Viper67857 t1_irz5sqi wrote on October 12, 2022 at 3:01 AM

Reply to comment by evolvedance in How did I burn out my brand new sensor switch for bathroom fan? Wiring woes! by evolvedance

Normally, you'd have 2 cables coming into a standard switch box. Neutral carries through, ground carries through with a jumper to the switch for safety, blacks go to the side terminals (one is constant, one is switched).

What you have is referred to as a switch-loop, where the source cable goes to the device first, the neutral is wired directly to the device, and the black is wired to that cable coming down to your switch. The white wire at the switch will be the hot wire going back up to the device. This setup is not compatible with a smart switch as it needs a neutral to power itself. You'd have to replace the cable between the switch and the fan with 14/3 to have a neutral at the box.

evolvedance OP t1_irzajfr wrote on October 12, 2022 at 3:43 AM

Whoa. Looking up switch-loop = mind blowing. Thanks for illuminating that for me. It's all starting to make more sense.

evolvedance OP t1_irz6jzu wrote on October 12, 2022 at 3:07 AM

Got it. Makes sense. I'll also google switch-loop to further understand what's going on.

Would my original normal switch work?

If so, did it make any sense that the green ground wire was connected into the old switch... and the white wire connected as well, but the black wire coming down was disconnected?

Viper67857 t1_irz7dvb wrote on October 12, 2022 at 3:15 AM

The green wire was probably at the very bottom of the switch, no? On a green ground screw? That is required for code purposes, to ground the frame of the switch for safety. It serves no purpose for functionality.

The white should be powering the fan while the black is incoming power (if it was originally wired correctly). If the black was taken loose, it was probably because something was fucked (maybe the switch, maybe the fan) and the old owners didn't feel like fixing it properly, though they should have at least capped the black with a wire-nut instead of leaving it dangling if it's a constant hot. I'd probe each wire with a multimeter to see wtf is actually going on before doing anything else. You should get no voltage between the white and green and 110-120 (or 220-240? I'm not sure what country you're in) between the black and each of the others.

evolvedance OP t1_is08vuf wrote on October 12, 2022 at 11:04 AM

>it was probably because something was fucked (maybe the switch, maybe the fan) and the old owners didn't feel like fixing it properly

That very well could have been the case - that old owner being my 80 year old dad. He may have attempted to disconnect the switch, not knowing how to do it properly when the fan went out. Pretty sure he didn't know it was a switch-loop either. He's a chief navy mechanic and is brilliant with automotive and almost anything mechanical, but, admittedly electric wasn't something he ever got to focus on. Which is part of the reason, I'm trying to learn a bit.

I'm in the U.S.

This is helpful though. I'm going to pick up a multimeter tomorrow to test. I had a voltage tester that only told me if there was any type of voltage.