Effects of electric current and sample orientation on flame spread over electrical wires

Abstract

Electrical wire is one of the primary causes of electrical fires. Experiments were conducted to study the effects of electric current and sample orientation on flame spread over polyethylene (PE) insulated copper wires. The flame spread velocity showed a non-monotonic trend with the inclination angle, i.e., the flame spread velocity firstly decreased and then increased with the increasing inclination angle. In the upward flame spread configuration, the molten polymer flew down along the wire if the wire was inclined, which resulted in a periodic flame spread phenomenon, and a sub-flame was observed behind the primary flame. The periodic time was shorter for the smaller inclination angle or the lower electric current. The downward spread seemed to be more susceptible to the electric current. A flame spread model considering the effects of inclination angle and electric current was developed. The heat transfer analyses in the preheating region were conducted to study the controlling mechanism of flame spread.