Ans. No. The covering should be made from a compound containing from 20 to 35 per cent. of pure rubber.
It would be difficult to place pure rubber on a wire, and moreover a covering made of pure rubber would not be durable and would deteriorate very rapidly, particularly at temperatures above 120° Fahr. Accordingly, it is mixed with other materials, such as French chalk, silicate of magnesia, sulphur, red lead, etc.
Weather Proof Conductors.—In this class of conductor, the wire is protected from the weather by a waterproof covering, consisting usually of braided cotton of two or three thicknesses saturated with a moisture resisting insulating compound.
Ques. Where are weather proof conductors used?
Ans. In places subject to dampness, such as cellars, tunnels, open sheds, breweries, etc.
Fig. 809.—Twisted weather proof wires. The insulation consists of two or three thicknesses of braided cotton saturated with a moisture resisting insulating compound.
Ques. What are the advantages of weather proof conductors?
Ans. The insulation is cheap, very durable, and does not deteriorate unless exposed to high temperatures such as will melt the compound.