Fan distribution box is a kind of equipment that can be used for fan power consumption. Fan distribution box is a massive parameter in data, which generally constitutes low voltage. According to electrical wiring, switchgear, measuring instruments, protective appliances and auxiliary equipment can be assembled in closed or semi closed metal cabinet or screen to form low voltage distribution box, During normal operation, the circuit can be connected or disconnected with the help of manual or automatic switch. During the use of fan distribution box, because the capacity selection of AC contactor is not very appropriate, AC contactors with the same capacity are installed for different outgoing circuits, and the imbalance of three-phase load is not considered, the current level of some outgoing contactors is not increased by one current level based on the normal selection model, Therefore, the AC contactor is burnt out during operation in high temperature season in summer, resulting in abnormal use of fan distribution box.