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My bathroom wall switch controls the old light above the old medicine cabinet but it only has 1 cable with a black and a white wire. I took off the old switch and put the black wire on the hot side of the GFCI and the white wire on the other side both in the "line" position. This new GFCI has both a switch and a outlet.

Turned the power back on and the swich does nothing but the outlet works and when I plug something in to it the light comes on. Turn the hair dryer off and the light goes off. What's the problem?

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You just tried to hook up an outlet to an old-style switch loop with no neutral wire. Right now, your hair dryer is wired in series with the light, and the switch is dangling in the electrical breeze.

(In other words: You'll need to find another place to put the GFCI function, or run a new /3 NM cable to the switch box so you can have a neutral there.)

  • Basically I wanted to get a new light fixture for the bathroom but my old one has an outlet on it but I don't won't the outlet on the light because it's too hard to reach so I thought the Pass & Seymour Switch/outlet combo would be perfect. Could someone provide a link to a diagram of how you think my bathroom is wired now? – MUMNUT Jan 5 '16 at 5:12
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    @MUMNUT -- You have to run new wires, or find a different home for the outlet. A switch loop can't do the job you're asking of it, because there's no return path for the current back to the panel, just a source of current and a path onward to the switched load. – ThreePhaseEel Jan 5 '16 at 5:16
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You made an assumption about the wiring: that power came from the breaker panel first to the light switch, then up to the fixture. Actually it goes to the light fixture first. Since the light switch only switches a hot, they didn't bother bringing a neutral to that location. (new code requires that.) One wire may be white, but it's not neutral. (It should have been marked with tape or paint.)

For outlets, you need neutral. That is only found in the light fixture, not the switch. So leave the switch the way you found it (but mark the white wire). You will have to run more wires from the light fixture to wherever you want the outlet. (Since this is new work, you may want to have a look at NEC and see what it requires for bathrooms.)

A simpler option is convert the light switch to an outlet-only box. Rewire, so the two wires to the former light switch actually are hot and neutral. And put the GFCI there. I would not do that if the light switch box is not grounded. Now you have no light switch. You could go hillbilly with a pull cord, or you could install one of the new home-automation gadgets to enable a wireless switch. (plus, if you left the bathroom light on, you could stay in bed and turn it off from your phone lol.)

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The problem is that the box where you put the gfci outlet is not meant to contain an outlet at all.

It is not supplied with a hot and neutral and ground as outlets require. It is bridging an opening in the hot or neutral of the light. This might apear to "work" with a hair dryer, but it will damage some types of appliances and possibly blow the bulb out. UNDO UNDO UNDO

Power runs from the source, to the light's junction box and then there's two wires to the switch that can interrupt current to the light.

If you need an outlet there, the best option is to find a light with a switch built into it, and then rewire the light's jbox so that the former swith leg is in parallel with the light. You'd still want a ground on that outlet probably. Especially if you chose a GFCI, and its next to a sink.... So hopefully when you said "only has 1 cable with a black and a white wire" you were ignoring the uninsulated ground wire.

Switches are also available from home automation vendors that can be concealed in a jbox or in the fixture housing and controlled wirelessly from wall mounted remotes.

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Sorry for my first answer, I didn't get that the power was coming from the light. The combo switch will not work for your setup since you can't get power back to the light separately, so put the old switch back.

However, since you are getting power from the light you should have the same 2-cables & 4-wires as you saw in the YT vids in your light's box. EXCEPT, since you had a lazy "professional" in there you don't want to do anything with the white going to the light, as that is hot & not labeled as it should be in either existing box.

From the light box you can run a new separate line for a new box & GFCI outlet. You'll plier & then wire-nut the blacks for your outlet & plier & wire-nut your new white to the white that's NOT connected to the light. If the medicine cabinet is recessed, just a hole in the wall, this can make the whole process an absolute breeze. If not, then the cabinet will still cover your very short fishing holes, still patch them though.

  • He doesn't have a neutral at his switch box. – ThreePhaseEel Jan 5 '16 at 5:17
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    You're right @ThreePhaseEel the outlet box only has 2 wires, a black and a white – MUMNUT Jan 5 '16 at 5:32
  • Sorry & thank you. My mistake with the YouTube reference, I'll edit my answer accordingly. – Iggy Jan 5 '16 at 5:45
  • @ThreePhaseEel Ok, figure i have to run new wire from breaker box, so can you diagram how to have a light (without an outlet) and my GFI Combo switch/outlet on the wall – MUMNUT Jan 6 '16 at 18:34
  • @MUMNUT If you must have that combo switch & not a separate light switch & separate outlet, you can do it only from the light's box & not from the switch's box. You should not need to run a new wire from the breaker box to get an outlet in. First, take the combo switch back & exchange it for a new outlet box, new 15-amp GFCI outlet & a 3' (or whatever your longer desire is) chunk of 14-2 Romex. I updated my Answer's last paragraph to detail the hook-up for a GFCI outlet to be right beside (or wherever) the medicine cabinet. – Iggy Jan 6 '16 at 20:52
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If you want a GFI outlet and don't need the old light, you might try this. Sacrifice the light. Twist the two wires that fed the light together and put a cover on the box that fed the old light. Then you will have power and ground in the switchbox. Then wire in your GFI outlet. (I am not an electrician, so this may not meet code. Perhaps one of the electricians on the site will tell us.)

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