An apparatus and method for detecting and locating electric current leakage paths along the length of an electrically conducting elongate member is disclosed. The apparatus has variable supply means (8, 10) and means for monitoring the impedance of the member (9, 11), the supply means being operable to drive current in opposite directions along the member, so that a movable node can be established, the node being where the net change in potential between the member and its surroundings is substantially zero. When the apparatus is in use, the position of the node is varied by varying the current driven along the member and the resultant impedance is monitored by the monitoring means (9, 11), whereby the position of the node at which there is a local minimum in the impedance indicates the position of a current leakage path.