Ignition phenomena of electrical wires by overheating have been investigated experimentally to gain a better understanding of the electrical fire and ignition mechanism of multilayer materials. In this study, several sample wires, made by nickel-chrome and copper, with different diameters and coating thickness of polyethylene have been used. In the experiments, a coil heater was adopted as the ignition source and the temperature distribution along the wire was monitored by thermocouples. The heat flux and heating time were selected as the main parameters to identify the flashpoint and spread point of electrical wires. Experimental results show that the difficulty of wire ignition is determined by the thermal conductivity, diameter and coating thickness of wire, collectively. Additionally, there may be a critical fuel mass flux and a critical wire temperature distribution that controls the flashpoint and spread point. We have also found that a critical heat flux for wire ignition exists and increases as pressure reduces. The ignition criterions of wire are summarized and qualitatively discussed.