Electrical – Testing 3-wire receptacles indicates no ground even though 12/2 w/ground wire is connected


I have an interesting question. I have a hundred-year-old house with electrical panel updated a few years ago by a professional electrician. I went around last week with a circuit tester just to make sure all the outlets were wired correctly. The former homeowner had added several outlets herself and some had reversed polarity, mixed-up ground/hot etc., which I was able to fix pretty easily.

However, most of the outlets are showing no ground. I opened the service panel and it is 60A service, Square D breakers, and two neutral bus bars. I'm not sure if one is a ground bus and one a neutral though. I assume they go to the same place anyway, since this is the only service panel (no sub-boxes).

The wires going into the buses are both neutral and ground.

So, assuming the neutral and ground bus bars are bonded (so, electrically the same), would this fact cause the tester to show no ground to a receptacle?

What I mean is, if a box had separate neutral bus and ground bus, would the tester show a good ground, whereas a shared bus would show open ground?

If the shared buses are not the issue, What other ideas do you have which may be causing the open ground reading?

Thank you.

Best Answer

The grounds should be bonded to the neutrals at the main panel. (If it's not, it's a serious problem, call an electrician.) If you are getting good grounds on some of the outlets, it's probably bonded at the main panel.

If the ground isn't spliced right* at a receptacle it will show no-good at that receptacle and at all the receptacles on the same circuit downstream from that receptacle. That would be a possible explanation. It fits with the miswiring by the previous owner. Tracking down the bad ones can be a bear. Still that may be better than tracking down and replacing a damaged wire.

*edit: by "spliced right" I mean all the ground conductors of all the cables and all the ground terminals of the devices are bonded together in the box, and the box itself it's a metal box ...

from electrical-online.com

If there was some creative wiring going on, some wiring can cause the receptacle tester to show a good ground where there isn't. For example jumpering the neutral to the ground terminal on the receptacle (non-code and a very bad idea) would show a good ground on the tester, but there isn't.

If you can double check with a different tester, that might be a good idea, you don't want to chase your tail if the tester is no good.