When the neutral conductors ares floated from the three-phase four-wire distribution power system, the three-phase voltage is distributed to the single-phase load device connected to the system in proportion to the impedance. An over-voltage is applied to a single-phase load device with a high internal impedance, and a fire may occur due to deterioration of an internal device of the load devices to which the over-voltage is applied, or dielectric breakdown of a coil or wire insulation coating. Therefore, in this study, the heating characteristics that appear in the process of applying an unbalanced voltage due to the departure of the neutral line and the risk of ignition through electrical signal analysis were confirmed with two types of load devices installed in the three-phase four-wire distribution system.