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I want to replace my regular bathroom lightswitch with a combo outlet/switch. Seems the wirebox only has 2 wires but i do see a 'mysterious' third wire in the back that is not connected to anything there. All videos i've viewed about installing combo outlet/switch requires 3 or more wires. My apartment building was built in the 1940s and our Super said the building wasn't wired with ground.

Anyone know if installing combo outlet/switch is a possibility with the wiring I have now?

Thanks!!

wiring

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  • Can you post a photo that shows the bottom of the box please? Something interesting is going on here... Jan 4 '21 at 1:28
  • You apartment appears to be wired with conduit, which is also ground...
    – Ecnerwal
    Jan 4 '21 at 1:37
  • @ThreePhaseEel - photo of bottom of box posted. i believe that's just a bunch of broken up old plaster/rocks.
    – Michael
    Jan 4 '21 at 1:48
  • @Ecnerwal - is that the weird looking wired with a pattern instead of a solid color? That wire doesn't seem to be used for anything in this box.
    – Michael
    Jan 4 '21 at 1:49
  • There aren't any holes in the bottom right of the box the weird wire could be extending out of I take it? Jan 4 '21 at 1:58
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That weird wire is your neutral, and the conduit's your ground

Your building was wired using what appears to be cloth-covered wires in metal conduit. This would not be atypical for a large or high-rise building in the 1940s, especially in an urban area with strict building codes. The mottled pattern you see on the wires in the back of the box is a simple fact of aging, by the way -- those two wires were originally white, and still are much lighter than the other wires in the box. As a result, we know that those two "weird" wires are actually white neutral wires, with power coming in from the top left and going to an in-line splice with a pigtail to the switch and an always-hot heading off to the top right, where the switched-hot also departs the box. Furthermore, since we have metal conduit here (from the lack of paper packing or jacketing peeking through), we know that the conduit itself provides grounding here.

As a result of that, and since this circuit serves only this bathroom, we are clear to install a GFCI/switch combo receptacle here. You'll have to cut the existing splice in the neutral out and add a neutral pigtail to do this, though, as well as cutting out the existing pigtail splice in the hots and replacing it with a new splice and pigtail that also joins one of the switch wires into the bundle of hots. The other switch lead gets connected to the switched-hot then, and the hot and neutral pigtails we created land on their respective LINE terminals on the GFCI. The LOAD terminals stay unused, and you can either use a grounding pigtail to connect the GFCI's ground screw to a 10-32 ground screw driven into the back of the box, or use a self-grounding GFCI/switch combo that's listed for grounding through the mounting screws.

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  • I posted the switch/receptacle combo I have. Not sure if it's GFCI. Can I use the one I have to install? If so, could you explain which wires would need to go to which screws?
    – Michael
    Jan 5 '21 at 3:02
  • @Michael -- it's not a GFCI, unfortunately, and you need it to be since you're putting this in a bathroom Jan 5 '21 at 3:04
  • So basically in a nutshell: 1. Combine the white neutral wires with another white neutral wire creating 1 neutral wire? 2. Combine the red and black hot wires with another hot wire together creating 1 hot wire? 3. The 1 neutral wire and 1 hot wire are to be placed in their line terminals? Is grounding necessary?
    – Michael
    Jan 5 '21 at 4:12
  • @Michael -- use a self-grounding type GFCI/switch combo. if you can't find one, you'll need to drive a Garvin GSST into the back of the box then run a pigtail to that screw from the ground screw on the GFCI/switch Jan 5 '21 at 4:26
  • Ok thanks! Am I correct with my novice wiring explanation or am i about to blow up my apartment?
    – Michael
    Jan 5 '21 at 4:48

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