I went to work in a 120/208 Panel in a large building getting near turnover.

Company policy is no live work and I happily shut down the transformer feeding the panel, checked the mains, it was dead.

I started moving some branch conductors around and Blam. Big flash. I checked my self and the coworker with me, we where fine.

What had happened was a 277 lighting circuit got tied into an outlet circuit.

The 120 volt branch breaker had not been turned on so the lighting circuit was working fine along with about 6 277 volt Duplex receptacles.

We commented that at least we found it before someone plugged in a tool, now I know what would have happened if they did [Linked Image]

Seriously, now I check all terminals.
Take nothing for granted.

Bob Badger
Construction & Maintenance Electrician
Massachusetts