An addition to my 1970's house has three outlets and my tester says each of them has an open ground. I checked each one and the incoming and outgoing copper wires are connected and a pigtail runs to the outlet. The boxes are plastic, so they don't need to be grounded. I checked back at the panel and it appears to me that the copper wire in the Romex is connected to the ground bus bar. I give up. It seems to me the grounding is fine, why do I get an open ground reading?

 

Have you checked EVERY junction box on the circuit?

 

Yes but I will do it again to make sure. Would switching to a metal box and grounding it make any difference? Of course, I could just punt and put two prong receptacles in the room, but if there is a problem with the grounding, I would rather fix it.

 

Switching to a metal box will not make any difference and would be difficult to do at this point.

Follow the circuit from the panel. Check for a proper ground at the first junction box, then at the second, etc. Somewhere you will find an open ground, if you are using your tester properly.

just out of curiosity, what type of tester are you using, and does your tester indicate a proper connection at a known properly wired receptacle?

 

Check in the closets. If any of the circuits pass through a porcelain closet light, then 99% of the time the electrician will not bother with the grounding wire and will either cut it or fold it back in the box,and that is where the break will be. I've bounced off the walls in older homes trying to find open grounds, and now I have an inside straight to the problem. Post if this is the case.

 

I am using the usual Home Deport bought Sperry tester, two yellow lights and one red on a three prong tester. Unfortunately, there are no closet lights on this circuit but that is good information for the future. At this point I am just going to bite the bullet and redo the grounding for each junction box on the circuit this weekend and see if that corrects the problem. If not, I will switch out the three prong outlets for two prong. Thanks for all the help.