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I own a house built in 1948 and want to update the duplex receptacle outlets in my kitchen. I was told by an electrician that our electrical box is grounded and I can see the grounding wires outside my back door.

The existing set has one set of 3 prong receptacles and the other set has only 2 prong receptacles. I want to put grounded outlets in each of the duplex slots, but there are only 2 black wires and two white wires in the box. The existing setup used a black wire and a white wire to bridge between the receptacles. Is that what I need to do for the new receptacles?

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existing receptacle setup

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    Good on ya for providing us a picture! If you can get another picture showing how the wires enter the box, that will be extra helpful. It's possible that there's a ground wire that's connected to the box, but if this is original 1948 wiring, that's unlikely. If there's been a wiring update since, it's possible. As noted above, a GFCI receptacle is now required in the kitchen and installing them adds protection even if they're not grounded. There are a number of questions here about that, if you'd do a search.
    – FreeMan
    Commented Feb 18 at 20:54
  • Also, maybe it's just the lighting, but the yoke on the receptacle on the left looks like it's been heat damaged. Probably a good thing you're replacing it.
    – FreeMan
    Commented Feb 18 at 21:15
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    Just brassy .vs. silvery on the yoke, I think, from experience with those. If the cable is BX (heavy armored metal) it was considered a suitable ground at the time, and would thus be grandfathered until replaced, IIRC. If it's just black and white wires with a cloth or plastic covering and no ground wire you'd need a retroit grounding wire to have grounded outlets. A clearer picture of the cable entering will help.
    – Ecnerwal
    Commented Feb 18 at 21:30
  • Can you post photos that show clearly where the cables enter the box at, please? Commented Feb 18 at 22:28
  • Whether it has threads or not, the little hole is where I put ground screws. I'm in EMT land, so there isn't even a wire. Anything new comes with one and there's never anything for me to do with it until I add a screw. Drilling a hole and threading it is a pita. Starting with a hole is much easier. - Adding a ground to an already (grandfathered) grounded box is one thing. You have cloth covered, two wire, ancient romex. :(
    – Mazura
    Commented Feb 19 at 22:12

2 Answers 2

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You cannot install a grounded (3-prong) receptacle except one of three ways. First, you have ground wires coming in on the cables, obviously. Second, you provide GFCI protection per 406.4(D) and label the outlet "No Equipment Ground". And third, you have a metal box and one of several things has happened.

  • Cables with ground wires come into the box, and the ground wires are attached to the metal box.
  • Armored cable which is legitimate for carrying ground has been used to reach the box, and the correct cable clamp has been used to attach the cable ground to the box.
  • Non-flexible metal conduit (EMT, IMC, FMC) connects to the box, and serves as the valid grounding path.
  • A ground wire has been retrofit, per NEC 250.130(C).

So, the box is grounded. How do we get that ground to the receptacle itself? The easiest way is to use the $3 "spec-grade" receptacles which come in a box instead of loose in a bin. These are marked "self-grounding" which means a wiper picks up ground off the standard 6-32 mounting screws.

If we're sure the receptacle is going to have hard, flat flush clean metal contact with the steel box, that is also acceptable and that lets you use the cheapie receptacles. The receptacle can't be floating above the box on the drywall ears; for that you need the self-grounding feature.

This trick always works with switches, even if they are floating and not marked self-grounding.

"But I have ground wires coming in on the cables. Can't I pigtail those straight to the outlets and ignore the metal box and treat it like a plastic box?" Nope, gotta ground the metal box first (at a higher priority than the outlets).

"What if I'm not sure the box is grounded?" Then you need to retrofit ground per 250.130(C) or use GFCI protected outlets per 406.4(D). That means either a GFCI receptacle marked "No Equipment Ground" or a plain receptacle wired off the LOAD terminals of a GFCI elsewhere, which then also requires a "GFCI Protected" label. Of course, no one uses the labels, and then they get mad when the home inspector correctly writes them up for the violation.

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It is a kitchen. If you don't find a ground at the box. Use a GFI at the first box from the breaker panel, use the load terminals on the GFI to connect to downstrean regular outlets. Label their cover plates " GFI protected" and "Not Grounded".

See 2023 code cycle. Joke- This will be eleventeen times safer than what you have, without doing a rewire.

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