The present study investigated experimentally the effect of electric fields on the characteristics of flame spread over insulated electric wire by varying AC voltage applied to the wire in the normal gravity condition. Polyethylene (PE) insulated electrical wires were tested. The wire was placed horizontally on electrically insulated posts and one end of the wire was connected to the high voltage terminal. Thus, the electrical system is the single electrode configuration. The insulator was ignited at one end and the flame spread rates along the wire have been measured by using a digital camera at various conditions of applied AC voltage and frequency. The result showed that the spread rate decreased with the applied AC voltage and over a certain critical voltage the flame was extinguished. For a fixed applied voltage, two distinct regimes existed depending on the applied AC frequency. In the low AC frequency regime, the flame spread rate decreased with the frequency, while in the high frequency regime, it increased with the frequency even over the spread rate without applying electric fields. This result implies that the fire safety code developed based on without applying electric fields needs to be modified in case of fire for electrical wires experiencing electric fields and suggest a need in conducting experiments in a microgravity condition to be applied for fire-safety in a spacecraft.