While putting in a line for the central air unit, the installers pointed out to me that there were sparks occurring where the white (common, neutral) wire was screwed into the ground bar attached to the back of the breaker panel. I followed the line and didn't immediately see any problems, but I know anything could be happening behind the wall on the way up to the top floor/garage. We unscrewed it and screwed it back in tight, and it's not sparking, so I thought maybe it was just loose, but here's my question: 1) I thought there was not supposed to be any power going through common, so how could there be sparking? 2) If there is power in it, wouldn't that be because a hot (black) is touching it somewhere, and if THAT's the case, how could it not trip the (20 amp) breaker? I mean, you don't get just SOME power going through when you touch hot to common, do you? isn't it just instantly enough to trip the breaker? This is a line that is the newer yellow 12 gauge; has hot, common, and ground. The ground appears to be scrwed in the breaker box fine, and the hot is scrwed tight onto the breaker. Any help would be appreciated; I'm looking to understand in what scenario you'd see sparks where the common is screwed into the breaker's ground bar, but the breaker doesn't trip. Thanks for any help, and for taking the time.

I have 1 inch conduit that I am bringing into the building with a pull box. It enters the cavity between 2x4(s) right below the Main panel. I need to take a sharp turn up and go another 2 to 3 feet into the panel. Can I use a regular PVC elbow to do this? I cant find a 90 degree elbow for 1 inch conduit. There is a 90 degree pull box, but I cant find that in 1 inch either. Isnt electrical PVC exactly the same as regular with the exception of color?