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In my bathroom, I currently have: one electrical outlet, one light fixture, and one fan. There are two switches at a 2-gang box (for the fan and the light). The fan is a simple fan without any other lights or speakers or anything.

I already set in the new light fixture and ran the wires through the attic. I am about to fish them down to the light switch box, planning to change it to a 3-gang and add a third switch.

But I found I don't quite understand the existing wiring. Specifically there is a red wire hooked to the fan's circuit in a way that is confusing to me. To accomplish my task, I was just going to wire a new switch to connect to the hot "line in" as well as the light, with the white return from the light going to the rest of the whites. But I wanted to make sure I understand the rest of the wiring.

Here's are diagrams: 1) what I observed in the box, and 2) what I infer is going on as well as my question regarding the wiring.

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  • How many wires actually arrive at the fan? – ThreePhaseEel Apr 28 '20 at 23:03
  • I believe a single 14-2 cable goes to the fan. So that kind of answers my question regarding which of those top cables actually travels to the fan. But I am still wondering what the 14-3 cable is doing in the circuit. Why is it there? Does it make sense that it is there, or could it be that I am misrepresenting something in the diagram? – user1323153 Apr 28 '20 at 23:09
  • It could have gone to a past fan location, perhaps? Have you accounted for all the junction boxes in the bathroom? – ThreePhaseEel Apr 28 '20 at 23:16
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I did not follow your question completely so I will explain how it should work (per code) A switch leg is where the power is supplied in the attic and then the hot black feed from the attic normally would go down on the white and come back on the black/ red after the switches. All work is done with the breaker off.

you have a fan and a light so at the switches you take the white to both switches (they should be marked as hot black or other color not green) then your red goes back from 1 switch and the black from the other switch.

At the attic tie the light and fan tie the neutrals (white) to the cable from the panel your supply white or neutral. the fan hot to the red (or black) The light hot to the black (or red)

The hot black from the panel to the white going to the switch (on the 14-3) this is always hot so it is harder to get confused but the white wire should be marked as a hot like the switches.

This would be the proper way to wire a switch leg to 2 devices through 2 switches.

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