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Renovating my bathroom (Bathroom A) and have all walls exposed to the studs. Power runs from the attic to the light and switch of the adjacent bathroom (Bathroom B), then to the light in Bathroom A, then from the light to the switch with a 14/2 wire (b/w). I want to add an exhaust fan controlled by a separate switch (preferably humidity sensor switch).

I initially thought I would run a new 14/3 from the exhaust fan to the new switch, and then connect the new switch to the existing switch with a pigtailed black (hot). But with the existing switch being at the end of the line with a 14/2, I don't think this is possible b/c that means both wires are operating as "hot" between the light and the switch, right? So how do I go about this? Do I run a new 14/3 from the light to the existing switch, then pigtail it to the new switch?

Excuse anything above that doesn't make sense, I'm a DIYer that is newer to electrical work and hoping this is feasible without hiring an electrician. Any help, especially a diagram, would be amazing!

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If I understand your question, you have power coming from the light junction box and from there it goes to the switch box with 14/2 wire as a switch loop. What you need is supply power, neutral, and two switched hots going back to the light/fan.

Rather than remove the 14/2, leave it in place with the black wire carrying the line voltage and white being neutral. Then install a new run of 14/3 from the switch to the fan light and use the black and red wires as the switched hot for the light and fan. At this point the white in the 14/3 would be redundant, but you get clarity and theres no question as to what each wire is for.


Edit below... I assumed a combo fan and light unit was going to be used, but the light and fan are separate.

Ok, so the above isn't the best way to handle this given the comments. You will want to remove the 14/2 that currently runs from the light to the switch and replace it with 14/3. I'll use colors to help illustrate the point. The 14/3 will have red, white and black. The black wire will carry the supply voltage to the light switch and the fan switch. The red wire will carry the switched power from the light switch back to the light. And the white will be neutral. In the light box all the whites will be bundled together, the incoming black will be connected to the black going to the switch and the red from the switch gets connected to the black wire of the light fixture. That takes care of the light.

Now you should run some 14/2 from the switch box to the new fan. Again, white is always neutral and the black will go from the fan switch to the black on the fan. You may be able to reuse the 14/2 that was going to the light, depending on the location of the light and fan.

If you buy 14/3 and have it on hand, feel free to run that to the fan and just leave one wire unused. Don't reuse damaged wire or splice wire that is too short.

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  • Thanks JPhi1618. I think you understood the current setup -- power runs from light junction to the switch box with a 14/2 loop. The part I'm unsure about is your reference to a "fan light". The light is existing and will be separate from the fan, which has no light. The end product will be a switch that controls the light, and a switch that controls the fan. So you said I would keep the 14/2 and run a new 14/3 from the existing switch to the "fan light". Do you mean the "fan switch"? Apologies again, I'm a visual person and have trouble imagining where each line comes and goes.
    – Travis
    Oct 13, 2021 at 23:45
  • That's a...questionable approach (300.3(B) issues with potential inductive heating of any ferrous metal that's between the two cable runs) Oct 13, 2021 at 23:45
  • As I mentioned, the goal would be to have two side-by-side switches -- one for the light, a second (w/ humidity sensor) for the fan. If this isn't possible, could I do a dual switch (not preferred)?
    – Travis
    Oct 13, 2021 at 23:56
  • If your hot feed comes into Bathroom A through the light then the 14/2 from the light to the switch is a simple switch loop. You should be able to supply power to a second switch in the switch box by pigtailing it. You'll then pigtail the neutral in the light with the fan. This is assuming I'm understanding the setup correctly.
    – HoneyDo
    Oct 14, 2021 at 0:34
  • @ThreePhaseEel, Thanks, addressed in the edit. Didn't think about that.
    – JPhi1618
    Oct 14, 2021 at 1:17

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