Faulted Circuit Indicator (Cable Network, Medium Voltage)

A compact, typically self-powered (via a current transformer around the cable or via battery) measuring and signalling device mounted at strategic points in a medium-voltage cable network (for example at ring main units or switching stations) to quickly determine, after a disturbance, in which section of the network a short circuit or earth fault has occurred. As soon as the indicator detects a fault current above a set threshold, it gives a local visual signal (for example a flashing LED or mechanical flag) and/or a signal to the control centre via remote communication, so that technicians do not have to check the entire network section by section but can go directly to the section between the last indicator without a fault signal and the first with a fault signal. Unlike time-domain reflectometry (TDR), which determines the exact distance to a cable fault within a section via a reflection measurement, a faulted circuit indicator only indicates whether a fault current has passed that point — the two techniques are often used complementarily: the indicator first narrows the search area down to a single cable section, after which TDR determines the exact fault location within that section.