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I've replaced some old GFCI receptacles in my kitchen, which live in metal electrical boxes. The old GFCIs did not have grounding conductors attached, but it seems that the boxes themselves are grounded. (I have tested for continuity between two of the boxes and I get a beep; I am assuming that the two boxes being electrically continuous is good evidence that they are both bonded to ground.)

I don't want to rely solely on the GFCI mounting screws for a ground connection and would like to connect a ground wire. The GFCI has a green ground screw, but the box does not have a green screw inside. How should I bond the wire to the box?

Here's a picture of the mid-run box. The other box is at the end of the run.

gfci box

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You should be able to find ground screws at any home improvement store. Most boxes have a tapped hole for this purpose. If yours does not, you should be able to find grounding clips at the home improvement store as well.

Keep in mind, however, that continuity does not equal an adequate ground. Just because you have continuity between two of the boxes, does not mean you have an adequate ground all the way back to the grounding electrode. For example, the boxes might have armored cable running between them. Armored cable is only rated as a grounding conductor, if there's an internal grounding strip (which is not always the case). Armored cable could/should connect the boxes in such a way, that a continuity test would pass but does not provide a proper ground.

If you don't have an adequate ground; or you're not sure if you do or not, the best bet is to not connect the grounding terminal of the GFCI to the box. You should also place the "No Equipment Ground" sticker on the receptacle, but this is often neglected in residential situations.

  • Thanks; I think the grounding clips will work for me. Is there a way to test if the box is truly grounded? My multimeter leads won't reach all the way back to the panel; I suppose I could just attach some long wires to them though.... – friedo Nov 17 '14 at 14:00
  • nm - I realized I could use my multimeter to test for voltage between the hot lead and the box and I do get 120v, so it looks like a good ground. Thanks for the help! – friedo Nov 17 '14 at 14:28
  • @friedo measuring 120 volts between the ungrounded (hot) conductor and the box, does not mean there's an adequate grounding conductor between the box and the grounding electrode. – Tester101 Nov 17 '14 at 18:12
  • How should I test it to make sure? – friedo Nov 17 '14 at 19:31
  • Sometimes with those old boxes, the ground screw can be on the top on the box. In the photo I don't see the ground wire coming from the 2wire. The original electrician could have pulled the hot and neutral into the box but kept the ground outside and it might be attached to the top (out of view). – justinw Nov 19 '14 at 3:07

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