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Full text of "Massachusetts electrical code"

INSERT NO. 1 



BOSTON PUBLIC LIBRARY 




3 9999 06588 182 1 
THE COMMONWEALTH OF MASSACHUSETTS 

DEPARTMENT OF PUBLIC SAFETY 

BOARD OF FIRE PREVENTION REGULATIONS 



MASSACHU 




E I AND REGULA' 
[RNING THE 
INSTALLATION, REPAIR AND MAimL'NvUMCi 
OF ELECTRICAL WIRING AND ELECTRICAL 
FIXTURES USED FOR LIGHT, HEAT AND POWER 
IN BUILDINGS AND STRUCTURES SUBJECT 
TO THE PROVISIONS OF SECTIONS 3 TO 60, 
CHAPTER 143, G. L, TER. ED., AS AMENDED 



FORM FPR-11 



THE COMMONWEALTH OF MASSACHUSETTS 

DEPARTMENT OF PUBLIC SAFETY 

BOARD OF FIRE PREVENTION REGULATIONS 

MASSACHUSETTS ELECTRICAL CODE 



In accordance with the provisions of G.L., C. 143, s. 3L, the Board of Fire 
Prevention Regulations herewith makes the following rules and regulations 
relative to the installation, repair and maintenance of electrical wiring and 
electrical fixtures used for light, heat and power purposes in buildings and 
structures subject to the provisions of G.L., C. 143, ss. 3 to 60, inclusive. 

NOTE: These regulations are identical with the 1965 Edition of the 
NATIONAL ELECTRICAL CODE (NFPA No. 70, ASA CI -1965) except as 
follows: 

1. Delete cover and pages 70-i through 70-x and pages 70-1 through 70-32. 
Substitute MASSACHUSETTS ELECTRICAL CODE INSERT #1 (cover 
through page 70-32). 

2. Delete pages 65 through 80. Substitute MASSACHUSETTS ELECTRICAL 
CODE INSERT #2 (pages 65 through 80). 

3. Amend the wording of the NATIONAL ELECTRICAL CODE by striking 
out the word "recommended" wherever it appears and substituting the 
word "shall"; and by striking out the words "NATIONAL 'ELECTRICAL 
CODE" wherever they appear and inserting the words "'MASSACHU- 
SETTS ELECTRICAL CODE". 

4. Delete pages 70-425 through 70-432 and remove the back cover. 
Substitute MASSACHUSETTS ELECTRICAL CODE INSERT #3 (signature 
page). 

5. Change the wording of the 1 965 Edition of the NATIONAL ELECTRICAL 
CODE in accordance with the attached list entitled: "Form FPR-11, 
Massachusetts Electrical Code, Amendments to the National Electrical 
Code". 



MASSACHUSETTS ELECTRICAL CODE 



Rule 1. All installations, repairs and maintenance of electrical wiring 
and electrical fixtures used for light, heat and power purposes in buildings 
and structures subject to the provisions of Sections 3 to 60, Chapter 143, 
G.L. Ter. Ed., as amended, shall be reasonably safe to persons and property. 

Rule 2. Conformity of installations, repairs and maintenance of electrical 
wiring and electrical fixtures used for light, heat and power with applicable 
regulations set forth in the code which is filed herewith with the Secretary 
of the Commonwealth shall be considered as complying with these require- 
ments. 

Rule 3. Additions or modifications to an existing installation shall be 
made in accordance with this code without bringing the remaining part of 
the installation to meet the requirements of this code. 



1 



Where an actual hazard exists, the owner of the property shall be notified 
in writing by the authority enforcing this code. 

Note: All references in this code to other standards shall be considered 
as advisory and not mandatory. 

With reference to the approval of specific items of equipment and ma- 
terials contemplated by the code, it is pointed out that in order to avoid 
the necessity for repetition of examinations by different examiners, fre- 
quently with inadequate facilities for such work, and to avoid the confusion 
which would result from conflicting reports as to the suitability of devices 
and materials examined for a given purpose, it is necessary that such ex- 
aminations should be made under standard conditions, and the record made 
generally available through promulgation by organizations properly equipped 
and qualified for experimental testing, inspections of the run of goods at 
factories, and service-value determination through field inspections. 

The approving authority may be guided in his approval by an indication 
that such equipment and materials have been tested and conform to suitable 
recognized industry standards. 



70-iii 



TABLE OF CONTENTS 



Article Page 

90 Introduction 70-1 

Chapter 1. General 

100 Definitions 70-4 

110 General 70-13 

Chapter 2. Wiring Design and 
Protection 

200 Use and Identification of 

Grounded Conductors .... 70-18 

210 Branch Circuits 70-21 

215 Feeders 70-27 

220 Branch Circuit and 

Feeder Calculations 70-28 

230 Services 70-37 

240 Overcurrent Protection 70-51 

250 Grounding 70-64 

280 Lightning Arresters 70-83 



Chapter 3. Wiring Methods and 
Materials 

300 Wiring Methods — General 

Requirements 70-85 

310 Conductors for General 

Wiring 70-90 

318 Continuous Rigid Cable 

Supports 70-112 

320 Open Wiring on Insulators 70-114 

324 Concealed Knob-and- 

Tube Work 70-118 

328 Bare-Conductor Feeders .... 70-119 

330 Mineral Insulated-Metal 

Sheathed Cable 70-120 

331 Aluminum Sheathed Cable 70-121 

334 Metal-Clad Cable 70-122 

336 Nonmetallic Sheathed 

Cable 70-125 

338 Service-Entrance Cable 70-127 

339 Underground Feeder and 

Branch Circuit Cable 70-128 

342 Nonmetallic Extensions 70-129 

344 Underplaster Extensions .... 70-131 

346 Rigid Metal Conduit 70-131 

347 Rigid Nonmetallic Conduit 70-135 

348 Electrical Metallic Tubing .. 70-138 



Article Page 

350 Flexible Metal Conduit 70-139 

351 Liquidtight Flexible 

Metal Conduit 70-140 

352 Surface Metal Raceways .... 70-141 

353 Multioutlet Assembly 70-142 

354 Underfloor Raceways 70-142 

356 Cellular Metal Floor 

Raceways 70-144 

357 Structural Raceways 70-145 

358 Cellular Concrete Floor 

Raceways 70-147 

362 Wireways 70-148 

364 Busways 70-149 

370 Outlet, Switch and Junction 

Boxes, and Fittings 70-151 

373 Cabinets and Cutout Boxes 70-156 

374 Auxiliary Gutters 70-159 

380 Switches 70-161 

384 Switchboards and 

Panelboards 70-164 

390 Prefabricated Buildings 70-167 

Chapter 4. Equipment for 
General Use 

400 Flexible Cords 70-169 

402 Fixture Wires 70-178 

410 Lighting Fixtures, Lamp- 
holders, Lamps, Recep- 
tacles and Rosettes 70-182 

422 Appliances 70-194 

430 Motors, Motor Circuits and 

Controllers 70-204 

445 Generators 70-238 

450 Transformers and Trans- 
former Vaults (Incuding 
Secondary Ties) 70-239 

460 Capacitors 70-245 

470 Resistors and Reactors 70-247 

480 Storage Batteries 70-248 

Chapter 5. Special Occupancies 

500 Hazardous Locations 70-251 

501 Class I Installations 70-255 

502 Class II Installations 70-264 

503 Class III Installations .... 70-274 
510 Hazardous Locations — 

Specific ! 70-278 



70-iv 



CONTENTS 



Article Page 

511 Commercial Garages, 

Repair and Storage 70-278 

512 Residential Storage Garages 70-280 

513 Aircraft Hangars 70-281 

514 Gasoline Dispensing and 

Service Stations 70-284 

515 Bulk-Storage Plants 70-286 

516 Finishing Processes 70-289 

517 Flammable Anesthetics ...... 70-292 

520 Theaters and Assembly 

Halls 70-296 

530 Motion-Picture Studios and 

Similar Locations 70-302 

540 Motion-Picture Projectors .. 70-305 

550 Mobile Homes 70-307 

551 Travel Trailers 70-315 

Chapter 6. Special Equipment 

600 Electric Signs and 

Outline Lighting 70-321 

610 Cranes and Hoists 70-327 

620 Elevators, Dumbwaiters, 

Escalators, and 

Moving Walks 70-332 

630 Electric Welders 70-338 

640 Sound-Recording and 

Similar Equipment 70-341 

650 Organs 70-344 

660 X-ray Equipment 70-345 

665 Induction and Dielectric 

Heating Equipment 70-348 

670 Metalworking Machine 

Tools 70-353 

680 Swimming Pools 70-354 

Chapter 7. Special Conditions 

700 Emergency Systems 70-358 

710 Over 600 Volts— General .. 70-362 



Article Page 

720 Circuits and Equipment 
Operating at Less Than 
50 Volts 70-368 

725 Remote-Control, Low- 
Energy Power, Low- 
Voltage Power and 
Signal Circuits 70-369 

730 Outside Branch Circuits 

and Feeders 70-374 

Chapter &, Communication Systems 

800 Communication Circuits .... 70-378 
810 Radio and Television 

Equipment 70-383 

Chapter 9. Tables and Examples 

Tables 70-389 

Examples 70-401 

Index 

Index 70-409 



MASSACHUSETTS ELECTRICAL CODE 70-1 



ARTICLE 90 — INTRODUCTION 

90-1. Purpose. 

(a) The purpose of this Code is the practical safeguarding of persons 
and of buildings and their contents from hazards arising from the use of 
electricity for light, heat, power, radio, signalling and for other purposes. 

(b) This Code contains provisions considered necessary 
for safety. Compliance therewith and proper maintenance will result in an 
installation essentially free from hazard, but not necessarily efficient, con- 
venient, or adequate for good service or future expansion of electrical use. 

Hazards often occur because of overloading of wiring systems by methods 
or usage not in conformity with the Code. This occurs because initial wiring 
did not provide for increases in use of electricity. For this reason it is 
recommended that the initial installation be adequate and that reasonable 
provisions for system changes be made as may be required for future increase 
in the use of electricity. 

(c) This Code is not intended as a design specification nor an instruction 
manual for untrained persons. 

90-2. Scope. 

(a) Covered. It covers the electric conductors and equipment installed 
within or on public and private buildings and other premises, including 
yards, carnival and parking lots, and industrial substations; also the 
conductors that connect the installations to a supply of electricity, and 
other outside conductors adjacent to the premises; also mobile homes and 
travel trailers. 

(b) Not Covered. It does not cover installations in mines, ships, rail- 
way cars, aircraft, automotive equipment, or the installations or equipment 
employed by a railway, electric or communication utility in the exercise 
of its function as a utility, and located outdoors or in buildings used ex- 
clusively for that purpose. 

90-3. Code Arrangement. Chapters 1, 2, 3 and 4 of the Code are of 
general application. Chapters 5, 6 and 7 apply to installations which involve 
special occupancies, special equipment or other special conditions. These 
chapters are supplementary to, or amendatory of, the general rules, and 
the latter apply under such circumstances except as so amended for the 
particular conditions. Chapter 8 governs installations of communication sys- 
tems, and is independent of the preceding Chapters except as they may 
be specifically referred to. Some tables and examples are included in Chap- 
ter 9. 



70-2 MASSACHUSETTS ELECTRICAL CODE 

90-4 Definitions. Article 100 contains definitions of a number of terms 
that are used in two or more Articles. In general, terms used only in a single 
Article are defined in the Article concerned. For electrical terms not defined 
in the Code, refer to the American Standard Definitions of Electrical Terms, 
ASA C-42. 

90-5. Fundamental Rules. Throughout the Code are paragraphs which 
state only fundamentals or objectives of safeguarding. These are followed 
by paragraphs setting forth the recognized methods and detail by which the 
purpose and intent of the fundamental may be satisfied. Accordingly, when 
employed, the rules stating a fundamental only will appear as the first 
paragraph of an Article or Section. 

90-6. 



DELETED 



90--7. Enforcement. 



This code shall be used by the authority enforcing the code. The administrative 
authority supervising such enforcement of the code shall have the responsi- 
bility for making interpretations of the rules and shall accept approved or 
labeled equipment and materials suitable for the purpose for which they are 
to be used. He may decide on the approval of unlisted equipment and may 
grant special permission contemplated in a number of the rules. 



90-8. Examination of Equipment for Safety. For approval of specific items 
of equipment and materials covered by the Code, examinations for safety 
should be made under standard conditions, and the record made generally 
available through promulgation by organizations properly equipped and 
qualified for experimental testing, inspections of the run of goods at fac- 
tories, and service-value determination through field inspections. This 
avoids the necessity for repetition of examinations by different examiners, 
frequently with inadequate facilities for such work, and the confusion that 
would result from conflicting reports as to the suitability of devices and ma- 
terials examined for a given purpose. 



ARTICLE 80 — INTRODUCTION 70-3 



90-9. Wiring Planning. 

(a) Electrical engineers and others when drawing plans and specifications 
shall make provision for ample raceways for wiring, spaces for equipment, 
and allowances for future increases in the use of electricity. In laying out 
an installation for constant-potential systems, provision shall be made for 
distribution centers located in easily accessible places for convenience and 
safety of operation. 

(b) It is elsewhere provided in this Code that the number of wires and 
circuits confined in a single enclosure be varyingly restricted. Electrical en- 
gineers and others who are planning installations shall provide similar re- 
strictions wherever practicable, to the end that the effects of breakdowns 
from short-circuits or grounds, even though resulting fire and similar damage 
are confined to wires, their insulation and enclosures, may not involve en- 
tire services to premises nor interruptions of essential and independent 
services. 

90-10. Revisions. It is customary to revise this Code periodically to con- 
form with developments in the art and the result of experience, and the 
latest edition of the Code should always be used. 



70- 4 MASSACHUSETTS ELECTRICAL CODE 

Chapter 1. General 
ARTICLE 100 — DEFINITIONS 

General guides for this Article on Definitions include: (1) for simplicity, 
only definitions essential to the proper use of this Code are included; (2) 
only those terms used in two or more Articles are defined in full in Article 
100, other definitions being defined in the individual Article where they 
apply; (3) in general, MASSACHUSETTS ELECTRICAL CODE 

definitions will be the same as definitions in the 

latest revision of ASA C-42, "Definitions of Electrical Terms," and are so 
identified by an asterisk*. 

* Accessible: (As applied to wiring methods.) Not permanently closed 
in by the structure or finish of the building; capable of being removed 
without disturbing the building structure or finish. (See "Concealed" and 
"Exposed.") 

* Accessible: (As applied to equipment.) Admitting close approach be- 
cause not guarded by locked doors, elevation or other effective means. (See 
"Readily Accessible.") 

Ampacity: Current-carrying capacity expressed in amperes. 

Anesthetizing Location: See Section 51 7-1 (b). 

Appliance: An appliance is utilization equipment, generally other than 
industrial, normally built in standardized sizes or types, which is installed 
or connected as a unit to perform one or more functions such as clothes 
washing, air conditioning, food mixing, deep frying, etc. 

Appliance — Fixed: An appliance which is fastened or otherwise secured 
at a specific location. 

Appliance — Portable: An appliance which is actually moved or can 
easily be moved from one place to another in normal use. 

Appliance — Stationary: An appliance which is not easily moved from 
one place to another in normal use. 

Approved: 

Acceptable to the authority enforcing this Code. The approval of any equip- 
ment, materials and appliances will be based on its compliance with accepted 
principles of recognized engineering practice. 

*Askarel: A synthetic nonflammable insulating liquid which, when de- 
composed by the electric arc, evolves only nonflammable gaseous mixtures. 

*Attachment Plug (Plug Cap) (Cap): An attachment plug is a device 
which, by insertion in a receptacle, establishes connection between the con- 
ductors of the attached flexible cord and the conductors connected perma- 
nently to the receptacle. 

* Automatic: Automatic means self-acting, operating by its own mech- 
anism when actuated by some impersonal influence, as for example, a change 
in current strength, pressure, temperature, or mechanical configuration. (See 
"Nonautomatic") 

Block (City, Town, or Village): See Section 800-2. 



ARTICLE 100 — DEFINITIONS 70-5 

* Branch Circuit: A branch circuit is that portion of a wiring system 
extending beyond the final overcurrent device protecting the circuit. 

A device not approved for branch circuit protection such as a thermal 
cutout or motor overload protective device is not considered as the over- 
current device protecting the circuit. 

* Branch Circuit' — Appliance: An appliance branch circuit is a circuit 
supplying energy to one or more outlets to which appliances are to be con- 
nected; such circuits to have no permanently connected lighting fixtures 
not a part of an appliance. 

Branch Circuit — General Purpose: A branch circuit that supplies a 
number of outlets for lighting and appliances. 

Branch Circuit — Individual: A branch circuit that supplies only one 
utilization equipment. 

Branch Circuit, Multiwire: A multiwire branch circuit is a circuit con- 
sisting of two or more ungrounded conductors having a potential difference 
between them, and an identified grounded conductor having equal potential 
difference between it and each ungrounded conductor of the circuit and 
which is connected to the neutral conductor of the system. 

BUILDING, a combination of any materials, whether portable or fixed, 
having a roof, to form a structure for the shelter of persons, animals 
or property. For the purpose of this definition "roof" shall include an awning 
or any similar covering, whether or not permanent in nature. The word "build- 
ing" shall be construed where the context requires as though followed by the 
words "or part or parts thereof". 

"Cabinet: An enclosure designed either for surface or flush mounting, 
and provided with a frame, mat or trim in which swinging doors are hung. 

Cell (As Applied to Raceways): See Section 356-1 and 358-1. 

Circuit Breaker: A device designed to open and close a circuit by 
nonautomatic means, and to open the circuit automatically on a predeter- 
mined overload of current, without injury to itself when properly applied 
within its rating. 

Communication Circuit: See Section 800-1. 

'Concealed: Rendered inaccessible by the structure or finish of. the 
building. Wires in concealed raceways are considered concealed, even though 
they may become accessible by withdrawing them. 

Conductor: 

BARE: A bare conductor is one having no covering or insulation 
whatsoever. (See "Conductor, Covered.") 

COVERED: A covered. conductor is one having one or more layers of 
nonconducting materials that are not recognized as insulation under the 
Code. (See "Conductor, Bare.") 

"Connector, Pressure (Solderless): A pressure wire connector is a de- 
vice which establishes the connection between two or more conductors or 
between one or more conductors and a terminal by means of mechanical 
pressure and without the use of solder. 

Continuous Load: A load where the maximum current is expected to 
continue for three hours or more. 



70-6 MASSACHUSETTS ELECTRICAL CODE 

Control Circuit: See Section 430-7 1 . 

Controller: A device, or group of devices, which serves to govern, 
in some predetermined manner, the electric power delivered to the ap- 
paratus to which it is connected. See also Section 430-81 (a) . 

Cooking Unit, Counter-Mounted: An assembly of one or more do- 
mestic surface heating elements for cooking purposes designed for flush 
mounting in, or supported by, a counter, and which assembly is com- 
plete with inherent or separately mountable controls and internal 
wiring. (See "Oven, Wall-Mounted.") 

Current Limiting Overcurrent Protective Device: (See Section 240-27.) 

* Cutout Box: An enclosure designed for surface mounting and 
having swinging doors or covers secured directly to and telescoping 
with the walls of the box proper. (See "Cabinet.") 

* Demand Factor: The demand factor of any system, or part of a 
system, is the ratio of the maximum demand of the system, or part of a 
system, to the total connected load of the system, or of the part of the 
system under consideration. 

Device: A unit of an electrical system which is intended to carry but 
not utilize electric energy. 

Disconnecting Means: A device, or group of devices, or other 
means whereby the conductors of a circuit can be disconnected from 
their source of supply. 

Dry: (See "Location — Dry.") 

Dust-Ignition-Proof: See Section 502-1. 

* Dust proof: So constructed or protected that dust will not interfere 
with its successful operation. 

* Dust-tight: So constructed that dust will not enter the enclosing 
case. 

Duty: 

*Continuous: Continuous duty is a requirement of service that 
demands operation at a substantially constant load for an indefinitely 
long time. 

* Intermittent: Intermittent duty is a requirement of service 
that demands operation for alternate intervals of (1) load and no load; 
or (2) load and rest; or (3) load, no load and rest. 

* Periodic: Periodic duty is a type of intermittent duty in which 
the load conditions are regularly recurrent. 

*Short Time: Short time duty is a requirement of service that 
demands operation at a substantially constant load for a short and 
definitely specified time. 

* Varying: Varying duty is a requirement of service that de- 
mands operations at loads, and for intervals of time, both of which may 
be subject to wide variation. 

See Table 430-22 (a — Exception) for illustrations of various types of duty. 

Duty Cycle (Welding): See Section 630-3 1(c). 



ARTICLE 100-DEFINITIONS 70-7 

♦Electric Sign: A fixed or portable, self-contained electrically il- 
luminated appliance with words or symbols designed to convey in- 
formation or attract attention. 

* Enclosed: Surrounded by a case which will prevent a person from 
accidentally contacting live parts. 

Equipment: A general term including material, fittings, devices, 
appliances, fixtures, apparatus and the like used as a part of, or in con- 
nection with, an electrical installation. 

* Explosion-proof Apparatus: Apparatus enclosed in a case which is 
capable of withstanding an explosion of a specified gas or vapor which 
may occur within it and of preventing the ignition of a specified gas or 
vapor surrounding the enclosure by sparks, flashes, or explosion of the 
gas or vapor within, and which operates at such an external tempera- 
ture that a surrounding flammable atmosphere will not be ignited 
thereby. 

Exposed: (As applied to live parts.) Exposed means that a live part 
can be inadvertently touched or approached nearer than a safe dis- 
tance by a person. It is applied to parts not suitably guarded, isolated or 
insulated. (See "Accessible" and "Concealed.") 

* Exposed: (As applied to wiring method.) Exposed means not con- 
cealed. 

♦Externally Operable: Externally operable means capable of being 
operated without exposing the operator to contact with live parts. 

This term is applied to equipment, such as a switch, that is enclosed in a 
case or cabinet. 

Feeder: A feeder is the circuit conductors between the service 
equipment, or the generator switchboard of an isolated plant, and the 
branch circuit overcurrent device. 

Fitting: An accessory such as a locknut, bushing or other part of a 
wiring system which is intended primarily to perform a mechanical 
rather than an electrical function. 

Garage: A building or portion of a building in which one or more 
self-propelled vehicles carrying volatile, flammable liquid for fuel or 
power are kept for use, sale, storage, rental, repair, exhibition or dem- 
onstrating purposes, and all that portion of a building which is on or 
below the floor or floors in which such vehicles are kept and which is 
not separated therefrom by suitable cutoffs. 

Ground: A ground is a conducting connection, whether intentional 
or accidental, between an electrical circuit or equipment and earth, or 
to some conducting body which serves in place of the earth. 

Grounded: Grounded means connected to earth or to some con- 
ducting body which serves in place of the earth. 

Grounded (Effectively Grounded Communication System): See Sec- 
tion 800-2(d). 

Grounded Conductor: A conductor which is intentionally grounded, 
either solidly or through a current limiting device. 



70-8 MASSACHUSETTS ELECTRICAL CODE 

Grounding Conductor: A conductor used to connect an equipment, 
device or wiring system with a grounding electrode or electrodes. 

Guarded: Covered, shielded, fenced, enclosed or otherwise pro- 
tected, by means of suitable covers or casings, barriers, rails or screens, 
mats or platforms, to remove the liability of dangerous contact or ap- 
proach by persons or objects to a point of danger. 

Hazardous Locations: See Article 500. 

Header: See Section 356-1. 

Header Ducts: See Section 358-1 . 

Hoistway: Any shaftway, hatchway, wall hole, or other vertical 
opening or space in which an elevator or dumbwaiter is designed to op- 
erate. 

Identified: Identified, as used in this Code in reference to a con- 
ductor or its terminal, means that such conductor or terminal is to be 
recognized as grounded. See Article 200. 

* Isolated: Isolated means that an object is not readily accessible to 
persons unless special means for access are used. 

Lighting Outlet: An outlet intended for the direct connection of a 
lampholder, a lighting fixture or a pendant cord terminating in a lamp- 
holder. 

Location: 

Damp Location : A location subject to a moderate degree of mois- 
ture, such as some basements, some barns, some cold storage ware- 
houses, and the like. 

Dry Location : A location not normally subject to dampness or 
wetness. A location classified as dry may be temporarily subject to 
dampness or wetness, as in the case of a building under construction. 

Wet Location: A location subject to saturation with water or 
other liquids, such as locations exposed to weather, washrooms in ga- 
rages, and like locations. Installations underground or in concrete slabs 
or masonry in direct contact with the earth shall be considered as wet 
locations. 

Low-Energy Power Circuit: A circuit which is not a remote-control 
or signal circuit but which has the power supply limited in accordance 
with the requirements of Class 2 remote control circuits. See Article 
725. 

Such circuits include electric door openers and circuits used in the opera- 
tion of coin operated phonographs. 

Multioutlet Assembly: A type of surface or flush raceway designed 
to hold conductors and attachment plug receptacles, assembled in the 
field or at the factory. 

*Nonautomatic: Nonautomatic means that the implied action re- 
quires personal intervention for its control. (See "Automatic") 

As applied to an electric controller, nonautomatic control does not neces- 
sarily imply a manual controller, but only that personal intervention is 
necessary. 



ARTICLE 100-DEFINITIONS 70-9 

♦Outlet: A point on the wiring system at which current is taken to 
supply utilization equipment. 

♦Outline Lighting: An arrangement of incandescent lamps or gas- 
eous tubes to outline and call attention to certain features such as the 
shape of a building or the decoration of a window. 

Oven, Wall-Mounted: A domestic oven for cooking purposes de- 
signed for mounting in or on a wall or other surface. 

Panelboard: A single panel or group of panel units designed for as- 
sembly in the form of a single panel; including buses, and with or with- 
out switches and/or automatic overcurrent protective devices for the 
control of light, heat or power circuits of small individual as well as 
aggregate capacity; designed to be placed in a cabinet or cutout box 
placed in or against a wall or partition and accessible only from the 
front. (See "Switchboard.") 

Projector, Nonprofessional: See Section 540-30. 

Projector, Professional: See Section 540-10. 

Qualified Person: One familiar with the construction and operation 
of the apparatus and the hazards involved. 

Raceway: Any channel for holding wires, cables or busbars, which 
is designed expressly for, and used solely for, this purpose. 

Raceways may be of metal or insulating material and the term includes 
rigid metal conduit, rigid nonmetallic conduit, flexible metal conduit, elec- 
trical metallic tubing, underfloor raceways, cellular concrete floor raceways, 
cellular metal floor raceways, surface metal raceways, structural raceways, 
wireways and busways. 

♦Raintight: So constructed or protected that exposure to a beating 
rain will not result in the entrance of water. 

♦Readily Accessible: Capable of being reached quickly, for opera- 
tion, renewal, or inspections, without requiring those to whom ready 
access is requisite to climb over or remove obstacles or to resort to 
portable ladders, chairs, etc. (See "Accessible.") 

Receptacle (Convenience Outlet): A receptacle is a contact device 
installed at an outlet for the connection of an attachment plug and flex- 
ible cord. 

♦Receptacle Outlet: An outlet where one or more receptacles are 
installed. 

Refrigeration Compressor, Sealed (Hermetic Type): See Section 430-2. 

Remote-Control Circuit: Any electrical circuit which controls any 
other circuit through a relay or an equivalent device. 

Sealable Equipment: Equipment enclosed in a case or cabinet that 
is provided with means of sealing or locking so that live parts cannot 
be made accessible without opening the enclosure. The equipment may 
or may not be operable without opening the enclosure. 

Sealed (Hermetic Type) Refrigeration Compressor: A mechanical 
compressor consisting of a compressor and a motor, both of which are 
enclosed in the same sealed housing, with no external shaft nor shaft 
seals, the motor operating in the refrigerant atmosphere. 



70-10 MASSACHUSETTS ELECTRICAL CODE 

Service: The conductors and equipment for delivering energy from 
the electricity supply system to the wiring system of the premises 
served. 

* Service Cable: The service cable is the service conductors made up 
in the form of a cable. 

Service Conductors: The supply conductors which extend from the 
street main, or from transformers to the service equipment of the prem- 
ises supplied. 

Service Drop: The overhead service conductors between the last 
pole or other aerial support and the first point of attachment to the 
building or other structure. 

Service-Entrance Conductors, Overhead System: The service conduc- 
tors between the terminals of the service equipment and a point usually 
outside the building, clear of building walls, where joined by tap or 
splice to the service drop. 

Service-Entrance Conductors, Underground System: The service con- 
ductors between the terminals of the service equipment and the point of 
connection to the service lateral. 

Where service equipment is located outside the building walls, there may 
be no service-entrance conductors, or they may be entirely outside the 
building. 

Service Equipment: The necessary equipment, usually consisting of 
circuit-breaker or switch and fuses, and their accessories, located near 
point of entrance of supply conductors to a building and intended to 
constitute the main control and means of cutoff for the supply to that 
building. 

Service Lateral: The underground service conductors between the 
street main, including any risers at a pole or other structure or from 
transformers, and the first point of connection to the service entrance 
conductors in a terminal box inside or outside the building wall. 
Where there is no terminal box, the point of connection shall be con- 
sidered to be the point of entrance of the service conductors into the 
building. 

Service Raceway: The rigid metal conduit, electrical metallic tub- 
ing, or other raceway, that encloses the service entrance conductors. 

Setting: (Of Circuit-breaker.) The value of the current at which it is 
set to trip. 

Show-Window: A show-window is any window used or designed to 
be used for the display of goods or advertising material, whether it is 
fully or partly enclosed or entirely open at the rear, and whether or not 
it has a platform raised higher than the street floor level. 

Sign: See "Electric Sign." 

Signal Circuit: Any electrical circuit which supplies energy to an 
appliance which gives a recognizable signal. 

Such circuits include circuits for door bells, buzzers, code-calling systems, 
signal lights, and the like. 



ARTICLE 100-DEFINITIONS 70-11 

Special Permission: The written consent of the authority enforcing 
this Code. 
Switches: 

*General Use Switch: A general use switch is a switch in- 
tended for use in general distribution and branch circuits. It is rated in 
amperes, and it is capable of interrupting its rated current at its rated 
voltage. 

General Use Snap Switch: A form of general use switch so 
constructed that it can be installed in flush device boxes, or on outlet 
box covers, or otherwise used in conjunction with wiring systems recog- 
nized by this Code. 

AC General Use Snap Switch: A form of general use snap 
switch suitable only for use on alternating current circuits for control- 
ling the following: 

(a) Resistive and inductive loads (including electric discharge 
lamps) not exceeding the ampere rating at the voltage involved. 

(b) Tungsten filament lamp loads not exceeding the ampere rating 
at 120 volts. 

(c) Motor loads not exceeding 80 per cent of the ampere rating of 
the switches at the rated voltage. 

All AC general use snap switches are marked "AC" in addition to their 
electrical rating. 

AC-DC General Use Snap Switch: A form of general use snap 
switch suitable for use on either direct or alternating current circuits 
for controlling the following: 

(a) Resistive loads not exceeding the ampere rating at the voltage in- 
volved. 

(b) Inductive loads not exceeding one-half the ampere rating at the 
voltage involved, except that switches having a marked horsepower 
rating are suitable for controlling motors' not exceeding the horsepower 
rating of the switch at the voltage involved. 

(c) Tungsten filament lamp loads not exceeding the ampere rating 
at 125 volts, when marked with the letter "T". 

AC-DC general use snap switches are not generally marked AC-DC, but 
are always marked with their electrical rating. 

*Isolating Switch: An isolating switch is a switch intended for 
isolating an electric circuit from the source of power. It has no inter- 
rupting rating, and it is intended to be operated only after the circuit 
has been opened by some other means. 

Motor Circuit Switch: A switch, rated in horsepower, capable 
of interrupting the maximum operating overload current of a motor of 
the same horsepower rating as the switch at the rated voltage. 

Switchboard: A large single panel, frame, or assembly of panels, on 
which are mounted, on the face or back or both, switches, overcurrent 
and other protective devices, buses and usually instruments. Switch- 
boards are generally accessible from the rear as well as from the front 
and are not intended to be installed in cabinets. (See "Panelboard.") 



70-12 MASSACHUSETTS ELECTRICAL CODE 

Thermal Cutout: An overcurrent protective device which contains a 
heater element in addition to and affecting a renewable fusible member 
which opens the circuit. It is not designed to interrupt short circuit cur- 
rents. 

Thermal Protection: (As applied to motors.) The words, "Thermal 
Protection," appearing on the nameplate of a motor indicate that the 
motor is provided with a thermal protector. 

Thermal Protector: (As applied to motors.) An inherent overheat- 
ing protective device which is responsive to motor current and tem- 
perature and which, when properly applied to a motor, protects the 
motor against dangerous overheating due to overload or failure to 
start. 

* Utilization Equipment: Utilization equipment is equipment which 
utilizes electric energy for mechanical, chemical, heating, lighting, or 
similar useful purposes. 

^Ventilated: Provided with a means to permit circulation of air 
sufficient to remove an excess of heat, fumes or vapors. 

Volatile Flammable Liquid: A flammable liquid having a flash point 
below 100°F. or whose temperature is above its flash point. 

* Voltage (of a circuit): Voltage is the greatest root-mean-square 
(effective) difference of potential between any two conductors of the 
circuit concerned. 

On various systems such as 3-phase 4 wire, single phase 3 wire and 3 wire 
direct current, there may be various circuits of various voltages. 

Voltage to Ground: In grounded circuits the voltage between the 
given conductor and that point or conductor of the circuit which is 
grounded; in ungrounded circuits, the greatest voltage between the 
given conductor and any other conductor of the circuit. 

Watertight: So constructed that moisture will not enter the enclos- 
ing case. 

^Weatherproof: Weatherproof means so constructed or protected 
that exposure to the weather will not interfere with successful op- 
eration. 

Raintight or watertight equipment may fulfill the requirements for 
"weatherproof." However, weather conditions vary and consideration 
should be given to conditions resulting from snow, ice, dust, or temperature 
extremes. 

Welder, Electric. 

Rated Primary Current: Section 630-3 1 (c) . 
Actual Primary Current: Section 630-3 1(c). 

Wet: ( See "Location — Wet." ) 

X-ray: 

Continuous Rating: Section 660-4. 
Long Time Rating: Section 660-4. 
Momentary Rating: Section 660-4. 



ARTICLE 110-GENERAL 70-13 



ARTICLE 110 — GENERAL 



110-1. Scope. This Article includes provisions applicable generally in 
installations of electric wiring and equipment. 

110-2. Approval. The conductors and equipment required or permit- 
ted by this Code shall be acceptable only when approved. See defini- 
tion of "Approved" in Article 100. 

110-3. Mandatory and Advisory Rules. Mandatory rules of this Code 
are characterized by the use of the word, "shall." Advisory rules are 
characterized by the use of the word, "should," or are stated as recom- 
mendations of that which is advised but not required. 

110-4. Examination of Equipment. Materials, devices, fittings, ap- 
paratus and appliances designed for use under this Code shall be 
judged chiefly with reference to the following considerations which 
also determine the classification by types, size, voltages, current ca- 
pacities, and specific use. 

(a) Suitability for installation and use in conformity with the pro- 
visions of this Code. 

(b) Mechanical strength and durability, including, for parts de- 
signed to enclose and protect other equipment, the adequacy of the 
protection thus provided. 

(c) Electrical insulation. 

(d) Heating effects under normal conditions of use and also under 
abnormal conditions likely to arise in service. 

(e) Arcing effects. 

110-5. Voltages. Throughout this Code the voltage considered shall 
be that at which the circuit operates, whether the current is supplied by 
a battery, generator, transformer, rectifier, or attiermopile. 

110-6. Conductor Gages. Conductor sizes are given in American 
Wire Gage (AWG). 

110-7. Conductors. Conductors normally used to carry current shall 
be of copper unless otherwise provided in this Code. Where conductor 
sizes are given in this Code, they shall apply to copper conductors. 
Where other materials are used, the size shall be changed accordingly. 

For aluminum conductors, see Tables 310-14 and 310-15. 

110-8. Wiring Methods. Only wiring methods recognized as suitable 
are included in this Code. The recognized methods of wiring may be 
installed in any type of building or occupancy except as otherwise pro- 
vided in this Code. 

110-9. Interrupting Capacity. Devices intended to break current shall 
have an interrupting capacity sufficient for the voltage employed and 
for the current which must be interrupted. 

110-10. Circuit Impedance and Other Characteristics. The overcur- 
rent protective devices, the total impedance and other characteristics of 



70-14 MASSACHUSETTS ELECTRICAL CODE 



the circuit to be protected shall be so selected and coordinated as to permit 
the circuit protective devices used to clear a fault without the occurrence of 
extensive damage to the electrical components of the circuit. This fault may 
be assumed to be between two or more of the circuit conductors; or between 
any circuit conductor and the grounding conductor or enclosing metal raceway. 

110-11. Deteriorating Agencies. Unless approved for the purpose, no 

conductors or equipment shall be located in damp or wet locations; where 
exposed to gases, fumes, vapors, liquids or other agents having a deteriorating 
effect on the conductors or equipment; nor where exposed to excessive tem- 
peratures. 

110-12. Mechanical Execution of Work. Electrical equipment shall be 
installed in a neat and workmanlike manner. 

110-13. Mounting of Equipment. Electrical equipment shall be firmly 

secured to the surface on which it is mounted. Wooden plugs driven into 
holes in masonry, concrete, plaster or similar materials shall not be depended 
on for security. 

Whenever bare conductors for grounding purposes are used with non-metallic 
sheathed cable, they must be joined together in some manner approved by 
this Code. The "wrap around" or "back wrap" method is prohibited. 

110-14. Connections to Terminals. Connection of conductors to terminal 
parts shall insure a thoroughly good connection without damaging the con- 
ductors and shall be made by means of pressure connectors (including set 
screw type), solder lugs or splices to flexible leads except that No. 8 or 
smaller solid conductors and No. 10 or smaller stranded conductors may be 
connected by means of clamps or screws with terminal plates having upturned 
lugs. Terminals for more than one conductor shall be of a type approved for 
the purpose. 

Because of different characteristics of copper and aluminum, devices such 
as pressure connectors and soldering lugs shall be suitable for the material 
of the conductor and shall be properly installed and used. Materials such as 
solder, fluxes, inhibitors, and compounds, where employed, shall be suitable 
for the use and shall be of a type which will not adversely affect the con- 
ductors, installation, or equipment. 

110-15. Splices. Conductors shall be spliced or joined with splicing devices 
approved for the use or by brazing, welding or soldering with a fusible metal 
or alloy. Soldered splices shall first be so spliced or joined as to be mechani- 
cally and electrically secure without solder and then soldered. All splices and 
joints and the free ends of conductors shall be covered with an insulation 
equivalent to that of the conductors. 

110-16. Working Space about Electrical Equipment. Sufficient access and 
working space shall be provided and maintained about all electrical equip- 
ment to permit ready and safe operation and maintenance of such equipment. 

(a) Horizontal Dimensions. Except as elsewhere required or permitted in 
this Code, the horizontal dimension of the working space in the direction of 
access to live parts, operating at not more than 600 volts, which are likely 
to require examination, adjustment, servicing or maintenance while alive, 
shall not be less than indicated in the following table. Distances are to be 
measured from the live parts if such are exposed or from the enclosure front 
or opening when such are enclosed. 



ARTICLE 110-GENERAL 70-15 



Voltage to Ground Minimum clear distance 

Condition: 1 2 3 

0-150 2^/2 ft. 2 1/2 ft. 3 ft. 

151-600 V/i 3Vi 4 

Where the "Conditions" are as follows: 

1 . Exposed live part on one side and no live or grounded part on the 
other side of the working space or exposed live parts on both sides ef- 
fectively guarded by suitable wood or other insulating materials. In- 
sulated wire or insulated bus bars operating at not more than 300 volts 
shall not be considered live parts. 

2. Exposed live parts on one side and grounded parts on the other 
side. Concrete, brick or tile walls shall be considered as grounded. 

3. Exposed live parts on both sides of the work space (not guarded 
as provided in Condition 1 ) with the operator between. 

Exception No. 1 . Working space is not required in back of assemblies 
such as dead-front switchboards or control centers when there are no 
renewable or adjustable parts such as fuses or switches on the back and 
when all connections are accessible from other locations than the back. 

Exception No. 2. Smaller spaces may be permitted by the authority 
having jurisdiction where it is judged that the particular arrangement of 
the installation will provide adequate accessibility. 

(b) Clear Spaces. Working space required by this section shall not 
be used as a passageway or for storage. When normally enclosed live 
parts are exposed for inspection or servicing, the working space, if ad- 
jacent to a passageway or general open space where other work is car- 
ried on, shall be suitably guarded. 

(c) Access and Entrance to Working Space. At least one entrance of 
sufficient area shall be provided to give access to the working space 
about electrical equipment. 

(d) Front Working Space. In all cases where there are live parts 
normally exposed on the front of switchboards or control centers, the 
working space in front of such boards or panels shall be not less than 3 
feet. 

(e) Illumination. Adequate illumination shall be provided for all 
working spaces about switchboards and control centers. 

(f) Headroom. The minimum headroom of working spaces about 
switchboards or control centers where there are live parts exposed at 
any time, shall be 6V4 feet. 

For higher voltages, see Article 710. 

110-17. Guarding of Live Parts. (Not more than 600 Volts) 

(a) Except as elsewhere required or permitted by this Code, live 
parts of electrical equipment operating at 50 volts or more shall be 
guarded against accidental contact by approved cabinets or other forms 
of approved enclosures, or any of the following means: 



70-16 MASS ACHUSETTS ELECTRICAL CODE 

(1) By location in a room, vault, or similar enclosure which is ac- 
cessible only to qualified persons. 

(2) By suitable permanent, substantial partitions or screens so ar- 
ranged that only qualified persons will have access to the space within 
reach of the live parts. Any openings in such partitions or screens shall 
be so sized and located that persons are not likely to come into acciden- 
tal contact with the live parts or to bring conducting objects into con- 
tact with them. 

(3) By a guard rail, provided the live parts operate at 600 volts or 
less and provided the location is such as to make contact with live parts 
unlikely. 

(4) By location on a suitable balcony, gallery, or platform so ele- 
vated and arranged as to exclude unqualified persons. 

(5) By elevation at least 8 feet above the floor or other working 
surface. 

(b) In locations where electrical equipment would be exposed to 
physical damage, enclosures or guards shall be so arranged and of such 
strength as to prevent such damage. 

(c) Entrances to rooms and other guarded locations containing ex- 
posed live parts shall be marked with conspicuous warning signs forbid- 
ding unqualified persons to enter. 

For motors see Sections 430-132 and 430-133. For additional require- 
ments at voltages over 600 see Article 710. 

110-18. Arcing Parts. Parts of electrical equipment which in ordinary 
operation produce arcs, sparks, flames or molten metal, shall be en- 
closed unless separated and isolated from all combustible material. 
For hazardous locations see Articles 500-517 inclusive. For motors see 
Section 430-14. 

110-19. Light and Power from Railway Conductors. Circuits for light- 
ing and power shall not be connected to any system containing trolley 
wires with a ground return, except in electric railway cars, car houses, 
power houses, or passenger and freight stations operated in connection 
with electric railways. 

110-20. Insulation Resistance. All wiring shall be so installed that 
when completed the system will be free from short-circuits and from 
grounds other than as provided in Article 250. In order that a reason- 
able factor of safety may be provided, the following table of insulation 
resistances is suggested as a guide where the insulation is subjected to 
test: 

(a) For circuits of No. 14 or No. 12 wire, 1,000,000 ohms. For cir- 
cuits of No. 10 or larger conductor, a resistance based upon the allow- 
able ampacities of conductors as fixed in Tables 310-12 through 310-15 
as follows: 

25 to 50 amperes, inclusive 250,000 ohms 

51 to 100 amperes, inclusive 100,000 ohms 

101 to 200 amperes, inclusive 50,000 ohms 

201 to 400 amperes, inclusive 25,000 ohms 

401 to 800 amperes, inclusive 12,000 ohms 

Over 800 amperes 5,000 ohms 



ARTICLE 110-GENERAL 70-17 



(b) The above values are to be determined with all switchboards, 
panelboards, fuseholders, switches, receptacles and overcurrent devices 
in place. 

(c) Where climatic or other conditions are such that the wiring or 
equipment is exposed to excessive humidity, it may be necessary to 
modify the foregoing provisions. 

110-21. Marking. The maker's name, trademark, or other identifica- 
tion symbol shall be placed on all electrical equipment. Other markings 
shall be provided giving voltage, current, wattage, or other ratings as 
are prescribed elsewhere in this Code. 

110-22. Identification. Each disconnecting means required by this 
Code for motors and appliances, and each ervice, feeder or branch 
circuit at the point where it originates, shall be legibly marked to indi- 
cate its purpose unless located and arranged so the purpose is evident. 
The marking shall be of sufficient durability to withstand the environ- 
ment involved. 



70-18 MASSACHUSETTS ELECTRICAL CODE 



Chapter 2. Wiring Design and Protection 

ARTICLE 200 — USE AND IDENTIFICATION 
OF GROUNDED CONDUCTORS 



200-1. Scope. This Article provides requirements for the use and 
identification of a grounded conductor in interior wiring systems. (See 
definitions of "grounded conductor" and "grounding conductor" in 
Article 100.) 

200-2. General. All interior wiring systems shall have a grounded 
conductor which is continuously identified throughout the system ex- 
cept as follows: 

Exception No. 1. A grounded conductor is not required in certain 
circuits or systems as provided in Sections 200-5 , 250-3 , 250-5, 250-6, 
250-7, 250-8, 503-13, and 517-6. 

Exception No. 2. Continuous identification throughout a length of 
a conductor between terminals is not required for certain conductors 
under Section 200-6 {a and b) . 

200-3. Connection to Grounded System. No interior wiring shall be 
electrically connected to a supply system unless the latter contains, for 
any grounded conductor of the interior system, a corresponding con- 
ductor which is grounded. 

Electrically connected implies connection capable of carrying current as 
distinguished from connection through electromagnetic induction. 

200-4. Circuits Derived from Auto-Transformers. Branch circuits as 
described in Article 210 shall not be supplied through auto-transform- 
ers (transformers in which a part of the winding is common to both 
primary and secondary circuits) unless the system supplied has an iden- 
tified grounded conductor which is solidly connected to a similar identi- 
fied grounded conductor of the system supplying the auto-transformer. 

200-5. Unidentified Circuits. 

(a) Two wire branch circuits and AC circuits of two or more con- 
ductors may be tapped from the ungrounded conductors of circuits 
having identified grounded neutrals. Switching devices in each tapped 
circuit shall have a pole in each ungrounded conductor. These poles 
shall manually switch together where the switching devices serve as 
the disconnecting means required by Section 422-23. 

Exception: Eor Motor Controllers see Section 430-84, and for heating 
equipment see Section 422-46. 

(b) Polyphase circuits need not have one conductor grounded and 
identified, except as required by Section 250-5, but where one conduc- 
tor is grounded it shall be identified. 



ARTICLE 200-GROUNDED CONDUCTORS 70-19 

(c) Other unidentified ungrounded systems or circuits may be used 
only by special permission. 

200-6. Means of Identification of Grounded Conductors. Identification 
for grounded conductors shall be as follows: 

(a) Insulated conductors of No. 6 or smaller, except conductors of 
Type MI cable, shall have an outer identification of white or natural 
gray color as specified in 310-2(g). The grounded conductors of Type 
MI cable shall be identified by distinctive marking at the terminals dur- 
ing the process of installation. 

(b) Insulated conductors larger than No. 6, shall have an outer iden- 
tification of white or natural gray color, or shall be identified by distinc- 
tive white marking at terminals during process of installation. 

(c) Where, on a 4-wire delta-connected secondary, the midpoint of 
one phase is grounded to supply lighting and similar loads, that phase 
conductor having the higher voltage to ground shall be indicated by 
tagging or other effective means at any point where a connection is to 
be made if the neutral conductor is present. 

200-7. Identified Conductor in Grounded Circuits Only. Conductors 
having white or natural gray covering shall not be used other than as 
conductors for which identification is required by Section 200-2, ex- 
cept under the following conditions, and then only where they are, in 
other respects, suitable for use as ungrounded conductors in the cir- 
cuit: 

Exception No. 1. Identified conductors, rendered permanently un- 
identified by painting or other effective means at each outlet where the 
conductors are visible and accessible, may be used as unidentified con- 
ductors. 

The foregoing permits the use of two-wire cable having one black and 
one white conductor on two-wire circuits tapped from the outside legs of a 
three-wire system or any two conductors of a multiwire system where the 
identified conductor of the two-wire cable is rendered permanently un- 
identified at terminals. 

Exception No. 2. Cable containing an identified conductor may be 
used for single-pole, three-way or four-way switch loops where the con- 
nections are so made that the unidentified conductor is the return con- 
ductor from the switch to the outlet. 

This exception makes it unnecessary to paint the terminal of the identi- 
fied conductor at the switch outlet. 

Exception No. 3. A flexible cord, for connecting a portable appli- 
ance, having one conductor identified as required by Section 400-13 
may be used even though there is no grounded conductor in the circuit 
supplying the outlet to which it is connected. 

200-8. Connections to Screw-Shells. An identified conductor, where 
run to a screw-shell lampholder, shall be connected to the screw-shell. 

200-9. Means of Identification of Terminals. The identification of ter- 
minals to which a grounded conductor is to be connected shall be by 
means of a metallic plated coating substantially white in color, such as 
nickel or zinc, or the terminals may be of material substantially white 



70-20 MASSACHUSETTS ELECTRICAL CODE 

in color. The other terminals shall be of a readily distinguishable dif- 
ferent color. 

200-10. Identification of Terminals. 

(a) Device Terminals. All devices provided with terminals for the 
attachment of conductors and intended for connection to more than 
one side of the circuit shall have terminals properly marked for identi- 
fication except as follows: 

Exception No. 1 . Marking may be omitted where the electrical con- 
nection of a terminal intended to be connected to the grounded con- 
ductor is clearly evident. 

Exception No. 2. Single-pole Devices. Devices to the terminals of 
which only one side of the line is connected need not have terminals 
marked for identification. 

Exception No. 3. Panelboards and Devices. The terminals of lighting 
panelboards and of devices having a normal current rating of over 30 
amperes need not be marked for identification, except as required in 
Section 200-1 0(b) for polarized receptacles for attachment plugs and 
polarized attachment plugs. 

(b) Plugs and Receptacles. Two-wire polarized receptacles for attach- 
ment plugs and polarized attachment plugs shall have the terminal in- 
tended for connection to the grounded conductor marked for identifi- 
cation. 

Exception No. 1. Two-wire attachment plugs, unless of the polarity 
type, need not have their terminals marked for identification. 

Exception No. 2. Three-wire and Four-wire Receptacles and Attach- 
ment Plugs. Three-wire and four-wire receptacles and attachment plugs, 
other than those of the grounding type which are rated within the limits 
outlined and required under Section 210-21 (b) , but on which one termi- 
nal may be used for the connection of either a grounding conductor or 
a grounded circuit conductor, shall have such a terminal marked to 
show other than a white or green finish. 

(c) Screw-Shells. In the case of devices with screw-shells, the identi- 
fied terminal shall be the one connected to the screw-shell. This does 
not apply to screw-shells which serve as fuseholders. 

(d) Screw-Shell Devices with Leads. In the case of screw-shell de- 
vices with attached leads, the conductor attached to the screw-shell 
shall have white or natural gray finish. The outer finish of the other 
conductor shall be of a solid color that will not be confused with the 
white or natural-gray finish which is to identify the grounded conduc- 
tor. 

(e) Fixed Appliances. The terminals of fixed appliances need not 
be marked to indicate the proper connection to the grounded conduc- 
tor unless a single-pole switch forms an integral part, then the terminal 
connected to the switch shall be the unidentified terminal. 

(f) Portable Appliances. The terminals of portable appliances need 
not be marked for identification. 



ARTICLE 210-BRANCH CIRCUITS 70-21 

ARTICLE 210 — BRANCH CIRCUITS 



210-1. Scope. The provisions of this Article shall apply to branch 
circuits supplying lighting or appliance loads or combinations of such 
loads. Where motors, or motor-operated appliances, are connected to 
any circuit supplying lighting or other appliance loads, the provisions 
of both this Article and Article 430 shall apply. Article 430 shall apply 
where branch circuit supplies only motor loads. 

210-2. Specific Purpose Branch Circuit. The provisions applying to 
branch circuits referred to in the following table are exceptions to the 
provisions of this Article or are supplementary thereto, and shall apply 
to branch circuits supplying the loads referred to therein: 

Busways Section 364-8 

Cranes and Hoists Section 610-42 

Elevators, Dumbwaiters and Escalators Section 620-61 

Infrared Industrial Heating Equipment Section 422-11 

Inductive and Dielectric Heat Generating 

Equipment Article 665 

Instruments Section 384-22 

Motion Picture Studios and Similar 

Locations Article 530 

Motors and Motor Controllers Article 430 

Organs Section 650-6 

Remote-Control, Low-Energy Power, Low- 
Voltage Power and Signal Circuits Article 725 

Signs and Outline Lighting Section 600-6 

Sound Recording and Reproduction Section 640-6 

Space Heating; Panel and Embedded Types Article 422 

Systems over 600 Volts Article 710 

Systems under 50 Volts Article 720 

Theaters and Assembly Halls Sections 520-41, 520-52, 

and 520-62 

Welders Article 630 

X-ray Equipment Section 660-3 

210-3. Classifications. Branch circuits recognized by this Article shall 
be classified in accordance with the maximum permitted rating or set- 
ting of the overcurrent device, and the classification for other than in- 
dividual branch circuits shall be 15, 20, 30, 40 and 50 amperes. When 
conductors of higher capacity are used for any reason, the rating or 
setting of the specified overcurrent device shall determine the circuit 
classification. 

A. General Provisions 

210-4. Multiwire Branch Circuits. Branch circuits recognized by this 
Article may be installed as multiwire circuits. 
See Article 100 for Definition. 

210-5. Color Code. Where installed in raceways, as aluminum 
sheathed cable, as open work, or as concealed knob-and-tube work, the 
conductors of multiwire branch circuits and two-wire branch circuits 



70-22 MASSACHUSETTS ELECTRICAL CODE 

connected to the same system shall conform to the following color 
code. Three-wire circuits — one black, one white, one red; four-wire 
circuits — one black, one white, one red, one blue; five-wire circuits — 
one black, one white, one red, one blue, one yellow. Where more than 
one multiwire branch circuit is carried through a single raceway the 
ungrounded conductors of the additional circuit may be of colors other 
than those specified. All circuit conductors of the same color shall be 
connected to the same ungrounded feeder conductor throughout the 
installation. 

Any conductor intended solely for grounding purposes shall be iden- 
tified by a continuous green color or a continuous green color with a 
yellow stripe unless it be bare. Branch circuit conductors and equip- 
ment lead wires to which branch circuit conductors attach having a 
continuous green color or a continuous green color with a yellow stripe 
shall not be used for other than grounding purposes. 

The above is not intended to prohibit the use of a conductor having a con- 
tinuous green color or a continuous green color with a yellow stripe, insula- 
tion for internal wiring of equipment, except where such wiring serves as the 
lead wires to which the branch circuit conductors attach. 

See Section 200-7 for use of white or natural gray for grounded or neutral 
conductors. 

210-6. Voltage. 

(a) Voltage to Ground. The voltage to ground on branch circuits 
supplying lampholders, fixtures, or standard receptacles of 15-ampere or 
less rating shall not exceed 150 volts, except as follows: 

Exception No. 1. In industrial establishments or in stores where the 
conditions of maintenance and supervision assure that only competent 
individuals will service the lighting fixtures the voltage of branch cir- 
cuits which supply only lighting fixtures that are equipped with mogul- 
base screw-shell lampholders or with lampholders of other types ap- 
proved for the application, mounted not less than eight feet from the 
floor, which do not have switch control as an integral part of the fixture 
shall not exceed 300 volts to ground; 

Exception No. 2. In industrial establishments, office buildings, 
schools, stores, and public and commercial areas of other buildings, 
such as hotels or transportation terminals, the voltage of branch cir- 
cuits which supply only the ballasts for electric discharge lamps 
mounted in permanently installed fixtures, by other than screw-shell 
type lampholders, which do not have manual switch control as an in- 
tegral part of the fixture shall not exceed 300 volts to ground. Where 
screw-shell type lampholders are used for electric discharge lamps the 
fixtures shall be installed not less than eight feet from the floor. 

Exception No. 3. For infrared industrial heating appliances as de- 
scribed in Section 422-11; 

Exception No. 4. In railway properties as described in Section 110-19; 

Exception No. 5. The branch circuits supplying the ballasts for 
electric discharge lamps mounted in permanently installed fixtures on 
poles for the illumination of areas such as highways, bridges, athletic 
fields, parking lots, at a height not less than 22 feet, or on other struc- 



ARTICLE 210-BRANCH CIRCUITS 70-23 

tures such as tunnels at a height not less than 18 feet, shall not exceed 
500 volts between conductors when installed as provided in Section 
730-7 {a). 

(b) Voltage Between Conductors — Dwellings. In dwelling occupan- 
cies, the voltage between conductors supplying lampholders of the 
screw-shell type, receptacles, or appliances, shall not exceed 150 volts, 
except as follows: 

Exception: The voltage between conductors may exceed 150 volts 
when supplying only: 

(7) Permanently connected appliances, 

(2) Portable appliances of more than 1 ,380 watts, 

(3) Portable motor-operated appliances of Va horsepower or 
greater rating. 

(c) Voltage Drop. The size of the conductors for branch circuits 
as defined in Article 100 should be such that the voltage drop would 
not exceed 3% to the farthest outlet for power, heating, lighting, or 
combinations thereof. Providing further that the maximum total voltage 
drop for feeders and branch circuits should not exceed 5% over all. 

210-7. Grounding Receptacles. Receptacles and cord connectors 
equipped with grounding contacts shall have those contacts effectively 
grounded. The branch circuit or branch circuit raceway shall include 
or provide a grounding conductor to which the grounding contacts of 
the receptacle or cord connector shall be connected. The metal armor 
of Type AC metal-clad cable, the sheath of aluminum sheathed cable, 
or a metallic raceway is acceptable as a grounding conductor. See Sec- 
tions 210-21 (b), 250-45 and 250-59. 

Exception: For extensions only in existing installations which do not 
have a grounding conductor in the branch circuit, the grounding con- 
ductor of a grounding type receptacle outlet may be grounded to a 
grounded cold water pipe near the equipment. 

21 0-8. Heavy-Duty Lampholders. Heavy-duty lampholders referred to 
in this Article shall include lampholders rated at not less than 750 
watts. 

Exception: Admedium lampholders rated at 660 watts shall be 
considered to be heavy duty type. 

B. Specific Requirements 
210-19. Conductors. Circuit conductors shall conform to the follow- 
ing: 

(a) Ampacity. Shall have an ampacity of not less than the rating 
of the branch circuit and not less than the maximum load to be served. 

(b) Minimum Size. Shall not be smaller than No. 8 for ranges of 
8 3 /i kw or more rating, nor smaller than No. 14 for other loads. 

(c) Exceptions: 

Exception No. 1. Range Loads. See Note 5 of Table 220-5. Where 
the maximum demand of a range of 8 3 A kw or more rating is computed 
according to Column A of Table 220-5, the neutral conductor of a 
three-wire branch circuit supplying a household electric range, a wall- 



70-24 MASSACHUSETTS ELECTRICAL CODE 

mounted oven or a counter-mounted cooking unit may be smaller than 
the ungrounded conductors but shall have an ampacity at least 70 per 
cent of the ampacity of the ungrounded conductors and shall not be 
smaller than No. 10. 

Cable assemblies with the neutral conductor smaller than the un- 
grounded conductors shall be so marked. 

Exception No. 2. Tap Conductors. Tap conductors may be of less 
capacity than the branch circuit rating provided no tap conductor is of 
less capacity than the load to be served and provided the rating is not 
less than 20 amperes for 40 or 50 ampere circuits or 15 amperes for 
circuits rated less than 40 amperes and only when these tap conductors 
supply either: 

(a) Individual lampholders or fixtures with taps extending not 
longer than 18 inches beyond any portion of the lampholder or fixture, 
except as required in Section 410-65 (b-2); or, 

(b) Individual outlets with taps not over 18 inches long; or, 

(c) Infra-red lamp industrial heating appliances. 

(d) Nonheating leads of snow and ice melting cables and mats. 

Exception No. 3. Fixture Wires and Cords. Fixture wires and cords 
may be of smaller size, but not less than the size specified in Exception 
No. 3 of Section 240-5. 

See Tables 400-9(b) and 402-4. 

Exception No. 4. Outlet Devices. Outlet devices may have less carry- 
ing capacity than the branch circuit rating, but not less than the types 
and ratings specified in Sections 210-21 (a-c) . 

Exception No. 5. Where tap conductors supply electric ranges, wall- 
mounted electric ovens and counter-mounted electric cooking units 
from 50 ampere branch circuits they shall be of suitable capacity for 
the load to be served, not less than 20 amperes in rating and no longer 
than necessary for servicing the appliance. 

210-20. Overcurrent Protection. The rating or setting of overcurrent 
devices shall conform to the following: 

(a) Rating. Shall not be in excess of the value specified in Section 

240-5. 

Exception: Tap Conductors and Fixture Wires. Tap conductors, fix- 
ture wire and cords as permitted in Section 210-19{c) may be consid- 
ered as protected by the circuit overcurrent device. 

(b) Single Appliance. Shall not exceed 150 per cent of the rating 
of the appliance, where the circuit supplies only a single appliance of 
10-ampere or more rating. 

(c) Continuous Loads. Where loads other than motor loads will con- 
stitute continuous loads see Sections 210-23(b), 220-2 and 240-2. 

210-21. Outlet Devices. Outlet devices shall have a rating not less than 
the load to be served and shall conform to the following: 



ARTICLE 210— BRANCH CIRCUITS 70-25 

(a) Lampkolders. Lampholders when connected to circuits having a 
rating of over 20 amperes shall be of the heavy-duty type. 

(b) Receptacles. Receptacles installed on 1 5 ampere and 20 ampere 

branch-circuits shall be of the grounding type and they shall be installed 

in accordance with Section 210-7. 

Grounding type receptacles which are of a type that reject non-grounding 
type attachment plugs or which are of the locking type may be used for 
specific purposes or in special locations. 

When grounding type receptacles are used as replacements for existing 
non-grounding types a grounding conductor installed in accordance with 
Section 250-57 shall be provided. If it is impractical to reach a source of 
ground a non-grounding type receptacle shall be used. The installation of 
grounding type outlets shall not be used as a requirement that all portable 
equipment be of the grounded type. See Article 250 for requirements for the 
grounding of portables. 

Receptacles required in Section 517-3(d) are considered as meeting the 
requirements of this Section. 

When connected to circuits having two or more outlets, receptacles shall 

conform to the following: 

15-amp. circuits Not over 15-amp. rating 

20-amp. circuits 20-amp. rating 

30-amp. circuits 30-amp. rating 

40-amp. circuits 40 or 50-armp. rating 

50-amp. circuits 50-amp. rating 

Receptacles connected to circuits having different voltages, frequencies 
or types of current (AC or DC) on the same premises shall be of such design 
that attachment plugs used on such circuits are not interchangeable. 

Grounding receptacles rated at 1 5 or 20 amperes and installed in circuits 
of less than 150 volts between conductors shall be approved for use only 
on potentials less than 150 volts. Grounding receptacles rated at 15 amperes 
and installed in circuits of 151 to 300 volts between conductors shall be 
approved for use only on potentials not less than 151 volts. 

Receptacles rated at 1 5 amperes connected to 20 ampere branch 

circuits serving two or more cutlets shall not supply a total load in excess 
of 12 amperes for portable appliances. Receptacles rated at 20 amperes 
connected to 20 ampere branch circuits serving two or more outlets shall 
not supply a total load in excess of 16 amperes for portable appliances. 
See Tentative Interim Amendment No. 128 at back of book. 

(c) Capacity of range receptacles may be based on single range loads 
as computed from Table 220-5. 

210-22. Receptacle Outlets Required. Receptacle outlets shall be installed 
as follows: 

(a) General. Where portable cords are used, except where the attach- 
ment of cords by other means is specifically permitted. 

A cord connector that is supported by a permanently connected cord 
pendant is considered a receptacle outlet. 



70-26 MASSACHUSETTS ELECTRICAL CODE 

(b) Dwelling Type Occupancies. 

In every kitchen, dining room, breakfast room, living room, parlor, library, 
den, sun room, recreation room and bedroom, receptacle outlet shall be in- 
stalled so that the maximum distance between any two successive receptacle 
outlets in any usable wall space shall not exceed twelve feet. To determine 
the minimum number of receptacle outlets required, divide the total horizontal 
linear footage of the four walls by twelve. If, after dividing by twelve, the 
remaining distance is less than twelve feet but greater than six feet, an- 
other receptacle outlet must be added. Receptacle outlets in floor shall not 
be counted as part of the required number of receptacle outlets unless 
located within six feet of the nearest wall receptacle. The receptacle outlets 
shall be placed in practical locations. 

(c) Guest rooms in hotels, motels, and similar occupancies shall have 
receptacles installed in accordance with Section 210-22(b). 

210-23. Maximum Load. The maximum load shall conform to the fol- 
lowing: 

(a) Appliances Consisting of Motors and Other Loads. Where a circuit 
supplies only motor operated appliance loads, Article 430 shall apply. For 
other than a portable appliance., the branch circuit size shall be calculated 
on the basis of 1 25 per cent of motor load where the motor is larger than 
V& hp plus the sum of the ether loads. 

(b) Other Loads. The total load shall not exceed the branch circuit 
rating, and shall not exceed 80 per cent of the rating when load will con- 
stitute a continuous load such as store lighting and similar leads. In com- 
puting the lead of lighting units which employ ballasts, transformers or 
auto-transformers, the lead shall be based on the total of the ampere rating 
of such units and not on the wattage of the lamps. 

Exception No. I . When the assembly including the overcurrent device 
protecting the branch circuit is approved for continuous operation at 100 
per cent of its rating, the total load may equal the branch circuit rating. 

Exception No. 2. Where branch circuits are derated in accordance with 
Note 8 of Tables 3/0-/2 through 3/0-/5 the derating factor for continuous 
loading shall not apply. 

Exception No. 3. Range Loads. See Note 5 of Table 220-5. 

210-24. Permissible Loads. Individual branch circuits may supply any 
loads. Branch circuits having twe or more outlets may supply only loads 
as follows: 

(a) 15- and 20-Ampere Branch Circuits. Lighting units and/or appli- 
ances. The rating of any one portable appliance shall not exceed 80 per 
cent of the branch circuit rating. The total rating of fixed appliances shall 
not exceed 50 per cent of the branch circuit rating when lighting units or 
portable appliances are also supplied. 

(b) 30-Ampere Branch Circuits. Fixed lighting units with heavy duty 
lampholders in other than dwelling occupancies; or appliances in any occu- 
pancy. The rating of any one portable appliance shall not exceed 24 amperes. 



ARTICLE 210-BRANCH CIRCUITS 



70-27 



(c) 40-Ampere Branch Circuits. Fixed or stationary cooking appli- 
ances or fixed water heaters; or clothes dryers; in other than dwelling 
occupancies fixed lighting units with heavy-duty lampholders or infra- 
red heating units. 

(d) 50-Ampere Branch Circuits. Fixed lighting units with heavy 
duty lampholders in other than dwelling occupancies; or fixed cooking 
appliances; or infra-red lamp industrial heating appliances. 

The term "fixed" as used in this Section recognizes cord connections where 
otherwise permitted. 

Fixed outdoor electric snow melting and deicing installations may be 
supplied by any of the branch circuits described herein provided the circuit 
supplies no other load. 

210-25. Table of Requirements. The requirements for circuits having 
two or more outlets [other than the receptacle circuits of Section 220- 
3(b)] as specifically provided for above are summarized in Table 210- 
25. 

Table 210-25 
Branch Circuit Requirements 

(Type FEP, FEPB, R, RW, RU, RUW, RH-RW, SA, T, TW, RH, RUH, 
RHW, RHH, THHN, THW, and THWN conductors in raceway or cable.) 



CIRCUIT RATING 


15 Amp. 


20 Amp. 


30 Amp. 


40 Amp. 


50 Amp. 


CONDUCTORS: 












(Min. Size) 












Circuit Wires* 


14 


12 


10 


8 


6 


laps 


14 


14 


14 


12 


12 


Fixture Wires 












and Cords 




Refer to Section 240-5, Exception No. 3 




OVERCURRENT 












PROTECTION 


15 Amp. 


20 Amp. 


30 Amp. 


40 Amp. 


50 Amp. 


OUTLET DEVICES: 












Lampholders 


Any 


Any 


Heavy 


Heavy 


Heavy 


Permitted 


Type 


Type 


Duty 


Duty 


Duty 


Receptacle 


15 Max. 


15 or 20 


30 


40 and 50 


50 


Rating 


Amp. 


Amp. 


Amp. 


Amp. 


Amp. 


MAXIMUM 












LOAD 


15 Amp. 


20 Amp. 


30 Amp. 


40 Amp. 


50 Amp. 


PERMISSIBLE 


Refer to 


Refer to 


Refer to 


Refer to 


Refer to 


LOAD 


Section 


Section 


Section 


Section 


Section 




210-24(a) 


210-24(a) 


210-24(b) 


210-24(c) 


210-24(d) 



* These ampacities are for copper conductors where derating is not re- 
quired. See Tables 310-12 through 310-15. 

ARTICLE 215 — FEEDERS 

215-1. Scope. This Article deals with installation requirements for, 
and, the size of conductors in the feeders needed to supply power to 
branch circuits and, the loads as calculated under Article 220. 
215-2. Conductor Size. Feeder conductors shall have a current rating 
not smaller than the feeder load as determined by Section 220-4. A 2- 
wire feeder supplying two or more 2-wire branch circuits, or a 3-wire 
feeder supplying more than two 2-wire branch circuits, or two or more 
3-wire branch circuits, shall be not smaller than No. 10. Where a 
feeder carries the total current supplied by the service-entrance con- 



70-28 MASSACHUSETTS ELECTRICAL CODE, 

ductors, such feeder, for services of No. 6 and smaller, shall be of the 
same size as the service-entrance conductors. 

Where at any time it is found that feeder conductors are, or will be, 
overloaded, the feeder conductors shall be increased in capacity to ac- 
commodate the actual load served. 

See Examples Nos. 1 to 7 of Chapter 9. 

215-3. Voltage Drop. The size of the conductors for feeders should 
be such that the voltage drop for the load as computed by Section 220-4 
would not be more than 3% for power, heating or lighting loads or 
combinations thereof. Providing further that the maximum total volt- 
age drop for conductors for feeders and branch circuits should not ex- 
ceed 5% over all. 

215-4. Overcurrent Protection. Feeders shall be protected against 
overcurrent in accordance with the provisions of Article 240. 

215-5. Common Neutral Feeder. A commen neutral feeder may be 
employed for two or three sets of 3-wire feeders, or two sets of 4-wire 
or 5-wire feeders. When in metal enclosures, all conductors of feeder 
circuits employing a common neutral feeder shall be contained within 
the same enclosure as provided in Section 300-20. 

215-6. Diagram of Feeders. If required by the authority enforcing 
this Code, a diagram showing feeder details shall be supplied previous 
to installation. This diagram should show: Area in square feet; load 
(before applying demand-factors); demand-factors selected; computed 
load (after applying demand-factors) ; and the size of conductors. 

215-7. Installation Requirements. Where a feeder supplies branch cir- 
cuits in which grounding conductors are required, the feeder shall in- 
clude or provide a grounding means to which the grounding conductor 
of the branch circuit shall be connected. 



ARTICLE 220 — BRANCH CIRCUIT AND FEEDER 
CALCULATIONS 



220-1. Scope. This Article provides the basis for calculating the ex- 
pected branch circuit and feeder loads and for determining the number 
of branch circuits required. 

220-2. Calculation of Branch Circuit Loads. The load for branch circuits 
shall be computed in accordance with the provisions of this Section. 

Where in normal operation the maximum load will constitute a con- 
tinuous load, such as store lighting and similar loads, the minimum unit 
loads specified in this Section shall be increased by 25 per cent. 

Exception No. 1. Where branch circuits are derated in accordance 
with Note 8 of Tables 310-12 through 310-15 the unit loads are not re- 
quired to be increased by 25 per cent. 

Exception No. 2. When the assembly including the overcurrent de- 
vices protecting the branch circuits and feeders are approved for opera- 



ARTICLE 220-BRANCH CIRCUIT AND FEEDER CALCULATIONS 70-29 

tion at 100 per cent of their rating the minimum unit loads need not be 
increased over those specified. 

(a) General Lighting Load. 

(1) In Listed Occupancies. In the occupancies listed in Table 220- 
2(a), a load of not less than the unit load specified shall be included 
for each square foot of floor area. 

In determining the load on the "watts per square foot" basis, the floor 
area shall be computed from the outside dimensions of the building, 
apartment or area involved, and the number of floors; not including 
open porches, garages in connection with dwelling occupancies, nor 
unfinished spaces and unused spaces in dwellings unless adaptable for 
future use. 

The unit values herein are based on minimum load conditions and 100 
per cent power factor, and may not provide sufficient capacity for the in- 
stallation contemplated. 

In view of the trend toward higher intensity lighting systems and increased 
loads due to more general use of fixed and portable appliances, each instal- 
lation should be considered as to the load likely to be imposed and the 
capacity increased to insure safe operation. 

Where electric discharge lighting systems are to be installed, high power- 
factor type should be used or the conductor capacity may need to be in- 
creased. 

(2) In Other Occupancies. In other occupancies, a load of not less 
than the unit load specified in Section 220-2 (b) shall be included for 
each outlet. 

(b) Other Loads. For lighting other than general illumination and 
for appliances other than motors, a load of not less than the unit load 
specified below shall be included for each outlet. 

*Outlets supplying specific appliances and other loads 

Amp. rating of appliance 

Outlets supplying heavy-duty lampholders 5 amperes 

tOther outlets Wz amperes 

*For motors, see Sections 430-22 and 430-24. 

$This provision shall not be applicable to receptacle outlets con- 
nected to the circuit specified in Section 220-3 (b) nor to receptacle out- 
lets provided for the connection of stationary equipment as provided 
for in Section 400-3. 

(c) Exceptions. The minimum load for outlets specified in Section 
220-2 (b) shall be modified as follows: 

Exception No. 1. Ranges. For household electric ranges, the branch 
circuit load may be computed in accordance with Table 220-5. 

Exception No. 2. Show-Window Lighting. For show-window light- 
ing a load of not less than 200 watts for each linear foot of show-win- 
dow, measured horizontally along its base, may be allowed in lieu of 
the specified load per outlet. 

Exception No. 3. Multioutlet Assemblies. Where fixed multioutlet as- 
semblies are employed, each five feet or fraction thereof of each sep- 



70-30 MASSACHUSETTS ELECTRICAL CODE 

arate and continuous length shall be considered as one outlet of not 
less than IV2 ampere capacity; except in locations where a number of 
appliances are likely to be used simultaneously , when each one foot or 
fraction thereof shall be considered as an outlet of not less than IV2 
amperes. The requirements of this Section are not applicable to dwell- 
ings or the guest rooms of hotels. 

Exception No. 4. Telephone Exchanges. Shall be waived for manual 
switchboards and switching frames in telephone exchanges. 



Table 220-2(a). General Lighting 


Loads by Occupancies 


Type of Occupancy 




Unit Load per 
Sq. Ft. (Watts) 


Armories and Auditoriums 






1 


Banks 






2 


Barber Shops and Beauty Parlors 






3 


Churches 






1 


Clubs 






2 


Court Rooms 






2 


♦Dwellings (Other Than Hotels) 






3 


Garages — Commercial (storage) 






V2 


Hospitals 






2 


"Hotels and Motels, including apartment houses 
without provisions for cooking by tenants 




2 


Industrial Commercial (Loft) Buildings 






2 


Lodge Rooms 






1% 


Office Buildings 






5 


Restaurants 






2 


Schools 






3 


Stores 






3 


Warehouses Storage 






y* 



In any of the above occupancies except single- 
familv dwellings and individual apartments 
of multifamily dwellings: 

Assembly Halls and Auditoriums 1 

Halls, Corridors, Closets % 

Storage Spaces % 

*A11 receptacle outlets of 15-ampere or less rating in single-family 
and multifamily dwellings and in guest rooms of hotels and motels 
[except those connected to the receptacle circuits specified in Section 
220-3 (b) ] may be considered as outlets for general illumination, and no 
additional load need be included for such outlets. 

The provisions of Section 220-2 (b) shall apply to all other receptacle 
outlets. 



ARTICLE 220-BRANCH CIRCUIT AND FEEDER CALCULATIONS 70-3 I 



(d) Existing Installations. Additions to existing installations shall con- 
form to the following: 

(1) Dwelling Occupancies. New circuits or extensions to existing circuits 
may be determined in accordance with Sections 220-2(a or b); except that 
portions of existing structures not previously wired, or additions to the 
building structure, either of which exceeds 500 square feet in area, shall be 
determined in accordance with Section 220-2(a). 

(2) Other Than Dwelling Occupancies. When adding new circuits 
or extensions to existing circuits in other than dwelling occupancies, the 
provisions of Section 220-2(a or b) shall apply. 

220-3. Branch Circuits Required. Branch circuits shall be installed as 
follows: 

(a) Lighting and Appliance Circuits. For lighting, and for appliances, 
including motor-operated appliances, not specifically provided for in Section 
220-3(b), branch circuits shall be provided for a computed load not less 
than that determined by Section 220-2. 

The number of circuits shall be not less than that determined from the 
total computed load and the capacity of circuits to be used. In every case 
the number shall be sufficient for the actual load to be served, and the 
branch circuit loads shall not exceed the maximum loads specified in Section 
210-23. 

Where the load is computed on a "watts per square foot" basis, the total 
load, in so far as practical, shall be evenly proportioned among the branch 
circuits according to their capacity. 

When lighting units to be installed operate at other than 100 per cent 
power factor, see Section 210-23(b) for maximum ampere load permitted 
on branch circuits. 

For general illumination in dwelling occupancies, not less than one branch 
circuit shall be installed for each 500 square feet of floor area in addition 
to the receptacle circuits called for in Section 220-3(b). 

See Examples No. 1, la, lb, 1 c, and 4, Chapter 9. 

(b) Receptacle Circuits, Dwelling Occupancies. For the small appliance 
load in kitchen, laundry, pantry, family room, dining room and breakfast room 
of dwelling occupancies, two or more 20 ampere branch circuits in addition 
to the branch circuits specified in Section 220-3(a) shail be provided for all 
receptacle outlets in these rooms, and such circuits shall have no other out- 
lets. 

Receptacle outlets supplied by at least two appliance receptacle branch 
circuits shall be installed in the kitchen. 

Receptacle outlets installed solely for the support of and the power supply 
for electric clocks may be installed on lighting branch circuits. 

A three wire 115/230 volt branch circuit is the equivalent of two 115 
volt receptacle branch circuits. 

(c) Other Circuits. For specific loads not otherwise provided for in 
Section 220-3(a or b), branch circuits shall be as required by other sections 
of the Code. 

220-4. Calculation of Feeder Loads. The computed load of a feeder 
shall be not less than the sum of all branch circuit loads supplied by 



70-32 



MASSACHUSETTS ELECTRICAL CODE 



the feeder, as determined by Section 220-2, subject to the following 
provisions: 

(a) General Lighting. The demand factors listed in Table 220-4(a) 
may be applied to that portion of the total branch circuit load com- 
puted for general illumination. These demand factors shall not be ap- 
plied in determining the number of branch circuits for general illumina- 
tion supplied by the feeders. 

See Section 220-4(g and h). 

The demand factors herein are based on minimum load conditions and 
100 per cent power factor, and in specific instances may not provide suffi- 
cient capacity for the installation contemplated. In view of the trend to- 
ward higher intensity lighting systems and increased loads due to more 
general use of fixed and portable appliances, each installation should be con- 
sidered as to the load likely to be imposed and the capacity increased to in- 
sure safe operation. Where electric discharge lighting systems are to be 
installed, high power-factor type should be used or the conductor capacity 
may need to be increased. 

Table 220-4 (a). Calculation of Feeder Loads by Occupancies 



Type of 
Occupancy 


Portion of Lighting Load 

to which Demand 

Factor Applies (wattage) 


Feeder 

Demand 

Factor 


Dwellings — other 
than Hotels 


First 3000 or less at 
Next 3001 to 120,000-at 
Remainder over 120,000 at 


100% 
35% 

25% 


*Hospitals 


First 50,000 or less at 
Remainder over 50,000 at 


40% 
20% 



Hotels and Motels — includ- First 20,000 or less at 50% 

ing Apartment Houses Next 20,001 to 100,000 at 40% 

without provision for Remainder over 100,000 at 30% 

cooking by tenants 



Warehouses 
(Storage) 



First 12,500 or less at 
Remainder over 12,500 at 



100% 

50% 



All Others 



Total Wattage 



100% 



* The demand factors of this Table shall not apply to the computed 
load of sub-feeders to areas in hospitals, hotels and motels where entire 
lighting is likely to be used at one time; as in operating rooms, ball- 
rooms, or dining rooms. 

(b) Show-Window Lighting. For show-window lighting, a load of 
not less than 200 watts shall be included for each linear foot of show- 
window measured horizontally along its base. 

(c) Motors. For motors, a load computed according to the provi- 
sions of Sections 430-24, 430-25 and 430-26 shall be included. 

(d) Neutral Feeder Load. The neutral feeder load shall be the 
maximum unbalance of the load determined by Section 220-4. The 
maximum unbalanced load shall be the maximum connected load be- 
tween the neutral and any one ungrounded conductor; except that the 
load thus obtained shall be multiplied by 140 per cent for 5-wire, 
2-phase systems. For a feeder supplying household electric ranges, wall- 



ARTICLE 220-BRANCH CIRCUIT AND FEEDER CALCULATIONS 70-33 

mounted ovens and counter-mounted cooking units, the maximum un- 
balanced load shall be considered as 70 per cent of the load on the un- 
grounded conductors, as determined in accordance with Table 220-5. 
For 3-wire DC or single-phase AC, 4-wire 3-phase and 5-wire 2-phase 
systems, a further demand-factor of 70 per cent may be applied to that 
portion of the unbalanced load in excess of 200 amperes. There shall 
be no reduction of the neutral capacity for that portion of the load 
which consists of electric discharge lighting. 

See Examples 1, la, lb, lc, 2, 3, 4 and 5, Chapter 9. 

(e) Fixed Electrical Space Heating. The computed load of a feeder 
supplying fixed electrical space heating equipment shall be the total 
connected load on all branch circuits. 

Exception No. 1. Where reduced loading of the conductors results 
from units operating on duty-cycle, intermittently , or from all units not 
operating at one time, the authority enforcing this code may grant per- 
mission for feeder conductors to be of a capacity less than 100 per cent, 
provided the conductors are of sufficient capacity for the load so de- 
termined. 

Exception No. 2. Section 220-4(e) does not apply when feeder ca- 
pacity is calculated in accordance with optional method in Section 
220-7 for one-family residences. 

(f) Noncoincident Load. In adding the branch circuit loads to de- 
termine the feeder load, the smaller of two dissimilar loads may be 
omitted from the total where it is unlikely that both of the loads will be 
served simultaneously. 

(g) Small Appliances. The computed branch circuit load for re- 
ceptacle outlets in other than dwelling occupancies, for which the al- 
lowance is not more than Wi amperes per outlet, may be included 
with the general lighting load and subject to the demand factors in Sec- 
tion 220-4(a). 

Dwelling Occupancies 

The requirements in following Sections 220-4 (h-k) apply to dwelling 
type occupancies and are supplemental to the preceding Sections 220-4 (a-g). 

(h) Small Appliances — Dwelling Occupancies. In single-family 
dwellings, in individual apartments of multifamily dwellings having 
provisions for cooking by tenants, and in each hotel suite having a 
serving pantry, a feeder load of not less than 1500 watts for each two- 
wire circuit installed as required by Section 220-3 (b) shall be included 
for small appliances (portable appliances supplied from receptacles of 
15 or 20 ampere rating) in pantry and breakfast-room, dining room, 
kitchen and laundry. Where the load is subdivided through two or 
more feeders, the computed load for each shall include not less than 
1500 watts for each two-wire circuit for small appliances. These loads 
may be included with the general lighting load and subject to the de- 
mand factors in Section 220-4 (a) . 

(i) Electric Ranges. The feeder load for household electric ranges 
and other cooking appliances, individually rated more than \ 3 A kw, may 
be calculated in accordance with Table 220-5. 



70-34 MASSACHUSETTS ELECTRICAL CODE 

In order to provide for possible future installation of ranges of higher 
ratings, where ranges of less than 8 3 /t kw ratings or 

wall-mounted ovens and counter-mounted cooking units are to be installed, 
the feeder capacity shall be not less than the maximum demand value 
specified in Column A of Table 220-5. 

Where a number of single-phase ranges are supplied by a 3-phase, 4- 
wire feeder, the current shall be computed on the basis of the demand of 
twice the maximum number of ranges connected between any two-phase 
wires. 

See Example 7, Chapter 9. 

(j) Fixed Electrical Appliances (Other than Ranges., Clothes Dryers, Air 
Conditioning Equipment or Space Heating Equipment). Where four or 
more fixed electrical appliances other than electric ranges, clothes dryers, 
air conditioning equipment or space heating equipment are connected to 
the same feeder in a single or multifamily dwelling, a demand factor of 75 
per cent may be applied to the fixed appliance load. 

(k) Space Heating and Air Cooling. In adding branch circuit loads for 
space heating and air cooling in dwelling occupancies, the smaller of the 
two loads may be omitted from the total where it is unlikely that both of 
the loads will be served simultaneously. 

(I) Farm Buildings. Feeders supplying farm buildings (excluding dwell- 
ings) or loads consisting of two or more branch circuits shall have minimum 
capacity computed in accordance with the following table: 

Table 220-4(1) 

Demand Computation for Farm Buildings or Loads 

Per Cent of 
Load in Amperes at 230 Volts Connected Load 

Loads expected to operate without diversity, 
but not less than 125% full load current of 
ihe largest motor and not less than first 

60 Amperes. 100% 

Next 60 Amperes of all other loads 50% 

Remainder of other load 25% 

NOTE 1: For services to farm dwellings, see Sections 220-2 through 220-7. 
NOTE 2: For service at main point of delivery to farmstead, see Section 
220-4(m). 

(m) Farm Services. 

(1) Service equipment and service entrance conductors for individual 
farm buildings (excluding dwellings) shall have minimum capacity com- 
puted in accordance with Section 220-4(1). 

(2) Minimum capacity of service conductors and service equipment, 
if any, at the main point of delivery to farms (including dwellings) 
shall be determined in accordance with the following formula: 

100 per cent of the largest demand computed in accordance with 
Section 220-4(1). 



ARTICLE 220-BRANCH CIRCUIT AND FEEDER CALCULATIONS 70-35 

15 per cent of the second largest demand computed in accordance 
with Section 220-4(1). 

65 per cent of the third largest demand computed in accordance with 
Section 220-4(1). 

50 per cent of the demands of remaining loads computed in accord- 
ance with Section 220-4(1). 

Note 1 : Consider as a single computed demand the total of the computed 
demands of all buildings or loads having the same function. 

Note 2: The demand of the farm dwelling, if included in the demands of 
this formula, should be computed in accordance with Note 1 of Ta- 
ble 220-4(1) 

Table 220-5. Demand Loads for Household Electric Ranges, 

Wall-Mounted Ovens, Counter-Mounted Cooking Units and 

Other Household Cooking Appliances Over 1 3 ,4 kw Rating 

Column A to be used in all cases except as otherwise permitted 

in Note 4 below. 





Maximum 












Demand 


Demand Fa 


ctors 




vi'ifcri} f\~v 


(See Notes) 


(See Note 


4) 






APPLIANCES 


COLUMN A 

(Not over 12 


COLUMN B 

Less than 3% 


COLUMN C 

(3% kw to 8% 






kw Rating; 


kw Rating) 


kw 


Rating) 




1 


8 


kw 


80% 




90% 




2 


11 


kw 


75 % 




65% 




3 


14 


kw 


70' 




55% 




4 


17 


kw 


66% 




50% 




5 


20 


kw 


62% 




45% 




6 


21 


kw 


59% 




43% 




7 


22 


kw 


56% 




40% 




8 


23 


kw 


53 




36% 




9 


24 


kw 


51% 




35 r c 




10 


25 


kw 


49% 




34% 




11 


26 


kw 


47% 




32% 




12 


27 


kw 


45- 




32% 




13 


28 


kw 


43 




32% 




14 


29 


kw 


41 




32% 




15 


30 


kw 


40% 




32% 




16 


31 


kw 


39% 




28% 




17 


32 


kw 


Vt 




28% 




18 


33 


kw 


37% 




28% 




19 


34 


kw 


36- 




28* 




20 


35 


kw 


35% 




28 




21 


36 


kw 


34% 




26% 




22 


37 


kw 


33% 




- ; ': 




23 


38 


kw 


32% 




21 




24 


39 


kw 


31% 




21 1 




25 


4'". 


kw 


30% 








26-30 


/15 kw plus 1 kw\ 


30% 




-, i 




31-40 


Ifor 


each ranged 


30 % 




22% 




41-50 


[25 kw plus fc] 


30% 








51-60 


\ kw for each \ 


30 




18% 




61 & over 


1 


range j 


34 % 




16% 





70-36 



MASSACHUSETTS ELECTRICAL CODE 



Note 1. Over 12 kw to 27 kw ranges all of same kw rating. For ranges, 
individually rated more than 12 kw but not more than 27 kw, the maximum 
demand in Column A shall be increased 5 per cent for each additional kw 
of rating or major fraction thereof by which the rating of individual 
ranges exceeds 12 kw. 

Note 2. Over 12 kw to 27 kw ranges of unequal ratings. For ranges in- 
dividually rated more than 12 kw and of different ratings but none exceed- 
ing 27 kw an average value of rating shall be calculated by adding together 
the ratings of all ranges to obtain the total connected load (using 12 kw 
for any range rated less than 12 kw) and dividing by the total number of 
ranges; and then the maximum demand in Column A shall be increased 5 
per cent for each kw or major fraction thereof by which this average value 
exceeds 12 kw. 

Note 3. This table does not apply to commercial ranges. The branch circuit 
load for a commercial range shall be the nameplate rating of the range. 

Note 4. Over 1 3 A kw to S 3 A kw. In lieu of the method provided in 
Column A, loads rated more than l 3 A kw but not more than 8% kw may be 
considered as the sum of the nameplate ratings of all the loads, multiplied 
by the demand factors specified in Columns B or C for the given number of 
loads. 

Note 5. Branch Circuit Load. Branch circuit load for one range may be 
computed in accordance with Table 220-5. The branch circuit load for one 
wall-mounted oven or one counter-mounted cooking unit shall be the name- 
plate rating of the appliance. The branch circuit load for a counter-mounted 
cooking unit and not more than two wall-mounted ovens, all supplied from a 
single branch circuit and located in the same room shall be computed by 
adding the nameplate ratings of the individual appliances and treating this 
total as equivalent to one range. 

Table 220-6 
Demand Factors for Household Electric Clothes Dryers 



Number of 
Dryers 


Demand Factor 
(per cent) 


1 


100 


2 


100 


3 


100 


4 


100 


5 


80 


6 


70 


7 


65 


8 


60 


9 


55 


10 


50 


11-13 


45 


14-19 


40 


20-24 


35 


25-29 


32.5 


30-34 


30 


35-39 


27.5 




25 



220-7. Optional Calculation for One-Family Residence. For a one-fam- 
ily residence served by a 115/230 volt, 3-wire, 100 ampere or larger 
service where the total load is supplied by one feeder or one set of 



ARTICLE 230-SERVICES 70-37 



service entrance conductors, the following percentages may be used in 
lieu of the method of determining feeder (and service) loads detailed in 
Section 220-4. 

All other load shall include 1500 watts for each 20 ampere appli- 
ance outlet circuit [Section 220-3 (b)]; lighting and portable appliances 
at 3 watts per square foot; all fixed appliances, (including four or more 
separately controlled space heating units [see Section 220-4(k)], 
ranges, wall-mounted ovens and counter-mounted cooking units) at 
nameplate rated load (kva for motors and other low power-factor 
loads). 

See Examples 1(b) and 1(c) of Chapter 9. 



Table 220-7 
Optional Calculation for One-Family Residence 

Per Cent 
LOAD (in kw or kva) of Load 

Air conditioning and cooling including heat pump compressors 

[see Section 220-4(k)] , 100% 



Central electrical space heating [see Section 220-4 (k)] 100% 



Less than four separately controlled electrical space heating 

units [see Section 220-4(k)] 100% 

First 10 kw of all other load 100% 

Remainder of other load 40% 



ARTICLE 230 — SERVICES 

A. General Requirements 

230-1. Scope. The provisions of this Article shall apply to the con- 
ductors and equipment for control and protection of services — cir- 
cuits that conduct electric power from the supply system or plant to 
the premises to be served. 

For over 600 volts see Section 230-100. 
230-2. Number of Services to a Building or Other Premises Served. In 
general, a building or other premises served shall be supplied through 
only one set of service conductors, except as follows: 

Exception No. 1. Fire Pumps. Where a separate service is required 
for fire pumps. 

Exception No. 2. Emergency Lighting. Where a separate service is 
required for emergency lighting and power purposes. 

Exception No. 3. Multiple-Occupancy Buildings. 

(a) By special permission, in multiple-occupancy buildings where 
there is no available space for service equipment accessible to all the 
occupants. 



70-38 MASSACHUSETTS ELECTRICAL CODE 

(b) Buildings of multiple occupancy may have two or more sep- 
arate sets of service-entrance conductors which are tapped from one 
service drop or lateral, or two or more sub-sets of service-entrance con- 
ductors may be tapped from a single set of main service conductors. 
See Section 230-75 and Section 230-90 (a) Exception No. 4. 

Exception No. 4. Capacity Requirements. Where capacity require- 
ments make multiple services desirable. 

Exception No. 5. Buildings of Large Area. By special permission, 
where more than one service is necessary due to the area over which a 
single building extends. 

Exception No. 6. Different Characteristics or Classes of Use. Where 
additional services are required for different voltages, frequency, or 
phase, or different classes of use. Different classes of use could be be- 
cause of needs for different characteristics, or because of rate schedule 
as in the case of controlled water heater service. 

230-3. Supply to a Building from Another. No overhead service, no 
underground service and no service from an isolated plant shall supply 
one building from another, unless such buildings are under single occu- 
pancy or management. See Sections 230-45 and 230-76. 

B. Insulation and Size of Service Conductors 

230-4. Insulation of Service Conductors. Service conductors shall 
have an insulating covering which will normally withstand exposure 
to atmospheric and other conditions of use and which shall prevent any 
detrimental leakage of current to adjacent conductors, objects, or the 
ground. 

Exception. Grounded Conductor. In the case of service conductors 
that have a nominal voltage to ground of not more than 300 volts, a 
grounded service conductor without an insulating covering may be in- 
stalled. 

For Service Drops — See Section 230-22. 

For Service Entrance Conductors — See Section 230-40. 

For Underground Services — See Section 230-30. 

For Farmstead Service Conductors — See Section 220-4(m). 

230-5. Size of Service Conductors. Service conductors shall have ade- 
quate ampacity to safely conduct the current for the loads supplied with- 
out a temperature rise detrimental to the insulating covering of the 
conductors, and shall have adequate mechanical strength. 

Minimum sizes are given in the following references: 
For Service Drops — Section 230-23. 
For Service Entrance Conductors — Section 230-41. 
For Underground Service Conductors — Section 230-31. 

C. Service Drops 

230-21. Number of Drops. No building shall be supplied through 
more than one service drop, except for the purposes listed in Section 
230-2. 

230-22. Service Drop Conductors. 



ARTICLE 230— SERVICES 70-39 

(a) In multiple-conductor cables, conductors shall be covered with 
rubber or thermoplastic, except a grounded conductor may be uninsulated 
where the maximum voltage to ground of any conductor is not over 300 volts. 

(b) All open individual conductors shall be insulated or covered. 
Conductors having extruded covering used for service drops have the 

same ampacities as covered conductors listed in Tables 310-13 and 310-15. 
230-23 Minimum Size of Service Drop Conductors. Conductors shall be 
of sufficient size to carry the load and shall not be smaller than No. 8 
copper or equivalent except for limited load as in Section 230-41, Excep- 
tion No. 4, where they may be net smaller than No. 12 and shall then be 
of hard drawn copper or equivalent. 

Conductors to a building from a pole on which a meter or disconnecting 
means is installed shall be considered as a service drop and installed accord- 
ingly. 

230-24. Clearance of Service Drops. Service drop conductors shall not 
be readily accessible and when not in excess of 600 volts, shall conform to 
the following: 

(a) Clearance Over Roof. Conductors shall have a clearance of not less 
than 8 ft. from the highest point of roofs over which they pass with the 
following exceptions: 

Exception No. 1 . Where the voltage between conductors does not exceed 
300 and the roof has a slope of not less than 4 inches in 12 inches thei 
clearance may be not less than 3 feet. 

Exception No. 2. Service drop conductors of 300 volts or less which da 
not pass over other than a maximum of 4 feet of the overhang portion of 
the roof for the purpose of terminating at a (through-the-roof) service race- 
way or approved support may be maintained at a minimum of 18 inches 
from any portion of the roof over which they pass. 

(b) Clearance from Ground. Conductors shall have a clearance of not 
less than 10 feet from the ground or from any platform or projection from 
which they might be reached. See Section 730-18. 

(c) Clearance from Building Openings. Conductors shall have a clearance 
of not less than 36 inches from windows, doors, porches, fire escapes, or 
similar locations. 

Conductors run above the top level of a window are considered out of 
reach from that window. 

For clearances of conductors of over 600 volts see National Electrical 
Safety Code. (Available from Superintendent of Documents, Government 
Printing Office, Washington 25, D.C.) 

230-25. Supports Over Buildings. Where practicable, conductors passing 
over a building shall be supported on structures which are independent 
of the building. Where necessary to attach conductors to roof they shall 
be supported on substantial structures. 

230-26. Point of Attachment. The point of attachment of a service 
drop to a building or other structure shall be not less than 10 feet above 
finished grade and shall be at a height to permit a minimum clearance 
for service drop conductors of 10 feet above sidewalks and 18 feet 



70-40 MASSACHUSETTS ELECTRICAL CODE 

above driveways, alleys and public roads. The attachment should not 
be more than 30 feet above ground unless a greater height is necessary 
for proper clearance. Where it is impractical to get the point of attach- 
ment high enough to obtain the above clearances, the clearance over 
residential driveways may be reduced, provided a clearance of 10 feet 
over sidewalks, 18 feet over alleys and public roads, and a minimum 
of 12 feet over residential driveways is obtained. 

In the event a mast type riser is required to attain the required height, 
it shall be of such construction and so supported that it will withstand 
the strain imposed by the service drop. Raceway fittings shall be of a 
type approved for the purpose. 

230-27. Means of Attachment. Multiple-conductor cables used for 
service drops shall be attached to buildings or other structures by fittings 
approved for the purpose. Open conductors shall be attached to non- 
combustible, nonabsorptive insulators securely attached to the building 
or other structure or by fittings approved for the purpose. 

D. Underground Services 
230-30. Insulation — Underground Service Conductors. 

(a) Underground conductors up to the point of attachment to serv- 
ice equipment shall be covered with rubber, cambric, thermoplastic, 
paper or other approved insulating material, except: 

Exception No. 1 . Uninsulated grounded neutral conductors of alumi- 
num or copper may be installed underground when part of an ap- 
proved cable assembly. 

Exception No. 2. Bare grounded neutral conductors of copper may 
be installed underground in duct or conduit. 

(b) Insulated service conductors installed underground, or in concrete 
slabs or masonry in direct contact with earth, shall be lead-covered or 
of other types specially approved for the purpose. 

230-31. Size of Underground Service Conductors. 

(a) Size of Underground Service Lateral. Conductors shall be of 
sufficient size to carry the load and shall not be smaller than No. 8 
copper or the equivalent except for limited load as in Section 230-41 
Exception No. 4 the conductors shall not be smaller than No. 12 cop- 
per or equivalent. 

(b) Size of Underground Service Entrance Conductors. Same as re- 
quired for overhead service entrance conductors. See Section 230-41. 

230-32. Protection Against Damage. 

(a) In the Ground. Underground service conductors shall be pro- 
tected against physical damage by being installed in duct, conduit, in 
cable of one or more conductors approved for the purpose, or by other 
approved means. See Sections 3 10-1 (b), 310-5 and 310-6. 

(b) On Poles. Where underground service conductors are carried 
up a pole the mechanical protection shall be installed to a point at least 
8 feet above the ground. Such mechanical protection may be provided 
by the use of approved cable, pipe, or other approved means. 



ARTICLE 230— SERVICES 70-41 

(c) Where Entering Building. Underground service conductors shall 
have mechanical protecticn in the form of rigid conduit, 

auxiliary gutters, the metal tape of an ap- 
proved service cable, or other approved means. The mechanical protection 
shall extend to the enclosure for the service equipment unless the service 
switch is installed on a switchboard, in which case a bushing shall be pro- 
vided which, except where lead-covered conductors are used, shall be of 
the insulating type. 

230-33. Raceway Seal. Where a service raceway or duct enters from an 
underground distribution system, the end within the building shall be sealed 
with suitable compound so as to prevent the entrance of moisture or 
gases. Spare or unused ducts shall also be sealed. 

230-34. Grounding Raceways and Cable Sheaths. See Section 230-63. 
230-35. Termination at Service Equipment. See Section 230-42, Exception 
No. 3, and Section No. 230-53. 

E. Service-Entrance Conductors 

230-40. Insulation of Service-Entrance Conductors. 

(a) Service-entrance conductors extending along the exterior of or enter- 
ing buildings or other structures shall be rubber-covered or thermoplastic- 
covered if in raceways, or in cables approved for the purpose, except a 
grounded conductor may be uninsulated where the maximum voltage to 
ground of any conductor is not over 300 volts. 

Where only on the exterior of the building or ether structure the con- 
ductors shali be insulated or covered. 

(b) Open individual conductors which enter the building or other struc- 
ture shall be rubber-covered or thermoplastic-covered. 

230-41. Size of Service-Entrance Conductors, Overhead System and Under- 
ground System. 

Service-entrance conductors shall have sufficient ampacity to carry the 
load as determined by Article 220 and in accordance with Tables 310-12, 
310-13, 310-14, 310-15. There shall be a minimum of 100 ampere 3-wire 
service for all individual residences except: 

Exception No. I . For installations consisting of not more than two 2-wire 
branch circuits they shall not be smaller than No. 8. 

Exception No. 2. By special permission due to limitations of supply source 
or load requirements they shall not be smaller than No. 8. 

Exception No. 3. For installations to supply only limited loads of a single 
branch circuit, such as small polyphase power, controlled water heaters and 
the like, they shall not be smaller than the conductors of the branch circuit 
and in no case smaller than No. 12. 

Exception No. 4. The neutral conductor which shall have an ampacity 
in conformity with Section 220-Md) , but shall not be smaller than the un- 
grounded conductors when these are No. 8 or smaller. 



70-42 MASSACHUSETTS ELECTRICAL CODE 

230-42. Service-bntrance Conductors without Splice. Service-entrance 
conductors shall be without splice except as follows: 

Exception No. 1. Clamped or bolted connections in a meter en- 
closure are permitted. 

Exception No. 2. Taps to main service conductors are permitted as 
provided in Section 230-2 Exception No. 3(b) or to individual sets of 
service equipment as provided in Section 2 30-70 (g) . 

Exception No. 3. A connection is permitted, when properly enclosed, 
where an underground service conductor enters a building and is to be 
extended to the service equipment or meter in another form of ap- 
proved service raceway or service cable. 

Exception No. 4. A connection is permitted where service conduc- 
tors are extended from a service drop to an outside meter location and 
returned to connect to the service-entrance conductors of an existing 
installation. 

230-43. Other Conductors in Service Raceway. Conductors other than 
service conductors, grounding conductors, or control conductors from 
time switches having overcurrent protection, shall not be installed in 
the same service raceway or service entrance cable. 

F. Installation of Service-Entrance Conductors 

230-44. Wiring Methods. Service-entrance conductors extending along 
the exterior, or entering buildings or other structures may be installed 
as separate conductors, in cables approved for the purpose, or enclosed 
in rigid conduit, or, for circuits not exceeding 600 volts, in electrical 
metallic tubing, wireways, auxiliary gutters, or as busways. 

Service-entrance conductors should not be run within the hollow spaces of 
frame buildings unless provided with overcurrent protection at their outer 
end. 

230-45. Conductor Considered Outside Building. Conductors placed 
under at least two inches of concrete beneath a building, or conductors 
within a building in conduit or duct and enclosed by concrete or brick 
not less than two inches thick shall be considered outside the building. 

230-46. Mechanical Protection. Individual open conductors or cables 
other than approved service-entrance cables, shall not be installed 
within 8 feet of the ground or where exposed to physical damage. 
Service-entrance cables, where liable to contact with awnings, shutters, 
swinging signs, installed in exposed places in driveways, near coal 
chutes or otherwise exposed to physical damage, shall be of the pro- 
tected type or be protected by conduit, electrical metallic tubing or 
other approved means. 

230-47. Individual Open Conductors Exposed to Weather. Individual 
open conductors exposed to weather shall be supported on insulators, 
racks, brackets, or other means, placed at intervals not exceeding 9 
feet and separating the conductors at least 6 inches from each other and 
2 inches from the surface wired over; or at intervals not exceeding 15 
feet if they maintain the conductors at least 12 inches apart. For 300 
volts or less, conductors may have a separation of not less than 3 inches 



ARTICLE 230-SERVICES 70-43 



where supports are placed at intervals not exceeding 4V2 feet and con- 
ductors are not less than 2 inches from the surface wired over. 

230-48. Individual Open Conductors Not Exposed to Weather. Indi- 
vidual open conductors not exposed to the weather may be supported 
on glass or porcelain knobs placed at intervals not exceeding 41/2 feet 
and maintaining the conductors at least one inch from the surface wired 
over and a separation of at least 2Vi inches between conductors. 

230-49. Individual Conductors Entering Buildings. Individual conduc- 
tors entering buildings shall pass inward and upward through slanting 
noncombustible, nonabsorptive insulating tubes, or shall enter through 
roof bushings, and shall conform to the provisions of Article 324. Drip 
loops shall be formed on the conductors before entering tubes. 

230-50. Service Cables. Service cables of a type not approved for 
mounting in contact with a building shall have insulating supports at in- 
tervals not exceeding 15 feet, and maintaining a distance of at least 2 
inches from the surface wired over. Service cables mounted in contact 
with the building shall be supported at intervals not exceeding 4V / 2 feet. 

230-51. Service Head. Service raceways shall be equipped with a rain- 
tight service head. Service cables, unless continuous from pole to serv- 
ice equipment or meter, shall be equipped with an approved raintight 
service head, or be formed in a gooseneck, taped and painted or taped 
with self-sealing weather-resistant thermoplastic. They shall be held se- 
curely in place by connection to service-drop conductors below the 
gooseneck or by a fitting approved for the purpose. Drip loops shall be 
formed on individual conductors. To prevent the entrance of moisture, 
service-entrance conductors shall be connected to the service-drop con- 
ductors below the level of the service head or the termination of serv- 
ice-entrance cable sheaths. Service drop conductors, and service en- 
trance conductors, shall be so arranged that water will not enter serv- 
ice raceway and equipment. Where service heads are used, conductors 
of opposite polarity shall be brought out through separately bushed 
holes. Service heads and goosenecks in service entrance cable shall be 
located above the point of attachment of the service drop conductors. 

Exception: Where building construction or location of service head 
or termination point of service drop conductors at the building is such 
as to be impractical for service head to be above the termination point 
of the service drop conductors, such service head may be located not 
more than twenty-four inches from the termination point of the service 
drop conductors and shall have a mechanical connector at the lowest 
point in the drip loop to prevent siphoning. 

230-52. Enclosing Raceways Made Raintight. When rigid metal race- 
ways are installed where exposed to weather the raceways shall be made 
raintight and arranged to drain. 

230-53. Terminating Raceway at Service Equipment. Where conduit, 
electrical metallic tubing, or service cable is used for service conduc- 
tors, the inner end shall enter a terminal box or cabinet, or be made up 
directly to an equivalent fitting, enclosing all live metal parts, except 
that where the service disconnecting means is mounted on a switch- 
board having exposed bus-bars on the back, the raceway may be 



70-44 MASSACHUSETTS ELECTRICAL CODE 

equipped with a bushing which shall be of the insulating type unless 
lead-covered conductors are used. 

230-54. Grounding Service Raceways and Cable Armor. See Section 
230-63. 

G. Service Equipment 

230-60. Hazardous Locations. Service equipment installed in hazard- 
ous locations shall comply with the requirements of Articles 500 to 517 
inclusive. 

230-61. Service Equipment Grouped. Where supplied at the same side 
of the building by more than one overhead service drop or more than 
one set of underground service conductors, the service equipment, ex- 
cept for services as permitted in Section 230-2, shall be grouped and 
equipment marked to indicate the load it serves. 

H. Grounding and Guarding 
230-62. Guarding. Live parts of service equipment shall be enclosed 
so that they will not be exposed to accidental contact, unless mounted 
on a switchboard, panelboard or controller accessible to qualified per- 
sons only and located in a room or enclosure free from easily ignitible 
material. Such an enclosure shall be provided with means for locking or 
sealing doors giving access to live parts. 

230-63. Grounding and Bonding. Service equipment shall be 
grounded as follows: 

(a) Equipment. The enclosure for service equipment shall be 
grounded in the manner specified in Article 250, unless (1) the volt- 
age does not exceed 150 volts to ground and such enclosures are (2) 
isolated from conducting surfaces, and (3) unexposed to contact by 
persons or materials that may also be in contact with other conducting 
surfaces. 

(b) Raceways. Service raceways, and the metal sheath of service 
cables, shall be grounded. Conduit and metal pipe from underground 
supply shall be considered sufficiently grounded where containing lead- 
sheathed cable bonded to a continuous underground lead-sheathed ca- 
ble system. 

(e) Flexible Conduit. Where a service run of rigid metal raceway is 
interrupted by flexible metal conduit, the sections of rigid metal race- 
way thus interrupted shall be bonded together by a copper conductor 
not smaller than specified for grounding conductors in Table 250-94 
(a), using clamps or other approved means. The conductor and bond- 
ing devices shall be protected from physical damage. Where the flexible 
conduit runs to the service cabinet, similar bonding shall be installed 
between the cabinet and the rigid raceway. 

J. Disconnecting Means 

230-70. General. (For multiple occupancy buildings see also Section 
230-75.) 

(a) Disconnection from Service Conductors. Means shall be pro- 
vided for disconnecting all conductors in the building or other structure 
from the service entrance conductors. 



ARTICLE 230— SERVICES 70-45 

(b) Location. The disconnecting means shall be located at a readily 
accessible point nearest to the entrance of the conductors, either inside or 
outside the building or other structure. See also Section 230-45 and Sec- 
tion 1 10-16. 

(c) Approval. The disconnecting means shall be of a type approved for 
service equipment and for prevailing conditions. 

(d) Types Permitted. The disconnecting means for ungrounded con- 
ductors shall consist of either: 

(1) A manually operable switch or circuit-breaker equipped with a 
handle or other suitable operating means positively identified and marked 
for mechanical operation by hand. 

(2) An electrically operated switch or circuit-breaker provided the 
switch or circuit-breaker can be opened by hand in event of a failure of 
the power supply and the open and closed positions are clearly indicated to 
the operator. 

(e) Externally Operable. An enclosed service switch or circuit-breaker 
shall be externally operable. See definition Article 100. 

Where the current of a single circuit, or group 
of circuits, is separately metered, as in apartment house installations, devices 
shall be installed in a convenient location to control each separately metered 
installation, such devices being enclosed and the switch or circuit breaker 
being externally operable. 

(f) Indicating. The disconnecting means shall plainly indicate whether 
it is in the open or closed position. 

(g) Switch and Circuit Breaker. It may consist of not more than six 
switches or six circuit breakers in a common enclosure, or in a group of 
separate enclosures. Two or three single pole switches or breakers, capable 
of individual operation, may be installed on multiwire circuits, one 
pole for each ungrounded conductor, as one multipole disconnect [where 
applicable, see Section 230-70(h)] provided they are equipped with "handle 
ties," "handles within 1/16 inch proximity," a "master handle," or "other 
means," making it practical to disconnect all conductors of the service with 
no more than six operations of the hand. 

See Section 200-5 and Section 384-1 6(a). 

(h) Simultaneous Openings. The disconnecting means shall simultane- 
ously disconnect all ungrounded conductors, except for 3-wire direct- 
current or single-phase circuits or multiwire circuits that do not supply 
polyphase motors. 

See Section 200-5(a). 

(i) Disconnection of Grounded Conductor. Where the switch or circuit 
breaker does not interrupt the grounded conductor, other means shall be 
provided in the service cabinet or on the switchboard for disconnecting the 
grounded conductor from the interior wiring. 
230-71. Rating of Service Equipment. 

(a) The service disconnecting means shall have a rating not less than 
the load to be carried determined in accordance with Article 220. In 
general the service disconnecting means shall have a rating of not less 



70-46 MASSACHUSETTS ELECTRICAL CODE 

than 60 amperes where a switch is used, and not less than 50 amperes 
where a circuit breaker is used, except: 



Exception No. I . For installations consisting of not more than two 2-wire 
branch circuits a service equipment of 30-ampere minimum rating may 
be used. 

(b) Where multiple switches or circuit breakers are used in accordance 
with Section 230-70(g) the combined rating shall not be less than required 
for a single switch or breaker. 

230-72. Connection to Terminals. The service conductors shall be at- 
tached to the disconnecting means by pressure connectors, clamps or other 
approved means, except that connections which depend upon solder shall 
not be used. 

230-73. Connections Ahead of Disconnecting Means. Service fuses, meters, 
high-impedance shunt circuits (such as potential coils of meters, etc.), 
supply conductors for time switches, surge protective capacitors, instrument 
transformers, lightning arresters and circuits for emergency systems, fire 
pump equipment, fire and sprinkler alarms as provided in Section 230-94, 
may be connected on the supply side cf the disconnecting means. Taps 
from service conductors to supply time switches, circuits for emergency 
lighting, etc., shall be installed in accordance with Section 230-44 and dis- 
connecting means shall be installed as required in Section 230-70. 

For detailed service provisions for fire alarm, sprinkler supervisory, or 
watchman systems, see appropriate Standards of the National Fire Protection 
Association. 

230-74. Safeguarding Emergency Supply. Where an emergency supply 
is provided to feed the conductors controlled by the service disconnecting 
means, the disconnector shall be of a design that will open all ungrounded 
conductors from the usual supply before connection is made to the emergency 
supply, unless agreed upon arrangements have been made for parallel 
operation and suitable automatic control equipment provided. See Article 700. 
230-75. Multiple Occupancy. In a multiple occupancy building, each occu- 
pant shall have access to his disconnecting means. A multiple occupancy 
building having individual occupancy above the second floor shall have service 
equipment grouped in a common accessible place, the disconnecting means 
consisting of not more than six switches or six circuit breakers. Multiple oc- 
cupancy buildings that do not have individual occupancy above the second 
floor may have service conductors run to each occupancy in accordance with 
Section 230-2, Exception No. 3 and each such service may have not more 
than six switches or circuit breakers. 

230-76. More Than One Building. In a property comprising more than 
one building under single management, the conductors supplying each 
building served shall be • provided with a readily accessible means, 



ARTICLE 230-SERVICES 70-47 



within or adjacent to the building, of disconnecting all ungrounded 
conductors from the source of supply. In garages and outbuildings on 
residential property the disconnecting means may consist of a snap 
switch, suitable for use on branch circuits, including switch controls at 
more than one point. 

K. Overcurrent Protection 

230-90. Where Required. Each ungrounded service-entrance con- 
ductor shall have overcurrent protection. 

(a) Ungrounded Conductor. Such protection shall be provided by 
an overcurrent device in series with each ungrounded service conduc- 
tor, having a rating or setting not higher than the allowable ampacity of 
the conductor, except as follows: 

Exception No. 1 . For motor-starting currents, ratings in conformity 
with Sections 430-52, 430-62, or 430-63 may be used. 

Exception No. 2. Circuit breakers may have a rating or setting in 
conformity with Section 240—5, Exceptions No. 1 and 2, also Section 
240-7; fuses shall conform to requirements of Section 240-6. 

Exception No. 3. Not more than six circuit breakers or six sets of 
fuses may serve as the overcurrent device. 

Exception No. 4. In a multiple occupancy building each occupant 
shall have access to his overcurrent protective devices. A multiple oc- 
cupancy building having individual occupancy above the second floor 
shall have service equipment grouped in a common accessible place, 
the overcurrent protection consisting of not more than six circuit 
breakers or six sets of fuses. Multiple occupancy buildings that do not 
have individual occupancy above the second floor may have service 
conductors run to each occupancy in accordance with Section 230-2, 
Exception No. 3(b) and each such service may have not more than six 
circuit breakers or six sets of fuses. 

A set of fuses is all the fuses required to protect all the ungrounded con- 
ductors of a circuit. Single pole breakers may be grouped as in Section 230- 
70(g) as one multiple protective device. 

(b) Not in Grounded Conductor. No overcurrent device shall be in- 
serted in a grounded service conductor except a circuit breaker which 
simultaneously opens all conductors of the circuit. 

(c) More Than One Building. In a property comprising more than 
one building under single management, the ungrounded conductors 
supplying each building served shall be protected by overcurrent de- 
vices, which may be located in the building served or in another build- 
ing on the same property, provided they are accessible to the occupants 
of the building served. 

230-91. Location. The service overcurrent device shall be an integral 
part of the service disconnecting means or shall be located immediately 
adjacent thereto, unless located at the outer end of the entrance. 

230-92. Location of Branch-Circuit Overcurrent Devices. Where the 
service overcurrent devices are locked or sealed, or otherwise not read- 
ily accessible, branch-circuit overcurrent devices shall be installed on 



70-48 MASSACHUSETTS ELECTRICAL CODE 

the load side, shall be mounted in an accessible location and shall be of 
lower rating than the service overcurrent device. 

230-93. Protection of Specific Circuits. Where necessary to prevent 
tampering, an automatic overcurrent device protecting service con- 
ductors supplying only a specific load such as a water heater, may be 
locked or sealed where located so as to be accessible. 

230-94. Relative Location of Overcurrent Device and Other Service 
Equipment. The overcurrent device shall protect all circuits and de- 
vices except as follows: 

(a) The service switch may be placed on the supply side. 

(b) High impedance shunt circuits (such as potential coils of me- 
ters, etc.), lightning arresters, surge protective capacitors, instrument 
transformers, may be connected and installed on the supply side of the 
service disconnecting means as permitted in Section 230-73. 

(c) Circuits for emergency supply and time switches may be con- 
nected on the supply side of the service overcurrent device where sep- 
arately provided with overcurrent protection. 

(d) Circuits used only for the operation of fire alarm, other protec- 
tive signalling systems, or the supply to fire pump equipment may be 
connected on the supply side of the service overcurrent device where 
separately provided with overcurrent protection. 

(e) Meters for alternating current service not in excess of 600 volts, 
provided the service contains a grounded conductor and the cases and 
enclosures of such meters are grounded by connection to the grounded 
circuit conductor (see Section 250-61) or to a common system and 
equipment ground electrode (see Section 250-54); or meters for alter- 
nating current service not containing a grounded service conductor and 
not in excess of 300 volts. 

L. Services Exceeding 600 Volts 

230-100. Scope. Service conductors and equipment used on circuits 
exceeding 600 volts shall comply with the applicable provisions of the 
preceding sections of this Article and with the following Sections which 
are additions to or modifications of the preceding Sections. 

Secondary conductors, not the primary conductors, are the service 
conductors to the building proper in the following cases : 

1 . Where step-down transformers are located outdoors. 

2. Where step-down transformers are located in a separate building 
from the one served. 

3. Where step-down transformers are located in the building served 
and in a transformer vault conforming to the requirements of 
Sections 450-41 to 450-48, and under the sole control of the sup- 
ply company. 

In all other cases, the primary conductors are the service conductors. 

In no case will the provisions of this Article apply to equipment not 
directly connected to service conductors, and consequently will not ap- 



ARTICLE 230-SERVICES 70-49 



ply to equipment in vaults under the sole control of the supply com- 
pany. 

230-101. Service-Entrance Conductors. 

(a) Conductor Size. Service conductors shall be not smaller than 
No. 6 unless in cable. Conductors in cable shall be not smaller than 
No. 8. 

(b) Wiring Methods. In locations accessible to other than qualified 
persons service-entrance conductors of more than 600 volts shall be in- 
stalled in rigid conduit, or as multiple conductor cable approved for the 
purpose. 

(c) Open Work. If open work is employed where not accessible to 
other than qualified persons, the service conductors shall be rigidly 
supported on glass, porcelain or other insulators approved for the pur- 
pose, which will keep them at least 8 inches apart, except at terminals 
of equipment. They shall be not less than 2 inches from the surfaces 
wired over and for voltages exceeding 2,500 not less than 3 inches. 

(d) Supports. Service conductors and their supports, including in- 
sulators, shall have strength and stability sufficient to insure mainte- 
nance of adequate clearance with abnormal currents in case of short 
circuits. 

(e) Guarding. Open wires shall be guarded where accessible to un- 
qualified persons. 

(f) Service Cable. Where cable conductors emerge from a metal 
sheath or raceway, the insulation of the conductors shall be protected 
from moisture and physical damage by a pothead or other approved 
means. 

(g) Draining Raceways. Unless conductors specifically approved 
for the purpose are used, raceways embedded in masonry, or exposed 
to the weather, or in wet locations shall be arranged to drain. 

(h) Over 15,000 Volts. Where the voltage exceeds 15,000 volts 
between conductors they shall enter either metal enclosed switchgear 
or a transformer vault conforming to the requirements of Section 450- 
41 to 450-48. 

(i) Conductor Considered Outside Building. Conductors placed un- 
der at least two inches of concrete beneath a building, or conductors 
within a building in conduit or duct and enclosed by concrete or brick 
not less than two inches thick shall be considered outside the building. 

230-102. Warning Signs. High voltage signs shall be posted where 
unauthorized persons might come in contact with live parts. 

230-103. Disconnecting Means. The circuit-breaker or the alternatives 
for it specified in Section 230-106 will constitute the disconnecting 
means required by Section 230-70 and shall comply with Section 230- 
70(h). The disconnecting means shall be capable of being closed on a 
fault within the maximum interrupting rating of the overcurrent pro- 
tection. 

230-104. Isolating Switches. Isolating switches shall be provided as 
follows: 



70-50 MASSACHUSETTS ELECTRICAL CODE 

(a) Air-break isolating switches shall be installed between oil 
switches or air or oil circuit breakers used as service switches and the 
supply conductor, except where such equipment is mounted on remov- 
able truck panels or metal-enclosed switchgear units which cannot be 
opened unless the circuit is disconnected, and which, when removed 
from the normal operating position, automatically disconnect the cir- 
cuit breaker or switch from all live parts. 

(b) When the fuses used with nonautomatic oil switches in accord- 
ance with Section 230-106 are of a type that may be operated as a dis- 
connect switch, they may serve as the isolating switch when they com- 
pletely disconnect the oil switch and all service equipment from the 
source of supply. 

(c) Air-break isolating switches shall be accessible to qualified attend- 
ants only. They shall be arranged so that a grounding connection on 
the load side can readily be made. Such grounding means need not be 
provided for duplicate isolating switches, if any, installed and main- 
tained by the supply company. 

230-105. Equipment in Secondaries. Where the primary service equip- 
ment supplies one or more transformers whose secondary windings con- 
nect to a single set of mains, and the primary load-interrupter switch 
or circuit-breaker is capable of being opened and closed from a point 
outside the transformer vault, the disconnecting means and overcurrent 
protection may be omitted from the secondary circuit provided the pri- 
mary fuse or circuit-breaker is rated or set to protect the secondary 
circuit. 

230-106. Overcurrent Protection. Overcurrent devices shall be pro- 
vided in accordance with the following: 

(a) In Vault or Consisting of Metal-Enclosed Switchgear. Where the 
service equipment is installed in a transformer vault meeting the provi- 
sions of Sections 450-41 to 450-48, or consists of metal-enclosed switch- 
gear, the requirements for overcurrent protection and disconnecting 
means may be fulfilled by the following: 

(1) A non-automatic oil switch, oil fuse cutout, air load-interrupter 
switch, or other approved switch, capable of interrupting the rated cir- 
cuit load, and suitable fuses may be used. 

(2) An automatic trip circuit-breaker of suitable current carrying 
and interrupting capacity with an overcurrent unit in each ungrounded 
conductor may be used. 

(3) A switch capable of interrupting the no-load current of the 
transformer supplied through the switch and suitable fuses may be used, 
provided the switch is interlocked with a single switch or circuit breaker 
on the secondary circuit of the transformer so that the primary switch 
cannot be opened when the secondary circuit is closed. 

(4) Vaults shall conform to the provisions of Sections 450-41 to 
450-48. 

(5) Metal-enclosed switchgear shall consist of a substantial metal 
structure and a sheet metal enclosure. Barriers between adjacent switch- 
gear units and internal metal barriers shall be not less than Va inch of 



ARTICLE 240-OVERCURRENT PROTECTION 70-51 

metal or No. 1 1 U.S.S. gage. All other covers, panels and doors shall 
be not less than No. 14 U.S.S. gage. Where installed over a wood floor, 
suitable protection thereto shall be provided. 

(b) Not in Vault or Not Consisting of Metal-enclosed Switchgear. 

Where the service equipment is not in a vault or metal-enclosed switch- 
gear, the requirements for the overcurrent protection and disconnecting 
means may be fulfilled by the following: 

(1) Air load-interrupter switches, or other approved switches, ca- 
pable of interrupting the rated circuit load may be used with suitable 
fuses on a pole or elevated structure outside the building provided the 
switch may be operated by persons using the building. 

(2) On circuits of any voltage, an automatic trip circuit-breaker of 
suitable ampacity and interrupting capacity with an overcurrent unit in 
each ungrounded conductor may be used. The circuit-breaker shall be 
located outside the building as near as practicable to where the service 
conductors enter the building. The location may be on a pole, roof, 
foundation, or other structure. 

(c) Fuses. Fuses used as permitted in Sections 230-1 06(a) and (b) 
shall have an interrupting rating at least equal to the maximum short- 
circuit current possible in the circuit. 

(d) Circuit Breakers. Circuit breakers shall be free to open in case 
the circuit is closed on an overload. This can be accomplished by means 
such as trip-free breakers or by multiple breakers having an operating 
handle per pole. A service circuit breaker shall indicate clearly whether 
it is open or closed, and shall be capable of interrupting the maximum 
short-circuit current to which it may be subjected. 

(e) Enclosed Overcurrent Devices. The restriction to 80 per cent of 
rating for an enclosed overcurrent device on continuous loads shall not 
apply to overcurrent devices installed in services operating at over 600 
volts. 

230-107. Lightning Arresters. Lightning arresters installed in accord- 
ance with the requirements of Article 280 shall be placed on each un- 
grounded overhead service conductor on the supply side of the service 
equipment, when called for by the authority enforcing this Code. 



ARTICLE 240 — OVERCURRENT PROTECTION 

A. Installation 

240-1. Scope. This Article provides the general requirements for the 
application of overcurrent protective devices. 

240-2. Purpose of Overcurrent Protection. Overcurrent protection for 
conductors and equipment is provided for the purpose of opening the 
electric circuit if the current reaches a value which will cause an exces- 
sive or dangerous temperature in the conductor or conductor insulation. 

240-3. Protection of Equipment. Equipment shall be protected against 
overcurrent as specified in the references in the following table: 



70-52 MASSACHUSETTS ELECTRICAL CODE 

Equipment Article No. 

Appliances 422 

Capacitors 460 

Cranes and Hoists 610 

Elevators, Dumbwaiters and Escalators 620 

Emergency Systems 700 

Generators 445 

Inductive and Dielectric Heat 

Generating Equipment 665 

Machine Tools 670 

Motion Picture Studios and Similar Locations 530 

Motors 430 

Organs 650 

Over 600 Volts 710 

Remote-Control, Low-Energy Power, Low- 
Voltage Power and Signal Circuits 725 

Services 230 

Signs and Outline Lighting 600 

Sound Equipment 640 

Switchboards and Panelboards 384 

Theaters and Assembly Halls : 520 

Transformers 450 

Welders 630 

X-ray Equipment 660 

240-4. Time-Delay Overcurrent Devices. Circuit breakers and plug 
fuses installed in residential occupancies on circuits of 20 amperes or 
less shall be of the time-delay type. 

240-5. Overcurrent Protection of Conductors. Conductors shall be pro- 
tected in accordance with their ampacities, as given in Tables 310-12 
through 310-15, except as follows: 

Exception No. 1. Rating of Nonadjustable Overcurrent Protection 
of 800 Amperes or Less. When the standard ampere ratings of fuses 
and nonadjustable circuit breakers do not correspond with the allow- 
able ampacities of conductors, the next higher standard rating may be 
used. 

Exception No. 2. Adjustable-Trip Circuit Breakers. Adjustable-trip 
circuit breakers of the thermal trip, magnetic time-delay trip or in- 
stantaneous-trip types shall be set to operate at not more than 125 per 
cent of the allowable ampacity of the conductor. 

The effect of the temperature on the operation of thermally controlled 
circuit breakers should be taken into consideration in the application of 
Such circuit breakers when they are subjected to extremely low or extremely 
high temperatures. 

Exception No. 3. Fixture Wires and Cords. Fixture wire or flexible 
cord, sizes No. 16 or No. 18, and tinsel cord shall be considered as 
protected by 20-ampere overcurrent devices except as provided in Sec- 
tion 620-61. Fixture wires of the sizes permitted for taps in Section 
210-19(c-2) shall be considered as protected by the overcurrent pro- 
tection of the 30-ampere and 50-ampere branch circuits of Article 210. 
Flexible cord approved for use with specific appliances shall be con- 



ARTICLE 240-OVERCURRENT PROTECTION 70-53 

sidered as protected by the overcurrent device of the branch circuit of 
Article 210 when conforming to the following: 

20 ampere circuits, No. 18 cord and larger. 

30 ampere circuits, cord of 10 amperes capacity and over. 

50 ampere circuits, cord of 20 amperes capacity and over. 

Exception No. 4. Motor Circuits. The conductors supplying motors 
and motor-operated appliances shall be considered as protected by 
the overcurrent protective devices specified in Sections 430-32, 430-34, 
430-52, 430-53 and 430-62. 

Exception No. 5. Remote Control. Except as provided in Article 725, 
the conductors of the control circuits of remote-control switches shall 
be considered as protected from overcurrent by overcurrent devices 
that are not of the so-called time-lag type and are rated or set at not 
more than 500 per cent of the ampacity of the remote-control conduc- 
tors, as specified in Tables 310-12 through 310-15. 

240-6. Fuses. 

(a) If the allowable ampacity of a conductor does not correspond 
to the rating of a standard-size fuse, the next larger size or rating of 
fuse may be used only where the rating is 800 amperes or less. 

(b) Standard ampere ratings for fuses are 15, 20, 25, 30, 35, 40, 45, 
50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 
400, 450, 500, 600, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 
5000 and 6000. Fuses with ampere rating other than the standard rat- 
ing listed may be used when they are of an ampere rating smaller than 
those included in the standard list. 

(c) Plug fuses and fuseholders shall not be used in circuits exceed- 
ing 125 volts between conductors except in circuits supplied from a 
system having a grounded neutral and no conductor in such circuits 
operating at more than 150 volts to ground. 

(d) Cartridge fuses and fuseholders rated at 300 volts shall not be 
used in circuits exceeding 300 volts between conductors except in cir- 
cuits supplied from a system having a grounded neutral and no conduc- 
tor in such circuits operating at more than 300 volts to ground. 

(e) The screw-shell of plug-type fuseholders shall be connected to 
the load side of the circuit. 

240-7. Nonadjustable-Trip Circuit Breakers. 

(a) Nonadjustable-trip circuit breakers, except as otherwise permit- 
ted in Note 10 to Tables 310-12 through 310-15 shall be rated in ac- 
cordance with the ampacity of the conductor. When the allowable am- 
pacity of a conductor does not correspond to the rating of a standard- 
size circuit breaker, the next larger size or rating of circuit breaker may 
be used only where the rating is 800 amperes or less. 

(b) Standard ampere ratings for circuit breakers are 15, 20, 30, 40, 
50, 60, 70, 100, 125, 150, 175, 200, 225, 250, 300, 350, 400, 500, 600, 
700, 800, 1000, 1200 and 1600. 

240-8. Thermal Devices. Thermal cutouts, thermal relays and other 
devices not designed to open short-circuits, shall not be used for protec- 



70-54 MASSACHUSETTS ELECTRICAL CODE 

tion of conductors against overcurrent due to short-circuits or grounds 
but may be used to protect motor branch circuit conductors from over- 
load if protected in accordance with Section 430-40. 

240-9. Feeders at Supply Stations. Each conductor of a constant-po- 
tential circuit entering or leaving a supply station, except grounded 
neutral conductors, shall be protected from excessive current by a cir- 
cuit breaker, or by an equivalent device of approved design. Such pro- 
tective devices shall be located as near as practicable to the point where 
the conductors enter or leave the building. For the outgoing circuits 
not connected with other sources of power, the protective devices may 
be placed on the supply side of transformers or similar devices. 

240-1 1 . Ungrounded Conductors. 

(a) An overcurrent device (fuse or overcurrent trip unit of a circuit 
breaker) shall be placed in each ungrounded conductor. The number 
and position of the overcurrent units such as trip coils or relays shall be 
as given in Table 240-28. 

(b) Circuit breakers shall open all ungrounded conductors of the 
circuit, except as follows: 

Exception: Individual single-pole circuit breakers may be used for 
the protection of each conductor of ungrounded 2-wire circuits, each 
ungrounded conductor of 3-wire direct-current or single-phase circuits, 
or for each ungrounded conductor of lighting or appliance branch cir- 
cuits connected to 4-wire three-phase systems, or 5-xvire 2-phase sys- 
tems, provided such lighting or appliance circuits are supplied from a 
system having a grounded neutral and no conductor in such circuits 
operates at a voltage greater than permitted in Section 210-6. 

240-12. Grounded Conductor. No overcurrent device shall be placed 
in any permanently grounded conductor, except as follows: 

Exception No. 1 . Where the overcurrent device simultaneously opens 
all conductors of the circuit. 

Exception No. 2. For motor-running protection as provided in Sec- 
tions 430-36 and 430-37. 

240-13. Change in Size of Grounded Conductor. Where a change oc- 
curs in the size of the ungrounded conductor, a similar change may be 
made in the size of the grounded conductor. 

240-14. Fuses in Multiple. For the protection of conductors having 
allowable ampacities exceeding the rating of the largest approved cart- 
ridge type fuse in Section 240-23 (a-1), such cartridge fuses arranged 
in multiple may be used, provided as few fuses as possible are used and 
the fuses are of the same type, characteristics, and rating, and provided 
the fuseholder terminals are mounted on a single continuous pair of 
bus-bars, or have an equivalent arrangement that will eliminate any po- 
tential difference between the terminals of the fuses. 

B. Location 

240-15. Location in Circuit. Overcurrent devices shall be located at 
the point where the conductor to be protected receives its supply, ex- 
cept as follows: 



ARTICLE 240-OVERCURRENT PROTECTION 70-55 

Exception No. 1. Service Conductors. An overcurrent protective 
device for service conductors may be located as specified in Section 
230-91. 

Exception No. 2. Smaller Conductor Protected. Where the overcur- 
rent device protecting the larger conductors also protects the smaller 
conductors in accordance with Tables 310-12 through 310-15. 

Exception No. 3. Branch Circuits. Taps to individual outlets and 
circuit conductors supplying a single household electric range shall be 
considered as protected by the branch circuit overcurrent devices when 
in accordance with the requirements of Sections 210-19 and 210-20. 

Exception No. 4. Feeder Taps. A conductor tapped from a feeder 
shall be considered as properly protected from overcurrent when in- 
stalled in accordance with Sections 210-25, 364-8 and 430-58. 

Exception No. 5. Feeder Taps Not Over 10 Feet Long. Where (1) 
the smaller conductor has an ampacity of not less than the sum of the 
allowable ampacities for the conductors of the one or more circuits or 
loads supplied, and (2) the tap is not over 10 feet long and does not 
extend beyond the switchboard, panelboard, or control devices which it 
supplies, and (3) except at the point of connection to the feeder, the tap 
is enclosed in conduit, electrical metallic tubing, or in metal gutters 
when not a part of the switchboard or panelboard. 

Exception No. 6. Feeder Taps Not Over 25 Feet Long. Where the 
smaller conductor has an ampacity at least one-third that of the con- 
ductor from which it is supplied, and provided the tap is suitably pro- 
tected from physical damage, is not over 25 feet long, and terminates 
in a single circuit breaker or set of fuses which will limit the load on the 
tap to that allowed by Tables 310-12 through 310-15. Beyond this point 
the conductors may supply any number of circuit breakers or sets of 
fuses. 

240-16. Location in Premises. Overcurrent devices shall be located 
where they will be: 

(a) Readily accessible, except as provided in Sections 230-91 and 
230-92 for service equipment and Section 364-1 1 for busways. 

(b) Not exposed to physical damage. 

(c) Not in the vicinity of easily ignitible material. 

C. Enclosures 
240-17. Enclosures for Overcurrent Devices. 

(a) General. Overcurrent devices shall be enclosed in cutout boxes 
or cabinets, unless a part of a specially approved assembly which af- 
fords equivalent protection, or unless mounted on switchboards, panel- 
boards or controllers located in rooms or enclosures free from easily 
ignitible material and dampness. The operating handle of a circuit 
breaker may be accessible without opening a door or cover. 

(b) Damp or Wet Locations. Enclosures for overcurrent devices in 
damp or wet locations shall be of a type approved for such locations 
and shall be mounted so there is at least one-fourth inch air space be- 
tween the enclosure and the wall or other supporting surface. 



70-56 MASSACHUSETTS ELECTRICAL CODE 

(c) Vertical Position. Enclosures for overcurrent devices shall be 
mounted in a vertical position unless in individual instances this is 
shown to be impracticable. 

(d) Rosettes. Fuses shall not be mounted in rosettes. 

D. Disconnecting and Guarding 

240-18. Disconnection of Fuses and Thermal Cutouts Before Handling. 

Disconnecting means shall be provided on the supply side of all fuses 
or thermal cutouts in circuits of more than 150 volts to ground and 
cartridge fuses in circuits of any voltage, where accessible to other than 
qualified persons, so that each individual circuit containing fuses or 
thermal cutouts can be independently disconnected from the source of 
electrical energy, except as provided in Section 230-73 and except that 
a single disconnecting means may be used to control a group of circuits 
each protected by fuses or thermal cutouts under the conditions de- 
scribed in Section 430-1 12. 

240-19. Arcing or Suddenly Moving Parts. Arcing or suddenly mov- 
ing parts shall comply with the following: 

(a) Location. Fuses and circuit breakers shall be so located or 
shielded that persons will not be burned or otherwise injured by their 
operation. 

(b) Suddenly Moving Parts. Handles or levers of circuit breakers, 
and similar parts which may move suddenly in such a way that persons 
in the vicinity are liable to be injured by being struck by them, shall be 
guarded or isolated. 

E. Plug Fuses and Fuseholders 

240-20. Plug Fuses of the Edison-Base Type. Plug fuses of the Edison- 
base type shall conform to the following: 

(a) Classification. Plug fuses of this type shall be classified at not 
over 125 volts, to 30 amperes. 

(b) Live Parts. Fuses and fuseholders when installed and assembled 
together shall have no live parts exposed. 

(c) Marking. Plug fuses of 15 amperes rating or less shall be dis- 
tinguished from those of larger rating by an hexagonal opening in the 
cap through which the mica or similar window shows, or by some 
other prominent hexagonal feature such as the form of the top or cap 
itself, or an hexagonal recess or projection in the top or cap. 

Plug fuses of the Edison-base type are recognized in this Code only as a 
replacement item in existing installations. 

240-21. Fuseholders for Plug Fuses. Fuseholders for plug fuses of 30 
amperes or less shall not be installed unless they comply with Section 
240-22 or are made to comply with Section 240-22 by the insertion of 
an adapter. 

240-22. Plug Fuses and Fuseholders of Type S. Where Type S plug 
fuses are to be used as the overcurrent device required by this Code, 
the fuses and fuseholders shall conform to the following requirements : 



ARTICLE 240-OVERCURRENT PROTECTION 70-57 

(a) Classification. Plug fuses and fuseholders of Type S shall be 
classified at not over 125 volts; to 15 amperes, 16 to 20 amperes, and 
21 to 30 amperes. 

(b) Use of Fuses in a Fuseholder of a Different Classification. Fuses 
of the 16 to 20 ampere and the 21 to 30 ampere classification shall not 
be usable with fuseholders or adapters of a lower ampere classification. 

(c) Fuseholders and Adapters. Fuses, fuseholders, and adapters 
shall be so designed that a fuse other than a Type S fuse cannot be 
used in a fuseholder or adapter designed for Type S fuses. 

(d) Tamperability. Fuses, fuseholders and adapters shall be so de- 
signed as to be subject to tampering or bridging only with difficulty. 

(e) Adapters to be Nonremovable. Fuse adapters shall be so de- 
signed that when once inserted in a fuseholder they cannot be removed. 

(f) Interchangeability. Fuses, fuseholders and adapters of various 
manufacturers shall be interchangeable with each other, and the plugs 
with adapters shall be suitable for use in the Edison-base type fuse- 
holder. 

(g) Plug Type. Fuses and fuseholders shall be of the plug type. 

(h) Ampere Rating. Each fuse, fuseholder and adapter shall be 
marked with its ampere rating. 

(i) Marking. Fuses of the to 15 ampere rating shall be distin- 
guished from those of larger rating by an hexagonal opening in the cap 
through which the mica or similar window shows, or some other prom- 
inent hexagonal feature such as the form of the top or cap itself, or an 
hexagonal recess or projection in the top or cap. 

F. Cartridge Fuses and Fuseholders 

240-23. Cartridge Fuses and Fuseholders. Cartridge fuses and fuse- 
holders shall conform to the following: 

(a) Classification. 

(1) 0-600 ampere cartridge fuses and fuseholders shall be classi- 
fied as regards current and voltage as follows: 

Not over 250 volts Not over 300 volts Not over 600 volts 

Amperes Amperes Amperes 

0- 30 0-15 0- 30 

31- 60 16-20 31- 60 

61-100 21-30 61-100 

101-200 31-60 101-200 

201-400 - 201-400 

401-600 - 401-600 

(2) 601-6000 ampere cartridge fuses and fuseholders shall be clas- 
sified at 600 volts as follows : 

601- 800 1601-2000 3001-4000 

801-1200 2001-2500 4001-5000 

1201-1600 2501-3000 5001-6000 

There are no 250 volt ratings over 600 amperes, but 600 volt fuses may 
be used for lower voltages. 



70-58 MASSACHUSETTS ELECTRICAL CODE 

(b) Noninterchangeable— 0-6000 Ampere Cartridge Fuseholders. 

Fuseholders shall be so designed that it will be difficult to put a fuse 
of any given class into a fuseholder which is designed for a current 
lower, or voltage higher, than that of the class to which it belongs. 
Fuseholders for current limiting fuses shall not permit insertion of 
fuses which are not current limiting. 

(c) Marking. Fuses shall be plainly marked with the ampere rating, 
voltage rating, interrupting rating when greater than 10,000 amperes, 
current limitation where it applies, and the name or trademark of the 
maker. The marking shall be either by direct printing on the fuse barrel 
or by means of an attached label. 

G. Link Fuses and Fuseholders 
240-24. Link Fuses and Fuseholders. Link fuses and fuseholders shall 
be used only by special permission and shall conform to the following: 

(a) Mounting. Link fuses shall be mounted on approved fusehold- 
ers. 

(b) Dimensions. Link fuses and fuseholders shall have the following 
dimensions in inches: 

Minimum Separation 

of Nearest Metal Minimum 
Parts of Opposite Break 

Amperes Capacity Polarity Distance 



Not over 125 volts 






601-1500 


V/2 


Wi 


Not over 250 volts 






601-1500 


2% 


2 



For 3-wire systems, link fuses, and fuseholders shall have the break 
distance required for circuits of the potential of the outside wires, ex- 
cept that in 125-250-volt systems with grounded neutral the fuses and 
fuseholders in 2-wire, 125-volt branch circuits may have the spacing 
specified for not over 125 volts. 

(c) Spacing. A space shall be maintained between the fuse termi- 
nals of link fuses of the same polarity of at least Vi inch for voltages 
up to 125, and of at least 3 A inch for voltages from 126 to 250. This is 
the minimum distance allowable and greater separation shall be pro- 
vided where practicable. 

(d) Material. Contact surfaces or tops of link fuses shall be of cop- 
per or aluminum having good electrical connections with the fusible 
part of the strip. 

(e) Minimum Rating. Link fuses and fuseholders shall be used only 
in sizes rated at more than 600 amperes, and only by special permission. 

(f) Marking. Link fuses shall be stamped with 80 per cent of the 
maximum current which they can carry indefinitely. 

H. Circuit Breakers 

240-25. Circuit Breakers. Circuit breakers shall conform to the fol- 
lowing: 



ARTICLE 240-OVERCURRENT PROTECTION 70-59 

(a) Method of Operation. In general, circuit breakers shall be ca- 
pable of being closed and opened by hand without employing any 
other source of power, although normal operation may be by other 
power such as electrical, pneumatic, and the like. Large circuit break- 
ers which are to be closed and opened by electrical, pneumatic, or 
other power shall be capable of being closed by hand for maintenance 
purposes and shall also be capable of being tripped by hand under 
load without the use of power. 

(b) Type of Operation. Circuit breakers of the to 30 ampere class 
should be of the time-delay type. 

(e) Injury to Operator. Circuit breakers shall be arranged and 
mounted so that their operation is not likely to injure the operator. 

(d) Indication. Circuit breakers shall indicate whether they are in 
the open or closed position. 

(e) Nontamperable. An air circuit breaker, used for the branch 
circuits described in Article 210, shall be of such design that any altera- 
tion of its trip point (calibration), or in the time required for its opera- 
tion, will be difficult. 

(f) Marking. Circuit breakers shall be marked with their rating in 
such a manner that the marking will be durable and visible after instal- 
lation except that it may be necessary to remove a trim or cover. The 
ampere rating of circuit breakers rated 100 amperes or less and 600 
volts or less shall be molded, stamped, etched, or similarly marked into 
the handle or the escutcheon area of the circuit breaker. Each circuit 
breaker intended to interrupt fault currents greater than 10,000 am- 
peres shall have its interrupting rating shown on the label or on the 
product. 

240-27. Current Limiting Overcurrent Protective Device. A current lim- 
iting overcurrent protective device is a device which, when interrupting 
a specified circuit, will consistently limit the short-circuit current in that 
circuit to a specified magnitude substantially less than that obtainable 
in the same circuit if the device were replaced with a solid conductor 
having comparable impedance. 

Table 240-28. Number of Overcurrent Units, Such as Trip 
Coils or Relays, for Protection of Circuits 

(See Diagrams 1 to 19 following this Table) 

(See Section 240-11 for the overcurrent protection of conductors in 
general, Section 230-90 for services, and Section 430-37 for motors). 

SYSTEMS *Number and Location of 
Overcurrent Units. 

2-Wire, Single-phase A.C. or D.C. Two (one in each conductor. 
Ungrounded. Diagram 1). 

2-Wire, Single-phase A.C. or D.C, One (in ungrounded conductor. 
One Wire Grounded. Diagram 2). 

2-Wire, Single-phase A.C. or D.C, Two (one in each conductor. 
Mid-point Grounded. Diagram 3). 



70-60 



MASSACHUSETTS ELECTRICAL CODE 



SYSTEMS 



*Number and Location of 
Overcurrent Units. 



2-Wire, Single-phase A.C. Derived 
from 3-Phase, with Ungrounded 
Neutral. 

2-Wire, Single-phase Derived from 
3-Phase, Grounded Neutral Sys- 
tem by Using outside Wires of 
3-Phase Circuit. 

3-Wire, Single-phase A.C. or D.C. 
Ungrounded Neutral. 

3-Wire, Single-phase A.C. or D.C. 
Grounded Neutral. 

3-Wire, 2-Phase, A.C. Common 
Wire Ungrounded. 

3-Wire, 2-Phase, A.C, Common 
Wire Grounded. 

4-Wire, 2-Phase Ungrounded, 
Phases Separate. 

4-Wire, 2-Phase, Grounded Neutral, 
or 5-Wire, 2-Phase, Grounded 
Neutral. 

3-Wire, 3-Phase, Ungrounded. 

3-Wire, 3-Phase, 1 Wire Grounded. 

3-Wire, 3-Phase, Grounded Neutral. 

3-Wire, 3-Phase, Mid-point of one 
phase grounded. 

4-Wire, 3-Phase, Grounded Neutral. 

4-Wire, 3-Phase, Ungrounded Neu- 
tral. 



Two (one in each conductor. 

Diagram 4). 

Two (one in each conductor. 

Diagram 5). 



Three (one in each conductor. 
Diagram 6). 

Two (one in each conductor ex- 
cept neutral conductor. Dia- 
gram 7). 

Three (one in each conductor. 
Diagram 8). 

Two (one in each conductor ex- 
cept common conductor. Dia- 
gram 9). 

Four (one in each conductor. 
Diagram 10). 

Four (one in each conductor ex- 
cept neutral conductor. 
Diagrams 11 and 12). 

Three (one in each conductor. 
Diagram 13**). 

Two (one in each ungrounded 
conductor. Diagram 14). 

Three (one in each conductor. 
Diagram 15**). 

Three (one in each conductor. 
Diagram 17**). 

Three (one in each ungrounded 
conductor. Diagram 18**). 

Four (one in each conductor. 
Diagram 19). 



Notes to Table 240-28 

*1. An overcurrent unit may consist of a series overcurrent tripping 
device or the combination of a current transformer and a secondary over- 
current tripping device. Either two or three secondary overcurrent tripping 
devices may be used with three current transformers on a 3-phase system 
similar to those shown in Diagrams 15 and 18. 

**2. When three current transformers are used instead of three series 
overcurrent tripping devices shown in Diagrams 13, 15, 17 and 18, the sec- 
ondary tripping devices may consist of three secondary overcurrent tripping 
devices or two secondary overcurrent tripping devices with a residual cur- 
rent tripping device of a lower range. See Diagram 16. 



ARTICLE 240-OVERCURRENT PROTECTION 



70-61 



3. Where standard devices are not available with three or four overcur* 
rent units as required in the Table, it is permissible to substitute two over- 
current units and one fuse where three overcurrent units are called for, two 
overcurrent units and two fuses where four overcurrent units are called for. 
The fuse or fuses are to be placed in the conductors not containing an over- 
current unit. This practice, however, of substituting fuses for overcurrent 
units is to be discouraged for obvious reasons. 



Diagrams 240-29 

Diagrams 1 to 19 showing- Number of Overcurrent Units such as 
Trip Coils or Relays for the Protection of Circuits as required by 
Table 240-28. 




f/WVVW\Aj 



FIG 6 



FIG 4 



.AA/Wl 



jA/WVWVN. 



FIG 2 



FIG. 7 



,/VYVV 




rsxi 



FIG 5 



FIG 3 



FIG. 8 



70-62 



MASSACHUSETTS ELECTRICAL CODE 



IN**! 
a 



FIG 9 



IX ^ 



FIGlO 



FIG II 




FIGI2 



ti y 



FIG.I3' 





FIG. 14 



*See Note 2 of Table 240-28 



ARTICLE 240-OVERCURRENT PROTECTION 70-63 




FIG 15 •• 




FIGI6 



!L !L 1 




FIG 17 




FIG. 18 




FIG 19 



**See Note 2 of Table 240-28. 



70-64 MASSACHUSETTS ELECTRICAL CODE 

240-30. Supplementary Overcurrent Protection. Where supplementary 
overcurrent protection is utilized in connection with appliances or other 
utilization equipment to provide individual protection for specific com- 
ponents or internal circuits within the equipment itself, this does not 
abrogate any of the requirements applicable to branch circuits and is 
not to be used as a substitute for branch-circuit protection. 

It is not the intent of the above requirement that supplementary overcur- 
rent protective devices be subject to the accessibility requirements as given 
elsewhere in this code for branch circuit overcurrent protective devices. 



ARTICLE 250— GROUNDING 



A. General 



250-1 . Scope. This Article treats of protection of electric installations 
by grounding. Insulation, isolation, and guarding are suitable alterna- 
J tives under certain conditions. See Section 110-17. 

(a) Systems and Circuits. Circuits are grounded for the purpose of 
limiting the voltage upon the circuit which might otherwise occur 
through exposure to lightning or other voltages higher than that for 
which the circuit is designed; or to limit the maximum potential to 
ground due to normal voltage. 

(b) Exposed Conductor Enclosures. Exposed conductive materials 
enclosing electric conductors are grounded for the purpose of prevent- 
ing a potential above ground on the enclosures. 

(c) Exposed Equipment Enclosures. Exposed conductive materials 
enclosing electric equipment, or forming a part of such equipment, are 
grounded for the purpose of preventing a potential above ground on 
the equipment. 



MASSACHUSETTS ELECTRICAL CODE— INSERT NO. 2 



ARTICLE 250-GROUNDING 70-65 

250-2. Other Articles. In other Articles, applying to particular cases 
of installation of conductors and equipment, there are requirements 
that are in addition to those of this Article or are modifications of 
them: 

Article Section 

Appliances 422 422-12 

Branch Circuits 210 210-5 

210-6 

Communications Circuits 800 

Conductors 200 

310 310-2 

Cranes and Hoists 610 

Elevators, Dumbwaiters, Escalators, 

and Moving Walks ... 620 

Fixtures & Lighting Equipment 410 410-91 

410-92 
410-93 
410-94 
410-95 
410-96 

Flexible Cords 400 400-13 

400-14 

Generators 445 445-8 

Grounding Receptacles (Outlets) 210 210-7 

210-21 
210-22 
Hazardous Locations 500-517 

Inductive and Dielectric Heat 

Generating Equipment 665 

Less Than 5.0 V 720 

Lighting Fixtures 410 

Metalworking Machine Tools 670 

Mobile Homes 550 

Motion Picture Studios 530 530-19 

530-66 

Motors and Controllers 430 

Organs 650 

Outlet, Switch and Junction Boxes, 

and Fittings 370 370-4 

370-15 
Radio and Television 810 





410-56 


725 


725-21 


422 


422-61 


230 




230 


230-63 


600 




640 


640-4 


680 




384 


384-11 


380 


380-1 




380-12 


520 


520-81 


450 


450-8 


551 




660 





70-66 MASSACHUSETTS ELECTRICAL CODE 

Receptacles & Attachment Plugs 410 410-55 

Remote Control Circuits 

Room Air Conditioners 

Services 

Service Equipment 

Signs and Outline Lighting 

Sound Recording Equipment 

Swimming Pools 

Sw i tchboa rds 

Switches 

Theaters & Assembly Halls 

Transformers 

Travel Trailers 

X-ray Equipment 

B. Circuit- and System' Grounding 

250-3. Two-Wire Direct-Current Systems. Two-wire direct-current systems 
supplying interior wiring, and operating at not more than 300 volts between 
conductors, shall be grounded, unless such system is used for supplying 
industrial equipment in limited areas and the circuit is equipped with a 
ground detector. 

All two-wire direct-current systems operating at more than 300 volts between 
conductors shall be grounded when a neutral point can be established such 
that the maximum difference of potential between the neutral point and any 
other point on the system does not exceed 300 volts. All two-wire direct- 
current systems shall not be grounded when the voltage to ground of either 
conductor would exceed 300 volts after grounding. 

250-4. Three-Wire Direct-Current Systems. The neutral conductor of all 
3-wire direct-current systems supplying interior wiring shall be grounded. 

250-5. Alternating-Current Systems. Secondary alternating-current systems 
supplying interior wiring, and interior alternating-current wiring systems, 
except those covered in Sections 250-6, 250-7 and 250-8, shall be grounded 
when they can be so grounded that the maximum voltage to ground does not 
exceed 150 volts. Where a service conductor is uninsulated in accordance 
with Section 230-4, the system shall be grounded. 

All alternating-current systems shall be grounded as provided in this article 
when the voltage to ground does not exceed 300 volts. Higher voltage 
systems may be grounded. 

Ungrounded systems supplying industrial equipment and operating at more 
than 150 volts and less than 600 volts shall be equipped with ground 
detectors. 



ARTICLE 250-GROUNDING 70-67 

250-6. Furnace Circuits. Electric furnace circuits need not be 
grounded. 

250-7. Electric Crane Circuits. Circuits for electric cranes operating 
over combustible fibers in Class III hazardous locations shall not be 
grounded. See Section 503-13. 

250-8. Circuits of Less than 50 Volts. Circuits of less than 50 volts 
need not be grounded, except as follows: 

(a) Where supplied by transformers from systems of more than 150 
volts to ground, except as provided in Section 250-45 (d). 

(b) Where supplied by transformers from ungrounded systems. 

(c) Where run overhead outside buildings. 

C. Location of Grounding Connections 

250-21. Current Over Grounding Conductors. The grounding of wiring 
systems, circuits, arresters, cable armor, conduit, or other metal race- 
ways as a protective measure shall be so arranged that there will be no 
objectionable passage of current over the grounding conductors. The 
temporary currents set up under accidental conditions, while the 
grounding conductors are performing their intended protective func- 
tions, are not to be considered as objectionable. Where an objection- 
able flow of current occurs over a grounding conductor, due to the use 
of multiple grounds, (1) one or more of such grounds shall be aban- 
doned, or (2) their location shall be changed, or (3) the continuity of 
the conductor between the grounding connections shall be suitably in- 
terrupted, or (4) other means satisfactory to the authority enforcing 
this Code shall be taken to limit the current. 

250-22. Grounding Connection for Direct-Current Systems. Direct-cur- 
rent systems which are to be grounded shall have the grounding con- 
nection made at one or more supply stations but not at individual 
services nor elsewhere on interior wiring. 

250-23. Grounding Connections for Alternating-Current Systems. 

(a) Secondary alternating-current circuits which are to be grounded 
shall have a connection to a grounding electrode at each individual 
service, except as provided for in Section 250-21. The connection shall 
be made on the supply side of the service disconnecting means. Each 
secondary distribution system which is grounded shall have at least one 
additional connection to a grounding electrode at the transformer or 
elsewhere. No connection to a grounding electrode shall be made to the 
grounded circuit conductor on the load side of the service disconnect- 
ing means, except as provided for in Section 250-24. 

(b) Where the secondary system is grounded at any point, the 
grounded conductor shall be run to each individual service. This con- 
ductor shall be not smaller than the required grounding conductor 
specified in Table 250-94(a). 

250-24. Two or More Buildings Supplied by a Single Service. Where 
more than one building is supplied by the same service, the grounded 
circuit conductor of the wiring system of any building utilizing one 
branch circuit supplied from such service may be connected to a 



70-68 MASSACHUSETTS ELECTRICAL CODE 

grounding electrode at such building, and in the case of any building 
housing equipment required to be grounded or utilizing two or more 
branch circuits supplied from such service, and in the case of a build- 
ing housing live stock, shall be so connected. 

250-25. Conductor to be Grounded. For alternating-current interior 
wiring systems the conductor to be grounded shall be as follows : 

(a) Single-phase, 2-wire: the identified conductor; 

(b) Single-phase, 3-wire: the identified neutral conductor; 

(c) Multiphase systems having one wire common to all phases: the 
identified common conductor; 

(d) Multiphase systems having one phase grounded: the identified 
conductor; 

(e) Multiphase systems in which one phase is used as in (b) : the 
identified neutral conductor. One phase only can be grounded. 

See Article 200. 

The identified conductor is commonly known as "the white wire." 

250-26. Isolated Systems. For an interior wiring system or circuit 
which is required to be grounded and which is not electrically con- 
nected to an exterior secondary distribution system, the grounding 
connection shall be made at the transformer, generator, or other source 
of supply, or at the switchboard, on the supply side of the first switch 
controlling the system. See fine print note following Section 200-3. 

D. Enclosure Grounding 

250-32. Service Conductor Enclosures. Service raceways, service cable 
sheaths or armoring, when of metal, shall be grounded. 

250-33. Other Conductor Enclosures. Metal enclosures for conductors 
shall be grounded, except they need not be grounded in runs of less 
than 25 feet which are free from probable contact with ground, 
grounded metal, metal lath or conductive thermal insulation and which, 
where within reach from grounded surfaces, are guarded against con- 
tact by persons. 

250-34. Spacing from Lightning Rods. Metal enclosures of conduc- 
tors shall, wherever practicable, be kept at least 6 feet away from light- 
ning rod conductors. Where it is not practicable to secure 6 feet sepa- 
ration, they shall be bonded together. 

E. Equipment Grounding 

250-42. Fixed Equipment— General. Under any of the following con- 
ditions, exposed, noncurrent-carrying metal parts of fixed equipment, 
which are liable to become energized, shall be grounded : 

(a) Where equipment is supplied by means of metal-clad wiring; 

(b) Where equipment is located in a wet location and is not isolated; 

(c) Where equipment is located within reach of a person who can 
make contact with any grounded surface or object; 

(d) Where equipment is located within reach of a person standing 
on the ground; 



ARTICLE 250-GROUNDING 70-69 

(e) Where equipment is in a hazardous location; see Articles 500-517 
inclusive; 

(f) Where equipment is in electrical contact with metal or metal lath; 

(g) Where equipment operates with any terminal at more than 150 
volts to ground, except as follows: 

(1) Enclosures for switches or circuit breakers where accessible 
to qualified persons only; 

(2) Metal frames of electrically heated devices, exempted by spe- 
cial permission, in which case the frames shall be permanently and 
effectively insulated from ground; 

(3) Transformers mounted on wooden poles at a height of more 
than 8 feet from the ground. 

250-43. Fixed Equipment— Specific. Exposed, noncurrent-carrying metal 
parts of the following kinds of equipment, regardless of voltage, shall 
be grounded : 

(a) Frames of motors as specified in Section 430-142; 

(b) Controller cases for motors, except lined covers of snap switches; 

(c) Electric equipment of elevators and cranes; 

(d) Electric equipment in garages, theatres and motion picture stu- 
dios, except pendant lampholders on circuits of not more than 150 volts 
to ground; 

(e) Motion-picture projection equipment; 

(f) Electric signs and associated equipment, unless these are inacces- 
sible to unauthorized persons and are also insulated from ground and 
from other conductive objects; 

(g) Generator and motor frames in an electrically operated organ, 
unless the generator is effectively insulated both from ground and from 
the motor driving it; 

(h) Switchboard frames and structures supporting switching equip- 
ment, except that frames of direct-current, single-polarity switchboards 
need not be grounded where effectively insulated; 

(i) Equipment supplied by Class 1 and Class 2 remote control and 
signaling circuits where Part B of this article requires those circuits to 
be grounded. 

250-44. Nonelectrical Equipment. The following metal parts shall be 
grounded: 

{a) Frames and tracks of electrically operated cranes; 

(b) The metal frame of a nonelectrically driven elevator car to which 
electric conductors are attached; 

(c) Hand-operated metal shifting ropes or cables of electric elevators; 

(d) Metal enclosures such as partitions, grill work, etc., around 
equipment carrying voltages in excess of 750 volts between conductors, 
unless in substations or vaults under the sole control of the supply com- 
pany. 



70-70 MASSACHUSETTS ELECTRICAL CODE 

Where extensive metal in or on buildings may become energized and is 
subject to personal contact, adequate bonding and grounding will provide 
additional safety. 

250-45. Portable Equipment. Under any of the following conditions, exposed 
noncurrent-carrying metal parts of portable equipment, which are liable to 
become energized, shall be grounded: 

(a) In hazardous locations (see Articles 500 to 517); 

(b) When operated at more than 1 50 volts to ground, except: 

(1) Motors, where guarded; 

(2) Metal frames of electrically heated appliances exempted by Sec- 
tion 422-12. 

(c) In residential occupancies, (1) clothes-washing, clothes-drying, and 
dish-washing machines, sump pumps, and (2) portable, hand held, motor 
operated tools and appliances of the following types: drills, hedge clippers, 
lawn mowers, wet scrubbers, sanders and saws. 

Exception: Such tools and appliances protected by an approved system of 
double insulation, or its equivalent, need not be grounded. Where such an 
approved system is employed the equipment shall be distinctively marked. 

Portable tools or appliances not provided with special insulating or 
grounding protection are not intended to be used in damD, wet or conductive 
locations. 

(d) In other than residential occupancies, (1) portable appliances used in 
damp or wet locations, or by persons standing on the ground or on metal 
floors or working inside of metal tanks or boilers, and (2) portable tools which 
are likely to be used in wet and conductive locations shall be grounded ex- 
cept that they need not be grounded where supplied through an insulating 
transformer with ungrounded secondary of not over 50 volts. 

The frames of all portable motors which operate at more than 50 volts and 
less than 150 volts to ground shall be grounded, where this can be readily 
accomplished. 

250-46. Spacing from Lightning Rods. Metal frames and enclosures of 
electric equipment shall, wherever practicable, be kept at least 6 feet away 
from lightning rod conductors. Where it is not practicable to secure 6 feet 
separation, they shall be bonded together. See Sections 250-34 and 250-86. 

F. Methods of Grounding 

250-51. Effective Grounding. The path to ground from circuits, equipment, 
and conductor enclosures shall (1) be permanent and continuous and (2) 
shall have ample carrying capacity to conduct safely any currents liable to 
be imposed on it, and (3) shall have impedance sufficiently low to limit the 
potential above ground and to facilitate the operation of the overcurrent de- 
vices in the circuit. 

250-52. Location of System Ground Connection. The grounding conductor 
may be connected to the grounded conductor of the wiring system at any 
convenient point on the premises on the supply side of the service discon- 
necting means. 



ARTICLE 250— GROUNDING 70-71 

High capacity services shall have the grounding conductor connected to the 
grounded circuit conductor within the service entrance equipment enclosure. 

250-53. Common Use of Grounding Conductor. The grounding conductor 
of a wiring system shall also be used for grounding equipment, conduit and 
other metal raceways or enclosures for conductors, including service con- 
duit or cable sheath and service equipment. 

Exception: The grounding connection as covered in the exception in Sec- 
tion 210-7 may be made to a grounded cold water pipe near the equipment. 

250-54. Common Grounding Electrode. Where the alternating-current 
system is connected to a grounding electrode in or at a building as specified 
in Sections 250-23 and 250-24, the same electrode shall be used to 
ground conductor enclosures and equipment in or on that building. 

250-55. Underground Service Cable. Where served from a continuous 
underground metal-sheathed cable system, the sheath or armor of under- 
ground service cable metallically connected to the underground system, or 
underground service conduit containing a metal-sheathed cable bonded to 
the underground system, need not be grounded at the building and may 
be insulated from the interior conduit or piping. 

250-56. Short Sections of Raceway. Isolated sections of metal raceway or 
cable armor, where required to be grounded, shall preferably be grounded 
by connecting to other grounded raceway or armor, but may be grounded 
in accordance with Section 250-57. 

250-57. Fixed Equipment. 

(a) Metal boxes, cabinets and fittings, or noncurrent-carrying metal parts 
of other fixed equipment, where metallically connected to grounded cable 
armor or metal raceway, are considered to be grounded by such connection. 

(b) Where not so connected they may be grounded in one of the following 
ways: 

(1) By a grounding conductor run with circuit conductors; this con- 
ductor may be uninsulated, but where it is provided with an individual 
covering, the covering shall be finished a continuous green color or a 
continuous green color with a yellow stripe. 

(2) By a separate grounding conductor installed the same as a ground- 
ing conductor for conduit and the like; 

(3) By a grounding conductor in the supply cord, when cord con- 
nected as permitted in Section 400-3; 

(4) By special permission, other means for grounding fixed equipment 
may be used. 

250-58. Equipment on Structural Metal. 

(a) Electric equipment secured to and in contact with the grounded struc- 
tural metal frame of a building, shall be deemed to be grounded. 



70-72 MASSACHUSETTS ELECTRICAL CODE 

(b) Metal car frames supported by metal hoisting cables attached to 
or running over sheaves or drums of elevator machines shall be deemed 
to be grounded where the machine is grounded in accordance with this 
Code. 

250-59. Portable Equipment. Noncurrent-carrying metal parts of portable 
equipment may be grounded in any one of the following ways: 

(a) By means of the metal enclosure of the conductors feeding such 
equipment, provided an approved grounding-type attachment plug is used, 
one fixed contacting member being for the purpose of grounding the metal 
enclosure, and provided, further, that the metal enclosure of the conductors 
is attached to the attachment plug and to the equipment by connectors ap- 
proved for the purpose; 

Exception: The grounding contacting member of grounding type attach- 
ment plugs on the power supply cord of hand-held tools or hand-held 
appliances may be of the movable self-restoring type. 

Attachment plug caps are not intended to be used as terminations for 
metal-clad cable or flexible metal conduit. 

(b) By means of a grounding conductor run with the power supply con- 
ductors in a cable assembly or flexible cord that is properly terminated in 
an approved grounding-type attachment plug having a fixed grounding 
contacting member. The grounding conductor in a cable assembly may be 
uninsulated; but where an individual covering is provided for such con- 
ductors it shall be finished a continuous green color or a continuous green 
color with a yellow stripe. 

Exception: The grounding contacting member of grounding type attach- 
ment plugs on the power supply cord of hand-held tools or hand-held 
appliances may be of the movable self-restoring type. 

(c) Separate flexible wire or strap, insulated or bare, when used for portable 

equipment shall be protected against physical damage. 

250-60. Frames of Electric Ranges and Electric Clothes Dryers. Frames of 
electric ranges and electric clothes dryers shall be grounded by any of 
the means provided for in Sections 250-57 and 250-59 or where served by 
120-240 volt, three-wire branch circuits, they may be grounded by con- 
nection to the grounded circuit conductors, provided the grounded circuit 
conductors are not smaller than No. 10 AWG. The frames of wall-mounted 
ovens and counter-mounted cooking units shall be grounded and may be 
grounded in the same manner as electric ranges. 

250-61. Grounding Equipment to Circuit Conductor. The grounded service 
conductor on the supply side of the service disconnecting means may be 
used for grounding meter housing and service equipment and metallic en- 
closures and guards. The grounded circuit conductor on the load side of 
the service disconnecting means shall not be used for grounding equipment, 
cable armor, or metal raceways except as provided in Section 250-57(b-4), 
and in Section 250-60. 



ARTICLE 250-GROUNDING 70-73 

G. Bonding 

250-71. Bonding at Service Equipment. The electrical continuity of 
the grounding circuit for the following equipment and enclosures shall 
be assured by one of the means given in Section 250-72. 

(a) The service raceways or service cable armor or sheath, except 
as provided in Section 230-63 (b) and Section 250-55; 

(b) All service equipment enclosures containing service entrance 
conductors, including meter fittings, boxes or the like, interposed in the 
service raceway or armor; 

(c) Any conduit or armor which forms part of the grounding con- 
ductor to the service raceway. 

250-72. Continuity at Service Equipment. Electrical continuity at 
service equipment shall be assured by one of the following means: 

(a) Bonding equipment to the grounded service conductor in a man- 
ner provided in Section 250-1 1 3. 

\a) Threaded couplings and threaded bosses on enclosures with 
joints shall be made up wrenchtight where rigid conduit is involved. 

(c) Threadless couplings made up tight for rigid conduit and electri- 
cal metallic tubing. 

(d) Bonding jumpers meeting the other requirements of this article. 
Bonding jumpers shall be used around concentric or eccentric knock- 
outs which are punched or otherwise formed so as to impair the elec- 
trical connection to ground. 

(e) Other devices (not locknuts and bushings) approved for the 
purpose. 

250-73. Metal Armor or Tape of Service Cable. With service cable 
having an uninsulated grounded service conductor in continuous elec- 
trical contact with its metallic armor or tape, the metal covering is con- 
sidered to be adequately grounded. 

250-74. Bonding at Grounding-Type Receptacles. Grounding continu- 
ity between a grounded outlet box and the grounding circuit of the re- 
ceptacle shall be established by means of a bonding jumper between 
the outlet box and the receptacle grounding terminal. 

Exception No. 1: When the box is surface-mounted, direct metal-to- 
metal contact between the device yoke and the box may be used to 
establish the grounding circuit. 

Exception No. 2: Contact devices or yokes designed and approved for 
the purpose may be used in conjunction with the supporting screws to 
establish the grounding circuit between the device yoke and flush-type 
boxes installed in walls. 

250-75. Continuity at Other Enclosures. The electrical continuity of 
metallic raceway systems and cable armor that are to serve as ground- 
ing conductors shall be assured. At points where raceway or armor 
connects to metal enclosures, any nonconducting coating which 
might interrupt such continuity shall be removed unless fittings are used 
which are so designed that such removal is unnecessary. 



70-74 MASSACHUSETTS ELECTRICAL CODE 

250-76. Voltages Exceeding 250 Volts. The electrical continuity of metal 
raceway or metal sheathed cable v/hich contains any conductor other than 
service entrance conductors of more than 250 volts to ground shall be as- 
sured by one of the methods specified in Section 250-72(b-e), or by one 
of the following methods: 

(a) Threadless fittings, made up tight, with conduit or metal-clad cable; 

(b) Two locknuts, one inside and one outside of boxes and cabinets. 

250-77. Loosely Jointed Metal Raceways. Expansion joints and telescoping 
sections of raceways shall be made electrically continuous by bonding jumpers 
or other approved means. Metal trough raceways used in connection with 
sound recording and reproducing, made up in sections, shall contain a ground- 
ing conductor to which each section shall be bonded. 

250-78. Hazardous Locations. In hazardous locations, regardless of the 
voltage involved, the electrical continuity of metallic racewdy, boxes and the 
like, shall be assured by one of the methods specified in Section 250-72(b-e). 

250-79. Bonding Jumpers. Bonding jumpers shall conform to the following: 

(a) Material and Size. Bonding jumpers shall be of copper or other 
corrosion-resistant material and shall be of sufficient size to have ampacity 
not less than is required in Table 250-94(a). 

(b) Attachment. Bonding jumpers shall be attached to cabinets and the 
like in a manner provided in Section 250-1 13; where used between ground- 
ing electrodes or around water meters and the like, they shall be attached in 
a manner provided for in Section 250-1 14. 



H. Grounding Electrodes 

250-81. Water Pipe. A metallic underground water piping system, either 
local or supplying a community, shall always be used as the grounding elec- 
trode where such a piping system is available. Where the buried portion of 
the metallic piping system is less than ten feet (including well casings bonded 
to the piping system) or there is some likelihood of the piping system being 
disconnected or isolated through the use of nonmetallic piping or insulated 
couplings, the piping svstem shall be supplemented by one or more of the 
grounding electrodes recognized in Sections 250-82 and 250-83. The interior 
metallic cold water piping system shall always be bonded to the one or more 
grounding electrodes. 

Expanding use of nonmetallic piping for water systems and insulating 
couplings on metallic water systems makes it more important that water 
piping within a building be adequately grounded without depending on con- 
nections to an outside piping system. The interior piping system should be 
electrically continuous. Bonding to sewer, hot water piping and metallic air 
ducts within the premises will provide additional safety. 

250-82. Other Available Electrodes. Where a water system as described in 
Section 250-81 is not available, the grounding connection may be made to 
any of the following: 

(a) The metal frame of the building, where effectively grounded. 



ARTICLE 250— GROUNDING 70-75 

(b) Underground gas service piping shall not be used as a grounding 
electrode. 



250-83. Made Electrodes. Where electrodes described in Sections 250-81 
and 250-82 are not available, the grounding electrode shall consist of a 
driven pipe, driven red, buried plate or other device approved for the pur- 
pose and conforming to the following requirements: 

(a) Plate Electrodes. Each plate electrode shall present not less than 2 
square feet of surface to exterior soil. Electrodes of iron, or steel plates shall 
be at least Va inch in thickness. Electrodes of nonferrous metal shall be 
at least 0.06 inch in thickness. 

(b) Pipe Electrodes. Electrodes of pipe or conduit shall be not smaller 
than of the 3 /£-inch trade size and, where of iron or steel, shall have the 
outer surface galvanized or otherwise metal-coated for corrosion protection. 

(c) Rod Electrodes. Electrodes of rods of steel or iron shall be at least 
Vq inch in diameter. Approved rods of nonferrous materials or their ap- 
proved equivalent used for electrodes shall be not less than V2 inch in 
diameter. 

(d) Installation. Electrodes should, as far as practicable, be imbedded 
below permanent moisture level. Except where rock bottom is encountered, 
pipes or rods shall be driven to a depth of at least 8 feet regardless of size 
or number of electrodes used. Pipes or rods when less than standard com- 
mercial length shall preferably be of one piece. Such pipes or rods shall 
have clean metal surfaces and shall not be covered with paint, enamel or other 
poorly conducting materials. Where rock oottom is encountered at a depth 
of less than 4 feet, electrodes shall be buried in a horizontal trench, and 
where pipes or rods are used as the electrode they shall comply with 
Section 250-83(b and c) and shall not be less than 8 feet in length. Each 
electrode shall be separated at least 6 feet from any other electrode, in- 
cluding those used for signal circuits, radio, lightning rods, or any other 
purpose. 

250-84. Resistance. Made electrodes shall, where practicable, have a re- 
sistance to ground not to exceed 25 ohms. Where the resistance is not 
as low as 25 ohms, two or more electrodes connected in parallel shall be used. 

Continuous metallic underground water piping systems in general 

have a resistance to ground of less than 3 ohms. Metal frames of buildings 
and local metallic underground piping systems, metal well casings, and the 
like, have, in general, a resistance substantially below 25 ohms. It is recom- 
mended that in locations where it is necesssary to use made electrodes for 
grounding interior wiring systems, additional grounds, such as connections 
to a system ground conductor be placed on the distribution circuit. It is also 



70-76 MASSACHUSETTS ELECTRICAL CODE 

recommended that single electrode grounds when installed, and periodically 
afterwards, be tested for resistance. 

250-85. Railway Tracks. Rails or other grounded conductors of electric 
railway circuits shall not be used (a) as a ground for other than railway 
lightning arresters and railway equipment, conduit, armored cable, metal 
raceway, and the like, where other effective grounds are available; and (b) 
in no case shall such rails or other grounded conductors of railway circuits 
be used for grounding interior wiring systems other than those supplied 
from the railway circuit itself. 

250-86. Use of Lightning Rods. Lightning rod conductors and driven pipes, 
rods or other made electrodes used for grounding lightning rods, shall not 
be used in lieu of the made grounding electrodes required by this Article 
for grounding wiring systems and equipment. The foregoing provision shall 
not be taken to forbid the bonding together of the several made electrodes 
that are respectively provided for electric wiring systems and equipment, 
for communication systems, and for lightning protection. See Section BOO- 
STS). 

All separate electrodes shall be bonded together to 
limit potential differences between them and between their associated wiring 
systems. 

J. Grounding Conductors 
250-91. Material. The material for the grounding conductors shall be as 
follows: 

(a) For System or Common Grounding Conductor. The grounding con- 
ductor of a wiring system shall be of copper or other corrosion-resistant ma- 
terial. The conductor may be solid or stranded, insulated or bare. Except in 
cases of bus-bars, the grounding conductor shall be without joint or splice 
throughout its length. Where the grounding conductor is not of copper, its 
electrical resistance per linear foot shall not exceed that of the allowable 
copper conductor for such a purpose. 

(b) For Conductor Enclosures and Equipment Only. The grounding con- 
ductor for equipment and for conduit and other metal raceways or enclosures 
for conductors, shall be a conductor of copper or other corrosion-resistant 
material, stranded or solid, insulated or bare, a bus-bar or a rigid conduit, 
steel pipe, electrical metallic tubing or the armor of Type AC metal-clad 
cable, except that under conditions favorable to corrosion, a suitable cor- 
rosion-resistant material shall be used. Where conduit is used as a grounding 
conductor, all joints and fittings shall be made wrenchtight. 

250-92. Installation. Grounding conductors shall be installed as follows: 

(a) System or Common Grounding Conductor. A grounding con- 
ductor, No. 4 or larger, may be attached to the surface on which it is 
carried without the use of knobs, tubes or insulators. It need not have 
protection unless exposed to severe physical damage. A No. 6 ground- 
ing conductor, which is free from exposure to physical damage, may 
be run along the surface of the building construction without metal 
covering or protection, where it is rigidly stapled to the construction; 



ARTICLE 250— GROUNDING 70-77 

otherwise, it shall be in conduit or electrical metallic tubing. 

Grounding conductors smaller than No. 6 shall be in conduit or electrical 
metallic tubing. Metallic enclosures for grounding 

conductors shall be electrically continuous from the point of attachment 
to cabinets or equipment to the grounding electrode, and shall be securely 
fastened with an approved fitting. Wheie rigid metallic conduit or steel pipe 
is used as protection for a grounding conductor, the installation shall com- 
ply with the requirement of Article 346; where electrical metallic tubing 
is used, the installation shall comply with the requirements of Article 348. 
Aluminum grounding conductors shall not be used where in direct contact 
with masonry or the earth or where subject to corrosive conditions. Where 
used outside, aluminum grounding . conductors shall not be installed within 
18 inches of the earth. 

(b) Conductor Enclosures and Equipment Only. A grounding conductor 
for conductor enclosures and equipment only shall meet the requirements of 
Section 250-92(a), except that where smaller than No. 6, as permitted by 
Section 250-95. 

Wires in a raceway where run through the hollow, spaces of a wall or partition 
shall be installed so as not to be subject to physical damage. 
250-93. Direct Current Systems. The ampacity of the grounding conductor 
for a direct-current supply system or generator shall be not less than that 
of the largest conductor supplied by the system, except that where the 
grounded circuit conductor is a neutral derived from a balancer winding or 
a balancer set protected in accordance with requirements of Section 445- 
4(d), the siz^of the grounding conductor shall not be less than that of the 
neutral conductor. The grounding conductor shall in no case be smaller than 
No. 8 copper. 
250-94. Alternating Current Systems. 

(a) Service and Common Grounding Conductor for Grounded Systems. 
Where the wiring system is grounded, the size of the grounding conductor 
for an alternating current system or for a common grounding conductor shall 
not be less than is given in Table 250-94. (a), except that where connected 
to made electrodes (as in Section 250-83.), that portion of the grounding 
conductor which is the sole connection between the grounding electrode and 
the grounded system conductor need not be larger than No. 6 copper wire 
or its equivalent in ampacity. 

(b) Service Equipment Grounding Conductor for Ungrounded Systems. 
Where the wiring system is ungrounded, the size of a grounding conductor 
for a service raceway, for the metal sheath or armor of a service cable, and 
for service equipment shall not be less than is given in Table 250-94. (b), 
except that where connected to made electrodes (as in Section 250-83) 
that portion of the grounding conductor which is the sole connection between 
the grounding electrode and the service equipment need not be larger than 
No. 6 copper wire or its equivalent in ampacity. 

250-95. Interior Raceway and Equipment. The size of the grounding con- 
ductor for conduit, cable sheath or armor, and other metal raceways or en- 
closures for conductors, and for equipment, shall be not less than given in 
Table 250-95. 



70-78 



MASSACHUSETTS ELECTRICAL CODE 



Table 250-94(a) 






Service and Common Grounding Conductor for Grounded Systems 


Size of Largest Service Conductor or 


Size 


of Grounding 


Equivalent for Multiple Conductors 


Conductor AWG No. 


Copper Aluminum 


Copper 


Aluminum* 


2 or smaller or smaller 


8 


6 


1 or 2/0 or 3/0 


6 


4 


2/0 or 3/0 4/0 or 250 MCM 


4 


2 


Over 3/0 to Over 250 MCM 


2 





350 MCM to 500 MCM 






Over 350 MCM Over 500 MCM 





3/0 


to 600 MCM to 900 MCM 






Over 600 MCM Over 900 MCM 


2/0 


4/0 


to 1100 MCM to 1750 MCM 






Over 1100 MCM Over 1750 MCM 


3/0 


250 MCM 



: See installation restrictions in Section 250-92(a). 



Table 250-94(b) 
Service Equipment Grounding Conductor for Ungrounded Systems 



Size of Largest Service Conductor or 
Equivalent for Multiple Conductors 



Size of Grounding 

Conductor AWG No. 

or Trade Size (Inch) 













Elec- 












trical 










Con- 


Metal- 










duit 


lic 






Cop- 


Alumi- 


or 


Tub- 


Copper 


Aluminum 


per 


num 


Pipe 


ing 


2 or smaller 


or smaller 


8 


6 


V2 


Vt 


1 orO 


2/0 or 3/0 


6 


4 


Vi 


1 


2/0 or 3/0 


4/0 or 250 MCM 


4 


2 


3 A 


Wa 


Over 3/0 to 


Over 250 MCM 


2 





3 /4 


IVa 


350 MCM 


to 500 MCM 










Over 350 MCM 


Over 500 MCM 





3/0 


1 


2 


to 600 MCM 


to 900 MCM 










Over 600 MCM 


Over 900 MCM 


2/0 


4/0 


1 


2 


to 1100 MCM 


to 1750 MCM 










Over 1100 MCM 


Over 1750 MCM 


3/0 


250 MCM 


1 


2 



ARTICLE 250-GROUNDING 



70-79 



Table 250-95. Sizes of Conductors for Grounding Interior 


Raceway 






and Equipment 






Rating or Setting 










of Automatic Over- 


Size 


of Grounding Conductor 




current Device in 










Circuit Ahead of 








Electrical 


Equipment, Con- 


Copper 


Aluminum* 


Conduit 


Metallic 


duit, etc., Not Ex- 


Wire 


Wire 


or Pipe 


Tubing 


ceeding (Amperes) 


No. 


No. 


(Inch) 


(Inch) 


20 


16** 


14** 


H 


y% 


30 


14 


12 


l A 


X A 


40 


12 


10 


V2 


X A 


60 


10 


8 


V2 


V* 


100 


8 


6 


l A 


l A 


200 


6 


4 


l A 


l 


400 


3 


1 


% 


IK 


600 


1 


00 


% 


IH 


800 





000 


l 


2 


1000 


00 


0000 


l 


2 


1200*** 


000 


250 MCM 


1 


2 



* See installation restrictions in Section 250-92 (a). 

* * Permissible only when part of an approved cable assembly. 

*** For ratings above 1200 amperes, the size of the grounding con- 
ductor shall be increased proportionately. 



250-96. Portable and Pendant Equipment. For grounding portable or 
pendant equipment, the conductors of which are protected by fuses 
or circuit breakers rated or set at not exceeding 20 amperes, No. 18 
copper wire may be used. Conductors of Nos. 16 or 18 copper which 
are used for grounding portable equipment shall be part of an approved 
flexible cord assembly. For grounding portable or pendant equipment 
protected at more than 20 amperes, Table 250-95 shall be followed. 

250-97. Outline Lighting. Isolated noncurrent-carrying metal parts of 
outline lighting systems may be bonded together by a No. 14 conductor 
protected from physical damage, where a conductor complying with 
Section 250-95 is used to ground the group. 

250-98. Common Raceway. A grounding conductor may be run in 
the same metal raceway with other conductors of the system to which it 
is connected. 

250-99. Continuity. No automatic cutout or switch shall be placed in 
the grounding conductor of an interior wiring system unless the open- 
ing of the cutout or switch disconnects all sources of energy. 

K. Grounding Conductor Connections 

250-111. To Raceway or Cable Armor. The point of connection of 
the grounding conductor to interior metal raceways, cable armor and 
the like shall be as near as practicable to the source of supply and shall 
be so chosen that no raceway or cable armor is grounded through a 
run of smaller size than is called for in Section 250-95. 



70-80 MASSACHUSETTS ELECTRICAL CODE 

250-112. To Electrode. The grounding connection to the electrode shall be 
located as follows: 

(a) To Water Pipes. System or common grounding conductors shall be 
attached to a water piping system on the street side of the water meter or 
on a cold water pipe as near as practicable to the water service entrance to 
the building. Where the source of the water supply is from a driven well in 
the basement of the premises, the connection shall be made as near as 
practicable to the well. Where practicable, the point of attachment shall be 
accessible. Where the point of attachment is not on the street side of the 
water meter, the water piping system shall be made electrically continuous by 
bonding together all parts between the attachment and the street side of 
the water meter or the pipe entrance which contain insulating sections or 
are liable to become disconnected, as at meters, valves and service unions. 

(b) To Gas Pipes. 

The attachment of a grounding conductor to gas piping shall be prohibited. 
An effective bonding shall be provided for all gas metallic piping within 
a building. 

(c) To Other Electrodes. The grounding conductor shall be attached to 
other electrodes permitted in Sections 250-82 and 250-83 at a point which 
will assure a permanent ground. Where practicable the point of attachment 
shall be accessible. 

250-113. Attachment to Circuits and Equipment. The grounding conductor, 
bond, or bonding jumper shall be attached to circuits, conduits, cabinets, 
equipment, and the like, which are to be grounded, by means of suitable lugs, 
pressure connectors, clamps, or other approved means, except that connec- 
tions which depend upon solder shall not be used. 

250-114. Continuity and Attachment of Branch Circuit Grounding Con- 
ductors to Boxes. Where more than one grounding conductor of a branch 
circuit enters a box, all such conductors shall be in good electrical contact 
with each other and the arrangement shall be such that the disconnection 
or removal of a receptacle, fixture, or other device fed from the box will not 
interfere with or interrupt the grounding continuity. 

(a) Metallic Boxes. A connection shall be made between the one or more 
grounding conductors and a metallic box by means of a grounding screw 
which shall be used for no other purpose, or an approved grounding device. 

(b) Nonmetallic Boxes. One or more grounding conductors brought into 
a nonmetallic outlet box shall be so arranged that a connection can be made 
to any fitting or device in that box which requires grounding. 

250-115. Attachment to Electrodes. The grounding conductor shall 
be attached to the grounding electrode by means of (1) an approved 
bolted clamp of cast bronze or brass or of plain or malleable cast iron, 
or (2) a pipe fitting, piug, or other approved device, screwed into the 
pipe or into the fitting, or (3) other equally substantial approved 
means. The grounding conductor shall be attached to the grounding 
fitting by means of suitable lugs, pressure connectors, clamps, or other 
approved means, except that connections which depend upon solder 



ARTICLE 250— GROUNDING 70-81 

shall not be used. Not more than one conductor shall be connected to the 
grounding electrode by a single clamp or fitting, unless the clamp or 
fitting is of a type approved for such use. 

250-116. 



DELETED 



DELETED 

250-118. Clean Surfaces. Where a nonconductive protective coating, such 
as paint or enamel, is used on the equipment, conduit, couplings or fittings, 
such coating shall be removed from threads and other contact surfaces in 
order to insure a good electrical connection. 

L. Instrument Transformers, Relays, etc. 
250-121. Instrument Transformer Circuits. The secondary circuits of cur- 
rent and potential instrument transformers shall be grounded where the 
primary windings are connected to circuits of 300 volts or more to ground, 
and where on switchboards, shall be grounded irrespective of voltage, ex- 
cept that such circuits need not be grounded where the primary windings 
are connected to circuits of 750 volts or less and no live parts or wiring are 
exposed or accessible to other than qualified persons. 

250-122. Instrument Transformer Cases. Cases or frames of instrument 
transformers shall be grounded where accessible to other than qualified 
persons, except that cases or frames of current transformers, the primaries 
of which are not over 150 volts to ground and which are used exclusively 
to supply current to meters, need not be grounded. 

250-123. Cases of Instruments, Meters and Relays — Operating Voltage 750 
or Less. Instruments, meters and relays which operate with windings or 
working parts at 750 volts or less shall be grounded as follows: 

(a) Not on Switchboards. Instruments, meters, and relays not located 
on switchboards, which operate with windings or working parts at 300 volts 
or more to ground, and accessible to other than qualified persons, shall have 
the cases and other exposed metal parts grounded; 

(b) On Dead Front Switchboards. Instruments, meters and relays (whether 
operated from current and potential transformers, or connected directly in 
the circuit) on switchboards having no live parts on the front of the panels 
shall have the cases grounded; 



70-82 MASSACHUSETTS ELECTRICAL CODE 

(c) On Live Front Switchboards. Instruments, meters and relays 
(whether operated from current and potential transformers, or con- 
nected directly in the circuit) on switchboards having exposed live parts 
on the front of panels shall not have their cases grounded. Mats of in- 
sulating rubber or other suitable floor insulation, shall be provided for 
the operator where the voltage to ground exceeds 150. 

250-124. Cases of Instruments, Meters and Relays— Operating Voltage 
Over 750. Where instruments, meters and relays have current-carry- 
ing parts over 750 volts to ground, they shall be isolated by elevation 
or protected by suitable barriers, grounded metal or insulating covers 
or guards. Their cases shall not be grounded, except as follows: 

(a) In electrostatic ground detectors the internal ground segments of 
the instrument are connected to the instrument case and grounded; the 
ground detector shall be isolated by elevation. 

250-125. Instrument Grounding Conductor. The grounding conductor 
for secondary circuits of instrument transformers and for instrument 
cases shall not be smaller than No. 12, where of copper or where of 
other metal, shall have equal conductance. Cases of instrument trans- 
formers, instruments, meters and relays which are mounted directly on 
grounded metal surfaces of enclosures or grounded metal switchboard 
panels shall be considered to be grounded and no additional grounding 
conductor will be required. 

M. Lightning Arresters 

250-131. On Secondary Services, 750 Volts or Less. Where a lightning 
arrester is installed on a secondary service, the connections to the serv- 
ice conductors and to grounding conductor shall be as short as prac- 
ticable. The grounding conductor may be (1) the grounded service 
conductor, or (2) the common grounding conductor, or (3) the serv- 
ice equipment grounding conductor. The bonding or grounding con- 
ductor shall be of copper not smaller than No. 14 or of equivalent 
corrosion-resistant material. 

250-132. On Primary Circuits. The grounding conductor of a lightning 
arrester protecting a transformer which supplies a secondary distribu- 
tion system may be interconnected as follows : 

(a) Metallic Interconnection. A metallic interconnection may be 
made to the secondary neutral provided that, in addition to the direct 
grounding connection at the arrester: 

(1) The grounded conductor of the secondary has elsewhere a 
grounding connection to a continuous metallic underground water 
piping system. However, in urban waterpipe areas where there are at 
least four waterpipe connections on the neutral and not less than four 
such connections in each mile of neutral, the metallic interconnection 
may be made to the secondary neutral with omission of the direct 
grounding connection at the arrester. 

(2) The grounded conductor of the secondary system is part of a 
multigrounded neutral system, of which the primary neutral has at least 
four ground connections in each mile of line in addition to a ground at 
each service. 



ARTICLE 280-LIGHTNING ARRESTERS 70-83 

(b) Through Spark Gap. Where the secondary is not grounded as 
in Section 250-1 32(a), but is otherwise grounded as in Sections 250- 
82 and 250-83, such interconnection, where made, shall be through a 
spark gap having a 60-cycle breakdown voltage of at least twice the 
primary circuit voltage but not necessarily more than 10 kv, and there 
shall be at least one other ground on the grounded conductor of the 
secondary not less than 20 feet distant from the lightning arrester 
grounding electrode. 

(c) By Special Permission. Except as above provided, intercon- 
nection of the arrester ground and the secondary neutral may be made 
only by special permission. 



ARTICLE 280 — LIGHTNING ARRESTERS 

A. Industrial Stations 

280-1. Where Required. Lightning arresters shall be provided in in- 
dustrial stations in locations where thunderstorms are frequent and 
adequate protection against lightning is not otherwise provided. 

For lightning arresters in hazardous locations, see Articles 500-517. 

280-2. Number Required. A lightning arrester shall be connected to 
each ungrounded overhead conductor entering or leaving the station, 
except that where there is more than one circuit, a single set of arresters 
may be installed on the station bus where means are provided to pro- 
tect circuits that may remain disconnected from the bus. 

280-3. Where Connected. The arrester shall be connected on the line 
side of all connected station apparatus. 

B. Other Occupancies 

280-11. Utilization Equipment. Lightning arresters installed for the 
protection of utilization equipment may be installed either inside or 
outside the building or enclosure containing the equipment to be pro- 
tected. Arresters, unless isolated by elevation or made otherwise inac- 
cessible to unqualified persons, shall be enclosed, and where the operat- 
ing voltage of the circuit exceeds 750 volts between conductors they 
shall be inaccessible to unqualified persons. 

Secondary lightning protection devices may reduce damage to wiring and 
equipment caused by lightning disturbances. (See Section 502-3.) 

C. General 

280-21. Location— Indoors. Arresters installed indoors shall be located 
well away from other equipment, passageways and combustible parts 
of buildings, and where containing oil shall be separated from other 
equipment by walls meeting the requirements of Section 450-42. 

280-22. Location— Outdoors. Where arresters containing oil are lo- 
cated outdoors, provision shall be made to drain away any accumula- 
tion of oil. 



70-84 MASSACHUSETTS ELECTRICAL CODE 

Oil may be drained away by ditches and drains or the oil may be absorbed 
and danger of spreading removed by paving the yard with cinders or other 
absorbent material to a depth of several inches. 

280-23. Connections— Size and Material. The connections between the 
arrester and the line wire or bus, and between arrester and ground shall 
be of copper wire or cable or the equivalent, and, except as provided on 
secondary services in Section 250-131, shall not be smaller than No. 6, 
and shall be made as short and as straight as practicable, avoiding as 
far as possible all bends and turns, especially sharp bends. 

280-24. Installation. Lightning-protection accessories such as gap 
electrodes, and choke coils where used, shall have an insulation from 
ground or from other conductors at least equal to the insulation re- 
quired at other points of the circuit. 

280-25. Switch for Isolating Arrester. Where isolating switches or dis- 
connecting devices are used, they shall withstand, in full open position, 
a voltage test between live parts 10 per cent in excess of the maximum 
voltage test they will withstand to ground. 

280-26. Grounding. Lightning arresters shall be grounded in the 
manner prescribed in Article 250. 



70-85 



Chapter 3. Wiring Methods and Materials 

ARTICLE 300 — WIRING METHODS — GENERAL 
REQUIREMENTS 



300-1. Scope. 

(a) The provisions of Chapter 3 apply to the electrical and mechani- 
cal requirements for the various methods of installing fixed electrical 
conductors for electric light, heat, power, and certain signal systems. 

(b) The provisions of this Article shall apply to all wiring installa- 
tions, except for remote-control, including low voltage relay switching, 
low-energy power and signal systems as provided in Article 725, and 
communication systems as provided in Article 800. 

(c) On premises where a continuous underground metallic water- 
piping network system is not available as a grounding electrode, and 
where it is not practicable otherwise to secure a ground of permanently 
low resistance, the use of a wiring method which does not employ 
metal enclosures for the wires is recommended, unless the character or 
occupancy of the building is such as to require the use of a metal-en- 
closed wiring system. 

(d) The provisions of this Article are not intended to apply to the 
conductors which form an integral part of equipment such as motors, 
motor controllers and the like. 

300-2. Voltage Limitations. Wiring methods specified in Chapter 3 
may be used for voltages not exceeding 600, unless specifically limited 
in some Article of Chapter 3. They may be used for voltages over 600 
where specifically permitted elsewhere in this code. 

300-3. Conductors of Different Systems. 

(a) Conductors of light and power systems of 600 volts or less may 
occupy the same enclosure, without regard to whether the individual 
circuits are alternating-current or direct-current, only where all con- 
ductors are insulated for the maximum voltage of any conductor within 
the enclosure. 

(b) Conductors of light and power systems of over 600 volts shall 
not occupy the same enclosure with conductors of light and power 
systems of 600 volts or less. 

(c) Secondary wiring to electric discharge lamps of 1,000 volts or 
less, insulated for the secondary voltage involved, may occupy the 
same fixture enclosure as the branch circuit conductors. 

(d) Primary leads of electric discharge lamp ballasts, insulated for 
the primary voltage of the ballast, when contained within the individual 
wiring enclosure may occupy the same fixture enclosure as the branch 
circuit conductors. 



70-86 MASSACHUSETTS ELECTRICAL CODE 

(e) Excitation, control, relay and ammeter conductors used in con- 
nection with any individual motor or starter may occupy the same en- 
closure as the motor circuit conductors. 

(f) Conductors of signal or radio systems shall not occupy the same 
enclosure with conductors of light or power systems except as permit- 
ted for elevators in Section 620-36; for sound recording in Section 
640-6; for remote-control, low-energy power and signal circuits in 
Sections 725-16 and 725-42; and communication system in Sections 
800-3 and 800-21. 

300-4. Protection Against Physical Damage. Where subject to physical 
damage, conductors shall be adequately protected. 

300-5. Protection Against Corrosion. Metal raceways, cable armor, 
boxes, cable sheathing, cabinets, metallic elbows, couplings and fittings 
shall be of materials suitable for the environment in which they are to 
be installed. 

(a) Ferrous raceways, cable armor, boxes, cable sheathing, cabinets, 
metallic elbows, couplings and fittings shall be suitably protected 
against corrosion inside and outside (except threads at joints) by a 
coating of approved corrosion resistant material such as zinc, cadmium, 
or enamel. Where protected from corrosion solely by enamel, they shall 
not be used out of doors or in wet locations as described in (c) be- 
low. 

(b) Unless made of materials judged suitable for the condition, or 
unless corrosion protection approved for the condition is provided, fer- 
rous or non-ferrous metallic raceways, cable armor, boxes, cable 
sheathing, cabinets, elbows, couplings and fittings shall not be installed 
in concrete or in direct contact with the earth, or in areas subject to se- 
vere corrosive influences. 

(c) In portions of dairies, laundries, canneries, and other indoor wet 
locations, and in locations where walls are frequently washed or where 
there are surfaces of absorbent materials, such as damp paper or wood, 
the entire wiring system, including all boxes, fittings, conduits and 
cable used therewith, shall be mounted so that there is at least one- 
quarter inch air space between it and the wall or supporting surface. 

Meat-packing plants, tanneries, hide cellars, casing rooms, glue houses, 
fertilizer rooms, salt storage, some chemical works, metal refineries, pulp 
mills, sugar mills, round houses, some stables, and similar locations are 
judged to be occupancies where severe corrosive conditions are likely to be 
present. 

300-6. Raceways Exposed to Different Temperatures. 

(a) Sealing. Where portions of an interior raceway system are ex- 
posed to widely different temperatures, as in refrigerating or cold- 
storage plants, provision shall be made to prevent circulation of air 
from a warmer to a colder section through the raceway. 

(b) Expansion Joints. Expansion joints for runs of raceway shall 
be provided where required to compensate for thermal expansion and 
contraction. 



ARTICLE 300-WIRING METHODS-GENERAL 70-87 

300-7. Underground Runs. Conductors run underground shall comply 
with the provisions of Section 230-32 as far as mechanical protection is 
concerned. 

Underground cable run under a building shall be in a raceway that is 
extended beyond the outside wall of the building. 

300-8. Through Studs, Joists and Rafters. 

(a) Where exposed or concealed wiring conductors in insulating 
tubes or cables are installed through bored holes in studs, joists or sim- 
ilar wood members, holes shall be bored at the approximate centers of 
wood members, or at least two inches from the nearest edge. 

(b) Where there is no objection because of weakening the building 
structure, metal-clad or nonmetallic sheathed cable, aluminum sheathed 
cable and Type MI cable may be laid in notches in the studding or 
joists when the cable at those points is protected against the driving of 
nails into it by having the notch covered with a steel plate at least 1/16 
inch in thickness before building finish is applied. 

300-9. Grounding Metal Enclosures. Metal raceways, boxes, cabinets, 
cable armor and fittings shall be grounded if and as prescribed in Article 
250. 

300-10. Electrical Continuity of Metal Raceways and Enclosures. Metal 
raceways, cable armor, and other metal enclosures for conductors, 
shall be metallically joined together into a continuous electrical con- 
ductor, and shall be so connected to all boxes, fittings and cabinets as 
to provide effective electrical continuity. Raceways and cable assem- 
blies shall be mechanically secured to boxes, fittings, cabinets and other 
enclosures, except as provided for nonmetallic boxes in Section 370-7. 

300-11. Secured in Place. Raceways, cable assemblies, boxes, cabi- 
nets and fittings shall be securely fastened in place, unless otherwise 
provided for specific purposes elsewhere in this Code. 

See Article 318 for Continuous Rigid Cable Supports. 

300-12. Mechanical Continuity— Raceways and Cables. Raceways and 
cable assemblies shall be continuous from outlet to outlet and from fit- 
ting to fitting. 

300-13. Mechanical Continuity— Conductors. Conductors shall be contin- 
uous between outlets, devices, etc., and, except as permitted for auxiliary 
gutters in Section 374-8, and for wireways in Section 362-6, there shall 
be no splice or tap within a raceway itself. 

300-14. Free Length of Conductors at Outlets and Switch Points. At least 
six inches of free conductor shall be left at each outlet and switch point 
for the making up of joints or the connection of fixtures or devices, 
except where conductors are intended to loop without joints through 
lampholders, receptacles and similar devices. 

300-15. Boxes or Fittings. Except as permitted in Sections 336-11 and 
410-60 a box or fitting shall be installed at each outlet, switch point, 
junction point or conductor splice connection joining sections of con- 
duit, electrical metallic tubing or surface metal raceway. A box shall 
be installed at each outlet, switch point, or conductor splice connec- 



70-88 MASSACHUSETTS ELECTRICAL CODE 

tion joining sections of metal-clad cable, aluminum sheathed cable, 
non-metallic sheathed cable or Type MI cable, and at each outlet and 
switch point of concealed knob-and-tube work. 

Exception: Straight through splice joints for Ml cable are permitted 
without a box provided the splice is accessible and a fitting approved 
for the purpose is used. 

300-16. Raceway or Cable to Open or Concealed Wiring. 

(a) A box or terminal fitting having a separately bushed hole for 
each conductor shall be used wherever a change is made from conduit, 
electrical metallic tubing, nonmetallic sheathed cable, metal-clad ca- 
ble, aluminum sheathed cable, or Type MI cable and surface metal 
raceway wiring to open wiring or to concealed knob-and-tube work. A 
fitting used for this purpose shall contain no taps or splices and shall 
not be used at fixture outlets. 

(b) A bushing may be used in lieu of a box or terminal fitting at 
ends of conduit or electrical metallic tubing where conductors leave the 
conduit or tubing behind a switchboard, or where more than 4 con- 
ductors leave the conduit or tubing at control apparatus or in similar 
locations, in which case the conductors shall be bunched, taped and 
painted with insulating paint. Such a bushing shall be of the insulating 
type except for lead-covered conductors. 

300-17. Number of Conductors in Raceway. In general the percent- 
age of the total interior cross-sectional area of a raceway occupied by 
conductors shall not be more than will permit a ready installation or 
withdrawal of the conductors and dissipation of the heat generated 
without injury to the insulation of the conductors. See the following 
Sections of this Code: conduit, Section 346-6; electrical metallic tub- 
ing, 348-6; flexible metal conduit, 350-3; surface metal raceways, 
352-4; underfloor raceways, 354-5; cellular metal floor raceways, 356- 
5; structural raceways, 357-6; cellular concrete floor raceways, 358-9; 
wireways, 362-5; auxiliary gutters, 374-5; theatres, 520-5; signs, 600- 
21(d); elevators, 620-33; and sound recording, 640-3 and 640-4; and 
Remote-Control, Low-Energy Power, Low-Voltage Power and Signal 
Circuits, Article 725. 

300-18. Inserting Conductors in Raceways. 

(a) Raceways shall first be installed as a complete raceway system 
without conductors, except those raceways exposed and having a re- 
movable cover or capping. 

(b) As far as possible, conductors shall not be inserted until the in- 
terior of the building has been physically protected from the weather, 
and all mechanical work on the building which is likely to injure the 
conductors has been completed. 

(c) Pull wires, if to be used, shall not be installed until the raceway 
system is in place. 

(d) Cleaning agents or materials used as lubricants that might have a 
deleterious effect on conductor coverings shall not be used. 

300-19. Supporting Conductors in Vertical Raceways. 

(a) Conductors in vertical raceways shall be supported at intervals 
not greater than those specified in the following table: 



ARTICLE 300-WIRING METHODS-GENERAL 



70-89 



Conductors 
Aluminum Copper 



100 feet 


100 feet 


200 feet 


100 feet 


180 feet 


80 feet 


135 feet 


60 feet 


120 feet 


50 feet 


95 feet 


40 feet 


85 feet 


35 feet 



No. 1 8 to No. 8 Not Greater than 

No. 6 to No. 

No. 00 to No. 0000 . . . 

211,601 CM to 350,000 CM 
350,001 CM to 500,000 CM 
500,001 CM to 750,000 CM 
Above 750,000 CM 

(b) One of the following methods of support, or a method of equal 
effectiveness is recommended : 

(1) By clamping devices constructed of or employing insulating 
wedges inserted in the ends of the conduits. With cables having var- 
nished cambric or thermoplastic insulation it may also be necessary to 
clamp the conductor. 

(2) By inserting boxes at the required intervals in which insulating 
supports are installed and secured in a satisfactory manner to with- 
stand the weight of the conductors attached thereto, the boxes being 
provided with covers. 

(3) In junction boxes, by deflecting the cables not less than 90 
degrees and carrying them horizontally to a distance not less than twice 
the diameter of the cable, the cables being carried on two or more in- 
sulating supports, and additionally secured thereto by tie wires if de- 
sired. When this method is used cables shall be supported at intervals 
not greater than 20 per cent of those mentioned in the preceding tabu- 
lation. 

300-20. Induced Currents in Metal Enclosures. When conductors car- 
rying alternating current are installed in metal enclosures they shall be 
so arranged as to avoid heating the surrounding metal by induction. To 
accomplish this all phase conductors and the neutral, where one is used, 
shall be grouped together. 

When a single conductor of a circuit passes through metal with 
magnetic properties the inductive effect shall be minimized by: 

(1) Cutting slots in the metal between the individual holes through 
which the individual conductors pass, or 

(2) Passing all the conductors in the circuit through an insulating 
wall sufficiently large for all of the conductors of the circuit. 

Exception: In the case of circuits supplying vacuum or electric dis- 
charge lighting systems or signs, or X-ray apparatus, the currents car- 
ried by the conductors are so small that the inductive heating effect may 
be ignored where these conductors are placed in metal enclosures or 
pass through metal. 

Aluminum being a nonmagnetic metal, there will be no heating due to 
eddy currents, however, induced currents will be present. These are not 
considered of sufficient magnitude to require grouping of conductors or 
special treatment in passing conductors through aluminum wall sections. 

300-21. Prevention of Spread of Fire. Electrical installations shall be 
so made that the possible spread of fire through fire-stopped partitions, 



70-90 MASSACHUSETTS ELECTRICAL CODE 

hollow spaces, fire walls or fire partitions, vertical shafts, ventilating or 
air-handling ducts is reduced to a minimum. 

300-22. Wiring in Ventilating and Exhaust Ducts. 

(a) Where it is necessary to run a wiring system through air handling 
ducts or plenum chambers, the wiring method shall be rigid conduit, 
electrical metallic tubing, flexible steel conduit with lead-covered con- 
ductors, Type ACL metal-clad cable with fittings suitable for the loca- 
tion, Type MI mineral insulated-metal sheathed cable, or Type ALS 
aluminum sheathed cable. The terminals of circuits of such wiring sys- 
tems shall be so located that it will not be necessary to install motors or 
control equipment in the ducts, except for temperature and humidity 
control. Raceways shall not interfere with the operation of automatic 
fire dampers in ducts. 

Exception No. 1. The above provisions shall not apply to integral fan 
systems specifically approved for the purpose. 

Exception No. 2. It is not the intent of this section to include habita- 
ble rooms or areas of a building, the prime purpose of which is not air 
handling. It may, however, include false ceiling space, hollow spaces in 
the wall, and the like if used for air handling purposes. 

Exception No. 3. In ventilating systems used solely for data process- 
ing systems the wiring method shall be rigid conduit, electrical metallic 
tubing, flexible steel conduit with lead-covered conductors, Type ACL 
metal-clad cable with fittings approved for the purpose, Type MI min- 
eral insulated-metal sheathed cable, Type ALS aluminum sheathed ca- 
ble, or flexible cords or cables specifically approved as a part Of the data 
processing system, when such cords or cables may be used in conform- 
ance with other sections of this code. 

(b) No wiring system of any type shall be installed in ducts used 
for dust, loose stock, vapor removal or ventilation of commercial type 
cooking equipment. 

300-23. Temporary Wiring. 

(a) Suitable disconnecting switches or plug connectors shall be in- 
stalled to permit the disconnection of all conductors of the temporary 
circuit by a single operation. 

(b) No bare conductors nor earth returns shall be used for the wiring 
of any temporary circuit. 



ARTICLE 310 — CONDUCTORS FOR GENERAL WIRING 

310-1. General. 

(a) The purpose of this Article is to assure that conductors have 
mechanical strength, insulation, and ampacity adequate for the particu- 
lar conditions under which they are to be used. 

(b) Conductors shall be insulated, except when covered or bare con- 
ductors are specifically permitted in this Code. 



ARTICLE 310-CONDUCTORS 



70-91 



(c) The provisions of this Article are not intended to apply to con- 
ductors which form an integral part of equipment such as motors, mo- 
tor controllers, and the like, or which are provided for elsewhere in this 
Code. 

310-2. Application and Construction. 

(a) Conductor Application. Conductor insulations as specified in the 
following Table 310-2(a) may be installed for any of the wiring meth- 
ods recognized in this Chapter, except as otherwise provided for in the 
Table or in Section 310-3, or as otherwise specified in this Code, They 
are suitable for 600 volts unless otherwise specified. 

(b) Conductor Construction. Insulated conductors for use at 600 
volts or less shall conform to the provisions of Table 3 10-2 (b) . 



Table 310-2 (a). Conductor Application 





Trade 
Name 


Type 
Letter 


Max. 
Operat- 
ing 
Temp. 


Application 
Provisions 




Rubber-Covered 
Fixture Wire 


*RF-1 


60°C 
140°F 


Fixture wiring. 
Limited to 300 V. 




Solid or 
7-Strand 


*RF-2 


60°C 
140°F 


Fixture wiring, and as 
mitted in Section 310-8. 


per- 


Rubber-Covered 
Fixture Wire 


*FF-1 


60°C 
140°F 


Fixture wiring. 
Limited to 300 V. 




Flexible 
Stranding 


*FF-2 


60°C 
140°F 


Fixture wiring, and as 
mitted in Section 310-8. 


per- 


Heat-Resistant 
Rubber-Covered 
Fixture Wire 
Solid or 
7-Strand 


*RFH-1 


75°C 
167°F 


Fixture wiring. 
Limited to 300 V. 




*RFH-2 


75°C 
167°F 


Fixture wiring, and as 
mitted in Section 310-8. 


per- 


Heat-Resistant 
Rubber-Covered 
Fixture Wire 
Flexible 
Stranding 


*FFH-1 


75°C 
167°F 


Fixture wiring. 
Limited to 300 V. 




*FFH-2 


75°C 
167°F 


Fixture wiring, and as 
mitted in Section 310-8. 


per- 


Thermoplastic- 
Covered Fixture 
Wire — Solid or 

Stranded 


*TF 


60°C 
140°F 


Fixture wiring, and as per- 
mitted in Section 310-8, and for 
circuits as permitted in Article 
725. 


Thermoplastic- 
Covered Fixture 
Wire — Flexible 
Stranding 


*TFF 


60°C 
140°F 


Fixture wiring, and as per- 
mitted in Section 310-8, and for 
circuits as permitted in Article 
725. 



♦Fixture wires are not intended for installation as branch circuit conductors nor 
for the connection of portable or stationary appliances. 



70-92 



MASSACHUSETTS ELECTRICAL CODE 





Trade 
Name 


Type 
Letter 


Max. 
Operat- 
ing 
Temp. 


Application 
Provisions 


Cotton-Covered, 
Heat-Resistant, 
Fixture Wire 


*CF 


90°C 
194°F 


Fixture wiring. 
Limited to 300 V. 


Asbestos-Covered 
Heat-Resistant, 
Fixture Wire 


*AF 


150°C 
302°F 


Fixture wiring. 

Limited to 300 V. and Indoor 

Dry Location. 


Silicone Rubber 
Insulated Fixture 
Wire 


*SF-1 


200°C 
392°F 


Fixture wiring. 
Limited to 300 V. 


Solid 

or 7 Strand 


*SF-2 


200°C 
392°F 


Fixture wiring and as per- 
mitted in Section 310-8. 


Silicone Rubber 
Insulated Fixture 
Wire 


♦ SFF-1 


150°C 
302°F 


Fixture wiring. 
Limited to 300 V. 


Flexible 
Stranding 


*SFF-2 


150°C 
302°F 


Fixture wiring and as per- 
mitted in Section 310-8. 


Code Rubber 


R 


60°C 
140°F 


Dry locations. 


Heat-Resistant 
Rubber 


RH 


75°C 
167°F 


Dry locations. 


Heat Resistant 
Rubber 


RHH 


90°C 
194°F 


Dry locations. 


Moisture- 
Resistant 
Rubber 


RW 


60°C 
140°F 


Dry and wet locations. 

For over 2000 volts, insulation 

shall be ozone-resistant. 


Moisture and RH-RW 
Heat Resistant 
Rubber 


60°C 
140°F 

75°C 
167°F 


Dry and wet locations. 

For over 2000 volts, insulation 

shall be ozone-resistant. 

Dry locations. 

For over 2000 volts, insulation 

shall be ozone-resistant. 


Moisture and 
Heat Resistant 
Rubber 


RHW 


75°C 
167°F 


Dry and wet locations. 

For over 2000 volts, insulation 

shall be ozone-resistant. 


Latex Rubber 


RU 


60°C 

140°F 


Dry locations. 



♦Fixture wires are not intended for installation as branch circuit conductors nor 
for the connection of portable or stationary appliances. 



ARTICLE 310-CONDUCTORS 



70-93 







Max. 




Trade 


Type 


Operat- 


Application 


Name 


Letter 


ing 
Temp. 


Provisions 



Heat Resistant 
Latex Rubber 


RUH 


75°C 


Dry locations. 




Moisture Resistant RUW 
Latex Rubber 


60°C 
140°F 


Dry and wet locations. 




Thermoplastic 


T 


60°C 
140°F 


Dry locations. 




Moisture- 
Resistant 
Thermoplastic 


TW 


60°C 
140°F 


Dry and wet locations. 




Heat-Resistant 
Thermoplastic 


THHN 


90°C 
194°F 


Dry locations. 




Moisture and 

Heat-Resistant 

Thermoplastic 


THW 


75°C 
167°F 


Dry and wet locations. 




Moisture and 

Heat-Resistant 

Thermoplastic 


THWN 


75°C 
167°F 


Dry and wet locations. 




Thermoplastic 
and Asbestos 


TA 


90°C 

194°F 


Switchboard wiring only. 




Thermoplastic 
and Fibrous 
Outer Braid 


TBS 


90°C 
194°F 


Switchboard wiring only. 




Synthetic 
Heat-Resistant 


SIS 


90°C 
194°F 


Switchboard wiring only. 





Mineral Insulation 
(Metal Sheathed) 


MI 


85 
185 

250 

482< 


3 C 

3 F 

F 


Silicone- 
Asbestos 


SA 


90°C 
194°F 

125°C 
257°F 



Dry and wet locations with 
Type termination fittings. 

For special application. 



Dry locations. 

For special application. 



70-94 



MASSACHUSETTS ELECTRICAL CODE 



Trade 
Name 


Type 
Letter 


Max. 
Operat- Application 
ing Provisions 
Temp. 


Fluorinated 

Ethylene 

Propylene 


FEP 

or 
FEPB 


90°C 
194°F 
200°C 
392 °F 


Dry locations. 

Dry locations — special applica 
tions. 


Varnished 
Cambric 


V 


85° C 

185°F 


Dry locations only. Smaller 
than No. 6 by special permis- 
sion. 


Asbestos and 

Varnished 

Cambric 


AVA 


110°C 
230°F 


Dry locations only. 


Asbestos and 

Varnished 

Cambric 


AVL 


110°C 
230°F 


Dry and wet locations. 


Asbestos and 

Varnished 

Cambric 


AVB 


90°C 
194°F 


Dry locations only. 


Asbestos 


A 


200°C 
392 °F 


Dry locations only. In race- 
ways, only for leads to or 
within apparatus. Limited to 
300 V. 


Asbestos 


AA 


200°C 
392 °F 


Dry locations only. Open wir- 
ing. In raceways, only for 
leads to or within apparatus. 
Limited to 300 V. 


Asbestos 


AI 


125°C 
257°F 


Dry locations only. In race- 
ways, only for leads to or 
within apparatus. Limited to 
300 V. 


Asbestos 


AIA 


125°C 
257°F 


Dry locations only. Open wir- 
ing. In raceways, only for 
leads to or within apparatus. 


Paper 




85°C 
185°F 


For underground service con- 
ductors, or by special permis- 
sion. 



ARTICLE 310-CONDUCTORS 



70-95 













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70-96 



MASSACHUSETTS ELECTRICAL CODE 







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ARTICLE 310-CONDUCTORS 



70-97 











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go w co go go co 


. GO w go 


t> O CJ o o o c 




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c c c c c c c 


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CO CO CO CO CO CC 


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CO CO CO 


CO CO T}< U3 CO t- OC 





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70-98 



MASSACHUSETTS ELECTRICAL CODE 



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CO ^ "3 CO t- 00 



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ARTICLE 310-CONDUCTORS 



70-99 



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****■ ■*■"*" — ~~^ — ' 


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CO ■"* tO CO t- OC 


CM rH CM CO "** Tf tO 














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Tf | | rHOC 


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70-100 



MASSACHUSETTS ELECTRICAL CODE 



p 

c 

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tM 



CO 



be 
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to 

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CO 



ARTICLE 310-CONDUCTORS 70-101 

(310-2 continued) 

(c) Marking. Insulated wires, cables and cords of all kinds except 
paper-insulated wire shall have a continuous distinctive marking so 
that their maker may be readily identified. All wires, cables and cords 
shall also be plainly tagged or marked as follows: 

(1) The maximum working voltage for which the wire was tested 
or approved. This may be omitted for asbestos-covered switchboard 
wires. 

(2) The words "National Electrical Code Standard," or "NEC 
Std." 

(3) Name of the manufacturing company and, if desired, trade 
name of the wire. 

(4) Month and year when manufactured. 

(5) The proper type letter for the particular style of wire or cable 
as given in the following sections. 

(d) Surface Marking. A durable marking on the surface shall be 
provided at intervals not exceeding 24 inches showing the name of the 
manufacturer or a significant abbreviation thereof, type letter or letters 
as specified in Article 310, Table 310-2(b) and Articles 336, 338, and 
339, the size Awg. or circular mils and the maximum voltage on the 
following types of wire and cable rated 600 volts or less: 

(1) Single conductor only, rubber insulated and thermoplastic in- 
sulated for General Wiring. 

(2) Non-Metallic Sheathed Cable. 

(3) Service-Entrance Cable. 

(4) Underground Feeder and Branch Circuit Cable. 

All other types of wire and cable, flexible cords, fixture wires, switch- 
board wires, and any of the above types with a metallic covering are 
not required to have a marking on the surface. 

(e) Classification. In addition to the type letters specified in Table 
310-2(b), the following letters shall apply: 

(1) A type letter or letters used alone indicates a single insulated 
conductor. 

(2) The letter "D" used as a suffix indicates a twin wire with two 
insulated conductors laid parallel under an outer nonmetallic covering. 

(3) The letter "M" used as a suffix indicates an assembly of two 
or more insulated conductors twisted together under an outer nonme- 
tallic covering. 

(4) The letter "L" used as a suffix indicates an outer covering of 
lead. 

(5) Voltage. Type letters, when used alone, indicate conductors 
for use at not more than 600 volts. Conductors for use at higher volt- 
ages shall be indicated by adding numerical suffixes to the type letters 
as follows: 



70-102 MASSACHUSETTS ELECTRICAL CODE 

1 — for use at not more than 1 000 volts. 

20 — for use at not more than 2000 volts. 

30 — for use at not more than 3000 volts. 

40 — for use at not more than 4000 volts. 

50 — for use at not more than 5000 volts. 
The working voltages referred to in the Table are the operating voltages 
between phases of single and two-phase systems, and three-phase systems 
with grounded or ungrounded neutral. 

(6) All conductors shall be examined and tested at 

the factory and, if approved, shall be labeled before shipment. 

(f) Identification of Insulation. All rubber-insulated conductors and all 
thermoplastic-insulated conductors, No. 14 and larger, shall have a readily 
recognizable durable marking to indicate the grade of insulation; except 
that single-conductor, code-rubber insulated conductors having a lead sheath; 
and multi-conductor cables, metal-clad cable, and nonmetallic-sheathed 
cable having code-rubber or nonmoisture-resistant thermoplastic-insulated 
conductors, need not be so marked. 

(g) Identified Conductors. Single insulated conductors of No. 6 or 
smaller, intended for use as identified conductors of circuits shall have an 
outer identification of a white or natural gray color. Twin and twisted-pair 
conductors and three-conductor cables shall have one conductor, and four- 
conductor cables shall have at least one conductor identified in this manner. 

Exception No. 1 — Multiple-conductor varnished cloth insulated cables. 

Exception No. 2 — Fixture wires as outlined below. 

Exception No. 3 — Mineral insuiated-metal sheathed cable. 
For fixture wires the identification shall be as above, or by means of 
(1) stripes, or (2) by the means described in Section 400-1 3(a), (b), (c), 
(d) and (e). 

For aerial cable the identification shall be as above, or by means of a 
ridge so located on the exterior of the cable as to identify it. 

Wires having their outer covering finished to show a white or natural gray 
color but having colored tracer threads in the braid, identifying the source of 
manufacture, are considered as meeting the provisions of this Section. 

(h) Single conductors, intended for use as unidentified conductors, and 
conductors other than the identified conductor in multi-conductor cabfes, 
shall be finished to show a color or combination of colors other than, and 
contrasting with, white or natural gray. The colors contrasting with white 
or natural gray, may be provided by means of an approved stripe or stripes 
on black conductors. For identification requirements for conductors larger 
than No. 6 see Section 200-6(b). 

(i) Insulation Thickness — Over 600 volts. The thickness of insulation 
for conductors for use at over 600 volts shall conform to Tables 310-2 
(i-1 thru i-4): 



ARTICLE 310-CONDUCTORS 



70-103 



Table 310-2(i) (1) 

Thickness of Rubber Insulation for Rubber-Covered Wire 
and Cable, in 64ths of an Inch 









Classification 




Size 

AWG. or 
MCM 


R10 

RH10 

RW10 

RHW10 


R20 
RH20 RW30f RW40f RW 50f 
RW 20 RH-RW 30t RH-RW 40f RH-RW 50f 
RHW20 RHW30f RHW 40f RHW 50f 


14-12 


4 


5 


. . 


, ^ 




10- 8* 


4 


5 


7 


9 


10* 


6- 2 


5 


6 


8 


9 


10 


1-4/0 


6 


7 


8 


9 


10 


213-500 


7 


8 


9 


10 


11 


501-1000 


8 


9 


9 


10 


11 


1001-2000 


9 


9 


10 


11 


12 



* No. 8 AWG. is the minimum conductor size for 5000 volts operation. 
f Shall be of approved ozone-resistant type for operation at voltages 
over 2000. 



Table 310-2(i) (2) 

Thickness of Varnished-Cambric Insulation for 
Single-Conductor Cable, in 64ths of an Inch 



Conductor Size 




For Voltages 


Not Exceeding 




AWG or MCM 


1000 


2000 


3000 


4000 


5000 


14 


4 


# m 


. a 


. # 


. . 


12 


4 


5 


. , 


. . 


. . 


10 


4 


5 


6 


. . 


. . 


8-2 


4 


5 


6 


7 


9 


1-4/0 


5 


6 


6 


7 


9 


213-500 


6 


6 


7 


8 


10 


501-1000 


7 


7 


7 


8 


10 


1001-2000 


8 


8 


8 


9 


10 



70-104 



MASSACHUSETTS ELECTRICAL CODE 



Table 310-2(i) (3) 

Thickness of Varnished-Cambric Insulation for 
Multiple-Conductor Cable, in 64ths of an Inch 









For Voltag 


es Not Exceeding 




AWG or MCM 


1000 
C B 


2000 
C B 


3000 
C B 


4000 
C B 


5000 
C B 


14 


4 





• . . . 


• . • • 


. . 


. . . . 


12 


4 





5 


. . 


. . 


. . . . 


10 


4 





5 


5 2 


. . 


. . 


8-2 


4 





5 


5 2 


6 3 


6 4 


1-4/0 


5 





6 


6 2 


6 3 


6 4 


213-500 


6 





6 


6 2 


6 3 


7 4 


501-1000 


6 


2 


6 2 


6 3 


6 4 


7 4 


1001-2000 


7 


2 


7 2 


7 3 


7 4 


7 5 



The thickness given in columns headed "C" are for the insulation on 
the individual conductors. Those given in the columns headed "B" are 
for the thickness of the overall belt of insulation. 



Table 310-2(i) (4) 

Thickness of Asbestos and Varnished-Cambric 

Insulation for Single-Conductor Cable, 

Types AVA, AVB and AVL, in Mils 



Conductor 


1st Wall 
Asbestos 




Varnished Cambric 




Asbestos 
2nd Wall 


AWG or 
MCM 




For Voltages 


Not Exceeding 






1000-5000 


1000 


2000 


3000 


4000 


5000 


1000-5000 


14-2 


15 


45 


60 


80 


100 


120 


25 


1-4/0 


20 


45 


60 


80 


100 


120 


30 


213-500 


25 


45 


60 


80 


100 


120 


40 


501-1000 


30 


45 


60 


80 


100 


120 


40 


1001-2000 


30 


55 


75 


95 


115 


140 


50 



ARTICLE 310 — CONDUCTORS 70-105 

310-3. Insulating Materials. 

(a) The rubber insulations include those made from natural and synthetic 
rubber, neoprene and other vulcanizable materials. 

(b) Thermoplastic insulation may stiffen at temperatures below minus 
10°C (14°F) and care should be used in its installation at such temperatures. 
It may be deformed when subject to pressure; care should be taken in its 
installation, as for example, at bushings, or points of support. See Section 
373-6(b). 

310-4. Temperature Limitations. No conductor shall be used under such 
conditions that its temperature, even when carrying current, will exceed 
the temperature specified in Table 310-2(a) for the type of insulation in- 
volved. 

310-5. Wet Locations. Insulated conductors used underground, in con- 
crete slabs or other masonry in direct contact with earth, in wet locations, 
or where condensation or accumulation of moisture within the raceway is 
likely to occur, shall be moisture-resistant, rubber-covered (Type RW); mois- 
ture- and heat-resistant (Type RH-RW); moisture- and heat-resistant, rubber- 
covered (Type RHW); moisture-resistant latex rubber (Type RUW); moisture- 
resistant, thermoplastic-covered (Type TW); moisture- and heat-resistant, ther- 
moplastic-covered (Type THW); moisture- and heat-resistant thermoplastic 
(Type THWN); lead covered; aluminum sheathed cable (Type ALS); mineral 
insulated-metal sheathed (Type Ml); or of a type approved for the purpose. 
Such conductors are not suitable for direct burial in the earth unless of 
a type specifically approved for the purpose. 

310-6. Buried Conductors. 

Cables of one or more conductors for direct burial in the earth shall be 
buried to a depth of at least 18" below finished grade in grass or seeded 
areas. Where passing under surfaced areas, such as driveways or roadways, 
they shall be buried to a depth of at least 24", shall be Type USE, except that 
branch circuit and feeder cable may be Type UF. 

Where single conductor cables are 
installed, all conductors of each service, feeder, sub-feeder or branch circuit, 
including the neutral conductor, shall be run continuously in the same 
trench or raceway. Supplementary mechanical protection, such as a covering 
board, concrete pad, raceway, etc., may be required by the authority enforc- 
ing the Code. See Section 339-3(c). 

310-7. Corrosive Conditions. Conductors exposed to oils, greases, vapors, 
gases, fumes, liquids or other substances having a deleterious effect upon 
the conductor or insulation shall be a type approved for the purpose. 
310-8. Minimum Size of Conductors. Conductors, whether solid or 
stranded, shall not be smaller than No. 14, except for printing press control 
circuits; as provided for flexible cords in Section 400-7; for fixture wire in 
Section 410-18; for fractional horsepower motors in Section 430-22; for 
cranes and hoists in Section 610-14; for elevator control and signal circuits 
in Section 620-12; and for remote-control, low energy power, low-voltage 
power and signal circuits in Section 725-13. 

310-9. Stranded Conductors. Except when used as bus bars or in Type Ml 
Cable, conductors No. 6 and larger, installed in raceways, shall be stranded. 
310-10. Conductors in Multiple. Conductors in sizes 1/0 and larger 
may be run in multiple provided the arrangement is such as to assure 



70-106 



MASSACHUSETTS ELECTRICAL CODE 



equal division of total current among all conductors involved. All of 
the multiple conductors shall be of the same length, of the same con- 
ductor material, circular-mil area, same insulation type and terminated 
in the same manner. Where run in separate raceways or cables, the 
raceways or cables shall have the same physical characteristics. 

When conductors are used in multiple, space in enclosures should be 
given consideration. 

310-11. Ampacity Reduction Factors. Where more than three conduc- 
tors are installed in a raceway or assembled into one or more cables 
the ampacity of each conductor shall be reduced in accordance with 
Note 8 to Tables 310-12 through 310-15. 

Notes To Tables 310-12 through 310-15. 

Ampacity. The maximum, continuous, ampacities of copper conductors 
are given in Tables 310-12 and 310-13. The ampacities of aluminum con- 
ductors are given in Tables 310-14 and 3 1 0- 1 5t 



1. Explanation of Tables. For ex- 
planation of Type Letters, and for 
recognized size of conductors for the 
various conductor insulations, see 
Sections 310-2 and 310-3. For in- 
stallation requirements, see Section 
310-1 through 310-7, and the various 
Articles of this Code. For flexible 
cords see Tables 400-9 and 400-11. 

2. Application of Tables. For 

open wiring on insulators and for 
concealed knob-and-tube work, the 
allowable ampacities of Tables 310- 
13 and 310-15 shall be used. For all 
other recognized wiring methods, 
the allowable ampacities of Tables 
310-12 and 310-14 shall be used, un- 
less otherwise provided in this Code. 

3. Aluminum Conductors. For 

aluminum conductors, the allowable 
ampacities shall be in accordance 
with Tables 310-14 and 310-15. 

4. Bare Conductors. Where bare 
conductors are used with insulated 
conductors, their allowable ampac- 
ities shall be limited to that permit- 
ted for the insulated conductors of 
the same size. 

5. Type MI Cable. The tempera- 
ture limitation on which the am- 
pacities of Type MI cable are based, 
is determined by the insulating ma- 
terials used in the end seal. Termina- 
tion fittings incorporating unimpreg- 
nated organic insulating materials 
are limited to 85 °C. operation. 

6. Ultimate Insulation Tempera- 
ture. In no case shall conductors be 



associated together in such a way 
with respect to the kind of circuit, 
the wiring method employed, or the 
number of conductors, that the limit- 
ing temperature of the conductors 
will be exceeded. 

7. Use of Conductors With Higher 
Operating Temperatures. Where the 
room temperature is within 10 de- 
grees C of the maximum allowable 
operating temperature of the insula- 
tion, it is desirable to use an insula- 
tion with a higher maximum allow- 
able operating temperature; although 
insulation can be used in a room 
temperature approaching its maxi- 
mum allowable operating tempera- 
ture limit if the current is reduced in 
accordance with the Correction Fac- 
tors for different room temperatures. 

8. More Than Three Conductors 
in a Raceway or Cable. Tables 310- 
12 and 310-14 give the allowable 
ampacities for not more than three 
conductors in a raceway or cable. 
Where the number of conductors in 
a raceway or cable exceeds three, 
the allowable ampacity of each con- 
ductor shall be reduced as shown in 
the following Table: 





Per Cent of Values in 


Number of 


Tables 310-12 and 
310-14 r 


Conductors 


4 to 6 


80 


7 to 24 


70 


25 to 42 


60 


43 and above 


50 



Exception No. 1 — When conduc- 
tors of different systems, as provided 



ARTICLE 310-CONDUCTORS 



70-107 



in Section 300-3, are installed in a 
common raceway the derating factors 
shown above apply to the number of 
Power and Lighting {Articles 210, 
215, 220 and 230) conductors only. 

Where the number of conductors 
in a raceway or cable exceeds three, 
or where single conductors or multi- 
conductor cables are stacked or bun- 
dled without maintaining spacing as 
required in Article 318 and are not 
installed in raceways, the individual 
ampacity of each conductor shall be 
reduced as shown in the above table. 

Exception No. 2 — The derating 
factors of Sections 21 0-23 (b) and 
220-2 (second paragraph) do not 
apply when the above derating fac- 
tors are also required. 

9. Application of Type RH-RW 
Wire. Where Type RH-RW rubber 
insulated wire is used in wet locations 
the allowable ampacities shall be 
that of Column 2 in Tables 310-12 
through 310-15. Where used in dry 
locations the allowable ampacities 
shall be that of Column 3 in Tables 
310-12 through 310-15. 

10. Overcurrent Protection. Where 
the standard ratings and settings of 
overcurrent devices do not corre- 
spond with the ratings and settings 
allowed for conductors, the next 
higher standard rating and setting 
may be used. 

Exception — Except as limited in 
Section 240-5. 



11. Neutral Conductor. A neutral 
conductor which carries only the un- 
balanced current from other con- 
ductors, as in the case of normally 
balanced circuits of three or more 
conductors, shall not be counted in 
determining ampacities as provided 
for in Note 8. 



In a 3-wire circuit consisting of two 
phase wires and the neutral of a 4-wire, 
3-phase WYE connected system, a com- 
mon conductor carries approximately the 
same current as the other conductors and 
is not therefore considered as a neutral 
conductor. 



12. Voltage Drop. The allowable 
ampacities in Tables 310-12 through 
310-15 are based on temperature 
alone and do not take voltage drop 
into consideration. 

13. Deterioration of Insulation. It 

should be noted that even the best 
grades of rubber insulation will de- 
teriorate in time, so eventually will 
need to be replaced. 

14. Aluminum Sheathed Cable. 

The ampacities of Type ALS cable 
are determined by the temperature 
limitation of the insulated conduc- 
tors incorporated within the cable. 
Hence the ampacities of aluminum 
sheathed cable may be determined 
from the columns in Tables 310-12 
and 310-14 applicable to the type of 
insulated conductors employed with- 
in the cable. See Note 9. 



70-108 



MASSACHUSETTS ELECTRICAL CODE 



Table 310-12. Allowable Ampacities of Insulated Copper 
Conductors 

Not More than Three Conductors in Raceway or Cable or 
Direct Burial (Based on Room Temperature of 30°C. 86°F. 



Size 


Temperature Rating 


of Conductor. See Table 310-21 


a) 


AWG 


60°C 


75°C 


85°-90°C 


110°C 


125°C 


200°C 


MCM 


(140°F) 


(167°F) 


(185°F) 


(230°F) 


(257°F) 


(392 °F) 


14 


15 


15 


25 t 


30 


30 


30 


12 


20 


20 


30 f 


35 


40 


40 


10 


30 


30 


40 f 


45 


50 


55 


8 


40 


45 


50 T 


60 


65 


70 


6 


55 


65 


70 


80 


85 


95 


4 


70 


85 


90 


105 


115 


120 


3 


80 


100 


105 


120 


130 


145 


2 


95 


115 


120 


135 


145 


165 


1 


110 


130 


140 


160 


170 


190 





125 


150 


155 


190 


200 


225 


00 


145 


175 


185 


215 


230 


250 


000 


165 


200 


210 


245 


265 


285 


0000 


195 


230 


235 


275 


310 


340 


250 


215 


255 


270 


315 


335 




300 


240 


285 


300 


345 


380 




350 


260 


310 


325 


390 


420 




400 


280 


335 


360 


420 


450 




500 


320 


380 


405 


470 


500 




600 


355 


420 


455 


525 


545 




700 


385 


460 


490 


560 


600 




750 


400 


475 


500 


580 


620 




800 


410 


490 


515 


600 


640 




900 


435 


520 


555 








1000 


455 


545 


585 


680 


730 




1250 


495 


590 


645 








1500 


520 


625 


700 


785 






1750 


545 


650 


735 








2000 


560 


665 


775 


840 







CORRECTION FACTORS, ROOM TEMPS. OVER 30° C. 86° F. 



C. F. 














40 104 


.82 


.88 


.90 


.94 


.95 




45 113 


.71 


.82 


.85 


.90 


.92 




50 122 


.5£ 


.75 


.80 


.87 


.89 




55 131 


.41 


.67 


.74 


.83 


.86 




60 140 




.58 


.67 


.79 


.83 


.91 


70 158 




.35 


.52 


.71 


.76 


.87 


75 167 






.43 


.66 


.72 


.86 


80 176 






.30 


.61 


.69 


.84 


90 194 








.50 


.61 


.80 


100 212 










.51 


.77 


120 248 












.69 


140 284 












.59 



These ampacities relate only to conductors described in Table 310-2(a). 

t The ampacities for Types FEP, FEPB, RHH and THHN conductors for 
sizes AWG 14, 12 and 10 shall be the same as designated for 75 °C conductors 
in this Table. 



ARTICLE 310-CONDUCTORS 



70-109 



Size 



Table 310-13. Allowable Ampacities of Insulated Copper 

Conductors 

Single Conductor in Free Air 
(Based on Room Temperature of 30° C. 86° F ) 

Temperature Rating of Conductor. See Table 3 IO-2(a) 



AWG 


60°C 


75°C 


85°-90°C 


110°C 


125°C 


200°C 


Bare & 


MCM 


(140°F) 


(167°F) 


(185°F) 


(230°F) 


(257°F) 


(392 °F) 


Coverec 

Conduct* 


14 


20 


20 


30 t 


40 


40 


45 


30 


12 


25 


25 


40 t 


50 


50 


55 


40 


10 


40 


40 


55 t 


65 


70 


75 


55 


8 


55 


65 


70 


85 


90 


100 


70 


6 


80 


95 


100 


120 


125 


135 


100* 


4 


105 


125 


135 


160 


170 


180 


130 


3 


120 


145 


155 


180 


195 


210 


150 


2 


140 


170 


180 


210 


225 


240 


175 


1 


165 


195 


210 


245 


265 


280 


205 





195 


230 


245 


285 


305 


325 


235 


00 


225 


265 


285 


330 


355 


370 


275 


000 


260 


310 


330 


385 


410 


430 


320 


0000 


300 


360 


385 


445 


475 


510 


370 


250 


340 


405 


425 


495 


530 






410 


300 


375 


445 


480 


555 


590 






460 


350 


420 


505 


530 


610 


655 






510 


400 


455 


545 


575 


665 


710 






555 


500 


515 


620 


660 


765 


815 






630 


600 


575 


690 


740 


855 


910 






710 


700 


630 


755 


815 


940 


1005 






780 


750 


655 


785 


845 


980 


1045 






810 


800 


680 


815 


880 


1020 


1085 






845 


900 


730 


870 


940 










905 


1000 


780 


935 


1000 


1165 


1240 






965 


1250 


890 


1065 


1130 












1500 


980 


1175 


1260 


1450 








i215 


1750 


1070 


1280 


1370 












2000 


1155 


1385 


1470 


1715 








1405 



CORRECTION FACTORS, ROOM TEMPS. OVER 30° C. 86° F. 



C. F. 
40 104 
45 113 
50 122 
55 131 


.82 
.71 
.58 
.41 


.88 
.82 
.75 
.67 




.90 
.85 
.80 

74 




.94 
.90 
.87 
.83 


.95 
.92 
.89 
.86 








60 140 
70 158 
75 167 
80 176 






.5 
.3 


8 
5 




.67 
.52 
.43 
.30 




79 
.71 
66 
61 


.83 
.76 
.72 
.69 


.91 

.87 
.86 
.84 






90 194 
100 212 
120 248 
140 284 
















.50 


.61 
.51 


.80 
.77 
.69 
.59 







These ampacities relate only to conductors described in Table 310-2(a). 

t The ampacities for Types FEP, FEPB, RHH and THHN conductors for 
sizes AWG 14, 12 and 10 shall be the same as designated for 75°C conductors 
in this Table. 



70-1 10 



MASSACHUSETTS ELECTRICAL CODE 



Table 310-14. Allowable Ampacities of Insulated Aluminum 

Conductors 

Not More than Three Conductors in Raceway or Cable or 
Direct Burial (Based on Room Temperature of 30°C. 86°F. 



Size 


Temperature Rating 


of Conductor. See Table 310-2 


a) 


AWG 


60°C 


75°C 


85°-90°C 


no°c 


125°C 


200°C 


MCM 


(140°F) 


(167°F) 


(185°F) 


(230°F) 


(257°F) 


(392°F) 


12 


15 


15 


25* 


25 


30 


30 


10 


25 


25 


30 1 


35 


40 


45 


8 


30 


40 


40 t 


45 


50 


55 


6 


40 


50 


55 


60 


65 


75 


4 


55 


65 


70 


80 


90 


95 


3 


65 


75 


80 


95 


100 


115 


*2 


75 


90 


95 


105 


115 


130 


*i 


85 


100 


110 


125 


135 


150 


*o 


100 


120 


125 


150 


160 


180 


*oo 


115 


135 


145 


170 


180 


200 


*ooo 


130 


155 


165 


195 


210 


225 


*oooo 


155 


180 


185 


215 


245 


270 


250 


170 


205 


215 


250 


270 




300 


190 


230 


240 


275 


305 




350 


210 


250 


260 


310 


335 




400 


225 


270 


290 


335 


360 




500 


260 


310 


330 


380 


405 




600 


285 


340 


370 


425 


440 




700 


310 


375 


395 


455 


485 




750 


320 


385 


405 


470 


500 




800 


330 


395 


415 


485 


520 




900 


355 


425 


455 








1000 


375 


445 


480 


560 


600 




1250 


405 


485 


530 








1500 


435 


520 


580 


650 






1750 


455 


545 


615 








2000 


470 


560 


650 


705 







CORRECTION FACTORS, ROOM TEMPS. OVE A i 30° C. 86° F. 



C. F. 














40 104 


.82 


.88 


.90 


.94 


.95 




45 113 


.71 


.82 


.85 


.90 


.92 




50 122 


.58 


.75 


.80 


.87 


.89 




55 131 


.41 


.67 


.74 


.83 


.86 




60 140 




.58 


.67 


.79 


.83 


.91 


70 158 




.35 


.52 


.71 


.76 


.87 


75 167 






.43 


.66 


.72 


.86 


80 176 






.30 


.61 


.69 


.84 


90 194 








.50 


.61 


.80 


100 212 










.51 


.77 


120 248 












.69 


140 284 












.59 



These ampacities relate only to conductors described in Table 3 10-2 (a). 

* For three wire, single phase service and sub-service circuits, the allow- 
able ampacity of RH, RH-RW, RHH, RHW, and THW aluminum conduc- 
tors shall be for sizes #2-100 Amp., #1-110 Amp., #1/0-125 Amp., #2/0-150 
Amp., #3/0-170 Amp. and #4/0-200 Amp. 

T The ampacities for Types RHH and THHN conductors for sizes AWG 
12, 10 and 8 shall be the same as designated for 75 °C conductors in this Table. 



ARTICLE 310-CONDUCTORS 



70-111 



Table 310-15. Allowable Ampacities of Insulated Aluminum 

Conductors 

Single Conductor in Free Air 
(Based on Room Temperature of 30° C. 86° F ) 



Size 



Temperature Rating of Conductor. See Table 310-2(a) 



AWG 


60°C 


75°C 


B5°-90°C 


110°C 


125°C 


200°C 


Bare & 

Coverec 

Conductc 


MCM 


(140°F) 


(167°F) 


(185°F) 


(230°F) 


(257°F) 


(392°F) 


12 


20 


20 


30 + 


40 


40 


45 


30 


10 


30 


30 


45 + 


50 


55 


60 


45 


8 


45 


55 


55 + 


65 


70 


80 


55 


6 


60 


75 


80 


95 


100 


105 


80 


4 


80 


100 


105 


125 


135 


140 


100 


3 


95 


115 


120 


140 


150 


165 


115 


2 


110 


135 


140 


165 


175 


185 


135 


1 


130 


155 


165 


190 


205 


220 


160 





150 


180 


190 


220 


240 


255 


185 


00 


175 


210 


220 


255 


275 


290 


215 


000 


200 


240 


255 


300 


320 


335 


250 


0000 


230 


280 


300 


345 


370 


400 


290 


250 


265 


315 


330 


385 


415 






320 


300 


290 


350 


375 


435 


460 






360 


350 


330 


395 


415 


475 


510 






400 


400 


355 


425 


450 


520 


555 






435 


500 


405 


485 


515 


595 


635 






490 


600 


455 


545 


585 


675 


720 






560 


700 


500 


595 


645 


745 


795 






615 


750 


515 


620 


670 


775 


825 






640 


800 


535 


645 


695 


805 


855 






670 


900 


580 


700 


750 










725 


1000 


625 


750 


800 


930 


990 






770 


1250 


710 


855 


905 












1500 


795 


950 


1020 


1175 








985 


1750 


875 


1050 


1125 












2000 


960 


1150 


1220 


1425 








1165 



CORRECTION FACTORS, ROOM TEMPS. OVER 30° C. 86° F. 



C. F. 
40 104 
45 113 
50 122 
55 131 




.82 
.71 
.58 
.41 


60 140 
70 158 
75 167 
80 176 






90 194 
100 212 
120 248 
140 284 







.82 
.75 
.67 



.58 
.35 



.94 
.90 

.87 
.83 



.79 
.71 
.66 
.61 



.50 



.95 
.92 
.89 
.86 



.83 
.76 
.72 
.69 



.61 
.51 



These ampacities relate only to conductors described in Table 310-2(a). 
t The ampacities for Types RHH and THHN conductors for sizes AWG 
12, 10 and 8 shall be the same as designated for 75 °C conductors in this Table. 



70-112 MASSACHUSETTS ELECTRICAL CODE 

ARTICLE 318 — CONTINUOUS RIGID CABLE SUPPORTS 



318-1. Definition. A continuous rigid cable support is a unit or an as- 
sembly of units or sections, and associated fittings, made of metal or 
other noncombustible materials forming a continuous rigid structure 
used to support cables. Continuous rigid cable supports include ladders, 
troughs, channels, and other similar structures. 

It is not the intent of this Article to require that cables be supported 
by continuous rigid cable supports or to recognize the use of conduc- 
tors described in Article 310 in continuous rigid cable supports for 
general wiring. 

318-2. Use. 

(a) Continuous rigid cable supports may be used as the mechanical 
support for only the following wiring methods under the conditions de- 
tailed in the Article for each wiring method: (1) Mineral-insulated metal- 
sheathed cables, (Article 330), (2) Aluminum sheathed cable, (Article 
331), (3) Metal-clad cable, (Article 334), (4) Non-metallic sheathed 
cable, (Article 336), (5) Service entrance cables, (Article 338), (6) 
Underground feeder and branch circuit cable, (Article 339), (7) Any 
approved conduit or raceway with its contained conductors. 

(b) Continuous rigid cable supports may be used as the mechanical 
support for factory-assembled, multiconductor control, signal, and power 
cables, which are specifically approved for installation in Continuous 
Rigid Cable Supports, in fire-resistive or non-combustible construction, 
but shall not be used (1) in hoistways, (2) where the cables supported 
are subject to severe physical damage, (3) in areas having readily com- 
bustible contents as determined by the authority enforcing this Code. 
Continuous Rigid Cable Supports may be used to support cables in 
hazardous locations when the cables are specifically approved for such 
use. (Refer to Section 501-4, 502-4, and 503-3.) 

318-3. Construction. Continuous Rigid Cable Supports shall be ap- 
proved for the purpose and shall comply with the following: 

(1) Shall have suitable strength and rigidity to provide adequate 
support for all contained wiring. 

(2) Shall not present sharp edges, burrs or projections injurious to 
the insulation or jackets of the wiring. 

(3) If made of metal, shall be adequately protected against cor- 
rosion or shall be made of corrosion-resistant material. 

(4) Shall have side rails or equivalent structural members. 

(5) Shall include fittings for changes in direction and elevation of 
runs. 

318-4. Installation. 

(a) Continuous Rigid Cable Supports shall be installed as a complete 
support system. 

(b) Each run of continuous rigid cable support shall be complete be- 
fore the installation of cables. 



ARTICLE 318-CABLE SUPPORTS 70-113 

(c) Continuous rigid cable supports shall be mechanically connected 
to any enclosure or raceway into which the cables contained in the 
continuous rigid cable support extend or terminate. 

(d) In portions of runs where additional physical protection is re- 
quired, noncombustible covers or enclosures providing the required 
protection shall be used. 

(e) Installations involving different electrical systems shall comply 
with Section 300-3 and, where separation is required, the separation 
shall be a solid noncombustible partition or compartment. Where ca- 
bles, as permitted by Section 318-2(b), are installed in the same con- 
tinuous rigid cable support as the cables permitted by Section 318-2 
(a), the requirements of this section shall apply 

(f) When continuous rigid cable supports are installed in tiers, the 
minimum vertical clearance between tiers shall be 12 inches. 

(g) Continuous rigid cable supports may extend transversely through 
partitions or walls, other than fire walls, provided the section of the 
support within the wall is continuous and unventilated. See Section 
300-21. 

(h) Continuous rigid cable supports may extend vertically through 
dry floors and platforms provided the continuous rigid cable support 
is totally enclosed where it passes through the floor or platform open- 
ing and for a distance of six feet above the floor or platform to provide 
protection from physical injury. See Section 300-21. 

(i) Continuous rigid cable supports may extend vertically through 
floors and platforms in wet locations where ( 1 ) there are curbs or other 
suitable means to prevent water flow through the floor or platform 
opening and (2) the continuous rigid cable support is totally enclosed 
where it passes through the floor or platform opening and for a distance 
of six feet above the floor or platform to provide protection from physi- 
cal injury. See Section 300-21. 

(i) Cable splices and cable taps shall be made only in junction boxes 
or fittings approved for the purpose. 

(k) In other than horizontal runs, and where side rails do not pro- 
vide adequate containment of the cables, they shall be fastened se- 
curely to transverse members of the continuous rigid cable support. 

(!) Where continuous rigid cable supports are located adjacent to 
one another an adequate working space of 24 inches minimum should 
be maintained on one side of each continuous rigid cable support, or 
where grouped in rows adjacent to each other a minimum working 
space of 32 inches should be maintained over each continuous rigid 
cable support. 

(m) A minimum vertical clearance of 6 inches should be maintained 
from the top of the continuous rigid cable support to all ceilings, beams, 
and other obstructions. 

318-5. Grounding. All metal sections of continuous rigid cable sup- 
ports and fittings shall be bonded and effectively grounded to provide 
a continuous circuit for fault current. A continuous rigid cable support 



70-114 MASSACHUSETTS ELECTRICAL COPE 

system shall not be used either as a grounded circuit conductor or as an 
equipment grounding conductor. See Section 250-33. 

318-6. Ampacity. The ampacities of cables installed in continuous 
rigid cable supports shall be as follows: 

(a) Where cables containing not more than three current-carrying 
conductors are installed in ventilated continuous rigid cable supports 
and spacing is maintained at from one-quarter to one cable diameter, 
the factors of Table 318-6 (a) shall be applied to the ampacities of the 
cables used. 

Table 318-6 (a) 
Factors for Cables with Maintained Spacing 









Horizontally 






Number of 














Cables 


1 


2 


3 


4 


5 


6 


Vertically 














1 


1.00 


0.93 


0.87 


0.84 


0.83 


0.82 


2 


0.89 


0.83 


0.79 


0.76 


0.75 


0.74 


3 


0.80 


0.76 


0.72 


0.70 


0.69 


0.68 


4 


0.77 


0.72 


0.68 


0.67 


0.66 


0.65 


5 


0.75 


0.70 


0.66 


0.65 


0.64 


0.63 


6 


0.74 


0.69 


0.64 


0.63 


0.62 


0.61 



(b) The ampacities of cables shall be in accordance with the require- 
ments of Note 8 of Notes to Tables 310-12 through 310-15 where (1) 
cables are not spaced, (2) spacing is maintained between cables of 
more than three current-carrying conductors, or (3) unventilated con- 
tinuous rigid cable supports are used. 



ARTICLE 320 — OPEN WIRING ON INSULATORS 



320-1. Definition. Open wiring is a wiring method using cleats, 
knobs, tubes and flexible tubing for the protection and support of in- 
sulated conductors run in or on buildings, and not concealed by the 
building structure. 

320-2. Use. 

(a) Open wiring on insulators may be used for exposed work, either 
inside or outside building; in dry or wet locations; where subject to 
corrosive vapors such as covered by Article 480; for services as covered 
by Article 230, provided the requirements of this Article are satisfied. 

(b) Open wiring on insulators shall not be used (1) in commercial 
garages, (2) in theaters, (3) in motion-picture studios, (4) in hoistways, 
and (5) in hazardous locations, except in storage compartments of Class 
III locations as provided in Section 503-3 (b) . 



ARTICLE 320-OPEN WIRING 70-115 

320-3. Other Articles. In addition to the provisions of this Article, 
open wiring shall conform to the other applicable provisions of this 
Code. See especially Articles 300 and 730. 

320-4. Conductors. The type of conductors shall conform to Article 
310. Only single conductors shall be used. 

(a) The allowable ampacities of insulated conductors as shown in 
Article 310 shall apply to open wiring on insulators. 

320-5. Supports. 

(a) Conductors shall not be in contact with any object other than 
their insulating supports. They shall be rigidly supported on noncom- 
bustible, nonabsorptive insulating material as follows: 

(1) Under ordinary circumstances, supports for wiring over flat 
surfaces shall be not more than 4Vi feet apart. Where the conductors 
are likely to be disturbed, the distance between supports shall be short- 
ened sufficiently to provide adequate support for conductors; 

(2) Conductors shall be supported within 6 inches of a tap; 

(3) Conductors shall not be dead ended at a rosette, lampholder, 
or receptacle unless the last support is within 12 inches of the device. 

(b) The following exceptions to the provisions of Section 320-5 (a) 
may be permitted: 

Exception No. 1. For use of nonmetallic flexible tubing, see Sec- 
tion 320-7. 

Exception No. 2. Conductors of No. 8 or larger installed in the 
open across open spaces where not likely to be disturbed, may be sup- 
ported at distances not greater than 15 feet provided that approved 
noncombustible, nonabsorptive insulating separators assuring not 
less than 2 V2 -inch separation between conductors, are installed at inter- 
vals of not over 4V2 feet. 

Exception No. 3. In buildings of mill construction where not likely 
to be disturbed^ feeders in the open, not smaller than No. 8, may be 
separated about six inches and installed direct from timber to timber, 
being supported from each timber only. 

(c) When nails are used to mount knobs they shall not be smaller 
than 10 penny. When screws are used to mount knobs, or when nails 
or screws are used to mount cleats, they shall be of a length sufficient 
to penetrate the wood to a depth equal to at least one-half the height of 
the knob and fully the thickness of the cleat. Cushion washers shall be 
used with nails. 

320-6. Conductor Separation. Open conductors shall be separated as 
follows: 

(a) For voltage not exceeding 300 volts between conductors, 2Vi 
inches from each other and shall be separated from the surface wired 
over at least V2 inch in dry locations. 



70-116 MASSACHUSETTS ELECTRICAL CODE 

(b) For voltages of 301 to 600 volts between conductors, 4 inches 
from each other and shall be separated from surface wired over at least 
1 inch. 

(c) In damp or wet locations, a separation of at least 1 inch from the 
surface wired over shall be maintained for all voltages. 

320-7. Flexible Nonmetallic Tubing. In dry locations, when not ex- 
posed to severe physical damage, conductors may be separately en- 
cased in flexible tubing. Tubing shall be in continuous length not ex- 
ceeding 15 feet, and secured to the surface wired over by straps spaced 
not exceeding AV2 feet apart. 

320-8. Tie Wires. No. 8 or larger conductors supported on solid 
knobs shall be securely tied thereto. Tie wires shall have a covering 
equivalent to conductors which they confine. 

320-9. Passing Through Walls and Floors. Open conductors shall be 
separated from contact with walls, floors, timbers or partitions through 
which they pass by tubes or bushings of noncombustible, nonabsorp- 
tive insulating material. Where the bushing is shorter than the hole, a 
waterproof sleeve of noninductive material shall be inserted in the hole 
and an insulating bushing slipped into the sleeve at either end in such a 
manner as to keep the conductors absolutely out of contact with the 
sleeve. Each conductor must be carried through a separate tube or 
sleeve. 

320-10. Separation from Metal Work. Open conductors shall be sep- 
arated at least 2 inches from metallic conduit, piping, or other con- 
ducting material, and from any exposed lighting, power or signal con- 
ductor, or shall be separated therefrom by a continuous and firmly 
fixed nonconductor additional to the insulation of the conductor. 
Where any insulating tube is used, it shall be secured at the ends. De- 
viation from this requirement may, when necessary, be allowed by the 
authority enforcing this Code. 

320-11. Separation from Piping in Damp Locations. Open conductors 
located close to water pipes or tanks, or in other damp locations, shall 
be so placed that an air space will be permanently maintained between 
them and pipes which they cross. Where practicable, conductors shall 
be installed over, rather than under, pipes upon which moisture is likely 
to gather or which may leak. 

320-12. Protection from Physical Damage. Where open conductors 
cross ceiling joists and wall studs, and are exposed to physical dam- 
age, they shall be protected by one of the following methods. Conduc- 
tors within 7 feet from the floor shall be considered exposed to physi- 
cal damage. 

(a) By guard strips not less than % inch in thickness and at least 
as high as the insulating supports, placed on each side of and close to 
the wiring. 

(b) By a substantial running board at least Vi inch thick back of the 
conductors with side protections. Running boards shall extend at 
least 1 inch outside the conductors, but not more than 2 inches and 
the protecting sides shall be at least 2 inches high and at least % inch 
thick. 



ARTICLE 320-OPEN WIRING 70-117 

(c) By boxing made as above and furnished with cover kept at least 
1 inch away from the conductors within. Where protecting vertical 
conductors on side walls the boxing shall be closed at the top and the 
holes through which the conductors pass shall be bushed. 

(d) By rigid metal conduit or electrical metallic tubing, in which 
case the rules of Articles 346 or 348 shall apply; or by metal piping, in 
which case the conductors shall be encased in continuous lengths of 
approved flexible tubing. The conductors passing through metal en- 
closures shall be so grouped that current in both directions is approxi- 
mately equal. 

320-13. In Accessible Attics. Conductors in unfinished attics or roof 
spaces shall be installed in accordance with the provisions of Section 
324-8. 

320-14. Entering Spaces Subject to Dampness, Wetness or Corrosive 
Vapors. Conductors entering or leaving locations subject to dampness, 
wetness or corrosive vapors shall have drip loops formed on them and 
shall then pass upward and inward from the outside of buildings, or 
from the damp, wet, or corrosive location, through noncombustible, 
nonabsorptive insulating tubes. See also Sections 230-49 and 730-21. 

320-15. Switches. 

(a) Surface-type snap switches shall be mounted in accordance with 
the provisions of Section 380-10. Metal boxes are not required. See 
Section 380-3. 

(b) Other types of switches shall be installed in accordance with the 
provisions of Section 380-3. 



70-) 18 M ASSACHUSETTS ELECTRICAL CQD& 

ARTICLE 324 — CONCEALED KNOB-AND-TUBE WORK 



324-1. Definition. Concealed knob-and-tube wiring is a wiring method 
using knobs, tubes and flexible nonmetallic tubing for the protection 
and support of insulated conductors concealed in hollow spaces of walls 
and ceilings of buildings. 

324-2. Use. Concealed knob-and-tube work may be used in the hol- 
low spaces of walls and ceilings. It shall not be used ( 1 ) in commercial 
garages, (2) in theaters, except as provided in Section 520-4, (3) in 
motion-picture studios, nor (4) in hazardous locations. 

324-3. Other Articles. In addition to the provisions of this Article, 
concealed knob-and-tube wiring shall conform to the other applicable 
provisions of this Code. See especially Article 300. 

324-4. Conductors. Only single conductors shall be used. The ampacity 
and type of conductor shall conform to Article 310. 

324-5. Supports. Conductors shall be supported at intervals not ex- 
ceeding AVz feet by knobs or tubes of noncombustible, nonabsorptive, 
insulating material. There shall be a knob within 6 inches from each 
tap. Tie wires shall comply with Section 320-8. Where such support is 
impracticable and the conductors are in a dry location, they may be 
fished when separately enclosed in flexible nonmetallic tubing extending 
in continuous lengths from one support to the next or to a box, or from 
one box to another. 

324-6. Conductor Separation. 

(a) Conductors, shall be separated at least 3 inches and maintained 
at least 1 inch from the surface wired over. 

(b) At distributing centers, meters, outlets, switches or other places 
where space is limited and the 3-inch separation cannot be maintained, 
each conductor shall be encased in a continuous length of flexible tub- 
ing. 

(c) Where practicable, conductors shall be run singly on separate 
timbers or studding. 

324-7. Separation from Other Objects and Protection. Conductors shall 
be separated from other conductors and objects as follows : 

(a) The provisions as to rigid supporting and clearance from foreign 
wires and other objects, as specified for open wiring in Sections 320-9, 
320-10, 320-1 1, and 320-15, shall be complied with. 

(b) Conductors passing through cross timbers in plastered partitions 
shall be protected by an additional noncombustible, nonabsorptive in- 
sulating tube extending at least 3 inches above the timber. 

324-8. In Unfinished Attics and Roof Spaces. Conductors in unfinished 
attics or roof spaces shall comply with the following: 

(a) Conductors in unfinished attics and roof spaces shall be run 
through or on the sides of joists, studs and rafters, except in attics and 
roof spaces having head room at all points of less than 3 feet in build- 
ings completed before the wiring is installed. 



ARTICLE 328-BARE-CONDUCTOR FEEDERS 70-119 

(b) Where conductors in accessible unfinished attics or roof spaces 
reached by stairway or permanent ladder are run through bored holes 
in floor joists or through bored holes in studs or rafters within 7 feet of 
the floor or floor joists, such conductors shall be protected by substan- 
tial running boards extending at least 1 inch on each side of the con- 
ductors and securely fastened in place. 

(e) Where carried along the sides of rafters, studs or floor joists, 
neither running boards nor guard strips will be required. 

324-9. Boxes of Insulating Material. Nonmetallic outlet boxes may 
be used as provided in Sections 370-3 and 370-7. 

324-10. Switches. See Sections 380-3 and 380-10. 



ARTICLE 328 — BARE-CONDUCTOR FEEDERS 

328-1. Use. By special permission, bare conductors installed in ac- 
cordance with the provisions of Sections 300-1 to 300-22 inclusive and 
in accordance with the provisions of the following Sections 328-2 to 
328-7 inclusive may be used for feeders only. Such bare conductors 
may be installed only in a chase, channel or shaft of noncombustible 
material in a building of fire-resistive construction; and only where the 
voltage between conductors does not exceed 600 volts. Bare conductors 
shall not be used in damp or wet locations, nor in any hazardous loca- 
tion, nor where subject to corrosive vapor, except in storage-battery 
rooms as provided in Section 480-7. 

328-2. Size and Capacity of Copper Conductors. The maximum per- 
missible current shall be 1000 amperes per square inch of cross-sec- 
tional area of conductor in unventilated enclosures, and 1200 amperes 
per square inch in ventilated enclosures. These provisions are not in- 
tended to apply to equipment such as controls and switchgear. 

328-3. Branch Taps. Branch taps from bare-conductor feeders may 
be installed as specified in Section 240-15; provided that the mechani- 
cal protection specified by Exceptions No. 5 and 6 of Section 240-15 
shall not be required for that portion of the conductor located in the 
chase, channel or shaft. 

328-4. Accessibility. The conductors shall not be accessible to other 
than qualified persons. 

328-5. Supports. Conductors shall be supported as follows: 

(a) Conductors shall be supported on noncombustible, nonabsorp- 
tive insulating supports of adequate mechanical strength. 

(b) Conductors shall be so supported that a separation between con- 
ductors, and between conductors and ground, of not less than that 
specified in Section 384-26 will be maintained under all conditions of 
operation. 

328-6. Fire Cutoffs. Where floors are pierced, suitable cutoffs against 
vertical travel of fire shall be provided. See also Section 300-21. 



70-120 MASSACHUSETTS ELECTRICAL CODE 

328-7. Special Safeguards. In addition to the provisions of the pre- 
ceding sections, the authority enforcing this Code may require other 
safeguards in view of special conditions that may be met in a particular 
installation. 



ARTICLE 330 — MINERAL INSULATED-METAL 
SHEATHED CABLE 

Type MI 

A. General 

330-1. Definition and Construction. For the purpose of this Article, 
mineral insulated-metal sheathed Type MI cable is a cable in which 
one or more electrical conductors are insulated with a highly com- 
pressed refractory mineral insulation and enclosed in a liquidtight and 
gastight metallic tube sheathing. It shall be used with approved fittings 
for terminating and connecting to boxes, outlets and other equipment. 

330-2. Use. Mineral insulated-metal sheathed cable may be used for 
services, feeders and branch circuits in both exposed and concealed 
work, in dry or wet locations; in Class I, Class II, and Class III hazard- 
ous locations as noted in the appropriate Articles; for under plaster ex- 
tensions as provided in Article 344; and embedded in plaster finish on 
brick or other masonry. It may be used where exposed to weather or 
continuous moisture, for underground runs and embedded in masonry, 
concrete or fill, in buildings in course of construction or where exposed 
to oil, gasoline, or other conditions not having a deteriorating effect on 
the metal sheath. The sheath of mineral insulated-metal sheathed cable 
exposed to destructive corrosive conditions, such as some types of cin- 
der fill, shall be protected by materials suitable for those conditions. 

330-3. Other Articles. In addition to the provisions of this Article, the 
installation of mineral insulated-metal sheathed cable shall comply 
with the other applicable provisions of this Code. See especially Article 
300. 

B. Installation 

330-4. Supports. Mineral insulated-metal sheathed cable shall be se- 
curely supported by approved staples, straps, hangers or similar fit- 
tings, so designed and installed as not to injure the cable. Cable shall be 
secured at intervals not exceeding 6 feet except where cable is fished. 

330-5. Through Studs, Joists and Rafters. See Section 300-8. 

330-6. Wet Locations. See Section 300-5. 

330-7. Bends. All bends shall be so made that the cable will not be 
damaged and the radius of the curve of the inner edge of any bend shall 
be not less than 5 times the diameter of the cable. 

330-8. Terminating Seal. At all points where mineral insulated-metal 
sheathed cable terminates an approved seal shall be provided imme- 
diately after stripping to prevent entrance of moisture into the mineral 



ARTICLE 331-ALUMINUM SHEATHED CABLE 70-121 

insulation. The conductors extending beyond the sheath shall be in- 
sulated with an approved insulating material. 

330-9. Fittings. When Type MI cable is connected to boxes or equip- 
ment, the fittings shall be approved for the conditions of service. When 
single conductor Type MI cables enter metal boxes through separate 
openings, refer to Section 300-20. 

330-10. Insulation Resistance. The completed wiring system shall be 
tested for insulation resistance in accordance with Section 1 10-20. 

C. Construction Specifications 

330-11. General. Type MI Cable for 600 volts shall conform to the 
following: 

(a) Conductors. The conductors are solid copper and have cross 
sectional areas corresponding to the standard American Wire Gage 
sizes. 

(b) Insulation. The insulation is a highly compressed refractory 
mineral which provides proper spacing for the conductors. 

(c) Outer Sheath. The outer sheath shall be of a continuous copper 
construction to provide mechanical protection and a moisture seal, 
and an adequate path for grounding purposes. 



ARTICLE 331 — ALUMINUM SHEATHED CABLE 

Type ALS 

A. General 

331-1. Definition and Construction. Aluminum sheathed type ALS 
cable is a factory assembled cable consisting of one or more insulated 
conductors enclosed in an impervious, continuous, closely fitting tube 
of aluminum. It shall be used with approved fittings for terminating 
and connecting to boxes, outlets and other equipment. 

331-2. Use. Aluminum sheathed cable may be used in both exposed 
and concealed work, in dry or wet locations. The sheath of aluminum 
sheathed cable exposed to destructive corrosive conditions such as en- 
vironments containing strong chlorides or caustic alkalis, or where 
vapors of chlorine or hydrochloric acid are present or where the cable 
is installed underground, shall be protected by materials suitable for 
those conditions. See Section 300-5. 

Aluminum sheathed cable and fittings shall not be embedded or 
buried directly in concrete or used in areas subject to severe corrosive 
influences unless suitable supplemental corrosion protection is provided. 

See Section 310-6. 

331-3. Other Articles. In addition to the provisions of this Article, 
the installation of aluminum sheathed cable shall comply with the other 
applicable provisions of this Code. See especially Article 300. 



70-122 MASSACHUSETTS ELECTRICAL CODE 

B. Installations 

331-4. Supports. Aluminum sheathed cable shall be securely sup- 
ported by staples, straps, hangers, or similar fittings so designed and 
installed as not to injure the cable. Cable shall be secured at intervals 
not exceeding 6 feet except where the cable is fished. 

331-5. Through Studs, Joists and Rafters. See Section 300-8. 

331-6. Wet Locations. See Section 300-5. 

331-7. Bends. All bends shall be so made that the cable will not be 
damaged and the radius of the curve on the inner edge of any bend 
shall be not less than: 

(a) Ten times the external diameter of the sheath for cable not more 
than 3 A inch in external diameter. 

(b) Twelve times the external diameter of the sheath for cable more 
than 3 A inch but not more than \Vi inches in external diameter; and 

(c) Fifteen times the external diameter of the sheath for cable more 
than 1 Vi inches in external diameter. 

331-8. Fittings. When aluminum sheathed cable is connected to boxes 
or equipment, the fittings shall be approved for the conditions of serv- 
ice. When single conductor aluminum sheathed cables enter metal 
boxes through separate openings refer to Section 300-20. 

C. Construction 

331-9. General. Type ALS cable shall conform to the following: 

(a) Conductors. The conductors shall be copper or electrical con- 
ductor (EC) grade aluminum, solid or stranded. 

(b) Insulation. The insulation shall be a type listed in Table 
310-2(b). 

(c) Insulation Covering. The covering over the insulation shall be 
the same as permitted for lead sheathed cable or multiple conductor 
cable. 

(d) Outer Sheath. The outer sheath shall be of a continuous, closely 
fitting tube of aluminum to provide mechanical protection, a moisture 
seal and an adequate path for equipment grounding purposes and shall 
conform with provisions of Section 331-2. The sheath shall not be used 
as a current-carrying conductor. 



ARTICLE 334 — METAL-CLAD CABLE 



Type MC and AC Series 

334-1. Definition. A metal-clad cable is a fabricated assembly of in- 
sulated conductors in a flexible metallic enclosure. See Section 334-4. 

334-2. Voltage. See Section 300-2. For systems in excess of 600 volts 
see Article 710. 



ARTICLE 334-METAL-CLAD CABLE 70-123 

334-3. Marking. The provisions of Section 310-2 shall apply, except 
that AC cable shall have ready identification of the maker by distinctive 
external markers in the cable sheath throughout its entire length. 

334-4. Construction. Metal-clad cable shall be an approved cable of 
Type MC or AC Series, with acceptable metal covering. The insulated 
conductors shall conform with Section 334-5. 

(a) Type MC. Type- MC cables are power cables limited in size, for 
the voltages of this article, to conductors of No. 4 AWG and larger for 
copper and No. 2 AWG and larger for aluminum. The metal enclosures 
shall be either a covering of interlocking metal tape, or an impervious, 
close fitting, corrugated tube. Supplemental protection of an outer cov- 
ering of corrosion-resistant material shall be required where such pro- 
tection is needed. See Section 300-5. The cables shall provide adequate 
path for grounding purposes. 

(b) Type AC. Type AC cables are branch circuit and feeder cables 
with armor of flexible metal tape. Cables of the AC type, except ACL, 
shall have an internal bonding strip of copper or aluminum, in intimate 
contact with the armor for its entire length. 

334-5. Conductors. Conductors for metal-clad cable shall conform 
with the following : 

(a) Type MC. For cables of Type MC, insulated conductors shall 
be of a type listed in Table 310-2(b) for rubber, thermoplastic, var- 
nished cloth, asbestos-varnished cloth, or of a type especially approved 
for the purpose. 

(b) Type AC. For cables of Type AC, insulated conductors shall 
be of a type listed in Table 310-2(b). In addition, the conductors shall 
have an over-all moisture-resistant and flre-retardant fibrous covering; 
for Type ACT, a moisture-resistant fibrous covering is required only 
on the individual conductors. 

334-6. Use. Except where otherwise specified elsewhere in this Code, 
and where not subject to physical damage, metal-clad cable may be in- 
stalled for branch circuits and feeders in both exposed and concealed 
work as follows: 

(a) Type MC. This type of power cable may be used in partially 
protected areas, such as in continuous rigid cable supports and the like, 
in dry locations and when any of the following conditions are met it 
may be used in wet locations : 

(1 ) The metallic covering is impervious to moisture. 

(2) A lead sheath or moisture impervious jacket is provided un- 
der the metal covering. 

(3) The insulated conductors under the metallic covering are ap- 
proved for use in wet locations. 

See Section 300-5. 

(b) Type AC. Metal-clad cable of the AC type may be used in dry 
locations; for under plaster extensions as provided in Article 344; and 
embedded in plaster finish on brick or other masonry, except in damp 
or wet locations. This cable may be run or fished in the air voids of 



70-124 MASSACHUSETTS ELECTRICAL C ODE 

masonry block or tile walls; where such walls are exposed or subject to 
excessive moisture or dampness or are below grade line, Type ACL 
cable shall be used. This cable shall contain lead-covered conductors 
(Type ACL), if used where exposed to the weather or to continuous 
moisture, for underground runs and embedded in masonry, concrete 
or fill in buildings in course of construction, or where exposed to oil, 
or other conditions having a deteriorating effect on the insulation. Type 
AC metal-clad cable shall not be used where prohibited elsewhere in 
this Code, including ( 1 ) in theatres, except as provided in Section 520-4; 
(2) in motion-picture studios; (3) in any hazardous locations; (4) where 
exposed to corrosive fumes or vapors; (5) on cranes or hoists, except as 
provided in Section 610-11 Exception No. 3; (6) in storage battery 
rooms; (7) in hoistways or on elevators, except as provided in Section 
620-21 ; or (8) commercial garages where prohibited in Article 511. 

334-7. Other Articles. In addition to the provision of this Article, 
metal-clad cable shall conform to other applicable provisions of this 
Code. See especially Article 300. 

334-8. Supports. Metal-clad cable shall be secured by approved sta- 
ples, straps, hangers or similar fittings so designed and installed as not 
to injure the cable. 

(a) Type MC cable shall be secured at intervals not exceeding six feet, 
and within two feet from every box or fitting, except where cable is 
fished. Cable may be installed on metal racks, trays, troughs, or con- 
tinuous rigid cable supports grounded as required by Article 250. The 
cables shall be separated from each other by a distance of not less than 
one-quarter of a cable diameter. There shall be no more than one layer 
of cables on a rack or other support member; each cable so installed 
shall be supported at intervals not exceeding six feet and within two 
feet from every box or fitting, and each cable shall be attached to the 
support at intervals of not more than ten feet horizontally and two feet 
vertically. 

(b) Type AC cable shall be secured at intervals of not exceeding AV2 
feet and within 12 inches from every outlet box or fitting, except where 
cable is fished and except lengths of not over 24 inches at terminals 
where flexibility is necessary. 

334-9. Bends. All bends shall be so made that the cable will not be 
injured, and the radius of the curve of the inner edge of any bend shall 
not be less than 7 times the diameter of Type MC cable nor 5 times the 
diameter of Type AC cable. 

334-10. Boxes and Fittings. 

(a) At all points where Type MC metal-clad cable terminates, suit- 
able fittings designed for use with the particular wiring cable and the 
conditions of service, shall be used. 

(b) At all points where the armor of AC cable terminates, a fitting 
shall be provided to protect wires from abrasion, unless the design of 
the outlet boxes or fittings is such as to afford equivalent protection, 
and in addition, an approved insulating bushing or its equivalent ap- 
proved protection shall be provided between the conductors and the 
armor. The connector or clamp by which the metal-clad cable is fas- 



ARTICLE 336 — NONMETALLIC SHEATHED CABLE 70-125 

tened to boxes or cabinets shall be of such design that the insulating bushing 
or its equivalent will be visible for inspection. This bushing is not required 
with lead-covered cables which shall be so installed that the lead sheath 
will be visible for inspection. Where change is made from metal-clad cable 
to other cable or raceway wiring methods, a box shall be installed at junction 
point as required in Section 300-15. 

334-11. Through Studs, Joists and Rafters. See Section 300-8. 

334-12. Exposed Work. Exposed runs of cable shall closely follow the 
surface of the building finish or of running boards, except: 

(a) Lengths of not more than 24 inches at terminals where flexibility is 
necessary. 

(b) Where suitably supported in accordance with Section 334-8(a). 

(c) On the underside of floor joists in basements where supported at each 
joist and so located as not to be subject to physical damage. 

334-13. In Accessible Attics. Type AC cables in accessible attics or roof 
spaces shall be installed as follows: 

(a) Where run across the top of floor joists, or within 7 feet of floor or 
floor joists across the face of rafters or studding, in attics and roof spaces 
which are accessible, the cable shall be protected by substantial guard strips 
which are at least as high as the cable. Where this space is not accessible by 
permanent stairs or ladders, protection will only be required within 6 feet 
of the nearest edge of scuttle hole or attic entrance. 

(b) Where cable is carried along the sides of rafters, studs or floor joists, 
neither guard strips nor running boards shall be required. 



ARTICLE 336 — NONMETALLIC 
SHEATHED CABLE 

Types NM and NMC 

336-1. Definition. A nonmetallic sheathed cable is an assembly of two or 

more insulated conductors having an outer sheath of moisture-resistant, 
flame-retardant, nonmetallic material. 

336-2. Construction. 

Non-metallic sheathed cable shall be an approved Type NM or NMC in sizes 
No. 14 through 2 AWG with copper conductors and in sizes No. 12 through 
2 AWG with aluminum conductors. 

(a) Type NM. The conductors shall comply with the requirements for the 
type of conductor used. Over-all fibrous coverings shall have a flame-re- 
tardant and moisture-resistant finish. 

(b) Type NMC. The cable shall be of a type approved for the purpose. 
The over-all covering shall be flame-retardant, moisture-resistant, fungus- 
resistant and corrosion-resistant. 

(c) Marking. In addition to the provisions of Section 310-2, the cable 
shall have a distinctive marking on the exterior for its entire 'ength specifying 
cable type. 



70-126 MASSACHUSETTS ELECTRICAL CODE 

336-3. Use. Nonmetallic sheathed cable may be installed for both ex- 
posed and concealed work as follows: 

(a) Type NM. This type of nonmetallic sheathed cable may be in- 
stalled for both exposed and concealed work in normally dry locations. 
It may be installed or fished in air voids in masonry block or tile walls 
where such walls are not exposed or subject to excessive moisture or 
dampness. Type NM cable shall not be installed where exposed to cor- 
rosive fumes or vapors; nor shall it be imbedded in masonry, concrete, 
fill or plaster; nor run in shallow chase in masonry or concrete and cov- 
ered with plaster or similar finish. 

(b) Moisture and Corrosion-Resistant Type NMC. This type of non- 
metallic sheathed cable may be installed for both exposed and con- 
cealed work in dry, moist, damp or corrosive locations, and in outside 
and inside walls of masonry block or tile. Where embedded in plaster 
or run in a shallow chase in masonry walls and covered with plaster 
within 2 inches of the finished surface, it shall be protected against 
damage from nails by a cover of corrosion-resistant coated steel at least 
1/16 inch in thickness and 3 A inch wide in the chase or under the final 
surface finish. 

(c) Uses Not Permissible for Either Type NM or NMC Nonmetallic 
Sheathed Cable. These types shall not be used as: ( 1 ) service-entrance 
cable, (2) in commercial garages, (3) in theatres except as provided in 
Section 520-4, (4) in motion picture studios, (5) in storage battery 
rooms, (6) inhoistways, (7) in any hazardous location, (8) embedded in 
poured cement, concrete or aggregate. 

336-4. Other Articles. In addition to the provisions of this Article, 
installations of nonmetallic sheathed cable shall conform to the other 
applicable provisions of this Code. See especially Article 300. 

336-5. Supports. Nonmetallic sheathed cable shall be secured by ap- 
proved staples, straps, or similar fittings, so designed and installed as 
not to injure the cable. Cable shall be secured in place at intervals not 
exceeding 4Vi feet and within 12 inches from every cabinet, box or 
fitting, except that in concealed work in finished buildings or finished 
panels for prefabricated buildings where such supporting is impractica- 
ble, the cable may be fished between points of access. 

336-6. Exposed Work — General. In exposed work, except as provided 
in Sections 336-8 and 336-9, the cable shall be installed as follows: 

(a) The cable shall closely follow the surface of the building finish 
or of running boards. 

(b) It shall be protected from physical damage where necessary, by 
conduit, pipe, guard strips or other means. Where passing through a 
floor the cable shall be enclosed in rigid metal conduit or metal pipe ex- 
tending at least 6 inches above the floor. 

336-7. Through Studs, Joists and Rafters. See Section 300-8. 

336-8. In Unfinished Basements. Where the cable is run at angles 
with joists in unfinished basements, assemblies not smaller than two No. 
6 or three No. 8 conductors may be secured directly to the lower edges 
of the joists; smaller assemblies shall either be run through bored holes 



ARTICLE 338-SERVICE-ENTRANCE CABLE 70-127 

in the joists or on running boards. Where run parallel to joists, cable 
of any size shall be secured to the sides or face of the joists. 

336-9. In Accessible Attics. Cable in accessible attics or roof spaces 
shall also conform with Section 334-13. 

336-10. Bends. Bends in cable shall be so made, and other handling 
shall be such, that the protective coverings of the cable will not be in- 
jured, and no bend shall have a radius less than 5 times the diameter of 
the cable. 

336-11. Devices of Insulating Material. Switch, outlet, and tap devices 
of insulating material may be used without boxes in exposed cable 
wiring, and for concealed work for rewiring in existing buildings where 
the cable is concealed and fished. Openings in such devices shall form 
a close fit around the outer covering of the cable and the device shall 
fully enclose that part of the cable from which any part of the cover- 
ing has been removed. 

Where connections to conductors are by binding screw terminals, 
there shall be available as many terminals as conductors, unless cables 
are clamped within the structure and terminals are of a type approved 
for multiple conductors. 

336-12. Boxes of Insulating Material. Nonmetallic outlet boxes ap- 
proved for the purpose may be used as provided in Section 370-3. 



ARTICLE 338 — SERVICE-ENTRANCE CABLE 



Types SE and USE 

338-1. Definition. Service-entrance cable is a conductor assembly pro- 
vided with a suitable over-all covering, primarily used for services and 
of the following types. When consisting of two or more conductors, one 
may be without individual insulation. 

(a) Type SE, having a flame-retardant, moisture-resistant covering, 
but not required to have inherent protection against mechanical abuse. 

(b) Type USE, recognized for underground use, having a moisture- 
resistant covering, but not required to have a flame-retardant covering 
or inherent protection against mechanical abuse. 

338-2. Use as Service-Entrance Conductors. Service-entrance cable 
used as service-entrance conductors shall be installed as required by 
Article 230. 

338-3. Use as Branch Circuit or Feeders. 

(a) Service-entrance cables may be used in interior wiring systems 
where all of the circuit conductors of the cable are of the rubber-cov- 
ered or thermoplastic type. 

(b) Service entrance cables without individual insulation on the 
grounded circuit conductor shall not be used as a branch circuit or as 
a feeder within a building, except a cable which has a final nonmetallic 



70-72 8 MASSACHUSETTS ELECTRICAL CODE 

outer covering and when supplied by alternating current at not exceed- 
ing 150 volts to ground, may be used: ( 1 ) As a branch circuit to supply 
only a range, wall-mounted oven, counter-mounted cooking unit, or 
clothes dryer, or (2) as a feeder to supply only other buildings on the 
same premises. It shall not be used as a feeder terminating within the 
same building in which it originates. 

The above provisions do not intend to deny the use of service entrance 
cable for interior use when the fully insulated conductors are used for cir- 
cuit wiring and the uninsulated conductor is used for equipment grounding 
purposes. 

(c) Service-entrance cable used to supply appliances shall not be sub- 
ject to conductor temperatures in excess of the temperature specified 
for the type of insulation involved. 

338-4. Installation Methods. 

(a) In addition to the provisions of this Article, service-entrance 
cable used for interior wiring shall comply with the applicable pro- 
visions of Article 300. 

(b) Unarmored cable shall be installed in accordance with the ap- 
plicable provisions of Article 336. 

(c) Cables through studs, joists and rafters shall be installed as re- 
quired in Section 300-8. 

338-5. Marking. Service-entrance cable shall conform with the mark- 
ing required in Section 310-2. Cable with the neutral conductor smaller 
than the ungrounded conductors shall be so marked. 



ARTICLE 339 — UNDERGROUND FEEDER AND 
BRANCH CIRCUIT CABLE 

Type UF 

339-1. Description and Marking. 

(a) Description. Underground feeder and branch circuit cable shall 
be an approved Type UF cable in sizes No. 14 to No. 4/0 AWG, in- 
clusive. The conductors shall be Types TW, RHW, or other conduc- 
tors approved for the purpose. In addition to the insulated conductors, 
the cable may have an approved size of uninsulated or bare conductor 
for grounding purposes only. The over-all covering shall be flame- 
retardant, moisture-resistant, fungus-resistant and corrosive-resistant, 
and suitable for direct burial in the earth. 

(b) Marking. In addition to the provisions of Section 310-2, the 
cable shall have a distinctive marking on the exterior for its entire length 
specifying cable type. 

339-2. Other Articles. In addition to the provisions of this Article, 
installations of underground feeder and branch circuit cable (Type 
UF) shall comply with other applicable provisions of this Code. See 
especially Article 300, and Section 310-2(b). 



ARTICLE 342-NONMETALLIC EXTENSIONS 70-129 

339-3. Use. 

(a) Underground feeder and branch circuit cable may be used un- 
derground, including direct burial in the earth, as feeder or branch cir- 
cuit cable when provided with overcurrent protection of the rated 
ampacity as required in Section 339-4. 

(b) Where single conductor cables are installed, all cables of the 
feeder circuit, sub-feeder circuit, or branch circuit, including the neu- 
tral conductor, if any, shall be run together in the same trench or race- 
way. 

(c) A minimum depth of 1 8 inches shall be maintained for conduc- 
tors and cables buried directly in the earth, when supplementary pro- 
tection from physical injury such as a covering board, concrete pad, 
raceway, etc., is not provided. 

(d) Type UF cable may be used for interior wiring in wet, dry, or 
corrosive locations under the recognized wiring methods of this Code, 
and when installed as nonmetallic sheathed cable it shall conform with 
the installation provisions of Article 336 and shall be of the multiple 
conductor type, except where recognized under the provisions of Sec- 
tion 422-44. 

(e) This type of cable shall not be used: (1) as service-entrance ca- 
bles; (2) in commercial garages; (3) in theatres except as provided in 
Section 520-4; (4) in motion picture studios; (5) in storage battery 
rooms; (6) in hoistways; (7) in any hazardous location; (8) embedded 
in poured cement, concrete or aggregate, except where recognized in 
Article 422; (9) when exposed to direct rays of the sun, unless ap- 
proved for the purpose. 

339-4. Overcurrent Protection. Overcurrent protection shall be pro- 
vided in accordance with provisions of Section 240-5. 

339-5. Rated Ampacity. The ampacities of conductors in Type UF 
cable shall be according to Tables 310-12 and 310-14. 



ARTICLE 342 — NONMETALLIC EXTENSIONS 



342-1. Description. Nonmetallic extensions are an assembly of two 
insulated conductors within a nonmetallic jacket or an extruded ther- 
moplastic covering. The classification includes both surface extensions, 
intended for mounting directly on the surface of walls or ceilings, and 
aerial cable, containing a supporting messenger cable as an integral 
part of the cable assembly. 

342-2. Other Articles. In addition to the provisions of this Article, 
nonmetallic extensions shall conform to other applicable provisions of 
this Code. 

342-3. Use Permitted. Nonmetallic extensions may be used only 
where all of the following conditions are met: 

(a) The extension is from an existing outlet on a 15 or 20 ampere 
branch circuit in conformity with the requirements of Article 210. 



70-130 M ASSACHUSETTS ELECTRICAL CODE 

(b) The extension is run exposed and in a dry location. 

(c) For nonmetallic surface extensions, the building is occupied for 
residential or office purposes. 

(d) For aerial cable, the building is occupied for industrial pur- 
poses, and the nature of the occupancy requires a highly flexible means 
for connecting equipment. 

342-4. Use Prohibited. Nonmetallic extensions shall not be installed: 

(a) As aerial cable to substitute for one of the general wiring meth- 
ods specified by this Code. 

(b) In unfinished basements, attics, or roof spaces. 

(c) Where voltage between conductors exceeds 150 volts for non- 
metallic surface extension and 300 volts for aerial cable. 

(d) Where subject to corrosive vapors. 

(e) Where run through a floor or partition, or outside the room in 
which it originates. 

342-5. Splices and Taps. Extensions shall consist of a continuous un- 
broken length of the assembly, without splices, and without exposed 
conductors between fittings. Taps may be made where approved fittings 
completely covering the tap connections are used. Aerial cable and its 
tap connectors shall be provided with an approved means for polariza- 
tion. Receptacle type tap connectors shall be of the locking type. 

342-6. Fittings. Each run shall terminate in a fitting which covers the 
end of the assembly. All fittings and devices shall be of a type approved 
for the purpose. 

342-7. Installation. Nonmetallic extensions shall be installed in con- 
formity with the following requirements: 

(a) Nonmetallic Surface Extensions. 

(1) One or more extensions may be run in any direction from an 
existing outlet, but not on the floor or within 2 inches from the floor. 

(2) Nonmetallic surface extensions shall be secured in place by 
approved means at intervals not exceeding 8 inches, except that where 
connection to the supplying outlet is made by means of an attachment 
plug the first fastening may be placed 12 inches or less from the plug. 
There shall be at least one fastening between each two adjacent outlets 
supplied. An extension shall be attached only to woodwork or plaster 
finish, and shall not be in contact with any metal work or other con- 
ductive material except with metal plates on receptacles. 

(3) A bend which reduces the normal spacing between the conduc- 
tors shall be covered with a cap to protect the assembly from physical 
damage. 

(b) Aerial Cable. 

(1) Aerial cable shall be supported by its messenger cable, securely 
attached at each end with approved clamps and turnbuckles. Interme- 
diate supports shall be provided at not more than 20 foot intervals. 
Cable tension shall be adjusted to eliminate excessive sag. The cable 
shall have a clearance of not less than 2 inches from steel structural 
members or other conductive material. 



ARTICLE 344-UNDERPLASTER EXTENSIONS 70-131 

(2) Aerial cable shall have a clearance of not less than 10 feet 
above floor areas accessible to pedestrian traffic, and not less than 14 
feet above floor areas accessible to vehicular traffic. 

(3) Cable suspended over work benches, not accessible to pedes- 
trian traffic, shall have a clearance of not less than 8 feet above the 
floor. 

(4) Aerial cable may serve to support lighting fixtures when the 
total load on the supporting messenger cable does not exceed that for 
which the assembly is intended. 

(5) The supporting messenger cable, when conforming to the ap- 
plicable provisions of Article 250 and when properly identified as a 
grounding conductor, may be used for the grounding of equipment. 
The messenger cable shall not be used as a branch circuit conductor. 



ARTICLE 344 — UNDERPLASTER EXTENSIONS 



344-1. Use. An underplaster extension installed as permitted by this 
Article, may be used only for extending an existing branch circuit in a 
building of fire-resistive construction. 

344-2. Materials. Such extensions shall be run in rigid or flexible con- 
duit, Type AC metal-clad cable, electrical metallic tubing, Type MI 
cable or metal raceways approved for the purpose. Standard sizes of 
conduit, cable, tubing and raceways shall be used except that for a 
single conductor only conduit or tubing having not less than 5/16 inch 
inside diameter, single-conductor Type AC metal-clad cable or single 
conductor Type MI cable may be used. 

344-3. Box and Fittings. See Article 370. 

344-4. Installation. An underplaster extension shall be laid on the face 
of masonry or other material and buried in the plaster finish of ceilings 
or walls. The methods of installation of the raceway or cable for such 
extension shall be as specified elsewhere in this Code for the particular 
type of material used. 

344-5. Extension to Another Floor. No such extension shall extend 
beyond the floor on which it originates unless installed in a standard 
size of rigid metal conduit, electrical metallic tubing, Type AC metal- 
clad cable, or MI cable. 



ARTICLE 346 — RIGID METAL CONDUIT 



Note: Where conduit is threaded in the field, it is assumed that a stand- 
ard conduit cutting die providing % inch taper per foot will be employed. 

346-1. Use. Rigid metal conduit may be used under all atmospheric 



70-132 MASSACHUSETTS ELECTRICAL CODE 

conditions and occupancies, except that ferrous raceways and fittings pro- 
tected from corrosion solely by enamel may be used only indoors and in 
occupancies not subject to severe corrosive influences. Where practicable 
dissimilar metals in contact anywhere in the system shall be avoided to 
eliminate the possibility of galvanic action. 

Unless made of a material judged suitable for the condition, or unless corro- 
sion protection approved for the condition is provided, aluminum, ferrous or 
non-ferrous metallic conduit, elbows, couplings, and fittings shall not be 
installed in concrete or in direct contact with the earth, or in areas subject to 
severe corrosive influences. Where dissimilar metals are used in conductors 
and couplings, the effects of galvanic action shall be eliminated by use of 
an approved material. 

See Section 300-5 for limitation in the use of ferrous raceways and fittings 
protected from corrosion solely by enamel. 

346-2. Other Articles. Installations of rigid metal conduit shall comply with 
the provisions of the applicable Sections of Article 300. 

A. Installation 

346-3. Cinder Fill. Conduit, unless of corrosion-resistant material suitable 

for the purpose shall not be used in or under cinder fill where subject to per- 
manent moisture unless protected on all sides by a layer of noncinder con- 
crete at least 2 inches thick or unless the conduit is at least 18 inches under 
the fill. 

346-4. Wet Locations. All supports, bolts, straps, screws, etc., shall be of 
corrosion-resistant materials or protected against corrosion by approved cor- 
rosion-resistant materials. 

See Section 300-5. 

346-5. Minimum Size. No conduit smaller than Vi inch, electrical trade 

size, shall be used, except as provided for underplaster extensions in Article 
344, and for enclosing the leads of motors as permitted in Section 430- 
145(b). 

346-6. Number of Conductors in Conduit. The number of conductors per- 
mitted in a single conduit shall be as follows: 

(a) New Work: 

(1) Where conductors are all of the same size, use Tables 1 and 2 of 
Chapter 9. 

(2) Where conductors are of various sizes to be used in combination, 
use Tables 3 and 4 of Chapter 9 and the dimensions of Column 3 of Table 
5 of Chapter 9. Where bare conductors are permitted by other Sections of 
this Code, the dimensions for bare conductors in Table 8 of Chapter 9 may 
be used. 

(b) Rewiring Existing Conduits: 

(1) For rewiring existing conduits where conductors are all of the same 
size use Tables 1, 1 A, and IB of Chapter 9. 

(2) Where conductors are of various sizes to be used in combination 
use Tables 3 and 4 of Chapter 9, and the dimensions of Column 3, 5, or 7 
of Table 5, Chapter 9. 



ARTICLE 346-RIGID METAL CONDUIT 



70-133 



Where bare conductors are permitted by other Sections of this Code, 
the dimensions for bare conductors in Table 8 of Chapter 9 may be 
used. 

346-7. Reaming. All cut ends of conduits shall be reamed to remove 
rough edges. 

346-8. Bushings. Where a conduit enters a box or other fitting, a 
bushing shall be provided to protect the wire from abrasion unless the 
design of the box or fitting is such as to afford equivalent protection. 
See Section 373-6 (b) for the protection of conductors at bushings. 

346-9. Couplings. 

(a) Threadless couplings and connectors used with conduit shall be 
made tight, Where installed in wet places or where buried in masonry, 
concrete, or fill, they shall be of a type to prevent water from entering 
the conduit. 

(b) Running threads shall not be used on conduit for connection at 
couplings. 

346-10. Bends — How Made. Bends of rigid conduit shall be so made 
that the conduit will not be injured, and that the internal diameter of 
the conduit will not be effectively reduced. The radius of the curve of 
the inner edge of any field bend shall not be less than shown in Table 
346-10. 

Table 346-10 
Radius of Conduit Bends 



Size of 
Conduit 



y 2 

i 

i% 

1% 

2 

2V 2 

3 

3V 2 

4 

5 

6 



in. 
in. 
in. 
in. 
in. 
in. 
in. 
in. 
in. 
in. 
in. 
in. 



Conductors 

Without 
Lead Sheath 


Conductors 

With 
Lead Sheath 


4 in. 


6 in. 


5 in. 


8 in. 


6 in. 


11 in. 


8 in. 


14 in. 


10 in. 


16 in. 


12 in. 


21 in. 


15 in. 


25 in. 


18 in. 


31 in. 


21 in. 


36 in. 


24 in. 


40 in. 


30 in. 


50 in. 


36 in. 


61 in. 



346-1 1. Bends — Number in One Run. A run of conduit between outlet 
and outlet, between fitting and fitting, or between outlet and fitting shall 
not contain more than the equivalent of 4 quarter bends (360 degrees, 
total), including those bends located immediately at the outlet or fitting. 



70-134 



MASSACHUSETTS ELECTRICAL CODE 



346-12. Supports. Rigid metal conduit shall be installed as a complete 
system as provided in Article 300 and shall be securely fastened in 
place. Conduit shall be firmly fastened within 3 feet of each outlet box, 
junction box, cabinet, or fitting. Conduit shall be supported at least 
every ten feet except that straight runs of rigid conduit made up with 
approved threaded couplings may be secured in accordance with Table 
346-12, provided such fastening prevents transmission of stresses to 
terminus when conduit is deflected between supports. 



Table 346-12 





Maximum distance 






between rigid metal 




Conduit Size 


cond 


uit supports 




(Inches) 




(Feet) 




Vi 




10 




Va 




10 




1 




12 




Wa 




14 




11/2 




14 




2 




16 




2V4 




16 




3 




20 





346-13. Boxes and Fittings. See Article 370. 

B. Construction Specifications 
346-14. General. Rigid metal conduit shall conform to the following: 

(a) Rigid conduit as shipped shall be in standard lengths of 10 feet 
including coupling, one coupling to be furnished with each length. Each 
length shall be reamed and threaded on each end. For specific applica- 
tions or uses, lengths shorter or longer than 10 feet, with or without 
couplings, may be shipped. 

(b) Steel conduit shall have an interior coating of a character and 
appearance so as to readily distinguish it from ordinary pipe commonly 
used for other than electrical purposes. 

(c) Nonferrous conduit of corrosion-resistant material shall have 
suitable markings. 

(d) Each length shall be clearly and durably identified in every 10 
feet with the manufacturer's name or trademark and type of material. 



ARTICLE 347-RIGID NONMETALLIC CONDUIT 70-135 

ARTICLE 347 — RIGID NONMETALLIC CONDUIT 



347-1. Description. The provisions of this Article shall apply to a type 
of conduit and fittings of suitable nonmetallic material which is resist- 
ant to moisture and chemical atmospheres. For use above ground, it 
shall also be flame retardant, resistant to impact and crushing, shall re- 
sist distortion due to heat under conditions likely to be encountered in 
service and shall be resistant to low temperature and sunlight effects. 
For use underground, the material shall be acceptably resistant to 
moisture and corrosive agents and shall be of sufficient strength to 
withstand abuse, such as by impact and crushing, in handling and dur- 
ing installation. Where intended for direct burial, without encasement 
in concrete, the material shall also be capable of withstanding con- 
tinued loading which is likely to be encountered after installation. 

Materials which have been recognized as having suitable physical charac- 
teristics when properly formed and treated include fiber, asbestos cement, 
soapstone, rigid polyvinyl chloride and high density polyethylene for under- 
ground use and rigid polyvinyl chloride for use above ground. 

347-2. Use Permitted. Rigid nonmetallic conduit and fittings ap- 
proved for the purpose may be used under the following conditions 
and where the potential is 600 volts or less except as noted in Section 
347-3. 

(a) Underground if encased in not less than two inches of con- 
crete. 

(b) Direct earth burial if of a type approved for the purpose and if 
buried not less than 24 inches below the surface. 

(c) In concrete walls, floors and ceilings. 

(d) In locations subject to severe corrosive influences as set forth in 
Section 300-5 and where subject to chemicals for which the materials 
are specifically approved. 

(e) Cinder fill. 

(f) Wet Locations. In portions of dairies, laundries, canneries or 
other wet locations and in locations where walls are frequently washed, 
the entire conduit system including boxes and fittings used therewith 
shall be so installed and equipped as to prevent water from entering the 
conduit. All supports, bolts, straps, screws, etc., shall be of corrosion- 
resistant materials or protected against corrosion by approved corro- 
sion-resistant materials. 

(g) In dry and damp locations not prohibited by Section 347-3. 
347-3. Use Prohibited. Rigid nonmetallic conduit shall not be used: 

(a) Less than 8 feet above ground outdoors unless protected against 
physical damage. 

(b) In hazardous locations except as covered in Section 514-8. 

(c) In the concealed spaces of combustible construction. 

(d) For the support of fixtures or other equipment. 



70-136 MASSACHUSETTS ELECTRICAL CODE 

(e) Where subject to physical damage. 

(f) Where subject to ambient temperatures exceeding those for which 
the conduit had been tested. 

(g) For conductors whose insulation temperature limitations would 
exceed those for which the conduit had been tested. 

(h) For potentials exceeding 600 volts unless encased in not less 
than 2 inches of concrete. 

(i) In the sunlight unless approved for the purpose. 

347-4. Other Articles. Installation of rigid nonmetallic conduit shall 
comply with provisions of the applicable sections of Article 300. 

A. Installations 

347-5. Trimming. All cut ends shall be trimmed inside and outside to 
remove rough edges. 

347-6. Joints. All joints between lengths of conduit, and between 
conduit and couplings, fittings and boxes shall be made by a method 
specifically approved for the purpose. 

347-8. Supports. Rigid nonmetallic conduit shall be adequately sup- 
ported as required in Table 347-8. In addition, there shall be a support 
within 4 feet of each box, cabinet or other conduit termination. 

Table 347-8 
Support of Rigid Nonmetallic Conduit 



Conduit Size 


Maximum 


Spacing between Supports 


Inches 






Feet 


H 






4 


H 






4 


l 






5 


IK 






5 


1H 






5 


2 






5 


2V 2 






6 


3 






6 


sy 2 






7 


4 






7 


5 






7 


6 






8 



347-9. Expansion Joints. Expansion joints for rigid nonmetallic con- 
duit shall be provided where required to compensate for thermal ex- 
pansion and contraction. 

347-10. Minimum Size. No conduit smaller than V2 inch electrical 
trade size shall be used. 

347-11. Number of Conductors. The number of conductors permitted 
in a single conduit shall be as follows: 



ARTICLE 347-RIGID NONMETALLIC CONDUIT 70-137 

(a) New Work: 

(1) Where conductors are all of the same size, Tables 1 and 2 of 
Chapter 9. 

(2) Where conductors are of various sizes to be used in combina- 
tion, use Tables 3 and 4 of Chapter 9 and the dimensions of conductors 
in Column 3 of Table 5 of Chapter 9. Where bare conductors are per- 
mitted by other Sections of this Code, the dimensions for bare conduc- 
tors in Table 8 of Chapter 9 may be used. 

(3) When equipment grounding is required by Article 250, a sep- 
arate grounding conductor shall be installed in the conduit. 

(b) Rewiring: Same as specified for new work. 

347-12. Bushings. Where a conduit enters a box or other fitting, a 
bushing or adapter shall be provided to protect the wire from abrasion 
unless the design of the box or fitting is such as to provide equivalent 
protection. See Section 373-6(b) for the protection of conductors at 
bushings. 

347-13. Bends, How Made. Bends of rigid nonmetallic conduit shall 
be so made that the conduit will not be injured and that the internal 
diameter of the conduit will not be effectively reduced. Field bends 
shall be made only with bending equipment specifically approved for 
the purpose, and the radius of the curve of the inner edge of such 
bends shall be not less than shown in Table 346-10. 

347-14. Bends, Number in One Run. A run of conduit between outlet 
and outlet, between fitting and fitting or between outlet and fitting shall 
not contain more than the equivalent of four quarter bends (360°) total 
including those bends located immediately at the outlet or fitting. 

347-15. Boxes and Fittings. See Article 370. 

B. Construction Specifications 

347-16. General. Rigid nonmetallic conduit shall conform to the fol- 
lowing: 

(a) Rigid nonmetallic polyvinyl chloride conduit as shipped shall be 
in standard lengths of 10 feet including couplings, one coupling to be 
furnished with each length. For specific applications or uses, lengths 
shorter or longer than 10 feet with or without couplings may be 
shipped. 

(b) High density polyethylene conduit as shipped shall be in standard 
lengths of 10 feet. One threaded coupling shall be furnished with each 
threaded length of high density polyethylene conduit. For specific ap- 
plications or uses, lengths shorter or longer than 10 feet with or without 
couplings may be shipped. 

(c) Each length of nonmetallic conduit shall be clearly and durably 
marked at least every ten feet with the manufacturer's name, trade 
name, or trademark, nominal trade size, and type of material. 

For conduit recognized for use above ground these markings shall be 
permanent. For conduit limited to underground use only, these mark- 
ings shall be sufficiently durable to remain legible until the material is 
installed. 



70-138 MASSACHUSETTS ELECTRICAL CODE 



ARTICLE 348 — ELECTRICAL METALLIC TUBING 

348-1. Use. Electrical metallic tubing may be used for both exposed and 
concealed work. Electrical metallic tubing protected from corrosion solely by 

enamel shall not be used. Electrical metallic tubing shall not be used (1) 
where during installation or afterward, it will be subject to severe physical 
damage; (2) in concrete, cinder concrete or fill where subject to permanent 
moisture. 

Unless made of a material judged suitable for the condition, or unless cor- 
rosion protection approved for the condition is provided, ferrous or nonferrous 
electrical metallic tubing, elbows, couplings and fittings shall not be installed 
in concrete or in direct contact with the earth, or in areas subject to severe 
corrosive influences. 

See Section 300-5 for limitation in the use of ferrous raceways and fittings 
protected from corrosion solely by enamel. 

348-2. Other Articles. Installations of electrical metallic tubing shall comply 

with the provisions of the applicable sections of Article 300. 



A. Installation 

348-4. Wet Locations. All supports, bolts, straps, screws, etc. shall be of 

corrosion-resistant materials or protected against corrosion by approved cor- 
rosion-resistant materials. See Section 300-5. 

348-5. Minimum and Maximum Sizes. No tubing smaller than Vi inch, 

electrical trade size, shall be used except as provided for underplaster exten- 
sions in Article 344 and for enclosing the leads of motors as permitted in 
Section 430-1 45(b). The maximum size of tubing shall be the 4-inch electrical 
trade size. 

348-6. Number of Conductors in Tubing. One tubing shall not contain more 
conductors than as provided in Section 346-6. 

348-7. Threads. Tubing shall not be coupled together nor connected to 

boxes, fittings, or cabinets by means of threads in the wall of the tubing, 
except by fittings approved for the purpose. Threads shall not be of the 
standard pipe thread dimensions. 

348-8. Couplings and Connectors. Threadless couplings and connectors used 
with tubing shall be made up tight. Where installed in wet locations, they 
shall be of the raintight type. 

348-9. Bends — How Made. Bends in the tubing shall be so made that the 
tubing will not be injured and that the internal diameter of the tubing will 
not be effectively reduced. The radius of the curve of the inner edge of 
any field bend shall not be less than shown in Table 346-10. 

348-1 0. Bends — Number in One Run. A run of electrical metallic tubing 
between outlet and outlet, between fitting and fitting, or between 



ARTICLE 350-FLEXIBLE METAL CONDUIT 70-139 

outlet and fitting, shall not contain more than the equivalent of four 
quarter bends (360 degrees, total), including those bends located imme- 
diately at the outlet or fitting. 

348-11. Reaming. All cut ends of electrical metallic tubing shall be 
reamed to remove rough edges. 

348-12. Supports. Electrical metallic tubing shall be installed as a 
complete system as provided in Article 300 and shall be securely fas- 
tened in place at least every 10 feet and within 3 feet of each outlet box, 
junction box, cabinet, or fitting. 

348-1 3. Boxes and Fittings. See Article 370. 

B. Construction Specifications 

348-14. General. Electrical metallic tubing shall conform to the fol- 
lowing: 

(a) Cross Section. The tubing, and elbows and bends for use with 
the tubing, shall have a circular cross section. 

(b) Finish. Tubing shall have such a finish or treatment of outer 
surfaces as will provide an approved durable means of readily distin- 
guishing it, after installation, from rigid conduit. 

(c) Connectors. Where the tubing is coupled together by threads, the 
connector shall be so designed as to prevent bending of the tubing at 
any part of the thread. 



ARTICLE 350 — FLEXIBLE METAL CONDUIT 



350-1. Other Articles. Installations of flexible metal conduit shall 
comply with the appropriate (or applicable) provisions of Articles 300, 
334, and 346. 

350-2. Use. Flexible metal conduit shall not be used (1) in wet loca- 
tions, unless conductors are of the lead-covered type or of other type 
specially approved for the conditions; (2) in hoistways, except as pro- 
vided in Section 620-21 ; (3) in storage-battery rooms; (4) in any hazard- 
ous location except as permitted in Sections 501-4(b), 502-4 and 503-3; 
nor (5) where rubber-covered conductors are exposed to oil, gasoline, 
or other materials having a deteriorating effect on rubber. 

350-3. Minimum Size. No flexible metal conduit less than one-half 
inch electrical trade size shall be used except ( 1 ) as permitted for un- 
derplaster extensions by Section 344-2; (2) as permitted for motors by 
Section 430-145 (b) ; and (3) for connection not over 48 inches in length, 
or longer on approved assemblies, to equipment where the use of one- 
half inch or larger size flexible metal conduit is not practicable, in 
which case flexible metal conduit of three-eighth inch electrical trade 
size may be used. 



70-140 MASSACHUSETTS ELECTRICAL CODE 

Table 350-3 

Maximum Number of Conductors in %" 
Flexible Metal Conduit 



Size 
AWG 


Types 
RF-32, R, 


RH 


Type 
RW-RHW 


TF, 


T, 


TW 


Types 

, RU, RUF, RUW 


18 


4 




— 








8 


16 


3 




— 








6 


14 


3 




2 








5 


12 


2 




2 








4 


10 


— 




— 








3 



350-4. Supports. When flexible metal conduit is installed it shall be 
secured by approved means at intervals not exceeding AVz feet and 
within 1 2 inches on each side of every outlet box or fitting, except where 
flexible conduit is fished, and except for lengths of not over 36 inches at 
terminals where flexibility is necessary. 



ARTICLE 351 — LIQUIDTIGHT FLEXIBLE 
METAL CONDUIT 



351-1. Purpose. Liquidtight flexible metal conduit is not intended as 
a general purpose raceway material. The provisions of this Article shall 
apply to a type of flexible conduit having an outer liquidtight jacket 
and employed with suitable terminal fittings approved for the purpose. 

351-2. Use. The use of this wiring material shall be restricted as fol- 
lows: 

(a) For the connection of motors or portable equipment where flex- 
ibility of connection is required. 

(b) Liquidtight flexible metal conduit shall not be used under the fol- 
lowing conditions: (1) where subject to physical damage; (2) where in 
contact with rapidly moving parts; (3) under conditions such that its 
temperature, with or without enclosed conductors carrying current, is 
above 60°C ( 140°F) ; (4) in any hazardous location, except as described 
in Section 501-4(b) and Sections 502-4 and 503-3, unless it is specially 
approved for such use. 

351-3. Maximum Size. The maximum size of liquidtight flexible 
metal conduit shall not exceed 3 inch electrical trade size. 

351-4. Conductor Size. The maximum size of conductor installed in 
liquidtight flexible metal conduit shall not exceed the following values: 



ARTICLE 352-SURFACE METAL RACEWAYS 70-141 

Table 351-4 

Trade Size of Conduit Size of Conductor 

% inch 16 Awg 

Vi inch 12 Awg 

3 A inch 8 Awg 

1 inch 6 Awg 

1 Va inch 2 Awg 
Wi inch 1 Awg 

2 inch 00 Awg 
2Vi inch 0000 Awg 

3 inch 350 MCM 

Liquidtight flexible metallic conduit in sizes V/i inch and larger shall 
be bonded in accordance with Section 250-79 unless specifically ap- 
proved for use without a separate bond. 



ARTICLE 352 — SURFACE METAL RACEWAYS 



352-1. Use. Surface metal raceways may be installed in dry locations. 
They shall not be used (1) where concealed, except that metal race- 
ways approved for the purpose may be used for underplaster exten- 
sions; (2) where subject to severe physical damage unless approved for 
the purpose; (3) where the voltage is 300 volts or more between con- 
ductors unless the metal has a thickness of not less than .040 inch; (4) 
where subject to corrosive vapors; (5) in hoistways; nor (6) in any 
hazardous location. 

352-2. Other Articles. Installations of surface metal raceways shall 
comply with the applicable provisions of Article 300. 

A. Installation 

352-3. Size of Conductors. No conductor larger than that for which 
the raceway is designed shall be installed in surface metal raceway. 

352-4. Number of Conductors in Raceways. The number of con- 
ductors installed in any raceway shall be no greater than the number 
for which the raceway is designed. 

352-5. Extension Through Walls and Floors. Except in multioutlet as- 
semblies, raceways may be extended through dry walls, dry partitions 
and dry floors, if in unbroken lengths where passing through. 

352-6. Combination Raceways. Where combination metal raceways 
are used both for signal and for lighting and power circuits, the different 
systems shall be run in separate compartments, identified by sharply 
contrasting colors of the interior finish, and the same relative position 
of compartments shall be maintained throughout the premises. 

B. Construction Specifications 

352-7. General. Surface metal raceways shall be of such construction 
as will distinguish them from other raceways. Surface metal raceways 
and their elbows, couplings, and similar fittings shall be so designed 



70-142 MASSACHUSETTS ELECTRICAL CODE 

that the sections can be electrically and mechanically coupled together, 
while protecting the wires from abrasion. Holes for screws or bolts in- 
side the raceway shall be so designed that when screws or bolts are in 
place their heads will be flush with the metal surface. 



ARTICLE 353 — MULTIOUTLET ASSEMBLY 



353-1. Other Articles. Installations of multioutlet assembly shall com- 
ply with applicable provisions of Article 300. See definition in Article 
100. 

353-2. Use. Multioutlet assembly may be installed in dry locations. It 
shall not be installed ( 1 ) where concealed, except that the back and 
sides of metal multioutlet assembly may be surrounded by the building 
finish and nonmetallic multioutlet assembly may be recessed in the base- 
board; (2) where subject to severe physical damage unless approved for 
the purpose; (3) where the voltage is 300 volts or more between conduc- 
tors unless assembly is of metal having a thickness of not less than .040 
inch; (4) where subject to corrosive vapors; (5) in hoistways; nor (6) in 
any hazardous locations. 

353-3. Metal Multioutlet Assembly Through Dry Partitions. Metal multi- 
outlet assembly may be extended through (not run within) dry parti- 
tions, providing arrangements are made for removing the cap or 
cover on all exposed portions and no outlet is located within the parti- 
tions. 



ARTICLE 354 — UNDERFLOOR RACEWAYS 



354-1. Other Articles. Installations of underfloor raceways shall com- 
ply with the applicable provisions of Article 300. 

354-2. Use. Underfloor raceways may be installed beneath the surface 
of concrete or other flooring material, or in office occupancies, where 
laid flush with the concrete floor and covered with linoleum or equiva- 
lent floor covering. Underfloor raceways shall not be installed ( 1 ) where 
subject to corrosive vapors nor (2) in any hazardous location. Unless 
made of a material judged suitable for the condition, or unless corro- 
sion protection approved for the condition is provided, ferrous or non- 
ferrous metallic underfloor raceways, junction boxes, and fittings shall 
not be installed in concrete or in direct contact with the earth, or in 
areas subject to severe corrosive influences. 

354-3. Covering. Raceway coverings shall conform to the following: 

(a) Raceways Not Over 4 Inches Wide. Half-round raceways not 
over 4 inches in width, and, except as permitted in (c) flat-top raceways 



ARTICLE 354-UNDERFLOOR RACEWAYS 70-143 

not over 4 inches in width, shall have not less than % inch of concrete 
or wood above the raceway. 

(b) Raceways 4 Inches Wide but Not Over 8 Inches Wide. Flat top 
raceways 4 inches wide with a minimum of 1 inch spacing between 
raceways shall be covered with concrete to a depth of not less than 1 
inch. Raceways spaced less than 1 inch apart shall be covered with 
concrete to a depth of 1 Vi inches. 

(c) Raceways Flush With Concrete. Approved flush raceways with re- 
movable covers may be laid flush with the floor surface. Such approved 
raceways shall be so designed that the cover plates will provide ade- 
quate mechanical protection and rigidity equivalent to junction box 
covers. 

354-4. Size of Conductors. No conductor larger than that for which 
the raceway is approved shall be installed in underfloor raceways and the 
largest size conductor allowed shall be 500,000 cm. 

354-5. Number of Conductors in Raceway. The combined cross-sec- 
tional area of all conductors shall not exceed 40 per cent of the interior 
area of the raceway; except that where the raceway contains only ar- 
mored cable or nonmetallic sheathed cable, these requirements shall not 
apply. 

354-6. Splices and Taps. Splices or taps shall be made only in junction 
boxes. 

See Tentative Interim Amendment No. 127 at back of book. 

354-7. Discontinued Outlets. When an outlet is abandoned, discontin- 
ued, or removed, the sections of circuit conductors supplying the outlet 
shall be removed from the raceway. No splices or reinsulated conduc- 
tors such as would be the case with abandoned outlets on loop wiring, 
shall be allowed in raceways. 

354-8. Laid in Straight Lines. Underfloor raceways shall be laid so 
that a straight line from the center of one junction box to the center of 
the next junction box will coincide with the center line of the raceway 
system. Raceways shall be firmly held in place to prevent disturbing 
this alignment during construction. 

354-9. Markers at Ends. At every end of line of raceway, and at other 
locations where the location of the raceway is not apparent, a suitable 
number of markers shall be installed extending through the floor for fu- 
ture location of inserts and for system identification. 

354-10. Dead Ends. Dead ends of raceways shall be closed. 

354-11. Low Points. Where practicable, raceways and their fittings 
shall be so arranged as to avoid low points that may form traps for wa- 
ter. 

354-12. Fittings at Angles. Where raceways are run at other than right 
angles, special fittings shall be provided. 

354-13. Junction Boxes. Junction boxes shall be leveled to the floor 
grade and sealed against the entrance of water. Junction boxes used 
with metal raceways shall be metal and shall be electrically continuous 
with the raceways. 



70-144 MASSACHUSETTS ELECTRICAL CODE 

354-14. Inserts. Inserts shall be leveled to the floor grade and sealed 
against the entrance of water. Inserts used with metal raceways shall 
be metal and shall be electrically continuous with the raceway. Inserts 
set in or on fiber raceways before the floor is laid shall be mechanically 
secured to the raceway. Inserts set in fiber raceways after the floor is 
laid shall be screwed into the raceway. In cutting through the raceway 
wall and setting inserts, chips and other dirt shall not be allowed to 
fall into the raceway, and tools shall be used which are so designed as 
to prevent the tool from entering the raceway and injuring conductors 
that may be in place. 

354-15. Connections to Cabinets and Wall Outlets. Connections be- 
tween raceways and distribution centers and wall outlets shall be made 
by means of rigid or flexible metal conduit or by means of fittings 
approved for the purpose. 



ARTICLE 356 — CELLULAR METAL FLOOR 
RACEWAYS 



356-1. Definitions. For the purposes of this Article, a "cellular metal 
floor raceway" shall be defined as the hollow spaces of cellular metal 
floors, together with suitable fittings, which may be approved as en- 
closures for electrical conductors; a "cell" shall be defined as a single, 
enclosed tubular space in a cellular metal floor member, the axis of the 
cell being parallel to the axis of the metal floor member; a "header" 
shall be defined as a transverse raceway for electrical conductors, pro- 
viding access to predetermined cells of a cellular metal floor, thereby 
permitting the installation of electrical conductors from a distribution 
center to the cells. 

356-2. Use. Conductors shall not be installed in cellular metal floor 
raceways (1) where subject to corrosive vapor; (2) in any hazardous lo- 
cation; nor (3) in commercial garages, except for supplying ceiling out- 
lets or extensions to the area below the floor but not above. No electric 
conductors shall be installed in any cell or header which contains a 
pipe for steam, water, air, gas, drainage, or other service than electrical. 

356-3. Other Articles. Installations of conductors in the raceways of 
cellular metal floor shall comply with the applicable provisions of Ar- 
ticle 300. 

A. Installation 

356-4. Size of Conductors. No conductor larger than No. shall be 
installed, except by special permission. 

356-5. Number of Conductors in Raceway. The total cross-sectional 
area of all conductors in a header or in an individual cell shall not ex- 
ceed 40% of the cross-sectional area of the header or cell in which 
they are located; except that where the raceway contains only Type AC 
metal-clad cable or nonmetallic sheathed cable, these requirements shall 
not apply. 



ARTICLE 357-STRUCTURAL RACEWAYS 70-145 

356-6. . Splices and Taps. Splices and taps shall be made only in header 
access units or junction boxes. 

356-7. Discontinued Outlets. When an outlet is discontinued, the con- 
ductors supplying the outlet shall be removed from the raceway. 

356-8. Markers. A suitable number of markers shall be installed ex- 
tending through the floor for the future locating of cells and for system 
identification. 

356-9. Junction Boxes. Junction boxes shall be levelled to the floor 
grade and sealed against the entrance of water. Junction boxes used 
with these raceways shall be of metal and shall be electrically continu- 
ous with the raceway. 

356-10. Inserts. Inserts shall be levelled to the floor grade and sealed 
against the entrance of water. Inserts shall be of metal and shall be elec- 
trically continuous with the raceway. In cutting through the cell wall 
and setting inserts, chips and other dirt shall not be allowed to fall into 
the raceway, and tools shall be used which are designer to prevent the 
tool from entering the cell and injuring the conductors. 

356-11. Connection to Cabinets and Extensions from Cells. Connections 
to cabinets and extensions from cells to outlets shall be made by means 
of rigid or flexible conduit or by means of fittings approved for the pur- 
pose. 

B. Construction Specifications 

356-12. General. Cellular metal floor raceways shall be so constructed 
that adequate electrical and mechanical continuity of the complete sys- 
tem will be secured. They shall provide a complete enclosure for the 
conductors. The interior surfaces shall be free from burrs and sharp 
edges, and surfaces over which conductors are drawn shall be smooth. 
Suitable bushings or fittings having smooth rounded edges shall be pro- 
vided where conductors pass. 



ARTICLE 357 — STRUCTURAL RACEWAYS 



357-1. Definitions. Structural raceways are formed steel members ap- 
proved for the installation of electrical wires or cables within them. 

(a) Vertical members used for studs or columns shall be tubes or 
channels. 

(b) Horizontal headers used as beams or top plates shall be provided 
with suitable covers, end closers, and fittings. 

357-2. Use. Structural raceways used to enclose electrical conductors 
shall be used only in single-family dwellings. 

357-3. Other Articles. Installation of conductors in structural race- 
ways shall comply with the applicable provisions of Article 300. 



70-146 MASSACHUSETTS ELECTRICAL CODE 

A. Installation 

357-4. Openings in Vertical Members. Vertical members may have 
openings provided in them for the purpose of installing wiring devices. 
Vertical members may be concealed. Openings in vertical members 
shall provide access to wiring. The size of such openings shall comply 
with the provisions of Section 300-15 and Article 370. Wiring devices 
may be installed in openings in vertical members without the use of 
individual boxes, provided that the back and sides of each device are 
surrounded by terminal barriers. 

357-5. Horizontal Headers. Horizontal headers shall be securely fas- 
tened to vertical members. 

357-6. Number of Conductors in Raceway. Structural raceways shall 
not contain more than 20 current-carrying conductors at any cross- 
section, and the total cross-sectional areas of all contained conductors 
shall not exceed 20 per cent of the interior cross-section. 

357-7. Splices and Taps. Splices and taps shall be made only in hori- 
zontal headers, or junction boxes. The conductors including splices and 
taps shall not fill the structural raceway to more than 75 per cent of its 
area at that point. All splices and taps shall be made and insulated by 
approved methods. 

357-8. Size of Conductors. No conductor larger than Number 6 
AWG shall be installed in vertical or horizontal members. 

357-9. Accessibility. The covers of the horizontal members shall be 
accessible after installation and shall not be obstructed by the wall fin- 
ish. 

357-10. Fittings. Fittings shall be designed and installed to prevent 
physical damage to electrical conductors. Fittings shall be free from 
burrs and sharp edges. 

357-11. Extensions from vertical structural members. Extensions from 
vertical structural members shall be made with rigid or flexible metal 
conduit, electrical metallic tubing, surface metal raceway or metal- 
clad cable. 

357-12. Dead Ends. Dead ends of structural raceways shall be closed. 

357-13. Installation of Electrical Devices. The installation of switches, 
receptacles, and outlets shall be in accordance with the requirements of 
Articles 380 and 410, except as otherwise permitted in this Article. 

357-14. Grounding. All elements of structural raceway systems shall 
be bonded and effectively grounded. 

B. Construction Specifications 

357-15. Marking. Structural raceways and fittings shall be marked 
with the manufacturer's name, trademark, or identification symbol. 

357-16. General. All metal components shall be properly coated to 
prevent corrosion. The interior shall be free from sharp edges and 
burrs. The structural raceway systems shall be constructed to provide 
electrical and mechanical continuity of the complete system. They shall 
provide a complete enclosure for the conductors. Enclosures shall be 
approved for the purpose. 



ARTICLE 358-CELLULAR CONCRETE FLOOR RACEWAYS 70-147 

ARTICLE 358 — CELLULAR CONCRETE FLOOR 

RACEWAYS 



358-1. Scope. Approved precast cellular concrete floor raceways shall 
comply with the applicable requirements of Article 300, and shall also 
comply with the provisions of Sections 358-2 to 358-11 inclusive. For 
the purpose of this Article, "precast cellular concrete floor raceways" 
shall be defined as the hollow spaces in floors constructed of precast 
cellular concrete slabs, together with suitable metal fittings designed to 
provide access to the floor cells in an approved manner. A "cell" shall 
be defined as a single, enclosed tubular space in a floor made of precast 
cellular concrete slabs, the direction of the cell being parallel to the di- 
rection of the floor member. "Header ducts" shall be defined as trans- 
verse metal raceways for electrical conductors, furnishing access to 
predetermined cells of a precast cellular concrete floor, thus providing 
for the installation of electrical conductors from a distribution center 
to the floor cells. 

358-2. Use. Conductors shall not be installed in precast cellular con- 
crete floor raceways ( 1 ) where subject to corrosive vapor; (2) in hazard- 
ous locations; nor (3) in commercial garages, except for supplying ceil- 
ing outlets or extensions to the area below the floor but not above. No 
electrical conductors shall be installed in any cell or header which con- 
tains a pipe for steam, water, air, gas, drainage, or any service other 
than electrical. 

358-3. Header Duct. The header duct shall be installed in a straight 
line, at right angles to the cells. The header duct shall be mechanically 
secured to the top of the precast cellular concrete floor. The end joints 
shall be closed by metallic closure fittings and sealed against the pene- 
tration of water. The header duct shall be electrically continuous 
throughout its entire length and shall be electrically bonded to the en- 
closure of the distribution center. 

358-4. Connection to Cabinets and Other Enclosures. Connection from 
header duct to cabinets and other enclosures shall be made by means of 
metallic duct and fittings approved for the purpose. 

358-5. Junction Boxes. Junction boxes shall be levelled to the floor 
grade and sealed against the entrance of water. Junction boxes shall be 
of metal and shall be mechanically and electrically continuous with 
the header ducts. 

358-6. Markers. Each hidden access point between a header and a 
cell intended for future use shall be provided with a marker extending 
through the floor covering. A suitable number of markers shall be in- 
stalled, extending through the floor covering, to locate the cells and to 
provide system identification. 

358-7. Inserts. Inserts shall be levelled to the floor grade and sealed 
against the entrance of water. Inserts shall be of metal and shall be 
fitted with receptacles of the grounded type. A ground conductor shall 
connect the insert receptacles to a positive ground connection provided 
on the header duct. In cutting through the cell wall for setting inserts or 



70-148 MASSACHUSETTS ELECTRICAL CODE 

other purposes (such as providing access openings between header duct 
and cells) chips and other dirt shall not be allowed to fall into the race- 
way, and the tool used shall be so designed as to prevent the tool from 
entering the cell and injuring the conductors. 

358-8. Size of Conductors. No conductor larger than No. shall be 
installed, except by special permission. 

358-9. Number of Conductors. The total cross-sectional area of all 
conductors in a header or in an individual cell shall not exceed 40% of 
the cross-sectional area of the header or cell in which they are located; 
except that where the raceway contains only Type AC metal-clad cable 
or nonmetallic sheathed cable, these requirements shall not apply. 

358-10. Splices and Taps. Splices and taps shall be made only in 
header duct access units or junction boxes. 

358-11. Discontinued Outlets. When an outlet is discontinued, the 
conductors supplying the outlet shall be removed from the header and 
cell. 



ARTICLE 362 — WIREWAYS 



362-1. Definition. Wireways are sheet-metal troughs with hinged or 
removable covers for housing and protecting electrical wires and cable 
and in which conductors are laid in place after the wireway has been 
installed as a complete system. 

362-2. Use. Wireways may be installed only for exposed work. Wire- 
ways intended for outdoor use shall be of approved raintight construc- 
tion. Wireways shall not be installed: (1) where subject to severe physi- 
cal damage or corrosive vapor; nor (2) in any hazardous location. 

362-3. Other Articles. Installations of wireways shall comply with the 

applicable provisions of Article 300. 

362-4. Size of Conductors. No conductor larger than 500,000 cm. 

shall be installed in any wireway. 

362-5. Number of Conductors. Wireways shall not contain more than 

30 current carrying conductors at any cross section. The sum of the 

cross-sectional areas of all contained conductors at any cross-section of 

a wireway shall not exceed 20 per cent of the interior cross-sectional 

area of the wireway. 

Exception No. 1 . See Section 620-32. 

The correction factors specified in Note 8 to Tables 310-12 through 
310-15 are not applicable to the foregoing. 

Exception No. 2. Conductors for signal circuits or controller con- 
ductors between a motor and its starter and used only for starting duty 
shall not be considered as current carrying conductors. 
362-6. Splices and Taps. Splices and taps, made and insulated by ap- 
proved methods, may be located within the wireway provided they are 
accessible. The conductors, including splices and taps, shall not fill the 
wireway to more than 75 per cent of its area at that point. 



ARTICLE 364— BUSWAYS 70-149 

362-7. Supports. Wireways shall be securely supported at intervals not 
exceeding 5 feet, unless specially approved for supports at greater intervals, 
but in no case shall the distance between supports exceed 10 feet. 

Exception: See Section 620-32. 

362-8. Extension Through Walls. Wireways may extend transversely 
through walls if in unbroken lengths where passing through. 

362-9. Dead Ends. Dead ends of wireways shall be closed. 

362-10. Extensions From Wireways. Extensions from wireways shall be 
made with rigid or flexible metal conduit, electrical metallic tubing, surface 
metal raceway or metal-clad cable. 

362-11. Marking. Wireways shall be marked so that their manufacturer's 
name or trademark will be visible after installation. 



ARTICLE 364 — BUSWAYS 

364-1. Other Articles. Installations of busways shall comply with the appli- 
cable provisions of Article 300. 

364-2. Use. Busways may be installed only for exposed work. Busways 
shall not be installed (1) where subject to severe physical damage or cor- 
rosive vapors; (2) in hoistways; (3) in any hazardous location; nor (4) out- 
doors or in wet or damp locations unless specially approved for the purpose. 

Busways may be used for service-entrance conductors. See Section 230-44. 

Where secondary systems are operated ungrounded, 
a combination ground detector and potentializer plug shall be used as an 
auxiliary fitting for busway systems to establish a definite potential difference 
between the bus-bars and the grounded casing of the busways. This will serve 
to drain off any static or other charge from the entire busway system includ- 
ing its connected apparatus, supply and branch circuit conductors. 

364-3. Support. Busways shall be securely supported at intervals not ex- 
ceeding 5 feet, unless specially approved for supports at greater intervals, 
but in no case shall the distance between supports exceed 10 feet. Where a 
busway is installed in a vertical position, the supports for the bus-bars shall 
be designed for vertical installation. 

364-4. Extension Through Walls. Busways may extend transversely 
through dry walls if in unbroken lengths where passing through. Busways 
may extend vertically through dry floors when totally enclosed (unventilated) 
where passing through and for a minimum distance of six feet above the 
floor to provide adequate protection from physical damage. 



70-150 MASSACHUSETTS ELECTRICAL CODE 

364-5. Dead Ends. A dead end of a busway shall be closed. 

364-7. Branches from Busways. Branches from busways shall be made 
with busways or with rigid or flexible metal conduit, electrical metallic 
tubing, surface metal raceway, metal-clad cable or with suitable cord 
assemblies approved for hard usage for portable equipment or for the 
connection of stationary equipment to facilitate their interchange. 

364-8. Overcurrent Protection. Overcurrent protection shall be pro- 
vided in accordance with Sections 364-9 to 364-13 inclusive. 

364-9. Rating of Overcurrent Protection — Feeders and Sub-Feeders. 

Where the allowable current rating of the busway does not correspond 
to a standard rating of the overcurrent device, the next higher rating 
may be used. 

364-10. Reduction in Size of Busway. Overcurrent protection may be 
omitted at points where busways are reduced in size, provided that the 
smaller busway does not extend more than 50 feet and has a current 
rating at least equal to one-third the rating or setting of the overcurrent 
device next back on the line, and provided further that such busway is 
free from contact with combustible material. 

364-11. Branch Circuits. Where a busway is used as a feeder, devices 
or plug-in connections for tapping off branch-circuits from the busway 
shall contain the overcurrent devices required for the protection of the 
branch circuits. 

Exception No. 1. For overcurrent protection of taps, see Section 
240-15. 

Exception No. 2. For fixed or semi-fixed lighting fixtures, the branch 
circuit overcurrent device may be part of the fixture cord plug on cord- 
connected fixtures. 

Exception No. 3. Where fixtures without cords are plugged directly 
into the busway, the overcurrent device may be mounted on the fixture. 

364-12. Rating of Overcurrent Protection — Branch Circuits. A busway 
may be used as a branch circuit of any one of the types described in 
Article 210. When so used, the rating or setting of the overcurrent de- 
vice protecting the busway shall determine the ampere rating of the 
branch circuit, and the circuit shall in all respects conform with the re- 
quirements of Article 210 that apply to branch circuits of that rating. 

364-13. Length of Busways Used as Branch Circuits. Busways which 
are used as branch circuits and which are so designed that loads can be 
connected at any point shall be limited to such lengths as will provide 
that in normal use the circuits will not be overloaded. 

In general, the length of such run in feet should not exceed three times 
the ampere rating of the branch circuit. 

364-14. Marking. Busways shall be marked with the voltage and cur- 
rent rating for which they are designed, and with the manufacturer's 
name or trademark in such manner as to be visible after installation. 



ARTICLE 370— BOXES AND FITTINGS 70-151 

ARTICLE 370 — OUTLET, SWITCH AND 
JUNCTION BOXES, AND FITTINGS 

A. Scope and General 
370-1. Scope. The provisions of this Article shall apply to the installation 
of outlet, switch and junction boxes, and fittings as required by Section 300- 
15. Installations in hazardous locations shall conform to Articles 500 to 
51 7 inclusive. 

370-2. Round Boxes. Round boxes shall not be used where conduits or 
connectors requiring the use of locknuts or bushings are to be connected to 
the side of the box. 

370-3. Nonmetallic Boxes. Nonmetallic boxes approved for the purpose 
may be used only with open wiring on insulators, concealed knob-and-tube 
work, nonmetallic sheathed cable, and with approved nonmetallic conduit. 
370-4. Metallic Boxes. Where used with knob-and-tube work or non- 
metallic sheathed cable, and mounted on metal or metal lath ceilings or walls, 
such boxes shall be insulated from their supports and from the metal or 
metal lath, or shall be grounded. 

B. Installation 
370-5 Damp or Wet Locations. In damp or wet locations, boxes and fittings 
shall be so placed or equipped as to prevent moisture or water from entering 
and accumulating within the box or fitting. Boxes and fittings installed in 
wet locations shall be weatherproof. For boxes in floors, see Section 410-53. 

Approved boxes of nonconductive material shall be used 
with nonmetallic sheathed cable or approved nonmetallic conduit when such 
cable or conduit is used in locations where there is likely to be occasional 
moisture present such as in dairy barns. 

370-6. Number of Conductors in a Box. Boxes shall be of sufficient size 
to provide free space for all conductors enclosed in the box. 

The limitations in Section 370-6(a and b) shall not apply to terminal 
housings supplied with motors, nor to types of boxes or fittings without 
knockout and having hubs or recessed parts for terminal bushings and 
locknuts. 

Section 370-6(a and b) does not apply to conductors used for rewiring 
existing raceways as referred to in Table 3, Chapter 9. 

(a) The maximum number of conductors, not counting fixture wires, 
permitted in cutlet and junction boxes shall be as in Tables 370-6(a-l and 
-2) with the exceptions noted. 

Tables 370-6(a-l and -2) apply where no fittings or devices, such as 
fixture studs, cable clamps, hickeys, switches or receptacles are con- 
tained in the box. Where one or more fixture studs, cable clamps, or 
hickeys are contained in the box, the number of conductors shall be 
one less than shown in the Tables, with a further deduction of one con- 



70-152 MASSACHUSETTS ELECTRICAL CODE 

ductor for one or several flush devices mounted on the same strap. A 
conductor running through the box is counted as one conductor and 
each conductor originating outside the box and terminating inside the 
box is counted as one conductor. Conductors of which no part leaves 
the box are not to be counted in the above computation. If single flush 
boxes are ganged, and each section is occupied by a flush device or 
combination of flush devices on the same strap, the limitations will 
apply to each section individually. 



Table 370-6(a-l)— Deep Boxes 



Maximum Number of Conductors 
Box Dimensions, Inches 



Trade Size No. 14 No. 12 No. 10 No. 8 No. 6* 

\y 2 x 33 i : octagonal. . 5 5 4 

l]/ 2 x 4 octagonal. . . . 8 7 6 5 

13^x4 square 11 9 7 5 

13^x4 11/16 square. 16 12 10 8 

2V S x 4 11/16 square. 20 16 12 10 '6 

2 xl^x2M 5 4 4 

2^ x 1^ x 2% 6 6 5 

3 xl^x2M 7 7 6 

Where there is not sufficient space for a deeper box, four No. 14 AWG conductors 
may enter a box provided with cable clamps and containing one or more devices on 
a single mounting strap. 

* See Section 370-18 where boxes are used as pull and junction boxes. 
Table 370-6(a-2)— Shallow Boxes 

Maximum Number of Conductors 
Box Dimensions, Inches 



Trade Size No. 14 No. 12 No. 10 

334 ~4~ 4 3 

4 6 6 4 

134 x 4 square 9 7 6 

4 11/16 8 6 6 

Any box less than 1 */< inch deep is considered to be a shallow box. 



(b For combinations not shown in the above Tables, Table 370-6(b) 
shall apply. 

370-7. Conductors Entering Boxes or Fittings. Conductors entering 
boxes or fittings shall be protected from abrasion, and shall conform to 
the following: 

(a) Openings to Be Closed. Openings through which conductors 
enter shall be adequately closed. 



TABLE 370-6(b) 70-153 



Size of Free Space Within Box 

Conductor for Each Conductor 

No. 14 2. cubic inches 

No. 12 2.25 cubic inches 

No. 10 2.5 cubic inches 

No. 8 3. cubic inches 

No. 6 5. cubic inches 

(b) Metal Boxes and Fittings. Where metal outlet boxes or fittings are 
installed with open wiring or concealed knob-and-tube work, conductors shall 
enter through insulating bushings or, in dry places, through flexible tubing 
extending from the last insulating support and firmly secured to the box 
or fitting. Where raceway or cable is installed with metal outlet boxes or fit- 
tings, the raceway or cable shall be secured to such boxes and fittings. 

(c) Nonmetallic Boxes. Where nonmetallic boxes are used with open 
wiring or concealed knob-and-tube work, the conductors shall enter through 
individual holes. Where flexible tubing is used to encase the conductor, the 
tubing shall extend from the last insulating support and may be run into the 
box or terminate at the wall of the box. If nonmetallic sheathed cable is used, 
the cable assembly shall enter the box through a knockout opening. Clamp- 
ing of individual conductors or cables to the box is not required where sup- 
ported within 8 inches of the box. Where nonmetallic conduit is installed 
with nonmetallic boxes or fittings, the conduit shall be secured to such boxes 
and fittings in an approved manner. 

(d) Where bond wires are provided, they shall be attached to the yoke of 
the device by a means suitable for the purpose. 

370-8. Unused Openings. Unused openings in boxes and fittings shall be 
effectively closed to afford protection substantially equivalent to that of 
the wall of the box or fitting. Metal plugs or plates used with nonmetallic 
boxes or fittings shall be recessed at least Va inch from the outer surface. 

370-9. Boxes Enclosing Flush Devices. Boxes used to enclose flush devices 
shall be of such design that the devices will be completely enclosed on back 
and sides, and that substantial support for the devices will be provided. Screws 
for supporting the box shall not be used in attachment of the device con- 
tained therein. 

370-10. In Wall or Ceiling. In walls or ceilings of concrete, tile or other 
noncombustible material, boxes and fittings shall be so installed that the 
front edge of the box or fitting will not set back of the finished surface more 
than Va inch. In walls and ceilings constructed of wood or other combustible 
material, outlet boxes and fittings shall be flush with the finished surface or 
project therefrom. 

370-11. Repairing Plaster. Except on walls or ceilings of concrete, 
tile or other noncombustible material, a plaster surface which is broken 



70-154 MASSACHUSETTS ELECTRICAL CODE 



or incomplete shall be repaired so that there will be no gaps or open 
spaces at the edge of the box or fitting. 

370-12. Exposed Extensions. In making an exposed extension from 
an existing outlet of concealed wiring, a box, extension ring or blank 
cover shall be mounted over the original box and electrically and 
mechanically secured to it. The extension shall then be connected to 
this box in the manner prescribed for the method of wiring employed 
in making the extension. 

370-13. Supports. 

(a) General. Boxes, fittings and cabinets shall be securely fastened 
in place. Boxes and fittings, not over 100 cubic inches in size, which 
are attached to firmly secured exposed raceway by threading or other 
connection designed for the purpose, are considered as so fastened. 

(b) Concealed Work. In concealed work, except as prescribed in 
Section 370-1 3(c), boxes and fittings, unless securely held in place by 
concrete, masonry or other building material in which they are em- 
bedded, shall be secured to a stud, joist or similar fixed structural unit, 
or to a metal or wooden support which is secured to such a structural 
unit. Wooden supports shall be not less than Vs inch in thickness. Lath 
of wood, metal or composition shall not be considered a structural unit. 
See Sections 410-15 and 410-16 for support of fixtures. 

(c) Exposed Work. In exposed work, and in concealed work in exist- 
ing buildings where conductors or cables are fished and boxes cannot 
be secured as provided in Section 370-13(b) without disturbing the 
building finish, the boxes may be mounted directly upon the plaster sur- 
face when securely fastened in place. 

370-14. Depth of Outlet Boxes for Concealed Work. Outlet boxes for 
concealed work shall have an internal depth of at least \Vi inches, ex- 
cept that where the installation of such a box will result in injury to the 
building structure or is impracticable, a box not less than Vi inch in- 
ternal depth may be installed. 

370-15. Covers and Canopies. In completed installations each outlet 
box shall be provided with a cover unless a fixture canopy is used. 

(a) Nonmetallic covers and plates or metallic covers and plates may 
be used with nonmetallic outlet boxes. When metallic covers or plates 
are used, they shall comply with the grounding requirements of Section 
250-42. 

See Section 410-95. 

(b) Where a fixture canopy or pan is used, any combustible wall or 
ceiling finish exposed between the edge of the canopy or pan and the 
outlet box shall be covered with noncombustible material. 

(c) Covers of outlet boxes having holes through which flexible cord 
pendants pass, shall be provided with bushings designed for the purpose 
or shall have smooth, well-rounded surfaces on which the cords may 
bear. So-called hard-rubber or composition bushings shall not be used. 

370-16. Fastened to Gas Pipes. Outlet boxes used where gas outlets 
are present shall be so fastened to the gas pipes as to be mechanically 
secure. 



ARTICLE 370-BOXES AND FITTINGS 70-155 

370-17. Boxes at Lighting Fixture Outlets. Boxes used at outlets for 
lighting fixtures shall be designed for the purpose. At every outlet used 
exclusively for lighting, the box shall be so designed or installed that a 
lighting fixture may be attached. 

370-18. Pull and Junction Boxes. Pull and junction boxes shall con- 
form to the following: 

(a) Minimum Size. For raceways of 1 inch trade size and larger, 
containing conductors of No. 6 or larger, and for cables* containing 
conductors of No. 6 or larger, the minimum dimensions of a pull or 
junction box installed in a raceway or cable run shall conform to the 
following: 

(1) Straight Pulls. In straight pulls the length of the box shall be 
not less than 8 times the trade diameter of the largest raceway. 

(2) Angle or U Pulls. Where angle or U pulls are made, the dis- 
tance between each raceway entry inside the box and the opposite wall 
of the box shall not be less than 6 times the trade diameter of the larg- 
est raceway. This distance shall be increased for additional entries by 
the amount of the sum of the diameters of all other raceway entries 
on the same wall of the box. The distance between raceway entries en- 
closing the same conductor shall not be less than 6 times the trade di- 
ameter of the larger raceway. 

Exception. The limitations of Section 370-18(a-l and a-2) are 
not intended to apply to terminal housings supplied with motors, nor 
to types of boxes or fittings without knockouts and having hubs or re- 
cessed parts for terminal bushings and locknuts. 

(b) Conductors in Pull or Junction Boxes. In pull boxes or junction 
boxes having any dimension over 6 feet, all conductors shall be cabled 
or racked up in an approved manner. 

See Section 373-6(b) for insulation of conductors at bushings. 

(c) Covers. All pull boxes, junction boxes and fittings shall be pro- 
vided with covers approved for the purpose. Where metallic covers are 
used, they shall comply with the grounding requirements of Section 
250-42. 

370-19. Junction, Pull and Outlet Boxes Be Accessible. Junction, pull 
and outlet boxes shall be so installed that the wiring contained in them 
may be rendered accessible without removing any part of the building, 
sidewalks or paving. 

C. Construction Specifications 

370-20. Metallic Outlet, Switch and Junction Boxes and Fittings. Out- 
let, switch and junction boxes and fittings, when of metal, shall conform 
to the following. 

(a) Corrosion-Resistant. Metallic boxes and fittings, unless of cor- 
rosion-resistant metal, shall be well galvanized, enameled, or otherwise 
properly coated, inside and out, to prevent corrosion. 

* When transposing cable size into raceway size in (1) and (2) 
above, the minimum trade size raceway required for the number and 
size of conductors in the cable shall be used. 



70- 1 56 MASSACHUSETTS ELECTRICAL CODE 

See Section 300-5 for limitation in the use of boxes and fittings protected 
from corrosion solely by enamel. 

(b) Thickness of Metal. For sheet steel boxes and fittings not over 100 
cubic inches in size, the metal shall not be less than No. 14 USS gage 
(0.0747 inch in thickness). Cast metal boxes shall have a wall thickness 
of not less than Vs inch, except that boxes of malleable iron shall have a 
wall thickness of not less than 3/32 inch. 

(c) Boxes Over 100 Cubic Inches. Boxes of over 100 cubic inches in 
size shall be composed of metal and shall conform to the requirements for 
cabinets and cutout boxes, except that the covers may consist of single 
flat sheets secured to the box proper by screws, or bolts instead of hinges. 
Boxes having covers of this form are for use only for enclosing joints in 
conductors or to facilitate the drawing in of wires and cables. They are not 
intended to enclose switches, cutouts or other control devices. 

370-21. Covers. Metal covers shall be of a thickness not less than that 
specified for the walls of the box or fitting of the same material and with 
which they are designed to be used, or shall be lined with firmly attached 
insulating material not less than 1/32 inch in thickness. Covers of porcelain 
or other approved insulating material may be used when of such form and 
thickness as to afford the requisite protection and strength. 

370-22. Bushings. Covers of outlet boxes and outlet fittings having holes 
through which flexible cord pendants may pass, shall be provided with ap- 
proved bushings or shall have smooth, well-rounded surfaces, upon which 
the cord may bear. Where conductors other than flexible cord may pass 
through a metal cover, there shall be provided a separate hole for each wire, 
said hole being equipped with a bushing of suitable insulating material. 

370-23. Nonmetallic Boxes. Provisions for supports, or other mounting 
means, for nonmetallic boxes, shall be outside of the box, or the box shall 
be so constructed as to prevent contact between the conductors in the box 
and the supporting screws. 



ARTICLE 373 — CABINETS AND CUTOUT BOXES 

373-1. Scope. The provisions of this Article shall apply to the installation 
of cabinets and cutout boxes. Installations in hazardous locations shall con- 
form to the provisions of Articles 500 to 5 1 7 inclusive. 

A. Installation 
373-2. Damp or Wet Locations. In damp or wet locations, cabinets and 
cutout boxes of the surface type shall be so placed or equipped as to 
prevent moisture or water from entering and accumulating within the 
cabinet or cutout box, and shall be mounted so there is at least Va inch 



ARTICLE 373 — CABINETS AND CUTOUT BOXES 70-1 57 

air space between the enclosure and the wall or other supporting surface. 
Cabinets or cutout boxes installed in wet locations shall be weatherproof. 

373-3. Position in Wall. In walls of concrete, tile, or other noncombustible 
material, cabinets shall be so installed that the front edge of the cabinet 
will not set back of the finished surface more than Va inch. In walls con- 
structed of wood or ether combustible material, cabinets shall be flush with 
the finished surface or project therefrom. 

373-4. Unused Openings. Unused openings in cabinet or cutout boxes 
shall be effectively closed to afford protection substantially equivalent to 
that of the wall of the cabinet or cutout box. Where metal plugs or plates 
are used with nonmetallic cabinets or cutout boxes, they shall be recessed 
at least Va inch from the outer surface. 

373-5. Conductors Entering Cabinets or Cutout Boxes. Conductors enter- 
ing cabinets or cutout boxes shall be protected from abrasion and shall con- 
form to the following: 

(a) Openings To Be Closed. Openings through which conductors enter 
shall be adequately closed. 

(b) Metal Cabinets and Cutout Boxes. Where metal cabinets or cutout 
boxes are installed with open wiring or concealed knob-and-tube work, con- 
ductors shall enter through insulating bushings or, in dry places, through 
flexible tubing extending from the last insulating support and firmly secured 
to the cabinet or cutout box. 

373-6. Deflection of Conductors. Conductors entering or leaving cabinets 
or cut out boxes and the like shall conform to the following: 

Table 373-6(a) — Minimum Bending Space in Inches 



AWGor 












Circular-Mil 




Wires 


per Terminal 






Size of Wire 


1 


2 


3 


4 


5 




Not 










14-8 
6 


Specified 
1 -Vi 


— 


— 


— 


— 


4-3 

2 

i 


2 

2i/ 2 

3 

31/ 2 


— 


— 


— 


— 


0-00 


_ 








000-0000 


4 


6 


8 








250 MOM 


41/2 


6 


8 


10 





300-350 MCM 


5 


8 


10 


12 





400-500 MCM 


6 


8 


10 


12 


14 


600 - 700 MCM 


8 


10 


12 


14 


16 


750-900 MCM 


8 














1,000- 1,250 MOM 


10 














1,500-2,000 MCM 


12 


— 


— 


— 


— 



70-158 MASSACHUSETTS ELECTRICAL CODE 

(a) Width of Gutters. Conductors shall not be deflected within a cabinet 
unless a gutter having a width in accordance with Table 373-6(a) is provided. 

(b) Insulation at Bushings. Where ungrounded conductors of No. 4 or 
larger enter a raceway in a cabinet, pull box, junction box, or auxiliary gut- 
ter, the conductors shall be protected by a substantial bushing providing a 
smoothly rounded insulating surface, unless the conductors are separated 
from the raceway fitting by substantial insulating material securely fastened 
in place. Where conduit bushings are constructed wholly of insulating ma- 
terial, a locknut shall be installed both inside and outside the enclosure to 
which the conduit is attached. 

373-7. Space in Enclosures. Cabinets and cutout boxes shall conform to 
the following; 

(a) To Accommodate Conductors. Cabinets and cutout boxes shall be 
selected which have sufficient space to accommodate all conductors installed 
in them without crowding. 

373-8. Switch Enclosures. Switch enclosures shall not be used as junction 
boxes, auxiliary gutters or raceways for conductors feeding through or tap- 
ping off to other switches unless designs suitable for the purpose are em- 
ployed to provide adequate space for this purpose. 

373-9. Side or Back Wiring Spaces or Gutters. Cabinets and cutout boxes 
shall be provided with back wiring spaces, gutters, or wiring compartments 
as required by Section 373-1 1 (c and d). 

B. Construction Specifications 
373-10. Material. Cabinets and cutout boxes shall conform to the fol- 
lowing: 

(a) Metal Cabinets and Boxes. Metal cabinets and cutout boxes shall 
be well galvanized, plated with cadmium or other approved metallic finish, 
enameled, or otherwise properly coated, inside and out, to prevent corrosion. 

(b) Strength. The design and construction of cabinets and cutout boxes 
shall be such as to secure ample strength and rigidity. If constructed of 
sheet steel, the metal shall be of not less than No. 16 US gage (.0598 inch) 
in thickness. 

(c) Composition Cabinets. Composition cabinets shall be submitted for 
approval prior to installation. 

373-11. Spacing. The spacing within cabinets and cutout boxes shall con- 
form to the following: 

(a) General. The spacing within cabinets and cutout boxes shall be suf- 
ficient to provide ample room for the distribution of wires and cables placed 
in them, and for a separation between metal parts of devices and apparatus 
mounted within them as follows: 

(1) Base. There shall be an air space of at least 1/16 inch, except 
at points of support, between the base of the device and the wall of any 
metal cabinet or cutout box in which the device is mounted. 



ARTICLE 374-AUXILIARY GUTTERS 70-159 

(2) Doors. There shall be an air space of at least 1 inch between 
any live metal part (including live metal parts of enclosed fuses) and 
the door, unless the door is lined with an approved insulating material 
or is of a thickness of metal not less than No. 12 USS gage (.1046 
inch) , when the air space shall be not less than Vz inch. 

(3) Doors and Walls — Link Fuses. There shall be a space of at 
least 2 inches between open link fuses and metal-lined walls or metal, 
metal-lined or glass-paneled doors. 

(4) Live Parts. Except as noted above, there shall be an air space 
of at least Vi inch between the walls, back, gutter partition, if of metal, 
or door of any cabinet or cutout box and the nearest exposed current- 
carrying part of devices mounted within the cabinet where the potentials 
do not exceed 250 volts. This spacing shall be increased to at least one 
inch where the potentials exceed 250 volts. 

(b) Switch Clearance. Cabinets and cutout boxes shall be deep 
enough to allow the closing of the doors when 30-ampere branch-cir- 
cuit panelboard switches are in any position, or when combination 
cutout switches are in any position, or when other single-throw 
switches are opened as far as their construction will permit. 

(c) Wiring Space. Cabinets and cutout boxes which contain de- 
vices or apparatus connected within the cabinet or box to more than 8 
conductors, including those of branch circuits, meter loops, sub-feeder 
circuits, power circuits and similar circuits, but not including the supply 
circuit or a continuation thereof, shall have back wiring spaces or one 
or more side wiring spaces, side gutters or wiring compartments. 

(d) Wiring Space — Enclosure. Side wiring spaces, side gutters or 
side wiring compartments of cabinets and cutout boxes shall be ren- 
dered tight enclosures by means of covers, barriers or partitions ex- 
tending from the bases of the devices, contained in the cabinet, to the 
door, frame, or sides of the cabinet; provided, however, that where the 
enclosure contains only those conductors which are led frfem the cabi- 
net at points directly opposite their terminal connections to devices 
within the cabinet, such covers, barriers or partitions may be omitted. 
Partially enclosed back wiring spaces shall be provided with covers to 
complete enclosure. Wiring spaces that are required by Section 373- 
11(c) and which are exposed when doors are open, shall be provided 
with covers to complete the enclosure. 



ARTICLE 374 — AUXILIARY GUTTERS 



374-1. Purpose. Auxiliary gutters, used to supplement wiring spaces 
at meter centers, distribution centers, switchboards and similar points 
of wiring systems, may enclose conductors or bus-bars, but shall not be 
used to enclose switches, overcurrent devices, appliances or other similar 
equipment. 

374-2. Extension Beyond Equipment. An auxiliary gutter shall not 
extend a greater distance than 30 feet beyond the equipment which it 



70-160 MASSACHU SE TTS ELECTRICAL CODE 

supplements except in elevator work. Any extension beyond this dis- 
tance shall comply with the provisions for wireways in Article 362 or 
with the provisions for busways in Article 364. 

374-3. Supports. Gutters shall be supported throughout their entire 
length at intervals not exceeding 5 feet. 

374-4. Covers. Covers shall be securely fastened to the gutter. 

374-5. Number of Conductors. Auxiliary gutters shall not contain 
more than 30 conductors at any cross section unless the conductors are 
for signal circuits or are controller conductors between a motor and its 
starter and used only for starting duty. The sum of the cross-sectional 
areas of all contained conductors at any cross section of an auxiliary 
gutter shall not exceed 20 per cent of the interior cross-sectional area 
of the gutter. 

For elevators see Section 620-35. 

374-6. Ampacity of Conductors. The ampacities of insulated copper 
and aluminum conductors are given in Tables 310-12 and 310-14 re- 
spectively. The correction factors specified in Note 8 of these tables 
shall not apply to conductors in auxiliary gutters. The current carried 
continuously in bare copper bars in auxiliary gutters shall not exceed 
1000 amperes per square inch of cross section of the conductor. For 
aluminum bars the current carried continuously shall not exceed 700 
amperes per square inch of cross section of the conductor. 

374-7. Clearance of Bare Live Parts. Bare conductors shall be securely 
and rigidly supported so that the minimum clearance between bare cur- 
rent-carrying metal parts of opposite polarities mounted on the same 
surface shall be not less than 2 inches, nor less than 1 inch for parts that 
are held free in the air. A clearance not less than 1 inch shall be secured 
between bare current-carrying metal parts and any metal surface. Ade- 
quate provisions shall be made for the expansion and contraction of 
bus-bars. 

374-8. Splices and Taps. Splices and taps shall conform to the fol- 
lowing : 

(a) Splices or taps, made and insulated by approved methods, may 
be located within gutters when they are accessible by means of re- 
movable covers or doors. The conductors, including splices and taps, 
shall not fill the gutter to more than 75 per cent of its area. 

(b) Taps from bare conductors shall leave the gutter opposite their 
terminal connections and conductors shall not be brought in contact 
with uninsulated current-carrying parts of opposite polarity. 

(c) All taps shall be suitably identified at the gutter as to the circuit 
or equipment which they supply. 

(d) Tap connections from conductors in auxiliary gutters shall be 
provided with overcurrent protection in conformity with the provisions 
of Section 240-15. 

374-9. Construction and Installation. Auxiliary gutters shall be con- 
structed in accordance with the following: 



ARTICLE 380-SWITCHES 70-161 

(a) Gutters shall be so constructed and installed that adequate elec- 
trical and mechanical continuity of the complete system will be se- 
cured. 

(b) Gutters shall be of substantial construction and shall provide a 
complete enclosure for the contained conductors. All surfaces, both in- 
terior and exterior, shall be suitably protected from corrosion. Corner 
joints shall be made tight and where the assembly is held together by 
rivets or bolts, these shall be spaced not more than 12 inches apart. 

(c) Suitable bushings, shields or fittings having smooth rounded edges 
shall be provided where conductors pass between gutters, through par- 
titions, around bends, between gutters and cabinets or junction boxes 
and at other locations where necessary to prevent abrasion of the in- 
sulation of the conductors. 

(d) Gutters shall be constructed of sheet metal of thicknesses not 
less than in the following table: 

Table 374-9(d) 

Maximum Width of the Widest Surface of Gutters 

Thickness (Manufacturers Standard Gage) 

Up to and including 6 inches No. 16; 0.0598 inch 

Over 6 in. and not over 18 in No. 14; 0.0747 inch 

Over 18 in. and not over 30 in No. 12; 0.1046 inch 

Over 30 inches No. 10; 0.1345 inch 

(e) Where insulated conductors are deflected within the auxiliary 
gutter, either at the ends or where conduits, fittings or other raceways 
enter or leave the gutter, or where the direction of the gutter is deflected 
greater than 30 degrees, dimensions corresponding to Section 373-6 
shall apply. 

(f) Auxiliary gutters intended for outdoor use shall be of approved 
raintight construction. 



ARTICLE 380 — SWITCHES 



A. Installation 

380-1. Grounded Conductors. No switch or circuit breaker shall dis- 
connect the grounded conductor of a circuit unless the switch or cir- 
cuit breaker simultaneously disconnects the ungrounded conductor or 
conductors, or unless the switch or circuit breaker is so arranged that 
the grounded conductor cannot be disconnected until the ungrounded 
conductor or conductors have first been disconnected. 

380-2. Three-Way and Four-Way Switches. Three-way and four-way 
switches shall be so wired that all switching is done only in the un- 
grounded circuit conductor. Wiring between switches and outlets shall, 



70-162 MASSACHUSETTS ELECTRICAL CODE 

where in metal enclosures, be run with both polarities in the same en- 
closure. 

380-3. Enclosures. Switches and circuit breakers shall be of the ex- 
ternally operable type enclosed in metal boxes or cabinets, except pen- 
dant and surface type snap switches and knife switches mounted on an 
open face switchboard or panelboard. 

380-4. Wet Locations. A switch or circuit breaker in a wet location or 
outside of a building shall be enclosed in a weatherproof enclosure or 
cabinet installed to conform to Section 373-2. 

380-5. Time Switches, Flashers, and Similar Devices. Time switches, 
flashers, and similar devices need not be of the externally operable 
type. They shall be enclosed in metal boxes or cabinets except: 

Exception No. 1 . Where mounted on switchboards or control panels. 

Exception No. 2. Where enclosed in approved individual housings. 

380-6. Position of Knife Switches. Single- Lhrow knife switches shall be 
so placed that gravity will not tend to close them. Double-throw knife 
switches may be mounted so that the throw will be either vertical or 
horizontal as preferred, but where the throw be vertical a locking de- 
vice shall be provided which will insure the blades remaining in the 
open position when so set. 

380-7. Connection of Knife Switches. Knife switches, unless of the 
double-throw type, shall be so connected that the blades are dead when 
the switch is in the open position. 

380-8. Accessibility and Grouping. Switches and circuit breakers, so 
far as practicable, shall be readily accessible and shall be grouped. 

Snap switches shall not be grouped or ganged in outlet boxes unless 
they can be so arranged that the voltage between exposed live metal 
parts of adjacent switches does not exceed 300 volts. 

380-9. Covers of Flush Snap Switches. Flush snap switches, that are 
mounted in ungrounded metal boxes and located within reach of con- 
ducting floors or other conducting surfaces, shall be provided with 
covers of nonconducting, noncombustible material. Metallic faceplates 
shall be of ferrous metal not less than 0.030 inch in thickness or of 
nonferrous metal not less than 0.040 inch in thickness. Faceplates of 
insulating material shall be noncombustible and not less than 0.10 inch 
in thickness but may be less than 0.10 inch in thickness if formed or 
reinforced to provide adequate mechanical strength. 

380-10. Mounting of Surface-Type Snap Switches. Snap switches used 
with open wiring on insulators shall be mounted on sub-bases of in- 
sulating material which will separate the conductors at least V2 inch 
from the surface wired over. 

380-11. Circuit Breakers as Switches. A circuit breaker operable di- 
rectly by applying the hand to a lever or handle may serve as a switch 
provided it has the number of poles required for such switch. 

380-12. Grounding of Enclosures. Enclosures for switches or circuit 
breakers on circuits of over 150 volts to ground shall be grounded in 
the manner specified in Article 250, except where accessible to quali- 
fied operators only. 



ARTICLE 380-SWITCHES 70-163 



380-13. Knife Switches. 

(a) Knife switches rated for more than 1200 amperes at 250 volts or 
less, and for more than 600 amperes at 251 to 600 volts, shall be used 
only as isolating switches and shall not be opened under load. 

(b) To interrupt currents greater than 1200 amperes at 250 volts or 
less, or 600 amperes at 251 to 600 volts, a circuit breaker or a switch 
of special design approved for such purpose shall be used. 

(c) Knife switches of lower rating may be used as general-use 
switches and may be opened under load. 

(d) Motor-circuit switches (see Definition) may be of the knife- 
switch type. 

380-14. Rating of Snap Switches. Snap switches installed for the fol- 
lowing types of loads shall be rated as follows : 

(a) Noninductive Loads. For noninductive loads other than tungs- 
ten-filament lamps, switches shall have an ampere rating not less than 
the ampere rating of the load. 

(b) Tungsten Filament Loads. For tungsten-filament lamp load and 
for combined tungsten-filament and noninductive loads, switches shall 
be "T" rated or, where on alternating-current circuits, may be a gen- 
eral use alternating-current snap switch. 

Exception. A switch that is not "T" rated may be installed to con- 
trol such loads provided all three of the following qualifications are 
satisfied: 

(1) Where switches are used in branch circuit wiring systems in 
private homes; in rooms in multiple-occupancy dwellings used only as 
living quarters by tenants; in private hospital or hotel rooms; or in simi- 
lar locations but not in public rooms or places of assembly; and 

(2) Only where such a switch controls permanently connected fix- 
tures or lighting outlets in one room only, or in one continuous hall- 
way where the lighting fixtures may be located at different levels, or 
on porches or in attics or basements not used for assembly purposes; 
and 

(3) The switch is rated at not less than 10A, 125V; 5A, 250V; or 
for the 4-way types, 5A,125 V; 2A, 250V. 

(c) Inductive Loads. Switches controlling inductive loads shall have 
an ampere rating twice the ampere rating of the load unless they are of 
a type approved as part of an assembly or for the purpose employed. 
On alternating-current circuits, general use alternating-current snap 
switches may be used to control inductive loads other than motors not 
exceeding the ampere rating of the switch. 

For switches on signs and outline lighting, see Section 600-2. 
For switches controlling motors, see Sections 430-83 and 430-110. 

B. Construction Specifications 

380-15. Marking. Switches shall be marked with the current and 
voltage and, if horsepower rated, the maximum rating for which they 
are designed. 



70-1 64 MASSACHUSETTS ELECTRICAL CODE 

380-16. 600-Volt Knife Switches. Auxiliary contacts of a renewable or 
quick-break type or the equivalent, shall be provided on all 600-volt knife 
switches designed for use in breaking currents over 200 amperes. 

Auxiliary contacts shall be provided on direct-current switches rated at over 
250 volts. 

380-17. Multiple Fuses. Switches rated above 600 amperes may be arranged 
for fuses in multiple provided as few fuses as possible sre used and the 
fuses are of the same type and rating and are so mounted as to eliminate a po- 
tential difference between the terminals of the fuses. (See Section 240-14.) 

ARTICLE 384 — SWITCHBOARDS AND 
PANELBOARDS 

384-1. Scope. The requirements of this Article shall apply to all switch- 
boards, panelboards, and distribution boards installed for the control of light 
and power circuits. 

Exception No. I. Switchboards in utility company operated central sta- 
tions or substations, which directly control energy derived from generators 
or transforming devices. 

Exception No. 2. Switchboards or portions thereof used exclusively to 
control signal circuits operated by batteries. 

The requirements of this Article shall apply to battery-charging panels 
where current is taken from light or power circuits. 

384-2. Application of Other Articles. Switches, circuit breakers and over- 
current devices used on switchboards, panelboards and distribution boards, 
the boards and their enclosures, shall conform to the requirements of Articles 
240, 250, 370, 380 and other Articles which apply. Switchboards and panel- 
boards in hazardous locations shall conform to the requirements of Articles 
500 to 51 7 inclusive. 

384-3. Support and Arrangement of Bus-bars and Conductors. 

(a) Conductors and bus-bars on a switchboard, panelboard or control board 
shall be so located as to be free from physical damage and shall be held 
firmly in place. 

(b) The arrangement of bus-bars and conductors shall be such as to avoid 
overheating due to inductive effects. 

(c) Each switchboard, switchboard section or panelboard, if used as service 
equipment, shall be provided with an equipment grounding means placed 
within the service disconnect section for connecting the neutral on its supply 
side to the switchboard or panelboard frame. The equipment grounding 
means for switchboards or panelboards rated more than 225 amperes shall 
have a cross sectional area of at least 25% of the cross sectional area of the 
service entrance conductors, but need not exceed the cross sectional area of 
the grounding conductors specified in Table 250-94(a). 



ARTICLE 384-SWITCHBOARDS AND PANELBOARDS 70-165 

It is recommended that the switchboard, if consisting of more than one 
section, be provided with a copper ground bus, and equipment ground strap 
be connected to the switchboard ground bus. 

A. Switchboards 

384-4. Location of Switchboards. Switchboards which have any ex- 
posed live parts shall be located in permanently dry locations and then 
only where under competent supervision and accessible only to quali- 
fied persons. 

384-5. Wet Locations. Where a switchboard is in a wet location or 
outside of a building, it shall be enclosed in a weatherproof enclosure 
or cabinet installed to conform to Section 373-2. 

384-6. Location Relative to Easily Ignitible Material. Switchboards 
shall be so placed as to reduce to a minimum the probability of com- 
municating fire to adjacent easily ignitible material. 

384-7. Clearance from Ceiling. Switchboards shall not be built up to 
a nonfireproof ceiling, a space of 3 feet being left between the ceiling 
and the board, unless an adequate fireproof shield is provided between 
the board and the ceiling. 

384-8. Clearance Back of Switchboard. Clearances around switchboards 
shall conform to the provisions for Working Space about Electrical 
Equipment as specified in Section 1 10-16 of this Code. 

384-9. Conductor Covering. Insulated conductors where closely 
grouped, as on the rear of switchboards, shall each have a flame-re- 
tardant outer covering. The conductor covering shall be stripped back 
a sufficient distance from the terminals so as to not make contact with 
them. Insulated conductors used for instrument and control wiring on 
the back of switchboards shall be flame-retardant, either inherently or 
by means of an outer covering, such as one of the following types: 
R, RH, RW, RHH, RHW, V, ALS, AVA, AVB, SIS, T, TA, TBS, TW, 
THW, MI, or other types specifically approved for the purpose. 

384-11. Grounding Switchboard Frames. Switchboard frames and 
structures supporting switching equipment shall be grounded, except 
that frames of direct-current single-polarity switchboards need not be 
grounded if effectively insulated. 

384-12. Grounding of Instruments, Relays, Meters and Instrument Trans- 
formers on Switchboards. Instruments, relays, meters and instrument 
transformers located on switchboards shall be grounded as specified in 
Sections 250-121 to 250-125. 

B. Panelboards 

384-13. General. All panelboards shall have a rating not less than the 
minimum feeder capacity required for the load as computed from Ar- 
ticle 220. Panelboards shall be durably marked by the manufacturer 
with the voltage and the current rating and the number of phases for 
which they are designed and with the manufacturer's name or trade- 
mark in such a manner as to be visible after installation, without dis- 
turbing the interior parts or wiring. 



70-166 MASSACHUSETTS ELECTRICAL CODE 

384-14. Lighting and Appliance Branch Circuit Panelboard. For the 

purposes of this Section, a lighting and appliance branch circuit panel- 
board is one having more than 10 per cent of its overcurrent devices 
rated 30 amperes or less, for which neutral connections are provided. 
384-15. Number of Overcurrent Devices on One Panelboard. Not more 
than 42 overcurrent devices (other than those provided for in the 
mains) of a lighting and appliance branch circuit panelboard shall be 
installed in any one cabinet or cutout box. 

A lighting and appliance branch circuit panelboard shall be pro- 
vided with physical means to prevent the installation of more overcur- 
rent devices than that number for which the panelboard was designed, 
rated and approved. 

For the purposes of this Article a two-pole circuit breaker shall be 
considered two overcurrent devices; a three-pole breaker shall be con- 
sidered three overcurrent devices. 
384-16. Overcurrent Protection. 

(a) Each lighting and appliance branch circuit panelboard shall be 
individually protected on the supply side by not more than two main 
circuit breakers or two sets of fuses having a combined rating not 
greater than that of the panelboard. 

Exception No. 1. Individual protection for a lighting and appliance 
panelboard is not required when the panelboard feeder has overcur- 
rent protection not greater than that of the panelboard. 

Exception No. 2. Individual protection for lighting and appliance 
branch circuit panelboards is not required where such panelboards are 
used as service equipment in supplying an individual residential oc- 
cupancy and where any bus supplying 15 or 20 ampere circuits is pro- 
tected on the supply side by an overcurrent device. 

(b) Panelboards equipped with snap switches rated at 30 amperes or 
less, shall have overcurrent protection not in excess of 200 amperes. 

(c) The total load on any overcurrent device located in a panelboard 
shall not exceed 80% of its rating where in normal operation the load 
will continue for 3 hours or more. 

Exception. Except where the assembly including the overcurrent de- 
vice is approved for continuous duty at 100% of its rating. 
384-17. Panelboards in Damp or Wet Locations. Panelboards in damp 
or wet locations shall be installed in conformity to Section 373-2. 
384-18. Enclosure. Panelboards shall be mounted in cabinets or cut- 
out boxes. 

384-19. Relative Arrangement of Switches and Fuses. Panelboards 
having switches on the load side of any type of fuses shall not be in- 
stalled except for use as service equipment as provided in Section 
230-94. 

C. Construction Specifications 

384-20. Panels. The panels of switchboards shall be made of mois- 
ture-resistant, noncombustible material. 

384-21. Bus-bars. Bus-bars may be of bare metal provided they are 
rigidly mounted. 

384-22. Protection of Instrument Circuits. Instruments, pilot lights, 
potential transformers, and other switchboard devices with potential 



ARTICLE 390-PREFABRICATED BUILDINGS 



70-167 



coils, except where the operation of the overcurrent device might in- 
troduce a hazard in the operation of devices, shall be supplied by a cir- 
cuit that is protected by standard overcurrent devices of a rating not 
greater than 15 amperes, except that for ratings of 2 amperes or less 
special types of enclosed fuses may be used. 

384-23. Component Parts. Switches, fuses, and fuseholders used on 
panelboards shall conform to the requirements of Articles 240 and 
380 so far as they apply. 

384-24. Knife Switches. Knife switches shall be so arranged that the 
blades, when exposed during operation, will be dead when the switches 
are open. 

384-25. Color-Coding. On switchboards or panelboards that are pro- 
vided with color markings to indicate the main bus-bars to which 
branch circuit bus-bars are connected, the colors shall conform to the 
color coding of Section 210-5. 

384-26. Spacings. Except at switches and circuit breakers, the dis- 
tance between bare metal parts, bus-bars, etc., shall be not less than 
specified in the following Table: 

Table 384-26— Spacings Between Bare Metal Parts 

Opposite Opposite 

Polarity Polarity 
When When 

Mounted on Held 

the Same Free *Live Parts 

Surface in Air to Ground 

Not over 125 volts % inch V 2 inch V2 inch 

Not over 250 volts I 1 /* inch % inch V2 inch 

Not over 600 volts 2 inches 1 inch 1 inch 

*For spacing between live parts and doors of cabinets, see subparagraph a of 
Section 373-11. 



It should be noted that the above distances are the minimum allow- 
able, and it is recommended that greater distances be provided wher- 
ever the conditions will permit. 

At switches, enclosed fuses, etc., parts of the same polarity may be 
placed as close together as convenience in handling will allow, unless 
close proximity causes excessive heating. 



ARTICLE 390 — PREFABRICATED BUILDINGS 



390-1. Scope. The intent and purpose of the following sections is to 
define approved methods for the wiring of prefabricated building sec- 
tions, panels, or units designed for later erection or assembly as integral 
parts of buildings whether wired in the process of manufacture or at 
the site of erection or assembly. 



70-168 MASSACHUSETTS ELECTRICAL CODE 

390-2. Wiring Methods. Only wiring methods recognized in this Code 
shall be used. 

390-3. Code Provisions to Apply. The provisions of this Code shall 
apply for the type of wiring method used and the type of construction 
employed. 



70-169 



Chapter 4. Equipment for General Use 
ARTICLE 400 — FLEXIBLE CORDS 



A. General and Types 

400-1. General. Flexible cords shall be suitable for the conditions of 
use and location. 

400-2. Types. Cords of the several types shall conform to the de- 
scriptions of Table 400-11. Types of flexible cords other than those 
listed in Table 400-1 1 and other uses for types listed in the Table, shall 
be the subject of special investigations and shall not be used before be- 
ing approved. 

B. Use and Installation 

400-3. Use. Flexible cord may be used only for (1) pendants; (2) 
wiring of fixtures; (3) connection of portable lamps or appliances; (4) 
elevator cables; (5) wiring of cranes and hoists; (6) connection of sta- 
tionary equipment to facilitate their frequent interchange; or (7) pre- 
vention of the transmission of noise or vibration; or (8) facilitating the 
removal or disconnection of fixed appliances for maintenance or re- 
pair. 

400-4. Prohibited Uses. Flexible cord shall not be used ( 1 ) as a sub- 
stitute for the fixed wiring of a structure; (2) where run through holes 
in walls, ceilings, or floors; (3) where run through doorways, windows, 
or similar openings; (4) where attached to building surfaces; or (5) 
where concealed behind building walls, ceilings, or floors. 

400-5. Splices. Flexible cord shall be used only in continuous lengths 
without splice or tap. 

400-6. Cords in Show-Windows and Show-Cases. Flexible cord used 
in show-windows and show-cases shall be of types S, SO, SJ, SJO, ST, 
SJT, or AFS, except for the wiring of chain supported fixtures, and for 
supplying current to portable lamps and other merchandise for exhibi- 
tion purposes. 

400-7. Minimum Size. Flexible cords shall not be smaller than No. 18, 
except that tinsel cords, or cords having equivalent characteristics, of 
smaller size may be approved for use with specific appliances. 

400-8. Insulation— Over 300 Volts. Where the voltage between any 
two conductors exceeds 300, but does not exceed 600, flexible cord of 
No. 10 and smaller shall have rubber or thermoplastic insulation on the 
individual conductors at least 3/64 inch in thickness, unless type S, SO 
or ST cord is used. — — — ~ 

400-9. Overcurrent Protection and Ampacities of Flexible Cords. 

(a) Overcurrent Protection. Flexible cords not smaller than No. 18, 



70-170 



MASSACHUSETTS ELECTRICAL CODE 



and tinsel cords, or cords having equivalent characteristics, of smaller 
size approved for use with specific appliances, shall be considered as 
protected against overcurrent by the overcurrent devices described in 
Section 240-5. Cords shall be not smaller than required in Table 400-9 
(b) for the rated current of the connected equipment. 

Table 400-9(b). Ampacity of Flexible Cord 

Table 400-9 (b) gives the allowable ampacity for not more than 
three current carrying conductors in a cord. If the number of current 
carrying conductors in a cord is from four to six, the allowable am- 
pacity of each conductor shall be reduced to 80 per cent of the values 
in the Table. The ampacities for the sizes and types of three conductor 
cords connected to utilization equipment, where the third conductor is 
used for equipment grounding only and does not carry any load current, 
are given in Notes 1 and 2 following the Table. 

(Based on Room Temperature of 30°C (86°F.). See Section 400-9 and Table 400-11.) 















Cotton Types 




Rubber Types i 


Rubber Types 1 
PO, C, PD, 


Rubber Types 
S, SO. SRD. 
SJ, SJO, SV, 
SVO, SP 






CFC* 
CFPO* 


Size 


TP. TS 


P. K, 
E, EO 


Types AFS, 
AFSJ, HC, 


Types AVPO, 
AVPD 


CFPD* 








AWG 






plastic Types 


Thermo- 


Thermo- 


HPD, HSJ, 




Types 




TPT, TSP 


plastic Type 


plastic Types 


HSJO, HS, 




AFC* 






ET 


ST, STO, 
SRDT, SJT, 
SJTO, SVT, 
SVTO, SPT 


HSO, HPN 




AFPO* 
AFPD* 


27** 


0.5 












18 




5 


7 


io 


17 


6 


17 








12 






16 




7 


10 


15 


22 


8 


15 








17 






14 




15 


15 


20 


28 


17 


12 




20 


20 


30 


36 


23 


10 




25 


25 


35 


47 


28 


8 




35 


35 




, . 


. . 


6 




45 


45 




. . 




4 




60 


60 




. . 




2 


80 






. . 




•These types are u 


sed almost ex 


clusively in : 


ixtures wher* 


; they are ex 


posed to high 


tempera 


tures and am 


pere ratings 


ire assigned 


accordingly. 







**Tinsel cord. 



Note 1. For Nos. 18, 16 and 14 AWG sizes of Types S, SO and ST 
Cords, the allowable ampacities are 10, 13 and 18 amperes respectively. 

Note 2. For Nos. 18 and 16 AWG sizes of SJ, SJO and SJT Cords, 
the allowable ampacities are 10 and 13 amperes respectively. 

Note 3. Ultimate Insulation Temperature. In no case shall conduc- 
tors be associated together in such a way with respect to the kind of cir- 
cuit, the wiring method employed, or the number of conductors, that 
the limiting temperature of the conductors will be exceeded. 



ARTICLE 400-FLEXIBLE CORDS 



70-171 



400-10. Pull at Joints and Terminals. Flexible cords shall be so con- 
nected to devices and to fittings that tension will not be transmitted to 
joints or terminal screws. This shall be accomplished by a knot in the 
cord, winding with tape, by a special fitting designed for that purpose, 
or by other approved means which will prevent a pull on the cord from 
being directly transmitted to joints or terminal screws. 



Notes to Table 400-11 



1. Except for Types AFPO, 
CFPO, PO-1, PO-2, PO, SP-1, SP-2, 
SPT-1, SPT-2, TP, TPT, and AVPO, 

individual conductors are twisted to- 
gether. 

2. Type PO-1 is for use only with 
portable lamps, portable radio re- 
ceiving appliances, portable clocks 
and similar appliances which are not 
liable to be moved frequently and 
where appearance is a consideration. 

3. Types TP, TPT, TS, and TST 

are suitable for use in lengths not 
exceeding eight feet when attached 
directly, or by means of a special 
type of plug, to a portable appli- 
ance rated at 50 watts or less and of 
such nature that extreme flexibility 
of the cord is essential. 

4. Type K is suitable for use on 
theatre stages. 

5. Rubber-filled or varnished 
cambric tapes may be substituted 
for the inner braids. 

6. Types S, SO, and ST are suit- 
able for use on theatre stages, in ga- 
rages and elsewhere, where flexible 
cords are permitted by this Code. 

7. Traveling cables for operating, 
control and signal circuits may have 
one or more nonmetallic fillers or 
may have a supporting filler of 
stranded steel wires having its own 
protective braid or cover. Cables ex- 
ceeding 100 feet in length shall have 



steel supporting fillers, except in lo- 
cations subject to excessive moisture 
or corrosive vapors or gases. Where 
steel supporting fillers are used, they 
shall run straight through the center 
of the cable assembly and shall not 
be cabled with the copper strands of 
any conductor. 

Type E and EO Cables may in- 
corporate in the construction #20 
Gauge Conductors formed as a pair, 
and covered with suitable metallic 
braided shielding for telephone cir- 
cuits. The insulation of the conduc- 
tors may be rubber or thermoplastic 
of thickness specified for Type E 
and EO Cables. The shield shall 
have its own protective covering. 
This component may be incorporated 
in any layer of the cable assembly, 
and shall not run straight through 
the center. 

8. A third conductor in these ca- 
bles is for grounding purposes only. 

9. The individual conductors of 
all cords except those of heat-resist- 
ant cords (Types AFC, AFPO, 
AFPD, AFS, AFSJ, AVPO, AVPD, 
CFC, CFPO and CFPD) shall have 
a rubber or thermoplastic insulation, 
except that the grounding conduc- 
tor where used, shall be in accord- 
ance with Paragraph 400- 14(b). A 
rubber compound shall be vulcan- 
ized except for heater cords (Types 
HC, HPD and HSJ) and for belt 
fillers in Types P-l, P-2, and P. 



70-172 



MASSACHUSETTS ELECTRICAL CODE 



CD 

co 


Not 
Hard 
Usage 


Not 
Hard 
Usage 


Not 
Hard 
Usage 


Not 
Hard 
Usage 


c 

2 


T3 bfi 

03 CO 


->- 

c 


i3 bo 

03 co 


CO 

2 O 
^Ph 

Q 


CO 

o CD 

2* cd 

J?Ph 

Q 


CO 
Cl CD 

J?Ph 


CO 

Cl CU 
e u 

S s 

Q 


CO 
CD 
CD 

>>* 
£Ph 
Q 


CO 
CD 
CD 

^;Ph 
Q 


T3 g 

cd ^ 

o 03.2 
03 ^-3 

< <j 


^ g 

O 03 03 
03 S 


CD ° 

cj o3 o3 
03 n -3 

^ < 


T3 g 

O o3 o3 
03 — 


c 

03 
C 

O) 
Ph 


c 

03 
13 

C 

CD 
Ph 


be 
.£ 

CD 
> 

O 

O 

t- 
<v 
-t-> 

3 
O 


>- 
cd 

Ph 


O O 

s^ 

C CO 

cd o3 


CD 


O CD 

6 '-3 

E CO 

CD 03 


CD 

c 
o 


CO 

O to 

r- CD 

O co 
o?< 

CD 
S oj 

r 9 ta 


CD 

c 

o 


C 

o 
>> 

03 

Ph 

O 

c 
o 

o 
U 


Braid 

on Each 

Conductor 


CD 

C 

o 
55 


CD 

C 

o 


<D 

o 


CD 

C 
O 


c 

o 

c >» 

O 03 

U o 


CD 

o 


o 

-i_j 03 
°Ph 


CD 

c 
o 


c 
.2 

co 

C 
i— i 


CD 

Ph 


1 

O <y 

£ - ^ 

£ to 
Eh n 


0) 

3 


i 

O cj 

6--J3 

E CO 

cd o3 

■ sz 'o. 




1 c 

£ So 


CO 

«« o 

6 -o 

z § 


CM 


CM 


CO 

o 

CM 


CO 

o 

CM 


CO 

° 

CM 


CM 


CO 

o 

CM 


CO 

o 

CM 


CM 


CO 
(-, 

o 

CM 


cyO 


cm 


CM 


CM 


<M 


O 

1 1 
CO 
1— 1 


o 

1 

CO 




„- co 

CD CD 


1 cu 

! CD CO CO 
1 C/2 CD 

CD CD CD 

Eh^S w-g 

1 Eh Eh 


SCO 
S/3 CD 


<3 


o 

Ph 

i- 


Q 

Ph 
&h 


o 

O 1 Ph 
&h fe 

O o 


Q 

Ph 

o 


CD 

s 

cd 

03 
t- 


'3 

03 

1 Cm 


CO ~ 

5 o 

hO 


T3- 

<D 

CD 

CD t 
03 
•-3 


co T3 

5 o 

hO 


i 
o 

CO 

CD 
CO 

1 < 


3 

- 
U -i 

> 

3: 


+ 
! 
C 

il 

D C 

CP 


5 
2 -3 

>i 

u o 

hU 


1 o 

1 o 


3 co ( 
V (V c 

dPhC 


3 

5 
3 



ARTICLE 400-FLEXIBLE CORDS 



70-173 



Not 
Hard 
Usage 


Not 
Hard 
Usage 


Not 
Hard 
Usage 


Not 
Hard 
Usage 


Not 
Hard 
Usage 


hrt 03 
— CO 


£ CD 
03 M 
M 03 
~ CO 


Dry 
Places 


CO 

cl cd 

^43 

43 Ph 
Q 


t/j 

Q. CD 
=? CD 

£43 

45 Ph 

Q 


co 

0. CD 
2* CD 

C43 
43 Ph 
Q 


Damp 
Places 


Dry 
Places 


co 

CD 
O 

>>-2 


(M 

CD 
+3 

o 
S3 

CD 
CD 
GO 


Pendant 

or 
Portable 


Pendant 

or 
Portable 


Refriger- 
tors or 

Room Air 
Condi- 
tioners 


Pendant 

or 
Portable 


Refriger- 
ators or 

Room Air 
Condi- 
tioners 


Pendant 
or Port. 


Pendant 
or Port. 


C 

o 
>> 

03 
t- 

o 

c 
o 

o 
U 


CD 

-a 

3 

Ph 


CD 
J3. 
dD 

PS 


Thermoplastic 


Thermoplastic 


CD 

c 



c 

>> 

03 

PS 

s_ 

O 

c 


-u 

O 
O 


e 
o 

o 
U 


CD 

c 



CD 

c 



CD 

c 



CD 

c 


5 


c 


-u 






c 


-t-> 






Rubber 


CD 
-D 

3 
Ph 


(-, 

CD 
-D 

3 
PS 


1 

O CD 

CD 03 
-*= O. 


1 
O CD 

£•-£ 

CD 03 

Eh ^ 


CD 

.a 

J3. 

PS 


CD 

PS 


CM 


CM 


cm 


CM 


CD 
(h 
O 

£ 



CM 


CD 
In 

O 

£ 


CM 


00 

1— ( 


CD 

1 

00 

T-H 


o I 

i-H 1 

1 | 
00 00 

T-H T-H 


CD 

T-H 

1 
00 

T-H 


CXI 

i 
00 


00 


CD 

T-H 

1 

00 

T— 1 


O 

T-H 

1 
00 

T-H 


O 

i-H 

1 
00 

T-H 


O 

T-H 

1 
00 

T-H 


,-H 

1 

o 

Ph 


1 

o 


o 

Ph 


T-H 

1 

Ph 

m 


SP-2 
See 
Note 8 


00 
CO CD 


T-H 

1 
Eh 

Ph 
CO 


SPT-2 

See 
Note 8 


SPT-3 
Note 8 





Q 

Ph 


1 


T3 
t- 

o 
U 

In 

o3 
Ph 




1 

PS" 


3 

3 
H 




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5 

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3 

H 


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CO — 

43~ 

33 o3 
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"73 

O 

Q. 

£ 

03 


1 

-(J 

(h 



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T3c3 

H o3 



70-174 



MASSACHUSETTS ELECTRICAL CODE 



CO 


Si Oi 

c3 M 

HH TO 
KM GO 


CD 

Si W 

C3>— } 


CD 
Si to 


'So; 

HM CO 

55 


CD 

T3 <a 

Si CO 




CO 
<D 

>»i2 

Q 


co 

cd 

g rt 
J?Ch 

Q 


CO 
O. CD 

4SE 

Q 


CO 

£42 

4? Cm 


+j CD 

42 *i «« 

C ° ** 

a, o 
Oh Ph 


+j CD 

42 s- s 3 

c ° fc 

O) 
Cm Cm 


+j CD 

42 s- <a 

c ° «- 
55 
Cm Cm 


+j CD 

45 s- * 

C ° fe 
Cm CU 


bo 

a> 
> 
o 
O 
t-, 

CD 

o 


4H 

*■» r3 

O Si 

On 
-u 3 
©PS 

o 


.2 ^ 

'0 o> 

S CO CO 
vJ 1 co 

O S C 

*3E 


Si 
CD 

3 

Cm 


co 

42 
13, 


S 

Si 
CD 


Si 

CD 

X3 

3 
Cm- 


C 
c«t3 

S a 

CO 

45 ft. 
K| 
.t: 
OU 


CO 

42 
"3. 


£ 

Si 

CD 


Braid 

on Each 

Conductor 


o 

■»-> 
o 
O 


C 
O 

-M> 

-u 






CD 

c 



cd 

C 
O 


c 
o 

42 

co 
C 


Si 

0> 

X5 

3 
Cm 


Si 
CD 

X> 
Xi 

3 
C4 


Si 

CD 

X5 

3 



£ 

Si 

CD 


Si 
CD 

-Q 

3 
C4 


^1 »-■ 

I 3 

cStf 
H 


<~ ° 

O o 

- 3 
^ o 


CD 

Si 

O 

£ 

o 
cm 


CD 

Si 

O 

£ 

s~ 



CM 


CM 


Si 

O 

CO 

cm" 


0,0 


oo 

H 


SO 

i-H 

1 
00 

H 




1-H 

1 
00 
1— 1 


O 

1— ( 

1 

00 


00 

1—1 


CD 

i-H 
1 

00 

1-H 


si 


1 

Cm 


CM 

1 

Cm 


Cm 


CD CD 

a z 


O 
> 

CO 

> 

Xfl 


.O °° 


1-9 


O 

•-3 


O 

Hj 1-3 

mm 


01 

g 


< 
I 

t 

e 

«* 
t 

'o 



3 
) 

2 O 

* 




T3 
O 

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PQ 


6| 
gJ 

> 


S 
JO 




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s-'>l 

.2 S3 « 
3 

»-9 


3 
5 
> 



ARTICLE 400-FLEXIBLE CORDS 



70-175 







Extra 
Hard 
Usage 




Portable 
Heaters 




Portable 
Heaters 


CD 

~ co 

^t CD 

»-. ™ 

o a> 
P<ffi 


CD 
J±i CO 

n ^ 

o <y 

cutn 




CO 
o CD 

£ oa 


Damp 
Places 

Dry 
Places 


CO 

Q, 9 

£i2 
Q 


CO 

o CD 

£iH 

^Ph 

Q 


Pendant 

or 
Portable 


Portable 


Portable 


Portable 


Portable 


Rubber 


Oil Resist. 
Compound 


CO 
O 

£ 

CD 


Oil Resistant 
Thermoplastic 


Rubber 


CD 

c 
o 


c 
o 
>i 
ca 

i-, 

o 

c 

o 

o 
O 


Cotton and Rubber 


Cotton and Oil Re- 
sistant Compound 


CD 
Xi 

Kg 
■gg 

c w 

O o 


i TJ 
CD £ 
Ph 3 

_ o 

~ Oh 

OS 

Tj ° 

CO 

C$ ^j 

C c 
O w 
+5 "^ 

-|j w 

<5» 


CD 

■ c 
o 


CD 

c 
o 


c 

o 

o 
U 


CD 

C 

o 


CD 

c 
o 


CD 

c 
o 


Rubber 


Q. CD 

oX) 

cdct: 
E- 1 c 


Impreg- 
nated 

Asbestos 


°3 «, 

Sin 

,Q CD 

3 to 


Rubber 
with As- 
bestos or 
All Neo- 
prene 


Rubber 
with As- 
bestos or 
All Neo- 
prene 


Rubber 
with As- 
bestos or 
All Neo- 
prene 


2 or more 


CO 

o 

CM 


o 

CO 

cm" 


o 

CO 

cm" 


-<* 

o 

CO 

cm" 


o 

CO 

cm" 


CM 

i 

00 

tH 


18-16 
18-16-14 


CM 

1 
00 
I— I 


CM 

1 
00 


CO 

1 

00 


rH 

1 
00 
T-H 


CM 

rH 

1 

■>* 

t— 1 


CM 
1 

tH 


S See 
Note 6 


O E-< 

CO CO 


STO 

AFSJ 
AFS 


u 

X 


1 
? 

Pi CO 

X X 


o 

CO 


CO 


o 

CO 

W 


c 

1 

1 
< 



T 
1 
( 

u 


j 
> 

Z 

1 i 
i 

3 C 

3<- 


3 

s 






Rubber-Jack- 
eted Heat-Re- 
sistant Cord 




o 
O 

t- 

CD 
■t-> 

CD 


Rubber Jack- 
eted Heater 
Cord 


c 

C 
5 

: 


3 cD* 

5fficj 
a 

5 





70-176 



MASSACHUSETTS ELECTRICAL CODE 





cp co 
-=. «-■ 
,q cd 

cd-^ 

Ph3h 


Not 
Hard 
Usage 


W CO 

cp j2 

bO 0/ 

s >» 

P^G 


cu g 
bo S 

s >» 

cd (- 

PhQ 


CO 

O 
§1 


Hazardous 
Locations 


CO 

O 

is <» 


CD 

en 
P 


CO 

Q 


CO 

g CO 

Q 


CO 

6,2 

Cd Q. 


CO 

a. ^ 
g « 

Q 




r2 

cd 

o 

Ph 


0) O 
PH Ph 


cd 
-t-> 
t-, 

O 
Ph 


a> 

03 

(-1 

O 


1,3 -^ _ h 


bfl 

.2 

cd 
> 

o 

U 
ki 

CD 
-t-> 

O 


bfl 

.s 

-(J 
0) 
CO 

o 

s 

a> 
EH 


1 
CD 

g £ 

cd 3 

- o c 
to -.22 

CD -*J CO 

n 0) 4) 

< 


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t-i »-. 

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Pn^ 


CO 

"3. 

o 

g 
«_ 
a> 
J= 
EH 


1 

O) . Cd +J 

e +j cy 

CD CP Cd J2 ^ U "^' 

£OP5^^ c^^ 
EH O 


S ■ 

^§S5t^ 


Braid 

on Each 

Conductor 


a> 

C 
o 


CD 

c 

o 


CP 

c 

o 


0) 

c 

o 


o 

o 
U 


c 
o 


c 
.2 

J2 
3 

co 

C 
i— i 


o bo 

S.S 


CO . 

2 *- 

0)> c 
^5 Cd 

< 


CP 


1 

o a 

E CO 
CD d 

•** a 
EH 


CD 


1 

O CD 

£'£ 

cp cd 

EH 


CO 

s- ° 

O y 

• 3 

O -73 

z § 
u 


<M 


CM 


CO 

«-. 

o 

CM 


o 

CO 


t-, 

o 

CO 


CD 
(-, 

O 

g 

o 

CM 


0,0 

M 3 


»— ( 

1 

00 

T-H 


O 

i—i 
1 

oo 

i— i 


1 

o 
i— i 


i 

o 


1 
00 


>— i 

i 

oo 

T-H 


8.5 




O 

Pm 
> 


Q 

Ph 

> 

< 


Q 

Xfl 


EH 
Q 
PS 

GO 




CD 
CU o 

S»2 


CD 
CD O 

S- z 


g 

0) 

OS 


i— i cd 
Ph 


i 

CO ■+ 

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cd * 


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J 


5g 


CP 

Q 

cp~ 
a 


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o <y 





ARTICLE 400-FLEXIBLE CORDS 70-177 

C. Construction Specifications 

400-12. Labels. Flexible cords shall be examined and tested at the 
factory and shall be labeled before shipment. 

400-13. Grounded Conductor Identification. One conductor of flexible 
cords shall have a continuous marker readily distinguishing it from the 
other conductor or conductors. The identification shall consist of one 
of the following: 

(a) Colored Braid. A braid finished to show a white or natural gray 
color and the braid on the other conductor or conductors finished to 
show a readily distinguishable solid color or colors. 

(b) Tracer in Braid. A tracer in a braid of any color contrasting 
with that of the braid and no tracer in the braid of the other conductor 
Qr conductors. No tracer shall be used in the braid of any conductor of 
a flexible cord which contains a conductor having a braid finished to 
show white or natural gray, except, in the case of Types C, PD and PO 
cords having the braids on the individual conductors finished to show 
white or natural gray. In such C, PD and PO cords the identifying 
marker may consist of the solid white or natural gray finish on one 
conductor provided there is a colored tracer in the braid of each other 
conductor. 

(c) Colored Insulation. A white or natural gray insulation on one 
conductor and insulation of a readily distinguishable color or colors on 
the other conductor or conductors for cords having no braids on the 
individual conductors (except cords which have insulation on the in- 
dividual conductors integral with the jacket). The insulation may be 
covered with an outer finish to provide the desired color. 

(d) Colored Separator. A white or natural gray separator on one 
conductor and a separator of a readily distinguishable solid color on 
the other conductor or conductors of cords having insulation on the 
individual conductors integral with the jacket. 

(e) Tinned Conductors. One conductor having the individual strands 
tinned and the other conductor or conductors having the individual 
strands untinned for cords having insulation on the individual conduc- 
tors integral with the jacket. 

(f) Surface Marking. A stripe, ridge or groove so located on the 
exterior of the cord as to identify one conductor for cords having in- 
sulation on the individual conductors integral with the jacket. 

400-14. Grounding Conductor Identification. A conductor intended to 
be used as a grounding conductor shall have a continuous identifying 
marker readily distinguishing it from the other conductor or conduc- 
tors. Conductors having a green covering shall not be used for other 
than grounding purposes. The identifying marker shall consist of one of 
the following: 

(a) Colored Braid. A braid finished to show a continuous green 
color or a continuous green color with a yellow stripe. 

(b) Colored Insulation or Covering. For cords having no braids on 
the individual conductors a continuous green color insulation or a con- 
tinuous green color with a yellow stripe covering on one conductor. 



70-178 M ASSACHUSETTS ELECTRICAL CODE 

400-15. Insulation Thickness. The nominal thickness of rubber or 
thermoplastic conductor insulation in Types TS, TST, PO-1, P-l, 
SV, and SVT shall be not less than 1/64 inch. The nominal thickness of 
rubber insulation in Types HC, HPD, HSJ, and HS shall be not less than 
1/64 inch for the Nos. 18-16 AWG sizes, and not less than 2/64 inch 
for the Nos. 14-12 AWG sizes. For heater cord other than Types 
HS and HPS, the all Neoprene insulation shall be 2/64 inch for 
No. 18 and No. 16 AWG sizes and 3/64 inch for No. 14 and No. 
12 AWG sizes. The nominal thickness of the thermoplastic insula- 
tion in Type ET elevator cable shall be not less than 20 mils for 
the No. 18 and No. 16 AWG size and not less than 1/32 inch for 
the No. 14 AWG size. The nominal thickness of the rubber insula- 
tion in Types E and EO elevator cables shall be not less than 20 mils for 
the No. 18 and 16 AWG sizes and not less than 2/64 inch for the No. 14 
AWG size for ratings not exceeding 300 volts. The nominal thickness 
of latex-rubber insulation, when employed, in Types SJ, SJO, S and SO 
shall be not less than 15 mils for the Nos. 18-16 AWG sizes and not less 
than 18 mils for the No. 14 AWG and larger sizes. The nominal thick- 
ness of conductor insulation in Types PO, P, SP-2, SPT-2, HPN, 
SRD, and SRDT shall be not less than 3/64 inch. The nominal thick- 
ness of thermoplastic insulation in Type SPT-3 shall be not less than 
4/64 inch for sizes 18-16 and 5/64 inch for No. 14, 6/64 inch for No. 
12 and 7/64 inch for No. 10 AWG. For other types, the minimum nom- 
inal thickness of rubber or thermoplastic conductor insulation shall be 
as follows: size AWG 27, and 18 to 16—2/64 inch; 14 to 10—3/64 
inch; 8 to 2 — 4/64 inch. 

400-16. Attached to Receptacle Plugs. Where a flexible cord is pro- 
vided with a grounding conductor and equipped with an attachment 
plug, the plug shall comply with Paragraphs 250-59(a and b). 



ARTICLE 402 — FIXTURE WIRES 



402-1. Use. Fixture wires are designed for installation in lighting fix- 
tures and in similar equipment where enclosed or protected and not 
subject to bending or twisting in use. Also, they are used for connecting 
lighting fixtures to the conductors of the circuit that supplies the fixtures. 

For application in lighting fixtures, see Article 410. 

Fixture wires are not intended for the connection of portable or station- 
ary appliances, nor for installation as branch circuit conductors, except as 
permitted in Article 725. 

402-2. Minimum Size. Fixture wires shall not be smaller than No. 18. 

402-3. Insulation. 

(a) The rubber insulations include those made from natural and 
synthetic rubber, neoprene and other vulcanized materials. 



ARTICLE 402-FIXTURE WIRES 70-179 

Thermoplastic insulation may stiffen at temperatures below minus 10°C. 
(14°F.) and care should be used in its installation at such temperatures. It 
may be deformed when subject to pressure; care should be taken in its in- 
stallation, as for example, at bushings, or points of support. See Section 
373-6(b). 

(b) No conductor shall be used under such conditions that its tem- 
perature, even when carrying current, will exceed the temperature 
specified in Table 310-2(a) for the type of insulation involved. 

Table 402-4. Allowable Ampacity of Fixture Wire 

(Based on Room Temperature of 30° C, 86°F.) 

Size AWG Fixture Wire 

Thermoplastic Types TF, TFF 

Rubber Types Cotton Type CF* 

RF-1, RF-2, FF-1, Asbestos Type AF* 

FF-2, RFH-1, RFH-2, Silicone Rubber Types 

FFH-1, FFH-2 SF-1*, SF-2*, SFF-1*, SFF-2* 



18 


5 


6 


16 


7 


8 


14 


•• 


17 



•These types are used almost exclusively in fixtures where they are exposed to high 
temperatures and ampere ratings are assigned accordingly. 

Ultimate Insulation Temperature. In no case shall conductors be 
associated together in such a way with respect to the kind of circuit, 
the wiring method employed, or the number of conductors, that the 
limiting temperature of the conductors will be exceeded. 

402-5. Overcurrent Protection. 

See Section 240-5. Exception No. 3. 



70-180 



MASSACHUSETTS ELECTRICAL CODE 



to 
C 

CD 

> 

o 
U 

u 

CD 

O 



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£* co 

£ s 



CD CD 
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55 



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cd 


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at 


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3 


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3 


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cd 


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70-182 MASSACHUSETTS ELECTRICAL CODE 

ARTICLE 410 — LIGHTING FIXTURES, LAMPHOLDERS, 
LAMPS, RECEPTACLES AND ROSETTES 



A. General 

410-1. Scope. Lighting fixtures, lampholders, pendants, receptacles, 
and rosettes, incandescent filament lamps, arc lamps, electric discharge 
lamps, the wiring and equipment forming part of such lamps, fixtures 
and lighting installations shall conform to the provisions of this Article, 
except as otherwise provided in this Code. 

410-2. Application to Other Articles. Equipment for use in hazardous 
locations shall conform to Articles 500 to 517. 

410-3. Live Parts. Fixtures, lampholders, lamps, rosettes and recepta- 
cles shall have no live parts normally exposed to contact, except in the 
case of cleat-type lampholders, receptacles and rosettes which are lo- 
cated at least 8 feet above the floor. Lampholders, receptacles and 
switches which have exposed accessible terminals shall not be installed 
in metal fixture canopies or in open bases of portable table or floor 
lamps. 

B. Provisions for Fixture Locations 
410-4. Fixtures in Damp, Wet or Corrosive Locations. 

(a) Fixtures installed in damp or wet locations shall be approved for 
such locations and shall be so constructed or installed that water can- 
not enter or accumulate in wireways, lampholders or other electrical 
parts. All fixtures installed outdoors, in damp or wet locations shall be 
marked "Suitable for Wet Locations." 

(b) Fixtures installed in corrosive locations shall be of a type ap- 
proved for such locations. 

See Section 210-21 (b) for receptacles in fixtures. 

410-5. Fixtures near Combustible Material. Fixtures shall be so con- 
structed, or installed, or equipped with shades or guards that combusti- 
ble material will not be subjected to temperatures in excess of 90° C 
(194° F). 

410-6. Fixtures over Combustible Material. Lampholders installed 
over highly combustible material shall be of the unswitched type and 
unless an individual switch is provided for each fixture, shall be lo- 
cated at least 8 feet above the floor, or shall be otherwise so located or 
guarded that the lamps cannot be readily removed or damaged. 

410-7. Fixtures in Show-Windows. Externally wired fixtures shall not 
be used in a show-window. 

Exception: Fixtures of the chain-supported type may be externally 
wired. 

410-8. Fixtures in Clothes Closets. 

(a) A fixture in a clothes closet shall be installed : 
(1) On the wall above the closet door, or 



ARTICLE 410— LIGHTING FIXTURES, ETC. 70-183 



(2) On the ceiling over an area which is unobstructed to the floor, or 

(3) So that the clearance from the fixture to any combustible material 
within the closet is not less than 1 8 inches. 

NOTE: A flush recessed fixture equipped with a solid lens is considered 
to be outside the closet area. 

(b) Pendants shall not be installed in clothes closets. 

410-9. Space for Cove Lighting. Coves shall have adequate space and shall 
be so located that lamps and equipment can be properly installed and main- 
tained. 

C. Provisions at Fixture Outlet Boxes, Canopies and Pans 
410-10. Space for Conductors. Canopies and outlet boxes taken together 
shall provide adequate space so that fixture conductors and their connecting 
devices may be properly installed. 

410-11. Temperature Limit of Conductors in Outlet Boxes. Fixtures shall 
be of such construction or so installed that the conductors in outlet boxes 
shall not be subjected to temperatures greater than that for which the con- 
ductors are approved. 

410-12. Outlet Boxes to be Covered. In a completed installation, each out- 
let box shall be provided with a cover unless covered by means of a fixture 
canopy, lampholder, receptacle, rosette, or similar device. 

410-13. Covering of Combustible Material at Outlet Boxes. Any combus- 
tible wall or ceiling finish exposed between the edge of a fixture, canopy or 
pan and an outlet box shall be covered with noncombustible material. 
410-14. 

CONNECTION OF FIXTURES. In general, fluorescent fixtures when supported 
independently of the outlet box shall be connected through metal raceways 
or armored conductors. This requirement may be waived when grounding type 
cord-equipped fixtures are suspended directly below the outlet box and the 
exposed cord is not subject to strain or physical damage. 

D. Fixture Supports 
410-15. Supports — General. Fixtures, lampholders, rosettes and recep- 
tacles shall be securely supported. A fixture which weighs more than 6 lbs. 
or exceeds 16 inches in any dimension shall not be supported by the screw 
shell of a lampholder. 

410-16. Means of Support. Where the outlet box or fitting will provide 

adequate support, a fixture shall be attached thereto; otherwise a fixture 
shall be supported as required by Section 370-13. A fixture which weighs 
more than 50 lbs. shall be supported independently of the outlet box. 

E. Wiring of Fixtures 
410-17. Fixture Wiring — General. Wiring on or within fixtures shall be 
neatly arranged and shall not be exposed to physical damage. Excess wiring 
shall be avoided. Conductors shall be so arranged that they shall not be 
subjected to temperatures above those for which they are approved. 



70-1 84 MASSACHUSETTS ELECTRICAL CODE 

410-18. Conductor Size. Fixture conductors shall not be smaller than No. 
1 8 AWG. 

410-19. Conductor Insulation. 

(a) Fixtures shall be wired with conductors having insulation suitable 
for the current, voltage, and temperature to which the conductors will be 
subjected. 

(b) Where fixtures are installed in damp, wet, or corrosive locations, con- 
ductors shall be of a type approved for such locations. 

(c) For ampacity of fixture wire, see Table 402-4. 

(d) For maximum operating temperature and voltage limitation of fixture 
wires, see Section 310-2. 

410-20. Conductors for Certain Conditions. 

(a) Fixtures provided with Mogul base screw-shell lampholders and operat- 
ing at not more than 300 volts between conductors shall be wired with Type 
AF, SF-1, SF-2, SFF-1 or SFF-2 fixture wire. 

(b) Fixtures provided with other than Mogul base screw shell lampholders 
and operating at not more than 300 volts between conductors shall be wired 
with Type AF, SF-1, SF-2, SFF-1, SFF-2 fixture wire or Type AFC, AFPO, 
or AFPD flexible cord. 

Exception No. 1. Where temperatures do not exceed 90° C (194° F), 
Type CF fixture wire or Type CFC, CFPD, or CFPO flexible cord may be used. 

Exception No. 2. Where temperatures exceed 60° C (140° F) but are 
not higher than 75° C (167° F) Type RH rubber-covered wire, Type RFH-1 , 
RFH-2, FFH-1 , and FFH-2 fixture wires may be used. 

Exception No. 3. Where temperatures do not exceed 60° C (140° F) , 
Type T thermoplastic wire, Types TF and TFF fixture wire, Type R rubber- 
covered wire, and Types RF-1 , RF-2, FF-1, FF-2 fixture wires may be used, 
including use in fixtures of decorative type on which lamps of not ovef 
60-watt rating are used in connection with imitation candles. 

See Sections 402-6 and 310-2 for fixture wires and conductors; also, Table 
400-9(b) for flexible cords. 

410-21. Conductors for Movable Parts . 

(a) Stranded conductor shall be used for wiring on fixture chains and on 
other movable or flexible parts. 

(b) Conductors shall be so arranged that the weight of the fixture or 
movable parts will not put a tension on the conductors. 

410-22. Pendant Conductors for Incandescent Filament Lamps. 

(a) Pendant lampholders with permanently attached leads, where used 
in other than festoon wiring, shall be hung from separate stranded rubber- 
covered conductors which are soldered directly to the circuit conductors but 
supported independently thereof. 

(b) Such pendant condgctors shall be not smaller than No. 14 AWG 
for heavy-duty or medium-base screw-shell lampholders, nor, except 



ARTICLE 410-UGHTING FIXTURES, ETC. 70-185 

for approved Christmas tree and decorative lighting outfits, smaller 
than No. 18 AWG for intermediate or candelabra-base lampholders. 

(c) Pendant conductors longer than 3 feet shall be twisted together 
where not cabled in an approved assembly. 

410-23. Protection of Conductors and Insulation. 

(a) Conductors shall be secured in a manner that will not tend to cut 
or abrade the insulation. 

(b) Conductor insulation shall be protected from abrasion where 
it passes through metal. 

(c) Fixtures in permanently installed (fixed) showcases or wall cases 
shall be supplied through a permanent connection to a recognized 
wiring system. Stationary equipment may be cord-connected as pro- 
vided in Section 400-3; item (6). 

410-24. Conductor Protection at Lampholders. Where a metal lamp- 
holder is attached to a flexible cord, the inlet shall be equipped with" 
an insulating bushing which, if threaded, shall not be smaller than 
nominal % inch pipe size. The cord hole shall be of a size appropriate 
for the cord and all burrs and fins removed in order to provide a 
smooth bearing surface for the cord. 

Bushings having holes 9/32 inch in diameter are suitable for use with 
plain pendant cord and holes 13/32 inch in diameter with reinforced 
cord. 
410-25. Connections, Splices and Taps. 

(a) Fixtures shall be so installed that the connections between the 
fixture conductors and the circuit conductors may be inspected without 
requiring the disconnection of any part of the wiring, unless the fixture 
is connected by means of a plug and receptacle. 

(b) Splices and taps shall not be located within fixture arms or 
stems. 

(c) No unnecessary splices or taps shall be made within or on a fix- 
ture. 

(d) For approved means of making connections, see Sections 110-14 
and 110-15. 

410-26. Fixture Raceways. Fixtures shall not be used as a raceway for 
circuit conductors unless the fixtures meet the requirements for ap- 
proved raceways, except that the conductors of the single branch cir- 
cuit supplying the fixtures may be carried through as follows : 

Exception No. 1. An installation of fixtures approved for end to end 
assembly to form a continuous raceway, or 

Exception No. 2. Fixtures which are connected together by approved 
wiring methods. 

Branch circuit conductors within 3 inches of a ballast within the bal- 
last compartment shall be recognized for use at temperatures not lower 
than90°C. (194°F.). 

410-27. Polarization of Fixtures. Fixtures shall be so wired that the 
screw-shells of lampholders will be connected to the same fixture or 
circuit conductor or terminal. For polarity identification of conductors 
to screw-shells of lampholders, see Section 200-8. 



70-186 MASSACHUSETTS ELECTRICAL CODE 

F. Construction of Fixtures 

410-28. Combustible Shades and Enclosures. Adequate air space shall 
be provided between lamps and shades or other enclosures of combusti- 
ble material. 

410-29. Fixture Rating. 

(a) All fixtures requiring ballasts or transformers shall be plainly 
marked with their electrical rating and the manufacturer's name, trade- 
mark or other suitable means of identification. 

(b) The electrical rating shall include the voltage and frequency, 
and shall indicate the current rating of the unit including the ballast, 
transformer or auto-transformer. 

410-30. Design and Material. Fixtures shall be constructed of metal, 
wood, or other approved material and shall be so designed and assem- 
bled as to secure requisite mechanical strength and rigidity. Wireways, 
including the entrances thereto, shall be such that conductors may be 
drawn in and withdrawn without injury. 

410-31. Nonmetallic Fixtures. In all fixtures not made entirely of 
metal, wireways shall be lined with metal unless approved armored 
or lead-covered conductors with suitable fittings are used. 

410-32. Mechanical Strength. 

(a) Tubing used for arms and stems where provided with cut threads 
shall be not less than 0.040 inch in thickness and when provided with 
rolled (pressed) threads shall be not less than 0.025 inch in thickness. 
Arms and other parts shall be fastened to prevent turning. 

(b) Metal canopies supporting lampholders, shades, etc., exceeding 
8 lbs., or incorporating attachment plug receptacles, shall be not less 
than 0.020 inch in thickness. Other canopies shall be not less than 0.016 
inch when made of steel and not less than 0.020 inch when of other 
metals. 

(c) Pull type canopy switches shall not be inserted in the rims of 
metal canopies which are less than 0.025 inch in thickness unless the 
rims are reinforced by the turning of a bead or the equivalent. Pull type 
canopy switches, whether mounted in the rims or elsewhere in sheet 
metal canopies, shall be located not more than 3Vi inches from the cen- 
ter of the canopy. Double set screws, double canopy rings, a screw 
ring, or equal method shall be used where the canopy supports a pull 
type switch or pendant receptacle. 

The above thickness requirements apply to measurements made on 
finished (formed) canopies. 

410-33. Wiring Space. Bodies of fixtures, including portable lamps, 
shall provide ample space for splices and taps and for the installation 
of devices, if any. Splice compartments shall be of nonabsorptive, non- 
combustible material. 

410-34. Fixture Studs. Fixture studs which are not parts of outlet 
boxes, hickeys, tripods, and crowfeet shall be made of steel, malleable 
iron, or other approved material. 



ARTICLE 410-UGHTING FIXTURES, ETC. 70-187 

410-35. Insulating Joints. Insulating joints shall be composed of ma- 
terials especially approved for the purpose. Those which are not de- 
signed to be mounted with screws or bolts shall have a substantial exte- 
rior metal casing, insulated from both screw connections. 

410-36. Portable Lamps. Portable table and floor lamps and fan mo- 
tors on ceiling fixtures may be wired with approved rubber-covered 
conductors, provided the wiring is not located so as to be subject to un- 
due heating from lamps. 

410-37. Portable Handlamps. Handlamps of the portable type sup- 
plied through flexible cords shall be of the molded composition or other 
type approved for the purpose. Metal-shell paper-lined lampholders 
shall not be used. Handlamps shall be equipped with a handle. Where 
subject to physical damage or where lamps may come in contact with 
combustible material, handlamps shall be equipped with a substantial 
guard attached to the lampholder or the handle. 

For garages, see Section 511-6. 

410-38. Cord Bushings. A bushing or the equivalent shall be provided 
where flexible cord enters the base or stem of a portable lamp. The 
bushing shall be of insulating material unless a jacketed type of cord is 
used. 

410-39. Tests. All wiring shall be free from short-circuits and 
grounds, and shall be tested for these defects prior to being connected 
to the circuit. 

410-40. Live Parts. 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 at least Vi 
inch between live parts and the mounting plane of the fixture. 

G. Installation of Lampholders 

410-41. Screw-Shell Type. Lampholders of the screw-shell type shall 
be installed for use as lampholders only. 

410-42. Double-Pole Switched Lampholders. Where used on unidenti- 
fied 2-wire circuits tapped from the ungrounded conductors of multi- 
wire circuits, the switching device of lampholders of the switched type 
shall simultaneously disconnect both conductors of the circuit. See Sec- 
tion 200-5. 

410-43. Lampholders in Damp or Wet Locations. Lampholders in- 
stalled in damp or wet locations shall be of the weatherproof type. 

H. Construction of Lampholders 

410-44. Insulation. The outer metal shell and the cap shall be lined 
with insulating material which shall prevent the shell and cap from be- 
coming a part of the circuit. The lining shall not extend beyond the 
metal shell more than V% inch, but shall prevent any current-carrying 
part of the lamp base from being exposed when a lamp is in the lamp- 
holding device. 

410-45. Lead Wires. Lead wires, furnished as a part of weatherproof 
lampholders and intended to be exposed after installation, shall be of 



70-188 MASSACHUSETTS ELECTRICAL CODE 

approved, stranded, rubber-covered conductors, not less than No. 14 
gage (No. 18 gage for candelabra sockets), and shall be sealed in place 
or otherwise made raintight. 

410-46. Switched Lampholders. Switched lampholders shall be of such 
construction that the switching mechanism interrupts the electrical con- 
nection to the center contact. The switching mechanism may also in- 
terrupt the electrical connection to the screw shell when connection to 
the center contact is simultaneously interrupted. 

J. Lamps 

410-49. Bases, Incandescent Lamps. An incandescent lamp for gen- 
eral use on lighting branch circuits shall not be equipped with a Me- 
dium base when rated over 300 watts, nor with a Mogul base when 
rated over 1,500 watts. Above 1,500 watts, special approved bases or 
other devices shall be used. 

410-50. Enclosures, Mercury-Vapor Lamp Auxiliary Equipment. Re- 
sistors or regulators for mercury-vapor lamps shall be enclosed in non- 
combustible cases and treated as sources of heat. 

410-51. Arc Lamps. Arc lamps used in theatres shall conform to 
Section 520-61, and arc lamps used in projection machines shall con- 
form to Section 540-20. Arc lamps used on constant-current systems 
shall conform to the general requirements of Article 710. 

K. Receptacles, Cord Connectors and Attachment Plugs (Caps) 
410-52. Rating and Type. 

(a) Receptacles installed -for the attachment of portable cords shall 
be rated at not less than 15 amperes, 125 volts, or 10 amperes, 250 
volts, and shall be of a type not suitable for use as lampholders. 

(b) Metallic faceplates shall be of ferrous metal not less than 0.030 
inch in thickness or of nonferrous metal not less than 0.040 inch in 
thickness. Faceplates of insulating material shall be noncombustible 
and not less than 0.10 inch in thickness but may be less than 0.10 inch 
in thickness if formed or reinforced to provide adequate mechanical 
strength. 

410-53. Receptacles in Floors. Receptacles located in floors shall be 
enclosed in floor boxes especially approved for the purpose. 

Exception: Where such receptacles are located in elevated floors of 
show-windows or other locations and when the authority enforcing 
this Code judges them to be free from physical damage, moisture and 
dirt, the standard approved type of flush receptacle box may be used. 

410-54. Receptacles in Damp or Wet Locations. Receptacles installed 
in damp or wet locations shall be of the weatherproof type. 

410-55. Receptacles and Cord Connectors — Grounding Type. Recep- 
tacles and cord connectors which are installed to provide for an equip- 
ment grounding connection for cord-connected equipment for a 2-wire 
power supply from a receptacle rated 15 or 20 amperes at a potential 
under 300 volts shall have one separate fixed grounding member. The 
terminal for connection to the grounding member shall be designated 



ARTICLE 410-LIGHTING FIXTURES, ETC. 70-189 

by a green-colored finish. The design of receptacles and cord connectors 
shall be such that the grounding connection shall be made before the 
current carrying connection. 

410-56. Attachment Plugs (Caps) — Grounding Type. An attachment 
plug (cap) for use with a grounding-type receptacle shall, when for use 
with a grounding type receptacle as described in Section 410-55, have 
one separate fixed grounding member which shall be so designed as 
to prevent it from being capable of touching any current-carrying con- 
tact of the receptacle. The terminal connection for this grounding mem- 
ber shall be designated by a green-colored finish. The design of attach- 
ment plugs (caps) shall be such that the grounding connection shall be 
made before the current carrying connection. 

Exception: The grounding contacting member of grounding type at- 
tachment plugs on the power supply cord of a hand-held tool or hand- 
held appliance may be of the movable self restoring type. 

L. Rosettes 
410-57. Approved Types. 

(a) Fusible rosettes shall not be installed. 

(b) Separable rosettes which make possible a change in polarity shall 
not be used. 

410-58. Rosettes in Damp or Wet Locations. Rosettes installed in 
damp or wet locations shall be of the weatherproof type. 

410-59. Rating. Rosettes shall be rated at 660 watts, 250 volts, with 
a maximum current rating of 6 amperes. 

410-60. Rosettes for Exposed Wiring. When designed for use with ex- 
posed wiring, rosettes shall be provided with bases which shall have at 
least two holes for supporting screws, shall be high enough to keep the 
wires and terminals at least V2 inch from the surface wired over, and 
shall have a porcelain lug under each terminal to prevent the rosette 
being placed over projections which would reduce the separation to 
less than Vi inch. 

410-61. Rosettes for Use with Boxes or Raceways. When designed for 
use with conduit boxes or wire raceways, rosette bases shall be high 
enough to keep wires and terminals at least 3 /s inch from the surface 
wired over. 

M. Special Provisions for Flush and Recessed Fixtures 

410-62. Approved Type. Fixtures which are installed in recessed cavi- 
ties in walls or ceilings shall be of an approved type and shall conform 
to Sections 410-63 to 410-70 inclusive. 

410-63. Temperature. 

(a) Fixtures shall be so constructed or installed that adjacent com- 
bustible material will not be subjected to temperatures in excess of 
90°C (194°F). 

(b) Where a fixture is recessed in fire-resistant material in a building 
of fire-resistant construction, a temperature higher than 90°C (194°F), 



70-190 MASSACHUSETTS ELECTRICAL CODE 

but not higher than 150°C (320°F) is acceptable if the fixture is plainly 
marked that it is approved for that service. 

410-64. Clearance. Recessed portions of enclosures, other than at points of 
support, shall be spaced at least Vi inch from combustible material. 

410-65. Wiring. 

(a) Conductors having insulation suitable for the temperature encountered 
shall be used. 

(b) Fixtures having branch circuit terminal connections which operate at 
temperatures higher than 60°C (140 C F) shall have circuit conductors as de- 
scribed in Sections 4 1 0-65 (b- 1 and b-2): 

(1) Branch circuit conductors having an insulation suitable for the 
temperature encountered may be run directly to the fixture. 

(2) Tap connection conductors having an insulation suitable for the 
temperature encountered shall be run from the fixture terminal connection 
to an outlet box placed at least one foot from the fixture. Such a tap shall 
extend for at least four feet but not more than six feet and shall be in a 
suitable metal raceway. 

N. Construction, Flush and Recessed Fixtures 

410-66. Temperature. Fixtures shall be so constructed that adjacent com- 
bustible material will not be subject to temperatures in excess of 90°C 
(194°F). 

410-67. Enclosure. Sheet metal enclosures shall be protected against corro- 
sion by galvanizing, plating, or other equivalent heat-resisting coating, and 
shall not be less than No. 22 USS gage. 

410-68. Lamp Wattage Marking. Incandescent lamp fixtures shall be 
marked to indicate the maximum allowable wattage of lamos. The markings 
shall be permanently installed, in letters at least Va. inch high, and located 
where visible during relamping. 

410-69. Solder Prohibited. No solder shall be used in the construction of 
the fixture box. 

410-70. Lampholders. Lampholders of the screw-shell type shall be of por- 
celain unless specially approved for the purpose. Cements, where used, shall 
be of the high-heat type. 

P. Special Provisions for Electric Discharge Lighting 

Systems of 1,000 Volts or Less 
410-71. General. 

(a) Equipment for use with electric discharge lighting systems and de- 
signed for an open-circuit voltage of 1,000 volts or less shall be of a type 
approved for such service. 

(b) The terminals of an electric discharge lamp shall be considered as 
alive where any lamp terminal is connected to a potential of more than 300 
volts. 

(c) Transformers of the oil-filled type shall not be used. 

(d) In addition to complying with the general requirements for lighting 
fixtures, such equipment shall conform to Part P of this Article. 

(e) Fluorescent fixtures for indoor installations shall have an approved 
thermally actuated protective device integral with the ballast. Such 
thermal unit shall be installed so as to interrupt the line current on the 



ARTICLE 410 — LIGHTING FIXTURES, ETC. 70-191 

supply side of both the primary and secondary windings of the ballast. Under 
no condition shall the thermal device permit the case temperature of the 
ballast to exceed 120° C. (230° F.). Simple reactance type ballast need not be 
thermally protected. 

This requirement 1 shall become effective January 1, 1967. 
410-72. Direct-Current Equipment. Fixtures installed on direct-current 
circuits shall be equipped with auxiliary equipment and resistors especially 
designed and approved for direct-current operation and the fixtures shall be 
so marked. 

410-73. Voltages — Dwelling Occupancies. 

(a) Equipment having an open-circuit voltage of more than 1000 volts 
shall net be installed in dwelling occupancies. 

(b) Equipment having an open-circuit voltage of more than 300 volts 
shall not be installed in dwelling occupancies unless such equipment is so 
designed that there shall be no exposed live parts when lamps are being 
inserted, are in place, or are being removed. 

410-74. Fixture Mounting. 

(a) Exposed- Ballasts. Fixtures having exposed ballasts or transformers 
shall be so installed that such ballasts or tranformers shall not be in contact 
with combustible material. 

(b) Combustible Low-Density Cellulose Fiberboard. Where a fixture con- 
taining a ballast is to be installed on combustible low-density cellulose fiber- 
board it shall, where surface mounted: 

(1) Be approved for this condition, or 

(2) Be spaced not less than 1 Vi inches from the surface of the fiber- 
board. 

(3) Where such fixtures are partially or wholly recessed, the provisions 
of Sections 410-62 to 410-70 shall apply. 

Combustible low-density cellulose fiberboard is considered to include 
sheets, panels and tiles which have a density of 20 pounds per cubic foot or 
less, and which are formed of bonded plant fiber material; but does not in- 
clude solid or laminated wood, nor fiberboard which has a density in excess 
of 20 pounds per cubic foot or is an approved material which has been in- 
tegrally treated with fire retarding chemicals to the degree that the flame 
spread in any plane of the material will not exceed twenty-five as determined 
by the method of NFPA No. 255, ASTM Designation E-84 or U.L. No. 723. 
410-75. Auxiliary Equipment Not Integral with Fixture. 

(a) Auxiliary equipment, including reactors, capacitors, resistors, and 
similar equipment, where not installed as part of a lighting fixture assembly 
shall be enclosed in accessible, permanently installed metal cabinets. 

(b) Where display cases are not permanently installed, no portion of a 
secondary circuit may be included in more than a single case. 

(c) Ballasts approved for separate mounting and for direct connection 
to an approved wiring system need not be separately enclosed. 

410-76. Auto-Transformers. An auto-transformer which is used as part 
of a ballast for supplying lighting units and which raises the voltage to 
more than 300 volts shall be supplied only by a grounded system. 
410-77. Switches. Snap switches shall conform to Section 380-14. 



70-192 MASSACHUSETTS ELECTRICAL CODE 

Q. Special Provisions for Electric Discharge Lighting 
Systems of More Than 1,000 Volts 

410-78. General. 

(a) Equipment for use with electric discharge lighting systems and 
designed for an open-circuit voltage of more than 1 ,000 volts shall be 
of a type approved for such service. 

(b) The terminal of an electric discharge lamp shall be considered as 
alive when any lamp terminal is connected to a potential of more than 
300 volts. 

(c) In addition to complying with the general requirements for light- 
ing fixtures, such equipment shall conform to Sections 410-78 to 410- 
90 inclusive. 

For signs and outline lighting, see Article 600. 

410-79. Control. 

(a) Fixtures or lamp installations shall be controlled either singly or 
in groups by an externally-operable switch or circuit breaker which 
shall open all ungrounded primary conductors. 

(b) The switch or circuit breaker shall be located within sight of the 
fixtures or lamps, or it may be located elsewhere if it is provided with 
means for locking in the open position. 

410-80. Lamp Terminals and Lampholders. Parts which must be re- 
moved for lamp replacement shall be hinged or fastened by an ap- 
proved means. Lamps or lampholders or both shall be so designed that 
there shall be no exposed live parts when lamps are being inserted or 
are being removed. 

410-81. Transformer Ratings. Transformers and ballasts shall have a 
secondary open-circuit voltage of not more than 15,000 volts with an 
allowance on test of 1,000 volts additional. The secondary current rat- 
ing shall be not more than 120 milli-amperes when the open circuit 
voltage is more than 7500 volts, and not more than 240 milli-amperes 
when the open circuit voltage is 7500 volts or less. 

410-82. Transformer Type. Transformers shall be of an approved 
enclosed type. Transformers of other than the askarel insulated or dry 
type shall not be used. 

410-83. Transformer Secondary Connections. 

(a) The high-voltage windings of transformers shall not be con- 
nected in series or in parallel, except that for two transformers, each 
having one end of its high-voltage winding grounded and connected to 
the enclosure, the high-voltage windings may be connected in series to 
form the equivalent of a mid-point grounded transformer. 

(b) The grounded ends shall be connected by an insulated conduc- 
tor not smaller than No. 14 AWG. 

410-84. Transformer Locations. 

(a) Transformers shall be accessible after installation. 

(b) The transformers should be installed as near to the lamps as 
practicable to keep the secondary conductors as short as possible. 



ARTICLE 410— LIGHTING FIXTURES, ETC. 70-193 

(c) Transformers shall be so located that adjacent combustible materials 
will not be subjected to temperatures in excess of 90° C (194° F). 

410-85. Transformer Loading. The lamps connected to any transformer 
shall be of such length and characteristics as not "to cause a condition of 
continuous over-voltage on the transformer. 

410-86. Wiring Method. Secondary Conductors. Approved gas-tube sign 
cable suitable for the voltage of the circuit shall be used. For installation of 
conductors, see Section 600-31 . 

410-87. Lamp Supports. Lamps shall be adequately supported as required 
in Section 600-33. 

410-88. Exposure to Damage. Lamps shall not be located where normally 
exposed to physical damage. 

410-89. Marking. Each fixture or each secondary circuit of tubing having an 
open-circuit voltage of more than 1 ,000 volts shall have a clearly legible mark- 
ing in letters not less than Va inch high reading "Caution .... volts." 
The voltage indicated shall be the rated open-circuit voltage. 
410-90. Switches. Snap switches shall conform to Section 380-14. 

R. Grounding 
410-91. General. Fixtures and lighting equipment shall be grounded as 
provided in Sections 410-92 to 410-96 inclusive. 

410-92. Metallic Wiring Systems. Metal fixtures installed on outlets wired 
with grounded metal raceway or grounded Type AC metal-clad cable shall 
be grounded. 

410-93. Nonmetallic Wiring Systems. Metal fixtures installed on outlets 
wired with knob-and-tube work, or nonmetallic sheathed cable, on circuits 
operating at 150 volts or less to ground, shall be grounded. 

Exception No. 1. Fixtures mounted on metal or metal lath ceilings or 
walls may be insulated from their supports and from the metal lath by 
the use of insulating joints or fixture supports, and canopy insulators. See 
Section 410-95. 

Exception No. 2. Fixtures not mounted on metal or metal lath ceilings 
or walls need not be insulated or grounded. See Section 410-95. 

Fixtures made of insulating materials, and lampholders with shells of insulating 
material, shall be used with wiring systems that do not afford a ready means 
for grounding the exposed noncurrent-carrying parts of fixtures and lamp- 
holders. 

410-94. Equipment of More Than 150 Volts to Ground. 

(a) Metal fixtures, transformers and transformer enclosures on circuits 
operating at more than 150 volts to ground shall be grounded. 

(b) Other exposed metal parts shall be grounded unless they are insulated 
from ground and other conducting surfaces and are inaccessible to unqualified 
persons, except that lamp tie wires, mounting screws, clips and decorative 
bands on glass lamps spaced not less than 1 Vi inches from lamp terminals 
need not be grounded. 



70-194 MASSACHUSETTS ELECTRICAL CODE 

410-95. Equipment Near Grounded Surfaces. 

(a) Ungrounded metal lighting fixtures, lampholders and face plates 
shall not be installed in contact with conducting surfaces nor within 8 
feet vertically or 5 feet horizontally of laundry tubs, bath tubs, shower 
baths, plumbing fixtures, steam pipes or other grounded metal work or 
grounded surfaces. 

(b) Metal pull chains used at these locations shall be provided with 
insulating links. 

410-96. Methods of Grounding. Equipment shall be considered as 
grounded where mechanically connected in a permanent and effective 
manner to metal raceway, the armor of Type AC metal-clad cable, the 
grounding conductor in nonmetallic sheathed cable, or to a sepa- 
rate grounding conductor not smaller than No. 14, provided that the 
raceway, armor, or grounding conductor is grounded in a manner spec- 
ified in Article 250. 



ARTICLE 422— APPLIANCES 



A. General 

422-1. Scope. This Article shall apply to electric appliances used in 
any occupancy. 

422-2. Branch Circuit Requirements. Every appliance shall be sup- 
plied by a branch circuit of one of the types specified in Article 210. 
Motor-operated appliances shall also conform to the requirements of 
Article 430. 

See Table 220-5 for the conductors of a household range branch circuit. 

B. Installation of Appliances 

422-3. Flexible Cords. Flexible cords used to connect heating appli- 
ances shall comply with the following: 

(a) Heater Cords Required. All smoothing irons and portable elec- 
trically heated appliances rated at more than 50 watts and which pro- 
duce temperatures in excess of 121 °C (250°F) on surfaces with which 
the cord is liable to be in contact shall be provided with one of the types 
of approved heater cords listed in Table 400-1 1. 

(b) Other Heating Appliances. All other portable electrically heated 
appliances shall be connected with one of the approved types of cord 
listed in Table 400-11, selected in accordance with the usage specified 
in that Table. 

422-4. Insulation of Appliances. Portable appliances shall be pro- 
vided with an adequate dielectric interposed between current-carrying 
parts and those external surfaces which persons can touch, except for 
toasters, grills or other heating appliances in which the current-carrying 
parts at high temperature are necessarily exposed. In locations where 



ARTICLE 422-APPLIANCES 70-195 

the dielectric is exposed to physical damage, it shall be suitably pro- 
tected. 

422-5. Portable Immersion Heaters. Electric heaters of the portable 
immersion type shall be so constructed and installed that current-car- 
rying parts are effectively insulated from electrical contact with the sub- 
stance in which immersed. The authority enforcing this Code may 
make exception of special applications of apparatus where suitable pre- 
cautionary measures are followed. 

422-6. Protection of Combustible Material. Each electrically heated 
appliance that is obviously intended by size, weight and service to be 
located in a fixed position shall be so placed as to provide ample pro- 
tection between the appliance and adjacent combustible material. 

422-7. Stands for Portable Appliances. Each smoothing iron and other 
portable electrically heated appliance which is intended to be applied 
to combustible material shall be equipped with an approved stand, 
which may be a separate piece of equipment or may be a part of the ap- 
pliance. 

422-8. Signals for Heated Appliances. In other than residence occu- 
pancies, each electrically heated appliance, or group of electrically 
heated appliances, intended to be applied to combustible material, shall 
be installed in connection with a signal unless the appliance is provided 
with an integral temperature-limiting device. 

422-9. Flatirons. Electrically heated smoothing irons intended for use 
in residences shall be equipped with approved temperature-limiting 
means. 

422-10. Water Heaters. Each water heater shall be equipped with tem- 
perature limiting means in addition to the control thermostats to dis- 
connect all ungrounded conductors and such means shall be: 

(1) installed to sense maximum water temperature. 

(2) trip-free manually reset or it shall use a replacement element. 

(3) in addition to any other devices protecting the tank against 
excessive temperature or pressure or both. 

422-1 1 . Infrared Lamp Industrial Heating Appliances. 

(a) Infrared heating lamps rated at 300 watts or less may be used 
with lampholders of the medium-base unswitched porcelain type, or 
other types approved for the purpose. 

(b) Screw-shell lampholders shall not be used with infrared lamps 
over 300 watts rating unless the lampholders are especially approved 
for the purpose. 

(c) Lampholders may be connected to any of the branch circuits of 
Article 210 and, in industrial occupancies, may be operated in series on 
circuits of more than 150 volts to ground provided the voltage rating 
of the lampholders is not less than the circuit voltage. 

Each section, panel or strip carrying a number of infrared lampholders 
(including the internal wiring of such section, panel or strip) is considered 
an appliance. The terminal connection block of each such assembly is 
deemed an individual outlet. 



70- 1 96 MASSACHUSETTS ELECTRICAL CODE 

422-12. Grounding. Metal frames of portable and stationary electrically 
heated appliances, operating on circuits above 150 volts to ground, shall 
be grounded in the manner specified in Article 250; provided, however, that 
where this is impracticable, grounding may be omitted by special permission, 
in which case the frames shall be permanently and effectively insulated from 
the ground. 

Frames shall be grounded in all cases. For methods 
of grounding frames of electric ranges and clothes dryers, see Sections 250- 
57 and 250-60. 

422-13. Wall-Mounted Ovens and Counter-Mounted Cooking Units. 

(a) Wall-mounted ovens and counter-mounted cooking units complete 
with provisions for mounting and for making electrical connections shall be 
considered as fixed appliances. 

(b) A separable connector or a plug and receptacle combination in the 
supply line to an oven or cooking unit used only for ease in servicing or for 
installation shall: 

(1) Not be installed as the disconnecting means required by Section 
422-20; 

(2) Be approved for the temperature of the space in which it is located. 

C. Control and Protection of Appliances 
422-20. Disconnecting Means. Each appliance shall be provided with a 
means for disconnection from all ungrounded conductors. 

422-21. Disconnection of Fixed Appliances. 

(a) For fixed appliances rated at not over 300 volt amperes or Vs hp. 
the branch circuit overcurrent device may serve as the disconnection means. 

(b) For fixed appliances of greater rating the branch circuit switch or cir- 
cuit breaker may, where readily accessible to the user of the appliance, 
serve as the disconnecting means. 

422-22. Disconnection of Portable Appliances. 

(a) For portable appliances a separable connector or an attachment plug 
and receptacle may serve as the disconnecting means. 

(b) The rating of a receptacle or of a separable connector shall not be less 
than the rating of any appliance connected thereto, except that demand 
factors authorized elsewhere in this Code may be applied. 

(c) Attachment plugs and connectors shall conform to the following: 

(1) Live Parts. They shall be so constructed and installed as to guard 
against inadvertent contact with live parts. 

(2) Interrupting Capacity. They shall be capable of interrupting their 
rated current without hazard to the operator. 

(3) Interchangeability. They shall be so designed that they will not 
fit into receptacles of lesser rating. 



ARTICLE 422-APPLIANCES 70-197 

422-23. Disconnection of Stationary Appliances. 

(a) For stationary appliances rated at not over 300 volt amperes or 
Vs horsepower, the branch-circuit overcurrent device may serve as the 
disconnecting means. 

(b) For stationary appliances of greater rating the branch-circuit 
switch or circuit breaker may, where readily accessible to the user of the 
appliance, serve as the disconnecting means. 

(c) For cord-connected appliances, such as household ranges and 
clothes dryers, a separable connector or an attachment plug and re- 
ceptacle may serve as the disconnecting means. 

For household electric ranges, a plug and receptacle connection at the rear 
base of a range, if it is accessible from the front by removal of a drawer, is 
considered as meeting the intent of this rule. 

422-24. Unit Switches as Disconnecting Means. Unit switches which 
are a part of an appliance shall not be considered as taking the place 
of the single disconnecting means required by Part C of this Article, 
unless there are other means for disconnection as follows : 

(a) Multi-Family Dwellings. In multi-family (more than two) dwell- 
ings, the disconnecting means shall be within the apartment, or on 
the same floor as the apartment in which the appliance is installed, and 
may control lamps and other appliances. 

(b) Two-Family Dwellings. In two-family dwellings, the disconnect- 
ing means may be outside of the apartment in which the appliance is 
installed. This will permit an individual switch for the apartment to be 
used. 

(c) Single-Family Dwellings. In single-family dwellings, the service 
disconnecting means may be used. 

(d) Other Occupancies. In other occupancies, the branch-circuit 
switch or circuit breaker, where readily accessible to the user of the 
appliance, may be used for this purpose. 

422-25. Switch and Circuit Breaker to Be Indicating. Switches and cir- 
cuit breakers used as disconnecting means shall be of the indicating 
type. 

422-26. Motor-Driven Appliances. A switch or circuit breaker which 
serves as the disconnecting means for a stationary motor-driven appli- 
ance of more than Vs horsepower shall be located within sight of the mo- 
tor controller or shall be capable of being locked in the open position. 

422-27. Overcurrent Protection. 

(a) Appliances, other than such motor-operated appliances as are 
required by Article 430 to have additional overcurrent protection, shall 
be considered as protected against overcurrent when supplied by one of 
the circuits of Article 210 and in accordance with the requirements 
therein specified. 

(b) A household type appliance with surface heating elements and 
which has a maximum demand of more than 60 amperes as calculated 
in accordance with Table 220-5 shall have its power supply subdivided 



70-198 MASSACHUSETTS ELECTRICAL CODE 

into two or more circuits each of which is provided with overcurrent 
protection rated at not more than 50 amperes. 

(c) Infrared lamp heating appliances shall have overcurrent protec- 
tion not exceeding 50 amperes. 

(d) Open coil or exposed sheathed-coil types of surface heating ele- 
ments in commercial type heating appliances shall be protected by 
overcurrent protection devices which are rated at not more than 50 
amperes. 

(e) A duct heater exceeding a 40 ampere rating shall have the heat- 
ing elements subdivided and each such subdivision shall be protected 
by overcurrent protection devices which are rated at not more than 50 
amperes. 

D. Marking of Appliances 

422-30. Nameplate. Each electric appliance shall be provided with 
a nameplate, giving the maker's name and the normal rating in volts 
and amperes, or in volts and watts. 

422-31. Marking of Heating Elements. Individual heating elements 
which are a part of an electric appliance containing more than one 
heating element shall each be legibly marked with normal rating in 
volts and amperes, or in volts and watts. 

422-32. Appliance Consisting of Motors and Other Loads. The mark- 
ing on an appliance shall specify the rating of the motor in volts and 
amperes, and the additional load (heaters, lights, etc.) in volts and 
watts or amperes. 

Exception No. 1 — Portable Appliances. 

Exception No. 2 — Eixed or stationary appliances employing a mo- 
tor 1/20 hp or less. 

E. Special Provisions For Fixed Indoor 
Electrical Space Heating 

422-40. General. 

(a) Equipment for use with electrical space heating systems shall be 
of a type approved for such service. 

(b) In addition to complying with the general requirements for ap- 
pliances, such equipment shall comply with Part E of this Article. 

(c) The special provisions of this Article shall apply to electrically 
energized units, panels and cables for space heating. They shall also in- 
clude central heating systems employing electrical heating units. 

(d) Electrical space heating systems employing methods of installa- 
tion other than covered by Part E of this Article may be used only by 
special permission. 

422-41. Use. Space heating systems shall not be used: 

(a) Where exposed to severe physical damage unless adequately pro- 
tected. 

(b) In wet or damp locations unless specially approved for the pur- 
pose. 



ARTICLE 422-APPLIANCES 70-199 

See also rules on Corrosive Conditions, Section 310-7. 

422-42. Temperature Limitations. The operating temperature of room 
surfaces where embedded elements and panels are used shall not exceed 
66°C. (150°F.). (Based on room temperature of 30°C.,86°F.) 

422-43. Appliances to Be Complete Units. 

(a) Panels and cables shall be installed in their complete sizes or 
lengths as supplied by the manufacturer. 

(b) Units which are shortened or from which the marking labels or 
nameplates are missing shall not be installed. 

(c) Units shall be suitable for use with approved wiring systems. 

422-44. Heating Cable Construction. Heating cables shall be furnished 
complete with factory-assembled nonheating leads at least 7 feet in 
length, and the leads shall consist of conductors and wiring approved 
for general use or other wiring approved for the purpose. 

422-45. Marking of Heating Cables. Each unit length of heating 
cable shall have a permanent marking located within 3 inches of the 
terminal end of the nonheating leads, and shall be legibly marked with 
the manufacturer's name or identification symbol, catalog number, and 
rating in volts and watts or amperes. 

The lead wires shall have the following color identifications: 230 
volts nominal — red, 115 volts nominal — yellow. 

422-46. Controllers and Disconnecting Means. 

(a) Thermostats and thermostatically controlled switching devices 
which indicate an "off" position and which interrupt line current shall 
open all ungrounded conductors in the "off" position. 

(b) Thermostats and thermostatically controlled switching devices 
which do not have "on" or "off" positions are not required to open all 
ungrounded conductors. 

See Sections 422-20, 422-23 and 422-24 for disconnecting means for sta- 
tionary appliances. 

(c) Switching devices consisting of combined thermostats and man- 
ually controlled switches which serve both as controllers and discon- 
necting means shall: 

(1) Open regardless of temperature all ungrounded conductors 
when manually placed in the "off" position; 

(2) Be so designed that the circuit cannot be energized automati- 
cally after the device has been manually placed in the "off" position. 

422-47. Clearances of Wiring in Ceilings. 

(a) Wiring located above heated ceilings and within thermal in- 
sulation shall be spaced not less than 2 inches above the heated ceiling 
and shall be considered as operating at an ambient of 50°C. The am- 
pacities of conductors shall be computed on the basis of the correction 
factors given in Tables 310-12 and 310-14. 

(b) Wiring located above heated ceilings and over thermal insulation 
having a minimum thickness of 2 inches requires no correction for 
temperature. 



70-200 MASSACHUSETTS ELECTRICAL CODE 

(c) Wiring located above heated ceilings and within a joist space 
having no thermal insulation shall be spaced not less than two inches 
above the ceiling and shall be considered as operating at an ambient of 
50°C. The ampacities of conductors shall be computed on the basis of 
the correction factors given in Tables 310-12 and 310-14. 

422-48. -'Clearances of Wiring in Walls. 

(a) Where located in exterior walls, wiring shall be located outside 
the thermal insulation. 

(b) Where located in interior walls or partitions, wiring shall be lo- 
cated away from the heated surfaces, and the wiring shall be considered 
as operating at an ambient of 40°C. (104°F.); and the ampacities of 
conductors shall be computed on the basis of the correction factors 
given in Tables 310-12 and 310-14. 

422-49. Area Restrictions. 

(a) Heating panels shall not extend beyond the room in which they 
originate. 

(b) Cables shall not be installed in closets, over cabinets which ex- 
tend to the ceiling, under walls or partitions or over walls or partitions 
which extend to the ceiling. 

Exception: Single runs of cable may pass over partitions where they 
are embedded. 

(c) This requirement shall not prohibit low-temperature heat sources 
in closets to control relative humidity. 

422-50. Clearance from Other Objects and Openings. Panels and cables 
shall be separated at least 8 inches from lighting fixtures, outlet and 
junction boxes, and 2 inches from ventilating openings and other such 
openings in room surfaces, or sufficient area shall be provided to assure 
that no heating cables or panels will be covered by surface mounted 
lighting units. 

422-51. Splices. Embedded cables may be spliced only where neces- 
sary and only by approved means, and in no case shall the length of the 
heating cable be altered. 

422-52. Installation of Heating Cables in Dry Board and Plaster. 

(a) Cables shall not be installed in walls. 

(b) Adjacent runs of cable not exceeding 2 3 A watts per foot shall be 
installed not less than 1 Vi inches on centers. 

(c) Heating cables may be applied only to gypsum board, plaster 
lath and similar fire-resistant materials. With metal lath or other con- 
ducting surfaces, a coat of plaster (brown or scratch coat) shall be ap- 
plied to completely cover the metal lath or conducting surface before 
the cable is attached. 

(d) The entire ceiling surface shall have a finish of thermally non- 
insulating sand plaster or other approved noninsulating material hav- 
ing a nominal thickness of Vi-inch. 

(e) Cables shall be secured at intervals not exceeding 16 inches by 
means of approved stapling, tape, plaster or other approved means. 
Staples or metal fasteners which straddle the cable shall not be used 
with metal lath or other conducting surface. 



ARTICLE 422-APPLIANCES 70-201 

(f) In dry board installations, after the heating cable is installed, the 
entire ceiling below it shall be covered with gypsum board not exceed- 
ing Vi-inch thickness. The void between the upper layer of gypsum 
board and the surface layer of gypsum board shall be filled with ther- 
mally conducting plaster or other approved material. 

(g) Cables shall be kept free from contact with metal or conducting 
surfaces. 

(h) Caution should be used in attaching a surface layer of gypsum 
so that the nails or other fastenings do not pierce the heating cable. 

422-53. Installation of Nonhealing Leads. 

(a) Nonheating leads of cables shall be installed in accordance with 
approved wiring methods from the junction box to a location on the 
underside of the ceiling. 

(b) Excess leads shall not be cut but shall be secured to the underside 
of the ceiling and embedded in plaster or other approved material, 
leaving only a length sufficient to reach the junction box with not less 
than 6 inches of free lead within the box. 

(c) The marking of the leads shall be visible in the junction box. 
422-54. Installation of Cables in Concrete or Poured Masonry Floors. 

(a) Adjacent runs of cable not exceeding 2 3 A watts per foot shall 
be installed not less than 1 inch on centers. 

(b) Cables shall be secured in place by nonmetallic frames or 
spreaders or other approved means while the concrete or other fini^ is 
applied. 

(c) A spacing of at least 1 inch shall be maintained between the heat- 
ing cable and other metallic bodies embedded in the floor. 

(d) Leads shall be protected where they leave the floor by rigid metal 
conduit, electrical metallic tubing, or by other approved raceways ex- 
tending to the junction box. 

(e) Bushings shall be used where the leads emerge in the floor slab. 
422-55. Tests During and After Installation. 

(a) Embedded cable installations shall be made with due care to pre- 
vent damage to the cable assembly and shall be inspected and approved 
before cables are covered or concealed. 

(b) Cable shall be tested for insulation resistance after plastering or 
the pouring of floors. See Section 1 10-20, Insulation Resistance. 

422-56. Installation of Resistance Heaters in Air Ducts. 

(a) A heater which is to be installed in an air duct or plenum shall 
be approved for the purpose and shall be installed in the manner ap- 
proved for the equipment. 

(b) Each duct heater shall be provided with an approved temperature 
limiting control to de-energize the circuit. 

(c) In addition a supplementary independent control shall also be 
provided in each duct heater to prevent overheating. This device shall 
be manually resettable or replaceable. 



70-202 MASSACHUSETTS ELECTRICAL CODE 

(d) Duct and plenum heater controller equipment shall be accessible 
with the disconnecting means installed at or within sight of the con- 
troller. 

(e) Where a duct heater is supplied by more than one source of 
supply, the disconnecting means serving the duct heater shall be 
grouped and identified. 

F. Provisions for Room Air-Conditioning Units 

422-60. General. The provisions of Sections 422-61 to 63 inclusive 
shall apply to electrically energized units and equipment which control 
temperature and humidity. 

See Section 422-56. 
422-61. Grounding. Exposed noncurrent-carrying metal parts which 
are liable to become energized shall be grounded under one or more 
of the following conditions: 

(a) Where permanently connected to metal-enclosed wiring; 

(b) When in a wet location and not isolated; 

(c) When within reach of a person standing on the ground outside of 
a building; 

(d) When in a hazardous location, see Article 500; 

(e) Where in electrical contact with metal or metal lath; 

(f) Where more than 150 volts to ground. 
422-62. Branch Circuit Requirements. 

(a) The total load of motor operated air-conditioning equipment 
shall not exceed 80 per cent of the rating of a branch circuit which 
does not supply lighting units or other appliances. 

(b) The total load of air-conditioning equipment shall not exceed 50 
per cent of the rating of a branch circuit where lighting units or other 
appliances are also supplied. 

(c) For air-conditioning units employing two or more motors, see 
Section 430-53 (d). 

422-63. Disconnecting Means. A separable connector or an attach- 
ment plug and receptacle may serve as the disconnecting means. 

G. Special Provisions for Fixed Outdoor 
Electric Deicing and Snow Melting Installations 

422-70. General. 

(a) Equipment for use with electric deicing and snow melting sys- 
tems shall be of a type approved for such service. 

(b) In addition to complying with the general requirements for ap- 
pliances, such equipment shall comply with Part G of this Article. 

(c) The special provisions of this Article shall apply to electrically 
energized heating units, panels, and cables, embedded in poured 
masonry or asphalt driveways, walks, steps, and other areas. 

(d) Electrical heating systems employing methods of construction or 



ARTICLE 422-APPLIANCES 70-203 

installation other than covered by Part G of this Article may be used 
only by special permission. 

422-71. Use. 

(a) Deicing and snow melting equipment may be installed only in the 
specific materials for which they are approved. 

(b) Deicing and snow melting units shall not be used where exposed 
to severe physical damage, unless adequately protected. 

422-72. Appliances To Be Complete Units. 

(a) Units, panels, and cables shall be installed in their complete sizes 
or lengths as supplied by the manufacturer. 

Exception: by special permission of the authority enforcing the Code. 

(b) Units which are shortened, or from which the marking name- 
plates are missing shall not be installed except that the non-heating lead 
may be shortened if the marking specified in Section 422-76 is retained. 

(c) Units shall be suitable for use with approved wiring systems. 

422-73. Non-Heating Leads. Non-heating leads on the cables, panels, 
or units shall be furnished as part of the factory assembly. The leads 
shall consist of conductors and wiring approved for general use, or 
other wiring approved for the purpose. 

422-74. Installation Of Heating Cables, Units, Or Panels. 

(a) The operating characteristics of embedded assemblies of heating 
equipment depend upon the specific materials involved and therefore 
embedded equipment should be installed as designed for use in such 
materials. 

(b) Panels or heating units shall not exceed 120 watts per square foot 
of heated area. 

(c) The spacing between adjacent cable runs is dependent upon the 
rating of the cable, but may in no case be less than 1 inch on centers. 

(d) Units, panels and cables shall be installed either: 

(1) On a substantial asphalt or masonry base at least 2 inches thick 
and have at least W2 inches of asphalt or masonry applied over the 
units, panels or cables, or 

(2) they may be installed over other approved bases and embedded 
within V/i inches of masonry or asphalt but not less than one inch from 
the top surface. 

(e) Cables shall be secured in place by frames or spreaders, or other 
approved means, while the masonry or asphalt finish is applied. 

(f) Cables, units and panels shall not be installed where they bridge 
expansion joints unless adequately protected from expansion and con- 
traction. 

422-75. Installation Of Non-Heating Leads. 

(a) Non-heating leads having a grounding sheath or braid may be 
embedded in masonry or asphalt similar to the heating cable with- 
out additional protection. 



70-204 MASSACHUSETTS ELECTRICAL CODE 

(b) Non-heating leads of type TW and other approved types not hav- 
ing a grounding sheath shall be enclosed in conduit, electrical metallic 
tubing or other raceways within the asphalt or masonry and the distance 
from the factory splice to the raceway shall be not less than 1 inch nor 
more than 6 inches. 

(c) Bushings shall be used in the asphalt or masonry where leads en- 
ter conduit, tubing or raceway. 

(d) Leads shall be protected in expansion joints and where they 
emerge from masonry or asphalt by conduit, electrical metallic tubing 
or other raceways. 

(e) Not less than 6 inches of non-heating lead shall be within the 
junction box. 

422-76. Marking. Each heating unit, panel and cable shall be legibly 
marked within 3 inches of the termination of the non-heating lead 
with the identification symbol, catalog number, and rating in volts and 
watts or amperes. 

422-77. Junction Boxes. All splices other than factory splices shall be 
made in properly installed boxes approved for the location. 

422-78. Grounding. 

(a) Grounding means such as copper braid, lead or copper sheath, 
or other approved means shall be provided as part of the heating section 
of the approved cable, panel or unit. 

(b) All non-current-carrying parts which are liable to become ener- 
gized shall be bonded together and positively connected to a continuous 
(unbroken) No. 14 AWG or larger covered copper wire extending to 
the distribution panelboard. Where the bonding conductor is subject to 
physical damage it shall be at least No. 10 AWG copper. 

422-79. Tests. Embedded heating installation shall be inspected and 
approved before being covered. 



ARTICLE 430 — MOTORS, MOTOR CIRCUITS AND 
CONTROLLERS 

A. General 
430-1. (a). Motor Feeder and Branch Circuits. (See Diagram 430-1 (a). 

(b) General. The following general requirements cover provisions 
for motors, motor circuits, and controllers which do not properly fall 
into the other parts of this Article. 

430-2. Sealed (Hermetic Type) Refrigeration Compressor. For the pur- 
poses of this Article, a sealed (hermetic-type) refrigeration compres- 
sor is a mechanical compressor consisting of a compressor and a mo- 
tor, both of which are enclosed in the same housing, with no external 
shaft nor shaft seals, the motor operating in the refrigerant atmosphere. 

430-3. Part Winding Motors. A part-winding-start induction or syn- 
chronous motor is one arranged for starting by first energizing part of 



ARTICLE 430-MOTOR CIRCUITS AND CONTROLLERS 70-205 



Diagram 430-1 (a) 



Genera/ Part A 

Pequ/remen/s for oyer GOOro/ts Par/ J 

Protec/ion of //Ve parts a// vo/tages • • • Part K 

Grounding- Part L 

Tab/es Part Nt 



Motor Feeder 



7b Supp/u 

k Part B 

Sec 430-23 and 43024 
430-25 and 430Z6 



Motor Feeder 
Orercurrent protec t/on 



Par/ £ 



Par/ F 



Motor Oisconnect/ng 
Means 



i 



Par/H 



Motor Branch Circuit 
Orercurr en/ protection 

Motor Circuit Conductor^ 



PartD 



PartB 



Motor Controller 
Motor Contro/ Circuits 



t 



PartG 



Par/F 



Motor Panning 
Overcarrent protection [ 



Parte 



Motor 



Inherent Protection C 



a 



"2T 



> 



IS' 



Part A 



Parte 



Secondary Controller 
Secondary Conductors LJ 



Secondary 
Pes/ s tor 



PartB 
Sec. 430- 23 



70-206 MASSACHUSETTS ELECTRICAL CODE 

its primary (armature) winding and, subsequently, energizing the re- 
mainder of this winding in one or more steps. The purpose is to reduce 
the initial values of the starting current drawn or the starting torque 
developed by the motor. A standard part-winding-start induction mo- 
tor is arranged so that one-half of its primary winding can be energized 
initially and, subsequently, the remaining half can be energized, both 
halves then carrying the same current. A sealed "hermetic type" re- 
frigeration compressor motor is not to be considered a standard part- 
winding-start induction motor. 

When separate overcurrent devices are used with a standard part- 
winding-start induction motor, each half of the motor winding shall be 
individually protected in accordance with Sections 430-32 and 430-37, 
except that the trip current shall be one-half that specified. 

Each motor winding connection shall have short circuit and ground 
fault protection rated at not more than one-half that specified by Sec- 
tion 430-52 except that a single device having this half rating may be 
used for both windings if this will allow the motor to start. 

430-4. In Sight From. Where in this Article it is specified that some 
equipment shall be "in sight from" another equipment, it means that 
the equipment must be visible and not more than 50 feet distant. 

430-5. Other Articles. Motors and controllers shall also comply with 
the applicable provisions of the following: 

Capacitors Section 460^9 

Cranes and Hoists Article 610 

Elevators, Dumbwaiters, Escalators, and Moving Walks Article 620 

Garages, Aircraft Hangars, Gasoline Dispensing and Service 
Stations, Bulk Storage Plants, Finishing Processes and 
Flammable Anesthetics. .. .Articles 511, 513, 514, 515, 516, and 517 

Hazardous Locations Articles 500-503 

Metalworking Machine Tools Article 670 

Motion-picture Projectors Sections 540-12, 540-17 

Motion-picture Studios Article 530 

Organs Section 650-3 

Resistors and Reactors Article 470 

Theaters Section 520-48 

430-6. Ampacity Determination. Ampacities shall be determined as 
follows: 

(a) General Motor Applications. Except as noted in Section 430-6 
(b), whenever the current rating of a motor is used to determine the 
ampacity of conductors, switches, branch-circuit overcurrent devices, 
etc., the values given in Tables 430-147, 430-148, 430-149, and 430- 
150, including notes, shall be used instead of actual current rating 
marked on the motor nameplate. Motor running overcurrent protection 
shall be based on the motor nameplate current rating. When a motor is 
marked in amperes, but not horsepower, the horsepower rating shall be 
assumed to be that corresponding to the value given in Tables 430-147, 
430-148, 430-149, and 430-150 interpolated if necessary. 

Exception: For multispeed motors, see Sections 430-22 {a) and 430- 

52. 

(b) Sealed (Hermetic-Type) Refrigeration Compressor Motors. For 

sealed (hermetic-type) refrigeration compressor motors the full-load 



ARTICLE 430-MOTOR CIRCUITS AND CONTROLLERS 70-207 

current marked on the nameplate for the compressor shall be used to 
determine the ampacity of the branch-circuit conductors (see Sections 
430-22 and 430-24), branch-circuit overcurrent protection, and motor- 
running overcurrent protection. For motor controllers and disconnect- 
ing means, see Section 430-83 Exception No. 3, and Section 430-1 10. 

430-7. Marking on Motors. 

(a) Usual Motor Applications. A motor shall be provided with a 
nameplate showing the maker's name, the rating in volts and amperes, 
including those of the secondary if a wound-rotor type of motor, the 
normal full-load speed and the interval during which it can operate at 
full load starting cold, before reaching its rated temperature. The time 
interval shall be 5, 15, 30, or 60 minutes, or cor :inuous. A motor rated 
at Vs horsepower or larger shall have the horsepower rating marked on 
the nameplate except that the motors of arc welders may be marked in 
amperes. A multispeed motor, except a shaded pole or permanent 
split-capacitor motor, shall have the amperes and horsepower at each 
speed marked on the name plate. A motor provided with a protective 
device integral with the motor, that complies with Secti )n 430-32(a-2) 
or 430-32 (c-2) shall be permanently marked "Thermally Protected." 
An alternating-current motor rated at Vi horsepower or larger, unless it 
is a polyphase wound-rotor motor, shall have the nameplate marked 
with a code letter to show its input in kilovolt-amperes with locked ro- 
tor, selected from Table 430-7(b). Motors complying with Section 430- 
32(c) (4) shall be marked "Impedance-Protected." 

(b) Locked Rotor Indicating Code Letters. Code letters marked on 
motor nameplates to show motor input with locked rotor shall be in 
accordance with Table 430-7(b). 

The code letter indicating motor input with locked rotor must be in 
an individual block on the nameplate, properly designated. This code 
letter is to be used for determining branch-circuit overcurrent protec- 
tion by reference to Table 430-152, as provided in Section 430-52. 

(1) Multi-speed motors shall be marked with the code letter desig- 
nating the locked-rotor KVA per horsepower for the highest speed at 
which the motor can be started, except constant horsepower motors 
which shall be marked with the code letter giving the highest locked- 
rotor KVA per horsepower. 

(2) Single-speed motors starting on Y connection and running on 
delta connections shall be marked with a code letter corresponding to 
the locked-rotor KVA per horsepower for the Y connection. 

(3) Dual-voltage motors which have a different locked-rotor KVA 
per horsepower on the two voltages shall be marked with the code let- 
ter for the voltage giving the highest locked-rotor KVA per horse- 
power. 

(4) Motors with 60- and 50-cycle ratings shall be marked with a 
code letter designating the locked rotor KVA per horsepower on 60 
cycles. 

(5) Part-winding-start motors shall be marked with a code letter 
designating the locked-rotor KVA per horsepower that is based upon 
the locked-rotor current for the full winding of the motor. 



70-208 


MASSACHUSETTS ELECTRICAL CODE 


Table 430-7(b). 


Locked Rotor Indicating Code Letters 


Code 
Letter 


Kilovolt- Amperes 

per Horsepower 

with Locked Rotor 



A — 3.14 

B 3.15 — 3.54 

C 3.55 — 3.99 

D 4.0 — 4.49 

E 4.5 — 4.99 

F 5.0 — 5.59 

G 5.6 — 6.29 

H 6.3 — 7.09 

J 7.1 — 7.99 

K 8.0 — 8.99 

L 9.0 — 9.99 

M 10.0 — 11.19 

N 11.2 — 12.49 

P 12.5 — 13.99 

R 14.0 — 15.99 

S 16.0 — 17.99 

T 18.0 — 19.99 

U 20.0 — 22.39 

V 22.4 — and up 

The above table is an adopted standard of the National Electrical 
Manufacturers Association. 

(c) Sealed (Hermetic-Type) Refrigeration Compressor Motors. Sealed 
(hermetic-type) refrigeration compressors shall be provided with a 
nameplate which shall give the manufacturer's name; the phase, volt- 
age, frequency, and the full load current in amperes of the motor 
(operating current when the compressor is delivering rated output). 
The locked-rotor current of single-phase motors having full load cur- 
rents in amperes of more than 9 amperes at 115 volts and more than 
4.5 amperes at 230 volts and all polyphase motors shall also be marked 
on the nameplate. When a protective device integral with a motor is 
used (see Section 430-32), the nameplate shall be marked with the 
words "Thermal Protection." 

Note: The words "Thermally Protected" are to replace words "Thermal 
Protection" on the nameplate effective January 1, 1967. 

430-8. Marking on Controllers. A controller shall be marked with 
the maker's name or identification, the voltage, the current or horse- 
power rating, and such other data as may be needed to properly indi- 
cate the motors for which it is suitable. 

Where a controller is built in as an integral part of a motor or of a motor- 
generator set, the controller need not be individually marked when the 
necessary data is on the motor nameplate. 



ARTICLE 430-MOTOR CIRCUITS AND CONTROLLERS 70-209 

430-9. Marking at Terminals. Terminals of motors and controllers 
shall be suitably marked or colored where necessary to indicate the 
proper connections. 

430-10. Wiring Space in Enclosures. Enclosures for controllers and 
disconnecting means for motors shall not be used as junction boxes, 
auxiliary gutters, or raceways for conductors feeding through or tap- 
ping off to the other apparatus unless designs are employed which pro- 
vide adequate space for this purpose. 

430-11. Protection Against Liquids. Suitable guards or enclosures 
shall be provided to protect exposed current-carrying parts of motors 
and the insulation of motor leads where installed directly under equip- 
ment, or in other locations where dripping or spraying oil, water, or 
other injurious liquid may occur, unless the motor is designed for the 
existing conditions. 

430-12. Motor Terminal Housings. Motor terminal housings shall be 
of ample size to properly make connections and shall be of substantial 
metal construction. 

430-13. Bushing. Where wires pass through an opening in an en- 
closure, conduit box or barrier, a bushing shall be used to protect the 
conductors from the edges of the openings having sharp edges. The 
bushing shall have smooth, well-rounded surfaces where it may be in 
contact with the conductors. If used where there may be a presence of 
oils, greases, or other contaminants, the bushing shall be made of ma- 
terial not deleteriously affected. 

For conductors, see Section 310-7. 

430-14. Location of Motors. 

(a) Ventilation and Maintenance. Motors shall be located so that 
adequate ventilation is provided and so that maintenance such as lubri- 
cation of bearings and replacing of brushes can be readily accom- 
plished. 

(b) Open Motors. Open motors having commutators or collector 
rings shall be located or protected so that sparks cannot reach adjacent 
combustible material. This does not prohibit the installation of these 
motors on wooden floors or supports. 

430-16. Overheating from Dust Accumulations. In locations where 
dust or flying material will collect on or in motors in such quantities 
as to seriously interfere with the ventilation or cooling of motors, and 
thereby caused dangerous temperatures, suitable types of enclosed 
motors which will not overheat under the prevailing conditions, shall 
be used. Especially severe conditions may require the use of enclosed 
pipe ventilated motors, or enclosure in separate dust-tight rooms, 
properly ventilated from a source of clean air. 

B. Motor Circuit Conductors 

430-21. General. The provisions of Part B specify sizes of conductors 
capable of carrying the motor current without overheating under the 
conditions specified. 

(a) The provisions of Articles 250 and 310 are not intended to ap- 
ply to conductors which form an integral part of equipment, such as 



70-210 



MASSACHUSETTS ELECTRICAL CODE 



motors, motor controllers, and the like. See Sections 300-1 (d) and 
310-l(c). 

430-22. Single Motor. 

(a) Branch-circuit conductors supplying a single motor shall have 
an ampacity not less than 125 per cent of the motor full-load current 
rating. 

In case of a multispeed motor, the selection of branch circuit con- 
ductors on the line side of the controller shall be based on the high- 
est of the full load current ratings shown on the motor name plate; 
selection of branch circuit conductors between the controller and the 
motor, which are energized for that particular speed, shall be based on 
the current rating for that speed. 

Exception: Conductors for a motor used for short-time, intermittent, 
periodic, or varying duty shall have an ampacity not less than the per- 
centage of the motor nameplate current rating as shown in Table 430- 
22 (a-Exception) unless the authority enforcing the Code grants special 
permission for conductors of smaller size. 

(b) The conductors between a stationary motor rated one horse- 
power or less, and the separate terminal enclosures permitted in Section 

Table 430-22 (a-Exception) 

Percentages of Nameplate 
Current Rating 



Classification of Service 



5- 15- 

Minute Minute 

Rated Rated 

Motor Motor 



30 & 60 Con- 
Minute tinuous 
Rated Rated 
Motor Motor 



Short-Time Duty 

Operating valves, raising or low- 
ering rolls, etc 110 120 150 

Intermittent Duty 

Freight and passenger elevators, 
tool heads, pumps, drawbridges, 
turntables, single-operator arc 
welders for manual welding, etc. 85 85 90 :: 

Periodic Duty 

Rolls, ore and coal-handling ma- 
chines, etc 85 90 95 

Varying Duty 110 120 150 



140 



140 
200 



*This figure also applies for conductors which supply a motor-gen- 
erator single-operator arc welder which has a 60 per cent duty cycle 
rating. 



Any motor application is considered to be for continuous duty unless 
the nature of the apparatus which it drives is such that the motor will 
not operate continuously with load under any condition of use. 

For long runs, it may be necessary in order to avoid excessive 
voltage drop, to use conductors of sizes larger than the minimum sizes 
selected from Tables 310-12 to 310-15 inclusive. 

See Example No. 8, Ch. 9, and Diagram in Section 430-1. 



ARTICLE 430-MOTOR CIRCUITS AND CONTROLLERS 70-211 

430-145(b) may be smaller than No. 14 but not smaller than No. 18, 
provided they have an ampacity as specified above. 

430-23. Wound-Rotor Secondary. 

(a) For continuous duty the conductors connecting the secondary of 
a wound-rotor alternating-current motor to its controller shall have 
an ampacity which is not less than 125 per cent of the full-load second- 
ary current of the motor. 

(b) For other than continuous duty, these conductors shall have an 
ampacity, in per cent of full load secondary current, not less than that 
specified in Table 430-22 (a-Exception) . 

(c). Where the secondary resistor is separate from the controller, the 
ampacity of the conductors between controller and resistor shall be 
not less than that given in Table 430-23 (c) . 

Table 430-23 (c) 

Ampacity of Wire in 
Resistor Duty Classification Per Cent of Full-Load 

Secondary Current 

Light starting duty 35 

Heavy starting duty 45 

Extra heavy starting duty 55 

Light intermittent duty 65 

Medium intermittent duty 75 

Heavy intermittent duty 85 

Continuous duty 110 

430-24. Conductors Supplying Several Motors. Conductors supplying 
two or more motors shall have an ampacity of not less than 125 per cent 
of the full-load current rating of the highest rated motor in the group 
plus the sum of the full-load current ratings of the remainder of the 
motors in the group. Where one or more motors of a group are used on 
short time, intermittent, periodic, or varying duty, the conductors shall 
have an ampacity of not less than 125 per cent of the name plate full 
load current of the highest rated continuous duty motor or the highest 
current obtained by multiplying the applicable percentage of Table 
430-22 (a-Exception), by the name plate full load current of any non- 
continuous duty motor, whichever is the larger, plus the name plate full 
load currents of the other motors, each multiplied by 100 per cent or 
the applicable percentage of the table, whichever is smaller. 

Exception: When the circuitry is so interlocked as to prevent the start- 
ing and running of a second motor or group of motors, the conductor 
size shall be determined from the larger motor or group of motors that 
are to he operated at a given time. 

See Example No. 8, Chapter 9. 

430-25. Combination Load. Conductors supplying a motor load, and 
in addition a lighting or appliance load as computed from Article 220 
and other applicable Sections, shall have an ampacity sufficient for the 
lighting or appliance load plus the required capacity for the motor load 
determined in accordance with Section 430-24, or, for a single motor, 
in accordance with Section 430-22. 



70-212 MASSACHUSETTS ELECTRICAL CODE 

430-26. Feeder Demand-Factor. Where a reduced heating of the con- 
ductors results from motors operating on duty-cycle, intermittently, or 
from all motors not operating at one time the authority enforcing this 
Code may grant permission for feeder conductors to be of a capacity 
less than specified in the Sections 430-24 and 430-25, provided the con- 
ductor is of sufficient ampacity for the maximum load determined by 
the sizes and number of motors supplied and the character of their 
loads and duties. 

430-27. Capacitors with Motors: For provisions covering conductors 
where capacitors are installed on motor circuits, see Sections 460-7, 
460-8, 460-9. 

C. Motor Running Overcurrent (Overload) Protection 

430-31. General. The provisions of Part C specify overcurrent de- 
vices intended to protect the motors, the motor-control apparatus, and 
the branch-circuit conductors against excessive heating due to motor 
overloads. 

(a) Overload in electrical apparatus is an operating overcurrent 
which, when it persists for a sufficient length of time, would cause 
damage or dangerous overheating of the apparatus. It does not include 
short circuits or ground faults. 

(b) These provisions shall not be interpreted as requiring overcurrent 
protection where it might introduce additional or increased hazards as 
in the case of fire pumps [see NFPA Standard for Centrifugal Fire 
Pumps (No. 20)]. 

430-32. Continuous Duty Motors. 

(a) More Than One Horsepower. Each continuous duty motor rated 
more than one horsepower shall be protected against running over- 
current by one of the following means: 

(1) A separate overcurrent device which is responsive to motor 
current. This device shall be rated or selected to trip at not more than 
125 per cent of the motor full-load current rating for sealed (hermetic- 
type) refrigeration compressor motors and motors marked to have a 
temperature rise not over 40° C, and at not more than 115 per cent for 
all other types of motors. This value may be modified as permitted by 
Section 430-34. For a multispeed motor, each winding connection 
shall be considered separately. 

(2) A thermal protector integral with the motor, approved for use 
with the motor which it protects on the basis that it will prevent dan- 
gerous overheating of the motor due to overload or failure to start. If 
the motor current interrupting device is separate from the motor and 
its control circuit is operated by a protective device integral with the 
motor, it shall be so arranged that the opening of the control circuit 
will result in interruption of current to the motor. 

(3) For motors larger than 1500 horsepower, a protective device 
employing embedded temperature detectors which cause current to the 
motor to be interruped when the motor attains a temperature rise 
greater than marked on the nameplate in an ambient of 40° C. 

Standards for the application of embedded temperature detectors are 
given in the American Standards for Rotating Electrical Machinery, ASA 
C50-1 andC50-2. 



ARTICLE 430-MOTOR CIRCUITS AND CONTROLLERS 70-213 

(b) One Horsepower or Less, Manually Started. Each continuous 
duty motor rated at one horsepower or less which is not permanently 
installed, is manually started and is within sight from the controller lo- 
cation, shall be considered as protected against overcurrent by the 
overcurrent device protecting the conductors of the branch circuit. 
This branch circuit overcurrent device shall not be larger than that 
specified in Table 430-146, except that any such motor may be used at 
125 volts or less on a branch circuit protected at 20 amperes. Any such 
motor which is not in sight from the controller location shall be pro- 
tected as specified in Section 430-32(c). Any motor rated at one horse- 
power or less which is permanently installed, shall be protected in ac- 
cordance with Section 430-32(c) . 

(c) One Horsepower or Less, Automatically Started. Any motor of 
one horsepower or less which is started automatically shall be pro- 
tected against overcurrent by the use of one of the following means: 

(1) A separate overcurrent device which is responsive to motor 
current. This device shall be rated or selected to trip at not more than 
125 per cent of the motor full-load current rating for sealed (hermetic- 
type) refrigeration compressor motors and motors marked to have a 
temperature rise not over 40° C, and at not more than 115 per cent for 
all other types of motors. This value may be modified as permitted by 
Section 430-34. For a multispeed motor, each winding connection shall 
be considered separately. 

(2) A thermal protector integral with the motor, approved for use 
with the motor which it protects on the basis that it will prevent dan- 
gerous overheating of the motor due to overload or failure to start. 
Where the motor current interrupting device is separate from the mo- 
tor and its control circuit is operated by a protective device integral 
with the motor, it shall be so arranged that the opening of the control 
circuit will result in interruption of current to the motor. 

(3) The motor shall be considered as being properly protected 
where it is part of an approved assembly which does not normally 
subject the motor to overloads and which is also equipped with other 
safety controls (such as the safety combustion controls of a domestic 
oil burner) which protect the motor against damage due to stalled rotor 
current. Where such protective equipment is used it shall be indicated 
on the nameplate of the assembly where it will be visible after installa- 
tion. 

(4) In case the impedance of the motor windings is sufficient to 
prevent overheating due to failure to start, the motor may be protected 
as specified in Section 430-32 (b) for manually started motors. 

Many alternating-current motors of less than 1/20 horsepower, 
such as clock motors, series motors, etc., and also some larger motors 
such as torque motors, come within this classification. It does not in- 
clude split-phase motors having automatic switches to disconnect the 
starting windings. 

(d) Wound-Rotor Secondaries. The secondary circuits of wound- 
rotor alternating-current motors, including conductors, controllers, 
resistors, etc., shall be considered as protected against overcurrent by 
the motor-running overcurrent device. 



70-214 MASSACHUSETTS ELECTRICAL CODE 

430-33. Intermittent and Similar Duty. A motor used for a condition 
of service which is inherently short time, intermittent, periodic, or 
varying duty, as illustrated by Table 430-22 (a-Exception), shall be 
considered as protected against overcurrent by the branch-circuit over- 
current device, provided the overcurrent protection does not exceed 
that specified in Tables 430-152 and 430-153. 

Any motor application shall be considered to be for continuous duty 
unless the nature of the apparatus which it drives shall be such that the 
motor cannot operate continuously with load under any condition of 
use. 

430-34. Selection or Setting of Protective Device. Where the values 
specified for motor-running overcurrent protection do not correspond 
to the standard sizes or ratings of fuses, nonadjustable circuit breakers, 
thermal cutouts, thermal relays, the heating elements of thermal trip 
motor switches, or possible settings of adjustable circuit breakers ade- 
quate to carry the load, the next higher size, rating, or setting may be 
used, but not higher than 140 per cent of the full-load current rating 
of sealed (hermetic-type) refrigeration compressor motors and mo- 
tors marked to have a temperature rise not over 40° C, and not 
higher than 1 30 per cent of the full-load current rating for all other 
motors. 

In case it is not shunted during the starting period of the motor 
(see Section 430-35), the protective device shall have sufficient time 
delay to permit the motor to start and accelerate its load. 
430-35. Shunting During Starting Period. 

(a) In the case of a motor that is manually started (including start- 
ing with a magnetic starter having push-button control), the running 
overcurrent protection may be shunted or cut out of circuit during the 
starting period of the motor, provided the device by which the over- 
current protection is shunted or cut out cannot be left in the starting 
position, and fuses or time-delay circuit breakers rated or set at not 
over 400 per cent of the full-load current of the motor, are so located 
in the circuit as to be operative during the starting period of the motor. 

(b) The motor-running overcurrent protection shall not be shunted 
or cut out during the starting period if the motor is automatically 
started. 

430-36. Fuses— In Which Conductor. Where fuses are used for motor- 
running protection, a fuse shall be inserted in each ungrounded con- 
ductor. 

Exception: A fuse shall also be inserted in a grounded conductor 
under the circumstances set forth in the note following Table 430-37. 
430-37. Devices Other Than Fuses— In Which Conductor. Where de- 
vices other than fuses are used for motor-running overload protection, 
Table 430-37 shall govern the minimum allowable number and loca- 
tion of overcurrent units such as trip coils, relays, or thermal cutouts. 
430-38. Number of Conductors Opened by Overcurrent Device. Motor- 
running protective devices, other than fuses, thermal cutouts, or ther- 
mal protectors, shall simultaneously open a sufficient number of un- 
grounded conductors to interrupt current flow to the motor. 
430-39. Motor Controller as Running Overcurrent Protection. A motor 
controller may also serve as the running overcurrent device where the 



ARTICLE 430-MOTOR CIRCUITS AND CONTROLLERS 70-215 

number of overcurrent units complies with Section 430-37 and where 
these overcurrent units are operative in both the starting and running 
position in the case of a direct-current motor, and in the running posi- 
tion in the case of an alternating-current motor. When a nonautomatic 
motor controller serves as the running overcurrent device, it is rec- 
ommended that all ungrounded conductors be opened. 

Table 430-37 



Kind of Motor 



Supply System 



Number and location of 

over-current units, such 

as trip coils, relays or 

thermal cutouts 



1-phase A.C. 2-wire, 1-phase A.C. or 
or D.C. D.C. ungrounded 

1-phase A.C. 2-wire, 1-phase A.C. or 
or D.C. D.C, one conductor 

grounded 

1-phase A.C. 3-wire, 1-phase A.C. or 
or D.C. D.C, grounded-neutral 

2-phase A.C. 3-wire, 2-phase A.C, 
ungrounded 

2-phase A.C. 3-wire, 2-phase A.C, one 
conductor grounded 

2-phase A.C 4-wire, 2-phase A.C. 

grounded or ungrounded 

2-phase A.C. 5-wire, 2-phase, A.C, 
grounded neutral or 
ungrounded 

3-phase A.C. 3-wire, 3-phase A.C, 
ungrounded 

3-phase A.C. 3-wire, 3-phase A.C, one 
conductor grounded 

3-phase A.C 3-wire, 3-phase A.C. 
grounded-neutral 



3-phase A.C 



1 in either conductor 



1 in ungrounded conduc- 
tor 



1 in either ungrounded 
conductor 

2, one in each phase 



2 in ungrounded conduc- 
tors 

2, one per phase in un- 
grounded conductors 

2, one per phase in any 
ungrounded phase 
wire 

*2 in any 2 conductors 



c 2 in ungrounded conduc- 
tors 

c 2 in any 2 conductors 



-'2 in any 2 conductors 
except the neutral 



4-wire, 3-phase A.C. 
grounded-neutral or 
ungrounded 

*Note: Three running overcurrent units shall be used 
where three-phase motors are installed in isolated, inacces- 
sible, or unattended locations, unless the motor is protected 
by other approved means. 

Unattended (Definition) : Lacking the presence of a person ca- 
pable of exercising responsible control of the motor under consideration. 



70-216 MASSACHUSETTS ELECTRICAL CODE 

430-40. Thermal Cutouts and Relays. Thermal cutouts, thermal re- 
lays, and other devices for motor-running protection which are not 
capable of opening short circuits, shall be protected by fuses or cir- 
cuit breakers with ratings or settings of not over 4 times the rating of 
the motor for which they are designed, unless approved for group in- 
stallation, and marked to indicate the maximum size of fuse by which 
they must be protected. 

430-42. Motors on General Purpose Branch Circuits. Overcurrent pro- 
tection for motors used on general purpose branch circuits as permit- 
ted in Article 210, shall be provided as follows: 

(a) One or more motors without individual running overcurrent 
protection may be connected to general purpose branch circuits only 
where the limiting conditions specified for each of two or more mo- 
tors in Section 430-53 (a) are complied with. 

(b) Motors of larger ratings than specified in Section 430-53 (a) may 
be connected to general purpose branch circuits only in case each mo- 
tor is protected by running overcurrent protection selected to protect 
the motor as specified in Section 430-32. Both the controller and the 
motor-running overcurrent device shall be approved for group in- 
stallation with the protective device of the branch circuit to which the 
motor is connected. See Section 430-53. 

(c) Where a motor is connected to a branch circuit by means of a 
plug and receptacle, and individual running overcurrent protection is 
omitted as provided in Section 430-42(a), a rating of the plug and 
receptacle shall not exceed 15 amperes at 125 volts or 10 amperes at 
250 volts. Where individual overcurrent protection is required as pro- 
vided in Section 430-42 (b) for a motor or motor-operated appliance 
provided with an attachment plug for attaching to the branch circuit 
through a receptacle, the running overcurrent device shall be an in- 
tegral part of the motor or of the appliance. The rating of the plug and 
receptacle shall be assumed to determine the rating of the circuit to 
which the motor may be connected, as provided in Article 210. 

(d) The overcurrent device protecting a branch circuit to which a 
motor or motor-operated appliance is connected shall have sufficient 
time delay to permit the motor to start and accelerate its load. 

430-43. Automatic Restarting. A motor-running protective device 
which can restart a motor automatically after overcurrent tripping 
shall not be installed unless approved for use with the motor which it 
protects. A motor which can restart automatically after shutdown shall 
not be installed so that its automatic restarting can result in injury to 
persons. 

D. Motor-Branch-Circuit Short Circuit and 
Ground Fault Protection 

430-51. General. The provisions of Part D specify overcurrent de- 
vices intended to protect the motor-branch-circuit conductors, the mo- 
tor control apparatus, and the motors against overcurrent due to short 
circuits or grounds. They are in addition to or amendatory of the pro- 
visions of Article 240. 

430-52. Rating or Setting for Individual Motor Circuit. The motor- 
branch-circuit overcurrent device shall be capable of carrying the start- 



ARTICLE 430-MOTOR CIRCUITS AND CONTROLLERS 70-217 

ing current of the motor. Overcurrent protection shall be considered as 
being obtained when this overcurrent device has a rating or setting not 
exceeding the values given in Table 430-152 or 430-153; provided that 
where the overcurrent protection specified in the Table is not sufficient 
for the starting current of the motor, it may be increased, but shall in 
no case exceed 225 per cent of the motor full load current for sealed 
(hermetic type) refrigeration compressor motors of 400 KVA locked 
rotor or less, nor more than 400 per cent for other motors. 

For a multispeed motor, a single short-circuit and ground fault pro- 
tective device may be used for one or more windings of the motor pro- 
vided the rating of the protective device does not exceed the above ap- 
plicable percentage of the name plate rating of the smallest winding 
protected. 

Branch circuit protective device ratings calculated on this basis are 
given in Columns 4, 5, 6, and 7, Table 430-146. 

Where maximum protective device ratings shown on manufacturer's 
heater table for use with a motor controller are less than 15 amperes, 
the protective device rating shall not exceed the manufacturer's values 
marked on the equipment. 

See Example No. 8, Chapter 9, and Diagram in Section 430-1. 

430-53. Several Motors on One Branch Circuit. Two or more motors 
may be connected to the same branch circuit under the following con- 
ditions: 

(a) Two or more motors each not exceeding one horsepower in rat- 
ing and each having a full-load rated capacity not exceeding 6 amperes, 
may be used on a branch circuit protected at not more than 20 amperes 
at 125 volts or less, or 15 amperes at 600 volts or less. Individual run- 
ning overcurrent protection is unnecessary for such motors unless re- 
quired by the provisions of Section 430-32. 

(b) If the branch circuit protective device is selected not to exceed 
that allowed by Section 430-52 for the motor of the smallest rating, two 
or more motors each having individual running overcurrent protection 
may be connected to a branch circuit when it can be determined that 
branch circuit protective device will not open under the most severe 
normal conditions of service which might be encountered. 

(c) Except as provided for in Section 430-53 (d), two or more mo- 
tors of any rating, each having individual running overcurrent protec- 
tion, may be connected to one branch circuit provided all of the follow- 
ing conditions are complied with: 

(1) Each motor-running overcurrent device must be approved for 
group installation. 

(2) Each motor controller must be approved for group installation. 

(3) The branch circuit shall be protected by fuses having a rating 
not exceeding that specified in Section 430-52 for the largest motor 
connected to the branch circuit plus an amount equal to the sum of the 
full load current ratings of all other motors connected to the circuit. 

(4) The branch circuit fuses must not be larger than allowed by 
Section 430-40 for the thermal cutout or relay protecting the smallest 
motor of the group. 



70-2 1 8 MASSACHUSETTS ELECTRICAL COD£ 

(5) The conductors of any tap supplying a single motor need not 
have individual branch circuit protection, provided they comply with 
either of the following: (1) no conductor to the motor shall have an 
ampacity less than that of the branch circuit conductors, or (2) no 
conductor to the motor shall have an ampacity less than one-third that 
of the branch circuit conductors, with a minimum in accordance with 
Section 430-22; the conductors to the motor-running protective device 
being not more than 25 feet long and being protected from physical 
damage. 

(d) The nameplate marking of a room air conditioner unit shall be 
used in determining the branch circuit requirements, and each unit 
shall be considered as a single-motor unit unless the nameplate is other- 
wise marked. For the purpose of this paragraph a room air conditioner 
is an alternating-current hermetic type air cooled window, console, or 
in-wall room air conditioner which is installed in the conditioned room. 
It covers equipment rated not greater than 250 volts, single phase. It 
also applies to such a room air conditioner, if it has provisions for 
heating. 

430-54. Combined Overcurrent Protection. Motor-branch-circuit over- 
current protection and motor-running overcurrent protection may be 
combined in a single overcurrent device when the rating or setting of 
the device provides the running overcurrent protection specified in 
Section 430-32. 

430-55. Overcurrent Devices— In Which Conductor. Overcurrent de- 
vices shall comply with the provisions of Section 240-11. 

430-56. Size of Fuseholder. Where fuses are used for motor-branch- 
circuit protection, the fuseholders shall not be of a smaller size than re- 
quired to accommodate the fuses specified by Table 430-146. 

Exception: Where fuses having time delay appropriate for the start- 
ing characteristics of the motor are used, fuseholders of smaller size 
than specified in Table 430-146 may be used. 

430-57. Rating of Circuit Breaker. A circuit breaker for motor branch- 
circuit protection shall have a continuous current rating of not less than 
1 1 5 per cent of the full load current rating of the motor. 

430-58. Feeder Taps in Inaccessible Location. If the location of the 
connection of a tap to the feeder conductors is not accessible, the mo- 
tor-branch-circuit overcurrent device may be placed where it will be 
accessible, provided the conductors between the tap and the overcurrent 
device have the same ampacity as the feeder, or provided they have 
an ampacity of at least 1/3 that of the feeder and are not more than 25 
feet long and are protected from physical damage. 

430-59. Selection or Setting of Protective Device. In case the values for 
branch circuit protective devices determined by Table 430-152 or 430- 
153 do not correspond to the standard sizes or ratings of fuses, non- 
adjustable circuit breakers, or thermal devices, or possible settings of 
adjustable circuit breakers adequate to carry the load, the next higher 
size, rating or setting may be used. See Sections 240-6 and 240-7 for 
Standard Ratings. 



ARTICLE 430-MOTOR CIRCUITS AND CONTROLLERS 70-219 

E. Motor-Feeder Short-Circuit and Ground Fault Protection 

430-61. General. The provisions of Part E specify overcurrent de- 
vices intended to protect feeder conductors supplying motors against 
overcurrents due to short circuits or grounds. 

430-62. Rating or Setting— Motor Load. 

(a) A feeder which supplies a specific fixed motor load and consist- 
ing of conductor sizes based on Section 430-24 shall be provided with 
overcurrent protection which shall not be greater than the largest rating 
or setting of the branch-circuit protective device, for any motor of the 
group (based on Tables 430-152 and 430-153), plus the sum of the 
full-load currents of the other motors of the group. 

Where two or more motors of equal horsepower rating are the larg- 
est in the group, one of these motors shall be considered as the largest 
for the above calculations. 

Where two or more motors of a group must be started simultaneously, 
it may be necessary to install larger feeder conductors and correspondingly 
larger ratings or settings of feeder overcurrent protection. 

See Example No. 8, Chapter 9. 

(b) For large capacity installations, where heavy capacity feeders 
are installed to provide for future additions or changes, the feeder over- 
current protection may be based on the rated ampacity of the feeder 
conductors. 

430-63. Rating or Setting— Power and Light Loads. Where a feeder 
supplies a motor load, and in addition a lighting or a lighting and ap- 
pliance load, the feeder overcurrent protective device may have a rating 
or setting sufficient to carry the lighting or the lighting and appliance 
load as determined in accordance with Articles 210 and 220, plus, for 
a single motor, the rating permitted by Section 430-52, and for two or 
more motors, the rating permitted by Section 430-62. 

F. Motor Control Circuits 

430-71. General. Part F contains modifications of the general re- 
quirements and applies to the particular conditions of motor control 
circuits. 

Control Circuit (Definition) : The control circuit of a control ap- 
paratus or system is the circuit which carries the electric signals direct- 
ing the performance of the controller, but does not carry the main 
power circuit. 

430-72. Overcurrent Protection. Conductors of control circuits shall 
be protected against overcurrent in accordance with Section 240-5, Ex- 
ception No. 5. 

Exception. Such conductors shall be considered as being properly 
protected by the branch-circuit overcurrent devices under any one of 
the following conditions: 

(1) Where the rating or setting of the branch-circuit overcurrent 
device is not more than 500 per cent of the ampacity of the control- 
circuit conductors. 



70-220 MASSACHUSETTS ELECTRICAL CODE 

(2) Where the controlled device and the point of control {start 
and stop buttons, pressure switch, thermostatic switch, etc.) are both 
located on the same machine and the control circuit does not extend 
beyond the machine. 

(3) Where the opening of the control circuit would create a haz- 
ard; as for example, the control circuit of fire-pump motors, and the 
like. 

430-73. Mechanical Protection of Conductor. Where damage to a con- 
trol circuit would constitute a hazard, all conductors of such remote- 
control circuit shall be installed in a raceway or be otherwise suitably 
protected from physical damage outside the control device itself. 

Control circuits shall be so arranged that an accidental ground in the 
remote control devices will not start the motor. 

430-74. Disconnection. 

(a) Control circuits shall be so arranged that they will be discon- 
nected from all sources of supply when the disconnecting means is in 
the open position. The disconnecting means may consist of two sepa- 
rate devices, one of which disconnects the motor and the controller 
from the source of power supply for the motor, and the other, the 
control circuit from its power supply. Where the two separate devices 
are used, they shall be located immediately adjacent one to the other. 

(b) Where a transformer or other device is used to obtain a reduced 
voltage for the control circuit and is located in the controller, such 
transformer or other device shall be connected to the load side of the 
disconnecting means for the control circuit. 

G. Motor Controllers 

430-81. General. The provisions of Part G are intended to require 
suitable controllers for all motors. 

(a) Definition. For definition of "Controller," see Article 100. For 
the purpose of this Article, the term "Controller" includes any switch 
or device normally used to start and stop the motor. 

(b) Stationary Motor of Vs Horsepower or Less. For a stationary 
motor rated at Vs horsepower or less, that is normally left running and 
is so constructed that it cannot be damaged by overload or failure to 
start, such as clock motors and the like, the branch-circuit overcurrent 
device may serve as the controller. 

(c) Portable Motor of 1/3 Horsepower or Less. For a portable mo- 
tor rated at 1/3 horsepower or less, the controller may be an attachment 
plug and receptacle. 

430-82. Controller Design. 

(a) Each controller shall be capable" of starting and stopping the 
motor which it controls, and for an alternating-current motor shall be 
capable of interrupting the stalled-rotor current of the motor. 

(b) Autotransformer. An autotransformer starter shall provide an 
off position, a running position, and at least one starting position. It 
shall be so designed that it cannot rest in the starting position, or in any 
position which will render inoperative the overcurrent protective device 
in the circuit. 



ARTICLE 430-MOTOR CIRCUITS AND CONTROLLERS 70-221 

(c) Rheostats. Rheostats shall conform to the following: 

(1) Internal Connections. Motor-starting rheostats shall be so de- 
signed that the contact arm cannot be left on intermediate segments. 
The point or plate on which the arm rests when in the starting position 
shall have no electrical connection with the resistor. 

(2) Under-voltage Release, Direct-Current Motors. Motor-starting 
rheostats for direct-current motors operated from a constant voltage 
supply shall be equipped with automatic devices which will interrupt 
the supply before the speed of the motor has fallen to less than one- 
third its.normal value. 

430-83. Rating. The controller shall have a horsepower rating, which 
shall not be lower than the horsepower rating of the motor, except as 
follows: 

Exception No. 1. Stationary Motor of 2 Horsepower or Less. For a 
stationary motor rated at 2 horsepower or less, and 300 volts or less, 
the controller may be a general-use switch having an ampere rating at 
least twice the full-load current rating of the motor. 

On AC circuits, general use snap switches suitable only for use on 
AC {not general use AC -DC snap switches) may be used to control a 
motor rated at 2 horsepower or less and 300 volts or less having a full- 
load current rating not exceeding 80 per cent of the ampere rating of 
the switch. 

Exception No. 2. Circuit Breaker as Controller. A branch circuit 
circuit breaker, rated in amperes only, may be used as a controller. 
Where this circuit breaker is also used for overcurrent protection, it 
shall conform to the appropriate provisions of this Article governing 
overcurrent protection. 

Exception No. 3. Sealed {Hermetic-type) Refrigeration Compres- 
sor Motors. The motor controller shall have both a continuous duty 
full-load current rating, and a locked-rotor current rating, not less than 
the nameplate full-load current and locked-rotor current, respectively, 
of the compressor. In case the motor controller is rated in horsepower, 
but is without one or both of the foregoing current ratings, equivalent 
currents shall be determined from the rating as follows: Use Table 
430-148, 430-149, or 430-150 to determine the equivalent full-load 
current rating. Use Table 430-151 to determine the equivalent locked- 
rotor current rating. 

430-84. Need Not Open All Conductors. Except when it serves also 
as a disconnecting means (see Section 430-111), the controller need 
not open all conductors to the motor. 

430-85. In Grounded Conductors. One pole of the controller may be 
placed in a permanently grounded conductor provided the controller is 
so designed that the pole in the grounded conductor cannot be opened 
without simultaneously opening all conductors of the circuit. 

430-86. Motor Not in Sight from Controller. Where a motor and the 
driven machinery are not in sight from the controller location, the in- 
stallation shall comply with one of the following conditions: 

(a) The controller disconnecting means is capable of being locked in 
the open position. 



70-222 MASSACHUSETTS ELECTRICAL CODE 

(b) A manually operable switch which will disconnect the motor 
from its source of supply is placed within sight from the motor location. 

430-87. Number of Motors Served by Each Controller. Each motor 
shall be provided with an individual controller. 

Exception: For motors of 600 volts or less a single controller may 
serve a group of motors under any one of the following conditions: 

(a) Where a number of motors drive several parts of a single ma- 
chine or piece of apparatus such as metal and woodworking machines, 
cranes, hoists, and similar apparatus. 

(b) Where a group of motors is under the protection of one over- 
current device as permitted in Section 430-5 3 {a) . 

(c) Where a group of motors is located in a single room within 
sight from the controller location. 

430-88. Adjustable-Speed Motors. Adjustable-speed motors that are 
controlled by means of field regulation shall be so equipped and con- 
nected that they cannot be started under weakened field, unless the 
motor is designed for such starting. 

430-89. Speed Limitation. Machines of the following types shall be 
provided with speed limiting devices. 

(a) Separately excited direct-current motors. 

(b) Series motors. 

(c) Motor-generators and converters which can be driven at excessive 
speed from the direct-current end, as by a reversal of current or de- 
crease in load. 

Exception No. 1. Unless the inherent characteristics of the ma- 
chines, the system, or the load and the mechanical connection thereto, 
are such as to safely limit the speed. 

Exception No. 2. Unless the machine is always under the manual 
control of a qualified operator. 

430-90. Combination Fuseholder and Switch as Controller. The rating 
of a combination fuseholder and switch used as a motor-controller 
shall be such that the fuseholder will accommodate the size of fuse 
specified in Table 430-146, for motor-running overcurrent protection. 

Exception: Where fuses having time delay appropriate for the start- 
ing characteristics of the motor are used, fuseholders of smaller size 
than specified in Table 430-146 may be used. 

H. Disconnecting Means 

430-101. General. The provisions of Part H are intended to require 
disconnecting means capable of disconnecting motors and controllers 
from the circuit. 

See Diagram in Section 430-1. 

430-102. In Sight from Controller Location. A disconnecting means 
shall be located in sight from the controller location, except as recog- 
nized in Section 422-26. 



ARTICLE 430-MOTOR CIRCUITS AND CONTROLLERS 70-223 

430-103. To Disconnect Both Motor and Controller. The disconnecting 
means shall disconnect both the motor and the controller from all un- 
grounded supply conductors. The disconnecting means may be in the 
same enclosure with the controller. See Section 430-1 13. 

430-104. To Be Indicating. The disconnecting means shall plainly in- 
dicate whether it is in the open or closed position. 

430-105. Grounded Conductors. One pole of the disconnecting means 
may disconnect a permanently grounded conductor, provided the dis- 
connecting means is so designed that the pole in the grounded conduc- 
tor cannot be opened without simultaneously disconnecting all conduc- 
tors of the circuit. 

430-106. Service Switch as Disconnecting Means. Where an installa- 
tion consists of a single motor, the service switch may serve as the dis- 
connecting means, provided it conforms to the requirements of this 
Article, and is within sight from the controller location, except as recog- 
nized in Section 422-26. 

430-107. Readily Accessible. One of the disconnecting means shall 
be readily accessible. 

430-108. Every Switch. Every switch in the motor branch circuit 
within sight from the controller location shall comply with the require- 
ments of Part H. 

430-109. Type. The disconnecting means shall be a motor-circuit 
switch, rated in horsepower, or a circuit breaker, except as permitted 
in Sections 430-109 (a, b, c, d, or e) . 

(a) One-Eighth Horsepower or Less. For stationary motors of 1/8 
horsepower or less, the branch-circuit overcurrent device may serve as 
the disconnecting means. 

(b) Two Horsepower or Less. For stationary motors rated at 2 
horsepower or less and 300 volts or less, the disconnecting means may 
be a general-use switch having an ampere rating not less than twice the 
full-load current rating of the motor. 

On AC circuits, general use snap switches suitable only for use on 
AC (not general use AC-DC snap switches) may be used to discon- 
nect a motor having a full-load current rating not exceeding 80 per cent 
of the ampere rating of the switch. 

(c) Over Two Horsepower to and Including 50 Horsepower. The sep- 
arate disconnecting means required for a motor with an autotrans- 
former type of controller may be a general-use switch where all of the 
following provisions are complied with: 

(1) The motor drives a generator which is provided with over- 
current protection. 

(2) The controller (1) is capable of interrupting the stalled-rotor 
current of the motor, (2) is provided with a no-voltage release, and 
(3) is provided with running-over-current protection not exceeding 
1 25 per cent of the motor full-load current rating. 

(3) Separate fuses or a circuit breaker, rated or set at not more 
than 150 per cent of the motor full-load current, are provided in the 
motor branch circuit. 



70-224 MASSACHUSETTS ELECTRICAL CODE! 

(d) Exceeding 50 Horsepower. For stationary motors rated at more 
than 50 horsepower, the disconnecting means may be a motor-circuit 
switch also rated in amperes, a general-use switch, or an isolating 
switch. 

Isolation switches for motors exceeding 50 horsepower, not capable 
of interrupting stalled-rotor currents, shall be plainly marked "Do not 
open under load." 

(e) Portable Motors. For portable motors an attachment plug and 
receptacle may serve as the disconnecting means. 

430-1 10. Ampacity and Interrupting Capacity. 

(a) The disconnecting means shall have an ampacity of at least 
115 per cent of the full-load current rating of the motor. 

(b) The disconnecting means for sealed (hermetic-type) refrigera- 
tion compressors shall be selected on the basis of the nameplate full- 
load current and locked-rotor current, respectively of the compressor 
motor as follows: 

(1) The ampacity shall be at least 115 per cent of the nameplate 
full-load current. 

(2) To determine the equivalent horsepower in complying with the 
requirements of Section 430-109, select the horsepower rating from 
Tables 430-148, 430-149, and 430-150 corresponding to the full-load 
current, and also the horsepower rating from Table 430-151 corre- 
sponding to the locked-rotor current. In case the nameplate full-load 
current and locked-rotor current do not correspond to the currents 
shown in Tables in Sections 430-148, 430-149, and 430-150, respec- 
tively, the horsepower rating corresponding to the next higher value 
shall be selected. In case two different horsepower ratings are obtained 
when applying Tables 430-148, 430-149, 430-150, and 430-151, a 
horsepower rating at least equal to the larger of the two values obtained 
shall be selected. 

430-111. Switch or Circuit Breaker as Both Controller and Disconnect- 
ing Means. A switch or circuit breaker complying with the provisions 
of Section 430-83 may serve as both controller and disconnecting 
means provided it opens all ungrounded conductors to the motor, is 
protected by an overcurrent device (which may be the branch circuit 
fuses) which opens all ungrounded conductors to the switch or circuit 
breaker, and is of one of the following types: 

(a) An air-break switch, operable directly by applying the hand to a 
lever or handle. 

(b) A circuit breaker operable directly by applying the hand to a 
lever or handle. 

(c) An oil switch used on a circuit whose rating does not exceed 
600 volts or 100 amperes, or by special permission on a circuit exceed- 
ing this capacity where under expert supervision. 

The oil switch or circuit breaker specified above may be both power 
and manually operable. If power operable, provision should be made 
to lock it in the open position. 

The overcurrent device protecting the controller may be part of the 
controller assembly or may be separate. 



ARTICLE 430-MOTOR CIRCUITS AND CONTROLLERS 70-225 

An autotransformer type of controller is not included above and will 
require a separate disconnecting means. 

430-112. Motors Served by a Single Disconnecting Means. Each mo- 
tor shall be provided with individual disconnecting means. 

Exception: For motors of 600 volts or less a single disconnecting 
means may serve a group of motors under any one of the following 
conditions: 

(a) Where a number of motors drive several parts of a single ma- 
chine or piece of apparatus such as metal and woodworking machines, 
cranes, and hoists. 

(b) Where a group of motors is under the protection of one set of 
overcurrent devices as permitted by Section 430-5 3 (a) . 

(c) Where a group of motors is in a single room within sight from 
the location of the disconnecting means. 

The disconnecting means shall have a rating not less than is re- 
quired by Section 430-109 for a single motor the rating of which equals 
the sum of the horsepowers or currents of all the motors of the group. 

430-113. Energy From More Than One Source. Equipment receiving 
electrical energy from more than one source shall be provided with dis- 
connecting means from each source of electrical energy adjacent to the 
equipment served. 

J. Requirements for Over 600 Volts 

430-121. General. The provisions of Part J recognize the additional 
hazard due to the use of high voltage. They are in addition to or amend- 
atory of the other provisions of this article. Other requirements for cir- 
cuits and equipment operating at more than 600 volts are in Article 
710. 

430-122. More Than 7500 Volts. Motors operating at more than 7500 
volts between conductors shall be installed in fire-resistant motor rooms. 

430-123. Motor Running Overcurrent (Overload) Protection. Running 
overcurrent protection for a motor of over 600 volts shall consist either 
of a circuit breaker, or of overcurrent units integral with the controller 
which shall simultaneously open all ungrounded conductors to the mo- 
tor. The overcurrent device shall have a setting as specified elsewhere 
in this Article for motor-running overcurrent (overload) protection. 

430-124. Short Circuit and Ground Fault Protection. Each motor 
branch circuit and feeder of more than 600 volts shall be protected 
against overcurrent by one of the following means: 

(a) A circuit breaker of suitable rating so arranged that it can be 
serviced without hazard. 

(b) Fuses of the oil-filled or other suitable type. Fuses shall be used 
with suitable disconnecting means or they shall be of a type which can 
also serve as the disconnecting means. They shall be so arranged that 
they cannot be re-fused or replaced while they are energized. 

(c) Differential protection may be employed to protect an alternat- 
ing-current motor, the motor control apparatus, and the branch-circuit 
conductors against overcurrent due to short circuits or grounds. When 



70-226 MASSACHUSETTS ELECTRICAL CODE 

all these elements are included within the protected zone of a differen- 
tial protective system, the ratings or settings specified in Section 430- 
52 do not apply. 

Differential protective system (definition) : A differential pro- 
tective system is a combination of two or more sets of current transform- 
ers and a relay or relays energized from their interconnected second- 
aries. 

The primaries of the current transformers are connected on both sides 
of the equipment to be protected, both ends of the motor phase windings 
being brought out for this purpose. All of the apparatus and circuits included 
between the sets of current transformer primaries constitute the protected 
zone. The current transformer secondaries and the relay elements are so 
interconnected that the relay elements respond only to a predetermined 
difference between the currents entering and leaving the protected zone. 
When actuated, the relay or relays serve to trip the branch-circuit circuit 
breaker, thus disconnecting the motor, control apparatus in the motor cir- 
cuit and the branch-circuit conductors from the source of power and, in 
the case of a synchronous motor, de-energizing its field circuit. 

430-126. Disconnecting Means. The circuit breaker or the fuses spec- 
ified in Section 430-124 may constitute the disconnecting means if they 
conform to the other applicable requirements of this Article. 

K. Protection of Live Parts — All Voltages 

430-131. General. The provisions of Part K specify that live parts 
shall be protected in a manner judged adequate to the hazard involved. 

430-132. Where Required. Exposed live parts of motors and control- 
lers operating at 50 volts or more between terminals, shall be guarded 
against accidental contact by enclosure, or by location as follows: 

(a) By installation in a room or enclosure which is accessible only to 
qualified persons; 

(b) By installation on a suitable balcony, gallery or platform, so ele- 
vated and arranged as to exclude unqualified persons; 

(c) By elevation 8 feet or more above the floor; 

(d) So that it will be protected by a guard rail when the motor oper- 
ates at 600 volts or less. 

Exception: Stationary motors having commutators, collectors and 
brush rigging located inside of motor end brackets and not conduc- 
tively connected to supply circuits operating at more than 150 volts to 
ground. 

430-133. Guards for Attendants. Where the live parts of motors or 
controllers operating at more than 150 volts to ground are guarded 
against accidental contact only by location as specified in Section 430- 
132, and where adjustment or other attendance may be necessary dur- 
ing the operation of the apparatus, suitable insulating mats or plat- 
forms shall be provided so that the attendant cannot readily touch live 
parts unless standing on the mats or platforms. Where necessary, steps 
and hand-rails should be installed on or about large machines to afford 
safe access to parts which must be examined or adjusted during opera- 
tion. 



ARTICLE 430— MOTOR CIRCUITS AND CONTROLLERS 70-227 

L. Grounding 

430-141. General. The provisions of Part L specify the grounding of motor 
and controller frames to prevent a potential above ground in the event of 
accidental contact between live parts and frames. Insulation, isolation, or 
guarding are suitable alternatives to grounding of motors under certain con- 
ditions. 

430-142. Stationary Motors. The frames of stationary motors shall be 
grounded where any of the following conditions exist: 

(a) supplied by means of metal-enclosed wiring. 

(b) located in a wet place and not isolated nor guarded. 

(c) in a hazardous location. (See Articles 500 to 517 inclusive.) 

(d) the motor operates with any terminal at more than 150 volts to ground. 

Grounding of the motor frame is preferable, but where the frame of the 
motor is not grounded, it shall be permanently and effectively insulated 
from the ground. 

430-143. Portable Motors. The frames of portable motors which operate 
at more than 150 volts to ground shall be guarded or grounded. See Section 
250-45(d) on grounding of portable appliances in other than residential oc- 
cupancies. 

Frames of motors which operate at less than 150 volts to ground shall be 
grounded where this can be readily accomplished. See Section 250-59(b) for 
color of grounding conductor. 

430-144. Controllers. Controller cases, except those attached to un- 
grounded portable equipment and except the lined covers of snap switches, 
shall be grounded regardless of voltage. 

430-145. Method of Grounding. Grounding where required shall be done 
in the manner specified in Article 250. 

(a) Grounding Through Terminal Housings. Where the wiring to fixed 
motors is in Type AC metal-clad cable or metal raceways, junction boxes to 
house motor terminals shall be provided, and the armor of the cable or the 
metal raceways shall be connected to them in the manner specified in Article 
250. 

(b) Separation of Junction Box from Motor. The junction box required 
by Section 430- 145(a) may be separated from the motor not more than 6 
feet provided the leads to the motor are Type AC metal-clad cable or ar- 
mored cord or are stranded leads enclosed in flexible or rigid conduit or elec- 
trical metallic tubing not smaller than 3 /s inch electrical trade size, the 
armor or raceway being connected both to the motor and to the box. Where 
stranded leads are used, protected as specified above, they shall not be 
larger than No. 10, and shall comply with other requirements of the Code 
for conductors to be used in raceways. 

(c) Grounding of Controller Mounted Devices. Instrument transformer 
secondaries, and exposed noncurrent-carrying metal or other conductive 
parts or cases of instrument transformers, meters, instruments, and relays 
shall be grounded as specified in Sections 250-121 through 250-125. 



70-228 



MASSACHUSETTS ELECTRICAL CODE 



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MASSACHUSETTS ELECTRICAL CODE 



Table 430-147. Full-Load Currents in Amperes 
Direct-Current Motors 



The following values of full-load currents are for motors 


running at base speed. 


HP 


120V 


240V 


% 


2.9 


1.5 


H 


3.6 


1.8 


V2 


5.2 


2.6 


% 


7.4 


3.7 


1 


9.4 


4.7 


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13.2 


6.6 


2 


17 


8.5 


3 


25 


12.2 


5 


40 


20 


7 l A 


58 


29 


10 


76 


38 


15 




55 


20 




72 


25 




89 


30 




106 


40 




140 


50 




173 


60 




206 


75 




255 


100 




341 


125 




425 


150 




506 


200 




675 



Table 430-148. Full-Load Currents in Amperes 

Single Phase Alternating Current Motors 

The following values of full-load currents are for motors running at usual 
speeds and motors with normal torque characteristics. Motors built for es- 
pecially low speeds or high torques may have higher full-load currents, and 
multispeed motors will have full load current varying with speed, in which 
case the nameplate current ratings shall be used. 

To obtain full-load currents of 208- and 200-volt motors, increase cor- 
responding 230-volt motor full-load currents by 10 and 15 per cent, respec- 
tively. 

The voltages listed are rated motor voltages. Corresponding nominal sys- 
tem voltages are 110 to 120, 220 to 240, 440 to 480. 



HP 


115V 


230V 


440V 




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4.4 


2.2 








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5.8 


2.9 








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7.2 


3.6 








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9.8 


4.9 








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13.8 


6.9 








i 


16 


8 








i% 


20 


10 








2 


24 


12 








3 


34 


17 








5 


56 


28 








7V 2 


80 


40 


21 




10 


100 


50 


26 





ARTICLE 430-MOTOR CIRCUITS AND CONTROLLERS 70-233 



Table 430-149. Full-Load Current 
Two-Phase A.C. Motors (4-wire) 

The following values of full-load current are for motors running at speeds 
usual for belted motors and motors with normal torque characteristics. Mo- 
tors built for especially low speeds or high torques may require more run- 
ning current, and multispeed motors will have full load current varying 
with speed, in which case the nameplate current rating shall be used. Cur- 
rent in common conductor of 2-phase, 3-wire system will be 1.41 times value 
given. 

The voltages listed are rated motor voltages. Corresponding nominal sys- 
tem voltages are 110 to 120, 220 to 240, 440 to 480 and 550 to 600 volts. 





Induction Type 

Squirrel-Cage and Wound Rotor 

Amperes 


Synchronous Type 
fUnity Power Factor 

Amperes 


HP 


110V 


220V 


440V 


550V 


2300V 


220V 


440V 


550V 


2300V 


H 

i 


4 

4.8 

6.4 


2 

2.4 
3^2 

4.4 
5.6 
8 


1 

1.2 

1.6 


.8 
1.0 
1.3 












2 
3 


8.8 
11.2 


2.2 
2.8 
4 


1.8 

2.2 
3.2 













5 
Vi 

10 




13 

19 
24 


7 

9 

12 


6 

8 

10 










15 

20 
25 




34 
45 
55 


17 
23 
28 


14 
18 

22 


6 


47 


24 


19 

23 
31 
38 


4.7 


30 
40 
50 




67 

88 

108 


34 
44 
54 


27 
35 
43 


7.5 
9 
11 


56 
75 
94 


29 
37 
47 


5.7 

7 

9 


60 

75 
100 




129 
158 
212 


65 

79 
106 


52 

63 
85 


13 
16 
21 


111 
140 

182 


56 

70 
93 


44 

57 
74 


11 
13 
17 


125 
150 
200 




268 
311 
415 


134 
155 
208 


108 
124 
166 


26 
31 
41 


228 


114 
137 
182 


93 
110 
145 


22 
26 
35 



tFor 90 and 80 per cent P. F. the above figures should be multiplied by 1.1 and 1.26 
respectively. 



70-234 



MASSACHUSETTS ELECTRICAL CODE 



Table 430-150. Full-Load Current* 
Three-Phase A.C. Motors 





Induction Type 

Squirrel-Cage and Wound Rotor 

Amperes 


Synchronous Type 

fUnity Power Factor 

Amperes 


HP 


110V 


220V 


440V 


550V 


2300V 


220V 


440V 


550V 


2300V 


1 


4 
5.6 

7 


2 

2.8 
3.5 


1 
1.4 

1.8 


.8 
1.1 
1.4 












1H 

2 
3 


10 
13 


5 

6.5 

9 


2.5 
3.3 
4.5 


2.0 
2.6 

4 












5 

7H 
10 




15 
22 

27 


7.5 
11 
14 


6 

9 

11 












15 
20 
25 




40 
52 
64 


20 
26 
32 


16 
21 
26 


7 


54 


27 


22 


5.4 


30 
40 
50 




78 
104 
125 


39 
52 
63 


31 

41 
50 


8.5 
10.5 
13 


65 

86 

108 


33 
43 
54 


26 
35 

44 


6.5 

8 
10 


60 

75 

100 




150 
185 
246 


75 

93 

123 


60 

74 
98 


16 
19 
25 


128 
161 
211 


64 

81 

106 


51 
65 

85 


12 
15 
20 


125 
150 
200 




310 
360 

480 


155 
180 
240 


124 
144 
192 


31 
37 

48 


264 


132 
158 
210 


106 
127 

168 


25 
30 

40 



For full-load currents of 208- and 200-volt motors, increase the corre- 
sponding 220-volt motor full-load current by 6 and 10 per cent, respectively. 

* These values of full-load current are for motors running at speeds 
usual for belted motors and motors with normal torque characteristics. Mo- 
tors built for especially low speeds or high torques may require more run- 
ning current, and multispeed motors will have full load current varying with 
speed, in which case the nameplate current rating shall be used. 

t For 90 and 80 per cent P. F. the above figures shall be multiplied by 1.1 
and 1.25 respectively. 

The voltages listed are rated motor voltages. Corresponding nominal sys- 
tem voltages are 1 10 to 120, 220 to 240, 440 to 480 and 550 to 600 volts. 



ARTICLE 430-MOTOR CIRCUITS AND CONTROLLERS 70-235 

Table 430-151 
Locked-Rotor Current Conversion Table 

As Determined from Horsepower and Voltage Rating 
For Use Only With Sections 430-83, Exception No. 3, and 430-110(b) 

Conversion Table 







Maximum 


Motor Locked-Rotor Amperes 




Max HP 

Rating 














Single 


Phase 




Two or Three Phase 






115V 


230 V 


110 V 


220 V 


440 V 


550 V 


X A 


58.8 


29.4 


24 


12 


6 


4.8 


% 


82.8 


41.4 


33.6 


16.8 


8.4 


6.6 


1 


96 


48 


42 


21 


10.8 


8.4 


1H 


120 


60 


60 


30 


15 


12 


2 


144 


72 


78 


39 


19.8 


15.6 


3 


204 


102 


— 


54 


27 


24 


5 


336 


168 


— 


90 


45 


36 


iy 2 


480 


240 


— 


132 


66 


54 


10 


600 


300 


— 


162 


84 


66 


15 


— 


— 


— 


240 


120 


96 


20 


— 


— 


— 


312 


156 


126 


25 


— 


— 


— 


384 


192 


156 


30 


— 


— 


— 


468 


234 


186 


40 


— 


— 


— 


624 


312 


246 


50 


— 


— 


— 


750 


378 


300 


60 


— 


— 


— 


900 


450 


360 


75 


— : 


— 


— 


1110 


558 


444 


100 





— 


— 


1476 


738 


588 


125 





— 


— 


1860 


930 


744 


150 





— 


— 


2160 


1080 


864 


200 


— 


— 


— 


2880 


1440 


1152 



70-236 



MASSACHUSETTS ELECTRICAL CODE 



Table 430-152. Maximum Rating or Setting of Motor- 
Branch-Circuit Protective Devices for Motors Marked 
with a Code Letter Indicating Locked Rotor KVA 



Per Cent of Full-Load Current 
Fuse Rating Circuit-Breaker Setting 

Type of Motor See also Table Instan- Time 

430-146, Columns taneous Limit 

4, 5, 6, 7) Type Type 



All AC single-phase and 






polyphase squirrel cage 






and synchronous motors 






with full-voltage, resis- 






tor or reactor starting: 






Code Letter A _. 


150 


150 


Code Letter B to E 


250 


200 


Code Letter F to V 


300 


250 


All AC squirrel cage and 






synchronous motors 






with auto-transformer 






starting : 






Code Letter A 


150 


150 


Code Letter B to £ 


200 


200 


Code Letter F to V 


250 


200 



For certain exceptions to the values specified see Sections 430-52 
and 430-54. The values given in the last column also cover the ratings 
of non-adjustable, time-limit types of circuit-breakers which may also 
be modified as in Section 430-52. 



Synchronous motors of the low-torque, low-speed type (usually 450 
RPM or lower), such as are used to drive reciprocating compressors, 
pumps, etc., which start up unloaded, do not require a fuse rating or 
circuit-breaker setting in excess of 200 per cent of full-load current. 

For motors not marked with a Code Letter, see Table 430-153. 



ARTICLE 430-MOTOR CIRCUITS AND CONTROLLERS 70-237 

Table 430-153. Maximum Rating or Setting of Motor- 
Branch-Circuit Protective Devices for Motors not Marked 
with a Code Letter Indicating Locked Rotor KVA 



Per Cent of Full-Load Current 
Fuse Rating Circuit-Breaker Setting 

Type of Motor (See also Table Ins tan- Time 

430-146, Columns taneous Limit 

4, 6, 6, 7 Type Type 

Single-phase, all types 300 .... 250 

Squirrel-cage and syn- 
chronous (full-voltage, 
resistor and reactor 
starting) 300 250 

Squirrel-cage and syn- 
chronous (auto-trans- 
former starting) 
Not more than 30 am- 
peres... 250 .... 200 

More than 30 amperes ... 200 .... 200 

High-reactance squirrel-cage 
Not more than 30 am- 
peres 250 250 

More than 30 amperes . . . 200 .... 200 

Wound-rotor 150 150 

Direct-current 

Not more than 50 H.P. . . 150 250 150 

More than 50 H.P 150 175 150 

Sealed (Hermetic Type) 
Refrigeration Compressor* 
400KVAlocked-rotororless **175 .... **175 

For certain exceptions to the values specified see Sections 430-52, 
and 430-59. The values given in the last column also cover the ratings 
of non-adjustable, time-limit types of circuit-breakers which may also 
be modified as in Section 430-52. 

Synchronous motors of the low- torque low-speed type (usually 450 
R.P.M. or lower) such as are used to drive reciprocating compressors, 
pumps, etc., which start up unloaded, do not require a fuse rating or 
circuit-breaker setting in excess of 200 per cent of full-load current. 

For motors marked with a Code Letter, see Table 430-152. 

*The locked rotor KVA is the product of the motor voltage and the 
motor locked rotor current (LRA) given on the motor nameplate di- 
vided by 1,000 for single-phase motors, or divided by 580 for 3-phase 
motors. 

**This value may be increased to 225 per cent if necessary to permit 
starting. 



70-238 MASSACHUSETTS ELECTRICAL CODE 

ARTICLE 445 — GENERATORS 

445-1. Location. Generators shall be located in dry places, and also so as 
to meet the requirements for motors in Section 430-14. Generators installed 
in hazardous locations as described in Articles 500-503, or in other locations 
as described in Articles 510-517, 520, 530, and 665, shall also comply with 
the provisions of those Articles. 

Waterproof covers shall be provided for use in emergency. 

445-2. Marking. Each generator shall be provided with a nameplate giving 
the maker's name, the rating in kilowatts or kilovolt-amperes, the normal 
volts and amperes corresponding to the rating, and the revolutions per 
minute. 

445-3. Drip Pans. Generators shall be provided with suitable drip pans if 
required by the authority enforcing this Code. 
445-4. Overcurrent Protection, 

(a) Constant-Potential Generators. Constant-potential generators, except 
alternating-current generators and their exciters, shall be protected from ex- 
cessive current by circuit breakers or fuses. 

(b) Two-Wire Generators. Two-wire, direct-current generators may have 
overcurrent protection in one conductor only if the overcurrent device is 
actuated by the entire current generated, except that in the shunt field. The 
overcurrent device shall not open the shunt field. 

(c) 65 Volts or Less. Generators operating at 65 volts or less and driven 
by individual motors shall be considered as protected by the overcurrent device 
protecting the motor if these devices will operate when the generators are 
delivering not more than 150 per cent of their full-load rated current. 

(d) Balancer Sets. Two-wire, direct-current generators used in conjunc- 
tion with balancer sets to obtain neutrals for 3-wire systems shall be equipped 
with overcurrent devices which will disconnect the 3-wire system in the case 
of excessive unbalancing of voltages or currents. 

(e) 3-Wire, Direct-Current Generators. Three-wire, direct-current genera- 
tors, whether compound or shunt wound, shall be equipped with overcurrent 
devices, one in each armature lead, and so connected as to be actuated by 
the entire current from the armature. Such overcurrent devices shall con- 
sist either of a double-pole, double-coil circuit breaker, or of a 4-pole circuit 
breaker connected in the main and equalizer leads and tripped by two 
overcurrent devices, one in each armature lead. Such protective devices shall 
be so interlocked that no one pole can be opened without simultaneously dis- 
connecting both leads of the armature from the system. 

445-5. Size of Conductors. The conductors from the generator terminals 
to supplied equipment shall have an ampacity not less than 115 per cent 
of the nameplate current rating of the generator. Neutral conductors shall 
be the same size as the conductors of the outside legs. 



ARTICLE 450-TRANSFORMERS AND VAULTS 70-239 

445-6. Protection of Live Parts. Live parts of generators of more than 
150 volts to ground shall not be exposed to accidental contact where ac- 
cessible to unqualified persons. 

445-7. Guards for Attendants. Where necessary for the safety of at- 
tendants the provisions of Section 430-133 shall be complied with. 
445-8. Grounding. If a generator operates at a terminal voltage in 
excess of 150 volts to ground, the frame shall be grounded in the man- 
ner specified in Article 250. If the frame is not grounded, it shall be 
permanently and effectively insulated from the ground. 
445-9. Bushings. Where wires pass through an opening in an enclo- 
sure, conduit box, or barrier, a bushing shall be used to protect the con- 
ductors from the edges of the opening having sharp edges. The bushing 
shall have smooth, well rounded surfaces where it may be in contact 
with the conductors. If used where there may be a presence of oils, 
grease, or other contaminants, the bushing shall be made of a material 
not deleteriously affected. 



ARTICLE 450 — TRANSFORMERS AND TRANS- 
FORMER VAULTS 

(Including Secondary Ties) 

450-1. Application. This Article applies to the installation of all trans- 
formers except: (1) current transformers; (2) dry-type transformers 
which constitute a component part of other apparatus and which con- 
form to the requirements for such apparatus; (3) transformers for use 
with X-ray and high-frequency; (4) transformers used with Class 1 
low-voltage power circuits or Class 2 remote control low energy power 
and signal circuits which shall conform to Article 725; (5) transform- 
ers for sign and outline lighting which shall conform to Article 600; 
and (6) transformers for electric discharge lighting which shall con- 
form to Article 410. 

This Article applies to the installation of transformers in hazardous 
locations except as modified by Article 500. 

Supplementary rules are found also in Article 710, Circuits and Equip- 
ment Operating at More than 600 Volts Between Conductors; and Service 
Installations Over 600 Volts as referred to in Article 230. 

A. General Provisions 

450-2. Location. Transformers and transformer vaults shall be readily 
accessible to qualified personnel for inspection and maintenance. The 
location of oil insulated transformers and transformer vaults is covered 
in Sections 450-24, 450-25, and 450-41; dry type transformers in Sec- 
tion 450-21 and askarel insulated in Section 450-23. 

450-3. Overcurrent Protection. Overcurrent protection shall conform 
to the following. As used in this Section, the word "transformer" means 
a transformer or polyphase bank of two or three single phase trans- 
formers operating as a unit. 



70-240 MASSACHUSETTS ELECTRICAL CODE 

(a) Primary Side. Each transformer shall be protected by an in- 
dividual overcurrent device in the primary connection, rated or set at 
not more than 250 per cent of the rated primary current of the trans- 
former, except that an individual overcurrent device is not required 
when the primary circuit overcurrent device provides the protection 
specified in this Section, and except as provided in Section 450-3 (b). 

(b) Primary and Secondary Side. A transformer having an over- 
current device in the secondary connection, rated or set at not more 
than 250 per cent of the rated secondary current of the transformer, or 
a transformer equipped with a coordinated thermal overload protection 
by the manufacturer, is not required to have an individual overcurrent 
device in the primary connection provided the primary feeder overcur- 
rent device is rated or set to open at a current value not more than six 
times the rated current of the transformer for transformers having not 
more than six per cent impedance, and not more than four times rated 
current of the transformer for transformers having more than six but 
not more than ten per cent impedance. 

(c) Potential (Voltage) Transformers. Potential transformers should 
be protected with primary fuses. The fuse rating should not exceed 10 
amperes for circuits of 600 volts or less, and 3 amperes for circuits of 
more than 600 volts. A resistor should be connected in series with high 
tension fuses when necessary to limit the possible short-circuit current 
to a value within the interrupting capacity of the fuse. 

450-5. Secondary Ties. As used in this Section, the word "trans- 
former" means a transformer or a bank of transformers operating as a 
unit. A secondary tie is a circuit operating at 600 volts or less between 
phases which connects two power sources or power supply points, such 
as the secondaries of two transformers. The tie may consist of one or 
more conductors per phase. 

(a) Tie Circuits. Tie circuits shall be provided at each end with over- 
current protection as required in Article 240 of this Code, except un- 
der the conditions described in Sections 450-5 (a-1 and a-2), in which 
cases the overcurrent protection may be in accordance with Section 
450-5 (a-3). 

(1) Loads at Transformer Supply Points Only. Where all loads 
are connected at the transformer supply points at each end of the tie 
and overcurrent protection is not provided in accordance with Article 
240, the rated ampacity of the tie shall be not less than 67 per cent of 
the rated secondary current of the largest transformer connected to the 
secondary tie system. 

(2) Loads Connected Between Transformer Supply Points. Where 
load is connected to the tie at any point between transformer supply 
points and overcurrent protection is not provided in accordance with 
Article 240, the rated ampacity of the tie shall be not less than 100 per 
cent of the rated secondary current of the largest transformer connected 
to the secondary tie system except as otherwise provided in Section 
450-5 (a-4). 

(3) Tie Circuit Protection. Under the conditions described in Sec- 
tions 450-5 (a-1 and 2), both ends of each tie conductor shall be 
equipped with a protective device which will open at a predetermined 



ARTICLE 450-TRANSFORMERS AND VAULTS 70-241 

temperature of the tie conductor under short circuit conditions. This 
protection shall consist of one of the following: (1) a fusible link ca- 
ble connector, terminal or lug, commonly known as a limiter, each be- 
ing of a size corresponding with that of the conductor and of approved 
construction and characteristics according to the operating voltage and 
the type of insulation on the tie conductors, or (2) automatic circuit 
breakers actuated by devices having comparable current-time charac- 
teristics. 

(4) Interconnection of Phase Conductors Between Transformer Sup- 
ply Points. Where the tie consists of more than one conductor per 
phase, the conductors of each phase shall be interconnected in order to 
establish a load supply point, and the protection specified in Section 
450-5 (a-3) shall be provided in each tie conductor at this point, except 
as follows: 

Exception: Loads may be connected to the individual conductors of 
a multiple-conductor tie without interconnecting the conductors of each 
phase and without the protection specified in Section 450-5(a-3) at 
load connection points provided; the tie conductors of each phase have 
a combined capacity not less than 133 per cent of the rated secondary 
current of the largest transformer connected to the secondary tie sys- 
tem; the total load of such taps does not exceed the rated secondary 
current of the largest transformer; the loads are equally divided on each 
phase and on the individual conductors of each phase as far as prac- 
ticable. 

(5) Tie Circuit Control. Where the operating voltage exceeds 150 
volts to ground, secondary ties provided with limiters shall have a 
switch at each end which when open will de-energize the associated tie 
conductors and limiters. The current rating of the switch shall be not 
less than the rated current of the conductors connected to the switch. 
It shall be capable of opening its rated current, and it shall be con- 
structed so that it will not open under the magnetic forces resulting 
from short-circuit current. 

(b) Overcurrent Protection for Secondary Connections. When sec- 
ondary ties are used an overcurrent device rated or set at not more 
than 250 per cent of the rated secondary current of the transformers 
shall be provided in the secondary connections of each transformer, 
and in addition an automatic circuit breaker actuated by a reverse-cur- 
rent relay set to open the circuit at not more than the rated secondary 
current of the transformer shall be provided in the secondary connec- 
tion of each transformer. 

450-6. Parallel Operation. Transformers may be operated in parallel 
and switched as a unit provided that the overcurrent protection for 
each transformer meets the requirements of 450-3. 

To obtain balanced division of load current, both transformers should 
have the same rated per cent impedance and be operated on the same voltage- 
ratio tap. 

450-7. Guarding. Transformers shall be guarded as follows : 

(a) Mechanical Protection. Appropriate provisions shall be made to 
minimize the possibility of damage to transformers from external causes 



70-242 MASSACHUSETTS ELECTRICAL CODE 

where the transformers are located where they are exposed to physical 
damage. 

(b) Case or Enclosure. Dry-type transformers shall be provided with 
a noncombustible moisture-resistant case or enclosure which will pro- 
vide reasonable protection against the accidental insertion of foreign 
objects. 

(c) Exposed Live Parts. The transformer installation shall conform 
with the provisions for guarding of live parts in Section 110-16. 

(d) Voltage Warning. The operating voltage of exposed live parts 
of transformer installations shall be indicated by signs or visible mark- 
ings on the equipment or structures. 

450-8. Grounding. Exposed noncurrent carrying metal parts of trans- 
former installations including fences, guards, etc., shall be grounded 
where required under the conditions and in the manner prescribed for 
electrical equipment and other exposed metal parts in Article 250. 

450-9. Marking. Each transformer shall be provided with a name- 
plate giving the name of the manufacturer; rated kilovolt-amperes, 
frequency, primary and secondary voltage; and the amount and kind 
of insulating liquid where used and the transformer rating exceeds 25 
kva. Where Class B insulation is used in the construction of dry-type 
transformers rated more than 100 kva, the nameplate shall indicate 
the temperature rise for this insulation system. 

B. Specific Provisions Applicable to Different 
Types of Transformers 

450-21. Dry-Type Transformers Installed Indoors. Transformers rated 
112V2 kva or less shall have a separation of at least 12 inches from 
combustible material unless separated therefrom by a fire-resistant 
heat-insulating barrier, or unless of a rating not exceeding 600 volts 
and completely enclosed except for ventilating openings. 

Transformers of more than 112Vi kva rating shall be installed in a 
transformer room of fire-resistant construction unless they are con- 
structed with 80° C rise (Class B) or 150° C rise (Class H) insulation, 
and are separated from combustible material not less than 6 feet hori- 
zontally and 12 feet vertically or are separated therefrom by a fire- 
resistant heat-insulating barrier. 

Transformers rated more than 35,000 volts shall be installed in a 
vault. See Part C of this Article. 

450-23. Askarel-lnsulated Transformers Installed Indoors. Askarel-in- 

sulated transformers rated in excess of 25 kva shall be furnished with 
a pressure-relief vent. Where installed in a poorly ventilated place they 
shall be furnished with a means for absorbing any gases generated by 
arcing inside the case, or the pressure relief vent shall be connected to a 
chimney or flue which will carry such gases outside the building. As- 
karel-insulated transformers rated more than 35,000 volts shall be in- 
stalled in a vault. 

450-24. Oil-Insulated Transformers Installed Indoors. Oil-insulated 
transformers shall be installed in a vault constructed as specified in this 
Article except as follows: 



ARTICLE 450-TRANSFORMERS AND VAULTS 70-243 

(a) Not Over 1 1 2Vi kva Total Capacity. The provisions for trans- 
former vaults specified in Part C of this Article apply except that the 
vault may be constructed of reinforced concrete not less than 4 inches 
thick. 

(b) Not Over 600 Volts. A vault is not required provided suitable 
arrangements are made where necessary to prevent a transformer oil 
fire igniting other materials, and the total transformer capacity in one 
location does not exceed 10 kva in a section of the building classified 
as combustible, or 75 kva where the surrounding structure is classified 
as fire-resistant construction. 

(c) Furnace Transformers. Electric furnace transformers of a total 
rating not exceeding 75 kva may be installed without a vault in a build- 
ing or room of fire-resistant construction provided suitable arrange- 
ments are made to prevent a transformer oil fire spreading to other 
combustible material. 

(d) Detached Buildings. Transformers may be installed in a build- 
ing which does not conform with the provisions specified in this Code 
for transformer vaults, provided neither the building nor its contents 
present a fire hazard to any other building or property, and provided 
the building is used only in supplying electric service and the interior 
is accessible only to qualified persons. 

450-25. Oil-Insulated Transformers Installed Outdoors. Combustible 
material, combustible buildings and parts of buildings, fire escapes, 
door and window openings shall be safeguarded from fires originating 
in oil-insulated transformers installed on, attached to, or adjacent to a 
building or combustible material. Space separations, fire-resistant bar- 
riers, automatic water spray systems and enclosures which confine the 
oil of a ruptured transformer tank are recognized safeguards. One or 
more of these safeguards shall be applied according to the degree of 
hazard involved in cases where the transformer installation presents a 
fire hazard. Oil enclosures may consist of fire-resistant dikes, curbed 
areas or basins, or trenches filled with coarse crushed stone. Oil en- 
closures shall be provided with trapped drains in cases where the ex- 
posure and the quantity of oil involved are such that removal of oil is 
important. 

C. Provisions for Transformer Vaults 

450-41. Location. Vaults shall be located where they can be ventilated 
to the outside air without using flues or ducts wherever such an ar- 
rangement is practicable. 

450-42. Walls, Roof, and Floor. The walls and roofs of vaults shall 
be constructed of reinforced concrete, brick, load bearing tile, concrete 
block, or other fire resistive constructions which have adequate struc- 
tural strength for the conditions, and a minimum fire resistance of 2Vi 
hours according to American Standard A2.1 — Methods of Fire Tests 
of Building Construction and Materials (ASTM Standard El 19-58; 
NFPA No. 251). The floors of vaults in contact with the earth shall be 
of concrete not less than 4 inches thick but when the vault is con- 
structed with a vacant space or other stories below it, the floor shall 
have adequate structural strength for the load imposed thereon and a 
minimum fire resistance of IVi hours. 



70-244 MASSACHUSETTS ELECTRICAL CODE 

450-43. Doorways. Vault doorways shall be protected as follows: 

(a) Type of Door. Each doorway leading into a building shall be pro- 
vided with a tight-fitting door of a type approved for openings in Class 
A situations as defined in the NFPA Standard for the Installation of 
Fire Doors and Windows, No. 80 (National Fire Codes, Vol. 4). The 
authority enforcing this Code may require such a door for an exterior 
wall opening or on each side of an interior wall opening where condi- 
tions warrant. 

(b) Sills. A door sill or curb of sufficient height to confine within 
the vault the oil from the largest transformer shall be provided and in 
no case shall the height be less than 4 inches. 

(c) Locks. Entrance doors shall be equipped with locks, and doors 
shall be kept locked, access being allowed only to qualified persons. 
Locks and latches shall be so arranged that the door may be readily 
and quickly opened from the inside. 

450-44. Ventilation. The ventilation shall be adequate to prevent a 
transformer temperature in excess of the values prescribed in ASA 
C57.12-58. 

450-45. Ventilation Openings. When required by Section 450-44, 
openings for ventilation shall be provided in accordance with the fol- 
lowing: 

(a) Location. Ventilation openings shall be located as far away as 
possible from doors, windows, fire escapes, and combustible mate- 
rial. 

(b) Arrangement. Vaults ventilated by natural circulation of air 
may have roughly half of the total area of openings required for ven- 
tilation in one or more openings near the floor and the remainder in 
one or more openings in the roof or in the sidewalls near the roof; or 
all of the area required for ventilation may be provided in one or more 
openings in or near the roof. 

(c) Size. In the case of vaults ventilated to an outdoor area without 
using ducts or flues the combined net area of all ventilating openings 
after deducting the area occupied by screens, gratings, or louvers, shall 
be not less than 3 square inches per kva of transformer capacity in 
service, except that the net area shall be not less than 1 square foot for 
any capacity under 50 kva. 

(d) Covering. Ventilation openings shall be covered with durable 
gratings, screens, or louvers, according to the treatment required in or- 
der to avoid unsafe conditions. 

(e) Dampers. Where automatic dampers are used in the ventilation 
openings of vaults containing oil-insulated transformers, the actuating 
device should be made to function at a temperature resulting from fire 
and not at a temperature which might prevail as a result of an over- 
heated transformer or bank of transformers. Automatic dampers should 
be so designed and constructed to minimize the possibility of acci- 
dental closing. 

(f) Ducts. Ventilating ducts shall be constructed of fire-resistant 
material. 



ARTICLE 460-CAPACITORS 70-245 

450-46. Drainage. Where practicable, vaults containing more than 
100 kva transformer capacity shall be provided with a drain or other 
means which will carry off any accumulation of oil or water in the 
vault unless local conditions make this impracticable. The floor shall 
be pitched to the drain when provided. 

450-47. Water Pipes and Accessories. Any pipe or duct systems for- 
eign to the electrical installation should not enter or pass through a 
transformer vault. Where the presence of such foreign systems cannot 
be avoided, appurtenances thereto which require maintenance at regu- 
lar intervals shall not be located inside the vault. Arrangements shall be 
made where necessary to avoid possible trouble from condensation, 
leaks and breaks in such foreign systems. Piping or other facilities pro- 
vided for fire protection or for water-cooled transformers are not 
deemed to be foreign to the electrical installation. 

450-48. Storage in Vaults. Materials shall not be stored in trans- 
former vaults. 



ARTICLE 460 — CAPACITORS 

460-1. Application. This Article applies to installation of capacitors 
on electric circuits in or on buildings. 

Exception No. 1. Capacitors that are components of other apparatus 
shall conform to the requirements for such apparatus. 

Exception No. 2. Capacitors in hazardous locations shall comply 
with additional requirements in Articles 500-517. 

460-2. Location. An installation of capacitors in which any single unit 
contains more than three gallons of combustible liquid shall be in a 
vault conforming to Part C of Article 450. 

460-3. Mechanical Protection. Capacitors shall be protected from 
physical damage by location or by suitable fences, barriers or other 
enclosures. 

460-4. Cases and Supports. Capacitors shall be provided with non- 
combustible cases and supports. 

460-5. Transformers Used with Capacitors. Transformers that are 
components of capacitor installations and are used for the purpose of 
connecting the capacitor to a power circuit shall be installed in accord- 
ance with Article 450. The kva rating shall not be less than 135 per 
cent of the capacitor rating in kvar. 

460-6. Drainage of Stored Charge. Capacitors shall be provided with 
a means of draining the stored charge. 

(a) Time of Discharge. The residual voltage of a capacitor shall be 
reduced to 50 volts or less within one minute after the capacitor is 
disconnected from the source of supply in the case of capacitors rated 
600 volts or less and in five minutes in the case of capacitors rated more 
than 600 volts. 



70-246 MASSACHUSETTS ELECTRICAL CODE 

(b) Means of Discharge. The discharge circuit shall be either per- 
manently connected to the terminals of the capacitor or capacitor bank, 
or provided with automatic means of connecting it to the terminals of 
the capacitor bank on removal of voltage from the line. Manual means 
of switching or connecting the discharge circuit shall not be used. The 
windings of motors, of transformers, or of other equipment directly 
connected to capacitors without a switch or overcurrent device inter- 
posed, constitutes a suitable discharge means. 

460-7. Power Factor Correction — Motor Circuit. The total kvar rating 
of capacitors which are connected on the load side of a motor con- 
troller shall not exceed the value required to raise the no-load power 
factor of the motor to unity. 

460-8. Conductor Rating. 

(a) The ampacity of capacitor circuit conductors shall be not less 
than 135 per cent of the rated current of the capacitor. The ampacity 
of conductors which connect a capacitor to the terminals of a motor or 
to motor circuit conductors, shall be not less than one-third the am- 
pacity of the motor circuit conductors but not less than 135 per cent of 
the rated current of the capacitor. 

(b) Overcurrent Protection. 

(1) An overcurrent device shall be provided in each ungrounded 
conductor. 

Exception: A separate overcurrent device is not required on the 
load-side of a motor running overcurrent device. 

(2) The rating or setting of the overcurrent device shall be as low 
as practicable. 

(c) Disconnecting Means. 

(1) A disconnecting means shall be provided in each ungrounded 
conductor. 

Exception: A separate disconnecting means is not required for a 
capacitor connected on the load side of a motor overcurrent device. 

(2) The disconnecting device need not open all ungrounded con- 
ductors simultaneously. 

(3) The disconnecting device may be used for disconnecting the 
capacitor from the line as a regular operating procedure. 

(4) The continuous ampacity of the disconnecting device shall be 
not less than 135 per cent of the rated current of the capacitor. 

460-9. Rating or Setting of the Motor-Running Overcurrent Device. 

Where a motor installation includes a capacitor connected on the load 
side of the motor-running overcurrent device, and the overcurrent de- 
vice used can be adjusted, the rating or setting of the motor overcurrent 
device shall be determined as provided in Section 430-32, except that 
instead of using the full-load rated current of the motor as provided in 
that Section a lower value corresponding with the improved power- 
factor of the motor circuit shall be used. Section 430-22 applies 
with respect to the rating of the motor circuit conductors. 



ARTICLE 470-RESISTORS AND REACTORS 70-247 

460-10. Grounding. Capacitor cases shall be grounded in accordance 
with Article 250. 

460-11. Guarding. All live parts of capacitors which are connected 
to circuits of more than 600 volts between conductors and are acces- 
sible to unqualified persons, shall be enclosed or isolated. For isolation 
by elevation, see Section 7 1 0-34 ( f ) . 

460-12. Marking. Each capacitor shall be provided with a nameplate 
giving the maker's name, rated voltage, frequency, kvar, or amperes, 
number of phases, and if filled with a combustible liquid, the amount 
of liquid in gallons. When filled with a nonflammable liquid, the 
nameplate shall so state. The nameplate shall also indicate if a capaci- 
tor has a discharge device inside the case. 



ARTICLE 470 — RESISTORS AND REACTORS 

For Rheostats see Section 430-82. 



470-1. Location. Resistors and reactors shall not be placed where ex- 
posed to physical damage. Where in the immediate vicinity of easily 
ignitible material they shall be of the oil-immersed type or shall be en- 
closed in metal boxes or cabinets. See Article 500 for Hazardous Loca- 
tions. 

470-2. Space Separation. Unless attached to a switchboard or other 
noncombustible material, or unless mounted as provided in Section 
470-3, resistors and reactors shall be separated from combustible ma- 
terial by a distance of not less than 1 foot. 

470-3. On or In a Proximity to Combustible Material. Where placed 
within a distance of 1 foot from combustible material, resistors and re 
actors shall be installed as follows : 

(a) Slab or Panel. They shall be attached to a slab or panel of non- 
combustible, nonabsorptive material such as slate, soapstone, or mar- 
ble. 

(b) Size of Slab. The slab shall extend beyond the edges of the 
device and shall have a thickness proportioned to the size and weight 
of the device but shall not be less than Vi inch thick. 

(c) Supports. The slab shall be secured in position by supports in- 
dependent of those fastening the device to the slab. Bolts which support 
the device shall be countersunk at least Ys inch below the rear surface 
of the slab and shall be covered with insulating material. 

470-4. Contacts. Fixed and movable contacts shall be so designed that 
arcing will be kept at a minimum. 

470-5. Reactor Materials. Reactors shall be composed of noncom- 
bustible materials, and shall be mounted on noncombustible bases. 

470-6. Mounting. Enclosures when mounted on plain surfaces shall 
make contact with such surfaces only at the point of support, an air 



70-248 MASSACHUSETTS ELECTRICAL CODE 

space of at least Va inch being maintained between the enclosures and 
surfaces. 

470-7. Conductor Insulation. Insulated conductors used for connec- 
tion between resistance elements and controllers shall be suitable for 
an operating temperature of not less than 90°C (194°F). For elevator 
motor starting service, see Section 620-1 1(a). 

Exception: For motor starting service other conductor insulations 
may be used. 

470-8. Incandescent Lamps as Resistors. Incandescent lamps may be 
used as protective resistors for automatic controllers, or may by special 
permission be used as resistors in series with other devices and shall 
conform to the following: 

(a) Mounting. They shall be mounted in porcelain receptacles on 
noncombustible supports. 

(b) Voltage. They shall be so arranged that they cannot have im- 
pressed upon them a voltage greater than that for which they are rated. 

(c) Nameplate. They shall be provided with a nameplate, perma- 
nently attached, giving the wattage and voltage of the lamp to be used 
in each receptacle. 

(d) Not Carry Main Current. They shall not carry or control the 
main current nor constitute the regulating resistance of the device. 



ARTICLE 480 — STORAGE BATTERIES 



480-1. Scope. The provisions of this Article shall apply to all station- 
ary installations of storage batteries using acid or alkali as the electro- 
lyte and consisting of a number of cells connected in series with a nom- 
inal voltage in excess of 16 volts. 

480-2. Definition of Nominal Battery Voltage. The nominal battery 
voltage shall be calculated on the basis of 2.0 volts per cell for the lead- 
acid type, and 1 .2 volts per cell for the alkali type. 

480-3. Wiring and Apparatus Supplied from Batteries. Wiring, ap- 
pliances, and apparatus supplied from storage batteries shall be subject 
to the requirements of this Code applying to wiring, appliances, and 
apparatus operating at the same voltage, except as otherwise provided 
for communication systems in Article 800. 

480-4. Insulation of Batteries of Not Over 250 Volts. The provisions 
of this Section shall apply to storage batteries having the cells so con- 
nected as to operate at a nominal battery voltage not exceeding 250 
volts. 

(a) Lead-Acid Batteries. Cells in lead-lined wood tanks, where the 
number of cells in series does not exceed 25, shall be supported indi- 
vidually on glass or glazed porcelain insulators. Where the number of 
the cells in series exceeds 25, the cells shall be supported individually 
on oil insulators. 



ARTICLE 480-BATTERIES 70-249 



(b) Alkali-Type Batteries. Cells of the alkali type in jars made of 
conducting material shall be installed in trays of nonconducting mate- 
rial, with not over 20 cells in a series circuit in any one such tray, or 
the cells may be supported singly or in groups on porcelain or other 
suitable insulators. 

(c) Unsealed Jars. Cells in unsealed jars made of nonconductive 
material shall be assembled in trays of glass or supported on glass or 
glazed porcelain insulators; or, where installed on a rack, shall be sup- 
ported singly or in groups on glass or other suitable insulators. 

(d) Sealed Rubber Jars. Cells in sealed rubber or composition con- 
tainers shall require no additional insulating support where the total 
nominal voltage of all cells in series does not exceed 150 volts. Where 
the total voltage exceeds 150 volts, batteries shall be sectionalized into 
groups of 150 volts or less and each group shall have the individual cells 
installed in trays or on racks. Where trays or racks are required for this 
type of cell, such trays or racks shall be supported on glass or glazed 
porcelain insulators or oil-type insulators. 

(e) Sealed Glass or Plastic Jars. Cells in sealed glass jars or in 
sealed jars of approved heat resistant plastic, with or without wood 
trays, require no additional insulation. 

480-5. Insulation of Batteries of Over 250 Volts. The provisions of 
Section 480-4 shall apply to storage batteries having the cells so con- 
nected as to operate at a nominal voltage exceeding 250 volts and, in 
addition, the provisions of this section shall also apply to such batteries. 
Cells shall be installed in groups having a total nominal voltage of not 
over 250 volts, in trays or on racks supported on oil insulators. 

Exception No. 1. Where each individual cell, or sub-group in the 
tray or rack, is supported on oil insulators, no additional insulation for 
the group need be provided. 

Exception No. 2. Cells of not over 10 ampere-hour capacity in sealed 
glass jars may be grouped in trays, the total nominal voltage of all cells 
in such group not to exceed 250 volts, and each such tray to be sup- 
ported on glass or glazed porcelain insulators, the trays being mounted 
on racks supported on oil insulators with a total nominal voltage of not 
over 500 volts for all cells in series on each such insulated rack. 

Maximum protection is secured by sectionalizing high-voltage batteries 
into cell groups insulated from each other. 

480-6. Racks and Trays. Racks and trays shall conform to the follow- 
ing: 

(a) Racks. Racks, as required in this Article, refer to frames de- 
signed to support cells or trays. They shall be substantial, and made of: 

(1) Wood, so treated as to be resistant to deteriorating action by 
the electrolyte; or 

(2) Metal, so treated as to be resistant to deteriorating action by 
the electrolyte, and provided with nonconducting members directly sup- 
porting the cells or with suitable insulating material on conducting 
members; or 

(3) Other similar suitable construction. 



70-250 MASSACHUSETTS ELECTRICAL CODE 

(b) Trays. Trays refer to frames such as crates or shallow boxes 
usually of wood or other nonconducting material, so constructed or 
treated as to be resistant to deteriorating action by the electrolyte. 

480-7. Battery Rooms. Battery rooms shall conform to the following: 

(a) Use. Separate battery rooms or enclosures shall be required 
only for batteries in unsealed jars and tanks where the aggregate ca- 
pacity at the 8-hour discharge rate exceeds 5 kilowatt hours. 

(b) Ventilation. Provision shall be made for sufficient diffusion and 
ventilation of the gases from the battery to prevent the accumulation 
of an explosive mixture in the battery room. 

(e) Wiring Method. In storage battery rooms, bare conductors, 
open wiring, Type MI cable, type ALS cable, or conductors in rigid 
conduit or electrical metallic tubing shall be used as the wiring method. 
Rigid metal conduit, or electrical metallic tubing, where used, shall be 
of corrosion-resistant material or shall be suitably protected from corro- 
sion. 

(d) Varnished-Cambric Conductors. Varnished-cambric-covered con- 
ductors, Type V, shall not be used. 

(e) Bare Conductors. Bare conductors shall not be taped. 

(f) Terminals. Where metal raceway or other metallic covering is 
used in the battery room, at least 12 inches of the conductor at the end 
connected to a cell terminal shall be free from the raceway or metallic 
covering and shall be bushed by a substantial glazed insulating bush- 
ing. The end of the raceway shall be sealed tightly to resist the entrance 
of electrolyte by spray or by creepage. Sealing compound, rubber in- 
sulating tape or other suitable material shall be used for this purpose. 



70-251 

Chapter 5. Special Occupancies 
ARTICLE 500 — HAZARDOUS LOCATIONS 

500-1. Scope. The provisions of Articles 500-503 apply to locations in 
which the authority enforcing this Code judges the apparatus and wiring to 
be subject to the conditions indicated by the following classifications. It is 
intended that each room, section or area (including motor and generator 
rooms, and rooms for the enclosure of control equipment) shall be considered 
individually in determining its classification. Except as modified in Articles 
500-503, all other applicable rules contained in this Code shall apply to 
electrical apparatus and wiring installed in hazardous locations. For defini- 
tions of "approved" and "explosion-proof" as used in these Articles, refer 
to Article 100; "dust-ignition-proof" is defined in Section 502-1. 

Equipment and associated wiring approved as intrinsically safe may be 
installed in any hazardous location for which it is approved, and the pro- 
visions of Articles 500-517 need not apply to such installation. Intrinsically 
safe equipment and wiring are incapable of releasing sufficient electrical 
energy under normal or abnormal conditions to cause ignition of a specific 
hazardous atmospheric mixture. Abnormal conditions will include accidental 
damage to any part of the equipment or wiring, insulation or other failure 
of electrical components, application of over-voltage, adjustment and main- 
tenance operations, and other similar conditions. 

Through the exercise of ingenuity in the layout of electrical installations 
for hazardous locations, it is frequently possible to locate much of the equip- 
ment in less hazardous or in nonhazardous areas and thus to reduce the 
amount of special equipment required. In some cases, hazards may be re- 
duced or hazardous areas limited or eliminated by adequate positive-pressure 
ventilation from a source of clean air in conjunction with effective safeguards 
against ventilation failure. 

It is recommended also that the Code enforcing authority be familiar with 
such recorded industrial experience as well as with such standards of the 
National Fire Protection Association as may be of use in the classification of 
various areas with respect to hazard. For further information see NFPA No. 
30, Flammable and Combustible Liquids Cede; No. 32, Standard for Dry 
Cleaning Plants; No. 35M, Organic Coatings Manufacture; and No. 36, 
Standard for Solvent Extraction Plants. 

For protection against static electricity hazards, refer to the standards of 
the National Fire Protection Association on this subject. 

Where rigid conduit is used in hazardous locations, it is necessary to have 
all threaded joints made up wrench tight to minimize sparking when fault 
current flows through the conduit system. Where it is impractical to make a 
threaded joint tight, a bonding jumper should be utilized. 

All conduit referred to herein shall be threaded with standard conduit 



70-252 MASSACHUSETTS ELECTRICAL CODE 

cutting die which provides %" taper per foot. Such conduit shall be 
made up wrench tight to minimize sparking when fault current flows 
through the conduit system. Where it is impractical to make a threaded 
joint tight, a bonding jumper shall be utilized. 

500-2. Special Precaution. The intent of Articles 500-503 is to require 
a form of construction of equipment, and of installation that will insure 
safe performance under conditions of proper use and maintenance. It, 
therefore, is assumed that inspection authorities and users will exercise 
more than ordinary care with regard to installation and maintenance. 

The characteristics of various atmospheric mixtures of hazardous 
gases, vapors and dusts depend on the specific hazardous material in- 
volved. It is necessary therefore that equipment be approved not only 
for the class of location but also for the specific gas, vapor or dust that 
will be present. 

For purposes of testing and approval, various atmospheric mixtures have 
been grouped on the basis of their hazardous characteristics, and facilities 
have been made available for testing and approval of equipment for use in 
the following atmospheric groups : 

Group A, Atmospheres containing acetylene; 

Group B, Atmospheres containing hydrogen, or gases or vapors of equiv- 
alent hazard such as manufactured gas; 

Group C, Atmospheres containing ethyl ether vapors, ethylene, or cyclo- 
propane; 

Group D, Atmospheres containing gasoline, hexane, naphtha, benzine, 
butane, propane, alcohol, acetone, benzol, lacquer solvent vapors, or 
natural gas; 

Group E, Atmospheres containing metal dust, including aluminum, mag- 
nesium, and their commerical alloys, and other metals of similarly hazardous 
characteristics. 

Group F, Atmospheres containing carbon black, coal or coke dust; 

Group G, Atmospheres containing flour, starch, or grain dusts. 

500-3. Specific Occupancies. See Articles 510 to 517 inclusive for 
rules applying to garages, aircraft hangars, gasoline dispensing and serv- 
ice stations, bulk storage plants, finishing processes, and flammable 
anesthetics. 

500-4. Class I Locations. Class I locations are those in which flam- 
mable gases or vapors are or may be present in the air in quantities 
sufficient to produce explosive or ignitible mixtures. Class I locations 
shall include the following: 

(a) Class I, Division 1. Locations (1) in which hazardous concen- 
trations of flammable gases or vapors exist continuously, intermittently, 
or periodically under normal operating conditions, (2) in which haz- 
ardous concentrations of such gases or vapors may exist frequently be- 
cause of repair or maintenance operations or because of leakage, or 
(3) in which breakdown or faulty operation of equipment or proc- 
esses which might release hazardous concentrations of flammable gases 
or vapors, might also cause simultaneous failure of electrical equipment. 

This classification usually includes locations where volatile flammable 
liquids or liquefied flammable gases are transferred from one container to 



ARTICLE 500-HAZARDOUS LOCATIONS 70-253 

another; interiors of spray booths and areas in the vicinity of spraying and 
painting operations where volatile flammable solvents are used; locations 
containing open tanks or vats of volatile flammable liquids; drying rooms or 
compartments for the evaporation of flammable solvents; locations con- 
taining fat and oil extraction apparatus using volatile flammable solvents; 
portions of cleaning and dyeing plants where hazardous liquids are used; gas 
generator rooms and other portions of gas manufacturing plants where flam- 
mable gas may escape; inadequately ventilated pump rooms for flammable 
gas or for volatile flammable liquids; the interiors of refrigerators and freez- 
ers in which volatile, flammable materials are stored in open, lightly stop- 
pered, or easily ruptured containers, and all other locations where hazard- 
ous concentrations of flammable vapors or gases are likely to occur in the 
course of normal operations. 

(b) Class I, Division 2. Locations (1) in which volatile flammable 
liquids or flammable gases are handled, processed or used, but in which 
the hazardous liquids, vapors or gases will normally be confined within 
closed containers or closed systems from which they can escape only 
in case of accidental rupture or breakdown of such containers or sys- 
tems, or in case of abnormal operation of equipment, (2) in which 
hazardous concentrations of gases or vapors are normally prevented by 
positive mechanical ventilation, but which might become hazardous 
through failure or abnormal operation of the ventilating equipment, or 
(3) which are adjacent to Class I, Division 1 locations, and to which 
hazardous concentrations of gases or vapors might occasionally be 
communicated unless such communication is prevented by adequate 
positive-pressure ventilation from a source of clean air, and effective 
safeguards against ventilation failure are provided. 

This classification usually includes locations where volatile flammable 
liquids or flammable gases or vapors are used, but which, in the judgment 
of the Code enforcing authority, would become hazardous only in case of 
an accident or of some unusual operating condition. The quantity of 
hazardous material that might escape in case of accident, the adequacy of 
ventilating equipment, the total area involved, and the record of the industry 
or business with respect to explosions or fires are all factors that should re- 
ceive consideration in determining the classification and extent of each 
hazardous area. 

Piping without valves, checks, meters and similar devices would not 
ordinarily be deemed to introduce a hazardous condition even though used 
for hazardous liquids or gases. Locations used for the storage of hazardous 
liquids or of liquefied or compressed gases in sealed containers would not 
normally be considered hazardous unless subject to other hazardous con- 
ditions also. 

Electrical conduits and their associated enclosures separated from 
process fluids by a single seal or barrier shall be classed as Division 2 
locations if the outside of conduit and enclosures is a nonhazardous 
area. 

500-5. Class II Locations. Class II locations are those which are haz- 
ardous because of the presence of combustible dust. Class II locations 
shall include the following: 

(a) Class II, Division 1. Locations (1) in which combustible dust is 
or may be in suspension in the air continuously, intermittently, or pe- 
riodically under normal operating conditions, in quantities sufficient to 
produce explosive or ignitible mixtures, (2) where mechanical failure 



70-254 MASSACHUSETTS ELECTRICAL CODE 

or abnormal operation of machinery or equipment might cause such 
mixtures to be produced, and might also provide a source of ignition 
through simultaneous failure of electrical equipment, operation of 
protection devices, or from other causes, or (3) in which dusts of an 
electrically conducting nature may be present. 

This classification usually includes the working areas of grain handling 
and storage plants; rooms containing grinders or pulverizers, cleaners, 
graders, scalpers, open conveyors or spouts, open bins or hoppers, mixers 
or blenders, automatic or hopper scales, packing machinery, elevator heads 
and boots, stock distributors, dust and stock collectors (except all-metal 
collectors vented to the outside), and all similar dust producing machinery 
and equipment in grain processing plants, starch plants, sugar pulverizing 
plants, malting plants, hay grinding plants, and other occupancies of similar 
nature; coal pulverizing plants (except where the pulverizing equipment is 
essentially dust-tight); all working areas where metal dusts and powders 
are produced, processed, handled, packed or stored (except in tight con- 
tainers); and all other similar locations where combustible dust may, under 
normal operating conditions, be present in the air in quantities sufficient to 
produce explosive or ignitible mixtures. 

Combustible dusts which are electrically nonconducting include dusts 
produced in the handling and processing of grain and grain products, 
pulverized sugar and cocoa, dried egg and milk powders, pulverized spices, 
starch and pastes, potato and woodflour, oil meal from beans and seed, 
dried hay, and other organic materials which may produce combustible 
dusts when processed or handled. Electrically conducting nonmetallic dusts 
include dusts from pulverized coal, coke and charcoal. Dusts containing mag- 
nesium or aluminum are particularly hazardous and every precaution must 
be taken to avoid ignition and explosion. 

(b) Class II, Division' 2. Locations in which combustible dust will 
not normally be in suspension in the air, or will not be likely to be 
thrown into suspension by the normal operation of equipment or ap- 
paratus, in quantities sufficient to produce explosive or ignitible mix- 
tures, but (1) where deposits or accumulations of such dust may be 
sufficient to interfere with the safe dissipation of heat from electrical 
equipment or apparatus, or (2) where such deposits or accumulations 
of dust on, in, or in the vicinity of electrical equipment might be ig- 
nited by arcs, sparks or burning material from such equipment. 

Locations where dangerous concentrations of suspended dust would not 
be likely, but where dust accumulations might form on, or in the vicinity of 
electrical equipment, would include rooms and areas containing only closed 
spouting and conveyors, closed bins or hoppers, or machines and equipment 
from which appreciable quantities of dust would escape only under ab- 
normal operating conditions; rooms or areas adjacent to locations de- 
scribed in Section 500-5 (a), and into which explosive or ignitible concentra- 
tions of suspended dust might be communicated only under abnormal 
operating conditions; rooms or areas where the formation of explosive or 
ignitible concentrations of suspended dust is prevented by the operation of 
effective dust control equipment; warehouses and shipping rooms where 
dust producing materials are stored or handled only in bags or containers; 
and other similar locations. 

500-6. Class III Locations. Class III locations are those which are haz- 
ardous because of the presence of easily ignitible fibers or flyings, but 
in which such fibers or flyings are not likely to be in suspension in air 
in quantities sufficient to produce ignitible mixtures. Class III locations 
shall include the following: 



ARTICLE 501-CLASS I INSTALLATIONS 70-255 

(a) Class III, Division 1. Locations in which easily ignitible fibers 
or materials producing combustible flyings are handled, manufactured 
or used. 

Such locations usually include some parts of rayon, cotton and other 
textile mills; combustible fiber manufacturing and processing plants; cotton 
gins and cotton-seed mills; flax processing plants; clothing manufacturing 
plants; woodworking plants; and establishments and industries involving 
similar hazardous processes or conditions. 

Easily ignitible fibers and flyings include rayon, cotton (including cotton 
linters and cotton waste), sisal or henequen, istle, jute, hemp, tow, cocoa 
fiber, oakum, baled waste kapok, Spanish moss, excelsior and other ma- 
terials of similar nature. 

(b) Class III, Division 2. Locations in which easily ignitible fibers 
are stored or handled (except in process of manufacture). 



ARTICLE 501 — CLASS I INSTALLATIONS — 
HAZARDOUS LOCATIONS 



501-1. General. The general rules of this Code shall apply to the in- 
stallation of electrical wiring and equipment in locations classified as 
Class I under Section 500-4 except as modified by this Article. 

501-2. Transformers and Capacitors. The installation of transformers 
and capacitors shall conform to the following: 

(a) Class I, Division 1. In Class I, Division 1 locations, transform- 
ers and capacitors shall conform to the following: 

(1) Containing a Liquid that Will Burn. Transformers and capac- 
itors containing a liquid that will burn shall be installed only in 
approved vaults, which shall conform to Sections 450-41 to 450-48 in- 
clusive, and in addition, ( 1 ) there shall be no door or other com- 
municating opening between the vault and the hazardous area, (2) 
ample ventilation shall be provided for the continuous removal of haz- 
ardous gases or vapor, (3) vent openings or ducts shall lead to a safe 
location outside of buildings, and (4) vent ducts and openings shall be 
of sufficient area to relieve explosion pressures within the vault, and 
all portions of vent ducts within the buildings shall be of reinforced 
concrete construction. 

(2) Not Containing a Liquid that Will Burn. Transformers and 
capacitors which do not contain a liquid that will burn shall (1) be 
installed in vaults conforming to the requirements of Section 50 1-2 (a- 
1 ), or (2) be approved for Class I locations (explosion-proof). 

(b) Class I, Division 2. In Class I, Division 2 locations, transform- 
ers and capacitors shall conform to Sections 450-21 to 450-25 inclu- 
sive. 

501-3. Meters, Instruments and Relays. The installation of meters, in- 
struments and relays shall conform to the following: 



70-256 MAS SACHUSETTS ELECTRICAL CODE 

(a) Class I, Division 1. In Class I, Division 1 location, meters, in- 
struments and relays, including kilowatt-hour meters, instrument trans- 
formers and resistors, rectifiers and thermionic tubes, shall be provided 
with enclosures approved for Class I locations. 

(b) Class I, Division 2. In Class I, Division 2 locations, meters, in- 
struments and relays shall conform to the following: 

(1) Contacts. Switches and circuit-breakers, and make and break 
contacts of push buttons, relays, and alarm bells or horns, shall have 
enclosures approved for Class I locations, unless general purpose en- 
closures are provided, and current interrupting contacts are (1) im- 
mersed in oil, (2) enclosed within a chamber hermetically sealed 
against the entrance of gases or vapors, or (3) in circuits which under 
normal conditions do not release sufficient energy to ignite a specific 
hazardous atmospheric mixture. 

(2) Resistors and Similar Equipment. Resistors, resistance devices, 
thermionic tubes, and rectifiers, which are used in or in connection 
with meters, instruments and relays, shall conform to Section 501-3 (a), 
except that enclosures may be of general purpose type when such 
equipment is without make and break or sliding contacts (other than as 
provided in Section 501-3 (b) (1) above) and when the maximum op- 
erating temperature of any exposed surface will not exceed eighty per 
cent (80% ) of the ignition temperature in degrees Centigrade of the gas 
or vapor involved as determined by A.S.T.M. test procedure (Designa- 
tion D286-30). 

(3) Without Make or Break Contacts. Transformer windings, im- 
pedance coils, solenoids, and other windings which do not incorporate 
sliding or make or break contacts shall be provided with enclosures 
which may be of general purpose type where vents adequate to permit 
prompt escape of any gases or vapors are provided. 

(4) General Purpose Assemblies. Where an assembly is made 
up of components for which general purpose enclosures are acceptable 
under Sections 501-3(b-l, 2, 3), a single general purpose enclosure is 
acceptable for the assembly. Where such an assembly includes any of 
the equipment described in Section 501-3(b-2) the maximum obtain- 
able surface temperature of any component of the assembly shall be 
clearly and permanently indicated on the outside of the enclosure. 

(5) Fuses. Where general purpose enclosures are permitted un- 
der Paragraphs 501-3.(b), (1), (2), (3), (4), fuses for overcurrent 
protection of the instrument circuits may be mounted in general pur- 
pose enclosures provided such fuses do not exceed 3 ampere rating at 
1 20 volts and provided each such fuse is preceded by a switch conf orm- 
ing to Paragraph 501-3.(b).(l). 

501-4. Wiring Methods. Wiring methods shall conform to the follow- 
ing: 

(a) Class I, Division 1. In Class I, Division 1 locations, threaded 
rigid metal conduit or Type MI cable with termination fittings approved 
for the location shall be the wiring method employed. All boxes, fittings, 
and joints shall be threaded for connection to conduit or cable termina- 
tions, and shall be explosion-proof. Threaded joints shall be made up 



ARTICLE 501 -CLASS I INSTALLATIONS 70-257 

with at least five threads fully engaged. Type MI cable shall be installed 
and supported in a manner to avoid tensile stress at the termination fit- 
tings. Where necessary to employ flexible connections, as at motor 
terminals, flexible fittings approved for Class I locations (explosion- 
proof) shall be used. 

(b) Class J, Division 2. In Class I, Division 2 locations, threaded 
rigid metal conduit or Type MI cable with termination fittings ap- 
proved for Class I locations, or approved Type MC or ALS cable with 
termination fittings approved for Class I locations shall be the wiring 
method employed. Type MI, MC or ALS cable shall be installed in a 
manner to avoid tensile stress at the termination fittings. Boxes, fittings 
and joints need not be explosion proof except as required by Sections 
501-5 (b) (1) and (2). Where provision must be made for limited flex- 
ibility, as at motor terminals, flexible metal fittings, flexible metal con- 
duit with approved fittings, or flexible cord approved for extra hard 
usage and provided with approved bushed fittings shall be used. An ad- 
ditional conductor for grounding shall be included in the flexible cord 
unless other acceptable means of grounding are provided. 

501-5. Sealing and Drainage. Seals are provided in conduit and ca- 
ble systems to prevent the passage of gases, vapors or flames from one 
portion oi the electrical installation to another through the conduit. 
Such communication through Type MI cable is inherently prevented 
by construction of the cable, but sealing compound is used in cable 
termination fittings to exclude moisture and other fluids from the cable 
insulation, and shall be of a type approved for the conditions of use. 
Seals in conduit and cable systems shall conform to the following : 

(a) Class I, Division 1. In Class I, Division 1 locations, seals shall 
be located as follows : 

(1) In each conduit run entering an enclosure for switches, circuit 
breakers, fuses, relays, resistors or other apparatus which may pro- 
duce arcs, sparks or high temperatures. Seals shall be placed as close 
as practicable and in no case more than 1"8 inches from such enclosures. 

(2) In each conduit run of 2-inch size or larger entering the en- 
closure or fitting housing terminals, splices or taps, and within 18 
inches of such enclosure or fitting. 

Where two or more enclosures for which seals are required under Sec- 
tions 501-5 ( a- 1, 2) are connected by nipples or by runs of conduit not 
more than 36 inches long, a single seal in each such nipple connection or 
run of conduit would be sufficient if located not more than 18 inches from 
either enclosure. Ordinary conduit fittings of the "L," "T" or "Cross" type 
would not usually be classed as enclosures when not larger than the trade 
size of the conduit. 

(3) In each conduit run leaving the Class I, Division 1 hazardous 
area. The sealing fitting may be located on either side of the boundary 
of such hazardous area, but shall be so designed and installed that any 
gases or vapors which may enter the conduit system, within the Divi- 
sion 1 hazardous area, will not enter or be communicated to the conduit 
beyond the seal. There shall be no union, coupling, box or fitting in 
the conduit between the sealing fitting and the point at which the con- 
duit leaves the Division 1 hazardous area. 



70-258 MASSACHUSETTS ELECTRICAL CODE 

(b) Class I, Division 2. In Class I, Division 2 locations, seals shall 
be located as follows: 

(1) For conduit connections to enclosures which are required to be 
approved for Class I locations, seals shall be provided in conformance 
to Sections 501-5(a-l, 2). All portions of the conduit run or nipple be- 
tween the seal and such enclosure shall conform to Section 501-4(a) . 

(2) In each conduit run passing from the Class I, Division 2 haz- 
ardous area into a nonhazardous area. The sealing fitting may be lo- 
cated on either side of the boundary of such hazardous area, but shall 
be so designed and installed that any gases or vapors which may enter 
the conduit system, within the Division 2 hazardous area, will not enter 
or be communicated to the conduit beyond the seal. Rigid conduit shall 
be used between the sealing fitting and the point at which the conduit 
leaves the hazardous area, and a threaded connection shall be used at 
the sealing fitting. There shall be no union, coupling, box or fitting in 
the conduit between the sealing fitting and the point at which the con- 
duit leaves the hazardous area. 

(c) Class I, Divisions 1 and 2. Where seals are required, they shall 
conform to the following: 

(1) Fittings. Enclosures for connections or for equipment shall 
be provided with approved integral means for sealing, or sealing fittings 
approved for Class I locations shall be used. Sealing fittings shall be 
accessible. 

(2) Compound. Sealing compound shall be approved for the pur- 
pose, shall not be affected by the surrounding atmosphere or liquids, 
and shall not have a melting point of less than 93 °C. (200°F.) . 

(3) Thickness of Compound. In the completed seal, the minimum 
thickness of the sealing compound shall be not less than the trade size 
of the conduit, and in no case less than %inch. 

(4) Splices and Taps. Splices and taps shall not be made in fit- 
tings intended only for sealing with compound, nor shall other fittings 
in which splices or taps are made be filled with compound. 

(5) Assemblies. In an assembly where equipment which may 
produce arcs, sparks or high temperatures is located in a compartment 
separate from the compartment containing splices or taps, and an in- 
tegral seal is provided where conductors pass from one compartment 
to the other, the entire assembly shall be approved for Class I locations. 
Seals in conduit connections to the compartment containing splices or 
taps shall be provided in Class I, Division 1 locations where required by 
Section 501 -5 (a-2). 

(d) Drainage. 

(1) Control Equipment. Where there is probability that liquid 
or other condensed vapor may be trapped within enclosures for control 
equipment or at any point in the raceway system, approved means shall 
be provided to prevent accumulation or to permit periodic draining of 
such liquid or condensed vapor. 

(2) Motors and Generators. Where the authority enforcing this 
Code judges that there is probability that liquid or condensed vapor 



ARTICLE 501 -CLASS I INSTALLATIONS 70-259 

may accumulate within motors or generators, joints and conduit systems 
shall be arranged to minimize entrance of liquid. If means to prevent 
accumulation or to permit periodic draining are judged necessary, such 
means shall be provided at the time of manufacture, and shall be 
deemed an integral part of the machine. 

(3) Canned Pumps, Process Connections for Flow, Pressure or Anal- 
ysis Measurement, Etc., frequently 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. 

See also the last paragraph of footnote in Section 500-4 (b) . 

501-6. Switches, Circuit Breakers, Motor Controllers and Fuses. 

Switches, circuit breakers, motor controllers and fuses shall conform 
to the following: 

(a) Class I, Division 1. In Class I, Division 1 locations, switches, 
circuit breakers, motor controllers and fuses, including push buttons, 
relays and similar devices, shall be provided with enclosures, and the 
enclosure in each case together with the enclosed apparatus shall be 
approved as a complete assembly for use in Class I locations. 

(b) Class I, Division 2. Switches, circuit breakers, motor controllers 
and fuses in Class I, Division 2 locations shall conform to the follow- 
ing: 

(1) Type Required. Circuit breakers, motor controllers and 
switches intended to interrupt current in the normal performance of 
the function for which they are installed shall be provided with enclo- 
sures approved for Class I locations, unless general purpose enclosures 
are provided and ( 1 ) the interruption of current occurs within a cham- 
ber hermetically sealed against the entrance of gases and vapors, or 
(2) the current interrupting contacts are oil-immersed and the device 
is approved for locations of this class and division. 

This includes service and branch circuit switches and circuit breakers; 
motor controllers, including push buttons, pilot switches, relays and motor- 
overload protective devices; and switches and circuit breakers for the con- 
trol of lighting and appliance circuits. Oil-immersed circuit breakers and 
controllers of ordinary general use type may not confine completely the arc 
produced in the interruption of heavy overloads, and specific approval for 
locations of this class and division is therefore necessary. 

(2) Isolating Switches. Enclosures for disconnecting and isolat- 
ing switches without fuses and which are not intended to interrupt 
current may be of general purpose type. 

(3) Fuses. For the protection of motors, appliances and lamps, 
except as provided in Section 501-6(b-4), (1) standard plug or car- 
tridge fuses may be used provided they are placed within enclosures 
approved for the purpose and for the location, or (2) fuses of a type 
in which the operating element is immersed in oil or other approved 
liquid, or is enclosed within a chamber hermetically sealed against the 
entrance of gases and vapors may be used provided they are approved 
for the purpose and are placed within general purpose enclosures. 



70-260 MASSACHUSETTS ELECTRICAL CODE 

(4) Fuses or Circuit Breakers for Overcurrent Protection. When 
not more than 10 sets of approved enclosed fuses, or not more than 10 
circuit breakers which are not intended to be used as switches for the 
interruption of current, are installed for branch or feeder circuit pro- 
tection in any one room, area or section of this class and division, the 
enclosures for such fuses or circuit breakers may be of general purpose 
type, provided the fuses or circuit breakers are for the protection of cir- 
cuits or feeders supplying lamps in fixed positions only. 

A set of fuses is construed to mean a group containing as many fuses as 
are required to perform a single protective function in a circuit. For ex- 
ample, a group of 3 fuses protecting an ungrounded three-phase circuit, and 
a single fuse protecting the ungrounded conductor of an identified two-wire 
single-phase circuit, would each be considered as a set of^fuses. Fuses con- 
forming to Section 501-6(b-3) need not be included in counting the 10 sets 
of fuses permitted in general purpose enclosures. 

501-7. Control Transformers and Resistors. Transformers, impedance 
coils and resistors used as or in conjunction with control equipment for 
motors, generators and appliances shall conform to the following: 

(a) Class I, Division 1. In Class I, Division 1 locations, transform- 
ers, impedance coils and resistors, together with any switching mech- 
anism associated with them, shall be provided with enclosures approved 
for Class I locations (explosion-proof) . 

(b) Class I, Division 2. In Class I, Division 2 locations, control 
transformers and resistors shall conform to the following: 

(1) Switching Mechanisms. Switching mechanisms used in con- 
junction with transformers, impedance coils and resistors shall con- 
form to Section 501 -6(b). 

(2) Coils and Windings. Enclosures for windings of transform- 
ers, solenoids or impedance coils may be of general purpose type, but 
shall be provided with vents adequate to permit prompt escape of gases 
or vapors that may enter the enclosure. 

(3) Resistors. Resistors shall be provided with enclosures and the 
assembly shall be approved for Class I locations, unless resistance is 
nonvariable and maximum operating temperature, in degrees Centi- 
grade, will not exceed eighty per cent (80%) of the ignition tempera- 
ture of the gas or vapor involved as determined by ASTM test proce- 
dure (Designation D 286-30). 

501-8. Motors and Generators. Motors and generators shall conform 
to the following: 

(a) Class I, Division 1. In Class I, Division 1 locations, motors, 
generators and other rotating electrical machinery shall be (1) ap- 
proved for Class I locations (explosion-proof), or (2) of the totally 
enclosed type supplied with positive-pressure ventilation from a source 
of clean air with discharge to a safe area, so arranged to prevent ener- 
gizing of the machine until ventilation has been established and the 
enclosure has been purged with at least ten (10) volumes of air, and 
also arranged to automatically de-energize the equipment when the 
air supply fails, or (3) of the totally enclosed inert-gas-filled type sup- 
plied with a suitable reliable source of inert gas for pressuring the en- 



ARTICLE 501 -CLASS I INSTALLATIONS 70-261 

closure, with devices provided to insure a positive pressure in the en- 
closure and arranged to automatically de-energize the equipment when 
the gas supply fails. Totally enclosed motors of types (2) or (3) shall 
have no external surface with an operating temperature in degrees 
Centigrade in excess of eighty per cent (80% ) of the ignition tempera- 
ture of the gas or vapor involved, as determined by ASTM test proce- 
dure (Designation: D-286-30). Appropriate devices shall also be pro- 
vided to detect any increase in temperature of the motor beyond design 
limits and automatically de-energize the equipment. Auxiliary equip- 
ment shall be of a type approved for the location in which it is in- 
stalled. 

(b) Class I, Division 2. In Class I, Division 2 locations, motors, 
generators and other rotating electrical machinery in which are em- 
ployed sliding contacts, centrifugal or other types of switching mech- 
anism (including motor overcurrent devices), or integral resistance de- 
vices, either while starting or while running, shall be approved for Class 
I locations (explosion-proof), unless such sliding contacts, switching 
mechanisms and resistance devices are provided with enclosures ap- 
proved for such locations. 

This rule does not prohibit installation of open or nonexplosion-proof 
enclosed motors, such as squirrel cage induction motors, without brushes, 
switching mechanism, etc., in Class I, Division 2 locations. 

501-9. Lighting Fixtures. Lamps shall be installed in fixtures which 
shall conform to the following: 

(a) Class I, Division 1 . In Class I, Division 1 locations, lighting fix- 
tures shall conform to the following: 

(1) Approved Fixtures. Each fixture shall be approved as a com- 
plete assembly for locations of this class, and shall be clearly marked 
to indicate the maximum wattage of lamps for which it is approved. 
Fixtures intended for portable use shall be specifically approved as a 
complete assembly for that use. 

(2) Physical Damage. Each fixture shall be protected against 
physical damage by a suitable guard or by location. 

(3) Pendant Fixtures. Pendant fixtures shall be suspended by 
and supplied through threaded rigid conduit stems and threaded joints 
shall be provided with set-screws or other effective means to prevent 
loosening. For stems longer than 12 inches, permanent and effective 
bracing against lateral displacement shall be provided at a level not 
more than 12 inches above the lower end of the stem, or flexibility in 
the form of a fitting or flexible connector approved for the purpose 
and for the location shall be provided not more than 12 inches from 
the point of attachment to the supporting box or fitting. 

(4) Supports. Boxes, box assemblies or fittings used for the sup- 
port of lighting fixtures shall be approved for the purpose and for 
Class I locations. 

(b) Class I, Division 2. In Class I, Division 2 locations, lighting fix- 
tures shall conform to the following: 

(1) Portable Lamps. Portable lamps shall conform to Section 
501-9(a-l). 



70-262 MASSACHUSETTS ELECTRICAL CODE 

(2) Fixed Lighting. Lighting fixtures for fixed lighting shall be 
protected from physical damage by suitable guards or by location. 
Where there is danger that falling sparks or hot metal from lamps or 
fixtures might ignite localized concentrations of flammable vapors or 
gases, suitable enclosures or other effective protective means shall be 
provided. Where lamps are of a size or type which may, under normal 
operating conditions, reach surface temperatures exceeding eighty per 
cent (80%) of the ignition temperature in degrees Centigrade of the 
gas or vapor involved, as determined by ASTM test procedure (Des- 
ignation D 286-30), fixtures shall conform to Section 501-9(a-l). 

(3) Pendant Fixtures. Pendant fixtures shall be suspended by 
threaded rigid conduit stems or by other approved means. For rigid 
stems longer than 12 inches, permanent and effective bracing against 
lateral displacement shall be provided at a level not more than 12 inches 
above the lower end of the stem, or flexibility in the form of a fitting 
or flexible connector approved for the purpose shall be provided not 
more than 12 inches from the point of attachment to the supporting 
box or fitting. 

(4) Supports. Boxes, box assemblies, or fittings used for the sup- 
port of lighting fixtures shall be approved for the purpose. 

(5) Switches. Switches which are a part of an assembled fixture 
or of an individual lampholder shall conform to the requirements of 
Section 501 -6 (b-1). 

(6) Starting Equipment. Starting and control equipment for mer- 
cury-vapor and fluorescent lamps shall conform to the requirements 
of Section 501 -7(b). 

501-10. Utilization Equipment, Fixed and Portable. Utilization equip- 
ment, fixed and portable, shall conform to the following: 

(a) Class I, Division 1. In Class I, Division 1 locations, utilization 
equipment, including electrically-heated and motor-driven equipment 
shall be approved for Class I locations. 

(b) Class I, Division 2. In Class I, Division 2 locations, utilization 
equipment, fixed and portable, shall conform to the following: 

(1) Heaters. Electrically-heated utilization equipment shall be 
approved for Class I locations. 

(2) Motors. Motors of motor-driven utilization equipment shall 
conform to Section 501 -8(b) . 

(3) Switches, Circuit-breakers, and Fuses. Switches, circuit-break- 
ers and fuses shall conform to Section 501 -6(b) . 

501-11. Flexible Cords, Class I, Divisions 1 and 2. A flexible cord 
may be used only for connection between a portable lamp or other 
portable utilization equipment and the fixed portion of its supply cir- 
cuit and where used shall (1) be of a type approved for extra hard 
usage, (2) contain, in addition to the conductors of the circuit, a 
grounding conductor conforming to Section 400-13, (3) be connected 
to terminals or to supply conductors in an approved manner, (4) be 
supported by clamps or by other suitable means in such a manner that 
there will be no tension on the terminal connections, and (5) suitable 



ARTICLE 501-CLASS I INSTALLATIONS 70-263 

seals shall be provided where the flexible cord enters boxes, fittings 
or enclosures of explosion-proof type. 

Refer to Section 501-13 when flexible cords are exposed to liquids having 
a deleterious effect on the conductor insulation. 

501-12. Receptacles and Attachment Plugs, Class I, Divisions 1 and 2. 

Receptacles and attachment plugs shall be of the type providing for 
connection to the grounding conductor of the flexible cord, and shall 
be approved for Class I locations. 

501-13. Conductor Insulation Class I, Divisions 1 and 2. Where con- 
densed vapors or liquids may collect on or come in contact with the in- 
sulation on conductors, such insulation shall be of a type approved for 
use under such conditions or the insulation shall be protected by a 
sheath of lead or by other approved means. 

501-14. Signal, Alarm, Remote-control and Communication Systems. 

Signal, alarm, remote-control and communication systems shall con- 
form to the following: 

(a) Class I, Division I. In Class I, Division 1 locations, all appa- 
ratus and equipment of signalling, alarm, remote-control and com- 
munication systems, irrespective of voltage, shall be approved for 
Class I locations, and all wiring shall conform to Sections 501-4(a) and 
501-5(aandc). 

(b) Class I, Division 2. In Class I, Division 2 locations, signal, 
alarm, remote-control and communication systems shall conform to 
the following: 

(1) Contacts. Switches and circuit breakers, and make and break 
contacts of push buttons, relays, and alarm bells or horns, shall have 
enclosures approved for Class I locations, unless general purpose en- 
closures are provided and current interrupting contacts are ( 1 ) im- 
mersed in oil, or (2) enclosed within a chamber hermetically sealed 
against the entrance of gases or vapors, or (3) in circuits which under 
normal conditions do not release sufficient energy to ignite a specific 
hazardous atmospheric mixture. 

(2) Resistors and Similar Equipment. Resistors, resistance de- 
vices, thermionic tubes and rectifiers shall conform to Section 501-3 
(b-2). 

(3) Protectors. Enclosures which may be of general purpose type 
shall be provided for lightning protective devices and for fuses. 

(4) All wiring shall conform to Section 501-4. (b) and 501-5. (b) 
and (c). 

501-15. Live Parts, Class I, Divisions 1 and 2. There shall be no ex- 
posed live parts. 

501-16. Grounding, Class I, Divisions 1 and 2. Wiring and equip- 
ment shall be grounded in conformity with the following: 

(a) Exposed Parts. The exposed noncurrent-carrying metal parts 
of equipment such as the frames or metal exteriors of motors, fixed or 
portable lamps or other utilization equipment, lighting fixtures, cabi- 
nets, cases, and conduit, shall be grounded as specified in Article 250 
of this Code. 



70-264 MASSACHUSETTS ELECTRICAL CODE 

(b) Bonding. The locknut-bushing and double-locknut types of con- 
tacts shall not be depended upon for bonding purposes, but bonding 
jumpers with proper fittings or other approved means shall be used. Such 
means of bonding shall apply to all intervening raceways, fittings, boxes, 
enclosures, etc. between hazardous areas and the point of grounding 
for service equipment. Where flexible conduit is used as permitted in 
Section 501-4(b), bonding jumpers with proper fittings shall be pro- 
vided around such conduit. 

(c) Lightning Protection. Each ungrounded service conductor of a 
wiring system in a Class I location, when supplied from an overhead 
line in an area where lightning disturbances are prevalent, shall be pro- 
tected by a lightning protective device of proper type. Lightning pro- 
tective devices shall be connected to the service conductors on the sup- 
ply side of the service disconnecting means, and shall be bonded to the 
raceway system at the service entrance. 

Also refer to Section 502-3. 

(d) Grounded Service Conductor Bonded to Raceway. Wiring in a 
Class I location, when supplied from a grounded alternating current 
supply system in which a grounded conductor is a part of the service, 
shall have the grounded service conductor bonded to the raceway sys- 
tem and to the grounding conductor for the raceway system. The bond- 
ing connection to the grounded service conductor shall be made on 
the supply side of the service disconnecting means. 

(e) Transformer Ground Bonded to Raceway. Wiring in a Class I 
location, when supplied from a grounded alternating current supply 
system in which no grounded conductor is a part of the service, shall 
be provided with a metallic connection between the supply system 
ground and the raceway system at the service entrance. The metallic 
connection shall have an ampacity not less than 1/5 that of the service 
conductors, and shall in no case be smaller than No. 10 when of soft 
copper, or No. 12 when of medium or hard-drawn copper. 

(f) Multiple Grounds. Where, in the application of Section 250-21, 
it is necessary to abandon one or more grounding connections to avoid 
objectionable passage of current over the grounding conductors, the 
connection required in Section 501-16(d and e) shall not be abandoned 
while any other grounding connection remains connected to the supply 
system. 



ARTICLE 502 — CLASS II INSTALLATIONS — 
HAZARDOUS LOCATIONS 



502-1. General. The general rules of this Code shall apply to the in- 
stallation of electrical wiring and apparatus in locations classified as 
Class II under Section 500-5 except as modified by this Article. 

"Dust-ignition-proof," as used in this Article, shall mean enclosed 
in a manner which will exclude ignitible amounts of dusts or amounts 



ARTICLE 502-CLASS II INSTALLATIONS 70-265 

which might affect performance or rating and which, when installation 
and protection are in conformance with this Code, will not permit arcs, 
sparks or heat otherwise generated or liberated inside of the enclosure, 
to cause ignition of exterior accumulations or atmospheric suspensions 
of a specified dust on or in the vicinity of the enclosure. 

Equipment installed in Class II locations shall be able to function at 
full rating without developing surface temperatures high enough to 
cause excessive dehydration or gradual carbonization of any organic 
dust deposits that may occur. Dust which is carbonized or is excessively 
dry is highly susceptible to spontaneous ignition. In general, maximum 
surface temperatures under actual operating conditions shall not exceed 
165°C. (329°F.) for equipment which is not subject to overloading, 
and 120°C. (248°F.) for equipment such as motors, power transform- 
ers, etc., which may be overloaded. 

Equipment and wiring of the type defined in Article 100 as explosion- 
proof is not required in Class II locations, and may not be acceptable unless 
approved for such locations. 

502-2. Transformers and Capacitors. The installation of transformers 
and capacitors shall conform to the following: 

(a) Class II, Division 1. In Class II, Division 1 locations, transform- 
ers and capacitors shall conform to the following: 

(1) Containing a Liquid that Will Burn. Transformers and ca- 
pacitors containing a liquid that will burn shall be installed only in ap- 
proved vaults conforming to Sections 450-41 to 450-48 inclusive, and 
in addition ( 1 ) door or other openings communicating with the haz- 
ardous area shall have self-closing fire doors on both sides of the wall, 
and the doors shall be carefully fitted and provided with suitable seals 
(such as weather stripping) to minimize the entrance of dust into the 
vault, (2) vent openings and ducts shall communicate only with the 
outside air, and (3) suitable pressure-relief openings communicating 
with the outside air shall be provided. 

(2) Not Containing a Liquid that Will Burn. Transformers and 
capacitors which do not contain a liquid that will burn shall (1) be 
installed in vaults conforming to Sections 450-41 to 450-48 inclusive, 
or (2) be approved as a complete assembly including terminal connec- 
tions for Class II locations. 

(3) Metal Dusts. No transformer or capacitor shall be installed 
in a location where dust from magnesium, aluminum, aluminum bronze 
powders, or other metals of similarly hazardous characteristics may be 
present. 

(b) Class II, Division 2. In Class II, Division 2 locations, transform- 
ers and capacitors shall conform to the following: 

(1) Containing a Liquid that Will Burn. Transformers and capac- 
itors containing a liquid that will burn shall be installed in vaults con- 
forming to Sections 450-41 to 450-48 inclusive. 

(2) Containing Askarel. Transformers containing askarel and 
rated in excess of 25 kva shall ( 1 ) be provided with pressure-relief 
vents, (2) be provided with means for absorbing any gases generated 
by arcing inside the case, or the pressure-relief vents shall be connected 



70-266 MASSACHUSETTS ELECTRICAL CODE 

to a chimney or flue which will carry such gases outside the building 
and (3) have an air space of not less than 6 inches between the trans- 
former cases and any adjacent combustible material. 

(3) Dry-Type Transformers. Dry-type transformers shall be in- 
stalled in vaults or shall ( 1 ) have their windings and terminal connec- 
tions enclosed in tight metal housings without ventilating or other 
openings, and (2) operate at voltages not exceeding 600 volts. 

502-3. Surge Protection, Class II, Divisions 1 and 2. In geographical 
locations where lightning disturbances are prevalent, wiring systems in 
Class II locations shall, when supplied from overhead lines, be suitably 
protected against high-voltage surges. This protection shall include 
suitable lightning protective devices, interconnection of all grounds, 
and surge-protective capacitors. 

Interconnection of all grounds shall include grounds for primary and 
secondary lightning protective devices, secondary system grounds if 
any, and grounds of conduit and equipment of the interior wiring sys- 
tem. For ungrounded secondary systems, secondary lightning protec- 
tive devices may be provided both at the service and at the point where 
the secondary system receives its supply, and the intervening second- 
ary conductors may be accepted as the metallic connection between 
the secondary protective devices, provided grounds for the primary 
and secondary devices are metallically interconnected at the supply 
end of the secondary system and the secondary devices are grounded 
to the raceway system at the load end of the secondary system. 

Surge protective capacitors shall be of a type especially designed for 
the duty, shall be connected to each ungrounded service conductor, 
and shall be grounded to the interior conduit system. Capacitors shall 
be protected by 30-ampere fuses of suitable type and voltage rating, or 
by automatic circuit breakers of suitable type and rating and shall be 
connected to the supply conductors on the supply side of the service dis- 
connecting means. 

502-4. Wiring Methods. Wiring methods shall conform to the fol- 
lowing: 

(a) Class II, Division 1. In Class II, Division 1 locations, threaded 
rigid metal conduit or Type MI cable with termination fittings approved 
for the location shall be the wiring method employed. Type MI cable 
shall be installed and supported in a manner to avoid tensile stress at 
the termination fittings. 

(1) Fittings and Boxes. Fittings and boxes shall be provided with 
threaded bosses for connection to conduit or cable terminations, shall 
have close fitting covers, and shall have no openings (such as holes for 
attachment screws) through which dust might enter, or through which 
sparks or burning material might escape. Fittings and boxes in which 
taps, joints or terminal connections are made, or which are used in lo- 
cations where dusts are of an electrically conducting nature shall be 
dust-ignition-proof and approved for Class II locations. 

(2) Flexible Connections. Where necessary to employ flexible 
connections, dust-tight flexible connectors, flexible metal conduit with 
approved fittings, or flexible cord approved for extra-hard usage and 



ARTICLE 502— CLASS II INSTALLATIONS 70-267 

provided with bushed fittings shall be used, except that where dusts are of 
an electrically conducting nature, flexible metal conduit shall not be used, 
and flexible cords shall be provided with dust-tight seals at both ends. An 
additional conductor for grounding shall be provided in the flexible cord 
unless other acceptable means of grounding is provided. Where flexible con- 
nections are subject to oil or other corrosive conditions, the insulation of the 
conductors shall be of a type approved for the condition or shall be protected 
by means of a suitable sheath. 

(b) Class II, Division 2. In Class II, Division 2 locations, rigid metal 
conduit, type Ml cable with approved termination fittings, or approved Type 
MC or ALS cable with approved termination fittings for Class II locations shall 
be the wiring method employed. 

(1) Fittings and Boxes. Fittings and boxes in which taps, joints or 
terminal connections are made shall be designed to minimize the entrance 
of dust, and (1) shall be provided with telescoping or close fitting covers, 
or other effective means to prevent the escape of sparks or burning material, 
and (2) shall have no openings (such as holes for attachment screws) through 
which, after installation, sparks or burning material might escape, or through 
which adjacent combustible material might be ignited. 

(2) Flexible Connections. Where flexible connections are necessary 
the provisions of Section 502-4(a-2) shall apply. 

502-5. Sealing, Class II, Divisions 1 and 2. Where a raceway provides com- 
munication between an enclosure which is required to be dust-ignition-proof 
and one which is not, suitable means shall be provided to prevent the en- 
trance of dust into the dust-ignition-proof enclosure through the raceway. 
This means may be (1) a permanent and effective seal, (2) a horizontal sec- 
tion not less than 10 feet long in the raceway, or (3) a vertical section of 
raceway not less than 5 feet long and extending downward from the dust- 
ignition-proof enclosure. Sealing fittings shall be accessible. 

502-6. Switches, Circuit Breakers, Motor Controllers, and Fuses. Switches, 
circuit breakers, motor controllers and fuses shall conform to the following: 

(a) Class II, Division 1. In Class II, Division 1 locations, switches, circuit 
breakers, motor controllers and fuses shall conform to the following: 

(1) Type Required. Switches, circuit breakers, motor controllers and 
fuses, including push buttons, relays and similar devices, which are intended 
to interrupt current in the normal performance of the function for which they 
are installed, or which are installed where dusts of an electrically conducting 
nature may be present, shall be provided with dust-ignition-proof enclosures 
which, together with the enclosed apparatus in each case, shall be approved 
as a complete assembly for Class II locations. 

This includes service and branch circuit fuses, switches and circuit breakers, 
motor controllers (including push buttons, pilot switches, relays, and motor 
overload protective devices), and switches, fuses and circuit breakers for the 
control and protection of lighting and appliance circuits. 



70-268 MASSACHUSETTS ELECTRICAL CODE 

(2) Isolating Switches. Disconnecting and isolating switches con- 
taining no fuses and not intended to interrupt current, and which are 
not installed where dusts may be of an electrically conducting nature, 
shall be provided with tight metal enclosures which shall be designed 
to minimize the entrance of dust, and which shall ( 1 ) be equipped with 
telescoping or close fitting covers, or with other effective means to pre- 
vent the escape of sparks or burning material, and (2) have no 
openings (such as holes for attachment screws) through which, after 
installation, sparks or burning material might escape, or through which 
exterior accumulations of dust or adjacent combustible material might 
be ignited. 

(3) Metal Dusts. In locations where dust from magnesium, alu- 
minum, aluminum bronze powders, or other metals of similarly haz- 
ardous characteristics may be present, fuses, switches, motor control- 
lers and circuit breakers shall have enclosures specifically approved 
for such locations. 

(b) Class II, Division 2. In Class II, Division 2 locations, enclosures 
for fuses, switches, circuit breakers and motor controllers including 
push buttons, relays and similar devices, shall conform to the require- 
ments of Section 502-6 ( a-2 ) . 

502-7. Control Transformers and Resistors. Transformers, solenoids, 
impedance coils and resistors used as or in conjunction with control 
equipment for motors, generators and appliances shall conform to the 
following: 

(a) Class II, Division 1. In Class II, Division 1 locations, control 
transformers, solenoids, impedance coils and resistors, and any over- 
current devices or switching mechanisms associated with them shall 
have dust-ignition-proof enclosures approved for Class II locations. 
No control transformer, impedance coil or resistor shall be installed in 
a location where dust from magnesium, aluminum, aluminum bronze 
powders, or other metals of similarly hazardous characteristics may be 
present unless provided with an enclosure specifically approved for 
such locations. 

(b) Class II, Division 2. In Class II, Division 2 locations, transform- 
ers and resistors shall conform to the following: 

(1) Switching Mechanisms. Switching mechanisms (including 
overcurrent devices) associated with control transformers, solenoids, 
impedance coils and resistors, shall be provided with enclosures con- 
forming to Section 502-6 (a-2) . 

(2) Coils and Winding. Where not located in the same enclosure 
with switching mechanisms, control transformers, solenoids and im- 
pedance coils shall be provided with tight metal housings without 
ventilating openings. 

(3) Resistors. Resitors and resistance devices shall have dust- 
ignition-proof enclosures approved for Class II locations, except that 
where the maximum normal operating temperature of the resistor will 
not exceed 120°C. (248°F.) nonadjustable resistors and resistors which 
are part of an automatically timed starting sequence may have enclos- 
ures conforming to Section 502-7 (b-2). 



ARTICLE 502-CLASS II INSTALLATIONS 70-269 

502-8. Motors and Generators. Motors and generators shall conform 
to the following: 

(a) Class II, Division 1. In Class II, Division 1 locations, motors, 
generators and other rotating electrical machinery shall be totally en- 
closed not ventilated, totally enclosed pipe ventilated, or totally en- 
closed fan-cooled, and shall be approved as dust-ignition-proof for 
Class II locations. Motors, generators or other rotating electrical ma- 
chinery shall not be installed in locations where dust from magnesium, 
aluminum, aluminum bronze powders, or other metals of similarly 
hazardous characteristics may be present unless such machines are to- 
tally enclosed, or totally enclosed fan-cooled, and specifically ap- 
proved for such locations. 

(b) Class II, Division 2. In Class II, Division 2 locations, motors, 
generators and other rotating electrical machinery shall be totally en- 
closed not ventilated, totally enclosed pipe ventilated, or totally en- 
closed fan-cooled, except that in locations where, in the judgment of 
the code enforcing authority, only moderate accumulations of non- 
conducting, nonabrasive dust are likely to occur, and where the equip- 
ment is readily accessible for routine cleaning and maintenance self- 
cleaning textile motors of the squirrel-cage type, standard open type 
machines without sliding contacts, centrifugal or other types of switch- 
ing mechanism (including motor overcurrent devices), or integral re- 
sistance devices, or standard open type machines having such contacts, 
switching mechanisms or resistance devices enclosed within tight metal 
housings without ventilating or other openings, may be installed. Mo- 
tors, generators or other rotating electrical machinery of partially en- 
closed or splashproof type shall not be installed in such locations. 

502-9. Ventilating Piping. Vent pipes for motors, generators or other 
rotating electrical machinery, or for enclosures for electrical apparatus 
or. equipment, shall be of metal not lighter than No. 24 USS gage, or 
of equally substantial noncombustible material, and shall ( 1 ) lead di- 
rectly to a source of clean air outside of buildings, (2) be screened at 
the outer ends to prevent the entrance of small animals or birds, (3) 
be protected against physical damage and against rusting or other cor- 
rosive influences. In addition, vent pipes shall conform to the follow- 
ing: 

(a) Class II, Division 1. In Class II, Division 1 locations, vent pipes, 
including their connections to motors or to the dust-ignition-proof en- 
closures for other equipment or apparatus, shall be dust-tight through- 
out their length. For metal pipes, seams and joints shall be ( 1 ) riveted 
(or bolted) and soldered, (2) welded, or (3) rendered dust-tight by 
some other equally effective means. 

(b) Class II, Division 2. In Class II, Division 2 locations, vent pipes 
and their connections shall be sufficiently tight to prevent the entrance 
of appreciable quantities of dust into the ventilated equipment or en- 
closure, and to prevent the escape of sparks, flame or burning material 
which might ignite dust accumulations or combustible material in the 
vicinity. For metal pipes, lock seams and riveted or welded joints may 
be used, and tight-fitting slip joints may be used where some flexibility 
is necessary as at connections to motors. 



70-270 MASSACHUSETTS ELECTRICAL CODE 

502-10. Utilization Equipment, Fixed and Portable. Utilization equip- 
ment, fixed and portable, shall conform to the following: 

(a) Class II, Division 1. In Class II, Division 1 locations, utiliza- 
tion equipment, including electrically heated and motor-driven equip- 
ment, shall be dust-ignition-proof approved for Class II locations. 
Where dust from magnesium, aluminum, aluminum bronze powders, 
or other metals of similarly hazardous characteristics may be present, 
such equipment shall be specifically approved for such locations. 

(b) Class II, Division 2. In Class II, Division 2, locations, utilization 
equipment, fixed and portable, shall conform to the following: 

(1) Heaters. Electrically heated utilization equipment shall be 
dust-ignition-proof approved for Class II locations. 

(2) Motors. Motors of motor-driven utilization equipment shall 
conform to Section 502-8 (b). 

(3) Switches, Circuit Breakers and Fuses. Enclosures for switches, 
circuit breakers, and fuses shall conform to Section 502-6(a-2). 

(4) Transformers, Impedance Coils and Resistors. Transformers, 
solenoids, impedance coils and resistors shall conform to Section 
502-7(b). 

502-11. Lighting Fixtures. Lamps shall be installed in fixtures which 
shall conform to the following: 

(a) Class II, Division 1. In Class II, Division 1 locations, lighting 
fixtures for fixed and portable lighting shall conform to the following: 

(1) Approved Fixtures. Each fixture shall be dust-ignition-proof 
and approved for Class II locations, and shall be. clearly marked to in- 
dicate the maximum wattage of the lamp for which it is approved. In 
locations where dust from magnesium, aluminum, aluminum bronze 
powders, or other metals of similarly hazardous characteristics may be 
present, fixtures for fixed or portable lighting, and all auxiliary equip- 
ment, shall be specifically approved for such locations. 

(2) Physical Damage. Each fixture shall be protected against 
physical damage by a suitable guard or by location. 

(3) Pendant Fixtures. Pendant fixtures shall be suspended by 
threaded rigid conduit stems or chains with approved fittings, or by 
other approved means. For rigid stems longer than 12 inches perma- 
nent and effective bracing against lateral displacement shall be provided 
at a level not more than 12 inches above the lower end of the stem, or 
flexibility in the form of a fitting or a flexible connector approved for 
the purpose and for the location shall be provided not more than 12 
inches from the point of attachment to the supporting box or fitting. 
Threaded joints shall be provided with set-screws or other effective 
means to prevent loosening. Where wiring between an outlet box or 
fitting and a pendant fixture is not enclosed in conduit, flexible cord ap- 
proved for hard usage shall be used, and suitable seals shall be pro- 
vided where the cord enters the fixture and the outlet box or fitting. 
Flexible cord shall not serve as the supporting means for a fixture. 

(4) Supports. Boxes, box assemblies or fittings used for the sup- 



ARTICLE 502-CLASS II INSTALLATIONS 70-271 

port of lighting fixtures shall be approved for the purpose and for 
Class II locations. 

(b) Class II, Division 2. In Class II, Division 2 locations, lighting 
fixtures shall conform to the following: 

(1) Portable Lamps. Portable lamps shall be dust-ignition-proof 
and approved for Class II locations. They shall be clearly marked to 
indicate the maximum wattage of lamps for which they are approved. 

(2) Fixed Lighting. Lighting fixtures for fixed lighting, when not 
of a type approved for Class II locations, shall provide enclosures for 
lamps and lampholders which shall be designed to minimize the de- 
posit of dust on lamps and to prevent the escape of sparks, burning ma- 
terial or hot metal. Each fixture shall be clearly marked to indicate the 
maximum wattage of lamp which may be used without exceeding a 
maximum exposed surface temperature of 165°C. (329°F.) under nor- 
mal conditions of use. 

(3) Physical Damage. Lighting fixtures for fixed lighting shall be 
protected from physical damage by suitable guards or by location. 

(4) Pendant Fixtures. Pendant fixtures shall be suspended by 
threaded rigid conduit stems or chains with approved fittings, or by 
other approved means. For rigid stems longer than 12 inches perma- 
nent and effective bracing against lateral displacement shall be pro- 
vided at a level not more than 12 inches above the lower end of the 
stem, or flexibility in the form of a fitting or a flexible connector ap- 
proved for the purpose shall be provided not more than 12 inches from 
the point of attachment to the supporting box or fitting. When wiring 
between an outlet box or fitting and a pendant fixture is not enclosed 
in conduit, flexible cord approved for hard usage shall be used. Flexi- 
ble cord shall not serve as the supporting means for a fixture. 

(5) Supports. Boxes, box assemblies and fittings used for the sup- 
port of lighting fixtures shall be approved for that purpose. 

(6) Electric Discharge Lamps. Starting and control equipment for 
mercury vapor and fluorescent lamps shall conform to the requirement 
of Section 502-7 (b). 

502-12. Flexible Cords, Class II, Divisions 1 and 2. Flexible cords 
used in Class II locations shall ( 1 ) be of a type approved for extra hard 
usage, (2) contain, in addition to the conductors of the circuit, a 
grounding conductor conforming to Section 400-13, (3) be connected 
to terminals or to supply conductors in an approved manner, (4) be 
supported by clamps or by other suitable means in such a manner that 
there will be no tension on the terminal connections, and (5) be pro- 
vided with suitable seals to prevent the entrance of dust where the flex- 
ible cord enters boxes or fittings which are required to be dust-ignition- 
proof. 

502-13. Receptacles and Attachment Plugs. 

(a) Class II, Division 1. In Class II, Division 1 locations, recepta- 
cles and attachment plugs shall be of the type providing for connection 
to the grounding conductor of the flexible cord, and shall be dust-igni- 
tion-proof approved for Class II locations. 



70-272 MASSACHUSETTS ELECTRICAL CODE 

(b) Class II, Division 2. In Class II, Division 2 locations, receptacles and 
attachment plugs shall be of the type providing for connection to the 
grounding conductor of the flexible cord and shall be so designed that con- 
nection to the supply circuit cannot be made or broken while live parts are 
exposed. 

502-14. Signal, Alarm, Remote-Control, and Local Loud-Speaker Intercom- 
munication Systems. Signal, alarm, remote-control and local loud-speaker 
intercommunication systems shall conform to the following: 

Refer to Article 800 for rules governing the installation of communication 
circuits as defined in Article 100. 

(a) Class II, Division 1. In Class II, Division 1 locations, signal, alarm, 
remote-control and local loud-speaker intercommunication systems shall con- 
form to the following: 

(1) Wiring Method. Where accidental damage or breakdown of insu- 
lation might cause arcs, sparks or high temperatures, rigid metal conduit, or 
Type Ml cable with approved termination fittings shall be the wiring method 
employed. For conduit the number of conductors shall be limited only by the 
requirement that the cross-sectional area of all conductors shall not exceed 
40 per cent of the area of the raceway. Where limited flexibility is desirable 
or where exposure to physical damage is not severe, flexible cord approved 
for extra-hard usage may be used. 

(2) Contacts. Switches, circuit breakers, relays, contactors and fuses 
which may interrupt other than voice currents, and current-breaking contacts 
for bells, horns, howlers, sirens and other devices in which sparks or arcs may 
be produced, shall be provided with enclosures approved for the location, un- 
kss current-breaking contacts are immersed in oil, or unless the interruption 
of current occurs within a chamber sealed against the entrance of dust, in 
which case enclosures may be of general purpose type. 

(3) Resistors and Similar Equipment. Resistors, transformers and 
choke coils which may carry other than voice currents, and rectifiers, ther- 
mionic tubes, and other heat generating equipment or apparatus shall be 
provided with dust-ignition-proof enclosures approved for Class II locations. 

4) Rotating Machinery. Motors, generators and other rotating electri- 
cal machinery shall conform to Section 502-8(a). 

(5) Electrical Conducting Dusts. Where dusts are of an electrically 

conducting nature, all wiring and equipment shall be approved for Class II 
locations. 

(6) Metal Dusts. Where dust from magnesium, aluminum, aluminum 
bronze powders, or other metals of similarly hazardous characteristics may be 
present, all apparatus and equipment shall be specifically approved for such 
conditions. 

(b) Class II, Division 2. In Class II, Division 2 locations, signal, alarm, 
remote-control and local loudspeaker intercommunication systems shall con- 
form to the following: 



ARTICLE 502-CLASS II INSTALLATIONS 70-273 

(1) Contacts. Enclosures shall conform to Section 502-1 4(a-2) or 
contacts shall have tight metal enclosures designed to minimize the 
entrance of dust, and shall have telescoping or tight fitting covers and 
no openings through which, after installation, sparks or burning ma- 
terial might escape. 

(2) Transformers and Similar Equipment. The windings and 
terminal connections of transformers and choke coils shall be provided 
with tight metal enclosures without ventilating openings. 

(3) Resistors and Similar Equipment. Resistors, resistance de- 
vices, thermionic tubes, and rectifiers shall conform to Section 502-14 
(a-3) except that enclosures for thermionic tubes, nonadjustable re- 
sistors or rectifiers for which maximum operati lg temperature will not 
exceed 120°C. (248°F.) may be of general purpose type. 

(4) Rotating Machinery. Motors, generators and other rotating 
electrical machinery shall conform to Section 502-8 (b) . 

502-15. Live Parts, Class II, Divisions 1 and 2. There shall be no ex- 
posed live parts. 

502-16. Grounding, Class II, Divisions 1 and 2. WLing and equip- 
ment shall be grounded in conformity with the following : 

(a) Exposed Parts. The exposed noncurrent-carrying metal parts 
of equipment such as the frames or metal exteriors of motors, fixed or 
portable lamps or other utilization equipment, lighting fixtures, cabi- 
nets, cases, and conduit, shall be grounded as specified in Article 250 of 
this Code. 

(b) Bonding. The locknut-bushing and double-locknut types of con- 
tact shall not be depended upon for bonding purposes, but bonding 
jumpers with proper fittings, or other approved means shall be used. 
Such means of bonding shall apply to all intervening raceways, fittings, 
boxes, enclosures, etc., between hazardous areas and the point of 
grounding for service equipment. Where flexible conduit is used as per- 
mitted in Section 502-4, bonding jumpers with proper fittings shall be 
provided around such conduit. 

(c) Lightning Protection. Each ungrounded service conductor of a 
wiring system in a Class II location, when supplied from an un- 
grounded overhead electrical supply system in an area where lightning 
disturbances are prevalent, shall be protected by a lightning protective 
device of proper type. Lightning protective devices shall be connected 
to the service conductors on the supply side of the service disconnecting 
means, and shall be bonded to the raceway system at the service en- 
trance. 

(d) Grounded Service Conductor Bonded to Raceway. Wiring in a 
Class II location, when supplied from a grounded alternating-current 
supply system in which a grounded conductor is a part of the service, 
shall have the grounded service conductor bonded to the raceway sys- 
tem and to the grounding conductor for the raceway system. The bond- 
ing connection to the grounded service conductor shall be made on the 
supply side of the service disconnecting means. 



70-274 MASSACHUSETTS ELECTRICAL CODE 

(e) Transformer Ground Bonded to Raceway. Wiring in a Class II 
location, where supplied from a grounded alternating-current supply 
system in which no grounded conductor is a part of the service, shall be 
provided with a metallic connection between the supply system ground 
and the raceway system at the service entrance. The metallic connec- 
tion shall have an ampacity not less than 1/5 that of the service con- 
ductors, and shall in no case be smaller than No. 10 when of soft cop- 
per, or No. 12 when of medium or hard-drawn copper. 

(f) Multiple Grounds. Where, in the application of Section 250-21, 
it is necessary to abandon one or more grounding connections to 
avoid objectionable passage of current over the grounding conductors, 
the connection required in Section 502-16(d or e) shall not be aban- 
doned while any other grounding connection remains connected to 
the supply system. 



ARTICLE 503 — CLASS III INSTALLATIONS — 
HAZARDOUS LOCATIONS 



503-1. General. The general rules of this Code shall apply to the in- 
stallation of electrical wiring and apparatus in locations classified as 
Class III under Section 500-6 except as modified by this Article. 

Equipment installed in Class III locations shall be able to function 
at full rating without developing surface temperatures high enough to 
cause excessive dehydration or gradual carbonization of accumulated 
fibers or flyings. Organic material which is carbonized or is excessively 
dry is highly susceptible to spontaneous ignition. In general, maximum 
surface temperatures under operating conditions shall not exceed 
165°C. (329°F.) for equipment which is not subject to overloading, and 
120°C. (248°F.) for equipment such as motors, power transformers, 
etc., which may be overloaded. 

503-2. Transformers and Capacitors, Class III, Divisions 1 and 2. 

Transformers and capacitors shall conform to Section 502-2(b). 

503-3. Wiring Methods. Wiring methods shall conform to the fol- 
lowing: 

(a) Class III, Division 1. In Class III, Division 1 locations, rigid 
metal conduit or Type MI cable shall be the wiring method employed. 

(1) Boxes and Fittings. Fittings and boxes in which taps, joints 
or terminal connections are made shall ( 1 ) be provided with telescoping 
or close fitting covers, or other effective means to prevent the escape 
of sparks or burning material, and (2) shall have no openings (such as 
holes for attachment screws) through which, after installation, sparks 
or burning material might escape, or through which adjacent combusti- 
ble material might be ignited. 

(2) Flexible Connections. Where flexible connections are neces- 
sary the provisions of Section 502-4(a-2) shall apply. 



ARTICLE 503-CLASS III INSTALLATIONS 70-275 

(b) Class III, Division 2. In Class III, Division 2 locations, the 
wiring method shall conform to Section 503-3 (a), except that in sec- 
tions, compartments or areas used solely for storage and containing 
no machinery, open wiring on insulators may be employed when in- 
stalled to conform to Article 320, but only on condition that protection 
as required by Section 320-12 be provided where conductors are not 
run in roof spaces, and well out of reach of sources of physical damage. 

503-4. Switches, Circuit Breakers, Motor Controllers and Fuses, Class 
III, Divisions 1 and 2. Switches, circuit breakers, motor controllers 
and fuses, including push buttons, relays and similar devices, shall be 
provided with tight metal enclosures designed to minimize entrance of 
fibers and flyings, and which shall ( 1 ) be equipped with telescoping or 
close fitting covers, or with other effective means to prevent escape of 
sparks or burning material, and (2) have no openings (such as holes for 
attachment screws) through which, after installation, sparks or burning 
material might escape, or through which exterior accumulations of fi- 
bers or flyings or adjacent combustible material might be ignited. 

503-5. Control Transformers and Resistors, Class III, Divisions 1 and 2. 

Transformers, impedance coils and resistors used as or in conjunction 
with control equipment for motors, generators and appliances, shall 
conform to Section 502-7 (b), with the exception that, in Class III, Di- 
vision 1 locations, when these devices are in the same enclosure with 
switching devices of such control equipment, and are used only for 
starting or short time duty, the enclosure shall conform to the require- 
ments of Section 503-4. 

503-6. Motors and Generators. Motors and Generators shall conform 
to the following: 

(a) Class III, Division 1. In Class III, Division 1 locations, motors, 
generators, and other rotating electrical machinery shall be totally 
enclosed not ventilated, totally enclosed pipe ventilated, or totally en- 
closed fan-cooled, except that in locations where, in the judgment of 
the Code enforcing authority, only moderate accumulations of lint and 
flyings will be likely to collect on, in, or in the vicinity of a rotating 
electrical machine, and where such machine is readily accessible for 
routine cleaning and maintenance, self-cleaning textile motors of the 
squirrel-cage type, standard open type machines without sliding con- 
tacts, centrifugal or other types of switching mechanism (including 
motor overload devices), or standard open type machines having such 
contacts, switching mechanisms or resistance devices enclosed within 
tight metal housings without ventilating or other openings, may be in- 
stalled. 

(b) Class III, Division 2. In Class III, Division 2 locations, motors, 
generators, and other rotating electrical machinery shall be totally en- 
closed not ventilated, totally enclosed pipe ventilated, or totally en- 
closed fan-cooled. 

(c) Partially Enclosed Type, Class III, Divisions 1 and 2. Motors, gen- 
erators or other rotating electrical machinery of the partially enclosed 
or splash-proof type shall not be installed in Class III locations. 

503-7. Ventilating Piping, Class III, Divisions 1 and 2. Vent pipes for 
motors, generators or other rotating electrical machinery, or for en- 



70-276 MASSACHUSETTS ELECTRICAL CODE 

closures for electrical apparatus or equipment, shall be of metal not 
lighter than No. 24 USS gage, or of equally substantial noncombusti- 
ble material, and shall (1) lead directly to a source of clean air outside 
of buildings, (2) be screened at the outer ends to prevent the entrance 
of small animals or birds, (3) be protected against physical damage 
and against rusting or other corrosive influences, and (4) vent pipes 
and their connections shall be sufficiently tight to prevent the entrance 
of appreciable quantities of fibers or flyings into the ventilated equip- 
ment or enclosure, and to prevent the escape of sparks, flame or burn- 
ing material which might ignite accumulations of fibers or flyings or 
combustible material in the vicinity. For metal pipes, lock seams and 
riveted or welded joints may be used, and tight fitting slip joints may 
be used where some flexibility is necessary as at connections to motors. 

503-8. Utilization Equipment, Fixed and Portable, Class III, Divisions 1 

and 2. Utilization equipment shall conform to the following: 

(a) Heaters. Electrically heated utilization equipment shall be ap- 
proved for Class III locations. 

(b) Motors. Motors of motor-driven utilization equipment shall 
conform to Section 503-6 (b ) . Utilization equipment which may be read- 
ily moved from one location to another should conform to requirements 
for the most hazardous location. 

(c) Switches, Circuit Breakers, Motor Controllers and Fuses. Switches, 
circuit breakers, motor controllers and fuses shall conform to Section 
503-4. 

503-9. Lighting Fixtures, Class III, Divisions 1 and 2. Lamps shall be 
installed in fixtures which shall conform to the following: 

(a) Fixed Lighting. Lighting fixtures for fixed lighting shall provide 
enclosures for lamps and lampholders which shall be designed to mini- 
mize entrance of fibers and flyings, and to prevent the escape of sparks, 
burning material or hot metal. Each fixture shall be clearly marked to 
show wattage of lamp which may be used without exceeding a maxi- 
mum exposed surface temperature of 165°C. (329°F.) under operating 
conditions of use. 

(b) Physical Damage. A fixture which may be exposed to physical 
damage shall be protected by a suitable guard. 

(c) Pendant Fixtures. Pendant fixtures shall be suspended by stems 
of threaded rigid conduit or threaded metal tubing of equivalent thick- 
ness. For stems longer than 12 inches, permanent and effective bracing 
against lateral displacement shall be provided at a level not more than 
12 inches above the lower end of the stem, or flexibility in the form of 
a fitting or a flexible connector approved for the purpose shall be pro- 
vided not more than 12 inches from the point of attachment to the 
supporting box or fitting. 

(d) Supports. Boxes, box assemblies or fittings used for the support 
of lighting fixtures shall be of a type approved for the purpose. 

(e) Portable Lamps. Portable lamps shall be equipped with handles 
and protected with substantial guards, and lampholders shall be of un- 
switched type with no exposed metal parts and without provision for 



ARTICLE 503— CLASS III INSTALLATIONS 70-277 

receiving attachment plugs. In all other respects, portable lamps shall con- 
form to Section 503-9(a). 

503-10. Flexible Cords, Class III, Divisions 1 and 2. Flexible cords shall 
conform to Section 502-12. 

503-11. Receptacles and Attachment- Plugs, Class III, Divisions 1 and 2. 

Receptacles and attachment plugs shall conform to Section 502-1 3(b). 

503-12. Signal, Alarm.. Remote-Control and Local Loud-Speaker Intercom- 
munication Systems, Class III, Divisions 1 and 2. Signal, alarm, remote- 
control and local loudspeaker intercommunication systems shall conform to 
Section 502- 14(a). 

503-13. Electric Cranes and Hoists, and Similar Equipment, Class III, Divi- 
sions 1 and 2. Where installed for operation over combustible fibers or 
accumulations of flyings, traveling cranes and hoists for material handling, 
traveling cleaners for textile machinery, and similar equipment shall con- 
form to the following: 

(a) Power supply to contact conductors shall be isolated from all other sys- 
tems and shall be ungrounded, and shall be equipped with an acceptable re- 
cording ground detector which will give an alarm and will automatically de- 
energize the contact conductors in case of a fault to ground, or with an 
acceptable ground fault indicator which will give a visual and audible alarm, 
and maintain the alarm as long as power is supplied to the system and the 
ground fault remains. 

(b) Contact conductors shall be so located or guarded as to be inaccessible 
to other than authorized persons, and shall be protected against accidental 
contact with foreign objects. 

(c) Current collectors shall be arranged or guarded to confine normal spark- 
ing and to prevent escape of sparks or hot particles. To reduce sparking, two 
or more separate surfaces of contact shall be provided for each contact con- 
ductor. Reliable means shall be provided to keep contact conductors and cur- 
rent collectors free of accumulations of lint or flyings. 

(d) Control equipment shall conform to Sections 503-4 and 503-5. 

Where the distance of travel permits, current to the crane shall be supplied 
through flexible cord approved for extra hard usage and equipped with ap- 
proved type of reel or takeup device. 

503-14. Electric Trucks. Electric trucks shall conform to NFPA Standard 
for the Use, Maintenance and Operation of Industrial Trucks (No. 505). 

503-15. Storage-Battery Charging Equipment. Class III, Divisions 1 and 2. 

Storage-battery charging equipment shall be located in separate rooms built 
or lined with substantial noncombustible materials so constructed as to ade- 
quately exclude flyings or lint, and shall be well ventilated. 

503-16. Live Parts, Class III, Divisions 1 and 2. There shall be no exposed 
live parts except as provided in Section 503-13. 

503-17. Grounding, Class III, Divisions 1 and 2. Wiring and equipment 
shall be grounded in conformity with Section 502-16. 



70-278 MASSACHUSETTS ELECTRICAL CODE 

ARTICLE 510 — HAZARDOUS LOCATIONS — SPECIFIC 



510-1. Scope. The provisions of Articles 511 to 517 inclusive shall 
apply to occupancies or parts of occupancies which are or may be 
hazardous because of atmospheric concentrations of hazardous gases or 
vapors, or because of deposits or accumulations of materials which may 
be readily ignitible. It is the intent to assist Code enforcing authorities 
in the classification of areas with respect to hazardous conditions which 
may or may not require construction and equipment conforming to 
Articles 501 to 503 inclusive, and to set forth such additional special 
requirements as are applicable to the specific occupancy. 

510-2. General. The general rules of this Code shall apply to the in- 
stallation of electrical wiring and equipment in occupancies within the 
scope of Articles 511 to 517 inclusive, except as such rules are modi- 
fied in those articles. Where unusual conditions exist in a specific oc- 
cupancy, the authority enforcing this Code shall judge with respect to 
the application of specific rules. 

It is recommended that the authority enforcing this Code be familiar 
with National Fire Protection Association standards applying to occupancies 
included within the scope of Articles 511 to 517 inclusive. 



ARTICLE 511 — COMMERCIAL GARAGES, REPAIR 

AND STORAGE 



51 1-1. Scope. These occupancies shall include locations used for serv- 
ice and repair operations in connection with self-propelled vehicles 
(including passenger automobiles, buses, trucks, tractors, etc.) in which 
volatile flammable liquids or flammable gases are used for fuel or 
power, and locations in which more than three such vehicles are or may 
be stored at one time. 

For further information regarding classification of garages, refer to the 
NFPA Standard for Garages (No. 88). 

511-2. Hazardous Areas. Classification under Article 500. 

(a) For each floor at or above grade, the entire area up to a level 18 
inches above the floor shall be considered to be a Class I, Division 2 
location. 

(b) For each floor below grade, the entire area up to a level 18 
inches above the bottom of outside doors or other openings which are 
at or above grade level shall be considered to be Class I, Division 2 lo- 
cation. Where adequate positive-pressure ventilation is provided, the 
authority enforcing this Code may judge that the hazardous location 
extends up to a level of only 1 8 inches above each such floor. 

(c) Any pit or depression below floor level shall be considered to be a 
Class I, Division 2 location which shall extend up to said floor level, 
except that any unventilated pit or depression may be judged by the 
authority enforcing this Code to be a Class I, Division 1 location. 



ARTICLE 511 -COMMERCIAL GARAGES 70-279 

(d) Adjacent areas in which hazardous vapors are not likely to be 
released such as stock rooms, switchboard rooms and other similar lo- 
cations, having floors elevated at least 18 inches above adjacent ga- 
rage floor, or separated therefrom by tight curbs or partitions at least 
18 inches high, shall not be classed as hazardous. 

511-3. Wiring and Equipment in Hazardous Areas. Within hazardous 
areas as defined in Section 511-2, wiring and equipment shall conform 
to applicable provisions of Article 501. 

511-4. Sealing. Approved seals conforming to the requirements of 
Section 501-5 shall be provided, and Section 501-5(b-2) shall apply to 
horizontal as well as to vertical boundaries of the defined hazardous 
areas. Raceways embedded in a masonry floor or buried beneath a 
floor shall be considered to be within the hazardous area above the 
floor if any connections or extensions lead into or through such area. 

511-5. Wiring in Spaces Above Hazardous Areas. 

(a) All fixed wiring shall be in metallic raceways or shall be Type MI 
or Type ALS cable. Cellular metal floor raceways may be used only 
for supplying ceiling outlets or extensions to the area below the floor, 
but such raceways shall have no connections leading into or through 
any hazardous area above the floor. No electrical conductor shall be 
installed in any cell, header or duct which contains a pipe for steam, 
water, air, gas, drainage, or other service except electrical. 

(b) For pendants, flexible cord suitable for the type of service and 
approved for hard usage shall be used. 

(c) For connection of portable lamps, motors or other utilization 
equipment, flexible cord suitable for the type of service and approved 
for extra hard usage shall be used. 

(d) When a circuit which supplies portables or pendants includes 
an identified grounded conductor as provided in Article 200, recepta- 
cles, attachment plugs, connectors, and similar devices shall be of po- 
larized type, and the identified conductor of the flexible cord shall be 
connected to the screw shell of any lampholder or to the identified 
terminal of any utilization equipment supplied. 

(e) When a pendant is used to supply a portable lamp or utilization 
equipment, the female portion of a polarized pin-plug connector or 
equivalent shall be attached to the lower end of the pendant, and the 
male portion shall be attached to the cord for the portable. The con- 
nector shall be designed to break apart readily in any position, and 
shall be suspended at a level not less than that specified in Section 511-2. 
Attachment plug receptacles in fixed position shall be located above the 
level specified in Section 511-2. 

51 1-6. Equipment Above Hazardous Areas. 

(a) Equipment which is less than 12 feet above floor level, and which 
may produce arcs, sparks or particles of hot metal, such as cutouts, 
switches, receptacles, charging panels, generators, motors, or other 
equipment (excluding lamps and lampholders) having make and break 
or sliding contacts, shall be of totally-enclosed type or shall be provided 
with suitable guards or screens to prevent escape of sparks or hot metal 
particles. 



70-280 MASSACHUSETTS ELECTRICAL CODE 

(b) Lamps and lampholders for fixed lighting which are located over 
lanes through which vehicles are commonly driven or which may other- 
wise be exposed to physical damage, shall be located not less than 12 
feet above floor level unless of totally enclosed type or provided with 
suitable guards, screens or covers to prevent escape of sparks or hot 
metal particles. 

(c) Portable lamps shall be equipped with handle, lampholder, hook 
and substantial guard attached to the lampholder or handle. All ex- 
terior surfaces which might come in contact with battery terminals, 
wiring terminals, or other objects shall be of nonconducting material or 
shall be effectively protected with insulation. Lampholders shall be of 
unswitched type, and shall not provide means for plug-in of attach- 
ment plugs. Outer shell shall be of moulded composition or other ma- 
terial approved for the purpose, and metal-shell, lined lampholders, 
either of switched or unswitched type, shall not be used. Unless the 
lamp and its cord are supported or arranged in such a manner that 
they cannot be used in the hazardous areas classified in Section 511-2, 
they shall be of a type approved for such hazardous locations. 

511-7. Battery-Charging Equipment. Battery chargers and their con- 
trol equipment, and batteries being charged shall not be located within 
hazardous areas classified in Section 511-2. Tables, racks, trays, and 
wiring shall, in addition, conform to the provisions of Article 480. 

51 1-8. Electric Vehicle Charging. 

(a) Flexible cords used for charging shall be suitable for the type of 
service and approved for extra hard usage. Their ampacity shall be 
adequate for the charging current. 

(b) Connectors shall have a rating not less than the ampacity of the 
cord, and in no case less than 50 amperes. 

(c) Connectors shall be so designed and installed that they will break 
apart readily at any position of the charging cable, and live parts shall 
be guarded from accidental contact. No connector shall be located 
within a hazardous area defined in Section 511-2. 

(d) Where plugs are provided for direct connection to vehicles, the 
point of connection shall not be within a hazardous area as defined in 
Section 511-2, and where the cord is suspended from overhead, it shall 
be so arranged that the lowest point of sag is at least 6 inches above the 
floor. Where the vehicle is equipped with an approved plug which will 
readily pull apart, and where an automatic arrangement is provided to 
pull both cord and plug beyond the range of physical damage, no addi- 
tional connector is required in the cable or at the outlet. 



ARTICLE 512 — RESIDENTIAL STORAGE GARAGES 



512-1. Definition. A residential storage garage is a building or room in 
which not more than three vehicles of the types described in Section 
511-1 are or may be stored, but which will not normally be used for 
other than minor service or repair operations on such stored vehicles. 



ARTICLE 513-AIRCRAFT HANGARS 70-281 

512-2. At or Above Grade. Where the lowest floor is at or above 
adjacent ground or driveway level, and where there is at least one out- 
side door at or below floor level, the garage area shall not be classed as 
a hazardous location. 

512-3. Below Grade. Where the lowest floor is below adjacent ground 
or driveway level, the following shall apply: 

(a) The entire area of the garage or of any enclosed space which in- 
cludes the garage shall be classified as a Class I, Division 2 location up 
to a level 1 8 inches above the garage floor. All electrical equipment and 
wiring within such hazardous location shall conform to applicable pro- 
visions of Article 501. 

(b) Wiring and equipment above the defined hazardous location 
shall conform to the requirements of this Code for nonhazardous loca- 
tions. 

(c) Adjacent areas in which hazardous vapors or gases are not likely 
to be released, and having floors elevated at least 18 inches above the 
garage floor, or separated therefrom by tight curbs or partitions at 
least 1 8 inches high, shall not be classed as hazardous. 



ARTICLE 513 — AIRCRAFT HANGARS 



513-1. Definition. This occupancy shall include locations used for 
storage or servicing of aircraft in which gasoline, jet fuels, or other 
volatile flammable liquids, or flammable gases, are used, but shall not 
include such locations when used exclusively for aircraft which have 
never contained such liquids or gases, or which have been drained and 
properly purged. 

513-2. Hazardous Areas. Classification under Article 500. 

(a) Any pit or depression below the level of the hangar floor shall 
be considered to be a Class I, Division 1 location which shall extend 
up to said floor level. 

(b) The entire area of the hangar including any adjacent and com- 
municating areas not suitably cut off from the hangar shall be consid- 
ered to be a Class I, Division 2 location up to a level 18 inches above 
the floor. 

(c) The area within 5 feet horizontally from aircraft power plants, 
aircraft fuel tanks or aircraft structures containing fuel shall be con- 
sidered to be a Class I, Division 2 hazardous location which shall ex- 
tend upward from the floor to a level 5 feet above the upper surface 
of wings and of engine enclosures. 

(d) Adjacent areas in which hazardous vapors are not likely to be 
released such as stock rooms, electrical control rooms, and other simi- 
lar locations, should not be classed as hazardous when adequately ven- 
tilated and when effectively cut off from the hangar itself by walls or 
partitions. 



70-282 MASSACHUSETTS ELECTRICAL CODE 

513-3. Wiring and Equipment in Hazardous Areas. All fixed and port- 
able wiring and equipment which is or may be installed or operated 
within any of the hazardous locations defined in Section 513-2 shall 
conform to applicable provisions of Article 501. All wiring installed in 
or under the hangar floor shall conform to the requirements for Class I, 
Division 1. When such wiring is located in vaults, pits, or ducts, ade- 
quate drainage shall be provided, and the wiring shall not be placed 
within the same compartment with any other service except piped com- 
pressed air. 

513-4. Wiring Not Within Hazardous Areas. 

(a) All fixed wiring in a hangar, but not within a hazardous area as 
defined in Section 513-2, shall be installed in metallic raceways or shall 
be Type MI or Type ALS cable, except that wiring in nonhazardous lo- 
cations as defined in Section 513-2(d) may be of any type recognized in 
Chapter 3 of this Code. 

(b) For pendants, flexible cord suitable for the type of service and 
approved for hard usage shall be used. Each such cord shall include a 
separate grounding conductor. 

(e) For portable utilization equipment and lamps, flexible cord suit- 
able for the type of service and approved for extra hard usage shall be 
used. Each such cord shall include a separate grounding conductor. 

(d) Where a circuit which supplies portables or pendants includes 
an identified grounded conductor as provided in Article 200, recepta- 
cles, attachment plugs, connectors, and similar devices shall be of po- 
larized type, and the identified conductor of the flexible cord shall be 
connected to the screw shell of any lampholder or to the identified 
terminal of any utilization equipment supplied. Acceptable means shall 
be provided for maintaining continuity of the grounding conductor 
between the fixed raceway system and the noncurrent-carrying metallic 
portions of pendant fixtures, portable lamps, and portable utilization 
equipment. 

513-5. Equipment not Within Hazardous Areas. 

(a) In locations other than those described in Section 513-2, equip- 
ment which is less than 10 feet above wings and engine enclosures of 
aircraft and which may produce arcs, sparks or particles of hot metal, 
such as lamps and lampholders for fixed lighting, cutouts, switches, re- 
ceptacles, charging panels, generators, motors, or other equipment hav- 
ing make and break or sliding contacts, shall be of totally enclosed type 
or shall be provided with suitable guards or screens to prevent escape 
of sparks or hot metal particles, except that equipment in areas de- 
scribed in Section 513-2(d) may be of general purpose type. 

(b) Lampholders of metal shell, fiber-lined types shall not be used 
for fixed incandescent lighting. 

(c) Portable lamps which are or may be used within a hangar shall 
be approved for Class I locations. 

(d) Portable utilization equipment which is or may be used within a 
hangar shall be of a type suitable for use in Class I, Division 2 loca- 
tions. 



ARTICLE 513-AIRCRAFT HANGARS 70-283 

513-6. Stanchions, Rostrums and Docks. 

(a) Electric wiring, outlets and equipment (including lamps) on or 
attached to stanchions, rostrums or docks which are located or likely to 
be located in a hazardous area as defined in Section 513-2(c) shall con- 
form to the requirements for Class I, Division 2 locations. 

(b) Where stanchions, rostrums, or docks are not located or likely 
to be located in a hazardous area as defined in Section 513-2(c), wiring 
and equipment shall conform to Sections 513-4 and 513-5, except that 
such wiring and equipment not more than 18 inches above the floor in 
any position shall conform to Section 513-6(a). Receptacles and attach- 
ment plugs shall be of locking type which will not break apart readily. 

(c) Mobile stanchions with electrical equipment conforming to Sec- 
tion 513-6(b) shall carry at least one permanently affixed warning sign 
to read: "WARNING — KEEP 5 FEET CLEAR OF AIRCRAFT 
ENGINES AND FUEL TANK AREAS." 

513-7. Sealing. Approved seals shall be provided in conformance 
with Section 501-5 and Section 501-5(a-3) and 501-5(b-2) and shall ap- 
ply to horizontal as well as to vertical boundaries of the defined haz- 
ardous areas. Raceways embedded in a masonry floor or buried beneath 
a floor shall be considered to be within the hazardous area above the 
floor when any connections or extensions lead into or through such 
area. 

513-8. Aircraft Electrical Systems. Aircraft electrical systems should 
be de-energized when the aircraft is stored in a hangar, and, whenever 
possible, while the aircraft is undergoing maintenance. 

513-9. Aircraft Battery — Charging and Equipment. 

(a) Aircraft batteries should not be charged when installed in an 
aircraft located inside or partially inside a hangar. 

(b) Battery chargers and their control equipment shall not be lo- 
cated or operated within any of the hazardous areas defined in Section 
513-2, and should preferably be located in a separate building or in an 
area such as described in Section 513-2(d). Mobile chargers shall carry 
at least one permanently affixed warning sign to read: "WARNING — 
KEEP 5 FEET CLEAR OF AIRCRAFT ENGINES AND FUEL 
TANK AREAS." Tables, racks, trays, and wiring shall not be located 
within a hazardous area, and shall, in addition, conform to the provi- 
sions of Article 480. 

513-10. External Power Sources for Energizing Aircraft. 

(a) Aircraft energizers shall be so designed and mounted that all 
electrical equipment and fixed wiring will be at least 18 inches above 
floor level and shall not be operated in a hazardous area as defined in 
Section 513-2(c). 

(b) Mobile energizers shall carry at least one permanently affixed 
warning sign to read: "WARNING — KEEP 5 FEET CLEAR OF 
AIRCRAFT ENGINES AND FUEL TANK AREAS." 

(e) Aircraft energizers should be equipped with polarized external 
power plugs and should have automatic controls to isolate the ground 



70-284 MASSACHUSETTS ELECTRICAL COD E 

power unit electrically from the aircraft in case excessive voltage is 
generated by the grounding power unit. 

(d) Flexible cords for aircraft energizers and ground support equip- 
ment shall be approved for the type of service and extra hard usage and 
shall include a ground conductor. 

513-1 1. Mobile Servicing Equipment with Electrical Components. 

(a) Mobile servicing equipment (such as vacuum cleaners, air com- 
pressors, air movers, etc.) having electrical wiring and equipment not 
suitable for Class I, Division 2 locations shall be so designed and 
mounted that all such fixed wiring and equipment will be at least 18 
inches above the floor. Such mobile equipment shall not be operated 
within the hazardous areas defined in Section 513-2(c) and shall carry 
at least one permanently affixed warning sign to read: "WARNING 
— KEEP 5 FEET CLEAR OF AIRCRAFT ENGINES AND FUEL 
TANK AREAS." 

(b) Flexible cords for mobile equipment shall be suitable for the type 
of service and approved for extra hard usage, and shall include a 
grounding conductor. Attachment plugs and receptacles shall be ap- 
proved for the location in which they are installed, and shall provide 
for connection of the grounding conductor to the raceway system. 

(c) Equipment not of a type suitable for Class I, Division 2 loca- 
tions should not be operated in areas where maintenance operations 
likely to release hazardous vapors are in progress. 

513-12. Grounding. All metallic raceways, and all noncurrent-carry- 
ing metallic portions of fixed or portable equipment, regardless of 
voltage, shall be grounded as provided in Article 250. 



ARTICLE 514 — GASOLINE DISPENSING 
AND SERVICE STATIONS 



514-1. Definitions. This classification shall include locations where 
gasoline or other volatile flammable liquids or liquefied flammable gases 
are transferred to the fuel tanks (including auxiliary fuel tanks) of self- 
propelled vehicles. 

Other areas used as lubritoriums, service rooms and repair rooms, 
and offices, salesrooms, compressor rooms and similar locations shall 
conform to Articles 510 and 511 with respect to electrical wiring and 
equipment. 

Where the authority enforcing the Code can satisfactorily determine that 
flammable liquids having a flash point below 100°F such as gasoline will 
not be handled, he may classify such an area as nonhazardous. 

For further information regarding safeguards for gasoline dispensing and 
service stations see NFPA Flammable and Combustible Liquids Code (No. 
30). 



ARTICLE 514-SERVICE STATIONS 70-285 

514-2. Hazardous Areas. 

(a) The space within the dispenser up to 4 feet from its base and the 
space within 18 inches extending horizontally from the dispenser up to 
4 feet from its base shall be considered a Class I, Division 1 location. 
This classification shall also apply to any space below the dispenser 
which may contain electrical wiring or equipment. 

(b) In an outside location, any area (excluding Class I, Division 1, 
but including buildings not suitably cut off) within 20 feet horizontally 
from the exterior enclosure of any dispensing pump shall be considered 
a Class I, Division 2 location which will extend to a level 18 inches 
above driveway or ground level. 

(c) In an outside location, any area (excluding Class I, Division 1, 
but including buildings not suitably cut off) within 10 feet horizontally 
from any tank fill-pipe shall be considered a Class I, Division 2 loca- 
tion which shall extend upward to a level 18 inches above driveway 
or ground level. 

(d) Electrical wiring and equipment, any portion of which is below 
the surface of areas defined as Class I, Division 1 or Division 2 in 
514-2(a), (b), (c) above shall be considered to be within a Class I 
Division 1 location which shall extend at least to the point of emer- 
gence above grade. 

(e) The spherical volume within a 3 foot radius from point of dis- 
charge of any tank vent-pipe shall be considered a Class I, Division I 
location and the volume between three foot to five foot radius from 
point of discharge of a vent shall be considered a Class I, Division 2 
location. For any vent that does not discharge upward, the cylindrical 
volume below both the Division 1 and 2 locations extending to the 
ground shall be considered a Class I, Division 2 location. The hazard- 
ous area shall not extend beyond an unpierced wall. 

514-3. Wiring and Equipment Within Hazardous Areas. All electrical 
equipment and wiring within the hazardous areas defined in Section 
514-2 shall conform to applicable provisions of Article 501. 

For special requirements for conductor insulation, see Section 501-13. 
514-4. Wiring and Equipment Above Hazardous Areas. Wiring and 
equipment above hazardous areas defined in Section 514-2 shall con- 
form to Sections 511-5 and 511-6. 

514-5. Circuit Disconnects. Each circuit leading to or through a dis- 
pensing pump shall be provided with a switch or other acceptable 
means to disconnect simultaneously from the source of supply all con- 
ductors of the circuit including the grounded neutral, if any. 

514-6. Sealing. 

(a) An approved seal shall be provided in each conduit run entering 
or leaving a dispenser or any cavities or enclosures in direct communi- 
cation therewith. The sealing fitting shall be the first fitting after the 
conduit emerges from the earth or concrete. 

(b) Additional seals shall be provided in conformance with Section 
501-5 and Sections 501-5(a-3) and 501-5(b-2) shall apply to horizontal 
as well as to vertical boundaries of the defined hazardous areas. 



70-286 MASSACHUSETTS ELECTRICAL CODE 

514-7. Grounding. Metallic portions of dispensing pumps, metallic 
raceways, and all noncurrent-carrying portions of electrical equipment, 
regardless of voltage, shall be grounded as provided in Article 250. 

514-8. Underground wiring shall be installed in rigid metal conduit, or, 
where buried under not less than 2 feet of earth, may be installed in 
non-metallic conduit conforming to the requirements of Section 
347-2. (d). Where non-metallic conduit is used, an additional grounding 
conductor shall be included to provide for metallic continuity of the 
raceway system and for grounding of noncurrent carrying metallic parts 
of equipment. 



ARTICLE 515 — BULK-STORAGE PLANTS 



515-1. Definition. This designation shall include locations where gas- 
oline or other volatile flammable liquids are stored in tanks having an 
aggregate capacity of one carload or more, and from which such prod- 
ucts are distributed (usually by tank truck). 

515-2. Hazardous Areas. 

(a) Pumps, Bleeders, Withdrawal Fittings, Meters and Similar Devices. 

(1) Adequately ventilated indoor areas containing pumps, bleeders, 
withdrawal fittings, meters and similar devices which are located in 
pipe lines handling flammable liquids under pressure shall be consid- 
ered as Class I, Division 2 locations within a 5 foot distance extending 
in all directions from the exterior surface of such devices. The Class I, 
Division 2 location shall also extend 25 feet horizontally from any sur- 
face of these devices and extend upward to 3 feet above floor or grade 
level. 

See Flammable and Combustible Liquids Code, NFPA No. 30, for dis- 
cussion of factors influencing adequacy of ventilation required to prevent 
formation of hazardous vapor-air mixtures. 

(2) Inadequately ventilated indoor areas containing pumps, bleeders, 
withdrawal fittings, meters and similar devices which are located in 
pipe lines handling flammable liquids under pressure shall be consid- 
ered as Class I, Division 1 location within a 5 foot distance extending 
in all directions from the exterior surface of such devices. The Class I, 
Division 1 location shall also extend 25 feet horizontally from any sur- 
face of the devices and extend upward to 3 feet above floor or grade 
level. 

(3) Outdoor areas containing pumps, bleeders, withdrawal fittings, 
meters and similar devices which are located in pipe lines handling 
flammable liquids under pressure shall be considered as Class I, Divi- 
sion 2 locations within a 3 foot distance extending in all directions from 
the exterior surface of such devices. The Class I, Division 2 location 
shall also extend up to 18 inches above grade level within 10 feet hori- 
zontally from any surface of the devices. 



ARTICLE 515-STORAGE PLANTS 70-287 

(b) Transfer of Flammable Liquids to Individual Containers. 

(1) In outdoor areas or where positive and reliable mechanical ven- 
tilation is provided in indoor areas in which flammable liquids are 
transferred to individual containers, such areas shall be considered to 
be a Class I, Division 1 location within 3 feet of the vent or fill opening 
extending in all directions and a Class I, Division 2 location within the 
area extending between a 3 foot and 5 foot radius from the vent or fill 
opening extending in all directions, and including the area within a 
horizontal radius of 10 feet from the vent or fill opening and extending 
to a height of 18 inches above floor or grade levels. 

See Flammable and Combustible Liquids Code, NFPA No. 30, for dis- 
cussion of factors influencing adequacy and reliability of mechanical venti- 
lation required to prevent formation of hazardous vapor-air mixtures. 

(2) When positive and reliable mechanical ventilation is not pro- 
vided in indoor areas in which flammable liquids are transferred to in- 
dividual containers, such areas shall be considered to be a Class I, Di- 
vision 1 location. 

(c) Loading and Unloading of Tank Vehicles and Tank Cars in Outside 
Locations. 

(1) The area extending 3 feet in all directions from the dome when 
loading through an open dome or from the vent when loading through 
a closed dome with atmospheric venting shall be considered a Class I, 
Division 1 location. 

(2) The area extending between a 3 foot and 5 foot radius from the 
dome when loading through an open dome or from the vent when 
loading through a closed dome with atmospheric venting shall be con- 
sidered a Class I, Division 2 location. 

(3) The area extending within 3 feet in all directions from a fixed 
connection used in bottom loading or unloading, loading through a 
closed dome with atmospheric venting, or loading through a closed 
dome with a vapor recovery system, shall be considered a Class I Di- 
vision 2 location. In the case of bottom loading or unloading this clas- 
sification shall also be applied to the area within a 10 foot radius from 
point of connection and extending 18 inches above grade. 

In deciding upon extent of hazardous area, consideration should be given 
to the total area within which loading and unloading operation may occur 
such as racks, platforms, driveways, etc. 

(d) Aboveground Tanks. 

(1) The area above the roof and within the shell of a floating roof 
type tank shall be considered a Class I, Division 1 location. 

(2) For all types of aboveground tanks the area within 10 feet 
from the shell, ends and roof of other than a floating roof shall be 
considered a Class I, Division 2 location. Where dikes are provided the 
area inside the dike and extending upward to the top of the dike shall 
be considered to be a Class I, Division 2 location. 

(3) The area within 5 feet of a vent opening and extending in all 
directions shall be considered a Class I, Division 1 location. 



70-288 MASSACHUSETTS ELECTRICAL CODE 

(4) The area between 5 and 10 feet of a vent opening and extend- 
ing in all directions shall be considered a Class I, Division 2 location. 

For underground tanks see Article 514. 

(e) Pits. 

(1) Any pit or depression, any part of which lies within a Division 
1 or Division 2 location as defined herein, shall be considered a Class 4, 
Division 1 location unless provided with positive and reliable mechan- 
ical ventilation. 

(2) Any such areas when provided with positive and reliable me- 
chanical ventilation shall be considered a Class I, Division 2 location. 

See Flammable and Combustible Liquids Code, NFPA No. 30, for dis- 
cussion of factors pertaining to positive and reliable mechanical ventilation 
required to prefent formulation of hazardous vapor-air mixtures. 

(3) Any pit or depression not within a Division 1 or Division 2 
location as defined herein, but which contains piping, valves or fittings 
shall be classified as a Class I, Division 2 location. 

(f) Storage and Repair Garages for Tank Vehicles shall be considered 
to be a Class I, Division 2 location up to 18 inches above floor or grade 
level unless in the judgment of the authority enforcing this Code condi- 
tions warrant more severe classification or a greater extent of the 
hazardous area. 

(g) Office Buildings, Boiler Rooms and Other Similar Locations which 
are outside the limits of hazardous areas as defined herein, and which 
are not used for handling or storage of volatile flammable liquids or 
containers for such liquids, shall not be considered to be hazardous lo- 
cations. 

515-3. Wiring and Equipment Within Hazardous Areas. All electrical 
wiring and equipment within the hazardous areas defined in Section 
515-2 shall conform to applicable provisions of Article 501. 

515-4. Wiring and Equipment Above Hazardous Areas. All fixed 
wiring above hazardous areas shall be in metallic raceways or shall be 
Type ALS cable. Fixed equipment which may produce arcs, sparks or 
particles of hot metal, such as lamps and lampholders for fixed light- 
ing, cutouts, switches, receptacles, motors, or other equipment having 
make and break or sliding contacts, shall be of totally enclosed type or 
shall be provided with suitable guards or screens to prevent escape of 
sparks or hot metal particles. Portable lamps or utilization equipment, 
and their flexible cords shall conform to the provisions of Article 501 
for the class of location above which they are connected or used. 

515-5. Underground Wiring. 

(a) Underground wiring shall be installed in rigid metal conduit, or, 
where buried under not less than 2 feet of earth, may be installed in 
nonmetallic conduit or duct, or in the form of cable approved for the 
purpose. Where cable is used, it shall be enclosed in rigid metal conduit 
from the point of lowest buried cable level to the point of connection 
to the aboveground raceway. 

(b) Conductor insulation shall conform to Section 501-13 of Article 
501. 



ARTICLE 516-FINISHING PROCESSES 70-289 

(e) Where cable with nonmetallic sheath or nonmetallic conduit is 
used, an additional grounding conductor shall be included to provide 
for metallic continuity of the raceway system and for grounding of 
noncurrent-carrying metallic parts of equipment. 

515-6. Sealing. Approved seals shall be provided in conformance 
with Section 501-5 and Sections 501-5(a-3) and 501-5(b-2) shall apply 
to horizontal as well as to vertical boundaries of the defined hazardous 
areas. Buried raceways under defined hazardous areas shall be consid- 
ered to be within such areas. 

515-7. Gasoline Dispensing. Where gasoline dispensing is carried on 
in conjunction with bulk station operations, applicable provisions of 
Article 514 shall apply. 

515-8. Grounding. All metallic raceways, and all noncurrent-carry- 
ing metallic portions of electrical equipment shall be grounded as pro- 
vided in Article 250. 



ARTICLE 516 — FINISHING PROCESSES 

516-1. Definition. This Article shall apply to locations where paints, 
lacquers or other flammable finishes are regularly or frequently applied 
by spraying, dipping, brushing or by other means, and where volatile 
flammable solvents or thinners are used or where readily ignitible de- 
posits or residues from such paints, lacquers or finishes may occur. 

For further information regarding safeguards for finishing processes, see 
the NFPA Standard for Spray Finishing Using Flammable Materials (No. 
33) and the NFPA Standard for Dip Tanks Containing Flammable or Com- 
bustible Liquids (No. 34). 

516-2. Hazardous Areas. Classification with respect to flammable va- 
pors. For deposits and residues, see Section 516-3. 

(a) The interiors of spray booths and their exhaust ducts, all space 
within 20 feet horizontally in any direction from spraying operations 
more extensive than touch-up spraying and not conducted within spray 
booths, all space within 20 feet horizontally in any direction from dip 
tanks and their drain boards, and all other spaces where hazardous 
concentrations of flammable vapors are likely to occur, shall be con- 
sidered to be Class I, Division 1 locations. 

(b) All space within 20 feet horizontally in any direction from the 
open face of a spray booth, and all space within the room but beyond 
the limits for Class I, Division 1 as defined in Section 5 16-2 (a) for ex- 
tensive open spraying, for dip tanks and drain boards and for other 
hazardous operations, shall be considered to be Class I, Division 2 loca- 
tions unless the authority enforcing this Code judges otherwise. 

(c) Adjacent areas which are cut off from the defined hazardous 
areas by tight partitions without communicating openings, and within 
which hazardous vapors are not likely to be released, shall be classed 
as nonhazardous unless the Code enforcing authority judges other- 
wise. 



70-290 MASSACHUSETTS ELECTRICAL CODE 

(d) Drying and baking areas provided with positive mechanical ven- 
tilation adequate to prevent formation of flammable concentrations of 
vapors, and provided with effective interlocks to de-energize all elec- 
tric equipment (other than equipment approved for Class I locations) 
in case the ventilating equipment is inoperative, may be classed as 
nonhazardous when the Code-enforcing authority so judges. 

516-3. Wiring and Equipment in Hazardous Areas. 

(a) All electrical wiring and equipment within the hazardous areas 
defined in Section 516-2 shall conform to applicable provisions of 
Article 501. 

(b) Unless approved for both readily ignitible deposits and the flam- 
mable vapor location, no electrical equipment shall be installed or 
used where it may be subject to hazardous accumulations of readily 
ignitible deposits or residues, except that wiring in rigid conduit or in 
threaded boxes or fittings containing no taps, splices or terminal con- 
nections may be installed in such locations. Type MI cable without fit- 
tings or boxes may be used. 

(c) Illumination of readily ignitible areas through panels of glass or 
other transparent or translucent material is permissible only where: (a) 
fixed lighting units are used as the source of illumination, (b) the panel 
effectively isolates the hazardous area from the area in which the light- 
ing unit is located, (c) the lighting unit is approved for its specific lo- 
cation, (d) the panel is of a material or is so protected that breakage 
will be unlikely and (e) the arrangement is such that normal accumu- 
lations of hazardous residue on the surface of the panel will not be 
raised to a dangerous temperature by radiation or conduction from the 
source of illumination. 

(d) Portable electric lamps or other utilization equipment shall not 
be used within a hazardous area during operation of the finishing proc- 
ess. When such lamps or utilization equipment are used during cleaning 
or repairing operations, they shall be of a type approved for Class I 
locations, and all exposed metal parts shall be effectively grounded. 

(e) Electrostatic spraying or detearing equipment shall be installed 
and used only as provided in Section 516-4. 

For more details, see NFPA No. 33. 

516-4. Fixed Electrostatic Equipment. Where electrostatic spraying and 
detearing equipment is installed, such equipment shall be of approved 
type, and shall conform to the following requirements. 

(a) No transformers, power packs, control apparatus, or other elec- 
trical portion of the equipment (except high voltage grids and their 
connections) shall be installed in any of the hazardous areas defined in 
Section 516-2 unless of a type approved for the location. 

(b) High voltage grids or electrodes shall be located in suitable non- 
combustible booths or enclosures provided with adequate mechanical 
ventilation, shall be rigidly supported and of substantial construction, 
and shall be effectively insulated from ground by means of nonporous 
noncombustible insulators. 



ARTICLE 516-FINISHING PROCESSES 70-291 

(c) High voltage leads shall be effectively and permanently supported 
on suitable insulators, shall be effectively guarded against accidental 
contact or grounding, and shall be provided with automatic means for 
discharging any residual charge to ground when the supply voltage is 
interrupted. 

(d) Goods being processed shall be supported on conveyors in such 
a manner that minimum clearance between goods and high voltage 
grids or conductors cannot be less than twice the sparking distance. A 
conspicuous sign indicating the sparking distance shall be permanently 
posted near the equipment. 

(e) Approved automatic controls which will operate without time de- 
lay to disconnect the power supply and to signal the operator in case 
of (a) stoppage of ventilating fans or failure of ventilating equipment 
from any cause, (b) stoppage of the conveyor carrying goods through 
the high voltage field, (c) occurrence of a ground or of an imminent 
ground at any point on the high voltage system, or (d) reduction of 
clearance below that specified in Section 516-4(d). 

(f) Adequate fencing, railings or guards which are electrically con- 
ducting and effectively grounded shall be provided for safe isolation 
of the process, and signs shall be permanently posted designating the 
process zone as dangerous because of high voltage. 

516-5. Electrostatic Hand Spraying Equipment. Electrostatic hand spray 
apparatus and devices used in connection with paint spraying operations 
shall be of approved types and shall conform to the following require- 
ments : 

(a) The equipment shall be so designed that the maximum surface 
temperature of the equipment in the spraying area can not exceed 
150°F. under any condition. The high voltage circuits shall be designed 
so as to be intrinsically safe and not produce a spark of sufficient in- 
tensity to ignite any vapor-air mixtures nor result in appreciable shock 
hazard upon coming in contact with a grounded object. The electro- 
statically charged exposed elements of the hand gun shall be capable of 
being energized only by a switch which also controls the paint supply. 

(b) Transformers, power packs, control apparatus, and all other elec- 
trical portion of the equipment, with the exception of the hand gun 
itself and its connections to the power supply, shall be located outside 
of the hazardous area. 

(c) The handle of the spraying gun shall be electrically connected to 
ground by a metallic connection and be so constructed that the opera- 
tor in normal operating position is in intimate electrical contact with 
the grounded handle. This requirement is to prevent build-up of a static 
charge on the operator's body. 

(d) All electrically conductive objects in the spraying area shall be 
adequately grounded. This requirement shall apply to paint containers, 
wash cans and any other objects or devices in the area. The equipment 
shall carry a prominent permanently installed warning regarding the 
necessity for this grounding feature. 



70-292 MASSACHUSETTS ELECTRICAL COD b' 

(e) Objects being painted shall be maintained in metallic contact 
with the conveyor or other grounded support. Hooks shall be regularly 
cleaned to insure this contact and areas of contact shall be sharp points 
or knife edges where possible. Points of support of the object shall be 
concealed from random spray where feasible and where the objects be- 
ing sprayed are supported from a conveyor, the point of attachment to 
the conveyor shall be so located as to not collect spray material during 
normal operation. 

(f) The spraying operation shall take place within a spray area which 
is adequately ventilated to remove solvent vapors released from the op- 
eration. The electrical equipment shall be so interlocked with the ven- 
tilation of spraying area that the equipment cannot be operated unless 
the ventilation fans are in operation. 

516-6. Wiring and Equipment Above Hazardous Areas. 

(a) All fixed wiring above hazardous areas shall be in metallic race- 
ways or shall be Type MI cable or Type ALS cable. Cellular metal 
floor raceways may be used only for supplying ceiling outlets or ex- 
tensions to the area below the floor of a hazardous area, but such race- 
ways shall have no connections leading into or through the hazardous 
area above the floor unless suitable seals are provided. No electrical 
conductor shall be installed in any cell, header or duct which contains a 
pipe for steam, water, air, gas, drainage, or for other service except 
electrical. 

(b) Equipment which may produce arcs, sparks or particles of hot 
metal, such as lamps and lampholders for fixed lighting, cutouts, 
switches, receptacles, motors, or other equipment having make and 
break or sliding contacts, where installed above a hazardous area or 
above an area where freshly finished goods are handled, shall be of 
totally enclosed type or shall be provided with suitable guards or 
screens to prevent escape of sparks or hot metal particles. 

516-7. Grounding. All metallic raceways, and all noncurrent-carry- 
ing metallic portions of fixed or portable equipment, regardless of 
voltage, shall be grounded as provided in Article 250. 



ARTICLE 517 — FLAMMABLE ANESTHETICS 



517-1. Definitions. 

(a) Flammable anesthetics are gases or vapors such as cyclopro- 
pane, divinyl ether, ethyl chloride, ethyl ether, and ethylene, which 
may form flammable or explosive mixtures with air, oxygen, or nitrous 
oxide. 

(b) For the purpose of this Article, anesthetizing locations are areas 
in hospitals in which flammable anesthetics are or may be administered 
to patients. Such locations will include operating rooms, delivery rooms 
and anesthesia rooms, and will also include any corridors, utility rooms 
or other areas which are or may be used for administering flammable 



ARTICLE 517-FLAMMABLE ANESTHETICS 70-293 

anesthetics to patients. Recovery rooms are not classed as anesthetizing 
locations unless used for administering flammable anesthetics. 

For further information regarding safeguards for hospital operating 
rooms, see the NFPA Code for the Use of Flammable Anesthetics (No. 56). 

517-2. Hazardous Areas. 

(a) Any room or space in which flammable anesthetics or volatile 
flammable disinfecting agents are stored shall be considered to be a 
Class I, Division 1 location throughout. 

(b) In an anesthetizing location as defined in Section 517-1, the en- 
tire area shall be considered to be a Class I, Division 1 location which 
shall extend upward to a level 5 feet above the floor. 

517-3. Wiring and Equipment Within Hazardous Areas. 

(a) In hazardous areas as defined in Section 517-2, all fixed wiring 
and equipment, and all portable equipment, including lamps and other 
utilization equipment, operating at more than 8 volts between conduc- 
tors, shall conform to the requirements of Sections 501-1 to 501-15 in- 
clusive and of Sections 50 1-1 6 (a and b) for Class I, Division 1 loca- 
tions, and all such equipment shall be specifically approved for the 
hazardous atmospheres involved. 

(b) Where a box, fitting or enclosure is partially but not entirely 
within a hazardous area, the hazardous area shall be considered to be 
extended to include the entire box, fitting or enclosure. 

(c) Flexible cords which are or may be used in hazardous areas for 
connection to portable utilization equipment, including lamps operat- 
ing at more than 8 volts between conductors shall be of a type ap- 
proved for extra hard usage, shall be of ample length, and shall include 
an additional conductor for grounding. A storage device for the flexi- 
ble cord shall be provided, and shall not subject the cord to bending at 
a radius of less than 3 inches. 

(d) Receptacles and attachment plugs shall be of the type with pro- 
vision for connection of the grounding conductor, and where located 
within a hazardous area, shall be approved for Class I location. Single 
phase, 125 volt receptacles and attachment plugs shall be of the type 
recognized in Section 2438 of NFPA Code for the Use of Flammable 
Anesthetics (No. 56). 

517-4. Wiring and Equipment Above Hazardous Areas. 

(a) Wiring above a hazardous area as defined in Section 517-2(b) 
shall be installed in metal raceways or shall be Type MI cable or Type 
ALS cable. 

(b) Equipment which may produce arcs, sparks or particles of hot 
metal, such as lamps and lampholders for fixed lighting less than 8 feet 
above the floor, cutouts, switches, receptacles, generators, motors, or 
other equipment having make and break or sliding contacts, shall be of 
totally enclosed type or shall be provided with suitable guards or 
screens to prevent escape of sparks or hot metal particles. 

(e) Surgical and other lighting fixtures shall conform to Section 
501 -9(b), except that surface temperature limitations set forth in Sec- 
tion 501-9(b-2) shall not apply, and except that integral or pendant 



70-294 MASSACHUSETTS ELECTRICAL CODE 

switches which are located above and cannot be lowered into the 
hazardous area need not be explosion-proof. 

517-5. Sealing. Approved seals shall be provided in conformance with 
Section 501-5, and 501-5(a-3) and shall apply to horizontal as well as 
to vertical boundaries of the defined hazardous areas. 

Exception. Seals may be located within 18 inches of the point at 
which a conduit emerges from a wall forming the boundary of an anes- 
thetizing location if all of the following conditions are met. 

(1) The junction box switch or receptacle contains a seal-off device 
between the arcing contacts and the conduit. 

(2) The conduit is continuous {without coupling or fitting) between 
the junction box and the sealing fitting within 18 inches of the point 
where the conduit emerges from the wall. 

517-6. Circuits in Anesthetizing Locations. 

(a) Except as provided in Section 517-6(e), each circuit within or 
partially within an anesthetizing location as defined in Section 517-1 (b) 
shall be controlled by a switch having a disconnecting pole in each cir- 
cuit conductor, and shall be supplied from an ungrounded distribution 
system which shall be isolated from any distribution system supplying 
areas other than anesthetizing locations. Such isolation may be ob- 
tained by means of one or more transformers having no electrical 
connection between primary and secondary windings, by means of mo- 
tor generator sets, or by means of suitably isolated batteries. 

(b) Circuits supplying primaries of isolating transformers shall op- 
erate at not more than 300 volts between conductors, and shall be pro- 
vided with proper overcurrent protection. Secondary voltage of such 
transformers shall not exceed 300 volts between conductors, and all 
circuits supplied from such secondaries shall be ungrounded and shall 
have an approved overcurrent device of proper rating in each conduc- 
tor. Circuits supplied from batteries or from generators or motor-gen- 
erator sets shall be ungrounded, and shall be protected against over- 
current in the same manner as transformer secondary circuits. 

(c) Transformers, motor-generator sets, batteries and battery charg- 
ers, together with their overcurrent devices shall be installed in non- 
hazardous locations, and shall conform to the requirements of this 
Code for such locations. 

(d) In addition to the usual control and protective devices, the un- 
grounded system shall be provided with an approved ground contact 
indicator so arranged that a green signal lamp conspicuously visible 
to persons in the anesthetizing location remains lighted while the sys- 
tem is isolated from ground. An adjacent red signal lamp and an audi- 
ble warning signal shall be energized when any conductor of the system 
becomes grounded through a resistance or a capacitive reactance of 
any value up to at least 60,000 ohms. The current through the ground 
indicator to the ground shall not exceed 2 milliamperes. The indicator 
and associated signals shall not be installed within a hazardous area. 

For maintenance tests of the ground indicator, see Section 3422 of the 
NFPA Code for the Use of Flammable Anesthetics (No. 56). 



ARTICLE 517-FLAMMABLE ANESTHETICS 70-295 

(e) Branch circuits supplying only fixed lighting fixtures above the 
hazardous location other than surgical lighting fixtures or supplying 
only approved permanently installed X-ray equipment which complies 
with Section 2434 of the NFPA Code for the Use of Flammable Anes- 
thetics (No. 56) may be supplied by a conventional grounded system, 
provided: (a) wiring for grounded and ungrounded circuits does not 
occupy the same raceways; (b) the lighting fixtures and the X-ray equip- 
ment (except the enclosed X-ray tube and the metal-enclosed high 
voltage leads to the tube) are located at least eight feet above the floor 
or outside the anesthetizing location; and (c) switches for the grounded 
circuits are located outside of the anesthetizing location. 

Note: Remote control stations for remote control switches may be in- 
stalled in the anesthetizing location if the remote control circuit is energized 
from the ungrounded distribution system. 

517-7. Low Voltage Equipment and Instruments. 

(a) Electrical apparatus and equipment used within a hazardous 
area, and which has exposed current-carrying elements or which is fre- 
quently in contact with the bodies of persons, shall be designed to op- 
erate at 8 volts or less unless it is entirely surrounded by a metallic 
casing or sheath. Power supply shall be ungrounded, and shall be elec- 
trically isolated from all circuits of higher voltage. 

(b) Where a low voltage unit receives current from an individual 
transformer located within a hazardous area, the flexible cord shall con- 
form to Section 517-3(d), the core and case of the transformer shall be 
effectively grounded, and the transformer shall be approved for Class 
I locations. 

(c) Where low voltage units within a hazardous area are supplied 
with current from a common source, such as a transformer, motor- 
generator set, or storage battery, such common source shall be installed 
in a nonhazardous location. Where located or used within a hazardous 
area, receptacles and attachment plugs shall be approved for Class I 
locations. Plugs shall be so designed that they cannot be inserted into 
receptacles for higher voltage. Flexible cords shall be of adequate 
length and ampacity, and shall be approved for extra hard usage. An 
extra conductor for grounding is not required. 

(d) Low voltage equipment and wiring (including flexible cords) 
shall be protected from dangerous overcurrents by suitable overcurrent 
devices or by inherent current limiting characteristics of the source of 
supply. Overcurrent devices shall not be installed in a hazardous area. 

(e) Resistance or impedance devices may be used to control low 
voltage units but shall not be used to limit maximum input voltage. 
Where a low voltage unit includes a switch or other make and break 
or sliding contact, or where it includes a resistor or resistance device 
which may under any operating condition reach a surface temperature 
exceeding eighty per cent (80%) of the lowest ignition temperature in 
degrees Centigrade (as determined by ASTM test procedure — Desig- 
nation D286-30) of the gases or vapors that may be present, the unit 
shall be of a type approved for Class I locations. 



70-296 MASSACHUSETTS ELECTRICAL CODE 

517-8. Other Equipment. 

(a) Suction, pressure, or insufflation equipment involving electrical ele- 
ments, and located or used within a hazardous area shall be approved for Class 
I locations. 

(b) X-ray equipment installed or operated in an anesthetizing location as 
defined in Section 5 17- Kb) shall be provided with approved means for pre- 
venting accumulation of electrostatic charges. All control devices, switches, 
relays, meters, and transformers shall be totally enclosed, and where installed 
or operated within a hazardous area, shall be approved for Class I locations. 
High voltage wiring shall be effectively insulated from ground and adequately 
guarded against accidental contact. 

(c) Equipment for generating high frequency currents or voltages used in 
electrocautery, diathermy, television, etc., where installed or used in an 
anesthetizing location, shall conform to Sections 517-3 and 517-4. 

517-9. Grounding. In any hazardous area, all metallic raceways, and all 
noncurrent-carrying metallic portions of fixed or portable equipment (except 
equipment operating at not more than 8 volts between conductors) shall be 
grounded as provided in Sections 50 1 - 1 6(a and b). 

ARTICLE 520— THEATERS 
AND ASSEMBLY HALLS 

A. General 
520-1. Scope. The requirements of this Article shall apply to all buildings, 
or part of a building, designed, intended, or used for dramatic, operatic, mo- 
tion-picture or other shows, and night clubs, dance halls, armories, sporting 
arenas, bowling alleys, public auditoriums, television studios and like build- 
ings used for public asssembly. 

520-2. Motion-Picture Projectors. Motion-picture equipment and its instal- 
lation and use shall comply with Article 540. 

520-3. Sound Reproduction. Sound-reproducing equipment and its installa- 
tion shall comply with Article 640. 

520-4. Wiring Method. The wiring method shall be metal raceways, Type 
ALS cable or Type Ml cable except as follows: 

Exception No. I. As provided in Article 640, Sound Reproduction, in 
Article 800, Communication Circuits, and in Article 725 for Class 2 Remote 
Control and Signal Circuits. 

Exception No. 2. Where the area intended for public assembly has a 
capacity of less than 200 persons, Type AC metal-clad cable as provided in 
Article 334 may be used, or for concealed work, concealed knob-and-tubei 
work or nonmetallic sheathed cable as provided in Articles 324 and 336 may 
also be used. 

For determination of population capacity, refer to Dept. of Public Safety 
B-l Regulation. 



ARTICLE 520— THEATERS AND ASSEMBLY HALLS 70-297 

Exception No. 3. The wiring for stage set lighting and stage effects and 
other wiring which is not fixed as to location shall be done with approved 
portable cables and approved flexible cords. 

520-5. Number of Conductors in Raceway. The number of conductors per- 
mitted in any metal conduit or electrical metallic tubing for border or stage 
pocket circuits or for remote control conductors shall not exceed that shown in 
Table 1 of Chapter 9. In the case of auxiliary gutters or wireways, the sum 
of the cross-sectional areas of all contained conductors at any cross-section 
shall not exceed 20 per cent of the interior cross-sectional area of the gutter 
or wireway. 

520-6. Enclosing and Guarding Live Parts. Live parts shall be enclosed or 
guarded to prevent accidental contact by persons and objects. All switches 
shall be of the externally operable type. Rheostats shall be placed in ap- 
proved cases or cabinets which enclose all live parts, having only the operat- 
ing handles exposed. 

B. Fixed Stage Switchboard 
520-21. Dead Front. Stage switchboards shall be of the dead-front type. 
520-22. Guarding Back of Switchboard. Stage switchboards having exposed 
live parts on the back of such boards shall be enclosed by the building walls, 
wire mesh grills, or by orher approved methods. The entrance to this en- 
closure shall be by means of a self-closing door. 

520-23. Control and Overcurrent Protection of Receptacle Circuits. Means 
shall be provided at the stage switchboard for the control and individual 
overcurrent protection of branch circuits to stage and gallery receptacles used 
for portable stage equipment. 

520-24. Metal Hood. A stage switchboard that is not completely enclosed 
dead-front and dead-rear or recessed into a wall shall be provided with a 
metal hood extending the full length of the board to protect all equipment 
on the board from falling objects. 

520-25. Dimmers. Dimmers shall conform to the following: 

(a) Disconnection and Overcurrent Protection. Where dimmers are in- 
stalled in ungrounded conductors, each dimmer shall have overcurrent pro- 
tection not greater than 125 per cent of the dimmer rating, and shall be 
disconnected from all ungrounded conductors when the master or individual 
switch or circuit-breaker supplying such dimmer is in the open position. 

(b) Resistance or Reactor Type Dimmers. Resistance or series reactor type 
dimmers may be placed in either the grounded or the ungrounded conductor 
of the circuit. Where designed to open either the supply circuit to the dimmer 
or the circuit controlled by it, the dimmer shall then comply with Section 
380-1. 

The resistance or reactor type dimmers shall be placed in the grounded neutral 
conductor of the circuit provided they do not open the circuit. 

(c) Auto-Transformer Type Dimmers. The circuit supplying an auto- 
transformer type dimmer shall not exceed 150 volts between 



70-298 MASSACHUSETTS ELECTRICAL CODE 

conductors. The grounded conductor shall be common to the input and 
output circuits. See Section 200-4. 

C. Stage Equipment — Fixed 

520-41. Circuit Loads. Footlights, border lights, and proscenium side 
lights shall be so arranged that no branch circuit supplying such equip- 
ment will carry a load exceeding 20 amperes; provided that where 
heavy-duty lampholders only are used, such circuits may conform to 
the provisions of Article 210 for circuits supplying heavy-duty lamp- 
holders. 

520-42. Conductor Insulation. Foot, border, proscenium, or portable 
strip light fixtures shall be wired with conductors having insulation 
suitable for the temperatures at which the conductors will be operated 
and not less than 125 °C (257°F). See Table 310-2(a). 

520-43. Footlights. 

(a) Where metal trough construction is employed for footlights, 
the trough containing the circuit conductors shall be made of sheet 
metal not lighter than No. 20 USS gage (.0359 inch in thickness) treated 
to prevent oxidation. Lampholder terminals shall be kept at least Vi 
inch from the metal of the trough. The circuit conductors shall be 
soldered to the lampholder terminals. 

(b) Where the metal trough construction specified in Section 520- 
43(a) is not used, footlights shall consist of individual outlets with 
lampholders, wired with rigid or flexible metal conduit, Type ALS ca- 
ble or Type MI cable. The circuit conductors shall be soldered to the 
lampholder terminals. Disappearing footlights shall be so arranged that 
the current supply shall be automatically disconnected when the foot- 
lights are replaced in the recess designed therefor. 

520-44. Borders and Proscenium Sidelights. 

(a) Borders and proscenium sidelights shall be constructed as pre- 
scribed in Section 520-43, shall be suitably stayed and supported, and 
shall be so designed that the flanges of the reflectors or other adequate 
guards will protect the lamps from mechanical injury and from acci- 
dental contact with scenery or other combustible material. 

(b) Cables for Border Lights. Cables for supply to border lights 
shall be types S, SO, or ST flexible cord. See Table 400-11. The cables 
shall be suitably supported. Such cables shall be employed only where 
flexible conductors are necessary. 

520-45. Receptacles. Receptacles intended for the supply of arc lamps 
shall have not less than 50 amperes capacity and shall be supplied by 
conductors not smaller than No. 6. Receptacles intended for the supply 
of incandescent lamps shall have not less than 20 amperes capacity 
and shall be supplied by conductors not smaller than No. 12. Plugs for 
arc and incandescent receptacles shall not be interchangeable. 

520-46. Stage Pockets. Receptacles intended for the cohnection of 
portable stage lighting equipment shall be mounted in suitable pockets 
or enclosures, and shall comply with the requirements of Section 520- 
45. 



ARTICLE 520-THEATERS AND ASSEMBLY HALLS 70-299 

520-47. Lamps in Scene Docks. Lamps installed in scene docks shall 
be so located and guarded as to be free from mechanical injury and 
provide an air space of not less than 2 inches between such lamps and 
any combustible material. 

520-48. Curtain Motors. Curtain motors having brushes or sliding 
contacts shall comply with one of the following conditions: 

(a) Be of the totally enclosed, enclosed-fan-cooled, or enclosed-pipe- 
ventilated types. 

(b) Be enclosed in separate rooms or housings built of noncombus- 
tible materials so constructed as to exclude flyings or lint, and properly 
ventilated from a source of clean air. 

(c) Have brush or sliding-contact end of motor enclosed by solid 
metal covers. 

(d) Have brushes or sliding contacts enclosed in substantial, tight, 
metal housings. 

(e) Have the upper half of brush or sliding-contact end of the motor 
enclosed by a wire screen or perforated metal and the lower half en- 
closed by solid metal covers. 

(f) Have wire screens or perforated metal placed at the commutator 
or brush ends. No dimension of any opening in the wire screen or 
perforated metal shall exceed .05 inch, regardless of the shape of the 
opening and of the material used. 

520-49. Flue-Damper Control. Where stage flue dampers are released 
by an electrical device, the circuit operating the latter shall be normally 
closed and shall be controlled by at least two externally operable 
switches, one switch being placed at the electrician's station and the 
other where designated by the inspection authority. The device shall be 
designed for the full voltage of the circuit to which it is connected, no 
resistance being inserted. The device shall be located in the loft above 
the scenery and shall be enclosed in a suitable iron box having a tight, 
self-closing door. 

D. Portable Switchboards on Stage 

520-51. Supply. Portable switchboards shall be supplied only from 
outlets especially provided for this purpose. Such outlets shall include 
externally operable, enclosed fused switches or circuit breakers 
mounted on the stage wall or at the switchboard in locations readily 
accessible from the stage floor. 

520-52. Overcurrent Protection. Circuits from portable switchboards 
directly supplying equipment containing incandescent lamps of not 
over 300 watts shall be protected by overcurrent devices having a 
rating or setting of not more than 20 amperes. Circuits for lampholders 
over 300 watts may be used where overcurrent protection conforms to 
the provisions of Article 210. Other circuits shall be provided with 
overcurrent devices with a rating or setting not higher than the current 
required for the connected load. 

520-53. Construction. Portable switchboards for use on stages shall 
comply with the following: 



70-300 MASSACHUSETTS ELEClKICAL CODE 

(a) Enclosure. Portable switchboards shall be placed within an en- 
closure of substantial construction which may be so arranged that the 
enclosure is open during operation. Enclosures of wood shall be com- 
pletely lined with sheet metal of not less than No. 24 USS gage (.0239 
inch), and shall be well galvanized, enamelled, or otherwise properly 
coated to prevent corrosion or be of a corrosion-resistant material. 

(b) Live Parts. Except as provided for dimmer face plates in Sec- 
tion 520-53 (e), there shall be no exposed live parts within the enclosure. 

(e) Switches and Circuit Breakers. All switches and circuit breakers 
shall be of the externally operable, enclosed type. 

(d) Circuit Protection. Overcurrent devices shall be provided in 
each ungrounded conductor of every circuit supplied through the 
switchboard. Enclosures shall be provided for all overcurrent devices 
in addition to the switchboard enclosure. 

(e) Dimmers. The terminals of dimmers shall be provided with en- 
closures, and dimmer face plates shall be so arranged that accidental 
contact cannot be readily made with the face-plate contacts. 

(f) Interior Conductors. All conductors within the switchboard en- 
closure shall be stranded and, except for cables feeding to or from the 
switchboard, shall be asbestos-covered type AA or other types approved 
for a maximum operating temperature of 200°C (392°F). Each con- 
ductor shall have an ampacity at least equal to the rating of the circuit 
breaker, switch or fuse which it supplies, except for conductors for in- 
candescent lamp circuits having overcurrent protection not exceeding 
20 amperes. Conductors shall be enclosed in metal troughs or securely 
fastened in position and shall be bushed where they pass through metal. 

(g) Pilot Light. A pilot light shall be provided within the enclosure 
and shall be so connected to the circuit supplying the board that the 
opening of the master switch will not cut off the supply to the lamp. 
This lamp shall be on an independent circuit having overcurrent pro- 
tection of a rating or setting of not more than 15 amperes. 

(h) Supply Connections. The supply to a portable switchboard shall 
be by means of flexible cord (types S, SO or ST) terminating within 
the switchboard enclosure or in an externally operable fused master 
switch or circuit breaker. The supply cable shall have sufficient am- 
pacity to carry the total load on the switchboard and shall be protected 
by overcurrent devices. 

(i) Cable Arrangement. Cables shall be protected by bushings 
where they pass through enclosures and shall be so arranged that 
tension on the cable will not be transmitted to the connections. 

(j) Terminals. Terminals to which stage cables are connected shall 
be so located as to permit convenient access to the terminals. At termi- 
nals not provided with approved pressure connectors the following con- 
struction shall be employed : 

(1) For conductors of No. 10 or larger, solder lugs shall be used. 

(2) For conductors smaller than No. 10, the strands shall be sol- 
dered together where connected to clamps or binding screws not spe- 
cifically approved as pressure connectors. 



ARTICLE 520-THEATERS AND ASSEMBLY HALLS 70-301 

E. Stage Equipment — Portable 

520-61. Arc Lamps. The construction of arc lamps shall be approved 
by the authorities having jurisdiction. 

520-62. Portable Plugging Boxes. Portable plugging boxes shall con- 
form to the following: 

(a) Enclosure. The construction shall be such that no current- 
carrying part will be exposed. 

(b) Receptacles and Overcurrent Protection. Each receptacle shall 
have a rating of not less than 30 amperes, and shall have overcurrent 
protection which shall be installed in an enclosure equipped with self- 
closing doors. 

(c) Busbars and Terminals. Busbars shall have an ampacity equal 
to the sum of the ampere ratings of all the receptacles. Lugs shall be 
provided for the connection of the master cable. 

520-63. Lights on Scenery. 

(a) Brackets on scenery shall be wired internally and the fixture 
stem shall be carried through to the back of the scenery where a bush- 
ing shall be placed on the end of the stem, except that externally wired 
brackets or other fixtures may be used when wired with cords de- 
signed for hard usage which shall extend through scenery and with- 
out joint or splice in canopy of fixture back and terminate in an ap- 
proved type stage connector located within 18 inches of the fixture, 
unless such location is impractical. 

(b) Fixtures shall be securely fastened in place. 

520-64. Portable Strips. Portable strips shall be constructed in ac- 
cordance with the requirements for border lights and proscenium side 
lights in Section 520-44 (a). The supply cable shall be protected by 
bushings where it passes through metal and shall be so arranged that 
tension on the cable will not be transmitted to the connections. See 
Section 520-42 for wiring of portable strips. 

520-65. Festoons. Joints in festoon wiring shall be staggered where 
practicable. Lamps enclosed in lanterns or similar devices of combus- 
tible material shall be equipped with approved guards. 

520-66. Special Effects. Electrical devices used for simulating light- 
ning, waterfalls, and the like, shall be so constructed and located that 
flames, sparks, or hot particles cannot come in contact with combustible 
material. 

520-67. Cable Connectors. Cable connectors for flexible conductors 
shall be so constructed that tension on the cord or cable will not be 
transmitted to the connections. See Section 400-9. The female half of 
the connector shall be attached to the line end of the cord or cable. 

520-68. Conductors for Portables. Flexible conductors used to supply 
portable stage equipment shall be Types S, SO or ST, except that re- 
inforced cord may be used to supply stand lamps where the cord is not 
liable to severe physical damage and is protected by an overcurrent 
protection rated at not over 20 amperes. 



70-302 MASSACHUSETTS ELECTRICAL CODE 

F. Dressing Rooms 

520-71. Pendant Lampholders. Pendant lampholders shall not be in- 
stalled in dressing rooms. 

520-72. Lamp Guards. All incandescent lamps in dressing rooms, 
where less than 8 feet from the floor, shall be equipped with open-end 
guards riveted to the outlet box cover or otherwise sealed or locked in 
place. 

520-73. Switches Required. All lights and receptacles in dressing 
rooms shall be controlled by wall switches installed in the dressing 
rooms. Each switch controlling receptacles shall be provided with a pilot 
light to indicate when the receptacle or receptacles are energized. 

G. Grounding 

520-81. Grounding. All metal raceways shall be grounded. The metal 
frames and enclosures of equipment including border lights shall be 
grounded, except the frames and enclosures of portable equipment on 
grounded circuits operating at not over 150 volts to ground and not 
within reach of grounded surfaces. Grounding, when employed, shall 
be done in the manner specified in Article 250. 



ARTICLE 530 — MOTION-PICTURE STUDIOS AND 
SIMILAR LOCATIONS 

A. General 

530-1. Scope. The requirements of this Article shall apply to television 
studios (except as covered in Section 520-1), motion-picture studios, 
exchange, factory, laboratory, stage, or a portion of the building in 
which motion-picture films more than % inch in width are manufac- 
tured, exposed, developed, printed, cut, edited, rewound, repaired or 
stored. 

For the purpose of this Article, a motion-picture studio is one in 
which photographic film is used to record action. A television studio 
shall mean one which employs the use of electronic cameras only. 

For recommendations for protection against cellulose nitrate film hazards 
refer to NFPA Standard for the Storage and Handling of Cellulose Nitrate 
Motion Picture Film (No. 40). 

B. Stage or Set 

530-11. Permanent Wiring. The permanent wiring shall be in ap- 
proved metal raceways Type ALS cable or Type MI cable. 

Exception. Communication circuits, and sound recording and re- 
producing equipment may be wired as permitted by the articles cover- 
ing those installations. {See Articles 640 and 800) . 

530-12. Portable Wiring. The wiring for stage set lighting and stage 
effects, and other wiring which is not fixed as to location, shall be done 



ARTICLE 530-MOTION-PICTURE STUDIOS 70-303 

with approved portable cables and approved flexible cords. This re- 
quirement shall not apply to portable lamps or other electrical equip- 
ment used as properties in a motion picture set, on a studio stage or 
lot, or on location. 

530-13. Stage Lighting and Effects Control. Switches used for studio 
stage set lighting and effects (on the stages and lots and on location) 
shall be of the externally operable type. When contactors are used as 
the disconnecting means for fuses, an individual externally operable 
type switch (such as a tumbler switch) for the control of each contac- 
tor, shall be located at a distance of not more than six feet from the 
contactor, in addition to remote control switches. 

Exception. A single externally operable switch may be used to si- 
multaneously disconnect all the contactors on any one location board, 
where located at a distance of not more than 6 feet from the location 
board. 

530-14. Plugging Boxes. Each receptacle of plugging boxes shall have 
an ampacity of not less than 30 amperes. 

530-15. Enclosing and Guarding Live Parts. 

(a) Live parts shall be enclosed or guarded to prevent accidental 
contact by persons and objects. 

(b) All switches shall be of the externally operable type. 

(c) Rheostats shall be placed in approved cases or cabinets which 
enclose all live parts, having only the operating handles exposed. 

(d) Current-carrying parts of "bull-switches," "location boards," 
"spiders," and plugging boxes shall be so enclosed, guarded, or located 
that persons cannot accidentally come into contact with them or bring 
conducting materials into contact with them. 

530-16. Portable Lamps. Portable lamps and work lights shall be 
equipped with approved portable cords, approved composition or 
metal-sheathed porcelain sockets and substantial guards. 

Exception. The requirements of this Section shall not apply to port- 
able lamps used as properties in a motion picture set or television stage 
set, on a studio stage or lot, or on location. 

530-17. Portable Arc Lamps. Portable arc lamps shall be substantially 
constructed. The arc shall be provided with an enclosure designed to 
retain sparks and carbons and to prevent persons or materials from 
coming into contact with the arc or bare live parts. The enclosures shall 
be ventilated. All switches shall be of the externally operable type. 

530-18. Overcurrent Protection — Short Time Rating.* 

(a) General. Automatic overcurrent protective devices (circuit 
breakers or fuses) for feeders, and subfeeders for moving-picture stu- 
dio stage set lighting and the stage cables for such stage set lighting, shall 
be rated or set to operate at not more than 400 per cent of the values 
given in Table 310-12 and Table 400-9. 

* Special consideration is given to motion-picture studios because filming 
periods are of only a few minutes duration and are rarely longer than 10 
minutes. 



70-304 MASSACHUSETTS ELECTRICAL CODE 

(b) Feeders. The feeders from the substations to the stages shall be 
protected by means of overcurrent devices having suitable ampacity 
(generally located in the substation). The overcurrent devices may be 
double-pole, or two single-pole devices may be used. There need be no 
pole or overcurrent coil in the neutral conductor. The overcurrent de- 
vice setting for each feeder shall not exceed 400 per cent of the am- 
pacity of the feeder, as given in Table 310-12 for the kind of insulation 
used. 

(c) "Location Boards." Overcurrent protection (fuses or circuit 
breakers) shall be provided at the "location boards." The fuses in the 
"location boards" shall be not larger in rating than 400 per cent of the 
ampacity of the cables between the "location boards" and the plugging 
boxes. 

(d) Plugging Boxes. Where plugging boxes are not provided with 
overcurrent protective devices, each cable or cord smaller than No. 8 
supplied through a plugging box shall be attached to the plugging box 
by means of a plug containing two cartridge fuses or a circuit breaker. 
The rating of the fuses or the setting of the circuit breaker shall be not 
more than 400 per cent of the safe ampacity of the cables or cords as 
given in Tables 310-12, 310-13 and 400-8 for the kind of insulation 
used. 

(e) Lighting. Work-lights, stand-lamps, and fixtures shall be con- 
nected to plugging boxes by means of plugs containing two cartridge 
fuses not larger than 20 amperes, or they may be connected to special 
outlets on circuits protected by fuses or circuit-breaker settings of not 
more than 20 amperes. Plug fuses shall not be used unless they are on 
the load side of the fuse or circuit breakers on the "location boards." 

530-19. Grounding. Conduit, armored cable or metal raceways, and 
all noncurrent-carrying metal parts of appliances, devices and equip- 
ment shall be grounded as prescribed in Article 250. This shall not ap- 
ply to pendant and portable lamps, nor to stage lighting and stage 
sound equipment, nor to other portable or semiportable special stage 
equipment, operating at not more than 150 volts to ground. 

C. Dressing Rooms 

530-31. Dressing Rooms. Fixed wiring in dressing rooms shall be in- 
stalled in accordance with wiring methods covered in Chapter 3. Wir- 
ing for portable dressing rooms shall be of an approved type. 

D. Viewing, Cutting and Patching Tables 

530-41. Lamps at Tables. Only approved composition or metal- 
sheathed porcelain keyless lampholders, equipped with suitable means 
to guard lamps from physical damage and from film and film scrap, 
shall be used at patching, viewing and cutting tables. 

E. Film Storage Vaults 

530-51. Lamps in Cellulose Nitrate Film Storage Vaults. Lamps in cel- 
lulose nitrate film storage vaults shall be rigid fixtures of the glass en- 
closed and gasketed type. Lamps shall be controlled by a switch hav- 
ing a pole in each ungrounded conductor. This switch shall be located 



ARTICLE 540-MOTION-PICTURE PROJECTORS 70-305 

outside of the vault and provided with a pilot light to indicate whether 
the switch is on or off. This switch shall disconnect from all sources of 
supply all ungrounded conductors terminating in any outlet in the vault. 

530-52. Motors and Other Electrical Equipment in Film Storage Vaults. 

No electric motors, heaters, portable lights, or other portable electric 
equipment shall be located in the film storage vaults. 

F. Substations 

530-61. Substations. Wiring and equipment above 600 volts shall con- 
form to Article 710. 

530-62. Low-Voltage Switchboards. On 600 volts or less switch- 
boards shall conform to Article 384. 

530-63. Overcurrent Protection of DC Generators. Three-wire DC gen- 
erators shall have protection consisting of overcurrent devices having 
current ratings or settings in accordance with the generator rating. The 
overcurrent protective devices may be single-pole or two-pole and need 
not have a pole or over-current coil in the neutral lead (whether it is 
grounded or ungrounded). 

530-64. Working Space and Guarding. Working space and guarding 
in permanent fixed substations shall conform to Sections 110-16 and 
110-17. For guarding of live parts on motors and generators, see Sec- 
tion 430-1 1 and 430-14. Switchboards for voltage of not more than 250 
volts DC between conductors when located in substations or switch- 
board rooms accessible to qualified persons only need not be dead- 
front. 

530-65. Portable Substations. Wiring and equipment in portable sub- 
stations shall conform to the sections applying to installations in perma- 
nent fixed substations, but, due to the limited space available, the work- 
ing spaces may be reduced, provided that the equipment shall be so 
arranged that the operator may do his work safely, and so that other 
persons in the vicinity cannot accidentally come into contact with 
current-carrying parts or bring conducting objects into contact with 
them while they are energized. 

530-66. Grounding at Substations. Noncurrent-carrying metal parts 
shall be grounded except the frames of DC circuit breakers installed on 
switchboards. 



ARTICLE 540 — MOTION-PICTURE PROJECTORS 



A. General 

540-1. Scope. This Article applies to motion-picture projectors and 
associated equipment of the Professional and Nonprofessional Types. 

B. Equipment and Projectors of the Professional Type 

540-10. Professional Projector — Definition. The professional projec- 
tor employs a 35-millimeter film which is 1% inch wide and has on 
each edge 5.4 perforations per inch. 



70-306 MASSACHUSETTS ELECTRICAL CODE 

540-11. Enclosure. The professional type of projector, such as is com- 
monly used in theaters and motion-picture houses, shall be located in an ap- 
proved enclosure. Such enclosure shall not be considered as a hazardous lo- 
cation as defined in Article 500. 

540-12. Motor-Driven Projectors. Motor-driven projectors shall be approved 
for the purpose as an assembly or shall comply with all of the following con- 
ditions: 

(a) An approved projector shall be used. 

(b) An approved projector lamp shall be used. 

(c) Motors shall be so designed or guarded as to prevent ignition of film 
by sparks or arcs. 

(d) Projectors shall be in charge of a qualified operator. 

540-13. Conductor Size. Conductors supplying cutlets for arc projectors 
of the professional type shall not be smaller than No. 8 and shall be of 
sufficient size for the projector employed. Conductors for incandescent type 
projectors shall conform to normal wiring standards as provided in Section 
210-25. 

540-14. Conductors on Lamps and Hot Equipment. Asbestos covered con- 
ductors type AA or other types of insulated conductors having a maximum 
operating temperature of 200 C C (392°F) shall be used en all lamps or other 
equipment where the ambient temperature at the conductors as installed will 
exceed 50°C (122°F). 

540-15. Flexible Cords. Cords approved for hard service in Table 400-11 
shall be used on portable equipment. 

540-16. Lamp Guards. Incandescent lamps in projection rooms or booths 
shall be provided with an approved lamp guard unless otherwise protected 
by noncombustible shades or other enclosures. 

540-17. Location of Equipment. Motor-generator sets, transformers, recti- 
fiers, rheostats, and similar equipment, for the supply or control of current 
to arc lamps on projectors shall, if practicable, be located in separate rooms. 
Where placed in the projector room, they shall be so located or guarded that 
arcs or sparks cannot come in contact with film, and motor-generator sets 
shall have the commutator end or ends protected as provided in Section 
520-48. 

540-18. 

DELETED 

540-19. Equipment Prohibited. Switches, overcurrent devices, or other 
equipment not normally required or used for projectors, sound reproduction, 
flood, or other special effect lamps or other equipment shall not be installed 
in such booths or rooms 

Exception. Remote-control switches for the control of auditorium lights or 
a switch for the motor operating the curtain at the motion-picture screen. 



ARTICLE 550 — MOBILE HOMES 70-307 



540-20. Approval. Projectors and enclosures for arc or incandescent lamps, 
rectifiers, transformers, rheostats, and similar equipment, shall be of an ap- 
proved type. 

540-21. Marking. Projectors and other equipment as set forth in Section 
540-20 shall be marked with the name or trademark of the maker and with 
the voltage and current for which they are designed. 

540-22. 

DELETED 

C. Nonprofessional Type Projectors 
540-30. Definition. The nonprofessional projector employs film other than 
that used on professional type projectors. 

540-31. Booth Not Required. Projectors of the nonprofessional or miniature 
type, when employing only approved slew-burning (cellulose acetate or equiv- 
alent) film, may be operated without a booth. 

540-32. Approval. Projectors, lamp enclosures, and current-controlling de- 
vices and similar devices shall be approved as component parts of the pro- 
jector equipment. 

540-33. Source of Illumination. The source of illumination shall be a lamp 
of a type approved for stereopticon use or for motion-picture projection. 

540-34. Marking. Projectors shall be marked with name or trademark of 
the maker, with the current and voltage for which they are designed, and 
for projectors of this type using the standard 35-millimeter film, with the 
wording "For use with slew-burning films only." 

540-35. Nonprofessional Film Marking. The slow-burning (cellulose acetate 
or equivalent) film shall have a permanent distinctive marker for its entire 
length identifying the manufacturer and the slow-burning character of the 
film stock. 

D. Sound Recording and Reproduction 
540-50. Sound Recording and Reproduction. Sound recording and repro- 
duction equipment shall comply with Article 640. 

ARTICLE 550 — MOBILE HOMES 

550-1. Scope. 

(a) The provisions of this Article cover the electric conductors and equip- 
ment installed within or on mobile hemes and also the conductors that 
connect mobile homes to a supply of electricity. 

Wherever the requirements of other Articles of the MASSACHUSETTS ELEC- 
TRICAL Code and Article 550 differ, the requirements of Article 550 shall 
apply. 



70-308 MASSACHUSETTS ELECTRICAL CODE 

(b) A mobile home not intended as a dwelling unit, as for example, 
equipped for sleeping purposes only, contractor's on-site offices, con- 
struction job dormitories, mobile studio dressing rooms, banks, clinics, 
mobile stores or intended for the display or demonstration of merchan- 
dise or machinery, shall not be required to meet the provisions of this 
Article pertaining to the number or capacity of circuits required. It 
shall, however, meet all other applicable requirements of this Article if 
provided with an electrical installation intended to be energized from 
a 1 15 volt or 1 15/230 volt AC power supply system. 

(c) The provisions of this Article apply to mobile homes intended for 
connection to a wiring system nominally rated 115/230 volts, 3-wire 
AC, with grounded neutral. 

550-2. Definition. Mobile Home: a vehicular, portable structure built 
on a chassis and designed to be used without a permanent foundation 
as a dwelling when connected to indicated utilities. 

550-3. Power Supply. The mobile home service equipment shall be 
located adjacent to the mobile home and not mounted in or on the mo- 
bile home. 

The power supply to the mobile home shall be feeder circuits con- 
sisting of not more than two mobile home supply cords each rated 50 
amperes or permanently installed circuits. 

Exception No. 1. A mobile home that is factory-equipped with gas 
or oil-fired central heating equipment and cooking appliances may be 
provided with a mobile home supply cord rated 40 amperes, minimum. 

(a) Each such mobile home supply cord shall be approved for the 
purpose and have four conductors, one of which shall be identified by 
a continuous green color or a continuous green color with a yellow 
stripe. The attachment plug, connectors and mating receptacles shall be 
of a 3-pole, 4-wire grounding type covered by American Standard — 
C73 Attachment Plugs and Receptacles. The mobile home power-supply 
cord shall be permanently attached to the mobile home distribution 
panel. A suitable clamp or the equivalent shall be provided at the dis- 
tribution panel to afford strain relief for the cord to prevent strain 
from being transmitted to the terminals. 

The power supply cord shall be not less than 21 feet nor more than 
26 Vi feet long. 

(b) Second Supply Cord. Where the calculated load of the mobile 
home is in excess of 50 amperes, or where a separately metered appli- 
ance is installed in the mobile home, a second 50 ampere mobile home 
supply cord shall be installed. Where two cord supply systems are in- 
stalled, they shall not be interconnected on either the line side or the 
load side except that the grounding circuits and grounding means shall 
be electrically interconnected. 

(c) Permanent Wiring. Where the calculated load exceeds 100 am- 
peres or where a permanent feeder is used the supply shall be by means 
of four permanently installed conductors in an approved wiring method, 
one conductor being identified by a continuous green color or a con- 
tinuous green color with a yellow stripe. 

550-4. Disconnecting Means and Branch Circuit Protective Equipment. 

The branch circuit equipment may be combined with the disconnecting 



ARTICLE 550-MOBILE HOMES 70-309 

means as a single assembly. Such a combination may be designated as 
a distribution panel. 

Plug fuses and fuseholders shall be tamper-resistant, type *'S," en- 
closed in dead-front fuse panels. 

(a) Disconnecting Means. Disconnecting means shall be provided 
in each mobile home and shall be approved service entrance equipment 
consisting of circuit-breakers or a switch and fuses and their accessories 
installed in a readily accessible location near the point of entrance of the 
supply cord or conductors into the mobile home. This equipment shall 
contain a solderless type of grounding connector or bar for the purposes 
of grounding with sufficient terminals for all grounding conductors. 
The neutral bar termination of the grounded circuit conductors shall be 
insulated. The disconnecting equipment shall have a rating suitable for 
the connected load. 

Where two power supply cords are installed disconnecting means 
shall be provided for each cord and may be combined in a single equip- 
ment but without electrical interconnections other than for grounding 
purposes. 

A distribution panel main circuit-breaker shall be rated 50 amperes 
and employ a 2-pole circuit breaker rated 40 amperes for a 40-ampere 
supply cord, or 50 amperes for a 50-ampere supply cord. A distribu- 
tion panel employing a disconnect switch and fuses shall be rated 60 
amperes and shall employ a single 2-pole 60-ampere fuseholder with 
40- or 50-ampere main fuses for 40- or 50-ampere supply cords, re- 
spectively. The outside of the distribution panel shall be plainly marked 
with the fuse size. The main circuit breakers or fuses shall be plainly 
marked "Main." 

(b) Branch Circuit Protective Equipment. Branch circuit distribution 
equipment shall be installed in each mobile home and shall include 
overcurrent protection for each branch circuit consisting of either cir- 
cuit breakers or fuses. 

Where circuit breakers are provided for branch-circuit protection, 
230-volt circuits shall be protected by 2-pole common or companion 
trip, or handle-tied paired circuit breakers. 

The branch-circuit overcurrent devices shall be rated : 

(1) not more than the circuit conductors; and 

(2) not more than 150 per cent of the rating of a single appliance 
rated 10 amperes or more; but 

(3) not more than the fuse size marked on the air conditioner or 
other motor-operated appliance. 

(c) Electrical Nameplates. A metal nameplate on the outside adja- 
cent to the supply cord entrance shall read, "This Mobile Home is 
Wired for 115/230 Volt, 3-wire, 60 Cycle Supply. Supply Cord 40 (or 
50) amp." The voltage marking may read 120/240 Volts instead of 
115/230 Volts. 

550-5. Branch Circuits. The number of branch circuits required shall 
be determined in accordance with the following: 



70-310 MASSACHUSETTS ELECTRICAL CODE 

(a) Lighting. Based on 3 watts per square foot times outside di- 
mensions of the mobile home (hitch excluded) divided by 115 volts to 
determine number of 15 or 20 ampere lighting area circuits, e.g., 

3 X Length X Width _ c , e , „^ . . 

= No. of 15 (or 20) ampere circuits. 

115 X 15 (or 20) 

(b) Portable Appliances. There shall be a minimum of two 20 am- 
pere branch circuits for receptacle outlets in the kitchen area, which 
may supply other receptacle outlets in the dining, laundry, and patio 
areas. These circuits shall supply only portable appliances. 

(c) General Appliances. (Including Furnace, Water Heater, Range, 
and Central or Room Air Conditioner, Etc.) There shall be one or 
more circuits of adequate rating in accordance with the following: 

(1) Ampere rating of fixed appliances not over 50 per cent of cir- 
cuit rating if lighting outlets (receptacles, other than kitchen, dining 
area, and laundry, considered as lighting outlets) are on same circuit; 

(2) For fixed appliances on a circuit without lighting outlets, the 
sum of rated amperes shall not exceed the branch-circuit rating for 
other than motor loads or 80 per cent of the branch-circuit rating for 
air conditioning or other motor loads; 

(3) The rating of a single portable appliance on a circuit having no 
other outlets shall not exceed 80 per cent of the circuit rating; 

(4) The rating of range branch circuit shall be based on the range 
demand as specified for ranges in Section 550-11 (b) (5). 

550-6. Receptacle Outlets. 

(a) All receptacle outlets: 

(1) shall be of grounding type; 

(2) shall be installed according to Section 210-7; and 

(3) except when supplying specific appliances, receptacles shall be 
parallel blade, 15-ampere, 125-volt, either single or duplex. 

(b) There shall be an individual outlet of the grounding type for 
each cord-connected fixed appliance installed. 

(c) Except in the bath and hall areas, receptacle outlets shall be in- 
stalled at all wall spaces 2 feet wide or more, so that no point along 
the floor line is more than 6 feet, measured horizontally, from an outlet 
in that space. Except as explained in the following, receptacle outlets 
are not required for wall spaces occupied by kitchen or wardrobe cabi- 
nets. 

In addition, a receptacle outlet shall be installed: 

(1) Over counter tops in the kitchen (at least one on each side of 
the sink if counter tops are on each side) ; 

(2) Adjacent to the refrigerator and free-standing gas-range space; 

(3) At counter top spaces for built-in vanities; 

(4) At counter top spaces under wall-mounted cabinets. 



ARTICLE 550-MOBILE HOMES 70-311 

(d) Receptacle outlets shall not be installed within or adjacent to a 
shower or bathtub space. 

550-7. Fixtures and Appliances. 

(a) Water heaters, refrigerators, air conditioning equipment, ranges, 
electric heaters, washers, dryers and other like appliances shall be of 
an approved type and shall be connected in an approved manner and 
securely fastened in position. (See Section 550-9 for provisions on 
grounding.) 

(b) (1) Specifically approved pendant-type fixtures or pendant cords 
may be installed in mobile homes. 

(2) If a lighting fixture is provided over a bathtub or in a shower 
stall, it shall be of the approved enclosed and gasketed type. 

(3) Switches shall not be located inside the tub or shower space. 

550-8. Wiring Methods and Materials. Except as specifically limited 
in this Section the wiring methods and materials included in the Na- 
tional Electrical Code shall be used in mobile homes. 

(a) Nonmetallic outlet boxes are acceptable only with nonmetallic 
sheathed cable. 

(b) Nonmetallic cable located 15 inches or less above the floor, if 
exposed, shall be protected from physical damage by covering boards, 
guard strips, or conduit. Cable likely to be damaged by stowage shall 
be so protected in all cases. 

(c) Metal-clad and nonmetallic cables may be passed through the cen- 
ters of the wide side of 2 by 4 studs. However, they shall be protected 
where they pass through 2 by 2 studs or at other studs or frames 
where the cable or armor would be less than \Vi inches from the inside 
or outside surface. Steel plates on each side of the cable, or a tube, 
with not less than No. 16 manufacturer's standard gage wall thickness, 
are required to protect the cable. These plates or tubes shall be securely 
held in place. 

(d) Where metallic faceplates are used they shall be effectively 
grounded. 

(e) If the range, clothes dryer, or similar appliance is connected by 
metal-clad cable or flexible conduit, a length of free cable or conduit 
should be provided to permit moving the appliance. The cable or flexi- 
ble conduit should be adequately secured to the wall. Clearance space 
behind a range may provide the required protection when a range is 
connected by Type SE cable. When used, Type SE cable shall have an 
identified and insulated neutral plus an equipment grounding conduc- 
tor. Nonmetallic cable (Type NM) shall not be used to connect a 
range. 

(f) Rigid metal conduit shall be provided with a locknut inside and 
outside the box, and a conduit bushing shall be used on the inside. 
Inside ends of the conduit shall be reamed. 

(g) Switches shall be rated as follows: 

(1) For lighting circuits, switches shall have a 10-ampere 125 volt 
rating; or higher, if needed for the connected load. 



70-312 MASSACHUSETTS ELECTRICAL CODE 

(2) For motors or other loads, switches shall have ampere or 
horsepower ratings or both adequate for loads controlled. (An "AC 
general use" snap switch may control a motor 2 horsepower or less with 
full-load current not over 80 per cent of the switch ampere rating.) 

(h) At least 4 inches of free conductor shall be left at each outlet box 
except where conductors are intended to loop without joints. 

(i) Under Chassis Wiring (Exposed to Weather) . 

(1) When outdoor or under chassis wiring is exposed to moisture 
and physical damage it shall be protected by rigid metal conduit or 
liquid-tight flexible metal conduit, except electrical metallic tubing may 
be used when closely routed against frames and equipment enclosures. 

(2) The conductors shall be Type NMC, RW, TW, or equivalent. 

550-9. Grounding. 

Grounding of both electrical and non-electrical metal parts in a mo- 
bile home is through connection to a grounding bus in the mobile home 
distribution panel. The grounding bus is grounded through the green- 
colored conductor in the supply cord or the feeder wiring to the service 
ground in the service entrance equipment located adjacent to the mo- 
bile home location. Neither the frame of the mobile home nor the frame 
of any appliance may be connected to the neutral conductor in the mo- 
bile home. 

(a) Insulated Neutral. 

(1) The grounded circuit conductor (neutral) shall .be insulated 
from the grounding conductors and from equipment enclosures and 
other grounded parts. The grounded (neutral) circuit terminals in the 
distribution panel and in ranges, clothes dryers, counter-mounted cook- 
ing units, and wall-mounted ovens are to be insulated from the equip- 
ment enclosure. Bonding screws, straps, or buses in the distribution 
panel or in appliances are to be removed and discarded. 

(2) Connection of ranges and clothes dryers shall be made with 4 
conductor cord and 3 -pole, 4- wire grounding type plugs, or by ar- 
mored cable or conductors enclosed in flexible steel conduit. 

(b) Equipment Grounding Means. 

(1) The green-colored grounding wire in the supply cord or perma- 
nent feeder wiring shall be connected to the grounding bus in the dis- 
tribution panel or disconnecting means. 

(2) The chassis shall be grounded. The grounding conductor may 
be solid or stranded, insulated or bare, and shall be an armored ground- 
ing conductor or routed in conduit if No. 8 AWG. The conductor, if 
No. 6 AWG or larger, may be run without metal covering. The 
grounding conductor shall be connected between distribution panel 
grounding terminal and a terminal on the chassis. Grounding termi- 
nals shall be of the solderless type and approved as pressure terminal 
connectors recognized for the wire size employed. 

(3) In the electrical system, all exposed metal parts, enclosures, 
frames, lamp fixture canopies, etc. shall be effectively bonded to the 
grounding terminal or enclosure of the distribution panel. 



ARTICLE 550-MOBILE HOMES 70-313 

(4) Cord-connected appliances, such as washing machines, clothes 
dryers, refrigerators, and the electrical system of gas ranges, etc. shall 
be grounded by means of an approved cord with grounding conductor 
and grounding type plug. 

(c) Grounding of Non-current-carrying Metal Parts. All major ex- 
posed metal parts that may become energized, including the water, 
gas and waste plumbing, the roof and outer metallic covering, the chas- 
sis and metallic circulating air ducts, shall be effectively bonded to the 
grounding terminal or enclosure of the distribution panel or to the metal 
chassis. See Section 550-9 (b) (2) for bonding of the chassis to the dis- 
tribution panel grounding terminal. 

550-10. Testing. Dielectric Strength Test. The wiring of each mobile 
home shall be subjected to a 1 -minute, 900-volt, dielectric strength test 
(with all switches closed) between live parts (including neutral) and 
the mobile home ground. Alternatively, the test may be performed at 
1,088 volts for 1 second. This test shall be performed after branch cir- 
cuits are complete and after fixtures or appliances are installed. 

Exception: Fixtures or appliances which are approved shall not be 
required to withstand the dielectric strength test. 

550-11. Calculations. The following method is to be employed in 
computing the supply cord and distribution panel load for each power 
supply assembly for each mobile home in lieu of the procedure shown 
in Article 220 and is based on 3 wire, 115/230 volt supply with 115 
volt loads balanced between the two legs of the 3 wire system. 

(a) Lighting and Small Appliance Load: 

Lighting Watts: Length times width of mobile home (outside di- 
mensions, exclusive of hitch) times 3 watts per square foot; e.g., 

Length X width X 3 = lighting watts. 

Small appliance Watts: Number of circuits times 1,500 watts for 
each 20-ampere appliance receptacle circuit (see definition of Appli- 
ance, Portable with note) ; e.g., 

Number of circuits X 1,500 = small appliance watts. 

Total: Lighting watts plus small appliance = total 

watts. 

First 3,000 total watts at 100 per cent plus remainder at 35 per 

cent = watts to be divided by 230 volts to obtain current 

(amperes) per leg. 

(b) Total load for determining power supply is the summation of: 

(1) Lighting and small appliance load as calculated in Section 
550-1 1(a). 

(2) Name plate amperes for motors and heater loads (exhaust 
fans, air conditioners,* electric, gas, or oil heating).** 

* Omit smaller of these two, except include blower motor if used as air 
conditioner evaporator motor. 

* * When an air conditioner is not installed and a 40-ampere power 
supply cord is provided, allow 15 amperes per leg for air conditioning. 

(3) 25% of current of largest motor in (2) . 



70-314 MASSACHUSETTS ELECTRICAL CODE 

(4) Total of nameplate amperes for: Disposal, Dishwasher, Water 
heater, Clothes dryer, Wall-mounted oven, Cooking units. 

Where number of these appliances exceeds three use 75% of 
total. 

(5) Derive amperes for free standing range (as distinguished from 
separate ovens and cooking units) by dividing values below by 230 
volts. 

Name Plate Rating Use 

10,000 w X or less 80 per cent of rating 

10,001-12,500 w 8,000 w 

12,501-13,500 w 8,400 w 

13,501-14,500 w 8,800 w 

14,501-15,500 w 9,200 w 

15,501-16,500 w 9,600 w 

16,501-17,500 w 10,000 w 

(6) If outlets or circuits are provided for other than factory in- 
stalled appliances include the anticipated load. 

See following Example for illustration of application of this calcula- 
tion. 

Example 

A mobile home is 70 X 10 feet and has two portable appliance 
circuits, a 1000 watt 230 volt heater, a 200 watt 115 volt exhaust 
fan, a 400 watt 115 volt dishwasher and a 7000 watt electric range. 

Lighting and small appliance load 

Lighting 70 X 10 X 3 = 2100 watts 

Small appliance 1500 X 2 = 3000 watts 

5100 watts 

1st 3000 watts at 100% 3000 

Remainder (5,100 — 3,000 = 2,100) at 35% 735 

3735 

3735 

= 16 amperes per leg 

1000 watt (heater) -t 230 = 

200 watt (fan) -s- 115 = 

400 watt (dishwasher) -^ 115 = 
7000 watt (range) X .8 -*■ 230 = 



Lighting and appliances 
Heater (230 volt) 
Fan (115 volt) 
Dishwasher (115 volt) 
Range 

Totals 46 48 

Based on the higher current calculated for either leg, use one 50 
ampere supply cord. 



4.4 amp 




1.7 amp 




3.5 amp 




24. amp 




Amperes 


per leg 


A 


B 


16 


16 


4 


4 


2 


— 


— 


4 


24 


24 



ARTICLE 551— TRAVEL TRAILERS 70-315 



ARTICLE 551— TRAVEL TRAILERS 

551-1. Scope. 

(a) The provisions of this Article cover the electric conductors and equip- 
ment installed within or on Travel Trailers and also on conductors that con- 
nect them to a supply of electricity. 

Wherever the requirements ot other Articles of the MASSACHUSETTS ELEC- 
TRICAL CODE and Article 551 differ, the requirements of Article 551 shall 
apply. 

(b) A Travel Trailer not intended as a dwelling unit, as for example, for 
use as a mobile store, an office, a schoolroom or designed for the display or 
demonstration of merchandise or machinery shall not be required to meet the 
provisions of this Article pertaining to the number or capacity of circuits 
required. It shall, however, meet all other applicable requirements of this 
Article if provided with an electrical installation intended to be energized 
from a 1 1 5 volt, AC power supply system. 

(c) The provisions of this Article apply to the electrical equipment and 
materials of Travel Trailers intended for connection to a wiring system nom- 
inally rated 1 15 volts, 2 wire, AC, with a grounded neutral. 

551-2. Definition. Travel Trailer: A vehicular portable structure built on 
a chassis, designed to be used as a temporary dwelling for travel, recreational, 
and vacation use, permanently identified "Travel Trailer" by the manufac- 
turer on the trailer, and when factory equipped for the road, being of body 
width not exceeding 8 feet and being of any length provided its gross Weight 
does not exceed 4,500 pounds, or being of any weight provided its body 
length does not exceed 29 feet. 

551-3. Power Supply. The Travel Trailer service equipment shall be located 
adjacent to the Travel Trailer parking location and not mounted in or on the 
Travel Trailer. 

(a) The power supply to the Travel Trailer shall be a feeder circuit supply 
cord approved for the purpose rated 15, 20 or 30 amperes, 1 15 volts, and 
shall have three conductors, one of which shall be identified by a continuous 
green color or a continuous green color with a yellow stripe. The attachment 
plug, connectors and mating receptacles shall be of a 2-pole, 3-wire grounding 
type covered by American Standard C73 Attachment Plugs and Receptacles. 

(b) The supply cord shall be not less than 20 feet nor more than 26 ] /2 
feet long and shall be either separable or permanently attached. 

(1) Separable Cord Set. When a separable cord set, consisting of a 
cord, male and female fittings, is provided by the travel trailer manufacturer, 
the travel trailer shall be equipped with a permanently-mounted, approved, 
male recessed-type attachment plug (motor base receptacle) wired directly 
to the distribution panel in an approved manner by means of approved service 
cable. The supply end of the cord set shall be equipped with an attachment 
plug of the type described in Section 551 -3(a). 



70-3 1 6 M ASSACHUSETTS E LECTRICAL CODE 

(2) Permanently Connected Power Cord. The cord shall be con- 
nected directly to the terminals of the distribution panel and provided 
with means to prevent strain from being transmitted to the terminals. 
The supply end of the cord shall be equipped with an attachment plug 
of the type described in Section 55 1-3 (a) . 

(d) Supply Cords shall be as follows: 

(1) 15 ampere No. 14/3 AWG for travel trailers which have a 
single 15 ampere general purpose branch circuit and gas or oil-fired 
heating and cooking appliance. 

(2) 20 ampere No. 12/3 AWG for travel trailers which have a 
single 20 ampere general purpose branch circuit and gas or oil-fired 
heating and cooking appliance. 

(3) 30 ampere No. 10/3 AWG for travel trailers with branch cir- 
cuits in accordance with Section 551-5 (b) . 

551-4. Disconnecting Means and Branch Circuit Protective Equipment. 

The branch circuit equipment may be combined with the disconnecting 
means as a single assembly. Such a combination may be designated as 
a distribution panel. 

Plug fuses and fuseholders shall be tamper-resistant, type "S" en- 
closed in dead-front fuse panels. 

(a) Disconnecting Means. Disconnecting means shall be provided 
in each travel trailer and shall be approved service entrance equipment 
consisting of circuit-breakers or a switch and fuses and their acces- 
sories installed in a readily accessible location near the point of entrance 
of the supply cord or conductors into the travel trailer. This equipment 
shall contain a solderless type of grounding connector or bar for the 
purposes of grounding with sufficient terminals for all grounding con- 
ductors. The neutral bar termination of the grounded circuit conductors 
shall be insulated. 

The disconnecting equipment shall have a rating suitable for the 
connected load. Travel trailers in which only a single branch circuit is 
installed may use a branch-circuit breaker or pull-out type of fuse- 
holder as disconnecting means if approved for use as service equipment. 

(b) Branch Circuit Protective Equipment. Branch circuit distribution 
equipment shall be installed in each travel trailer and shall include over- 
current protection for each branch circuit consisting of either circuit 
breakers or fuses. 

The branch-circuit overcurrent devices shall be rated : 

(1) not more than the circuit conductors; and 

(2) not more than 150 per cent of the rating of a single appliance 
rated 1 amperes or more. 

(c) Labeling at Electrical Entrance. Each travel trailer shall have 
permanently affixed to the exterior skin, at or near the point of en- 
trance of the power supply cord, a metal tag reading: "This travel trailer 
is wired for 110/125 volt AC service. Do not connect to higher volt- 
age. 



ARTICLE 551 -TRAVEL TRAILERS 70-317 

551-5. Branch Circuits. 

(a) Travel trailers with not more than six general appliance and re- 
ceptacle outlets combined shall have not less than either: 

(1) One general purpose (lighting) branch circuit, 15 amperes, 
No. 14 AWG circuit, to supply these outlets, or 

(2) One general purpose (lighting and appliance) branch circuit, 
20 amperes, No. 12 AWG circuit, to supply these outlets, provided 
that the total rating of fixed appliances connected to this circuit shall 
not exceed 5 amperes or 600 watts. 

Note: Travel trailers, wired in accordance with (1) and (2) shall be 
equipped with gas or oil-fired heating and cooking appliances. 

(b) Travel trailers with more than six general appliance and recep- 
tacle outlets combined shall have not less than : 

(1) One general purpose (lighting and appliance) branch circuit, 
20 amperes or No. 12 gage conductors, minimum, which shall supply 
current to lighting outlets and receptacles only (shall not supply re- 
ceptacles in cooking and dining areas) and may supply fixed or porta- 
ble appliances such as electric water heaters. The total rating of such 
fixed or factory installed appliances shall not exceed 9 amperes or 
1,000 watts, and 

(2) One appliance branch circuit, as follows: 20 amperes, No. 12 
gage conductors, minimum, which shall supply current to receptacle 
outlets only in cooking and dining areas. 

551-6. Receptacle Outlets. 

(a) All receptacle outlets; (1) shall be of the grounding type; (2) 
shall be installed according to Section 210-7; and (3) shall be of the 
parallel blade, 1 5 ampere, 1 25 volt type either single or duplex. 

(b) There shall be an individual outlet of the grounding type for 
each cord-connected fixed appliance installed. 

(c) Except in the bath area, receptacle outlets shall be installed at 
all wall spaces 2 feet wide or more, so that no point along the floor 
line is more than 6 feet, measured horizontally, from an outlet in that 
space. Except as explained in the following, receptacle outlets are not 
required for wall spaces that are partially or fully occupied by kitchen 
cabinets, wardrobes, built-in furniture, or similar facilities. 

In addition, a receptacle outlet shall be installed: 

(1 ) Over counter tops in the kitchen and dining area. 

(2) Adjacent to the refrigerator space, except when a gas-operated 
refrigerator containing no electrical circuit is factory installed. 

(3) Adjacent to a gas range space, except when a gas cooking ap- 
pliance containing no electrical circuit is factory installed. 

(4) At counter top spaces for built-in vanities. 

(d) No receptacle outlet shall be provided adjacent to a shower or 
bathtub. 



7Q-318 MASSACHUSETTS ELECTRICAL CODE 

551-7. Fixtures and Appliances. 

(a) Fixed Appliances: 

(1) All fixed appliances shall be of an approved type and shall be 
connected in an approved manner and securely fastened in position. 
(See Section 551-9 for provisions on grounding.) 

(b) Lighting Fixtures: 

(1) Pendant-type fixtures or pendant cords shall not be installed. 

(2) If a lighting fixture is provided over a bathtub or in a shower 
stall, it shall be of the approved enclosed and gasketed type. 

(3) Switches shall not be located inside the tub or shower space. 

551-8. Wiring Methods and Materials. Except as specifically limited 
in this section, the wiring methods and materials included in the Na- 
tional Electrical Code shall be used in Travel Trailers. 

(a) Nonmetallic outlet boxes are acceptable only with nonmetallic 
sheathed cable. 

(b) Nonmetallic cable located 1 5 inches or less above the floor, if ex- 
posed, shall be protected from physical damage by covering boards, 
guard strips, or conduit. Cable likely to be damaged by stowage shall 
be so protected in all cases. 

(c) Metal-clad and nonmetallic cables may be passed through the cen- 
ters of the wide side of 2 by 4 studs. However, they shall be protected 
where they pass through 2 by 2 studs or at other studs or frames where 
the cable or armor would be less than IVi inches from the inside or 
outside surface. Steel plates on each side of the cable, or a tube, with 
not less than No. 16 manufacturer's standard gage wall thickness, are 
required to protect the cable. These plates or tubes shall be securely 
held in place. When the thickness of studs or frames make it imprac- 
tical or impossible to use metal plates or tubes, particular care shall be 
exercised in the design and production of the travel trailer so as to 
avoid contacting the cables with nails, screws, or other fasteners, such 
care in design shall include appropriate routing of the cables through 
studs or frames at locations where the likelihood of their being con- 
tacted by nails, screws, or other fasteners subsequent to production is 
remote. 

(d) Where metallic faceplates are used they shall be effectively 
grounded. 

(e) Switches shall be rated as follows: 

(1) For lighting circuits, switches shall have a 10-ampere, 125 
volt rating; or higher, if needed for the connected load. 

(2) For motors or other loads, switches shall have ampere or 
horsepower ratings or both adequate for loads controlled. (An "AC 
general use" snap switch may control a motor 2 horsepower or less 
with full-load current not over 80 per cent of the switch ampere rat- 
ing.) 

(f) At least 4 inches of free conductor shall be left at each outlet 
box except where conductors are intended to loop without joints. 



ARTICLE 551-TRAVEL TRAILERS 70-319 

(g) Under Chassis Wiring (Exposed to Weather). 

(1) When outdoor or under chassis wiring is exposed to moisture 
and physical damage it shall be protected by rigid metal conduit or 
liquid-tight flexible metal conduit, except electrical metallic tubing may 
be used when closely routed against frames and equipment enclosures. 

(2) The conductors shall be type NMC, RW, TW, or equivalent. 
551-9. Grounding. 

Grounding of both electrical and non-electrical metal parts in a 
Travel Trailer is through connection to a grounding bus in the Travel 
Trailer distribution panel. The grounding bus is grounded through the 
green-colored conductor in the supply cord or the feeder wiring to the 
service ground in the service entrance equipment located adjacent to 
the Travel Trailer location. Neither the frame of the Travel Trailer nor 
the frame of any appliance may be connected to the neutral conductor 
in the Travel Trailer. 

(a) Insulated Neutral. The ground circuit conductor (neutral) shall 
be insulated from the grounding conductors and from equipment en- 
closures and other grounded parts. The grounded (neutral) circuit 
terminals in the distribution panel and in countermounted cooking 
units are to be insulated from the equipment enclosure. Bonding screws, 
straps or buses in the distribution panel or in appliances are to be re- 
moved and discarded. 

(b) Equipment Grounding Means. 

(1) The green-colored grounding wire in the supply cord or perma- 
nent feeder wiring shall be connected to the grounding bus in the dis- 
tribution panel or disconnecting means. 

(2) The chassis shall be grounded. The grounding conductor may 
be solid or stranded, insulated or bare, and shall be an armored 
grounding conductor or routed in conduit if No. 10 AWG. The con- 
ductor, if No. 8 AWG stranded or larger, may be run without metal 
covering. The grounding conductor shall be connected between distribu- 
tion panel grounding terminal and a terminal on the chassis. Grounding 
terminals shall be of the solderless type and approved as pressure termi- 
nal conductors recognized for the wire size employed. The grounding 
conductors shall be routed so as not to be exposed to physical damage; 
protection can be afforded by following the configuration of the chassis. 

(3) In the electrical system, all exposed metal parts, enclosures, 
frames, lamp fixture canopies, etc. shall be effectively bonded to the 
grounding terminal or enclosure of the distribution panel. 

(4) Cord-connected appliances, such as refrigerators, and the 
electrical system of gas ranges, shall be grounded by means of an ap- 
proved cord with grounding conductor and grounding type plug. 

(c) Grounding of Noncurrent-Carrying Metal Parts. All major ex- 
posed metal parts that may become energized, including the water, gas, 
and waste plumbing, the roof and outer metallic covering, the chassis 
and metallic circulating air ducts, shall be effectively bonded to the 



70-320 MASSACHUSETTS ELECTRICAL CODE 

grounding terminal or enclosure of the distribution panel or to the metal 
chassis. See Section 551-9 (b) (2). 

551-10. Testing. Dielectric Strength: The wiring of each Travel 
Trailer shall be capable of withstanding, without breakdown, for a 
period of 1 minute, the application of an alternating potential of 900 
volts between live parts and noncurrent-carrying metal parts. 

Fixtures or permanently installed appliances shall not be required to 
withstand the dielectric test if they have been approved. 



70-321 



Chapter 6. Special Equipment 

ARTICLE 600 — ELECTRIC SIGNS AND 
OUTLINE LIGHTING 



A. General 

600-1. Scope. The provisions of this Article shall apply to the in- 
stallation of conductors and equipment for electric signs and outline 
lighting as defined in Article 100. 

600-2. Disconnect Required. Each outline lighting installation, and 
each sign of other than the portable type, shall be controlled by an ex- 
ternally operable switch or breaker which will open all ungrounded 
conductors and shall be suitable for conditions of installation, such as 
exposure to the weather. 

(a) In Sight of Sign. The switch or breaker required by Section 
600-2 shall be within sight of the sign or outline lighting which it con- 
trols or may be located elsewhere when capable of being locked in the 
open position. 

(b) Control Switch Rating. Switches, flashers, and similar devices 
controlling transformers shall be either of a type approved for the pur- 
pose, or have a current rating not less than twice the current rating of 
the transformers. On alternating-current circuits, general use alternat- 
ing-current snap switches may be used to control inductive loads other 
than motors, not exceeding the ampere rating of switch. See Section 
380-14. 

600-5. Grounding. 

(a) Signs, troughs, tube terminal boxes and other metal frames shall 
be grounded in the manner specified in Article 250 of this Code, unless 
they are insulated from ground and from other conducting surfaces 
and are inaccessible to unauthorized persons. 

(b) Isolated noncurrent-carrying metal parts of outline lighting may 
be bonded by No. 14 conductors and grounded in accordance with 
Article 250. 

(c) Signs of the portable incandescent or fluorescent-lamp type in 
which the open circuit voltage does not exceed 150 volts to ground are 
not required to be grounded. 

600-6. Load of Branch Circuit. Circuits shall be so arranged that the 
load imposed by outlets, lamps, and transformers connected to them, 
shall in no case exceed the rating of the branch circuit. 

Circuits which supply lamps, ballasts, and transformers or combina- 
tions thereof may be rated not to exceed 20 amperes. 

Circuits containing electric discharge lighting transformers exclusively 
shall not be rated in excess of 30 amperes. 



70-322 MASSACHUSETTS ELECTRICAL CODE 

600-7. Marking. 

(a) Signs shall be marked with the maker's name, and for incan- 
descent-lamp signs with the number of lampholdeis, and for electric 
discharge signs with input amperes at full load and input voltage. The 
marking of the sign shall be visible for inspection after installation. 

(b) Transformers shall be marked with the maker's name, and trans- 
formers for electric discharge signs shall be marked with the input 
rating in amperes or volt-amperes, the input voltage and the open-cir- 
cuit high-tension voltage. 

600-8. Enclosures. Enclosures for signs and outline lighting shall con- 
form to the following: 

(a) Conductors and Terminals. Conductors and terminals in sign 
boxes, cabinets, and outline troughs shall be enclosed, except the sup- 
ply leads. 

(b) Cutouts, Flashers, Etc. Cutouts, flashers, and similar devices 
shall be enclosed in metal boxes the doors of which shall be arranged 
so that they can be opened without removing obstructions or finished 
parts of the enclosure. 

(c) Strength. Enclosures shall have ample strength and rigidity. 

(d) Material. Except for portable signs of the indoor type, signs 
and outline lighting shall be constructed of metal or other noncombus- 
tible material. Wood may be used for external decoration if placed not 
less than 2 inches from the nearest lampholder or current-carrying part. 

(e) Minimum Thickness — Enclosure Metal. Sheet copper shall be at 
least 20 ounce (0.028 inch). Sheet steel may be of No. 28 USS gage 
(.0149 inch) except that for outline lighting and for electric discharge 
signs sheet steel shall be of No. 24 USS gage (.0239 inch), unless ribbed, 
corrugated or embossed over its entire surface, when it may be of No. 
26 USS gage (.0179 inch). 

(f) Protection of Metal. All steel parts of enclosures shall be gal- 
vanized or otherwise protected from corrosion. 

(g) Enclosures Exposed to the Weather. Enclosures for outside use 
shall be weatherproof and shall have an ample number of drain holes, 
each not larger than Vi inch or smaller than Va inch. Wiring connections 
shall not be made through the bottoms of enclosures exposed to the 
weather unless the enclosures are of the raintight type. 

B. Signs and Outline Lighting — 600 Volts or Less 

600-21. Installation of Conductors. Conductors shall be installed as 
follows: 

(a) Wiring Method. Conductors shall be installed as open conduc- 
tors on insulators, in rigid metal conduit, flexible metal conduit, elec- 
trical metallic tubing, metal-clad cable, metal troughing, Type ALS 
cable or Type MI cable. 

(b) Insulation and Size. Conductors shall be of a type approved for 
general use and shall be no smaller than No. 14. 



ARTICLE 600-ELECTRIC SIGNS 70-323 

Exception No. 1. Conductors in portable signs, short leads perma- 
nently attached to lampholders or ballasts, and leads in wiring chan- 
nels which are permanently attached to electric discharge lampholders 
or electric discharge ballasts and which are not longer than 8 feet may 
be smaller than No. 14 but shall not be smaller than No. 18 and shall 
be of a type approved for the purpose. 

Exception No. 2. Conductors, for signs with multiple incandescent 
lamps requiring one conductor from a control to one or more lamps 
whose total load does not exceed 250 watts, may be smaller than No. 
14 but shall not be smaller than No. 18 if in an approved cable assem- 
bly of two or more conductors. 

(c) Exposed to the Weather. Conductors in raceways, armored ca- 
ble or enclosures exposed to the weather, shall be of the lead-covered 
type or other type specially approved for the conditions, except where 
rigid conduit, electrical metallic tubing or enclosures are made raintight 
and arranged to drain. 

(d) Number of Conductors in Raceway. Number of conductors in 
raceway for sign flashers may be in accordance with Table 1 of Chap- 
ter 9. 

(e) Open Conductors. Open conductors on insulators shall comply 
with the provisions of Sections 300-2 to 300-22 inclusive, and, if out- 
doors, Article 730, except that the separation between conductors need 
be only 2 inches. 

Exception: Open conductors may be supported by lampholders lo- 
cated not more than 1 foot apart. 

(f) Conductors Soldered to Terminals. Where the conductors are 
fastened to lampholders other than of the pin type, they shall be sol- 
dered to the terminals and the exposed parts of conductors and termi- 
nals shall be treated to prevent corrosion. Where the conductors are 
fastened to pin-type lampholders which protect the terminals from the 
entrance of water, and which have been found acceptable for sign use, 
the conductors shall be of the stranded type but need not be soldered 
to the terminals. 

600-22. Lampholders. Lampholders shall be of the unswitched type 
having bodies of suitable insulating material and shall be so constructed 
and installed as to prevent turning. Miniature lampholders shall not be 
employed for outdoor signs and outline lighting. 

C. Signs and Outline Lighting — Exceeding 600 Volts 

600-31. Installation of Conductors. Conductors shall be installed as 
follows : 

(a) Wiring Method. Conductors shall be installed as open work, as 
concealed conductors on insulators, in rigid or flexible metal conduit, 
or in electrical metallic tubing. 

(b) Insulation and Size. Conductors shall be of a type approved for 
the purpose and for the voltage of the circuit and shall be not smaller 
than No. 14. 



70-324 MASSACHUSETTS ELECTRICAL CODE 

Exception No. 1. Leads in wiring channels which are permanently 
attached to electric discharge lampholders or electric discharge ballasts 
and which are not longer than 8 feet may be smaller than No. 14 but 
shall not be smaller than No. 18 and shall be of a type approved for the 
purpose. 

Exception No. 2. Leads in show-window displays or small portable 
signs that run from the line ends of the tubing to the secondary wind- 
ings of the transformer where they are permanently attached within the 
transformer enclosure and which are not longer than eight (8) feet 
may be smaller than No. 14, but shall not be smaller than No. 18 and 
shall be of a type approved for the purpose. 

(c) Bends in Conductors. Sharp bends in the conductors shall be 
avoided. 

(d) Open Conductors — Indoors. Open conductors indoors shall be 
mounted on noncombustible, nonabsorptive insulators. Insulators of 
porcelain shall be glazed on all exposed surfaces. A separation of at 
least Wi inches shall be maintained between conductors and between 
conductors and other objects. Conductors shall not be located where 
subject to physical damage. 

(e) Concealed Conductors on Insulators — Indoors. Concealed con- 
ductors on insulators shall be separated from each other and from all 
objects other than the insulators on which they are mounted by a spac- 
ing of not less than \Vi inches for voltages above 10,000 volts, and 
not less than 1 inch for voltages of 10,000 or less. They shall be in- 
stalled in channels lined with noncombustible material and used for no 
other purpose, except that the primary circuit conductors may be in 
the same channel. The insulators shall be of noncombustible, nonab- 
sorptive material. 

(f) Conductors in Raceways. Where the conductors are covered with 
lead or other metal sheathing, the covering shall extend beyond the end 
of the raceway, and the surface Of the cable shall not be injured where 
the covering terminates. 

(1) In damp or wet locations, the insulation on all conductors 
shall extend beyond the metal covering or raceway at least 4 inches for 
voltages over 10,000, 3 inches for voltages over 5,000 but not exceed- 
ing 10,000, and 2 inches for voltages of 5,000 or less. 

(2) In dry locations the insulation shall extend beyond the end of 
the metal covering or raceways not less than 2Vi inches for voltages 
over 10,000, 2 inches for voltages over 5,000 but not exceeding 10,000, 
and 1 Vi inehes for voltages of 5,000 or less. 

(3) For conductors at grounded midpoint terminals, no spacing is 
required. 

(4) A metal raceway containing a single conductor from one sec- 
ondary terminal of a transformer shall not exceed twenty feet in length. 

(g) Open Conductors — Outdoors. Open conductors outdoors shall 
be mounted on noncombustible, nonabsorptive insulators. Insulators of 
porcelain shall be glazed on all exposed surfaces. A separation of at 
least two inches shall be maintained between conductors, and between 
conductors and other objects. 



ARTICLE 600-ELECTRIC SIGNS 70-325 

Where subject to physical damage, or where within reach from 
ground, roof, or window, conductors shall be enclosed in raceways or 
suitably guarded. Where guarded, a spacing of not less than Wi 
inches shall be maintained between conductors and the enclosure un- 
less the enclosure is nonconducting and noncombustible. 

(h) Show Windows and Similar Locations. Conductors that hang 
freely in the air, away from combustible material, and where not sub- 
ject to physical damage, as in some show-window displays, need not 
be otherwise protected. 

(i) Conductors may be run from the ends of tubing to the grounded 
midpoint of transformers specifically designed for the purpose and 
provided with terminals at the midpoint. Where such connections 
are made to the transformer grounded midpoint, the connections be- 
tween the high-voltage terminals of the transformer and the line ends 
of the tubing shall be as short as possible. 

600-32. Transformers. Transformers shall comply with the following: 

(a) Voltage. The transformer secondary open-circuit voltage shall 
not exceed 15,000 volts with an allowance on test of 1000 volts addi- 
tional. In end-grounded transformers the secondary, open-circuit volt- 
age shall not exceed 7,500 volts with an allowance on test of 500 volts 
additional. 

(b) Type. Transformers shall be of a type approved for the pur- 
pose and shall be limited in rating to a maximum of 4,500 volt-amperes. 

Open core-and-coil type transformers, shall be limited to 5,000 volts 
with an allowance on test of 500 volts, and to indoor applications in 
small portable signs. 

Transformers for outline lighting installations shall have secondary 
current ratings not in excess of 30 milliamperes except where they and 
all wiring connected to them are installed in accordance with the pro- 
visions of Article 410 for electric discharge lighting of the same voltage. 

(c) Exposed to Weather. Transformers used outdoors shall be of 
the weatherproof type or shall be protected from the weather by en- 
closure in the sign body or in a separate metal box. 

(d) Transformer Secondary Connections. The high-voltage windings 
of transformers shall not be connected in parallel; and shall not be con- 
nected in series, except that two transformers each having one end of 
its high-voltage winding connected to the metal enclosure may have 
their high-voltage windings connected in series to form the equivalent 
of a midpoint grounded transformer. The grounded ends shall be con- 
nected by insulated conductors not smaller than No. 14. 

Exception: Transformers for small portable signs, show windows, 
and similar locations that are equipped with leads permanently attached 
to the secondary winding of the transformer enclosure and that do not 
extend more than eight (8) feet beyond the enclosure for attaching to 
the line ends of the tubing may have leads smaller than No. 14, but 
shall not be smaller than No. 18 and shall be of a type approved for 
the purpose. 

(e) Accessibility. Transformers shall be accessible. 



70-326 MASSACHUSETTS ELECTRICAL CODE 

600-33. Electric Discharge Tubing. Electric discharge tubing shall con- 
form to the following: 

(a) Design. The tubing shall be of such length and design as not 
to cause a continuous over-voltage on the transformer. 

(b) Support. Tubing shall be adequately supported on noncombus- 
tible, nonabsorptive supports. Tubing supports should, where practi- 
cable, be adjustable. 

(c) Contact with Flammable Material and Other Surfaces. The tub- 
ing shall be free from contact with flammable material and shall be 
located where not normally exposed to physical damage. Where operat- 
ing in excess of 7,500 volts, the tubing shall be supported on noncom- 
bustible, nonabsorptive, insulating supports which maintain a spacing 
of not less than Va inch between the tubing and the nearest surface. 

600-34. Terminals and Electrode Receptacles for Electric Discharge Tub- 
ing. Terminals and electrode receptacles for electric discharge tub- 
ing shall comply with the following: 

(a) Terminals. Terminals of the tubing shall be inaccessible to un- 
qualified persons and isolated from combustible material and grounded 
metal or shall be enclosed. Where enclosed they shall be separated from 
grounded metal and combustible material by noncombustible, nonab- 
sorptive, insulating material approved for the purpose or by YVi inches 
of air. Terminals shall be relieved from stress by the independent sup- 
port of the tubing. 

(b) Tube Connections Other Than With Receptacles. Where tubes do 
not terminate in receptacles designed for the purpose, all live parts of 
tube terminals and conductors shall be so supported as to maintain a 
separation of at least \ l /i inches between conductors or between con- 
ductors and any grounded metal. 

(c) Receptacles. Electrode receptacles for the tubing shall be of 
noncombustible, nonabsorptive insulating material approved for the 
purpose. 

(d) Bushings. Where electrodes enter the enclosure of outdoor 
signs or of an indoor sign operating at a voltage in excess of 7,500 
volts, bushings shall be used unless receptacles are provided or the sign 
is wired with bare wire mounted on approved supports which maintain 
the tubing in proper position. Bushings shall be of noncombustible, 
nonabsorptive material. Where bare wiring is used, the conductor shall 
be not less than No. 14 solid copper, shall be supported so as to prevent 
sagging and lessening of the spacing required elsewhere in this Article, 
and electrode terminal assemblies shall be of an approved type and sup- 
ported not more than 6 inches from the electrode terminals. 

(e) Show Windows. In the exposed type of show-window signs, 
terminals shall be ( 1 ) enclosed by receptacles approved for the purpose 
or (2) where hanging in air, free from grounded surfaces, enclosed in 
sleeves of vulcanized fiber, phenolic composition, or other suitable ma- 
terial which overlaps all live parts by at least Vi inch. 

(f) Receptacles and Bushing Seals. A flexible, nonconducting seal 
may be used to close the opening between the tubing and the recep- 



ARTICLE 610-CRANES AND HOISTS 70-327 

tacle or bushing against the entrance of dust or moisture. This seal 
shall not be in contact with grounded conductive material and shall not 
be depended upon for the insulation of the tubing. 

(g) Enclosures of Metal. Enclosures of metal for electrodes shall be 
of not less than No. 24 USS gage (.0239 inch) sheet metal. 

(h) Enclosures of Insulating Material. Enclosures of insulating ma- 
terial shall be noncombustible, nonabsorptive and approved for the 
voltage of the circuit. 

600-35. Switches on Doors. Doors or covers giving access to unin- 
sulated parts of indoor signs or outline lighting exceeding 600 volts 
and accessible to the general public, shall either be provided with in- 
terlock switches which on the opening of the doors or covers discon- 
nect the primary circuit, or shall be so fastened that the use of the other 
than ordinary tools will be necessary to open them. 



ARTICLE 610 — CRANES AND HOISTS 



A. Scope and Use 

610-1. Scope. The provisions of this Article shall apply to the installa- 
tion of cranes, crane runways, hoists, and monorails, and shall be addi- 
tional to, or amendatory of, the requirements prescribed in Articles 100 
to 480, inclusive, of this Code. 

For definition of various kinds of cranes and hoists see American Standard 
Safety Code for Cranes, Derricks, and Hoists, ASA B30.2 — 1943. 

610-2. Particular Locations. 

(a) Ignitible Material Hazards. Installations in hazardous locations 
shall comply with the provisions of Section 503-13. 

(b) Combustible Materials. Where a crane operates over readily 
combustible material, the resistors shall be placed in a well-ventilated 
cabinet composed of noncombustible material so constructed that it 
will not emit flames or molten metal. 

Exception: Resistors may be located in a cage or cab constructed of 
noncombustible material which encloses the sides of the cage or cab 
from the floor to a point at least 6 inches above the top of the resistors. 

B. Wiring 

610-11. Wiring Method. Conductors shall be enclosed in raceways or 
be Type ALS cable or Type MI cable. 

Exception No. 1. Bare Conductors. Bare conductors used as contact 
conductors. 

Exception No. 2. Open Conductors. Short lengths of open conduc- 
tors at resistors, collectors, and other equipment. 

Exception No. 3. Flexible Connections. Where flexible connections 
are necessary to motors and similar equipment, flexible metal conduit, 



70-328 MASSACHUSETTS ELECTRICAL CODE 

liquidtight flexible metal conduit, metal-clad cable, multiple conductor 
rubber-covered cable or an approved nonmetallic enclosure may be 
employed. 

Exception No. 4. Pendant Push-Button Stations. Where multiple 
conductor cable is used with a suspended push-button station, the sta- 
tion must be supported in some satisfactory manner that will protect 
the electrical conductors against strain. 

610-12. Raceway Terminal Fittings. Conductors leaving raceways shall 
comply with the provisions of Section 300-16. 

610-13. Types of Conductors. Conductors shall be of the rubber-cov- 
ered or the thermoplastic type except: 

Exception No. 1 . Contact Conductors. Contact conductors along run- 
ways, crane bridges and monorails may be bare and may be of hard 
drawn copper, or aluminum, or steel in the form of tees, angles, tee 
rails, or other stiff shapes. 

Exception No. 2. Flexible Conductors. Flexible conductors may be 
used to convey current and where practicable, cable reels or take-up 
devices may be employed. 

Exception No. 3. Varnished Cambric Conductors. Varnished-cambric 
conductors (Type V) or asbestos varnished cambric (Types AVA and 
A VB) may be used in dry locations. 

Exception No. 4. Type Ml Cable. Type Ml cable may be used in wet 
or dry locations within its specified temperature ratings. 

Exception No. 5. Exposed to High Temperatures. Conductors ex- 
posed to external heat or connected to resistors shall have an insulation 
approved for the temperature and location as specified in Section 310-2. 
Where conductors not having a flame-resistant outer covering are 
grouped together, the group shall be covered with a flame-resistant tape. 

610-14. Conductors 

(a) Ampacity. The allowable ampacities of conductors shall be as 
shown in Table 6 10-1 4 (a). For the ampacities of conductors between 
controllers and resistors, see Section 430-23. 

(b) Minimum. Conductors shall not be smaller than No. 14. 

Exception: No. 16 may be used for crane and hoist motor and con- 
trol circuits only when the application meets Section 610-14(a) am- 
pacity, and provided the conductors are protected against physical dam- 
age. 

(c) Contact Conductors. The size of contact wires shall be not less 
than the following: 

Distance between end Size of 

strain insulators wire 



0-30 feet No. 6 

31-60 feet No. 4 

over 60 feet No. 2 

(d) Calculation of Motor Load. The ampacity of the power supply 
conductors on the crane shall be not less than the combined short time 



ARTICLE 610-CRANES AND HOISTS 



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70-330 MASSACHUSETTS ELECTRICAL CODE 

full load ampere rating of the largest motor or group of motors for any 
single crane motion plus 50 per cent of the combined short time full 
load ampere rating of the next largest motor or group of motors. 

(e) Other Loads. Additional loads, such as heating, lighting, and air 
conditioning, shall be provided for by application of the appropriate 
sections of this Code. 

610-15. Common Return. Where a crane or hoist is operated by more 
than one motor, a common-return conductor of proper ampacity may 
be used. 

C. Contact Conductors 

610-21. Installation of Contact Conductors. Bare contact conductors 
shall conform to the following: 

(a) Contact Wires. Wires that are used as contact conductors shall 
be secured at the ends by means of approved strain insulators and shall 
be so mounted on approved insulators that the extreme limit of displace- 
ment of the wire will not bring the latter within less than Wi inches 
from the surface wired over. 

(b) Supports Along Runways. Main contact conductors carried 
along runways shall be supported on insulating supports placed at in- 
tervals not exceeding 20 feet, and these supports shall be insulating 
except for grounded rail conductors as provided in Section 610-21 (e). 
Such conductors shall be separated not less than 6 inches except for 
monorail hoists where a spacing of not less than 3 inches may be used. 
Where necessary, intervals between insulating supports may be in- 
creased up to 40 feet, the separation between conductors being in- 
creased proportionately. 

(c) Supports on Bridges. Bridge contact conductors shall be kept at 
least 2V2 inches apart and, where the span exceeds 80 feet, insulating 
saddles shall be placed at intervals not exceeding 50 feet. 

It is recommended that the distance between wires be greater than 2Vi 
inches where practicable. 

(d) Supports for Rigid Conductors. Conductors along runways and 
crane bridges, which are of the rigid type specified in Section 610-13 
Exception No. 1, shall be carried on insulating supports spaced at in- 
tervals of not more than 80 times the vertical dimension of the conduc- 
tor, but in no case greater than 15 feet, and spaced apart sufficiently to 
give a clear electrical separation of conductors or adjacent collectors of 
not less than 1 inch. Hardwood supports covered with, or impregnated 
with, insulating paint shall be acceptable insulators. 

(e) Track as Circuit Conductor. Monorail, tramrail or crane-runway 
tracks may be used as a conductor of current for one phase of a three- 
phase alternating-current system furnishing power to the carrier, crane 
or trolley, provided all of the following conditions are fulfilled: 

(1) The conductors for supplying the other two phases of the 
power supply shall be insulated. 

(2) The power for all phases shall be obtained from an insulating 
transformer. 



ARTICLE 610-CRANES AND HOISTS 70-331 

(3) The voltage shall not exceed 300 volts. 

(4) The rail serving as a conductor shall be effectively grounded 
at the transformer and may also be grounded by the fittings used for 
the suspension or attachment of the rail to a building or structure. 

(f) Electrical Continuity of Contact Conductors. All sections of bare 
rigid contact conductors shall be mechanically joined to provide a con- 
tinuous electrical connection. 

(g) Not to Supply Other Equipment. Contact conductors shall not 
be used as feeders for any equipment other than the crane or cranes 
which they are primarily designed to serve. 

(h) Locating or Guarding Contact Conductors. Contact conductors 
shall be located or guarded in such a manner that unqualified persons 
cannot inadvertently touch energized current-carrying parts. 

610-22. Collectors. Collectors shall be so designed as to reduce to a 
minimum sparking between them and the contact conductor, and when 
operated in rooms used for the storage of easily ignitible combustible 
fibers and materials the requirements of Section 503-13 shall be com- 
plied with. 

D. Control 

610-31. Runway Conductor Disconnecting Means. A disconnecting 
means shall be provided between the runway contact conductors and 
the power supply. Such disconnecting means shall consist of a motor- 
circuit switch or circuit breaker, except that a general-use switch may 
be used when the disconnecting means is provided in accordance with 
Section 610-32. This disconnecting means shall be readily accessible 
and operable from the ground, shall be arranged to be locked in the 
open position, shall open all ungrounded conductors simultaneously, 
and shall be placed within sight of the crane or hoist and the runway 
contact conductors. 

610-32. Disconnecting Means for Crane. A motor-circuit switch or cir- 
cuit breaker shall be provided in the leads from the runway contact 
conductors on all bridge cranes. Where this disconnecting means is not 
readily accessible from the crane operating station, means shall be pro- 
vided at the crane operating station to open the power circuit to the 
crane motors. 

610-33. Rating of Disconnecting Means for Crane. On both alternat- 
ing-current and direct-current crane protective panels, the continuous 
ampacity of the switch or circuit breaker required by Section 610- 
32, and mainline contactors, shall be not less than 50 per cent of the 
combined short-time ampacities of the motors, nor less than 75 per 
cent of the sum of the short-time ampacities of the motors required 
for any single crane motion. 

610-34. Limit Switch. A limit switch shall be provided for upper limit 
of travel of crane hoists. 

E. Overcurrent Protection 

610-41. Contact Conductors. The main contact conductors shall be 
protected by an overcurrent device. 



70-332 MASSACHUSETTS ELECTRICAL CODE 

610-42. Crane Motors. Where more than one motor is employed on 
a crane, each motor shall have individual overcurrent protection as 
provided in Article 430, except that where two motors operate a single 
hoist, carriage, truck, or bridge, and are controlled as a unit by one con- 
troller, the pair of motors with their leads may be protected by a single 
overcurrent device. 

F. Grounding 

610-51. Grounding. All exposed metal parts of cranes, hoists, and 
accessories, including pendant controls, shall be metallically joined to- 
gether into a continuous electrical conductor so that the entire crane or 
hoist will be grounded on installation in accordance with Article 250. 
Moving parts, other than removable accessories or attachments having 
metal-to-metal bearing surfaces, i.e., such as bridge wheels running on 
a track, shall be considered to be electrically connected to each other 
through the bearing surfaces for grounding purposes. 



ARTICLE 620 — ELEVATORS, DUMBWAITERS, 
ESCALATORS, AND MOVING WALKS 

A. Scope and General 

620-1. Scope. This Article shall apply to electrical equipment and 
wiring used in connection with elevators, dumbwaiters, escalators, and 
moving walks. 

620-2. Voltage Limitations. The nominal voltage used for elevator, 
dumbwaiter, escalator, and moving walk operating control and signal 
circuits, operating equipment, driving machine motors, machine brakes, 
and motor-generator sets shall not exceed the following : 

(a) For operating control and signal circuits and related equipment 
including door operator motors: 300 volts except that higher potentials 
may be used for frequencies of 25 through 60 cycles alternating cur- 
rent or for direct current provided the current in the system cannot, 
under any conditions, exceed 8 milliamperes for alternating current or 
30 milliamperes for direct current. 

(b) Driving machine motors, machine brakes, and motor-generator 
sets: 600 volts, except that higher potentials may be used for driving 
motors of motor-generator sets. 

620-3. Live Parts Enclosed. All live parts of electrical apparatus in the 
hoistways, at the landings, or in or on the cars of elevators and dumb- 
waiters or in the wellways or the landings of escalators or moving walks 
shall be enclosed to protect against accidental contact. 

B. Conductors 

620-11. Insulation of Conductors. The insulation of conductors in- 
stalled in connection with elevators, dumbwaiters, escalators and mov- 
ing walks, shall comply with the following: 



ARTICLE 620-ELEVATORS, DUMBWAITERS 70-333 

(a) Control Panel Wiring. Conductors from panels to main circuit 
resistors shall be flame-retardant and suitable for a temperature of not 
less than 90°C. (194°F.) All other wiring on control panels shall be 
flame-retardant, moisture-resistant. 

(b) Traveling Cables. Traveling cables used as flexible connections 
between the elevator or dumbwaiter car and the raceway shall be Type 
E, EO, or ET elevator cable or other approved types and shall have a 
flame-retardant, moisture-resistant outer covering. 

(c) Other Wiring. All conductors in the raceways and in or on the 
cars of elevators and dumbwaiters and in the wellways of escalators 
and moving walks and in the machine room of elevators, dumbwaiters, 
escalators and moving walks shall have flame-retardant and moisture- 
resistant insulation. 

(d) Thickness of Insulation. The thickness of the insulation of all 
conductors shall be suitable for the voltage to which the conductors are 
subjected. 

620-12. Minimum Size of Conductors. The minimum size of conduc- 
tors used for elevator, dumbwaiter, escalator, and moving walk wiring, 
except for conductors which form an integral part of control equip- 
ment, shall be as follows : 

(a) Traveling Cables. 

(1) For lighting circuits: No. 14, except that No. 20 or larger con- 
ductors may be used in parallel provided the ampacity is equivalent to 
at least that of No. 14 wire. 

(2) Operating control and signal circuits: No. 20. 

(b) Other Wiring. All operating control and signal circuits: No. 20. 

620-13. Motor Circuit Conductors. Conductors supplying elevator, 
dumbwaiter, escalator, or moving walk motors shall have an ampacity 
conforming to (a), (b) and (c) below based on the nameplate current 
rating of the motors. With generator field control, the ampacity shall 
be based on the nameplate current rating of the driving motor of the 
motor-generator set which supplies power to the elevator motor. 

The heating of conductors depends on root mean square current values 
which, with generator field control, are reflected by the nameplate current 
rating of the motor-generator set driving motor rather than by the rating of 
the elevator motor which represents actual but short time and intermittent 
full-load current values. 

(a) Conductors Supplying a Single Motor. Conductors supplying a 
single motor shall have an ampacity in conformance with Section 430- 
22, Table 430-22 (a-Exception). 

(b) Conductors Supplying Several Motors. Conductors supplying 
several motors shall have an ampacity of not less than 125 per cent of 
the nameplate current rating of the highest rated motor in the group 
plus the sum of the nameplate current ratings of the remainder of the 
motors in the group. 

(c) Feeder Demand Factor. Feeder conductors of less capacity than 
required by (b) above may be furnished subject to the requirements of 
Section 430-26. 



70-334 MASSACHUSETTS ELECTRICAL CODH 

C. Wiring 

620-21. Wiring Methods. Conductors located in hoistways and esca- 
lators and moving walk wellways, in or on cars and machine and con- 
trol rooms, not including the traveling cables connecting the car and 
hoistway wiring, shall be installed in rigid conduit, electrical metallic 
tubing, metal wireways, Type ALS cable or Type MI cable subject to 
the following exceptions: 

Exception No. 1 . Flexible conduit or Type AC metal-clad cable may 
be used in hoistways and in escalator and moving walk wellways be- 
tween risers and limit switches, interlocks, operating buttons, and sim- 
ilar devices. 

Exception No. 2. Short runs of flexible conduit or Type AC metal- 
clad cable may be used on cars where so located as to be free from oil 
and if securely fastened in place. 

Exception No. 3. Types S, SO, and ST cords may be used as flexible 
connections between the fixed wiring on the car and the switches on 
car doors or gates. 

Exception No. 4. Conductors between control panels and machine 
motors, machine brakes, and motor generator sets, not exceeding six 
feet in length, may be grouped together and taped or corded without 
being installed in a raceway provided the taping or cording is painted 
with an insulating paint. Such cable groups shall be supported at inter- 
vals of not more than three feet and so located as to be free from phys- 
ical damage. 

Where motor generators and machine motors are located adjacent 
to or underneath control equipment, and are provided with extra length 
terminal leads not exceeding six feet in length, such leads may be ex- 
tended to connect directly to controller terminal studs without regard 
to the carrying capacity requirements of Articles 430 and 445. Auxili- 
ary gutters may be used in machine and control rooms between con- 
trollers, starters and similar apparatus. 

D. Installation of Conductors 

620-31. Raceway Terminal Fittings. Conductors leaving raceways 
shall comply with the provisions of Section 300-16. In no case shall the 
raceway terminate less than 6 inches from the floor. 

620-32. Metal Wireways. Section 362-5 shall not apply to wireways. 
The sum of the cross sectional area of the individual conductors in a 
metallic wireway shall not be more than 50 per cent of the interior cross 
sectional area of the wireway. 

Vertical runs of wireways shall be securely supported at intervals not 
exceeding 15 feet and shall have not more than one joint between sup- 
ports. Adjoining wireway sections shall be securely fastened together to 
provide a rigid joint. 

620-33. Number of Conductors in Other Raceways. The number of 
operating and control circuit conductors in other raceways may be in 
accordance with Table 1 of Chapter 9. 

620-34. Supports. Supports for Type ALS cable or conductor race- 
ways in the hoistway or escalator or moving walk wellway shall be se- 



ARTICLE 620-ELEVATORS, DUMBWAITERS 70-335 

curely fastened to the guide rail or to the hoistway or wellway con- 
struction. 

620-35. Auxiliary Gutters (Wiring Troughs). Auxiliary gutters shall 
not be subject to the restrictions of Section 374-2 as to length or of Sec- 
tion 374-5 as to number of conductors. 

620-36. Different Systems in One Raceway or Traveling Cable. Con- 
ductors for operating, control, power, signal, and light circuits of 600 
volts or less may be run in the same traveling cable or raceway sys- 
tem provided that all conductors are insulated for the maximum voltage 
found in the cables or raceway system and all live parts of the equip- 
ment are insulated from ground for this maximum voltage. Such a trav- 
eling cable or raceway may also include a pai " of telephone conduc- 
tors for the car telephone provided such conductors are insulated for 
the maximum voltage found in the cable or raceway system. 

620-37. Foreign Wires. Main feeders for supplying power to elevators 
and dumbwaiters shall be installed outside the hoistway, except in exist- 
ing structures subject to special permission of the enforcing authority. 
Only such electrical wiring, conduit and cable used directly in connec- 
tion with the elevator or dumbwaiter, including wiring for signals, for 
communication with the car, for lighting and ventilating the car and 
wiring for low voltage fire detecting systems for the hoistways, may be 
installed inside the hoistway. 

E. Traveling Cables 

620-41. Suspension. Traveling cables shall be so suspended at the car 
and hoistway end as to reduce the strain on the individual copper con- 
ductors to a minimum. 

Cables exceeding 100 feet in length and which have steel support- 
ing fillers shall be suspended directly by the steel supporting fillers. 

Where nonmetallic fillers are used, the cables shall be suspended by 
looping the cables around the supports. 

620-42. Hazardous Locations. In hazardous locations, traveling ca- 
bles shall be Type EO and shall be secured to explosion proof cabi- 
nets by heavy-duty rubber-bushed threaded connector bushings sealed 
off at the enclosure as provided in Section 501-5. 

620-43. Location of and Protection for Cables. Traveling cable sup- 
ports shall be so located as to reduce to a minimum the possibility of 
damage due to the cables coming in contact with the hoistway construc- 
tion or equipment in the hoistway. Where necessary, suitable guards 
shall be provided to protect the cables against damage. 

F. Control 

620-51. Disconnecting Means. There shall be in addition to the ele- 
vator controller, a means for disconnecting all conductors of the cir- 
cuit to the elevator motor, or in the case of generator field control, to 
the motor of the motor-generator set which supplies current to the ele- 
vator motor. 

(a) Type. The disconnecting means shall be an enclosed externally 
ooerable motor circuit switch or circuit breaker arranged to be locked 
in he open position. 



70-336 MASSACHUSETTS ELECTRICAL CODE 

(b) Location. It shall be located adjacent to and be visible from the 
elevator machine, unless a disconnect switch in the control circuit of 
the motor-generator set is placed adjacent to and is visible from the 
elevator machine. 

620-52. Electrical Equipment in Garages and Similar Occupancies. 

Electrical equipment and wiring used for elevators, dumbwaiters, es- 
calators, and moving walks in garages shall conform to the require- 
ments of Article 511. Wiring and equipment located under the car plat- 
form shall be considered as being located in the hazardous area. 

620-53. Phase Protection. Elevators driven by polyphase alternating 
current machine motors shall be provided with means to prevent start- 
ing of the elevator motor when: 

(a) The phase rotation is in the wrong direction, or 

(b) There is a failure in any phase. . 

G. Overcurrent Protection 

620-61. Overcurrent Protection. Overcurrent protection shall be pro- 
vided as follows: 

(a) Control and Operating Circuits. Control and operating circuits 
and signal circuits shall be protected against overcurrent in accordance 
with the requirements of Section 725-18. 

(b) Motors. 

(1) Duty on elevator and dumbwaiter driving machine motors and 
driving motors of motor generators used with generator field control 
shall be classed as intermittent. Such motors shall be protected against 
overcurrent in accordance with Section 430-33. 

(2) Duty on escalator and moving walk driving machine motors 
shall be classed as continuous. Such motors shall be protected against 
overcurrent in accordance with Section 430-32. 

(3) Elevator, dumbwaiter, escalator, and moving walk driving ma- 
chine motors and driving motors of motor generator sets shall be pro- 
tected against running overcurrent as provided in Table 430-37, except 
that no more than two overcurrent protective units shall be required. 

H. Machine Room 

620-71. Guarding Equipment. Elevator, dumbwaiter, escalator, and 
moving walk driving machines, motor generator sets, controllers and 
auxiliary control equipment shall be installed in a space secured against 
unauthorized access. 

Such equipment may be located in rooms or spaces containing other 
equipment essential to the operation of the building provided it is sepa- 
rated therefrom by a substantial metal grill enclosure of a design 
which will reject a ball two inches in diameter and is at least six feet 
high equipped with a self-closing and self-locking door. 

It is not intended to prohibit the installation of dumbwaiter, esca- 
lator, or moving walk controllers outside the spaces herein specified, 
provided they are enclosed in cabinets with doors or removable panels 



ARTICLE 620-ELEVATORS, DUMBWAITERS 70-337 

capable of being locked in the closed position; nor is it intended to pre- 
vent the installation of dumbwaiter controllers within the hoistway 
without cabinets, provided removable or hinged panels capable of be- 
ing locked in the closed position are installed in the hoistway enclo- 
sures to provide access to the controllers. 

620-72. Clearance Around Control Panels. There shall be provided 
sufficient clear working space around control panels to provide safe 
and convenient access to all live parts of the equipment necessary for 
maintenance and adjustment. The minimum clear working space about 
live parts on control panels shall not be less than set forth in Section 
620-72 (a and b) unless otherwise specified. 

(a) Elevator and Dumbwaiter Panels. 

(1 ) In the front — 30 inches to live panel parts. 

(2) In the rear — 24 inches to live panel parts. 

(3) On one side of a panel or a group of panels — 18 inches except 
this clearance can be waived if there is a clear passageway, not less than 
18 inches wide at any point, from the front to the rear of the panel or 
panels. 

It shall be permissible to mount control panels on, over or against the 
hoisting machine or motor generator set or to place auxiliary control 
equipment in the front or rear of control panels provided the clearances 
to the live parts are not less than specified and provided there is safe ac- 
cess to the front and/or back of the controller from at least one side. 

Where control panels are mounted in cabinets with swing doors or 
removable panels, sufficient clear space shall be provided to fully open 
the doors or remove the panels. 

(b) Escalator and Moving Walk Control Panels. The minimum 
working clearance for escalator and moving walk control panels shall 
be as specified in Section 620-72 (a) provided that where the control 
panel is mounted in the same space as the escalator or moving walk 
drive machine and the clearances specified cannot be provided, they 
may be waived where the entire panel is arranged so that it can be read- 
ily removed from the machine space and is provided with flexible leads 
to all external connections. 

Where control panels are not located in the same space as the drive 
machine they shall be so located in cabinets with doors or removable 
panels capable of being locked in the closed position. Such cabinets may 
be mounted in the balustrading on the side away from the moving steps 
or moving treadway. 

J. Grounding 

620-81. Metal Raceways Attached to Cars. Conduit, Type ALS cable 
or Type AC metal-clad cable attached to elevator cars shall be bonded 
to grounded metal parts of the car with which they come in contact. 

620-82. Electric Elevators. For electric elevators, the frames of all mo- 
tors, elevator machines, controllers and the metal enclosures for all 
electrical devices in or on the car or in the hoistway shall be grounded. 



70-338 MASSACHUSETTS ELECTRICAL CODE 

620-83. Nonelectric Elevators. For elevators other than electric, 
when any electrical conductors are attached to the car, the metal frame 
of the car, where normally accessible to persons, shall be grounded. 

620-84. Hand-Operated Cables. All hand-operated metallic shifting 
ropes or cables shall be grounded. 

620-85. Inherent Ground. Equipment mounted on members of the 
structural metal frame of a building shall be deemed to be grounded. 
Metal car frames supported by metal hoisting cables attached to or run- 
ning over sheaves or drums of elevator machines shall be deemed to be 
grounded when the machine is grounded in accordance with Article 
250. 

K. Overspeed 

620-91. Overspeed Protection for DC Elevators. Under overhauling 
load conditions, means shall be provided on the load side of each 
elevator power disconnecting means to prevent the elevator from at- 
taining a speed equal to the governor tripping speed or a speed in ex- 
cess of 125 per cent of the elevator rated speed, whichever is the lesser. 

620-92. Motor Generator Overspeed Device. Motor generators driven 
by direct current motors and used to supply direct current for the op- 
eration of elevator machine motors shall be provided with speed limit- 
ing devices as required by Section 430-89 (c), which will prevent the 
elevator from attaining at any time a speed of more than 125 per cent 
of its rated speed. 



ARTICLE 630 — ELECTRIC WELDERS 



A. General 

630-1. Scope. This Article covers electric arc welding, resistance weld- 
ing apparatus, and other similar welding equipment that is connected to 
an electrical supply system. 

630-2. Other Articles. This Article amplifies or modifies parts of Chap- 
ters 1 to 4 inclusive of this Code in order to properly cover the operat- 
ing conditions to which electric welder installations are subjected. Ac- 
cordingly, the appropriate provisions of Chapters 1 to 4 inclusive apply 
to the component parts of electric welder installations except as other- 
wise provided in this Article. 

B. AC Transformer and DC Rectifier Arc Welders 

630-11. Ampacities of Supply Conductors. The ampacities of conduc- 
tors shall be as follows: 

(a) Individual Welders. The rated ampacities of the supply conduc- 
tors shall be not less than the current values determined by multiplying 
the rated primary current in amperes, given on the welder nameplate, 
and the following factor based upon the duty cycle or time rating of the 
welders: 



ARTICLE 630-ELECTRIC WELDERS 70-339 

Rated Per Cent Duty 
Cycle of Welders Multiplying Factor 

20 or less 0.45 

30 0.55 

40 0.63 

50 6.71 

60 0.78 

70 0.84 

80 0.89 

90 0.95 

100 1.00 

For a welder having a time rating of one hour, the multiplying factor shall 

be 0.75. 

(b) Group of Welders. The rated ampacities of conductors which sup- 
ply a group of welders may be less than the sum of the currents, as de- 
termined in accordance with Section 630-1 1.( a) of the welders supplied. 
The conductor rating shall be determined in each case according to 
the welder loading based on the use to be made of each welder and the 
allowance permissible in the event that all the welders supplied by the 
conductors will not be in use at the same time. The load value used for 
each welder shall take into account both the magnitude and the dura- 
tion of the load while the welder is in use. 

Conductor ratings based on 100 per cent of the current, as determined 
in accordance with Section 630-11 (a), of the two largest welders, 85 per 
cent for the third largest welder, 70 per cent for the fourth largest welder, 
and 60 per cent for all the remaining welders, should provide an ample mar- 
gin of safety under high production conditions with respect to the maximum 
permissible temperature of the conductors. Percentage values lower than 
those given are permissible in cases where the work is such that a high op- 
erating duty cycle for individual welders is impossible. 

630-12. Overcurrent Protection. Overcurrent protection shall be as 
provided in Section 630-12(a and b). Where the nearest standard rat- 
ing of the overcurrent device used is under the value specified in this 
Section, or where the rating or setting specified results in unnecessary 
opening of the overcurrent device, the next higher rating or setting may 
be used. 

(a) For Welders. Each welder shall have overcurrent protection 
rated or set at not more than 200 per cent of the rated primary current 
of the welder, except that an overcurrent device is not required for a 
welder having supply conductors protected by an overcurrent device 
rated or set at not more than 200 per cent of the rated primary current 
of the welder. 

(b) For Conductors. Conductors which supply one or more welders 
shall be protected by an overcurrent device rated or set at not more 
than 200 per cent of the conductor rating. 

630-13. Disconnect Means. A disconnect means shall be provided in 
the supply connection of each welder which is not equipped with a dis- 
connect mounted as an integral part of the welder. 

The disconnect means shall be a switch or circuit breaker and its 
rating shall be not less than that necessary to accommodate overcur- 
rent protection as specified under Section 630-12. 



70-340 MASSACHUSETTS ELECTRICAL CODE 

630-14. Marking. A nameplate giving the following information shall 
be provided: name of manufacturer; frequency; primary voltage; rated 
primary current; maximum open-circuit secondary voltage; rated sec- 
ondary current; basis of rating, i.e., the duty cycle, number of phases, 
60-minute rating. 

C. Motor-Generator Arc Welders 

630-21. Other Sections Which Apply. Motor-generator arc welder in- 
stallations are covered by the appropriate Sections of Chapters 1 to 4 
inclusive applicable to conductors, motors, generators and associated 
equipment. Referring specifically to the motor supply connections, the 
following Sections apply in addition to such other provisions as may be 
applicable. Conductor rating, Sections 430-22 and 430-26. Overcurrent 
protection for motors, Section 430-33; for conductors, Section 430-52. 
Controllers, Sections 430-7, 430-8 and 430-83. Disconnecting means, 
Section 430-1 11. 

D. Resistance Welders 

630-31. Ampacities of Supply Conductors. The ampacities of the sup- 
ply conductors necessary to limit the voltage drop to a value permissible 
for the satisfactory performance of the welder are usually greater than 
that required to prevent overheating as prescribed in Section 630-31 
(a and b). 

(a) Individual Welders. The rated ampacities for conductors for in- 
dividual welders shall conform to the following: 

(1) Varying Operations. The rated ampacities of the supply con- 
ductors for a welder which may be operated at different times at differ- 
ent values of primary current or duty cycle shall be not less than 70 
per cent of the rated primary current for seam and automatically fed 
welders, and 50 per cent of the rated primary current for manually op- 
erated nonautomatic welders. 

(2) Specific Operation. The rated ampacities of the supply con- 
ductors for a welder wired for a specific operation for which the actual 
primary current and duty cycle are known and remain unchanged shall 
be not less than the product of the actual primary current and the mul- 
tiplier given below for the duty cycle at which the welder will be op- 
erated. 

Duty Cycle 

(percent) 50 40 30 25 20 15 10 7.5 5.0 or less 

Multiplier 71 .63 .55 .50 .45 .39 .32 .27 .22 

(b) Groups of Welders. The rated ampacities of conductors which 
supply two or more welders shall be not less than the sum of the value 
obtained as explained in Section 630-3 1(a) for the largest welder sup- 
plied, and 60 per cent of the values obtained as explained in Section 
630-3 1(a) for all the other welders supplied. 

(c) Explanation of Terms. ( 1 ) The rated primary current is the rated 
kva multiplied by 1 ,000 and divided by the rated primary voltage, using 
values given on the nameplate. (2) The actual primary current is the 
current drawn from the supply circuit during each welder operation at 
the particular heat tap and control setting used. (3) The duty cycle is 



ARTICLE 640-SOUND-RECORDING, SIMILAR EQUIPMENT 70-341 

the percentage of the time during which the welder is loaded. For in- 
stance, a spot welder supplied by a 60-cycle system (216,000 cycles per 
hour) making four hundred 15-cycle welds per hour would have a duty 
cycle of 2.8 per cent (400 multiplied by 15, divided by 216,000, multi- 
plied by 100). A seam welder operating 2 cycles "on" and 2 cycles "off" 
would have a duty cycle of 50 per cent. 

630-32. Overcurrent Protection. Overcurrent protection shall be as 
provided in Section 630-32(a and b). Where the nearest standard rat- 
ing of the overcurrent device used is under the value specified in this 
Section, or where the rating or setting specified results in unnecessary 
opening of the overcurrent device, the next higher rating or setting may 
be used. 

(a) For Welders. Each welder shall have an overcurrent device 
rated or set at not more than 300 per cent of the rated primary current 
of the welder, except that an overcurrent device is not required for a 
welder having a supply circuit protected by an overcurrent device rated 
or set at not more than 300 per cent of the rated primary current of the 
welder. 

(b) For Conductors. Conductors which supply one or more welders 
shall be protected by an overcurrent device rated or set at not more 
than 300 per cent of the conductor rating. 

630-33. Disconnecting Means. A switch or circuit breaker shall be 
provided by which each welder and its control equipment can be iso- 
lated from the supply circuit. The ampacity of this disconnecting means 
shall be not less than the supply conductor rating determined as ex- 
plained in this Article. The supply circuit switch may be used as the 
welder disconnecting means where the circuit supplies only one welder. 

630-34. Marking. A nameplate giving the following information shall 
be provided: name of manufacturer, frequency, primary voltage, rated 
kva at 50 per cent duty cycle, maximum and minimum open-circuit sec- 
ondary voltage, short-circuit secondary current at maximum secondary 
voltage and specified throat and gap setting. 



ARTICLE 640 — SOUND-RECORDING AND 
SIMILAR EQUIPMENT 



640-1. Scope. This Article shall apply to installations of equipment 
and wiring used for sound-recording and reproduction, centralized dis- 
tribution of sound, public address, speech-input systems and electronic 
organs. 

640-2. Application of Other Articles. 

(a) Except as modified by this Article, wiring and equipment from 
source of power to and between devices connected to the interior wir- 
ing systems shall comply with the requirements of Chapters 1 to 4, in- 
clusive, of this Code. 



70-342 MASSACHUSETTS ELECTRICAL CO DE 

(b) Wiring and equipment for public-address, speech-input, radio- 
frequency, audio-frequency systems, and amplifying equipment asso- 
ciated with radio receiving stations in centralized distribution systems, 
shall comply with Article 725. 

640-3. Number of Conductors in Raceway. The number of conductors 
in a conduit or other raceway shall comply with Tables 1 to 7 inclusive 
of Chapter 9 except as follows: 

Exception No. 1. Special permission may be granted for the installa- 
tion of two 2-conductor lead-covered cables in 3 A-inch conduit, pro- 
vided the cross-sectional area of each cable does not exceed .11 square 
inch. 

Exception No. 2. Special permission may be granted for the installa- 
tion of two 2-conductor No. 19 lead-covered cables in V2-inch con- 
duit, provided the sum of the cross-sectional areas of the cables does 
not exceed 32 per cent of the internal cross-sectional area of the con- 
duit. 

640-4. Wireways and Auxiliary Gutters. 

(a) Wireways and auxiliary gutters shall comply with the require- 
ments of Articles 362 and 374. 

(b) Where used for sound-recording and reproduction the following 
exceptions are made: 

Exception No. 1 . Number of Conductors in Raceway. Conductors in 
wireways or gutters shall not fill the raceway to more than 75 per cent of 
its depth. 

Exception No. 2. Auxiliary-Gutter Covers. Where the cover of aux- 
iliary gutters is flush with the flooring and is subject to the moving of 
heavy objects it shall be of steel at least : A inch in thickness; where not 
subject to moving of heavy objects, as in the rear of patch or other 
equipment panels, the cover shall be at least No. 10 USS gage (0.1345 
inch ) . 

Exception No. 3. Metal-Trough Raceways. Metal-trough raceways 
may be installed in concealed places provided they are run in a straight 
line between outlets or junction boxes. Covers of boxes must be acces- 
sible. Edges of metal must be rounded at outlet or junction boxes and 
all rough projections smoothed to prevent abrasion of insulation or 
conductors. Raceways made of sections shall be bonded and grounded 
as prescribed in Section 250-76. 

Exception No. 4. Grounding Wireways and Auxiliary Gutters. Metal 
wireways and auxiliary gutters shall be grounded in accordance with 
the requirements of Article 250. Where the wireway or auxiliary gutter 
does not contain power supply wires, the grounding conductor need 
not be larger than No. 14 copper or its equivalent. Where the wireway 
or auxiliary gutter contains power supply wires, the grounding conduc- 
tor shall not be smaller than the size called for in Section 250-95. 

640-5. Conductors. Amplifier output circuits carrying audio-program 
signals of 70 volts or less and whose open circuit voltage will not ex- 
ceed 100 volts, may employ Class 2 wiring as covered in Article 725. 



ARTICLE 640-SOUND-RECORDING, SIMILAR EQUIPMENT 70-343 

The above is based on amplifiers whose open-circuit voltage will not ex- 
ceed 100 volts when driven with a signal at any frequency from 60 to 100 cps 
sufficient to produce rated output (70.7 volts) into its rated load. This also 
accepts the known fact that the average program material is 12 db below the 
amplifier rating — thus the average RMS voltage for an open-circuit 70 volt 
output would be only 25 volts. 

640-6. Grouping of Conductors. Conductors of different systems 
grouped in the same conduit or other metallic enclosure, or in portable 
cords or cables, shall comply with the following requirements: 

(a) Power-Supply Conductors. Power-supply conductors shall be 
properly indicated and shall be used solely for supplying power to the 
equipment to which the other conductors are connected. 

(b) Leads to Motor-Generator or Rotary Converter. Input leads to a 
motor-generator or rotary converter shall be run separately from the 
output leads. 

(c) Conductor Insulation. The conductors shall be insulated indi- 
vidually, or collectively in groups, by insulation at least equivalent to 
that on the power-supply and other conductors. 

Exception: Where the power-supply and other conductors are sepa- 
rated by a lead sheath or other continuous metallic covering. 

640-7. Flexible Cords. Flexible cords and cables shall be of types P, 
K, S, SJ, ST, SJO, and SJT or other types specifically approved for the 
purpose for which they are to be used. The conductors of flexible cords, 
other than power-supply conductors, may be of a size not smaller than 
No. 26 provided such conductors are not in direct electrical connection 
with the power-supply conductors and are equipped with current-limit- 
ing means so that the maximum power under any condition will not ex- 
ceed 150 watts. 

640-8. Terminals. Terminals shall be marked to show their proper 
connections. Terminals for conductors other than power-supply con- 
ductors shall be separated from the terminals of the power-supply con- 
ductors by a spacing at least as great as the spacing between power- 
supply terminals of opposite polarity. 

640-9. Storage Batteries. Storage batteries shall comply with the fol- 
lowing: 

(a) Installation. Storage batteries shall be installed in accordance 
with Article 480. 

(b) Conductor Insulation. Storage-battery leads shall be rubber- 
covered or thermoplastic-covered. 

640-10. Overcurrent Protection of "A", "B" and "Q" Circuits. Over- 
current protection shall be provided as follows: 

(a) "A" circuit, where supplied by branch-lighting circuits, or by 
storage batteries of more than 20-ampere-hour capacity, shall have 
overcurrent protection not exceeding 15 amperes. 

(b) k 'B" circuits shall have overcurrent protection not exceeding one 
ampere. The overcurrent protection shall be placed in each positive 
lead. 



70-344 MASSACHUSETTS ELECTRICAL CODE 

(c) "C" circuits where supplied from branch lighting circuits or 
from storage batteries of more than 20 ampere-hour capacity shall have 
overcurrent protection not exceeding one ampere. 

(d) Overcurrent devices shall be located as near as practicable to the 
battery. 

640-1 1 . Amplifiers and Rectifiers— Type. 

(a) They shall be suitably housed and shall be of a type approved for 
the purpose unless otherwise expressly permitted by the authority en- 
forcing this Code. 

(b) Amplifiers and rectifiers shall be so located as to be readily acces- 
sible. 

(c) Amplifiers and rectifiers shall be so located as to provide suffi- 
cient ventilation to prevent undue temperature rise within the housing. 

640-12. Hazardous Locations. Equipment used in hazardous locations 
shall be specifically approved for the purpose. 

640-13. Protection Against Physical Damage. Amplifiers, rectifiers, 
loud-speakers and other equipment shall be so located or protected as 
to guard against physical damage such as might result in fire or per- 
sonal hazard. 



ARTICLE 650 — ORGANS 



650-1. General. This Article shall apply to those electric circuits and 
parts of electrically operated organs which are employed for the con- 
trol of the sounding apparatus and keyboards. Electronic organs shall 
comply with the appropriate provisions of Article 640. 

650-2. Source of Energy. The source of energy shall have a potential 
of not over 15 volts and shall be a self-excited generator, a two-coil 
transformer type rectifier or a primary battery. 

650-3. Insulation— Grounding. The generator shall be effectively in- 
sulated from the ground and from the motor driving it, or both the gen- 
erator and the motor frames shall be grounded in the manner pre- 
scribed in Article 250. 

650-4. Conductors. Conductors shall comply with the following: 

(a) Size. No conductor shall be smaller than No. 26, and the 
common-return conductor shall be not smaller than No. 14. 

(b) Insulation. Conductors shall have rubber, thermoplastic, as- 
bestos, cotton, or silk insulation, except the common-return conductor 
which shall be rubber-covered, thermoplastic, asbestos-covered (types 
AA, AI, or AIA), or slow-burning (type SB). The cotton or silk may be 
saturated with paraffin if desired. 

(c) Conductors to Be Cabled. Except the common-return conductor, 
and conductors inside the organ proper, the organ sections and the or- 



ARTICLE 660-X-RAY EQUIPMENT 70-345 

gan console, conductors shall be cabled. The common-return conduc- 
tor may be placed under an additional covering enclosing both cable 
and return conductor, or may be installed as a separate conductor and 
may be in contact with the cable. 

(d) Cable Covering. The cable shall be provided with one or more 
braided outer coverings, provided that a tape may be used in place of 
an inner braid. Where not installed in metal raceways the outer braid 
shall be flame-retardant or shall be covered with a closely-wound fire- 
proof tape. 

650-5. Installation of Conductors. Cables shall be securely fastened in 
place and may be attached directly to the organ structure without in- 
sulating supports. Cables shall not be placed in contact with other con- 
ductors. 

650-6. Overcurrent Protection. Circuits shall be so arranged that all 
conductors, except the main supply conductors and the common-return 
conductor, shall be protected from overcurrent by an overcurrent de- 
vice of not greater than 15-ampere rating. 



ARTICLE 660 — X-RAY EQUIPMENT 



A. Scope and Installation 

660-1. Scope. The provisions of this Article shall apply to all X-ray 
equipment operating at any frequency or voltage for medical or indus- 
trial use, or for any other purpose. 

Nothing in this Article shall be construed as specifying safeguards against 
the useful beam or stray X-ray radiation. 

Recommendations for radiation protection by the National Committee on 
Radiation Protection and Measurement are published as National Bureau of 
Standards Handbooks obtainable from Superintendent of Documents, Wash- 
ington 25, D.C. 

660-2. Hazardous Locations or 600 Volt Supply. Unless approved for 
the location, X-ray and related equipment shall not be installed or oper- 
ated in hazardous locations or operated on a supply potential of more 
than 600 volts. 

660-3. Connection to Supply Circuit. 

(a) Stationary Equipment. X-ray equipment permanently installed 
shall be connected to the power supply by means of a wiring method 
meeting the general requirements of this Code, except that equipment 
properly supplied by branch circuits not larger than a 30-ampere 
branch circuit may be supplied through suitable plug and hard service 
cable or cord. 

(b) Portable and Transportable. Individual branch circuits shall not 
be required for portable X-ray equipment requiring a capacity not ex- 
ceeding 50 amperes. Portable type X-ray equipment of any capacity 
shall be supplied through a suitable plug and hard service cable or cord. 



70-346 MASSACHUSETTS ELECTRICAL CODE 

Transportable X-ray equipment of any capacity may be connected to 
its power supply by suitable temporary connections and hard service 
cable or cord. 

660-4. Disconnecting Means. A disconnecting means of adequate ca- 
pacity for at least 50 per cent of the input required for the momentary 
rating of the X-ray equipment shall be provided in the supply circuit and 
it shall be operable from a location readily accessible from the X-ray 
control. For equipment requiring 125 volt line fuses of 30 ampere or 
less, a plug and receptacle of proper size and of an approved make 
may serve as a disconnecting means. Disconnecting means shall not be 
required for portable X-ray equipment of any capacity which complies 
with section 660-1 1. 

Definitions: 

Continuous rating. Continuous rating is a constant load which can be 
carried for an indefinite period of time. 

Long time rating. A long time rating is the rating based on an operating 
interval of 5 minutes or longer. 

Momentary rating. A momentary rating is the rating based on an oper- 
ating interval that does not exceed 5 seconds. 

660-5. Branch Circuit and Overcurrent Protection Requirements. Fifty 
per cent of the momentary rating of the X-ray equipment shall be used 
in determining the ampacity requirements for branch circuits and over- 
current protection devices. 

The ampacities of the branch circuit conductors and the ratings of discon- 
necting means and overcurrent protection for X-ray equipment is usually 
recommended by the manufacturer for the specific installation. 

660-6. Wiring Terminals. Unless provided with a permanently at- 
tached cord or a cord set, X-ray equipment shall be provided with suit- 
able wiring terminals or leads for the connection of conductors of at 
least the size required by the input load corresponding to the long time 
rating of the equipment. 

660-7. Number of Conductors in Raceway. The number of control 
circuit conductors installed in a raceway may be in accordance with 
Table 1 of Chapter 9. 

660-8. X-ray Installations. 

(a) Shockproof Installations. All new equipment used on new in- 
stallations of X-ray equipment, or used or reconditioned equipment 
moved to and reinstalled at a new location, shall be of the approved 
shockproof type, except as provided for in Section 660-8 (b). All con- 
trols, tables, X-ray tube stands, transformer tanks, shockproof cables, 
and X-ray tube heads, etc. shall be suitably grounded to prevent acci- 
dental shock to patient or operator. 

(b) Nonshockproof Re-installations. No nonshockproof X-ray equip- 
ment shall be reinstalled in a new location without special permission 
from the authority enforcing this Code. Any such equipment shall be 
reinstalled in an approved manner. 

660-9. On Fluoroscopic Tables. Where permitted in accordance with 
Section 660-8 (b), leads on fluoroscopic tables shall be adequately in- 



ARTICLE 660-X-RAY EQUIPMENT 70-347 

sulated or be provided with barriers which will guard against inadvert- 
ent contact. 

B. Control 

660-10. Stationary Equipment. A manually controlled device shall be 
incorporated in the X-ray control supply or in the primary circuit to 
the high voltage transformer, and shall be adequate to control the load 
resulting from failures in the high voltage circuit. This device shall be 
a part of the X-ray equipment, but may be located in a separate en- 
closure immediately adjacent to the X-ray control unit. 

660-11. Portable Equipment. Portable equipment shall comply with 
Section 660-10, but the manually controlled device shall be located in or 
on the equipment. 

660-12. General. 

(a) Radiographic Type. There shall be provided a timer or auto- 
matic exposure terminating device and also a switch of a type which 
opens automatically except when held closed by the operator. 

(b) Fluoroscopic Type. A switch shall be provided which shall be 
designed to open automatically except when held closed by the opera- 
tor. 

(c) Therapy. A timer or automatic exposure terminating device 
shall be provided which is not of the repeating type. 

C. Industrial Apparatus 
660-13. Industrial X-ray Apparatus. 

(a) Radiographic and Fluoroscopic Types. A switch which shall be 
designed to open automatically except when held closed by the oper- 
ator, or a timer, shall be provided except on equipment or installations 
effectively enclosed or provided with interlocks to prevent ready access 
to live current-carrying parts during operation. 

(b) Industrial or Laboratory Apparatus — Diffraction or Irradiation 
Types. Positive indication of energization by pilot lights, readable 
meter deflections or equivalent means shall be provided except on 
equipment or installations effectively enclosed or provided with inter- 
locks to prevent ready access to live current-carrying parts during op- 
eration. 

660-14. Independent Control. Where more than one piece of appara- 
tus is operated from the same high-voltage circuit, each piece or each 
group of apparatus as a unit shall be provided with a high-voltage 
switch or equivalent disconnecting means. This disconnecting means 
shall be constructed, enclosed, or located so as to avoid contact by per- 
sons with its live parts. 

D. Transformers and Capacitors 

660-15. General. Transformers and capacitors which are part of an 
X-ray apparatus shall not be required to conform to the requirements 
of Articles 450 and 460 of this Code. 



70-348 MASSACHUSETTS ELECTRICAL CODE 

660-16. Draining Capacitor Charge. Capacitors shall be provided with 
an automatic means for discharge and grounding the plates whenever 
the transformer primary is disconnected from the source of supply. 

Exception No. 1. Where all current-carrying parts of capacitors, and 
of the conductors connected therewith, are at least 8 feet from the floor 
and are inaccessible to unauthorized persons. 

Exception No. 2. Where within 8 feet from the floor are within en- 
closures of grounded metal or insulating material. 

E. Guarding and Grounding 
660-17. General. 

(a) High Voltage Parts. All high voltage parts, including X-ray 
tubes, shall be mounted within grounded enclosures. Either air, oil, gas 
or other suitable insulating media may be used to insulate the high 
voltage from the grounded enclosure. The connections from the high 
voltage equipment to X-ray tubes and other high voltage components 
shall be made with high voltage cables of the shockproof type. 

(b) Low Voltage Cables. Low voltage connecting cables to oil filled 
units such as transformers, condensers, oil coolers, and high voltage 
switches which are not completely sealed shall be of the oil resistant 
type. 

660-18. Grounding. Noncurrent-carrying metal parts of tube stands, 
fluoroscopic and other equipment shall be grounded in the manner 
prescribed in Article 250. 

(a) Portables. Portable equipment shall be provided with an ap- 
proved grounding type plug. 



ARTICLE 665 — INDUCTION AND DIELECTRIC 
HEATING EQUIPMENT 



A. Scope and General 

665-1. Scope. The provisions of this Article shall apply to the con- 
struction and installation of induction and dielectric heating equipment 
and accessories for industrial, scientific and medical applications, but 
not for appliances. 

665-2. Definitions. The term "heating equipment" as used in this 
Article includes any equipment used for heating purposes whose heat 
is generated by induction or dielectric methods. 

Induction heating is the heating of a nominally conducting material 
due to its own P'R losses when the material is placed in a varying electro- 
magnetic field. 

Dielectric heating is the heating of a nominally insulating material 
due to its own dielectric losses when the material is placed in a vary- 
ing electric field. 



ARTICLE 665-INDUCTION, DIELECTRIC HEATING 70-349 

The term "therapeutic high frequency equipment" as used in this 
Article shall be understood to mean generating equipment capable of 
producing alternating currents having frequencies greater than those 
frequencies which elicit neuromuscular response. In order to comply 
with the above, the output frequency of the therapeutic high frequency 
equipment shall not be less than 2 megacycles. 

665-3. Application of Other Articles. Wiring from the source of power 
to the heating equipment shall comply with the Code Chapters 1 to 4 
inclusive. Circuits and equipment operating on a supply circuit of 
more than 600 volts shall comply with the provisions of Article 710. 

665-4. Hazardous Locations. Induction and dielectric heating equip- 
ment shall not be installed in hazardous locations as defined in Article 
500 unless the equipment and wiring is designed and approved for the 
locations. 

B. Motor-Generator Equipment 

665-5. Scope. Motor generator equipment shall include all rotating 
equipment designed to operate from an AC or DC motor, or by me- 
chanical drive from a prime mover, producing an alternating current 
of any frequency for induction and/or dielectric heating. 

665-6. Ampacities of Supply Conductors. Ampacities of supply con- 
ductors shall be determined by Article 430 of this Code. 

665-7. Overcurrent Protection. Overcurrent protection shall be pro- 
vided as specified in Article 430 of this Code for the electrical supply 
circuit. 

665-8. Disconnecting Means. The disconnecting means shall be pro- 
vided as specified in Article 430 of this code. 

A readily accessible disconnecting means shall be provided by which 
each heating equipment can be isolated from the supplying circuit. The 
ampacity of this disconnecting means shall be not less than the name- 
plate current rating of the equipment. The supply circuit disconnect 
means may be used as a heating equipment disconnecting means where 
the circuit supplies only one equipment. 

665-9. Output Circuit Definition. The output circuit shall include all 
high frequency output components external to the generator, including 
contactors, transformers, bus-bars, and transmission lines. The same 
definition shall apply to all off line frequencies obtained from motor 
generators, or generators used with induction heating loads. 

665-10. Output Circuits. Output circuits shall conform to the follow- 
ing: 

(a) Generator Output. The output circuit shall be isolated from 
ground, except for the capacitive coupling inherent in the generator, 
which, in effect causes the generator terminals to have voltages from 
terminal to ground that are equal. 

When rated at more than 500 volts, the output circuit shall incor- 
porate a DC ground protector unit. The DC impressed on the output 
circuit shall not exceed 30 volts and shall not exceed a current capabil- 
ity of 5 milliamperes. 



70-350 MASSACHUSETTS ELECTRICAL CODE 

An isolating transformer for matching the load and the source may 
be used in the output circuit wherein the secondary is not at DC ground 
potential. 

(b) Component Interconnections. The various components required 
for a complete induction heating equipment installation shall be con- 
nected by properly protected multiconductor cable, bus bar, or coaxial 
cable. Cables shall be installed in non-ferrous conduit raceways. Bus 
bar shall be protected where required by nonferrous enclosures. 

665-11. Control-Enclosures. Low frequency AC or DC may be used 
in the control portion of the heating equipment. This shall be limited to 
a value of 150 volts. Solid or stranded wire, properly sized in No. 18 
AWG or larger shall be used. Sixty cycle components may be used to 
control HF when properly rated by the induction heating equipment 
manufacturer. Electronic circuits utilizing solid state devices and tubes 
may use printed circuits or wire sizes, properly sized smaller than No. 
18 AWG. 

665-12. Remote Control 

(a) When remote controls are used for applying power, a "Local- 
Remote" switch shall be provided and interlocked so as to prevent the 
possibility of applying power from other than one selected control 
point or points. 

(b) Switches operated by foot pressure shall be provided with a 
shield over the contact button to avoid accidental closing. 

C. Equipment Other Than Motor Generator 

665-13. Scope. Equipment other than motor generator includes all 
static multipliers and oscillator type units utilizing vacuum tubes and/or 
solid state devices. The equipment shall be capable of converting AC, 
or DC to a frequency suitable for induction and/or dielectric heating. 

665-14. Ampacities of Supply Conductors. Ampacities of supply con- 
ductors shall be determined as follows: 

(a) The ampacity of the circuit shall be not less than the nameplate 
current rating of the equipment. 

(b) The ampacities of conductors supplying two or more equipments 
shall be not less than the sum of nameplate current ratings on all 
equipment except as follows: Where, when supplying two or more 
equipments from the same feeder, simultaneous operation of said 
equipments is not possible, the ampacity of the feeder shall be not less 
than the sum of the nameplate currents for the largest group of ma- 
chines capable of simultaneous operation, plus 100 per cent of the 
standby currents of the remaining machines supplied. 

665-15. Overcurrent Protection. Overcurrent protection shall be pro- 
vided as specified in Article 430 for the equipment as a whole. This 
overcurrent protection shall be provided separately or as a part of the 
equipment. 

665-16. Disconnecting Means. A readily accessible disconnecting 
means shall be provided by which each heating equipment can be 
isolated from the supplying circuit. The ampacity of this disconnecting 



ARTICLE 665-INDUCTION, DIELECTRIC HEATING 70-351 

means shall not be less than the nameplate current rating of the equip- 
ment. The supply circuit disconnect means may be used for disconnect- 
ing the heating equipment where the circuit supplies only one equip- 
ment. 

665-17. Output Circuit Definition. The output circuit shall include all 
high frequency output components external to the converting device 
including contactors, transformers, bus-bars, and transmission lines. 
The same definition shall apply to all off line frequencies obtained from 
the converting device, or devices used with induction and/or dielec- 
tric heating loads. 

665-18. Output Circuits. Output circuits shall conform to the follow- 
ing: 

(a) Converter output. The output circuit (direct or coupled) shall 
be at DC ground potential. 

(b) Converter and Applicator Connection. When the connections 
between the converter and the work applicator exceed two feet in length 
the connections shall be enclosed or guarded with noncombustible ma- 
terial. 

665-19. Line Frequency in Converter Equipment Output. Commercial 
frequencies of 25 to 60 cycle alternating current output may be cou- 
pled for control purposes, but shall be limited to a value of 150 volts 
available only during periods of circuit operation. 

665-20. Keying. Where high-speed keying circuits dependent on the 
effect of "oscillator blocking" are employed, the peak R.F. output volt- 
age during the blocked portion of the cycle shall not exceed 100 volts 
in units employing R.F. converters. 

665-21. Remote Control. 

(a) When remote controls are used for applying power, a "Local Re- 
mote" switch shall be provided and interlocked so as to prevent the pos- 
sibility of applying power from other than one selected control point or 
points. 

(b) Switches operated by foot pressure shall be provided with a 
shield over the contact button to avoid accidental closing. 

D. Guarding and Grounding 

665-22. Enclosures. The converting apparatus (including the DC line) 
and high frequency electrical circuits (excluding the output circuits 
and remote control circuits), shall be completely contained in an en- 
closure or enclosures of noncombustible material. 

665-23. Panel Controls. All panel controls shall be of "dead front" 
construction. 

665-24. Access to Internal Equipment. Doors or detachable panels 
may be. employed for internal access. Where doors are used giving 
access to voltages from 500 to 1000 volts AC or DC, either door 
locks shall be provided or interlocking shall be installed with the 
choice of precaution optional. Where doors are used giving access to 
voltages above 1000 volts AC or DC, either mechanical lockouts, with 
a disconnect means to prevent access until voltage is removed from the 



70-352 MASSACHUSETTS ELECTRICAL CODE 

cubicle, or both door interlocking and mechanical door locks shall be 
provided. Detachable panels not normally used for access to such 
parts shall be fastened in a manner which will make them inconvenient 
to remove. 

665-25. Warning Labels. "Danger" labels shall be attached on the 
equipment, and shall be plainly visible even when doors are opened 
or panels are removed from compartments containing voltages above 
250 volts AC or DC. 

665-26. Capacitors. When capacitors in excess of 0.1 Mfd. are used 
in DC circuits, either as rectifier filter components, or suppressors, 
etc., having circuit voltages exceeding 230 volts above ground, bleeder 
resistors or grounding switches shall be used as grounding devices. The 
time of discharge shall be in accordance with Article 460-6. (a). 

Where auxiliary rectifiers are used with filter capacitors in the output 
for bias supplies, tube keyers, etc., bleeder resistors shall be used even 
though the DC voltage may not exceed 230 volts. 

665-27. Work Applicator Shielding. Protective cages or adequate 
shielding shall be used to guard work applicators other than induction 
heating coils. Induction heating coils may be protected by insulation 
and/or refractory materials. Interlock switches shall be used on all 
hinged access doors, sliding panels or other easy access to the appli- 
cator. All interlock switches shall be connected in such a manner as to 
remove all power from the applicator when any one of the access doors 
or panels is open. Interlocks on access doors or panels are not required 
when the applicator is an induction heating coil at DC ground poten- 
tial or operating at less than 150 volts AC. 

665-28. Grounding and Bonding. Grounds and/or inter-unit bonding 
shall be used wherever required for circuit operation and for limiting 
to a safe value radio frequency potentials between all exposed noncur- 
rent-carrying parts of the equipment and earth ground, also between all 
equipment parts and surrounding objects and between such objects and 
earth ground. Such grounding and bonding shall be installed in accord- 
ance with Article 250 of this Code. 

665-29. Marking. Each heating equipment shall be provided with a 
nameplate, giving the manufacturer's name and model identification, 
and the following input data: line volts, frequency, number of phases, 
maximum current, full load KVA and full load power factor. 

E. Therapeutic Equipment 
665-30. Installation. 

(a) Where portability is not essential, equipment shall be permanently 
installed in accordance with Chapters 1 to 3 inclusive of this Code. 

(b) Where portability is essential, the power supply cord shall be a 
three-conductor hard service type with an ampacity not less than the 
marked rating of the equipment. One conductor having a continuous 
green color or a continuous green color with a yellow stripe insulation 
shall be used solely for equipment grounding. The cord shall terminate 
in an approved grounding attachment-plug cap as described in Section 
250-59. (b). 



ARTICLE 670-METALWORKING MACHINE TOOLS 70-353 

665-31. Applicators for Therapeutic Equipment. Application of the 
high frequency power to the patient may be made by means of an elec- 
tric field or of an induction field. Current-carrying parts of applicators 
shall be so insulated or enclosed that reliable isolation of the patient 
shall be assured. 

665-32. Enclosure. The converting apparatus including the DC line, 
and high frequency electrical circuits, but excluding the line cord for 
portable units and the output circuits, shall be contained in an enclosure 
of noncombustible material. 

665-33. Panel Controls. All panel controls shall be of "dead front" 
construction. 

665-34. Access to Internal Equipment. Access shall be through panels 
not conveniently removable. Panels which need removal for access to 
fuses, tubes, adjustments, overload reset devices, internal top switches, 
and the like, shall be labeled to indicate danger if and when removed, or 
shall be provided with suitable electrical interlock devices. 



ARTICLE 670 — METALWORKING MACHINE TOOLS 

For further information see NFPA Standard on 
Metalworking Machine Tools (No. 79). 

670-1. Scope. The provisions of this Article apply to the size and 
overcurrent protection of supply conductors to metalworking machine 
tools and to the nameplate data required on each such tool. 

670-2. Definition of Metalworking Machine Tools. For the purpose of 
this Article, metalworking machine tools are defined as follows: 

(a) A metal-cutting machine tool is a power driven machine, not 
portable by hand, used for the purpose of removing metal. 

(b) A metal-forming machine tool is a power driven machine, not 
portable by hand, used to press, forge, emboss, hammer, blank, or 
shear metal. 

670-3. Machine Tool Nameplate Data. A permanent nameplate listing 
supply voltage, phase, frequency, full load currents (see note), ampere 
rating of largest motor, short circuit interrupting capacity of the ma- 
chine overcurrent protective device if furnished, and diagram number 
shall be attached to the control equipment enclosure or machine where 
plainly visible after installation. 

Note 1 . The full load current shall be not less than the sum of the 
full load currents required for all motors and other equipment which 
may be in operation at the same time under normal conditions of use. 
Where unusual type loads, duty-cycles, etc., require oversized conduc- 
tors, the required capacity shall be included in the marked "full load 
current." 

Note 2. Where more than one incoming supply circuit is to be pro- 
vided, the nameplate shall state the above information for each circuit. 



70-354 MASSACHUSETTS ELECTRICAL CODE 

670-4. Conductors Supplying a Machine Tool. 

(a) The supply circuit conductor shall have an ampacity of not less 
than the marked full load current rating plus 25 per cent of the full 
load current rating of the highest rated motor as indicated on the name- 
plate. For the protection of supply conductors to the machine tool, re- 
fer to Section 240-5. 

(b) A machine tool conforming with NFPA No. 79 shall be consid- 
ered individual unit equipment. It is provided with a disconnecting 
means and may be supplied by branch circuits protected by either fuses 
or circuit breakers. 

(c) The disconnecting means may or may not incorporate overcur- 
rent protection. Where the machine tool nameplate is marked "Over- 
current protection provided at machine supply termials," the supply 
conductors are to be considered either as feeders, or taps as covered 
by Section 240-15. 

"Overcurrent protection provided at machine supply terminals" means 
that provision has been made in the machine tool for each set of supply con- 
ductors to terminate in a single circuit breaker or set of fuses. 



ARTICLE 680 — SWIMMING POOLS 



680-1. Scope. The provisions of this Article apply to the construction 
and installation of electric wiring for equipment in or adjacent to 
swimming pools, to metallic appurtenances in or within 5 feet of the 
pool, and to the auxiliary equipment such as pumps, filters and similar 
equipment. No electric appliances or wiring shall be installed in the wa- 
ter or in the enclosing walls of a swimming pool, except as provided for 
in this Article. 

680-2. Approval of Equipment. All equipment shall be approved for 
the purpose. 

680-3. Application of Other Articles. Except as modified by this Ar- 
ticle, wiring and equipment in or adjacent to swimming pools shall 
comply with the applicable requirements of Chapters 1 to 4, inclusive, 
of this Code. 

See Article 720 for low voltage lighting. 
680-4. Lighting. 

(a) The provisions of this Section apply to lighting fixtures installed 
below the pool surface. 

(b) No lighting fixture shall be installed for operation at more than 
150 volts. 

(c) A nonmetallic fixture shall not be used with a grounded power 
supply. 

(d) All noncurrent carrying metal parts of lighting fixtures shall be 
grounded whether exposed or enclosed in nonconducting materials. 
The fixture shall be secured and grounded to the forming shell by a posi- 



ARTICLE 680-SWIMMING POOLS 70-355 

tive locking device which will assure a low resistance contact and 
which will require a tool to remove the fixture from the forming shell. 

Definition. A forming shell is a metal housing designed to contain a 
lighting fixture assembly for mounting into a swimming pool structure. 
The forming shell provides a bond between the raceway and the non- 
current carrying metal parts of the fixture. 

(e) Fixtures approved for the purpose may be installed outside the 
walls of the pool in closed recesses which are adequately drained and 
accessible for maintenance. 

(f) Approved metal fixture housings (forming shells) shall be in- 
stalled for the mounting of all wet niche underwater fixtures and shall 
be equipped with provisions for threaded conduit entries. Metal parts 
of the fixtures and fixture housings in contact with the pool water and 
the supply conduit below grade level shall be of brass or other approved 
corrosion-resistant metal. The rigid conduit shall extend from the fix- 
ture housing (forming shell) to a suitable junction box located as pro- 
vided in Section 680-5 of this Article. 

(g) Underwater lighting fixtures shall perform reliably under any 
likely combination of fault conditions so that there is no shock hazard. 
Compliance with this requirement shall' be assured by one of the follow- 
ing: 

(1) The design and construction of the fixtures; or 

(2) The use of differential type circuit protection; or 

(3) The use of a transformer complying with Section 680-4 (h) 
and further provided with a ground detector if the circuit voltage is 
greater than 15 volts; or 

(4) Other acceptable means. 

(h) Transformers used for the supply of fixtures, together with the 
transformer enclosure, shall be approved for the purpose. The trans- 
formers shall be a two-winding type having a grounded metal barrier 
between the primary and secondary voltage windings. 

(i) Within the fixture the cord termination, all splices, and the 
ground connection shall be covered with a suitable compound to pro- 
tect them from the deteriorating effect of exposure to pool water in 
the event of a failure causing water to enter the fixture. 

680-5. Junction Boxes and Transformer Enclosures. 

(a) Junction boxes installed on the supply side of conduits extend- 
ing to underwater pool lights shall be provided with threaded hubs for 
conduit connection. These boxes shall be located not less than 8 
inches above ground, pool deck, or maximum pool water level, which- 
ever provides the greatest elevation, nor less than 4 feet from the 
perimeter of the pool unless part of an approved fixture assembly. 
Junction boxes mounted above the grade of the finished walkway 
around the pool shall not be located in the walkway unless afforded 
additional protection such as by location under diving boards, adjacent 
to fixed structures, and the like. 



70-356 MASSACHUSETTS ELECTRICAL CODE 

(b) Transformer enclosures shall be located not less than 12 inches 
above ground, pool deck, or maximum pool water level, whichever 
provides the greatest elevation, nor less than 4 feet from the perimeter 
of the pool. Transformer enclosures mounted above the grade of the 
finished walkway around the pool shall not be located in the walkway 
unless afforded additional protection such as by location under diving 
boards, adjacent to fixed structures, and the like. 

(e) Boxes shall be provided with means for independently terminat- 
ing not less than two grounding conductors. 

680-6. Attachment Plug Receptacles. No attachment plug receptacles 
shall be installed within 10 feet of the inside walls of the swimming 
pool. 

Exception. Attachment plug receptacles of other than the standard 
15 ampere parallel slot type may be installed where an integral part of 
the lighting fixture assembly and where used for the installation, main- 
tenance, or servicing of the fixture. 

Note: In determining the 10-foot dimension, the distance to be measured 
is the shortest path which the supply cord of an appliance connected to the 
receptacle would follow without piercing a building floor, wall or ceiling. 

680-7. Grounding. 

(a) All metallic conduit, piping systems, pool reinforcing steel, light- 
ing fixtures, lighting fixture housings, metal parts of ladders, diving 
boards and their supports, and the like shall be bonded together and 
grounded to a common ground. The bonding conductor shall be not 
smaller than No. 8 copper. 

Exception: The usual steel tie wires are considered suitable for 
bonding the reinforcing steel together and welding or special clamping 
will not be required. 

(b) An unbroken No. 12 AWG, or larger, insulated copper wire 
shall be provided for a grounding conductor from the junction box to 
the distribution panel ground. This conductor shall be installed in rigid 
metallic conduit with the circuit conductors from the pool junction box 
to the distribution panel ground terminal. 

(c) Metallic raceways shall not be depended upon for grounding. 
Where exposed to pool water and in other corrosive areas such as in 
pump houses or adjacent to water treating and other equipment, the 
grounding of the non-current carrying parts shall be by means of an 
insulated copper conductor sized in accordance with Section 250-95 
and not smaller than No. 12 AWG. 

680-8. Methods of Grounding and Bonding. 

(a) Metal wiring enclosures shall be grounded in accordance with 
Article 250, in addition to other requirements of this Article. 

(b) In addition to other requirements of this Article, lighting fixtures 
that are supplied by flexible cord or cable shall have all metal parts 
grounded by means of an insulated grounding conductor that is an in- 
tegral part of the cord or cable. This grounding conductor shall be con- 
nected to a grounding terminal in the supply junction box. This con- 



ARTICLE 680-SWIMMiNG POOLS 70-357 

ductor shall be equal in size to the supply conductors but not smaller 
than No. 16AWG. 

(c) Nonelectrical equipment shall be grounded to a common ground 
in accordance with Section 680-7. 

Structural reinforcing steel may be used as a common bonding conductor 
for nonelectrical parts where connections can be made in accordance with 
Section 250-113. 

680-9. Clearances. Service drop conductors and any other open over- 
head wiring shall not be installed above the swimming pool or sur- 
rounding area extending 10 feet horizontally from the pool edge, or 
diving structure, observation stands, towers or platforms. 

See Section 90-2 (b). 



70-358 MASSACHUSETTS ELECTRICAL CODE 

Chapter 7. Special Conditions 
ARTICLE 700 — EMERGENCY SYSTEMS 

A. General 
700-1. Scope. The provisions of this Article apply to the installation, opera- 
tion and maintenance of circuits, systems and equipment intended to supply 
illumination and power in the event of failure of the normal supply or in the 
event of accident to elements of a system supplying power and illumination 
essential for safety to life and property where such systems or circuits are 
legally required by Municipal, State, Federal or other Codes, or by any gov- 
ernmental agency having jurisdiction. 

Emergency systems are generally installed in places of assembly where 
artificial illumination is required, such as buildings subject to occupancy by 
large numbers of persons, hotels, theaters, sports arenas, hospitals and similar 
institutions.. Emergency systems may provide power for such functions as 
essential refrigeration, operation of mechanical breathing apparatus, ventila- 
tion when essential to maintain life, illumination and power for hospital op- 
erating rooms, fire alarm systems, fire pumps, industrial processes where cur- 
rent interruption would produce serious hazards, public address systems and 
similar functions. 

See NFPA Building Exits Code (NFPA No. 101) for specification of loca- 
cations where emergency lighting is considered essential to life safety. 

700-2. Other Requirements. 

All requirements of the MASSACHUSETTS ELECTRICAL Code shall apply to 
emergency systems, except as modified by this article. 

700-3. Equipment- Approval. All equipment shall be approved for use on 
emergency systems. 

700-4. Tests and Maintenance. 

(a) The authority having jurisdiction shall conduct or witness a test on 
the complete system upon installation and periodically afterward. 

(b) Systems shall be tested periodically on a schedule acceptable to the 
authority having jurisdiction to assure their maintenance in proper operating 
condition. 

(c) Where battery systems or unit equipments are involved, including 
batteries used for starting or ignition in auxiliary engines, the authority having 
jurisdiction shall require periodic maintenance. 

(d) A written record shall be kept of such tests and maintenance. 

700-5. Capacity. Emergency systems shall have adequate capacity and 
rating for the emergency operation of all equipment connected to the system. 

B. Sources of Power 
700-6. Systems. Current supply shall be such that in event of failure 
of the normal supply to or within the building or group of buildings con- 
cerned, emergency lighting, or emergency power, or both emergency 
lighting and power, will be immediately available. The supply system 



ARTICLE 700— EMERGENCY SYSTEMS 70-359 

for emergency purposes may comprise one or more of the types of system 
covered in Section 700-7 to Section 700-10. Unit equipments in accordance 
with Section 700-22 shall satisfy the applicable requirements of this Article. 

Consideration must be given to the type of service to be rendered, whether 
of short time duration, as for exit lights of a theater, or of long duration as 
for supplying emergency power and lighting due to a long period of current 
failure from trouble either inside or outside the building, as in the case of 
a hospital. 

Assignment of degree of reliability of the recognized emergency supply 
system depends upon the careful evaluation of the variables at each particular 
installation. 

700-7. Storage Battery. One service, in accordance with Article 230, and 
a storage battery of suitable rating and capacity to supply and maintain at not 
less than 91 per cent of system voltage the total load of the circuits supplying 
emergency lighting and emergency power for a period of not less than one 
and one-half hours. 

Batteries whether of the acid or alkali type shall be designed and con- 
structed to meet the requirements of emergency service. When of the lead- 
acid type, this shall include low gravity acid (1.20 to 1.22 SP-GR), relatively 
thick and rugged plates and separators, and a transparent jar. 

700-8. Generator Set. One service, in accordance with Article 230, and a 
generator set driven by some form of prime mover and of sufficient capacity 
and proper rating to supply circuits carrying emergency lighting or lighting 
and power, with suitable means for automatically starting the prime mover 
on failure of the normal service. For hospitals, the transition time from in- 
stant of failure of the normal power source to the emergency generator source 
shall not exceed ten seconds. 

See Section 700-4. 

700-9. Separate Service. Two services, each in accordance with Article 230, 
widely separated electrically and physically to minimize possibility of simul- 
taneous interruption of supply. 

700-10. Connection Ahead of Service Disconnecting Means. Connections 
on the line side of the main service if sufficiently separated from main service 
to prevent simultaneous interruption of supply through an occurrence within 
the building or group of buildings served. 

700-11. Auxiliary Source. The requirements of Section 700-5 and Section 
700-6 shall also apply to installations where the entire electrical load on a 
service or sub-service is arranged to be supplied from a second source. Cur- 
rent supply from a standby power plant shall satisfy the requirements of 
availability in Section 700-6. 

700-12. Derangement Signals. Audible and visual signal devices shall be 
provided where practicable for the following purposes: 

(a) To give warning of derangement of the emergency or auxiliary source. 

(b) To indicate that the battery or generator set is carrying load. 

(c) To indicate when battery charger is properly functioning. 



70-360 MASSACHUSETTS ELECTRICAL CODE 

C. Emergency Circuits for Lighting and Power 

700-13. Loads on Emergency Branch Circuits. No appliances and no 
lamps, other than those specified as required for emergency use shall 
be supplied by emergency lighting circuits. 

700-14. Emergency Illumination. Emergency illumination shall include 
all required exit lights and all other lights specified as necessary to pro- 
vide sufficient illumination. 

Emergency lighting systems should be so designed and installed that the 
failure of any individual lighting element, such as the burning out of a light 
bulb, cannot leave any space in total darkness. 

700-15. Circuits for Emergency Lighting. Branch circuits intended to 
supply emergency lighting shall be so installed as to provide service im- 
mediately when the normal supply for lighting is interrupted. Such in- 
stallations shall provide either one of the following: 

(a) An emergency lighting supply, independent of the general light- 
ing system with provisions for automatically transferring, by means of 
devices approved for the purpose, the emergency lights upon the event 
of failure of the general lighting system supply. 

(b) Two or more separate and complete systems with independent 
power supply, each system providing sufficient current for emergency 
lighting purposes. Unless both systems are used for regular lighting 
purposes and are both kept lighted, means shall be provided for auto- 
matically energizing either system upon failure of the other. Either or 
both systems may be part of the general lighting system of the protected 
occupancy if circuits supplying lights for emergency illumination are 
installed in accordance with other sections of this article. 

700-16. Circuits for Emergency Power. For branch circuits which sup- 
ply equipment classed as emergency, there shall be an emergency sup- 
ply source to which the load will be transferred automatically and im- 
mediately upon the failure of the normal supply. 

700-17. Independent Wiring. Emergency circuit wiring shall be kept 
entirely independent of all other wiring and equipment and shall not 
enter the same raceway, box or cabinet with other wiring except: 

Exception No. I. In transfer switches. 

Exception No. 2. In exit or emergency lighting fixtures supplied 
from two sources. 

D. Control 

700-18. Switch Requirements. The switch or switches installed in 
emergency lighting circuits shall be so arranged that only authorized 
persons will have control of emergency lighting except: 

Exception No. I . Where two or more single throw switches are con- 
nected in parallel to control a single circuit, at least one of these 
switches shall be accessible only to authorized persons. 

Exception No. 2. Additional switches which act only to put emer- 
gency lights into operation but not disconnect them are permissible. 

Switches connected in series or three and four way switches shall not 
be used. 



ARTICLE 700— EMERGENCY SYSTEMS 70-361 

700-19. Switch Location. 

(a) All manual switches for controlling emergency circuits shall be in 
locations convenient to authorized persons responsible for their actuation. In 
places of assembly such as theaters a switch for controlling emergency light- 
ing systems shall be located in the lobby or at a place conveniently accessible 
thereto. 

(b) In no case shall a control switch for emergency lighting in a theater 
or motion-picture theater be placed in a motion-picture projection booth or 
on a stage, except that where multiple switches are provided, one such switch 
may be installed in such location when so arranged that it can energize, but 
not disconnect, the circuit. 

700-20. Other Switches 

(a) Exterior Lights. Those lights on the exterior of the building which 
are not required for illumination when there is sufficient daylight may be 
controlled by an automatic light-actuated device approved for the purpose. 

(b) Hospital Corridors. Switching arrangements to transfer corridor light- 
ing in patient areas of hospitals from overhead fixtures to fixtures designed 
to provide night lighting may be permitted, provided the switching system is 
so designed that switches can only select between two sets of fixtures and 
cannot extinguish both sets at the same time. 

E. Overcurrent Protection 

700-21. Accessibility. The branch-circuit overcurrent devices in emergency 
circuits shall be accessible to authorized persons only. 

F. Unit Equipments 

700-22. Unit Equipments. Where permitted by the authority having jurisdic- 
tion, in lieu of other methods specified elsewhere in this Article, individual 
unit equipments for emergency illumination shall consist of (a) a battery, 
(b) battery charging means when a storage battery is used, (c) one or more 
lamps, and (d) a relaying device arranged to energize the lamps automatically 
upon failure of the normal supply to the building. 

The batteries shall be of suitable rating and capacity to supply and maintain 
at not less than 91 per cent of rated lamp voltage the total lamp load associ- 
ated with the unit for a period of not less than one and one-half hours. 

Storage batteries whether of the acid or alkali type shall be designed and 
constructed to meet the requirements of emergency service. When of the 
lead-acid type the storage battery shall have a transparent jar. 

Unit equipments shall be permanently fixed in place (i.e., not portable) and 
shall have all wiring to each unit installed in accordance with the requirements 
of any of the wiring methods in Chapter 3. They shall not be connected by 
flexible cord. The supply circuit between the unit equipment and the service, 
feeders, or the branch circuit wiring shall be installed as required by Section 
700-17. Emergency illumination fixtures which obtain power from a unit 
equipment and are not part of the unit equipment shall be wired to the 
unit equipment as required by Section 700-17 and by one of the wiring 
methods of Chapter 3. 



70-362 MASSACHUSETTS ELECTRICAL CODE 

ARTICLE 710 — OVER 600 VOLTS — GENERAL 

A. General 

710-1. Scope. This Article applies in general to all circuits and equip- 
ment operated at more than 600 volts. For specific installation see the 
Articles referred to in Section 710-2. 

710-2. Installations Covered in Other Articles. Provisions applicable 
to specific types of installations are included in Article 230, Services; 
Article 346, Rigid Metal Conduit; Article 347, Rigid Nonmetallic 
Conduit; Article 430, Motors, Motor Circuits and Controllers; Article 
450, Transformers and Transformer Vaults; Article 460, Capacitors; 
Article 730, Outside Branch Circuits and Feeders; Article 410, Lighting 
Fixtures, Lampholders, Lamps, Receptacles and Rosettes; Article 600, 
Electric Signs and Outline Lighting; Article 660, X-ray Equipment, 
and Article 665, Inductive and Dielectric Heat Generating Equip- 
ment. 

710-3. Wiring Methods. Circuit conductors shall be suitable for the 
voltage and the conditions under which they are installed. They shall 
be installed in rigid metal conduit, in raceways or ducts or as open runs 
of metal. armored cable suitable for the use and purpose. 

When installed in the ground they shall be suitable for the purpose 
and buried at least 36 inches deep. Where this is impractical they may 
be not less than 24 inches deep provided they are installed in suitable 
raceways or encased in 2 inches of concrete. (See Articles 346 and 
347.) 

Exception. In locations accessible to qualified persons only, open 
runs of nonmetallic sheathed cable, bare conductors and bare bus-bars 
may also be used. 

710-4. Braid-Covered Insulated Conductors — Open Installation. Open 

runs of braid-covered insulated conductors shall have a flame-retard- 
ant braid. When the conductors used do not have this protection, a 
flame-retardant saturant shall be applied to the braid covering after in- 
stallation. This treated braid covering shall be stripped back a safe 
distance at conductor terminals, according to the operating voltage. 
This distance should be not less than one inch for each kilovolt of the 
conductor-to-ground voltage of the circuit, where practicable. 

710-5. Shielding of Rubber Insulated Conductors. Where rubber-in- 
sulated conductors for permanent installations operate at voltages 
higher than those indicated in Table 710-5 and under the conditions 
mentioned, they shall be of a type having metallic shielding for the pur- 
pose of confining their dielectric field. 

710-6. Grounding of Shielding Tape. The metallic shielding or any 
other static voltage shields on shielded cable shall be stripped back to a 
safe distance according to the circuit voltage, at all terminations of the 
shielding, as in potheads and joints. At such points, suitable methods 
such as the use of potheads, terminators, stress cones or similar devices 
shall be employed for stress reduction and the metallic shielding tape 
shall be grounded. 



ARTICLE 710-OVER 600 VOLTS-GENERAL 



70-363 



Table 710-5 
Shielding of Rubber-Insulated Conductors 

Voltage in Kv (L-L) Above which 
Shielding is Required 

Neutral Grounded Neutral Ungrounded 



Method of Installation 



Fibrous 
Covered 



Ozone- 
Resistant 

Jacket 
Covering 



Fibrous 
Covered 



Ozone- 
Resistant 

Jacket 
Covering 



In metallic conduit or 
trough above grade lo- 
cated indoors and in 
dry locations 

Single conductor ... 2 

Multi-conductor .... 2 

Underground ducts and 
conduits and other wet 
locations 

Single conductor ... 2 

Multi-conductor .... 2 



5* 
5 



3** 
5 



On insulators — 
Only multi-conductor Not required under 5 Kv. 

Directly in soil — 

Single conductor ... — 3 

Multi-conductor .... — 5 



•It is presumed that installation conditions will be such as to maintain a high level 
of jacket surface resistivity and so minimize the possibility of destructive discharge. 
Pulling dry or the use of insulating type pulling lubricants will help attain these 
conditions. Where surface contamination cannot be prevented and high surface resis- 
tivity cannot be maintained, metallic shielding shall be used at over 3 kv. 

Note : Metallic sheathed single or 3 conductor cables require no metallic shielding 
for voltages 5 kv and less. In the case of portable equipment cables it is good practice 
to specify shielding for all voltages above 2 kv. 

**For three single conductor cables, cabled together without overall outer covering, 
the value is 5 kv. 

710-7. Grounding. Wiring and equipment installations shall conform 
with the applicable provisions of Article 250. 

710-8. Moisture or Mechanical Protection for Metal Sheathed Cables. 
Where cable conductors emerge from a metal sheath and where pro- 
tection against moisture or mechanical injury is necessary, the insula- 
tion of the conductors shall be protected by a pothead or other ap- 
proved means. 

B. Equipment — General Provisions 

710-10. Indoor Installations. Indoor electrical equipment installations 
shall conform with Sections 710-10(a-c). 

(a) In Public Places. In places which are regularly open to the pub- 
lic, electrical installations shall conform with Sections 710-31 to 710-34 
inclusive. Metal-enclosed switch-gear, unit substations, transformers, 



70-364 MASSACHUSETTS ELECTRICAL CODE 

pull boxes, connection boxes, and other similar associated equipment 
shall be marked with appropriate caution signs. Openings in ventilated 
dry-type transformers or similar openings in other equipment shall be 
designed so that foreign objects inserted through these openings will be 
deflected from energized parts. 

(b) In Places Frequented Only By Persons Employed on the Premises.. 

In places where access is normally restricted to persons employed on 
the premises, enclosure of electrical installations is not mandatory pro- 
vided that: (1) No live parts are exposed or readily accessible; (2) The 
associated conduits or Type AC metal-clad cables terminate in, and 
are securely fastened to, the terminal chamber, casing or enclosure of 
the equipment; (3) Openings in ventilated dry-type transformers or 
similar openings in other equipment are designed so that foreign ob- 
jects inserted through these openings will be deflected from energized 
parts. 

(c) In Places Accessible to Qualified Persons Only. Electrical installa- 
tions shall conform with Sections 7 1 0-3 1 to 7 1 0-34 inclusive. 

710-11. Outdoor Installations. Outdoor installations having exposed 
live parts shall be accessible to qualified persons only. Installations are 
considered to be accessible to qualified persons only where enclosed as 
provided in Section 710-31 or when isolated by elevation. Live parts are 
deemed to be isolated by elevation ( 1 ) where the clearance to ground 
and to buildings conforms with Article 730 for outdoor installations, 
and (2) as provided in Section 710-34(f) for locations accessible to 
qualified persons only. 

710-12. Metal Enclosed Equipments. Installations consisting of metal 
enclosed equipments such as metal clad switchgear, transformers, and 
the like, which have no exposed live parts, need not comply with Sec- 
tion 710-31. Ventilating or similar openings in equipment shall be so 
designed that foreign objects inserted through these openings will be de- 
flected from energized parts. Where exposed to physical damage from 
vehicular traffic suitable guards shall be provided. 

C. Equipment — Specific Provisions 

See also references to specific types of installations in Section 710-2. 
710-21. Circuit Interrupting Devices. 
(a) Circuit Breakers. 

(1) Indoor installations shall consist of metal-enclosed units or 
fire-resistant cell-mounted units except that open mounting of circuit 
breakers is permissible in locations accessible to qualified persons only. 

(2) Circuit breakers shall be trip-free in all positions. In every in- 
stallation the circuit breaker rating in respect to closing, carrying or in- 
terrupting capabilities shall not be less than the short circuit duty at the 
point of application. 

(3) Circuit breakers used to control oil-filled transformers should 
be located outside the transformer vault. 

(4) Circuit breakers shall have a means of indicating the open and 
closed position of the breaker at the point (s) from which they may be 
operated. 



ARTICLE 710-OVER 600 VOLTS-GENERAL 70-365 

(5) Oil circuit breakers shall be so arranged or located that adjacent 
readily combustible structures or materials are safeguarded in an ap- 
proved manner. Adequate space separation, fire-resistant barriers or en- 
closures, trenches containing sufficient coarse crushed stone and prop- 
erly drained oil enclosures such as dikes or basins are recognized as 
suitable for this purpose. 

(b) Fuseholders and Fuses. 

(1) Fuses which expel flame in opening the circuit shall be so de- 
signed or arranged that they will function properly without hazard to 
persons or property. 

(2) Fuseholders shall be designed so that they can be de-energized 
while replacing a fuse unless the fuse and fuseholder are designed to 
permit fuse replacement by qualified persons using equipment designed 
for the purpose without de-energizing the fuseholder. 

(3) When high voltage fused cutouts are installed in a building or 
a transformer vault, they shall be of a type designed for use in build- 
ings. Where such cutouts are not suitable to interrupt the circuit man- 
ually while carrying full load, an approved switch or contactor shall 
be provided which is capable of interrupting the entire load. In addi- 
tion, the cutouts shall be interlocked with the approved interrupter or 
bear a conspicuous sign reading "Do Not Open Cutout Under Load." 

The cutouts shall be so located that they may be readily and safely 
operated and re-fused. Fuses shall be accessible from a clear floor 
space. 

(c) Load Interrupters. Load interrupter switches may be used pro- 
viding suitable fuses or circuit breakers are applied in conjunction with 
these devices to interrupt fault currents. When these devices are used in 
combination they shall be so coordinated electrically that they will 
safely withstand the effects of closing, carrying or interrupting all pos- 
sible currents up to the assigned maximum short circuit rating. 

710-22. Isolating Means. Means shall be provided to completely 
isolate an item of equipment. The use of isolating switches is not nec- 
essary where there are other ways of de-energizing the equipment for 
inspection and repairs such as metal-enclosed switchgear units, and 
removable truck panels. Isolating switches should be interlocked with 
the associated circuit interrupting device to prevent their being opened 
under load, otherwise signs warning against opening them under load 
shall be provided. Barriers should be provided on both sides of each 
pole of indoor open-type isolating switches. A fuseholder and fuse, de- 
signed for the purpose, may be used as an isolating switch. 

D. Installations Accessible To Qualified Persons Only 

710-31. Enclosure for Electrical Installations. Electrical installations 
in a vault, room, closet or in an area surrounded by a wall, screen or 
fence, access to which is controlled by lock and key or other approved 
means, are considered to be accessible to qualified persons only. The 
height of the wall, screen or fence should not be less than eight feet 
over-all, unless designed to provide an equivalent degree of isolation. 
The type of enclosure used in a given case shall be designed and con- 
structed according to the nature and degree of the hazard (s) associ- 



70-366 MASSACHUSETTS ELECTRICAL CODE 

ated with the installation. Article 450 covers minimum construction 
requirements for oil-filled transformer vaults. 

Isolation by elevation is covered in Sections 710-11 and 710-34. 

710-32. Circuit Conductors. They may be installed in conduit; in duct 
systems; as metal-armored cable; as bare wire, cable and buses, or as 
nonmetallic sheathed cables or conductors as provided in Sections 710-3 
to 710-6 inclusive. Bare live conductors shall conform with Sections 
710-33 and 710-34. 

Insulators, together with their mounting and conductor attachments, 
when used as supports for wires, single conductor cables and bus-bars, 
shall be capable of safely withstanding the maximum magnetic forces 
which would prevail when two or more conductors of a circuit were 
subjected to short-circuit current. 

Open runs of insulated wires and cables, having a bare lead sheath or 
a braided outer covering, shall be supported in a manner designed to 
prevent physical damage to the braid or sheath. Supports for lead cov- 
ered cables shall be designed to prevent electrolysis of the sheath. 

710-33. Minimum Space Separation Between Live Parts and Adjacent 
Surfaces. The minimum indoor air separation between bare live con- 
ductors and between such conductors and adjacent surfaces shall be 
not less than the values given below. This Section applies to interior 
wiring design and construction. It does not apply to the space separation 
provided in electrical apparatus and wiring devices. 

Table 710-33. Minimum Air Separation in Inches, Indoors* 

Between Bare Live 
Circuit Between Bare Live Conductors and 

Voltage Conductors Adjacent Surfaces 

5,000 3.5 2.5 

15,000 7 5.5 

25,000 11 8.5 

*The values given are the minimum permissible space separation 
under favorable service conditions. They should be increased under 
unfavorable service conditions or wherever space limitations permit. 
Proportional values may be used for intermediate voltages. 

710-34. Work Space and Guarding. 

(a) Working Space. The minimum clear working space in front of 
electrical equipment, such as switchboards, control panels, switches, 
circuit breakers, motor controllers, relays and similar equipment shall 
not be less than set forth in the following table unless otherwise speci- 
fied in this Code. 

Table 710-34(a) 
Minimum Clear Working Space in Front of Electrical Equipment 

Voltage to Ground Conditions 
J 2 3_ 

601-2500 3 ft. 4 ft. 5 ft. 

2501-7500 4 ft. 5 ft. 6 ft. 

over 7500 5 ft. 6 ft. 9 ft. 



ARTICLE 710-OVER 600 VOLTS-GENERAL 70-367 

Where the "Conditions" are as follows: 

(1) Exposed live parts on one side and no live or grounded parts 
on the other side of the working space or exposed live parts on both 
sides effectively guarded by suitable wood or other insulating materials. 
Insulated wire or insulated bus bars operating at not more than 300 
volts shall not be considered live parts. 

(2) Exposed live parts on one side and grounded parts on the other 
side. Concrete, brick or tile walls will be considered as grounded sur- 
faces. 

(3) Exposed live parts on both sides of the work space (not 
guarded as provided in Condition 1 ) with the operator between. 

Exception: Working space is not required in back of assemblies such 
as dead-front switchboards or control assemblies when there are no 
renewable or adjustable parts such as fuses or switches on the back 
and when all connections are accessible from other locations than the 
back. 

(b) Separation from Low-Potential Equipment. When switches, cut- 
outs or other equipment operating at 600 volts or less are installed in a 
room or enclosure where there are exposed live parts or exposed 
wiring operating at more than 600 volts the high potential equipment 
shall be effectively separated from the space occupied by the low po- 
tential equipment by a suitable partition, fence, or screen. 

Exception: Switches or other equipment operating at 600 volts or 
less and serving only equipment within the high-voltage vault, room 
or enclosure may be installed in the high-voltage enclosure, room or 
vault if accessible to qualified persons only. 

(c) Locked Rooms or Enclosures. The entrances to all buildings, 
rooms or enclosures containing exposed live parts or exposed conduc- 
tors operating in excess of 600 volts shall be kept locked, except where 
such entrances are at all times under the observation of a qualified at- 
tendant. 

Where the voltage exceeds 600 volts permanent and conspicuous 
warning signs shall be provided, reading substantially as follows: 
"Warning — High Voltage — Keep Out." 

(d) Illumination. Adequate illumination shall be provided for all 
working spaces about electrical equipment. The light outlets shall be 
so arranged that persons changing lamps or making repairs on the light- 
ing system will not be endangered by live parts or other equipment. 

The points of control shall be so located that persons are not liable 
to come into contact with any live part or moving part of the equip- 
ment while turning on the lights. 

(e) Headroom. The minimum headroom above working spaces 
about switching equipment where there are live parts exposed at any 
time shall be not less than 6Y2 feet. 

(f) Elevation of Unguarded Live Parts. Unguarded live parts above 
working space shall be maintained at elevations not less than required 
by the following table. 



8 





9 





9 


3 


9 


6 


9 


10 


10 


5 


11 





11 


7 


12 


2 



70-368 MASSACHUSETTS ELECTRICAL CODE 

Table 710-34(f) 
Elevation of Unguarded Live Parts Above the Working Space 

Minimum Vertical Clearance of 
Voltage Between Phases Unguarded Parts 
Feet Inches 

601-6600 
6601-11000 
11001-22000 
22001-33000 
33001-44000 
44001-66000 
66001-88000 
88001-110000 
110001-132000 



ARTICLE 720 — CIRCUITS AND EQUIPMENT 
OPERATING AT LESS THAN 50 VOLTS 



720-1. General. This Article shall apply to installations operating at 
less than 50 volts, direct current or alternating current, except such 
as are treated in Articles 650 and 725. 

720-2. Hazardous Locations. Circuits or equipment coming within the 
scope of this Article and installed in hazardous locations shall comply 
with the appropriate provisions of Articles 500-517 inclusive. 

720-3. Larger Current at Lower Voltage. Conductors, devices, and 
equipment shall have current ratings sufficient for the greater current 
required to deliver equal power at the lower voltage than at usual volt- 
ages. 

720-4. Conductors. Conductors shall be not smaller than No. 12, and 
for appliance branch circuits supplying more than one appliance or 
appliance receptacle, conductors shall be not smaller than No. 10. (See 
Section 300-1.) 

720-5. Lampholders. Standard lampholders of rating not less than 
660 watts shall be used. 

720-6. Receptacle Rating. Receptacles shall have a rating not less 
than 15 amperes. 

720-7. Receptacles Required. Receptacles of not less than 20-ampere 
rating shall be provided in kitchens, laundries, and other locations 
where portable appliances are likely to be used. 

720-8. Overcurrent Protection. Overcurrent protection shall comply 
with the provisions of Article 240. 

720-9. Batteries. See Article 480. 

720-1 0. Grounding. See Sections 250-8 and 250-45 (c) . 



ARTICLE 725-REMOTE-CONTROL AND SIGNAL CIRCUITS 70-369 

ARTICLE 725 — REMOTE-CONTROL, LOW- 
ENERGY POWER, LOW- VOLTAGE POWER AND 
SIGNAL CIRCUITS 

A. Scope and General 

725-1. Scope. Provisions of this Article shall apply to remote-control 
circuits, including low voltage relay switching, low-energy power cir- 
cuits, low-voltage power circuits and signal circuits, as defined in Article 
100, Definitions. 

The provisions of this Article are not intended to apply to remote-control, 
low-energy or signal circuits which form an integral part of a device or ap- 
pliance. 

725-2. Hazardous Locations. Circuits or equipment coming within the 
scope of this Article and installed in hazardous locations shall also 
comply with the appropriate provisions of Articles 500-517 inclusive. 

725-3. Classification. Remote-control and signal circuits shall be clas- 
sified as follows: 

(a) Class 1 Circuits. Control and signal circuits in which power is 
not limited in accordance with Section 725-3 1 . 

(b) Class 2 Circuits. Control and signal circuits in which the power 
is limited in accordance with Section 725-31. 

725-4. Low-Energy Power Circuits. Circuits which are neither remote- 
control nor signal circuits, but which have the power limited in accord- 
ance with Section 725-31 shall, for the purpose of this Code, be treated 
as Class 2 remote-control circuits. 

725-5. Low-Voltage Power Circuits. Circuits which are neither remote- 
control nor signal circuits but which operate at not more than 30 volts, 
where the current is not limited in accordance with Section 725-31, and 
which are supplied from a source not exceeding 1000 volt-amperes 
shall for the purpose of this Code be treated as Class 1 remote-control 
circuits. 

725-6. Safety-Control Devices. Remote-control circuits to safety-con- 
trol devices, the failure of operation of which would introduce a direct 
fire or life hazard, shall be considered as Class 1 circuits. 

Room thermostats, service hot-water temperature regulating devices, and 
similar controls used in conjunction with electrically controlled domestic 
heating equipment, are not considered to be safety-control devices. 

725-7. Remote-Control and Signal Circuits in Communication Cables. 

Remote-control and signal circuits, which use conductors in the same 
cable with communication circuits, shall, for the purpose of this Article, 
be classified as communication circuits and meet the requirements of 
Article 800, of this Code. 

B. Class 1 System 

725-11. Wiring Method. Conductors and equipment of Class 1 re- 
mote-control and signal systems and low voltage power circuits shall be 



70-370 MASSACHUSETTS ELECTRICAL CODE 

installed in accordance with the requirements of the appropriate Articles 
in Chapter 3 of this Code, except as provided in Sections 725-12 to 
725-15 inclusive. 

725-12. Other Articles. The wiring method required in Section 725-11 
does not apply where other Articles of this Code specifically permit or 
require other methods for remote-control or signal circuits. See Article 
620, Elevators, for example. 

725-13. Conductor Sizes. Nos. 18 and 16 gage conductors may be 
used provided they are installed in a raceway or a cable approved for 
the purpose, or in flexible cords in accordance with the provisions of 
Article 400. 

725-14. Conductor Insulation. Conductors larger than No. 16 shall 
be rubber-covered Type R, thermoplastic-covered Type T, or other 
approved type. Fixed conductors Nos. 18 and 16 gage shall have an 
insulation at least equal to that of Type TF thermoplastic-covered fixture 
wire. Conductors approved for the purpose having insulation of a thick- 
ness less than specified above or having other kinds of insulation may 
be used. 

725-15. Number of Conductors in Raceways. The number of conduc- 
tors of remote-control or signal circuits in a raceway may be determined 
according to Section 300-17 and Note 8 of Tables 310-12 through 310- 
15 need not be observed. Where there are four or more conductors in 
a raceway, some of which are remote-control, as permitted by Section 
300-3, the provisions of Note 8 of Tables 310-12 through 310-15 shall 
apply, as determined by the number of power and lighting circuit con- 
ductors only. 

725-16. Conductors of Different Systems. Conductors of two or more 
Class 1 remote-control and/or signal circuits may occupy the same en- 
closure or raceway without regard to whether the individual systems or 
circuits are alternating or direct current, provided all conductors are 
insulated for the maximum voltage of any conductor in the enclosure 
or raceway. Conductors of remote-control, low-energy power and sig- 
nal circuits, in which the current is limited as for Class 2 systems, shall 
be considered as Class 1 system conductors for the purpose of this re- 
quirement if insulated and installed in accordance with the provisions 
for Class 1 system conductors. Power supply conductors may occupy 
the same enclosure or raceway with Class 1 system conductors when 
supplying only equipment to which Class 1 system conductors are 
connected. 

725-17. Mechanical Protection of Remote-Control Circuits. Where dam- 
age to a remote-control circuit would introduce a hazard as covered 
in Section 725-6, all conductors of such remote-control circuits shall 
be installed in conduit, electrical metallic tubing, Type MI cable or be 
otherwise suitably protected from physical damage. 

725-18. Overcurrent Protection. Conductors shall be protected against 
overcurrent in accordance with the ampacities of Tables 310-12 through 
310-15 except as follows: 

Exception No. 1. Other Articles. Where other Articles of this Code 
specifically permit or require other overcurrent protection. See Sections 
430-72 and 620-61. 



ARTICLE 725-REMOTE-CONTROL AND SIGNAL CIRCUITS 70-371 

Exception No. 2. Conductors of Nos. 18 and 16. Conductors of Nos. 
18 and 16 shall be considered as protected by overcurrent devices of 20- 
ampere rating or setting. 

Exception No. 3. Omission of Overcurrent Protection. In remote- 
control and signal circuits having main and branch circuits, the branch 
circuits need not be individually protected against overcurrent where 
the operating voltage does not exceed 30 volts. 

725-19. Location of Overcurrent Protection. Overcurrent devices shall 
be located at the point where the conductor to be protected receives its 
supply unless the overcurrent device protecting the larger conductor 
also protects the smaller conductor in accordance with Tables 310-12 
through 310-15. 

725-20. Circuits Extending Beyond One Building. Class 1 circuits 
which extend aerially beyond one building shall also meet the require- 
ments of Article 730. 

725-21. Grounding. Class 1 remote-control and signal circuits and 
equipment shall be grounded in accordance with Article 250. 

C. Limitation of Low-Voltage Power Circuit 

725-22. Overcurrent Protection. Transformer devices supplying low- 
voltage power circuits shall be provided with overcurrent protection in 
the secondary circuit rated or set at not more than 250 per cent of the 
rated secondary current of the transformer. Such protection and mount- 
ing shall be approved for the purpose. Overcurrent protection required 
shall not be interchangeable with protection of a higher rating. The 
overcurrent protection may be an integral part of a transformer or 
other power supply device approved for the purpose. 

725-23. Transformer Rating. Transformer devices supplying low-volt- 
age power circuits shall be approved for the purpose and be restricted 
in their rated output to not exceeding 1000 volt-amperes and to not 
exceeding 30 volts. They shall be marked where plainly visible to show 
their rated output and the voltage to be applied to the circuit. 

A transformer is considered as meeting the 1000 volt-ampere requirement 
where the approximate temperature limit is reached at 1000 volt-ampere 
load. 

D. Class 2 System Voltage and 
Current Limits 

725-31. Limits of Class 2 Systems. Class 2 remote-control and signal 
systems, depending on the voltage shall have the current limited as fol- 
lows: 

(a) Maximum 15 Volts: 5 Amperes. Circuits in which the open-cir- 
cuit voltage does not exceed 15 volts and having overcurrent protec- 
tion of not more than 5-amperes rating. Where the current supply is 
from a transformer or other device having energy-limiting character- 
istics and approved for the purpose, or from primary batteries, the 
overcurrent protection may be omitted. 

(b) 15 to 30 Volts: 3.2 Amperes. Circuits in which the open-circuit 
voltage exceeds 15 volts but does not exceed 30 volts and having over- 



70-372 MASSACHUSETTS ELECTRICAL CODE 

current protection of not more than 3.2 amperes rating. Where the 
current supply is from a transformer or other device having energy- 
limiting characteristics and approved for the purpose, or from primary 
batteries, the overcurrent protection may be omitted. 

(c) 30 to 60 Volts: 1.6 Amperes. Circuits in which open-circuit 
voltage exceeds 30 volts but does not exceed 60 volts and having over- 
current protection of not more than 1.6 amperes rating. Where the 
current supply is from a transformer or other device having energy- 
limiting characteristics and approved for the purpose, the overcurrent 
protection may be omitted. 

(d) 60 to 150 Volts: 1 Ampere. Circuits in which the open-circuit 
voltage exceeds 60 volts but does not exceed 150 volts, and having over- 
current protection of not more than 1 -ampere rating, provided that such 
circuits are equipped with current-limiting means other than overcur- 
rent protection which will limit the current as a result of a fault to not 
exceeding 1 ampere. 

725-32. Overcurrent Protection and Mounting. Where current is lim- 
ited in Class 2 systems by means of overcurrent protection, such pro- 
tection and its mounting shall be approved for the purpose. Overcur- 
rent protection required shall not be interchangeable with protection of 
a higher rating. The overcurrent protection may be an integral part of a 
transformer or other power supply device approved for the purpose. 

725-33. Transformer Rating. Transformer devices supplying Class 2 
systems shall be approved for the purpose and be restricted in their 
rated output to not exceeding 100 volt-amperes. Such devices shall not 
be paralleled or otherwise interconnected. They shall be marked where 
plainly visible to show the voltage to be applied to the circuit. 

A transformer is considered as meeting the 100 volt-ampere requirement 
if the approximate temperature limit is reached at a 100-volt-ampere load. 

725-34. Transformer Leads. The primary leads of transformers sup- 
plying Class 2 remote-control and signal circuits may be smaller than 
No. 14 but not smaller than No. 18, provided they are not over 12 
inches long, have insulation at least equal to type RF-2 rubber-cov- 
ered fixture wire, or approved equivalent. 

E. Installation of Class 2 Remote-Control and 
Signal Circuits 

725-41. On Supply Side of Overcurrent Protection, Transformers or 
Current-Limiting Devices. Conductors and equipment on supply side 
of overcurrent protection, transformers or current-limiting devices shall 
be installed in accordance with the appropriate requirements of Chap- 
ter 3 of this Code. Transformers or other devices supplied from elec- 
tric light and power circuits shall be protected by an overcurrent device 
with a rating or setting not exceeding 20 amperes. 

725-42. On Load Side of Overcurrent Protection, Transformer or Current- 
Limiting Devices. Conductors on load side of overcurrent protection, 
transformer or current-limiting devices shall be insulated and shall 
comply with the following: 

(a) Separation from Other Conductors. Conductors shall be sepa- 
rated from conductors of electric light and power circuits as follows: 



ARTICLE 725— REMOTE-CONTROL AND SIGNAL CIRCUITS 70-373 

(1) Open Conductors. Conductors shall be separated at least 2 inches 
from any light or power conductors not in a raceway unless permanently 
separated from the conductors of the other system by a continuous and firmly 
fixed nonconductor, such as porcelain tubes or flexible tubing, additional to 
the insulation on the wire. 

(2) In Raceways and Boxes. Conductors of Class 2 remote-control and 
signal circuits shall not be placed in any raceway, compartment, outlet box 
or similar fitting with conductors for either light and power circuits or Class 
1 signal and control circuits, unless the conductors of the different systems 
are separated by a partition; provided that this shall not apply to conductors 
in outlet boxes, junction boxes or similar fittings or compartments where 
power supply conductors are introduced solely for supplying power to the 
remote-control or signal equipment to which the other conductors in the en- 
closure are connected. (See Section 725-16.) 

(3) In Shafts. Conductors may be run in the same shaft with con- 
ductors for light and power where the conductors of the two systems are 
separated at least 2 inches, or where the conductors of either system are en- 
cased in noncombustible tubing. In hoistways conductors shall be installed in 
rigid conduit or electrical metallic tubing except as provided for in Section 
620-21 Exception No. 1. 

(b) Vertical Runs. Conductors in a vertical run in a shaft or partition 
shall have a fire resistant covering capable of preventing the carrying of fire 
from floor to floor except where conductors are encased in tubing or other 
outer covering of noncombustible material or are located in a fireproof shaft 
having fire stops at each floor. 

Where 3 or more conductors are used, such conductors shall be grouped under 
a common braid or covering. 

(c) Conductor Insulation. Conductor insulation shall comply with the 
following: 

(1) 30 Volts or Less. The insulation shall be suitable for the particular 
application. 

The kind of insulation for the conductors is not specified in further detail 
as reliance is placed on current limitation to stop dangerous currents. 

(2) 30 to 150 Volts. Conductors of a cable shall be of solid or 
stranded copper not smaller than No. 22 AWG, and shall have thermoplastic 
insulation of not less than 0.012 inch nominal (0.010 inch minimum) thick- 
ness. The cable conductors shall have a thermoplastic jacket overall having a 
nominal thickness of not less than 0.035 inch (0.030 inch minimum). Where 
the number of conductors in a cable exceeds 4, the thickness of the thermo- 
plastic jacket overall shall be increased so as to provide equivalent perform- 
ance characteristics. Similarly, where the size of conductors in a cable exceeds 
No. 16 gage, the thickness of the conductor insulation shall be increased so 
as to provide equivalent performance characteristics. 

Two-conductor assemblies of No. 16 gage or smaller, may be in flat paral- 
lel construction with 1/32 inch nominal integral-insulation jacket and an 
0.047 inch minimum web. Approved low-energy circuit cable may be used. 



70-374 MASSACHUSETTS ELECTR ICAL CODE 

Other insulation having equivalent performance characteristics may 
be acceptable. 

Where single conductors are used they shall be not smaller than No. 
18 AWG and shall be insulated in conformity with Section 725-14. 

725-43. Circuits Extending Beyond One Building. Class 2 remote- 
control and signal circuits which extend beyond one building and are 
so run as to be subject to accidental contact with light or power conduc- 
tors operating at a potential exceeding 300 volts, shall also meet the re- 
quirements of Sections 800-2, 800-1 1 and 800-12. 

725-44. Grounding. Class 2 remote-control and signal circuits and 
equipment shall be grounded in accordance with Article 250. 



ARTICLE 730 — OUTSIDE BRANCH CIRCUITS 
AND FEEDERS 



730-1. Scope. This Article applies to electrical equipment and wiring 
for the supply of utilization equipment located on or attached to the 
outside of public and private buildings, or run between buildings, struc- 
tures or poles on other premises served; but, shall not apply to equip- 
ment or wiring of an electric or communication utility used in the ex- 
ercise of its function as a utility. 

730-2. Application of Other Articles. Application of other Articles, 
including additional requirements to specific cases of equipment and 
conductors, are as follows: 

Articles 

200 — Polarity Identification. 

210 — Branch Circuits. 

215 — Feeders. 

230 — Services. , 

250 — Grounding. 

500 — Hazardous Locations, General. 

510 — Hazardous Locations, Specific. 

600 — Signs and Outline Lighting. 

710 — Circuits and Equipment Operating at More than 600 Volts. 

725 — Remote Control and Signal Circuits. 

800 — Communication Circuits. 

810 — Radio and Television Circuits. 

730-3. Calculation of Load. 

(a) Branch Circuits. The load on every outdoor branch circuit is 
to be determined by the applicable provisions of Article 220. 

(b) Feeders. The load to be expected on every outdoor feeder is to 
be determined by the procedure specified in Article 220. 

730-4. Conductor Covering. Where within 10 feet of any building or 
structure, open conductors supported on insulators shall be insulated or 
covered. Conductors in cables or raceways, except Type MI Cable, 



ARTICLE 730-OUTSIDE BRANCH CIRCUITS AND FEEDERS 70-375 

shall be of the rubber-covered type or thermoplastic type and in wet lo- 
cations shall comply with Section 310-5. Conductors for festoon light- 
ing shall be of the rubber-covered or thermoplastic type. 

730-5. Size of Conductors. The ampacity of outdoor branch circuits 
and feeder conductors shall be according to the rating in Tables 310-12 
through 310-15 in order to carry the loads determined under Section 
730-3. 

730-6. Minimum Size of Conductor. 

(a) Overhead Spans. Overhead conductors shall not be smaller than 
No. 10 for spans up to 50 feet in length, and not smaller than No. 8 for 
longer spans. 

(b) Festoon Lighting. Overhead conductors for festoon lighting shall 
not be smaller than No. 12 unless supported by messenger wires. (See 
Section 730-25.) 

(c) Over 600 Volts. Overhead conductors operating at more than 
600 volts shall not be smaller than No. 6 when open individual con- 
ductors nor smaller than No. 8 when in cable. 

730-7. Lighting Equipment on a Pole. 

(a) For the supply of lighting equipment installed on a single pole 
or structure, the branch circuits shall comply with the requirements of 
Article 210. 

(b) For multiwire branch circuits, a common neutral may be em- 
ployed for the branch circuits, provided not more than 8 ungrounded 
conductors are used. Such a common neutral shall have an ampacity of 
not less than the maximum load of all the ungrounded conductors con- 
nected to any phase or polarity. 

730-8. Disconnection. 

(a) For branch circuits as required in Article 210. 

(b) For feeders as required in Article 215. (At each building supplied 
by a feeder see Section 230-76.) 

730-9. Overcurrent Protection. 

(a) For branch circuits as required in Article 210. 

(b) For feeders as required in Article 215. 

730-10. Wiring on Buildings. Outside wiring on surfaces of buildings 
may be installed, for circuits of 600 volts or less, as open conductors 
on insulating supports, as multiple-conductor cable approved for the 
purpose, as aluminum sheathed cable, in rigid metal conduit, in bus- 
ways as provided in Article 364, or in electrical metallic tubing. Circuits 
of more than 600 volts shall be installed as provided for services in Sec- 
tion 230-101. Circuits for sign and outline lighting shall be installed as 
provided in Article 600. 

730-11. Circuit Exits and Entrances. Where outside branch and feeder 
circuits exit from or enter into buildings the installation shall comply 
with those requirements of Article 230 which apply to service entrance 
conductors. 

730-12. Open Conductor Supports. Open conductors shall be sup- 
ported on glass or porcelain knobs, racks, brackets, or strain insulators, 
approved for the purpose. 



70-376 MASSACHUSETTS ELECTRICAL CODE 

730-13. Festoon Supports. In spans exceeding 40 feet the conductors 
shall be supported by a messenger wire supported by approved strain 
insulators. Conductors or messenger wires shall not be attached to any 
fire escape, downspout, or plumbing equipment. 

730-14. Open Conductor Spacings. Conductors shall conform to the 
following spacings: 

(a) Open Conductors Exposed to the Weather. As provided in Sec- 
tion 230-47. 

(b) Open Conductors Not Exposed to Weather. As provided in Sec- 
tion 230-48. 

(c) Over 600 Volts. As provided in Section 230-101 (c) . 

(d) Separation from Other Circuits. Open conductors shall be sep- 
arated from open conductors of other circuits or systems by not less 
than 4 inches. 

(e) Conductors On Poles. Conductors on poles shall have a separa- 
tion of not less than 1 foot except when placed on racks or brackets. 
Conductors supported on poles shall provide a horizontal climbing 
space not less than the following: 

Power conductors, below communication 

conductors 30 inches 

Power conductors alone or above communication conductors : 

Less than 300 volts 24 inches 

Exceeding 300 volts 30 inches 

Communication conductors below power 

conductors same as power conductors 

Communication conductors alone or above power 

conductors no requirement 

730-1 5. Supports Over Buildings. See Section 230-25. 

730-1 6. Point of Attachment to Buildings. See Section 230-26. 

730-1 7. Means of Attachment to Buildings. See Section 230-27. 

730-18. Clearance from Ground. Open conductors of not over 600 
volts shall conform to the following: 

(a) Over Driveways. Conductors above alleys and above driveways 
on other than residential property shall have a clearance above ground 
of not less than 1 8 feet. 

(b) Over Lots. Conductors supplying lights in automobile parking 
lots, drive-in establishments, and similar commercial areas shall have 
clearances above ground of not less than 1 2 feet. 

(c) Over Footwalks, etc. On residential property, and elsewhere 
across spaces accessible to pedestrians only, conductors between build- 
ings shall have a clearance of not less than 10 feet. 

Note : For clearances of conductors of over 600 volts see National Electri- 
cal Safety Code. 



ARTICLE 730-OUTSIDE BRANCH CIRCUITS AND FEEDERS 70-377 

730-19. Clearances from Buildings for Conductors not in Excess of 600 
Volts. 

(a) Over Roofs. Open conductors shall not be less than 8 feet from 
the highest point of roofs. Conductors attached to roof structures shall 
be substantially supported. Wherever practicable, conductors crossing 
over buildings shall be supported on structures which are independent 
of the building. 

For Service Drop Conductors see Section 230-24(a). 

(b) Horizontal Clearances. Open conductors not attached to a build- 
ing shall have a minimum horizontal clearance of 36 inches. 

(c) Final Spans. Final spans of feeders or branch circuits to build- 
ings which they supply or from which they are fed may be attached to 
the building but they shall be kept 3 feet from windows, doors, porches, 
fire escapes or similar locations. 

(d) Zone for Fire Ladders. Where buildings exceed 3 stories, or 50 
feet in height, overhead lines shall be arranged where practicable so 
that a clear space (or zone) at least 6 feet wide will be left either ad- 
jacent to the buildings or beginning not over 8 feet from them, to facili- 
tate the raising of ladders when necessary for fire fighting. 

Note: For clearance of conductors over 600 volts, consult National Elec- 
trical Safety Code. 

730-20. Mechanical Protection of Conductors. Mechanical protection 
of conductors on buildings, structures or poles shall be as provided for 
services, Section 230-46. 

730-21. Conductors Entering Buildings. Conductors entering buildings 
shall be as provided for services, Sections 230-44, -49, and -51. 

730-22. Multiple Conductor Cables on Exterior Surfaces of Buildings. 

Multiple conductor cables on exterior surfaces of buildings shall be as 
provided for service cable, Section 230-50. 

730-23. Raceways on Exterior Surfaces of Buildings. Raceways on 
exterior surfaces of buildings shall be made raintight and suitably 
drained. 

730-24. Underground Circuits. Underground circuits shall be as pro- 
vided for services, Sections 230-32 to -34. 

730-25. Outdoor Lighting Equipment — Lampholders. Lampholders 

shall be of molded composition, or other approved material of the 
weatherproof type, and where they are attached as pendants shall have 
the connections to the circuit wires staggered. Where lampholders have 
terminals of a type which puncture the insulation and make contact 
with the conductors, they shall be attached only to conductors of the 
stranded type. 

730-26. Outdoor Lighting Equipment — Location of Lamps. Location 
of lamps for outdoor lighting shall be below all live conductors, trans- 
formers, or other electrical equipment, unless clearances or other safe- 
guards are provided for relamping operations, or unless the installation 
is controlled by a disconnecting means which can be locked in the open 
position. 



70-378 MASSACHUSETTS ELECTRICAL CODE 

Chapter 8. Communication Systems 
ARTICLE 800 — COMMUNICATION CIRCUITS 

A. General 

800-1. Scope. The provisions of this Article shall apply to telephone, 
telegraph (except radio), district messenger, fire and burglar alarms 
and similar central station systems and to telephone systems not con- 
nected to a central station system but using similar type of equipment, 
methods of installation and maintenance. 

Such protective measures as are essential to safeguard these systems un- 
der the various conditions to which they are subjected are outlined in these 
rules. 

For detailed service requirements for fire alarm, sprinkler supervisory or 
watchman systems, see the Standards of the National Fire Protection Asso- 
ciation.* 

B. Protection 

800-2. Protective Devices. A protector approved for the purpose shall 
be provided on each circuit, aerial or underground, so located within 
the block containing the building served as to be liable to accidental 
contact with light or power conductors operating at a potential exceed- 
ing 300 volts, and on each circuit run partly or entirely in aerial wire or 
cable not confined within a block. 

The word "block" as used in this Article shall be construed to mean a 
square or portion of a city, town, or village enclosed by streets and includ- 
ing the alleys so enclosed but not any street. 

(a) Location. The protector shall be located in or on the building as 
near as practicable to the point where the conductors enter. In the 
case of an underground entrance the protector may be located at the 
junction of the underground and the aerial wires. 

(b) Hazardous Locations. The protector shall not be located in any 
hazardous location as defined in Article 500, nor in the vicinity of eas- 
ily ignitible material. 

(c) Protector Requirements. The protector shall be mounted on a 
noncombustible, nonabsorptive insulating base and shall consist of an 
arrester between each line conductor and the ground, and a fuse in 
each line conductor, the fuses protecting the arrester except as spec- 
ified in Section 800-2(d). The protector terminals shall be plainly 
marked to indicate line, instrument, and ground. 

(d) Omission of Fuses. A protector without fuses may be used under 
any of the following conditions: 

''The NFPA standards on fire alarm and supervisory systems are pub- 
lished by the NFPA in the National Fire Codes, Vol. 7 and in separate pam- 
phlet form by the NFPA (NFPA Nos. 71, 72A, 72B, 72C, 72D, and 73). 



ARTICLE 800-COMMUNICATION CIRCUITS 70-379 

(1) Where circuits enter a building through metal-sheathed cable, 
or through a nonmetallic sheathed cable having a metal grounding 
shield between the sheath and the conductor assembly, provided the 
metal sheath or shield of the cable is effectively grounded and the con- 
ductors in the cable shall safely fuse at currents less than the ampacity 
of the protector, the associated insulated conductors, and the protector 
grounding conductor. 

(2) Where insulated conductors in accordance with Section 800-1 1 
(c-1 and -2) are used to extend circuits to a building from a metal- 
sheathed cable or from a nonmetallic-sheathed cable having a metal 
grounding shield between the sheath and the conductor assembly pro- 
vided the metal sheath or shield is effectively grounded and the con- 
ductors in the cable or cable stub shall safely fuse at currents less than 
the ampacity of the protector, the associated insulated conductors, and 
the protector grounding conductor. 

(3) Where insulated conductors, in accordance with Section 800-1 1 
(c-1) or (c) (2) are used to extend circuits to a building from other 
than grounded metal-sheathed or shielded cable, provided (a) the pro- 
tector is approved for this purpose and (b) the protector grounding 
conductor is connected to a water pipe electrode or the grounding con- 
ductor or grounding electrode of a multi-grounded neutral power sys- 
tem and (c) the connections of the insulated conductors to the exposed 
plant or the conductors of the exposed plant shall safely fuse at currents 
less than the ampacity of the protector, the associated insulated conduc- 
tors, and the protector grounding conductor. 

(4) Where insulated conductors in accordance with Section 800- 
1 1 (c-1 and -2) are used to extend circuits aerially to a building from an 
unexposed buried or underground circuit. 

Effectively grounded means permanently connected to earth through a 
ground connection of sufficiently low impedance and having sufficient am- 
pacity to prevent the building up of voltages which may result in undue 
hazard to connected equipment or to persons. 

800-3. Installation of Conductors. Conductors from the protector to 
the equipment or, where no protector is required, conductors attached 
to the outside of, or inside the building shall comply with the follow- 
ing: 

(a) Separation from Other Conductors. Conductors shall be sepa- 
rated from conductors of electric light and power circuits as follows: 

(1) Open Conductors. Conductors shall be separated at least 2 
inches from any light or power conductors not in metallic raceways or 
metal-sheathed cable unless permanently separated from the conduc- 
tors of the other system by a continuous and firmly fixed nonconduc- 
tor, additional to the insulation on the wire, such as porcelain tubes 
or flexible tubing. 

(2) In Raceways and Boxes. Communication conductors shall 
not be placed in any raceway, compartment, outlet box, junction box 
or similar fitting with conductors for light and power circuits or Class 
1 signal and control circuits unless the conductors of the different sys- 
tems are separated by a partition; provided that this shall not apply to 



70-380 MASSACHUSETTS ELECTRICAL CODE 

conductors in outlet boxes, junction boxes or similar fittings or com- 
partments where such conductors are introduced solely for power sup- 
ply to communication equipment or for connection to remote-control 
equipment. 

(3) In Shafts. Conductors may be run in the same shaft with 
conductors for light and power provided the conductors of the two 
systems are separated at least 2 inches, or where the conductors of ei- 
ther system are encased in noncombustible tubing. 

(b) Vertical Runs. Conductors bunched together in a vertical run 
in a shaft shall have a fire-resistant covering capable of preventing the 
carrying of fire from floor to floor, except where conductors are en- 
cased in noncombustible tubing or are located in a fireproof shaft hav- 
ing fire stops at each floor. 

The conductors referred to in this Section would ordinarily be insulated 
but the kind of insulation is not specified as reliance is placed on the protec- 
tive device to stop all dangerous voltages and currents. 

C. Outside Conductors 

800-11. Overhead Conductors. Overhead conductors entering build- 
ings shall comply with the following: 

(a) On Poles. Where communication conductors and light or power 
conductors are supported by the same pole, the following conditions 
shall be met: 

(1) Relative Location. The conductors should preferably be lo- 
cated below the light or power conductors. 

(2) Attachment to Crossarms. Conductors shall not be attached 
to a crossarm which carries light or power conductors. 

(3) Climbing Space. The climbing space through signal con- 
ductors shall comply with the requirements of Section 730-14. 

(b) On Roofs. Conductors passing over buildings shall be kept at 
least 8 feet above any roof which may be readily walked upon, except 
small auxiliary buildings such as garages and the like. 

(c) Circuits Requiring Protectors. Circuits which require protectors 
(see Section 800-2) shall comply with the following: 

(1) Insulation, Single or Paired Conductors. Each conductor, 
from the last outdoor support to the protector, shall have 1/32-inch 
rubber insulation, except that when such conductors are entirely within 
a block the insulation on the conductor may be less than 1/32 inch, but 
not less than 1/40 inch in thickness. In addition, the conductor, either 
individually or over the pair, shall be covered with a substantial fibrous 
covering or equivalent protection. Conductors approved for the pur- 
pose having rubber insulation of a thickness less than specified above, 
or having other kinds of insulation may be used. 

(2) Insulation, Cables. Conductors within a cable of the metal- 
sheathed type, or within a cable having a rubber sheath of at least 1/32- 
inch thickness and covered with a substantial fibrous covering, may 
have paper or other suitable insulation. Where the metal or rubber 



ARTICLE 800-COMMUNICATION CIRCUITS 70-381 

sheath is omitted, each conductor shall be insulated as required in Sec- 
tion 800-1 l(c-l), and the bunched conductors shall be covered with a 
substantial fibrous covering or equivalent covering. 

(3) On Buildings. Open conductors shall be separated at least 4 
inches from light or power conductors not in conduit or cable, unless 
permanently separated from conductors of the other system by a con- 
tinuous and firmly fixed nonconductor additional to the insulation 
on the wires, such as porcelain tubes or flexible tubing. Open conduc- 
tors exposed to accidental contact with light and power conductors 
operating at over 300 volts, and attached to buildings, shall be sepa- 
rated from woodwork by being supported on glass, porcelain or other 
insulating material approved for the purpose except that such separa- 
tion is not required where fuses are omitted as provided for in Section 
800-2 (d) or where conductors approved for the purpose are used to 
extend circuits to a building from a cable having a grounded metal 
sheath. 

(4) Entering Buildings. Where a protector is installed inside the 
building, the conductors shall enter the building either through a non- 
combustible, nonabsorptive insulating bushing, or through a metal race- 
way. The insulating bushing may be omitted where the entering con- 
ductors (1) are in metal-sheathed cable, (2) pass through masonry, 
( 3 ) are approved for the purpose and fuses are omitted as provided for 
in Section 800-2 (d), or (4) are approved for the purpose and are used 
to extend circuits to a building from a cable having a grounded metal 
sheath. Raceways or bushings shall slope upward from the outside or, 
where this cannot be done, drip loops shall be formed in the conductors 
immediately before they enter the building. Raceways shall be equipped 
with an approved service head. More than one conductor may enter 
through a single raceway or bushing. Conduits or other metallic race- 
ways located ahead of the protector shall be grounded. 

800-12. Lightning Conductors. Where practicable, a separation of at 
least six feet shall be maintained between open conductors of com- 
munication systems on buildings and lightning conductors. 

D. Underground Circuits 

800-21. Underground Circuits. Underground conductors of communi- 
cation circuits entering buildings shall comply with the following: 

(a) With Electric Light or Power Conductors. Underground conduc- 
tors in a duct, handhole, or manhole containing electric light or power 
conductors, shall be in a section separated from such conductors by 
means of brick, concrete, or tile partitions. 

(b) Underground Block Distribution. Where the entire street circuit 
is run underground and the circuit within the block is so placed as to be 
free from liability of accidental contact with electric light or power cir- 
cuits of over 300 volts, the insulation requirements of Section 800-11 
(c-1 and c-4) shall not apply, the conductors need not be placed on in- 
sulating supports and no bushings shall be required where the conduc- 
tors enter the building. 



70-382 MASSACHUSETTS ELECTRICAL CODE 

E. Grounding 
800-31. Grounding. Equipment shall be grounded as follows: 

(a) Cable Sheath. The metal sheath of aerial cables entering buildings 
which are liable to contact with electric light or power conductors shall be 
grounded or shall be interrupted close to the entrance to the building by an 
insulating joint or equivalent device. 

(b) Protector Ground. The protector ground shall comply with the fol- 
lowing: 

(1) Insulation. The grounding conductor shall have a 1/32-inch rubber 
insulation and shall be covered by a substantial fibrous covering. Conductors 
approved for the purpose having less than 1/32-inch rubber insulation or 
having other kinds of insulation may be used. 

(2) Size. The grounding conductor shall not be smaller than No. 
1 8 copper. 

(3) Run in Straight Line. The grounding conductor shall be run in as 
straight a line as practicable to the grounding electrode. 

(4) Physical Damage. Where necessary, the grounding conductor shall 
be guarded from physical damage. 

(5) Electrode. The grounding conductor shall preferably be connected 
to a water pipe electrode. Where a water pipe is not readily available and the 
grounded conductor of the power service is connected to the water pipe at 
the building, the protector grounding conductor may be connected to the 
power service conduit, service equipment enclosures, or grounding conductor 
of the power service. 

Gas piping shall not be used for grounding. In the absence of a water pipe, 
connection may be made to an effectively grounded metallic structure, or to 
a ground rod or pipe driven into permanently damp earth. Steam or hot water 
pipes, or lightning rod conductors shall not be employed as electrodes for 
protectors. A driven rod or pipe used for grounding power circuits shall not 
be used for grounding communication circuits unless the driven rod or pipe 
is connected to the grounded conductor of a multigrounded neutral power 
system. The requirements for separate made electrodes for power and light- 
ing system grounds, those for communication systems, and those for a 
lightning rod installation shall not prohibit the bonding together of all such 
made electrodes. See Section 250-86. 

All separate electrodes shall be bonded together to limit potential dif- 
ferences between them and between their associated wiring systems. 

(6) Electrode Connection. The grounding conductor shall be attached 
to a pipe electrode by means of a bolted clamp to which the conductor is 
soldered or otherwise connected in an effective manner. 

In every case the connection to the grounding electrode shall be made as 
close to the earth as practicable. 



ARTICLE 810— RADIO AND TV EQUIPMENT 70-383 

ARTICLE 810 — RADIO AND TELEVISION 
EQUIPMENT 

A. General 

810-1. Scope. This Article shall apply to radio and television receiving 
equipment and to amateur radio transmitting and receiving equipment, but 
shall not apply to equipment and antennas used for coupling carrier current 
to power line conductors. 

The authority enforcing this Code shall be freely consulted as to the 
specific methods to be followed in any case of doubt relative to installation 
of antenna conductors and that the National Electrical Safety Code, Part 5, 
be followed. 

810-2. Application of Other Articles. Wiring from the source of power to 
and between devices connected to the interior wiring system shall comply with 
Chapters 1 to 4, inclusive, except as modified by Sections 640-3, 640-4 and 
640-5. Wiring for radio-frequency and audio-frequency equipment and loud- 
speakers shall comply with Article 640. 

810-3. Community Television Antenna. The antenna shall comply with 
the requirements of this Article. The distribution system shall comply with 
Article 800. 

810-4. Radio Noise Suppressors. Radio interference eliminators, inter- 
ference capacitors or radio noise suppressors connected to power supply leads 
shall be of a type approved for the purpose. They shall not be exposed to 
physical damage. 

B. Receiving Equipment Only 

Antenna Systems — Genera! 

810-11. Material. Antenna and lead-in conductors shall be of hard-drawn 
copper, bronze, aluminum alloy, copper-clad steel or other high-strength, 
corrosion-resistant material. Soft-drawn or medium-drawn copper may be 
used for lead-in conductors where the maximum span between points of 
support is less than 35 feet. 

810-12. Supports. Outdoor antenna and lead-in conductors shall be se- 
curely supported. They shall not be attached to poles or similar structures 
carrying electric light or power wires or trolley wires of more than 250 volts 
between conductors. Insulators supporting the antenna conductors shall have 
sufficient mechanical strength to safely support the conductors. Lead-in con- 
ductors shall be securely attached to the antenna. 

810-13. Avoidance of Contacts with Conductors of Other Systems. Out- 
door antenna and lead-in conductors from an antenna to a building shall 
not cross over electric light or power circuits and shall be kept well away from 
all such circuits so as to avoid the possibility of accidental contact. Where 
proximity to electric light and power service conductors of less than 250 
volts between conductors cannot be avoided, the installation shall be such 
as to provide a clearance of at least two feet. Antenna conductors shall be so 
installed as not to cross under electric light or power conductors. 



70-384 MASSACHUSETTS ELECTRICAL CODE 

810-14. Splices. Splices and joints in antenna spans shall be made with 
approved splicing devices or by such other means as will not appreciably 
weaken the conductors. 

810-15. Grounding. Masts and metal structures supporting antennas shall 
be permanently and effectively grounded, without intervening splice or con- 
nection. 

Antenna Systems — Receiving Station 
810-16. Size of Wire-Strung Antenna. 

(a) Outdoor antenna conductors for receiving stations shall be of a size 
not less than given in Table 8 10- 16(a). 

Table 81 0-1 6(a) 

Size of Receiving-Station 

Outdoor Antenna Conductors 

Minimum Size of Conductors 



When Maximum Open Span Length is 
Material Less than 35 feet to Over 

35 feet 150 feet 150 feet 

Aluminum alloy, hard-drawn copper 19 14 12 

Copper-clad steel, bronze or other high 

strength material 20 17 14 



For very long span lengths larger conductors will be required, depending* 
on the length of the span and the ice and wind 1 loading. 

(b) Self-Supporting Antennas. Outdoor antennas, such as vertical rods or 
dipole structures, shall be of noncorrodible materials and of strength suitable 
to withstand ice and wind loading conditions, and shall be located well away 
from overhead conductors of electric light and power circuits of over 150 
volts to ground so as to avoid the possibility of the antenna or structure 
falling into or accidental contact with such circuits. 

810-17. Size of Lead-In. Lead-in conductors from outside antenna for 
receiving stations, shall, for various maximum open span lengths, be of 
such size as to have a tensile strength at least as great as that of the con- 
ductors for antenna as specified in Section 810-16. Where the lead-in con- 
sists of two or more conductors which are twisted together or are enclosed 
in the same covering or are concentric, the conductor size shall, for various 
maximum open span lengths, be such that the tensile strength of the com- 
bination will be at least as great as that of the conductors for antenna as 
specified in Section 810-16. 



ARTICLE 810-RADIO AND TV EQUIPMENT 70-385 

810-18. Clearances. 

(a) On Buildings Outside. Lead-in conductors attached to buildings 
shall be so installed that they cannot swing closer than two feet to the 
conductors of circuits of 250 volts or less between conductors, or ten 
feet to the conductors of circuits of more than 250 volts between con- 
ductors, except that in the case of circuits not exceeding 150 volts be- 
tween conductors, where all conductors involved are supported so as 
to insure permanent separation, the clearance may be reduced but shall 
not be less than four inches. The clearance between lead-in conductors 
and any conductor forming a part of a lightning rod system shall be 
not less than six feet unless the bonding referred to in Section 250-86 is 
accomplished. 

(b) Antennas and Lead-ins — Indoors. Indoor antennas and in- 
door lead-ins shall not be run nearer than two inches to conductors of 
other wiring systems in the premises unless 

(1) such other conductors are in metal raceways or cable armor, or 

(2) unless permanently separated from such other conductors by a 
continuous and firmly fixed nonconductor such as porcelain tubes or 
flexible tubing. 

810-19. Electric Supply Circuits Used in Lieu of Antenna. Where an 
electric supply circuit is used in lieu of an antenna, the device by which 
the radio receiving set is connected to the supply circuit shall be spe- 
cially approved for the purpose. 

Lightning Arresters 

810-20. Lightning Arresters — Receiving Stations. Each conductor of 
a lead-in from an outdoor antenna shall be provided with a lightning 
arrester approved for the purpose, except that where the lead-in con- 
ductors are enclosed in a continuous metallic shield the lightning ar- 
rester may be installed to protect the shield or may be omitted where 
the shield is permanently and effectively grounded. Lightning arresters 
shall be located outside the building, or inside the building between the 
point of entrance of the lead-in and the radio set or transformers, and 
as near as practicable to the entrance of the conductors to the building. 
The lightning arrester shall not be located near combustible material 
nor in a hazardous location as defined in Article 500. 

Grounding Conductors — General 

810-21. Material. The grounding conductor shall, unless otherwise 
specified, be of copper, aluminum, copper-clad steel, bronze, or other 
corrosion-resistant material. 
810-22. Insulation. The grounding conductors may be uninsulated. 

810-23. Supports. The grounding conductors shall be securely fas- 
tened in place and may be directly attached to the surface wired over 
without the use of insulating supports. Where proper support cannot be 
provided the size of the grounding conductor shall be increased propor- 
tionately. 



70-386 MASSACHUSETTS ELECTRICAL CODB 

810-24. Mechanical Protection. The grounding conductor shall be 
protected where exposed to physical damage or the size of the ground- 
ing conductor shall be increased proportionately to compensate for the 
lack of protection. 

810-25. Run in Straight Line. The grounding conductor shall be run in 
as straight a line as practicable from the antenna mast and/or lightning 
arrester to the grounding electrode. 

810-26. Grounding Electrode. The grounding conductor shall be con- 
nected to a metallic underground water piping system as specified in 
Section 250-81. Where the building is not supplied with a water system 
the connection shall be made to the metal frame of the building when 
effectively grounded or to a grounding electrode as specified in Section 
250-83. At a penthouse or similar location the ground conductor may 
be connected to a water pipe or rigid conduit. 

Grounding Conductors — Receiving Stations 

810-27. Inside or Outside Building. The grounding conductor may 
be run either inside or outside the building. 

810-28. Size. The grounding conductor shall be not smaller than No. 
10 copper or No. 8 aluminum or No. 17 copper-clad steel or bronze. 

810-29. Common Ground. A single grounding conductor may be used 
for both protective and operating purposes. 

Where a single conductor is so used, the ground terminal of the equip- 
ment should be connected to the ground terminal of the protective device. 

C. Amateur Transmitting and Receiving Stations 

Antenna System 

810-51. Other Sections. In addition to conforming to the requirements 
of Part C, antenna systems for amateur transmitting and receiving sta- 
tions shall also comply with Sections 810-11 to 810-15 inclusive. 

810-52. Size of Antenna. Antenna conductors for amateur transmit- 
ting and receiving stations shall be of a size not less than given in Table 
810-52. 

Table 810-52 
Size of Amateur-Station Outdoor Antenna Conductors 

Minimum Size of Conductors 



When Maximum Open Span Length Is 
Material Less than Over 

150 feet 150 feet 

Hard-drawn copper 14 10 

Copper-clad steel, bronze 

or other high strength 

material 14 12 

For very long span length larger conductors will be required, de- 
pending on the span length and the ice and wind loadings. 



ARTICLE 810-RADIO AND TV EQUIPMENT 70-387 

810-53. Size of Lead-in Conductors. Lead-in conductors for transmit- 
ting stations shall, for various maximum span lengths, be of a size at 
least as great as that of conductors for antenna as specified in Section 
810-52. 

810-54. Clearance on Building. Antenna conductors for transmittin