I read the above article posted by another member with great interest. Seems the guy was probing with a standard DVM, and it failed, causing the arc flash. I still don't get how this caused the incident because a DVM has rather thin leads, so any fault current would be limited by the probe, and guage of the prove lead.
Even if he had an aligator clip to ground, usually they are not the greatest connections.
Am I missing something ???
needless to say, I don't like going into 480/277v panels any more....