The location of opens in toll telephone cables

Improved methods have recently been developed for the location of opens in toll cable conductors. The discussion of these methods is prefaced by a review of older practices. This improved open location method and equipment are sufficiently accurate that in practically all cases a fault in a 60-mile length of cable may be located within a maximum variation of plus or minus one half the length of a cable section (a section is the length of cable between splices — about 750 feet), and therefore enables one to select, prior to the opening of the cable, one or the other of the two splices between which the fault lies. This degree of accuracy is very desirable for practical reasons. In this development, the line characteristics are considered. The accuracies of calculated locations, assuming no errors in measurements, arc compared for different lengths of lines. The impedance bridge circuit is treated to bring out the method of obtaining a balance. The effects of several frequencies of testing potential are analyzed. The probable errors and inaccuracies of measurement which would interfere with the correct location of faults are classified and methods for their correction are developed. The accuracy of the method and the sensitivity of the apparatus are given.