Bridge Methods for Locating Resistance Faults on Cable Wires

N the toll telephone plant, insulation faults such as " g r o u n d s " and "crosses" are usually located by the " Varley l o o p " method, which involves essentially the measurement of the d.-c. resistance of the faulty wire between the point of fault and one end of the cable, and the comparison of this resistance with the total conductor resistance of the wire to obtain the "percentage location" of the fault on a resistance basis. Corrections are then applied to account for such factors as the resistance of the leads between the cable and the bridge, the resistances of loading coils, and non-uniformity of conductor resistance caused by temperature differences between underground and aerial sections of the cable. After all corrections are applied the corrected percentage location is converted into distance from one cable end to the fault.