I'm trying to take a switched duplex outlet and make it half-switched. I turned off the breaker and pulled the receptacle out and this is what I found. When tested with a voltage pen tester everything inside the circuit was off except for the black wires in the back that run through the box.

I'm assuming what I need to do is: 1) first find the breaker that the black wire is on and shut it off. 2) break the tab on the side with the red connector with some pliers 3) run a new wire from the nut holding the red wires together at the back of the box to the other terminal on the red side of the outlet

Does this make sense? I'm a little confused why there is already two neutrals coming off this box and why the black wire wasn't off when I switched the breaker.

Any help would be appreciated.

1st angle 2nd angle

  • The fact that you have to turn off 2 breakers is very important and there's a safety issue here. Are the breakers next to each other in the service panel? Have you had the service panel cover off? Commented Sep 26, 2017 at 4:07
  • The breakers aren't side by side but they are "near" each other. It's an old panel. It seems like it is for lights (and maybe outlets?) in an adjacent room.
    – mrwest09
    Commented Sep 26, 2017 at 21:50
  • Uh... Oh... Commented Sep 27, 2017 at 3:16

2 Answers 2


The two white wires are "common coming in" and "common going out". Leave them alone.

Your red group might be "power in" and "power out to switch", with the separate red being "switched power returning from switch". Or the red group might be switched, or something entirely different.

I'd suggest that you turn the breakers back on, and see what wires are switched. That will tell you if the red nut group is good to use.

If the red nut group is switched also, then you'll have to take power from the black nut group for your unswitched half.

  • 1
    Okay that makes sense. What gauge and color of wire should I use once I determine the correct nut group? Should the wire color be the same as the nut group?
    – mrwest09
    Commented Sep 25, 2017 at 22:21
  • 2
    I would suggest black for the "unswitched" outlet. You've already got all your other wires.
    – aghast
    Commented Sep 25, 2017 at 22:27
  • Thanks for all your help. I just tested the outlet. The red group is not switched. It maintains voltage when the switch is flipped on and off. The black wires in the back are on a different breaker. So I'll get some black 12# wire to run from the red group? Seems weird to have a black wire running out of the red group. Or is it that alright by code.
    – mrwest09
    Commented Sep 26, 2017 at 0:02
  • 1
    Should be okay. Now, before you get too happy: are you sure that red group isn't switched by some other switch? :-)
    – aghast
    Commented Sep 26, 2017 at 0:47
  • Shoot. I've been at it for a while and I can't figure this out. I broke the tab yet there is still power at the second screw. When using my voltage tester it still switches as though it is still connected to the red cable from the switch. I haven't even tied the permanent connection in yet. Any ideas? Is it possible for some outlets to be connected at another location in the outlet?
    – mrwest09
    Commented Sep 26, 2017 at 1:42

I'm afraid this may be a real mess, and dangerous

The problem is you have 2 hots fed by 2 separate circuits, fed by a common neutral. This configuration is called a multi-wire branch circuit or MWBC. There is nothing wrong with these, but they need to folow special rules to be safe - and yours don't.

The single most important thing is they must be on opposite poles. There must be 240V between the two "hots". That is the only way the circuit can avoid overloading the neutral. Experience has shown careful breaker placement is not reliable, because people move breakers around. The modern rule is to put the circuits on a 2-pole breaker which is designed for 240V. Then, the panel's design will assure you place the two hots on opposite poles.

You identify problem MWBCs in the panel by looking for 3-wire cable (black red white) whose black and red wires do not already go to a 2-pole breaker.

Because two hots share a neutral, neutrals must be pigtailed like grounds are - and for the same reason: removing a device must not break the wire for downstream loads. If you tried removing that receptacle right now, you would be shocked when you tried to remove the neutral wires, by the current flowing down the other circuit. This is the other reason to use a 2-pole breaker - it assures when you shut one off for maintenance, it shuts both off.

Once that's fixed

It looks like we are joining this MWBC "already in progress". The red wire carries switched-hot from one leg of the MWBC... And the black carries (presumably) always-hot from the other leg.

So get a short stretch of /3 Romex cable, because you need to make some pigtails: first to the bundle of blacks, to get an always-hot for one side of your outlet. Then don't forget you need to pigtail the neutral.

Don't break off the tab on the neutral side, and connect the neutral pigtail to that.

Do break off the tab on the hot side, and connect the black pigtail to the unoccupied side.

I would continue to ignore the red pushed into the back of the box, since we know nothing about it.

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