A 1 1/4 inch liquatite coming from a wireway had been left where the non-electrician maintenance guys removed it from an air compressor. Actually, they pulled it in through the hole in the wall and left it there. It was #2 copper THHN and thus was stiff enough so the last 3 feet stuck up in the air inside that electrical room. No tape on the bare copper ends, just sitting there dead, no problem, breaker is off, right?
WRONG! These dummiies can't be made to fear this 480/277 stuff. One leg of the 3 phase breaker DID NOT BREAK and this just sat there live, 277 volts to ground. High dust area, no care given to dust proofing electrical equip. I am guessing that's what compomised the breaker's ability to make/break.
I found this while trying to find a breaker to feed the new compressor now situated 100 feet away (to get it out of the dusty environment that ruined the old comp.) My wand waved at these bare conductors tipped me off. These are a combination of truck mechanics and welders and such who are real good at their own stuff but HAVE NO FEAR of the voltages involved at these plants.
Never assume a breaker or disconnect has broken all connections. Use your meter!!