Distributing System and Lamps Volume 2

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1906 edition. Excerpt: ...very high voltages. For local distribution, especially within the limits of cities and towns, electric light and power overhead wires are covered throughout with insulating material, to reduce the danger of accidental contact with persons or with other wires or conducting bodies. The insulation of overhead wires is in two parts. One /of insulating material impervious to moisture, placed next to the wire, and the other of some substance fitted to resist abrasion or like mechanical injury. Fig. 199. Prom Glass Insulator. The inner coating is a rubber compound, or for lower grades some cheaper substitute. Before this is laid on the wire it is first tinned to prevent the sulphur contained in the rubber compound from corroding the wire. This inner coating is then covered with a hard braid of cotton or hemp, woven on to the wire, or the wire is served with a tape and insulating compound. Where the wire is to be continually moist, gutta percha is better than rubber, but it is more costly. In the more expensive grades of wire the coatings are greater than two in number, and they alternate, insulating compound and then braid or tape. In Figs. 201-203 are shown 2oa Loeke H, gh Potant"u "uu'ator the manner of application of the insulation and the braid. Joints in Overhead Lines.--Whether an electrical conductor is bare or insulated it is necessary that any joint made in it shall be nearly equal in conductivity and in mechanical strength to the Fig. 201. Insulated Line Wire. rest of the conductor. The ordinary "lineman's splice" (Fig. 204) has been the standard practice for galvanized wire iron, in telegraph lines; but the use of copper wire, both hard and soft drawn, and the necessity for better connection with heavy currents, has...