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surrounding material, or that the insulation of the conductor will be ultimately injured or destroyed by the elements.
3. So constructed or placed that difficulty will be experienced in removing or replacing the conductors.
4. Subject to mechanical injury by saws, chisels, or nails.
5. Supplied with a twin conductor in a single tube where a current of more than 10 amperes is expected.
G. Depended upon for insulation. The conductors must be covered with moisture-proof material.
The object of a tube or conduit is to facilitate the insertion or extraction of the conductors, to protect them from mechanical injury, and as far as possible, from moisture.
Twin tube conductors must not be separated from each other by rubber or similar material, but by cotton or other readily carbonizable substance.
Conductors passing through walls or ceilings must be encased in a suitable tubing, which must extend at least one inch beyond the finished surface until the mortar or other similar material be entirely dry, when the projection may be reduced to half an inch.
Double Pole Safety Cut-outs—Must be:
1. Placed where the overhead or underground conductors enter a building and join the inside wires.
2. Placed at every point where a change is made in the size of wires (unless the cut-out in the larger wire will protect the smaller.) This includes all flexible conductors. All such junctions must be in plain sight.
3. Constructed with bases of non-combustible and moisture-proof material.
4. So constructed and placed that an arc cannot be maintained between the terminals by the fusing of the metal.
5. So placed that on any combination fixture, no group of lamps requiring a current of six amperes or more shall be ultimately dependent upon one cut-out.
6. Wherever used for more than six amperes (or where the plug or equivalent device is not used) equipped with fusible strips or wires provided with contact surfaces or tips of harder metal soldered or otherwise having perfect electrical connection with the fusible part of the strip.
Safety Fuses must be so proportioned to the conductors they are intended to protect that they will melt before the maximum safe carrying capacity of the wire is exceeded.
All fuses, where possible, must be stamped or otherwise marked with the number of amperes equal to the safe carrying capacity of the wire they protect.
All cut-out blocks, when installed, must be similarly marked.
The safe carrying capacity of a wire changes under different circumstances, being about 40 per cent. less when the wire is closed in a tube or piece of molding than when bare and exposed to the air, when the heat is rapidly radiated. It must be clearly understood that the size of the fuse depends upon the size of the smallest conductor it protects, and not upon the amount of current to be used on the circuit. Below is a table showing the safe carrying capacity of conductors of different sizes in Birmingham, Brown & Sharpe and Edison gauges, which must be followed in the placing of interior conductors.
'-Brown & Sharpe.—. . Birmingham. . —Edison Standard—.
Gauge No. Amperes. Gauge No. Amperes. Gauge No. Amperes.
1. Be mounted on moisture-proof and incombustible bases, such as slate or porcelain.
2. Be double pole when the circuits which they control are connected to fixtures attached to gas pipes, and when six amperes or more are to pass through them.
3. Have a firm and secure contact, must make and break readily, and not stick wheo motion has once been imparted by the handle.
4. Have carrying capacity sufficient to prevent heating above the surrounding atmosphere.
5. Be placed in dry accessible places, and be grouped as far as possible, being mounted, when practicable, upon slate or equally indestructible back boards.
Motors.—In wiring for motive power, the same precautions must be taken as with the current of the same volume and potential for lighting. The motor and resistance box must be protected by a double-pole cut-out and controlled by a double-pole switch. Arc Lights On Low Potential Circuits— —Must be:
1. Supplied by branch conductors not smaller than No. 12 B. & S. gauge.
2. Connected with main conductors only through double-pole cut-outs.
3. Only furnished with such resistances or regulators as are inclosed in non-combustible material, such resistances being treated as sources of heat.
4. Supplied with globes protected as in the case of arc lights on high potential circuits.
1. In all cases where conductors are concealed within or attached to fixtures, the latter must be insulated from the gas pipe system Ci the building.
2. When wired outside, the conductors must be so secured as not to be cut or abraded by the pressure of the fastenings, or motion of the fixtures.
3. All conductors for fixture work must have a waterproof insulation that is durable and not easily abraded, and must not in any case be smaller than No. 16 B. & S., No. 18 B. W. G.. or No. 3 E. S. G.
4. All burrs or fins must be removed before the conductors are drawn into a fixture.
5. The tendency to condensation within the pipes must be guarded against by sealing the upper end of the fixture.
6. No combination fixture in which the conductors are concealed in a space less than onefourth inch between the inside pipe and the outside casing will be approved.
7. Each fixture must be tested for possible "contacts" between conductors and fixture, and for "short circuits," before the fixture is connected to its supply conductors.
8. The ceiling blocks of fixtures should be made of insulating material.
Where electric gas-lighting is to be used on the same fixture with the electric light:
1. No part of the gas piping or fixture shall be in electrical connection with the gas-lighting circuit.
2. The wires used with the fixture must have a non-inflammable insulation, or where