Fig. 810.—Slow burning wire, formerly known as Underwriter's Wire. The insulation is triple braided, saturated with a white fireproof compound. Solid conductor.
Ques. Where should slow burning wires be used?
Ans. In hot dry places, where ordinary insulations would be injured, and where wires are bunched, as on the back of a large switchboard or in a wire tower.
A slow burning covering is considered good enough when the wires are entirely on insulating supports. Its main object is to prevent the copper conductors coming into contact with each other or anything else.
Ques. What must be done before using weather proof wire?
Ans. Permission to use the wire must first be obtained from the local Inspection Department.
Slow Burning Weather Proof Wire.—The covering of this type wire is a combination of the underwriters and weather proof insulations. The fireproof coating comprises a little more than half of the total covering. When the fireproof coating is placed on the outside, the wire is called "slow burning weather proof."
Fig. 811.—Slow burning weather proof wire. The insulation is composed of two braids thoroughly saturated with a fire proof composition, over which is a highly polished weather proof third braid. This wire was formerly known as "fire and weather proof" wire.