Phase back-chaining preventing apparatus and method of three phase power source

A phase back-chaining preventing apparatus and method of three phase power source is provided to prevent miss-connection of three phase power sources when installing an air-conditioner. In a three phase power source reverse phase preventing apparatus, a zero-crossing detection unit(301) detecting zero-crossing in each phase between signals of three phase power source. A microcomputer(302) determines whether the angular power source was normally connected or not by using zero-crossing information. A power switching stage(303) turns on/off the main power source applied to air-conditioner with on/OFF by the control of the microcomputer.