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SP 30 (2011) : National Electrical Code of India

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BUREAU OF INDIAN STANDARDS

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NATIONAL ELECTRICAL CODE 2011
( First Revision )

BUREAU OF INDIAN STANDARDS

SP 30: 2011

FIRST PUBLISHED AUGUST 1985
FIRST REVISION FEBRUARY 20 1 1

ICS 01.120; 91.160.01

PRICE Rs. 4070.00

PUBLISHED BY BUREAU OF INDIAN STANDARDS, MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR
MARQNEWDELHI 110 002, PRINTED BY VIBA PRESS PVT. LTD., NEW DELHI 110 020

INTRODUCTION

India is on the path of development and its infrastructure sector has grown progressively. The buildings and
services so constructed depend on power for their construction and effective utilization. In fact, power is one of
the prime movers of development and electrical energy is the predominant form of energy being used due to ease
of generation/conversion, transmission, and final utilization.

Specific regulations to be adhered to in the supply and use of electrical energy had been laid down by the Indian
Electricity Act, 1910 and the Indian Electricity Rules, 1956 framed thereunder. However, a need was felt to
elaborate upon these regulations since the agencies involved have varied practices in view of their diverse interests
and different accessibility levels to technological developments. In order to rationalize these practices, India's
first National Electrical Code, formulated in 1985, was a compendium of several well established codes of practice
which provided assistance on economic selection, installation and maintenance of electrical equipment employed
in the usage of electrical energy. The code complemented and elaborated on the Indian Electricity Rules, 1956
for the ease of application by the system engineers by recommending the best practices for electrical installations
in a consolidated form in order to provide for unified practices and procedures along with consideration for
safety and economic usage of energy in the design, execution, inspection and maintenance of electrical installations
of various locations.

During the formulation of the National Electrical Code in 1985, it was realized that the referred codes, for
example, those on wiring practice, earthing, lightning protection etc need to be revised in line with the practice
and technology available at that time. It had also been planned that after the relevant codes are revised, the
National Electrical Code would also need to be revised. After the publication of NEC 1985, the referred Codes
were revised. However, the task of revision of NEC could not be taken up in earnest immediately after the
revision of various codes of practice. Over the years, there have been yet more changes in the technology; new
practices have evolved and got modified. There have been tremendous socio-economic changes, and corresponding
change in the pattern of the usage of electricity. Electricity Act 2003 has been notified and power sector reforms
have been firmly established. During the Ninth Plan, it was realized that it is necessary to have an Energy
Conservation Act. Accordingly, the Government has enacted the Energy Conservation Act, 2001 to meet the legal
requirement needed to enforce energy efficiency and conservation measures. Due to all such changes, the present
scenario is at great variance with that of 1985, when the Code was first formulated. Therefore, an urgent need was
felt to revise the NEC at the earliest to maintain its relevance in the present context.

The task for revision of NEC was taken up by the Electrical Installations Sectional Committee, ETD 20 considering
the above factors. This revision follows the earlier structure of NEC, with modifications and additions being
incorporated in line with IEC 60364 series on 'Electrical Installations' as well as the changes and developments
that took place since the publication of NEC 1985. It is visualized that in future, further harmonization with
international codes may be considered.

Electrical installation should be carried out in accordance with the Indian Electricity Rules, 1956 and relevant
regulations as amended or brought into force from time to time. All material, accessories, appliances etc., used in
an electrical installation should conform to Indian Standards wherever they exist. There should be good
workmanship and proper coordination and collaboration between the architect, building engineer and the electrical
engineer from the planning stage itself. The design of electrical installation is required to take into account the
characteristics of available supply, nature of demand, environmental conditions, type of wiring and methods of
installations, protective equipment, emergency control, disconnecting devices, preventing of mutual influence
between electrical and non electrical installations, accessibility etc.

The Code is divided into eight parts, which are further divided into sections. Part 1 covers the General and
common aspects, which would apply to all types of electrical installations. Wiring installations are an important

aspect of any electrical installation. These have been revised to align with international practice and it is proposed
to revise the relevant code of practice for wiring installations also. The Sections related to Earthing and Lightning
protection have been modified and corresponding modification is also being initiated to respective codes. Aspect
of voltage surges has also been included. Energy conservation aspects had been emphasized in NEC 1985.
Meanwhile, Energy Conservation Act, 2001 has been notified. Therefore, energy conservation aspects have been
further elaborated and energy audit has also been included.

This Code excludes the requirements coming under the purview of utilities, namely, the large generating stations,
distribution substations and associated transmission system, or captive generator sets of very large capacity. It
covers the requirements relating to standby or emergency generating stations and captive substations intended
for serving an individual occupancy and intended to serve a building or a group of buildings normally housed in
and around it. It gives guidelines on layout and building construction aspects, selection of equipment, transformer
installations, switching stations and station auxiliaries. Reference to pollution norms as laid down in Environment
Protection Act 1986 for diesel generator sets has now been included.

Non-industrial buildings include domestic dwellings, office buildings, shopping and commercial centers and
institutions, recreational & assembly buildings, medical establishments, hotels and sports buildings etc. Optimum
benefits from the use of electricity can be obtained only if the installation is of sufficient capacity and affords
enough flexibility. Safety, economy, efficiency, reliability, convenience as well as provision for future expansion
are major considerations in planning the electrical layout. Guidelines are provided based on general characteristics
of installations, supply characteristics and parameters. Switchgear for control and protection, service lines, metering,
earthing, building services, fire protection and miscellaneous provisions have been covered. Miscellaneous
provisions include telephone wiring, call bell system, clock system, group control, audio visual systems, closed
circuit TV where applicable, emergency lights for critical areas of the dwelling. Provision of increased number of
points for residential units in order to accommodate the gadgets available and to avoid overloading of points by
consumer and reference to miniature circuit breakers in addition to fuses under requirement of switchgear for
control and protection has been made.

Electrical networks in industrial buildings serve the purpose of distributing the required power to the consuming
points where it is used for a multitude of purposes in the industry. The design of electrical installation in industrial
premises is therefore more complicated than those in non-industrial buildings. Industrial installation has to take
care of load requirements and supply limitations in a simple and economic manner, ensuring at the same time full
protection to human life and loss of property by fire. The network layout should also facilitate easy maintenance
and fault localization. A particular feature of electrical installations in industrial buildings is the reliability of
supply to essential operations for which standby and emergency supply sources/networks are available. The
needs of such systems would depend on the type and nature of the industrial works.

Locations in industrial buildings which are by their nature hazardous, require special treatment in respect of
design of electrical installations therein. Industrial installations have been classified depending on the specified
criteria therein in order to help identify the specific nature of each industry and the locations therein, for assisting
the design engineer in the choice of equipment and methods.

Electrical installations are often required to be designed and erected for use for short periods of time ranging
from a few hours to few months and are connected to the supply source in open ground. Such installations are
generally unprotected from environmental hazards as compared to installations in buildings. Major risks in the
use of power in such installation arise from short circuit resulting in fire accidents and exposure to live wire
resulting in shock. Outdoor installations are required to comply not only with the general requirements, but also
additional requirements regarding supply intake arrangements, control of circuits, earthing, and protection against
overload, short circuit and earth leakage.

There is increased use of electricity for essential purposes in agriculture with the increase in sophistication in
organising the farm output of the country. Installations in agricultural premises are different as the external
influences on the electrical services are quite different from those encountered elsewhere. Even though the overall
power requirements for such installations could be small, the presence of livestock and other extraneous factors
necessitate laying down specific requirements to ensure safety. Specific requirements of electrical installations in
agricultural premises which include premises where livestock are present and farm produce are handled or stored
have been covered. Agricultural processing at the farm premises has now been included.

Any area, where during normal operations a hazardous atmosphere is likely to occur in sufficient quantity to
constitute a hazard had to be treated in a special manner from the point of the design of electrical installation.

Many liquids, gases and vapours which in industry are generated, processed, handled and stored are combustible.
When ignited these may burn readily and with considerable explosive force when mixed with air in the appropriate
proportions. With regard to electrical installations, essential ignition sources include arcs, sparks or hot surfaces
produced either in normal operation or under specified fault conditions. NEC provides guidelines for electrical
installations and equipment in locations where a hazardous atmosphere is likely to be present with a view to
maximizing electrical safety. When electrical equipment is to be installed in or near a hazardous area, effort is to
be made to locate much of the equipment in less hazardous or non-hazardous areas and thus reduce the amount
of special equipment required. Hazardous areas can be limited in extent by construction measures, that is, walls
or dams. Ventilation or application of protective gas also reduces the probability of the presence of explosive gas
atmosphere so that areas of greater hazard can be transformed to areas of lesser hazard or to non-hazardous areas.
A number of product standards offering different types of protection are available. Regulatory requirements are
to be adhered to for such installations. Standards pertaining to classification of hazardous areas having flammable
gases and vapours for electrical installation and guide for selection of electrical equipment for hazardous area
have been revised and the changes have been incorporated in the NEC.

Excessive reliance on fossil fuel resources to meet the energy requirement of the country is considered unsustainable
in the long-run and has an adverse impact on the environment and ecology. This has resulted in the quest of
renewable sources of energy as a viable option to achieve the goal of sustainable development. Harnessing of
solar energy is one such area which is expected to supplement energy supply efforts. Hence a new part on solar
photovoltaic installations has been added.

The Code excludes guidance on tariff. Product details are also excluded from the Code as separate product
standards are available for these. When these standards are revised subsequent to the revision of NEC, there
could be instances where the latest Codes differ from the revised NEC. It is therefore recommended to follow the
provisions of the latest standards/codes of practice. In order to avoid instances where the Indian Standards and
provisions of this Code differ, attention has been drawn to the relevant standard. However, for certain provisions
in this Code, the relevant requirements from corresponding Indian Standards have been extracted and reproduced.
In all cases, for detailed guidance, reference should be made to the individual standard and should any contradiction
be observed between the provisions in individual standard and those reproduced herein, the provisions of the
former shall be considered accurate. As a general rule, technological innovations such as better materials or new
and better method also proved as 'good practice' would first be introduced in the individual standard as appropriate
than in the National Electrical Code. In order to keep pace with such changes and to incorporate the additional
knowledge that will be gained through the implementation of the Code, a continuous review is envisaged. Thus,
the users of this Code are encouraged to bring to the notice of Bureau of Indian Standards, need of modifications
that may be required in the light of changes in technology or other factors, as this is a continuous process.

The National Electrical Code (hereafter referred to as the Code) is intended to be advisory. It contains guidelines,
which can be immediately adopted for use by the various interests concerned. Its provisions are presently not
mandatory but are expected to serve as a model for adoption in the interest of safety and economy and with the
intent to keep our electrical installation practices at par with the best practices in the world.

COMMITTEE COMPOSITION
Electrical Installations Sectional Committee, ETD 20

Chairman
SHRI N. NAGARAJAN

Chief Engineer
Central Public Works Department, New Delhi

Organization
Areva Transmission and Distribution, Noida
BEST Undertaking, Mumbai

BSES Rajdhani Power Ltd, New Delhi
Central Electricity Authority, New Delhi

Chief Electrical Inspectorate (Kerala), Thiruvananthapuram

Chief Electrical Inspectorate (Madhya Pradesh), Bhopal

Chief Electrical Inspectorate (Orissa), Behrampur

Chief Electrical Inspectorate (Tamil Nadu), Chennai

Chief Electrical Inspectorate (Uttranchal), Nainital

Central Public Works Department, New Delhi

Development Consultant Limited, Kolkata

Representative(s)

Shri Biswajit Saha

Shri S. A. Puranik

Shri P. R. B. Nair (Alternate)

Shri Shantanu Dastfdar

Shri R. K. Verma

Shri B. R. Singh (Alternate)

Shri K. S. Beena

Shri K. K. Unni (Alternate)

Shri S. S. Mujalde

Shri A. K. Dubey (Alternate)

Shri G. C. Choudhury

Shri S. H. Rahman (Alternate)

Shri R. Subramaniyan

Shri S. Appavoo (Alternate)

Shri Anupam Kumar

Shri Girish Chand (Alternate)

Shri M. K. Verma

Shri S. Chopra (Alternate)

Shri Jiban K. Chowdhury

Shri Ranjit K. Das (Alternate)

Director General Factory Advisory Services & Labour Institute, Mumbai Shri V. B. Sant

Shri S. C. Sharma (Alternate)

Department of Telecommunications, New Delhi
Electrical Contractors Association of Maharashtra, Mumbai
Electrical Contractors Association of Tamil Nadu, Chennai
Engineers India Ltd, New Delhi
Gujarat Electricity Board, Vadodara

Shri Pradeep Nettur

Shri J. S. Yadav (Alternate)

Shri U. S. Chitre

Shri Anil Gachke (Alternate)

Shri A. K. Venkataswamy

Shri T. M. Bhikkaji (Alternate)

Shri J. M. Singh

Shri Neeraj Sethi (Alternate)

Shri R. O. Gandhi

Shri K. M. Dave (Alternate)

Indian Electrical and Electronics Manufacturers' Association, Mumbai Shri Amitabha Sarkar

Shrimati Anita Gupta (Alternate)

Larsen & Toubro Ltd, Chennai

Metallurgical & Engineering Consultants (I) Ltd, Ranchi
Ministry of Defence, New Delhi

National Thermal Power Corporation Ltd, Noida
Nuclear Power Corporation, Mumbai

Shri S. Rajavel

Shri D. Maheswaran (Alternate)

Shri G. Mishra

Shri A. K. Mittal

Shri R. K. Tyagi (Alternate)

Shri Atul Shrivastava

Shri Rahul Aggarwal (Alternate I)
Shri Vikram Talwar (Alternate II)

Shri M. L. Jadhav

Organization
Power Grid Corporation of India Ltd, Gurgaon

Rural Electification Corporation Ltd, New Delhi

Siemens Ltd, Chennai

Tariff Advisory Committee, Ahmedabad

Tata Consulting Engineers; Mumbai

Tamil Nadu Electricity Board, Chennai

BIS Directorate General

Representative(s)

SHRr S. V. Sarma

Shri Subir Sen (Alternate)

Shri Dinesh Kumar

Shri R S. Hariharan (Alternate)

Shri T. Prabhakar

Shri K. Gurumurthy (Alternate)

Shri M. M. Bhuskute

Shri P. K. Roy Chowdhury (Alternate)

Shri Murli Muthana

Shri Utpal Priyadarshi (Alternate)

Shri Sukumaran

Shri S. Kabbab (Alternate)

Shri R. K. Trehan Scientist T' & Head (Electrotechnical)
Representing Director General (Ex-officio Member)

Member Secretary

Shrimati Nishat S. Haque

Scientist E (Electrotechnical)

CONTENTS

Page No.

INTRODUCTION
COMPOSITION

in
vi

PARTI GENERAL AND COMMON ASPECTS

Section 1 Scope of the National Electrical Code

Section 2 Definitions

Section 3 Graphical Symbols for Diagrams, Letter Symbols and Signs

Section 4 Guide for Preparation of Diagrams, Charts, Tables, and Marking

Section 5 Units and Systems of Measurement

Section 6 Standard Values

Section 7 Fundamental Principles

Section 8 Assessment of General Characteristics of Buildings

Section 9 Wiring Installations

Section 10 Short-Circuit Calculations

Section 1 1 Electrical Aspects of Building Services

Section 12 Selection of Equipment

Section 13 Erection and Pre-commissioning Testing of Installations

Section 14 Earthing

Section 15 Lightning Protection

Section 1 6 Protection Against Voltage Surges

Section 17 Guidelines for Power-Factor Improvement

Section 18 Energy Efficiency Aspects

Section 19 Safety in Electrical Work

Section 20 Tables

4
6

101

110

130

131

136

163

171

180

184

186

190

PART 2 ELECTRICAL INSTALLATIONS IN STAND-BY GENERATING STATIONS 195
AND CAPATIVE SUBSTATIONS

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS 201

Section 1 Domestic Dwellings 204

Section 2 Office Buildings, Shopping and Commercial Centres and Institutions 214

Section 3 Recreational, Assembly Buildings 220

Section 4 Medical Establishments 224

Section5 Hotels 250

Section 6 Sports Buildings 259

Section 7 Specific Requirements for Electrical Installations in Multi-storeyed Buildings 265

PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS 271

PART 5 OUTDOOR INSTALLATIONS 301

Section 1 Public Lighting Installations 304

Section 2 Temporary Outdoor Installations 325

Section 3 Permanent Outdoor Installations 330

PART 6 ELECTRICAL INSTALLATIONS IN AGRICULTURAL PREMISES 343

PART 7 ELECTRICAL INSTALLATIONS IN HAZARDOUS AREAS 351

PART 8 SOLAR PHOTOVOLTAIC (PV) POWER SUPPLY SYSTEMS 379

NATIONAL ELECTRICAL CODE

PART1

SP 30: 2011

PART 1 GENERAL AND COMMON ASPECTS

FOREWORD

Electrical installations require adequate planning right from concept stage to layout and designing, selection of
proper equipment, their installation and their maintenance. Fundamental aspects of installation practice are common
for most of the types of electrical installations. Part 1 of the National Electrical Code covers these aspects under
its various Sections.

An account has been taken of the Indian Standards existing on different aspects of electrical installation practice.
However, some practices have changed over time and corresponding Codes of practice either do not exist or are
yet to be modified. An attempt has been made through this Code to refer to the present good practices. A reference
has also been made to product standards in order to inform the user of the Code about the availability and
desirability to use them.

Aspects concerning specific occupancies are covered in other Parts and Sections of this Code. The fundamental
principles of installation practice covered under Part 1 of this Code generally apply, unless modified or
supplemented by subsequent Parts. This Part 1 would also be a useful reference for occupancies not explicitly
covered by the scope of subsequent Parts of the Code.

PART 1 GENERAL AND COMMON ASPECTS 3

SP 30 : 2011

SECTION 1 SCOPE OF THE NATIONAL ELECTRICAL CODE

FOREWORD

Each Part/Section of the National Electrical Code
covers the requirements relating to electrical
installations in specific occupancies. The fundamental
and general principles governing electrical installation
practice together with common aspects applicable to
all types of installations has been brought out in a
separate Part in order to serve as a reference document
on such matters.

The details enumerated in this Part are generally
applicable to all types of occupancies and are to be
read as modified or supplemented with the information
provided in the relevant Parts of the Code.

Effort has been made to make this part self-contained,
so that users of the Code can derive utmost advantage
in using it for application in the field even for
occupancies not explicitly covered by the scope of
subsequent Parts of the Code. Efforts have also been
made to ensure that all the relevant details required for
the understanding of the Code are available to the extent
possible within Part 1 and effort has been made to keep
the references of individual standards to the minimum.

1 SCOPE

This Part 1 /Section 1 of the Code describes the scope
of the National Electrical Code.

2 REFERENCES

The National Electrical Code takes into account the
stipulations in several Indian Standards dealing with
the various aspects relating to electrical installation
practice. Several product standards also exist, and
compliance with relevant Indian Standards is
desirable. It is therefore recommended that individual
Parts/Sections of the Code should be read in
conjunction with the relevant Indian Standards. List
of such Indian Standards is given at relevant Part/
Section of the Code.

At the time of publication, the editions indicated were
valid. All standards are subject to revision, and parties
to agreements based on this standard are encouraged
to investigate the possibility of applying the most recent
editions of the standards.

3 SCOPE OF THE NATIONAL ELECTRICAL
CODE

3.1 The National Electrical Code covers the following:

a) Standard good practices for selection of

various items of electrical equipment forming
part of power systems;

b) Recommendations concerning safety and
related matter in the wiring of electrical
installations of buildings or industrial
structures, promoting compatibility between
such recommendations and those concerning
the equipment installed;

c) General safety procedures and practices in
electrical work; and

d) Additional precautions to be taken for use of
electrical equipment for special environmental
conditions like explosive and active
atmosphere.

3.2 The Code applies to electrical installations such as
those in:

a) Standby/emergency generating plants and
building substations;

b) Domestic dwellings;

c) Office buildings, shopping and commercial
centres and institutions;

d) Recreation and other public premises;

e) Medical establishments;

f) Hotels;

g) Sports buildings;
h) Industrial premises;

j) Temporary and permanent outdoor

installations;
k) Agricultural premises;
m) Installations in hazardous areas; and
n) Solar photovoltaic installations.

NOTES

1 Any type of installation not covered by the above shall be
classified in the group which most nearly resemble its existing
or proposed use.

2 Where change in the occupancy places it under the scope
of a different Section of the Code, the same installation shall
be made to comply with the requirements of the Code for
the new occupancy.

33 The Code applies to circuits other than the internal
wiring of apparatus.

3*4 The Code does not apply to traction, motor vehicles,
installations in rolling-stock, on board-ships, aircraft
or installations in underground mines.

3.5 The Code covers only electrical aspects of lightning
protection of buildings and in so far as the effects of
lightning on the electrical installations are concerned.

NATIONAL ELECTRICAL CODE

SP 30 : 2011

It does not cover lightning protection aspects from b) Power generation and transmission for such

structural safety point of view. systems.

3.6 The Code is also not intended to apply to, 3.7 The Code also does not cover guidelines on the

. _ .,..,. „ lt . payment for electrical work done in installations,
a) Systems of distribution of energy to public;

and

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

SECTION 2 DEFINITIONS

FOREWORD

Each Part of the Code gives, where necessary,
definitions of terms and phrases relevant for the
comprehension of the requirements stipulated therein.
Users may find it convenient to refer to a detailed list
of terms and their definitions contained in this section
that are relevant to electrical installation practice. It
may however be noted that for further guidance,
recourse should be made to IS 1885 (series) on
electrotechnical vocabulary containing a compendium
of terms in the field.

The definitions contained in the Code are based on the
current international terminology as far as possible.
Some definitions are based on the terminology drawn
up by the relevant expert groups under the
Electrotechnical Division Council with the object of
striking a correct balance between absolute precision
and simplicity. The principal object of this exercise is to
provide definitions which are sufficiently clear so that
each term is understood with the same meaning by all
concerned. It may sometimes be felt that the definitions
are not identical with those which may be found in other
publications designed with different objectives and for
other readers. Such differences are inevitable and should
be accepted in the interest of clarity.

1 SCOPE

This Part 1/Section 2 of the Code covers definitions of
terms.

2 REFERENCES

A list of Indian Standards on electrotechnical
vocabulary relevant for the purpose of the Code is given
at Annex A.

3 TERMINOLOGY

3.0 For the purpose of the National Electrical Code,
the following definitions shall apply, in addition to
those contained in individual Parts/Sections and
relevant Indian Standards.

3.1 Fundamental Definitions

3.1.1 Capacitor — A system of two conductors (plates)
separated over the extent of their surfaces by an
insulation medium which is capable of storing electrical
energy as electrical stress.

3.1.2 Conductor — A substance or body which allows
current of electricity to pass continuously.

3.1.3 Dielectric — A material medium in which an
electric field can exist in a stationary state.

3.1.4 Electrode — A conducting element used for
conveying current to and from a medium.

3.1.5 Current — The elementary quantity of electricity
flowing through a given section of a conductor divided
by the corresponding indefinitely small time.

3.1.6 Electric Circuit — An arrangement of bodies or
media through which a current can flow.

3.1.7 Electric Current — The movement of electricity
in a medium or along a circuit. The direction of the
current is accepted as opposite to that of the motion of
negative electricity.

3.1.8 Voltage, Potential Difference — The line of
integral from one point to another of an electric field,
taken along a given path.

3.1.9 Arc — A luminous discharge of electricity across
a gas, characterized by a large current and a low voltage
gradient, often accompanied by partial volatilization
of the electrodes.

3.1.10 Flashover — The passage of a disruptive
discharge round in insulating material.

3.1.11 Spark — A brilliantly luminous phenomenon
of short duration which characterized a disruptive
discharge.

3.1.12 Connection of Circuits

3.1.12.1 Series — An arrangement of elements so that
they all carry the same current or flux.

3.1.12.2 Parallel — An arrangement of elements so
that they all carry a portion of total current or flux
through them

3.1.12.3 Series parallel — An arrangement of elements
of which some are connected in series and others in
parallel.

3.1.13 Earth Fault — Accidental connection/contact
of a conductor to earth. When the impedance is
negligible, the connection is called a dead earth.

3.1.14 Earth Leakage Current — The current flowing
to earth on account of imperfect insulation.

3.1.15 Insulation Fault — An abnormal decrease in
insulation resistance.

3.1.16 Overload — Operating conditions in an
electrically undamaged circuit which causes an
overcurrent.

3.1.17 Short-circuit — The intentional or accidental
connection of two points of a circuit through a
negligible impedance. The term is often applied to the

NATIONAL ELECTRICAL CODE

SP 30 : 2011

group of phenomena which accompany a short circuit
between points at different potentials.

3.2 Equipment

3.2.1 Electrical Equipment — The electrical machines,
apparatus and circuits forming part of an electrical
installation or a power system.

NOTES

1 Outdoor electrical equipment are those suitable for
installation in open air.

2 For the purpose of this Code, the term electrical equipment
can in general be used to any item used for such purposes as
generation, conversion, transmission, distribution or utilization
of electrical energy such as machines, transformers, apparatus,
measuring instruments, protective devices, wiring material and
appliances.

3.2.2 Current Using Equipment — Equipment intended
to convert electrical energy into another form of energy,
for example, light, heat or motive power.

3.2.3 Portable Equipment — Equipment which is
moved while in operation or which can easily be moved
from one place to another while connected to the
supply.

3.2.4 Hand- he Id Equipment — Portable equipment
intended to be held in the hand during normal use, in
which the motor, if any, forms an integral part of the
equipment.

3.2.5 Stationary Equipment — Either fixed equipment
or equipment not provided with a carrying handle and
having such a mass that it cannot easily be moved.

3.2.6 Fixed Equipment — Equipment fastened to a
support or otherwise secured in a specific location.

3.2.7 Generator — A machine for converting mechanical
energy into electrical energy.

3.2.8 Electric Motor — A machine for converting
electrical energy into mechanical energy.

3.2.9 Induction Motor — An alternating current motor
without a commutator in which one part only, the rotor
or a stator, is connected to the supply network, the other
working by induction.

3.2.10 Motor Generator Set — A machine which
consists of an electric motor mechanically coupled to
a generator.

3.2.11 Auto-transformer — A transformer in which the
primary and secondary windings have common part
or parts.

3.2.12 Transformer — A piece of apparatus, without
continuously moving parts, which by electromagnetic
induction transforms variable voltage and current in
one or more other windings usually at different values
of voltage and current and at the same frequency.

3.2.13 Relay (Including Gas-operated Relay) — A
device designed to produce sudden pre-determined
changes in one or more physical systems on the
appearance of certain conditions in the physical system
controlling it.

3.2.14 Switchgear and Controlgear — A general term
covering switching devices and their combination with
associated control, measuring, protective and
regulating equipment, also assemblies of such devices
and equipment with associated inter-connections,
accessories, enclosures and supporting structures
intended in principle for use in connection with
generation, transmission, distribution and conversion
of electric energy. Controlgears are switching devices
intended in principle for the control of electrical energy
consuming equipment.

3.2.15 Switch (Mechanical) — A mechanical switching
device capable of making carrying and breaking
currents under normal circuit conditions which may
include specified operating overload conditions and
also carrying for a specified time currents under
specified abnormal circuit conditions such as those of
a short-circuit.

3.2.16 Switch-fuse — A switch in which one or more
poles have a fuse in series in a composite unit.

3.2.17 Fuse-switch — A switch in which a fuse-link
or a fuse-carrier with fuse-link forms the moving
contact of the switch.

3.2.18 Circuit-Breaker (Mechanical) — A mechanical
switching device capable of making carrying and
breaking currents under normal circuit conditions and
also making, carrying for a specified time and breaking
currents under specified abnormal circuit conditions
such as those of a short-circuit.

3.2.19 Fuse — device that, by the fusing of one or
more of its specially designed and proportioned
components, opens the circuit in which it is inserted
by breaking the current when this exceeds a given value
for a sufficient time

NOTE — The fuse comprises all the parts that form the
complete device.

3.2.20 Enclosed Distribution Fuse-board — An
enclosure containing bus-bars, with fuses, for the
purposes of protecting, controlling or connecting more
than one outgoing circuit fed from one or more
incoming circuits.

3.2.21 Enclosed Fuse-link — Fuse-link in which the
fuse-element is totally enclosed, so that during
operation within its rating it cannot produce any
harmful external effects, for example, due to
development of an arc, the release of gas or the ejection
of flame or metallic particles.

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

3.2.22 Fuse- link — Part of a fuse including the fuse-
elements) intended to be replaced after the fuse has
operated.

3.2.23 Miniature Circuit-breaker — A compact
mechanical device for making and breaking a circuit
both in normal conditions and in abnormal conditions
such as those of overcurrent and short-circuit.

3.2.24 D-Type Fuse — A non-interchangeable fuse
comprising a fuse-base a screw type fuse-carrier, a
gauge piece and a fuse-link.

3.2.25 Distribution Pillar — A totally enclosed
structure cubicle containing bus-bars connected to
incoming and outgoing distribution feeders controlled
through links fuses.

3.2.26 Interconnecting Bus-bar — A conductor other
than cable, used for external connection between
terminals of equipment.

3.2.27 Bimetallic Connector — A connector designed
for the purpose of connecting together two or more
conductors of different materials (normally copper and
aluminium) for preventing electrolytic corrosion.

3.2.28 Fuse-element (Fuse-wire in Rewirable Fuse) —
That part of a rewirable fuse, which is designed to melt
when the fuse operates.

3.2.29 Fuse-base (Fuse-mount) — The fixed part of a
fuse provided with contacts and terminals for
connection to the system. The fuse-base comprises all
the parts necessary for insulation.

3.2.30 Fuse-carrier — The movable part of a fuse
designed to carry a fuse-link. The fuse-carrier does not
include any fuse-link.

3.2.31 Lightning Arrester (Surge Diverter) — A device
designed to protect electrical apparatus from high
transient to protect electrical apparatus from high
transient voltage and to limit the duration and
frequently the amplitude of follow-current. The term
'lightning arrester' includes any external series gap
which is essential for the proper functioning of the
device as installed for service, regardless of whether
or not it is supplied as an integral part of the device.

3.3 Wiring Practice

3.3.1 Accessory — Any device, associated with the
wiring and electrical appliance of an installation, for
example, a switch, a fuse, a plug, a socket-outlet, a
lamp holder, or a ceiling rose.

3.3.2 Apparatus — Electrical apparatus including all
machines, appliances and fittings in which conductors
are used for of which they may form a part.

3.3.3 Aerial Conductor — Any conductor which is

supported by insulators above the ground and is directly
exposed to the weather.

NOTE — The following four classes of aerial conductors are
recognized:

a) Bare aerial conductors,

b) Covered aerial conductors,

c) Insulated aerial conductors, and

d) Weatherproof neutral-screened cable.

3.3.4 Bunched — Cables are said to be 'bunched' when
two or more are contained within a single conduit, duct
or groove or, if not enclosed, are not separated from
each other.

3.3.5 Cable — A length of single-insulated conductor
(solid or stranded), or two or more such conductors,
each provided with its own insulation, which are laid
up together. The insulated conductor or conductors may
or may not be provided with an overall mechanical
protective covering.

3.3.6 Cable, Armoured — A cable provided with a
wrapping of metal (usually in the form of tape or wire)
serving as a mechanical protection.

3.3.7 Cable, Flexible — A cable containing one or more
cores, each formed of a group of wires, the diameters
of the cores and of the wires being sufficiently small
to afford flexibility.

3.3.8 Circuit — An arrangement of conductor or
conductors for the purpose of conveying energy and
forming a system or a branch of a system.

3.3.9 Circuit, Final, Sub — An outgoing circuit
connected to one-way distribution fuse-board and
intended to supply electrical energy at one or more
points to current-using appliances, without the
intervention of a further distribution fuse-board other
than a one-way board. It includes all branches and
extensions derived from that particular way in the
board.

3.3.10 Cleat — An insulated incombustible support
normally used for insulated cable.

3.3.11 Conductor, Bare — A conductor not covered
with insulating material.

3.3.12 Conductor, Earthed — A conductor with no
provision for its insulation from earth.

3.3.13 Conductor, Insulated — A conductor adequately
covered with insulating material of such quality and
thickness as to prevent danger.

3.3.14 Connector Box or Joint Box — A box forming
a part of wiring installation provided to contain joints
in the conductors of cables of the installation.

3.3.15 Conductor for Portable Appliances — A
combination of a plug and socket arranged for

NATIONAL ELECTRICAL CODE

SP 30: 2011

attachment to a portable electrical appliance or to a
flexible cord.

3.3.16 Consumer's Terminals — The ends of the
electrical conductors situated upon any consumer's
premises and belonging to him at which the supply of
energy is delivered from the service line.

3.3.17 Cord, Flexible — A flexible cable having
conductor of small cross-sectional area. Two flexible
cords twisted together are known as 'Twin Flexible
Cord'.

NOTE — For the maximum diameter and minimum number
of wires for flexible cord, see relevant standard.

3.3.18 Cut-out — Any appliance for automatically
interrupting the transmission of energy through any
conductor when the current rises above a
predetermined amount, for example, fusible cut-out.

3.3.19 Dead — At or about earth potential and/or
disconnected from any live system.

3.3.20 Direct Earthing System — A system of earthing
in which the parts of an installation are so earthed as
specified but are not connected within the installation
to the neutral conductor of the supply system or to earth
through the trip coil of an earth leakage circuit-breaker.

3.3.21 Distribution Fuse-board — An assemblage of
parts including one or more fuses arranged for the
distribution of electrical energy to final sub-circuits.

3.3.22 Earth — A connection to the general mass of
earth by means of an earth electrode. An object is said
to be 'earthed' when it is electrically connected to an
earth electrode; and a conductor is said to be 'solidly
earthed' when it is electrically connected to earth
electrode without a fuse, switch, circuit-breaker,
resistance or impedance in the earth connection.

3.3.23 Earth Continuity Conductor — The conductor,
including any clamp, connecting to the earthing lead
or to each other those parts of an installation which
are required to be earthed.

3.3.24 Earth Electrode — A metal plate, pipe or other
conductor electrically connected to the general mass
of the earth.

3.3.25 Earthing Lead — The final conductor by which
the connection to the earth electrode is made.

3.3.26 Fitting, Lighting — A device for supporting or
containing a lamp or lamps (for example, fluorescent
or incandescent) together with any holder, shade, or
reflector, for example, a bracket, a pendant with ceiling
rose, or a portable unit.

3.3.27 Flammable — A material capable of being easily

ignited.

3.3.28 Disconnector — A device used to open (or close)
a circuit when either negligible current is interrupted
(or established) or when the significant change in the
voltage across the terminal of each of the pole of the
disconnector occurs; in the open position it provides
an isolating distance between the terminals of each
pole.

3.3.29 Double Insulation

a) Of a conductor — A conductor is said to have
double insulation when insulating material
intervenes not only between the conductor and
its surrounding envelope (if a cable) or
immediate support (if bare), but also between
the envelope or support and earth.

b) Of an appliance — An appliance having
accessible metal part is doubly insulated when
protective insulation is provided in addition
to the normal functional insulation, in order
to protect against electric shock in case of
breakdown of the functional insulation.

3.3.30 Live or Alive — Electrically charged so as to
have a potential difference from that of earth.

3.3.31 Multiple Earthed Neutral System — A system
of earthing in which the parts of an installation,
specified, to be earthed are connected to the general
mass of earth and, in addition, are connected within
the installation to the neutral conductor of the supply
system.

3.3.32 Neutral or Neutral Conductor — Includes the
neutral conductor of a three-phase four-wire system,
the conductor of a single-phase or dc installation which
is earthed by the supply undertaking (or otherwise at
the source of the supply), and the middle wire or
common return conductor of a three- wire dc or single-
phase ac system.

3.3.33 Point — A point shall consist of the branch
wiring from the branch distribution board, together
with a switch as required, as far as and including the
ceiling rose or socket-outlet or suitable termination. A
three-pin socket-outlet point shall include, in addition,
the connecting wire or cable from the earth pin to the
earth stud of the branch distribution board.

3.3.34 Service — The conductors and equipment
required for delivering energy from the electric supply
system to the wiring system of the premises served.

3.3.35 Socket-outlet and Plug — A device consisting
of two portions for easily connecting portable lighting
fittings or other current-using appliances/devices to the
supply. The socket-outlet is an accessory having socket
contacts designed to engage with the pins of a plug
and having terminals for the connection of cable(s).

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

The plug portion has pins designed to engage with the
contacts of a socket-outlet, also incorporating means
for the electrical connection and mechanical retention
of flexible cable(s).

3336 Switchboard — An assemblage of switchgear
with or without instruments but the term does not apply
to a group of local switches or a final sub-circuit where
each switch has its own insulating base.

3337 Voltage, Low - — The voltage which does not
normally exceed 250 V.

3338 Voltage, Medium — The voltage which normally
exceeds 250 V but does not exceed 650 V.

3339 Voltage, High — The voltage which normally
exceeds 650 V (but less than 33 kV).

3.3,40 Voltage, Extra- High — The voltage exceeding
33 kV under normal conditions.

NOTE — The Indian Electricity Rules, 1956 define four ranges
of voltages, namely, low (up to 250 V), medium (250-650 V),
high (650 V-33 kV) and extra-high (greater than 33 kV). The
definitions given in 3.3.37 to 3.3.40 are based on the provisions
of IE Rules. It may however, be noted that voltage ranges as
defined internationally are at variance with the above
definitions.

3.4 Miscellaneous Terms

3.4.1 Building — Any structure for whatsoever purpose
and of whatsoever materials constructed and every part
thereof whether used as human habitation or not and
includes foundation, plinth, walls, floors, roofs,
chimneys, plumbing and building services, fixed
platforms, verandah, balcony, cornice or projection,
part of a building or any thing affixed thereto or any
wall enclosing or intended to enclose any land or space
and signs and outdoor display structures. Tents,
shamianahs, tarpaulin shelters, etc, erected for
temporary of the Authority shall not be considered as
building.

3.4.2 Occupancy or Use Group — The principal
occupancy for which a building or a part of a building
is used or intended to be used; for the purposes of
classification of a building according to occupancy,
an occupancy shall be deemed to include the subsidiary
occupancies which are contingent upon it

3.4.3 Room Height — The vertical distance measured
from the finished floor surface to the finished ceiling
surface. Where a finished ceiling is not provided, the
underside of the joints or beams or tie beams shall
determine the upper point of measurement for
determining the head room.

3.4.4 Impulse — Usually an aperiodic transient voltage
or current which rises rapidly to a peak value and then
falls, generally more slowly, to zero. Ideally it

approximates a double exponential form. Other forms
are sometimes used for special purposes.

3.4.5 Clearance — The distance between two
conducting parts along a string stretched the shortest
way between these conducting parts.

3.4.6 Creepage Distance — The shortest distance
between two conducting parts along the surface of the
insulating material or along the joint of two insulating
bodies.

3.4.7 Simultaneously Accessible Parts — Conductors
or conductive parts that can be touched simultaneously
by a person or where applicable by livestock.

NOTE — Simultaneously accessible parts may be;

a) live parts,

b) exposed conductive parts,

c) extraneous conductive parts,

d) protective conductors, and

e) earth electrodes.

3.4.8 Arm } s Reach — A zone extending from any point
on a surface where persons usually stand or move about
to the limits which a person can reach with the hand in
any direction without assistance.

3.4.9 Enclosure — A part providing protection of
equipment against certain external influences and, in
any direction, protection against direct contact.

3.4.10 Barrier — A part providing protection against
direct contact from any usual direction of access.

3.4.11 Obstacle — A part preventing unintentional
direct contact, but not preventing deliberate action.

3.4.12 Leakage Current (in an Installation) — A
current which flows to earth or to extraneous
conductive parts in a circuit in the absence of a fault.

NOTE — This current may have a capacitive component
including that resulting from the deliberate use of capacitors.

3.4.13 Nominal Voltage (of an Installation) — Voltage
by which an installation or part of an installation is
designated.

NOTE — The actual voltage may differ from the nominal
voltage by a quantity within permitted tolerances.

3.4.14 Supply Terminals — The point at which a
consumer received energy.

3.4.15 Service Line, Service — A line for connecting a
current consuming installation to the distribution
network.

3.4.16 Distribution Undertaking — The party
supplying electricity to consumers entirely from
external sources of power via a distribution network.

3.4.17 Consumer or Customer — The party who

NATIONAL ELECTRICAL CODE

SP 30: 2011

receives electricity from the supply or distribution
undertaking for his own needs or for further
distribution.

3.4.18 Demand — The magnitude of electricity supply,
expressed in kW or kVA.

3.4.19 Installed Load — The sum of the rated inputs
of the electrical apparatus installed on the consumer's
premises,

3.4.20 Connected Load — The part of the installed
load of consumer supplied by the supply undertaking.

3.4.21 Kilowatthour Rate (kWh Rate) — The amount
to be paid per unit of energy (kWh) consumed.

3.4.22 Meter Rent — An amount to be paid for a
specified period for metering, and associated
equipment installed.

3.4.23 Tariff — A statement setting out the components
to be taken into account and the methods to be
employed in calculating the amounts to be charged by
the supply/distribution undertaking to the consumer,
according to the characteristics of the supply.

3.4.24 Domestic Tariff — A tariff applicable
particularly or exclusively to domestic consumers.

3.4.25 Industrial Tariff — A tariff applicable
exclusively to industrial consumers.

3.4.26 Lighting Tariff — A tariff applicable to
electricity supplies taken mainly for lighting and other
small appliances, for example, fans and radios.

3.4.27 Heating Tariff — A tariff applicable to electricity
supplies taken for space heating or for thermal
applications or for both.

3.4.28 Power Factor Clause — A clause setting out
increase in charges to be applied if the ratio of the kWh
to kVAh consumed by a consumer during a specified
period below a set limit; the same clause may provide
for a decrease in charges in the opposite case.

NOTE — The power factor is generally measured by the ratio
of kWh to kVAh consumed during the specified period.

3.4.29 Load Factor — The ratio, expressed as a
numerical value or as a percentage, of the energy
consumption within a specified period (year, month,
day, etc) to the energy consumption that would result
from continuous use of the maximum kW demand
occurring within the same period.

NOTE — The load factor for a given demand is also equal to
the ratio of the utilization time to the time in hours within the
same period.

ANNEX A
(Clause 2)

LIST OF INDIAN STANDARDS ON ELECTROTECHNIC AL VOCABULARY

IS No.

1885
(Part 1) : 1961
(Part 8) : 1986

(Part 9): 1992/

IEC 60050 (446)

1983

(Part 10) : 1993/

IEC 60050 (448)

1986

(Part 11): 1966

(Part 14) : 1967

(Part 15) : 2003/

IEC 60050 (481)

1996

(Part 16/Sec 1) :

1968

Title

Electrotechnical vocabulary:

Fundamental definitions

Secondary cells and batteries (first

revision)

Electrical relays (second revision)

Power system protection (first
revision)

Electrical measurements
Nuclear power plants
Primary cells and batteries (first
revision)

Lighting, Section 1 General aspects

IS No.

(Part 16/Sec 2) :
1968

(Part 16/Sec 3) :

1967

(Part 17) : 1979

(Part 27): 1993/

IEC 60050 (551)

1982

(Part 28) : 1993/

IEC 60050 (321)

1986

(Part 29): 1971

(Part 30): 1971

Title

Lighting, Section 2 General

illumination, lighting fittings and

lighting for traffic and signalling

Lighting, Section 3 Lamps and

auxiliary apparatus

Switchgear and controlgear (first

revision)

Power electronics (second

revision)

Instrument transformers (first
revision)

Mining terms

Overhead transmission and

distribution of electrical energy

PART 1 GENERAL AND COMMON ASPECTS

SP 30:- 2011

IS No.

(Part 32) : 1993/

IEC 60050 (461):

1984

(Part 34) : 1972

(Part 35) : 1993/

IEC 60050 (411);

1996

(Part 37) : 1993/

IEC 60050 (691):

1973

(Part 38): 1993/

IEC 60050 (421):

1990

(Part43):1977

(Part 51): 1993/
IEC 60050 (841) :
1983

(Part 53) : 1980
(Part 54) : 1993/
IEC 60050 (471):
1984

(Part 55): 1981
(Part 57): 1993/
IEC 60050 (131):
1978

(Part 60) : 1993/
IEC 60050 (426) :
1990

(Part61):1985
(Part 62); 1993/
IEC 60050 (212):
1990

(Part 69): 1993/
DEC 60050 (602) :
1993

(Part 70) : 1993/
IEC 60050 (604) :
1987

Title
Electric cables (first revision)

Cinematography

Rotating machinery (first revision)

Part 37 Tariffs for electricity (first
revision)

Power transformers and reacto
(second revision)

Electrical equipment used in

medical

Industrial electro-heating

Mica

Insulators (first revision)

Electric fans

Electric and magnetic circuits (first

revision)

Electrical apparatus for explosive
atmospheres (first revision)

Nuclear medical instruments
Solid insulating materials (first
revision)

Generation, transmission and dis-
tribution of electricity — Generation

Generation, transmission and dis-
tribution of electricity —
Operation

IS No.

(Part 71): 1993/

IEC 60050 (605) :

1983

(Part72):1993/

IEC 60050 (101):

1977

(Part73/Secl):

1993/IEC60050

(111-1): 1984

(Part73/Sec2):

1993/IEC 60050

(111-2): 1984

(Part73/Sec3):

1993/IEC 60050 :

(111-3): 1977

(Part 74): 1993/

IEC 60050 (151):

1978

(Part 75): 1993/

IEC 60050 (351):

1975

(Part 77): 1993/

IEC 60050 (466) :

1990

(Part78):1993/

IEC 60050 (601):

1985

(Part 79): 1993/

IEC 60050 (603) :

1986

(Part 80): 1994/

IEC 60050 (301) :

1983

(Part 81): 1993/

IEC 60050 (302) :

1983

Title
Generation, transmission and
distribution of electricity —
Substations
Mathematics

Physics and chemistry, Section 1
physical concepts

Physics and chemistry — Section
2 Electrotechnical concepts

Physics and chemistry — Section 3

Concepts related to quantities and

units

Electrical and magnetic devices

Automatic control

Overhead lines

Generation, transmission and
distribution of electricity —
General

Generation, transmission and
distribution of electricity — Power
system planning and management
General terms on measurements
in electricity

Electrical measuring instruments

NATIONAL ELECTRICAL CODE

SF 30: 2011

SECTION 3 GRAPHICAL SYMBOLS FOR DIAGRAMS, LETTER

SYMBOLS AND SIGNS

FOREWORD

Several graphical symbols are used for installation
diagrams. Considerable amount of standardization has
been achieved in the field of

symbols for electrotechnology that it is now possible
to device electrical network schematics using them so
that these schematic diagrams could be uniformly
understood by all concerned.

The symbols contained in this Section of the Code have
been drawn up by individual expert groups under the
Electrotechnical Division Council. They represent a
consensus of opinion in the discipline and are
recommended for direct adoption. Assistance has also
been drawn from International Electrotechnical
Commission (IEC) database IEC 60617 'Graphical
symbols for diagrams'.

It has also been felt essential for the purposes of this
Section to draw the attention of practicing engineers
to standardized letter symbols and signs.

1 SCOPE

This Part 1 /Section 3 of the Code covers graphical
symbols for diagrams, letter symbols and signs which
may be referred to for further details.

2 REFERENCES

A list of relevant Indian Standards on graphical
symbols is given at Annex A.

3 GRAPHICAL SYMBOLS

3.0 For the purposes of the Code, the graphical symbols
given below shall apply.

NOTE — A list of Indian Standards on graphical symbols used
in electrotechnology relevant to the Code is given in Annex A.

3.1 Fundamental Symbols
3.1.1 Direct Current

3.1.2 Alternating Current, General Symbol

a) Alternating current, single-phase, 50 Hz

r\jsoHz

b) Alternating current, three-phase, 415 V.
50 Hz

/"\ J 50Hz «
r \-/ 415V

c) Alternating current, three-phase with neutral.
50 Hz

3.1.3 Neutral

3nT\J 50Hz

3.1.4 Positive Polarity

3.1.5 Negative Polarity

3.1.6 Direct Current, 2 Conductors 110 V

2 110V

3.1.7 Direct Current, 3 Conductors including Neutral,
220V

2N _ 220V

3.1.8 Underground Cable

3.1.9 Overhead Line

3.1.10 Winding, Delta

3.1.11 Winding, Star

3.1.12 Terminals

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

3.1.13 Resistance/Resistor

3.1.13.1 Variable resistor

*■

3.1.14 Impedance

3.1.15 Inductance/Inductor

3.1.16 Winding

3.1.17 Capacitance, Capacitor

3.1.18 Earth

3.1.19 Fault

3.2 Equipment

3.2.1 Flexible Conductor

3.2.2 Generator

3.2.2.1 AC generator

3.2.2.2 DC generator

3.2.3 Motor

3.2.4 Synchronous Motor

[MS

3.2.5 Mechanically Coupled Machines

o=o

3.2.6 Induction Motor, Three-Phase, Squirrel Cage

3.2.6.1 Induction motor with wound rotor

3.2.7 Transformers with Two Separate Windings

3.2.8 Auto-Transformer

3.2.9 3-Phase Transformer with Three Separate
Windings — Star — Star — Delta

NATIONAL ELECTRICAL CODE

SP 30 : 2011

3.2.10 Starter

3.2.19 Isolator

3.2.11 Direct-on-Line Starter for Reversing Motor

3.2.12 Star-Delta Starter

3.2.13 Auto -Transformer Starter

3.2.14 Rheostatic Starter

3.2.15 Switch

3.2.16 Contactor

i
i

3.2.17 Relay

•tfSft**"

W2I

3.2.18 Circuit-Breaker

PART 1 GENERAL AND COMMON ASPECTS

3.2.20 Earth Leakage Circuit Breaker

3.2.21 Residual Current Circuit Breaker

h*-

3.2.22 Surge Protective Device

\-T7^H

3.2.23 Fuse

3.2.24 Signal Lamp

3.2.25 Link

3.2.26 Distribution Board, Cubicle Box, Main Fuse
Board with Switches

■ — i

3.2.27 Socket Outlet, 5A

Y°*A

SP 30: 2011

Socket Outlet, ISA

3.2.28 Plug

3.2.29 Voltmeter

3.2.30 Ammeter

3.2.31 Wattmeter

3.2.32 Varmeter

3.2.33 Power Factor Meter

3.2.34 Ohmmeter

3.2.35 Indicating Instrument (general symbol)

3.2.36 Recording Instrument (general symbol)

3.2.37 Integrating Meter

3.2.38 Watthour Meter

3.2.39 Clock

3.2.4© Master Clock

3.2.41 Current Transformer

3.2.42 Voltage Transformer

3.2.43 Wiring on the Surface

3.2.44 Wiring in Conduit

3.2.45 Lamp

NATIONAL ELECTRICAL CODE

SP 30 : 2011

3.2.46 Lamp Mounted on a Ceiling

3.2.47 Emergency Lamp

3.2.57 Aerial

3.2.48 Spot Light

(8=

3.2.49 Flood Light

3.2.50 Heater

-am-

3.2.51 Storage Type Water Heaters

-US-

3.2.52 5e//

3.2.53 Buzzer

3.2.54 Ceiling Fan

3.2.55 Exhaust Fan

3.2.56 Fan Regulator

3.2.58 Radio Receiving Set

3.2.59 Television Receiving Set

3.2.60 Manually Operated Fire Alarm

3.2.61 Automatic Fire Detector Switch

4 LETTER SYMBOLS AND SIGNS

4.0 General

4.0.1 Quantities and units used in electrotechnology
cover in addition to electricity and magnetism other
subjects such as radiation and light, geometry,
kinematics, dynamics and thermodynamics. Several
disciplines interact with the result that terminology used
in one discipline becomes closely interrelated with that
of the other. In order to enable uniform understanding
of the meaning they represent, the letter symbols and
signs used in abbreviations for denoting quantities, their
functions and units shall conform to those recommended
in IS 3722 (Part 1) and IS 3722 (Part 2).

4.0.2 Guidance on the choice of alphabet and their type,
representation of vector quantities, symbols of units,
numerical values, and guidance on the use of subscripts
are covered in IS 3722 (Part 1).

Ready reference tables for symbols and subscripts are
contained in IS 3722 (Part 2). For the purposes of this
Code, a list of symbols, names of quantities and of
constants and subscripts referred to frequently is given
in 4.1.

4.1 Symbols and Subscripts

4.1.1 Table 1 of IS 3722 (Part 2) gives a reference list
of symbols and subscripts used in electrotechnology.

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

ANNEX A
(Clause 2)

LIST OF INDIAN STANDARDS ON GRAPHICAL SYMBOLS

IS No.

2032

(Part 15) : 1976
(Part 19) : 1977

(Part 25): 1980
3722

(Part 1) : 1983

(Part 2) : 1983

10381 : 1982

11353: 1985

12032 (Parti):
1987/IEC
60617-1 (1985)

12032 (Part 2):
1987/IEC
60617-2 (1983)

Title

Graphical symbols used in electro-
technology:

Aircraft electrical symbols
Electrical equipment used in
medical practice
Electrical installations in ships
Letter symbols and signs used in
electrical technology:
General guidelines on symbols
and subscripts

Reference tables for symbols and
subscripts

Terms (and their Hindi
equivalents) commonly used for
name plates and similar data of
electrical power equipment
Guide for uniform system of
marking and identification of
conductors and apparatus terminals
Graphical symbols for diagrams in
the field of electrotechnology:
Part 1 General information, general
index, cross reference table
Graphical symbols for diagrams in
the field of electrotechnology:
Part 2 Symbols elements,
qualifying symbols and other

IS No.

12032 (Part 3) :

12032 (Part 4):

1987/IEC

60617-4 (1984)
12032 (Part 6):

1987/IEC

60617-6 (1983)

12032 (Part 7):
1987/IEC
60617-7 (1983)

12032 (Part 8):
1987/IEC
60617-8 (1983)

12032 (Part 11):
1987/IEC
60617-11 (1983)

Title

symbols having general

application

Graphical symbols for diagrams

in the field of electrotechnology:

Part 3 Conductors and connecting

devices

Graphical symbols for diagrams in

the field of electrotechnology:

Part 4Passive components

Graphical symbols for diagrams in

the field of electrotechnology:

Part 6 Production and conversion

of electrical energy

Graphical symbols for diagrams in

the field of electrotechnology:

Part 7 Switchgear, controlgear and

protective

Graphical symbols for diagrams in

the field of electrotechnology: Part 8

Measuring instruments, lamps

and signalling devices

Graphical symbols for diagrams in

the field of electrotechnology: Part

1 1 Architectural and topographical

installation plans and diagrams

NATIONAL ELECTRICAL CODE

SP 30: 2011

SECTION 4 GUIDE FOR PREPARATION OF DIAGRAMS,
CHARTS, TABLES AND MARKING

FOREWORD

Various types of diagrams and charts are required to be
prepared during the planning and execution stages of
an electrical installation work. It is therefore necessary
to define the different types of diagrams, charts and
tables, their purposes and format and the guiding
principles for preparing them for the sake of uniformity.

This Section 4 of the Code covers general guidelines
on the subject. A list of relevant Indian Standards is
given at Annex A.

The guidelines for marking of conductors given in 3.6.
Table 1 are in line with the guidelines accepted
internationally on such matters. They provide for a
common basis for understanding and identifying
conductors and apparatus terminals, but more
important, ensure safety to operating, maintenance
personnel.

1 SCOPE

This Part 1 /Section 4 of the Code covers guidelines
for preparation of diagrams, charts and tables in
electrotechnology and for marking of conductors.

2 REFERENCES

A list of Indian Standards on general guidelines on various
types of diagrams and charts is given at Annex A.

3 PREPARATION OF DIAGRAMS, CHARTS
AND TABLES

3.0 General

3.0.1 Diagram

A diagram may show the manner in which the various
parts of a network, installation, group of apparatus or items
of an apparatus are interrelated and or interconnected.

3.0.2 Chart

A chart may show the interrelation between;

a) different operations.

b) operations and time.

c) operations and physical quantities, and

d) states of several items.

3.0.3 Table

A table replaces or supplements a diagram or a chart.

3.1 Classification According to Purpose
3.1.0 The main classifications are:

a) Explanatory diagrams,

b) Explanatory charts or tables,

c) Wiring diagrams or wiring tables, and

d) Location diagrams or tables.

3.1.1 Explanatory Diagrams

Explanatory diagrams are intended to facilitate the
study and understanding of the functioning of an
installation or equipment. Three types are defined
below:

a) Block diagram — Relatively simple diagram
to facilitate the understanding of the principle
of operation. It is a diagram in which an
installation or equipment together with its
functional interrelationships are represented
by symbols, block symbols or pictures
without necessarily showing all the
connections.

b) Circuit diagram — Explanatory diagram
intended to facilitate the understanding of the
functioning in detail. It shows by symbols an
installation or part of an installation and the
electrical connections and other links
concerned with its operation.

c) Equivalent circuit diagram — Special type
of circuit diagram for the analysis and
calculation of circuit characteristics.

3.1.2 Explanatory Charts or Tables

Explanatory charts or tables are intended to facilitate
the study of diagrams and to give additional
information. Two examples are given below:

a) Sequence chart or table — gives the
successive operation in a specified order, and

b) Time sequence chart or table — is one which
in addition takes account of the time intervals
between successive operations.

3.1.3 Wiring Diagrams or Wiring Tables

Wiring diagrams are intended to guide the making and
checking of the connection of an installation or
equipment. For an equipment, they show the internal
or external connections or both. The diagrams may
sometimes show the layout of the different parts and
accessories, such as terminal blocks and the wiring
between them.

3.1.3.1 Unit wiring diagram

Diagram is representing all connections within a unit
of an installation.

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

3.1.3.2 Interconnection diagram

Diagram representing the connections between the
different units of an installation.

3.1.3.3 Terminal diagram

Diagram showing the terminals and the internal and/or
external conductors connected to them.

NOTE — Any of the wiring diagram may be replaced or
supplemented by a table.

3.1,4 Location Diagrams or Tables

A location diagram or table contains detailed
information about the location of parts of the
equipment, for example, terminal blocks, plug-in units,
sub-assemblies, modules, etc. It shows the item
designations used in related diagrams and tables.

NOTES

1 A location diagram need not necessarily be to scale.

2 Several types of diagrams may be combined into a single
diagram, forming a mixed diagram. The same drawing may
form both an explanatory and wiring diagram.

3.2 Classification According to Method of
Representation

3.2,1 The method of representation is distinguished by:

a) the number of conductors, devices or elements
represented by a single symbol (see 3.2.1 J);

b) the arrangement of the symbols representing
the elements or parts of an item of apparatus
(for example, detached or assembled) (see
3.2.1); and

c) the placing of the symbols to correspond with
the topographical layout of the devices (see
3.2.1.3).

3.2.1.1 Number of conductors

According to the number of conductors, devices or
elements represented by a single symbol, the two
methods of representation as given below may be

distinguished.

a) Single -line representation — Two or more
conductors are represented by a single line.

In particular, a single line may represent:

1 ) circuits of a multi-phase system,

2) circuits which have a similar electrical
function,

3) circuits or conductors which belong to
the same signal path,

4) circuits which follow the same physical
route, and

5) conductor symbols which would follow
the same route on the diagram.

Several similar items of apparatus may
accordingly be represented by a single
symbol,
b) Multi-line representation — Each conductor
is represented by an individual line.

3.2.1.2 Arrangement of symbols

According to the arrangement of the symbols
representing the elements or parts of an item of
apparatus on the diagram, the methods of
representation are given below:

a) Assembled representation — The symbols for
the different parts of an item of apparatus or
of an installation or equipment are drawn in
close proximity on the diagram.

b) Semi-assembled representation — The
symbols for the different parts of an item of
apparatus or of an installation are separated
and arranged in such a way that the symbols
for mechanical linkages between the parts
which work together may be drawn easily.

c) Detached representation — The symbols for
the different parts of an item of apparatus or
of an installation are separated and arranged
in such a way that the circuits may easily be
followed.

3.2.1.3 Topographical representation

The positions of the symbols on the diagram
correspond wholly or partly to the topographical
(physical) location of items represented.

The following are examples where topographical
representation may be used.

a) Wiring diagrams,

b) Architectural diagrams, and

c) Network diagrams.

NOTE — Several of these methods of representation may be
used on the same diagram.

3.3 Item Designation

3.3.1 Item is a term used for component equipment,
plant, unit, etc, which is represented by a graphical
symbol on a diagram. The item designation is shown
at an appropriate place near the graphical symbol of
the item. This designation correlates the item on
different diagrams, parts list, circuit descriptions and
in the equipment.

3.3.2 An item designation may be used for general or
special purposes depending on the kind of information
required. Guidelines on assignment of item
designation, groups together with standard letter codes
for the same are covered in IS 8270 (Part 2).

NATIONAL ELECTRICAL CODE

SF 30 : 2011

3.4 General Rules for Diagrams

3.4.1 Paper sizes for drawings shall preferably be
according to the international A-series (see IS 1064).
The choice of drawing sizes should be decided after
taking into account the necessary factors enumerated
in 2.2 of IS 8270 (Part 2).

3.4.2 In IS 2032, different kinds of symbols as well as
symbols of different forms are shown. All the possible
examples are also not covered there. Any symbol may
be composed using the guidance from relevant Part of
IS 2032 and Part 1/Section 3 of the Code. The basic
rules for the choice of symbols shall be:

a) to use the simplest form of symbol adequate
for the particular purpose,

b) to use a preferred form wherever possible, and

c) to use the chosen form consistently
throughout the same set of documentation.

3.4.3 Specific guidelines on the application of IS 2032
(All parts) from the point of view of choice of
alternative symbols, symbol sizes, line thickness,
orientation of symbols and methods of indicating
symbol location are covered in IS 8270 (Part 3).

3.5 Interconnection Diagrams and Tables

3.5.1 Interconnection diagrams and tables provide
information on the external electrical connections
between equipment in an installation. They are used
as an aid in the fabrication of wiring and for
maintenance purposes. Information on the internal
connections of units are normally not provided but
references to the appropriate circuit diagram [see
IS 8270 (Part 4)] may be provided.

3.5.2 The diagrams may employ single or multiple
representation and may be combined with or replaced
by tables, provided clarity is maintained. Tables are
recommended when the number of interconnections
is large.

3.5.3 Guidance on layout, identification and types of
interconnection diagrams and tables are given in
IS 8270 (Part 5).

3.6 Marking and Arrangement of Conductors

3.6.0 General

3.6.0.1 The purpose of marking is to provide a means
whereby conductors can be identified in a circuit and
also after they have been detached from the terminals
to which they are connected. Main marking is a system
of marking characterizing each conductor or group of

conductors irrespective of their electrical function.
Supplementary marking is used as supplement to a
main marking based on the electrical function of each
conductor or group of conductors.

3.6.0.2 The various methods of marking applicable to
electrical installations and the equipment which form
part of them are covered in IS 5578.

3.6.1 Identification of Insulated and Bare Conductors

For the purposes of this Code, the provisions of Table 1
shall apply for the general application of marking
conductors in installation. The rules also apply for
marking conductors in assembles, equipment and
apparatus. Reference is also drawn to the provision
contained in relevant Indian Standard.

3.6.2 Arrangement of Conductors

3.6.2.0 Bus-bars and main connections which are
substantially in one plane shall be arranged in the order
given in either 3.6.2.1 or 3.6.2.2 according to the
system. The relative order remains applicable even if
any poles of the system are omitted.

3.6.2.1 AC systems

The order of phase connection shall be red, yellow and
blue:

a) When the run of the conductors is horizontal,
the red shall be on the top or on the left or
farthest away as viewed from the front.

b) When the run of the conductors is vertical,
the red shall be on the left or farthest away as
viewed from the front.

c) When the system has a neutral connection in
the same place as the phase connections, the
neutral shall occupy an outer position.

d) Unless the neutral connection can be readily
distinguished from the phase connections, the
order shall be red, yellow, blue and black.

3.6.2.2 DC systems

The arrangement shall be as follows:

a) When the run of the conductors is horizontal,
the red shall be on the top or on the left or
farthest away as viewed from the front.

b) When the run of the conductors is vertical,
the red shall be on the left or farthest away as
viewed from the front.

c) When the system is 3-wire with the
conductors in the same place, the neutral shall
occupy the middle position.

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

Table 1 Alphanumeric Notation, Graphical Symbols and Colours

(Clause 3.6.1)

SI No.

Designation of Conductors

Identification by

''Alphanumeric

Graphical

Colour ^

Notation

Symbol

(1)

(2)

(3)

(4)

(5)

Phase 1

Red

Supply ac system Phase 2

Yellow

Phase 3

Blue

Neutral

Black

Phase 1

Red

Phase 2

Yellow

ii)

Apparatus ac system phase 3

Blue

Neutral

Black

Positive

L+

Red

iii)

Supply dc system Negative

L-

Blue

Midwire

Black

iv)

Phuse
Supply dc system (single phase) NeutraJ

Red

Black

Protective conductor

Green and Yellow

vi)

Earth

No colour other than the colour of the

bare conductor. If insulated, the

colour for insulation so chosen to

avoid those listed above for

designation of other conductors

vii)

Noiseless (clean earth)

Under consideration

viii)

Frame or chassis

—

ix)

Equipotential Terminal

—

ANNEX A
(Clause 2)

LIST OF INDIAN STANDARDS ON DIAGRAMS, CHARTS, TABLES AND MARKING

IS No.

Title

IS No.

1064 : 1980

Specification for paper standard

8270

2032

sizes

Graphical symbols used in

electrotechnology :

(Part 1) :

: 1976

(Part 15): 1976

Aircraft electrical symbols

(Part 2) :

1976

(Part 19) : 1977

Electrical equipment used in

(Part 3) :

1977

medical practice

(Part 4) :

: 1977

(Part 25) : 1980

Electrical installations in ships

(Part 5) :

: 1976

5578 : 1984

Guide for marking of insulated

conductors

(Part 6) :

1983

Title

Guide for the preparation of

diagrams, charts and tables for

electrotechnology:

Definitions and classification

Item designation

General requirements for diagrams

Circuit diagram

Interconnection diagrams and

tables

Unit wiring diagrams and tables

NATIONAL ELECTRICAL CODE

SF 30: 2011

SECTION 5 UNITS AND SYSTEMS OF MEASUREMENT

FOREWORD

The International System of Units (SI) have received
worldwide acceptance and are accepted in most of the
countries. It had been introduced in India under the
Weights and Measures Act, 1976. Use of SI Units in
matters relating to electrical engineering practice has
many advantages.

This Section 5 of the Code for reasons of brevity is
restricted to electrical units only.

1 SCOPE

This Part 1 /Section 5 of the Code covers units and
systems of measurement in electrotechnology.

2 REFERENCE

The following Indian Standard may be referred for
further information:

'IS 10005 : 1994/ISO 1000 : 1992 SI units and
recommendations for the use of their multiples and of
certain other units'.

3 UNITS AND SYSTEMS OF MEASUREMENT

3.1 Absolute Units

3.1.1 Ampere (Unit of Electric Current)

A constant current which, maintained in two parallel
straight conductors of infinite length, of negligible
circular cross-section an placed at a distance of one
metre apart in a vacuum will produce a force of
2 x 10~ 7 Newton per metre length between the
conductors.

3.1.2 Coulomb (Unit of Quantity of Electricity)

The quantity of electricity conveyed in one second by
a current of one ampere.

3.1.3 Farad (Unit of Electric Capacitance)

The capacitance of an electric capacitor having a
difference of electric potential of one volt between the

plates, when it is charged with a quantity of electricity
of one coulomb.

3.1.4 Henry (Unit of Electric Inductance)

The inductance of a closed circuit in which an emf of
one volt is produced when the current in the circuits
varies at the uniform rate of one ampere per second.

3.1.5 Ohm (Unit of Electrical Resistance)

The electrical resistance between two points of a
conductor when a constant potential difference of one
volt, applied to these points, produces a current of one
ampere in the conductor, provided no emf is generated
in the conductor.

3.1.6 Volt (Unit of Electric Potential Difference)

The difference of electric potential which exists
between two points of a conductor carrying a constant
current of one ampere, when the power dissipated
between these points is one watt.

3.1.7 Weber (Unit of Magnetic Flux)

The magnetic flux which, linked with a circuit
composed of a single turn produces in it an emf of one
volt if it is uniformly reduced to zero in one second.

3.1.8 Watt (Unit of Electric Power)

The power which results in the production of energy
at the rate of 1 J/s.

3.1.9 Siemens (Unit of Electric Conductance)

The conductance of a conductor of resistance 1 ohm
and is numerically equal to 1 ohm -1 .

3.1.10 Tesla

The tesla is a magnetic flux density of 1 Wb/m 2 .

3.2 The electrical units defined in 3.1, together with
their expression in terms of other units,
recommendations on the selection of their multiples
and submultiples and supplementary remarks (if any)
are enumerated in Table 1 .

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

Table 1 Electrical Units of Measurement

(Clause 3.2)

No.
(1)

Quantity

(2)

Name Symbol Expression in Terms Expression in Terms

of Other Units of SI Base Units

(3) (4) (5) (6)

Selection of Multiples

(7)

Electric current

ampere

—

kA, mA, juA, nA, pA

ii)

Power

watt

J/s

m 2 .kgs~ 3

GW, MW, kW, mW, j/W

iii)

Quantity of electricity,
electric charge

coulomb

—

s.A

kC, juC, nC, pC

iv)

Electric potential,
potential difference,
electromotive force

volt

W/A

mlkgs^A- 1

MV,kV,mV,^V

Capacitance

farad

C/V

m 2, kg.s" 1 .A~ 1

mF, jjF, nF, pF

vi)

Electrical resistance

ohm

V/A

m 2 kg.s- 1 .A- 2

Ga,MQ.KQ,ma, ...vQ

vii)

Conductance

Siemens

A/V

m^kg-'.s" 1

kS, mS, uS

viii)

Magnetic flux

weber

V.s

m^kg.s-lA" 1

mWb

ix)

magnetic flux density

tesla

Wb/m 2

kg.s-'.A- 1

mT, juT. nT

Inductance

henry

Wb/A

m 2 kg.s- 2 .A- 2

mH,juH,nH,/?H

xi)

Conductivity

siemens/metre

S/m

—

m'kg-'.S 1 , A 1

MS/m, kS/m

xii)

Electric field strength

volt/metre

V/m

—

m.kg.s~ 1 .A~ l

M V/m, kV/m or V/mra, V/m,
raV/m, ju V/m

xiii)

Permeability

henry/metre

H/m

—

m.kg.s- 2 A- 2

jt/H/m, nH/m

xiv)

Permittivity

farad per metre

F/m

—

m-^kg-'.s 4 ^ 2

//F/m, nF/m, pF/m

xv)

Reluctance

1 per henry

H- 1

—

m^kg-'.slA 2

—

xvi)

Resistivity

ohm/metre

Q.m

—

m^kg.s^.A -2

G^m, MQ m, kQm, Clem,
mOm, /iUm, nQm

NATIONAL ELECTRICAL CODE

SF 30: 2011

SECTION 6 STANDARD VALUES

FOREWORD

Standardization of basic parameters such as voltage,
currents and frequency is one of the primary exercizes
undertaken at the national level. This standardization
helps in laying a sound foundation for further work
relating to product or installation engineering. The
values of voltages recommended as standard in this
Section are based on the contents of IS 12360 : 1988
'Voltage bands for electrical installations including
preferred voltages and frequency'.

This history of standardization of system voltages
particularly those of systems operating below medium
voltage levels is enumerated in IS 12360. Reference
to Indian Electricity Rules may also be made.

1 SCOPE

This Part 1/Section 6 of the Code covers standard values
of ac and dc distribution voltages, preferred values of
current ratings and standard system frequency.

2 REFERENCES

This Part 1 /Section 6 of the Code may be read in
conjunction with the following Indian Standards:

IS No. Title

1076 (Part 1) : 1985/ Preferred numbers: Part 1 Series
ISO 3 : 1973 of preferred numbers

12360 : 1988 Voltage bands for electrical

installations including preferred
voltages and frequency

3 STANDARD VALUES OF VOLTAGES

3.0 General

3.0.1 For the sake of completeness, all the standard
values of voltages given in IS 12360 relating to ac
transmission and distribution systems are reproduced
in this Section. However, it is noted that for most of the
types of installations covered in subsequent parts of the
Code, only the lower voltage values would be relevant.

3.0.2 For medium and low voltage of distribution
system, the original recommended standard values of
nominal voltages were 230 V for single-phase
and 230/400 V for three-phase system. However,
during 1959, to align with IEC recommendations and
in view of the economic advantages they offered,
values of 240 V single-phase and 240/415 V three-
phase had been adopted with a tolerance of ± 6 percent.
However, in view of the latest international
developments, it was decided to align Indian
Standards nominal system voltages with IEC

recommendations and accordingly revise the values
of ac nominal system voltages from 240/415 to
230/400 with the tolerance of ± 10 percent and it was
also decided to effect the complete transition by
31 December 2009, as given in IS 12360. IS 12360
may be referred for the latest values.

3.0.3 In the case of voltages above 1 kV, the importance
of highest system voltage, which are generally 10
percent above the corresponding nominal voltages
given in 2.1.2.1 is recognized and product standards
relate the voltage rating of equipment with respect to
highest system voltages only.

3.1 Standard Declared Voltage

3.1.1 Single-phase, Two -Wire System

The standard voltage shall be 240 V(see 3.0.2).

3.1.2 Three-phase System

3.1.2.1 The standard voltages for three-phase system
shall be as under:

415 V (see 3.0.2) (Voltage to neutral—

240 V) (see 3.0.2)

3.3 kV

66 kV

6.6 kV

110 kV

11 kV

132 kV

22 kV

220 kV

33 kV

400 kV

NOTES

1 However, in view of the latest international developments,
it was decided to align Indian Standards nominal system
voltages with IEC recommendations and accordingly revise
the values of a.c. nominal system voltages from 240/415 to
230/400 with the tolerance of ± 10 percent and it was also
decided to effect the complete transition by 31 December 2009,
as given in IS 12360

2 These voltages refer to the line-to-line voltage.

3 1 10 kV is not a standard voltage for transmission purposes
but this value has been included for the sake of equipment that
are required for use on the 1 10 kV systems already in existence.
It is realized that because of economic and other considerations,
extensions to existing systems at this voltage may have to be
made at the same voltage.

3.1.3 The standard dc distribution voltage shall be
220/440 V

3.2 Voltage Limits for ac Systems

3.2.1 The voltage at any point of the system under
normal conditions shall not depart from the declared
voltage by more than the values given below:

a) 6 percent in the case of low or medium voltage
(see 3.0.2); or

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

NOTE — Supply variation will become 230 V ± 10 percent
with effect from 31 December 2009. See IS 12640 : 1988 for
the latest provision.

b) 6 percent on the higher side or 9 percent on
the lower side in the case of high voltage; or

c) 12.5 percent in the case of extra high voltage.

NOTE — The permissible variations given above are in
accordance with Indian Electricity Rules, 1956, and are
applicable to the supply authorities.

3.2.2 For installation design purposes, the limits of
voltage between which the system and the equipment
used in the system shall be capable of operating
continuously are as follows:

System Voltage

Highest Voltage

Lowest Voltage

(U n )

(UJ

(1)

(2)

(3)

240 V

264 V

216 V

415 V

457 V

374 V

3.3 kV

3.6 kV

3.0 kV

6.6 kV

7.2 kV

6.0 kV

11 kV

12 kV

10 kV

22 kV

24 kV

20 kV

33 kV

36 kV

30 kV

66 kV

72.5 kV

60 kV

System Voltage

(1)

Highest Voltage

(2)

Lowest Voltage
(3)

132 kV

145 kV

120 kV

220 kV

245 kV

200 kV

400 kV

420 kV

380 kV

NOTES

1 This variation in voltage should not be confused with the
permissible variation from the declared voltage as given
in 3.2.1.

2 For system voltage 230/400 highest voltage and lowest
voltage shall be ±10 percent.

4 PREFERRED CURRENT RATINGS

4.1 The preferred current ratings shall be selected from
the R5 series. If intermediate values are required, the
same shall be selected from R10 series [see IS 1076
(Part 1)].

5 STANDARD SYSTEM FREQUENCY

5.1 The standard system frequency shall in 50 Hz.

5.2 The limits within which the frequency is to be
maintained are governed by the Indian Electricity
Rules.

NATIONAL ELECTRICAL CODE

SP 30: 2011

SECTION 7 FUNDAMENTAL PRINCIPLES

FOREWORD

The basic criteria in the design of electrical
installation are enumerated in this Section which
could be taken note of in the planning stages. The
specific nature of each occupancy calls for additional
information which are summarized in the respective
Sections of the Code.

Assistance has been derived for this Section from IEC
60364- 1 'Low- voltage electrical installations — Part 1 :
Fundamental principles, assessment of general
characteristics, definitions' issued by the International
Electrotechnical Commission. Measures for achieving
protection against the various hazards are under
consideration by the National Electrical Code Sectional
Committee. It may be added that subsequent
requirements of the Code would, however, provide
sufficient guidelines in respect of achieving the desired
level of safety.

1 SCOPE

This Part 1 /Section 7 of the Code enumerates the
fundamental principles of design and execution of
electrical installations.

2 REFERENCE

Reference has been made to the following Indian
Standard:

IS No. Title

IS 3792 : 1978 Guide for heat insulation of non-

industrial buildings

3 FUNDAMENTAL PRINCIPLES

3.0 General

3.0,1 Conformity with Indian Electricity Rules

The installation shall generally be carried out in
conformity with the requirements of the Indian
Electricity Rules, 1956 as amended from time to time,
and also the relevant regulations of the electric supply
authority concerned.

3.0.2 Materials

All materials, fittings, equipment and their accessories,
appliances, etc, used in an electrical installation shall
conform to Indian Standards wherever they exist. In
case an Indian Standard does not exist, the materials
and other items shall be those approved by the
competent authority.

3.0.3 Workmanship

Good workmanship is an essential requirement for
compliance with this Code. Unless otherwise exempted
under the Indian Electricity Rules, the work on
electrical installations shall be carried out under the
supervision of a person holding a certificate of
competency issued by a recognized authority. The
workmen shall also hold the appropriate certificate of
competency.

3.1 Coordination

3.L1 Exchange of Information

3.1.1.1 Proper coordination and collaboration between
the architect, building engineer and the electrical
engineer shall be ensured from the planning stage of
the installation. The provisions that would have to be
made for the accommodation of substation, transformer
switchgear rooms, lift wells and other spaces required
to be provided for service cable ducts, openings, etc.
in the civil work, and such other relevant data shall be
specified in advance.

3.1.1.2 In all cases, that is, whether the proposed
electrical work is a new installation or an extension to
the existing one, or a modification, the relevant
authority shall be consulted. In all such cases, it shall
also be ensured that the current carrying capacity and
the condition of the existing equipment and accessories
are adequate.

3.1.1.3 Sufficient coordination shall be ensured with
the civil architect in the initial stages itself to ensure
that sufficient building space be allotted for electrical
installation purposes such as those required for sub-
station installation, from the point of safety.

3.1.1.4 The building services plan shall also include
at the early stages all the details of services that
utilize electrical energy and the requirements of the
electrical installation in order to enable the designers
and others involved to decide the coordination to
be ensured.

3.2 Distance from Electric Lines

No building shall be allowed to be erected or re-
erected, or any additions or alterations made to the
existing building, unless the following minimum
clearances are provided from the overhead electric
supply lines:

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

No.

Type of

Supply

Line

(1) (2)

Voltage

(3)

Clearance

Vertical Hori-
m zontal, m

(4) (5)

ii)

Low and
medium
voltage

High
voltage

Up to and
including
11000V
Above 11 kVup
to and including
33 kV

iii) Extra high
voltage

2.5.

3.7

3.7
(see

Note)

1.2

2.0

■2.0

(see

Note)

NOTE — For extra high voltage lines apart from the minimum
clearances indicated, a vertical and horizontal clearance of
0.30 m for every additional kV or part thereof shall be provided.

3.3 Lighting and Ventilation

From the point of view of conserving energy, it is
essential to consider those aspects of design of
buildings as vital, which would enable use of natural
lighting and ventilation to the maximum. Attention is,
however, drawn to the general requirements stipulated
in Part 1/Section 14.

3.4 Heat Insulation

3.4.1 For information regarding recommended limits
of thermal transmittance of roofs and walls and
transmission losses due to different constructions,
reference shall be made to IS 3792.

3.4.2 Proper coordination shall be ensured to provide
for necessary arrangements to install and serve the
electrical equipment needed for the air-conditioning
and heating services in the building.

3.5 Lifts and Escalators

For information of the electrical engineer, the lift/
escalator manufacturer in consultation with the building
planners, shall advise of the electrical requirements
necessary for the lifts and escalators to be installed in
the building. General provisions are outlined in
Part 1/Section 14.

3.6 Location and Space for Electrical Equipment

Even though specific provisions regarding the choice
of location and space requirements for electrical
installation in buildings have been provided in the
relevant parts of the Code. The following aspects shall
be taken note of in general while planning the building
design:

a) Need for and location and requirements of
building substation.

b) Load centre and centre of gravity of buildings,

c) Layout,

d) Room/spaces required for electrical utility,

e) Location and requirements of switch rooms,

f) Levels of illumination, and

g) Ventilation.

4 DESIGN OF ELECTRICAL INSTALLATION

4.0 General

4.0.1 The design of the electrical installation shall take
into account the following factors:

a) The protection of persons, livestock and
property in accordance with 4.1, and

b) The proper functioning of the electrical
installation for the use intended.

4.0.2 The following factors shall therefore be kept in
view:

a) Characteristics of the available supply or
supplies,

b) Nature of demand,

c) Emergency supply or supplies,

d) Environmental conditions,

e) Cross-section of conductors,

f) Type of wiring and methods of installations,

g) Protective equipment,
h) Emergency control,

j) Disconnecting devices, and
k) Preventing of mutual influence between
electrical and non-electrical installations.

4.1 Protection for Safety

4.1.0 The requirements stated in 4.1.1 to 4.1.6 are
intended to ensure the safety of persons, livestock and
property against dangers and damage which may arise
in the reasonable use of electrical installations.

NOTE — In electrical installations, two major types of risks
exist.

a) Shock currents; and

b) Excessive temperatures likely to cause burns, fires and other
injurious effects.

4.1.1 Protection Against Direct Contact

Persons and livestock shall be protected against danger
that may arise from contact with live parts of the
installation.

The protection can be achieved by one of the following
methods:

a) Preventing a current from passing through the
body of any person or any livestock, and

NATIONAL ELECTRICAL CODE

SP 30: -2011

b) Limiting the current which can pass through
a body to a value lower than the shock
current.

4.1.2 Protection Against Indirect Contact

Persons and livestock shall be protected against dangers
that may arise from contact with exposed conductive
parts.

This protection can be achieved by one of the following
methods:

a) Preventing a fault current from passing
through the body of any person or any
livestock.

b) Limiting the fault current which can pass
through a body to a value lower than the shock
current.

c) Automatic disconnection of the supply on the
occurrence of a fault likely to cause a current
to flow through a body in contact with
exposed conductive parts, where the value of
that current is equal to or greater than the
shock current.

4.1.3 Protection Against Thermal Effects in Normal
Service

The electrical installation shall be so arranged that there
is no risk of ignition of flammable materials due to
high temperature or electric arc. Also, during normal
operation of the electrical equipment, there shall be
no risk of persons or livestock suffering burns.

4.1.4 Protection Against Overcurrent

Persons or livestock shall be protected against injury,
and property shall be protected against damage due to
excessive temperatures or electromechanical stresses
caused by any overcurrents likely to arise in live
conductors.

This protection can be achieved by one of the following
methods:

a) Automatic disconnection on the occurrence
of an overcurrent before this overcurrent
attains a dangerous value taking into account
its duration, and

b) Limiting the maximum overcurrent to safe
value and duration.

4.1.5 Protection Against Overvoltage

Persons or livestock shall be protected against injury
and property shall be protected against any harmful
effects of a fault between live parts of circuits supplied
at different voltages.

Persons or livestock shall be protected against injury
and property shall be protected against damage from

any excessive voltages likely to arise due to other
causes (for example, atmospheric phenomena or
switching voltages).

4.1.6 Methods for Protection for Safety

While the general principles of protection against
hazards in an electrical installation are given in 4.1.1
to 4.1.6 guidelines on the methods for achieving
protection and the choice of a particular protective
measure are under consideration.

4.2 Other Factors of Design

4.2.1 Characteristics of the Available Supply or Supplies

a) Nature of current: ac and/or dc,

b) Nature and number of conductors:

1) For ac:

i) phase conductors(s),
ii) neutral conductor, and
iii) protective conductor.

2) For dc:

i) conductors equivalent to those listed
above.

c) Values and tolerances;

1) voltage and voltage tolerances (see
Part 1 /Section 6),

2) frequency and frequency tolerances {see
Part 1/Section 6),

3) maximum current allowable, and

4) prospective short-circuit current (see
Part 1/Section 13).

d) Protective measures inherent in the supply,
for example, earthed (grounded) neutral or
mid- wire.

e) Particular requirements of the supply
undertaking.

4.2.2 Nature of Demand

The number and type of the circuits required for
lighting, heating, power, control, signalling,
telecommunication, etc, are to be determined by:

a) locations of points of power demand,

b) loads to be expected on the various circuits,

c) daily and yearly variation of demand,

d) any special conditions,

e) requirements for con trol, signaling,
telecommunication, etc.

4.2.3 Emergency Supply or Supplies (see also Part 2
of the Code)

a) Source of supply (nature, characteristics), and

b) Circuits to be supplied by the emergency
source.

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

4.2.4 Environmental Conditions ( see Part 1/Section 8)

4.2.5 Cross-section of Conductors

The cross- section of conductors shall be determined
according to;

a) their admissible maximum temperature,

b) the admissible voltage drop,

c) the electromechanical stresses likely to occur
due to short-circuits,

d) other mechanical stresses to which the
conductors may be exposed, and

e) the maximum impedance stresses to which the
conductors of the short-circuit protection.

4.2.6 Type of Wiring and Methods of Installations

The choice of the type of wiring and the methods of
installation depend on:

a) nature of the location,

b) nature of the walls or other parts of the
building supporting the wire,

c) accessibility of wiring to persons and livestock,

d) voltage,

e) electromechanical stresses likely to occur due
to short-circuits, and

f) other stresses to which the wiring may be
exposed during the erection of the electrical
installation or in service.

4.2.7 Protective Equipment

The characteristics of protective equipment shall be
determined with respect to their function which may
be, for example, protection against the effects of:

a) overcurrent (overload, short-circuit)

b) earth-fault current,

c) overvoltage, and

d) undervoltage and no- voltage.

The protective devices shall operate at values of current,
voltage and time which are suitably related to the
characteristics of the circuits and to the possibilities of
danger.

4.2.8 Emergency Control

Where in case of danger, there is necessity for
immediate interruption of supply, in interrupting
device shall be installed in such a way that it can be
easily recognized and effectively and rapidly
operated.

4.2.9 Disconnecting Devices

Disconnecting devices shall be provided so as to permit
disconnection of the electrical installation, circuits or
individual items of apparatus as required for
maintenance, testing, fault detection or repair.

4.2.10 Prevention of Mutual Influence Between
Electrical and Non-electrical Installations

The electrical installation shall be arranged in such a
way that no mutual detrimental influence will occur
between the electrical installation and non-electrical
installations of the building.

4.2.11 Accessibility of Electrical Equipment

The electrical equipment shall be arranged so as to
afford as may be necessary:

a) sufficient space for the initial installation and
later replacement of individual items of
electrical equipment, and

b) accessibility for operation, testing, inspection,
maintenance and repair.

NATIONAL ELECTRICAL CODE

SP 30: 2011

SECTION 8- ASSESSMENT OF GENERAL CHARACTERISTICS

OF BUILDINGS

FOREWORD

An assessment of the general characteristics of
buildings is essential before planning for the needs
of an electrical installation. This Part 1 /Section 8
covers a checklist of various factors that require
assessment.

This Part 1 /Section 8 follows the internationally
recommended method of identification of the external
influences on the electrical installation such as
environment, utilization and method of construction of
the building. Out of these influences, those which are
specifically important for specific occupancies are listed
at the relevant Sections of the Code. However, it is hoped
that this Section 8 would also enable understanding of
installations not explicitly covered by the Code.

The contents of this Part 1 /Section 8 are primarily
intended for installations inside buildings though to
the extent possible they could be utilized for outdoor
sites. However more severe conditions may prevail
at outdoor sites and these require special
considerations.

1 SCOPE

This Part 1 /Section 8 of the Code covers guidelines
for assessing the characteristics of buildings and the
electrical installation therein.

2 ASSESSMENTOFGENERALOH^yt4CIERISTICS
OF BUILDINGS

An assessment of the general characteristics of
buildings as enumerated below is essential from the
point of view of design and protection for safety of the
electrical installation. These characteristics when
assessed shall also be taken into consideration in the
selection and erection of equipment.

2.1 Identification of General Characteristics
2.1.1 Purposes, Supplies and Structure
The following shall be assessed;

a) Maximum demand and diversity from the
point of view of economic and reliable design
{see 3.2.2 of Part 1/Section 7).

b) Type of distribution system, which includes,
types of systems of live conductors and types
of system earthing.

NOTE — For types of system earthing, see Part 1/
Section 14.

c) Supply characteristics such as nature of
current, nominal voltage, prospective short-
circuit currents.

NOTE — This assessment shall include those
characteristics of main, standby and safety supply
services.

d) Division of installation from the point of view
of control, safe operation, testing and
maintenance.

2.2 Identification of External Influences on the
Electrical Installation

2.2.1 The characteristics of the following external
influences shall be assessed:

a) Environments

Ambient temperature,

Atmospheric humidity,

Altitude,

Presence of water,

Presence of foreign solid bodies,

Presence of corrosive or polluting

substances,

Mechanical stresses,

Presence of flora and/or mould growth,

Presence of fauna,

10) Electromagnetic, electrostatic or ionizing

influences,

11) Solar radiation,

12) Seismic effects,

13) Lighting, and

14)

Wind.

Utilization

Capability of persons,

Electrical resistance of human body,

Contact of persons with earth potential,

Conditions of evacuation in an

emergency, and
5) Nature of processed or stored material.
c) Construction of Buildings

1) Constructional materials, and

2) Building design.

2.2.2 Table 1 suggests the classification and
codification of external influences which require
assessment in the design and erection of electrical
installation.

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

Table 1 Assessment of General Characteristics of Buildings

(Clause 2.2.2)

No.

(1)

Class Designation

(2)

Characteristics

(3)

Application and Examples Code

(4) (5)

i) Environment

1) Ambient
temperature

The ambient temperature to be considered for
the equipment is the temperature at the place
where the equipment is to the installed
resulting from the influence of all other
equipment in the same location, when
operating, not taking into account the thermal
contribution of the equipment to be installed.
Lower and upper limits of range of ambient
temperature:

Lower Limits

Upper Limits

-60°C

+5°C

-40°C

+5°C

-25°C

+5°C

-5°C

+40°C

+5°C

+40°C

-5°C

+60°C

2) Atmospheric humidity

3) Altitude

4) Presence of water:
a) Negligible

The average temperature over a 24 hour period
must not exceed 5°C below the upper limits.
Combination of two ranges to define some
environments may be necessary. Installation
subject to temperatures outside the ranges
require special consideration.
Under consideration

< 2 000 m
> 2 000 m

Probability of presence of water is negligible

b) Free-falling drops Possibility of vertically falling drops

c) Sprays

d) Splashes

e) Jets

f) Waves

g) Immersion

h) Submersion

5) Presence of foreign
solid bodies:

a) Negligible

b) Small objects

c) Very small objects

Possibility of water falling as spray at an
angle up to 60°C from the vertical
Possibility of splashes from any direction

Possibility of jets of water from any direction

Possibility of water waves

Possibility of intermittent partial or total
covering by water

Possibility of permanent and total covering by
water

The quantity of nature of dust or foreign solid
bodies is not significant
Presence of foreign solid bodies where the
smallest dimension is not less than 2.5 mm
Presence of foreign solid bodies where the
smallest dimension is not less than 1 mm

Locations in which the walls do not
generally show traces of water but may do so
for short periods, for example, in the form of
vapour which good ventilation dries rapidly
Locations in which water vapour
occasionally condenses as drops or where
steam may occasionally be present
Locations in which sprayed water forms a
continuous film on floors and/or walls
Locations where equipment may be
subjected to splashed water, this applies, for
example, to certain external lighting fittings,
construction site equipment, etc
Locations where hosewater is used regularly
(yards, car-washing bays)
Seashore locations such as piers, beaches
quays, etc

Locations which may be flooded and or
where water may be at least 150 mm above
the highest point of equipment, the lowest
part of equipment being not more than 1 m
below the water surface
Locations such as swimming pools where
electrical equipment is permanently and
totally covered with water under a pressure
greater than 0. 1 bar

Tools and small objects of which the smallest
dimension is at least 2.5 mm
Wires are examples of foreign solid bodies
of which the smallest dimension is not less
than 1 mm

AA1
AA2
AA3
AA4
AA5
AA6

AC1

AC2

AD1

AD2

AD3
AD4

ADS
AD6

AD7

AD8

AE1
AE2
AE3

NATIONAL ELECTRICAL CODE

SP 30 : 2011

Table 1 — (Continued)

Class Designation

Characteristics

(1)

(2)

(3)

Application and Examples Code

(4) (5)

d) Dust
6) Presence of corrosive
or polluting substances:

a) Negligible

b) Atmospheric

c) Intermittent or
accidental

d) Continuous

7) Mechanical stresses:

a) Impact

Low severity
Medium severity
High severity

b) Vibration
Low severity
Medium severity
High severity

c) Other mechanical
stresses
8) Presence of fungus
and/or mould growth:

a) No hazard

b) Hazard

9) Presence of vermin:

a) No hazard

b) Hazard

NOTE — In conditions AE1 and AE3, dust
may be present but is not significant to
operation of the electrical equipment
Presence of dust in significant quantity

The quantity or nature of corrosive or
polluting substances is not significant
The presence of corrosive or polluting
substance of atmospheric origin is significant

Intermittent or accidental subjection to
corrosive or polluting chemical substances
being used or produced

Continuously subject to corrosive or polluting
chemical substances in substantial quantity

Installation situated by the sea or industrial
zones producing serious atmospheric
pollution, such as chemical works and
cement works; this type of pollution arises
especially in the production of abrasive,
insulating or conductive dusts
Location where some chemical products are
handled in small quantities and where these
products may come only accidentally into
contact with electrical equipment; such
conditions are found in factory, laboratories,
other laboratories or in locations where
hydro-carbons are used (boiler-rooms,
garages, etc)
For example, chemical works

Household and similar conditions
Usual industrial conditions
Severe industrial conditions

NOTE — Provisional classification.
Quantitative expression of impact severities is
under consideration.

NOTE — Provisional classification.
Quantitative expression of vibration severities
is under consideration.

No hazard of fungus and/or mould growth
hazard of fungus and/or mould growth

No hazard

Hazard from fauna (insects, birds, small

animals)

Household and similar conditions where the

effects of vibration are generally negligible

Usual industrial conditions

Industrial installations subject to severe

conditions

Under consideration

The hazard depends on local conditions and
the nature of fungus. Distinction should the
made between harmful growth of vegetation
or conditions for promotion of mould growth

The hazard depends on the nature of the
vermin. Distinction should be made
between:

a) presence of insects in harmful quantity or

of an aggressive nature.

b) presence of small animals or birds in

harmful quantity or of an aggressive
nature

AE4

AF1

AF2

AF3

AF4

AG1
AG2
AG3

AH1
AH2
AH3

AK1
AK2

AL1
AL2

10) Electro magnetic,

electrostatic or ionizing
influences:

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

Table 1 — (Continued)

SI Class Designation

No.

(1) (2)

Characteristics

(3)

Application and Examples Code

(4) (5)

a) Negligible

b) Stray currents

c) Electromagnetics

d) Ionization

e) Electrostatics

f) Induction

11) Solar radiation:

a) Negligible

b) Significant

12) Seismic effects:

a) Negligible

b) Low severity

c) Medium severity

d) High severity

13) Lightning:

a) Negligible

b) Indirect exposure

c) Direct exposure

14) Wind

(Under consideration)

ii) Utilization
1 ) Capability of persons:

a) Ordinary

b) Children

c) Handicapped

d) Instructed

e) Skilled

No harmful effects from stay currents,
electromagnetic radiation, electrostatic fields,
ionizing radiation or induction
Harmful hazards of stray currents
Harmful presence of electromagnetic radiation
Harmful presence of ionizing radiation
Harmful presence of electrostatic fields
Harmful presence of induced currents

Solar radiation of harmful intensity and/or
duration

Up to 30 gal (1 gal=lcm/s 2 )
Over 30 up to and including 300 gal
Over 300 up to and including 600 gal
Greater than 600 gal

Hazard from supply arrangements
Hazard from exposure of equipment

2) Electrical resistance of
the human body
classification

(Under consideration)

3) Contact of persons with
earth potential:

a) None

b) Low

c) Frequent

d) Continuous

Uninstructed persons

Children in locations intended for their

occupation.

NOTE — This class does not necessarily apply to

family dwellings

Persons not in command of all their physical and

intellectual abilities (sick persons, old persons)

Persons adequately advised or supervised by

skilled persons to enable them to avoid

dangers which electricity may create

(operating and maintenance staff)

Persons with technical knowledge or

sufficient experience to enable them to avoid

dangers which electricity may create

(engineers and technicians)

Persons in non-conducting situations
Persons do not in usual conditions make
contact with extraneous conductive parts or
stand on conducting surfaces
Persons are frequently in touch with
extraneous conductive parts or stand on
conducting surfaces
Persons are in permanent contact with
metallic surroundings and for whom the
possibility of interrupting contact is limited

Vibration which may cause the destruction
of the building is outside the classification.
Frequency is not taken into account in the
classification; however, if the seismic wave
resonates with the building, seismic effects must
be specially considered. In general, the frequency
of seismic acceleration is between and 10 Hz

Installations supplied by overhead lines.
Part of installations located outside
buildings. The risks AQ2 and AQ3 relate to
regions with a particularly high level of
thunderstorm activity

AMI

AM2
AM3
AM4
AM5
AM6

AN1
AN2

API
AP2
AP3

AP4

AQ1
AQ2
AQ3

Nurseries

Hospitals

Electrical operating areas

Closed electrical operating areas

Non-conducting locations

Locations with extraneous conductive parts,
either numerous or of large area

Metallic surroundings such as boilers and
tanks

BA1
BA2

BA3
BA4

BA5

BC1
BC2

BC3

BC4

NATIONAL ELECTRICAL CODE

SP 30 : 2011

Table 1 — (Concluded)

No.

Class Designation

Characteristics

Application and Examples

Code

(1)

(2)

(3)

(4)

(5)

4) Conditions of
evacuation in an
emergency

Low density occupation, easy conditions of

evacuation

Low density occupation, difficult conditions

of evacuation

High density occupation, easy conditions of

evacuation

High density occupation, difficult conditions

of evacuation

5) Nature of processed or
stored materials

a) No significant risks

b) Fire risks

c) Explosion risk

d) Contamination
risks

iii) Constructions of
Building

1) Constructional
materials:

a) Non-combustible

b) Combustible

2) Building Design:

a) Negligible risk

b) Propagation of fire

c) Movement

d) Flexible or unstable

Manufacture, processing or storage of
flammable materials including presence of dust
Processing or storage of explosive or low
flashpoint materials including presence of
explosive dusts

Presence of unprotected foodstuffs, pharma-
ceutics, and similar products without protection

Buildings mainly constructed of
combustible materials

Buildings of which the shape and

dimensions facilitate the spread of fire (for

example, chimney effects)

Risks due to structural movement (for

example, displacement between a building

and the ground, or settlement of ground or

building foundations)

Structures which are weak or subjects to

movement (for example, oscillation)

Buildings of normal or low height used for

habitation

High-rise buildings

Locations open to the public (theatres,

cinemas)

High-rise buildings open to the public (hotels,

hospitals, etc)

Barns, wood-working shops, paper factories
Oil refineries, hydrocarbon stores

Foodstuff industries, kitchen

NOTE — Certain precautions may be necessary in
the event of fault, to prevent processed materials
being contaminated by electrical equipment, for
example, by broken lamps

Wooden buildings

High-rise buildings, Forced ventilation
systems

Buildings of considerable length or erected on

unstable ground.

Contraction or expansion joints

Tents, air-support structures, false ceilings,

removable partitions

Flexible wiring, Installations needing support

BD1
BD2
BD3
BD4

BE1
BE2

BE3

CM
CA2

CB1
CB2

CB3

CB4

NOTES

1 Each condition of external influence is designated by a code comprising a group of two capital letters and a number as follows:

The first letter relates to the general category of external influence

A = environment

B = utilization

C = construction of buildings

The second letter relates to the nature of the external influence

A,.,

B ...

C...

The number relates to the class within each external influence

1 ...
2...
3...

For example, the code AC2 signifies:

A = environment

AC = environment altitude, and

AC2 = environment altitude > 2 000 m.

The Code given here is not intended to be used for marking equipment.

2 The characteristics defined for electrical installations are those accepted by the IEC and as applicable for electrical installations in
buildings. Influences on outdoor installations are separately defined in the respective parts of the Code.

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

For the time being, the characteristics of influences
(Table 1 , col 3) are given in descriptive language only.
Codification for the same {see Note 1), as
recommended by IEC are given at Table 1 col 5 for
information.

2.3 Compatibility

An assessment shall be made of any characteristics of
equipment likely to have harmful effects upon other
electrical equipment or other services or likely to impair
the supply. Those characteristics include, for example:

a) Transient overvoltages,

b) Rapidly fluctuating loads,

c) Starting currents,

d) Harmonic currents,

e) dc feedback,

f) High-frequency oscillations, and

g) Earth leakage currents .

2.4 Maintainability

An assessment shall be made of the frequency and
quality of maintenance the installation can reasonably
be expected to receive during its intended life. Where
an authority is to be responsible for the operation of
the installation, that authority shall be consulted. Those
characteristics are to be taken into account in applying
the requirements of this Code so that, having regard to
the frequency and quality of maintenance expected,

a) Any periodic inspection and testing and
maintenance and repairs likely to be necessary
during the intended life can be readily and
safely carried out,

b) Effectiveness of the protective measures for
safety during the intended life is ensued, and

c) Reliability of equipment for proper
functioning of the installation is appropriate
to the intended life.

NATIONAL ELECTRICAL CODE

SP 30: 2011

SECTION 9 WIRING INSTALLATIONS

FOREWORD

A major portion of fixed installation design in a
building relates to wiring installation. This Section of
the Code is primarily intended to cover guidelines on
design and construction of wiring installations which
are commonly applicable to all types of occupancies.
The requirements specified in this Section are based
on safety and reliability considerations.

The general design guidelines for wiring given in this
Section have to be carefully considered while applying
them to specific occupancies and a proper selection of
the method is to be decided depending on local
conditions. Guidance on such matters is covered in
respective Sections of the Code.

Assistance for this Section has been derived from
IEC 60364-5-52 (20001) 'Electrical installations
of buildings — Part 5-52: Selection and erection of
electrical equipment — Wiring systems'.

1 SCOPE

This Section 9 of the Code covers the essential design
and constructional requirements for electrical wiring

installations.

2 REFERENCES

A list of relevant Indian Standards on electrical wiring
is given at Annex A.

3 TERMINOLOGY

For the purpose of this Part 1 /Section 9, the definitions
given in Part 1/Section 2 of this Code and the following
shall apply.

3.1 Cabfie Ducting System — A system of closed
enclosure of non-circular sections for insulated
conductors, cable and cords in electrical installations,
allowing them to be drawn in and replaced.

3.2 Conduit Fitting — A device designed to join or
terminate one or more components of a conduit system,
or change direction.

3.3 Conduit Joint — An interface between two or more
components of a conduit system, or between a conduit
system and other equipment.

3.4 Cable Trunking System — A system of closed
enclosures comprising a base with a removable cover
intended for the complete surrounding of insulated
conductors, cables, cords and/or for the
accommodation of other electrical equipment.

3.5 Conduit System — A closed wiring system
consisting of conduits and conduit fittings for the
protection and management of insulated conductors
and/or cables in electrical or communication
installations, allowing them to be drawn in and/or
replaced, but not inserted laterally.

NOTE — Within the conduit system there shall be no sharp
edges, burrs or surface projections which are likely to
damage insulated conductors or cables or inflict injury to
the installer or user. The manufacturer shall be responsible
for providing guidelines to assist the safe installation of the
conduit system.

3.6 Distribution Board — A unit comprising one or
more protective devices against over current and
ensuring the distribution of electrical energy to the
circuits.

3.7 Luminaire — Apparatus which distributes, filters
or transforms the light transmitted from one or more
lamps and which includes all the parts necessary for
supporting, fixing and protecting the lamps, but not
the lamps themselves, and where necessary circuit
auxiliaries together with the means for connecting them
to the supply.

4 GENERAL AND COMMON ASPECTS FOR
SELECTION OF WIRING SYSTEMS

4.1 Cable and Conductors for Low/Medium Voltage

Every non-flexible cable cord for use at low/medium
voltage, busbar trunking system, and every conductor
other than a cable for use as an overhead line operating
at low medium voltage shall comply with the
appropriate Indian Standards.

Flexible cable or flexible cord shall be used for fixed
wiring only where the relevant provisions of this Code
are met.

4.1.1 Cable for ac Circuits — Electromagnetic Effects

Single-core cables armoured with steel wire or tape
shall not be used for ac circuits. Conductors of ac
circuits installed in ferromagnetic enclosure shall be
arranged so that the conductors of all phases and the
neutral conductor (if any) and the appropriate
protective conductor of each circuit are contained in
the same enclosure.

Where such conductors enter a ferrous enclosure they
shall be arranged so that the conductors are not
individually surrounded by a ferrous material, or other
provision shall be made to prevent eddy (induced)
currents.

PART 1 GENERAL AND COMMON ASPECTS

SF 30 : 2011

4.1.2 Electromechanical Stresses

Every conductor or cable shall have adequate strength
and be so installed as to withstand the
electromechanical forces that may be caused by any
current, including fault current it may have to carry in
service.

4.2 Conduits and Conduit Fittings

A conduit or conduit fitting shall comply with the
appropriate Indian Standard.

4.3 Trunking, Ducting and Fittings

Where applicable, trunking, ducting and their fittings
shall comply with IS 14927. Where IS 14927 does not
apply, non-metallic trunking, ducting and their fittings
shall be of insulating material complying with the
ignitability characteristic 'P' of relevant Indian
Standard.

4.4 Lighting Track Systems

A lighting track system shall comply with relevant
Indian Standard

4.5 Methods of Installation of Cables and
Conductors

The methods of installation of a wiring system for
which the Code specifically provides are at 6. Other
methods can be used provided that compliance with
the Code is maintained.

A bare live conductor shall be installed on insulators.
Non-sheathed cables for fixed wiring shall be enclosed
in conduit, ducting or trunking. Where cables having
different temperature ratings are installed in the same
enclosure, all the cables shall be deemed to have the
lowest temperature ratings.

4.6 Selection and Erection in Relation to External
Influences

Table 1 of Part 1/Section 8 contains a concise list of
external influences which need to be taken into account
in the selection and erection of wiring systems.

4.6.1 Ambient Temperature (AA)

A wiring system shall be selected and erected so as to
be suitable for the highest and lowest local ambient
temperature likely to be encountered. The components
of a wiring system, including cables and wiring
enclosures shall be installed or handled only at
temperatures within the limits stated in the relevant
product specification or as recommended by the
manufacturer.

4.6.2 External Heat Sources

To avoid the effects of heat from external sources one

or more of the following methods, or an equally
effective method, shall be used to-protect the wiring
system:

a) shielding.

b) placing sufficiently far from the source of
heat.

c) selecting a system with due regard for the
additional temperature rise which may occur.

d) reducing the current-carrying capacity.

e) local reinforcement or substitution of
insulating material.

NOTE — Heat from external sources may be radiated,
convected or conducted, for example

a) from hot water systems,

b) from plant appliances and luminaires,

c) from manufacturing process,

e) through heat conducting materials,

f) from solar gain of the wiring system or its surrounding
medium.

Parts of a cable or flexible cord within an accessory,
appliance or luminaire shall be suitable for the
temperatures likely to be encountered, or shall be provided
with additional insulation suitable for those temperatures.

4.6.3 Presence of Water (AD) or High Humidity (AB)

A wiring system shall be selected and erected so that
no damage is caused by high humidity or ingress of
water during installation, use and maintenance. Where
water may collect or condensation may form in a wiring
system provision shall be made for its harmless escape
through suitably located drainage points. Where a
wiring system may be subjected to waves (AD6),
protection against mechanical damage shall be afforded
by one or more of the methods given in 4,6.6 to 4.6.8.

4.6.4 Presence of Solid Foreign Bodies (AE)

A wiring system shall be selected and erected to
minimize the ingress of solid foreign bodies during
installation, use and maintenance. In a location where
dust or other substance in significant quantity may be
present (AE4: Light dust, AE5: Moderate dust or AE6:
Heavy Dust) additional precautions shall be taken to
prevent its accumulation in quantities which could
adversely affect the heat dissipation from the wiring
system.

4.6.5 Presence of Corrosive or Polluting Substances

(AF)

Where the presence of corrosive or polluting substances
is likely to give rise to corrosion or deterioration, parts
of the wiring system likely to be affected shall be
suitably protected or manufactured from materials
resistant to such substances. Metals liable to initiate
electrolytic action shall not be placed in contact with

NATIONAL ELECTRICAL CODE

SP 30: 2011

each other. Materials liable to cause mutual or
individual deterioration or hazardous degradation shall
not be placed in contact with each other.

4.6.6 Impact (AG)

A wiring system shall be selected and erected so as to
minimize mechanical damage. In a fixed installation
where an impact of medium severity (AG2) or high
severity (AG3) can occur, protection shall be afforded
by:

a) the mechanical characteristics of the wiring
system, or

b) the location selected, or

c) the provision of additional local or general
mechanical protection,

or by any combination of the above.

Except where installed in a conduit or duct which
provides equivalent mechanical protection, a cable
buried in the ground shall be of a construction
incorporating an armour or metal sheath or both, or be
of insulated concentric construction. Such cable shall
be marked by cable covers or a suitable marking tape
or by suitable identification of the conduit or duct and
be buried at a sufficient depth to avoid being damaged
by any disturbance of the ground reasonably likely to
occur.

A wiring system buried in a floor shall be sufficiently
protected to prevent damage caused by the intended
use of the floor.

Where a cable is installed under a floor or above a
ceiling it shall be run in such a position that it is not
liable to be damaged by contact with the floor or the
ceiling or their fixings. Where a cable passes through
a timber joist within a floor or ceiling construction or
through a ceiling support ( for example, under
floorboards), the cable shall be at least 50 mm measured
vertically from the top, or bottom as appropriate, of
the joist or batten. Alternatively, cable shall incorporate
an earthed metallic sheath suitable for use as a
protective conductor or shall be protected by enclosure
in earthed steel conduit securely supported, or by
equivalent mechanical protection sufficient to prevent
penetration of the cable by nails, screws, and the like.

Where a cable is to be concealed within a wall or
partition at a depth of less than 50 mm from the surface
its method of erection shall be that the cable shall be
installed within 150 mm of the top of the wall or
partition within 150 mm of an angle formed by two
adjoining walls or partitions. Where the cable is
connected to a point or accessory on the wall or
partition, the cable may be installed outside these zones
only in straight runs, either horizontally or vertically,
to the point or accessory or switch gear.

Where compliance as above is impracticable, the
concealed cable shall incorporate an earthed metallic
covering which complies with the requirements of this
Code for a protective conductor of the circuit
concerned, or shall be enclosed in earthed conduit,
trunking or ducting satisfying the requirements of this
Code for a protective conductor, or by mechanical
protection sufficient to prevent penetration of the cable
by nails, screws and the like.

4.6.7 Vibration (AH)

A wiring system supported by, or fixed to, a structure
or equipment subject to vibration of medium severity
(AH2) or high severity (AH3) shall be suitable for the
conditions and in particular shall employ cable with
fixings and connections suitable for such a situation.

4.6.8 Other Mechanical Stresses (AJ)

A wiring system shall be selected and erected so as to
minimize during installation, use and maintenance,
damage to the sheath and insulation of cables and
insulated conductors and their terminations.

Where the wiring system is designed to be
withdrawable there shall be adequate means of access
for drawing cable in or out and, if buried in the
structure, a conduit or cable ducting system for each
circuit shall be completely erected before cable is
drawn in. The radius of every bend in a wiring system
shall be such that conductors and cables shall not suffer
damage. Where a conductor or a cable is not
continuously supported it shall be supported by suitable
means at appropriate intervals in such a manner that
the conductor or cable does not suffer damage by its
own weight. Every cable or conductor used as fixed
wiring shall be supported in such a way that it is not
exposed to undue mechanical strain and so that there
is no appreciable mechanical strain on the terminations
of the conductors, account being taken of mechanical
strain imposed by the supported weight of the cable or
conductor itself. A flexible wiring system shall be
installed so that excessive tensile and torsional stresses
to the conductors and connections are avoided.

4.6.9 Presence of Flora and/or Mould Growth (AK)

Where expected conditions constitute a hazard (AK2),
the wiring system shall be selected accordingly or
special protective measures shall be adopted.

4.6.10 Presence of Fauna (AL)

Where expected conditions constitute a hazard (AL2),
the wiring system shall be selected accordingly or
special protective measures shall be adopted.

4.6.11 Solar Radiation (AN)

Where significant solar radiation (AN2) is experienced

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

or expected, a wiring system suitable for the conditions
shall be selected and erected or adequate shielding shall
be provided.

4.6.12 Building Design (CB)

Where structural movement (CB3) is experienced or
expected, the cable support and protection system
employed shall be capable of permitting relative
movement so that conductors are not subjected to
excessive mechanical stress.

For flexible or unstable structures (CB4) flexible wiring
systems shall be used.

4.7 Current — Carrying Capacity of Conductors

The current to be carried by any conductor for sustained
periods during normal operation shall be such that the
appropriate temperature limit specified is not exceeded.
See various parts of IS 3961 for details.

4.8 Voltage Drop in Consumer's Installations

Under normal service conditions the voltage at the
terminals of any fixed current-using equipment shall
be greater than the lower limit corresponding to the
Indian Standard relevant to the equipment wherever
existing. In the absence of such a standard, then the
Voltage at the terminals shall be such as not to impair
the safe functioning of the equipment.

The voltage drop between the origin of the installation
(usually the supply terminal) and the fixed current-
using equipment should not exceed 4 percent of the

normal voltage of the supply.

A greater voltage drop maybe accepted for a motor
during starting periods and for other equipment with
high inrush currents provided it is verified that the
voltage variations are within the limits specified in the
relevant Indian Standards for the equipment or, in the
absence of a Indian Standard, in accordance with the
manufacturer's recommendations. Temporary
conditions such as voltage transients and voltage
variation due to abnormal operation may be
disregarded.

4.9 Cross-sectional Areas of Conductors

4.9.1 Phase Conductors in ac Circuits and Live
Conductors in dc Circuits

The nominal cross-sectional area of phase conductors
in ac circuits and of live conductors in dc circuits shall
be not less than the values specified in Table 1.

4.10 Neutral Conductors

For a polyphase circuit in which imbalance may occur
in normal service, through significant inequality of
loading or of power factor in the various phases, or
through the presence of significant harmonic currents
in the various phases, the neutral conductor shall have
a cross-sectional area adequate to afford compliance
with permissible conductor operating temperature for
the maximum current likely to flow in it.

For a polyphase circuit in which serious imbalance is
unlikely to occur in normal service, other than a

Table 1 Minimum Nominal Cross-sectional Area of Conductor

{Clause 4.9.1)

No.

(1)

Type of Wiring System

(2)

Use of the Circuit

(3)

Conductor

-«**_

Material

Minimum permissible nominal

cross-sectional area

mm 2

(4)

(5)

1.5

J~Cu

Lai

2.5

10 (see Note 1)

0.5 (see Note 2)

As specified in the relevant

Indian Standard

0.5 {see Note 2)

0.5

Cables and insulated conductors f Lighting circuits
) Power Circuits

ii) Bare conductors

iii)

L Signalling and control circuits
[Power circuits

Is,

Flexible connections with
insulated conductors and cables

gnalling and control circuits
For a specific appliance

For any other application

Extra low voltage circuits for special

applications

NOTES

1 Connectors used to terminate aluminium conductors shall be tested and approved for this specific use.

2 In multicore flexible cables containing 7 or more cores and in signalling control circuits intended for electronic equipment a
minimum nominal cross-sectional area of 0. 1 mm is permitted.

NATIONAL ELECTRICAL CODE

SP 30: -2011

discharge lighting current, multi-core cables
incorporating a reduced neutral conductor in
accordance with the appropriate Indian Standard may
be used. Where single — core cables are used in such
circuits, the neutral conductor shall have a
cross-sectional area appropriate to the expected value
of the neutral current.

In a discharge lighting circuit the neutral conductor
shall have a cross- sectional area not less than that of
the phase conductor(s).

4.11 Electrical Connections

4.11.1 Connections Between Conductors and Between
a Conductor and Equipment

Every connection between conductors and between a
conductor and equipment shall provide durable
electrical continuity and adequate mechanical strength
{see 4.6.8).

4.11.2 Selection of Means of Connection

The selection of the means of connection shall take
account, as appropriate, of the following:

a) material of the conductor and its insulation.

b) number and shape of the wires forming the
conductor.

c) cross- sectional area of the conductor.

d) number of conductors to be connected
together.

e) temperature attained by the terminals in
normal service such that the effectiveness of
the insulation of the conductors connected to
them is not impaired.

f) where a soldered connection is used the design
shall take account of creep, mechanical stress
and temperature rise under fault current
conditions.

g) provision of adequate locking arrangements
in situations subject to vibration or thermal
cycling.

'4.11.3 Enclosed Connections

Where a connection is made in an enclosure. The
enclosure shall provide adequate mechanical protection
and protection against relevant external influences.
Every termination and joint in a live conductor or a
PEN conductor shall be made within one of the
following or a combination thereof:

a) a suitable accessory complying with the
appropriate Indian Standard.

b) an equipment enclosure, complying with the
appropriate Indian Standard.

c) a suitable enclosure of material complying

with the relevant glow wire test requirements
of IS 11000 (Part 2/Secl).

d) an enclosure formed or completed with
building material considered to be non-
combustible when tested appropriate Indian
Standard relating to IS 3808.

e) an enclosure formed or completed by part of
the building structure, having the ignitability
characteristic 'P' as specified in appropriate
Indian Standard.

Cores of sheathed cables from which the sheath has
been removed and non-sheathed cables at the
termination of conduit, ducting or trunking shall be
enclosed as per specified enclosure at (b) above.

4.11.4 Accessibility of Connections

Except for the following, every connection and joint
shall be accessible for inspection, test and maintenance:

a) a compound-filled or encapsulated joint.

b) a connection between a cold tail and a heating
element (for example, a ceiling and floor
heating system, a pipe trace-heating system).

c) a joint made by welding, soldering, brazing
or compression tool.

4.12 Selection and Erection to Minimize the Spread

of Fire

4. 12. 1 Risk of Spread of Fire

The risk of spread of fire shall be minimized by
selection of an appropriate material and erection in
accordance with this Code. The wiring system shall
be installed so that the general building structural
performance and fire safety are not materially reduced.
A part of a wiring system which complies with the
requirements of the relevant Indian Standard, which
standard has no requirement for testing for resistance
to the propagation of flame, shall be completely
enclosed in non-combustible building material having
the ignitability characteristic "P".

Where a wiring system passes through elements of
building construction such as floors, walls, roofs,
ceilings, partitions or cavity barriers, the openings
remaining after passage of the wiring system shall be
sealed according to the degree of fire resistance
required of the element concerned (if any).

Where a wiring system such as conduit, cable ducting,
cable trunking, busbar or busbar trunking penetrates
elements of building construction having specified fire
resistance it shall be internally sealed so as to maintain
the degree of fire resistance of the respective element
as well as being externally sealed to maintain the
required fire resistance. A non-flame propagating

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

wiring system having a maximum internal
cross-section of 710 mm 2 need not be internally sealed.

Except for fire resistance over one hour, this
requirement is satisfied if the sealing of the wiring
system concerned has been type tested by the method
specified in relevant Indian Standard.

Each sealing arrangement used as above shall comply
with the following requirements:

a) It shall be compatible with the material of the
wiring system with which it is in contact, and

b) It shall permit thermal movement of the
wiring system without reduction of the sealing
quality,

c) It shall be removable without damage to
existing cable where space permits future
extension to be made, and

d) It shall resist relevant external influences to
the same degree as the wiring system with
which it is used.

4.12.2 Erection Conditions

During the erection of a wiring system temporary
sealing arrangements shall be provided as appropriate.
During alteration work sealing which has been
disturbed shall be reinstated as soon as practicable.

4.12.3 Verification

Each sealing arrangement shall be visually inspected
at an appropriate time during erection to verify that it
conforms to the manufacturer's erection instructions
and the details shall be recorded.

4.13 Proximity to Other Services

4.13.1 Proximity to Electrical Services

4.13.1.1 Neither an extra-low voltage nor a low voltage
circuit shall be contained within the same wiring system
as a circuit of nominal voltage exceeding that of low
voltage unless every cable is insulated for the highest
voltage present or one of the following methods is
adopted:

a) each conductor in a multicore cable is
insulated for the highest voltage present in
the cable, or is enclosed within an earthed
metallic screen of current-carrying capacity
equivalent to that of the largest conductor
enclosed within the screen, or

b) the cables are insulated for the irrespective
system voltages and installed in a separate
compartment of a cable ducting or cable
trunking system, or have an earthed metallic
covering.

4.13.1.2 A low voltage circuit shall be separated from
an extra-low voltage circuit.

4.13.1.3 Where an installation comprises circuits for
telecommunication, fire-alarm or emergency lighting
systems as well as circuits operating at low voltage
and connected directly to a mains supply system,
appropriate precautions shall be taken to prevent
electrical contact between the cables of the various
types of circuit.

4.13.1.4 Fire alarm and emergency lighting circuits
shall be segregated from all other cables and from each
other.

4.13.1.5 Where a common conduit, trunking, duct or
ducting is used to contain cables of category 1 and
category 2 circuits, all cables of category 1 circuits
shall be effectively partitioned from the cables of
category 2 circuits, or alternatively the latter cables
shall be insulated in accordance with the requirements
of the clauses for the highest voltage present in the
category 1 circuits {see also 4.13.1.8).

4.13.1.6 Where a category 3 circuit is installed in a
channel or trunking containing a circuit of any other
category, the circuits shall be segregated by a
continuous partition such that the specified integrity
of the category 3 circuit is not reduced. Partitions shall
also be provided at any common outlets in a trunking
system accommodating a category 3 circuit and a
circuit of another category. Where mineral-insulated
cable, or cable whose performance complies with
appropriate Indian Standard relating to specification
for performance requirements for cables required to
maintain circuit integrity under fire conditions, is used
for the category 3 circuit such a partition is not normally
required.

4.13.1.7 In conduit, duct, ducting or trunking systems,
where controls or outlets for category 1 and category 2
circuits are mounted in or on a common box,
switchplate or block, the cables and connections of the
two categories, of circuit shall be segregated by a
partition which, if of metal, shall be earthed. .

4.13.1.8 Where cores of a category 1 and a category 2
circuit are contained in a common multicore cable,
flexible cable or flexible cord, the cores of the category
2 circuit shall be insulated individually or collectively
as a group, in accordance with the requirements of this
Code, for the highest voltage present in the category 1
circuit, or alternatively shall be separated from the cores
of the category 1 circuit by an earthed metal screen of
equivalent current-carrying capacity to that of the cores
of the category 1 circuit. Where terminations of the
two categories of circuit are mounted in or on a

NATIONAL ELECTRICAL CODE

SP 30 : 2011

common box, switchplate, or block, they shall be
segregated in accordance with 4.13.1.7.

4.13.2 Proximity to Non-electrical Services

4.13.2.1 Where a wiring system is located in close
proximity to a non-electrical service both the following
conditions shall be met:

a) the wiring system shall be suitably protected
against the hazards likely to arise from the
presence of the other service in normal use, and

b) protection against indirect contact shall be
afforded in accordance with Part 1 /Section 7
of this Code.

4.13.2.2 A wiring system shall not be installed in the
vicinity of a service which produces heat, smoke or
fume likely to be detrimental to the wiring, unless
protected from harmful effects by shielding arranged
so as not to affect the dissipation of heat from the wiring.

4.13.2.3 Where a wiring system is routed near a service
liable to cause condensation (such as water, steam or
gas services ) precautions shall be taken to protect the
wiring system from deleterious effects.

4.13.2.4 Where a wiring system is to be installed in
proximity to a non-electrical service it shall be so
arranged that any foreseeable operation carried out on
either service will not cause damage to the other.

4.13.2.5 Any metal sheath or armour of a cable
operating at low voltage, or metal conduit, duct, ducting
and trunking or bare protective conductor associated
with the cable which might make contact with fixed
metalwork of other services shall be either segregated
from it, or bonded to it.

4.13.2.6 No cable shall be run in a lift (or hoist) shaft
unless it forms part of the lift installation as defined in
the appropriate Indian Standard relating to Lifts and
Service Lifts.

4.14 Selection and Erection in Relation to
Maintainability, Including Cleaning

Where any protective measure must be removed in
order to carry out maintenance, reinstatement of the
protective measure shall be practicable without
reducing the original degree of protection. Provision
shall be made for safe and adequate access to all parts
of the wiring system which may require maintenance.

5 MAINS INTAKE AND DISTRIBUTION OF
ELECTRICAL ENERGY IN. CONSUMERS'

PREMISES

5.1 Distribution Board System

Distribution board system, also known as 'Distribution
Fuse Board System' or 'Distribution Miniature Circuit

Breaker (MCB) Board System' is most commonly
adopted for distribution of electrical energy in a
building. Appropriate protection shall be provided at
distribution boards and at all levels of panels and
switchboards for all circuits and sub-circuits against
short circuit, over-current and other parameters as
required. The protective device shall be capable of
interrupting maximum prospective short circuit current
that may occur, without danger. The ratings and settings
of fuses and the protective devices shall be co-ordinated
so as to afford selectivity in operation. Where circuit-
breakers are used for protection of a main circuit and
of the sub-circuits derived there from, discrimination
in operation may be achieved by adjusting the
protective devices of the sub-main circuit breakers to
operate at lower current settings and shorter time-lag
than the main circuit-breaker. It is recommended to
provide residual current device (RCD) of 300/500 mA
rating as part of the main board at the entry of the
building and of 30 mA rating as part of the sub-
distribution board.

Where high rupturing capacity (HRC) type fuses are
used for back-up protection of circuit breakers, or
where HRC fuses are used for protection of main
circuits, and circuit-breakers for the protection of sub-
circuits derived therefrom, in the event of short-circuits
protection exceeding the short-circuits protection
exceeding the short-circuits capacity of the circuit
breakers, the HRC fuses shall operate earlier than the
circuit-breakers; but for smaller overloads within the
short-circuit capacity of the circuit-breakers, the circuit-
breakers shall operate earlier than the HRC fuse blows.
If rewireable type fuses are used to protect sub-circuits
derived from a main circuit protected by HRC type
fuses, the main circuit fuse shall normally blow in the
event of a short-circuit or earth fault occurring on sub-
circuit, although discrimination may be achieved in
respect of overload currents. The use of rewireable
fuses is restricted to the circuits with short-circuit level
of 4 kA; for higher level either cartridge or high
rupturing capacity (HRC) fuses shall be used.

A fuse carrier shall not be fitted with a fuse element
larger than that for which the carrier is designed. The
current rating of a fuse shall not exceed the current
rating of the smallest cable in the circuit protected by
the fuse. Every fuse shall have its own case or cover
for the protection of the circuit and an indelible
indication of its appropriate current rating in an
adjacent conspicuous position.

In Fig. 1, the two copper strips (busbars) fixed in a
distribution board of hard wood or metal or other non-
metal insulating case are connected to the "supply
mains" through a linked switch with fuse or linked
circuit breaker on each live conductor, so that the
installation can be switched off as whole from both

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

DISTRIBUTION
BOARD

CIRCUIT N0.2

Fig. 1 A Typical Distribution Board System

poles of the supply, if required. A fuse or MCB is
inserted in the phase pole of each circuit, so that each
circuit is connected up through its own particular fuse
or MCB. The lamps, fans, socket outlets for other
domestic appliances consisting each circuit need not
necessarily be in the same room or even on the same
floor in case of a small building and simply allocated
to each circuit in such a way that the raceways or runs
for connecting them is most convenient and
economical. The distribution board has 4 ways for four
circuits but the number of ways and the circuits can be
more, provided the cable feeding the board is large
enough to carry the total load current.

The practice in residential and similar commercial
buildings is to restrict the maximum number of points
of lights, fans and socket outlets in a final circuit. In
order to ensure safety, in case more points are required
to be connected to the supply, then it is to be done by
having more than one final circuits.

5.1.1 Main and Branch Distribution Board Systems

5.1.1.1 The rating or setting of over-current protection
devices shall be so chosen as to be suitable for
protection of cables and conductors used in the circuit.
Main distribution board shall be provided with a circuit-
breaker on each pole of each circuit, or a switch with a
fuse on the phase or live conductor and a link on the
neutral or earthed conductor of each circuit. The
switches shall always be linked. Main and branch
distribution boards shall be provided, along with surge
protective device and earth leakage protective device
(incoming), with a fuse or a miniature circuit breaker
or both of adequate rating/setting on the live conductor
of each sub-circuit and the earthed neutral conductor

shall be connected to a common link and be capable
of being disconnected individually for testing purposes.
At least one spare circuit of the same capacity shall be
provided on each branch distribution board. Further,
the individual branching circuits (outgoing) shall be
protected against overcurrent with miniature circuit
breaker of adequate rating. In residential/industrial
lighting installations, the various circuits shall be
separated and each circuit shall be individually
protected so that in the event of fault, only the particular
circuit gets disconnected.

5.1.1.2 Functionally the residential installation wiring
shall be separate for ceiling and higher levels in walls,
portable or stationery plug in equipments. For devices
consuming high power and which are to be supplied
through supply cord and plug, separate wiring shall be
done. For plug-in equipment provisions shall be made
for providing ELCB protection in the sub-distribution
board. It is preferable to have additional circuit for
kitchen and bathrooms. Such sub-circuit shall not have
more than a total of ten points of light, fans and 6 A
socket outlets. The load of such circuit shall be
restricted to 800 W. If a separate fan circuit is provided,
the number of fans in the circuit shall not exceed ten.
Power sub-circuit shall be designed according to the
load but in no case shall there be more than two 16A
outlets on each sub-circuit. The circuits for lighting of
common area shall be separate. For large halls 3 -wire
control with individual control and master control shall
be made for effective conservation of energy.

5.1.1.3 In industrial and other similar installations
requiring the use of group control for switching
operation circuits for socket outlets may be kept
separate from fans and lights. Normally, fans and lights

NATIONAL ELECTRICAL CODE

SP 30 : 2011

may be wired on a common circuit, however, if need
is felt separate circuits may be provided for the two.
The load on any low voltage sub-circuit shall not exceed
3 000 W. In a case of new installation, all circuits and
sub-circuits shall be designed by making a provision
of 20 percent increase in load due to any future
modification. Power sub-circuits shall be designed
according to the load but in no case shall there be more
than four outlets on each sub-circuit. In industrial
installations the branch distribution board shall be
totally segregated for single-phase distribution and
wiring.

5.1.1.4 In wiring installations at special places like
construction sites, stadium, shipyards, open yards in
industrial plants, etc, where a large number of high
wattage lamp may be required, there shall be no
restriction of load on any circuit but conductors used
in such circuits shall be of adequate size for the load
and proper circuit protection shall be provided.

5.1.1.5 In large buildings, however, if only one
distribution board were used, some of the points would
be at a considerable distance from it and in such cases
it is advisable to employ sub-distribution boards
(known as final circuit distribution boards) known as
branch distribution boards either to save cable or to
prevent too great voltage drop at the more distant points
(lamps, fans or other appliances). In such cases, the
main distribution board controls the distribution circuits
to each sub-distribution board from which the final
circuits to loads are taken as shown in Fig. 2.

5.1.1.6 The number of,

a) sub-main circuits (also called distribution
circuits) from main distribution board to sub-
distribution boards.

b) sub-distribution boards, also called branch
distribution boards or final circuit distribution
boards.

c) final circuits to loads, are decided as per the
number of points to be wires and load to be
connected per circuit and total load to be
connected to the supply system.

5.1.1.7 For determination of load of an installation,
the following ratings may be assumed, unless the values
are known or specified:

Connected Device

Rating for Calculating
Connected Load

Fluorescent lamp
Incandescent lamp, fan
6A socket outlet

16A socket outlet

Exhaust fans, fluorescent
lamps other than single
lamp, compact fluorescent
lamps, HVMV lamps,
HVSV lamps

40 W

60 W

100 W unless the actual

value of loads are

specified

1000 W unless the

actual value of loads are

specified

according to their

capacity, control gear

losses shall be also

considered as applicable

5.2 Distribution Boards

Distribution boards which provide plenty of wiring
space having terminals of adequate size to
accommodate the cables which will be connected to
them should be selected. Very often it is necessary to
install a cable which is larger than would normally be
required, in order to limit voltage drop, and take

sua MAIN

--, DISTRIBUTION

t BOARD /NO.A

4-,

SUB-CIRCUIT
N0.2
i M 1-2 L3

C-L

It »-3

SUB-CIRCUIT N0.1

Fig. 2 Typical House- wiring Circuit

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

account of the presence of harmonics, variation of
voltage; and sometimes the main terminals are not of
sufficient size to accommodate these larger cables.
Therefore distribution boards should be selected with
main terminals of sufficient size for these larger cables.

5.2.1 Branch Distribution Boards

Branch distribution boards shall be provided, along
with surge protective device and earth leakage
protective devices (incoming), with a fuse or a
miniature circuit breaker or both of adequate rating /
setting chosen in accordance with IS 732 on the live
conductor of each sub-circuit and the earthed neutral
conductor shall be connected to a common link and be
capable being disconnected individually for testing
purposes. At least one spare circuit of the same capacity
shall be provided on each branch distribution board.
Further the individual branching circuits (outgoing)
shall be protected against over current with miniature
circuit-breaker of adequate rating. In residential /
industrial lighting installation, the various circuits shall
be separated and each circuit shall be individually
protected so that in the event of fault, only the particular
circuit gets disconnected.

There are three types of distribution boards,

a) those fitted with rewirable fuse links;

b) those fitted with HBC fuse links; and

c) those fitted with circuit-breakers.

Refer to Fig. 3 for the above mantioned protective
devices.

There are several reservations to the use of rewirable
fuses. It is difficult to prevent the replacement of
rewirable fuse link by a larger size fuse link than the
fuse link chosen at the time of the installation. If the
fuse links are not of appropriate size to match the
current carrying capacity of the installed circuit, it
would lead to short-circuit and earth fault.

Distribution boards can be fitted with MCBs or HBC
fuse links. Distribution boards fitted with miniature
circuit-breakers are more expensive in their first cost,
but they have an advantage that they can incorporate
an earth leakage trip. Miniature circuit-breakers are
obtainable in ratings from 6 A to 63 A, all of which are
of the same physical size, and are therefore easily
interchangeable. However, they must not be
interchanged without first making sure that are of the
correct rating for the circuits they protect. Another
advantage of using MCBs is that they can easily be
reset after operation.

FUSE BASE

HEAT-RESISTANT
PADDING

FUSE ELEMENT

3A Semi-enclosed Rewirable Fuses
PORCELAIN BODY DETECTOR STRIP CONNECTION LUG

QUARTZ FILLING

FUSE. ELEMENT

METAL CAP

3B High Breaking Capacity (HBC) Fuse
Fig. 3 Protective Devices {Continued)

NATIONAL ELECTRICAL CODE

SP 30: 2011

3C High Breaking Capacity (HBC) Fuse

3D Miniature Circuit Breaker
Fig. 3 Protective Devices

5.2.2 Installation of Distribution Boards

5.2.2.1 The distribution boards shall be located as near
as possible to the centre of the load they are intended
to control. The location should be convenient and
economical for installation and use. Where two and/or
more distribution fuse-boards feeding low voltage
circuits are fed from a supply of medium voltage, these
distribution boards shall be:

a) arranged so that it is not possible to open two
at a time, namely, they are interlocked and
the metal case is marked 'Danger 415 Volts'
and identified with proper phase marking and
danger marks; or

b) installed in a room or enclosure accessible to
only authorized persons.

5.2.2.2 In wiring branch distribution board, total load
of consuming devices shall be divided as far as possible
evenly between the number of ways in the board
leaving spare circuits for future extension. All low
voltage distribution boards shall be marked 'Lighting'
or 'Power' or 'Lighting and Power', as the case may
be, and also marked with the voltage and number of
phases of the supply. Each shall be provided with a
circuit list giving diagram of each circuit which it

controls and the current rating of the circuit and size
of fuse element. If a distribution board is recessed into
a wall which is constructed of combustible materials
such as wood, the case must be of metal or other non-
combustible material.

5.2.2.3 Distribution boards shall be of either metal-
clad type, or air insulated type. But, if exposed to
weather or damp situations, these shall be of the
weatherproof type and, if installed where exposed to
explosive dust, vapour or gas, these shall be of
flameproof type in accordance with IS 5571. In
corrosive atmospheres, these shall be treated with anti-
corrosive preservative or covered with suitable plastic
compound.

5.2.3 Wiring of Distribution Boards

5.2.3.1 The wiring shall be done on a distribution
system through main and/or branch distribution boards.
Main distribution board shall be controlled by a linked
circuit-breaker or linked switch with fuse. Each
outgoing distribution circuit or sub-main circuit from
main distribution board to sub-distribution boards shall
be provided with linked disconnector switch or linked
MCB. Each outgoing final circuit from a main
distribution board or branch distribution board shall

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

be controlled by a miniature circuit-breaker (MCB) or
a fuse on the phase or line conductor as in the case of
single phase neutral (SPN) distribution board or three
phase neutral distribution board. The branch
distribution board shall be controlled by a linked
switchfuse or linked circuit-breaker. Each outgoing
circuit shall be provided with a fuse or miniature circuit
breaker (MCB) of specified rating on the phase or live
conductor.

5.2.3.2 Three pole neutral (TPN) distribution boards
are not generally recommended to be used for single
phase 2 wire final circuit distribution. However, the
use of TPN fuse distribution boards or TPN MCB
distribution boards for single phase 2 wire final circuit
distribution have come to practice and the same is
permissible, provided the size of the neutral conductor
wire is carefully designed, taking the unbalanced load
condition, harmonic generation of loads etc.

5.2.3.3 The neutral conductors (incoming and
outgoing) shall be connected to a common link (multi-
way connector) in the distribution board, and be
capable of being disconnected individually for testing
purposes. The wiring throughout the installation shall
be such that there is no break in the neutral wire except
in the form of a linked switchgear.

5.2.3.4 There shall be at least two ring circuits — one
for light current (known as light power) 6A socket
outlets and another for heavy current (known as heavy
power) 16A socket outlets to connect heavy current
domestic appliances. Similarly, heavy current wiring
shall be kept separate and distinct from "light current"
wiring, from the level of circuits, that is, beyond the
branch distribution boards. Lights, fans and call bells
shall be wired in the light current circuits.

5.2.3.5 Wiring shall be separate or essential loads, that
is, those fed through standby supply and non essential
loads throughout. Wiring for the safety services shall
be separate and distinct. Unless and otherwise
specified, wiring shall be done only by the "Looping
System". Phase or live conductors shall be looped at
the switch boxes and neutral conductors at the point
outlets. Where "joint box system" is specified for
installation, all joints in the conductors shall be made
by means of approved mechanical connector in suitable
and approved junction boxes.

5.2.3.6 The balancing of circuits in three wire or poly
phase installations shall be arranged before hand.

5.2.4 Location of Distribution Boards

5.2.4.1 Distribution boards should preferably be sited
as near as possible to the centre of the loads they are
intended to control. This will minimize the length and
cost of final circuit cables, but this must be balanced
against the cost of submain cables. Best location of

distribution boards depends on the availability of
suitable stanchions or walls, the case with which circuit
wiring can be run to the position chosen, accessibility
for replacement of fuselinks, and freedom from
dampness and adverse conditions (if exposed to the
weather or damp conditions, a distribution board must
be of the weather proof type) The distribution boards
shall not be more than 2 m above room floor level.

5.2.4.2 Where distribution boards (which are fed from
a supply exceeding 230 V) feed circuits with a voltage
not exceeding 230 V then precautions must be taken
to avoid accidental shock at the higher voltage between
the terminals of two lower voltage boards. Where the
voltage exceeds 230 V, a clearly visible warning label
must be provided, worded "400/415 V BETWEEN
ADJACENT ENCLOSURES". These warning notices
should be fixed on the outside of busbar chambers,
distribution boards or switchgear, whenever voltage
exceeding 230 V exists.

5.2.5 Feeding Distribution Board

When more than one distribution board is fed from a
single submain cable or from a rising bus bar trunking,
it is advisable to provide local isolation near each
distribution board {see Fig 4). It is also good practice
to provide a local isolator for all distribution boards
which are situated remote from the main switchboard
{see Fig. 5). If the main or submain cables consist of
bare or insulated conductors in metal trunking, it is
very often convenient to fit the distribution board
adjacent to the rising trunking, and to control each with
fusible cutouts or switchfuse.

5.2.6 Circuit Charts and Labelling

The diagrams, charts or tables shall be provided to
indicate for each circuit:

a) The outlets served,

b) Size and type of cable, and

c) Rating of fuse or protective device.

These should be fixed in, or in the vicinity of the
distribution board, and fitted in glazed frames or in
plastic envelops for protection.

5.2.7 Marking Distribution Boards

a) All distribution boards should be marked with
a letter or number, or both, preferably with
the prefix *L' for lighting, 'S' for socket and
'P' for power.

b) They should also be marked with the voltage
and the type of supply, and if the supply exceeds
230V a DANGER notice must be fixed.

c) When planning an installation, a margin of
spare fuseways should be provided usually
about 20 percent of the total.

NATIONAL ELECTRICAL CODE

SP 30: 2011

FINAL CIRCUITS

MAIN FUSeSWITCM

NOTE — The cables feeding the ring will share the load and may therefore be reduced accordingly. This arrangement enables the ring
to be broken by one of the isolators in the event of a fault a one end of the ring, in which case the load must be reduced.

Fig. 4 Single Line Diagram of a Typical Ring Main Feeding Six Distribution Boards

O-

6-WAY 15A

DISTRIBUTION

SOARDS

I I

SPARS
WAYS

Ha™

fOWAV 9 $OOA

D1STRI3UTION

8QARD

MAIN
J SWITCH

NOTE — It is recommended that distribution boards located remote from main switchgear be provided with local isolators.

Fig. 5 Single Line Diagram Showing Six Final Distribution Boards Fed by
Radial Submains from a Main Distribution Board

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

d) Metal distribution boards should be provided
with plugged holes to enable additional
conduits or multicore cables to be easily
connected in future.

53 Approximate Estimates of Allowable Voltage
Drop in Different Farts of Wiring System of a Large
Building

There is no hard and fast rule in this respect. Ordinarily,
however, in a lighting circuit containing lights and fans,
the total voltage drop is kept within 3 percent of the
declared voltage. The maximum allowable voltage drop
is 1 V from main fuse to main distribution board, 4.5 V
from main distribution board to each sub-distribution
board and 1.5 V in each final sub-circuit. The voltage
drop in the connection line of a pump motor in a house
may go up to 7.5 percent of the declared voltage, but
as is the case with a lighting circuit, it is recommended
to keep this drop within 3 percent, if possible.

5.4 Correct Estimation of Sizes of Cables

5.4.1 If the size of cable is determined on the basis of
total load connected in the circuit, that is, on the basis
of sum of wattage of all lamps, fans, wall-plugs, etc,
the size will be very large. However, all lamps, fans,
wall-plugs etc, may not be in use simultaneously at a
given time, and it is possible that all the points are not
loaded to their full capacity. For these reasons it is
considered to be sufficiently accurate if an estimate is
prepared according to 5.1.1.7 and the criteria of
considering two-thirds of total wattage of the circuit,
that is, the total wattage of every final sub-circuit is
obtained by adding up the wattage of individual loads
connected to that circuit and two-thirds of this total
wattage should be taken into consideration for
determining the size of cable to be used for this sub-
circuit. But the current corresponding to this wattage
must not be less than the current drawn by the single
maximum wattage point. If a sub-circuit has only one
point, cable suitable for full load current of that point
is to be used. However, if a sub-circuit has three 6 A
plug-sockets, the size of the cable can be determined
on the basis of two-thirds of 180 W (that is, 120 W).

The above applies to ordinary dwelling-house, but not
to all buildings. Three-fourths of the total wattage is to
be considered for hotels, boarding houses etc, and nine-
tenths for office etc. For the auditorium of cinema, theatre
etc, cables suitable for full connected load are to used.

5.4.2 If in a house there is electric cooker or electric
oven, full load up to 10 A and one-half of any extra
load (in excess of 10 A) should be taken into account.
The load of every sub-circuit is thus calculated, and
the current drawn by a sub-distribution board is
determined.

5.4.3 The load of wall-plug connected to a sub-
distribution board in a dwelling house where there are
wall-plugs of various sizes will be the full-load of the
plug drawing maximum current plus four-tenths of all
the remaining plugs. In hotels etc, three-fourths of the
total load of all the remaining plugs have to be added
to the full-load of the plug drawing maximum current.

a) At first currents for the sub-circuits are to be
determined, one by one.

b) Sizes of fuse should be determined according
to capacity to continuously carry the
respective current.

c) The size of cable for each sub-circuit is
determined according to the current drawn by
that sub-circuit.

d) Finally, the sizes of flexible cord and wall-
socket for the respective sub-circuit to be
determined.

5.5 Diversity and Maximum Demand

In determining the maximum demand of an installation
or parts thereof, diversity may be taken into account.

Table 2 gives guidance on diversity, but it is emphasized
that the calculation of diversity would have to take into
account several factors which would need special
knowledge and experience. By consulting Table 2, a
reasonable estimate can be obtained as to what the
maximum load is likely to be, but it must be stressed
that each installation must be dealt with on its own
merits.

Table 2 Typical Allowances for Diversity
(Clause 5.5 )

SI Purpose of Final Circuit Fed from
No. Conductors or Switchgear to
which Diversity Applies

(1)

(2)

Type of Premises

Individual house- hold
installations, including
individual dwelling of a block
(3)

Small shops, stores offices
and business premises

(4)

Small hotels, boarding houses
etc

(5)

66 percent of total current 90 percent of total current 75 percent of total current
demand demand demand

i) Lighting

NATIONAL ELECTRICAL CODE

SP 30: 2011
Table 2 — (Concluded)

_0) (2) (3) (4) (5)

ii) Heating and power [also see SI. No. 100 percent of tota] current 100 percent of full load of 100 percent of full load of
(iii) to (iv) below] demand upto 10 A largest appliance largest appliance

+50 percent of any current +75 percent of remaining +80 percent of second largest
demand in excess of 10A appliances appliances

+60 percent of remaining
appliances
iii) Cooking appliances 10A 100 percent of full load of 100 percent of largest

+30 percent of full load of largest appliance appliance

connected cooking appliances +80 percent of full load of +80 percent of full load 1 of
in excess of 10 A + 6 A if second largest appliance second largest appliance
socket-outlet incorporated in +60 p ercent of M load of +60 percent of full load of
umt remaining appliances remaining appliances

iv) Motors (other than lift motors which 100 percent of full load of 100 percent of full load of

are subject to special consideration) largest motor largest motor

+80 percent of full load of +50 percent of full load of
second largest motor remaining motors.

+60 percent of full load of
remaining motors

v) Water heater (instantaneous type 1} ) 100 percent of full load of 100 percent of full load of 100 percent of full load of

largest appliance largest appliance largest appliance

+100 percent of full load of +100 percent of full load of +100 percent of full load of
second largest appliance second largest appliance second largest appliance

+25 percent of full load of +25 percent of full load of +25 percent of full load of
remaining appliances remaining appliances remaining appliances

vi) Water heaters (thermostatically No diversity allowable 2) +25 percent of full load of

controlled) remaining appliances

vii) floor warming installations No diversity allowable 2)

viii) Water heaters thermal storage space No diversity allowable 2)
heating installations

ix) Standard arrangements of final 100 percent of current demand 100 percent of current
circuits in accordance with IS 732 of largest circuit demand of largest circuit

+40 percent of current demand +50 percent of current
of every other circuit demand of every other circuit

x) Socket outlets other than those 100 percent of current demand 100 percent of current 100 percent of current demand

included in SI No. (ix) above and of largest point demand of largest point of largest point

stationary equipment other than ^q percent of cumnt demand +?5 percent of current +75 percent of current demand

those listed above Q f ever y ot h er point demand of every other of every point in main rooms

point (dinning rooms, etc)

+40 percent of current demand
of every other point

For the purpose of the table an instantaneous water heater is deemed to be a water heater of any loading which heats water only while
the tap is turned on and therefore uses electricity intermittently.

It is important to ensure that the distribution boards are of sufficient rating to take the total load connected to them without the
application of any diversity.

An example of estimation of maximum demand for a domestic installation with a single tariff is given below:

Connected Load Expected Maximum Demand

Installed lighting — 10A 66 percent of installed load = 6.6A

Installed fixed heating— 30A 100 percent of first 10 A plus = 20A

50 percent of excess of 10 A
Installed general-purpose socket-outlet — 40A 100 percent current demand of largest = 28 A

circuit (20A) plus 40 percent current

demand of other circuits (8A)
Installed cooker — 45A 10A plus 30 percent of full load of = 22A

remaining connected appliances plus 6A

for socket in unit

Total 125A 76.6A

PART 1 GENERAL AND COMMON ASPECTS 51

SP 30: 2011

In this case a 100A main switch should be provided.
Unless it is anticipated to increase the load considerably
in the foreseeable future, in which case a larger switch
fuse should be installed.

However, for a small restaurant where electric lighting
and heating is installed, it would be most likely that
the whole load will be switched on at one time and
therefore the main switchgear must be suitable for the
total installed load.

5.6 MV/LV Busbar Chambers (400/230V)

Bus bar chambers which feed two or more circuits must
be controlled by a main disconnector (TP and N), or
isolating links, or (three) fuses and neutral link, to
enable them to be disconnected from the supply.

5.7 Earthed Neutrals

To comply with Indian Electricity Rules, 1956 no fuses
or circuit-breakers other than a linked circuit-breaker
shall be inserted in an earthed neutral conductor, and a
linked switch or linked circuit-breaker shall be arranged
to break all the related phase conductors. If this neutral
point of the supply system is connected permanently
to earth, then the above rule applies throughout the

installation including 2-wire final circuits (see Fig. 6).
This means that no fuses may be inserted in the neutral
or common return wire and the neutral should consist
of a bolted solid link, or part of a linked switch which
completely disconnects the whole system from the
supply. This linked switch must be arranged so that
the neutral makes before, and breaks after the phases.

5.8 General Design of Feeder Circuit, Distribution
Circuit and Final Circuit

5.8.1 Every distribution board must be connected to
either a main switch fuse or a separate way on a main
switch board. Every final circuit must be connected to
either a switch fuse, or to one way of a distribution
board. In either case the rating of the protective device
must not exceed the current rating of the circuit cable.

5.8.2 The circuit which is connected to single-way of
switch board/sub-switch board or fuse/MCB distribution
board for supplying current to one or more load point
known as 'final circuit' . In the case of domestic and
commercial supply, the suppliers' line or cable comes
to the energy meter through supplier's scaled cut-out
and from the meter it goes to consumer's main switch.
This line is called 'supply main' or 'main line'.

& SOUD W&UT9AL
MMRV&

OOUSLC POLf

UNtttD &wtrcnt&

WITH ftlNCU
POU PVSC &
SOU© MluraAl

NOTE — When the neutral point of a supply or one pole of transformer on consumer's premises is earthed permanently, a fuse, non-

linked switch or circuit-breaker is not permitted in the line connected to earth.

Fig. 6 Single Pole Fusing

NATIONAL ELECTRICAL CODE

SP 30: 2011

5.8.3 On account of heavy load in big factories of
horizontal distribution, very often feeder line is drawn
from the main incomer switch to busbar chamber of
main switch board and the feeder line is called 'supply
main' or 'main feeder'. If sub-switch board or
distribution board is installed next in sequence to
another sub-main switch, the feeder line upto sub-
switch board or main distribution, the line from main
switch board up to sub switch board or main
distribution board is called 'sub-main feeder'. If main
distribution board is installed next in sequence to sub-
(main) switch board, the line upto main distribution
board is called 'main distribution feeder' line. And from
there line is drawn through different sub-busbar
chambers of sub-switch boards to distribution boards,
or from the main switch board and direct to main
distribution boards.

5.8.4 Also on account of heavy load in large buildings
of vertical distribution, very often main feeder line is
drawn from the main incomer switch to main busbar
chambers and from there upto different sub-busbar
chambers and or main distribution boards, the feeder
line from consumer's main switch to busbar chamber
that rises from the ground floor upto the top most floor
in multistoried building is known as 'main raising
main'. If sub-(main) busbar chamber or main
distribution board is installed next in sequence in
different floors through another submain switch, feeder
line upto sub-(main) busbars or main distribution
boards is called 'sub-main raising bars' and considered
sub-main feeder line. If main distribution is installed
next in sequence to sub-main busbars, the line upto
main distribution board is called 'distribution busbar'
and considered main distribution feeder line. Circuit
lines drawn from main distribution boards upto final
circuit fuse districution boards /MCB distribution
boards may be as 'sub-main distribution feeder'.

5.8.5 Every circuit line which runs from final circuit
fuse distribution board towards load points is called
'final circuit'. Sometimes a circuit line may go to a
load point from a main distribution board/main
distribution busbar chamber, a sub-main switch board/
sub-main rising main, a main switch board /main rising
main etc; in that case every line is regarded as a final
circuit.

5.8.6 Every final circuit must come out of a separate
way of a (final circuit) distribution board. Where there
is only one final circuit, it may be connected directly
to the main switch board.

5.8.7 Wiring of every final circuit will be completely
separated from that of another final circuit which can
be on or off with a single-pole switch. Care must be
taken to see that every pair of live or neutral wires are

kept together properly in order in the distribution board
for the convenience of testing or disconnecting current
flowing towards load points must not exceed the circuit-
carrying capacity of wires used for final circuit.

5.8.8 Use of Plug Point with Lamp Circuit

In a house wiring, usually lamp, wall-plug etc., are
connected to the same circuit. The actual limit of the
current that the cables used in the wiring can safely
carry should be known. Considering the final circuit
which includes discharge lamps, the sum total of
currents taken by all discharge lamps together must
not exceed the current carrying capacity of the final
circuit. If the lamps are lighted by means of only the
normal circuit, current carrying capacity of the final
circuit should be 1.256 times the total current of all
the lamps together.

If in a final circuit both incandescent lamps and
inductor-lighted discharge lamps are used,

(Power taken by inductor- + (Power taken by incan-
lighted discharge lamps x 2) descent lamps x 1)
Line voltage

Must not exceed the current carrying capacity of the
final circuit.

5.8.9 Exception in Case of Temporary Wiring

In case of temporary load points where bayonet holders
for lamps have been used, total power demand of load
must not exceed 1 000 W per final circuit.

5.8.10 Splitter Unit

This kind of distribution board is very much in use
now-a-days. This board can be installed anywhere and
is known as 'splitter unit' or 'splitter box'. The unit is
prepared by setting a pair of main switches as well as
a pair of main fuses or a single fuse inside a cast iron
box. An external handle is attached to the body of the
box. It is so arranged that the cover of the box cannot
be opened when the switch is in the on position or the
switch cannot be switched on when the cover is open,
that is the cover cannot by any means be opened unless
the switch is off. It is for this arrangement that the unit
is quite good from the point of view of safety. The box
is also known as Iron-clad Switch-Fuse Box. The
switch-fuse box is installed at a point where from
consumer's zone starts. Cables are drawn from the
switch and connected to the bus-bars of a fuse board.
This is the main distribution board, Now-a-days iron-
clad fuse-box is very much in use. A screw is attached
to the body of this box. The risk of electric shock is
avoided by connecting earth wires to that screw. The
box is to be earthed by two separate and distinct earth
connections.

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

5.8.11 Lamps of the Same Room are Supplied from
More Than One Final Circuit Distribution Boards

When outlets from a sub-distribution board or a fuse
board are divided into 'ways' and each final sub-circuit
is connected to a separate way, the advantage is that in
the event of a short-circuit in anyone sub-circuit, the
other sub-circuits remain unaffected and continue to
function normally. But if a fault occurs in a distribution
board, all the sub-circuits coming out of it are affected.
There are some places such as hospital, operation
theatre; cash room in a bank, engine room, workshop
etc, where the entire room cannot be allowed to be
dark under any circumstance. A lot of risks may have
to be faced if such places suddenly become totally dark.
Wherever special attention must be paid to avoid any
inconvenience in business, every room is equipped with
more than one lamp and these are invariably taken from
different ways. Even sometimes these lamps are
supplied from fully separate distribution board.
Suppose the wiring of a three-storeyed building is to
be done in such a way that no room of that building
shall be totally dark (except in the event of discontinuity
of supply). In that case there must be a separate sub-
distribution board in each floor. But it is not that the
sub-distribution board will control the load points of
that floor only. Depending on the convenience of a
circuit, sub-distribution board in the lower floor will
supply power to some lamps etc, of the lower floor
and to some lamps etc, of the upper floor. Every room
will be provided with two sets of cables — one set will
be supplied from sub-distribution board of the upper
floor and the other set will be supplied from sub-
distribution board of the lower floor. With these
arrangements if a fault develops in a sub-distribution
board, there is no possibility of any room becoming
totally dark. In such cases, operation theatre etc, are
provided not only with connection from separate
distribution boards but with alternative source of supply
such as gas plant or charged battery.

5.8.12 Pilot Lamp

Arrangements should be made for fixing a bracket
above each main board and for connecting a 20 W lamp
on it. Cables connecting this lamp will come out
directly from the bus bars of the board through a
separate switch arid fuse. This lamp is called a Pilot
Lamp. The purpose behind this arrangement is to keep
the main board always illuminated so that fuse etc, can
easily be changed.

5.8.13 Arrangements for Taking Cable Connections
from One House to Another

If wiring is to be done to supply current from one house
in which consumer's main switch has been installed to
another house, whichever of the following

arrangements is suitable (for a particular case) is to be
adopted for the wiring and its protection:

If the distance between the house in which the main
meter board has been installed and the other house (for
example garage, servant's room etc) does not exceed
3 m and if there be no thoroughfare between the two
houses, electric lines may be drawn from the former to
the latter through a galvanized iron (G.I.) pipe of
suitable dimensions at a height of at least 2.5 m above
the ground level. Also the G.L pipe has to be properly
earthed. But in case the distance between the two houses
exceeds 3 m or if there is a thoroughfare between them,
a separate main or sub-main has to be drawn from one
house to another by means of weather-proof cables tied
up with G.I. bearer wire (see Fig. 7A).

If current is to be taken from one house to another by
means of cleat wiring, the cable used in the wiring will
be weather-proof. This is also known as H.S.O.S.
(House Service Overhead System) cable. Use of cable
with 'polychloroprine' sheath or PVC cable or cable
with PVC sheath is also approved by many. This
arrangement of drawing a supply line is allowed up to
a distance of 3 m between two buildings. Using cables
as described above and drawing these cables over a
separate catenary wire or using those cables which have
in-built bearer wires (at the time of manufacture), the
supply line may be drawn.

Other methods of drawing cables over bearer wires
are also in use, one of these methods is shown in
Fig. 7B. In this method a piece of leather strap loops a
hard rubber- sheathed cable at certain intervals for
hanging it, while the upper part of the strap is fastened
to the catenary wire by means of wire hook. This is
also an arrangement for taking a supply cable from
one building to another. If such a cable, as has in-built
bearer wire, is used, the limit of distance between two
buildings will depend upon the load-bearing capacity
of the bearer wire.

Besides these a cable may be drawn from one house to
another as shown in Fig. 7C. Main earth pit should be
at least 1.5 m away from the building.

5.8.14 Identification of Cables and Conductors

IS 1 1353 gives guidance on uniform system of marking
and identification of conductors and apparatus
terminals (see Table 3). Colours of the cores shall be
as per relevant Indian Standard for cables. The
following shall be ensured:

a) Non-Flexible Cables and Bare Conductors —
Every single core non-flexible cable, and
every core of twin or multicore non-flexible
cable used as fixed wiring shall be identifiable
throughout its length by appropriate methods.

NATIONAL ELECTRICAL CODE

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7 A Gl Bearer Wire Stretched Between Two Houses and Supply Cable Tied-
Up with this Wire by Means of Link Clips

7B Leather Strap Loops for Hanging Hard Rubber-sheathed Cable at Intervals

NOTE — Leather strap loops are used for hanging hard rubber- sheathed cable at intervals while the upper part of the strap is fastened
to the catenary wire by means of wire hook

Earth

7C Drawing of Supply Cable from One House to Another
Fig. 7 Arrangements for Taking Cable Connections from One House to Another

b) Rubber or PVC Insulated Cables — Core f)
colours to be in accordance with respective

Indian Standard or colour sleeves at the
termination of these cables.

c) Multicore PVC Cables — If colouring of g)
cores is not used, then cores to be identified

in accordance with relevant Indian Standards.

d) MI Cables — At the termination of these
cables, sleeves shall be fitted.

e) Bare Conductors — To be fitted with sleeves

or painted. h)

PART 1 GENERAL AND COMMON ASPECTS

Colour coding of fixed wiring cables applies
to all wiring up to the final distribution board,
and also for circuit wiring, except that red may
be used for any phase.
When wiring to motors the colours specified
in Indian Standard should be used right up to
the motor terminal box. For slipring motors
the colours for the rotor cables should be the
same as those for the phase cables, or could
be all of one colour except black or green.
For star delta connections between the starter

SP 30 : 2011

and the motor, use red for Al and A0, yellow
for Bl and BO, and blue for CI and CO. The
"1" cables should be marked to distinguish
them from the "0" cables.

j) For 2-wire circuits, such as for lighting or
sockets, the neutral of middle wire must
always be black, and the phase or outer wire
(whichever phase it is derived from) should
be red.

k) For lighting the red wire will always feed the
switch, and a red wire must be used from the
switch to the lighting point.

For flexible cables and cords the distinctive colours
are not the same as for fixed wiring, and the colours of
these are given in Table 4.

5.8.15 Sub-main Cables

Sub-main (feeder) cables are those which connect
between a switch fuse/MCCB feeding sub distribution
boards of main switchboard, to incomer of subsidiary
main switch board or direct to a main distribution
board. The size of these cables will be determined by
the total connected load which they supply, with due
consideration for diversity and voltage drop, and the
other factors described in Wiring Regulations.
Sub-main cables may be arranged to feed more than
one distribution board if desired; they may be arranged
to form a ring circuit, looping from one main
distribution board to another. Where a sub-main cable
feeds more than one distribution board in a ring circuit,
its size must not be reduced when feeding the second

Table 3 Colour Identification of Cores of Non-fiexible Cables and Bare Conductors for Fixed Wiring

(Clause 5.8.14 )

SI No.

Function

(2)

Colour Identification of Core of Rubber or PVC

Insulated Non-flexible Cable, or of Sleeve or Disc to

be Applied to Conductor or Cable Code

(3)

i)
ii)
iii)
iv)
v)
vi)
vii)
viii)
ix)

xi)

xii)

xiii)

Protective or earthing

Phase of ac single-phase circuit

Neutral of ac single or three-phase circuit

Phase R of 3-phase ac circuit

Phase Y of 3-phase ae circuit

Phase B of 3-phase ac circuit

Positive of dc 2-wire circuit

Negative of dc 2-wire circuit

Outer (positive or negative) of dc 2-wire circuit derived from 3 wire

system

Positive of 3-wire system (positive of 3-wire dc circuit)

Middle wire of 3-wire dc circuit

Negative of 3-wire dc circuit

Functional earth-telecommunication

Green and yellow

Red [or yellow or blue (see Note 1)]

Black

Red

Yellow

Blue

Red

Black

Red

Red
Black
Blue
Cream

NOTES

1 As alternative to the use of red, if desired in large installations, up to the final distribution board.

2 For armoured PVC-insulated cables and paper-insulated cables, see relevant Indian Standard.

Table 4 Colour, Identification of Cores of Flexible Cables and Flexible Cords

(Clause 5.8.14)

SI No.

Number of Cores

Function of Core

(1)

(2)

(3)

Phase

Neutral

Protective or earthing

ii)

Phase
Neutral

iii)

Phase

Neutral

Protective or earthing

iv)

or 5

Phase

Neutral

Protective or earthing

Colour(s) of Core

(4)

Brown
(Light) Blue
Green and yellow
Brown

(Light) Blue
Brown

(Light) Blue
Green and yellow
Brown or black
(Light) Blue
Green and yellow

} Certain alternatives are allowed in Wiring Regulations.

NATIONAL ELECTRICAL CODE

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or subsequent board, because the cable must have a
current rating not less than the fuse or circuit breaker
protecting the sub-main. If a fuse or circuit-breaker is
inserted at the point where a reduction in the size of
the cable is proposed, the reduced size of cable may
be used, providing that the protective device is rated
to protect the cable it controls.

5.8.16 Protective Multiple Earthing (PME)

5.8.16.1 Protective multiple earthing system uses the
protective conductor as a combined earth/neutral
conductor. It is sometimes used where there is overhead
distribution, and where it is difficult to obtain a
sufficiently low earth resistance from supply
transformer to the consumer's terminal. In such a case
the neutral conductor is also the earth conductor and it
is bonded to earth, not only at the transformer position,
but also at the consumer terminal position. The
condition of approval for this system contain very
stringent requirements. The wiring for consumers
installations, including sub-mains and circuits wiring
may (if approved) be carried out on the PME system.
Some of the requirements for consumer's installation
are as follows:

a) The supply undertaking shall be consulted to
determine any special requirements
concerning the size of protective conductors.

b) All precautions must be taken to avoid the
possibility of an open circuit in the neutral
conductor.

c) Bonding leads must be connected to the
earthing terminals of all metal structures,
metal pipes and other metal services that are
(or may reasonably be expected to become)
in electrical contact with the general mass of
earth, and that are so situated that
simultaneous contact may reasonably be
expected to be made by any person with such
structures, pipes or other metal work on the
one hand, and with the exposed non-current-
carrying metalwork of the consumer's
installation, or any metal work in electrical
contact therewith, on the other hand.

d) Earth electrodes shall be provided at points
not less remote from the transformer than the
most remote service line or connection point,
and at such other points as will ensure that
the resistance to earth in the neutral conductor
is satisfactory and the protection system
operative. The overall resistance shall not
exceed 20 times.

e) There shall be a wire connection from the
neutral earth conductor to both the neutral and
the earth terminal of every socket outlet.

Wiring from plugs or spur units to lamps and
appliances shall be carried out by a phase
conductor, a conductor and a separate earth
conductor,
f) There shall be electrical continuity of the
neutral earth sheathing of multicore armoured
cables. All connections and joints shall be
made in accordance with the
recommendations of the cable manufacturer.
At every joint in the outer conductor (that is
neutral earth) and at terminations, the
continuity of the conductor shall be ensured
by bonding conductor additional to the means
used for sealing and clamping the outer
conductor.

5.8.16.2 The use of a PME system in petrol filling
stations is specifically prohibited. The reason for the
prohibition is to prevent the risk of electrical return
currents flowing back to earth through the metallic
parts of the underground supply pipes and storage
tanks. Special armoured multicore cables may be used
for the PME system. Such cables may be with XLPE
(cross linked polyethylene) insulation, Aluminium
conductors and sheath are used, and the cables have a
PVC oversheath. The armouring in these cables is laid
upon such a way that sufficient amount can be pulled
away from the cable without the necessity of cutting
it, to enable access to the phase conductor for the
purpose of jointing. These special cables are only
manufactured in minimum lengths of about 200 m, and
it may not be economical to employ the PME system
for sub-main cables when only short runs are involved.

5.8.16.3 Circuit wiring

a) Circuit ring for PME system may also use a
common neutral earth (CEN) conductor, but
in some instances this may not result in any
cost savings.

b) For mineral-insulated copper sheathed
systems the outside sheathing lends itself
readily to the system, but special glands
should be used to ensure satisfactory low
impedance in the earth conductor.

c) For screwed-conduit systems it is sometimes
difficult to guarantee satisfactory low
impedance in the conduit system during the
life of the installation, and it is recommended
that a circuit protective conductor (CPC)
neutral conductor be drawn into the conduit.

d) The same recommendation applies to wiring
is steel trunking, because it is imperative that
there be no risk during the life of the
installation that an open circuit, or a high
resistance joint, could occur.

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

e) Before planning any PME installation careful
study must be made of the actual conditions
of approval issued by the concerned
regulatory authority.

5.9 Computer Data Transmission and Control
System

Cables required for data transmission and control
systems are those that are required between the
computer and the outstations and those used between
the machine and the associated peripheral equipment.
Generally, the field wiring is multicore and may have
screening applied to each core, to each pair or, simply,
overall. There is a large range of cables used by different
computer manufacturers. One of the commonly used
cables for peripheral equipment is the ribbon form
which is also produced as multicore cable, with and
without screening and various types of insulation.
Although ribbon cables are produced in widths upto
approximately 80 mm and with over 60 cores, they are
extremely thin and, therefore, flexible.

5.10 Multiplex Systems

One of the advantages gained by the use of electronic
equipment is that the amount of field wiring required
is far less, in both quantity and size, than for the earlier
power circuitry entailed by mechanical relay systems.
Even further improvements are made possible by the
use of multiplexing systems, that is, the ability to
convey a large number of signals each way along the
same conductor, and these are, therefore, particularly
suitable for installations requiring a large number of
outstations, whether for data transmission or process
control. Optical fibre cables provide further advantages
for light-current installations of all types; they have
low attenuation and high bandwidth, which reduces
the necessity for repeaters, and are not subject to
interference from heavy electrical equipment. In
hazardous areas, optical fibres give even greater safety
than intrinsically safe circuits as the form of energy
transmitted is, of course, light waves and not current.

5.11 Domestic Systems

5.11.1 The smaller domestic type of installation is
adequately catered for with twin and circuit protective
conductor (CPC) PVC cables or single-core PVC cable
in some form of enclosure; the installation of the first
is less labour-intensive than conduit work although the
second provides better mechanical protection. Due to
the amount of space that is occasionally available
between floorboards and ceilings (modern construction
methods include solid floors) and in lofts, installation
is relatively simple and protection is rarely necessary
for horizontal runs. Where droppers are required for
switches and wall-fittings, however, it is essential to

provide oval conduit or capping over the cables.
Although PVC has a much longer anticipated life than
the previously used rubber covered cables, MICC is a
suitable alternative which has an even longer life. It is
not commonly used on very small installations except,
possibly, for exterior lighting or feeds to remote
buildings.

5.11,2 To avoid undue disruption and damage to
existing floorboards, plastering, etc, a number of
enclosed surface systems are available which
incorporate mini-trunking, dado-trunking and cornice-
trunking. For each system, accessories are available
for accommodating different types of outlet and for
negotiating corners, doorways, etc, a correctly designed
installation is effective and relatively inconspicuous,
although even where obvious, such as across ceilings,
it presents an aesthetically pleasing appearance.

5.12 Telephone Cables

As the user finds it more convenient to install his own
internal telephone systems, a large range of cables
available for the purpose. The conventional type of
multipair or multitriple cable consists of tinned copper
conductors, PVC-insulated and sheathed with, in some
cases, a non-metallic rip-cord laid under the sheath to
simplify stripping while, for under-the-carpet
installations or situations where the conventional round
cables are inconvenient or too bulky, ribbon cables are
again available with upto 50 ways. Where such cables
may be subject to damage or heavy traffic, such as
under floor coverings, ribbon cables insulated with
cross-linked PVC (XLPVC) which is more robust than
standard PVC may be used. XLPVC are different from
XLPE-insulated cables which, among other
advantages, have fire-retardant properties.

5.13 Cable Jointing and Termination

5.13.1 Although the methods employed for jointing
and terminating cables of all types have been
simplified, largely due to the use of improved materials
for insulation and sheathing, the importance of utilizing
correct techniques and methods cannot be too strongly
emphasized. All joints and terminations introduce
potentially dangerous points; in power circuits a faulty
joint will lead to local hot-spots with ultimate failure
of the cable, while in light- current installations for
process control, data transmission and
communications, a high resistance connection (dry
joint) can prevent equipment from operating
satisfactorily.

5.13.2 Multicore cables, whether for mains, voltages
or light-current duty, generally present the greater
problem as the crutch, that is, the point at which
conductors are splayed out from the normal formation,

NATIONAL ELECTRICAL CODE

SP 30 : 2011

constitutes a naturally weak area in which air may be
trapped if a termination or joint is not correctly formed,
leading to breakdown at a later stage.

5.13.3 Single-core cables should, preferably, never be
jointed, but where this is essential it should be effected
only in purpose-made joint boxes equipped with
suitable mechanical or compression- type connectors.
These may be of the ferrule type with pinching screws
or, as with terminators, bolted clamps requiring the
bare conductor to be either wound around the bolt
between shaped washers or enclosed in crimped type
terminals which are then threaded over the screw thread
and clamped. It is essential with all types of stranded
cable to ensure that every strand is included in the joint
or termination and, particularly with aluminium
conductors, to follow cable manufacturers'
recommendations for tightening torques. Aluminium,
although lighter in weight and less expensive than
copper, unfortunately has a higher co-efficient of
expansion and this has, at times, caused connections
to slacken shortly after commissioning. It is therefore
advisable for the installer of aluminium cables to
recheck all clamp-type connections after electrical load
has been applied. This does not imply, however, that a
similar procedure is unnecessary with copper
conductors but that it may not be so essential provided
that connections are fully checked in the first instance.

5.13.4 Crimped terminals are quite adequate for the
smaller, relatively lightly loaded cables but, otherwise,
compression sleeves and lugs, provided that the
recommended torques are applied, are unlikely to give
rise to problems during the life of a cable under the
most arduous circumstances.

5.14 Special Cabling Requirements

5.14.0 Although PVC insulated cables are suitable for
most of the general wiring requirements in domestic,
commercial and industrial situations, circumstances
may dictate, either through technical necessity or
statutory demands, that further precautions are
necessary to prevent the possibility of danger or to give
increased security, as detailed below.

5.14.1 Lighting

The two main areas of concern are related to heat build-
up in luminaries and surges created by discharge
lighting. In totally enclosed luminaries, high
temperatures may arise due to the lack of ventilation.
Though luminaires complying with the relevant Indian
Standards take into account the temperature rise,
however, during installation of luminaires it should
ensured that wiring in proximity to the fittings is
suitable. Discharge-type fittings may entail the use of
higher current rated cables to avoid unnecessary
temperature rises. The effects of high discharge

currents during switching operations may have more
drastic effects by causing a cable to disintegrate
completely. Some cables are susceptible to current and
voltage surges which may be avoided by the use of
current limiting devices. Where electrical equipment
in normal operation has a surface temperature sufficient
to cause a risk of fire, suitable methods of protection
should be adopted.

5.14.2 Emergency Lighting

Emergency lighting is very critical for at hospitals,
theatres, hotels, factories, offices, shops, cinemas and
certain specified places of entertainment and practically
all types of premises excluding houses. Generally, the
cable installation for an emergency lighting system
should comply with Wiring Regulations but care must
be taken to ensure that all wiring possesses inherently
high resistance to attack by fire and adequate
mechanical strength. This allows the use of various
standard types of cable, provided that suitable means
of protection are employed. When emergency
luminaries are supplied from a remote source, the
wiring system must be mechanically separated from
other systems by rigid and continuous partitions of
non-combustible materials. Consequently,
multicompartment enclosures are suitable, also mineral
insulated copper clad cables without further
precautions. Segregation is not a requirement when
self-contained luminaries are installed, as a failure of
the supply will only cause them to operate. Precautions
to be taken at the source of supply for an emergency
lighting system are that cables between the source and
a battery charger combination should be a fixed
installation, which precludes plugs and sockets, while
those cables from the battery to a protective device,
that is the load circuit cables, must be separated from
each other and not enclosed within metal conduit,
ducting or trunking. Segregation must also be applied
between the dc and any ac cables.

5.14.3 Fire Alarms and Detection

The requirements in the previous section regarding
mechanical protection, high fire resistance and
segregation, etc apply. Where high frequency circuits
are installed, adequate screening is applied between
the different circuits in order to avoid false alarms.

5.14.4 Power System

5.14.4.1 Some of the problems arising in the installation
of power cables are high or low ambient temperatures,
grouping, thermal insulation, type of protective device
employed and voltage drop considerations. Under
normal circumstances, correctly chosen protective
devices are adequate to deal with disruptions such as
overloads, short-circuits and earth-faults on low voltage
systems but, on high voltage networks, transients may

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

occur which create high stresses on cable insulation
and therefore, it may be advisable to install screened
cables which have the effect of grading such stresses
between cores or between cores and earth.

5.14.4.2 The handling and installation of all types of
cable is an important consideration. Some PVC cables,
for instance, should not be installed during
temperatures below 0°C as flexing will damage the
insulation, while high temperatures will soften the
PVC, causing it to strip if pulled into conduit, ducting,
etc. Damage may also be caused to cables by drawing
them into rough-edged enclosures, for example burred
conduits, over stony surfaces or bending them tighter
than the recommended radii. Large armoured cables
are impressively strong, but even these, when being
drawn into ducts, may be damaged if the correct type
of grip-sleeve (or sock) and hauling equipment is not
used, as too high a torque may stretch the cable cores
or strip off the insulation and sheathing.

5.14.4.3 Particularly with the smaller armoured cables,
if armouring is to be used as the protective conductor,
the impedance must be checked to ensure that it
complies with the relevant requirements; otherwise
additional conductive material must be incorporated
in the protective circuit.

5.14.5 Control and Instrumentation

Modern systems for control and instrumentation utilize
electronic means (rather than power circuitry) which
are more likely to be affected by low voltage systems,
and precautions such as segregation and screening must
be employed. Cables are available to suit all types of
system but, as requirements vary between
manufacturers of electronic equipment, advice should
be sought at an early stage. The increasing use of
multiplex systems and fibre-optics cables simplify
installation work by reducing the number of cores
required for the most complex systems and, in the case
of the latter, eliminate completely the possibility of
interference from other circuits.

5.14.6 Hazardous Areas

Danger in a hazardous area arises initially from the
type of materials being processed rather than from the
electrical installation, but a great degree of
responsibility rests upon the designer to ensure that
the installation does not contribute to the hazard by
the introduction of flammable materials, high surface
temperatures, arcs or sparks to the atmosphere. For
these reasons, every care must be taken to avoid the
overloading of cables or the inclusion of sheathing
materials which easily burn and give off toxic gases.

See IS 5572 for classification of hazardous areas and
IS 5571 for selection of equipment in hazardous areas.

Different degrees of hazard exist and, consequently,
these affect the type of electrical installation,
particularly with regard to equipment. It is essential,
therefore, to ascertain which zone is applicable before
commencing the electrical design, this information
generally being available from the process plant user.
See also Part 7 of the Code.

6 WIRING SYSTEMS

6.0 General

6*0.1 The following systems are usually adopted for
house wiring:

a) Cleat wiring;

b) Casing and capping wiring;

c) Metal sheathed wiring (for example lead-
covered wiring);

d) Cab tyre sheathed (C.T.S.) or tough rubber
sheathed (T.R.S.) wiring;

e) PVC sheathed wiring;

f) All insulated wiring — surface wiring and
concealed wiring;

g) Enclosed wiring system — conduit wiring and
cable trunking; and

h) Conduit wiring — steel, plastic and flexible.

A particular type of wiring is selected for a particular
place on the basis of type of work, place and expenses
involved. Insulated wires are used in all systems of
wiring. These systems have been named according to
either constructional details of wires or modes of fixing
these wires on the wall. The voltage grade of wires
depends on supply voltage of the circuit, that is, the
voltage grade of wires must not be less than the highest
root mean square or effective value of supply voltage.
In case of house wiring where working voltage
normally does not exceed 250 V, wires of 250 V grade
can be used.

6.0.2 Size of Wires

The wire used should have such cross-sectional area that
when the maximum current drawn by the circuit flows
continuously through it, the voltage drop between main
distribution board and the farthest point of the lighting
circuit does not exceed 3 percent of the supply voltage
(in a 230 V circuit this drop is 3/100 x 230 = 6.9 - 7.0
V). At the same time it should be ensured that the wire
is not excessively heated when the maximum current
flows continuously through it. Normally, the wire is not
excessively heated when the amount of voltage drop
remains within the limited value.

If the size of a wire in a circuit has to be increased with a
view to reduce the drop of voltage, it may be noted that
the wire will carry as much current as has been determined

NATIONAL ELECTRICAL CODE

SP 30: -2011

for the circuit to carry. Further, the size of a wire specified
for a circuit must be suitable for continuous flow of current
which is not less than the current-carrying capacity of the
fuse of that circuit. Recommended current ratings for
cables are as per IS 3961 .

6.0.3 Protection of Wiring from Damage

V.I. R. (vulcanized rubber) wire, plastic-insulated wire
with or without braided cotton cover, C.T.S. (or T.R.S.)
wire normally need not be further covered with separate
covering. But situations and circumstances have to be
taken into account, and if necessary, the outermost
insulation has to be protected from probable damage.

Where there is probability of conduit, duct, casing, etc,
becoming hurtful, adequate arrangements have to be
made to protect them. Where metal- sheathed wire or
armoured cable is installed inside concrete or plaster,
there is usually no need for further protection. However,
depending upon site condition, sometimes additional
arrangements may have to be made.

Wires used for lift, hoist (an electrically operated
machine used for lifting goods), etc, must be metal-
sheathed [see also IS 4289 (Part 1) and IS 4289 (Part 2].
Where the wiring will pass under the floor, the wire
should be so installed that it will not be damaged as a
result of coming in contact with the floor or some fitting.

Where a cable will enter the iron part of a house or the
shed of a factory, every such entry should be provided
with a bush in such a manner that the cable will not
suffer abrasion from rubbing.

Where the sheath of a C.T.S. cable made of rubber or
some compound mixed with rubber will be exposed to
direct sunlight, arrangements must be made to cover it
with some special covering. If the sunlight comes
through glass panes of windows, it is not a direct sunlight.
Wiring should be done in as dry a place as possible.

6.0.4 Permissible Temperature Rise of Ordinary
Insulated Wires and Flexible Cables

Ordinary insulated cables and flexible cables, which
are not specially manufactured for withstanding

excessive heat, should not be used in places where the
temperature may exceed the limit given in Table 5.

In cases where the temperature of lamp fittings and
other accessories are excessively high, cables and
flexible cords which are not specially made to
withstand such high temperatures should not be
brought near these fittings and accessories. Where there
is probability of temperature exceeding 60°C, high
temperature resisting cables like flexible cord, specially
covered with conditioned asbestos, must be used.
Further, they should be so connected that their
temperatures do not exceed 85°C. If however, the
flexible cord is connected with a portable heater with
which there is not possibility of excessive rise of
temperature, a temperature rise up to 66°C may be
allowed, provided that the insulation of wires should
remain covered with beads or insulating sleeves
suitable for high temperature, and there is no
dependence on rubber insulation of cable for the
prevention of earth fault of cable conductors or short-
circuit among them. These arrangements are to be
specially provided for lamps rated 200 W or more and
for immersion heater.

Where a cable with rubber, PVC or polythene insulation
or a flexible cord remains connected with bare
conductor or a busbar, the insulation of the cable or
cord should be peeled off and wires should remain bare
for a length of about 1 5 cm from the point of connection
even when the temperature of the bare conductor or
the bus bar is 90°C. But in places where this cannot be
done, the current flowing through the bare conductor
or the busbar should be so reduced as not to allow a
rise of temperature above 90° C.

6.1 Cleated Wiring System

6.1.0 Cleat wiring is one of the most economical
methods of wiring. The wires remain exposed to view,
and these wires are drawn through cleats made of
porcelain or plastic or some other approved material.
Cleat wiring is most suitable for temporary wiring. The
wiring can be completed quickly and the wiring
materials can be recovered easily while dismantling.

Table 5 Permissible Maximum Temperature of Surrounding Space for Ordinary Insulated Cables

(Clause 6.0.4 )

SI No.

Types of Insulation

*"*"""

— %

Cable

Flexible Cable

(1)

(2)

(3)

Rubber

ii)

PVC

iii)

Polythene

—

iv)

Oil-soaked Paper

—

Cloth impregnated with

varnish

—

vi)

—

Rubber or cloth mixed with
conditioned asbestos

Maximum Temperature of Surrounding
Space or Space Inside Conduit Pipes

(°C)
(4)

45
45
45
75
75
80

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

Moreover, additions and alterations as well as
inspection of wiring system can be easily made. Cleat
wiring is not recommended for damp places and also
for permanent wiring. After a certain period of
installation the wires sag at some places, dust and dirt
collect over them and the whole of the wiring system
may look shabby.

6.1.1 The wires used are either vulcanized rubber
insulated cables, single-core PVC or polyethylene
cables, which can be used without further protection.
Conductors should be visible all throughout a cleat
wiring.

6.1.2 The cleats are made in two parts, called base
and cap. The base is grooved to receive the wire and
the cap is placed over it, and the whole of it is placed
on a wooden plug which is fixed into the wall. The
cleats are tightened up on wooden plugs by means of
wooden screws which also tighten the grip of the wires
between two halves of the cleat. The cleats are usually
of two types having two or three grooves so as to
receive two or three wires. These cleats are shown in
Fig. 8.

6.1.3 Installation of Cleats

a) Wooden plugs are to be properly cemented in
the wall or ceiling, and the distance between
two adjacent plugs should be such that the
cleats are not more than 60 cm apart
horizontally or vertically.

b) Cleats shall be of such dimensions that for
low voltage installation the distance between
two wires shall not be less than 2.5 cm centre
to centre for branch lines and 4 cm for sub-
main lines.

c) In no case two wires shall be placed in the
same groove of the cleats. Also the wires shall
be laid stretched between the cleats so that
they do not touch the wall.

d) Joint cut-outs or fuse cut-outs shall not be used
in this type of wiring. Where joints become
unavoidable, wooden junction boxes with
porcelain connectors inside should be used.

e) Wiring should be enclosed in a conduit when
passing through a wall or a floor. The wires
should run through a conduit upto a height of
1.5 m level. In case of a metallic conduit, it
should be properly earthed. Wooden bushings
are to be provided at both ends of the conduit,
otherwise insulation of the wires may be
spoiled when drawn through it.

f) When two wires cross each other, they should
be separated by an insulating bridge piece
which should maintain a distance of atleast
1.3 cm between the wires.

g) The wires should not run near water or gas
pipes or structural work.

h) A special pattern of cleat may be used where
conductors pass round corners, so that there
may be no risk of the conductors touching
the walls owing to sagging or stretching.

j) Cleats shall be fixed at distances not greater
than 60 cm apart and at regular intervals.

6.1.4 In temporary installations wiring is often done
over bobbin or knob insulators in place of cleats.
Whenever the wires pass through a floor or through a
space where some damage is apprehended, they should
be provided with an additional protection of a special
strong covering upto a height of 1 .5 m above the floor
level. For this purpose, while the wiring passes through
a wall or a partition, it should be taken inside a tube or
a pipe or a conduit made of non-inflammable and non-
hygroscopic material. Porcelain wall-pipe, lead wall-
tube, iron conduit, etc, are the examples of this type of
covering. Various components of cleat wiring are
described below.

6.1.5 Installation of Cleat Wiring

6.1,5.1 Cleat wiring is installed along the wall below
the beam. If there are wooden beams in a house, cleats
may be directly fixed on the beam for drawing wires
up to ceiling roses. But if there is an iron beam, then
space permitting, a piece of wood may be tightly fitted
on one side of the beam and cleat is fitted on this piece
of wood. This is shown in Fig. 9. If space is not
sufficient for fixing a piece of wood on the side of the

(i) Cleat with two grooves

f I
11

(ii) Cleat with three grooves

Fig. 8 Types of Cleat

NATIONAL ELECTRICAL CODE

SP 30 : 2011

iron beam, at first pieces of wood are clamped at
intervals to the bottom of the beam and then the cleats
are fixed on these wood pieces. This is shown in Fig. 10.
The spacing between two consecutive pieces of wood
should be such that the wiring must not sag due to its
own weight. If wiring is to be taken from one room
into the next, a hole is drilled into the common wall
and wiring is taken through porcelain or metal tube
(wall-tube) set into the hole.

Fig. 9 Cleat is Fixed on an Wood Piece Which is
Tightly Attached on One Side of an Iron Beam

SCREW

ROOF

HOOP IRON CLAMP FIXED
WITH WOODEN BEAM BY
SCREW

Fig. 10 Arrangement for Drawing Wires
Under Iron Beam

If the wires are to be drawn under the iron beam from
one cleat to the next, arrangements are provided as
shown in Fig. 1 IB using hoop iron or flat iron clamp.
For heavy wiring or for lasting and durable job, two
wrought iron clamps are used as shown in Fig. 1 1 A.

SET SCREW

BEAM

WOOD BELOW
IRON BEAM

HOOP IRON CLAMP

a WIRE
CLEAT

Fig. 11 Use of Clamps

PART 1 GENERAL AND COMMON ASPECTS

6.1.5.2 Spacing between wires in cleat wiring

The spacing between wires drawn through the cleats
depends upon the line voltage, and the type of circuit
as given at Table 6. An example of cleat wiring system
is given at Fig. 12.

Table 6 Spacing of Wires in Cleat Wiring
(Clause 6.1.5.2 )

Voltage

Type of

Centre to Centre

No.

Circuit

Distance Between
Two Adjacent Wires

(1)

(2)

(3)

(4)

i) Not exceeding 250 V

ii) Exceeding 250 V

Branch

Sub-main

Main

Not less than 2.5 cm
Not less than 4 cm
Not less than 7.0 cm
10.0 cm distance;
2.5 cm spacing all
around

6.1.5.3 Drawing a wire through wall

Wall tube or pipe is usually set near the ceiling corner
(see Fig. 13). The space within the pipe should be
sufficient to accommodate with comfortable inter-
space the maximum number of wires to be drawn
through it. With too many number of wires more than
one tube may be necessary. In that case pipes are set
together at one place side by side. Such a tube may be
made of porcelain or metal. Among metals lead, iron
or steel is used. The pipe is set inside the wall by means
of cement. If conduit is used, its two rough ends are
properly filed and two bushes made of hard wood or
ebonite are fitted at these ends. This eliminates the
possibility of damage of the insulation of wires when
drawn through the pipes. In case of ac wiring all the
wires must be drawn through the same metal conduit.
Where wires are drawn outside from a room, the outer
end of the pipe should be a bit more widened. Also
this end should have a downward bend so that rain
water or water from other sources may not get inside
the pipe along the wires.

6.1.5.4 Drawing of wires through floors

If the wires are to be drawn through a hole made in the
floor, these must be drawn through a conduit pipe upto
a height of 1 .5 m above the floor level, and the lower
end of the conduit should be flush with the ceiling
below. As usual two ends of the conduit must be fitted
with insulating bushes.

6.2 Casing Wiring

In this system of wiring narrow grooved planks of hard
wood are fixed on wooden plugs grouted in the wall
instead of cleats and wires drawn along the grooves.
These narrow planks are called wood casing. Usually
two long grooves are made in each casing, although
three-grooved casing is also available. The top of the

SP 30 : 2011

LEADS FOR FAN CONNECTION

JUNCTION BOX

WIRES DRAWN
TO NEXT ROOM

CUT-OUT

OF CONNECTOR

CjplEP WIRE FOR FAN
CONNECTION "

WIRE FOR LAMP
CONNECTION

1.5 METRES ABOVE
GROUND LEVEL

r4-

.o.

BRANCH
LINES

jpL© (pi

1. SWITCH FOR LAMP

2. SWITCH FOR FAN

3. SWITCH FOR
WALL-PLUG

4. WALL-PLUG

Fig. 12 An Example of Cleat Wiring System

Fig. 13 Use of Wall-tube for Drawing Wires from One Room
into the Other Through Partition Wall

NATIONAL ELECTRICAL CODE

SP 30 : 2011

casing is covered by a rectangular strip of wood of the
same width as that of casing. It is known as capping
which remains screwed to the casing (see Fig. 14). On
the surface of the capping a bouble bed is cut to show
the position of wires so that the screws may not be
driven through wrong position damaging the insulation
of the cables laid under the capping. Casing wiring is
generally adopted for low voltage installations such as
office and residential buildings. This type of wiring is
not suitable for places exposed to rain or sun or having
dampness. It should not also be used in places where
acids and alkalies are likely to be present.

6.2.1 The wood used for casing and capping must be
first class seasoned teak wood or any other hard wood
free from knots, shakes and saps. The sides should be
well varnished both inside and outside with pure shellac
varnish. The size of casing and capping depends upon
the number of wires drawn through the grooves in a
particular length of run.

CAPPING

CASING

Fig. 14 Wooden Capping and Casing

6.2.2 The size of wood casing and capping and number
of cables that may be drawn in one groove of the casing
is given in Table 2 of Part 1 /Section 20 of this Code.

6.2.3 Installation of Casing Wiring

Casing generally used for installation is about 44 mm
wide and 16 mm in thickness (height). However, for
cables of higher sizes, 80-100 mm wide and
proportionally higher in thickness casings are also in
use. Casings may be .5.5 m to 6.0 m long, but smaller
lengths are also available. Lengths of about 2.5 m to
3.0 m are convenient for handling. Very good
workmanship is required to make the job perfect, and
this results in costlier installation. There is also risk of
fire from wood.

There are two grooves in each casing. The width of
the strip of wood separating the two grooves should
be carefully observed so that it is not less than 13 mm,
and the portion of wood below each groove shall not
be less than 7 mm in thickness. In case the cable has a
large cross-section or a number of cables are to be
drawn, the size of casing should increase accordingly.
At the time of wiring the cables laid in the grooves are
covered by a very thin and long strip of wood which is
as wide as the casing. This is known as capping. The

thickness of capping should be about 7 mm. The
following precautions need to be taken:

a) Any number of wires of the same polarity may
be laid in the same groove, but in no case wires
of opposite polarities are laid in one groove.

b) Casing should be fixed on dry wall and
ceiling. Casing shall not be embedded into
cement or plaster. It shall neither be so set as
to get contact with a water pipe, nor it shall
be laid just below a water pipe. It shall not
also be used in a place where moisture
accumulates and drips.

c) A clear space of 3 mm shall be kept between
wall or ceiling and the casing. This could be by
means of porcelain insulators (spacing insulator)
or cleats (either upper half or lower half).

d) Wooden plugs of approved sizes shall be fixed
at a distance of 90 cm apart for casing of sizes
upto 63.5 mm. For higher sizes of casing this
distance shall not exceed 60 cm.

e) While passing through floors or walls, heavy
gauge conduit of approved sizes shall be used .
The conduit should be securely entered into
casing, and it should be extended upto a height
of 1.5 m above floor level.

f) All joints shall be made with good
workmanship as per IS 732.

g) After the wires are laid in the grooves, the
capping is attached to casing by brass screws
in a proper way. The screws must not be so
fixed as to pierce through the insulation of
the wires.

h) Capping should be fixed on the casing only
by screws. The screw used for fixing the casing
must be long enough to pass through the
casing, capping, central hole in the bobbin
insulator or spacing insulator and the wooden
plug in the wall. The capping is fixed on the
casing by means of small screws. If the width
of the casing is less than 50 mm, a series of
screws are fixed on the central line of the
capping, and in case the width is more, two
rows (or columns) of screws are fixed on two
sides of the capping. For this reason the width
of the strips of wood on both sides of the casing
shall not be less than 10 mm. Screws used for
fixing the capping may be made of brass.

j) Provision must be there for easy insertion of
cables into the casing. Before fixing the
casing, it is necessary to smear its sides and
back properly with two coats of shellac
varnish. Further protection is provided by
painting or varnishing the casing wiring once
again on all sides after the wiring is finished.

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

k) Spacing insulators may be used at a place
where the casing is passing below an iron
beam. Preferred sizes of casings is given in
Part 1/Section 20.

6.2.4 Joints in Casing Wiring

In casing wiring work starts from the farthest point of
the load circuit, gradually proceeds towards the main
board and finally ends there.

a) Joint while fixing lamp — The ceiling rose of
the lamp bracket is set on a round wooden
block. This block should have a thickness
(height) of 4 cm with two coats of varnish
applied on it. It has a saw-cut on one side in
such a manner that the tip of the casing closely
fits on to it {see Fig. 15).

FIXED WITH THE
WOODEN PLUG
EMBEDDED IN
THE WALL

FIXED WITH THE
WOODEN PLUG

WIRES COME OUT
THROUGH THESE TWO
HOLES AND GO TO
SWITCH, CELLING ROSE
OR BRACKET

Fig. 15 Joint for Fixing Lamp

Joints for casing/capping — When two pieces
of casing or of capping are to be joined together,
the joint should be completed as shown
in Fig. 16 A (Lap Joint). The joint of capping
shall be an oblique one {see Fig. 16B), Care
must be taken to see that cappings are not joined
together at a point where there is already a joint
of casing, and also no screw for fixing the
capping pierces any side wall of the casing.

1 . Joint at the corner — The kind of joint
necessary at the corner round is shown
in Fig. 17. The two tips of casings that
are to be joined together are placed on
the floor, cut at an angle of 45° and finally

16A Joint of Casing

16B Joint of a Caping with Another
Caping Out in Oblique

Fig. 16 Joints for Casing/Capping

screwed to each other. The corners of the
grooves should be flush with each other
so as to prevent any damage to the
insulation of the cables. The general
appearance of the joint where the casing
is taken from one wall to another is at
Fig. 18 or somewhat similar. The shape
of such a joint should be such that the
radius of curvature of the joint should not
be less than 75 mm so that the insulation
of cables is not damaged due to twist etc.
For a corner joints, the piece of casing
can be abtained as shown in Fig. 19.

45*

90°

45°

SCREW

Fig, 17 Joint at a Corner

CORNER JOINT
Fig. 18 Shape of Joint at a Corner

NATIONAL ELECTRICAL CODE

SP 30 : 2011

l\\\\\\\\\\\\\\\\\\\\\\\\s
7////////////////////////

- \\\\\\\\\\\\\\\\\NV\\\\\\

Fig. 19 How a Small Piece of Casing is
Obtained for a Corner Joint

2) Bending on cables — To bend a VIR or
PVC cable, the internal radius of bend
shall be atleast four times the diameter
of the cable. Where the casing will go
from one wall to another on the external
side, the joint should be as per Fig. 20.

Fig. 20 Joint of Casing on the External
Sides of Walls

T- Joint — From a point in the continuous
run of the casing, sometimes connection
is to be taken out for lamp point, fan
point, etc, through a joint of the casing,
known as T- Joint. Where such a joint is
to be adopted, a V-shaped piece of casing
is to be cut off upto the middle of the
casing used in the continuous run.
Later, the tip of another casing to be
joined to it is cut off in the shape of V
and is made flush with the V-groove of
the former casing as shown in Fig. 21.

Fig. 21 T- joint
PART 1 GENERAL AND COMMON ASPECTS

Bridge — When it is required to draw
one circuit over another, a small piece of
casing, named 'bridge', is used so that
the cable of one circuit does not come in
touch with that of another. At first the
bridge is fixed on the casing and then the
second cable is drawn over it. Where a
T-joint is necessary, a one-half bridge is
fixed there along with a full bridge. This
additional one-half portion is known as
'half-bridge' . A bridge is also used where
cable of one circuit crosses that of another
circuit. Figure 22 depicts 'half bridge'
and 'bridge'. The joint of casings at this
point is called 'cross joint'. T-joint and
cross-joint of casings are shown in
Fig. 23 and Fig. 24 respectively.

HALF BRIDGE

BRIDGE

Fig. 22 Half Bridge and Bridge

Fig. 23 T-joint of Casing with Bridges

Fig. 24 Cross-joint of Casings with Bridge

6.2.5 Installation of Wiring

a) Leading a cable from one room to another
— When leading from one room to another,
a cable may be drawn either through a casing
or through a wall-tube. If casing is used, the
hole in the wall must be large enough to leave

SP 30 : 2011

a clearance of at least 25 mm all around the
casing. The purpose of this clearance is to
keep the casing dry through ventilation of air.
If a wall-tube is to be used, the two ends of
the tube project a little from the wall. The
partition wall between the grooves at the end
of casing remaining in contact with the wall-
tube must be cut off to the same extent as the
amount of projection of the tube from the wall
(see Fig. 25). This will keep the wall-tube
properly fitted with the casing. But in case
the diameter of the tube is larger than the
height of the casing or where more than one
wall-tubes are used, it will not be possible to
fix the capping over the casing. In such cases,
the height of the casing is increased with the
help of a half bridge.

For continuous earthing system a single
galvanized iron wire is drawn continuously
outside the casing along with the cables and
finally earthed. This is called 'Earth continuity
conductor'. The outer metallic covers of fan
regulator iron-clad distribution box, earth
terminal of the wall socket etc, remain
connected with this wire. Usually a separate
wall-tube is used for leading earth continuity
conductor through the wall. For this work a
half bridge on the casing near the wall is
indispensable.

Fig. 25 Cutting Off a Portion of Casing in Order
to Fit it with a Wall-tube

There should be three sockets instead of two
in every wall socket and three pins instead of
two with every wall plug. Also the flexible
cables used in this system must have three
lengths of insulated wires instead of two.
b) Leading a cable through the floor — In the
casing wiring if cables are to be drawn from a
lower floor to a upper floor, a piece of conduit
is pushed through a hole made in the floor.
The sizes of wires of all the circuits to be drawn
from lower to upper floor are calculated at first,
and then the size and number of conduits are
determined accordingly. If continuous earthing

system is adopted, another extra conduit is to
be provided for drawing earth continuity
conductor. At the ceiling of the lower floor all
conduits must project atleast 25 mm. At both
ends of a conduit insulating bushes are to be
fitted. In the upper floor conduit will rise up
to a height of 1.5 m above the floor level. At
this end of the conduit one end of a casing
should remain properly fitted. For proper
fitting the lower end of the casing is cut to size
as shown in Fig. 26. If necessary, the spacing
of the casing from the wall may be increased
by using a half bridge. Besides, every piece of
conduit should remain well-earthed.

INSULATING BUSH

EARTH WIRE

HALF-BRIDGE FIXED ON
CASING

EARTHING CLAMP FOR
t CONDUIT

2.5

(1 Inch)

FLOOR
INSULATING BUSH

Fig. 26 Leading of Cable Through the Floor

c) Utility of looping -in- system — Like cleat
wiring, casing wiring can also be done by
means of connectors inside junction boxes as
well as by looping-in-system. Loop wiring has
many advantages. No joint is necessary and
the insulation resistance is better retained by
this system than any other system of wiring.
The reason for no joint is that, one piece of
cable is joined with another piece only
through brass screws of switches and ceiling
roses. What is meant by jointing of cables does
not at all happen in this system. Its main
disadvantage, however, is that the length of
cable required for wiring is somewhat more.

6.3 Metal-sheathed Wiring

6.3.1 The wiring system completed with wires having
metallic (for example lead) covering over rubber
insulation is known as 'metal-sheathed' or 'lead-
covered' wiring. Here the conductors are rubber
insulated and covered with an outer sheath of lead alloy
containing about 95 percent lead which provides

NATIONAL ELECTRICAL CODE

SP 30:2011

protection against mechanical injury. Lead sheath
should be properly earthed.

6.3.2 The cables may remain exposed to sun or rain,
but it should not be used where acids and alkalies are
likely to be present. The cables are laid on wooden
battens and remain fixed on it by means of brass or
aluminium link clips spaced at intervals not exceeding
10 cm horizontally and 15 cm vertically. The thickness
of the batten should not be less than 10 mm.

6.3.3 Installation of Metal Sheath

a) Sharp bends should be avoided. A round bend
of radius not less than 10 cm may be adopted
for a change of direction.

b) Supporting clips used for the cables must not
set up any chemical reaction with the metal
sheath.

c) Lead sheath must be electrically continuous
and properly earthed. For maintaining
electrical continuity, bonding of sheaths is
necessary at joint-boxes and switch boards.

d) When passing through a floor or crossing a
wall, the cable must be drawn through
conduits. Conduits should go up to a height
of 1.5 m above the floor level. Both ends of
the conduit should be fitted with ebonite,
plastic or hard rubber bushings in order to
protect metal sheath and rubber insulation of
cables from being damaged.

6.3.4 Joints for Metal Sheathed Wiring

a) Connectors — Some special types of
connector are used for jointing wires or for a
T-joint to lead a cable to switch board etc.
These types of connector are more or less the
same for almost all types of wiring. As per
requirement two, three or four holes are
provided in small pieces of porcelain or
plastic, and inside those holes there are
connectors in the form of brass tubes. At the
two ends of the connector there are brass
screws for fixing the wires. The porcelain or
plastic portion acts as insulators. When only
one piece of wire is to be joined with another
piece, the smallest size connector with a single
piece of brass tube is used. For jointing twin-
wire (2-core) from a single cable, a connector
with two pieces of brass tubes is needed. In
place of junction cut-outs connector is used
even in cleat and casing wirings. There are
holes on the top of all connectors with screws
to connect wires with the connector (the left
hand one shows single-joint connector).
Sometimes the outer cover of a connector is

made of PVC or bakelite in place of porcelain.
But as an insulator the use of porcelain is
better than PVC or bakelite.
b) Thimbles — Thimble is made of porcelain or
plastic and looks like a cap as shown in
Fig. 27. A thimble is threaded inside and it
becomes pointed towards the upper end.
Where two or more wires are to be connected
together, about 6.4 mm of end insulation of
each wire is taken off and all the ends are then
twisted together. The combination is then put
inside a thimble which is turned like a screw
driver. As a result the thimble pulls the
combination of twisted ends in by means of
threads and thus holds it tightly.

Fig. 27 Wires Connected with Thimble

c) T- Joint — Where T-connection is taken for a
point, connectors used there and the mode of
connection are shown in Fig. 28. A small box,
called 'joint-box', is used to cover the joint.
The box may be made of metal or wood. The
box shall prevent access of insects, dust or
lime-water (during white washing). The
advantage of a metal box is that the speciality
of a lead-sheathed wiring to maintain
electrical continuity of metal sheath of the
cables everywhere beginning from the main
board upto the farthest point of the load circuit
is automatically retained in it, whereas in case
of a wooden box it is not so. If a wooden box
is to be used, an additional bonding clamp
must be provided in the box and the lead
sheaths of all the cables taken in for
connection shall remain fixed with this clamp
so that electrical continuity is established
among them. If metal sheath of the cable is to
be used as an earth continuity conductor, then
in case of non-metal box, a strip of metal is to
be used for maintaining continuity of metal
sheath, and the resistance of such metal strip
shall be negligible in comparison to that of

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

the largest size of cable coming into the box
(see Fig. 29). Joint-box must not be installed
in a damp place due to possibility of leakage
of current in the joint-box installed in a damp
place. Arrangement for maintaining
continuity between wires near a ceiling rose
is shown in Fig. 30. In this way, maintaining
continuity and electrical connections among
lead sheaths, finally the sheath is connected
to earth at the main distribution board. If this
is not done, the insulation of the cable gets
damaged in a very short time in metal-
sheathed wiring. If two or more lead-covered
wires are laid side by side and one wire has
leakage and its sheath is not well-bonded,
there will be sparking between them, causing
damage to the cable. In metal-sheathed
wiring, electrical continuity of sheath must
be maintained, and this sheath must not only
be well-earthed, but the earth connection must
also be well-maintained.

Bonding Strip and Unk'ClIp

Fig. 28 How Wires are Drawn and how These are
Connected in a T-joint

wwv

Tinned UnN Ctfp

/fy/Yh

Fig. 29 Use of Bonding Metal Strip in
a Wooden Joint-box
Lead-sheathed cables with earth wire —
Continuous earthing system ensures safety of
circuits. According to this system metallic
covers of table fan, electric iron, electric
heater, table lamp etc, are to be earthed. In
case of cleat or casing wiring a single G.I.
wire is to be drawn as the earth wire along
with the wiring throughout the house. Use of

cables having a single earth wire provided
along with insulated copper wire or wires
within the same lead sheath can be made.
While jointing two or more wires, a separate
connector should also joint all related earth
wires. If the outer cover and inner lever is
made of metal, the switch should also be
earthed as per rule. In such cases lead-
sheathed cables with earth wire inside is used.
Connection of earth wire of a circuit with earth
in the distribution board is shown in Fig. 31.
Descriptions of different methods and systems
of wiring (for example cleat or casing wiring)
are also applicable to metal-sheathed system.
Looping-in-system of wiring may also be
adopted with lead-sheathed cables where
necessary.

Fig. 30 Maintenance of Continuity
of Wires Near a Ceiling Rose

&&:* «M S

EARTH CONTINUITY BAR

EARTH WIRE

Fig. 31 Earth Continuity Bar and Arrangement

for Connection of Earth Wires

of Different Circuits

6.3,5 Installation of Wiring

a) Drawing of Cables through the Floor — The
lead-sheathed cable should be drawn through
a heavy gauze conduit pipe when the cable is
drawn from lower floor to upper floor. The
conduit length shall remain extended upto a

71)

NATIONAL ELECTRICAL CODE

SP 30 : 2011

height of 1.5 m above the floor level in the
upper floor, while the lower end of the conduit
shall remain flush with the ceiling of the lower
floor. Both ends of the conduit should be fitted
with bushes made of wood or ebonite or some
other insulating material.

b) Drawing of cables through partition wall
between two adjacent rooms — Like other
systems of wiring metal-sheathed cable
should also be drawn through porcelain wall-
tube or steel conduit or hard PVC conduit as
straight as possible.

c) Concealed wiring through the wall — Lead-
sheathed cable cannot be laid direct under
plaster. For concealed wiring it should be
either drawn through conduit pipe or by some
other means after which the whole thing is
covered with plaster.

6.4 Cab-Tyre Sheathed (C.T.S.) or Tough Rubber-
Sheathed (T.R.S.) Wiring

6.4.0 This type of wiring is adopted only for low voltage
circuits. C.T.S. wiring is used in open space in place
of drawing bare conductors. This system of wiring is
very useful in workshops or places where fumes are
generated continuously from acids etc, which may
damage the insulation of ordinary cables or wear out
conduits etc, or corrode the lead sheath of cables. No
other insulation is applied on the conductor except hard
rubber sheath, and in the wiring system cable may not
be drawn through conduit, casing etc. The advantages
of this system is that wiring can be done very easily
and quickly. As a result wiring is economical on the
whole, although the cable may cost more. C.T.S. wiring
can be used with a variety of fittings and also in case
of concealed wiring. The T.R.S. (C.T.S.) system has
however, now become almost obsolete; as it has been
replaced by the PVC insulated and sheathed system.

6.4.1 Installation of C.T.S. Wiring

When the sheath of C.T.S. cable made of rubber or
some other compound mixed with rubber remains
exposed to direct sunlight, arrangement must be
provided to cover it up properly. It should, however,
be noted that when sunlight comes through the glass
of a window, it is not regarded as direct sunlight. Where
weather proof or lead- sheathed cable is to be drawn
with the help of catenary wire, either the cable should
be taken by binding it continuously with the catenary
wire or it should remain fixed with catenary wire by
means of link clips at intervals of about 15 cm. C.T.S.
cable is drawn over the wall in the same way as lead-
sheathed cable. At first wooden plugs are grouted or
cemented in the wall at intervals of about 75 cm and
polished thin batten of teak wood as wide as or a little

wider than the cable is screwed to these plugs. Tinned
brass or aluminium link clips are then fixed on this
batten with the help of iron pins at intervals not
exceeding 10 cm horizontally and 15 cm vertically.
For the sake of convenience of work, sometimes clips
are fixed on the batten at equal intervals in a straight
line first and then the batten is screwed to the wooden
plugs. Finally the cable is laid neatly on the clips which
are then folded. In some cases a batten with clipped
cable is screwed to the wooden plugs. A single clip
may be used to fix upto two twin-core, 0.019 4 cm 2
cables. If the cross- section of the cable is greater than
this, a single clip may hold only one cable. Where there
are fumes from acids etc, clips are made of lead strips
cut out from then lead sheets and iron pins are already
painted with acid-proof paint. This prevents the iron
pins being rusted when in contact with acid fumes.
For a neat and clean look of C.T.S. wiring or for saving
it from mechanical injury, the wiring may be covered
by wooden channeling or any other suitable cover. Also
C.T.S. cables may be drawn through conduit pipes, if
necessary. During installation of C.T.S. wiring the
following points are to be kept in mind:

a) C.T.S. cables should be laid on well seasoned,
well varnished and perfectly straight hard
wood of thickness 10 mm and width sufficient
enough to carry the required number of
cables.

b) Wooden batten should remain fixed to rawl
or phil plugs grouted in the wall or ceiling by
means of wood screws at an interval not
exceeding 75 cm.

c) C.T.S. cables shall never be turned at right
angles. Wherever there is a bend, the radius
of curvature shall not be less than six times
the outer diameter of the cable. While passing
through wall or floor, cable must be drawn
through conduit pipes. Metal conduit should
be properly earthed.

d) C.T.S. cables shall never be buried under
plaster. These should be drawn through
conduit or wooden channeling.

e) While taking through a floor, the cable shall
be drawn through a heavy conduit. The two
ends of the conduit should be fitted with
bushes made of wood or rubber or any other
suitable insulating material. The bottom of the
conduit should be flush with the ceiling of
the lower floor, while its top must rise upto a
height of 1.5 m above the floor level of the
upper floor. Porcelain tubes may also be used
when the cables are drawn through a wall.

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

6.5 Polyvinyl Chloride (PYC) Sheathed Wiring

6.5.0 PVC sheathed cable is used extensively in house
wiring. This cable is available in single-core, twin-core
or three-core, and its cost is comparatively less than
that of other wires. PVC cable may be used for wiring
in open space in place of bare conductor or C.T.S. cable.
The rubber sheath of C.T.S. cable deteriorates quickly
in places where there is oil, but PVC insulation is highly
suitable in such places. PVC insulation can withstand
acid, alkali, ozone and also direct sunlight. Owing to
gaps in the sheath it does not dry up, harden and crack
like rubber. But at higher temperatures PVC softens
because of which it should not be used at places where
it is expected to get excessively heated. Also, PVC
insulation becomes brittle in very cold atmosphere
therefore it should not be used in places where there is
ice or snow fall. Wiring systems of PVC wire is similar
to that of C.T.S. wiring. However, as the PVC wire is
comparatively lighter than C.T.S. wire, link clips are
to be fixed on wooden battens at comparatively closer
intervals. The distance between two adjacent link clips
should be 6 cm horizontally and 7.5 cm vertically. For
conduit wiring as well as for concealed wiring, PVC
cables are drawn through conduit pipes in place of
V.I.R. wires. The first all-insulated wiring system
consisted of vulcanized insulated conductors with a
tough cables sheath (T.R.S.). When first introduced the
system was known as "cab-type" system (C.T.S.). The
T.R.S. (C.T.S.) system has now become almost
obsolete; as it has been replaced by the PVC insulated
and sheathed system. PVC and similar sheathed cables
if exposed to direct sunlight shall be of a type resistant
to damage by ultraviolet light. PVC cable should not
be exposed to contact with oil, creosote and similar
hydrocarbons, or should be of a type capable of
withstanding such exposure. The cables may be
installed without further protection, except where
exposed to mechanical damage, in which case they
must be suitably protected. The all-insulated wiring
system is used extensively for lighting and socket
installation in small dwellings, and is one of the most
economical methods of wiring for this type of work.
See IS 14772 for joint boxes and IS 371 for ceiling
roses. An alternative method for wiring with PVC
sheathed cables for lighting is to use 2-core and circuit
protective conductor cables with 3 plate ceiling roses
instead of joint boxes. At the positions of joint boxes,
switches, sockets and luminaries the sheathing must
terminate inside the box or enclosure, or could be partly
enclosed by the building structure if constructed of
combustible material.

6.5.1 Installation of PVC Wiring

a) Bends in Wiring — The wiring shall not in
any circumstances be bent so as to form a right

angle but shall be rounded off at the corners
to a radius not less than six times the overall
diameter of the cable.

b) Keeping cables away from pipework —
Insulated cables must not be allowed to come
into direct contact with gas pipes or non-
earthed metal work, and very special care
must be exercised to ensure they are kept away
from hot water pipes.

c) Precautions for cables passing through walls,
ceiling, etc — Where the cables pass through
walls, floors, ceilings, partitions, etc, the holes
shall be made good with incombustible
material to prevent the spread of fire. It is
advisable to provide a short length of pipe or
sleeving suitable bushed at these positions and
the space left inside the sleeve should be
plugged with incombustible material. Where
the cables pass through holes in structural
steelwork, the holes must be bushed so as to
prevent abrasion of the cable. Where run
under wood floors, the cables should be fixed
to the side of the joists, and if across joists,
should be threaded through holes drilled
through the joists in such a position as to avoid
floorboard nails and screws. In any case,
screwed 'traps' should be left over all joint
boxes and other positions where access may
be necessary.

d) Fixing cables by suspension on catenary wires
— Cables can be taken across a lofty building,
or outside between buildings, if protected
against direct sunlight by suspending them on
catenary wires. Galvanized steel wires should
be strained tight and the cables clipped to the
wire with wiring clips. Alternatively, they can
be suspended from the wire with 'rawhide'
hangers; this provides better insulation
although not so neat as the former method.
The catenary wire must be bonded to earth.

e) Multicore cables have cores of distinctive
colours, the red should be connected to phase
terminals, the black to neutral or common
return and the protective conductor to the
earth terminal. Clips are much neater than
saddles, but when more than two cables are
run together it is generally best to use large
saddles. If a number of cables have to be run
together on concrete or otherwise where the
fixings are difficult to obtain, it is advisable
to fix a wood batten and then to clip or saddle
the cables to the batten. Cable runs should be
planned so as to avoid cables having to cross
one another, and additional saddles should be
provided where there is change in directions.

NATIONAL ELECTRICAL CODE

SP 30 : 2011

PVC sheathed cables should not be used for
any systems where the normal voltage exceed
1000 V.
f) Wiring to socket outlets — When PVC cables
is used for wiring to socket outlets of other
outlets demanding an earth connection, it is
usual to provide 2-core and circuit protective
conductor cables. These consist of two
insulated conductors and one uninsulated
conductor, the whole being enclosed in the
PVC sheathing. The protective conductor
shall comply with IS 3043. When wiring to
16-amps standard domestic sockets, the cable
will have to be taken into standard box which
is designed for these sockets and which
includes an earth terminal.

6*6 All-Insulated Wiring

The first all-insulated wiring system consisted of
vulcanized insulated conductors with a tough cables
sheath (T.R.S.). The system was initially know as "cab-
type" system (C.T.S.). The T.R.S. (C.T.S.) system has
now become almost obsolete; as it has been replaced
by the PVC insulated and sheathed system. The PVC
system has many advantages over the old T.R.S. system
because it is not so inflammable, and will stand up
better to direct sunlight and chemical action. The cables
may be installed without further protection, except
where exposed to mechanical damage, when they must
be suitably protected. This all-insulated wiring system
is used extensively for lighting and socket installation
in small dwellings, and is probably the most
economical method of wiring for this type of work. It
is customary to use 2 and 3 -core cables with an integral
protective or 4-terminal ceiling roses for making the
necessary connections.

An alternative method for wiring with PVC sheathed
cables for lighting is to use 2-core and CPC cables
with 3 plate ceiling roses instead of joint boxes.
Terminations of joints in these cables must be enclosed
in non-ignitable material, such as a box complying with
IS 14772.

NOTE — An accessory is a device, other than current using
equipment associated with such equipment or with the wiring
of installation.

At the positions of joint boxes, switches, sockets and
luminaries the sheathing must terminate inside the box
or enclosure, or could be partly enclosed by the
building structure if constructed of combustible
material.

6.6.1 Surface Wiring

When cables are run on the surface, a box is not
necessary at outlet positions providing the outer
sheathing is brought into the accessory or luminaries,

or into a block or recess lined with incombustible
materials, or into a plastic patress. For vertical-run
cables which are installed in accessible positions and
unlikely to be disturbed, support shall be provided at
the top of the cable, and then at intervals of not less
than 5 m. For horizontal runs the cables may rest with-
out fixing in positions which are in accessible and are
not likely to be disturbed, provided that the surface is
dry, reasonably smooth and free from sharp edges. For
cables installed in accessible portions the fixing space
for cable is 100 to 250 mm for horizontal runs and
150 to 400 mm for vertical runs.

Link clips for electrical wiring shall be used for fixing
the cables installed in accessible positions. Link clips
shall be so arranged that one single clip shall not hold
more than two twin-core T.R.S. or PVC-sheathed
cables up to 1.5 mm 2 above which single clips shall
hold a single twin-core cable. The clips shall be fixed
on varnished wood battens with any rust resisting pins
or screws. For the wiring and runs of mains exposed to
heat and rain, clip specially made for outdoor use from
a durable metal, resistant to weather and atmospheric
corrosion shall be used (see IS 2412 for link clips).

6.6.2 Concealed Wiring

PVC wiring, concealed in ceiling partition, is an
effective method of providing a satisfactory installation
where appearance is of prime importance as in
domestic, display or office situations. Where it is
impractical to run concealed wiring at these locations,
special precautions are necessary, appropriate
protection must be provided. This may take the form
of a cable incorporating an earthed metal sheath, or by
enclosing the cables in earthed metallic conduit,
trunking or ducting. PVC sheathed cables shall not be
buried direct in cement or plaster. The disadvantage is
that cables once buried in cement or plaster cannot be
withdrawn should any defect occur. It is better to
provide a plastic conduit to the switch or outlet
positions, so that the PVC cables can be drawn into
the conduit, and withdrawn should the need arise. Such
an arrangement must also comply with the location
constraints. Whichever construction is employed, it is
necessary to provide a box at all light, switch and socket
outlet position. The boxes must be provided with
earthing terminals to which the protective conductor
in the cable must be connected. If the protective
conductor is a bare wire in multicore cable, a green/
yellow sheath must be applied where the cable enters
the box.

6.7 Enclosed Wiring System

6.7.0 Many of the original installations consisted of
single-core cable supported in cleats. With increasing
awareness of the possibility of hazard, the necessity

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

for greater protection created the demand for
enclosures such as conduit and, later, trunking of which
there are many different types now available to suit
different situations.

6.7.1 Conduit Wiring Systems

6.7.1.0 Wiring done by insulated wires drawn through
iron or steel pipes is known as conduit wiring. Conduit
systems, when assembled in accordance with the
manufacturer's instructions, shall have adequate
resistance to external influences according to the
classification declared by the manufacturers with a
minimum requirement of IP 30. A conduit system
which conforms to IS 14930 (Part 1) is deemed safe
for use. To ensure safety in electrical installations, use
of metallic conduits as earth continuity conductor is
not permitted.

NOTES

1 Certain conduit systems may also be suitable for use in
hazardous atmosphere. Regard should be taken for the extra
requirement necessary for equipment to be installed in such
condition.

2 Earthing conductors may or may not be insulated. Earthing
conductors may or may not be insulated if laid outside, but
invariably be insulated.

See IS 14930 (Part 2) for requirements and tests for
conduit systems buried underground, including
conduits and conduit fittings for the protection and
management of insulated conductors and/or cables in
electrical installations in communication systems and
IS 9537 (various parts) for conduits. Conduit diameters

shall be preferably according to Table 7 and points of
support in accordance with Table 8. Classification
coding of conduit systems is given at Annex B.

6.7.1.1 Types of Conduits

a). Steel conduit system — IS 9537 (Part 2)
specifies the requirement of rigid steel
conduits. The screwed steel conduit system
is used extensively for permanent wiring
installations, especially for modern
commercial and industrial buildings (see
Fig. 32). Its advantages are that it affords the
conductors good mechanical protection,
permits easy rewiring when necessary and
minimizes fire risks. The disadvantages are
that it is expensive compared with other
systems, is difficult to install under wood
floors in houses and flats, and is liable to
corrosion when subjected to acid, alkali and
other fumes. Moreover, under certain
conditions, moisture due to condensation may
form inside the conduit. Solid drawn conduit
is much more expensive than welded conduit,
due to which its use is generally restricted to
gas-tight and explosion-proof installation
work. Welded screwed conduit is, therefore,
generally used for most installation.

b) Copper conduit — At some places, copper
conduit is used as it resists corrosion and
provides excellent continuity. However, the

Table 7 Outside Diameters — Preferred Values
(Clause 6.7.1.0)

SI No.

Nominal Size

Outside Diameter

Tolerance

Inside Diameter, Min

(1)

(2)

(3)

(4)

(5)

+0.5

ii)

+0.6

iii)

+0.8

iv)

+ 1.0

+ 1.2

vi)

+ 1.4

vii)

+ 1.7

viii)

110

+2.0

ix)

120

+2.2

125

+2.3

xi)

140

+2.6

106

xii)

160

+2.9

120

xiii)

180

+3.3

135

xiv)

200

+3.6

150

xv)

225

+4.1

170

yvH

750

?50

+45

188

NOTES

1 Tolerance on outside diameters are given as follows:

a) Outside diameter specified are nominal dimensions.

b) Outside diameter maximum is nominal outside diameter + (0,018 x nominal outside diameter values) rounded off to + 0.1 mm.

c) Minimum inside diameter is nominal outside diameter divided by 1.33.

2 Any other sizes other than those mentioned in Table 7 shall be as per the agreement between the buyer and the seller.

NATIONAL ELECTRICAL CODE

SP 30 : 2011

use is limited because the cost could prove to
be prohibitive. Copper conduit can be screwed
in the same manner as steel conduit although
the screwing of copper is more difficult than
mild steel. Connections are generally made
by soldering. Bronze junction boxes should
preferably be used.

SMOOTH
BRASS

32A With Smooth Bore Bush and Coupling

BRASS
BUSH

32B With Brass Ring Bush and Back Nut

Fig. 32 Methods of Fixing Screwed Conduit at
Clearance Entries in Metal Casing or Boxes

c) PVC conduit — When first introduced, such
conduits had many disadvantages compared
to steel — the material was mechanically

weak, greatly affected by changes in
temperature, did not retain sets, maintained
combustion (and emitted toxic fumes) and
tended to separate at joints. These problems
have now been overcome and, in some
respects, plastics conduits have many
advantages over steel. It is much lighter and,
therefore, easier to handle and install, provides
a smoother surface for the drawing of the
cables, is not subject to corrosion and rusting,
and the super high impact materials now used
make it suitable for most applications,
d) Flexible conduit — Several different types of
flexible conduit are available, ranging from
convoluted plastics to reinforced corrugated
steel covered both internally and externally
with self-extinguishing plastics, the latter
being the most appropriate for general use. It
is particularly useful for final connections to
machinery subject to vibration in place of the
alternative methods of flexible cable or coiled
mineral insulated copper cables (MICCs).
Flexible conduit shall conform to relevant
Indian Standard.

6.7*1.2 Cables in conduits

The types of cables which may be installed in conduits
are PVC single-core insulated, butyl or silicone rubber
insulated, with copper or aluminium conductors. PVC
insulated and sheathed cables are sometimes installed
in conduits when the extra insulation and protection is
desirable. Under no circumstances may ordinary
flexible cords be drawn into conduit.

6.7.1.3 Selection of correct size of conduit

After selection of the correct size of cables for a given
electrical load is made, the selection of the appropriate
size of conduit to accommodate these cables is to be
done. The number of cables which may be drawn into
any conduit must be such that it allows easy drawing

Table 8 Spacing of Supports for Conduits

(Clause 6.7.1.0)

SI No.

Nominal Size of
Conduit

Maximum Distance between Supports

*r— '

~~~—~*.

Rigid Metal

Rigid

Insulation

Pliable

• ■*—

,-*-,

~*~

*•

*^~~

-*\

Horizontal

Vertical

Horizontal

Vertical

Horizontal

Vertical

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

Not exceeding 16

0.75

1.0

0.75

1.0

0.3

0.5

ii)

Exceeding 16 and not
exceeding 25

1.75

2.0

1.5

1.75

0.4

0.6

iii)

Exceeding 25 and not
exceeding 40

2.0

2.25

1.75

2.0

0.6

0.8

iv)

Exceeding 40

2.25

2.5

2.0

0.8

1.0

NOTE

— A flexible conduit is no

t normally required to be supported

in its run.

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

in, and in no circumstances may it be in excess of the
maximum given in Part 1/Section 20 of this Code. For
larger cables it is preferable to install cables in trunking.
As the number of cables or circuits in a given conduit
or trunking increase, the current-carrying capacities
of the cables decrease. Therefore it is advisable not to
increase the size of the conduit or trunking in order to
accommodate more cables, but to use two or more
conduits. The conduit installation must be complete
before cables are drawn in. This is to ensure that
subsequent wiring can be carried out just as readily as
the original. Also the installation must be arranged so
that cables are not drawn round more than two rigid-
angle bends. This conduit is complete and ready for
wiring, and will be concealed when the wall panels
are fitted.

6.7.1.4 Conduit system

There are two distinct conduit systems, the surface
system, and the concealed system.

6,7.1.4.1 Surface system

a) Choice of runs — The most suitable 'run'
should be chosen for the conduits. When there
are several conduits running in parallel, they
must be arranged to avoid crossing at the point
where they take different directions. The
routes should be chosen so as to keep the
conduits as straight as possible, only deviating
if the fixings are not good. The 'runs' should
also be kept away from gas and water pipes
and obstructions which might prove difficult
to negotiate. Locations where they might
become exposed to dampness or other adverse
conditions should be avoided.

b) Conduit fittings — Bends, inspection tees and
elbows, made in accordance with relevant
Indian Standards may be used. However,
bends can be made by setting the conduit, and
where there are several conduits running in
parallel which change direction, it is necessary
for these bends to be made so that the conduits
follow each other symmetrically which is not
possible if manufactured bends are used. The
use of inspection elbows and tees is not good
practice, as there is insufficient room for
drawing in cables and, in addition, the
installation presents a shoddy appearance.
Round boxes in accordance with relevant
Indian Standards may, instead be used. These
boxes have a much better appearance, provide
plenty of room for drawing in cables, and can
accommodate some slack cable which should
be stowed in all draw-in points. For conduits
up to 25 mm diameter, the small circular boxes

should be used. Circular boxes are not suitable
for conduits larger than 32 mm, and for these
larger sizes rectangular boxes should be used
to suit the size of cables to be installed. The
inspection sleeve is a very useful draw-in
fitting, because its length permits the easy
drawing in of cables and its restricted width
enable conduits to be run in close proximity
without the need to * set' the conduits at draw-
in points. Where two or more conduits run in
parallel, it is a good practice to provide at
draw-in points an adaptable box which
embraces all of the conduits. This presents a
much better appearance than providing
separate draw-in boxes and has the advantage
of providing junctions in the conduit system
which might prove useful if alterations have
to be made at a later date. Where two or more
conduits are run in parallel, it is good practice
to embrace all conduits with an adaptable box
as shown in Fig. 35. An advantage of the
conduit system is that the cables can be
renewed or altered easily at any time. It is,
therefore, necessary that all draw-in boxes
should be readily accessible, and subsequently
nothing should be fixed over or in front of
them so as to render them inaccessible. The
need for the conduit system to be complete
for each circuit, before cables are drawn in,
is to ensure that subsequent wring can be
carried out just as readily as the original; it
prevents cables becoming damaged where
they protrude from sharp ends of conduit, and
avoids the possibility of drawing the conduit
over the cables during the course of erection.

c) Radius of conduit bends — Facilities such as
draw-in boxes, must be provided so that cables
are not drawn round more than two right-angle
bends or their equivalent. The radius of bends
must not be less than the standard normal bend
(see also Fig. 36 and Table 9).

d) Methods of fixing conduit — There are several
methods of fixing conduit, and the one chosen
generally depends upon what the conduit has
to be fixed to.

1) Conduit clips — Conduit clips take the
form a half saddle, and have only one
fixing lug. The reason for using clips
instead of saddles is to save an additional
fixing screw. They are not satisfactory if
the conduit is subjected to any strain.

2) Ordinary saddles — Ordinary saddles
provide a very secure fixing (see Fig. 37).
They should be fixed by means of two

NATIONAL ELECTRICAL CODE

SP 30 : 2011

Multiple
Saddle"

Two-way through-box
-Two-way through-box

Bending of conduit is
Shown in the diagram

Conduit Fitting
Fig. 33 Bending of Conduit

Right side
angle box

Fig. 34 Fittings of Conduits

NOTE — Where two or more conduits are run in parallel it is good practice to embrace all conduits with an adaptable box.

Fig. 35 Conduits Run in Parallel

NOTE — Cable must not be drawn round more than two right angle bends or their equivalent. The four bends in the lower diagram are
each 45° making a total of 180° in all.

Fig. 36 Drawing of Cables in Bends

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

Table 9 Minimum Internal Radii of Bends in Cables for Fixed Wiring
[Clause 6.7.1.4.1(c)]

SI No.

(1)

Insulation

(2)

Finish

(3)

Overall Diameter

(4)

Factor to be Applied to

Overall Diameter 1} of Cable

to Determine Minimum

Internal Radius of Bend

(5)

i) XLPE, PVC or rubber (circular, or

Non-armoured

Not exceeding 10 mm

circular stranded copper or aluminium
conductors)

Not exceeding 25 mm
Exceeding 25 mm
Armoured Any

ii) XLPE, PVC or rubber (solid aluminium Armoured or non-armoured Any

or shaped copper conductors)
iii) Mineral Copper of aluminium sheath

with or without PVC overing

3(2) 2)
4(3) 2)
6
6

1} For flat cables the factor is to be applied to the major axis.

2) The figure in brackets relates to single-core circular conductors of stranded construction installed in conduit, ducting or trunking.

screws and should be spaced not more
than 1.3 m apart. Nails must not be used
for fixing (see Fig. 37). The conduit
boxes to which luminaries are to be fixed
should be drilled at the back and fixed,
otherwise a saddle should be provided
close to each side of the box (see Fig. 38).

Fig. 37 Spacing Saddles with Oval Holes

Fig. 38 Saddle

3) Spacer bar saddles — Spacer bar saddles
are ordinary saddles mounted on a
spacing plate. This spacing plate is
approximately the same thickness as the
sockets and other conduit fittings and,
therefore, serves to keep the conduit
straight where it leaves these fittings as
well as to prevent the conduit from

making intimate contact with damp
plaster and cement walls and ceilings
which would result in corrosion of the
conduit and discoloration of the
decorations. When conduit is fixed to
concrete a high percentage of the
installation time is spent in plugging for
fixing, and the use of the spacer-bar
saddle which has only a one-hole fixing
in its centre has an advantage over the
ordinary saddle. Some types of spacer bar
saddles are provided with saddles having
slots instead of holes. The idea is that the
small fixing screws need only be loosened
to enable the saddle to be removed,
slipped over the conduit and replaced (see
Fig. 31 and 40). This advantage is offset
by the fact that when the saddle is fixed
under tension there is tendency for it to
slip sideways clear of its fixing screws,
and there is always a risk of this
happening during the life of the
installation if a screw should be come
slightly loose. For this reason holes rather
than slots are generally more satisfactory
in these saddles. When selecting the larger
sizes of spacer-bar saddles it is important
to make sure that the slotted hole which
accommodates the counter-sunk fixing
screw is properly proportioned.
Distance saddles — These are designed
to space conduits approximately 10 mm
from the wall or ceiling. Distance saddles
are generally made of malleable cast iron.
They are much more substantial than other
types of saddles, and as they space the
conduit from the fixing surface they
provide better protection against

NATIONAL ELECTRICAL CODE

SP 30 : 2011

corrosion. The use of this type of saddle
eliminates the possibility of dust and dirt
collecting behind and near the top of the
conduit where it is generally inaccessible.
For this reason distance saddles are usually
specified for hospitals, kitchens, and other
situation where dust traps must be avoided.
Multiple saddles — Where two or more
conduits follow the same route it is
generally an advantage to use multiple
saddles as it saves a considerable amount
of fixing time because only two screws are
required, and also all conduits are properly
and evenly spaced (see Fig. 39 and 42).

Fig. 39 Multiple Saddle

Fig. 40 Installation of Conduit
with Spacing Saddle

Fig. 41 Multiple Saddle

6) Girder clips — Where conduits are run
along or across girders, trusses or other
steel frame work, standard spring clips
may be used for be quick and easy fitting.
Other methods include a range of bolt-

on devices and if it is intended to run
number of conduits on a particular route
and standard clips are not suitable, it may
be advisable to make these to suit site
conditions, multiple girder clips can be
made to take a number of conduits run in
parallel. As an alternative to girder clips,
multiple saddles can be welded to
steelwork, or the steelwork could be
drilled in case there is no adverse effect
on its structural properties.
When conduits are suspended across
trusses or steel work there is a possibility
of sagging, especially if luminaries are
suspended from the conduit between the
trusses. These conduits should either be
of sufficient size to prevent sagging, or
be supported between the trusses. They
can sometimes be supported by iron rods
from the roof above (see Fig. 42 and 43).
If the trusses are spaced 3 mm or more
apart it is not very satisfactory to attempt
to run any conduit across them, unless
there is additional means of support. It is
far better to take the extra trouble and run
the conduit at roof level where a firm
fixing may be found.

Fig. 42 A U-section Fastened to a Concrete
Ceiling with Rag-Bolts Used to Carry a
Number of Saddles of the Required Size

PART 1 GENERAL AND COMMON ASPECTS

SF 30: 2011

Avoidance of gas, water and other pipes —
All conduits must be kept clear of gas and
water pipes, either by spacing or insulation.
They must also be kept clear of cables and
pipes which feed telephones, bells and other
services, unless these are wired to the same
standard as lighting, heating or power circuits.
One exemption to this is that conduits may
be fitted to electrically operated gas valves,
and the like, if they are constantly under
electrically skilled supervision. Another is that
conduits may make contact with water pipes
if they are intentionally bonded to them. They
must not make casual contact with water
pipes. If conduits have to be run near gas or
water pipes and there is a risk of their making
contact, they should be spaced apart with
wood or other insulating material. If the
conduit system reaches a high potential due
to defective cables in the conduit and
ineffective earth continuity, and this conduit
makes casual contact with a gas or water pipe,
either of which would be at earth potential,
then arcing would take place between the
conduit and the other pipe. This might result
in puncturing the gas pipe and igniting the
gas. There is greater likelihood of this
happening if the gas or water pipe is of lead.

[ ANGLE

1 IRON

TRUSS

40 X 3mm
FLAT IRON
CUP

Fig. 43 Supporting Several Conduits from
Angle Iron Truss

f) Protection of conduits — Although heavy
gauge conduit affords excellent mechanical
protection to the cables it encloses, it is
possible for the conduit itself to become
damaged if stuck by heavy objects. Such
damage is liable to occur in workshops where
the conduit is fixed near the floor level and
may be struck by trolley or heavy equipment

being moved or slung into position. Protection
can be afforded by threading a water pipe over
the conduit during erection, or by screening
it with sheet steel or channel iron. Another
method of protection is, of course, to fix the
conduit behind the surface of the wall.

r^-\

NOTE — The conduit is fixed to the ceiling with spacer bar
saddles.

Fig. 44 A Supporting Fitting from
Tangent Tee Box

TRUSS

SUPPORT
FROM ROOF
TO PREVENT
SAGGING

CONDUIT

STANCHION

Fig. 45 A Conduit Suspended Across
Roof Trusses

g) Termination of conduit at switch positions —
At switch positions the conduit must terminate
with a metal box or into an accessory or recess
lined with incombustible material.

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SP 30: 2011

Termination of conduit at other than switch
positions — Where conduit terminates a
ceiling or wall points other than at switch
positions, it must terminate with a meal box,
or recess, or a block of incombustible material.

WALL

SURFACE CONDUIT &
SURFACE SWITCH

FLUSH CONDUIT &
FLUSH SWITCH

NOTE — At switch positions, conduit must terminate with
metal box or other suitable enclosure.

Fig. 46 Typical Methods of Terminating Surface
and Concealed Systems

CONDUIT
BOX

CONDUIT
SET OUT
CLEAR OF
WALL

OUTLET
BOX

METAL
BOX

NOTE — A box or suitable enclosure must be fitted at all outlet
positions. Terminations as shown at B, C and D are not
permitted.

Fig. 47 Outlet Positions

j) Removal of burrs from ends of conduit —
When steel conduit is cut by a hacksaw, a burr
is formed upon the inner bore of the conduit.
If this burr were not removed it would cause
considerable damage to the insulation of the
cables drawn into the conduit. Ends of lengths
of conduit should be free from burrs, and
where they terminate at boxes, trunking and
accessories not fitted with spout entries, should
be treated so as to eliminate damage to cables.

k) Conduit Installed in damp conditions — If
metallic conduits are installed externally or in
damp situations, they should either be
galvanized, sherardized, or be made of copper,
and all clips and fixings (including fixing
screws) shall be of corrosion-resisting material

and should be free from burrs. When there is a
danger of condensation forming inside conduit
(for example, where there may be changes of
temperature) suitable precautions should be
taken. Holes may be drilled at the lowest points
of the conduit system or, alternatively, conduit
boxes with drainage holes should be fitted.
Drainage outlets should be provided where
condensed water might otherwise collect.
When ever possible conduit runs should
designed so as to avoid traps for moisture.

Continuity of the conduit system — A screwed
conduit system must be mechanically and
electrically continuous across all joints so that
the electrical resistance of the conduit,
together with the resistance of the earthing
lead, measured from the earth electrode to any
position in the conduit system shall be
sufficiently low so that the earth fault current
operates the protective device. To achieve this
it is necessary to ensure that all conduit
connections are tight and that the enamel is
removed form adaptable boxes and other
conduit fittings where screwed entries are not
provided. To ensure the continuity of the
protective conductor throughout the life of the
installation, a separate circuit protective
conductor is drawn into the conduit for each
circuit in the conduit._Conduits must always
be taken direct into distribution boards,
switchfuses, switches, isolators, starters,
motor terminal boxes, etc, and must be
electrically and mechanically continuous
throughout. Conduits must not be terminated
with a bush and unprotected cables taken into

COUPLER AND LOCKNUT
IN POSITION

Fig. 48 Connecting Two Lengths of Conduit

Neither of Which can be Turned, by Use of

Coupler and Lockout

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

switchgear and other equipment. The
switchgear must be connected mechanically
either with solid conduits, or with flexible
metallic conduits,
n) Flexible metallic conduit — Flexible metallic
conduits are used for final connections to
motors so as to provide for the movement of
the motor if fixed on slide rails. It also prevents
any noise or vibration being transmitted from
the motor, or the machine to which it may be
coupled, to other parts of the building through
the conduit system (see Fig. 49). These
flexible conduits should preferably be of the
watertight pattern and should be connected
to the conduit by means of brass adaptors.
These adaptors are made to screw on to the
flexible tubing and also into the conduit. It is
good practice to braze the adaptor to the
metallic tubing, otherwise it is likely to
become detached and expose the cables to
mechanical damage. The use of flexible
metallic tubing which is covered with PVC
sleevings is recommended as this outer
protection prevents oil from causing damage
to the rubber insertion in the joints of the
tubing.

CPC TERMINATES
WITHIN MOTOR
CONNECTION BOX

NOTE — Figure 49A shows the wrong method, which is
frequently adopted because proper conduit outlets are not
always provided on starters and motors. The lengths of
unprotected cable are subject to mechanical damage which may
lead to electrical breakdown. Figure 49B illustrates the right
method. Conduit is either taken direct into the equipment or
terminated with flexible metallic conduit and a suitable c.p.c.

Fig. 49 Termination Conduit at
Switch and Starter

p) Surface conduit feeding luminaires and clocks
— When surface conduit run to feed wall or
ceiling accessory like luminaries/clock etc
which are fixed direct to the wall or ceiling, it
is advisable, if possible, to set the conduit into
the wall a short distance from the position of
the accessory as shown in Fig. 50.

Fig. 50 Surface Conduit System when Fitting/
Accessory must be Flush on Wall or Ceiling

q) Drawing cables into conduits

1) Cables must not be drawn in to conduits
until the conduit system for the circuit
concerned is complete, except for
prefabricated flexible conduit systems
which are not wired in-situ.

2) When drawing in cables they must first
of all be run off the reels or drums, or the
reels must be arranged to revolve freely,
otherwise if the cables are allowed to
spiral off the reels they will become
twisted, and this would cause damage to
the insulation. If only a limited quantity
of cable is to be used it may be more
convenient to dispense it direct from one
of the boxed reels which are now on the
market.

3) Cable must not be allowed to spiral off
reels or it will become twisted and the
insulation damaged.

4) If a number of cables are being drawn
into conduit at the same time, the cable
reels should be arranged on a stand or
support so as to allow them to revolve
freely.

5) In new buildings and in damp situations
the cable should not be drawn into
conduits until it has been made certain
that the interiors of the conduits are dry
and free from moisture. If in doubt, a draw
wire with a swab at the end should be
drawn through the conduit so as to

NATIONAL ELECTRICAL CODE

SP 30 : 2011

remove any moisture that may have
accumulated due to exposure or building
operations.

6) It is usual to commence drawing in cables
from a mid-point in the conduit system
so as to minimize the length of cable
which has to be drawn in. A draw-in tape
should be used from one draw-in point
to another and the ends of the cables
attached. The ends of the cables must be
bared for a distance of approximately
50 mm and threaded through a loop in
the draw tape. When drawing in a number
of cables they must be fed in very
carefully at the delivery end whilst some
one pulls them at the receiving end.

7) The cables should be fed into the conduit
in such a manner as to prevent any cables
crossing, and also to avoid them being
pulled against the sides of the opening
of the draw-in box. In hot weather or
under hot conditions, the drawing-in can
be assisted by rubbing French chalk on
the cables. Always leave some slack
cable in all draw-in boxes and make sure
that cables are fed into the conduit so as
not to finish up with twisted cable at the
draw-in point.

8) This operation needs care and there must
be synchronization between the person
who is feeding and the person who is
pulling. If in sight of each other this can
be achieved by a movement of the head,
and if with in speaking distance by word
of command given by person feeding the
cables. If the two persons are not with in
earshot, then the process is somewhat
more difficult. A good plan is for the
individual feeding the cables to give pre-
arranged signals by tapping the conduit
with a pair of pliers.

9) In some cases, it may be necessary for a
third person to be stationed midway
between the tow positions to relay the
necessary instructions from the person
feeding to the person pulling. Otherwise
cables may become crossed and this
might result in the cables becoming
jammed inside the conduit.

10) The number of cables drawn into a
particular size conduit should be such that
no damage is caused to either the cables
or to their enclosure during installation.
It will be necessary, after deciding the
number and size of cables to be placed

in a particular conduit run, to determine
the size of conduit to be used. Each cable
and conduit size is allocated a factor and
by summing the factors for all the cables
to be run in a conduit route, the
appropriate conduit size to use can be
determined.

6.7.1.4.2 Concealed conduit system

6.7.1.4.2.1 Screwed metal conduit is particularly
suitable for concealed wiring. The conduit can be
installed during building operations and can be safely
buried in floors and walls whether the floors or walls
are constructed of wood, brick, hollow tiles or solid
concrete, in such a manner that the cables can be drawn
in at any time after the completion of the building. The
conduit system, if property installed, can be relied upon
adequately to protect the cables and allows them to be
replaced at any time if desired. Most modern buildings,
including blocks of flats, are constructed with solid
floors and solid walls and it is necessary for the conduit
(if concealed) to be erected during the construction of
the building. In other types of building where there
are wooden joists and plaster ceilings, conduit will have
to be run between and across the joists.

Running conduit in wooden floors — Where
conduit is run across the joists, they will have
to be slotted to enable the conduit to be kept
below the level of the floor boards. When slots
are cut in wooden joists they must be kept as
near as possible to the bearings supporting
the joists, and the slots should not be deeper
than absolutely necessary, otherwise the joists
will be unduly weakened {see Fig. 51). The
slots should be arranged so as to be in the
centre of any floorboards, if they are near the
edge there is the possibility of nails being
driven through the conduit. The slots cut in
the joists should be no deeper than necessary
and kept as near as possible to the bearing of
the joints so as not to weaken them unduly.
'Traps' should be left at the position of all
junction boxes. These traps should consist of
a short length of floor board, screwed down
and suitably marked.

FLOOR BOARDS

Fig. 51 Running Conduit in Wood Floors to Feed
Lighting Points

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

b) Running conduits in solid floors — Where c)

there are solid floors, it is impossible to leave
junction boxes in the floors, unless there is a
cavity above the top of the floor slab, in which
case the conduits may be run in the cavity
and inspection boxes arranged so as to be
accessible below the floor boards. Otherwise
the conduit needs to be arranged so that cables
can be drawn in through ceiling or wall points.
This methods is known as the' looping-in
system' , and it is shown in Fig. 52 and Fig. 53
and conduit boxes are provided with holes at
the back to enable the conduit to be looped
from one box to another. These boxes are
made with two, three or four holes so that it
is possible also to tee off to switches and
adjacent ceiling or wall points. If the floors
are of reinforced concrete, it may be necessary
to erect the conduit system on the shuttering
and to secure it in position before the concrete
is poured. Wherever conduit is to be buried
by concrete, special care must be taken to d)

ensure that all joints are tight, otherwise liquid
cement may enter the conduit and form a solid
block inside. Preferably the joints should be
painted with bitumastic paint, and the conduit
itself should also be painted where the enamel
has been removed during threading of setting.
Sometimes the conduits can be run in chases
cut into concrete floors; these should be
arranged so as to avoid traps in the conduit
where condensation may collect and damage
the cables.

Conduit runs to outlets in walls — Sockets
near skirting level should preferably be fed
from the floor above rather than the floor
below, because in the latter case it would be
difficult to avoid traps in the conduit (Fig. 54),
When the conduit is run to switch and other
positions in walls it is usually run in a chases
in the wall. These chases must be deep
enough to allow at least 10 mm of cement
and plaster covering; otherwise rust from the
conduit may come through to the surface.
Conduits buried in plaster should be given a
coat of protective paint, or should be
galvanised. The plaster should be finished
neatly round the outside edges of flush switch
and socket boxes, otherwise the cover plates
may not conceal any deficiencies in the
plaster finish. When installing flush boxes
before plastering, it is advisable to stuff the
boxes with paper to prevent their being filled
with plaster.

Ceiling points — At ceiling points the conduit
boxes will be flush with the finish of the
concrete ceiling. If the ceiling is to have a
plaster rendering, this will leave the front of
the boxes recessed above the plaster finish.
To overcome this it is possible to use extension
rings for standard conduit boxes. At the
position of ceiling points pit is usual top
provide a standard found conduit box, with
an earth terminal, but any metal box or
incombustible enclosure may be used,
although an earth terminal must be provided.

-NUMBERS INDICATE NUMBER OF CABLES IN THE
CONDUITS

Fig. 52 Typical Arrangement of Concealed Conduits Feeding Lighting Points by Looping the Conduit

into the Back of Outlet Boxes

NATIONAL ELECTRICAL CODE

SP 30 : 2011

///^///MMMK^^^mm////M

Fig. 53 Details of Conduit Box and Method of Hastening Conduit

WRONG
METHOD

SOCKET OUTLET
BOXES

FLOOR

fazZZa2Z3%?7^

CORRECT METHOD

LOOPING BOXES

SOCKET OUTLET
BOXES

CEILING

FLOOR

NOTE — If the sockets are fed from the floor below, it is difficult to avoid a trap for moisture.

Fig. 54 Right and Wrong Methods of Feeding Socket Near Skirting Level

e) Running sunk conduits to surface distribution
boards — Where surface mounted
distribution boards are used with a sunk
conduit, the problems arises as to the best
method of terminating flush conduits into the
surface boards. One method is to 'set' the
conduits out to the required distance into the
surface boards but this is not recommended.
A better method is to fit a flush adaptable box

in the wall behind the distribution board and
to take the flush conduits directly into it. Holes
can be drilled in the back of the distribution
board and bushed. Spare holes should be
provided for future conduits. Alternatively, an
adaptable box can be fitted at the top of the
distribution board, partly sunk into the wall
to receive the flush conduits, and partly on
the surface to bolt on the top of the distribution

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

board. Distribution boards must be bonded to
the adaptable boxes.

f) Before wiring sunk conduit - — Before wiring,
the conduits for each circuit must be erected
complete. Not only should they be complete
but they must be clean and dry inside
otherwise the cables may suffer damage. No
attempt should be made to wire conduits
which are buried in cement until the building
has dried out and then the conduits should be
swabbed to remove any moisture or
obstruction which may have entered them.

g) The light mechanical stress unscrewed conduit
system — The light mechanical stress conduit
system consists of conduits, the walls of which
are not of sufficient thickness to allow them
to be threaded. Instead of screwed sockets and
fittings grip type fittings are used.

h) Insulated conduit system — Non-metallic
conduits are now being increasingly used for
all types of installation work, both for
commercial and house wiring. The PVC rigid
conduit is made in various sizes and there are
various types of conduit fittings, including
boxes available for use with this conduit. The
type of universal conduit box is made of a
plastic material, and fitted with special
sockets, and enable the conduit to be merely
slipped into position, and secured by locking
ring. No cement is required, except that it is
recommended in damp situations. The
advantage of the insulated conduit system is
that it can be installed much more quickly than
steel conduit, it is non-corrosive, impervious
to most chemicals, weatherproof, and it will
not support combustion. The disadvantages
are that it is not suitable for temperatures
below -5°C or above 60°C, and where
luminaries are suspended from PVC conduit
boxes, precautions must be taken to ensure
that the heat from the lamp does not result in
the PVC box reaching a temperature
exceeding 60°C. For surface installations it is
recommended that saddles be fitted at
intervals of 800 mm for 20 mm diameter
conduit, and intervals of 1 600 mm to
2 000 mm for larger sizes. The special sockets
and saddles for this type of conduit must have
provision to allow for longitudinal expansion
that may take place with variations in ambient
temperature. It is necessary to provide a circuit
protective conductor in all insulated conduit,
and this must be connected to the earth
terminal in all boxes for switches, sockets and
luminaries. The only exception is in

connection with Class 2 equipment, that is,
equipment having double insulation. In this
case a protective conductor must not be
provided. Flexible PVC conduits are also
available, and these can be used with
advantage where there are awkward bends,
or under floorboards where rigid conduits
would be difficult to install.

6.7.1.4.2.2 Installation of plastic conduit

Plastic conduits and fittings can be obtained from a
number of different manufacturers and the techniques
needed to install these are not difficult to apply. Care
is however needed to assemble a neat installation and
the points given below should be borne in mind. As
with any other installation good workmanship and the
use of good quality materials is essential.

It should be noted that the thermal expansion of plastic
conduit is about six times that of steel, and so whenever
surface installation of straight runs exceeding 6 m is
to be employed, some arrangement must be made for
expansion. The saddles used have clearance to allow
the conduit to expand. Joints should be made with an
expansion coupler, which is attached with solvent
cement to one of the lengths of tube, but allowed to
move in the other.

Cutting the conduit can be carried out with a fine tooth
saw or using the special tool. As with steel conduit, it
is necessary to remove any burrs and roughness at the
end of the cut length.

Bending the small sizes of plastic conduit up to 25 mm
diameter can be carried out cold, A bending spring is
inserted so as to retain the cross sectional shape of
the tube. It is important to use the correct size of
bending spring for the type of tube being employed.
With cold bending, the tube should initially be bent
to about double the required angle, and then returned
to the angle required, as this reduces the tendency of
the tube to return to its straight form. To bend larger
sizes of tube, 32 mm diameter and above, judicious
application of heat is needed. This may be applied by
blowlamp, electric fire or boiling water. If a naked
flame is used, extreme care must be taken to avoid
overheating the conduit. Once warm, insert a bending
spring and bend the tube round a suitable former. A
bucket is suitable, but do not use a bending machine
former, as this conduits away the heat too rapidly. The
formed tube should as soon as possible be saddled
after bending.

Joints are made using solvent adhesives, which can be
obtained specifically for the purpose. These adhesives
are usually highly flammable and care is needed in
handling and use. Good ventilation is essential, and it

NATIONAL ELECTRICAL CODE

SP 30: 2011

is important not to inhale any fumes given off. The
manufacturers' instructions for use of the solvent
adhesive should be strictly followed. If sealing is
needed to waterproof the joint, use a special non-setting
adhesive or grease. Threaded adaptors are available
for use when it is required. Drawing in cables is carried
out by making use of a nylon draw-in tape. The smooth
bore of the plastic tube aids the pulling in operation.
Liquid soap or French chalk maybe used to provide
lubrication to help the pulling in process. Capacities
of plastic conduits maybe calculated in a similar way
to that used for steel systems. Each type of cable is
allocated a factor, and corresponding factors are
allocated for various sizes of conduit. Table 10 and
Table 1 1 give the factors applicable to cables and
conduits. This requires that when cables are drawn into
conduit damage to both cables and conduit is avoided.
The use of plastic conduit is suitable when cable runs
require to be located in pre-cast concrete. As will be
appreciated it is essential that sound joints are made
so that when the concrete is cast, the conduit runs do
not separate. The maximum permissible number of
1 . 1 kV grade cables that can be drawn into rigid steel
conduits are given at Table 3 of Part 1 /Section 20 of
this Code. The maximum permissible number of
1 . 1 kV grade single-core cables that may be drawn into
rigid non-metallic conduits are given in Table 4 of
Part 1/Section 20 of this Code. Table 1 of Part 1/
Section 20 gives diameter and maximum allowable
resistance of fusewires of tinned copper.

6.7*2 Cable Trunking and Ducting Systems

6.7.2.0 General

Cable trunking and cable ducting systems are used for
the accommodation, and where necessary for the
segregation of conductors, cables or cords and/or other
electrical equipment in electrical installations
{see Fig. 55). The systems are mounted directly on walls
or ceilings , flush or semi-flush or indirectly on walls or
ceilings, or on structures away from on walls or ceilings.
See IS 14927 (Part 1) for general requirements of the
cable trunking and ducting systems. For general use,
cable trunking is now available in various materials such
as steel, PVC, aluminium and phenylene oxide (Noryl),
in a wide range of sizes of both square and rectangular
cross-section. Steel cable trunking is supplied in various
standard lengths with provision for slotting together and
bolting to maintain electrical continuity for bonding. If
required, trunking is available with pin supports at
regular intervals for separating circuits and, where it is
essential to completely segregate wiring, such as safety
services and extra-low voltage, continuous barriers are
provided.

Where a large number of cables has to be run together,
it is often convenient to put them in trunking. Trunking

for electrical purposes is generally made of 1.2 mm
sheet steel, and is available is size ranging from 50 mm
x 50 mm to 600 mm x 150 mm, common sizes being
50 mm x 50 mm, 75 mm x 100 mm, 150 mm x 75 mm
and 150 mm x 150 mm although 50 mm x 100 mm
and 100 mm x 100 mm are also available. See Table
12 for spacing of supports for trunking and Table 13
for preferred dimensions of cable trunking and
ducting.

6.7.2.1 Types of trunking

a) Metallic trunking — Trunking for industrial
and commercial installations is often used in
place of the larger sizes of conduit. It can be
used with advantage in conjunction with 16
mm to 32 mm conduits, the trunking forming
the background or framework of the system
with conduits running from the trunking to
lighting or socket outlet points. For example,
in a large office building, trunking can be run
above the suspended ceiling along the
corridors to feed corridor points, and rooms
on either side can be fed from this trunking
by conduit.

In multistorey ed buildings trunking of suitable
capacity, and with the necessary number of
compartments, is to be provided and run
vertically in the riser ducts and connected to
distribution boards; it can also accommodate
circuit wiring, control wiring, also cables
feeding fire alarms, telephones, emergency
lighting and other services associated with a
modern building.

Cables feeding fire alarms and emergency
circuits need to be segregated by fire-resisting
barriers from those feeding low-voltage
circuits (that is 50 V to 1 000 V ac). It is usual
for telecommunications companies to insist
that their cables are completely segregated
from all other wiring systems. It may therefore
be necessary to install 3 or 4 compartment
trunking to ensure the requirements for data
and telecommunications circuits are complied
with. Cables feeing emergency lighting and
fire alarm must also be segregated from the
wiring of any other circuits by means of rigid
and continuous partitions of non-combustible
material.

b) Non-metallic trunking — A number of
versatile plastic trunking systems have been
developed in recent years and these are often
suitable for installation work in domestic or
commercial premises, particularly where
rewiring of existing buildings is required.

PART 1 GENERAL AND COMMON ASPECTS

§§ Table 10 Conduit Factors for Runs Incorporating Bends Eg

(Clause 6.7.1.4.2.2) g

8
>

w
n

SI No.

Length of Run

(2)

Straight

One Bend

Two Bends

Three Bends

Four Bends

(1)

(3)

20
(4)

25
(5)

32
(6)

16
(7)

20
(8)

25
(9)

32
(10)

16
(11)

20
(12)

25
(13)

32
(14)

16
(15)

20
(16)

25
(17)

32
(18)

16
(19)

20
(20)

25
(21)

32
(22)

188

303

543

947

177

286

514

900

158

256

463

818

130

213

388

692

ii)

1.5

182

294

528

923

167

270

487

857

143

233

422

750

111

182

333

600

iii)

177

286

514

900

158

256

463

818

130

213

388

692

159

292

529

iv)

2.5

171

278

500

878

150

244

442

783

120

196

358

643

141

260

474

167

270

487

857

143

233

422

750

111

182

333

600

vi)

3.5

179

290

521

911

162

263

475

837

136

222

404

720

103

169

311

563

vii)

177

286

514

900

158

256

463

818

130

213

388

692

159

292

529

viii)

4.5

174

282

507

889

154

250

452

800

125

204

373

667

149

275

500

ix)

171

278

500

878

150

244

442

783

120

196

358

643

141

260

474

167

270

487

857

143

233

422

750

111

182

333

600

xi)

162

263

475

837

136

222

404

720

103

169

311

563

xii)

158

256

463

818

130

213

388

692

159

292

529

xiii)

154

250

452

800

125

204

373

667

149

275

500

xiv)

150

244

442

783

120

196

358

643

141

260

474

SP 30 : 2011

Recessed screw

Locking bar

Gusset bend

Gusset tee

Elbow bend

Fig. 55 Cable Trunking

Table 11 Cable Factors for Long Straight Runs,

or Runs Incorporating Bends in Conduit

(Clause 6.7.1.4.2.2)

Type of Conductor

Conductor, Cross-
Sectional Area

Factor

1.0

Solid or stranded

1.5

2.5

4.0

6.0

10.0

105

c) Mini trunking — For domestic or similar small
installations, mini-trunking systems similar in
form to cable trunking but of less obstructive
cross-section, ranging from 16 mm to 75 mm
wide by 12 mm to 30 mm deep can be used.
There are numerous accessories for bends,
junctions and outlets and, with the exception
of the outlets which are usually surface
mounted. A complete installation can be made
quite inconspicuously by close fitting to
skirtings, picture rails and door architraves.
Because of the small section, runs on walls or
across ceilings can be used without spoiling the
aesthetics of an area.

Mini-trunking and cove-trunking are
particularly suitable for areas which may be
subject to changes of layouts, or for rewiring,
to avoid major unheavals in addition to new
installations. The simplicity of installations
and the degree of accessibility provided by
these systems can reduce labour costs
tremendously.

d) Lighting trunking system — Steel or alloy
lighting trunking was originally designed to
span trusses other supports in order to provide
an easy an economical method of supporting
luminaries in industrial premises at high level.

e) Underfloor trunking system/Floor distribution
system — Open plan office and other types of
commercial buildings may well need power
and data wiring to outlets at various points in
the floor area. The most appropriate way of
providing this is by one of the underfloor
wiring systems now available. Both steel and
plastic construction trunking can be obtained,
and if required 'power poles' can be inserted
at appropriate locations to bring the socket
outlets to a convenient hand height. With the
increasing use being made of computers, and

Table 12 Spacing of Supports for Trunking
(Clause 6.7.2.0)

SI No.

(1)

Cross-sectional Area, mm 2

(2)

Maximum Distance Between Supports

*-— *

-x

Metal

Insulating

^*^

*-\

/"*■"

Horizontal

Vertical

Horizontal

Vertical

(3)

(4)

(5)

(6)

0.75

1.0

0.5

1.25

1.5

0.5

1.75

2.0

1.25

3.0

1.5

2.0

3.0

1.75

2.0

i) Exceeding 300 and not exceeding 700

ii) Exceeding 700 and not exceeding 1 500

iii) Exceeding 1 500 and not exceeding 2 500

iv) Exceeding 2 500 and not exceeding 5 000

v) Exceeding 5 000

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

other electronic data transmission systems, the
flexibility of the underfloor wiring can be
used to good advantage.

f) Steel floor trunking — Under floor trunking
made of steel is used extensively in commercial
and similar buildings, and it can be obtained
in very shallow sections with depth of only
22 mm, which is very useful where the
thickness of the floor screed is limited.

g) Plastic underfloor trunking — Plastic
materials are now often used instead of their
metal counterparts for the enclosures of
underfloor systems. Under floor trunking
systems made with this material can be
divided into two main types, these being
raised floor systems and underfloor systems.

h) Carpet trunking system — A carpet trunking
is provided for fixing to a finished floor, which
has a total depth of 9.6 mm. It is complete
with a snap on overlapping lid which, when
it place, forms a retainer for abutting carpet.

NOTE — There are many different designs, the
particular requirements of which are covered in other
parts of IS 14927.

6.7.2.2 Trunking and ducting systems shall be so
designed and constructed that where required they
ensure reliable mechanical protection to the conductors
and/or cables contained therein. Where required, the
system shall also provide adequate electrical protection.
In addition, the system components shall withstand the
stresses likely to occur during transport, storage,
recommended installation practice and usage. System
Components are parts used within the system, which
include lengths of trunking or ducting, trunking or
ducting fittings, fixing devices, apparatus mounting
devices, and other accessories.

NOTE — The above mentioned components may not
necessarily be included all together in a system. Different
combinations of components may be used.

In addition, for cable trunking and ducting systems
intended for mounting on walls or ceilings, the
manufacturer's instruction on classification of the CT/
DS and on installation of the system should be
followed. If the system is intended for the suspension
of loads, the manufacturers on the maximum load and
method of suspension should be followed.

The sizes of the cable trunking and ducting other than
those specified are also acceptable as per the agreement
between the purchasers and the manufacturers provided
that the height and width are from the combination of
the following dimensions having tolerances of ±0.2
mm on both height and width dimensions. 12 mm,
16 mm, 20 mm, 25 mm, 32 mm, 38 mm, 50 mm,
75 mm and 100 mm.

Wall thickness for cable trunking and ducting for any
type of combination with respect to height and width
as given in clause shall be as follows:

a) Any combination where size is up to 32 mm
the wall thickness shall be at least 1.20 mm.

b) Any combination where size is up to 38 mm,
the wall thickness shall be at least 1.30 mm.

c) Any combination where size is up to 50 mm
the wall thickness shall be atleast .1.50 mm.

d) Any combination where size is above 50 mm
the wall thickness shall be at least 1.80 mm.

6.7.2.3 Access to live parts

Trunking/ducting systems shall be so designed that
when they are installed and fitted with insulated
conductors and apparatus in normal use, parts are not
accessible.

6.7.2.4 Designs of conduit system

A schematic of trunking and ducting systems for wall,
ceiling installation and floor installation is given at
Fig. 56.

Table 13 Preferred Dimensions of Cable Trunking and Ducting
{Clause 6.7.2.0 )

Size

Approximate Internal Cross-

Outer

Wall Thickness

Sectional

Width

Height

Min

mm 2

(1)

(2)

(3)

(4)

(5)

12x12

119.50

12.0 ± 0.2

16x12

153.00

16.0 ± 0.2

12.0 ± 0.2

16x16

196.00

16.0 ± 0.2

25 x 12

239.10

25.0+ 0.2

12.0 + 0.2

25x16

307.40

25.0+ 0.2

16.0 + 0.2

25 x 25

510.80

38x16

474.40

25.0±0.2

25.0 ± 0.2

38x25

793.00

38.0 ± 0.2

16.0 ± 0.2

50x16

611.00

38.0 ± 0.2

25.0 + 0.2

50x50

2 209.00

50.0 ± 0.2

16.0 ±0.2

75x75

5 098.00

50.0 ± 0.2

100x50

4 473.00

75.0+ 0.2

75.0 ± 0.2

100.0 ± 0.2

50.0 ± 0.2

1.20
1.20
1.20
1.20
1.20
1.20
1.30
1.30
1.50
1.50
1.80
1.80

NATIONAL ELECTRICAL CODE

SP 30 : 2011

«®

<(D

«<D

^3L

i ii i

11 Ef

NOTE — No. 5 represents an apparatus in a trunking system.

a) Types and Application of Trunking and Ducting System for Wall and Ceiling Installation

No. on
Fig. 56

Definition

(2)

For

(3)

Counting
(4)

1
7
11
12
13
15

3
9

10
8

Trunking and
accessories

Ducting and
accessories

Insulated conductors, cables, Surface on wall and ceiling, on walls
cords mounted horizontally or vertically, ceiling

suspended

Insulated conductors, cables, Flush in wall and ceiling, in walls mounted

cords horizontally or vertically

Insulated conductors, cables, Surface on wall and ceiling, on walls

cords, mounting devices for mounted horizontally or vertically
apparatus (switches, socket-
outlets, circuit-breakers, etc

Insulated conductors, cables, Surface on wall and ceiling, on walls

cords mounted horizontally or vertically, ceiling

suspended

Insulated conductors, cables,
cords

Embedded in wall and ceiling, in walls
mounted horizontally or vertically

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

b) Trunking and Ducting Systems for Floor Installation

No. on
Fig. 56

(1)

Definition

(2)

For

(3)

Mounting

(4)

Trunking and accessories
Trunking and accessories

Ducting and accessories

Ducting and accessories
Electrical service unit

Electrical service unit
Skirting systems

Insulated conductors, cables, cords Flush floor

Insulated conductors, cables, cords Surface on floor

Insulated conductors, cables, cords, Flush floor

Insulated conductors, cables, cords In floor (embedded)

Apparatus Flush floor

Apparatus

Surface on floor

15
Not shown

Skirting trunking and accessories Insulated conductors, cables, cords Surface on wall and ceiling

Skirting trunking and accessories Insulated conductors, cables, cords, Surface on wall and ceiling

counting devices for apparatus

Not shown Socket plinth

Mounting apparatus (socket-outlets) Surface on wall

Fig. 56 Types of Trunking and Ducting Systems

7 EQUIPMENT, FITTINGS AND ACCESSORIES

7,0 An important stage of electrical installation work
is the fixing of accessories, such as ceiling roses,
holders, switches, socket outlets and luminaries. This
work requires experience and a thorough knowledge
of the regulations which are applicable, because
danger from shock frequently results from the use of
incorrect accessories or accessories being wrongly
connected.

All equipment shall be suitable for the maximum power
demanded by the current using equipment when it is
functioning in its intended manner. In wiring other than
conduit wiring, all ceiling roses, brackets, pendants and
accessories attached to walls or ceilings shall be
mounted on substantial teak wood blocks twice
varnished after all fixing holes are made in them.
Blocks shall not be less than 4 cm deep. Brass screws
shall be used for attaching fittings and accessories to
their base blocks. Where teak or hardwood boards are
used for mounting switches, regulators, etc, these
boards shall be well varnished with pure shellac on all
four sides (both inside and out side), irrespective of
being painted to match the surroundings. The size of
such boards shall depend on the number of accessories
that could conveniently and neatly be arranged. Where
there is danger of attack by white ants, the boards shall
be treated with suitable anti-termite compound and
painted on both sides.

Similar part of all switches, lampholders, distribution
fuse-boards, ceiling roses, brackets, pendants, fans and
all other fittings shall be so chosen that they are of the
same type and interchangeable in each installation.
Electrical equipment which form integral part of wiring
intended for switching or control or protection of
wiring installations shall conform to the relevant Indian
Standards wherever they exist.

7.1 Ceiling Roses

7.1.1 Ceiling rose shall not be used on a circuit the
voltage of which normally exceeds 250 V. Ceiling
roses may be of the 2-plate pattern and must have an
earth terminal. The 3-plate type is used to enable the
feed to be looped at the ceiling rose rather than to use
an extra cable which would be needed to loop it at the
switch. Figure 57 gives different types of ceiling roses.

7.1.2 For PVC sheathed wiring it is possible to
eliminate the need for joint boxes if 3-plate ceiling roses
are employed. No ceiling rose may be used on a circuit
having a voltage normally exceeding 250 V. Not more
than two flexible cords may be connected to any one
ceiling rose unless the later is specially designed for
multiple pendants.

7.1.3 Special 3 and 4-pin fittings rated at 2 or 6 A
may be obtained and these can be installed where
lighting fittings need to be removed or rearranged.
The ability to remove lighting easily can assist in

NATIONAL ELECTRICAL CODE

SP 30 : 2011

57A Porcelain Ceiling Rose
with Two Plates

57B Porcelain Ceiling Rose
with Three Plates

57C Ceiling Rose Made of
Bakelite or Plastic

Fig. 57 Ceiling Rose

carrying our maintenance. Although the fitting is a
socket outlet, it cannot be used for supplying hand
held equipment.

7.1.4 For the conduit system of wiring it is usual to fit
ceiling roses which screw direct on to a standard
conduit box, the box being fitted with an earth
terminal.

7.2 Luminaries

7.2.1 Every luminaire or group of luminaries must be
controlled by a switch or a socket outlet and plug,
placed in a readily accessible position. Luminaire
should conform to relevant Indian Standard where
existing.

7.2.2 In damp situations, every luminaire shall be of
the water proof type, and in situations where there is
likelihood of presence of flammable or explosive dust,
vapour, or gas, the luminaries must be of the flameproof
type in accordance with the recommendation of Part 7
of this Code and relevant Indian Standard (see IS 5571).
Flammable shade shall not form a part of lighting
fittings unless such shade is well protected against all
risks of fire. Celluloid shade or lighting fittings shall
not be used under any circumstances. General and
safety requirements for electrical lighting fittings shall
be in accordance with good practice. The lighting
fittings shall conform to relevant Indian Standards
where they exist.

The use of fittings- wire shall be restricted to the internal
wiring of the lighting fittings. Where fittings wire is
used for wiring fittings, the sub-circuit loads shall
terminate in a ceiling rose or box with connectors from
which they shall be carried into the fittings

7.2.3 Flexible Cords and Cables

7.2.3 .1 The conductor of flexible cords and cables shall
be according to flexibility Class 5 of IS 8130. Flexible

cords, if not properly installed and maintained, can
become a cause of fire and shock. Flexible cords must
not be used for fixed wiring. Flexible cords must not
be used where exposed to dampness or immediately
below water pipes. They should be open to view
through out their entire length, except where passing
through a ceiling when they must be protected with a
properly bushed non-flammable tube. Flexible cords
must never be held in position by means of insulated
staples. Connections between flexible cords and cables
shall be effected with an insulated connector, and this
connector must be enclosed in a box or in part of a
luminaire. If an extension of a flexible cord is made
with a flexible cord connector consisting of pins and
sockets, the sockets must be fed from the supply, so
that the exposed pins are not alive when disconnected
from the sockets. All flexible cords used for portable
appliances shall be of the sheathed circular type and,
therefore twisted cords must not be used for portable
handlamps, floor and table lamps, etc. All flexible cords
should be frequently inspected, especially at the point
where they enter lampholders and other accessories,
and renewed if found to be unsatisfactory. Flexible
cords used in workshops and other places subjected to
risk of mechanical damage shall be sheathed or
armoured.

7.2.3.2 Where flexible cords support luminaries the
maximum weight which may be supported is as
follows:

Nominal Cross-sectional

Maximum

Area of Flexible Cord

Permissible Weight

mm 2

(1)

(2)

0.5

0.75

1.0

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

If necessary two or more flexible cords shall be used
so that the weight supported by any cord does not
exceed the above values.

7.2.3.3 In kitchens and sculleries, and in rooms with a
fixed bath, flexible cords shall be of the PVC sheathed
or an equally waterproof type.

7.2.3.4 In industrial premises luminaries shall be
supported by suitable pipe/conduits, brackets fabricated
from structural steel, steel chains or similar materials
depending upon the type and weight of the fittings.
Where a lighting fitting is supported by one or more
flexible cords, the maximum weight to which the twin
flexible cords may be subjected shall be as follows:

Nominal Cross -sectional

Maximum Permissible

Area of Twin Cord

Weight

mm 2

(1)

(2)

0.5

0.75

1.0

1.5

5.3

2.5

8.8

4.0

1.4.0

7.2.3.5 Where the temperature of the luminaire is likely
to exceed 60° C, special heat-resisting flexible cords
should be used, including for pendant or enclosed type
luminaries. The flexible cord should be insulated with
heatproof insulation such as butyl or silicone rubber.
Ordinary PVC insulated cords are not likely to
withstand the heat given off by tungsten filament lamps.
Flexible cords feeding electric heaters must also have
heatproof insulation such as butyl or silicone rubber.

7.3 Lamp Holders

7.3.1 Insulated lampholders should be used wherever
possible. Lampholders fitted with switches must be
controlled by a fixed switch or socket outlet in the same

room. Lamp holder should conform to relevant Indian
Standards.

7.3.2 Lamp holders for use on brackets and the like
shall be in accordance with Indian Standards and all
those for use with flexible pendants shall be provided
with cord grip. All lampholders shall be provided with
shade carriers. The outer screwed contact of Edison
screw-type lampholders must always be connected to
the neutral of the supply. Small Edison screw
lampholders must have a protective device not
exceeding 6 A, but the larger sizes may have a protective
device not exceeding 1 6 A. The small Bayonet Cap (BC)
lampholder must have a protective device not exceeding
6 A, and for the larger BC lampholders the protective
device must not exceed 16 A. Figure 58 shows different
types of BC lamp holders.

7.3.3 No lampholder may be used on circuits exceeding
250 V and all metal lampholders must have an earth
terminal. In bathrooms and other positions where there
are stone floors or exposed extraneous conductive parts,
lampholders should be fitted with insulated skirts to
prevent inadvertent contact with live pins when a lamp
is being removed or replaced.

7.4 Lamps

7.4.1 All lamps unless otherwise required and suitably
protected, shall be hung at a height of not less than

2.5 m above the floor level. All electric lamps and
accessories shall conform to relevant Indian Standards.
Portable lamps shall be wired with flexible cord. Hand
lamps shall be equipped with a handle of moulded
composition or other material approved for the purpose.
Hand lamps shall be equipped with a substantial guard
attached to the lamp holder or handle. Metallic guards
shall be earthed suitably.

7.4.2 A bushing or the equivalent shall be provided
where flexible cord enters the base or stem of portable
lamp. The bushing shall be of insulating material unless
a jacketed type of cord is used. All wiring shall be free

58A Pendant Holder

58B Bracket Holder 58C Batten Holder

Fig. 58 Different Types of Bayonet Holders

58D Push-pull Holder

NATIONAL ELECTRICAL CODE

SP 30: 2011

from short-circuits and shall be tested for these defects
prior to being connected to the circuit. Exposed live
parts within porcelain fixtures shall be suitably recessed
and so located as to make it improbable that wires will
come in contact with them. There shall be a spacing of
atleast 125 mm between live parts and the mounting
plane of the fixture.

7.4.3 External and road lamps shall have weatherproof
fittings of approved design so as to effectively prevent
the ingress of moisture and dust. Flexible cord and cord
grip lamp holders shall not be used where exposed to
weather. In verandahs and similar exposed situations
where pendants are used, these shall be of fixed rod
type.

7.5 Socket Outlets and Plugs

7.5.1 Socket outlets are used for circuits not exceeding
250 V. Figure 59 shows various accessories and their
use. Each 16A socket-outlet provided in buildings for
the use of domestic appliances shall be provided with
its own individual fuse or miniature circuit-breaker
(MCB), with suitable discrimination with back-up fuse
or miniature circuit-breaker provided in the
distribution/sub-distribution board. The socket-outlet
shall not necessarily embody the fuse or MCB as an
integral part of it. Each socket-outlet shall also be
controlled by a switch which shall preferably be located
immediately adjacent thereto or combined therewith.
The switch controlling the socket-outlet shall be on

the live side of the line. Ordinary socket-outlet may be
fixed at any convenient place at a height above 20 cm
from the floor level and shall be away from danger of
mechanical injury. Socket outlets installed in old
people's homes and in domestic premises likely to be
occupied by old or disabled people, should be installed
at not less than 1 m from floor level.

In situations where a socket-outlet is accessible to
children, it is necessary to install an interlocked plug
and socket or alternatively a socket-outlet which
automatically gets screened by the withdrawal of plug.
In industrial premises socket-outlet of rating 16 A and
above shall preferably be provided with interlocked
type switch. Socket outlets should conform to relevant
Indian Standards.

7.5.2 In an earthed system of supply, a socket-outlet
with plug shall be of three-pin type with the third
terminal connected to the earth. When such socket-
outlets with plugs are connected to any current
consuming device of metal or any non-insulating
material or both, conductors connecting such current-
consuming devices shall be of flexible cord with an
earthing core and the earthing core shall be secured by
connecting between the earth terminal of plug and the
body of current-consuming devices.

In industrial premises three phase and neutral socket-
outlets shall be provided with a earth terminal either
of pin type or scrapping type in addition to the main

FIXED SOCKET OUTLET

PLUG (NON-REWIRABLE)

CORD EXTENSION SET

|j£»— *»

PLUG AND SOCKET-OUTLET

PORTABLE SOCKET-OUTLET
(NON'REWIREABLE)

PLUG (NON-REWiREABLE>;

CONNfCTOR
(NON-REWIR6ABLE)

APPLIANCE COUPLER

Fig. 59 Plug Socket Outlet and Associated Accessories

PART 1 GENERAL AND COMMON ASPECTS

SF 30 : 2011

pins required for the purpose. In wiring installations,
metal clad switch, socket-outlet and plugs shall be used
for power wiring.

A recommended schedule of socket-outlets in a residential
building is given at Table 2 of Part 3 of this Code.

Although 16 A socket-outlet is extensively used in
industrial premises, other industrial type socket-outlets
include single-phase and three-phase sockets with
ratings up to 125 A.

The low voltage electrical equipment (safety) standards
require equipment to be safe. Any part intended to be
electrified should be adequately protested such that it
is not accessible to a finger, including that of a child.
This protection can be achieved by partly shrouding
the live pins of plugs so that when the plug is in the
process of being inserted even the smallest finger
cannot make contact with live metal.

When installing socket outlets the cables must be
connected to the correct terminals, which are;

a) red wire (phase or outer conductor) to
terminal marked L.

b) black wire (neutral or middle conductor) to
terminal marked N.

c) yellow/ green earth wire to terminal marked
E.

7.5.3 If wrong connections are made to socket outlets
it may be possible for a person to receive an electric
shock from an appliance when it is switched off.
Socket-outlet adaptors which enable two or more
appliances to be connected to a single socket should
contain fuses to prevent the socket-outlet from
becoming overloaded,

7.6 Switches

7.6.1 There are various types of switches available, the
most common being the 6 A switch which is used to
control lights. There is also the 16 A switch for circuits
carrying heavier currents. For ac circuits the micro-
gap switch is also being used; it is much smaller than
the older type and more satisfactory for breaking
inductive loads.

Quick-make and slow-break switches are
recommended for ac. A quick-break switch connected
to an ac supply and loaded near to its capacity will
tend to break down to earth when used to switch off an
inductive load (such as fluorescent lamps).

7.6.2 In a room containing a fixed bath, switches must
be fixed out of reach of the person in the bath,
preferably out side the door, or be of the ceiling type
operated by a cord. All single pole switches shall be
fitted in the same conductor though out the installation,
which shall be the phase conductor of the supply.

7.6.3 In damp situations, every switch shall be of the
waterproof type with suitable screwed entries or glands
to prevent moister entering the switch. To prevent
condensed moisture from collecting inside a watertight
switchbox, a very small hole should be drilled in the
lowest part of the box to enable the moisture to drain
away.

7.6.4 Flame proof switches must be fitted in all
positions exposed to flammable or explosive dust,
vapour, gas.

7.7 Fans

7.7.1 Ceiling Fans

Ceiling fans including their suspension shall conform
to Indian Standards. The following should be adhered
to during installation:

a) Control of a ceiling fan shall be through its
own regulator as well as a switch in series.

b) All ceiling fans shall be wired with normal
wiring to ceiling roses or to special connector
boxes to which fan rod wires shall be
connected and suspended from hooks or
shackles with insulators between hooks and
suspension rods. There shall be no joint in the
suspension rod, but if joints are unavoidable
then such joints shall be screwed to special
couplers of 50 mm minimum length and both
ends of the pipes shall touch together within
the couplers, and shall in addition be secured
by means of split pins; alternatively, the two
pipes may be welded. The suspension rod shall
be of adequate strength to withstand the dead
and impact forces imposed on it. Suspension
rods should preferably be procured along with
the fan.

c) Fan clamps shall be of suitable design
according to the nature of construction of
ceiling on which these clamps are to be fitted.
In all cases fan clamps shall be fabricated from
new metal of suitable sizes and they shall be
as close fitting as possible. Fan clamps for
reinforced concrete roofs shall be buried with
the casting and due care shall be taken that
they shall serve the purpose. Fan clamps for
wooden beams, shall be of suitable flat iron
fixed on two sides of the beam and according
to the size and section of the beam one or two
mild steel bolts passing through the beam shall
hold both flat irons together. Fan clamps for
steel joist shall be fabricated from flat iron to
fit rigidly to the bottom flange of the beam.
Care shall be taken during fabrication that the
metal does not crack while hammer to shape.

NATIONAL ELECTRICAL CODE

SP 30 : 2011

Other fan clamps shall be made to suit the
position, but in all cases care shall be taken to
see that they are rigid and safe.

d) Canopies on top and bottom of suspension
rods shall effectively conceal suspensions and
connections to fan motors, respectively.

e) The lead-in-wire shall be of nominal cross-
sectional area not less than 1 .0 mm 2 copper or
1.5 mm 2 aluminium and shall be protected
from abrasion.

f) Unless otherwise specified, the clearance
between the bottom most point of the ceiling
fan and the floor shall be not less than 2.4 m.
The minimum clearance between the ceiling
and the plane of the blades shall be not less
than 300 mm.

NOTE — All fan clamps shall be so fabricated that fans
revolve steadily.

7.7.2 Exhaust Fans

For fixing of an exhaust fan, a circular hole shall be
provided in the wall to suit the size of the frame which
shall be fixed by means of rag-bolts embedded in the
wall. The hole shall be neatly plastered with cement
and brought to the original finish of the wall. The
exhaust fan shall be connected to exhaust fan point
which shall be wired as near to the hole as possible by
means of a flexible cord, care being taken that the
blades rotate in the proper direction.

7.7.3 Fannage

7.7.3.1 Where ceiling fans are provided, the bay sizes

of a building, which control fan point locations, play
an important part. Fans normally cover an area of 9 m 2
to 10 m 2 and therefore in general purpose office
buildings, for every part of a bay to be served by the
ceiling fans, it is necessary that the bays shall be so
designed that full number of fans could be suitably
located for the bay, otherwise it will result in ill-
ventilated pockets. In general, fans in long halls may
be spaced at 3 m in both the directions. If building
modules do not lend themselves for proper positioning
of the required number of ceiling fans, such as air
circulators or bracket fans would have to be employed
for the areas uncovered by the ceiling fans. For this,
suitable electrical outlets shall be provided although
result will be disproportionate to cost on account of
fans.

7.7.3.2 Proper air circulation could be achieved either
by larger number of smaller fans or smaller number of
larger fans. The economics of the system as a whole
should be a guiding factor in choosing the number and
type of fans and their locations.

Exhaust fans are necessary for spaces, such as
community toilets, kitchens, canteens and godowns to
provide the required number of air changes
(see Part 1/Sec 1 1 of this Code). Since the exhaust fans
are located generally on the outer walls of a room
appropriate openings in such walls shall be provided
for in the planning site.

Positioning of fans and light fittings shall be chosen to
make these effective without causing shadows and
stroboscopic effect on the working planes.

ANNEX A
(Clause 2)

LIST OF INDIAN STANDARDS RELATED TO INSTALLATION

IS No. Title IS No.

371 : 1999 Ceiling roses — Specification 2412 : 1975

732 : 1989 Code of practice for electrical wiring 2667 : 1988

installations
1255 : 1983 Code of practice for installation and 3043 : 1987

maintenance of power cables upto 3419 : 1938

and including 33 kV rating
1293 : 2005 Plugs and socket-outlets of rated 3439 : 1966

voltages up to and including 250 V

and rated current up to and including 3gQg . j 979

16 A — Specification
1646 : 1997 Code of practice for fire safety of ^%y] • 1975

buildings (general): Electrical

installations

Title

Link clips for electrical wiring
Fittings for rigid steel conduits for
electrical wiring
Code of practice for earthing
Fittings for rigid non-metallic
conduits

Flexible steel conduits for electrical
wiring

Method of test for non-
combustibility of building materials
Accessories for rigid steel conduits
for electrical wiring

PART 1 GENERAL AND COMMON ASPECTS

SP 30 : 2011

ISNa
3854 : 1997

3961

(Part 1) : 1967
(Part 2) : 1967

(Part 3) : 1968
(Part 5) : 1968
4289

(Part 1) : 1984
(Part 2) : 2000
4649 : 1968

5571 : 2000

5572 : 1994

6946 : 1990

8130: 1984

8623

(Part 1) : 1993/
IEC 60439-1 :
1985

(Part 2): 1993/
IEC 60439-2 :
1987

(Part 3) : 1993/
IEC 60439-3 :
1990
9537

(Part 2): 1981
(Part 3): 1983

(Part 4); 1983

(Part 5) : 2000

Title

Switches for domestic and similar

purposes

Recommended current ratings for

cables:

Paper insulated lead sheathed cables

PVC insulated and PVC sheathed

heavy duty cables

Rubber insulated cables

PVC insulated light duty cables

Specification for flexible cables for

lifts and other flexible connections:

Elastomer insulated cables

PVC insulated circular cables

Adaptors for flexible steel conduits

Guide for selection of electrical

equipment for hazardous areas

Classification of hazardous areas

(other than mines) having flammable

gases and vapours for electrical

installation

PVC insulated cables for working

voltages upto and including 1 100 V

Conductors for insulated electric

cables and flexible cords

Specification for low-voltage

switchgear and controlgear assemblies:

Requirements for type-tested and

partially type-tested assemblies

Particular requirements for busbar
trunking systems (busway)

Particular requirements for

equipment where unskilled persons

have access for their use

Conduits for electrical installations:

Rigid steel conduits

Rigid plain conduits of insulating

materials

Pliable self-recovering conduits of

insulating materials

Pliable conduits of insulating

material

IS No. Title

(Part 6) : 2000 Pliable conduits of metal or

composite materials
(Part 8) : 2003 Rigid non-threadable conduits of

aluminium alloy

Fire hazard testing: Part 2 Test

methods, Section 1 Glow-wire test

and guidance

11000(Part2/
Seel): 1984/
IEC 695-2-1 :
1980

11353: 1985

13703 (Part 1) :
1993 /IEC 269-
1 : 1986

14255 : 1995

14763 : 2000

14768 (Part 1) :
2000

14772 : 2000

14927

(Part 1) : 2001
(Part 2): 2001

14930

(Part 1) : 2001
(Part 2): 2001

SP 69 : 2000

Guide for uniform system of marking

and identification of conductors and

apparatus terminals

LV Fuses for voltages not exceeding

1000 V ac or 1500 V dc: Part 1

General requirements

Aerial bunched cables for working

voltages upto and including 1 100 V

— Specification

Conduits for electrical purposes —
Outside diameters of conduits for
electrical installation and threads for
conduits and fittings — Specification
Conduit fittings for electrical
installations — Specification: Part 1
General requirements
General requirements for enclosures
of accessories for household and
similar fixed electrical installations

— Specifications for an accessory or
luminaries

Cable trunking and ducting systems

for electrical installations:

General requirements

Cable trunking and ducting systems

intended for mounting on walls or

ceilings

Conduit systems for electrical

installations:

General requirements

Particular requirements — Conduit

systems buried underground

Banking and related financial

services — Information security

guidelines

NATIONAL ELECTRICAL CODE

SP 30: 2011

ANNEX B
(Clause 6.7.1.0)

CLASSIFICATION CODING FOR CONDUIT SYSTEMS

The classification coding format for declared properties
of the conduit system which may either be incorporated
in the manufacturer's literature or marked on the
product shall be as shown below. When the conduit is
marked with the classification code, it includes at least
the first four digits.

a) First digit — Resistance to compression

[See 6.1.1 of IS 14930 (Part 1)]

Very light compression strength
Light compression strength
Medium compression strength
Heavy compression strength
Very heavy compression strength

b) Second digit — Resistance to impact

[See 6.1.2 of IS 14930 (Part 1)]

Very light impact strength
Light impact strength
Medium impact strength
Heavy impact strength
Very heavy impact strength

c) Third digit — Lower temperature range

[See Table 1 of IS 14930 (Part 1)]

+ 5°C
-5°C
-15°C
-25°C
-45°C

d) Fourth digit — Upper temperature range

[See Table 2 of IS 14930 (Part 1)]

+ 60°C
+ 90°C
+ 105°C
+ 120°C
+ 150°C
+ 250°C
+ 400°C

e) Fifth digit — Resistance to bending

[See 6.1.3 of IS 14930 (Part 1)]

Rigid

Pliable

Pliable/Self recovering

Flexible

2
3
4
5

1
2
3
4

2
3
4

f) Sixth digit — Electrical characteristics

[See 6.3 of IS 14930 (Part 1)]

None declared

With electrical continuity characteristics
With electrical insulating characteristic
With electrical continuity and insulating
characteristics

g) Seventh digit — Resistance to ingress of solid
objects

[See 6.4.1 of IS 14930 (Part 1)]

Protected against solid foreign objects

2.5 mm diameter and greater
Protected against solid foreign objects

1.0 diameter and greater
Dust protected
Dust tight

h) Eight digit — Resistance to ingress of water

[See 6.4.2 of IS 14930 (Part 1)]

None declared

Protected against vertically falling water drops
Protected against vertically falling water drops
when conduit system tilted up to an angle of 15°
Protected against spraying/ water
Protected against splashing water
Protected against water jets
Protected against powerful water jets
protected against the effects of temporary
immersion in water

j) Ninth digit — Resistance against corrosion

[See 6 A3 of IS 14930 (Part 1)]

Low protection inside and outside 1

Medium protection inside and outside 2

Medium protection inside, high protection outside 3
High protection inside and outside 4

k) Tenth digit — Tensile strength
[See, 6.1.4 of IS : 14930 (Part 1)]

5
6

3
4
5
6

None declared
Very light tensile strength
Light tensile strength
Medium tensile strength
Heavy tensile strength
Very heavy tensile strength

PART 1 GENERAL AND COMMON ASPECTS

SP 30: 2011

m) Eleventh digit — Resistance to flame None declared

propagation Very light suspended load capacity 1

Light suspended load capacity 2

[See 6.5 of IS 14930 (Part 1)] j^ ^^ loa / capa y dty 3

Non-flame propagating 1 Heavy suspended load capacity 4

Flame propagating 2 Very heavy suspended load capacity 5

n) Twelfth digit — Suspended load capacity p) Thirteenth digit — Fire effects

[See 6.1.5 of IS 14930 (Part 1)] (Under consideration)

100 NATIONAL ELECTRICAL CODE

SP 30: 2011

SECTION 10 SHORT-CIRCUIT CALCULATIONS

FOREWORD

Circuit calculations are performed for checking the
adequacy of the electrical equipment for any electrical
system that is characterized by the type of distribution
system comprising of transformers, bus, cables etc.

The essential requirements and methods associated
with following calculations are covered in this Section:

a) Short circuit calculations in 3 phase ac systems.

b) Current carrying capacity and Voltage drop
calculations for cables and flexible cords.

Assistance for this Section has been derived from the
following standards:

IS No. Title

13234 : 1992 Guide for short circuit calculation

in three phase ac systems

1 3235 : 1 99 1/ Calculation of the effects of short
IEC 865 (1986) circuit currents

1 SCOPE

This Part 1/Section 10 covers guidelines and general
requirements associated with circuit calculations,
namely, short circuit calculations and voltage drop
calculations for cables and flexible cords.

2 REFERENCES

The following Indian Standards have been referred in
this Section:

IS No.
2086 : 1993

9926: 1981

13703 (Part 2/
Sec 1) : 1993/DEC
60269-2 : 1986

13703 (Part 2/
Sec 2) : 1993/IEC
60269-2 : 1987

IS/IEC 60898-1 :
2002

Title

Carriers and bases used in
rewirable type electric fuses for
voltages upto 650V
Fuse wires used in rewirable type
electric fuses upto 650 V
Specification for low-voltage
fuses for voltages not exceeding
1 000 V ac or 1 500 V dc : Part 2
Fuses for use by authorized
persons, Section 1 Supplementary
requirements

LV fuses for voltages not
exceeding 1000 V ac or 1500 V dc:
Part 2 Fuses for use by authorized
persons, Section 2 Examples of
standardized fuses
Electrical accessories — Circuit
breakers for over protection for
household and similar installations:
Part 1 Circuit breakers for ac
operation

3 GENERAL CONSIDERATIONS

3*0 General

3.0*1 This subject of circuit calculations covers the
guidelines relating to the short circuit withstand
capability of the electrical equipment and to check
permissible voltage drop in cables and flexible cords
upto the equipment terminals.

3.0.2 The objective of the circuit calculation is to ensure
that the selection of equipment under consideration is
designed for safe and reliable long period of operation.

4 CIRCUIT CALCULATIONS

4.1 Short Circuit Calculations

4.1.1 Design Considerations

4.1.1.1 A complete calculation of the short-circuit
currents should give the currents as a function of time
at the short circuit location from the initiation of the
short circuit up to its end, corresponding to the
instantaneous value of the voltage at the beginning of
the short-circuit.

4.1.1.2 In most of the practical cases it is sufficient to
determine the r.m.s value of symmetrical AC
component and the peak value / p of the short-circuit
current following the occurrence of a short circuit. The
value of i depends on time constant of the decaying
aperiodic component i DC with frequency depending on
the X/R ratio of the short-circuit impedance.

4.1.1.3 For determination of asymmetrical short-circuit
breaking current, the decaying aperiodic component
/ DC may be calculated with sufficient accuracy by:

i DC - V2 I k e

■iKfiT

where

/£ = initial symmetrical short circuit current (A),

/ = nominal system frequency (Hz),

t = time duration of fault(s), and

x = time constant based on system X/R.

4.1.1.4 The calculation of maximum and minimum
short circuit current are based on the following
considerations:

a) For the duration of the short-circuit there is
no change in the number of circuits involved,
that is, a three phase short-circuit remains as
three phase and similarly a line-to-earth short-
circuit remains line-to-earth during the short
circuit.

PART 1 GENERAL AND COMMON ASPECTS

101

SP 30 : 2011

b) Tap changers of the transformer are at
nominal position.

c) Arc resistances are not taken into account.

4.1.1.5 In situations where there will be no significant
change in ac component decay due to far distance from
generator (see Fig. 1), short-circuit current can be
considered as the sum of the following two
components:

a) The ac component with constant amplitude
during the whole short-circuit.

b) The aperiodic component beginning with
initial value A and decaying to zero.

4.1,1.6 For the systems where there will be significant
change in ac component decay due to close location
near Generator (see Fig. 2), short circuit- current can be
considered as the sum of the following two components:

Current

Top envelope

dec aying (aperiodic) component /qq

Time

Bottom envelope

Fig. 1 Short-Circuit Current at a System Far-from-Generator

Current

Top envelope

decaying (aperiodic) component j'qq

Time

/ k = initial symmetrical short-circuit current

/ p = peak short-circuit current

/ k = steady-state short-circuit current

/ DC = decaying (aperiodic) component of short-circuit current

A = initial value of the aperiodic component / DC

Fig. 2 Short-Circuit Current at a System Near-to-Generator

102

NATIONAL ELECTRICAL CODE

a) The ac component with decaying amplitude
during the whole short circuit.

b) The aperiodic component beginning with
initial value A and decaying to zero.

4.1.2 Calculation Methods

4.1.2.1 General

Equivalent circuits are to be drawn for the system
before calculation of short-circuit current with example
as per Fig. 3.

4*1.2.1.1 Balanced short-circuit

The balanced three-phase short-circuit of a three-phase
ac system often leads to the highest values of
prospective (available) short-circuit current and the
calculation becomes particularly simple on account of
the balanced nature of the short circuit.

In calculating the short-circuit current, it is sufficient
to take into account only the positive sequence short-
circuit impedance, Z (1) = Z^ as seen from the fault
location.

4.1.2.1.2 Unbalanced short-circuit

The following types of unbalanced (asymmetrical)
short-circuits are to be considered:

'KQ

<3>

< t :1

SP 30 : 2011

a) line-to-line short-circuit without earth
connection

b) line-to-line short-circuit with earth connection

c) line-to-earth short-circuit

Normally, the three-phase short-circuit current is the
largest among the above listed type of faults. In the
event of a short-circuit near to a transformer with
neutral earthing or a neutral earthing transformer, the
line-to-earth short-circuit current may be greater than
the three-phase short-circuit current. This applies in
particular to transformers of vector group Yz, Dy and
Dz when earthing the y- or z-winding on the low
voltage side of the transformer.

In three-phase systems the calculation of the current
values resulting from unbalanced short-circuits is
simplified by the use of the method of symmetrical
components which requires the calculation of three
independent system components, avoiding any
coupling of mutual impedances.

Using this method, the currents in each line are found
by superposing the currents of three symmetrical
component systems:

a) positive-sequence current 7 (

(i)>

•tih

NON F

ROTATING

LOAD

jEZI ROTATING
LOAD

3A System Diagram

R Qt x qt Q Rt

X't

R L X l F

^
J3

3B Equivalent Circuit Diagram (Positive Sequence System)

Fig. 3 Illustation for Calculating the Initial Symmetrical Short-Circuit Current I" k in Compliance
with the Procedure for the Equivalent Voltage Source

PART 1 GENERAL AND COMMON ASPECTS

183

SP 30 : 2011

b) negative- sequence current 7 (2) , and

c) zero-sequence current Z (0) .

Taking the line LI as reference the currents / L1 / L2 and
Z L3 are given by:

(la)
(lb)
(lc)

i-L\~ -(1) + HI) + -(0)

42 = S 2 Z (J) + aZ (2) + / (0)
Z L3 = a/ (J) + a Z( 2 ) + Z(0)

Each of the three symmetrical component systems has
its own impedance.

The method of the symmetrical components postulates
that the system impedances are balanced, for example
in the case of transposed lines. The results of the short-
circuit calculation have an acceptable accuracy also in
the case of un-transposed lines.

4.1.2.1.3 Short-circuit impedances

While calculating the impedances, there shall be
clear distinction between short-circuit impedances
at the short-circuit location and short-circuit
impedances of individual electrical equipment.
Accordingly the calculations with symmetrical
components namely, positive-sequence, negative-
sequence and zero-sequence short-circuit
impedances to be performed.

4.1.3 Effects Due to Short Circuit

4.1.3.1 The electromagnetic effect on rigid and slack
(line) conductors

With the calculation methods, forces on insulators,
stresses in rigid conductors and tensile forces in slack
conductors are to be estimated.

4.1.3.1.1 Mechanical forces due to short-circuit
currents

Currents in parallel conductors will induce
electromagnetic forces between the conductors. When
the parallel conductors are long compared to the
distance between them, the forces will act evenly
distributed along the conductors.

When the currents are in opposite directions the
electromagnetic force is a repulsion which tends to
induce deformations that would increase inductance
of the circuit.

The value of the force in a given direction can be
calculated by considering the work done in the case of
a virtual displacement in the actual direction. As the
work is done by the electromagnetic force, it must be
equal to the change in the energy in the magnetic field
caused by this virtual displacement.

The force between two conductors is proportional to
the square of the current, or to the product of the two

currents. As the current is a function of time, the force
will also be a function of time. In the case of a short-
circuit current without a dc component the force will
vary with twice the frequency of the current. A dc
component in the short-circuit current will give rise to
an increase of the peak value of the force and to a
component of force varying with the same frequency
as the current. The peak value of the force is of
particular interest in the case of mechanically rigid
structures.

The force will result in bending stress on rigid
conductors, tension stress and deflection in flexible
conductors and bending, compression or tension loads
on the supports.

4.1.3.1.2 Stresses in rigid conductors and forces on
supports

The conductors may be supported in different manners,
either fixed or simple or in a combination of both, and
may have two, three, four or several supports.
Depending on the kind of support and the number of
supports, the stress in the conductors and the forces on
the supports will be different for the same short-circuit
current.

The stresses in the conductors and the forces on
supports also depend on the ratio between the natural
frequency of the mechanical system and the frequency
of the electromagnetic force. Especially in the case of
resonance, or near to resonance, the stresses and forces
in the system may be amplified.

4.1.3.1.3 Tensile forces in slack conductors (line
conductors)

A short-circuit current in a slack conductor will cause
a tensile force in the conductor which will affect
insulators, support structures and apparatus. It is
necessary to distinguish between the tensile force
during short-circuit and the tensile force after short-
circuit, when the conductor falls back to its initial
position.

4.1.3.2 Thermal effect on bare conductors

The heating of conductors due to short-circuit currents
involves several phenomena of a non-linear character
and other factors that have to be either neglected or
approximated in order to make a mathematical
approach possible.

For the purpose of this calculation, the following
assumptions can been made:

a) Proximity-effect (magnetic influence of nearby
parallel conductors) has been disregarded.

b) Resistance-temperature characteristic has
been assumed linear.

104

NATIONAL ELECTRICAL CODE

SP 30 : 2011

c) The specific heat of the conductor is
considered constant.

d) The heating is generally considered adiabatic.

4.1.3.2.1 Calculation of temperature rise

The loss of heat from a conductor during the short-
circuit is very low, and the heating can generally be
considered adiabatic. Hence the calculation for this can
also be based on adiabatic conditions.

When repeated short-circuits occur with a short-time
interval between them (that is rapid auto-reclosure) the
cooling down in the short dead-time is of relatively
low importance, and the heating can still be considered
adiabatic. In cases where the dead-time interval is of
longer duration (that is delayed auto-reclosure) the heat
loss may be taken into account.

The calculation need not take into account the skin
effect, that is the current is regarded as evenly
distributed over the conductor cross-section area. This
approximation is not valid for large cross-sections, and
therefore for cross-sections above 600 mm 2 the skin
effect shall be taken into account.

NOTE — If the main conductor is composed of sub-conductors,
uneven current distribution between the sub-conductors will
influence the temperature rise of sub-conductors.

4.1.3.2.2 Calculation of thermal equivalent short-
circuit current

The thermal equivalent short-circuit current is to be
calculated using the short-circuit current r.m.s. value
and the factors m and n for the time-dependent heat
effects of the dc and ac components of the short-circuit
current

The thermal equivalent short-circuit current can be
expressed by:

and

Ah ~ ^ k V m + n

where m and n are numerical factors, /' k the r.m.s. value
of the initial symmetrical short-circuit current; in a
three-phase system, the balanced three-phase short-
circuit is decisive. The values m and n are usually
defined as functions of the duration of the short-circuit
current. For a distribution network usually n = 1.

NOTE — The relation /" k // k is dependent on the impedance
between the short-circuit and the source.

When a number of short-circuits occur with a short
time interval in between, the resulting thermal
equivalent short-circuit current is obtained from:

r k =5X

i-l

4.1.3.2.3 Calculation of temperature rise and rated
short-time current density for conductors

The temperature rise in a conductor caused by a short-
circuit is a function of the duration of the short-circuit
current, the thermal equivalent short-circuit current and
the conductor material.

NOTE — The maximum permitted temperature of the support
has to be taken into account.

4.1.3.2.4 Calculation of the thermal short-circuit
strength for different durations of the short-circuit
current

Electrical equipment has sufficient thermal short-circuit
strength as long as the following relations hold for the
thermal equivalent short-circuit current 7 th :

/ th </ thr forr v <r kr

^ for T k >T k

where I thv is the rated short-time current and T^ the
rated short- time.

The thermal short-circuit strength for a bare conductor
is sufficient when the thermal equivalent short-circuit
current density S th satisfies the following relation:

S t u < S*

1 n
y k I = i

thi ^ki

With Tfo =1 s and for all T k the rated short time current
density S tht is shown in Fig 4.

4.2 Calculations for Current Carrying Capacity and
Voltage Drop for Cables and Flexible Cords

4.2.1 Conductor Operating Temperature

The current to be carried by any conductor for sustained
periods during normal operation shall be such that the
conductor operating temperature given in the
appropriate table of current-carrying capacity in this
section is not exceeded.

Where a conductor operates at a temperature
exceeding 70 °C it shall be ascertained that the
equipment connected to the conductor is suitable for
the conductor operating temperature.

4.2.2 Cables Connected in Parallel

Except for a ring final circuit, cables connected in

PART 1 GENERAL AND COMMON ASPECTS

105

a) Full lines: Copper

Dotted lines: Flat product of unalloyed steel and steel cables.

b) Aluminium, aluminium alloy, aluminium conductor steel reinforced (ACSR).

Fig. 4 Relation Between Rated Short-time Current Density (T kr =1 s) and Conductor Temperature
106 NATIONAL ELECTRICAL CODE

SP 30: 2011

parallel shall be of the same construction, cross-
sectional area, length and disposition, without branch
circuits and arranged so as to carry substantially equal
currents.

4.2.3 Cables Connected to Bare Conductors or Bus
Bars

Where a cable is to be connected to a bare conductor
or busbar its type of insulation and/or sheath shall be
suitable for the maximum operating temperature of the
bare conductor or busbar.

4.2.4 Cables in Thermal Insulation

Where a cable is to be run in a space to which thermal
insulation is likely to be applied, the cable shall
wherever practicable be fixed in a position such that it
will not be covered by the thermal insulation. Where
fixing in such a position is impracticable the cross-
sectional area of the cable shall be appropriately
increased.

For a single cable likely to be totally surrounded by
thermally insulating material over a length of more
than 0.5 m, the current-carrying capacity shall be taken,
in the absence of more precise information, as 0.5 times
the current-carrying capacity for that cable clipped
direct to a surface and open.

Where a cable is to be totally surrounded by thermal
insulation for less than 0.5 m the current-carrying
capacity of the cable shall be reduced appropriately
depending on the size of cable, length insulation and
thermal properties of the insulation. The de-rating
factors have to be appropriate to conductor sizes.

4.2.5 Metallic Sheaths and/or Non-Magnetic Armour
of Single-Core Cables

The metallic sheaths and/or non-magnetic armour of
single-core cables in the same circuit shall normally
bonded together at both ends of their run (solid
bonding). Alternatively the sheaths or armour of such
cables having conductors of cross-sectional area
exceeding 50 mm 2 and a non-conducting outer sheath
may be bonded together at one point in their run (single
point bonding) with suitable insulation at the un-
bonded ends, in which case the length of the cables
from the bonding point shall be limited so that, at full
load, voltages from sheaths and/or armour to Earth,

a) do not exceed 25 V

b) do not cause corrosion when the cables are
carrying their full load current, and

c) do not cause danger or damage to property
when the cables are carrying short-circuit
current.

4.2.6 Correction Factors for Current-Carrying
Capacity

The current-carrying capacity of cable for continuous
service is affected by ambient temperature and by
frequency. This Clause provides correction factors in
these respects as follows.

4.2.6.1 Ambient temperature

In practice the ambient air temperatures may be
determined by thermometers placed in free air as close
as practicable to the position at which the cables are
installed or are to be installed, subject to the proviso
that the measurements are not to be influenced by the
heat arising from the cables; thus if the measurements
are made while the cables are loaded, the thermometers
should be placed about 0.5 m or ten times the overall
diameter of the cable whichever is the lesser, from the
cables, in the horizontal plane, or 150 mm below the
lowest of the cables.

Where cables are subject to such radiation due to solar
or other infra-red, the current-carrying capacity may
need to be specially calculated.

4.2.6.2 Grouping

Appropriate correction factors to be applied to the
manufacture declared current-carrying capacity where
cables or circuits are grouped.

4.2.7 Effective Current-Carrying Capacity

The current-carrying capacity of cable corresponds to
the maximum current that can be carried in specified
conditions without the conductors exceeding the
permissible limit of steady state temperature for the
type of insulation concerned.

The values of current calculated represent the effective
current- carrying capacity only where no correction
factor is applicable. Otherwise the current-carrying
corresponds to the value multiplied by the appropriate
factors for ambient temperature, grouping and thermal
insulation, as applicable.

Irrespective of the type of over current protective device
associated with the conductors concerned, the ambient
temperature correction factors to be used when
calculating current- carrying capacity (as opposed to
those used when selecting cable size).

4.2.8 Overload Protection

Where overload protection is required, the type of
protection provided does not affect the current-carrying
capacity of a cable for continuous service (/ z ) but it
may affect the choice of conductor size. The operating
conditions of a cable are influenced not only by the
limiting conductor temperature for continuous service,
but also by the conductor temperature which might be

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attained during the conventional operating time of the
overload protection device, in the event of an overload.

This means that the operating current of the protective
device must not exceed 1.45/ 2 . Where the protective
device is a fuse as per IS 13703 (Part 2/Section 1)
and IS 13703 (Part 2/Section 2) or IS 2086 or a
miniature circuit breaker as per IS/IEC 60898, this
requirement is satisfied by selecting a value of / z not
less than I n

In practice, because of the standard steps in nominal
rating of fuse and circuit breakers, it is often necessary
to select a value of I n exceeding I b . In that case, because
it is also necessary for I z in turn to be not less than the
selected value of In, the choice of conductor cross-
sectional area maybe dictated by the over load
conditions and the current-carrying capacity (I z ) of the
conductors will not always by fully used.

The size needed for a conductor protected against
overload by a IS 9926 fuse fix in rewirable type fuse
can be obtained by the use of a correction factor,
1.45/2 = 0.725 which results in the same degree of
protection as that afforded by other overload protective
devices. This factor is to be applied to the nominal
rating of the fuse as a divisor, thus indicating the
minimum value of 7 t required of the conductor to be
protected. In this case also, the choice of conductor
size is dictated by the overload conditions and the
current carrying capacity (7 Z ) of the conductors can not
be fully used.

4.2.9 Determination of the Size of Cable to be Used

Having established the design current (7 b ) of the circuit
under consideration, the conductor size has to be sized
necessarily from consideration of the conditions of
normal load and overload is then determined. All
correction factors affecting 7 Z (that is, the factor for
ambient temperature, grouping and thermal insulation)
can, if desired, be applied to the values of 7 t as
multipliers. This involves a process of trial and error
until a cross-sectional area is reached which ensures
that 7 Z is not less than 7 b and not less than 7 n of any
protective device it is intended to select. In any event,
if a correction factor for protection by a semi-enclosed
fuse is necessary, this has to be applied to 7 n as a divisor.
It is therefore more convenient to apply all the
correction factors to 7 n as divisors.

4.2.10 Voltage Drop in Consumers' Installations

4.2.10.1 Acceptable values of voltage drop

Under normal service conditions the voltage at the
terminals of any fixed current-using equipment shall
be greater than the lower limit corresponding to the
Indian Standard relevant to the equipment.

Where the fixed current-using equipment concerned
is not the subject of Indian Standard the voltage at the
terminals shall be such as not to impair the safe
functioning of the equipment.

The requirements are deemed to be satisfied for a
supply given if the voltage drop between the origin of
the installation (usually the supply terminal) and the
fixed current-using equipment does not exceed
5 percent of the normal voltage of the supply.

A greater voltage drop may be accepted for a motor
during starting periods and for other equipment with
high in-rush currents provided it is verified that the
voltage variations are within the limits specified in the
relevant Indian Standards for the equipment or, in the
absence of an Indian Standard, in accordance with the
manufacturer' s recommendations .

4.2.10.2 Calculation of voltage drop

For a given run, to calculate the voltage drop (mV/A/m)
the value for the cable concerned has to be multiplied
by the length of the run in metres and by the current
the cable is intended to carry, namely the design current
of the circuit (7 b ) in amperes.

For three-phase circuits the calculated mV/A/m values
relate to the line voltage and balanced conditions have
to be assumed.

The direct use of the calculated (m/V/A/m) r or
(mV/A/m) z values, as appropriate may lead to
pessimistically high calculated values of voltage drop
or, in other words, to unnecessarily low values of
permitted circuit lengths.

Where the design current of a circuit is significantly
less than the effective current-carrying capacity of the
cable chosen, the actual voltage drop would be less
than the calculated value because the conductor
temperature (and hence its resistance) will be less than
that on which the calculated mV/A/m had been based.

In some cases it may be advantageous to take account
of the load power factor when calculating voltage drop.

4.2.10.3 Correction Factor for operating temperature

For cables having conductors of cross-sectional area
16 mm 2 or less the design value of mV/A/m is obtained
by multiplying the calculated value by a factor C t , given by

230 + t p -

C t =

r 2 ^

(* p -30)

230+ u

where t = maximum permitted normal operating
temperature, in ° C.

NOTE — For convenience, the above formula is based on the
resistance-temperature coefficient of 0.004 per °C at 20°C for
both copper and aluminum conductors.

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For very large conductor sizes where the resistive
component of voltage drop is much less than the
corresponding reactive part (that is when xlr > 3) this
correction factor need not be considered.

4.2.10.4 Correction for load power factor

For cables having conductors of cross-sectional area
of 16 mm 2 or less the design value of mV/A/m is
obtained approximately by multiplying the calculated
value by the power factor of the load, cos 9.

For cables having conductors of cross-sectional area
greater than 16 mm 2 the design value of m/V/A/m is
approximately:

Cos (p [Calculated (m/V/A/m) r ] + sin (p [Calculated
(m/V/A/m)J

For single-core cables in flat formation the calculated

values apply to the outer cables and may under-estimate
for the voltage drop between an outer cable and the
centre cable for cross-sectional areas above 240 mm 2
and power factors greater than 0.8.

4.2.10.5 Combined correction for both operating
temperature and load power factor

Where it is considered appropriate to correct the
calculated mV/A/m value so for both operating
temperature and load power factor, the design values
of mV/A/m are given by:

for cable having conductors of 16 mm 2 or less
cross-sectional area
C t cos (p (Calculated mV/A/m)
for cables having conductors of cross-
sectional area greater than 16 mm 2
C t cos cp (Calculated mV/A/m) r ) + sin (p

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SECTION 11 ELECTRICAL ASPECTS OF BUILDING SERVICES

FOREWORD

Most of the modern day services in buildings depend
on electrical energy. These services, broadly; are:

a) Lighting and ventilation,

b) Air-conditioning and heating, and

c) Lifts and escalators.

From the point of view of conservation of energy and
safety in its use, it is found essential to draw attention
to essential design principles for building services.

Apart from the three major power consuming services
in a building there are other functional/safety services
that are basically light current installations, whose
proper functioning is important. These are:

a) Electrical audio systems,

b) Fire-alarm and fighting systems,

c) Electric call-bell systems,

c) Electric clock systems,

d) Computer system,

e) Telephone systems, and

f) Building management systems.

Attention should be paid to the requirements to be
complied within the design and construction of
building services. This Section provides basic
information on the electrical aspects of building
services. Further details can be had from the relevant
Indian Standards.

1 SCOPE

This Part 1 /Section 1 1 of the Code covers requirements
for installation work relating to building services that
use electric power.

NOTE — SP 7 'National Building Code of India' should be
referred for non-electrical aspects of building services.

2 REFERENCES

A list of Indian Standards related to building services
is given at Annex A.

3 GENERAL GUIDELINES

3.1 Extensive guidelines on building design aspects
have been covered in SP 7 from the point of view of
ensuring economic services in an occupancy. These
shall be referred to from the point of view of ensuring
good design of building services and early coordination
amongst all concerned.

3.2 Orientation of Building

3.2.1 The chief aim of orientation of buildings is to
provide physically and psychologically comfortable
living inside the buildings by creating conditions which
suitably and successfully ward off the undesirable
effects of severe weather to a considerable extent by
judicious use of the recommendations and knowledge
of climatic factors.

3.2.2 From the point of view of lighting and ventilation,
the following climatic factors influence the optimum
orientation of the buildings:

a) Solar radiation and temperature,

b) Clouds,

c) Relative humidity, and

d) Prevailing winds.

IS 7662 (Part 1) gives recommendations on orientation
of buildings.

4 ASPECTS OF LIGHTING SERVICES

4.1 Principles of Good Lighting

4.1.1 Good lighting is necessary for all buildings and
has three primary aims. The first is to promote the work
and other activities carried on within the buildings; the
second is to promote the safety of people using the
building; and the third is to create, in conjunction with
the structure and decoration, a pleasing environment
conducive to interest and a sense of well-being.

Realization of these aims involves:

a) Careful planning of the brightness and colour
patterns within the working area and the
surroundings so that attention is drawn
naturally to the important areas, detail is seen
quickly and accurately and the room is free
from any sense of gloom or monotony.

b) Using directional lighting, where appropriate,
to assist preception of task detail and to give
good modelling.

c) Controlling direct and reflected glare from
light sources to eliminate visual discomfort,

d) In artificial lighting installations, minimizing
flicker from certain types of lamp and paying
attention to the colour rendering properties
of the light.

e) Correlating lighting throughout the building
to prevent excessive differences between
adjacent areas and so as to reduce the risk of
accidents, and

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f) Installing emergency lighting systems where
necessary.

4.1.2 Good lighting design shall take into account the
following:

a) Planning the brightness pattern from the point
of view of visual performance, safety and
amenity and surroundings;

b) Form of texture in the task area and
surroundings;

c) Controlling glare, stroboscopic effect and flicker;

d) Colour rendering;

e) Lighting for movement;

f) Provision for emergency;

g) Maintenance factors in lighting installation;
and

h) Maximum energy effectiveness of the lighting
system used consistent with the specific needs
of visual tasks performed.

4.1.3 Guidelines on principles of good lighting design
can be had from IS 3646 (Part 1). Reference should be
made to National Lighting Code, which covers all
aspects of lighting.

4.2 Design Aspect

4.2.1 Illumination Levels

The level of illumination for a particular occupation
depends on the following criteria:

a) Adequacy for preventing both strain in seeing
and liability to accidents caused by poor
visibility,

b) Adequacy for realizing maximum visual
capacity,

c) Adequacy for the performance of visual tasks
at satisfactory high levels of efficiency, and

d) Adequacy for pleasantness or amenity.

4.2.2 Designing for Daylight

Reference shall be made to IS 2440 and National
Lighting Code.

4.2.3 Lighting Problems and Economics

Reference is drawn to Annexes C and D of IS 3646
(Part 1) and National Lighting Code.

5 ASPECTS OF VENTILATION

5.0 General

5.0.1 Ventilation of buildings is required to supply fresh
air for respiration of occupants, to dilute inside air to
prevent vitiation by body odours and to remove any
products of combustion or other contaminants in air
and to provide such thermal environments as will assist

the maintenance of heat balance of the body in order
to prevent discomfort and injury to health of the
occupants.

5.0.2 The following govern design considerations:

a) Supply of fresh air for respiration,

b) Removal of combustion products or other
contaminants and to prevent vitiation by body
odours,

c) Recommended schedule of values of air
changes for various occupancies, and

d) The limits of comfort and heat tolerance of
the occupants.

5.1 Methods of Ventilation

General ventilation involves providing a building with
relatively large quantities of outside air in order to
improve general environment of building. This may
be achieved in one of the following ways:

a) Natural supply and natural exhaust of air,

b) Natural supply and mechanical exhaust of air,

c) Mechanical supply and natural exhaust of air,
and

d) Mechanical supply and mechanical exhaust
of air.

5.2 Mechanical Ventilation

Reference should be made to IS 3103 and IS 3362
which cover methods of mechanical ventilation.

6 ASPECTS OF AIR-CONDITIONING AND
HEATING SERVICES

6.1 General

The object of air-conditioning facilities in buildings
shall be to provide conditions under which people can
live in comfort, work safely and efficiently. It shall aim
at controlling and optimizing factors in the building
like air purity, air movement, dry bulb temperature,
relative humidity, noise and vibration, energy efficiency
and fire safety.

6.1.1 The design of the system and its associated
controls should take into account the following:

a) The nature of the application,

b) The type of construction of building,

c) External and internal load patterns,

d) Desired space conditions,

e) Permissible control limits,

f) Control methods for minimizing use of
primary energy,

g) Opportunities for heat recovery,

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SP 30 : 2011

h) Economic factors (including probable future

cost and availability of power),

j) Outdoor air quality,

k) Energy efficiency,

m) Filteration standard,

n) Hours of use,

p) Outdoor air quality, and

q) Diversity factor.

6.1.2 The operation of the system in the following
circumstances should be considered when assessing
the complete design:

a) In summer;

b) In monsoon;

c) In winter;

d) In intermediate seasons;

e) At night;

f) At weekends and holidays;

g) Under frost conditions, where applicable;

h) If electricity supply failure occurs and when
the supply is restored; and

j) If extended low voltage conditions persist.

6.1.3 Consideration should be given to changes in
building load and the system design so that maximum
operational efficiency is maintained under part load
conditions. Similarly, the total system should be
separated into smaller increments having similar load
requirements so that each area can be separately
controlled to maintain optimum operating conditions.

6.2 Electrical Requirements

6.2.1 Conduits

Where conduits are used for carrying insulated
electrical conductors and when such conduits pass from
a non-air-conditioned area into an air-conditioned area
or into a fan chamber of duct, a junction box shall be
installed or other means shall be adopted to break the
continuity of such conduit at the point of entry or just
outside, and the conduit should be sealed round the
conductors to prevent air being carried from one area
into the other through the conduit and thereby giving
rise not only to leakage and inefficiency but also to the
risk of condensation of moisture inside the conduits.
The same method applies equally to other types of
wiring, like wood sheathing or ducts which allow air
to pass through around the conductors.

6.2.2 In case of air-conditioning plants where re-
heating is used, a safety device shall be incorporated
in the installation to cut off automatically the source

of heating, such as steam or electricity by means of a
thermostat or some other device, as soon as the
temperature of the room reaches a predetermined high
level not exceeding 44°C, unless a higher temperature
is required for an industrial process carried on in the
air-conditioned enclosure.

6.2.3 In case of air-conditioning plants where heating
by means of an electric heater designed to operate in
an air current is used, a safety device shall be
incorporated in the installation to cut off the supply of
electricity to the heating device whenever there is
failure of the air current in which the heater is required
to operate. Serious harm to the plant and sometimes
fires may be caused by negligence in this respect.

The surface temperature of all electric heaters used in
an air-conditioned plant should be limited, preferably
to 400°C, and in any case it shall not exceed 538°C,
when measured in still air.

6.2.4 Air-conditioning and ventilating systems
circulating air to more than one floor or fire area shall
be provided with dampers designed to close
automatically in case of fire and thereby prevent
spread of fire or smoke. Such system shall also be
provided with automatic controls to stop fans in case
of fire, unless arranged to remove smoke from a fire,
in which case these shall be designed to remain in
operation.

6.2.5 Air-conditioning system serving large places of
assembly (over 1 000 persons), large departmental
stores or hotels with over 100 rooms in a single block
shall be provided with effective means for preventing
circulation of smoke through the system in the case of
a fire in air filters or from other sources drawn into the
system even though there is insufficient heat to actuate
heat sensitive devices controlling fans or dampers. Such
means shall consist of suitable photo-electric or other
effective smoke sensitive controls, or may be manually
operated controls.

7 ELECTRICAL ASPECTS OF LIFTS AND
ESCALATOR SERVICES

7.0 General

7.0.1 For the information of the electrical engineer,
the lift/escalator manufacturer should advise the
architect/engineer of the building of his structural and
electrical requirements. This should be available early
in the planning stage to ensure proper electrical
provisions to be made for the service and suitable cables
and switchgears. During preliminary planning of the
building, the aspect of lifts and escalators installation
shall be discussed with all concerned parties namely,
client, architect, consulting engineer and/or lift
manufacturer.

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7,0.2 The following aspects shall be taken into account
to decide the electrical requirements for lifts:

a) Number of lifts, size, capacity and position;

b) Number of floors served by the lift;

c) Height between floor levels;

d) Provisions for machine room and proper
access to it;

e) Provisions for ventilation and lighting;

f) Electric supply required;

g) Details of wiring and apparatus required;
h) Quantity/quality of service;

j) Occupant load factors;

k) Car speed;

m) Control system;

n) Operation and maintenance;

p) Provision for lift and depth;

q) Number of entrances;

r) Provision of telephone or alarm bell inside
the lift car;

s) Provision of battery backup emergency light

inside the lift car; and
t) Providing battery backup automatic rescue

device or uninterrupted power supply (UPS).

7.1 Design and Operation

Reference is drawn to IS 14665 (Part 2/Sec 1), IS 14665
(Part 2/Sec 2), IS 14665 (Part 3/Sec 1) and IS 14665
(Part 3/Sec 2).

7.2 Electrical Installation Requirements

7.2.1 General

The requirements for main switches and wiring with
reference to relevant regulations may be adhered to.
The lift maker should specify, on a schedule, particulars
of full load current, starting current, maximum
permissible voltage drop, size of switches and other
details to suit requirements. For multiple lifts a diversity
factor may be used to determine the cable size and
should be stated by the lift manufacturer.

It is important that the switches at the intake and in the
machine room which are provided by the electrical
contractor are of correct size, so that correctly rated
fuses can be fitted. No form of 'No Volt' trip relay
should be included anywhere in the power supply of
the lift.

The lift maker should provide overcurrent protection
for power and control circuits, either on the controller
or by a circuit-breaker, but the following are not
included in the contract.

a) Power supply mains — The lift sub-circuit

from the intake room should be separate from
other building service.
Each lift should be capable of being isolated
from the mains supply. This means of
isolation should be lockable.

b) For banks of interconnected lifts, a separate
sub-circuit is required for the common
supervisory system, in order that any car may
be shut down without isolating the
supervisory control of the remainder.

c) Lighting — Machine rooms and all other
rooms containing lift equipment should be
provided with adequate illumination and with
a switch fixed adjacent to the entrance. At least
one socket outlet, suitable for lamps or tools,
should be provided in each room.

The car lighting supply should be independent of the
power supply mains and should be connected to the
inverter system with battery backup.

Pits should be provided with a light, the switch for
which should be in the lift well, and accessible from
the lower terminal floor entrance.

When the alarm system is connected to a transformer
or trickle-charger, the supply should be taken from the
machine room lighting.

7.2.2 Electrical Wiring and Apparatus

7.2.2.1 All electrical supply lines and apparatus in
connection with the lift installation shall be so
constructed and shall be so installed, protected, worked
and maintained that there may be no danger to persons
therefrom.

7.2.2.2 All metal casings or metallic coverings
containing or protecting any electric supply lines of
apparatus shall be efficiently earthed.

7.2.2.3 No bare conductor shall be used in any life car
as may cause danger to persons.

7.2.2.4 All cables and other wiring in connection with
the lift installation shall be of suitable grade for the
voltage at which these are intended to be worked and if
metallic covering is used it shall be efficiently earthed.

7.2.2.5 Suitable caution notice shall be affixed near
every motor or other apparatus operating at a voltage
exceeding 250 V.

7.2.2.6 Circuits which supply current to the motor shall
not be included in any twin or multicore trailing cable
used in connection with the control and safety devices.

7.2.2.7 A single trailing cable for lighting control and
signal circuit shall be permitted, if all the conductors
of this trailing cable are insulated for maximum voltage
running through any one conductor of this cable.

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SP 30: 2011

7.2.2.8 Emergency signal or telephone

It is recommended that lift car should be provided either
with an emergency signal that is operative from the
lift car and audible outside the lift well or with a
telephone.

When an alarm bell is to be provided, each car is fitted
with an alarm push which is wired to a terminal box in
the lift well at the ground floor by the lift maker. This
alarm bell, to be supplied by the lift maker (with
indicator for more than one lift), should be fixed in an
agreed position and wired to the lift well. The supply
may be from a battery (or transformer) fixed in the
machine room or, when available, from the building
fire alarm supply.

When a telephone is to be provided in the lift car, the
lift maker should fit the cabinet in the car and provide
wiring from the car to a terminal box adjacent to the
lift well.

7.2.2.9 Building Management System — Interface for
Lifts

Where more than three lifts are provided in a building
and especially when these are provided at different
locations in the building, a form of central monitoring
may be provided. Such central monitoring may be
through a Building Management System, if provided
in the building or through a display panel.

7.2.2.10 Earthing

The terminal for the earthing of the frame of the motor,
the winding machine, the frame of the control panel,
the cases and covers of the tappet switch and similar
electric appliances which normally carry the main
current shall be at least equivalent to a 10 mm diameter
bolt, stud or screw. The cross -sectional area of copper
earthing conductor shall be not smaller than those
specified in Part 1/Sec 14 of the Code.

The terminal for the earthing of the metallic cases and
covers of doors interlocks, door contacts, call and
control buttons, stop buttons, car switches, limit
switches, junction boxes and similar electrical fittings
which normally carry only the control current shall
be, at least equivalent to a 5 mm brass screw, such
terminal being specially provided for this purpose.

The earthing conductor shall be secured to earthing
terminal in accordance with the recommendations
made in IS 3043 and also in conformity with the
provisions of Indian Electricity Rules 1956.

Where screwed conduit screws into electric fittings
carrying control current and making the case and cover
electrically continuous with the conduit, the earthing
of the conduit may be considered to earth the fitting.
Where flexible conduit is used for leading into a fitting,

the fitting and such length of flexible conduit shall be
effectively earthed.

One side of the secondary winding of bell transformers
and their cases shall be earthed.

73 Additional Requirements for Escalators

7.3.1 Connection Between Driving Machine and Main
Drive Shaft

The driving machine shall be connected to the main
drive shaft by toothed gearing, a coupling, or a chain.

7.3.2 Driving Motor

An electric motor shall not drive more than one
escalator.

7.3.3 Brake

Each escalator shall be provided with an electrically
released, mechanically applied brake capable of
stopping the up or down travelling escalator with any
load up to rated load. This brake shall be located either
on the driving machine or on the main drive shaft.

Where a chain is used to connect the driving machine
to the main drive shaft, a brake shall be provided on
this shaft. It is not required that this brake be of the
electrically released type, if an electrically released
brake is provided on the driving machine.

7.3.4 No bare conductor shall be used in any escalator
as may cause danger to persons.

7.3.5 Electrical conductors shall be encashed in rigid
conduits, electrical tubings or wireways which shall
be security fastened to the supporting structure.

7.3.6 All electrical supply lines and apparatus in the
escalator shall be of suitable construction and shall be
so installed, protected, worked and maintained that
there is no danger to persons from them.

All metal casings or metallic coverings, containing or
protecting any electric supply line or apparatus shall
be efficiently connected with earth.

7.3.7 Disconnect Switch

An enclosed, fused switch or a circuit-breaker shall be
installed and shall be connected into the power supply
line to the driving machine motor. Disconnecting
switches or circuit-breakers shall be of the manually
closed multi-pole type. The switch shall be so placed
that it is closed to and visible from the escalator
machine to which the supply is controlled.

With dc power supplies the main disconnecting switch
and any circuit-breaker shall be so arranged and
connected that the circuit of brake magnet coil is
opened at the same time that the main circuit is opened.

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73.8 Enclosure of Electrical Parts

All electric safety switches and controllers shall be
enclosed to protect against accidental contact.

7.3.9 Caution Notice

Suitable 'CAUTION' notice shall be affixed near every
motor or other apparatus operating at a voltage
exceeding 250 V.

7.3.10 Insulation

The electrical parts of starting and stopping devices,
other operating and similar devices, controllers and
similar other parts shall be efficiently insulated and
the insulation shall be capable of withstanding for a
period of one minute the continuous application of a
ac test voltage equal to ten times the voltage at which
these electrical parts are energized, subject to a
maximum voltage of 2 000 V when the test voltage is
applied between contacts or similar parts in the open
position, and between such contacts and earthed parts.

8 ELECTRICAL ASPECTS OF AUDIO SYSTEM
SERVICES

8.0 General

8.0.1 This clause covers essential installation design
aspects of electrical audio systems for indoor and
outdoor use both for temporary and permanent
installations.

8.0.2 This applies to sound distribution systems and
public address systems but does not cover installations
in conference halls where both microphones and
loudspeaker are distributed amongst the audience.

8.0.3 Specific requirements if any, for individual
occupancies are covered in individual Sections of the
Code.

8.0.4 For guidance on selection of equipment and their
installation and maintenance, reference shall be made
to IS 1881 and IS 1882.

8.1 Exchange of Information

8.1.1 The initial and ultimate requirements of the
installations should be ascertained as accurately as
possible by prior consultations. Plans shall show,

a) details of the installation proposed,

b) accommodation and location of the central
amplifier equipment, and

c) ducts and overhead lines required for wiring.

8.2 Design Requirements

8.2.0 The output from the microphone, gramophone,
tape-recorder or radio receiver or CD player from a
sound film is amplified and presented through a system

of loudspeakers installed at chosen locations. The
design of this installation shall be such that, depending
on the nature of occupancy, the quality of reproduction
is as desired. Reference is drawn to 5.2 of IS 1881 and
IS 1882 on the quality of reproduction suitable for
different purposes, and the acoustic power
requirements therein. The choice of equipment such
as these for input signals, amplifying equipment/system
and loudspeaker shall be governed by the
considerations enumerated in IS 1881 and IS 1882.

8.2.1 Wiring for Audio System

8.2.1.0 All equipments shall be securely installed in
rooms guarded against unauthorized access.
Precautions shall be taken to keep dust away.

8.2.1.1 All present controls should be mounted behind
cover plates and designed for adjustment only with the
help of tools. All controls shall be mechanically and
electrically noiseless.

8.2.1.2 The positioning of equipment shall be such that
the lengths of the interconnecting cables is kept to the
minimum.

8.2.1.3 In case the number of the equipment is large, they
shall be mounted on racks of suitable dimensions of metal
or wood, in such a manner that the controls are within
easy reach. The patch cords shall be neatly arranged.

8.2.1.4 In determining the positioning of the
microphones and loudspeakers in the installation,
advice of an acoustical expert shall be sought for best
accuracy and reproducibility.

8.2.1.5 For outdoor installations, the line-matching
transformers shall be mounted in weather-proof
junction boxes.

8.2.1.6 In large open grounds such as an outdoor
stadium, care shall be taken to ensure that the sound
heard from different loudspeakers do not have any
noticeable time lag.

8.2.1.7 The plugs and sockets used in electrical audio
systems shall not be interchangeable with those meant
for power currents.

8.2.1.8 Microphone and gramophone cables shall
preferably use twisted pairs of conductors with
sufficient insulation screened continuously with a close
mesh of tinned-copper braid. The copper braiding
should be sheathed with an insulating covering. These
shall be isolated from power, loudspeaker and
telephone cables. Joints in the cables shall be avoided.
Microphone cables shall be laid without sharp bends.
Indoor cables can be laid on the floor along the walls
or under the carpet. When laid in the open, they shall
be either buried in the ground at a depth not less than
20 cm, or inside an iron-pipe at that depth if heavy

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mechanical movement is expected above. This may
also be laid overhead at a height not less than 3.5 m,
clipped securely to a bearer wire. Any wiring required
to be run along corridors or outside walls below 1.8 m
shall be protected by a conduit.

8.2.1.9 The loudspeaker cables shall be so chosen that
the line losses do not exceed the values given in Table 1
of IS 1882.

8.2.2 Power Supplies

8.2.2.1 The equipment should normally operate from
230 V, single phase 50 Hz ac mains supply. A voltage
regulating device shall be provided if the regulation is
poorer than ±5 percent. In the absence of ac mains
supply the system shall be suitable for operating from
a storage battery.

8.2.2.2 The supply mains shall be controlled by a MCB
of adequate capacity.

8.2.3 Earthing

Proper earthing of the equipment shall be made in
accordance with good practice.

8.3 Inspection and Testing

The completed installation shall be inspected and tested
by the engineer to ensure that the work has been carried
out in the manner specified.

8.4 Miscellaneous Provisions

Where necessary, that is in installations where the
breakdown of the sound distribution systems should
be restored instantaneously or within a limited time,
the stand-by equipment shall be readily available.

9 ELECTRICAL ASPECTS OF FIRE ALARM
AND FIGHTING SYSTEMS

9.0 General

9.0.1 This clause covers the electrical aspects of the
installation of fire alarm/protection system in buildings.

9.0.2 This clause is applicable in general to all types
of occupancies, while specific requirements if any or
individual situations are covered in the respective
sections of the Code.

9.0.3 For total requirements for fire protection of
buildings, including non-electrical aspects such as
choice and disposition of fire-fighting equipment,
depending on the nature of occupancy installation and
maintenance aspects, etc., reference shall be made to
SP 7 and the relevant Indian Standards.

9.1 Fire Detectors

9.1.1 The following types of fire detectors are available
for installation in buildings:

a) Heat detectors {see IS 2175):

1) 'Point' or 'spot' type detector

2) Line type detector.

NOTE — These may be of fixed temperature
detector or rate of rise detector.

b) Smoke detectors:

1) Optical detectors.

2) Ionization chamber detector,

3) Chemically sensitive detector.

c) Flame detectors.

9.1.2 For guidance on their choice and siting in the
installation, see SP 7.

9.2 Wiring for Fire Alarm Systems

9.2.1 The equipment and wiring of the fire alarm system
shall be independent of any other equipment or wiring,
and shall be spaced at least 5 cm away from each other
and other wiring. The wiring of the fire alarm systems,
shall be in metallic conduits. The wiring shall be kept
away from lift shafts, stair cases and other flue-like
opening.

9.2.2 Alarm sounders shall be of the same kind in a
particular installation.

9.2.3 For large or intricate premises, it is necessary
that the origin of a call be indicated. For this, the
premises shall be divided into sections zones. All call
points in a section shall be connected to the same
indicator. The various drops or lamp indicators shall
be grouped together on the main indicator board or
control panel. When the premises are extensive, a
number of main indicator boards may be used covering
different sectors. These shall be supplemented by sector
indicators for the various sectors at a central control
point.

9.2.4 At the control point the indicator board or the
zone and section indicating boards and all common
control apparatus and supervisory equipment shall be
located. For every installation a control point shall be
provided, where it can be under constant observation.
The main control centre shall be located on the ground
floor and should be segregated from the rest of the
building by fire-break wall.

9.2.5 No section shall have more than 200 fire detectors
connected together.

9.2.6 The origin of the calls may be indicated by the
use of lamp indicators. Each indicator shall include:

a) two lamps connected in parallel associated
with each indication, so arranged that failure
of either of the lamps is readily apparent, or

b) one lamp glowing during normal operation
of the system for each section and the alarm

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indicated by the extinguishing of the lamp for
the section where the call originates. Alarms
should not sound on the failure of the
indicator.

9.2.7 The arrangement of the circuits and the electrical
connections shall be such that a call or fault in any
circuit does not prevent the receipt of calls on any other
circuit.

9.2.8 The indicating device associated with the various
call points and sections shall be grouped together on
the main indicator board. If necessary remote indicating
panel, with audible alarms in the night quarters of the
caretaker of the building should be provided.

9.2.9 The silencing switches/push buttons in their off
position shall give an indication of this fact on the main
control panel operation of silencing switches shall not
prevent sounding of alarm from any other zone
simultaneously, or cancel the other indications of the
alarm or fault.

9.2.10 For fire alarm systems, cables of the following
types shall be used:

a) Mineral insulated aluminium sheathed cables;

b) PVC insulated cables,

c) Rubber insulated braided cables,

d) PVC or rubber insulated armoured cables, and

e) Hand metal sheathed cables.

The laying of the cables shall be done in accordance
with Part 1/Section 1 of the Code.

9.2.11 The source of supply for the alarm system shall
be a secondary battery continuously trickle/float
charged from ac mains, with facilities for automatic
recharging in 8 h sufficiently to supply the maximum
alarm load at an adequate voltage for at least 2 h. The
capacity of battery shall be such that it is capable of
maintaining the maximum alarm load on the system at
an adequate voltage for at least 1 h plus the standing
load or losses for at least 48 h. Suitable overload
protective devices shall be provided to prevent
discharging of the batteries through the charging
equipment.

9.3 Fire Fighting Equipment

9.3.0 The choice of fire fighting equipment and their
installation details shall be governed by the
requirements specified in SP 7.

9.3.1 Requirements for Electrical Drives for Pumps in
Hydrant and Sprinkler Systems

9.3.1.1 Full details of the electric supply shall be
furnished together with details of generator plant to
the appropriate authorities.

9.3.1.2 Sufficient power shall be made available for
the purpose and the power source shall be entirely
independent of all other equipment in the premises and
shall not be interrupted at any time by the main switch
controlling supply to the premises. An indicator lamp
shall continuously glow in a prominent position to
indicate status of power in the substation and in the
fire-pump room.

9.3.1.3 Pumping sets shall be direct coupled type, and
shall work satisfactorily at varying load.

9.3.1.4 All motors and electrical equipment shall be
continuously rated, drip-proof with air inlets and outlets
protected with meshed wire panels where required
motors shall have a suitable fixed warming resistance
to maintain them in dry condition.

9.3.1.5 The starting equipment of the set shall
incorporate an ammeter and clearly marked to show
full load current. They shall not incorporate no-volt
trips.

9.3.1.6 The electric circuit for fire fighting system shall
be provided at its origin with a suitable switch for
isolation, but overload and no- volt protection shall not
be provided in the switch.

10 ELECTRICAL CALL BELL SERVICES

10.0 General

10.0.1 Guidance on installation of electric bells and
call systems are covered in IS 8884.

10.0.2 On the basis of information collected on the
extent of installation of electric bells and buzzers, or
indicator call system in the building, the following
aspects shall be ascertained in collaboration with the
parties concerned:

a) Accommodation required for control
apparatus, location and distribution points;
and

b) Details of chases, ducts and conduits required
for wiring.

10.1 Equipment and Materials

10.1.1 If wooden bases are used for bells and buzzers,
the component parts shall be rigidly held together
independently of the base, so that they are unaffected
by any warping.

10.1.2 Bells and buzzers which have a make or break
contact shall be provided with means of adjusting the
contact gap and pressure and means for locking the
arrangement.

10.1.3 Equipment for outdoor use shall be suitably
protected against the environmental conditions.

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SP 30 : 2011

10.1.4 Bell push switches shall be of robust
construction. Terminals shall be of adequate size and
should be so arranged that the loosening of a terminal
screw does not disturb the contact assembly. Any
flexible chords attached to them should be covered with
hard wearing braid.

10.1.4.1 Relays may be required for the following
situations:

a) Where mains operated device is to be
controlled by a circuit operating at a voltage
not exceeding 24 V,

b) For repeating a call indication until at a distant
point or points, and

c) For maintaining a call indication until an
indication is reset.

10.1.5 The indications shall be one of the following
types:

a) Lamp type — where sound of bell is
undesirable; for example in hospitals or in
noisy locations such as forges, mills, etc.

b) Flag type — where positive indication is
required which remain in position until
restored.

c) Pendulum type — for small installations
having up to 20 call points.

10.2 Choice of Call Bell System

The following guidelines are recommended:

a) Simple call bell system — For dwellings and
small offices (see Fig. 1).

b) Multiple call bell system — Hotels, hospitals
or similar large buildings where call points
are numerous (see Fig. 2).

c) Time bell system — Factories, schools.

10.3 Power Supply

The system may be operated at the normal mains
voltage, though it is preferable for the control circuit
to be operated at a voltage not exceeding 24 V.

10.4 Wiring

The wiring shall be done in accordance with
Part 1/Section 9 of the Code.

11 CLOCK SYSTEMS

11.1 Design Considerations

11.1.1 Reference is drawn to 5.1 of IS 8969. A
schematic diagram is shown in Fig. 3.

11.1.2 The enclosure of the clocks shall have no
openings giving access to live parts or functional

SUPPLY

Fig. 1 Simple Electric Call Bell System

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BELL PUSH
SWITCHES

^Hr

BELL PUSH
SWITCHES

N s INDICATOR

BELL PUSH
SWITCHES

tHt

BELL PUSH
SWITCHES

INDICATOR

BELLPU&H
SWITCHES

THif

bHTpuSFT

SWITCHES

I V INDICATOR

BELL PUSH
SWITCHES

tHt

BELL PUSH
SWITCHES

N i INDICATOR

SUPPLY

CENTRAL SWITCHROOM
WITH FLOOR INDICATOR

Fig. 2 Multiple Call Bell System

insulated parts or functional insulation other than the
openings necessary for the use and working of the
clocks. Where such openings are necessary, sufficient
protection against accidental contact with live parts
shall be provided.

11.1.3 To ensure necessary continuity of supply, direct
connection of the system to the supply mains is not
recommended. Batteries should always be provided.
The capacity of the battery shall be at least sufficient
to supply the installation for 48 h, not less than 10 Ah.

11.1.3.1 Where the supply is ac, single battery on
constant trickle charge is recommended, means being
provided for charging at a higher rate when necessary.

11.1.3.2 Where the supply is dc, two batteries should
be provided with changeover switch.

11.2 Location of Clocks

11.2.1 The master clock shall be placed in a room not
smaller than 2.4 m x 3.6 m.

11.2.2 The location and size of slave clocks may
frequently depend upon aesthetic requirements, but
from the point of view of readability, a ratio of
0.30 m diameter of dial to every 2.7 m of height is
acceptable. The following is adequate:

Dia of Clock

Height from Floor

0.30 m

2.70 m

0.45 m

3.30 m

0.60 m

4.50 m

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SP 30: 2011

11.3 Wiring

The wiring shall be done in accordance with Part 1/
Section 9 of the Code. Special conductor shall be
provided, or the conduit may be colour coded for
distinction from other circuits.

12 ELECTRICAL ASPECTS OF COMPUTER
CONTROL OF ENVIRONMENTAL SYSTEMS

12.0 General

12,0.1 Building users require services to meet the
environmental and functional needs associated with a
particular type of building, and these services vary
considerably according to the type of building involved.
However, the basic requirements are for comfort, safety
security, efficiency, reliability and operational utilities.
The increased application requirement calls for
coordinated and efficient control of the various systems
and their sub-systems. Configuration of these systems
in a computer programme is a necessicity now.

12.0.2 General building classifications are residential,

commercial, industrial, public, medical establishments
and industrial premises. The requirements differ
according to the particular purpose of the building. The
complexities of the services also relate to the
requirements and additionally to the size and class-
type of the building.

12.1 Exchange of Information

12.1.0 The architect should exchange information with
the engineer concerned when the building plans are
being prepared. The chief purpose of such an exchange
is to obtain information regarding the architectural and
electrical features of the building so that due provision
may be made to retain the aesthetic features and the
essential services while planning the locations of the
various devices and equipment of the environmental
services. Information may also be obtained at an early
stage regarding other services, such as electrical
installation, gas and water pipes etc.

12.1.1 Scale drawings showing plans and elevations
of the structure, electrical wirings shall be obtained

AC SUPPLY

Fig. 3 Impulse Master Clock System

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and the nature and location of the devices, sensors and
controllers of the environmental services shall be
indicated on them.

12.1.2 The initial and final requirements of the
installations should be ascertained as accurately as
possible by prior consultations. Plans shall show,

a) details of the installations proposed;

b) accommodation and locations of the central
control units, server, monitor, etc; and

c) ducts and cable routing required for wiring.

12.2 Building Management System (BMS)

12.2.0 Thermal comfort, lighting, ventilation, air-
conditioning, security, safety, fire detection and control
system and electrical power are always required, and
residential building represents this basic level of need.

12.2.1 The management of building services systems
for a larger establishment is more difficult due to the
variety, increased complexity, lack of individual
responsibility and high capital and operating costs for
the systems involved. The more complex control
systems are termed building management systems
(BMS). They are employed in commercial, public and
industrial buildings and control the services of heating,
ventilation, air-conditioning, steam, refrigeration, gas,
water, general and emergency lighting, emergency
electrical systems, power distribution, mechanical
transportation, fire detection alarm and fighting
systems, general and noxious fume ventilation, security
and waste disposal.

12.2.2 The building management systems (BMS)
means that all services can be monitored and reset from
a central location without delay or movement by the
engineer. BMS can also advise on preventative
maintenance schedules, thereby improving overall
plant reliability and operating efficiency. Consequently,
plant operation is greatly simplified by allowing an
engineer to reset any control level, monitor energy con-
sumption, organize maintenance and make fault
diagnosis from a central location. Remedial action is
quicker and can often be carried out by a smaller
engineering staff than would be required otherwise.

12.3 BMS Architecture

12.3.1 BMS architecture and performance
requirements shall be based on a distributed system of
intelligent, stand alone controllers, operating BMS
incorporates control and monitoring of all systems such
as environmental, fire and security but, in some cases,
separate dedicated fire protection systems are favoured
by the authorities and reference to local fire codes and
regulations is essential. The integration of fire
protection and security systems into BMS shall be

subject to the approval of the local fire prevention
authority. It is possible to keep the fire protection
system panel separate while still providing
communication links with the BMS for alarm and
reporting purposes.

12.3.2 Back-up power supplies such as the UPS
systems, although required for any BMS, need more
consideration for centralized intelligence systems. A
parallel systems structure and duplication of equipment
to provide redundancy facilities may also be necessary,
depending on the level of reliability required or the
importance of the functions.

12.4 Design Requirements

12.4.1 The BMS shall include all workstation software
and hardware, Process Control Units (PCU), Terminal
Controllers, Local Controller, Local Area Network
(LAN), sensors, control devices, actuators, system
software, Interconnecting cable, installation and
calibration, supervision, Distributed intelligence
systems also have a central computer, with the addition
of remote intelligent outstations capable of carrying
out all control functions independent of the main
computer. Outstations are located near to the building
zone which they serve, as in the earlier systems, and
are programmed to perform the required control
functions. The outstation can, however, be interrogated
and reset from the main computer and also
communicate routine information and alarms as
required by the plant operator.

12.4.2 System administration shall be available from
the Workstation in Control Room on Ethernet LAN
(Local Area Network) WAN (Wide Area Network) in
the system. The system specifically must have the
capability to support multiple workstations, depending
on complexity and magnitude of the services,
connected on the LAN or WAN network at the same
time. The building management system shall allow all
connected workstations to function in a true multi-user,
multi-tasking environment employing user-friendly
Windows platform using TCP/IP Protocol or any other
open protocol.

12.4.3 The system architecture shall be capable of
supporting single site and/or campuses as well as
multiple sites located in different geographical
locations.

12.4.4 The system shall be capable of modular
expansion without software upgrades or wiring
revisions.

12.5 General Characteristic of Software

12.5.1 Software shall be modular in design for
flexibility in expansion or revision of the system.

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SP 30 : 2011

12.5.2 The software shall include a General Purpose
Operating System, which will be based on a user-
friendly open platform. The architecture of the system,
and the application software/firmware shall generally
be compiled for faster execution speeds.

12.6 Hardware Requirements

12.6.0 The BMS consists of many subsystems and
equipment, sensors and peripheral devices. However,
the servers provide a single interface point for
operations, maintenance and management analysis.
Various subsystems and systems are connected to
provide information on different parameters at different
locations.

12.6.1 The on-site operator workstation shall be user
friendly, operator interface with the complete system.
As an example, the requirements of a workstation
equipment are given below:

a) Workstation equivalent to Pentium-IV 1GHz
or higher processor,

b) 256 MB Random Access Memory,

c) 40 GB Hard Disk or better,

d) 3.5 IN, 1.44 MB Diskette Drive,

e) Read/Write CD ROM 52X or Faster;

f) Serial Port,

g) Parallel Printer Port,
h) USB Port,

j) 19" SVG Colour Monitor,

k) Colour Graphics Card with at least 6 MB

RAM,
m) 101 Keyboard,
n) 3 button track ball with scroll wheel/optical

mouse,
p) 3COM Etherlink III with modem, and
q) Printer.

12.6.2 System Controllers

It is desirable to monitor and/or control all points in
the system through 'Intelligent' Distributed Control
Units. Each Distributed Control Unit in the system shall
contain its own microprocessor and memory with a
minimum 300 h battery backup. Each distributed
control unit shall be a completely independent stand-
alone 'master' with its own hardware clock calendar
and all firmware and software to maintain complete
on an independent basis.

12.6.2.1 Communication backbone

12.6.2.2 The central computer communicates with the
outstations through a standard interface and either a
dedicated line, a leased line or a telephone switched
line. Smaller systems on one site are usually connected

using a twisted pair in either a ring, star or tree network.

12.6.2.3 Optic fibre transmission is currently being
installed and allows very fast and high bandwidth
transmission. As BMS becomes more widely accepted,
it is likely that system capacities will increase to a level
that will make optic fibre technology an attractive
proposition.

12.6.2.4 For transmission distances within the building
or site up to about 1.6 km, telephone lines are usually
employed. The computer and outstations are connected
to the telephone line via a modem, which converts the
input signals to pulses which are transmittable on the
telephone line, thus enabling information to be
transmitted and received.

12.6.2.5 In many cases, particularly for remote sites
an autodial modem restricts the use and cost of
telephone lines by automatically communicating only
when required. Autodial modems are therefore used
for large or multiple sites and the telephone lines are
accessed through the existing telecom system. Modems
generally operate over a range of speeds (baud rate)
with generally increased cost for the higher speed, for
example, 9 600 baud is now common. (1 baud = 1 bit/
second.) The baud rate is software set to suit the
particular system, and some manufacturers use higher
transmission rates for directly wired systems.

12.6.2.6 Autodial communication with the computer
can be either direct dialling by the operator,
programmed down-loading of data at predetermined
times, or priority alarm reports.

12.6.2.7 It is advisable to have more than one line per
station, one of which is dedicated to priority reporting
and the other to routine reporting and monitoring. This
allows each function to be effective without conflict
with the other.

12.6.3 Control Monitoring Stations

12.6.3.1 A typical control monitoring station consists
of a microcomputer, visual display unit (VDU),
backing store and printer. One station is usually
installed in a central location, but systems with several
stations working on a master/slave principle can be
obtained for large sites.

12.6.3.2 Buildings under phased development can be
provided with a distributed intelligence system without
a central computer. Under these circumstances, the
outstation can be programmed and interrogated directly
by portable hand-held microcomputers, which are
taken around the site by personnel and plugged into
the outstation as required. A central computer can be
added to the system at a later date, when the
development is complete or finances allow.

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12.6.33 The location of the central computer requires
careful consideration and should be provided with a
clean power supply with back-up, as referred to
previously. If connected to fire safety systems, it should
be located where it can be easily accessed and
interrogated by the fire brigade. The fire alarm
protection system may be connected directly to the fire
brigade, but the information supplied at the control
station is likely to be more comprehensive and useful
for directing fire-fighting operations and controlling
services that may affect safety or the spread of fire.
Smoke removal and staircase pressurization systems
for high rise buildings are often an integral part of the
mechanical ventilation or air conditioning system.
When this is the case, ready access by the fire brigade
for system status and control is essential.

12.6.4 VDUs and Key Boards

12.6.4.1 High resolution VDUs enable text and
graphics to be displayed. Communication with the
system software can be through keyboard, mouse or
touch screen. The touch screen is the simplest but least
flexible method and has not been widely adopted by
BMS manufacturers.

12.6.5 Printers

12.6.5.1 The output of data and information from the
system is transferred to paper copy by a printer. This
is essential so that a readable log of the system
performance is available for distribution to other
interested members of the engineering and
management team.

12.6.6 LANs

12.6.6.1 The Controller LAN utilizes a peer-to-peer,
token passing protocol to communicate between nodes
on the network. The Process Control Unit shall provide
direct control and monitoring of process functions from
a Teer-to-Peer' LAN based controller. These process
functions include environmental control, trending,
energy management, and process control, which may
be executed locally in a stand-alone mode or
'globalized' across the Token Passing LAN, reports.

12.6.7 Data Communications

12.6.7.1 The standard specifications of generally
acceptable ratings are indicated hereunder:

a) PC port

1 ) Protocol: Asynchronous, Polling, RS-232

2) Baud Rate: 300, 1 200, 2 400 or 9 600
Bps

b) Host LAN

1) Protocol: Token Passing, RS-485

2) Baud Rate: 9 600 or 19 200 Bps

c) Cables

1) LAN

22 AWG (0.324 mm) shielded, twisted
pair (Belden 9184), 5 000' (1 500 mm)
maximum or 24 AWG (0.206 mm)
shielded, twisted pair (Belden 9841)
4 000' (1200 mm) maximum per
segment.

2) Communication ports

i) Controller LAN: RS-485; 19,200 or
9 600 baud, SDLC, token-passing.

ii) Hand Held Console Port: RJ11
Modular, 1 200 baud, TTL.

iii) RS-232 Port: PC @ 9 600 baud
(7801 TAP function), or Hayes direct
dial asynchronous modem @ 1 200,
2 400 baud or 9 600 baud.

iv) RS-232 Expansion Board Port:
Supports synchronous modem,
direct or two-way dial SDLC (78061
or 78035 TAP functions) @ baud
rates of 1 200 to 9 600 baud.
Requires optional plug on module.

3) Network wiring requirements

Cable Supported: Twisted pair, shielded.
22 AWG (0.324 mm 2 ) or larger, 30 pF/ft.
or less between conductors, 55 pF/ft. or
less conductor to shield, 85 to 150 Ohm
impedance Belden 9841 or equivalent.

4) Controller LAN length

i) 1 500 m per segment,
ii) 7 600 m with repeaters

5) Controller LAN

RS-485; 19 200 or 9 600 baud, SDLC,
token-passing.

6) Door controller LAN

RS-485; 9 600 baud, asynchronous,
polling.

7) Hand held console port

RJII Modular; 1 200 baud, TTL.

8) RS-232 port

PC @ 9 600 baud (7801 TAP function)
or Hayes direct-dial a synchronous
modem @ 1.200, 2 400 or 9 600 baud.

9) RS-232 expansion board port
Supports synchronous modem, direct or
two-way dial SDLC (78061 or 78035
TAP functions) @ baud rate of 1 200 to
9 600 baud, Requires optional plug on
module.

PART 1 GENERAL AND COMMON ASPECTS

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SP 30 : 2011

10) Network wiring requirements
i) Controller LAN length

1 500 m per segment; 7 600 m with

repeaters
ii) Micro controller sub-LAN length

1 500 m

1) Cable supported

Twisted pair, shielded, 22 AWG
(0.324 mm 2 ) or larger, 30 pF/ft.
or less between conductors, 55
pF/ft. or less conductor to
shield, 85 to 150 ohm
impedance.

2) Auto dial support telephone
numbers

8; stored in NOVRAM, Number
of Digits — 31 per phone
number; Supported — Phone,
Beeper, Pager.

12.6,8 Input/Output Sensors

The input devices, depending on application and usage
are:

a) Space air temperature sensor,

b) Relative humidity sensor,

c) Air flow switch,

d) Water flow switch,

e) Water flow measuring transducer,

f) Tank float switch,

g) Current sensor,
h) kWh transducer,

j) Current, voltage and watt transducers,

k) Occupancy sensor,

m) Personal attendance sensor,

n) Motion detector,

p) Electronic door lock,

q) Card reader,

r) Access controller,

s) Damper and valve and their actuators, and

t) Electronic to pneumatic transducers.

12.7 Installation

All devices shall be installed in pre-engineering
locations to be shown on the drawings in accordance
with standard industry practice.

12.7.1 Cables

12.7.1.1 Cables in conduits

It shall be secured from building structure, not from
other services.

12.7.1.2 Cables on trays and ladders

Cables shall be fixed neatly to trays and ladders in
single layers and parallel to the tray edge to avoid
unnecessary crossovers. Cables shall be fixed at
intervals not exceeding 48" by means of non-corrosive
fastening materials.

12.7.13 Segregation

Data cabling shall be physically segregated from power
and SMS input/output cabling and mains cabling.

12.7 \1 Panels

12.7.2.1 General

Panels and Controllers shall be installed within a
dedicated metal enclosure.

12.7.2.2 Documentation

Terminal numbers, points list, point addresses and short
and long descriptions shall be described inside a plastic
fade-free in a pocket.

12.7.3 Small Point Controllers

Small point controllers shall be installed adjacent to
the controlled device, accessible for maintenance and
contained in a suitable enclosure.

12.7.4 Transmission Systems

12.7.4.1 The BMS shall utilize the above LAN
architecture to allow all of the Control Units to share
data as well as to globalize alarms. The Controller LAN
shall be based on a peer-to-peer, token passing
technique with a data speed of not less than 19.2 kB.
The turnaround time for a global point to be received
by any node, including operator stations, shall be less
than 3 s.

12.7.4.2 Fiber Optic Pathways, Fiber Optic Media shall
be used, as required, between buildings for the
Controller LANs. Wherever the Optical Fiber enters
or leaves the building, provide a fiber to hard copper
interface device. The FOI shall regenerate data prior
to transmitting this data to either the fiber or hard
copper channels, so as not to result in the degradation
of signal and to minimize the accumulation of errors
between multiple FOIs. The FOI shall include ' 'jabber"
protection, such that continuous data from a defective
component will not destroy communications on the
LAN. Provide visual indication of receiving and
transmitting data activity on the hardwired drop.
Provide visual indication of data transmission on the
fiber media, jabber presence of fiber and hard copper
channels, and bad signal quality on the hard copper
channel.

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12.8 Testing and Commissioning

12.8.1 General

The contractor shall perform all tests submitted in the
Test Procedure and remain on site until the BMS is
fully operational.

12.8.2 Factory Testing

Demonstrate such control loop shall be demonstrated
including all calculations and global functions. Analog
values shall be simulated, if required. Attendance by
three (3) persons nominated by the Owner shall be
allowed. After Test, summary of results and necessary
modifications shall be submitted.

12.8.3 Final Acceptance Test

Acceptance of the system shall require a demonstration
of the standby of the system. This test shall not start
until the customer has obtained 30 days beneficial use
of the system.

13 TELEPHONE SYSTEMS

13.0 General

13.0.1 Telephone systems are classified as
communications systems. Telephone communication
through the public network is in most countries the
responsibility of the Telecom administrations. These
are systems, which must meet more stringent
requirements for reliability of transmission.

13.0.2 Electronic Private Automatic Branch Exchanges
(EPABX)

Electronic private branch exchanges are connected to
the public exchanges through exchange lines.
Operationally they form part of the subscriber
equipment of the public telephone system. EPABX
permit internal communication between the extensions
of a system and external communication, for approved
branch systems, over the exchange lines.
Communication within the private branch system,
normally, does not attract charges.

13.0.3 Backbone Cabling

Generally the inter-floor/inter-building backbone
cabling is included in the scope of main building
design. The backbone cabling should accommodate
analog voice signal alone or analog and data signals
simultaneously, as the case may be. It is the speed of
data transmission and bandwidth, which matter most
in the design of the communication backbone.

13.1 Exchange of Information

13.1.1 The exact requirement of the subscribers shall
be assessed before drawing out the specification of the

EPABX system. This means that information on
number of subscribers in the building, distribution of
the phones in the floors and other areas, nature of traffic
etc are to be collected.

13.1.2 The initial and final requirements of the
installations should be ascertained as accurately as
possible by prior consultations. Plans shall show:

a) details of the installations proposed;

b) the accommodation and location of the
EPABX console, monitor, etc; and

c) the ducts and cable routing required for
wiring.

13.2 Design Requirements

13.2.1 The basic architecture and performance
requirements of the modern day communication system
is microprocessor-based pulse code modulated (PCM)/
Time Division Multiplexing (TDM) technology.

13.2.2 The environmental conditions for the EPABX
should preferably be controlled so that the room air
temperature is maintained between 10 °C and 40 °C
and relative humidity between 50 percent and
95 percent.

13.2.3 Integrated Services Digital Network (ISDN) is
a common requirement now-a-days for commercial
buildings since it is possible to handle simultaneous
calls of different types namely voice, data and images
transfer (Tele & Video conferencing) without any loss
of data, at a minimum speed of 64 kBps, which can be
increased further depending on requirement. EPABX
system shall be capable of interfacing with other
EPABX system through appropriate protocol.

13.2.4 Hardware Requirement

13.2.4.1 Electronic private automatic branch exchange

In EPABX system the individual call stations are
connected each by a twisted pair of wires to the
automatic exchange (see Fig.4). This is also the
termination for the exchange lines and, where
necessary.

13.2.4.2 Power supply

Depending on the size and type of installation, the
telephone system requires for its operation a dc power
supply of 24 V or 48 V, which is obtained from the
power mains through a rectifier. The rectifiers, provided
with closed-loop control and for small and medium
sized systems, are accommodated in the exchange
housing. For large systems rectifiers (controlled) are
supplied in separate cabinets.

13.2.5 Standby Batteries

Standby batteries can be provided as an adjunct to the

PART 1 GENERAL AND COMMON ASPECTS

125

SP 30: 2011

rectifier. These are necessary for important installations
such as police stations, fire stations, etc, to cover
possible main supply failures.

13.2.6 Space Requirements

13.2.6.1 The switching equipment for the telephone
systems and small EPABX's takes up little room. Apart
from the telephones, only relatively small wall-
mounted junction boxes or exchange units are required.
The exchanges, furthermore, produce little or no noise,
so that they can be accommodated in an office if
desired. For large systems a separate room should be
provided for the exchange equipment, and similarly
for the answering panel. Space should be allowed in
planning for additional cabinets or racks, exchange
equipment platforms etc that may be necessitated by
future enlargement of the systems. The size of the
battery room depends upon the type of power supply
equipment used.

13.2.7 Features

There are various features available with the present
day EPABX with introduction of concerned cards and
features to be incorporated have to be decided

depending on functional requirement. Some of the most
common features included are Abbreviated Dialing,
Recorded Announcement System, Last number redial,
Executive override, multi-party conference, call
forwarding, Direct Inward Dialing (DID), Automatic
alarm make-up call, STD barring, group hunting,
networking facility.

13.3 Installation

13.3.1 Wiring Installation

For wiring within buildings, wire is mainly installed in
embedded PVC conduit, or wiring cables with
conductors of 0.6 mm or 0.8 mm diameter for surface
wiring.

13.3.1.1 In running the wires it is important to maintain
a separation of at least 10 mm between the
communications wiring and power cables.

13.3.1.2 If conductors belonging to different
communications systems are run together — for
example, telephone wires and loudspeaker wires, or
heavily loaded slave clock circuits — there is a risk of
mutual interference between them. In such cases it is
advisable to use screened cables.

Building 1

4th floor

Branch lines
o—

Sub- distribution
assembly

3rd floor

2nd floor -a
as

1st floor &

Ground floor

Building 2

Building 3

Conduit

Main distribution
assembly

Basement

Conduit

Building distribution
assembly

Conduit

Building distribution
assembly

o 3>

126

Main cable

Fig. 4 Example of the Arrangement of a Basic EPABX System in Large Building

NATIONAL ELECTRICAL CODE

SF 30 : 2011

13.3,1.3 In communication cables the cores are twisted
together either in pairs or in star quad formation. For
speech transmission — to avoid crosstalk — either a
twisted pair or, in the case of the star quad a pair of
opposite cores — should be used.

13.3.2 Ducts, Apertures and Channels

In the course of constructing the shell of the building the
appropriate channels and ducts should be formed in the
masonry and lead-through apertures provided in walls,
ceilings, joists and pillars. Suitable accommodation should
be provided for the distribution boards in large
communications system (for example recesses, shafts
etc).

13.3.2.1 Conduits

PVC conduit can be used for the individual sections of
conduit networks in residential buildings for the riser

conduit from floor to floor, horizontal branches in the
floors up to the distribution boxes in the apartments,
and between the distribution boxes in the apartments
and the flush-type junction boxes.

13.3.3 Connection of Telephones

13.3.3.1 At the positions allocated for the telephones
the conduit should be terminated in flush- type boxes.
For junction boxes and socket outlets for the connection
of telephones, flush-type boxes (switch boxes) to
standards are adequate. A maximum of two telephones
can be connected to a junction box.

13.3.3.2 In most cases the telephone is connected
permanently to the subscriber's line through a junction
box. If it is required to be able to use it in a number of
rooms, socket outlets and plugs should be provided.
Units for flush and surface mounting are available for
both methods of connection.

3rd floor

Plastic conduit

— 16 mm conduit

Flush 1
connection jox y

Distribution

network to call
station

box

2nd floor

Flush
distribution box

PI a clip ro-

nduit 23 mm

Branch conauit

1st floor

IP"

Plastic co-
nduit 29 mm

Ground floor

Conduit network
to several call

stations
(e.g. shops)

Ground floor or basement

Riser conduit

Distribution box
for cable connection

Cable

Fig. 5 Typical Conduit Wiring System
PART 1 GENERAL AND COMMON ASPECTS

127

SP 30: 2011

13.3.4 Installation of Telephone Wiring

13.3.4.1 Wiring in residential building

In residential buildings a concealed wiring arrangement
is most conveniently and economically installed in an
adequately dimensioned conduit network. It has been
found satisfactory to provide riser conduits or cable
ducts and horizontal branch conduits to the apartments,
with distribution boxes at the junctions (Fig. 5). With
a concealed installation of this kind it is possible at
any time to alter the wiring or add to it without
inconvenience to the occupier.

13.3.4.2 Wiring in non-residential buildings

In office buildings, manufacturing plants, department
stores etc. particular importance is attached to flexible
arrangement and utilisation of the accommodation. To
this end the, communication wiring can be run in
underfloor trunking systems or window-sealed
trunking rather than on the walls.

13.3.5 Accessory Installation

13.3.5.1 Main distribution board

All the lines are collected in the main distribution board.
The main distribution board should be located in the
same part of the building in the immediate vicinity of
the telephone equipment. If the telephone equipment
extends over several buildings, each building is
connected to the main distribution board by a main
cable.

13.3.5.2 Floor distribution board

The floor distribution boards should be accommodated
close to the stair well. The rising mains are run
vertically to the floors.

13.3.5.3 Preventive fire precautions (for example
fireproof barriers) should be considered at an early
stage of planning

13.3.5.4 Riser cables

The ducts and ceiling apertures for the riser cables
should be sufficiently large to permit the later addition
of cables or PVC conduits without great expense.

13.3.5.5 Spare conduits

In addition at least one extra conduit should be provided
from one floor distribution board to the next.

13.4 Inspection and Testing

13.4.1 The completed installation shall be inspected
and simulation testing to be done to ensure that all the
designed functions are available as per the standards
and norms of specified by the manufacturer.

14 SUPPLIES FOR SAFETY SERVICES

14.0 General

14.0.1 For a safety service, a source of supply shall be
selected which will maintain a supply of adequate
duration.

14.0.2 For a safety service required to operate in fire
conditions, all equipment shall be provided, either by
construction or by erection, with protection providing
fire resistance of adequate duration.

14.0.3 A protective measure against indirect contact
without automatic disconnection at the first fault is
preferred. In an IT system, continuous insulation
monitoring shall be provided to give audible and visible
indications of a first fault.

14.0.4 Equipment shall be arranged to facilitate
periodic inspection, testing and maintenance.

14.1 Sources

14.1.1 A source for safety services shall be one of the
following:

a) A primary cell or cells.

b) A storage battery.

c) A generator set capable of independent
operation.

d) A separate feeder effectively independent of
the normal feeder (provided that an
assessment is made that the two supplies are
unlikely to fail concurrently).

14.1.2 A source for a safety service shall be installed
as fixed equipment and in such a manner that it cannot
be adversely affected by failure of the normal source.

14.1.3 A source for a safety service shall be placed in
a suitable location and be accessible only to skilled or
instructed persons.

14.1.4 A single source for a safety service shall not be
used for another purpose. However, where more than
one source is available, such sources may supply stand-
by systems provided that, in the event of failure of one
source, the energy remaining available will be sufficient
for the starting and operation of all safety services;
this generally necessitates the automatic off-loading
of equipment not providing safety services.

14.1.5 Clauses 14,1,3 and 14.1.4 do not apply to
equipment individually supplied by a self-contained
battery.

14.1.6 The location of the source shall be properly and
adequately ventilated so that any exhaust gases, smoke
or fumes from the source cannot penetrate, to a
hazardous extent, areas occupied by persons.

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14.2 Circuits

14.2.1 The circuit of a safety service shall be
independent of any other circuit and an electrical fault
or any intervention or modification in one system shall
not affect the correct functioning of the other.

14.2.2 The circuit of a safety service shall not pass
through any location exposed to abnormal fire risk unless
the wiring system used is adequately fire resistant.

14.23 The protection against overload in the circuit
may be omitted.

14.2.4 Every over-current protective device shall be
selected and erected so as to avoid an over-current in
one circuit impairing the correct operation of any other
safety services circuit.

14.2.5 Switchgear and control gear shall be clearly
identified and grouped in locations accessible only to
skilled or instructed persons.

14.2.6 Every alarm, indication and control device shall
be clearly identified.

14.3 Utilization Equipment

14.3.1 In equipment supplied by two different circuits,

a fault occurring in one circuit shall not impair the
protection against electric shock nor the correct
operation of the other circuit.

14.4 Special Requirements for Safety Services
Having Sources not Capable of Operation in

Parallel

14.4.1 Precautions shall be taken to prevent the
paralleling of the sources, for example by both
mechanical and electrical interlocking.

14.4.2 The requirements of the regulations for
protection against fault current and against indirect
contact shall be met for each source.

14.5 Special Requirements for Safety Services
Having Sources Capable of Operation in Parallel

14.5.1 The requirements of the regulations for
protection against short-circuit and indirect contact
shall be met whether the installation is supplied by
either of the two sources or by both in parallel.

14.5.2 Precautions shall be taken, where necessary, to
limit current circulation, particularly thereof third
harmonics or multiples thereof, in the connection
between the neutral points of sources.

IS No.

1881 : 1998

1882 : 1993
2175 : 1988

2440 : 1975
3103 : 1975

3043 : 1987
3362 : 1977

3646 (Part 1): 1992

7662 (Part 1): 1974

8884 : 1978

ANNEX A
(Clause 2)

LIST OF INDIAN STANDARDS RELATED TO BUILDING SERVICES
Title IS No. Title

Code of practice for indoor instal-
lation of public address systems
Code of practice for outdoor instal-
lation of public address system
Specification for heat sensitive
fire detectors for use in automatic
fire alarm system
Guide for day lighting of buildings
Code of practice for industrial
ventilation

Code of practice for earthing
Code of practice for natural
ventilation of residential buildings
Code of practice for interior
illumination: Part 1 General
requirements and recommenda-
tions for welding interiors
Recommendations for orientation
of buildings: Part 1 Non-industrial
buildings

Code of practice for the installation
of electric bells and call system

8969 : 1978

14665 (Part 2/
Sec 1) : 2000

14665 (Part 2/
Sec 2) : 2000

14665 (Part 3/
Sec 1) : 2000

14665 (Part 3/
Sec 2) : 2000

SP 7 : 2005
SP 72: 2010

Code of practice for installation
and maintenance of impulse and
electronic master and slave
electric clock systems
Electric traction lifts: Part 2
Code of practice for installation,
operation and maintenance,
Section 1 Passenger and goods
lifts

Electric traction lifts: Part 2
Code of practice for installation,
operation and maintenance,
Section 2 Service lifts
Electric traction lifts: Part 3
Safety rules, Section 1 Passenger
and goods lifts

Electric traction lifts: Part 3
Safety rules, Section 2 Service
lifts

National Building Code of India
National Lighting Code

PART 1 GENERAL AND COMMON ASPECTS

129

SP 30: 2011

SECTION 12 SELECTION OF EQUIPMENT

FOREWORD

Several Indian Standards exist, which cover details of
selection, installation, and maintenance of electric
power equipment. This Part 1/Section 12 of the Code
is formulated in such a manner as to bring out only the
essential criteria for selection of equipment, and users
of the Code are recommended to make reference to
individual product codes for detailed guidelines.

1 SCOPE

This Part 1/Section 12 of the Code covers general
criteria for selection of equipment.

NOTE — This Part 1/Section 12 shall be read in conjunction
with the Indian Standard/Codes on individual equipment.

2 SELECTION OF EQUIPMENT

2.1 Conformity to Indian Standards

Every item of electrical equipment used in the
installation shall conform to the relevant Indian
Standards, wherever available.

2.2 Characteristics

Every item of electrical equipment selected shall have
suitable characteristics appropriate to the values and
conditions on which the design of the electrical
installation (see 3.2 of Part 1/Section 7) is based and
shall, in particular, fulfill the requirements given
to 2.2.1 to 2.2.4.

2.2.1 Voltage

Electrical equipment shall be suitable with respect to
the maximum steady voltage (rms value for ac) likely
to be applied, as well as overvoltages likely to occur.

NOTE — For certain equipment, it may be necessary to take
account of the lowest voltage likely to occur.

2.2.2 Current

All electrical equipment shall be selected with respect
to the maximum steady current (rms value for ac)
which it has to carry in normal service, and with respect
to the current likely to be carried in abnormal
conditions and the period (for example, operating time

of protective devices, if any) during which it may be
expected to flow.

2.2.3 Frequency

If frequency has an influence on the characteristics of
electrical equipment, the rated frequency of the
equipment shall correspond to the frequency likely to
occur in the circuit.

2.2.4 Power

All electrical equipment to be selected on the basis of
its power characteristics, shall be suitable for the duty
demanded of the equipment, taking into account the
load factor and the normal service conditions.

2.3 Conditions of Installation

All electrical equipment shall be selected so as to
withstand safely the stresses and the environmental
conditions (see 3.2 of Part 1/Section 7 of this Code)
characteristic of its location to which it may be exposed.
The general characteristics of building installations are
assessed according to the guidelines given in Part 1/
Section 8 of this Code. If, however, an item of
equipment does not have by design the properties
corresponding to its location it may be used on
condition that adequate additional protection provided
as part of the completed electrical installation.

2.4 Prevention of Harmful Effects

All electrical equipment shall be selected so that it will
not cause harmful effects on, other equipment or impair
the supply during normal service including switching
operations. In this context, the factors which may have
an influence include;

a) Power factor,

b) Inrush current,

c) Asymmetrical load, and

d) Harmonics.

2.5 Guidelines on the selection of specific equipment
are covered in the relevant Indian Standards. Guidelines
on selection of protective devices are given at Part 1/
Section 14 of this Code.

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SECTION 13 ERECTION AND PRE-COMISSIONING TESTING

OF INSTALLATION

FOREWORD

Testing and ensuring that the installation conforms to
the predetermined conditions before the installation
could be energized, is a necessary prerequisite under
the statutory provisions. Several aspects/parameters are
required to be verified before an installation could be
certified as ready for energizing and use.

While a general check list of items to be checked and
necessary tests to be done are included in this Section,
individual product standards and individual Codes of
practice cover more detailed guidelines on
pre~commissioning checks for individual equipment.

In addition to initial testing, periodic testing and
preventive maintenance checks are necessary, the
nature and frequency of such measures depending on
the nature of the electrical installation in question.
Guidelines on such aspects are outside the purview of
the Code. However, a reference could be made to
individual equipment codes which cover maintenance
schedules.

1 SCOPE

This Part 1/Section 13 of the Code covers general
principles of erection of installation and guidelines on
initial testing before commissioning.

2 REFERENCES

A list of relevant Indian Standards is given at
Annex A.

3 ERECTION

3.1 For the erection of the electrical installation, good
workmanship by suitably qualified personnel and the
use of proper materials shall be ensured.

3.2 The characteristics of the electrical equipment, as
determined in accordance with Part 1/Section 12 shall
not be impaired in the process of erection.

3.3 Protective conductors and neutral conductors shall
be identifiable at least at their terminations by colouring
or other means. These conductors in flexible cords or
flexible cables shall be identifiable by colouring or
other means throughout their length (see 3.6 of
Part 1/Section 4).

3.4 Connections between conductors and between
conductors and other electrical equipment shall be
made in such a way that safe and reliable contacts are
ensured. For electrical wiring installation, IS 732
should be followed. Also see Part 1/Section 14 of the
Code.

3.5 All electrical equipment shall be installed in such
a manner that the designed cooling conditions are not
impaired.

3.6 All electrical equipment likely to cause high
temperatures or electric arcs shall be placed or guarded
so as to eliminate the risk of ignition of flammable
materials. Where the temperature of any exposed parts
of electrical equipment is likely to cause injury to
persons, these parts shall be so located as to prevent
accidental contact therewith.

3.7 Several Indian Standards exist on installation of
specific electrical equipment. These shall be adhered
to during erection of the installation.

4 INSPECTION AND TESTING

4.1 Genera! Requirements

4.1.1 Before the completed installation, or an addition
to the existing installation, is put into service, inspection
and testing shall be carried out in accordance with the
Indian Electricity Rules, 1956. In the event of defects
being found, these shall be rectified, as soon as
practicable, and the installation retested.

4.1.2 After putting the installation into service periodic
inspection and testing shall be carried out in order to
maintain the installation in a sound condition.

4.1.3 Where an addition is to be made to the fixed
wiring of an existing installation the latter shall be
examined for compliance with recommendations of
this Code.

4.2 Inspection of the Installation

4.2.0 General

At the completion of wiring, a general inspection shall
be carried out by competent personnel to verify that
the provisions of this Code and that of Indian Electricity
Rules, 1956 have been complied with. This, among
other things, shall include checking whether all
equipment, fittings, accessories, wires and cables, used
in the installation are of adequate rating and quality to
meet the requirements of the load. General
workmanship of the electrical wiring with regard to
the layout and finish shall be examined for neatness
that would facilitate easy identification of circuits of
the system, adequacy of clearances, soundness of
termination with respect to tightness, contact pressure
and contact area. A complete check shall also be made
of all the protective devices, with respect to the rating,
range of settings and for co-ordination between the
various protective devices.

PART 1 GENERAL AND COMMON ASPECTS

131

SP 30 : 2011

4.2,1 Substation Installations

In substation installation it shall be checked whether,

1) the installation has been carried out in
accordance with the approved drawings;

2) phase-to-phase and phase-to-earth clearances
are provided as required;

3) all equipments are efficiently earthed and
properly connected to the required number
of earth electrodes;

4) the required ground clearance to live terminals
is provided;

5) suitable fencing is provided with gate with
lockable arrangements;

6) the required number of caution boards, fire-
fighting equipments, operating rods, rubber
mats, etc, are kept in the substation;

7) in case of indoor substation, sufficient
ventilation and draining arrangements are
made;

8) all cable trenches are provided with non-
flammable covers;

9) free accessibility is provided for all equipment
for normal operation;

10) all name-plates are fixed and the equipment
are fully painted;

11) all construction materials and temporary
connections are removed;

12) oil levels, bus bar tightness, transformer tap
position, etc, are in order;

13) earth pipe troughs and cover slabs are
provided for earth electrodes/earth pits.
Neutral and lightning arrester earth pits are
marked for easy identification;

14) earth electrodes are of GI pipes or CI pipes or
MS rods or copper plates. For earth
connections, brass bolts and nuts with lead
washers are provided in the pipes/plates;

15) earth pipe troughs, oil sumps/pits are free
from rubbish and dirt and stone jelly and the
earth connections are visible and easily
accessible;

16) Panels and switchgears are all vermin and
damp proof and all unused openings or holes
are blocked properly;

17) the earth bus bars for tightness and for
corrosion free joint surface;

18) control switchfuses are provided at an
accessible height from ground;

19) adequate head room is available in the
transformer room for easy topping up of oil,
maintenance, etc;

20) safety devices, horizontal and vertical

barriers, bus bar covers/shrouds, automatic
safety shutters/doors interlock, handle
interlock for safe and reliable operation in all
panels and cubicles;

21) clearances in the front, rear and sides of the
switchboards, are adequate;

22) the gap in the horngap fuse and the size of
fuse adequate;

23) the switch operates freely, all the blades make
contact at the same time. The arcing horns
contact in advance, and the handles are
provided with locking arrangements;

24) Insulators are free from cracks, and are clean;

25) in the case of transformers, there is any oil leak;

26) connections to bushings in transformers are
tightened and have good contact;

27) bushings are free from cracks and are clean;

28) accessories of transformers like breathers,
vent pipe, buchholz relay, etc, are in order;

29) connections to gas relay in transformers are
in order;

30) oil and winding temperature are set for
specific requirements in transformers;

31) in case of cable cellars, adequate
arrangements to pump out water that has
entered due to seepage or other reason is
provided; and

32) all incoming and outgoing circuits of panels
are clearly and indelibly labelled for
identifications both at the front and at the rear.

4.2.2 Installation at Voltage not exceeding 650 V

It shall be checked whether:

a) all blocking materials that are used for safe
transportation in switchgears, contractors,
relays, etc, are removed;

b) all connections to the earthing system are
feasible for periodical inspection;

c) sharp cable bends are avoided and cables are
taken in a smooth manner in the trenches or
alongside the walls and ceilings using suitable
support clamps at regular intervals;

d) suitable linked switch or circuit-breaker or
lockable push button is provided near the
motors/apparatus for controlling supply to the
motor apparatus in any easily accessible
location;

e) two separate and distinct earth connections
are provided for the motor apparatus;

f) control switchfuse is provided at an accessible
height from ground for controlling supply to
overhead travelling crane hoists, overhead bus
bar trunking;

132

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g) the metal rails on which the crane travels are
electrically continuous and earthed and
bonding of rails and earthing at both ends are
done;

h) four core cables are used for overhead
travelling crane and portable equipments, the
fourth core being used for earthing, and
separate supply for lighting circuit is taken;

j) if flexible metallic house is used for wiring
to motors and equipments, the wiring is
enclosed to the full lengths, and the hose
secured properly;

k) the cables are not taken through areas where
they are likely to be damaged or chemically
affected;

m) the screens and armours of the cables are
earthed properly;

n) the belts of the belt driven equipments are

properly guarded;
p) adequate precautions are taken to ensure that

no live parts are so exposed as to cause danger;
q) ammeters and voltmeters are tested and

calibrated;

r) the relays are inspected visually by moving

covers for deposits or dusts or other foreign

matter;
s) flat washers backed up by spiring washers are

used for making end connections; and
t) number of wires in a conduit conform to

provisions of this Code.

43 Testing of Installation

4.3.0 General

After inspection, the following tests shall be carried
out, before an installation or an addition to the existing
installation is put into service, any testing of the
electrical installation in an already existing installation
shall commence after obtaining permit to work from
the engineer-in-charge and after ensuring the safety
provisions.

4.3.1 Switchboards

Switchboards shall be tested in the manner indicated
below:

a) all switchboards shall be tested for di-electric
test in the manner recommended in IS 8623
(Part 1),

b) all earth connections shall be checked for
continuity,

c) the operation of all protective devices shall
be tested by means of secondary or primary
injection tests,

d) the operation of the circuit-breakers shall be
tested from all control stations,

e) indication/signalling lamps shall be checked
for working,

f) the operation of the circuit-breakers shall be
tested for all interlock,

g) the closing and opening timings of the circuit-
breakers shall be tested wherever required for
autotransfer schemes,

h) contact resistance of main and isolator
contacts shall be measured, and

j) the specific gravity of the electrolyte and the
voltage of the control battery shall be
measured.

4.3.2 Transformers

All commissioning tests as listed in IS 10028 (Part 2)
shall be carried out.

4.3.3 Cables

Cable installations shall be checked as laid down in
IS 1255.

4.3.4 Motors and Other Equipment

The following tests are made on motor and other
equipment:

a) The insulation resistance of each phase
winding against the frame and between the
windings shall be measured. Megohm-meter
of 500 V or 1 000 V rating shall be used. Star
points should be disconnected. Minimum
acceptable value of the insulation resistance
varies with the rated power and the rated
voltage of the motor.

The following relation may serve as a
reasonable guide:

*i=-

20x£ n
1000 -f IP

where

R x - insulation resistance in MQ at 25°C,
E n = rated phase-to-phase voltage, and
P = rated power kW.

If the resistance is measured at a temperature
different from 25°C, the value shall be
corrected to 25°C.
b) The insulation resistance as measured at
ambient temperature does not always give a
reliable value, since moisture might have been
absorbed during shipment and storage. When
the temperature of such a motor is raised, the
insulation resistance will initially drop

PART 1 GENERAL AND COMMON ASPECTS

133

SP 30: 2011

considerably, even below the acceptable
minimum. If any suspicion exists on this
score, motor winding shall be dried out.

4.3.5 Energymeters

IS 15707 should be followed in case of energymeters,

4.3.6 Wiring Installation

The following tests shall be done:

a) The insulation resistance shall be measured by
applying between earth and the whole system
of conductor or any section thereof with all
fuses in place and all switches closed, and
except in earthed concentric wiring, all lamps
in position or both poles of installation
otherwise electrically connected together, a dc
voltage of not less than twice the working
voltage, provided that it does not exceed 500 V
for medium voltage circuits . Where the supply
is derived from three-wire (ac or dc) or a
polyphase system the neutral pole of which is
connected to earth either direct or through
added resistance, the working voltage shall be
deemed to be that which is maintained between
the outer or phase conductor and the neutral.

b) The insulation resistance in megohms of an
installation measured as in (a) shall be not less
than 50 divided by the number of points on
the circuits, provided that the whole
installation need not be required to have an
insulation resistance greater than 1MQ.

c) Control rheostats, heating and power
appliances and electric signs, may, if desired,
he disconnected from the circuit during the
test, but in that event the insulation resistance
between the case or framework, and all live
parts of each rheostat, appliance and sign shall

be not less than that specified in the relevant
Indian Standard or where there is no such
specification shall be not less than 0.5 MQ.

d) The insulation resistance shall also be
measured between all conductors connected
to one pole or phase conductor of the supply
and all the conductors connected to the middle
wire to the neutral on to the other pole of phase
conductors of the supply. Such a test shall be
made after removing all metallic connections
between the two poles of the installation and
in these circumstances the insulation
resistance between conductors of the
installation shall be not less than that specified
in(b).

e) On completion of an electrical installation (or
an extension to an installation) a certificate
shall be furnished by the contractor,
countersigned by the certified supervisor
under whose direct supervision the
installation was carried out. this certificate
shall be in a prescribed form as required by
the local electric supply authority.

4.3.7 Earthing

For checking the efficiency of earthing the following
tests are recommended (see IS 3043):

a) The earth resistance of each electrode is
measured.

b) The earth resistance of earthing grid is
measured.

c) All electrodes are connected to the grid and
the earth resistance of the entire earthing
system is measured.

These tests shall preferably be done during the summer
months.

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ANNEX A
(Clause 2)

LIST OF INDIAN STANDARDS ON INSTALLATION

IS No.
732 : 1989

1255 : 1983
1646 : 1997

3043 : 1987
4051 : 1967

5571 : 2000

8623 (Part 1) : 1993/
IEC 60439-1:
1985

Title IS No.

Code of practice for electrical

wiring installations

Code of practice for installation 10028 (Part 2) :

and maintenance of power 1981

cables upto and including 33 kV

rating 14927

Code of practice for fire safety of

buildings (general): Electrical (Part 1) : 2001

installations (Part 2) : 2001

Code of practice for earthing

Code of practice for installation

and maintenance of electrical 14930

equipment in mines

Guide for selection of electrical (Part 1) : 2001

equipment for hazardous areas (Part 2) : 2001

Specification for low-voltage

switchgear and controlgear

assemblies: Part 1 Requirements 15707 : 2006

Title

for type-tested and partially type-
tested assemblies
Code of practice for selection,
installation and maintenance of
transformers: Part 2 Installation
Cable trunking and ducting
systems for electrical installations :
General requirements
Cable trunking and ducting
systems intended for mounting on
walls or ceilings

Conduit systems for electrical
installations:
General requirements
Particular requirements —
Conduit systems buried
underground

Testing, evaluation, installation
and maintenance of ac electricity
meters — Code of practice

PART 1 GENERAL AND COMMON ASPECTS

135

SP 30 : 2011

SECTION 14 EARTHING

FOREWORD

Earthing provides safety of persons and apparatus
against earth faults. Any system is characterised by
the type of distribution system, which include types of
systems of live conductors and types of system
earthing. The different types of earthing systems are
also covered under this Part 1/Section 14 of the Code.
The choice of one system or the other would depend
on several considerations as each offer different degree
of performance/safety.

This Part 1/Section 14 of the Code summarises the
essential requirements associated with earthing in
electrical installations. These relate to general conditions
of soil resistivity, design parameters of earth electrode,
earth bus and earth wires and methods of measurements.
Particular requirements for earthing depending on the
type of installation are covered in respective Sections of
the Code.

1 SCOPE

This Part 1/Section 14 of the Code covers general
requirements associated with earthing in electrical
installations. Specific requirements for earthing in
individual installations are covered in respective Parts
of the Code.

NOTES

1 This Section shall be read in conjunction with the provisions
of IS 3043.

2 Additional rules applying to earth leakage circuit-breaker
systems are covered in Annex A.

2 REFERENCES

For further details, the following standards may be
referred:

3 GENERAL REMARKS

3.0 General

IS No.
732 : 1989

3043 : 1987

IS 8437(Part 1) :
1993

IS 8437(Part 2) :
1993

IS/IEC 60947-2 :

2006
IS/IEC 60947-4-1:

2002

Title

Code of practice for electrical
wiring installations (third revision)
Code of practice for earthing (first
revision)

Guide on effects of current passing
through human body: Part 1
General aspects

Guide on effects of current passing
through human body: Part 2
Special aspects

Low voltage switchgear and
controlgear: Part 2 Circuit breakers
Low-voltage switchgear and
controlgear: Part 4 Contactors and
motor-starters, Section 1 Electro-
mechanical contactors and motor-
starters

3.0.1 The subject of earthing covers the problems
relating to the conduction of electricity through earth.
The terms earth and earthing have been used in this
Code, irrespective of reliance being placed on the earth
itself, to denote a low impedance return path of the
fault current. As a matter of fact, the earth now rarely
serves as a part of the return circuit but is being used
mainly for fixing the voltage of system neutrals. The
earth connection improves service continuity and avoids
damage to equipment and danger to human lives.

3.0.2 The object of an earthing system is to provide as
nearly as possible a surface under and around a station
which shall be at a uniform potential and as nearly
zero or absolute earth potential as possible. The purpose
of this is to ensure that in general all parts of apparatus,
other than live parts, shall be at earth potential, as well
as to ensure that operators and attendants shall be at
earth potential at all times. Also by providing such an
earth surface of uniform potential under and
surrounding the station, as nearly as possible, there
can exist no difference of potential in a short distance
big enough to shock or injure an attendant when short-
circuits or other abnormal occurrence take place.

3.0.3 Earthing associated with current-carrying
conductor is normally essential to the security of the
system and is generally known as system earthing,
while earthing of non-current carrying metal work and
conductor is essential to the safety of human life, of
animals and of property and is generally known as
equipment earthing.

3.0.4 Earthing shall generally be carried out in
accordance with the requirements of Indian Electricity
Rules, 1956 as amended from time to time, and the
relevant regulations of the electricity supply authority
concerned. The following clauses of The Indian
Electricity Rules, 1956 are particularly applicable:

32, 51, 61, 62, 67, 69, 88 (2) and 90.

3.0.5 Al medium voltage equipment shall be earthed
by two separate and distinct connections with earth
through an earth electrode. In the case of high and extra
high voltages the neutral points shall be earthed by
not less than two separate and distinct connections with
earth each having its own electrode at the generating
station or sub- station and may be earthed at any other
point provided no interference is caused by such
earthing. If necessary, the neutral may be earthed
through a suitable impedance.

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3.0.5.1 In cases where direct earthing may prove
harmful rather than provide safety (for example, high
frequency and mains frequency coreless induction
furnaces), relaxation may be obtained from the
competent authority.

3.0.6 Earth electrodes shall be provided at generating
stations, substations and consumer premises in
accordance with the requirements.

3.0.7 All far as possible all earth terminals shall be
visible.

3.0.8 All connections shall be carefully made; if they
are poorly made or inadequate for the purpose for
which they are intended, loss of life or serious personal
injury may result.

3.0.9 Each earth system shall be so devised that the
testing of individual earth electrode is possible. It is
recommended that the value of any earth system
resistance shall not be more than 5.0, unless otherwise
specified.

3.0.10 It is recommended that a drawing showing the
main earth connection and earth electrodes be prepared
for each installation.

3.0.11 No addition to the current-carrying system either
temporary or permanent, shall be made, which will
increase the maximum available earth fault current or
its duration until it has been ascertained that the existing
arrangement of earth electrodes, earth busbar, etc, are
capable of carrying the new value of earth fault current
which may be obtained by this addition.

3.0.12 No cut-out, link or switch other than a linked
switch arranged to operate simultaneously on the
earthed or earthed neutral conductor and the live
conductors shall be inserted on any supply system. This
however, does not include the case of a switch for use
in controlling a generator or a transformer or a link for
test purposes.

3.0.13 All materials, fittings, etc, used in earthing shall
conform to Indian Standards wherever these exist. In
the case of materials for which Indian Standard
specifications do not exist, the materials shall be
approved by the competent authority.

3.1 Design Considerations

3.1.1 System Earthing

3.1.1.1 The regulations that every medium, high and
extra high voltage equipment shall be earthed by not
less than two separate and distinct connections with
earth is designed primarily to preserve the security of
the system by ensuring that the voltage on each live
conductor is restricted to such a value with respect to
the potential of the general mass of the earth as is

consistent with the levels of insulation applied. Distinct
connection with the earth shall be provided for
lightning protection system for buildings or other
installations. Distinct earthing system shall be provided
for centralized electronic system of any building.

3.1.1.2 The earth system resistance should be such that
when any fault occurs against which earthing is
designed to give protection, the protective gear will
operate to make the faulty portions of plant harmless.
In most cases such operation involves isolation of the
faulty main or plant by circuit-breaker or fuses. In the
cases of underground system there may be no difficulty,
but in the case of overhead line system protected only
by fuses there may be difficulty in so arranging the
value of the earth resistance that a conductor falling
and making good contact with earth shall cause the
fuses in the supply to operate.

NOTE — Earthing may not give protection against faults which
are not essentially earth faults. For example, if a phase
conductor of an overhead spur line breaks, and the part remote
from the supply falls to the ground, it is unlikely that any
protective gear relying on earthing will operate since the major
fault is the open-circuit against which earthing gives no
protection.

3.1.2 Equipment Earthing

The object of equipment earthing is to ensure effective
operation of the protective gear in the event of leakage
through such metal work, the potential of which with
respect to neighbouring objects may attain a value
which would cause danger to life or risk or fire.

3.1.3 Soil Resistivity

3.1.3.1 The resistance to earth of an electrode of given
dimensions is dependent on the electrical resistivity of
the soil in which it is installed. It follows, therefore,
that an overriding consideration in deciding which of
the alternative method of protection is to be adopted
for a particular system or location is the soil resistivity
in the area concerned.

3.1.3.2 The type of soil largely determines its resistivity
and representative values for soils generally found in
India are given at Annex B. Earth conductivity is,
however, essentially electrolytic in nature and is
affected therefore by moisture content of the soil and
its chemical composition and concentration of salts
dissolved in the contained water. Grain size and
distribution and closeness of packing are also
contributory factors since they control the manner in
which the moisture is held in soil. Many of these factors
vary locally and some seasonally and, therefore, the
values given in Annex B should be taken only as a
general guide. Local values should be verified by actual
measurement and this is especially important where
the soil is stratified, as owing to the disposition of earth
current, the effective resistivity depends not only on

PART 1 GENERAL AND COMMON ASPECTS

137

SP 30: 2011

the surface layers but also on the underlying geological
formation.

3.1.33 The soil temperature also has some effect on
soil resistivity but is important only near and below
freezing point, necessitating the installation of earth
electrode at depths to which frost will not penetrate.

3.1.3.4 While the fundamental nature and properties
of a soil in a given area cannot be changed, use can be
made of purely local conditions in choosing suitable
electrode sites and of methods of preparing the site
selected, to secure optimum resistivity. Reference is
drawn to IS 3043.

3.1.4 Potential Gradients

It is necessary to ensure, especially in case of large
electrical installations, that a person walking on the
ground or touching an earthed objects, in or around the
premises shall not have large dangerous potential
differences impressed across his body in case of a fault
within or outside the premises. Such danger may arise
if steep potential gradients exist within the premises or
between boundary of the premises and an accessible
point outside. For this the step potential and touch
potential should be investigated and kept within safe
limits. Within an earthing grid, the step and touch
potentials may be lowered to any value by reducing
the mesh interval of the grid. The situation is more
difficult in the zone immediately outside the periphery
where the problems may exist even for the theoretical

case of a single plate covering the sub- station area. This
problem may be serious in small stations where the grid
may cover only a limited area. Attempts should be made
to design a substation so as to eliminate the possibility
of touch contact beyond the earth-system periphery,
when the limitations on step potential become less
exacting. While assessing the touch potential, the
method of earthing of the object touched, for example,
whether it is earthed directly below or remotely should
be kept in view in order to consider the possibility of
occurrence of large potential differences.

Special attention should be paid to the points near the
operating handles of apparatus and, if necessary,
potential equalizer grillages of closer mesh securely
bonded to the structure and the operating handle should
be buried below the surface where the operator may
stand when operating the switch.

3.1.5 At consumer's premises where the apparatus is
protected by fuses, the total earth circuit impedance
shall not be more than that obtained by graphs given
in Fig. 1.

4 EARTH ELECTRODES

4.1 Material

4.1.1 Although electrode material does not affect initial
earth resistance, care should be taken to select a
material which is resistant to corrosion in the type of
soil in which it will be used.

4 6 8 10 12 14

FUSE RATING IN AMPERES

Fig. 1 Recommended Earth Circuit Impedance of Resistance for Different Values of Fuse Rating
138 NATIONAL ELECTRICAL CODE

SP 30: 2011

4.1.2 Under ordinary conditions of soil, use of copper,
iron or mild steel electrodes is recommended.

4.1.3 In cases where soil conditions point to excessive
corrosion of the electrode and the connections, it is
recommended to use either copper electrode or copper
clad electrode or zinc coated (galvanized) iron
electrodes.

4.1.4 In direct current system, however, due to
electrolytic action which causes serious corrosion, it
is recommended to use only copper electrodes.

4.1.5 The electrode shall be kept free from paint,
enamel and grease.

4.1.6 It is recommended to use similar material for earth
electrodes and earth conductors or otherwise
precautions should be taken to avoid corrosion.

4.2 Current Loading

4.2.1 An earth electrode should be designed to have a
loading capacity adequate for the system in which it
forms a part, that is, it should be capable of dissipating
without failure, energy in the earth path at the point at
which it is installed under any condition of operation
of the system. Failure is fundamentally due to excessive
rise of temperature at the surface of the electrode and
is thus a function of current density and duration as
well as electrical and thermal properties of soil.

4.2.2 Two conditions of operation occur in system
operation, namely;

a) Long duration overloading as with normal
system operation, and

b) Short time overloading as under fault
conditions in directly earthed system.

4.3 Voltage Gradient

4.3.1 Under fault conditions the earth electrode is raised
to a potential with respect to the general mass of the
earth. This results in the existence of voltages in the
soil around the electrode which may be injurious to
telephone and pilot cables whose cores are substantially
at earth potential owing to the voltage to which the
sheaths of such cables are raised. The voltage gradient
at the surface of the earth may also constitute danger
to life.

4.3.2 Earth electrodes should not be installed in
proximity to a metal fence to avoid the possibility of
the fence becoming live, and thus dangerous at points
remote from the substation, or alternatively giving rise
to danger within the resistance area of the electrode
which can be reduced only by introducing a good
connection with the general mass of the earth. If the
metal fence is unavoidable, it should be earthed.

4.4 Types of Earth Electrodes

The following types of earth electrodes are considered
standard:

a) Rod and pipe electrodes,

b) Strip or conductor electrodes,

c) Plates electrodes, and

d) Cable sheaths.

For details regarding their design, reference shall be
made to IS 3043.

4.5 Design Data on Earth Electrodes

4.5.1 The design data on the various types of earth
electrodes is given in Table 1.

4.5.2 Effect of Shape on Electrode Resistance

The resistance of any electrode buried in the earth is in
fact related to the capacitance of that electrode and its
image in free space. The relationship is given by:

100 p

AtiC

where

R - resistance in an infinite medium;

p = resistivity of the medium (soil); in ohm-
metre; and

C = capacitance of the electrode and its image
in free space.

In practical case, the capacitance is divided into two
by the plane of earth's surface so that,

100 p

a) For rod or pipe electrodes, the formula is

100p log e 2/ohms

~ AkC d

where

/ = length of rod or pipe, in cm; and
d - diameter of rod or pipe, in cm.

b) For strip or round conductor electrodes,

100 p log e 4/ ohms

AnC

where

= length of the strip, in cm; and

PART 1 GENERAL AND COMMON ASPECTS

139

SP 30 : 2011

/ = width (strip) or twice the diameter
(conductors), in cm.

c) For plate electrodes,

p I /r ohms
~4VA

where

A = area of both sides of plate, in m 2 .

4.5.3 Effect of Depth of Burial

To reduce the depth of burial without increasing the
resistance, a number of rods or pipes shall be connected
together in parallel (see Fig. 4). The resistance in this
case is practically proportional to the reciprocal of the
number of electrodes used so long as each is situated
outside the resistance area of the other. The distance
between two electrodes in such a case shall preferably
be not less than twice the length of the electrode.

5 EARTH BUS AND EARTH WIRES

5.0 General

5.0.1 The minimum allowable size of earth wire is
determined principally by mechanical consideration for
they are more liable to mechanical injury and should
therefore be strong enough to resist any strain that is
likely to be put upon them.

5.0.2 All earth wires and earth continuity conductors
shall be of copper, galvanized iron, or steel or
aluminium.

NOTE — Bare aluminium shall not be used underground.

5.0.3 They shall be either stranded or solid bars or flat
rectangular strips and may be bare provided due care
is taken to avoid corrosion and mechanical damage to
it. Where required, they shall be run inside metallic
conduits.

5.0.4 Interconnections of earth- continuity conductors
and main and branch earth wires shall be made in such
a way that reliable and good electrical connections are
permanently ensured.

NOTE — Welded, bolted and clamped joints are permissible.
For stranded conductors, sleeve connectors (for example,
indented, riveted or bolted connectors) are permissible. Bolted
connectors and their screws shall be protected against any
possible corrosion.

5.0.5 The path of the earth wire shall, as far as possible,
be out of reach of any person.

5.0.6 If the metal sheath and armour have been used
as an earth continuity conductor the armour shall be
bonded to the metal sheath and the connection between
the earth wire and earthing electrode shall be made to
the metal sheath.

5.0.7 If a clamp has been used to provide connection

Table 1 Design Data on Earth Electrodes
(Clause 4.5.1 )

All dimensions in millimetres.

SI No.

Measurement

Type of Electrodes

Rod

Pipe

Strip

Round Conductor

Plate

(see Note 1)

(see Note 2)

(1)

(2)

(3)

(4)

(5)

(6)

(7)

Diameter
(not less than)

16 mm"
12.5 mm 2)

38 mm 1 '
100mm 2)

ii)

Length of
conductor/rod

3 500 mm

500 mm

15 000 mm

1 500 mm

iii)

Depth upto
which buried

3 750 mm

3 550 mm

3 200 mm

iv)

Size

25mmx 1.60 mm 2)
25 mm x 4 mm 11

3.0mm 22)
6mm 21)

1200
600

immx 1200 mm 3)
mm x 600 mm 1 '

Thickness

3.15 mm 1 '

6.30 mm 2)

3.5 mm 1 '

1} Steel or

galvanized iron.

2) Copper.

3) Cast iron.

NOTES

1 A typical illustration of pipe earth electrode is given in Fig. 2.

2 A typical illustration of plate electrode is given in Fig. 3. If two or more plates are used in parallel, they shall be separated by not less
than 3.0 m.

3 Adequate quantity of water to be poured into sump every few days to keep the soil surrounding the earth pipe permanently moist.

140

NATIONAL ELECTRICAL CODE

SP 30 : 2011

J15.

TO GROUNDING
CONDUCTOR

400

Mg|~— ^P*

C 1 COVER HINGED
TO C I FRAME

NOTES

1 All dimensions in millimetres.

2 After laying the earth from the earth bus to the electrode through the PVC conduits at the pit entry conduits should be sealed with
bitumin compound.

Fig. 2 A Typical Illustration of Pipe Earth Electrode

FART 1 GENERAL AND COMMON ASPECTS

141

2
>

n
o

r
r>
o

CAST IRON OR
C I COVER

ITO^W^

WELDED

50X12

G I STRIP WXl

1000X500X600

THSHBblK ft

CHAMBER

CEMENT

CONCRETE .

.0 5OGIPIPE

1200x1200X12 Ci PLATE

CHARCOAL AND SALT

50 x 1-2 G I STRIP

012X60 LONG G I
&6L.TS & NUTS, CHECK NUT
& WASHER (AFTER FIXING, THE
OUTSIDE SURFACE SHOULD
BE COVERED WITH BITUMIN)

DETAIL A

800

I f t t fc

G I STRIP

1200X1200X12
Ci PLATE

DETAIL B

12X6OLQNGGI
BOLTS & NUTS t CHECK NUT
& WASHER (AFTER FIXING, THE
OUTSIDE SURFACE SHOULD
BE COVERED WITH BITUMIN)

10 G I BOLT LENGTH
50 (AFTER FIXING, THE
OUTSIDE SURFACE SHOULD
BE COVERED WITH BmifUtlN)

50 x 12 G I STRIP

DETAIL C

All dimensions in millimetres.

3A Earthing with GI Plate
Fig. 3 A Typical Illustration of Plate Earth Electrode

Continued

o
m

o
S
S
o

H
as

CAST IRON OR
CI COVER

35 X 6 COPPER STRIP

12X40 LONG BRASS

BOLTS & NUTS, CHECK NUT
a WASHER (AFTER FIXING, THE
OUTSIDE SURFACE SHOULD
BE COVERED WITH BiTUMIN)

600X600X3

DETAIL B

12X40 LO NG BRASS
BOLTS & NUTS, CHECK NUT
& WASHER (AFTER FIXING, THE
OUTSIDE SURFACE SHOULD
BE COVERED WITH BITUMIN)

COPPER PLATE

10 BRASS BOLT LENGTH
30 (AFTER FIXING, THE
OUTSIDE SURFACE SHOULD
BE COVERED WTTH BITUMIN)

25 X 4 COPPER STRIP
FOR CLAMP

DETAIL C

All dimensions in millimetres.

3B Earthing with Copper Plate
Fig. 3 A Typical Illustration of Plate Earth Electrode

SP 30 : 2011

2 4 6 8 10 12 14 16

INDIVIDUAL RESISTANCE IN OHMS

Fig. 4 Resistance of Electrode at Various Depths and Soil Resistances

between the earth wire and the metal sheath and armour,
it shall be so designed and installed as to provide reliable
connection without damage to the cable.

5.0.8 The neutral conductor shall not be used as earth
wire.

5.0.9 The minimum sizes of earth-continuity
conductors and earth wires shall be as given in the
relevant part of the Code.

6 MEASUREMENT OF EARTH ELECTRODE
RESISTANCE

6.1 Fall of Potential Method

In this method two auxiliary earth electrodes,
besides the test electrode, are placed at suitable
distances from the test electrode (see Fig. 5). A
measured current is passed between the electrode
'A' to be tested and an auxiliary current electrode
'C and the potential difference between the
electrode 'A' and the auxiliary potential electrode
'5' is measured. The resistance of the test electrode
'A' is then given by:

where

R = resistance of the test electrode, in ohms;
V = reading of the voltmeter, in V; and
/ = reading of the ammeter, in amperes.

144

<*>

^AMMETER

CURRENT ~ ~V ^

SOURCE Q / y VVOLTME TER

Y777?.

777777777,

777777777?

* » tro

>/7777Z

TEST

ELECTRODE

POTENTIAL
ELECTRODE

CURRENT
ELECTRODE

Fig. 5 Method of Measurement of Earth
Electrode Resistance

6.1.1 If the test is made at power frequency, that is,
50 Hz, the resistance of the voltmeter should be high
compared to that of the auxiliary potential electrode
'IT and in no case should be less than 20 000 Q.

NOTE — In most cases there will be stray currents flowing in
the soil and unless some steps are taken to eliminate their effect,
they may produce serious errors in the measured value. If the
testing current is of the same frequency as the stray current,
this elimination becomes very difficult and it is better to use
an earth tester incorporating a hand-driven generator. These
earth testers usually generate direct current and have rotary
current-reverser and synchronous rectifier mounted on the
generator shaft so that alternating current is supplied to the
test circuit and the resulting potentials are rectified for
measurement by a direct-reading moving-coil ohm-meter. The
presence of stray currents in the soil is indicated by a wandering
of the instrument pointer, but an increase or decrease of
generator handle speed will cause this to disappear.

6.1.2 The source of current shall be isolated from the
supply by a double by a double wound transformer.

NATIONAL ELECTRICAL CODE

SP 30 : 2011

6.1.3 At the time of test, where possible, the test
electrode shall be separated from the earthing system.

6.1.4 The auxiliary electrodes usually consist of
12.5 mm diameter mild steel rod driven up to 1 m into
the ground.

6.1.5 All the test electrodes and the current electrodes
shall be so placed that they are independent of the
resistance area of each other. If the test electrode is in
the form of rod, pipe or plate, the auxiliary current
electrode ' C shall be placed at least 30 m away from
it and the auxiliary potential electrode '/?' shall be
placed midway between them.

6.1.6 Unless three consecutive readings of test electrode
resistance with different spacings of electrodes agree,
the test shall be repeated by increasing the distance
between electrodes 'A' and 'C up to 50 m and each
time placing the electrode *#' midway between them.

6.2 Alternative Method

6.2.1 The method described in 6.1 may not give
satisfactory results if the test electrode is of very low
impedance (1 ohm or less). This applies particularly
while measuring the combined resistance of large
installations. In these cases, the following method may
be adopted.

6.2.1.1 Two suitable directions, at least 90° apart, are
first selected. The potential lead is laid in one direction
and an electrode is placed 250 to 300 m from the fence.
The current lead is taken in the other direction and the
current electrode located at the same distance as the
potential electrode. A reading is taken under this
condition. The current electrode is then moved out in
30 m steps until the same reading is obtained for three
consecutive locations. The current electrode is then left
in the last foregoing position and the potential electrode
is moved out in 30 m steps until three consecutive
readings are obtained without a change in value. The
last readings then correspond to the true value of earth
resistance.

7 EARTHING OF INSTALLATIONS IN
BUILDINGS

7.1 The earthing arrangements of the consumer's
installation shall be such that on occurrence of a fault
of negligible impedance from a phase or non-earthed
conductor to adjacent exposed metal, a current
corresponding to not less than three-and-a-half times
the rating of the fuse or one-and-a-half times the setting
of the overload earth leakage circuit- breaker will flow
except where residual current operated devices or
voltage operated earth leakage circuit-breakers are used
and make the faulty circuit dead. Where fuses are used
to disconnect the faulty section of an installation in

the event of an earth fault, the total permissible
impedance of the earth fault path may be computed
from the following formula (for a normal three-phase
system with earthed neutral).

Z = -

Phase-to-earth voltage of system
Minimum fusing current off ues x Factor of safety

where

Z = permissible impedance, in ohm.

NOTE — The factor of safety in calculating the permissible
impedance should be left to the discretion of the designer.

7.1.1 The factor of safety in the above formula ensures
that in most cases the fuse will blow in a time which is
sufficiently short to avoid danger and allowing for a
number of circumstances, such as the grading of fuse
rating, increase of resistance due to drying out of the
earth electrodes in dry weather, inevitable extensions
to installations involving increase in length of the circuit
conductors and the earth-continuity conductors, etc.

7.1.2 It will be observed that this requirement
determines the overall impedance and does not contain
a specific reference to any part of the circuit such as
the conduit or other earth-continuity conductor together
with the earthing lead. In fact, in large installations the
overall impedance permissible may be less than 1 ohm,
so that considerably less than this might be allowable
for the earth-continuity system.

7.2 It is desirable when planning an installation to
consult the supply authority or an electrical contractor
having knowledge of local conditions, in order to
ascertain which of the two, namely, the use of fuses of
overload circuit-breakers, for protection against earth-
leakage currents is likely to prove satisfactory.

7.3 It is recommended that the maximum sustained
voltage developed under fault conditions between
exposed metal required to be earthed and the
consumer's earth terminal shall not exceed 32 V rms.

7.4 Only pipe, rod or plate earth electrodes are
recommended and they shall satisfy the requirements
of 4.5.

7.5 Earth-Continuity Conductors

7.5.1 Connection to earth of those parts of an
installation which require to be earthed shall be made
by means of an earth-continuity conductor which may
be a separate earth conductor, the metal sheath of the
cables or the earth continuity conductor contained in a
cable, flexible cable or flexible cord.

7.5.2 Earth-Continuity Conductors and Earth Wires
not Contained in the Cables

The size of the earth-continuity conductors should be

PART 1 GENERAL AND COMMON ASPECTS

145

SP 30: 2011

correlated with the size of the current carrying
conductors, that is, the sizes of earth-continuity
conductors should not be less than half of the largest
current carrying conductors, provided the minimum
size of earth-continuity conductors is not less than
1.5 mm 2 for copper and 2.5 mm 2 for aluminium and
need not be greater than 70 mm 2 for copper and
120 mm 2 for aluminium. As regards the sizes of
galvanized iron and steel earth-continuity conductors,
they may be equal to size of current-carrying
conductors with which they are used. The size of earth-
continuity conductors to be used along with aluminium
current-carrying conductors should be calculated on
the basis of equivalent size of the copper current-
carrying conductors.

7.5.3 Earth-Continuity Conductors and Earth Wires
Contained in the Cables

For flexible cables, the size of the earth-continuity
conductors should be equal to the size of the current-
carrying conductors and for metal sheathed, PVC and
tough rubber sheathed cables the sizes of the earth-
continuity conductors shall be in accordance with
relevant Indian Standards.

7.5.4 Cable Sheaths Used as Earth-Continuity
Conductors

Where the metal sheaths of cables are used as earth-
continuity conductors, every joint in such sheaths shall
be so made that its current-carrying capacity is not less
than that of the sheath itself. Where necessary, they
shall be protected against corrosion.

Where non-metallic joint boxes are used, means shall
be provided to maintain the continuity, such as a metal
strip having a resistance not greater than that of the
sheath of the largest cable entering the box.

7.5.5 Metal Conduit Pipe Used as on Earth-Continuity
Conductor

Metal conduit pipe should generally not be used as an
earth-continuity conductor but where used as very high
standard of workmanship in installation is essential.
Joints shall be so made that their current-carrying
capacity is not less than that of the conduit itself.
Slackness in joints may result in deterioration and even
complete loss of continuity. Plain slip or pin-grip
sockets are insufficient to ensure satisfactory electrical
continuity of joints. In the case of screwed conduit,
lock nuts should also be used.

7.5.6 Pipes and Structural Steel Work

Pipes, such as water pipe, gas pipe, or members of
structural steel work shall not be used as earth-
continuity conductor.

8 MEASUREMENT OF EARTH LOOP
IMPEDANCE

8.1 The current which will flow under earth fault
conditions and will thus be available to operate the
overload protection depends upon the impedance of
the earth return loop. This includes the line conductor,
fault, earth-continuity conductor and earthing-lead,
earth electrodes at consumer's premises and substations
and any parallel metallic return to the transformer
neutral as well as the transformer winding. To test the
overall earthing for any installation depending for
protection on the operation of overcurrent devices, for
example, fuses, it is necessary to measure the
impedance of this loop under practical fault conditions.
After the supply has been connected this shall be done
by the use of an earth loop impedance tester as shown
in Fig. 6. The neutral is used in place of the phase
conductor for the purpose of the test. The open-circuit
voltage of the loop tester should not exceed 32 V.

9 TYPES OF SYSTEM EARTHING

9.1 Internationally, it has been agreed to classify the
earthing systems as TN System, TT System and IT
System.

9.1.1 TN System

This type of system has one or more points of the source
of energy directly earthed, and the exposed and
extraneous conductive parts of the installation are
connected by means of protective conductors to the
earthed point(s) of the source, that is, there is a metallic
path for earth fault currents to flow from the installation
to the earthed point(s) of the source. TN systems are
further sub-divided into TN-C, TN-S and TN-C-S
systems.

9.1.2 TT System

This type of system has one or more points of the source
of energy directly earthed and the exposed and
extraneous conductive parts of the installation are
connected to a local earth electrode or electrodes and
are electrically independent of the source earth(s).

9.1.3 IT System

This type of system has the source either unearthed or
earthed through a high impedance and the exposed
conductive parts of the installation are connected to
electrically independent earth electrodes.

9.1.4 It is also recognized that, in practice, a system
may be an admixture of types. For the purpose of this
Code, earthing systems are designated as follows:

a) TN-S system (for 240 V single-phase domestic/
commercial supply) — Systems where there
are separate neutral and protective conductors

146

NATIONAL ELECTRICAL CODE

SP 30: 2011

V) VOLTMETER

A = ammeter

B = neon indicator

C = main switch

D = test switch

E - consumer's earth electrode

F = supply fuse

P = polarity switch

S - substation earth electrode

V = voltmeter

At FF y jacks are provided for insertion of plugs for connection to externa) neutral and/or earth conductors, if desired.

NOTES

1 Arrows shows current flow in neutral or earth loop.

2 Supply system is shown in dotted.

Fig. 6 Circuit Diagram of Earth Loop Impedance Tester

throughout the system. A system where the
metallic path between the installation and the
source of energy is the sheath and armouring
of the supply cable (see Fig. 7 A).

b) Indian TN-S System (for 415 V three-phase
domestic commercial supply) — An
independent earth electrode within the
consumer's premises is provided (see Fig. 7B).

c) Indian TN-C System — The neutral and
protective functions are combined in a single
conductor throughout the system (for example
earthed concentric wiring (see Fig. 7C).

SOURCE OF ENERGY

rz>

SOURCE
EARTH

EQUIPMENT IN
INSTALLATION

-12
-13

-PE

' *

w-"

EXPOSED

CONOUCTIVE

PART
CONSUMER
INSTALLATION

NOTE — The protective conductor (PE) is the metallic covering
(armour or load sheath of the cable supplying the installation
or a separate conductor). All exposed conductive parts of an
installation are connected to this protective conductor via main
earthing terminal of the installation.

7A TN-S System Separate Neutral and Protective
Conductors Throughout the System, 230V Simple
Phase. Domestic/Commercial Supply for 3 ~ TN-S

d) TN-C-S System — The neutral and protective
functions are combined in a single conductor
but only in part of the system (see Fig. 7D).

e) T-TN-S System (for 6. 6/1 1 kV three-phase bulk
supply) — The consumers installation, a TN-
S system receiving power at a captive
substation through a delta connected
transformer primary (see Fig. 7E).

f) 7T System (for 415V three-phase industrial
supply) — Same as 9.1.2 (see Fig. 7F)

g) IT System — Same 9.1.3 (see Fig. 7G).

SOURCE OF ENERGY

ZZ3 : : <

S 1

> i

► i

> «

■""71 L, |

► i

► <

12
13
H

NOTE — For 415 V Three Phase Domestic/Commercial
Supply Having 3-Phase and 1-Phase Loads. All exposed
conductive parts of the installation are connected to protective
conductor via the main earthing terminal of the installation.
An independent earth electrode within the consumer's premises
is also provided.

7B Indian TN-S System

Fig. 7 Types of System Earthing — (Continued)

PART 1 GENERAL AND COMMON ASPECTS

147

SP 30 : 2011

SOURCE OF ENERGY

3 ^CONSUME

NOTE — All exposed conductive parts are connected to the
PEN conductor. For 3~ consumer, local earth electrode has to
be provided in addition.

7C Indian TN-C System (Neutral and Protective

Functions Combined in a Single Conductor

Throughout System)

COMBINED
PE tN

=5— H

> i "

—

-]I

UAjj

1
1

NOTE — The usual form of a TN-C-S system is as shown,
where the supply is TN-C and the arrangement in the
installations in TN-S. This type of distribution is known also
as Protective Multiple Earthing and the PEN conductor is
referred to as the combined neutral and earth (CNE) conductor.
The supply system PEN conductor is earthed at several points
and an earth electrode may be necessary at or near a consumer' s
installation. All exposed conductive parts of an installation are
connected to the PEN conductor via the main earthing terminal
and the neutral terminal, these terminals being linked together.
The protective neutral bonding (PNB) is a variant of TN-C-S
with single point earthing.

7D TN-C-S System, Neutral and Protective

Functions Combined in a Single Conductor in a

Part of the System

SOURCE OF ENERGY

tza-

IAI

CONSUMER

INSTALLATION

■JT

-12

6 6 6

3*^> LOAD

CONSUMER
INSTALLATION

^13

IviLOAD

— I

3^L0A0

- ?

-2
-3

6.6/1 1 kV Three phase bulk supply.

7E T-TN-S System

Fig. 7 Types of System Earthing — (Continued)

SOURCE
EARTH

CONSUMER f
INSTALLATION

fi=

INSTALLATION

EARTH
ELECTRODE

415 V Three phase industrial supply having 3-phase and
1 -phase loads.

NOTE — All exposed conductive parts of the installation are
connected to an earth electrode which is electrically
independent of the source earth. Single phase TT system are
not present in India.

7F TT System

SOURCE OF
ENEROY

** lJ r ?_i l

-L2

-13

NOTE — All exposed conductive parts of an installation are
connected to an earth electrode.

The source is either connected to earth through a deliberately
introduced earthing impedance or is isolated from earth.

7G IT System
Fig. 7 Types of System Earthing

10 SELECTION OF DEVICES FOR
AUTOMATIC DISCONNECTION OF SUPPLY

10.1 General

In general, every circuit is provided with a means of
overcurrent protection. If the earth fault loop
impedance is low enough to cause these devices to
operate within the specified times (that is, sufficient
current can flow to earth under fault conditions), such
devices may be relied upon to give the requisite
automatic disconnection of supply. If the earth fault
loop impedance does not permit the overcurrent
protective devices to give automatic disconnection of
the supply under earth fault conditions, the first option
is to reduce that impedance. It may be permissible for
this to be achieved by the use of protective multiple
earthing or by additional earth electrodes. There are
practical limitations to both approaches.

In case of impedance/arcing faults, series protective
devices may be ineffective to clear the faults. An
alternate approach is to be adopted for the complete
safety of the operating personnel and equipment from
the hazards that may result from earth faults. This is to

148

NATIONAL ELECTRICAL CODE

SP 30: 2011

use residual current devices with appropriate settings
to clear the faults within the permissible time, based
on the probable contact potential. This method is
equally applicable where earth loop impedances cannot
be improved.

In TT systems, there is an additional option of the use
of fault voltage operated protective devices; whilst
these devices will always give protection against shock
risk, provided they are correctly installed, the presence
of parallel earths from the bonding will reduce the
effectiveness of the fire risk protection they offer. These
are, therefore, more suited for isolated installations that
do not have interconnections to other installations. It
should also be remembered that every socket outlet
circuit that do not have earthing facility in a household
or similar installation should be protected by a residual
current device having a rated residual operating current
not exceeding 30 mA.

On all other systems where equipment is supplied by
means of a socket outlet not having earthing facility or
by means of a flexible cable or cord used outside the
protective zone created by the main equipotential
bonding of the installation such equipment should be
protected by a residual current operated device having
an operating current of 30 mA or less.

NOTE — Information on cascading, limitation and
discrimination is given at Annex C.

10.2 Use of Over-Current Protective Devices for
Earth Fault Protection

Where over-current protective devices are used to give
automatic disconnection of supply in case of earth fault
in order to give shock risk protection, the basic
requirement is that any voltage occurring between
simultaneously accessible conductive parts during a
fault should be of such magnitude and duration as not
to cause danger. The duration will depend on the
characteristic of the overcurrent device and the earth
fault current which, in turn, depends on the total earth
fault loop impedance. The magnitude will depend on
the impedance of that part of the earth fault loop path
that lies between the simultaneously accessible parts.

The basic requirement can be met if,

a) a contact potential of 65 V is within the
tolerable limits of human body for 10 s. Hence
protective relay or device characteristic should
be such that this 65 V contact potential should
be eliminated within 10 s and higher voltages
with shorter times.

b) a voltage of 250 V can be withstood by a
human body for about 100 ms, which requires
instantaneous disconnection of such faults,
giving rise to potential rise of 250 V or more
above the ground potential.

The maximum earth fault loop impedance
corresponding to specific ratings of fuse or miniature
circuit-breaker that will meet the criteria can be
calculated on the basis of a nominal voltage to earth
(U ) and the time current characteristics of the device
assuming worst case conditions, that is, the slowest
operating time accepted by the relevant standards.
Thus, if these values are not exceeded, compliance with
this Code covering automatic disconnection in case of
an earth fault is assured.

Where it is required to know the maximum earth fault
loop impedance acceptable in a circuit feeding, a fixed
appliance or set of appliances and protected by an over
current device, the minimum current that may be
necessary to ensure operation of the overcurrent device
within the permissible time of 10 s for a contact
potential of 65 V is found from the characteristic curve
of the device concerned. Application of the Ohm's Law
then enables the corresponding earth fault loop
impedance to be calculated.

For circuits supplying socket outlets, the corresponding
earth fault loop impedance can be found by a similar
calculation for earthed equipment. When equipment
are not earthed and connected to socket outlets without
earthing facility, disconnection should be ensured for
30 mA within 10 s and with appropriate decrements in
time for higher currents.

This method requires a knowledge of the total earth
loop impedance alone (rather than individual
components) and is, therefore, quick and direct in
application. Its simplicity does exclude some circuit
arrangements that could give the required protection.

While calculations give the maximum earth fault loop
or protective conductor impedance to ensure shock risk
protection under fault conditions it is also necessary to
ensure that the circuit protective earth conductor is
protected against the thermal effects of the fault current.
The earth fault loop impedance should, therefore, be low
enough to cause the protective device to operate quickly
enough to give that protection as well. This consideration
places a second limit on the maximum earth loop
impedance permissible and can be checked by
superimposing on the time current characteristic of the
overload device, the 'adiabatic' line having the equation:

k 2 A 2
I 2

-or A =

Iyft

Details of the maximum permissible earth loop
impedance for the thermal protection of cables by fuses
can also be computed. However, the time current
characteristics of a miniature circuit-breaker are such
that if the loop impedance is low enough to give
automatic disconnection within safe disconnecting time

PART 1 GENERAL AND COMMON ASPECTS

149

SP 30 : 2011

so providing shock risk protection, it will also give
the necessary thermal protection to the earth conductor
likely to be used with a breaker of that specific rating.
Figure 8 shows the relationship between the adiabatic
line and the characteristic of fuses and miniature circuit-
breaker.

FUSE CHARACTERISTICS

A DIABATIC LINE

CURRENT I -

8A Fuses

MCB CHARACTERISTICS

CURRENT I -

8B Miniature Circuit-breaker

Fig. 8 Relationship Between Adiabatic Lines
and Characteristics

In order that the devices will give thermal protection
to the protective conductor, operation has to be
restricted to the area to the right of point A where these
curves cross. Thus, the maximum earth fault loop
impedance for thermal protection of the cable is that
corresponding to the minimum earth fault current for
which the device gives protection. The value of this
current can be read from the curve and the
corresponding loop impedance can be calculated from:

where

Z s = earth fault loop impedance,
U = nominal voltage to earth, and

I t = earth fault current.

For a given application, the maximum permitted earth
fault loop impedance would be the lower of the two
values calculated for shock risk protection or thermal
restraint respectively.

It will be noted that the adiabatic line crosses the
characteristic curve for a miniature circuit-breaker at
a second point B. This denotes the maximum fault
current for which a breaker will give thermal protection
but it will generally be found in practice that this value
is higher than the prospective short circuit current that
occurs in the circuit involved and cannot, therefore, be
realized.

10.3 Earth Fault Protective Devices

There are two basic forms of such devices that can be
used for individual non-earthed/earthed (with limited
application) equipment as follows:

10.3.1 Residual Current Operated Devices (RCD)

An RCD incorporates two component items. A core
balance transformer assembly with a winding for each
recognizing the out of balance current that the fault
produces in the main conductors. This induces a current
that is used to operate the tripping mechanism of a
contact system. For operating currents of 0.5 A or more,
the output from such a transformer assembly can
operate a conventional trip coil directly. For lower
values of operating current, it is necessary to interpose
a delay device, either magnetic or solid state.

Devices for load currents greater than 100 A usually
comprise a separate transformer assembly with a circuit-
breaker or contact relay, mounted together within a
common enclosure. Devices for load currents below
100 A usually include the transformer and contact
system within the same single unit, which is then
described as a residual current operated circuit- breaker
(RCB). Such an RCB should be considered a particular
type of RCB although it is the most usual form.

A wide choice of operating currents is available (typical
values are between 10 mA and 20 A ) RCB's are normally
non-adjustable whilst RCD's are often manufactured so
that one of several operating currents may be chosen.
Single phase and multiphase devices with or without
integral overcurrent facilities are available.

Where residual current breakers of 30 mA operating
current or less are being used, there is a choice between
devices that are entirely electromechanical in operation
and those that employ a solid state detector. The
electromechanical types are generally small and compact
and will operate on the power being fed to the fault alone
whereas the solid state type which tend to be bulkier to
require a power supply to ensure operation. Where this
power supply is derived from the mains, it may be

150

NATIONAL ELECTRICAL CODE

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necessary to take added precaution against failures of
part of that mains supply. Devices suitable for time
grading are more likely to be of the solid state form as
are those having higher through fault capacity.

A test device is incorporated to allow the operation of
the RCD to be checked. Operation of this device creates
an out of balance condition within the device. Tripping
of the RCD by means of the test device establishes the
following:

a) The integrity of the electrical and mechanical
elements of the tripping device; and

b) That the device is operating at approximately
the correct order of operating current.

It should be noted that the test device does not provide
a means of checking the continuity of the earthing lead
or the earth continuity conductor, nor does it impose
any test on the earth electrode or any other part of the
earthing circuit.

Although an RCD will operate on currents equal to or
exceeding its operating current, it should be noted that
it will only restrict the time for which a fault current
flows. It cannot restrict the magnitude of the fault percent
current which depends solely on the circuit conditions.

10.3.2 Fault Voltage Operated Earth Leakage Circuit
Breakers (ELCB)

A voltage operated earth leakage circuit-breaker
comprises a contact switching system together with a
voltage sensitive trip coil. On installations, this coil is
connected between the metal-work to be protected and
as good a connection with earth as can be obtained.
Any voltage rise above earth on that metal-work
exceeding the setting of the coil will cause the breaker
to trip so giving indirect shock risk protection.

Tripping coils are designed so that a fault voltage
operated device will operate on a 40 V rise when the
earth electrode resistance is 500 W or 24 V on a 200 W
electrode. Single and multiphase units, with or without
overcurrent facilities, are available for load currents
up to 100 A.

A test device is provided on a voltage operated unit to
enable the operation of the circuit breaker to be
checked, operation of the device applies a voltage to
the trip coil so simulating a fault. Tripping of the circuit
breaker by means of the test device shows the integrity
of the electrical mechanical elements that the unit is
operating with the correct order of operating voltage
and, in addition, proves the conductor from the circuit
breaker to the earth electrode. It can not prove other
features of the installation.

Whilst the voltage operated ( ELCB ) will operate when
subjected to a fault voltage of 20 V or more, it should

be noted that it cannot restrict the voltage in magnitude
only in duration.

10.3.3 Current Operated Earth Leakage Circuit -Breakers

For industrial applications, earth leakage circuit-
breakers operating on milliampere residual currents or
working on fault voltage principle are of little use, since
milliamperes of earth leakage current for an extensive
industrial system is a normal operating situation.
Tripping based on these currents will result in nuisance
for the normal operation. Milliamperes of current in a
system, where exposed conductive parts of equipments
are effectively earthed and fault loop impedance is
within reasonable values, will give rise only to a ground
potential/contact potential rise of a few millivolts. This
will in no way contribute to shock or fire hazard. Here
objectionable fault currents will be a few or a few tenths
of amperes. In such cases, residual current operated
devices sensitive to these currents must be made use
of for earth fault current and stable operation of the
plant without nuisance tripping. This is achieved either
by separate relays or in-built releases initiating trip
signals to the circuit-breakers

10.4 Selection of Earth Fault Protective Devices

In general, residual current operated devices are
preferred and may be divided into two groups
according to their final current operating
characteristics.

10.4.1 RCDs having Minimum Operating Currents
Greater than 30 mA

These devices are intended to give indirect shock risk
protection to persons in contact with earthed metal.

10*4.2 RCDs having Minimum Operating Current of
30 mA and Below

These devices are generally referred to as having 'high
sensitivity' and can give direct shock risk protection
to persons who may come in contact with live
conductors and earth provided that the RCD operating
times are better than those given in IS 8437 (Part 1)
and IS 8437 (Part 2). It should be noted that such RCDs
can only be used to supplement an earth conductor
and not replace one.

In addition to giving protection against indirect contact
or direct contact RCDs may also give fire risk
protection, the degree of protection being related to
the sensitivity of the device.

An RCD should be chosen having the lowest suitable
operating current. The lower the operating current the
greater the degree of protection given, it can also
introduce possibilities of nuisance tripping and may
become unnecessarily expensive. The minimum
operating current will be above any standing leakage

PART 1 GENERAL AND COMMON ASPECTS

151

SP 30: 2011

that may be unavoidable on the system. A further
consideration arises if it is intended to have several
devices in series. It is not always possible to introduce
time grading to give discrimination whereas a limited
amount of current discrimination can be obtained by
grading the sensitivities along the distribution chain.

The maximum permitted operating current depends on
the earth fault loop impedance. The product of the net
residual operating current loop impedance should not
exceed 65 V.

It is often acceptable on commercial grounds to have
several final circuits protected by the same residual
current devices. This, however, does result in several
circuits being affected if a fault occurs on one of the
circuits so protected and the financial advantages have
to be weighed against the effects of loosing more than
one circuit.

It should also be noted that different types of RCD in
different circuits may react differently to the presence
of a neutral to earth fault on the load side. Such an
earth connection together with the earthing of the
supply at the neutral point will constitute a shunt across
the neutral winding on the RCD transformer.
Consequently, a portion of the neutral load current will
be shunted away from the transformer and it may result
in the device tripping. On the other hand, such a shunt
may reduce the sensitivity of the device and prevent
its tripping even under line to earth fault conditions.
In general, therefore, care should be taken to avoid a
neutral to earth fault where RCDs are in use, although

there are some designs being developed that will detect
and operate under such conditions. On installations
with several RCDs, care should be taken to ensure that
neutral currents are returned via the same device that
carries the corresponding phase current and no other.
Failure to observe this point could result in devices
tripping even in the absence of a fault on the circuit
they are protecting.

When using fault voltage operated ELCBs, the
metal-work to be protected should be isolated from
earth so that any fault current passes through the
tripping coil gives both shock and fire risk protection.
However, this isolation is not always practicable and
the presence of a second parallel path to earth will
reduce the amount of fire risk protection offered.
Because the coil is voltage sensitive, the presence of
such a parallel path will not reduce the shock risk
protection offered provided that this second path goes
to earth well clear of the point at which the earth
leakage circuit-breaker trip coil is earthed. It is required
that the earthing conductor is insulated to avoid contact
with other protective conductors or any exposed
conductive parts or extraneous conductive parts so as
to prevent the voltage sensitivity element from being
shunted, also the metal- work being protected should
be isolated from that associated with other circuits in
order to prevent imported faults.

NOTE — For hybrid Indian TN-S system it is recommended
that RCD protection is provided in addition to the overcurrent
protection provided for earth fault protection. This will ensure
required protection in case of any break in continuity of the
protective earth conductor.

ANNEX A
(Clause 1)

ADDITIONAL RULES FOR EARTHINGS

A-l ADDITIONAL RULES APPLYING TO THE
DIRECT EARTHING SYSTEM

Where a driven or buried electrode is used, the earth
resistance shall be as low as possible.

NOTE — The value of earth resistance is under consideration.

A-2 ADDITIONAL RULES APPLYING TO THE
MULTIPLE EARTH NEUTRAL SYSTEM

This system shall be used only where the neutral and
earth is low enough to preclude the possibility of a
dangerous rise of potential in the neutral.

A-3 ADDITIONAL RULES APPLYING TO THE
EARTH LEAKAGE CIRCUIT-BREAKER SYSTEM

A-3.1 Installation of the Earth Leakage Circuit-
Breaker System (see Fig. 9)

All parts required to be earthed shall be connected to
an earth electrode through the coil of an earth leakage
circuit-breaker which controls the supply to all those
parts of the installation which are to be protected; and
to a separate earth electrode.

A-3 2 Selective Protection

If selective operation of earth leakage circuit-breaker
is required, the circuit-breaker, electrodes and earthing
conductors shall be installed in one of the following
ways:

a) Arrangement Giving Complete Selectivity —
All metal frames, conduits, earthing
conductors, etc, which are to be protected as
a unit shall be electrically separated from all
other such parts and from any other earthed
metal. Each part to be protected as a unit shall

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E.LC.B.

PLUG - SOCKET
OUT LETS

.EQUIPMENT
Fig. 9 Connection of Earth Leakage Circuit-Breaker Simple Installation

INSULATED
CONDUCTOR

MAY BE BARE

CONDUITS SHALL
NOT TOUCH
<mirt. RESIS-
TANCE 5000
DHMS)

10A Complete Separation of the Exposed Metal of 10B By Use of a Double-Insulated Wiring System,

One Installation from that of Other Installation Where There are no Conduits to be Earthed

Fig. 10 Connection of Earth Leakage Circuit-Breaker for Complete Selectivity
PART 1 GENERAL AND COMMON ASPECTS 153

SP 30:' 2011

be connected to an earth electrode through
the coil of an earth leakage circuit-breaker.
(see Fig. 10)

All the separately protected portions of the
installations may be connected to one
electrode to the earth leakage circuit-breaker.

b) Arrangement Giving Partial Selectivity
(Complete Selectivity with Respect to Faults
in Apparatus, but no Selectivity with Respect
to Faults in Wiring in Conduit) (see Fig. 9) —
All the conduits and associated fittings shall
be bonded together and connected to an earth
electrode, all shall also be connected to
another earth electrode through an earth
leakage circuit-breaker which controls all the

active conductors supplying the whole or
portions of the installations concerned. Each
part to be protected as a unit shall be
connected to an earth electrode through the
coil of a separate earth leakage circuit-breaker
which controls all the active conductors
supplying that portion of the installation only.
All these portions may be connected to one
electrode, but this electrode shall be separated
from the electrode to which the conduits are
connected.

NOTES

1 A double-insulated wiring system is used, for example,
tough rubber-sheathed cables. Any conduit used does
not then need to be earthed.
2 The earthing conductor is insulated from the conduit.

ANNEX B
(Clause 3.1.3.2)

REPRESENTATIVE VALUES OF SOIL RESISTIVITY IN VARIOUS PARTS OF INDIA

Locality

Type of Soil

Order of

Remarks

No.

Resistivity
Q m

(1)

(2)

(3)

(4)

(5)

1 . Kakarapar, Distt Surat, Gujarat

2. Taptee Valley

3. Narmada Valley

4. Purna Valley (Deogaon)

5. Dhond, Mumbai

6. Bijapur Distt, Karnataka

7 . Garimenapenta, Distt Nellore
Andhra Pradesh

8. Kartee

9. Delhi

a) Najafgarh

b) Chhatarpur

Clayey black soil 6-23

Alluvium 6-24

Alluvium 4-11

Agricultural 3-6

Alluvium 6-40

a) Black cotton soil 2-10

b) Moorm 10-50
Alluvium (highly 2
clayey)

a) Alluvium 3-5

b) Alluvium 9-21

a) Alluvium 75-170
(dry sandy soil)

b) Loamy to clayey 38-50
soil

c) Alluvium (saline) 1.5-9
Dry soil 36-109

Underlying
trap

bedrock-Deccan

Underlying bedrock-sand-
stone shale and lime-stones,
Deccan trap and gneisses
Underlying bedrock-Deccan
trap

do
Underlying bedrock-gneisses

Underlying bedrock- sand-
stone, trap or gneisses

do
Underlying bedrock-
quartzites

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Locality

Type of Soil

Order of

Remarks

No.

Resistivity
Q m

(1)

(2)

(3)

(4)

(5)

10.

Korba, M.P.

a) Moist clay

b) Alluvium soil

2-3
10-20

Underlying bedrock-sand-
stone or shale

11.

Cossipur, Kolkata

Alluvium

25
(approx)

—

12.

Bhagalpur, Bihar

a) Alluvium

9-14

Underlying bedrock-traps,
sand-stone or gneisses

13.

Kerala (Trivandrum Distt)

Lateritic clay

2-5

Underlying bedrock-laterite,
charnockite or granites

14.

Bharatpur

Sandy loam (saline)

6-14

—

15.

Kalyadi, Mysore

Alluvium

60-150

Underlying bedrock-gneisses

16.

Kolar Gold Fields

Sandy surface

45-185

17.

Wajrakarur, Andhra Pradesh

Alluvium

50-150

18.

Koyana, Satara Distt

Lateritic

800-1 200

(dry)

Underlying bedrock-sand-
laterite or trap

19.

Kutch-Kandla (Amjar Area)

a) Alluvium (clayey)

4-50

Underlying bedrock-sand-
stone, shale or tap

b) Alluvium (sandy)

60-200

20.

Villupuram, Chennai

Clayey sands

Underlying bedrock-granite

21.

Ambaji, Banaskantha, Gujarat

Alluvium

170

Underlying bedrock-granites
and gneisses

22.

Ramanathapuram Distt, Chennai

a) Alluvium

2-5

Underlying bedrock-sand-
stones and gneisses

b) Lateritic soil

300
(approx)

NOTE — The soil resistivities are subject to wide seasonal variation as they depend

very much on t

he moisture content.

PART 1 GENERAL AND COMMON ASPECTS

155

SP 30 : 2011

ANNEX C
(Clause 10.1)

CASCADING, DISCRIMINATION AND LIMITATION

C-l CASCADING

The utilization of the current limiting capacity of a
circuit-breaker at a given point to enable installation
of lower-rated circuit-breakers in branch is known as
'cascading' or 'back-up protection*. The main
(upstream) circuit-breakers acts as a barrier against
short-circuit currents and branch (downstream) circuit-
breakers with lower breaking capacities than the
prospective short-circuit (at their point of installation)
operate under their normal breaking conditions. The
limiting circuit-breaker helps the circuit-breaker placed
downstream by limiting high short-circuit currents thus
enabling use of downstream circuit-breaker with a
breaking capacity lower than the short-circuit current
calculated at its installation point thus enabling
economical selection of circuit-breakers.

Cascading concerns all devices installed downstream
of the circuit-breaker, and can be extended to several
consecutive devices, even if they are used in different
switchboards. The upstream device must have an
ultimate breaking capacity greater than or equal to the
assumed short-circuit current at the installation point.
For downstream circuit-breakers, the ultimate breaking
capacity to be considered is the ultimate breaking
capacity enhanced by coordination.

The association of the upstream and downstream circuit-
breakers allows an increase in performance of the
breakers. Thus, the electromagnetic, electrodynamic and
thermal effects of short-circuit currents are reduced.
Installation of a single limiting circuit-breaker alongwith
lower rated circuit-breakers results in considerable
economy and simplification of installation work.

D } and D 2 are the two circuit-breakers (see Fig. 11).

t(s) A ^ «i

As soon as the two circuit-breakers trip (as from point
/ B ), an arc voltage U AD] on separation of the contacts
of D } is added to voltage ?7 AD2 and helps, by additional
limitation, circuit-breaker D 2 to open.

The association D x + D 2 allows an increase in
performance of D 2 as shown in Fig. 12, which depicts,

limitation curve of D 2 ,

enhanced limitation curve of D 2 by D v

I cu D 2 enhanced by D v

Annex A of IS/IEC 60947-2 defines coordination under
short-circuit conditions between circuit-breaker and
another short-circuit protective device (SCPD)
associated in the same circuit and the tests to be
performed. Cascading is normally verified by tests for
critical points. The tests are performed with an
upstream circuit-breaker D 2 with a maximum
overcurrent setting and a downstream circuit-breaker
D 2 with a minimum setting.

C-2 LIMITATION

C-2.1 The technique of limitation allows the circuit-
breaker to considerably reduce short-circuit currents.
It ensures attenuation of the harmful electromagnetic,
thermal and mechanical effects of short-circuits and is
the basis of the cascading technique.

The assumed fault current / sc is the short-circuit current
that would flow at the point of the installation where
the circuit-breaker is placed, if there were no limitation.
Since the fault current is eliminated in less than one
half-period, only the first peak current (asymmetrical
peak 7) is considered. This is a function of the
installation fault cos 9. Reduction of this peak / to

Fig. 1 1 Operation of Circuit-Breakers in Cascade

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SP 30 : 2011

*cuD2 ^citBI enhanced

D 1 helps D 2 t e break tie current

— LimltattoH of H 2 @n§iaEie@fi§ by Dj

•- Limitation of D»

Llmltatloii of D 4

Fig. 12 Limitation Curves for Circuit-Breakers

Fig. 13 Effect of Limitation on Fault Current

limited I L characterizes circuit-breaker limitation.
Limitation consists of creating a back-electromotive
force opposing the growth of the short-circuit current.
Effectiveness of limitation depends on intervention
time, that is the time t s when the back-electromotive
force (b cmf ) appears, the rate at which b tmi increases
and the value of b cmf . The back-electromotive force is
the arc voltage £/ a due to the resistance of the arc
developing between the contacts on separation. Its
speed of development depends on the contact separation
speed. As shown in Fig. 13, as from the time t s when
the contacts separate, the back less than the assumed
fault current flow through when a short-circuit occurs.

C-2.2 Circuit-Breaker Limitation Capacity

The circuit-breaker limitation capacity defines the way

how it reduces the let through current in short-circuit
conditions (see Fig. 14 and 15). The thermal stress of the
limited current is the area (shaded) defined by the curve
of the square of the limited current I s 2 c (t) . If there is no
limitation, this stress would be the area, far larger, that
would be defined by the curve of the square of the assumed
current. For an assumed short-circuit current I sc , limitation
of this current to 10 percent results in less than 1 percent
of assumed thermal stress. The cable temperature rise is
directly proportional to the thermal stress.

NOTE — On a short-circuit, adiabatic temperature-rise of
conductors occurs (without heat exchange with the outside due
to the speed of the energy supply). The increased temperature
for a conductor with a cross-section S is:

B . = jrvy*

where I 2 dt is the thermal stress (A 2 s)

100% --

— ^ss^— Assumed transient p@a§s I

10%

assumed st@
p#aw *„

_!a — limited peak J w

Fig. 14 Current Limitation

Assumed m iy100%

Limited energy < 1%

Fig. 15 Thermal Stress Limitation

Limitation considerably attenuates the harmful effects
of short-circuits on the installation. Consequently,
limitation contributes to the durability of electrical
installations. Due to limitation, the harmful effects of
short-circuits on a motor feeder are greatly attenuated.
Proper limitation ensures easy access to a Type 2
coordination as per IS/IEC 60947-4-1, without
oversizing of components. This type of coordination
ensures optimum use of their motor feeders.

PART 1 GENERAL AND COMMON ASPECTS

157

SP 30 : 2011

C-2.3 Limitation Curves

A circuit-breaker's limiting capacity is expressed by
limitation curves that give,

a) the limited peak current as a function of the
rms current of the assumed short-circuit
current. For example on a 160 A feeder where
the assumed lsc is 90 kA rms, the non-limited
peak lsc is 200 kA (asymmetry factor of 2.2)
and the limited 7 SC is 26 kA peak.

b) the limited thermal stress (in A2s) as a
function of the rms current of the assumed
short-circuit current. For example, on the
previous feeder, the thermal stress moves from
more than 100 x 106 A2s to 6 x 106 A2s.

C-3 DISCRIMINATION

C-3.1 Discrimination is the co-ordination of the
operating characteristics of two or more over-current
protective devices such that, on the incidence of over-
currents within stated limits, the device intended to
operate within these limits does so, while the other(s)
does (do) not (see Fig. 16).

Distinction is made between series discrimination
involving different over-current protective devices
passing substantially the same over-current and
network discrimination involving identical protective
devices passing different proportions of the over-
current. In LV networks, discrimination is
recommended in order to obtain higher levels of supply
continuity and protection, ensuring better safety of
installations and minimum cost overruns.

Cascading principle in limiting CBs can enhance the
discrimination levels. It is recommended that the
manufacturer provide the relevant data in terms of
discrimination charts and cascading levels for various
combination of CBs (upstream and downstream) and
fault current as per the laboratory test results.

A discrimination current 7 S is defined such that if;

a) / fau]t > / s : both circuit-breakers trip, and

b) / fault < 7 S : only D 2 eliminates the fault.

C-3.2 Discrimination Quality

^mmmmmmH^mmmmmm^ o

F®2

D 2 oniy

trips

Fig. 16 Discimination and Sequence of Tripping

The value J s is compared with assumed / sc (Z) 2 ) at point
ft

D 2 of the installation

total discrimination: I s > 7 SC (D 2 );
discrimination is qualified as total, that is
whatever the value of the fault current, D 2 only
will eliminate it.
b) partial discrimination: I s < 7 SC (7) 2 );
discrimination is qualified as partial, that is
up to 7 S , only D 2 eliminates the fault. Beyond
7 S , both 7), and D 2 open.

where

7 SC (£>,): short-circuit current at the point where
D x is installed,

7 CU Dj : ultimate breaking capacity of D } .

C-3.3 Types of Discriminations

C -3.3,1 Current Discrimination

This technique is directly linked to the staging of the
Long Time (LT) tripping curves of two serial-connected
circuit-breakers (see Fig. 17).

t(s)

**ra *ri -*sda s«ii

Fig. 17 Current Discrimination

The discrimination limit 7 S is,

a) 7 S = 7 sd2 if the thresholds 7 sd] and 7 sd2 are too close
or merge, and

b) ^ s = hdi^ tne thresholds 7 sdl and 7 sd2 are
sufficiently far apart.

Current discrimination is achieved when,

a) / rl // r2 <2

b) / sdl // sd2 >2

The discrimination limit being

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C-3.3.1.1 Discrimination quality

Discrimination is total if / s > / SC (£> 2 X that is 7 S dl > / SC (D 2 ).

This normally implies,

a relatively low level I SC (D 2 ),
a large difference between the ratings of circuit-
breakers D ] and D r

Current discrimination is normally used in final
distribution.

C -3.3.2 Time Discrimination

This is the extension of current discrimination and is
obtained by staging over time of the tripping curves.
This technique consists of giving a time delay of t to
the Short Time (ST) tripping of D x (see Fig. 18).

Fig. 18 Time Discrimination

The thresholds (7 rl , 7 sdl ) of D x and (7 r2 , 7 sd2 ) comply
with the staging rules of current discrimination. The
discrimination limit 7 S of the association is at least equal
to 7 U , the instantaneous threshold of D v

C-3.3.2.1 Discrimination quality

For discrimination on final and/or intermediate feeders,
A category circuit-breakers can be used with time-
delayed tripping of the upstream circuit-breaker. This
allows extension of current discrimination up to the
instantaneous threshold I u of the upstream circuit-
breaker: 7 S > 7 n . If 7 SC (D 2 ) is not too high (case of a
final feeder) total discrimination can be obtained.

On the incomers and feeders of the MSB, as continuity
of supply takes priority, the installation characteristics
allow use of B category circuit-breakers designed for
time-delayed tripping. These circuit-breakers have a
high thermal withstand (7 CW > 50 percent 7 cn for t = 7 S ):
7 S > 7 cwl . Even for high 7 SC (D 2 ), time discrimination
normally provides total discrimination: 7 cwi > 7 SC (D 2 ).

NOTE — Use of B category circuit-breakers means that the
installation must withstand high electrodynamic and thermal
stresses. Consequently, these circuit-breakers have a high
instantaneous threshold / k that can be adjusted and disabled in
order to protect the busbars if necessary.

C-3.4 Enhancement of Current and Time
Discrimination

C-3.4.1 Enhancement by Limiting Downstream
Circuit-Breakers

Use of a limiting downstream circuit-breaker enables
the discrimination limit to be pushed back.

noiHImltliig

gt»rt*elreult
limlter

Fig. 19 Enhancement of Discrimination

On referring to Fig. 19, a fault current / d will be seen
by D l9

equal to / d for a non-limiting circuit-breaker, and equal
to 7 Ld < / d for a limiting circuit-breaker.

The limit of current and time discrimination 7 S of the
association D t + Z) 2 is thus pushed back to a value that
increases when the downstream circuit-breaker is rapid
and limiting.

C-3.4.2 Discrimination Quality

Use of a limiting circuit-breaker is extremely effective
for achievement of total discrimination when threshold
settings (current discrimination) and/or the
instantaneous tripping threshold (time discrimination)
of the upstream circuit-breaker D x are too low with
respect to the fault current I d in D 2 - I SC (D 2 ).

C-3.4.2. 1 Logic discrimination or "Logic
Discrimination Zone (ZSI) "

This type of discrimination can be achieved with
circuit-breakers equipped with specially designed
electronic trip units. Only the Short Time Protection
(STP) and Ground Fault Protection (GFP) functions
of the controlled devices are managed by Logic
Discrimination. In particular, the Instantaneous
Protection function (inherent protection function) is
not concerned.

PART 1 GENERAL AND COMMON ASPECTS

159

SP 30 : 2011

pilot wir@

Interlocking

m4m

gnt©r8oegcB«i

Fig. 20 Logic Discrimination(ZSI)

C-3.4.2.2 Settings of controlled circuit-breakers

a) Time delay: staging (if any) of the time delays
of time discrimination to be applied (t D { >
t D 2 > t D 3 )

b) Thresholds: natural staging of the protection
device ratings must be complied with (7 cr Dj >

'cA>'cA)-

NOTE — This technique ensures discrimination even with
circuit-breakers of similar ratings.

C -3.4.2.3 Principles

Activation of the Logic Discrimination function is via
transmission of information on the pilot wire for ZSI
input,

a) Low level (no downstream faults): the
Protection function is on standby with a
reduced time delay (< 0.1)

b) High level (presence of downstream faults):
the relevant Protection function moves to the
time delay status set on the device.

Activation of the Logic Discrimination function is via
transmission of information on the pilot wire for ZSI
output,

a) Low level: the trip unit detects no faults and
sends no orders.

b) High level: the trip unit detects a fault and
sends an order.

C-3.4.2.4 Operation

A pilot wire connects in cascading form the protection
devices of an installation (see Fig. 20). When a fault
occurs, each circuit-breaker upstream of the fault
(detecting a fault) sends an order (high level output)
and moves the upstream circuit-breaker to its natural
time delay (high level input). The circuit breaker placed
just above the fault does not receive any orders (low
level input) and thus trips almost instantaneously.

C-3A2.5 Discrimination quality

This technique enables easy achievement as standard
of discrimination on 3 levels or more, easy achievement
of downstream discrimination with non-controlled
circuit-breakers, elimination of important stresses on
the installation, relating to time-delayed tripping of the
protection device, in event of a fault directly on the
upstream busbars. All the protection devices are thus
virtually instantaneous.

C-3.5 Discrimination Rules

C -3.5.1 Overload Protection

For any overcurrent value, discrimination is guaranteed
on overload if the non-tripping time of the upstream
circuit-breaker D { is greater than the maximum
breaking time of circuit-breaker D 2 .

The condition is fulfilled if the ratio of Long Time (LT)
and Short Time (ST) settings is greater than 2. The
discrimination limit 7 S is at least equal to the setting
threshold of the upstream Short Time (ST) time delay.

C-3.5.2 Short-circuit Protection

C-3.5.2.1 Time discrimination

Tripping of the upstream device Dj is time delayed by
r, the conditions required for current discrimination
must be fulfilled and the time delay t of the upstream
device Dj must be sufficient for the downstream device
to be able to eliminate the fault. Time discrimination
increases the discrimination limit / s up to the
instantaneous tripping threshold of the upstream
circuit-breaker D { (see Fig. 21).

Discrimination is always total if circuit-breaker D, is
of category B, has an / cw characteristic equal to its 7 CU .

Discrimination is total in the other cases if the
instantaneous tripping threshold of the upstream
circuit-breaker D l is greater than the assumed 7 SC in D 2 .

C-3.5.2.2 Logic discrimination

Discrimination is always total.

C-3.5.2.3 General case

There are no general discrimination rules. The time/
current curves clearly supply a value of 7 SC (limited or
assumed) less than the Short Time tripping of the
upstream circuit-breaker; discrimination is then total.
If this is not the case, only tests can indicate
discrimination limits of coordination, in particular
when circuit-breakers are of the limiting type. The
discrimination limit 7 S is determined by comparison of
curves,

a) in tripping energy for the downstream circuit-
breaker, and

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NATIONAL ELECTRICAL CODE

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b) in non-tripping energy for the upstream
circuit-breaker.

The potential intersection point of the curves gives the
discrimination limit I s . The manufacturers indicate in
tables the tested performance of coordination.

C-3.6 Earth Leakage Protection Discrimination

C-3.6.1 According to the Earthing System,
discrimination only uses coordination of overcurrent
protection devices. When the insulation fault is treated
specifically by earth leakage protection devices (for
example in the TT system), discrimination of the
residual current devices (RCDs) with one another must
also be guaranteed. Discrimination of earth leakage
protection devices must ensure that, should an
insulation fault occur, only the feeder concerned by
the fault is de-energized. The aim is to optimize energy
availability.

en ©2

Fig. 21 Discrimination at Various Fault Currents

C-3.6.2 Types of Earth Leakage Protection
Discrimination

C-3.6.2.1 Vertical discrimination

In view of requirements and operating standards,
discrimination must simultaneously meet both the time
and current conditions (see Fig. 22).

C-3.6.2. 1.1 Current condition

The RCD must trip between / n and I n 12, where I n is the
declared operating current. There must therefore exist
a minimum ratio of 2 between the sensitivities of the
upstream device and the downstream device. In
practice, the standardized values indicate a ratio of 3.

C-3.6.2.1. 2 Time condition

The minimum non-tripping time of the upstream device
must be greater than the maximum tripping time of
the downstream device for all current values.

NOTE — The tripping time of RCDs must always be less than
or equal to the time specified in the installation standards to
guarantee protection of people against indirect contacts.

•A

°1\

RESIDUAL
CURRENT

Fig. 22 Vertical Discrimination

For the domestic area, standards IS 12640 (Part 1)
(residual current circuit-breakers) and IS 12640 (Part
2) (residual current devices) define operating times.
The values in the table correspond to curves G and S.
Curve G (General) correspond to non-delayed RCDs
and S (Selective) to those that are voluntarily delayed
(see Fig. 23).

t(HiS) ii

2@9

500

Fig. 23 Operating Time Curves

C-3.6.2.2 Horizontal discrimination

Sometimes known as circuit selection, it allows savings
at the supply end of the installation of an RCD placed
in the cubicle if all its feeders are protected by RCDs.
Only the faulty feeder is de-energized, the devices
placed on the other feeders do not see the fault (see
Fig. 24).

PART 1 GENERAL AND COMMON ASPECTS

161

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1
\

risidum.

CURRENT
DEVICE

RESIDUAL
CURRENT
DEVICE

Fig. 24 Horizontal Discrimination

Table 2 Standardized Values of Operating Times

Type /„

h n

Standardized Values of Operating

Time and Non

-operating Time (in s) at:

lAn

2Ia

5Ia„

500A

General instantaneous All values
Selective >25

All values
>0.030

0.3
0.5
0.13

0.15
0.2
0.06

0.04
0.15
0.05

0.04
0.15
0.04

Maximum operating time
Maximum operating time
Maximum operating time

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SECTION 15 LIGHTNING PROTECTION

FOREWORD

For the purposes of the National Electrical Code, the
fixed installation for lightning protection is considered
part of the electrical installation design and constitutes
a major area where the installation design engineer has
to ensure proper coordination.

This Section covers the essential design and
construction details of lightning protective systems. It
is, however, intended to serve only as a guide of general
nature on the principles and practices in the protection
of structures against lightning, and account has to be
taken of several other local conditions such as
variations in the architecture, topography of the region,
atmospheric conditions, etc.

Lightning protection of industrial installations which
are categorized as hazardous, require special
considerations. These are summarised in Part 7 of the
Code.

Assistance has been derived from IS 2309 : 1989 'Code
of practice for the protection of buildings and allied
structures against lightning (second revision)* for this
Section.

1 SCOPE

1.1 This (Part 1/Section 15) of the Code covers
guidelines on the basic electrical aspects of lightning
protective systems for buildings and the electrical
installation forming part of the system.

1.2 Additional guidelines if any, for specific
occupancies from the point of lightning protection are
covered in respective sections of the Code.

2 REFERENCES

The following Indian Standards on lightning protection
may be referred for further details:

IS No.
IS 2309 : 1989

IS 15086 : Part 5/
IEC 60099-5 : 1996

Title

Code of practice for the protection
of buildings and allied structures
against lightning (second revision)
Surge arresters : Part 5 Selection
and application recommen-
dations

3 TERMINOLOGY

For the purposes of this Section, the following
definitions shall apply.

3.1 Air Termination (Lightning Conductor) or Air

Termination Network — Those parts of a lightning

protective system that are intended to collect the
lightning discharges from the atmosphere.

3.2 Bonds — Electrical connection between the
lightning protective system and other metal work, and
between various portions of the latter.

3.3 Down Conductors — Conductors which connect
the air terminations with the earth terminations.

3.4 Earth Terminations or Earth Terminations
Network — Those part of the lightning protective
system which are intended to distribute the lightning
discharges into the general mass of the earth. All parts
below the testing point in a down conductor are
included in this term.

3*5 Earth Electrodes — A metal plate, pipe or other
conductor or any array of conductors electrically
connected to the general mass of the earth; these
include those portions of the earth terminations that
make direct electrical contact with the earth.

3.6 Fasteners — Devices used to fasten the conductors
to the structures.

3.7 Isoceraunic Level — It is the number of days in a
year on which the thunder is heard in the particular
region averaged over a number of years.

3.8 Joints — The mechanical and electrical junctions
between two or more portions of the lightning
protective system or other metal bonded to the system
or both.

3.9 Lightning Protective System — The whole system
of interconnected conductors used to protect a structure
from the effects of lightning.

3.10 Metal-clad Building — A building with sides
made of or covered with sheet metal.

3.11 Metal-roofed Building — A building with roof
made of or covered with sheet metal.

3.12 Side Flash — A spark occurring between nearby
metallic objects or between such objects and the
lightning protective system or to earth.

3.13 Testing Points — Joints in down conductors or
in bonds or in earth conductors connecting earth
electrodes, so designed and situated as to enable
resistance measurements to be made.

3.14 Zone of Protection — The space within which
the lightning conductor is expected to provide
protection against a direct lightning stroke.

4 EXCHANGE OF INFORMATION

4.1 The architect should exchange information with

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the engineer concerned when the building plans are
being prepared. The primary object of such an
exchange is to obtain information regarding the
architectural features of the structure so that due
provision may be made to retain the aesthetic features
of the building while planning the location of the
lightning conductors and down conductors of the
lightning protective system. Information may also be
obtained at an early stage regarding other services, such
as electrical installation, gas and water pipes as well
as climatic and soil conditions.

4»2 Scale drawings showing plans and elevations of
the structure should be obtained, and the nature, size
and position of all the metal component parts of the
lightning protective system should be indicated on
them. In addition, a ground plan should show all the
tall objects, such as, buildings, masts, transmission
towers, tall trees, etc, within the zone of protection.

5 CHARACTERISTICS OF LIGHTNING
DISCHARGES

5.1 The principal effects of lightning discharge to
structure are electrical, thermal and mechanical. These
effects are determined by the current which is
discharged into the structure. These currents are
unidirectional and may vary in amplitude from a few
hundred amperes to about 200 kA. The current in any
lightning discharge rises steeply to its crest value in a
few microseconds and decays to zero in a few
milliseconds. Many lightning discharges consist of a
single stroke but some others involve a sequence of
strokes which follow the same path and which
discharge separate currents of amplitude and duration
as mentioned above. A complete lightning discharge
may thus last a second or even longer.

5.2 Electrical Effects

The principal electrical effects of a lightning discharge
are two-fold.

5.2.1 The lightning current which is discharged to earth
through the resistance of the lightning conductor and
earth electrode provided for a lightning protective
system, produces a resistive voltage drop which
momentarily raises the potential of the protective
system with respect to the absolute earth potential to a
very high value. The lightning current also produces,
around the earth electrode, a high voltage gradient
which may be dangerous to persons and animals.

5.2.2 The lightning current rises steeply to its crest
value (approximate at the rate of 10 kA/ms) and as a
first approximation may be regarded as equivalent to
high frequency discharge. A vertical conductor of the
dimensions generally used in a lightning protective
system has an inductance of about 16 x 10" 5 H/100 m.

The rate of rise of current in conjunction with the
inductance of the discharge path produces an inductive
voltage drop which would be added, with due regard
to the time relationship, to the resistive (ohmic) voltage
drop across the earthing system.

5.3 Thermal Effects

The thermal effect of lightning discharge results in rise
in temperature of the conductor through which the
lightning current is discharged to the earth. Although
the amplitude of the lightning current may be very high,
its duration is so short that the thermal effect on a
lightning protective system is usually negligible. This
ignores the fusing or welding effects which occur
locally consequent upon the rupture of a conductor
which was previously damaged or was of inadequate
cross- sectional area. In practice the cross-sectional area
of a lightning conductor is determined primarily by
mechanical considerations.

5.4 Mechanical Effects

When a high electric current is discharged through
parallel conductors which are in close proximity to each
other, these are subjected to large mechanical forces.
The lightning conductors should, therefore, be
provided with adequate mechanical fixings.

5.4.1 A different mechanical effect exerted by a
lightning discharge is due to the fact that the air channel,
that is, the space between the thunder cloud and the
lightning conductor, along which the discharge is
propagated, is suddenly raised to a very high
temperature. This results in a strong air pressure wave
which is responsible for damages to buildings and other
structures. It is not possible to provide protection
against such an effect.

6 DETERMINATION OF THE NEED FOR
PROTECTION

6.1 Risk Index

In determining how far to go in providing lightning
protection for specific cases or whether or not it is
needed at all, it is necessary to take into account the
following factors:

a) Usage of structure,

b) Type of construction,

c) Contents or consequential effects,

d) Degree of isolation,

e) Type of isolation,

f) Height of structure, and

g) Lightning prevalance.

6. LI IS 2309 gives the details of various factors that
affect the risk of the structure being struck and the

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consequential effects of a stroke. Certain values called
'index figures', have been assigned to these factors
which help in arriving at an overall 'risk index' to serve
as an aid to judging whether lightning protection. The
examples of such structures are:

a) those in or near which large number of people
congregate.

b) those concerned with the maintenance of
essential public services,

c) those in areas where lightning strokes are
prevalent,

d) very tall or isolated structures,

e) structures of historic or cultural importance,
and

f) structures containing explosives and highly
flammable materials.

7 ZONE OF PROTECTION

7.1 The zone of protection of a lightning conductor
denotes the space within which a lightning conductor
provides protection against a direct lightning stroke
by diverting the stroke to itself. Examples of the
protection of different types and shapes of buildings
along with zone of protection provided by their
lightning protective systems are given in 8.2 of
IS 2309.

8 MATERIALS AND DIMENSIONS

8.1 Materials

The materials of lightning conductors, down
conductors, earth termination network, etc, of the
protective system shall be reliably resistant to corrosion
or be adequately protected against corrosion. The
following materials are recommended:

a) Copper — When solid or stranded copper
wire or flat copper strips are used, they
shall be of grade ordinarily required for
commercial electrical work, generally
designated as being of 98 percent
conductivity when annealed. They shall
conform to relevant Indian Standards.

b) Copper-clad Steel — Where copper-clad
steel is used, the copper covering shall
be permanently and effectively welded
to the steel core. The proportion of copper
and steel shall be such that the
conductance of the material is not less
than 30 percent of the conductance of
solid copper of the same total cross-
sectional area.

c) Galvanized Steel — If there is any
difficulty in the use of copper or

aluminium, galvanized steel of the same
cross section as recommended for copper
may be used, in line with the provisions
of IS 2309. Where steel is used it shall
be thoroughly protected against corrosion
by a zinc coating. Galvanized steel may
be preferred for some short life
installations, such as exhibitions. Copper
is preferred to galvanized iron where
corrosive gases, industrial pollution or
saltaden atmospheric conditions are
encountered.

d) Aluminium — Aluminium wire and strips
are increasingly finding favour for use as
lightning conductors in view of the fact
that aluminium has a conductivity almost
double that of copper mass for mass.
When used, it shall be least 99 percent
pure, of sufficient mechanical strength
and effectively protected against
corrosion.

e) Alloys — Where alloys of metals are used
they shall be substantially as resistant to
corrosion as copper under similar
conditions.

NOTE — Aluminium should not be used
underground or in direct contact with walls.

8.2 Shapes and Sizes

The recommended shape and minimum sizes of
conductors for use above ground and below ground
are given in Table 1 and Table 2 respectively.

Table 1 Shapes and Minimum Sizes of Conductors

for Use Above Ground
{Clause 8.2)

SI Material and Shape

No.

(1) (2)

Minimum Size

(3)

i) Round copper wire or 6 mm diameter
copper-clad steel wire

ii) Stranded copper wire 50 mm 2 (or 7/3.00 mm diameter)

iii) Copper strip 20 mm x 3 mm

iv) Round galvanized iron wire 8 mm diameter

v) Galvanized iron strip 20 mm x 3 mm

vi) Round aluminium wire 9 mm diameter

vii) Aluminium strip 25 mm x 3.15 mm

8.3 Corrosion

Where corrosion due to atmospheric, chemical,
electrolytic or other causes is likely to impair any part
of the lightning protective system, suitable precautions
should be taken to prevent its occurrence. The contact
of dissimilar metals is likely to initiate and accelerate
corrosion unless the contact surfaces are kept

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165

SP 30: 2010

completely dry and protected against the ingress of
moisture.

Table 2 Shapes and Minimum Sizes of Conductors

for Use Below Ground

{Clause 8.2)

Material and Shape

Minimum Size

No.

(2)

(3)

Round copper wire or copper-clad
steel wire

8 mm diameter

ii)

Copper strip

32 mm x 6 mm

iii)

Round galvanized iron wire

10 mm diameter

iv)

Galvanized iron strip

32 mm x 6 mm

8.3.1 Dissimilar metal contacts can exist where a
conductor is held by fixing devices or against external
metal surfaces. Corrosion can arise also where water
passing over one metal comes into contact with another.
Run-off water from copper, copper alloys and lead can
attack aluminium alloys and zinc. The metal of the
lightning protective system should be compatible with
the metal or metals used externally on the structure
over which the system passes or with which it may
make contact.

9 DESIGN

9.0 General

Lightning protective systems should be installed with
a view to offering least impedance to the passage of
lightning current between air-terminals and earth.
There shall be at least two parts, and more if practicable.
This is done by connecting the conductors to form a
cage enclosing the building. The basic design
considerations for lightning protective systems are
given in IS 2309.

The principal component of a lightning protective
system are:

a) air terminations,

b) down conductors,

c) joints and bends,

d) testing points,

e) earth terminations,

f) earth electrodes, and

g) fasteners.

9.1 Air Terminations

For the purpose of lightning protection, the vertical
and horizontal conductors are considered equivalent
and the use of pointed air terminations or vertical finials
is, therefore, not regarded as essential except when
dictated by practical considerations. An air termination
may consist for a vertical conductor as for a spire, a

single horizontal and vertical conductors for the
protection of bigger buildings.

9.1.1 A vertical air termination need not have more
than one point and shall project at least 30 cm above
the object, salient point or network on which it is fixed.

9.1.2 Horizontal air terminations should be so
interconnected that no part of the roof is more than 9
m away from the nearest horizontal conductor except
that an additional 30 cm may be allowed for each 30 cm
by which the part to be protected is below the nearest
protective conductor. For a flat roof, horizontal air
terminations along the outer perimeter of the roof are
used. For a roof of building with larger horizontal
dimensions a network of parallel horizontal conductors
should be installed as shown in IS 2309.

NOTE — Salient points even if less than 9 m apart should each
be provided with an air termination.

9.1.3 Horizontal air terminations should be coursed
along contours, such as ridges, parapets and edges of
flat roofs, and where necessary over flat surfaces in
such a way as to join each air termination to the rest
and should themselves form a closed network.

9.1.4 The layout of the network may be designed to
suit the shape of the roof and architectural features of
the buildings.

9.1.5 The air termination network should cover all
salient points of the structure.

9.1.6 All metallic finials, chimneys, ducts, vent pipes,
railings, gutters and the like, on or above the main
surface of the roof of the structure shall be bonded to,
and form part of, the air termination network. If
portions of a structure vary considerably in height, any
necessary air termination or air termination network
of the lower portions should, in addition to their own
conductors, be bonded to the down conductors of the
taller portions.

9.1.7 All air terminals shall be effectively secured
against overturning either by attachment to the object
to be protected or by means of substantial braces and
fixings which shall be permanently and rigidly attached
to the building. The method and nature of the fixings
should be simple, solid and permanent, due attention
being given to climatic conditions and possible
corrosion.

9.2 Down Conductors

The number and spacing of down conductors shall
largely depend upon the size and shape of the building
and upon aesthetic considerations. The minimum
number of down conductors may, however, be decided
on the following considerations:

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a) A structure having a base area not exceeding
1 00 m 2 may have one down conductor only if
the height of the air termination provides
sufficient protection. However, it is advisable
to have at least two down conductors except
for very small buildings.

b) For structures having a base area exceeding
100 m 2 , the number of down conductors
required should be worked out as follows:

1) One for the first 100 m 2 plus one more
for every additional 300 m 2 or part
thereof, or

2) One for every 30 m of perimeter.
The small of the two shall apply.

c) For a structure exceeding 30 m in height
additional consideration as given in IS 2309
shall apply.

9.2.1 Down conductors should be distributed round
the outside walls of the structure. They shall preferably
be run along the corners and other projections, due
consideration being given to the location of air
terminations and earth terminations. Lift shaft shall not
be used for fixing down conductors.

9.2.2 It is very important that the down conductors shall
follow the most direct path possible between the air
termination and the earth termination, avoiding sharp
bends, upturns and kinks. Joints shall as far as possible
be avoided in down conductors. Adequate protection
may be provided to the conductors against mechanical
damage. Metal pipes should not be used as protection
for the conductors.

9.2.3 Metal pipes leading rainwater from the roof to
the ground may be connected to the down conductors
but cannot replace them. Such connections shall have
disconnecting joints for testing purposes.

9.2.4 Where the provision of suitable external routes
for down conductors is impracticable or inadvisable,
as in buildings of cantilever construction, from the first
floor upwards, down conductors may be used in an air
space provided by a non-metallic non-combustible
internal duct. Any covered recess not smaller
than 75 mm x 15 mm or any vertical service duct
running the full height of the building may be used for
this purpose, provided it does not contain an
unarmoured or non-metal- sheathed cable.

9.2.5 Any extended metal running vertically through
the structure should be bonded to the lightning
conductor at the top and the bottom unless the clearance
are in accordance with IS 2309 for tall structures.

9.2.6 A structure on bare rock, should be provided with
at least down conductors equally spaced.

9.2.7 In deciding on the routing of the down conductor,
its accessibility for inspection, testing and maintenance
should be taken into account.

9.3 Joints and Bonds

9.3.1 Joints

The lightning protective system shall have as few joints
in it as necessary. In the down conductors below ground
level these shall be mechanically and electrically
effective and shall be so made as to exclude moisture
completely. The joints may be clamped, screwed,
bolted, crimped, riverted or welded. With overlapping
joints the length of the overlap should not be less
than 20 mm for all types of conductors. Contact
surfaces should first be cleaned and then inhibited from
oxidation with a suitable non-corrosive compound.
Joints of dissimilar metal should be suitably protected
against bimetallic action and corrosion.

9.3.1.1 In general, joints for strips shall be tinned,
soldered, welded or brazed and at least double-riveted,
welded or brazed and at least double-riveted. Clamped
or bolted joints shall only be used on test points or on
bonds to existing metal, but joints shall only be of the
clamped or screwed type.

9.3.2 Bonds

External metal on or forming part of a structure may
have to discharge the full lightning current. Therefore,
the bond to the lightning protective system shall have
a cross-sectional area not less than that employed for
the main conductors. On the other hand, internal metal
is not so vulnerable and its associated bonds are, at
most, only likely to carry a portion of the total lightning
current, apart from their function of equalizing
potential. These latter bonds may, therefore, be smaller
in cross-sectional area than those used for the main
conductors. All the bonds should be suitably protected
against corrosion. Bonds shall be as short as possible.

9.4 Testing Points

Each down conductor shall be provided with a testing
point in a position convenient for testing but
inaccessible for interference. No connection, other than
one direct to an earth electrode, shall be made below a
testing point. Testing points shall be phosphorbronze,
gunmetal, copper or any other suitable material.

9.5 Earth Terminations

Each down conductor shall have an independent earth
termination. It should be capable of isolation for testing
purposes. Suitable location for the earth termination
shall be selected after testing and assessing the specific
resistivity of the soil and with due regard to reliability
of the sub-soil water to ensure minimum soil moistness.

PART 1 GENERAL AND COMMON ASPECTS

167

SP 30 : 2010

9.5.1 Water pipe system should not be bonded to the
earth termination system. However, if adequate
clearance between the two cannot be obtained, they
may be effective bonded and the bonds should be
capable of isolation and testing. The gas pipes,
however, should in no case be bonded to the earth
termination system.

9.5.2 It is recommended that all earth terminations
should be interconnected. Common earthing, besides
equalizing the voltage at various earth terminations also
minimizes any risk to it of mechanical damage. The
condition for limiting earthing resistance given in 12
does not apply and in such a case no provision need be
made for isolation in earth.

9.5.3 A structure standing on bare rock should be
equipped with a conductor encircling and fixed to the
structure at ground level and following reasonably
closely the contour of the ground. This conductor
should be installed so as to minimize any risk to it of
mechanical damage. The condition for limiting
earthing resistance given in 12 does not apply and in
such a case no provision need be made for isolation in
earth termination for testing. Where there is a risk to
persons or to valuable equipment, expert advice should
be sought.

9,6 Earth Electrodes

Earth electrodes shall be constructed and installed in
accordance with Part 1/Section 14 of the Code.

9.6.1 Earth electrodes shall consist of rods, strips or
plates. Metal sheaths of cables shall not be used as
earth electrodes.

9.6.2 When rods or pipes are used they should be driven
into the ground as close as practicable but outside the
circumference of the structure. Long lengths in sections
coupled by screwed connectors or socket joints can be
built up where necessary to penetrate the substrate of
low resistivity. Where ground conditions are more
favourable for the use of shorter lengths of rods in
parallel, the distance between the rods should
preferably be not less than twice the length of the rods.
The arrangement of earth electrodes are given in Fig. 24
of IS 2309.

9.6.3 When strips are used, these should be buried in
trenches or beneath the structure at a suitable depth,
but not less than 0.5 m deep to avoid damage by
building or agricultural operations. The strips should
preferably be laid radially in two or more directions
from the point of connection to a down conductor. But
if this is not possible they may extend in one direction
only. However, if the space restriction requires the strips
to be laid in parallel or in grid formation the distance
between two strips should not be less than 2 m.

9.6.4 When plate electrodes are used they shall be
buried into the ground so that the top edge of the plate
is at a depth not less than 1.5 m from the surface of the
ground. If two plate electrodes are to be used in parallel
the distance between the two shall not be less than 8 m.

9.6.5 In the neighbourhood of structure where high
temperatures are likely to be the encountered in the
sub-soil, for example brick kilns, the earth electrodes
may have to be installed at such a distance from the
structure where the ground is not likely to be dried
out.

9.7 Fasteners

Conductors shall be securely attached to the building
or other object to be protected by fastners which shall
be substantial in construction, not subject to breakage,
and shall be made of galvanized steel or other suitable
material. If fasteners are made of steel, they should be
galvanized to protect them against corrosion. If they
are made of any other material suitable precautions
should be taken to avoid corrosion. Some samples of
fasteners are shown in IS 2309.

9.8 Earth Resistance

Each earth termination should have a resistance in
ohms to earth not exceeding numerically the product
of 10 and the number of earth terminations to be
provided. The whole of the lightning protective system
should have a combined resistance to earth not
exceeding 10 ohms before any bonding has been
effected to metal in or on the structure or to surface
below ground.

10 ISOLATION AND BONDING

10.0 When a lightning protective system is struck with
a lightning discharge, its electrical potential with
respect to earth is raised, and unless suitable
precautions are taken, the discharge may seek
alternative paths to earth by side flashing to other metal
in the structure. Side flashing may be avoided by the
following two methods:

a) Isolation, and

b) Bonding.

10.1 Isolation

Isolation requires large clearances between the
lightning protective system and other metal parts in
the structure. To find out the approximate clearances,
the following two factors should be taken into account:

a) The resistive voltage drop in the earth
termination, and

b) The inductive voltage drop in the down
conductors.

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10.1*1 The resistive voltage drop requires a clearance
of 0.3 m ohm of earthing resistance while the inductive
voltage drop requires a clearance of 1 m for each 15m
of structure height. For two or more down conductors
with a common air termination this distance should be
divided by the number of down conductors. The total
clearance required is the sum of the two distances and
may be expressed by the following simple equation:

D = 03R

I5n

where

D
R

= required clearance in m;

- combined earthing resistance of the earth
termination, in ohms;

= structure height in m, and

= number of down conductors connected to a
common air termination.

10.1.2 The above clearance may be halved if a slight
risk of occurrence of a side flash can be accepted.

10.1.3 The drawback of isolation lies in obtaining and
maintaining the necessary safe clearance and in
ensuring that isolated metal has no connection via the
water pipes or other services with the earth. In general,
isolation can be practised only in small buildings.

10.2 Bonding

In structures which contain electrically continuous
metal, for example, a roof, wall, floor or covering, this
metal, suitably bonded, may be used as part of the
lightning protective system, provided the amount and
arrangement of the metal render it suitable for use in
accordance with 9.

10.2.1 If a structure is simply a continuous metal frame
without external coverings it may not require any air
termination or down conductors provided it can be
ensured that the conducting path is electrically
continuous and the base of the structure is adequately
earthed.

10.2.2 A reinforced concrete structure or a reinforced
concrete frame structure may have sufficiently low
inherent resistance to earth to provide protection
against lightning and if connections are brought out
from the reinforcement at the highest points during
construction, a test may be made to varify this at the
completion of the structure.

10.2.3 If the resistance to earth of the steel frame of a
structure or the reinforcement of a reinforced concrete
structure is found to be satisfactory a suitable air
termination should be installed at the top of the
structure and bonded to the steel frame or to the

reinforcement. Where regular inspection is not
possible, it is recommended that a corrosion resistant
material be used for bonding to the steel or to the
reinforcement and this should be brought out for
connection to the air termination. Down conductor and
earth terminations will, of course, be required if the
inherent resistance of the structure is found to be
unsatisfactory when tested.

10.2.4 Where metal exists in a structure as
reinforcement which cannot be bonded into a
continuous conducting network, and which is not or
cannot be equipped with external earthing connections,
its presence should be disgarded. The danger
inseparable from the presence of such metal can be
minimized by keeping it entirely isolated from the
lightning protective system.

10.2.5 Where the roof structure is wholly or partly
covered by metal, care should be taken that such metal
is provided with a continuous conducting path to earth.

10.2.6 In any structure, metal which is attached to the
outer surface or projects through a wall or a roof and
has insufficient clearance from the lightning protective
system, and is unsuitable for use as part of it, should
preferably be bonded as directly as possible to the
lightning protectives system. If the metal has
considerable length (for example, cables, pipes, gutters,
rain-water pipes, stair-ways, etc) and runs
approximately parallel to a down conductor or bond,
it should be bonded at each and but not below the test
point. If the metal is in discontinuous lengths, each
portion should be bonded to the lightning protective
system; alternatively, where the clearance permits, the
presence of the metal may be disregarded.

10.-2,7 Bonding of metal entering or leaving a structure
in the form of sheathing or armouring of cable, electric
conduit, telephone, steam, compressed air or other
services with earth termination system, should be
avoided. However, if they are required to be bonded,
the bonding should be done as directly as possible to
the earth termination at the point of entry or exist
outside the structure on the supply side of the service.
The gap pipes should in no case be bonded with other
metal parts. However, water pipes may be bonded to
other metal parts, if isolation and adequate clearance
cannot be obtained. In this operation all the statutory
rules or regulations which may be in force should be
followed and the competent authority should be
consulted for providing lightning protection in such
cases.

10.2.8 Masses of metal in a building, such as bell-frame
in a tower, should be bonded to the nearest down
conductor by the most direct route available.

10.2.9 Metal clading or curtain walling having a

PART 1 GENERAL AND COMMON ASPECTS

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SP 30 : 2010

continuous conducting path in all directions may be
used as part of a lightning protective system.

10.2.10 In bonding adjacent metalwork to the lightning
protective system careful consideration should be given
to the possible effects such bonding would have upon
metalwork which may be cathodically protected.

11 PROTECTION OF SPECIAL STRUCTURES

For guidance on design of lightning protection systems
for special structures, reference shall be made to
IS 2309. Guidance for the appropriate authorities shall
also be obtained.

12 INSPECTION AND TESTING

12.1 Inspection

All lightning protective systems shall be examined by
a competent engineer after completion, alteration or
extensions, in order to verify that they are in accordance
with the recommendations of the Code. A routine
inspection shall be made at least once a year.

12.2 Testing

12.2.1 On completion of the installation or of any
modification, the resistance of each earth termination
or section thereof, shall, if possible, be measured and
the continuity of all conductors and the efficiency of
all bonds and joints shall be verified.

12.2.2 Normally annual measurement of earth resistance
shall be carried out but local circumstances in the light
of experience may justify increase or decrease in this
interval but it should not be less than once in two years.
In the case of structures housing explosives or flammable
materials, the interval shall be six months.

12.2.3 Earth resistance shall be measured in accordance
with Part 1/Section 14 of the Code.

12.2.4 The actual procedure adopted for the test shall
be recorded in detail so that future tests may be carried
out under similar conditions. The highest value of
resistance measured shall be noted as the resistance of
the soil and details of salting or other soil treatment,
should be recorded.

12.2.5 The record shall also contain particulars of the
engineer, contractor or owner responsible for the
installation or upkeep or both of the lightning protective
system. Details of additions or alterations to the system,
and dates of testing together with the test results and
reports, shall be carefully recorded.

12.3 Deterioration

If the resistance to earth of a lightning protective system
or any section of it exceeds the lowest value obtained
at the first installation by more than 100 percent,
appropriate steps shall be taken to ascertain the causes
and to remedy defects, if any.

12.4 Testing Continuity and Efficacy of Conductors
and Joints

12.4.1 The ohmic resistance of the lightning protective
system complete with air termination, but without the
earth connection should be measured and this should
be a fraction of an ohm. If it exceeds 1 ohm, then there
shall be some fault either electrical or mechanical,
which shall be inspected and the defect rectified.

12.4.2 For this system is best divided into convenient
sections at testing points by suitable joints. A
continuous current of about 10 A shall be passed
through the portion of the system under test and the
resistance verified against its calculated or recorded
value. Suitable portable precision testing sets for this
purposes should be used.

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SECTION- 16 PROTECTION AGAINST VOLTAGE SURGES

FOREWORD

A sudden change in the established operating
conditions in an electrical network causes transient
phenomena to occur. Transients may be generated
outside of the home or business by lightning, other
utility customers, animals, and even normal utility
switching operations. Inside the home or business,
transients are generated by motors starting and
stopping, flourescent lighting, copiers, vending
machines, welders, and many other sources. In a dry
environment, electrical charges accumulate and create
a very strong electrostatic field. Protection to mitigate
the larger transients coming from outside the home or
business, and point-of-use surge protection for
equipment sensitive to transients generated within the
building need to be considered.

Assistance for this Section has been derived from
IEC 61643-12-2008 'Low-voltage surge protective
devices — Part 12: Surge protective devices connected
to low-voltage power distribution systems — Selection
and application principles'.

1 SCOPE

1.1 This Part 1/Section 16 covers the protection
requirements in low voltage electrical installation of
buildings.

1.2 This part does not cover the primary protection
against lightning which is covered under Part 1/
Section 15.

2 REFERENCES

A list of Indian Standards relevant to protection against
voltage surges is given at Annex A.

3 TERMINOLOGY

The definitions given in Part 1 /Section 2 of this Code
and the following shall apply.

3.1 Continuous Operating Current (/ c ) — Current
that flows in an SPD when supplied at its permament
full withstand operating voltage (U c ) for each mode. I c
corresponds to the sum of the currents that flow in the
SPD's protection component and in all the internal
circuits connected in parallel.

3.2 Disruptive Discharge — The phenomena
associated with the failure of insulation under electrical
stress which include a collapse of voltage and the
passage of current; the term applies to electrical
breakdown in solid, liquid and gaseous dielectrics and
combinations of these.

NOTE — A disruptive discharge in a solid dielectric produces
permanent loss of electrical strength; in a liquid or gaseous
dielectric the loss maybe only temporary.

3.3 Flashover — A disruptive discharge over a solid
surface.

3.4 Impulse — A unidirectional wave of voltage or
current which, without appreciable oscillations, rises
rapidly to a maximum value and falls, usually less
rapidly, to zero with small, if any, loops of opposite
polarity. The parameters which define a voltage or
current impulse are polarity, peak value, front time,
and time to half value on the tail.

3.5 Impulse Current (/ imp ) — It is defined by a current
peak value / peak and the charge a tested according to
the test sequence of the operating duty test. This is
used for the classification of the SPD for Class I test.

3.6 Maximum Continuous Operating Voltage (U c )
— The maximum r.m.s. or d.c. voltage which may be
continuously applied to the SPDs mode of protection.
This is equal to the rated voltage.

3.7 Maximum Discharge Current for Class II Test
(J Max ) — Crest value of a current through the SPD
having an 8/20 waveshape and magnitude according
to the test sequence of the Class II operating duty test.
W is g reater than 7 n-

3.8 Nominal Discharge Current (/ n ) — The crest
value of the current through the SPD having a current
waveshape of 8/20. This is used for the classification
of the SPD for the Class II test and also for
pre-conditioning of the SPD for Class I and II tests.

3.9 Puncture — A disruptive discharge through a solid.

3.10 Rated Network Voltage (U n ) — The rated voltage
of the network.

3.11 Residual Voltage (t/ res ) — The peak value of the
voltage that appears between the terminals of an SPD
due to the passage of discharge current.

3.12 Sparkover of an Arrester — A disruptive
discharge between the electrodes of the gaps of an
arrester.

3.13 Surge Arrester — A device designed to protect
electrical apparatus from high transient voltage and to
limit the duration and frequently the amplitude of
follow-current. The term 'surge arrester' includes any
external series gap which is essential for the proper
functioning of the device as installed for service,
regardless of whether or not it is supplied as an integral
part of the device.

PART 1 GENERAL AND COMMON ASPECTS

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SP 30 : 2011

NOTE — Surge arresters are usually connected between the
electrical conductors of a network and earth although they may
sometimes be connected across the windings of apparatus or
between electrical conductors.

3.14 Surge Protective Device (SPD) — A device that
limits transient voltage surges and runs current waves
to ground to limit the amplitude of the voltage surge
to a safe level for electrical installations and
equipment. Surge protective devices (SPDs) are used
to protect, under specified conditions, electrical
systems and equipment against various overvoltages
and impulse currents, such as lightning and switching
surges.

3.15 Switching Overvoltages — These stresses are
usually lower than lightning stresses in terms of peak
current and voltage, but may have longer duration.
However, in some cases, particularly deep inside a
structure or close to switching overvoltage sources, the
switching stress can be higher than the stresses caused
by lightning. The energy related to these switching
surges needs to be known to permit the choice of
appropriate SPDs. The time duration of the switching
surges, including transients due to faults and fuse
operations, can be much longer than the lightning surge
duration.

3.16 Temporary Overvoltages (U T0X ) — Any SPD
can be exposed to a temporary overvoltage U T0W during
its lifetime that exceeds the maximum continuous
operating voltage of the power system. A temporary
overvoltage has two dimensions, magnitude and time.
The time duration of the overvoltage primarily depends
upon the earthing of the supply system (this includes
both the high- voltage supply system as well as the low-
voltage system to which the SPD is connected). In
determining the temporary overvoltages, consideration
should be given to the maximum continuous operating
voltage of the power system (l/ cs ).

3.17 Voltage Protection Level (U p ) — A parameter
that characterizes the performance of the SPD in
limiting the voltage across its terminals, which is
selected from a list of preferred values. This value shall
be greater than the highest value of the measured
limiting voltages.

The most common values for a 230/400 V network
are:

1 kV -1.2 kV -1.5 kV -1.8 kV - 2 kV - 2.5 kV

3.18 Voltage Surge — A voltage impulse or wave
which is superposed on the rated network voltage (see
Fig. 1). A voltage surge disturbs equipment and causes
electromagnetic radiation. The duration of the voltage
surge (T) causes a surge of energy in the electrical
circuits which is likely to destroy the equipment.

4 GENERAL

4.1 Voltage Surges

A voltage surge disturbs equipment and causes
electromagnetic radiation. Furthermore, the duration
of the voltage surge (T) causes a surge of energy in the
electrical circuits which is likely to destroy the
equipment. There are four types of voltage surges
which may disturb electrical installations and loads:

a) Atmospheric voltage surges,

b) Operating voltage surges,

c) Transient overvoltage at industrial frequency,
and

d) Voltage surges caused by electrostatic
discharge,

4.1.1 Atmospheric Voltage Surges

Atmospheric voltage surges, that is, lightning, comes
from the discharge of electrical charges accumulated
in the cumulo-nimbus clouds which form a capacitor
with the ground. Storm phenomena cause serious
damage. Lightning is a high frequency electrical
phenomenon which produces voltage surges on all
conductive elements, and especially on electrical loads
and wires. Protection against lightning is covered under
Part 1 /Section 15.

4.1.2 Operating Voltage Surges

A sudden change in the established operating
conditions in an electrical network causes transient
phenomena to occur. These are generally high
frequency or damped oscillation voltage surge waves
(see Fig. 1).

They are said to have a slow gradient — their frequency
varies from several ten to several hundred kilohertz.

Operating voltage surges may be created by:

The opening of protection devices (fuse, circuit-
breaker), and the opening or closing of control devices
(relays, contactors, etc).

Inductive circuits due to motors starting and stopping, or
the opening of transformers such as MVILV substations

Capacitive circuits due to the connection of capacitor
banks to the network

All devices that contain a coil, a capacitor or a transformer
at the power supply inlet: relays, contactors, television
sets, printers, computers, electric ovens, filters, etc.

4.1.3 Transient Overvoltages at Industrial Frequency

These overvoltages (see Fig. 2) have the same
frequency as the network (50, 60 or 400 Hz); and can
be caused by:

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VOLTAGE

LIGHTING TYPE IMPULSE

( duration = 100JL/S)

(Operating impulse)
type dumped ring wave
F-IQQkHzl MHz)

Trms

Fig. 1 Voltage Surge Examples

VOLTAGE (V or kV)

50%

Voltage surge duration (T)

Fig. 2 Transient Overvoltage at Industrial Frequency

a) Phase/frame or phase/earth insulating faults on
a network with an insulated or impedant neutral,
or by the breakdown of the neutral conductor.
When this happens, single phase devices will
be supplied in 400 V instead of 230 V.

b) A cable breakdown, for example a medium
voltage cable which falls on a low voltage line.

c) The arcing of a high or medium voltage
protective spark-gap causing a rise in earth
potential during the action of the protection
devices. These protection devices follow
automatic switching cycles which will
recreate a fault, if it persists,

4.1.4 Voltage Surges Caused by Electrical Discharge

In a dry environment, electrical charges accumulate
and create a very strong electrostatic field. For example,
a person walking on carpet with insulating soles will
become electrically charged to a voltage of several

kilovolts. If the person walks close to a conductive
structure, he will give off an electrical discharge of
several amperes in a very short rise time of a few
nanoseconds. If the structure contains sensitive
electronics, a computer for example, its components
or circuit boards may be damaged.

4.2 Main Characteristics of Voltage Surges

The surge protective device includes one or several
non-linear components. The surge protective device
eliminates voltage surges:

a) In common mode : Phase to earth or neutral to
earth.

b) In differential mode: Phase to phase or phase
to neutral.

When a voltage surge exceeds the U c threshold, the
surge protective device (SDP) conducts the energy to
earth in common mode. In differential mode the

PART 1 GENERAL AND COMMON ASPECTS

173

SP 30 : 2011

diverted energy is directed to another active conductor
(see Annex B). Table 1 sums up the main characteristics
of voltage surges.

The surge protective device has an internal thermal
protection device which protects against burnout at its
end of life. Gradually, over normal use after
withstanding several voltage surges, the SPD degrades
into a conductive device. An indicator informs the user
when end-of-life is close.

Some surge protective devices have a remote
indication. In addition, protection against short-circuits
is ensured by an external circuit-breaker.

4.3 Basic Functions of Surge Protection Devices
(SPDs)

The functions of surge protection devices are as
follows:

a) In power systems in the absence of surges:
the SPD shall not have a significant influence
on the operational characteristics of the
system to which it is applied.

b) In power systems during the occurrence of
surges: the SPD responds to surges by
lowering its impedance and thus diverting
surge current through it to limit the voltage
to its protective level. The surges may initiate
a power follow current through the SPD.

c) In power systems after the occurrence of
surges: the SPD recovers to a high-impedance
state after the surges and extinguishes any
possible power follow current.

The characteristics of SPDs are specified to achieve
the above functions under normal service conditions.
The normal service conditions are specified by the
frequency of the power-system voltage, load current,
altitude (that is, air pressure), humidity and ambient
air temperature.

4.4 Surge Protective Device Tests

4.4.1 Three test classes are defined for surge protective

devices connected to low-voltage power distribution
systems:

a) Class I tests: They are conducted using
nominal discharge current (/ n ), voltage
impulse with 1.2/50 us waveshape and
impulse current / imp .

The Class I tests is intended to simulate
partial conducted lightning current impulses.
SPDs subjected to Class I test methods are
generally recommended for locations at
points of high exposure, for example line
entrances to buildings protected by lightning
protection systems.

b) Class II tests: They are conducted using
nominal discharge current (7 n ), voltage
impulse with 1.2/50 us waveshape.

c) Class HI tests: They are conducted using the
combination waveform (1.2/50 and 8/20 us).

4.4.2 SPDs tested to Class II or III test methods are
subjected to impulses of shorter duration. These SPDs
are generally recommended for locations with lesser
exposure. SPDs are classified in the following three
categories:

a) Type 1 : SPD tested to Class I,

b) Type 2: SPD tested to Class II, and

c) Type 3 : SPD tested to Class III.

4.4.3 The SPD is characterised by J7 C , l/ p , I n and 7 Max
(see Fig. 3).

4.4.4 To test the surge arrester, standardized voltage
and current waves have been defined Voltage wave for
example, 1.2/50 us (see Fig. 4) Current wave for
example, 8/20 us (see Fig. 5).

Other possible wave characteristics 4/10 jus, 10/1 000 us,
30/60 us, 10/350 us.

Comparison between different surge protective devices
must be carried out using the same wave characteristics,
in order to get relevant results.

Table 1 Characteristics of Voltage Surges
(Clause 4.2)

SI No.

(1)

Type of Voltage Surge

(2)

Voltage Surge Coefficient

(3)

Duration

(4)

Front Gradient or
Frequency

(5)

Industrial frequency (insulation fault)

<1.7

Long

30 to 1 000 ms

Industrial frequency
(50-60-400 Hz)

ii)
iii)

Operation
Atmospheric

2 to 4
>4

Short

1 to 100 ms

Very short

1 to 100 us

Average
1 to 200 kHz
Very high

1 to 1 000 kV/^is

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<1 RtA

Fig. 3 Voltage/Current Characteristics

Fig. 4 1.2/50 ps Wave

Fig. 5 8/20 jus Wave

5 SELECTION OF PROTECTION DEVICE

5.1 For the selection of protection device, the value of
the equipment to be protected should be estimated. To
estimate its value, the cost of the equipment in financial
terms and the economic impact if the equipment goes
down needs to be taken into account. Protection devices
shall be selected according to their environmental
conditions and the acceptable failure rate of the
equipment and the protective device. These factors
include equipment to be protected and system
characteristics, insulation levels, overvoltages, method
of installation, location of SPDs, co-ordination of
SPDs, failure mode of SPDs and equipment failure
consequences etc.

5.2 Rated residual voltage i/ res of protection devices
must not be higher than the value in the voltage impulse
withstand category II (see Table 2).

5.3 Choice of Disconnector

The disconnector is necessary to ensure the safety of
the installation.

One of the surge arrester parameters is the maximum
current (/ Max 8/20 jis wave) that it can withstand without
degradation. If this current is exceeded, the surge
arrester will be destroyed; it will be permanently short
circuited and it is essential to replace it.

The fault current must therefore be eliminated by an
external disconnector installed upstream.

The disconnector provides the complete protection
required by a surge arrester installation, that is:

a) it must be able to withstand standard test
waves:

1 ) it must not trip at 20 impulses at 7 n , and

2) it can trip at 7 Max without being destroyed.

b) the surge arrester disconnects if it short-
circuits.

Surge arrester/disconnection circuit breaker
correspondence table are generally supplied by
manufacturers.

5.4 Additional Requirements

5.4.0 Depending upon the application of the SPD,
additional requirements may be needed such as
protection of SPDs against direct contact, safety in the
event of SPD failures etc. An SPD may fail subjected to
a surge greater than its designed maximum energy and
discharge current capability. Failure modes of SPDs are
usually divided into open-circuit and short circuit mode.

5.4.1 End-of-life Indication of the Surge Arrester

In the open-circuit mode the system to be protected is
no longer protected. In this case, failure of an SPD is
usually difficult to detect since it has almost no
influence on the system. To ensure that the failed SPD
is replaced before the next surge, an indication function
may be required. Various indication devices are
provided to warn the user that the loads are no longer
protected against voltage surges. Many surge arresters
have a light indicating that the module is in good
working order.

5.4.2 Use of Disconnecting Devices

In the short-circuit mode, the system is severely
influenced by the failed SPD. The short-circuit current
flows through the failed SPD from the power source.
Energy dissipated during the conduction of short circuit
current may be excessive and cause a fire hazard. The
short-circuit withstand capability test of covers this
problem. In cases where the system to be protected
has no suitable device to disconnect the failed SPD

PART 1 GENERAL AND COMMON ASPECTS

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SP 30 : 2011

Table 2 Selection of Equipment for the Installation
(Clause 5.2)

SI No.

Nominal Voltage of the Installation

Required Impulse Withstand Voltage for

->*^.

__^t^, ,„

Three-Phase

Single-Phase

Equipment at the

Appliances

Specially Protected

Systems

System with
Middle Point

Origin of the
Installation

Equipment

(Impulse Withstand

Category IV)

Category III)

Category I)

(1)

(2)

(3)

(4)

(5)

(6)

(7)

120-240

2.5

1.5

0.8

ii)

230/400

277/480

(see Note 1)

1.5

400/690

—

2.5

iv)

1000

—

Values subject to system engineers

NOTES

1 For voltages to earth higher than 300 V, the impulse withstand voltage corresponding to the next higher voltage in col (2) applies.

2 Category I is addressed to particular equipment engineering.

3 Category II is addressed to equipment for connection to the mains.

4 Category III is addressed to installation material and some special products.

5 Category IV is addressed to supply authorities and system engineers.

from its circuit, a suitable disconnecting device may
be required to be used in conjunction with a SPD which
has a short-circuit failure mode.

6 INSTALLATION OF SURGE PROTECTION
DEVICES

When installing surge protective devices, several
elements must be considered, such as the earthing
system, positioning with respect to residual current
devices, the choice of disconnection circuit-breakers
and cascading.

6.1 Protection Devices According to the Earthing
System

a) Common mode overvoltage: Basic protection
involves the installation of a common mode
surge arrester between phase and PE or phase
and PEN, whatever type of earthing system
is used.

b) Differential mode overvoltage: In the IT and
TN-S earthing systems, earthing the neutral
leads to dissymmetry due to earthing
impedances, which causes differential mode
voltages to appear, whereas the overvoltage
induced by a lightning strike is a common
mode voltage.

6.2 Internal Architecture of Surge Arresters

a) 2P, 3P, 4P surge arresters (see Fig. 6):

They provide protection against common-mode
overvoltages only and are appropriate for TN-C
and IT earthing systems.

Fig. 6 2P, 3P, 4P Surge Arresters

b) 1P+N, 3P+N surge arresters (see Fig. 7):

They provide protection against common-mode
and differential-mode overvoltages and are
appropriate for TT, TN-S, and IT earthing systems.

Fig. 7 1P+N, 3P+N Surge Arresters
c) Single-pole (IP) surge arresters (see Fig. 8).

They are used to satisfy the demand of different
assemblies (according to the manufacturer's
instructions) by supplying only one product.

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However, special dimensioning will be required for
N-PE protection.

Fig. 8 Connection Example

6.3 Installation of Protection Devices

The overvoltage protection study of an installation may
show that the site is highly exposed and that the
equipment to be protected is sensitive. The surge
arrester must be able to discharge high currents and
have a low level of protection. This dual constraint
cannot always be handled by a single surge arrester. A
second one will therefore be required (see Fig. 9).

The first device, P x (incoming protection) will be
placed at the incoming end of the installation.

Fig. 9 Cascading of Surge Arresters

Its purpose will be to discharge the maximum amount
of energy to earth with a level of protection = 2 000 V
that can be withstood by the electrotechnical equipment
(contactors, motors, etc).

The second device (fine protection) will be placed in a
distribution enclosure, as close as possible to the
sensitive loads. It will have a low discharge capacity
and a low level of protection that will limit overvoltages
significantly and therefore protect sensitive loads
( = 1500 V). Cascading protection requires a minimum

distance of at least 10 m between the two protection
devices. This is valid whatever the field of application,
domestic, tertiary or industrial.

In Fig. 10, the fine-protection device P 2 is installed in
parallel with the incoming protection device P l .

If the distance L is too small, at the incoming
overvoltage, P 2 with a protection level of U 2 = 1 500 V
will operate before P x with a level of U x = 2 000 V. P 2
will not withstand an excessively high current. The
protection devices must therefore be coordinated to
ensure that P x activates before P 2 . This depends on
length L of the cable, that is the value of the self-
inductance between the two protection devices. This
self-inductance will block the current flow to P 2 and
cause a certain delay, which will force P x to operate
before P 2 . A metre of cable gives a self inductance of
approximately 11 JH.

The rule AU= Ldi/dt causes a voltage drop of
approximately 100 V/m/kA, 8/20 jus wave.

For L = 10 m, we get UL X = UL 2 =1 000 V.

To ensure that P 2 operates with a level of protection of
1 500 Y requires

U x = UL X + UL 2 +£/ 2 =1000V+1000V+l 500 V
= 3 500 V.

Consequently, P x operates before 2 000 V and therefore
protects P 2 .

NOTE — If the distance between the surge arrester at the
incoming end of the installation and the equipment to be
protected exceeds 30 m, cascading the surge arresters is
recommended, as the residual voltage of the surge arrester may
rise to double the residual voltage at the terminals of the
incoming surge arrester; as in the above example, the fine
protection surge arrester must be placed as close as possible to
the loads to be protected. It should be ensured that the
connection between the surge arrester and its disconnection
circuit breaker does not exceed 50 cm.

6.4 Surge Protection Device Installation Conditions

a) According to supply system configuration:
The maximum continuous operating voltage
U c of SPDs shall be equal to or higher than
shown in Table 3.

b) At the origin of the installation: If the surge
arrester is installed at the source of an
electrical installation supplied by the utility
distribution network, its rated discharge
current may be lower than 5 kA.

If a surge arrester is installed downstream from
an earth leakage protection device, an RCD of
the S type, with immunity to impulse currents
of less than 3 kA (8/20 jus), must be used.

c) Protection against overcurrent at 50 Hz and
consequences of a SPD failure: Protection

PART 1 GENERAL AND COMMON ASPECTS

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SP 30 : 2011

UL1

r UL2 P

Fig. 10 Coordination of Surge Arresters

against SPDs short-circuits is provided by the
overcurrent protective devices which are to
be selected according to the maximum

recommended rating for the overcurrent
protective device given in the manufacturer's
SPD instructions.

Table 3 Minimum Required U c of the SPD Dependent on Supply System Configuration

(Clause 6.4)

SI SPDs Connected

System Configuration of Distribution Network

_^*^

TN-C

TN-S IT with Distributed
Neutral

IT without
Distributed Neutral

(1) (2)

(3)

(4)

(5) (6)

(7)

i) Line conductor and neutral

1.1 Uo

Not applicable

1.1 Uo 1.1 Uo

Not applicable

conductor

ii) Each line conductor and PE

1.1 Uo

Not applicable

1.1 Uo 3 Uo

Line-to-the voltage

conductor

(see Note 3)

iii) Neutral conductor and PE

Not applicable

Uo(l) Uo

Not applicable

conductor

(see Note 3)

iv) Each line conductor and PEN

Not applicable

1.1 Uo

NA NA

Not applicable

conductor

(see Note 3)

NOTES

1 Uo is the line-to-neutral voltage of the low-voltage system.

2 These values are related to worst case fault conditions, therefore the tolerance of 10 percent is not taken into account.

3 In extended IT systems, higher values of U c may be necessary.

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ANNEX A
(Clause 2)

LIST OF INDIAN STANDARDS RELEVENT TO PROTECTION AGAINST VOLTAGE SURGES

IS No.
732 : 1989

2309 : 1989
11548: 1986

15086 (Part 1) :
2001

15086 (Part 3) :

2003/IEC

60099-3 : 1990
15086 (Part 5):

2001/IEC

60099-5 : 1996

Title

Code of practice for electrical wiring

installations

Code of practice for the protection

of buildings and allied structures

against lightning

Capacitors for surge protection for

use in voltage system above 650 V

and upto 33 kV

Surge arresters: Part 1 Non-linear

resistor type gapped surge arresters

for ac systems

Surge arresters: Part 3 Artificial

pollution testing of surge arresters

Surge arresters: Part 5 Selection
and application recommendations

IS No.

QC 420100 :
1994 /IEC QC

420100 : 1991
QC 420101

: 1994 /IEC QC

420101 : 1991

QC 420102 :
1993 /IEC QC
420102 : 1991

Title

Varistors for use in electronic
equipment — Sectional specification
for surge suppression varistors
Varistors for use in electronic
equipment — Blank detail
specification for silicon carbide surge
suppression varistors assessment
level E

Varistors for use in electronic
equipment — Blank detail
specification for zinc oxide surge
suppression varistors — Assessment
level E

ANNEX B
(Clause 4.2)

DIFFERENT PROPAGATION MODES OF VOLTAGE SURGE

B-l COMMON MODE

Common mode voltage surges occur between the live
parts and the earth: phase/earth or neutral/earth
(see Fig. 11), They are especially dangerous for devices
whose frame is earthed due to the risk of dielectric
breakdown.

B-2 DIFFERENTIAL MODE

Differential mode voltage surges circulate between live
conductors: Phase to phase or phase to neutral
(see Fig. 12). They are especially dangerous for
electronic equipment, sensitive computer equipment, etc.

Fig. 1 1 Common Mode

Fig. 12 Differential Mode

PART 1 GENERAL AND COMMON ASPECTS

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SECTION 17 GUIDELINES FOR POWER-FACTOR I IMPROVEMENT

FOREWORD

The various advantages of maintaining a high power
factor of a system reflects on the national economy of
a country. The available resources are utilized to its
fullest possible extent. More useful power is available
for transmission and utilization without any extra cost.
Moreover, the life of individual apparatuses
considerably increased and the energy losses reduced.

Guidance to the consumers of electrical energy who
take supply of low and medium voltage for
improvement of power factor at the installation in their
premises is provided in this Section. The guidelines
provided are basically intended for installation
operating at voltages below 650 V. For higher voltage
installations, additional or more specific rules apply.

Assistance has been derived from IS 7752
(Part 1) : 1975 'Guide for the improvement of power
factor in consumer installations: Part 1 Low and
medium supply voltages'.

1 SCOPE

This Part 1 /Section 17 of the Code covers causes for
low power factor and guidelines for use of capacitors
to improve the same in consumer installations.

1.2 Specific guidelines, if any, for individual
installation on improvement of power factor are
covered in the respective sections of the Code.

2 REFERENCE

The following Indian Standard on power factor
improvement may be referred for details:

IS 7752 (Part 1) :
1975

3 GENERAL

Guide for the improvement of
power factor in consumer
installations: Part 1 Low and
medium supply voltages

3.1 Conditions of supply of electricity boards or
licensees stipulate the lower limit of power factor which
is generally 0.85 and consumer is obliged to improve
and maintain the power factor of his installation to
conform to these conditions.

3.1.1 When the tariffs of Electricity Boards and the
licensees are based on kVA demand or kW demand
with suitable penalty rebate for low high power factor,
improvement in the power factor would effect savings
in the energy bills.

3.2 Power factor is dependent largely on consumers'
apparatus and partly on system components such as

transformers, cables, transmission lines, etc. System
components have fixed parameters of inductance,
capacitance and resistance. The choice of these
components to bring up the power factor depends on
economics.

3.3 In case of ac supply, the total current taken by
almost every item of electrical equipment, except that
of incandescent lighting and most forms of resistance
heating, is made up of two parts, namely:

a) in-phase component of the current (active or
useful current) which is utilized for doing
work or producing heat; and

b) quadrature component of the current (also
called 'idle' or 'reactive' current) and used
for creating magnetic field in the machinery
or apparatus. This component is not
convertible into useful output.

4 POWER FACTOR

4.1 The majority of ac electrical machines and
equipment draw from the supply an apparent power
(kVA) which exceeds the required useful power (kW).
This is due to the reactive power (kVAR) necessary
for alternating magnetic field. The ratio of useful power
(kW) to apparent power (kVA) is termed the power
factor of the load. The reactive power is indispensable
and constitutes an additional demand on the system.

4.2 The power factor indicates the portion of the current
in the system performing useful work. A power factor
of unity (100 percent) denotes 100 percent utilization
of the total current for useful work whereas a power
factor of 0.70 shows that only 70 percent of the current
is performing useful work.

4.3 Principle Causes of Lower Power Factor

4.3.1 The following electrical equipment and apparatus
have a lower factor:

a) Induction motors of all types particularly
when they are underloaded,

b) Power transformers and voltage regulators,

c) Arc welders,

d) Induction furnaces and heating coils,

e) Choke coils and magnetic systems, and

f) Fluorescent and discharge lamps, neon signs,
etc.

4.3.2 The principal cause of a low power factor is due
to the reactive power flowing in the circuit. The reactive
power depends on the inductance and capacitance of
the apparatus.

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4.4 Effect of Power Factor to Consumer

4.4.1 The disadvantages of low power factor are as

follows:

a) Overloading of cables and transformer,

b) Decreased line voltage at point of application,

c) Inefficient operation of plant, and

d) Penal power rates.

4.4.2 The advantages of high power factor are as
follows:

a) Reduction in the current;

b) Reduction in power cost;

c) Reduced losses in the transformers and cables,

d) Lower loading of transformers, switchgears,
cables, etc;

e) Increased capability of the 'power system'
(additional load can be met without additional
equipment);

f) Improvement in voltage conditions and
apparatus performance; and

g) Reduction in voltage dips caused by welding
and similar equipment.

4.5 Economics of Power Factor Improvement

4.5.1 Static capacitors, also called static condensers,
when installed at or near the point of consumption,
provide necessary capacitive reactive power, relieve
distribution system before the point of its installation
from carrying the inductive reactive power to that
extent.

4.5.2 The use of the static capacitors is an economical
way of improving power factor on account of their
comparatively low cost, ease of installation loss
maintenance, low losses and the advantage of extension
by addition of requisite units to meet the load growth.
Installation of capacitors also improve the voltage
regulation and reduces amperes loading and energy
losses in the supply apparatus and lines.

4.5.3 When considering the economics connected with
power factor correction, it is most important to
remember that any power factor improving equipment
will, in general, compensate for losses and lower the
loadings on supply equipment, that is, cables,
transformers, switchgear, generating plant, etc.

4.5.4 The minimum permissible power factor
prescribed in the conditions of supply of Electricity
Boards or Licensees and the reduction in charges
offered in supply tariffs for further improvement of
power factor shall, along with other considerations such
as reduction of losses, etc, determine the kVAR
capacity of the capacitors to be installed.

4*5.5 In case of two port tariff with kVA demand
charged, the value of economic improved power factor
(cos <|> 2 ) may be obtained as follows:

Let the tariff be Rs. A per kVA of maximum demand
per annum plus Rs. P per kWh.

cos (^ is the initial power factor,

cos <t) 2 is the improved power factor after installing the
capacitors

The economic power factor cos (t> 2 is obtained from
the expression

cos0 = Jl -

where

B = total cost per kVAR per year of capacitor
installation inclusive of interest, depreciation
and maintenance.

NOTE — The explanation for the derivation of the
formula for economic power factor cos f 2 is given in
Annex A of IS 7752 (Parti).

5 USE OF CAPACITORS

5.1 In order to improve the power factor, the consumer
shall install capacitors where the natural power factor
of this installation is low.

5.2 The average values of the power factor for different
types of 3 phase electrical installations as measured
by one of major utilities in the country are given in
respective Sections of the Code.

5.3 Capacitors for power factor improvement may be
arranged as described in IS 7752 (Part 1). The
successful operation of power factor improvement
depends very largely on the positioning of the capacitor
on the system. Ideal conditions are achieved when the
highest power factor is maintained under all load
conditions.

5.4 Individual Compensation

Wherever possible the capacitor should be connected
directly across the terminals of the low power factor
appliance or equipment. This ensures the control to be
automatic through the same switching devices of the
apparatus of appliance.

5.5 Group Compensation

In industries where a large number of small motors or
other appliances and machines are installed and whose
operation is periodical it is economical to dispense with
individual installation of capacitors. A bank of
capacitors may be installed to connect them to the

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distribution centre of main bus-bars of the group of
machines.

5.6 Central Compensation

Capacitors may also be installed at a central point,
that is, at the incoming supply or service position. In
order to overcome problems of drawing leading
currents on light loads, these capacitors may be
operated manually or automatically as required. The
automatic control is preferred as it eliminates human
errors. Automatic operation may be arranged by
means of suitable relays in which a contractor controls
the capacitors bank and maintains the correct amount
of kVAR in the circuit.

5.7 Combined Compensation

Capacitors may be connected directly across the
terminals of higher capacity inductive appliances or
equipments, in addition to the capacitors with
Automatic Power Factor Correction Relay for Central
Compensation connected at the incoming supply or
service position

5.8 The methods of connecting power factor capacitors
to supply line and motors are given in Fig. 1 and Fig. 2.

6 SELECTION AND INSTALLATION OF
CAPACITORS

6.1 Capacitor current shall not exceed magnetization
current of the motor when directly connected across
motor terminals.

6.2 Capacitors shall not be connected directly across
motor terminals if solid state starters/soft starters are
used.

6.3 Capacitors shall not be connected directly to motor
terminals if variable speed drive is adopted.

6.4 Capacitors connected to same bus-bars discharge,
instantaneously to uncharged capacitors, at the time
of switching on, with high in-rush current. This shall
be taken care of while providing central compensation
with automatic power factor correction relay.

6.5 Harmonics may reduce life of capacitors.

6.6 Switching/controlling devices for capacitors shall
have required capacitor switching duty.

6.7 Chances of resonating shall be considered.

6.8 Energy loss/Power consumption of capacitors shall
be taken care of.

6.9 Capacitor banks shall be properly ventilated.

6.10 Chances of over voltage shall be looked into.

6.11 Resistors shall be provided across capacitor
terminals for discharging.

7 POWER FACTOR IMPROVEMENT AND
CAPACITOR RATING

For calculating the size of the capacitor for power factor
improvement reference should be made to Table 5 of
Part 1/Section 20 of the Code.

TO STARTER

TO STAR DELTA
STARTER

Fig. 1 Methods of Connecting Capacitors to Motors for Improvement of Power Factor
182 NATIONAL ELECTRICAL CODE

SF 30 : 2011

CIRCUIT BREAKER,
CONTACTOR, OR
FUSE SWITCH, AS
RECOMMENDED
( SUITABLE FOR
GROUP OPERATION )

060

A^^jX,-^

ISOLATOR SWITCH
X ^X „X TOBEOPENEDAT
NO LOAD (SUITABLE
FOR GROUP OPERATION)

11 t v/

HRC FUSE

Fig. 2 Methods of Connecting Capacitors to Supply Line for Improvement of Power Factor

FART 1 GENERAL AND COMMON ASPECTS

183

SP 30: 2011

SECTION 18 ENERGY EFFICIENCY ASPECTS

FOREWORD

Efficient use of energy inputs acquires added
significance since energy saved is energy generated.
Economic growth is desirable for developing countries
and energy is essential for economic growth. This
means commensurate input of energy is required.
However, due to the fact that our fossil fuel reserves
are limited, energy conservation is essential. Electrical
energy input is utilized in various industrial plants,
agricultural sector, commercial buildings and
establishments, in the form of mechanical motive
power, heating, lighting, air conditioning and
ventilation etc. The Indian Industrial Sector accounts
for half of the total commercial energy used in the
country. Energy conservation aims at eliminating the
waste of energy and minimization of losses. In this
context proper selection of electrical equipment
assumes greater importance. The Energy Conservation
Act, 2001, also emphasises the need of energy
conservation.

This Section provides guidance to the consumers of
electrical energy, with regard to the selection of
equipment from energy conservation point of view and
on energy audits.

1 SCOPE

This Part 1/Section 18 of the Code covers the aspects
to be considered for selection of equipment from
energy conservation point of view and guidance on
energy audit.

2 REFERENCE

The following Indian Standard has been referred to in
this Section:

IS No
IS 12615 : 2004

3 GENERAL

Title

Energy efficient induction motors
— Three phase squirrel cage

Energy conservation aims at eliminating wastage of
energy and minimizing losses. The major factors to be
looked into in this regard include system design,
selection of equipment, operation and maintenance
practices, capacity utilization factors etc. Improving
efficiency typically costs less than the energy tariffs.

In order to standardize and benchmark the level of
efficiency of various electrical and other energy
consuming equipment, the Bureau of Energy Efficiency
was instituted in March 2002. The standards and

labelling/rating standards for various equipment
proposed by Bureau of Energy Efficiency shall be
followed while selecting equipment. Provisions of the
Energy Conservation Act, 2001 may also be taken into
account.

4 EQUIPMENT SELECTION

The main criterion for equipment selection, from
energy conservation point of view, is that the power
loss has to be minimum. In other words the operating
efficiency should be high. Proper sizing of equipment
is essential to ensure optimum utilization of energy. It
is also necessary to avoid over rating or under rating
the equipment. It should be ensured that operating
power factor of equipment is high.

Most commonly encountered equipments in electrical
systems are mentioned below:

4.1 Motor

Motors should preferably be energy efficient motors,
conforming to IS 12615. Preferably, motors shall
conform to efficiency class 'eff V as per IS 12615 as
these are more efficient than motors with efficiency
class 'eff 2' . Motors with higher operating power factor
shall be considered during selection as this results in
lower current and consequently lower losses. Use of
variable speed drives will bring substantial energy
saving wherever different flow conditions/speeds are
encountered in the process industry. Use of variable
speed drives is a highly efficient means of achieving
flow control etc. as compared to throttling of valves,
dampers etc. or the use of stepped pulleys.

4.2 Transformers

While procuring transformers, normal loading shall be
indicated so as to optimize transformer efficiency to
be maximum at projected load for minimizing losses
under normal operating conditions. Losses should be
accounted while selecting equipment, by way of loss
capitalization or specifying the minimum acceptable
value for maximum efficiency.

4.3 Cables Equipment

Optimizing cable route/length can best reduce cable
losses. Though the losses can also be reduced by over
sizing the conductors, this is not recommended due to
the practical problems encountered with termination
of over sized cables.

4.4 Lighting

An efficient lighting system can substantially reduce

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the energy consumption. The selection criteria for
lighting shall include among other factors, luminaries
with light sources of higher luminous efficiency such
as tubular fluorescent as well as compact fluorescent
lighting. Street lighting and other tasks where colour
rendering properties of light are not of significance
can be more efficiently achieved by the use of sodium
vapour lamps compared to mercury vapour lamps. The
use of incandescent lamps should be avoided except
for DC lighting in critical areas such as escape routes.
Newer technologies such as LED based lighting
systems, building automation systems for optimizing
power consumption through natural lighting, reduction
in HVAC load demand through the use of solar films,
lights controlled by sensors which get activated by
movement/human presence etc. which can significantly
optimize the use of electrical energy, also need to be
promoted. The use of solar energy for lighting, heating
etc. also needs to be maximized.

Low loss electronic ballasts can be employed, where
feasible, after taking care that the harmonic distortion
is within permissible limits.

5 ENERGY AUDIT

5.1 'Energy Audit' means the verification, monitoring
and analysis of the use of energy including submission
of a technical report containing recommendations for
improving energy efficiency with cost benefit analysis
and an action plan to reduce energy consumption.

5.2 The function of an energy audit broadly includes:

— Review of level of energy consumption.

— Creating a data base.

— Identifying energy conservation potential.

— Preparation of norms/guidelines for
implementation of energy conservation
measures.

— Recommending the use of energy efficient
appliances.

5.3 Energy Conservation Act, 2001 has been enacted
and the regulations issued under the said act shall be
complied with, with reference to Energy Audit.
Accordingly, designated consumers as notified under
Energy Conservation Act, 2001, shall get the energy
audit carried out through an accredited energy auditor/
firms and implement techno-economic viable
recommendations/measures. Every designated consumer
shall appoint or designate a certified energy manager,
whose responsibility shall be to assist the designated
consumer in complying with the energy consumption
norms and standards and other mandatory provisions.

5.4 Energy Conservation Building Code formulated
by the Bureau of Energy Efficiency and prescribed by
the Central Government shall be implemented for new
buildings having connected load of 500 kW and above
or contract demand of 600 kVA and above, once the
same or modified version has been notified by the
respective State Governments. List of energy intensive
industries and other establishments specified as
designated consumers is given in the Energy
Conservation Act, 2001 .

PART 1 GENERAL AND COMMON ASPECTS

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SP 30: 2011

SECTION 19 SAFETY IN ELECTRICAL WORK

FOREWORD

Safety procedures and practices are essential in
electrical work. Basic approaches to electrical work
from the point of view of ensuring safety which include
inbuilt safety in procedures such as permit-to-work
system, safety instructions and safety practices are
covered in this Section.

It is essential that safety should be preached and
practiced at all times in the installation, operation and
maintenance work. The real benefit to be derived from
the guidelines covered in this Section will be realized
only when the safety instructions it contains are
regarded as normal routine duty and not as involving
extra and laborious operations.

1 SCOPE

This Part 1 /Section 19 of the Code covers guidelines
on safety procedures and practices in electrical work.

2 REFERENCES

A list of Indian Standards on safety in electrical work
are as follows:

IS No.

Title

2551 : 1982

Specification for danger notice

plates

IS 5216 (Part 1) :

Recommendations on safety

1982

procedures and practices in

electrical work: Part 1 General

IS 5216 (Part 2):

Recommendations on safety

1982

procedures and practices in

electrical work: Part 2 Life saving

techniques

8923 : 1978

Warning symbol for dangerous

voltages

SP31 : 1986

Method of treatment of electric

shock

3 PERMIT-TO-WORK SYSTEM

3.1 All work on major electrical installations shall be
carried out under permit-to-work system which is now
well established, unless standing instructions are issued
by the competent authority to follow other procedures.
In extenuating circumstance, such as for the purpose
of saving life or time in the event of an emergency, it
may become necessary to start the work without being
able to obtain the necessary permit-to-work; in such
cases, the action taken shall be reported to the person-
in-charge as soon as possible. The permit-to-work
certificate from the person-in-charge of operation to
the person-in-charge of the men selected to carry out

any particular work ensure that the portion of the
installation where the work is to be carried out is
rendered dead and safe for working. All work shall be
carried out under the personal supervision of a
competent person. If more than one department is
working on the same apparatus, a permit-to-work
should be issued to the person-in-charge of each
department.

NOTE — The words 'permit-to-work' and 'permit' are
synonymous for the purpose of this Section.

3.2 No work shall be commenced on live mains unless
it is specifically intended to be so done by specially
trained staff. In such cases all possible precautions shall
be taken to ensure the safety of the staff engaged for
such work, and also of others who may be directly or
indirectly connected with the work. Such work shall
only be carried out with proper equipment provided
for the purpose and, after taking necessary precautions,
by specially trained and experienced persons who are
aware of the danger that exists when working on or
near live mains or apparatus.

3.3 On completion of the work for which the permit-
to-work is issued, the person-in-charge of the
maintenance staff should return the permit duly
discharged to the issuing authority.

3.4 In all cases, the issue and return of permits shall be
recorded in a special register provided for that purpose.

3.5 The permits shall be issued not only to the staff of
the supply undertakings, but also to the staff of other
departments, contractors, engineers, etc, who might be
required to work adjacent to live electrical mains or
apparatus.

3.6 A model form of permit-to- work certificate is given
in IS 5216 (Parti).

NOTES

1 The permit is to be prepared in duplicate by the person-in-
charge of operation on the basis of message, duly logged, from
the person-in-charge of the work.

2 The original permit will be issued to the person-in-charge of
work and the duplicate will be retained in the permit book.
For further allocation of work by the permit receiving officer,
tokens may be issued to the workers authorizing them
individually to carry out the prescribed work.

3 On completion of the work, the original shall be returned to
the issuing officer duly discharged for cancellation.

3.7 Permit books should be treated as important
records. All sheets in the permit books and the books
themselves should be serially numbered. No page
should be detached or used for any other except
bonafide work. If any sheet is detached, a dated and

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initiated statement shall then and there be recorded in
the book by the person responsible for it.

3.8 Permit books shall be kept only by the person-in-
charge of operation who shall maintain a record of the
receipts and issues made by him.

4 SAFETY INSTRUCTIONS

4.1 Safety Instructions for Working on Mains and
Apparatus Up to and Including 650 Y

4.1.1 Work on Dead Low and Medium Voltage Mains
and Apparatus

Unless a person is authorized to work on live mains
and apparatus all mains and apparatus to be worked
upon shall be isolated from all sources of supply before
starting the work, proved dead, earthed and short-
circuited. For earthing and short-circuiting, only
recognized methods should be used. Measures shall
be taken against, the inadvertent energizing of the
mains and apparatus.

4.1.2 Work on Live Mains and Apparatus

Only competent, experienced and authorized persons
shall work on live mains and apparatus, and such
persons should take all safety measures as may be
required.

Warning boards shall be attached on or adjacent to the
live apparatus and at the limits of the zone in which
work may be carried out.

Immediately before starting work, rubber gauntlets, if
used, shall be thoroughly examined to see whether they
are in sound condition. Under no circumstances shall
be person work with unsound gauntlets, mass, stools,
platforms or other accessories and safety devices.

No live part should be within unsafe distance of a
person working on live low and medium voltage mains
so that he does not come in contact with it unless he is
properly protected.

4.1.3 Testing of Mains and Apparatus

No person shall apply test voltage to any mains unless
he has received a permit-to-work and has warned all
persons working on the mains of the proposed
application of test voltage. If any part which will thus
become alive is exposed, the person-in-charge of the
test shall take due precautions to ensure that the
exposed live portion does not constitute danger to any
person. It should also be ensured before the application
of test voltage, that no other permit-to-work has been
issued for working on this mains.

4.1.4 Connecting Dead Mains to Live Mains
When dead mains are connected to live mains, all

connections to the live parts shall be made last, and in
all cases the phase sequence should be checked to
ensure that only like phases are connected together.
Before inserting fuses or links in a feeder or distribution
pillar controlling the cable on which a fault has been
cleared, each phase shall first be connected through a
test switch fuse.

4.2 Safety Instructions for Working on Mains and

Apparatus at Voltages Above 650 V

4.2.1 General

All mains and apparatus shall be regarded as live and
a source of danger and treated accordingly, unless it is
positively known to be dead and earthed.

a) No person shall work on, test or earth mains
or apparatus unless covered by a permit-to-
work and after proving the mains dead except
for the purpose of connecting the testing
apparatus, etc. which is specially designed for
connecting to the live parts.

b) The operations of proving dead, earthing and
short-circuiting of any mains shall be carried
out only by an authorized person under the
instructions of the person-in-charge of
maintenance;

c) While working on mains, the following
precautions shall be taken:

1) No person, after receiving a permit-to-
work, shall work on, or in any way
interfere with, any mains or conduits or
through containing a live mains except
under the personal instructions and
supervision, on the site of work, of
competent person,

2) When any live mains is to be earthed, the
procedure prescribed in 4.2.4 shall be
scrupulously followed, and

3) The earths and short-circuits, specified
on the permit-to-work shall not be
removed or interfered with except by
authority from the person-in-charge of
the work.

4.2.2 Minimum Working Distance

No person shall work within the minimum working
distance from the exposed live mains and apparatus.
The minimum working distance depends upon the
actual voltages. It does not apply to operations carried
out on mains and apparatus which are so constructed
as to permit sale operation within these distances.
Exposed live equipment in the vicinity shall be
cordoned off so that persons working on the released
equipment in service. The cordoning off shall be done
in such a way that it does not hinder the movement of

PART 1 GENERAL AND COMMON ASPECTS

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SP 30 : 2011

the maintenance personnel. If necessary, a safety
sergeant could be posted.

4.2.3 Isolation of Mains

Isolation of mains shall be effected by the following
methods:

a) The electrical circuits shall be broken only by
authorized persons by disconnecting switches,
isolating links, unbolting connections or
switches which are racked out. Where possible,
the isolation should be visibly checked, and

b) Where the means of isolation are provided
with a device to prevent their reclosure by
unauthorized persons, such a device shall be
used.

4.2.4 Devices for Proving Mains and Apparatus Dead

4.2.4.1 High voltage neon lamp contact indicators rods
are often used for proving exposed mains and apparatus
dead. Each rod is fitted with an indicating neon tube
or other means which glows when the contact end of
the rod comes in contact with exposed live parts. Each
rod is clearly marked for the maximum voltage on
which it may be safely used and shall not, under any
circumstances, be used on higher voltages.

4.2.4.2 Contact indicator and phasing rods are provided
for phasing and proving exposed mains and apparatus
dead. A set consists of two rods connected in series by
a length of insulated cables. Both rods are fitted with
contact tips and indicating tubes. When the contact tip
of one rod is applied to exposed live parts and that of
the other earth or other exposed live parts provided
there is sufficient voltage difference between the two,
the indicating tubes should glow. Each set of rods is
normally marked for the maximum voltage on which
it may be used and shall not, under any circumstances,
be used on higher voltages.

4.2.4.3 Use of contact indicator and phasing rods

While using the high voltage contact indicator and
phasing rods for proving the mains or apparatus dead,
following precautions should be taken:

a) Ensure that the rod is clean and dry,

b) Check the rod by applying it to known live
parts of the correct voltage, the indicating tube
shall glow,

c) Apply the rod to each phase required to be
proved dead, the indicating tube shall not
glow. Be very careful to be in a position to
see the glow, if any, appearing in the indicating
tube, and

d) Again check the rod by applying it to live parts
as in 4.2.4.3 (b). Again the indicating tubes
shall glow.

NOTES

1 All the above operations shall be carried out at the same place
and at the same time, if no live parts are available on the site,
rods up to 1 1 kV may be tested by applying them to the top of
the spark plug in a running motor car engine. If the rod is in
order the indicating tube will glow each time the plug sparks.
Therefore, the glow will to intermittent, but the indicating tube
should glow on this test or the rod is useless as a means of
proving the mains or apparatus dead.

2 The rod should be tested both before and after the use.

4.2.4.4 Testing and marking of devices

It shall be ensured that all devices for proving high
voltage mains and apparatus dead are marked clearly
with the maximum voltage for which they are intended
and should be tested periodically.

4.2.4.5 Identification of cables to be worked upon

A cable shall be identified as that having been proved
dead prior to cutting or carrying out any operation
which may involve work on or movement of the cable.
A non-contact indicating rod, induction testing set or
spiking device may be used for proving the cable dead.

4.2.4.6 Earthing and short-circuiting mains

a) High voltage mains shall not be worked upon
unless they are discharged to earth after
making them dead and are earthed and short-
circuited with earthing and short-circuiting
equipment is adequate to carry possible short-
circuit currents and specially meant for the
purpose. All earthing switches wherever
installed should be locked up.

b) If a cable is required to be cut, steel wedge
shall be carefully driven through it at the point
where it is to be cut or preferably by means
of a spiking gun of approved design.

c) After testing the cable with dc voltage, the
cable shall be discharged through a 2 megohm
resistance and not directly, owing to dielectric
absorption which is particularly prominent in
the dc voltage testing of high voltage cables.
The cable shall be discharged for a sufficiently
long period to prevent rebuilding up of
voltage.

d) The earthing device when used shall be first
connected to an effective earth. The other end
of the device shall then be connected to the
conductors to be earthed.

e) Except for the purpose of testing, phasing, etc,
the earthing and short-circuiting devices shall
remain connected for the duration of the work.

4.2.4.7 Removing the earth connections

On completion of work, removal of the earthing and
short-circuiting devices shall be carried out in the
reverse order to that adopted for placing them

188

NATIONAL ELECTRICAL CODE

SP 30: 2011

(see 4.2A.6), that is, the end of the earthing device
attached to the conductors of the earthed mains or
apparatus shall be removed first and the other and
connected to earths shall be removed last. The
conductor shall not be touched after the earthing device
has been removed from it.

4.2.4.8 Safety precautions for earthing

The precautions mentioned below should be adopted
to the extent applicable and possible:

a) Examine earthing devices periodically and
always prior to their use,

b) Use only earthing switches or any other
special apparatus where provided for earthing,

c) Verify that the circuit is dead by means of
discharging rod or potential indicator. The
indicator itself should first be tested on a live
circuit before and after the verification,

d) Earthing should be done in such a manner that
the persons doing the job are protected by
earth connections on both sides of their
working zone, and

e) All the three phases should be effectively
earthed and short-circuited though work may
be proceeding on one phase only.

4.2.4.9 Working on mains where visible isolation
cannot be carried out

Where the electrical circuit cannot be broken visibly
as set out in 4.23 the circuit may be broken by two
circuit opening devices, one on each side of the work
zone, where duplicate feed is available and by one
circuit opening device where duplicate feed is not
available provided the following conditions are fulfilled:

a) The position of the contacts of the circuit
opening device(s) — 'open' or 'closed' — is
clearly indicated by the position of the
operating handle or by signal lights or by other
means.

b) The circuit opening device(s) can be locked
mechanically in the open position.

c) The mains and apparatus to be worked on are
adequately earthed and short-circuited
between the circuit opening device and the
position of the work.

d) In cases where duplicate feed is available,
both the circuit opening devices are in series

between the mains and apparatus to be worked
on and any source of supply,
e) In cases where duplicate feed is not available,
the circuit opening device is between the
mains to be worked on and any source of
supply.

The circuit opening devices mentioned above shall be
locked in the open position before the work on the
mains and apparatus is commenced. The locking
devices shall be removed only by a competent person
and not until the work has been completed, any short-
circuiting and earthing removed and the permit-to- work
form duly returned and cancelled.

4.2.4.10 Work on mains with two or more sections

When the mains to be worked upon are to be divided
into two or more sections, the provisions of 4.2.3,
4.2.4.6 and 4.2.4.9 shall be observed with regard to
each section.

5 SAFETY PRACTICES

5.1 In all electrical works, it is very necessary that
certain elementary safety practices are observed. It has
been found that quite a large number of accidents occur
due to the neglect of these practices. The details of
such practices are given in Annex C of IS 5216 (Part 1).

5.2 Equipment, Devices and Appliances

General guidelines on equipment, devices and
appliances are given in IS 5216 (Part 1).

6 SAFETY POSTERS

6.1 The owner of every medium, high and extra high
voltage installation is required to fix permanently, in a
conspicuous position a danger notice in Hindi or
English and the local language of the district on every
motor, generator, transformer, all supports or high and
extra high voltage etc. The danger notice plate shall
conform to IS 2551.

6.2 It is also recognized as good practice to indicate by
means of the symbol recommended in IS 8923 on
electrical equipment where the hazards arising out of
dangerous voltage exist.

7 ACCIDENTS AND
ELECTRIC SHOCK

TREATMENT FOR

See SP 31 and IS 5216 (Part 2),

PART 1 GENERAL AND COMMON ASPECTS

189

SP 30: 2011

SECTION 20 TABLES

FOREWORD

In electrical engineering work, frequent need arises to
make reference to certain data, which, when made
available in the form of ready reference tables facilitates
the work. Those tables which basically provide
fundamental data not necessarily required for the
understanding of the Code but are required to be
referred to in designing the installation are given in
this Section.

1 SCOPE

This Part 1 /Section 20 gives frequently referrred tables
in electrical engineering work.

2 REFERENCES

The following Indian Standards may be referred for
further details:

IS No.

Title

3961

Recommended current ratings for
cables:

(Part 1) :

: 1967

Paper insulated lead sheathed cables

(Part 2) :

: 1967

PVC insulated and PVC sheathed
heavy duty cables

(Part 3) :

1968

Rubber insulated cables

(Part 4) :

: 1968

Polyethylene insulated cables

IS 11955:

: 1987

Preferred current ratings

Table 1 Diameter and Maximum Allowable Resistance of Fuse- Wire, Tinned Copper

SI No.

Rated Current of

Nominal Diameter

Tolerance

Permissible Resistance at 20°C

Fuse-Wire

Max

Q/m

ft/m

(1)

(2)

(3)

(4)

(5)

(6)

0.20

±0.003

0.564 4

0.525

ii)

0.35

±0.004

0.183 4

0.173

iii)

0.50

± 0.005

0.089 8

0.084 8

iv)

0.63

±0.006

0.056 6

0.053 5

0.75

±0.008

0.040

0.037 6

vi)

0.85

±0.009

0.031 1

0.029 3

vii)

1.25

±0.011

0.014 3

0.013 6

viii)

1.50

±0.015

0.009 9

0.009 4

ix)

1.80

±0.018

0.006 9

0.006 5

100

2.00

±0.020

0.005 6

0.005 3

Table 2 Size of Wood Casing and Capping, and Number of Cables that may be
Drawn in One Groove of the Casing

SI No. Width of Casing of Capping, mm

102

i) No. of grooves

ii) Width of grooves, mm

iii) Width of dividing fillet, mm

iv) Thickness of outer wall, mm

v) Thickness of casing, mm

vi) Thickness of capping, mm

vii) Thickness of the back under the groove, mm

viii) Length, m

10
2.5 to 3.0

190

NATIONAL ELECTRICAL CODE

SP 30 : 2011

Table 2 — (Concluded)

Size of Cable

Number of Cables that

may

be Drawn in

One Groove

Nominal Cross-
Sectional Area, mm 2

Number and Diameter
(in mm) of Wires

1.0

1/L12 ,}

1.5

1/1.40

2.5

1/1.80
3/1 .60 n

1/2.24
7/1.85 1}

—

1/2.80
7/1.06

—

l/3.55 2)
7/1.40

—

7/1.70

—

7/2.24

—

___

—

7/2.50

—

7/3.00 2)

■s only,
ictors only.

°For copper conductoi
2) For aluminium condi

Table 3 Maximum Permissible Number of 1.1 kV Grade Cables that can be Drawn into

Rigid Steel Conduits

Size of Cable

Size of Conduit, mm

Nominal Number and
Cross- Diameter

Sectional Area (in mm)
mm 2 of Wires

Number of Cables, Max

(1)

(2)

S B S B S B S B S B S B S B

(3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)

1.0
1.5

2.5

6
10

25
35
60

1/1.12°

1/1.40

1/1.80

3/1.06 !)

1/2.24

7/0.85 ,}
11/2.80

7/0.6 S)
ll/3.55 2)

7/1. 40"

7/1.70

7/2.24

7/2.50
19/1.80

7/3.007 2)

2 —

13
12
10

10
10

20
20
18

8
6

4
3

14
14
12

6 9 7

5 8 6

4 9 5

NOTE — The table shows the maximum capacity of conduits of the simultaneous drawing of cables, the table applies to 1.1 kV grade
cables. The columns headed S apply to runs of conduit which have distance not exceeding 4.25 m between draw-in-boxes, and which
do not deflect from the straight by an angle of more than 15°. The columns headed B apply to runs of conduit which deflect from the
straight by an angle of more than 15°.

]) For copper conductors only.
a) For aluminium conductors only.

PART 1 GENERAL AND COMMON ASPECTS

191

SP 30: 2011

Table 4 Maximum Permissible Number of 1.1 kV Grade Single-Core Cables that may be Drawn into

Rigid Non-metallic Conduits

Size of Cable

Size of Conduit, mm

Nominal Cross-
Sectional Area

Number and
Diameter of

mm 2

Wires, mm

Number of Cables, Max

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

1.0

1/1.12 1}

1.5

1/1.40

—

2.5

1/1.80
3/1.06 ])

—

1/2.24
7/0.85 ,}

1/2.80
7/1. 40 u

—

l/3.55 2)
7/1.40 1)

—

7/1.70

—

7/2.24

—

7/2.50

—

7/3.00 2}
19/1.80

n For copper

conductors only.

2) For aluminium conductors only.

Table 5 Capacitor Sizes for Power Factor Improvement

Existing
Power

Improved Poi

^er Facte
0.94

Factor

0.80

0.85

0.90

0.91

0.92

0.93

0.95

0.96

0.97

0.98

0.99

1.00

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)

(12)

(13)

(14)

Multiplying

Factors

0.40

1.537

1.668

1.805

1.832

1.861

1.895

1.924

1.959

1.998

2.037

2.085

2.146

2.288

0.41

1.474

1.605

1.742

1.769

1.798

1.831

1.860

1.896

1.935

1.973

2.021

2.082

2.225

0.42

1.41.3

1.544

1.681

1.709

1.738

1.771

1.800

1.836

1.874

1.913

1.961

2.022

2.164

0.43

1.356

1.487

1.624

1.651

1.680

1.713

1.742

1.778

1.816

1.855

1.903

1.964

2.107

0.44

1.290

1.421

1.558

1.585

1.614

1.647

1.677

1.712

1.751

1.790

1.837

1.899

2.041

0.45

1.230

1.360

1.501

1.532

1.561

1.592

1.626

1.659

1.695

1.737

1.784

1.846

1.988

0.46

1.179

1.309

1.446

1.473

1.502

1.533

1.567

1.600

1.636

1.677

1.725

1.786

1.929

0.47

1.130

1.260

1.397

1.425

1.454

1.485

1.519

1.552

1.588

1.629

1.677

1.758

1.881

0.48

1.076

1.206

1.343

1.370

1.400

1.430

1.464

1.497

1.534

1.575

1.623

1.684

1.826

0.49

1.030

1.160

1.297

1.326

1.355

1.386

1 .420

1.453

1.489

1.530

1.578

1.639

1.782

0.50

0.982

1.112

1.248

.276

1.303

1.337

1.369

1.403

1.441

1.481

1.529

1.590

1.732

0.51

0.936

1.066

1.202

1.230

1.257

1.291

1.323

1.357

1.395

1.435

1.483

1.544

1.686

0.52

0.894

1.024

1.160

1.188

1.215

1.149

1.281

1.315

1.353

1.393

1.441

1.502

1.644

0.53

0.850

0.980

1.116

1.144

1.171

1.205

1.237

1.271

1.309

1.349

1.397

1.458

1.600

0.54

0.809

0.939

1.075

1.103

1.130

1.164

1.196

1.230

1.268

1.308

1.356

1.417

1.559

0.55

0.769

0.899

1.035

1.063

1.090

1.124

1.136

1.190

1.228

1.268

1.316

1.377

1.519

0.56

0.730

0.860

0.996

1.024

1.051

1.085

1.117

1.151

1.189

1.229

1.277

1.338

1.480

0.57

0.692

0.822

0.958

0.986

1.013

1.047

1.079

1.113

1.151

1.191

1.239

1.300

1.442

0.58

0.655

0.785

0.921

0.949

0.976

1.010

1.042

1.076

1.114

1.154

1.202

1.263

1.405

0.59

0.618

0.748

0.884

0.912

0.939

0.973

1.005

1.039

1.077

1.117

1.165

1.226

1.368

0.60

0.584

0.714

0.849

0.878

0.905

0,939

0.971

1.005

1.043

1.083

1.131

1.192

1.334

0.61

0.549

0.679

0.815

0.843

0.870

0.904

0.936

0.970

1.008

1.048

1.096

1.157

1.299

192

NATIONAL ELECTRICAL CODE

SP 30 : 2011

Table 5 — (Concluded)

Existinj

Improved Power Factor

Power
Factor

0.80

0.85

0.90

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1.00

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)

(12)

(13)

(14)

0.62

0.515

0.645

0.781

0.809

0.836

0.870

0.902

0.936

0.974

1.014

1.062

1.123

1.265

0.63

0.483

0.613

0.749

0.777

0.804

0.838

0.870

0.902

0.942

0.982

1.030

1.091

1.233

0.64

0.450

0.580

0.716

0.744

0.771

0.805

0.837

0.871

0.909

0.949

0.997

1.058

1.200

0.65

0.419

0.549

0.685

0.713

0.740

0.774

0.806

0.840

0.878

0.918

0.966

1.027

1.169

0.66

0.388

0.518

0.654

0.682

0.709

0.743

0.775

0.809

0.847

0.887

0.935

0.996

1.138

0.67

0.358

0.488

0.624

0.652

0.679

0.713

0.745

0.779

0.817

0.857

0.905

0.966

1.108

0.68

0.329

0.459

0.595

0.623

0.650

0.684

0.716

0.750

0.788

0.828

0.876

0.937

1.079

0.69

0.299

0.429

0.565

0.593

0.620

0.654

0.686

0.720

0.758

0.798

0.840

0.907

1.049

0.70

0.270

0.400

0.536

0.564

0.591

0.625

0.657

0.691

0.729

0.769

0.811

0.878

1.020

0.71

0.242

0.372

0.508

0.536

0.563

0.597

0.629

0.663

0.701

0.741

0.785

0.850

0.992

0.72

0.213

0.343

0.479

0.507

0.534

0.568

0.600

0.634

0.672

0.712

0.754

0.821

0.963

0.73

0.186

0.316

0.452

0.480

0.507

0.541

0.573

0.607

0.648

0.685

0.727

0.794

0.936

0.74

0.159

0.289

0.425

0.453

0.480

0.514

0.546

0.580

0.618

0.658

0.700

0.740

0.909

0.75

0.132

0.262

0.398

0.426

0.453

0.487

0.519

0.553

0.591

0.631

0.673

0.713

0.882

0.76

0.105

0.235

0.371

0.399

0.426

0.460

0.492

0.526

0.564

0.604

0.652

0.687

0.855

0.77

0.079

0.209

0.345

0.373

0.400

0.434

0.466

0.500

0.538

0.578

0.620

0.661

0.829

0.78

0.053

0.183

0.319

0.347

0.374

0.408

0.440

0.474

0.512

0.552

0.592

0.634

0.803

0.79

0.026

0.156

0.292

0.320

0.347

0.381

0.413

0.447

0.485

0.525

0.567

0.608

0.776

0.80

0.130

0.266

2.294

0.321

0.355

0.387

0.421

0.459

0.499

0.541

0.582

0.750

0.81

—

0.104

0.240

0.268

0.295

0.329

0.361

0.395

0.433

0.473

0.515

0.556

0.724

0.82

—

0.078

0.214

0.242

0.269

0.303

0.335

0.369

0.407

0.447

0.489

0.530

0.698

0.83

—

0.052

0.188

0.216

0.243

0.277

0.309

0.343

0.381

0.421

0.463

0.504

0.672

0.84

—

0.026

0.162

0.190

0.217

0.251

0.283

0.317

0.355

0.395

0.417

0.450

0.620

0.85

—

0.136

0.164

0.191

0.225

0.257

0.291

0.329

0.369

0.417

0.450

0.620

0.86

—

0.109

0.140

0.167

0.198

0.230

0.264

0.301

0.343

0.390

0.424

0.593

0.87

—

0.083

0.114

0.141

0.172

0.204

0.238

0.275

0.317

0.364

0.395

0.567

0.88

—

0.054

0.085

0.112

0.143

0.175

0.209

0.246

0.288

0.309

0.369

0.512

0.89

___

—

0.028

0.059

0.086

0.117

0.149

0.183

0.230

0.262

0.309

0.369

0.512

0.90

—

0.031

0.058

0.089

0.121

0.155

0.192

0.234

0.281

0.341

0.484

0.91

—

___

—

0.027

0.058

0.090

0.124

0.161

0.203

0.250

0.310

0.453

0.92

—

0.027

0.063

0.097

0.134

0.176

0.223

0.283

0.426

0.93

—

0.032

0.066

0.103

0.145

0.192

0.252

0.395

0.94

—

0.034

0.071

0.113

0.160

0.220

0.363

0.95

—

0.037

0.079

0.126

0.186

0.329

0.96

—

0.042

0.089

0.149

0.292

0.97

—

___

—

0.047

0.107

0.250

0.98

—

__„

—

0.060

0.203

0.99

—

0.143

NOTE — The consumer is advised to make proper allowance for lower supply voltages where these exist during the working hours
and may choose slightly higher kVAR than recommended in the table for such cases.

PART 1 GENERAL AND COMMON ASPECTS

193

NATIONAL ELECTRICAL CODE

PART 2

SP 30 : 2011

PART 2 ELECTRICAL INSTALLATIONS IN

STAND-BY GENERATING STATIONS AND

CAPTIVE SUBSTATIONS

FOREWORD

This National Electrical Code (Part 2) is primarily intended to cover the requirements relating to stand-by generating
stations and captive substations intended for serving an individual occupancy. As the general provisions relating
to such installations are common and are themselves elaborate in nature, it was felt essential to cover them in a
separate part preceding the other parts which cover the requirements for specific installations.

Generating stations covered by this Part 2 are the stand-by or emergency supply and captive substations normally
housed in or around the building in question. This Code does not include the switching stations and other large
generating plants coming solely under the preview of the electric supply authority of a metropolis even though to
some extent the requirements stipulated herein could also be applicable to them.

Specific requirements if any, for generating and switching substations for individual buildings that might vary
depending on the nature of the occupancy or the size of the building are enumerated in the respective sections of
the Code.

In the formulation of this Code, note has been taken of the requirements stipulated in installation Codes of
individual equipment as well as the fire- safety Codes for generating stations and substations. It is generally not
feasible to draw very strict guidelines for the design and layout for such installations owing to the complexity of
the needs of building installations and hence only the essential safety considerations are listed out for compliance.
It is essential to take recourse to the assistance of local authorities for further details.

Specific requirements pertaining to stand-by generating stations and captive substations for multistoreyed/high-
rise buildings are covered in Part 3/Section 7 of this Code.

PART 2 ELECTRICAL INSTALLATIONS IN STAND-BY GENERATING STATIONS AND CAPTIVE SUBSTATIONS 197

SP 30: 2011

1 SCOPE

1.1 This Code (Part 2) covers essential requirements
for electrical installations in stand-by generating
stations and captive substations intended to serve a
building or group of buildings.

1.2 This Part is not intended to cover 'captive generator
sets' of very large capacities. This Part 2 covers only
the stand-by generating sets upto the capacity of 5 MW.
Similarly the substations upto the capacities of 10 MVA
and 33 kV are covered. This Part 2 also does not apply
to the generating stations coming under the jurisdiction
of the Electric Supply Authority in a city or metropolis.

2 REFERENCES

This Part 2 should be read in conjunction with the
following Indian Standards:

IS No.
1641 : 1988

1642 : 1989

1646 : 1997

1946 : 1961

2309 : 1989

3034 : 1993

3043 : 1987

10028 (Part 2) :
1981

10118 (Part 3):
1982

Title

Code of practice for fire-safety of
buildings (general): General
principles of fire grading and
classification

Code of practice for fire safety of
buildings (general): Details of
construction (first revision)
Code of practice for fire-safety of
buildings (general): Electrical
installation (second revision)
Code of practice for use of fixing
devices in walls, ceilings and of
solid construction
Code of practice for the protection
of buildings and allied structures
against lightning (second revision).
Fire-safety of industrial buildings:
Electrical generating and
distributing stations — Code of
practice (second revision)
Code of practice for earthing (first
revision)

Code of practice for selection,
installation and maintenance of
transformers: Part 2 Installations
Code of practice for selection,
installation and maintenance of
switchgear: Part 3 Installation

3 TERMINOLOGY

For the purpose of this Part, the definitions given in
Part 1/Section 2 of this Code shall apply.

4 GENERAL CHARACTERISTICS OF STATION
INSTALLATIONS

4.1 In determining the general characteristics of

stand-by generating plants and building substations in
a building, the assessment of characteristics of the
buildings based on its occupancy shall be taken note
of as specified in individual Parts/Sections of this Code.

4.2 Depending on the exact location of the station in
the building premises, and depending on whether the
equipment are installed indoor or outdoor, the degree
of external influence of the environment shall
be determined based on the guidelines given in
Part 1/Section 8 of this Code.

4.3 It is generally presumed that generating stations
and substations are restricted areas not meant for
unauthorized persons, and such electrical operating
areas fall under the category of BA4 utilization for
instructed personnel (see Part 1/Section 8), which are
adequately advised or supervised by skilled persons
to avoid dangers that may arise owing to the use of
electricity.

5 EXCHANGE OF INFORMATION

5.1 Information shall be exchanged amongst the
personnel involved regarding the size and nature of
substation and supply station requirements to be
provided for an occupancy so that the type of
equipment and their choice, as well as their installation
shall be governed by the same. An assessment shall
also be made of the civil construction needs of the
station equipment keeping in view a possible expansion
in future.

5.2 Before ordering the equipment, information shall
be exchanged, regarding the installation and location
conditions, including such building features as access
doors, lifting beams, oil pumps, cable trenches,
foundation details for heavy equipment, ventilating
arrangement, etc.

6 LAYOUT AND BUILDING CONSTRUCTION
ASPECTS

6.1 The constructional features of all building housing
the station installation shall comply with IS 1641,
IS 1642 and IS 3034. Locating of substation in lowest
basement is not recommended.

6.2 Switchgears, circuit-breaker and transformers
(except outdoor types) shall be housed preferably in
detached single storey buildings of Type 1 construction.
In the case of built up areas in cities, multistoreyed
construction may also be adopted. Construction of such
buildings shall conform to IS 1946.

6.3 Construction of fire separation walls shall conform
with the requirements of relevant Indian Standards.
Doorway openings in separating walls of transformer
or switchgear rooms shall be provided with sills not
less than 15 cm in height. Reference is drawn to

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IS 3034, Where risk of spread of possible fire exists,
interconnecting doors should have a 2 h fire rating.

6.4 The foundation of the stand-by generating sets shall
preferably be isolated from that of the other structures
of the building so that vibrations are not carried over.

6.5 The diesel generating (DG) set should be provided
with integral acoustic enclosure conforming to the
requirements as laid down in Environment Protection
Act

7 SELECTION OF EQUIPMENT

7.1 The selection of equipment shall be done in
accordance with the guidelines provided in Part 1/
Section 9 of this Code.

8 GENERATING SETS

8.0 Stationary generating sets of 5 kVA and above are
normally driven by diesel engine as this drive is most
economical. Smaller sets are driven by petrol. During
the planning of the building, the dimensions of the
power plant room and the transport ways shall be agreed
to between the architect and electrical contractor.

8.1 In case of large capacity sets which generate
appreciable heat, the rooms shall be well ventilated
and provided with air exhaust equipment.

8.2 The capacity of the stand-by set for an installation
should be such that in an event of power failure, the
essential loads can be supplied power. For instance in
case of hospitals such loads comprise operation theatres
and their supporting auxiliaries; intensive care units,
cold storage in laboratories, emergency lifts, etc. In
the case of industries having continuous processes,
such loads are required to be supplied with power all
the time. In commercial premises and high-rise
buildings, a few lifts and circulation area lights and
fire-fighting equipment have to be kept working by
supply from stand-by sets. Similar is the case of
essential loads in large hotels. Such sets can either be
manually started and switched on to essential loads
with the use of changeover switches or they could be
auto-start on mains failure and loads autochanged over
to generator supply.

8.3 In case of large electrical installation in which
essential loads are widely scattered it becomes
necessary to run the generating set supply cables to
these essential loads and in the event of mains failure,
changeover to generator supply, either manually or
through auto-changeover connectors,

8.4 The fire safety requirements for fuel oil storage
shall conform to 5.3 of IS 3034.

8.5 The fire safety requirements for oil and gas fired
installations shall conform to IS 3034.

8.6 All equipment of prime mover shall conform to
relevant Indian Standard (where they exist) for
construction, temperature-rise, overload and
performance.

8.7 The diesel generator set should meet the pollution
norms of the Central and State Statutory Authorities.

9 TRANSFORMER INSTALLATIONS

9.1 Reference is drawn to the requirements given in
IS 10028 (Part 2).

9.2 Transformer of capacity up to 3 MVA may be
housed indoor or outdoor. The larger ones, because of
their size, are usually of outdoor type.

9.3 Indoor transformer will require adequate ventilation
to take away as much heat as possible. Oil drainage
facilities and partition walls between transformers and
between transformer and other equipment such as oil
circuit-breakers are necessary to reduce the risk of
spread of fire.

9.4 As a transformer station normally has a high voltage
and a low voltage switchgear, all such equipment
should be adequately separated.

9.5 Only dry type transformer(s) shall be used for
installation inside the residential/commercial buildings.
The transformer room should be located on ground
floor inside a well ventilated room.

10 HIGH VOLTAGE SWITCHING STATIONS

Reference is drawn to the requirements stipulated in
IS 101 18 (Part 3).

11 LOW VOLTAGE SWITCHING STATIONS
AND DISTRIBUTION PANELS

Reference is drawn to the requirements stipulated in
IS 10118 (Part 3).

12 STATION AUXILIARIES

12.0 Station auxiliaries could consist of:

a) batteries for stand-by generating sets,

b) batteries for short time emergency lighting,

c) battery charging equipment,

d) fuel oil pumps,

e) ventilating equipment, and

f) fire-fighting equipment.

12.1 Batteries

12.1.1 Batteries shall have containers of glass or any
other non-corrosive, non-flammable materials.

12.1.2 Batteries shall be installed in a separate
enclosure away from any other auxiliary equipment or
switchgear. The enclosure shall be free from dust and

PART 2 ELECTRICAL INSTALLATIONS IN STAND-BY GENERATING STATIONS AND CAPTIVE SUBSTATIONS

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well ventilated. Care shall be taken to ensure that direct
sunlight does not fall on the batteries.

NOTE — Provision shall be made for sufficient diffusion and
ventilation of gases from the battery to prevent the
accumulation of an explosive mixture.

12.1.3 The batteries shall stand directly on durable, non-
ignitable, non-absorbent and non-conducting material,
such as glass, porcelain or glazed earthenware. These
materials shall rest on a bench which shall be kept dry
and insulated from earth. If constructed of wood it shall
be slatted and treated with anti-sulphuric enamel.

12.1.4 The batteries shall be so arranged on the bench
that a potential difference exceeding 12 V shall not
exist between adjoining cells. The batteries not
exceeding 20V shall not be bunched or arranged in
circular formation.

12.1.5 All combustible materials within a distance
of 60 cm measured horizontally from, or within 2.0 m
measured vertically above, any battery shall be
protected with hard asbestos sheets.

12.2 Battery Charging Equipment

12.2.1 The battery charging equipment with necessary
switch and controlgear shall be mounted separately and
away from the batteries.

12.3 Fuel Oil Pump

12.3.1 Fuel oil pump shall be installed close to the
engine room or inside the engine room.

12.3.2 The electric cable provided to run the pump
motor shall be protected with oil-resistant outer sheath.

12.4 Ventilating Equipment

12.4.1 The engine room shall be fitted with hot-air
extractors.

12.4.2 The battery room shall be fitted with exhaust
fans. The exhaust gases be let off to atmosphere where
no other equipment is installed.

13 WIRING IN STATION PREMISES

All cabling and electrical wiring inside generation or
substation premises shall be done in accordance with
the practice recommended in (Part 1/Section 9) of this
Code.

14 EARTHING

The provision of 17 of IS 3043 shall apply (see also
Part 1/Section 14).

IS BUILDING SERVICES

15.1 Lighting

15.1.1 The general principal of good lighting for any
occupancy shall be as given in Part 1/Section 11 of
this Code. For the purpose of station installations the
values of lumen level and limiting value of glare index
shall be as given in Table 1 .

Table 1 Recommended Values of Illumination
and Glare Index

No.

Location

Illumi-
nation,

lux

Laminating
Glare
Index

(1)

(2)

(3)

(4)

Indoor Locations

Stand-by generator hall

300

Auxiliary equipment;
battery room, blowers,
switchgear

Basements

100

Control rooms:

1) Vertical control panels

300

2) Control desks

300

3) Rear of control panel

150

ii)

Outdoor Locations

a)
b)

Fuel oil storage area
Transformers, outdoor
switchgear

50
50

19
19

15.2 The luminaires used shall be of dust-proof
construction and shall be energy efficient with compact
fluorescent lamps (CFL)/fluorescent lamps with
electronic ballasts.

16 FIRE-SAFETY REQUIREMENTS

16.1 The provisions of IS 3034 and IS 1646 shall apply
for station installations.

16.2 All wiring for automatic fire-fighting installation
shall be of fire-resistant outer sheath.

17 LIGHTNING PROTECTION
The provisions of IS 2309 shall apply.

18 TESTING AND INSPECTION

The guidelines provided in Part 1/Section 13 of this
Code shall apply. In the case of diesel sets which come
into operation only in emergency as stand-by sets, it is
necessary that such sets are regularly checked run up
and mechanical and electrical system tested to ensure
that the set is in operable conditions all the time.

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PART 3. ELECTRICAL INSTALLATIONS IN
NON-INDUSTRIAL BUILDINGS

FOREWORD

For the purposes of this Code, electrical installations
in buildings have been broadly classified as those in
non-industrial and industrial . While a majority of
installations could be categorically classified as non-
industrial, an industrial complex would necessarily
incorporate sub-units such as offices, residential
quarters and support services which are either housed
or fall in the category of non-industrial buildings. The
requirement stipulated in Part 3 and Part 4 of this Code
would therefore require judicious application.

With the current trend in power utilization, it would
also be extremely difficult to classify electrical
installations based on power requirement or the
voltage of supply, as large buildings for non-industrial
purposes consume sufficient power to consider them
at par with the consumption of light industrial
establishments. It is therefore necessary to consider
for initial assessment of the installation the guidelines
given in Part 1/Sec 8 this Code, which are better
defined than the earlier terminology used for
classifying installations.

Part 3 of this Code, therefore covers requirements

for major types of non-industrial occupations. It is
felt that a large number of occupancies would fall
in one of the categories, and for typical buildings
which do strictly fall into any of these, recourse shall
be made to the general guidelines stipulated in
Parti.

This Part consists of the following Sections:

Section 1 Domestic Dwellings

Section 2 Office Building, Shopping and

Commercial Centres and Institutions
Section 3 Recreational, Assembly Building
Section 4 Medical Establishments
Section 5 Hotels
Section 6 Sports Buildings
Section 7 Specific Requirements for Electrical

Installations in Multistoried Buildings

Sections 1-6 of this Part cover requirements applicable
to buildings which are of nominal heights less than
15 m. It is recognized that from the point of view fire-
safety of buildings more than 15 m height require
specific considerations. These are summarized in
Section 7 of this Part.

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS

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SP 30: 2011

SECTION 1 DOMESTIC DWELLINGS

FOREWORD

Electrical installations in domestic dwellings and in
buildings providing living accommodation for people
are by far the simplest form of installation. Use of
electrical appliances, both portable and fixed has now
become very common and popular even in single
family dwellings. The optimum benefits from the use
of electricity can be obtained only if the installation
is of sufficient capacity and affords enough
flexibility.

The primary considerations in planning the electrical
layout in domestic dwellings are economy and safety.
Besides these, other considerations such as efficiency
and reliability, convenience and provisions for future
expansion are also valid.

Domestic installations are characterized mainly by a
circuit voltage of 250 V to earth except in the case of
large power consumers where three-phase supply is
given. A brief description of the type of installations
covered in this Section is given in 4. It may, however,
be noted that lodging and rooming houses, though
utilized as living accommodation for short periods of
time (by different occupants) are covered under scope
of Part 3/Section 5 of this Code.

Specific requirements for installations in rooms
containing a bath tub or shower basin, namely,
bathrooms are separately covered in Annex A. These
requirements also apply to similar locations in other
occupancies, such as hotels. For convenience, these
requirements are covered in this Section.

1 SCOPE

This Part 3/Section 1 of the Code covers requirements
for electrical installations in domestic dwellings.

2 REFERENCES

This Part 3/Section 1 of the Code should be read in
conjunction with the following Indian Standards:

IS No. Title

3646 (Part 2) : 1966 Code of practice for interior
illumination: Part 2 Schedule for
values of illumination and glare
index

7689 : 1989 Guide for the control of

undesirable static electricity

8061 : 1976 Code of practice for design,

installation and maintenance of
service lines upto and including
650 V

IS No.

13450 (Parti):

1994 /IEC

60601-1 : 1988
14665(Part 1) :
2000

15707 : 2006

SP7.-2005
SP 72: 2010

Title

Medical electrical equipment —
Part 1: General requirements for
safety

Electric traction lifts — Part 1:
Guidelines for outline dimensions
of passenger, goods, service and
hospital lifts

Testing, evaluation, installation
and maintenance of ac electricity
meters — Code of practice
National Building Code of India
National Lighting Code

3 TERMINOLOGY

For the purpose of this Section, the definitions given
in Part 1/Section 2 of this Code shall apply.

4 CLASSIFICATION

4.1 The electrical installations covered in this Section,
are those in buildings intended for the following
purposes:

4.1.1 Domestic Dwellings/ Residential Buildings

These shall include buildings in which sleeping
accommodation is provided for normal residential
(domestic) purposes with cooking and dining facilities.

Such buildings shall be further classified as follows:

a) One or two family dwellings — These shall
include any private dwelling which is
occupied by members of a single family and
has a total sleeping accommodation for not
more than 20 persons.

b) Apartment houses (flats) — These shall include
any building or structure in which living quarters
are provided for three or more families, living
independently of each other and with
independent cooking facilities. For example
apartment houses, mansions and chawls.

NOTE — If accommodation is provided for more than
20 persons, such buildings are considered lodging or
rooming houses, (dormitories) and the provisions of
Part 3/Section 5 shall apply.

5 GENERAL CHARACTERISTICS
INSTALLATIONS

General guidelines on the assessment of characteristics
of installations in buildings are given in Part 1/Sec 8
of this Code. For the purposes of installations falling
under the scope of this Section, the characteristics
defined below specifically apply.

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5.1 Environment

The following environmental factors shall apply to
electrical installations in domestic dwellings:

Environment

Characteristics

Remarks

(1)

(2)

(3)

Presence of

Probability of

water

presence of water
is negligible

Presence of

The quantity or

foreign solid

nature of dust or

bodies

foreign solid
bodies is not
significant

Presence of

The quantity and

Applicable for

corrosive or

nature of

most of the

polluting

corrosive or

locations except

substances

polluting

for dwellings

substances is not

situated by sea or

significant

in industrial zone
in which case
categorization AF2
applies (see Part
1/Sec 8)

Mechanical

Impact and

Household and

stresses

vibration of low
severity

similar conditions

Seismic effect

Depends on the

and lighting

location of the
building

5.2 Utilization

The following aspects utilization shall apply:

Utilization

Characteristics

Remarks

(1)

(2)

(3)

Capability of

Uninstructed

Applies to all

persons

domestic
installations

Contact of

Persons in

persons

normally

conducting

situations

Conditions of

Low density

Buildings of

evacuation

occupation, easy

normal or low

during

conditions of

height used for

emergency

evacuation

one or two
family dwellings

Low density

Apartment

occupation,

houses including

difficult

high-rise flats

conditions of

evacuation

Nature of

No significant

processed of

risks

stored material

6 SUPPLY CHARACTERISTICS AND
PARAMETERS

6.0 Exchange of Information

6.0.1 Genera] aspects to be taken note of before
designing the electrical installations are enumerated
in Part 1/Section 7 of this Code. However, the
following points shall be noted particularly in respect
of domestic dwellings.

6.0.2 Before starting wiring and installation of fittings
and accessories, information should be exchanged
between the owner of the building or architect or
electrical contractor and the local supply authority in
respect of tariffs applicable, types of apparatus that
may be connected under each tariff, requirement of
space for installing meters, switches, service lines, Qtc,
and for total load requirement of lights, fans and power.

6.0.3 While planning an installation, consideration
should be given to the anticipated increase in the use
of electricity for lighting, general purpose socket-
outlet, kitchen, heating, etc. It is essential that adequate
provision should be made for all the services which
may be required immediately and during the intended
useful life of the building, for the householder may
otherwise be tempted to carry out extension of the
installation himself or to rely upon use of multiplug
adaptors and long flexible cords, both of which are
not recommended. A fundamentally safe installation
may be rendered dangerous, if extended in this way.

6.0.4 Electrical installation in a new building should
normally begin immediately on the completion of the
main structural building work. For conduit wiring
system, the work should start before finishing work
like plastering has begun. For surface wiring system,
however, work should begin before final finishing work
like white washing, painting, etc. Usually, no
installation work should start until the building is
reasonably weatherproof, but where electric wiring is
to be concealed within the structures, the necessary
conduits and ducts should be positioned after the
shuttering is in place and before the concrete is poured,
provision being made to protect conduits from damage.
For this purpose, sufficient coordination shall be
ensured amongst the concerned parties.

6.1.1 Estimation of Load Requirements

The extent and form of electrical installations in
domestic dwellings is basically designed to cater to
light and fan loads and for electrical appliances and
gadgets. In estimating the current to be carried by any
branch circuit unless the actual values are known, these
shall be calculated based on the following
recommended ratings:

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS

205

SP 30: 2011

Table 2 Recommended Schedule of J

SI Item

Recommended

Docket-Outlets

No.

Rating

(W)
(3)

(Clause

6.1.3)

(1) (2)

SI No.

Description

Number of Socket- Outlets

i) Incandescent lamps

16A

ii) Ceiling fans

(1)

(2)

(3)

(4)

Bedroom

2-3

iii) Table fans

ii)

Living room

2-3

iv) 6A, socket-outlet point unless

100

iii)

Kitchen

the actual value of loads

are

specified

IV)

Dining room

Garage

v) Fluorescent tubes:

vi)

For refrigerator

Length 600 mm

vii)

For air-conditioner

—

1 (for each)

1 200 mm

viii)

Verandah

1 per 10 m 2

1 500 mm

>A)

90
1000

ix)

Bathroom

vi) Power socket outlet (1(

unless the actual value

loads are specified

6.1.6 Balancing of circuits in three-wire or polyphase
installation shall he nlanneH beforehand Tn p.anh rase

6.1.2 Number of Points in Branch Circuits

The recommended yardstick for dwelling units for
determining the number of points is given in Table 1.

Table 1 Number of Points for Dwelling Units

SI Description

Area for the Main Dwelling Unit (m 2 )

No.

'-N

55 85

140

(1) (2)

(3)

(4)

(5) (6)

(7)

i) Light points

10 12

ii) Ceiling fans

2-2

3-2

4-3 5-4

7-5

iii) 6 A Socket outlets

4 5

iv) 16A Socket outlets

—

2 3

v) Call-bell (buzzer)

—

1 1

NOTE — The figures in table

against

SI No. (ii) indicate the

recommended number of points and the number of fans.

Example — For main dwelling

I unit of 55 m 2 , 4 points

with 3

fans are recommended.

6.1.3 Number of Socket-Outlets

The recommended schedule of socket-outlets for the
various sub-units of a domestic are given in Table 2.

6.1.4 Selection of Size of Conductors

Provisions of Part 1/Section 9 of this Code shall apply.

6.1.5 'Power' sub-circuits shall be kept separate and
distinct from 'lighting-and fan' sub-circuit. All wiring
shall be done on the distribution system with main and
branch distribution boards located at convenient
physical and electrical load centres. All types of wiring,
whether recessed or surface should be capable of easy
inspection. The surface wiring when run along the walls
should be as near the ceiling as possible. In all types
of wirings due consideration shall be given for neatness
and good appearance and safety.

it is recommended that all socket-outlets in a room are
connected to one phase. The conductors shall be so
enclosed in earthed metal or incombustible insulating
material that it is not possible to have ready access to
them. If the points between which a voltage exceeding
250 V is present are 2 m or more apart, the covers or
access doors shall be clearly marked to indicate the
voltage present.

6.1.7 It is recommended to provide at least two
lighting sub-circuits in each house. It is also
recommended that a separate lighting circuit be
utilized for all external lighting of steps, walkways,
driveways, porch, car park, terrace, etc., with a master
double-pole switch for the sub-circuit in addition to
the individual switches.

6.1.8 Wherever the load to be fed is more than 1 kW, it
shall be controlled by an isolator switch or miniature
circuit-breaker.

6.2 Selection of Wiring

Any one of the following types of wiring may be used
in a residential building (see Part 1/Section 9 of this
Code).

a) Tough rubber sheathed or PVC insulated PVC
sheathed wiring on wood batten,

b) PVC insulated wiring in steel/non-metallic
surface conduits, and

c) PVC insulated wiring in steel7non -metallic
recessed conduits.

However, if aesthetics is the main consideration,
recessed conduit wiring system may be adopted.

The wiring for 16 A plug outlets (power circuits) shall
invariably be carried out either in surface/recessed conduit
wiring system where general wiring is on wood batten.

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NATIONAL ELECTRICAL CODE

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Wiring for staircase lights and garage lights may be
done in recessed conduit wiring systems.

7 SWITCHGEAR FOR CONTROL AND

PROTECTION

7.1 Location

7.1.1 All main switches or miniature circuit-breakers
shall be either of metal-clad enclosed pattern or of any
insulated enclosed pattern which shall be fixed at close
proximity to the point of entry of supply.

7.1.2 Open type switch boards shall be placed only in
dry situation and in well ventilated rooms. They shall
not be placed in the vicinity of storage batteries and
exposed to chemical fumes.

7.1.3 Main switch boards shall be installed in rooms
or cupboards having provision for locking so as to
safeguard against operation by unauthorized persons.

7.1.4 In a damp situation or where inflammable or
explosive dust, vapour or gas is likely to be present,
the switch boards shall be totally enclosed or made
flame-proof as may be necessitated by the particular
circumstances.

7.1.5 Switch boards shall not be erected above gas
stoves or sinks or within 2.5 m of any washing unit in
the washing room.

7.1.6 Switch boards, if unavoidably fixed in places
likely to be exposed to weather, to drip, or to abnormal
moist atmosphere, their outer casing shall be
weatherproof and shall be provided with glands or
bushings or adopted to receive screwed conduit
according to the manner in which cables are run. PVC
and double flanged bushes shall be fitted in the holes
of the switches for entry and exit of wires.

7.1.7 A switch board shall not be installed so that its
bottom is within 1.25 m above the floor, unless the
front of the switch board is completely enclosed by a
door, or the switch board is located in a position to
which only authorized persons have access.

7.1.8 Where so required, the switch boards shall be
recessed in the wall. The depth of recess provided at
the back for connection and the space at the front
between the switchgear mountings shall be adequate.

7.1.9 Equipment's which are on the front of a
switchboard shall be so arranged that inadvertent
personal contact with live parts is unlikely during the
manipulation of switchgears, changing of fuses or
similar operations.

7.1.10 No mounting shall be mounted within 2.5 cm
of any edge of the panel and no hole other than the
holes by means of which the panel is fixed shall be
drilled closer than 1.3 cm from any edge of the panel.

7.2 General Requirements of Switchboards

7.2.1 The various live parts, unless they are effectively
screened by insulating material shall be so spaced that
an arc cannot be maintained between such parts and
earth.

The arrangement of the gear shall be such that they
shall he readily accessible and their connections to all
instruments and apparatus shall also be traceable.

7.2.2 In every case in which switches and fuses are
fitted on the same pole, these fuses shall be so arranged
that the fuses are not alive when their respective
switches are in the 'off position.

7.2.3 No fuse other than fuses in instrument circuit
shall be fixed on the back of or behind a switchboard
panel or frame.

7.2.4 All metal switchgears and switchboards shall be
painted and maintained during service.

7.2.5 All switchboards connected to medium voltage
and above shall be installed in accordance with
Part 1/Section 9 of this Code.

7.2.6 The wiring throughout the installation shall be
such that there is no break in the neutral wire in the
form of a switch or fuse unit.

7.2.7 The neutral shall also be distinctly marked.

7.2.8 The main switch shall be easily accessible.

7.3 Types of Switchboards

7.3.1 In dwelling units, the metal clad switchgears shall
preferably be mounted on any of the following types
of boards:

a) Hinged type metal boards — Such boards
shall be suitable for mounting of metal clad
switchgear consisting of not more than one
switchgear and ICDB 4 way or 6 way, 15 A
per way.

b) Fixed type metal boards — Such boards shall
be suitable for large switchboards for
mounting large number of switchgears and
or higher capacity switchgear.

c) Wooden hoards — For small installations
connected to a single phase 240 V supply,
these boards may be used as main board or
sub-boards. These shall be of seasoned and
durable wood with solid back impregnated
with varnish with joints dove-tailed.

NOTE — See also Part 1/Section 9 of this Code.

Where a board has more than one switchgear, each
such switchgear shall be marked to indicate the section
of the installation it controls. The main switchgear shall
be marked as such. Where there is more than one main

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS

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SP 30 : 2011

switchboard in the building, each switchboard shall
be marked to indicate the section of the installation
and building it controls.

7.4 Distribution Boards

7.4.1 Distribution boards shall preferably be of metal
clad type.

7.4.2 Main distribution boards shall be controlled by a
linked switchfuse or circuit-breaker. Each outgoing
circuit shall be provided with a fuse on the phase or
live conductor.

7.4.3 Branch distribution boards shall be controlled
by a switchfuse or circuit-breaker. Each outgoing
circuit shall be provided with a fuse MCB on the phase
or live conductor. The earthed neutral conductor shall
be connected to a common link and be capable of being
disconnected individually for testing purposes. At least
one spare circuit of the same capacity shall be provided
on each branch distribution board.

7.4.4 Triple pole distribution boards shall not
generally be used for final circuit distribution. Where
use of triple pole distribution boards is inevitable,
individual single phase circuit shall be controlled by
double pole isolator.

7.4.5 All distribution boards shall be marked 'Lighting'
or Tower' as the case may be and also with the voltage
and number of phases of the supply.

7.4.6 The distribution boards for light and power
circuits shall be different.

8 SERVICE LINES

The relevant provisions of IS 8061 shall apply.

9 METERING

9.1 It is recommended to have two distinct circuits,
one for lights and fans and the other for high wattage
(power) appliances particularly when the tariff is
different for light and power.

9.2 Energymeters shall be installed at such a place
which is readily accessible to both the owner of the
building and the authorized representatives of the
supply authority. These should be installed at a height
where it is convenient to note the meter reading, it
should preferably not be installed at a height less than
1 m from the ground. The energymeters should either
be provided with a protective covering, enclosing it
completely, except the glass window through which
the readings are noted or should be mounted inside a
completely enclosed panel provided with a hinged or
sliding doors with arrangement for locking it. The
room/space where energy meters are installed shall be
kept clear from any obstruction {see also IS 15707).

9.3 Means for isolating the supply to the building shall
be provided immediately after the energymeter.

10 EARTHING IN DOMESTIC INSTALLATIONS

10.0 Means shall be provided for proper earthing of
all apparatus and appliances in accordance with
Part 1/Section 14 of this Code.

10.1 Plugs and Sockets

All plugs and sockets shall be of three-pin type, one of
the pins being connected to earth.

10.2 Lighting Fittings

If the bracket type lamp holders are of metallic
construction, it is recommended that they should be
earthed. All pedestal lamp fittings of metallic
construction shall be earthed.

10.3 Fans and Regulators

Bodies of all table fans, pedestal fans, exhaust fans,
etc., shall be earthed by the use of three-pin plugs. The
covers of the regulators, if of metallic construction shall
be earthed by means of a separate earth wire.

10.4 Domestic Electric Appliances

Bodies of hot-plates, kettles, toasters, heaters, ovens
and water boilers shall all be earthed by the use of
three-pin plugs. However, if fixed wiring has been used,
then a separate earth wire shall be used for earthing
these appliances.

10.5 Bath Room

The body of automatic electric water heaters shall be
earthed by the use of a three-pin plug or by a separate
earth wire, if fixed wiring has been done. All non-
electrical metal work including the bath tub, metal
pipes, sinks and tanks shall be bonded together and
earthed.

10.6 Radio Sets

From the point of view of good reception it is
recommended that radio sets should be earthed through
an electrode different from that of the main earth
system for other electrical appliances. However, if it is
not possible to have separate earth electrode, radio sets
may be earthed through the main earth system.

10.7 Miscellaneous Apparatus

Where appliances utilizing gas and electricity are in
use, for example, gas-heated electricity-driven washing
machines, the inlet end of the gas supply shall be either
fitted with a strong insulating bush, substantial enough
to stand a flash test of 3 500 V and so designed as to
be difficult to detach, or, where it is desirable or
necessary that metal work in proximity to electrical

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apparatus be bonded to the earthed metal work of the
latter, as for example, in kitchens, the gas supply shall
be introduced through a non-conducting plastic pipe
from a point not in proximity to earthed metal work.
Where separation is not easily achieved, for example,
as in cases of direct-coupled motor-driven gas boosters
and motorized gas valves, the metal work of the
electrical equipment, shall be bonded to the metal or
pipework of gas equipment. In such cases the addition
to the motor control gear of a differential or current-
balance type of circuit-breaker, designed to operate at
low values of fault current, would afford a desirable
safeguard against fault current transfer specially where
the rating of the plant is of a size and capacity which
entails correspondingly high ratings for the normal
overload protective devices.

The refrigerators, air-conditioners and coolers, electric
radiators, electric irons, etc, shall all be earthed by the
use of three-pin plugs.

11 BUILDING SERVICES

11.1 Lighting

The general rules laid down in Part 1/Section 1 1 of
this Code shall apply. The choice of lamps, lighting
fittings shall be based on the recommended values of
illumination given in Table 3. See SP 72 for detailed
guidance.

Tabfie 3 Recommended Levels of Illumination for

Different Parts of Domestic Dwellings
(Clauses 11.1 and 14.3)

SI No.

Location

Illumination Level

lux

(1)

(2)

(3)

Entrances, hallways

100

ii)

Living room

300

iii)

Dining room

150

iv)

Bedroom:

a) General

300

b) Dressing tables, bed heads

200

Games or recreation room

100

vi)

Table games

300

vii)

Kitchen

200

viii)

Kitchen sink

300

ix)

Laundry

200

Bathroom

100

xi)

Bathroom mirror

300

xii)

Sewing

700

xiii)

Workshop

200

xiv)

Stairs

100

xv)

Garage

xvi)

Study

300

11.2 Air-conditioning

11,2.1 The general rules laid down in Part 1/Section 1 1
of this Code shall apply. For domestic dwellings, by

and large, the following types of air-cooling equipment
are used:

a) Evaporative coolers,

b) Packaged air-conditioners, and

c) Room air-conditioners.

11.2.2 The power requirements, layout and design of
electrical installation shall take into account the number
and type of such equipment.

11.3 Lifts

11.3.1 Whenever lifts are required to be installed in
residential buildings, the general rules laid down in
Part 1/Section 11 of this Code shall apply. However,
the design of lifts shall take into account the following
recommendations.

11.3.1.1 Occupant load

For residential (domestic) dwellings, the occupant load
(the number of persons within any floor area) expressed
in gross area in mVperson shall not be less than 12.5.

11.3.1.2 Passenger handling capacity (H)

Expressed as the estimated population that has to be
handled in the buildings in the 5-minute peak period,
the passenger handling capacity for residential
buildings shall be 5 percent.

11.3.1.3 Car speed

Car speed for passenger lifts shall be as follows:

a) In low and medium class flats 0.5 m/s, and

b) Large flats (No. of floors served 6-12)
0.754.5 m/s.

11.3.2 Where a lift is arranged to serve two, three or
four flats per floor, the lift may be placed adjoining
the staircase, with the lift entrances serving direct on
to the landings. Where the lift is to serve a considerable
number of flats having access to balconies or corridors,
it may be conveniently placed in a well ventilated tower
adjoining the building.

12 FIRE PROTECTION

The following protection systems are recommended:

a) One or two family private dwellings — Fire
detection/extinguishing systems not required.

b) Apartment houses/flats

1) Up to 2 storey — Not required.

2) 3 storey and above

i) Floor area less than 300 m 2 — Not

required,
ii) Floor area more than 300 m 2 —

Manually operated electric fire alarm.

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS

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SP 30: 2011

SP 7 may be referred for detailed guidance.

13 TESTING OF THE INSTALLATION

The provisions of Part 1/Section 13 of this Code shall
apply.

14 MISCELLANEOUS PROVISIONS

14.1 Telephone Wiring

Facilities for telephone wiring shall be provided in all
residential buildings where telephones are likely to be
installed. In high rise residential buildings, a riser of
adequate size shall be provided for telephone wiring
cables.

14.2 Safety Requirements

Some of the important safety requirements in electrical
installations in domestic dwellings are summarized
below:

a) All outlets for domestic electrical appliances
shall be of three-pin socket type, third socket
being connected to the earth.

b) All the single pole switches shall be on phase
or live conductor only.

c) The electrical outlets for appliances in the
bathrooms shall be away from the shower or
sink (see Annex A).

d) Wiring for power outlets in the kitchen shall
be preferably done in metallic conduit wiring.

e) The electrical outlets shall not be located
above the gas stove.

f) The clearance between the bottom most point
of the ceiling fan and the floor shall be not
less than 2.4 m.

g) The metallic body of the fan regulator if any,
shall be earthed effectively.

h) Earth leakage circuit-breaker at the intake of
power supply at the consumer's premises (see
Part 1/Section 14 of this Code) shall be
provided.

14.3 Guidelines on Power Factor Improvement in
Domestic Dwellings

General guidelines on principal causes of low power
factor and methods of compensation are given in
Part 1/Section 17 of this Code. For guidance on natural
power factor available for single phase appliances and
equipment in domestic use, see Table 3.

ANNEX A

[Clause 14.2 (c)]

PARTICULAR REQUIREMENTS FOR LOCATIONS CONTAINING A BATH TUB OR

SHOWER BASIN

A-l SCOPE

The particular requirements of this Annex apply to bath
tubs, shower basins and the surrounding zones where
susceptibility of persons to electric shock is likely to
be increased by a reduction in body resistance and
contact with earth potential.

A-2 CLASSIFICATION OF ZONES

A-2.1 The requirements given in this Annex are based
on the dimensions of four zones as described in Fig. 1

and Fig. 2.

a) Zone — is the interior of the bath tub or
shower basin.

b) Zone 1 — is limited:

1) by the vertical plane circumscribing the
bath tub or shower basin, or for a shower
without basin, by the vertical plane 0.6 m
from the shower head; and

2) by the floor and the horizontal plane
2,25 m above the floor.

c) Zone 2 — is limited:

1) by Zone 1 and the vertical parallel plane
0.60 m external to Zone 1, and

2) by the floor and horizontal plane 2.25 m
above the floor.

d) Zone 3 — is limited:

1) by Zone 2 and the parallel vertical plane
2.40 m external to Zone 2, and

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2) by the floor and the horizontal plane

2.25 m above the floor.

NOTE — The dimensions are measured taking account
of walls and fixed partition.

A-3 PROTECTION FOR SAFETY

A-3.1 Where safety extra low voltage is used, whatever
the nominal voltage, protection against direct contact
shall be provided by:

a) barriers or enclosures affording at least the
degree of protection IP2X, or

b) insulation capable of withstanding a test
voltage of 500 V for 1 min.

A-3.2 A local supplementary equipotential bounding
shall connect all extraneous conductive parts in Zones
1, 2 and 3 with protective conductors of all exposed
conductive parts situated in these zones.

A-4 SELECTION OF EQUIPMENT

A-4.1 Electrical equipment shall have at least the
following degrees of protection:

a) Zone : IP X 7

b) Zone 1: IPX 5

c) Zone 2 : IP X 4

d) Zone 3 : IP X 1

IP X 5 in public baths

A-4.2 In Zones 0, 1 and 2, wiring systems shall be limited
to those necessary to the supply of appliances situated
in those zones. Junction boxes are not permitted in Zones
0, 1 and 2. In Zone 3, they are permitted if the necessary
degree of protection is available.

A-4.3 In Zones 0, 1 and 2 no switchgear and accessories
shall be installed.

A-4.4 In Zone 3, socket-outlets are permitted, only if
they are either:

a) supplied individually by an isolating
transformer, or

b) supplied by safety extra-low voltage, or

c) protected by a residual current protective device.

A-4.S Any switches and socket outlets shall be at a
distance of at least 0.60 m from door of the shower
cabinet.

A-4.6 In Zone 0, only electrical appliances specially
intended for use in the bath tub are permitted. In Zone 1
only water heaters may be installed. In Zone 2 only
water heaters and Class II luminaries may be installed.

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS

211

SP 30 : 2011

Bath Tub

ZONE 2 * ZONE 3

:^nix

0.8 m

ZONE 1

Shower Basin

.ZONE 1 ] ZONE 2

o »- |

M z z I
M o o

Y, Y ,1 Y ,Y V V \ V \ \*m\,}

TTT

2.40 m

' ZONE 3

Shower without Basin but with fixed partition

ZONE 1

0.6 m

\ \ \ \ \ \

ZONE 3

£
to

^S^^^CE^TE^^C^

FIXED PARTITION WALL

Fig. 1 Zone Dimensions (Elevation)

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SP 30 : 2011

£2,

roi

a) Bath Tub

b) Bath Tub with flxea Partition

ZONEI ZONE 3
2 i
i

JLfir?^ 2.40m

_^-"

-#J

c> Shower Basin

ZONE

ZONEizone 3

4- •*.-*

i
i
i

d) Shower Basin with Fixed Partition

^^^^2

ZONE

zaszx szzzza

V 0.6m ,'

Z ° NE JZ0NE 3 (
1 ! 2.40m

♦*• :

e) Shower without Basin

SHOWER \ \ [

f) Shower without Basin but with Fixed Partition

-SHOWER HEAD

Fig. 2 Zone Dimensions (Plan)

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS

213

SP 30: 2011

SECTION 2 OFFICE BUILDINGS, SHOPPING AND COMMERCIAL CENTRES

AND INSTITUTIONS

FOREWORD

Office buildings, shopping and commercial centres can
be of various types depending on the size of the civil
structure or the extent of activity involved in the
building. High-rise buildings housing office complexes
are common, calling for a coordinated planning while
designing the electrical services therein.

In small buildings with comparatively moderate loads,
supply is normally at medium voltage and the
distribution of power is less complex. However, in the
case of multi- storied office-cwm-commercial complex,
where the large number of amenities is to be provided
calls for a more complex distribution system. Some of
such buildings has to incorporate a standby/emergency
power plant for essential service needs.

For editorial convenience, and keeping in view the
similarly with the type of buildings covered in this
section, educational and other institutional buildings
are also covered here. Should any special provisions
apply to them, they are identified at the relevant clauses.

It is not possible to define strictly the type of buildings
covered in this Section except in broad terms, an
attempt has been made to identify the nature of the
occupancy. Reference may, however, be made to 3
wherein a description is provided for the various types
of installations covered in this Section.

1 SCOPE

This Part 3/Section 2 of this Code covers requirements
for electrical installations in office buildings, shopping
and commercial centres and educational and similar
institutional buildings.

2 REFERENCES

This Part 3/Section 2 of the Code should be read in
conjunction with the following Indian Standards:

IS No.
3646 (Part 2) : 1966

8061 : 1976

15707 : 2006

Title
Code of practice for interior
illumination: Part 2 Schedule for
values of illumination and glare
index

Code of practice for design,
installation and maintenance of
service lines upto and including
650 V

Testing, evaluation, installation
and maintenance of ac electricity
meters — Code of practice

3 TERMINOLOGY

For the purpose of this Section, the definitions given
in Part 1/Section 2 of this Code shall apply.

4 CLASSIFICATION

The electrical installations covered in this Section, are
those in buildings intended for the following purposes:

a) Office Buildings/Business Buildings — These
include buildings for the transaction of business,
for the keeping of accounts and records and
similar purposes, professional establishments,
offices, banks, research establishments, data
processing installations, etc.

b) Shopping/Commercial Centres/Mercantile
Buildings — These include buildings used as
shops, stores, market, for display and sale of
merchandise, wholesale or retail,
departmental stores, etc.

c) Educational Buildings — These include
buildings used for schools, colleges and
daycare purposes for more than 8 hours per
week involving assembly of people for
instruction and education (including
incidental recreation), etc.

NOTE — Larger assembly buildings recreational
occupancies are covered in Part 3/Section 3 of this Code.

5 GENERAL CHARACTERISTICS OF
INSTALLATIONS

5.0 General guidelines on the assessment of
characteristics of installations in buildings are given
in Part 1 /Section 8 of this Code. For the purpose of
installations falling under the scope of this Section the
characteristics defined below generally apply.

5.1 Environment

The following environmental factors shall apply to
office buildings, shopping and commercial centres and
educational/institutional buildings.

Environment

Characteristics

Remarks

(i)

(2)

(3)

Presence of

Probability of

water

presence of water
is negligible

Presence of

The quantity or

foreign solid

nature of dust or

bodies

foreign solid
bodies is not
significant

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Environment
(1)

Characteristics
(2)

Remarks

(3)

Utilization

(i)

Characteristics
(2)

Remarks
(3)

Presence of
corrosive or
polluting
substances

The quantity and
nature of
corrosive or
polluting
substances is not
significant

Mechanical
stresses

Seismic effect
and lighting

Impact and
vibration of low
severity

Locations where
some chemical
products are
handled in small
quantities, (for
example, labora-
tories in schools
and colleges) will
be categorized as
AF3. For office
and other build-
ings covered by
this Section
situated by the sea
or in industrial
zones, producing
serious pollution,
the categorization
AF2 applies (see
Part 3/Section 8)

Depends on the
location of the
building

5.2 Utilization

The following aspects of utilization shall apply:

Utilization

Cha racteristics

Remarks

(1)

(2)

(3)

Capability of

Uninstructed

A major percentage

persons

of occupants

Children

Applies to schools

Persons

Applies to areas

adequately

such as building

advised or

substations and for

supervised by

operating and

skilled persons

maintenance staff

Contact of

Persons in non-

persons

conducting
situations

Conditions of

Low density

Small offices and

evacuation

occupation, easy

shops

during

conditions of

emergency

evacuation.

High density

Departmental stores

occupation,

difficult

conditions of

evacuation

High density

High rise office

occupation,

commercial centres,

difficult

underground

Nature of
processed of
stored material

conditions of
evacuation
No significant
risks

Existence of
fire risk

shopping arcades,

etc

Small shops

In view of large
volume of paper
and furniture, for
example, office
buildings, furni-
ture shops, etc.

6 SUPPLY CHARACTERISTICS AND
PARAMETERS

6.0 Exchange of Information

6,0.1 Proper coordination shall be ensured between the
architect, building contractor and the electrical engineer
on the various aspects of installations design. From
the point of view of the design of the various
installations, the following shall be considered.

a) Maximum demand and diversity;

b) Type of distribution system, mains and sub-
mains;

c) Nature of supply (current, frequency, nominal
voltages);

d) Prospective short-circuit current at the supply
intake point;

e) Division of the installation;

f) Nature of the external influences (see 4);

g) Maintainability of the installations;

h) Nature and details of building services;

1) Lighting,

2) Air-conditioning, and

3) Lifts.

j) Other details as relevant such as, pumps for
fire fighting, lighting, fire-alarm systems,
telephones, call-bells, clock systems, etc;

k) Telephone circuits including extensions and
intercom facilities;

m) CCTV for information display and security;

n) Computer installation facility where
applicable; and

p) Metering system for different loads.

NOTE — Fire protection system shall include such
details such as locations of detectors, zonal indicators,
central control console, public address system for fire
fighting, cable runs and their segregation from the other
cable system.

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS

215

SP 30: -2011

A complete drawing of layout of the electrical
installation shall be prepared together with associated
floor plans indicating the details mentioned in (a) to
(p). This wiring diagram shall include outlets for lights,
sockets, bells, ceiling fans, exhaust fans, location of
sectionalized control switches, distribution boards, etc.
In special occupancies such as school or college
laboratories, the dc circuits be identifiable in the layout
diagram.

6.1 Branch Circuits

6.1.1 The general design of wiring of branch circuits
shall conform to those laid down in Part 1 /Section 1 1
of this Code. However, for special cases such as for
communication networks, fire-alarm system and wiring
for data-processing equipment, the recommendations
of the manufacturer shall apply.

6.1.2 The branch circuit calculations shall be done
according to the general provisions laid down in Part 3/
Section 1 of this Code. However, the specific demands
of the lighting, appliance and motor loads as well as
special loads encountered in the types of buildings
covered in this Section shall be taken into account.

6.1.3 In offices and showrooms, the interior decoration
normally include false ceiling, carpets and curtails. Any
wiring laid above the false ceiling should be adequately
protected such as by drawing the wires in metallic
conduits and nor run in open. Wires shall not be covered
by carpets. They shall be run at skirting level and
encased for mechanical protection.

6.1.4 Adequate number of socket-outlets shall be
provided for electrically operated office machines such
as electrical typewriter, calculators, etc, to avoid
training of wires and use of multiple outlets from one
socket.

6.1.5 Areas where corrosive or polluting substance are
present intermittently or continuously, such as school
laboratories and other buildings located in high
industrial pollution zones, socket-outlets shall
preferably be of metal clad weatherproof type with
covers.

6.1.6 Lighting circuits shall preferably be combined
in switched groups so that lighting can be limited to
desks which are occupied.

6.2 Service Lines

The general provisions laid down in IS 8061 shall
apply.

6.3 Building Substations

6.3.0 General

The designer of power supply for office buildings and
commercial centres shall take into account the great

concentration of power demand of the electrical loads.
Air-conditioning in office buildings absorbs an
especially high proportion of the total power used.
Consequently, such occupancies have to be provided
with their own substation with vertical and horizontal
forms of power distribution.

6.3.1 If the load demand is high, requiring supply at
high voltage, accommodation for substation equipment
will be required. Main switch room will serve feeders
to various load centres such as air-conditioning plant,
elevators, water pumps, etc. Other loads are taken to
local distribution boards.

6.3.2 The transformer power rating for the supply of
the building shall be sufficient to cater to the highest
simultaneous power requirements of the building.
Typical proportions of power usage are given as
follows:

Part of Electrical

Part of the Total

Diversity

Installation

Power Requirement
Percent

Factor

(1)

(2)

(3)

Ventilation, heating

1.0

(air-conditioning)

Power plant (drives)

0.65

Lighting

0.95

Lifts

1.0

63.3 The location and layout of building substation
shall conform to the general rules laid down in Part 2
of this Code. The substation room shall be well
ventilated and inaccessible to birds and reasonably
reptile-, rodent- and insect-proof. Only authorized
persons be allowed to enter the substation for
operations/maintenance of any kind. Cables leading
from the substation to the main building shall
preferably be carried underground through ducts or
pipes of adequate dimensions. Such pipes shall be
properly sealed at both ends to reduce the possibility
of rain water flowing through the pipes and flooding
the trenches.

6.3.4 Emergency Supply

Wherever emergency supply is considered necessary,
it can be in the form of separate and independent feeder
from the undertaking terminated in equipment isolated
from the regular supply line. In case of standby supply
from diesel generator set, it will be installed as per the
general rules laid down in Part 2 of this Code.

6.3.4.1 In office buildings, certain safety and essential
services shall be supplied even in the case of mains
failure. These are governed by the rules and regulations
of the respective authorities. Essential services include
amongst others, water-pressure pumps, ventilation

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NATIONAL ELECTRICAL CODE

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installations, essential lighting and lifts. The power
requirement of these essential loads is generally about 25
percent of the total power requirement of the building.

6.3.5 Switchboards and Panel Boards

All current carrying equipment shall be totally
enclosed, dust-and vermin-proof and if mounted
outdoor, shall be of weatherproof construction or
housed in weatherproof kiosk or cabin. Switchboards
shall be of open type or cubicle type. Cubicle type
boards shall be with hinged doors interlocked with
switch-operating mechanisms. All switches shall bear
labels indicating their functions. Switchboards shall
be located away from areas likely to be crowded by
the public.

6.3.6 Selection of equipment shall be made according
to the guidelines laid down in Part 1 /Section 9 of this
Code. For the purposes of office buildings, shopping
and commercial centres, miniature circuit-breakers of
adequate capacity shall be preferred to switchfuse units.
They can also be effectively used in place of fuses in a
distribution board.

6.4 Metering

In multi-storied buildings, a number of offices, and
commercial centres occupy various areas. Electrical
load for each of them would have to be metered
separately; the meter-room normally is situated in the
ground floor (see IS 15707 for further guidance).

6.5 System Protection

6.5.0 General

The general rules for protection for safety laid down
in Part 1/Section 7 of this Code shall apply. Reference
is also drawn to SP 7 on guidelines for fire protection
of buildings. The general rules given below shall apply.

6.5.1 The type of buildings covered in this Section fell
under Group B (educational buildings). Group E
(business buildings) and Group F (mercantile
buildings) from the point of view of fire safety
classification (see SP 7). Typical fire fighting
installation requirements are also covered therein. The
electrical needs for the appropriate type of installation
shall, therefore, be decided accordingly.

6.5.1.1 Educational buildings (Group B)

Educational buildings above 2- storeys having an area
of more than 500 m 2 per floor shall have besides fire-
fighting equipment, manually operated electrical fire
alarm and automatic fire alarm systems.

6.5.1.2 Business buildings (Group E)

Besides fire-fighting equipment, automatic fire alarm
systems are recommended for offices, banks,

professional establishments, etc, where the buildings
are more than 2 storey with floor area above 500 m 2
per floor, and for laboratories with delicate instruments
as well as computer installations.

6.5.1.3 Mercantile buildings (Group F)

Besides fire-fighting equipment, automatic sprinkles
and automatic fire alarm systems are recommended
for wholesale establishments, warehouses, transport
booking agencies, etc, as well as for shopping areas
inside buildings with area more than 500 m 2 on each
floor. For other premises and shopping lines with
central corridors open to sky, automatic fire-alarm
systems shall be installed. Underground shopping
centres shall be provided with automatic sprinkles.

6.6 Building Services

6.6.1 Lighting

6.6.1.1 The general rules laid down in Part 1/Section 1 1
of this Code shall apply. The choice of lamps, lighting
fittings and general lighting design together with power
requirement shall be planned based on the
recommended values of illumination and limiting
values of glare index given in Table 1.

6.6.1.2 In commercial premises, a fairly high level of
glare free lighting on working planes and subdued
lighting in circulation areas are necessary. Aesthetics
and interior decoration also play a part. Lighting design
in showrooms includes high level of lighting in the
vertical and horizontal planes, depending on the
merchandise exhibited and their layout. Colour
temperature characteristics of the light source shall
also be taken into account in the case of showroom
lighting.

6.6.2 Air-conditioning

6.6.2.1 The general rules laid down in Part 1/Section 14
of this Code shall apply. The design of the air-
conditioning system, shall take into account the
requirements stipulated in the following clauses.

6.6.2.2 In case of large air-conditioning installations
(500 tonne and above) it is advisable to have a separate
isolated equipment room together with electrical
controls. All equipment rooms shall have provision for
mechanical ventilation.

6.6.3 Lifts and Escalators

6.6.3.1 The general rules laid down in Part 1/
Section 14, of this Code shall apply. However, the
design of lifts shall take into account the following
recommendations :

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS

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SP 30: 2011

Table 1 Recommended Values of Illumination and Glare Index

{Clause 6.6.1)

SSNo.

(l)

BuiBding

(2)

Illumination

Limiting Glare Index

lux

(3)

(4)

300 ■

150

70-150

150-300

300-700

150-300

150

300

450

—

100

—

100

—

200

150

300

200-300

—

700

450

{see SI No. ii above.)

[see appropriate trades

in IS 3646 (Part 2)]

300

150

—

100

—

150-300

200

Banks:

a) Counters, typing accounting book areas

b) Public areas

ii) Libraries;

Shelves

Reading rooms (newspaper, magazines)

Reading tables

Book repair and binding

Cataloging, sorting, stock rooms

iii) Off

ices:

Entrance halls and reception area

Conference rooms, executive offices

Genera] offices

Business machine operation

Drawing offices

Corridors and lift cars

Stairs

Lift landings

Telephone exchanges;

1) Manual exchange rooms (on desk)

2) Main distribution frame room

iv) Schools and colleges:

Assembly halls:

1) General

2) When used for exams

3) Platforms

Class and lecture rooms:

1) Desks

2) Black board

Embroidery and sewing rooms

Art rooms

Libraries

Manual training

Offices

Staff rooms, common rooms

Corridors

Stairs

v) Shops and stores^:

General areas

Stock rooms

Does not cover display (showroom lighting).

6.6.3.2 Occupant load
These shall be as follows:

Occupancy

Occupation

No.

Load Gross Area
in m 2 /Person

(1)

(2)

(3)

Educational

ii)

Business

iii)

Mercantile:

1) Ground floor and sales

2) Upper sale floor

6.6.3.3 Passenger handling capacity (H)

These are expressed in terms of percent of the estimated
population that has to be handled in the building in the
5 min peak period as follows:

SI
No.
(1)

Occupancy

(2)

(Percent)
(3)

i) Diversified (mixed) office occupancy 10-15
ii) Single purpose office occupancy 15-25

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6.6.3.4 Car speed — These shall be as follows:

Occupancy

No. of

Car

No.

Floors

Speed

Served

20 m/s

(1)

(2)

(3)

(4)

Office building

4-5

0.5-0.75

6-12

0.75-1.5

13-20

Above 1.5

ii)

Shops and departmental

stores

2-2.5

6.6.3,5 For office buildings, it is desirable to have at
least a battery of 2 lifts at two or more convenient
points. If this is not possible, it is advisable to have at
least two lifts side by side at the main entrance and
one lift each at different sections of the building for
inter-communication. When two lifts are installed side
by side, the machine room shall be suitably planned.
All machines and switchgear may be housed in one
machine room.

7 TESTING OF INSTALLATION

The various tests on the installation shall be carried
out as laid down in Part 1/Section 13 of this Code.

8 MISCELLANEOUS PROVISIONS

8.1 Group Control

8.1.1 The lighting circuits shall preferably be combined
in switched groups as well as coordinated to functional
groups of desks in an open plan office. The switching
points may be combined centrally at the entrance
passageways. In order to ensure proper co-ordination
with design of the building for daylight use of devices
such as photoelectric switches shall be encouraged for
controlling lighting groups near windows.

8.2 Telephones/Intercoms

8.2.1 Adequate coordination shall be ensured right from
the planning stages with the telephone authorities to
determine the needs for the telephone system catering
to the various units in office buildings. For private
intercom systems, entirely under the control of the user,
it is necessary to pre-plan the coordination of external
and intercom systems.

8.3 Electric Call Bell System

8.3.1 The general guidelines laid down in Part 1/
Section 11, regarding installation of electric bells and
call system shall be referred to. Depending on the final
requirements of the type of occupancy, the type of
equipment to be used, wiring and other details shall be
agreed to.

8.3.2 A simple call bell system is suitable for small
offices whereby service staff may be called to a
particular position by the caller. A visible- cwm-audible
indicator/bell panel shall be used. When call points are
too numerous on a single indicator panel, such as in
large offices, multiple call system shall be preferred.
The layout in such a case would be determined by the
size of building and staff. Time bell systems shall be
installed in schools to give Start-work and Stop-work
signals.

8.4 Clock Systems

8.4.1 The general guidelines contained in Part 1/
Section 14 shall apply regarding installation and
maintenance of master and slave clock systems.

8.4.2 In simple installations, impulse clocks designed
to operate at the same current may be connected in
one series circuit, with a battery having sufficient
voltage to ensure satisfactory operation. In a more
complex installation like multi-storeyed office
buildings with large number of slave clocks, the
impulse clocks may be arranged in number of series
circuits. Each of which is connected to a pair of
contact on a relay which is operated from the contacts
of master clock.

8.4.3 Master clock shall be placed in a dust free
location, readily accessible for maintenance at all
times.

8.5 Closed Circuit TV

8.5.1 Commercial buildings may require the
installations of CCTVs for one of more of the following
purposes:

a) Security, and

b) Information display.

Educational/institutional buildings may use CCTV as
a teaching aid for pre-recorded educational
programmes. Reference shall be made to good practice
for installations of such facilities.

8.6 Emergency Lights for Critical Areas

Battery powered (at least 2 h rating) emergency lights
should be installed at critical and strategic locations
including emergency exit points. These will provide
illumination by self contained battery source even on
failure of a.c. mains. On resumption of a.c. power supply,
they will switch back to mains automatically and
simultaneous recharge the battery to the required level.

8.7 Emergency Exit Signage

Photo luminescent safety signage should be provided
at different strategic locations.

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS

219

SP 30 : 2011

SECTION 3 RECREATIONAL, ASSEMBLY BUILDING

FOREWORD

A variety of buildings are being used for public assembly
for purposes that are recreational, amusement, social or
religious. These include cinema halls, theatres, auditoria
and the like, the primary feature being a congregation
of people of all age groups for a short period of time
during a day or a group of days. Buildings such as those
catering to display of regular programmes demands a
continuous power supply. In view of the nature of use
of such occupancies, certain specific safety and
reliability considerations become necessary for the
electrical installations.

The lighting design of such buildings are generally
sophisticated, required to be properly coordinated with
the electro-acoustic demands. On the physical aspects
of lighting and sound systems in recreational buildings,
it is recommended that assistance should be derived
from specialists as such details are beyond the scope
of this Code.

Sports buildings, which are also basically assembly
buildings, are covered separately under Part 3/Sec 6
of this Code, in view of their unique nature. The type
of buildings covered in this Section are enumerated
in 4. It shall also be noted that assembly buildings
forming part of other building complex, say,
educational or office-commercial-cum-cinema
complex shall also comply with this Section.

1 SCOPE

1.1 This Part 3/Section 3 of the Code covers
requirements for electrical installation in buildings,
such as those meant for recreational and assembly
purposes,

1.2 This Part 3/Section 3 does not cover sports
buildings.

2 REFERENCES

This Part 3/Section 1 of the Code should be read in
conjunction with the following Indian Standards:

IS No. Title

8061 : 1976 Code of practice for design,

installation and maintenance of
service lines upto and including
650V

SP 72 : 2010 National Lighting Code

3 TERMINOLOGY

For the purpose of this Section, the definitions given
in Part 1 /Section 2 of this Code shall apply.

4 CLASSIFICATION

4,1 The electrical installations covered in this Section,
are those in buildings intended for the following purposes:

Assembly/Recreational Buildings — These shall
include any building where groups of people
congregate or gather for amusement, recreation, social,
religious, patriotic, civil and similar purposes, for
example, theatres, motion-picture (cinema) houses,
assembly halls, auditoria, exhibition halls, museums,
restaurants, places of worship, dance halls, clubs, etc.

NOTE — Theatres are also classified further as permanent (air-
conditioned and non-air-conditioned), temporary or traveling
depending on the nature or construction of the premises.
Temporary installations shall also conform to the additional
provisions laid down in Part 5/Section 2 of this Code.

5 GENERAL CHARACTERISTICS OF
INSTALLATIONS

5.0 General guidelines on the assessment of
characteristics of installations in buildings are given
in Part 1/ Section 8 of this Code. For the purpose of
installations falling under the scope of this section, the
characteristics defined below generally apply.

5.1 Environment

The following environmental factors shall apply to
recreational and assembly buildings:

Environment Characteristics Remarks

(1) (2) (3)

Presence of

Probability of

—

water

presence of
water is
negligible

Presence of

The quantity or

—

foreign solid

nature of dust or

bodies

foreign solid
bodies is not
significant

Presence of

The quantity

—

corrosive or

and nature of

polluting

corrosive or

substances

polluting
substances is
not significant

Mechanical

Impact and

—

stresses

vibration of low
severity

Seismic effect

—

Depends on the

and lighting

location of the
building

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NATIONAL ELECTRICAL CODE

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5.2 Utilization

The following aspects of utilization shall apply:

Utilization

Characteristics

Remarks

(1)

(2)

(3)

Capability of Uninstructed persons

Majority of

persons

the occupants

Persons adequately

Electrical

advised or supervised by

operating

skilled persons

areas

Conditions

High density occupation,

Small theatres

of evacuation easy conditions of

and cinemas

during

evacuation

emergency

High density occupation

Multiple

difficult conditions of

cinema halls,

evacuation

cultural and

theatrical

buildings

Nature of

Existence of fire risk

In view of

processed of

large quantum

stored

of furniture

material

and drapings

6 SUPPLY CHARACTERISTICS AND
PARAMETERS

6.0 Exchange of Information

6.0.1 Proper coordination shall be ensured between the
architect, building contractor and the electrical engineer
on the various aspects of the installation design in a
building intended for recreational or assembly
purposes. For large projects, the advice of the
appropriate specialists shall be obtained, in particular
on the following aspects:

a) Audio- visual systems,

b) Stage lighting and control, and

c) General auditorium lighting and other special
service needs.

6.0.2 The installation work shall conform to the
provisions of Indian Electricity Rules as well as other
Rules applicable for assembly buildings formulated by
the State Authorities.

6.1 Branch Circuits

6,1.0 The branch circuits shall in general cater to the
following individual load groups:

a) Power installation:

1) Stage machinery,

2) Ventilation and
installation,

air-conditioning

3) Lifts, and

4) Additional power connections.

b) Lighting:

1) In front of the theatre, such as general
lighting of outdoor, foyer, corridors and
stairs, and auditorium; and

2) In the rear of the theatre for stage, work
place dressing rooms, workshops and
storehouses.

c) Emergency supply.

6.1.1 The electrical lighting of the main building shall
have at least three separate and distinct main circuits
as follows:

a) For the enclosures (cabin) and hence through
a dimmer regulator to the central lighting of
the auditorium;

b) For one-half of the auditorium, passage ways,
stairways, exit and parts of the building open
to the public; and

c) For the remaining half of the auditorium,
passage ways, stairways, exit and parts of the
building open to the public.

6.1.2 The control of the circuits in respect of the two
halves of the auditorium referred to in 6.1.1 shall be
remote from each other.

6.1.3 The cabin shall be provided with two separate
circuits, one feeding the cabin equipments and the other
lights and fans.

6.1.4 Wiring shall be of the conduit type. Ends of
conduits shall enter and be mechanically secured to the
switch, control gears, equipment terminal boxes, etc.
Ends of conduits shall be provided with screwed bushes.
Within the enclosure, all cables shall be enclosed in
screwed metal conduits adequately earthed. PVC
conduits may be used in the auditorium and other places.

6.1.5 Temporary wiring shall not be allowed in cabin,
rewinding room, queue sheds and similar places.

6.1.6 The cabin equipment shall be accessible at all
times. Nothing shall impede access to any part of the
equipment or its controls.

6.1.7 Linked tumbler switches shall not be used for
the control of circuits.

6.1.8 Branch and main distribution boards shall be
mounted at suitable height not higher than 2 m from
the floor level. A front clearance of 1 m should also be
provided.

6.1.9 Wood work shall not be used for the mounting of
or construction of the framework for iron-clad switch
and distribution boards and controlgear.

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS

221

SP 30 : 2011

6.1.10 All the lighting fittings shall be at a height of
not less than 2.25 m.

6.1.11 The single pole switches for the individual lights
and fans shall be mounted on sheet steel boards suitably
earthed.

6.1.12 Suitable socket outlets with controls shall be
provided on the side walls near the stage for tapping
supply to screen motor; stage focusing lights, audio
systems and portable lights.

6.1.13 In the queue sheds, bulk head fittings shall be used. 6 * 5 s y stem Protection

a) As there will be concentration and movement
of people, the substation should be located
away from the area where people and vehicles
move about, preferably at the rear of the
building.

b) The substation should not be in the way of
people and fire-fighting vehicles and
personnel where they are likely to attend to
an emergency.

6.1.14 For outdoor lighting, water-tight fittings shall
be used and fittings may be so mounted without
spoiling the aesthetic view of the recreation buildings.

6.1.15 The installation in a traveling cinema should
generally conform to the above requirements and the
building should be sufficiently away from the nearest
conductor of power lines {see 3.2 of Part 1 /Section 7
of this Code).

6.1.16 The plug points shall be provided at a height of
about 1.5 m from the floor, in assembly buildings.

6.1.17 In case of travelling cinemas, the wiring for the
open yard lighting shall be done with weather-proof
cables threaded through porcelain reel insulators
suspended by earthed bearer wire at a height of not
less than 5 m from ground level. The reel insulators
shall be spaced 0.5 m from each other.

6.1.18 When a tapping is taken from the open yard
wiring, it should be taken only at a point of support
through porcelain connectors housed in a junction box,
fixed to the supporting pole.

6.2 Feeders

6.2.1 Feeder circuits shall generally conform to the
requirements laid down in Part 1 /Section 1 1 of this
Code.

6.2.2 Separate feeders shall be taken to air-conditioning
units, lifts and the lighting and fan circuits.

6.3 Service Lines

Service lines shall conform to IS 8061.

6.4 Building Substation

6.4.0 The electrical power demand of an assembly
building can vary from 30 kVA to more than 1 000 kVA
according to the size of the building. Usually, supply
at voltages above 1 kV is given for large theatres and
auditoria. Building substations shall conform to the
general requirements specified in Part 2 of this Code.

6.4.1 The following aspects shall be taken note of while
deciding the location of substation:

6.5.0 The rules for protection for safety laid down in
Part 1 /Section 7 of this Code shall apply. Reference
may also be made to SP 7 on guidelines for fire
protection of buildings. The general rules given below
shall apply.

6.5.1 The type of occupancies covered in this Section
fall under Group D (assembly buildings) from the point
of view of fire safety classification. Such occupancies
can be further classified into groups depending on the
capacity of the theatre [auditorium to hold the
congregation {see SP 7)]. Typical fire-fighting installation
requirements are also covered therein. The following shall
be provided besides fire-fighting equipment:

a) Building having a theatrical stage and fixed
seats:

1) Stage — Automatic sprinkler; and

2) Auditoria, corridor, green rooms, canteen
and storage Automatic fire-alarm system.

b) Buildings without a stage but no permanent
seating arrangement — Automatic fire alarm
system.

c) All other structures designed for assembly —
Manually operated electrical fire-alarm
system.

6.6 Building Services

6.6.1 Lighting

The general rules laid down in Part 1 /Section 1 1 of
this Code shall apply. The choice of lamps, lighting
fitting and general lighting design together with power
requirement shall be planned based on the
recommended values of illumination and glare index
given in Table 1 {see SP 72).

6.6.2 Air-conditioning

6.6.2.1 The general rules laid down in Parti/Section 1 1
of this Code shall apply.

6.6.2.2 In air-conditioned assembly buildings, inside
temperature shall be 22 ± 2°C.

6.6.2.3 Provisions shall be made to record the
temperature inside the auditorium.

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NATIONAL ELECTRICAL CODE

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Table 1 Recommended Values of Illumination

and Glare Index
(Clause 6.6.1)

Part of Building

Illumination

Limiting Value of

No.

lux

Glare Index

(1)

(2)

(3)

(4)

Assembly and concert:

a) Foyers, auditoria

100450

—

b) Platforms

450

—

c) Corridors

—

d) Stairs

100

—

Cinemas:

a) Foyers

150

—

b) Auditoria

—

c) Corridors

—

d) Stairs

100

—

Museums:

a) General

150

b) Display

Special lighting

Art Galleries:

a) General

100

b) Paintings

200

Theatres:

a) Foyers

150

—

b) Auditoria

—

c) Corridors

—

d) Stairs

100

—

NOTE — The above is

meant for general

guidelines and

does not include special lighting effects.

6.6.2.4 In the event of a breakdown of the air-
conditioning plant, alternate arrangements should be
available for ventilation and air circulation.

6.6.3 Lifts and Escalators

The general rules laid down in Part 1/Section 11 of
this Code shall apply. However, the design of the lifts
shall take into account the following recommendations:

Occupant load

This shall be as follows:

Occupancy

Occupant Load, Gross
Area (m 2 /Person)
0.6

Assembly halls with

fixed or loose seats

and dance floors

Without seating 1.5

facilities including

dining rooms

Passenger handling capacity and car speed
As given in Part 3/Section 2 of this Code.

7 TESTING OF INSTALLATIONS

The various tests on the installations shall be carried
out as laid down in Part 1/Section 13 of this Code.

8 MISCELLANEOUS PROVISIONS

8.1 Emergency Supply
See also Part 2 of this Code.

8.1.1 In all recreational and assembly buildings,
sufficient number of emergency lights in all the
locations which includes all the emergency exit.

8.1.2 Battery powered (at least 2 h rating) emergency
lights should be installed at critical and strategic
locations to avoid catastrophic in case of total power
failure. These will provide illumination by self
contained battery source even on failure of a.c. mains.
On resumption of a.c. power supply, they will switch
back to mains automatically and simultaneous recharge
the battery to the required level.

8.1.3 Depending on the total capacity required for
standby supply for the occupancy, suitable standby
generator set shall be installed. The location and
installation of the standby DG set should be in
accordance with the norms specified in Part 2 of this
Code.

8.2 Stage Lighting

On the stage of a theatre, a great number of spotlights,
border lights, projectors, etc, are required for
illumination, including portable light sources. The
various possibilities of switching each fittings shall be
kept in view while designing the lighting circuits. For
same lighting schemes, dimmer-control equipment
may be required.

8.3 Group Control

The lighting in the auditorium shall be suitably
combined into control groups to facilitate group
switching. In the special case of stage lighting control,
the lighting operator shall have a good view of the stage
in order to be able to follow the performance.
Therefore, the control-room shall be situated in a
convenient position.

8.4 Audio- Visual System

Installation of amplifying and sound distribution
systems shall conform to the guidelines contained in
Part 1/Section 11 of this Code!

8.5 Luminous Sign

Photo luminescent safety signage should be provided
at different strategic locations.

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUS TRIAL BUILDINGS

223

SP 30: 2011

SECTION 4 MEDICAL ESTABLISHMENTS

FOREWORD

Hospitals in the country vary in size from simple
premises used for medical purposes in villages to a
well-equipped, multidisciplinary hospital in big cities.
The lattser type will have several units functioning
simultaneously with a variety of support services to
cater to the needs of doctors and patients.

Safety requirements for electrical equipment used in
medical practice are covered IS 13450 series.
Additional safety provisions in the electrical
installations of medically used rooms and medical
establishments are covered in this Section of the Code.
This Section 4 is based on the following
considerations:

a) The patient may not be in a condition to react
normally to the effects of hazardous events;

b) The electrical resistance of the skin, which is
normally an important protection against
harmful electric currents is bypassed in certain
examinations or treatments;

c) Medical electrical equipment may often be
used to support or substitute vital body
functions, the breakdown of which may cause
a dangerous situation;

d) Specific locations in medical establishments
where flammable atmosphere exists, call for
special treatment; and

e) Electric and magnetic interference may
disturb certain medical examinations or
treatments.

1 SCOPE

This Part 3/Section 4 of this Code applies to the
electrical installations in medical establishments. This
Section is also applicable to rooms for veterinary
medicine and dental practice.

2 REFERENCES

This Part 3/Section 4 of the code should be read in
conjunction with the following Indian Standards:

IS No. Title

3646 (Part 2) : Code of practice for interior

1966 illumination : Part 2 Schedule for

values of illumination and glare

index
7689 : 1989 Guide for the control of

undesirable static electricity
8061 : 1976 Code of practice for design,

installation and maintenance of

IS No.

13450 (Parti):

1994 /IEC

60601-1 : 1988
14665 (Part 1) :

2000

SP 7 : 2005
SP 72 : 2010

Title

service lines upto and including

650 V

Medical electrical equipment :

Part 1 General requirements for

safety

Electric traction lifts : Part 1
Guidelines for outline dimensions
of passenger, goods, service and
hospital lifts

National Building Code of India
National Lighting Code

3 TERMINOLOGY

In addition to the definitions contained in Part 1/
Section 2 of this Code the following shall apply.

3,1 Rooms

3.1.1 Anaesthetic Room — Medically used room in
which general inhalation anesthetics are intended to
be administered.

NOTE — Anaesthetic room comprises for instance the actual
operating theatre, operating preparation room, operating plaster
room and surgeries.

3.1.2 Angiographic Examination Room — Room
intended for displaying arteries or veins, etc, with
contrast media.

3 A3. Central Monitoring Room — Room in which the
output signals of several patient monitors are displayed,
stored or computed.

NOTE — A centra] monitoring room is considered to be part
of a Room Group, if a conductive connection (for example, by
signal transmission lines) between the rooms of such a group
exists.

3.1,4 Central Sterilization Room — Room, not spatially
connected to a medically used room, in which medical
equipment and utensils are sterilized.

3.1.5 Delivery Room -
takes place.

- Room in which the actual birth

3.1.6 Endoscopic Room — Room intended for
application of endoscopic methods for the examination
of organs through natural or artificial orifices.

Examples of endoscopic methods are bronchoscopic,
laryngoscopy, cystoscopic, gastroscopic and similar
methods, if necessary, performed under anaesthesia.

3.1.7 Heart Catheterization Room — Room intended
for the examination or treatment of the heart using
catheters.

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NATIONAL ELECTRICAL CODE

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Examples of applied procedures are measurement of
action potentials of the haemodynamics of the heart,
drawing of blood samples, injection of contrast agents
or application of pacemakers.

3.1.8 Hemodialysis Room — Room in a medical
establishment intended to connect patients to medical
electrical equipment in order to detoxicate their blood.

3.1.9 Hydrotherapy Room — Room in which patients
are treated by hydrotherapeutic methods.

Examples of such methods are therapeutic treatments
with water, brine, mud, slime, clay, steam, sand, water
with gases, brine with gases, inhalation therapy,
electrotherapy in water 1 } , massage thermotherapy and
thermotherapy in water 1} .

Swimming pools for general use and normal bath-
rooms are not considered as hydrotherapy rooms.

3.1.10 Intensive Care Room — Room in which bed
patients are monitored independently of an operation
by means of electromedical equipment Body actions
may be stimulated, if required.

3.1.11 Intensive Examination Room — Room in which
patients are connected for the purpose of intensive
examination, but not for the purpose of treatment,
simultaneously to several electromedical measuring or
monitoring devices.

3.1.12 Intensive Monitoring Room — Room in which
operated patients are monitored, using electromedical
equipment. Body actions (for example, heart
circulation, respiration) may be stimulated, if required.

3.1.13 Labour Room — Room in which patients are
prepared (waiting) for delivery.

3.1.14 Medical Establishment — Establishment for
medical care (examination, treatment, monitoring,
transport, nursing, etc) of human beings or animals.

3.1.15 Medically Used Room — Room intended to be
used for medical, dental or veterinary examination,
treatment or monitoring of persons or animals.

3.1.16 Minor Surgical Theatre — Room in which
minor operations are performed on ambulant or non-
ambulant patients, if necessary using anesthetics or
analgesics.

3.1.17 Operating Plaster Room — Room in which
plaster of Paris or similar dressings are applied while
anaesthesia is maintained.

NOTE — Such a room belongs to the operating room group
and is usually spatially connected to it.

3.1.18 Operating Preparation Room — Room in which

l) With or without additives.

patients are prepared for an operation, for example,
by administering anaesthetics.

NOTE — Such a room belongs to the operating room group
and is spatially connected to it.

3.1.19 Operating Recovery Room — Room in which
the patient under observation recovers from the
influence of anesthesia.

NOTE — Such a room is usually very close to the operating
room group but not necessarily part of it.

3.1.20 Operating Sterilization Room — Room in which
utensils required for an operation are sterilized.

NOTE — Such a room belongs to the operating room group
and is spatially connected to it.

3.1.21 Operating Theatre — Room in which surgical
operations are performed.

3.1.22 Operating Wash Room — Room in which
medical staff at an operation can wash for disinfection
purposes.

NOTE — Such a room belongs to the operating room group
and is spatially connected to it.

3.1.23 Physiotherapy Room — Room in which patients
are treated by physiotherapeutic methods.

3.1.24 Radiological Diagnostic Room — Room
intended for the use of ionizing radiation for display
of internal structures of the body by means of
radiography or fluoroscopy or by the use of radio-active
isotopes or for other diagnostic purposes.

3.1.25 Radiological Therapy Room — Room intended
for the use of ionizing radiation to obtain therapeutic
effects on the surface of the body or in internal organs
by means of X-radiation, gamma radiation or
corpuscular radiation or by the use of radio-active
isotopes.

3.1.26 Room Group — Group of medically used rooms
linked with each other in their function, by their
designated medical purpose or by interconnected
medical electrical equipment.

3.1.27 Urology Room — Room in which diagnostic or
therapeutic procedures are performed on the urogenital
tract using electromedical equipment, such as X-ray
equipment, endoscopic equipment and high-frequency
surgery equipment.

3.1.28 Ward — Medically used room or room group
in which patients are accommodated for the duration
of their stay in a hospital, or in any other medical
establishment.

3.2 Zones of Risk (see also Annex A).

3.2.1 Flammable Anaesthetic Atmosphere — Mixture
of a flammable anaesthetic vapour and/or a vapour of
a flammable disinfection or cleaning agent with air in

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SP 30 : 2011

such a concentration that ignition may occur under
specified conditions.

3.2.2 Flammable Anaesthetic Mixture — Mixture of a
flammable anaesthetic vapour with oxygen or with
nitrous oxide in such a concentration that ignition may
occur under specified conditions.

3.2.3 Zone G — Volume in a medically used room in
which continuously or temporarily small quantities of
flammable anaesthetic mixtures may be produced, guided
or used including the surroundings of a completely or
partly enclosed equipment or equipment part up to a
distance of 5 cm from parts of the equipment enclosure
where leakage may occur because such parts are:

a) unprotected and liable to be broken,
c) subject to a high rate of deterioration, or
c) liable to inadvertent disconnection.

Where the leakage occurs into another enclosure which
is not sufficiently (naturally or forcedly) ventilated and
enrichment of the leaking mixture may occur, such an
enclosure and possibly the surroundings of it (subject
to possible leakage) up to a distance of 5 cm from said
enclosure or part of it is regarded as a Zone G.

3.2.4 Zone M — Volume in a medically used room in
which small quantities of flammable anaesthetic
atmospheres of flammable anaesthetics with air may
occur. A Zone M may be caused by leakage of a
flammable anaesthetic mixture from a Zone G or by
the application of flammable disinfection or cleaning
agents. Where a Zone M is caused by leakage, it
comprises the space surrounding the leakage area of a
Zone G up to a distance of 25 cm from the leakage
point.

3.3 Special Terms

3.3.1 Equipotential Bonding — Electrical connection
intended to bring exposed conductive parts or
extraneous conductive parts to the same or
approximately the same potential.

3.3.2 Essential Circuit — Circuit for supply of
equipment which is kept in operation during power
failure.

NOTE — Provisions for supply of such circuit separately from
the remainder of the electrical installation are present.

3.3.3 Generator Set — Self-contained energy convenor
including all essential components to supply electrical
power (for example, engine driven generator).

3.3.4 Hazard Current — Total current for a given set
of connections in an isolated power system that would
flow through a low impedance if it were connected
between either — isolated conductor and earth.

The following hazard currents are recognized:

a) Total hazard current — Hazard current of an
isolated system with all supplied equipment,
including the line isolation monitor,
connected.

b) Fault hazard current — Hazard current of an
isolated system with all supplied equipment,
except the line isolation monitor, connected.

c) Monitor hazard current — Hazard current of
the line isolation monitor.

NOTE — This current is expressed in milliamperes
(mA).

3.3.5 Insulation Impedance Monitoring Device — A
device measuring the ac impedance at mains frequency
from either of the conductors of an isolated circuit to
earth and predicting the hazard current that will flow
when an earth fault occurs and providing an alarm when
a preset value of that current is exceeded.

3.3.6 Insulation Monitoring Device — Instrument
indicating the occurrence of an insulation fault from a
live part of an isolated electrical supply system to the
protective conductor of the installation concerned.

3.3.7 Insulation, Resistance Monitoring Device —
Instrument measuring the ohmic resistance between
the monitored isolated circuit and earth providing an
alarm when the value of this resistance becomes less
than a given limit.

3.3.8 Medical Isolating Transformer — Electrical
equipment used in medical practice intended to supply
isolated power to medical electrical equipment in order
to minimize the likelihood of discontinuity of supply
in case of a failure to earth in the isolated power source
or in equipment connected to it.

3.3.9 Medical Safety Extra-Low Voltage (MSELV) —
Voltage not exceeding a nominal value of 25 V ac or
up to and including 60 V dc or peak value at rated
supply voltage on the transformer or converter between
conductors is an earth-free circuit isolated from the
supply mains by a medical safety extra-low voltage
transformer or by a converter with separate windings.

3.3.10 Operating Residual Current — Value of a
residual current causing a protective device to operate
under specified conditions.

3.3.11 Patient Environment — Any area up to 1.5 m
distance from the intended location of the patient in
which intentional or unintentional contact between
patient and equipment or some other person touching
the equipment can occur (see Annex B).

3.3.12 Touch Voltage — Voltage appearing, during an
insulation fault, between simultaneously accessible
parts.

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4 CLASSIFICATION

4.1 The electrical installations covered in this Section
are those in buildings intended for the following purposes:

a) Hospitals and sanatoria — This includes any
building or group of buildings, which is used
for housing treating persons suffering from
physical limitations because of health, age,
injury or disease. This also includes
infirmaries, sanatoria and nursing homes.

b) Custodial institutions — This includes any
building or group of buildings which is used
for the custody and care of persons, such as
children (excluding schools), convalescents
and the aged, for example, home for the aged
and infirm, convalescent homes, orphanages,
mental hospitals, etc.

5 GENERAL CHARACTERISTICS OF
MEDICAL ESTABLISHMENTS

5.0 General guidelines on the assessment of
characteristics of installations in buildings are given
in Part 1/Section 8, of this Code. For the purpose of
installations falling under the scope of this Section,
the characteristics given below apply.

5.1 Environment

The following environmental factors shall apply to
hospitals:

Environment Characteristics Remarks
(1) (2) (3)

Presence of Probability of

water presence of

water is

negligible

The quantity or —

nature of dust or

foreign solid

bodies is not

significant

The quantity and

nature of

corrosive or

polluting

substances is not

significant

Presence of
foreign solid
bodies

Presence of
corrosive or
polluting
substances

Locations where
some chemical
products are
handled (for
example,
laboratories in
hospitals) will be
categorized as in
Part 1/Section 8

Mechanical

stresses

Seismic effect
and lighting

Impact and
vibration of low
severity

Depends on the
location of the
building

5.2 Utilization

The following aspects of utilization shall apply:

Utilization

Characteristics
(2)

Remarks

(3)

Capability of
persons

Contact of
persons with
earth potential

Conditions of
evacuation
during
emergency

Nature of
process fire or
risk or stored
materials

Children in
locations
intended for
their occupation
Handicapped

Persons
adequately
advised or
supervised by
skilled persons
Persons do not in
usual conditions
make contact
with extraneous
conductive parts
or stand on
conducting
surfaces
Difficult
conditions of
evacuation

Fire or risk

Applies to
child-care homes,
orphanages, etc.

Applies to
hospitals in
general, sanatoria,
nursing homes,
etc, where the
occupants are not
in command of all
their physical and
intellectual
abilities

Applies to areas
such as building
substations,
operations and
maintenance staff

Applies in general
to hospitals and
similar buildings,
irrespective of
density of
occupation
Many locations in
hospital buildings
in general would
fall under
category BE 1 of
no significant fire
or explosion risk,
specific locations
like, operation
theatre, casualty
medicine store,
X-Ray block fall
under BE 2 and
BE 3

{see Part 1/Section
8 of this Code)

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6 SAFETY CONSIDERATIONS

6.0 General

6.0.1 In the context of this Section 'installation' means
any combination of interconnected electrical
equipment within a given space or location intended
to supply power to electrical equipment used in medical
practice.

6.0.2 As such, some parts of the installation may be
present in the patient's environment, where potential
differences, that could lead to excessive currents
through the patient, must be avoided. For this purpose
a combination of earthing of equipment and potential
equalization in the installation seems to provide the
best solution. A disadvantage of such a system is that
in the case of an insulation fault in circuits directly
connected to supply mains, the fault current may cause
a considerable voltage drop over the protective earth
conductor of the relevant circuit. Since a reduction of
such a voltage drop by the application of increased
cross-sectional areas of protective conductors is usually
impractical, available solutions are the reduction of the
duration of fault currents to earth by special devices or
the application of a power supply which is isolated
from earth,

6.0.3 Generally a power supply system including a
separated protective conductor is required (TN-S-
system).

In addition the following provisions may be required,
depending upon the nature of the examinations or
treatments performed:

a) Additional requirements concerning
protective conductors and protective devices
to restrict continuous voltage differences.

b) Restriction of voltage differences by
supplementary equipotential bonding. During
the application of equipment with direct contact
to the patient, as least a potential equalized zone
around the patient shall be provided with a
patient centre bonding bar to which the
protective and functional earth conductors of
the equipment are connected. All accessible
extraneous conductive parts in the zone shall
be connected to this potential equalization bar.

c) Restriction of the potential equalization zone
to the zone around one patient, meaning
practically around one operation table or
around one bed in an intensive care room.

d) If more than one patient is present in an area,
connection of the various potential
equalization centres to a central potential
equalization busbar, which should preferably
be connected to the protective earth system
of the power supply for the given area.

In its completed form the equipotential
bonding network may consist partly of fixed
and permanently installed bonding and partly
of a number of separate bondings which are
made when the equipment is set up near the
patient. The necessary terminals for these
bonding connections should be present on
equipment and in the installation.

e) Restriction of the duration of transient voltage
difference by the application of residual
current operated protective devices (earth
leakage circuit-breakers).

f) Continuity of power supply to certain
equipment in the case of a first insulation fault
to earth and restriction of transient voltage
differences by application of isolating
transformers.

g) Monitoring of a first insulation fault to earth
in an IT-system (the secondary side of an
isolating transformer) with sufficiently high
impedance to earth.

h) Prevention of ignitions and fire in rooms
where flammable anesthetics or flammable
cleaning or disinfection agents are used by
ventilation, anti- static precautions and careful
layout of the installation.

j) Safety supply system for major parts of the
hospital, usually a diesel-powered generator.
Recommendations for essential circuits to be
connected to it.

k) Special safety supply system for critical
equipment as life-supporting equipment and
operating room lamps.

The power supply is taken over by these
devices in a short time. The device may
consist of rechargeable batteries possibly
combined with converters or special
generating sets.
m) Suppression of electromagnetic interference
achieved by the layout of the building and wiring
and provision of screening arrangements.

Limits for magnetic fields of mains frequency
are necessary for a number of sensitive
measurements.

6.1 Safety Provisions

6.1.1 Safety measures are divided into a number of
provisions as given in Table 1 .

6.1.2 Provision P Q shall be applicable to all buildings
containing medically used rooms. Provision P 1 shall
be applicable for all medically used rooms.

Other requirements of this Section, need not be
complied with if:

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Table 1 Safety Provisions
(Clause 6.1.1)

Provisions

No.

(1)

(2)

ii)

Principal Requirements

(3)

Installation Measures

(4)

iii)

iv)

Duration of touch voltages restricted to a safe limit

As Po but additionally: Touch voltages in patient
environment restricted to a safe limit

As P] but additionally: Resistance between extraneous
conductive parts and the protective conductor but bar of
the room not exceeding 0.1Q.

As P\ or P 2 but additionally: Potential difference
between exposed conductive parts, extraneous
conductive parts and the protective conductor bus bar
not exceeding 10 mV in normal condition (see Note )

As Pi or P 2 . Additional protection against electric shock
by limitation of disconnecting time

Continuity of the mains supply maintained in case of a
first insulation fault to earth and currents to earth
restricted

Reduction of fault currents and touch voltages in case
of a fault in the basic insulation

Prevention of dangerous touch voltages in normal
condition and in single fault condition (see Note )

No interruption of the power supply of the essential
circuits of the hospital for more than 15 s

No interruption of the power supply of life-supporting
equipment for more than 15 s

No interruption of the power supply of the operating
lamp for more than 0.5 s

Prevention of explosions, fire and electrostatic charges

No exercise interference from electric and magnetic
fields

NOTE — Normal condition means without any fault in the installation.

vi)

vii)

viii)

ix)

xi)

E 2

xii)

xiii)

TN-S,TT or IT system

Additional to P : Supply system with additional
requirements for protective earthing, etc.

Additional to P { : Supplementary equipotential
bonding

As P { or P 2 : Measurement necessary, corrective
action possibly necessary

Additional to P\ or P 2 : Residual current operated
protective device

Additional to P h P 2 or P 3 : Isolated supply system
with isolation monitoring

Additional P\ or P 2 : Medical isolating transformer
supplying one individually piece of equipment

Additional to P\ or P 2 : Supply with medical
safety, extra low voltage

Safety supply system

Special safety supply system

Special safety supply system for operating lamp

Measures concerning explosion and fire hazards
Layout of building and installation, screening

a) a room is not intended for the use of medical
electrical equipment, or

b) patients do not come intentionally in contact
with medical electrical equipment during
diagnosis or treatment, or

c) only medical electrical equipment is used which
is internally powered or of protection Class II.

The rooms mentioned under (a), (b) and (c) may be
massage rooms, general wards, doctor's examining
room (office, consulting room), where medical
electrical equipment is not used.

6.1.3 Guidance on the application of the provisions
are given in Table 2.

6.1.4 A typical example of an installation in a hospital
is given in Annex C.

7 SUPPLY CHARACTERISTICS AND
PARAMETERS

7.0 Exchange of Information

7.0.1 Proper coordination shall be ensured between the

architect, building contractor and the electrical engineer
or the various aspects of installation design. The
necessary special features of installations shall be
ascertained beforehand with reference to Table 2.

7.1 Circuit Installation Measures for Safety

Provisions — See Table 1, col 3.

7.1.1 Provision P : General

7.1.1.1 All buildings in the hospital area which contain
medically used rooms shall have a TN-S, TT or IT
power system. The conventional touch voltage limit
(U L ) is fixed at 50 Vac.

NOTE — The use of TN-C-S system (in which the PEN-
conductor may carry current in normal condition) can cause
safety hazards for the patients and interfere with the function
of medical electrical equipment, data processing equipment,
signal transmission lines, etc.

7.1.2 Provision F, ; Medical TN-S System

7.1.2.1 The conventional touch voltage limit (U L ) is
fixed at 25 V ac.

7.1.2.2 Protective conductors inside a medically used

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SP 30 : 2011

Table 2 Examples of Application of Safety Provisions

(Clause 6.1.3)

SI Medically Used Room
No.

Protective Measures

Safety Sup
System

Explosions
and Fire

Measures

Against
EM Fields

*^~~

-**.

/ —

jP</Pi

p s p*

Pi.

E 2

(1) (2)

(3)

(4)

(5)

(6)

(7) (8)

(9)

(10)

(11)

(12)

(13)

(14)

i) Message room

ii) Operating wash room

iii) Ward general

iv) Delivery room

v) ECG, EEG, EMG room

vi) Endoscopic room

vii) Examination or treatment room

viii) Labour room

ix) Operating sterilization room

x) Urology room (not being an
operating theatre)

xi) Radiological diagnostic and
therapy room, other than
mentioned under SI No. (xx) and
(xxiv)

xii) Hydrotherapy room

xiii) Physiotherapy room

xiv) Anaesthetic room

x t

xv) Operating theatre

xvi) Operating preparation room

xvii) Operating plaster room

X t

xviii) Operating recovery room

xix) Outpatient operating theatre

xx) Heart catheterization room

xxi) Intensive care room

xxii) Intensive examination room

xxiii) Intensive monitoring room

xiv) Angiographic examination room

xxv) Hemodialysis room

xxvi) Central monitoring room {see
Note)

NOTE — Only if such a room is part of a medical room group and therefore installed in the same way as an intensive monitoring room.
Central monitoring room having no conductive connection to the medically used room (for example, by use of isolating coupling
devices for signal transmission) may be installed as non-medically used room (provision P only).

Explanation; M = Mandatory measure.

X = Recommended measure.

Xj = As X, but only for equipment described in 7.1.6.7.

O = Additional measure, may be considered desirable.

room shall be insulated: their insulation shall be
coloured green-yellow (see Part l/Section4 of this
Code).

7.1.2.3 Exposed conductive parts of equipment being
part of the electrical installation used in the same room
shall be connected to a common protective conductor.

7.1.2.4 A main equipotential bonding with a main
earthing bar shall be provided near the main service

entrance. Connections shall be made to the following
parts by bonding conductors:

a) lightning-conductor;

b) earthing systems of the electric power
distribution system;

c) the central heating system;

d) the conductive water supply line;

e) the conductive parts of the waste water line;

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NATIONAL ELECTRICAL CODE

f) the conductive parts of the gas supply; and

g) the structural metal framework of the building,
if applicable.

Main equipotential bonding conductors shall have
cross-sectional areas not less than half the cross-
sectional area of the largest protective conductor of
the installation, subject to a minimum of 6 mm 2 . The
cross-sectional area need not, however, exceed 25 mm 2 ,
if the bonding conductor is of copper or a cross-
sectional area affording equivalent current-carrying
capacity in other metals.

7.1.2.5 Each medically used room or room group shall
have its own protective conductor bus bar, which should
have adequate mechanical and electrical properties and
resistance against corrosion.

This bus bar may be located in the relevant power
distribution box. The leads connected to terminals of
such a protective conductor bar shall be identified and
shall be similarly designated on drawings of the
installation system.

7.1.2.6 The impedance (Z) between the protective
conductor bar and each connected protective conductor
contact in wall sockets or terminals should not exceed
0.2 Q, if the rated current of the overcurrent protective
device is 16 A or less. In case of a rated current
exceeding 1 6 A the impedance should be calculated
using the formula:

Z = Q in all cases Z shall not exceed 0.2 H.

6.1,

where

7 r = rated current of overcurrent protective

device in amperes (A).

NOTE — The measurement of the protective conductor
impedance should be performed with an ac current not less
than 10 A and not exceeding 25 A from a source of current
with a no-load voltage not exceeding 6 V, for a period of at
least 5 s.

7.1.2.7 The cross-sectional area of the protective
conductor shall be not less than the appropriate value
shown in Table 3.

Table 3 Cross-sectional Area of Conductors

Cross-sectional Area of

Minimum Cross-sectional

No.

Phase Conductor, S,

Area of the Corresponding

mm 2

Protective Conductor, PE,

mm 2

(1)

(2)

(3)

S<16

ii)

\6<S<35

iii)

S>35

NOTE — If the application of this table produces non-
standard sizes, conductors having the nearest standard cross-
sectional area are to be used.

SP 30: 2011

The values given in Table 3 are valid only if the
protective conductor is made of the same metal as the
phase conductors. If this is not so, the cross- sectional
area of the protective conductor is to be determined in
a manner which produces a conductance equivalent to
that which results from the application of Table 3.

The cross- sectional area of every protective conductor
which does not form part of the supply cable or cable
enclosure shall be, in any case, not less than:

a) 2.5 mm 2 , if mechanical protection is provided,
and

b) 4 mm 2 , if mechanical protection is not
provided.

7.1.2.8 It may be necessary to run the protective
conductor separate from the phase conductors, in order
to avoid measuring problems when recording
bioelectric potentials.

7.1.3 Provision P 2 : Supplementary Equipotential
Bonding

7.1.3.1 In order to minimize the touch voltage, all
extraneous conductive parts shall be connected to the
system of protective conductors.

An equipotential conductor bar shall be provided. It
should be located near the protective conductor bar
(see also 7.1.2.5). A combined protective conductor
and equipotential bonding bar may be used, if all
conductors are clearly marked according to 7.1.2.5
and 7.1.3.3 (e).

7.1.3.2 Connections shall be provided from the
equipotential bonding bar to extraneous conductive
parts, such as pipes for fresh water, heating, gases,
vacuum and other parts with a conductive surface area
larger than 0.02 m 2 or a linear dimension exceeding
20 cm, or smaller parts that may be grasped by hand.

Additionally the following requirements supply:

a) Such connections need not be made to:

1) Extraneous conductive parts inside of
walls (for example structural metal frame
work of buildings) having no direct
connection to any accessible conductive
part inside the room, and

2) conductive parts in a non-conductive
enclosure.

b) In locations where the position of the patient
can be predetermined this provision may be
restricted to extraneous conductive parts
within the patient environment (see
Annex B)

c) In operating theatres, intensive care rooms,
heart catheterization rooms and rooms

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SP 30 : 2011

intended for the recording of bioelectrical
action potentials all parts should be connected
to the equipotential bonding bar via direct and
separate conductors.

7.1.3.3 The following requirements shall be fulfilled:

a) The impedance between extraneous
conductive parts and the equipotential
bonding bar shall not exceed 0.1.

NOTE — The measurement of this impedance should
be performed with a current not less than 10 A and not
exceeding 25 A during not less than 5 s from a current
source with a no-load potential not-exceeding 6 V ac.

b) All equipotential bonding conductors shall be
insulated, the insulation being coloured green/
yellow.

NOTE — Insulation of the equipotential bonding
conductors is necessary, to avoid loops by contact and
to avoid picking up of stray currents.

c) Equipotential conductors between
permanently installed extraneous conductive
parts and the equipotential bonding bar shall
have a cross-sectional area of not less than
4 mm 2 copper or copper equivalent.

d) The equipotential bonding bar, if any, should
have adequate mechanical and electrical
properties, and resistance against corrosion.

e) The conductors connected to the equipotential
bonding bar shall be marked and shall be
similarly designated on drawings of the
installation system.

f) A separate protective conductor bar and an
equipotential bonding bar in a medically used
room or in a room group shall be inter-
connected with a conductor having a cross-
sectional area of not less than 16 mm 2 copper
or its equivalent (see also 7.1.3.1).

g) An adequate number of equipotential bonding
terminals other than those for protective
conductor contacts or pins of socket outlets
should be provided in each room for the
connection of an additional protective
conductor of equipment or for reasons of
functional earthing of equipment.

7.1.4 Provision P 3 : Restriction of Touch Voltage in
Rooms Equipped for Direct Cardiac Application

7.1.4.1 The continuous current through a resistance of
1 000 connected between the equipotential bonding bar
and any exposed conductive part as well as any
extraneous conductive part in the patient environment
shall not exceed 10 pA in normal condition for
frequencies from dc to 1 kHz.

For a description of patient environment, see Annex B.

Where the measuring device has an impedance and a
frequency characteristics as given in Annex D, the
current may also be indicated as a continuous voltage
with a limit of 10 mV between the parts mentioned
above.

a) During the test it is assumed that fixed and
permanently installed medical electrical
equipment is operating.

b) 'Normal conditions' means 'without any fault
in the installation and in the medical electrical
equipment'.

Compliance with this requirement may be achieved
through one or more of the following methods:

a) Extraneous conductive parts may be:

1) connected to the equipotential bonding
bar by a conductor of a large cross-
sectional area in order to reduce the
voltage drop across such a conductor,

2) insulated so that it is not possible to touch
them unintentionally, and

3) provided with isolating joints at those
places where they enter and leave the
room.

b) Exposed conductive parts of permanently
installed equipment may be isolated from the
conductive building construction.

7.1.5 Provision P 4 : Application of Residual- Current
Protective Devices

7.1.5.1 The use of a residual-current protective device
is not recognized as a sole means of protection and
does not obviate the need to apply the provisions P l
and P v

7.1.5.2 Each room or each room group shall be
provided with at least one residual-current protective
device.

7.1.5.3 A residual-current protective device shall have
a standard rated operating residual-current / A < 30 mA.

7.1.5.4 A medical isolating transformer and the circuits
supplied from it shall not be protected by a residual-
current protective device.

7.1.5.5 Electrical equipment such as general lighting
luminaries, installed more than 2.5 m above floor level
need not be protected by a residual-current protective
device.

7.1.5.6 Fixed and permanently installed electromedical
equipment with a power consumption requiring an
overcurrent protective device of more than 63 A rated
value may be connected to the supply mains by use of
a residual-current protective device with / A < 300 mA.

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7.1.6 Provision P 5 : Medical IT-System

7.1.6.0 The use of a medical IT- system for the supply
of medically used rooms for example operating
theatres, may be desirable for different reasons:

a) A medical IT-system increases the reliability
of power supply in areas where an interruption
of power supply may cause a hazard to patient
or user;

b) A medical IT-system reduces an earth fault
current to a low value and thus also reduces
the touch voltage across a protective
conductor through which this earth fault
current may flow;

c) A medical IT-system reduces leakage currents
of equipment to a low value, where the
medical IT-system is approximately
symmetrical to earth;

It is necessary to keep the impedance to earth
of the medical IT-system as high as possible.
This may be achieved by:

1) restriction of the physical dimensions of
the medical isolating transformer,

2) restriction of the system supplied by this
transformer.

3) restriction of the number of medical
electrical equipment connected to such a
system, and

4) high internal impedance to earth of the
insulation monitoring device connected
to such a circuit.

If the primary reason for the use of medical IT-system
is the reliability of the power supply, it is not possible
to define for such a system a hazard current and an
insulation resistance monitoring device should be used.

If on the other hand the restriction of leakage current
of equipment is the main reason for the use of the
medical IT-system, an insulation impedance
monitoring device should be used.

7.1.6.1 For each room or each room group at least one
fixed and permanently installed medical isolating
transformer shall be provided.

7.1.6.2 A medical isolating transformer shall be
protected against short circuit and overload.

In case of a short circuit or a double earth fault in parts
of opposite polarity of the medical IT-system the
defective system shall be disconnected by the relevant
overcurrent protective device.

If more than one item of equipment can be connected
to the same secondary winding of the transformer, at
least two separately protected circuits should be
provided for reasons of continuity of supply.

7.1.6.3 Overcurrent protective devices shall be easily
accessible and shall be marked to indicate the protected
circuit.

7.1.6.4 An insulation monitoring device shall be
provided to indicate a fault of the insulation to earth of
a live part of the medical IT-system.

7.1.6.5 Fixed and permanently installed equipment
with a rated power input of more than 5 kVA and all
X-ray equipment (even with a rated power input of
less than 5 kVA) shall be protected by provision P 4 .
Electrical equipment such as general lighting, more
than 2.5 m above floor level, may be connected directly
to the supply mains.

7.1.6.6 General requirements for insulation monitoring
devices

A separate insulation resistance or impedance
monitoring device shall be provided for each secondary
system. It shall comply with the requirements given
below:

a) It shall not be possible to render such a device
inoperative by a switch. It shall indicate
visibly and audibly if the resistance or
impedance of the insulation falls below the
value given in 7.1.6.7 and 7.1.6.8.

The arrangement may be provided with a stop
button for the audible indication only.

b) A test button shall be provided to enable
checking the response of the monitor to a fault
condition as described in 7.1.6.4.

c) The visible indication mentioned in (a) of the
insulation monitoring device shall be visible
in the monitored room or room group.

d) The insulation monitoring device should be
connected symmetrically to the secondary
circuit of the transformer.

7.1.6.7 Insulation resistance monitoring device

The ac resistance of an insulation resistance monitoring
device shall be at least 100 k. The measuring voltage
of the monitoring device shall exceed 25 V dc, and the
measuring current (in case of a short circuit of an
external conductor to earth) shall not exceed 1 mA.
The alarm shall operate if the resistance between the
monitored isolated circuit and earth is 50 k or less,
setting to a higher value is recommended.

7.1.6.8 Insulation impedance monitoring device

An insulation impedance monitoring device shall give
readings calibrated in total hazard current with the
value of 2 mA near the centre of the meter scale.

The device shall not fail to alarm for total hazard
currents in excess of 2 mA. In no case, however, shall

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the alarm be activated until the fault hazard current
exceeds 0.7 mA.

During the checking of the response of the monitor to
a fault condition the impedance between the medical
IT-system and earth shall not decrease.

NOTE — The values of 2 mA or 0.7 mA are based on practical
experience with 1 10 to 120 V power supplies. For a 220-240 V
power supply it may be necessary to increase these values to
4 mA and 1.4 mA because of the higher leakage current
of equipment.

7.1.7 Provision P 6 : Medical Individual Electrical
Separation

7.1.7.0 Individual electrical separation of a circuit is
intended to prevent shock currents through contact with
exposed conductive parts which may be energized by
a fault in the basic insulation.

7.1.7.1 The source of supply shall be a medical isolating
transformer.

7.1.7.2 Only one item of equipment shall be connected
to one source of supply.

7.1.7 J The voltage of the secondary circuit shall not
exceed 250 V.

7.1.7.4 Live parts of the separated circuit shall not be
connected at any point to any other circuit or to earth.

7.1.7.5 To avoid the risk of a fault to earth, particular
attention shall be paid to the insulation of such circuits
from earth, especially for flexible cables and cords.

7.1.7.6 Flexible cables and cords shall be visible
throughout any part of their length where they are liable
to mechanical damage.

7.1.7.7 All conductors shall be physically separated
from those of other circuits.

7.1.8 Provision P 1 : Medical Safely Extra-Low Voltage
(MSELV)

7.1.8.1 Medical safety extra-low voltage shall not
exceed 25 V ac or 60 V dc peak value.

7.1.8.2 A supply transformer for medical safety extra-
low voltage shall comply with relevant Indian
Standards.

7.1.8.3 A source of medical safety extra-low voltage
other than a transformer shall have at least the same
separation and insulation to other circuits and earth as
required for the transformer under 7.1.8.2.

7.1.8.4 Live pans at medical safety extra-low voltage
shall not be connected to live parts or protective
conductors forming part of other circuits or to earth.

7.1.8.5 Exposed conductive parts shall not intentionally
be connected to:

a) earth, or

b) protective conductors or exposed conductive
parts of another system, or

c) extraneous conductive parts except that,
where electrical equipment is inherently
required to be connected to extraneous
conductive parts, it is ensured that those parts
cannot attain a voltage exceeding medical
safety extra-low voltage.

7.1.8.6 Live parts of circuits at medical safety extra-
low voltage shall be electrically separated from other
circuits. Arrangements shall ensure electrical
separation not less than required between the input and
output of a medical safety extra-low voltage
transformer.

In particular, electrical separation not less than that
provided between the input and output windings of a
medical safety extra-low voltage transformer shall be
provided between the live parts of electrical equipment
such as relays, conductors, auxiliary switches and any
part of a circuit with a higher voltage.

7.1.8.7 Medical safety extra-low voltage circuit
conductors shall either be physically separated from
those of any other circuit or where this is impracticable,
one of the following arrangements is required:

a) Medical safety extra-low voltage circuit
conductors shall be enclosed in a non-metallic
sheath additional to their basic insulation.

b) Conductors of circuits at different voltages
shall be separated by an earthed metallic
screen or an earthed metallic sheath.

c) Where circuits at different voltages are
contained in a multi-conductor cable or
other grouping of conductors, medical
safety extra-low voltage circuits shall be
insulated, individually or collectively, for
the highest voltage present.

NOTE — In the above arrangements, basic-insulation
of any conductor should comply only with the
requirements for the voltage of the circuit of which it
is a part.

7.1.8.8 Plugs and socket-outlets shall comply with the
following requirements:

a) Supply systems of different voltages or
different kinds or nature shall not have
interchangeable plugs and sockets, and

b) Socket-outlets shall not have a protective
conductor contact.

7.2 Wiring

7.2.1 The general design of wiring shall conform to
Part 1/Section 9 of this Code.

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7.2.2 All panel boards and switchboards shall
preferably be of dead front type, enclosed in metal
cabinet. Where locked cabinets are provided, all locks
should be keyed alike. Switchboard and panel boards
shall be installed in non-hazardous locations.

7.2.3 Circuit-breakers are preferred to switchfuse units
in power and lighting feeders.

7.2.4 Inside the wards only silent type wall mounted
switches should be used to reduce noise. The lighting
points shall be so grouped so that minimum lighting
may be switched on during night time.

7.2.5 Separate circuits shall be provided for X-ray,
electrotherapy, diathermy, electrocardiograph, etc.
Advice of equipment manufacturers shall also be
sought in their installation.

7.2.6 In corridors and spaces accessible to public
provisions shall be made for lighted signs.

7.2.7 Special convenience outlets in corridors spaced
about 12 m apart are desirable for portable treatment
equipment and cleaning machines.

7.3 Feeders

The general provisions laid down in Part 1 /Section 9
of this Code shall apply.

7.4 Service Lines

7.4.1 The general provisions laid down in IS 8061 shall
apply.

7.4.2 The main supply conductors shall preferably be
brought into the building underground to reduce the
possibility of interruption of power supply.

7.5 Building Substation

7.5.0 General

The design of power supply for hospital and similar
buildings shall take into account the concentration of
power demand for the various electrical loads. If the
load demand is high requiring supply at high voltage,
accommodation of substation equipment will be
required. Emergency and standby power- supply needs
of hospital buildings shall also be taken into account
in designing the building substation.

7.5.1 While calculating the power requirement, the
diversity factor for different electrical appliances and
installations shall be considered. For guidance, Table 4
gives reference values of power requirement and
diversity factor for the different parts in a hospital
installation.

7.5.2 The location and layout of building sub-station
and emergency diesel generating set/s shall conform
to the general rules laid down in Part 2 of this Code.

Table 4 Power Requirement

(Clause 7.5.1)

SI No.

Part of Electrical

Proportion of

Diversity

Installation

Total Power
Requirement

Percent

Factor

(1)

(2)

(3)

(4)

Lighting

0.9

ii)

Air-conditioning

1.0

»i)

Kitchen

0.6

iv)

Sterilizer

0.6

Laundry

0.6

vi)

Lifts

1.0

vii)

Electromedical
installations and
other loads

0.6

7.6 System Protection

7.6.0 General

The general rules for protection for safety laid down
in Part 1 of this Code shall apply. Reference should
be made to SP 7 for guidelines for fire-protection of
buildings. The additional rules given below shall
apply.

7.6.1 The type of buildings covered in this Section fall
under Group CI (hospitals and sanatoria), C2 (custodial
institution), and C3 (panel institutions — - for mental
hospitals, and similar buildings) from the fire-safety
classification point of view.

7.6.2 In hospitals and similar buildings, besides fire-
fighting equipment manually operated electrical fire
alarm system and automatic fire-alarm system shall
be provided. Restricted paging system arrangement
with sound alarm/indicators in the duty rooms/nurses
rooms shall be made.

7.6.3 For guidelines on selection of fire detectors, see
SP 7. The wiring for fire-fighting systems shall be
segregated from other wiring to reduce risk of damage
to them in the case of fire. For high-rise buildings, the
fire-fighting pump motors are generally large and they
draw heavy current. Sufficient care shall be taken to
ensure that the supply to such motors is maintained
properly.

7.7 Fire-protection

Where electrical equipment contains pipes or tubes of
combustion supporting gases, such as oxygen or nitrous
oxide, the following additional requirements apply:

a) Gas outlets shall be located at least 20 cm
away from electrical components which, in
normal use or in case of a fault, could generate
sparks.

b) The gas-flow shall not be directed towards
such electrical components.

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c) Electrical wiring shall only be allowed to be
run in a common enclosure, for example in a
common conduit for channel, with tubes for
combustion supporting gases, such as oxygen
or nitrous oxide, if in the relevant circuit the
product of the no-load voltage in volts (V)
and the short-circuit current in amperes (A)
does not exceed 10.

d) If the requirements in (c) cannot be. fulfilled
gas-tight separation shall be provided between
the electrical wiring and the tubes for gases.
The gas-tight separation shall be electrically
conducting and shall be connected to the
protective earth busbar.

e) Where electrical leads are close to a pipeline
guiding ignitable gases or oxygen, a short-
circuit of these leads or a short-circuit of one
lead with a metal duct or pipeline shall not
result in a temperature which may cause
ignition.

8 ADDITIONAL REQUIREMENTS FOR
HAZARDOUS LOCATIONS IN HOSPITALS

8.1 Provision A: Explosion and Fire Protection

8.1.1 Explosion Protection: General

a) When the administration of flammable
anaesthetic atmospheres or flammable
anesthetics or flammable cleaning and/or
disinfection agents with air or oxygen and
nitrous oxide is intended, special measures to
avoid ignitions and fire are necessary. These
measures include mainly the use of antistatic
flooring.

b) Effective ventilation and the application of a
suction system on anaesthesia equipment
assists in reducing flammable concentrations
of flammable anaesthetic mixtures in the
patient environment, the anaesthetists
working-place and the operating table. The
effectiveness of a ventilation, system may be
subjected to National Regulations.

c) Limits of zones of risk are given in Annex A.
Zones of risk exist only when flammable
anesthetics or flammable cleaning and/or
disinfection agents are used.

d) Requirements on construction, marking and
documentation of medical electrical
equipment of category AP or APG are given
in IS 13450 (Parti).

Allocation of equipment of the categories AP
or AG to zones of risk in operating theatres
or other anaesthetic rooms are under
consideration.

e) Mains plug connections, switches, power
distribution boxes and similar devices, which
may cause ignition shall be kept outside zones
of risk.

8.2 Antistatic Floor

8.2.1 Antistatic floors shall be used in rooms where
zones of risk occur.

Where antistatic floors are used in conjunction with
non-antistatic floors marking should be provided,
which should be described in the application code.

8.2.2 The resistance of an antistatic floor shall not
exceed 25 MQ at any time during the lifetime of the
floor when measured according to IS 7689.

NOTE — The fact that during the lifetime of the floor the
resistance may changes should be taken into consideration. The
resistance of terrazzo floors increases, while that of PVC floors
decreases with time.

8.2.3 If floors of low resistance (< 50 k) are used.
Provision P 4 and/or P 5 shall be used to effectively limit
the effects of fault currents.

9 BUILDING SERVICES

9.1 Lighting

9,1.1 The general rules laid down in Part 1/Section 1 1
of this Code shall apply. The choice of lamps, lighting
fittings and the general lighting design together with
the power requirement shall be plane based on the
recommended values of illumination and glare index
given in Table 5 (see also SP 72).

9.2 Heating, Ventilation and Air- Conditioning

The provisions of Part 1 /Section 11 of this Code shall
apply. Provision shall be made to maintain positive
air pressure and induct increased quantity of fresh air
to avoid entry of gases from one room to another.

9.3 Lifts

9.3.1 The general rules laid down in Part 1 /Section 1 1
of this Code shall apply. However, the design of lifts
in hospitals and similar buildings shall be made taking
into account the criteria given Table 5.

9.3.2 Dimensions

The outline dimensions of hospitals lifts shall conform
to those laid down in Table 3 of IS 14665 (Part 1).

9.3.3 Occupant Load

For the types of buildings covered in this Section, the
occupant load expressed as gross area in m 2 per person,
shall be 15.

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Table 5 Recommended Values of Illumination

and Limiting Glare Index
(Clauses 9.1.1 and 9.3.1)

S! Buildings Illumination Limiting

No. Glare Index

(1) (2) (3) (4)

i) Hospitals

a) Reception and waiting rooms

150

b) Wards

1) General

100

13 1 '

2) Beds

150

c) Operating theatres/Dental

surgeries

1) General

300

2) Tables/chairs

(Special
lighting)

—

d) Laboratories

300

e) Radiology department

100

—

f) Casualty and outpatient
department

150

g) Stairs, corridors

100

___

h) Dispensaries

300

ii) Doctor's Surgeries

a) Consulting rooms

150

b) Corridors

—

c) Sight testing (acuity) wall
charts and near vision

450

—

types

iii) Laundries/Dry -cleaning Works

a) Receiving, sorting, washing,
drying

200

b) Dry-cleaning, bulk machine
work

200

c) Ironing, pressing, mending,
spotting, dispatch

300

iv) Offices

(see Part 3/Section 2 of this
Code)

v) Kitchens

200 2)

l} Care shall be taken to screen all bright light and areas from

view of patients in bed.
2) Special local lighting required over kitchen equipment.

9.3.4 Car Speed

These shall be as follows:

SI Type of Lift

'. of Floors Car Speed

No.

Served

(m/sec)

(1) (2)

(3)

(4)

i) Hospital passenger

}

13-20

Above 1.5

lift

4-5

0.5 to 0.75

ii) Hospital bed lifts

a) Short travel lifts

—

0.25

small hospitals

b) Normal

—

0.5

c) Long travel lifts

—

0.6-1.5

general hospitals

9.3.5 Position

It is convenient to position the hospital passenger lifts
near the staircases. Hospital bed lifts shall be situated
conveniently near the ward and operating theatre
entrances. There shall be sufficient space near the
landing door for easy movement of stretcher/trolley.

10 TESTING OF INSTALLATION

10.1 The various tests on the installation shall be carried
out as laid down in Part 1/Section 13 of this Code.

10.2 The initial testing of the installation shall also
include:

a) Testing of the effectiveness of protective
measures (provisions P to P t );

b) Testing of the resistance of protective
conductors and of the equipotential bonding;

c) Testing of the insulation resistance between
live conductors and earth in each separately
fused circuit;

d) Testing of the resistance of antistatic floors;

e) Testing of the general safety supply system
and

f) Testing of the special safety supply system.

11 STANDBY, SAFETY AND SPECIAL SAFETY
SUPPLY SYSTEM

11.1 Provision GE

System

Standby and Safety Supply

11.1.1 Electrical systems for medical establishments
shall comprise essential circuits capable of supplying
a limited amount of lighting and power service which
is considered essential for safety, life support and basic
hospital operation during the time the normal electrical
service is interrupted (see also Annex E).

11.1.2 All medical establishments containing life-
supporting equipment shall be provided with a safety
supply system.

11.1.3 Essential circuits shall provide facilities for
charging batteries of a special safety supply system.

11.1.4 Operation of a safety supply system shall not
impair the function of protective measures.

11.1.5 All parts of essential circuits shall be marked.

11.1.6 An example of safety supply systems of a
hospital is given in Annex F.

11.1.7 A safety supply system shall be capable of
automatically taking over the load of essential circuits
in the event of a failure of the normal power supply.

11.1.8 The taking-over procedure shall not start earlier
than after a period of 2 s has elapsed during which the

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SP 30 : 2011

system voltage has dropped below 90 V of the nominal
value and shall be completed within 15 s after the
starting of the taking-over procedure.

Return to normal power supply should be delayed. For
diesel- generators the delay should be at least 30 min.

11,1.9 To prevent simultaneous damage, the main
feeders for the safety supply system shall be segregated
from the normal system wherever possible.

11.2 Provisions E x and E 2 t Special Safety Supply
System

11.2.1 Provision E{. Special Safety Supply System,
Medium Break

11.2.1.1 A special safety supply system shall
automatically take over the load within 15 s after a
failure of the power supply at the medical establishment
containing life- supporting equipment.

11.2.1.2 It shall be possible to resume operation of
equipment for maintaining important body functions,
in particular breathing equipment, or equipment for
resuscitation, within 15 s and to maintain operation
for a period of 3 h subsequently, for example, via a
battery with inverter or via a motor driven generator.

11.2.1.3 Where the rating of the special safety supply
system is sufficient the circuits of a medical IT-sy stem
according to 7.1.6 may be connected to it.

11.2.1.4 Where not all socket outlets in a medically
used room are connected to the special safety supply
system the connected socket outlets shall be marked
clearly as such.

11.2.2 Provision E 2 : Special Safely Supply System,
Short Break

11.2.2.1 A special safety supply system shall
automatically take over the load within 0.5 s after a
failure of the power supply at the operating lamp.

11.2.2.2 Operation of at least one operating lamp shall
be resumed after a switchover time not exceeding 0.5 s
and operation shall be maintained for at least 3 h.

11.2.3 Common Recommendations for the Provisions
E ] and E 2

11.2.3.1 The rated power of the source of a special
safety supply system shall not be less than required by
the connected functions. At least the loads which
require continuity of supply shall be connected to the
special supply system.

11.2.3.2 Operation of a special safety supply system
shall not impair the function of protective measures.

For diesel-generators the requirements of 11,1.8 shall
apply.

11.2.3.3 Voltage deviations under normal conditions
shall be less than 10 percent for periods of time
exceeding 5s.

11.2.3.4 Frequency deviations shall be less than
1 percent for periods of time exceeding 5 s.

11.2.3.5 The special safety supply system source shall
be located outside the medically used rooms, if possible
close to the relevant distribution point, so that physical
damage to the cables connecting the source to the
distribution point is unlikely.

11.2.3.6 Operation of the special safety supply system
shall be indicated by visual means in all rooms
concerned.

NOTE — It is recommended to provide additionally a total
load indicator in each room connected to the same special safety
supply system.

11.2.3.7 Automatic means shall be provided to keep
batteries optimally charged.

11.2.3.8 The charging device shall be designed so that,
starting from the fully charged conditions, it is possible
to discharge continuously during 3 h at nominal output,
and subsequently to re-change during 6 h after which
it shall be possible to discharge once more for 3 h under
the conditions mentioned above.

11.2.3.9 It shall be possible to supply the charging
circuit of a special safety supply system from the safety
supply system, so that the special safety supply system
batteries can be charged even during a failure of the
normal power supply.

12 MEASURES AGAINST INTERFERENCE

PROVISION!

12.1 Measures Against ac Interference

12.1.1 In rooms where measurements of bioelectric
potentials are performed measures against interference
in the room and in the surrounding area should be
affected, if such interference may cause incorrect
measurements. Such rooms are:

a) rooms intended for measurement of bio-
electric potentials (EEG, ECG, etc);

b) intensive examination rooms;

c) intensive care and monitoring rooms;

d) catheterization rooms;

e) angiographic examination rooms; and

f) operating theatres.

12.2 Measures Against Interference Caused by
Mains-Induced Electric Fields

12.2.1 The electrical wiring on both sides of or inside
walls, floor and ceiling of the rooms concerned should

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be screened by means of metal shielding of cables or
by metal conduits for cables and wiring.

If such metal shielding is applied it should be connected
to protective earth at one point only.

12.2o2 Metal enclosures or pans of enclosures of fixed
and permanently installed electrical equipment of
Class II and III (such as of lighting fittings) should be
connected to the equipotential bonding system.

12.23 Where adequate measures according to 11.1
cannot be applied and ECG and EEG monitoring is to
be undertaken, it is recommended to shield the room
or a part of the room against electric fields by installing
a room screening within the wall structure.

12.3 Measures Against Interference Caused by
Mains-Induced Magnetic Fields

12.3.1 It is recommended to provide sufficient distance
between electrical components and equipment which
may, cause magnetic interference and the place for the
examination of patients. In practice the following
values of magnetic field strength have been found to
be sufficiently low to avoid magnetic interference:

a) 4 x 10 7 T pp for ECG recording, and

b) 2 x 10 7 T pp for EEG recording.

NOTE — Ballasts incorporated in fluorescent lamp fittings
generate an alternating magnetic field; those on the ceiling of
the room immediately below the examination room are the ones
most likely to cause interference. In some cases it may be
necessary to remove ballasts of a certain type from the lighting
fitting and to mount them at sufficient distance.

12.3.2 Sufficient distance should be provided when
installing units with strong stray magnetic fields such
as transformers and motors. This applies also to the
isolating transformer of provision P 5 . The distance
should be 3 m or more.

12.3.3 The rooms listed in 12.1 should not have large
power cables passing through or adjacent to them.
Suggested minimum distances are:

Conductor Cross-
Sectional Area

10 to 70
95 to 185

240

Distance, Min
m

NOTES

1 Cables, either single phase or three phase, will have a
negligible external field if the load is correctly distributed
between phase or between phase and neutral but in practice
faults between neutral and earth or incorrectly distributed loads
between lines and neutral, and leakage currents will cause
alternating magnetic fields in the vicinity of power cables.

2 The values apply only to twisted cables. When bar systems
or separated single cables are used, the distances may have to
be substantially larger.

12.4 Measures Against Interference from Radio
Frequency Electromagnetic Fields

12.4.0 Powerful radio frequency fields may cause
interference in sensitive electromedical equipment.

12.4.1 Normally such fields exist only where short-wave
diathermy or surgical diathermy equipment is used and
close to transmitting aerials used for such purposes as
staff location and ambulance communications. The
simplest measure against such interference is to locate
equipment which causes it well away from areas where
sensitive equipment is used. Additional measures are
the inclusion of radio frequency rejection circuits in
sensitive equipment and the use of short-wave diathermy
equipment with a low modulation factor.

If the measures described here are not sufficiently
effective it may be necessary to use sensitive equipment
with a screened room.

NOTE — The construction of such a screened room should be
entrusted to a specialist. An attenuation of 40 dB over the
frequency range 150 kHz to 30 MHz is considered to be
adequate.

12.5 Electric Heating Cables

12.5.0 The following requirement applies to electric
heating cables embedded in or attached to surfaces in
buildings. It does not apply to removable appliances
which may be mounted on the surface of walls.

12.5.1 Electric heating cables of any type should not
be used in rooms where bioelectric potentials are
recorded.

NOTE — Due to the construction of such heating cables it is
very likely, that the electric and magnetic fields will interfere
with the recording of bioelectric potentials. Appropriate
measures according to 12.2 and 12.3 should be taken.

13 MISCELLANEOUS PROVISIONS

13.1 Call Systems

13.1.0 Electrical call and signal system when provided
in hospitals should comply with the requirements given
in 13.1.1 to 13.1.4.1 The following are the important
call and signal system:

a) Nurses call,

b) Doctors' paging, and

c) In-and-out register.

NOTE — It is recommended that electrical call and signal
system should be provided in all hospitals so that patients may
receive prompt service and the doctors, nurses and attendants
may work more efficiently.

13.1.1 Nurses' Call System

The nurses call system should be a wired electrical
system whereby patients may signal for a nurse from
the bed site. Two types of systems are recommended:

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239

SP 30 : 2011

a) A simple one-way signal system which con-
nects the bed side call stations with a signal
at the nurses' station, utility room and floor
pantry of the nursing unit. It simultaneously
lights a dome light over the door of the room
from which the call originated. The signal at
the nurses' station may be in the form of an
annunciator with a buzzer or a single light
with a buzzer. Two or more lights in the ceiling
of the corridor at the nurses' station to indicate
the direction from which the call came are
desirable for the latter arrangement.

b) A central control panel should be set up pre-
ferably on the ground floor incorporating a
set of indicating panels according to the
number of wards. Each indicating panel
should have a number of small lamps
according to the number of beds. At each bed
there could be 4 push buttons. First for
'Calling Nurses', second for 'Nurse Present',
third for 'Setting Combination' and fourth for
'Call for Doctor'. When any patient presses
the push button the indication is at the central
control room from where intimation to nurses
can be sent. After reaching the bed site the
nurse presses the 'Nurse Present' button which
gives an indication to operator at the central
control panel that the nurse is available near
the particular bed. After attending the patient,
the nurse presses the resetting button which
puts the whole equipment to the original
condition. If the patient needs further help of
a doctor then the nurse again presses the fourth
push button and the central control panel
operator sends message to the doctor for that
particular bed.

13.1.1.1 For emergency call of nurse by the patient
when he/she is inside a bath or water-closet, suitable
pull cord switches shall be provided inside bath and
water-closet. These switches when operating will give
an indication at the central control panel from where
intimation to nurse can be sent.

13.1.1.2 Nurses call system may also be of the
intercommunicating type with a microphone and
loudspeaker at the bed connected to the nurses' station.
The patient can signal for a nurse or speak to her and
receive an answer. For maximum benefit and service,
this system should include all the features described
in 13.1.1 for the one-way signal system in addition to
the inter-communicating features.

13.1.2 Doctors Paging System

This may consist of loudspeakers located throughout
the hospital, clinics on which doctors' numbers can be

sounded or the flasher type which indicates the doctors'
numbers. The loudspeaker and other audible calls
should not be used as they may disturb the patients
and attendants. The flasher system consists of a
keyboard and flasher at the telephone switchboard. The
telephone operator may set the board to flash as many
as three doctors' numbers automatically in rotation.
The numbers appear on annunciators located in all
sections of the corridors. The same number of
numerals, at least three, should be used for each doctor
so that a burnt out lamp may be located.

13,1.2.1 These paging systems could be used for calling
interns, administrators, heads of departments and their
assistants and engineers. These flashers may also be
used for other general calls such as 'fire' with a red 'F'
and buzzer. The flasher call system has its shortcomings
as the individual may fail to see the numbers when
flashed. For this reason the flasher system should be
supplemented with loudspeakers at points where
interns, heads of departments and doctors may
congregate, that is, in doctors' lounge, staff dining
room, laboratory and engineers' office and such other
areas where the calls may not disturb the patients.

13.1.3 VHF Paging System

This system consists of a low powered transmitting
station from which calls are broadcast throughout the
hospital to miniature receiving sets which the doctors
and others may carry in their pockets.

13.1.4 In-and-Out Register

The doctors' in-and-out register permits the doctor to
register 'IN' and 'OUT' with the minimum of effort
and delay. The register consists of a board, at one or
more entrances, on which all staff doctor, upon entering
or leaving, operates a switch opposite his name which
indicates whether or not he is in the building. The
switch controls a light at or back of the name on all
boards connected in the system.

13.1.4.1 Except in very small hospitals, it is
recommended to install register system with a board
at two or more entrances and at the telephone
switchboard. Such a system should include a recall
feature which consists of a flasher unit, having a motor
driven interrupter. This flasher unit, controlled at the
telephone switchboard, will actuate a flashing light at
the doctors' name on all register boards which indicates
there is a massage for the doctors, and attracts the
attention of doctor upon entering or leaving the
building. Call back systems are used for nurses' and
interns' bedrooms. With such system the nurses and
interns can be awakened, called for duty, or called to
the telephone by push-buttons in the office which
operate buzzers in the rooms. The room called can

240

NATIONAL ELECTRICAL CODE

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answer by pushing a button which registers on an
annunciator in the office. The main office buzzers may
be connected through a selector switch so that serial
rooms or sections may be called by one button.

13.2 Telephones

13.2 .0 A centralized EPABX System with adequate
number of P&T lines shall be installed for internal and
external communication. Interconnecting telephones
should be provided for each important department and
at patients' bed. These shall be interconnected to permit
internal communication without operator's assistance.
Facility shall be provided for external communication
with these departments through operator's assistance.
Some of the most important departments shall have
direct access facility for external communication. At all
special and important beds, telephone jacks should be
installed so that a telephone may be plugged in any time.

13.2.1 In case of operation theatre and rooms where
surgical operations and dressing is done, concealed
wiring should be provided to avoid risk of
contamination. In other places, any type of general
wiring may be acceptable.

13.2.2 The concealed wiring and switch-socket outlets
in the operation theatres shall be kept at a minimum

height of 1.5 m from the floor as anaesthetic gases are
heavier than air and gravitate to the floor.

13.3 Clocks

Electric clock system when provided, should have
clocks at nurses' stations, main lobby, telephone
switchboard, kitchen, laundry, dining room and boiler
room, as well as in the operating and delivery rooms.
The clocks should be of the recessed type, preferably
with a narrow frame. Clocks in operating and delivery
rooms should have sweep second hands. The general
guidance provided in Part 1 /Section 11 of this Code
shall apply.

13.4 Other Special Installations

The list of other special circuits in installations in
hospitals are given below:

Closed-circuit television in surgery depart-
ment (for teaching purposes);
Television sets in wards;
Short-wave, ultraviolet rays or sterile ray
lamps in ceilings of operating and delivery
rooms around the operating light, to reduce
the bacteria count; and
Luminous signs.

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS

241

SP 30: 2011

ANNEX A
{Clauses 3.2 and 8.1.1)

ZONES OF RISK IN THE OPERATING THEATRE WHEN USING FLAMMABLE ANAESTHETIC
MIXTURES OF ANAESTHETIC GASES AND CLEANING AGENTS

ZONE G

ZONE M

Legend

1 = Ventilation system

2 - Ceiling outlet with sockets for electric power gases

(for example, oxygen), vacuum and exhaust
ventilation system for medical electrical equipment

3 = Operation lamp
4= Equipment

5 = Operating table

Legend

6 = Foot switch

7 = Additional zone M due to use of flammable

disinfection and/or cleaning agents

8 = Anaesthesia apparatus

9 = Exhaust system for anaesthesia gases

10 = Exhaust ventilation system

1 1 = Parts unprotected and likely to the broken

242

NATIONAL ELECTRICAL CODE

ANNEX B

[Clauses 3.3.11, 7.1.3.2(b) and! A A]

PATIENT ENVIRONMENT

SP 30 : 2011

/ m

fT) OPERATION TABLE

(7) MEDICAL ELECTRICAL
^^ EQUIPMENT

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS

243

SP 30: 2011

ANNEX C
(Clause 6,1 A)

EXAMPLE OF AN ELECTRICAL INSTALLATION IN A MEDICAL ESTABLISHMENT

Legend

1 = Heating pipes

2 = Water supply

3 = Gas supply

4 = Distribution board

5 = General ward

6 = Hospital bed

7 = Heating and water pipes

8 = Medical IT-system for Operation Theatre

9 = Insulation monitoring device

10 = Medical isolating transformer

11 - Socket outlet

12 - Main distribution board.

Legend

13 = Main earthing bar

14 = Joint

15 = Water meter

16 = Gas meter

17 = Waste water

18 = Earth electrode

19 = Lighting protective system

20 = From public electric power system

L v L 2 , L 3 = phase conductors
N - neutral conductors
EC = bonding conductor
PE = protective conductor

244

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SP 30 : 2011

ANNEX D
(Clause 7*1.4.1)

SCHEMATIC PRESENTATION OF PROTECTIVE CONDUCTORS AND EQUIPOTENTIAL

BONDING IN OPERATING THEATRES

Legend

1 = Feeder from the main service entrance

(main distribution board)

2 = Distribution of the floor

3 = Operating theatre distribution panel

4 = Safety supply system

5 = Medical isolating transformer

6 = Insulation monitoring device

7 = Special safety supply system, E 2

8 - Special safety supply system E,

9 = Central heating

10 = Metal window-frame

1 1 = Metal cabinet for instruments

12 = Meal washing-basin and water supply

13 = Ceiling stand with outlets for gas supply

14 = Ceiling stand with mains socket outlets

(with terminals for equipotential bonding,
enclosure connected to the protective
conductor bar)

15 = Alarm device for the insulation monitoring

device (example)

16 = Operating table (electrically driven)

Legend

17 = Operating lamp

18 = Ampere meter for special safety

supply system

19 = X-ray equipment

20 = Sterilizer

21 = Residual-current protective device

22 = Protective conductor bar

23 = Equipotential conductor bar

24 = Terminals for equipotential bonding

25 = Operation

26 = Warning

27 = Green

28 = Red

29 = Buzzer

30 = Stop button for buzzer

31 = Test button

PE = protective conductor
EC = equipotential bonding
L v L 2 , L 3 = phase conductors
N = neutral conductor

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS

245

SP 30: 2011

ANNEX E
(Clause 11.1.1)

SAFETY SUPPLY SYSTEM

E-0 GENERAL

E-0.1 This Annex contains recommendations for the
design of the safety supply system in medical
establishments.

Priority is given to all aspects ensuring safe working
conditions in medically used rooms.

Interruption of normal electrical service in medical
establishments may cause hazardous situations.
Therefore, it is necessary to provide for continuity of
power supply for vital services at all times.

In some medically used rooms a special safety supply
system should be provided additionally. It supplies life
supporting equipment and the operating table lighting
for 3 h only, that is, for a relatively short time if the
mains supply or the safety supply system fails or the
switch-over time cannot be tolerated.

The safety supply system is intended to supply
electrical energy for a longer period of time to essential
circuits of the medical establishment if the mains
supply fails by external causes.

E-l ESSENTIAL SERVICES — LIGHTING

E-l.l Essential lighting requirements will vary
considerably in different locations, depending on the
importance and nature of the work. In some instances,
for example, operating table lighting in operating
suites, and the critical working areas in the delivery
room and recovery rooms, the degree and quality of
emergency lighting should be approximately equal to
that of the normal lighting. Even in these areas,
however, considerable reduction in the general lighting
may be acceptable. Ample socket-outlets connected to
essential circuits should be available to enable portable
lighting fittings to be used for any tasks outside the
critical working area-which require a higher standard
of lighting.

E-1.2 No general recommendations can be made for
the emergency lighting arrangements for stairs and
corridors as needs will differ considerably according
to the design and size of the hospital. As a general
guide, safety lighting should be provided to enable
essential movement of staff and patients to be carried
out in reasonable safety. Safety lighting should also
be provided in public waiting spaces, at entrances and
exits, and in corridors used by members of the public,
ambulance staff, etc. External emergency lighting will

normally be restricted to the accident and emergency
entrance areas.

E-l. 3 Three grades of emergency lighting are
suggested, namely:

a) Grade A lighting of intensity and quality equal
or nearly equal to that provided under normal
supply conditions;

b) Grade B reduced standard of lighting, for
example, about half the normal standard,
sufficient to enable essential activities to be
properly carried out; and

c) Grade C safety lighting of a much reduced
standard but sufficient to allow the free
movement of persons, trolleys, etc.

Levels for Grades A, B and C are under consideration.

E-1.4 Table 6 is intended as a general guide. Emergency
lighting may be needed in areas not mentioned in the
table.

E-2 ESSENTIAL CIRCUITS — SOCKET-
OUTLETS

E-2.1 Socket-outlets should be so distributed that in
each area where essential equipment will be used,
socket-outlets connected to at least two separate sub-
circuits are available.

Table 7 is intended as a general guide.

E-2. 2 Socket outlets in operating rooms for the
connection of X-ray equipment for fluoroscopy should
be supplied from an essential circuit.

E-2.3 Electrical services, including automatic controls,
which are essential for the safe operation of sterilizing
equipment in operating theatre and the central sterile
supply department should be supplied from an essential
circuit.

E-2.4 Blood banks and other clinical refrigerators are
usually equipped with temperature retaining facilities
which will satisfactorily safeguard against power
failures of several hours' duration. Nevertheless, they
shall be supplied from an essential circuit.

E-2.5 Motors of surgical suction plant should be
connected to an essential circuit. It is desirable that
the motors should be so arranged that once they are
switched on they will restart automatically, following
an interruption of supply.

246

NATIONAL ELECTRICAL CODE

SP 30: 2011

Table 6 Emergency Lighting

(Clause "EA A)

Table 6 — (Concluded)

Department or

Area

Grade of

No.

Location

Lighting

(1)

(2)

(3)

(4)

Major Operating
Suites

Operating theatre

Critical working area

Grade A

Operating theatre

General working area

Grade B

Anaesthetic rooms

General working area

Grade A

Post operative

General working area

Grade A

Intensive care room

Circulating areas

Grade C

ii)

Delivery Suites

Critical working area

Grade A

Delivery rooms

Other nursing areas

Grade B

Circulating areas

Grade C

iii)

Accident and

Emergency

Departments

Operating theatres

Critical working area

Grade A

Intensive care rooms

Critical working area

Grade A

General working area

Grade B

Circulating areas

Grade C

iv)

Out-Patient
Department

Operating theatres

Critical working area

Grade A

Treatment rooms

General working areas

Grade B

Consulting rooms

General working areas

Grade B

Circulating areas

Grade C

Pathological

Essential working areas

Grade B

department

Blood bank

Grade A

Transfusion laboratory

Grade A

Diagnostic X-ray

General working area

Grade B

department

(where portable X-ray
machines may be used)

Circulation areas

Grade C

Radiotherapy

Treatment areas

Grade A

department

Public circulating areas

Grade C

Pharmacy

Dispensing areas

Grade B

Laboratory

Grade B

Ward Areas

Intensive therapy

Intensive nursing area

Grade A

units

Other nursing areas

Grade B

Nurses' station or duty

Grade B

room

vi)

Special Baby Care
Units

Nurseries

General working area

Grade B

Psychiatric wards

General working area

Grade B

Treatment rooms

General working area

Grade A

Other nursing areas

General working area

Grade C
(night-
lighting)

vii)

Central Sterile Supply General working area

Grade B

Department

iii)

Telephone Exchanges

Essential working area

Grade B

ix)

Operators Room

Grade B

Lifts

Lifts cars

Grade A

Entrance and exit of

Grade A

elevators

xi)

General circulating
Areas

Public entrances and

—

Grade C

exits

Corridors and

—

Grade C

SI Department or
No. Location

(1) (2)

Area

(3)

Grade of
Lighting

(4)

Corridors and —

Grade C

circulating spaces of

deep planned designs

ii) Assembly Areas

Assembly rooms and —

Grade C

associated exists

Public waiting space - —

Grade C

Plant rooms housing Working area

Grade B

essential plant

Kitchens Essential working areas

Grade B

Table 7 Socket-Outlets in Essential Circuits
(Clause E-2.1)

Department

Number of Socket-

No.

Outlets Connected to

Essential Circuits (see

Note)

(1)

(2)

(3)

i) Operating suits
ii) Intensive care room and
operating rooms in accident
and emergency department
iii) Delivery rooms
iv) Post-anaesthetic recovery

rooms
v) Intensive therapy units
vi) Radiological diagnostic room
vii) Ward accommodation set aside
for patents dependent on
electrically driven equipment,
for example, respirators,
rocking beds, artificial kidney
machines, etc.
viii) Special baby care units
ix) Pathology laboratories
x) Wards where essential
equipment such as suction
apparatus will be used

All
All

All
All
All

All

staircases forming
recognized means of
escape

2 sockets outlets for wards
containing 1 to 4 beds and,
pro rata, where the number
of beds exceeds 4.

NOTE — It is reasonable to assume that only essential
equipment will be used in these areas during periods of power
failure. The recommendation that all socket are connected to
the Essential Circuits provide the most convenient choice of
sockets outlets at any time, and to simplify installation.

E-2.6 Safety supply systems for facilities for ventilation
and air-conditioning purposes will usually apply only
to plants which serve areas which are entirely
dependent on mechanical ventilation and have no
facilities for natural ventilation or where mechanical
ventilation services are essential for clinical reasons.
Where ventilation requirements are met by duplicate
plants it will usually only be necessary for one of the
plants to be supplied from the emergency source, thus
ensuring air supplies of approximately 50 percent of
the normal rate. Changeover switches, however, should
be provided, to enable either of the plants to be
connected to the emergency service.

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS

247

SP 30: 2011

E-2.7 Any mains-energized alarm and control circuits
should be so arranged that they are automatically
connected to the safety supply system in the event of a
power failure.

E-2.8 In biochemical laboratories and in the pharmacy
about 50 percent of the normal load should be supplied
from essential circuits.

E-3 PARTS OF ESSENTIAL CIRCUITS

E-3.1 Deep-freeze refrigerators and food storage
refrigerators will normally operate within a temperature
range of -10 to -23°C and be fitted with a temperature
alarm device to give a warning when the refrigerator
temperature approaches the upper safety limit. It may
be desirable for one deep-freeze refrigerator at each
hospital to be supplied from the essential circuits where
this can be conveniently arranged.

E-3. 2 In milk kitchen, all refrigerators should be
supplied from an essential circuit.

E-3.3 Where electrically operated pumps are used to
maintain essential water supplies (including that for
fire fighting purposes) it will be necessary to make
suitable arrangements for the pumps to be connected
to the safety supply system.

E-3.4 Telephone exchange equipment is usually

energized from float charged batteries having sufficient
capacity for at least 24 h normal working.

E-3.5 Where lifts are provided for the movement of
patients it is desirable that one lift in each separate
section of the hospital should be so arranged that it is
normally connected to the essential circuits of the
installation having automatic changeover facilities.
These lifts will be regarded as emergency or fire lifts,
and should be suitably indicated by markings at each
landing.

Suitable manually-operated switching arrangements
should be provided to enable the general safety supply
system to be switched from the emergency lift to each
of the other lifts in turn to eliminate the possibility of
occupants being trapped in the lifts during power
failures. Under normal supply conditions the
emergency lifts only will be connected to the essential
circuit of the installation.

E-3.6 Communication equipment should be connected
to essential circuits.

E-3.7 All boiler house supplies should be fed from
essential circuits.

E-3.8 Emergency supplies for computers should be
examined in each case.

248

NATIONAL ELECTRICAL CODE

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C/5

SP 30 : 2011

SECTION 5 HOTELS

FOREWORD

Hotels lodging or rooming houses are of a wide variety,
ranging from simple dormitory type accommodation
for guests, where only a common bath is provided with
no facility for dining/kitchen to the sophisticated star
hotels. Increasing competition in the hotel industry as
such, coupled with the demand by guests for a variety
of comforts, calls for an electrical installation in a hotel
with increased sophistication.

The electrical needs of a hotel depend on the type and
extent of facilities being provided and the rating of the
hotel. The system design would in general be identical
with that of any other large building, the actual power
requirement expressed in terms of per-unit area or per
guest room.

Specific requirements for installations in swimming
pool are covered in Annex A to this Section. These
requirements also apply to swimming pools in other
occupancies, say sports buildings. For editorial
convenience, these specific requirements form part of
this section of the Code.

1 SCOPE

This Section 5 of the Code covers requirements for
electrical installations in buildings such as hotels and
lodging houses.

2 REFERENCES

This Part 3/Section 5 of the Code should be read in
conjunction with the following Indian Standards:

IS No, Title

3646 (Part 2): 1966

8061 : 1976

IS AEC 60309-1:

2002

IS/EEC 60309-2
2002

SP 7 : 2005
SP 72 : 2010

Code of practice for interior
illumination: Part 2 Schedule for
values of illumination and glare
index

Code of practice for design,
installation and maintenance of
service lines upto and including
650 V

Plugs, socket-outlets and couplers
for industrial purposes: Part 1
General requirements (first revision)
Plugs, socket-outlets and couplers
for industrial purposes: Part 2
Dimensional interchangeability
requirements for pin and contact
tube accessories (first revision)
National Building Code of India
National Lighting Code

3 TERMINOLOGY

For the purpose of this Section, the definitions given
in Part 1 /Section 2 of the Code shall apply.

4 CLASSIFICATION

4.1 The electrical installations covered in this Section
are those in buildings intended for the following
purposes:

a) Lodging or rooming houses — These include
any building or group of buildings in which
separate sleeping accommodation for a total
of not more than 15 persons on either transient
or permanent basis with or without dining
facilities, but without cooking facilities for
individuals, is provided.

NOTE — The above is distinct from single or two family
private dwellings which are covered in Part 3/Sec 1 of
this Code.

b) Hotels — These include any building or group
of buildings in which sleeping
accommodation is provided with or without
dining facilities for hire to more than 15
persons, who are primarily transient such as
hotels, inns, clubs and motels.

NOTE — For the purpose of this Code, restaurants other
than those forming part of a large hotel are treated as
assembly buildings and are covered in Part 3/Sec 3 of
this Code.

4.2 The electrical installations in hotels covered in this
Section include the following services:

a) Supply intake,

b) Main distribution centre,

c) Ventilation and exhaust systems,

d) Kitchen,

e) Laundry,

f) Cold storage,

g) Health club,

h) Swimming pool and filtration plants,

j) Restaurants and bars,

k) Interior lighting,

m) Telephones,

n) Channelized music,

p) Service lifts and passenger lifts,

q) Offices,

r) Fire protection and alarm systems,

s) Banquet halls and conference facilities,

t) Gardens and parking lots and illumination
systems therein,

250

NATIONAL ELECTRICAL CODE

SP 30 : 2011

u) Illuminated signs, display lights and

decorative illuminations, and
v) Emergency system.

5 GENERAL CHARACTERISTICS OF
INSTALLATIONS

General guidelines on the assessment of characteristics
of installations in buildings are given in Part 1/Sec 8 of
this Code. For the purposes of installations falling under
the scope of this Section, the characteristics defined
below generally apply (see also SP 7).

5*1 Environment

5.1.1 The following environmental factors apply to
hotels:

Environment Characteristics Remarks

(1) (2) (3)

Utilization

(i)

Characteristics

(2)

Remarks

(3)

Presence of
water

Probability of
presence of water
is negligible

Presence of
foreign solid
bodies

Presence of
corrosive or
polluting
substances

Possibility of jets
of water from any
direction

Possibility of

permanent and

total covering by

water

The quantity or

nature of dust or

foreign solid

bodies is not

significant

The quantity and

nature of corrosive

or polluting

substances is not

significant

Majority of
locations in hotels.
Traces of water
appearing for short
periods are dried
rapidly by good
ventilation.
Applies to gardens

Locations such as
swimming pools

For hotels situated
by the sea or
industrial zones,
other

categorization
applies (see
Part 1/Section 8 of
this Code)

Mechanical Impact and
stresses vibration of low

severity
Seismic
effect and
lighting

Depends on the
location of the
building

5.2 Utilization

5.2.1 The following aspects of utilization shall apply:

Capability of Ordinary,
persons uninstructed

persons

Persons
adequately
advised or
supervised by
skilled persons

Persons in non-
conducting
situations

A major
proportion of
occupants in
Hotels

Applies to areas,
such as building
substation and for
operating and
maintenance staff

Contact of
persons with
earth
potential

Condition of
evacuation
during
emergency

Low density
occupation, easy
conditions of
evacuation

High density
occupation,
difficult
conditions of
evacuation

Nature of No significant
processed of risks
stored
material

Contamination
risks due to
presence of
unprotected food
stuffs

Applies to lodging
houses

Large hotels, high-
rise buildings.

Applies to
kitchens

6 SUPPLY CHARACTERISTICS AND
PARAMETERS

6.0 Exchange of Information

6.0.1 Proper coordination shall be ensured between the
architect, building contractor and the electrical engineer
on the various aspects of installation design. In addition
to the general aspects which require coordination and
identified in other sections, information shall be
obtained on the following services:

a) Whether central air-conditioning system is
intended. If so, layout of air handling units,
fan coil units, ducting, false ceiling and chilled
water lines should be obtained.

b) Whether centrally controlled fire-fighting is
intended. If so, layout of fire-fighting
installation should be obtained.

c) Whether telephone and TV facilities are
intended in each room. If so, layout of the

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS

251

SP 30 : 2011

telephone installation and TV circuits should
be obtained,
d) Whether centrally heated out water system is
intended. If so, layout of hot water pipe-line
be obtained.

6.1 Branch Circuits

6.1.1 The general provisions for the design of wiring
of branch circuits shall conform to those laid down in
Part 1/Section 9 of this Code. However, for special
cases such as for communication networks, fire-alarm
system, etc, as well as in areas such as kitchen, laundry,
etc, the recommendation of the manufacturer shall
apply.

6.1.2 The branch circuit calculations shall be done as
laid down in Part 1/Section 1 of this Code. The specific
demands of the lighting, appliance and motor loads,
as well as special loads encountered in hotel building
shall be taken into account.

6.1.3 In hotel buildings, the interior decor normally
includes false ceiling, carpets and curtains. Any wiring
laid above the false ceiling should be adequately
protected, such as by drawing the wires in metallic
conduits and not run in open. Wires shall not be laid
under carpets. They shall be run at skirting level and
encased for mechanical protection.

6.1.4 Panel Boards and Switch-boards

The provisions of Part 1/Section 9 of this Code shall
apply.

6.1.5 Socket-outlets and Plugs

6.1.5.0 These should be provided in all places where
plug-in service is likely to be required, to reduce the
need for alterations and extensions of wiring after the
hotel building is completed. Duplex or other suitable
outlets should be provided as required in the offices
and work places for fans, lamps and appliances. The
socket-outlets shall preferably have covers. Corridors
and staircases shall be provided with sufficient socket-
outlets for floor cleaning appliances. These shall be
connected in a circuit separate from the circuits for
the guest rooms.

6.1.5.1 If provided, use of a central radio receiving
system wired with multi-channels piped music system
to each room is recommended so that the occupant may
choose one of the broadcasts. For such reception,
special aerials and related wiring are required. Aerial
outlets at rooms are required for portable radios in areas
and buildings where reception is poor but in general
the aerial built in the set may be adequate.

6.1.5.2 Special convenience outlets in corridors at
suitable locations are desirable for use of portable

equipment such as floor cleaning appliances. They
should be of the 3 -pin type, suitably rated with one-
pin earthed.

Heavy duty sockets should also be provided in pantries,
kitchens, toilets and utility rooms for use of appliances.

Adequate plug-in sockets at proper locations should
be provided in banquet halls and other meeting places
for flood lights and other appliances.

6.2 Feeders

The general provisions laid down in Part 3/Section 9
of this Code shall apply.

6.3 Service Lines

The general provisions laid down in IS 8061 shall
apply.

6.4 Building Substation

6.4.1 If the load demand is high which requires supply
at voltage above 650 V a separate indoor
accommodation, as near the main load centre of the
hotel as possible shall be provided to accommodate
switchgear equipment of supply undertaking and
indoor/outdoor accommodation for the transformers.
The main distribution equipment of the hotel shall
preferably be located next to the substation. Separate
feeders shall be provided for major loads like central
air-conditioning, kitchen, laundry, swimming pool,
lighting of main building and other essential loads.

6.4.2 The supply line should preferably be brought into
the building underground to reduce the possibility of
interruption of power supply. The accommodation for
substation equipment as well as for main distribution
panel shall be properly enclosed so as to prevent access
to any unauthorized person. It shall be provided with
proper ventilation and lighting arrangement.

6.4.3 The location and layout of building sub-station
and emergency diesel generating set(s) shall be in
conformance with Part 2 of this Code.

6.5 System Protection

6.5.1 General

The general rules for protection for safety laid down
in Part 1/Section 7 of this Code shall apply. Reference
should be made to SP 7 for guidelines for fire protection
of buildings.

6.5.2 For lodging and rooming houses of 3 storey and
above, with a floor area more than 200 m 2 with central
corridor and rooms on either side, besides fire fighting
equipment, manually operated electric fire-alarm system
shall be provided. Both manually operated and automatic
fire-alarm systems shall be provided in large hotels.

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6.6 Building Services

6.6.1 Lighting

6.6. LI The general rule laid down in Part 1 /Section 14
of this Code shall apply. The choice of lighting fittings
and general lighting design together with power
requirements shall be planned based on the
recommended values of illumination and limiting
values of glare index given in Table 1 [see also IS 3646
(Part 2) and SP 72].

Table 1 Recommended Values of Illumination
and Glare Index for Hotels

SI Building Illumination, Limiting Glare

No. lux Index

(1) (2) (3) (4)

i) Entrance halls, lobby

150

—

ii) Reception and accounts

300

—

iii) Dining rooms (tables)

100

—

iv) Lounges

150

—

v) Bedrooms:

a) General

100

—

b) Dressing tables, bed

200

—

heads, etc.

vi) Writing tables

300

vii) Corridors

—

viii) Stairs

100

—

ix) Laundries

200

x) Kitchens

200

xi) Goods/passenger lifts

xii) Cloakrooms/toilets

100

—

xiii) Bathrooms

100

—

xiv) Shops/stores

150-300

NOTE — The lighting

some of these

locations is

determined primarily by

aesthetic considerations and the

above values should be taken as a guide only.

6.6.1.2 In guest bedrooms, it shall be possible to switch
the general lighting not only from the entrance but also
from the bedside (see also 8.4.2)

6.6.1.3 In bathrooms, the lights should be mounted at
head level on both sides of the mirror. Care shall be
taken to ensure that there is no glare.

6.6.1.4 Lighting in banquet halls shall be given special
consideration in view of its multipurpose utility such
as fairs, dances, fashion shows, conferences, exhibition
or concerts. Sufficient number of controlled socket-
outlet circuits shall be combined in a switching station
from which the entire hall shall be visible.

6.6.1.5 In designing outdoor lighting installations, care
shall be taken to ensure that disturbing glare does not
reach the rooms of the guests.

6.6.2 Air-conditioning

The provisions of Part 1 /Section 14 of this Code shall
apply.

6.6.3 Lifts and Escalators

6.6.3.0 The general rules laid down in Part 1 /Section 14
of this Code shall apply. However, the design of lifts
shall take into account the following recommendations.

6.6.3.1 Occupant load

For hotel buildings, an occupant load of 12.5 gross
area, in m 2 per person is recommended.

6.6.3.2 Passenger handling capacity

The passenger handling capacity expressed in percent
of the estimated population that has to be handled in
the 5 min peak period shall be 5 percent for hotel
buildings.

6.6.3.3 Car speed — This shall be as follows:

Occupancy Floors Served Car Speed

m/s

(1) (2) (3)

Passenger lifts for low
and medium class
lodging houses
Hotels

4-5

0.5

0.5-0.75

6.6,3.4 For hotel buildings, it is desirable to have at
least a battery of two lifts at convenient points of a
building. If this is not possible, it is advisable to have
at least two lifts side by side at the main entrance, and
one lift at different sections of the building for
intercommunication.

7 TESTING OF INSTALLATION

The various tests on the installation shall be carried
out as laid down in Part 1/Section 10 of this Code.

8 MISCELLANEOUS PROVISIONS

8.1 Call System

The general provisions for electrical bells and call
system shall conform to those laid down in Part 1/
Section 14 of this Code. The call system should be a
wired electrical system whereby customer may signal
for attendance from his room. Two types of systems
are recommended:

a) A simple one-watt signal system which
connects the room side call stations with a
signal at the attendant station. It
simultaneously lights a dome light over the
door of the room from which the call is
originated. The signal at the attendant station
may be in the form of an annunciator with a
buzzer or a light with a buzzer.

b) A central control panel shall, be set up

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SF 30 : 2011

preferably on the ground floor incorporating
a set of indicating panels according to the
number of wings. Each indicating panel
should have a set of small lamps according to
the number of rooms. After- attending the
customer, the attendant presses the resetting
button which puts the whole equipment to the
original condition.

8.2 Telephones

A centralized EPABX System with sufficient P&T lines
shall be installed for internal and external
communications with the help of operator's assistance
as well as directly through this system. These may be
connected on a dial system which permits internal
communication through the hotel switchboard without
the assistance of the operator. At all the rooms,
telephone jacks shall be installed so that a telephone
may be plugged in any time at any convenient location.
Parallel telephones may be provided in the bedrooms.
Each room shall also be provided with jacks for Broad
Band Multi Service facility /internet facility.

8.3 Clock Systems

The general provisions for clock systems shall conform
to those laid down in Part 1/Sec 14. The following
locations may be provided with clocks:

a) Guest rooms,

b) Main lobby,

c) Telephone switchboard,

d) Dining room,

e) Banquet halls,

f) Kitchen, and

g) Restaurant and bar rooms.

8.4 Emergency Supply

See also Part 2 of this Code.

8.4.1 In the event of a failure of supply, a large standby
power supply usually a diesel driven generating set
could be used to partly or entirely supply the loads in
the hotel. Emergency lighting shall be confined to
essential areas, and the standby power supply shall feed
essential and safety installations in the hotel.

8.4.2 Part of the kitchen, storage and refrigeration
rooms in the hotel shall also be supplied by the
emergency supply. A part of the lighting in each room,
corridor, staircases and other circulation areas shall be
connected to emergency supply.

8.5 Other Special Installations

The list of such installations is given below:

a) TV sets at main assembly areas and in guest
rooms,

b) Lighting in banquet halls,

c) Fire-fighting system,

d) Swimming pool (see Annex A),

e) Cold storage,

f) Sauna Heaters (see Annex B), and

g) Broad Band Multi Service facility /internet
facility.

H.6 For particular requirements for locations containing
a bathtub or shower basin, see Annex A of Part 3/
Section 1 of this Code.

8.7 Luminous Sign

Photo luminescent safety signage should be provided
at different strategic locations.

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ANNEX A
(Clause 8.5)

PARTICULAR REQUIREMENTS FOR SWIMMING POOL

A-l SCOPE

This Annex applies to the basins of swimming pools
and paddling pools and their surrounding zones where
susceptibility to electric shock is likely to be increased
by the reduction of body resistance and contact with
earth potential.

A-2 CLASSIFICATION OF ZONES

A-2.1 Reference is drawn to Fig. 1 and Fig. 2.

Zone — is the interior of the basin.

Zone 1 — is limited by a vertical plane 2 m from the
rim of the basin by the floor or the surface expected to
be occupied by persons and the horizontal plane 2.50 m
above the floor of the surface.

Zone 2 — is limited by the vertical plane external to
Zone 1 and a parallel plane 1.50 m from the former,
by the floor or surface expected to be occupied by
persons and the horizontal plane 2.50 m above the floor
or surface.

NOTE — Where the pool contains diving boards, spring boards,
starting blocks or a chute, Zone 1 comprises the zone limited
by a vertical plane situated 1.50 m around the diving boards,
spring boards and starting blocks, and by the horizontal plane
2.50 m above the highest surface expected to be occupied by
the persons.

A-3 PROTECTION FOR SAFETY

A-3.1 Where safety extra-low voltage is used, whatever
the nominal voltage, protection against direct contact
shall be provided by barriers or enclosures affording
at least a protection of IP2X, or insulation capable or
withstanding a test voltage of 500 V for 1 min.

A-3.2 All extraneous conductive parts in Zones 0, 1
and 2 shall be bonded with protective conductors of
ail exposed conductive parts situated in these Zones.

A-4 SELECTION OF EQUIPMENT

A-4.1 Electrical equipment shall have at least the
following degrees of protection:

a) Zone

b) Zone 1

IPX 8
IPX 4

c) Zone 2 : IP X 2 for inside swimming pools.
IP X 4 for outside swimming pools.

A-4.2 For Zone 1 and Zone 2, water jet is likely to be
used for clearing purpose : IP X 5

This requirement does not apply to instantaneous water
heaters complying with IS 302 (Part 2/Sec 35).

A-5 WIRING SYSTEMS

A-5.1 In Zone and Zone 1, wiring systems shall be
limited to those necessary to the supply of appliances
situated in those zones.

A-5.2 Junction boxes are not permitted in Zone and
Zone 1. In Zone 2, they are permitted provided they
have the necessary degree of protection as given
in A-4.1.

A-5.3 In Zone and Zone 1 no switchgear and
accessory shall be installed. In Zone 2 socket-outlets
are permitted only if they are either:

a) supplied individually by an isolating
transformer, or

b) supplied by safety extra low voltage, or

c) protected by a residual current protective
device.

A-5.4 If it is not possible to locate socket-outlets
may be installed only if they are complying

a) Outside 1.25 m from the Zone border, and

b) protected by residual current protection device.

A-5.S The socket-outlets shall comply IS/IEC 60309
(Part 1) and IS/IEC 60309 (Part 2).

A -5.6 An electric heating unit embedded in the floor
in Zones 1 and 2 shall incorporate a metallic sheath
connected to the local supplementary equipotential
bonding and shall be covered by the metallic grid
required by A-3.2.

A-5.7 In Zone 2, only water heaters are permitted
excepting that other equipment supplied by SELV
(Safety Extra Low Voltage) at a nominal voltage not
exceeding 12 V may be installed.

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS

255

SP 30 : 2011

ZONE 2

20fl£ 1

« h J"

lit I I

L ^-Sm ■ Hj J

I
I
I

' t

I ZONE 2

Fig. 1 Zone Dimensions for Basins Above Ground

ZONE 2

r~--~-T-r-T

ZONE 1

/?/////}////////

1-S m ' 2*0

-■ m ^ m

£ — ^

%///////\>/////\'

I- 2-0m

ZONE 2

I
I

m hSm -«|

Fig. 2 Zone Dimensions of Swimming Pools and Paddling Pools

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ANNEX B
(Clause 8.5)

PARTICULAR REQUIREMENTS FOR LOCATIONS CONTAINING SAUNA HEATERS

1 SCOPE

The particular requirements of this Annex apply to
locations in which hot air sauna heating equipment is
installed.

B-2 CLASSIFICATION OF TEMPERATURE
ZONES

B-2.1 The assessment of the general characteristics of
the location shall take due consideration of the
classification of the four temperature zones which are
illustrated in Fig. 3.

B-3 PROTECTION FOR SAFETY

B-3.1 Where Safety Extra Low Voltage (SELV) is
used, irrespective of the nominal voltage, protection
against direct contact shall be provided by one or more
of the following:

a) insulation capable of withstanding a test
voltage of 500 V ac, rms for 1 min.

b) barriers or enclosures, affording at least
degree of protection IP 24.

B-3,2 All extraneous conductive parts shall be bonded
with protective conductors of all exposed conductive
parts situated in these zones and earthed.

B-4 SELECTION OF EQUIPMENT

B-4.1 All equipment shall have at least the degree of
protection IP 24.

B-4.2 Equipment should be selected in accordance with
the temperature zones as depicted in Fig. 3 as per the
following details:

a) Zone A: only the sauna heater complying with
relevant safety standard and equipment

"T"

0.3 m

0.5 m

0.5m-

£T

0.5m

Fig. 3 Classification of Temperature Zones

PART 3 ELECTRICAL INSTALLATIONS IN NON-INDUSTRIAL BUILDINGS

257

SP 30: 2011

directly associated with it shall be installed.

b) Zone B: there is no special requirement
concerning heat resistance of equipment.

c) Zone C: equipment shall be suitable for an
ambient temperature of 125°C.

d) Zone D: only luminaries and their associated
wiring, and control devices for the sauna
heater and their associated wiring shall be
installed. The equipment shall be suitable for
an ambient temperature of 125°C.

B-5 WIRING SYSTEMS

B-5.1 Flexible elastomer insulated and mechanically

protected cords complying with appropriate standard,
suitable for 150°C should be used.

B-5.2 Switchgear not built into sauna heater, other than
a thermostat and a thermal cut-out shall be installed
outside the hot air sauna.

B-5. 3 Except as permitted in B-4.2 and B-5.2
accessories shall not be installed within the hot air
sauna.

B-6 OTHER FIXED EQUIPMENT

B-6.1 Luminaries shall be so mounted as to prevent
overheating.

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SECTION 6 SPORTS BUILDINGS

FOREWORD

The design and erection of electrical installation in a
sports building have to take into account a multitude
of factors that are unique to the type of use to which it
is put. In a way the electrical power needs and the
external influences in a sports building are quite
identical to those for theatres and other multipurpose
buildings for cultural events excepting that for
international events exacting standards of services and
flexibility had to be provided in a multipurpose sports
stadia.

Several stadia, especially those of the indoor type are
meant for staging a variety of games which between
themselves require varying standards of lighting levels.
The design of illumination system in a sports building
therefore requires consultations with a specialist and
the guidelines provided in this Section are purely
recommendatory in nature in this respect.

In indoor stadia where large number of people
congregate it is essential to inbuild adequate fire
precautions from the point of view of safety. Assessing
the need for adequate strength of a standby supply for
essential services requires special consideration.

It is to be noted that a sports stadia should preferably
be designed for use for other purposes as well, such as
the staging of cultural events and this aspect shall be
borne in mind while designing the electrical needs of
the complex so as to ensure optimum utilization of the
facilities.

With the advent of sophisticated stadia in the country
as well as keeping in view the accent on sports, this
Section of this Code has been set aside to cover such
of those specific requirements applicable to sports
buildings from the electrical engineering point of view.
Taking note of the fact that the type of buildings and
their needs for the purposes of sports and games would
be quite different between them, only broad guidelines
are outlined in this Section. It is recommended that
assistance of experts shall be sought in the design of
the installation at the early stages itself.

1 SCOPE

This Part 3/Section 6 of the Code covers requirements
for electrical installations in sports buildings and stadia,
indoor and outdoor.

2 TERMINOLOGY

For the purpose of this Section, the definitions given
in Part 1/Section 2 of this Code shall apply.

3 CLASSIFICATION OF SPORTS BUILDINGS

3.1 The buildings for the purposes of conducting sports
and games are characterized by the criteria that large
number of people congregate. Sports complexes not
basically meant for exhibition purposes, and not likely
to be utilized for other purposes, such as for staging
special or cultural events, shall however conform to
the special requirements of this Section. The type of
building shall therefore be classified as follows:

a) Based on type of building:

1) Indoor stadia.

2) Outdoor stadia: Stadia meant for use in
daylight. Stadia meant for use during
night under artificial lighting.

b) Based on type of game/sport:

1) Single game sports hall/stadia.

2) Multigames hall/stadia.

c) Based on utility:

1) Stadia meant for games only.

2) Multipurpose stadia for other amuse-
ments as well.

d) Based on audience-factor:

1) Stadia/halls meant for exhibition pur-
poses — where groups of people con-
gregate.

2) Stadia/halls meant for training and pass-
time — where audience may not normal-
ly be present.

NOTE — Classification d (1) includes stadia meant for
staging tournaments and events, and d (2) includes
games halls in educational institutions and the like
where normally no exhibition is intended.

3.1.1 Reference should be made to 5.5.1.2 for
classification from lighting consideration.

3.2 The electrical installation needs in sports buildings
would therefore be governed by the type of use
indicated in 3.1(a) to (d). A large sports complex may
include the following sub-units:

a) Supply intake/voltage of supply;

b) Main substation and satellite substations, if
any;

c) Central control room/switch rooms;

d) Electrification of restaurant, health clubs;
hospitals, offices and other support structures;

e) Communication facilities (telephone, telex,
telegraph, data processing TV, radio and press
facilities);

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SP 30: 2011

f) Fire protection services;

g) External electrification of gardens and
parking lots, service routes, lake fountains (if
any);

h) Emergency electric supply system including
uninterrupted power requirements;

j) Audio systems, public address/security;

k) De-watering arrangements, sewage disposal,
water supply systems;

m) Gas/oil arrangements for sports flame if
required; and

n) Miscellaneous requirements for power-
socket, microphone outlets, score-boards, etc.

4 GENERAL CHARACTERISTICS OF SPORTS
BUILDINGS

General guidelines on the assessment of characteristics
of installations in buildings are given in Part 1/Section 8
of this Code. For the purposes of installations falling
under the scope of this Section, the characteristics given
below shall apply.

4.1 Environment

4.1.1 The following environmental factors apply to
sports buildings:

Environment Characteristics Remarks

(1) (2) (3)

Presence of
water

Presence of
foreign solid
bodies

Submersion, Locations such as

possibility of swimming pools

permanent and total where electrical
covering by water equipment is

permanently and
totally covered
with water under
pressure greater
than J bar.

The quantity or Indoor stadia,
nature of dust or
foreign solid bodies
is not significant

Presence of dust in Outdoor stadia,
significant quantify

Presence of
corrosive or
polluting
substances

Negligible

Lighting Negligible

260

Covers majority
of cases. Stadia
and games
complexes
situated by the sea
or industrial zones
require special
consideration.

Covers category
d(2) (see 3.1) type
of installations.

Environment Characteristics Remarks
(1) (2) (3)

Indirect exposure Installations

to lighting, where supplied by

hazard from overhead lines.

supply

arrangements

exists

Direct exposure or Lighting towers
hazard from in outdoor stadia,

exposure of
equipment is
present

4.2 Utilization

The following aspects utilization shall apply:

Utilization

(i)

Characteristics
(2)

Remarks
(3)

Capability of

Uninstructed

In sports stadia the

persons

sportsmen and
spectators fall under
this category. However,
electrical operating
areas are accessible to
instructed persons only.

Conditions of Low density

Training halls and the

evacuation in

occupation, easy

like where people do

an emergency

conditions of
evacuation

not congregate.

High density

Large multipurpose

occupation,

stadia for exhibition

difficult conditions

purposes.

of evacuation

Nature of

Existence of fire-

Due to furniture and

processed of

risks.

false floor for playing

stored

area

material

5 SUPPLY CHARACTERISTICS AND
PARAMETERS

5.0 Exchange of Information

5.0.1 Proper coordination shall be ensured between the
architect building contractor and the electrical engineer
on the various aspects of the installation design. In
addition to the general aspects which require
coordination and identified in other sections, the
following data shall specifically be obtained:

a) The total electrical power needs of the stadium
including the standby power arrangements,
which will decide the voltage of supply,
number of substations and their preferred
locations, capacity of diesel engine generating

NATIONAL ELECTRICAL CODE

SP 30: 2011

sets for standby supply, transformers,
switchgear, voltage stabilizers, uninterrupted
power supply requirements, etc;

b) In case of indoor stadia, whether air-
conditioning is required and if so, the capacity
and locations of main plants, air-handling
units, pumps, ducting, layout, route of chilled
water lines, etc. In case of outdoor stadium,
the covered portions like offices, restaurants,
are to be air-conditioned or not and their
details as above;

c) Details of fire fighting system/fire alarm
system envisaged;

d) Details of water supply arrangements, storm
water drainage, sewage disposals and pump
capacities, locations, etc;

e) Locations of substations, switchrooms,
distribution boards, etc;

f) Requirements of audio-communication
system for the stadium which includes public
address system, car calling system, ambulance
call, fire service call, intercom stations,
wireless paging system, inter-stadia commu-
nication facilities, computer-aided results
information, etc;

g) Details of score-boards — that is whether and
their power etc, centralized manual or
automatic, etc, needs, voltage stability, clock
system, etc;

h) Special requirements of press, TV, Radio,
telecommunication, games federations, etc;

j) Requirements of lighting, the location of
lighting luminaries, type of light source, level
of illumination required for various stages like
training, TV (black and white or colour)
coverage, etc;

k) Requirements for power outlets, speaker
outlets, microphone outlets, etc., in playing
arena and field; and

m) Other miscellaneous items like electrification
of ancillary buildings in the sports complex,
restaurants, gas/oil requirements for flame
and their controls, fountain lighting system,
car park, path way and external electrifi-
cation.

5.0.2 The following drawings are recommended to be
prepared before commencing the installations work:

a) Single line diagram for electrical distribution;

b) Complete layout drawings indicating type and
mounting of luminaries and conduit/cable
installations for various services. This shall

be prepared in coordination with civil and
structural engineers;

c) Wiring diagrams showing switching sequence
of luminaries, firealarm system, public
announcement systems, etc;

d) In case of air-conditioning, layout of plants,
chilled water piping routes, ducts/grill layout,
etc;

e) Layout of public address system envisaged;
and

f) Site plan indicating the location of pump
houses for storm water drains, water supply,
sewage and fire fighting systems, with the
proposed source and route of power supply.

5.1 Branch Circuits

5.1.1 The general rules as laid down for other large
assembly buildings (see Part 3/Section 3) and as laid
down in Part 1 of this Code shall apply.

5.1.2 Wiring installations for general purpose lighting
and ventilation needs of the sports buildings shall
conform to the requirements laid down in Part 1/Sec 1
of this Code. It is preferable to avoid temporary wiring
in electrical central control room.

Whenever floodlight luminaries of more than 1 000
W are installed, it is preferable to have individual
branch, circuits to each of the luminaries after
considering the economic aspects.

Junction boxes shall be installed near the luminaries
from which connection to the light source may be taken
by flexible conduits. This will help maintenance work
to be carried out without disturbing the positioning of
the lighting fittings.

5.1.3 Panel Boards and Switchboards

The provision of Part 1 /Section 9 of this Code shall
apply. In large stadia, the areas covered by the
services shall be segregated into zones and the sub-
distribution and distribution boards shall be so
arranged and marked keeping in view their
accessibility in times of need.

5.1.4 Socket-outlets and Plugs

For small stadia/halls, the provisions of Part 3/Section 3
of this Code shall apply. The need for special
convenience outlets shall be considered for services
enumerated in 3.2(e). Utility socket outlets shall be
provided at a height of about 0.3 m from the floor
except in field/arena. These shall be of weather-proof
type.

5.2 Feeders

5.2.1 The utility shall be consulted as to the type of

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SP 30 : 2011

service available, whether primary or secondary,
single-phase or three-phase star or delta.

5.2.2 Outdoor floodlighting installations can be made
with either overhead or underground distribution
feeders. From the point of view of appearance and
minimum interference, the underground system is more
desirable where large playing areas are involved.

5.2.3 The underground system shall either be cables
directly buried or cables in conduits.

5.3 Building Substation

5.3.1 The electrical needs of sports stadia may vary
from 30 kVA to 1 000 kVA, according to the size of
the installation. Usually HV supply is used for large
multipurpose stadia where power demand is in excess
of 500 kVA. The design of location of substation and
the diesel generating set, if provided, shall conform to
the requirements specified in Part 2 of this Code.

5.3.2 The main substation for a sports building shall
preferably be located in such a place that does not
interfere with the movement of people congregating.
All electrical operating areas, and control rooms shall
preferably be segregated from public routes for the
sporting events.

5.3.3 Some installations may justify a separate
transformer on each pole of the floodlighting tower
with primary wiring to each tower. In smaller
installations, it may be more economical to reduce
the number of transformers by serving several
locations from a single transformer through secondary
wiring.

5.3.4 For buildings staging national and international
sports events, it shall be provided with duplicate power
supply so that in the event of failure of one power
supply, other one can be able to cater the total load
intended to serve. The changeover should be
automatic.

5.3.5 Emergency power supply by DG set/s shall be
provided at strategic locations to keep the general
lighting and ventilation of the sport buildings in case
of normal ac power failure. The changeover should be
automatic.

5.4 System Protection

5.4.0 The general rules for the protection of safety laid
down in Part 1 /Section 7 of this Code shall apply.

5.4.1 Sports buildings are classified as 'assembly
buildings' (Group D) from fire-safety point of view.
Besides fire fighting equipment fire-detection and
extinguishing system shall be provided as
recommended below (see also SP 7):

Description

Fire Detection System

(1)

(2)

Big halls for over 5 000

Automatic sprinkler and

persons

alarm system

Small halls, health clubs,

Automatic sprinkler

arena, gymnasiums, etc,

Automatic fire alarm

indoor with or without

system

fixed seats corridors for

about 1 000 persons

Same as above,

Same as above

occupancy for less than

1 000 persons

Small indoor games halls Automatic fire alarm

for less than 300 persons

system

Grandstands, stadia for

Manually operated fire

outdoor gathering

alarm systems, in offices

and automatic fire alarm

system in stadia, machine

room, control room, etc

5.5 Building Services
5.5.1 Lighting

5.5.1.0 The general rules laid down in Part 1/Section 1 1
of this Code shall apply {see also SP 72).

5.5.1.1 Special design features

Design of sports lighting, especially in large stadia
require considerations of not only the objects to be
seen, the background brightness, etc, but the observer's
location in the grandstand as well. The following shall
be taken into account;

a) Observers have no fixed visual axis or field
of view. During the shifting of sight, even the
ceiling and luminaries are likely to come into
the line of vision.

b) While the game is in play, the objects of regard
are not fixed, and mostly moving in a three-
dimensional space.

c) It is important for observers to be able to
estimate accurately the object velocity and
trajectory.

5.5.1.2 For the purposes of artificial lighting design, it
is recommended to divide the location of sport play
into general areas for more than one sport and areas
for particular sport.

General areas include field houses, gymnasiums,
community centre halls and other multipurpose areas.
For the purposes of lighting design, the nature of sports
shall be divided as follows:

a) Aerial sports (sports which are aerial in part
or whole) — Badminton, basketball,
handball, squash, tennis and volleyball.

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b) Low level (games which are close to the
ground level) — Archery, billiards, bowling,
fencing, hockey, swimming and boxing.

5.5.1.3 Levels of illumination

For some representative types of sport, the
recommended values of illumination are as given in
Table 1.

Table 1 Recommended Values of Illumination

Sport

Illumination, lux

No.

(1)

(2)

(3)

Archery

Target

540

Shooting line

220

Badminton

320

Basketball

540

Billiards (on table)

540

Boxing and wrestling

540

ii)

Football (see Notes 1 and 2)

Class I

1 100

540

III

320

220

iii)

Gymnasiums

Matches

540

General exercising

320

Hockey (field)

220

iv)

Racing

Bicycle

320

Horse

220

v)-

Rifle (outdoor)

Targets

540 (vertical)

Firing point

110

Range

vi)

Swimming

a) Indoor Exhibition

540

Underwater

100 W/m 2 of surface
area

b) Outdoor Exhibition

220

Underwater

60 percent of indoor

Tennis (laws) Indoor

540

Outdoor

320

Table tennis

540

Volleyball

220

NOTES

1 It is generally conceded that the distance between the
spectators and the play is primary consideration for
football, as well as the potential seating capacity of the
stand. The following classification is therefore described.
Class I — 30 000 spectators, over 30 m minimum

distance.
Class II — 10 000-30 000 spectators,

minimum distance.
Class III — 5 000-10 000 spectators,

minimum distance.
Class IV — 5 000 spectators, over 10 m minimum

distance.

2 For football, uniform illumination shall be provided at
ground level as well as vertically for 15 m above ground.

1} Levels recommended are for incandescent lamps. For
discharge lamps W/m 2 would be reduced depending upon

over 1 5-30 m

over 10-15 m

the efficiency of light source,
flux.

In order that the installed

5.5.1.4 Selection of light sources

For sports lighting, the following light sources are
advantageous together with the considerations
indicated against each:

a) Incandescent lamps (including tungsten
halogen) — Where necessary, over- voltage
operation can be used to advantage especi-
ally as in sports installations, the lighting
systems are used for less than 500 h a year.

b) Fluorescent lamps — Advantageous where
mounting heights are low and short projec-
tion distances are acceptable, for example
tennis, bowling, trampoline and a variety of
indoor sports.

c) High intensity discharge lamps — These are
characterized by long life and high human
efficiency. However, the inherent time delay
for full glow when first energized or when
there is power interruption may necessitate
use of incandescent lighting system to provide
emergency standby illumination in spectator
areas.

For sports events, where colour rendition is important,
use of fluorescent mercury lamps is recommended.

5.5.1.5 Miscellaneous considerations for lighting

a) While selecting and installing high intensity
discharge or fluorescent lamps in multipur-
pose stadia, it is necessary to connect lamps
on alternate phases of supply to avoid flicker
on rapidly moving objects. Where a quite
surrounding is required in order to avoid
ballast hum, remote mounting of ballasts shall
be considered.

b) Efforts shall be required to coordinate the
lighting design for sports events with the
illumination requirements for TV or film
coverage. A horizontal illumination in excess
of 300 lux is considered adequate for
operation of black and white TV and film
recording. Colour recording calls for more
stringent requirements. Colour filming may
also need lamps having correlated colour
temperature of between 3 000 K to 7 000 K.
For film/TV coverage, data on the following
shall be necessary:

1 ) Camera sensitivity,

2) Exposure time, and

3) Effective aperture.

c) Group switching — Group switching of
luminaries is recommended to have maximum
energy saving, after considering the following
factors as well:

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1) Separate switching for lighting outside
the stadia,

2) Requirement of lighting for training
purpose,

3) Requirement of lighting for tournaments
with film and TV coverage, and

4) Separate switching for playing arenas.

5.5.2 Air-conditioning

5.5.2.1 The requirements for air-conditioning and
ventilation as laid down in Part 1/Sec 14 of this Code
shall apply.

5.5.3 Lifts and Escalators

The general rules laid down in Part 1 /Section 14 of
this Code shall apply.

6 TESTING OF INSTALLATIONS

The various tests on the installation shall be carried
out as laid down in Part 1 /Section 10 of this Code.

7 MISCELLANEOUS PROVISIONS

7.1 Electrical Audio Systems

The general provisions for the installation of public
address systems shall be as laid down in Part 1/

Section 1 1 of this Code.

In large grandstand stadia, the effect of time delay for
the sound from the loudspeakers to reach different
sections of the audience would be significant. This shall
be avoided in taking proper precautions in the design
of electrical audio systems.

7.2 Control Room

The various communication needs of large stadia is
normally met with by electronic equipment centrally
controlled, requiring specific power supply, and other
installation conditions. This would call for special
wiring systems with synchronizing systems. The
technical requirements for these systems concerning
voltage and frequency stability are very high. These
shall be considered before designing the electrical
services of the same.

7.3 Electrical/Electronic Score Board

The power requirements for such equipment would
depend on the type of equipment to be installed.
Guidelines of the manufacturer shall be adhered to.

7.4 Clock System

Reference shall be made to the provisions in Part 1/
Section 1 1 of this Code.

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SECTION 7 SPECIFIC REQUIREMENTS FOR ELECTRICAL
INSTALLATIONS IN MULTISTORIED BUILDINGS

FOREWORD

The design and construction of electrical installations
in multistoried buildings call for special attention to
details pertaining to fire-safety of the occupancy.
While on the one hand, the civil design aspects are
more stringent for high-rise buildings than for
buildings of low heights, the electrical design
engineer, on his part had to ensure that the fire hazards
from the use of electric power is kept to the lowest
possible limit.

In drafting the requirements of electrical installations
in various occupancies it was felt that a separate
compendium giving the specific requirements
applicable to multistoried buildings should be brought
out. For editorial convenience, such details have been
stated in this Section where the major non-industrial
occupancies have been covered.

In applying the provisions of this Section, note shall
also be taken of the nature of occupancy of the high-
rise buildings and a judicious choice of alternative
features shall be made.

1 SCOPE

1.1 This Part 3/ Section 7 is intended to cover specific
requirements for electrical installations in multistoried
buildings.

1.2 The requirements specified here are in addition to
those specified in respective sections of the Code, and
are specifically applicable for buildings more than 15 m
in height.

2 REFERENCES

This Part 3/Section 7 of the Code should be read in
conjunction with the following Indian Standards:

IS No. Title

SP 7 : 2005
2309 : 1989

10028 (Part 2)
1981

National Building Code of India
Code of practice for the protection
of buildings and allied structures
against lightning
Code of practice for selection,
installation and maintenance of
transformers: Part 2 Installation

4 SPECIAL CONSIDERATIONS

Special considerations shall have to be given in respect
of the following requirements for the electrical
installations in multistoried buildings:

b)
c)
d)
e)
f)
g)
h)

J)
k)
m)

Internal wiring for lighting, ventilation, call

bell system, outlets for appliances, power and

control wiring for special equipments like

lifts, pumps, blowers, etc;

Distribution of electric power;

Generators for standby electric supply;

Telephone wiring;

Fire safety;

Lightning protection;

Common antenna system;

Clock system;

Building Management System (BMS);

EPABX with P&T lines; and

Broad Band Multi Service facility.

3 TERMINOLOGY

For the purposes of this Section, the definitions given
in Part 1 /Section 2 of the Code shall apply.

5 EXCHANGE OF INFORMATION

5.1 The detailed requirements of the owner shall be
assessed at the planning stage.

5.2 It is necessary that right at the planning stages, the
requirements of space for accommodating the
distribution equipment for the various electrical
services and openings required in slabs for vertical
risers for such services are assessed and incorporated
in drawings in due coordination with the architect and
structural designer. Care shall be taken to provide
adequate and where necessary, independent spaces for
the equipment for electrical services for different
functions.

5.3 Multistoried buildings are usually in framed design.
Coordination with the architect is required in evolving
suitable layout of lights, fans and other outlets and the
position for their switch controls to take care of
functional utility and flexibility.

5.4 While designing the electrical services, due
consideration should be given for conservation of energy.

5.5 The voltage of supply and location of energy meters
(especially in multistoried buildings meant for
residential purposes) shall be agreed to between the
utility and the owner of the building. Spaces for
accommodating the distribution and metering
equipment of utility should be accordingly provided
for by coordinating with the architect and licensee.

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5.6 The telephone authorities shall be consulted for
the requirements of space for accommodating the
distribution equipment, battery, etc, for the telephone
services.

5.7 The local fire brigade authorities shall be consulted
in the matter of system layout for fire detection and
alarm systems to comply with local bye-laws. The
locations of control panel and indication panel shall
be decided in consultation with the owner.

5.8 Runs of roof conductors and down conductors for
lightning protection shall be coordinated with the
architects of the building. The requirements as laid
down in Part 1/Section 15 of this Code shall be
complied with.

6 ASSESSMENT OF CHARACTERISTICS OF
MULTISTORIED BUILDINGS

6.0 The general characteristics of buildings depending
on the type of occupancy are assessed based on me
guidelines given in relevant sections of this Code,
together with those given in Part 1 /Section 8.

6.1 For the purposes of multistoried buildings in
addition to other external influences depending on the
type of occupancy, the electrical installation engineer
shall specifically take note of characteristics BD2, BD4
and CB2 given in Table 1 of Part 1 /Section 8 of this
Code.

7 DISTRIBUTION OF ELECTRIC POWER

7.0 Load Assessment and Equipment Selection

7.0.1 The electrical load shall be assessed considering
the following:

a) Lighting and power loads;

b) Special loads of equipments as in laborato-
ries, hospitals, data processing areas, etc;

c) Air-conditioning/evaporative cooling/heating
services;

d) Water supply pumps;

e) Fire fighting pumps;

f) Electric lifts; and

g) Outdoor and security lighting.

The anticipated increase in load shall also be given
due consideration.

7.0.2 Suitable demand factors and diversity factors shall
be applied depending on the operational and functional
requirements. The distribution equipments shall be
selected by adopting standard ratings. Adequate spare
capacity should be provided for every component in
the distribution system.

7.0.3 The fault level at the point of commencement of

supply should be obtained from the licencee and fault
levels at salient points in the distribution system
assessed. Distribution system component should be
selected to satisfy the same.

7.1 Building Substation

7.1.1 The provisions contained in Part 2 of this Code
shall apply.

7.1.2 A substation or a switch- station with apparatus
having, more than 2 000 litre of oil shall not ordinarily
be located in the basement where proper oil drainage
arrangements cannot be provided. If transformers are
housed in the building below the ground level, they
shall necessarily be in the first basement in a separate
fire-resisting room of 4-h rating. The room shall
necessarily be at the periphery of the basement. The
entrance to the room shall be provided with a fire-
resisting door of 2-h fire rating. A curb (sill) of a
suitable height shall be provided at the entrance in order
to prevent the flow of oil from a ruptured transformer
into other parts of the basement. Direct access to the
transformer room shall be provided, preferably from
outside. The switchgears shall be housed in a room
separated from the transformer bays by a fire-resisting
wall with fire resistance of not less than 4 h.

7.1.3 The transformer, if housed in basement, shall be
protected by an automatic high velocity water spray
system. The transformer may be exempted from such
protection if their individual oil capacity is less than
5 000 litres.

7.1.4 In case the transformers are housed in the
basements, totally segregated from other areas of the
basements by 4-h fire-resisting wall/walls with an
access directly from outside, they may be protected
by carbon dioxide or BCF (bromochloro difluro
methane) or BTM (bromotrifluro methane) fixed
installation system.

7.1.5 When housed at ground floor level, it/they shall
be cut off from the other portion of premises by fire-
resisting walls of 4-h fire resistance.

7.1.6 Oil-filled transformers shall not be housed on
any floor above the ground floor.

7.1.7 Soak pit of approved design shall be provided
where the aggregate oil capacity of the apparatus does
not exceed 2 000 litres. Where the oil capacity exceeds
2 000 litre, a tank of RCC construction of capacity
capable of accommodating entire oil of the
transformers shall be provided at a lower level to collect
the oil from the catch-pit in case of emergency. The
pipe connecting the catch-pit to the tank shall be of
non-combustible construction and shall be provided
with a flame-arrester [see IS 10028 (Part 2)].

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7.1.8 Only dry type of transformers should be used for
installation inside the residential/commercial buildings.

7.2 Distribution System

7.2.0 Capacity and number of system components and
the electrical distribution layout should be decided
considering the likely future requirements, security,
grade of service desired and economics. The choice
between cables and metal rising mains for distribution
of power should be done depending on the load and
the number of floors to be fed.

7.2.1 In multistoried buildings where large number of
people gather (for example office buildings), there shall
be at least two rising mains located in separate shafts.
Each floor shall have a changeover switch for
connection to either of the two mains.

7.2.2 When cables are used for distribution to different
floors, it may be desirable that cables feeding adjacent
floors are interconnected for use when distribution
cables in either of the floors fail.

7.2.3 It is essential to provide independent feeders for
installations such as fire lift, fire alarm, fire pumps,
etc.

7.2.4 In the case of residential buildings, submain
wiring to the flats/apartments shall be independent for
each flat/apartment.

7.2.5 Twin earthing leads of adequate size shall be
provided along the vertical runs of rising mains.

7.3 Siting of Distribution Equipment

7.3.1 The following aspects shall be considered in
deciding the location of electric substation for
multistoried buildings:

a) Easy access for purpose of movement of
equipment in and out of the substation
including fire fighting vehicles;

b) Ventilation;

c) Avoidance of flooding by rain water;

d) Feasibility of provision of cable ducts (keep-
ing in view the bending radius of the cable),
oil soak pits (for large transformers) and entry
of utility 'scable(s);

e) Transformer hum (and noise and vibration
from diesel generating sets where provided
as part of the substation);

f) Where a separate building for substation is
not possible, the same should preferably be
at ground floor level of the multistoried
building itself. In the case of a complex with
a number of buildings, the substation should
be located, as far as possible, near the load
centre; and

g) In the cases of certain high rise buildings,
provision of substation at intermediate floors
may be necessary for case of distribution. In
such cases, non-inflammable cooling medium
shall be used for substation equipment from
the point of view of fire safety.

7.3.2 The vertical distribution mains should be located
considering the following aspects:

a) Proximity to load centre;

b) Avoiding excess lengths of wiring for final
circuits and points;

c) Avoiding crossing of expansion joint, if any,
by horizontal runs of wiring;

d) Avoiding proximity to water bound, areas like
toilets, water coolers, sanitary/air-
conditioning shafts, etc;

e) Easy maintainability from common areas like
lobbies, corridors, etc; and

f) Feasibility to provide distribution switch-
boards in individual floors vertically one over
the other.

7.4 Wiring Installation

7.4.1 The electrical wiring shall be carried out in
conformity with Part 1/Section 9 of this Code.

7.4.2 Aluminium conductor may be used for wiring
cables, but copper conductor may be preferred for fire-
alarm, telephones, control circuits, etc.

7.4.3 Where excessively long lengths of wiring runs
are inevitable to suit the building layout, the conductor
sizes shall be suitably designed to keep the voltage
drop within limits {see Part 1/Section 9 of this Code).

7.4.4 The type and capacity of control switches shall
be selected to suit the loading, such as room air-
conditioners, water coolers, group control of
fluorescent lights, etc.

7.4.5 All switchgear equipment used for main-
distribution in multistoried buildings shall be metal
enclosed. Woodwork shall not be used for the
construction of switchboards.

7.4.6 The electric distribution cables/wiring shall be
laid in a separate duct. The duct shall be sealed at every
alternative floor with non-combustible materials having
the same fire resistance as that of the duct. Low and
medium voltage wiring running in shaft and in false
ceiling shall run in separate conduits.

7.4.7 Water mains, telephone lines, intercom lines, gas
pipes or any other service line shall not be laid in the
duct for electric cables.

7.4.8 Separate circuits for water pumps, lifts,

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staircases and corridor lighting and blowers for
pressurizing system shall be provided directly from
the main switchgear panel and these circuits shall
be laid in separate conduit pipes, so that fire in one
circuit will not affect the others. Master switches
controlling essential service circuits shall be clearly
labelled.

7.4.9 The inspection panel doors and any other opening
in the shaft shall be provided with airtight fire doors
having the fire resistance of not less than 1 h.

7.4.10 Medium and low voltage wiring running in
shafts, and within false ceiling shall run in metal
conduit. Any 230 V wiring for lighting or other
services, above false ceiling, shall have 660 V grade
insulation. The false ceiling, including all fixtures used
for its suspension, shall be of non-combustible material.

7.4.11 An independent and well-ventilated service
room shall be provided on the ground floor with direct
access from outside or from the corridor for the purpose
of termination of electric supply from the licensees,
service and alternative supply cables. The doors
provided for the service room shall have fire resistance
of not less than 2 h.

7.4.12 If the utility agree to provide meters on upper
floors, the utility's cables shall be segregated from
consumers' cable by providing a partition in the duct.
Meter rooms on upper floors shall not open into
staircase enclosures and shall be ventilated directly to
open air outside.

7.4.13 The staircase and corridor lighting shall be on
separate circuits and shall be independently connected
so as it could be operated by one switch installation on
the ground floor easily accessible to fire fighting staff
at any time irrespective of the position of the individual
control of the light points, if any. It should be of MCB
type of switch so as to avoid replacement of fuse in
case of crisis.

7.4.14 Staircase and corridor lighting shall also be
connected to alternative supply as defined in 8.1 for
buildings exceeding 24 m in height. For assembly
institutional buildings of height less than 24 m, the
alternative source of supply may be provided by battery
continuously trickle charged from the electric mains.

7.4.15 Suitable arrangements shall be made by
installing double throw switches to ensure that the
lighting installed in the staircase and the corridor
does not get connected to two sources of supply
simultaneously. Double throw switch shall be
installed in the service room for terminating the
standby supply.

7.4.16 Emergency lights shall be provided in the
staircase/corridor.

8 PROVISION OF STAND-BY GENERATING SET

8.1 A centralized EPABX System with P&T lines shall
be installed for internal connection as well as for
external communication with essential services. The
following loads shall be fed from the stand-by
generating set, to enable continuity of supply in the
event of failure of mains:

a) Lighting in common areas, namely corridors,
staircases, lift lobbies, entrance hall, common
toilets, etc;

b) Fire lift;

c) Fire fighting pump, smoke extraction and
damper systems;

d) Fire alarm control panel;

e) Security lighting;

f) Obstruction light(s);

g) Water supply pump; and

h) Any other functional and critical loads.

8.2 The norms specified in Part 2 of this Code is
applicable for locating DG sets.

9 TELEPHONE WIRING SYSTEM

9.1 On the basis of assessment of demand of direct
telephones and EPABX lines, the conduit runs for
telephone wiring should be designed in consultation
with telephone department. Where telephone wiring
is intended to be taken on any other method, this should
be coordinated with the architect and the telephone
department.

9.2 Lighting, ventilation and flooring in battery rooms
should be designed in accordance with the guidelines
in Part 2 of this Code.

9.3 Suitable provisions should be made for cable entry
and spaces for distribution components.

9.4 Where the layout of intercom telephones is known
in advance, provisions for wiring for the same may
also be made.

10 FIRE SAFETY

10.1 Consideration in respect of the following
provisions is necessary from fire safety point of view:

a) Fire detectors and alarm system;

b) Fire fighting arrangements;

c) Fire lift;

d) First-aid and fire fighting appliances;

e) Construction of lift shafts, cable and rising
main shafts, lobbies, substation, etc, from fire
safety considerations; and

f) Provision for pressurization of stairwells, lift
shafts, lobbies, etc.

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10.2 Provisions contained in Part 1/Section 11 of this
Code and SP 7 shall be applicable in respect of the
above aspects. Any regulations of fire safety by local
municipal/fire authorities shall also be complied with.

10.3 The following specific guidelines shall be kept in

view.

103.1 All buildings with heights of more than 15 m
shall be equipped with manually operated electrical
fire alarm (MOEFA) system and automatic fire alarm
system. However, apartment and office buildings
between 15 m and 24 m in height may be exempted
from the installation of automatic fire alarm system
provided the local fire brigade is suitably equipped for
dealing with fire above 15 m height and in the opinion
of the Authority, such building does not constitute
hazard to the safety of the adjacent property or the
occupants of the building itself.

103.1.1 Manually operated electrical fire alarm system
shall be installed in a building with one or more call
boxes located at each floor. The call boxes shall
conform to the following:

a) The location of call boxes shall be decided
after taking into consideration the floor plan
with a view to ensuring that one or the other
call box shall be readily accessible to all
occupants of the floor without having to travel
more than 22.5 m.

b) The call boxes shall be of the 'break-glass' type
where the call is transmitted automatically to
the control room without any other action on
the part of the person operating the call box.
The mechanism of operation of the call boxes
shall preferably be without any moving parts.
However, where any moving part is
incorporated in the design of the call box, it
shall be of an approved type, so that there shall
be no malfunctioning of the call box.

c) All call boxes shall be wired in a closed circuit

to a control panel in the control room in
accordance with good practice so located that
the floor number/zone where the call box is
actuated is clearly indicated on the control panel.
The circuit shall also include one or more
batteries with a capacity of 48 hours normal
working at full load. The battery shall be
arranged to be continuously trickle charged from
the electric mains. The circuit may be connected
to alternative source of electric supply.

d) The call boxes shall be arranged to sound one
or more sounders so as to ensure that all
appropriate occupants of the desired floor(s)
shall be warned whenever any call box is
actuated.

e) The call boxes shall be so installed that they
do not obstruct the exit-ways and yet their
location can easily be noticed from either
direction. The base of the call box shall be at
a height of 1 m from the floor level.

103.1.2 The installation of call boxes in hostels and
such other places where these are likely to be misused,
shall as far as possible be avoided. Location of call
boxes in dwelling units shall preferably be inside the
building.

NOTES

1 Several types of fire detectors are available in the market,
but the application of each type is limited and has to be carefully
considered in relation to the type of risk and the structural
features of the building where they are to be installed. For
guidelines for selection of fire detection reference may be made
to relevant Indian Standard.

2 No automatic detector shall be required in any room or portion
of building which is equipped with an approved installation of
automatic sprinklers.

11 LIGHTNING PROTECTION

Provisions of lightning protection of multistoried
buildings shall be made in conformity with Part 1/
Section 15 of this Code and IS 2309.

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PART 4

SP 30 : 2011

PART 4 ELECTRICAL INSTALLATIONS IN
INDUSTRIAL BUILDINGS

FOREWORD

Industrial installation has to take care of load requirements and supply limitations in a simple and economic
manner, ensuring at the same time full protection to human life and loss of property by fire. The network layout
should also facilitate easy maintenance and fault localization. Keeping in view the tariff structures as also the
economic necessity of conserving power to the maximum extent, power factor compensation assumes special
importance.

A particular feature of electrical installations in industrial buildings is the reliability of supply to essential operations
for which standby and emergency supply sources/networks had to be designed. The needs of such systems would
depend on the type and nature of the industrial works.

Locations in industrial buildings which are by their nature hazardous, require special treatment in respect of
design of electrical installations therein. Such special rules for hazardous areas are covered in Part 7 of the Code
and these shall be complied with in addition to the general rules specified in this Part {see also Part 7 of this
Code).

In clause 4 of this Part, an attempt has been made to classify industrial installations depending on the specified
criteria therein. Such a classification, it is hoped would help identify the specific nature of each industry and the
locations therein, assisting the design engineer in the choice of equipment and methods.

PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS 273

SP 30 : 2011

1 SCOPE

1.1 This Part 4 of the Code covers the guidelines for
design and construction of electrical installations in
industrial buildings.

1.2 This Part 4 does not cover specific areas in industrial
sites, such as office buildings, workers rest rooms,
medical facilities, canteen annexe, etc, for which
requirements stipulated in the relevant sections of Part 3
of the Code apply.

1.3 This Part 4 also does not cover locations in
industrial sites that are by nature hazardous for which
the provisions of Part 7 of the Code apply.

2 REFERENCES

This Part 4 should be read in conjunction with the
Indian Standards listed at Annex A.

3 TERMINOLOGY

For the purpose of this Part 4, the definitions given in
Part 1 /Section 2 of the Code and the following shall
apply:

3.1 Pollution — Any condition of foreign matter, solid,
liquid or gaseous (ionized gases), that may affect
dielectric strength or surface resistivity

3.2 Pollution Degree (of Environmental Conditions)
— Conventional number based on the amount of
conductive or hygroscopic dust, ionized gas or salt and
on the relative humidity and its frequency of
occurrence, resulting in hygroscopic absorption or
condensation of moisture leading to reduction in
dielectric strength and/or surface resistivity.

4 CLASSIFICATION OF INDUSTRIAL

BUILDINGS

Industrial buildings by definition include any building
or part of building or structure, in which products or
materials of all kinds and properties are stored,
fabricated, assembled, manufactured or processes, for
example, assembly plants, laboratories, dry cleaning
plants, pumping stations, refineries, dairies, saw mills,
chemical plants, workshops, distilleries, steel plants, etc.

Industrial installations are of various types and in a
single industrial site, electrical loads of varying
requirements are to be met. For the purpose of this
Part, industries are classified based on three criteria as
given in 4.1 to 4.3.

4.1 Classification Based on Fire Safety

4.1.1 Industrial buildings are classified into Group G
from the fire safety point of view in SP 7. Buildings
under Group G are further subdivided as follows:

a) Subdivision G-l — Buildings used for low hazard
industries — Includes any building in which the
contents are of such low combustibility and the
industrial processes or operations conducted
therein are of such a nature that there are no
possibilities for any self-propagating fire to occur
and the only consequent danger to life and
property may arise from panic, fumes or smoke,
or fire from some external source.

b) Subdivision G-2 — Buildings used for
moderate hazard industries — Includes any
building in which the contents or industrial
processes of operations conducted therein are
liable to give rise to a fire which will burn
with moderate rapidity and give off a
considerable volume of smoke but from which
neither toxic fumes nor explosions are to be
feared in the event of fire.

c) Subdivision G-3 — Buildings used for high
hazard industries — Includes any building in
which the contents or industrial processes or
operations conducted therein are liable to give
rise to a fire which will burn with extreme
rapidity or from which poisonous fumes or
explosions are to be feared in the event of fire.

NOTE — SP 7 includes Group J buildings for such
location where storage, handling, manufacture or
processing of highly combustible or explosive materials
or products are being carried out. Such installations
including such high hazard locations in Group G
classification shall comply with the special rules of
Part 7 of. the Code.

4.1.2 Typical list of industries for different class of fire
hazard are given in Annex B.

4.2 Classification Based on Power Consumption

4.2.1 Industrial buildings are also classified depending
on the quantum of electric power requirements for its
services as given in Table 1 .

4.2.2 Loads within the industrial site could be divided
depending on their nature and size. For guidance, the
classification given in Table 2 shall be referred to.

4.3 Classification Based on Pollution

For the propose of evaluating creepage distances and
clearances, the following four degrees of pollution in
the micro-environment are established:

a) Pollution degree 1 — No pollution or only
dry, non-conductive pollution occurs. The
pollution has no influence.

b) Pollution degree 2 — Only non-conductive
pollution occurs except that occasionally a
temporary conductivity caused by
condensation is to be expected.

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Table 1 Classification Based on Power
Consumption

(Clause 4.2.1)

SI No.

(1)

Description l)

(2)

Average

Power

Requirement

(3)

Examples

(4)

i) Light

industries
ii) Average

industries

iii) Heavy
industries

Up to 50 kVA

Above 50 kVA
up to 2 000
kVA

Above 2 000
kVA

' and

Hosiery, tailoring
jewellery
Machinery, engine
fitting, motor cars,
aircraft, light pressings,
furniture, pottery, glass,
tobacco, electrical
manufacturing and
textile (see Note)

Heavy electrical
equipment, rolling
mills, structural steel
works, tube making,
foundries, locomotives,
ship-building and
repairing, chemical
factories, factories for
metal extraction from
ores, etc.

NOTE — Average factory installations are set apart from
heavy industries in that the former has no conditions
requiring specialized or exceptional treatment.

^Terminology based on IS 732. Where different degrees of
hazard occupancy exist in different parts of building, the
most hazardous of those shall govern the classification for
the purpose.

Table 2 Load Groups in Industrial Buildings
(Clause 4.2.2)

SI.

Groups

Type to Load

Examples

Corrected

No.

Power
Factor

(1)

(2)

(3)

(4)

(5)

>0.85

i) 1 Small and large loads Repair shop,

fairly evenly distributed automatic

over the whole area and lathe,

loaded constantly during workshop,

the working day spinning

(precision mechanical mill,

engineering) weaving mill

ii) 2 Loads fairly evenly
distributed over the
whole area, but varying
loads and with peak load
at different times (for
example metal working
industry)

iii) 3 Loads having very high
power requirement in
conjunction with smaller
loads of negligible size
compared to the total
load (for example, raw
material, industry)

c) Pollution degree 3 — Conductive pollution
occurs or dry non-conductive pollution occurs

Press shop

Machine
shop

Welding
shop

Heat
treatment
shop, steel
works,
rolling mills

which becomes conductive due to
condensation — which is to be expected,
d) Pollution degree 4 — Continuous
conductivity occurs due to conductive dust,
rain or other wet conditions.

NOTES

1 Clearances and creepage distances according to the different
pollution degrees are given in Tables 13 and 15 of IS/IEC
60947-1. Unless otherwise stated by the relevant product
standard, equipment for industrial applications is generally for
use in pollution degree 3 environment. However, other pollution
degrees may be considered to apply depending upon particular
applications or the micro-environment.

2 The pollution degree of the micro-environment for the
equipment may be influenced by installation in an enclosure.
Means may be provided to reduce pollution at the insulation
under consideration by effective use of enclosures,
encapsulation or hermetic sealing. Such means to reduce
pollution may not be effective when the equipment is subject
to condensation or if, in normal operation, it generates
pollutants itself.

3 Pollution will become conductive in the presence of humidity.
Pollution caused by contaminated water, soot, metal or carbon
dust is inherently conductive. Small clearances can be bridged
completely by solid particles, dust and water and therefore
minimum clearances are specified where pollution may be
present in the micro — environment.

5 GENERAL CHARACTERISTICS OF
INDUSTRIAL BUILDINGS

General guidelines on the assessment of characteristics
of installations in buildings are given in Part 1 of the
Code. For the purposes of installations falling under
the scope of this Part 4, the characteristics given below
shall apply.

5.1 Environment

5.1.1 The following environmental factors shall apply
to industrial installations:

Environment Characteristics Remarks

(1) (2) (3)

Presence of
water

Presence of
foreign solid
bodies

Presence of
corrosive

Presence of water
negligible, or
possibilities of free
falling drops or
sprays

These conditions
include possibilities
of presence of
foreign solid bodies
of various sizes
likely to affect
electrical equipment
(such as tools,
wires, dust, etc.)

Atmospheric where
the presence of

Depends on the
location. For
further details
see Part 1/Sec 8
of the Code

Industrial
installations,

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Environment

Characteristics

Remarks

Utilization

Characteristics

Remarks

(1)

(2)

(3)

(1)

(2)

(3)

polluting

corrosive or

situated by the

Contact of

Persons are

Locations with

substances

polluting substances

sea, chemical

persons with

frequently in touch

extraneous

is significant

works, cement

earth

with extraneous

conducting

works where the

potential

conductive parts or

parts, either

pollution arises

stand on conducting

numerous or

due to abrasive,

surfaces

large area

insulating or

Persons are in

Metallic

conducting

permanent contact

surrounding

ducts

with metallic

such as boilers

Intermittent or

Factory

surroundings and

and tanks

accidental

laboratories

for whom the

subjection to

boiler rooms,

possibility of

corrosive or

etc.

interrupting contact

polluting chemical

is limited

substances being

Conditions

Low density

This category

used or produced

occupation, easy

applies to

Continuous

Chemical works

evacuation

conditions of

buildings of

pollution

evacuation

normal or low

Mechanical

Impact and

Household and

height

stresses

vibration of low

similar

Nature of

Existence of fire-

Wood- working

severity

conditions

processed or

risks, where there

shop, paper

Impact/vibration of

Industrial

stored

is manufacture,

factories, textile

high severity

installations
subject to severe
conditions

material

processing or
storage of
flammable
materials, including

mills, etc

Seismic
effect and

Depends on the
location of the

presence of dust

lighting

buildings

Processing or

Oil refineries,

storage of low-
flash-point

hydrocarbon
stores

5.2 Utilization — The following aspects utilization

materials including

shall apply:

presence of
explosive dust

Utilization

(i)

Characteristics
(2)

Remarks
(3)

Capability of Instructed persons,
persons adequately advised

or supervised by
skilled persons
(operating and
maintenance staff)

Persons with

technical

knowledge and

sufficient

experience

(engineers and

technicians)

Majority of
persons utilizing
the industrial
installations are
in this category.
However specific
zones or
operations
involving
uninstructed
persons shall also
be kept in view

Closed operating
areas

5.3 Compatibility

In industrial installations, an assessment shall also be
made of any characteristics of equipment likely to have
harmful effects upon other equipment or other services
{see Part 1/Section 8 of the Code).

5.4 Maintainability

Assessment shall also be made of the frequency and
quality of maintenance of the installation (see
Part 1/Section 8 of the Code).

6 SUPPLY CHARACTERISTICS AND
PARAMETERS

6*0 General

6.0.1 The arrangement of the electrical system in
industrial plants and the selection of electrical
equipment depends largely on the type of

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manufacturing process, the reliability of supply and
adequate reserve of electrical capacity are the most
important factors to avoid interruption of supply.

6.0.2 All electrical installation shall be suitable for the
voltage and frequency of supply available.

6.0.3 For large loads, the relative advantage of high
voltage three-phase supply should be considered.
Though the use of high voltage supply entails the
provision of space and the capital cost of providing a
suitable transformer substation on the consumer's
premises, the following advantages are gained:

a) Advantage in tariff,

b) More effective earth fault protection for heavy
current circuits,

c) Elimination of interference with supplies to
other consumers permitting the use of large
size motors, welding plant, etc., and

d) Better control of voltage regulation and more
constant supply voltage.

6.0.4 In very large industrial buildings where heavy
electric demands occur at scattered locations, the
economics of electrical distribution at high voltage
from the main substation to other subsidiary
transformer substations or to certain items of plant,
such as large motors, furnaces, etc, should be evaluated.
The relative economy attainable by use of medium or
high voltage distribution and high voltage plant is a
matter for expert judgement and individual assessment
in the light of experience by a professionally qualified
electrical engineer.

6.1 Industrial Substations

6.1.0 The general requirements for substation
installations given in Part 2 of the Code shall apply in
addition to those given below.

6.1.1 If the load demand is high, which requires supply
at voltages above 650 V, a separate substation should
be set up. For an outdoor substation general guidelines
as given in Part 2 of the Code shall apply. For bringing
the supply into the factory building, a separate indoor
accommodation, as close as possible to the main load
centre, should be provided to house the switchgear
equipment.

6.1.2 The supply conductors should preferably be
brought into the building underground to reduce the
possibility of interruption of power supply. The
accommodation for substation equipment as well as
for main distribution panel shall be properly chosen
so as to prevent access by any unauthorized person.
It shall be provided with proper ventilation and
lighting.

6.1.3 In cases where the load currents are very high,
and the transformers are located just outside the
building, a bus-trunking arrangement may be desirable.
These trunkings should, however, be straight, as far as
possible, and also as short as possible on economic
grounds.

6.1.4 Location of Transformers and Switchgear

Oil filled transformers are preferably located outdoors
while the associated switchgear is located in a room of
the building next to the transformer. In certain cases,
however, it may be considered desirable to locate the
transformer inside the room.

For reasons of safety, however, it may be considered
desirable to locate the transformer also inside the room.
The transformer could be connected to the switchgear
by cables for small loads, however it may often be
found desirable to avoid cable joints and connect the
transformer directly to the switchgear placed on either
side of the transformer. For oil-filled transformer,
special means should be available for remote operation
of the main switches/circuit-breakers in an emergency
created by explosion/fire in the transformers.

6.1.5 In order to ensure the reliability and safety of
industrial sub-station, it is desirable to have circuit
breakers as the main switching elements on both sides
of the transformers. However, a high voltage sizes,
switches and fuses may also be used for this purpose
upto the limit specified under Rule 50, sub-rule 1 of
Indian Electricity Rules, 1956.

6.1.6 For small substations up to 1 600 kVA capacity,
it is also possible to locate the substation at the load
centre, without a separate room. This yields
considerable economies in cost. In such cases, the
transformer shall be of dry type.

6.1.7 Isolation of Switchgear

For installations where the system voltage exceeds
650 V, the typical circuits and the recommended
location of isolating switches in such circuits are
illustrated in IS 732. Reference should be made to the
same for guidance regarding isolation depending on
the type of supply system.

6.2 Distribution of Power

6.2.1 From the main receiving station, power is taken
to the loads, either directly as in the case of small
factories, or through further load centre substations as
would be the case with bigger installations.

Distribution is done on HV through circuit breaker/
load break switches depending on quantum of load to
be transferred, distance to be covered, and on similar
factors. MV/LV distribution is possible through one
of the following:

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a) Wall-mounted distribution boards,

b) Floor mounted distribution boards,

c) Local fuse distribution boards, and

d) Overhead bus bar system with tap-off holes.

6.2.2 In every layout, however, specific care shall be
taken for:

a) Human safety,

b) Fire/explosion hazards,

c) Accessibility for repair/checking,

d) Easy identification, and

e) Fault localization.

6,23 Switchgear

6.23.0 All switchgear equipment used in industrial
installations shall be metal enclosed. Woodwork shall
not be used for mounting off switchboards.

6.23.1 MV switchgear isolation and protection of
outgoing circuits forming main distribution system may
be effected by means of circuit-breakers, or switchfuse
units mounted on the main switchboards. The choice
between alternative types of equipment may be
influenced by the following considerations:

a) In certain installations where supply is from
remote transformer substations, it may be
necessary to protect main circuits with circuit-
breakers operated by earth leakage trips, in
order to ensure effective earth fault protection.

b) Where large electric motors, furnaces or other
heavy electrical equipment is installed, the
main circuits shall be protected by metal-clad
circuit-breakers or contactors of air-break or
oil-immersed type fitted with suitable
instantaneous and time delay over current
devices together with earth leakage and back-
up protection where necessary.

c) In installations other than those referred to in
(a) and (b) or where overloading of circuits
may be considered unlikely to occur, HRC
type fuses will normally afford adequate
protection for main circuits. Where means for
isolating main circuits is required, fuse switch
or switch fuse units shall be used or fuses with
switches forming part of the mean switch-
board shall be used.

6.23.2 It may be necessary to provide for connection
of capacitors for power- factor correction; and when
capacitors are to be installed advice of capacitor and
switchgear manufacturers shall be sought.

6.233 Adequate passageways shall be allowed so that
access to all switchboards for operation and
maintenance is available. Sufficient additional space
shall be provided for anticipated future extensions.

6.23.4 Switchboards should, preferably, be located in
separate rooms to ensure:

a) adequate protection against weather elements
like heat, dust, corrosion, etc; and

b) protection against entry of factory material
like cotton, wood dust, water during clean-
ing, etc.

Where necessary the control rooms should be designed
to avoid wide fluctuations in ambient temperature, and
against entry of excessive dust or corrosive gases.

6.2.3.5 Certain applications may necessitate location
of the switchboards on the factory floor itself, without
separate rooms. In such cases, the switchboards shall
be specifically designed and protected against hazards
mentioned above.

63 Main Distribution

63.1 For power distribution from a substation or main
switchboard to a number of separate buildings, use shall
preferably be made of;

a) metal-sheathed, bedded and armoured cable,
served, installed overhead/underground, or

b) mineral-insulated metal-sheathed cable,
served with PVC, laid overhead/direct in the
ground, or

c) PVC-insulated, armoured and PVC-sheathed
cable installed overhead/underground, or

d) XLPE insulated, armoured and PVC-sheathed
cable installed overhead/underground.

63.1.1 Cables shall not be laid in the same trench or
alongside a water main.

63.1.2 Cable trenches shall be made with sufficient
additional space to provide for anticipated future
extensions.

63.2 Cables at difference voltage levels should be
laid with separation at least 250 mm and clearly
identified. Cables at voltages above 1 000 V should be
laid at the lowest level in trenches, and at the highest
level on walls, keeping in view the requirements of
human safety. The cable routes where buried should
be properly identified by route markers, as a precaution
against accidents. The marker should necessarily
indicate the voltage level. Cables laid underground or
at low working levels, should either be with armouring,
or should be adequately protected against mechanical
damage, for example, by the use of conduits.

6.4 Sub-circuits

6.4.0 The sub-circuit wiring shall conform in general
to the requirements given in IS 732.

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6.4.1 In 3-phase distribution systems, a neutral
conductor may preferably be provided in all sub-
main circuits even when there is no immediate
requirement for the supply of single-phase circuits.
Control devices are often designed for connection
between one phase and neutral and considerable
extra cost may be involved, if a four-wire sub-main
has to be installed in place of a three-wire sub-main
previously installed.

6.4.2 In workshops and factories where alterations and
additions are frequent, it may be economical and
convenient to install wiring in ducts or trunking.
Alternatively, cables may be conveniently run on
perforated metal cable trays. In this case earth
continuity conductor shall be bonded to each section
of ducts or trunking to provide permanency of the
electrical continuity of the joints of the ducts.

6.4.3 In machine shops and factories where alterations
in layout may repeatedly occur, consideration shall be
given to the replacement of local distribution boards
by overhead bus-bar or cable systems, to which
subcircuit are connected through fused plugs in tapping
boxes wherever required.

6.4.4 In industrial installations, the branch distribution
boards shall be totally segregated for single phase
wiring.

6.4.5 Where more than one distribution system is
necessary, the socket outlets shall be so selected as to
obviate inadvertent wrong connections.

6.4.6 In industrial premises, 3-phase and neutral socket
outlets shall be provided with earth terminal either of
pin type or scrapping type in addition to the main pins
required for the purpose.

In industrial installations, socket outlets of rating 30 A
and above shall be provided with interlocked type
switch. These shall be of metal clad type.

6.4.7 Where non-luminous heating appliance is to be
used, pilot lamps shall be arranged to indicate when
the circuit is live.

6.4.8 Final sub-circuits for lighting shall be so arranged
that all the lighting points for a given area are fed from
more than one final sub-circuit.

6.4.9 Individual sub-mains shall be installed to supply
passenger and goods lifts from the main or sub-main
switchgear, and the lift manufacturer shall be
consulted as to the appropriate rating of cables to be
employed.

The supply to small hoists and service lifts shall not
be taken from a distribution board controlling final sub-
circuits for lighting, unless the maximum current,
including the starting and accelerating current, of the

motor is less than 20 percent of the total rating of all
the ways of the distribution boards. Where the supply
is taken from such a distribution board, the motor
circuit shall be clearly labelled.

6.5 Selection of Wiring Systems

The selection of a wiring system to be adopted in a
factory depends upon the factors enumerated in Part 1/
Section 9 of the Code.

The wiring system available for general use are listed
in Annex C. Selection from a group of alternative
systems shall be made in accordance with Annex C,
keeping in view the particular circumstances of each
circuit having regard to,

a) location, structural conditions, liability to
mechanical damage and the possibility of
corrosion;

b) protection against corrosion, nature of the
corrosive elements being taken into account
in conjunction with the protective coverings
available;

c) occupancy of the building; and

d) presence of dust, fluff, moisture and tem-
perature conditions.

6.6 Earthing in Industrial Premises

6.6.0 In factories and workshops all metal conduits,
trunking, cable sheaths, switchgear, distribution fuse
boards, starters, motors and all other parts made of
metal shall be bonded together and connected to an
efficient earth system. The electricity regulations made
under the Factories Act require that adequate
precautions shall be taken to prevent non-current-
carrying metal work of the installation from becoming
electrically charged.

In larger installations, having one or more substations,
it is recommended to parallel all earth-continuity
system.

6.6.1 Earth Electrodes

Any of the earth electrodes as mentioned in Part 1 of
the Code except cable sheath, may be used in industrial
premises.

6.6.2 Earth-continuity Conductor

6.6.2.1 Earth-continuity conductors and earth wires
not contained in the cables

The size of the earth-continuity conductors should be
correlated with the size of the current carrying
conductors, that is, the sizes of earth-continuity
conductors should not be less than half of the largest
current-carrying conductor, provided the minimum size
of earth-continuity conductors is not less than 1.5 mm 2

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for copper and 2.5 mm 2 for aluminium and need not be
greater than 70 mm 2 for copper and 120 mm 2 for
aluminium. As regards the sizes of galvanized iron and
steel earth-continuity conductors, they may be equal to
the size of the current carrying conductors with which
they are used. The size of earth-continuity conductors to
be used along with aluminium current-carrying
conductors should be calculated on the basis of equivalent
size of the copper current-carrying conductors.

6.6.2.2 Earth-continuity conductors and earth wires
contained in the cables

6.6.2.3 Conduits may be used as earth-continuity
conductors provided they are permanently and securely
connected to the earth system. However, where by
nature of the process, metal conduits cannot be used
as earth-continuity conductor on account of corrosion,
etc, the tough rubber or PVC sheathed cables may be
used in which case they shall incorporate an earth-
continuity conductor.

6.6.2.4 Flexible conduits shall not be used as earth-
continuity conductors. A separate earth wire shall be
provided either inside or outside the flexible conduits
which shall be connected by means of earth clips to
the earth system at one end and to the equipment at the
other end.

6.6.2.5 Earth leakage protection

Use of earth leakage protection shall be made where
greater sensitivity than provided by overcurrent
protection is necessary. With a good earth electrode,
overload protective devices may be used as earth
leakage protective device.

In addition to the advantage of sensitivity gained by
such methods, the circuits may be relieved of the
thermal and mechanical socks associated with the
clearance of heavy faults.

Some degree of discrimination may, in certain cases,
be introduced with advantage by providing the delay
in the operation of an earth-leakage trip, so that earth
faults on smaller subsidiary circuits protected by fuses
have time to clear and prevent the opening of the circuit-
breaker, controlling a larger part of the installation.

6.6.3 Earthing of Portable Appliances and Tools

6.6.3.1 Good electrical continuity between the body
of a portable appliance and the earth-continuity
conductor shall always be maintained.

6.6.3.2 It shall be ascertained that the fixed wiring at
the appliance inlet terminals has been done correctly
and in accordance with relevant Indian Standard.

6.6.3.3 A single pole switch shall not be connected in
the earth conductor.

6.6.3.4 No twisted or taped joints shall be used in earth
wires.

6.6.3.5 Additional security may be obtained by
arranging the earth-continuity conductor in the flexible
cable between the socket outlet and the portable
appliance in the form of a loop through which a light
circulating current provided by a small low-voltage
transformer is passed when the appliance is in use. Any
discontinuity in this loop will interrupt the circulating
current and can thus be caused to operate a relay and
disconnect the supply from the portable appliance.

6.6.4 Earthing of Electrically Driven Machine Tools

In all types of machine tools connected to medium
voltage, the body of all motors and bed plate of the
machine shall be earthed at two places by means of a
strip or conductors of adequate cross-sectional area.
The strip or conductor shall be securely fastened to
the bed plate by means of bolts.

6.6.5 Earthing of Electric Arc Welding Equipment

6.6.5.1 All components of electric arc welding
equipment shall be effectively bonded and connected
to earth. The transformers and separate regulators
forming multioperator sets and capacitors for power
factor correction, if used, shall be included in the
bonding.

6.6.5.2 All terminals on the output side of a motor
generator set shall be insulated from the car case and
control panel, as the generator is not connected
electrically to a motor and therefore the welding circuit
is electrically separate from the supply circuit including
the earth.

6.6.5.3 In case of transformer sets, which for welding
purpose are double wound, an 'earth and work' terminal
shall be provided. In single phase sets this terminal
shall be connected to one end of the secondary winding
and in case of three-phase sets this shall be connected
to the neutral point of the secondary winding.

6.6.6 Earthing of Industrial Electronic Apparatus

6.6.6.0 The earthing of these apparatus shall follow
normal practice but attention shall be paid to the points
discussed below.

6.6.6.1 Any industrial electronic apparatus which
derives its supply from two-pin plugs incorporates
small capacitors connected between the supply and the

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metal case of the instrument to cut down interference.
This capacitor shall be securely earthed.

6.6.6.2 When an oscilloscope is being used to examine
the wave-form of a high frequency source, the
oscilloscope shall be earthed by a conductor entirely
separate from that used by the source of high frequency
power. However, when an oscilloscope is being used
on a circuit where the negative is above earth potential
and also connected to its metallic case, the earthing of
the oscilloscope is not possible. Precautions shall be
taken that in such a case the oscilloscope is suitably
protected from other apparatus.

6.6.6.3 High frequency induction heating apparatus
shall be earthed by means of separate earth wire by as
direct a route as possible.

6.6.6.4 Dielectric loss heating equipment work at
frequencies between 10 MHz to 60 MHz according to
its use. These should not be directly earthed. At
30 MHz, for example, a quarter wavelength is nearly
250 cm and an earth wire of this length or odd multiples
of it is capable of being at earth potential at one end
but several hundred volts at the other end. This is due
to the presence of standing waves on the earth
conductors which besides being dangerous can result
in energy being radiated to the detriment of
communication services. In such a case it is
recommended to mount the equipment on a large sheet
of copper or copper gauze, the earth conductor being
connected to it at several points.

6.6.6.5 In case where direct earthing may prove harmful
rather than provide safety, for example, high frequency
and mains frequency coreless induction furnaces,
special precautions are necessary. The metal of the
furnace charge is earthed by electrodes connected at
the bottom of the charge, and the furnace coils are
connected to the mains supply but are unearthed. A relay
is connected by a detection circuit which itself is earthed
to the coils. The object is to prevent dangerous break-
through of hot metal through the furnace lining, the earth
detection circuit giving a continuous review of the
conditions for the furnace lining. When leakage current
attains a certain set maximum it becomes necessary to
take the furance out of service and to re-line.

7 EMERGENCY/STANDBY POWER SUPPLIES
7.1 The provisions of Part 2 of the Code shall apply.

8 SYSTEM PROTECTION
8.1 Protection of Circuits

8.1.1 Appropriate protection shall be provided at
switchboards and distribution boards for all circuits
and sub-circuits against overcurrent and earth faults,
and the protective apparatus shall be capable of

interrupting any short-circuit current that may occur,
without danger. The ratings and settings of fuses and
the protective devices shall be coordinated so as to
afford selectivity in operation where necessary.

8.1.2 Where circuit-breakers are used for protection
of a main circuit and of the sub-circuits derived
therefrom, discrimination in operation may be achieved
by adjusting the protective devices of the sub- main
circuit-breakers to operate at lower current settings and
shorter time-lag than the main circuit-breaker.

8.1.3 Where HRC type fuses are used for backup
protection of circuit-breakers, or where HRC fuses are
used for protection of main circuits and circuit-breakers
for the protection of sub-circuits derived therefrom, in
the event of short circuits exceeding the breaking
capacity of the circuit-breakers, the HRC fuses shall
operate earlier than the circuit-breakers; but for smaller
overloads within the breaking capacity of the circuit-
breakers, the circuit-breakers shall operate earlier than
the HRC fuse.

8.1.4 If rewirable type fuses are used to protect
sub-circuits derived form a main circuit protected by
HRC type fuses, the main circuit fuse shall normally
blow in the event of a short-circuit or earth fault
occurring on a sub-circuit, although discrimination may
be achieved in respect of overload currents. The use of
rewirable fuses is restricted to the circuits with short-
circuit level of 4 kA; for higher level either cartridge
or HRC fuses shall be used.

8.1.5 Provision shall also be made for control of general
lighting and other emergency services through separate
main circuits and distribution boards from the power
circuits.

8.1.6 If necessary, independent source of supply for
emergency service in particular installations may be
provided.

8.1.7 Search suppressors shall be provided at the
incomers of the sub distribution boards as considered
necessary.

8.1.8 Wherever necessary to control the harmonics
within permissible limits, passive/active filters may be
used.

8.2 Fire-safety Requirements

8.2.1 Besides fire fighting equipment, the fire detection
and extinguishing systems, as recommended in Part 4
of SP 7 shall be followed.

8.2.2 Reference is also drawn to IS 1646 regarding
rules and regulations relating to electrical installations
from the point of fire safety. Annex D covers specific
requirements for fire safety for representative
industries.

PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS

281

SP 30: 2011

9 BUILDING SERVICES

9.1 Lighting

9.1.0 Industrial lighting encompasses seeing tasks,
operating conditions and economy. With each of the
various visual task conditions, lighting should be
suitable for adequate visibility. Physical hazards exist
in many manufacturing processes, therefore, lighting
contribute to the utmost as a safety factor in preventing
accidents. The speed of many manufacturing
operations might also be hampered due to poor lighting.
The general considerations for design of lighting in
industrial areas are enumerated in IS 6665 (see also
SP72).

9.1.1 Equipment for Lighting

The choice of light sources and luminaries shall be
governed by the guidelines given in IS 6665. The
recommended values of illumination and limiting
values of glare index are given in Annex E for guidance.

.9.2 Air-conditioning, Heating and Ventilation

9.2.1 The electrical installation meant for the services
such as air-conditioning heating and ventilation in
industrial buildings shall conform to the requirements
given in Part 1/Sec 1 1 of the Code. The specific needs
of individual locations requiring these services in each
factory shall be ascertained in consultation with the
concerned personnel before designing the electrical
system. Reference should be made to the guidelines
given in SP 7.

9.3 Lifts

9.3.1 The general rules laid down in Part 1/Section 1 1
of the Code shall apply regarding lift installations.
However, the design of lifts in industrial buildings shall
take into account the following requirements:

a) Occupant load — The occupant load ex-
pressed in terms of gross area in m 2 /person
shall be 10 for industrial buildings.

b) Car-speed for goods lifts — These shall be as
follows:

1) Normal load carrying lifts — 2-2.5 m/s

2) Lifts serving many floors — 1 m/s

9.3.2 The location of lifts in factories, warehouses and
similar buildings should be planned to suit the
progressive movement of goods through the buildings
having regard to the nature of processes carried out,
position of loading platform, railway slidings, etc. The
placing of a lift in a fume or dust laden atmosphere, or
where it may be exposed to extreme temperatures shall
be avoided. Where it is impossible to avoid extreme
environmental conditions. The selection of electrical
equipment shall be such that they are suitable to meet
the conditions involved.

10 MISCELLANEOUS/SPECIAL PROVISIONS

10.1 Control of Static Electricity

See IS 7689 regarding recommendations for controlling
static electricity generated incidentally by processes
in industries which may pose a hazard or
inconvenience. Specific control methods are also given
for some industries therein.

10.2 Safety in Electro-Heat Installations

Industrial process include in many instances, electro-
heat installations such as;

a)
b)

e)
f)

Arc furnaces;

Induction furnaces;

Appliances for direct and indirect resistance

heating;

Medium and high frequency induction

heating, radio frequency heating and

dielectric heating appliances;

Infra-red radiatum heating appliances; and

Microwave heating.

For safety requirements in such electro-heat
installations reference shall be made to IS 9080 (Parts 2
and 4) and IS/IEC 60519 (Parts 1, 3, 5 and 9).

103 POWER FACTOR COMPENSATION

10,3.1 The provisions of Part 1/Section 17 of the Code
shall apply. For specific guidance for installations
covered by this Part (see Annex F).

282

NATIONAL ELECTRICAL CODE

SP 30 : 2011

ANNEX A -

(Clause 2)

IS No.

Title

IS No.

732:

1989

Code of practice for electrical
wiring installations

7689 : 1989

1646

: 1997

Code of practice for fire safety of
buildings (general): Electrical
installations

9109 : 2000

2726

: 1988

Code of practice for fire safety of

industrial buildings: Cotton

9080 (Part 2/

ginning and pressing (including

Sec 2) : 1980

cotton seed delintering) factories

3058

: 1990

Code of practice for fire safety of
industrial buildings: Viscose
rayon yarn and/or staple fibre

plants

9080 (Part 2/

3079

: 1990

Code of practice for fire safety of
industrial buildings: Cotton textile
mills

Sec 4): 1981

3594

: 1991

Code of practice for fire safety of

industrial buildings: General

IS/IEC 60519-1

storage and warehousing

1984
IS/IEC 60519-3

including cold storage

3595

:2002

Code of practice for fire safety of
industrial buildings : Coal
pulverizers and associated
equipments

1988

3836:

:2000

Fire safety of industrial buildings

IS/IEC 60519-5

— Jute mills — Code of practice

1980

4226:

: 1988

Code of practice for fire safety of

industrial building: Aluminium/

IS/IEC 60519-9

Magnesium powder factories

1987

4886:

: 1991

Code of practice for fire safety of
industrial buildings: Tea factories

6329:

:2000

Code of practice for fire safety of

IS/IEC 60947-1

industrial buildings — Saw mills

2004

and wood works

6665:

: 1972

Code of practice for industrial

SP 7 : 2005

lighting

SP 72: 2010

Title

Guide for the control of
undesirable static electricity
Fire safety of industrial buildings
— Pradio frequency paint and
varnish factories — Code of
practice

Safety requirements in electro-
heat installations: Part 2 Particular
requirements for resistance
heating equipment, Section 2
Protection in indirect resistance
heating installations
Safety requirements in electro-
heat installations: Part 2 Particular
requirements for resistance heating
equipment, Section 4 Protection in
installations used for drying
varnishes and other similar products
Safety in electroheat installation:
Part 1 General requirements
Safety in electroheat installations:
Part 3 Particular requirements for
induction and conduction heating
and induction melting
installations

Safety in electroheat installation:
Part 5 Specification for safety in
plasma installation
Safety in electroheat installations:
Part 9 Particular requirements for
high-frequency dielectric heating
installations

Specification for low-voltage
switchgearandcontrolgear: Part 1
General rules

National Building Code of India
National Lighting Code

PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS

283

SP 30: 2011

ANNEX B
(Clause 4.1.2)

EXAMPLES OF INDUSTRIES BASED ON FIRE-SAFETY

B-l The following is a representative list of industries
classified according to the degree of fire hazard
enumerated in 4.1.1:

a) Low Hazard Industries

Abrasive manufacturing premises
Aerated water factories
Agarbatti manufacturing premises
Aluminium copper and zinc factories
Asbestos steam packing and lagging

manufacturers
Battery manufacturers
Bone mills
Breweries
Canning factories
Carbon dioxide plants
Cardamom factories
Cement factories
Cement and/or asbestos or concrete products

manufacturing premises
Ceramic and crockery factories
Clay works

Clock and watch manufacturing premises
Confectionery manufacturers
Electric generating houses
Electric lamps and fluorescent tube

manufacturers
Electronic goods manufacturing premises
Electroplating workshops
Engineering workshops
Fruit products and condiment factories
Gold thread factories/gilding factories
Glass factories
Gum and glue factories
Ice candy and ice cream manufacturing

premises
Ice factories

Ink factories (excluding printing inks)
Milk pasteurising plants and dairy farms
Mica products manufacturing premises
Potteries/tiles and brick works
Rice mills

Refractories works and firebrick kilns
Salt crushing factories and refineries
Silicate (other than sodium silicate) factories
Soap and detergent factories

Sugar candy manufacturers

Sugar factories

Tanneries

Tea colouring factories

Umbrella factories

Vermicelli factories

Wire drawing works

b) Moderate Hazard

Aeronaut/betelnut factories

Atta and cereal grinding premises

Bakeries and/or biscuit factories

Beedi factories

Book binders and paper cutting premises

Book sellers and stationers' shops

Boot and shoe factories and other leather

goods factories
Boat builders and ship repairing docks
Button factories
Candle works

Canvas sheet manufacturers
Cardboard box manufacturers
Carbon paper manufacturing premises
Carpet and durries factories
Carpenter's workshops
Camphor boiling premises
Cashew nut factories (using open fire)
Cloth processing works
Coffee curing premises
Coffee roasting and grinding works
Colour/dyes mixing and/or blending factories
Coir factories
Cork factories
Cork stopper and other cork products

manufacturing premises
Collieries

Chemical manufacturers
Cotton mills

Dyeing and dry cleaning works
Electric wire and cable manufacturing

premises
Enamel factories
Essential oil distillation plants
Flour mills
Garment makers

284

NATIONAL ELECTRICAL CODE

SP 30 : 2011

Ghee manufacturing premises
Ginning and pressing factories
Grains and/or seeds disintegrating factories
Grease manufacturing works
Gunning and pressing factories
Hat and topee factories
Hosiery factories

Incandescent gas mantle manufacturers
Jute mills and jute presses
Mineral oil blending and processing works
Mutton tallow manufacturers
Manure and/or fertilizer works (blending,
mixing and granulating only)

Mattresses and pillow making premises

Oxygen plants

Paper mills

Pencil factories

Plastic goods manufacturers

Printing press premises

Pulverizing and crushing mills (hazardous

materials)
Rice mills
Rope factories

Rubber goods manufacturers
Shellac factories
Spray painting works
Starch factories

Synthetic fibre manufacturing premises
Tea factories
Thermal power stations
Tobacco (chewing), zarda, kimam and pan

masala making premises
Tobacco grinding and crushing and snuff

manufacturing premises
Tobacco curing and redrying factories
Tobacco pressing works
Upholsterers
Weaving factories
Woollen mills

Wool cleaning/pressing factories
Yarn gassing plants.

c) High Hazard
Acetylene plants

Alcohol distillers

Aluminium and magnesium powder plants

Bituminished paper/hessian cloth

manufacturing premises

Bobbin factories

Cinematograph film production studies

Calcium carbide plants

Cotton waste factories

Coal/coke/charcoal ball and briquettes

factories
Celluloid goods manufacturers
Cigarette filter manufacturers
Cotton seed cleaning or deliniting premises
Duplicating and stencil paper manufacturers
Fertilizer plants
Explosive manufacturers
Fireworks factories
Foam plastics and foam rubber goods

manufacturers

Grass, hay, fodder and bhoosa (chaff) pressing

factories
Match factories
Oil mills

Oil extraction plants
Oil and leather cloth factories
Paint (including nitrocellulose paints) and

varnish factories
Petrochemical plants
Plywood factories
Printing ink manufacturers
Resin and lamp black manufacturers
Rubber substitute manufacturers
Surgical cotton manufacturers
Tar distilleries

Tar felt manufacturing premises
Tarpauplin and canvas proofing factories
Timber and woodworkers' premises
Tin printers (where more than 50 percent of

floor area is occupied as engineering

workshop this may be taken as moderate

hazard risk)
Terpentino distilleries
Tyre retreading and resoling factories
Woodmeal manufacturers

PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS

285

SP 30: -2011

ANNEX C
(Clause 6.5)

SELECTION OF WIRING SYSTEMS

C-l WIRING SYSTEMS FOR GENERAL

APPLICATION

a) Bare solid or tubular conductors supported on
insulators in metal or incombustible structural
ducts or chases (main connections).

b) Tough rubber-sheathed or PVC-sheathed
cables protected as necessary against
mechanical damage, say, buried in plaster or
installed in concrete ducts.

NOTE — Polythene-insulated PVC-sheathed cable
provides an alternative having the advantage of high
insulation-resistance.

c) Elastomer-insulated braided and compounded
or PVC-insulated cable installed in heavy-
gauge screwed conduit.

NOTE — The use of galvanized conduit and PVC-
insulated cable is to be preferred where the situation
may be damp or long life is required.

d) Elastomer-insulated braided and compounded
or PVC-insulated cable installed in light-
gauge steel conduit with lug grip.

e) Elastomer-insulated braided and compounded
or PVC-insulated cable installed in PVC or
other insulated conduit and provided with a
bare copper or copper-alloy earth-continuity
conductor as necessary.

f) Grid suspension wiring system comprising
elastomer-insulated or PVC insulated cables
laid around a galvanized steel catenary wire,
braided overall or otherwise protected to
withstand corrosive conditions where
necessary.

g) Elastomer-insulated braided and compounded
or PVC-insulated cable installed in metal
trunking or ducts.

NOTE — Incombustible insulated trunking and ducts
provide an alternative and where these are used a bare
copper or copper-alloy earth-continuity conductor may
be required.

h) Elastomer-insulated braided and compounded
or PVC-insulated cable installed on cleats,
with appropriate protection where cable
passes through floors or walls.

j) Elastomer-insulated lead-alloy-sheathed
cables incorporating an earth continuity
conductor, or elastomer-insulated aluminium-
sheathed cable, protected as necessary against
mechanical damage and corrosion.
NOTE — Where a lead-sheathed cable has plumbed
joints a separate earth-continuity conductor may not be
required.

k) Mineral-insulated metal-sheathed cable with

or without protective sheathing with suitable
watertight glands.

C-2 ADDITIONAL WIRING SYSTEMS
PARTICULARLY SUITABLE FOR USE IN
FACTORIES AND THE LIKE

n) PVC-insulated and steel tape or wire

armoured and PVC-sheathed cable buried

directly in the ground or used in special

conditions,
p) PVC-insulated steel tape or wire armoured

and PVC-sheathed cable with cleat or hook

suspensions,
q) PVC-insulated and PVC-sheathed cable,

installed in underground earthenware ducts

or metal pipes.

r) PVC-insulated and PVC-sheathed cable,
mounted on porcelain or hardwood cleats or
in trenches or ducts, and so installed as to be
protected against mechanical damage.

s) Tough rubber-sheathed or PVC-sheathed
cable mounted on insulating non-hygro-
scopic cleats affixed to treated, teak
battens by screws of corrosion-resisting
material, such as Monel metal or phosphor-
bronze.

t) Elastomer-insulated braided and compounded
or PVC-insulated cable installed in galvanized
solid-drawn screwed conduit with flameproof
couplings and inspection fittings.

u) Varnished-cambric insulated, lead-alloy or
aluminium-sheathed cable.

v) Elastomer-insulated, tough rubber- sheathed
cable, steel wire armoured.

NOTE — Varnished cambric insulated cables without
metal sheath should be used only for short connections
on switchboards and the like in dry situations.

w) Cross-linked polyethylene insulated
thermoplastic sheathed, armoured cable.

C-3 SELECTION OF WIRING SYSTEMS FOR
FACTORIES

C-3.1 Wiring systems suitable for installations in
different categories of factories are given in Table 3.

C-4 SPECIAL RESTRICTIONS

C-4.1 Even though guidance may be taken from the
selection chart (see Table 3) for wiring systems, the
following restrictions to their use apply:

286

NATIONAL ELECTRICAL CODE

SP 30 : 2011

Wiring

Restrictions

Wiring

Restrictions

System (see

C-l, C-2)

(1)

(2)

(1)

(2)

b) and g) If the ducts are in the form of under
floor trenches then the following
provisions should be observed:

1) Cables shall preferably be so
mounted on suitably earth cracks
or other supports and has to be at
least 75 mm above the bottom.

2) Top of trenches shall be covered
with chequered plates or concrete
slabs,

3) In case of long trenches, it is
recommended that trenches of
more than 1 000 cm 2 cross-
sectional area be divided by
incombustible barriers at
intervals not exceeding 45 m.
The barriers shall be at least
50 mm in thickness and of the
same height as of cable trench.
The cables shall be carried
through holes in the barriers,
which shall be made good
thereof to prevent the passage of
fire beyond the barriers,

4) The combined cross- sectional
area of all conductors or cables
shall not as far as possible exceed
40 percent of the internal cross-
sectional area of the trench, and

5) The cable trenches shall be kept
free from accumulation of water,
dusts and waste materials.

c) Trunking or ducting systems for cables

above ground shall not be used where:

1) they are exposed to physical
damage,

2) they are exposed to corrosive
vapours.

3) the atmosphere is likely to
contain flammable gases or
vapours,

4) the wet processes are carried out,
or

5) in concealed spaces.
Ordinary steel conduits shall not be
permitted in areas where flammable
vapour may be present, unless it is of
type conforming with wiring system (t)
and shall not be permitted in locations:
1) where wiring height is less than

2.5 m above working floor level,
unless protected against
mechanical damage,

PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS

h) and s)

m), n), p)

and v)

4)
5)

they are exposed to corrosive

vapours.

where atmosphere is likely to

contain flammable gases or

vapours,

where wet processes are carried

out, or

in concealed spaces.
Ordinary steel conduits shall not be
permitted in areas where flammable
vapour may be present, unless it is of
type conforming with wiring system (t)
and shall not be permitted in locations:

1) where wiring height is less than
2.5 m above working floor level,
unless protected against
mechanical damage,

2) where ambient temperature is
likely to be above 55°C at
sometime or other during the year,

3) in concealed spaces of
combustible construction,

4) where atmosphere is likely to
contain flammable gases or
vapours, or

5) where conductor operates at
voltage above 650 V.

It shall be permitted only where voltage
is below 650 V and in locations where
the atmosphere is unlikely to contain
any flammable vapours or gases.
Same as in case of wiring system (d).
This system shall not be permitted in
locations:

1) where exposed to severe physical
damage,

2) where exposed to corrosive
vapours,

3) where wet processes are carried
out, or

4) in concealed places.

These systems should only be
permitted for voltage below 250 V and
that too only if use of such system is
essential.

Same as in case of wiring system (d).
Armoured cables shall not be permitted
in following locations unless the cable
is of PVC-sheathed type, and shall not
be permitted in locations exposed to
corrosive fumes or vapour; and battery
rooms.

287

SP 30: 2011

Table 3 Selection Chart for Wiring Systems for Installations in Factories
(Clauses C-3.1 and C-4.1)

SI No.

Section of Installation

Category of Factory

Average Factory

Heavy Industry Light Industry

Chemical Industry

Factories
Involving
Fire Risk

(11)

r" -\ r- —>> r "\ r

1st 2nd 1st 2nd 1st 2nd

Choice Choice Choice Choice Choice Choice

(2) (3) (4) (5) (6) (7) (8)

1st 2nd

Choice Choice

(9) (10)

i) Main distribution at
medium or low voltage

k
w
n

k
w
n
r

k
w
n

ii)

Sub-main distribution to
local distribution boards

iii) Sub-circuit wiring

c
f
k
w
P

f
g

c
f
k
w

P
r

b
h
J

g
k
w
P

NOTE — For description of a, b, c w, see C-l and C-2.

ANNEX D
(Clause 8.2.2)

REQUIREMENTS FOR FIRE SAFETY IN SPECIFIC INDUSTRIES

Type of Industry

Ref.IS

Motors

Other Equipment

Fittings

Miscellaneous

(1)

(2)

(3)

(4)

(5)

(6)

Jute spinning and

3836

All motors shall be

All equipment shall

Lighting fittings

Supply shall be at <

weaving, jute rope,

totally enclosed type

be metal clad, dust-

shall be dust-tight

250 V in jute

carpet making factories

and in wet locations
shall be drip-proof

tight

godowns

Cotton ginning cotton

2726

All equipment shall

seed delintering and

be metal clad, dust-

pressing factories

tight

Plants making viscose

3058

All equipment in the

Vapour-proof

All current carrying

rayon yarn or staple

Xanthation

lighting fittings in

parts, contacts liable

fibre or both

disulphide plant

areas where

for corrosion shall

shall comply with

corrosive gases are

be cadmium plated

Part 8 of the Code

evolved

288

NATIONAL ELECTRICAL CODE

SP 30 : 2011

Type of Industry

Ref.lS

Motors

Other Equipment

Fittings

Miscellaneous

(1)

(2)

(3)

(4)

(5)

(6)

Textile mills using

3079

Totally enclosed

Metal clad and dust-

Dust-tight lighting

Machines for

cotton, cotton waste

type, the cooling air

tight. Equipment

fittings at willowing,

singeing yarn shall

regenerated cellulose,

for variable speed

shall be flameproof

lap breaking, waste

be protected to

man-made fibres or

motor taken from

in gas singeing

opening, mixing,

ensure that heating

any grouping of these

outside the building

rooms. Stop motion

blow and raising

elements are not

devices provided on

rooms

switched on while

frames shall be dust-

yarn is stationary

tight

Places where paints

9109

—

Wiring in steel

Provisions shall be

and varnishes are

conduits. Lighting

made for switching

stored or processed

fittings of enclosed
type

off the whole factory
at more than one
control point

Factories where

4226

Motors shall be

All equipment of

Wiring in steel

Provisions shall be

powders of aluminium,

flameproof dust-

the enclosed type

conduits. Enclosed

made for switching

magnesium and their

protected (see Part 7

lighting fittings

off the whole factory

alloys are processed or

of the Code)

at more than one

used

control point

Coal pulverizing mills,

3595

Totally enclosed,

Lighting fittings

Use of flexible

as also equipment

flameproof, dust-

shall be dust-tight.

cables to be kept to

therein for power

proof (see Part 7 of

Only conduits;

the minimum

generation cole or

the Code)

armoured or mineral

briquette making

insulated type of
wiring

Tea factories

4886

Where practicable,
totally enclosed
type

Fan motors of
dryers and
withering troughs
and other control
equipment shall be
dust proof tape

Godowns, ware-houses,

3594

Driving motors for

All switchgear

Screwed steel

All control

outdoor storage sites

overhead cranes

equipment metal

conduits mineral

equipment switches,

forming part of

totally enclosed

enclosed. For mains

insulated, copper or

etc., outside

industrial complexes or

operated electrical

aluminium sheathed

godown where

others; cold storage

stackers, switch and

cable. Lighting

fibrous goods,

buildings

socket shall be

fittings to be

flammable liquids,

water-tight. Flexible

positioned not

nitro-cellulose, fire

connection to the

below 45 cm below

works or explosives

stacker through

roof A clearance of

are stored

rubber compound

not less than 75 cm

sheathed trailing

to be provided from

cable with hard cord

highest stacking

braiding

level. Flexible
lighting pendants or
portable lamps not
allowed

Saw mills, furniture

6329

Motors shall be

All equipment shall

Electrical heaters

factories, coach and

totally enclosed or

be dust-tight and

shall be metal cases,

body build works, up-

pipe ventilated

where spray painting

totally enclosed,

holsteries and other

is done shall comply

immersion type or

wood working shops.

with Part 7 of the

totally enclosed low

Plywood hard-wood,

Code

temperature type

wood wool, insulation

with external

boards, wood flour, etc

surface below 92°C

PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS

289

SP 30 : 2011

ANNEX E
(Clause 9.1.1)

RECOMMENDED VALUES OF ILLUMINATION AND LIMITING VALUES OF
GLARE INDEX — INDUSTRIAL BUILDINGS

SI No. Industrial Buildings and Processes

(1) (2)

Average Limiting Glare
Illumination, lux Index

(3) (4)

150
100
100

i) General factor areas:

a) Canteens

b) Cloakrooms

c) Entrances, corridors, stairs
ii) Factory outdoor areas:

Stockyards, main entrances, exit roads, car parks, internal factory roads
iii) Aircraft factories and maintenance hangers:

a) Stock parts productions

b) Drilling, riveting, screw fastening, sheet aluminium layout and
template work, wing sections, cowling welding, sub-assembly,
final assembly, inspection

c) Maintenance and repairs (Hangers)
iv) Assembly shops:

a) Rough work, for example, frame assembly, assembly of heavy
machinery

b) Medium work, for example, machined parts, engine assembly,
vehicle body assembly

c) Fine work, for example, radio and telephone equipment, typewriter
and office machinery assembly

d) Very fine work, for example, assembly of very small precision
mechanisms, instruments

v) Bakeries:

a) Mixing and make-up rooms, oven rooms, wrapping rooms

b) Decorating and icing
vi) Boiler houses (industrial):

a) Coal and ash handling

b) Boiler rooms:

1) Boiler fronts and operating areas

2) Other areas

c) Outdoor plants:

1) Catwalks

2) Platforms
vii) Bookbinding:

a) Pasting, punching and stitching

b) Binding and folding; miscellaneous machines

c) Finishing, blocking and in laying
viii) Boot and shoe factories:

a) Sorting and grading

b) Clicking and closing, preparatory operations

c) Cutting table and presses, stitching

d) Bottom stock preparation, lasting and bottoming, finishing

450

300

150

300

700

1 500' >

150

200

100

100 2)

' —

20 to 25

—

200

300

1 000 3)

700

1000

700

290

NATIONAL ELECTRICAL CODE

SP 30 : 2011

150

200

Special lighting

—

450

300

200

300

450

—

200

450

SI No. Industrial Buildings and Processes Average Limiting Glare

Illumination, lux Index
(1) (2) (3) (4)

e) Shoe rooms 700 22

ix) Breweries and distilleries:

a) General working areas

b) Brewhouse, bottling and canning plants

c) Bottle inspection
x) Canning and preserving factories;

a) Inspection of beans, rice, barley, etc

b) Preparation: kettle areas, mechanical cleaning, dicing, trimming

c) Canned and bottled goods: retorts

d) High speed labelling lines

e) Can inspection
xi) Carpet factories:

a) Winding, beaming

b) Designing, Jacquard and cutting, setting pattern, tufting, topping,
cutting, hemming, fringing

c) Weaving, mending, inspection 450 22
xii) Ceramics — See pottery and clay products

xiii) Chemical works:

a) Hand furnaces, boiling tanks, stationery driers, stationery or gravity 150 28
crystalizers, mechanical driers, evaporators, filtration plants,
mechanical crystallising bleaching, extractors, percolators,
nitrators. electrolytic cells

b) Controls, gauges, values, etc 100 —

c) Control rooms:

1) Vertical control panels

2) Control desks
xiv) Chocolate and confectionery factories:

a) Mixing, blending, boiling

b) Chocolate husking, winnowing, fat extraction, crushing and
refining, feeding, bean cleaning, sorting, milling, cream making

c) Hand decorating, inspection, wrapping, packing 300 22
xv) Clothing factories:

a) Matching-up 450 3) 19

b) Cutting sewing:

1) Light

2) Medium

3) Dark

4) Pressing

c) Inspection:

1) Light

2) Medium

3) Dark

d) Hand tailoring:

1) Light

2) Medium

3) Dark

PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS 291

200-300

300

150

200

300

450

700

300

450

1000

1 500

450

1000

1500

SP 30 : 2011

SI No. Industrial Buildings and Processes

(1) (2)

Average Limiting Glare
Illumination, lux Index

(3) (4)

xvi)

Collieries (surface buildings):

Coal preparation plant:
1) Working areas

150

2) Other areas

100

—

3) Picking belts

300

—

4) Winding houses

150

—

Lamp rooms:

1) Main areas

2) Repair sections

3) Weigh cabine

100
150
150

—

Fan houses

100

—

xvii)

Dairies:

General working areas

200 2)

Bottle inspection

Special lighting

—

Bottle filling

450

xviii)

Die sinking:

General

300

—

Fine

1000

xix)

Dye works:

Reception, 'grey' perching

700

—

Wet processes

150 2 >

Dry processes

200 2)

Dyers' offices

700 3}

Final perching

2 000 3)

—

xx)

Electricity generating stations: Indoor locations

Turbine halls

200

Auxiliary equipment; battery rooms, blowers
switchgear and transformer chambers

auxiliary generators,

100

—

Boiler houses (including operating floors) platforms, coal conveyors,
pulverizers, feeders, precipitators, soot and slag blowers

70-100

—

Boiler house and turbine house

100

—

Basements

—

Conveyor houses, conveyor gantries, junction

towers

70-100

—

Control rooms:

1) Vertical control panels

200-300

2) Control desks

300

3) Rear of control panels

150

4) Switch houses

150

Nuclear reactors and steam, raising plants:

1) Reactor areas, boilers, galleries

150

2) Gas circulator days

150

3) Reactor charge/discharge face

200

xxi)

Electricity generating stations: Outdoor locations

Coal unloading areas

—

Coal storage areas

—

292

NATIONAL ELECTRICAL CODE

SP 30: 2011

SI No. Industrial Buildings and Processes

(1) (2)

Average Limiting Glare
Illumination, lux Index

(3) (4)

c) Conveyors

—

d) Fuel oil delivery headers

—

e) Oil storage tanks

—

f) Catwalks

—

g) Platforms, boiler and turbine decks

—

h) Transformers and outdoor switchgear

100

—

xxii)

Engraving:

a) Hand

1000

b) Machine (see Die sinking)

—

xxiii)

Farm buildings (dairies)

a) Boiler houses

—

b) Milk rooms

150

c) Washing and sterilizing rooms

150

d) Stables

—

e) Milking parlours

150

xxiv)

Flour mills:

a) Roller, purifier, sifting and packing floors

150

b) Wetting tables

300

xxv)

Forges: General

150

xxvi)

Foundries:

a) Charging floors, tumbling cleaning, pouring, shaking out, rough

150

moulding and rough core making

b) Fine moulding and core making, inspection

300

xxvii)

Garages:

a) Parking areas (interior)

b) Washing and polishing, greasing, general servicing, pits

150

c) Repairs

300

xxviii

) Gas works:

a) Retort houses, oil gas plants, water gas plants, purifiers, coke

30-50 4)

screening and coke handling plants (indoor)

b) Governor, meter, compressor, booster and exhauster houses

100

c) Open type plants:

—

1) Catwalks

20 4)

—

2) Platforms

50 4)

—

xxix)

Gauge and tool rooms: General

700 5)

xxx)

Glass works and processes:

a) Furnace rooms, bending, annealing lehrs

100

b) Mixing rooms, forming (blowing, drawing, pressing, rolling)

150

c) Cutting to size, grinding, polishing, toughening

200

d) Finishing (bevelling, decorating, etching, silvering)

300

e) Brilliant cutting

700

f) Inspection:

1) General

200

2) Fine

700

PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS

293

SP 30 : 2011

SI No. Industrial Buildings and Processes

(1) (2)

Average Limiting Glare
Illumination, lux Index

(3) (4)

300

450

700

300

450

700

xxxi) Glove making:

a) Pressing, knitting, sorting, cutting 300 22

b) Sewing:

1) Light

2) Medium

3) Dark
xxxii) Hat making

a) Stiffening, braiding, cleaning, refining forming, sizing, 150 22
pouncing, flanging, finishing ironing

b) Sewing:

1) Light

2) Medium

3) Dark
xxxiii) Hosiery and knitwear:

a) Circular and flat knitting machines universal winders, cutting 300 22
out, folding and pressing

b) Lock stitch and overlooking machines:

1) Light

2) Medium

3) Dark

c) Mending

d) Examining and hand finishing, light, medium, dark

e) Linking or running-on
xxxiv) Inspection shops (Engineering)

a) Rough work, for example, counting, rough checking of stock
parts, etc.

b) Medium work, for example, 'Go' and 'No-go' gauges,
sub-assemblies

c) Fine work, for example, radio and telecommunication equipment,
calibrated scales, precision mechanisms, instruments

d) Very fine work, for example, gauging and inspection of small
intricate parts

e) Minute work, for example, very small instruments
xxxv) Iron and steel works

a) Marshalling and outdoor stockyards

b) Stairs, gangways, basements, quarries, loading docks

c) Slab yards' melting shops, ingot stripping soaking pits, blast
furnace working areas, picking and cleaning lines, mechanical
plants, pump houses

d) Mould preparation, rolling and wire mills, mills motors rooms,
power blower houses

e) Slab inspection and conditioning, cold strip mills, sheet and plate
finishing, tinning, galvanizing, machine and roll shops

f) Plate inspection

g) Tinplate inspection

300

450

700

1500

700

450

150

300

700

1500

3 000 2 >

10-20

100

—

100

150

200

300

— -

;ial lighting

—

294

NATIONAL ELECTRICAL CODE

SP 30 : 2011

SI No. Industrial Buildings and Processes

(1) (2)

Average Limiting Glare
Illumination, lux Index

(3) (4)

xxxviii)

a)
b)
c)

xl)

xli)

xlii)

xliii)

xliv)

xlv)

700"

3 000"

1 500 3 >

—

300

450

200

300

150

200

450

700

1 000 3)

150

300

xxxvi) Jewellery and watchmaking

a) Fine processes

b) Minute processes

c) Gem cutting, polishing, setting
xxx vii) Laboratories and test rooms

a) General laboratories, balance rooms
Electrical and instrument laboratories
Laundries and drycleaning works

Receiving, sorting, washing, drying, ironing (calendering), despatch
Drycleaning, bulk machine work

Fine hand ironing, pressing, inspection mending, spotting
xxxix) Leather dressing

a) Vats, cleaning, tanning, stretching, cutting, fleshing and stuffing

b) Finishing, staking, splitting and scrafing
Leather working

a) Pressing and glazing

b) Cutting, scarfing, sewing

c) Grading and matching
Machine and fitting shops
a) Rough bench and machine work

Medium bench and machine work, ordinary automatic machines,
rough grinding, medium buffing and polishing
Fine bench and machine work, fine automatic machines, medium
grinding fine buffing and polishing
Motor vehicle plants

a) General sub-assemblies, chassis assembly, car assembly

b) Final inspection

c) Trim shops, body sub-assemblies, body assembly

d) Spray booths
Paint works

a) General automatic processes

b) Special batch mixing

c) Colour matching
Paint shops and spraying booths:

a) Dipping, firing rough spraying

b) Rubbing, ordinary painting, spraying and finishing

c) Fine painting, spraying and finishing

d) Retouching and matching
Paper- works:
a) Paper and board making:

1) Machine houses, calendering pulp mills, preparation plants,
cutting, finishing, trimming

2) Inspection and sorting (over hauling)
Paper converting processes:
1) Corrugated board, cartons, containers and paper sack

manufacture, coating and laminating processes

700

300

450

300

450

—

200

450

700 3 >

150

300

450

700 3 >

200

300

200

PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS

295

SP 30: 2011

SI No, Industrial Buildings and Processes

(1) (2)

Average Limiting Glare
Illumination, lux Index

(3) (4)

2) Associated printing
xlvi) Pharmaceuticals and fine chemicals works:
a) Raw material storage

Control laboratories and testing

Pharmaceuticals manufacturing: grinding, granulating, mixing

and drying, tableting, sterilizing and washing, preparation of

solutions and filling, labelling, capping, cartoning and wrapping,

inspection

Fine chemical manufacture:

1 ) Plant processing

2) Fine chemical finishing
xlvii) Plastics works:

a) Manufacture (see Chemical works)

b) Processing:

1) Calendering, extrusion

2) Moulding-compression, injection

3) Sheet fabrication:
i) Shaping

ii) Trimming, machining, polishing
iii) Cementing
xlviii) Plating shops:

a) Vat and baths, filter pressing, kin rooms, moulding, pressing,
cleaning, trimming, glazing, firing

b) Enamelling, colouring, decorating
xlix) Printing works:

a) Type foundries:

1) Matrix making, dressing type, hand and machine casting

2) Front assembly, sorting

b) Printing plants:

1) Machine composition, imposing stones

2) Presses

3) Composing room

4) Proof reading

c) Electrotyping:

1) Block-making, electroplating, washing, backing

2) Moulding, finishing, routing

d) Photo-engraving:

1) Block-making, etching, masking

2) Finishing, routing

e) Colour printing: Inspection area
1) Rubber processing:

a) Fabric preparation creels

b) Dipping, moulding, compounding calendars

c) Tyre and tube making

300

200
300

200

300

25
25

300

200

300

200

150

450 3 >

200

450

200

300

450

300

200

300

200

300

700 3)

200

150

200

296

NATIONAL ELECTRICAL CODE

SP 30: 2011

SI No. Industrial Buildings and Processes

(1) (2)

Average Limiting Glare
Illumination, lux Index

(3) (4)

li) Sheet metal works:

a) Benchwork, scribing, pressing, punching shearing, stamping, 200 25
spinning, folding

b) Sheet inspection Special lighting
lii) Soap factories:

a) Kettle houses and ancillaries, glycerine evaporation and
distillation, continuous indoor soap making, plants:

1) General areas

2) Control panels

b) Batch or continuous soap cooling, cutting and drying, soap milling,
plodding:

1) General areas

2) Control panels, key equipment

c) Soap stamping, wrapping and packing, granules making, granules
storage and handling, filling and packing granules:

1) General areas

2) Control panels, machines

d) Edible products processing and packing
liii) Structural steel fabrication plants:

a) General

b) Marking off
liv) Textile mills (cotton or linen):

a) Bale breaking, blowing, carding, roving, slubbing, spinning
(ordinary counts), winding, heckling, spreading, cabling

b) Warping, slashing, dressing and dyeing, doubling (fancy), spinning
(fine counts)

c) Healding (drawing-in) 700

d) Weaving:

1) Patterned cloths, fine counts dark

2) Patterned cloths, fine counts light

3) Plain 'grey' cloth

e) Cloth inspection
lv) Textile mills (silk or synthetics):

a) Soaking, fugitive tinting, conditioning or setting of twist

b) Spinning

c) Winding, twisting, rewinding and coning, quality slashing:

1) Light thread

2) Dark thread

d) Warping

e) Healding (drawing-in)

f) Weaving

g) Inspection
lvi) Textile mills (woollen):

a) Scouring, carbonizing, teasing, preparing, raising, brushing, 150 25

pressing, back-washing, gilling, crabbing and blowing

150

200-300

150

200-300

150

200-300

200

150

300

150

200

700

300

200

700'>

—

200

450

200

300

700

—

700

L000 3 >

PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS

297

SP 30: 2011

SI No. Industrial Buildings and Processes Average Limiting Glare

Illumination, lux Index
_0) (2) . (3) (4)

b) Blending, carding, combing (white), tentering, drying, cropping

c) Spinning, roving, winding, warping, combing (coloured), twisting

d) Healding (drawing-in)

e) Weaving:

1) Fine worsteds

2) Medium worsteds, fine woollens

3) Heavy woollens

f) Burling and mending

g) Perching:

1) Grey

2) Final
lvii) Textile mills (jute):

a) Weaving, spinning, flat, jacquard carpet looms, cop winding

b) Yarn calender
lviii) Tobacco factories: All processes

lix) Upholstering, furniture and vehicles
lx) Warehouses and bulk stores:

a) Large material, loading bays

b) Small material, racks

c) Packing and despatch
Ixi) Welding and soldering:

a) Gas and arc welding, rough spot welding

b) Medium soldering, brazing and spot welding, for example,
domestic hardware

c) Fine soldering and spot welding, for example, instruments, radio
set assembly

d) Very fine soldering and spot welding, for example, radio valves
lxii) Woodworking shops:

a) Rough sawing and bench work

b) Sizing, planning, rough sanding, medium machine, and bench
work, gluing, veneering, cooperage

c) Fine bench and machine work, fine sanding and finishing 300 22

200

450

700

—

700

450

300

700

2 000 3 >

—

200

150

300 3)

300

100

150

300

700

150

200

Optical aids should be used where necessary.

2) Supplementary local lighting may be required for gauge glasses and instrument panels.

3) Special attention should be paid to the colour quality of the light.

4) Supplementary local lighting should be used at important points.

53 Supplementary local lighting and optical aids should be used where necessary.

298 NATIONAL ELECTRICAL CODE

SP 30 : 2011

ANNEX F
(Clause 10)

POWER FACTOR IN INDUSTRIAL INSTALLATIONS

F-l The general guidelines for power factor compensation
is given in Part 1/Sec 17 of the Code. For guidance, the
natural power factor for some three phase electrical

installations are given in Table 4. The recommended
capacitor ratings at rated voltage, for direct connection
to ac induction motor in industries are given in Table 5.

Table 4 Power Factor for Three Phase Electrical Installations

(Clause F-l)

Type of Installation

Natural Power

Type of Installation

Natural Power

No.

Factor

No.

Factor

(1)

(2)
Cold storage and fisheries

(3)
0.76-0.80

(1)

(2)

(3)

xviii)

Flour mills

0.61

ii)

Cinemas

0.78-0.80

xix)

Gas works

0.87

iii)

Metal pressing

0.57-0.72

xx)

Textile mills

0.86

iv)

Confectionery

0.77

xxi)

Oil mills

0.51-0.59

Dyeing and printing (textile)

0.60-0.87

xxii)

Woolen mills

0.70

vi)

Plastic moulding

0.57-0.73

xxiii)

Potteries

0.61

vii)

Film studios

0.65 to 0.74

xxiv)

Cigarette manufacturing

0.80

viii)

Newspapers

0.58

xxv)

Cotton press

0.63-0.68

ix)

Heavy engineering works

0.48-0.75

xxvi)

Foundries

0.59

Rubber extrusion and moulding

0.48

xxvii)

Tiles and mosaic

0.61

xi)

Pharmaceuticals

0.75-0.86

xxviii)

Structural engineering

0.53-0.68

xii)

Oil and paint manufacturing

0.51-0.69

xxix)

Chemicals

0.72-0.87

xiii)

Silk mills

0.58-0.68

xxx)

Municipal pumping stations

0.65-0.75

xiv)

Biscuit factory

0.60

xxxi)

Oil terminals

0.64-0.83

xv)

Printing press

0.65-0.75

xxxii)

Telephone exchange

0.66-0.80

xvi)

Food products

0.63

xxxiii)

Rolling mills

0.72-0.60

xvii)

Laundries

0.92

xxxiv)

Irrigation pumps

0.52-0.70

Table 5 Capacitor Ratings at Rated Voltage

(Clause F-l)

Rated Output

of Motors

Capacitor Rating in

kVAR for Motor Speed

3 000

1500

1000

750

600

500

rev/min

(1)

(2)

(3)

(4)

(5)

(6)

(7)

2.25

1.5

2.5

3.7

2.5

3.5

5.7

2.5

3.5

4.5

5.5

7.5

4.5

5.5.

6.5

11.2

7.5

8.5

18.7

10.5

14.5

22.5

12.5

102

150

187

NOTES

1 The reference to speed of motor has been made since the manufacturers provide information on that basis.

2 The capacitive current supplied by condensers directly across induction motor terminals should not exceed the magnetizing current of
the induction motors, to guard against excess transient torques and overvoltages.

3 Should a consumer desire to improve the power factor beyond a value which is limited by considerations of magnetizing kVAR of the
motor as stated in Note 2, then he may install the calculated capacitor kVAR as a separate circuit with its independent controlgear.

PART 4 ELECTRICAL INSTALLATIONS IN INDUSTRIAL BUILDINGS

299

NATIONAL ELECTRICAL CODE

PART 5

SP 30: 2011

PART 5 OUTOGO: I INSTALLATIONS

FOREWORD

As compared to the various types of indoor installations covered in other Parts of this Code, outdoor installations
are distinct in nature by virtue of their being exposed to moderate to heavy environmental conditions. In addition,
electric power in outdoor installations is normally utilized for specific purposes such as, lighting or for meeting
the needs of heavy machinery (example, open cast mines). In the case of the latter, the duties would be more
onerous than those normally encountered in indoor situations, thereby calling for special considerations in their
design.

Keeping the above in view, Part 5 of this Code deals with installations erected outdoor. Some outdoor installations
are erected to serve for a small duration of time after which they are meant to be dismantled. Such installations
are called temporary installation. For convenience, and keeping other aspects of safety provisions in view, this
duration is defined as not exceeding six months. Permanent outdoor installations are those which are generally in
use for longer periods of time. This Part 5 of this Code basically deals with these two types of outdoor installations.

Part 5 consists of the following Sections:

Section 1 Public Lighting Installations
Section 2 Temporary Outdoor Installations
Section 3 Permanent Outdoor Installations

Even though installations for lighting of public thoroughfares are permanent in nature, they are dealt with separately
in Section 1.

It may, however, be noted that small outdoor locations around building installations (example, gardens around
hotel installations or storage yards in industries) do not fall under the scope of Part 5 . For requirements pertaining
to this, reference should be made to relevant parts of this Code.

PART 5 OUTDOOR INSTALLATIONS 303

SP 30 : 2011

SECTION 1 PUBLIC LIGHTING INSTALLATIONS

FOREWORD

One of the most common forms of permanent outdoor
installations is the public lighting installations intended
for lighting of public thoroughfares. With the
availability of variety of light sources for such
installations and the need for proper illumination of a
variety of traffic routes and city centres it has been
found necessary to lay down guidelines for designing
on efficient and economical lighting installation.

This Section of this Code is intended to cover general
principles governing the lighting of public
thoroughfares and to lay down recommendations on
the quantity and quality of lighting to be provided. The
actual details of design would entirely depend on the
local circumstances.

The requirements given in this Section are, as far as
practicable aligned with the recommendations of the
International Commission on Illumination (CIE)
modified to suit the local conditions and regulations.

1 SCOPE

1.1 This Part 5/Section 1 of the Code covers requirements
of public lighting installations in order to provide
guidance to those concerned with the preparation of
public lighting schemes, their installation and
maintenance (see also SP 72).

1.2 This Section deals only with electric lighting
sources and does not include gas or other types of
lighting.

1.3 This Section also does not cover exterior lighting
installations, such as those which apply for parks,
shopping enclaves, flood lighting of routes and
structures of architectural importance, etc.

2 REFERENCES

This Part 5/Section 1 of the Code should be read in
conjunction with the following Indian Standards:

IS No. Title

SP 72 : 2010 National Lighting Code

1 885 (Part 16/ Electrotechnical vocabulary : Part

Sec 2) : 1968 16 Lighting, Section 2 General

illumination lighting fittings and

lighting for traffic and signalling

1944 (Parts 1 Code of practice for lighting of

and 2): 1970 public thoroughfares: Part 1

General principles; Part 2

Lighting of main roads (first

revision)

IS No.
1944 (Part 5): 1981

1944 (Part 6): 1981

Title

Code of practice for lighting of
public thoroughfares: Part 5
Lighting of grade separated
junctions, bridges and elevated
road (Group D)

Code of practice for lighting of
public thoroughfares: Part 6
Lighting of town and city centres
and areas of civic importance
(Group E)

3 TERMINOLOGY

3.0 For the purpose of this Section, the following terms
together with those provided in IS 1885 (Part 16/
Section 2) shall apply.

3.1 Terms Relating to Highways

3.1.1 Highway — A way for the passage of vehicular
traffic over which such traffic may lawfully pass.

3.1.2 Layout — All those physical features of a highway
other than the surfacing of the carriageway, which have
to be taken into account in planning a lighting
installation.

3.1.3 Carriageway — That portion of a highway
intended primarily for vehicular traffic.

3.1.4 Dual Carriageway — A layout of the separated
carriageways, each reserved for traffic in one direction
only.

3.1.5 Central Reserve -
a dual carriageway.

- A longitudinal space dividing

3.1.6 Service Road — A subsidiary road between
principle road and buildings or properties facing
thereon or a parallel road to the principal road and
giving access to the premises and connected only at
selected points with the principle road".

3.1.7 Cycle Track — A way or part of a highway for use
by pedal cycles only.

3.1.8 Footway — That portion of a road reserved
exclusively for pedestrians.

3.1.9 Verge — The unpaved area flanking a carriageway,
forming part of the highway and substantially at the
same level as the carriageway.

3.1.10 Shoulder — A strip of highway adjacent to and
level with the main carriageway to provide an
opportunity for vehicles to leave the carriageway in an
emergency.

304

NATIONAL ELECTRICAL CODE

SP 30: 2011

3.1.11 Refuge — A raised platform or a guarded area
so sited in the carriageway as to divide the streams of
traffic and to provide a safety area for pedestrians.

3.1.12 Kerb — A border of stone, concrete or other
rigid material formed at the edge of a carriageway.

3.2 Terms Relating to Lighting Installation

3.2.1 Lighting Installation — The whole of the
equipment provided for lighting the highway
comprising the lamps, luminaires, means of support
and electrical and other auxiliaries.

3.2.2 Lighting System — An array of luminaires having
a characteristic light distribution sited in a manner
concordant with this distribution. (Lighting systems
are commonly designated by the name of the
characteristic light distribution, for example, cut-off,
semi-cut-off, etc.)

3.2.3 Luminaire — A housing for one or more lamps,
comprising a body and any refractor, reflector, diffuser
or enclosure associated with the lamp(s).

3.2.4 Outreach — The distance measured horizontally
between the centre of the column or wall face and the
centre of a luminaire {see Fig. 1).

3.2.5 Overhang — The distance measured horizontally
between the centre of a luminaire mounted on a bracket
and the adjacent edge of the carriageway {see Fig. 1).

3.2.6 Mounting Height — The vertical distance between
the centre of the luminaire and the surface of the
carriage (see Fig. 1).

3.2.7 Spacing — The distance, measured along the
centre line of the carriageway, between successive
luminaires in an installation (see Fig.l).

NOTE — In a staggered arrangement, the distance is measured,
along the centre line of the carriageway, between a luminaire
on one side of the carriageway and the next luminaire, which
is on the other side of the carriage. It is not the distance
measured on the diagonal joining them, nor the distance
between successive luminaires on the same side of the
carriageway.

3.2.8 Span — That part of the highway lying between
successive luminaires in an installation.

3.2.9 Width of Carriageway — The distance between
kerb lines measured at right angles to the length of the
carriageway (see Fig. 1).

3.2.10 Arrangement — The pattern according to which
luminaires are sited on plan, for example, staggered,
axial, opposite.

3.2.11 Geometry (of a Lighting System) — The inter-
related linear dimensions and characteristics of the
system, namely the spacing, mounting height, width,
overhang and arrangement.

3.3 Photometric Terms

3.3.1 Luminous Flux — The light given by a light
source or a luminaire or received by a surface
irrespective of the directions in which it is distributed.
The unit of the luminous flux is the lumen (lm).

3.3.2 Lower Hemispherical Flux or Downward Flux
— The luminous flux emitted by a luminaire in all
directions below the horizontal.

.77/

/ m/ F

o = location of columns

h - mounting height of luminaires

d - width of the carriage way

p = outreach
$ = overhang
c = clearance

Fig. 1 Siting of Luminaries: Characteristic Dimensions
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3.3.3 Luminous Intensity — The quantity which
describes the light-giving power of a luminaire in any
particular direction. The unit of luminous intensity is
the candela (cd).

3.3.4 Illumination — The luminous flux incident on a
surface per unit area. The unit of. illumination is the
lumen per square metre (lux).

33.5 Luminance (at a Point of Surface and in a Given
Direction) — The luminous intensity per unit projected
area of a surface. If a very small portion of a surface has
an intensity / can del as in a particular direction and its
orthogonal projection (that is, its projection on a plane
perpendicular to the given direction) has an area D, the
luminance in this direction is I/D candelas per unit area.
The usual unit is the candela per square metre (cd/m 2 ).

3.3.6 Luminosity — The attribute of visual sensation
according to which an area appears to emit more or
less light. It is some time called brightness.

NOTE — Luminosity is the visual sensation which correlates
approximately with the photometric quantity 'luminance'.

3.3.7 Light Output — The luminous flux emitted by a
luminaire.

3.3.8 Light Distribution — The distribution of luminous
intensity from a luminaire in various directions in
space.

3.3.9 Symmetrical (Converse Asymmetrical)
Distribution — A distribution of luminous intensity
which is substantially symmetrical (conversely
asymmetrical) about the vertical axis of the luminaire.

3.3.10 Axial (Converse Non-axial) Distribution — An
asymmetrical distribution in which the directions of
maximum luminous intensity lie (do not lie) in vertical
planes substantially parallel to the axis of the
carriageway.

3.3.11 Peak Intensity Ratio — The ratio of the
maximum intensity to the mean hemispherical intensity
of the light emitted below the horizontal.

3.3.12 Mean Hemispherical Intensity — The
downward flux divided by 6.28 (2rc) (This is the
average intensity in the lower hemisphere).

3.3.13 Intensity Ratio (in a Particular Direction) —
The ratio of an actual intensity from the luminaire (in
a particular direction) to the mean hemispherical
intensity.

3.3.14 Beam — The portion of the light output of the
luminaire contained by the solid angle subtended at
the effective centre of the luminaire containing the
maximum intensity, but no intensity less than 90
percent of the maximum intensity.

3.3.15 Beam Centre — A direction midway between

the directions for which the intensity is 90 percent of
the maximum in a vertical plane through the maximum
and on a conical surface through the maximum.

3.3.16 Isocandela Curve — A curve traced on an
imaginary sphere with a source at its centre and joining
all the points corresponding to those directions in which
the luminous intensity is the same or a plane projection
of this curve.

3.3.17 Isocandela Diagram — An array of Isocandela
curves.

3.3.18 Polar Curve — Curve of light distribution using
polar co-ordinates.

3.4 Terms Relating to Luminaires

3.4.1 Street Lighting Luminaire — A housing for a light
source or sources, together with any refractor, reflector,
dispersive surround or other enclosure which may be
associated with the source in order to modify the light
distribution in a desired manner and protect the light
source from weather conditions and insects and/or for
the sake of appearance, brightness and other lighting
characteristic the source.

3.4.2 Cut-off Luminaire — Luminaire employing the
technique used for concealing lamps and surfaces of
high luminance from direct view in order to reduce
glare.

3.4.3 Semi-cut-off Luminaire — Luminaire employing
the technique for concealing lamps and surfaces of high
luminance from direct view in order to reduce glare
but to a lesser degree than cut-off luminaire.

3.4.4 Integral Luminaire — Luminaire with all its
accessories such as ballasts, starters, igniters,
capacitors, etc. However integrally with the body of
the luminaire.

3.4.5 Post Top Luminaire — Luminaire with
arrangement for mounting the same symmetrically on
the top of the column.

4 CLASSIFICATION

4.0 Ideally, both from the points of view of traffic safety
and comfort, a high standard of lighting is advisable
on all roads. The system of lighting, from good
engineering point of view as well as economy should
take into account all the relevant factors, such as the
presence of factories, places of public resort, character
of the street (whether a shopping area or a ring-road in
non-built-up area), aesthetic considerations, the
properties of the carriageway surface, the existence of
lumps, bends or long straight stretches and overhanging
trees.

4.1 The classification of lighting installations in public
thoroughfares given in 4.2 is based on volume, speed

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and composition of the traffic using them. It is left to
the local engineer to decide upon the category of the
lighting for the given road. Further amplification of
the types of thoroughfares can be had from Annex A,
wherein description of terms are given for guidance.

4.2 Types of Roads

For the purposes of this Section, roads are classified
as given in Table 1 .

5 GENERAL PRINCIPLES

5.1 Aims of Public Lighting Installations

5.1.1 Main Roads

The aim of public lighting along main roads, bridges
and flyovers (Groups A, B and D) is to permit users of
the roads at night to move about with greatest possible
safety and comfort so that the traffic capacity of the
road at night is as much equal to that planned for day
time as possible. Towards this end consideration has
to be given while designing the lighting on road
junctions and pedestrian crossings so that these can be
easily identified by the drivers.

5.1.2 Roads in Residential Areas

The principle aim of public lighting along roads in
residential areas (Group C) is to provide light along
the stretch of carriage way and footpath for safety and
comfort of road users mainly the pedestrians;
consideration has to be given to ensure that the lighting
is soft and does not cause glare.

5.1.3 Roads in City Centres

The main consideration while designing the lighting
in city centres (Group E) is proper illumination of
footpaths for pedestrians, besides the comfort of the
drivers. Also care is required to easily identify flow of
traffic and road dividers, islands, roundabouts, etc.

5.1.4 Roads with Special Requirements (Group F)

Separate considerations are required to be given for
each of the following:

a) Airports — The main consideration in
designing lighting of roads in the vicinity of
airports is to ensure that under no
circumstances, would a pilot mistake the
stretch of the road as airport landing strip at
night time. Also the lamps should not cause
glare to the pilot either while taking off or
more specifically while landing, which may
interfere with his/her judgement.

b) Railways and docks — The driver of the
railway is required to observe a number of
signals along the tracks in the course of his
work. It is necessary that none of the street
lamps cause either glare to the driver or is
mistaken by the driver for track signals.
Similar considerations are applicable to
navigators in the vicinity of docks.

5.2 Principles of Vision in Public Lighting

5.2.0 Though public lighting has to satisfy both drivers

Table 1 Road Classification

{Clause 4.2)

Group

No.

{as in IS : 1944

(Part 1 and 2)}

(1)

(2)

Description

(3)

i) A Main Roads:

Al Very important routes with rapid and dense traffic where safety, speed of traffic and comfort to drivers
are the only consideration.

A2 Other main roads with considerable mixed traffic like main city streets, arterial roads, etc.

ii) B Secondary roads — Roads which do not require lighting up to Group A standard.

Bl Secondary roads of considerable traffic such as principal local traffic routes, shopping streets, etc.

B2 Secondary roads with comparatively light traffic,

iii) C Residential and unclassified roads. These are roads not included in Groups A and B.

iv) D Grade separated junctions, bridges and elevated roads {see Note 2).

v) E Town and city centres and areas of civic importance {see Note 2).

vi) F Roads with special requirements {see Note 3).

vii) G Tunnels (roads underground).

NOTES

1 For the purposes of lighting installations, bridges are classified short or long when their lengths are less than or greater than 60 m.

2 Such areas are set apart in view of the fact that their standard of lighting is different from and higher than that described for other
groups. Group E also includes important shopping streets, boulevards, promenades and such other places which are the focus of
special activities after dark.

3 Group F includes roads in the vicinity of aerodromes, railways, docks and navigable waterways; where special lighting requirements
are to be met in addition to compliance with general principles.

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and pedestrians, it is in practice the requirements of
the drivers which are more stringent. The following
principles are considered essential [see also IS 1944
(Parts 1 and 2)].

5.2.1 Requirements of Drivers

These are as follows:

b)
c)
d)
e)
f)

Visibility of the whole of the road and its

details such as entry of side-roads, traffic

signs, etc;

Visual guidance on the alignment of the road;

Clear visibility of objects in time;

Good seeing condition by silhouette vision;

Continuity and uniformity of lighting; and

General or special lighting of signs.

5.2.2 Visual Field of the Driver

The visual field of the driver comprises, in order of
decreasing importance;

a) The carriageway;

b) The surrounds to the road, including signs; and

c) The sky, including the bright luminaires.

5.2.3 Visibility

The phenomenon of visibility is directly related to
contrast. Good contrast should always be produced:

a) between the carriageway and all objects which
indicate its boundaries; and

b) between any obstacles which may be present
and the background against which it appears;
since the characteristics of the obstacles may
vary over a very wide range, any factor which
tends to increase contrast should be exploited.

5.2.4 Glare and Visual Comfort

Glare in public lighting is generally caused by the
luminaires. Other factors that can lead to glare are
presence of undesirable large surface of high reflection
factor, specular surfaces, excessively bright shop
windows, advertisement signs or road direction signs.

5.3 Criteria of Quality

5.3.0 The following four factors contribute to the
fundamental criteria of quality of public lighting:

a) Level of luminance,

b) Uniformity of luminance,

c) Limitation of glare, and

d) Optical guidance.

5.3.1 Level of Luminance

The level of luminance should be adequate to provide
visibility which guarantee for the user a maximum of

safety and sufficient visual comfort. It is obvious that
it is the road surface luminance rather than the
illumination level which provides for an accurate
measure of the effective light in a street lighting
installation. However, with the present state of
technique and the knowledge of reflection properties
of road surfaces, the calculation and measurement of
luminance are likely to present difficulties. Reference
may be made to 8.1 regarding illumination values to
be provided on the road surfaces.

5.3.2 Uniformity of Luminance

This provides visual comfort for the driver.

5.3.3 Limitation of Glare

It is required to control the glare due to luminaires at a
value which keeps the visual discomfort below an
acceptable level.

5.3.4 Visual Guidance

A good visual guidance is required especially in long
stretches of the road and even more on complicated
intersections, roundabouts, etc. Most of the long range
guidance is offered by the luminaires.

6 DESIGN

6.1 Layout for Roads

The design, spacing and column heights are governed
by the road- width and the classification of the roads.
Typical layouts for various road width are given in
Table 2.

Table 2 Classification of Roads and
Recommended Arrangement of Columns

Width of

Group Arrangement

Column

Spacing

No.

Carriage

as in Fig.

Height

Way

(1)

(2)

(3)

(4)

(5)

(6)

9-14

2.5-3.0//

ii)

2.5 H

iii)

18-20

9-14

2.5-3.0 H

iv)

2.5 H

vi)

2.5 H

vii)

3.0 H

viii)

2.5 H

ix)

3.0 H

xi)

2.0 H

xii)

3.0 H

xiii)

3.5 H

xiv)

3.5 H

6.2 Layout for Flyovers

The design and column heights for flyovers are
governed by the layout of flyovers, height above

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_=£

L 6 TO 9 m 2A

S ■&*>

! _ „ ■ & ^ " —

i .. .— „_- " * —

L-9 TO 12 m

•12 TO 20 m 2C

H« S »H

M8 TO 20m
r 24m

2 ff' ; - ~_z^jr^~_r"_"^.~_"Lr_re"i_ri.^z<E_- — isLiirirff

Fig. 2 Standard Layouts for Roads (Six Alternatives)
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normal ground level and the width of the low level
roads. The spacing may be governed by the structural
design of the flyovers. The layout of typical flyovers
is given in Fig. 3A to 3D.

6.2.1 The layout with recommended arrangements,
column heights and spacing for various road widths
on flyover are given in the Table 3.

Table 3 Recommended Arrangement of Columns

on Flyovers

No.

(1)

Width of Group Arrangement Column Spacing
Carriage as in Fig. Height 1

Wfl y h s

(5)

(2)

(3)

(4)

(6)

i) 12 D 3C

ii) D 3B

Hi) 9 D 3A

Above the flyover road level.

2-2.5 H
2H
2H

6.2.2 The layouts with recommended arrangements,
column heights and spacing for various road widths of
low level road are given in Table 4.

Table 4 Recommended Arrangement of Columns

on Flyovers (Low Level Roads)

Width of Group

Arrangement

Column

Spacing

No.

Carriage

as in Fig.

Height

Way

(1)

(2) (3)

(4)

(5)

(6)

Over 20 D

2.5 H

ii)

10-20 D

1.5 H

iii)

Upto 10 D

2.5 H

Above low level road

6.3 Junctions

Spacing of the junction columns should be 50 to 75
percent of the normal spacing of columns on the main
roads. These columns may be installed on the traffic
islands located at the junctions.

6.3.1 The level of illumination of the junction should
be substantially different from the nearby roads. The
junctions may be lighted by either of the following
methods:

a) Higher level of illumination — In case this
scheme is adopted the level of illuminations
should be 150 percent of that of the roads.

b) Change in height of columns — The size of
columns adopted at the junction should be
higher than those adopted on roads.
Recommended sizes are given in Table 5.

c) Change in the colour of the light source — In
case the main road is lit by HPMV lamps, the

junction could be lit by HPSV lamps or vice

Table 5 Recommended Variation in Height of
Columns of Junctions

(Clause 6.3.1)

SI No. Height of Columns
on Roads

(1) (2)

Recommended Height of
Columns at Junctions

(3)

i)
ii)
iii)

7
9

High mast

6.3.2 The different types of junctions commonly
encountered are discussed below in details as they
require special consideration:

a) Simple two road junction — This type of
junction should be illuminated by locating the
columns in such configuration that the
junction is noticed by fast moving traffic. The
design would depend upon existence of traffic
islands at the junctions. Typical layout of such
junctions are shown in Fig. 4A to Fig, 4C.

b) Junction of two major roads — These
junctions would generally be provided with
traffic island at suitable locations to regulate
flow of traffic. The lighting columns could
be located in the islands to advantage.
However, if the junctions are too wide or the
islands do not permit planting of poles within
the desired spacing, special considerations are
required.

Typical layout of such junctions are shown in
Fig. 5Ato5C.

c) Multiple road junctions — The lighting of
multiple road junction would depend upon the
geographical layout of the roads, the width
of the various roads and most important, the
traffic conditions. At such junctions invariably
entry for traffic may not be permitted on all
the roads. Similarly, the traffic islands design
would change from location to location.
Special consideration will have to be given to
the design of lighting of such junction.

Typical layout of such junctions are shown in
Fig. 6Ato6D.

6A Roundabouts

6.4.0 Multiple road junctions with roundabouts are
much easier to design as a definite central roundabout
is available to locate the columns. Two types of
roundabouts are discussed below:

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NATIONAL ELECTRICAL CODE

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9 C

» €

^ff

l 3 ^4 $ ^ |j

frl

$ €

i„ +lj + I

C> C

£1 c

^ -c

& c

D £

a C

»- «

» €

9 CI

Fig. 3 Standard Layouts for Flyovers (Four Alternatives)

PART 5 OUTDOOR INSTALLATIONS

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SP 30: 2011

a) Islands which are clear or have only parking
lots — The lighting of these could be
advantageously achieved by use of high mast
as given in Fig. 7A and 7B or semi-high mast

lighting as in Fig. 7C and Fig. 7D.
b) Islands which have gardens or other
construction which would be obstruction to
line of vision of traffic — The lighting of these

-a^

• !

1 1

' 1

\#**

<§>

r r

• = Locations of Columns
Fig. 4 Simple Two Road Junctions (Three Alternatives)

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NATIONAL ELECTRICAL CODE

could be either by semi-high mast as in
Fig. 8 A or conventional lighting as in Fig. 8B
and 8C.

SP 30: 2011

6.5 Road Lighting in the Vicinity of Aerodrome

6,5. 1 General Requirements

When a proposed road lighting scheme is within 5 km
of the boundary of an aerodrome it is essential that

i i
i i
i i

/ « J s

I©

•*■

U I!

o Location of Columns
Fig. 5 Junction of Two Major Roads (Three Alternatives)

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313

SP 30: 2011

appropriate aviation authority is consulted regarding
any restrictions and precautions to be observed that
may be necessary.

6.5.2 The aviation authority may have a specific interest
in the pattern of the layout, the mounting height, the
colour and intensity, distribution of light emitted above
the horizontal so that lighting installation does not
present any danger to the air navigation. The following
points should, therefore, be kept in view while

designing lighting scheme in the vicinity of the
aerodromes:

a) The light provided in the vicinity of an
aerodrome shall be properly screened so as
to avoid any glare which may otherwise
endanger safety of an aircraft arriving and
departing from an aerodrome.

b) Lights mounted on the electric poles/pylons
shall not cause an obstruction to the arriving

Fig. 6 Multiple Road Junctions (Four Alternatives)

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HIGH

MAST

LUMINAIRE

HIGH MAST
LUMINAtRE-^

7 A

SEMI HISH-MAST.LUMINAtKES

Fig. 7 Use of High Mast, Semi-High-Mast Luminaires in Roundabouts (Four Alternatives)
PART 5 OUTDOOR INSTALLATIONS 315

SP 30: 2011

SEMI HIGH-MAST LUMINALS

SEMI HIGH-MAST LUMINAIRES

i e

-c*

*%.....

m
1 1
it

9 i

e e

srtt OK

Fig. 8 Use of Semi-Mast or Conventional Lighting in Roundabouts (Three Alternatives)
316 NATIONAL ELECTRICAL CODE

SP 30: 2011

and departing aircraft from an aerodrome in
terms of obstacle limitation specified by the
airport authorities.
c) It is particularly important to ensure that
lighting of the road cannot ever be confused
with the ground lighting of the flight paths
by the pilots. Following conditions should be
ensured:

1) In case roads are not parallel to landing
strips,

i) Uniform design and spacing of
columns is not recommended.

ii) Arrangement of mounting columns
on opposite as in Fig. 2D is not
recommended.

2) In case roads are parallel to landing strips,
no lighting should be provided on the
stretch of road near the landing strip.

6.6 Road Lighting in Vicinity of Railways, Docks

and Navigable Waterways

6.6.0 General

In lighting for roads in the vicinity of railways, docks
and navigable waterways, because of the colour of the
light source may interfere with the proper recognition
of signal system, it is essential that this interference is
avoided, but local conditions vary so widely that it is
not possible to lay down any rigid code applicable to
all circumstances.

6.6.1 Requirements

The following requirements are likely to apply in all
places where roads are so located that their lighting
installation may affect the operation of railways, docks
and navigable waterways.

6.6.2 Consultations

It is essential that prior consultation is made with the
appropriate authorities regarding any special provision
that may be necessary. These provisions should be met
in a way that is mutually acceptable so that they may
be incorporated at the design stage.

6.6.3 Colour

Where any form of road lighting is employed there is
a risk of confusion with signal light. This may
necessitate careful selection of light source, siting of
luminaires or the use of appropriate screened luminaire
at certain points and heights.

6.6.4 Glare and Masking

The position of individual light source on the road may
fall in line with signal lights and even when fairly
remote may mask them or make them difficult to
recognise or may hamper the vision because of glare.

If these cannot be avoided by re-siting, it may be
necessary to employ screening to obviate the
interference even though the colour of the light source
is not objectionable.

6.6.5 Screening

In all cases where screening of a light source is required
this should preferably be achieved by means of
properly designed luminaires and not by addition of
unsightly screens to normal luminaires.

6.6.6 Siting

If the road is bordered by water (lake, river or canal)
and if the lighting is single sided, it is recommended
that the columns be sited, if possible, on the waterside.

7 SELECTION OF EQUIPMENT

7.1 Electric Light Sources

7.1.0 The choice of source for public lighting is guided
by the following considerations:

a) Luminous flux,

b) Economy (determined by lumens/watt and
life),

c) Dimensions of the light sources, and

d) Colour characteristics.

7.1.1 The sources normally used in public lighting are:

a) Incandescent lamps,

b) Mixed incandescent and high pressure
mercury vapour lamps,

c) High pressure mercury vapour lamps with
clear or fluorescent bulbs,

d) Tubular fluorescent lamps,

e) Sodium vapour lamps,

f) Mercury-halide lamps, and

g) High pressure sodium vapour lamps.

7.1.1.1 Incandescent lamps

For new installations the employment of incandescent
lamps is very limited in practice. They are sometimes
used for residential streets when initial cost is to be
kept low. They are not usually employed in traffic
routes.

7.1.1.2 Mixed incandescent and mercury vapour lamps

These lamps may sometimes be employed in
modernising an installation to obtain higher levels
without the need for ballasts required for discharge
lamps.

7.1.1.3 High pressure mercury vapour lamps (HPMV)

These lamps have higher luminous efficacy.and longer
life than mixed incandescent and mercury lamps. These

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SP 30: 2011

are suitable for installations where colour rendering is
of lesser importance and where high powers are
needed.

7.1.1.4 Tubular fluorescent lamps

These lamps have high luminous efficacy and long life.
They are suitable for installations where colour
appearance and colour rendering are important and
where large multiple lamp luminaires are acceptable.
The choice between high pressure mercury vapour
fluorescent lamps and fluorescent tubes is in general
determined by local considerations of aesthetics and
cost of installation.

7.1.1.5 Sodium vapour lamps

The use of sodium lamps is convenient when colour
rendering is not important and when a high luminous
efficacy is desired. Their colour is sometimes useful
to provide visual guidance. It is also particularly
suitable under foggy conditions.

7.1.1.6 Mercury halide lamps

These lamps are improved versions of HPMV lamps
and having very much higher efficiencies in the order
of 80 lm/W combined with good colour characteristics.

7.1.1.7 High pressure sodium vapour lamps

These lamps are improved versions of sodium vapour
with efficiency of the order of to 100 lm/W with colour
rendering satisfactory and of dimensions suited to
fittings of small size and accurate light control.

7.2 Luminaires

7.2.0 The luminaire has double role of protecting the
light source from the weather and redistributing the
luminous flux of the source.

In the choice of the luminaire the following points
should be considered:

a) Nature and power of the source or sources;

b) Nature of the optical arrangements and the
light distribution which they provide;

c) Light output ratio;

d) Whether the luminaire is open or closed type;

e) Resistance to heat, soiling and corrosion;

f) Protection against collection of dust and
insects;

g) Resistance to atmospheric conditions;
h) Ease of installation and maintenance;
j) Presence or absence of auxiliaries; and

k) Fixing arrangements, the weight and area
exposed to wind pressure.

The influence of all these factors varies according to
local circumstances and it is difficult to recommend

one solution rather than another, but the attention of
lighting designers may be drawn to the fact that the
most economical installation can be achieved only by
the choice of the most suitable luminaire, selected
according to the relative importance of the above
mentioned factors. There is, however, one essential
characteristic of luminaires the choice of which directly
influences the quality of the lighting, that is, the general
form of its distribution curves of luminous intensity
particularly in directions near the usual directions of
vision.

7.2.1 The following general forms of light distribution
are considered according to the degree of glare which
is acceptable:

a) Post top integral luminaires,

b) Post top non-integral luminaires,

c) Cut-off integral luminaires,

d) Cut-off non-integral luminaires,

e) Semi-cut-off integral.

f) Non-cut-off tubular luminaires, and

g) Flood-lighting luminaires.

7.2.1.1 Cut-off luminaire

A luminaire whose light distribution is characterised by
a rapid reduction of luminous intensity in the region
between 80° and the horizontal. The intensity at the
horizontal should not exceed 10 cd per 1 000 1m of flux
from the light sources and the intensity at 80° is of the
order of 30 cd per 1 000 1m. The direction of the
maximum intensity may vary but should be below 65°.

The principal advantage of the cut-off system is the
reduction of glare and its use is favoured under the
following conditions:

a) Matt carriageway surfaces;

b) Absence of buildings;

c) Presence of large trees;

d) Long straight sections;

e) Slight humps, bridges; and

f) Few intersections and obstructions.

7.2.1.2 Semi-cut-off luminaire

A luminaire whose light distribution is characterised
by a less severe reduction in the intensity in the region
80° to 90°. The intensity at the horizontal should not
exceed 50 cd per 1 000 1m of flux from the light sources
(see Note) and the intensity at 80° is of the order of
1 000 cd per 1 000 1m. The direction of the maximum
intensity may vary but should be below 75°. The
principal advantage of the semi-cut-off system is a
greater flexibility in siting, and its use is favoured under
the following conditions:

a) Smooth carriageway surfaces;

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b) Buildings close to carriageway, especially
those of architectural interest; and

c) Many intersections and obstructions.

NOTE — Subject to a maximum value of 1 000 cd whatever is
the luminous flux emitted.

7.2.1.3 Non-cut-off luminaire

A luminaire whose luminous intensity in directions
making an angle equal to or greater than 80° from the
downward vertical is not reduced materially and the
intensity of which at the horizontal may exceed the values
specified for the semi-cut-off distribution, but should not
nevertheless exceed 1 000 cd. Non-cut-off luminaires are
permissible only when a certain amount of glare may be
accepted and when the luminaires are of large size and
of reduced brightness. In certain cases they have some
advantages in increasing the illumination of facades.

7.2.1.4 Inclination

Attention should be given to the inclination of
luminaires. An upward inclination which is generally
called for reasons of aesthetics, should be employed
with care. Too great an inclination of the luminaire
may modify, particularly in certain directions, the cut-
off qualities of the luminaires and in certain situations
(for example, when there are roads at several levels,
bends, roundabouts, etc) this inclination may lead to
unexpected glare.

8 GUIDELINES FOR SPECIFIC LOCATIONS

8.1 Several factors contribute to good public lighting
and those are enumerated for guidance in various parts
of IS 1944. Recommendations are made on the various
components of design of public lighting installations
and those require detailed calculations of the level and
uniformity of illumination on the road surface and of
glare. Several criteria may not be satisfied for want of
data such as characteristics of surface, etc. To get some
idea of the extent to which the installation would
perform, it may be preferable to make a temporary trial
installation of a few luminaires on a stretch of road to
be lighted.

8.2 Tables 6 to 8 give a summary of recommendations
on the various types of thoroughfares. These shall be
used as ready reckoners, though for a detailed guidance
reference should be made to the relevant part of
IS 1944.

NOTE — Recommendations for Groups C, F and G lighting
are under consideration.

9 POWER INSTALLATION REQUIREMENTS

9.1 The electrical design aspects of public lighting
installations not only take into account the illumination
principles, but also economic considerations giving
allowance for cost of electrical control units, cable
ducts, switching, etc.

Table 6 Lighting Installation in Group A and B Roads
{Clause 8.2)

SINo.

Description

(2)

Group Al

(3)

Group A2

(4)

Group Bl

(5)

Group B2

(6)

Average level of illumination on road surface, lux

ii)

Ratio minimum/average illumination ratio

0.4

0.3

iii)

Transverse variation of illumination, percent

iv)

Preferred
Type of luminaire:

Cut-off

Cut-off or
Semi-cut off

Cut-off or
Semi-cut-off

Permitted

Semi-cut-off

Non-cut-off

Mounting height, m

9-10

7.5-9

vi)

Maximum spacing of luminaire/height ratio

Cut-off^

= 3

Cut-off ■-

= 3

Semi-cut-off :

= 3.5

Semi-cut-off :
Non-cut-off :

= 3.5
= 4

NOTES

1 In Group A lighting, the level and uniformity of illumination shall be as high as possible and the glare strictly reduced.

2 In Group B lighting, greater tolerances on uniformity and glare are admitted, which may be justified by the character of the roads
and by the presence of facades .

3 Mounting heights less than 7.5 m are undesirable except in special cases, such as lighting of residential roads or roads bordered by
trees.

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Table 7 Lighting Installations in Group D Roads

(Clause 8.2)

SI No.

(1)

Description

(2)

Remarks

(3)

A. Grade Separated Junctions

1) Lighting by conventional street lighting
technique

Complex junctions:

a) General principles

b) Mounting height, m

c) Luminaire

d) Light sources

2) Lighting by high-mast lighting

a) Minimum service level value (lux)

As in IS 1944 (Parts 1 and 2)

10-12

cut-off

HPMV or HPSV lamps

b) Uniformity ratio

-'Avg

c) Height of masts, m

d) Choice of luminaire

ii) B. Bridges

1) Short bridges (<60 m)

2) Long bridges (> 60 m)

3) Bridges of historical importance

4) Parapet lighting

a) Mounting height, m

b) Separation between rows of lighting, m

c) Choice of lamps

5) Foot-bridges

a) Illumination, lux

iii) C. Elevated Roads

a) General lighting

b) Choice of luminaire

0.4

Not less than 20

see IS 1944 (Parts 1 and 2)

Normal street lighting techniques with minor adjustments
[see IS 1944 (Part 5)]

See IS 1944 (Part 5)

Special considerations apply

Not greater than 1

Not greater than 12

Tubular fluorescent lamps, HPSV lamps or other linear
sources of luminance weatherproof, dustproof, verminproof,
robust

Not less than 6

Similar to heavy traffic roads
Cut-off

9.1.1 Lamps and Luminaire s

9.1.1.1 All lamps and luminaires and other fittings used
in public lighting installations shall conform to the
relevant Indian Standards.

9.2 Cables

9.2.1 Underground cables shall be laid for power supply
to the street lamps. For roads under Groups A, B and D,
separate mains shall be laid for group control of lamps
on these roads. The street lighting cables shall be
terminated in separate junction boxes or street lighting
pillars. The pillars shall be provided with electrically

operated contactors of suitable current rating. Auxiliary
terminals of these contactors could provide facility of
return indication in case of supervisory remote control.
The contactor circuits shall be provided with externally
mounted switches for local manual operation. A typical
street lighting pillar with control circuit is shown in Fig. 9,

9.2.2 The cable circuits for each section of the roads shall
be so designed as to prevent important section of the roads
from being completely off in case of a fault on the
underground cables. For roads under Groups Al , A2 and
D, each stretch of road shall be lit by two independent
circuits, preferably emanating from two separate street

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Table 8 Lighting Installations in Group E Roads

(Clause 8.2)

Si No.

(1)

Description

(2)

Remarks

(3)

ii)
iii)

iv)

Main squares [see IS 1944 (Part 6)]:

1) Average level of illumination, lux

2) Mounting height, m
Shopping streets/promenades
Pedestrian precincts

1) Average horizontal illuminance (footway level), lux

2) Average horizontal illuminance (under canopies), lux

3) Mounting height, m

4) Luminaires

Public carparks (above ground)

1) Average horizontal illuminance, lux

2) Luminaires preferred
Pedestrian stairways/footbridges

1 ) Average level of illuminance (surface of footbridge), lux

2) Average level of illuminance (sub-ways), lux

10-15

Special considerations

20
50
5-6
Special considerations

Floodlight luminaries on high masts

6
10

lighting pillars. For junctions also, the lamps shall be
divided into at least two circuits in such a way that in
case of fault on one circuit the entire junction or a section
of it does not become completely dark.

9.2.3 In case of roads in groups A, B and D, the cables
shall preferably be terminated into the column junction
boxes by looping rather than T* joints.

9.2.4 Underground cables of suitable sizes should be
utilised for the purpose of control. The recommended
sizes of the cables for various installation are shown
in Table 9.

Table 9 Recommended Types and Sizes of Cables

Road

Minimum Size

Type of Cables

No.

Group

of Cables

mm 2

(1)

(2)

(3)

(4)

3-phase, 4-core

ii)

3 -phase, 4-core

iii)

3-phase, 4-core

iv)

Single phase/3-phase, 4-core

vi)

3-phase, 4-core

9.2.5 The junction boxes with suitable sized contactors
with independent fuses shall be provided for each phase.
The contactors shall be controlled by electrically operated
switches mounted for external manual/local operation.

9.3 Power Supply

The supply to the street lights may be either through
overhead wires or underground cables. The supply to lamps
on roads under Groups A, B and D, should preferably be
by underground cables laid specially for street lighting

purposes. In case overhead wires are employed these should
also be suitable for street lighting purposes.

9.4 Control of Street Lighting Installations

9.4.1 The contactors may be provided with additional
circuitry for remote/automatic control. Following
schemes for remote control are recommended:

a) Special relay control — This may be achieved
by special control cables laid up to the street
lighting pillar. Special relays operated by
normal supply or electronic impulses may be
provided. This scheme enables return
indication of the operation by auxiliary
contacts of the contactors.

b) Ripple control — This may be achieved by
injecting audio frequency impulse through
suitable power supply network and installing
suitable sensors at control points.

9.4.2 Automatic Control

The contactors may, alternately, be controlled
automatically by use of auto-control devices. The
following controls are recommended:

a) Photoelectric control — This may be achieved
by installing suitably mounted photoelectric
switches near the control points. The
photoelectric switch shall be mounted so as to
be free from the glare caused by headlights of
motor vehicles and protected from the weather.

b) Time Switches — The local electrically
operated contractors may be controlled through
time switches. The time switches may be
manually spring would or electrically operated.
In case of electrical operation the time switches

PART 5 OUTDOOR INSTALLATIONS

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SP 30 : 2011

HANOLE WELDED
UU Td DOOR~\ S

DOUBLE HINGED
DOORS

V GL

>%&;

V*?

m < >—

FUSEWAYS

I 1 1 u. y -

FUSEWAYS

CONTACTOR

CONTROL
UNIT

9A Typical Street Lighting Pillar

9B Inside Layout

-Or @—

N-

u. L 3 «

9C Typical Contactor Wiring (Manual)

m in
un-
ci x
»- i»
en 3

□

ROTARY

SWITCH

(INTERNAL)

ROTARY

SWITCH

(EXTERNAL)

9D Typical Wiring For Remote/Auto Control
Fig. 9 A Typical Street Lighting Pillar

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should be of electrically- wound mechanically-
operated variety so as to prevent their being
affected by variations in supply frequency.
However, these would need to be regulated
from time to time due to seasonal variations.

c) Electronic Control Switches — It should be
possible to install pre-programmed electronic
micro-processors, with one year seasonal
variations. These could be installed for each
individual lamp. With suitable design these
could also be utilised to switch off unwanted
lights after peak traffic hours are over.

8.4.3 Black-out Control — Black-out control may be
required to be adopted in case of war in vulnerable areas.
This could be achieved by either of the following schemes:

a) Remote Control — Special control cables are
laid (alternatively, use of telephone cables)
to give control impulse to group control
points. The control could then be utilised to
switch off the lamps instantaneously on
demand by civil defence authorities.

b) Ripple Control — In case special control cables
are not available, ripple control equipment could
be used with suitable sensing devices at the control
points. When the need arises, the entire area could
be switched off by ripple control impulse.

c) UHF control — Electronic relays responding
to pre-determined control frequency could be
installed at each switching point. This could
be programmed to switch off on demand by a
pre-determined control frequency signal.

9.4.4 Brown-out Control

Brown-out control is necessary in vulnerable cities with
heavy vehicular traffic at the time of war, where
complete black-out is not practicable. Even in such
cases, complete black-out would be necessary at the
time of possible air raids. Following alternatives for
brown-out control are recommended:

a) Voltage control — This could be advantageously
adopted in areas where the source of lighting is
filament lamp. Applying reduced voltage to such
lamps would automatically reduce the illumi-
nation to any desired level. In case of discharge
lamps this scheme would not be suitable.

b) Ripple control — In case ripple control is
adopted, it would be possible to programme
alternate (or any other combination) lamps to
respond to specified ripple control signals. In
case of necessity, brown-out could be effected
by switching off alternate lamps and complete
black-out by switching off all the lamps.

c) Multiple Lamp Luminaires — On main roads
the luminaires adopted could have two or more
lamps, each controlled either by different phase

or by separate ripple control signals. In case of
necessity, either one or two phases could be
switched off, or alternately alternate lamps be
switched off by suitable ripple control signals,
d) Replacement of lamps — In case of prolonged
brown-out operations, the wattage of the lamps
could be reduced by replacing the same with
lower wattage lamps. This, though could not
be achieved on short notice is recommended
in case of prolonged operations.

10 MISCELLANEOUS CONSIDERATIONS

10.1 Aesthetics

The aesthetics of a lighting installation are principally
judged by day. Half of the time, the lighting installation
serves no useful purpose; an attractive or at least a non-
disturbing daytime appearance which harmonises well
with the surroundings is, therefore, of great importance.
Aesthetic considerations should relate to the unit
formed by the luminaire and its support and the
situation in which it is placed.

Firstly, the unit formed by the luminaire and its support
should be considered. Secondly, the siting of the
luminaires in the scene may lead to unpleasant effects
even if the luminaires themselves considered in
isolation, are aesthetic.

There are no simple or universal rules for aesthetically
satisfactory design and layout since every city, town
and village has its own character and what may look
well in one place may be incongruous in another.

The points of general application are:

a) Design and siting;

b) Columns and surroundings:

c) Size and type of luminaire;

d) Form of bracket;

e) Assembly of column, bracket and luminaire;

f) Arrays of luminaires; and

g) Material and colour.

10.2 Lighting Columns as Hazards

A motor vehicle involved in an accident frequently
leaves the carriageway and the probability of this
happening increases with the speed of the vehicle. If
the vehicle collides with a lighting column the severity
of injuries to the occupants is likely to be increased.
There is evidence to suggest that the number of such
collisions decreases with the increase of distance of
the column from the edge of the carriageway.

Normally the clearance between column and
carriageway should be at least 1.5 m. Where there is a
footway close to the carriageway, the column should
be sited behind the footway. In exceptional cases a
smaller clearance may be used.

PART 5 OUTDOOR INSTALLATIONS

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SP 30: 2011

ANNEX A
{Clause A A)

TYPES OF ROADS

SI No, Term Description of Type of Road

(1) (2) (3)

i) Road

ii) Street

iii) Motorway

iv) Express road

v) All purpose
road

vi) Trunk road/
Major road

vii) Minor road

viii) Ring road

ix) Radial road

A general term denoting any
public way for purposes of
vehicular traffic

A road which has become partly
or wholly defined by buildings
along one or both frontages

A road reserved for motor traffic,
accessible only from interchanges
and on which, in particular,
stopping and parking are
prohibited. Roads of this type
should have two or several separate
and one-way carriageways

A road similar to, but lacking
some feature of a motorway, for
example:

a) not dual-carriageway

b) not fully access-controlled

c) not all intersections grade-
separated

Road usable by all traffic (includ-
ing pedestrians and cyclists)

Used to distinguish other roads
from motorways

A main route in the through com
munication system of a country

A road which has, or to which
is assigned, a lesser traffic value
than that of a major road

A road round an urban area
enabling traffic to avoid the
urban centre

A road providing direct
communication between the
centre of an urban area and the
outer districts

SI No. Term Description of Type of Road

(1) (2) (3)

x) Commercial
street

xi) Shopping
street

xii) Resident street

Street with frontages comprising
a high proportion of commercial
premises (usually unlit at night),
and with a high proportion of
heavy goods vehicles in the
traffic stream

Street with frontages comprising
a high proportion of shops or
other premises which may be lit
at night and with heavy
pedestrian (and possibly pedal
cycle) traffic

Street with the majority of
frontages comprising private
houses

xiii) Collector road/ A link between the radial or ring
Distributor road roads and the local access streets

xiv) Local street

xv) Service road

xvi) Footway
xvii) Cycle track

Street giving direct access to
buildings and land with a
minimum of through traffic

A subsidiary road between
principle road and buildings or
properties facing thereon or a
parallel road to the principal
road and giving access to the
premises and connected only at
selected points with the
principle road

That portion of a road reserved
exclusively for pedestrians

A way, or part of a road, reserved
for use only by bicycles

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SECTION 2TEMPORARY OUTDOOR INSTALLATIONS

FOREWORD

The major risks in the use of power in such installation
arise from short circuit resulting in fire accidents and
exposure to live wire resulting in shock. It is, therefore,
imperative to lay down the necessary precautions to
be observed for such installations from the point of
view of safety.

Temporary installations covered in this section are
enumerated in 5 and are classified based on the duration
of their existence in use. It may be noted that this
section basically intends to lay down additional safety
measures to be adopted in the design of temporary
installations, and the general guidelines for outdoor
installations under heavy conditions from the point
of view of selection and use of equipment given in
Part 5/Section 3 shall also be referred to.

1 SCOPE

This Part 5/Section 2 of the Code covers the
requirements for outdoor electrical installations of
temporary use.

2 REFERENCES

This Part 5/Section 2 of the code should be read in
conjunction with the following Indian Standards:

IS No.

5613 (Parti/
Sec 1) : 1985

5613 (Part 1/
Sec 2) : 1985

SP 7 : 2005

Title

Code of practice for design,
installation and maintenance of
overhead power lines: Part 1
Lines up to and including 1 1 kV,
Section 1 Design
Code of practice for design,
installation and maintenance of
overhead power lines: Part 1 Lines
upto and including 1 1 kV, Section
2 Installation and maintenance
National Building Code of India

3 TERMINOLOGY

For the purpose of this Section 2, the following
definition in addition to those given in Part 1 /Section 2
of this Code shall apply.

3.1 Temporary Installations (Outdoor) — An
electrical installation open to sky or partially covered,
intended to be used for a temporary period not
exceeding 6 months.

NOTE — In special cases, the guidelines specified in this
Section shall be applicable for longer durations subject to fresh
inspection and tests with the prior approval of the supply
authority (see also 9.3).

4 CLASSIFICATION

4.1 The temporary outdoor electrical installations
covered in this Section are those intended for the
following purposes:

a) Temporary installations for durations not
exceeding 6 months — Outdoor installations
open to sky or partially covered, erected in
the vicinity of construction sites solely for the
purposes of supplying the electrical needs of
building construction work such as lighting
and power loads.

NOTES

1 Construction site installations for very long periods
of times, where the equipment are quite similar to those
in heavy conditions shall conform to the requirements
in Part 5/Sec 3 of this Code.

2 Construction site installations are those which include
sites where the following are carried out:

a) Construction of new building;

b) Works of repair, alternation, extension or
demolition of existing buildings; and

c) Public engineering works.

The construction site installations are also characterised
by frequent modifications.

b) Temporary installations for durations not

exceeding 45 days — These include fairly

large loads such as for exhibitions, fairs, etc.

NOTE — Exhibition or fair site lighting installations of
the permanent type shall conform to the requirements
specified in Part 5/Section 1 of this Code.

c) Temporary installations for durations not
exceeding 1 days — These include
installations site of temporary nature intended
for a week long public function or outdoor
lighting installations of buildings and parts
in view of festival and other reasons.

d) Temporary installations for durations not
exceeding 24 hours — These include
temporary installations which cater to loads
for the purposes of marriages, reception,
religious and other public function, etc.

PART 5 OUTDOOR INSTALLATIONS

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SP 30 : 2011

5 GENERAL CHARACTERISTICS OF

Utilisation

Characteristics

Remarks

TEMPORA!

EtY INSTALLATIONS

slines on the assessment of characteristics

(1)

(2)

(3)

General guide

Capability of Uninstructed

Majority of

of installations in buildings are given in Part 1/Sec 8

persons

occupants say in

of this Code.

For the purposes of installations falling

an exhibitions

under the scope of this section,

the characteristics

circus fairs

defined below generally apply.

Instructed persons

Applies to

5.1 Environment

adequately advised

operating staff

or supervised by

The following environmental factors shall apply to

skilled persons

temporary outdoor installations:

Contact of

Frequent

Construction sites

persons with
earth

Environmeni

t Characteristics

Remarks

(2)

(3)

potential

Conditions of Low density

Presence of

Possibility of

External lighting

Small gatherings,

water

splashes from any

fittings,

evacuation

occupation easy

such as for

direction

construction site

during

conditions of

marriages and

equipment, etc

emergency

evacuation

similar functions

Possibility of jets of

Temporary

High density

Circus, large

water in any

installations in

occupation, difficult public gatherings

direction

parts

conditions of

inside an

Partial or total

evacuation

enclosure, etc.

covering by water

Nature of

Fire risk

Shamianahs,

Presence of

Presence of small

processed

tents

foreign solid

objects

Construction

Combustible

The nature of

bodies

Presence of dust in
significant quantity

of structure

construction
materials used in
temporary
installations may
be combustible.

Impact

High severity

Construction

demolition sites

Such as wooden

Vibrations

Medium severity

Constructions,
demolitions sites

cloth structures in
tents

Presence of

No harmful hazard

Structural design

Structures which

flora/mould

flexible or unstable

are weak or

growth

subject to

Presence of

Hazard from fauna

movement, such

fauna

(insects, birds, small
animals)

as tents,
removable

Solar

Solar radiation of
harmful intensity

partitions etc.

radiation

and/or duration

6 GENERAL REQUIREMENTS FOR

Seismic

—

Depends on the

TEMPORARY OUTDOOR INSTALLATIONS

effects

location of the

installation

6,1 Temporary installation shall in

general conform to

Lighting

Hazard from

Generally
applicable for
installations

the requirements stipulated in the relevant Section of

exposure of
equipment

Part 1 of this Code, in respect wiring of circuits,

location and installation of equipment, etc. Additional

located outdoors

requirements

are given in 7 (see also SP 7).

5.2 Utilization

The following factors of utilization apply:

6.2 If the equipment used in temporary and provisional
places of work in the open, such as building sites are
similar to those used in surface mining applications,
references shall be made to the guidelines contained
in Part 5/Section 3 of this Code.

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7 ADDITIONAL REQUIREMENTS FOR
TEMPORARY OUTDOOR INSTALLATIONS

7.1 Supply Intake Arrangements

7.L0 The type of outdoor installations will depend
on the magnitude and duration of the installation.
Depending on the availability of spare capacity, of
the existing distribution system, the supply intake
arrangements could be through either of the
following:

a) A HV feeder,

b) A HV feeder and step-down transformer,

c) A service line at voltages below 250 V, or

d) A tapping form one of the existing service
connection.

One construction site may be served by several sources
of supply, including fixed or mobile power generators.
All the circuits supplied from the same point of supply
comprise one installation and it is important to clearly
differentiate them; in particular, a single distribution
point, cabinet or distribution board shall consist of only
components belonging to one and the same installation
except for circuits for standby supplies, signalling or
control.

7.1.1 Commissioning of Substation

In case the loads at construction sites or to exhibitions,
circuses, etc, are large and the power supply authority
has no network in the vicinity of the temporary
installation that could be utilised then it would be
necessary to establish a temporary substation where
the switchgear and transformer can be installed. The
substation site shall be so selected that it is as close to
the load centre as possible.

The power supply authority's line should be brought
up to the substation in a separate enclosure. If overhead
line is laid up to the temporary substation, then the
supporting poles, conductors, materials of the line,
insulation and the method of stringing the conductors
and the mechanical strength of the line as a whole shall
conform to the relevant provisions of IS 5613 (Part 1/
Section 1) and IS 5613 (Part 1/Section 2). In case
supply at voltages above 650 V is required, a suitable
enclosure to install the switchgear and the metering
arrangement shall also be erected.

7.1.2 Power Distribution

7.1.2.1 At the origin of each installation a unit
containing the main control gear and the principal
protective device shall be provided. The main switch
shall be installed in an earthed metallic enclosure and
as close to the metering point as possible (see
also 7.2.1.1).

7.1.2.2 Means of emergency switching shall be
provided on the supply to all current using equipment
on which it may be necessary to disconnect all live
conductors in order to remove a hazard.

7.1.2.3 The enclosure or the cupboard in which the
main-switch is installed shall be such that the
equipment within shall be unaffected by the
environmental conditions (see 5.1).

7.1.2.4 The main switch on the installation shall be
connected to the point of supply by means of an
armoured cable or insulated wires and the termination
of this cable shall be adequately protected from rain
water.

7.1.2.5 The main switches shall be located at a height
not exceeding 1.5 m so as to be accessible in
emergencies.

7.1.2.6 The cable shall be laid either underground or
supported in the air. Precautions shall be taken to ensure
that this cable when laid underground is done so with
the same meticulous care as is, done for a permanent
installation. In case the cable passes underneath the
passages, it shall be laid in whole or split pipes. When
laid over ground, the cables shall either be cleated with
saddles of proper size along the walls of a permanent
structure if available, or alternatively, it shall be
supported on rigid poles. The height of the cable shall
not be less than 2 m when run inside the compound
and at least 5 m when run along or across road.
Crossing of the road shall preferably be avoided. An
independent earthing shall be established inside the
installation premises. In case overhead wires are used
in the installation they should conform to the relevant
Indian Standards mentioned in 7.1.1.

7.1.2.7 In selecting the equipment and cables, the rating
shall be decided taking the environmental conditions
into account.

7.1.2.8 The supply intake point shall be placed outside
the periphery of area which is accessible to the general
public.

7.1.2.9 In cities, towns and thickly populated localities,
it is advisable to wire up the installation with insulated
wires including for main circuits in open compounds
or running along or across roads. For main circuits,
cables shall be used, preferably laid underground.
Alternatively, they shall be cleated along the walls of
structures with proper saddles. When laid underground,
the cable shall be laid at a depth of 900 mm, covered
with sand, bricks and earth for providing mechanical
protection.

7.1.2.10 For temporary installations in cities and towns
for purposes described under 4.1(b), (c) and (d), bare

PART 5 OUTDOOR INSTALLATIONS

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SF 30 : 2011

conductors shall not be used. Only in the case of load
for purposes mentioned under 4.1(a) especially outside
cities and town bare conductors are permitted.

7.1.2.11 In cities and towns, if the premises where
temporary electric supply required is isolated, then:

a) mixed wiring of insulated and bare conductor
— overhead wiring, and

b) mixed wiring, partly underground and partly
overhead may be used.

In such an event, the underground part of the
installation and the overhead part of the installation
shall separately conform to the requirements as
mentioned in this Section.

7.2 Control of Circuits

7.2.1 Main Circuit

7.2.1.1 A device shall be provided on the incoming
cable to each supply unit and each distribution unit for
switching and isolating. With this type of arrangement
it shall be possible to switch off the supply at the intake
point or at the distribution point.

7.2.1.2 The main switch shall be adequately protected
from ingress of water. The incoming and outgoing
cable/wires of the main switch shall be firmly supported
so that cable and wire ends connected to the main
switch shall not be subjected to any mechanical force,
transmitted to it from any portion of the cables and
wires.

7.2.1.3 The main switch shall be installed on a firm
and vertical surface, which can withstand the
mechanical vibrations created at the installation site
as well as the wind pressure at the location.

7.2.1.4 There shall be adequate ventilation in the room
where main switches are installed and there shall be
operational space around the switch in accordance with
good practice. The switch room shall be accessible at
any time of the day or night to authorised persons.

7.2.2 Sub-circuit

7.2.2.1 On large temporary installations like those on
construction sites, at exhibitions, circuses, etc, the
outgoing end of the main switch shall be connected to
busbar of adequate size and various sub-circuits shall
be connected to this busbar through double or triple
pole switches, depending upon whether they are single
phase or 3 phase circuits. The switches shall be
mounted on a firm support and shall be at a height
between 1 m and 2 m from the floor level. The sub
circuit switch shall be so spaced that there shall be a
minimum clear distance of 60 mm between the
switches for ease of operation.

7.2.2.2 The outgoing wires from the sub-circuit
switches inside the enclosure shall be cleated firmly
on wooden battens or taken through conduits which
are fixed by means of saddles to the masonry wall or
wooden partition wall. The lead wires connected to
the sub circuits switches shall be suitably supported
on wall with clips and shall not be left hanging. Spans
more than 2 m shall have guide wire support.

7.2.2.3 The distribution boards the sub-circuits shall
be at an accessible height but not less than 1 m. The
distribution boards shall be fixed on firm supports or
on pole firmly planted in the ground.

7.2.2.4 Taped joints shall not be used at heights less
than 3 m. The taped joints shall be properly supported
and preferably clamped on either side of the joint so
that the joint is not subject to a strain. For series lights
used for decorative purposes no taped joint shall be
used.

7.2.2.5 A broken bulb of a lamp in a series circuit is a
risk and therefore series lamps shall not be strung or
hung at heights less than 3 m. A defective series lamp
shall not be allowed to remain in its position and shall
be immediately removed.

7.2.2.6 Installation at construction sites

The entire area where the temporary supply will be
used, shall be indicated beforehand and in case the
electric supply is required at construction site for pipe
lines, then a drawing may also be given to the electric
supply authority. On this drawing various points from
where different appliances/equipment are intended to
be used, may also be indicated. All switches, sockets
and fixed appliances shall be protected from rain by
enclosing these in cubicles. Sub-circuit distribution
board shall be installed, at a place where it is safe from
atmospheric conditions. If such a place is not available,
the distribution board shall be placed in a cubicle. In a
3 phase circuit the loads on the 3 phases shall be
balanced. At the point of supply the load on the neutral
shall not be more than 20 percent of the computed value
of the load in the phases.

7.2.3 Earthing

7.2.3.1 All appliances and equipment on temporary
installation shall be connected to a system of duplicate
earthing — one of the power supply Authority and one
local. Wherever armoured cables are used, the
armouring shall be connected to earthing arrangement
of power supply Authority. For local earthing, an
independent earth continuity wire shall be used.

7.2.3.2 For local earthing the earth electrode shall be
buried near the supply intake point. The earth
continuity wire shall be bare round conductors/strips

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and shall be a single core insulated wire and shall be
connected to the local earth plate and taken along the
cable connecting the supply intake point and the main
switch in the installation. The connection from this
earth continuity wire shall be taken to various sub-
distribution boards and terminated on a busbar. All
appliances and equipment connected to sub-
distribution board shall get their duplicate earth
connection from the earth continuity busbar on the sub-
distribution board.

8 PROTECTION AND SAFETY

8.1 The installation as a whole shall be protected
against overload, short circuit and earth leakage by
suitable protective devices.

8.2 Temporary supply is generally used at public places
and for public functions and, therefore, extreme care
shall be taken to ensure that there is no risk of any type
of hazard either from electrical shock or fire.

No flammable material shall be stored near the service
intake point or the operational area of electrical
equipment or appliances. For large public functions,
exhibitions, etc, suitable fire extinguishers shall be kept
at the supply intake point and near the main switch of
the installation.

In construction sites, protection of persons against
indirect contact shall be assured by automatic

disconnection of supply appropriate to the system
of earthing. Socket outlet shall either be protected
by residual current devices having operating current
not exceeding 30 mA or be supplied by safety extra-
low voltage or electrical separation of circuit each
socket outlet being supplied by a separate
transformer.

9 TESTING AND COMMISSIONING

9.1 Supply to all temporary installations should be
connected by a specific date for the user and therefore
the installation work meant for types of installations
in 4.1(a), (b) and (c) shall be ready at least 24 h prior
to connection of supply, so as to properly test the
installation and find the loads in different sub-circuits.
In the case of installation described in 4.1(c) there
should be a period of at least 6 h after completion of
the work and prior to connecting supply for the purpose
of testing the installation and visual inspection.

9.2 The various tests on the installation shall be carried
out as laid down in Part 1 /Section 10 of this Code.

9.3 When the specified duration of use of the
installation as defined in 3.1 is required to be extended
beyond the stipulated period of 6 months, the guidelines
specified in this Section shall be applicable subject to
fresh inspection and tests as above, with the prior
approval of the supply authority.

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SECTION 3 PERMANENT OUTDOOR INSTALLATIONS

0FOREWORD

Outdoor installations of the permanent nature require
special treatment as compared to temporary
installations of short durations (less than 6 months)
primarily owing to the continuous exposure of the
former installation and equipment forming part of it to
heavy conditions of service at site. The design and
selection of equipment and components have to take
into consideration the expected loading, operating
characteristics and cycle duty, as well as the special
and arduous environmental, operational, transportation
and storage conditions.

This Section of the Code attempts to cover the general
requirements applicable to equipment and auxiliaries
for a variety of permanent outdoor site installations
which are enumerated in 4. It is intended to provide
necessary guidelines for such installations in this
Section for the purposes of the practicing engineers
and the relevant authorities.

The general characteristics of permanent outdoor
installations are enumerated in 5. The object of this
Section is to set out the guiding principles so as to
ensure the safety of persons, livestock, property and
the proper functioning.

In the preparation of this Section considerable
assistance has been derived from IEC 60621 : 1987
'Electrical installations for outdoor sites under heavy
conditions including open-cast mines and quarries',
issued by the International Electrotechnical
Commission.

1 SCOPE

1.1 This Part 5/Section 3 of this Code covers
requirements for permanent outdoor installations, for
operations of equipment and machinery therein used
for the purposes such as:

a) Winning, stacking and primary processing;

b) Secondary processing;

c) Transport conveying;

d) Associated pumping and water supply
systems;

e) Haulage trucks;

f) Power generating and distribution systems;

g) Control, signal supervisory and
communication system; and

h) Ancillaries.

1.2 This Section does not cover temporary and
provisional places of work of durations less than

6 months for which reference shall be made to Part 5/
Section 2 of this Code.

NOTE — However this Section shall be applicable to building
sites and earth-moving sites as far as the equipment used therein
are similar to those used in surface mining application.

2 REFERENCES

This Part 5/Section 3 of this Code should be read in
conjunction with the following Indian Standards:

IS No.
1255 : 1983

Title

Code of practice for installation
and maintenance of paper
insulated power cables (up to and
including 33 kV)

10028 (Part 2) : 1981 Code of practice for selection,
installation and maintenance of
transformers : Part 2 Installation

IS/IEC 60947 Specification for low voltage

(Part 1) : 2003 switchgear and controlgear: Part 1

General rules

3 TERMINOLOGY

3.0 For the purpose of this Section, the definitions given
in Part 1 along with the following shall apply:

3.1 Operations (Electrical) — The process of
performing work through the controlled application of
electrical power. This process includes:

a) Operating — which means, switching,
adjusting, controlling and supervision,

b) Servicing — which means maintenance,
alterations, removal of faults and testing.

3.2 Operating Area — An area accessible to operating
personnel in the normal performance of their duties.

3.3 Electrical Operating Area — An area accessible
only by the opening of a door or the removal of a
barrier. The area shall be clearly and visibly marked
by appropriate signs.

3.4 Closed Electrical Operating Area — An area
accessible only through the use of a tool or key the
area shall be clearly and visibly marked by appropriate
signs.

3.5 Working Level (Bench) — That part of an open-
cut mine or quarry on which machinery and/or rolling
stock are in operation. The working level and/or
working area may change location with the progress
of operations.

3.6 Winning and Stacking Machinery — Winning
and stacking machines are used in the process of

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uncovering or detaching materials from the earth's
surface or stacking such material. These machines are
designed to be able to change location according to
operational requirements. They include the following:

a) Excavators, namely: bucket-wheel excavators,
bucket-chain excavators, draglines, shovels
and other excavators, reclaimers, ditch bunker
loaders, etc;

b) Spreaders and stackers;

c) Mobile conveyor bridges;

d) Mobile conveyors, including tripper carriages;

e) Loading stations, including hoppers and surge
bins;

f) Floating dredgers; and

g) Mobile electric drills,

3.7 Transport Conveying System — A movable or
stationary mechanical item of plant designed for the
conveying of materials continuously from one location
to another.

They include the following:

a) Belt conveyors,

b) Chain conveyors,

c) Bucket conveyors,

d) Paddle or scraper conveyors,

e) Screw conveyors, and

f) Hydraulic conveyors systems.

3.8 Primary Processing Machinery — Any
machinery necessary to prepare material won from the
earth prior to its transport to the final processing or
utilization areas.

3.9 Secondary Processing Machinery — Any

machinery necessary to process at a point remote from
the open cut or quarry, material won from the earth.

3.10 Fixed Apparatus — An apparatus or assembly of
apparatus which is permanently installed in a determined
place and which is not normally moved during or between
periods of use.

3.11 Portable Apparatus — An apparatus or assembly
of apparatus intended to be normally held in the hand
during use and which can be carried by a person.

NOTE — Cables are not included as part of apparatus.

3.12 Mobile Apparatus — An apparatus or assembly
of apparatus which is too heavy to be portable but which
is capable of being moved without discontinuity of
electric power during use.

3.13 Movable Apparatus — An apparatus or assembly
of apparatus which is too heavy to be portable, but
which is moved between periods of use, with its electric
power source disconnected.

3.14 Haulage Truck — An electrically powered
vehicle usually operating on rubber tyres used for
transport of materials and which may have a self-
contained or external power supply.

3.15 Movable Railway System — A railway system
which is designed to be movable to another location
without dismantling.

3.16 Self-Contained Power Supply — An electrical
installation in which the generation and utilization
plants are housed within the same structure.

3.17 External Power Supply — An electrical
installation in which the generation and utilization
plants are not housed within the same structure.

3.18 Exposed Conductive Part — A conductive part
which can be touched readily and which normally is
not live but which may become live under fault
conditions.

NOTE — Typical exposed conductive parts are walls of
enclosures, operating handles, etc.

3.19 Earthable Point — That point of the power
system, for example, of the transformer and/or
generator, which would be connected to earth if the
system were to be earthed.

NOTE — The earthable point may be the neutral point
depending on the type of power system.

3.20 Insulation Monitoring and Warning Device —

A device which causes a signal to be given in the event
of reduced insulation resistance to earth.

3.21 Movable Distribution Cable — An insulated
cable that may be moved from time to time according
to the operation without necessarily following the
movements of the machinery.

3.22 Drum Cable — An insulated cable specially
designed to be frequently reeled on and off a cable
drum or reeler mounted on a mobile machine.

3.23 Trailing Cable — An insulated cable specially
designed to be towed by a mobile machine.

3.24 Overhead Traction (Trolley) Wire — An
electric line having bare conductors used for supplying
vehicles (for example, locomotives) by means of a
collector or pantograph.

3.25 Overhead Traction Distribution Line (Feeder)
— An electric line having bare conductors used for
the interconnecting line between the power source and
traction wire.

3.26 Overhead Collector Wire — An electric line
used for supplying moving machinery, such as a
reclaimer, by means of a collector.

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3.27 Overhead Distribution Line (Feeder) — An
interconnecting electric line between distribution
substation and load point.

3.28 Return Conductors — Conductors (which may
be rails) used for carrying the return current.

3.29 Safety Circuits and Devices — Circuits and
devices designed to prevent danger to personnel or
livestock and damage to plant in the event of abnormal
or unintentional operation.

4 TYPES OF PERMANENT OUTDOOR
INSTALLATIONS

The types of permanent outdoor installations covered
by this Section are given in 4.1. The general
characteristics and service conditions enumerated in 5.1
cannot be made uniformly applicable to all such
installations. Depending on the site conditions and the
nature of the operation involved, a judicious estimate
has to be made of the environmental factors that
influence the performance of the installation.

4.1 The following are the types of permanent outdoor
installations covered by this Section:

a) Open-cut or open-cast mine — An open air
site for the extraction of materials or minerals
such as coal, bauxite, iron-ore, etc.

NOTE — Underground mines are excluded from the
scope of this Section. However surface installations of
underground mines are covered by this Section, to the
extent that the operations therein are identical with those
described in 1.1.

b) Quarry — An open air site for the extraction
of materials such as limestone, gravel, clay,
etc.

c) Dockyards — Includes loading and unloading
areas, container terminal, railway yards, repair
docks, passenger berths, jetty's, etc.

d) Airport aprons — A defined area on a land
aerodrome, intended to accommodate aircraft
for the purposes of loading and unloading
passengers, mail or cargo, refuelling parking
or maintenance.

e) Railway marshalling yards — A yard with
facilities for receiving classifying and
dispatching railway rolling stock.

5 GENERAL CHARACTERISTICS OF
PERMANENT OUTDOOR INSTALLATIONS

The design and the selection of components shall be
on the basis of expected loading, operating
characteristics and cyclic duty taking into consideration
the protection required in special and arduous
environmental, operational, transportation and storage
conditions.

5.1 Some of these conditions, are listed below which
may differ from their normal values:

a) Altitude;

b) Low and/or high ambient temperature;

c) Supply voltage variations;

d) Supply frequency variations;

e) Insecure power supply and transients;

f) High or low humidity;

g) Environment (dust, wind pressure, marine
atmosphere, etc);

h) Flammable and/or explosive material/or

atmosphere;
j) Vermin, including rodents or other small

animals;
k) Localities prone to natural calamities; and
m) Ecological impact.

6 RULES FOR EQUIPMENT AND AUXILIARIES

6.0 General

6.0.1 Exchange of Information

Before ordering electrical equipment for outdoor sites,
information regarding the duties, location and
installation conditions under which they would operate,
should be gathered by the engineers responsible for
their procurement, installation and maintenance so that
the electrical equipment or apparatus is procured to
suit those conditions. Necessity for special measures
may be decided in consultation with all concerned.

6,0.2 Relevant Standards

The electrical specifications of all components shall
be not less than that required by the relevant Indian
Standard.

6.0.3 Materials

Materials used in component construction shall be
appropriate for the environmental conditions, including
temperature, altitude, moisture, etc.

6.0.4 Protection

Protection shall be provided against damage and/or
overheating during normal operation or in expected
fault conditions.

6.0.5 Operating Conditions

Components shall be designed to meet such conditions
as vibration, acceleration, deceleration, slewing and
angles of inclination (tilting and mounting) which may
occur under expected operational conditions.

6.0.6 Site Conditions

Components shall be installed so that design features

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such as cooling systems shall not be impaired by
external factors such as position, blocking of ventilation
ducts, hostile environment, etc.

6.0.7 Combustible Materials

If combustible material (for example, gas, dust or
liquid) is present in such quantity as to create a hazard
and contact is possible between any exposed part of
the component and the combustible material, the
temperature of the exposed part shall not exceed the
limits specified in Part 7 of this Code.

6.0.8 Noise Limitations

Consideration shall be given in the design to limit the
noise level in accordance with local rules.

6.1 Selection of Equipment and Ancilfiaries

6.1.1 Rotating Machines

Rotating machines used in applications where high
acceleration, overspeed, reversing or braking may be
employed shall be so selected that they are capable of
withstanding the expected stresses on parts such as
rotor windings or cages, stators, stator end windings,
shafts and couplings, rotating machines shall be so
located or guarded to prevent inadvertent contact with
moving parts.

6.1.2 Transformers
Transformers shall be so selected that:

a) the bracing of the core, coils, internal leads
and the tank of transformers on mobile and
movable installations are capable of
withstanding vibrations;

b) they are totally enclosed; and

c) dry type transformers including cooling
system are protected against harmful ingress
of dust.

The following additional protective measures are
suggested from fire:

a) Use of dry type transformers,

b) Use of flame-retardant cooling medium, and

c) Protective measures as specified in IS 10028
(Part 2) for transformers with flammable
cooling medium.

Adequate precautions shall be taken to prevent spillage
of the cooling medium causing pollution.

6.1.3 Static Converters

The following precautions are recommended:

a) Protection against harmful effects of over-
voltage, and transient over-voltage
conditions;

b) Protection against interference with
communication or electrical control
equipment;

c) Protection against spurious operation due to
electrical coupling with other apparatus;

d) Protection against interaction between
earthing systems of the input, output and
control circuits;

e) Feedback supervision, where necessary; and

f) Measures to limit harmonics.

6.1.4 Switching Devices

The following measures are recommended for
switching devices for outdoor sites:

a) Selection of proper design that no uninten-
tional switching may be caused under
expected operational and risk conditions;

b) Ensuring, where required suitable means to
enable isolators to be locked;

c) Suitable labelling of switching devices which
are not meant for interrupting load or fault
currents; and

d) Suitable installation precautions to prevent
hazards to personnel from electric areas,
automatic movement of the mechanism,
etc.

6.1.5 Cables

6.1.5.1 Phase conductors

Selection of phase conductor size should take into
consideration the expected load current, short-circuit
current and duration of fault, voltage drop and the
mechanical strength required for the expected method
of handling. The voltage drop should be calculated for
both starting and maximum load conditions. Where
supplying cyclic loads, the current-carrying capacity
should be based on the long time (for example, 10 min)
rms current expected.

6.1.5.2 Protective conductor

All multicore cables of the movable distribution, drum
and trailing types, shall contain a protective conductor.
In high voltage systems, special measures shall be taken
to guard against deterioration of the earthing circuit.
This may be achieved by either:

a) monitoring the protective conductor against
increase in resistance by the use of pilot cores,
high frequency monitoring or other means,
or

b) cables should be specially designed and used
in accordance with the requirements of
relevant Indian Standard whether or not they
are used on a drum.

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The protective conductor may be in the form of core(s)
and/or screen(s).

For certain classes of movable distribution cables, the
armouring may, subject to the requirements of 6.1.5,3,
form the protective conductor.

6.1.5.3 Armouring as protective conductor

Where the cross-sectional area of a single composite
strand of the armouring is greater than 6 mm 2 , the
metallic armouring of a movable distribution cable may
be used as a protective conductor provided that the
security against breakage of the armouring (taking into
account strength, elongation, lay, etc) is at least equal
to that of all the conductors; and provided that the
armour conductivity is at least equal to that of a
protective conductor of the required nominal cross-
sectional area which would otherwise be required.

6.1.5.4 Limiting temperatures under short circuit

Cables shall be selected so as to ensure that the
maximum allowable conductor temperature,
considering the type of insulation, is not exceeded
under expected short-circuit fault conditions.

6.1.5.5 Protection against partial discharge

For flexible cables having nominal voltages greater
than 3.8/6.6 kV, measures shall be provided to
minimize internal partial discharge or to render such
effects harmless (for example, field gradient control).

Suitable protective measures shall be applied to reduce
the touch and step voltages. Such measures may consist
of:

a) metallic screens, or

b) substantial semi-conductive elements in
contact with the protective conductor.

6.1.5.6 Semi-conducting layers

Where cables are fitted with substantial longitudinal
semi conducting layers for the purpose of providing a
current path to the protective conductor in the event of
a fault, the resistance between the semi conducting
element and the protective conductor should be tested
to ensure that it is suitable to carry the prospective fault
current.

6.1.5.7 Provision of screens and/or armouring for
cables above 1 000 V

Where flexible cables are handled manually while
energized, they shall have metallic screens and/or
armouring or shall be provided with conducting
elastomeric screens of substantial cross-sectional area
and so placed as to limit the touch and step voltages
that may arise in the event of a cable fault.

In cases where cables are handled only by means of
special insulated tools, these requirements shall apply
only for voltages above 3.8/6.6 kV.

6.1.5.8 Identification of protective conductor
Unless otherwise required, the following applies:

a) For cables rated at up to and including 1 000
V, in which the protective conductor is
insulated, such insulation, or outer taping,
shall be distinctly and indelibly coloured
green and yellow also (see Part 1 /Section 4
of this Code) over its whole length so that in
any 15 mm length one of these colours shall
cover at least 30 percent and not more than
70 percent of the surface, the other colour
covering the remainder of the surface; and

b) For cables rated at above 1 000 V, in which
the protective conductor is insulated, such
insulation or outer taping shall at least be
identified at each end by the green/yellow
colour combination applied in accordance with
the foregoing paragraph. Suitable
supplementary identification may also be used.

6.1.5.9 Partial discharge performance

For cables rated at above 3.8/6.6 kV each production
length (minimum length 150 m) of movable distribution
cable, drum cable and trailing cable shall be tested by
the cable manufacturer for partial discharge.

6.1.5.10 Terminations of flexible cables

Flexible cables shall be terminated in such a way that
their ends are not under stress or under tension effects,
and that excessive bending and compressing are
avoided.

6.1.5.11 Power cable twist limitation

Where the normal mode of operation of the machine
requires infrequent rotation through an arc of up to
360° in either direction, the distance between the
clamping supports of the cable shall be not less than
50 times the largest cable diameter in the cable run.
Where the normal mode of operation of the machine
requires frequent rotation through an arc of up to 360°
in either direction, the distance between the clamping
supports of the cable shall be not less than 100 times
the largest cable diameter in the cable run. Where cables
designed specially for this purpose are used, the above
ratios may be reduced to 25 and 50 times respectively.

6.1.5.12 Sheathing

Cables may be laid directly on or in the ground
provided that the outer sheath is designed for the
operating conditions.

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Cables having extruded metallic sheaths, for example,
cables with lead alloy or aluminium sheaths or mineral-
insulated metal-sheathed cables, shall not be used
where fatigue may occur, due to vibration, frequent
handling or ground movement.

6.1.5.13 Segregation of power and control cores

a) Single-core cables — Single-core cables
which are installed in a common duct, conduit
or sleeving may be used for several circuits,
both power and control.

All such cables (except bare earthing
conductors) shall be insulated for the
maximum voltage applied to any cable in the
duct, conduit or sleeving.
When using single-core cables for alternating
current circuits, all conductors of a given
circuit shall follow the same magnetic path
to neutralize the resultant magnetic flux.

b) Multicore cables — For voltages up to and
including 1 000 V, multicore cables may be
used for several circuits, both power and
control.

For voltages above 1 000 V, the only control
core(s) which may be included in a multicore
cable, shall be the earth continuity check pilot.
Multicore cables containing power and
control cores shall comply with the following
requirement as appropriate:

1) Any cable containing pilot, control and,
supervisory cores shall have such cores
insulated from all other conducting ele-
ments of the cable;

2) Cables operating at above 1 000 V in an
unearthed system shall have either
metallic screens or individual conductive
rubber screens separating the power cores
from the pilot core(s);

3) Cables operating at above 1 000 V in an
earthed system shall have metallic
screens separating the power cores from
the pilot core(s); and

4) Cables operating at up to and including
1 000 V shall have pilot, control or
supervisory cores separated from power
cores by conductive rubber screens if on
an unearthed system or metallic screens
if on an earthed system. Alternatively, for
either system, the pilot, control or
supervisory cores shall be insulated to a
voltage level equal to that of the power
cores.

c) Composite multicore cables on reeling drums
— Multicore cable which contain power, pilot,

control or supervisory cores may be used for
reeling drum applications, subject to the
voltage limitations given in (b) above
provided that the cable is specially designed
for such reeling duty.

6.1.5.14 Separation of cables in racks

Where power and control cables, multicore and single-
core are used on a common rack, tray or duct, the
degree of mutual interference shall be considered.

6.1.5.15 Bending radius for flexible cables over 25 mm
diameter

The recommended minimum bending radius for
flexible cables during installation and handling in
service is six times the cable diameter for cable not
constructed in accordance with 6.1.5.5(a) or (b), and
eight times the cable diameter for cables which are
constructed in accordance with 6.1.5.5(a) or (b).

6.1.6 Cable Connectors

6.1.6.1 Use of plug/socket connectors

Where plug and socket connectors are used at voltages
above 1 000 V, measures shall be taken to prevent the
plug from being engaged with, or disengaged from,
the socket while the circuit is energized.

The measures shall consist of one or both of the
following:

a) The provision of isolating switches which are
interlocked with the plug/socket so as to
prevent connection or disconnection while the
circuit is energized and to prevent switching
the circuit when the plug/socket connection
is incomplete.

b) The provision of protective conductor
monitoring by means of either a pilot core,
by high frequency monitoring, or by other
means.

The measures under (b) are intended as a safety feature
and should not be used for normal isolation purposes.

6.1.6.2 Use of bolted plug/socket connectors and bolted
connections

Where bolted plug/socket connectors or bolted
connections are used, interlocking is not required
provided suitable and adequate operational procedures
are implemented.

6.1.7 Control Circuits and Control Devices

Control circuits and control devices shall not
automatically reset after tripping unless resetting of
the control device either does not cause automatic
restarting of the device or there is no hazard to
personnel created by automatic restarting or fire.

PART 5 OUTDOOR INSTALLATIONS

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SP 30 : 2011

For unearthed control circuits, measures shall be taken
to limit the leakage and capacitance currents that they
shall not exceed 70 percent of the drop-out currents.
For unearthed control devices, an insulation monitoring
device shall also be provided for safety.

6.1.8 Safety Circuits and Safety Devices

Any safety circuits shall incorporate fail-safe principle
as far as reasonably possible. Some of the principles
suggested are:

a) closed circuit principle,

b) proving function operation principle, and

c) fail-safe principles with solid state switching
devices.

7 GENERAL RULES FOR PROTECTION IN
OUTDOOR INSTALLATIONS

The general rules for protection for electrical
installation inside buildings, as enumerated in Part 1/
Section 7 of this Code are applicable for outdoor
installations of permanent nature covered by the Scope
of this Section. The additional requirements applicable
for permanent outdoor installations are given in the
following clauses.

7.1 Protection Against Direct Contact

7.1.1 Complete Protection by Means of Barriers or
Enclosures

7.1.1.1 The minimum electrical clearances in air
between field installed bare conductors and between
such conductors and earthed parts (such as barriers
and enclosures) shall be in accordance with Table 1
or 2.

NOTES

1 These tables need not apply within electrical apparatus wiring
devices or manufactured assemblies nor when the installation
is covered by other sections of this Code.

2 Tables 1 and 2 take into consideration the fact that the system
voltage may vary up to 20 percent from the rated operating
voltage.

3 Tables 1 and 2 may be used to indicate clearance distances
between conductors and earth in a TN or TT system by using
the phase-to-earth voltage.

4 These minimum clearance distances in Tables 1 and 2 do not
take into consideration such factors as creepage distances,
different voltage levels in the same area nor extreme
environmental conditions, etc.

7.1.1.2 All live parts shall be inside enclosures or
behind barriers providing at least the degrees of
protection in accordance with Table 3.

7.1.1.3 Barriers and enclosures shall be firmly secured
in place, and taking into account their nature, size and
arrangement, they shall have sufficient stability and
durability to resist the strains and stresses likely to
occur in outdoor conditions.

7.1.1.4 Where access to the installation is necessary
by removal of barriers, opening of enclosures, etc, these
shall:

a) necessitate the use of key or tool; or

b) involve provision of an interlocking device
such that the removal, opening or withdrawal
without the use of a key or tool necessitates
previous switching off of all live parts; or

c) ensure automatic disconnection when
removal, opening or withdrawal without the
use of a key or tool is attempted.

7.1.2 Partial Protection by Placing Live Parts Out of
Reach {see Table 3)

7.1.3 Partial Protection by the Provision of Obstacles
{see Table 3)

7.2 Protection Against Indirect Contact

7.2.1 The provisions of Part 1/Section 7 of this Code
shall apply.

8 REQUIREMENTS FOR PERMANENT
OUTDOOR INSTALLATIONS

8.1 Winning, Stacking and Primary Processing
Machinery

8.1.1 Mounting of Components

For the mounting of motors, limit switches, sockets, etc,
special protective connections to the structural parts of
the installation are not required if the connecting surfaces
between the electrical equipment housing and structural
parts provide an adequate conducting area. In such cases,
the normal mounting bolt or screw connection is adequate.

This is also applicable for the mounting of all types of
electrical equipment in cubicles, termination boxes, etc.

Where the equipment is required to operate under
corrosive atmospheric conditions or extreme vibrating
conditions, a separate protective conductor shall be
connected to motors, limit switches, etc.

8.1.2 Off -Board Mobile and Movable Auxiliary
Equipment

For mobile and movable off -board auxiliary equipment
(such as welding equipment, vulcanising transformers,
etc.) where the protective conductor is not monitored
nor visible, a visible main equipotential bonding
conductor shall be provided between such auxiliary
equipment and plant.

8.1.3 Insulation Monitoring Device for IT Systems

In the case of an IT system, an insulation monitoring
device is not required for power circuits which are
supplied by a power source from within the machine,

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Table 1 Clearance Distances for Indoor Installations

(Clause 7.1.1.1)

SP 30: 2011

Maximum rms value of rated operating voltage, kV 1

Minimum distance for installations subject to 40
overvoltages, mm

Minimum distance for installations protected 40
against overvoltages or connected to cables, mm

110

115

215

325

520

700

1 100

160

270

380

520

950

Table 2 Clearance Distances for Outdoor Installations

(Clause 7.1.1.1)

Maximum rms value of rated operating voltage, kV

Minimum distance for installations subject to
overvoltages, mm

Minimum distance for installations protected 150
against overvoltages or connected to cables, mm

110

150

220

150

215

325

520

700

1 100

1550

2 200

160

270

380

520

950 1 350

1850

Table 3 Minimum Protection Against Direct Contact by Barriers or Enclosures
(Applicable to Live Parts Only)
(Clauses 7.1.1.2, 7.1.2 and 7.1.3)

No.

(1)

Voltage Band

(ac) *
(2)

Within Operating Areas

(3)

Within Electrical Operating

Areas
(4)

Within Closed Electrical
Operating Areas

(5)

50<f/<1000V

ii)

Complete protection IP2X 1) or IP4X
for top surfaces or barriers or
enclosures which are readily
accessible. This applies in particular
to those parts of enclosures which
might serve as a standing surface

See Note 1

U > 1 000 V Complete protection IP5X within

arm's reach

Partial protection IP2X beyond arm's
reach

U = rated voltage of the installation between lines

Partial protection IP1X 1} if U
< 660 V or no simultaneously
accessible parts at different
voltages are situated within
arm's reach

Complete protection IP2X if
£/>600V or IP4X if
U > 660 V for top surfaces or
barriers or enclosures which
are readily accessible

This applies in particular to
those parts of enclosures
which might serve as a
standing surface

See Note 1

Complete protection
within arm's reach

Partial protection
beyond arm's reach

No protection IP0X if U < 660 V

Partial protection IP0X° if
£/>660V or no simultaneously
accessible parts at different voltages
are situated within arm's reach

See Note 1

IP5X° Partial protection IP1X 1}

IPlX n

NOTES

1 The use of floor plug and socket connector is not precluded but such sockets shall be covered when not in use.

2 For details on IP classifications, see IS/IEC 60947 (Part 1). As used in the present standard, the IP classification is intended to
specify only the degree of protection required to protect persons from contact with live parts. Additional protection may be required
for protection from contact with moving parts or to prevent ingress of solid foreign bodies, such as dust.

3 In the case of dc voltages, the voltage bands in the above table may be increased in the ratio of 1 : 1.5, namely, up to 1 500 V and
above.

]) For electrical operating areas and closed electrical operating areas, protection equivalent to IP1X is also considered to be achieved by
placing out of reach or by the interposition of obstacles, for example, by means of protective barriers or handrails.

PART 5 OUTDOOR INSTALLATIONS

337

SP 30 : 2011

such as by a transformer having electrical isolated
windings or by a generator or storage battery.

8.1.4 Insulation Monitoring Devices for Vulcanising
Heating Platens

In IT systems, insulation monitoring devices are not
required for vulcanising heating platens where the
power circuit is supplied from a transformer having
electrically isolated windings.

8.1.5 Electric Hand Tools
Under consideration.

8.1.6 Electric Hand Lamps
Under consideration.

8.1.7 Drives

The following recommendations apply to drives with
a periodic or cyclic duty as well as to certain other
drives with a continuous duty.

8.1.7.1 Effect on voltage levels

The effects of equipment starting and of the duty cycle
on voltage levels, which may result in damage or the
malfunction of equipment, shall be taken into
consideration to ensure the safety of personnel and
equipment.

8.1.7.2 Supply systems

The effect of load fluctuations on the supply system
shall be considered, taking account any restrictions
imposed by the electricity supplier.

8.1.8 External Power Supply Systems

8.1.8.1 System design

The supply system shall meet the requirements of cyclic
or periodic loads, motor starting, and inherent ac motor
oscillations due to transient load changes. For
protection requirements, see 7.

8.1.8.2 Overcurrent protection

Overload and short-circuit protection for transformers,
cables, etc, shall take into consideration the starting
requirements and cyclic nature of the load.

8.1.8.3 Automatic reclosing or transferring

Where regeneration may delay the operation of
undervoltage devices, automatic reclosing or
transferring devices should not be used in the power
distribution system unless such device has sufficient
time delay to allow motor disconnection, the device is
fitted with 'out of step' protection, or the combination
of supply system and motor design characteristics is
such as to permit automatic re-energisation.

8.1.8.4 System voltage

It is important that the equipment manufacturer and
user mutually understand whether the voltage specified
is under no-load or full load conditions.

8.1.9 Self-Contained Power Systems

8.1.9.1 System design

The power generation systems shall meet the
requirements of motor starting, regeneration, peak load,
rms load and frequency stability.

8.1.9.2 Eire protection

Consideration should be given to the need for special
and/or additional fire protection due to the fuels used
(see 6).

8.1.9.3 Earthing

When the supply of electrical energy is self-contained
within stationary, mobile, or movable items of
equipment and there is no external supply, such
equipment need not be connected to the general mass
of the earth.

8.1.9.4 Supply to off -board equipment

When power is supplied to off-board mobile and
movable equipment conditions given in 8.1.2 are
applicable.

8.1.10 Cable Types
Under consideration.

8.1.11 Control Circuits and Control Devices

8.1.11.1 Shock vibration and voltage fluctuations

The effect of shock, vibration or voltage fluctuations
on control devices shall be taken into consideration,
ensuring that safety of personnel and equipment is not
endangered by inadvertent operation of control
devices.

When mechanically latched control devices are used
and re-energisation following loss of supply power
would endanger personnel or equipment, means shall
be provided to automatically trip the latched control
device on loss of supply power. The device shall also
be tripped on operation of protective devices.

8.1.11.2 Synchronous motor control

a) Automatic field removal — Where
synchronous motors are used to drive any part
of the installation, automatic motor field
removal on disconnection is required.

b) Automatic field excitation control — Where
synchronous motors are used to drive periodic

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or cyclic loads, an automatic field excitation
control is recommended.

c) Power loss protection — Where synchronous
motors are used to drive loads which may be
regenerative, means shall be provided to trip
the motor starting switch or incoming line
switch upon loss of power supply. Frequency
sensitive devices are recommended. When
automatic reclosing or transferring devices are
used in the distribution system, conditions
given in 8.1.8.3 are applicable.

8.1.11.3 Stop control

The devices described in the following paragraphs shall
not be used for purposes of isolation or immobilisation
to allow work to be carried out on parts which would
otherwise be electrically energised or moving:

a) Stop control circuits — The circuits of stop
control and of other safety protection devices
should be as simple, reliable and direct acting
as is practical.

b) Location of stop controls — A stop control
shall be located near each start control, except
for lift call control. Additional stop controls
may be provided.

c) Locking of stop controls — Where required,
provision shall be made to guard against
unauthorised starting. Acceptable methods
include locking of stop controls in the 'off'
position or ensuring that only the person
operating the stop control has access to the
start control.

d) Pullwire stop controls — Stop controls
operated by a pullwire shall be arranged so
that a pull on the wire in any direction will
stop the controlled equipment. The stop
controls shall be of a type in which the
contacts are opened by a positive mechanical
action and can only be reclosed by a further
mechanical action.

8.1.11.4 Interlocking of start controls

Where equipment can be started from more than one
location, the control system shall permit operation from
only one nominated location at anyone time, unless
start-up alarms are used, the equipment is in sight from
all starting locations, or the equipment is guarded
against inadvertent access.

8.1.12 Emergency Stopping and Emergency Devices

8.1.12.1 Emergency stopping

Disconnection of power or other equally effective
means shall be provided for stopping the drive under
emergency conditions. The power disconnect device

may be a manually or remotely operated power circuit-
breaker, contactor, etc.

Emergency stopping can be accomplished by means
other than disconnection of power, provided that such
means otherwise comply with the intent of 8.1.11.3.
For example, when rotation conveners are used,
disconnection of the external excitation is permitted if
protection against self excitation is provided.

8.1.12.2 Emergency devices

Where the cut-out devices are actuated remotely they
will be arranged as series tripping system. However,
shunt tripping devices may be used providing the
tripping device and its stored energy tripping supply
are monitored and regularly maintained.

Emergency devices may be arranged to operate
simultaneously in a number of different circuits. A
number of emergency devices may be arranged in
groups; each group may operate in single or multiple
circuits.

Where several circuits are divided the respective
contact elements shall be connected in series. However,
shunt tripping systems may be used providing the
abovementioned conditions are maintained.

The emergency device may use remote control systems,
for example, audio-frequency of time-multiplex
operations, providing at least the same protective
measures as for the above devices are applied to ensure
positive and reliable operations. However, the
simultaneous existence of two or more faults within
the remote controls system need not be expected.

8.1.13 Provision for Supply Isolation

A means of mains supply isolation shall be provided
to isolate the power circuits from the equipment or parts
thereof inclusive of control and motor circuits.

However, separate means of isolation may be provided
for control circuits, which may remain energised after
disconnection of power circuits, provided special
measures for the safety of personnel and equipment
have been implemented.

8.2 Secondary Processing Machinery

Under consideration.

8.3 Transport Conveyor Systems

8.3.1 Mounting of Components {see 8.1.1)

8.3.2 Equipotential Bonding Conductor and
Conductivity of Structural Parts

Where electrical equipment supplied at a voltage in
excess of 50 V is mounted on a conveyor structure
and the cable to the equipment does not include a

PART 5 OUTDOOR INSTALLATIONS

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SP 30 : 2011

protective conductor, an equipotential bonding
conductor shall be provided to the electrical equipment
unless the structural parts of the conveyor are
mechanically fastened and/or electrically bonded
together. The conductivity of the metallic structural
parts of the conveyor and its fastenings shall be at least
equal to that of the otherwise necessary equipotential
bonding conductor.

8.3.3 Off-board Mobile and Movable Auxiliary
Equipment (see 8.1.2)

8.3.4 Insulation Monitoring Device for IT Systems

(see 8.1.3)

8.3.5 Insulation Monitoring Devices for Vulcanising
Heating Platens (see 8.1.4)

8.3.6 Electric Hand Tools
Under consideration.

8.3.7 Electric Hand Lamps
Under consideration.

8.3.8 Cables

8.3.8.1 General

Where cables without semi conductive sheaths,
metallic screens or armouring are suspended from
structures or frames of movable conveyors, such
structures and frames shall be considered as extraneous
conductive parts and shall be included as part of the
whole plant in the design of the protective measures
against indirect contact, that is, by ensuring that all
metallic parts are linked together.

8.3.8.2 Power supply cables
Under consideration.

8.3.9 Stop Controls

The devices described in the following clauses shall
not be used for purposes of isolation or immobilisation
to allow work to be carried out on parts which would
otherwise be electrically energised or moving.

8.3.9.1 Stopping sequence

The operation of a stop control on a conveyor shall
stop that conveyor and:

a) all upstream conveyors to a controlled loading
point,

b) cause the material from all upstream conveyors
to be diverted to an alternative route,

c) initiate braking to stop the conveyor in safe
time, and

d) prevent run-back.

On very long conveyor systems, however, the operation
of a stop control within one stop zone need not stop all
upstream conveyors beyond that zone, provided that
the conveyor upstream of the zone is proved to be
unloaded, such as by sensors.

Although the stop control may be reset automatically,
restarting shall be initiated manually.

8.3.9.2 Location of stop controls

Stop controls shall be provided. It is recommended that
stop controls be located at the head and tail ends of a
conveyor and that pullwire stop controls be used along
the length of the conveyor. All accessible points along
the pull wire operated stop control are considered as stop
controls. Where individual stop controls are used, they
shall be located not more than 15 m from any accessible
point along the conveyor. Stop controls shall be accessible
from any side of a conveyor to which there is access.

NOTE — Manually operated stop controls may also provide
the function of an emergency stop.

8.3.10 Stopping of Downhill Conveyors

Under consideration.

8.4 Pumping and Water Supply Systems
8.4.1 Deep -we 11 Type Pumps

8.4.1.1 Risers as protective conductors

Where a continuous metallic riser pipe is fitted between
the motor and the well head, no protection conductor is
required between the motor and the protective conductor
connected directly to the fixed riser provided that:

a) the supply cable is terminated close to the well
head,

b) the conductivity of the metallic riser (stand
pipe) and the connections (couplings) shall
be at least equal to the conductivity of the
protective conductor which would otherwise
be necessary, and

c) personnel do not have access down the well.

8.4.1.2 Continued operation after first earth fault

Operation may continue after the first earth fault only
when all of the following conditions are met:

a) An IT system is used,

b) Personnel do not have access down the well,
and

c) Equipotential bonding is provided.

NOTE — Electrically initiated explosive devices should
not be stored or used in the vicinity of such installations
as hazards may exist due to fault currents flowing in the
ground when systems continue to operate following the
first earth fault.

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8.4.1.3 Equipotential bonding

An equipotential bonding conductor shall be installed
between the main earth terminals of the supply and the
well head(s), where the conductor shall be connected
directly to the fixed riser. Where transformers are located
at the well head, their enclosures shall be connected to
this bonding conductor.

The equipotential bonding conductor shall be so
dimensioned that the voltage drop between any two
points (of resistance value R) that may be contacted
simultaneously shall not exceed 50 V. That is:

ohms

Kxl n

where I n (in amperes) is the rated current of the power
fuses or, in the case of circuit-breakers, 0.2 times the
releasing current for the instantaneous or short-time
delay trip; and A' is a multiplying factor.

NOTE — A value of K = 2.5 is suggested for the time being.

8.4.14 Exemption from insulation monitoring device

An insulation monitoring device (or earth fault
detector) is not necessary.

8.4.1.5 Double line to earth faults

Protection shall be provided to disconnect the supply
in the case of a double fault (phase-earth-phase).

A device such as one which detects a change in neutral
displacement on the occurrence of the first and second
earth faults, may be provided. Disconnection follows
the second fault.

8.5 Pumps Other than Deep-well Types

Under consideration.

8.6 Power Supply Cables

Under consideration.

8.7 Control Circuits and Control Devices

Under consideration.

8.8 Safety Circuits and Safety Devices
Under consideration.

9 ADDITIONAL GUIDELINES FOR
INSTALLATIONS IN SPECIFIC AREAS

9.0 General

9.0.1 The requirements given in 4 to 8 are applicable
to the specific areas described in this Section in so far
as the operations are identical with those described.

9.0.2 Guidance from relevant experts shall be taken in
respect of specific areas before installation work
begins.

9.1 Lighting of Aircraft Aprons

The provisions of relevant Indian Standards shall apply.

9.2 Lighting of Ports and Harbours

The provisions of relevant Indian Standards shall apply.

9.3 Lighting Installations in Railway Marshalling

Yards

9.3.1 Classification

9.3.1.1 The classification in respect of yard area is
based on the speed and intensity of traffic both
vehicular and otherwise.

a) Multipurpose yard — A marshalling yard with
facilities for receiving, classifying and
despatching vehicles to their several
destination. They also deal with traffic
originating at or destined for centres.

b) A reception yard — A yard in which the loads
of incoming trains may stand clear of running
lines while waiting for their turn to be dealt with.

c) A classification yard — A yard in which trains
are broken up on the different lines for the
various directions or stations irrespective of
station order, so as to form them into trains
and prepare them for correct marshalling.

9.3.1.2 The railway yards are also classified into five
main categories depending on their handling capacity
and way of working:

a) Gravity yard — A yard where natural
gradient is available. It is utilized for
classification and sorting of loads. Shunting
is done without engine.

b) Hump yard — Hump yard created by raising
track levels in specified crest of 2 to 2.5 m
height. Hump yards are those where shunting
necks have shape of a camel hump. These
yards are mechanized where wagon level
crosses 2 500 wagons/day. Normally one
hump handles 1 000 to 1 500 wagons/day. The
number of humps can be increased depending
on the work-load.

c) Flat yard — Yards with flat shunting neck are
called flat yard. It deals from 300 to 700 wagons/
day. It is mostly suitable for metre gauge.

d) A sorting yard — This is a yard in which
wagons are separated in station order and
reformed into trains in special order to meet
the requirements of the section ahead or any

PART 5 OUTDOOR INSTALLATIONS

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SP 30 : 2011

other special transportation requirements,
e) A departure yard — This is a yard in which
loads are kept waiting for departure.

9.3.1.3 Each yard can be of anyone of the three
formations based on method of construction:

a) Baloon or classification type,

b) ladder type, and

c) Grid type.

NOTE — Yards with grid type formation are reception-
cwra-despatch yards.

9.3.1.4 For the purpose of illumination, most important
locations are 'king points' and 'queen points' and order
of priority for lighting is determined accordingly.

NOTES

1 King points are the first pair of points that the wagon meets
after passing over the hump summit and these divide the hump
yard into two portions.

2 Queen points are the second pair of points the wagon meets
on either of the two diverging lines taking off from the king
points and these divide the classification lines into four sub-
portion. These are two in each hump yard.

9.3.2 Different segments (functions) of yards are:

a) classification yard — zone- wise,

b) sorting yard — station- wise,

c) reception yard,

d) despatch yard, and

e) through goods yard.

9.3.3 Design

9.3.3.1 For the purpose of designing the lighting
system, the recommended height of tower is 30 m.

9.3.3.2 Selection of equipments

a) Light sources — The following sources of
light are recommended for the purpose of yard
lighting.

1) High pressure mercury vapour lamps.

2) High pressure sodium vapour lamps.

Each luminaire may be provided with 2
lamps of 400 W or 1 lamps of 1 000 W.
b) Luminaires — Flood lighting types of

luminaires are recommended for yard lighting

installation.

9.3.3.3 Levels of illumination would depend on the
type of marshalling yard. The levels given below are
recommendatory:

Type Minimum Maximum Special Location

Like Shunting
Neck, King
Points, etc

(1) (2) (3) (4)

Important
yard
Small yards

1.2 lux
0.5 lux

5 lux
1.2 lux

10 lux
5 lux

9.3.4 Power Installation Requirements

9.3.4.0 The source of electric supply shall be located
at a suitable place nearest to the yard.

9.3.4.1 The power supply to the towers shall be through
underground armoured cables.

Minimum size of cable shall be 10 to 16 mm 2 4 core.

9.3.4.2 Means shall be provided to control supply to
group of towers with controlgear located in feeding
substation/switching substation.

9.3.4.3 The cables shall be preferably terminated on
column junction boxes by looping joints, rather than
T' joint.

9.3.4.4 The junction boxes shall be provided with
suitable sized contactors with independent fuses for
each phase. The contactors shall be controlled by
electrically operated switch mounted for external
manual local operation.

Laying of cables in yard, along the track and across
the tracks should be done in accordance with IS 1255.

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PART 6

SP 30 : 2011

PART 6 ELECTRICAL INSTALLATIONS IN
AGRICULTURAL PREMISES

FOREWORD

This Part of the Code is primarily intended for covering the specific requirements of electrical installations in
agricultural premises which include premises where livestock are present and farm produce are handled or stored.
With the increase in sophistication in organising the farm output of the country, and the use of electricity for
certain essential purposes, it has been felt necessary to cover the requirements of such installations as a part of the
Code.

Installations in agricultural premises are different from those covered in other Sections of the Code in that the
external influences on the electrical services are quite different from those encountered elsewhere. Even though
the overall power requirements for such installations would be small, the presence of livestock and other extraneous
factors necessitate laying down specific requirements.

PART 6 ELECTRICAL INSTALLATIONS IN AGRICULTURAL PREMISES 345

SP 30 : 2011

1 SCOPE

1.1 This Part 6 of the Code covers requirements for
the fixed electrical installations in agricultural premises
excluding dwellings or similar locations situated in
these premises.

1.2 This Part applies to premises where livestock are
present.

NOTE — Examples of such premises are stables, cow houses,
sheepfolds, stalls, hen-houses, piggeries, etc.

2 TERMINOLOGY

For the purpose of this Part, the definitions given in
Part 1/Section 2 of the Code shall apply.

3 CLASSIFICATION

3.1 Installations in agricultural premises shall be
broadly classified into:

a) Farm houses and agricultural processing units,
and

b) Livestock houses.

3.1.1 Farm Houses and Agricultural Processing Units

Farm houses and agricultural processing units are
premises where livestock are not normally present and
are those utilized solely for the purposes of handling,
processing or storing farm inputs and produce.

3.1.2 Livestock Houses

Livestock houses are premises where livestock are
present for long periods of time during the day (such
as in a dairy farm) with or without associated farm units.

3.1.2.1 Livestock houses are further classified
depending on the type of climatic conditions:

a) Plain areas with moderate rainfall,

b) Arid areas and high altitude areas, and

c) Heavy rainfall areas and high rainfall
humidity areas.

3.1.2.2 Livestock houses can also be classified
depending on the type of animal or bird housed. For
example:

Animal/Bird
Housing

Sub-Classification

Animal/Bird
Housing

Sub-Classification

Poultry housing

Sheepfolds
(sheep and goats)
Piggeries
Horse stables or
equine houses
Cattle housing

Layer house
Brooder house

Stationary
Portable

calves and pair of bullocks)

Cattle sheds for rural milk

producer (average of about 20

animals)

Organized milk produces (130

animals)

Large dairy farm (about 500

animals)

4 GENERAL CHARACTERISTICS OF
AGRICULTURAL PREMISES

General guidelines on the assessment of general
characteristics of buildings are given in Part 1/
Section 8. For the purpose of installations covered by
this Part the conditions given below apply.

4.1 Environment

The following conditions generally apply:

Environment
(1)

Characteristics

(2)

Remarks
(3)

Presence of
water

Presence of
foreign solid
bodies

Presence of
corrosive or
polluting
substances

Cattle sheds for average farmer
(3 milch animals with their

Presence of
flora and/or
mould growth
Presence of
fauna

Electromagnetic
influences

Possibility of
splashes from
any direction

Possibility of jets
of water from
any direction
Presence of dust
in significant
quantity

a) Intermittent
or accidental
subjection to
corrosive or
polluting
substances

b) Continuously
subjected to
corrosive or
polluting
substances

Harmful hazard
present

Harmful hazard Insects, birds
present and small animal

Harmful presence
of induced
currents

Locations where
equipment may
be subjected to
splashed water,
for example
external lighting
fittings

Locations where
hose-water is
used regularly

Applies to barns,
stores and stalls

Applies to
locations in
which livestock
are present or
fertilizers or plan
protective
products are
stored or handled

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4.2 Utilization

The following conditions apply:

Utilization

(i)

Characteristics

(2)

Remarks

(3)

Electrical

Low to resistance

—

resistance

due to wet

of human

conditions

body

Contact of

Persons are

persons

frequently in

with earth

touch with

potential

extraneous
conductive parts
or stand on
conducting
surfaces

Conditions

Low density

Special

occupation

precautions to

evacuation

difficult

be taken where

during

conditions of

animals are

emergency

evacuation
High density
occupation easy
conditions of
evacuation

present

Nature of

Flammable

Barns

processed

material

or stored

including dust

materials

Building

Propagation of

design

fire is facilitated
and risks due to
structural
movement of
structures which
are weak

5 SUPPLY CHARACTERISTICS AND
PARAMETERS

5.1 Information shall be exchanged among the people
concerned on the electrical needs of the premises before
installation work begins. Each installation may have
to cater to the services required in the subunits of the
premises which depend on the type of agricultural
premises as enumerated in 4.

5.1.1 In agricultural farms the following sub-units are
present:

a) Outdoor processing,

b) Indoor processing,

c) Heating/cooling,

d) Cold storage,

e) Stores, and

f) Office.

5.1.2 In sheepfolds, the following sub-units are present:

a) Sheds such as flock shed, ram or buck shed,
sick shed, etc;

b) Sheering and store room; and

c) Shepherd house.

5.1.3 In cattle housing, the following sub-units are
present:

a) Sheds for animals,

b) Milk recording and testing room,

c) Utensils room,

d) Ration room,

e) Stores, and

f) Office.

5.1.4 In meat houses and abattoirs, the following sub-
units are present:

a) Animal sheds before slaughter,

b) Slaughter shed,

c) Flaying, dressing and washing,

d) By-products handling,

e) Inspection,

f) Laboratory, and

g) Office.

5.2 Wiring Systems

5.2.1 Main switchgear shall not be installed

a) within reach of livestock, or

b) in any position where access to it may be
impeded by livestock.

5.2.2 Where an installation serves more than one
building, it shall be possible to isolate and control the
buildings individually.

5.2.3 Means of access to all live parts of switchgear
and other fixed live parts where different nominal
voltages exist shall be marked to indicate the voltages
present.

5.2.4 Cables

5.2.4.1 All cables shall be placed out of reach of
livestock and clear of all vehicular movement.

5.2.4.2 Where additional protection against mechanical
damage to cables is required, it shall, wherever
possible, be provided by the use of non-metallic
materials.

5.2.4.3 Where long runs of cable must be placed along
the sides of buildings, they shall wherever possible be
placed on the outside of the buildings, and as high as
practicable.

5.2.4.4 Where conductors or cables are carried

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overhead supported by buildings or by poles, the
minimum height above ground shall be 6 m.

5.2.4.5 Cable couplers shall not be used in agricultural
premises.

5.3 Selection and Erection of Equipment

Equipment shall be so selected that they suit the
environmental conditions of use and shall be installed
in such a way that their normal functioning is not
affected by the external influences enumerated in 4.

5.3.1 It is recommended to protect final sub-circuits
by residual current devices, the rated operating residual
current not exceeding 30 mA and as low as practicable
but avoiding nuisance tripping.

5 A System Protection

5.4.1 Protection Against Electric Shock

For the application of protective measure by safety
extra-low voltage in locations in which livestock are

present or situated outside, protection against direct
contact shall be provided by:

a) barriers or enclosures affording at least the
degree or protection IP2X, or

b) insulation capable of withstanding a test
voltage of 500 V for 1 min.

For achieving protection by automatic disconnection
of supply, the conventional voltage limit in locations in
which livestock are present or situated outside is U L =
25 V. These conditions are also applicable to locations
directly connected through extraneous conductive parts
to the locations where livestock are present.

Where electrical equipment is installed in livestock
building, supplementary equipotential bonding shall
connect all exposed conductive parts which can be
touched by livestock and the protective conductor of
the installation.

NOTE — A metallic grill connected to the protective conductor
laid in the floor is recommended (see Fig. 1).

Earth conductor

Sheet metal and foil partitions

Water pipe

10.

Manure removal device

11.

Potential equalization, for example,

12.

structural steel mat

13.

Tethering device

14.

Automatic watering device

15.

Feeding apparatus

Milking apparatus

Steel structure

Protective earth conductor (PE)

Earth electrode

Busbar for equipotential bonding

Earth electrode for lightning protection

Earth electrode for electric fences

Fig. 1 Example of Equipotential Bonding on Agricultural Premises

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5.4.2 Protection Against Fire

Heaters used in the rearing and tending of livestock
shall be secured or hung on a safe mounting so that an
adequate spacing from both animals (risk of burns) and
combustible materials (fire hazard) is assured. Due
consideration shall be given to the evacuation of
animals in case of emergency. Due considerations shall
also be given to locations presenting fire-risks.

5.43 Isolation and Switching

For fire safety purposes, a residual current protective
device shall be installed having a rated residual
operating current of 0.5A. Devices for emergency
electrical switching including emergency stopping shall
not be installed within reach of livestock or in any
position where access to them may be impeded by
livestock, account being taken of the condition likely
to arise in the event of panic by livestock.

6 SERVICES IN AGRICULTURAL PREMISES

Farm houses and livestock houses do not in general
require sophisticated electrical services, but in the case
of the latter, lack of proper ventilation or lighting leads
to insanitation and discomfort to the livestock thereby
leading to retarded growth, high mortality or poor
fertility. The houses are required to be maintained
reasonably cool in summer and warm in winter, with a
regular supply of fresh air and light. The guidelines
given in 6.1 to 6.3 shall be adhered to.

6.1 Poultry Housing

A minimum of 14 h day length shall be provided to
the birds and artificial lighting shall be provided for
the same. For the purposes, 1 W (GLS) or 0.75 W
(fluorescent) per bird or 1 W per 28-38 cm are
considered adequate. The light sources shall be hung
at a height not less than 1.8 m above floor. For poultry
sheds of 6 m width and below, one row of bulbs in
the centre shall be adequate. For sheds of larger width
two rows of lamps properly interspaced may be
desirable.

6.2 Abattoir

In meat houses and abattoirs, in halls where meat or
carcasses are hung, a temperature of not greater than
10°C would be required and air-conditioning may be
required. In unrefrigerated work rooms, ample artificial
light and ventilation shall be provided by electrical
means. The overall intensity in every abattoir shall not
be less than 200 lux throughout the slaughter hall and
workroom and at places where meat inspection is
carried out, the illumination shall be at least 500 lux.

6.3 Farm Cattle Housing

In large dairy farms, roof-lights shall be provided to
give 50-200 lux of artificial lighting. The lamps shall
be hung at a height not less than 2 m above floor level.

7 TESTING OF INSTALLATION

Before commissioning the installation shall be tested
and inspected as given in Part 1/Section 13 of the Code.

8 MISCELLANEOUS PROVISIONS

8.1 For large scale livestock keeping, such as in a dairy
farm, it shall be essential to provide:

a) a warning device for indicating failure of air
circulation system; and

b) for continuity of supply, a fast acting
emergency supply system is recommended.

8.2 Electric Fences

Where electric fences are in the vicinity of overhead
lines, appropriate distances shall be observed to take
account of induction currents, falling lines, etc.

Any earth electrode connected to the earth terminal of
an electric fence controller shall be separate from the
earthing system of any other circuit and shall be
situated outside the resistance area of any electrode
used for protective earthing.

83 Circuits of wirings which are only occasionally
used, for example, during threshing time, shall be fitted
with a separate switch marked accordingly.

PART 6 ELECTRICAL INSTALLATIONS IN AGRICULTURAL PREMISES

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PART 7

SP 30 : 2011

PART 7 ELECTRICAL INSTALLATIONS
IN HAZARDOUS AREAS

FOREWORD

Explosive gas atmosphere is the atmosphere where mixture with air, under atmospheric conditions, of flammable
substances in the form of gas or vapour, which, after ignition, permits self-sustaining flame propagation. Area in
which an explosive gas atmosphere is present, or may be expected to be present, in quantities such as to require
special precautions for the construction, installation and use of equipment is referred as a hazardous area and has
to be treated in a special manner from the point of the design of electrical installation.

Many liquids, gases and vapours which in industry are generated, processed, handled and stored are combustible.
When ignited, these may burn readily and with considerable explosive force when mixed with air in the appropriate
proportions. With regard to electrical installations, essential ignition sources include arcs, sparks or hot surfaces,
produced either in normal operation or under specified fault conditions.

This Part 7 of the Code is intended to provide guidelines for electrical installations and equipment in locations
where a hazardous atmosphere is likely to be present, with a view to maximising electrical safety. The scope of
this Part therefore includes installations in hazardous areas such a petroleum refineries and petrochemical and
chemical industries. The requirements laid down herein are in addition to those specified in Part 4 of this Code.

It is recognized that when electrical equipment is to be installed in or near a hazardous area, it is frequently
possible, by taking care in the layout of the installation, to locate much of the equipment in less hazardous or
non-hazardous areas and thus reduce the amount of special equipment required.

NOTE — Hazardous areas can be limited in extent by construction measures, that is, walls or dams. Ventilation or application of
protective gas will reduce the probability of the presence of explosive gas atmosphere so that areas of greater hazard can be transformed
to areas of lesser hazard or to non-hazardous areas.

This Part includes generalised statements and recommendations on matters on which there are diverse opinions.
It is, therefore, important that sound engineering judgement should be exercised while applying these guidelines.

PART 7 ELECTRICAL INSTALLATIONS IN HAZARDOUS AREAS 353

SP 30: 2011

1 SCOPE

1.1 This Part 7 of the Code covers recommendations
for electrical installations in chemical industries,
petroleum refineries and other similar areas where
hazards of explosion due to gases and vapours exist,
and in which flammable gases and volatile liquids are
processed, stored, loaded, unloaded or otherwise
handled.

1.2 In addition to the recommendations given in this
Part 7, the electrical installations in hazardous areas
shall comply, with the requirements for industrial
installation in non-hazardous areas laid down in Part 4
of this Code.

1.3 This Part does not apply to installations in
hazardous areas having ignitable dusts and fibres. As
distinct from the hazardous areas on the surface,
environmental conditions in mines demand special
consideration. This Part of the Code does not include
provisions for installations in underground mines.

1.4 In any plant installation, irrespective of size, there
may be numerous sources of ignition apart from those
associated with electrical apparatus. Precautions may
be necessary to ensure safety but guidance on this
aspect is outside the scope of this Part.

NOTE — Some examples of industrial locations which require
application of the guidelines in this Part are given in Annex A.

2 REFERENCES

A list of standards for electrical equipment for
explosive atmospheres is given at Annex B. Some of
these standards deal with particular construction
techniques, others with aspects of standardization
which are relevant to more than one technique.

3 TERMINOLOGY

For the purpose of this Part, the following definitions
shall apply, in addition to those given in Part 1 of this
Code.

3.1 Flammable Material — A flammable material is
a gas, vapour, liquid and/or mist which can react
continuously with atmospheric oxygen and which may
therefore, sustain fire or explosion when such reaction
is initiated by a suitable spark, flame or hot surface.

3.2 Flammable Gas-Air Mixture — A mixture of
flammable gas, vapour or mist with air, under
atmospheric conditions, in which after ignition,
combustion spreads throughout the unconsumed
mixture.

3.3 Hazard — The presence, or the risk of presence,
of a flammable gas-air mixture.

3.4 Explosive Gas Atmosphere — Mixture with air,

under atmospheric conditions, of flammable substances
in the form of gas or vapour, which, after ignition,
permits self-sustaining flame propagation.

3.5 Hazardous Area — Area in which an explosive
gas atmosphere is present, or may be expected to be
present, in quantities such as to require special
precautions for the construction, installation and use
of equipment.

3.6 Explosive (Flammable) Limits — The extreme
values for the concentration of a flammable gas or
vapour in air under atmospheric conditions, under
which flammable gas-air mixture can be ignited by an
electrical arc or spark. These limits are called the 'lower
explosive limit' (LEL) and the 'upper explosive limit'
(UEL).

3.7 Flammability Range — The range of gas or
vapour mixtures with air between the flammable limits
over which the gas mixtures are continuously
explosive.

3.8 Flammable Gas or Vapour — Gas or vapour
which, when mixed with air in certain proportions, will
form an explosive gas atmosphere.

3.9 Flammable Liquid — A liquid capable of
producing a flammable vapour, gas or mist under any
foreseeable operating conditions.

3.10 Flammable Mist — Droplets of flammable
liquid, dispersed in air, so as to form an explosive gas
atmosphere.

3.11 Liquefied Flammable Gas — Flammable gas
which, under normal ambient pressures and
temperatures, is in gaseous state but which is handled
in a liquid state under the applied conditions of pressure
and/or temperature.

3.12 Flash Point — The temperature at which the
liquid gives so much vapour that this vapour, when
mixed with air, forms an ignitable mixture and gives a
momentary flash on application of a small pilot flame
under specified conditions of test.

3.13 Boiling Point — The temperature of a liquid
boiling at an ambient pressure of 101.3 kPa.

NOTE — For liquid mixtures the initial boiling point shall be
considered. 'Initial boiling point' is used for liquid mixtures
to indicate the lowest value of the boiling point for the range
of liquids present.

3.14 Ignition Temperature — The lowest temperature
at which ignition occurs in a mixture of explosive gas
and air when the method specified in IS 7820 is
followed.

3.15 Source of Release — A source of release is a
point or location from which a gas, vapour, mist or

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liquid may be released into the atmosphere so that an
explosive gas atmosphere could be formed.

3.16 Restricted Release — A release (normal or
abnormal) of flammable gas or vapour which can be
diluted below the lower flammable limit.

3.17 Unrestricted Release — A release (normal or
abnormal) of flammable gas or vapour which cannot
be diluted below the lower flammable limit.

3*18 Adequate Ventilation — Adequate ventilation is
that which is sufficient to prevent accumulations of
significant quantities of gas-air mixtures in
concentration over one-fourth of the lower flammable
limit.

Adequately ventilated area could be naturally
ventilated or artificially ventilated.

3.19 Relative Density of Gas or Vapour — The
density of a gas or a vapour relative to the density of
air at the same pressure and the same temperature.

3.20 Non-hazardous (Safe) Area — Area in which
an explosive gas atmosphere is not expected to be
present in quantities such as to require special
precautions for the construction, installation and use
of equipment

3.21 Electrical Apparatus for Hazardous Areas —

Electrical apparatus which will not ignite the
surrounding flammable atmosphere in which it is used.

3.22 Ignition Capable Apparatus — Apparatus which
in normal operation produces sparks, hot surfaces, or
a flame which can ignite a specific flammable mixture.

3.23 Safety Measures — Measures taken to ensure
that electrical apparatus cannot cause an explosion.

3.24 Type of Protection — Specific measures applied
to electrical equipment to avoid ignition of a
surrounding explosive atmosphere.

3.25 Maximum Surface Temperature — Highest
temperature which is attained in service under the most
adverse operating conditions (but within recognized
tolerances) by any part or surface of the electrical
equipment, which would be able to produce an ignition
of the surrounding explosive atmosphere.

NOTES

1 The most adverse conditions include recognized overloads
and fault conditions recognized in the specific standard for
the type of protection concerned.

2 The relevant surface temperature may be internal and/or
external depending upon the type of protection concerned.

3.26 Flame Arrester — A device for releasing gas
from an enclosure in such a way that in case of an
internal explosion there is no appreciable increase in
internal pressure and the released gas will not ignite

the surrounding flammable atmosphere.

3.27 Inert Gas — A gas which cannot be ignited when
mixed with a flammable gas or vapour in any
concentration.

4 STATUTORY REGULATIONS

4.1 In following the recommendations of this Part 7,
the various statutes and regulations in force in the
country, applicable to the installation and use of
electrical apparatus in hazardous areas shall be kept in
view.

4.2 Attention is invited to the fact that the manufacture
and use of equipment in hazardous areas is controlled
by the statutory authorities listed below for the area of
their jurisdiction:

a) The Directorate General of Mines Safety,
Dhanbad (Bihar);

b) The Chief Controllerate of Explosives,
Petroleum and Explosives Safety
Organisation, Nagpur (Maharashtra); and

c) The Directorate General Factory Advice
Services and Labour Institute, Mumbai
(Maharashtra).

4.3 Testing

Equipment to be installed in hazardous area have to be
certified by a recognised testing authority.

4A Marking of equipment shall conform to
IS/IEC 60079-0.

5 FUNDAMENTAL CONCEPTS

5.1 Flammable gases and vapours may cause a fire or
explosion when the following three basic conditions
are satisfied:

a) Presence of sufficient quantity of a flammable
gas or vapour,

b) Mixing of flammable gas or vapour with air
or oxygen in the proportions required to
produce an explosive or ignitable mixture, and

c) Occurrence of ignition.

In applying this principle to any potential hazard, the
quantity of the substance that might be liberated, its
physical characteristics and the natural tendency of
vapours to disperse in the atmosphere shall be
recognised. Flammable substances, the potential
release of which shall be considered in area
classification of electrical installations (see 6) include
the following:

a) Non-liquefiable gases,

b) Liquefied petroleum gas, and

c) Vapour or flammable gas.

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5.2 It is recommended that plants and installations in
which flammable materials are handled or stored be
so designed that the degree and extent of hazardous
areas are kept to a minimum. Similarly consideration
should be given to design and operation of process
equipment to ensure that even when it is operating
abnormally, the amount of flammable material released
to the atmosphere is minimized in order to reduce the
extent of the area made hazardous.

Once a plant has been classified, it is important that no
modification to equipment or operating procedures is
made without discussion with those responsible for the
area classification. Unauthorized action may invalidate
the area classification.

It is necessary to ensure that process equipment which
has been subjected to maintenance shall be carefully
checked during and after re-assembly to ensure that
safety aspect or integrity of the original design has been
maintained before it is returned to service.

53 Where it is necessary to use electrical apparatus in
an environment in which there may be an explosive
gas atmosphere and it is not possible to:

a) eliminate likelihood of an explosive gas
atmosphere occurring around the source of
ignition, or

b) eliminate the source of ignition.

Then measures should aim at reducing the likelihood
of occurrence of either or both of the above factors so
that the likelihood of coincidence is so small as to be
negligible.

5.4 In most practical situations where flammable
materials are used it is difficult to ensure that an
explosive gas atmosphere will never occur. It may also
be difficult to ensure that the electrical apparatus will
never give rise to a source of ignition. Reliance is
therefore placed on using electrical apparatus which has
an extremely low likelihood of creating a source of
ignition in situations where a flammable atmosphere has
a high likelihood of occurring. Conversely where the
likelihood of an explosive gas atmosphere is reduced,
electrical apparatus which has an increased likelihood
of becoming a source of ignition may be used.

flammable atmospheres (explosive concentrations of
combustible gas or vapour) may arise in installations
in terms of both the frequency of occurrence and the
probable duration of existence on each occasion.

6.1 Area Classification

The area classification is given in Table 1 ,

6.2 Extent of Hazardous Area

6.2.1 A complete knowledge of the physical properties
of the flammable materials involved is essential for
classifying a hazardous area. Properties of primary
interest from an ignition standpoint are:

a) relative density,

b) flammable limits,

c) flash point,

d) volatility,

e) ignition temperature, and
ignition energy.

Some of these characteristics have a direct influence
on the degree and extent of hazardous areas while the
others affect the design of electrical equipment.

6.2.1. 1 Relative density

Where a substantial volume of gas or vapour is released
into the atmosphere from a localized source, a relative
density less than one, that is, lighter-than-air, for the
combustible indicates the gas or vapour will rise in a
comparatively still atmosphere. A vapour density
greater than one, that is, heavier-than-air, indicates the
gas or vapour will tend to sink, and may thereby spread
some distance horizontally and at a low level. The latter
effects will increase with compounds of greater relative
vapour density.

NOTE — In process industries, the boundary between
compounds which may be considered lighter-than-air is set at
a relative vapour density of 0.75. This limit is chosen so as to
provide a factor of safety for these compounds whose densities
are close to that of air and where movement may not, therefore,
be predicted without a detailed assessment.

6.2.1.2 Flammable limits

The lower the 'lower flammable limit' the larger may
be the extent of the hazardous area.

6 CLASSIFICATION OF HAZARDOUS AREAS 6.2.1.3 Flash point

6.0 General

The objective of the hazardous area classification is to
ensure an adequately safe level of operation of
electrical apparatus in flammable atmospheres using
the fundamental concepts outlined in 5.

The basis for hazardous area classification recognizes
the differing degrees of probability with which

A flammable atmosphere cannot exist if the flash point
is significantly above the relevant maximum
temperature of the flammable liquid. The lower the
flash point, the larger may be the extent of the
hazardous area.

6.2.1.4 Volatility

Boiling point can be used for comparing the volatility

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Table 1 Area Classification

(Clause 6.1)

SI No.

(1)

Area Classification

(2)

Description

(3)

Remarks

(4)

ZoneO

ii)

iii)

Zone 1

Zone 2

Place in which an explosive atmosphere
consisting of a mixture with air of
flammable substances in the form of gas,
vapour or mist is present continuously or
for long periods or frequently

Place in which an explosive atmosphere
consisting of a mixture with air of
flammable substances in the form of gas,
vapour or mist is likely to occur in normal
operation occasionally

Place in which an explosive atmosphere
consisting of a mixture with air of
flammable substances in the form of gas,
vapour or mist is not likely to occur in
normal operation but, if it does occur, will
persist for a short period only

This classification is applicable only where the
hazard will exist continuously. In the petroleum
industry such a condition is rarely encountered
except in confined spaces, such as the vapour
space of closed process vessels, storage tanks or
closed containers. In Zone 0, any arc or spark
would almost certainly lead to fire or explosion.
Any electrical apparatus must afford a degree of
protection as near as practicable to absolute. It is
recommended to avoid installing electrical
equipment in Zone areas to the extent possible.

In Zone 1, the hazard is likely to occur at any
time requiring fullest practicable application of
measures.

Zone 2 is applicable to areas where hazard is
unlikely and may be caused only by the highly
improbable and simultaneous occurrence of an
arc or spark together with a hazardous
atmosphere arising out of failure of conditions of
control. It presupposes that any abnormal
occurrence is rapidly dispersed so that possible
contact with electrical apparatus is of minimum
duration.

NOTES

1 Earlier, classified areas were called divisions.

2 This area classification deals only with risks due to combustible gases and vapours and combustible mists. It does not deal with
dusts since these material can be quiescent for long periods of time until they are disturbed into suspension by a suitable mechanism
(see also 1.3).

3 By implication, an area not classified as Zone 0, Zone 1 or Zone 2, is deemed non-hazardous or safe and no special precautions are
necessary.

of flammable liquids. The more volatile a liquid and
the lower its flash point, the more closely it
approximates a flammable gas.

6,2.1.5 Ignition temperature and ignition energy

Ignition temperature and ignition energy of a
flammable gas or vapour are taken into account in the
design of electrical apparatus for hazardous areas so
that these do not present an ignition risk.

6.2.2 Factors Affecting Extent of Hazard

6.2.2.0 In addition to the properties of flammable
materials involved, the following factors need to be
considered for determining the degree and extent of
hazardous areas while applying the guidelines given
in IS 5572.

6.2.2.1 Risk points

Normal operation is the situation in which all plant
equipment is operating within its design parameters.
Minor releases of flammable material may be part of

normal operation but leakages which entail repair or
shut down are not part of normal operation.

Some examples of persistent risk points are as follows:

a) Interior of pressure vessels and pipes
containing gas-air mixtures;

b) Free space above liquid level in tanks;

c) Free space immediately above open dipping
baths, etc; and

d) The immediate vicinity of vapour exhausts
and liquid outlets where these are designed
to discharge as part of normal plant function.

Examples of occasional risk points are the immediate
vicinity of mechanical glands, seals relying on wetting
by the fluid being pumped and other localized spillage
points and of vapour exhausts and liquid outlets
designed to discharge only on plant malfunction.

6.2.2.2 Temperature of process liquid

The extent of a hazardous area may increase with

PART 7 ELECTRICAL INSTALLATIONS IN HAZARDOUS AREAS

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SP 30 : 2011

increasing temperature of process liquid provided the
temperature is above the flash point. It should be noted
that the liquid or vapour temperature after the release
maybe increased or decreased by the ambient
temperature or other factors (for example, a hot
surface).

NOTE — Some liquids (such as certain halogenated
hydrocarbons) do not possess a flash point although they are
capable of producing a flammable atmosphere; in these cases,
the equilibrium liquid temperature corresponding to saturated
concentration at lower flammable limit should be compared
with the relevant maximum liquid temperature.

6.2.2.3 Concentration of vapour

For flammable liquids, the concentration of the released
vapour is related to the vapour pressure at the relevant
maximum liquid temperature. The lower the initial
boiling point a the greater the vapour pressure for a given
liquid temperature and hence the greater concentration
of vapour at the release source resulting in greater
extent of hazardous area.

6.2.2.4 Rate of release

The extent of hazardous area may increase with
increasing rate of release of flammable material.

6.2.2.5 Release velocity

Due to an improved dilution for release of flammable
gases, vapours and/or mists in the air, the extent of
hazardous area may decrease if, with constant release
rate, the release velocity increases above that which
causes turbulent flow.

NOTE — Elevated or depressed sources of release will alter
the areas of potential hazard.

6.2.2.6 Air current

Air currents may substantially alter the outline of the
limits of potential hazard. A very mild breeze may serve
to extend the area in those directions to which vapours
might normally be carried. However, a stronger breeze
may so accelerate the dispersion of vapours that the
extent of potentially hazardous area would be greatly
reduced.

6.2.2.7 Ventilation

With an increased rate of ventilation, the extent of
hazardous area may be reduced. The extent may also
be reduced by an improved arrangement of the
ventilation system.

6.2.2.8 Obstacles

Obstacles (for example, dykes, walls) may impede the
ventilation and thus may enlarge the extent. On the
other hand, they may limit the movement of a cloud of
an explosive gas atmosphere and thus may reduce the
extent.

6.2.2.9 For vapours released at or near ground level,
the areas where potentially hazardous concentrations
are most likely to be found are below ground, those at
ground are next most likely, and as the height above
ground increase, the potential hazard decreases.

NOTE — For lighter-than-air gases, the opposite is true, there
being little or no potential hazard at and below ground and
greater potential hazard above ground.

6.2.3 Internal Hazards

6.2.3.0 In cases where electrical apparatus, like those
used for measurement and control of process variable,
are connected directly to gas or a liquid process
equipment, this may introduce additional source of
internal and/or external release and consequently
influence the external area classification.

6.2.3.1 The hazards created inside the electrical
apparatus by an internal release of flammable gas or
vapour may be compared to the external area
classification as follows:

a) Where pressurization with inert gas is applied,
the internal releases cannot create a flammable
gas atmosphere, because no oxygen is present.

b) Where dilution with air is applied in case of a
restricted normal release the internal hazards
are comparable to those in a safe area. This
applies also when the abnormal release (when
occurring) would be restricted. When, however,
the abnormal release would be unrestricted, the
internal hazards are comparable to the external
hazards in Zone 2.

c) In all other types of protection, the internal
hazards are comparable to the external
hazards in Zone 2, provided that there is no
normal release and that an abnormal release
would be very infrequent and of a relatively
short duration. When there is a normal release,
the internal hazards are comparable to the
hazards in Zone and the abnormal release
is not relevant.

6.2.3.2 When apparatus in which the internal hazards
are comparable to Zone 2 is installed in a safe area or
in Zone 2, the internal hazards determine the actual
hazard condition, but when the same apparatus is
installed in Zone 1 or Zone the external hazards
determine the actual hazard condition. When an
apparatus in which the internal hazards are
comparable to Zone 1 is installed in a Zone
hazardous area, the area classification would
determine the actual hazard.

6.2.4 Extent of Zones of Hazard

6.2.4.1 The treatment of hazardous area, from the point
of view of determining the extent of hazardous zones

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(and their classification) around the source of hazard
differ in the following broad situations:

a) Open-air situations (freely ventilated process
area):

1) Source of hazard located near ground
level, and

2) Source of hazard above ground level,

b) Enclosed premises and surrounding area
(process area with restricted ventilation).

c) Storage tanks:

1) Floating roof, and

2) Fixed roof tank with vent.

6.2.4.2 Detailed guidelines on the above situations can
be had from IS 5572.

7 SPECIFIC GUIDELINES FOR ELECTRICAL
INSTALLATIONS IN HAZARDOUS AREAS

7.1 General

7.1.1 Mechanical Strength

All apparatus shall be installed with due regard to the
possibility of external mechanical damage. Where
adequate protection cannot be ensured, for example,
by location, reference should be made to the impact
test requirements according to IS/IEC 60079-0 for the
apparatus before deciding on any additional measures
such as the provision of guards for transparent parts.

7.1.2 Earthing and Bonding

7.1.2.1 Earthing shall be in accordance with Part 1/
Section 14 of this Code. The connection between metal
part to be grounded and the grounding conductor shall
be made secure mechanically and electrically by using
adequate metallic fitting. The earthing conductors shall
be sufficiently strong and thick, and the portions of
conductor which are likely to be corroded or damaged
shall be well protected. Grounding conductors which
shall not reach a hazardously high temperature due to
the anticipated maximum earth fault current flowing,
shall be used.

7.1.2.2 Protection against lightning shall be provided
in accordance with Part 1/Section 15 of this Code.
Specific guidelines for installations in hazardous
locations are given in Annex C. Interconnection system
with other buried metal services and/or earth
terminations for equipment earthing for the purpose
of equalizing the potential distribution in the ground
should preferably be made below ground.

7.1.2.3 Portable and transportable apparatus shall be
earthed with one of the cores of flexible cable for power
supply. The earth continuity conductor and the metallic
screen wherever provided for the flexible cable should

be bonded to the appropriate metal- work of the
apparatus and to the earthing pin of the plug.

7.1.2.4 Efficient bonding should be installed where
protection against stray currents or electrostatic charges
is necessary.

7.1.2.5 Earthing and bonding of pipelines and pipe-
racks

Unless adequately connected to earth elsewhere, all
utility and process pipelines should be bonded to a
common conductor by means of earth bars or pipe
clamps and connected to the earthing system at a point
where the pipelines enter or leave the hazardous area*
except where conflicting with the requirements of
cathodic protection. In addition, it is recommended that
steel pipe racks in the process units and off-site areas
should be earthed at every 25 m.

7.1.3 Automatic Electrical Protection

7.1.3.1 It is essential that the severity and duration of
faults internal or external to the electrical apparatus be
limited, by external means, to values that can be
sustained by the apparatus without disruptive effect.

7.1.3.2 All circuits and apparatus in hazardous areas
shall be provided with means to ensure disconnection
quickly in the event of excessive overloads,
overcurrent, internal short-circuit or earth-fault
conditions. In case of distribution systems with isolated
neutral, an automatic earth-fault alarming device may
be considered adequate, in addition to overload/
overcurrent and short-circuit protection.

7.1.3.3 Protection and control apparatus shall be
normally located in a non-hazardous area. Where its
installation in a potentially hazardous area cannot be
avoided, such apparatus should be provided with the
appropriate type of protection.

7.1.3.4 Apart from self-powered apparatus and hand
lamps, earth-leakage protection or earth monitoring,
or both should be included in the protection of the
portable and transportable apparatus. Protection of the
circulating-current type a which automatically cuts off
the supply in the event of the earth continuity conductor
becoming disconnected, may, with advantage, be
adopted as the earth-monitoring device.

7.1.4 Isolation

7.1.4.1 All electrical circuits should be provided with
an effective means of complete circuit isolation,
including the neutral. Such means of isolation should
be provided for each item of electrical apparatus and/or
each sub-circuit.

7.1.4.2 The means of isolation, when located in a
hazardous area, shall be a switch which breaks all poles,
including the neutral, and which is provided with an

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appropriate type of protection against explosive
hazards. This applies equally to single phase sub-
circuits. When the means of isolation is located in a
non-hazardous area, the switch shall break all poles,
the neutral being isolated by a removable link. The
means of isolation shall be capable of being locked in
the 'OFF' position.

7.1.4.3 When the means of isolation is not
immediately adjacent to the associated apparatus,
effective provision should be made to prevent the
restoration of supply to the apparatus while the risk
of exposure of live conductors to a flammable gas-
air mixture continues.

7.1.5 Operation and Maintenance

7.1.5.1 None of the protection techniques for electrical
equipment for explosive gas atmospheres are effective
unless the apparatus is operated within the limits
indicated by its nameplate marking and is properly
maintained according to the recommendations of
appropriate Indian Standards.

7.1.5.2 Care shall be taken when inspecting equipment
in hazardous areas; circuits shall be made dead before
removing covers. Flexible cables are a potential source
of hazard; they should be frequently inspected, together
with the portable apparatus. Equipment should be
examined for mechanical faults, cracked glasses,
deterioration of cement, slackened conduit joints and
corrosion. Electrical tests should be carried out at fixed
intervals.

7.2 Wiring Installation

7.2.0 General

Types of wiring and systems which may be used for
installation in hazardous areas are:

a) cables drawn into screwed, solid drawn or
seamless conduits, and

b) cables which are otherwise suitably protected
against mechanical damage.

Requirements for the installation of general power
systems may not apply to the installation of apparatus
and systems with type of protection T (intrinsic safety).
For intrinsically safe circuits, there is normally no need
to have special enclosures for the conductors. However,
some protection will have to be afforded to such
conductors primarily to prevent contact between
conductors of intrinsically safe circuits and those of
any other system, to avoid the possibility of arcing
occurring at the point of contact or invasion of the
intrinsically safe circuits by current arising from
contact or electrostatic or electromagnetic induction.
In addition, the conductors should be protected against
mechanical damage (see 7.2.1.5).

The diameter of each strand of the conductor shall be
not less than 0.300 mm of copper or equivalent size of
conductor in the case of aluminium conductors as
specified in relevant Indian Standard.

For (b) the following types of cables may be used in
principle:

1) Lead-sheathed and armoured cable;

2) Plastics or rubber-sheathed steel screen
protected or armoured cable, with overall
sheath;

3) Cables enclosed in a seamless aluminium
sheath with or without armour, with an outer
protective sheath;

4) Mineral insulated metal sheathed cable; and

5) Braided screen-protected flexible cables.

Unarmoured lead-covered cable is not acceptable. The
sheath of a metal- sheathed cable should not be used as
the neutral conductor.

7.2.1 Factors Affecting Choice of Wiring System

7.2.1.1 Screwed steel conduit systems are satisfactory
for many situations but should not be used where
vibration might cause fracture or loosening of joints
and where excessive stress may be imposed as a result
of its rigidity or where corrosion or excessive internal
condensation of moisture is likely to occur.

7.2.1.2 Lead-sheathed and armoured cables are suitable
for underground installation. Steel-wire/flat armour is
preferred for underground use.

7.2.1.3 PVC-insulated and armoured cable, complying
with IS 1554 (Part 1) with an extruded plastic outer
sheath may be used for above ground or underground
installation. Lead-sheathed cable should be used where
spillages may affect the integrity of the cable and or
allow migration of the liquid through the cable.

7.2.1.4 For telecommunication circuits, plastic-
insulated and armoured telephone cables may be used.

7.2.1.5 In Zone areas only intrinsically safe circuits
shall be installed and its use shall be kept to an
unavoidable minimum. Wiring of circuits which have
been approved as intrinsically safe may follow the
requirements of general electrical wiring except that
the following requirements shall be observed:

a) The conditions of use laid down on the test
certificate issued by the approving authority
shall be observed,

b) The wiring shall be so made as to avoid
contact with other circuits,

c) The wiring shall be so made as to avoid
electromagnetic or electrostatic induction
from other circuit(s).

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d) The wiring shall be adequately protected
against mechanical damage, and

e) Aluminium armoured or sheathed cable shall
not be used in Zone areas.

7.2.2 Wiring Design

7.2.2.1 Correctly designed terminations complete with
armour clamps shall be provided for armoured cables.
The armouring should be carried into the clamps to
provide mechanical support to the cable and to ensure
electrical continuity. Where such cable is lead covered
and armoured, the lead-sheath should be plumbed or
mechanically gripped and sealed and the armouring
should be carried over the lead joint.

7.2.2.2 Where circuits traverse a hazardous area in
passing from one non-hazardous area to another, the
wiring in the hazardous area should comply with the
requirements of this standard.

7.2.2.3 Where practicable, contact either deliberate or
accidental, should be avoided between electrical
apparatus, conduit or cables, and any equipment or
pipework used for carrying combustible gases, vapours
or liquids.

7.2.2.4 Where, owing to particular circumstances,
contact between components referred to in 7.2.2.3 is
unavoidable, the armouring, conduit or sheathing of
the cable should be bonded to the equipment or
pipework in such a manner and at such intervals as to
ensure that under the worst fault conditions, the passage
of any current will not give rise to incendive sparking
or bring about a temperature rise approaching the
ignition temperature of the combustible gas, vapour
or liquid which may be present. Alternatively, in the
case of cable, the insulation of the sheath may be
sufficient to prevent danger.

7.2.2.5 Where cables or conduits pass through a floor,
wall, partition or ceiling, the hole provided for them
should be sealed with cement or similar incombustible
material to the full thickness of the floor, wall, partition
or ceiling, so that no space remains around the cable
through which combustible gas liquid or vapour might
spread. Alternatively cable glands may be used for this
purpose.

7.2.2.6 Where trunking, ducts, pipes or trenches are
used to accommodate cables, precautions should be
taken to prevent the passage of combustible gases,
vapours or liquids from one area to another, and to
prevent the collection of combustible gases, vapours
or liquids in trenches. Such precautions may involve
the sealing of trunking, ducts and pipes, and the
adequate ventilation or sand filling of trenches.

7.2.2.7 Where an overhead supply line is used for either
power or telecommunication circuits, it should be

terminated outside the hazardous area and be fitted at
or near the terminal pole with an effective surge-
protection apparatus. The cable used to connect the
overhead line with the installation in the hazardous area
should comply with the recommendations for wiring
systems in hazardous areas. Conduit should not be used
if it is likely to be subjected to vibration. The casing,
armouring or sheathing and armouring should be
electrically continuous and the end adjacent to the point
of connection with the overhead line should be bonded
to the earth electrode of the overhead line. In addition,
the casing or sheathing should be independently
earthed as near as possible to the junction of the cable,
with the installation and bonded to the earthing lead
of any lightning protective system associated with the
hazardous area. If convenient, a common electrode may
be used for this independent earth and for the lightning-
protective system of the installation.

Where the overhead line supplying a building forming
a hazardous area is supported by the building, and the
connecting cable to the installation consequently is
short, the earth electrodes for the surge-protection
apparatus on the overhead line may be used for earthing
the cable sheath or casing and for any lightning
protective system associated with the hazardous area.

7.2.2.8 The wiring entry to the apparatus, direct or
indirect, should maintain the type of protection used.

7.2.2.9 Unused cable entries in electrical apparatus
should be closed with plugs suitable for the type of
protection used.

7.2.2.10 Where cable terminals are used in apparatus
and accessories with the type of protection 'e' or V
they shall be fixed in position so as to ensure
maintenance of the creepage and clearance distances
as specified in 'IS/EEC 60079-7 and IS /IEC 60079-15.

7.2.3 Laying of Conduits

7.2.3.1 Conduits shall be solid-drawn or seamless,
screwed and galvanized.

Conduit, having an external diameter of more than
25 mm, should be fitted with a stopper box at each
point of connection with apparatus or fittings, unless a
self-contained assembly, independent of external
connections, has been certified.

7.2.3.2 Elbows of the solid type may be used for the
immediate connection of conduit to apparatus.

7.2.3.3 The lengths of the screwed part of any conduit
should be in accordance with the requirements of
IS/IEC 60079-1.

7.2.3.4 Where, in a run of conduit, it is necessary to
employ a joint other than a screwed coupler, certified
unions approved for flame-proof purposes should be

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used. The use of running couplings is not recommended
but where it is impracticable to avoid their use, factory
made assemblies should be used and the running
coupling should be secured by locknuts.

7.2.3.5 All screwed joints should be pulled up tight
and should, in addition, be provided with locknuts.

7.2.3.6 Surface-mounted conduit should be supported
by spacing saddles.

7.2.3.7 Elbows or tees, other than those of the
inspection type, should not be used except for the
immediate connection of conduit to apparatus, and all
inspection fittings should be of the flameproof type.

7.2.3.8 All joints in an assembly or conduit should be
painted after assembly with moisture-resisting paint
to inhibit the development of rust.

NOTE — It is important to ensure efficient earthing and
bonding in a flameproof installation. In view of the operating
conditions associated with the use of flameproof apparatus,
attention is drawn to the necessity of ensuring that the resistance
of all joints, including those in or between flameproof
enclosures and conduit, or cable sheaths and armour, is such
as to prevent a dangerous rise of temperature or voltage from
the passage of fault current, and that the total resistance of the
earth-fault current path, measured from any point in the
installation, is such as to ensure reliable operation of the
protection devices in all seasons.

7.2.3.9 Where a run of conduit, irrespective of size,
passes from a hazardous area to a non-hazardous area,
a stopper or sealing box or appropriate sealing device
shall be inserted on the side remote from the hazardous
area. There shall be no union, coupling, box or fitting
in the conduit between the sealing fittings and point at
which the conduit leaves the hazardous locations.

7.2.3.10 Seals shall be provided within 450 mm where
conduit run is terminated on the apparatus.

7.2.3.11 Metal conduit containing no unions,
couplings, boxes or fittings that passes through a
hazardous location with no fittings less than 300 mm
beyond each boundary may not be sealed if the
termination points of the unbroken conduit are in non-
hazardous locations.

7.2.3.12 For canned pumps, process connections for
instruments, etc, that depend upon a single seal
diaphragm or tube to prevent process fluids from
entering the electrical conduit system, an additional
approved seal or barrier shall be provided with an
adequate drain between the seals in such a manner that
leaks would be obvious.

7.2.3.13 Where there is a probability that any vapour
or moisture in the air may be condensed into liquid
within the conduit runs, boxes or sealing fittings, proper
means shall be provided to prevent accumulation of or
to permit drainage of such liquid periodically.

7.2.4 Laying of Cables

7.2.4.1 Cable systems include cables laid above ground
or cables laid underground directly buried, in concrete
trenches, or in cable ducts. The types of the cable for
use in hazardous areas shall be as specified in this
Section.

7.2.4.2 Cable runs should, where practicable, be
uninterrupted, that is, continuous and therefore, free
from intermediate joints. Where discontinuities cannot
be avoided, either during installation or subsequently,
the apparatus used for interconnection should be
provided with the type of protection appropriate to the
zone.

7.2.4.3 All cables shall be provided with adequate
mechanical protection. Cables shall be adequately
supported throughout their length, care being taken to
avoid excessive pressure when clamp supports are used.
Horizontal cables may be carried on supports, cable
trays or through protective troughs or tubes. Rising
cables should be clipped, cleated or otherwise attached
to suitable supports which provide adequate
mechanical protection.

7.2.4.4 Where paper-insulated armoured cables are
used, and particularly where such cables may be
exposed to high temperature, preference should be
given to non-draining cables. In the case of other types
of paper-insulated armoured cables, vertical runs
should be avoided.

7.2.4.5 The passage of cables from a hazardous area
to a non-hazardous area should, if necessary, be
provided with adequate means to prevent the
transmission of flammable material into the non-
hazardous area consideration should also be given to
the treatment of cables against fire transmission.

7.2.4.6 Where trunking, ducts, pipes or trenches are
used to accommodate cables, precautions should be
taken to prevent the passage of combustible gases,
vapours or liquids from one area to another, and to
prevent the collection of combustible gases, vapours
or liquids in trenches. Such precautions may involve
the sealing of trunking, ducts and pipes and the
adequate ventilation or sand filling of trenches.

7.2.4.7 Cables capable of transmitting gases or vapours
through the core shall be sealed in the hazardous
location in such a manner as to prevent passage of gases
or vapours into a non-hazardous location.

7.2.4.8 Correctly designed terminations complete with
armour clamps shall be provided for armoured cables,
the armouring should be carried into the clamps to
provide mechanical support to the cable and to ensure
electrical continuity. Where such cables are lead
covered and armoured, the lead sheath should be

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plumbed or mechanically gripped and sealed and the
armouring should be carried over the lead joint.

7.2.4.9 Cable glands, where used, shall be flameproof
type for flameproof enclosure and double-compression
type for enclosure having type of protection other than
flameproof.

7.2.4.10 Cable fittings for mineral insulated cables shall
be suitable for use with the appropriate apparatus to
which they are to be attached. Fittings should be
arranged for sealing the cable insulation and be
provided with means for ensuring adequate earth
continuity.

7.2.4.11 Where electrolytic corrosion of copper sheath
of mineral insulated cable may result from contact with
walls or other surfaces to which the cable is attached,
it should be kept clear of such surface or covered with
a protective sheath.

7.2.4.12 Where there is risk of mineral-insulated cables
being exposed to excessive voltages such as inductive
surges; surge suppression devices should be fitted.
Where surge suppression devices are installed in
hazardous areas, they should be suitably explosion-
protected.

7.2.4.13 Aluminium sheathed cables, unless sheathed
with a protective covering, should not be installed in
contact with walls or floor. Consideration should be
given to the avoidance of frictional contact with such
cables.

7.2.5 Plugs and Sockets

7.2.5.1 Plugs and sockets for installation in Zone 2
areas shall be flameproof type. Those shall be of
interlocked switch type.

7.2.5.2 Plugs and sockets shall be of the type that
provides for connections to the earthing conductor of
the flexible cables. The contacts of the grounding
conductor shall be mechanically and electrically of at
least the same quality as the main contacts and when
the plug is inserted it shall make connection before or
at the same time as the main contacts are made.

7.2.6 Connections to Portable and Transportable
Apparatus

7,2.6.1 Flexible cables of the types specified below
may be used for connection between a fixed source of
supply and the portable transportable apparatus through
flameproof plugs and sockets:

a) Ordinary tough rubber sheathed flexible cables,

b) Ordinary tough polychloroprene sheathed
flexible cables,

c) Heavy tough rubber sheathed flexible cables,
and

d) Plastic insulated cables equivalent to ordinary
tough rubber sheathed flexible cables.

Use of screened cables is also permitted.

All flexible cables shall be provided with braiding for
mechanical protection.

7.2.6.2 An effective cable clamping device so designed
as not to damage the insulation of the flexible cable,
should be provided at the points of entry of the flexible
cable to the apparatus and plug. In addition, means
should be provided to prevent sharp bending of the
cable at both points of entry.

7.2.7 Protective Measures from Dangerous Sparking

7.2.7.1 Dangers from live parts

In order to avoid the formation of sparks liable to ignite
the explosive gas atmosphere, any contact with bare
live parts other than intrinsically safe parts shall be
prevented.

Where this requirement is not met by construction other
precautions shall be taken. In certain cases a warning
label such as 'Isolate elsewhere before opening' may
be sufficient.

7.2.7.2 Dangers from exposed and extraneous
conductive parts

It is impracticable to cover all possible systems in this
case but the basic principles on which safety depends
are the limitation of earth currents (magnitude and
potentials on equalizing conductors).

NOTE — The term extraneous conductive parts is defined as a
conductive part likely to propagate a potential and not forming
part of the electrical installation.

Guidance on permissible power systems is given below:

a) If a power system with an earthed neutral is
used, the type TN-S system with separate
neutral (N) and protective conductor (PE)
throughout the system is preferred.

The neutral and the protective conductor shall
not be connected together, or combined in a
single conductor, in a hazardous area.
A power system of type TN-C (having
combined neutral and protective functions in
a single conductor throughout the system) is
not allowed in hazardous areas.

b) If a type IT power system (separate earths for
power system and exposed conductive parts)
is used in Zone 1 , it shall be protected with a
residual current device even if it is a safety
extra-low voltage circuit (below 50 V).
The type TT power system is not permitted
in Zone 0.

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c) For an IT power system (neutral isolated from
earth or earthed through impedance), an
insulation monitoring device should be used
to indicate the first earth fault. However
equipment in Zone shall be disconnected
instantaneously in case of the first earth fault,
either by the monitoring device or by a
residual current operated device.

d) For all power systems installed in Zone 0,
irrespective of the voltages., due attention should
be paid to the limitation of earth fault currents
in magnitude and duration. Instantaneous earth
fault protection shall be installed.

NOTE — It may also be necessary to provide
instantaneous earth fault protection devices for certain
applications in Zone 1 .

7.2.7.3 Potential equalization

To avoid dangerous sparking between metallic parts
of structures, potential equalization is, always required
for installations in Zone and Zone 1 areas and may
also be necessary for installations in Zone 2 areas.
Therefore, all exposed and extraneous conductive parts
shall be connected to the main or supplementary
equipotential bonding system.

The bonding system may include normal protective
conductors, conduits, metal cable sheaths, steel wire
armouring and metallic parts of structures but shall not
include neutral conductors. The conductance between
metallic parts of structures shall correspond to a cross
section of at least 10 mm 2 of copper.

Enclosures need not be separately connected to the
equipotential bonding system if they are secured to and
are in metallic contact with structural parts or piping
which are connected to the equipotential bonding
system. For additional information, see relevant Indian
Standards.

However, there are certain pieces of equipment, for
example some intrinsically safe apparatus, which are
not intended to be connected to the equipotential
bonding system.

NOTE — Potential equalization between vehicles and fixed
installations may require special means, for example, when
insulated flanges in connecting pipelines are used.

7.2.7.4 Cathodically protected metallic parts

Cathodically protected metallic parts located in
hazardous areas are live extraneous conductive parts
which shall be considered potentially dangerous
(especially if equipped with the impressed current
method) despite their low negative potential. No
cathodic protection shall be provided for metallic parts
in Zone unless they are specially designed for this
application.

7.2.7.5 Electromagnetic radiation

Account should be taken of the effects due to strong
electromagnetic radiation.

7.3 Selection of Equipment

7.3.1 General

7.3.1.1 The selection of electrical apparatus for
explosive gas atmospheres is based on the general
principle that the likelihood of the simultaneous
presence of a hazardous atmosphere and a source of
ignition is reduced to an acceptably low level.

7.3.1.2 When the electrical apparatus does not have an
internal release of flammable material, the
classification of the hazardous area surrounding the
electrical equipment decides the selection of an
adequate type of protection.

7.3.1.3 When the electrical apparatus has an internal
release of flammable material, the actual hazard is a
combination of the external and internal hazards and
both must be taken into account when selecting an
adequate type of protection.

7.3.1.4 The selected apparatus will normally have a
recognized type of protection and should also be
selected for the appropriate temperature class and the
appropriate apparatus group applicable. Where gases
of different degrees of hazard exist in the same area,
the type of protection appropriate for the highest degree
of hazards shall be applicable.

7.3.1.5 The selected electrical apparatus shall be
adequately protected against corrosive and solvent
agencies, and against water ingress and thermal and
mechanical stresses as determined by the
environmental conditions. These construction
requirements should ensure that the protection against
explosion is not reduced when the apparatus is used in
the specified conditions of service.

7.3.1.6 Particular consideration shall be given to the
location of apparatus which incorporates aluminium
or light alloys in the construction of its enclosure. These
have been outlined in IS 5571 reference to which
should be made {see also IS/IEC 60079-1).

7.3.1.7 As electrical apparatus for flammable gas
atmospheres requires special safety maintenance after
they are installed, the selection of electrical apparatus
shall be made with full considerations to the facility
and frequency of inspection and maintenance,
preparation for spares and repairing materials and the
extent of allowable interruption of power supply during
maintenance work.

7.3.1.8 It is advisable that the selection of electrical
apparatus be made after full considerations have been

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given not only to the initial cost of installation but also
to the expected life and expenses for operation and
maintenance of the apparatus.

7.3.1.9 Unless otherwise specified for particular
equipment, the guidance provided in Table 2 shall be
followed in the selection of equipment for hazardous
areas. However, any equipment which in the opinion
of the authorised inspector affords a degree of safety
not less than that afforded by the equipment specified
may be accepted as an alternative.

7.3.1.10 The necessity for equipment with flameproof
enclosures or other enclosures may sometimes be
eliminated by the adoption of special design, such as
pressurised equipment.

7.3.2 Selection Procedure

7.3.2.1 In order that electrical apparatus may be
selected for use in hazardous area, the following
information is necessary:

a) The classification of the area, that is, the zone
(see 7.2.1.1).

b) The ignition temperature of the gas or vapour
involved, or the lowest values of ignition
temperature if more than one combustible
material is present.

This will permit determination of the
temperature classification required for the
apparatus, or the upper-limit temperature
for any unprotected surface according to
IS/IEC 60079-0 (see 7.3.2.3).

c) The characteristics of the gas or vapour
involved in relation to (see 7.3.2.3).

1) Ignition current or minimum ignition
energy in the case of installations of
intrinsically safe apparatus, or

2) Safe gap data in the case of installations
for flameproof enclosures.

Apparatus certified to the constructional and design
requirements for a particular group may also be used
with compounds of lesser risk and which would be
allocated therefore to a lesser group, subject again to
consideration of temperature classification and
chemical compatibility.

Similarly electrical apparatus which is designed so that
it may be used with certain flammable materials in a
particular zone may be used with flammable materials
in zone of lesser risk without restriction provided it is
determined that the flammable materials likely to be
present are compatible with the following
characteristics of the apparatus:

a) Apparatus grouping (where this is applicable).

b) Temperature classification.

c) Chemical compatibility.

7.3.2.2 Selection of type of protection

The selection of type of protection of the equipment
for different zone of hazardous areas shall be made in
accordance with Tables 2, 3 and 4 as applicable.

7.3.2.3 Temperature classes

Besides the danger of explosion caused by an electric
spark or arc, there is also a danger of ignition at a hot
surface exposed to a flammable atmosphere. The
maximum surface temperature of any unprotected
surface of electrical equipment should not exceed the
ignition temperature of the gas or vapour.

Flammable gases and vapours fall into fairly well-
defined groups when classified with reference to their
ignition temperature. To simplify the manufacture of
apparatus, therefore, the permitted maximum surface
temperatures have been classified in IS/IEC 60079-0
as follows:

Temperature

Ignition

Allowable

Class

Temperature

Required by

of Gas or

Classes of

the Area

Vapour

Equipment

Classification

(°C)

>450

T1-T6

>300

T2-T6

>200

T3-T6

>135

T4-T6

>100

T5-T6

>85

If the marking of the electrical equipment does not
include an ambient temperature range, the equipment
shall be used only within the temperature range
-20 °C to +40 °C. If the marking of the electrical
equipment includes an ambient temperature range, the
equipment shall only be used within this range.

If there is an influence from an ambient temperature
outside the temperature range, the process temperature
or exposure to sun light, the effect on the equipment
shall be verified as suitable for the application and
documented.

Ambient temperatures do not consider solar radiation.
Where applicable, additional factors should be applied.

Junction boxes and switches in intrinsically safe
circuits, however, can be assumed to have a temperature
classification of T6 because, by their nature, they do
not contain heat dissipating components. Simple
apparatus used within an intrinsically safe circuit shall

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Table 2 Types of Protection for Different Hazardous Areas
(Clauses 7.3.1.9 and 7.3.2.2)

SI No. Area

Classification

(1) (2)

Type of Protection

(3)

Description

(4)

Zone Electrical equipment and

circuits can be used in Zone 0,
if they are constructed in
accordance with following:
a) Intrinsic safety
(category "i a ") according
to IS 5780

b) EPL "Ga"

Intrinsic Safety (Ex-i)

A circuit or part of a circuit is intrinsically safe when any spark or thermal
effect produced normally (that is, by breaking or closing the circuit) or
accidentally (for example by short-circuit or earth fault) is incapable, under
prescribed test conditions, of causing ignition of a prescribed gas or vapour.

EPL "Ga"

Equipment for explosive gas atmospheres, having a "very high" level of
protection, which is not a source of ignition in normal operation, expected
malfunction or when subject to rare malfunction. Such equipment will have a
form of protection which will remain effective even in the presence of two
potential faults (for example, intrinsic safety, level of protection i a ), or will
have two independent means of protection (for example, Ex-e and Ex-d acting
independently of each other).

ii)

Zone 1

Electrical equipment can
be used in Zone 1 if it is
constructed in accordance
with the requirements for
Zone or one or more of
the following types of
protection:
a) EPL"Gb"

b) Flameproof enclosures
"d" according to
IS/IEC 60079-1

c) Pressurized enclosures
"p" according to IS 7389

d) Powder filling "q"
according to IS 7724

e) Oil immersion "o"
according to IS 7693

EPL "Gb"

Equipment for explosive gas atmospheres, having a "high" level of protection,
which is not a source of ignition in normal operation or when subject to faults
that may be expected, though not necessarily on a regular basis

Flameproof enclosures (Ex-d)

An enclosure for electrical apparatus that will withstand when the covers or
other access doors are properly secured, an internal explosion of the flammable
gas or vapour which may enter it or which may originate inside the enclosure,
without suffering damage and without communicating the internal flammation
to the external flammable gas or vapour for which it is designed, through any
joints or structural openings in the enclosure.

Pressurized Enclosure (Ex-p)

An enclosure for electrical apparatus in which the entry of flammable gas or
vapour is prevented by maintaining the air (or other non-flammable gas)
within the enclosure at a pressure above that of the external atmosphere.
This type of protection has the following categories (for choice see Table 3):

5)
6)

Pressurization with air and alarm in case of loss of air pressure

[Ex-p(l)].

Pressurization with air and automatic switching off from electric supply

in case of loss of air pressure [Ex-p (2)].

Pressurization with inert gas and alarm in case of loss of inert gas

pressure [Ex-p (3)].

Pressurization with inert gas and automatic switching off from electric

supply in case of less of inert gas pressure [Ex-p (4)].

Dilution with air and alarm in case of loss of air supply [Ex-p (5)].

Dilution with air and automatic switching off from electric supply in case

of loss of air supply [Ex-p (6)].

Sand-filled apparatus (Ex-q)

Electrical apparatus which has all its live parts entirely embedded in a mass of

powdery material, in such a way that under the conditions of use for which the

apparatus has been designed no arc occurs within the outer explosive

atmosphere either by the transmission of flame or by the overheating of the

walls of the enclosure.

Oil Immersed Apparatus (Ex-o)

Electrical apparatus in which all parts in which an arc may occur in normal

service are immersed in oil to a sufficient depth to prevent ignition of an

explosive gas mixture that may be present above the surface of the oil, and all

live parts in which arcs do not occur in normal service are either immersed in

oil or protected bv some other recognised techniques (see Notes 3 and 5).

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Table 2 — (Concluded)

SI No,

Area
Classification

(1) (2)

Type of Protection

(3)

Description

(4)

f) Intrinsic safety "i b "
according to IS 5780

g) Encapsulation "m"
according to IS/IEC
60079-18

Intrinsically Safe Apparatus (Ex-ib)

Electrical apparatus in which all the circuits are intrinsically safe.

Encapsulation "m" (Ex-m)

Type of protection whereby parts that are capable of igniting an explosive
atmosphere by either sparking or heating are enclosed in a compound in such a
way that the explosive atmosphere cannot be ignited under operating or
installation conditions.

iii) Zone 2

h) Electrical Heat Tracers
and equipment which
are certified for use in
Zone 1 areas

a) Electrical equipment can
be used in Zone 2 if it is
constructed in
accordance with the
requirements for Zone 0/
Zone 1 or one or more
of the following types of
protection:

EPL "Gc"

b) Non-sparking "n"
according to IS/IEC
60079-15 (see Note 2)

c) Intrinsic safety "i c "
according to IS/IEC
60079-11

d) Increased safety "e"
according to IS/IEC
60079-7 (see Note 2)

e) Electrical Heat Tracers
and equipment, which are
certified for use in Zone 2

EPL "Gc"

Equipment for explosive gas atmospheres, having a "enhanced" level of
protection, which is not a source of ignition in normal operation and which
may have some additional protection to ensure that it remains inactive as an
ignition source in the case of regular expected occurrences (for example failure
of a lamp).

Non-sparking Apparatus (Ex-n)

Apparatus which in normal operation is not capable of igniting a surrounding

explosive atmosphere, and a fault capable of causing ignition is not likely to occur.

Intrinsically Safe Apparatus (Ex-i c )

Electrical apparatus in which all the circuits are intrinsically safe.

Increased Safety (Ex-e)

A method of protection in which measures additional to those adopted in ordinary
industrial practice are applied, so as to give increased security against the possibility
of excessive temperatures and the occurrence of arcs or sparks in electrical
apparatus which does not produce arcs or sparks in norma] service.

NOTES

1 Special protection category is reserved for those types of protection that cannot be classified as belonging wholly to anyone of the
above types. It may be that a combination of several types of protection is incorporated within one piece of apparatus.

2 For outdoor installation, the apparatus with type of protection 'e' and 'n' should be used with enclosures providing at least the
following degree of protection:

a) IP 55 where there are uninsulated conducting parts internally, and

b) IP 44 for insulated parts.

3 Oil-immersed apparatus may be used only in case its security will not be impaired by tilting or vibration of the apparatus.

4 For apparatus with type of protection *p\ 'c\ 'n' and where applicable, 'q' only area classification and ignition temperature are
required. However, where apparatus is protected by Ex-'i' or Ex-'d' in addition to one of these types of protection, it is necessary to
determine the appropriate apparatus grouping according to IS/IEC 60079-1 1 and IS/IEC 60079-1 respectively.

5 Type "o" equipment shall not be used in Zone 1 area in Oil mines.

6 Even though, in general, use of increased safety equipment in Zone 1 area is not permitted, certain equipment having a combination of Ex-i,
Ex-e and Ex-d protection may be used in Zone 1 areas, provided the Ex-e protection is limited to the termination of cables / wires only.

7 Various Indian standards for electrical equipment for hazardous areas have been aligned with IEC Standards to facilitate
manufacturers and testing bodies. However selection and installation of these equipment in hazardous areas shall follow IS 5571.

8 Requirements of diesel engines for hazardous areas are covered in Annex D.

Table 3 Minimum Actions on Failure of Protective Gas for Type of Protection 'p'

(Clause 7.3.2.1)

SI. No

(1)

Area Classification

(2)

Enclosure Does not Contain Ignition-
Capable Apparatus

(3)

Enclosure Contains Ignition-Capable
Apparatus

(4)

i)
ii)

Zone 1
Zone 2

Alarm

No action required

Alarm and switch off
Alarm

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Table 4 Adequate Types of Protection for Electrical Apparatus with an Internal Source of Release

(Clause 7.3.2.1)

SI No.

Normal
(1) (2)

Internal Release
^ s

Abnormal

Area

Classification - —

Type of Protection

(3)

(4)

(5)

e
(6)

(7)

ib
(8)

(9)

P(l) P(2) P(3) P(4) P(5) P(6)
(10) (11) (12) (13) (14) (15)

Restricted
Unrestricted
Restricted
Unrestricted
iii) Unrestricted Not relevant
iv) Not relevant Not relevant

i) None

ii) Restricted

NH, Zone 2
Zone 1

NR Zone 2
Zone 1
ZoneO

•

2
>/
2
S

NOTE

NH : Non-hazardous area.

S : Adequate.

1 : Adequate, if the internal components of circuits have type of protection adequate for Zone-1.

2 : Adequate, if the internal components of circuits are not ignition-capable during normal operation.
— : Not adequate

2
2
2

2
2

be temperature classified in accordance with IS 5571.

Cable glands in normal service do not create a heat
source and therefore do not have a temperature class
or ambient operating temperature range marked on
them. In general cable glands will be marked with
service temperature. If no marking exists it is assumed
that the service temperature is -20°C to +80°C.

NOTE — Consideration of the capability of the equipment
and cables to operate in the required temperature range should
include normal operating limits as well as temperature rise.

7.3.2.4 Apparatus groups

For the purpose of flameproof enclosures and intrinsic
safety, gases and vapours have been classified
according to the groups or sub-groups of apparatus
required for use in the particular gas or vapour
atmosphere. The groups of the apparatus are:

a) Group I — for mining applications,

susceptible to fire damp

b) Group II — applications in industries with

an explosive gas atmosphere,
other than mines susceptible to
firedamp

c) Group II — apparatus is sub-divided

according to the requirements
appropriate to the nature of the
flammable atmosphere for which
the apparatus is intended. These
sub-groups with a representative
gas and the design parameters are
as follows:

Appara-

Represent-

Maximum

Minimum

tus

ative Gas

Experimental Ignition Current

Sub-

Safe Gap

Ratio

group

(1)

(2)

(3)

(4)

IIA

Propane

>0.9mm

Above 0.8

IIB

Ethylene

Greater than

Between

0.5 mm less

0.45 and 0.8

than 0.9 mm

IIC

Hydrogen

< 0.5 mm

Below 0.45

Various gases and vapours, for which a particular group
of enclosure is suitable are listed in IS 9570.

NOTE — For flameproof enclosures, gases and vapours are
classified according to their maximum experimental safe gap
(MESG). For intrinsic safety, gases and vapours are classified
according to the ratio of their minimum igniting currents (MIC)
with that of laboratory methane {see also IS 9735).

7.3.3 Individual Features of Electrical Equipment for
Hazardous Areas

The essential features of individual equipment for
installation in hazardous areas are indicated in Table 5.

7.4 Miscellaneous Requirements

7.4.1 Exceptional Circumstances

7.4.1.1 In exceptional circumstances (for example,
research, development or repair-work, and in
emergency situations) apparatus may be used which is
not specially designed for use in Zone 1 or Zone 2

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hazardous areas, provided that adequate measures have
been taken to ensure an adequate level of safety.

7.4.1,2 Apparatus which is intended to be used for short
periods only may be of normal industrial design but
only when operating in Zone 2, it is either regularly
supervized by trained personnel or gas-free conditions
are regularly monitored.

7.4.2 Static Electricity (See IS 7689)

7.4.3 Pressurized Rooms

7.4.3.1 Where unavoidable, electrical switchgear and
equipment may be located in a pressurized room within
a hazardous area meeting the following requirements:

a) The pressurized room shall be situated in such
area within a hazardous location, which is least
hazardous and from which the operators
working in the room can easily evacuate in
the event of an accident.

b) Main structural parts such as wells, pillars,
ceiling, floor, doors and the like shall be on
non-combustible materials and shall be
sufficiently resistant to explosion blasts or
other mechanical effects.

c) Structural materials and construction of the
room shall be such as not to allow gases or
vapours to penetrate easily through them.

d) More than one doorway shall be provided, and
at least one of them shall face the direction of
no source of hazard as for as practicable.

e) The design of the doorway facing the
hazardous area shall be such that the doors
can only be opened outwards from the interior
and they shall be double doors.

f) In case it is necessary to provide a window
facing the hazardous area, the window shall
have enough strength to resist an explosion
blast, blowout of gases or other possible
mechanical effects.

g) The source of air shall be free of hazardous
concentrations of flammable gases and
vapours contaminants and any other foreign
matter. It shall be determined from the nature
of the process and the physical layout.

h) The volume and pressure of supply air shall
be such that the air pressure in the vicinity of
doorways is maintained higher than the
atmospheric pressure outside the room.

j) An alarm or other device shall be provided
so that any disorder in the pressurization
system may be assuredly noticed.

k) Openings to lead wirings or pipings from the
hazardous locations into the room shall be so
constructed as not to admit explosive gases

into the room, by filling tightly the space
around conduits or pipes with cement or
similar incombustible materials.

NOTE — Elevated ambient temperatures can be
expected in pressurized rooms. Accordingly, it is
advisable that due account be taken while selecting
electrical equipment for installation in pressurized
rooms.

7.4.3.2 Prior to commissioning apparatus protected by
pressurization or continuous dilution, it shall be verified
by competent personnel that the installation of the
equipment fulfils the requirements of relevant Indian
Standards, either by inspection of the reference
documents, or by tests if necessary.

The following shall be considered:

a) the protective gas supply is suitable, that is,
impurities in the protective gas will not reduce
the level of safety such as by attacking the
enclosure or ducting material or introducing
flammable material into the enclosure.

b) The apparatus design and safety provisions
are such that purging can be completed
satisfactorily.

c) The minimum pressure required is maintained
with the minimum protective gas supply stated
by the manufacturer.

d) The maximum temperature limits stated are
not exceeded.

NOTE — Satisfactory completion of purging would
include passing a volume of protective gas of at least
five times the free internal volume of the protected
enclosure and associated ducting, prior to energizing
the electrical apparatus.

With regard to installation practices, the following shall
be considered:

a) For wiring systems:

1) When cable wiring systems are used, the
cable entries shall prevent excess leakage
of the protective gas and ensure that
sparks or incandescent particles do not
escape from the enclosure.

2) When conduit wiring systems are used,
it is recommended that all conduit
entrances to an enclosure be sealed to
prevent excess leakage of protective gas
unless the conduit system is being used
as a duct for supplying the protective gas.

b) The point at which the protective gas enters
the supply duct or ducts should be situated in
a non-hazardous area.

c) Ducting should, as far as possible, be located
in a non-hazardous area. If ducting passes
through a hazardous area, it shall be checked

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Table 5 Features of Electrical Equipment

(Clause 7.3.3)

SI No. Equipment ZoneO

(1) (2) (3)

Zone 1

(4)

Zone 2

(5)

Motors

No motor shall be
used in this area

ii)

Transformers
and capacitors

No transformer or
capacitor shall be
used in this area

iii)

iv)

vi)

Lighting fittings
(.see Notes 1 and

Switchgear and
control gear

Generators

No lighting fitting
shall be used

No switchgear and
control gear shall
be used. When not
practicable use
type T protection

No generator shall
be used

Diesel engines Unacceptable

vii)

Storage batteries Shall not be used

a) Motor with type of
protection 'd'

b) Motors with type of
protection 'p'

a) All power and distribution
transformers and capacitors
with type 'd' protection.

b) Type T protection for
control and instrumentation,
with transformers and
capacitors forming part of
flameproof or intrinsically
safe equipment.

All switches, circuit
breakers, fuses and other
equipment shall be housed in
an enclosure with type 'd'
protection.

All switches circuit breakers,
fuses and other equipment,
the enclosure together with
the enclosed apparatus shall
be type 'd' protection.

Generators with Type *d'
and 'p* protection

a) Motor suitable for Zone-1 area.

b) Motors with type of protection 'n' and 'e\ However,
all normally sparking parts such as slip-rings and brushes
shall be provided with type of protection 'd' or 'p\ .

Motors provided with a combination of the above forms
of protection. For example, slip-ring motors in which the
main enclosures and windings are of type 'e' but the
normally sparking parts of type 'd' protection

Transformers and capacitors suitable for Zone 1 area.
Transformers and capacitors that are dry type or
containing liquids need not have any special enclosure
provided that the following requirements are satisfied:

a) Cable boxes shall be suitable for specified level of
current and fault clearing time.

b) Only off-circuit manually operated tap changers shall
be allowed with provision for locking the operating
handle in position.

c) Auxiliary devices shall be intrinsically safe or if they
have sparking contacts, these shall be:

l)Type'd'

2) Under adequate head of oil.

3) of mercury in glass type with adequate mechanical
protection.

4) of enclosed break type or, alternatively, auxiliary devices
may be deleted or installed in a safe zone.

d) Any other sparking accessories or switches shall
comply with the requirements for Zone 1 area. Where oil
filled transformers are used, necessary precautions against
spread of fire (see IS 1646) shall be complied with.

a) Lighting fittings for Zone 1 .

b) Lighting fittings with type of protection 'e' or 'n\

All equipment where arcing may occur under normal
conditions of operating shall be of type 'd', unless the
current interrupting contacts are oil-immersed, or the
switches are enclosed break type with flameproof
breaking chamber or having mercury in glass switches or
enclosed break micro switches.

Equipment suitable for Zone 1 areas. Generators with
type 'n' protection or V and having brushless excitation
system and sparking parts, if provided shall comply with
Zone 1 requirements.

a) The use of permanently installed diesel engines to be
avoided.

b) Equipment suitable in Zone 1 areas.

The use of permanently
installed diesel engines to be
avoided.

Where necessary, they shall
satisfy the requirements as
given in Annex D.

Storage batteries shall not be Storage batteries shall be of type V protection (see also

installed in Zone 1 areas, except Annex E).

those in portable torches where

the enclosures housing the bulb,

switch and battery shall be

flameproof type.

NOTES

1 Low-pressure sodium lamps shall not be used in a hazardous area owing to the risk of ignition from the free sodium from a broken lamp.

2 If luminaires with fluorescent lamps are used in a hazardous area, then the area should be confirmed to be free from group IIC
gas/vapour before lamps are transported through the area or changed, unless suitable precautions are taken to prevent tubes being broken.

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for leaks prior to start-up of the electrical
apparatus to ensure that the requirements of
7.4.3.2 (a) are met.
d) Exhaust ducting shall vent to a non-hazardous
area or otherwise be designed to prevent the
emission of sparks or hot particles such as by
the use of spark arrestors or baffles. Care
should be taken to ensure that the exhaust does
not result in a secondary hazardous source in
an otherwise non-hazardous area.

7.4,4 Intrinsically Safe Installations

A fundamentally different installation philosophy has
to be recognized in the installation of intrinsically safe
circuits. In comparison with all other types of
installations, where care is taken to confine electrical
energy to the installed system as designed so that a
hazardous environment cannot be ignited, the integrity
of an intrinsically safe circuit has to be electrically
protected from the environment in order that the safe
energy limitation in the circuit is not exceeded, even
when breaking, shorting or earthing of the circuit
occurs.

As a consequence of this principle the aim of the
installation rules for intrinsically safe circuits is to
maintain separation from other circuits.

7.4.4.1 Intrinsically safe circuits may be installed
either;

a) isolated from earth, or

b) connected at one point to the potential
equalization conductor if this exists in the
whole area of the installation of the
intrinsically safe circuits, or

c) connected to earth at one point only, if
earthing is required for functional or
protective purposes.

The installation method shall be chosen with regard to
the functional requirements of the circuits according
to the manufacturers' instructions.

If the circuit is isolated from earth, particular attention
should be given to any possible danger due to static
charges.

More than one earth connection is permitted on a
network provided that the network is galvanically
separated into circuits each of which has only one earth
point.

7.4.4.2 Where a safety barrier is used, the maximum
fault voltage in apparatus connected to the barrier input
terminals shall not exceed the fault voltage rating of
the barrier, for example, 250 V. Where a safety barrier
requires a connection to earth, the connecting load to

the earthing terminal of the safety barrier should be as
short as possible. The cross-section of the connecting
load shall take account of the short circuit current to
be expected, and shall have a minimum value of 1.5 m 2
copper.

Consideration should be given to the need for earthing
of the supply system connected to the barrier input
terminals.

7.4.4.3 In installations with intrinsically safe circuits,
for example, in measuring and control cabinets, the
terminals shall be reliably separated from the non-
intrinsically safe circuits (for example, by a separating
panel, or a gap of at least 50 mm). The terminals of the
intrinsically safe circuits shall be marked as such. All
terminals shall satisfy the requirements of relevant
Indian Standards.

Where terminals are arranged to provide separation of
circuits by spacing alone, care shall be taken in the
layout of terminals and the wiring method used, to
prevent contact between circuits should a wire become
disconnected.

7.4.4.4 Enclosures and wiring of intrinsically safe
circuits should meet the requirements which would be
applied to similar types of equipment which are
intended to be installed in non-hazardous areas
otherwise having the same environmental conditions.
If an enclosure contains both intrinsically safe circuits
and non-intrinsically safe circuits, the intrinsically safe
circuits shall be clearly identified.

In installation containing both intrinsically safe
apparatus and apparatus having another type of
protection, the intrinsically safe circuits shall be clearly
marked.

7.4.4.5 Marking may be achieved by labelling or colour
coding of enclosure, terminals and cables. Where a
colour is used for this purpose it shall be light blue.

7.4.4.6 Where intrinsically safe circuits may be exposed
to disturbing magnetic or electric fields, suitable
attention shall be given to transposition or shielding to
ensure that these fields do not adversely affect the
intrinsic safety of the circuit.

7.4.4.7 Unless specifically permitted, conductors of
intrinsically safe circuits and conductors of non-
intrinsically safe circuits shall not be run together in
cables, cords, conduits, or bundles. In cable ducts and
trays, intrinsically safe cables shall be separated from
non-intrinsically safe cables by a mechanical barrier.
Such a barrier is not required if all cables are provided
with additional protective sheathing or sleeves which
provide equivalent separation, or if the cables are

PART 7 ELECTRICAL INSTALLATIONS IN HAZARDOUS AREAS

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securely fastened to ensure that physical separation is
maintained.

7.4.4.8 A flexible cable may contain more than one
intrinsically safe circuit if the cable installation is such
as to minimize the risk of damage which could cause
interconnection between different circuits.

7.4.4.9 The installation of intrinsically safe circuits
shall be such that the extreme permitted values, such
as capacitance, inductance and inductance to resistance
ratio, are not exceeded. The permissible values shall
be taken from the certificate, the nameplate of the
apparatus, or from the installation instructions.

7.4.4.10 Where intrinsically safe circuits are
interconnected to form a system, due account shall be
taken by calculation or by measurement of the resultant
combination of electrical parameters, such as
inductance, and capacitance, which may affect the
intrinsic safety of the system as a whole.

NOTE — In addition to electrical sparking due account should
be taken of thermal effects particularly where non-certified
apparatus is used.

7.4.4.11 The following equipment is considered to be
intrinsically safe without certification:

Devices whose electrical parameters, according to the
manufacturer's specification, do not exceed any of the

values 1 .2 V, 0. 1 A, 20 J or 25 mW need not be certified

or marked. They will be subject, however, to the
requirements of relevant Indian Standard, if they are
connected to a device which contains a source of energy
which could cause the circuit to exceed these parameters.

8 TESTING OF INSTALLATION

8.0 All equipment intended for use in hazardous areas
shall be approved by a recognized, testing and
certifying authority (see 4.2).

8.1 Installation tests should include insulation
resistance and earth continuity resistance and the
checking of fused ratings and other protection devices,
settings and operation.

8.2 For periodical electrical testing, the following
precautions shall be followed:

a) Insulation tests should, in general, be carried
out with certified intrinsically safe insulation
tester for use in hazardous areas.

b) Earth continuity tests, in general, be carried
out with certified intrinsically safe earth tester
embodying a hand-driven generator suitable
for use in hazardous areas.

c) The rating of fuses and the settings of
protective devices, where practicable, and the
operation of other protective devices should
be checked.

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SP 30: 2011

ANNEX A
(Clause 1.4)

EXAMPLE OF INDUSTRIES AND THEIR WORKING PLACES WHICH REQUIRE
CONSIDERATIONS IN REGARD TO HAZARDOUS LOCATIONS

A-l Though it is difficult to determine hazardous
locations merely according to kind of industries or kind
of working places, typical industries and working
places, which require considerations in regard to
hazardous locations are listed below:

1) Ammonium sulphate manufacturing
industry — Places where gaseous raw
materials are produced, electrolysis of water
is conducted or synthesis of ammonia is
carried out.

2) Soda manufacturing industry — Working
places of electrolysis, synthetic hydrochloric
acid manufacturing and liquid chlorine
handling.

3) Electric furnace industry — Working places
where calcium carbide is pulverised and stor-
age of it.

4) Compressed or liquefied flammable gas
industry — Working places where flammable
gases are produced, compressed or filled.
Storage of containers filled with flammable
gases.

5) Coal tar products industry — Working places
where coal tar is fractionally distilled or light
oil extracted from coal is refined or
fractionally distilled. Places where benzene
or the other volatile flammable liquids are
filled or stored.

6) Dyestuffs and their intermediates
manufacturing industry — Working places
where flammable gases or volatile flammable
liquids are handled in large quantity.

7) Fermentation industry — Working places
where volatile flammable liquids are distilled
or filled. Storage of volatile flammable
liquids.

8) Acetylene, ethylene or methanol derivative
manufacturing industries — Working places
where gaseous raw materials or volatile
flammable liquids are produced, refined
reacted, distilled, filled, or stored.

9) Synthetic resin and plastic manufacturing
industry — Working places where flammable
gases or volatile flammable liquids are hand-
led in large quantity.

10) Synthetic fibres manufacturing industry —
Working places where flammable gases or
volatile flammable liquids are added, reacted,
produced, recovered or stored.

11) Vegetable oil industry, solvent extraction
plants — Working places where extraction
or recovery is conducted using volatile
flammable liquids. Storage of volatile
flammable liquids. Hydrogeneration plants.

12) Fatty acids, hardened oil and glycerin
manufacturing industry — Working places
where hydrogen is produced or added. Other
working places where flammable gases or
volatile flammable liquids are used in large
quantity.

13) Wood dry distillation industry — Working
places where dry distillation or rectification
is conducted. Places where volatile flammable
liquids are filled or stored.

14) Drugs and medicine manufacturing indus-
try — Working places where flammable gases
or volatile flammable liquids are handled in
large quantity. Storage of the gases and liquids.

15) Paints manufacturing industry — Working
places where volatile flammable paints or
thinners are produced. Places where volatile
flammable raw materials or finished products
are stored.

16) Insecticides and germicides manufacturing
industry — Working places where flammable
gases or volatile flammable liquids are
handled in large quantity.

17) Perfumes and cosmetics manufacturing
industry — Working places where volatile
flammable liquids are added, prepared,
distilled or extracted. Storage of these liquids.

18) Photographic sensitive materials manufactur-
ing industry — Working places where volatile
flammable liquids are added, prepared,
applied, recovered or distilled. Storage of
these liquids.

19) Oil refining and petrochemical industry —
Working places where various refining pro-
cesses or chemical reactions are conducted.
Places where volatile flammable liquids are
transported, filled or stored.

20) Gum products industry — Working places
where gum arabic is produced or applied.
Storage of volatile flammable liquids.

21) Brewing industry — Places where alcohol is
distilled, added or stored.

22) Processed paper or coated cloth
manufacturing industry — Working places

PART 7 ELECTRICAL INSTALLATIONS IN HAZARDOUS AREAS

373

SP 30 : 2011

where volatile flammable liquids are added,
applied or recovered.

23) Dry-cleaning industry — Working places
where washing using flammable liquids and
recovery of the said liquids are conducted.
Storage of the said liquids.

24) Finishing processes — Working places where
preparation of volatile flammable paints,
locations where paints, lacquers or other
flammable finishers are regularly or
frequently applied by spraying, dipping,
brushing or by other means, where flammable
thinners are used, and where readily ignitable

deposits or residues from such paints, lacquers
finishers may occur.

25) Printing industry — Working places where
printing is done using inks with addition of
volatile flammable liquids.

26) Aircraft hangars — Location used for storage
or servicing of aircraft in which gasoline, jet
fuels or other volatile flammable liquid or
flammable gases are used.

27) Petrol bunks and service stations — Location
where petrol or other volatile flammable
liquids, or liquefied flammable gases are
transferred to the fuel tanks of vehicles.

ANNEX B
{Clause 2)

INDIAN STANDARDS FOR ELECTRICAL EQUIPMENT FOR
USE IN EXPLOSIVE ATMOSPHERES

IS No.

1554 (Parti): 1988

1646 : 1997

2309 : 1989

5571 : 2009

5572 : 2009

7689 : 1989

7724 : 2004/
IEC 60079-5

7820 : 2004/
IEC 60079-4

9570 : 1980/
IEC -60079-12:

1978

9735 : 2003/
IEC 60079-1-1

Title

PVC insulated (heavy duty) electric

cables: Part 1 For working voltages

upto and including 1 1 00 V

Code of practice for fire safety of

buildings (general): Electrical

installations

Code of practice for the protection

of buildings and allied structures

against lightning

Guide for selection and

installation of electrical

equipment for hazardous areas

Classification of hazardous areas

(other than mines) having

flammable gases and vapours for

electrical installation

Guide for the control of

undesirable static electricity

Electrical apparatus for explosive

gas atmoshperes — Powder filling

"q"

Electrical apparatus for explosive

gas atmospheres — Method of test

for ignition temperature

Classification of flammable gases

or vapours with air according to

their maximum experimental safe

gaps and minimum igniting

currents

Electrical apparatus for explosive

gas atmospheres — Flameproof

IS No.

Title

2002

enclosures "d" — Method of test

for ascertainment of maximum

experimental safe gap

IS/IEC 60079-0 :

Explosive atmospheres: Part

2004

General requirements

IS/IEC 60079-1:

Explosive atmospheres: Part 1

2007

Equipment protection by

flameproof enclosures "d"

IS/IEC 60079-2 :

Explosive atmoshperes: Part 2

2007

Equipment protection by

pressurized enclosures "p"

IS/IEC 60079-6 :

Explosive atmospheres : Part 6

2007

Equipment protection by oil-

immersed "o"

IS/IEC 60079-7 :

Explosive atmoshpheres :

2006

Part 7 Equipment protection by

increased safety *e'

IS/IEC 60079-11:

Explosive atmospheres : Part 1 1

2006

Equipment protection by intrinsic

safety "i"

IS/IEC 60079-15:

Explosive atmospheres: Part 15

2005

Construction, test and marking of

type of protection "n" electrical

apparatus

IS/IEC 60079-18:

Explosive atmospheres: Part 18

2004

Construction, test and marking of

type of protection encapsulation

"m" electrical apparatus

374

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SP 30: 2011

ANNEX C
(Clause 7.1.2.2)

LIGHTNING PROTECTION OF STRUCTURES WITH EXPLOSIVE OR HIGHLY

FLAMMABLE CONTENTS

C-0 The presence of explosives or highly flammable
materials in a structure may increase the risk to persons
or to the structure and the vicinity in the event of a
lightning stroke. For this reason higher degree of
protection is essential for these structures. Protection
of a different degree may be secured in the case of
both inherently self-protecting and other structures by
installation of various types of protection equipment,
such as vertical and horizontal air terminations and
other means. The recommendations given in C-l
to C-5.4 should be followed for structures in which
explosive or highly flammable solids, liquids, gases,
vapours or dusts are manufactured, stored or used or
in which highly flammable or explosive gases, vapours
or dusts may accumulate.

C-l PRECAUTIONS

C-l.l Following precautions should be taken for the
protection of structures and their contents from
lightning.

a) Storage of flammable liquids and gases in all-
metal structures, essentially gas-tight,

b) Closure or protection of vapour or gas
openings against entrance of flames,

c) Maintenance of containers in good condition,
so far as potential hazards are concerned,

d) Avoidance, so far as possible, of the
accumulation of flammable air-vapour
mixtures about such structures,

e) Avoidance of spark gaps between metallic
conductors at points where there may be an
escape or accumulation of flammable vapours
or gases.

f) Location of structures not inherently self-
protecting in positions of lesser exposure with
regard to lightning, and

g) For structures not inherently self -protecting, the
establishment of zones of protection through use
of earthed rods, masts, or the equivalent.

C-2 GENERAL PRINCIPLES OF PROTECTION

C-2.1 For the protection of structures with explosives
or highly flammable contents the general principles
are given below. In case of doubt, expert advice should
be sought.

C-2.2 An air termination network should be suspended
at an adequate height above the area to be protected. If

one horizontal conductor only is used, the protective
angle adopted should not exceed 30°. If two or more
parallel horizontal conductors are installed, the
protective angle to be applied may be as much as 45°
within the space bonded by the conductors, but it
should not exceed 30° outside that space. The height
of the horizontal conductor should be sufficient to avoid
all risk of flashover from the protective system to the
structure to be protected. The supports of the network
should be adequately earthed.

C-2.3 Where the expense of the method given in C-2.2
is unjustified, and where no risk is involved in
discharging the lightning current over the surfaces of
the structure to be protected, a network of horizontal
conductors with a spacing of 3 m to 7.5. m, according
to the risk, should be fixed to the roof of the structure.

C-2.4 If the vertical conductor is separate from the
structure to be protected, the minimum clearance
between it and the protected structure shall be not less
than 2 m; this clearance should be increased by 1 m for
every 10 m of structure height above 15 m to prevent
side flashes. Also the minimum clearance between the
suspended horizontal air termination and the highest
projection on the protected structure shall be 2 m.

C-2.5 A structure which is wholly below ground and
which is not connected to any services above ground
may be protected by an air termination network in
accordance with C-2.2 by virtue of the fact that soil
has an impulse breakdown strength which can be taken
into account when determining the risk of flashover
from the protective system to the structure to be
protected, including its services. Where the depth of
burying is adequate, the air termination network may
be replaced by a network of earthing strips arranged
on the surface in accordance with expert advice. Where
this method is adopted, the recommendations for
bonding between metal in the structure, or metal
conductors entering the structure given in C-4, should
be ignored.

C-3 TYPES OF LIGHTNING PROTECTION
SYSTEM

C-3.1 These should generally be of the integral
mounted system with the horizontal air terminals
running along the perimeter of the roof in all cases
except for buildings containing highly sensitive
explosives and very small buildings. The following
types of protection are recommended:

PART 7 ELECTRICAL INSTALLATIONS IN HAZARDOUS AREAS

375

SP 30: 2011

Type of Building

(1)

Recommended Type of

Protection

(2)

Building with explosives
dust or flammable
vapour risk

Explosives storage

building and explosives
workshops

Small explosives storage
buildings

Buildings storing more
dangerous types of
explosives, for example,
nitroglycerine (NG) and
for initiatory explosives
manufacturing

Integrally mounted

system with vertical air
terminals 1.5 m high and
horizontal air terminals
spaced 3 to .7.5 m from
each other depending on
the type of storage and
processes involved

Integrally mounted

system with vertical air
terminals 0.3 m high and
horizontal air terminals
spaced 7.5 m.

Vertical pole type.

Suspended horizontal air
terminations at least 2 m
higher than the structure
and with a spacing of 3 m.

C-3.2 Each separate structure protected in accordance
with C-2.3 should be equipped with twice the number
of down conductors recommended in Part 1 /Section 15
of this Code.

C-3.3 The earth terminations of each protective system
should be interconnected by a ring conductor. This ring
conductor should preferably be buried to a depth of at
least 0.5 m unless other considerations, such as the need
for bonding other objects to it, testing, or risk of
corrosion make it desirable to leave it exposed in which
case it should be protected against mechanical damage.
The resistance value of the earth termination network
should be maintained permanently at 10 Q. or less. If
this value proves to be unobtainable, the methods
recommended in IS 2309 should be adopted, or the
ring conductor should be connected to the ring
conductors of one or more neighbouring structures until
the above value is obtained.

C-4 BONDING

C-4.1 All major members of the metallic structure,
including continuous metal reinforcement and services,
should be bonded together and connected to the
lightning protective system. Such connections should
be made at least in two places and should, so far as is
possible, be equally spaced round the perimeter of the
structure at intervals not exceeding 15 m.

C-4.2 Major metal work inside the structure should be
bonded to the lightning protective system.

C-4.3 Electrical conductors entering a structure of this
category should be metal-cased. This metal casing
should be electrically continuous within the structure.
It should be earthed at the point of entry outside the
structure on the supply side of the service and bonded
directly to the lightning protective system.

C-4.4 Where the electrical conductors are connected
to an overhead electric supply line, a length of buried
cable with metal sheath or armouring should be inserted
between the overhead line and the point of entry to the
structure and a surge protective device, for example,
of the type containing voltage-dependent resistors,
should be provided at the termination of the overhead
line. The earth terminal of this protective device should
be bonded direct to the cable sheath or armouring. The
spark over voltage of the lightning protective device
should not exceed one-half the breakdown withstand
voltage of the electrical equipment in the structure. On
account of the low impulse strength of mineral-
insulated metal-sheathed cable, such cables are not
recommended for the above purpose.

C-4.5 Metallic pipes, electrical cable sheaths, steel
ropes, rails or guides not in continuous electrical
contact with the earth, which enter a structure of this
kind, should be bonded to the lightning protective
system. They should be about 75 m away and the other
a further 75 m away.

C-5 MISCELLANEOUS REQUIREMENTS

C-5.1 For a buried structure or underground excavation
to which access is obtained by an adit or shaft, the
recommendation in C-4.5 as regards extra earthing
should be followed for the adit or shaft at intervals not
exceeding 75 m.

C-5.2 The metal uprights, components and wires of
all fences, and of retaining walls in close proximity to
the structure, should be connected in such a way as to
provide continuous metallic connection between
themselves and the lightning protective system.
Discontinuous metal wire fencing on non-conducting
supports or wire coated with insulating material should
not be employed.

C-5.3 The vents of any tanks containing flammable
gas or liquid and exhaust stacks from process plants
emitting flammable vapours or dusts should either be
constructed of non-conducting material or be filled with
flame traps.

C-5, 4 Structures of this category should not be
equipped with a tall component, such as spire or
flagstaff or radio aerials on the structure or within 1 5 m
of the structure. This clearance applies also to the
planting of new trees, but structures near existing trees
should be treated in accordance with IS 2309.

376

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SP 30 : 2011

ANNEX D
[Table 5, SI No. (vi)]

RECOMMENDATIONS FOR THE PROTECTION OF DIESEL ENGINE FOR PERMANENT

INSTALLATION IN HAZARDOUS AREAS

D-0 To ensure a maximum degree of safety in the event
of a permanently installed diesel engine being
necessary in Zone 1 or Zone 2 it is recommended that
it should have the following protection.

D-l The starter shall be either of flameproof electrical
type (usually operated from the mains supply) or of
the following non-electric types:

a) Pneumatic,

b) Hydraulic,

c) Spring recoil,

d) Inertia, or

e) Hand start.

Any other electrical equipment associated with the
engine shall be flameproof, Electrical equipment shall
be effectively earthed and bonded.

D-2 Cooling fan blades shall be made from non-
metallic materials, which do not accumulate
electrostatic charge.

D-3 All belts shall be of antistatic fire resistant type.

D-4 In order to contain discharge of sparks or flames
from the exhaust system; a gas conditioner box and a
flame trap shall be installed. Alternatively, the exhaust
should be designed to discharge to a location within a
safe area.

D-5 To prevent flash back through induction system,
wherever possible, air intakes for engines shall be
located in a safe area. Alternatively, a flame trap should
be installed.

D-6 The surface temperature of the engine and exhaust
system shall not exceed 250°C, when tested under full
load conditions. In some situations cooling of the
exhaust manifold and piping may be necessary, using
water-jacketing or finned coolers and/or high
temperature cut outs or alarms should be provided.

However, when either the free movement of air is
restricted by thermal or acoustic shielding or the
ignition temperature of the surrounding flammable
atmosphere is below 200°C, exposed surface
temperature of engine shall not exceed the minimum
ignition temperature of the gases involved.

D-7 To prevent over speeding of the engine due to
induction of flammable gases or vapours, means shall
be provided to stop the engine. It can be either:

a) a valve to close the air intake, or

b) a system to inject carbon dioxide into the air
intake.

D-8 Alarms or automatic shutdown devices shall be
provided, activated by excessive water temperature and
low lube oil pressure

D-9 A system using an alarm or trip device to protect
the engine from excessive vibration should be
considered.

D-10 An engine having a crankcase volume of over
0.5 m 3 shall be provided with relief devices. Relief
valves or breathers on engines shall be fitted with flame
traps or discharge into the induction system
downstream of the flame trap, if fitted, and upstream
of the shut-off valve, if fitted, as specified in D-7.
Dipsticks and/or filler caps should be screwed or
effectively secured by other means.

D-ll Intake and exhaust system design shall meet the
following minimum requirements:

a) The length of the flame path through or across
any joint shall be not less than 13 mm;

b) Suitable metal-clad or other acceptable j ointing
material shall be interposed between all joint
faces to ensure that leakage does not occur;

c) Where valve spindles pass through the walls
of any component of the induction system.
The diametrical clearance shall not exceed
0.13 mm for an axial length of not less than
25 mm unless end caps are fitted; and

d) No screw, stud or bolt hole shall pass through
the wall of any component of the system.

D-12 Decompression system should not normally be
provided. However, if they are essential, then the
decompression parts should be provided with flame
traps and ducted away to safe area.

D-13 The fuel injection pump land governor, where
fitted, should be so designed that reverse running of
the engine is not possible.

PART 7 ELECTRICAL INSTALLATIONS IN HAZARDOUS AREAS

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SP 30 : 2011

ANNEX E
[Table 5, Item (vii)]

RECOMMENDATIONS FOR STORAGE BATTERIES FOR USE IN ZONE 2 AREAS

E-0 Storage batteries for use in Zone 2 areas shall be
of increased safety type. These shall meet the following
requirements.

E-l Celluloid and similar combustibles shall not be
used as constructional materials.

E-2 Battery containers as well as fittings and insulating
parts outside the enclosed cells shall not consist of
porous materials, for example, wood or other
flammable materials and shall be resistant to flame and
the action of electrolytes.

E-3 Openings of cells necessary for the escape of the
gases given off shall be so constructed as to prevent
splashing of the electrolyte.

E-4 The exterior of the cells shall be so constructed as
to resist impact, and the cell cases shall be firmly fixed.

E-5 The cells shall be so built into the containers that
working loose of connection of the cells with one
another is impossible and normally a discharge voltage
exceeding 24 V shall not appear between adjacent rows
of cells.

The creepage distance between two poles of adjacent
cells shall not be less than 35 mm. Where the discharge

voltage exceeds 24 V, the creepage distance shall be
correspondingly increased by 1 mm/2 V.

Where voltage of batteries is not less than 50 V either
the battery case shall be sub-divided by partitions or
the batteries shall be grouped into containers so that in
no grouping does a voltage exceeding 50 V occur. In
these cases, the partitions or the containers shall have
heights at least half that of the battery case.

E-6 The battery case shall be so constructed as to ensure
sufficient ventilation in order to prevent accumulation
of gases given off from the battery, and the free space
within the case shall be as small as possible.

E-7 The metallic cover of the battery case shall be lined
with materials resistant to electrolyte.

E-8 The cover of the battery case shall have special
fastenings.

E-9 Exposed live parts of battery contained in a case
shall be protected with rubber or equivalent insulating
materials. However, the opening for checking voltage
may be provided.

NOTE — Charging of storage batteries shall be conducted in
non-hazardous location, while the cover of the battery enclosure
is kept open.

378

NATIONAL ELECTRICAL CODE

PART 8

SP 30 : 2011

PART 8 SOLAR PHOTOVOLTAIC (PV) POWER
SUPPLY SYSTEMS

FOREWORD

Solar energy is a natural resource which is, for practical purposes, free, renewable and inexhaustible and can
supplement/augment the depleting fossil fuel resources. Greenhouse gases and pollutant emissions which result
from fossil fuel generation can be offset by solar photovoltaic power generation. It can be used in decentralized/
distributed mode. The energy converter (namely, solar photovoltaic cells which convert solar energy directly in
dc electric power) does not have moving parts and has a comparatively long lifetime. It is expected that such
advantages would lead to further growth of solar photovoltaic power supply systems.

This Part 8 of the Code is primarily intended to cover the requirements relating to electrical installations of power
supply system based on the solar photovoltaic energy.

PART 8 SOLAR PHOTOVOLTAIC (PV) POWER SUPPLY SYSTEMS 381

SP 30 : 2011

1 SCOPE

This Part 8 of the Code covers essential requirements
for electrical installations for power supply system
based on the solar photovoltaic energy including
systems with ac modules.

2 REFERENCES

This Part 8 of the code should be read in conjunction
with the following Indian Standards:

IS No,
2309 : 1989

Title

3034 : 1993

3043 : 1987
8623 (Part 1)

Code of practice for the protection
of buildings and allied structures
against lightning
Fire safety of industrial buildings:
Electrical generating and
distribution stations — Code of
practice

Code of practice for earthing
1993 Specification for low voltage
switchgear and controlgear
assemblies: Part 1 Requirements
for type-tested and partially type
tested assemblies

8623 (Part 2) : 1993 Specification for low voltage
switchgear and controlgear
assemblies: Part 2 Particular
requirements for busbar trunking
systems (busways)

8623 (Part 3) : 1993 Specification for low voltage
switchgear and controlgear
assemblies: Part 3 Particular
requirements for equipment
where unskilled persons have
access for their use

IS 14153 : 1994

Guide for general description of
photovoltaic(PV) power generat-
ing systems

3 TERMINOLOGY

The following terminology related to solar photovoltaic
energy systems will apply.

3.1 PV Cell — Basic PV device which can generate
emf by the absorption of photons from source such as
solar radiation.

3.2 PY Module — Smallest complete environmentally
protected assembly of interconnected PV cells.

3.3 PV String — Circuit in which PV modules are
connected in series, in order for a PV array to generate
the required output voltage.

3.4 PV Array — Mechanically integrated assembly
of PV modules, together with support structure, but
exclusive of foundation, tracking apparatus, thermal

control and other such components, to form a dc power
producing unit.

3.5 PV Array Junction Box — Enclosure where all
PV strings of any PV array are electrically connected
and where protection devices can be located if
necessary.

3.6 PV Generator — Assembly of PV arrays.

3.7 PV Generator Junction Box — Enclosure where
all PV arrays are electrically connected and where
protection devices can be located if necessary.

3.8 PV String Cable — Cable connecting PV modules
to form a PV string.

3.9 PV Array Cable — Output cable of a PV array.

3.10 PV dc. Main Cable — Cable connecting the PV
generator junction box to the dc terminals of the PV
inverter.

3.11 PV Inverter -
into an ac output.

Device which changes dc input

3.12 PV Supply Cable — Cable connecting the ac
terminals of the PV inverter to a distribution circuit of
the electrical installation.

3.13 PV ac Module — Integrated module/inverter
assembly where the electrical interface terminals are
ac only. No access is provided to the dc side.

3.14 PV Installation — Erected equipment of a PV
power supply system.

3.15 Standard Test Conditions (STC) — Reference
testing values of cell temperature (35 °C), in-plane
irradiance (1 000 W/m 3 ), air mass solar reference
spectrum (AM = 1 .5) for a PV module or PV cell testing.

3.16 Open-Circuit Voltage under Standard Test
Conditions U oc$TC — Voltage under standard test
conditions across an unloaded (open) PV module, PV
string, PV array, PV generator or on the dc side of the
PV inverter.

3.17 Short-circuit Current under Standard Test
Conditions 1 SC stc — Short-circuit current of a PV
module, PV string, PV array or PV generator under
standard test conditions.

3.18 dc Side — Part of a PV installation from a PV
cell to the dc terminals of the PV inverter.

3.19 ac Side — Part of a PV installation from the ac
terminals of the PV inverter to the point of connection
of the PV supply cable to the electrical installation.

3.20 Simple Separation — Separation between
circuits or between a circuit and earth by means of
basic insulation.

NOTE — The abbreviation TV is used for 'solar photovoltaic' .

382

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SP 30: 2011

4 CLASSIFICATION

The major PV power- generating configurations are as
follows:

a) Stand alone system — an independent power-
producing system that is not connected to
utility.

b) Utility connected system — a power
producing system interconnected with an
electric power utility.

NOTE — The term 'utility' is also referred to as the
'grid'.

5 GENERAL CHARACTERISTICS OF
INSTALLATIONS

General guidelines on the assessment of
characteristics of installations in buildings are given
in Part 1/Sec 8 of the Code. An overview of PV
power-generating systems including functional
description of major components and interfaces and
also possible configurations is given in IS 14153.
PV modules shall comply with the requirements of
the relevant equipment standard where such
standards exist. PV modules of class II construction
or with equivalent insulation are recommended if
U 0CSTC of the PV strings exceeds 120 V dc. The PV
array junction box, PV generator junction box and
switchgear assemblies shall be in compliance with
IS 8623.

NOTE — General information on solar photovoltaics is given
at Annex A.

6 OPERATIONAL CONDITIONS AND
EXTERNAL INFLUENCES

6.1 Electrical equipment on the dc side shall be suitable
for direct voltage and direct current. PV modules may
be connected in series up to the maximum allowed
operating voltage of the PV modules and the PV
inverter, whichever is lower. Specifications for this
equipment shall be obtained from the equipment
manufacturer

6.2 As specified by the manufacturer, the PV modules
shall be installed in such a way that there is adequate
heat dissipation under conditions of maximum solar
radiation for the site.

7 WIRING

7.1 All cabling and electrical wiring of the installation
shall be done in accordance with the practice
recommended in Part 1/Sec 9 of this Code.

7.2 Selection and Erection in Relation to Externa!
Influences

7.2.1 PV string cables, PV array cables and PV dc main

cables shall be selected and erected so as to minimize
the risk of earth faults and short-circuits.

NOTE — This may be achieved for example by reinforcing the
protection of the wiring against external influences by the use
of single-core sheathed cables.

7.2.2 Wiring systems shall withstand the expected
external influences such as wind, ice formation,
temperature and solar radiation.

8 EARTHING

8.1 The provision of 17 of IS 3043 shall apply (see
also Part 1 /Section 14 of the Code). Earthing of one of
the live conductors of the dc side is permitted, if there
is at least simple separation between the ac side and
the dc side.

NOTE — Any connections with earth on the dc side should be
electrically connected so as to avoid corrosion

8.2 Earthing Arrangements, Protective Conductors
and Protective Bonding Conductors

Where protective equipotential bonding conductors are
installed, they shall be parallel to and in close contact as
possible with dc cables and ac cables and accessories.

9 PROTECTION FOR SAFETY

9.1 Protection Against Electric Shock

PV equipment on the dc side shall be considered to be
energized, even when the system is disconnected from
the ac side. The selection and erection of equipment
shall facilitate safe maintenance and shall not adversely
affect provisions made by the manufacturer of the PV
equipment to enable maintenance or service work to
be carried out safely.

9.2 Protection Against Both Direct and Indirect
Contact

9.2.1 Protection by Extra-low Voltage: SELVandPELV

For SELV and PELV systems, U oc STC replaces U n and
shall not exceed 120 V dc.

9.3 Fault Protection

9.3.1 Protection by Automatic Disconnection of Supply

On the ac side, the PV supply cable shall be connected
to the supply side of the protective device for automatic
disconnection of circuits supplying current-using
equipment.

Where an electrical installation includes a PV power
supply system without at least simple separation
between the ac side and the dc side, a Residual Current
Device (RCD) installed to provide fault protection by
automatic disconnection of supply shall be Type B
according to Indian Standards.

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9.4 Protection Against Overload on the dc Sides

9.4.1 Overload protection may be omitted to PV string
and PV array cables when the continuous current-
carrying capacity of the cable is equal to or greater
than 1 .25 times 7 SC STC at any location.

9.4.2 Overload protection may be omitted to the PV
main cable if the continuous current-carrying capacity
is equal to or greater than 1 .25 times 7 SC STC of the PV
generator.

9.5 Protection Against Short-circuit Currents

9.5.1 The PV supply cable on the ac side shall be
protected by a short circuit or an overcurrent protective
device installed at the connection to the ac mains.

9.6 Protection Against Electromagnetic Interference
(EMI) in Buildings

9.6.1 To minimize voltages induced by lightning, the
area of all wiring loops shall be as small as possible.

9.7 Lightning Protection

9.7.1 The provisions of IS 2309 shall apply.

10 ISOLATION, SWITCHING AND CONTROL

10.1 To allow maintenance of the PV inverter, means
of isolating the PV inverter from the dc side and the ac
side shall be provided.

10.2 Devices for isolation and Switching

10.2.1 In the selection and erection of devices for
isolation and switching to be installed between the PV
installation and the public supply, the public supply
shall be considered the source and the PV installation
shall be considered the load.

10.2.2 A switch disconnector shall be provided on the
dc side of the PV inverter.

10.2.3 All junction boxes (PV generator and PV array
boxes) shall carry a warning label indicating that active
parts inside the boxes may still be live after isolation
from the PV inverter.

11 FIRE-SAFETY REQUIREMENTS
The provisions of IS 3034 shall apply.

ANNEX A
(Clause 5)

GENERAL INFORMATION ON SOLAR PHOTOVOLTAICS

A-l SUN AS AN ENERGY SOURCE

A-l.l The sun is a spherical mass of hot gases, with a
diameter of about 1.39 x 10 9 m and at an average
distance of 1.5 x 10 ]1 m from the earth. Energy is
being continuously produced in the sun through
various nuclear fusion reactions, the most important
one being where four protons combine to form a
helium nucleus.

H 2 + H 2 -»He+ 15MeV

The mass lost in the process is converted into energy.
These reactions occur in the innermost core of the sun,
where the temperature is estimated to be (8-40) x 10 6 K.
The various layers of differing temperatures and
densities emit and absorb different wavelengths making
the solar spectrum quite composite. However, the sun
essentially acts as a black body having a temperature
of 5 800 K. The spectral distribution of solar radiation
at the earth's mean distance is shown in Fig. 1.

A-1.2 Photon is a particle of light that acts as an
individual unit of energy. Its energy depends on
wavelength. Solar radiation is in the form of photons.

A-1,3 Solar photovoltaic effect is the phenomenon that
occurs when photons, the 'particles' in a beam of solar
radiation (light), knock electrons loose from the atoms
they strike. When this property of solar radiation (light)
is combined with the properties of semiconductors,
electrons flow in one direction across a junction, setting
up a voltage. With the addition of circuitry, current
will flow and electric power will be available.

A-2 SOLAR RADIATION AT THE EARTH'S
SURFACE

A-2.1 Solar Constant (G )

It is the radiant flux density incident on a plane normal
to the sun's rays at a distance of 1.49 x 10 8 km from
the sun and is given by the area under the curve in
Fig. 1 . It has a value of 1 367 W/m 2 in space and about
1 000 W/m 2 at sea level at the equator at solar noon.

NOTE — The received flux density varies by ±1.5 percent
during the day's course due to variations in the sun's output,
and by about ± 4 percent over the year due to the earth's elliptic
orbit.

Irradiance is the solar power incident on a surface. It

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2000

9 1000 -

ABOVE THE ATMOSPHERE

AT MEAN SEA LEVEL

1000

2000

A(nm)

Fig. 1 Spectral Distribution of the Sun's Radiation

is usually expressed in kW/m 2 . The product of
irradiance and time equals insolation.

A-3 CLASSIFICATION OF SOLAR SPECTRUM

The solar spectrum can be classified based on spectral
distribution; the basis of type of radiation or the energy
received.

A-3.1 Classification Based on Spectral Distribution

The solar spectrum can be divided into three main
regions:

a) Ultraviolet region : 9 percent
(X < 400 urn)

b) Visible region : 45 percent
(400 nm < X < 700 nm)

c) Infrared region : 46 percent

(X > 700 nm)

The radiation in the wavelengths above 2 500 nm are
negligible.

The earth's atmosphere absorbs various components
of the radiation to different levels. The short wave UV
and X-ray regions are almost completely absorbed by
oxygen and nitrogen gases and irons; the ozone absorbs
UV rays. The atmosphere unaffected by dust or clouds
acts as an open window for the visible region. Up to 20
percent of the IR (Infrared) radiation is absorbed by
the water vapour and C0 2 The carbon dioxide
concentration in the atmosphere is about 0.03 percent

by volume and is beginning to rise with pollutants being
let off into the atmosphere. The water vapour
concentration can very greatly (up to 4 percent by
volume). Dust, water droplets and other molecules
scatter the sun's radiation.

A-3.2 Classification Based on Beam and Diffuse
Radiation

A-3.2.1 The sun's radiation at the earth's surface is
composed of two components: beam radiation and
diffuse radiation. Beam or direct radiation consists of
radiation along the line connecting the sun and the
receiver as shown in Fig. 2A. Diffuse radiation is the
radiation scattered by the atmosphere without any
unique direction as in Fig. 2B. There is also a reflected
component due to terrestrial surface. Total radiation is
shown in Fig. 2C.

It follows from these figures that

G bc = G b *cos8

For a horizontal surface, the relation becomes

G bh = G b * cos 6 Z

Here Q z (called the Zenith angle) is the angle of
incidence of beam component of solar radiation for a
horizontal surface. Zenith Angle is the angle between
directly overhead and the line intersecting the sun.
(90°-zenith) is the elevation angle of the sun above the
horizon.

G h * is intensity of beam component of normally

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A Beam Component G bc B Diffuse G dc C Total G tc

Fig. 2 Components of Solar Reacting Earth

incident solar radiation on a surface. Adding the beam
of the diffuse components,

G = G U

G bc + ^dc

A -3.2.2 Equation Used to Determine Monthly Average
Daily Global Radiation:

■ = a + i

f S A

V. "Max J

where

H — monthly average daily global radiation, in
kWh/m 2 day;

H = monthly average daily extraterrestrial
radiation, in kWh/m 2 day; and

5 = the monthly average sunshine h and 5 Max is
the monthly average maximum sunshine h.

A-3.2.2.1 Monthly average daily diffuse radiation

For Indian cities linear equation used to compute
monthly average daily diffuse radiation is.

^J. = i .41 1 - 1.696 x -=£• and is valid for 0.3 < -=*■ < 0.7

A-3.2.2.2 Monthly average total radiation on tilted
surface

The tilt angle or slope of collector governs the amount
of energy intercepted by the flat plate collector and is

hence an important specification for design of fixed
or non-tracking collectors. The following relation is
used to calculate the optimum tilt using the available
solar radiation data,

A™ = tan -

£(/f b xtan(0>-(5)

where O is the latitude of the location and 8 is the
angle of tilt of the beam. Optimum tilt for the entire
year typically for Bangalore is p opt = 11.7°.

The optimum tilt for any location for the whole year is
almost equal to 0.9® and is equal to 1 1 .7° and it is also
nearly equal to latitude of the location <£. For practical
considerations the optimal tilt is taken as latitude +15°.

The following relation is used to calculate monthly
average total radiation on tilted surface:

1-2*.

M
xfr+^J-xRi + R

H t = monthly average daily global radiation on
tilted surface,

H % - monthly average daily global radiation on
horizontal surface,

H d = monthly average daily diffused radiation on

horizontal surface, and
R b = conversion factor for beam solar radiation.

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A-3.3 Classification by Energy

A-3.3.1 Solar energy as an energy source has the
following characteristics:

a) The peak global (beam + diffuse) solar
radiation received in India is - 1 kW/m 2 .

b) The power output follows a parabolic trend
with the maximum value at noon.

c) The maximum daily load factor (P Average /P Max )
is 33 percent. This implies that if the capacity
of the SPV panel is 100 kW the maximum
average power input over the day (12 h)
cannot exceed 33 kW. The maximum annual
load factor (£P Average /XP Max ) is 25 percent. This
implies that if the capacity of the SPV panel
is 100 kW the maximum average power input
over the year (12 h/day x 365 days/year)
cannot exceed 25 kW.

d) The total annual global energy input (beam +
diffuse radiation) in India is typically
1970-2 100 kWh/year.

e) An average of 0.5 kWh/m 2 day of energy
available for over 300 days per annum.

Even the hottest regions on earth, have solar radiation
flux rarely to exceed 1 kW/m 2 amounting to 7 kWh/
m 2 /day. Typical solar radiation profile for Bangalore
is given at Annex B. Annex C gives typical daily,
monthly and annual data for Bangalore. Typical daily
solar radiation is in the range of 5-6 kWh/ m 2 /day. The
measured solar radiation data is recorded by mainly
by the Indian Meteorological Department using
Thermo-electric Pyraonometer with sensor placed at a
distance of 19.2 m from ground level.

A Pyranometer is an instrument used for measuring
global solar irradiance. A Pyrheliometer is an
instrument used for measuring direct beam solar
irradiance. It has an aperture of 5.7° to transcribe the
solar disc.

Peak sun hours is the equivalent number of h per day
when solar irradiance averages 1 000 W/m 2 . For
example, six peak sun hours means that the energy
received during total daylight h equals the energy that
would have been received had the irradiance for 6 h
been 1 000 W/m 2 .

A-3.3.2 Effect of Cloud Cover

Cloud cover is measured in Okta [0 Okta: clear sky; 8
Okta: fully covered sky]. Cloud cover directly reduces
solar radiation. There are between 20 and 100 cloudy
days in an year in different Indian locations.

A-3.3.3 Effect of Rainfall, Relative Humidity and Dry
Bulb Temperature

Rainfall is normally associated with cloud cover and

with increase in cloud cover the global solar radiation
is reduced. Relative humidity (0-100 percent) and dry
bulb temperature (-2 to 45 °C) do not affect the solar
radiation significantly but affects the performance of
SPV cells negatively.

A-3.3.4 Effect of Latitude and Longitude

The effect of location on the optimal collector tilt angle
is already given above.

A-3.3 .5 Effect of Altitude

The effect of altitude on solar radiation is not very
significant.

A-3.3.6 Effect of Wind Velocity

Average wind velocities range between and 20 m/s.
Wind does not directly affect solar radiation but affects
the performance of SPV cells in a positive way by
increasing the heat removal from the top cover.

A-4 CLASSIFICATION OF CELLS

a) In terms of materials: non-crystalline silicon,
polycrystalline silicon, amorphous silicon,
gallium arsenide, cadmium telluride,
cadmium sulphide, idium arsenide, etc.

b) In terms of technology for fabrication: single
crystal bonds (or cylinders), ribbon growth,
thin-film, etc.

A-4,1 Some of the definitions under this section are as
follows:

a) Amorphous Semiconductor — A non-
crystalline semiconductor material that has no
long-range order.

b) Amorphous Silicon — A thin-film PV silicon
cell having no crystalline structure.
Manufactured by depositing layers of doped
silicon on a substrate.

c) Cadmium Telluride (CdTe) — A
polycrystalline thin-film photovoltaic
material.

d) CIS (Copper --Indium- Diselelide) — A base
material for SPV cells.

e) Crystalline Silicon — A type of PV cell made
from a single crystal or polycrystalline slice
of silicon.

f) Czochralski Process — A method of growing
large size, high quality semiconductor crystal
by slowly lifting a seed crystal from a molten
bath of the material under careful cooling
conditions.

g) EFG (Edge defined Film Growth) — A
method for making sheets of polycrystalline
silicon in which molten silicon is drawn
upward by capillary action through a mold.

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h) EVA (Ethylene-Vinyl- Acetate Foil) — It is a
material to be used by module production for
covering the cells.

j) GaAs (Gallium Arsenide) — A crystalline,
high-efficiency semiconductor/ photovoltaic
material.

k) MOS-FET (Metal-Oxide-Silicon Field Effect
Transistor) — used as semiconductor power
switch in charge regulators, inverters etc.

m) N-Type Silicon — Silicon material that has
been doped with a material that has more
electrons in its atomic structure than does
silicon.

n) Poly crystalline Silicon — A material used to
make PV cells which consist of many crystals
as contrasted with single crystal silicon.

p) Single Crystal Silicon — Material with a
single crystalline formation. Many PV cells
are made from single crystal silicon.

q) Silicon (Si) — A chemical element, atomic
number 14, semi-metallic in nature, dark gray,
a semiconductor material. A common
constituent of sand and quartz (as the oxide).
Crystallizes in face-centered cubic lattice like
a diamond. This is the most common
semiconductor material used in making
photovoltaic cells.

r) Thin Film PV Module — A PV module
constructed with sequential layers of thin film
semiconductor materials.

s) Wafer — A thin sheet of semiconductor
material made by mechanically sawing it from
a single-crystal or multi-crystal ingot or
casting.

Some of the important characteristics of various types
of SPV cells, measured at normal temperature (25 °C)
and under illumination level of 1 .0 kW/m 2 , are listed
in Table 1.

A-5 BASIC STRUCTURE OF PV CELL

A-5.1 The basic structure of typical PV cell is shown
in Fig. 3 A and 3B. Various layers from top to bottom
and their function are as follows:

a) Top layer is glass cover, transparency 90-95
percent. Its purpose is to protect the cell from
dust, moisture, etc.

b) The next is a transparent adhesive layer which
holds the glass cover.

c) Underneath the adhesive is an antireflection
coating (ARC) to reduce the reflected sunlight
to below 5 percent.

d) Then follows a current carrier bus (aluminium
or silver) Fig. 3B which collects the charge
carriers, generated by the cell under incidence
of sunlight, for circulating to outside load.

e) Under the lower side of the metallic grid lies a
/?-layer followed by n-layer forming a pn-
junction at their interface. The thickness of the
top p-layer is so chosen that enough photons
cross the junction to reach the lower n-layer.

INCIDENT SUNLIGHT

T~r^

p - Type

GLASS COVERING

• TRANSPARENT
ADHESIVE

-ANTI-REFLECTION
COATING

- METALLIC GRID

• METALLIC CONTACT

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3A Cross Sectional View
Fig. 3 Basic Structure of Typical PV Cell — (Continued)

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, METALIC GRID

3B Top View
Fig. 3. Basic Structure of Typical PV Cell

f) The follows another bus in contact with the
lower rc-layer. This forms the second terminal
of the cell.

Table 1 Characteristics of SPY Cells

(Clause A-4.1)

SPV Cell

Fill

Conversion

No.

Factor

Efficiency (percent)

(1)

(2)

(3)

(4)

Mono-crystalline silicon

0.85

13-14

ii)

Polycrystalline silicon

0.85

9-12

iii)

Amorphous silicon

0.66

5-6

iv)

Gallium arsenide

0.87

20-25

(when load is connected across the cell terminals),.
There is also the thermally generated small reverse
saturation current 7 S (minority carrier flow in same
direction as 7 G ) also called dark current as it flows even
in absence of light. 7 G flows in opposite direction to
7 D , the forward diode current of the junction. The cell
feeds current 7 L to load with a terminal voltage V.

The above operation suggests the circuit model of a PV
cell as drawn in Fig. 4. The following can be written from
the circuit model and the well-known expression for:

/ D = / s ^ v -U-* =

A-5.2 Operation and Circuit Model for Analysis

The incidence of photons (sunlight) causes the
generation of electron-hole pairs in both/? and n-layers.
Photons generated minority carriers (electrons in
p-layer and hole in n-layer) freely cross the junction.
This increases the minority carrier flow manifolds. Its
major component is the light generated current 7 G

where

k = Boltsman constant,
e = electronic change and
T = cell temperature in K.

7 L = / G -/ D = / G -/ s ^-lj

Fig. 4 Circuit Model of PV Cell

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Hence,

and

V O c(Il = 0)=J

/ SC (V = 0) = / G

-In

-2- + 1

where V oc is the open circuit voltage and / sc is the short
circuit current.

Solar radiation generated current I G is dependent on
the intensity of light. The I-V characteristics of the cell
are drawn in Fig. 5 A for various values of intensity of
solar radiation. One typical I-V characteristic of the
cell is drawn in Fig. 5B. Each point on this curve
belongs to a particular power output. The point Q
indicated on the curve pertains to the maximum power
output at which the cell should be operated. At this
point.

°Max = M> Max ^ P, Max

The fill-factor (ff) of a cell is defined as:

FF =

he Vs.c

The cell efficiency is given as:

1 =

where P out is the power delivered to load ( W) and P in is
the solar power incident on die cell (W).

A-5.3 Effect of Temperature on Solar Cell Efficiency

As the temperature increases, the diffusion of electrons
and holes in the length of Si (or GaAs) increases
causing an increase in the dark current and decrease in
V oc The overall effect causes a reduction in the
efficiency of solar cell as the temperature increases.
The practical efficiency of Si solar cell is about 12
percent and that of GaAs solar cell is 25 percent at the
normal temperature of 300 K. With each degree rise in
temperature, the efficiency decreases by a factor of
A> 0.004 2 percent.

Ar|

■ 0.0042A7 7

where AT is the rise in temperature above 300 K and
Ar| is the change in efficiency. The factor K may vary
depending on the type of cell.

ASA Spectral Response

It is seen from the spectral response curves of Fig. 6
that the Selenium cell response curve nearly matches
that of the eye. The spectral response of the human
eye is 550 nm, Because of this, Se cell has a widespread
application in photographic equipment such as

exposure meters and automatic exposure diaphragm.
Silicon response also overlaps the visible spectrum but
has its peak at the 0.8 um (8 000 A) wavelength, which
is in the infrared region. In general, silicon has higher
conversion efficiency and greater stability and is less
subject to fatigue. It is therefore widely used for present
day commercial solar cells.

A-5.5 Fabricating Silicon PV Cell

The most commonly used methods of manufacturing
silicon PV cell from purified silicon feedstock are as
follows:

a) Single crystal silicon with a uniform chemical
structure.

b) Polycrystalline silicon-series of crystalline
structures within a PV cell.

c) Amorphous silicon with a random atomic
chemical structure.

Most PV power uses flat-plate modules of cut and
polished wafer like cells of crystalline silicon, which
are now have an efficiency of about 12 percent.

A-5.5.1 Thin-film technologies

There are two main reasons why thin film offers
promise of significant cost reduction. These are as
follows:

a) Thin-film cells use only a few microns of
direct material, instead of tens of mills used
by crystalline, polycrystalline or ribbon
silicon modules,

b) Construction of monolithic thin-film modules
can be done at the same time that the cells are
formatted, thus eliminating most of the cost of
module fabrication. These two aspects of thin-
film technology are further explained below:

Cadmium telluride can absorb 99 percent of
the sun's energy in less than 0.5 um thickness
as opposed to the 0.2 mm requirement for
crystalline silicon. In conventional
technologies, cells cut into individual parts
are then circuited back together as discrete
elements. Monolithic interconnection during
cell fabrication eliminates labour and in
addition produces a superior looking product
because of its uniform finish.

A-6 TESTING OF SPV CELLS

A-6.1 Typical Procedure for Testing of SPV Cells

Some of the definitions under this section are as
follows:

a) NOCT (Nominal Operating Cell Temperature)
— It is the estimated temperature of a SPV

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' l

2000

f c,

^SC2
^SC1

No Light

N. |\

N^OC1

VfA.

Fig. 5 Current-Voltage Characteristics of a PV Cell

module when operating under 800 W/m 2
irradiance, 20°C ambient temperature and
wind speed of 1.0 m/s, NOCT is used to
estimate the nominal operating temperature
of a module in its working environment.

PART 7 ELECTRICAL INSTALLATIONS IN HAZARDOUS AREAS

b) Standard test conditions — Conditions under
which a module is typically tested in a
laboratory:

1) Irradiance intensity of 1 000 W/m 2 ,

2) AM 1 .5 solar reference spectrum; and

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3) Cell (module) temperature of 25 °C,
±2°C.

c) System operating voltage — The array output
voltage under load. The system operating
voltage is dependent on the load or batteries
connected to the output terminals.

d) Rated module current — The current output
of a PV module measured at standard test
conditions of radiation level of 1 000 W/m 2
and a cell temperature of 25 °C. .

e) Short circuit current — The current produced
by an illuminated PV cell, module, or array
when its output terminals are shorted.

f) Full sun — The full sun condition is the
amount of power density received at the
surface of the earth at noon on a clear day —
about 1 000 W/m 2 . Lower levels of sunlight
are often expressed as 0.5 sun or 0.1 sun. A
figure of 0.5 sun means that the power density
of the sunlight is one-half of that of a full sun
(that is 500 W/m 2 ).

The procedure for testing of SPV panels is as follows:

a) Soaking in natural sunlight for 7 days.

b) Measurement of the following parameters
under condition of 1 Sun (1000 W/m 2 ) from
a solar simulator (with a non-uniformity of
light source within ± 3 percent) at 25 °C:

1) Kc4 :

2)
3)

n power point, I n

n power point;

4) 'load' 'load.

Calculation of parameters from the above
measured data:

1)
2)
3)
4)

'Max,

Fill factor,

Cell efficiency, and

Module efficiency.

A-7 APPLICATION OF SPV PANELS FOR BULK
ENERGY CONVERSION

SPV cell produces dc power which is maximum at a
particular point on its I-V characteristics (which
responds to solar radiation input). There are several;
ways in which this power can be used:

a) Direct use for applications such as lighting,
pumping, mechanical power, conversion to ac
for ac loads, etc.

b) Conditioning of power: SPV power is used
as ac after conditioning. The process of
conversion and re-conversion into ac with
solid stage devices like SCR (Silicon
Controlled Rectifier), IGBT (Insulated Gate
Bi-polar Transistor) is called power
conditioning.

c) Storage in batteries and used for mobile power
plants.

d) Hybrid system which is a SPV system that
includes other sources of electricity
generation, such as wind or diesel generators.

^series' ^shunP anC ^

% RESPONSE

SILICON

2000 4000 6000 8000 10000 12000

A(A°)

Fig. 6 Spectral Response of Si, Se and the Naked Eye

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e) Combination of stationary plants with battery
storage which can be of two types:

1) Minigrids:

i) dc bus (because many renewable

sources generate dc power),
ii) ac bus
iii) ac and dc bus

2) Generalized ac and dc bus based system
can also be connected to conventional
power grid at the LT (0.415 kV) or HT
(11 kV) level.

f) BIPV (Building integrated SPV) — It is the
design and integration of PV into the building

SP 30: 2011

envelope, typically replacing conventional
building materials. This integration may be in
vertical facades, replacing view glass, spandrel
glass, or other facade material; into semi-
transparent skylight systems; into roofing
systems, into shading "eyebrows" over
windows; or other building envelope systems.

Usually the SPV panel is the costliest element in the
SPV system. Balance of system (BOS) which is
composed of the parts or components of a SPV system
other than the photovoltaic array usually const only a
small fraction of the total cost. Hence it is economical
to install the most efficient sub-systems (inverters,
battery bank, etc.) in the BOP.

PART 7 ELECTRICAL INSTALLATIONS IN HAZARDOUS AREAS

393

ANNEX B
(Clause A-3. 3. 1)

TYPICAL PROFILE OF SOLAR RADIATION DATA (kW/m 2 ) FOR BANGALORE

SI No.

(1)

Time (h) — »
Month

(2)

06:00 07:00

(3)

(4)