I was working installing a 2 pole 50A 240V GFCI breaker and trying to debug an appliance. I turned off the GFCI breaker I was working on, but the main breaker was on. About the time I had one of the wires undone I put my hand on the metal enclosure of the breaker box and received a shock. What could possibly have caused this? The main was on, and the GFCI breaker was connected to the box via the pigtail to the neutral terminal. Any heuristics/diagnostics to determine why the external enclosure became electrified?
The subpanel (in a detached garage) has 4 wires coming in: 2 hot to the main breaker, one to the grounding bus, and neutral to the neutral bus. In addition, there is a very thick copper wire running outside the conduit that appears to terminate in the ground below the deck on the outside of the building.
There is continuity between the neutral and ground bus, which I understand is not normal for a subpanel.
Am I right in suspecting that the grounding electrode is not grounded? How would I test this?
Best Answer
First I would like to say, thank god you weren't seriously injured. Second this is a very serious situation. The reason someone is shocked when touching a metal enclosure is because you are grounded and the enclosure is not.
You're neutrals and grounds are tied together at the first means of disconnect. It will be bonded at the main breaker and if there is no separate main it will be done at the Panel's main breaker. Check to make sure the bonding screw is properly installed and the grounding bus is bonded with the neutral bus. Then check to see if your grounding electrode conductor actually runs to a proper grounding electrode. Check for corrosion and loose connections. If everything is properly done, if you have a problem you should get a trip on the breaker having a problem.
If you're not getting a trip then you probably have a piece of 240V equipment that is missing a phase, the neutral, or the ground is not connected properly and you are getting one phase trying to seek a path back to the Panel and the breaker. I noticed that you said you were trying to debug an appliance. I would start there.
Under no circumstances should you be trying to troubleshoot this problem under power. Disconnect all power and troubleshoot with a continuity tester or an ohmmeter. If all of this seems to technical I would advise you seek professional help.