Simple phase failure protection circuit composed of intermediate relay

In general, the power supply for the contactor to attract the motor control circuit is drawn from two phases. Conventional methods may cause the motor to run in two phases. In the ordinary motor start-stop circuit, an intermediate relay KA is added, and its attracting voltage is 380V. This allows KA to close its normally open contacts only when the three-phase power supply is powered, thereby ensuring that the three phases L1, L2, and L3 are powered, and the contactor KM can be powered to work, playing the role of motor phase failure protection. The circuit is shown in the figure below.

This circuit is generally used in working places where the motor load is heavy. If the motor load is light, once the fuse blows during the operation of the motor and one phase is powered off, the other two phases of power can be returned to the coil of the other phase that is powered off through the motor. Although the voltage is low, the contactor coil can still be attracted, so it is difficult to protect the motor.