ECN Forum Forums General Topics of the Trade General Discussion Area 70E quandry

Thank you all for your responses.
We evaluated the possible cause and isolated all loads before we reset the main breaker. We had an outside contractor with 30cal suit reset the breaker to keep everyone happy. We then turned on the unrelated breakers to the suspected cause. Suspected Load: A motor control center feeder breaker had also tripped with the mains and there was a report of a BANG when a pump was started. Then we investigated and found that the Motor Control Center bucket for the pump had melted its buss clips and damaged the buss. Hard to tell if it flashed to ground or phase to phase.

Nice to see a thread on 70E. Seems most people in this trade never even heard of it. I bring this up all the time. I made my employer get me a Proper Arc Flash shield. I use it every time I remove a panel cover. If I suspect a problem, I will than put on my FR shirt.
I have been in your circumstance many times. Show the ignoramous the literature., ie 70E

0 Risk as stated by others. However I personaly will put on FR shirt, hot gloves and shield/hard hat to reset such a breaker. You never know.

While we are on this topic I would like to pose a question...not to hijack the thread:
Many years ago, a instructor I had in my 3rd year apprenticeship, was explaining about how a breaker can store energy, enough to kill you if you closed it. If I remember correctly it was along the lines of say there is a lightning strike, the utilities circuit breaker is antiquated and doesn't open. Current travels through line to residence or building with improper grounding. That or some of the e=nergy could store in your tripped main. seems impossible however he was pretty convincing! You reset breaker and that energy comes out of panel and basically cuts you in half. I have never read or heard of this.
1) Is this possible?
2) Have any of you heard of this?

If so, a 0 Risk for resetting tripped breaker with panel cover on seems egregious.

Breakers do not store any energy, nor does any energy actually flow through an open one.
What does happen is enormous amounts of energy can be released when the contacts close on a bolted fault.

Greg's right on that.
Having repaired and rebuilt breakers all the way up the 15kV ones I can confirm that a circuit breaker is basically just a knife switch with tons of stuff to make it move quickly and a fair amount of stuff to snuff out the arc that is created at the moment that the breaker opens. Once it has opened, it's dead and harmless (unless there are charged springs in it waiting to break an unwary finger).

As Greg stated, there is no 'stored' energy within a circuit breaker.

Closing a cb with a fault on the load side can cause catastrophic situations.

Check out the Bussmann website for a lot of graphic info on fault current situations.