The use of DC current splitting to locate resistive faults in cable pairs

Northern Telecom engineers have developed a “cable-fault locator,” which allows for the rapid and accurate location of resistive faults in metallic cable pairs. Finding resistive or “wet” faults in cable pairs is a very important activity for public utilities, since these types of faults present service interruptions to the utility´s customers. Rapid and accurate location of the faults is essential to utility repair personnel. Using a dc current-splitting technique, single-point resistive faults can be located to an accuracy of 1 Ω, within 30 s, using a Northern Telecom loop test unit. This type of accuracy allows repair personnel to dig up buried cable with a high level of confidence that they are near the fault. The cable-fault locator is fully automatic, requiring the tester to enter only essential information, such as which wire the fault is on, and whether the fault is to ground, to battery, or is a short to the other wire in the pair. In addition, the meter can be placed in remote locations, using a standard modem to communicate via the telephone network. In this paper, the Northern Telecom method is compared to standard fault location methods.