CHAPTER XXXVIII INSIDE WIRING

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N. Hawkins

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.

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.

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.

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.

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.

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 ? 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.

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.

Fig. 858.—Method of protecting exposed wiring on low ceilings by two guard strips.

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.

Figs. 860 to 866.—Various porcelain knobs and cleats. In open work various forms of these devices are used.

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.

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.

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?

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?

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.

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.

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.

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.

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.

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 ? 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.

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 ? 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 ? 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.

Figs. 883 and 884.—Elevation and sectional view showing arrangement of switch outlet in concealed knob and tube wiring.

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 ? 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.

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 ? 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.

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.

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.

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.

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.

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.

Figs. 895 to 897.—Greenfield flexible steel conduit and fish plug, showing method of insertion. Fish plugs are made for ? 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.

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.

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.

Fig. 903.—Service entrance to interior conduit system; showing method of preventing moisture reaching the interior of the conduit system.

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.

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.

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.

Fig. 911.—Commercial form of hickey or conduit bender.

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.

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.

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.

                                                                                                                                                                                                                                                                                                           

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