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I've been replacing all the outlets in my house (built in 1949, wiring is newer than that) with white outlets to please the SO. I came across an outlet where I had to shut off two circuits to get the the plug not to be hot.

After doing some reading, it seems like some of the likely possibilities are

1) mis-wired breaker-box

2) possibly the two circuits are connected in a junction box somewhere.

The second seems likely, as almost every outlet has 4 wires, two hot wires and two neutral wires, and it's easy to discern the pairs. In general I've just been wiring them like they were, not taking the tabs off the outlets because they weren't off the old outlets.

After reading about this, I realized that if any two of those pairs of wires are on different circuits, I'll have joined the circuits (at least I think that's what I got out of it).

My question is, if there are four wires, is there any reason not to break the tabs on every outlet I'm wiring?

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Yes, there is a reason not to break the tabs on every receptacle that has four wires (2 black and 2 white). With the tabs in place the receptacle is a way of joining an incoming line from the panel to a cable which is feeding more receptacles and lights further on. If you would break the tabs on all receptacles, you would have to make these connections with lengths of wire and wire nuts. It would be a lot of trouble.

The only reason to break these tabs is if you want the two receptacles in a duplex receptacle to be powered through two different breakers.

If you have a receptacle with one or both tabs broken and you want to restore the connection between the receptacles, there is a kind of pigtail with wire that can be used to connect the two receptacles, but it is trouble and takes up space.

  • Ah okay, thats kind of what I thought. So as far as my suspicion that there is a box where two circuits are being connected, whats the appropriate way to test that for certain? – Iron_Teapot Jul 26 '17 at 23:34
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    Have you been checking for broken tabs as you have been replacing the receptacles? It's real common to get on a roll and forget to check. Everybody does it lol. – Harper Jul 26 '17 at 23:55
  • I believe the issue existed before I started (or at the very least i noticed it on the third outlet I started on). Perhaps I'll recheck the first two. This should be test-able by unwiring those guys and turning on one breaker, testing the black wires, then turning on the other breaker and testing the black wires right? Is there a better way? – Iron_Teapot Jul 27 '17 at 0:04
  • Yeah, that should work fine. You can just break it in one place and see what happens. Cap or tape unused wires including neutral. – Harper Jul 27 '17 at 0:07

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