I have searched this forum and read some answers on similar issues to what I am having but I still need clarity. I had an old exhaust fan that went. In the box for the switch I have two romex wires. It was a double pole rocker switch. You needed to turn the light on if you also wanted to turn the fan on. The fan would NOT work without the light switched to on. Both black wires were wired into the switch, only one neutral wire out of the 2 were used, and the grounds were connected. I wired in the new fan the same exact way and the light worked but the fan didnt. The new fan came with a humidity switch that I didn’t want to use but I tried it figuring maybe the fan needed it to run. It had line and then also load for the fan. I wired the switch line to one of my black wires, and wired in the switch fan load into the other romex black wire. The fan worked but the light didn’t. Now I am at a loss. Any help would be appreciated. I am looking at a double pole humidity switch from leviton, but the wiring is for branch line in and then 2 loads. It seems I only have 1 load and 1 line in, or just two load wires. Currently I have just the light wired to a rocker switch and it works. I can send a picture if needed. enter image description here

  • 1
    Please edit to provide pictures of the wiring as connected (at switch and at fan) showing all the cables in the boxes, along with the "and this worked and this didn't" information. Generally if you have 2 cables coming into a switch box, one has power and the other is for switched power, or one is a switch loop (where white isn't neutral) and the other is doing something not exactly right by code to switch something else.
    – Ecnerwal
    Jan 7 at 1:34
  • Looked at this again. The left side is my line in but it also controls the light. The right side romex has no voltage unless switched on. Doesn’t make sense to me that my fan isn’t switching on when I connect the switching load to my 2nd pole of my rocker switch. Jan 7 at 2:39

1 Answer 1


Connections in the fan box will matter.

You appear to have a switch loop for the left cable. That means you don't have an "incoming line" you only have hot and switched hot for the light. That would mean the white wire in that cable is NOT neutral. The white wire in the other cable might or might not be neutral - depends what's connected to what at the far end.

So, if the switch controls the light by connecting it to the left cable, one of the wires in that cable (should be the white, and it should be marked with black, red or some other hot color at both ends, but may not be) is always hot, and the other wire is switched hot to the light. Neutral for the light will not appear in the switch box, only in the fan/light box.

For a fan/light setup, the always-hot could be brought to one side of both switches, or, as you had before, the switched hot of the light could be brought to one terminal of the fan switch, and the fan connected to the other terminal of the fan switch, so the fan only worked with the light switched on.

  • Yes that should work, But it doesnt and its driving me nuts. The fan won’t turn on when connected as you described. Maybe I need a neutral for the fan that I don’t have. The right side wire is connected to the fan, black white green. Leaving the white wire off the switch and connecting black and ground it doesn’t work, but the old one did. Jan 7 at 13:13
  • The neutral for the fan would be, as I presume the neutral for the light is, in the fan/light junction box. So if the fan is connected to the right cable here, no, it's not going to work, because there is no neutral here, so there's no circuit for the fan. The white in that cable could be used to get a neutral to this box if you WANTED to use the humidity-sensor-thing that needs a neutral, but it would need to be connected to the line neutral in the fan/light box to do so.
    – Ecnerwal
    Jan 7 at 13:23
  • Yes I was just thinking about this. When I took the old fan out there were two wires. The wire from the switch i am currently using and then another wire going into a j box in the attic. Forgetting the humidity sensor, can I run this fan and light without a neutral? If so, what combo would I use. Jan 7 at 13:51
  • Please SHOW the wiring in the fan box, and at the light box. Are fan and light fed together from one box, or not? You must have a neutral connected to the light, or it would not work. That does not mean you have a neutral in the switch box. If the fan is completely separate from the light, the "cable into the attic" is probably the completely separate power to the fan circuit, in which case the right cable probably should also be wired as a switch loop for the fan, and the two switches should not be joined at all.
    – Ecnerwal
    Jan 7 at 13:59
  • They are fed from the same box. I will try to get a picture in the attic. Jan 7 at 14:32

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