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I attempted to replace an electrical outlet that was not working. My voltage tester indicated nothing was working. A receptacle analyzer indicated nothing was working as well. but when opening it up, I was surprised to discover that the outlet was wired using two black wires and one white wire. There was a bare ground as usual. Surprisingly, I didn't see an additional white wire in the group of wires, so I got confused. I wired it back up the same way it was just with a new outlet and it still didn't work.

Why would this wiring configuration be like this? Was it a mistake?

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    2 black 1 white would possibly indicate a 220V circuit. Do you have a photo of the wiring you could post?
    – The Evil Greebo
    Aug 5, 2013 at 13:02
  • With the new switch wired, the cover off and the power on, have you tested (very carefully) both black wires with a non-contact tester to see of either or both are live?
    – bib
    Aug 5, 2013 at 14:40
  • I don't have a non-contact tester (I can buy one if I need it), but I do have this: homedepot.com/p/… ... I'm wondering if I carefully place one end on the white wire and one on the black, maybe this should tell me if the wires are live?
    – paneerlovr
    Aug 5, 2013 at 19:46
  • Place the black probe on the white (neutral) then test each of the black leads. Also post a photo of the side of the outlet, is the little bridge broken off? The new outlet must have the tab broken off ALSO to prevent problems.
    – Bryce
    Aug 6, 2013 at 4:00
  • Most likely the second black wire simply carries the power from that outlet to the next outlet in the circuit.
    – Norm
    Apr 12, 2018 at 12:49

1 Answer 1

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Assuming you are in the US, this could be a half-switched outlet. Do you still have the old outlet? Look at the side and see if the metal tab between the screws is broken off on one or both sides. If it is, then (at least) one of those black wires is probably controlled by a wall switch somewhere, resulting in one outlet being on all of the time and the other switched.

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  • I'll look for it, I have two of them and am not sure which one was on this wall. Does the tab effectively function to make each outlet function independently? If both outlets were controlled by the switch, would you expect that the tab would not be broken off?
    – paneerlovr
    Aug 5, 2013 at 17:56
  • Yes, breaking off the tab on the hot side makes each outlet function independently, but with a shared neutral. Yes, if both outlets were controlled by the same switch, I would expect the tab to still be attached.
    – longneck
    Aug 5, 2013 at 18:26
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    Thanks longneck, you were completely right. A switch was connected. It didn't need the tab broken off, both outlets are simply controlled by the switch. It all makes sense now, thank you!
    – paneerlovr
    Aug 6, 2013 at 12:29
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    In a similar situation, I was trying to replace a 125V 15Amp outlet, but the new onw kept tripping the breaker. It had a red and black hot, one neutral and one ground. No switch associated with the outlet. After reading longneck's answer, I checked the old outlet and saw the tab joining the two hot side terminals was broken. I did the same on the new and all worked great. Thanks for the great tip and puting an end to hours of frustration.
    – user20304
    Mar 7, 2014 at 4:14

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