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To preface this, I'm experienced with wiring up AC outlets/switches/etc - but when it comes to looking at work someone else has done - this is what's throwing me for a loop. And maybe someone else more experienced will recognize it.

When we moved into our home - and this is all from my memory so may not be 100% accurate - but in this room I believe there was no light switch. We wanted to install one, and add a fan to center of the ceiling. Contractor did this for us, by putting in one of those drywall blue boxes for the switch. We want to upgrade this to a "smart" z-wave style switch - that has two terminals for the load on one side, and then a "traveler" (for 3-way, which we don't need) - and then a neutral terminal.

Here's what I found inside the box:

The situation in the box

I see a black and white wire, and a ground coming from the left side of the box. The white and black are twisted together and capped off. Another piece of Romex comes in from the right, has it's white capped off, ground tied to the other ground, and the black and red wires go to a light switch.

If I use my Klein voltage tester, the black wire going to the switch appears to always be "hot". The black and white twisted pair also shows "hot". The shorter white wire from right Romex shows nothing as far as I can tell.

I haven't climbed up to rip open the wiring harness for the fan, but I guess I can if I need to.

I tried to connect a lead from the black/white twisted pair into "neutral" on the new switch - and it worked to turn on the light but then would immediately shut off.

Am I stuck here/unable to put a smart switch in this location without some additional work? I would hope my contractor had done something "typical" in this scenario, but maybe he didn't.

Thanks for any guidance/direction. And yes, I asked the contractor but he does not recall how he did it (he's getting kinda old).

Here’s an enhanced picture of back. Left side is black and white and ground wire. Right side is Romex with black, red, white and ground wires.

enter image description here

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  • Can you post a photo that shows the back of the box more clearly please? Dec 29 '20 at 22:34
  • @ThreePhaseEel I added another picture, enhanced. If that’s not good enough I can take it apart again. Hopefully I described the wiring well enough but glad to answer questions. Thanks! Dec 29 '20 at 22:59
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    This switch actually may have already been there but controlling an outlet. The fan circuit was definitely added by contractor. I think he wired the outlet to be on constantly instead of switched. Dec 29 '20 at 23:43
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My bet: you have two switch loops in the same box here, one old and one new

From what you've said so far, my bet is that you have not one, but two switch loops in this box. Fortunately, while the switch loop for the old receptacle appears to be an "old style" loop with just a hot and a switched-hot, the new switch loop for the fan appears to be use the current Code configuration where neutral is brought down to the switch location alongside the hot and switched wires for precisely the reason you're asking this question. So, I'd leave the black/white pair alone, and wire your switch as follows:

  • Hot/Line -- solo black wire
  • Switched/Load -- solo red wire
  • Neutral -- solo white wire
  • Ground -- bundle of bare wires in the back of the box

This should get the fan to work normally without disturbing the old receptacle circuit.

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  • Might be the new fan 3-wire cable was not "to have neutral" but rather "to have separate switched hots for fan & light". But either way, that gives enough wires to get the job done. Dec 30 '20 at 2:51
  • @manassehkatz-Moving2Codidact -- if it was fitted to have 2x switched hots, then I'd expect white to be live (as the always hot) Dec 30 '20 at 3:06
  • You're right. I missed that in OP's text. Dec 30 '20 at 3:20
  • Thanks so much for the help. I’ll give this a try tomorrow. Dec 30 '20 at 3:38

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