This invention relates to a method of detecting faults on an electrical power line (7) and a sensor (5) for use in such a method. Preferably, the sensor is a line-mounted sensor (5). The method comprises the initial step of determining an initial impedance profile for the power line (7), and thereafter the method comprises the subsequent steps of the line-mounted sensor (5) transmitting a conducted communication signal (41) along the power line, receiving a reflected signal (43) particular to the transmitted communication signal and correlating the transmitted signal and the reflected signal. By correlating the signals, it is possible to determine the actual impedance of the power line. The actual impedance of the power line may then be compared with the initial impedance profile and it is possible to ascertain whether a fault exists on the power line. Preferably, the method uses an adaptive filter to determine the location of the fault.