Ignition and Flame Spreading Features of Excessively Overloaded Polyvinyl Chloride Copper Wires.

This work investigated the ignition and flame spreading features over an excessively overloaded wire coated with polyvinyl chloride (PVC) to provide valuable information for determining fire behavior caused by this typical type of wire failure. The wires with a core/wire diameter of 3.3/4.1 mm carried various overload currents from 130 A to 240 A at intervals of 10 A. Experimental results revealed that occurrence of a parting arc as the core melted into two parts was indispensable for ignition of the overloaded PVC wire without an external ignition source. The current increase reduced the time for energizing the wire to a parting arc. For this special piloted flame, with the current increase, the intensity of the heating of the core became higher; thus, the flame spread distance (FSD) became longer due to the thermal decomposition of the PVC insulation intensifying, and the average flame spread rate reached its maximum value of approximately 1.0 m/s as the current increased to 220 A. However, the FSD declined as the currents reached higher than 220 A because the faulting wire melted so quickly that it did not have enough time for the insulation materials to decompose and produce sufficient flammable gases. [ABSTRACT FROM AUTHOR]