Simple three-phase motor phase loss protection circuit

The working principle of this circuit is as follows:

Close the three-phase air switch, and the intermediate relay is energized. Press the K2 normally open button, K2 is self-locked, and the AC contactor K is closed. If the A phase is missing due to a fault, the K coil loses power and the AC contactor K is disconnected. If the B phase or C phase is missing, the coils of the intermediate relay J and the AC contactor K lose power at the same time, and J and K are disconnected at the same time, which plays a double protection role.

Component Selection

J is the intermediate relay, K is the AC contactor, the coil voltage is 380V, and the size of the AC contactor depends on the load.

The circuit is simple and reliable, the components are easy to purchase, the cost is low, and it can effectively protect three-phase electrical equipment.