I have a box with a switch and a dimmer side by side. Last year I replaced them with smart switch/dimmer and had no problem until the dimmer stopped working. I am replacing the dimmer, but foolishly and overconfidently didn’t document the wiring and now I have confused myself.
The bundle for the switch has a black and a white wire. The bundle for the dimmer has black, red, and white. (There are also grounds for both.) Both the smart switch and dimmer need ground, neutral, load, and live.
The leaves one short on the switch (the bundle has white and black). Originally, there was a wire bridging the dimmer and the switch. I think the load went from the switch, to the dimmer, and then to the red in the second bundle, but I am not certain enough to test.
Using a tester, the only hot wire I detect is the black from the two-wire bundle. None of the wires in the three-wire bundle read as hot.
How should I wire this? (Keeping in mind that this was working fine until I decided to mess with it this morning.)
And obviously, never forget to document!
Top photo is the current situation. Bottom is the original (pre-smart).
Best Answer
The black wire from the /2 cable needs to be pigtailed to the LINE terminals on both devices
We know, from your testing, that the black wire from the /2 cable is the incoming always-hot wire; this means that the black and red wires from the /3 cable are the outgoing switched-hots for the two sets of lights this box controls. Therefore, we wire the box as follows:
Then you can button the box up, turn the power back on, and enjoy your new smart switch!