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I have an outlet and light switch combo box in a bathroom that I’d like to upgrade to a dimmer switch and a GFCI outlet. The dimmer switch replacement works fine, but there are two white cables and one black going into the former outlet.

I thought that the black line would go into the line connector on the GFCI and that the white line from the same cable bundle would go into the line connector while the white cable from the red, white and black bundle would go into load connector.

How would I reconnect this to a GFCI outlet that has line and load connectors?

Outlet that I’d like to replace with GFCI outlet that I’d like to replace with GFCI

There are two white cables and one black connected to the outlet. there are two white cables and one black connected to the outlet.

It appears that two wires could be inserted on the white line on the back of the GFCI, should I try that? it appears that two wires could be inserted on the white line on the back of the GFCI, should I try that?

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    Something isn't quite adding up. Either you have some wacky neutral problems (which will cause problems with the GFCI) or there is a missing jumper wire or something else funny going on. Is power coming in to this box from the black of black/red/white or from the black of black/white? Are there other receptacles that used to work and are not working right now? Jan 2 at 0:39
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    What I see is the left cable has a black and a white; the right cable has a black, a red, and a white. Possibly you won't need the white in the cable with the red and you can cap it and fold it back. So possibly you use only the line connections on the GFCI: black wire in the left cable to the hot side of the GFCI and white in the left cable (neutral) to the neutral side. As Katz says you should really try to get strainght what other receptacles this is connected to if any. I am assuming that there are not other receptacles on following this bathroom one. Jan 2 at 0:41
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    Presumably you have a light/fan controlled together by the switch or is it only a light? If you are putting in a dimmer, then presumably the switch only controls a light? Jan 2 at 0:46
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    The white wire in the cable to the switch is probably a neutral which is not needed for the switch you have. You probably should NOT connect it to the GFCI receptacle. Just cap or cut off the exposed stripped end and curl it up and push it to the back. The left cable has a white which is presumably the neutral for the hot (black) in that cable. Do you have any test equipment? Non contact voltage tester? Plug in circuit tester?. If not, just wire it the way I specified, turn on the power and see if it works. Do you have ground wires? Jan 2 at 1:02
  • Thanks, Jim. That’s very helpful. I think you may be right that the neutral that’s not needed by the switch could be disconnected. There’s no fan, just a light controlled by this switch and no ground wires and no other receptacles that this is connected to. I have a circuit tester and multimeter.
    – sudocity
    Jan 2 at 2:37

1 Answer 1

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If the lights work properly when only the switch is connected as in your second photo, then you have two (independent) circuits in that box.

  • 1 circuit with hot (black) and neutral (white) for the receptacles
  • 1 circuit with switched-hot (red presumably), permanent hot (black presumably) and neutral (white)

Even if those circuits end up at the same breaker, it is best to treat them as independent circuits and not connected wires from the different cables together.

Use the black/white cable only for the receptacles. Use the black/red/white cable only for the switch. If the switch doesn't need a neutral now, cap off that white wire so that it is available for the next (smart?) switch that does need neutral.

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