Vent: Had a panel in a San Antonio house nearly fry from a bad ground loop

Last week I was finishing a job on a new build off I-10, and the main panel started throwing random trouble signals. Turns out the electrician had tied the alarm's ground to a water pipe that wasn't actually bonded to the main house ground, creating a nasty loop. The voltage difference was almost 2 volts AC, and the board was getting hot. Anyone else run into weird grounding issues in new construction lately?

3 comments

3 Comments

wyatt_green15d agoTop Commenter

Yeah the "bad ground loop" thing is a classic. I had to run a new 6 AWG bonding jumper back to the main panel last month for the same reason.

theawest15d agoMost Upvoted

Wait, isn't 2 volts AC a bit low to make a board get hot? Honestly, I've seen ground loops cause weird signals, but the heat usually comes from a bigger voltage difference or a direct short. Tbh, the hot board makes me think there might be a loose neutral connection on that circuit too, letting current find a path through the alarm ground. That would explain the heat and the weird voltage reading.

sanchez.mia10d ago

So they're still using water pipes as grounds on new builds? I read a whole thread on a trade forum last month about how that's becoming a huge problem with PEX plumbing, since the plastic sections break the ground path. That 2 volt difference could totally mess with sensitive boards, especially if it's not a clean sine wave. The heat is weird but maybe the board was trying to correct for the noise constantly.

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