Unprotected faults of electrical cords and extension cords in AC and DC systems

Abstract

In electrical power systems all the wiring exposed to mechanical damages and other insulation stresses, such as flexible cords, can be involved in overheating, arcing and burning. Mechanical damages of the stranded bare conductors can degrade locally the effective sizing of the cross section and cause anomalous local conditions. The circuit protective devices can be unfit to detect the faults of cords that remain so energized and available to electric shock and fire hazards. Some fire ignitions result so special unprotected faults. To highlight the local incident energy in case of fault, the paper introduces the parameters steady current and transient current densities that assist to analyze these fault events. An efficient protection can be achieved by integration of active and passive techniques: - adopting Arc-fault Circuit Interrupters (AFCI) that recognize the arcing faults; - wiring the circuits with a grounding protection conductor to involve the ground in every faults that in AC systems are rapidly protected by residual current protective devices (RCDs or GFPDs). At this aim it is recommendable the use of special cables, Ground-Fault-Forced Cables, GFFCs particularly for cords and extension cords also supplying Class II equipment. The protection of DC systems requires a special care.