Just as an aside in case it might apply, a friend of mine in New Zealand (where Dairies are one of their only stable industries) did a lot of work on the effects of stray voltages that are created by the more extensive use of VFDs now. He boiled his work down to this web page. Worth a look.
I haven’t gotten around to the GF detection yet. The above metallic gutter mounted between two pvc faulted and energized the building frame. Some one noticed it smoking.. PVC was temp fix. Covers inline setscrew Splices we had in our used parts area. Field engineering.