a fault sensing electrical wire utilized one or more sensor strips which provide an impedance change when the wire is subject to an overtemperature condition or mechanical damage of the wire . a control unit measures the impedance of the sensor strips of the fault sensing wire and provides a control signal to initiate an alarm or protective action based on the severity of the condition . the control unit may monitor a number of fault sensing sires simultaneously or in sequence . the apparatus may be used to sense an electrical arc occurring in the insulation of the wire .