So I've been installing a ceiling fan and I'm encountering an issue I didn't come across in 2 other rooms, same fan model etc. At the ceiling box I've got Ground, Neutral, Red, and Black. In the other rooms I've been able to wire the light to the switch and the fan motor/remote to constant power no problem to keep them separate. I want to be able to run the fan without the light at night. Here, while I am able to get the light working off the switch (black wire), I am unable to get the fan running off the constant (red wire.) When I put my multimeter to the switched wire in the ceiling (black), I get 120V when the switch is on. Red wire has .5V with the switch off and 15V with it on (?) I looked in the box behind the switch and I've got a loose red wire in there capped off. Is that my problem? Seems like maybe it was wired for a fan but not connected? How could I make this work? Do I need to wire nut the red to another wire in the switch? Thanks in advance.

UPDATE: Ok, so I flipped the breaker labeled for the bedroom lights which also includes the hallway light (share walls with the dining room) and THAT is now killing the switch and the fan successfully. Weird. Is this what's called a multi-wire branch circuit (MWBC)? Should I make sure to also flip the breaker called Dining Room since that was successfully shutting off the power to the light in the fan (but not the motor)? Bottomline, I don't mind adding a note on the breaker box to remind myself or whoever, but is is safe? Thanks.

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The change in voltage is coupling between the floating red wire and the live wire.

You can change the switch to a duplex switch. That will allow you to control the light and fan separately.

If you want constant power to the fan then add the red wire to the wire nut with all the blacks.

  • It's a single switch in the other rooms. Is there a way for me to make this work without doing that? I only want to control the fan with the remote. I just want this red wire to get constant power. I'm guessing this is the same wire going to the ceiling that's not getting 120V. What do I tap into? Twist the red in with the black in the switch? – Intromission Jul 19 '19 at 13:14
  • Also, want to be able to control fan speed. – Intromission Jul 19 '19 at 13:32
  • Thanks! It's working now. – Intromission Jul 19 '19 at 14:50
  • The only odd thing is, now, flipping the breakers in the basement for this room doesn't do anything when it comes to the fan or light. I am able to turn on the light with the switch and operate the fan on the remote with the breakers flipped off. Is that bad? – Intromission Jul 19 '19 at 15:06
  • 1
    There should be a single breaker that will turn it off. if that is not the case then there is a issue. – ratchet freak Jul 19 '19 at 15:12

I seriously doubt it's a multi-wire branch circuit. That would require 3-conductor (black white red) cable, and there's only one such cable in this box, and that's for the fan/light. I suspect your circuit is miswired in some way, with hots (and possibly neutrals) from 2 circuits bridged together somewhere. This box is just the kind of place that could happen.

It might be a switch loop

I would try joining the black, white and red wires from the fan cable, and see if the fan and light come on. (power off before doing this; power up after). If that's the case, then this fan/light circuit is a switch loop and there is a different circuit also in this box. In this case, the switch-loop should not be intermixed with any other wires in the box (except ground).

In a switch loop, you get to source always-hot from right up in the junction box. In your application you can use black for always-hot, red for light switched-hot, and white gets held in reserve for actual neutral.

If it's not a switch loop...

Then the preferred colors for the wires are white for neutral (this is mandatory), black for either fan-control or always-hot, and red for switched-hot/lamp.

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