Why does the motor trip after soft start

- Oct 10, 2019-

If start trip, first look at the soft start reported what fault, if jump circuit breaker, estimated start current is large.

If the trip in operation, estimated to be a protective action, first confirm the motor load, is not overload or broken phase.

1: the reason of circuit breaker trip when soft start starts the motor

This tripping situation, more occurred in the start and stop, should be carefully recalled is just a start or stop that jump, or start or stop after a few seconds jump.

  1. Start or stop immediately jump, should check the motor side whether short circuit, the mechanism stuck or blocked rotation.

  2. When tripping during starting or stopping, the current is too large or the time is too long, and the circuit breaker trip curve has been reached.

2: soft start start motor circuit breaker trip solution

  1. Reset the setting value of circuit breaker to make the trip curve larger than the start current curve.

  2. Adjust the current limiting multiple of soft start to make the current within the specified range.

  3. reduce the start or stop time.


The above is the reason and solution of circuit breaker trip when soft start starts the motor. Under normal circumstances, it will not occur, but only when the load is especially heavy, it may occur. Take ABB soft start as an example, the default start time is 10S, which can be applied in almost 90% of the occasions.And the pump can be said to be 99% problem free.