Precautions for Adding Disconnect between Drive and Motor

Precautions when installing at motor disconnects or contactors on output of VFD

PowerFlex Drives

The disconnect can be opened while the drive is running.

It’s when closing that is a concern. If the drive runs full speed and you close the contactor, it puts undo stress on the IGBTs and may cause premature failure.

Suppose you have multiple motor applications. Let's say you have 4 motors on one drive. You will probably be fine when closing the contactor to 1 motor while running the drive because the inrush of 1 small motor on a larger drive is negligible.

Ideally, we want the drive to be at 0 speed or stopped when the contactors are close to the motor.


In general, It’s recommended not to open or close the disconnect to the motor while the drive is running. In the past, this has been seen to damage the IGBTs very easily, even in multiple motor applications.

Use the Enable on the drive from an early break aux contact on the contactor or disconnect. That way, the drive goes into a Not Enable state (coast) before the drive is fully powered off.