Abstract: The invention provides method and apparatus for identifying the faulted phases on the occurrence of a single phase fault simultaneously on both circuits of a double circuit electric power transmission line using measurements taken at one end only of the line. Using measurements of voltage and current at the one end of the line and a knowledge of various parameters of the line, a signal representative of the travelling wave arriving at the one end of the line in consequence of the faults is derived. This derived signal is used to deduce the values of the components of the derived signal attributable to the different faults for each of a number of assumptions as to which phases are faulted. The deduced values for the different assumptions are then used to determine which assumption is most likely to be correct.