We recently found a tripped GE SGLB series breaker. The breaker fed a VFD and it fed a large motor on the roof. Per the display on the breaker it appeared to have tripped on a GF. While testing things we got to the point of wanting to re-energize the VFD and a discussion ensued questioning how to confirm the drive was ok so we didn't close the beaker into a faulty piece of equipment. Needless to say the discussion left me scratching my head and realizing I didn't have the correct answer.

What is the proper way to "test" a drive so you can be confident you energize it safely?

Thanks for your help

I would either reach out to the manufacturer or review the VFD manual. There may be troubleshooting or initial power up procedure.

Disclaimer: It is imperative that you follow all guidelines recommended by the manufacturer. For low voltage VFD's, many manufacturers recommend checking the resistance phase to phase and phase to ground at the power input terminals before energizing the drive. A very low resistance or dead short would indicate that the VFD's protection or power structure components have been damaged. However, most VFD's have capacitors and various input semiconductor structures so the results can be misleading unless you follow the manufacturers instructions precisely. Take the manufacturers troubleshooting training for that specific model of VFD before attempting this.

We have had similar issues on VFD. Manufacturer usually has static testing that needs to be done prior to commissioning and on a fault. Here is a document we use for our drives when a fault has occurred on the line side of the drive to trip a breaker or blow a fuse.

Thanks to everyone for the input.





I've downloaded this and appreciate it very much.