ELECTRIC
WIRING AND LIGHTING
A HANDBOOK OF APPROVED MODERN METHODS
OF LIGHTING BY ELECTRICITY, AND OF
INSTALLING CONDUCTORS FOR THE
TRANSMISSION AND UTILIZATION
OF ELECTRICITY FOR POWER,
LIGHTING, HEATING,
AND OTHER USES
Part I ELECTRIC WIRING
By CHARLES E. I^NOX, E. E.
CONSULTING ELECTRICAL ENGINEER
Part II ELECTRIC LIGHTING
By GEORGE E. SHAAD, E. E.
PROFESSOR OF ELECTRICAL ENGINEERING, UNIVERSITY OF KANSAS
ILLUSTRATED
AMERICAN TECHNICAL SOCIETY
CHICAGO
1916
Copyright 1908, 1913 by
AMERICAN TECHNICAL SOCIETY
Copyright Great Britain
AH Rights Reserved
CONTENTS
PART I
ELECTRIC WIRING
PAGE
Wires run concealed in conduits 1
Wires run in rigid conduit 1
Wires run in flexible metal conduit 4
Wires run in moulding 9
Fibrous tubing 15
Wires run exposed on insulators 16
Two-wire and three-wire systems 20
Calculation of sizes of conductors 25
Planning a wiring installation 29
Wiring methods 29
Wiring systems 30
Location of outlets 30
Location of distributing centers 31
Branch circuits ."*". 32
Voltage drop in conductors 34
Feeders and mains 36
Testing circuits 36
Alternating-current circuits 40
Comparison with direct-current circuits 40
Skin effect 42
Mutual induction 42
Line capacity 43
Calculation of drop in a. c. lines 44
Single-phase circuits 48
Polyphase circuits 53
346638
CONTENTS
PAGE
Wiring an office building 54.
Current supply '. . . 54
Switchboard 55
Load ' 55
Feeders and mains 55
Wiring plans for eacli floor :..... 56
Interconnection system 58
Outlet-boxes, cut-out panels and accessories 63
Overhead linework 68
Poles 69
Pole guying 72
Corners 75
Cross arms 75
Service mains 77
Lightning arresters 78
Lamp supports on poles 79
Underground linework 79
Iron pipe 80
Vitrified tile conduit 80
Laying conduit 82
Fibre conduit . . 83
PART II
ELECTRIC LIGHTING
PAGE
History and development 1
Classification 2
Incandescent lamps 2
Manufacture of carbon filament lamps V 3
Voltage and candle-power 5
Efficiency 6
Selection of lamps 8
Distribution curves 11
Gem metallized- filament lamp 12
Metallic filament lamps 14
Helion lamp 21
Nernst lamp 21
Comparison of different types 25
CONTENTS
PAGE
Special lamps 27
Mercury vapor lamp 27
Moore tube light 29
Arc lamps 32
Control mechanisms 33
Types of 38
Direct-current arcs 38
Alternating-current arcs 39
Flaming arcs 42
Power distribution systems 46
Illumination '.,." 53
Residence lighting 56
Types of lamps 56
Illumination calculations . .". 56
Intensity constants for incandescent lamps. . 59
Intensity constants for arc lamps 59
Arrangements of lamps. 55
Lighting of public halls, offices, etc 64
Street lighting 67
Shades and reflectors 72
Frosted globes 73
Holophane globes 74
Opal enclosed globes 76
Photometry ,. 76
Light standards .......;.. . . . .- * 76
Photometers 79
Lummer-Brodhun 80
Weber 83
Portable 85
Integrating 86
Incandescent lamp photometry 88
Arc light photometry 93
INTRODUCTION
T~^ LECTEIC lighting virtually started with the invention of the
' J Edison incandescent lamp in 1878, the discovery of this very
useful and flexible lighting unit marking an epoch not only in home
lighting., but also in the actual development of the electrical industry
itself. This invention had been preceded by the invention of the higher
powered but less flexible arc lamp, and these two fundamental lighting
sources have been the standards of electrical illumination since that
time.
C The last few years have seen many notable improvements,, not only
in the methods of lighting but in the light units themselves. The
enclosed arc, the flaming arc, the Moore tubes, and the Nernst lamp
have all contributed to this wonderful development, but the recent
improvement in metallic filament lamps, notably the Tungsten, has
given an impetus which is second onty to the original invention of the
incandescent lamp itself. To cut the energy consumption per candle-
power from 3.5 watts to 1.25 watts is certainly a triumph, and this
improvement has opened up many fields of activity hitherto closed to
incandescent lighting. It has even made the beautifully effective, but
criminally inefficient, method of indirect lighting economically pos-
sible.
C In addition to the progress in the lighting phases of this interesting
subject, the many precautions and safeguards which the building
departments of our cities and the National Board of Fire Underwriters
demand in connection with lighting and power circuits, make it all the
more necessary that everyone actively engaged or interested in lighting
and wiring should have a reliable handbook giving standard specifica-
tions and requirements as to materials and methods, and adequate
descriptions of recommended devices.
C The material in this volume is especially adapted for purposes of
self-instruction and home study. The utmost care has been used to
make the treatment of each subject appeal not only to the technically
trained expert, but also to the beginner and the self-taught practical
man who wishes to keep abreast of modern progress. The language
is simple and clear; heavy technical terms and the formulae of the
higher mathematics have been avoided, yet without sacrificing any of
the requirements of practical instruction.
C For purposes of ready reference and timely information when
needed, it is believed that this handbook will be found to meet every
requirement.
ELECTRIC WIRING
METHODS OF WIRING
The different methods of wiring which are now approved by the
National Board of Fire Underwriters, may be classified under four
general heads, as follows:
1. WIRES RUN CONCEALED IN CONDUITS.
2. WIRES RUN IN MOULDING.
3. CONCEALED KNOB AND TUBE WIRING.
4. WIRES RUN EXPOSED ON INSULATORS.
WIRES RUN CONCEALED IN CONDUITS
Under this general head, will be included the following:
(a) Wires run in rigid conduits.
(6) Wires run in flexible metal conduits.
(c) Armored cable.
Wires Run in Rigid Conduit. The form of rigid metal conduit now
used almost exclusively, consists of plain iron gaspipe the interior sur-
face of which has been prepared by removing the scale and by remov-
ing the irregularities, and which is then coated with flexible enamel.
The outside of the pipe is given a thin coat of enamel in some cases,
and, in other
cases, is galvan-
i z e d . Fig. 1
shows one make
11 , Fig. 1. Rigid Enameled Conduit, Unlined.
OI enameled (nu- Courtesy of American Conduit Mfg. Co., Pittsburg, Pa.
lined) conduit.
Another form of rigid conduit is that known as the armored con-
duit, which consists of iron pipe with an interior lining of paper
impregnated with asphaltum or similar compound. This latter form
of conduit is now rapidly going out of use, owing to the unlined pipe
being cheaper and easier to install, and owing also to improved methods
of protecting the iron pipe from corrosion, and to the introduction of
additional braid on the conductors, which partly compensates for the
ELECTRIC WIRING
pipe being unlined. The introduction of improved devices such as
outlet insulators, for protecting the conductors from the sharp edges of
the pipe, at outlets, cut-out cabinets, etc. also decreases the neces-
sity of the additional protection afforded by the interior paper lining.
Rigid Conduits are made in gaspipe sizes, from one-half inch to
three inches in diameter. The following table gives the various data
relating to rigid, enameled (unlined) conduit:
TABLE I
Rigid, Enameled Conduit Sizes, Dimensions, Etc.
NOMINAL
NUMBER OF
ACTUAL
NOMINAL
STANDARD
PIPE SIZE
THICKNESS
WEIGHT
PER
THREADS
PER INCH
OUTSIDE
DIAMETER.
INSIDE
DIAMETER.
100 FEET
OF SCREW
INCHES
INCHES
j
.109
84
14
.84
.62
|
.113
112
14
1.05
.82
1
.134
167
11*
1.31
1.04
H
.140
224
11*
1.66
1.38
i*
.145
268
11*
1.90
1.61
2
.154
361
111
2.37
2.06
2i
.204
574
8
2.87
2.46
3
.217
754
8
3.50
3.06
Tables II, III, and IV give the various sizes of conductors that
may be installed in these conduits. Caution must be exercised in
TABLE II
Single Wire in Conduit
SIZE WIRE, B. & S. G.
LORICATED CONDUIT, UNLINED; D. B. WIRE
No. 14-4
\ inch
2
1 '
1
i '
f inch or 1 '
00
1
000
1 '
0000
1
t
250,000 C. M.
H
(
300,000 C. M.
H
(
350,000 C. M.
H
i
400,000 C. M.
H " or if
t
450.000 C. M.
l|
i
SOOiOOO C. M.
1*
i
600,000 C. M.
H " or 2
1
700,000 C. M.
2
i
800,000 C. M.
2
*
900,000 C. M.
2
t
1,000,000 C. M.
2 " or 2
i .
1,500,000 C. M.
2*
t
1,700,000 C. M.
(
2,000,000 C. M.
3
i
ELECTRIC WIRING
TABLE III
Two Wires in One Conduit
SIZE WIRE, B. & S. G.
LORICATED CONDUIT, UNLINED; D. B. WIRE
No. 14
\ inch.
12
\ irch or f
'
10
|
<
8
1
<
6
1
'
5
1 " or \\
'
4
H
t
3
H
(
2
U " or \\
1
1
lj
1
H
f
00
H " or 2
'
000
2
1
0000
2
1
250,000 C. M.
2 " or 2i
1
300,000 C. M.
2i
t
350,000 C. M.
2^
i
400,000 C. M.
2 " or 3
i
450,000 C. M.
3
<
500,000 C. M.
3
:
600,000 C. M.
3
t
700,000 C. M.
3
(
TABLE IV
Three Wires in One Conduit
SIZE WIRE, B. & S. G.
LORICATED TUBE, UNLINED;
Outside
Center
D. B. WIRE
No.
14
No.
12
f inch
12
10
"
10
8
1
8
6
1
6
4
1*
5
2
H
4
1
1| inch or 1^
3
1*
2
2/0
li " or 2
1
3/0
2
4/0
2
2/0
250
M.
2 " or 2J
3/0
300
M.
2*
4/0
400
M.
2*
250
M.
450
M.
2J " or 3
250
M.
500
M.
3
300
M.
600
M.
3
350
M.
700
M.
3
400
M.
800
M.
3
450
M.
900
M.
3
4 ELECTRIC WIRING
using these tables, for the reason that the sizes of conductors which
may be safely installed in any run of conduit depend, of course, upon
the length of and the number of bends in the run. The tables are
based on average conditions where the run does not exceed 90 to 100
feet, without more than three or four bends, in the case of the smaller
sizes of wires for a given size of conduit ; and where the run does not
exceed 40 to 50 feet, with not more than one or two bends, in the case
of the larger sizes of wires, for the same sizes of conduit.
Unlined conduit can be bent without injury to the conduit, if the
conduit is properly made and if proper means are used in making the
bends. Care should be exercised to avoid flattening the tube as a result
of making the bend over a sharp curve or angle.
In installing iron conduits, the conduits should cross sleepers or
beams at right angles, so as to reduce the amount of cutting of the
beams or sleepers to a minimum.
Where a number of conduits originate at a center of distribution,
they should be run at right angles for a distance of two or three feet
from the cut-out box, in order to obtain a symmetrical and workman-
like arrangement of the conduits, and so as to have them enter the
cabinet in a neat manner. While it is usual to use red or white lead
at the joints of conduits in order to make them water-tight, this is
frequently unnecessary in the case of enameled conduit, as there is
often sufficient enamel on the thread to make a water-tight joint.
When iron conduits are installed in ash concrete, in Keene
cement, or, in general, where they are subject in any way to corrosive
action, they should be coated with asphaltum or other similar protec-
tive paint to prevent such action.
While the cost of circuit work run in iron conduits is usually
greater than any other method of wiring, it is the most permanent
and durable, and is strongly recommended where the first cost is not
th'e sole consideration. This method of wiring should always be
used in fireproof buildings, and also in the better class of frame build-
ings. It is also to be recommended for exposed work where the work
is liable to disturbance or mechanical damage.
Wires Run in Flexible Metal Conduit. This form of conduit,
shown in Fig. 2, is described by the manufacturers as a conduit com-
posed of "concave and convex metal strips wound spirally upon each
other in such a manner as to interlock several concave surfaces and
ELECTRIC WIRING
Fig. 2. Flexible Steel Conduit.
Courtesy of Sterling Electric Co., Troy, N. 7.
present their convex surfaces, both exterior and interior, thereby
securing a smooth and comparatively frictionless surface inside and
out."
The field for the use of this form of conduit is rapidly increasing.
Owing to its flexibility, conduit of this type can be used in numerous
cases where the
rigid conduit
could not possi-
bly be em-
ployed. Its use
is to be recom-
mended above
all the other forms of wiring, except that installed in rigid conduits.
For new fireproof buildings, it is not so durable as the rigid conduit,
because not so water-tight; and it is very difficult, if not impossible,
to obtain as workmanlike a condu't system with the flexible as with the
rigid type of conduit. For completed or old frame buildings, however,
the use of the flexible conduit is superior to all other forms of wiring.
Table V gives the inside diameter of various sizes of flexible con-
duit, and the lengths of standard coils. inside diameter of this
conduit is the same as that of the rigid conduit; and the table given
for the maximum sizes of conductors which may be installed in the
various sizes of conduits, may be used also for flexible steel conduits,
except that a little more margin should be allowed for flexible steel
conduits than for the rigid conduits, as the stiffness of the latter makes
it possible to pull in slightly larger sized conductors.
TABLE V
Greenfield Flexible Steel Conduit
INSIDE DIAMETER
APPROXIMATE FEET IN COIL
ft inch
?
inches
200
200
100
50
50
50
50
Random Lengths
6
ELECTRIC WIRING
This conduit should, of course, be first installed without the con-
ductors, in the same manner as the rigid conduit. Owing to the
flexibility of this conduit, however, it is absolutely essential to fasten
it securely at all elbows, bends, or offsets; for, if this is not done, con-
siderable difficulty will be ex-
perienced in drawing the con-
ductors in the conduit.
The rules governing the in-
stallation of this conduit are
the same as those covering
rigid conduits. Double-braided
Fig. 3. use of Elbow ciamp for Fastening Flex- conductors are required, and
ible Conduit in Place. ' , . . _ _ . /
the conduit should be grounded
as required by the Code Rules. As already stated, the conduit should
be securely fastened (in not less than three places) at all elbows; or
else the special elbow clamp made for this purpose, shown in Fig. 3,
.should be used.
In order to cut flexible steel conduit properly, a fine hack saw
should be employed. Outlet -boxes are required at all outlets, as well
as bushing and wires to rigid
conduit. Fig. 4 shows a coil
of flexible steel conduit. Figs.
5, 6, and 7 show, respectively,
an outlet box and cover, outlet
plate, and bushing used for this
conduit.
Armored Cable. There
are many cases where it is im-
possible to install a conduit
system. In such cases, prob-
bably the next best results may
be obtained by the use of steel
armored cable. The rules gov-
erning the installation of armored cable are given in the National
Electric Code, under Section 24-A, and Section 48 ; also in 24r-S. This
cable is shown in Fig. 8.
Steel armored cable is made by winding formed steel strips over
the insulated conductors. The steel strips are similar to those used
Fig. 4. A 100-Foot Coil of Flexible Steel Conduit.
Courtesy of Sprague Electric Co., New York,N.Y.
ELECTRIC WIRING 7
for the steel conduit. Care is taken in forming the cable, to avoid
crushing or abraiding the insulation on the conductors as the steel
Fig. 5. Outlet Box for Flexible Steel Conduit.
strips are fed and formed over the same. In the process of manufac-
ture, the spools of steel ribbon are of irregular length, and when a
Fig. 6. Outlet Plate for Flexible Steel Fig. 7. Outlet Bushing.
Conduit. Courtesy of SpragueElectric Co.,NewYork, 2V. F.
spool is empty, the machine is stopped, and the ribbon is started on
the next spool, the process being continued. There is no reason why
Fig. 8. Flexible Armored Cable. Twin Conductors.
Courtesy of Sprague Electric Co., New York, N. Y.
the conduit cables could not be made of any length ; but their actual
lengths as made are determined by convenience in handling. Armored
8
ELECTRIC WIRING
cable is made in single conductors from No. 1 to No. 10 B. & S. G.;
in twin conductors, from No. 6 to No. 14 B. & S. G.; and three-conduc-
tor cable, from No. 10 to No. 14 B. & S. G. Table VI gives various
data relating to armored conductors:
TABLE VI
Armored Conductors Types, Dimensions, Etc.
SIZE
B.&S
GAUGE
TYPE AND NUMBER OF CONDUCTORS
OUTSIDE
DIAMETER
(INCHES)
No. 14
BX twin conductor
.63
" 12
it ti it
.685
" 10
(t (t (t
.725
" 8
ti tt it
.875
" 6
<t it ti
1.3125
" 14
BM twin conductor (for marine work ship wiring)
.725
" 12
a it u
.725
" 10
tt <t tt
.73
" 14
BX3 three conductor
.71
" 12
ti it tt
.725
tt 10
ti tt tt
.73
" 14
BXL twin conductor, leaded
.725
" 12
it tt ti tt
.725
" 10
tt ti tt a
.87
" 14
BXL3 three conductor, leaded
.90
" 12
ti tt tt ti
.90
" 10
tt n tt tt
.94
" 10
" 8
Type D single conductor, stranded
.550
.550
" 6
it t
.575
" 4
tt i
.700
" 2
tt t
.900
" 1
tt t
.965
" 10
11 8
Type DL single conductor, stranded, leaded
if tt -i (i
.625
.710
" 6
it ft t (t
.700
4
tt ti t n
.760
" 2
ti tt tt
.920
" 1
u K t it
.910
STEEL ARMORED FLEXIBLE CORD
" 18
" 16
Type E twin conductor
it tt ti ti
.40
.40
" 14
ti ft ti it
.47
" 18
" 16
Type EM twin conductor, re-inforced
if ti tt ti tt
.575
.585
" 14
<t tt tt ti ti
.595
In Table VI, Tvpes D (single), BX (twin), and BX3 (3 conduc-
ELECTRIC WIRING 9
tors) are armored cable adapted for ordinary indoor work. Type
BM (twin conductors) is adapted for marine wiring. Types DL
(single), BXL (twin), and BXL 3 (3 conductors) have the conductors
lead -encased, with the steel armor outside, and are especially adapted
for damp places, such as breweries, stables, and similar places.
Type E is used for flexible-cord pendants, and is suitable for
factories, mills, show windows, and other similar places. Type EM
is the same as Type E; but the flexible cord is reinforced, and is suit-
able for marine work,' for use in damp places, and in all cases where it
will be subject to very rough handling.
While this form of wiring has not the advantage of the conduit
system namely, that the wires can be withdrawn and new wires
inserted without disturbing the building in any way whatever yet it
has many of the advantages of the flexible steel conduit, and it has
some additional advantages of its own. For example, in a building
already erected, this cable can be fished between the floors and in the
partition walls, where it would be impossible to install either rigid
conduit or flexible steel conduit without disturbing the floors or
walls to an extent that would be objectionable.
Armored conductors should be continuous from outlet to outlet,
without being spliced and installed on the loop system. Outlet boxes
should be installed at all outlets, although, where this is impossible,
outlet plates may be used under certain conditions. Clamps should
be provided at all outlets, switch-boxes, junction-boxes, etc., to hold
the cable in place, and also to serve as a means of grounding the steel
sheathing.
Armored cable is less expensive than the rigid conduit or the
flexible steel conduit, but more expensive than cleat wiring or knob
and tube wiring, and is strongly recommended in preference to the
latter.
WIRES RUN IN MOULDING
Moulding is very extensively used for electric circuit work, in
extending circuits in buildings which have already been wired, and
also in wiring buildings which were not provided with electric circuit
work at the time of their erection. The reason for the popularity of
moulding is that it furnishes a convenient and fairly good-looking
runway for the wires, and protects them from mechanical injury.
10
ELECTRIC WIRING
i
y T
*a
3
IT
d co
CQ J_
Ac k Ab 4* Aa4*- Ab *| Ac
A
Fig. 9. Two- Wire Wood Moulding.
It seems almost unwise to place conductors carrying electric current,
in wood casing; but this method is still permitted by the National
Electric Code, although it is not allowed in damp places or in places
where there is liability to damp-
ness, such as on brick walls,
in cellars, etc.
The dangers from the use of
moulding are that if the wood
becomes soaked with water,
there will be a liability to leak-
age of current between the conductors run in the grooves of the mould-
ing, and to fire being thereby started, which may not be immediately dis-
covered. Furthermore, if the conductors are overloaded, and conse-
quently overheated, the wood is likely to become charred and finally ig-
nited. Moreover, the moulding itself is always a temptation as affording
a good "round strip" in which to drive nails, hooks, etc. However, the
convenience and popularity of moulding cannot be denied; and until
some better substitute is found, or until its use is forbidden by the
Rules, it will continue to be used to a very great extent for running
circuits outside of the walls and on the ceilings of existing build ings.
Figs. 9, 10, 11, and 12 show two- and three-wire moulding respectively;
and Table VII gives complete data as to sizes of the moulding required
for various sizes of conductors.
While the Rules recommend the use of hardwood moulding, as a
matter of fact probably 90 per cent of the moulding used is of white-
wood or other similar cheap, soft wood . Georgia pine or oak ordinarily
Q
^ ^1
t
o
00
d 1
Q i
Ac-
Ab
-Aa-
-Ab-
*-Ac^
c
i
I
Fig. 10. Two-Wire Wood Moulding.
costs about twice as much as the soft wood. In designing moulding
work, if appearance is of importance, the moulding circuits should
be laid put so as to afford a symmetrical and complete design. For
ELECTRIC WIRING
11
example, if an outlet is to be located in the center of the ceiling,
the moulding should be continued from wall to wall, the portion beyond
the outlet, of course, having no conductors inside of the moulding.
If four outlets are to be placed on the ceiling, the rectangle of moulding
should be completed on the fourth side, although, of course, no con-
i
z E
I
-
Jl ?
Ac]*-Ab-j-Aa4-Ab j-A
aT~Ab-*mc
. A
Fig. 11. Three- Wire Wood Moulding.
ductors need be placed in this portion of the moulding. Doing this
increases the cost but little and adds greatly to the appearance.
Moulding is frequently used in combination with other methods
of wiring, including armored cable, flexible steel tubing, and fibrous
tubing. In many instances, it is possible to fish tubing between
beams or studs running in a certain direction; but when the conduc-
tors are to run in another direction or at right angles to the beams or
studs, exposed work is necessary. In such cases, a junction-box or
outlet-box must be placed at the point of connection between the
moulding and the armored cable or steel tubing.
Where circuits are run in moulding, and pass through the floor,
additional protection must be provided, as required by the Code Rules,
Q
D
^ x
DC
DQ
|J
Ac
Ab-*
Act
Ab
ACL
Ab-
-Ac-
Q
Fig. 12. Three-Wire Wood Moulding.
to protect the moulding. As a rule, it is better to use conduit for all
portions of moulding within six feet of the floor, so as to avoid the
possibility of injury to the circuits. Where a combination of iron
conduit or flexible steel tubing is used with moulding, it is well to use
double-braided conductors throughout, because, although only single-
12
ELECTRIC WIRING
TABLE VII
Sizes of Mouldings Required for Various Sizes of Conductors
OF
DING
Y
M
A-2
MBER
WIRES
MAXIMUM
SIZE OF WIRE
BANDS.
SOLID
12
STRANDED
14
DIMENSIONS IN INCHES
AaAb
Ac
5
Ba
Bb
32
DC
Ca
A-4
6
10
_
16
h
29
32
16
32
'fl
16
A-6
It
A-6
A-9
10
A-IO
55QOOO
C.M.
16
10
A-l
C.M.
\i
.
16
1 1
B-2
12
14
.
32
27
32
32
i 1
B-4-
6
10
L5
32
.
16
16
29
32
16
32
1 I
B-6
13
32
1 1
B-8
_
32
16
9_
32
1 1
B-9
3/0
16
15
32
.
32
9.
32
12
B-IO
25QOOO
C.M.
23
32
23
32
.
16
12
B-ll
4-OQOOO
C.M.
16
braided conductors are required with moulding, double-braided con-
ductors are required with unlined conduit, and if double-braided con-
ductors were not used throughout, it would be necessary to make a
joint at the outlet-box where the moulding stopped and the conduit
work commenced. Where the conductors pass through floors, in
moulding work, and where iron conduit is used, the inspection authori-
ties, in order to protect the wire, usually require that a fibrous tubing
be used as additional protection for the conductors inside of the iron
pipe, although, if double-braided wire is used, this will not usually be
required. Fig. 13 shows a f useless cord rosette for use with moulding
work. Fig. 14 shows a device for making a tap in moulding wiring.
Moulding work, under ordinary conditions, costs about one-half
as much as circuit run in rigid conduit, and about 75 per cent, under
ELECTRIC WIRING 13
ordinary conditions, of the cost of armored cable. Where the latter
method of wiring or the conduit system can be employed, one or the
other of these two methods should be used in preference to moulding,
Fig. 13. Fuseless Cord Fig. 14. Device for Making "Tap" in
Rosette. Moulding.
Courtesy of Grouse- TRnds Co., Courtesy of II. T. Paiste CD.,
Syracuse, 'N. Y. Philadelphia, Pa.
as the work is not only more substantial, but also safer. Various forms
of metal moulding have been introduced, but up to the present time
have not met with the success which they deserve.
CONCEALED KNOB AND TUBE WIRING
This method of wiring is still allowed by the National Electric
Code, although many vigorous attempts have been made to have it
abolished. Each of these attempts has met with the strongest
opposition from contractors and central stations, particularly in small
towns and villages, the argument for this method being, that it is the
cheapest method of wiring, and that if it were forbidden, many places
which are wired according to this method would not be wired at all,
and the use of electricity would therefore be much restricted, if not
entirely done away with, in such communities. This argument, how-
ever, is only a temporary makeshift obstruction in the way of inevitable
progress, and in a few years, undoubtedly, the concealed knob and
tube method will be forbidden by the National Electric Code.
The cost of wiring according to this method is about one-third
of the cost of circuits run in rigid conduit, and about one-half of the
cost of circuits run in armored cable. The latter method of wiring
14
ELECTRIC WIRING
is rapidly replacing knob and tube wiring, and justly so, wherever
the additional price for the latter method of wiring can be obtained.
As the name indicates, this method of wiring employs porcelain knobs
Fig. 15. Knob and Tube Wiring.
and tubes, the circuit work being run concealed between the floor beams
and studs of a frame building. The knobs are used when the circuits
run parallel to the floor beams ; and the porcelain tubes are used when
the circuits are run at right angles to the floor beams.
Fig. 15 shows an example of knob and tube wiring. In concealed
knob and tube wiring, the wires must be separated at least five inches
from one another, and at least one inch from the surface wired over,
that is, from the beams, flooring, etc., to which the insulator is fas-
tened. Fig. 16 shows a
good type of porcelain
knob for this class of
wiring. For knob and
tube wiring, it will be
noted that, owing to the
fact that the wiring is
concealed, the conductors Fig " 1G Porcelain Knob '
must be kept further apart than in the case of exposed or open wiring
on insulators, where, except in damp places, the wires may be run on
cleats or on insulators only one-half inch from the surface wired ovei,
ELECTRIC WIRING
15
Fibrous Tubing. Fibrous tubing is frequently used with knob
and tube wiring, and the regulations governing its use are given in
Rule 24, Section S, of the National Electric Code. This tubing, as
stated in this Rule, may be used where it is impossible and impracticable
to employ knobs and tubes, provided the difference in potential
between the wires is not over 300 volts, and if the wires are not sub-
Fig. 17. Flexible Tubing, "Flexduct" Type.
Courtesy of National Metal Molding Co., Pittsburg, Pa.
ject to moisture. The cost of wiring in flexible fibrous tubing is
approximately about the same as the cost of knob and tube wiring.
Duplex conductors, or two wires together are not allowed in fibrous
tubing.
Fibrous tubing is required at all outlets where conduit or armored
cable is not used (as in knob and tube wiring) ; and, as required by the
Rules, it must extend back from the last porcelain support to one inch
beyond the outlet. Fig. 17 shows one make of fibrous tubing.
Table VIII gives the maximum sizes of conductors (double-
braided) which may be installed in fibrous conduit.
TABLE VIII
Sizes of Conductors in Fibrous Conduit
OUTSIDE DIAMETER
INSIDE DIAMETER
ONE WIRE IN
TUBE
\l inch
i inch
No. 12
11
1
" 8
If
^
" 6
f
" 1
" 2/0
ii^
1
250,000
C. M.
i&
H
400,000
C. M.
ill
1*
750,000
C. M.
If
1,000,000
C. M.
21
2
1,500,000
C. M.
2|
2i '
2,000,000
C. M.
16 ELECTRIC WIRING
WIRES RUN EXPOSED ON INSULATORS
This method of wiring has the advantages of cheapness, durability,
and accessibility.
Cheapness. The relative cost of this method of wiring as com-
pared with that of the concealed conduit system, is about fifty per cent
of the latter if rubber-covered conductors are used, and about forty
per cent of the latter if weatherproof slow-burning conductors are used.
As the Rules of the Fire Underwriters allow the use of weatherproof
slow-burning conductors in dry places, considerable saving may be
effected by this method of wiring, provided there is no objection to it
Fig. I& Large Feeders Run Exposed on Insulators.
from the standpoint of appearance, and also provided that it is not
liable to mechanical injury or disarrangement.
Durability. It Is a well-known fact that rubber insulation has a
relatively short life. Inasmuch as in this method of wiring, the insula-
tion does not depend upon the insulation of the conductors, but on
the insulators themselves, which are of glass or porcelain, this system
is much more desirable than any of the other methods. Of course,
if the conductors are mechanically injured, or the insulators broken,
the insulation of the system is reduced ; but there is no gradual dete-
rioration as there is in the c^se of other methods of wiring, where
ELECTRIC WIRING
17
rubber is depended upon for insulation. This is especially true in hot
places, particularly where the temperature is 120 F. or above. For
such cases, the weatherproof slow-burning conductors on porcelain
or glass insulators are especially recommended.
Accessibility. The conductors being run exposed, they may be
readily repaired or removed, or connections may be made to the same.
This method of
wiring is especially
recommended for
mills, factories, and
for large or long
feeder conductors.
Fig. 18 shows ex-
amples of exposed
large feeder con-
ductors, installed in the New York Life Insurance Building, New
York City. For small conductors, up to say No. 6 B. & S.
G-auge each, porcelain cleats may be used to support one, two,
or three conductors, provided the distance between the conduc-
Fig. 19. Two- Wire Cleat.
Fig. 20. One- Wire Cleat.
Fig. 21. Porcelain Insulator for
Large Conductors.
tors is at least 2J inches in a two-wire system, and 2J inches
between the two outside conductors in a three-wire system where the
potential between the outside conductors is not over 300 volts. The
cleat must hold the wire at least one-half inch from the surface to which
the cleat is fastened; and in damp places the wire must be held at
least one inch from the surface wired over. For larger conductors,
18
ELECTRIC WIRING
from No. 6 to No. 4/ OB. & S. Gauge, it is usual to use single porcelain
cleats or knobs. Figs. 19 and 20 show a good form of two-wire
Fig. 22. Iron Rack and Insulators for Large Conductors.
Courtesy of General Electric Co., Schenectady, N. Y.
cleat and single-wire cleat, respectively.
For large feeder or main conductors
from No. 4/0 B. & S. Gauge upward, a
more substantial form of porcelain insu-
lafoi should be used, such as shown in
Fig. 21. These insulators are held in
iron racks or angle-iron frames, of which
two forms are shown in Figs. 22 and 23.
The latter form of rack is particularly de-
sirable for heavy conductors and where a
number of conductors are run together.
In this form of rack, any length of con-
ductor can be removed without disturb-
ing the other conductors.
As a rule, the porcelain insulators
should be placed not more than 4J feet
apart; and if the wires are liable tc be
disturbed, the distance between supports
should be shortened, particularly for small
conductors. If the beams are so far
apart that supports cannot be obtained
every 4J feet, it is necessary to provide a
running board as shown in Fig. 24, to
which the porcelain cleats and knobs
can be fastened. Figs. 25 and 26 show
two methods of supporting small con-
ductors, For conductors of No. 8 B. & S.
Fig. 23. Elevation and Plan of
Insulators Held in Angle-
Iron Frames.
ELECTRIC WIRING
19
Gauge, or over, it is not necessary to break around the beams, provided
they are not liable to be disturbed ; but the supports may be placed on
each beam.
Where the dis-
tance between the
supports, however,
is greater than 4J
feet, it is usually
necessary to provide
intermediate SUp-
ports, as shown in
Fig. 27, or else to provide a running-board. Another method which
may be used, where beams are further than 4J feet apart, is to
pi gt2 4. insulators MOUK ted on Running-Board across Wide-
Spacec
Fig. 25. Method of Supporting Small Conductors.
(B
H
\\f
H
_N- .._ , n
-i_ _ y. .
Fig. 27. Intermediate Support for Conductor between Wide-Spaced Beams.
run a main along the wall at right angles to the beams, and to
have the individual circuits run between and parallel to the beams.
nm
y
"
y.
*-*
Fig. 26. Method of Supporting a Small
Conductor.
Fig. 28. Conductors Protected by Wooden
Guard-Strips on Low Ceiling.
In low-ceiling rooms, where the conductors are liable to injury,
it is usually required that a wooden guard strip be placed on each side
of the conductors, as shown in Fig. 28.
Where the conductors pass through partitions or walls, they must
20 ELECTRIC WIRING
be protected by porcelain tubes, or, if the conductors be of rubber, by
means of fibrous tubing placed inside of iron conduits.
All conductors on the walls for a height of not less than six feet
from the ground, either should be boxed in, or, if they be rubber-covered,
should (preferably) be run in iron conduits; and in conductors having
single braid only, additional protection should be provided by means of
flexible tubing placed inside of the iron conduit.
Where conductors cross each other, or where they cross iron pipes,
they should be protected by means of porcelain tubes fastened with
tape or in some other substantial manner that, will prevent the tubes
from slipping out of place.
TWO=WIRE AND THREE=WIRE SYSTEMS
As both the two-wire and the three-wire system are extensively
used in electric wiring, it will be well to give some consideration to the
advantages and disadvantages of each system, and to explain them
somewhat in detail.
Relative Advantages. The choice of either a two-wire or a three-
wire system depends largely upon the source of supply. If, for ex-
ample, the source of supply will always probably be a 120-volt, two
wire system, there would be no object in installing a three-wire system
for the wiring. If, on the other hand, the source of supply is a 120-
240-volt system, the wiring should, of course, be made three-wire.
Furthermore, if at the outset the supply were two-wire, but with a pos-
sibility of a three-wire system being provided later, it would be well
to adapt the electric wiring for the three-wire system, making the
neutral conductor twice as large as either of the outside conductors,
and combining the two outside conductors to make a single conductor
until such time as the three-wire service is installed. Of course, there
would be no saving of copper in this last-mentioned three-wire system,
and in fact it would be slightly more expensive than a two-wire system,
as will be shortly explained.
The object of the three-wire system is to reduce the amount of
copper and consequently the cost of wiring necessary to transmit a
given amount of electric power. As a rule, the proposition is usually
one of lighting and not of power, for the reason that by means of the
three-wire system we are able to increase the potential at which the
current is transmitted, and at the same time to take advantage of the
FT?
ELECTRIC WIRING 21
greater efficiency of the lower voltage lamp. If current for power
(motors, etc.) only were to be transmitted, it would be a simple matter
to wind the motors, etc., for a higher voltage, and thereby reduce the
weight of copper.
If, however, we in-
crease the voltage
of lamps, we find
that they are not so
efficient, nor is their
life SO long. With F *&' 39 Three-Wire System, with Neutral Conductor between
the Two Outside Conductors.
the standard carbon
lamp, it has been found that the 240-volt lamp, with the same
life, requires about 10 to 12 per cent more current than the cor-
responding 120-volt lamp. Furthermore, in the case of the more
efficient lamps recently introduced (such as the Tantalum lamp,
Tungsten lamp, etc.), it has been found impracticable, if not impos-
sible, to make them for pressures above 125 volts. For this reason
the three-wire system is employed, for by this method we can use 240
volts across the outside conductors, and by the use of a neutral con-
ductor obtain 120 volts between the neutral and the outside conductor,
and thereby be enabled to use 120-volt lamps. Furthermore, if a
240-volt lamp should ever be placed on the market that was as economi-
cal as the lower voltage lamp, the result would be that the 240-480-
volt system would be introduced, and 240-volt lamps used. As a
-. matter of fact, this
has been tried in
several cities and
particularly in
Providence, Rhode
^ Island. As a rule,
Fig. 30. Lamps Arranged in Pairs in Series, Dispensing with however the 1 20-
Necessity for Third or Neutral Conductor.
volt lamp has been
found so much more satisfactory as regards life, efficiency, etc., that
it is nearly always employed.
The two-wire system is so extremely simple that no explanation
whatever is required concerning it.
The three-wire system, however, is somewhat confusing, ana
will now be considered.
22 ELECTRIC WIRING
Details of Three-Wire System. The three-wire system may be
considered as a two-wire system with a third or neutral conductor
placed between the two outside conductors, as shown in Fig. 29.
This neutral conductor would not be required if we could always have
the lamps arranged in pairs, as shown in Fig. 30. In this case, the
two lamps would burn in series, and we could transmit the current
at double the usual voltage, and thereby supply twice the number of
lamps with one-quarter the weight of copper, allowing the same loss
in pressure in the lamps. The reason for this is, that, having the
lamps arranged in series of pairs, we reduce the current to one-half,
and, as the pressure at which the current Is transmitted is doubled,
we can again reduce the copper one-half without increasing the loss
in lamps. We therefore see that we have a double saving, as the cur-
rent is reduced one-half, which reduces the weight of copper one-half,
and we can again reduce the copper one-half by doubling the loss in
volts without increasing the percentage loss. For example,' if in one
case we had a straight two-wire system transmitting current to 100
lamps at a potential of 100 volts, and this system were replaced by one
in which the lamps were placed in series of pairs, as shown in Fig. 30,
and the potential increased to 200 volts 100 lamps still being used
we should find, in the latter case, that we were carrying current really
for only 50 lamps, as we would require only the same amount of cur-
rent for two lamps now that we required for one lamp before. Fur-
thermore, as the potential would now be 200 instead of 100 volts,
we could allow twice as much loss as in the first case, because the loss
would now be figured as a percentage of 200 volts instead of a percent-
age of 100 volts. From this, it will readily be seen that in the second
case mentioned, we would require only one-quarter the weight of
copper that would be required in the first case.
It will readily be seen, however, fchat a system such as that out-
lined in the second scheme having two lamps, would be impracticable
for ordinary purposes, for the reason that it would always require the
lamps to be burned in pairs. Now, it is for this very reason that the
third or neutral conductor is required ; and, if this conductor be added,
it will no longer be necessary to burn the lamps in pairs. This, then,
is the object of the three-wire system to enable us to reduce the
amount of copper required for transmitting current, without increasing
the electric pressure employed for the lamps.
w
g*
on
ELECTRIC WIRING 23
With regard to the size of the neutral conductor, one important
point must be borne in mind ; and that is, that the Rules of the National
Electric Code require the neutral conductor in all interior wiring to be
made at least as large as either of the two outside conductors. The
reasons for this from a fire standpoint are obvious, because, if for
any reason either of the outside conductors became disconnected, the
neutral wire might be required to carry the same current as the out-
side conductors, and therefore it should be of the same capacity. Of
course, the chances of such an event happening are slight; but, as
the fire hazard is all-important, this rule must be complied with for
interior wiring or in all cases where there would be a probability of
fire. For outside or underground work, however, where the fire
hazard would be relatively unimportant, the neutral conductor might
be reduced in size; and, as a matter of fact, it is made smaller than
the outside conductors.
The three-wire system is sometimes installed where it is desired
to use the system as a two-wire, 125-volt system, or to have it arranged
so that it may be used at any time also as a three-wire, 125-250-volt
system. Of course, in order to do this, it is necessary to make the
neutral conductor equal to the combined capacity of the outside con-
ductors, the latter being then connected together to form one con-
ductor, the neutral being the return conductor. This system is not
recommended except in such instances, for example, as where an
isolated plant of 125 volts is installed, and where there is a possibility
of changing over at some future time to the three-wire, 125-250-volt
system. In such a case as this, however, it would be better, where
possible, to design the isolated plant for a three-wire, 125-250-volt
system originally, and then to make the neutral conductor the same
size as each of the two outside conductors.
The weight of copper required in a three-wire system where the
neutral conductor is the same size as either of the two outside conduct-
ors, is f of that required for a corresponding two-wire system using
the same voltage of lamps.* It is obvious that this is true, because,
*NOTE. If, in the two-wire system, we represent the weight of each of the two con-
ductors by i, the weight of each of the outside conductors in a three-wire system would
be represented by ; and if we had three conductors of the same size, we would have
i + i + i^fof the weight of copper required in a three-wire system, which would be
required in a corresponding two-wire system having the same percentage of loss and
using the same voltage of lamps.
If the neutral conductor were made \ of the size of each of the outside conductors,
as is sometimes done in underground work, the total weight of copper required would be
i ^ i f T'S = A of that required in the corresponding two- wire system.
24 ELECTRIC WIRING
as the discussion proved concerning the arrangement shown in Fig.
30, where the lamps were placed in series of pairs, we found that the
weight of copper for the two conductors was one-quarter the weight
of the regular two-wire system. It is then of course true, that, if we
had another conductor of the same size as each of the outside conduct-
ors, we increase theweight of copper one-half, or one-quarter plus
one-half of one-quarter that is, three-eighths.
In the three-wire system frequently used in isolated plants in
which the two outside conductors are joined together and the neutral
conductor made equal to their combined capacity, there is no saving
of copper, for the reason that the same voltage of transmission is used,
and, consequently, we have neither reduced the current nor increased
the potential. Furthermore, though the weight of copper is the same,
it is now divided into three conductors, instead of two, and naturally
it costs relatively more to insulate and manufacture three conductors
than to insulate and manufacture two conductors having the same
total weight of copper. As a matter of fact, the three-wire system,
having the neutral conductor equal to the combined capacity of the
two outside ones, the latter being joined together, is about 8 to 10
per cent more expensive than the corresponding straight two-wire
system.
In interior wiring, as a rule, where the three-wire system is used
for the mains and feeders, the two-wire system is nearly always em-
ployed for the branch circuits. Of course, the two-wire branch cir-
cuits are then balanced on each side of the three-wire system, so as to
obtain as far as possible at all times an equal balance on the two sides
of the system. This is done so as to have the neutral conductor carry
as little current as possible. From what has already been said, it is
obvious that in case there is a perfect balance, the lamps are virtually
in series of pairs, and the neutral conductor does not carry any current.
Where there is an unbalanced condition, the neutral conductor carries
the difference between the current on one side and the current on the
other side of the system. For example, if we had five lamps on one
side of the system and ten lamps on the other, the neutral conductor
would carry the current corresponding to five lamps.
In calculating the three-wire system, the neutral conductor is
disregarded, the outer wires being treated as a two-wire circuit, and
the calculation is for one-half the total number of lamps, the per-
ELECTRIC WIRING 25
centage of loss being based on the potential across the two outside
conductors.
The three-wire system is very generally employed in alternating-
current secondary wiring, as nearly all transformers are built with
three-wire connections.
While unbalancing will not affect the total loss in the outside
conductors, yet it does affect the loss in the lamps, for the reason that
the system is usually calculated on the basis of a perfect balance, and
the loss is divided equally between the two lamps (the latter being
considered in series of pairs). If, however, there is unbalancing to
a great degree, the loss in lamps will be increased ; and if the entire
load is thrown over on one side, the loss in the lamps will be doubled
on the remaining side, because the total loss in voltage will now occur
in these lamps, whereas, in the case of perfect balance, it would be
equally divided between the two groups of lamps.
CALCULATION OF SIZES OF CONDUCTORS
The formula for calculating the sizes of conductors for direct
currents, where the length, load, and loss in volts are given, is as fol-
lows:
The size of conductor (in circular mils) is equal to the current multiplied
by the distance (one way), multiplied by 21.6, divided by the loss in volts; or,
CM = C X F X 21 - 6 (I)
in which C = Current, in amperes;
D Distance or length of the circuit (one way, in feet) ;
V = Loss in volts between the beginning and end of the circuit.
The constant (21.6) of this formula is derived from the resistance
of a mil foot of wire of 98 per cent conductivity at 25 Centigrade or
77 Fahrenheit. The resistance of a conductor of one mil diam-
eter and one foot long, is 10.8 at the temperature and conduc-
tivity named. We multiply this figure (10.8) by 2, as the length of a
circuit is usually given as the distance one way, and in order to obtain
the resistance of both conductors in a two-wire circuit, we must
multiply by 2. The formula as above given, therefore, is for a two-
wire circuit; and in calculating the size of conductors in a three-wire
system, the calculation should be made on a two- wire basis, as ex-
plained hereinafter.
26 ELECTRIC WIRING
Formula 1 can be transformed so as to obtain the loss in a given
circuit, or the current which may be carried a given distance with a
stated loss, or to obtain the distance when the other factors are given,
in the following manner:
Formula for Calculating Loss in Circuit when Size, Current, and Distance are Giver,
77 _ C X DX 21.6 f ^^
CM ...... (*)
Formula for Calculating Current which may be Carried by a Given Circuit of Specified
Length, and with a Specified Loss
CMXV
D X 21.6
Formula for Calculating Length of Circuit when Size, Loss, and Current to be Carried
are Given
CM X V /A \
D = ex 21.6 ( 4 )
Formulae are frequently given for calculating sizes of conductors,
etc., where the load, instead of being given in amperes, is stated in
lamps or in horse-power. It is usually advisable, however, to reduce
the load to amperes, as the efficiency of lamps and motors is a variable
quantity, and the current varies correspondingly.
It is sometimes convenient, however, to make the calculation
in terms of watts. It will readily be seen that we can obtain a formula
expressed in watts from Formula 1. To do this, it is advisable to
express the loss in volts in percentage, instead of actual volts lost. It
must be remembered that, in the above formulae, V represents the
volts lost in the circuit, or, in other words, the difference in potential
between the beginning and the end of the circuit, and is not the
applied E. M. F. The loss in percentage, in any circuit, is equal to
the actual loss expressed in volts, divided by the line voltage, multiplied
by 100; or,
P = -Q- X 100.
From this equation, we have:
100
If, for example, the calculation is to be made on a loss of 5 per cent,
with an applied voltage of 250, using this last equation, we would have:
5 X 250
V = -QQ- = 12.5 volts.
P F
Substituting the equation V= -y^r- in Formula 1 , we have:
ELECTRIC WIRING 27
n ,, C X D X 21.6
100
C X D X 21.6 X 100
PE
C X D X 2,160
P E
This equation it should be remembered, is expressed in terms of
applied voltage. Now, since the power in watts is equal to the applied
voltage multiplied by the current (W = EC), it follows that
C---
E
By substituting this value of C in the equation given above ( C M
C X D X 2 160\
* - | , the formula is expressed in terms of watts instead
r L /
of current, thus:
CM= ^ V/-. ............ (5)
in which W = Power in watts transmitted;
D = Length of the circuit (one way) that is, the length of one
conductor;
P = Figure representing the percentage loss;
E*= Applied voltage.
All the above formulae are for calculations of two-wire circuits.
In making calculations for three-wire circuits, it is usual to make the
calculation on the basis of the two outside conductors; and in three
wire calculations, the above formulae can be used with a slight modifi-
cation, as will be shown.
In a three-wire circuit, it is usually assumed in making the cal-
culation, that the load is equally balanced on the two sides of the
neutral conductor; and, as the potential across the outside conductors
is double that of the corresponding potential across a two- wire circuit,
it is evident that for the same size of conductor the total loss in volts
could be doubled without increasing the percentage of loss in lamps.
Furthermore, as the load on one side of the neutral conductor, when
the system is balanced, is virtually in series with the load on the
third side, the current in amperes is usually one-half the sum of the
current required by all the lamps. If C be still taken as the total
*NOTE. Remember that V in Formulae 1 to 4 represents the volts lost, but that
E in Formula 5 represents the applied voltage.
28 ELECTRIC WIRING
current in amperes (that is, the sum of the current required by all of
the lamps) in Formula 1, we shall have to divide this current by 2,
to use the formula for calculating the two outside conductors for a
three-wire system. Furthermore, we shall have to multiply the
voltage lost in the lamps by 2, to obtain the voltage lost in the two out-
side conductors, for the reason that the potential of the outside con*
ductors is double the potential required by the lamps themselves.
In other words, Formula 1 will become:
CX DX 21.6
CM
2 X V X 2
CX DX 21.6
in which C = Sum of current required by all of the lamps on both sides of
the neutral conductor;
D = Length of circuit that is, of any one of the three conductors;
V = Loss allowed in the lamps, i, e., one-half the total loss in the
two outside conductors.
In the same manner, all of the other formulse may be adapted for
making calculations for three-wire systems. Of course the calcula-
tion of a three-wire system could be made as if it were a two-wire
system, by taking one-half the total number of lamps supplied, at
one-half the voltage between the outside conductors.
It is understood, of course, that the size of the conductor in
Formula 6 is the size of each of the two outs'de ones; but, inasmuch
as the Rules of the National Electric Code require that for interior
wiring the neutral conductor shall be at least equal in size to the outside
conductors, it is not necessary to calculate the size of the neutral
conductor. It must be remembered, however, that, in a three-wire
system where the neutral conductor is made equal in capacity to the
combined size of the two outside conductors, and where the two
outside conductors are joined together, we have virtually a two-wire
system arranged so that it can be converted into a three- wire system
later. In this case the calculation is exactly the same as in the case
of the two-wire circuits, except that one of the two conductors is split
into two smaller wires of the same capacity. This is frequently done
where isolated plants are installed, and where the generators are wound
for 125 volts and it may be desired at times to take current from an
outside three-wire 125-250-volt system.
ELECTRIC WIRING 29
METHOD OF PLANNING A WIRING
INSTALLATION
The first step in planning a wiring installation, is to gather all
the data which will affect either directly or indirectly the system of
wiring and the manner in which the conductors are to be installed.
These data will include: Kind of building; construction of building;
space available for conductors; source and system of electric-current
supply; and all details which will determine the method of wiring
lo be employed. These last items materially affect the cost of the
work, and are usually determined by the character of the building
and by commercial considerations.
Method of Wiring. In a modern fireproof building, the only
system of wiring to be recommended is that in which the conductors
are installed in rigid conduits; although, even in such cases, it may be
desirable, and economy may be effected thereby, to install the larger
feeder and main conductors exposed on insulators using weatherproof
slow-burning wire. This latter method should be used, however,
only where there is a convenient runway for the conductors, so that
they will not be crowded and will not cross pipes, ducts, etc., and
also will not have too many bends. Also, the local inspection authori-
ties should be consulted before usin^ this method.
For mills, factories, etc., wires exposed on cleats or insulators
are usually to be recommended, although rigid conduit, flexible con-
duit, or armored cable may be desirable.
In finished buildings, and for extensions of existing outlets,
where the wiring could not readily or conveniently be concealed,
moulding is generally used, particularly where cleat wiring or other
exposed methods of wiring would be objectionable. However, as
has already been said, moulding should not be employed where there
is any liability to dampness.
In finished buildings, particularly where they are of frame con-
struction, flexible steel conduits or armored cable are to be recom-
mended.
While in new buildings of frame construction, knob and tube
wiring are frequently employed, this method should be used only
where the question of first cost is of prime importance. While armored
cable will cost approximately 50 to 100 per cent more than knob and
30 ELECTRIC WIRING
tube wiring, the former method is so much more permanent and is
so much safer that it is strongly recommended.
Systems of Wiring. The system of wiring that is, whether
the two-wire or the three-wire system shall be used is usually deter-
mined by the source of supply. If the source of supply is an isolated
plant, with simple two-wire generators, and with little possibility
of current being taken from the outside at some future time, the
wiring in the building should be laid out on the two-wire system. If,
on the other hand, the isolated plant is three-wire (having three-wire
generators, or two-wire generators with balancer sets), or if the cur-
rent is taken from an outside source, the wiring in the building should
be laid out on a three-wire system.
It very seldom happens that current supply from a central station
is arranged with other than the three-wire system inside of buildings,
because, if the outside supply is alternating current, the transformers
are usually adapted for a three-wire system. For small buildings,
on the other hand, where there are only a few lights and where there
would be only one feeder, the two-wire system is used. As a rule,
however, when the current is taken from an outside source, it is best
to consult the engineer of the central station supplying the current,
and to conform with his wishes. As a matter of fact, this should be
done in any event, in order to ascertain the proper voltage for the
lamps and for the motors, and also to ascertain whether the central
station will supply transformers, meters, and lamps for, if these
are not thus supplied, they should be included in the contract for the
wiring.
Location of Outlets. It is not within the scope of this treatise
to discuss the matter of illumination, but it is desirable, at this point,
to outline briefly the method of procedure.
A set of plans, including elevation and details, if any, and show-
ing decorative treatment of the various rooms, should be obtained
from the Architect. A careful study should then be made by the
Architect, the Owner, and the Engineer, or some other person qualified
to make recommendations as to illumination. The location of the
outlets will depend: First, upon the decorative treatment of the
room, which determines the aesthetic and architectural effects; second*
upon the type and general form of fixtures to be used, which should
be previously decided on; third, upon the tastes of the owners or
ELECTRIC WIRING 31
occupants in regard to illumination in general, as it is found that
tastes vary widely in regard to amount and kind of illumination.
The location of the outlets,' and the number of lights required
at each, having been determined, the outlets should be marked on
the plans.
The Architect should then be consulted as to the location of the
centers of distribution, the available points for the risers or feeders,
and the available space for the branch circuit conductors.
In regard to the rising points for the feeders and mains, the fol-
lowing precautions should be used in selecting chases :
1. The space should be amply large to accommodate all the feeders and
mains likely to rise at that given point. This seems trite and unnecessary,
but it is the most usual trouble with chases for risers. Formerly architects
and builders paid little attention to the requirements for chases for electrical
work; but in these later days of 2-inch and 2^-inch conduit, they realize that
these pipes are not so invisible and mysterious as the force they serve to dis-
tribute, particularly when twenty or more such conduits must be stowed away
in a building where no special provision has been made for them.
2. If possible, the space should be devoted solely to electric wiring.
Steam pipes are objectionable on account of their temperature; and these and
all other pipes are objectionable in the same space occupied by the electrical
conduits, for if the space proves too small, the electric conduits are the first to
be crowded out.
The chase, if possible, should be continuous from the cellar to the roof,
or as far as needed. This is necessary in order to avoid unnecessary bends or
elbows, which are objectionable for many reasons.
In similar manner, the location of cut-out cabinets or distributing
centers should fulfil the following requirements:
1. They should be accessible at all times.
2. They should be placed sufficiently close together to prevent the cir-
cuits from being too long.
3. Do not place them in too prominent a position, as that is objectionable
from the Architect's point of view.
4. They should be placed as near as possible to the rising chases, in
order to shorten the feeders and mains supplying them.
Having determined the system and method of wiring, the location
of outlets and distributing centers, the next step is to lay out the branch
circuits supplying the various outlets.
Before starting to lay out the branch circuits, a drawing showing
the floor construction, and showing the space between the top of the
beams and girders and the flooring, should be obtained from the Archi-
tect. In f "-proof buildings of iron or steel construction, it is almost
the invariable practice, where the work is to be concealed, to run *he
32
ELECTRIC WIRING
conduits ove* the beams, under the rough flooring, carrying them
between the sleepers when running parallel to the sleepers, and notch-
ing the latter when the conduits run across them (see Fig. 31). In
wooden frame buildings, the conduits run parallel to the beams and
to the furring (see Fig. 32); they are also sometimes run below the
Finished Floorv
Fig. 31. Running Conductors Concealed under Floor in Fireproof Building.
beams. In the latter case the beams have to be notched, and this is
allowable only in certain places, usually near the points where the
beams are supported. The Architect's drawing is therefore necessary
in order that the location and course of the conduits may be indicated
on the plans.
The first consideration in laying out the branch circuit is the
number of outlets and number of lights to be wired on any one branch
circuit. The Rules of the National Electric Code (Rule 21-D) require
that "no set of incandescent lamps requiring more than 660 watts,
whether grouped on one fixture or on several fixtures or pendants,
will be dependent on one cut-out." While it would be possible to
have branch circuits supplying more than 660 watts, by placing various
cut-outs at different points along the route of the branch circuit, so
as to subdivide it into small sections to comply with the rule, this
method is not recommended, except in certain cases, for exposed wiring
in factories or mills. As a rule, the proper method is to have the
cut-outs located at the center of distribution, and to limit each branch
circuit to 660 watts, which corresponds to twelve or thirteen 50-watt
lamps, twelve being the usual limit. Attention is called to the fact
that the inspectors usually allow 50 watts for each socket connected
to a branch circuit; and although 8-candle-power lamps may be
placed at some of the outlets, the inspectors hold that the standard
lamp is approximately 50 watts, and for that reason th^T? is always
the likelihood of a lamp of that capacity being used, and their mspec-
ELECTRIC WIRING
33
tion is based on that assumption. Therefore, to comply with the
requirements, an allowance of not more than twelve lamps per branch
circuit should be made.
In ordinary practice, however, it is best to reduce this number
still further, so as to make allowance for future extensions or to increase
the number of lamps that may be placed at any outlet. For this
reason, it is wise to keep the number of the outlets on a circuit at the
lowest point consistent with economical wiring. It has been proven
by actual practice, that the best results are obtained by limiting the
number to five or six outlets on a branch circuit. Of course, where
all the outlets have a single light each, it is frequently necessary, for
reasons of economy, to increase this number to eight, ten, and, in
some cases, twelve outlets.
We have already referred to the location of the wires or conduits.
This question is generally settled by the peculiarities of the construc-
tion of the building. It is necessary to know this, however, before
laying out the circuit work, as it frequently determines the course of
a circuit.
Now, as to the course of the circuit work, little need be said,
as it is largely influenced by the relative position of the outlets, cut-
Stud or
Wall
Wooden Beam
Furring Strips
Rough Flooring"
/Con du.1 t
Stud or
Wall
Fig. 32. Running Conductors Concealed under Floor in Wooden Frame Building.
outs, switches, etc. Between the cut-out box and the first outlet, and
between the outlets, it will have to be decided, however, whether
the circuits shall run at right angles to the walls of the building or
room, or whether they shall run direct from one point to another,
irrespective of the angle they make to the sleepers or beams. Of
course, in the latter case, the advantages are that the cost is some-
what less and the number of elbows and bends is reduced. If the
34 ELECTRIC WIRING
tubes are bent, however, instead of using elbows, the difference in
cost is usually very slight, and probably does not compensate for the
disadvantages that would result from running the tubes diagonally.
As to the number of bends, if branch circuit work is properly laid
out and installed, and a proper size of tube used, it rarely happens
that there is any difference in "pulling" the branch circuit wires.
It may happen, in the event of a very long run or one having a large
number of bends, that it might be advisable to adopt a short and
most direct route.
Up to this time, the location of the distribution centers has been
made solely with reference to architectural considerations; but they
must now be considered in conjunction with the branch circuit work.
It frequently happens that, after running the branch circuits
on the plans, we find, in certain cases, that the position of centers of
distribution may be changed to advantage, or sometimes certain
groups may be dispensed with entirely and the circuits run to other
points. We now see the wisdom of ascertaining from the Architect
where cut-out groups may be located, rather than selecting particular
points for their location.
As a rule, wherever possible, it is wise to limit the length of each
branch circuit to 100 feet; and the number and location of the dis-
tributing centers should be determined accordingly.
It may be found that it is. sometimes necessary and even desirable
to increase the limit of length. One instance of this may be found in
hall or corridor lights in large buildings. It is generally desirable,
in such cases, to control the hall lights from one point; and, as the
number of lights at each outlet is generally small, it would not be
econonrcaJ. to run mains for sub-centers of distribution. Hence,
in instances of this character, the length of runs will frequently exceed
the limit named. In the great majority of cases, however, the best
results are obtained by limiting the runs to 90 or 100 feet.
. There are several good reasons for placing such a limit on the
length of a branch circuit. To begin with, assuming that we are going
to place a limit on the loss in voltage (drop) from the switchboard to
the lamp, it may be easily proven that up to a certain reasonable
limit it is more economical to have a larger number of distributing
centers and shorter branch circuits, than to have fewer centers and
longer circuits. It is usual, in the better class of work, to limit the
ELECTRIC WIRING 35
loss in voltage in any branch circuit to approximately one volt. As-
suming this limit (one volt loss), it can readily be calculated that the
number of lights at one outlet which may be connected on a branch
circuit 100 feet long (using No. 14 B. & S. wire), is jour] or in the
case of outlets having a single light each, -five outlets may be con-
nected on the circuit, the first being 60 feet frcrn the cut-out, the others
being 10 feet apart.
These examples are selected simply to show that if the branch
circuits are much longer than 100 feet, the loss must be increased
to more than one volt, or else the number of lights that may be con-
nected to one circuit must be reduced to a very small quantity, pro-
vided, of course, the size of the wire remains the same.
Either of these alternatives is objectionable the first, on the
score of regulation; and the second, from an economical standpoint.
If, for instance, the loss in a branch circuit with all the lights turned
on is four volts (assuming an extreme case), the voltage at which a
lamp on that circuit burns will vary from four volts, depending on the
number of lights burning at a time. This, of course, will cause the
lamp to burn below candle-power when all the lamps are turned on,
or else to diminish its life by burning above the proper voltage when
it is the only lamp burning on the circuit. Then, too, if the drop in
the branch circuits is increased, the sizes of the feeders and the mains
must be correspondingly increased (if the total loss remains the same),
thereby increasing their cost.
If the number of lights on the circuit is decreased, we do not use
to good advantage the available carrying capacity of the wire.
Of course, one solution of the problem would be to increase the
size of the wire for the branch circuits, thus reducing the drop. This,
however, would not be desirable, except in certain cases where there
were a few long circuits, such as for corridor lights or other special
control circuits. In such instances as these, it would be better to
increase the sizes of the branch circuit to No. 12 or even No. 10
B. & S. Gauge conductors, than to increase the number of centers
3f distribution for the sake of a few circuits only, in order to reduce
the number of lamps (or loss) within the limit.
The method of calculating the loss in conductors has been given
elsewhere; but it must be borne in mind, in calculating the loss of a
branch circuit supplying more than one outlet, that separate calcu-
36 ELECTRIC WIRING
lations must be made for each portion of the circuit. That is, a
calculation must be made for the loss to the first outlet, the length in
this case being the distance from the center of distribution to the first
outlet, and the load being the total number of lamps supplied by the
circuit. The next step would be to obtain the loss between the first
and second outlet, the length being the distance between the two out-
lets, and the load, in this case, being the total number of lamps sup-
plied by the circuit, minus the number supplied by the first outlet;
and so on. The loss for the total circuit would be the sum of these
losses for the various portions of the circuit.
Feeders and Mains. If the building is more than one story, an
elevation should be made showing the height and number of stories.
On this elevation, the various distributing centers should be shown
diagrammatically ; and the current in amperes supplied through
each center of distribution, should be indicated at each center. The
next step is to lay out a tentative system of feeders and mains, and to
ascertain the load in amperes supplied by each feeder and main.
The estimated length of each feeder and main should then be deter-
mined, and calculation made for the loss from the switchboard to
each center of distribution. It may be found that in some cases it
will be necessary to change the arrangement of feeders or mains, or
even the centers of distribution, in order to keep the total loss from the
switchboard to the lamps within the limits previously determined.
As a matter of fact, in important work, it is always best to lay out the
entire work tentatively in a more or less crude fashion, according to
the "cut and dried" method, in order to obtain the best results, because
the entire layout may be modified after the first preliminary layout
has been made. Of course, as one becomes more experienced and
skilled in these matters, the. final layout is often almost identical with
the first preliminary arrangement.
TESTING
Where possible, two tests of the electric wiring equipment should
be made, one after the wiring itself is entirely completed, and switches,
cut-out panels, etc., are connected; and the second one after the
fixtures have all been installed. The reason for this is that if a ground
or short circuit is discovered before the fixtures are installed, it is
more easily remedied; and secondly, because there is no division oi
ELECTRIC WIRING 37
the responsibility, as there might be if the first test were made only
after the fixtures were installed. If the test shows no grounds or
short circuits before the fixtures are installed, and one does develop
after they are installed, the trouble, of course, is that the short circuit
or ground is one or more of the fixtures. As a matter of fact, it is a
wise plan always to make a separate test of each fixture after it is
delivered at the building and before it is installed.
While a magneto is largely used for the purpose of testing, it is
at best a crude and unreliable method. In the first place, it does
not give an indication, even approximately, of the total insulation
resistance, but merely indicates whether there is a ground or short
circuit, or not. In some instances, moreover, a magneto test has
led to serious errors, for reasons that will be explained. If, as is
nearly always the case, the magneto is an alternating-current instru-
ment, it may sometimes happen particularly in long cables, and
especially where there is a lead sheathing on the cable that the
magneto will ring, indicating to the uninitiated that there is a ground
or short circuit on the cable. This may be, and usually is, far from
being the case; and the cause of the ringing of the magneto is not a
ground or short circuit, but is due to the capacity of the cable, which
acts as a condenser under certain conditions, since the magneto produc-
ing an alternating current repeatedly charges and discharges the cable
in opposite directions, this changing of the current causing the magneto
to ring. Of course, this defect in a magneto could be remedied by
using a commutator and changing it to a direct-current machine;
but as the method is faulty in itself, it is hardly worth while to do this.
A portable galvanometer with a resistance box and Wheatstone
bridge, is sometimes employed; but this method is objectionable
because it requires a special instrument which cannot be used for
many other purposes. Furthermore, it requires more skill and time
to use than the voltmeter method, which will now be described.
The advantage of the voltmeter method is that it requires merely
a direct-current voltmeter, which can be used for many other purposes,
and which all engineers or contractors should possess, together with
a box of cells having a potential of preferably over 30 volts. The volt-
meter should have a scale of not over 150 volts, for the reason that if
the scale on which the battery is used covers too wide a range (say
1,000 volts) the readings might be so small as to make the test inac-
38
ELECTRIC WIRING
curate. A good arrangement would be to have a voltmeter Having
two scales say, one of 60 and one of 600 which would make the
voltmeter available for all practical potentials that are likely to be
used inside of a building. If desired, a voltmeter could be obtained
with three connections having three scales, the lowest scale of which
would be used for testing insulation resistances.
Before starting a test, all of the fuses should be inserted and
switches turned on, so that the complete test of the entire installation
can be made. When this has been done, the voltmeter and battery
should be connected, so as to obtain on the lowest scale of the volt-
meter the electromotive force of the entire group of cells. This
connection is shown in Fig. 33. Immediately after this has been done,
the insulation resistance to be tested
is placed in circuit, whether the
insulation to be tested is a switch-
board, slate panel-board, or the
entire wiring installation; and the
connections are made as shown in
Fig. 34. A reading should then
again be taken of the voltmeter;
and the leakage is in proportion
to the difference between the first
and second readings of the volt-
meter. The explanation given below
will show how this resistance may be calculated: It is evident that
the resistance in the first case was merely the resistance of the volt-
meter and the internal resistance of the battery. As a rub, the internal
resistance of the battery is so small in comparison with the resistance
of the voltmeter and the external resistance, that it may be entirely
neglected, and this will be done in the following calculation. In the
second case, however, the total resistance in circuits is the resistance
of the voltmeter and the battery, plus the entire insulation resistance
on all the wires, etc., connected in circuit.
To put this in mathematical form, the voltage of the cells may
be indicated by the letter E; and the reading of the voltmeter when
the insulation resistance is connected by the circuit, by the letter E'.
Let R represent the resistance of the voltmeter and R x represent the
insulation resistance of the installation which we w r ish to measure.
Fig. 33. Connections of Voltmeter and
Battery for Testing Insulation
Resistance.
ELECTRIC WIRING
39
It is a fact which the reader undoubtedly knows, that the E. M. F. as
indicated by the voltmeter in Fig. 34 is inversely proportional to the
resistance: that is, the greater the resistance, the lower will be the
reading on the voltmeter, as this reading indicates the leakage or cur-
rent passing through the resistance. Putting this in the shape of a
formula, we have from the theory of proportion :
E : E' :: R + R x : R ;
or,
Transposing,
and
;' R + E' R x = E R .
7 R X = E R - E' R = R (E-E'\
R(E- E'}
Or, expressed in words, the insulation resistance is equal to the resist-
ance of the volt-
meter multiplied by
the difference be-
tween the first read-
ing (or the voltage
in the cells) and
the second reading
(or the reading of
the voltmeter with
the insulation re-
sistance in series with the voltmeter), divided by this last reading of
the voltmeter.
Example. Assume a resistance of a voltmeter (R) of 20,000 ohms,
and a voltage of the cells (E) of 30 volts; and suppose that the insula-
tion resistance test of a wiring installation, including switchboard,
feeders, branch circuits, panel-boards, etc., is to be made, the insula-
tion resistance being represented by the letter R x . By substituting
in the formula
R(E- E'}
+BUS
Fig. 34. Insulation Resistance Placed in Circuit, Ready :or
Testing.
Rx =
E'
and assuming that the reading of the voltmeter with the insulation
resistance connected is 5, we have :
R =
20,000 X (30-5)
100,000 ohms.
If the test shows an excessive amount of leakage, or a ground or
40 ELECTRIC WIRING
short circuit, the location of the trouble may be determined by the
process of elimination that is, by cutting out the various feeders
until the ground or leakage disappears, and, when the feeder on which
the trouble exists has been located, by following the same process
with the branch circuits.
Of course, the larger the installation and the longer and more
numerous the circuits, the greater the leakage will be; and the lower
will be the insulation resistance, as there is a greater surface exposed
for leakage. The Rules oj the National Electric Code give a sliding
scale for the requirements as to insulation resistance, depending upon
the amount of current carried by the various feeders, branch circuits,
etc. The rule of the National Electric Code (No. 66) covering this
point, is as follows:
"The wiring in any building must test free from grounds; i. e., the com-
plete installation must have an insulation between conductors and between
all conductors and the ground (not including attachments, sockets, recepta-
cles, etc.) not less than that given in the following table:
Up to 5 amperes 4,000,000 ohms
10
25
50
100
200
400
800
1,600
2,000,000.
800,000
400,000
200,000
100,000
50,000
25,000
12,500
"The test must be made with all cut-outs and safety devices in place. If
the lamp sockets, receptacles, electroliers, etc., are also connected, only one-
half of the resistances specified in the table will be required."
ALTERNATING-CURRENT CIRCUITS
It is not within the province of this chapter to treat the various
alternating-current phenomena, but simply to outline the modifications
which should be made in designing and calculating electric light
wiring, in order to make proper allowance for these phenomena.
The most marked difference between alternating and direct cur-
rent, so far as wiring is concerned, is the effect produced by self-
induction, which is characteristic of all alternating-current circuits.
This self-induction varies greatly with conditions depending upon
the arrangement of the circuit, the medium surrounding the circuit,
the devices or apparatus supplied by or connected in the circuit, etc.
ELECTRIC WIRING 41
For example, if a coil having a resistance of 100 ohms is included in
the circuit, a current of one ampere can be passed through the coil
with an electric pressure of 100 volts, if direct current is used ; while
it might require a potential of several hundred volts to pass a current
of one ampere if alternating-current were used, depending upon the
number of turns in the coil, whether it is wound on iron or some other
non-magnetic material, etc.
It will be seen from this example, that greater allowance should
be made for self-induction in laying out and calculating alternating-
current wiring, if the conditions are such that the self-induction will
be appreciable.
On account of self-induction, the two wires of an alternating-
current circuit must never be installed in separate iron or steel con-
duits, for the reason that such a circuit would be virtually a choke coil
consisting of a single turn of wire wound on an iron core, and the self-
induction would not only reduce the current passing through the cir-
cuit, but also might produce heating of the iron pipe. It is for this
reason that the National Electric Code requires conductors constitut-
ing a given circuit to be placed in the same conduit, if that conduit
is iron or steel, whenever the said circuit is intended to carry, or is
liable to carry at some future time, an alternating current. This does
not mean, in the case of a two-phase circuit, that all four conductors
need be placed in the same conduit, but that the two conductors of a
given phase must be placed in the same conduit. If, however, the
three-wire system be used for a two-phase system, all three conductors
should be placed in the same conduit, as should also be the case in a
three-wire three-phase system. Of course, in a single-phase two- or
three-wire system, the conductors should all be placed in the same
conduit.
In calculating circuits carrying alternating current, no allowance
usually should be made for self-induction when the conductors of the
same circuit are placed close together in an iron conduit. When,
however, the conductors are run exposed, or are separated from each
other, calculation should be made to determine if the effects of self-
induction are great enough to cause an appreciable inductive drop.
There are several methods of calculating this drop due to self-induc-
tionone by formula, and one by means of chart and table which will
be described.
ELECTRIC WIRING
Skin Effect. Skin effect in alternating-current circuits is caused
by an incorrect distribution of the current in the wire, the current
tending to flow through the outer portion of the wire, it being a well-
known fact that in alternating currents, the current density decreases
toward the center of the conductor, and that in large wires, the current
density at the center of the conductor is relatively quite small.
The skin effect increases in proportion to the square of the diam-
eter, and also in direct ratio to the frequency of the alternating current.
For conductors of No. 0000 B. & S. Gauge, and smaller, and for
frequencies of 60 cycles per second, or less, .the skin effect is negligible
and is less than one-half of one per cent.
For very large cables and for frequencies above 60 cycles per
second, the skin effect may be appreciable; and in certain cases, allow-
ance for it should be made in making the calculation. In ordinary
practice, however, it may be neglected. Table IX, taken from Alter-
nating-Current Wiring and Distribution, by W. R. Emmet, gives the
data necessary for calculating the skin effect. The figures given in
the first and third columns are obtained by multiplying the size of the
conductor (in circular mils) by the frequency (number of cycles per
second) ; and the figures in the second and fourth columns show the
factor to be used in multiplying the ohmic resistance, in order to
obtain the combined resistance and skin effect.
TABLE IX
Data for Calculating Skin Effect
PRODUCT OF CIRCULAR
MILS X CYCLES PER SEC.
FACTOR
PRODUCT op CIRCULAR
MILS X CYCLES PER SEC.
FACTOR
10,000,000
.00
70,000,000
1.13
20,000,000
.01
80,000,000
1.17
30,000,000
.03
90,000,000
1.20
40,000,000
.05
100,000,000
1.25
50,000,000
.08
125,000,000
1.34
60,000,000
.10
150,000,000
1.43
The factors given in this table, multiplied by the resistance to direct cur-
rents, will give the resistance to alternating currents for copper conductors of
circular cross-section.
Mutual Induction. When two or more circuits are run in the
same vicinity, there is a possibility of one circuit inducing an electro-
motive force in the conductors of an adjoining circuit. This effect
may result in raising or lowering the E. M. F. in the circuit in which a
ELECTRIC WIRING 43
mutual induction takes place. The amount of this induced E. M. F.
set up in one circuit by a parallel current, is dependent upon the cur-
rent, the frequency, the lengths of the circuits running parallel to each
other, and the relative positions of the conductors constituting the
said circuits.
Under ordinary conditions, and except for long circuits carrying
high potentials, the effect of mutual induction is so slight as to be
negligible, unless the conductors are improperly arranged. In order
to prevent mutual induction, the conductors constituting a given
circuit should be grouped together. Figs. 35 to 39, inclusive, show
te>ooo Alt. .035 Volts,
O O 7200 AH. ,016 Volts,
Fig. 35.
O O I6 > 000 Alt - -' 5 Volts.
7,200 Alt. .0065Volts.
Fig. 36.
A r\ s-\ A 13000 Ait. .070 Volts.
7,800 Alt. .038 Volts.
Fig. 37.
O/~\ A fa I^OOO Alt. .006 Volts.
^ 7200 Alt. .0027 Volts.
Fig. 38.
0O O A I6 POO Alt. .112 Volts.
^ 7 f aoo Alt .0^0 Volts,
Fig. 39.
Various Groupings of Conductors in Two Two- Wire Circuits, Giving Various
Effects of Induction.
five arrangements of two two-wire circuits; and show how relatively
small the effect of first induction is when the conductors are properly
arranged, as in Fig. 38, and how relatively large it may be when im-
properly arranged, as in Fig. 39. These diagrams are taken from
a publication of Mr. Charles F. Scott, entitled Polyphase Trans-
mission, issued by the Westinghouse Electric & Manufacturing
Company.
Line Capacity. The effect of capacity is usually negligible,
except in long transmission lines where high potentials are used ; no
calculations or allowance need be made for capacity, for ordinary
circuits.
44 ELECTRIC WIRING
Calculation of Alternating=Current Circuits. In the instruction
paper on 'Tower Stations and Transmission," a method is given for
calculating alternating-current lines by means of formulae, and data are
given regarding power factor and the calculation of both single-phase
and polyphase circuits. For short lines, secondary wiring, etc., how-
ever, it is probably more convenient to use the chart method devised
by Mr. Ralph D. Mershon, described in the American Electrician of
June, 1897, and partially reproduced as follows:
DROP IN ALTERNATINQ=CURRENT LINES
When alternating currents first came into use, when transmission
distances were short and the only loads carried were lamps, the ques-
tion of drop or loss of voltage in the transmitting line was a simple one,
and the same methods as for direct current could without serious
error be employed in dealing with it. The conditions existing in
alternating practice to-day longer distances, polyphase circuits,
and loads made up partly or wholly of induction motors render
this question less simple; and direct-current methods applied to it
do not lead to satisfactory results. Any treatment of this or of
any engineering subject, if it is to benefit the majority of engineers,
must not involve groping through long equations or complex diagrams
in search of practical results. The results, if any, must be in avail-
able and convenient form. In what follows, the endeavor has b?en
made to so treat the subject of drop in alternating-current lines tliat
if the reader be grounded in the theory the brief space devoted to
it will suffice; but if he do not comprehend or care to follow the
simple theory involved, he may nevertheless turn the results to his
practical advantage.
Calculation of Drop. Most of the matter heretofore published
on the subject of drop treats only of the inter-relation of the E. M. F. J s
involved, and, so far as the writer knows, there have not appeared
in convenient form the data necessary for accurately calculating this
quantity. Table X (page 47) and the chart (page 46) include, in a
form suitable for the engineer's pocketbook, everything necessary
for calculating the drop of alternating-current lines.
The cnart is simply an extension of the vector diagram (Fig. 40),
giving the relations of the E. M. F.'s of line, load and genera tpi\ In
ELECTRIC WIRING
45
Fig. 40, E is the generator E. M. F. ; e, the E. M. F. impressed upon
the load ; c, that component of E which overcomes the back E. M. F.
due to the impedance of the line. The component c is made up of two
components at right angles to each other. One is a, the component
overcoming the IR or back E. M. F. due to resistance of the line.
The other is 6, the component overcoming the reactance E. M. F. or
back E. M. F. due to the alternating field set up around the wire by
the current in the wire. The drop is the difference between E and
e. It is d, the radial distance between two circular arcs, one of which
is drawn with a radius e, and the other with a radius E.
The chart is made by striking a succession of circular arcs with
Oasacenter. x
The radius of the
smallest circle cor-
responds to e, the
E. M. F. of the
load, which is taken
as 100 per cent.
The radii of the suc-
ceeding circles in-
crease by 1 per cent
of that of the small-
est circle; and, as
the radius of the
last or largest cir-
cle is 140 per cent
of that of the smallest, the chart answers for drops up to 40 per cent of
the E. M. F. delivered.
The terms resistance volts, resistance E. M. F., reactance volts,
and reactance E. M. F., refer, of course, to the voltages for overcom-
ing the back E. M. F. J s due to resistance and reactance respectively.
The figures given in the table under the heading "Resistance-Volts
for One Ampere, etc." are simply the resistances of 2,000 feet of the
various sizes of wire. The values given under the heading "React-
ance-Volts, ptc./' are, a part of them, calculated from tables published
some time ago by Messrs. Houston and Kennelly. The remainder
were obtained by using Maxwell's formula.
The explanation given in the table accompanying the chart
Fig. 40. Vector Diagram.
46
ELECTRIC WIRING
9 .7
LOAD POWER
O 10 20 3
DROP IN PERCENT OF E.1M.F. DELIVERED
Cnart for Calculating Drop in Alternating-Current Lines.
ELECTRIC WIRING
47
TABLE X
Data for Calculating Drop in Alternating=Current Lines
To be used in conjunction with Chart on opposite page.
By means of the table, calculate the Resistance- Volts and the Reactance-Volts in the
line, and find what per cent each is of the E. M. F. delivered at the end of the line.
Starting from the point on the chart where the vertical line corresponding with the
power-factor of the load intersects the smallest circle, lay off in per cent the resistance
E. M. F. horizontally and to the right; from the point thus obtained, lay off upward
in per cent the reactance-E. M. F. The circle on which the last point falls gives the
drop, in per cent, of the E. M. F. delivered at the end of the line. Every tenth circle
arc is marked with the per cent drop *-o which it corresponds.
en
m
1
8
en
52
"*"bC
e^
03 "^
O) O
!,
P +^
||0
PHW*O
Throughout the table the lower figures in the squares give
values for ONE MILE of line, corresponding to those of the
upper figures for 1,000 feet of line.
Upper figures are REACTANCE-VOLTS in 1,000 ft. of Line (=
2,000 ft. of Wire) for One Ampere at 7,200 Alternations per
Minute (60 Cycles per Second) for the distance given between
Centers of Conductors.
w
1"
2"
3"
6"
9"
12"
18"
24"
30"
36"
0000
639
3,376
.098
.518
.046
.243
.079
.417
.111
.586
.130
.687
.161
.850
.180
.951
.193
1.02
.212
1.12
.225
1.19
.235
1.24
.244
1.29
000
00
507
2,677
.124
.653
.052
.275
.085
.449
.116
.613
.135
.713
.167
.882
.185
.977
.199
1.05
.217
1.15
.230
1.22
.241
1.27
.249
1.32
.254
1.34
.259
1.37
402
2,123
.156
.824
.057
.301
.090
.475
.121
.639
.140
.739
.172
.908
.190
1.00
.204
1.08
.222
1.17
.236
1.25
.246
1.30
319
1,685
.197
1.04
.063
.332
.095
.502
.127
.671
.145
.766
.177
.935
.196
1.04
.209
1.10
.228
1.20
.233
1.23
.238
1.26
.241
1.27
.251
1.33
1
2
253
1,335
.248
1.31
.068
.359
.101
.533
.132
.687
.151
.797
.183
.966
.201
1.06
.214
1.13
.246
1.30
.256
1.35
.265
1.40
201
1,059
.313
1.65
.074
.391
.106
.560
.138
.728
.156
.824
.188
.993
.206
1.09
.220
1.16
.252
1.33
.262
1.38
.270
1.43
3
159
840
.394
2.08
.079
.417
.112
.591
.143
.755
.162
.856
.193
1.02
.212
1.12
.225
1.19
.244
1.29
.257
1.36
.267
1.41
.275
1.45
.281
1.48
4
126
666
.497
2.63
.085
.449
.117
.618
.149
.787
.167
.882
.199
1.05
.217
1.15
.230
1.22
.249
1.32
.254
1.34
.262
1.38
.272
1.44
5
100
528
.627
3.31
.090
.475
.121
.639
.154
.813
.172
.908
.204
1.08
.223
1.18
.236
1.25
.268
1.42
.278
1.47
.286
1.51
6
79
419
.791
4.18
.095
.502
.127
.671
.158
.834
.178
.940
.209
1.10
.214
1.13
.228
1.20
.233
1.23
.241
1.27
.246
1.30
.260
1.37
.265
1.40
.270
1.43
.272
1.44
.278
1.47
.283
1.49
,291
1.54
.296
1.56
.302
1.60
7
63
332
.997
5.27
.101
.533
.132
.697
.164
.866
.183
.966
.288
1.52
8
50
263
1.260
6.64
.106
.560
.138
.729
.169
.893
.188
.993
.220
1.16
.238
1.26
.252
1 33
.284
1.50
.293
1.55
48 ELECTRIC WIRING
(Table X) is thought to be a sufficient guide to its use, but a few
examples may be of value.
Problem. Power to be delivered, 250 K.W. ; E. M. F. to be delivered,
2,000 volts; distance of transmission, 10,000 feet; size of wire, No. 0; distance
between wires, 18 inches; power factor of load, .8; frequency, 7,200 alterna-
tions per minute. Find the line loss and drop.
Remembering that the power factor is that fraction by which
the apparent power of volt-amperes must be multiplied to give the
true power, the apparent power to be delivered is
250 K.W. A __ w
- =312.5 apparent K.W,
.8
The current, therefore, at 2,000 volts will be
312,500 1K . _
_-:=156.25 amperes.
From the table of reactances under the heading "18 inches," and
corresponding to No. wire, is obtained the constant .228. Bearing
the instructions of the table in mind, the reactance-volts of this line
are, 156.25 (amperes) X 10 (thousands of feet) X .228=356.3 volts,
which is 17.8 per cent of the 2,000 volts to be delivered.
From the column headed "Resistance-Volts" and corresponding
to No. wire, is obtained the constant .197. The resistance-volts
of the line are, therefore, 156.25 (amperes) X 10 (thousands of feet)
X .197=307.8 volts, which is 15.4 per cent of the 2,000 volts to be
delivered.
Starting, in accordance with the instructions of the table, from
the point where the vertical line (which at the bottom of the chart
is marked "Load Power Factor" .8) intersects the inner or smallest
circle, lay off horizontally and to the right the resistance-E. M. F. in
per cent (15 .4) ; and from the point thus obtained, lay off vertically the
reactance-E. M. F. in per cent (17.8). The last point falls at about
23 per cent, as given by the circular arcs. This, then, is the drop, in
per cent, of the E. M. F. delivered. The drop, in per cent, of the genera-
tor E. M. F. is, of course,
23
8.7 per cent.
The percentage loss of power in the line has not, as with direct
current, the same value as the percentage drop. This is due to the
fact that the line has reactance, and also that the apparent power
ELECTRIC WIRING 49
delivered to the load is not identical with the true power that is,
the load power factor is less than unity. The loss must be obtained
by calculating P R for the line, or, what amounts to the same thing,
by multiplying the resistance-volts by the current.
The resistance-volts in this case are 307.8, and the current
156.25 amperes. The loss b 307.8 X 156.25 = 48.1 K. W. The
percentage loss is
48.1
250+48.1
Therefore, for the problem taken, the drop is 18.7 per cent, and the
loss is 16 . 1 per cent. If the problem be to find the size wire for a given
drop, it must be solved by trial. Assume a size of wire and calculate
the drop ; the result in connection with the table will show the direction
and extent of the change necessary in the size of wire to give the
required drop.
The effect of the line reactance in increasing the drop should be
noted. If there were no reactance, the drop in the above example
would be given by the point obtained in laying off on the chart the
resistance-E. M. F. (15.4) only. This point falls at 12.4 per cent,
and the drop in terms of the generator E. M. F. would be
12 4
' =11 per cent, instead of 18 . 7 per cent.
11.2 .4
Anything therefore which will reduce reactance is desirable.
Reactance can be reduced in two ways. One of these is to
diminish the distance between wires. The extent to which this can
be carried is limited, in the case of a pole line, to the least distance at
which the wires are safe from swinging together in the middle of the
span; in inside wiring, by the danger from fire. The other way of
reducing reactance is to split the copper up into a greater number of
circuits, and arrange these circuits so that there is no inductive inter-
action. For instance, suppose that in the example worked out above,
two No. 3 wires were used instead of one No. wire. The resistance-
volts would be practically the same, but the reactance-volts would be
244
less in the ratio \ X ~ = 535, since each circuit would bear half the
current the No. circuit does, and the constant for No. 3 wire i? . 244,
instead of . 228 that for No. 0. The effect of subdividing the copper
is also shown if in the example given it is desired to reduce the drop
50 ELECTRIC WIRING
to, say, one-half. Increasing the copper from No. to No. 0000 will
not produce the required result, for, although the resistance-volts will
be reduced one-half, the reactance-volts will be reduced only in the
ratio .212. If, however, two inductively independent circuits of No.
.228*
wire be used, the resistance- and reactance-volts will both be reduced
one-half, and the drop will therefore be diminished the required
amount.
The component of drop due to reactance is best diminished by sub-
dividing the copper or by bringing the conductors closer together. It
is little affected by change in size of conductors.
An idea of the manner in which changes of power factor affect
drop is best gotten by an example. Assume distance of transmission,
distance between conductors E. M. F., and frequency, the same as in
the previous example. Assume the apparent power delivered the
same as before, and let it be constant, but let the power factor be given
several different values; the true power will therefore be a variable
depending upon the value of the power factor. Let the size of wire
be No. 0000. As the apparent power, and hence the current, is the
same as before, and the line resistance is one-half, the resistance-
E. M. F. will in this case be
15 4
, or 7 . 7 per cent of the E. M. F. delivered.
Also, the reactance-E. M. F. will be
.212X17.8 _ .
228~ - 16. 5 per cent.
Combining these on the chart for a power factor of .4, and deducing
the drop, in per cent, of the generator E. M. F., the value obtained is
15.3 per cent; with a power factor of .8, the drop is 14 per cent;
with a power factor of unity, it is 8 per cenl. If in this example the
true power, instead of the apparent power, had been taken as constant,
it is evident that the values of drop would have differed more widely,
since the current, and hence the resistance- and reactance-volts,
would have increased as the power factor diminished. The condition
taken more nearly represents that of practice.
If the line had resistance and no reactance, the several values
of drop, instead of 15.3, 14, and 8, would be 3.2, 5.7, and 7.2 per
cent respectively, showing that for a load of lamps the drop will not
ELECTRIC WIRING 51
be much increased by reactance; but that with a load, such as induc-
tion motors, whose power factor is less than unity, care should ba
taken to keep the reactance as low as practicable. In all cases it is
advisable to place conductors as close together as good practice will
permit.
When there is a transformer in circuit, and it is desired to obtain
the combined drop of transformer and line, it is necessary to know
the resistance- and reactance-volts of the transformer. The resist-
ance-volts of the combination of line and transformer are the sum of
the resistance-volts of the line and the resistance-volts of the trans-
former. Similarly, the reactance-volts of the line and transformer
are the sum of their respective reactance-volts. The resistance- and
reactance-E. M. F.s of transformers may usually be obtained from
the makers, and are ordinarily given in per cent.* These per-
centages express the values of the resistance- and reactance-E. M. F/s
when the transformer .delivers its normal full-load current; and they
express these values in terms of the normal no-load E. M. F. of the
transformer.
Consider a transformer built for transformation between 1,000
and 100 volts. Suppose the resistance- and reactance-E. M. F.'s given
are 2 per cent and 7 per cent respectively. Then the corresponding
voltages when the transformer delivers full-load current, are 2 and 7
volts or 20 and 70 volts according as the line whose drop is required
is connected to the low-voltage or high-voltage terminals. These
values, 2 7 and 20 70, hold, no matter at what voltage the trans-
*When the required values cannot be obtained from the makers, they may be
measured. Measure the resistance of both coils. If the line to be calculated is attached
to the high- voltage terminals of the transformer, the equivalent resistance is that of the
high-voltage coil, plus the resistance obtained by increasing in the square of the ratio of
transformation the measured resistance of the low-voltage coil That is, if the ratio of
transformation is 10, the equivalent resistance referred to the high-voltage circuit is
the resistance of the high- voltage coil, plus 100 times that of the low- voltage coil. This
equivalent resistance multiplied by the high-voltage current gives the transformer
resistance-volts referred to the high-voltage circuit. Similarly, the equivalent resist-
ance referred to the low- voltage circuit is the resistance of the low-voltage coil, plus that
of the high- voltage coil reduced in the square of the ratio of transformation. It follows,
of course, from this, that the values of the resistance- volts referred to the two circuits
bear to each other the ratio of transformation. To obtain the reactance-volts, short-
circuit one coil of the transformer arid measure the voltage necessary to force through
the other coil its normal current at normal frequency. The result is, nearly enough,
the reactance-volts. It makes no difference which coil is short-circuited, as the results
obtained in one case will bear to those in the other the ratio of transformation. If a
close value is desired, subtract from the square of the voltage reading the square of the
resistance-volts, and take the square root of the difference as the reactance- volts.
52 ELECTRIC WIRING
former is operated, since they depend only upon the strength of cur-
rent, providing it is of the normal frequency. If any other than the
full-load current is drawn from the transformer, the reactance- and
resistance-volts will be such a proportion of the values given above
as the current flowing is of the full-load current. It may be noted, in
passing, that when the resistance- and reactance-volts of a trans-
former are known, its regulation may be determined by making use
of the chart in the same way as for a line having resistance and
reactance.
As an illustration of the method of calculating the drop in a
line and transformer, and also of the use of table and chart in calculat-
ing low-voltage mains, the following example is given :
Problem. A single-phase induction motor is to be supplied with 20 am-
peres at 200 volts; alternations, 7,200 per minute; power factor, .78. The
distance from transformer to motor is 150 feet, and the line is No. 5 wire, 6
inches between centers of conductors. The transformer reduces in the ratio
2 000
' , has a capacity of 25 amperes at 200 volts, and, when delivering this
current and voltage, its re&Istance-E. M. F. is 2.5 per cent, its reactance-
E. M. F. 5 per cent. Find the drop.
The reactance of 1,000 feet of circuit consisting of two No. 5
wires, 6 inches apart, is .204. The reactance-volts therefore are
.204 X ~ X 20 = .61 volts.
1 ,uUU
The resistance-volts are
.627 X r X 20 = 1.88 volts.
At 25 amperes, the resistance-volts of the transformer are 2.5 per
20
cent of 200, or 5 volts. At 20 amperes, they are of this, or 4 volts.
u
Similarly, the transformer reactance-volts at 25 amperes are 10,
and at 20 amperes are 8 volts. The combined reactance-volts of
transformer and line are 8 + .61 = 8.61, which is 4.3 per cent of
the 200 volts to be delivered. The combined resistance-volts are 1.88
+4, or 5.88, which is 2.94 per cent of the E. M. F. to be delivered.
Combining these quantities on the chart with a power factor of .78,
the drop is 5 per cent of the delivered E. M. F.,
or - = 4.8 per cent
105
of the impressed E. M. F. The transformer must be supplied with
ELECTRIC WIRING 53
= 2 ,100 volts,
in order that 200 volts shall be delivered to the motor.
Table X (page 47) is made out for 7,200 alternations, but will
answer for any other number if the values for reactance be changed
in direct proportion to the change in alternations. For instance,
i f\ nnn
for 16,000 alternations, multiply the reactances given by '
,^UU
For other distances between centers of conductors, interpolate the
values given in the table. As the reactance values for different sizes
of wire change by a constant amount, the table can, if desired, be
readily extended for larger or smaller conductors.
The table is based on the assumption of sine currents and
E. M. F.'s. The best practice of to-day produces machines which
so closely approximate this condition that results obtained by the
above methods are well within the limits of practical requirements.
Polyphase Circuits. So far, single-phase circuits only have
been dealt with. A simple extension of the methods given above
adapts them to the calculation of polyphase circuits. A four-wire
quarter-phase (two-phase) transmission may, so far as loss and regula-
tion are concerned, be replaced by two single-phase circuits identical
(as to size of wire, distance between wires, current, and E. M. F.)
with the two circuits of the quarter-phase transmission, provided that
in both cases there is no inductive interaction between circuits. There-
fore, to calculate a four-wire, quarter-phase transmission, compute
the single-phase circuit required to transmit one-half the power at
the same voltage. The quarter-phase transmission will require two
such circuits.
A three-wire, three-phase transmission, of which the conductors
are symmetrically related, may, so far as loss and regulation are
concerned, be replaced by two single-phase circuits having no in-
ductive interaction, and identical with the three-phase line as to
size, wire, and distance between wires. Therefore, to calculate a
three-phase transmission, calculate a single-phase circuit to ca^ry
one-half the load at the same voltage. The three-phase transmis-
sion will require three wires of the size and distance between centers
as obtained for the single-phase.
SL three-wire, two-phase transmission may be calculated
54 ELECTRIC WIRING
exactly as regards loss, and approximately as regards drop, in the
same way as for three-phase. It is possible to exactly calculate
the drop, but this involves a more complicated method than the
approximate one. The error by this approximate method is gen-
erally small. It is possible, also, to get a somewhat less drop and
loss with the same copper by proportioning the cross-section of
the middle and outside wires of a three-wire, quarter-phase circuit
to the currents they carry, instead of using three wires of the same
size. The advantage, of course, is not great, and it will not be con-
sidered here.
WIRING AN OFFICE BUILDING
The building selected as a typical sample of a wiring installation
is that of an office building located in Washington, D. C. The figures
shown are reproductions of the plans actually used in installing the
work.
The building consists of a basement and ten stories. It is of
fireproof construction, having steel beams with terra-cotta flat arches.
The main walls are of brick and the partition walls of terra-cotta
blocks, finished with plaster. There is a space of approximately five
inches between the top of the iron beams and the top of the finished
floor, of which space about three inches was available for running
the electric conduits. The flooring is of wood in the offices, but of
concrete, mosaic, or tile in the basement, halls, toilet-rooms,
etc.
The electric current supply is derived from the mains of the local
illuminating company, the mains being brought into the front of the
building and extending to a switchboard located near the center of the
basement.
As the building is a very substantial fireproof structure, the only
method of wiring considered was that in which the circuits would be
installed in iron conduits.
Electric Current Supply. The electric current supply is direct
current, two-wire for power, and three-wire for lighting, having a
potential of 236 volts between the outside conductors, and 118 volte
between the neutral and either outside conductor.
ELECTRIC WIRING 55
Switchboard. On the switchboard in the basement are mounted
wattmeters, provided by the local electric company, and the various
switches required for the control and operation of the lighting and
power feeders. There are a total of ten triple-pole switches for light-
ing, and eighteen for power. An indicating voltmeter and ampere
meter are also placed in the switchboard. A voltmeter is provided
with a double-throw switch, and so arranged as to measure the poten-
tial across the two outside conductors, or between the neutral con-
ductor and either of the outside conductors. The ampere meter is
arranged with two shunts, one being placed in each outside leg; the
shunts are connected with a double-pole, double-throw switch, so
that the ampere meter can be connected to either shunt and thus
measure the current supplied on each side of the system.
Character of Load. The building is occupied partly as a news-
paper office, and there are several large presses in addition to the usual
linotype machines, trimmers, shavers, cutters, saws, etc. There are
also electrically-driven exhaust fans, house pumps, air-compressors,
etc. The upper portion of the building is almost entirely devoted
to offices rented to outside parties. The total number of motors
supplied was 55; and the total number of outlets, 1,100, supplying
2,400 incandescent lamps and 4 arc lamps.
Feeders and Mains. The arrangement of the various feeders
and mains, the cut-out centers, mains, etc., which they supply, are
shown diagrammatically in Fig. 41, which also gives in schedule the
sizes of feeders, mains, and motor circuits, and the data relating to the
cut-out panels.
Although the current supply was to be taken from an outside
source, yet, inasmuch as there was a probability of a plant being in-
stalled in the building itself at some future time, the three-wire system
of feeders and mains was designed, with a neutral conductor equal
to the combined capacity of the two outside conductors, so that
120-volt two-wire generators could be utilized without any change in
the feeders.
Basement. The plan of the basement, Fig. 42, shows the branch
circuit wiring for the outlets in the basement, and the location of the
main switchboard. It also shows the trunk cables for the inter-
connection system serving to provide the necessary wires for telephones,
FEEDERS
X ALL CONDUCTORS IN ONE CONDUIT.
XX SEPARATE CONDUIT FOR E ACH CONDUCTOR
XXX THIS FEEDER IS TO BE DIVIDED INTO FOUR (-*)
CONDUCTORS OF H 2OOOOOO CM. EACH.
" EACH CONDUCTOR IS TO BE INSTALLED IN A SEP-
- ARATE 3" (INSIDE DIAM) CONDUIT
I_S?- LIGHTING SUPPLY
P.S.=POWER
XXX* SEPARATE 3" (INSIDE DIAt^CONDUIT FOR EACH
CONDUCTOR
X ALL CONDUCTORS IN ONE CONDUIT
MOTOR CIRCUITS
i
SUPPLIED BY
s !
Si
oc ^
0?
LENGTH i
JO 3ZIS | W
."-"-o
E
id
i
Z3
3
u.
1 INSID
r; DIAM.C
j!J CONOU
,-
a
,.-'
5
20
5.0
s
zz
',-
E
-
_L5_
15
6O
-$-
^3
eo.
-i-
W-
3t
0-10
o
10 Th-
3O
u->
-&-
-4-
BOTH CONDUCTORS IN ONE CONDUIT
CUT-OUTS
TH
HAS CONNECTIONS FOR
fr
FE SWITCHES
8
Fig. 41. Wiring of an Office Building. Diagram Showing Arrangement of
Feeders and Mains, Cut-Out Centers, etc.
ELECTRIC WIRING
57
SCHEDULE OF CIRCUITS'
CABt_E NO. & RISES TO S^d FLOOR
Showing Explanation
Of Various Symbols used in
Figs. 41 to 46 Inclusive
Ceiling Chandelier
Wall Bracket
--Gooseneck Bracket
Wall Socket
Drop Cord
Arc Lamp
Cooper-Hewitt Lamp
Cluster
Floor Outlet
-Desk Light
Extension Outlet
Push Button Switch
Snap Swltchi
-Junction Box
Electric Clock
Master Clock
Motor Starter
Cut-Out Panel .
Interconnection Box
Power Panel
-Pull Box
Circuit under Floor
" " " above
"' on Ceiling- Exposed
Service Line under Floor
Fig. 42. Wiring an Office Building. Basement Plan Showing Branch Circuit Wiring for
Outlets in Basement, Location of Main Switchboard, and Trunk Cables of the
Interconnection System Providing Wires for Telephone,
Ticker, and Messenger Call Service, etc,
58 ELECTRIC WIRING
tickers, messenger calls, etc., in all the rooms throughout the building,
as will be described later.
To avoid confusion, the feeders were not shown on the basement
plan, but were described in detail in the specification, and installed
in accordance with directions issued at the time of installation. The
electric current supply enters the building at the front, and a service
switch and cut-out are placed on the front wall. From this point, a
two-wire feeder for power and a three-wire feeder for lighting, are
run to the main switchboard located near the center of the basement.
Owing to the size of the conduits required for these supply feeders, as
well as the main feeders extending to the upper floors of the building,
the said conduits are run exposed on substantial hangers suspended
from the basement ceiling.
First Floor. The rear portion of the building from the basement
through the first floor, Fig. 43, and including the mezzanine floor,
between the first and second floors, at the rear portion of the building
only, is utilized as a press room for several large and heavy, modern
newspaper presses. The motors and controllers for these presses are
located on the first floor. A separate feeder for each of these press
motors is run directly from the main switchboard to the motor con-
troller in each case. Empty conduits were provided, extending from
the controllers to the motor in each case, intended for the various
control wires installed by the contractor for the press equipments.
One-half of the front portion of the first floor is utilized as a news-
paper office; the remaining half, as a bank.
Second Floor. The rear portion of the second floor, Fig. 44, is
occupied as a composing and linotype room, and is illuminated chiefly
by means of drop-cords from outlets located over the linotype machines
and over the compositors' cases. Separate ^-horse-power motors
are provided for each linotype machine, the circuits for the same being
run underneath the floor.
Upper Floors. A typical plan (Fig. 45) is shown of the upper
floors, as they are similar in all respects with the exception of certain
changes in partitions, which are not material for the purpose of illus-
tration or for practical example. The circuit work is sufficiently
intelligible from the plan to require no further explanation.
Interconnection System. Fig. 46 is a diagram of the intercon-
nection system, showing the main interconnection box located in the
ELECTRIC WIRING
59
SCHEDULE OF CIRCUITS
~J3>
RISE TO CONTROLLI
7-0" FF
RISE TO CONTROLLED
"-^-"rrB^'-O" 1 FRpMJF
i
^---*---S-^ L*
U UJ I '^
Mife^^l
z
SUP-
PLED
5
1
OUTLETS
SUPPLIED
TOTAL
AT WHAT
POINT
CONTROLLED
1
1
\r>
til
/)
j
I
B
'N^?
ci
1
8
Sa.tQ
LL
t'
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tocde
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44
f
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TV
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16
76
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3 Receptacles
Q
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38
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5
ID
it * it
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o
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" fc "
NOTE: THE CLOCKS IN STORE AND COUMTr
ING ROOM ARE TO BE LOCATED
AS DIRECTED BY ARCHITECT.
WALL BETWEEN
PRESS ROOM &
PAPER STORAGE
PRESS R'M
SKETCH SHOWING ROUTE OF
EMPTY CONDUITS RISIN3 TO COSH
TROLLER PLATFORM IN PRESS
ROOM..
NOTE: ALL CONDUITS FOR THE PRESSES MUST COME
THROUGH THE CONTROLLER PLATFORM 2 1" FROM
THE WALL.
ALL CONDUITS ARE; TO TERMINATE IN PRESS Aia
DIRECTE.P.
Fig. 43. Wiring of an Office Building.
First-Floor Plan, Showing Press Room in Rear, Containing Motors and Controllers for
Newspaper Presses, Fed Directly from Main Switchboard in Basement;
also, in front, Newspaper Counting Room and Bank Offices.
SCHEDULE o* CIRCUITS
SUP-
PLIED
NS^/BRANCMES
OUTLETS
SUPPLIED
TCfTA
AT WHAT
POINT
CONTROLLED
b
il
NIVW^Ti
OUTLETS
LIGHTS
J 7T-
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a.
1
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4 *
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16 **
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13 **
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TERMINATE ALL. MOTOR CIRCUITS
AT MOTOR CONTROLLER AS
DIRECTED
MOTOR CIRCU ITS
* BOTH CONDUCTORS IN ONE CONDUIT
* *2N- P - REDUCED TO ^ H.F?
z
SUPPLIED
BY
O
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CURRENT
IN AMPERES
if
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FEtDER NO
FLOOR
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41
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3
OB
"
Fig. 44. Wiring of an Office Building. Plan of Second Floor. Rear Portion Occupied a
a Composing and Linotype Room.
ELECTRIC WIRING
61
SCHEDULE OF CIRCUITS
su
PL
P-
ED
s
TOT
AL
i-OP.
d
z
!
Z
1
1
OUTLETS
SUPPLIED
|j
LIGHTS
AT WHA
POINT C
TROLLE
I
A
Dcd
4-
TT
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-7
TT
t
m
2
3Z"
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16
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17
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fe4
46
23
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m" n"
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Sat B
24
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25
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b
M
Fig. 45. Wiring of an Office Building.
Typical Plan of Upper Floors, Showing Circuit Work, Schedule, etc. All the Floors above
the Second are Similar to One Another in Plan, Differing Only in Comparatively
Unimportant Details of Partitions.
CABLES.
FIXTURES.
* EMPTY CONDUIT ONLY
SEiCTON
BOX FOR TlCKERSJvCSSENGER
OO.LS.ETCo
4 Of IKTURCOWCCTION
BOX fUft TELCPHONCS.BELl.
CAO5.ETC.
;
-::.
BOXES.
^aREOUWroOF VAR.OUS '
Fig. 46. Wiring of an Office Building. Diagram of the Interconnection System.
ELECTRIC WIRING 63
basement; adjoining this main box is located the terminal box of the
local telephone company. A separate system of feeders is provided
for the ticker system, as these conductors require somewhat heavier
insulation, and it was thought inadvisable to place them in the same
conduits with the telephone wires, owing to the higher potential of
ticker circuits. A separate interconnection cable runs to each floor,
for telephone and messenger call purposes; and a central box is placed
near the rising point at each floor, from which run subsidiary cables
to several points symmetrically located on the various floors. From
these subsidiary boxes, wires can be run to the various offices requiring
telephone or other service. Small pipes are provided to serve as race-
ways from office to office, so as to avoid cutting partitions. In this
way, wires can be quickly provided for any office in the building with-
out damaging the building in any way whatever; and, as provision is
made for a special wooden moulding near the ceiling to accommodate
these wires, they can be run around the room without disfiguring the
walls. All the main cables and subsidiary wires are connected with
special interconnection blocks numbered serially; and a schedule is
provided in the main interconnection box in the basement, which
enables any wire originating thereat, to be readily and conveniently
traced throughout the building. All the main cables and subsidiary
cables are run in iron conduits.
OUTLET=BOXES, CUT-OUJ PANELS, AND
OTHER ACCESSORIES
Outlet-Boxes. Before the introduction of iron conduits, outlet-
boxes were considered unnecessary, and with a few exceptions were
not used, the conduits being brought to the outlet and cut off after the
walls and ceilings were plastered. With the introduction of iron con-
duits, however, the necessity for outlet-boxes was realized; and the
Rules of the Fire Underwriters were modified so as to require their use.
The Rules of the National Electric Code now require outlet-boxes to
be used with rigid iron and flexible steel conduits, and with armored
cables. A portion of the rule requiring their use is as follows :
All interior conduits and armored cables "must be equipped at every
outlet with an approved outlet-box or plate.
"Outlet-plates must not be used where it is practicable to install outlet-
boxes.
64
ELECTRIC WIRING
"In buildings already constructed, where the conditions are such that
neither outlet-box nor plate can be installed, these appliances may be omitted
by special permission of the inspection department having jurisdiction, pro-
viding the conduit ends are bushed and secured."
Fig. 47 shows a typical form of outlet-box for bracket or ceiling
outlets of the universal type. When it is desired to make an opening
for the conduits, a blow from a hammer
will remove any of the weakened portion
of the wall of the outlet-box, as may be re-
quired. This form of outlet-box is fre-
quently referred to as the knock-out type.
Other forms of outlet-boxes are made with
the openings cast in the box at the re-
quired points, this class being usually
stronger and better made than the univer-
sal type. The advantages of the universal
type of outlet-box are that one form of box will serve for any ordinary
conditions, the openings being made according to the number of
conduits and the directions in which they enter the box.
Fig. 48 shows a waterproof form of outlet-box used out of doors,
or in other places where the conditions require the use of a water-
tight and waterproof outlet-box.
It will be seen in this case, that the box is threaded for the con-
Fig. 47. Universal and
Knock-Out Type of
Outlet Box.
OD
Fig. 48. Water-Tight Outlet Box.
Courtesy of H. Krantz Manufacturing Co., Brooklyn, N. 1 .
duits, and that the cover is screwed on tightly and a flange provided
for a rubber gasket.
ELECTRIC WIRING
65
Figs. 49 and 50 show water-tight floor boxes which are for outlets
located in the floor. While the rules do not require that the floor outlet-
box shall be water-tight, it is strongly recommended that a water-
tight outlet be used in all cases for floor connections. In this case
also, the conduit opening is threaded, as well as the stem cover through
which the extension is made in the conduit to the desk or table. When
the floor outlet connection is not required, the stem cover may be
removed and a flat, blank cover be used to replace the same.
A form of outlet-box used for flexible steel cables and steel ar-
mored cable, has already been shown (see Fig. 5).
There is hardly any limit to the number and variety of makes of
outlet-boxes on the market, adapted for ordinary and for special con-
Fig. 49.
Types of Floor Outlet-Boxes.
Fig. 50.
ditions; but the types illustrated in these pages are characteristic and
typical forms.
Bushings. The Rules of the National Electric Code require that
conduits entering junction-boxes, outlet-boxes, or cut-out cabinets
shall be provided with approved bushings, fitted to protect the wire
from abrasion.
Fig. 51 shows a typical form of conduit bushing. This bushing
is screwed on the end of the conduit after the latter has been intro-
duced into the outlet-box, cut-out cabinet, etc., thereby forming an
insulatec[ orifice to protect the wire at the point where it leaves the
conduits, and to prevent abrasion, grounds, short circuits, etc. A
lock-nut (Fig. 52) is screwed on the threaded end of the conduit before
the conduit is placed in the outlet-box or cut-out cabinet, and this
lock-nut and bushing clamp the ronduH securely in position. Fig.
66
ELECTRIC WIRING
Fig. 51. Conduit Bushing.
53 shows a terminal bushing for panel-boxes used for flexible steel
conduit or armored cable.
The Rules of the National Electric Code require that the metal
of conduits shall be permanently and effectually grounded, so as to
insure a positive
connection for
grounds or leak-
ing currents, and
in order to pro-
vide a path of
least resistance
to prevent the
current from
finding a path
through any source which might cause a fire. At outlet-boxes, the
conduits and gaspipes must be fastened in such a manner as to
insure good electrical connection; and at centers of distribution,
the conduits should be joined by suitable bond
wires, preferably of copper, the said bond wires
being connected to the metal structure of the
building, or, in case of a building not having
an iron or steel structure, being grounded in a
permanent manner to water or gas piping.
Fuse-Boxes, Cut-Out Panels, etc. From the very outset, the
necessity was apparent of having a protective device in circuit with
the conductor to protect it from overload, short circuits, etc. For
this purpose, a fusible
metal having a low
melting point was em-
ployed. The form of
this fuse has varied
greatly. Fig. 54 shows
ohar^ctpristiV form
of what is known as
the link fuse with copper terminals, on which are stamped the ca-
pacity of the fuse.
The form of fuse used probably to a greater extent than any other,
although it is now being superseded by other more modern forms,
Fig. 52. Lock-Nut.
Fig. 53. Panel-Box Terminal Bushing.
Courtesy of Sprague Electric Co., New York, N. 1.
ELECTRIC WIRING
67
is that known as the Edison fuse-plug, shown in Fig. 55. A porcelain
cut-out block used with the Edison fuse is shown in Fig. 56.
Within the last four or five years, a new form of fuse, known as
the enclosed fuse, has been introduced and used to a considerable
Fig. 54. Copper-Tipped Fuse Link.
Fig. 55. Edison Fuse-Plug,
Courtesy of 'General Electric Co., Schenectady.N. Y.
Fig. 56. Porcelain Cut-Out Block.
Courtesy ofGeneralElectricCo.,
Schenectady, Jf. Y.
extent. A fuse of this type is shown in Fig. 57. Fig. 58 gives a sec-
tional view of this fuse, showing the porous filling surrounding the
fuse-strips, and also the device for indicating when the fuse has
blown. This form of fuse is made with various kinds of terminals;
it can be used with spring clips in small
sizes, and with a post screw contact in
larger sizes. For ordinary low potentials
this fuse is desirable for currents up to
25 amperes; but it is a debatable ques-
tion whether it is desirable to use an en-
closed fuse for heavier currents. Fig. 59
shows a cut-out box with Edison plug
fuse-blocks used with knob and tube wiring. It will be seen that
there is no connection compartment in this fuse-box, as the circuits
enter directly opposite the terminals with which they connect.
Fig. 60 shows a cut-out panel adapted for enclosed fuses, and
installed in a cab-
inet having a con-
nection compart-
ment. As will be
seen from the cut,
the tablet itself is
surrounded on the
Fig. 58. Section of Enclosed Fuse.
four sides by slate,
which is secured in the corners by angle-irons. The outer box may
be of wood lined with sheet iron, or it may be of iron. Fig. 61
shows a door and trim for a cabinet of this type. It will be seen that
Fig. 57. Enclosed or "Cartridge" Fuse.
ELECTRIC WIRING
i i
the door opens only on the center panel, and that the trim covers and
conceals the connection compartment. The inner side of the door
should be lined with slate, and the inner side of the trim should be
lined with sheet iron. Fig. 62 shows a sectional view of the cabinet
and panel. In this type of cabinet, the conduits may enter at any
point, the wires being
run to the proper con-
nectors in the connection
compartment.
Figs. 63 and 64 illus-
trate a type of panel-
board and cabinet hav-
ing a push-button switch
connected with each
branch circuit and so
arranged that the cut-
out panel itself may be
enclosed by locked doors,
and access to the switches
may be obtained through
two separate doors pro-
vided with latches only.
This type of panel was arranged and designed by the author of this
instruction paper.
OVERHEAD LINEWORK
The advantages of overhead linework as compared with under-
ground linework are that it is much less expensive; it is more readily
and more quickly installed ; and it can be more readily inspected and
repaired.
Its principal disadvantages are that it is not so permanent as
underground linework; it is more easily deranged; and it is more
unsightly.
For large cities, and in congested districts, overhead linework
should not be used. However, the question of first cost, the question
of permanence, and the municipal regulations, are usually the factors
which determine whether overhead or underground linework shall
be used.
:
Fig. 59. Porcelain Cut-Outs in Wooden Box.
Courtesy of H. T. Paiste Co., Philadelphia, Pa.
ELECTRIC WIRING
The principal factors to be considered in overhead linework will
be briefly outlined.
Placing of Poles. As a general rule, the poles should be set from
100 to 125 feet apart, which is equivalent to 53 to 42 poles per mile.
Under certain conditions, these spacings given will have to be modified ;
but if the poles are spaced too far apart, there is danger of too great
a strain on the poles themselves, and on the cross-arms, pins, and
Fig. 60. Plan View, Cover, and
Section of Double Cut-Out Box. Fig. 61.
conductors. If, on the other hand,
they are placed too close together,
the cost is unnecessarily increased.
The size and number of conduct-
ors, and the potential of the line- Fig. 62.
work, determine to a great extent
the distance between the poles; the smaller the size, the less the num-
ber of conductors; and the lower the potential, the greater the distance
between the poles may be made. Of course, the exact location of
the poles is subject to variation because of trees, buildings, or other
obstructions. The usual method employed in locating poles, is first
to make a map on a fairly large scale, showing the course of the line-
work, and then to locate the poles en the ground according tc the actual
conditions.
70 ELECTRIC WIRING
Poles. Poles should be of selected quality of chestnut or cedar,
and should be sound and free from cracks, knots, or other flaws.
Experience has proven that chestnut and cedar poles are the most
durable and best fitted for linework. If neither chestnut nor cedar
poles can be obtained, northern pine may be used, and even other
timber in localities where these poles cannot be obtained; but it is
found that the other woods do not last so long as those mentioned,
Pig. 63. Cut-Otit Panel with Push-Button Switches. Cover Removed.
and some of the other woods are not only less strong initially, but are
apt to rot much quicker at the "wind and water line" that is, just
above and below the surface of the ground.
The proper height of pole to be used depends upon conditions.
In country and suburban districts, a pole of 25 to 30 feet is usually
of sufficient height, unless there are more than two or three cross-arms
required. In more densely populated districts and in cities where a
great number of cross-arms are required, the poles may have to be
ELECTRIC WIRING
71
40 to 60 feet, or even longer. Of course, the longer the pole, the
greater the possibility of its breaking or bending; and as the length
increases, the diameter of the butt end of pole should also increase.
Table XI gives the average diameters required for various heights of
poles, and the depth the poles should be placed in the ground. These
data have been compiled from a number of standard specifications.
TABLE XI
Pole Data
LENGTH OF POLE
DIAMETER 6 IN.
FROM BUTT
DIAMETER AT Top
DEPTH POLE SHOULD
BE PLACED IN
GROUND
25 feet
9 to 10 in.
6 to 8 in.
5 feet
30
11
5^
35
12
5|
40
13
6
45
14
6^
50
15
7
55
16 to 17
7
60
18
7*
65
19
8
70
20
8
75
21
8
80
22
9
As it is somewhat difficult, because of irregularities in size, to measure the diame-
ter of some poles, the circumference may be measured instead: then, by multiplying
the diameters given in the above table, by 3,1416, the measurements may be reduced
to the circumference in inches.
The minimum diameters of the pole at the top, which should be
allowed, will depend largely on the size of the conductors used, and
on the potential carried by the circuits; the larger the conductors
and the higher the potentials, the greater should be the diameter at
the top of the pole.
Poles should be shaved, housed, and -gained, also cleaned and
ready for painting, before erection.
Poles should usually be painted, not only for the sake of appear-
ance, but also in order to preserve them from the weather. It is par-
ticularly important that they should be protected at their butt end, not
only where they are surrounded by the ground, but for a foot or two
above the ground, as it is at this point that poles usually deteriorate
most rapidly. Painting is not so satisfactory at this point as the us6
of tar, pitch, or creosote. The life of the pole can be increased con
siderably by treating it with one or another of these preservatives.
72
ELECTRIC WIRING
Before any poles are erected, they should be closely inspected for
flaws and for crookedness or too great departure from a straight line.
Where appearance is of considerable importance, octagonal poles
may be used, although these cost considerably more than round poles.
Gains or notches for the cross-arms should be cut in the poles before
they are erected, and should be cut square with the axis of the pole,
and so that the cross-arms will fit snugly and tightly within the space
thus provided. These gains should be not less than 4J inches wide,
Fig. 64. Cut-Out Panel with Push-Button Switches. With Cover.
nor less than J inch deep. Gains should not be placed closer than 24
inches between centers, and the top gains should be at least 9 inches
from the apex of the pole.
Pole Guying. Where poles are subject to peculiar strains due
to unusual stress of the wires, such as at corners, etc., guys should be
employed to counteract the strain and to prevent the pole from being
bent and finally broken, or from being pulled from its proper position.
ELECTRIC WIRING
73
Where there are a consider-
able number of wires on the poles,
or in case of unusually long
poles, or where the linework is
subject to severe storms, it is
frequently necessary to guy the
poles even on straight linework.
In such cases, the guys should
extend from a point near the top
of the pole to a point near the
butt of the adjacent pole.
Straight guying should also be
employed at the terminal pole,
the guy extending to a stub
beyond the last pole, to counter-
act the strain of the wires pull-
ing in the opposite direction. On
particularly heavy lines, it is
sometimes necessary to use
straight guys for the second and
even the third pole from the ter-
minal pole, to prevent undue
strain on the terminal pole itself,
as shown in Fig. 65.
Where there are three or
more cross-arms, either two sets
of guys should be employed, or
else a "Y" form of guy should
be used. If a single guy is used
on a long pole or on a pole car-
rying a number of cross-arms, or
on which there is unusual strain,
the pole is apt to break where
the guy is attached. Figs. 66 and
67 show respectively a proper and
an improper method of guying,
and their effect.
74
ELECTRIC WIRING
At corners, or wherever the direction of the linework changes,
guys should be provided to counteract the strain due to the change in
direction. Guys are also necessary at points where poles are set in
other than a vertical position.
Where the soil is not firm or solid, or where poles are subject to
unusual stress, it is sometimes necessary to obtain additional stiffness
by what is known as crib-bracing, as may be seen from Fig. 68. This
consists of placing two short logs at the butt of the pole. These
logs need not be more than 4 to 5 feet long, or more than 8 to 9 inches
Fig. 66. Proper Method of Guying where there are Three or More Cross- Arms.
A Y-form of Guy is Used at Left; Double Guy at Right.
in diameter. This crib-bracing is sometimes also necessary to give
greater stability to stubs or short poles to which guys are fastened.
W r hile, as a rule, it is not advisable to use trees for guy supports,
it is sometimes necessary to do this, but the trees should be sound and
should be protected in a proper manner from injury. On private
property, permission should first be obtained from the owner to use
the tree for such purpose.
The guy itself should be of standard cable, consisting of 7 strands
of No. 12 B. & S. Gauge iron or steel wire. This is the standard
guy cable, and should be used in all cases, except for very light poles
and light linework, where a smaller cable having a minimum diameter
of \ inch may be used. The guy wires should be fastened at the ends
by means of suitable clamps. All guy cables and clamps should be
heavily galvanized, to prevent rusting,
ELECTRIC WIRING
75
Corners. In cases of heavy linework where there are a con-
siderable number of wires and cross-arms, the turns should be made,
Fig. 67. Improper Method of Guying where there are Three or More Cross-Arms.
Strain is Concentrated at one Point, Causing Rupture of Pole.
if possible, by the use of two poles. In cases where there are only a
few wires, a double cross-arm may be employed, using a single pole.
The two methods are illustrated in Figs. 69 and 70.
Fig. 68. Additional Stiffness Secured by Use of Crib-Bracing.
Cross-Arms. Cross-arms, where possible, should be of long
leaf yellow pine, or of Oregon or Washington fir, of sound wood,
76
ELECTRIC WIRING
thoroughly seasoned and free from sap, cracks, cr large knots. They
should be not less than 3J inches thick by 4J inches deep, the length
depending upon the number of pins required.
Cross-arms, after being properly seasoned, should be painted
with two coats of lead paint before erection. They should then be
snugly fitted into the gain of the pole, and securely fastened with
a bolt not less than f inch in
diameter driven through a
hole of slightly less diameter
previously bored in the pole.
A galvanized-iron washer
not less than 2 inches
diameter should be placed
under the head and nut of
Fig. 69. Two-Poles Used in Making Turn
on Heavy Line.
each bolt. The cross-
arms should be at right
angles to the pole, and
should be parallel to one
another where two or
more arms are used on
the same pole.
The cross-arms
should be braced with
galvanized-iron braces approximately 1J inches wide, \ inch thick,
and from 18 to 30 inches in length. The braces should be fastened
to the cross-arm by means of f-inch galvanized-iron bolts passing
through the brace and the cross-arm, washers being used under the
nut and head of each bolt. Guys should be provided for the cross-
arms in case of unusual strain. The dimensions of cross-arms re-
quired for various numbers of pins, are given verv completely in a
ELECTRIC WIRING
77
O
LJ
paper read by Mr. Paul Spencer before the Atlantic City Convention
of the National Electric Light Association in 1906, and reprinted
in a number of the technical journals.
Wherever practicable, cross-arms should be placed on the poles
before the poles are erected, as not only can they be more securely
fastened when the poles are on the ground, but the cost of erection
is thereby considerably reduced.
Pins. Pins should be of selected locust, not less than f inch
diameter at the shank portion, and not less than 1 J inches in diameter
at the point where
they rest upon the
cross-arm. For po-
tentials of 20,000
volts or over, the
pins should be of (
metal, to avoid car-
bonization of the (
wood due to static
leakage. The top
portion of the pin
(if of wood) should
be not less than one
inch in diameter.
The length of both
the shank and the
upper portion Fig>70>
should be each ap-
proximately 4J inches, making the total length approximately 9
inches. The pin should be threaded and tapered, and accurately cut.
The pin should fit the hole in the cross-arm snugly, and should be
nailed to the cross-arm with a sixpenny galvanized-iron wire nail
driven straight through the center of the shank of the pin.
Insulators. For potentials of 3,000 volts or less, insulators
should be of flint glass, of double-petticoat, deep-grooved type. For
potentials of over 3,000 volts, they should be of the triple-petticoat
type, and preferably of porcelain, and should be of special pattern
adapted for the potential.
Service Mains, Pole Wiring, etc. For service connections-
Double Cross-Arm Used on Single Pole to Make Turn
in Heavy Line Carrying Only a Few Wires.
78 ELECTRIC WIRING
that is, for the mains run to service switches in consumers' residences
or other buildings, conductors of not less than No. 8 B. & S. Gauge
should be used in order to obtain the necessary tensile strength.
Where possible, the circuits should be arranged in such a manner as to
have the service main connect with the line on the lowest cross-arm,
in order to prevent crossing of wires. The transformers should be
installed either on poles or in vaults outside of the building, or, where
this is impracticable, in a fireproof vault or other enclosed space
inside of the building itself. Small transformers may be fastened to
a pair of cross-arms secured to the pole itself. For transformers of
25 K. W. and over, it is usually best to provide special poles. It is
inadvisable to place transformers on building walls.
Where appearance is of importance, when the transformer is
placed underground, or when the wires enter the lower portion of a
building, the conductors must be run underground. In such cases, a
splice should be made between the weatherproof conductors and
rubber-insulated lead-sheathed conductors, at a height of about 15
to 20 feet above the ground, and the mains run in iron pipe down the
pole to a point underground, where they may be continued either in
iron pipe or in vitrified or fiber conduits underground to the point
of entrance.
All circuit wiring on poles should be so arranged as to leave one
side free for the linemen to climb the poles without injuring the con-
ductors. As a rule, all poles on which transformers, lightning arresters,
or fuse-boxes are located, should be provided with steps.
In order to limit the area of disturbance of a short circuit or
overload, fuses should be inserted in each leg of a primary circuit
in making connections to transformers, or where tap or branch con-
nections are made. The fuses should have a capacity of approxi-
mately 50 per cent greater than the transformer or conductor which
they protect. Of course, it would be undesirable to have an excessive
number of fuses, and for short branch lines they might frequently
be undesirable; but for important branch lines, they should be em-
ployed in order to prevent the fuse on the main feeder from being
blown in case of disturbance en the branch line.
Lightning arresters should be placed on the linework in places
particularly exposed to lightning discharges, and at all points where
connections are made to enter a building. The location and number
ELECTRIC WIRING
79
of lightning arresters will depend upon local conditions, the likelihood
and frequency of thunderstorms, etc. Where lightning arresters are
provided, it is essential that a
good ground connection be obtained.
The ground connection should be
made by a fairly good-sized insu-
lated rubber conductor, not less
than No. 6 B. & S. Gauge, con-
necting either with a water pipe
to which it should be clamped, or
fastened in such a manner as to
obtain a good electric contact, or
else to a ground-plate of copper
embedded in crushed charcoal or
coke.
The neutral wire of a three-
wire of both secondary alternating-
current systems and direct-current
systems, should be properly
Fig. 71. Method of Wiring to and Sup-
porting Lamp on Pole.
grounded as required by the National Electric Code (see Rules 12,
13, and 13-A).
Lamps on Poles. Fig. 71 shows the method of wiring to and
supporting a lamp located on a pole.
UNDERGROUND LINEWORK
In large cities, or in congested districts, or where the appearance
of overhead linework is objectionable, it is generally necessary to
place the conductors underground instead of overhead.
The advantages of underground linework are first, that of
appearance; second, it is more permanent and less liable to inter-
ruption than overhead work.
The principal disadvantage of underground work is the greater
first cost. In overhead linework, conductors having weatherproof
insulators consisting of cotton dipped in a special compound similar
to pitch, are used, the cost of which is relatively small. For under-
ground linework, however, the conductors must not only have rubber
insulation, but also a lead sheathing for mechanical protection.
80 ELECTRIC WIRING
Furthermore, the cost of the ducts, trenching, concrete work, laying
the ducts, etc., is much greater than the cost of poles, cross-arms, etc.
As in the case of inside wiring, underground linework should
be so arranged that the conductors may be readily removed and re-
placed without disturbing the underground conduits or ducts. The
system should be arranged with manholes, and in such a manner that
changes or additions or branches may be readily and conveniently
made. In order to provide for the removal and replacing of con-
ductors, and also for growth in the system, the method formerly in
vogue, of embedding the conductors in wooden boxes, or in trenches
underground, has been abandoned; and the conductors are now
placed in conduits or ducts. A number of different forms of ducts and
conduits have been introduced, some of which have been dropped as
cheaper and better forms have been introduced. The forms of con-
duits or ducts now most generally employed include iron pipe, vitrified
conduits, and fibre conduit. As all three of these forms of conduit
are very generally employed, they will now be described, as well as the
method of installing them.
Iron Pipe. Three-inch iron conduit is frequently used for under-
ground linework, particularly for short runs or where there are not
more than two or three ducts required, or where the soil is bad and
where the longer lengths and more stable joints of the iron conduit
would make it more desirable than vitrified duct or fibre conduit.
This conduit, however, is generally undesirable on account of its
greater first cost, and also on account of its liability to deterioration
from rust or corrosion. Where iron conduit is used, and where it is
subject to corrosion, it should be coated with asphaltum or other
similar protective composition. While it is not necessary to have a
concrete bed under iron pipe, it is better to provide such a bed, especi-
ally where the soil is shifting or not solid.
Vitrified Tile Conduit. This type of conduit in both the single-
and multiple-duct form, is used more extensively than any other form
of conduit for underground work. It is made in lengths of 18 inches
for the single-duct form, and in considerably greater lengths in the
multiple-duct form. Fig. 72 shows the single-duct conduit, and
Fig. 73 shows a multiple-duct form of conduit.
Vitrified conduit requires less space for the same number of
ducts than any other form, and is particularly desirable where a great
ELECTRIC WIRING
81
number of ducts are required in a small space. The advantages of
this form of conduit are that it is cheap in first cost; after being
laid, it is practically indestructible; it is not subject to corrosion or
Fig. 72. Self-Centering Duct,
Vitrified Conduit.
Courtesy of Standard Vitrified Conduit Co.,
New York, N. Y.
Fig. 73. Multiple Duct, Vitrified
Conduit.
Courtesy of Standard Vitrified Conduit Co.,
New York, N. Y.
deterioration; it is not combustible; it is fairly strong mechanically;
and it does not require skilled labor to install.
Table XII gives the principal data of one of the well-known
makes of vitrified conduit
TABLE XII
Standard Vitrified Conduit
STYLE OF CONDUIT
DIMENSION
OF SQUARE
DUCT
(INCHES)
DIMENSION
OF ROUND
DUCT
(INCHES)
OUTSIDE
DIMENSIONS
OF END SEC-
TION (!N.)
REG.
STOCK
LENGTHS
(INCHES)
SHORT
LENGTHS
(INCHES)
APPROX.
WEIGHT
PERDUCT
(FOOT)
2-ducfc multiple. . .
3-duct multiple. . .
4-duct multiple. . .
6-duct multiple. . .
9-duct multiple. . .
Common single
duct
3| sq.
3| sq.
3f sq.
3f sq.
3f sq.
COCOCOCOCO CO CO CO
f
\
5x 9
5x13
9x 9
9x 13
13x 13
5x5
5x5
5 in. round
24
24
36
38
36
18
18
18
6, 9, 12
6,9, 12
6, 9, 12
6,9, 12
6,9, 12
6,9, 12
6,9, 12
6,9, 12
0000000000 00 O O
1 I 1 I
Single duct, self-
centering
Round single duct,
self-centering. . .
In installing vitrified conduit, a trench following as straight
lines as possible should be dug to such a depth that there will be a
space of at least 18 inches from the top layer of the duct to the street
surface. The bottom of the trench should be level; and a bed of
good cement concrete not less than 3 inches thick should be laid.
The following instructions* for installing vitrified conduit may be
considered as typical of the best up-to-date practice:
*From the Catalogue of the Standard Underground Conduit Company.
82 ELECTRIC WIRING
Laying of Conduit. When the trench has been properly pre-
pared and the concrete foundation set, the laying of conduit should be
begun. The ends of the conduit should be butted against the shoulder
of the conduit terminal brick; short length should be used for the
breaking of joints.
Care should be taken, when each length of conduit is laid, that
the duct hole is perfectly clear and the conduit level. The work may
then proceed; and if the following instructions are carried out, no
difficulty will be encountered after the duct are laid.
When the first piece of conduit is laid and the keys inserted,
one on the top and one on the side of the duct, the burlap for joints
should be slipped partly under the conduit, and the next piece brought
up and connected. The burlap is then brought up and wrapped
around the conduit. After this operation is completed, a thin layer
of cement mortar is plastered around the burlap, extending over the
edges, so as to cover the scarified portion of the conduit so that it
may adhere to it, thus making the joint practically water-tight.
The burlap should be first prepared in strips of not less than 6
inches in width, and of suitable length to wrap around the conduit,
overlapping about 6 inches. If possible, the burlap should be satur-
ated in asphaltum or pitch; but if this is not convenient, it may be
dipped in water so as to stick to the conduit until the joint has been
cemented. The engineer or foreman in charge should personally
oversee the making of the joint, and especially see that the keys are
inserted, as in many instances they are left out by the workmen,
causing considerable trouble and expense. Sufficient time should be
allowed for the joints to harden.
After the duct are laid, the sides are filled in with either concrete
or dirt, as specified, care being taken that the conduit are not forced
out of alignment by the careless filling-in of the sides. The top layer
of concrete may then be laid and leveled.
After this the trench is ready for filling in.
In the laying of our self-centering single-duct conduit, no dowel-
pins are used, the ducts being self-centering one piece of conduit
socketing into the other. Burlaping and cementing of joint is not
necessary. Otherwise the instructions for the laying of multiple-
duct should be followed. The use of a mandrel in laying self-
centering conduit is superfluous.
ELECTRIC WIRING 83
As each section of the system that is, from manhole to man-
hole is completed, it should be rodded to insure the duct being clear.
For this purpose wooden rods are employed, the rods being from
3 to 4 feet long by one inch in diameter and provided with brass
couplings on the ends. The first rod is pushed into the duct chamber,
the second one is then attached, and then the third and so on, until the
first rod appears in the manhole at the opposite end,
A wooden mandrel about 10 inches long, made to conform to
the shape of the duct, but about J inch smaller in diameter, is attached
to the last rod, and a galvanized -iron wire is then attached to the other
end of the mandrel. The rods are drawn through the duct and
uncoupled, until the mandrel has passed through the ducts. The
wire is left remaining in the chamber, and secured in the manhole to
prevent its being pulled out. The same operation is repeated until
all the ducts are tested and wired. Should obstructions be met with
and the mandrel bind, the location of the obstructions can readily be
ascertained from the length of rod yet remaining in the duct, and can
easily be removed. This method is far better than pulling the
mandrel through as the ducts are laid, as in many cases the duct is
obstructed or thrown out of alignment by the filling-in of the con-
crete or trench, and this would not be noticed until an attempt was
made to draw the cable. The wire left in the duct is used in drawing
the cables.
Fibre Conduit. This type of conduit consists of wood fibre
formed into a tube over a mandrel under pressure. After the tube
Fig. 74. Socket-Joint Fibre Conduit.
is formed on the mandrel, it is removed, and, after being dried in
air, is placed in a tank of preservative and insulating compound.
Fibre conduits are made in three different styles namely, the
socket- joint, sleeve- joint, and screw- joint types, shown respectively in
Figs. 74, 75, and 76. The forms of conduit here shown are made by
the Fibre Conduit Company, of Orangeburg, New York.
In the socket-joint type, the connections between the lengths
84
ELECTRIC WIRING
of conduit are made by means of male and female joints turned on
the ends of the conduit so that it is necessary only to push one length
within the other to secure alignment without the use of a sleeve-
coupling or other device. While this is the cheapest and simplest
Fig. 75. Sleeve-Joint Fibre Conduit.
form of fibre conduit, the joint is not so secure as in either of the other
two types.
The sleeve-joint fibre conduit has the ends of each joint turned
so that a sleeve may be slipped over the turned portion and butted up
against the shoulder on the tubes. These sleeves are about 4 inches
long and f inch thick. While this form of joint is more secure than
the socket type, it is not so secure as the screw-joint type.
The screw-joint type of fibre conduit is manufactured with a
slightly thicker wall than the socket-joint type, in order to obtain the
necessary thickness for getting the thread on the end of the pipe. The
sleeve in this case is threaded; and, instead of being slipped on the
conduit, as in the case of the sleeve-joint type, it is screwed on, and
the thread may be filled with compound and a water-tight joint thereby
obtained. Various special forms of elbows, bends, junction-boxes,
tees, etc., are provided for this conduit, for special connections.
Couplings are also made so that joints can be made between fibre
conduit and iron pipe, where it is desirable to make such a connection.
The advantages of fibre conduit are -first, that it is lighter than
any of the other forms of conduit, which reduces the cost of trans-
Fig. 76. Screw-Joint Fibre Conduit.
portation, carting, and handling; and second, that the cost of labor
for installing it is less than in the case of iron pipe, and less than that
of the single-duct tile pipe. Table XIII edves the principal data
relating to fibre conduit,
ELECTRIC WIRING
85
TABLE XIII
Fibre Conduit
INSIDE
DIAMETER
(INCHES)
TYPE OF CONDUIT
LENGTH
(FEET)
THICKNESS op
WALL, (INCHES)
APPROX.
WEIGHT PER
FOOT (LBS.)
1
Socket -joint
2-i
0.50
1*
5
0.70
2
5
J
0.85
2i
5
1.02
3
5
1.20
3
5
1.40
4
5
1.60
li
Sle
eve-joi
it
5
0.80
2
5
0.95
2|
5
i
1.15
3
5
1 7 6
2.40
3*
5
A
2.90
4
5
J
3.33
1*
Scr
ew-joir
t
5
I 5 e
1.00
2
5
1
1.45
2*
5
f
1.75
3
5
T 7 6
2.40
3
5
TV
2.90
4
5
J
3.33
Fig. 77 shows the method of laying fibre conduit in a trench.
A concrete bed should be provided for all three types of fibre
conduit. Where the ground is moist or where there is likelihood of
water getting in the joints, it is advisable to make a complete envelope
around the conduit.
The joints should be carefully dipped in or coated with a special
liquid compound provided for this purpose, so as to insure water-
tightness. The cables should be spaced about 1J inches apart, by
means of wooden separators; and the spaces between the ducts, and
between the walls of the trench and the outer ducts, should be filled
with a thin grouting of cement and sand. If more than one horizontal
row of ducts are installed, the grouting of each row should be smoothed
over so as to prepare a base for the next row of ducts.
To fish the conductors in fibre conduit, it is not necessary to fol-
low the method of rodding usually required with vitrified conduits;
but it is found that by utilizing a solid No. 6 iron wire, and fishing
from one manhole to the next, the mandrels and brush can be attached
to the end of the wire and pulled through the conduits, thus insuring
that the joints are smooth and that there are no obstructions in the
conduit. To prevent accidental clogging of the ends of the con-
86
ELECTRIC WIRING
duit, wooden plugs should be installed in the openings of all un-
finished conduit work, or in all unoccupied cable ducts at manholes.
Drawing In the Cables. After the conduits have been tested by
means of the mandrel to ascertain that they are continuous and that
the joints are smooth, the work of installing the cables may be started.
Special precaution should be taken to prevent sharp bending of the
cables, and thus to prevent injury to the lead sheathing of the rubber
insulation. If the
cable is light and
of small diam-
eter, the distance
not over 300 feet,
and the run fairly
straight, the ca-
ble can usually
be pulled in by
hand; but often
other mean s
must be provided
so as to secure
sufficient power.
Pr e cautions
should be taken,
however, to
avoid placing too
great a strain on
the cables, as it
is liable to in-
jure them, and
the injuries may
not show up immediately, but may cause trouble later. The remedy
is to avoid placing the manholes too far apart, and to have the runs as
straight as possible; also to properly test the conduits for continuity
and smoothness before starting to install the cables. Enough slack
should be left in each manhole to allow the cables to pass close to
the side walls of the manhole, and to have the centers free and acces-
sible for a man to enter the manhole. Where there are a great
number of cables in a manhole, shelves or other supports should be
Fig. 77. Method of Laying Fibre Conduit in Trench.
ELECTRIC WIRING
87
provided for holding the cables apart and in position. Where two
or more conductors are placed in the same duct, they should always
be pulled in at the same time, for otherwise the cables last pulled in
are apt to injure those already installed.
Manholes. Manholes should be provided about every 300 feet,
in order to facilitate
the installation of the
conductors in the duct.
The exact distance be-
tween manholes
should be determined
by conditions; in some
?ases they should be
placed even closer to-
gether than the figure
given, while in other
cases their distance
apart mi gh t be
slightly greater.
Manholes are
built of concrete or
brick, and provided
with a cast-iron frame
or cover. The man-
holes may be of
square, round, rect-
angular, or oval sec-
tion, the last-men- Fig. 78.
tioned form of man-
hole being probably the best, as it avoids the liability to sharp bends
or kinks being made in the cable. The manhole cover may be of
the same form as the manhole itself, or it may be of different form; but
round or square covers are usually used. Fig. 78 shows a standard
form of manhole used in New York City. This manhole is substan-
tially built, and adapted for heavy traffic passing over the cover. For
suburban or country work, manholes may be made of lighter con-
struction.
Plan and Sectional Elevation of Standard Form
of Manhole Used in New York City.
AERIAL CONSTRUCTION
Telephone and Electric Light Wires.
ELECTRIC LIGHTING
HISTORY AND DEVELOPMENT
The history of electric lighting as a commercial proposition begins
with the invention of the Gramme dynamo, by Z. J. Gramme, in
1870, together with the introduction of the Jablochkoff candle or
light, which was first announced to the public in 1876, and which
formed a feature of the International Exposition at Paris in 1878.
Up to this time, the electric light was known to but few investigators,
one of the earliest being Sir Humphrey Davy who, in 1810, produced
the first arc of any great magnitude. It was then called the voltaic
arc, and resulted from the use of two wood charcoal pencils as elec-
trodes and a powerful battery of voltaic cells as a source of current.
From 1840 to 1859, many patents were taken out on arc lamps,
most of them operated by clockwork, but these were not successful,
due chiefly to the lack of a suitable source of current, since all de-
pended on primary cells for their power. The interest in this form
of light died down about 1859, and nothing further was attempted
until the advent of the Gramme dynamo.
The incandescent lamp was but a piece of laboratory apparatus
up to 1878, at which time Edison produced a lamp using a platinum
spiral in a vacuum, as a source of light, the platinum being rendered
incandescent by the passage of an electric current through it. The
first successful carbon filament was made in 1879, this filament being
formed from strips of bamboo. The names of Edison and Swan are
intimately connected with these early experiments.
From this time on, the development of electric lighting has been
very rapid, and the consumption of incandescent lamps alone has
reached several millions each year. When we compare the small
amount of lighting done by means of electricity twenty-five years ago
with the enormous extent of lighting systems and the numerous
applications of electric illumination as they are to-day, the growth
and development of the art is seen to be very great, and the value of
a study of this subject may be readily appreciated. While in many
Copyright, 1909, by American School of Correspondence.
2 ELECTRIC LIGHTING
cases electricity is not the cheapest source of power for illumination,
its admirable qualities and convenience of operation make it by far
the most desirable.
CLASSIFICATION
The subject of electric lighting may be classified as follows:
1. The type of lamps used.
2. The methods of distributing power to the lamps.
3. The use made of the light, or its application.
4. Photometry and lamp testing.
The types of lamps used may be subdivided into:
1. Incandescent lamps: Carbon, metallic filament; Nernst.
2. Special lamps: Exhausted bulb without filament, such as the Cooper-
Hewitt lamp and Moore tube lamp.
3. Arc lamps: Ordinary carbon, flaming arc.
INCANDESCENT LAMPS
The incandescent lamp is by far the most common type of lamp
used, and the principle of its operation is as follows:
If a current I is sent through a conductor whose resistance is
R, for a time t, the conductor is heated, and the heat generated =
PR t, PR t representing joules or watt-seconds.
If the current, material, and conditions are so chosen that the
substance may be heated in this way until it gives out light, becomes
incandescent, and does not deteriorate too rapidly, we have an in-
candescent lamp. Carbon was the first successful material to be
chosen for this conductor and for ordinary lamps it is formed into a
small thread or filament. Very recently metallic filament lamps
have been introduced commercially with great success but the carbon
incandescent lamp will continue to be used for some time, especially
in the low candle-power units operated at commercial voltages. Car-
bon is a successful material for two reasons:
.1. The material must be capable of standing a very high tem-
perature, 1,280 to 1,330 C., or even higher.
2. It must be a conductor of electricity with a fairly high re-
sistance.
Platinum was used in an early stage of the development, but,
as we shall see, its temperature cannot be maintained at a value high
enough to make the lamp as efficient as when carbon, or a metal
ELECTRIC LIGHTING 3
having a melting point higher than that of platinum, is used. Nearly
all attempts to substitute another substance in place of carbon have
failed until recently, and the few lamps which are entirely or partially
successful will be treated later. The nature of the carbon employed
in incandescent lamps has, however, been much improved over the
first forms, and owing to the still very great importance of this lamp,
the method of manufacture will be considered.
Manufacture of Carbon Incandescent Lamps. Preparation of
the Filament. Cellulose, a chemical compound rich in carbon, is
prepared by treating absorbent cotton with zinc chloride in proper
proportions to form a uniform, gelatine-like mass. It is customary
to stir this under a partial vacuum in order to remove bubbles of air
which might be contained in it and destroy its uniformity. This
material is then forced, "squirted," through steel dies into alcohol, the
W
BODE.
Fig. 1. Fonr.s of Filaments now in Use.
alcohol serving to harden the soft, transparent threads. These threads
are then thoroughly washed to remove all trace of the zinc chloride,
dried, cut to the desired lengths, wound on forms, and carbonized by
heating to a high temperature away from air. During carbonization,
the cellulose is transformed into pure carbon, the volatile matter being
driven off by the high temperature to which the filaments are subjected.
The material becomes hard and stiff, assuming a permanent form,
shrinking in both length and diameter the form being specially con-
structed so as to allow for this shrinkage. The forms are made of
carbon blocks which are placed in plumbago crucibles and packed
with powdered carbon. The crucibles, which are covered with
loosely fitting carbon covers, are gradually brought to a white heat,
at which temperature the cellulose is changed to carbon, and then
allowed to cool. After cooling, the filaments are removed, measured,
and inspected, and the few defective ones discarded.
4 ELECTRIC LIGHTING
In the early days, these filaments were made of cardboard or
bamboo, and later, of thread treated with sulphuric acid.
A few of the shapes of filaments now in use are shown in Fig. 1,
the different shapes giving a slightly different distribution of light.
As here shown they are designated as follows: A, U-shaped; B,
single-curl; C, single-curl anchored; D, double-loop; E, double-
curl; F, double-curl anchored.
Mounting the Filament. After carbonization, the filaments
are mounted or joined to wires leading into the globe or bulb. These
wires are made of platinum platinum being the only substance, so
far as known, that expands and contracts the same as glass, with
change in temperature and which, at the same time, will not be melted
by the heat developed in the carbon. Since the bulb must remain
air-tight, a substance expanding at a different rate from the glass
cannot 'be used. Several methods of fastening the filament to the
leading in wires have been used, such as forming a socket in the end
of the wire, inserting the filament, and then squeezing the socket
tightly against the carbon; and the use of tiny bolts when cardboard
filaments were used; but the pasted joint is now used almost exclu-
sively. Finely powdered carbon is mixed with some adhesive com-
pound, such as molasses, and this mixture is used as a paste for fasten-
ing the carbon to the platinum. Later, when current is sent through
the joint, the volatile matter is driven off and only the carbon remains.
This makes a cheap and, at the same time, a very efficient joint.
Flashing. Filaments, prepared and mounted in the manner
just described, are fairly uniform in resistance, but it has been found
that their quality may be much improved and their resistance very
closely regulated by depositing a layer of carbon on the outside of the
filament by the process of flashing. By flashing is meant heating the
filament to a high temperature when immersed in a hydrocarbon gas,
such as gasoline vapor, under partial vacuum. Current is passed
through the filament in this process to accomplish the heating. Gas
is used, rather than a liquid, to prevent too heavy a deposit of the
carbon. Coal gas is not recommended because the carbon, when
deposited from this, has a dull black appearance. The effects of
flashing are as follows:
1. The diameter of the filament is increased by the deposited
carbon and hence its resistance is decreased. The process must be
ELECTRIC LIGHTING
discontinued when the desired resistance is reached. Any little irregu-
larities in the filament will be eliminated since the smaller sections,
having the greater resistance, will become hotter than the remainder
of the filament and the carbon is deposited more rapidly at these
points.
2. The character of the surface is changed from a dull black
and comparatively soft nature to a bright gray coating which is much
harder and which increases the life and efficiency of the filament.
Exhausting. After flashing, the filament is sealed in the bulb
and the air exhausted through the tube A in Fig. 2, which shows the
lamp in different stages of its
manufacture. The exhaustion
is accomplished by means of
mechanical air pumps, sup-
plemented by Sprengle or mer-
cury pumps and chemicals.
Since the degree of exhaustion
must be high, the bulb should
be heated during the process
so as to drive off any gas which
may cling to the glass. When
chemicals are used, as is now
almost universally the case, the
chemical is placed in the tube
A and, when heated, serves
to take up much of the remain-
ing gas. Exhaustion is neces-
sary for several reasons:
1. To avoid oxidization of the filament.
2. To reduce the heat conveyed to the globe.
3. To prevent wear on the filament due to currents or eddies in the gas.
After exhausting, the tube A is sealed off and the lamp com-
pleted for testing by attaching the base by means of plaster of Paris.
Fig. 3 shows some of the forms of completed incandescent lamps.
Voltage and Candle=Power. Incandescent lamps of the carbon
type vary in size from the miniature battery and candelabra lamps to
those of several hundred candle-power, though the latter are very
seldom used. The more common values for the candle-power are
Fig. 2. Different Stages in Lamp Manufacture.
ELECTRIC LIGHTING
8, 16, 25, 32, and 50, the choice of candle-power depending on the
use to be made of the lamp.
The voltage will vary depending on the method of distribution
of the power. For what is known as parallel distribution, 110 or
220 volts are generally used. For the higher values of the voltage,
long and slender filaments must be used, if the candle-power is to be
low; and lamps of less than 16 candle-power for 220- volt circuits are
not practical, owing to difficulty in manufacture. For series dis-
tribution, a low voltage and higher current is used, hence the fila-
ments may be quite heavy. Battery lamps operate on from 4 to 24
volts, but the vast majority of lamps for general illumination are
operated at or about 110 volts.
Fig. 3. Several Forms of Completed Lamps.
Efficiency. By the efficiency of an incandescent lamp is meant
the power required at the lamp terminals per candle-power of light
given. Thus, if a lamp giving an average horizontal candle-power
of 16 consumes J an ampere at 112 volts, the total number of watts
consumed will be 112 X J = 56, and the watts per candle-power
will be 56 -f- 16 = 3.5. The efficiency of such a lamp is said to be
3.5 watts per candle-power, or simply watts per candle. Watts
economy is sometimes used for efficiency.
The efficiency of a lamp depends on the temperature at which
the filament is run. In the ordinary lamp this temperature is between
1,280 and 1,330 C, and the curve in Fig. 4 shows the increase of
efficiency with the increase of temperature. The temperature attained
ELECTRIC LIGHTING 7
by a filament depends on the rate at which heat is radiated and the
amount of power supplied. The rate of radiation of heat is propor-
tional to the area of the filament, the elevation in temperature, and
the emissivity of the surface.
By emissivity is meant the number of heat units emitted from
unit surface per degree rise in temperature above that of surrounding
bodies. The bright surface of a flashed filament has a lower emis-
sivity than the dull surface of an unheated filament, hence less
energy is lost in heat radiation and the efficiency of the filament is
increased.
As soon as incandescence is reached, the illumination increases
much more rapidly than the emission of heat, hence the increase in
1400
3 4 56 78 9
Fig. 4. Efficiency Curve for Incandescent Lamp.
10
efficiency shown in Fig. 4. Were it not for the rapid disintegration
of the carbon at high temperature, an efficiency higher than 3.1 watts
could be obtained.
By a special treatment of the carbon filaments, the nature of the
carbon is so changed that the filaments may be run at a higher tem-
perature and the lamps still have a life comparable to that of the 3.1-
watt lamp. Lamps using these special carbon filaments are known
as gem metallized filament lamps, or merely as gem lamps, and they
will be described more fully later.
Relation of Life to Efficiency. Ordinary Carbon Lamp. By
the useful life of a lamp is meant the length of time a lamp will burn
before its candle-power has decreased to such a value that it would
be more economical to replace the lamp with a new one than to con-
tinue to use it at its decreased value. A decrease to 80% of the initial
candle-power of carbon lamps is now taken as the point at which a
lamp should be replaced, and the normal life of a lamp is in the
8
ELECTRIC LIGHTING
neighborhood of 800 hours. To obtain the most economical results,
such lamps should always be replaced at the end of their useful life.
In Table I are given values of efficiency and life of a 3.5-watt,
110-volt carbon lamp for various voltages impressed on the lamp.
These values are plotted in Fig. 5. The curves show that a 3%
increase of voltage on the lamp reduces the life by one-half, while an
increase of 6% causes the useful life to fall to one-third its normal
value. The effect is even greater w r hen 3.1-watt lamps are used, but
not so great with 4-watt lamps. From this we see that the regulation
of the voltage used on the system must be very good if high efficiency
lamps are to be used, and this regulation will determine the efficiency
of the lamp to be installed.
Selection of Lamps. Ordinary Carbon Type. Lamps taking 3.1
watts per candle-power will give satisfaction only when the regulation
of voltage is the best practically a constant voltage maintained at the
normal voltage of the lamp.
TABLE I
Effects of Change in Voltage
Standard 3. 5- Watt Lamp
V OT/TAGE
PER CENT. OF
NORMAL
CANDLE-POWER
PER CENT. OF
NORMAL
WATTS PER
CANDLE-POWER
LIFE PER CENT.
OF NORMAL
DETERIORATION
PER CENT. OF
NORMAL
90
53
5.36
91
56
5.09
92
61
4.85
93
65
4.63
94
69
4.44
394
25
95
73
4.26
310
32
96
78
4.09
247
44
97
83
3.93
195
51
98
88
3.78
153
65
99
94
3.64
126
79
100
100
3.5
100
100
101
106
3.38
84
118
102
111
3.27
68
146
103
116
3.16
58
173
104
123
3.05
47
211
105
129
2.95
39
253
106
137
2.85
31
316
107
143
2.76
26
380
108
152
2.68
21
474
109
159
2.60
17
575
110
167
2.53
16
637
Lamps of 3.5 watts per candle-power should be used when the
regulation is fair, say with a maximum variation of 2% from the
normal voltage.
ELECTRIC LIGHTING
90
92 94 93 98 100 102 104 103 108
Fig. 5. Curves of Efficiency and Life of Carbon Filament Lamps.
110
Lamps of 4 watts per candle-power should be installed when the
regulation is poor. These values are for 110-volt lamps. A 220- volt
lamp should have a lower efficiency to give a long life. This is on
100 200 300 400 500 00
HOURS
Fig. 6. Life Curves of Incandescent Lamps.
account of the fact that, for the same candle-power, the 220-volt lamp
must be constructed with a filament which is long and slender com-
pared to that of the 110-volt lamp, and if such a filament is run at a
high temperature its life is short. The 220-volt lamp is used to some
considerable extent abroad but it is not employed extensively in the
United States. It is customary to operate such lamps at an efficiency
of about 4 watts per candle-power.
10
ELECTRIC LIGHTING
Lamps should always be renewed at the end of their useful life,
this point being termed the smashing-point, as it is cheaper to replace
the lamp than to run it at the reduced candle-power. Some recom-
mend running these lamps at a higher voltage, but that means at a
reduced life, and it is not good practice to do this.
Fig. 7. Horizontal Distribution Curve for Single-Loop Filament.
Fig. 6 shows the life curves of a series of incandescent lamps.
These curves show that there is an increase in the candle-power of
some of the lamps during the first 100 hours, followed by a period
during which the value is fairly constant, after which the light given
by the lamp is gradually reduced to about 80% of the initial candle-
power.
ELECTRIC LIGHTING
11
Distribution of Light. In Fig. 1 are shown various forms of
filaments used in incandescent lamps, and Figs. 7 and 8 show the dis-
tribution of light from a single-loop filament of cylindrical cross-
section. Fig. 7 shows the distribution of light in a horizontal plane, the
lamp being mounted in a vertical position, and Fig. 8 shows the dis-
o
Fig. 8. Vertical Distribution Curve for Single-Loop Filament.
tribution in a vertical plane. By changing the shape of the filament.,
the light distribution is varied. A mean of the readings taken in
the horizontal plane forms the mean horizontal candle-power, and
this candle-power rating is the one generally assumed for the ordinary
incandescent lamp. A mean of the readings taken in a vertical plane
gives us the mean vertical candle-power, but this value is of little use.
12
ELECTRIC LIGHTING
Mean Spherical Candle=Power. When comparing lamps which
give an entirely different light distribution, the mean horizontal
candle-power does not form a proper basis for such comparison, and
the mean spherical or the mean hemispherical candle-power is used
instead. By mean spherical candle-power is meant a mean value of
the light taken in all directions. The methods for determining this
will be taken up under photometry. The mean hemispherical candle-
power has reference, usually, to the light given out below the horizon-
tal plane.
The Gem Metallized Filament Lamp. When the incandescent
lamp was first well established commercially, the useful life of a unit,
when operated at 3.1 watts per candle, was about 200 hours. The
improvements in the process of manufacture have been continuous
from that time until now, and the useful life of a lamp operated at
that efficiency to-day is in the neighborhood of 500 hours. Experi-
ments in the treatment of the carbon filament have led to the intro-
duction of the gem metallized filament lamp. This lamp should not
be confused with the metallic filament lamps, to be described later,
because the material used is carbon, not a metal. As a result of
special treatment the carbon filament assumes many of the character-
istics of a metallic conductor, hence the term metallized filament.
The word graphitized has been proposed in place of metallized.
TABLE II
* Data on the Gem Metallized Filament Lamp
WATTS
HORIZONTAL
C. P.
WATTS PER
CANDLE
tSPHERICAL
REDUCTION
FACTOR
$ USEFUL
LIFE
10
16
2.5
.816
450 hrs.
50
20
2.5
.825
450
80
32
2.5
.816
450
100
40
2.5
;
460
125
50
2.5
;;
450
187.5
75
2.5
;;
450
250
100
2.5
%
450
* These lamps are normally rated at three voltages, 114, 112, and 110 volts, but
data referring to the highest voltage only are given.
t By spherical reduction factor is meant the factor by which the horizontal candle-
power must be multiplied to obtain the mean spherical candle-power.
J The larger units are almost invariably used with reflectors, hence no spherical
reduction factor is given.
$ The life of the lamps when operated at the lower voltage is increased to about
950 hours, and the efficiency is changed to 2.83 watts per candle.
ELECTRIC LIGHTING
13
When a filament, as treated in the ordinary manner, is run at a
high temperature in a lamp there is no improvement of the filament,
but it was discovered that, if the treated filaments were subjected to
the extremely high temperature of the electric resistance furnace
3,000 to 3,700 degrees C. at atmospheric pressure, the physical
nature of the carbon was changed and the resulting filament could be
operated at a higher temperature in the lamp and a higher efficiency,
/J*
30'
IS' 30
Fig. 9. Typical Distribution Curves of Gem Lamp with Different Types of Reflectors.
and still maintain a life comparable to that of a 3.1-watt lamp. This
special heating of the filament, which is applied to the base filament
before it is flashed, as well as to the treated filament, causes the cold
resistance of the carbon to be very materially decreased and the fila-
ment, as used in the lamp, has a positive temperature coefficient
rise in resistance with rise in temperature a desirable feature from
the standpoint of voltage regulation of the circuit from which the
lamps are operated. The high temperature also results in the driving
off of considerable of the material which, in the ordinary lamp, causes
the globe to blacken after the lamp has been in use for some time.
The blackening of the bulb is responsible to a considerable degree
14
ELECTRIC LIGHTING
for the decrease in candle-power of the incandescent lamp. The
metallized filament lamp is operated at an efficiency of 2.5 watts pel
candle with a useful life of about 500 hours. The change in candle-
power with change in voltage is less than in the ordinary lamp on
account of the positive temperature coefficient of the filament. These
lamps are not manufactured for very low candle-powers, owing to the
difficulty of treating very slender fila-
ments, but they are made in sizes con-
suming from 40 to 250 watts. Table II
gives some useful information in connec-
tion with metallized filament lamps. The
filaments are made in a variety of shapes
and the distribution curves are usually
modified in practice by the use of shades
and reflectors. The general appearance
of the lamp does not differ from that of
the ordinary carbon lamp. Fig. 9 shows
typical distribution curves of the metallized
filament lamp as it is installed in practice.
Metallic Filament Lamps. The Tan-
talum Lamp. The first of the metallic
filament lamps to be introduced to any considerable extent com-
mercially was the tantalum lamp. Dr. Bolton of the Siemens &
Halske Company first discovered the methods of obtaining the pure
metal tantalum. This metal is rendered ductile and drawn into
slender filaments for incandes-
cent lamps. Tantalum has a high
tensile strength and high melting
point, and tantalum filaments are
operated at temperatures much
higher than those used with the
carbon filament lamp. On ac-
count Of the comparatively low Fig - n - Tantalum Filament Before and
J After 1,000 Hours' Use.
specific resistance of this material
the filaments, for 110-volt lamps must 'be long and slender, and
this necessitates a special form of support. Figs. 10, 11, and 12
show some interesting views of the tantalum lamp and the fila-
ment. This lamp is operated at the efficiency of 2 watts per
10.
Hound Bulb Tantalum
Lamp.
ELECTRIC LIGHTING
15
candle-power, with a life comparable to that of the ordinary lamp.
By special treatment it is possible to increase the resistance of the
filaments so that they may be shorter and heavier than those used in
Fig. 12.
Appearance of Filament After Filament Frame Showing
Having Been Used. Broken Filament.
the first of the tantalum lamps. It should be noted that the life of
this type of lamp on alternating-current circuits is somewhat uncer-
tain; it is much more satisfactory for operation on direct-current
circuits. Tables III and IV give some general data on the tantalum
lamp, and Figs. 13 and 14 show typical distribution curves for the
units as installed at present.
TABLE III
Data on Tantalum Lamp
GENERAL ELECTRIC CO., MFTRS.
SIZE OF BULB
ESTIMATED LIFE
DIAMETER OF
BULB IN INCHES
REGULAR
ROUND
ON A. C.
ON D. C.
40 watt
2i 5 6
350
800
50 "
2&
350
800
80 "
3i
400
800
40 watt
31
350
800
80 "
o
400
800
16
ELECTRIC LIGHTING
TABLE IV
Data on the Life of a 25-C. P. Unit
No. OF HOURS BURNED
CANDLE-POWER
WATTS PER CANDLE
19.8
2.17
25
23.6
1.865
50
23.1
1.90
125
22.3
1.98
225
22.4
1.96
350
22.3
1.97
450
22.2
1.98
550
21.2
2.05
650
19.6
2.20
Fig. 13. Vertical Distribution Curve Without Reflector.
The Tungsten Lamp. Following closely upon the development
of the tantalum lamp came the tungsten lamp. Tungsten possesses
a very high melting point and an indirect method is employed in
farming filaments for incandescent lamps. There are several of these
methods in use. In one method a fine carbon filament is flashed in
an atmosphere of tungsten oxy chloride mixed with just the proper
proportion of hydrogen, in which case the filament gradually changes
ELECTRIC LIGHTING
17
to one of tungsten. A second method consists of the use of powdered
tungsten and some binding material, sometimes organic and in other
cases metallic. The powdered tungsten is mixed with the binding
material, the paste squirted into filaments, and the. binding material is
then expelled, usually by the aid of heat. Another method of manu-
facture consists of securing tungsten in colloidal form, squirting it
Fig. 14. Distribution Curves for Tantalum Lamp. No. 1, 40 Watts; No. 2, 80 Watts.
into filaments, and then changing them to the metallic form by passing
electric current through the filaments.
The tungsten lamp has the highest efficiency of any of the com-
mercial forms of metallic filament lamps now in use, about 1.25 watts
per candle-power when operated so as to give a normal life, and lamps
for 110-volt service and consuming but 40 watts have recently been
put on the market. A 25-watt lamp for this same voltage appears to
be a possibility. The units introduced at first were of high candle-
power because of the difficulty of manufacturing the slender filaments
required for the low candle-power lamps.
18
ELECTRIC LIGHTING
The advantages of these metals, tantalum and tungsten, for
incandescent lamps are in the improved efficiency of the lamps and
the good quality of the light, white or nearly white in both cases.
In either case the change in candle-power with change in voltage is
less than the corresponding change in an ordinary carbon lamp. The
disadvantage lies in the fact that the filaments must be made long and
slender, and hence are fragile, for low candle-power units to be used
Fig. 15. Multiple Tungsten Lamp.
Fig. 1 6. Series Tungsten Lamp.
on commercial voltages. In some cases tungsten lamps are con-
structed for lower voltages and are used on commercial circuits through
the agency of small step-down transformers. Improvements in the
process of manufacture of filaments and of the method of their sup-
port have resulted in the construction of 110-volt lamps for candle-
powers lower than was once thought possible. Figs. 15 and 16 show
the appearance of the tungsten lamp, and Figs. 17 and 18 give some
ELECTRIC LIGHTING
19
typical distribution curves. Tables V and VI give data on this lamp
as it is manufactured at present. One very considerable application
20* Jo
Fig. 17. C. P. Distribution Curves of 100- Watt Gen. Elec. Tungsten
Incandescent Units with B-3, C-3, and D-3 Holophanes.
of the tungsten lamp is to incandescent street lighting on series cir-
cuits, in which case the lamp may be made for a low voltage across
its terminals and the filament may be made comparatively short and
w'o
60
60*
50 40 3O 20 /O" O" W 20 3O 4O' 50"
Fig. 18. Candle-Power Distribution Given with 40 c. p Gen. Elec. Tungsten
Series Lamp and Radial Wave Reflector.
heavy. The tungsten lamp is also being introduced as a low voltage
battery lamp.
The Just lamp, the Z lamp, the Osram lamp, the Zircon- Wolfram
lamp, the Osmin lamp, etc., are all tungsten lamps, the filaments
being prepared by some of the general methods already described or
modifications of them.
20
ELECTRIC LIGHTING
TABLE V
Tungsten Lamps
MULTIPLE
WATTS
VOLTS
CANDLE-
POWER
WATTS
PER
C. P.
TIP CANDLE-
POWER
SPHERICAL
REDUCTION
FACTOR
40
100
32
1.25
5
76.3
60
125
40
1.25
5.6
76.3
TABLE VI
Tungsten Lamps
SERIES
AMPERES
VOLTS
CANDLE-POWER
WATTS PER C. P.
4
13.5
40
1.35
20.25
60
5.5
9.8
40
1.35
14.7
60
6.6
8.2
40
1.35
12.3
60
7.5
7.2
40
1.35
10.8
60
The Osmium Lamp. Very efficient incandescent lamps have
been constructed using osmium for the filament. An indirect method
is resorted to in the formation of these filaments. Osmium lamps
have not been successful for commercial voltages because the fila-
ment is too fragile if it is made to have a high resistance, so these
lamps must be operated in series or through the agency of reducing
transformers if they are to be applied to 110-volt circuits. At 25
volts, lamps are constructed giving an efficiency of about 1.5 watts per
candle-power with a life comparable to that of a 3.5-watt carbon lamp.
Owing to the introduction of the tungsten lamp, the osmium lamp
will probably never be used to any great extent.
Other Metallic Filament Lamps. Table VII gives the melting
points of several metals which are highly refractory and those already
mentioned are not the only ones which have been successfully used
in incandescent lamps. Titanium, zirconium, iridium, etc., have
been successfully employed, but the tantalum and tungsten lamps are
the only ones which are used to any extent in the United States.
ELECTRIC LIGHTING
21
TABLE VII
Melting Point of Some Metals
METAL
APPROXIMATE MELTING POINT
IN DEGREES C.
Tungsten
3080-3200
Titanium
3000
Tantalum
2900
Osmium
2500
Platinum
1775
Zirconium
1500
Silicon
1200
Carbon (not a metal)
3000
The Helion Lamp. The helion lamp, which gives considerable
promise of commercial development, is a compromise between the
carbon lamp and the metallic filament lamp. A slender filament of
carbon is flashed in a compound of silicon (gaseous state) and a fila-
ment composed of a carbon core more or
less impregnated with silicon and coated
with a metallic layer is formed. The
emissivity of such a filament is high, the
light is white in color, and the filament is
strong. The efficiency of the helion fila-
ment as far as it has been developed is
higher than that of a carbon filament
when operated at the same temperature.
At 1,500 degrees C. the efficiency of the
helion filament is 2.15 watts per candle-
power, while for a carbon filament it is
about 3.5 watts per candle-power. Fila-
ments of this type have been made which
may be heated to incandescence in open
air without immediate destruction. This
lamp is not yet on the market.
The Nernst Lamp. The Nernst lamp
is still another form of incandescent
lamp, several types of which are shown in Figs. 19, 20, 21, and 22.
This lamp uses for the incandescent material certain oxides of the
rare earths, the oxides being mixed in the form of a paste, then
squirted through a die into a string which is subjected to a roast-
Fig. 19. Westinghouse Nernst
Multiple-Glower Lamp.
22
ELECTRIC LIGHTING
ing process forming the filament or glower material of the lamp as
represented by the lower white line in Fig. 23. The more recent
glowers are made hollow instead of solid. The glowers are cut to
the desired length and platinum ter-
minals attached. The attachment
of these terminals to the glowers is
an important process in the manu-
facture of the lamp. The recent
discovery of additional oxides has
led to the construction of glowers
which show a considerable gain in
efficiency over those previously used.
The glowers are heated to incan-
descence in open air, a vacuum not
being required.
As the glower is a non-conductor
when cold, some form of heater is
t necessary to bring it up to a tem-
./ p^wMA \\ perature at which it will conduct.
X r j\t/( r ^ wo f rms f neater nave been
M^, =S3Jy& used. One of them consists of a
porcelain tube shown just above
the glower, Fig. 23, about which a
fine platinum wire is wound; the
wire is in turn coated with a cement.
Two or more of these tubes are
mounted directly over the glower, or
glowers, and serve as a reflector
as well as a heater. The second
form of heater consists of a slender
rig. 20. sectional view of Multiple- rod of refractory material about
Glower Westinghouse Nernst Lamp. wm ' c h a platinum wire is WOUnd,
the wire again being covered with
a cement. This rod is then formed into a spiral which surrounds the
glower in the vertical glower type, or is formed into the wafer heater,
Fig. 24, now universally employed in the Westinghouse Nernst lamp
with horizontal glowers. The wafer heater is bent so that it can be
mounted with several sections parallel to the glower or glowers.
ELECTRIC LIGHTING
23
The heating device is connected across the circuit when the lamp
is first turned on, and it must be cut out of circuit after the glowers
become conductors in order to save the energy consumed by the
Fig. 21. Sectional Views of Single-Glower Westinghouse Nernst Lamp.
heater and to prolong the life of the heater. The automatic cut-out
is operated by means of an electromagnet so arranged that current
flows through this magnet as soon as the glower becomes a conductor,
and contacts in the heater circuit
are opened by this magnet. The
contacts in the heater circuit are
kept normally closed, usually by the
force of gravity.
The conductivity of the glower
increases with the increase of tem-
perature the material has a nega-
tive temperature coefficient hence
if it were used on a constant poten-
tial circuit directly, the current
and temperature would continue
to rise until the glower was de-
Fig. 22. Westinghouse Nernst Screw
stroyed. To prevent the current Burner.
24
ELECTRIC LIGHTING
from increasing beyond the desired value, a ballast resistance is
used in series with the glower. As is well known, the resistance of
iron wire increases quite rapidly with increase in temperature, and
the resistance of a fine pure iron wire
is so adjusted that the resistance of the
combined circuit of the glower and the
ballast becomes constant at the desired
temperature of the glower. The iron
wire must be protected from the air
to prevent oxidization and too rapid
temperature changes, and, for this
reason, it is mounted in a glass bulb
filled with hydrogen. Hydrogen has
been selected for this purpose because
Fig 23. Westinghouse Nernst Screw it is an inert gas and conducts the heat
Bur Z,;S 0"^' frm the ballast to the walls of the
Tubular Heater. bulb better than other gases which
might be used.
All of the parts enumerated, namely, glower, heater, cut-out, and
ballast, are mounted in a suitable manner; the smaller lamps have but
one glower and are arranged to fit in an incandescent lamp socket,
while the larger types are constructed at present with four glowers
Fig. 24. Wafer Heater and Mounting.
and are arranged to be supported in special fixtures, or the same as
small arc lamps. All parts are mechanically arranged so that renew-
als may be easily made when necessary and it is not possible to insert
a part belonging to one type of lamp into a lamp of a different type.
ELECTRIC LIGHTING
25
The advantages claimed for the Nernst Jamp are : High effi-
ciency; a good color of light; a good distribution of light without the
use of reflectors: a long life with low cost of maintenance; and a
complete series of sizes of units,
thus allowing its adaption to prac-
tically all classes of illumination. If |
The lamp is constructed for
both direct- and alternating-current
service and for 110 and 220 volts.
When the alternating-current lamp
is used on a 110- volt circuit a small
transformer, commonly called a
converter coil, Fig. 25, is utilized to
raise the voltage at the lamp ter-
minals to about 220 volts.
Data on the Nernst lamp in its present form are given in Table
VIII, and Figs. 26 and 27 show the form of distribution curves.
TABLE VIII
General Data on the Nernst Lamp
Fig. 25. Converter Coil.
LAMP
RATING
IN WATTS
VOLTAGE
CURRENT
IN
AMPERES
MAX.
CANDLE-
POWER
MEAN
HEMISPHER-
ICAL C. P.
WATTS PER M. II. S. c. P.
FROM TEST
66
110
.6
74
50
1.38
88
220
.4
105
77
1.2
A.C.
1-Glower or
110
110
1.0
131
96.4
1.2
D.C.
220
.5
132
110
1.2
156
114
1.2
220
.6
264
220
1.2
345
231
1 .2 [2-Glower-i . -,
396
220
1.8
528
359
1.15 J3-Glower [ or
528
220
2.4
745
504
1.09 }4-Glower j D - C *
Comparison of the Different Types of Incandescent Lamps. A
direct comparison of the different types of incandescent lamps can-
not be made but it is desirable at this time to note the following points :
The lamps which are considered commercial in the United States
at the present time are the carbon, gem, tantalum, tungsten, and
Nernst lamp. The efficiencies ordinarily accepted run in the order
26
ELECTRIC LIGHTING
given, approximately 3.1, 2.5, 2, 1.25, and 1.2 watts per candle respec-
tively. The figure of 1.2 watts per candle for the Nernst lamp is
based upon the mean hemispherical candle-pov/er and it should not
be compared directly with the other efficiencies. The color of the
light in all of the above cases is suitable for the majority of classes of
illumination, the light from the higher efficiency units being some-
what whiter than that from the carbon lamp. All of these lamps are
constructed for commercial voltages and for either direct or alternating
current. The use of the tantalum lamp on alternating current is not
60'
75'
SO' 75" 60'
Fig. 26. Distribution Curve of 132- Watt Type Westinghouse Nernst Lamp.
Single Glower.
always to be recommended as the service is unsatisfactory in some
cases. The minimum size of units for 110 volts is about 4 candle-
power for the carbon lamp, 20 candle-power for the metallic filament
lamp, and 50 candle-power (mean hemispherical) for the Nernst
lamp. Some of the metallic filament lamps are constructed for a
consumption of as high as 250 watts, while the largest size of the
Nernst lamp uses 528 watts. The light distribution of any of the
units is subject to considerable variation through the agency of re-
flectors, but the Nernst lamp is ordinarily installed without a reflec-
ELECTRIC LIGHTING
27
tor. Practically all of the other units of high candle-power use re-
flectors and only a few of the typical curves of light distribution curves
with reflectors have been shown in connection with the description
of the lamps. The life of all of the commercial lamps described is
considered as satisfactory. The minimum life is seldom less than
500 hours and the useful life is generally between 500 and 1,000 hours.
On account of the slender filaments employed in the metallic filament
45-
60 75" 90 75" 60
Fig. 27. Distribution of Light from Multiple-Glower "Westinghouse Nernst Lamps with
8" Clear Globes. No. 1, 2 Glower; No. 2, 3 Glower; No. 3, 4 Glower.
lamps they are not made for low candle-powers at commercial vol-
tages. The introduction of transformers for the purpose of changing
the circuit voltage to one suitable for low candle-power units has not
become at all general as yet in this country.
SPECIAL LAMPS
The Mercury Vapor Lamp. The mercury vapor lamp in this
country is put on the market by the Cooper-Hewitt Electric Company
and it is being used to a considerable extent for industrial illumination.
In this lamp mercury vapor, rendered incandescent by the passage
of an electric current through it, is the source of light. In its standard
form this lamp consists of a long glass tube from which the air has
been carefully exhausted, and which contains a small amount of
metallic mercury. The mercury is held in a large bulb at one end of
28 ELECTRIC LIGHTING
the tube and forms the negative electrode in the direct-current lamp.
The other electrode is formed by an iron cup and the connections
between the lamp terminals and the electrodes are of platinum where
this connection passes through the glass. Fig. 28 gives the general
appearance of a standard lamp having the following specifications:
Total watts (110 volts, 3.5 amperes) = 385
Candle-power (M. H. with reflector) = 700
Watts per candle = 0.55
Length of tube, total = 55 in.
Length of light-giving section = 45 in.
Diameter of tube = 1 in.
Height from lowest point of lamp to ceiling plate = 22 in.
For 220-volt service two lamps are connected in series.
The mercury vapor, at the start, may be formed in two ways:
First, the lamp may be tipped so that a stream of mercury makes
contact between the two elec-
trodes and mercury is vaporized
when the stream breaks. Second,
by means of a high inductance
and a quick break switch, a very
high voltage sufficient to pass a
current from one electrode to the
Fig. 28. Cooper-Hewitt Mercury Vapor ,1 ,1 1,1
Lamp other through the vacuum, is in-
duced and the conducting vapor
is formed. The tilting method of starting is preferred and this
tilting is brought about automatically in the more recent types of
lamp Fig. 29 shows the connections for automatically starting two
lamps in series. A steadying resistance and reactance are connected
as shown in this figure.
The mercury vapor lamp is constructed in rather large units,
the 55-volt, 3.5-ampere lamp being the smallest standard size. The
color of the light emitted is objectionable for some purposes as there
is an entire absence of red rays and the light is practically monochro-
matic. The illumination from this type of lamp is excellent where
sharp contrast or minute detail is to be brought out, and this fact
has led to its introduction for such classes of lighting as silk mills and
cotton mills. On account of its color the application of this lamp is
limited to the lighting of shops, offices, and drafting rooms, or to disc
ELECTRIC LIGHTING
29
play windows where the goods shown will not be changed in appear-
ance by the color of the light. It is used to a considerable extent in
photographic work on account of the actinic properties of the light.
Special reactances must be provided for a mercury arc lamp operating
on single-phase, alternating-current circuits.
The Moore Tube Light. The Moore light makes use of the
familiar Geissler tube discharge discharge of electricity through a
vacuum tube as a source of illumination. The practical application
of this discharge to a system of lighting has involved a large amount
t03-I2O volts
3.5 Ampere
Switch
H Inductance
\
j
I|LKJ | induct once
1 Coil
==#^J
Fig. 29. Wiring Diagram. Two H Automatic Lamps in Series.
of consistent research on the part of the inventor and it has now been
brought to such a stage that several installations have been made.
The system has many interesting features.
In the normal method of installation, a glass tube If inches in
diameter is made up by connecting standard lengths of glass tubing
together until the total desired length is reached, and this continuous
tube, which forms the source of light when in operation, is mounted
in the desired position with respect to the plane of illumination. In
many cases the tube forms a large rectangle mounted just beneath
the ceiling of the room to be lighted. The tube may be of any reason-
able length, actual values running from 40 to 220 feet. In order to
30
ELECTRIC LIGHTING
Tube distributed, in
cmy form des~ire<4 to
ofsoofeet.
provide an electrical discharge through this tube it is customary to
lead both ends of the tube to the high tension terminals of a trans-
former, the low tension side of which may be connected to the alter-
nating-current lighting mains. This transformer is constructed so
that the high tension terminals are not exposed and the current is
led into the tube by means of platinum wires attached to carbon
electrodes. The electrodes are about eight inches in length. The
ends of the tube and the high tension terminals are enclosed in a steel
casing so as to effectually prevent anything from coming in contact
with the high potential of the system. As stated, the low tension side
of the trans-
former is con-
nected to the
usual 60-cycle
lighting mains.
If direct current
is used for distribution, a motor-
generator set for furnishing alter-
nating current to the primary of
the transformer is required. Any
frequency from 60 cycles up is
suitable for the operation of these
tubes. At lower frequencies there
is some appreciable variation of
the light emitted. One other de-
vice is necessary for the suitable
operation of this form of light and
this is known as the regulator. In order to maintain a constant pres-
sure inside the tube, and such a constant pressure is necessary for
its satisfactory operation, there must be some automatic device which
will allow a small amount of gas to enter the tube at intervals while
it is in operation. The regulator accomplishes this purpose. Fig.
30 shows a diagram of the very simple connections of the system and
gives the relative positions occupied by the transformer, tube, and regu-
lator. Fig. 31 gives an enlarged view of the regulator, a description
of which and its method of operation is given as follows:
A piece of -inch glass tubing is supported vertically and its bottom end
is contracted into a f -inch glass tube which extends to the main lighting tube.
Fig. 30. Diagram Showing Essentia
Features of the Moore Light. 1 . Light-
ing Tube; 2. Transformer Case;
3. Lamp Terminals; 4. Trans-
former; 5, 6, 7, 8, Regulators.
ELECTRIC LIGHTING
31
At the point of contraction at the bottom of the f-inch tube there is sealed
by means of cement a | inch carbon plug, the porosity of which is not great
enough to allow mercury to percolate through it but which will permit gases
easily to pass, due- to the high vacuum of the
lighting tube connected to the lower end of the
plug, and approximately atmospheric pressure
above it. This carbon plug is normally com-
pletely covered with what would correspond to
a thimbleful of mercury which simply seals the
pores of the carbon plug, and therefore has
nothing whatever to do with the conducting
properties of the gas in the main tube which
produces the light. Partly immersed in the
mercury and concentric with the carbon plug,
is another smaller and movable glass tube, the
upper end of which is filled with soft iron wire,
which acts as the core of a small solenoid con-
nected in series with the transformer. The
action of the solenoid is to lift the concentric
glass tube partly out of the mercury, the sur-
face of which falls and thereby causes the
minute tip of the conical shaped carbon plug
to be slightly exposed for a second or two.
This exposure is sufficient to allow
a small amount of gas to enter the tube,
the current decreases slightly, and the
carbon plug is again sealed. The process
above described takes place at intervals
of about one minute when the tube is in
operation.
The color of the light emitted by the
tube depends upon the gas used in it.
The regulator is fitted with some chem-
ical arrangement whereby the proper gas
is admitted to it when the tube is in opera-
tion. Nitrogen is employed when the tube
gives the highest efficiency and the light
emitted when this gas is used is yellowish
in color. Air gives a pink appearance to
the tube and carbon dioxide is employed when a white light is desired.
Table IX gives general data on the Moore tube light. The
advantages claimed for this light are: High efficiency, good color, and
low intrinsic brilliancy.
Fig. 31. Regulating Valve.
32
ELECTRIC LIGHTING
TABLE IX
Data on the Moore Tube Light
LENGTH OF
TUBE
TRANSFORMER
CAPACITY
POWER FACTOR
OF CIRCUIT
VOLTAGE AT LAMP TERMINALS
40-70 ft.
80-125 "
2 kw.
2.75 "
65-84%
3,146 for 40-ft. tube, at
12 Hefners per ft.
130-180 "
3.5 "
190-220 "
4.5 "
12,441 for 220-ft. tube, at
12 hefners per ft.
Pressure in tube, about ^ mm. of mercury.
Watts per hefner, 3.2 for 20-foot tube including transformer.
Watts per hefner, 1.4 for 180-foot tube including transfo.'mer.
Hefner per foot, normal, 12.
Note that one hefner equals 0.88 candle-power.
ARC LAMPS
The Electric Arc. Suppose two carbon rods are connected in
an electric circuit, and the circuit closed by touching the tips of these
rods together; on separating the carbons again the circuit will not
be broken, provided the space between the carbons be not too great,
but will be maintained through the arc
formed at these points. This phenom-
enon, which is the basis of the arc
light, was first observed on a large scale
by Sir Humphrey Davy, who used a
battery of 2,000 cells and produced an
arc between charcoal points four inches
apart.
As the incandescence of the carbons
across which an arc is maintained, to-
gether with the arc itself, forms the
source of light for a large portion of arc
lamps, it will be well to study the
nature of the arc. Fig. 32 shows the
general appearance of an arc between two carbon electrodes when
maintained by direct current.
Fig. 32. The Electric Arc between
Carbon Terminals.
ELECTRIC LIGHTING
33
Here the current is assumed as passing from the top carbon to
the bottom one as indicated by the arrow and signs. We find, in the
direct-current arc, that the most of the light issues from the tip of the
positive carbon, or electrode, and this portion is known as the crater
of the arc. This crater has a temperature of from 3,000 to 3,500 C.,
the temperature at which the carbon vaporizes, and gives fully 80 to
85% of the light furnished by the arc. The negative carbon becomes
pointed at the same time thai the positive one is hollowed out to form
the crater, and it is also incandescent but not to as great a degree as
the positive carbon. Between the electrodes there is a band of violet
light, the arc proper, and this
is surrounded by a luminous
zone of a golden yellow color.
The arc proper does not fur-
nish more than 5% of the light
emitted when pure carbon
electrodes are used.
The carbons are worn
away or consumed by the
passage of the current, the
positive carbon being con-
sumed about twice as rapidly
as the negative.
The light distribution
curve of a direct-current arc,
taken in a vertical plane, is
shown in Fig. 33. Here it is seen that the maximum amount of light
is given off at an angle of about 50 from the vertical, the negative
carbon shutting off the rays of light that are thrown directly down-
ward from the crater.
If alternating current is used, the upper carbon becomes positive
and negative alternately, and there is no chance for a crater to be
formed, both carbons giving off the same amount of light and being
consumed at about the same rate. The light distribution curve of
an alternating-current arc is shown in Fig. 34.
AroLamp Mechanisms. In a practical lamp we must have not
only a pair of carbons for producing the arc, but also means for sup-
porting these carbons, together with suitable arrangements for leading
Fig. 33.
Distribution Curve for D. C. Arc
Lamp (Vertical Plane).
34
ELECTRIC LIGHTING
the current to them and for maintaining them at the proper distance
apart. The carbons are kept separated the proper distance by the
operating mechanisms which must perform the following functions:
1. The carbons must be in contact, or be brought into contact, to start
the arc when the current first flows.
2. They must be separated at the right distance to form a proper arc
immediately afterward.
Fig. 34. Distribution Curve for A. C. Arc Lamp (Vertical Plane).
3. The carbons must be fed to the arc as they are consumed.
4. The circuit should be open or closed when the carbons are entirely
consumed, depending on the method of power distribution.
The feeding of the carbons may be done by hand, as is the case
in some stereopticons using an arc, but for ordinary illumination the
striking and maintaining of the arc must be automatic. It is made
so in all cases by means of solenoids acting against the force of gravity
or against springs. There are an endless number of such mechanisms,
ELECTRIC LIGHTING
35
but a few only will be described here. They may be roughly divided
into three classes:
1. Shunt mechanisms.
2. Series mechanisms.
3. Differential mechanisms.
Shunt Mechanisms. In shunt lamps, the carbons are held apart
before the current is turned on, and the circuit is closed through a
solenoid connected in across the
gap so formed. All of the cur-
rent must pass through this coil
at first, and the plunger of the
solenoid is arranged to draw the
carbons together, thus starting
the arc. The pull of the solenoid
and that of tha springs are ad-
justed to maintain the arc at its
proper length.
Such lamps have the disad-
vantage of a high resistance at
the start 450 ohms or more
and are difficult to start on series
circuits, due to the high voltage
required. They tend to maintain
a constant voltage at the arc, but
do not aid the dynamo in its
regulation, so that the arcs are
liable to be a little unsteady.
Series Mechanisms. With
the series-lamp mechanism, the
carbons are together when the lamp is first started and the current,
flowing in the series coil, separates the electrodes, striking the arc.
When the arc is too long, the resistance is increased and the current
lowered so that the pull of the solenoid is weakened and the carbons
feed together. This type of lamp can be used only on constant-
potential systems.
Fig. 35 shows a diagram of the connection of such a lamp. This
diagram is illustrative of the connection of one of the lamps manu-
factured by the Western Electric Company, for use on a direct-current,
Fig. 35. Series Mechanism for D. C.
Arc Lamp.
36
ELECTRIC LIGHTING
constant-potential system. The symbols + and refer to the termi-
nals of the lamp, and the lamp must be so connected that the current
flows from the top carbon to the bottom one. R is a series resistance,
adjustable for different voltages by means of the shunt G. F and D
are the controlling solenoids connected in series with the arc. B and
C are the positive and negative carbons respectively, while A is the
switch for turning the current on and off. H is the plunger of the
solenoids and I the carbon clutch,
^ this being what is known as a
carbon-feed lamp. The carbons
are together when A is first closed,
the current is excessive, and the
plunger is drawn up into the so-
lenoids, lifting the carbon B until
the resistance of the arc lowers the
current to such a value that the
pull of the solenoid just counter-
balances the weight of the plunger
and carbon. G must be so adjusted
that this point is reached when the
arc is at its normal length.
Differential Mechanisms. In
the differential lamp, the series and
shunt mechanisms are combined,
the carbons being together at the
start, and the series coil arranged
so as to separate them while the
shunt coil is connected across the
arc, as before, to prevent the carbons from being drawn too far apart.
This lamp operates only over a low-current range, but it tends to aid
the generator in its regulation.
Fig. 36 shows a lamp having a differential control, this also being
the diagram of a Western Electric Company arc lamp for a direct-
current, constant-potential system. Here S represents the shunt coil
and M the series coil, the armature of the two magnets A and A' being
attached to a bell-crank, pivoted at B, and attached to the carbon
clutch C. The pull of coil S tends to lower the carbon while that of
M raises the carbon, and the two are so adjusted that equilibrium is
Fig. 36.
Differential Mechanism for
D. C. Arc Lamp.
ELECTRIC LIGHTING
37
reached when the arc is of the proper length. All of the lamps are
fitted with an air dashpot, or some damping device, to prevent too
rapid movements of the working parts.
The methods of supporting the carbons and feeding them to
the arc may be divided into two classes:
1. Rod-feed mechanism.
2. Carbon-feed mechanism.
Rod-Feed Mechanism.
Lamps using a rod feed have
the upper carbons supported
by a conducting rod, and the
regulating mechanism acts on
this rod, the current being fed
to the rod by means of a sliding
contact. Fig. 37 shows the ar-
rangement of this type of feed.
The rod is shown at R, the
sliding contact at B, and the
carbon is attached to the rod
atC.
These lamps have the ad-
vantage that carbons, which
do not have a uniform cross-
section or smooth exterior, may
be used, but they possess the
disadvantage of being very
long in order to accommodate
the rod. The rod must also be
kept clean so as to make a
good contact with the brush.
Carbon-Feed Mechanism. In carbon-feed lamps the controlling
mechanism acts on the carbons directly through some form of clutch
such as is shown at C in Fig. 38. This clamp being lifted grips the
carbon, but allows the carbon to slip through it when the tension
is released. For this type of feed the carbon must be straight and
have a uniform cross-section as well as a smooth exterior. The
current may be led to the carbon by means of a flexible lead and a
short carbon holder
Fig. 37. Rod-Feed Mechanism.
38
ELECTRIC LIGHTING
TYPES OF ARC LAMPS
Arc lamps are constructed to operate on direct-current or alter-
nating-current systems when connected in series or in multiple. They
are also made in both the open and the enclosed forms.
By an open arc is meant an arc lamp in which the arc is exposed
to the atmosphere, while in the enclosed arc an inner or enclosing
Fig. 38. Enclosed Arc Lamp with Carbon Feed Mechanism.
globe surrounds the arc, and this globe is covered with a cap which
renders it nearly air-tight. Fig. 38 is a good example of an enclosed
arc as manufactured by the General Electric Company.
Direct=Current Arcs. Open Types of Arcs for direct-current
systems were the first to be used to any great extent. When used
they are always connected in series, and are run from some form of
ELECTRIC LIGHTING 39
special arc machine, a description of which may be found in "Types
of Dynamo Electric Machinery."
Each lamp requires in the neighborhood of 50 volts for its opera-
tion, and, since the lamps are connected in series, the voltage of the
system will depend on the number of lamps; therefore, the number
of lamps that may be connected to one machine is limited by the
maximum allowable voltage on that machine. By special construction
as many as 125 lamps are run from one machine, but even this size
of generator is not so efficient as one of greater capacity. Such gen-
erators are usually wound for 6.6 or 9.6 amperes. Since the carbons
are exposed to the air at the arc, they are rapidly consumed, requiring
that they be renewed daily for this type of lamp.
Double-carbon arcs. In order to increase the life of the early
form of arc lamp without using too long a carbon, the double-carbon
type was introduced. This type uses two sets of carbons, both sets
being fed by one mechanism so arranged that when one pair of the elec-
trodes is consumed the other is put into service. At present nearly
all forms of the open arc lamp have disappeared on account of the
better service rendered by the enclosed arc.
Enclosed arcs for series systems are constructed much the same
as the open lamp, and are controlled by either shunt or differential
mechanism. They require a voltage from 68 to 75 at the arc, and are
usually constructed for from 5 to 6.8 amperes. They also require a
constant-current generator or a rectifier outfit if used on alternating-
current circuits.
Constant-potential arcs must have some resistance connected in
series with them to keep the voltage at the arc at its proper value.
This resistance is made adjustable so that the lamps may be used on
any circuit. Its location is clearly shown in Fig. 38, one coil being
located above, the other below the operating solenoids.
Alternating-Current Arcs. These do not differ greatly in con-
struction from the direct-current arcs. When iron or other metal
parts are used in the controlling mechanism, they must be laminated
or so constructed as to keep down induced or eddy currents which
might be set up in them. For this reason the metal spools, on which
the solenoids are wound, are slotted at some point to prevent them
from forming a closed secondary to the primary formed by the solen-
oid winding. On constant-potential circuits a reactive coil is used
40
ELECTRIC LIGHTING
in place of a part of the resistance for cutting down the voltage at the
arc.
Interchangeable Arc. Interchangeable arcs are manufactured
which may be readily adjusted so as to operate on either direct or
alternating current, and on voltages from 110 to 220. Two lamps
may be run in series on 220-volt circuits.
The distribution of light, and the resulting illumination for the
different lamps just considered, will be taken up later. Aside from
the distribution and quality of light, the enclosed arc has the advan-
tage that the carbons are not consumed so rapidly as in the open lamp
because the oxygen is soon exhausted from the inner globe and the
combustion of the carbon is greatly decreased. They will burn
from 80 to 100 hours without retrimming.
TABLE X
Rating of Enclosed Arcs
WATTS CONSUMED
MEAN INTENSITY
IN H. U.
MEAN WATTS
Oi
a
a
2
SPHERICAL
aj , M
^. S a
SPHERICAL
H. U.
^ i ^
3
H
(X
a
o
M
a
ti
llsi
g
MK d
P.
&
M
A
H
00
CO
CLEAR
OUTER
00
oo
CLEAR
OUTER
235
332
2.37
1.66
1
5.01
551
401
150
172
256*
362*
3.10
2.18*
1 .52*
3
5.08
559
406
252
195
216
282
2.85
2.60
1.99
4
4.76
524
381
143
127
139
208
4.12
3.76
2.52
5
4.16f
458
333
125
154
174
221
2.96
2.63
2.07
7
4.76
524
381
143
203
333
317
2.63
2.20
1.65
9
4.84
532
387
145
182
226
281
2.83
2.38
1.89
10
4 99
549
399
150
202
242
309
2.74
2 24
1 .77
12
4.87
536
3CO
146
178
195
230
3.05
2^66
2.33
Mean
4.9
529
384
144
176
207
272
3.03
2.60
1.98
a
1
Jj
H
cu
P5
o
tf
55
W
"i O
i O
M
d
tf
PH
j
* o S
o u
^
< !
<! PS
w
<
I I
M
5
101
6.40
448
.63
340
.82
108
127
141
206
3.52
3.17
2.17
203
236
2.26
1 .94
102
6.79
459
.61
375
.73
84
146
176f
226t
3.31
2.60t
1.72t
103
5.89
424
.65
344
.75
80
116
130
147
3.66
3.15
2.88
105
6.20
414
.61
382
.80
32
128
187
219
3.24
2.20
1.89
153
169
2.56
2.23
106
6.12
378
.56
298
.70
80
132
182t
284
2.82
2.19t
1.48f
108
6.48
457
.64
383
.80
74.5
133
175
211
3.20
2.61
2.16
110
6.18
339
.49
276
.72
63
140*
126
143
2.41*
2.68
2.37
Mean
6.29 417
.60
342
.76
74.5
130
159
190
3.31
2.66
2.23
*Condition of no outer globe. fCondition with shade on lamp. H.U. Hefner Units.
Rating of Arc Lamps.
follows :
Open arcs have been classified as
ELECTRIC LIGHTING 41
Full Arcs, 2,000 candle-power taking 9.5 to 10 amps, or 450-480 watts.
Half Arcs, 1,200 candle-power taking 6.5 to 7 amps, or 325-350 watts.
These candle-power ratings are much too high, and run more
nearly 1,200 and 700, respectively, for the point of maximum intensity
and less than this if the mean spherical candle-power be taken. For
this reason, the ampere or watt rating is now used to indicate the
power of the lamp. It is now recommended that specifications for
street lighting should be based upon the illumination produced. This
point is considered later under the topic of street lighting. Enclosed
arcs use from 3 to 6.5 amperes, but the voltage at the arc is higher
than for the open lamp. Table X gives some data on enclosed arcs
on constant-potential circuits.
Efficiency. The efficiency o e arc lamps is given as follows:
Direct-Current Arc (enclosed) 2.9 watts per candle-power.
Alternating-Current Arc (enclosed) 2.95 watts per candle-power.
Direct-Current Arc (open) .6-1.25 watts per candle-power.
Carbons for Arc Lamps. Carbons are either moulded or forced
from a product known as petroleum coke or from similar materials
such as lampblack. The material is thoroughly dried by heating to a
high temperature, then ground to a find powder, and combined with
some substance such as pitch which binds the fine particles of carbon
together. After this mixture is again ground it is ready for moulding.
The powder is put in steel moulds and heated until it takes the form
of a paste, when the necessary pressure is applied to the moulds. For
the forced carbons, the powder is formed into cylinders which are
placed in machines which force the material through a die so arranged
as to give the desired diameter. The forced carbons are often made
with a core of some special material, this core being added after the
carbon proper has been finished. The carbons, whether moulded
or forced, must be carefully baked to drive off all volatile matter.
The forced carbon is always more uniform in quality and cross-
section, and is the type of carbon which must be used in the carbon-
feed lamp. The adding of a core of a different material seems to
change the quality of light, and being more readily volatilized, keeps
the arc from wandering.
Plating of carbons with copper is sometimes resorted to for
moulded forms for the purpose of increasing the conductivity, and,
by protecting the carbon near the arc* prolonging the life.
42 ELECTRIC LIGHTING
The Flaming Arc. In the carbon arc the arc proper gives out
but a small percentage of the total amount of light emitted. In order
to obtain a light in which more of the source of luminosity is in the
arc itself, experiments have been made with the use of electrodes im-
pregnated with certain salts, as well as with electrodes of a material
different than carbon. The result of these experiments has been to
place upon the market the flaming arc lamps and the luminous arc
lamps lamps of high candle-power, good efficiency, and giving vari-
ous colors of light. These lamps may be put in two classes : One class
uses carbon electrodes, these electrodes being impregnated with certain
salts w T hich add luminosity to the
arc, or else fitted with cores which
contain the required material;
the other class covering lamps
which do not employ carbon, the
most notable example being the
magnetite arc which uses a copper
segment as one electrode and a
magnetite stick as the other
electrode.
Flaming arcs of the first class
Fig. 39. Diagram of Bremer Flaming Arc. are made in two general types:
One in which the electrodes are
placed at an angle, and the other in which the carbons are placed
one above the other as in the ordinary arc lamp. The term lumi-
nous arc is usually applied to arcs of the flaming type in which the
electrodes are placed one above the other. The minor modifications
as introduced by the various manufacturers are numerous and include
such features as a magazine supply of electrodes by which a new pair
may be automatically introduced when one pair is consumed; feed
and control mechanisms; etc. The flaming arc presents a special
problem since the vapors given off by the lamp may condense on the
glassware and form a partially opaque coating, or they may interfere
with the control mechanism.
Bremer Arc. The Bremer flaming arc lamp was introduced
commercially in 1899, and since some of its principles are incorporated
in many of the lamps on the market to-day, it will be briefly described
here. The diagram shown in Fig. 39 illustrates the main features of
ELECTRIC LIGHTING
43
this lamp. The electrodes are mounted at an angle and an electro-
magnet is placed above the arc for the purpose of keeping the arc from
creeping up and injuring the economizer, and also for the purpose of
spreading the arc out and increasing its surface. The vapor from
the arc is condensed on the economizer and this coating acts as a re-
flector, throwing the light downward. The economizer serves to
limit the air supplied to the arc and thus increases the life of the elec-
trodes. The inclined position of the carbons was suggested by the
fact that in the impregnated carbons a slag was formed which gave
trouble when the electrodes were mounted in the usual manner. By
using the electrodes in
this position there is little
if any obstruction to the
light which passes di-
rectly downward from
the arc.
Bremer's original
electrodes contained
compounds of calcium,
strontium, magnesium,
etc., as well as boracic
acid. Electrodes as em-
ployed in the various
lamps to-day differ
greatly in their make-up.
Some use impregnated
carbons, others use carbons with a core containing the flaming ma-
terials, and metallic wires are added in some cases. The life of
electrodes for flaming lamps is not great, depending upon their length
and somewhat upon the type of lamp. The maximum life of the
treated carbons is in the neighborhood of 20 hours.
The color of the light from the flaming arc is yellow when cal-
cium salts are used as the main impregnating compound, and the
majority of the lamps installed use electrodes giving a yellow light.
By employing more strontium, a red or pink light is produced, while
if a white light is wanted, barium salts are used. Calcium gives the
most efficient service and strontium comes between this and barium.
The distribution curves in Fig. 40 illustrate the relative economies
Fig. 40. Distribution Curves of a Luminous Arc.
44
ELECTRIC LIGHTING
of the different materials. Modern electrodes contain not more than
15% of added material and it is customary to find the salts applied
as a core to the pure carbon sticks. The electrodes are made of a
small diameter in order to maintain a steady light and this partially
accounts for their short life.
The feeding mechanisms employed differ greatly. They may be
classified as: Clock, gravity-feed, clutch, motor, and hot-wire mech-
anisms. Fig. 41 illustrates a clock mechanism. This is a dif-
ferential mechanism in which the
shunt coils act to release a detent /
which allows the electrodes to feed
down and when they come in con-
tact the series coils separate them
to the proper extent for maintaining
a suitable arc. In the gravity feed
an electromagnet is used to operate
one carbon in springing the arc and
the other carbon is fed by gravity,
it being prevented from dropping
too far by means of a special rib
formed on the electrode which comes
in contact with a part of the lamp
structure. Gravity feed is also em-
ployed in the clutch mechanism but
here the carbons are held in one
position by an electrically operated
clutch which releases them only when
the current is sufficiently reduced by
the lengthening of the arc. In the
hot-wire lamp, the wire is usually in series with the arc; the contrac-
tion and expansion of this wire is balanced against a spring and the
arc is regulated by such contraction or expansion of the wire. Such
a lamp is suitable for either direct or alternating current. In the
motor mechanism, as applied to alternating-current lamps, a metallic
disk is actuated by differential magnets and its motion is transmitted
to the electrodes to lengthen or shorten the arc accordingly as the
force exerted by the series or shunt coils predominates.
Magnetite Arc. The magnetite arc employs a copper disk as
Fig. 41. Clock Feeding Mechanism for
Luminous Arc Lamp.
ELECTRIC LIGHTING
45
one electrode; and a magnetite stick formed by forcing magnetite,
to which titanium salts are usually added, into a thin sheet steel tube
is used as the other electrode. This lamp gives a luminous arc of
good efficiency and the magnetite electrode is not consumed as rapidly
as the treated carbons with the result that magnetite lamps do not
require trimming as frequently. The life of the magnetite electrode
as at present manufactured is from 170 to 200 hours. A diagram of
the connections of this lamp as manufactured by the General Electric
Starting
Maonet
(s
B
=
f or ting Resist an c
1
Fig. 42. Diagram of Connections for Magnetite Arc Lamp.
Company is shown in Fig. 42. The magnetite electrode is placed be-
low. The copper electrode has just the proper dimensions to prevent
its being destroyed by the arc and yet it is not large enough to cause
undue condensation of the arc vapor. Direct current must be used
with this lamp, the current passing from the copper to the magnetite.
Table XI gives some general data on the flaming arc, while Figs.
43 and 44 give typical distribution curves. The advantages of the
flaming arc over lamps using pure carbon electrodes are: High effi-
ciency; better light distribution; and better color of light for some
46
ELECTRIC LIGHTING
purposes. A greater amount of light can be obtained from a single
unit than is practical with the carbon arc. The disadvantages lie
in the frequent trimming required and the expense of electrodes.
Flaming arcs have been introduced abroad, especially in Germany,
to a much greater extent than in the United States.
TABLE XI
General Data on Flaming Arcs
VOLTS
AMPERES
WATTS
MEAN SPHERICAL
CANDLE-POWER
WATTS PER MEAN
SPHERICAL c. P.
55
6
330
480
.68
8
440
800
.55
10
550
1100
.5 -
12
660
1300
.5
15
825
1700
.49
20
1100
2250
.48
POWER DISTRIBUTION
The question of power distribution for electric lamps and other
appliances is taken up fully in the section on that subject, therefore
it will be treated very briefly here. The systems may be divided into :
1. Series distribution systems.
2. Multiple-series or series-multiple systems.
3. Multiple or parallel systems.
They apply to both alternating and direct current.
The Series System. This is the most simple of the three; the
lamps, as the name indicates, are connected in series as shown in
Fig. 45. A constant load is necessary if a constant potential is to be
used. If the load is variable, a constant-current generator, or a
special regulating device is necessary. Such devices are constant-
current transformers and constant-current regulators as applied to
alternating-current circuits.
The series system is used mostly for arc and incandescent lamps
when applied to street illumination. Its advantages are simplicity
and saving of copper. Its disadvantages are high voltage, fixed by
the number of lamps in series; the size of the machines is limited
since they cannot be insulated for voltage above about 6,000; a single
open circuit shuts down the whole system.
Alternating-current series distribution systems are being used to
a very large extent. By the aid of special transformers, or regulators,
ELECTRIC LIGHTING
47
any number of circuits can be run from one machine or set of bus bars,
and apparatus can be built for any voltage and of any size. It is not
customary, however, to build transformers of this type having a capac-
o
6O 75" 90' 75 SO'
Fig. 43. Distribution Curve for Flaming Arc Lamp.
ity greater than one hundred 6.6-ampere lamps because of the high
voltage which would have to be induced in the secondary for a larger
number of lamps.
Fig. 45 gives a dia-
gram of the connection
of a single-coil trans-
fermer in service. The
constant-current trans- oV- IL^I^ JCJ4--UI jo
/o"
20'
Luminous Arc Lamp
Direct current series circuit
Distribution
30
former most in use for
lighting purposes is the 20"
one manufactured by the
General Electric Com-
pany and commonly
known as a tub trans-
former. Fig. 46 shows such a transformer (double-coil type) when
removed from the case.
Referring to Fig. 46, the fixed coils A form the primaries which
are connected across the line; the movable coils B are the secondaries
40" 50' 6 0' TO'SCrSO* 80 70*60' 50 4-0
Fig. 44. Distribution Curve for a 4-Ampere,
75-\olt, Magnetite Luminous Arc Lamp.
48
ELECTRIC LIGHTING
SECONDARY
-X X X X X X-
LAMPS
connected to the lamps. There is a repulsion of the coils B by the
coils A when the current flows in both circuits and this force is bal-
anced by means of the weights at W, so that the coils B take a position
such that the normal current will flow in the secondary. On light
loads, a low voltage is sufficient, hence the secondary coils are close
together near the middle of
the machine and there is a
heavy magnetic leakage.
When all of the lamps are
on, the coils take the posi-
tion shown when the leak-
age is a minimum and the
voltage a maximum. When
first starting up, the trans-
former is short-circuited and
the secondary coils brought
close together. The short
circuit is then removed and
the coils take a position
corresponding to the load
on the line.
These transformers regu-
late from full load to J rated
load within T V ampere of
normal current, and can be
run on short circuit for
C PRIMARY PLUG SWITCH several hours without over-
heating. The efficiency is
given as 96% for 100-light
transformers and 94.6% for
50-light transformers at full
load. The power factor of the system is from 76 to 78% on full
load, and, owing to the great amount of magnetic leakage at less than
full load the effect of leakage being the same as the effect of an in-
ductance in the primary the power factor is greatly reduced, falling
to 62% at f load, 44% at J load, and 24% at J load.
Standard sizes are for capacities of 25-, 35-, 50-, 75-, and 100-6.6
ampere enclosed arcs, and they are also made for lower currents in
SHORT CIRCUITING
PLUG SWITCH
CURRENT
TRANSFORMER
OMIT FOR
25 LIGHTS
OPEN CIRCUITING
PLUG SWITCHES
CONSTANT CURRENT
TRANSFORMER
RESISTANCE
FUSE
WMV
POTENTIAL
TRANSFORMER
PRIMARY
BACK VIEW
Fig. 45.
Wiring Diagram for Single-Coil
Transformer.
ELECTRIC LIGHTING
49
50
ELECTRIC LIGHTING
the neighborhood of 3.3 amperes for incandescent lamps. The low
power factor of such a system on light loads shows that a transformer
should be selected of such a capacity that it will be fully or nearly
fully loaded at all times. The primary winding can be constructed
for any voltage and the open circuit voltages of the secondaries are
as follows :
25 light transformer, 2,300 volts.
35 " " 3,200 "
50 " " 4,600 "
75 light transformer, 6,900 volts.
100 " " 9,200 "
The 50-, 75-, and 100-light transformers are arranged for multiple
circuit operation, two circuits
used in series, and the vol-
tages at full load reach 4,100
for each circuit on the 100-light
machine.
The second system, used
for series distribution on
alternating-current circuits
consists of a constant-potential
transformer, stepping down the
line voltage to that required
for the total number of lamps
on the system, allowing 83
volts for each lamp, and in
series with the lamps is a
reactive coil, the reactance of
which is automatically regu-
lated, as the load is increased
or decreased, in order to keep
Fig. 47. Current Regulator for A. C. Series ^
Distribution Systems. the current in the line con-
stant. Fig. 47 shows such a regulator and Fig. 48 shows this regu-
lator connected in circuit. The inductance is varied by the move-
ment of the coil so as to include more or less iron in. the magnetic
circuit. Since the inductance in series with the lamps is high on light
loads, the power factor is greatly reduced as in the constant-current
transformer; and the circuits should, preferably, be run fully loaded.
60 to 65 lamps on a circuit is the usual maximum limit.
While used primarily for arc-light circuits, the same systems,
ELECTRIC LIGHTING
51
designed for lower currents, are very readily applied to series incan-
descent systems.
The introduction of certain flaming or luminous arcs requiring
direct current for their operation has led to the use of the mercury arc
rectifier in connection with series circuits on alternating-current
systems. A constant-current transformer is used to regulate for the
proper constant current in its second-
ary winding, and this secondary current
is rectified by means of the mercury arc
rectifier for the lamp circuit. In the
recent outfits the rectifier tubes are
immersed in oil for cooling. While
this rectifier was first introduced for
the operation of luminous arc lamps,
there is no reason why it should not
be used with any series lamp requiring KICKING
direct current, provided the system is
designed for the current taken by such
lamps. With this system any commer-
cial frequency may be used. Sets are
constructed for 25-, 50-, and 75-light
circuits. They have a combined effi-
ciency, transformer and rectifier tube,
of 85% to 90%, and operate at a power
factor of from 65% to 70%. Fig. 49
gives a diagram of the circuit and
rectifier connections USed with a single- Fig. 48. Wiring Diagram Showing In-
, n , troduction of the Current Regulator.
tube outfit.
Multiple= Series or Series= Multiple Systems. These combine
several lamps in series, and these series groups in multiple, or several
lamps in multiple and these multiple groups in series, respectively.
They have but a limited application.
Multiple or Parallel Systems of Distribution. By far the largest
number of lamps in service are connected to parallel systems of dis-
tribution. In this system, the units are connected across the lines
leading to the bus bars at the station, or to the secondaries of con-
stant-potential transformers. Fig. 50 shows a diagram of ten lamps
connected in parallel. The current delivered by the machine de-
C.P. STEP UP
OR STtlPDOWN
TRANSFORMER
UGHTNING
ARRESTERS
52
ELECTRIC LIGHTING
pends directly on the number of lamps connected in service, the vol-
tage of the system being kept constant.
Inasmuch as the flow of current in a conductor is always accom-
. panied by a fall
-tzsACBusses\
Fig. 49.
various
systems
1.
2.
3.
4.
of potential equal
to the product of
the current flow-
ing into the resist-
ance of the con-
ductor, the lamps
at the end of the
system shown
will not have as
high a voltage
impressed upon
them as those
nearer the ma-
chine. This
drop in potential
is the most seri-
ous obstacle that
we have to over-
AViring Diagram for A. C. System Showing Introduc- come in multiple
tion of Mercury Arc Rectifier.
systems, and
schemes have been adopted to aid in this regulation. The
may be classified as :
Cylindrical conductors, parallel feeding.
Conical
Cylindrical anti-parallel feeding.
Conical
In the cylindrical conductor, parallel-feeding system, the con-
ductors, A, B,C, D, Fig. 50, are of the same size throughout and are
fed at the same end by the generator. The voltage is a minimum
at the lamps E and a maximum at the lamps F; the value of the
voltage at any lamp being readily calculated.
By a conical or tapering conductor is meant a conductor whose
diameter is so proportioned throughout its length that the current,
divided by the cross-section, or the current density, is a constant
ELECTRIC LIGHTING
53
Fig. 50. Parallel Feeding System.
Fig. 51. Anti-parallel Feeding System.
quantity. Such a conductor is approximated in practice by using
smaller sizes of wire as the current in the lines becomes less.
In an anti-parallel system, the current is fed to the lamps from
opposite ends of the system, as shown in Fig. 51.
Multiple=Wire Systems. In order to take advantage of a higher
voltage for distribution of power to the lighting circuits, three- and
five-wire systems have been introduced, the three-wire system being
used to a very large extent. In this system, three conductors are
used, the voltage from each A B
outside conductor to the
middle neutral conductor
being the same as for a
simple parallel system. Fig.
52 gives a diagram of this.
By this system the amount
of copper required for a giv-
en number of lamps is from
five-sixteenths to three-
eighths of the amount
required for a two-wire dis-
tribution, depending on the
size of the neutral con- Fig 52 Three . wire System .
ductor. The saving of
copper together with the disadvantages of the system is more fully
treated in the paper on "Power Transmission."
ILLUMINATION
Illumination may be defined as the quality and quantity of light
which aids in the discrimination of outline and the perception of
color. Not only the quantity, but the quality of the light, as well as
the arrangement of the units, must be considered in a complete study
of the subject of illumination.
Unit of Illumination. The unit of illumination is the joot-
candle and its value is the amount of light falling on a surface at a
distance of one foot from a source of light one candle-power in value.
The law of inverse squares namely, that the illumination from a
given source varies inversely as the square of the distance from the
source shows that the illumination at a distance of two feet from a
54
ELECTRIC LIGHTING
single candle-power unit is .25 foot-candles. For further con-
sideration of the law of inverse squares, see "Photometry."
Illumination may be classified as use/lit when used for the
ordinary purposes of furnishing light for carrying on work, taking
the place of daylight; and scenic when used for decorative lighting
such as stage lighting, etc. The two divisions are not, as a rule,
distinct, but the one is combined with the other.
Intrinsic Brightness. By intrinsic brightness is meant the
amount of light emitted per uirt surface of the light source. Table
XII gives the intrinsic brightness of several light sources.
TABLE XII
Intrinsic Brilliancies in Candle-Power per Square Inch
SOURCE
BRILLIANCY
NOTES
Sun in zenith
600,000 )
Sun at 30 degrees elv.
500,000
Rough equivalent values, tak-
Sun on horizon
2,000 )
ing account of absorption
10,000)
Arc light
to [
Maximum about 200,000 in
100,000 )
crater
Calcium light
5,000
Nernst "glower"
1,000
Unshaded
Incandescent lamp
200-300
Depending on efficiency
Enclosed arc
75-100
Opalescent inner globe
Acetylene flame
75-100
Welsbach light
20 to 25
Kerosene light
4 to 8
Variable
Candle
3 to 4
Gas flame
3 to 8
Variable
Incandescent (frosted)
2 to 5
Opal shaded lamps, etc.
0.5 to 2
Regular Reflection. Regular reflection is the term applied to
reflection of light when the reflected rays are parallel. It is of such
a nature that the image of the light source is seen in the reflection.
The reflection from a plane mirror is an example of this. It is useful
in lighting in that the direction of light may be changed without com-
plicating calculations aside from deductions necessary to compensate
for the small amount of light absorbed.
Irregular Reflection. Irregular reflection, or diffusion, consists
of reflection in which the reflected rays of light are not parallel but
take various directions, thus destroying the image of the light source.
Rough, unpolished surfaces give such reflection. Smooth, unpolished
surfaces generally give a combination of two kinds of reflection.
ELECTRIC LIGHTING 55
Diffused reflection is very important in the study of illumination
inasmuch as diffused light plays an important part in the lighting of
interiors. This form of reflection is seen in many photometer screens.
Light is also diffused when passing through semi-transparent shades
or screens.
In considering reflected light, we find that, if the surface on
which the light falls is colored, the reflected light may be changed in
its nature by the absorption of some of the colors. Since, as has been
said, in interior lighting the reflected light forms a large part of the
source of illumination, this illumination will depend upon the nature
and the color of the reflecting surfaces.
Whenever light is reflected from a surface, either by direct or
diffused reflection, a certain amount of light is absorbed by the surface.
Table XIII gives the amount of white light reflected from different
materials.
TABLE XIII
Relative Reflecting Power
MATERIAL
White blotting paper
White cartridge paper
Chrome yellow paper
Orange paper
Yellow wall paper
Light pink paper
Yellow cardboard
Light blue cardboard
Emerald green paper
Dark brown paper
Vermilion paper
Blue-green paper
Black paper
Black cloth
Black velvet
82
80
62
50
40
36
30
25
18
13
12
12
5
1.2
From this table it is seen that the light-colored papers reflect the
light well, but of the darker colors only yellow has a comparatively
high coefficient of reflection. Black velvet has the lowest value, but
this only holds when the material is free from dust. Rooms with
dark walls require a greater amount of illuminating power, as will be
seen later.
Useful illumination may be considered under the following
heads:
56 ELECTRIC LIGHTING
1. Residence Lighting.
2. Lighting of Public Halls, Offices, Drafting Rooms, Shops, etc.
3. Street Lighting.
RESIDENCE LIGHTING
Type of Lamps. The lamps used for this class of lighting are
limited to the less powerful units namely, incandescent or Nernst
lamps varying in candle-power from 8 to 50 per unit. These should
always be shaded so as to keep the intrinsic brightness low. The
intrinsic brilliancy should seldom exceed 2 to 3 candle-power per
square inch, and its reduction is usually accomplished by appropriate
shading. Arc lights are so powerful as to be uneconomical for
small rooms, while the color of the mercury-vapor light is an additional
objection to its use.
Plan of Illumination. Lamps may be selected and so located
as to give a brilliant and fairly uniform illumination in a room; but this
is an uneconomical scheme, and the one more commonly employed
is to furnish a uniform, though comparatively weak, ground illumi-
nation, and to reinforce this at points where it is necessary or desirable.
The latter plan is satisfactory in almost all cases and the more eco-
nomical of the two.
While the use of units of different power is to be recommended,
where desirable, lights differing in color should not be used for lighting
the same room. As an exaggerated case, the use of arc with incan-
descent lamps might be mentioned. The arcs being so much whiter
than the incandescent lamps, the latter appear distinctly yellow when
the two are viewed at the same time.
Calculation of Illumination. Jn determining the value of illumi-
nation, not only the candle-power of the units, but the amount of re-
flected light must be considered for the given location of the lamps.
Following is a formula based on the coefficient of reflection of the
walls of the room, which serves for preliminary calculations:
d*
I = Illumination in foot-candles.
c.p. = Candle-power of the unit.
Jc = Coefficient of reflection of the walls.
d = distance from the unit in feet.
ELECTRIC LIGHTING 57
Where several units of the same candle-power are used this
formula becomes:
> ( 1
d 2 d 2 t d 2 ^ I - k
c.p. j p
( -77- 4~ 79 + ~~TT ~f~
1- k
where d, d v d v etc., equal the distances from the point considered to
the various light sources. If the lamps are of different candle-power,
the illumination, may be determined by combining the illumination
from each source as calculated separately. An example of calculation
is given under "Arrangement of Lamps."
The above method is not strictly accurate because it does not
take account of the angle at which the light from each one of the
sources strikes the assumed plane of illumination. If the ray of
C T)
light is perpendicular to the plane, the formula I = ^ gives cor-
rect values. If a is the angle which the ray of light makes with a line
drawn from the light source perpendicular to the assumed plane,
then the formula becomes I = C + X %*** ' Therefore, by
or
multiplying the candle-power value of each light source in the direc-
tion of the illuminated point by the cosine of each angle a, a more
accurate result will be obtained.
It is readily seen that the effect of reflected light from the ceilings
is of more importance than that from the floor of a room. The value
of k, in the above formula, will vary from 60% to 10%, but for rooms
with a fairly light finish 50% may be taken as a good average value.
The amount of illumination will depend on the use to be made of
the room. One foot-candle gives sufficient illumination for easy
reading, when measured normal to the page, and probably an illumi-
nation of .5 foot-candle on a plane 3 feet from the floor forms a suffi-
cient ground illumination. The illumination from sunlight reflected
from white clouds is from 20 foot-candles up, while that due to moon-
light is in the neighborhood of .03 foot-candles. It is not possible to
produce artificially a light equivalent to daylight on account of the
58 ELECTRIC LIGHTING
great amount of energy that would be required and the difficulty of
obtaining proper diffusion.
The method of calculating the illumination of a room that has
just been described is known as the point-by-point method and it
gives very accurate results if account is taken of the angle at which
the light from each source strikes the plane of illumination and if
the light distribution curves of the units, and the value of k, have been
carefully determined. Under these conditions the calculations be-
come extended and complicated and methods only approximate, but
simpler in their application, are being introduced. One method,
which gives good results when applied to fairly large interiors, makes
the flux of light from the light sources the basis of calculation of the
average illumination.
Flux of light is measured in lumens and a lumen may be defined
as the amount of light which must fall on one square foot of surface
in order to produce a uniform illumination of an intensity of one foot-
candle. A source of light giving one candle-power in every direction
and placed at the center of a sphere of one foot radius would give an
illumination of one foot-candle at every point in the surface of the
sphere and the total flux of light would be 4?r, or 12.57, lumens since
the area of the sphere would be 4?r, or 12.57, sq. ft. A lamp giving
one mean spherical candle-power gives a flux of 12.57 lumens and
the total flux of light from any source is obtained by multiplying its
mean spherical candle-power by 12.57. In calculating illumination
it is customary to determine the illumination on a plane about 30
inches from the floor for desk work, and about 42 inches from the
floor for the display of goods on counters. If we determine the total
number of lumens falling on this plane and divide this number by
the area of the plane, we obtain the average illumination in foot-
candles. This of course tells us nothing about the maximum or
minimum value of the illumination and such values must be obtained
by other methods if they are desired. Reflected light, other than that
covered by the distribution curve of the light unit including its re-
flector, is usually neglected in this method of calculation.
We may assume that in large rooms the light coming from the
lamp within an angle of 75 degrees from the vertical reaches the plane
of illumination. In smaller rooms this angle should be reduced to
about 60 degrees. In order to determine the flux of light within this
ELECTRIC LIGHTING 59
angle a Rousseau diagram, which is described later, should be drawn.
By the means of this diagram the average candle-power of the light
source within the angle assumed may be readily determined and this
mean value, multiplied by 12.57, will give the flux of light in lumens.
This method of calculation, together with some guides for its rapid
application, is described by Messrs. Cravath and Lansingh in the
"Transactions of the Illuminating Engineering Society, 1908." The
same authorities give the following useful data:
To determine the watts required per square foot of floor area,
multiply the intensity of illumination desired by the constants given
as follows:
INTENSITY CONSTANTS FOR INCANDESCENT LAMPS
Tungsten lamps rated at 1.25 watts per horizontal candle-power; clear
prismatic reflectors, either bowl or concentrating; large room; light
ceiling; dark walls; lamps pendant; height from 8 to 15 feet .25
Same with very light walls 20
Tungsten lamps rated at 1.25 watts per horizontal candle-power; pris-
matic bowl reflectors enameled; large room; light ceiling; dark
walls; lamps pendant, height from 8 to 15 feet .29
Same with very light walls 23
Gem lamps rated at 2.5 watts per horizontal candle-power; clear pris-
matic reflectors either concentrating or bowl; large room; light
ceiling; dark walls; lamps pendant; height from 8 to 15 feet 55
Same with very light walls 45
Carbon filament lamps rated at 3.1 watts per horizontal candle-power;
clear prismatic reflectors either bowl or concentrating; light ceiling;
dark walls; large room; lamps pendant; height from 8 to 15 feet. . .65
Same with very light walls 55
Bare carbon filament lamps rated at 3.1 watts per horizontal candle-
power; no reflectors; large room; very light ceiling and walls;
height from 10 to 14 feet .75 to 1.5
Same; small room; medium walls 1 .25 to 2.0
Carbon filament lamps rated at 3.1 watts per horizontal candle-power;
opal dome or opal cone reflectors; light ceiling; dark walls; large
room; lamps pendant; height from 8 to 15 feet 70
Same with light walls 60
INTENSITY CONSTANTS FOR ARC LAMPS
5-ampere, enclosed, direct-current arc on 110-volt circuit; clear inner,
opal outer globe; no reflector; large room; light ceiling; medium
walls; height from 9 to 14 feet 50
Arrangement of Lamps. An arrangement of lamps giving a
uniform illumination cannot be well applied to residences on account
of the number of units required, and the inartistic effect. We are
60
ELECTRIC LIGHTING
limited to chandeliers, side lights, or ceiling lights, in the majority
of cases, with table or reading lamps for special illumination.
When ceiling lamps are used and the ceilings are high, some
form of reflector or reflector lamp is to be recommended. In any
case where the coefficient of reflection of the
I ceilings is less than 40%, it is more economical
to use reflectors. When lamps are mounted
on chandeliers, the illumination is far from
uniform, being a maximum in the neighbor-
hood of the chandelier and a minimum at the
corners of the room. By combining chande-
liers with side lights it is generally possible to
I ro e ^ a satisfactory arrangement of lighting for
J small or medium-sized rooms.
<v| As a check on the candle-power in lamps
I . . require^ we have the following :
I *^
* *' T For brilliant illumination allow one candle-
6'-
Fig. 53. Diagram Showing P ower P er two square feet of floor space. In some
Method of Calculating particular cases, such as ball rooms, this may be
Room Illumination. increased to one candle-power per square foot.
For general illumination allow one candle-power
for four square feet of floor space, and strengthen this illumination with the
aid of special lamps as required. The location of lamps and the height of
ceilings will modify these figures to some extent.
As an example of the calculation of the illu- y
mination of a room with different arrangements
of the units of light, assume a room 16 feet |
square, 12 feet high, and with walls having a S
coefficient of reflection of 50%. Consider first
the illumination on a plane 3 feet above the
floor when lighted by a single group of lights
mounted at the center of the room 3 feet below
the ceiling. If a minimum value of .5 foot-
candle is required at the corner of the room,
we have the equation (first method outlined) :
.5 = c. v. ^^ X
12.8 2
1 - .5
Since d =i/8 2 + 8 2 + 6 2
Fig. 53)
= 12.8 (see
f ^ m m s f r n Four
'side Vail.
ELECTRIC LIGHTING
Solving the above for the value of c. p., we have
c. p. =- - ' 5 .5 X 82 == 41
^
.5
Three 16-candle-power lamps would serve this purpose very
well.
Determining the illumination directly under the lamp, we have:
I = 48 X ~ X - ^r- = |J X 2 =
6 2 1 - .5 36
2.7 foot-candles, or five times the value of the illumination at the
corners of the room.
Next consider four 8-candle-power lamps located on the side
walls 8 feet above the floor, as shown in Fig. 54. Calculating the
illumination at the center of the room on a plane three feet above
the floor, we have:
T
N
1 - .
89 89 89 89 1 - .5
ft = 8 2 + 5 2 = 64 + 25 - 89
I = 8 X -- X 2 = .72 foot-candles
Ot/
The illumination at the corner of the room would be:
\ on on o A e o/ic '
89 89 345 345 ' 1 - .5
) X 2 = .45 foot-candles.
In a similar manner the illumination may be calculated for any
point in the room, or a series of points may be taken and curves plotted
showing the distribution of the light, as well as the areas having the
same illumination. Where refined calculations are desired, the dis-
tribution curve of the lamp must be used for determining the candle-
power in different directions. Fig. 55 shows illumination curves for
the Meridian lamp as manufactured by the General Electric Com-
pany. This is a form of reflector lamp made in two sizes, 25 or 50
candle-power. Fig. 56 gives the distribution curves for the 50-
candle-power unit. Similar incandescent lamps are now being
manufactured by other companies.
ELECTRIC LIGHTING
Table XIV gives desirable data in connection with the u^ of
the Meridian lamp.
Fig. 55. Illumination Curves for a G. E. Meridian Lamp.
TABLE XIV
Illuminating Data for Meridian Lamps
No. 1 Lamp (60 Watts) No 2 Lamp(120 Watts)
Class Service
Light
Intensity
in Foot-
candles
Height of
Lamp and
Diameter
of Uni-
formly
Lighted
Distance
between
Lamps
when Two
or more
are Used
Height of
Lamp and
Diameter
of Uni-
formly
Lighted
Distance
between
Lamps
when Two
or more
are Used
per Sq. Ft.
of Area
Lighted
with
either
Lamp
Desk or Reading
Tnhlp
3
2
2.9 feet
3.5
4 . 9 feet
6
4 feet
5
7 feet
8.5 '
2.50
1.66
1?
4
7 "
5.75 '
9.8 '
1.25
1
5
8.5 "
7
12
0.83
General Lighting
1
5.75
9.8 "
8.2 '
13.9 '
0.62
I
7
12
10
11
0.41
By means of the Weber, or some other form of portable photom-
ete*, carves as plotted from calculations may be readily checked
after the lamps are installed. When lamps are to be permanently
located, the question of illumination becomes an important one, and
it may be desirable to determine, by calculation, the illumination
curves for each room before installing the lamps. This applies to
the lighting of large interiors more particularly than to residence
lighting. The point-by-point method of calculation is used for
ELECTRIC LIGHTING
63
very accurate work when the system of illumination admits of this
method. Other methods are often simpler and sufficiently accurate
for practical work.
no
30 20 10 10 20 30
Fig. 56. Distribution Curve for a G. E. 50-c. p. Meridian Lamp.
Dr. Louis Bell gives the following in connection with residence
lighting:
TABLE XV
Residence Lighting Data
ROOM
8
C. P.
16
C. P.
32
C.P.
SQ. FT.
PER C.P.
REMARKS
Hall, 15' X 20'
Library 20' X 20'
8
12
1
4.7
*5 1
8-c p reflector lamps
Reception room, 15' X 15' ..
Music room, 20' X 25'
Dining room, 15' X 20'
Billiard room, 15' X 20'
p orc h
4
12
14
2
4
1
7.0
3.0
2.7
2.3
8 reflector lamps
32-c.p.with reflectors
Bedrooms (6), 15' X 15'
Dressing rooms (2), 10' X 15'.
Servants' rooms (3), 10' X15'
Bathrooms (3), 8' X 10'
Kitchen, 15' X 15' )
14
4
3
3
3
7.0
4.7
9.4
5.0
Pantry, 10' X 15' f '
Halls )
10
3
Cellar f
Closets (4)
4
Reflector lamps
Total
64
30
8
^64 ELECTRIC LIGHTING
LIGHTING OF PUBLIC HALLS, OFFICES, ETC.
Lighting of public halls and other large interiors differs from the
illumination of residences in that there is usually less reflected light,
and, again, the distance of the light sources from the plane of illumi-
nation is generally greater if an artistic arrangement of the lights is
to be brought about. This in turn reduces the direct illumination.
The primary object is, however, as in residence lighting, to produce
a fairly uniform ground illumination and to superimpose a stronger
illumination where necessary. An illumination of .5 foot-candle for
the ground illumination may be taken as a minimum.
In the lighting of large rooms it is permissible to use larger light
units, such as arc lamps and high candle-power Nernst or incan-
descent units, while for factory lighting and drafting rooms, where
the color of the light is not so essential, the Cooper-Hewitt lamp is
being introduced. High candle-power reflector lamps, such as the
tungsten lamp, are being used to a large extent for offices and drafting
rooms.
The choice of the type of lamp depends on the nature of the
work. Where the light must be steady, incandescent or Nernst
lamps are to be preferred to the arc or vapor lamps, though the latter
are often the more efficient. When arcs are used, they must be care-
fully shaded so as to diffuse the light, doing away with the strong
shadows due to portions of the lamp mechanism, and to reduce the
intrinsic brightness. Such shading will be taken up under the head-
ing " Shades and Reflectors." Arcs are sometimes preferable to
incandescent lamps when colored objects are to be illuminated, as in
stores and display windows.
In locating lamps for this class of lighting, much depends on the
nature of the building and on the degree of economy to be observed.
For preliminary determination of the location of groups, or the illumi-
nation when certain arrangement of the units is assumed, the prin-
ciples outlined under "Residence Lighting" may be applied. It has
been found that actual measurements show results approximating
closely such calculated values.
When arcs are used they should be placed fairly high, twenty
to twenty-five feet when used for general illumination and the ceilings
are high. They should be supplied with reflectors so as to utilize
the light ordinarily thrown upwards. When used for drafting-room
ELECTRIC LIGHTING
65
work, they should be suspended from twelve to fifteen feet above
the floor, and special care must be taken to diffuse the light.
Incandescent lamps may be arranged in groups, either as side
lights or mounted on chandeliers, or they may be arranged as a frieze
running around the room a few feet below the ceiling. The last
named arrangement of lights is one that may be made artistic, but it
is uneconomical and when used should serve for the ground illumina-
tion only. Reflector lights may be used for this style of work and
the lights may be entirely concealed from view, the reflecting prop-
erty of the walls being utilized for distributing the light where needed.
Ceiling lights should preferably be supplied with reflectors,
especially when the ceilings are high.
Indirect lighting is employed to some extent. By indirect
lighting \ve mean a system af illumination in which the light sources
are concealed and the light from them is reflected to the room by the
walls, or ceilings, or other surfaces; or in which the light sources are
placed above a diffusing panel. In the latter case the diffusing plate
appears to be the source of light. In some cases the walls themselves
are shaped and constructed so as to form the reflectors for the light
units (cove lighting), but in others all of the reflecting surfaces, except
the side walls and ceiling, are made portions of the lamp fixtures.
Tables XVI and XVII give data on arc and mercury-vapor
lamps for lighting large rooms. Table XVII refers to arc lights as
aerially installed.
TABLE XVI
Cooper=Hewitt Lamps
SERVICE
HEIGHT OF LAMP
C. P. OF UNIT
Av. AREA PER LAMP
IN SQUARE FEET
Foundry
10-15 ft.
300
900
20-25
700
2250
Machine shop
10-15
300
500
Erecting shop
Drafting room
20-30
15
700
300
1250
300
(i
20
700
400
Offices
10-15
300
400
20-25
700
750
< Vdinary labor
10-15
300
1100
' a
20-25
700
2750
66
ELECTRIC LIGHTING
K a
pj
W
I:
8
00 CO
8 38
o*
11
P
o 10
-O<N ^H
E
->1
Si
-3 d
03 ^
JS
bJC
C
8
O01 CO
.-H ^HCOCO
3 . ^
|^^ :
3 ^ :
<N
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fi :
,o5
{ H 1-1
S
OTH
TO
<N . O
a :
rt c3
: -8 :
a -a
:.* i
ELECTRIC LIGHTING 67
Measurements taken in well-lighted rooms having a floor space
of from 1,000 to 5,000 square feet show an average of 3 to 3.5 square
feet per candle-power. About 2.5 square feet per candle-power
should be allowed when brilliant lighting is required or the ceilings
are very high, while 3.75 square feet per candle-power will give good
illumination when lights are well distributed and there is considerable
reflected light.
In factory and drafting room lighting, the lamps must be arranged
to give a strong light where most needed, and located to prevent such
shadows as would interfere with the work.
STREET LIGHTING
In studying the lighting of streets and parks, we find that, except
in special cases, such as narrow streets and high buildings, there is
no reflected light which aids the illumination aside from that due to
special shades or reflectors on the lamp itself. Such reflectors are
necessary if the light ordinarily thrown above the horizontal plane is
to be utilized.
In calculating the illumination due to any type of lamp at a given
point it is necessary to know the distribution curve of the lamp used
and the distance to the point illuminated. The approximate illumi-
nation of a plane normal to the rays of light is given by the formula,
_ _ c.p.
h 2 + d 2
when I = illumination in foot-candles.
c.p. = candle-power of the unit, determined from the distri-
bution curve of the lamp.
h = distance the, lamp is mounted above the ground, in feet,
and d = distance from the base of
the pole supporting the lamp to the
point where the illumination is being
considered, Fig. 57.
While this will give the illumi-
nation in foot-candles, the nature of Fi &- 57 - street Li ^ ht illumination
Diagram.
the lighting cannot be decided from
this alone, but the total amount of light must also be considered.
Thus, a street lighted with powerful units and giving a minimum
68
ELECTRIC LIGHTING
Fig. 58.
Ideal Distribution Curve for a Street
Light.
illumination of .05 foot-candles would be considered better illumi-
nated than one having smaller units so distributed as to give the
same minimum value. . \
* \ A
Since a uniform distribu-
tion of light is desirable, for
economic reasons, the ideal
distribution curve of a lamp
for street lighting would be a
curve which shows a low value
of candle-power thrown di-
rectly downward, but with the
candle-power increasing as we
approach the horizon tal . Su ch
an ideal distribution curve is shown in Fig. 58.
Actual distribution curves taken from commercial arc lamps are
given in Fig. 59, in which
Curve A shows distribu-
tion curve for a 9.6-ampere,
gQ 50 40 30<s open, direct-current arc.
Curve B shows distribu-
tion curve for a 6.6-ampere,
D.C. enclosed arc
Curve C shows distribu-
tion curve for a 7.5-ampere,
A.C. enclosed arc.
Globes used with B and
C are opal inner globes,
clear outer globes.
Globes used with A are
clear outer globes.
A street reflector was
used with the enclosed arcs.
Typical curves for
flaming and luminous
arc lamps are shown in
Figs. 40, 43, and 44.
A series of curves
known as illumination
curves may be readily
calculated showing the
illumination in foot-
Distribution Curves for Commercial Arc ,, . ,.
Lamps Used in street Lighting. candles at given distance
10
30
1300
Fig. 59.
ELECTRIC LIGHTING
69
from the foot of the pole supporting the lamp. Illumination curves
corresponding to the distribution curves in Fig. 59 are given in Fig. 60
where A', B f , andC" correspond to A, B, and C in Fig. 59. These
curves correspond to actual readings taken with commercial lamps.
Similar curves for incandescent lamps fitted with suitable reflectors
are shown in Fig. 61. A value o e .03 foot-candles is about the min-
Fig. 60. Illumination Curves Drawn to Data given in Fig. 59.
imum for street lighting. Open arcs should be placed at least 25 feet
above the ground; 30 to 40 feet is better, especially if the space to be
illuminated is quite open. With enclosed arcs it is often advan-
tageous to place them as low as 18 to 20 feet from the ground.
Table XVIII gives the distance between lights for different types
of arcs for fair illumination.
In considering the type of arc light to be used we must turn to
the illumination curves as shown in Fig. 60. These curves show that
the illumination from a direct-current open arc in its present form
is superior to that from a direct-current enclosed arc, taking the
70
ELECTRIC LIGHTING
TABLE XVIII
DISTANCE
KIND OF LIGHT
BETWEEN
LIGHTS PEK
LIGHTS
MILE
6.6-ampere enclosed D.C. arc
340 feet
15
9.6-ampere open D.C. arc
6.6-ampere enclosed A C. arc
315 "
275 "
17
19
6.6-ampere open D.C arc
260 "
20
same amount of power, in the vicinity of the pole; but at a distance of
100 feet, the illumination from the enclosed arc is better. This
illumination is still more effective on
account of the absence of such strong
light as is given by the open arc near
the pole. The pupil of the eye adjusts
itself to correspond to the brightest
40' so- cor light in the field of vision, and we are
unable to see as well in the dimly-
Fig. 61. Illumination Curves for r , , -, , i ,1
street incandescent Lamps. lighted section as when the maximum
intensity is less. The characteristics
of the open and enclosed direct-current arc lamps are as follows:
The mean spherical candle-power and energy required at the arc are
variable with the open arc.
Fluctuations of light are marked, due to wandering of the arc, flickering
due to the wind and lack of uniformity of the carbons.
Dense shadows are cast by the side rods and the lower carbon, while the
light is objectionably strong in the vicinity of the pole.
With the enclosed arc the mean spherical candle-power and the watts
consumed at the arc are fairly constant.
No shadows are cast by the lamps, and the illumination is not subject to
such wide variations. The enclosed arc is much superior to the open arc using
the same amount of energy. This applies to the open arc as it is now used.
With proper reflection and diffusion of the light such as might be accomplished
by extensive or special shading, we ought to be able to get as good distribution
from the open arc with a greater total amount of illumination.
In comparing the direct-current with the alternating-current
enclosed arc, we see that the direct-current arc gives slightly more light
than the alternating lamp, but this may be more than counterbalanced
by the better distribution of light from the alternating-current lamp.
The selection of A.C. or D.C. enclosed lamps will usually depend on
other conditions, such as method of distribution of power, efficient
of plant, etc.
ELECTRIC LIGHTING
71
TABLE XIX
Street- Lamp Data
APPROX.
APPROX.
LAMP
AMPERES
WATTS AT
LAMP
VALUE op
X AS
TERMINALS
PROPOSED
D. C. Series, open arc, clear globe
J6.6
{9.6
330
450
3.5
4
D, C. Series, enclosed, clear outer globe
J5.0
]6.6
370
480
3.5
4
(5.5
345
3
Opalescent inner globe, street reflectors
J6.6
430
3.5
A. C. Series as above
(7.5
480
4
D. C. Series "Magnetite"
4.0
310
5.5
The question of street lighting has been given considerable
attention by the National Electric Light Association and this society
recommends the following form of specification for street lights:
1. Under ordinary conditions of street lighting, with lamps spaced 200
to 600 feet apart, specifications for street lamps should define the mean illumi-
nation thrown by the individual lamp, in position in the street, as measured at
the height of the observer's eye and perpendicular to the rays, at some point
not less than 200 feet nor more than 300 feet distant, along a level street, from
a position immediately below the lamp, with all extraneous light screened off
and with no reflection from surrounding objects not forming part of the lamp
equipment.
2. When using smaller units of light, such as series incandescent lamps
spaced shorter distances apart, a correspondingly shorter distance from the
lamp should be chosen in measuring the illumination.
3. The lamp contracted for should give a mean normal illumination at
the test point (selected as in Sections 1 and 2) not less than the illumination
given by the stationary standard incandescent lamp of 16 candle-power at 1/X
of the distance. The said standard incandescent lamp should be a stand-
ardized seasoned lamp having a determined candle-power in a fixed direction.
4. When the lamp tested fluctuates in intensity, a number of observa-
tions of the maximum normal illumination should be made at a distance of not
less than 200 feet horizontally from beneath the lamp, and the average of these
measurements should be taken as the average maximum illumination. A
similar number of observations of the minimum normal illumination should be
made, the average of which should be taken as the average minimum illumi-
nation. The arithmetical mean of the said average maximum and minimum
illuminations should be taken as the mean normal illumination called for in
Section 1.
5. A reasonable number of the lamps covered by the contract should
be tested.
6. For measuring the mean normal illumination of a lamp, comparison
with the standard incandescent lamp may be made either with a suitable portable
72 ELECTRIC LIGHTING
photometer or with a reading distance instrument, such as the so-called lumi-
nometer.
7. The unobstructed mean normal illumination must not be less at
shorter distances than at the point of test.
8. An approximate value of the mean normal illuminations thrown by
street lamps of standard manufacture, at horizontal distances within the 200-
300-foot range, hung approximately 20 feet above the observer's eye, may be
determined from Table XIX.
Series incandescent lamps are used considerably for lighting
the streets in residence sections of cities or where shade trees make
it impracticable to use arcs. These vary in candle-power from 16
to 50 or even higher, and are usually constructed so as to take from
two to four amperes. The best arrangement of these is to mount
them on brackets a few feet from the curb, with alternate lamps on
opposite sides of the street. The distance between the lamps depends
on their power. 50 candle-power lamps spaced 100 feet between
lamps, give a minimum illumination of .02 foot-candle. 25 candle-
power lamps spaced 75 feet between lamps will serve where economy
is necessary.
TABLE XX
PER CENT
Clear glass
10
Alabaster glass
15
Opaline glass
20-40
25-30
Opal glass
25-60
Milkv glass
30-60
Ground glass
24 4
Opal glass
32 2
Opaline glass ...
23
SHADES AND REFLECTORS
Lamps, as ordinarily constructed, do not always give a suitable
distribution of light, while the intrinsic brightness is often too high
for interior lighting. Shades are intended to modify the intensity
of the light, while reflectors are used for the purpose of changing its
direction. Frequently the two are combined in various ways. Shades
are also used for decorative purposes, but, if possible, these should
be of such a nature as to aid illumination rather than to reduce its
efficiency.
ELECTRIC LIGHTING
73
A considerable amount of light is absorbed by the material used
for the construction of shades. Table XX shows the approximate
amount absorbed by some materials.
Of the great number of styles of shades
and reflectors in use, only a few of the more
important will be considered here.
Frosted Globes. One of the simplest
methods of shading incandescent lamps is by
the use of frosted bulbs. These serve to
reduce the intrinsic brightness of the lamp, and
should be freely used for residence lighting
when separate shades are not installed. Frosted
globes are also used in connection with reflec-
tors for the purpose of diffusing the reflected
light. The McCreary shade as shown in Fig.
62, is an example of such a combined shade
and reflector. Fig. 63 shows the distribution Fig 62 Mc creary Shade,
curve taken from an incandescent lamp using
a McCreary shade. Fig. 64 shows the distribution of light from a con-
ical shade. Fig. 56 shows the distribution of light brought about by
means of a spiral filament and a reflector as used in the Meridian lamp.
4-C5 C.P.
Fig. 63. Distribution Curve for Incan-
descent Lamp Provided with
McCreary Shade.
Fig. 64. Distribution Curve for Incan-
descent Lamp Provided with
Conical Shade.
74 ELECTRIC LIGHTING
Holophane Globes. These are made for both reflecting and
diffusing the light, and they can be made to bring about almost any
desired distribution with but a small amount of absorption of light.
These consist of shades of clear glass having horizontal grooves
forming surfaces which change the direction of light by refraction or
total reflection as is necessary. The diffusion of light is effected by
means of deep, rounded, vertical grooves on the interior surface of
the globe. While these globes are of clear glass and absorb an amount
of light corresponding to clear glass, the light is so well diffused that
the filament of the lamp cannot be seen, and the globe appears as if
Fig. 65. Enclosed Arc Lamp Fitted with Shade and Concentric Diffuser.
made of some semi-transparent material. The holophane glassware
is made in a large variety of artistic designs and for all types of in-
candescent lamps. By the proper selection of a reflector the dis-
tribution of the light of the unit used may be made that which is best
suited to the particular case of lighting in hand. Figs. 9, 13, 14,
15, 16, 17, and 18 give some idea of what can be accomplished by these
shades.
Fig. 65 shows an enclosed arc lamp fitted with a shade and a
concentric diffuser. The effect of this combination is best shown
in Fig. 66. Fig. 67 shows the change in the illumination curve pro-
.duced by such shading. Inverted arcs have some application where
ELECTRIC LIGHTING
75
Fig. 66. Diagram Showing Effect of the Concentric Diffuser.
the light may be readily reflected and diffused as in lighting large
rooms with light finish. Reflectors of this general type are now being
manufactured in such a form that they may be built in and become
part of the ceiling of the room to be illuminated.
LAMPS WITH OPAL GLASS SHADES.
LAMPS WITH CONCENTRIC LIGHT DIFFUSERS.
Fig. 67. Illumination Curves for Lamps \rithand without Light Diffusers.
76 ELECTRIC LIGHTING
Opal Enclosing Globes. The use of opal enclosing globes is
recommended for arc lamps used for street lighting for the reason
that they change the distribution of the light so that it covers a greater
area, and the light is so diffused as to obliterate shadows in the vicinity
of the lamp. Table XXI gives the efficiency of different globe com-
binations for street lighting assuming the opal inner and the clear
outer globes as 100%.
TABLE XXI
O pal enclosing and clear outer
Clear " " clear " .
" opal " .
Opal " " opal " .
100 per cent
91.2
85.1
82.7
PHOTOMETRY
Photometry is the art of comparing the illuminating properties
of light sources, and forms one branch of scientific measurement.
Its use in electric illumination is to determine the relative values of
different types of lamps as sources of illumination, together with their
efficiency; also by means of the principles of photometry, we are able
to study the distribution of illumination for any given arrangement
of light sources.
LIGHT STANDARDS
Inasmuch as sources of light are compared with one another in
photometry, we must have some standard, or unit, to which all light
sources are reduced. This unit is usually the candle-power and the
rating of most lamps is given in candle-power.
While the candle-power remains the unit and is based on the
standard English candle, other light standards have been introduced
and are much more desirable.
The English Candle. The English candle is made of spermaceti
extracted from crude sperm oil, with the addition of a small quantity
of beeswax to reduce the brittleness. Its length is ten inches, and its
diameter .9 inch at the bottom and .8 inch at the top, and its weight
is one-sixth of a pound. Great care is taken in the preparation of
the wick and spermaceti. This candle burns with a normal height
of flame of 45 millimeters and consumes 120 grains per hour when
ELECTRIC LIGHTING 77
burning in dry air at normal atmospheric pressure. Under these
conditions, the light given by a single candle is one candle-power.
When used for measurements, the candle should be allowed to
burn at least fifteen minutes before taking any readings. At the end
of this period the wick should be trimmed, if necessary, and when the
flame height reaches 45 millimeters, readings can be taken. The
candle should not require trimming when the proper height of flame
has been reached. It is best to weigh the amount of material con-
sumed by balancing the candle on a properly arranged balance when
the first reading is taken, and again balancing at the end of a suitable
period ten to fifteen minutes. The candle-power of the unit is
then, practically, directly proportional to the amount of the material
consumed.
The objections to the candle as a unit are that it burns with an
open flame which is subject to variation in height and to the effect of
air currents. The color of the light is not satisfactory, being too
rich in the red rays, and the composition of the spermaceti is more or
less uncertain.
The German Candle is made of very pure paraffine, burns
with a normal flame height of 50 millimeters, and is subject to the
same disadvantages as the English candle. It may be necessary to
trim the wick to keep the flame height at 50 millimeters. The light
given is a trifle greater than for the spermaceti candle.
The Carcel Lamp is built according to very careful specifications
and burns colza (rape seed) oil. It has been used to a large extent
in France, but its present application is limited.
The Pentane Lamp is a specially constructed lamp burning
pentane, prepared by the distillation of gasoline between narrow
limits of temperature. This standard is not extensively used.
The Amyl Acetate Lamp. This lamp, known also as the Hefner
lamp, is at present the most desirable standard. It is a lamp built
to very careful specifications, especially with regard to the dimension
of the wick tube. It burns pure amyl acetate and the flame height
should be 40 millimeters. This flame height must be very carefully
adjusted by means of gauges furnished with the lamp. Amyl acetate
is a colorless hydrocarbon prepared from the distillation of amyl
alcohol obtained from fusel oil, with a mixture of acetic and sulphuric
acids, or by distillation of a mixture of amyl acetate, sulphuric acid,
78
ELECTRIC LIGHTING
and potassium acetate. It has a definite composition, and must be
pure for this use.
The most serious disadvantage of this standard is the color of
the light, inasmuch as it has a decidedly red tinge and is not readily
compared with whiter lights. Its value is affected somewhat by the
moisture in the air and the atmospheric pressure, but it excels all other
standards in that it is quite readily reproduced.
Table XXII gives the value of the candle-power units of different
laboratories in terms of the unit of the Bureau of Standards and also
the values of the units of the Carcel and Vernon-Harcourt in terms of
the Hefner, as accepted by the International Photometric Commission.
TABLE XXII
Photometric Units
Bureau of Standards Unit, United" States
1.000
Reichsanstalt Unit, Germany
0.998
X 0.88
National Physical Laboratory Unit, England
0.984
Laboratoire Central Unit, France
0.982
CARCEL
HEFNER
VERNON-
HARCOURT
Carcel
Hefner
Vernon-Harcourt (pentane)
1.00
0.0930
1.020
10.75
1.00
10.95
0.980
0.0915
1.0
The above values are at a barometric pressure of 760 mm. of mercury and a humid-
ity for the Carcel and Vernon-Harcourt standards of 10.0 liters of water per cubic meter
of dry air. The humidity for the hefner unit is 8.8 liters of water to one cubic meter
of dry air.
Working Standards. Incandescent Lamp. The units just de-
scribed, together with some others, form reference standards, but an
incandescent lamp is generally used as the working standard in all
photometers. An incandescent lamp, when used for this work, should
be burned for about two hundred hours, or until it has reached the
point in the life curve where its value is constant, and it should then
be checked by means of some standard when in a given position and
at a fixed voltage. It then serves as an admirable working standard
if the applied voltage is carefully regulated. Two such lamps should
always be used the one to serve as a check on the other; the checking
lamp to be used for very short intervals only.
ELECTRIC LIGHTING
79
PHOTOMETERS
Two light sources are compared by means of a photometer
which; in one of its simplest forms, consists of what is known as a
Bunsen screen mounted on a carriage between the two lights being
compared, with its plane at right angles to a line passing through
the light sources, and arranged with mirrors or prisms so that both
sides of the screen may be observed at once. The Bunsen screen
consists of a disk of paper with a portion of either the center, or a
section around the center, treated with paraffine so as to render it
translucent. If the light falling on one side of this screen is in ex-
cess, the translucent spot will appear dark on that side of the screen
and light on the opposite side.
Care must be taken to see that
the two sides of the screen are
exactly alike, otherwise there will
be an error introduced in using
the screens. It is well to reverse
the screen and check readings
whenever a new lot of lamps are
to be tested. When the light
falling on the two sides of the
screen is the same, the trans-
parent spot disappears. The
values of the two light sources are
then directly proportional to the
square of their distances from the
screen. As an example, consider a 16 candle-power lamp being
compared with a standard candle on a photometer with a 300-centi-
meter bar. Say the translucent spot disappears when the screen
is distant 60 centimeters from the standard candle, we then have
the proportion,
x : 1 - (240) 2 : (60) 2 == 16 : 1,
showing that the lamp gives 16 candle-power.
The above law is known as the law of inverse squares, and holds
true only when the dimensions of the light sources are small com-
pared with the distance between them, and when there are no reflecting
surfaces present as when the readings are taken in a dark room.
Fig. 68. Proof of the Law of Inverse
Squares by the Method of Con-
centric Spheres.
80
ELECTRIC LIGHTING
The proof that the light varies inversely with the square of dis-
tance from the source is as follows:
Consider two spherical surfaces, Fig. 68, illuminated by a source
of light at the center. The same quantity of light falls on both sur-
faces.
Area of 8 = lirR 2 sq. ft. (R is in feet.)
Area of $ x = 4 r n-R 2 1 sq. ft.
Let Q = total quantity of light and q = light falling on unit
surface. Then,
Q
Q
Q
Q
Fig. 69 shows the relation in another way. The area of C. dis-
tant two units from the
source of light A, is four
times that of B which is
distant one unit.
The Lummer=Brodhun
Photometer. In addition
to the Bunsen screen de-
scribed, there are several
other forms of photom-
eters, the most important
Fig. 69. Proof of the Law of Inverse Sqiiares by , . , . T
Method of Screen Shadow. of wnicn is the Lummer-
Brodhun. The essential
feature of this instrument is the optical train which serves to bring
into contrast the portions of the screen illuminated by the two sources
of light. Referring to Fig. 70 the screen S is an opaque screen which
ELECTRIC LIGHTING
81
reflects the light falling upon it from Z, to the mirror M, when it is
again reflected to the pair of glass prisms A, B. The surfaces sr are
ground to fit perfectly and any light falling on this surface will pass
through the prisms. Light falling on the surface ar or bs will be re-
flected as shown by the arrows. We see then that the light from L,
which falls on ar and bs, is reflected to the eye piece or telescope T,
while that falling on sr is transmitted to and absorbed by the black
interior of the containing box. Likewise, the light from the screen
Fig. 70. Diagram of Lummer-Brodhun Screen.
L 1 is reflected by the screen M^ to the pair of prisms A, B. The
rays falling on the surface sr pass through to the telescope T, while
the rays falling on ar and bs are reflected and absorbed by the black
lining of the case. The field of light, as then viewed through the
telescope, appears as a disk of light produced by the screen L v sur-
rounded by an annular ring of light produced by L. When the
illumination on the two sides of the screen is the same, the disk and
ring appear alike and the dividing circle disappears.
In using this screen, it is mounted the same as the Bunsen screen
and readings are taken in the same manner. The screen and prisms
are arranged so that they can be reversed readily and two readings
82
ELECTRIC LIGHTING
should always be taken to compensate for any inequalities in the sides
of the screen and the reflecting surfaces, a mean of the two readings
Fig. 71. Complete Photometer with Liunmer-Broclhun Screen.
serving as the true reading. This form of screen is used when es-
pecially accurate comparisons are required.
Fig. 71 shows a complete photometer with a Lummer-Brodhun
screen, while Fig. 72 shows a Bunsen screen and sight box. In Fig.
71, the lamps are shaded by means of curtains so as to leave only a
ELECTRIC LIGHTING
83
smtill opening toward the screen. If the lights are properly screened
photometric measurements may be made in rooms having light-
colored walls.
Fig. 72. Bunsen Screen and Sight Box.
The Weber Photometer. As an example of a portable type of
photometer, we have the Weber. This photometer, shown in Fig. 73,
is very compact and is especially adapted to measuring intensity of
illumination as well as
the value of light sources ;
it may be used for ex-
ploring- the illumination
of rooms or the lighting
of streets.
This apparatus con-
sists of a tube A, Fig. 74,
which is mounted hori-
zontally and contains a
circular, opal glass plate
/, which is movable by
means of a rack and
pinion. To this screen is
attached an index finger
which moves over a scale
attached to the outside of
the tube. A lamp L,
burning benzine, is mounted at the end of this tube. The benzine
used should be as pure as possible, and the flame height should be
Fig. 73. Weber Portable Photometer.
84
ELECTRIC LIGHTING
carefully adjusted to 20 mm. when taking readings. At right angles
to the tube A is mounted the tube B which contains an eye piece at
0, a Lummer-Brodhun contrast prism at p, and a support for opal or
colored glass plates at g.
Operation. The tube B is turned toward the source of light to
be measured, the distance from the light to the screen at g being noted.
The light from this source is diffused by the screen at g, while that
from the standard is diffused by the screen /. By moving (he screen
/, the light falling on either side of the prism p can be equalized.
The value of the unknown source can be determined from the reading
of the screen /, the photometer having previously been calibrated by
means of a standard lamp
in place of the one to be
measured. The calibra-
tion may be plotted in the
form of a curve or it may be
denoted by a constant C,
when we have the formula,
n
r = c ~
C corresponds to a par-
ticular plate at g, I = dis-
tance of screen / from the
benzine lamp, and L = dis-
tance from the screen g to
the light source being
measured. Screens of dif-
ferent densities may be
used at g, depending on
the strength of the light source.
When used for measuring illumination, a white screen is used
in connection with this photometer. The screen is mounted in front
of the opening at g } and turned so that it is illuminated by the source
being considered. Readings of the screen / are taken as before. A
calibration curve is plotted for the instrument, using a known light
source at a known distance from the white screen when the instru-
ment is mounted in a dark room.
Fig. 74. Diagram of Weber Photometer.
ELECTRIC LIGHTING
85
Portable Photometers, There is a large variety of portable
photometers available and giving more or less satisfactory results.
An instrument especially designed with a view to portability and to
overcoming some of the
defects of instruments
already on the market
has recently been intro-
duced. The instrument
referred to is called a
Universal photometer but
it is more commonly
known as the Sharp-
Millar photometer from the names of its inventors. Views of this
instrument are shown in Figs. 75 and 76. It is adapted to the meas-
urement of the intensity of light sources as well as to the illumination
at any point, as is the Weber photometer. The photometer screen
or photometric device is shown at B, and consists of a special form of
Fig. 75. Universal Photometer.
Fig. 76. Sectional View of Universal Photometer.
Lummer-Brodhun optical screen. A standardized incandescent
lamp C is used as the photometric standard and this may be con-
nected to a battery, or be adapted to use on the mains supplying the
lamps in the room where measurements are to be taken. All stray
light is carefully screened from the interior of the box by a series of
screens G. The instrument scale is calibrated in foot-candles and in
candle-powers.
86 ELECTRIC LIGHTING
When illumination is to be measured, a specially selected trans-
luscent screen is placed at A and the illumination of this plate, which
is placed at the point and in the plane where the value of the illumi-
nation is desired, is reflected to the photometric device by the mirror
at H. A second plate K is mounted so as to be illuminated by the
standard lamp and the photometer is balanced by making the illumi-
nation of A and K the same. When the intensity of a light source
is to be determined, the screen at A is replaced by a small aperture
and a diffusing surface I is put in place of the mirror H. The illumi-
nation of 7 is now compared with the illumination of K, and when
the two are made equal, the photometer reads the candle-power of the
light source, or some multiple of this candle-power. The range of
this instrument is increased by the use of suitably arranged absorbing
screens which may be readily inserted or removed, and as ordinarily
equipped, the range in foot-candles is approximately from .004 to
2,000. The variety of uses which can be made of such a photometer
is large, and some idea of its portability can be obtained from the
dimensions of the box, 24" x 4J" x 5", and its weight, fully equipped,
of 8 pounds. It is very accurate considering its compactness.
Integrating Photometers. Matthews. This photometer is used
to some extent and a very good idea of its construction can be ob-
tained from Fig. 77. By means of a system of mirrors, the light
given by the lamp in several directions may be integrated and throw r n
on the photometer screen for comparison with the standard, the result
giving the mean spherical candle-power from one reading. By cover-
ing all but one pair of screens, the light given in any one direction
is easily determined.
Another type of integrating photometer is known as the inte-
grating sphere or globe photometer. If a light source is placed within
a sphere, the interior walls of which are coated with a white diffusing
surface, the illumination of that surface at any point is due partly
to the light falling on it directly, and partly to the light reflected from
the remainder of the surface of the sphere. The reflected light is
proportional to the total flux of light from the light source and so,
if the direct light is screened from the point considered, its illumina-
tion is proportional to the total flux of light, and hence to the mean
spherical candle-power of the light source.
The practical application of this principle is to so arrange our
ELECTRIC LIGHTING
87
properly coated sphere that the lamp to be tested may be readily
inserted; to replace a small portion of the sphere by a piece of un-
polished white glass; to shut off the direct rays of the lamp to be
Fig. 77. Integrating Photometer.
measured from this glass surface; and to so mount a photometer
screen and standard lamp that the illumination of the glass section
can be measured. Under these conditions the illumination of the
glass screen is proportional to the mean spherical candle-power of the
lamp under test. A substitution method is used in practice. A
88
ELECTRIC LIGHTING
standardized lamp of the general type of the one to be tested is mounted
in the sphere and the constant of the instrument for this type of lamp
is determined. The unknown lamps are then put in place and their
candle-power is readily determined, once the constant of the instru-
ment is known. Figs. 78 and 79 give some views of the integrating
Fig. 78. Eighteen -Inch Integrating Sphere Equipped with Photometer.
sphere and indicate the range of the sizes in which it may be con-
structed.
INCANDESCENT LAMP PHOTOMETRY
Apparatus. Some sort of screen, either the Bunsen type or the
Lummer-Brodhun screen preferred, should be mounted on a carriage
moving on a suitable scale, and the lamp holders, one for the standard,
the other for the lamp to be tested, are mounted at the ends of this
scale. There are several types of so-called station photometers
arranged so as to be very convenient for testing incandescent lamps.
Fig. 80 shows one form of station photometer manufactured by
Queen & Co. The controlling rheostats and shielding curtains are
not shown here. Fig. 81 shows a form of portable photometer for
ELECTRIC LIGHTING
89
incandescent lamps. The length of scale should not be less than
100 centimeters, and 150 to 200 centimeters is preferred. This scale
may be divided into centimeters or, for the purpose of doing away
with much of the calculation, the scale may be a proportional scale.
This scale is based on the law of inverse squares and reads the inverse
ratio of the squares of the distances from the two lights being compared.
Fig. 79. Interior of 80-Inch Integrating Sphere.
If the standard used always has the same value, the scale may be
made to read in candle-powers directly.
For mean horizontal candle-power measurements, the lamp
should be rotated at 180 revolutions per minute, when mounted in a
vertical position.
For distribution curves a universal lamp holder which will
allow the lamp to be placed in any position, and which indicates this
position, is used.
^or mean spherical candle-power, the following method is used
when the Matthews photometer is not available :
90 ELECTRIC LIGHTING
The lamp is placed in an adjustable holder and readings taken
with the lamp in thirty-eight positions, as follows :
The measurement of the spherical intensity. For convenience
the tip of the lamp and its base may be termed the north and south
poles respectively.
Fig. 80. Station Photometer.
The mean of 13 readings taken at intervals of 30,. is taken to give the
mean horizontal candle-power.
Beginning again at azimuth, thirteen readings are made in the prime
meridian or vertical circle, the interval again being 30, and the last reading
checking the first.
Fig. 81. Portable Photometer for Incandescent Lamps.
It will be noticed that four readings, two being check readings, have been
made at azimuth in each case. The mean of the four is taken as the standard
reading, it being the value of the intensity, in this position, should the lamp be
used as a standard.
Additional sets of thirteen readings each the last reading checking the
first one are similarly made on each of the vertical circles through 45, 90,
and 135 azimuth.
ELECTRIC LIGHTING 91
In combining the readings for the mean spherical intensity, a note is
taken of the repetitions.
Neglecting the repetitions, which may also be omitted in part, in the
practice of the method, there remain thirty-eight points, as follows:
DISTRIBUTED
VALUES
The mean of four measurements at the north pole of the lamp 1
Four measurements on each of the vertical circles through and 90
azimuth at vertical circle readings of 60, 120, 240, and 300... . 8
Four measurements on each of the vertical circles through 0, 45, 90,
and 135 azimuth at vertical circle readings of 30, 150, 210, and
330 16
Twelve measurements 30 apart at the equator 12
Four null values at the south pole of lamp 1
Total number of effective measurements 38
The points thus laid off on the reference sphere are approximately equi-
distant, being somewhat closer together at the equator than at the poles.
When the lamp is rotated, readings are taken for each 15 or 30
in inclination, from to 90, and from to 270. These are inte-
grated values for their corresponding parallels of latitude on the unit
sphere.
The mean spherical candle-power from these readings may best
be obtained by plotting a distribution curve from the readings, deter-
mining the area of this closed curve by means of a planimeter and
taking the radius of an equivalent circle as the value for the mean
spherical candle-power.
The Rousseau diagram may be used for determining the mean
spherical candle-power of a lamp when its vertical distribution curve
is known. Fig. 82 shows such a diagram made up for a gem lamp
with a bowl reflector. Where the horizontal distribution curve of the
lamp is net uniform the values for the vertical distribution curve
should be taken with the lamp rotating so as to give average values
at each angle. One-half of the distribution curve is drawn to scale A
and a circle B is drawn with the source of light as a center. Radii
C are drawn at equal angles about the light source and extended until
they intersect the circle B. The points of intersection of these lines
with the circle are projected upon the straight line D E. Distances
from this line are laid off on the verticals F equal to the distances
from the center of the circle to the points where the corresponding
radii cut the distribution curve. The area enclosed between the
straight line D E and a curve drawn through the points just deter-
mined, G H, divided by the base line, is equal to the mean spherical
92
ELECTRIC LIGHTING
candle-power of the lamp. If the mean candle-power ot the lamp
within a certain angle is desired, it is only necessary to find the area
of the diagram within the space indicated by that angle and divide
by the corresponding base.
, Vertical o
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W |^7^>?^^^VN>x"/^
-V^
n I
'I I
' I
n i
li
/ - ' Jr~* \
;;! i
\ X
C
/^
80
6
60
40
20
K'-
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Fig. 82. Rousseau Diagram for Gem Lamp with Bowl Reflector.
In all tests the voltage of the lamp must be very closely regulated.
A storage battery forms the ideal source of current for such purposes.
In testing incandescent lamps, a standard similar to the lamp being
tested is desirable and it should, preferably, be connected to the same
leads. Any variation in the voltage of the mains then affects both
lamps and the error introduced is slight.
ELECTRIC LIGHTING 03
ARC LIGHT PHOTOMETRY
Owing to the variation of the amount of light given out by an
arc lamp in one direction at any time, due to variation of the qualities
of the carbons, position of the arc, and also on account of the color
of the light, etc., the photometry of arc lamps is much more difficult
than that of incandescent lamps. The curves shown in Figs. 33 and
34 are average distribution curves taken from several lamps and will
vary considerably for any one lamp. If the arc is enclosed, this
variation is not so great.
The working standard should be an incandescent lamp run at
a voltage above the normal so that the quality of the light will com-
pare favorably with that of the arc. Since an incandescent lamp
deteriorates rapidly when run at over voltage, the standard can be
used only for short intervals and must be frequently checked.
Since an arc lamp can be mounted in one position only, mirrrors
must be used to obtain distribution curves. A mirror is used mounted
at 45 with the axis of the photometer, and arranged so as to reflect
the arc when in different positions. A mirror absorbs a certain per
cent of the light falling upon it and this percentage must be deter-
mined by using lamps previously standardized. The length of the
photometer bar must include the distance from the mirror to the arc.
The Weber photometer is well adapted to arc-light measure-
ments inasmuch as appropriate screens may be used to cut down
the intensity of the light.
A special form of the Matthews photometer is also used for
testing arc lamps.
For the comparison of the illumination from arc lamps as in-
stalled in service, an instrument known as an illuminometer is some-
times used. This consists of a light wooden box, readily portable,
having a black interior and arranged with two openings. One
of these openings is for the purpose of admitting light from the source
being considered, to a printed card. The other opening is for the
purpose of viewing this card when illuminated by the light source.
The printing on the card is made up from type of different sizes, and
the smallest size which is legible, together with the distance from the
light source, is noted. Another method of application is to select
some definite size of type and then to move the instrument from the
94 ELECTRIC LIGHTING
light source to a point where this type is just legible and note the dis-
tance. From similar measurements taken on different lamps a good
comparison may be obtained. Such an instrument is very convenient
to use, and results obtained by different observers check very closely.
The flicker photometer is used for the comparison of different
colored lights, the basis for comparison being that each light, though
different in color, shall produce light sensations equally intense for the
purpose of distinguishing outlines. It consists, in one form, of an
arrangement by means of which a sectored disk is rotated in front of
each light source, these disks being so arranged that the light from
one source is cut off while the other falls on the screen, and vice versa,
any form of screen being used for making the comparison. The disks
must be revolved at such a rate that the light, viewed from the oppo-
site side, will appear continuous. When the illumination of the two
sides of the screen, under these conditions, is not the same, there will
be a perceptible flicker and the screen should be so adjusted that this
flicker disappears. The value of the light source can then be calcu-
lated from the screen reading in the usual manner. Another device
consists of the use of a special lens mounted in front of a wedge-
shaped screen, the lens being constructed so as to reverse the image
of the two sides of the screen, as viewed by the eye, when such lens
is in front of the screen. The lens is so mounted that it can be oscil-
lated rapidly in front of the screen, giving the same result as would be
obtained were it possible to reverse the screen at such a rapid rate as
to cause the illumination on the two sides to appear continuous. The
setting of this screen is accomplished as with the more simple forms.
Still another flicker photometer, the Simmance-Abady, makes
use of a rotating wheel. This wheel is made of a white material
having a diffusing surface, and its edge is so beveled that during part
of a revolution a surface illuminated by one of the light sources is
viewed through the eye-piece of the instrument, and during the other
part of the revolution a surface viewed by the second light source is
observed. The flicker occasioned by this change disappears when
the screen is brought to a point where it is equally illuminated by the
two light sources.
By the use of such forms of photometers it is found that results
with different colored lights can be obtained, which are comparable
with results obtained with lights of the same color.
INDEX
PART PAGE
Alternating-current circuits I ? 40
calculation of I, 44
line capacity I, 43
mutual induction I, 42
skin effect I, 42
Alternating-current lines, drop in I, 44
Amyl acetate lamp II, 17
Arc lamps II, 32
carbons for II, 41
efficiency II, 41
electric arc II, 32
flaming arc II, 42
Bremer II, 42
magnetite II, 44
mechanisms II, 33
carbon-feed II, 37
rod-feed II, 37
series II, 35
shunt . , II, 35
rating of II, 40
types of II, 38
alternating-current II, 39
direct-current II, 38
interchangeable II, 40
Arc light photometry II, 93
B
Bremer arc lamp II, 42
Bushings I, 65
C
Carbon incandescent lamps, manufacture of II, 3
Carcel lamp II, 77
Concealed knob and tube wiring I, 13
Conductors, calculation of sizes of I, 25
Cross-arms : I, 75
Cut-out panels I, 66
i
ii INDEX
E
PART PAGE
Electric lighting II, 1.94
arc lamps II, 32
arc light photometry II, 93
classification II, 2
history and development II, 1
illumination II, 53
incandescent lamp photometry .'. II, 88*
incandescent lamps II, 2
light standards II, 76
lighting of public halls, offices, etc II, 64
photometers : II, 79
photometry II, 76
power distribution II, 46
residence lighting II, 56-
shades and reflectors II, 72
special lamps II ? 27
street lighting II, 67
Electric wiring I, 1-87
alternating-current circuits I, 40
alternating-current lines, drop in I, 44
concealed knob and tube wiring I, 13
conductors, calculation of sizes I, 25
methods of wiring I, 1
outlet-boxes, cut-out panels, and other accessories I, 63
overhead linework ; . I, 68
testing I, 36
two- wire and three-wire systems I, 20
underground linework I, 79
wires run concealed in conduits I, 1
wires run exposed on insulators I, 16
wires run in moulding I, 9
wiring installation I, 29
wiring an office building I, 54
English candle II, 76
F
Fibre conduit I, 83
Fibrous tubing . I, 15
Frosted globes II, 73
Fuse-boxes I, 66
G
Gem metallized filament lamp II, 12
German candle i II, 77
INDEX iii
H
PART PAGE
Helion lamp 1I ? 21
Holophane globes n, 74
I
Illumination n, 53
intrinsic brightness II ? 54
irregular reflection n, 54
regular reflection n, 54
unit of II, 53
Incandescent lamp photometry n, 88
Incandescent lamps !' II, 2
comparison of types II ? 25
distribution of light II., H
efficiency II, 6
gem metallized filament lamp II, 12
helion lamp II, 21
manufacture of carbon incandescent lamps. II, 3
mean spherical candle-power II, 12
metallic filament lamps II, 14
Nernst lamp II, 21
selection of lamps II, 8
voltage and candle-power ( II, 5
Insulators I, 77
L
Light standards II, 76
amyl acetate lamp II, 77
carcel lamp II, 77
English candle II, 76
German candle II, 77
pentane lamp II, 77
working standards II, 78
Lighting of public halls, offices, etc II, 64
Lightning arresters I, 78
Lummer-Brodhun photometer II, 80
M
Mercury vapor lamp II, 27
Metal conduit, wires run in I, 4
Metallic filament lamps II, 14
Moore tube light II, 29
Mutual induction , , . . I, 42
iv INDEX
N
PART PAGE
Nernst lamp II, 21
Opal enclosing globes II, 76
Osmium lamp II, 20
Outlet-boxes I, 63
Overhead Hnework I, 68
corners I, 75
cross-arms I, 75
insulators I, 77
lamps on poles I, 79
lightning arresters I, 78
pins I, 77
poles ' I, 70
guying of I, 72
placing of I, 69
service mains, pole wiring, etc I, 77
P
Pentane lamp II, 77
Photometers \ II, 79
integrating II, 86
Lummer-Brodhun II, 80
portable II, 85
Weber II, 83
Photometry II, 76
arc light II, 93
incandescent lamp II, 88
light standards II, 76
photometers II, 79
Poles I, 70
Polyphase circuits I, 53
Power distribution II, 46
multiple or parallel systems of distribution II, 51
multiple-series or series-multiple systems II, 51
multiple-wire systems II, 53
series system II, 46
E
Residence lighting II, 56
arrangement of lamps II, 59
calculation of illumination II, 56
plan of illumination II, 56
types of lamps II, 56
Rigid conduit, wires run in I, 1
INDEX v
s
PART PAGE
Shades and reflectors H, 72
frosted globes II, 73
holophane globes II, 74
opal enclosing globes II, 76
Skin effect I, 42
Special lamps II, 27
mercury vapor lamp II, 27
Moore tube light II, 29
Street lighting II, 67
T
Table
absorption loss for different shades II, 72
arc lights per mile II, 70
armored conductors types, dimension, etc I, 8
change in voltage, effects of II, 8
conductors in fibrous conduit, sizes of I, 15
Cooper-Hewitt lamps - II, 65
drop in alternating-current lines, data for calculating. I, 47
efficiency of transmission of arc light globes II, 76
flaming arcs, general data on II, 46
gem metallized filament lamp data II, 12
Greenfield flexible steel conduit I, 5
illuminating data for meridian lamps II, 62
intrinsic brilliancies in candle-power per square inch . . II, 54
life of a 25 c. p. unit data II, 16
lighting data for arc lamps II, 66
melting point of some metals II, 21
Moore tube light data II, 32
mouldings, sizes of required for various sizes of con-
ductors I, 12
Nernst lamp data II, 25
photometric units II, 78
pole data I, 71
relative reflecting power II, 55
residence lighting data 4 II, 63
rigid, enameled conduit sizes, dimensions, etc I, 2
single wire in conduit I, 2
standard vitrified conduit I, 81
street-lamp data II, 71
tantalum lamp data II, 15
three wires in one conduit I, 3
tungsten lamps (multiple and series) II, 20
two wires in one conduit I,
Testing electric wiring I, 36
vi INDEX
.... , i.
PART PAGE
Three-wire system,, details of -I, 22
Tungsten lamp II, 16
Two-wire and three-wire systems I, 20
details of three-wire system . . . . I, 22
relative advantages I, 20
U
Underground linework I ? 79
fibre conduit I, 83
iron pipe I, 80 .
laying of conduit I, 82
vitrified tile conduit I, 80
w
Weber photometer II, 83
Wires run concealed in conduits I, 1
armored cable I, 6
in flexible metal conduit I, 4
in rigid conduit . I, 1
Wires run exposed on insulators I, 16
accessibility I, 17
cheapness I, 16
durability I, 16
Wires run in mouldings I, 9
Wiring installation I., 29
feeders and mains. I, 36
location of outlets . I, 30
method of wiring I, 29
systems of wiring I, 30
Wiring an office building I, 54
basement . I, 55
character of load I, 55
electric current supply I, 54
feeders and mains I, 55
first floor I, 58
interconnection system I, 58
second floor I, 58
switchboard I, 55
upper floors I, 58
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WILL INCREASE TO 5O CENTS ON THE FOURTH
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OVERDUE.
FEBs
MA? 10 ...
JUN 10 1941
'49'
*6
SEP 2 3 1952 UJ
1933
LD 21-50m-l,'3
-o
YC 19518
346638
UNIVERSITY OF CALIFORNIA LIBRARY