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UNDERGROUND TRANSMISSION

AND

DISTRIBUTION

McGraw-Hill Book Company

Electrical World The Engineering andMining Journal
Engineering Record Engineering News

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Signal E,ngin<?<?r American Engineer

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Metallurgical and Chemical Engineering Power

UNDERGROUND

TRANSMISSION AND

DISTRIBUTION

FOR

ELECTRIC LIGHT AND POWER

BY
E. B. MEYER

MEMBER AMERICAN INSTITUTE OF ELECTRICAL ENGINEERS; MEMBER AMERICAN
8OCIETT OF MECHANICAL ENGINEERS; MEMBER AMERICAN ELECTRIC RAIL-

WAY ASSOCIATION; MEMBER NATIONAL ELECTRIC LIGHT ASSOCIATION;

CHAIRMAN, N. E. L. A. COMMITTEE ON UNDERGROUND CONSTRUCTION
AND ELECTROLYSIS, 1915-1916

FIRST EDITION

McGRAW-HILL BOOK COMPANY, INC.

239 WEST 39TH STREET. NEW YORK

LONDON: HILL PUBLISHING CO., LTD.

6 & 8 BOUVERIE ST., E. C.

1916

THK MAPLE PRESS V Cl R K PA

PREFACE

The rapid growth of the electric light and power industry
with the resultant increase in the number of overhead wires,
has brought about the policy on the part of municipal authori-
ties of compelling utility companies to operate their systems
underground. This has led to the development of a more or less
specialized branch of electrical engineering; it involves large
expenditures annually and gives rise to operating difficulties
in many cases not clearly understood by the central station
engineer.

While there are various treatises which deal with special
branches quite fully, there appears to be no work which covers
the general field of underground construction, transmission and
distribution. The writing of this book was undertaken by the
author because of repeated requests from engineers engaged in
the construction and operation of underground systems, for
information bearing on many of the details of this branch of
central station work.

In the preparation of this volume, the author has not included
such data as can readily be obtained from handbooks. The
treatment of the subject assumes on the part of the reader a
general knowledge of the fundamentals of electrical theory.
The subject matter has been treated from the American
point of view, since European practice differs considerably from
that followed in America, due to the difference in conditions
under which electric lighting properties are operated.

A part of the material contained in this volume originally
appeared in the various reports of the National Electric Light
Association Committee on Underground Construction, on which
committee the author has served for the past five years, and
acknowledgment is hereby made to the Association for per-
mission to use data from these reports.

The author wishes to acknowledge the assistance and ready
cooperation of the various cable manufacturers and others who
have contributed for publication much valuable information

349327

vi PREFACE

and many photographs and cuts, and is indebted to Messrs.
J. T. Foster, H. S. Vassar and Paul Liipke for valuable sugges-
tions received during the preparation of the manuscript.

E. B. MEYER.

NEWARK, N. J.,
November, 1916.

CONTENTS

PAGE

PREFACE v

CHAPTER I

HISTORICAL 1

Periods of Development — Built-in Systems — Drawing-in Sys-
tems— Present Forms of Construction.

CHAPTER II

PRELIMINARY SURVEY 19

Planning the System — Maps — Test Holes — Permits and Right-of-
way — Form of Agreement — Regulations.

CHAPTER III

CONDUIT AND MANHOLE CONSTRUCTION 30

Selection of Materials — Installation of Conduit — Concrete — Tile
Duct — Stone Duct — Fibre Duct — Manhole Construction— Sewer
and Illuminating Gas — Sealing Ducts in Manholes — Types of Man-
hole Construction — Building Manholes in Quicksand — Roof Con-
struction— Types of Covers — Waterproofing Manholes — Design of
Manholes for Transmission and Distribution — Transformer Man-
holes— Concrete Manhole Forms — Distribution Manholes — Cable
Tunnels — Specification and Contract — Form of Specification, Con-
tract and Bond — Construction Costs.

CHAPTER IV

METHODS OP DISTRIBUTION 81

Street Distribution — Interior Block Distribution — Sidewalk Dis-
tribution— Duct Arrangement — Parallel Routing — Solid System —
Service Connections — Armored-cable System — Installing Steel-
Taped Street-lighting Cable — Comparative Costs of Installation.

CHAPTER V

CABLES 102

General — Terminology — Conductors — Insulating Wall — Rubber
Insulation — Paper Insulation — Varnished Cambric Insulation —
Graded Insulation — Lead Covering — Types of Cables — Diameter
and Length of Cables — Fibre Core Cables — Transmission Cables —
General Data — Sector Cable — Submarine Cable — Specifications,
General — Rubber Cable Specifications — Paper Cable Specifications
— High Tension Cable Specifications — Moisture in Cable Insulation.-

vii

viii CONTENTS

CHAPTER VI

PAGE

INSTALLATION OP GABLES 151

Handling Lead Cables — Choice of Ducts — Rodding Ducts —
Obstructions in Ducts — Drawing-in Cables — Cable-pulling Grips —
Draw Rope — Drawing Apparatus — Power Trucks — Slack — Joint-
ing Cables — General Directions for Jointing — Jointing Rubber-
insulated Cables — Jointing Armored Cables — Paper and Cambric
Tape Joints — Paper Tube Joints — Advantages of Paper Tube
Joints — Sleeve Filling Material — Conducell Cable Joint Insulators
— High-voltage Vacuum Joint — Unit Package of Joint Material
— Protection of Cables in Manholes — Current-carrying Capacity
of Cables — Cooling Duct Lines — Connections to Overhead Lines —
Lightning Arresters — Splicing Equipment, Tools and Safety
Devices.

CHAPTER VII

TESTING CABLES 227

International Electrical Units — Standardization Rules — Electrical
Tests — Insulation Resistance — Electrostatic Capacity — Capacity
of Testing Apparatus — Locating and Repairing Cable Failures —
Loop Test — Fault-locating Equipment — Periodic High-potential
Testing.

CHAPTER VIII

DISTRIBUTION SYSTEMS AND AUXILIARY EQUIPMENT 241

General — Alternating-current Distribution — Single-phase System
— Two-phase Systems — Three-phase Systems — Secondary Mains —
Underground Transformers — Cable Junction Boxes — Service Bus
— Manhole Oil Switches — A. C. Network Protector — Service Con-
nections from Underground Mains — Armored Services — Protection
of Transmission Systems — Relays — Current Limiting Reactance
Coils — Selective Fault Localizer — Arcing Ground Suppressor —
Grounded Neutral Systems — Merz System of Cable Protection.

CHAPTER IX

ELECTROLYSIS 281

General — Drainage Systems — Protective Coatings — Insulating
Joints — Protecting Cable Sheaths — General Practice — Coopera-
tion of Utilities — Electrolysis Surveys.

CHAPTER X

OPERATION AND MAINTENANCE 296

Records — Identification of Cables — Record of Cable and Equip-
ment Failures — Cleaning Manholes — Care of Cables — Bonding
Cables in Manholes — Rules and Requirements.

INDEX . 309

UNDERGROUND TRANSMISSION
AND DISTRIBUTION

CHAPTER I
HISTORICAL

Periods of Development. — For a number of years after electric
lighting was first introduced, the distribution of current was
effected almost entirely by means of overhead wires carried on
poles. The development in many of the large cities where the
early market for electricity was found, proceeded at such a rapid
rate that it soon became practically impossible to take care of
the number and size of feeders required for distribution by means
of overhead construction.

Large amounts of money had been expended in attempting
to beautify various cities, but these improvements were offset
to a great extent by the erection of unsightly overhead lines.
To remedy this condition and eliminate the fire hazard, it was
realized by engineers that some other form of construction would
be necessary.

When the idea was first conceived of relieving the streets and
boulevards of the presence of electric wires, by placing them
underground, there were few engineers who believed the innova-
tion practicable, either from the viewpoint of service or economy.
The cry immediately arose that the first cost of an underground
installation would be prohibitive and it was firmly believed that
the efficiency and capacity of the wires would be greatly lessened.
This view was supported by the failures which attended the early
attempts to bury electric wires.

The earliest recorded attempt to lay a cable in the United
States for the purpose of transmitting an electric current appears
to be that made by Samuel F. B. Morse on Oct. 18, 1842. That
evening he hired a boat at the Battery water front, in New York,
and paid out a reel of copper wire laboriously insulated with
pitch, tar and rubber, as he was being rowed to Governor's
Island. He set up and prepared to demonstrate his electromag-

2 UNDERGROUND TRANSMISSION AND DISTRIBUTION

netic telegraph instruments at Castle Garden and the Island on
the following day. Only a few signals had been exchanged,
however, when an anchor fouled the cable, and it was cut by
ignorant- sailors who dragged it up. Thus this first effort ended
in failure.

After strenuous exertion Morse secured from Congress, on the
last day of the session, March 3, 1843, an appropriation of
$30,000 "to test the practicability and efficacy" of his telegraph
system. He decided on a line from Washington to Baltimore
and planned to use underground construction, supposing that

FIG. 1. — Calvert and German Streets, Baltimore, Md. Before removal of
poles and overhead wires. (By courtesy of Mr. Chas. E. Phelps, Chief
Engineer, Baltimore Electrical Commission.)

this method had already been successfully used in England by
Professor Wheatstone for his indicating needle telegraph. Morse
figured on four No. 16 copper wires covered with cotton and
insulating varnish and drawn into a lead pipe. The estimated
cost was about $600 per mile. The cable was constructed under
the supervision of an assistant who was supposed to carefully
test it. However, when part of the cable had been put down,

HISTORICAL 3

it was found to be faulty due to charring of the insulation in the
"hot process" employed in applying the lead. The assistant
was reluctantly dismissed and the faithful Ezra Cornell, who took
his place, dexterously managed to smash the cable-laying outfit
by skillfully guiding the trenching plow against a rock, thereby
furnishing a convenient excuse for the change to overhead
construction which brought about the success of the enterprise.
The precedent thus established dominated future developments
for a considerable period. Lack of care caused failure of under-
ground construction in this case, and the same cause can probably
be held responsible for more subsequent failures than any other.

FIG. 2. — Damage to overhead wires resulting from snow and sleet storm.

In the years following, the use of overhead wires for trans-
mission of electric currents multiplied. Besides telegraphic
communication, various signal systems, such as fire alarms and
police telegraphs, district-messenger-call systems and stock-
ticker circuits, were established. Beginning in about 1876,
commercial application of the telephone entered the field, in-
creasing the number of overhead wires at a rapid rate, so that
when in 1878 the first series-arc circuits made their appearance

4 UNDERGROUND TRANSMISSION AND DISTRIBUTION

there was already a conspicuous tangle of wires strung indis-
criminately above the public highways. The situation was
aggravated by the neglect of defunct enterprises to remove the
"dead wires."

This abandoned and ownerless equipment in combination with
poorly insulated electric light wires constituted a real menace,
that soon led to a public outcry against further increase of over-
head wires and the immediate undergrounding of those already
in use.

Ill-considered and impracticable legislation was the natural
consequence of this situation.

A remarkable exception to the general practice was the radical
departure from accepted methods made by Mr. Edison in the
introduction of his low-tension multiple system.

As one of the items in Mr. Edison's programme for the
development of his " system, " we find in Dyer and Martin's
book, " Edison, His Life and Inventions," the following:

"To elaborate a system or network of conductors capable oj being
placed underground or overhead, which would allow of being tapped
at any intervals, so that service wires could be run from the main
conductors in the street into each building. Where these mains
went below the surface, as in large cities, there must be protective
conduit or pipe for the copper conductors, and these pipes must
allow of being tapped wherever necessary. With these conductors
and pipes must also be furnished manholes, junction boxes, connec-
tions and a host of varied paraphernalia insuring perfect general
distribution."

The development of such a "system or network" with all the
necessary accessories was accomplished, and on Sept. 4, 1882,
current from the Pearl Street Station was turned into under-
ground wires laid under the streets of a downtown section of
New York City, supplying 225 houses wired for about 5,000
lamps.

However, this system was not applicable to the high-tension
series currents used for arc lighting and the number of overhead
wires for this purpose continued to increase until in the congested
sections of the larger cities the situation became unbearable.

The general unsightliness, the menace to firemen, the dangers
to the employees of the companies and to the public at large
were too apparent to be further ignored. In 1884 the New York
Legislature passed a law requiring the removal of wires from the

HISTORICAL 5

streets before the first day of November, 1885. The physical
impossibility of compliance with this law and the concrete fact
that at the date set for their disappearance the overhead wires
were still very much in evidence led to the passage of another
act in 1885 which provided "that, if no suitable place should be
proposed for placing the said wires underground it should be the
duty of the said Board of Commissioners (created by this act)
to cause to be devised, and made ready for use, such a general
place as would meet the requirements of the said Acts of 1884r-5
and the said Board should have full authority to compel all com-
panies to use such subways so prepared. "

A great variety of schemes was submitted to this Board, by
outside parties, about 450 in all, but the electric light companies
generally opposed the placing of electrical conduits underground,
claiming that it was a physical impossibility to accomplish
the feat successfully, and that in any event the cost would be
prohibitive.

Finally the Board entered into a contract with a conduit
company and a system of iron pipe conduit was put down in
certain streets of the city. On these streets the authorities
proceeded, in 1889, to cut down the poles and to remove the over-
head wires and thus ruthlessly compelled progress in underground
construction.

In Europe the situation had become acute before it was felt
in this country, and various methods were tried with but little
success, including the plan of running the wires on supports
located on the roofs of the buildings.

In France there was developed the Berthoud-Borel System
employing copper wires wrapped with cotton saturated with
linseed oil, which had been previously treated by heating.
The heat treatment appears to have made the oil more stable
in character and to have increased its insulating properties.

One of the earliest forms of underground construction was
the trench system, in which an attempt was made to use the same
general methods as were used in overhead lines. The system
consisted of a closed trench in which were placed conductors,
either bare or insulated, fastened to insulating supports.

Professor Jacoby, of St. Petersburg, laid a form of armored
cable consisting of cotton-covered cord, laid in lead pipe with
the intervening spaces filled in with resin. There were many
attempts along similar lines, none of which were successful

6 UNDERGROUND TRANSMISSION AND DISTRIBUTION

until, with the discovery of petroleum in 1856, paraffine came into
the market as a cheap and satisfactory insulating material.

The principal difficulty seemed to be in finding an insulation
which could be made to adhere to the conductor. Many sub-
stances were found which were good insulators in dry places,
but there were few which would stand the acid and alkali fumes
and the ravages of sewer and illuminating gas to which the con-
ductors were exposed when buried under the streets of our large
cities.

Attempt was made to use oil as an insulation for cables and
what was known as the Brook's System, Fig. 3, was employed
for a time to some extent. It was found that wires insulated with
resin and oil were difficult to short-circuit, even under a high
potential difference. Of course, no pure oil could be used in

FIG. 3. — Brooks system of service-box cable and oil pipe.

the construction of cable, even when encased in lead, as in the
jointing process the oil leaked out before the joint was sealed.
It was proposed to lay iron pipe for the distance to be traversed,
the pipes to terminate in hermetically sealed boxes. Cables
which were carefully dried out to get rid of the moisture and then
covered with jute and boiled in oil were drawn into these pipes,
after which the pipes were filled with oil so that no moisture could
enter. The oil was kept under pressure by means of a standpipe
or pump, the theory being that if small leaks developed and
allowed the oil to escape, the pressure on the oil would prevent
the entry of either air or moisture. In addition, insulation
break-downs would be self-healing.

However, it was found exceedingly difficult to obtain oil
sufficiently heavy for good insulation, and that the pressure
from the standpipe or pump could not be transmitted for any
great distance.

HISTORICAL 7

Experiments with this type of construction were made by
the Pennsylvania Railroad Co. and the Western Union Tele-
graph Co., between Newark and Jersey City, across the salt
marshes.

In England, a system was developed by Johnson and Phillips,
which gave satisfactory service. In their system the idea of
using oil under pressure was abandoned and more attention was
paid to the laying of pipes without leaks, taking especial pre-
cautions to seal the junction boxes and the pipe ends.

This system was particularly adapted for electrical lines
crossing private grounds and for long trunk lines in which there
was little probability of their being disturbed after laying.
It was very difficult, however, to keep this sj^stem in proper repair,
as leaks in the pipe line necessitated the placing of additional
junction boxes which were difficult to install without removing
the cable and refilling the entire length of the pipe. Other
disadvantages lay in the objection of workmen to handling cables
saturated with heavy oils and in difficulty in making extensions
or branch connections to the system.

The failure to obtain an insulation which would stand up
under moisture and other deteriorating influences brought
about the development of the solid or built-in system.

Built-in Systems. — Numerous solid or built-in underground
systems using both insulated and bare conductors were tried as
a substitute for overhead electrical wires. The enormous expense
of making the change, as well as the utter lack of experience with
buried circuits, made this a very difficult problem from the start,
and as is usual in such cases, extraordinary methods were devised
for overcoming the difficulties.

In England, the Crompton System, Fig. 4, of bare copper
strips was used quite extensively. This system used bare con-
ductors supported at intervals on insulators and laid in a specially
prepared trench. The system was tried in two forms: In the
first, sag or strain bars were placed at a suitable distance apart.
These took up most of the strain and very little came upon the
insulating supports which were located about 50 ft. apart and
carried on cast-iron cross-bars. In the other form of this system,
no strain bars were used, but the number of supporting insulators
was increased. In both forms, but particularly in the latter,
trouble was experienced due to leakage of current to earth at the

8 UNDERGROUND TRANSMISSION AND DISTRIBUTION

insulator supports, probably caused by water leaking along the
support and reaching the conductor.

The system, in both its forms, was abandoned because of the
high cost of construction and maintenance and because of inher-
ent defects, due principally to the following:

FIG. 4. — Section of Crompton and Kennedy conduit.

1. Temperature changes caused buckling of the strips, result-
ing in heavy short-circuits and interruptions to service.

2. Lack of efficient drainage and ventilation which caused
leakage of current due to moisture and the collection of gases

in the trench. Arcing at a poor
connection ignited these gases, caus-
ing disastrous explosions.

3. Heavy short-circuits set up
electromagnetic forces between con-
ductors, causing them to buckle and
communicate the trouble by com-
ing into contact with other circuits.
What is known as the Callender
Solid System, Fig. 5, consisting of
a series of cast-iron troughs laid
along the bottom of a trench, was
also used to some extent. The re-
quired number of insulated conductors were strung in a cast-iron
trough. After stringing the conductors, the trough was filled with
an asphalt compound and closed with cast-iron covers. Experi-
ments were carried on with other forms of cast-iron troughs, some
of which were made in short sections and bolted together, the cable

FIG. 5. — Section of Callender
system.

HISTORICAL 9

being placed in the troughs as laid . The troughs were usually filled
with some kind of compound to exclude moisture. These methods
of providing underground distribution, however, were so expen-
sive as to be almost prohibitive. Moreover, all systems which em-
ployed tarry or bituminous filling had two serious disadvantages.
It was difficult to keep them rigid under all conditions of tem-
perature, as at high temperatures the softening of the material
caused sagging of the system under the weight of the earth above,
resulting in damage to both the ducts and the wires which they
carried. At the low winter temperatures the conduit was likely
to crack and admit moisture. The second disadvantage lay
in the fact that in making extensions to the system it was neces-
sary to tear up the street to get at the cable on which work was to
be done.

The first objection was finally overcome by the use of iron
pipe filled with compound to give the necessary rigidity, but the
second was an inherent defect and was to a large extent respon-
sible for the final abandonment of the built-in system.

In the early eighties, the Edison Tube System of underground
construction was devised and later commercially adopted by a
number of the larger cities in the United States and Europe.

This system consists of 20-ft. lengths of iron pipe inside which
the conductors are embedded in a bituminous compound. The
conductors, which are not removable, are usually in the shape of
round copper rod, the main tubes being designed for use on the
three-wire system. Each rod is wound with a layer of rope which
serves to keep the rods separated in case a softening of the insu-
lating material in the tubes should occur. After the rods have
been provided with the layer of rope, they are bound together
by means of a wrapping of rope and inserted in the iron pipe,
the rods projecting for a short distance at each end. The whole
tube is then filled with an insulating compound which becomes
hard when cold. The 20-ft. lengths are made in various sizes
of conductors from No. 1 gage up to 500,000 cm. for mains, and
1,000,000 cm. for feeders. Sections of the tube are designed
for use as distributing mains, and are made with three conductors
of the same size, while those designed for feeders are often made
with one conductor about half the area of the others. This
small conductor is used as the neutral for which, in a balanced
system, little capacity is required. Tubes are also provided
with potential leads to indicate at stations or substations the

10 UNDERGROUND TRANSMISSION AND DISTRIBUTION

voltage at the outer end of the feeder. The tubes are laid in
the ground about 30 in. below the surface of the pavement and
are joined together by means of coupling boxes. The conductors
are connected together by means of short flexible copper cables
provided with lugs to fit over the rods and soldered in place.
The coupling boxes are made in two similar halves. After being
placed in position the two sections are securely bolted together
by means of flanged bolts. After this is done, melted compound
is poured through an opening in the upper casting and the joint
completed. Branch connections are made with T coupling boxes

FIG. 6. — Edison tube coupling joint.

which are filled with compound in a similar manner. At centers
of distribution junction boxes are provided at which the main
feeders and the supply wires from the station join. The junc-
tion boxes are provided with fuses and water-tight covers to
allow inspection and testing. When trouble occurs, the usual
method of procedure is to dig a hole at one of the couplings and
separate the ends. By making a number of breaks in this way
at different locations, the section in which the ground or short-
circuit occurs is located and the defective length of tube replaced.
The Edison System remained standard for low-tension distribu-
tion for about 15 years, when cables drawn into ducts began to be
employed for the heavy feeders. It is still used to some extent
in cities where a large investment had been made for such work
before the development of the drawing-in system.

HISTORICAL 11

In some instances, especially in European countries, armored
cables laid directly in the earth have been employed for under-
ground distribution. The armor, which is in the form of a steel
wire or tape, is relied upon for mechanical protection. This
form of installation which is used quite extensively at the present
time has advantages for certain purposes, as described elsewhere
in this volume. However, the ease with which repairs may be
made in the drawing-in systems has caused these systems to
become standard throughout the United States.

FIG. 7. — Edison tube junction box.

Drawing-in Systems. — With the development of the alternat-
ing-current system of distribution and the use of high-potential
circuits of from 1,000 to 7,000 volts for street-lighting circuits,
the need was felt for some form of insulation sufficiently flexible
to permit of drawing cables into the ducts. The built-in system
had been abandoned to a large extent because of its failure to
stand high potential and because it was found necessary to dig
up the streets when increased load demanded reinforcements or
additions. The constant tearing up of the pavement for these
purposes created an antagonistic feeling on the part of the munici-
pal authorities and in many cases they were reluctant to grant
permits for the laying of additional conductors in the streets.

12 UNDERGROUND TRANSMISSION AND DISTRIBUTION

In the early forms of drawing-in systems the chief difficulty
appears to have been the lack of an insulating material capable
of withstanding the high potential of arc circuits. Some trouble
was also experienced on account of disintegration of the lead
sheath itself.

Lead-covered cables were being operated successfully at low
voltages, but with the undergrounding of arc-light wires failures
of the insulation soon resulted.

The difficulties which were experienced in the early days of
the drawing-in system were due not to the fact that the under-
ground system was fundamentally wrong, but rather to the fact
that in cable manufacture lack of experience prevented the intel-

JO1NT.

FIG. 8. — Dorset conduit.

ligent design of the subsurface structure which was to carry the
conductors.

The problem resolved itself into three parts:

1. The insulation of the conductors.

2. The protection of the insulation from the effects of moisture
and corrosion.

3. The protection of both conductors and insulation from
mechanical injury.

Elaborate experiments were conducted with all kinds of cable
and with a variety of conduits, but it was found that copper
conductors insulated with any of the compounds which had
thus far been tried failed under high potential within a short
time. Where lead was used to protect the insulation the life
of the cable was materially increased.

HISTORICAL 13

The Dorsett Conduit System which consisted of sections of
duct made with bituminous concrete was at one time largely
used in New York and Minneapolis and proved a complete failure
on account of the fact that it was impossible to make sure that
the compound between the ducts effected a thorough cementing
and in consequence after construction the blocks were frequently
found to have cracked apart and fallen out of alignment, thus
sacrificing all the insulating properties and reducing the cross-
section of the duct.

This type of construction was somewhat modified by General
Webber, of the British Postal Telegraph Co., and he was able
to construct a satisfactory cable-carrying conduit, but could not
make the system entirely waterproof.

In Webber's System, the 4-in. or 5-in. space between ducts
was filled with the same material of which the ducts were formed
in a molten state. This molten material melted enough of the
conduit surface to form the whole into a solid mass. The system,
however, did not permit of the use of uninsulated wires.

The system used in Minneapolis by the Interior Conduit Co.
consisted of impregnated paper tubes with paper ferrules at the
joint laid in a trench. The trench was filled with a compound
composed of asphaltum and coal tar, poured while hot, entirely
covering the paper tubes. Bare copper wires were drawn into
the ducts and manholes were provided. These consisted of
double wooden boxes sealed with compound and covered with
water-tight covers. The system worked well for several years,
but was finally abandoned because of the original use of unsatis-
factory material. The paper ducts were found to be not abso-
lutely impervious to moisture and as the supporting wooden
blocks in time became saturated with moisture which seeped
through the paper conduits, short-circuits were frequent. The
installation was not water-tight and in many instances the whole
duct structure was filled with water after heavy rains.

The Interior Conduit Co. later used a system of paper tubes
one within the other, designed to be laid with broken joints.
The tubes were protected externally by an iron pipe or laid in
asphaltic concrete supported on blocks of earthenware. Iron
manholes were substituted for the double wooden boxes used in
the earlier systems.

Another system, known as the Gumming Duct, was used to
some extent. Four wooden ducts were enclosed in an iron pipe,

14 UNDERGROUND TRANSMISSION AND DISTRIBUTION

the intervening space being filled with an asphaltic compound.
This system was limited to the use of low-potential conductors
where a small number of cables were installed.

In Milwaukee, three systems were tried and abandoned:
namely, a wooden-trench plan, tarred iron pipe, and grooved
wood. In Detroit, the Thomson-Houston Co. employed a cable
of the most expensive and approved character in the Dorsett

FIG. 9. — Types of wooden duct.*

conduit, and the mechanical work was of the best quality. The
conduit was made of a so-called concrete consisting of asphal-
tum and sand moulded into 3J^-ft. lengths, with the desired
number of ducts. One end of each section was flanged and two
sections were jointed and fitted together by means of hot concrete,
the manholes being made of the same material. In this installa-
tion it was found that while the cables were new the results were

HISTORICAL

fair, but the loss by leakage rendered it impossible to provide
proper voltage regulation at the lamps.

Creosoted wood, or what is commonly known as pump-log
conduit, was used in a number of installations. This conduit
though cheap was found to deteriorate very rapidly and to cause
much trouble by catching fire when a cable burnout occurred.
In many installations the decay of the wood formed acetic acid
which attacked the lead sheathing of the cable. As the result
of these difficulties the use of wood as a conduit was soon
abandoned.

Cement-lined pipe was largely used about 15 years ago. This
consisted of sections of thin wrought-iron pipe, No. 26, B.W.G.,
0.018 in. thick, securely held by rivets 2 in. apart. The tube was

RIVCTS

•pJ *~*

HH^I -.Wv^ffi:.:^S

//POM

FIG. 10. — Details of cement-lined pipe.

lined with a wall of Rosendale cement % in. thick, the inner sur-
face of which was polished while drying, so as to form a perfectly
smooth tube. The ends of the tubes were provided with a cast-
iron beveled socket joint to obtain perfect alignment. The
cement lining in this form of conduit, after several years service,
separated from the outer iron form, causing considerable trouble
in the installation and withdrawal of cables. In some cases the
cement lining was porous and with the absorption of moisture
the conduit soon disintegrated so that this form of construction
had a very short life.

Wrought-iron or steel pipes screwed together by means of
couplings were used for a number of years, particularly where
the high cost was not a serious objection. Wrought-iron pipe
laid up in cement and additionally protected with 2-in. plank
was for a long time considered standard construction in New York

16 UNDERGROUND TRANSMISSION AND DISTRIBUTION

City. Its special advantages are: great strength to resist the
severe strains caused by the pressure of the earth, and that it
is well adapted to withstand blows from workmen's shovels and
tools, to which conduits in large cities are subjected because of
the frequency of street excavation work. The pipes are standard
3-in. and 4-in. diameter and are made gas- and water-tight by
means of a tapering screw-thread coupling. The pipes are laid
about an inch apart and the spaces around them filled with con-
crete. It is evident that this form of construction is extremely

>. - • •- o •
•*~ • "-.•' *V4'-». '»'•'«' *;>~

,', " ^
o _

& 'o

^^^^8^<S^

*>v* '*.«•' *."*••*•''• -'i ^2

FIG. 11. — Cross-section of iron-pipe conduit.

substantial and will withstand the most severe mechanical
stresses, but because of its high first cost it has been superseded
by cheaper systems.

In the city of Paris, the sewers, which are egg-shaped in form,
are purposely constructed much larger than necessary for carry-
ing sewage, so that the upper portion may be rented for pipe and
conduit lines. Service connections are made through the sewer
pipes connected to each house, thus avoiding the use of manholes.
The sewers are large enough to allow a man to stand upright,
while the main sewers are often 27 ft. in diameter. Perforated
manhole covers are provided at intervals to allow for ventilation
and give access for cleaning. The air in the sewers is fresh,

HISTORICAL 17

although a slight musty odor associated with sewage is notice-
able. Gas mains are not carried in the sewers as they are con-
sidered a danger on account of the possibility of an explosion.
Electric service connections are carried through the individual
service connections to the buildings.

Present Forms of Construction. — Tile and fiber conduits are
now used almost exclusively. The first is manufactured from
vitrified clay in single duct and multiples of two, three, four and
six ducts, in either round or square bore. The ducts are laid
end to end and usually surrounded with an envelope of concrete
which reinforces the structure. The joints are staggered and
wrapped with either burlap or iron and covered with cement.

While there is some difference of opinion among engineers as
to which type of conduit is the better, the clay-duct system is
more generally used in distribution work. The newer material,
known as fiber conduit, is rapidly coming into general favor, and
at present is considered standard construction and used success-
fully by a number of the larger companies.

In some locations stone pipe is being used to advantage and
its cost compares favorably with that of tile and fiber conduit.
An ideal conduit would provide absolute protection for the
cables from every destroying influence. It should be proof
against acids, alkalies, gases and all other chemical elements;
it is likewise essential that it be non-corrosive and absolutely
permanent in character and composition; it should also have
high insulating qualities to protect the cables from outside cir-
cuits and avoid electrolysis. The joints should be self -aligning
and insure permanently fixed alignment, and the duct should
have a hole with a smooth and strictly non-abrasive inner
surface, to entirely prevent injuries to the covering of cables
while drawing them in and out of the ducts. The ducts should
be light in weight to save expense in freighting, handling, and
laying, and should be strong and tough for proper protection of
cables and to avoid loss from breakage, in shipping and handling,
and lastly the first cost should not be excessive.

It is a well-established fact that when a system is properly
designed, the saving in the cost of maintenance, the increase
in efficiency, the superior service and absolute insulation, in a
very short time unquestionably repay for the increased first
cost. The cost of the subsurface structures among the larger
central-station companies may be said to amount to one-fourth

18 UNDERGROUND TRANSMISSION AND DISTRIBUTION

of the entire investment, and for the reason that these structures
are themselves as important as any link in the chain of central-
station equipment, and because of the relatively large investment
involved, great care should be exercised in determining the kind
and type of underground construction to be used. In the suc-
ceeding chapters the types of construction which are in use to-day
are described in detail, together with specifications, costs, and
other data to be used as a guide for the central-station engineer
in the design and operation of underground systems of trans-
mission and distribution.

CHAPTER II
PRELIMINARY SURVEY

Planning the System. — In planning a conduit system for
general use in housing both transmission and distribution feeders,
as well as mains and service cable, the first thing to be decided
upon is the method of distribution. The system of distribution
depends to a large extent upon local conditions and in many cases
will follow the general plan of the existing overhead system, except
in large cities where obstructions in the streets and the expense
of approved paving methods will frequently determine to a great
extent the route to be followed.

In some cities, local ordinances prescribe the use of poles in
alleys for block distribution, and in such cases the conduits are
usually laid on the main streets or thoroughfares. Where the use
of overhead alley distribution is permissible, the problem of
eliminating pole lines from the streets is relatively easy and the
cost of underground construction is materially reduced.

Maps. — When the method of distribution has been decided
upon and the streets on which the ducts are to be laid have been
determined, a map should be prepared showing the location and
size of the proposed duct line.

The problems presented to the engineer who is responsible
for the installation of an underground system are many, but he
has a comparatively large field from which to choose methods and
materials. Local conditions will determine to a large extent the
character of the construction to be employed. Conduit systems
are usually laid subsequent to other subsurface structures such
as water and sewer pipes and gas mains, and it is therefore neces-
sary in preparing specifications and estimates that locations of
existing subsurface structures be known in advance as definitely
as possible. The engineer should, therefore, provide himself
with a map of the- district to be covered in order that he may
determine what streets can best be used after considering the load
on the system and determining the method of distribution. Maps
or surveys should be drawn to scale in order that the locations
of foreign structures may be plotted thereon.

20 UNDERGROUND TRANSMISSION AND DISTRIBUTION

A record of the subsurface structures can generally be obtained
by applying to the municipal authorities. While this informa-
tion will frequently be found of great value in making a pre-
liminary layout, too much dependence should not be placed
thereon, as such records are not always accurate and are quite
often incomplete.

It is, therefore, necessary to check up these records in the streets
where underground structures are numerous, particularly in
cases where the space available for a conduit installation is limited
by such structures.

Test Holes. — Obstructions are most likely to be encountered
at street intersections, and these obstructions should be located
as accurately as possible before beginning the trench excavation.

FIG. 12. — Method of building manhole around obstructions.

It is best to find obstructions, such as water and gas mains
and the service connections of other utilities by digging test holes
along the line of work, and so laying out the work as to avoid
them when possible.

These test holes are usually about 2 ft. in width, extend from
curb to curb and are of sufficient depth to show the locations of
the lowest structures. Only one-half of the street is opened at
one time in order not to interfere with traffic. To determine
definitely that the proposed location of the conduit line is clear
of other underground structures and obstructions, these test
holes should be dug at intervals along the line far enough in
advance of the trench so that any errors in records of previous
work in the streets or in the location of the conduit line will be
disclosed before incurring the expense of digging the trench.

PRELIMINARY SURVEY

Where possible, test holes should be dug at the proposed man-
hole sites with the double purpose of utilizing the extra excava-
tion and of obtaining definite information as- to the availability
of the proposed manhole location.

/Curb

-Gas

FIG. 13. — Street main cut around manhole.

£P»Ce AKOUND f/fC

FIG. 14. — Method of building conduit around service pipes.

It is frequently found after measurements are taken in the test
holes, that while there is sufficient space for the conduit, the space

22 UNDERGROUND TRANSMISSION AND DISTRIBUTION

for manhole construction is so limited as to make it necessary to
provide a special form of construction. In Fig. 12 is illustrated
a method of installing a manhole in a congested street where
foreign obstructions make it necessary to resort to an unusual
design. In some cases it may be cheaper to have the water
or gas pipes cut around the manhole as shown in Fig. 13. The
conduit, when installed parallel to water or gas mains, should be
placed at a grade which will not interfere with the water- or
gas-service connections. But where this is impossible, the
service pipe is usually run through the conduit, the ducts being
divided and the space around the service pipe, where it passes
through the conduit, filled with sand, as shown in Fig. 14. Gas
mains should not be run through manholes except only in very
special cases. Where it is necessary to take a gas main into a
manhole, it should be encased in concrete.

Permits and Right-of-way. — Before proceeding with any
actual construction work in the streets, the engineer should
acquaint himself with the local municipal laws, ordinances and
regulations or other requirements relating to the excavation or
the occupancy of space in the public streets. Notes as to ob-
structions or any other points relating to the work should be
made and arranged in a form convenient for reference.

In some cities pavements are laid by contractors under bond
with the municipal authorities to keep such pavements in good
repair for a period of years. In such cases it is usually necessary
to restore the pavement after street excavations have been made.
In many instances it is impossible to obtain permits for street
opening after a new pavement has been installed, and this should
be given consideration in laying out a route for the conduit system,
as it has often been found advisable to install a conduit system
in advance of the laying of a permanent pavement in order to
keep the cost within reasonable limits.

The engineer should confer with the local authorities in the
matter of obtaining permits for the opening of streets, the use of
fire hydrants and the methods of obtaining permits and the rates
of payment for water used for construction purposes.

In many European cities it is the practice to install the subsur-
face structures of the utilities beneath the sidewalk. Regulations
are in force prescribing the exact location beneath the sidewalk
within which each utility must be placed. In some places a
movable pavement is provided which may be removed and re-

PRELIMINARY SURVEY 23

placed without great expense, allowing repairs to be made to the
subsurface structures. The advantages of locating utilities be-
neath the sidewalks as compared with their placement beneath
the street pavement are that it is less expensive to remove a
cheap sidewalk than a costly pavement, and the maintenance
cost is lowered. Structures placed under the sidewalk are not
subjected to the shock and vibration from heavy overhead
traffic, and the installation of transportation subways is made
considerably less expensive where no underground utilities have
to be maintained in service during construction.

In some of the larger cities in the United States, the streets
have become so congested with both surface and subsurface
structures that the matter of subsurface construction has been
placed under the control of a Municipal Board consisting of the
Chiefs of Bureaus of Highways, Surveys, City Property, Electri-
cal Bureaus, etc., the idea being to have all departments concerned
with surface or subsurface construction of streets represented
on the Board. One of the most important duties of this Board
is the obtaining, compiling and mapping of all possible informa-
tion concerning existing or projected structures under streets.
For carrying out the work, a corps of field inspectors and drafts-
men is maintained, and necessary authority and power given the
Board to enable it to obtain the required information and to con-
trol the action of both corporations and individuals in their
use of the streets.

In some cities it is required that plans showing all existing
underground structures be filed in duplicate together with com-
plete details of proposed construction. All work and material
used must be satisfactory to the Chief of the Electrical Bureau
and any work and material condemned must be at once replaced
in acceptable form. After work is completed, the party to whom
the permit is issued is required to file complete plans in detail
showing the work as constructed, with all previously existing
structures encountered during the construction work.

The foregoing applies to only a few cases where subsurface
structures and transportation subways occupy practically all
of the available space under the street surface.

When electrical companies are required to remove overhead
wires and poles from streets or public highways, it is the usual
practice to confer with the authorities and arrange for some satis-
factory manner of procedure. While franchise requirements will

24 UNDERGROUND TRANSMISSION AND DISTRIBUTION

govern the form of the agreement in any particular case, the
following is submitted as a specimen:

FORM OF AGREEMENT

AN ORDINANCE granting permission to (name of company), its suc-
cessors and assigns, to lay and maintain underground conduits, cables,
wires and manholes for electrical conductors in the streets, avenues and pub-
lic places of the city (or town) of for the use and purposes of its

business, and providing for the removal of certain overhead wires and pole
lines.

BE IT ORDAINED by the Common Council of the city (or town) of ....
as follows :

SECTION I. — That (name of company), its successors and assigns, be and
it is hereby authorized and empowered to construct and maintain for the
use and purposes of its business, a system of subways and underground con-
duits, laterals, service conduits, service boxes and manholes beneath the
surface of the streets, avenues, and other public places of the city (or town)

of as the boundaries thereof are now or may hereafter be, and to place,

maintain and operate therein wires, cables and other electrical conductors
necessary for such purposes; provided that said subway shall be confined
within a space of four (4) feet in width, except the manholes, which may be
constructed of the usual size and shape necessary or advantageous for the
conduct of the business of said company.

SECTION II. — That (name of company) shall, within six (6) months after
the passage and acceptance of this ordinance, proceed to construct its sub-
ways or underground conduits with the necessary laterals, service conduits,
service boxes, manholes and street openings in (state requirements of first
year's work, giving names of streets and avenues in which conduits are to
be installed). After the completion of the subways or underground conduits
in the above-mentioned streets, said (name of company) may extend its
conduits and subways through the other streets, avenues, and public places

of the city (or town) of from time to time, as the requirements of its

business shall demand.

SECTION III. — That within one year from the laying of subways or con-
duits in any street, avenue or public place in the city (or town) of or

any section thereof, said company shall remove its electrical conductors,
poles and fixtures from above the surface of those sections of said streets,
avenues or public places beneath which said subways or conduits shall be
constructed, except where said poles and fixtures are used for supporting
public lights, or for the purpose of supporting or connecting with wires in
intersecting streets, and thereupon the right of said company to maintain the
poles so required to be removed shall cease and become void; and the said
company shall repair the sidewalks from which said poles shall have been
removed.

SECTION IV.— That the said (name of company) before opening any street
for the doing of any part of the work hereby authorized, shall from time to
time file in the office of the city (or town) of a map or plan showing

PRELIMINARY SURVEY 25

the proposed location and dimensions of the subways, underground conduits
and manholes, or any portion thereof, proposed to be constructed in any
such street, avenue or highway, which location or locations shall become
operative from the time of such filing. The said subway or underground
conduits shall be made of (specify the kind and types of construction), and
shall be laid not iess than two (2) feet beneath the surface of the streets,
and not less than one (1) foot outside of the curb lines, except where neces-
sary to avoid obstructions; and shall conform to the laws of the State govern-
ing the laying of subways for the transmission of electricity for light, heat
or power.

The manholes shall be located beneath the surface of said streets at such
points along the line of the subways or underground conduits as may be
necessary or convenient for placing, reaching and operating the electrical
conductors which the said company may from time to time place in sub-
ways or underground conduits, and shall be so constructed as not to inter-
fere with the passage of the public over and along the said streets; and the
said company shall restore such street or avenue which may be disturbed
in the construction and maintenance of the subways, conduits, laterals,
or manholes to the condition in which it was at the commencement of the
work thereon, and free from any cost or expense whatever to the city (or

town) of In backfilling of the trenches, the earth shall be put in

layers of not more than six (6) inches at a time ; it shall be thoroughly rammed
and compacted before another layer of dirt is placed thereon, and where
necessary it shall be carefully and thoroughly puddled. The electrical
conductors and conduits therefor shall be so placed as to do no injury to any
shade tree or to the property of any person or persons, or to any public
or private sewer, or to any water or gas pipe, or to the wires or conduits
of any other company. At least forty-eight (48) hours before the opening
of any street or avenue, the said company shall notify, in writing, the city
(or town) engineer of the desire of the said company so to do, stating the
place and purpose of such proposed opening, and the said company and its
servants and employees, in the laying of any wires or conduits, in excavating
and replacing the earth in any street or avenue, and in replacing the pave-
ment thereon, shall be under the supervision of the city (or town) engineer,
or the proper officer appointed by him having supervision of streets and high-
ways. The earth removed in making any excavation shall be restored, and
the pavement taken up and relaid by the said company in a thorough and
workmanlike manner, and in such manner as to prevent any future sinking
of the pavement. The pavement so disturbed or taken up, either in the
original construction of said work or in any subsequent repairs to the work,
shall thereafter be maintained by the said company for a period of one (1)
year, unless said street is repaved within such time, in as good condition
as the surrounding pavement. No street, avenue or public place shall be
encumbered for a longer period than shall be necessary. In prosecuting
said work not more than one thousand (1,000) feet of any street, avenue
or highway shall be opened at one time, and in all cases and at all times dur-
ing the prosecution of such work in any street, avenue or highway, a proper
passageway for vehicles shall be kept open and free at the intersection of
streets.

26 UNDERGROUND TRANSMISSION AND DISTRIBUTION

The cost of restoring the earth or otherwise and the cost of replacing the
pavement and repairs thereto, caused by the opening of any such street
or avenue, shall be paid for by said company, and the said company shall
likewise pay the cost of an inspector appointed by the city (or town) of

to supervise the work. The expense of such supervision and the cost

of such inspector shall be paid by said company upon the presentation of
bills therefor, certified by the proper officer of the city (or town) and the

expense to which the city (or town) of shall be put from the neglect

of said company, or its employees or the doing of any work in an unwork-
manlike manner in the digging of trenches or holes, or in the restoring of
the earth, or of the relaying or replacing of any pavement, shall in like
manner be paid by said company. In case the work or any part thereof
shall not be done to the satisfaction of the city (or town) engineer, or the
person appointed by him having the supervision of streets and highways,
the said city (or town) engineer may, without waiving any of its rights
hereunder, cause the said work to be performed or material to be supplied
to its satisfaction; and the company agrees upon the presentation of bills
therefor, certified by the proper officer in the city (or town) to pay at once
the same, including the cost of both inspection and of labor and material;
provided, however, that before any work shall be done or material supplied

by the city (or town) of for the cost of which (name of company)

under this section shall be liable, the city (or town) engineer shall give
notice in writing to (name of company) of the work required to be done and
the material required to be supplied, and the company shall have ten (10)
days within which to begin the work and supply material by such notice
required to be done or provided, and shall have a reasonable time thereafter
within which to complete the said work.

SECTION V. — The said company shall indemnify and save harmless the

city (or town) of , its officers, servants and agents, against all loss,

and shall assume all liability and pay all damages which may at any time

arise, come or occur to the city (or town) of ,its officers or agents, from

any injury to person or property, from the doing of any work hereinbefore
mentioned, or from the doing of said work negligently or unskillfully,
or from the neglect of said company or its employees to comply with the

provisions of any ordinance of the city (or town) of relative to the

use of the streets, or from the failure to put up proper lights and barriers at
or around excavations, or from the failure to support properly the tracks of
steam railroads or street railways during the prosecution of the work and
thereafter, and the acceptance by the company of this ordinance shall be

an agreement by said company to pay the city (or town) of on any

sum of money for which the city (or town) of may become liable

from or by reason of any injury or damage.

SECTION VI. — The said company shall file with the city (or town) of

its acceptance of this ordinance within thirty (30) days from the date on
which it shall take effect.

SECTION VII. — That the company shall repay the city (or town) of

the amount of the cost and expense to the city (or town) of

of all official publication of this ordinance.

SECTION VIII. — That this ordinance shall take effect immediately.

PRELIMINARY SURVEY 27

Other forms of agreement provide for the removal of overhead
wires and poles in certain definitely prescribed sections of the city
or town, covering a period of from 5 to 20 years. In such cases
the operating company has the advantages of being in a position
to lay out definitely its work from year to year, and to make
plans for the entire system, thus providing at the very start for
the ultimate number and size of conduit and manholes.

Still other forms of agreement provide for the expenditure of
a certain sum ranging from $5,000 to $50,000, depending on
the size of the city and the financial condition of the operating
company.

Some companies have agreed to construct each year a certain
number of lineal feet of underground conduit, the municipality
exercising the right to designate the streets in which it desires
to have conduit installed, covering not more than one-half of
the total amount, the remainder being left to the judgment of
the company. The streets designated by the city (or town) must
be contiguous to the present subway system. The forms of
agreement regarding the amount of work to be done are de-
pendent entirely on local conditions, and the foregoing outline is
given merely to aid the engineer in determining a proper method
of procedure.

Regulations. — Many states have enacted laws to regulate the
construction and maintenance of subway systems, with a view to
safeguarding workmen.

In some cases these laws fix the size of manholes so as to pro-
vide sufficient working space for the necessary jointing and
repairs, and the size and location of manhole covers. The
proposed National Electrical Safety Code, in the preliminary
edition issued by the Bureau of Standards, April 29, 1915, con-
tains the following recommendations covering manholes, hand-
holes and ducts:

LOCATION

Underground systems of electrical conductors should be so located as to
be subject to the least practicable amount of disturbance. When being
designed and installed, care should be exercised to avoid catchment basins,
street railway tracks, gas pipes, or other underground structures which
have been installed or are planned for the future.

To facilitate installing and withdrawing cables and conductors, the
ducts between adjacent manholes or other outlets should be installed in
straight lines, except when it is necessary to install curves, in which case

28 UNDERGROUND TRANSMISSION AND DISTRIBUTION

they should be of not less than 25 ft. radius, and manholes or other outlets
spaced closer together than on straight runs.

GRADING

Manholes should be so located and ducts so graded that drainage of
ducts will always be toward manholes or handholes. To insure satisfactory
drainage, the ducts should be so installed as to provide a grade of not less
than 3 in. in 100 ft. of length.

ACCESSIBILITY

Manholes should be so located as to provide safe and ready access, and,
if possible, so that the least horizontal distance from any rail of a railroad
track to the nearest edge of a manhole opening is not less than 3 ft.

MECHANICAL DETAILS

The mechanical design and construction of manholes and handholes shall
be such as to provide sufficient strength to safely sustain the mechanical
loads which will be imposed upon them.

The entrance to all manholes shall be not less than 24 in. minimum
diameter. Round openings are recommended.

Manholes should be so constructed when practicable that the least
inside dimension will be not less than 3 ft. 6 in., and should be so arranged
as to maintain a clear working space whose least dimensions are not less
than 3 ft. horizontally and 6 ft. vertically, except that where the opening is
within 1 ft. on each side of the full size of the manhole the depth may be less.
Where conditions will permit, a larger working space than the above should
be provided.

Manholes and handholes shall be so arranged, if practicable, as to provide
permanent drainage through trapped sewer connections or otherwise for
such surface or drainage water as may flow into them.

MANHOLE COVERS

Manholes and handholes while not being worked in shall be securely
closed by covers of sufficient strength to sustain such mechanical loads as
will be imposed upon them, and so secured in place that a tool or appliance
is required for their opening or removal.

MECHANICAL BARRIERS AND GUARDS

Manhole openings shall be so arranged that they may, when uncovered,
be surrounded by substantial metal barrier guards.

MATERIAL, SIZE, AND FINISH OF DUCTS

Ducts used in underground systems of distribution for electrical supply
and signal conductors shall be of such material, size, mechanical strength,
and finish as to permit the safe installation and maintenance of all con-
ductors or cables to be maintained in them.

PRELIMINARY SURVEY 29

INSTALLATION OF DUCTS

Conduits should, where necessary, be laid on suitable foundations of
sufficient mechanical strength to protect them from settling and be pro-
tected by covers where necessary to prevent their disturbance by workmen
when digging, or by other causes. A sufficient depth shall be provided
between the top of the duct covering and pavement surface or other surfaces
under which the duct run is constructed.

Ducts shall have clear bores and be freed from burrs before laying. They
shall be laid in line in such manner as to prevent shoulders at joints.

Duct openings into manholes, handholes, or other permanent openings
of underground systems shall be provided with an effective bushing.

Duct runs should provide as great a clearance from other underground
structures as practicable. Conduits for underground conduit systems to be
occupied by signal conductors for public use should, where practicable,
be separated from underground conduit systems for supply conductors by
not less than 3 in. of concrete or its equivalent.

Joints in duct runs shall be made reasonably water-tight and mechanically
secure to maintain individual ducts in alignment.

No duct should enter any manhole, handhole, or other permanent open-
ing of underground systems of distribution at a distance of less than 6 in.
above the floor line or below the roof line.

Ducts of laterals supplying service to buildings should be effectively
plugged or cemented by the use of asphaltum, pitch, or other suitable means
to prevent gas entering the consumers' premises through the ducts.

The foregoing notes are included with the idea that they may
be useful to companies in their dealings with commissions and
municipal bodies.

CHAPTER III
CONDUIT AND MANHOLE CONSTRUCTION

Selection of Materials. — "Whether it is the intention of the
central-station engineer to build the conduit line himself, or to
have it built by contract, there will be certain material and labor
used, and these should be the best of their kind in either case."1
Having decided on the routes of the conduit, the type of conduit
line to be constructed should be determined.

A few years ago a 3-in. diameter duct was considered suffi-
ciently large, but for feeder cables called for today, which are
often over 3 in. in diameter, nothing less than a 3J^-in. bore
conduit should be used.

If the material selected is of the best, and the workmanship
all that it should be, there is no reason why a first-class conduit
should not last indefinitely and the repair and maintenance
charges be low.

Installation of Conduit. — In the laying of conduit, trenches
should be dug to a line stretched along the street to keep the
ditch straight, and the width should be kept constant by means
of a stick cut to the required length and used as a gage. The
ditch should be dug in the rough, somewhat narrower than the
finished width, the exact width being obtained by trimming.
This method produces a straight smooth finish on the sides of the
trench and will aid materially in keeping the ducts straight and
also in reducing the quantity of concrete required for any given
duct section.

The bottom of the trench should be carefully leveled and
graded to the required depth and grade stakes should be driven
at intervals throughout the length of the ditch for the purpose of
limiting the thickness of the concrete base and of fixing the exact
grade of the finished conduit.

Ducts should be so laid as to drain toward manholes, for if
pockets are formed and the duct line is submerged it is likely
to freeze in winter weather and injure the insulation of the cable,
and possibly, damage the conduit.

1 HANCOCK, N. E. L. A., 1904.

CONDUIT AND MANHOLE CONSTRUCTION 31

In the laying of conduit great care should be taken to insure
that the alignment of the ducts is not disturbed previous to or
during the process of filling in the space between the ducts and
sides of the trench, or in placing the top cover on the concrete.

In digging the trench, paving materials or old concrete should
be carefully separated from the earth and all excavated material
should be thrown well back from the brows of the ditch to pro-
vide wheeling space for concrete and other materials, in order to
prevent them from being brushed into the ditch by workmen.
Where deep ditches are required, and the soil is of an unstable
character, shoring or bracing will be necessary. This is especially
necessary in case of severe rains during the progress of the work,
and the force engaged in the work should always be so arranged
that the smallest possible amount of trench consistent with
economical working, will be opened at one time.

In many cities there is a limit set on the amount of street which
may be opened at one time.

Where it is the intention of the engineer to furnish his own
labor and material in the construction of the conduit line, it is
essential that he provide himself with a general foreman, or
general superintendent, who is thoroughly familiar with the
laying out of the work, handling the men and attending to the
details of city-street construction. It will be necessary to place
considerable confidence in this man and his ability should be
such that the payroll will be reduced to a minimum and the
amount of work completed each day be consistent with the
number of men employed.

The superintendent of construction should be familiar with
all of the details of the work, and see that his assistant properly
protects the life and property of others observing the city
regulations and providing bridges over openings at intersecting
streets. Proper barriers should be placed where required, and
excavations should be flagged at all times, to avoid accidents to
pedestrians, or interference with traffic. The trench should be
properly patroled at night by a watchman, whose duty it should
be to see that the lanterns are kept lighted throughout the
night.

It is important that records be made of the progress of each
day's work and that measurements be taken showing the actual
location of the work, foreign conduits, pipes, and any other ob-

32 UNDERGROUND TRANSMISSION AND DISTRIBUTION

structions encountered in the installation, as well as any troubles
experienced during the construction period.

The principal object in keeping itemized records is to enable the
engineer to determine the unit cost for similar work, and to analyze
expenditures with a view to improving the method of working,
as well as the class of labor to be employed. The records should
show the amount of each class of work completed daily so that
the many kinds of work may be divided into units and the unit
cost obtained.

In all forms of conduit construction which require the formation
of ducts, the base or foundation section of concrete should be
not less than 3 in. in thickness. The laying of the conduit should
be immediately followed by the concrete required to fill in between
the sides of the trench and the conduit line, in order to give sup-
port to the sides of the trench and to insure a proper joining of the
concrete in the base and side sections.

Concrete. — The concrete required for conduit work should be
mixed in a thorough and careful manner. Where the streets are
surfaced with a smooth, clean pavement, and the municipal
authorities will permit the use of the pavements, no mixing board
will be required. Where the work is being done on unimproved
streets or rough pavements, mixing boards should be provided
if the concrete is to be mixed by hand. Mixing boards made of
a sheet of boiler iron will be found convenient. These should
be about 8 ft. square and J4 m- thick, and provided with holes
and rings at the corners to which a length of chain can be fastened
to facilitate moving from place to place.

TABLE I. — MATERIALS REQUIRED FOR A CUBIC YARD OP RAMMED CONCRETE

Mixtures

Stone 1 in. and
under, dust
screened out

Stone 2^ in. and
under, dust
screened out

Stone 2J4 in. with
most small stone
screened out

Gravel H in.
and under

•g

«r

.
•*»

03 U

2.0

4.0

1.46

0.44

0.89

1.48 0.45

0.90

1.53

0.47

0.93

1.34

0.41 0.81

2.5

5.0

1.19

0.461 0.91

1.21

0.46

0.92J 1.26

0.48

0.96

1.10

0.42 0.83

3.0

5.0

1.11

0.51

0.851 1.14

0.52

0.87

1.17

0.54

0.89

1.03

0.47J °-78

3.0

6.0

1.01

0.46 0.92

1.02

0.47

0.93

1.06

0.48

0.97

0.92

0.42

0.84

3.0

7.0

0.91

0.42 0.97

0.92

0.421 0.98

0.94

0.42

1.05

0.84

0.38

0.89

4.0

7.0

0.83

0.51 0.89

0.84

0.51

0.90

0.87

0.53

0.93

0.77

0.47

0.81

4.0

8.0

0.77

0.47

0.93

0.78

0.48

0.95

0.81

0.49

0.98

0.71

0.43

0.86

CONDUIT AND MANHOLE CONSTRUCTION 33

Concrete for conduit work should be mixed from good Port-
land cement and clean sand and gravel, or broken stone, in the
proportions of 1 part cement to 3 parts of sand and 5 parts of
gravel or broken stone, with sufficient water to thoroughly wet
the mix, and allow a small amount of water to come to the surface
when the concrete is ready for pouring.

Most brands of Portland cement manufactured at the present
time appear to be satisfactory and will pass the strength tests
if the cement is a representative sample of the manufacturer's
output.

It is customary to test cement for tensile strength, the reason
being that concrete is weaker in tension than compression.

Specifications for cement may be obtained from any of the
members of the Association of Portland Cement Manufacturers,
and they will, therefore, not be printed here. It is customary to
test samples of cement from each shipment received, some engi-
neers testing one sample from each 8 or 10 bbl. received, others
testing only one sample from each carload. The number of
samples to be tested depends on the importance of the work,
but in ordinary conduit work and manhole construction one test
from each carload should be sufficient.

There are several important considerations to be observed in
the selection of aggregates for concrete. The material entering
into the concrete must be of such structure and quality as to suit
the use to which the concrete is to be put. Aggregates should
remain in an unaltered physical state as long as the concrete lasts
and should be so graded as to give a maximum density, strength
and impermeability. The material selected should show a definite
strength in combination with the cement.

The matter of using a good quality of sand is very important.
All sands are derived from the decomposition of natural rock of
various kinds. It is frequently stated in specifications that clean
sharp sand must be used, and while this is important, it is more
important that sand be properly graded so as to secure a dense
mass. Sand containing loam or clay should not be used, for if
it has been properly washed all such foreign materials will have
been removed.

When mixed by hand, the cement, sand and stone should
be turned at least three times dry and twice wet, and the concrete
should be placed immediately after mixing. When all the con-
crete has been placed in the trench, it should be allowed to take

34 UNDERGROUND TRANSMISSION AND DISTRIBUTION

its initial set before the trench is filled in and tamped, and the
pavement replaced in order to avoid throwing the conduit out
of line or fracturing the concrete while it is still weak.

Tile Duct. — Tile duct is made of clay which has been worked
up in a pug mill to the proper consistency, passed through a press
from which it emerges in the desired shape, carefully dried, and
burned until it is thoroughly vitrified. It is then given a salt
glaze and allowed to cool slowly.

FIG. 15. — Single- and multiple-tile duct.

The quality of the duct is very materially affected by many of
the processes, and it is, therefore, important that it be purchased
on carefully drawn specifications.

The clay should be free from gravel and of such composition
that it will work up into a solid homogeneous mass, 60 per cent,
fire clay and 34 per cent, shale making a very desirable com-
bination.

The duct, when moulded and dried, should be burned thor-
oughly, but not scorched or fused. The glaze should thoroughly
cover the inside -of the ducts so that they will present a smooth

CONDUIT AND MANHOLE CONSTRUCTION 35

surface to the cable. Single duct should not have a bend of over
J^ in. from a straight line, and multiple duct should not have
more than %Q in. bend. Twisted or distorted pieces should be
rejected as these cannot be lined up and may interfere with the
installation of the cable. No duct having salt blisters or drips
which project more than J^ in. inside, or J4 in. outside should
be used. Air- and fire-checked pieces should also be rejected.
The test for straightness should be made by passing through the
duct a mandril of the length of the piece and % in. smaller than
the inside diameter of the duct. If the mandril will not pass, the
duct is too crooked to be installed.

If the tile is properly vitrified, it will give a clear ringing sound
when struck by a piece of tool steel. If it gives a dead sound, it
indicates softness and porosity, which will result in a high break-
age in handling.

Tile conduit will last indefinitely, and when free from iron it
possesses high insulating properties. It also has great mechan-
ical strength, and shows an average puncture test of 25,000 volts
dry, and 21,000 volts after immersion in water for several days.
While the dielectric strength of the tile is very high, the insulation
resistance of the system is greatly lowered in consequence of the
number of joints which are made with cement or other moisture-
absorbing material. Instead of the entire system withstanding
20,000 volts, it will be found that, due to the presence of joints,
the installation will not be able to stand more than 5,000 volts,
depending, however, on the general characteristics of the soil
surrounding the ducts.

Multiple-tile conduit is usually made in lengths of 3 ft., the
number of ducts varying from two to nine, and in some special
installations even more.

The pieces are laid end to end and are usually held in align-
ment during the construction period by iron dowel pins which fit
into the holes formed in the ends of each section.

In making joints in multiple-duct tile, it is impossible to pre-
vent communication between the ducts, and, owing to this con-
dition, multiple-duct affords the least protection to the cables.
If the streets in which the conduit is to be installed are congested
under the surface, the use of single-tile duct permits of a more
flexible installation, whereas, the multiple-tile duct is used to
good advantage in suburban districts where there are few ob-
structions to interfere with the course of the line.

36 UNDERGROUND TRANSMISSION AND DISTRIBUTION

Multiple-tile duct is better adapted for telephone, telegraph
and other similar wires than for use in connection with power
cables, since, as explained, the ducts communicate at each
joint between the sections of tile, and in case of trouble on a
cable, in addition to the communication at each joint, the thin
tile is apt to be melted and evaporated, permitting the burning
cable to damage other cables in the same conduit line.

In the laying of single-duct tile, the ordinary methods of brick
laying are used and the joints are made by simply putting the

FIG. 16. — Section of tile conduit illustrating use of mandril.

two pieces of tile together. Alignment is secured by the aid of a
mandril. Since the length of the sections is shorter and the
area much less than in the case of multiple-tile, a more perfect
butt joint can be obtained in a single-duct installation.

It is not customary in laying single-duct tile to wrap the joint
with any form of protection to prevent the mortar or concrete
running through the joint. It is almost certain, however, that
some mortar will work its way through the joint and in order that
this may be removed before it hardens, a wooden mandril, such
as is shown in Fig. 16, 3 in. in diameter and about 30 in. in length,
is used. At one end is provided an eye (a), which maybe engaged
by a hook, in order to draw it through the conduit, while at

CONDUIT AND MANHOLE CONSTRUCTION

the other end is secured a rubber gasket (6) having a diameter
slightly larger than that of the interior of the duct. One of these
mandrils is placed in each duct when the work of laying is begun.
As the work progresses, the mandril is drawn along through the
duct by the workmen by means of an iron hook at the end of a

6 DUCT'S.

/£ &UCTS.

FIG. 17. — Single-tile duct sections.

rod about 3 ft. long. By this means the formation of shoulders
on the inner walls of the ducts at the joints is prevented, and
any dirt that may have dropped into the duct is also removed.
The cylindrical part of the mandril insures good alignment of the
ducts, thus securing a perfect tube from manhole to manhole.
The use of such a device will leave a smooth inner surface, free

38 UNDERGROUND TRANSMISSION AND DISTRIBUTION

from projections and burrs, which if left would be likely to dam-
age the sheaths of the cables during the drawing-in process.

The principal advantage to be gained from the use of single-
duct lies in the ability to break joints in all ducts. Provided a
jacket of concrete or mortar surrounds each individual longitu-
dinal row of tiles, perfectly solid ducts may be produced. If the
tiles are not completely surrounded by such a jacket, a burning
cable is very likely to discharge the gases produced by the arc
through the butt joints with such force that the hot gases and the
flame which results from their combustion will cause damage to
the cables in adjacent ducts.

Single-duct tile, being vitrified, requires the same general
provisions for inspection as multiple-duct and all duct purchased
should be rigidly inspected at the factory before shipment is
made.

The weight of 3J^-in. tile is approximately 8 Ib. per duct ft.
and this heavy weight increases the freight cost and the labor
cost of laying.

The question of breakage is an item which must be taken into
consideration. This will vary from 5 to 10 per cent, of the total
shipment, depending upon the composition, quality and firing
of the clay of which the duct is made.

TABLE II. — TABLE OP INFORMATION ON STANDARD VITRIFIED CONDUIT

Style ofjconduit

Dimension
of square
duct, in.

Dimension
of round
duct, in.

Outside
dimen-
sions of
end section,
in.

Reg.
stock
lengths,
in.

Short
lengths,
in.

Approx.
weight
per duct
ft., Ib.

2-duct multiple
3-duct multiple
4-duct multiple
6-duct multiple
9-duct multiple

3%sq.
3%sq.
3Hsq.
3X sq.
3Hsq.

3M
3H
3H

3tf
3H

5 by 9
5 by 13
9 by 9
9 by 13
13 by 13

24
24
36
36
36

6, 9 and 12
6, 9 and 12
6, 9 and 12
6, 9 and 12
6, 9 and 12

8
8
8
8
8

5 by 5

6, 9 and 12

Single duct, self-cen-
tering

3?£

5 by 5

6, 9 and 12

Round single duct,
self-centering

5 in.
round

6, 9 and 12

Minimum car lot, 5,000 duct ft. or 40,000 Ib.
Maximum car lot, 7,500 duct ft. or 60,000 Ib.

Where very cheap work is desired, multiple-duct tile is some-
times laid either without concrete or with a single bottom layer
for a foundation and with perhaps a top layer for protection

CONDUIT AND MANHOLE CONSTRUCTION

against future excavations. The concrete in such cases gives
little or no support to the tile and should the earth shift or settle,
the tile is apt to give way under the strain, resulting in damage
to the cables. Such construction is not recommended and in
no case should it be used where permanency is desired.

In the laying of tile duct both of the single and multiple type
the ducts should all be thoroughly cleaned out by drawing through

^£#£&££

DUCT.

/s"

« DUCT:

DUCT:

££££&£

/s'

4 DUCT.

/2 OUCT

FIG. 18. — Multiple-tile duct sections.

them a wire brush or flue cleaner slightly larger than the duct.
Any particles of sand or loose bits of mortar left in the duct may
be removed by following up the brush or cleaner with a cotton-
rope mop. It is essential that the cleaning be done as soon as
possible after the placing of the concrete in order that concrete
or mortar which may have been introduced into the ducts through

40 UNDERGROUND TRANSMISSION AND DISTRIBUTION

the joints may be removed before it has a chance to harden.
Where it is necessary to cut pieces of the tile for fitting lengths
together, the tile is notched all around at the desired point by
means of a hammer and cold chisel. It should break off at the
mark after continued chipping, though it frequently happens that
the cracks run off in some other direction. It is, preferable,
therefore, to have fitter lengths, furnished by the manufacturer.

Stone Duct. — Stone duct has been used quite extensively in the
City of Chicago. It is made of a high grade of limestone and
Portland cement, in the proportions of 4.75 to 1.00, the materials
being thoroughly blended together with water.

Moulded-stone duct is manufactured under the Graham process
and is moulded in two half moulds or sections in especially
designed machines. This mould contains a mandrel form that is
displaced by a larger mandrel having a tapered steel point.
Both mandrels are revolved by means of individual motors and
the tables holding the moulds are moved parallel with the
mandrels. As the form is displaced by the tapered steel points,
all inequalities in filling are eliminated.

This method insures a perfectly smooth inner and outer sur-
face of the pipes. After being removed from the conduit
machines, the ducts are allowed to stay in the lower half of
the mould for 48 hr. to take their initial set. They are then
placed in racks and sprinkled continuously for about 6 weeks to
insure their perfect curing, after which they are allowed to dry
for 2 weeks. They are then ready for use. The ducts are made
in 5-ft. lengths and the units are provided with metal rings.
These rings, which are used for connecting two sections together
afford a tight joint, making it impossible for any foreign material
to get into the duct. It is claimed that this type of conduit is
not injured even by the short-circuiting of heavy power cables.
In this way communication of trouble from one duct to another
is avoided.

This conduit is laid with an envelope of concrete. It forms a
monolithic mass as the envelope makes an excellent bond with
the duct. The ducts can be readily cut with an ordinary cross-
cut saw, and the weight of the duct is approximately the same
as that of tile duct. With the use of metal sleeves, unskilled
labor may be employed in its installation. Its length permits of
the same staggering as is obtained with the use of fiber conduit.
The conduit is made up in various forms and in split sections,

CONDUIT AND MANHOLE CONSTRUCTION 41

thus allowing repairs to be made in ducts carrying cables. It
weighs approximately 7J£ Ib. per ft., has a bore of 3^ in., with
a wall % in. thick and approximately 4,000 ft. can be loaded for
shipment on a standard car.

Fiber Duct. — Fiber conduit is the most recent addition to the
materials used for subway construction, and has come into very
general use for all classes of underground electrical work. This
type of conduit has been in use approximately 15 years, and the
writer has had occasion to examine fiber duct which has been

FIG. 19. — Stone conduit.

installed in moist soil for about 10 years. The inspection failed
to show the slightest signs of deterioration. Fiber pipe was
originally used for irrigation purposes and was installed under the
most unfavorable conditions in all kinds of soil, both wet and
dry, and in a number of cases without any concrete or cement
protection. It is made of wood pulp which has been thoroughly
saturated with a bituminous compound containing about 6
per cent, of creosote in solution. The creosote prevents rotting
by killing the organisms which might act on the vegetable
matter in the pulp. The conduit is made in various styles of

42 UNDERGROUND TRANSMISSION AND DISTRIBUTION

joint to suit the particular service conditions; sleeve, drive or
screw joints may be obtained as required. The joints, which are
turned up true in a lathe during the process of manufacture,
are self-aligning.

TABLE III. — DATA ON FIBER CONDUIT

Inside diameter,
in.

Type of conduit

Approximate
average weight
per ft.-lb.

Feet in mini-
mum car ship-
ped in bulk

Average load
one-team
truck, ft.

Socket joint

0.38

80,000

10,500

Socket joint

0.70

42,000

5,700

Socket joint

0.85

35,000

4,700

Socket joint

1.02

30,000

4,000

Socket joint

1.20

25,000

3,300

Socket joint

1.45

21,000

2,750

Socket joint

1.62

18,000

2,450

Sleeve joint

0.74

40,000

5,400

Sleeve joint

0.90

33,000

4,400

Sleeve joint

1.10,

27,000

3,600

Sleeve joint

1.30

23,000

3,000

Sleeve joint

2.50

12,000

1,600

Sleeve joint

3.20

9,400

1,250

Harrington joint

0.90

33,000

4,400

Harrington joint

1.10

27,000

3,600

Harrington joint

1.30

23,000

3,000

Harrington joint

1.55

19,300

2,550

Harrington joint

1.90

15,500

2,100

Screw joint

2.20

13,600

1,800

Screw joint

2.50

12,000

1,600

Screw joint

3.20

9,400

1,250

"Linaduct"

0.55

54,000

7,300

"Linaduct"

0.65

42,000

6,100

"Linaduct"

0.75

24,000

5,300

"Linaduct"

0.85

21,500

4,700

These joints make it possible to lay the sections in the trench
unit by unit with great rapidity. No wrapping with burlap
or other material is required and no trowel work is necessary,
thus permitting employment of unskilled labor in laying the
duct.

Where it is desirable to make a perfectly water-tight joint,
liquid compound is usually applied to the male end of each section
as it is placed in position. The simplicity of this form of duct
and the ease of handling give it an important advantage over
other classes of duct. When the ends are properly fitted together,
they remain in perfect alignment.

CONDUIT AND MANHOLE CONSTRUCTION 43

Tests which have been conducted on fiber, show that it will
withstand a puncture test of 32,000 volts when dry and 24,000
volts after immersion in water for about 200 hr. It is impervious
to moisture, gases, acids and other corrosive elements and as it
is a non-conductor, troubles from stray currents are negligible.

The non-abrasive feature of the conduit is very important,
as it permits of drawing cables into the ducts without injury to
the sheaths by such grinding or cutting action as often results

FIG. 20. — Installation of fiber and multiple duct.

when the ducts are composed of a hard material and the inner
wall is not perfectly smooth.

Absence of abrasive or gritty surfaces adds to the ease and
rapidity with which the cable may be installed. The lightness
of the conduit gives it a decided advantage not only as regards
handling and laying, but also as regards shipping, since about
20,000 ft. can be loaded in a standard box-car, owing to the light-
ness of the conduit. It is made in 5-ft. lengths, which is a con-
venient length for shipping and handling in the trenches; this
also results in fewer joints, thereby effecting a considerable
saving in labor.

44 UNDERGROUND TRANSMISSION AND DISTRIBUTION

Bearing in mind its light weight, the lengths of the sections
in which it is manufactured, and the simplicity in the method of
jointing, it is readily seen that a greater amount can be laid in
less time by a less number of men than is the case with other forms
of duct. Unskilled labor can be used in its installation and the

20 DUCTS.

<7 &UCTS.

& DUCTS.

/G> DUCTS.

S3"

WSSSKSS*

:•.'*>.• ^ ?.-•?•.•.• • •."..>

4- DUCTS.

FIG. 21. — Fiber-duct sections.

cost of laying is thereby considerably reduced. Breakage
amounts to practically nothing owing to the great tensile strength
and the shock-resisting properties of the material.

In the laying of fiber conduit a concrete base 3 in. thick is
provided similar to that used in other forms of construction.
There is also provided a side and top cover with 1 in. of concrete
separating the adjacent duct, and with fiber conduit, as well as
with other forms, it is well to avoid water pockets in the ducts.

CONDUIT AND MANHOLE CONSTRUCTION

After the foundation of concrete has been placed, the first or
bottom row of pipes is laid directly on its surface and these are
spaced by means of a wooden spacing block or comb, illustrated
in Fig. 22. The desired duct section is then built up in succes-
sive tiers and a 1-in. spacing is maintained throughout the line
of conduit by means of the spacing block just mentioned. In
laying the duct care should be taken to stagger the joints in the
adjacent pipes in the conduit, and it is important that all joints
be perfectly tight, otherwise the concrete is apt to work into
the duct and cause obstructions.

The concrete should be worked thoroughly around each pipe
to prevent voids in the structure, and for this kind of work the
concrete should be mixed with gravel or broken stone, which will

"HT

(A) THtS D/MEMS

FIG. 22. — Detail of comb for spacing fiber ducts.

pass through a sieve of %-in. mesh. In laying the fiber duct,
each piece should be inspected to see that it is perfect and that no
foreign material has lodged inside the tube.

In considering the merits of the numerous kinds of conduit
material, which are used in underground systems, it must be
understood that each has its particular field and the conditions
which will govern the type of installations are to be carefully
considered, not only from the standpoint of interest and depre-
ciation on the investment, but also with a view to securing free-
dom from interruptions to service.

The question of the relative mechanical strength of fiber, tile
and stone conduit is of minor importance, because the strength
of the surrounding concrete will determine the strength of the
structure as a whole. Since the best grade of concrete will
stand a compression test of about 3,000 Ib. per sq. in., it will be
seen that, regardless of the duct material, the structure will

46 UNDERGROUND TRANSMISSION AND DISTRIBUTION

have sufficient strength to meet the most exacting demands of
service conditions.

Manhole Construction. — Manholes are usually built at street
intersections or turns in the conduit line, to afford a place for
jointing the cables. The distance between these manholes
depends on local conditions. It is safe to say that this limiting
distance, where large cables are to be employed, should be
500 ft.

In pulling in long runs of cable, the sheath is subjected to
severe strains which are to be limited as much as possible.

Manholes designed for high-tension cables should be spacious
and should have good drainage facilities. Their design should
be such as to avoid sharp bends between the point where the
cables enter and the position on the manhole wall where they are
to be jointed and racked.

Ample facilities should be provided in each manhole for the
shelves or racks on which the cables are to be supported. Many
cables have had to be renewed on account of insufficient manhole
room and careless racking.

It is also wise to give some attention to the location of the lower
and top ducts in the manholes to permit drawing in cables
without damaging them.

Manhole covers are preferably located at the center of the
manhole making it easy to set and rack cables and rendering it
impossible for careless workmen to ruin the cables by using them
as steps in entering and leaving manholes.

In transmission systems it is very desirable, as previously
stated, to limit the distance between manholes to less than 500
ft., as this permits of carrying in stock standard lengths of cable
which can be used in any part of the transmission line. Wher-
ever practicable manholes should be connected to sewers so
that the water will run off. A suitable trap should be employed
to prevent the sewer water from backing up and filling the man-
hole or conduit line. Where it is impossible to make the neces-
sary connection to the sewer, the following method may be used
to advantage:

When excavating for manhole work, a hole a trifle deeper
and larger than an ordinary barrel is dug and a barrel without
top or bottom placed in it; the outside of the barrel is surrounded
with a concrete covering about 3 in. thick and the barrel filled
with gravel or small stones. The concrete foundation of the

CONDUIT AND MANHOLE CONSTRUCTION 47

manhole should then be laid and the top of the barrel set flush
with the floor.

The tendency in the past has been to give too little attention
to the matter of future requirements and this has resulted in
the very congested condition of cables and equipment now found
in the manholes of many of our large cities. The importance of
providing adequate facilities will be appreciated when it is con-
sidered that the efficiency of men, when working under cramped
conditions, is seriously impaired.

Sewer and Illuminating Gas. — In the construction of manholes,
provisions should be made for sufficient ventilation to carry off
any gases which may accumulate.

The gases most commonly found in manholes are sewer gas
and illuminating gas, and now, with the extensive use of automo-
biles, we may find gasolene vapors mixed with the sewer gas.

Sewer gas consists of approximately 90 parts of nitrogen,
2 to 4 parts of oxygen, 1 to 3 parts of carbon dioxide, 3 to 5
parts of carbon monoxide, methane and other gases. It has an
odor due to the organic decomposition constantly going on in the
sewers. It is not poisonous in the true sense of the word, but,
due to its high percentage of nitrogen and its low percentage of
oxygen, there is not a sufficient amount of oxygen to support
respiration, and hence a person is slowly smothered in an
atmosphere of this gas. It is non-explosive in itself, and, due to
its high nitrogen and low oxygen content, would, undoubtedly,
prevent the explosion of otherwise explosive gas when mixed with
it. This gas easily finds its way into the conduit lines through the
entrapped connections which the manholes have with the sewers.

Illuminating gas, or city gas, as generally distributed, may be
coal gas, water gas, Solvay gas, or a mixture of any two or all of
these gases. It is colorless, but usually has a strong penetrating
odor, so that a small percentage may readily be detected by the
sense of smell. It is very poisonous in itself and with air forms
a highly explosive mixture. Gas mains and distribution lines are
closely interwoven with the conduit lines and breaks or leaks in
the gas system lead to the escape of the gas into the conduits and
manholes.

Sealing of Ducts in Manholes. — When troubles occur in which
there is an arc in series with considerable resistance, the lack of
sufficient oxygen for the combustion of the gases, which are gener-
ated, will cause these gases to flow through the conduits and burn

48 UNDERGROUND TRANSMISSION AND DISTRIBUTION -

in adjacent manholes, unless there is some positive barrier to
prevent the gas flowing between manholes. It is, therefore,
considered advisable to cement the ducts in each manhole along
the heavier runs of cable where the spreading gas could cause
the greatest damage. Some companies using concentric cables,
subject to creeping on account of expansion and contraction
at periods of heavy and light loads, do not consider it advisable
to cement the ducts. They also consider the omission of the
sealing of the ducts an advantage from the standpoint of provid-
ing more ventilation to the manholes and, therefore, less chance
of accumulation of gases, and perhaps increased heat radiation
in the ducts. All ducts or pipes leading from manholes to the
premises of customers should be cemented in the subway and
at the entrance into the customer's buildings to prevent obnoxious
gases entering the premises. Several devices are on the market
which have been designed to be placed in the duct before apply-
ing a mortar to aid in removing the latter. A weak cement
mortar is sufficient for this purpose.

Types of Manhole Construction. — Manhole construction may
be classified under three headings :

(a) Brick construction.

(6) Monolithic concrete construction.

The design of each of these three types of construction may be
divided into two classes: namely, design to properly facilitate
the training of cables for transmission purposes; and design to
provide for the training of cables for distribution purposes, in-
cluding the installation of transformers, boxes, and other sub-
surface equipment.

Monolithic concrete seems to be advocated for manhole con-
struction, particularly where a number of manholes of the same
size are to be built, and where local conditions and the space
available in the street will permit the use of a standard form.
One of the advantages of the use of monolithic concrete for man-
hole construction is the fact that common labor may be employed
for mixing and placing the concrete, whereas, with brick construc-
tion, the service of experienced masons is necessary. Brick
construction seems to be very desirable in congested sections
where the use of either a wooden or metal form for concrete work
would be almost prohibitive on account of the high cost of special
forms to meet the local conditions.

CONDUIT AND MANHOLE CONSTRUCTION 49

One of the disadvantages in the use of concrete manholes lies
in the fact that the soil in many locations is sandy clay, which
will not stand unless properly supported by bracing. The result
of this soil condition is that in the locations where the absence
of other constructions permits the use of concrete manholes, the
soil requires an outer as well as an inner form. In such cases the
resulting cost is higher than for brick manholes. The presence
of water in some localities at a depth of 3 or 4 ft. makes it neces-
sary to build brick manholes. In such locations, a manhole of
brick can be built by driving sheet piling and using a sufficient
number of pumps' to remove the water from the hole. The brick-
work is started directly upon the sand and the manhole is rilled
up with sand as the work progresses. This prevents the water
which seeps into the hole washing out the mortar of the
brickwork.

Building Manholes in Quicksand. — It is frequently necessary
to build manholes in a sandy soil when the permanent water level
is only 2 or 3 ft. below the surface, and in such cases manholes
have been successfully built by using a modified form of open-
caisson construction. The excavation to the quicksand is made
in the ordinary manner. Then a wooden framework is built,
having the same horizontal section as the manhole wall. This
framework is built up of 2-in. planks to a total thickness of 6 in.,
the corners being well fastened to eliminate diagonal bracing and
leave the center of the framework free for the excavation. The
framework is then placed in a level position on the quicksand and
the manhole is built of brick to the required height, the walls
being well plastered on the outside.

After setting for 3 or 4 days, the excavation of the manhole
proceeds. By digging along the walls inside of the manhole and
under the wooden framework, the manhole will usually settle
to the required depth. During the excavation only sufficient
water should be removed to allow the men to work to advantage,
as otherwise the sand becomes quite hard. The settlement, if
slow, can be accelerated by placing bags of sand or other weights
on top of the manhole walls. Ordinarily the excavation and
settlement of the manholes to the required depth will not require
more than 8 or 10 hr. unless obstructions are encountered. After
the manhole has reached the proper depth, the settlement is
stopped by backfilling the excavation and tamping around the
outside of the manhole wall.

50 UNDERGROUND TRANSMISSION AND DISTRIBUTION

Upon completion of the settlement, the water is removed from
the manhole, the sand excavated to the level of the bottom of the
wooden framework and a heavy concrete bottom is placed in the
manhole. The openings for the conduit are cut in the manhole
walls after it is entirely completed and has settled to the proper
depth.

In building such manholes, the labor cost is about double that
of the ordinary manholes. The wooden framework is the only
other additional item of expense.

Concrete blocks have not been used to any considerable extent
for building manholes, although this form of construction would,
undoubtedly, be the cheapest if a considerable number of man-
holes of a standard size were to be built. One reason why this
type of construction is not more common is the difficulty of
making connections between the manhole and the conduit lines.
Concrete manholes are limited to localities in which the under-
ground conditions permit the use of standard sizes and shapes,
and where the ground is of sufficiently firm composition as to
require no outer form for the concrete. Moreover, concrete
manholes should be allowed at least 48 hr. for setting, which
practically prevents their use in streets with dense traffic. The
brick manhole is preferable where irregular shapes only can be
used and where a large number of future connections are to be
made, it being much less liable to damage by these connections
than the concrete manholes.

Roof Construction. — Manhole roofs are sometimes built of
second-hand T-rails laid in two layers crosswise and filled in
with concrete. I-beams and other standard shapes are also
used, and sometimes, on moderate spans, concrete reinforced
with expanded metal. The iron roof framing should be
thoroughly embedded in the concrete for protection and to
avoid corrosion.

While cables and other manhole equipment are usually so
constructed as to operate successfully when submerged in water,
it is desirable to have manholes free of water. It is the general
practice to install sewer connections, which are usually provided
with a back-trap valve. Drains are particularly necessary for
those manholes which contain transformers and other equipment
that should not be flooded.

Type of Cover. — There are several types of manhole heads in
use, both round and rectangular, the round type being more

CONDUIT AND MANHOLE CONSTRUCTION

3>f

PL. AM AN** SfCT/ON.

'^MerAi. TO *£ KNOCKED
OUT Off LEFT IN AS

&£TA/t.5 Or/^/VAME

Coves?.

FIG. 23. — Small round manhole head and cover.

37*'

COUNTERSUNK ~\ xx- ft. METAL. TO ae KNOCKED

AMD

FIG. 24. — Large "round manhole head and cover.

52 UNDERGROUND TRANSMISSION AND DISTRIBUTION

generally used. The use of rectangular covers should be avoided
as far as possible, as in the hands of careless workmen the cover
may be dropped into the manhole causing damage to cables and
equipment. Some companies use an inner cover, which is
fastened tightly to the outer frame by means of a lock bar and nut
and made waterproof by a rubber gasket. In some installations
this inner cover is intended only for a pan to catch the dirt which

UUoU

OOSOO

SECTION Or FRAME AMD COVEF?.
FIG. 25. — Square manhole frame and cover.

falls through the ventilated outer cover. Such pans, however,
are not in general use. Ventilated covers are quite necessary in
streets where conduits and gas mains parallel each other in close
proximity, as without ventilation there is always danger of gas
explosions and fires in the manholes.

When manholes are constructed in unimproved streets, it is
well to allow for any uncertainty regarding the exact grade of the
finished paving. If, therefore, the roof is built about 4 in. low

CONDUIT AND MANHOLE CONSTRUCTION

and the head casting is brought to the surface by being set on
bricks instead of directly on the iron frame, it will allow a space
of 4 in. for lowering the head without disturbing the roof frame in

3~^tll i "5J*""'T*"~6?4~*1-I 8%"

/w!i^"

DETAILS OF RIB

FIG. 26. — Manhole cover for asphalt filling.

case the grade of the street is changed when permanent pavement
is laid. Manhole heads should be set J^ in. above street grade
to prevent surface water draining into the hole.
Fig. 26 shows details of a manhole cover with space at the

54 UNDERGROUND TRANSMISSION AND DISTRIBUTION

top which can be filled with asphalt. This cover is for use in
locations where the noise made by wagons running over an iron
cover is objectionable, or where the authorities object to the
appearance of the standard type of cover. Covers of this type
can be developed to match any kind of street pavement.

Waterproofing Manholes. — Few attempts seem to have been
made to waterproof manholes. In a few special cases tarred
paper painted over in the usual manner with waterproofing
compounds has been employed to coat the exterior surface of the
manholes to prevent seeping of water. This method of water-

;^^^^^^^t^:^^:^^^^':^

FIG. 27. — Waterproof manhole.

proofing has not been entirely satisfactory owing to the number
of corners and outlets, such as duct lines and service connections,
around which it is very difficult to make a water-tight joint.
Concrete manholes, in which the concrete is mixed with some form
of waterproofing compound, have been built below tide water and
made quite waterproof. Probably the most satisfactory method
of securing this result is to keep the manhole as dry as possible
when pouring the concrete, and to use a rich cement mortar,
tamping it carefully. A cement waterproof coating applied on
the inside of a concrete manhole has given very good results.

Design of Manholes for Transmission and Distribution Work.
— Manholes are either two-way, three-way or four-way, Fig. 28,
according to the number of conduit outlets, which is determined

CONDUIT AND MANHOLE CONSTRUCTION

largely by service requirements. For transmission purposes
the two-way manhole of elliptical or oblong octagonal shape is
well-suited, because it provides sufficient wall space for the mak-
ing of cable joints and at the same time eliminates the necessity
for sharp bends in the cable. The three-way manhole practically
follows the lines of the two-way manhole on the outlet sides
excepting that the side free from ducts is built straight. The

OVftL

XOUHDPO COfttffffS

FIG. 28. — Types of manholes.

7W/ff£ Mt/.

ideal shape of a four-way manhole is rectangular, but with the
opposite duct entrances centrally displaced. This provides
sufficient spacing for the training of cables in all cases.

Transformer Manholes. — Frequently separate manholes or
vaults are provided for transformers. These manholes are in-
stalled, usually, immediately adjacent to one of the main-line
manholes, and are very desirable when the space in the street
will allow construction of this type to be followed. Manholes
in which there is likely to be any considerable amount of work

56 UNDERGROUND TRANSMISSION AND DISTRIBUTION

should have a clear head room of at least 6 ft., to provide working
space for cable splicers.

In the design of manholes for the installation of underground
transformers consideration should be given to the fact that
manholes must be well-ventilated and so constructed that they
can be kept reasonably free from water during rain storms.
Where sewer connections are not possible, a dry well for drain-

FIG. 29. — Transformer manhole.

ing moisture from the bottom of the manholes is advocated as
an efficient means of disposing of surface drainage which may
enter the manholes. Natural ventilation is preferred in all
cases where the conditions are favorable, and sufficient space
should be allowed so that at least 3 cu. ft. per kva. of transformer
capacity is provided.

In general, where the total capacity of the transformers in-
stalled in a manhole does not exceed 100 kw., the natural heat

CONDUIT AND MANHOLE CONSTRUCTION

FIG. 30.— Ducts
grouped in center of
manhole.

FIG. 31. — Double manhole with divided
duct lines.

58 UNDERGROUND TRANSMISSION AND DISTRIBUTION

radiation from the manhole through the ground is sufficient to
keep the transformer within safe temperature limits. In ex-
treme cases it is advisable to provide artificial means of ventila-
tion. Many advantages are derived from the use of separate
manholes for transformers, and in cases where it is necessary to
install transformers of large capacity in underground systems it
is frequently found advisable to arrange with large consumers

pol Fool
oo too

Fool
loon loo

FIG. 32. — Double manhole with ducts separated.

for the installation of transformers in the basement of buildings
where they are accessible for inspection and repairs.

In some cases it is necessary to provide separate manholes,
sometimes called subsidiary manholes, which are installed some
distance from the main conduit line, either in intersecting streets
or underneath a sidewalk. No cables pass through these holes
other than the cables feeding the transformers installed therein,
with the result that the heating effect is reduced to a minimum.

Double manhole construction is very desirable where it is
necessary to install transmission and low-tension power feeders

CONDUIT AND MANHOLE CONSTRUCTION 59

in the same conduit line. In such installations a dividing wall
in the manhole permits the complete separation of high-tension
and low-tension cables.

The ducts in some cases run straight through the manhole
wall, Fig. 30, to the center of the manhole, where the cables divide,
half going to one side and half to the other, the cables being
racked on the manhole wall. Grouping of ducts in this manner
is very objectionable on account of the sharp bends in the cable,
which may crack the insulation and cause breakdowns. Rise
in temperature in one cable is readily communicated to another
when the ducts are grouped in this manner.

The form of construction adopted by the Niagara Falls Power
Co. for one of their recent installations is shown in Fig. 31.
Where the space in the street will permit of this design, very
satisfactory results may be obtained.

In places where rock is near the surface necessitating shallow
excavation and affording excellent conditions for the - radiation
of heat, the type of construction illustrated in Fig. 32 will give
good service.

All of these special methods depend upon local conditions in
the streets and can be used only where foreign structures do not
interfere.

In Fig. 33 is illustrated a typical design of a two-way manhole,
as recommended by the Committee on Power Distribution of the
Railway Engineering Association. This type of hole is well-
adapted to railway service, as it permits the installation of heavy
power cables in almost a straight line, very little bending of the
cable being required, and the slack in the manhole being reduced
to a minimum. It will be noted that every third layer of bricks
is projected to act as a shelf for the cables, and while this may be
good construction for railway feeders which as a rule run straight
through the manhole, for electric light and power cables, the
installation of shelves of this type is not so desirable. Manholes
for electric light and power cables frequently contain junction
boxes and other equipment, and to facilitate their installation,
smooth walls are desirable, the cables being racked on the wall
by means of portable hangers conveniently arranged. The
installation of eye-bolts, as shown in the sketch, is a very good
feature, as by their use the drawing in of cables is much simpli-
fied. Bolts, of this type should be installed in all manholes, as it

60 UNDERGROUND TRANSMISSION AND DISTRIBUTION

CONDUIT AND MANHOLE CONSTRUCTION

62 UNDERGROUND TRANSMISSION AND DISTRIBUTION

greatly facilitates the rigging of cable tackle as described else-
where, under the heading of " Cable Installation."

Manholes of the four-way type, as illustrated in Fig. 34 are
usually placed at intersecting streets where two main conduit
lines cross.

Concrete Manhole Forms. — The choice of forms will be gov-
erned by the character of the work to be done. Usually forms
are made of wood but where there is considerable repetition and

G. Board

FRAME MADE IK 4 SECTIONS

SECTION A-B

FIG. 35. — Wood form for concrete manholes.

no obstacles are encountered steel forms have been used to ad-
vantage. They may be used a number of times because they
retain their shape. They, moreover, produce a very smooth
finish on the interior of the manhole wall.

In Fig. 35 is shown a manhole form constructed of wood so
designed as to permit of the building of manholes of various
sizes by simply changing the spacing between the end sections.
The outer surface of the form should be of dressed lumber in

CONDUIT AND MANHOLE CONSTRUCTION 63

order to insure a smooth surface on the inside wall of the man-
hole. Usually forms are removed the second day following the
placing of the concrete, but some consideration should be given
to temperature conditions and the kind of cement used. It will
take concrete considerably longer to set in winter weather and
under unfavorable atmospheric conditions, than during the
summer months.

In order that the forms may not adhere to the concrete after
it has set, it is customary to oil them before the concrete is
placed.

The concrete should be of a consistency known as "wet mix-
ture/7 and should be thoroughly paddled and worked in around
the form so as to avoid a porous or honeycombed structure.

The mixture most commonly used is 1 part cement, 3 parts
sand and 5 parts stone. The proper portions in any particular
case must be determined by a knowledge of the conditions under
which the structure is to be installed and operated and of the
quality of materials making up the aggregate.

After the removal of the forms any rough surfaces should be
smoothed off and the voids filled with cement mortar. How-
ever, if care is taken in the paddling of the concrete, by spading
it well around the forms, there should be no need of smoothing
over rough surfaces after the forms have been removed.

Distribution Holes. — Service or distribution holes should be
located at intervals of 100 to 150 ft. between manholes in order
to reduce the length of service runs. These service holes should
be of ample size to allow room for the proper racking of cable and
placing of subway boxes. They should be not less than 3 ft.
square and of sufficient depth to allow a man to work in them.
In Fig. 36 two methods of installing distribution holes are shown.
Where the space in the street will allow, the holes should be built
on the side of the main conduit, as shown in the illustration.
In congested streets, however, this plan is not always feasible and
under such conditions the hole may be placed on top of the main
conduit and sufficient ducts run therein for distribution cable.

A suitable concrete foundation should be laid not less than 3
in. in thickness. The walls should be built of brick or concrete,
depending on the type of construction to be used.

Reinforcing I-beams or old scrap rail are used in the roof of
the hole for supporting the iron frame or cover, which is of the
same design as those used on manholes, except that it may be of

64 UNDERGROUND TRANSMISSION AND DISTRIBUTION

smaller diameter to conform to the size of the hole. The type
and size of the hole depends entirely upon the service require-
ments, loads and other local conditions.

Cable Tunnels. — In some cities which are divided into two or
more parts by a river, it has been found expedient to build tunnels
for carrying cables across the river. The tunnels are built in
the shape of an inverted U, with a vertical height 6 ft. 6 in. in
the clear, and the width 6 ft. with 9-in. concrete wall. The

FIG. 36. — Methods of building distribution hole in main conduit line.

tunnel has a slope of 1 or 2 per cent, toward a sump at the foot
of one of the shafts so that the tunnel can be pumped out pre-
liminary to cable pulling. At each end of the tunnel is a shaft
6 ft. 6 in. internal diameter, with 15-in. walls built of concrete.
At the upper end of each shaft is a manhole which forms the
terminus of the conduits leading to and from the tunnel. It is
advisable to have the tunnel shaft extend 2 ft. above the bottom
of the manhole for convenience in working and as a protection

CONDUIT AND MANHOLE CONSTRUCTION

to the workmen. A permanent galvanized-iron grating is placed
over the unoccupied portion of the upper end of the shaft so as
to prevent accidents.

On completion of the tunnel a standard conduit is installed in
a horizontal position, and in each of the shafts, leaving a gap at
the junction of the tunnel with the shafts to allow for proper
training of the cables. This junction should be built with a curve
having a radius of about 6 or 8 ft., to give proper working space
and permit the cable to be installed with easy curves. The
vertical conduit in the shafts can be built with single-duct,
vitrified tile, fiber pipe or stone conduit. Tee irons are fitted
into the shafts at intervals of about 2 ft., so as to leave a clear

TUNNEL SHAFT

VERTICAL CONDUIT

FIG. 37.— Cable tunnel shaft.

space in the center of the shaft about 2 ft. wide. With the
dimensions given for the shaft about 35 or 40 ducts can be
installed between the tee irons and the shafts on each side.

A brick or concrete pier under the curve in the cables at the
lower end of the shaft will support a considerable portion of the
weight of the vertical cable. Some additional means of support
for each cable should be installed at the top of the shaft. Care
should be exercised to avoid clamping the cable too tightly or
placing too great a strain on the lead sheath.

Fig. 37 illustrates the method of training cable in the manhole
over a tunnel shaft.

66 UNDERGROUND TRANSMISSION AND DISTRIBUTION

The telephone company in Chicago has used iron pipes exclu-
sively for the vertical conduits in shafts and has made the connec-
tions between these vertical pipes and the conduits in the tunnel
with bends of 6 or 8 ft. radius in such a manner that the duct is
continuous from the top of one shaft to the top of the other.
Copper lead-wires are installed at the time that the conduit is
built, so as to avoid difficulty, which might be experienced with
iron wires. This provision allows the pulling in of cables at any
future time without pumping out the tunnel, and at the same time
eliminates all joints from the bottom of the shafts. It is probable
that the same scheme could be used with smaller cables for elec-
tric light and power purposes, but this is not the usual practice.

A useful auxiliary in connection with such tunnels is a motor-
driven pump of about 15 hp. capacity for removing the water
from the tunnel. Such pumps can be obtained with either a
direct-current or alternating-current motor, and can be readily
lowered in the clear space in the tunnel. These outfits are
preferably built with a vertical shaft, and for convenience in
assembling, are made in two parts.

The tunnel shaft should be erected from 25 to 50 ft. away from
the river edge, depending on local conditions. Where the river
bank consists of filled ground, it may be necessary to use a steel
shield, extending into the impervious clay below the river. With
a stiff clay the depths of the tunnel below the lowest portion of the'
river should be about 15 or 20 ft. If there is not sufficient depth
of clay above the rock to give this amount of clearance to the
river, the tunnel should be built in the rock. In Chicago these
tunnels are located at least 15 ft. below the surface of the rock,
so as to avoid the danger of letting in any water while blasting.

The cost of such a tunnel, if in clay, will be about $25 to $35
per lin. ft., plus $50 to $60 per ft. for the shaft. If built in
rock the expense will be increased about 50 per cent.

These prices do not include manholes at the top of the shafts,
or the conduits in the tunnel and shaft.

Very little water has been encountered in building tunnels in
hard blue clay. Considerable water is usually present in build-
ing tunnels through rock, as the surrounding rock is somewhat
shattered by the blasting, opening up water seams, which adds
considerable difficulty to the construction of the tunnel. When
completed, the tunnels through clay are generally dry, while
those through rock are somewhat leaky.

CONDUIT AND MANHOLE CONSTRUCTION 67

Slight leaks that do not interfere with the construction work
or prevent pumping the tunnel out for cable installations are
not objectionable as it is the practice to allow the tunnel to fill
up with water after the cables are installed. Tunnels built in the
manner just described have been in service for as much as 12
years and no serious operating difficulties have been experienced.

Specification and Contract. — It is very often desirable to have
subway construction work done by an outside contractor, and
while contracts are frequently drawn by engineers, it is necessary
that the subject matter be in legal form. Specifications should
be clear and so written that the precise meaning of each sentence
is understood and that no doubt exists in the mind of the con-
tractor as to their intent. It is not necessary in preparing a
specification to model the language after that used in many legal
documents, but the specifications should be complete in every
detail and, as far as possible, the use of long or involved sentences
should be avoided. This is particularly desirable in view of the
fact that such specifications are often placed in the hands of con-
struction foremen whose knowledge of legal phraseology is limited.
Short and simple wording is preferable and it should be the aim
of the engineer to make the language crisp and concise, rather
than to produce a literary masterpiece.

The specifications should describe in detail the work to be
covered and should give directions as to how it is to be done.
Specifications are usually accompanied by plans of the work and
the drawings should be mentioned in the specification giving the
number, date and title of the drawing. Contractors are usually
required to give a bond which provides for the payment to the
owner of an indemnity in case the contractor fails to live up to
a part or all of his agreement. While there are many forms of
specifications in use, the following specimens cover most classes
of conduit and manhole construction.

SPECIFICATION AND CONTRACT

THIS AGREEMENT, made and concluded this day

of in the year between

a Corporation of the State of of the first part, and

of the State of , of the second

part:

WITNESSETH: That the said party of the second part (hereinafter
designated Contractor) has agreed and by these presents does agree with the

68 UNDERGROUND TRANSMISSION AND DISTRIBUTION

said party of the first part (hereinafter designated Company) for the con-
sideration hereinafter mentioned and under the penalty expressed on a bond
bearing even date with these presents, and hereunto annexed, at his own
proper cost and expense, to do all the work and furnish all the material called
for, in the manner and under the conditions set forth in the following speci-
fications, and the attached plans, which constitute a part of this contract.
It is understood that the work covered by this contract is intended for

1. Wherever the term "Engineer" appears it shall mean the engineer
employed by the company and in charge of the work and construction to be
done hereunder.

2. The subways for electrical wires and cables covered by this contract,
and these specifications and plans herewith attached, are to be built in the

following streets, alleys, lanes and public places of the city of

in the State of . . viz : .

and in such other streets, alleys, lanes and public places in said city of

as may hereafter be designated by the company.

The foregoing schedules of streets and alleys contain those upon which
are to be located the conduits, manholes and service boxes that it is now
intended to be built, but it is agreed that, during the progress of the work,
any additional extensions or subtractions to the conduits, manholes, serv-
ice boxes or laterals shall be constructed by the contractor as required

by The terms and conditions of this agreement shall apply

to and cover all such conditions, provided that such work is reasonably

similar to that which is now specified. It is also agreed that

may decrease the amount of work in any way it shall deem advisable with-
out becoming liable to the contractor for any compensation or damage for
such change, provided shall notify the contractor in writ-
ing before instructions are given to commence the portion of the work. If
said change in combination of ducts and trench feet now shown on plans
herewith attached, should be altered so as not to be substantially similar to
the schedule figured on, then a revised figure is to be agreed upon and made
the basis upon which payment is to be made.

3. Due notice will be given by the company as to the location of certain
divisions of the work and when same shall be commenced, in order to insure
perfect cooperation between the company and the contractor in prosecuting
the work without delay.

4. The company will obtain the rights-of-way and street permits needed
for the prosecution of the work contemplated under this agreement.

5. The work to be done by the contractor is to include the furnishing of
all materials (except the conduit, service-box castings, manhole castings,
eye beams, expanded metal for manhole roofs, and form for drain opening in
floor of manhole), all labor, tools, night lights, bridging, guard rails, shoring,
and so forth. The contractor is also to remove the pavements along the
route of the work to excavate for trenches and manholes, and to refill the
same, and to repave the streets in a complete and workmanlike manner in
accordance with the original specifications under which the street pavement
is laid. For refilling the trenches the best and most substantial part of the

CONDUIT AND MANHOLE CONSTRUCTION 69

materials excavated shall be used, it shall be thoroughly tamped, rammed,
rolled or flushed, as may be deemed necessary to the engineer or required
by the city authorities, and shall be done with the proper tools and in a man-
ner to prevent, as far as possible, a settlement of the earth after completion.

6. The backfilling of the trenches shall be done according to the regula-
tions of the city of and the requirements of the city civil

engineer and all new or other material required for this purpose and the haul-
ing thereof shall be furnished and done by the contractor at his expense.
The contractor shall furnish all materials and labor required for installing
walls and floors of manholes and labor for setting forms for the drain open-
ing in floor of the manholes and shall set manhole and service-box covers.

7. The work is to be done under the line of streets, alleys, lanes and public
places as designated by the engineer.

8. The trenches, manholes, and service boxes are to be located according
to the position assigned by the engineer in charge of work under approval
of the city authorities.

9. The work performed and material supplied under this specification
shall be subject to inspection of the engineer of the company, and the
contractor must remove and make good, at his own cost, all material that
does not fully comply with the specification. The decision of the engineer
shall be final on all matters under this contract.

10. The company shall maintain engineering inspection of the work dur-
ing its progress, and should the contractor fail to fulfill the specifications or
any portion of the contract, or in any particular fail to perform the work
herein specified, he shall be given a written notification of such failure, and
must correct the same and proceed with the work within twenty-four (24)
hours of such notice, and his failure to correct the faults or to so proceed with
the work shall be deemed sufficient cause for voiding of the contract which
the company may at its option do.

11. Should the contractor cease work hereunder for ten (10) consecutive
days unless prevented from proceeding therewith from stress of weather or
unavoidable casualty or accidents, or by act or default of the company, the
company may, at its option, treat the work and contract as abandoned and
proceed as is herein provided to be done in case of such abandonment.

12. Should the contractor abandon said work, or if this contract should be
terminated by the company as above provided, all material delivered and on
the line of the work shall become the property of the company, and such
material and all tools, implements, vehicles and machinery along the line of
the work may be used by the company or its agents or employees to complete
the construction provided for by its contract.

13. If the contractor shall refuse or neglect to proceed immediately with
the correction of any default, or to proceed with the work as required by the
engineer, said company may employ men and teams and purchase material
to effect the requisite corrections or to complete the work at the expense of
the contractor, the cost thereof to be deducted from any moneys due to the
contractor or to be recovered from him and the sureties on his bond.

14. In case the contractor shall not be present upon the work at any time
when it may be necessary to give instructions, the foreman in charge for the
time being shall receive and obey any orders that the engineer may give.

70 UNDERGROUND TRANSMISSION AND DISTRIBUTION

15. The engineer may require the discharge from the work of any incom-
petent or unfaithful employees who may neglect to execute the work in

. accordance with the specifications and the direction of the engineer, and the
contractor shall not again employ such person on any part of the work with-
out the consent of the engineer.

16. The handling of materials and all work relating thereto must be done
in compliance with the regulation established by the city authorities of the

city of The contractor shall immediately remove all

surplus material as fast as the work is finished and dispose of same at his
own cost.

17. The contractor shall furnish all necessary watchmen, place sufficient
and proper guards for the prevention of accident, and shall put up and
keep at night suitable and sufficient danger lights and barricades as required
by the ordinance of said city, and shall indemnify and save harmless the
company, its officers, agents and servants against and from all damages,
cost and expense, which they may suffer, or to which they may be put by
reason of injuries to person or property of another, resulting from negligence
or carelessness or accident on the part of said contractor.

18. The contractor must furnish all necessary guard rails, staging or
bridging that may be necessary to cover over the trenches so as to not ob-
struct public travel at crossings.

19. If, in the excavation of trenches a water main or pipe service, a line
of gas pipe, or any private or public underground service of any character
is encountered, all necessary protection from injury thereof must be provided
by the contractor, and if necessary to make any changes thereto same must
be done entirely by the contractor and to the approval of the owners; pay-
ment for same should be agreed upon in writing.

20. The contractor must assume all responsibility for damage of any kind
caused by his employees to any sewer, gas pipe, conduit or other underground
system and must make such damage good at his own cost and expense. The
repairs must be satisfactory to the owners.

21. The contractor will assume, and shall be held liable for, any damage
to property, or any accident to men or material, connected with the work
described in these specifications which may occur prior to the final comple-
tion of the work and its acceptance.

22. The contractor shall pay, discharge and satisfy all claims for material
furnished and labor done in carrying out this contract and shall fully protect

the company and from all such claims or liens on account

thereof and the bond to be given by the contractor shall comply with this
clause.

23. The contractor is to furnish such a force of men and teams, and such
labor-saving devices, such as concrete mixers, rock drills, tools, machinery,
and so forth, as in the judgment of the engineer is necessary to prosecute
the work with satisfactory speed.

24. If the contractor does not prosecute said work as rapidly as in the
opinion of the engineer he should, the contractor shall employ and put
to work so many additional men, teams and labor-saving devices as the
engineer may require, and if the contractor fails to do so, the company may

CONDUIT AND MANHOLE CONSTRUCTION 71

employ and put to work such additional men, teams and labor-saving
devices, and shall charge the contractor with the cost thereof.

25. The work shall be prosecuted in such a manner as to cause as little
inconvenience as possible to public travel and to property owners on the
streets, alleys, lanes and public places where the conduit is laid. The order
in which the work shall be prosecuted and the sections which shall be first
laid will be indicated by the engineer. The work shall be commenced within

days of the execution of the contract and completed on or

before

26. The paving, if any, removed from the trench, shall be neatly and
compactly piled along the trench on the curb line, except in cases of cross
streets, when a modified disposition may be advisable, but the flow of water
in gutters or drains shall not be obstructed.

27. All pavements disturbed by the contractor must be replaced by him
with a paving of the same character and equal quality and he must give
bond guaranteeing the maintenance of the pavement during the term of
one year from the completion and acceptance of the work to be done under
this contract, all new material required to replace pavement as aforesaid
shall be furnished by the contractor. Where it is necessary to disturb
pavements which have been laid under a guaranty the contractor is to ar-
range with the municipal authorities to have this pavement replaced under
the original guaranty. In such case the contractor is to make temporary
repairs to the pavement, which he shall maintain for a period of at least sixty
(60) days or until such time that the pavement is permanently restored to
its originaUcondition.

28. All excavations and openings of streets must be done in compliance
with the regulations established by the city authorities of the city of

29. The engineer will give any explanations or directions required to
complete or give proper and due effect to the provisions of the specifications,
and will appoint such assistants and inspectors as he may deem necessary
to secure compliance with the same.

30. The engineer shall determine all questions that may arise in regard
to lines, levels, locations, dimensions, materials and workmanship.

31. If, in the opinion of the engineer, it is necessary to make changes in
said plans, the same may be made by him and the work shall be done in
accordance with the plans as changed, and the contractor shall not be en-
titled to extra pay therefor, unless the engineer shall certify that work re-
quired by the changes is in addition to, or of a different and more costly
character than, that embraced in the original plans, and such extra pay
shall be agreed upon before the extra work is done.

32. The trench shall be excavated by the contractor to such width and
depth as may be required to receive the number of ducts required by the
company, as designated by the engineer. There shall be an allowance of
three (3) inches for work space on each side of the completed duct. The
grade of the trench shall be such as will conform to the requirements of
the street route for making a continuous line of conduit from manhole to
manhole, and where the obstructions or other underground service are met
with, the excavation shall be done as far as may be required to afford facilities
for laying of conduits around, under or over such obstructions. Should it

72 UNDERGROUND TRANSMISSION AND DISTRIBUTION

be found necessary for the conduit to straddle gas or water pipes or any
other obstructions, either vertically or horizontally, the excavation must
be made accordingly, and in these details, as the inspecting engineer on the
work may direct.

LOOSE DIRT

33. Loose dirt on bottom of trenches is to be tamped solid previous to
laying conduits, and any sharp stones or rocks which are encountered in
bottom of trench, or in filling dirt, must be removed to prevent injuring
conduits.

34. The sides of the trenches will be vertical, and wherever required the
contractor must shore the trenches to prevent caving. The contractor
must assume all responsibility for the safety of -the work and no extra charge
will be recognized for the shoring and other protection of the work. During
the progress of the work the trenches must be kept absolutely free from
water. All pumping that may be necessary must be done by the contractor
without extra cost.

LAYING

35. Conduits to be laid so as to break joints and true to line, so that no
shoulders or offsets shall be formed in the bores, to be built up in tiers to the
required arrangement and bedded in cement mortar. Conduits must be
laid to drain to the manholes. Conduits may be laid to vary slightly from
a straight line, providing there are no "sags" or "pockets" which will not
drain themselves. Where multiple-duct is used the joints are to be thor-
oughly protected by a strip of tarred burlap not less than six (6) inches
wide and long enough to go around the conduit in a continuous piece and
overlapping on the top by not less than four (4) inches. This burlap must
be applied before applying the cement mortar. A mandrel shall be drawn
through each duct as work progresses. Conduits must be laid with at
least thirty (30) inches between the top layer of ducts and the finished
street surface. This distance may be modified by the engineer of the com-
pany, if the exigencies of the work demand it and the engineer thinks it
advisable. Wherever it may be deemed expedient or necessary by the com-
pany's engineer, ducts shall be reamed by the contractor in a manner
approved by the company's engineer and at the sole expense of the
contractor.

MORTAR

36. Mortar for laying conduit to be mixed of one (1) part of

cement, to two (2) parts clean sharp sand, and must be used within

after being mixed.

CONCRETE

37. A concrete bed three (3) inches in depth and of width sufficient to
extend three (3) inches beyond the sides of the conduits must be placed on
the bottom of the trenches and brought to smooth even surface of uniform
grade. After the conduits are in place, three (3) inches of concrete must be

CONDUIT AND MANHOLE CONSTRUCTION 73

placed on the sides and top. If the space between sides of conduits and sides
of trench is too great to be entirely filled with concrete, and boards are used,
these must be left in place or else withdrawn so as not to disturb concrete
or earth filling and in a manner acceptable to the engineer. All concrete

to be made of one (1) part cement, two (2) parts clean sharp

sand, and five (5) parts of screened gravel. Cement and sand to be first
thoroughly mixed dry, then a sufficient quantity of water added to form a
soft mortar; the gravel to be afterward added and thoroughly mixed. The
concrete when placed in trench to be tamped till water flushes to the sur-
face. The placement of concrete to be so conducted as not to disturb the
conduits while mortar is setting.

38. Service laterals shall be installed by the contractor at the places
designated by the engineer and run into the basement or cellar. These
laterals will be run with single conduit and under same specifications as the
other conduit work.

PLUGS

39. Wherever and whenever work is suspended, the open end of all ducts
must be plugged with hard-wood plugs conforming accurately to the shape
of the duct, and at the larger end at least one-quarter (^) of an inch greater
in dimension than the duct.

BLASTING

40. Where blasting is required, moderate charges of explosive must be
used, and the blast covered with heavy logs and chains, or other measures
taken to protect life and property. Excavation of ledge, rock or such boul-
ders as may contain ten (10) cubic feet or more will be subject to extra pay-
ments at rates hereinafter named.

ROBBING

41. Upon completion of the entire work and before acceptance by the
company, the contractor will be required to pass through each duct, from
manhole to manhole, an iron or iron-shod mandrel conforming in shape
to that of the duct, and of not more than one-quarter (%) inch smaller di-
mension. Any obstruction to the free passage of the mandrel through the
ducts must be removed by the contractor at his own expense.

EXTRAS

42. No claim for extra payment is to be made except for extra work
done in obedience to written orders from the engineer approved by the
company.

MANHOLES

43. Manholes and service boxes will be as shown on accompanying plans,
unless otherwise directed by the inspecting engineer. They are to be con-
structed of the best cement. Concrete mixed over one (1)

hour, or that has commenced to set, shall not be retempered or used. All

74 UNDERGROUND TRANSMISSION AND DISTRIBUTION

manholes shall be drained by means of a round opening located in the floor
of the manholes at such points as shall be designated by the engineer, and the
form for this opening will be furnished by the company. All service holes
must have drain tubes, supplied by the company, installed in the walls of
same, at points designated by the engineer of the company.

MANHOLE FRAMES

44. Manhole and service-hole frames and covers to be as per plans.
Each manhole and service-hole frame when set shall be bedded in cement
mortar and must be set to a line not exceeding one-half (££) inch above grade
of finished pavement, and shall not in any event be below said grade after
settlement.

MEASUREMENT

45. The number of duct feet to be paid for under these specifications shall
be according to the actual measurements of the finished work from face to
face of manhole walls. The manhole and service manholes will be paid
for at so much per manhole complete. Service laterals will be paid for accord-
ing to the actual measurements of the finished work from face of service
box or manhole to face of basement or cellar wall or floor line where there is
no basement or cellar. Where, owing to obstructions, manholes cannot be
built to a specified dimension, and in order to get the desired working space,
it is necessary that the manhole be constructed of a shape and size not
shown on the plans; the contractor is to be paid at a unit price per cubic
yard of brick work or concrete, in the sides, top and bottom of the hole.

46. Contractor shall use every care hi handling conduit, and any damage
through carelessness on his part to be replaced at his expense.

47. Any work proving defective within one (1) year after completion of
the work, if due to the use of poor material or faulty construction, or both,
shall be replaced free of charge by the contractor.

48. All walls when broken through in installing laterals as provided for
in Paragraph 38, shall be, by the contractor at his own expense, left in as good
condition as they were before such laterals were installed.

49. Test pits shall be put down at the contractor's expense wherever
thought desirable and of such size as is necessary to determine the feasible
location for the trench, manholes and service holes.

50. Particular care shall be taken not to obstruct access to fire hydrants,
manholes, catch basins and grates belonging to the city or any other cor-
poration or individual in the vicinity of the work and to arrange free passage
ways for the fire department.

51. Such ducts as may be deemed necessary for the installation of the
said conduit system across any canal or river shall be installed in proximity
to the various bridges crossing the canal or river at such points as may be
designated and approved by the company's engineer.

BOND

52. The contractor will be required to execute a bond in the sum of

with such sureties as shall be approved

by the company.

CONDUIT AND MANHOLE CONSTRUCTION 75

53. The undersigned contractor hereby proposes to build subway for
the undersigned as itemized in, and shall do so all in accordance with the
foregoing specifications and the attached plans, and agrees to receive the
following prices in full compensation for furnishing all materials (including
or excepting manhole castings) and all labor necessary for the complete
installation :

For 4-duct subway under (?) pavement, per duct foot

For 6-duct subway under (?) pavement, per duct foot

For 12-duct subway under (?) pavement, per duct foot

For 24-duct subway under (?) pavement, per duct foot

For manholes under (?) pavement, each

NOTE. — Above may be specified the various sizes of conduits and man-
holes, as well as kinds of pavement under which they are constructed.

For service laterals under (?) pavement, per foot

The price for extra work is as follows:

Per cubic yard for dirt excavation and removal.

Per cubic yard for dirt excavation and refilling :

Per square yard for repaving

(Here mention various kinds of paving work to be done.)

Per cubic yard of concrete in place

Per cubic yard for rock excavation and removal

Per cubic yard for clean, sharp building, sand, delivered on the work

Per barrel of cement, delivered on the work

Per cubic yard for clean, freshly crushed stone, delivered on the work

Per thousand brick, delivered on the work

Per thousand brick, laid in place

Per day of ten (10) hours for double team, truck and driver

Per day of ten (10) hours for common labor

The undersigned company, by its duly authorized officer or representative,
hereby accepts the proposal of the undersigned contractor, and agrees that
it will cause to be made each month, approximate monthly statements of
the work done and material delivered, and it will pay to the contractor on or

before the day of each month per cent.

(%) of the value of the estimated work done and materials delivered during
the next previous month. The company further agrees to pay to the con-
tractor at or before the expiration of ( ) days after the

work has been completed in accordance with the agreement and formally
accepted by the company, the whole amount of money then remaining due.

IN WITNESS WHEREOF, the undersigned have hereunto set their
hands and seals the year and day first above mentioned.

FORM OF BOND

KNOW ALL MEN BY THESE PRESENTS: That we

a corporation of the State of as principal, and

as sureties, are hereby held and firmly bound

unto a corporation of the State of

76 UNDERGROUND TRANSMISSION AND DISTRIBUTION

in the sum of Dollars

(S ) lawful money of the United States of America, to be paid to the said

or its certain attorney, its successors and

assigns for which payment, well and truly made, we bind ourselves, our heirs,
executors and administrators, jointly and severally, firmly by these presents:

Sealed with our seals, dated the day of

in the year one thousand, nine hundred and

WHEREAS, the said has entered into a con-
tract with the said for the building of conduits for

electrical wires in the City of in the State of

bearing date the day of

one thousand, nine hundred and

NOW, THE CONDITION OF THIS OBLIGATION IS SUCH, that if

the said shall well and truly keep and perform all

the terms and conditions of the said contract on its part to be kept and

performed, and shall indemnify and save harmless the said

as herein stipulated, then this obligation shall be of no effect; otherwise

it shall remain in full force and virtue.

(Witnesses) (Signed) ,

Construction Costs. — The cost of construction and of materials
varies so much with different localities that it is impossible to
give data which could be considered standard for all classes of
work; and the following schedule, which is compiled to serve as
a guide in making up estimates, is such as to cover average
conditions. The figures include the cost of all materials, excava-
tion, removing dirt, mixing and placing concrete, hauling and
laying duct, replacing pavement and the expense of city inspec-
tion. In the conduit cost, the figures provide for the duct line
to be surrounded on all sides by a 3-in. envelope of concrete, the
top row of ducts being 30 in. beneath the surface.

The cost of removal of obstructions is an item which cannot
be estimated with any degree of certainty. The expense of this
work will vary from 5 to 50 cts. per ft., depending on the size
of conduit and the number of obstructions.

Since it is difficult for workmen to carry on the work in a trench
less that 18 in. wide, it is necessary to remove a strip of pavement
of at least this width. Engineering expense will also vary con-
siderably, depending on whether the work involves any special
features.

Table IV gives the estimated cost of single-tile duct under
various kinds of pavement, and a similar cost for fiber conduit
is given in Table V.

CONDUIT AND MANHOLE CONSTRUCTION

TABLE IV. — SINGLE TILE DUCT COSTS. ESTIMATED COST PER 100 FT. OP

CONDUIT

Based on 3-in. tile duct, 3 in. of concrete on all sides and top of conduit
30 in. below the grade of the street

Amounts

Items

Number of duct

Excavation and re-
moval, cu. yd
Excavation and re-
filling, cu. yd . . .

4.12

11.77
200
3.05
184

5.98

11.77
400
3.78
184

7.85

15.43
600
4.51
217

10.29

15.43
900
5.25
217

12.73

15.43
1,200
5.98
217

15.76

19.10
1,600
6.92
260

18.78

19.10
2,000
7.45
260

Duct, ft

Concrete, cu. yd
Paving, sq ft

Cost of conduits

Excavation and re-
moval, $1.00 per cu.
yd . .

$4 12

$5 98

$7 85

$10 29

$12 73

$15 76

$18 78

Excavation and refill-
ing, 60cts. per cu.

7 06

9 26

11 46

Duct, 6 cts. per ft.
laid

12.00

24.00

36.00

54.00

72.00

96.00

120.00

Concrete, $7.00 per
cu. yd .

21.35

26.46

31.57

36.75

41.86

48 44

52.15

Plus 20 per cent.1. . .
Total cost : . .

8.91
53.44

12.70
76.20

16.94
101.62

22.06
132.36

27.17
163.02

34.33
205.99

40.48
242.87

Cost of p.aving

Macadam, 10 cts. per
sq. ft

$18.40

$21.70

$26 00

Belgian block on
sand, 15 cts. per sq.
ft

27.60

32 55

32.55

39 00

Asphalt, 25 cts. per
sq ft

46 00

54 25

65 00

Granite block and
brick, 35 cts. per sq.
ft

64 40

75 95

91 00

Wood block, 37 cts.
per sq. ft

68.08

80.29

£0.29

80.29

96.20

Total cost of conduits

Macadam
Belgian block on
sand

$71.84
81 04

$94.60
103 80

$123.32
134 17

$154.06
164 91

$184.72
195 57

$231.99
244 99

$268.87
281 87

Asphalt

99 44

122 20

155 87

186 61

217 27

270 99

302 87

Granite block and
brick

117 84

140 60

177 57

208 31

238 97

296 99

333 87

Wood block

121 52

144.28

181 91

212 65

243 31

302 19

339 07

1 Covers Engineering, Inspection, Sheathing, Obstructions, Insurance, eto.

78 UNDERGROUND TRANSMISSION AND DISTRIBUTION

TABLE V. — FIBER DUCT COSTS. ESTIMATED COST PER 100 FT. OP CONDUIT

Based on 3-in. Fiber Duct, 3 in. of Concrete on all Sides and Top of

Conduit 30-in. Below the Grade of the Street

Amounts

Items

Number of duct

Excavation and re-
moval, cu. yd
Excavation and re-
filling, cu. yd
Duct, ft

3.42

10.80
200
2.93
166

5.04

10.80
400
4.05
166

6.66

14.27
600
5.19
200

8.80

14.27
900
6.58
200

10.95

14.27
1,200
7.99
200

13.61

17.75
1,600
9.65
250

16.27

17.75
2,000
11.33
250

Concrete, cu. yd ....
Paving, sq. f t

Cost of conduits

Excavation and re-
moval $1.00 per cu.

yd
Excavation and re-
filling, 60 cts. per
cu. yd

$ 3.42

6.48
10.00

20.51
8.08
48.49

$ 5.04

6.48
20.00

28.35
11.97

71.84

$ 6.66

8.56
30.00

36.33
16.31
97.86

$ 8.80

8.56
45.00

46.06
21.68
130.10

$ 10.95

8.56
60.00

55.93
27.09
162.53

$ 13.61

10.65
80.00

67.55
34.36
206.17

$ 16.27

10.65
100.00

79.31
41.25
247.48

Duct, 5 cts. per ft.
laid

Concrete, $7.00 per
cu. yd
Plus 20 per cent.1 . . .
Total cost

Cost of paving

Macadam, 10 cts. per
sq. ft
Belgian block on
sand. 15 cts. persq.
ft. .

$ 16.60

24.99
41.59

58.19
61.42

$ 16.60

24.99
41.59

58.19
61.42

$ 20.00

30.00
50.00

70.00
74.00

$ 20.00

30.00
50.00

70.00
74.00

$ 20.00

30.00
50.00

70.00
74.00

$ 25.00

37.50
62.50

87.50
92.50

$ 25.00

37.50
62.50

87.50
92.50

Asphalt, 25 cts. per
sq ft . .

Granite block and
brick 35 cts. per
sq. ft

Wood block 37 cts.
per sq. ft

Total cost of conduit

Macadam

$ 64.09

$ 88 44

$117.86

$150.10

$182.53

$231 . 17

$272.48

Belgian block on
sand

73 44

96 83

127 86

160 10

192 53

243 67

284.98

Asphalt..

90 08

113 43

147 86

180 10

212 53

268 67

309.98

Granite block and
brick. ...

106 68

130 03

167 86

200 10

232 53

293.67

334 . 98

Wood block

109 91

133 26

171 86

204 10

236 53

298.67

339.98

1 Covers engineering, inspection, sheathing, obstructions, insurance, etc.

CONDUIT AND MANHOLE CONSTRUCTION

As these tables include unit quantities, the costs may be revised
to suit local conditions where actual unit costs are known.

As in the case of conduit construction, the cost of manholes
also varies with different localities. For city work, and especially
in congested districts, brick is sometimes more suitable than
other forms. Where numerous obstructions are met with, a
manhole made of brick can readily be made of such shape as to
avoid other structures. In cross-country work the concrete man-
hole is cheaper, since the iron or wooden forms can be used a
number of times. The figures given in Table VI and Table VII
may safely be used for estimating. These include all material
and labor (exclusive of paving) and the cost of the cast-iron frame
and cover.

TABLE VI. — BRICK CONSTRUCTION
Estimated Costs of Manholes

8 by 10 ft.
by 6 ft.
6 in.

7 by 9 ft.
by 6 ft.
6 in.

6 by 8 ft.
by 6 ft.
6 in.

6 by 6 ft.
by 6 ft.
6 in.

5 by 7 ft.
by 6 ft.
6 in.

4 by 7 ft.
by 6 ft.
6 in.

Excavation and removal

$ 37.00

$ 34.00

$ 30.00

$ 23.00

$ 21.00

$ 18.00

Brick in place

120.00

110.00

96.00

86.00

L60.00

Rail

22.00

18.00

15.00

14.00

9.00

f9.00

Head and cover

26.00

Concrete

13.00

12.00

9.00

7.00

Incidentals

20.00

18.00

15.00

12.00

Supervision

5 00

4 00

3 00

$243.00

$225.00

$199.00

$175.00

$168.00

$135.00

TABLE VII. — MONOLITHIC CONCRETE CONSTRUCTION

8 by 10 ft.
by 6 ft.
6 in.

7 by 9 ft.
by 6 ft.
6 in.

6 by 8 ft.
by 6 ft.
6 in.

6 by 6 ft.
by 6 ft.
6 in.

5 by 7 ft.
by 6 ft.
6 in.

4 by 7 ft.
by 6 ft.
6 in.

Excavation and removal

$37.00
84 00

$ 34.00
78 00

$ 30.00
63 00

$ 23.00
54 00

$ 21.00
52 00

$ 18.00
48 00

Rail -.

22.00

18.00

15.00

14.00

9.00

8 00

Head and cover

26.00

26 00

10 00

8 00

7 00

Incidentals

18.00

17.00

14.00

12.00

12 00

10 00

Supervision

5.00

4 00

3 00

$202.00

$188.00

$163.00

$141.00

$132.00

$120.00

The above estimated costs are exclusive of paving.

When the area and type of the pavement is known, the cost
can be estimated and added to the figures given in the table
to obtain a total cost.

80 UNDERGROUND TRANSMISSION AND DISTRIBUTION

As previously stated, under certain conditions concrete man-
holes may be constructed at a cost somewhat less than that of
brick construction, and the relation between the cost of the two
forms of construction is shown in Fig. 37a. This curve is com-

1.00

100

200

300

400

500

Cubic Feet
FIG. 37 a. — Approximate cost of manholes exclusive of paving.

puted on the basis of the cost per cubic foot of manholes of various
sizes.

For further details the reader is referred to the various elec-
trical handbooks which include underground construction costs.

CHAPTER IV

METHODS OF DISTRIBUTION

Street Distribution. — In large cities the arrangement of service
laterals and subsidiary connections from the main duct line to
the consumer's premises is a matter of importance because it
forms a large part of the underground investment. A single-
conduit system with service connections is shown in Fig. 38.
In some cases it is advisable to install duplicate conduit lines in
the same street; one conduit consisting of a sufficient number of
ducts to carry all the main cables, and the other usually consist-
ing of about four ducts on the opposite side of the street for dis-
tribution cables, Fig. 39. The main conduit also carries about

FIG. 38. — Service handholes and laterals, single-conduit system,

four ducts reserved for these purposes. In Fig. 40 is shown a
single-conduit system with crossings.

The desirability of installing duplicate conduit depends en-
tirely upon local conditions and the width of the street. With
duplicate-conduit systems the service or lateral connections are
usually of a shorter length than in the single-conduit system and
the service holes are placed about 100 ft. apart. Where the
streets are more than 100 ft. wide a double-conduit line installa-
tion is convenient as it saves long lateral connections. In
some localities a single service connection serves several buildings,
the intermediate buildings being connected by means of interior

6 81

82 UNDERGROUND TRANSMISSION AND DISTRIBUTION

wiring through the side wall or basement. While this method is
considerably cheaper than supplying individual service to each
building, and requires fewer distribution holes, it has the dis-
advantage that a fault in the main wiring will interrupt service
in all the buildings connected thereto. If such a fault develops
in the service connection supplying a building which is closed

FIG. 39. — Service handholes and laterals, double-conduit system.

during certain hours of the day while the other buildings are
still open, it is sometimes difficult to gain entrance in order to
make necessary repairs and to restore service to other buildings
tied in on the same service. Still another system which is simi-
lar to the duplicate conduit is to provide crossings at each dis-

I \ J

Ml 1 M 1

FIG. 40. — Service handholes and laterals, single-conduit system with

crossings.

tribution hole from which the service connections are run on
each side of the street.

Interior Block Distribution. — What is commonly known as
back-yard or block system of distribution, Fig. 41, has been used
quite extensively in the suburban sections of a number of large

METHODS OF DISTRIBUTION

cities. From the results obtained through its introduction
there seems to be good reason for the enthusiastic way in which
it has been taken up. So far as appearances go this plan pos-
sesses nearly all the advantages of the complete duct system and
the cost of reaching suburban houses with electrical service
in sections where the underground connections in streets would
be necessitated, is not much greater than would be entailed by
the straight overhead system. In the larger cities arrangements
have been made whereby the lighting companies have deeded
to them by the owner of the property the ground on which poles
may be erected in the rear of houses, together with the right of

FIG. 41. — Plan of back-yard pole lines, with overhead-service connection
fed from main subway.

free access at all times, the company in return for this privilege
placing on the street an improved type of lamp post. In this
method of distribution the mains are run to the back-yard lines
and the high-potential circuits are run underground to the trans-
former manhole nearest the desired streets. From this point
low-potential circuits run to the street opposite the pole line
whence they branch and run underground to the end pole on the
other side. The mains are then brought up through conduits
to the crossarm. Service connections are made to the main and
brought in to the rear of the house, thus relieving the front of the
property from overhead wires and service connections. The
pole line extends from block to block, depending on the number of

84 UNDERGROUND TRANSMISSION AND DISTRIBUTION

houses to be connected. The property owner usually appreciates
the 'effort to keep the streets free from poles and the shade trees
from being killed or marred owing to the presence of overhead
wires in the street. Few difficulties, therefore, are encountered
in securing free grant of the ground and the right of access.

The scheme has met with public approval in many cities where
detached houses abound. With this system of distribution the
problem of street lighting becomes more difficult as it involves the
use of long overhead branches to each lamp, or underground
laterals of the same length at a considerably greater cost.

The need of a cheap, yet good system, of subway distribution
in suburban districts is being felt at this time when there is so
much agitation about the injurious effects of wires in trees. The
springing up of shade tree commissions in the larger cities has
particularly aggravated the situation. It is believed that in
sections where the business would not warrant a complete installa-
tion of an underground system the combination of an under-
ground system with the overhead system just described will be
most satisfactory and economical.

Sidewalk Distribution. — In the sidewalk system of distribu-
tion the conduit is usually laid under the grass plot between the
curb and the sidewalk with han dholes located at every second
property line from which the service pipes lead in to the meter
board on the consumer's premises. Sometimes the ducts are
sunk below the sidewalk level, the record of their exact location
being kept so that they may be quickly located in case of trouble.
The box as shown in Fig. 42 is well adapted to this type of con-
struction. It is constructed of cast iron with a removable cover
and is cast with holes of a convenient size to receive the duct
and the service pipe.

Handholes may also be installed with a cast-iron cover which
is set flush with the sidewalk. Fig. 42 illustrates an installation
of this type.

The duct may be either fiber or iron pipe, the fiber duct, how-
ever, being considerably cheaper than the iron pipe. It is not
necessary to lay the duct in concrete, as a special sleeve may be
employed, which has sufficient strength to insure proper align-
ment of the duct during the refilling of the earth. The ends of
the duct should fit tightly in the sleeve, which is about 5 in. long.
Cement covered joints are also used to good advantage when the
conduit is not entirely laid in concrete. In this case slip joints

METHODS OF DISTRIBUTION

are wrapped with muslin tape before the protective covering of
cement is applied, thus preventing any water from entering the
conduit. This system, however, has its limitations and is
practicable only in suburban sections where the houses set well
back from the property line and have no vaults extending to the
curb.

In the larger cities where real estate promoters have built
blocks of houses, and desire to keep all overhead wires off the
property, it is customary for them to install subway services to
the sidewalk distribution system, since the revenue from the

FIG. 42. — Sidewalk distribution.

customers is very often not sufficiently large to justify the ex-
penditure on the part of the lighting company of the amount
necessary to install underground connections. An agreement
with the owner is made whereby the latter will install the conduit
at his own expense under the supervision of the company, the
company agreeing to install the necessary wiring without any
future expense to the owner.

Duct Arrangement. — Conduit lines of a large number of ducts
are undesirable and should be avoided wherever possible. More
than 20 or 24 cables entering a manhole by one conduit line are
difficult to properly train around the manhole walls and a man-

86 UNDERGROUND TRANSMISSION AND DISTRIBUTION

hole fire with so many exposed cables may cause great trouble
and damage.

Unless conditions are such as to make it absolutely necessary,
it is not good practice to use more than 20 ducts, partly because
of the limiting of the current-carrying capacity, due to the diffi-
culty in dissipating the heat from the line and partly because
of the danger of shutting down the whole duct line due to
communication of trouble from one cable to another.

The layout of the conduit system should be one which will
give the shortest cable lengths and at the same time avoid
the bunching of cables in any one manhole or conduit run. It
is advisable to divide into two or more runs at the supply point
or center of distribution, such as the generating station or sub-
station. When the number of cables for present and future use
has been ascertained, the various duct sections to be laid should
be determined by increasing the number of ducts required by
25 or 30 per cent.

This increase is advisable on account of the relative cheapness
of the ducts so installed as compared with the high cost of
installing needed ducts at some future time when unforeseen
contingencies require their use.

While the number of ducts will be fixed by requirements, there
must be sufficient to care for local distribution and distribution
feeders and transmission lines, as well as to care for future
requirements.

It is not advisable to lay less than four ducts in a line except
in side streets or for lateral connections and where there is no
probability of the line becoming part of a through line.

In selecting a route for conduits, due consideration should be
given to the character of the streets or alleys in which the work
is to be done. It often develops that it is cheaper to lengthen
the conduit and cables to some extent than to install them in
streets where very expensive pavement is laid or where rock
excavation or difficult obstructions will be encountered.

Parallel Routing. — Because of the likelihood of large cables
in one conduit or in one street to be interrupted by accidents, the
attempt is usually made, in case of important lines running from
a power house for some distance, to route them in separate con-
duit lines or even in separate streets, and it is, therefore, advisable,
instead of using a large number of ducts, to provide parallel
conduit lines with fewer ducts. Among some of the causes

METHODS OF DISTRIBUTION

which might interrupt such lines are burning of cables by severe
short-circuits, by caving in of streets due to excavation for
building foundations, sewers or subway construction, explosions
due to illuminating gases, blasting, malicious mischief, washing
out of pavement and conduit due to bursting of water mains,
collapse of large buildings in case of fires, earthquakes or faulty
construction.

In Fig. 43 is shown a system with all main cables installed in
a single-conduit system.

Sue STATIO/V

FIG. 43. — Feeder cables routed in same duct lines.

While much of this constitutes an ever-present menace, any
real danger of interruption of service on any line from these causes
is quite remote and the justification of any increased investment
to provide a duplicate route should be gaged accordingly. Some
engineers are of the opinion that the greatest protection warrant-
able would be to provide duplicate routes for conduit lines in the
same streets. Others go to the extreme of providing a duplicate
route for a single line, which necessitates a much longer run than
the original route.

Inquiries among a number of the leading companies show that
some would not provide a duplicate if it required any material

88 UNDERGROUND TRANSMISSION AND DISTRIBUTION

increase in the length of the second line, while others in some
special cases would favor the use of a duplicate route, as shown
in Fig. 44.

In order to avoid more than two cables paralleling along the
wall of the manhole at the same elevation, the conduit should be
so arranged that not more than four ducts in width enter a man-
hole. Where the conduit is several ducts wide, it is frequently
found advantageous to separate the ducts where they enter the
manhole. The arrangement of the ducts, however, is usually
determined by the space available in theL street.

FIG. 44. — Feeder cables routed in different duct lines.

Where conditions will allow, a good form of duct arrangement
is as follows:

Two-, four- and six-duct conduit Two ducts wide.

Nine- and twelve-duct conduit Three ducts wide.

Sixteen-, twenty- and twenty-four-duct

conduit Four ducts wide.

Solid System. — The need for an inexpensive system of under-
ground distribution in suburban sections where the complete
installation of a drawing-in system would be prohibitive on ac-
count of the cost, has led some companies to experiment with

METHODS OF DISTRIBUTION

a so-called "solid" system. One of the large illuminating com-
panies several years ago constructed a system which consisted
of fiber conduit laid directly in the ground without concrete,
but with a protective covering of "kyanized" planking resting
directly on the fiber tube.

The conductors consisted of ordinary line wire and were
arranged for three-wire distribution with the center or neutral

2 Plank

Compound

Fibre Conduit '
Omitted here
to show Jointing

INTERIOR VIEW OF BOX
SHOWING SERVICE CONNECTION

SECTION OF
FIBRE PIPE

FIG. 45. — Experimental solid system.

wire lying directly in the earth between the two outside con-
ductors.

After laying the wire the fiber tubes were filled with an insulat-
ing compound. A complete installation of this type is shown in
Fig. 45. Service connections for customers were made by remov-
ing a short section of the covering and connecting service wires
to the mains, after which the joint was filled with compound and

90 UNDERGROUND TRANSMISSION AND DISTRIBUTION

the covering restored. The writer has been advised that this
system has been in service for about 8 years in suburban sections,
without showing any indication of deterioration, and with no
displacement of the compound during the summer months even
when laid on 5 per cent, grades.

The compound used in the installation shows a dielectric
strength of about 2,300 volts per in. and an expansion from solid
to liquid from 5 to 10 per cent. It is not affected by moisture
and has a flash test of about 700°F.

Service Connections. — Service or lateral connections from man-
holes to the consumers' premises are usually installed in wrought-
iron or steel pipe. The pipe should be thoroughly coated with
an asphaltic compound or other suitable protection to prevent
corrosion. Galvanized or sherardized pipe is sometimes used
in order to prolong the life of the service. In a number of
installations the iron pipe is used only in the street between the
manhole and the curb line where the traffic is heavy, and under
the sidewalk or on private property fiber pipe or some other form
of conduit may be used. It is customary in installing service
connections in a street which is about to be improved with a
permanent pavement, to install the laterals not only to present
consumers, but also to prospective customers, terminating the
pipe at the curb, a record being taken of the exact location in
order that the service may be continued to the consumers,
premises as the occasion requires.

For convenience in locating the pipe services, markers are fre-
quently placed in the sidewalk to fix the location.

These service markers consist of an iron rod which is driven
into the ground to the end of the pipe. The rod is capped with
a cast-iron plate which indicates the class of service.

Wooden plugs or metal caps are placed at the end of the pipe
in order to prevent earth or other material entering the pipe
when the excavation is being refilled.

It is frequently found necessary to install service pipes under
cement sidewalks or under highways, and since such installations
require, a permit and the expenditure of considerable money
for restoration of the pavement, the use of a pipe-forcing jack
will be found economical. This jack is specially designed for
forcing pipe horizontally through the ground and may be used
advantageously where it is desired to install pipe under the con-
ditions mentioned above, or under railroad tracks or other cross-

METHODS OF DISTRIBUTION 91

ings. The device effects a considerable saving in both time and
money. This jack, which is illustrated in Fig. 46 consists of a
carriage which travels on a track so designed that when the
carriage reaches the limit of its travel it can be drawn back to
the starting point to permit of a new section of pipe being in-
serted. The operation of this apparatus is thus carried on
until the desired distance to which the pipe is to be forced has
been reached. It has been found advisable to provide for the
driving in of a section of pipe 1 or 2 ft. long and of a size larger
than the pipe to be laid. . This short length of pipe is equipped

FIG. 46. — Pipe forcing jack showing pipe and steel nose mounted in position.

with a steel nose so that it can readily cut its way^through a
reasonable amount of earth, rock and stones or roots in its path.
Under favorable soil conditions this jack will force pipe up to
4 in. in diameter for a reasonable distance. In using the jack
in public highways, however, care should be taken to avoid coming
into contact with any foreign structures, as the writer has known
of several cases where lack of care has caused damage to under-
ground pipes or other conduits. The jack should, therefore, be
used only where the operator is certain that no obstructions of
this nature will be encountered in the path of the pipe being forced.
Underground construction, when employed for service con-
nections of small capacity, usually requires an abnormal invest-

92 UNDERGROUND TRANSMISSION AND DISTRIBUTION

ment in comparison with the business to be served. Where a
number of customers in a single building are to be served by a
single service, local municipal regulations usually require that
the main service switch be placed in a location accessible at all
times for the replacement of fuses, etc.

This is usually easily accomplished in a building one or more
stories in height, where there are no partitions or dividing walls
cutting the building vertically into several parts by locating
the service in the main entrance or in some position in the base-
ment which is used in common by all tenants.

In the case of a block of one-story buildings, as shown
in Fig. 47 constructed with or without basements, each having

FIG. 47. — Method of installing service box in buildings.

its own entrance, recourse must be had to installing a separate
service connection to each subdivision of the block, as shown in
Fig. 48.

In many cases such services may serve a load of only % kw.
or even less, thus involving a heavy and unwarranted expenditure
for the business served.

In efforts to reduce the cost of this form of construction, a
material saving has been effected by the introduction of a service
box adapted for the supply of an entire block or group of cus-
tomers of the character last described.

The service box comprises a suitable weatherproof iron box
built into the wall of the building at the street level in a manner
to conform to the general architecture of the building and in no
way to detract from its appearance. The company terminates

METHODS OF DISTRIBUTION

its service in this box, installing a main switch properly fused
for the supply of the entire premises to be served. The owner of
the building installs a common main from the service box, run-
ning the same horizontally to connect with all the separate
premises to be served.

This main, when installed in conduit, in strict accordance
with the rules of the National Board of Fire Underwriters, intro-

Manhole

BLUE HILL AVE.

Manhole

Handholes

-?*

Bowling Alley

Manhole

COMMONWEALTH AVE.

FIG. 48. — Method of installing separate underground services.

duces no hazard of any character, and simply duplicates the
conditions under which vertical mains or risers are installed to
serve tenants in buildings of one or more stories in height. In
both cases branch connections are taken from the main on each
tenant's premises, thus giving the tenant access at all times to the
devices controllingjhis service.

94 UNDERGROUND TRANSMISSION AND DISTRIBUTION

The main service box, located in the outside wall of the building,
is always accessible to the company's employees for re-fusing,
inspection, etc., and also to firemen or other municipal agents who
might desire to discontinue the service in the building in emer-
gencies. While the box is ordinarily locked, provision is made
for forcing the door without damage to the box itself.

Armored-cable System. — In Europe the installation of armored
cable is practically standard for all underground systems
supplying large, as well as small, service requirements.

These systems employ armored cables with or without lead
sheaths, laid directly in the ground or in insulated troughs
which are sometimes filled with compound as may best suit the
local conditions governing the installation.

Junction or distribution boxes are employed at the center
of distribution and service connections for customers are made
by means of wiped joints where lead-sheath cables are employed
and by connection boxes where non-leaded cables are used.

In the latter case these connection points are filled with com-
pound after the connection is completed. In this country the
armored-cable system has demonstrated its advantages for use
in cities where service requirements are of a difficult nature and
are subject to radical changes, and for residence streets where
there is a strip of land between the curb and the sidewalk line.

It can readily be installed in places where the dra wing-in
system would be impossible owing to the necessity of passing
around large obstacles such as rocks, trees, etc.

The necessity for a safe and inexpensive conduit system in
many of the smaller cities or towns, and in the parks, playgrounds
and boulevards of larger cities, has brought about a great demand
for steel-tape cable. This cable is made in various sizes and is
adapted for any voltage. The conductors are insulated with a
rubber compound and taped. After the required number of
conductors has been laid and covered with jute and tape, a
lead sheath is applied and the whole served with jute. The
armor is then applied. This usually consists of two layers of
steel tape over which is applied the asphalt and jute which
serves for the outside or final layer, as illustrated in Fig. 49.

Such construction is closely analogous to that of the standard
submarine cable and each layer or cover has its special function.
The outer jute covering protects the steel armor against the ac-
tion of water and chemicals and the steel tape affords mechanical

METHODS OF DISTRIBUTION

strength and protection to the conductors. The layer of jute
under the armor acts as a cushion between the armor and the
lead sheath. The lead sheath absolutely excludes moisture.
The economies effected by this type of installation have allowed
a number of municipalities to install street-lighting systems at a
minimum cost. The growing demand for improved methods in
the installation of ornamental street-lighting systems using under-
ground conductors seems to have been met by the use of steel-
armored cable, as it permits the installation of a complete system

FIG. 49. — Forms of steel taped cable.

in the minimum time and at the least cost, in any kind of weather
and with practically no interruptions to traffic.

One of the largest installations of this type is in Central Park,
New York City, where over 500,000 ft. of steel-tape street-
lighting cable is in use.

Installations of steel-armored cables have been in service in
this country for a number of years and have operated very
satisfactorily. The cable is usually laid about 1 ft. deep in a
trench of spade width, as illustrated in Fig. 50. No reinforce-
ment or protection is provided except at street crossings and

96 UNDERGROUND TRANSMISSION AND DISTRIBUTION

roadways where there is apt to be heavy traffic. At such places
it is customary to run the cable through an iron pipe.

Where the ground is sufficiently level the cable may be laid
directly from the reel mounted on a pair of wheels. Where neces-
sary the same cables may be used as submarine cable for crossing
lakes or streams. No joints are made in the cable as it is usually
looped in through the lamp post. Terminal blocks are located
in the bases of the posts as shown in Fig. 51.

Steel-tape cable, being frostproof and waterproof, may be laid
just deep enough to prevent accidental damage or injury.

FIG. 50. — Installation of armored cable.

Cable has been used to good advantage where it has been found
necessary to cross railroad tracks, in which case the above type
of installation furnishes an ideal solution of the problem. When
crossing under tracks, excavation is sometimes avoided entirely
by boring through the ground with an auger and slipping the
cable through the hole thus made.

The writer's investigation regarding the experience of a number
of companies using this type of cable indicates that troubles
which have developed have been due chiefly to mechanical
injury to the system caused by carelessness or accidents.

METHODS OF DISTRIBUTION

If, therefore, the cable is carefully manufactured and properly
installed, it is rarely necessary to take it up again to locate and
repair faults.

3 WIRE BLOCK

CONTROL SWITCH
Neutral Solid Uo Switch

FIG. 51. — Terminal blocks.

Installing Steel-taped Street-lighting Cable. — When used for
ornamental street lighting, the usual practice is to bury the cable
in the street close to the curb and just beneath the paving.
Where the street is paved with brick, cobbles, granite or wood

98 UNDERGROUND TRANSMISSION AND DISTRIBUTION

blocks, the installation simply requires the removal of one or two
rows of the paving material and the cable is laid 3 in. below the
pavement, filled over with sand and the paving replaced.

Another method largely used is to remove one course of brick
or block next to the curb, lay the cable in and cover with concrete
to the pavement level. This method may also be used with
asphalt or macadam pavements, a shallow groove being chopped
or chiseled away, the cable laid in, and the groove filled flush with
concrete. In either of these cases, the cable is brought up to the
lighting post either under the curbing or through it, and up
through a hole in the sidewalk.

Another style of construction sometimes used in business
districts where the sidewalks run out to the curb, is to cut a
channel in the walk just inside the curb (about 2 in. by 2 in. in
section) in which the cable is buried in concrete.

Where there is a parkway between the sidewalk and curb,
the cable can be laid in a narrow, shallow trench, dug in the sod
inside the curb. Where an intersecting walk is encountered,
it can be crossed in a narrow channel chiseled out and filled with
concrete.

When crossing intersecting streets, a row of brick or block
is removed and the cable laid beneath; or the asphalt or macadam
is channeled, the cable laid in, and the surface restored. If car
tracks must be crossed, a hole is bored beneath the track and the
cable pulled through. The right-of-way is not disturbed and
the car service need not be interrupted.

Where obstructions of any kind are encountered in the trench,
the cable is simply pulled under, or laid around the obstacle.

Where the standards can be set upon concrete walks of suffi-
cient thickness and sound quality, no other footing is necessary.
The base can be set on the walk, holes marked and drilled, and
the foundation bolts set in head down, bedded in lead, sulphur
or grout. A hole for the cable is drilled through the walk, and
another through or under the curb. The cable is brought up
through, the standard set over it and bolted in place.

When there is no cement walk, or where the concrete is not
strong enough, it will be necessary to build a concrete base or put
in a cast-iron sub-base for the lamp standard. Fig. 52 shows a
simple form of concrete base made in a plain square wood form.

Instead of the curved tile shown, a wood box may be used, or
a piece of steel conduit or iron pipe. In some cases the cable has
been bedded directly in the green concrete base.

METHODS OF DISTRIBUTION

It is advisable to connect the conductors of the cable to a cut-
out in the base of the lamp standard, at least a foot above ground.
The jute is cut away, the steel tape rolled back the right distance
and cut off, and the lead casing removed to within about 1 in.
of the end of the steel tape. The copper conductors are then
separated, bared, and fitted or bent into loops at the end, for
connection to the cutout. The end of the lead sheath should be
carefully taped and painted with waterproof compound, to seal
it against moisture. The steel tape should be bound with wire

FIG. 52. — Design for concrete base for lamp standard.

at the end and the outside woven covering taped or wrapped with
twine to prevent fraying.

At the point where the cable connects with overhead lines, the
best practice is to carry the cable to the top of the pole and make
connection in a suitable pothead for protection against weather.

In an installation of steel-taped cable for ornamental street
lighting at Maryville, Mo., 74 five-light standards are used, the
top light being a 100-watt Mazda and the four lower lights
being 40-watt Mazdas. The top light burns all night, and the
others up to 11:00 p. m. Three- wire cable is used, being placed
under the brick pavement at the curb.

100 UNDERGROUND TRANSMISSION AND DISTRIBUTION

TABLE VIII.— STEEL TAPED CABLE
Dimensions and Weights

600 Volts

Single conductor

Two-conductor flat

Three-conductor

Size of conductors

ness of
rubber,
in.

Outside
diame-
ter, in.

Approx.
shipping
weight per
M ft., Ib.

Outside
diameter,
in.

Approx.
shipping
weight
per M ft.,
Ib.

Outside
diameter,
in.

Approx.
shipping
weight
per M ft.,
Ib.

Solid

12 B & S

0 687

850

0 970

1 375

1 030

1 750

10 B & S

0 720

1,200

1 000

1 545

1 062

1 900

8 B & S

0 750

1 300

1 062

1 700

1 125

2 100

6B. &S

0.782

1,365

1.125

2,045

1.187

2,500

Stranded

4B. &S

0.875

1,700

1.312

2,185

1.375

3,430

2B. &S

0.906

1,875

1.437

2,810

1.500

4,010

1 B. &S

.000

2,065

1.625

3,320

1.687

5,120

OB. &S

564

.030

2,200

1.687

3,650

1.812

5,650

00 B. & S

.062

2,400

1.750

3,900

1.906

6,250

000 B. &S

.125

2,600

1.875

4,620

2.030

7,125

0000 B. &S

.187

2,850

2.000

5,145

2.156

8,950

2,400 Volts

Solid

12 B & S

442

0.781

1,415

1. 188

2,100

1.281

2,790

10 B. & S

TO&

0.813

1,500

1.213

2,265

1.328

3,070

8B. &S

0.828

1,550

1.250

2,365

1.375

3,165

6 B & S

0.859

1,640

1.313

2,535

1.453

3,415

Stranded

4B. &S

*J2

0.938

1,865

.469

2,970

1.609

4,075

2B. &S

1.015

2,085

.625

3,700

1.734

5,250

IB. &S

1.047

2,200

.688

3,840

1.828

5,600

OB. &S

' 1.034

2,360

.781

4,120

1.921

6,110

00 B. & S

1.140

2,550

.875

4,575

2.046

6,825

000 B. & S

1.218

2,765

.969

4,950

2.156

7,950

0000 B. & S

te*

1.281

3,500

2.094

6,140

2.281

8,800

5,000 Volts

8B. &S. solid...

1.062

1,680

1.375

2,680

1.656

3,920

6 B. & S. solid.. .

1.094

1,800

1.500

2,900

1.719

4,220

4 B. & S. stranded

1.156

2,075

1.719

3,685

1.906

5,430

The diagram (Fig. 53) shows the wiring scheme. Two trans-
formers and two primary circuits are required. Switches at the
station control each primary circuit and by this means constant
load is carried on each transformer. The usual practice in a
system of this kind is to control the lights by means of switches
placed at some convenient point on the secondary lines.

METHODS OF DISTRIBUTION 101

Table VIII lists the standard specifications for steel-taped cable
in the voltages for which it is regularly manufactured. Special
sizes and voltages not listed may be obtained when required.

Comparative Costs of Installation. — It is impossible to state
just what the saving realized by a system of steel-taped cable will
be over a conduit system, without a careful analysis of the con-
ditions. In general it may be said that the saving will rarely
be less than 30 per cent., and may run higher, under conditions

CUTOUT 1600! CUTOUT

/=>OST

VWW WvW

^/VW\
A/»./

FIG. 53. — Wiring diagram for street lamps.

peculiarly adverse to the conduit. In fact, the cable has been
successfully and cheaply installed under conditions which abso-
lutely prohibited the use of conduit.

The following comparison has been worked out on some arbi-
trary assumptions, with a special effort to make the figures just
in each case. A length of 1,000 ft. is taken as a basis of compari-
son, laid in brick-paved streets:

Cost of lead-encased, 600-V.R.C. cable in fiber duct:

1,000 ft. No. 6 three-conductor cable $200

1,000 ft. 2-in. fiber conduit 50

Cost of installing in loop system 420

$670
Cost of steel-taped, 600-V.R.C. cable:

1,000 ft. No. 6 three-conductor, 600-volt steel-taped

cable $260

Cost of installing in loop system 165

$425
Saving by the use of steel-tape cable, $245, or 36 per cent.

CHAPTER V
CABLES

General. — In present-day practice of underground construction
lead-covered insulated cables are used almost exclusively. The
three essential members of such a cable are: The conductor itself,
the wall of insulating material and the outer protective covering,
and they will be considered in the order named.

Terminology. — The following definitions relating to wire and
cables are based on Bulletin No. 37, issued by the Bureau of
Standards, January, 1915.

WIRES AND CABLES

Wire. — A slender rod or filament of drawn metal.

Conductor. — A wire, a combination of wires not insulated from one an-
other, suitable for carrying a single electric current.

Stranded Conductor. — A conductor composed of a group of wires, or of
any combination of groups of wires.

Cable. — (1) A stranded conductor (single-conductor cable) ; or (2) a com-
bination of conductors insulated from one another (multiple-conductor
cable).

Strand. — One of the wires or groups of wires of any stranded conductor.

Stranded Wire. — A group of small wires used as a single wire.

Cord. — A small and very flexible cable, substantially insulated to with-
stand wear.

Concentric Strand. — A strand composed of a central cord surrounded by
one or more layers of helically laid wires or groups of wires.

Duplex Cable. — Two insulated conductor cables, twisted together.

Twin Cable. — Two insulated single-conductor cables, laid parallel, hav-
ing a common covering.

Triplex Cable. — Three insulated, single-conductor cables twisted together.

Twisted Pair. — Two small insulated conductors twisted together without
a common covering.

Twin Wire. — Two small insulated conductors laid parallel, having a com-
mon covering.

Conductor. — Theoretically the transmission of electricity
through any substance is a matter of degree; practically we may
make a distinction between conducting and insulating materials.

102

CABLES 103

The following table gives a list of materials approximately ar-
ranged in order of their conducting powers.

Conductors Non-conductors or insulators

All metals Dry air Ebonite

Well-burned charcoal Shellac Gutta percha

Plumbago Paraffine India rubber

Acid solutions Rosins Silk

Metallic ores Sulphur Dry paper

Living vegetable substances Wax Dry leather

Moist earth Glass Porcelain

Water Mica Oils

The conducting power of any substance depends largely upon
its physical state, and the conductivity of all substances materi-
ally alters with a change of temperature.

The general trend of this change in conductivity with rising
temperature is toward a decrease with metals and toward an
increase with other substances.

In commercial transmission of electricity we are limited to
the use of three metals: copper, iron and aluminum, although
abnormal conditions of late have added zinc in certain countries.
Copper ranks first in importance, with aluminum next, and iron
last, and whether or not the use of zinc will survive after normal
conditions are restored appears uncertain. Pure copper, in
addition to its high conductivity, possesses many other physical
properties of special value in cable work.

Its strength, malleability and cost in comparison with that of
other metals makes it an ideal material for cable work. The
malleability, ductility, tensile strength and electrical conduc-
tivity of copper are somewhat modified by impurities. These,
when present, usually are of one or more elements such as bis-
muth, arsenic, antimony, sulphur, etc.; however, the electrolytic
wire bars so largely used in the manufacture of wires and cables
for electrical purposes are almost pure.

Refining of copper and its separation from the multitude of
alloying metals is a complex metallurgical process, but a very
necessary one. Even traces of other metals affect the con-
ductivity to a remarkable degree, as the following table will
show:

104 UNDERGROUND TRANSMISSION AND DISTRIBUTION

Element ^er cen*- present Per cent, con-

in copper ductivity

Carbon 0.05 77.87

Sulphur 0.18 92.08

Arsenic 0 . 10 73 .89

Silver 1.22 90.34

Tin 1.33 50.44

Aluminum 0. 10 86.49

Copper enters readily into combination with the constituents
of rubber insulation and must be coated with a protective such
as tin, which is not easily attacked.

Copper is easily soluble in nitric acid, aqua regia and strong
boiling sulphuric acid; and in diluted sulphuric acid, when ex-
posed to the air, it dissolves slowly.

The tensile strength of annealed copper is usually about 30,000
Ib. per sq. in., but when it is hard-drawn or medium hard-drawn,
its strength is increased to 50,000 and 65,000 Ib., depending upon
the size of the wire.

Table IX gives the average values of breaking weight for
various sizes.

TABLE IX. — TENSILE STRENGTH OP PURE COPPER WIRE IN POUNDS

Hard-drawn

Annealed

Hard-drawn

Annealed

Size
B. &S.

Actual

Average
per sq.

Actual

Average
per sq.

Size
B. &S.

Actual

Average
per sq.

Actual

Average
per sq.

in.

an.

in.

0000

8,260

49,700

5,320

32,000

1,050.0

64,200

556.0

34,000

000

6,550

49,700

4,220

32,000

843.0

65,000

441.0

34,000

5,440

52,000

3,340

32,000

678.0

66,000

350.0

34,000

4,530

54,600

2,650

32,000

546.0

67,000

277.0

34,000

3,680

56,000

2,100

32,000

343.0

67,000

174.0

34,000

2,970

57,000

1,670

32,000

219.0

68,000

110.0

34,000

2,380

57,600

1,323

32,000

138.0

68,000

68.9

34,000

1,900

58,000

1,050

32,000

86.7

68,000

43.4

34,000

1,580

60,800

884

34,000

68.8

68,000

34.4

34,000

1,300

63,000

700

34,000

54.7

68,000

27.3

34,000

Many experiments have been made determining the 'effect of
temperature on the tensile strength of copper, and a summary of
the results may be stated as follows:

Up to about 400°F. the loss in strength is about 10 per cent. ;

CABLES 105

at 500°F. it is about 16 per cent, and above 500°F. it is so great
as to make the metal almost useless.

As the conductivity of any one wire will, in general, differ
from that of any other, it is necessary in comparing or specifying
wires to refer to some standard.

The present practice in copper specifications for cable work,
is to refer to the standardization rules of A.I.E.E. of which the
following shall be taken as normal values of standard annealed
copper.

1. At a temperature of 20°C., the resistance of a wire of standard annealed
copper, 1 meter in length, and of a uniform section of 1 sq. mm. is ^g onm =
0.017241 ohm.

2. At a temperature of 20°C., the density of standard annealed copper is
8.89 grams per c.c.

3. At a temperature of 20°C., the "constant mass" temperature coeffi-
cient of resistance of standard annealed copper measured between two poten-
tial points rigidly fixed to the wire is 0.00393 = Ms 4- 45 • • • • Per degree
Centigrade.

4. As a consequence, it follows from (1) and (2) that, at a temperature of
20°C., the resistance of a wire of standard annealed copper of uniform sec-
tion, 1 meter in length, and weighing 1 gram, is (^s) X 8.89 = 0.15328 . . .
ohm.

Table X gives a comparison of wire gages of the Brown &
Sharpe, or American ("B. & S."), the Birmingham (B.W.G.)
and the British Standard (S.W.G.) wire gages.

In Table XI is given the diameter, weight and resistance of
copper wires.

The following Table XII gives data regarding standard con-
centric strands of different sizes of cable, as recommended by
the General Electric Co.

The area of the finished cable is that of the individual wires
cut at right angles to their axes, when laid straight, multiplied by
the number of wires in the cables. Special attention is called
to this point, since in some cases the area of the individual wires
is figured as if cut after twisting, i.e., on the "bias," thus using a
figure larger than the actual area of the finished conductor, and
results in a cable having less copper than if the area was correctly
figured.

Insulating Wall. — The principal materials used for insulating
power cables are rubber, saturated-paper tapes, varnished cam-
bric or cloth and graded insulation usually consisting of a
combination of the foregoing.

106 UNDERGROUND TRANSMISSION AND DISTRIBUTION

-S — O
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OS

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rj< »c t^ oo cs

TJH •* rt rf - 1

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MH Tj< CO CO (N IN CN CN
° ° ° ° ° °

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SSS QOt-'O^^eOfNrH O 05 05 00 00 t^ «>

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d d d d d o* d d d d d d d d d d o* d d d d d d d

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I (N (N <N C

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ICO O5 Tj< rH CO 00 CD CN »C
<TJH 00!>OOO5OOOO<N

iSSoS^rH -^C^^"5

o o oooo

rH O CO <N TH

CO CO O5 CO CO

•<* -^ TJH CO CO CO

iCt^COOOOOCO O»C»C>COO»C
(N CO >C t>CN t» CM 00 »C O 1C TH
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00 CO Tt* CM O
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CABLES 107

TABLE XI. — DIAMETER, WEIGHT AND RESISTANCE OP COPPER WIRE

Weight, bare wire

Resistance at 75°F.

No.
B.&S.

Diame-
ter, mils

Area, cir-
cular mils

Pounds
per 1,000
ft.

Pounds
per
mile

Ohms

i.oSTft.

Ohms
per mile

Feet
per ohm

0000

460.000

211,600.00

640.73

3,383.0400

0.04904

0.25891

20939 . 2000

000

409.640

167,805.00

508.12

2,682.8500

0.06184

0.32649

16172.1000

364.800

133,079.00

402.97

2,127.6600

0.07797

0.41168

12825.4000

324.950

105,592.50

319.74

1,688.2000

0.09827

0.51885

10176.4000

289.300

83,694.50

253.43

1,338.1000

0.12398

0.65460

8066.0000

257.630

66,373.20

200 . 98

1,061.1700

0.15633

0.82543

6396.7000

229.420

52,633.50

159.38

841.5000

0.19714

1 . 04090

5072.5000

204.310

41,742.60

126.40

667.3800

0.24858

1.31248

4022.9000

181.940

33,102.20

100.23

529.2300

0.31346

1 . 65507

3190.2000

162.020

26,250.50

79.49

419.6900

0.39528

2.08706

2529.9000

144.280

20,816.70

63.03

332.8200

0.49845

2.63184

2006.2000

128.490

16,509.70

49.99

263 . 9600

0.62849 3.318431 1591.1000

114.430

13,094.20

39.65

209.3500

0.79242 4.18400

1262.0000

101.890

10,381.60

31.44

165.9800

0.99948

5.27726

1000 . 5000

90.742

8,234.11

24.93

131 . 6500

1 . 26020

6.65357| 793.5600

80.808

6,529.94

19.77

104.4000

1 . 58900

8. 39001 i 629.3200

71.961

5,178.39

15.68

82.7920

2 . 00370

10.57980 499.0600

64.084

4,106.76

12.44

65.6580

2.52660

13.34050

395.7900

57.068

3,256.76

9.86

52.0690

3.18600

16.82230

313.8700

50.820

2,582.67

7.82

41.2920

4.01760

21.21300

248.9000

45.257

2,048.20

6.20

32.7460

5.06600

26.74850

197.3900

40.303

1,624.33

4.92

25.9700

6.38800

33 . 72850

156.5400

35.890

1,288.09

3.90

20.5940

8.05550

42.53290

124.1400

31.961

1,021.44

3.09

16.3310

10.15840

53.63620

98.4400

28.462

810.09

2.45

12.9520

12.80880

67.63020

78.0700

25.347

642.47

1.95

10.2720

16.15040

85.27430

61.9200

22.571

509.45

1.54

8.1450

20.36740

107.54000

49 . 1000

20.100

404.01

1.22

6.4593

25.68300

135.60600

38.9400

17.900

320.41

0.97

5.1227

32.38330

170.98400

30.8800

15.940

254.08

0.77

4.0623

40.83770

215.62300

24.4900

14.195

201 . 50

0.61

3.2215

51.49520

271.89500

19.4200

12.641

159.80

0.48

2.5548

64.93440

342.85400

15.4000

11.257

126.72

0.38

2.0260

81.88270

432.34100

12.2100

10.025

100.50

0.30

1 . 6068

103.24500

545.13300

9 . 6860

8.928

79.71

0.24

1 . 2744

130.17600

687.32700

7.6820

7.950

63.20

0.19

1.0105

164.17400

866.83700

6.0910

7.080

50.13

0.15

0.8014

207.00000

1092.96000

4.8310

6.304

39.74

0.12

0.6354

261.09900

1378.60000

3.8300

5.614

31.52

0.10

0.5039

329.22500

1738.31000

3.0370

5.000

25.00

0.08

0.3997

415.04700

2191.45000

2.4090

4.453

19.83

0.06

0.3170

523.27800

2762.91000

1.9110

3.965

15.72

0.05

0.2513

660.01100

3484.86000

1.5150

3.531

12.47

0.04

0.1993

832.22800

4394.16000

1 . 2020

3.144

9.88

0.03

0.1580

1049.71800 5542.51000

0.9526

If the insulating body is of paper, it is necessary to saturate
it with an insulating compound and the character of the com-
pound is of utmost importance in determining the quality and
permanence of the cable. In varnished-cloth insulation, specially
prepared cotton fabric, coated on both sides with multiple films
of insulating varnish is used.

Paper and varnished-cloth insulation, being composed of
staple commercial fabrics, impregnated with compound of well-

108 UNDERGROUND TRANSMISSION AND DISTRIBUTION

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<N~ Of

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dddddddd o

-g § popt-qiopTt!5? rnwocDiotope?

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t^^rHO»OO3COI> t-lrJ<i-IOOt>-OOI>iO

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S-p

I
I
I

eocococbcocbco'cb

LJL

ri S"fg"8"S8"S"S §§8§|||

r-T rH rH Cl

SS^SSSSS^ og^r^iS^?

i.a

oooooooo oooooooo

t>- CO <N 00 l> rH

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^Ci r-li-lr-IC^C<|CO

IJI^

O.t) eceoeoiocooococo

•^fe THOOOOOrHOOt^CO

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ors.S oooooooo ooooo^o

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b-O>OSOSO5Oit-t>.

1H 1-4 TH l-l r-l CO CO

1
g° °

CABLES 109

known oils, etc., are not readily susceptible to adulteration or
imitation, and consequently do not suffer much in quality from
attempts by the manufacturers to lessen the cost of production.

Rubber compounds, on the other hand, being made of any
material mixed with any amount or grade of rubber, are easily
adulterated and even imitated. The extent to which this is
sometimes carried makes it necessary for engineers to insist
on complete mechanical and electrical tests of the compound.

Rubber Insulation. — Rubber-producing trees and vines of one
kind or another are found in all tropical countries. Various
grades of crude rubber are known by the name of the country or
seaport whence they come; hence the terms "Para," "Ceylon,"
etc., as names of the particular grades of rubber. In the prepara-
tion of rubber for insulating purposes, the first step is to free it
from all impurities, which is done by passing it between corru-
gated steel rolls, revolving at different speeds and under a constant
stream of water. In this manner the rubber is washed and pre-
pared in sheets ready to be dried. As crude rubber is affected very
much by the changes in temperature and readily oxidizes in the
uncured state, the rubber must be compounded with other mate-
rials to obtain the properties needed in the insulation of a wire.
Compounding consists chiefly of adding other substances, such
as powdered minerals, including a small percentage of sulphur.
After the crude rubber has been warmed to a plastic condition
in heated mixing rolls, it is thoroughly kneaded until the resulting
compound is homogeneous in nature and of suitable physical
condition for the work that is expected of it. Another reason
for compounding is that the cost of pure rubber for insulating
purposes is excessive. The matter of compounding is of prime
importance and requires exhaustive tests and experiments to
develop a suitable insulating material for various conditions of
service. Compounded rubber before vulcanizing is plastic and
cohesive, and carr be shaped into any form desired. In order to
apply it to a wire, two different methods are commercially em-
ployed; in one a machine similar to a lead press is used and the
rubber is forced by a revolving worm into a closed chamber at
high pressure, the wire entering this chamber through a nozzle
of its own diameter and leaving from a nozzle having the
diameter of the intended insulation. The wire thus comes out
with a seamless coat of rubber, forced on at high pressure.

In the other method of application, the rubber is sheeted on

110 UNDERGROUND TRANSMISSION AND DISTRIBUTION

a calendar having heavy smooth rolls, and the sheets thus made
are cut into narrow strips, the width and thickness of which
depend on the wire to be insulated, and the number of covers to
be used. By this method a wire is passed between two or more
curved rolls, running in tangent to each other. As the wire
enters each pair of rolls, strips of rubber enter at the same
time and the grooves form a uniform thickness of rubber about
the wires, the edges meeting in a continuous seam.

Surplus rubber is cut off the rolls and the seams, being made
between two pieces of the same unvulcanized cohesive stock
under pressure, become invisible in the wire, and can be deter-
mined only by a ridge along the insulation.

In the process of vulcanization, the rubber at the seams is
kneaded together so that the rubber at this point is as dense and
homogeneous as at any other part of the insulation.

FIG. 54. — Crude rubber.

Good rubber compound will last indefinitely in pure or salt
water, but if the water contains sewage, acids, oils, or other
destroying agents, it will have a short life unless protected with
some outer covering, such as a lead sheath.

In order to vulcanize rubber compounds, they are subjected
to temperatures somewhat above the melting point of sulphur,
which temperatures are usually obtained by steam under pres-
sure. This operation causes the sulphur in the compound to
chemically unite with the rubber and other ingredients with the
result that the rubber is no longer plastic; it becomes firm, strong,
elastic, susceptible neither to heat nor cold, and not readily
affected at ordinary temperatures by the usual solvents of unvul-
canized rubber. Its mechanical properties depend considerably
on the time and temperature of vulcanization, as well as the
amount of sulphur used. In producing high-grade insulation,
proper vulcanization is fully as important as the selection of the
crude materials. Rubber insulation is usually protected by a

CABLES 111

winding of tape or braid, or a tape and one or more braids,
depending upon the class of service for which it is to be used.
When used for station work it is sometimes provided with an
outer braid of asbestos or other form of flameproof covering, to
serve as a fire protection. When installed in underground con-
duits where it is subjected to the severest conditions, it should be
covered with a lead sheath.

Paper Insulation. — The use of paper-insulated cables for elec-
tric light and power work is rapidly increasing, and when prop-
erly constructed and installed such cables give excellent service.

Various kinds of paper have been used for cable insulation;
the extremes of quality are represented by that made from wood
pulp, which is the poorest, and that made from manila rope fiber,
which is the best. Between these extremes there are combina-
tions of wood pulp with jute, jute with manila fiber and wood
pulp, jute and manila fiber. A paper containing any appre-
ciable amount of pulp will "felt down" when saturated with
insulating oils. In other words, the fibers of the paper stand
up before saturation, giving a thickness of insulating wall, which
is greatly diminished during impregnation; because of this "felt-
ing down" even the most tightly wound insulations composed of
pulp paper, will be found quite loose after saturation. Wood
fiber or pulp paper is apt to be injured during the drying process
to which it is subjected before impregnation, and it has been
known to rot badly under the influence of certain of the substances
used in the impregnating solution. A paper containing any
appreciable amount of jute, either alone or in combination with
pulp and manila, will have practically all the disadvantages of
pulp paper and in addition the jute will saturate very slowly,
which sometimes may result in an unevenly saturated cable.
Manila-rope paper is free from this objection and its structure is
hard, close and even. It may be dried perfectly without loss
of strength and will not rot under the action of properly prepared
impregnating oils.

Manila-rope paper of the very highest grade should be used
in all paper-insulated cable. The impregnating oils now used
by the majority of cable manufacturers consist of solutions of
rosin and rosin oil, and solutions of rosin and petroleum oil, or
a mixture of these solutions. Commercial rosin, as ordinarily
found on the market, is a mixture of what may be termed rosin,
some undecomposed turpentine gum, some water, acetic acid and

112 UNDERGROUND TRANSMISSION AND DISTRIBUTION

butyric acid, together with light turpentine naphthas and turpen-
tine. These impurities are found to a much larger extent in
second-run rosin oil. The method of preparing rosin oil for im-
pregnation varies with different manufacturers in accordance
with their particular formula, and the lack of uniformity in
commercial rosin oil requires that great care be taken in the
preparation of the oil for insulating purposes. The dielectric
value of paper, depends not only on the quality of the paper and
the manner of applying it to the conductor, but to a great extent
upon the composition of the insulating compound. Increasing
the fluidity of the compound within certain limits will improve
the puncture test and will increase the flexibility of the cable, but
will reduce the megohm tests and vice versa. A dense, thick
compound will result in a very stiff cable, but one having a higher
insulation resistance. The insulation of such a cable is apt to
crack or break if bent at a low temperature. In the preparation
of paper-insulated cables automatic machines are employed to
wind narrow strips of paper spirally around the conductors
until there are enough layers to secure the requisite dielectric
strength. If the cable is to consist of two or more conductors,
the necessary number of conductors, each encased in its wrapping
of paper, are laid up together and the whole encased in an outer
wrapping, or belt, composed of additional layers of paper.

Before the outer wrapping of paper is applied, the cable is
filled with jute laterals to make the whole cylindrical. For
high-tension cables some manufacturers use a fine grade of twisted
tissue paper in place of the jute laterals. The cable, after being
insulated, is placed in the vacuum drying and impregnating
tanks. Here every particle of moisture and air should be re-
moved even from its inner interstices, and the hot impregnating
oil is forced under pressure into every crevice filling the pores of
the paper and making it one homogenous structure. The
cable is then put through a hydraulic press and covered with a
closely fitting lead sheathing so as to exclude all air and moisture
and to retain the insulating compound. Paper cables are
generally cheaper and have a lower electrostatic capacity than
rubber or varnished-cambric cables. The insulation is strong
and uniform in quality and, except when frozen solid, is quite
flexible. Paper cables can be worked safely at higher tempera-
ture than can other kinds, but experience has demonstrated that
their usual life is determined by the integrity of the lead sheath.

CABLES 113

Paper is less liable than rubber to deterioration from excessive
electrostatic strains; in fact, paper-insulated cables, when
properly constructed and sheathed, can be recommended as the
best for most conditions.

Varnished -cambric Insulation. — Varnished-cambric cables
are made by winding strips of even-varnished cotton or muslin
served separately about the conductor in a sufficient number of
smooth, tightly drawn layers to make the required thickness of
dielectric. It is customary to place a separator of treated paper,
cloth or rubber over the copper core to prevent any possible
action of the varnished- cambric film on the copper, and over the
separator a taped strip of fabric which has been coated with
special insulating varnish. The dielectric strength of this
material is very high, as single thicknesses of cotton well-treated
with varnish will withstand potentials of approximately 10,000
volts for 5 sec., depending upon the number of coats of varnish
with which the cloth has been treated.

The varnish prevents the tape from unwrapping when the
cable is cut and permits the adjoining layers of varnished cam-
bric to slide upon each other. It also prevents capillary absorp-
tion of moisture between the layers of tape, seals any possible
skips in films and precludes air spaces.

In multiple-conductor cables it is usual to place a portion of the
required thickness of insulation in the form of a belt about the
core of conductors as is the case in paper cables. This class of
cables is in general more flexible than paper cable, more imper-
vious to moisture and lower in cost than rubber cables, and can
be used for station work without lead sheathing. It is especially
suitable for the insulation of wire and cables for generators,
motors and transformer leads, for high- and low-tension switch-
board connections and wherever the following conditions are to
be met in service: namely, moisture, oil drippings, or spasmodic
increases of voltage of considerable amount but of short duration.

Where this type of cable is to be used in locations where it is
likely to be submerged in water, it should, of course, be used with
a lead cover, since it has been found that no material suitable for
wire or cable insulation is permanently lasting in non-leaded
form when subjected to alternating periods of heat and cold,
wetness and dryness. The jointing of varnished-cambric cables
is simpler than that of paper-insulated cables as the insulation
of the former does not absorb moisture and, not being attacked

114 UNDERGROUND TRANSMISSION AND DISTRIBUTION

by mineral oil, is. particularly adapted for use in connecting to
apparatus submerged in oil, such as switches and transformers.
It can be operated at a temperature higher than rubber insula-
tion but not quite as high as impregnated paper insulation.
When the cable is to be used on insulators or through insulating
bushings, and exposed only to such moisture as is held in sus-
pension in the surrounding air, the lead cover is usually replaced
by one or more coverings of a weatherproof, flameproof or
asbestos braid.

Graded Insulation. — For exceptionally high -voltage work
graded insulation has been employed and insulating material
having different capacities has been used.

It is a well-known fact that the potential gradient of insulated
wire is much higher in that portion of the insulation near the
conductor than in the outer layers; and the fall of potential across
a series of insulators of varying specific inductive capacity is
inversely proportional to those capacities. Cables insulated
with two or more materials so proportioned as to their relative
thickness and specific inductive capacities as to take advantage
of this law, have been on the market for some time and the
advantages to be secured are that a smaller diameter of cable
may be used with the same factor of safety or a cable may be
operated at a higher voltage, the outside diameter and factor of
safety remaining the same. Cables have also been constructed
with rubber and paper, or rubber and cambric insulation, not
with the view of obtaining the results to be secured by grading,
but primarily for the purpose of reducing the cost. In some
cases multiple-conductor cables have been insulated with a
covering of paper or varnished cloth on the individual conductor
and a reinforced rubber jacket, the outer rubber jacket being
made up of several layers of rubber and cloth as a protection
against moisture.

In ordinary underground work the use of graded cables is
unnecessary and the cost of such cable apparently is unwarranted
except in special cases. For more detail information on the
subject of the grading of cables, the reader is referred to the
Transactions of the American Institute of Electrical Engineers,
vol. 29, part 2, page 1553, " Potential Stresses in Dielectrics,"
by Harold S. Osborne.

Lead Covering. — In order to protect the insulation of cables
from injurious effects common to most underground systems,

CABLES 115

and provide a protection of the insulation from mechanical
injury, they should be covered with a lead sheath. While rubber-
insulated cables have been used in a limited way without a
metallic covering, it is not considered good engineering practice
to use such cables in installations of a permanent character,
as the dependable life of the insulation does not exceed 10 years;
whereas the same insulation, if protected by a lead sheath, would
last indefinitely.

Lead, or a composition of lead and tin, is the most usual
material for sheathing in this country.

While lightning, electrolysis, heat, long-continued vibrations
and mechanical injuries have been considered about the only
cause for breakdown or disintegration of the lead sheaths, there
are cases on record where the lead has been destroyed by a species
of lead-eating insect. These insects have been found in Australia
and in the southeastern portion of the United States. An inter-
esting paper on this subject was read before the International
Congress of Electrical Engineers, at the Convention in St. Louis,
in 1904, by Mr. John Hesketh.

Lead is the heaviest metal used to any large extent for com-
mercial purposes, and the only metal used for the protection
of hygroscopic insulating media. It is not used in a chemically
pure state for commercial purposes; and the slight traces of
arsenic, antimony, copper, tin, etc., which are sometimes found
in the extra high-grade lead used for pipe and cable sheaths are
rather a benefit than an objection, as they tend to slightly harden
the metal. Lead is also hardened by hammering, but easily
regains its original softness on being annealed.

When lead is alloyed with small percentages of tin, its melting
point is lowered and its hardness and tensile strength increased.
The melting point continues to decrease with increasing amounts
of tin up to a critical value of 63 per cent, when the alloy then
becomes a definite chemical compound. Further addition of the
tin results in an increased (instead of a decreased) melting point.

Lead, as is well known, is very malleable, but lacking in
ductility.

No very reliable data are obtainable as to the tensile and com-
pressive strength of lead, the discrepancy in results arrived at
by different experimenters being due, doubtless, to the influence
of impurities and temperature variations.

The purest commercial lead obtainable is generally used for a

116 UNDERGROUND TRANSMISSION AND DISTRIBUTION

sheathing. It is sometimes necessary to harden and strengthen
the lead sheath by the addition of 1, 2 or more per cent, of tin,
but it is a question as to whether much is gained by this addition.
The two metals do not alloy uniformly and in sheaths where
much tin is used, hard or brittle sections may develop, due to the
segregation of one of the metals. The purpose of tin in the lead
sheath is, not to prevent chemical action, but to stiffen the
sheath so that it may better retain its cylindrical form when the
enclosed core is soft, as is the case in some of the dry-core tele-
phone cables. It appears to be a waste of money to put tin in lead
sheaths of cables used for electric light and power purposes, as
the introduction of tin adds at least 10 per cent, to the cost of the
cable and the slight advantages gained therefrom do not warrant
the extra expense. If tin is desired as a protection against
chemical action, or the lead cover, the proper place for it is on, not
in, the latter, for that places it where it will do the most good.

As to the thickness of lead, especially in connection with paper-
insulated cables, some manufacturers advocate a slightly heavier
thickness than for rubber cables as the life of the cable is entirely
dependent on the permanency of the lead sheath.

The following Table XIII shows the thickness of lead for various
outside diameters of the cable core as determined by the best
engineering practice.

TABLE XIII. — THICKNESS OP LEAD SHEATH

Diameter of core,
mils

Corresponding thick-
ness of sheath, in.

Diameter of core,
mils

Corresponding thick-
ness of sheath, in.

0-299
300-699
700-1,249

«4

1,250-1,999
2,000-2,699
2,700-over

H
&

The sheath should have an average thickness of approximately
that indicated in the foregoing table, and the minimum thickness
should in no place be less than 90 per cent, of the required
thickness.

Types of Cables. — Electric light and power cables may be
divided into the following classes: namely, single conductor,
duplex, concentric and multiple-conductor cables consisting of
three, four or more conductors under the one sheath as shown in
Fig. 55.

Single-conductor cables are most commonly used for low-ten-

CABLES 117

sion electric-lighting, power and arc-light service, but they are
also used -under special circumstances for high-tension trans-
mission. For railway feeders and direct-current power mains,
single-conductor cables are almost always used, as the size of
conductor required for this class of service is usually too large to
permit the installation of a multi-conductor cable of equal con-
ductivity in a single duct. In general, single-conductor cable
is most frequently employed for service mains where a number of
taps are required. Duplex cables are employed for feeders

Concentnc

Conductor

3~Conducfor
Conductor

FIG. 55. — Types of underground cables.

which do not require frequent taps, such as alternating-current,
single-phase circuits where both legs of the circuit cover the same
routes. For arc-light circuits or portions thereof, or for low-
pressure distribution mains, duplex cables are frequently used.
Relatively less duct space is required and duplex cables are safer
to handle than two single-wire cables and in addition are less
expensive in first cost. Double- and triple-concentric cables
have the same advantage as just stated for duplex cable, and they
are preferable in large conductor sizes where the side-by-side
arrangement of duplex cable would be difficult to bend. The
concentric arrangement is frequently employed for large feeders
and low-tension Edison direct-current service when a feeder of
750,000 cm. or larger would require two ducts, if single-con-

118 UNDERGROUND TRANSMISSION AND DISTRIBUTION

ductor cable were used. Where numerous feeders are employed
and the duct space is limited, this item is of much importance.

In some cases, particularly in the Edison direct-current feeder,
pressure wires are used to indicate and regulate, at the station,
the pressure or difference in potential existing at outlying points.
A No. 14 or No. 16 insulated pressure wire can be incorporated
at some suitable point in the cable, generally in the outer layer
of the stranded conductor, or in the valleys or interstices of
bunched cables as shown in Fig. 56.

In alternating-current two- and three-phase circuits, feeders
of two, three and four conductors are preferable on account of
their lower cost. For this class of service paper-insulated cables
are employed as they are considerably cheaper than either var-
nished-cloth or rubber-insulated cables. In the case of multiple-
conductor cables, the wires are twisted together with a suitable

'Pressure Mre

Pffperlnsu/atfon
Outer Conductor
'Inner Corx/uc tor

FIG. 56. — Concentric cable with pressure wires.

lay, the interstices are filled with jute or paper laterals to make
the core substantially round, and a further covering (called
"the belt") of the same insulating material is placed around the
core, generally to the same thickness as the insulation around
the individual wires. In the case of rubber cables the belt is
sometimes made of paper instead of rubber, depending upon the
pressure at which it is to be used, and especially if it is intended
for comparatively low pressure. Even in paper cables for low-
tension service, the belt is not always made of the same thick-
ness as the insulation in the individual wires, but for high-
tension service, the usual practice is to " split" the insulation
(from which these cables are sometimes spoken of as cables with
"split insulation") equally between the conductors and the belt.

CABLES 119

When it is desired to connect multiple-conductor cables to
overhead lines, single-conductor cables have been employed, but
with multiple-conductor pole terminals, as described in another
chapter, the use of multiple-conductor cables for the lateral pole
connection is now rapidly becoming general practice.

In single-conductor cables, or an alternating-current system,
carrying heavy loads, there is apt to be an inductive action and
the magnetic field may become strong enough to induce an appre-
ciable difference of potential between the lead sheaths of single-
conductor cables of a circuit, resulting in the flow of sufficient
current to cause damage to the sheaths where they come into
contact with each other. For connections to subway transform-
ers, junction boxes and manhole switches, single-conductor cables
are used to tap on or connect to the multiple-conductor feeders,
as they facilitate the making of such connections.

Diameter and Length of Cables. — As a rule cables having a
diameter of over 3% in. should not be specified on account of the
difficulty of handling and drawing into the conduits. The greater
the diameter, the greater the danger of the lead cover buckling
or breaking when bent, and abrading in the operation of pulling
in. For underground cables, the net diameter of the duct will
control the maximum diameter of the cable, which latter should
be approximately one-sixth less than the former, and in no case
less than one-eighth smaller in diameter. A margin or difference
of one-fourth the duct diameter represents the best condition for
ease and safety of drawing in cables.

Cable may be made in almost any length, but it is desirable,
on account of manufacturing operations, to confine the length to
certain practical economic limits. Extraordinary lengths re-
quire the temporary adoption of extraordinary methods and de-
vices in manufacture, shipment and installation, at an increased
cost quite out of proportion to the safer and simpler expedient,
practicable in most cases, of making a few more splices or building
a few more manholes. Cables weighing 1 Ib. or less per ft. can
usually be supplied in lengths of 2,500 to 3,500 ft. on a single reel,
and heavier cables in approximately inverse proportions; thus
for cables weighing 6 Ib. per ft., the reel should contain something
under 600 ft. of cable.

Table XIV gives the maximum length in feet of cable that
can be shipped on standard reels.

120 UNDERGROUND TRANSMISSION AND DISTRIBUTION

TABLE XIV.— CABLE REEL DATA1

Overall
dia. of
cable, in.

Reel No. 6,
24 by 12 in
max. length,
ft.

Reel No. 5,
30 by 21 in.
max. length,
ft.

Reel No. 4,
48 by 24 in.
max. length,
ft.

Reel No. 3,
60 by 24 in.
max. length,
ft.

Reel No. 2,
60 by 41 in.
max. length,

Reel No. 1,
66 by 41 in.
max. length,
ft.

0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70

0.75
0.80
0.90
1.00
1.10
1.20
1.30
1.40
.50
.60

.70
.80
.90
2.00
2.25
2.50
3.00

2,000
1,500
1,100
900
600
500
400
300
300
225

200

7,000
4,800
3,350
2,500
2,000
1,750
1,450
1,200
1,000
850

750
700
550
400

5,000
4,500
4,200
3,400
2,900

2,700
2,250
2,000
1,600
1,200
950
750
700
650

4,500
4,000

3,500
3,100
2,400
2,100
1,750
1,400
1,200
975
800
750

700
625
550
460
325
275
210

4,200
3,500
2,800
2,400
1,950
1,600
1,500

1,400
1,250
1,100
920
650
550
420

3,900
3,300
2,800
2,300
2,100
1,750

1,650
1,500
1,225
1,100
850
700
525

.....

:::::

Approximate Maximum Weight of Cable per Reel, Ib.

225

650

1,500

3,100

6,200

8,000

Approximate Weight of Empty Reel, Ib.

190

345

415

465

Approximate Weight of Reel with Slats, Ib.

100

240

495

650

760

1 General Electric Co.

For example: 1,000 ft. of any cable % in. in diameter and weigh-
ing 650 Ib. would require a No. 5 reel.

Fiber Core Cables. — Owing to the fact that alternating current
flowing in large cables has greater density on the surface of the

CABLES

121

conductor than in the center (so-called skin effect), ordinary
cable will not carry as much alternating current with the same
temperature rise as direct current. In order to overcome this
it is advisable on single-conductor cables, 700,000 cm. and larger
for 60-cycle circuits and 1,250,000 cm. and larger for 25-cycle
circuits, to make up the cable with a fiber core with the copper
stranded around it. The weight of the copper in this type of
cable is the same per foot as in an ordinary cable, but owing to
its annular cross-section the cable is much more efficient in
carrying alternating current and also has a somewhat greater
current-carrying capacity due to the larger radiating surface.
These copper strands can be insulated with any desired type of
insulation.

Table XV gives the diameter of core recommended for various
sizes, and the overall diameter as well as the ampere capacity at
30°C. and 60°C.

TABLE XV.— FIBER CORE CABLE DATA1

Size

Dia. fiber
core, in.

No. of wires
in strand

Size wire in
strand, in.

Overall dia.
copper core,
in.

Ampere capacity

30°C.

60°C.

2,000,000

210

0.099

2.065

1,400

1,750'

1,750,000

2^2

210

0.091

.870

1,300

1,625'

1,500,000

iMe

182

0.091

.780

1,200

1,500

1,250,000

91 6

168

0.086

.590

1,150

1,400

1,000,000

0.102

.280

900

1,150

800,000

»Ha

0.125

.100

• 775

925,

700,000

0.117

0.990

700

830J

1 General Electric Co.

Transmission Cables. — In no branch of the underground-cable
problem have the conditions been more difficult than in that of
transmission with high-tension current, for the reason that the
far greater pressure considerably increases the tendency to dis-
rupt the insulation, allowing the current to escape from its con-
ductor. Great difficulties were encountered, and failures were
experienced, principally due to inexperience or utter disregard of
proper care on the part of those in charge of the laying, jointing,
or operating of the cables, but each failure led to a better under-
standing of the conditions to be provided for and the invention
and adoption of the means of overcoming them, so that now it
is entirely practicable to manufacture and install cables for trans-

122 UNDERGROUND TRANSMISSION AND DISTRIBUTION

mission to operate at 25,000 and 30,000 volts. Several hundred
miles of such cables are now in successful daily operation.

Transmission lines, which are usually three-phase, are almost
universally of three-conductor cable with a thickness of insulation
on each conductor sufficient for voltages between phases. One
of the first installations of three-phase, high-tension cables was
made in St. Paul, Minn., in 1900. The highest potential used
underground prior to that time was 11,000 volts. Since this
time cables of 25,000 and 30,000 volts have been installed in a
number of places. In certain sections of Europe extensive
underground cable systems operating at 30,000 volts have been
very successful and results obtained by certain cable manu-
facturers through the use of improved insulating material and
processes of manufacture definitely indicate that satisfactory
cable may now be obtained to operate at 30,000 volts. As it is
both inconvenient and expensive to change the maximum voltage
of a cable system once established, recognition of the present
situation should be given and cables purchased for future exten-
sion which may be operated at the highest convenient voltage.

General Cable Data.— The following Table XVI gives the
working and test voltages for any size cable with a given thickness
of insulation, or the proper thickness of insulation may be
determined for various voltages.

The working voltages in the foregoing tabulation are based on
all conductors of the circuit being insulated. For three-phase
" Y "-connected circuits with grounded neutral with three-con-
ductor cables, thickness of insulation between conductors and
ground need only be seven-tenths of that between conductors.
The required thickness of insulation can be placed about each
separate conductor before it is laid up into the core, or, as is
more general, especially with paper and varnished cloth, a por-
tion of the required amount of insulation can be placed in the
form of a belt about the assembled conductors. This latter
method makes a more even distribution of the insulating material
and is the one most commonly used.

The approximate outside diameters of three-conductor cables
with various thickness of insulation and with J^-in. lead sheath
throughout is given in Table XVII.

The largest size outside-diameter cable which can safely and
conveniently be installed in a standard 3-in. duct is approxi-
mately 2.7 in. It will, therefore, be noted from the foregoing

CABLES

123

TABLE XVI. — WIRES AND CABLES
Working and Test Voltages1

Kilovolts,
work, press.

Sizes

Thick.,
insulation

Test in kilovolts

At factory

After installation

5 min. 30 min.

60min.

5 min.

30 min.

60min.

0.6
0.6
0.6

14-2
1-4/0
225,000-500,000

Ht
Hi

2.0
2.0
2.0

1.6
1.6
1.6

.3
.3
.3

1.6
1.6
1.6

1.3
1.3
1.3

1.0
1.0
1.0

0.6
1.0
1.0

550,000-1,000,000
12-2
1-4/0

9fe

2.0
2.5
2.5

1.6
2.0
2.0

.3
.6
.6

1.6
2.0
2.0

1.3
1.6
1.6

1.0
1.3
1.3

1.0
1.0
2.0

225,000-500,000
550,000-2,000,000
10-4/0

fa
tit

2.5
2.5
5.0

2.0
2.0
4.0

.6
.6
3.2

2.0
2.0
4.0

1.6
1.6
3.2

1.3
1.3
2.5

2.0
2.0
3.0

225,000-500,000
550,000-2,000,000
8 and larger

5.0
5.0
7.5

4.0
4.0
6.0

3.2
3.2
4.8

4.0
4.0
6.0

3.2
3.2

4.8

2.5

2.5
3.8

4.0
5.0
6.0

8 and larger
6 and larger
6 and larger

3/le

H,
M

10.0
12.5
15.0

8.0
10.0
12.0

6.4
8.0
9.6

8.0
10.0
12.0

6.4
8.0
9.6

5.1
6.4

7.7

7.0
9.0
11.0

5 and larger
5 and larger
4 and larger

17.5
22.5
27.5

14.0
18.0
22.0

11.2
14.4
17.6

14.0
18.0
22.0

11.2
14.4
17.6

9.0
11.5
14.1

13.0
15.0
17.0

4 and larger
3 and larger
3 and larger

32.5
37.5
42.5

26.0
30.0
34.0

20.8
24.0
27.2

26.0
30.0
34.0

20.8
24.0
27.2

16.6
19.2
21.7

19.0
21.0
23.0

2 and larger
2 and larger
1 and larger

47.5
52.5
57.0

38.0
42.0
46.0

30.4
33.6
36.8

38.0
42.0
46.0

30.4
33.6
36.8

24.3
26.8
29.4

25.0

1/0 and larger

62.5

50.0

40.0

50.0

40.0

31.9

Kilovolts = 1,000 volts.

Above working voltages are based on all conductors of the circuit being insulated. For
d.c. 600-volt railway single conductor use, 2000-volt class. For three-phase " Y" connected
circuits with grounded neutral with three-conductor cables, thickness of insulation between
conductors and ground need only be seven-tenths of that between conductors. Tests on
such cable in proportion to thickness of insulation: Example, three-phase 13,000-voIt cir-
cuit " Y," neutral grounded, insulation on each conductor jHo in. (total between conductors
H in.), outer belt Hz in. (total j&j in.); test pressure at factory for 5 min., between conduct-
ors 32,500 volts, each conductor to earth 17,500 volts.

1 General Electric Co., Bulletin No. 4787.

table that the largest conductor size for %2 by %% cable with J^-
in. lead (7,000 volts working pressure) is 350,000 cm.; whereas,
for i%2 by l%2 and >£-in. lead (25,000 volts working pressure)

124 UNDERGROUND TRANSMISSION AND DISTRIBUTION

the largest conductor size to be installed in a 3-in. duct is No. 4
wire.

TABLE XVII. — APPROXIMATE OUTSIDE DIAMETERS OP THREE-CONDUCTOR

COPPER CABLES

(^ Lead Throughout)

Insulation Thickness on Each Conductor, and Over Bunch Respectively

Equal to

Sue

%a + *$2

M* + %i

%2 + %2

9$2 + ?ia

1%2+l&»

Diam.

1,735

1,930

2,129

2,324

2,717

1,795

1,990

2,189

2,384

2,777

1,864

2,059

2,258

2,453

2,845

1,950

2,145

2,344

2,539

2,933

2,038

2,233

2,432

2,627

3,020

2,137

2,332

2,531

2,726

000

2,246

2,442

2,640

2,839

0000

2,371

2,567

2,765

2,960

Cm.

250,000

2,472

2,668

2,866

300,000

2,588

2,785

2,983

350,000

2,700

2,895

400,000

2,803

3,000

450,000

2,898

500,000

2,988

Tables XVIII and XIX give the thickness of insulation as
specified by the cable manufacturers for rubber, paper and
varnished-cambric insulation.

TABLE XVIII. — THICKNESS OP CAMBRIC INSULATION1

Normal working voltage

Insulation about each
conductor, in.

Insulation about three
conductors, in.

7,000

10,000

13,000

9*2

17,000

Jfa

20,000

*fc

23,000

»»«

'%4

25,000

»H«

1*4

i General Electric Co. Bulletin No. 4591.

In the table furnished by the Safety Insulated Wire & Cable
Co. no jacket is provided with the rubber-insulated cables in-
tended for use at the lower voltages. This is due to the fact
that a thin rubber jacket will be reduced in thickness by the

CABLES

125

pressure from the insulated conductors, as it appears to be
impossible to maintain a uniform pressure of the jute and the
conductors against the jacket.

TABLE XIX. — THICKNESS OF RUBBER AND PAPER INSULATION. l

Normal working
voltage

Rubber insulation

Paper insulation

About each
conductor, in.

About three
conductors, in.

About each
conductor, in.

About three
conductors, in.

5,000

None

7,000

Jfa

None

10,000

13,000
17,000

20,000

25,000

l%2

!%2

1%2

30,000

'Hi

2J;

1^2

S. I. W. & C. Co.

TABLE XX. — DATA ON PAPER CABLE OPERATION

Company

Line
vol-
tage

Insu-
lation

Thickness of insulation in thou-
sandths of an inch

Between
conduct-
ors

Between
conduct-
ors and
ground

Per 1,000 volts

Neutral
grounded

Between
conduct-
ors

Between
conduct-
ors and
ground

New York Edison

6,600
6,600
6,600
6,600
6,600
6,900
9,000
9,500
11,000
11,000
11,000
11,000
11,000
11,500
13,000
13,200
13,200
15,000
20,000
23,000
25,000
25,000
26,400

Paper
Paper
Paper
Paper
Paper
Paper
Paper
Paper
Paper
Paper
Paper
Paper
Paper
Paper
Paper
Paper
Paper
Paper
Paper
Paper
Paper
Paper
Paper

312
342
312
436
312
436
375
374
436
436
436
436
406
500
375
375
436
500
562
562
562
562
562

312
342
312
343
312
436
312
374
468
436
436
375
406
406
375
375
436
437
375
375
484
406
531

47
52
47
66
47
63
42
39
40
40
40
40
37
43
29
28
33
33
28
24
22
22
21

47
52
47
52
47
63
60
39
43
40
69
59
37
35
50
28
33
29
32
28
19
16
20

No
No
No
No
No
No
Yes
No
No
No
Yes
Yes
No
No
Yes
No
No
No
Yes
Yes
No
No
No

Brooklyn Edison
Phila. Elec. Co
N. Y. Metropolitan

St. Louis. . . .

Boston

Chicago. ....

Hartford .

New York Subway

New York Manhattan
Long Is. R. R

New York Central
Niagara

Buffalo

Minneapolis
Philadelphia

P. S.-N. J .

Milwaukee

Chicago
Detroit Edison
St. Paul.. .

Montreal. .

P. S.-N. J

126 UNDERGROUND TRANSMISSION AND DISTRIBUTION

It is rather difficult to determine mathematically the proper
thickness of insulation to use for a given potential and it is, there-
fore, better to rely on tables furnished by cable manufacturers.
Certain difficulties in the manufacture, such as unevenness of
the application of insulation on the conductors, eccentric placing
of the insulation and mechanical considerations of strength,
make such tables of insulation required for different voltages
and sizes of conductors more valuable and reliable than formulae.

As illustrating the difference of opinion among engineers
as to the proper factors of safety to use in the design of high-
voltage cables, the following tabulation (Table XX) shows the

FIG. 57. — Sector-type three-conductor transmission cable.

practice of a number of important operating companies using
three-conductor high-tension cables.

Sector Cables. — With the growth of electric service and the
increase in size of conductors for transmission systems the maxi-
mum size of three-conductor cable which can be safely installed
in a duct nominally 3 in. in diameter has been reached. To
meet this condition and make it possible to install cables having
larger conductors or thicker insulation, cables have recently
been constructed in a clover leaf or sector form, as illustrated in
Fig. 57.

Cables of this form of construction have been in use in Europe
for a number of years, but American manufacturers have taken

CABLES

127

up the making of sector cables only within the last 5 years. This
form of conductor permits of a more economical utilization of duct
space and the cable is slightly less expensive than round-conductor
in sizes of No. 000 B. & S. gage or greater. Several large central-
station companies have adopted this form of cable for transmis-
sion purposes where it has been impossible to secure space for
large-sized round-conductor cables.

Clover-leaf or sector cable in sizes under No. 00 B. & S. gage
is not manufactured to any extent, due to the fact that difficulty
is experienced in maintaining the shape of the conductor when
forming the cable.

-3.1
-3.0
-2.9
•2.8
-2.7
-2.6
-2.5
-2.4
-2.3
-2.2
-2.1

222j^*

200,000 300,000 400,000 500,000 500,000

Copper Area of each of Three Conductors in Circular Mils

FIG. 58. — Relative outside dimensions of round and sector cable having 1 ^4-
inch insulation on each conductor, ^2-incn belt and-^£ inch lead.

In determining the rating for the various sizes of sector cable,
it should be noted that, due to its shape, a larger portion of the
periphery of each conductor is nearer the lead sheath than in an
equivalent round-conductor cable. This allows a greater radia-
tion with a consequent higher current rating of the cable. No
fixed standard governing the carrying capacity of cables can
be given as this depends largely on the conditions governing
heat radiation. The position of cables in duct lines, the nature of
the soils through which the duct lines run, and their exposure to
the elements, are all factors to be considered in determining the
rating of a cable. Data obtained from operating companies on
sector cable is given in Table XXI, the information being

128 UNDERGROUND TRANSMISSION AND DISTRIBUTION

TABLE XXI. — DATA ON SECTOR CABLE USED BY FIVE LARGE ELECTRIC-
SERVICE COMPANIES*

Name of
company

Amount,
ft.

Service,
voltage

Thickness in
H2 in. of
insulation
around

Conductor
cross-sec-
tion, circ.
mils

Carrying
capacity,
permitted

Each
con-
ductor

Insu-
lated
Con-
ductors

New York Edi-
son Co.1

459,360
163,680

19,324.50
14,127.10
3,861.20
141,472.51
910.00
72,284.10
2,730.00

8,000
Same to
cable
shell

15,000
Same to
cable
shell

7,500
7,500
7,500
15,000
15,000
23,000
23,000

13,500
6,600"

4,600-volt
trunk line
4,800-volt
distribu-
tion to
overhead
lines

5^2
6^3

7*
75
8«
S*4»

6
6

5
5

7
8
4
8

6
6

5
5

350,000
350,000

350,000
350,000
350,000
350,000
350,000
350,000
350,000

350,000

350,000
2.78 to 2.89
in. outside
diameter

450,000
450,000

3,500 kva., with
50 per cent,
overload
for 1 hr. at
6,600 volts
6,000 kva., with
same per cent-
age of over-
load rating

7,500 kva.

3,000 kva. «
3,000 kva.«

United Electric
Light & Power
Co

Public Service
Electric Co. of
New Jersey
Brooklyn Rapid
Transit Co.">. . .

Detroit Edison
Co

258,081. 4 1»

200,000
209,668

64,416
11,616

1 Specifications call for 31 strands per conductor. Thickness of sheath is \b in. Alter-
nating-current test voltage for 5 min. between conductor and ground, 25,000 volts, and be-
tween conductors, 25,000 volts.

2 7,500 volts between conductors and sheath.

8 In generating stations and substations to afford additional reliability.
« In generating stations to permit changing to 15,000-volt service.

5 15,000-volt service, same pressure to sheath.

6 15,000-volt submarine section to permit changing to 23,000 volts.
* 23,000-volts half voltage to sheath.

• 8 23,000-volt service, submarine section.

9 Includes 3,372 ft. of odd sizes representing older practice.

10 Specifications call for 49 strands per conductor, the diameters of the individual strands
being largest at the cores of the conductors and graded off toward the outside to permit
flexibility and maintenance of the sector shape. Tin is not specified in the lead sheath.
Break-down test between each of two conductors and the other two connected to lead sheath
of 30,000 volts for ft hr. (at factory) and 23,000 volts for 10 min. (after installation).
Limits of insulation resistance in megohm miles, 100-400 corrected to 15.5°C.

11 Cables are designed for 11,500 volts to permit changing to that pressure in the future.

12 This low rating has been given because the 450,000-circ. mil cables are mixed in with
heavily loaded 200,000-circ. mil cables, so it is necessary to restrict the loading on the larger
ones to about 350 amp. to prevent high temperatures in ducts.

* Electrical World, Feb. 19, 1916.

CABLES

129

based on safe operating practice as predetermined for specific
conditions.

It will be noted in the foregoing Table XXI that the maximum
voltage under which sector cable has been operated is 23,000
volts and considerable discussion has arisen as to the advis-
ability of operating this type of cable at high voltages, due to
the excessive dielectric stresses produced at the corners of the
individual conductors.

Fig. 58 shows the relative outside dimensions of cables of
the round and sector types, the copper area and thickness of
insulation being the same for each type.

of In
Inch

Round

Type

100,000

200,000

300,000 400,000 500,000 600,000

Copper Area in Circular Mils

FIG. 59. — Increase in thickness of insulation possible by using sector
instead of round conductors, the outside diameter and copper area being
the same for each type. Insulation around conductors the same as outer
belt.

Fig. 59 shows the increased wall of insulation which can be
put on a cable of the sector type, the copper area and outside
diameter being the same for each type.

Submarine Cables. — For crossing rivers, small lakes, bays or
ponds, the beds of which are mud or sand and free from pebbles,
stones or sharply defined channels, ordinary lead-covered cables
have been used, but the addition of one or two well-saturated
stout braids has been found advantageous. If fiber or paper
insulation is used, it should be thoroughly saturated and filled
so as to limit the damage in case of injury to the lead cover, even
though the cables be also armored with steel tape or wires.

As a rule, however, and especially where long lines of cables

130 UNDERGROUND TRANSMISSION AND DISTRIBUTION

are to be laid under water, it is best to use rubber-insulated
conductors so that in case the protective covering should be
broken or cut, the insulation will still exclude moisture for a
considerable period of time, if not permanently.

Where the submarine cable is at all likely to be subjected to
considerable tensile strains, the lead sheath should be protected
with a heavy serving of tarred jute, and armored with galvanized-
steel wires of a size varying with the size of the cable and the
conditions under which the cable is to be laid and operated.
Heavily galvanized and pliable medium-strength steel is used
for armor wire and the size and thickness of armor for various
diameters of cable is given in the Standard Armor Table XXII.

When the bottom on which the cables lie is soft and there is
no danger from boats or dragging anchors, paper cables with
extra heavy lead, with or without additional fibrous covering
over the lead, have been used very successfully.

It is impossible to give instructions covering the installation
of submarine cables under all conditions but in general the
following method will be found practicable:

After procuring a tug or boat of suitable size to carry the cable
reel and crew, the reel is mounted on heavy trusses at the bow
of the boat, using a heavy shaft to support the weight and allow
the reel to revolve readily.

The cable should pass from the bottom of the reel over rollers
or pulleys back to the stern of the boat and should be securely
fastened on the shore at its proper location.

The reel should be provided with a brake so that it will not
overrun as the boat moves, and men should be stationed at the
reel and cable roller to guard against an}r damage to the cable.

The boat should move slowly to the point where the cable is
to land, and should anchor, or beach, bow on. The remainder
of the cable is then unreeled and dropped alongside, and the shore
end carried to the point at which it is to meet the underground
or aerial line.

The shore end should be laid in a trench extending far enough
into the water to protect the cable against ice and boats which
may ground at such points. In navigable waters a sign, " Cable
Crossing/' should be prominently displayed at the cable landings
to prevent damage from boats inadvertently anchoring along
or near the line of the cable.

In the laying of a submarine cable the boat should not be

CABLES 131

TABLE XXII. — STANDARD ARMOR TABLE*

O.D. cable, mils1

Band iron

Wire armor

Thickness

Weight, Ib.

Sizes

Weight, Ib.

300

0.095

655

400

....

0.095

783

500

0.030

748

0.134

171

600

0.030

843

0.134

1,298

700

0.030

927

0.134

1,426

800

0.030

1,020

0.148

1,741

900

0.030

1,107

0.148

1,891

1,000

0.030

1,198

0.148

2,045

1,200

0.030

1,374

0.148

2,348

1,400

0.030

1,555

0.180

3,202

1,600

0.050

2,454

0.180

3,562

1,800

0.050

2,703

0.180

3,913

2,000

0.050

2,953

0.180

4,265

2,200

0.050

3,202

0.203

5,107

2,400

0.050

3,450

0.203

5,600

2,600

0.050

3,700

0.203

6,100

* General Electric Co.

1 Overall diameter of cable in mils before armor is applied.

NOTE: For jute and 0.030 band steel add 0.60 to diameter.

For jute and 0.050 band steel add 0.70 to diameter.

For jute and 0.095 wire armor add 0.60 to diameter.

For jute and 0.134 wire armor add 0.68 to diameter.

For jute and 0.148 wire armor add 0.70 to diameter.

For jute and 0.180 wire armor add 0.80 to diameter.

For jute and 0.203 wire armor add 0.85 to diameter.

ARMOR TABLE

O.D. cable, mils

10 B.W.G.

weight

8 B.W.G.
weight

6 B.W.G.
weight

4 B.W.G.
weight

300

915

1,200

400

1,050

1,390

....

500

,185

1,590

2,100

....

600

,290

1,790

2,400

2,880

700

,430

1,980

2,600

3,250

800

,550

2,180

2,800

3,500

900

,690

2,380

3,000

3,750

1,000

,940

2,580

3,300

4,000

1,200

2,200

2,780

3,620

4,500

1,400

2,450

3,180

4,120

5,000

1,600

2,710

3,570

4,500

5,500

1,800

3,040

3,970

5,000

6,000

2,000

3,300

5,500

6,550

2,200

3,550

5,880

7,060

2,400

3,880

....

6,370

7,560

2,600

4,200

6,750

8,060

allowed to drift with the stream current, as a loop is apt to be
formed in the cable if a straight course is not maintained. If

132 UNDERGROUND TRANSMISSION AND DISTRIBUTION

the cable is allowed to slack off the reel resulting in the forming
of a loop, there is a possibility of creating a kink in the cable
when the strain is again put upon it.

Fig. 60 illustrates the result of a condition such as just
described. This piece of cable was cut from a length of three-
conductor, 13,200-volt, No. 2/0, paper-insulated, lead-covered
and armored cable, and in spite of this extraordinary physical
abuse the cable continued to operate and was still in service
when the kink was discovered.

In a recent installation of two submarine cables across the
Golden Gate at San Francisco, a messenger wire was first laid
from shore to shore and anchored securely at both ends.
This cable is approximately 13,000 ft. long and as it could not

FIG. 60. — Twisted submarine cable.

be made in one continuous length it was necessary to make a
number of splices. The messenger, which was a 37-wire galvan-
ized-steel strand 1% in. in diameter, was used to take the
strain, thus relieving the cable and joints from all tension. In
laying the cable a barge of 125 tons capacity was used, the cable
reels being mounted with their axes parallel to the long axis of
the barge; in this way the barge was least affected by the pre-
vailing action of the tide and waves in the channel. The tow for
the cable-laying equipment was a 50-hp. launch; during very
heavy tide runs two launches were necessary for towing the
equipment. When ready to lay the cable, the messenger was
picked up at the shore and laid across the barge. Two No. 6
galvanized wires were wound around the messenger and cable.
These wires were applied by a serving machine driven by a gaso-
line motor. Every 20 ft. the movement of the barge was stopped
by means of a grip and a considerable number of turns wound

CABLES

133

around the cable and the messenger at one point. The speed,
when laying the cable, was about 8 ft. per min. and when the
cable laying was once started the barge remained attached to the
messenger until the load had been paid out.

& Tarred Jute .

42 //o. 4 Q. W£. Ga/v. armor ft /'res

^Tarred jute.

'Leaof

"Varnished c/oth be/t
r Telephone, joa/r • 2 //a /J D&5. 75trand
}£Varn/5hedc/ofh, coffon brd/'d

& Yarn r shed c/of/7 .

igZubber 3o%Pzra

250000 c/*.(37t/nned strands)

FIG. 61. — Section of submarine power cable, 11,000 volts working pressure.

The submarine cables (Fig. 61) are three-conductor, 250,000-
cm. copper, each conductor having an insulation of %2 m-> 30
per cent. Para rubber over which was placed a ^4-in. layer of

Anchor Chain

METHOD OF ANCHORING CABLE SECTION C-C

FIG. 61a. — Details of power cable-anchor, showing method of taking the
strain on the armor wires.

varnished cambric. The three conductors are laid together in
circular form (a jute-filler being used), a 1%4-in. varnished
cambric belt being applied over all. The enclosing sheath is
m- Pure lead. Over the lead two layers of jute are applied,

134 UNDERGROUND TRANSMISSION AND DISTRIBUTION

to a total thickness of ^2 m- The jute forms a cushion for the
steel-wire armor, consisting of 42 wires of No. 4 B.W.G. extra
heavy galvanized iron and this armor is in turn covered with
a layer of jute %2 m- thick, to which was applied a sand and
asphaltum finish for mechanical protection.

Each cable contains a twisted pair of telephone wires of No.
13 B. & S. copper. Fig. 61a shows the detail of the power-cable
anchor and method of taking the strain on the armor wires.

Specifications. — In submitting specifications to cable manu-
facturers, it is well to state the conditions under which the cable
will be used as this will assist the manufacturer in determining
the particular cable which will best suit the operating conditions.
When the specific requirements covering details of construction,
tests and guarantees of cable are furnished, a more perfect under-
standing is established and the manufacturer can better serve the
customer's needs. Specifications are of all classes, good, bad and
indifferent, and taken collectively, indicate a wide difference in
ideas. On the cable depends the success of the electrical system
of transmission and distribution as a poorly constructed or
improperly insulated wire or cable will surely imperil the service.
The insulation should be of the proper kind and quality for the
purpose intended. To insure the service the cable must be
properly tested, properly installed and properly protected.

Gable should be tested at the manufacturer's plant before
shipment, at a potential somewhat higher than the maximum
working voltage and it is essential that a similar test be made
after installation. There still seems to be a difference of opinion
as to the proper pressure and duration of such tests and there is
a great tendency on the part of engineers to make this test too
severe. In general it may be said that tests of two and one-half
times working pressure for 30 min. at the factory and twice
the working pressure after installation for 15 min. are considered
conservative. Cables tested under these conditions have given
no indication in practice that the margin of safety was not ample.
High-potential tests are not intended to show the ultimate strength
of the cable, but to show that the cable is safe and satisfactory
for the purpose for which it is intended.

In many cases engineers have specified high-puncture tests on
cables and it was considered that if the insulation passed these
exacting tests it was in first-class condition. High-potential
tests frequently strain the insulation to such an extent that the

CABLES 135

cable fails after the first physical or potential strain is imposed
upon it. A high-potential test is not always conclusive proof of
insulating merit, but on the other hand it should not be assumed
that puncture tests are of no value. The object of puncture tests
is to disclose imperfections in the insulating wall of the cable and
in this respect 'they are of great importance. A cable may be
well made of poor material or it may be imperfectly made of the
very best material. In the one case there is good workmanship
with poor material, and in the other, bad workmanship with
good material.

Cable specifications in general should provide for the fixing
of the copper conditions, the insulating material, the sheath or
braid and the mechanical, electrical and chemical tests. They
should include clauses providing for the methods of tests and
apparatus to be used and, finally, instructions as to the method
of packing and shipping. It should not be the intent of the
specification to tell the manufacturer how he shall make the cable.
The main purpose should be to state the operating conditions
which the cable must satisfy in order that the manufacturer may
endeavor to meet these conditions.

Details of installation and service may radically affect the
design of any cable and it is, therefore, necessary that full infor-
mation be given the manufacturer in order to secure intelligent
consideration and to insure correct design.

Rubber-insulated Cable Specifications. — The numerous speci-
fications for 30 per cent, rubber compound do not materially
differ as to chemi cal tests, nor in their requirements for mechani-
cal properties as determined by stretch, return, and ultimate
break. Many requirements for chemical and mechanical prop-
erties now found in specifications for 30 per cent, compounds
appeared originally in specifications for wires and cables intended
for low-tension service. The same requirements were later
incorporated in specifications for high-tension service and ac-
cepted as satisfactory, but experience has developed the fact that a
change should have been made to secure the best results for this
work. The ingredients of a compound govern its characteristics,
and a change in the proportion of a given ingredient may improve
one characteristic to the detriment of another. Many engineers
leave the thickness of the insulation to be determined by the
manufacturer from specified tests. This practice has the dis-
advantage of permitting the various competing manufacturers

136 UNDERGROUND TRANSMISSION AND DISTRIBUTION

to submit their bids based on different thicknesses of insulation
and safety factors.

There are many different grades of rubber, all varying in
price as in quality, and it is only by a knowledge and recognition
of this wide diversity of character that an engineer can intelli-
gently make up specifications and rigidly enforce them. The
better grades of rubber insulation contain from 20 to 40 per cent.
Para rubber.

The specific gravity of rubber compounds varies from 1.10
to 2.0 depending on the ingredients used. The higher the per
cent, of rubber, the lower the specific gravity. The tensile
strength of high-grade rubber compound is about 1,200 Ib. per
sq. in.

Rubber insulation, owing to its composition, attacks copper and
it is, therefore, necessary that the conductor be properly tinned
before the insulation is applied. In testing rubber-covered
cables it is customary to apply the potential test at the factory
while the cables are immersed in testing tanks in which the water
is maintained at a constant temperature. These tests are made
when the conductor is covered with the vulcanized compound
and before the application of any covering other than a non-
waterproof tape. The analysis of rubber compounds presents
extraordinary difficulties and in the present state of the art no
one procedure is applicable to all compounds. Serious difficul-
ties have arisen in the past, due to the want of standard methods.
For several years no attempt was made to standardize specifica-
tions, and much trouble was given the manufacturers by the di-
versity of requirements contained in the various specifications.
In 1911, Mr. E. B. Katte, chief engineer of electric traction
of the New York Central and Hudson River Railroad Co.,
invited a number of manufacturers and consumers to a confer-
ence in order to discuss the possibility of standardizing specifica-
tions and analytical methods for rubber insulation. As a result
of this conference which was held in New York on Dec. 7, 1911, a
committee was appointed to devise a specification and analytical
procedure for rubber insulation. The committee, which has
become known as the Joint Rubber Insulation Committee, was
composed of men representing the various interests, and a report
was submitted on the procedure for chemical analysis and the
interpretation of the results obtained. A specification and chem-
ical limits for a 30 per cent, compound was also included.

CABLES 137

The procedure applies only to a limited class of compounds
and is not ordinarily applicable to compounds containing less
than 30 per cent, of rubber. The committee report is printed
in full in the Proceedings of the American Institute of Electrical
Engineers, vol. 33, 1914.

The following specification for 30 per cent, rubber insulating
compound is submitted for lead-sheathed cables for operating
at pressure in excess of 2,000 volts. The general clauses cover-
ing conductors, sheaths, patents, quantities, shipments, reels,
terms of payment, permits, measurements, etc., as given under
the heading of paper-insulated cable specification, will also apply
for rubber cable specifications.

SPECIFICATION FOB RUBBER-INSULATED CABLES

1. Conductors shall be properly tinned.

2. The insulating compound shall be made exclusively from pure, dry,
raw, wild South American Para rubber, of best quality of the grade known
as "fine," solid waxy hydrocarbons, suitable mineral matter and sulphur.

3. It shall be properly and thoroughly vulcanized.

4. The vulcanized compound shall show on analysis, freedom from all
foreign organic or injurious mineral matter; not less than 30 nor more than
33 per cent, of above-specified rubber; not more than 4 per cent, of solid
waxy hydrocarbons; not more than 1.5 per cent, of rubber resins; not more
than 0.7 per cent, of free sulphur and not more than 2.65 per cent, of total
sulphur in any form.

5. The manufacturer shall submit to the company a method of procedure
for chemical analysis of his compound for the guidance of the company's
chemist in order that intelligent comparisons may be made in the event of
dispute between the manufacturer and company.

6. The compound must be homogeneous hi character, tough, elastic,
adhere strongly to, and be placed concentrically about the wire, and in
section as stripped from the wire must have a specific gravity of not less than
1.75 as compared with distilled water at 60°F.

7. A sample of the vulcanized compound not less than 4 in. in length
and of uniform cross-section shall be cut from the wire and marks placed on
it 2 in. apart. The sample shall be stretched longitudinally at the rate of 12
in. per min. until the marks are 6 in. apart and then immediately released.
One minute after such release the marks shall not be over 2^ in. apart.
The sample shall then be stretched until the marks are 10 in. apart before
breaking.

8. The compound shall have a tensile strength of not less than 1,000 Ib.
per sq. in., based on the original cross-section of the test piece before stretch.

9. The above mechanical tests shall be made at a temperature of not
less than 50°F.

10. Each and every length of conductor shall comply with the mechanical

138 UNDERGROUND TRANSMISSION AND DISTRIBUTION

and electrical requirements indicated in the following tables "A" and "B."
The tests at the works of the manufacturer shall be made when the con-
ductor is covered with the vulcanized compound and before the application
of any covering other than a non-waterproof tape.

11. Electrical tests at the factory on single-conductor cables shall be
made after at least 12 hr. submersion in water and while still immersed.
The insulation test shall follow the voltage test and shall be made with a
battery of not less than 100 volts or more than 500 volts and the reading
shall be taken after 1 min. electrification.

TABLE "A"

Voltage tests on single-conductor cables insulated with high-tension rubber
compound. Duration of test at factory 5 min.; after installation, 30 min.
Tests at factory as per table; after installation at table values for 5 min., then
at 80 per cent, for 25 min.

Size conductor

Minimum thickness of insulation in inches

3/32

7/64

4/32

5/32

6/32

7/32

8/32

14/32

Stranded
1,000 M.C.M

6,000
6,000
7,000
7,000
8,000
8,000
8,000
9,000

9,000
9,000
9,000
9,000
9,000
9,000

8,000
8,000
9,000
9,000
10,000
10,000
10,000
11,000

11,000
11,000
10,000
10,000
10,000
10,000

12,000
12,000
13,000
13,000
13,000
13,000
13,000
14,000

14,000
14,000
11,000
11,000
11,000
11,000

16,000
16,000
16,000
16,000
16,000
16,000
16,000
16,000

16,000
16,000
12,000
12,000
12,000
12,000

19,000
19,000
19,000
19,000
19,000
19,000
19,000
18,000

18,000
18,000

22,000
22,000
22,000
22,000
22,000
22,000
22,000
20,000

20,000
20,000

30,000
30,000
30,000
30,000
30,000
30,000
30,000
30,000

30,000
30,000

750 M.C.M

500 M.C.M
350 M.C.M
4/0 A W G

5,000
5,000
6,000
6,000
6,000
7,000

7,000
7,000
7,500
7,500
7,500
7,500

2/0 A.W.G
1/0 A W G

2 A WG

Solid
4 A.W.G
6 A.W.G. . .

8 A.W.G
10 A WG

12 A.W.G
14 A.W.G

13. Samples of the cables 6 ft. in length taken from any reel of cable
must show an ultimate dielectric strength capable of resisting the applica-
tion of twice the voltage specified above for a period of 5 min. without
failure.

14. Insulation resistance and electrostatic capacity tests made (before
and after voltage tests as per Table "A") and under equivalent temperature
conditions must not indicate fatigue or overstrain of dielectric.

CABLES

139

15.

TABLE "B"

Insulation tests on single-conductor cables insulated with high-tension
rubber compound. Tests at factory as per table; after installation 80 per cent,
of table value.

MINIMUM MEGOHMS PER MILE AT 60°F.

Size conductor

Minimum thickness of insulation in inches

5/64

3/32

7/64

4/32

5/32

6/32

7/32

8/32

14/32

Stranded
1,000 M C M

300
350
410
520
610
740
800
1,070

1,260
1,480
1,720
1,990
2,270
2,560

340
400
460
580
680
820
980
1,170

1,380
1,610
1,870
2,150
2,440
2,740

420
490
570
700
820
980
1,060
1,380

1,610
1,860
2,140
2,440
2,750
3,060

490
570
660
810
940
1,130
1,210
1,560

1,800
2,070
2,360
2,680
3,000
3,320

560
650
750
910
1,060
1,260
1,350
1,720

1,980
2,260
2,570
2,890
3,220
3,550

630
730
830
1,010
1,170
1,380
1,470
1,870

2,140
2,430
2,750
3,000
3,420
3,750

750 M C M

500 M C M

350 M C M

4/0 A W G

530
650
710
950

1,130
1,330
1,560
1,810
2,080
2,360

2,000
2,240
2,400
2,750

3,200
3,600

2/0 A W G

1/0 A W G

2 A.W.G....
Solid
4 A.W.G....
6 A.W.G....
8 A W G

10 A.W.G....
12 A.W.G....
14 A.W.G....

1,860
2,120

SPECIFICATIONS
FOR

PAPER-INSULATED,
LEAD-ENCASED CABLES

FOR

ELECTRIC-LIGHTING, RAILWAY AND POWER SERVICE

1. GENERAL

(a) The word "Company" where occurring in these specifications shall
mean the purchaser »f the cable herein referred to, or its duly authorized
representative.

(6) The word "Manufacturer" where occurring in these specifications
shall mean the manufacturer of the cable herein referred to, or his duly
authorized representative.

2. RATING OP CABLE

(a) The rating of a cable shall be understood to be the highest equivalent
working pressure in volts corresponding to any of the specified conditions
of service or test. Such rating shall be determined from the following

140 UNDERGROUND TRANSMISSION AND DISTRIBUTION

Rating Table XXIII, all unlisted intermediates taking the next higher listed
figure.

TABLE XXIII. — VOLTAGE RATING OP CABLES

Working
pressure
volts

rr> 4. 4. t 4. IA Test after installation by manufac-
Test at factory, volts turer> voits *

5 min.

30 min.

60 min.

5 min.

30 min.

60 min.

500
1,000
1,500

1,250 1,000
2,500 2,000
3,750 3,000

1,000 1,000
1,600 2,000
2,400 3,000

1,000 1,000
1,600 1,300
2,400 1,950

2,000
2,500
3,000

5,000
6,250
7,500

4,000
5,000
6,000

3,200 4,000
4,000 5,000
4,800 6,000

3,200 2,600
4,000 3,250
4,800 3,900

4,000
5,000
6,000

10,000 8,000
12,500 10,000
15,000 12,000

6,400 8,000
8,000 10,000
9,600 12,000

6,400 5,200
8,000 6,500
9,600 7,800

7,000
8,000
9,000

17,500 14,000
20,000 16,000
22,500 18,000

11,200 14,000
12,800 16,000
14,400 18,000

11,200
12,800
14,400

9,100
10,400
11,700

10,000
11,000
12,000

25,000 20,000
27,500 22,000
30,000 24,000

16,000 20,000
17,600 22,000
19,200 • 24,000

16,000
17,600
19,200

13,000
14,300
15,600

13,000
14,000
15,000

16,000
17,000
18,000

32,500
35,000
37,500

40,000
42,500
45,000

26,000
28,000
30,000

32,000
34,000
36,000

20,800
22,400
24,000

25,600
27,200
28,800

26,000
28,000
30,000

32,000
34,000
36,000

20,800
22,400
24,000

25,600
27,200
28,800

16,900
18,200
19,500

20,800
22,100
23,400

19,000
20,000
21,000

47,500
50,000
52,500

38,000
40,000
42,000

30,400
32,000
33,600

38,000
40,000
42,000

30,400
32,000
33,600

24,700
26,000
27,300

22,000
23,000
24,000

55,000
57,500
60,000

44,000
46,000
48,000

35,200
36,800
38,400

44,000
46,000
48,000

35,200
36,800
38,400

28,600
29,900
31,200

25,000
26,000
27,000

62,500
65,000
67,500

50,000
52,000
54,000

40,000
41,600
43,200

50,000
52,000
54,000

40,000
41,600
. 43,200

32,500
33,800
35,100

28,000
29,000
30,000

70,000
72,500
75,000

56,000
58,000
60,000

44,800
46,400
48,000

56,000
58,000
60,000

44,800
46,400
48,000

36,400
37,700
39,000

Factors.. . . 2.5

2.0

1.6 2.0

1.6

1.3

For street railway service (nominal 500-volt d.c.), the e.w.p. shall be 2,500 volts for all
cables to be operated with a maximum regular working voltage not exceeding 750 volts
d.c. and a maximum momentary pressure (30 sec. or less ) not exceeding 1,500 volts d.c.

(6) For street-railway service nominal 600 volts d.c., the equivalent

CABLES 141

working pressure shall be 2,500 volts for all cables to be operated with a
maximum regular working voltage not exceeding 750 volts d.c., and a
maximum momentary pressure (30 sec. or less) not exceeding 1,500 volts d.c.
(c) For three-conductor three-phase "Y "-connected circuits with
grounded neutral, the thickness of insulation between any conductor and
ground need be only seven-tenths of that between conductors, and the test
voltage between any conductor and ground may be taken at seven-tenths
of the above tabulated figures for the corresponding equivalent working
pressure.

3. CONDUCTOKS

(a) Each conductor shall consist of not less than the following number
of soft-drawn copper wires free from splints, flaws, joints, or defects of any
kind, and having at least 98 per cent, conductivity of that of pure annealed
copper, as defined by the American Institute of Electrical Engineers
Standardization Rules. The conductors shall be concentrically stranded
together having an aggregate cross-sectional area when measured at right
angles to the axes of the individual wires at least equal to that corresponding
to the specified size, viz:

No. 4 B. & S. G and smaller Solid

No. 3 B. & S. G to No. 2 B. & S. G. . . 7-wire strand

No. 1 B. & S. G to No. 4/0 B. & S. G. . 19-wire strand

250,000 cm to 500,000 cm 37-wire strand

600,000 cm to 1,000,000 cm 61-wire strand

1,100,000 cm to 2,000,000 cm 97-wire strand

2,100,000 cm and larger 127-wire strand

Intermediate sizes take the stranding of the next larger listed size.

4. INSULATION

(a) The insulation shall consist of the best manila paper free from jute,
wood fiber or other foreign material applied helically and evenly on the con-
ductor, and shall be capable of withstanding the test and service conditions
corresponding to the highest equivalent working pressure as determined from
the rating table set forth hi paragraph 2 hereof. In the case of the cables
consisting of more than one conductor (except concentric cables) and Fig.
8 or flat form of duplex cables, the separately insulated conductors shall be
twisted together with a suitable lay, and interstices rounded out with the
jute' before the belt insulation is applied. The minimum insulation thick-
ness or thicknesses shall in no case be less than 90 per cent, of the agreed
average thickness or thicknesses. The completed core shall be thoroughly
insulated with an insulating compound.

5. SHEATH

(a) The sheath shall have an average thickness of not less than that
indicated in the tabulation next following and the minimum thickness
shall in no case be less than 90 per cent, of the required average thickness.

142 UNDERGROUND TRANSMISSION AND DISTRIBUTION

Diameter of core Corresponding thickness

in mils of sheath in inches

0-299 5/64

300-699 3/32

700-1,249 7/64

1,250-1,999 1/8

2,000-2,699 9/64

2,700-over 5/ 32

(b) The sheath shall consist of commercially pure lead, freshly mined
and shall contain no scrap, and shall be free from blow holes, cracks, scales
or imperfections of any kind.

6. FACTORY TESTS

(a) The manufacturer shall, when so stipulated in the order, notify the
company in writing when the cables are ready for test, so that proper tests
may be made at the works of the manufacturer by the duly accredited repre-
sentative of the company. Free access to the testing department shall be
given to said representative at all times while the cables are being tested
hereunder, and the requisite facilities and apparatus for the tests described
in these specifications shall be supplied by the manufacturer without extra
charge. In case the representative appointed by the company to make
factory tests is not wholly and permanently in the employ of the company,
said appointment shall be subject to the approval of the manufacturer.

(b) Conductivity. — The conductivity of the copper shall be determined
at least once for each day's output.

(c) Dielectric Strength. — Each length of cable shall withstand tests at
factory of a voltage corresponding to the rating (highest equivalent
working pressure) of the cable as determined from the rating table. The
condition and conduct of test shall conform to the Standardization Rules
of the American Institute of Electrical Engineers.

(d) Insulation Resistance. — The insulation resistance shall be deter-
mined on each length of cable and shall not be less than 50 megohms when
measured at, or corrected to, 60°F. This test shall be made subsequent to
the tests for dielectric strength. (Higher insulation resistance can be fur-
nished, but necessitates the use of a harder insulating compound, which is
more inclined to dry out and cannot safely be bent in cold weather.)

(e) Testing Apparatus and Methods. — Any disagreement as to the accuracy
of testing apparatus or method not specifically covered by this specification
shall be referred to the Bureau of Standards, Washington, D. C.

7. PATENTS

(a) The manufacturer, shall, at his own expense, defend any or all suits
or proceedings that may be instituted against the company for the in-
fringement or alleged infringement of any patent or patents, by the use of
any cable or goods covered by this specification, and sold to the company
by the manufacturer provided such infringement shall consist in the use by
the company, in the regular course of its business, of any of said cable or

CABLES 143

goods or parts thereof, and provided the company gives to the manufacturer
immediate notice in writing, of the institution of the suit, or proceedings,
and permits the manufacturer through his counsel, to defend the same and
gives all needed information, assistance, and authority to enable the manu-
facturer so to do, and thereupon, in case of an award of the damages, the
manufacturer shall pay such award and in case of an injunction against the
company, the manufacturer shall, upon return of the article, the use of
which has been enjoined, repay to the company the amount paid by it for
the same.

8. QUANTITIES

(a) The quantity of each cable specified in the order shall be subject
to an increase or decrease of not exceeding 5 per cent., at the option of the
company, provided that such option is exercised by the company in writing
not less than 30 days before the date fixed for final shipment on account of
said order.

9. SHIPMENTS

(a) Unless otherwise provided all deliveries shall be f.o.b. factory of the
manufacturer. Any material not called for by the company in time to
permit the manufacturer (at the agreed shipping rates) to make shipment
within the agreed time, and for which final shipping instructions are not
filed by the company with the manufacturer at least 1 month prior to the
expiration of said agreed time, shall be paid for as if shipped at the expiration
of said agreed time. Provided, however, that said agreed time shall not be
more than 6 months after date of order. A receipt given by the company
or its representatives for any material .shipped by the manufacturer, and
which fails to note any apparent injury to or bad condition of reels, cases or
contents shall terminate the manufacturer's responsibility for the condition
of said material.

10. REELS

(a) All reels and lagging shall not be included in the contract price, but
shall be charged separately therefrom and shall be paid for in accordance
with paragraph 11 thereof, "Terms of Payment," and when returned f.o.b
shipping factory in good condition complete with all lagging (reasonable
wear and tear excepted) within 6 months from date of shipment shall be
credited at the price charged. Reels and lagging thus returned after 6
months from date of shipment shall be credited at one-half the price originally
charged.

(6) Each reel shall be plainly marked, giving the length of cable, pur-
chaser's order number, and date of manufacture. Each reel shall have a
numbered metal tag, permanently attached.

11. TERMS OF PAYMENT

(a) Net cash within 30 days from date of payment by manufacturer; or
per cent, discount for cash within 10 days from said date of shipment.

144 UNDERGROUND TRANSMISSION AND DISTRIBUTION

12. INSTALLATION BY MANUFACTURER

(a) The following additional conditions contained in paragraphs 12 to
22, both inclusive, hereof shall apply when cable is installed in underground
ducts and manholes by the manufacturer, and then only; in which case the
conditions of paragraphs 10 and 11 hereof shall be cancelled.

13. PERMITS AND INFORMATION

(a) The company shall provide all necessary permits and information
to enable the manufacturer to carry on the work uninterruptedly.

14. MEASUREMENTS

(a) The company shall furnish the manufacturer correct measurements
for detail manufacturing lengths, but in case the company so elects at the
time of placing the order, the manufacturer shall make said measurements,
which shall be approved by the company before the manufacture of the
cable is begun. In either case the lengths as thus determined shall be paid
for under paragraph 21 hereof, relating to "payments," and the scrap or
excess cable, if any, shall become the property of the company.

15. CONDUITS, MANHOLES, ETC.

(a) All conduits, manholes, or locations provided by the company for
the reception of cable shall be clean and free from obstructions, safe and
suitable for the purpose intended. The ducts shall be such as to permit the
passing through them of a steel mandrel, 3 ft. in length and of a diameter at
least % in. greater than that of the cable to be installed therein, but in no
case of a smaller diameter than Y± in. less than that of the nominal diameter
of the ducts; in case obstructions or defects in the ducts assigned by the
company cause unavoidable delay to the manufacturer or damage to cable
through attempts to install therein, the company shall pay to the manu-
facturer the actual loss resulting from said delay, and cost of repairing said
damage.

16. JOINTING

(a) The manufacturer shall make all joints in a substantial and work-
manlike manner, using proper connectors of the proper conductivity, which
shall be sweated to the conductor so as to furnish perfect continuity at all
points. Sufficient insulating material shall be supplied to insure insulation
and dielectric strength equal to the average obtained to equal lengths of the
cable as manufactured. The joints shall be provided with lead sleeves of
thickness not less than that of the sheath of the cable; they shall be thor-
oughly made, wiped, and filled with compound to prevent the probability
of moisture, reaching the insulation.

CABLES 145

17. INSTALLED TEST

(a) After the cable is pulled in and jointed by the manufacturer, and
before being put into service, it shall be subjected to an installed test at a
voltage corresponding to the rating or highest equivalent working pressure
of the cable as determined from the rating table set forth in paragraph 2
hereof. Unless otherwise specified by the company in writing at or prior
to time of test, the latter shall be the listed test for 5 min. set forth in said
rating table. The necessary current and apparatus for making the test
shall be supplied by the company, the conditions and conduct of tests shall
conform to the recommendation of the Standardization Rules of the Ameri-
can Institute of Electrical Engineers.

18. TERMINALS AND JUNCTION BOXES

(a) Terminals, junction boxes, manhole cable supports and in general
all cable accessories or auxiliary apparatus not necessarily required to be
used in connection with the pulling in and jointing of the cable, shall be
provided by the company.

(6) If so instructed by the company, the manufacturer shall make con-
nection between the cable and terminals, junction boxes, or equivalent, but
shall not be required to guarantee the same hereunder unless said terminals
and junction boxes or equivalent are approved by him.

Each straight joint counts as one joint.

Each additional branch or tap cable from a straight joint counts as one
joint.

Each cable entering or leaving a junction box, test box, terminal, pothead
or equivalent, counts as one joint.

19. GUARANTEE

(a) In case any cable furnished hereunder fails within 1 year from date of
shipment by the manufacturer, and said failure results from defects of
material or workmanship for which the manufacturer is shown to be solely
responsible, the manufacturer shall be immediately notified and shall
(being given suflficient time to enable him to do so) at his own expense make
all necessary repairs to make the cable affected, in every way equal to its
condition previous to its failure.

(6) Should the manufacturer fail to attend to the repairs promptly, or
should the exigencies of the company's business be such as to necessitate
repairs before the manufacturer can be notified, the company shall have the
right to make the necessary repairs at the manufacturer's expense, preserving
the available evidence of the cause of the failure.

(c) Should the evidence fail to show the liability of the manufacturer
under this specification, the company shall pay to the manufacturer the
cost of repairs made by the latter.

146 UNDERGROUND TRANSMISSION AND DISTRIBUTION

20. ACCIDENT LIABILITY

(a) The manufacturer shall save the company free and harmless from
any and all claims or demands of the manufacturer's employees or his
legal representatives for injury which may be substained while employed
in the construction of the work herein contemplated, or while going to or
from the place where said work is to be performed, unless such injury is
due to negligence on the part of the company or its employees; also from
any and all claims or demands for damages, for injury to other parties,
caused by the fault or neglect of the manufacturer, his agents, servants, 01
employees in the construction of said improvements.

(6) Provided that in the event of any action or actions which may be
instituted either by the agent, servants, or employees of the manufacturer
against the company, or by third persons who may claim injuries to have
been sustained, within the meaning of the foregoing clause (which injuries
are alleged to be the result of the fault or neglect of the agents, employees,
or servants of the manufacturer), the company shall immediately notify the
said manufacturer thereof, and shall permit him to institute suit or action
and appear and participate in the trial by counsel of his own selection.
Provided, further, however, that this proviso shall not in anywise prevent
the said company from defending against suit or action with as full force
and effect as though the preceding paragraph in the said contract, to which
this is a proviso, had not been inserted in contract.

21. TERMS OF PAYMENT

(a) Net cash for 80 per cent, of the installed price shall be paid within
30 days from date of shipment. Ten per cent, of the installed price (one-
half of the remaining 20 per cent.) shall be paid upon the tenth day of each
calendar month for all cable pulled in and jointed during the preceding
calendar month, and the remaining 10 per cent, due for each separate cable,
shall be paid within 10 days from the date when each such cable shall have
been tested and accepted such test and final acceptance or rejection of each
separate cable to be made within 10 days from notice by the manufacturer
to the company that such cable is ready for final test. If the installation
of any cable or part thereof be delayed for more than 3 months by failure
or inability of the company to provide the manufacturer with the necessary
facilities for prosecuting the installation, or by other causes not attributable
to the manufacturer, the full balance remaining unpaid for such cable
(taking into consideration the due proportion of installation work done upon
the cable, if any), also the unpaid balance for all cable accessories furnished
in connection therewith and the manufacturer's customary charge for the
reels thus retained by the company, shall be due and shall be paid forthwith.

High-tension Cable Specification. — The National Electric
Light Association Committee on Underground Construction
suggest the following specification for three-conductor paper-
insulated cable. It will be noted that in this specification a

CABLES 147

bending test is included. In European cables the bending test
is applied three times to a radius of six times the cable diameter.
American manufacturers consider as too severe a bending test,
first in one direction and then in the other, twice repeated, to a
radius of six times the cable diameter. The specification here-
with presented, therefore, increases the radius of bending to seven
and one-half times the cable diameter.

INSULATING MATERIAL

The insulating material shall be of the best manila paper,
free from jute, wood fiber, or other foreign material. It shall be
cut in strips and helically and evenly applied to the conductor

to a uniform thickness of /32 in. After insulation the three

conductors shall be laid together, with a uniform twist, having
a pitch not exceeding 25 times the diameter of one conductor
measured over the insulation. The interstices shall be filled with
jute or paper so as to form a true firm cylinder without openings
or air spaces, over which is to be applied a paper-insulating
jacket in the same manner, and of the same quality as specified
for each conductor.

During the process of applying the paper insulation and the
jute or paper filler and immediately before the insulation is
impregnated, the cable shall be subjected to such treatment as
will insure the expulsion of all air and moisture, incident to
which treatment the cable shall be impregnated with an insulat-
ing compound of low specific inductive capacity, guaranteed not
to run appreciably and to retain its sticky adhesive qualities
during the life of the cable, and also guaranteed not to develop
any chemical action within itself or with any other component of
the completed cable.

TESTS

The following electrical tests shall be made by the manufacturer
at his works and without expense to the purchaser, the manu-
facturer supplying all necessary apparatus and the purchaser
to have the privilege of being represented when these tests are
conducted. The manufacturer shall furnish the purchaser with
copies of data sheets showing the behavior of the cable during
these tests.

(a) Voltage Test. — Each length of cable is to be tested with alternating
current, having a frequency preferably the same as that of the system of

148 UNDERGROUND TRANSMISSION AND DISTRIBUTION

which the cable is to be a part. The test voltage is to be applied between
all three conductors and between conductors and lead sheath at a tem-
perature of 150°F. If the cable is to form part of a system having a per-
manently grounded neutral, the neutral point of the test generator shall be
connected to the cable sheath during the test. If the cable is to form part
of a system with an ungrounded neutral, two tests shall be made, the first
with conductor A, the second with conductor B, grounded to the cable
sheath. The apparatus supplying the energy for the voltage test must
have a kilovolt-ampere capacity at least four times the kilovolt-ampere
capacity absorbed by the length under test, and in any event must not be
less than 25 kva. capacity. The time of application of the test and test
pressure shall be: 5 min. at a voltage having a peak value two and one-
half times the peak value of the normal working pressure as determined by
spark-gap in accordance with the American Institute of Electrical Engineers
Standardization Rules.

(6) Insulation Resistance Test. — (1) An insulation-resistance test shall be
made immediately before and after the voltage test. (2) The measurement
shall be made with a direct-current voltage of not less than 100 volts, the
reading to be taken after 1 min. electrification, and shall show no appreciable
decrease in the value of the insulation resistance between the two successive
measurements. Measurements shall be made between each conductor
and each of the other two and between each conductor and the lead sheath.
Any section of cable which shows a marked variation from others of the
same type manufactured at the same time shall be held for further examina-
tion and if such variations cannot be satisfactorily explained the section shall
be rejected.

(c) Breakdown Test. — Samples from 10 to 25 ft. long and selected by the
purchaser at random from any cable lengths shall not break down under
five times the working pressure applied for 5 min. between all three con-
ductors and between conductors and lead sheath, after samples with ends
sealed have remained at a temperature of 150°F. for 100 hr. in straight single
lengths with axes inclined 15° to the horizontal.

(d) Bending Test. — A sample from any length of cable shall be bent around
a cylinder having a diameter equal to 15 times the outside diameter of the
cable over lead sheath, and then be straightened out. It shall then be bent
in the opposite direction around the cylinder and straightened out. This
operation shall be performed twice in succession, after which the cable
shall be capable of withstanding a voltage test two and a half times working
pressure applied for a period of 5 min. between the conductors and between
the conductors and the lead sheath, and shall show no signs of mechanical
injury or electrical injury when dissected.

Test after Installation. — The cable shall be capable of withstanding twice
normal working pressure applied between all three conductors and between
conductors and lead sheath for a period of 10 min., after being drawn into the
ducts and jointed. An insulation-resistance test shall be made immediately
before and after the breakdown test, using the method specified under (6-2)
above, and the insulation resistance shall not be materially reduced as a
result of this test.

CABLES 149

Moisture in Cable Insulation. — Some companies, in their
high-tension paper-insulated cable specifications, include a clause
to limit the percentage of moisture in the insulating compound.
This appears to be a step in the right direction but such specifica-
tions should be accompanied by an exact description of the
method to be employed in determining the percentage of water
in the insulating compound.

Different methods of tests give different results, some of which
are accurate only to within approximately 25 per cent. It is
evident that in order to have accurate results the insulation
must be removed from the lead and copper and the difficulty is
to accomplish this without exposing the insulation to the air,
thus allowing it to absorb moisture, so that tests made from the
same cable show variations in accordance with the percentage
of moisture in the atmosphere at the time the tests are made.

In the production of high-grade transformer oils, great care
is used to eliminate even minute percentages of moisture. In
ordinary cases Jfo Per cent, is considered objectionable, and it
is believed that where trouble is experienced with impregnated-
paper cables it is due to the lack of this same attention to the
question of moisture in the original compound or in the paper
itself.

The rosin of commerce which is used for a base in most paper
cables is the residue from a steam-distillation process for turpen-
tine and contains from 8 to 10 per cent, of water. The rosins
obtained from the so-called "dry process" contain less moisture
than this, but are of an inferior grade.

In usual methods of making rosin-oil compound the mixture
of rosin and oil is heated so that the water is boiled off. This
method, if carried to an extreme, may result in the reduction
of the water to as low as 1 per cent., but in common practice rarely
reaches this minimum. There is also water present in unstable
molecular combination with the rosin and when cable is operated
above normal temperatures this molecular condition is destroyed,
and actual water and a further liberation of volatile ingredients
results. This fact apparently accounts for some cable troubles
which are otherwise unexplainable.

However, the present-day methods of paper-cable manufacture
have reached a degree of perfection where very little trouble
need be feared from overheating due to the presence of residual
moisture in the insulation, if the cable is operated within the

150 UNDERGROUND TRANSMISSION AND DISTRIBUTION

limits of voltage for which it has been designed. Only in cases
where the insulation has not been properly treated will excessive
dielectric losses be noticed.

Numerous tests have been made to determine heating due to
dielectric losses, but in no case have these losses been found to
be abnormal provided the cable insulation has been properly
treated and applied.

It would, therefore, seem that there is no good reason for
believing that there is ever enough residual moisture in the cable
insulation to cause any appreciable increase in normal dielectric
hysteresis, and that where companies are experiencing trouble
of this nature the cause is not due to residual moisture in the
compound, but to moisture entering the cable after installation,
either through small holes in the lead sheath, or when joints are
made under unfavorable conditions in damp weather.

CHAPTER VI
INSTALLATION OF CABLES

Handling Lead Cables. — No attempt will be made to indicate
all the details of cable installation; it is the intention rather to
outline the general method of installing underground cables and
to emphasize the importance of some parts of the work in con-
nection therewith. Cables are shipped from the manufacturers
on wooden reels of suitable size to accommodate one or more
lengths of cable.

When coiling a cable on a reel, the first end, usually termed the
test end, is put through a slanting smooth hole in the side of the
reel so as to have both ends of the cable accessible for testing
before shipment. After testing, both ends are capped or sealed,
thus protecting the cable insulation from moisture. The test
end of the cable is usually left protruding through the side of
the reel from 12 to 18 in. and is boxed over. It is customary to
lag the reel from flange to flange with heavy wooden slats nailed
to the flanges and further secured by wires encircling the slats
to protect the cable thoroughly from injury in transit or while
standing on the street.

Transporting reels of cable from the railroad to the manhole
should be entrusted only to experienced truckmen; and if a low
wagon is not available, and a high wagon must be used, the reels
of cable should be carefully lowered from the wagon by means of
a windlass and skids and not allowed to drop to the ground. To
avoid the loosening of the cable, the reels should be rolled in the
direction of the point of the arrow painted on the side of the reel.

The reel of cable is then placed at the manhole, over the duct
into which the cable is to be drawn, in such a way that the cable
will unwind from the top of the reel. It should next be mounted
on jacks and not until that is done should the slats be removed,
care being taken that no nails come into contact with the cable
or are left in the flanges to do damage.

An improved form of jack designed to handle cable reels of
varying sizes is shown in Fig. 62. It is provided with three

151

152 UNDERGROUND TRANSMISSION AND DISTRIBUTION

forged-steel hooks, as well as a swivel top, so that the reel can
be picked up on the hook nearest its center and suspended with
a very small amount of ratcheting, at the same time being just
high enough to clear the ground.

A pair of these jacks will safely support cable reels of any
ordinary size, the combined safe carrying capacity of a pair being

FIG. 62.— Reel jack.

over 6 tons on the top hook. Reels weighing from 6 to 10 tons
may be raised on the swivel top or, if the diameter of the reel
permits, on either of the two lower hooks.

The jack is superior to the screw type of cable-reel jack, as it
raises or lowers the load faster and by the use of the hook arrange-
ment, which is not applicable to an ordinary screw jack, one pair
of jacks can handle almost any size reel.

The utmost care should be taken not to bend the cable sharply,

INSTALLATION OF CABLES 153

nor to break through, cut, abrade, kink or dent the lead sheath;
and, above all, not to allow the slightest trace of moisture to
enter the ends of the cable after the seals have been broken. A
failure to observe these points may result in the loss of the cable.
The useful life of an underground cable is determined by that of
the insulation, which in turn usually depends upon the integrity
of the lead sheath.

Choice of Ducts. — Before drawing cables into a new conduit
system, there is often a question as to which of the ducts shall be
used first. Workmen, when about to install cables, may have
been told to use any one of the ducts, and naturally they draw
the cable into those which are most convenient, without any
consideration for the cables which are to be installed later.
There are cases where a manhole has been completely blocked
by the first few cables installed. There is another important
reason for using care in the selection of the ducts to be used for
power cables, as will be seen from the following:

It is not possible to foretell the current-carrying capacity of
a cable without previous knowledge of all the controlling factors
which will influence temperature rise in such a cable. Some
of the most important factors are: natural temperature of the
ducts and manholes; amount of moisture present; condition and
action of soil surrounding the conduit; and exact location of the
cable in the conduit with respect to other cables which have
previously been installed. All of these greatly influence both the
radiation and dissipation of heat generated in each conductor or
cable and consequently the current-carrying capacity of the
conductor.

Usually the ducts which dissipate heat most rapidly, and there-
fore run coolest, are those located at the lower corners of the
conduit. Those nearest to the outside of the system run fairly
cool, but the middle and top ducts, which not only take up heat
from the lower cables but must dissipate heat through adjoining
ducts, operate at a fairly high temperature. Attention to these
points, when planning a new system, may prove very profitable
in the end.

Regarding the selection of cables, it should be borne in mind
that other conditions being equal, those insulated with rubber
compound dissipate heat more readily than those insulated with
paper or other fibrous material. On the other hand, it has been
found that a cable insulated with an oil-saturated paper will

154 UNDERGROUND TRANSMISSION AND DISTRIBUTION

operate for a longer time at a high temperature without deteriora-
tion than when insulated with rubber compound. This, however,
does not hold true if too much resinous material has been used in
making up the paper insulation.

To economize in space, as many as six cables are, at times,
drawn into one duct. While this may be an advantage, it is
accompanied by the danger of losing all six cables through the
failure of one.

A cable should never be drawn over one already in position,
as the wear of the rubbing lead is excessive; and one cable,

-O

FIG. 63. — Rodding sticks and snake wire.

usually the one in place, is almost sure to be damaged by the
lead being worn through.

Rodding Ducts. — After having decided upon the duct into
which the cable is to be drawn, preparations are made to wire the
duct and to clean it thoroughly, freeing it from any obstructions
which might injure the cable when being drawn in. To accom-
plish this, a snake wire or rodding stick, of which there are
several types, Fig. 63, is worked through the duct. If the sec-
tions between manholes are short, rods are not required, a
snake wire alone being used. The latter is also better adapted
to wiring ducts with curves, but cannot be used in very long
lengths owing to the friction encountered. By means of a gal-

INSTALLATION OF CABLES 155

vanized wire a suitable rod to which is attached a scraper,
gage, brush, or swab is next drawn through the duct to insure
a clear passage for the cable. Gages so used should be about
% in. larger than the cable to be installed.

It is customary to rod long sections of conduit, using wooden
rods about 1 in. in diameter and 3 or 4 ft. long, provided at each
end with coupling devices by means of which the various sec-
tions may be jointed together. These coupling devices consist
of either screw connections or a sliding coupling which may be
more quickly joined.

The method of rodding is as follows :

A bundle of rods is placed in the manhole; a workman standing
in the hole pushes one rod into the duct, attaches a second to the
first and pushes it ahead, continuing this operation until the first
rod appears at the next hole. A rope is then fastened to the
rod at the distant manhole and the rods with the rope attached
are drawn back into the first hole and disconnected as they are
drawn from the duct until the rope appears. If a large quantity
of duct is to be rodded, it is, of course, impracticable to draw a
rope into each section, yet it is advisable to have the line rodded
somewhat in advance of the cable gang. In this case a small
piece of steel wire (No. 10 or No. 12 B.W.G.) is drawn into the
duct by the rods and left in place to be later used to draw in the
rope. This wire, if properly handled, and drawn out and reeled
or coiled neatly, may be used several times. Obviously, rods
may be drawn out at the distant manhole and there disconnected
from the wire fed in at the first hole. This method is usually
adopted when a long straight run of duct is to be wired, the rods
being shoved into the next duct section as they are drawn out and
disconnected from the first section. If the ducts are in a straight
line across the manhole, the rods may often be passed into the
next section without disconnecting.

Obstructions in Ducts. — A completed conduit system should
always be tested for obstructions previous to its acceptance
from the contractor by drawing through each duct a test mandrel
about 24 in. in length and Y± in. less in diameter than the bore
of the duct.

Ordinary obstructions, such as pieces of cement or dirt, may
be removed by mounting a mandrel consisting of a piece of steel
pipe on the end of the first rod and drilling away the projecting
cement Sometimes obstructions are met which cannot be so

156 UNDERGROUND TRANSMISSION AND DISTRIBUTION

removed. These must be located by a measurement of the rods
pushed into the ducts until the trouble is reached, the street
opened at that point and the ducts repaired or replaced by new
sections.

Several forms of mandrels or duct cleaners have been used, but
attention is called to Fig. 64 which shows a flexible cleaner so
designed that, when drawn through the conduit, particles of
cement are broken off and removed from the duct. It is usual,
when cleaning ducts, to attach to the cleaner a swab or brush
of some sort to remove properly the loose particles from the duct
line.

FIG. 64. — Flexible duct cleaner.

Drawing in Cables. — Before drawing the cable into the duct
the ends should be examined to see that they are perfect. A wire-
pulling grip of some form is then drawn through the cable end.
To the end of this grip is next fastened a flexible steel or manila
pulling-rope, which in the meantime has been drawn through the
duct ready for pulling. Proper cable protectors are placed in
the mouth of the duct. These protectors are usually made of
leather and placed in the end of the duct to prevent damage to
the sheath. The cable from the top of the reel should enter the
mouth of the duct by a curve of large radius, Fig. 65, without
touching at any intermediate point. The pulling can be done
by capstan, winch, motor truck, horses, or, in the case of a
small cable, by hand. When guiding the cable into the duct, a
small amount of common grease should be spread on the cable
so as to allow it to slide more easily and lessen the strain on the
cable. Enough extra cable should be drawn into the manhole
to provide for racking around the manhole and the making of
joints. During the installation, no cable should be bent sharper

INSTALLATION OF CABLES

157

than to a radius equal to ten diameters of the cable. If it is not
intended to joint the cables as soon as they are drawn in, the caps
or seals should be examined to see that they are safe before leav-
ing the work. The cable should be protected at the edge of the
duct, and should not be left hanging loosely or lying on the bottom
of the manhole, but should be placed on the racks provided for it.
Paper-insulated cables should not be installed at temperatures
below 40°F. without first warming them up by charcoal fires, or
other means, so as to make them more flexible and avoid any
possibility of cracking the insulation. Also when cables are being
racked around the manhole wall they should be thoroughly
warmed if the temperature is low. Before jointing, the ends
should be cut back far enough to positively insure against the
presence of moisture. No matter how excellent a cable the

FIG. 65. — Setting up cable reel.

manufacturer may produce, if it is not carefully installed and
properly cared for thereafter, it will inevitably fail, and it is,
therefore, necessary that the work be done by experienced and
reliable workmen. It will generally be found more satisfactory
for a small company to have its cables installed by the manu-
facturer. A large company, however, frequently finds it cheaper
to install its own cables. All large-sized cables should be ordered
in exact lengths, making the proper allowance for training in
manholes and necessary waste.

Cable-pulling Grips. — Many devices for fastening the cable
and draw rope together have been used and abandoned as un-
reliable. Where the ducts are dry, a good serviceable grip is
obtained by punching two holes through the center of the cable
from side to side, the holes being spaced about 3 in. away from
each side of the cable end. A No. 10 or No. 12 B.W.G. steel

158 UNDERGROUND TRANSMISSION AND DISTRIBUTION

wire is then passed several times through the eye of the rope
and the holes in the cable, and the ends of the wire are twisted
firmly together. This method is not recommended where there
is any danger of water in the ducts, as the water is certain to
enter the cable through the holes; and in case of paper cable,
to penetrate so far that the ends often cannot be cut back far
enough to clear the trouble thus introduced. A better form of
grip, and the one which is used almost universally to-day is shown
in Fig. 66 A.

FIG. 66. — Wire-cable grips.

A block of wood about 3 in. wide is placed against the end of
the cable, and steel wire of No. 10 or No. 12 B.W.G. cut in
6-ft. lengths is then bent in the middle of the wood block and
wrapped around the cable sheath in opposite directions, the
number of wires required depending on the severity of the pull.
When the pull of the rope comes on these wires, they bind harder
on each other, on the lead, the insulation, and the conductors,
as the pull grows harder, and the strain is equally distributed.

INSTALLATION OF CABLES

159

With this type of grip, the seal on the lead of the cable is not
broken and no water can, therefore, get into the insulation. A
form of basket-wire grip which has been used to good advantage
is illustrated in Fig. 66, B, D, E.

Where a section of cable is to be installed in a duct of a bore
only slightly larger than the diameter of the cable, the ordinary
woven-wire cable grip often fails, the reason for its failure being
that the diameter of the cable is increased by the wire of the
grip leaving insufficient clearance. The excessive strain, more-
over, has a tendency to strip the lead sheath from the cable.

FIG. 67. — Construction of a cable grip suitable for pulling cables up to
2^ inches outside diameter.

Considerable thought has been given to the various methods
utilized in fastening the pulling-rope to the cable ends when large-
sized cable is to be pulled into a duct line. A very satisfactory
method is to use what is known as a cable eye. This cable eye
is made of round steel about % in. in diameter, and an eyelet,
approximately 1^ in. in size turned on one end. The proper
procedure to be followed in fastening this eyelet to the
cable is to strip back the lead sheath 6 or 8 in., remove the
insulation from the conductors, then place the eyelet between the
conductors and wind them securely around it and solder them
fast. Next the portion of the lead sheath, which was stripped
back, is moulded around the conductors and eyelet, the whole

160 UNDERGROUND TRANSMISSION AND DISTRIBUTION

soldered and sealed so that it is waterproof. In using this eyelet
all the strain is placed on the conductors and there is no danger
of moisture entering the cable during the process of installation
due to damaged ends or improper seals.

What may be termed a "basket grip" is described in the
Electrical World, March 25, 1916. This grip may be cast of iron
or phosphor bronze. The grip illustrated in Fig. 67 is suitable
for pulling cables having an outside diameter up to 2% in.
About 4 in. of the lead and insulation is cut away from the end
of the cable and the bare conductors are tinned and pushed
up through the basket. The conductors are then spread in the
upper part of the basket, which is tapered to accommodate this
process and molten solder is poured over the spread conductors.
After the solder has cooled, the hooks attached to the pulling-
rope are passed through the loop of the basket, and the cable
can then be drawn through the ducts. However, if the duct is
wet or muddy, it is best to prevent water getting into the cable
end by winding a good quality of rubber-filled tape around the
lower end of the basket and the adjacent lead sheath of the
cable.

If the cable to be installed is single-conductor instead of multi-
conductor, the basket grip is equally adaptable. The method
of procedure is similar to the above, and the cable can be pre-
vented from slipping out of the basket by spreading the individual
strands of the conductor.

Draw Rope. — For general purposes a manila rope of best
quality and from % to 1J^ in. in diameter will be found most
satisfactory for pulling in cables. A steel hoisting rope is some-
times used, but it deteriorates rapidly from rust and hard usage
on the street unless protected by some form of covering. What-
ever style of rope is used, the ends should be provided with an
"eye" around a steel thimble fastened to a short length of chain
provided with a swivel at the end. In very hard pulls any rope
tends to untwist, and unless a swivel is inserted between the rope
and cable, this twist will be imparted to the cable itself and may
injure the lead or the conductors. It is advisable to terminate
the swivel with a pair of sister-hooks, Fig. 68. These are readily
inserted in the loop of the wire grip on the cable and prevented
from opening by several wraps of wire.

What is known as a "durable steel-stranded" rope is used by
a number of companies for pulling in cable. The rope is made up

INSTALLATION OF CABLES

161

with a flexible core and the strands are covered with specially
prepared braided hemp, which binds the strands together forming
a cushion between strands and protecting the rope from wear.
The rope is rustproof and will outwear a number of coils of
ordinary manila rope. The ^-in. size replaces the ordinary
IJ^-in. manila rope. It is especially desirable when power-
driven winches are used.

Drawing Apparatus. — If the cable is light and short, it may be
pulled in by hand, but usually some apparatus will be found
necessary to secure sufficient power.

Horses are sometimes used to
haul in the cable by hitching them
directly to the cable rope which
passes from the manhole over
snatch blocks or sheaves. This
method is undesirable as it is im-
possible to stop horses instantly in
case of an accident to the reel or
to the cable at the mouth of the
duct, or in case of meeting other
unforeseen obstructions; and serious
damage to the cable is liable to
ensue.

In some cities where great quan-
tities of cable are installed yearly,
winches as shown in Fig. 69 run by
electricity or gasoline engines
mounted on a wagon, are used for
pulling in the cables, but this de-
vice is too expensive in the first
cost and maintenance for profitable use unless large quantities
of cable are handled regularly.

For drawing in underground cables, in many locations a small
ship's capstan mounted on a stout framework fastened to the
pavement has been used. The frame on which the capstan is
fastened is provided with wheels easily removable to facilitate
moving the apparatus from place to place. The draw rope is
led over pulleys from the duct in the manhole to the capstan on
the street and is wrapped several times around the drum to give
the required purchase. The power is furnished by men in the
regular way.
11

FIG. 68.— Sister hooks.

162 UNDERGROUND TRANSMISSION AND DISTRIBUTION

In some locations manholes are so near car tracks or other
obstacles that there is not sufficient space for either form of
capstan with the projecting handle bars. In such cases a winch,

FIG. 69. — Electric motor-driven winch.

Fig. 70, mounted on a strong framework is most convenient.
The framework is placed directly over the manhole opening and
the rope is led from the duct through a snatch block directly to
the drum of the winch, the power being applied by two cranks

FIG. 70. — Hand winch.

(revolving handles) one on each side of the drum and directly
opposite each other, so placed that when one crank is down the
other is up. The snatch block in the manhole may be fastened

INSTALLATION OF CABLES

163

in place by attaching it to eye-bolts built into the walls or by
suitable blocking.

When constructing manholes, it is advisable to provide facili-
ties for drawing cables through ducts so that special guide sup-
ports do not have to be used. The accompanying illustration,
Fig. 71, shows how manholes may be equipped for this purpose.
In the wall opposite and about 12 in. below each duct entrance
is an eye-bolt which extends through the wall and is bent over
on the end to bear on an iron plate which reduces the unit pressure

FIG. 71. — Diagram showing equipment of manhole to facilitate cable

installation.

on the manhole wall. This eye-bolt may be employed to support
a guide block during the usual installation of a cable, or it may
be connected to a block and tackle when it is necessary to draw
a cable into place for splicing in cases where sufficient length has
not been left for this operation.

A flexible arrangement of the pulleys may be secured by means
of two steel channels or guide sheaves of such length as to reach
from the bottom of the manhole to a point about 3 ft. above
the surface of the ground. The channels are provided with
holes every few inches along the entire length, through which
heavy steel [pins secured by cotter pins may be placed, thus

164 UNDERGROUND TRANSMISSION AND DISTRIBUTION

providing movable shafts for the pulleys, as shown in Fig. 72.
The lower pulley is placed opposite the duct and the rope leav-
ing the duct passes under this pulley up to and over the upper
pulley just above the street surface. The bottoms of the chan-

Hot.es

FIG. 72. — Guide sheave for cable pulling.

nels rest against the wall of the manhole and the tops against
the manhole cover frame.

Power Trucks. — In the 1916 report of the National Electric
Light Association Committee on Underground Construction,
under the heading, " Use of Power Trucks for Underground Work "
the following data is given. Of the 12 large operating companies

INSTALLATION OF CABLES 165

reporting, all use power trucks for their cable work. Nearly
all companies use electric trucks, but some use both electric and
gasoline engine-driven trucks.

The electric truck most suitable for underground work should
have a speed of 10 to 12 miles an hour, and designed to run at
least 35 miles on one charge.

In addition to the use for pulling in cable, the trucks are used
for hauling reels of cable to the jobs, delivering material, and for
emergency work. Specially designed bodies with compartments
for tools are very desirable, Fig. 73. Compartments may be
built along both sides of the truck to hold tools, fire extinguishers,
sand buckets, etc. A compartment for the records of the dis-

FIG. 73.— Cable truck.

tribution system may also be provided and so arranged that the
cover of the pocket forms a desk on which the records rest while
being used by the emergency man.

There are two methods of pulling in cable :

1. By means of pulleys set on I-beam uprights.

2. By means of a pulley or snatch block anchored in some
manner in the manhole.

In Fig. 74 is illustrated various ways of arranging the trucks
and cable-pulling apparatus which represents the practice of
several of the large electric companies.

When manholes are near car tracks, it is sometimes impossible
to use the I-beam upright method of pulling cable without inter-
fering with street-car traffic. For this reason it is a good plan

166 UNDERGROUND TRANSMISSION AND DISTRIBUTION

to have the truck equipped with facilities for pulling cable with
a rope leading from the rear or from the front. A New York
company has its trucks provided with facilities for pulling from
either side as well.

MILWAUKEE

NEWARK

BOSTON

DETROIT

Side or Ends

NEW YORK

SAN FRANCISCO

CHICAGO BROOKLYN

ALL TRUCKS ARE ELECTRIC UNLESS OTHEWISE SPECIFIED
MOTOR WINCH SHOWN SOUD

FIG. 74. — Methods of pulling cable.1

Some difficulty has been encountered in maintaining the I-
beam uprights in position when pulling heavy cable on account
of the enormous strain. In order to obviate this difficulty, a
Chicago company has devised an anchor with wing bolts that may
be adjusted to any manhole. This anchor holds the uprights in

1 N. E. L. A. Report, 1916.

INSTALLATION OF CABLES 167

position by a strain on the roof of the hole, as illustrated in the
figure.

When the rope is passed through the hole in the floor of the
truck, the strain on the truck as well as on the winch is downward
and very little difficulty is experienced in holding the winch to
its fastenings. When this method is used, the truck is placed
over the manhole, a position which takes up less working space
in the streets and eliminates the hazard of injuries to pedestrians
on account of an unprotected open manhole. It may be difficult
to design the truck so that the rope leading directly downward
through the trap door will not interfere with the battery or run-
ning gear. Having a rolling spool for the rope on the side of the
truck and an eye-bolt for a snatch block in the center of the
floor, a method which a New York company uses, accom-
plishes the same results as the trap-door method without intro-
ducing its objectionable features. To prevent accident, cable-
pulling winches which are motor-driven should have all of the
gears or movable parts covered with guards.

It is recommended that trucks for underground work be
wired with socket for an extension cord to both the front and the
rear of the truck. This will greatly facilitate locating trouble
at night. For splicing cable at night, however, a portable
storage battery outfit is more suitable and efficient. The use of
an outfit of this kind eliminates the hazard encountered by the
use of candles or lanterns in gassy manholes, besides providing
the light necessary for good jointing work.

Most central stations have provided charging stations for
electric vehicles throughout their territory. Where the territory
is not too great, one central charging station is adequate for a
truck that will make 35 miles on one charge. A boosting charge
during the noon hour, however, is recommended where the
facilities are at hand.

Slack. — Enough slack must be left in each manhole to enable
the cables to pass around the sides, to make and place the joints
on the wall supports and to keep the center of the hole free from
cables. When extra slack is needed, employ a short rope with
one end frayed for 5 or 6 ft. and wrap the soft end spirally
around the cable near the duct so as to obtain a tight grip with-
out denting or kinking the cable. Pass the rope around the
capstan or winch and draw the cable out until the fastening
reaches the drum or block, slip the hitch back to the duct and

168 UNDERGROUND TRANSMISSION AND DISTRIBUTION

repeat the operation until sufficient cable has been secured.
Always determine the location of the splice in the manhole and
provide the foreman of the drawing-in gang with a diagram and
list showing exactly how much cable should project from the
duct into the manhole at each end of each section.

After a cable has been drawn in, an experienced workman
should examine the ends to see if the solder seal is intact or, if
broken, whether any moisture is present. If moisture is dis-
cernible, boil it out thoroughly or (if enough stock is available)
cut back the cable until all dampness is removed; and in all cases
leave the end carefully soldered up.

The cable should be protected at the edge of the duct, and it
should not be left hanging loosely or lying on the bottom of
the manhole, but should be placed on the racks provided for it.
If the cables have paper insulation and the temperature is below
40°F., they should be warmed by torch or other means, so as to
make them more flexible and avoid any possibility of cracking the
insulation when the cables are being racked around the manhole
walls.

Jointing of Cables. — It is generally admitted that the greater
part of cable trouble is due to poorly made joints or to the
presence of moisture or cracks in the insulation near the joints.
With good material and careful and competent workmen, the
insulation of the joint can be made as reliable and as durable
as that of any part of the cable. The construction of a joint
is, therefore, of prime importance, and unless the engineer has
at his command experienced and thoroughly reliable cable work-
men, he would do well to contract with the manufacturers, who
have every facility for doing this class of work, for the complete
installation of the cable.

In the making of a perfect joint, the following points are
especially worthy of comment and caution :

(a) The work should be done by reliable and experienced
cablemen.

(6) High-grade insulating materials should be carefully chosen
to suit the special conditions.

(d) The layers of insulating tape should be made to overlap
each other and should be drawn tight to exclude air.

INSTALLATION OF CABLES

169

(e) The sleeve should be well-filled with suitable compound
which should be sufficiently hot before pouring.

(/) The joint should be in proportion to the size of the conduc-
tor, and the insulation on the joint should be at least 20 per cent.

LEAD SLEEVE

COMPOUND

LEAD '/^LATION |
SHEATH/ i/

INT INSULATION
COPPER SLEEVE

OPENING FOR COMPOUND
/ (| WIPED JOINT

Straight-way single-conductor cable joint.

Single-conductor Y-shape branch joint.

Single-conductor right-angle branch joint.

Two-parallel-conductor branch joint.

FIG. 75. — Various types of cable-joint construction.

thicker than on the cable itself. Fig. 75 illustrates various types
of joint construction.

While not a part of joint making, it is perhaps well to say a
few words regarding the training of cables in manholes. Great
care should be exercised in bending cables into position. Sharp

170 UNDERGROUND TRANSMISSION AND DISTRIBUTION

Two-right-angle conductor branch joint.

Straight-way three-conductor cable joint.

Three-conductor right-angle branch joint.

Insulated single-conductor cable connection to a bare cable.

FIG. 75.— (Continued.)

INSTALLATION OF CABLES 171

bends in high-voltage cables should be avoided, and the cable
should never be bent against the edge of the duct but should be
shaped around a form to avoid abrading the lead. It should be
the duty of the jointer to see that protectors of some sort are left
under the cable at the edge of the duct to act as a cushion . Care-
lessness in observing the above precautions is frequently the
cause of considerable trouble.

GENERAL DIRECTIONS FOR MAKING JOINTS ON LEAD-
COVERED CABLES

The cables are usually left by the pulling-in gang without very
much reference to final arrangement, and it should be the jointer's
first duty to inspect the cable thoroughly from the edge of the
duct to the sealed end in order to discover any mechanical injury
or intrusion of moisture. Where there are several cables to be
jointed in one hole, care must be exercised that the corresponding
incoming and outgoing sections are spliced together. Absurd
as it may seem, such mistakes are sometimes made. After plac-
ing protectors in the mouth of the ducts, the cables should be
neatly bent and stored around the sides of the manhole and the
ends brought into position for jointing at the designated point
which should always be such that the joint, when finished, will
be between two supports or hangers so that there will be no
strain on the joint itself when completed and stowed away.

When the ends of the cables have been allowed to lie for any
length of time in manholes where there is water, a very slight
imperfection in the soldered end will admit more or less moisture
to the insulation. A careful examination should always be made,
and if any moisture is evident, the cable should be cut back a
little at a time until all evidence of moisture disappears, care
being taken not to cut back so far as to render it too short to
make the joint. When no more cable can be cut off and moisture
is still present, as shown by bubbles when the cable is dipped into
hot insulating compound, apply heat to the lead cover of the cable,
beginning at the point nearest the duct and very slowly approach-
ing the end of the cable, the object being to drive all moisture to
the open end. Wherever it is allowable, a furnace or gasoline
torch may be used for this purpose; and if the cable is covered
with saturated fiber, a metal screen should be interposed between
the flame and the cable to prevent ignition of the fiber. If the

172 UNDERGROUND TRANSMISSION AND DISTRIBUTION

use of a furnace or torch is forbidden, or it is unsafe on account
of the presence of gas, the heating should be effected by pouring
very hot insulating compound over the cable, catching it in a
vessel held underneath. Where there is still doubt as to freedom
from moisture, it is best to make a careful insulation test before
the joint is made. This test may indicate the necessity of re-
placing the cable section. Never cut off the second section until
sure that there is no moisture in the first. There will thus be an
opportunity to change the location of the splice in case tjje other
end must be cut back for moisture.

SCORING THE LEAD

When the cables are placed in position and ready for joint,
the ends should be marked at the point to which the lead is to
be removed, and scored or cut entirely around. This cutting is
easily and accurately accomplished by means of a tool which
works on the principle of an ordinary pipe cutter.

REMOVING THE LEAD

The lead sheath is then cut lengthwise of the cable from the
circular score to the end by the chipping knife, and the piece of
lead is removed with a pair of pliers. In making the longitudinal
cut which goes entirely through the lead, great care must be
exercised not to injure the insulation. The knife should be held
at such an angle that it will go through the lead tangent to the
insulation (i.e., so that the knife will pass between the insulation
and the lead and not cut the insulation) , or a special tool may be
used.

After the lead has been removed, the parts where the lead was
scored should be carefully examined and all sharp edges or pro-
jections, which might tend to penetrate the insulation of the cable,
should be removed by a knife, or the lead should be slightly
belled out by some blunt instrument such as the end of a pair of
pliers.

LEAD SLEEVE

When the lead covers of the two cable sections have been
thus treated, a lead sleeve, which will later be used in jointing,
is slipped over the more convenient end and pushed back out of
the way. The lead of this sleeve should be at least as thick as

INSTALLATION OF CABLES

173

the lead of the cable itself, and in view of its exposed position,
may (in the case of thin lead on the cable) be made somewhat
heavier to give greater mechanical strength.

Before slipping it on the cable, each end of the sleeve is
thoroughly scraped with a shave hook or knife for a length of
about 2 in., and the cleaned portion thoroughly smeared with
some suitable flux (usually a tallow candle), which, by prevent-
ing the formation of the usual film of lead salts, insures a close
union of the lead and the wiping metal which is used to make the
joint between sleeve and cable sheath. The internal diameter
of the sleeve should exceed the diameter over the lead of the cable
by y% in. in the case of single-conductor cables, and by 1 to 1J^
in. in the case of multi-conductor cables, or cables for high voltage
where high insulation of the splice and maximum separation
between the conductors and lead are necessary. The following
Table XXIV is somewhat more liberal in allowances for clearance
between inside of sleeve and outside of cable, but it is fairly
representative of average practice in this respect, as well as in
the sleeve lengths.

TABLE XXIV. — APPROXIMATE DATA AS TO LEAD SLEEVES, WEIGHTS OP
SOLDER AND SPLICING COMPOUND FOR STRAIGHT JOINTS (Two-WAY)1

Outside diam.
of cable, mils

Inside diam
sleeve, in.

Length of
sleeve, in.

Ozite per
joint, gal.

Wiping sol-
der per
joint, Ib.

•

Single conductor E. L. &

Up to 550

0.05

0.9

P., up to 6,600 volts. .

551— 950

0.10

1.7

951—1,350

0.20

2.8

1,351—1,750

0.30

4.2

1,751—2,150

0.50

5.5

2,151—2,550

0.60

6.8

Single conductor E. L. &

Up to 550

0.05

0.9

P., above 6,600 volts. .

551— 950

0.10

1.7

951—1,350

0.20

2.8

1,351—1,750

0.40

4.2

1,751 — 2,150

0.60

5.5

2,151—2,550

0.80

6.8

Multi-conductor E. L. &

Up to 800

0.20

1.5

P , all voltages

801 — 1,200

0.25

2.5

1,201—1,600

0.35

3.7

1,601—2,000

0.60

5.0

2,001—2,400

0.80

6.3

2,401—2,800

1.00

7.6

2,801—3,200

1.40

8.3

Standard Underground Cable Co.

174 UNDERGROUND TRANSMISSION AND DISTRIBUTION

COPPER CONNECTORS

One of the important features to be considered in the making
of joints, as already mentioned, is in the choice of proper copper
jointing sleeves. They should be made in suitable lengths for
regular underground joints, tinned and well-finished. They are
usually provided with an opening along the entire length so as
to permit of the solder flowing freely throughout the joint when
made, thus insuring a good soldered union. Both ends of the
sleeve should be beveled off, to remove sharp edges which would
have a tendency to cause a puncture through the insulation after
the joint has been finished. Table XXV gives the A. S. & W.
Co. standard dimensions of copper sleeves for jointing cables.

TABLE XXV. — STANDARD DIMENSIONS OP COPPER SLEEVES FOR JOINTING

CABLES1

Size of
conductor

Outside
diameter of
Conductor, in.

Outside
diameter of
sleeve, in.

Thickness
of copper, in.

Length of
sleeve, in.

Weight per
100 sleeves, Ib.

2,000,000

1.6302

2.168

0.268

6.00

280

1,750,000

1.5246

2.027

0.251

5.65

242

1,500,000

1.4124

1.879

0.233

5.30

200

1,250,000

1.2892

1.715

0.212

4.90

150

1,000,000

1.1520

1.532

0.190

4.45

110

900,000

1.0935

1.454

0.180

4.25

800,000

1.0305

1.360

0.170

4.05

750,000

0.9981

1.327

0.162

3.95

700,000

0.9639

1.282

0.159

3.80

600,000

0.8928

1.187

0.147

3.60

500,000

0.8134

1.082

0.134

3.35

400,000

0.7280

0.968

0.120

2.10

300,000

0.6321

0.841

0.104

2.75

250,000

0 . 5754

0.766

0.095

2.60

0000

0.5275

0.702

0.087

2.45

000

0.4700

0.625

0.078

2.25

0.4180

0.556

0.068

2.10

0.3730

0.496

0.062

1.95

0.3315

0.441

0.055

.80

0.2919

0.388

0.048

.70

0.2601

0.347

0.043

.60

0.2316

0.308

0.038

.50

0.2061

0.275

0.034

.40

0.1836

0.244

0.030

.25

0.1635

0.218

0.027

.25

0.1455

0.194

0.024

.25

0.1305

0.172

0.022

.25

0.1155

0.154

0.020

.25

American Steel & Wire Co.

INSTALLATION OF CABLES 175

The removal of sharp projections of solder from the copper
connectors is of utmost importance in the case of high-voltage
cables where sharp points or edges act as discharge points to
induce puncture of the insulation.

INSULATING THE CONDUCTOR

After the conductors have been connected and soldered
together, they are thoroughly insulated with tape of the same
material as is used on the cable itself, and to a thickness some-
what greater than that of the cable insulation, as tape applied
by hand is never as compact and free from air spaces as when
put on by machinery. Where the insulation is thicker than the
copper connector, it should be tapered down with a sharp knife
to the same thickness as the connector so as to leave no abrupt
edges, and to allow the tapes, when applied, to run evenly from
connectors to insulation without ridges.

The insulated splice should be thoroughly boiled out with
hot insulating compound, which is usually heated in a large
pot, the ordinary plumber's gasoline furnace being used. The
compound should be of such a temperature as to throw off
moisture readily, and yet not hot enough to ignite a piece of
heavy paper dipped into it.

The determination of the proper temperature is a matter of
practice and is one of the many points in which an expert's
experience is of the utmost value.

A large pan held under the splice serves to catch the surplus
compound, which can be returned to the pot, reheated and used
again. A hot closed pot of compound should not be taken down
into a manhole unless it has first been opened on the surface of the
ground to ascertain that it is at the proper temperature. Paraf-
fine especially and, in a lesser degree, all insulating compounds,
when unduly heated, will ignite when poured on damp insulation,
and the result may be to destroy the cable and severely burn the
workman.

WIPED SOLDER JOINT

The lead sleeve previously slipped on the cable is now brought
into position so as to extend equally over the lead on each
cable end, and the ends of the sleeve are dressed down close to
the lead of the cable, care being exercised to have the lead sleeve

176 UNDERGROUND TRANSMISSION AND DISTRIBUTION

concentric with the cable. The sleeve and the cables are then
joined by a wiped solder joint.

FILLING THE SLEEVE

The joint is next filled with hot compound, except in the case
of rubber-insulated cables. Two holes are tapped in the sleeve,
hot insulation is poured slowly in one hole until it appears at the
other, and then in each hole alternately until the joint is com-
pletely filled.

If any moisture appears in the joint, as shown by frothing of
the insulation, the compound should be allowed to flow freely
out of one hole until all moisture is removed.

The joint should be allowed to cool for a suitable period
before moving it, and any shrinkage or settling of the insulation
should be compensated for by the addition of more compound.
This is a particularly important point in the splicing of high-
tension cables, and should be carefully watched.

Jointing Rubber-insulated Cables. — The splices on rubber-
insulated cables differ from splices on other forms of cable only
in the kind of tapes used.

The wire splice is made precisely as hereinbefore described.
This splice is then covered by a layer or layers of pure rubber
tape spirally applied to a thickness of Y§± to J^2 m- This is
covered by rubber-compound tapes applied spirally until a total
thickness slightly greater than the insulation of the cable is
secured. Over all is placed a layer of linen tape thoroughly im-
pregnated with rubber to render it adhesive. The lead joint is
then made in the regular manner, but is not filled with hot
compound. In some instances it is necessary to vulcanize thor-
oughly the rubber tapes so as to cure the rubber and render it
homogeneous, elastic and water-tight. This process should be
entrusted only to experts.

Jointing Armored Cables.— When lead-covered cables are
provided with steel-wire armor, a joint in the armor wires is
required in addition to the joint on the cable, the latter being
made in the regular manner. While making the lead-covered
joint, the armor wires should be bound by tie wire on either side,
and bent back out of the way. When the cable is spliced and
the lead joint completed, the cable should be protected with
wrappings of jute over the lead sleeve and the armor wires, from

INSTALLATION OF CABLES 177

one side, bent down and spaced uniformly over the sleeve. The
sleeve being larger than the original cable, there will be space
between the armor wires, and these are filled by the armor wires
from the other side of the joint, the two sets of wires being
thus interlaced. If there is not space enough between the wires
from one side for all the wires from the other, the surplus wires
are cut off short on one section and the corresponding wires on
the other section left long enough to butt against the short wires,
thus covering the joint completely and evenly with the armor
wires. Where the armor wires are thus placed, they are firmly
bound together by a tight serving of wires wound in a short
spiral around the entire length of the splice and carefully soldered
to the armor. A joint thus made will be mechanically as strong
as any other part of the cable.

As the durability of a joint is dependent upon the proper exe-
cution of what might seem to be the most minute details, a
description of some of the methods of making up joints on three-
conductor paper cables is printed herewith.

Paper and Cambric Tape-insulated Joints. — The ends of the
cable are prepared in the usual manner by stripping off the lead.
The paper insulation is trimmed away to expose the conductors.
Split copper sleeves are slipped over the conductors that are to
be joined and the sleeve is then sweated on with solder. No
acid should be used as a flux in soldering, as it is likely to injure
the insulation.

The insulation on the conductors on each side of the sleeve
should be cut down to a pencil point so as to allow the tape to be
built up evenly without butt joints. The best work that can
be done by hand will be considerably looser than the machine-
wrapped insulation on the main cable, and for that reason the
tape should be put on thicker than the original insulation. In
applying tape on cables used for voltages over 10,000, a suitable
compound should be applied with a brush to each layer of tape.
This will tend to prevent the formation of air cells which invari-
ably accompany the taping of a joint and which have been found
to impair seriously the insulation of a high- voltage joint. During
the progress of the wrapping, the insulation should be boiled out
thoroughly by pouring hot compound over the layers of tape to
exclude all moisture. Moisture from the hands of the splicer
may be sufficient to destroy an otherwise perfect joint.

After all conductors are thoroughly taped and boiled out, a

178 UNDERGROUND TRANSMISSION AND DISTRIBUTION

FIG. 76. — Steps in making three-conductor paper-insulated lead-covered

cable joint.

INSTALLATION OF CABLES 179

small roll of tape should be placed between the conductors to
separate them. An outer wrapping of tape should be applied,
which is drawn tight and wrapped until it is considerably larger
than the original insulation but not too large to permit the lead
sleeve to be placed over it. Numerous incisions are then made
in the outer wrapping in order to allow the compound to fill up
all the voids on the inside. Great care must be taken in punch-
ing these holes not to injure the insulation on the individual
conductors.

The lead sleeve which has previously been prepared and
placed over one of the cable ends, is now beaten into proper
form and placed evenly over the joint. The sleeve is then
soldered to the cable sheath with a regular wiped joint. The
wipes must be absolutely water-tight and should be carefully
inspected, especially on the underside of the joint, by means
of a small mirror to insure smoothness, solidity, and absence of
air holes. This is most important as the presence of small blow-
holes is known to have caused perhaps more trouble than any
other feature in joint making. The various steps in the making
of a three-conductor high-tension cable joint are fully illustrated
in Fig. 76.

For filling the joint, two holes are punched in the top of the
lead sleeve about 3 in. from each end, one to pour compound
through and the other to serve as an air vent. The compound
should be poured very hot and the pouring continued until the
compound overflows at the opposite end. After standing for
half an hour or more, the sleeve is refilled, after which the
openings in the sleeve are sealed by soldering a small lead patch
over each.

Paper-tube Joints. — The Standard Underground Cable Co.
recommend the following procedure for making high-voltage
paper-tube joints:

Cut off ends of cable square. Cut off lead on one cable at a
point approximately 6 in. back from end; and on the other cable
approximately 9 in. back from end. (CAUTION. — The longi-
tudinal cut in lead should be made by inserting cutting knife
tangential with the inside curve of the lead sheathing. Circum-
ferential cut should be made by nicking lead only part way
through and then tearing by pulling it apart with pliers.) Re-
move belt insulation to a point about 1J^ in. from edge of lead.
(CAUTION. — Inner layers of paper of belt should be torn rather

180 UNDERGROUND TRANSMISSION AND DISTRIBUTION

than cut, to prevent damaging insulation on individual con-
ductors.) Pull jute filler back and cut off at point close to end
of belt insulation. The individual conductors will now be found
to be about 3 in. longer on one cable than the other.

Strip individual conductors of insulation for a distance J^ in.
greater than one-half the length of the copper sleeve.

Thread lead sleeving over one of the abutting ends of cable and
move back out of the way. Thread large enclosing joint tube,
when used, back over cable end and back out of the way. Thread
the small jointing tubes over the ends of the long-length indi-
vidual conductors (i.e., the conductors on the cable and whose
lead sheathing was trimmed back 9 in.), and push back far enough
to leave copper ends of conductors easily accessible.

Tin conductors thoroughly with hot solder applied by ladle.
Insert ends of conductors intended to be connected together,
into the split copper connectors, which should preferably be of
such size that even when compressed upon the conductor, the
longitudinal split will remain open Jf g or %2 m- With split
in copper sleeve uppermost, apply hot solder with a ladle, and
when thoroughly heated, compress copper tube. Then sweat
tube and connectors thoroughly together, keeping joint as full
of solder as possible. Wipe off all fins or points before solder
sets. (CAUTION. — Do not file off fins or sharp points unless the
tubes and insulation of all the conductors are protected from
falling particles of metal. Do not move the sleeve or joint,
otherwise the solder, if it be at about the critical temperature
when mealiness appears, may not unite the parts satisfactorily.)

Fill space between end of copper sleeves and insulation on
each side with loosely woven and easily impregnated cotton
tape. (For previous preparation of cotton tape see below.)
Apply similar tape in layers over the copper connector to a
diameter equal to the diameter of the insulated conductor. Boil
out tape and adjacent cable ends carefully with insulating com-
pound at a temperature of about 375°F. (CAUTION. — As the
tape must have its moisture boiled out in case any is present,
and be thoroughly impregnated besides, nothing but very hot
compound will suffice.)

After all conductors have thus been connected, move each of
the splicing tubes back to cover thoroughly the completed joint
on the conductor. (CAUTION. — Proper position for splicing tube
is such that the middle of the tube shall be over the middle of

INSTALLATION OF CABLES 181

the copper sleeve, or so that the tube shall equally overlap the
original conductor insulation at each end.) Fasten each end of
a piece of dry cotton tape to the conductor at each side of and
bridging the tube, thus holding it permanently in place. Move
the enclosing or large splicing tube back over the smaller tubes
so that it occupies a middle position. Bind in place with tape
in a manner similar to that just described for individual conductors.
(CAUTION. — Do not put wrappings of any sort — either paper,
linen or rubber — over the tubes, as this prevents the proper
ingress of filling compound into the interstices between tubes and
conductors, and between inner and outer tubes, a condition abso-
lutely essential to complete success in a joint of this type.)

Move lead sleeving back into proper position, i.e., so that at
each end it overlaps equally the lead sheathing of the abutting
cables. Dress down ends of sleeves to fit neatly around cable
sheathing. Wipe joint carefully with edges of the wipe at least
% in. back from the line at which the lead sheathing and the lead
sleeving meet. Make two holes, one at each end and on top of
the lead sleeving. One of these is for admission of the hot com-
pound, the other for its overflow. These holes should be of V--
shaped form, and the one selected for filling should be preferably
on the end farthest away from the paper tubes, and so located
that the stream of hot filling compound will strike the paper-belt
insulation of the jointed cable. Tilt the joint slightly so that
the filling hole will be slightly above the level of the other hole.
Pour in filling compound heated to a temperature of from 325°.
to 350°F. until it issues from the other hole; and if bubbles appear,
indicating moisture in the joint, continue pouring at upper hole
and emptying through lower hole until every evidence of mois-
ture disappears. After allowing to settle for % or % hr., pour
in additional compound, after which seal both holes carefully
with solder. (CAUTION. — A heavy soldering iron properly
heated must be used to insure adhesion of plenty of solder around
the opening.)

The illustration shown in Fig. 77 indicates the various steps in
the making of a tube joint as just described.

Advantages of Paper-tube Joint. — The following points of
superiority are claimed for the above type of joint:

(a) Absolute certainty of proper insulation and separation
between conductors and between conductors and lead, the judg-
ment of the workmen as to these points being entirely eliminated.

182 UNDERGROUND TRANSMISSION AND DISTRIBUTION

(b) Freedom from moisture, the tubes being thoroughly im-
pregnated with insulation at the factory by immersion in hot
compound.

(c) Freedom from air spaces. The fact that there are no con-
volutions of tape to be penetrated by the compound used in
filling the sleeve, makes it certain that the entire joint will be
thoroughly filled.

INSTALLATION OF CABLES

183

(d) Ease of application, with consequent saving in labor and
expense.

Sleeve -filling Material. — There seems to be a general impres-
sion among cable users who have not carefully investigated the
matter, that almost any compound is good enough for a cable
joint. Paraffine has met with general favor in spite of its inher-
ent disadvantages. Some of the properties which are considered
desirable for a good jointing compound are:

1. High melting point.

2. Adhesiveness.

3. Not brittle at ordinary temperatures.

4. Resists high-puncture tests.

5. Low coefficient of contraction.

FIG. 78. — Sections of high-voltage cable joints filled with different com-
pounds.

Some of the objections to the use of paraffine are: It does not
have the property of sticking tightly to smooth surfaces. It
becomes extremely fluid at about 125° or 130°F. At the time of
cooling, paraffine has an excessive contraction coefficient which
results frequently in voids which have a dielectric strength lower
than ordinary atmospheric air.

There are cases where very good results have been secured with
compounds of an inferior grade but this constitutes no argument
in favor of the reduction of the factor of safety through the use
of such inferior compounds since the unfavorable conditions for
jointing and operating underground cables almost everywhere
existent in cities imperatively demand the use of the best com-
pound available.

184 UNDERGROUND TRANSMISSION AND DISTRIBUTION

In Fig. 78 are illustrated sections of actual test joints on high-
voltage cables. A and D are joints filled with high-grade com-
pound; B and C with inferior compound offered for similar use.
A and B were exposed to a temperature of 110°F. for 2 hr.;
C and D to a temperature of 80° to 85°F. for 6 weeks. Note the
way the high-grade compound held its place in the sleeve, al-
though it remained soft and rubbery to the touch and showed no
signs of brittleness. The other compound, soft enough to almost
empty the sleeve, was so brittle that at 85°F. a slight blow with
a lead pencil broke the streamers into fragments.

Breakdowns solely attributable to the use of inferior insulat-
ing compounds or to good compounds which are ill adapted to

FIG. 79. — Viscosity test of cable-sleeve-filling compounds.

the conditions under which they are being used, are of frequent
occurrence.

A high coefficient of expansion is indeed somewhat objection-
able, but a moderate one must be accepted as unavoidable, if
the other desirable characteristics of a good insulating compound
are to be obtained in anything like a satisfactory degree.

The necessity for having compound which will keep its place
in the joint cannot be overemphasized. In many manholes
the joints are somewhat higher than the cables themselves, and
where compounds with too light a base are used, there is almost
always danger of the compound slowly moving away from the
joint into the abutting cable end, it being a peculiar character-
istic of some of these compounds that they flow no matter what
the temperature is. In such joints, even when they appear very
hard and brittle, the compound will be capable of flowing out

INSTALLATION OF CABLES

185

of extremely small openings, the rate of flow being dependent
upon the pressure and temperature. This is well illustrated in
Fig. 79, which shows one compound flowing, even though it
is hard and brittle, the other compound retaining its elasticity
to a large degree and showing almost no sign of movement.

There is an additional reason, however, particularly in high-
voltage cable, for keeping the joint full of compound. If any-
one will take the trouble to experiment with a copper conductor
surrounded with thin layers of insulating material and over which
is a thin metallic sheath, he will discover that when various vol-
tages are applied (starting with say 1,500 volts) between the con-

CONDUCTOf?

SHEATH

WWWWVWVVWW1

AAAAAAA

FIG. 80.— Electrical discharge between insulation and conductor of a *

cable.

ductor and sheath, there will appear, when the experiment is
made in a sufficiently dark room, an electric discharge accom-
panied by a glow of light, where the metallic sheathing comes
into contact with the cable insulation (see Fig. 80). This elec-
trical discharge is of the corona or brush type, and with it there is
given off a considerable quantity of ozone, dependent in amount,
among other things, upon the thickness of insulation which
separates the conductor and the sheath, and upon the voltage
applied. Now this ozone is being produced in a manner very
similar to that which has been adopted so extensively during the
last few years for sterilizing water by oxidation of its vegetable
and animal impurities. Its effect upon vegetable insulating
material, such as paper, fiber, varnished cloth, rubber, etc., is
very deleterious, and ultimate destruction of the insulation
almost invariably ensues where it is exposed to the action of

186 UNDERGROUND TRANSMISSION AND DISTRIBUTION

newly produced or nascent ozone for any considerable time. So
long as the edge of the sheath and the neighboring wall of cable
insulation are thoroughly covered by insulating compound, so
that air is excluded, there will be little or no deterioration of
the insulation at these points.

Jnsu/at/ng 5/eeve
/nclos/ng Ce//s

fitting
Compound

Interlocking Ce//
Partition.

FIG. 81. — Conducell cable-joint insulators.

Conducell Cable-joint Insulators. — There has lately been
placed on the market a new design of insulating form for use in
making cable joints. These forms are made of thin sheets of
mica, cemented together and made up over an iron form.
The insulators for the individual conductors are so made as to fit

FIG. 82. — Cable joint made with Conducell insulators.

into one another, as illustrated in Fig. 81, giving a round outer
surface, over which the outer cylindrical sleeve is slipped. A
porcelain spacer at each end holds the separators symmetrically
about the three conductors and centrally in the lead sleeve,
Fig. 82.

INSTALLATION OF CABLES

187

The advantages claimed for this construction are:

1, It is not necessary to cut the insulation back so far as when
tubes or hand wrapping are used, as the forms do not have to
be slipped back on the conductors but can be put into position
from the side after the conductors are jointed.

2. The conductors do not have to be bent as much as when
hand- wrapped. This bending is apt to crack the paper near the
edge of the belt.

30 40 50 60 70 80 90 100 110 120 130 Cent.
68 86 104 122 140 158 176 194 212 230 248 266 .Eahx,
Temperature

FIG. 83. — Hardness of Conduline compound and comparative dielectric

losses in cables.

3. The joint can be made up in about one-half the time
required to make a hand-wrapped joint.

4. The material used possesses very high dielectric properties
and does not absorb atmospheric moisture to any appreciable
extent.

Advantages 1 and 4 are peculiar to the joint material here
mentioned, while 2 and 3 would apply to any type of tube
joint.

For the filling of these joints, a compound has been developed
which is especially suited to the purpose.

The curve, Fig. 83, illustrates the properties claimed for the
filling compound mentioned.

188 UNDERGROUND TRANSMISSION AND DISTRIBUTION
The mica forms are supplied in three different grades:

4-in., No. 209 for use on from 2,000 to 9,000 volts.
4-in., No. 1,014 for use on from 10,000 to 14,000 volts.
5-in., No. 1,525 for use on from 15,000 to 25,000 volts.

Laboratory tests indicate that joints made up with the No.
1,014 material break down at from 90,000 to 100,000 volts be-
tween conductors. On other tests, joints heated to 70°C. stood
50,000 volts 2 hr. or more after a 14-hr, preliminary run at
50,000 volts at room temperature.

In none of these tests did the breakdown occur in the joint
proper, but all were in the cable beyond the joint, usually under
or beyond the wipe.

Several companies have these joints in service on 8,000- and
15,000-volt circuits without failure and have adopted the material
as standard construction on emergency work because of the
reduced time required to return feeders to service.

High-voltage Vacuum Joint. — The tendency toward centraliza-
tion of power generation has recently necessitated the operation
of underground cables at considerably increased transmission
voltages.

While the cable itself is so designed as to operate satisfactorily
at high voltages, a great deal of trouble has been experienced
due to breakdowns in the cable joints. The joints employed
when cables were first used to transmit at voltages higher than
13,000 to 15,000 were of essentially the same type of construction
as the joints which had been in general use and which had given
satisfactory service at the lower voltages.

Experience has shown, however, that joints as ordinarily con-
structed frequently fail at operating voltages in excess of 15,000.

A series of high-voltage tests made by a large operating com-
pany on joints using various types of compound failed to give
uniform and satisfactory results. Paraffine compounds shrink
during cooling and leave voids in the joint space. High-melting-
point gum compounds, because of their viscosity, do not com-
pletely fill the crevices and have the additional disadvantage
that short-circuit conditions develop cracks in the compound
which are not self-healing.

These disadvantages are not serious enough to cause much
trouble at lower voltages, but under high-voltage stresses the
danger of joint breakdowns is greatly increased.

INSTALLATION OF CABLES 189

Experiments have been made on a joint insulated with liquid
fillers, such as rosin or mineral oil, which are fluid at low tempera-
tures. These joints gave uniformly good results, but some diffi-
culty was experienced from the leaking of the oil from the joint
space along the cables. This difficulty was overcome after con-
siderable experimenting; and a very satisfactory high-voltage
joint has been designed and patented by Mr. Philip Torchio,
chief electrical engineer of the New York Edison Co.

In making this joint the cutting of the insulation and the
application of new insulation conforms to a special gage which
is part of the cable-splicers' equipment. The lead sheath is
stripped off in the usual way preparatory to jointing. After
the conductors are soldered, all metal points and burrs are re-
moved by filing and with emery cloth, and the space between the
conductors is thoroughly cleansed of all particles of emery and
copper. A liberal application of compound is given to the con-
ductor to be insulated, and impregnated-paper tape % in. wide
and 3 mils thick is wrapped tightly around it. Each layer of tape
receives an application of compound before the next is applied
and each turn of the tape is drawn tight so as to squeeze out any
air bubbles which might collect in the space between the layers.
The hand-applied insulation at its thickest point is about one and
one-quarter times that of the mill-applied insulation.

After each of the three conductors has received its applied
insulation, the space between the conductors is filled with com-
pound, and strips of jute, laid parallel to the conductors, are
packed into the space so as to completely fill it; and the whole is
then saturated with compound. The belt insulation of impreg-
nated-paper tape, 1 in. wide and 6 mils thick, is next applied, and
the same general method of application is adhered to as was used
in insulating the individual conductors, so as to eliminate pockets
and voids.

The finished belt is pierced in six places with the idea of facili-
tating the removal of air and complete impregnation with the
compound, and is encased in a metal sleeve, made of 30-mesh No.
30 copper wire gauze, which covers the joint and extends about
% in. under the belled ends of the lead sheath. The metal sleeve
is drawn tight so as to bear evenly on all parts of the splice, and
the belled ends of the sheath are beaten down and soldered to the
gauze.

The use of this metal sleeve is important in that it establishes

190 UNDERGROUND TRANSMISSION AND DISTRIBUTION

•33f2g

a 08 5 » »

03 _.^ B C

I It si

!l!l!
ilfll

INSTALLATION OF CABLES 191

permanently the potential gradient between the inner conductors
and ground regardless of the dielectric material in the annular
space between the sleeve and the sheath.

Over the gauze sleeve is wound a cotton wick, 1 J^ in. wide and
about %2 in. thick. The middle of the splice is covered by only

FIG. 85. — Connections of apparatus for creating vacuum in joint and filling

with compound.

At the upper-left-hand corner of the illustration is a reservoir and kerosene furnace for
heating compound, to 275°F. Attached to the reservoir is a thermometer with a
range of 50 deg. to 450°F. and a gage glass for indicating the height 9f compound
in the tank. At the right is a 3-in. by 3.5-in. vacuum pump which is belt-driven by a 90-
volt 0.5 hp. motor. Attached to the right-hand end of the cable-joint sleeve is a suction
chamber equipped with a vacuum gage. This chamber is connected with the pump by a
0.5-in. flexible spiral-metal hose capable of withstanding more than 29-in. vacuum. The
hose between the compound reservoir and the left-hand end of the splice is 1 in. in diameter.
Valves Nos. 1, 2 and 3 are Lunkenheimer quick-acting lever-type and valves Nos. 4, 5, 6
and 7 are two-way straight pet cocks.

one layer, but at the ends the covering is several layers thick, and
when the wick is saturated with compound, these end layers
act as a reservoir which supplies the center layer with compound
by capillary attraction, thus keeping the splice saturated at

192 UNDERGROUND TRANSMISSION AND DISTRIBUTION

all times. The joint is then filled with compound under high-
vacuum conditions. The various steps in making this joint are
shown in Fig. 84.

FIG. 86. — Joint-filling apparatus mounted on electric vehicle.

Fia. 87. — Apparatus supplying compound to compensate for absorption

by cable.

Fig. 85 illustrates an assembly of the apparatus necessary for
filling and sealing the joint; and the illustration in Fig. 86 shows

INSTALLATION OF CABLES 193

the vacuum machine in use on an electric truck. When tests
show that there are no leaks in the connections or joints and at
least 27 in. of vacuum is obtained, the pumping is continued for
about 15 min. to increase the vacuum to 28 in. or more. Then
the compound is allowed to flow in, after which the apparatus is
disconnected.

A pressure cup, Fig. 87, is connected to one of the splice plugs
and the compound is forced through until it overflows at the other
nipple, which is then capped. The cup is rilled up with compound,
the T-handle screwed out to its furthest position and the spring-
actuated piston forces compound into the joint space to compen-
sate for any contraction which may occur during cooling. The
pressure cup is left in place until the joint space is completely

FIG. 88. — Completed cable joint with apertures closed by plugs.

filled; the cup is then disconnected, the nipple capped, Fig. 88,
and the joint is ready for operation.

This method of joint construction has been used on three
25,000-volt feeders of the United Electric Light & Power Co. for
supplying power to the New Haven Railroad at the West Farms
Substation.

Unit Packages for Cable-Joint Material.1 — Considerable advan-
tage may be gained in putting the material for cable joints in
unit packages. One company has used this method in the con-
struction of joints for three-conductor, 350,000-cm., sector-type,
25,000-volt cable feeders. Reference to the special construction
of this type of joint is made in another part of this chapter, but
it may be stated here that each joint was made to a template and
the necessary material was delivered on the job in cans or pack-
ages, Fig. 89, two cans being used, one for the filling compound
and one for the paper tape and other miscellaneous insulating
material.

All of this insulating material was prepared at the cable factory,

1 N.E.L.A. Underground Committee report, 1916,

194 UNDERGROUND TRANSMISSION AND DISTRIBUTION

submitted to 29 in. vacuum and impregnated with the same
compound which was used in filling the joint. The insulating
material is placed in the can in layers in the order required to
make up the joint, so that all of the material in each layer has
to be used in its entirety in each successive operation. The
illustration shows all the material used to make one complete
joint of this type.

Another company reports the following practice :

When the lead sleeve is 3 in. or larger in diameter, this sleeving

is cut to the exact length required for the joint, wooden end plugs

and through bolts are used to seal the ends, and the tape, solder,

copper sleeves and soldering paste are placed within the sleeve.

FIG. 89. — Contents of sealed-unit package.

If the package is sent out in advance of the work, the ends are
sealed by dipping in melted paraffine.

When the sleeve is smaller than 3 in. in diameter, a pasteboard
or sheet-metal container is used to hold the lead sleeve and other
material. The material is placed in the pasteboard container if
it is to be used immediately, and in the sheet-metal container if
it is to remain on the job a day or two before being used. The
latter is necessary in order to keep the tape dry. Each package
made up for No. 6 and No. 0 single-conductor cable contains
material for four joints.

As the exact quantity of material required is sent out in each
package, uniform joints are secured. Less time is required on the

INSTALLATION OF CABLES 195

job to get material ready for the joints because the lead sleeve
is cut to the proper length and all material is in a form convenient
to handle. There is also considerable saving in the storeroom,
as these packages can be made up during slack time and are more
quickly and easily handled when delivered.

Protection of Cables in Manholes. — In an underground system
where cables are carrying from 2,000 to 5,000 kw., damage to
such cables becomes a matter of serious consequence, and their
protection from mechanical injury, especially in manholes, is very
important.

In order to prevent trouble on one cable from communicating
to the other cables in the same manhole, it is desirable to cover
the cables in manholes with some type of fireproof covering. The
principal types of protection used are as follows:

1. Concrete shelves.

2. Asbestos tape saturated with silicate of soda.

3. Asbestos tape covered with a soft-steel band armor.

4. Split-tile duct with cemented joints.

5. A cement-mortar coating with % in. rope bond.
Concrete shelves make a good protection between cables on

the several shelves but, without other protection, do not prevent
trouble in one cable from extending to others on the same shelf.
Nor is it feasible under ordinary conditions to extend the shelves
right up to the conduit end, so that with this scheme of protec-
tion the cables are ordinarily exposed to damage when they enter
and leave the manhole. These are the most vulnerable points
in any scheme of protection, and are also the points at which
repairs to cables are the most awkward and expensive.

In some cases specially designed octagonal-shaped manholes
have been used, receiving but two cables on the same horizontal
plane, one turning to the right and one to the left, giving very
gradual bends and resting throughout their length on reinforced-
cement shelves 1 in. thick. In the construction of these shelves
expanded metal of 1 in. mesh is stretched in forms, into which
the concrete is poured, a mixture of 1 part cement to 2 of sand
being used. A plan and elevation of a cable manhole of this
type is shown in Fig. 90.

The shelves are removable and are laid upon angle irons built
into the manhole walls. These barriers protect the cables from
being walked upon by careless workmen, or struck by ladders,
falling tools, etc. They also are considered a protection above

196 UNDERGROUND TRANSMISSION AND DISTRIBUTION

and below in case of severe short-circuit in adjacent conductors;
moreover, the weight of the cables is quite uniformly distributed,
which is a considerable advantage over the method of support-
ing them from manhole cable racks. These shelves cost about 12
to 15 cts. per sq. ft. They need be manufactured and added
only as the multiplication of cables in the conduit line warrants.
The several forms of asbestos-tape protection that have been
used for many years serve to protect cable from flame due to gas

FIG. 90. — Concrete shelves in manhole.

burning in the manhole or from similar flames, but will not with-
stand the action of an arc at short range. Asbestos, therefore,
cannot be considered a reliable form of protection where im-
munity from troubles of this kind is desired. The asbestos
coverings, furthermore, are not suitable for the protection of
cable sheaths in wet manholes where stray currents are in evi-
dence. Electrolytic action appears to be accelerated by the
presence of the asbestos wrapping, the cause apparently being
due to chemical decomposition of the contents of the asbestos

INSTALLATION OF CABLES 197

covering under conditions which promote rapid destruction of
cable sheaths.

Split tile laid on concrete or other types of shelves has been
used by a number of companies as a protective covering. Several
manufacturers make split tile in straight sections of regular length
as well as in short, straight lengths and with various degrees of
curvature. There still exists with this type of protection the
difficulty of applying the protection right up to the end of the
conduit; and while it has been used in the past in large quantities,
its use has been abandoned in favor of the cement-mortar cover-
ing. Although tile is fireproof in the ordinary sense, it will melt
and flow in the case of a severe electric arc, and when this occurs,
the cable is exposed to the arc which melted the tile. The tile
is also injured by manhole explosions. It is difficult to cement
the joints properly so that there are, in general, a number of
weak points in the covering in each manhole. In addition, there
is considerable difficulty in a crowded manhole in tracing indi-
vidual cables after all have been covered with tile. The prices
demanded by the tile manufacturers for the split-tile duct in
straight pieces and in bends were of considerable influence in
the decision to abandon this type of covering.

The cement-mortar coating is not affected by manhole explo-
sions, and although the quality of the concrete and its strength
may be seriously affected by the arc, it will in general remain in
place and serve as a protection until it has been mechanically
removed. The companies that have tried this type of protection
are highly impressed with its value, and freely recommend its
adoption.

In determining the type of protection to be used, the heat-
resisting qualities of the covering are of more importance than
the heat-conducting qualities. Even when covered with the
best non-conductor, the cables in the manholes will probably be
cooler than the cables in the conduit. The type of covering used,
therefore, has little, if any, influence on the carrying capacity
of the cables.

The cost of protecting cables by the several methods described
will, under ordinary circumstances, range between 20 and 30 cts.
per lin. ft. of cable.

Recent tests made to determine the relative value of two
types of protective covering for cables show very clearly the
marked superiority of cement mortar as compared with asbestos

198 UNDERGROUND TRANSMISSION AND DISTRIBUTION

and steel-tape covering. Briefly, the tests showed that a cable
protected with cement mortar was much less damaged by an arc
of 425 amp. for 101 sec. than was a similar cable with asbestos
and steel-tape covering by an arc of 450 amp. for 35 sec.

An objectionable feature connected with the asbestos covering
is the presence of the iron banding tape which may become
grounded and so actually involved in the arc circuit, which con-
dition could not exist where the cement covering is used.

Ci-EA/veO. COAT/KG
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FIG. 91. — Method of fire proofing cables in manhole.

Fig. 91 shows the method of fireproofing cables with cement
mortar. In applying the cement mortar, the lead sheath of the
cable is first cleaned and then coated with paraffine brushed on
evenly. A cover of cheese cloth is then applied, over which the
rope is wound, spaced about J^-in. centers. The cement mortar
of a mixture of 1 part Portland cement and 2 parts of clean sharp
sand is then placed over the rope by hand with leather pad and
smoothed down with a trowel to a thickness of %-in. The
method of protection illustrated in Fig. 91 provides for asbestos
listing to be wrapped around the cable 3 in. inside and 4 in.
outside the duct. This plan need not be followed when the space

INSTALLATION OF CABLES 199

in the manhole will allow the cement covering to be carried right
up to the duct and so make the protection practically continuous
with the conduit.

Cement armor has been found to be of considerable protection
to cables in cases where they might be accidentally struck by tools,
etc., and serves also to prevent the cables from being bent and
twisted by men not conversant with the proper handling of this
material.

Current-carrying Capacity of Cables. — The current-carrying
capacity of insulated copper cables sheathed with lead depends
primarily upon :

(a) The size and number of conductors and their relative
position.

(6) The ability of the insulating material to withstand high
temperatures and to conduct heat away from the copper con-
ductors; this latter being in turn dependent upon the kind of
insulation and its thickness.

(d) The ability of the medium surrounding the cable to
dissipate heat with small temperature rise.

(e) The number of operating cables in close proximity and
their relative position.

Where a number of insulated conductors are under the same
sheath, they are subject to an interchange of heat somewhat
similar to that which takes place when a number of separate
cables are laid closely together; and for that reason each conductor
of a multi-conductor cable will have a smaller current-carrying
capacity than a single-conductor cable. If the various con-
ductors are separately insulated and laid together in the form
of flat or round duplex or triplex cables, their carrying capacity
will be greater than if they are laid up in the form of concentric
cables. Assuming that unity represents the carrying capacity
of single-conductor cables, the capacity of multi-conductor
cables would be given by the following :

Two-conductor, flat or round form 0. 87

Three-conductor, triplex form 0 . 75

Two-conductor, concentric form 0.79

Three-conductor, concentric form 0 . 60

In any cable the area from which heat is dissipated is pro-
portional to the circumference of the conductor or (since the

200 UNDERGROUND TRANSMISSION AND DISTRIBUTION

circumference varies as the diameter) upon the diameter of the
conductor, while the cross-section of the conductor varies as
the square of the diameter. Hence the size of conductor varies
much more rapidly than its heat-radiating surface, and, in conse-
quence, the amperage per square inch or circular mil of copper
section must be less for large size conductors than for small in
order to have the same rise of temperature under the same con-
ditions. The usual formula for carrying capacity, Current =

(Diam. of Cond.)% • , . ,. . ,.

— r— — > takes account of this fact but not to a

A constant

sufficient degree, and we find that for cables as ordinarily used
in underground work, a more correct expression is Current =
(Diam. of Cond.)%
A constant

Rubber insulation is a somewhat better heat conductor than
dry or saturated paper, and, therefore, when applied to the same
size conductor in equal thickness will permit of a larger current
flowing in the conductor for the same rise of temperature above
the surrounding air. On the other hand, rubber deteriorates
much more rapidly at high temperatures than does saturated
paper, and while this disadvantage is apparently compensated
for up to about 150°F. by its superior heat-dissipating qualities,
at higher temperatures deterioration takes place, finally becoming
so serious that the value of the material as an insulating medium
disappears in a comparatively short time.

As the thickness of the insulation is increased, the temperature
of the conductor, with any given current flowing, gradually
increases and, therefore, the current-carrying capacity is reduced.
This reduction in capacity, however, is not very great, being in
the ratio of about 93 for 1^2~m- insulation to 100 for %2~m-
insulation, so that the values in the table given below should be
slightly decreased when greater thicknesses than %2~m- are used.

As it is the final temperature reached which really affects the
carrying capacity, the initial temperature of the surrounding
medium must be taken into account. If, for instance, the con-
duit system parallels steam or hot water mains, the temperature
of 150°F. (which has been assumed in Table XXVI to be a
maximum for safe continuous work on cables) will be reached
with lower values of current than would otherwise be the case;
and as 70° is the actual temperature which has been assumed
to exist in the surrounding medium prior to loading the cables,

INSTALLATION OF CABLES

201

any increase over 70° must be compensated for by reducing
the current carried.

•

TABLE XXVI. — RECOMMENDED CURRENT CARRYING CAPACITIES FOR
CABLES AND WATTS LOST PER FOOT*

For each of four equally loaded paper-insulated lead-covered cables,
installed in adjacent ducts in the usual type of conduit system where the
initial temperature does not exceed 70°F., the maximum safe temperature
for continuous operation being taken at 150°F.

(Copyright by Standard Underground Cable Co.)

Size
B. & S. G.

Safe current,
amp.

Watts' lost
per ft. at
150°F.

Size, cm.

Safe current,
amp.

Watts i lost
per ft. at
150°F.

0.97

300,000

323

4.22

1.03

400,000

390

4.61

1.09

500,000

450

4.91

1.15

600,000

505

5.16

1.25

700,000

558

5.36

1.39

800,000

607

5.56

1.53

900,000

650

5.71

1.67

1,000,000

695

5.86

1.85

1,100,000

740

6.01

2.08

1,200,000

780

6.13

2.31

1,300,000

820

6.25

108

2.54

1,400,000

857

6.37

125

2.77

1,500,000

895

6.49

146

3.00

1,600,000

933

6.61

168

3.23

1,700,000

970

6.73

195

3.46

1,800,000

1,010

6.85

000

225

3.69

1,900,000

1,045

6.97

0000

260

3.92

2,000,000

1,085

7.09

* Standard Underground Cable Co.

1 This column represents the amount of energy which is transformed into heat and which
must be dissipated. It is what is usually called the IzR loss and it is figured by using for
I the current values given; and for R the resistance of the respective conductor at a tempera-
ture of 150°F.

NOTE: The table is compiled from a long series of tests made by the Standard Underground
Cable Co., in conjunction with the Niagara Falls Power Co.

For rough calculations, it will be safe to use the following
multipliers to reduce the current-carrying capacity given in
Table XXVI to the proper value for the corresponding initial
temperatures:

Initial temperature 70 80 90 100 110 120 130 140 150

Multipliers 1.00 0.93 0.86 0.78 0.70 0.60 0.48 0.34 0.00

The formulae and tables prepared by Mr. H. W. Fisher, and
given in the handbook of the Standard Underground Cable Co.,

202 UNDERGROUND TRANSMISSION AND DISTRIBUTION

have been found to give excellent satisfaction in practice, and
are here reproduced through the courtesy of that company.

TABLE XXVII. — EQUIVALENT CONDUCTOR AREAS

Of Single Conductor of Any Size, from 0000 to 15, in a Stated Number
of Smaller Conductors1

B. & S.
G. No.

In 2 con-
ductors

In 4 con-
ductors

In 8 con-
ductors

In 16 con-
ductors

In 32 con-
ductors

In 64 con-
ductors

In 2 conductors,
one each of

0000

No. 0

No. 3

No. 6

No. 9

No. 12

No. 15

Nos. 00 and 1

000

Oand 2

land 3

9
10

12
13

15
16

2 and 4
3 and 5

2
3

5
6

8
9

14
15

17
18

4 and 6
5 and 7

6 and 8

7 and 9

9
10

12
13

15
16

8 and 10
9 and 11

10 and 12

11 and 13

12 and 14

13 and 15

14 and 16

15 and 17

16 and 18

For the same temperature rise more current can be carried by using divided circuits and
the greater the number of divided circuits for the same equivalent cross-section the greater
the amount of current that can be carried. See Table XXVI, Carrying Capacities.

1 Standard Underground Cable Co.

The temperature which the insulation of underground cables
will withstand is the condition which limits the current which
may be carried, and it is extremely important that this tempera-
ture shall not exceed its critical value. Within a limited range
the temperature increments are directly proportional to the
increments of PR, but a point will be reached where this propor-
tionality no longer exists, and it will be found that the tempera-
ture increase per unit increase in PR continually becomes larger.
In the case of cables used for direct current, the temperature
rise of the cable (other conditions being equal) depends solely
upon the PR loss; and for low-voltage alternating-current
cables this is approximately true.

However, when a cable is used for carrying alternating current
at a high voltage, the heat due to dielectric hysteresis is added to

INSTALLATION OF CABLES

203

the heat produced by ohmic resistance, and the effect is a lower-
ing of the temperature at which the insulation may be safely
operated.

The operation of high-tension alternating-current cables of
over 10,000 volts at too high a temperature is especially dangerous
because the effect of dielectric losses on temperature rise is cumu-
lative. It has been found that after the safe temperature has
been passed, the leakage currents through the dielectric increase
rapidly, causing increased heating and facilitating the passage
of more and more leakage current. If this process continues
unchecked, the failure of the insulation will quickly result.

Excessive operating temperature, if continued for a consider-
able length of time, has a deteriorating effect which is permanent
and which reduces very materially the useful life of a cable.

There is a lack of accurate information such as would enable
an operating company to know when the danger point in cable,
operation is reached. It is believed that, because of this lack of
information, the tendency, in underground practice, is to under-
load rather than overload the cable system. When the magni-

TABLB XXVIII. — RECOMMENDED POWER-CARRYING CAPACITY IN KILO-
WATTS OP DELIVERED ENERGY1

Three-conductor, Three-phase Cables

Size in

V Ull>O

B. & S. G.

1,100

2,200

3,300

4,000

6,600

11,000

13,200

22,000

Kilowatts

183

275

333

549

915

1,098

1,831

109

217

326

395

652

1,087

1,304

2,174

130

260

390

473

781

1,301

1,562

2,603

154

309

463

562

927

1,544

1,854

3,089

179

35S

536

650

1,073

1,788

2,145

3,575

209 ]

418

626

759

1,253

2,088

2,506

4,176

240

481

721

874

1,442

2,402

2,884

4,805

279

558

836

1,014

1,674

2,788

3,347

5,577

000

322

644

965

1,172

1,931

3,217

3,862

6,435

0000

372

744

1,115

1,352

2,231

3,717

4,462

7,435

250,000

413

827

1,240

1,503

2,480

4,132

4,960

8,264

These tables are based on the recommended current-carrying capacity of cables given in
Table XXVI. A power factor =» 1, was used in the calculation and hence the values found
in the last table are correct for direct currents. For alternating current the kilowatts given
in both tables must be multiplied by the power factor of the delivered load.

1 Standard Underground Cable Co.

204 UNDERGROUND TRANSMISSION AND DISTRIBUTION

TABLE XXVIII. — RECOMMENDED POWER-CARRYING CAPACITY IN KILO-
WATTS OP DELIVERED ENERGY. — Continued.

Single-conductor Cables, A.C. or D.C.

Volts

Size in

B. & S. G.

125

250

500

1,100

2,200

3,300

6,600

11,000

Kilowatts

8.0

16.0

141

211 422 704

9.5

19.0

167

251 502 836

11.4

22.8

100

200 i 300 601 | 1,001

13.5

27.0

119

238

356

713

1,188

15.6

31.2

138

275

413

825

1,375

18.3

36.5

161

321

482

964

1,606

21.0

42.0

185

370

554

1,109

1,848

24.4

48.8

215

429

644

1,287

2,145

000

28.1

56.3

113

248

495

743

1,485

2,475

0000

32.5

65.0

130

286

572

858

1,716

2,860

300,000

40.4

80.8

162

355

711

1,066

2,132

3,553

400,000

48.8

97.5

195

429

858

1,287

2,574

4,290

500,000

56.3

112.5

225

495

990 j 1,485

2,970

4,950

600,000

63.1

126.3

253

556

1,111

1,667

3,333

5,555

700,000

69.8

139.5

279

614

1,228

1,841

3,683

6,138

800,000

75.9

151.8

304

668

1,335

2,003

4,006

6,677

900,000

81.3

162.5

325

715

1,430

2,145

4,290

7,150

1,000,000

86.9

173.8

348

764

1,529

2,294

4,587

7,645

1,100,000

92.5

185.0

370

814

1,628

2,442

4,884

8,140

1,200,000

97.5

195.0

390

858

1,716

2,574

5,148

8,580

1,400,000

107.1

214.3

429

943

1,885

2,828

5,656

9,427

1,500,000

111.9

223.8

448

985

1,969

2,954

5,907

9,845

1,600,000

116.6

233.3

467

1,026

2,053

3,079

6,158

10,263

1,700,000

121.3

242.5

485

1,067

2,134

3,201

6,402

10,670

1,800,000

126.3

252.5

505

1,111

2,222

3,333

6,666

11,110

2,000,000

135.6

271.3

543

1,194

2,387

3,581

7,161

11,935

tude of the investment called for in this branch of the industry
is considered, the importance of increasing the carrying capacity
of cables to the maximum possible value is realized.

The current-carrying capacity of rubber, cambric and paper
insulated cables, as recommended by the General Electric Co.,
is given in Table XXIX.

The problem of determining the proper loading for under-
ground cables remains to a large extent unsolved, but more and
more attention is being given to this subject, and it is, therefore,
very desirable that operating companies and cable manufacturers

INSTALLATION OF CABLES

205

work in conjunction with the view to the formulation of a set of
standard rules.

TABLE XXIX. — CURRENT-CARRYING CAPACITY
Rubber, Cambric and Paper Cables1

Under ordinary conditions a cable will attain about 60 per cent, of its
total rise in temperature during the first hour, 30 per cent, during the second
hour, the final maximum being gradually reached during several following
hours.

Concentric cables will safely carry about 20 per cent, less current on each
conductor than the same size of single conductor cable. Four-conductor
cables, 10 per cent, less than same size triple conductor. All temperatures
refer to temperatures of copper core.

Initial Temperature, 20°C.

Low tension cable
single conductor

High tension
cable three
conductor

Size of cable,
circ. mils

National electric
code, rubber

Rubber, 30°C.
rise

Var. cam. or
paper, 60°C. rise

Rubber and var.
cam., 30°C. rise;
paper, 35°C. rise

Amp.

Amp. on each
conductor

2,000,000

1,050

1,400

1,750

1,500,000

350

1,200

1,500

1,000,000

650

900

1,150

750,000

525

750

900

500,000

390

550

660

440

400,000

330

460

560

360

300,000

270

370

450

290

250,000

235

320

390 250

200,000

200

270

310

210

150.000

160

220

260

175

125,000

140

180

210

140

100,000

120

160

190

125

80,000

104

140

165

110

60,000

110

130

40,000

6 B. & S. solid

8 B. & S. solid

33 30

10 B. & S. solid

24 20 24

1 General Electric Co.

Cooling Duct Lines. — The heating of a duct line depends upon
the composition of the duct itself, the arrangement of the ducts
relative to one another, and the nature of the surrounding medium.
Where a duct line is of the multiple type, the ducts furthest
away from the heat-dissipating surfaces will run hottest, and the
top row of ducts will run at a higher temperature than the lower
rows. Care should, therefore, be taken in assigning ducts to the

206 UNDERGROUND TRANSMISSION AND DISTRIBUTION

various cables that those cables which are expected to carry the
heaviest load be placed in the ducts which can best dispose of
the heat generated.

The nature of the surrounding medium is of importance in
determining the temperature of a duct line. It is a well-known
fact that the temperature of a duct of any given construction
will vary with changes in the character of the soil through which
it runs. Thus a line may give no trouble from overheating where
it runs through moist soil but is very likely to overheat in sections
where the soil is dry or sandy. Attempts have been made to
produce artificially the conditions favorable to rapid heat
dissipation, and various methods of cooling overheated duct
lines have been proposed, but as yet none has shown results which
would justify general adoption. A method of cooling by the
use of a porous-tile drain laid in a trench above the conduit
line was described in detail by Mr. L. E. Imlay in a paper pre-
sented before the American Institute of Electrical Engineers in
February, 1915. It was shown that the soil surrounding a buried
conduit containing active electric cables may become hot, dry
and powdery, a condition which would reduce its thermal con-
ductivity to a minimum. The addition of moisture to the soil,
either from above or from below through a vacant duct, brought
about a very distinct reduction in the temperature of the cables
as well as in the temperature of the surrounding soil. It seems
readily possible that future installations of heavily loaded con-
ducting cables, buried in conduits, will have special water-cooling
ducts laid in their immediate vicinity for the purpose of keeping
down the cable temperatures. A noteworthy point brought out
by the observations of the author is the relatively great distances
to which the heat liberated from active cables in the buried con-
duit can appreciably raise the temperature of the ground. It
appears that the temperature of the soil 1 meter below the surface
was raised by some 20°C. at a distance of half a dozen meters
from the buried conduit.

The method employed by the Niagara Falls Power Co. for
cooling its underground cables was to circulate water through
one of the vacant ducts adjacent to the occupied ducts. Later
porous drain tiles were installed parallel to and above the cable
ducts so that water flowing through the tile could percolate
through the ground surrounding the cable and finally be carried
away through agricultural tile drains installed below the ducts.

INSTALLATION OF CABLES

207

The approximate temperatures of the cables were ascertained by
inserting resistance thermometers in ducts adjacent to the cables
which were supposed to be the source of heat.

Tests were made by the Consolidated Gas, Electric Light &
Power Co. of Baltimore in sections of their conduit system where
cable burnouts were frequent. Most of the troubles in this
part of the insulation were due to the high temperature of the
duct line during the summer months. The soil around the ducts

FIG. 92. — Duct temperature before installing cooling system.

was to a great extent dried out and it seemed logical to conclude
that some method of supplying water to the duct line would
improve conditions. Studies were made of the temperatures
existing in the duct line under regular operating conditions.
The conduits which were used principally for carrying 13,000-
volt cables were laid in made earth with some ash. Thermome-
ters were placed in an idle duct some distance from a manhole
and the observations showed that the temperatures in the duct
line responded to the variations in load and to atmospheric

208 UNDERGROUND TRANSMISSION AND DISTRIBUTION

temperatures. The response to the changes in load followed
within a few hours, but atmospheric temperature variations
produced no effect for some days.

The records as has been stated were taken as a result of repeated
cable failures. During the year 1912 there were 15 failures;
during 1913, 7; and during 1914, 19. Nearly all the troubles
occurred during the summer months, and most of them were
in the section of the duct where the temperature records were
observed.

FIG. 93. — Duct temperature after installing cooling system

During the summer of 1915, a sprinkler system was installed
in the three sections where the greatest number of burnouts
had occurred. The cooling system consisted of a %-in. iron
pipe with M4-in. perforations at a 3-ft. spacing installed in a
vacant duct. About 4,000 gal. of water per day at a temperature
of about 55°F. were supplied to the system and it was found that
the duct temperature was reduced about 10°F. Some trouble
appears to have been experienced due to plugging up of the per-

INSTALLATION OF CABLES

209

forations. The charts shown in Figs. 92 and 93 show the tempera-
ture conditions before and after the sprinkler system was installed.
The results are not conclusive and serve merely to show the possi-
bilities of this method of cooling.

In some instances, transmission cables run through manholes
containing transformers and heavily loaded cables both of which
tend to raise the temperature of the duct line. In such special
cases it may be cheaper to provide a cooling system rather than
additional cables in order that the existing cables may be operated
at their maximum rating during the summer peak-load period.

The radiation of heat from a duct line differs from that from
other classes of electrical apparatus around which the air is
free to circulate; therefore,
changes in the temperature of a
duct line will not follow changes
in load as closely as in the case
of station apparatus, but instead
will lag to such an extent that
the line may not reach its final
temperature for several days.
This is especially true during cer-
tain seasons of the year when the
earth around the duct line is dry-
ing out.

The drying out of the earth in summer when the atmospheric
temperature is around 90°F. affects the carrying capacity of
cables quite materially, since the maximum copper temperature
at which it is safe to operate high- voltage cables is something
like 150°F. A number of companies change the rating of the
cables according to the seasons of the year. In one case where
there are a number of cables in a duct line it has been necessary
to limit the rating of the cables in summer to about half the
winter rating.

In order to facilitate radiation from cables, duct lines have
been constructed, as shown in Fig. 94, so that earth would be in
direct contact with each duct.

Connections to Overhead Lines. — In most primary distri-
bution systems in which part of the lines are underground, there
are connections made between the underground cable and over-
head aerial wires. It is usual to run feeders and important
mains underground for some distance from the station in large

FIG. 94.— Method of separating
ducts.

210 UNDERGROUND TRANSMISSION AND DISTRIBUTION

cities and then connect with overhead lines in the more scattered
area.

Where back-yard and alley distribution is general, the main
lines are placed underground in streets, and the local distributing
taps taken off the overhead lines. It is quite frequently neces-
sary that underground lines be carried across railroads, main
bouleyards and streams. This class of distribution was for
many years very troublesome because of the difficulty of properly
caring for the cable ends which are brought up the pole to the
overhead line.

Plain joints, made up by stripping the lead back a few inches
and covering by tape and compound, were succeeded by lead
joints rilled with compound and left open at the end where the
live wire came out. In some cases joints were protected by en-
closing them in boxes. All of these various forms were susceptible
to the action of the sun and rain, and were sooner or later located
by lightning flashes, or potential surges, as the weak spots in
.the line.

In recent years many of the large distributing systems have
been equipped with potheads or pole terminals designed to meet
such conditions. Outdoor potheads for pole connections should
serve the double function of connecting the insulated conductor
of the underground cable to the overhead aerial wire, and of
sealing properly the end of the lead-covered cable to protect the
insulation from moisture. Protection of the cable insulation
from moisture requires a structure which will not only prevent
the direct action of water in the form of rain, snow or sleet, but
will also prevent the indirect action of moisture in the form of
fog and water vapor.

Effective devices of this kind are today an absolute necessity
in every underground cable system. A single-conductor form
of terminal is shown in Fig. 95. This terminal consists essen-
tially of three parts : a conducting stem (a) which acts as a con-
tinuation of the underground cable conductor; an insulator (6);
and a connecting pin (c) between the insulator and lead sheath
(forming, in reality, an expanded extension to the lead sheath),
which may be called the bell.

The advantages claimed for this type of terminal are as
follows :

1. Protection of the insulation from injury by electrostatic
discharges, or by any deteriorating influence, such as moisture,

INSTALLATION OF CABLES 211

either held in suspension in the air or in the form of rain, snow
or sleet.

2. Separation of, and efficient insulation of, conductor from
conductor, and conductor from grounded lead sheath, when
exposed to usual weather conditions.

3. Connection of underground conductor with aerial conductor
in an approximately straight line, thus avoiding bending heavy
conductors or wasting cable in goose-necks or rain loops.

FIG. 95. — Single-conductor terminal.

4. Facility in connecting and disconnecting the aerial
extension.

5. Rigid structural unity — the terminal, the cable con-
ductors and the lead sheath being tied together in a rigid
mechanical union.

6. Ease of installation, the lead bell being adaptable to any
diameter of cable.

7. Connection of current-carrying parts in an effective manner,
securing good electrical and convenient mechanical connection
between the conductors of the cable and their aerial extensions.

Another form of single conductor terminal is shown in Fig.
96. This terminal consists of a porcelain sleeve which, when

212 UNDERGROUND TRANSMISSION AND DISTRIBUTION

filled with compound, serves to seal the end of the cable insulation
from moisture, and a porcelain cap which fits over the top and
has ample overlap, excluding water in a driving rain and when
submerged. The cap carries a copper plug which is attached

FIG. 96. — Single-conductor terminal.

to the outgoing terminal. The tube carries a recessed member
in which the plug seats, and this member is soldered to the cable
conductor. The circuit is thus opened and closed by merely
removing and replacing the cap.

INSTALLATION OF CABLES

213

This type of pothead is made in various forms for voltages up
to and including 30,000 and with either wiping sleeves, stuffing
boxes, or plain entrances for the cable. It has a very wide appli-
cation to distribution work and in many instances the device is
used merely as a disconnector in place of a blade or oil switch.
Because of its small unit form, it permits the installation of any
complicated switching arrangement
in a safe, neat and complete man-
ner.

A form of multi-conductor ter-
minal is shown in Fig. 97. This
type of terminal is particularly
suitable for heavy power-trans-
mission cables. Some companies
using multi-conductor terminals
made of iron have experienced
trouble due to heating caused by
eddy currents set up when the ter-
minal is used on cables carrying
alternating currents. This trouble,
however, has been overcome by
making the metal forked cap of
the terminal of non-magnetic ma-
terial such as aluminum or brass.

The pole shown in Fig. 98 is of
particular interest on account of
the considerable number of 13,200-
volt, three-conductor cables which
terminate at this point; and while
it may not be good practice to
bring out so many cables on one
pole, it shows what can be done when the conditions require it.

In all cases where underground cables are connected to over-
head lines, some suitable covering should be provided at the end
of the lateral pipe to prevent the entrance of water. There are
several devices on the market which are arranged to fit around
the cable and slip over the pipe. A very satisfactory pipe cap
can be made of sheet lead from the cable sheath which is formed
into a bell shape soldered to the cable and hammered over and
around the pipe, as shown in Fig. 99. Unless the top of the pipe

FIG. 97. — Three-conductor
head.

pot

214 UNDERGROUND TRANSMISSION AND DISTRIBUTION

is covered, water will enter during rain storms, and in winter
weather will freeze and damage the cable.

The National Electric Light Association line-construction
specification for joint use of poles provides that connection to

FIG. 98. — Terminal pole.

electric-light lines for supplying service, or for street lamps, trans-
formers, fuses, switches or lightning arresters or connections
to underground wires and, in general, connections forming a

INSTALLATION OF CABLES

215

part of the electric-light system may be run vertically upon a
pole, and, if necessary, through telephone wires, provided such
electric-light wires and connections are so constructed, placed
and maintained as to conform to the following requirements:

Lead-sheathed cable shall be inclosed within a pipe or conduit
of solid insulating material wherever such cable shall be run upon

Cement
i pound

SKETCH A

Cable Moulding

D Diameter Depends on

Size of Cable Installed

Cable Protected
with Wood Moulding
See Detail A

Bell

Cotton Waste
Packing

Lead Wipe
Lead Bell

To Manho

FIG. 99. — Terminal pole, showing methods of protecting cable.

the pole between a point not less than 40 in. above the highest
telephone wire, connection or attachment, and a point not less
than 6 ft. below the lowest telephone wire, connection or
attachment.
Ground wires or wires throughout the entire length of attach-

216 UNDERGROUND TRANSMISSION AND DISTRIBUTION

ment to the pole shall be inclosed within an insulating conduit,
or otherwise effectually insulated and protected. All cables,
wires, connections and conduits forming a part of the electric-
light system and carried vertically upon a pole within the terms
of this article shall be placed upon the same circumference of the
pole on the crossarm side or face of the pole, it being further
provided that the poles jointly used and having such vertical
attachment shall be furnished with pole steps and that no vertical
attachment shall be so placed as to interfere with the use of pole
steps. Where vertical attachments of the lighting company pass
telephone crossarms, they shall be run behind the telephone cross-
arm and not across the face of such arms.

Lightning Arresters. — Where underground cables connect with
overhead wires, protection of cables against lightning is necessary;
and suitable arresters and fuses should be installed for this
purpose as well as to protect the station apparatus. Resonance
invariably produces high potentials at the junction of overhead
and underground lines, and these potentials are often of sufficient
value to break down the insulation of the cables and also the
insulation of apparatus installed on the system.

Whenever lines contain both inductance and capacity in ap-
preciable amounts, high voltages, which endanger the insulation
of the whole system and which it is impossible to detect on
ordinary switchboard instruments, may exist. Abnormal vol-
tages are, therefore, often found in circuits containing a com-
bination of underground and overhead circuits.

It is difficult, however, to determine the proper arresters for
such circuits on account of the various conditions to be met.
Where it is necessary to install lightning arresters, the acces-
sibility, ease of inspection, voltage and power of the system, as
well as the length of underground and overhead lines, will be
important factors in the selection of a proper type. In all light-
ning-arrester installations it is of the utmost importance to make
proper ground connections, as many lightning-arrester troubles
can be traced to bad grounds.

For grounding pole arresters, one or two 1-in. or lj^-m- iron
pipes should be driven into the ground at the base of the pole
and connected to the arrester by means of a copper wire not less
than No. 2. The ground wire should be protected for some
distance up the pole to prevent its being injured. The pipes

INSTALLATION OF CABLES 217

should be driven far enough from the pole so that movement of
the pole will not loosen them.

Splicing Equipment, Tools and Safety Devices. — In the laying,
splicing and connecting of cables, certain tools and accessories
are necessary and useful; and every cable splicer should be sup-
plied with a kit of tools, as follows:

Gasoline furnace. 10-in. flat file.

Solder pot and ladle. 10-in. round file.

3- or 4-lb. soldering iron. Hacksaw frame and blades.

8-in. side-cutting pliers. Wiping cloths.

Gas pliers. Kettle for compound.

Chipping knife. Small and large pan.

Pein hammer. Mason's bag.

As a great many accidents of a minor character are constantly
occurring due to methods employed in raising and lowering tools
and material from manholes, these accidents occurring princi-
pally from want of particular kinds of devices to prevent the
spilling of solder and the tipping over of tool and material pans,
the following tools or devices which have been found very effec-
tive are suggested for use.1

(a) A very effective and useful rope for lowering the solder
pot, compound kettle, tool pan, etc., consists of a small hemp
rope on one end of which is fastened a snap hook for engaging
in the handles or bails on the compound kettle and solder pot.
On the other end of this rope there is a "sister-hook" which is
useful in forming a loop or safety belt which may be used in
emergency cases, Fig. 100.

The sister-hook, as shown in the figure, consists of two separate
hooks turned in opposite directions. The flat sides fit snugly
together, forming a complete ring about the bail of a kettle, or
anything which is placed within the hook, and make it prac-
tically impossible to jolt it out accidentally. The iron rod at the
other end is used when lowering hot solder pots or anything which
may burn or cut the rope.

(6) A solder pot which has eliminated many accidents due
to the spilling of solder is provided with a flange on the inside
which allows the pot to be tipped at a considerable angle with-
out spilling the contents. This pot also has a ring turned in
the handle which prevents it from losing its balance by the
handle slipping in the hook of the lowering rope.

1 N.E.L.A. Underground Report, 1915.

218 UNDERGROUND TRANSMISSION AND DISTRIBUTION

(c) The compound kettle may also have a ring turned in the
handle to prevent slipping in the lowering hook and consequent
spilling of the contents on the workmen below.

(d) A great deal of trouble has been experienced by the use of
the ordinary baking pan as a means for lowering into the man-
hole small tools, tape, etc., which are commonly used on cable-
splicing work. To prevent the pan from tipping over, handles
may be put on each corner of the pan and joined together in the

FIG. 100. — Tool lowering rope.

center, forming a ring in which the snap hook on the lowering
line engages. This form of handle for the material pan will
always keep the pan in balance and prevent spilling the contents.
(e) An effective cable-sheath knife has recently come into use.
This knife is very much the same as the sheath knife formerly
used, except for the provision of a fiber shield on each side of the
blade. These shields are set back just far enough from the cut-

INSTALLATION OF CABLES 219

ting edge to permit the sharp edge of the knife to penetrate the
lead sheath only, without cutting the insulation beneath.

(/) A new type of cable-sheath cutter for cutting around the
cable has recently been introduced. It has proved very effec-
tive and where used has reduced the number of short-circuits
due to the old style of cutting wheel, which cut through both
lead sheath and insulation. This cutter is of the plier type, the
cutting blades being mounted on the sides of the plier jaws
extending only far enough beyond the inside edge of the jaws to
allow the cutter to cut through the lead sheath without disturbing
the insulation beneath.

(g) Hacksaw frames used on cable work may be insulated in
several different ways, one of which is to wind the metal parts

FIG. 101. — Hacksaw frame.

of the frame with insulating tape. Another method is to have the
metal parts covered with rubber and vulcanized. A very satis-
factory form of hacksaw frame is one made entirely of fiber,
Fig. 101. The all-fiber hacksaw frame has been used by one of
the larger companies for some time and has proved very
satisfactory.

(h) To prevent the many short-circuits which occur by junc-
tion-box catch nuts and bolts falling across terminals of opposite
polarity, insulated wrenches may be used with good effect.
These wrenches are of the socket type and have a setscrew with
a fiber head which may be tightened on the nut of screw bolt
which is to be removed. This holds the nut or bolt tightly in
the head of the wrench and permits its safe removal from the
junction box. Another very successful form of wrench for remov-
ing junction-box catch nuts and bolts is one in which the nut or
bolt head is held tightly in the wrench by a set of springs.

(i). For removing the compound in low-voltage service boxes,

220 UNDERGROUND TRANSMISSION AND DISTRIBUTION

a hard-fiber chisel has been found very effective and should form
part of the equipment of every service wagon.

(/) The ship-auger type of socket wrench for removing the
nuts on the inside cover of junction boxes is a very satisfactory
tool, as it permits the workman to tighten the nuts or bolts in
a very easy position, and it also allows him to be on his guard
against being struck by vehicles or pedestrians.

TOOLS FOR HANDLING FUSES AND CATCHES

(a) The use of wooden pliers in handling fuses has eliminated
a great many accidents which occur from the careless handling
of fuses.

(6) A safe and useful tool for removing catches in junction
boxes under short-circuit conditions consists of a long insulated

FIG. 102. — Furnace shield.

handle with a clamp and setscrew on the end for holding the
catch. By using this device the workman may stand some
distance from the catch when it is withdrawn.

(c) A useful instrument for tracing the cause of blown fuses
consists of an insulated handle on which is mounted a fuse wire.
This fuse wire bridges the fuse terminals, and by blowing indi-
cates which of the wires of the circuit is short-circuited or
grounded.

FURNACES AND ACCESSORIES

(a) Kerosene furnaces for melting solder and compound, and
for the heating of soldering irons, are recommended in place

INSTALLATION OF CABLES 221

of the gasoline furnace which has caused many accidents on ac-
count of the inflammability of the gasoline. To prevent furnaces
from tipping over, it is the practice of some of the companies to
fill the bottom of the furnace with lead, giving it a heavy base.

(6) A very efficient device which allows the compound kettle
to be heated at the same time the solder pot is on the furnace,
consists of a shield which envelops the solder pot and carries the
compound kettle on top at the same time. A hole may be cut
in the side of the shield in which a soldering iron may be heated.
Many of these shields are now in use with very satisfactory
results, Fig. 102.

(c) When it is necessary to use gasoline, a very safe can or
container is one that cannot be exploded by igniting the gasoline
at the filling hole. A can of this type is on the market in several
different styles and thicknesses of material.

TEST LAMPS

Several styles of test lamps are in use.

(a) In one of these the lamps are enclosed in a small wooden
frame which prevents the lamps from being broken and is easily
packed in the tool kit. The contact points in connection with
this type of test lamp are made of common brad awls, the wires
being soldered to the awl points at the wooden handles, forming
not only an insulated handle but at the same time allowing the
workmen a firm grip on the contact points which is much more
desirable than having loose and flabby wires in his hand.

(&) Another form of test lamp has metal guards, but this is
found to be undesirable on account of the number of short-
circuits that have occurred by these guards falling across live
wires.

OPENING AND GUARDING MANHOLES

(a) Hooks for removing and replacing manhole covers, which
engage in a hole in the manhole cover, are found to be very con-
venient. On the end opposite the hook there is a ring handle.
In using these hooks the covers are dragged from the manhole,
which is preferable to prying them up and turning them over by
hand, as this method frequently results in injury to the hands
and feet on account of the covers slipping or falling.

(6) A guard rail may be made either of pipe, Fig. 103, or angle

222 UNDERGROUND TRANSMISSION AND DISTRIBUTION

FIG. 103. — Wrought-iron pipe manhole guard.

FIG. 104. — Warning flag.

INSTALLATION OF CABLES 223

iron, both forms of which are used extensively. The guard rail
should be made collapsible so that it may be stored in a tool cart
or wagon.

(c) It is customary to have a red flag displayed, and it seems
advisable to have, as a further safeguard, a danger sign, as in
many places very little attention is paid to a red flag. A flag
which is kept extended at all times by a wire device which folds
back against the staff when the flag is furled is shown in Fig. 104.

(d) Several types of gratings are used to cover open manholes.
Covers made of flat bar iron or heavy wire mesh are commonly

FIG. 105. — Manhole grating.

used. An excellent type of grating is one which is hinged in the
center, allowing one side of the grating to be raised for lowering
tools and materials into the manhole, as shown in Fig. 105.
Gratings for manholes are especially useful near railroad tracks
and places where the regular manhole railing cannot be kept in
place.

TESTING FOR LIVE CABLES

(a) There are several devices for testing cables to determine
whether they are alive before working on them. The first is a
pointed tool on the end of an insulated handle. The tool is
provided with a short piece of cable and clamp for attaching to
the cable sheath, Fig. 106. This insures the passage of the cur-

224 UNDERGROUND TRANSMISSION AND DISTRIBUTION

FIG. 106.— Tool for testing cable.

FIG. 107. — Geissler tube.

INSTALLATION OF CABLES 225

rent through to ground if the cable is alive when the tool is driven
into it.

(b) A similar device, but of different form, is the spear type
which, on account of the length of the handle, may be driven into
the cable from the street surface.

(c) Another method for determining the cable to be worked on
is to put a current of high frequency through the cable, and this
cable may be readily detected in the manhole by the use of an
exploring coil and telephone headpiece. The high-frequency
note that is struck when the exploring coil comes into contact
with the high-frequency cable is readily distinguished from the
note of the cables of lower frequency.

(d) The electroscope is sometimes used for detecting the pres-
ence of a live conductor. The electroscope is used by high-ten-
sion cable splicers to test a line after the lead sheath has been
removed.

(e) Recently the Geissler tube has been used for work of this
kind. The tube is connected between conductor and ground,
and if the cable is alive it is denoted by the illumination given
off by the tube, Fig. 107.

VENTILATION OF MANHOLES

(a) The most effective method of ventilating manholes con-
taining illuminating or other gases is by the use of either a motor-
driven fan or one operated by hand.

(6) There is another very efficient device for ventilating man-
holes which, however, is not recommended for removing gases.
This device consists of a canvas shield hung on the handrail
and passing down to a point near the bottom of the hole. This
canvas is always placed facing the wind, which passes down in
front of it and comes out of the hole on the opposite side of the
shield. This device has been found to give entire satisfaction
and is highly recommended for this work.

MISCELLANEOUS

(a) A very effective lamp guard made of fiber is found useful
around live low-tension work, as it eliminates the danger of
short-circuits should the lamp fall from the man's hand upon a
live terminal.

226 UNDERGROUND TRANSMISSION AND DISTRIBUTION

(b) Smoke helmets and respirators are very useful in man-
holes that are full of gas. There are several satisfactory respira-
tors in use today. Some of the less complicated types of smoke
helmets are very effective for rescue work in manholes, as it is
possible to wear them for periods of 30 min. or more without
the operator suffering any inconvenience.

(c) Storage-battery lamps for illumination of manholes should
be used when current from the mains is not available. The use
of open-flame lamps or torches should be avoided.

(d) On account of the many cases of employees getting dirt in
their eyes, and receiving other injuries to their eyes while working
in manholes, the wearing of an approved type of safety goggle is
advisable.

(e) It is good practice to display red lamps upon piles of
material and around openings at night and also on dark days, as
a great many accidents have been caused by employees and
others stumbling over material in dark places and also falling
through unprotected openings.

(/) Emergency wagons equipped with smoke helmets, pul-
motors, and first-aid outfits, along with tools for quick repairs,
etc., have proven very efficient.

(g) To prevent short-circuits between conductors of Edison
tube joints and prevent undue heating of conductors adjacent
to the one being worked on, the use of sheets of asbestos between
conductors has met with considerable favor.

(h) The use of rubber mats in manholes and junction boxes
has recently come into use. By their use the cable to be worked
on can be isolated, and the workman does not need to be as careful
as formerly, not having to consider burning the sheaths of the
adjoining cables while using solder; and, furthermore, the pos-
sibility of live cable ends falling on the other cable sheaths is
eliminated, the rubber shield completely blanketing all cables
with the exception of the one being worked on.

CHAPTER VII
TESTING OF CABLES

International Electrical Units. — The following resolutions were
adopted by the International Congress of Electricians, held at
Chicago in 1893. They were legalized by act of Congress and
approved by the president on July 12, 1894, and are now recog-
nized as the International Units of value for their respective
purposes.

Resolved, That the several governments represented by the
delegates of the International Congress of Electricians be, and
they are hereby, recommended to formally adopt as legal units
of electrical measure the following:

1. As a unit of resistance, the International Ohm, which is
based upon the ohm equal to 109 units of resistance of the
c.g.s. system of electromagnetic units, and is represented by the
resistance offered to an unvarying electric current by a column of
mercury at a temperature of melting ice, 14.4521 grams in mass,
of a constant cross-sectional area, and of the length 106.3 cm.

2. As a unit of current, the International Ampere, which is
one-tenth of the unit of current of the c.g.s. system of electro-
magnetic units, and which is represented sufficiently well for
practical use by the unvarying current which, when passed
through a solution of nitrate of silver in water, in accordance
with the accompanying specification (A) deposits silver at the
rate of 0.001118 gram per second.

3. As a unit of electromotive force, the International Volt,
which is the e.m.f. that, steadily applied to a conductor whose
resistance is one International Ohm, will produce a current of
one International Ampere, and which is represented sufficiently

1 000
well for practical use by T^TOT of the e.m.f. between the poles

or electrodes of the voltaic cell, known as Clark's cell, at a
temperature of 15°C., and prepared in the manner described
in the accompanying specification (B).

4. As the unit of quantity, the International Coulomb, which

227

228 UNDERGROUND TRANSMISSION AND DISTRIBUTION

is the quantity of electricity transferred by current of one
International Ampere in one second.

5. As the unit of capacity, the International Farad, which is
the capacity of a conductor charged to a potential of one Inter-
national Volt by one International Coulomb of electricity.

6. As the unit of work, the joule, which is 107 units of work
in the c.g.s. system, and which is represented sufficiently well for
practical use by the energy expended in one second by an Inter-
national Ampere in an International Ohm.

7. As the unit of power, the watt, which is equal to 107 units
of power in the c.g.s. system, and which is represented sufficiently
well for practical use, by the work done at the rate of one joule
per second.

8. As the unit of induction, the henry, which is the induction
in the circuit when the e.m.f. induced in this circuit is one Inter-
national Volt, while the inducing current varies at the rate of
one International Ampere per second.

NOTE. — Specifications (A) and (B), omitted here, may be
found in the original publication and in the electrical handbooks.

Standardization Rules. — In the Standardization Rules of the
American Institute of Electrical Engineers, approved June 30,
1915, the following recommendations are made in regard to
cable tests:

HEATING AND TEMPERATURE OF CABLES

677. Maximum Safe Limiting Temperatures. — The maximum
safe limiting temperature in degrees C. at the surface of the
conductor in a cable shall be:

For impregnated-paper insulation (85-E)

For varnished-cambric insulation (75-E)

For rubber insulation (60-0.251?) .

Where E represents the r.m.s. operating e.m.f. in kilovolts be-
tween conductors.

Thus, at a working pressure of 3.3 kv., the maximum safe
limiting temperature at the surface of the conductor or conduct-
ors, in a cable would be:

For impregnated-paper insulation (81.7°C.)

For varnished-cambric insulation (71.7°C.)

For rubber insulation (59.2°C.)

TESTING OF CABLES 229

ELECTRICAL TESTS.

678. Lengths Tested. — Electrical tests of insulation on wires and
cables shall be made on the entire lengths to be shipped.

679. Immersion in Water. — Electrical tests on insulated con-
ductors not enclosed in a lead sheath, shall be made while im-
mersed in water after an immersion of 12 hr., if insulated with
rubber compounds, or if insulated with varnished cambric.
It is not necessary to immerse in water insulated conductors
enclosed in a lead sheath.

In multiple-conductor cables, without waterproof overall
jacket of insulation, no immersion tests should be made on
finished cables, but only on the individual conductors before
assembling.

680. Dielectric-strength Tests. — Object of Tests. — Dielectric tests
are intended to detect weak spots in the insulation and to de-
termine whether the dielectric strength of the insulation is
sufficient for enabling it to withstand the voltage to which it is
likely to be subjected in service, with a suitable factor of
assurance.

The initially applied voltage must not be greater than the
working voltage, and the rate of increase shall not be over 100
per cent, in 10 sec.

681. Factor of Assurance. — The factor of assurance of wire or
cable insulation shall be the ratio of the voltage at which it is
tested to that at which it is used.

682. Test Voltage. — The dielectric strength of wire and cable
insulation shall be tested at the factory, by applying an alter-
nating test voltage between the conductor and sheath or water.

683. The magnitude and duration of the test voltage should depend
on the dielectric strength and thickness of the insulation, the
length and diameter of the wire or cable, and the assurance factor
required, the latter in turn depending upon the importance of
the service in which the wire or cable is employed.

684. The following test voltages shall apply unless a departure
is considered necessary, in view of the above circumstances.
Rubber-covered wires or cable for voltages up to 7 kv. shall be
tested in accordance with the National Electric Code. Stand-
ardization for higher voltages for rubber-insulated cables is
not considered possible at the present time.

Varnished-cambric and impregnated-paper insulated wires or

230 UNDERGROUND TRANSMISSION AND DISTRIBUTION

cables shall be tested at the place of manufacture for 5 min.
in accordance with the Table XXX below:

TABLE XXX. — RECOMMENDED TEST KILOVOLTS CORRESPONDING TO OPER-
ATING KILOVOLTS

Operating kv.

Test kv.

Operating kv.

Test kv.

Below 0.5

2.51

0.5

3.0

1.0

4.0

2.0

6.5

, 3.0

9.0

4.0

11.5

1 The minimum thickness of insulation shall be He in- (1-6 mm.).

Different engineers specify different thickness of insulation
for the same working voltages. Therefore, at the present time
the test kilovoltage corresponding to working kilovoltage given
in Table XXX are based on the minimum thickness of the insula-
tion specified by engineers and operating companies.1

685. The frequency of the test voltage shall not exceed 100 cycles
per sec., and should approximate as closely as possible to a sine
wave. The source of energy should be of ample capacity.

686. Where ultimate breakdown tests are required, these shall be
made on samples not more than 6 meters (20 ft.) long. The
maximum allowable temperature at which the test is made for
the particular type of insulation and the particular working
pressure, shall not be greater than the temperature limits given
in paragraph 677.

687. Multiple-conductor Cables. — Each conductor of a multiple-
conductor cable shall be tested against the other conductors
connected together with the sheath or water.

INSULATION RESISTANCE.

688. Definition. — The insulation resistance of an insulated
conductor is the electrical resistance offered by its insulation,
to an impressed voltage, tending to produce a leakage of current
through the same.

1 The Standards Committee does not commit itself to the principle of
basing test voltages on working voltages, but it is not yet in possession of
sufficient data to base them upon the dimensions and physical properties
of the insulation.

TESTING OF CABLES 231

689. Insulation resistance shall be expressed in megohms for
a specified length (as for a kilometer or a mile or) 1,000 ft., and
shall be corrected to a temperature of 15.5°C., using a tempera-
ture coefficient determined experimentally for the insulation
under consideration.

690. Linear insulation resistance, or the insulation resistance
of unit length, shall be expressed in terms of the megohm-kilo-
meter, or the megohm-mile, or the megohm-1,000 ft.

691. Megohms Constant. — The Megohms Constant of an
insulated conductor shall be the factor (K in the equation)

R = K logio -£

where R = the insulation resistance, in megohms, for a specified
unit length.

D = the outside diameter of insulation.

d = the diameter of conductor.

Unless otherwise stated, K will be assumed to correspond to
the mile unit of length.

692. Test. — The apparent insulation resistance should be meas-
ured after the dielectric strength test, measuring the leakage
current after a 1-min. electrification, with a continuous e.m.f. of
from 100 to 500 volts, the conductor being maintained positive
to the sheath of water.

693. Multiple-conductor Cables. — The insulation resistance of
each conductor of a multiple-conductor cable shall be the insula-
tion resistance measured from such conductor to all the other
conductors in multiple with the sheath or water.

CAPACITANCE OR ELECTROSTATIC CAPACITY.

694. Capacitance is ordinarily expressed in microfarads. Linear
Capacitance or Capacitance per unit length, shall be expressed
in microfarads per unit length (kilometer, or mile, or 1,000ft.).
and shall be corrected to a temperature of 15.5°C.

695. Microfarads Constant. — The Microfarads Constant of an
insulated conductor shall be the factor K in the equation:

c- K

Log10 -

232 UNDERGROUND TRANSMISSION AND DISTRIBUTION

where C = the capacitance in microfarads per unit length.
D = the outside diameter of insulation.
d = the diameter of conductor.

Unless otherwise stated, K will be assumed to refer to the mile
unit of length.

696. Measurement of Capacitance. — The capacitance of low-
voltage cable shall be measured by comparison with a standard
condenser for long units of high-voltage cables, where it is neces-
sary to know the true capacitance the measurement should be
made at a frequency approximating the frequency of operation.

697. Paired Cables. — The capacitance shall be measured be-
tween the two conductors of any pair, the other wires being
connected to the sheath or ground.

698. Electric Light and Power Cable. — The capacitance of low-
voltage cables is generally of but little importance. The capaci-
tance of high-voltage cables should be measured between the
conductors and also between each conductor and the other
conductors connected to the lead sheath or ground.

699. Multiple-conductor Cables (Not Paired). — The capaci-
tance of each conductor of a multiple-conductor cable shall be
the capacitance measured from such conductor to all of the
other conductors in multiple with the sheath or the ground.

NOTE. — The paragraph numbers refer to sections in the Ameri-
can Institute of Electrical Engineers Standardization Rules.

CAPACITY OF TESTING APPARATUS.

The size of electrical apparatus necessary in voltage testing,
with alternating current is not generally appreciated. This
may be due to the fact that as these tests are made on open cir-
cuits, many persons assume no current is required. However,
there is current flowing and the amount is shown by the formula:

2<irfCE
1,000,000
where

I = current flowing into the cable.

E = testing voltage.

/ = frequency.

C = electrostatic capacity of cable in microfarads.

But .the size of apparatus is dependent upon the watts required
or

TESTING OF CABLES 233

Size = Watts = / X E

' "

1,000,000 " 1,000,000

This means that the watts are proportional to the frequency
capacity and the square of the voltage, and on high-voltage tests
this means large apparatus. For instance, 1,000 ft. of a 500,000-
cm. cable with %2~m- wall of 30 per cent. Para has a capacity of
about 0.33 microfarads. With a frequency of 25 cycles, this for-
mula shows that 1.3 kw. capacity is required to test at 5,000 volts.
If this cable were to be tested at 30,000 volts, apparatus 36 times
as large, or of about 47 kw., would be required. If 60 cycles
instead of 25 were used, a 30,000-volt test would mean that the
apparatus would have to have a capacity of about 113 kw.

According to the best information available, there appears to
be no appreciable difference in severity between testing at 25 or
60 cycles on ordinary factory tests.

Locating and Repairing Cable Failures. — Numerous methods
have been tried for locating faults in underground transmission
cables, some companies depending upon the use of an intermittent
current on the damaged cable, which is then explored by means
of an induction coil and telephone receiver, while other companies
make use of the Murray loop test. Most companies avail them-
selves more or less of the method of inspection when locating
faults by sending men over the route of the cable.

As stated by W. A. Durgin, in a paper presented before the
National Electric Light Association in 1910, fault location ir
high-tension power cables requires quite a different procedure
from that usually outlined in texts upon cable testing, due to the
wide difference in the characteristics of construction between
power and intelligence transmissions. The "cut-and-try"
method is applicable to both, but if a quicker and less expensive
system is desired testing equipment of special design must be
provided.

Most of the larger companies have provided themselves with
a testing transformer which is used in connection with a motor-
driven generator to supply current of varying voltage for the
purpose of breaking down a faulty cable or applying a high-
tension test. For the purpose of expediting, as much as possible,
the work of locating and repairing a cable fault, specific rules

234 UNDERGROUND TRANSMISSION AND DISTRIBUTION

should be prepared governing the procedure of station, substa-
tion and underground men in such cases.

In the Proceedings of the National Electric Light Association,
Underground Committee, 1911, the report of two companies
gives the various methods by which the cable breaks are located,
and the percentage of breaks which are discovered by each
method as follows:

Method

Company A, per cent.

Company B, per cent.

Loop test

15 0

Examination. . .

36 5

Cut-and-try

17.5

Reported..

24 3

Exploring coil

1 3

Miscellaneous

5 4

Most companies, before applying the loop test, attempt to
obtain a dead ground on one phase of the cable by breaking it
down with a special transformer or generator. Following a
cable breakdown, and while the location of the break is being
determined it is customary to assemble a gang of underground
repair men, with tools and proper means of transportation at some
convenient location where they may be hurried to the place of
the burnout as soon as this is determined.

Loop Test. — Where one conductor of a multiple-conductor
cable is grounded and another conductor is clear, the following
adaption of the loop test can be used to advantage. This
method also applies to single-conductor cable where another
conductor is available for the return. The two conductors must
be of the same size or corrections will have to be made for the
difference in the resistance of the two sizes.

The grounded conductor is jointed to the good conductor at
the end opposite that at which the test is to be made. A resist-
ance wire is used, made up in the form of a straight wire bridge
or wound on a threaded drum. The wire is calibrated through-
out its length. Contact C, referring to Fig. 108, is arranged
that it can be moved along the resistance wire throughout its
entire length. A battery is connected between the contact C,
and the galvanometer between the terminals A and B. In
making test, C is set preferably at the middle point of the resist-
ance to start with. When contact is made, the galvanometer

TESTING OF CABLES

235

will swing to either one side or the other, depending on the
location of the ground. Contact C is then moved along the
resistance wire until no deflection is obtained upon the galva-
nometer. It will be evident that the distance from A to C of

FIG. 108. — Loop method of locating grounds on underground cables.

the resistance wire will represent the distance from A to G on
the conductor which is grounded.

This can be represented by the following formula, wherein
L represents the total length of the conductors joined together,

FIG. 109.— Portable fault localizes

and AC and BC represents the relative distance measured on the
resistance arm.

AC AG AC AG

Solving,

BC BG] or BG ~ L -AG'

AG =

AC (L - AG)
CB

236 UNDERGROUND TRANSMISSION AND DISTRIBUTION

A portable fault localizer is illustrated in Fig. 109.

It is an application of the Wheatstone bridge with all the
necessary apparatus contained in one portable case wired for
connection to the circuit to be tested.

Its use assumes that the cable is grounded at only one point
and that a parallel conductor of the same length and resistance
as the faulty cable is available.

After all electrical connections to the defective feeder have been
removed and before the fault localizer has been connected to the
cable, the cable is tested by means of a temporary connection
through a lamp bank or battery for the grounded conductor.
If the lamps do not burn brightly, a high-resistance ground is

l-=>>\

,000

>ooo

FIG. 110. — Diagram of connections for cable fault localizer.

indicated and should be broken down by applying a sufficiently
high voltage.

The fault localizer is connected as shown in the diagram (110)
and the dial revolved by means of the knob in the middle of the
localizer until the galvanometer shows no deflection when the
key is closed. The reading of the instrument then shows the
per cent, of length of the feeder from the point where the test is
being made to the location of the ground, assuming the total
length of the feeder to be 100 per cent. ; the red scale indicating
that the ground is on the conductor connected to the binding post
marked red, and the black scale indicating that it is on the
conductor connected to the binding post marked black.

Only direct current is used in these tests.

In this instrument all necessary apparatus is contained in
one case and it has the further advantage of easy adjustment.
The position of the ground may be read directly on the dial in
terms of per cent, of length of cable.

TESTING OF CABLES 237

Fault-locating Equipment. — In any central-station system the
most important work in connection with trouble finding is the
quick and accurate location of a break in a three-phase trans-
mission cable. With the advent of high-tension cables came a
problem which hitherto had not obtained to any great extent,
namely, the difficulty of obtaining a closed circuit for testing
current across the break, as on this closing of the signaling cir-
cuit through the fault hinges the success of all methods employ-
ing interrupted or varying current, with the exploring coil and
telephone receiver. Almost invariably in high-tension cable
breaks, there is no metallic path between conductors, or between
conductor and sheath; a thick wad of paper or other insulation
intervening, through which a path must be carbonized to com-
plete the testing circuit. With the application of sufficient pres-
sure and current this path through the insulating medium can
be made and maintained, while the fault is being located with
the exception of cases where the break is submerged in water,
or where the cable is burned completely open.

There is a wide variation in the resistance in faults in high-
tension cables; a cable may break down with a working pressure
of 13,000 volts, and upon applying a 100-volt test show practi-
cally a short-circuit through the fault. The next breakdown in
the same cable may take 5,000 volts to even indicate the existence
of trouble. It is, therefore, obvious that it is necessary to have
a test set of sufficient pressure to obtain a flow of current across
the break. It is also desirable to be able to vary this pressure
as in the use of signaling currents; the best results are obtained
with the testing voltage as low as possible. Again, on account
of the electrostatic capacity of long cables, a certain amount of
current-carrying capacity in the apparatus is required. While
it is unnecessary that this be as large as is required for a break-
down test on a sound cable, yet it should be of a considerable
value depending upon the length and working voltage of the line
in trouble.

There are some cable faults through which it is necessary to
maintain a steady flow of current at a certain pressure in order
to hold the conducting path across the break. This current
should be of a small value so as to obviate the danger of damaging
the adjacent cable and also to reduce the prospect of destroying
the conducting path by combustion. These conditions are met
by the use of the method and apparatus herein described which

238 UNDERGROUND TRANSMISSION AND DISTRIBUTION

has been used for a number of years in a large central-station
system. With this device it is possible to locate quickly and
accurately grounds, short-circuits, crosses and opens in under-
ground and overhead lines, whether the lines are carrying work-
ing current or not, also to identify for tagging different wires
and cables alive or dead, and to pick out the phase wires of an
alternating circuit on the poles, in the manholes, or on the
customer's premises, without any interruption or interference
whatever in the operation of the system.

The test set comprises two parts, the apparatus for the reduc-
tion of the fault resistance and carbonizing of the path across
the insulation medium, and the signaling device with exploring
coils and telephone receivers.

For the location of faults in No. % paper^insulated cables
of 5 miles and under, the capacity of the set is 7.5 kw. and for
over 5 miles in length, 15 kw. In general, the maximum pres-
sure of the apparatus should be one-half the greatest working
pressure of the underground system, and in the set in question
the pressures obtainable are 115-230-575-1,150-2,300-3,450-
4,600-5,750-6,900 volts. These voltages are derived from
standard lighting transformers connected in different combina-
tions to obtain varying pressures. The signaling part of the
apparatus consists of a very powerful sound-producing device
which takes current directly from either alternating current or
direct current mains. A specially designed motor-driven inter-
rupter produces a signal current of a frequency to which the tele-
phone receiver and the human ear are most responsive and which,
though extremely small in value, produces signals which are
easily heard. The voltage, current, and tone of the signaling
circuit can be varied at will. It will interrupt either alternating
current or direct current giving a distinctly different tone on
each. Wherever alternating current is available it is used in
preference to direct current as the apparatus is somewhat simpler.

This interrupter is of rugged construction, can be used on the
system voltage, in conjunction with the ordinary transformer,
and will run for hours without any attention whatever, giving
out a never- varying signal.

While this outfit is designed to be set up permanently in the
station, a portable set of about 3 kw. capacity can be used where
necessary. This is capable of handling practically all faults
except those submerged in water or of very high resistance.

TESTING OF CABLES 239

The apparatus is designed to be used by the ordinary trouble
hunter without the. use of laboratory instruments, and it can be
used to advantage in conjunction with the power bridge loop
and capacity instruments, etc., to locate faults exactly without
opening any joints in cables.

The signaling system can be adapted to any existing type of
breakdown apparatus.

It is often desirable to be able to pick out the different legs or
phases of an alternating circuit, at some point distant from the
source of supply. This can be done by superposing the inter-
rupted currents on the primary line through an ordinary trans-
former without any interference in the working of the circuit.
By applying the exploring coils to the different wires of the cir-
cuit it can be determined to which pair the interrupter is con-
nected. Likewise, if it is desired to know which phase supplies
a certain customer, by attaching a plug to a lamp socket and
listening through a telephone receiver connected to a special
type of coil, this can be readily determined.

A diagnosis and a somewhat predictive location of faults can
be made with a little experience in working the apparatus.
Faults in water show certain characteristics and the wet holes
being known, some idea is given of the location of the breaks.
Experience in carbonizing a fault shows whether it is in a section
of cable or in a joint by measuring the charging current the
distance to an open end can be approximately figured. If there
is a cross between the live side of a grounded secondary and a
primary or street-lighting circuit, this can be shown in advance.
Advantage can be taken of the phenomenon of resonance to
discriminate between the natural leakage and charging current
of a circuit, and fault current, all of which makes it much easier
to locate trouble.

For secondary networks, and breaks in low resistance, on
isolated lines and cables, a portable vibrating interrupter, which
will operate on two dry cells, has been developed. This inter-
rupter gives a very good signal and can be heard through 1,000
ohms resistance. While the foregoing apparatus is intended
primarily for underground cables it can be used with the same
success on overhead lines.

The method and apparatus was devised by James A. Vahey, of
the Edison Electric Illuminating Co, of Boston, Mass,

240 UNDERGROUND TRANSMISSION AND DISTRIBUTION

Periodic High-potential Testing of Transmission Cables.—
There is a great variation of opinion in regard to the advisability
of periodically testing transmission cables. It is the practice of
most companies to apply a breakdown test of 150 to 200 per
cent, of working voltage on new lines for an average time of 5
min. In some cases cables are subjected to high-potential test
only after meager tests show a low value or after a series of
breakdowns.

The following regarding high-potential testing is taken from
the National Electric Light Association, Underground Committee
report.

Some companies subject their cables to a high-potential test,
once, twice and even three times a year, with pressures as high
as three times normal working voltage. Other companies make
insulation tests only, unless the record of any cable should show a
gradual decrease in insulation resistance, in which case it would be
subjected to a high-potential test to break down the developing
defect. Several cases of incipient trouble have been discovered
and eliminated by this method, but it has not always proved
successful.

One large company started to make high-potential tests on all
of its cables twice a year, but for various reasons this practice
was soon abandoned. With the numerous changes in its under-
ground system and the practice of subjecting cables to a high-
potential test after any changes have been made on them, many
of the lines thus obtained a test indirectly. A few cases occurred
in which lines withstood the test but broke down shortly after-
ward, notably one case in which the lead sheath of the cable
was damaged by electrolysis. This cable burned out a few days
after the high-potential test, and an examination of the cable
showed that there must have been a hole in the lead sheath for
several weeks previous to the test.

Several companies are now installing apparatus with the view
of making periodic high-potential breakdown tests on all of their
transmission lines, while other companies which already have the
necessary equipment have abandoned the practice of making such
test.

In general, it might be said that high-potential tests increase
the liability to subsequent breakdowns and often do not disclose
existing points of weakness.

CHAPTER VIII
DISTRIBUTION SYSTEMS AND AUXILIARY EQUIPMENT

General. — In dealing with systems of distribution, no attempt
will be made to take up the solution of all of the electrical prob-
lems involved, numerous text-books and reports of engineering
associations having covered this subject in considerable detail.
Modern three-wire direct-current distributing systems consist
essentially of a three-wire network of distributing mains with
numerous cable feeders delivering current at different points
in the network, the current being supplied by a system of sub-
stations. Since the direct-current system of underground dis-
tribution is confined so largely to the Edison system, which
has been developed to a high degree of perfection and in which
most of the problems in handling low-potential current have
been solved, it is thought unnecessary to include this subject in
the discussion.

Alternating-current Distribution. — The secondary network in
an alternating-current system is practically identical in its es-
sential details with its predecessor, the direct-current network,
and, therefore, had a number of its problems already solved.
However, the higher voltages employed in the alternating-current
system brought about difficulties which have been satisfactorily
overcome only after years of experience and effort.

The distribution of alternating current for general commercial
purposes is accomplished in America almost universally by 2,200-
volt mains supplying step-down transformers located near groups
of consumers who are served by secondary mains at 110 to 220
volts. Lighting service is quite generally single-phase; while
power service is more frequently two-phase or three-phase.
Two-phase systems are in use chiefly where this method of dis-
tribution was established in the early period of development and
is too extensive to warrant changing to the three-phase system.
Three-phase systems are now standard for nearly all new power
installations. Alternating-current underground distribution in
general conforms to established overhead practice so far as voltage,
16 241

242 UNDERGROUND TRANSMISSION AND DISTRIBUTION

character of service and regulation are concerned. Alternating-
current systems are divided into primary and secondary dis-
tribution, which may be subdivided into single-phase, two-phase
(three- and four- wire), and three-phase (three- and four- wire)
systems.

Single-phase. — In the early days of the industry all distribu-
tion was single-phase. This system is very simple to install and
maintain but has the serious disadvantage of not being well
adapted for power loads except where the motors are of small
rating. Single-phase motors are not, as a rule, manufactured in
large sizes because their design is complicated and expensive and,

FIG. 111. — Single-phase two and three-wire system. The fuses on the
secondary side of the transformer may be omitted.

since they are not self-starting, a costly split-phase starting con-
trol is a necessary part of the motor equipment.

As a rule, straight single-phase primary distribution is not
employed except in scattered districts where the diversity factor
is such as to make the loading of a single-phase circuit more
economical than that of a polyphase circuit.

A single-phase, two- , and three-wire system is illustrated in
Fig. 111.

Two-phase. — A two-phase system is supplied by a generator
which generates two voltages which are in quadrature, i.e., one
voltage is a quarter cycle behind the other. This system pos-
sesses the same advantages as the single-phase system as regards
economical loading of circuits butjias, in addition, the important

DISTRIBUTION SYSTEMS

243

advantage that it may be used to take care of motor loads
without the use of the expensive starting apparatus required
by a single-phase motor.

3 F>HA 5£ 2 f

3 W//?£ 5

FIG. 112. — Two-phase, three-wire system.

7>
n

P.4/V
/J^

'J.

'» 1

[

r«S£S \

} i

-^
— £

) [

' /=»//>? 3^

FIG. 113. — Two-phase, four-wire system.

The two-phase system may be either three or four-wire.
Where used as a four-wire system, the transmission of energy

244 UNDERGROUND TRANSMISSION AND DISTRIBUTION

is in effect single-phase. The distribution of energy, however,
is a combination of single- and two-phase, since the lighting load
is taken care of on a number of single-phase taps made in such a
way that the load is balanced between A and B phases, while
the motor load makes use of both phases.

In the two-phase, three-wire system, two of the four wires
are replaced by a single wire called the neutral, the cross-section
of which is theoretically 41.4 per cent, greater than either of the
other two. The three-wire system requires less copper than the

V CONNECT/ON

FIG. 114. — Three-phase, three-wire system.

four-wire for the same current-carrying capacity but it is less
flexible, and good regulation is difficult because load conditions
on one phase will affect the other phase, thereby producing un-
balanced voltages.

Two-phase, three-wire, and two-phase, four-wire systems are
shown in Fig. 112 and 113.

Three-Phase. — The three-phase system may be used with
either three or four wires. The three-wire system may be either
A- or 7-connected; and where good load balances may be obtained,
it is very satisfactory. However, a balanced load is difficult to
obtain; and where the load is unbalanced, there is a shifting
of the neutral, with the result that voltage regulation is

DISTRIBUTION SYSTEMS

245

difficult. For this reason the four-wire system has many
advantages over the three-wire system and has been adopted
in many of the best installations. In this system, which is
7-connected, a neutral wire carries the unbalanced current,
making it possible to obtain good voltage regulation on all three
phases even when a condition of considerable unbalance exists.
Since this neutral wire is at approximately ground potential; it
will be seen that it is possible to transmit at considerably higher
voltage between phases without increasing the potential of the
system with respect to ground. For instance, a three-phase,

S/NGLE /=>HAS£

A S£COM0A#Y A SECOMOA/PY V CONNECT/O/

YSECONOARY Y SECONDARY SCOTT COfSM£CT/ON

FIG. 115. — Three-phase, four-wire system.

three-wire system with 2,400 volts between phases may be re-
placed by a three-phase, four-wire system with approximately
4,100 volts between phases without raising the voltage to ground.
This results in a reduction in the size of the conductors, which
is only partly offset by the increased cost of the neutral wire.

Three-phase, three-wire, and three-phase, four-wire systems
are shown in Figs. 114 and 115.

The following table gives a comparison of the weights of wire
required by the various systems based on the single-phase system
as 100 per cent, transmitted load and other conditions being
equal.

246 UNDERGROUND TRANSMISSION AND DISTRIBUTION

TABLE XXXI

System

Size of wire

Per cent, of
single-phase,
two- wire

Single-phase, two-wire

100.00

Two-phase, three-wire

Neutral equal to outside

75 00

Two-phase, three-wire
Two-phase, four-wire

Neutral 1.41 times outside.. . .

72.90
100.00

Three-phase three-wire

75 00

Three-phase four-wire .

Neutral equal to outside

33 30

Three-phase, four-wire .

Neutral one-half outside.

29 16

Secondary Mains. — The arrangement of secondary mains
depends largely upon the density of the load. In outlying dis-
tricts where the load runs from 1 to 10 kw. in each block, the

FIG. 116. — A. C. primary and secondary distribution system, showing use of
junction boxes and fuses.

size of secondary wires is comparatively small and the distance
between transformers is such that the interconnection of adjacent
secondary mains is not commonly considered desirable. In
the denser parts of a city, where business buildings are served,
a cross-connected network is frequently developed. The inter-
connection of secondary mains has the advantages of making
use of spare capacity, by equalizing loads on adjacent trans-
formers. The network is the last step in the development of a
system of secondary mains, the gradual extension of mains on all

DISTRIBUTION SYSTEMS

247

intersecting streets resulting in a system of lines which is inter-
connected thus forming a network. In the design of networks,
the selection of sizes of secondary cable is restricted by the practi-
cal conditions in each locality. The smaller and more widely dis-
tributed consumers are carried on mains of proper size to deliver
the total energy demanded. Large consumers, such as theatres
and department stores are usually more economically cared for
by a separate installation of transformers in the immediate
vicinity of the consumer's premises.

The desirability of establishing centers of distribution to
which a circuit is run directly from the substation without other

VNV™™*V™VYW

-a-

FIG. 1 17. — A. C. distribution system, showing use of oil switches.

connections has led to the development of several schemes for
interconnecting or disconnecting circuits at central distributing
points, as may be required in the operation of the system.
Among these methods attention is called to the use of junction
boxes equipped with fuses or solid connectors, adapted for easy
removal or manipulation in order to accomplish the desired result.
Another scheme includes the use of manual non-automatic oil
switches connected in distributing circuits for sectionalizing and
disconnecting purposes. In a few instances recourse has been had
to automatic switches, or special forms of high-tension fuses of
either the oil or cartridge type, arranged to automatically discon-
nect faulty sections of primary circuits from the main circuit.

248 UNDERGROUND TRANSMISSION AND DISTRIBUTION

Typical arrangements of these schemes are outlined in Figs,
lift and 117, which show the method of applying the various
devices referred to for sectionalizing and interconnecting pur-
poses, as well as for disconnecting circuits to improve working
conditions.

Underground Transformers. — The method of installing trans-
formers, standard subway types of which are on the market,
plays a very important part in the successful operation of an
alternating-current underground distribution system. Trans-
formers as now manufactured, when properly installed and cared
for, will give reasonably reliable service without automatic pro-
tection. The practice, however, varies with different companies,
some using fuses or automatic protection in connection with
every manhole transformer, and others connecting them solid.
Transformers for underground installation must possess certain
features in order successfully to meet all service conditions. The
following may be mentioned as especially important.

They must be water-tight, as subways are not always dry.
They must be properly proportioned for the limited space
available in manholes, and they must have small iron losses
because they are continuously connected to the mains. The
radiating surface must be large and the temperature rise small,
since the manholes are practically air-tight, limiting the dissi-
pation of heat. While in the past manufacturers have considered
that underground transformers should be provided with
emergency relief valves or vents in order to prevent the creation
of dangerous pressures within the transformer cases, it may
be definitely stated that the use of such devices is entirely unneces-
sary and their omission is recommended in all cases. An exhaus-
tive study of underground transformer troubles by the National
Electric Light Association Committee on Underground Construc-
tion reveals the fact that many troubles may be traced directly
or indirectly to the use of relief devices or to poor electrical con-
nections resulting from careless or improper installation methods.
Troubles caused by the occasional flooding of transformer
manholes where relief devices have been in use may be emphasized
as a reason for their omission, as many cases of transformer
failures are directly traceable either to water or moisture enter-
ing the relief device or the transformer case through loose covers
or other points of entrance which have not been properly sealed
at the time of installation.

DISTRIBUTION SYSTEMS 249

The importance of maintaining the oil in underground trans-
formers in perfect condition, free from moisture or sediment,
cannot be too strongly emphasized, as the life of the transformer
depends on the elimination of these conditions.

Precautions should be taken by operating companies to insure
proper installation and operation of transformers, and in addi-
tion to an inspection of the oil at least once a year, air pressure
should be applied to the transformer cases after installation to
detect leaks. Transformers should be so placed in the under-
ground chamber that the oil gage and oil drain are readily visible
and accessible.

The transformer should be subjected to an air pressure of
about 6 Ib. per sq. in. when full of oil and after the line and feeder
connections have been made. To make the air-pressure test,
any convenient device, such as a small air pump used to inflate
automobile tires, can be used to establish the required pressure.

The chief transformer difficulties which most companies
encounter are caused by the flooding of subways and manholes.
Occasional failures in the cable connections to the transformers
have also contributed to the list of troubles in this class of service.
If water gets into the transformer tank, it will be necessary to
dry out the transformer before it is again placed in service.
The simplest method of doing this is as follows: Drain off all
the oil from the transformer. Then, with the cover off, circulate
sufficient current through the coils to maintain a temperature of
about 80°C. With the secondary coils short-circuited, about
1^2 to 3 per cent, of the rated voltage applied to the primary
windings should be sufficient to produce the required heating.
The temperature may be determined by a thermometer between
the coils and in good contact with them. During the first hour
of this operation the temperature should be carefully observed
so that the coils will not attain a temperature exceeding the
above-mentioned value. Under ordinary circumstances 10
or 12 hr. should be a sufficient length of time to properly drive
out all moisture from the coils. If, however, there are evidences
of moisture at the end of this time, the heating should be
continued several hours longer.

Transformers should be provided with cutout subway boxes
on both primary and secondary sides if they feed an underground
distribution network. If they feed only isolated sections, the
cutout on the secondary side may be omitted. These boxes need

250 UNDERGROUND TRANSMISSION AND DISTRIBUTION

not necessarily be fused, as a number of companies consider that
fuses give more or less trouble. Several companies recommend
the omission of fuses on both the primary and secondary sides,
and depend for protection entirely upon the automatic devices
in the station. Fuses, where used, are between 150 and 200 per
cent, of cable capacity. The neutral is connected solid in all
cases, and is usually not brought into the junction box. The
secondary neutral of the transformer should be a solid copper
conductor where it enters the transformer case. If stranded
wire is used, water is apt to be siphoned into the transformer when
manholes are flooded, and special precaution should, therefore,
be taken to see that this connection is made water-tight.

The location of transformers at street intersections is especially
desirable as it permits of the supply of electricity in four direc-
tions from one unit. With alley lines, where the high-tension
distribution is overhead, it is sometimes preferable to locate
the transformers for the underground secondaries on poles. In
large installations, transformers are usually located in separate
manholes or in vaults on the customer's premises.

It is usual in subway systems to connect transformers in
multiple so that in case of a transformer failure the service may
not be interrupted, although there may be a temporary drop in
voltage until part of the load can be transferred to an adjacent
transformer bank.

Some trouble has been experienced due to transformers not
operating satisfactorily in parallel and it has been necessary in
some instances to install reactors in the transformer cases so that
the load may be properly shared by the different units. The
operation of subway transformers in multiple, however, has
proved a valuable means of safeguarding service, and many
failures of transformers or transformer bushings have resulted in
no interruption of service, the only indication of trouble being a
slight lowering of voltage at the immediate load supplied by the
defective transformer.

No particular precaution seems to be necessary to conduct heat
away from transformer manholes except with large installations,
where a cold-air intake is provided at the bottom of the manhole
and a vent at the top, as illustrated in Fig. 118. These are
usually placed alongside of an adjoining building where such ar-
rangements can be made.

In temperate zones, transformers of moderate capacities may

DISTRIBUTION SYSTEMS

251

be safely installed in manholes where 3 cu. ft. of space per kva.
is provided, without installing any special means of ventilation
other than that afforded by a perforated manhole cover. When
the concentration of transformer capacity in a single manhole
reaches 200 kva. or more, under conditions where the space

No.l Ventilated Cover

Ventilated
Cover

FIG. 118. — Methods of ventilating transformer manholes.

factor must be reduced below the limit given above, some special
facilities for ventilation must be provided to avoid temperature
rises in excess of those allowed and guaranteed as permissible by
manufacturers. Natural ventilation is to be preferred in all

252 UNDERGROUND TRANSMISSION AND DISTRIBUTION

cases where conditions are favorable for the installation of suitable
means for promoting a rapid circulation of air through the man-
hole. In some cases recourse may be had to artificial circulation
by placing small blowers in manholes to draw air in or out, as
may be convenient.

In general, it may be said that 8 watts of transformer losses
may be allowed per sq. ft. of wall surface. In moist soil with
ventilated chamber, 12 watts may be allowed; while under
unfavorable conditions not more than 6 watts per sq. ft. would be
permissible. The total surface, including roof and floor, should
be included when determining wall surface.

It is recommended that transformers be installed directly in
contact with the bottom of manholes, and not blocked up off the
bottom in any case unless the transformer case is reliably
grounded.

Some of the most serious accidents on record have been either
indirectly or directly the results of shocks received from trans-
former cases placed on wooden blocks in manholes, all of these
accidents being primarily due to a failure of the transformer or
wiring connections, whereby high potential was impressed upon
the ungrounded transformer case.

Cable Junction Boxes. — Due to the wide extent of territory
covered by alternating-current feeders and mains, and to the large
load connected to same, suitable emergency ties, junction boxes,
oil fuses, etc., must be provided to sectionalize the portions of
the system which may be affected or upon which work must be
performed. The necessity of these auxiliary devices is apparent
when one considers the high potential of the alternating-current
system as compared with the low potential of the direct-current
system.

Undoubtedly the greatest difficulty has been in the develop-
ment of primary fuses and junction boxes. If one is to judge by
the widely differing types of these devices in use, engineers are
not agreed as to the best solution of this problem. Underground
alternating-current distribution would probably now be more
extensively used but for lack of confidence in the primary fuse and
means for quickly and safely cutting in and out portions of a,
primary network in case of trouble.

Low- voltage cable junction boxes for 250- and 500-volt opera-
tion have been in general use for a number of years, but the
development of the alternating-current underground system of

DISTRIBUTION SYSTEMS

253

distribution has brought about a demand for similar subway
boxes for use at higher voltages. Primary fuse boxes in which
the fuses were immersed in oil have been used by some companies,
but in a number of cases their operation has been very unsatis-
factory. One general defect of a number of oil fuse boxes which
have been on the market in the past is that little or no effort had
been made to dampen the effect of the explosion when the fuse
was blown, the explosion of the fuse often bursting the box casting
itself, and also at times throwing the oil over the workmen.
Boxes of recent design, however, have been constructed to

FIG. 119. — Subway box with fuse immersed in oil.

operate successfully by the use of a special form of fuse holder,
which has been able to withstand satisfactorily the explosion
and arc of a blowing fuse without damage to the box and without
disturbing the oil contained therein to any noticeable extent.
This form of box, which is shown in Fig. 119, is not provided with
a relief valve, but the fuse holder consists of a special form of
cartridge holder with an insulating handle which carries the wire
fuse through the center and connects the ends to the fuse clip by
ordinary knife blades. The fuse wire itself is so built that the
overload current blows it at the center, and the result of the
explosion is greatly dampened by means of a cushion of air
trapped in the upper part of the horizontal tube mounted in the

254 UNDERGROUND TRANSMISSION AND DISTRIBUTION

center of the fuse holder. Tests with this type of box made
close to a source of power of 2,000 kw. failed to cause any
explosive action or throwing of oil under short-circuit.

220

I 18

0 100 200 300 400 500 600 700 800 900 1000 1100
Amperes

FIG. 120. — Fusing current of copper wire immersed in oil.

FIG. 121. — Four-way three-conductor subway box.

The boxes are usually fused'for short-circuit and not for over-
load protection. The curve shown in Fig. 120 shows the relation
between fusing current and size of wire.

DISTRIBUTION SYSTEMS

255

The first essential in the successful operation of any system
is continuity of service. While all systems are more or less sub-
ject to interruptions; each system should be so designed that
these interruptions will be reduced to a minimum, both as to
duration and area affected.

Fig. 121 shows a four- way, three-conductor interconnecting
junction box suitable for 4,500 volts working pressure. All live

FIG. 122. — Backview four-way three-conductor subway box.

parts are mounted in porcelain cells, one cell taking care of one
cable conductor. The bus connections are made on the rear
by copper straps connecting from the various studs to give the
desired combination. Flexible insulated cable leads are extended
through the side of the box from the other stud of each individual
porcelain cell, thereby making it possible to assemble all current-
carrying parts in the porcelain cells which are mounted in a
frame.

Fig. 122 shows a rear view of the arrangement and electrical
connections, which, when the box is assembled, are all imbedded

256 UNDERGROUND TRANSMISSION AND DISTRIBUTION

FIG. 123. — Two-way three-conductor sectionalizing box.

FIG. 124. — Single-pole primary cutout box.

DISTRIBUTION SYSTEMS

257

in insulating compound. A two-way sectionalizing box of the
same construction, built for three-conductor cable operated at
4,500 volts, is illustrated in Fig. 123.

A single-pole primary cutout box for fusing 2,500-volt cables
is shown in Fig. 124. In this particular design the ends of the
cable are sealed and thoroughly protected from moisture by a
nipple terminal which extends through the wall of the box casting
and at the same time acts as a support for the spring clip which
takes the enclosed fuse.

Oils

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FIG. 125. — Three-pole low-voltage sectionalizing box.

Fig. 125 shows a three-pole sectionalizing box, designed for
low voltage. The box may be arranged for multiple- or single-
conductor cables, depending upon local conditions. All cables
whether single or multiple form are terminated by sealed nipple
terminal structures; and disconnecting straps extend between the
stems in these nipples so that all slate or other bases may be
entirely eliminated.

In some installations spare feeders have been provided to be
used in case of emergency. These feeders are usually equipped
with suitable subway boxes so that they may be connected to any
of the feeders in trouble and supply service while repairs are being

258 UNDERGROUND TRANSMISSION AND DISTRIBUTION

made. Practice seems to have demonstrated that the fusing
of mains is unsatisfactory; and in most installations no fuses are
used in the primary system except on transformers.

Safety to workmen and continuity of service demand the use
of more reliable apparatus on an alternating-current system than
is required on a direct-current system. The additional cost of
sectionalizing devices for the alternating-current underground
system is small as compared with the cost of the direct-current
system. Load and service will be important factors in the choice
of the system.

FIG. 126. — Manhole service bus.

Service Bus. — In many systems, subway branch boxes are
used on the main cable for taking care of the service connections
to consumers. These boxes add considerably to the cost of the
service installation, and it is frequently necessary to install
additional boxes in cases where the number of outlets in the
original box installation is insufficient to take care of the ultimate
number of service connections. A novel method of taking care
of service connections is by the use of a rubber-insulated bus
mounted on the wall of the manhole or distribution hole, as shown
in Fig. 126. In this type of construction a hand splice is made
on the main paper-insulated lead-covered cable with rubber-

DISTRIBUTION SYSTEMS

259

insulated lead-covered cable; the lead sheath on the branch cable
terminating a short distance below the bus rack. Service con-
nections are made to the bus with rubber-insulated cable covered
with weatherproof braid, the bus cable being a solid conductor
in order to avoid any moisture siphoning into the paper cable
in case the rubber insulation or service-connection joints become
defective while the manhole is filled with water. Installations
of this character have proved very successful and have been in
operation on 220-volt alternating-current systems for a period
of about 10 years without failure. The principal advantage with

FIG. 127. — A.C. and D.C. service bus with sectionalizing box in manhole.

this form of construction is that the services of a lead jointer are
not required to make connections to the service bus; and any
number of services up to the capacity of the bus may be installed
as the occasion requires. In Fig. 127 is shown a bus arrangement
as just described, with sectionalizing boxes on the secondary
alternating-current and 500- volt direct-current mains mounted
on the wall of the manhole.

Manhole Oil Switches. — Manhole oil switches have been used
quite extensively by a number of companies for disconnecting
sections of cable when failures occur or when it is desired to work
on a feeder without interrupting the service. Multiple-pole
hand-operated oil switches of various capacities and potentials
up to 10,000 volts are in successful operation.

260 UNDERGROUND TRANSMISSION AND DISTRIBUTION

FIG. 128. — Triple-pole 10,000-volt manhole oil switch.

FIG. 129. — Triple-pole 2,500-volt manhole oil.switch.

DISTRIBUTION SYSTEMS 261

These switches are made for mounting on flat vertical surfaces
in manholes or in locations where there is danger of flooding.
The frame, cover and oil vessel are cast iron, and by means of
gaskets, all joints are made water-tight. The switch is provided
with an operating handle on the outside of the frame of such
design that the switch can be operated with a hook.

Manhole automatic overload switches are not recommended
due to the effect of low temperature on the automatic features
and the tendency of the oil to congeal or thicken at extremely
low temperatures. While the thickening of the oil would not
interfere with the opening and closing of a non-automatic hand-
operated switch, automatic switches must depend in a large
measure upon gravity as the actuating force in opening, and the
thickened oil would have a tendency to delay or entirely pre-
vent the opening of the switch. Further, the gases generated
by an automatic switch in opening the circuit under short-circuit
conditions would, in spite of any vent which might be provided,
have a deteriorating effect upon the gaskets, with consequent
danger of water getting into the switch and causing serious
damage. In Figs. 128 and 129 two types of manhole oil switches
are shown.

Alternating-current Network Protector. — The use of the alter-
nating-current network has become standard practice in sections
where the load is dense. This system has the advantage of
permitting the use of a smaller number of transformers, a more
economical loading of the transformers and a greater flexibility
in the distribution system.

The principal difficulty which has attended the interconnec-
tion of transformer secondaries has been the progressive blowing
of fuses when a defect developed in any of the transformers.
In the case of a failure not only does the transformer drop its
load but the defect develops into a short-circuit into which all
the other transformers feed, with the result that the fuses blow
progressively, starting with those nearest the fault, until the whole
network is shut down.

To eliminate the disadvantages of the network there has been
developed commercially a device known as the "A.C. Network
Protector" designed to disconnect automatically a faulty
transformer.

This device, which has no moving parts to stick or get out of
order, consists of a small transformer with primary and secondary

262 UNDERGROUND TRANSMISSION AND DISTRIBUTION

FIG. 130. — A.C. network protector.

3 WIRE SECONDARY

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Eia. 131. — Connections of A.C. network protector for three-wire network,

DISTRIBUTION SYSTEMS 263

windings in series with the corresponding windings in the power
transformer, and a third coil wound on the iron core. The wind-
ings are so designed that under normal conditions the ampere-
turns in one coil neutralize those in the other and the flux in the
core is zero. When a defect develops and there is a reversal of
current in the secondary, the ampere-turns add their effects
together, producing a heavy flux in the iron core, upon which is
wound the third coil consisting of a few turns of heavy-wire
short-circuited through a V-fuse. This flux sets up in the local
circuit a heavy current which instantly blows the fuse and
isolates the faulty transformer.

Fig. 130 shows the general appearance of the protector; and
Fig. 131 shows a diagram of connections for use on a three- wire
system.

Service Connections from Underground Mains. — The central
station, in furnishing service to all classes of consumers under
varying conditions, is required in many installations to change
existing overhead services to an underground system of dis-
tribution. In some cases the entire cost of making the change
from overhead to underground is borne by the customer, and in
other cases the company bears the entire cost, the practice fol-
lowed being dependant on local conditions. It is the practice
of some of the larger central-station companies to issue " Rules
and Regulations for Wiring" to the end that wiring contractors
doing construction work for customers to be connected to the
company's mains will so arrange and carry out their work as to
protect the interests of customers and at the same time conform
to such regulations as experience has shown are necessary in
order for the company to supply uniform and satisfactory
service.

Wherever it is desired to supply current from underground
mains, the customers' wiring should terminate and the meter-
board be placed at the front wall of cellar or vault nearest the
street. In some cases where wiring is done by local contractors
and service is not actually being supplied from subways at the
time service is desired, the central station companies require an
additional temporary overhead service to be installed until the
underground system is provided.

Armored Services. — In the early periods of underground con-
struction, the service end of the system was somewhat neglected
and very little thought was given to the real importance of an

264 UNDERGROUND TRANSMISSION AND DISTRIBUTION

ideal service installation. Services were usually treated as an
adjunct to the main system and no special attention was given
to the installation as long as the connection was made with the
property to be served.

As the underground system increased, the matter of adequate
protection at the consumer's end of services was taken up by the
underwriters with the result that certain rules and regulations
were formulated governing the methods of installation. At
first many companies made their service connections with lead-
covered cable which was buried in the ground. This, of course,
proved impractical, as a failure in the cable necessitated the
tearing up of both the street and sidewalk in effecting repairs.
Another method of furnishing service was to bring the feed into
a building at a street intersection extending it to adjacent build-
ings through the various cellars. The objections to this type
of service were that it materially increased the fire hazard and
the danger of interruptions to service and afforded ample means
for the unscrupulous to obtain current by theft.

There are many other arguments against the installation of
such services but the three previously mentioned were sufficient
to condemn such practice and to show clearly the need for indi-
vidual service connections. The next step was the installation
of individual services consisting of iron pipe or duct through which
the cable was drawn. Fire risk, however, was not materially
reduced until a few years ago when it was realized that the old
type of terminal block was inadequate. These terminal blocks
consisted of an ordinary fuse block which was not protected
against dampness nor against short-circuits caused by accidental
contact.

The writer recalls a case in a large eastern city where an investi-
gation of service trouble showed that a serious short-circuit had
been caused by the piling against the fuse block of a number of
steel-banded packing cases filled with fireworks. There are
still such services in existence but central-station companies are
gradually eliminating them, and with the advance in design of
equipment for underground services to meet the severe operating
conditions, a water-tight service box with enclosed fuses was
produced. This equipment was installed adjacent to the duct
holding the service wires which were carried by knobs or cleats
to the service box where porcelain-bushed holes provided an

DISTRIBUTION SYSTEMS 265

entrance for the wires. After leaving the service box, the main
wire ran to the meter, usually located on the board.

After a time the underwriters revised the rules governing wiring,
condemning the practice of using moulding in cellars. This
left conduit or open wiring as alternatives. Conduit was more
generally accepted, as the underwriters had also ruled that all
switches and cutouts be enclosed in iron boxes. With the in-
creased number of consumers came an alarming number of
current thefts, and the larger percentage of these occurred at
services which were more or less obscured. The underground
box which was located in basements afforded a temptation to
the unscrupulous, and a constant watch was necessary to detect

FIG. 132. — Service box with meter loop in wood moulding.

cases of theft. The plans for full meter and service protection
have been taken up within the past few years and now nearly
all of the larger operating companies have been equipping
their underground services with protective devices. As most
underground districts had been primarily supplied by overhead
services, whose entrance was usually above the first floor, con-
siderable expense is incurred in changing the location of meters
from upper floors to basements. This involves an entire new
meterboard and necessary wiring to connect the same with origi-
nal distributing centers. The old method was as shown in Fig.
132. This is inadequate in preventing theft of current and does
not furnish an absolute protection to the wires. Devices are
now on the market by the use of which it is possible to get full

266 UNDERGROUND TRANSMISSION AND DISTRIBUTION

protection from theft as well as to provide an absolutely iron-
clad service at a very slight cost over that of open-wired boards.
Such boards have many additional features for facilitating the
handling and testing of meters in service. An ideal board, as
used by some of the larger operating companies, can be con-
structed at a very reasonable cost.

In changing over from the old overhead to new underground
installations, considerable wiring is necessary to connect new ser-
vices to points of distribution. When making such changes in
large buildings it is advisable to bring all meters to a point ad-
jacent to the service. The following is an outline of the method
employed by a few of the companies making extensive changes
from overhead to underground systems.

Prior to starting the actual work, a service inspector is sent
out to select the most advantageous point to make the service
entrance. In making this selection attention must be given to
the physical conditions outside of the building, such as location
of hydrants, poles and other obstructions which would interfere
with service pipes. After having familiarized himself with the
outside, he selects the most desirable point for the location of the
service entrance, choosing the point, where possible, which is
least likely to be obstructed by an accumulation of material
usually found in cellars. If sufficient wall space can be secured at
the point of entrance of service, the meterboard will be located
at that point unless a large amount of interior wiring is involved.
Should this be the case, a meter location is selected which will
allow a more economical installation by eliminating some of the
wiring. Such a case would be where there are a number of meters
located at various points in a building.

After the service pipe is installed, the interior wiring changes
are started. Service wire is pulled in as the first step, and the
service board is mounted at the point selected. The best form
of meterboard is constructed of angle iron made up in the form
of a frame, upon which may be mounted backboards to support
meters. If service and meters are to be located at the same point,
an approved water-tight service box is bolted to the side of the
frame. Service wires are calked in the service pipe with oakum
soaked in a sealing compound to exclude gases. Service wires
are then incased in a flexible-steel conduit, one end of which is
pushed back in the service pi pe until it reaches the calking . To the
other end is attached a connector which is made up to a fitting

DISTRIBUTION SYSTEMS

267

on the service box and wires are then soldered into the service
box. This method gives a full armored protection to the service
and is highly recommended by the fire underwriters.

The service box should be of a type which will be accepted by
the underwriters as a switch and cutout. The usual type of box
used is that which provides for extraction of fuses when the cover
is opened. The load side of the service box is equipped with a
fitting similar to that which receives the flexible conduit on the
service side of box, and from this the wires are carried to the switch

FIG. 133. — Apartment house meter installation.

cabinet of the first meter and then on through the various cabinets
until the end of the bank has been reached. Each meter has an
independent switch and cutout located between the service and
the meter. These are placed in a steel cabinet which is sealed and
effectually protects the service against tampering. As most
companies use a three- wire bank form of distributing through
their underground system, it becomes necessary to balance
the load on each service as far as practical, as many of the over-
head services are apt to be two-wire. It has been found that
where an office or other similar building has a number of meters,
the installation may be practically balanced by using all two-wire

268 UNDERGROUND TRANSMISSION AND DISTRIBUTION

meters and connecting these in staggered position on a three-wire
service. This does not apply to larger two- wire installations,
as in the larger installations the periods of consumption do not
occur simultaneously. Installations of 1,000 watts or larger
should be changed to three-wire. This invariably means a
larger amount of rewiring but can usually be done by extending

FIG. 134. — Improper meter installation.

the three-wire mains from the meter to the center of distribution
and there balancing one subcircuit against another.

In all such three-wire systems, it is recommended that the
neutral wire be made solid from the manhole or transformer
to the point of distribution. Solid or dummy fuses should be

DISTRIBUTION SYSTEMS 269

installed in the service box and so arranged as not to be removed
when cover is opened and other fuses are extracted. This has
one distinct advantage in changeover jobs, especially where the
old jobs have had a grounded service. Such services are apt to
have local grounds on the building, and in changing over if no
secondary ground was on the original service these local grounds
are apt to appear on the live leg of the distributing main and blow
fuses. The current will then find a path back through load, and
owing to the resistance of the ground, will probably cause a fire.
With the solid neutral, this difficulty may be overcome safely by

FIG. 135. — Iron-clad meter installation.

transposing the circuit wires on which the ground appears. The
best form of neutral wires to install from street to service box is
a stranded bare tinned copper of not less capacity than that of
the outside wires, and in no case should this be less than No. 6
B. & S. gage. Fig. 133 shows a model service installation for
apartment houses and large buildings. The service is installed
in iron conduit from the manhole to the service box as described
before. This installation is equipped with meter protective and
testing devices in which are also incorporated consumer's fuses
and switch control. This represents an iron-clad installation in
which there are no wires or current-carrying parts exposed from
the manhole to the first point of distribution. The features of
the testing devices are that a meter may be tested, replaced if
necessary, or repaired, without interruption of service to the con-
sumer. Shunting arrangements are made by which meters may

270 UNDERGROUND TRANSMISSION AND DISTRIBUTION

be entirely isolated from the line for purpose of repairs or changes,
thus eliminating danger to the operator. It is also possible to
discontinue service for non-payment or other causes and lock
same out until such time as it becomes desirable to reinstate
service. This is very convenient where there is a change of
tenants and it is desirable to make a meter transfer. Fig. 134
shows a job which was changed over and shows the hazardous
condition of wires both from a fire and theft of current standpoint.
Many old installations have reached such a condition and should
be rebuilt.

Fig. 135 shows a service equipped with armor. Such in-
stallations as are shown in Fig. 135 can be made for less than
$2.50 per meter, which includes complete outfit installed as
shown.

Protection of Transmission Systems. — The growth in the
central-station industry and the use of high-voltage transmission
cable has brought about numerous problems which have made it
necessary to resort to various methods for protection of the
system.

The increase in size of generating and substation equipment,
together with the increase in size and voltage of the connected
cables, has made it exceedingly difficult to handle short-circuit-
ing values. The change from engine-driven units of compara-
tively small capacity and slow speeds to turbine-driven units of
large capacity and high speeds is perhaps one of the largest
factors in the problem.

Experience has shown that no single part of an electrical sys-
tem is free from the possibility of injury, and that it is incumbent
upon operating and designing engineers to protect their systems
as far as possible from such occurrences through the use of pro-
tective devices suitably designed to afford such protection.

Relays. — Oil-break switches and carbon-break circuit-breakers
are commonly used to open electrical circuits at some given
overload and on short-circuit. To secure additional protection
under a variety of abnormal conditions or to provide for a certain
predetermined operation or sequence of operation, relays may be
advantageously employed. The connections between the relays
and circuit-opening devices are usually electrical and are ex-
tremely flexible since they admit of the use of a number of devices,
each having a different function, with a single oil switch or circuit-

DISTRIBUTION SYSTEMS

271

breaker as well as with one or more switches to secure the desired
operation or protection.

Relay protection for transmission lines varies with the type
and method of operating different systems, but, in general, either
instantaneous, inverse time-limit or definite time-limit types of

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location of relays.1

relays have been used according to engineering judgment. The
arrangement of relays on a feeder or transmission line must be
such that the occurrence of a short-circuit between any two wires
will open the breaker. On single-phase circuits one relay is

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272 UNDERGROUND TRANSMISSION AND DISTRIBUTION

sufficient to accomplish this. One of the fundamental condi-
tions beginning to be more fully appreciated by engineers is that
each particular line should be treated individually with respect
to its relay setting instead of having a certain definite setting
for the relays of all lines in a given class.

In order to determine the proper setting of instantaneous over-
load, time-limit and inverse time-limit relays which are more
commonly used on a system of distribution, it is necessary to
know the characteristics of the system as well as the character-
istics of the generators, automatic apparatus, circuit-breakers,
regulators, etc.

In systems operating radial feeders, with each feeder connect-
ing to only one substation and not operating in parallel at sub-
station ends, reasonably satisfactory service has been rendered
by the type of relays referred to.

In systems operating ring systems of feeders, or radial feeders
with several substations in tandem on a single feeder, where
selective action is required in order to prevent interruption of
service from all stations between a fault and the source of power,
satisfactory results have rarely been continuously attained with
any of the types of relays mentioned.

In Fig. 136 is shown a one-line diagram which will be of assist-
ance in making a selection from the various types of relays to
meet the requirements of power-house and substation layouts.

It should be noted that the selection of relays to meet actual
operating conditions is an important problem and should receive
careful attention when a new system is being laid out or exten-
sions are being made to a system already installed.

The successful operation, selective cutting out of trouble, and
the continuity and safety of service, depend entirely on the opera-
tion of automatic oil switches and circuit-breakers, which in turn
must be tripped by means of relays. There are many types of
relays, each type designed to perform certain functions, and
before any of these types are installed, a careful study should be
made of the conditions under which they must operate.

Current-limiting Reactance Coils. — When short-circuits occur
in the cable system, a tremendous current flow is set up which
reaches its maximum during the first cycle. When it is realized
that for this first cycle every generator connected to the bus is
able to assume a short-circuiting value of at least ten times its
rated capacity, it is readily seen that heavy stresses are imposed

DISTRIBUTION SYSTEMS

273

on the switches, cables and apparatus. The stresses on the
feeder switches at such times are enormous, and it has become
necessary of late years to lock knife switches in position and to
take steps to protect the oil switches against these effects. To
relieve this condition and protect the system, various types of
apparatus have been employed. The use of reactances, both
external and internal, on generators, as well as on the bus and
feeder circuits, has perhaps been one of the most effective means
of protecting the central station and cable system.

FIG. 137. — Cast-in-concrete type of current-limiting reactance.

In general, it may be said that in stations of large capacity,
external current-limiting reactance coils, in one form or another,
have become a necessity for the protection of oil switches and
service. Local conditions will govern the type of reactances to
be used, but wherever possible, it is now generally admitted that
the best protection to service is obtained from the use of
reactances on the individual feeder circuits.

A large company, which has recently completed the installation
of 5 per cent, reactance coils on all 13,200-volt, 60-cycle feeders
has noticed a very material improvement in the selective opera-
tion of relays, with the resultant benefit to the system. Short-
circuits, which formerly caused an interruption to service on
several multiple feeders, have now become minimized to such an

274 UNDERGROUND TRANSMISSION AND DISTRIBUTION

extent that only the short-circuited feeder releases and the syn-
chronous apparatus in the system is not affected.

No combination of generator and bus reactances will give this
protection to service, as their installation is intended primarily
to protect station apparatus. The percentage of reactances to
be used is still an open question and cannot be standardized as it
depends largely upon operating conditions. The practice is to
have a total reactance of 8 to 12 per cent, on generator circuits and
about 2 to 5 per cent, on feeder circuits.

Current-limiting reactances should be of the air-core type, and
their capacity should correspond to the full -load capacity of the

FIG. 137a. — Semi-porcelain-clad type of current-limiting reactance.

line which they are intended to protect. They are generally
built with a core of non-magnetic material such as wood, concrete,
porcelain, or of several such materials in combination. Two types
of feeder reactance coils are illustrated in Figs. 137 and 137a. In
general, they are so bulky that it is difficult to find room for their
installation in a station already built. In some cases separate
structures adjacent to the generating station or the switch-house
have been found necessary for their proper housing. When these
reactance coils are properly constructed and placed, their in-
stallation involves no additional hazard.

Selective Fault Localizer. — The localizer is designed primarily
to indicate on which feeder a ground occurs when there are a
number of radial lines connected to a high-tension busbar. The
device necessitates a relay for each feeder. One of these relays
is shown in Fig. 138. They are connected to the respective cur-
rent transformers of the lines on which it is desired to localize,
in such a manner that all load currents are balanced out, as shown

DISTRIBUTION SYSTEMS

275

in Fig. 139. The various relays are interconnected in such a way
that only the relay on the grounded line is operative. All the

FIG. 138. — Relay for localizer of faulty feeders.

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other relays are rendered non-operative by balancing the mag-
netic pulls, one against the other in successive pairs. When a

276 UNDERGROUND TRANSMISSION AND DISTRIBUTION

ground occurs on a high-tension system, the proper relay operates
and illuminates its signal lamp to indicate the grounded feeder.
This device is used as an auxiliary appliance to the arcing-
ground suppressor. When the two devices are used in combina-
tion, it is possible to have a ground occur upon a system without
interrupting the service. As soon as a ground develops, the
localizer operates being followed immediately by the arcing-
ground suppressor, which automatically cuts out the arc to
ground.

FIG. 140. — Three-phase electro-magnetic selective relay for arcing-ground

suppressor.

If this arc were allowed to play for any length of time it would
develop into a short-circuit in the cable system. With the ac-
cidental arc suppressed, the station operator can now substitute a
good cable for the faulty one and open the switch of the arcing-
ground suppressor, thus clearing the system.

Arcing-ground Suppressor. — There are two essential parts
to the arcing-ground suppressor: first, a selector of a grounded
phase, Fig. 140; and second, a single-phase switch between each
phase of the busbar and ground. When an accidental ground
takes place in the system, the potential of that phase to ground is
reduced, which causes the selector to pick out and operate the
corresponding single-phase switch. This single-phase switch

DISTRIBUTION SYSTEMS 277

extinguishes the arc no matter where it occurs on the system,
and thus stops further development of the trouble as well as
preventing surges which accompany an arcing ground. When a
substitute cable is switched in, the faulty cable is taken out and
then the switch of the arcing-ground suppressor is opened. The
single-phase switches are designed with two contacts in series,
with resistances between contacts. A circuit is never made nor
broken without this resistance in series to damp out oscillations.

Grounded-neutral Systems. — Some companies in order to
gain additional protection operate on a grounded-neutral system,
while others resort to the use of various types of arcing-ground
suppressors. The practice of grounding the neutral on trans-
mission systems has not so far been standardized, and it is the
practice of some companies to operate with the neutral free from
ground, while others ground the neutral through varying amounts
of resistance, and in still other cases the neutral is grounded
without any resistance.

In a system with the neutral ungrounded, when one conductor
becomes grounded, the arc may establish and extinguish itself
in rapid succession, creating an arcing ground .which would have
been eliminated if the neutral had been grounded. The presence
of an arcing ground of high-frequency oscillation is liable to
create surges destructive to the cable and apparatus. Where
the neutral is grounded through a resistance, the high-frequency
voltage between two of the conductors and ground is minimized
when the other conductor is grounded. This same result is
accomplished also in an ungrounded system by the use of an
arcing-ground suppressor, when the faulty conductor is grounded
through the suppressor switch. This operation is accomplished
in a fraction of a second and eliminates the arcing ground and
with it the attending high-frequency voltage, thus leaving the
cable with line voltage between the other two conductors and
ground. This operation causes no interruption to the system,
and the faulty feeder may be taken out of service at leisure.
Another feature of the arcing-ground suppressor is that in cases
of accidental contacts with the bus by employees working in
the vicinity, the suppressor may act with sufficient promptness
to prevent fatal accidents. A number of instances of this kind
have been reported to the writer.

In the grounded system the voltage to ground decreases as the
resistance between the neutral and ground decreases, and in-

278 UNDERGROUND TRANSMISSION AND DISTRIBUTION

creases as the generator capacity increases. It is necessary to
decrease the resistance in the neutral as the capacity of the
system increases in order to confine the voltage strains to the same
limits. But since the current that can flow over a short-circuit
between one conductor and ground may be limited by the
resistance in the neutral, most of the companies using the resist-
ance prefer, in case one conductor becomes grounded, to use
such resistance as will allow the necessary current to flow to
operate the relays properly without regard to the voltage rise.

In expanding the idea of decreasing the resistance between the
neutral and ground in order to minimize the voltage strains to
ground, one large company, after operating with the neutral,
grounded through a resistance for several years, has decided to
ground the neutral without resistance. Under this condition,
when one conductor becomes grounded, the current on that con-

fYtfCK INSULATION

'rHfv* INSULATION

INSULATION
TWISTED f*Af>e* LflTKRII-S.

FIG. 141. — 350,000 c.m. 13,200-volt split-conductor paper insulated-sector

cable.

ductor approximates that flowing over a short-circuit between
conductors, which will cause the selective relays to operate in
the same manner as when a short-circuit occurs between con-
ductors, the condition for which the relays are set.

There is considerable difference of opinion regarding the
advisability of grounding the neutral and the relative advantages
and disadvantages resulting therefrom. For more detailed
information regarding the practice of grounding the neutral and
the operation of arcing-ground suppressors, the reader is referred
to the Proceedings of the American Institute of Electrical
Engineers.

Merz System of Cable Protection. — The Merz system of cable
protection consists of the usual equipment of current trans-
formers, relays and oil switches, but the current transformers at

DISTRIBUTION SYSTEMS

279

Bus Bar

.=. Tripping
Battery

Divided Main
Conductor

opposite ends of the transmission line are connected in opposition
through an independent pilot cable paralleling the main trans-
mission line. By this arrangement no current will flow through
the secondaries of the current transformers so long as the same
amount of current flows in the same direction in each of their
primaries; but should there be a breakdown of the cable insula-
tion between the transformers, conditions
would be so changed that current would
flow through the secondaries of both trans-
formers, actuate the relays and open the oil
switches at both ends of the line. There
would then be remaining in service the
transmission-ring system with one section
cut out but with a service to all substa-
tions unimpaired and supplied through the
lines remaining in service.

The disadvantages of this method of pro-
tection are the complications of the addi-
tional three-conductor pilot cable and the
fact that a short-circuit of the control
cable would operate the relays of the sec-
tion of the main cable it protects.

The objections to the installation of the
pilot-wire cable and the difficulties en-
countered in its maintenance have led to
the present development of split-conductor
cables in the application of the balanced
system of protection to transmission lines.
In Fig. 141 is illustrated a sector type of
split-conductor cable as manufactured and
now used in this country by several large
central-station companies.

This balanced system of protection has
been developed and patented by Mr. J. C.
Hunter, of the firm of Merz & McLellan.
In the balanced-current method of con-
trol in connection with main-line conductors, each conductor is
divided into two parts of equal resistance and carrying capacity.
The currents in these conductors are balanced against each other
in the usual manner to operate secondary relays, thereby avoid-
ing all necessity of using the pilot cable. A method of connect-

.=. Tripping
J . ^ Battery

Main
Swltc

Bus Bar

FIG. 142.— One-line
diagram, illustrating
the split-c onductor
scheme of feeder pro-
tection.

280 UNDERGROUND TRANSMISSION AND DISTRIBUTION

ing a split-conductor scheme of feeder protection is shown in Fig.
142. The general adoption of this type of cable in many trans-
mission undertakings abroad indicates that the advantages to be
derived from its use are considered as effecting material im-
provements in the reliability of service and are, therefore, worthy
of recognition in American practice.

CHAPTER IX
ELECTROLYSIS

General. — Electrolysis as here referred to is the chemical
decomposition of metallic structures by electric currents. Soil,
when entirely dry, has a very high resistance, but under normal
conditions street soils contain varying amounts of water-holding
salts in solution, thus making the earth a fair conductor of elec-
tricity. The specific resistance of soils varies widely, ranging
from a few hundred ohms per cm.3 for moist soils to 25,000 or
30,000 ohms per cm.3 in the case of dry sandy soils.

Since it is to a large extent the moisture which makes soil a
conductor, the passage of currents through the earth is by elec-
trolytic conduction, and is accompanied by a decomposition of the
metal at the point where the current leaves an underground struc-
ture to take a path of lower resistance through the earth. This is
true of both direct and alternating currents except that the rate
of decomposition by an alternating current is only about 1 per
cent, of that caused by a direct current of the same value.

The rate of oxidation is proportional to the current strength,
and from a consideration of the theoretical amount of metal
changed into the oxide it will be seen that even though the de-
composition of underground structures does not follow the
electrochemical law exactly, the amount of metal oxidized in a
year is very considerable. The constant for iron (converted into
the ferrous condition) is 1.042, and for lead 3.858 grams per
amp-hr. The amount of iron oxidized in a year will be 1.042 X
8,760 X 0.002205 = 20.2 Ib. per amp. The amount of lead will
be 3.858 X 8,760 X 0.002205 = 74.1 Ib. per year per amp.

Either more or less (but generally less) than this theoretical
amount is realized under actual conditions, depending upon
soil conditions.

The effects of electrolytic action would be far less serious if
this loss of metal were distributed evenly over the structure,
but this unfortunately is not the case. Actually the currents
discharge from a number of small areas, causing pitting. Thus

281

282 UNDERGROUND TRANSMISSION AND DISTRIBUTION

the usefulness of a structure may be destroyed by being badly
corroded in a few spots while the amount of oxidation over the
rest of its surface is negligible.

Electrolytic corrosion in most cases is caused by stray currents
which have leaked from grounded electrical systems. The
stray currents from grounded telegraph and telephone lines and,
in general, from direct-current distribution systems are so small
as to be negligible.

Railway return conductors, since they carry comparatively
heavy curents, are the only sources of stray currents which
need be considered in connection with the problem of electrolysis.

VOl. TS

FIG. 143. — Diagram showing stray railway currents with assumed distribu-
tion of potentials caused by these currents.

Trouble from electrolysis followed close upon the introduction
of electric traction. In the early days of the industry engineers
did not foresee the danger, and very little attention was paid to
the proper bonding of the track return, with the result that the
greater part of the return current left the rails to take a path of
lower resistance through the earth or along adjacent metallic
structures. Even after the necessity of proper bonding came to
be realized, a considerable part of the current returned to the
negative bus through the earth. Fig. 143 shows a simple trolley
system in which the return current divides, part returning along
the rail, part through the earth, and part along the iron water
main. The greatest damage to the main will occur at A where
the current leaves the pipe to pass through the ground to the

ELECTROLYSIS 283

negative bus. Corrosion will also occur at the joints, due to the
fact that where the joint resistance is high the current will by-
pass the joint through the earth, returning to the pipe on the
other side.

Before attempting to utilize any of the systems for the mitiga-
tion of electrolysis, attention should be given to the matter of
proper rail bonding and the limiting of the distance between
substations.

Rails may be bonded by the installation of copper ribbon or
wire soldered or brazed to the webs of the rails or by welding
together the ends so as to make practically a continuous rail.

In many installations not only are the separate rail sections
bonded but the two rails or (in the case of a double-track road)
all four rails are electrically connected.

The method of bonding rails by the use of a welding outfit
has been used to a considerable extent and is apparently satisfac-
tory since it provides mechanical reinforcement in addition
to a good electrical connection.

A great deal of attention has been given to the matter of rail
bonding; and since the methods in use to-day produce bonds which
show a conductivity of about 80 per cent, as compared with an
equivalent continuous rail, it is doubtful whether any further
relief for electrolytic conditions can be expected from attempts
to improve upon the present bonding methods.

The number of, and the distance between, stations or substa-
tions which supply a railway line will govern to a very large
extent the amount of current which will leak to pipe lines or
other foreign structures.

Where too small a number of stations are used to supply
a railway line, the return current to the negative bus will be large
and the distance between stations comparatively long. These
two factors bring about the condition of excessive voltage drop
along the rails and aggravate the tendency of current to return
through the ground.

American engineers apparantly did not have as thorough a
grasp of the situation as did engineers on the Continent. As
soon as the problem of electrolysis became serious in Europe,
regulations were adopted limiting the voltage drop between
any two points in the track to about 7 or 8 volts. These regula-
tions forced railway companies to install better bonds, to limit
the distance between stations and, in some cases, to install

284 UNDERGROUND TRANSMISSION AND DISTRIBUTION

insulated return feeders, with the result that troubles from
electrolytic corrosion disappeared almost entirely.

American practice, on the other hand, has not sought to
remove the underlying causes of electrolysis but has attempted
merely to relieve acute local conditions. The measures adopted
in this country, in addition to track bonding, have consisted
of "pipe drainage" or bonds to other systems. It must not be
inferred that the drainage system is inherently bad, for up to
the present time it has undoubtedly relieved acute cases of elec-
trolysis and has apparently imposed no serious hardship on the
owners of structures tied in by the bonds. In spite of the results
obtained by the drainage system, it does not cure electrolysis
nor remove the fundamental causes, and it is to be regretted
that the large investment necessary for the development of an
adequate bonding system was not used to develop some positive
cure such as the return-feeder system. It is true that where
a large system has adopted drainage bonds as a remedy the
cost of a change to the return-feeder system would be almost
prohibitive; and the writer believes that in most cases the drain-
age system is very nearly as satisfactory a remedy as the return-
feeder system, provided careful and systematic tests are made.

Drainage Systems. — The aim in all drainage systems is to
lower the potential of the structure with respect to the earth
by draining off the current through metallic bonds. The proper
location for these bonds is determined by tests, and the drainage
conductors are installed at points where the structure is danger-
ously positive to the adjacent track. The current is drained
either to the track or else direct to the negative railway bus by
means of return feeders. If all the current could be drained from
the structure by means of bonds, the bonding system would be
an excellent means of relieving conditions on the particular
structure so drained. The problem is not solved, however, by
indiscriminate bonding. Drainage of any one structure lowers
its potential with respect to neighboring structures, with the
result that the latter will drain through the ground to the bonded
pipe line. It is, therefore, clear that while bonding may clear up
conditions in one place it may work to the injury of structures
not tied into the network.

Where the drainage bonds are so installed that a pipe line be-
comes a parallel return for the track circuit, it is practically im-
possible to control the amount of current carried on the pipe line,

ELECTROLYSIS 285

and serious overheating may result. If the pipe joints offer a
high resistance, the current will leak around the joint and corrode
the metal at the point where the current passes into the soil. The
use of such bonds to a pipe line where high-resistance joints occur
may place the line in a worse condition than would obtain in the
absence of any bonds at all. In the unbonded condition the
total yearly loss of metal would be greater but under some condi-
tions of bonding the action is localized and intensified so as to
cause the structure to corrode through in a number of places.

In addition to the above objection, the system is not permanent
in that any radical change in conditions will necessitate a complete
change in the bonding system in the locality affected.

In any system where the pipe parallels the track, the current
will divide approximately in inverse proportion to the resistance;
and in such a system, when the current carried by the pipe be-
comes excessive, the current on the pipe can be decreased only by
an increase in rail conductivity. This method requires the use
of a very costly installation of copper as an auxiliary return.

Excessive currents on pipe lines are a source of danger not only
to the pipe itself but to buildings into which service connections
are run. There are cases on record of very serious overheating
of pipe connections inside buildings. However, this danger is
remote, and is due not to the use of bonds but to the installation
of bonds in the wrong place.

Probably the best way to drain a pipe line is by the installation
of insulated drainage feeders running from the negative bus in the
station to various points on the structure. It is possible by the
use of such a system to control very closely the distribution of
current on the pipe line by varying the resistance of the drainage
leads.

This method is better than the preceding, but all drainage sys-
tems have the disadvantage that with growth in the railway
system it may be necessary to drain very large currents from pipe
lines, and that in many cases the trouble is merely transferred
from one area to another.

Numerous attempts have been made to protect pipe lines from
the effects of electrolysis by means other than the use of bonds.

Protective Coatings. — Protective coatings in the form of
paint, dips of asphalt, coal tar or pitch, and wrappings of paper
or cambric have been used to some extent, but tests have failed
to show that any one method is universally satisfactory.

286 UNDERGROUND TRANSMISSION AND DISTRIBUTION

It is difficult to apply any coating so as to obtain a uniform
smooth surface free from pinholes or bare spots. Where these
exist, a pipe line may fail much more quickly than where the pipe
is uncoated due to the fact that corrosion will be localized in
a small number of areas, the effect of electrolytic action being
intensified.

Even if the coating is very carefully applied, it is likely to be
scratched in handling; and after the pipe is laid, blisters often
form on the coating and expose the metal to corrosion.

Insulation in the form of wrappings of cloth or paper fail in
most instances because they are not entirely impervious to mois-
ture. The coating becomes damp in spots and affords a conduct-
ing path, with the result that the pipe fails.

Dips consisting of coal tar or pitch which are applied hot and
allowed to cool and harden on the pipe surface are very likely to
develop cracks. It is possible to make coatings absolutely im-
pervious, but only at an excessive cost. Such an installation re-
quires the construction of a trench in which the pipe is laid, the
pitch being poured in and allowed to cool. This method is
not recommended except in special cases where continuity of
service is of such importance as to make the cost of the installa-
tion a minor consideration.

Cement coverings, even when several inches in thickness,
will not afford certain protection because concrete is not imper-
vious to moisture, and moist concrete is a fairly good conductor.

Electrolytic conditions on a pipe line could be cleared up if
it were possible to cover the pipe with a conducting coating
which would not be corroded when the current passed from the
pipe line into the earth. Most of the non-corrosive metals are
so expensive as to make their use commercially impracticable.
Black oxide, or coke particles in a suitable binder, fulfill the
requirement as regards non-corrosive properties, but the same
difficulties are here encountered as in the use of paints and dips.
It is very difficult to get a uniform surface free from flaws. In
addition, black oxide is electronegative to iron and there is
danger of local galvanic action being set up.

Insulating Joints. — Very beneficial results have attended the
practice of breaking up the electrical continuity of pipe lines by
the use of an insulating medium at every joint. If the installa-
tion cost is too great to warrant the insulation of every joint,
the insulation may be used at greater intervals in the line pro-

ELECTROLYSIS 287

vided test readings are taken to detect excessive potential drop
between insulated sections. If the voltage difference between
two sections is too great, there will be a shunting of the current
around the insulation and a corrosion of the pipe on one side of
the joint.

Cement is very commonly used as the insulating medium;
and while it is not strictly an insulator, if used at intervals
sufficiently frequent, its resistance will be high enough to reduce
the current carried. Various special types of insulated joints
using fiber, wood, leadite or other substances have been used with
apparent success.

The use of insulating joints is especially recommended at the
point where service connections are made to a building. These
joints prevent loading up the pipes inside a building with stray
current and minimize fire hazard.

FIG. 144. — Cable damaged by electrolysis.

Insulating joints are valuable as an auxiliary means of reducing
trouble from electrolysis but should not be used as a substitute
for some of the more positive methods, such as the limitation
of voltage drop along railway returns.

Protecting Cable Sheaths. — Thus far the problem of electroly-
sis has been considered only with a view to protecting such struc-
tures as gas and water pipes. Where conditions are favorable to
electrolysis, the destruction of the sheaths of lighting, power, and
telephone cables is much more rapid and disastrous.

Since the electrochemical equivalent of lead is about four
times that of iron, and the lead in the sheath is just thick enough
to give sufficient protection and mechanical support to the
insulation, it will be seen that a cable will fail in a much shorter
time than a pipe line carrying the same current.

Fig. 144 is a photograph of a section of a three-conductor
transmission cable which was damaged by electrolysis in a wet
manhole.

288 UNDERGROUND TRANSMISSION AND DISTRIBUTION

The character of the duct construction will determine to a
large extent the amount of current leaking from railway systems
to the cable sheaths. All duct structures will admit moisture
to a greater or less degree, but fiber duct laid in concrete admits
less than other forms of construction. Where water does enter,
there will in general be an exchange of current either from sheath
to sheath through the concrete or between sheaths and external
structures. It is, therefore, important that duct lines be so
graded as to drain toward manholes, and that, as far as possible,
manholes, be kept dry by drain connections to sewers.

The usual method of protecting cable sheaths is by the use
of a drainage system similar to that used for the protection of
pipe lines. The object of draining the sheaths is to make them
slightly lower in potential than the surrounding earth or neigh-
boring structures, thus preventing current flowing off the sheaths.
Since there is danger of overdraining in making the sheath po-
tential considerably lower that that of ground or adjacent
grounded structures, it is sometimes necessary to insert suitable
resistances in the drainage leads. Overdrained cable sheaths
are a source of danger to neighboring pipe lines because of the
tendency of these lines to be injured by the drainage of their
current to the cable sheaths. To prevent electrolysis of the
sheath of cables by an exchange of current between sheaths,
it is standard practice to attach a common bond in every manhole
which equalizes the sheath potential of all the cables in the
duct line.

It is inadvisable to bond direct to the track or railway return,
since this makes a cable system a parallel return to the railway
system. Where bonds are so installed, an accidental high
resistance in the railway return will throw upon the sheaths the
burden of carrying a large part of the return current. This
condition will result in serious overheating of the sheaths and,
in the case of power cables, in a considerable reduction of current-
carrying capacity.

To prevent excessive currents on cable sheaths, the use of
insulating joints in a run of cable is sometimes resorted to. This
method should be used only with great care since there is danger
of setting up excessive potentials across the joint or between
the sheath and ground. As in the case of insulated pipe joints,
insulated sheath joints are used] chiefly to prevent the entrance
of stray currents into buildings through lateral connections.

ELECTROLYSIS 289

The use of insulated return feeders provides the most satis-
factory means of preventing electrolysis. The cost of this
system compares favorably with those now in use, and except
in cases where there exists a large investment in bonding or other
systems, its use is recommended.

Where insulated return feeders are used, the connection
between the tracks or other return conductors and the station
negative bus is removed, and insulated leads are run out to
various points in the track. By draining the track at numerous
points, the potential gradient along the rail is reduced to any
desired value, and high-current densities are avoided. It will
be seen from Fig. 145 that the current flows from both directions
into the return lead, thus preventing the existence of a high-
Track

Substation

FIG. 145. — Reduction of track gradient by use of insulated return feeders.

voltage difference between any two points in the track. It is
possible to obtain practically any desired reduction in potential
gradient along the track and to eliminate excessive drop between
foreign structures and rails by proper design of the return feeders.
It is true that by the use of this system some of the conductivity
of the track is sacrificed, but this sacrifice seems justified by the
excellent results obtained in practice.

Insulated return-feeder systems are in use in New York City,
Springfield, Ohio, and St. Louis, Mo. For a complete description
of this system and of the methods of calculating, the number and
size of feeders, the reader is referred to Technologic Paper No. 52
of the Bureau of Standards. The simple insulated return-
feeder system will serve the purpose in most cases but where
long or heavily loaded railway lines are used, it is sometimes
necessary to make use of either direct or inverted boosters.

290 UNDERGROUND TRANSMISSION AND DISTRIBUTION

Another remedial measure has been proposed for the relief
of electrolysis. This consists in a periodic reversal of polarity
on the railway system ; and while this method would theoretically
reduce materially the corrosion, in a large and complicated system,
the operating difficulties would make the scheme impractical
even if the reversal were as infrequent as once in 24 hr.

Other schemes such as the double-trolley and negative-trolley
systems have been proposed. The first is open to the objec-
tion of excessive cost and increased operating difficulties. The
second, while it would undoubtedly delay the ultimate destruc-
tion of other structures, would impose a serious hardship on com-
panies which had installed drainage systems.

General Practice. — A canvass of 56 of the larger lighting companies
operating about 200,000 miles of underground lighting and power cables
yielded the following information as to practice as regards electrolysis
mitigation.

CONDUITS

Vitrified-clay tile, of both single and multiple type, is used exclusively by
43 per cent, of the companies. Vitrified tile and indurated fiber is used by
43 per cent, of the companies. In recent years the use of vitrified tile has
been abandoned in favor of fiber in most of these systems. Indurated
fiber is being used exclusively by 12.5 per cent, of the companies. The
remaining 1.5 per cent, is made up of companies who either have not specified
the type of conduit used or else have in use a type which is not yet standard.

The tendency to abandon the use of sectional tile conduit in favor of
fiber is significant. Not only does fiber conduit afford a continuous runway,
but its waterproofing and insulating properties must inevitably serve to
minimize the danger of electrolytic corrosion at some point outside of a
manhole where the destruction action might continue undetected until the
cable failed.

ELECTROLYSIS

Electrolysis was reported as existing on the cable system by 64 per cent,
of the companies. Evidence that the trouble is confined to isolated cases
is furnished by the fact that in only three instances was electrolysis reported
as generally existent throughout an entire system. The cause of the elec-
trolytic action was in most cases attributed to stray railway currents leaving
the cable sheaths to select paths of lower resistance to the railway return
systems. Two companies state that attempts have been made to remedy
the condition by insulating sections of the cable. Of these, one appears to
have been successful, and the other reports that the trouble still exists in
spite of the fact that each insulated section is drained to a driven ground
connection.

ELECTROLYSIS 291

BONDING OP CABLE SHEATHS

The practice of bonding the cable sheaths together as a means of equaliz-
ing sheath potentials and of preventing electrolysis between sheaths of
adjacent cables is shown to be quite general.

Bonds are used by 89 per cent, of the companies, leaving only 11 per cent,
which use no bonds. Except in the case of three companies, which employ
lead strip, the universal practice is either to use copper wire or copper ribbon
sweated directly to the cable sheaths. In one instance a company reports
sweating the bonding ribbon into one end of the cable joint sleeve, a method
which is at once unique and effective.

The necessity of insulating cable sheaths from their supporting racks in
manholes appears to be doubtful.

Of the replies received, 60 per cent, of the companies do not insulate.
It would appear that the companies who do attempt to insulate have more
trouble from electrolysis where cables are insulated from racks than where
they are not. This is probably due rather to local conditions than to the
method of racking cables.

Of those using some form of rack insulation, 23 per cent, use porcelain
saddle blocks. Slate, brick, alberene or concrete shelves are used by 14
per cent. Wood blocks, old rubber hose or fiber sections cut from old lengths
of conduit are employed by 35 per cent. An unintentional insulation is
obtained by 27 per cent, which use a non-conducting form of cable fire-
proofing.

Except in the case of those who use porcelain saddle blocks, the value of
such forms of insulation for establishing conditions adverse to the action of
electrolysis appears very doubtful.

Probably the only real value of any of these materials is to furnish a form
of mechanical support which protects the lead sheaths against the rough
edges of the manhole racks. A more effective protection would be obtained
by the use of a piece of sheet lead cut from the cable strippings.

The practice of draining a cable system to the street railway return
system at the negative bus in substations, or to negative conductor or tracks
at points close to substations is rapidly becoming standard.

That the drainage system affords real protection to cable sheaths is proved
by the fact that 66 per cent, use this system and have noted that electrolysis
under this method of bonding is negligible.

Many companies connect also to other grounded systems. Connections
to gas or water pipes are made by 25 per cent, of the companies, to system
neutrals by 16 per cent., and to cable sheaths of other systems by 7 per cent.
Bonding direct to street-railway tracks is practised by 18 per cent.

The fear that such apparently indiscriminate connections to other
systems would result in loading up the cable sheaths with return currents
from other systems has been dispelled by the results obtained by companies
using the drainage system.

It would appear that the troubles from electrolysis are in inverse propor-
tion to the number of drainage connections employed. This is borne out
by the experience of two companies which report that severe electrolytic
conditions have almost entirely disappeared from their systems as a result

292 UNDERGROUND TRANSMISSION AND DISTRIBUTION

of the free use of drainage bonds. This improvement in conditions has
not been obtained at the expense of the adjacent systems since tests show a
marked decrease in electrolytic action on neighboring structures tied into the
drainage network.

A large company operating in a city of about 500,000 population, and
which reports no drainage taps of any kind, appears to be suffering severe
damage by electrolytic corrosion. On the other hand, a company which
bonds both to its own grounded neutral conductors and to street railway
negative return cables notes absolutely no electrolysis in spite of the fact
that much of its system is permanently submerged in salt water.

In several cases the drainage connections used consist of a network of
conductors paralleling the cable system. One report states that a network
of this kind was installed by the railway company for the purpose of pro-
tecting adjacent cables and structures.

There appears to be no ground for the belief that sheath currents may
reach such a value as to result in serious overheating. Forty-two companies
making up 75 per cent, of the systems reporting state that they allow their
cable sheaths to carry return currents. Of these, four limit the currents by
the use of resistance inserted in the drainage leads; four make periodic in-
spection and test, limiting the current when necessary by the installation of
additional drainage bonds. The rest make no attempt to limit the current.
It is worthy of note that not a single case of damage to a cable or a limiting
of capacity due to overheating has been reported.

UNINSULATED NEUTRAL

An uninsulated neutral or return conductor is used on either their high-
or low-tension distribution systems, or both, by 54 per cent, of the companies
reporting. Of the companies using this system, 53 per cent, use their cable
sheaths either wholly or in part for carry ing these neutral currents. Where
this practice is followed, it appears that in most cases the neutral wire itself
is used chiefly as a common bond to which all cable sheaths are connected.
The return currents divide inversely as the resistance of the paths, and,
except in cases where there are few cables in a duct line, the cable sheaths
carry the major portion of the neutral return currents.

One company reports the use of the cable sheaths as a neutral for a trans-
mission system, and several use their sheaths as the neutral of their 2,300-
volt or 4,000-volt distribution feeders.

Only five cases of trouble are reported as resulting from the use of cable
sheaths as neutral return conductors. In one instance bond wires were
burned off and cable sheaths damaged due to the use of bonds of insufficient
size. The trouble was cleared up by the installation of bonds of larger
cross-section. The second case was the destruction of a neutral by elec-
trolytic action. This neutral was a service connection tapped off from an old
Edison iron-tube system and carried through a wooden plug into a joint-box.
A bond between the neutral and the iron tube caused a disappearance of the
dangerous condition.

The remaining three cases of trouble consisted of a distortion of neutral
potentials on Edison three-wire direct-current networks by earth-potential

ELECTROLYSIS 293

gradients caused by street-railway return currents. In two instances the
difficulty was overcome by installing additional feeder copper, but in the
third case it was found necessary to run insulated neutral wires from the load
center affected back to the substation.

COOPERATION OP UTILITIES

Cooperation with the railway companies is reported by 36 per cent, of the
companies; with the telephone companies by 28 per cent.; and with water
companies or municipalities by 25 per cent. Only 11 per cent, report any
cooperation on the part of the gas interests. It should be noted that in
many cases the reporting companies are connected either directly or
indirectly with the railway systems.

Since there is no reported instance of failure to cure electrolytic action
where proper cooperation existed between utilities, it seems clear that there
should be little difficulty in correcting conditions favorable to electrolytic
corrosion. The advantages of the standard methods in use have been
proved conclusively, and there is no reason to believe that the protection
gained by their use could not be extended to the underground structures of
other utilities provided these utilities were willing to take up the problem
in a real spirit of cooperation.

Electrolysis Surveys. — Where trouble from electrolytic cor-
rosion is suspected, accurate data as to the intensity and extent
of the trouble may be obtained from an electrolysis survey.
Such a survey is made by reading, at intervals along the streets
on which railways are located, the potential difference between
one structure and all the others. Where an electric central-sta-
tion company is making the survey it is usual to assume the
cable sheaths as the datum or potential zero. The potential
difference between the cables in each manhole and neighboring
tracks, water pipes or gas pipes is read by means of a high-
resistance voltmeter. A meter well-adapted for electrolytic work
is the Weston duplex instrument illustrated in Fig. 146.

For the potential readings, contact is secured by means of rods
for the cable sheaths and a screw-driver point for other structures
or the earth.

The rods are approximately 6 ft. long and are usually in two
parts so that they can be easily carried about. Heavy reinforced
lamp cord is used for the leads from the rods to the instrument.
In Fig. 147 rods are shown which have been used to advantage
by the testing department of the Brooklyn Edison Co. In taking
current readings, flexible rubber-covered wire of the proper re-
sistance is used to give the correct millivolt reading. The bare

294 UNDERGROUND TRANSMISSION AND DISTRIBUTION

ends of these leads are held on the cable sheaths by one man while
another reads the meter.

The field notes should be copied on cards similar to that shown
in Fig. 148 and made a part of a special electrolysis file. These
cards, in addition to the voltage readings, have space for a gen-
eral description of the conditions existing at the time of the test.
After the collection of the field data a skeleton map of the city or
district affected is used to give a graphic presentation of the ex-

FIG. 146. — Weston duplex electrolysis instrument.

isting conditions. The railway lines, duct lines, water pipes, and
other structures are drawn in their proper location and the poten-
tial difference between the cable sheaths and other structures are
platted normal to the direction of these structures. Positive
voltages are laid off in one direction and negative voltages in the
other.

Since the Weston test meter is a duplex instrument, it is possi-
ble also to measure the current carried on the cable sheaths by
obtaining the millivolt drop over a given length. The amperes

ELECTROLYSIS

295

per millivolt is a constant for a given cable, and by using the
constant as a multiplier, the value of sheath current is obtained.
By measuring the current carried on the cables in every man-
hole, it is possible to learn the approximate location of the point

I Q

NOTE:

X Steel Dowel Pin

Attach 15 ft. piece of reinforced lamp cord
soldering an end on snrface of coupling anc
taping entire rod with friction tape.

NOTE:

Attach 85 ft. piece of reinforced lamp cord
soldering an end on surface of coupling and
taping entire rod with friction tape.

Brass Coupling

Steel Dowel Pin

Mach. Steel Tempered

— 30--

Iron Rod'

30-,

Ji"lron Rod v

FIG. 147. — Electrolysis testing rods.

where the current is leaving. Where a marked discrepancy exists
in the sheath currents in adjacent manholes, an investigation
should be made with a view to installing metallic drains to pre-
vent the current leaving through the ground.

PUBLIC SERVICE ELECTRIC CO.
ELECTROtYTIC TEST

FIG. 148. — Electrolysis record card.

The value of the electrolysis survey is to show the danger
points in a cable system and to indicate the places where drain-
age bonds should be installed.

CHAPTER X
OPERATION AND MAINTENANCE

Records. — One of the essential things in connection with
the operation of an underground system is the keeping of de-
tailed permanent records. It should be the duty of every cable
and underground engineer to keep a system of records which will
enable him to tell at any time the exact amount and the location
of the cable installed.

Suitable forms should be provided to make it an easy matter for
the foreman on the work to make the necessary notes, and these
foremen's reports should be carefully transferred to the perma-
nent office records. A good system of records will be found of
great value in locating and taking care of trouble and in laying out
new work. Such records will also be of assistance to the commer-
cial department in considering new business. It frequently hap-
pens, where complete records are not kept, that the company
depends to a large extent upon the memory of certain employees,
and if these employees leave the company the information is lost.

Diagrammatic layouts of the conduit system and manhole
system are most conveniently kept in loose-leaf or card form.
These records are not drawn to scale, but show a diagram of the
street with a line to represent the conduit, while manholes are
indicated in their proper location by rectangles or other figures
corresponding to the shape of the manhole. Measurements are
indicated, showing distances between centers of covers and also
their location with respect to curb lines. The latter is quite
important, particularly in locations where, during the winter
months, snow covers the ground. Knowing the exact location
of the center of a cover will save considerable time for the cable
men when inspecting manholes on locating trouble. In Fig. 149
is illustrated a system of conduit record, while a manhole record
card is shown in Fig. 150. The number of records necessary will
depend on the size of the company and the nature of the work.
For a comparatively small expense, however, records will be made
which will always be accessible.

296

OPERATION AND MAINTENANCE

297

Identification of Cables. — All cables should be properly
tagged in every manhole, these tags to indicate the size,
voltage, and cable number. With a view to ascertaining the
general practice and experience of the larger companies in regard

PUBLIC SERVICE ELECTRIC COMPANY

CABLE RECORD

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FIG. 149. — Conduit and cable record card.

to cable tagging and numbering scheme, the Underground Com-
mittee of the National Electric Light Association sent out to
member companies a series of questions relating to cable tagging.
The replies received indicated a great diversity of opinion and
practice. With the exception of a few of the companies, who

298 UNDERGROUND TRANSMISSION AND DISTRIBUTION

embody some very good features in their methods of tagging and
numbering, it appears that the matter has received very little
attention.

Tags have been made of various metals, including brass, lead,
zinc, aluminum, copper and galvanized iron ; brass being the most
common in use. Usually symbols or figures are stamped into the
metal. A good form of tag is one in which the figures are cut

PUBLIC SERVICE ELECTRIC COMPANY

MANHOLE. INSPECTION CARD
MANHOLE H0+O/-S.£.Corner ^Qctcr\o^^aing First Strs. C)TY Mewar-k,N.*J.

BUILT /V7>1>»-/?/* KINO CO/MC*ET.£. SIZE 6 ^ X B ^T And £ &. pe &JO,

-Z—

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OAS

NECESSARY REPAIRS OR CHANGES

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TRANSFORMER AND BOX RECORD

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FIG. 150. — Manhole record card.

through the middle in the form of a stencil. With the figures or
symbols punched through the metal, the legibility should not be
affected by any ordinary corrosion. The punching should form
plain open figures without any frail bars of metal left to cause
confusion. A tag as just described is shown in Fig. 151, the
shape of the tag illustrated indicating the class of service for which
the cable is used.

A tag made of sheet lead, similar to the lead sheath of the

OPERATION AND MAINTENANCE

299

Hole for Fastening

cable and subject to the same exposure, would not be seriously

affected by corrosion, and when made in the form of a strap,

as shown in Fig. 152 can be passed around

the cable like a collar. Glass tags made to

receive a card bearing the cable number

have been used by some companies, but as

far as is known to the writer have nowhere

been in service long enough to have

thoroughly demonstrated their usefulness.

Tags were formerly fastened to the cables
with copper wire in pendant fashion ; but due
to corrosion, tags frequently became de-
tached from the cable. For this reason a
tinned copper bonding ribbon is now used
for fastening the tags to the cable. As shown in Fig. 153, two
holes are punched in the tag to allow an additional wire to be

FIG. 151.— Round-
cable tag.

e for Fastening

(A) DEPENDS ON DIAMETER OF CABLE

FIG. 152. — Lead-cable tag.

used in supporting the tag, thus insuring its proper fastening
to the cable. Tags should be fastened to the cables at or close

to the joint. This makes them

^^ ^ find ^ congegted man_

holes.

There are various numbering
schemes in use for designating
cables and in some cases attempts
have been made to indicate, in
addition to the serial number of
the cable itself, the voltage, class
of service, source and destination.

FIG. 153.— High-tension-cable tag. TaSs of different shapes have been

used to advantage and some com-
panies have adopted sharp-pointed tags, Fig. 153, for marking

300 UNDERGROUND TRANSMISSION AND DISTRIBUTION

high-tension feeders. By choosing different ranges of numbers
for different classes of distribution, distinction can be made as
to the class of service. Letters of the alphabet are sometimes
combined with numerals to show class distinction. The follow-
ing method of numbering is submitted as a simple and ready
means of identification.

Secondary mains, 110-volt numbers 100 to 199 inclusive.

Secondary mains, 220-volt numbers 200 to 299 inclusive.

Primary feeder, single-phase, 2, 400-volt. numbers 2,400 to 2,499 inclusive.

Primary feeder, two-phase numbers 4,800 to 4,899 inclusive.

Series-arc circuits numbers 7,500 to 7,599 inclusive.

From the foregoing it is noted that a number may be used
which readily indicates the voltage of the circuit. While num-
bering schemes are good, it must be remembered that, as a rule
a given method is applicable only to its particular cable system.
The design and development of any scheme is influenced by so
many local factors that each must be worked out independently
to suit the requirements. Whether the numbers are placed on
tags or in record books, they must be simple, capable of expansion
without complications, and they should preferably be indicative
to some degree of some function the cable performs.

The use of loose-leaf cable-record books in which duct loca-
tions are given and which can be used as a reference in the field
to check the cable tagging is very desirable. This form of record
has proved highly satisfactory for both field and office use.

In addition to proper tagging some additional safeguard is
usually desirable in order to remove every possibility of workmen
cutting into a live cable. An exploring coil has been used to
advantage in the field to pick up a signal on the desired cable
which has a special signal current impressed upon its conductor
terminals. This same exploring coil and interrupter is also used
in many cases in the field to phase out the conductors of a multi-
ple-conductor cable. Spiking is often resorted to as a last precau-
tion before cutting into a supposedly dead cable, but is not recom-
mended as good practice, because of its unreliability as it is done
by some cablemen.

In Chapter VI, under the heading "Testing for Live Cable,"
several methods which are considered good practice are described.

Record of Cable and Equipment Failures. — A system of
recording cable failures and subway troubles is of considerable
value. Interruption to service caused by the failure of a cable

OPERATION AND MAINTENANCE 301

or other equipment should be thoroughly investigated by the
foreman or cableman in charge, and a complete report giving
full details should be kept on file for future reference. If the
troubles are numerous a detailed record will greatly assist in
determining what changes are necessary to improve the system.

PUBLIC SERVICE ELECTRIC COMPANY

REPORT OF HIGH TENSION FEEDER TROUBLE

.Date --------------- .Time _____________ Feeder No ________ . ___ from _____________

To -------------- Size ------------- Operating voltage ____________ Frequency ______

Insulating material ------------------ Insulation thickness __________ Condition _____

Made by -------------------------- Installed, date ______________ by ___________

Length of underground portion ________________ ft. overhead ___________________ ___ ft.

First indication of trouble __________________________

Nature of. trouble ___________________________ Eeported by ______________________

Trouble occnrred during test. ___________________ or feeder in service ________________

Previous to breakdown, load on feeder. _____________________ Max. air temperature ________

LOCATION OF FAULT
Fault located by; Fault located in:

Inspection ------------------------- Manhole in joint _____________________

Report of _________________________ , in bend __________________

in straight
loop test ------------------------- length ____________________

Fault detector. _____________________ Duct _ ft. from duct edge.

Cut and try. ------ No. of cuts __________ ' Eepairs completed at __________________

Time required to locate ---------------- Feeder ready for service at

Section of conduit ------------------ '.. Location of duct occupied _______________

PROBABLE CAUSE OF TROUBLE

(a) Mechanical injury:

1. Extraneous mechanical ________________________________

2. 'Electrolysis ________________________________________

3. Sharp bend __________________________

.4. Overheating _____________________________________

(5 Surge on system) _____

(6) .Defect in cable:

1. Defective insulation ________________________________

2. Defective sheath _______________________________ J

3. Defective joint _________________ Made by _____________

^Resulting damage in conduit or manhole

" " " station or substation

Detail report of trouble of on cable No.

On reverse side give detailed report

FIG. 154.— Cable-trouble sheet.

In order to secure comparative information it is desirable that
reports be made up on a standard form such as that submitted
herewith, Fig. 154, for reporting high-tension feeder trouble.
This form which has been drawn up to cover all ordinary cases
of trouble, may be made up in card form for convenience in filing.

302 UNDERGROUND TRANSMISSION AND DISTRIBUTION

If this is done, some reduction may be made in the size of the
report. It is very desirable, however, that in entering the in-
formation under the headings ' 'Location of Fault" and " Probable
Cause of Injury" the foreman should have the accompanying
form of report at hand and make entries on the form under
one of the several subheadings. The back of the report should
be used for describing previous troubles on the same line or in
the same conduit, which may possibly have had a bearing upon
the fault, as well as other items of interest which cannot be
readily tabulated.

Cleaning Manholes. — Underground systems require much less
attention than overhead lines, but it is a mistake to suppose that
when lines are once underground they will care for themselves.
There is always a chance for trouble. Provision should be made
for cleaning manholes at regular intervals, these cleanings being
sufficiently frequent to prevent insanitary conditions in manholes.
A number of companies maintain portable pumping equipments
which are used by a regular inspection and cleaning division
employed solely in maintaining the underground system in a
satisfactory condition. Before beginning work in manholes
where obnoxious odors or other disagreeable conditions exist,
an effort should be made to supply forced ventilation or adopt
other expedients which will make the conditions in the manhole
tolerable for the workmen. Increasing interest in the welfare
of employees is daily becoming more evident both on the part
of the operating companies and the public authorities having to
deal with such matters. In a large system a considerable saving
in the cleaning of manholes can be affected by a systematic pro-
cedure in the use of large dump wagons and a small gang of men,
who, when work on the cleaning of manholes is slack, join the
various conduit and cable gangs.

Care of Cables. — If a large number of loaded cables pass
through one manhole it is well to take temperature readings
in the manhole to determine when a temperature unsafe for
the cable is reached; these can be taken either with a recording
thermometer or one giving maximum temperature. In cold
weather, or when the streets are muddy, it is sometimes advisable
to have an inspector go over heavily loaded conduit lines to
make sure that the ventilating holes in the manholes covers
are open.

In Fig. 155 are shown curves of manhole temperature, tern-

OPERATION AND MAINTENANCE

303

perature of outside air and load on the cables passing through
a manhole. The hole, which is 7 by 7 ft., and 7 ft. deep, contains
two 50~kw. transformers. It will be noted from the size of the
manhole that there are 3.43 cu. ft. of space per kw. of trans-
former capacity. This is considered conservative and in this
particular case did not result in excessive manhole temperatures.
Periodic insulation resistance tests are valuable, as they furnish
indications of abnormal conditions and often lead to the detection
of faults on the system. A new cable should not be connected
to the main busbars without being previously tested with full
working pressure. This is usually accomplished through a suit-

ump

-•rat

ire

anh

jle

^— *

, -1

— —

~-~_

- — -^

— —

—.

- —

/
_/

70
60

oad

— '

Tor

nper

•*-

—

,—

-~.

—

SIZE OF MANHOLE 7'X 7'X 7'DEEP
TOTAL SQUARE FEET INCLUDING TOP
AND BOTTOM 294
Transformer 60 Kw. Core Loss 297
Copper Loss 596
Total 893
Losses for Two Transformers 178C Watts
Watts Loss Square Foot 6.08
8.48 Cu. Ft. per Kw. of Transformers Capacity

^**

— •

^-*

—— ^

looos

800|
600 a

400§

200 g,

10A.M.12Noon 2P.M. 4P.M. 6P.M. 8P.M. 10P.M. 12 P-M, 2A.M. 1A.M. 6A.M. 8A.M.

FIG. 155.— Manhole-temperature chart showing comparison of temperature
with load on cables.

able transformer properly fused, or by inverting a rotary conver-
ter with a fuse on the low-tension side.

The feeder readings, taken in stations and substations, should
be carefully followed up to make sure that no feeders are over-
loaded and the load on the mains should also be noted. For
the purpose of checking the load on single-conductor cables,
particularly transformer leads, a split-core current-testing
transformer will be found convenient. This instrument, which
is illustrated in Fig. 156, consists of a special transformer having
a hinged magnetic circuit and a standard portable ammeter.
Flexible duplex leads are supplied with each set, of sufficient
length so that the transformer can be clamped in position around
the conductor and the ammeter removed to a more convenient

304 UNDERGROUND TRANSMISSION AND DISTRIBUTION

place for reading. When a test is to be conducted, the terminals
of the duplex leads should be inserted in the ammeter binding
posts and the transformer jaws firmly clamped in position around
the cable. The transformer will maintain within commercial
limits its ratio accuracy from one-eighth to 25 per cent, overload.
Occasions constantly arise for using this set in determining
the load on feeders and in the case of distribution networks,
where it has been found particularly valuable.

FIG. 156. — Split-core cable-testing transformer.

A regular inspection of the manholes, covers, cables, junction
boxes and other equipment should be made from two to four
times a year depending on the size of the system, and a record
kept of such inspection, together with all necessary work done
to maintain the entire system at maximum efficiency.

Cables should not be disturbed after once in place, if it is possi-
ble to avoid it. If they must be moved, it should be done with
the greatest care, one cable at a time and without any strain
on the cable joints.

OPERATION AND MAINTENANCE 305

Cables should never be used as steps for entering or leaving
manholes. A small portable ladder should always be used for
this purpose.

It is not possible to estimate accurately the life of cables and
what will be the cost of maintenance after several years' installa-
tion. The cost of repairs for the first year is usually very low
and the other items of maintenance are the expenses for periodic
inspection and testing.

Bonding Cables in Manholes. — The following recommenda-
tions are made by the Underground Committee of the National
Electric Light Association in the matter of the bonding of all
cables in each manhole.

It is of prime importance when faults occur in underground
cables; that the current flowing in the short-circuit should be
sufficient to operate the safety devices or in the absence of safety
devices to make a sufficient disturbance so that the existence of
the trouble will be quickly brought to the attention of the station
operator. In the case of single-conductor cables, whether for
use on Edison three- wire systems having a normal voltage of 115
or 230, or on railway systems having a normal voltage of about 600,
it is entirely possible that a short-circuit may occur between the
conductor and the lead at a point remote from the power supply
station without a sufficient rise in the current to enable the opera-
tor to distinguish it from some unusual load. The lead sheaths
of 1,000,000- and 1,500,000-cm. cables, which are the sizes fre-
quently used, are equivalent to about 70,000 and 80,000 cm. in
copper, respectively, so that if the current which passes through
the short-circuit from the conductor to the lead is required to tra-
verse only a few blocks of the lead of that particular cable before
it can find other paths to the station, the resistance may be suffi-
cient to limit the current to the normal carrying capacity of the
copper. The radiating surface of the lead is so great that this
large amount of current may be carried for quite an appreciable
time without seriously overheating the lead. The result is that
the arc at the point where the trouble started has in series with it
sufficient resistance so that it burns quite steadily and without
the knowledge of the station operator. This is probably the most
dangerous trouble that can occur on an underground system and
every effort should be made to avoid the occurrence of such a
condition.

The use of concentric cable eliminates the above-mentioned
20

306 UNDERGROUND TRANSMISSION AND DISTRIBUTION

difficulty, as an arc of this kind, even if it starts in the outer con-
ductor, is very quickly communicated to the inner, and enough
current will flow in the short-circuit to eliminate any doubt on the
part of the operator as to the nature of the trouble. Where
single-conductor cables are already installed, the condition can
generally be improved by bonding the lead sheaths of all cables
in each manhole. This will, in general give sufficient conductiv-
ity in the return path to cause enough current to flow at the point
of the trouble so that the existence of the trouble is immediately
apparent. The calculations to determine the possible amount
of current that will flow are, however, very simple and should
always be made as a check whenever there is any doubt on this
point.

The bonding of the cables in all manholes also reduces the
liability of damage due to electrolytic action by stray currents of
electric railways, as well as similar damage due to leaky joints
and other troubles on the lighting cables. While there is some
difference of opinion among experts on the subject as to the ex-
act scheme of protection that should be adopted for lead-covered
cables operated by a lighting company, they are in accord on the
proposition that the lead sheaths of all cables be bonded together
in all manholes.

When bonding cables the important feature, necessary for good
results, are a positive low-resistance connection to the lead
sheath and a conducting medium from one cable sheath to the
other. Experience has proved that either copper ribbon or
copper-tinned wire give the best results. A choice between the
two is simply a matter of opinion and minor manhole require-
ments, the wire having the advantage of a more flexible bond than
the ribbon, when such is an advantage.

Rules and Requirements. — In large systems it is impor-
tant to devise a set of rules for the guidance of the men in the
different departments. These rules must be rigidly complied
with so as to eliminate any danger of injury to men making
tests or repairs to cable or switchboards. While it is impossible
to include in a brief summary complete instructions covering
every detail in connection with underground work, the follow-
ing rules are intended to lay down certain fundamental princi-
ples, which should be observed in all cases. To avoid accidents
to employees or the public, the following rules and cautions are
recommended.

OPERATION AND MAINTENANCE 307

SUBWAY RULES

Every splicer, inspector, and helper, must observe the follow-
ing:

LOOK OUT FOR GAS

Immediately upon opening a manhole or vault and before en-
tering same, make a careful examination for illuminating, sewer,
or other harmful gas. Never enter a manhole where poisonous
gas is found, but report same promptly to foreman or superintend-
ent in charge.

If it is necessary to work in a manhole which does not venti-
late properly after the cover has been removed, an air pump must
be used. A rope must be attached to the body of the workman
in the manhole and fastened above, so that in case of necessity,
he can be drawn to the surface. Work of this character must be
done only when expressly ordered by the foreman or superinten-
dent and under his direct supervision.

AVOID EXPLOSIONS

Do not use matches, lamps or candles in or near manholes. If
artificial illumination is required use only incandescent lamps or
approved safety lanterns.

Never carry a gasolene or other furnace or torch into or near
a manhole.

Do not smoke or carry lighted cigars, cigarettes or pipes into
or near a manhole.

Avoid sparks in connecting or disconnecting cables or apparatus
in manholes.

Exercise care in soldering and wiping joints so as not to ignite
the flux.

WATCHING AND GUARDING

After removing a cover from a manhole, place around the open-
ing the guard provided, to which should be attached a red flag.
When working at night, substitute a red light. Always have a
man at the surface to guard the opening. Replace cover, noting
that it is properly seated, upon completion of work. If excava-
tions are made, see that they are properly fenced, lighted and
guarded.

308 UNDERGROUND TRANSMISSION AND DISTRIBUTION

GLOVES, BOOTS, ETC.

When working on any cable or piece of apparatus, wear rubber
gloves and rubber boots, and before beginning work satisfy your-
self that these are in good condition. Do not wear boots with
nails in the heels. Use a dry board to stand on, and an insulating
barrier around live parts where possible. All conducting parts
of tools or appliances that need not be exposed must be insulated.
Be sure your tools are in good condition. Never leave tools lying
around loose where they may come into accidental contact with
live parts. Keep sleeves down and avoid contact between any
part of your body and live cable or apparatus.

BE SURE You HAVE THE RIGHT CABLE

When sent out to do any work, be positive you understand
exactly what you are to do. Be sure you have the right cable
before beginning any work. If tags are missing or if from any
cause, there is difficulty in locating the proper cable, report
promptly to the foreman or superintendent.

LIVE WORK

Treat every cable and piece of apparatus as alive until you
have satisfied yourself that it is dead and until then observe all
precautions.

HIGH-VOLTAGE WORK

Do not work on live high-tension cable or apparatus, without
express and definite orders from the foreman or superintendent.
Never attempt to splice a high-voltage cable alive. When in-
structed to have the current disconnected before beginning work,
make certain that the switchboard attendant understands upon
which circuit you are to work and do not begin until he tells you
the circuit is dead. As soon as you have notified the station
to put the current on, consider the circuit alive. Make certain
that no other workman is engaged on the same circuit before
having current connected.

REPORT DEFECTS

Report without delay to the foreman or superintendent the
presence of gas or water in manholes, or any defect or unusual
condition you may observe.

INDEX

Agreement, form of franchise, 24
Arcing ground suppressor, 276
Armored cable, 94, 129

cables, jointing of, 176

services, 263
Arresters, lightning, 216

Balanced system of protection, 278
Block distribution, 82
Bond, form of indemnity, 75
Bonds, drainage, 284
Bonding of cables, 305
Boxes, junction, 252

sectionalizing, 252
Brooks system, 6
Built-in system, 7, 88
Bus service, 258

Cable pulling grips, 157

reels, 120

systems, operation of, 296

testing equipment, 237

tunnels, 64
Cables, armored, 94, 129

bonding of, 305

current carrying capacity of,
199

diameter and length of, 119, 124

faults in, 233

fibre core, 120

general data on, 102-122

heating of, 228

installation of, 151-157

location of faults in, 233

protection of, 195

sector, 126

Cables, specifications, 134, 135, 139-
146|

splicing of, 168

split conductor, 278

submarine, 129

tagging of, 297

terminology, 102

testing of, 229

transmission, 121

types of, 116
Callender system, 8
Cambric covered cables, 177
Choke coils, 272
Cleaning manholes, 302
Comb, conduit, 45
Concrete, 32

manholes, 62
Conduit installation, 30
Conducell insulators, 187
Conductors, 102-103
Connections to overhead lines, 209
Construction, early forms of, 5

present form of, 17
Contract, form of, 67
Cooling of duct lines, 205
Copper, properties, 104-105

sleeves, 174

Corrosion, electrolytic, 281
Costs, construction, 76
Cost of steel-taped cable, 101
Crompton system, 7
Gumming duct, 13
Current carrying capacity of cables,
199

Design of manholes, 54
Development, periods of,
Distribution, block, 82

holes, 63

sidewalk, 84

309

310

INDEX

Distribution, street, 81

systems of, 241
Dorsett conduit, 13
Drainage systems, 284
Draw rope, 160
Dra wing-in apparatus, 161

systems, 11
Duct cleaners, 155

fibre, 41

lines, routing of, 86

stone, 40

tile, 34
Ducts, arrangement of, 85

choice of, 153

rodding of, 154

sealing of, 47

Early underground systems, 5
Edison system, 4, 9
Electrolysis, 281

prevention of, 290

surveys, 293

Failures, records of cable, 300
Fault localizer, 274
Faults, location of, 233

locating equipment, 237
Fibre core cables, 120

duct, 41

Fireproofing cables, 198
Forms, concrete manhole, 62
Franchise agreement, 24

Gas in conduit systems, 47
Graded insulation, 114
Grips for cable pulling, 157
Ground suppressor, 276
Grounded neutral systems, 277

Heating of cables, 228
of duct lines, 205
of manholes, 302

High tension cable specifications,

146

voltage testing of cables, 240
Holes, distribution, 63

Identification of cables, 297
Installation of conduits, 30
Insulating compound, 183

pipe joints, 286
Insulation, graded, 114

kinds of, 105

paper, 111

rubber, 109

varnished cambric, 113
Interior conduit system, 13
Iron clad services, 263

Jack, pipe forcing, 91

reel, 151
Jointing material, 193

of cables, 168
Junction boxes, 252

Kennedy system, 8
L

Lamp standards, concrete, 99
Lead, properties of, 115

sheath, 114

sleeves, weights of, 173
Lightning arresters, 216
Loop test, 234

Mains, secondary, 246
Maintenance of cable systems, 296-

302

Mandril, 36
Manhole covers, 50

roof construction, 50

switches, 259

waterproofing, 54

INDEX

311

Manholes, cleaning of, 302

concrete, 62

construction of, 46

cost of, 79

design of, 54

distribution, 54

heating of, 302

in quicksand, 49

transformer, 55

transmission, 54

types of, 48

ventilation of, 225, 250
Maps of conduit systems, 19
Materials, selection of, 30
Merz system of cable protection,

278

Meter protection, 263
Mica tube joints, 186
Moisture in cable insulation, 149
Multiple tile duct, 34
Municipal regulation, 23-27

Network protector, 261
Neutral, grounding of, 277

Obstructions, 20

Oils, impregnating, 111

Operation of cables, 125

of cable systems, 296-302

Paper cables, jointing of, 177
ca'ble specifications, 139
insulation, 111
tube joints, 179

Periodic testing of cables, 240

Permits, 21

Pipe forcing jack, 91

Plans for conduit construction,
19

Pole terminals, 209

Potheads, 209

Power trucks, 164

Present forms of construction, 17

Protecting sheaths against electrol-
ysis, 287
Protection of cables, 195

of transmission systems, 270
Protective pipe coatings, 285
Protector on A. C. networks, 261

Rating of cables, 199
Reactance coils, 272
Records of cable failures, 300

installations, 296
Reels, cable, 120
Reel jack, 151

Regulations, municipal, 23-27
Relays, 270

Repairing cable failures, 233
Right-of-way, 22
Rodding ducts, 154
Rope for pulling cables, 160
Routing of duct lines, 86
Rubber cable specifications, 135

covered cable, jointing of, 176

insulation, 109
Rules, safety, 306

standardization, 228

Safety devices, 217

regulations, 306
Sealing of ducts, 47
Secondary mains, 246
Sectionalizing boxes, 252
Sector cables, 126, 278
Selective fault localizer, 274
Service bus, 258

connections, 90
Services, protection of, 263
Sheath, lead, 114
Sheaves for cable pulling, 164
Sidewalk distribution, 84
Single tile duct, 34
Slack in cables, 167
Sleeve-filling material, 183
Sleeves, copper, 174

lead, 173
Solid system, 88

312

INDEX

Specifications, cable, 134, 135, 139-
146

conduit and manhole, 67
Splicing cables, 168

equipment, 217
Split conductor cables, 278

core transformer, 303
Standardization rules, 228
Steel-pipe systems, 14

taped cable, 94-100

cost of, 101
Stone duct, 40
Street distribution, 81

lighting cable, 97
Submarine cables, 129
Subway transformers, 248
Suppressor, arcing ground, 276
Surveys, electrolysis, 293
Switches, oil, 259

manhole, 259

Tagging of cables, 297
Temperature of cables, 228
Terminal blocks, 97
Terminals, pole, 209
Terminology, cable, 102
Test holes, 20

voltages, 123
Tests, high voltage, 240

periodic, 240

Testing equipment, 237

of cables, 229

for live cables, 223
Tile duct, 34
Tools for splicing, 217
Transformer manholes, 55

split core, 303

Transformers, underground, 248
Transmission cables, 121

systems, protection of, 270
Trucks, power, 164
Tunnels, cable, 64

Underground transformers, 248
Units, electrical, 227

Vacuum joints, 188
Varnished cambric, 113
Ventilation of manholes, 225, 250
Voltages, wroking and test, 123

Waterproofing manholes, 54

Webber system, 13

Winch, cable pulling, 161

Wooden duct, 14

Wrought iron pipe systems, 14

UNIVEESITY OF CALIFORNIA LIBRARY,
BERKELEY

THIS BOOK IS DUE ON THE LAST DATE
STAMPED BELOW

Books not returned on time are subject to a fine of
50c per volume after the third day overdue, increasing
to $1.00 per volume after the sixth day. Books not in
demand may be renewed if application is made before
expiration of loan period.

JUN 2

it»

SEP 1 19?5

APR 4 1927

MAR IS

20m-ll,'20

UNIVERSITY OF CALIFORNIA LIBRARY

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