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When wiring a three way switch using a light, I like the method of running the 12/3 wire to the other switch as the traveler method.

I want to wire a light/fan using two switches to control light and fan differently from both sides of the room.

Should I just use two 12/3 runs to each switch on the other side of the room and run the power to the light like I normally do?

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  • Is using ENT+THHN instead of NM for the wire runs an option? Sep 18 at 17:22
  • Is the power supply coming into the light or one of the switches? If power comes to a switch, is the spur to the lamp departing from that same switch? Sep 18 at 23:52

2 Answers 2

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You need to check if the fan has separate neutrals for light and fan or a single neutral. If it has two neutrals then you can use two 12/3 (or 14/3 if this is a 15A circuit). However, if there is only a single neutral then you have to have a single neutral everywhere. That would require a 5 wire cable (2 travelers for fan, 2 travelers for light, 1 neutral) which would be a bit of a problem. There may be some way around to make it all work, but it gets...messy.

This is actually be a very good application for a smart fan/light control with the 2nd 3-way switch being a wired (but wired to the switch with fewer wires) or wireless (battery powered) in-wall remote. For example, you could use (no connection, just searching and sticking with a major brand for safety) Lutron:

  • PD-FSQN - Primary fan control
  • PJ2-3BRL-Gxx-F01 - Pico fan remote
  • PKG1W-PICOMNT-BNDL - Light control and Pico remote (this is a Home Depot part number, actual Lutron number may be different)

Note that the Pico remotes can be mounted on any junction box or all by themselves. Pico remotes have wiring instructions that really amount to "connect load and line together, cap the neutral if there is one, don't connect anything to the Pico".

Pico remotes do use a battery. Manufacturer claims a 10-year battery life. Battery is a very standard CR2032 - the same batteries have been used in computer motherboards for many years, so they are readily available.

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    You could make the 5 wire method work quite readily using ENT + THHN... Sep 18 at 17:22
  • @ThreePhaseEel Absolutely. But based on the 12/3 references and typical DIY abilities (myself included) and an assumption (which could be wrong...) that the walls and ceilings are all finished (no drop ceiling, no open walls), running ENT would likely be quite a bit tougher than getting 12/3 NM cable through. Sep 18 at 17:26
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I want to wire a light/fan using two switches to control light and fan differently from both sides of the room.

If this means that you want one set of switches on opposite sides of the room to control the light, and another set of switches to control the fan, then yes, you can install two runs of the traveler cable.

However, code is now requiring neutrals in the switch boxes to be able to handle powered smart switches. How to include this code requirement depends on the kind of 3-way switching setup you are going to have.

One form of 3-way wiring is where the power/neutral/ground comes to one 3-way switch, then two-travelers/neutral/ground go to the other 3-way, then power/neutral/ground continues on to the load. If this is your setup, then neutral is present in the switch boxes and /3 is fine.

The other setup is where one is adding a branch off an existing normal switched load: where power/neutral/ground comes into the box, power gets switched, then power/neutral/ground continues on to the load. In this case power goes to the 3-way, then there must be two-travelers/return-power/neutral/ground: that's three powered wires, neutral, & ground, which is /4. If you're planning this second setup, you need to run 12/4 instead of 12/3. (Cap the neutrals in the remote boxes if you don't need them for your switches.)

However^2, do you need 12 gauge? Seems high for light & fan. If your circuit that you're powering the light & fan from is a 14-gauge circuit protected by a 15-Amp circuit-breaker, you can continue to use 14-gauge traveler cable. If the circuit is 12-gauge 20 Amp, I'm not certain if you could go to 14 for the light & fan, or must remain using 12. The code gurus would have to weigh in.

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  • can you provide a link to the new code requirement?
    – Jason
    Sep 18 at 13:44
  • Regrettably, no, I've just been reading a lot here, and it's something I've picked up from the gurus. Sep 18 at 13:47
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    The code requirement is 404.2(C). It basically says you need a neutral at every light switch except ... there are quite a few exceptions but as I understand it what they come down to is you don't need one if there's access to install one later without opening the wall.
    – trawson
    Sep 18 at 13:56
  • This code is claiming to use 12/3 which is what I’m running to the switch boxes and has 4 wires. What am I missing here?
    – Jason
    Sep 18 at 14:37
  • Thanks, @trawson, for the code reference! Sep 18 at 16:12

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