Fondazione Policlinico Universitario Agostino Gemelli / Rome, Italy

Localized fire ignition hazard in branch circuits, cords and connected equipment

Abstract.  In electrical power systems, the fire ignition can be originated by incident energy of faults. Faults involve overheating, arcing and burning for all the wiring exposed to mechanical damage and other insulation stresses especially wiring connected by flexible cords and cables. The mechanical damage of the stranded bare conductors can degrade the effective sizing of the total cross section, causing anomalous conditions of local overcurrent. To highlight the local incident energy in case of fault, the parameters steady current and transient current densities can assist in analyzing the event. The conductors size reduction, degrading locally the thermal withstand capability, makes ineffective the protection coordination amplifying the anomalous effect of current no detectable adequately by overcurrent protective devices. The faulted cords remain so energized and present electric shock and fire hazards. Generally and especially in strategic buildings as hospitals, preventing ignition is better than promptly extinguishing. An efficient protection can be achieved by integration of active and passive techniques : by adoption of the special device Arc-fault Circuit Interrupter (AFCI) that recognize the arcing; by wiring the circuits, particularly extension cords, with Ground-Fault-Forced Cables, GFFCs, that convert faults into ground faults easily protected by ground fault protective devices (GFPDs).

Fondazione Policlinico Universitario Agostino Gemelli / Rome, Italy