File:Electrical instruments and telephones of the U.S. Signal corps (1911) (14753416431).jpg

Identifier: electricalinstru00unitrich (find matches)
Title: Electrical instruments and telephones of the U.S. Signal corps
Year: 1911 (1910s)
Authors: United States. Army. Signal Corps
Subjects: Military telegraph -- United States Military telephone -- United States
Publisher: Washington, Govt. print. off.
Contributing Library: University of California Libraries
Digitizing Sponsor: MSN

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le: and if the insulation is good, in one second so small an amount of this chaigo Avill be lost by leakage that little or no sound will be produced bj^ subsequent contacts, as cable will still be 242 ELECTEICAL INSTRUMENTS U. S. SIGNAL CORPS. 243 charged. Care should be taken that wire / and telephone terminalattached to it are well insulated, otherwise leakage from them maygive false indications. Having found the faulty conductors, the location of these fauhsnniy then be proceeded witli by the methods suggested below (figs. 160and IGl). It is applicable to cables having two or more similar con-ductors, or to a single conductor cable when both ends are available,as when it is coiled in a tank or on a reel. It is the Murray loop testwith a slide wire. in which simple relations of resistance to lengthsexist, owing to the uniformity of resistance along the wires in thecable conductors and slide wires, respectively. It is, in fact, a com-bination of several well-known instrument methods.
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coe Fig. 159. To prevent serious errors care must be taken that one of the con-ductors in this test has sound insulation. No resistance measurements are involved, and the only apparatarequired are a few cells of battery, a telephone receiver, and from10 to 50 feet of bare resistance wire. Of this latter about No. 28• Climax or S. B. wire is suitable. However, if resistance wireis not to be had, fair results may be obtained by using No. 36 bare cop-per wire. First taking the case of a multiple-conductor cable, say 3,000 yardslong, in which there is one or more conductors with defective insula-tion and at least one good one. join the defective one to be tested Aviththe good one at the distant end. Drive two small bright nails (.1 andC in fig. IGO) and convenient to the terminals of the conductors at 244 ELECTRICAL INSTRUMENTS U. S. SIGNAL CORPS. the testing end and stretch from these a piece of the resistance wirearound another nail (Z>) and back, making each equal branch of thewir

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