Experimental study on thermal and fire behaviors of energized PE-insulated wires under overload currents

Abstract

The electric fires are highly likely caused by the combustible wire insulation material ignited by a short circuiting or overload current in residential and commercial buildings, nuclear power plants, etc. It is important to know fire behaviors of the insulation materials over energized wires under overload currents, so fire behaviors are investigated experimentally over high-current energized polyethylene (PE)-insulated copper wires A and B with different sizes (d_c/d_o = 0.9 mm/3.0 mm and 1.3 mm/4.2 mm for wires A and B, respectively, where d_c and d_o denote the core and outer diameter of wire, respectively). The results show that the flame height rises firstly and then remains steady with the increasing current under low current, which is similar with the previous research, while the flame height drops sharply when the current is extremely high over 40 A. The flame width also drops with current under high-current condition. In addition, the surface temperature of wire, measured by infrared thermography, agrees well with the predicted balance temperature of wire under low current, but deviates from the balance temperature under high currents. Correspondingly, the measured flame spread rate agrees well with the prediction model based on the thermal balance temperature at low currents, while shows an obvious deviation under large currents. The flame spread rate grows approximately with the square of the current, but tends to increase slowly and even remains steady under high current. Moreover, the effects of wire size on flame spread are also investigated. The flame of wire with large diameter is wider, but its flame spread rate is lower and rises slower with current. The results of this work provide important information about fire behaviors over energized wires under overload currents and may guide the design of future electric fire safety.