ECN Forum Forums General Topics of the Trade Business Related Discussion Bonding screw

I just wondered if anyone wanted to speculate on something I saw the other day.

In a new steel storage building, a 200A Sq D panel was being fed directly from the meter. A grounding kit was installed in the panel. The GEC and bonding jumper to the steel building were the only wires on the grounding bar, and any neutrals were on the other (neutral bar). Conduit was run for all circuits with no EG. What caught my attention was arcing (just the marks) around the bonding screw. I checked the screw to see if it was tight, and turned it about 3 full turns.

I'm just wondering what caused this arcing. Did something short out to the conduit and return to the panel and arc between the screw and bar? I think I can imagine how this would happen, but would like to hear some ideas.

Thanks for all your help in the forum. I rarily post, but lurk everyday.

Welcome to the forum, rusty.

The most likely cause of the arcing is part of the neutral current is flowing through the GECs (probably the water line) back to the power company transformer.

This is normal and now that you tightened the screw you are all set.