Strange Dimmer Switch Wiring

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AlGreen

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I went to replace an old dimmer switch with one that's LED compatible (I was hearing a buzz), when I was presented with this wiring setup.

2017-01-06 19.04.34.jpg


In case it's hard to see from the photo, there are two separate NM cables feeding into the box. The neutral and ground wires have been twisted together, and the hots both go to the dimmer. I assume one of the NM cables goes to an outlet. Is this kosher?
 

Cacher_Chick

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It would be pretty common for there to be an NM cable coming from the panel, and another going to the fixture. The neutrals are tied together, the hots go through the switch, and the grounds should be tied together with pigtals grounding the metal box and the switch.
 

AlGreen

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That all makes sense. So with the circuit on but the light switch off, I need to use my non contact voltage tester to check which black wire is hot and that will tell me that the other is the switched leg.
 

DonL

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That all makes sense. So with the circuit on but the light switch off, I need to use my non contact voltage tester to check which black wire is hot and that will tell me that the other is the switched leg.

A volt meter would be the proper tool to use.

You can turn the dimmer all the way down, The one feeding it will remain hot, The switched leg will be low with a bulb in the socket. (The bulb puts a load on the dimmer SCR thru the neutral)
 

AlGreen

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Thanks. I had a major brain fart last night when I was confused about the wiring I was seeing. As HJ and cacher_chick noted, it was completely normal.

And DonL, you're right: I used my multimeter to find the hot wire.
 
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