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This is going to sound like a duplicate question but it's actually reversed.

We live in a house built in the 1960's (in the US). We have metal conduit throughout and surprisingly a ground wire that is terminated at each electrical box. Many of the outlets were 2-prong, and I've been replacing them with 3-prong.

I came across one outlet today that confused me. Instead of the standard 4 wires coming in, I only saw 3. And to make things stranger, it was 2 neutrals (white) and one hot (red) attached to a 2-prong screw terminal duplex-X receptacle (all 4 holes are T-shaped). Also it is a switched outlet.

Has anyone ever seen something like this? Is there a way to convert this to a 3-prong receptacle?

wires connected to device front of device

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  • Is this outlet switched? What is T shaped? – JACK Jul 6 '20 at 1:57
  • Jack, yes it appears to be a switched outlet, I've updated the post with a picture of the receptical. – Person Jul 6 '20 at 2:10
  • Are the side tabs which connect the two receptacles broken off and if so on which sides are they broken off? Often the switched receptacles are connected so that one receptacle is switched and the other is always on. Do you have a non-contact voltage tester or a VOM? Prolly the red is switched hot and the blacks (not currently connected to the receptacle) are always hot. The red and the black may be on the same breaker or may not be. – Jim Stewart Jul 6 '20 at 2:23
  • Both measure 10V when powered off and 122V when powered on. I didn't notice any tabs, so maybe they are both broken off. I'll use a non contact voltage tester on the black when I open it up next to check your theory. Thanks! – Person Jul 6 '20 at 2:39
  • How many bare copper ground wires are in the box? – Jim Stewart Jul 6 '20 at 17:29
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That's a combination 120/240v outlet that could be wired for 120 volt or 240 Volt. You're wired for 120 Volt so just turn off the power, remove the old outlet and get your regular grounded outlet and hook the red, switched hot, to the brass screw and the two whites to the silver screws. A better way to work with the two neutrals would be to pigtail both together with a 8" piece of white wire using a wire nut. Then connect the single white wire to the outlet. Make sure you use the right wire size. Since you have a bare ground wire, hook it to the ground screw on the new outlet.

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  • Thanks JACK! So was the previous person who wired it just being lazy hooking up both neutrals to separate screw terminals? – Person Jul 6 '20 at 2:33
  • Could the OP connect the new duplex receptacle so that one receptacle would switched and the other always on? Do you think the blacks are on the same breaker as the red? – Jim Stewart Jul 6 '20 at 2:34
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    @Person not being lazy, it's done a lot when daisy chaining outlets. Maybe he didn't have a wire nut. I have always pigtailed... makes replacing an outlet much easier. – JACK Jul 6 '20 at 12:20
  • @JimStewart I'm guessing they're on the same breaker and yes, the OP could wire one always hot and the other switched... I'm waiting to see if he asks that... And they could possibly be on different breakers, afterall, that a 120/240 V outlet, maybe originally wired that way. – JACK Jul 6 '20 at 12:29
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    @JimStewart One of the total drawbacks of this old plug and believe it or not, you can still buy them, with grounding but the ones I've found aren't UL listed. – JACK Jul 6 '20 at 13:03
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First, the outlet is just a red herring; it is just an older style of outlet.

There’s more going on in this box than you know

Note the extra black wires that you haven’t discussed at all.

What’s actually happening is that one black-white pair is delivering power from supply. The other black-white pair is delivering power onward to another point-of-use.

The red is delivering power to this outlet, with the white as neutral. That means one of (at least) two things:

  • The outlet is, or was, switched. And the red wire is (or was) coming back from the switch to deliver switched-hot to the outlet. Perhaps it’s been wired to bypass the switch and be permanently on.

  • The circuit is a Multi-wire branch circuit or MWBC, with this outlet receiving one 120V “leg” of the circuit, and the black onward wires are the other 120V “leg”. However there’s at least one defect with this setup: in an MWBC you are not allowed to use a device to splice the shared neutral. It must be pigtailed.

It’s normally allowed to use the 2 screws on a (non-tab-broken) outlet as a splice point. However that is not allowed in MWBCs.

Fortunately, you don’t need to care. Just use a red wire-nut to join the 2 existing white wires to a short pigtail, and connect that to the new outlet.

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