Abstract: A fault distance indicator (FDI), locates a fault in a power line by modeling pulses of reflected travelling wave signals which are generated from electrical arcs that occur as a result of the fault. Open loop power distribution circuits are arranged in two halves, each half comprising a circuit length from the overhead feed point to an open point with transformers and cable sections located along the circuit length. An FDI is inserted in each half of the loop. The FDI device monitors the circuit using an antenna which receives radio-frequency signals emitted by line faults and records the signatures of these faults. When the “trouble crew” arrives at the scene the recorded signature is downloaded to a portable PC via a radio, infra-red or other telemetry link. The downloaded data is analyzed first to generate a model of the reflected travelling wave signal and then parameters of the model are adjusted to minimize differences between the model and the actual data.