SECTIONALISER A method of isolating a spur line of an electrical power system protected by a multi-shot resetting circuit breaker is disclosed wherein at least two successive current surges in the spur line which activate the circuit breakers are detected. In response to the detection the spur line is isolated during a subsequent current dead period. A sectionaliser is described for isolating a spur line of an electrical power system protected by a multi-shot resetting circuit breaker. The sectionaliser comprises a metal casing 22 providing a current path across a fuse mounting 10 whilst the sectionaliser is in a conducting position. An electrical circuit 23 inside the tune detects at least two successive current surges in the casing and during the following dead period actuates a chemical actuator 14 to trip the sectionaliser out of its conducting position.
