INSIDE WIRING
The term _wiring_ is commonly understood to mean the methods employed
in laying the conductors used for the transmission and distribution of
electrical energy for lighting, power, and other purposes. Interior
wiring, comprises the various methods of installing the conductors from
the entrance devices in the walls or other parts of the buildings to
the lamps, motors, and other electrical apparatus within the buildings.
The different methods of interior wiring may be conveniently grouped
into the following general classes:
1. Open or exposed wiring;
2. Wires run in mouldings;
3. Concealed knob and tube wiring;
4. Rigid conduit wiring;
5. Flexible conduit wiring;
6. Armoured cable wiring.
=Open or Exposed Wiring.=—This method of wiring possesses the
advantages of being cheap, durable and accessible. It is used a great
deal in factories, mills and buildings where the unsightly appearance
of the wires exposed on the walls or ceilings is of no consequence.
=Ques. What kinds of wires are suitable for this method of wiring?=
Ans. Either rubber covered or slow burning weather proof wire.
Rubber insulation should always be used where the wire is in
a damp place, such as a cellar, and either weather proof or
rubber insulation may be used to protect it against corrosive
vapors.
[Illustration: FIGS. 842 to 844.—Open or exposed wiring. Fig. 842,
wires passing through beams. The holes are bored at an angle and wire
run through in zig-zag course. Porcelain tubes are used where the wire
passes through beams; fig. 843, cleat work across beams, the cleats are
carried by boards attached to the beams; fig. 844, method of carrying
wires on cleats around beams.]
=Ques. How are the wires installed?=
Ans. They are laid on some cornice, wainscoting, beam, or other
architectural feature suitable for the purpose, by means of porcelain
knobs and cleats, as shown in figs. 842 to 844.
Porcelain knobs should preferably be of the two piece type
(fig. 863) in which the wire is carried between the upper and
lower portions rather than being tied to a one piece knob with
a tie wire as in fig. 860. Various porcelain knobs and cleats
are shown in figs. 860 to 866.
=Ques. What are the disadvantages of open wiring?=
Ans. The wiring is not sufficiently protected from moisture, and the
effects of fire which will destroy the insulation of the wires; it is
also liable to mechanical injury.
[Illustration: FIGS. 845 to 847.—Splicing. Figs. 845 and 846, making
a wire splice, and the twist completed; fig. 847, a wrapped joint on
large wire. Splicing of wires or joining a branch to a main wire should
always be made by twisting the wires together or twisting one wire
around the other, so that the joint will be mechanically strong enough
to carry all strain which may come upon it, without any soldering.
The joint should then be carefully tinned and soldered in order to
give good electrical contact and to avoid corrosion along the contact
surface. Where wires are too large to be twisted together, the ends
are given a short bend and the two wires wrapped firmly together with
a smaller bare copper wire, after which the joint is thoroughly tinned
and soldered, preferably by pouring hot solder over the joint. The
joint is then insulated by wrapping it with two layers of pure rubber,
and three layers of tape, sufficient to make the insulation thickness
equal to that of the wire, after which the whole joint should be
painted with water proof paint.]
=Ques. How far apart should the wires be placed?=
Ans. When installed in dry places and for pressures below 300 volts,
the insulators should separate the wires 2½ inches from each other
and ½ inch from the surface along which they pass. For voltages from
300 to 500, the wires should be separated four inches from each other
and one inch from the surface along which they pass.
If the wiring be in a damp place, the wires should be at least
one inch from the surface.
[Illustration: FIGS. 848 to 850.—Crossing of wires. Where wires cross
each other, tubes should be used except in case of large stiff wires
as in fig. 848; here one wire may be bent down and carried under the
other; fig. 849, short bushing strung on the wire—this method is
usually unsatisfactory, especially where a large number of wires cross
each other; fig. 850, wires crossing each other through tubes. Flexible
tubing, such as circular loom may be used in crossing wires in dry
locations. Insulators should always be provided where wires cross to
support the wires, thus preventing the upper wires sagging and touching
those below.]
[Illustration: FIGS. 851 to 853.—Methods of wiring across pipes. The
wires should preferably run over rather than under the pipes. Fig. 851
shows crossing with circular loom, and fig. 852, one in which a tube is
used. Both of these methods are satisfactory in the case of gas pipes,
but for steam pipes or water pipes which are liable to leak or sweat
and drip moisture, the crossing should be above as shown in fig. 853.
On side walls where vertical wires run across horizontal water pipes,
the latter should be enclosed and the moisture deflected to one side.]
=Ques. How should wires be protected when run vertically on walls?=
Ans. They should be boxed in or run in a pipe as shown in fig. 854, the
covering extending 6 feet above the floor.
When placed inside a box there should be a clearance of at
least one inch around the wires; the box should be closed at
the end as shown, and the wires protected where they enter the
top with bushings. When the wires are placed in a pipe they
should be first encased in a piece of flexible tubing that will
extend from the insulator below the end of the pipe to the
first one above it.
[Illustration: Fig. 854.—Methods employed in open wiring when run
vertically on walls. Either a box casing or iron pipe should be used
to protect the wires. The covering need only extend six feet above the
floor.]
=Ques. What kind of incandescent lamp receptacle or wall socket is best
adapted to exposed wiring?=
Ans. One which does not have exposed contact ears, an approved form
being shown in fig. 859.
=Practical Points Relating to Exposed Wiring.=—Some of the principal
points which should be remembered in this connection, together with the
methods which may be applied to special cases, may be briefly stated as
follows:
1. In interior wiring no wires smaller than No. 14 B. & S.
gauge should be used, except as allowed by the underwriters,
and no more than 660 watts should be allowed to a circuit.
2. Tie wires should have an insulation equal to that of the
conductors which they secure.
3. In all cases, whether the wires be run on knobs, split
insulators, or cleats, the wires should be supported at
intervals of at least 4½ feet, and if exposed to mechanical
injury, the supporters should be placed at closer intervals.
4. Wires run on bare ceilings of low basements, especially
where they are liable to injury, should be protected by two
wooden guard strips as shown in fig. 858. The protective strips
should be at least ⅞ inch in thickness and slightly higher
than the knobs, insulators, or cleats. The two circuit wires
should not be run closer than 6 inches apart, and wires run
near water tanks must be rubber covered so as to render them
moisture proof.
5. Cleats should be used for the wiring of stores, offices,
or buildings having flat ceilings, provided the wiring is
installed in dry locations.
6. When the installation is exposed to dampness or acid fumes
such as those developed in stables, bakeries, etc., the wires
should run on knobs or split insulators, and should be rubber
covered.
[Illustration: Figs. 855 to 857.—Methods of carrying wires through
floors. In passing through floors (or walls) the wires often come in
contact with concealed pipes or other grounded material, hence the only
way they can be properly protected is by making the bushing continuous.
This may consist of continuous porcelain tubes as shown in fig. 855,
or short bushings may be arranged in iron pipes as in fig. 856. The
method followed in case of an offset in the wall is shown in fig. 857.
Sometimes the floor can be taken up and an iron conduit, properly
bent, put in place, the wires being reinforced with flexible tubing.
Another method is to attach the wires to insulators; in this case the
floor must not be put down until the wiring has been examined by the
inspector.]
7. When wires are run at right angles to beams which are more
than 4½ feet apart, a running board should be used and the
wires cleated to it as shown in fig. 843. It is desirable,
however, to avoid the use of running boards, whenever possible
by running the wires parallel with the beams, thus reducing the
cost of insulation.
8. In factories or other buildings of open mill construction,
mains of No. 8 B. & S. gauge or larger wire, where they are
not exposed to injury, may be placed about 6 inches apart and
run from timber to timber, not breaking around, and may be
supported at each timber only.
[Illustration: Fig. 858.—Method of protecting exposed wiring on low
ceilings by two guard strips.]
[Illustration: Fig. 859.—Receptacle suitable for use with open wiring,
the requirement being that the contact ears should not be exposed.]
9. The best location for feeders is on the walls. In dry
buildings the fire and weather proof wire can be used with
safety; but covered wire must be used on buildings subject to
any form of dampness. In all cases where feeders are run on
the walls, they should be protected from mechanical injury by
boxings at least 6 feet high on each floor. If floor switches
be used, they may be mounted on the front of the boxing. In
such cases, the holes in the boxing through which the wires
pass to the switches should be provided with porcelain bushings.
10. The rosettes, receptacles, sockets, snap switches, etc.,
used in connection with exposed wiring should conform in all
respects to the standards specified by the underwriters.
[Illustration: FIG. 860 to 866.—Various porcelain knobs and cleats. In
open work various forms of these devices are used.]
[Illustration: FIG. 867.—Porcelain tube for entrance of wire into
a building. There must be a drip loop outside to drain off water,
and the hole through which the conductor passes must be bushed with
a non-combustible, non-absorptive insulating tube slanting downward
toward the outside. The object of the inclination is to allow any water
that might enter the tube to gravitate to the drip loop.]
[Illustration: FIG. 868.—Interior bushing. Wires must be separated
from contact with walls, floors, timbers or partitions through which
they may pass by non-combustible, non-absorptive, insulating tubes,
such as glass or porcelain, except at outlets where approved flexible
tubing is required. Bushings must be long enough to bush the entire
length of the hole in one continuous piece, or else the hole must
first be bushed by a continuous water proof tube. This tube may be a
conductor, such as iron pipe, but in that case an insulating bushing
must be pushed into each end of it, extending far enough to keep the
wire out of contact with the pipe.]
=Wires Run in Mouldings.=—Wooden mouldings are extensively used in
connection with the wiring of stores, factories and buildings. The
advantages of this type of construction are: simplicity, cheapness, and
accessibility, and when the moulding is run straight and accurately
mitred it makes a neat job. Any class of wooden moulding wiring,
however, is not sufficiently impervious to moisture to render it
suitable for use in damp places, and it is liable to be crushed or
punctured. Furthermore, it is naturally very combustible. These
difficulties are overcome to a certain extent by impregnating the
moulding with some kind of moisture repellant, or by coating it both
inside and out with water proof paint. Hardwood moulding should be used
wherever possible, but soft wood moulding usually conforms much better
to the wall line.
[Illustration: FIG. 869.—Standard wooden moulding for encasing wires.
Wooden moulding must not be used in concealed or damp places, nor be
placed directly against a brick wall where sweating may introduce
moisture that may ultimately cause a short circuit. Wooden moulding for
concealing electrical conductors is prohibited by ordinances in some
cities.]
=Ques. For what conditions is wiring in mouldings suitable?=
Ans. It is adapted to installations in which the wires have to be laid
after the completion of the buildings.
=Ques. Describe the moulding usually employed.=
Ans. It is made of hardwood in two pieces, a backing and cap, so
constructed as to thoroughly encase the wire.
It should provide a one-half inch tongue between the conductors
and a solid backing which should not be less than three-eighths
of an inch in thickness under the grooves; it should be able to
give suitable protection from abrasion.
The inside of the moulding and the cap must have at least two
coats of waterproof material, or else the whole moulding must
be impregnated with moisture repellant.
Only one conductor is placed in a groove.
The backing is secured to the walls or ceilings by means of
wire nails. The wires are then laid in the grooves and the
capping put in place and fastened by small brads.
The wires should be continuous, and only rubber covered wire
should be employed.
Wooden moulding is made in a great variety of size and design.
The general appearance of this type of moulding being shown in
fig. 869.
=Ques. What other kind of moulding is used?=
[Illustration: FIGS. 870 to 872.—Metal moulding. An approved form
consists, as shown, of two pieces: base (fig. 870), and cap (fig. 871),
so formed as to snap together, the cap snapping over the base as in
fig. 872. The entire moulding should be galvanized or coated with a
rust preventive. When the base is held in place by screws or bolts from
the inside surface, depressions must be provided so that the heads of
the screws will be flush with the surface of the moulding.]
Ans. Metal moulding, as shown in figs. 870 to 872.
Metal moulding is permitted on circuits requiring not more than
660 watts and where the pressure is not over 300 volts. Special
fittings must be used with this class of moulding so that it
is continuous both mechanically and electrically. The moulding
should be grounded. The installation rules are practically the
same as those governing conduit work.
=Ques. What is a kick box?=
[Illustration: FIG. 873.—"Kick box;" a device used to protect wires
encased in porcelain tubes where they pass through floors.]
Ans. A fitting, as shown in fig. 873, for protecting wires at the
points where they enter or emerge from the floor.
=Ques. How is moulding work installed on brick or plaster walls which
are liable to dampness?=
Ans. A backing board must be put on before the moulding is used.
=Ques. How should moulding be placed on a ceiling with respect to
appearance?=
Ans. The appearance is improved if the moulding be carried through to
the side of the room, even if part of it be not used. This will give a
neat and finished appearance to the ceiling as shown in fig. 874.
Moulding should always be run in as inconspicuous position as
possible, and if it be necessary to run it on the open ceiling,
it should be arranged so as to form regular panels. Often it
can be run so as to take the place of a picture moulding or as
a part of the baseboard so that it becomes merely a part of the
wooden trim of the building; and in certain cases it should be
made of material to match the rest of the trim.
[Illustration: FIG. 874.—Treatment of moulding work on ceilings. All
installations should be planned out so as to conform to symmetrical
designs, as far as practicable with the proper distribution of the
lights, etc., and all runs finished off, whenever necessary, by "dead"
mouldings continued to the walls to improve the appearance. In the
figure the sectioned portions show the location of the dead moulding.
Sometimes, especially in the wiring of private houses the use of
special moulding is necessary. In such cases the shape and kind of
wood should match that of the finish or trim of the room, and the
receptacles should be stained to match the moulding. When the moulding
is run along the walls, the capping may be made to match the trim
or the picture moulding already in place, thus giving an apparently
concealed job. In this kind of work the feeders can be run through
the spaces between the walls, and if flexible tubes such as circular
loom or flexiduct be used, no splice box will be necessary where the
system of wiring changes and single braided rubber wire may be used
throughout.]
=Ques. What is the usual character of moulding work?=
Ans. Usually, a certain part of the work will be run as concealed, that
is, inside the partitions, the wires being "fished" from the moulding
to the outlet.
=Practical Points Relating to Wiring in Mouldings.=—The following
practical points will be found useful in the satisfactory execution of
any class of wiring with wooden moulding:
1. Wooden moulding should never be concealed, and should not be
used in damp places or in buildings subject to acid fumes, such
as ice houses, breweries, or stables, etc.
2. Wooden moulding selected for use should be formed of good
straight stock and free from knots, knot holes and other
imperfections. The saving effected in the lower cost of second
hand moulding does not compensate for the additional cost
increase in its working.
3. When wooden moulding is used in connection with solid pipe
or flexible tube conduit, an iron box or conduitlet must be
installed where the system of wiring changes, as shown in fig.
875. The pipe conduit is secured to the box by means of lock
nuts, with porcelain bushings or flexible tubes protecting the
wires. In all cases the loom should run up to the moulding.
[Illustration: FIG. 875.—Method of tapping outlets for feeder circuits
when wiring with wooden moulding.]
=Arc Light Wiring.=—All wiring for high voltage arc lighting
circuits should be done with rubber covered wire. The wires
should be arranged to enter and leave the building through an
approved double contact service switch which should close the
main circuit and disconnect the wires in the building when
turned "off" and be so constructed that they will be automatic
in their action, not stopping between points when started and
to prevent arcing between points under any circumstances, and
should indicate plainly whether the current is "on" or "off."
Never use snap switches for arc lighting circuits. All arc
light wiring of this class should be in plain sight and never
enclosed, except when required, and should be supported on
porcelain or glass insulators which separate the wires at least
one inch from the surface wired over. The wires should be kept
rigidly at least eight inches apart, except, of course, within
the lamp, hanger board or cut out box or switch. On side walls,
the wiring should be protected from mechanical injury by a
substantial boxing, retaining an air space of one inch around
the conductors, closed at the top (the wires passing through
bushed holes) and extending not less than seven feet from the
floor. When crossing floor timbers in cellars or in rooms,
where they are liable to be injured, wires should be attached
by their insulating supports to the under side of a wooden
strip not less than one-half an inch in thickness.
=Arc Lamps on Low Pressure Service.=—For this service there
should be a cut out for each lamp or series of lamps. The
branch conductors for such lamps should have a carrying
capacity about 50 per cent. in excess of the normal current
required by the lamp or lamps to provide for the extra current
required when the lamps are started or should a carbon become
stuck without over fusing the wires. If any resistance coils be
necessary for adjustment or regulation, they should be enclosed
in non-combustible material and be treated as sources of heat;
it is preferable that such resistance coils be placed within
the metal framework of the lamp itself. Incandescent lamps
should never be used for resistance devices. These lamps should
be provided with globes and spark arresters, as in the case
of arc lamps on high voltage series circuits, except when the
closed arc lamps are used.
4. Wooden moulding should never be run in elevator shafts, or
shafts of any kind, and should never be run on the inner side
of the outside walls of the buildings, as these locations are
usually subject to dampness.
5. In laying out feeders it is usually cheaper to use iron
conduit in a shaft, than to run moulding through the floor
timbers.
6. When tapping outlets for feeder circuits, an iron outlet box
with cover should be used, as shown in fig. 886. The one splice
box is held up to the outlet box already installed by means of
two long screws, and the loom is run right up to the moulding
so as to leave no exposed wire.
[Illustration: FIG. 876.—Circular fixture block for outlet from
moulding work on ceiling.]
7. Wherever fixture outlets are installed, a circular fixture
block as shown in fig. 876 should be used, to give a good
support for the fixture and to make a neat backing for the
fixture canopy. The wires should be brought through the fixture
without cutting and disfiguring the canopy.
=Concealed Knob and Tube Wiring.=—This method of wiring should be
discouraged as far as possible, as it is subject to mechanical injury,
is liable to interference from rats, mice, etc. As the wires run
according to this method are liable to sag against beams, laths, etc.,
or are likely to be covered by shavings or other inflammable building
material, a fire could easily result if the wires become overheated or
short circuited.
[Illustration: FIG. 877.—Concealed knob and tube wiring. The wires are
carried on porcelain knobs attached to the beams. If run perpendicular
to the beams, holes are bored in the latter and porcelain tubes with
a shoulder at one end, inserted in the holes through which the wires
pass. The knobs should support the wires at least one inch from the
surface over which they run, and should not be spaced further than
4½ feet apart. The wires should be attached with tie wires having an
insulation equal to that of the conductor which it secures to the knob.
The use of split knobs does away with the necessity of using tie wires.
The conductors must be at least 5 inches apart and it is better to
support them on separate beams when possible. Each wire must be encased
in a piece of flexible tube at all switches, outlets, etc., and this
piece of tubing should be sufficiently long to extend from the last
insulator and project at least one inch beyond the outlet.]
Concealed knob and tube wiring is still allowed by the
Underwriters, although many vigorous attempts have been made to
have it abolished. Each of these attempts has met with strong
opposition from electric light companies and contractors,
especially in small villages and towns the argument being that
it is the cheapest method of wiring, and if 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 dispensed with in such
communities. This argument, however, is only a temporary
makeshift obstruction against progress, and in the near future,
no doubt, concealed knob and tube wiring will be forbidden by
the underwriters.
[Illustration: FIGS. 878 to 880.—Methods of making fixture outlets in
concealed knob and tube wiring. A cleat consisting of a piece of board
at least ⅞ in. thick, should be nailed between the joists or studs
into which the wood screws supporting the electrolier can be secured.
Holes are then bored through the cleat, through which the flexible
tubing can pass. With a combination gas and electric fixture as shown
in fig. 879, no cleat is necessary, because the gas pipe supports
the fixture. The flexible tubing should be wired to the gas pipe, to
prevent displacement by artisans who have occasion to work around the
outlet.]
=Ques. Describe the method of concealed knob and tube wiring.=
Ans. It consists in running the wires concealed between the floor beams
and studs of a building, knobs being used to support the wires when run
parallel to the beams or studs, and porcelain tubes, when run at right
angles through the beams, or studs as shown in fig. 877.
In this method of wiring, usually nothing need be disturbed on
the first floor as the various outlets can be reached from the
basement and from the second floor.
[Illustration: FIG. 881 and 882.—Arrangement of switch and receptacle
outlets in knob and tube wiring. In wiring for switches, flexible
tubing must be used on the conductor ends from the last porcelain
support, as shown, the same as on conductor ends for other outlets. A
pressed steel switch box should be used to encase each flush switch
mechanism, even though it already be encased in porcelain. A ⅞ in.
wood cleat or cleats are arranged to support the switch box. These
wooden cleats should not be set out flush with the outer edges of the
studs, but should be set about ⅜ in. back, as illustrated, to allow a
space in which the plaster can take a "grip."]
For instance, if it be necessary to make an outlet for the
center fixture in the parlor, a strip of flooring can be
removed from the floor above so as to expose the beams. Then
the wireman can bore two holes through each of the beams,
insert porcelain tubes therein, slip the wires through the
outlet and replace the strip of flooring.
Various simple methods may be employed for carrying the wires
to the outlets on the side walls. For example: a small hole
can be made in the wall, and the wire may be dropped through
the spaces between the walls, or they may be pulled up from
the basement by means of a cord lowered with a weight attached
to its end. Outlets for switches and base receptacles may be
provided for, in a similar manner.
[Illustration: FIGS. 883 and 884.—Elevation and sectional view showing
arrangement of switch outlet in concealed knob and tube wiring.]
[Illustration: FIG. 885.—Arrangement of surface switch in concealed
knob and tube wiring. For a surface snap switch outlet, an iron box is
not necessary, but a ⅞ in. cleat must be installed to hold the tubing
in place and to provide a proper support for the screws that hold
the switch. In wiring old buildings where supporting cleats were not
provided back of the plaster, a ¾ in. wooden block or plate should be
installed on the surface, to which the switch can be attached.]
=Ques. What are the advantages of concealed knob and tube wiring?=
Ans. Its cheapness, especially in wiring completed buildings, and the
absence of any wires or casings on the walls or ceilings.
=Ques. What kind of wire must be used?=
Ans. Wire having an approved rubber insulating covering.
[Illustration: FIGS. 886 to 888.—Switch boxes for concealed knob and
tube wiring. These are for flush switches and are formed from sheet
steel. A single switch box can be expanded for any number of switches,
by using the proper number of spacers. Single and double switch boxes
can be supplied already assembled and are used where feasible, because
it is cheaper to buy them this way than to assemble them. Holes
partially punched, which can be knocked out with a hammer blow, are
provided in the sides and back through which the flexible conduit wire
protection can be extended.]
=Rigid Conduit Wiring.=—The installation of wires in conduits not
only affords protection from mechanical injury, but also reduces the
liability of a short circuit or ground on the wires producing an arc
which would set fire to the surrounding material; the conduit being of
sufficient thickness to blow a fuse before the arc can burn through the
conduit.
=Ques. Describe the unlined type of conduit.=
Ans. It consists of an iron or steel pipe, similar in size, thickness,
and in every other way to gas pipe, except that special precautions
are taken to free it inside from scale or any irregularities; it is
then coated inside with enamel, outside it is sometimes enameled and
sometimes galvanized.
=Ques. Describe the lined type of conduit.=
Ans. It usually consists of a plain iron pipe lined with a tube of
paper which has been treated with an asphaltic or similar compound;
this paper tube is cemented or fastened to the inside of the iron pipe
so that it forms practically an integral part of the same.
=Ques. What are the advantages of unlined conduit?=
Ans. It is cheaper, because having no lining a smaller size of conduit
can be used for any given size of conductor; it is also cheaper to
install, as it can be bent, threaded, and cut more readily than the
lined conduit. Wires may be more easily inserted and withdrawn as the
inside is smoother than that of the lined conduit.
NOTE.—Conduits for inside wiring which are subject to
inspection, must have an inside diameter of not less than
⅝ inch. They must be continuous from outlet to outlet or
to junction bores, and must properly enter and be secured to
all fittings, and the entire system be mechanically secured
in position. In case of service connections and main wires,
this involves running each conduit continuously into a main
cut out cabinet or gutter surrounding the panel board as the
case may be. Conduits must first be installed without the
conductors, and 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 bores. The outlet box or
plate must be so installed that it will be flush with the
finished surface, and if this surface be broken, it shall be
repaired so that it will not show any gaps or open spaces
around the edge of the outlet box or plate. 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, providing the conduit ends
are bushed and secured. It is suggested that outlet boxes and
fittings having conductive coatings be used in order to secure
better electrical contact at all points throughout the conduit
system. Metal conduits where they enter junction boxes, and
at all other outlets, etc., must be provided with _approved_
bushings or fastening plates, fitted so as to protect wire from
abrasion, except when such protection is obtained by the use
of _approved_ nipples, properly fitted in boxes or devices.
Conduits must have the metal of the conduit permanently and
effectually grounded. Conduits and gas pipes must be securely
fastened in metal outlet boxes so as to secure good electrical
connections. If conduit, couplings, outlet boxes or fittings
having protective coating of insulating material, such as
enamel, be used, such coating must be thoroughly removed from
threads of both couplings and conduit and from surfaces of
boxes and fittings where the conduit is secured in order to
obtain requisite good connection. Where boxes used for centers
of distribution do not afford good electrical connection, the
conduits must be joined around them by suitable bond wires.
Where sections of metal conduit are installed without being
fastened to the metal structure of buildings or grounded metal
piping, they must be bonded together and joined to a permanent
and efficient ground connection. Junction boxes must always be
installed in such a manner as to be accessible. All elbows or
bends must be so made that the conduit or lining of same will
not be injured. The radius of the curve of the inner edge of
any elbow must not be less than three and one-half inches. Must
have not more than the equivalent of four quarter bends from
outlet to outlet, the bends at the outlets not being counted.
[Illustration: FIG. 889.—Conduit box showing arrangement for
combination side outlet with open cover. Outlet or junction boxes are
of two general types: 1, those which are made for a particular position
and have a given number of outlets, and 2, those which have a variable
number of outlets which are plugged with metal discs in such a manner
that the latter can be knocked out by a slight blow of a hammer. The
illustration shows a universal plugged steel conduit box, which can be
used as a straight electric, or combination gas and electric, ceiling
or side wall outlet, or for flush rotary or push button switches, or
for flush receptacles. When rigid conduits are used, they are screwed
to the outlets by means of lock nuts and washers. In the case of
flexible conduits, the entering ends of the conduits are provided with
clamp bushings which are secured to the outlet by means of lock nuts.
All outlet boxes are fitted with covers of various designs, which
permit their use for various types of construction such as ceiling and
wall work in lath or plaster, fireproofing ceiling work, etc., while
many designs of outlet plates and receptacle plates may be obtained
from the supply houses to satisfy the requirement of any special case.]
=Ques. What are the disadvantages of the unlined conduit?=
Ans. The Underwriters require the use of double braided conductors
instead of single braided which are allowed for lined conduits.
=Ques. Where may unlined conduits be used?=
Ans. In buildings where the conduit is not liable to corrosive action.
=Flexible Conduit Wiring.=—Flexible conduits are used to advantage
in many cases where rigid conduits would not be desirable. It is
especially adapted to completed buildings where it is desired to
install the wiring by "fishing" without greatly disturbing the walls,
floors, or ceilings.
[Illustration: FIGS. 890 and 891.—Greenfield flexible steel conduit;
fig. 890 single strip type; fig. 891 double strip type. The former
(fig. 890) is formed with a single strip of galvanized steel,
interlocked and gasketed in such a manner as to be suitable for
concrete construction. The double strip type (fig. 891) is constructed
of a concave and convex steel strip, spirally wound upon each other
in such a manner as to interlock their concave surfaces. Thus the
convex surfaces of the two strips form respectively the outer and inner
surfaces of the conduit. This construction insures a smooth interior
surface, thus reducing the possibility of friction in the drawing in
of conductors. A gasket is provided between the inner and outer strips
rendering the conduit moisture proof. This form of flexible conduit
is especially adapted to use where the wiring is installed after
completion of building, because it is very flexible.]
=Ques. How is a flexible conduit installed by "fishing"?=
Ans. It is "fished" under floors, in partitions between the floor and
ceiling, by making pockets in the floors, walls or ceilings, say every
15 or 20 feet, and fishing through first a stiff metal wire called a
"snake," and then attaching the conduit to same and pulling the conduit
in place from pocket to pocket.
[Illustration: FIG. 892.—Insulating joint. This fitting is used
in fixture work. The part A screws on to the gas pipe and B to the
fixture. The parts are separated by insulating material E, and
the outside of the joint is covered with moulded insulation D. In
connecting fixtures to the wiring, all wires should be kept away
from the gas pipe above the joint, but they may be bunched in below
the insulating joint after the wires have been spliced, soldered,
and taped. It is important to protect the gas pipe at this point.
Insulating joints should be tested before being used.]
[Illustration: FIG. 893.—Canopy insulator. This fitting should be
installed wherever there are metal ceilings against which the canopies
of fixtures might come. The canopy is the brass cup shaped piece used
at the top of fixtures to cover the joint, and is simply an insulating
ring placed between the canopy and the ceiling. It is in contact with
the fixture; hence, it is important that it be insulated from metal
ceilings, or else all the benefits derived from an insulating joint
will be lost.]
=Ques. How is the conduit fished on vertical runs?=
Ans. A chain or weighted string is used which is dropped from the
outlet to the floor and its lower end located by sound of the chain end
or weight striking the floor.
[Illustration: FIG. 894.—Section of flooring illustrating use of
fishing hook. In fishing wires, punch a hole through the plastering
at the required position, being careful that there is no studding at
that place. Use a brad awl and cut the hole large enough to permit
running of the wires. With a short length of small brass spring wire,
push through the opening a few inches of number 19 double jack chain
such as is used for general fishing purposes, first having connected
the end of the chain with a piece of heavy linen thread. Run out the
thread between the laths and the outside wall until the chain touches
the floor beneath; move the thread and locate the chain by the sound;
bore a hole through the baseboard or floor, as the case may be, toward
the chain. Use a two or three foot German twist gimlet. With a small
brass spring wire bent at the end in the shape of a hook, fish for the
chain and draw it out. At the other end of the thread attach the wire
and draw it through with the thread. Passing under the floor bore a
second hole through the floor as near the other as possible. Run into
this a piece of snake or fishing wire with a hook at the end, until it
comes to an obstruction. Locate the obstruction by sound. In running
wires under the flooring first carefully examine all parts and find
the direction in which the beams and timbers run, and run the wires
parallel with these. After locating the end of the fishing wire see
if the obstruction be a timber; if so, find the center and bore from
the middle diagonally through it in the direction of the fishing wire.
Drop the jack chain and thread through the hole; fish for it and draw
it through hole number 2; attach the insulated wire and draw it back.
Starting hole number 3, bore hole number 4 diagonally through the
timber in the direction in which the wire is to be run, making holes
3 and 4 form an inverted "V" through the timber. Run the fishing wire
through hole number 4 until it meets an obstruction. If at the end of
the room, bore through the floor, drop the chain, fish it out, attach
wire and draw it home. Putty up holes after having finished the work,
in case of hard finish, plug them up with wood. In lightly built houses
it is often found easier to take off the moulding above the baseboard
and run the wire under it. In such cases care should be taken to break
off the old nails, as any attempt to drive them out would cause a bad
break. In closets and around chimneys it is usually found easy to work.
A "mouse" or lead weight attached to a string may often be dropped from
the attic to the cellar ceiling through the space outside the chimney.]
=Ques. What is the difference between flexible conduit and flexible
tubing?=
Ans. Flexible conduits are made of metal while flexible tubing is
non-metallic.
=Ques. Describe a flexible conduit.=
Ans. It is a continuous flexible steel tube composed of convex and
concave metal strips, wound spirally upon each other in such a way as
to interlock their concave surfaces.
=Ques. What are the advantages of this form of flexible conduit?=
Ans. It possesses considerable strength and can be obtained in long
lengths (50 to 200 feet); elbow fittings are not required as the
conduit may be bent to almost any radius. The fissures of the conduit
provide some ventilation; this is an advantage in some places and a
disadvantage in others.
[Illustration: FIGS. 895 to 897.—Greenfield flexible steel conduit
and fish plug, showing method of insertion. Fish plugs are made for
⅜ inch, ½ inch, and ¾ inch conduit and are useful in drawing in
the conduit in finished buildings where it is desired to fish it under
doors or in partitions. After the conduit has been cut off square in
the special vise, the fish plug may be screwed into the tube and the
fish wire or drawing-in line should then be attached to the eyelet on
the end of the plug.]
=Ques. In what places are flexible conduits not desirable?=
Ans. In damp places.
=Ques. Why?=
Ans. Because of the fissures.
=Practical Points Relating to Inside Conduit Wiring.=—The following
instructions apply to the installation of wiring in both rigid and
flexible conduit:
1. All conduits should be made continuous from one junction or
outlet box to another, or to the various fixtures. A conduit
installation is made a complete system by the use of outlets,
outlet boxes, switch or junction boxes, and panel boxes with
doors and locks, which serve to thoroughly protect the circuit
at all points.
[Illustration: FIGS. 898 to 901.—Pull boxes and their use in conduit
work. A pull box is a convenient device used for the purpose of
avoiding the disadvantages of having too many bends in one continuous
line of conduit; too many bends will give trouble when the conductors
are drawn in. Pull boxes are also useful in places where the
arrangement of the conduit is such that trouble would be experienced in
bending it to a fit, and also in the case of conduits which are first
run on a side wall and then have to be carried across the ceiling at
right angles to the wall. Fig. 898 shows an example of objectionable
bends, and fig. 899, the method of overcoming the difficulty by the use
of a pull box. It is evident that it would be impossible to make some
of these bends so as to permit the drawing in of the conductors. This
difficulty is overcome, as shown, by placing a pull box on the wall,
with its top close to the ceiling. A board B, having the proper size
holes for the conduits is fastened to the front of the box and close
to the ceiling. After the conductors have been drawn into the conduits
along the wall as far as the pull box, they can be readily pulled away
from the box through the holes in the board into the corresponding
conduit on the ceiling. Fig. 901, shows the use of a pull box in a case
where it is necessary to run conduit through partitions at right angles
to each other. Pull boxes can be designed to suit any condition liable
to occur in practice, and when properly used will always save much
time and labor. Locknuts should be placed on the ends of all conduits,
both inside and outside the pull box in order to prevent their being
displaced when drawing in the conductors. After all the conductors have
been drawn into the conduit, all the outlets should be plugged up with
wood or fibre plugs made in parts to fit around the wires and cables,
and the outlets given a coating of some compound which will render the
whole system air tight and moisture proof. A final test should then be
made to ascertain that there are no grounds on the different parts of
the wiring, and that the insulation comes up to the requirements of the
underwriters. The metal of all conduits, and the sheathing of steel
armoured cables should be effectually and permanently grounded.]
2. In the installation of interior conduit wiring, the tubes
are usually put in place as soon as the partitions of the
buildings have been constructed. In non-fireproof buildings,
the tubes are usually supported from the underside of the floor
beams, but in fireproof buildings they are placed on top of the
floor beams and under the floor as in fig. 902.
3. When conduit is used in damp places, lead encased wires
should be used, and the wires drawn in very carefully so as to
prevent any injury to the casings.
4. For wiring installations in buildings constructed entirely
of reinforced concrete, the preliminary work should be laid out
during the progress of the building operations so as to avoid,
as much as possible, the necessity of drilling holes in the
finished concrete work.
[Illustration: FIG. 902.—Method of installing conduits in fire proof
buildings. The installation of the conduit includes the placing of
all outlet boxes, and when this has been completed, the lathing or
plastering work is executed, and after that is finished, the wire is
pulled into the tubes, and the receptacles, switches, etc., put in
position. The work of pulling in the wires may be greatly facilitated
by the use of _pull boxes_ as shown in figs. 899 and 901.]
5. For concealed wiring, the location of all the outlets
should be marked by sheet iron tubes large enough to hold the
conduits. These tubes should be properly plugged, and set in
the false work before the concrete is poured in. In a similar
manner, threaded pieces of conduit of the proper size, should
be placed in the false work for risers.
6. For exposed wiring on concrete walls and ceilings, suitable
cast iron supports should be set in the moulds at regular
intervals. When liberally used, these supports will also serve
as good supports for other pipes.
7. Where a conduit line terminates on the outside of a building
some suitable fitting such as a pipe cap should be used, as
shown in fig. 903, to prevent the entrance of moisture into the
conduit system. A variety of devices suitable for this purpose
are available at supply houses; but those having porcelain
covers which spread the wires the proper distance apart are the
most satisfactory.
8. Where it is desirable or necessary to continue open wiring
from conduits, or where the character of the wiring makes it
necessary to bring the wires over from the conduit, as in an
arc lamp, neat and safe work can be done by use of a suitable
form of _condulet_ as shown in fig. 904.
[Illustration: FIG. 903.—Service entrance to interior conduit system;
showing method of preventing moisture reaching the interior of the
conduit system.]
[Illustration: FIG. 904.—Outlet to arc lamp from conduit by use of
condulet. The wires are brought out from the conduit system at a
distance of 2½ inches apart. Conduits are made in a great variety
of design with interchangeable porcelain covers which render them
adaptable to almost all cases requiring the installation of outlet
boxes.]
9. Where a conduit line terminates in a switch or panel box,
the lining or casing of the panels should be of iron, and the
conduit firmly secured to it so as to make good electrical
contact. Vertical lines of conduit should be fastened to the
wall or other supports in such a manner as to prevent the
weight of the conduit coming on the panel box, and each length
of conduit installed should be fastened so as to bear only
its own weight. The best method of fastening conduit to brick
walls is by the use of expansion bolts and screws. In the case
of fire brick ceilings or other plastered walls, toggle bolts
should be used. When conduits are run on wooden or iron beams,
various kinds of pipe hanger may be employed.
10. There are numerous devices on the market for bending
conduit for the making of elbows, offsets, etc., but the
majority possess the disadvantage that the conduit must be
taken to them to be bent. In the case of the smaller sizes,
this difficulty is avoided by the use of some form of conduit
bender such as shown in figs. 910 and 911.
[Illustration: FIGS. 905 to 909.—Sprague multilet covers. Fig. 905,
six wire porcelain cover; 906, P & S. rec. cover; 907, cover for five
ampere snap switch; 908, G. E. and P. & S. rec. cover; 909, cover for
ten ampere snap switch.]
11. In all cases, the interior diameter of the conduit
installed should be amply sufficient to permit of the wires
being drawn in easily, thus providing a substantial raceway for
the conductors. The practice of pulling wires through conduit
by means of a block and tackle is very objectionable. It is
evident that if the wires be pulled in by the application of
much force the insulation is very liable to become damaged;
furthermore, much difficulty will be experienced in pulling
them out again, especially in warm places where the heat tends
to soften the lining of the conduit, and also the rubber
covering of the wire. Powdered soapstone put in the pipe while
the wires are being drawn in will lessen the friction and
permit the wire to go in more readily.
[Illustration: FIG. 910.—Ordinary form of hickey or conduit bender. It
consists of a piece of one inch steam pipe about three feet long with a
one-inch cast iron tee screwed onto one end of the pipe. This device is
used as follows: the conduit to be bent is placed on the floor and the
tee slipped over it. The workman then places one foot on the conduit
close to the tee, and pulls the handle of the bender towards him. As
the bending progresses, the workman should take care to continually
move the bender away from himself, to prevent the buckling of the
conduit.]
[Illustration: FIG. 911.—Commercial form of hickey or conduit bender.]
[Illustration: FIGS. 912 and 913.—Methods of bending large conduits. A
substantial support is necessary which may consist, as in fig. 912, of
two pieces of 2 × 4 studding A and B securely fastened to an upright.
The conduit is placed under the block A and over the block B, and then
bent by a downward pressure exerted at C, the conduit in the meantime
being gradually advanced in the direction D to give a curve of the
required radius. The method shown in fig. 913, may be used wherever
a ring A can be attached to a beam or girder by means of clamps or
otherwise to serve as a support. In this case the conduit is slipped
through the ring and placed on the top of blocking B. The bending is
accomplished by means of a block and tackle rigged to an overhead beam
as shown. Where ring supports cannot be arranged, the application of
frame bending methods give the most satisfactory results.]
=Armoured Cable Wiring.=—Where a conduit system cannot be conveniently
installed, armoured cable is used. Armoured cable is made by winding
steel strips over the insulated conductors, the latter being
permanently retained inside the steel casing. Armoured cable is
manufactured in long lengths, the actual lengths being determined by
convenience in handling.
[Illustration: FIGS. 914 and 915.—Greenfield flexible steel armoured
conductors. The armour is composed of convex and concave galvanized
metal strips, wound spirally upon each other and over the insulated
conductors. A gasket is placed between the inner and outer metal
strips, thus further rendering the conductor moisture proof.
FIG. 916.—Greenfield flexible steel armoured lead covered conductors
for use in wet places, such as breweries, packing houses, cold
storage buildings, coal breakers and the like, and for underground
construction, in which classes of work these materials are being
extensively and satisfactorily used.]
=Ques. What are the features of armoured cable?=
Ans. It is flexible and the conductors are well protected from
mechanical injury. 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.
[Illustration: FIGS. 917 to 920.—Greenfield flexible conduit tools.
Special tools are necessary for installing this type of conduit. Fig.
917, universal reamer; fig. 918, bushing tool; fig. 919, cable armour
cutter; fig. 920, vice for holding conduit. To remove cable armours,
clamp the conductor firmly in the armour cutter and with a pair of
cutting pliers back the armour off, one strip at a time, to the point
of contact with the cutting edge of the tool. The vise for holding
conduit takes all sizes. The conduit can be cut with an ordinary
hacksaw. To protect the insulation against any possible injury while
the wire is being drawn in, a soft metal bushing should be inserted in
the end of the tube and secured permanently thereto by means of the
bushing tool. The bushing provided for this purpose has an outside
thread, which permits its being screwed into the end of the tube and
then expanded by the use of the tool. The tool should always be used
after the bushing has been screwed into the pipe, then the bushing tool
should be inserted.]
=Ques. How should armoured cable be installed?=
Ans. It 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.
=Ques. Is armoured cable wiring expensive?=
Ans. It 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.