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23. Double Pole Safety Cut-outs: —
a. Must be in plain sight or enclosed in an approved box readily accessible. (See Definitions).
b. Must be placed at every point where a change is made in the size of the wire (unless the cut-out in the larger wire will protect the smaller).
c. Must be supported on bases of non-combustible, insulating, moistureproof material.
d. Must be supplied with a plug (or other device for enclosing the fusible strip or wire) made of non-combustible and moisture-proof material, and so constructed that an arc cannot be maintained across its terminals by the fusing of the metal.
e. Must be 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. Special permission may be given in writing by the Inspector for departure from this rule in case of large chandeliers.
/. All cut-out blocks must be stamped with their maximum safe-carrying capacity in amperes.
24. Safety Fuses:—
a. Must all be stamped or otherwise marked with the number of amperes they will carry indefinitely without melting.
b. Must have fusible wires or strips (where the plug or equivalent device is not used), with contact surfaces or tips of harder metal, soldered or otherwise, having perfect electrical connection with the fusible part of the strip.
c. Must all 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.
25. Table Of Capacity Of Wires:—
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 Brown & Sharpe gauge, which must be followed in the placing of interior conductors:
Table A. Table B.
Note.—By "open work" is meant construction which admits of all parts of the surface of the insulating covering of the wire being surrounded by free air. The carrying capacity of 16 and 18 wire is given, but no wire smaller than 14 is to be used except as allowed under Rules 18 (a) and 27 (d). 26. Switches:—
a. Must be mounted on moistureproof and non-combustible bases, such as slate or porcelain.
b. Must be double pole when the circuits which they control supply more than six 16-candle-power lamps, or their equivalent.
c. Must have a firm and secure contact; must make and break readily, and not stop when motion has once been imparted by the handle.
d. Must have carrying capacity sufficient to prevent heating.
e. Must be placed in dry, accessible places, and be grouped as far as possible, being mounted—when practicable—upon slate or equally noncombustible backboards. Jackknife switches, whether provided with friction or spring stops, must be so placed that gravity will tend to open rather than close the switch.
27. a. In all cases where conductors are concealed within or attached to gas fixtures, the latter must be insulated from the gas-pipe system of the building by means of approved joints. The insulating material used in such joints must be of a substance not affected by gas, and that will not shrink or crack by variation in temperature. Insulating joints, with soft rubber in their construction, will not be approved. (See Definitions).
b. Supply conductors, and especially the splices to fixture wires, must be kept clear of the grounded part of gas pipes, and where shells are used the latter must be constructed in a manner affording sufficient area to allow this requirement.
c. When fixtures are 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 fixture.
d. 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. 18 B. & S., No. 20 B. W. G., No. 2 E. S. G.
e. All burrs or fins must be removed