This application relates to methods and apparatus for determining the location of a fault in a power cable of a power distribution network. The method involves monitoring at least one electrical parameter of the power distribution network to detect the occurrence of a fault and determine at least one time window for the occurrence of the fault The method involves analysing a first set of measurement signals is obtained by a distributed fibre optic sensor having a sensing optical fibre deployed along the path of the power cable. The first set of measurement signals include signals indicative of the extent of any disturbances along the sensing fibre over a known time period. The measurement shallots are analysed based on the at least one time window for measurement signals and the location of the fault in the power cable is identified based on the location of one or more longitudinal sensing portions of the sensing fibre.