Oddity repaired without conclusion
We had a large station, (foreign made machining equipment) which began taking out the bus duct when it was turned off for periodic maintenance, (ground fault indicated). This was obviously a problem for our facilities department, (wear & tear on the 800 amp breaker), and the production department, (other machines affected, including several identical); so two separate maintenance groups were looking into this.
I do remember making some improvements on the machine's 400 volt transformer grounding & bonding connections, (not normally installed with an outside contractor, but these were in an relocation agreement from another plant), but I don't recall finding any "Ah Ha" problems.
The problem went away without the other maintenance group reporting any specific findings, but I'm not so certain they would. Either way, this was an odd problem that none had a valid explanation for what exactly could cause it. I had an admittedly wild thought, knowing that a car's ignition spark is caused by the collapsing field in the coil when the points break, (old school); I wondered if there was any correlation with this. Has anyone had a similar incident? Or know exactly what occurred?