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I recently noticed that a three-prong outlet stopped working. Short version: I checked the wiring and there are only two wires running to the outlet and no visible ground wire. I checked another outlet in the room and it's setup the same. So I'm guessing these are both incorrectly setup?

Longer version is that I tested with a working light plus an outlet tester and tested resetting the breakers. The outlet tester has previously shown these outlets as "correct" as grounded outlets. Is this because the box is grounded? I want to get the outlet fixed, but not sure if I should try replacing the fixture or get someone in to fix the wiring?

  • Your house may be old enough to have non grounded wire. It also be a metallic sheathed cable, which could be acting as a ground. Looking deep inside the box, you may see a tiny bit of red where the wires come into the box, this red thing is a plastic piece which protects the wire where the metal sheathing is cut to expose the wire inside for tying in. It is a small clue if you have that type of cable. – Jack Nov 15 '15 at 7:23
  • The receptacle tester has some limitations - there are problems that they may miss. If the tester indicates OK ground, there should be wire on the ground terminal on the receptacle. What is it connected to? – batsplatsterson Nov 15 '15 at 14:23
  • What's the age of the house? Could you post a photo of the wires behind the outlet in question, and your incoming service box? – Bryce Feb 13 '16 at 23:49
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Note that if you can't put in a grounded outlet, a gfci outlet is an acceptable alternative for safety. I've done that at several places in my old house. When installing without a ground, there's a sticker that should be applied essentially saying "yes, we know there's no ground, don't panic if the tester tells you so but also don't expect to use anything plugged in here as a ground."

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The method in older houses was to wrap the ground wire around the cable and then insert it into the cable clamp in the box. This grounded the box. If the receptacle is a "self grounding" type than the receptacle is now grounded through the mounting screw.

It could have stopped working if it is downstream (on the load side) from a GFCI receptacle. Check that you don't have a tripped GFCI in the house somewhere. Usually the wiring does not go bad in a lifetime.

  • This still isn't a Code-compliant grounding means -- early W/G NM's EGC was undersized! – ThreePhaseEel Nov 15 '15 at 19:43
  • Hmm I don't think the EGC of NM cable was ever "undersized" but if it was it would have been code complient since NEMA would have made it that way, but that is beside the point. When the wrapped EGC grounding method was used in the 40's and 50's it was code complient. – ArchonOSX Nov 15 '15 at 20:17
  • Thanks for the suggestions. The GFCI was a good idea and I thought I had some upstream, but I realized (of course) I don't have any GFCI's (old houses are great!). That's on the list. I still need to investigate the box grounding but will probably just get someone to come in and look at this. I need estimates for a few other things too :) – Rob Nov 18 '15 at 16:09

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