Ignition and Flame Propagation of Externally Heated Electrical Wires with Electric Currents

This paper describes the results of an experimental and numerical study of the effect of electric current on the ignition and flame propagation propensity of polyethylene-insulated copper conductor electrical wire. Two simplified models were developed to describe the ignition and steady flame propagation of energized electrical wires exposed to an external heat flux, respectively. The models predict that for a higher-conductance wire it is more difficult to achieve ignition and flame propagation. Experiments were performed on three types of electrical wires with different conductor diameter of 0.5 mm, 0.8 mm and 1.1 mm and the same insulation thickness of 0.15 mm. A 20 mm long coil heater was used as the ignition source to generate a controlled heat flux. Experiments show that increasing the current of wire leads to a convexly decreasing critical heat flux for ignition, agreeing with model predictions. Effects of different currents on insulation temperature and flame height are discussed. The flame width of three types of wires could be considered invariable with the current, which are 9.06 mm, 12.45 mm and 15.07 mm respectively. The heat release rate of flame is discussed through the volume of flame and a correlation is presented that ΔV _F  ∝ I ². The likelihood for molten PE dripping is determined by the absolute and relative fuel load for different wires. Finally, the correlation between the flame propagation velocity and the current of wire, Δv _f  ∝ I ², is demonstrated.