# Intermittent Ground Fault on AB 525 VFD



## BenD (Jun 21, 2017)

I'm hoping someone can help out on this. I have a 3HP 525VFD that after running fine for several months is now occasionally returning a ground fault. It only happens occasionally and only when starting the conveyor. Before you ask, no, I have not meggered the motor yet. I only have a programmer onsite at the moment and he doesn't have a megger. We have checked for visible damage on the motor leads and used a multimeter and found no issues. If this were a new installation I would immediately suspect a damaged wire, but since it ran for months without issue it seems a little less likely, though still quite possible. We forced the VFD on with the motor disconnect off and didn't experience the fault. The next step will be to swap the motor leads in the panel with a same sized motor and run the system for awhile (it will be a week or more before I can get out there with a megger). 
At any rate, I'm looking for input on what else it could be. Application listed below:

2HP 480V motor powering a conveyor belt, part of a series of belts controlled from one control panel
3 speed settings (no encoder feedback)
2 second ramp time
Belt typically stops and starts around 20 times in a 4 hour period. Stops last a few seconds at most. We experience the fault once or twice a sort, and only on starting, never while running.
It is a pretty long run on the motor leads. I know that this can cause some issues with sensorless speed control. But I don't know if phantom ground faults is one of those issues. Also we have done this exact same set up several times over the past 3 years without issue.

Thoughts?


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## scotch (Oct 17, 2013)

You need a 1000v megger to start troubleshooting the wiring ...seen this problem often with575vac VSDs and 600vac rated wiring .


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## JRaef (Mar 23, 2009)

I agree, 1000V megger and PLEASE disconnect the VFD terminals when you do that!

If the cable megs out OK, it might be cable capacitance issues. How are the output cables run, individual conductors in _*steel *_conduit or did you use VFD cable? Has anything else changed in the system, as in ANYTHING, even mechanical?


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