I am replacing some of the receptacles in my house and encountered a strange wiring today. One of my receptacle boxes have hot wires coming from two different breakers from the electrical panel. I have also just realized that another receptacle on the opposite wall also has the same thing going on. Here is the situation:

  1. Breaker 1 is off, breaker 2 is on: the black and white wires on the right are hot
  2. Breaker 1 is on, breaker 2 is off: the black wire on the left is hot only

The way this was connected to the existing outlet was as in the 2nd photo.The tabs are in place.

Any idea what is going on here? I don't want to just wire it as before without understanding. If there was something wrong with this, I would like to fix it now.

enter image description here

enter image description here

enter image description here

enter image description here

enter image description here

  • 1
    It sounds very wrong if the tab/s are in place with two breakers. Add a picture of the two breakers in your panel. It sounds like a badly wired multi wire branch circuit. Do you have a multi meter and can read the voltages? If the breakers are in the right place, you should read 240v on two blacks, 120v on black and white. With tabs in place the breakers should have tripped.
    – crip659
    Nov 18 at 21:40
  • Just added a photo. Do you mean tabs in the breakers? I meant the tabs in the outlets.
    – Seyhan Gul
    Nov 18 at 21:57
  • Tabs on the outlets, yes. I don't know enough about those half size breakers to know if they are on the same phase, or different phases. I will need the let others more knowledgeable to answer.
    – crip659
    Nov 18 at 22:08
  • 3
    @crip659 Those are on the same phase. In all panels I know of, any tandem pair in the location of a single ordinary breaker is by definition on the same phase/leg. It is when you have quads or pairs of tandems that things get more interesting. Nov 18 at 23:45
  • 1
    Aside: The 30A breaker (with green handles) just above the main breaker in the bottom right corner has black and white wires connected. The white wire has far too much of the conductor exposed (It wasn't stripped or inserted correctly.) and is missing marking to indicate that it is a hot, not neutral, wire, e.g. black or red tape.
    – HABO
    Nov 19 at 1:55

1 Answer 1


You likely (can't guarantee it) have a series of mistakes that happened to work out OK in this particular instance.

The typical setup of wires from two different breakers coming to a duplex receptacle is to have one breaker for the top receptacle and one for the bottom receptacle. Technically this can be for a bunch of reasons, but the usual reason is a Multi-Wire Branch Circuit or MWBC. An MWBC lets you use three wires (normally black, red, white) in one cable to power a pair of 120V circuits instead of using two separate black/white cables. The advantage is that you can power twice as much stuff while saving on wire compared to two totally separate circuits. However, an MWBC only works correctly if the two breakers are on different phases/legs. That can be done with a typical double breaker or with two side-by-side single breakers with a handle tie (because common shutoff is required to avoid exactly the problem you found of a single breaker being turned off not cutting all power to the yoke) or with the proper set of tandem breakers (which gets a little tricky and varies by panel - basically the middle pair of a quad set).

However, in ye olden times an MWBC did not have to be a pair of breakers or fuses next to each other and so mistakes were made. I actually found one when (with my electrician) replacing old fuse panels with a new breaker panel. A common situation is that an MWBC will get rearranged in such a way that the two breakers end up on the same phase/leg, which I believe is what happened here.

But there is a second issue: separating the receptacles. The tabs on the sides are supposed to be removed when two receptacles in a duplex are powered (MWBC) or operated (half-switched) separately. But again, mistakes are common and that's how you end up with situations such as this one, and also one of the ways you get a switch that doesn't seem to do anything because it is switching one receptacle but power never goes away because the tab is there and the unswitched hot powers both receptacles.

And then the fun part:

If you rewire an MWBC to be one one phase/leg and then replace a receptacle that had the tabs removed without removing the tabs on the new receptacle then you get exactly what you found here.

On the other hand, if you replace a proper MWBC duplex receptacle without removing the tabs then sparks will fly until the breaker (normally very quickly) trips.

There is a remaining mystery though: Normally an MWBC is about saving wire, so you typically have a /3 (black, red, white) going to at least the first receptacle and then it might continue that way (with tabs removed on hot side but not on neutral side), or it splits at some point (negating some of the savings) into two /2 cables, each with hot from one breaker and sharing (at the point of the split) neutral. But the reasons to do that is if, for example, you run an MWBC to the first location in a kitchen and then split to other receptacles - but if you do that then you wouldn't have those two /2 cables in one location except at the initial split.

So something else may be going on. The next step is to carefully remove the front cover of the breaker panel so you can see whether this is a /3 from the pair of breakers (in which case it is a very serious issue because that neutral can get overloaded) or two separate /2 cables (in which case the mystery still exists but things area little bit safer).

Based on the picture and breaker identification, these are both black wires. So presumably two separate circuits, not an MWBC. Why? I have no idea. But be careful about disconnecting either one, as it is possible that one could be paired with a red wire on one of the breakers a few spaces down. Need to trace out the wires to the top of the panel box where the cables come in to see what goes with the reds.

As for the existing receptacle problem, capping one set of wires and using an ordinary (tabs not removed) receptacle would be perfectly safe. But figuring out what is going one is still a good idea. Step 2 (step 1 is to check the cables at the breakers) is to see what other receptacles, lights, etc. are powered by each breaker.

  • Thank you for the wonderful explanation. Lots of information, I will have to read it a few more times to understand. Let me take a photo after removing the front panel. I noticed another weird thing. When the receptacle is wired with the tabs, all of a sudden the white wire is not hot anymore. Does that give you any more clues?
    – Seyhan Gul
    Nov 19 at 1:07
  • Hard to say. The white wires are supposed to be neutral (well, all neutral is white, not all white is neutral, but in this case they are definitely both neutral). However a non-contact voltage tester can often trigger based on phantom current, so it isn't that surprising. Nov 19 at 1:12
  • Added photos of the breakers to the original post now.
    – Seyhan Gul
    Nov 19 at 1:41
  • I now understand what you mean. Mistakes somehow canceled each other here, seems like. Now, what is the way to check if I have a /3 from the pair of breakers or two separate /2 cables?
    – Seyhan Gul
    Nov 19 at 2:43
  • Well, I measured with a multimeter now and here is my findings: (i) voltage difference between ground and black 1 is 120 V; (ii) between ground and black 2 is 100 V; (iii) between ground and white is 100 V. The other white is 0 V.
    – Seyhan Gul
    Nov 19 at 19:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.