Just trying to rule out the possibility of someone hacking a leg for something. I'm guessing you would have cleared any major dust during initial t/s. How many grounding points between each machine and ground system? It sounds like one or both machines has an open in the egc somewhere. Your meter will tell you which leg is shorting, then where the ground is compromised. I hope they're ok with you taking the machines out of service for a bit-i hate when the brass won't ok a little down time... be safe.This is 480 3-phase. There would be no possibility of an outlet and zero branch circuits. The operators were subjected to the shock by accident. They did not intentionally touch both machines just to see if the voltage was present. The operation is very dusty. MAybe the extreme dust is conducting?