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when the circuit is broken is inconsiderable.

It is also of little importance here, that the switch cut off completely all the wiring beyond it. For these reasons the rules allow single-pole switches under the conditions stated.

The motor must be insulated from the ground for the same reasons that apply to the generator. (Page 58.) A motor is, however, used in all sorts of places and usually has not a special space set apart for it as a generator has, so there is need of greater precaution. Mounting the motor on filled dry wood and raising it eight inches from the surrounding floor keeps it well insulated, away from dirt that might gather on the floor, and less liable to water damage in case the floor becomes flooded during a fire. Drip-pans are required so that all surplus oil may be caught, and everything about the machine thus kept clean and less combustible.

The waterproof cover serves the same purpose that it serves in the case of the generator. (Page 60.)

Rule 1 (c) requires that a generator shall not be placed in a room where there are flyings of combustible material. It is obviously not always practicable to confine motors to rooms altogether free from this sort of thing, and where there is dust or dirt, or flyings of any kind, the motor is enclosed in a case that will isolate it from bad conditions. Usually the case

advised by the underwriters is a small room or closet built about the motor and lined with sheet metal.

Rules 9 (a) and 9 (6) are made for the reasons that 5 (a) and 5 (b) are made. In the case of a motor, however, a wooden resistance-box is still more unfit, for it is used only in starting the motor, and resistance is not supposed to be left in circuit, but to be all cut out as the motor reaches full speed. When through carelessness or accident some of the resistance is left in circuit, the coils are very likely to overheat, for they are frequently of too small carrying capacity to carry for any length of time the current that will flow through them.

CLASS B.

HIGH-POTENTIAL SYSTEMS.

OVER 300 VOLTS.

Any circuit attached to any machine, or combination of machines, which develops over 300 volts difference of potential between any two wires, shall be considered as a high-potential circuit and coming under that class, unless an approved transforming device is used, which cuts the difference of potential down to less than 300 volts.

10. Outside Conductors

(including services):

All outside, overhead conductors

a. Must be covered with some approved insulating material, not easily abraded, firmly secured to properly insulated and substantially built supports, all tie-wires having an insulation equal to that of the conductors they confine.

[Section a. Insulation that will be approved for servicewires must be solid, at least three sixty-fourths of an inch in thickness, and covered with a substantial braid. It must not readily carry fire, must show an insulating resistance of one megohm per mile after two weeks' submersion in water at 70 degrees Fahr., and three days' submersion in limewater, with a current of 550 volts, and after three minutes' electrification.]

[The following list of wires have been tested and found to comply with the requirements for an approved insulation under Rule 10 (a), Rule 12 (d), and Rule 18 (a) :·

:

Acme, Ajax, Americanite, Bishop, Canvasite, Clark, Columbia, Crescent, Crown, Edison Machine, Globe, Grimshaw (white core), Habirshaw (red core), Kerite, National India Rubber Company (N. I. R.), Okonite, Paranite, Raven Core, Safety Insulated: Requa white core, Safety black core; Salamander (rubber covered), Simplex (caoutchouc), United States (General Electric Company).

None of the above wires to be used unless protected with a substantial braided outer covering.]

"Services," or service-wires, are the wires that lead from the main distributing wires to any special installation, just as the service water-pipes are the small pipes that lead from the street mains to a building.

"Tie-wires" are the short pieces of wire that are used to tie or fasten the line-wire to the insulators. (Fig. 25.)

b. Must be so placed that moisture cannot form a crossconnection between them, not less than a foot apart, and not in contact with any substance other than their insulating supports.

c. Must be at least seven feet above the highest point of flat roofs, and at least one foot above the ridge of pitched roofs over which they pass or to which they are attached.

d. Must be protected by dead insulated guard irons or wires from possibility of contact with other conducting wires or substances to which current may leak. Special precautions of this kind must be taken where sharp angles occur, or where any wires might possibly come in contact with electric-light or power wires.

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A "cross-connection" might perhaps be quite as well termed simply a connection. Thus, in Figure 26, if both wires are lying on the wet wood, A, there may be sufficient leakage through the wood to form an electrical connection, or cross-connection, between the two wires.

In a similar way, if the two wires in Figure 27 were fastened to the front of a building, and the upper wire were to become loose and to hang near the lower, water

G

dripping from the upper wire might be the cause of a connection between the two.

Long stretches of wire are apt to sag, and to make sure that this sagging will not bring the wire in contact with roofs, the provisions in Rule 10 (c) are made.

“Guard-irons” are used to keep a wire from coming in contact with conducting material when the wire fails to be properly supported by its insulators. Thus, in Figure 28, where a wire is passing round the corner of a building, if the pin holding the insulator A should break, the attached wire would, on account of the strain upon it, come against the wires B if there were not the guard-iron, C, to catch it.

If a wire passes over another wire, and there is any liability of the upper wire's sagging, coming loose from its fastenings, or breaking, a guard-wire, fastened to insulated supports and passing under the upper wire, will receive this upper wire if it fall, and will prevent its falling on the wire below.

Wires that carry current for running motors, or for furnishing power in distinction from light, are commonly called "power-wires."

e. Must be provided with petticoat insulators of glass or porcelain. Porcelain knobs or cleats and rubber hooks will not be approved.

f. Must be so spliced or joined as to be both mechanically and electrically secure without solder. The joints must

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