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I have a bathroom fan/light/night light combo unit that allows for all 3 features to be switched separately (a connector for each). I want a timer for the fan, and separate switches for each light. I'm wondering the best way to wire that.

I could just add a 12/3 cable with two hot wires and a 12/2 cable to control all three features. Or 3 12/2 cables. But I was wondering, if one were starting from scratch would they run 3 separate cables from the switch to the fan combo? Or something else?

So my thought was, could I run conduit and put a ground, neutral, and 3 hots through it, between the switches and the fixture. I realize that would mean all 3 things going through the same neutral, but that would be the case anyway if I just ran 3 cables from the switches.

So is that a valid use of conduit? I also looked for existing cables with 1 neutral and 3 hots (grounded). I think they exist but I can't tell if they're for home wiring or to any sort of electrical code or anything.

I'm having a hard time finding the answer because I don't know how to ask. Being an amateur, I want to go with something I know is correct so I'm wary with this.

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Conduit is a fine way to do it. One of the luxuries of working in conduit is you can install any wires the circuit requires. This is safer too, because it assures that hots and neutrals actually are together. There's no problem with transitioning between cable and conduit of any kind, so long as you are in locations appropriate to both types.

It's also easier to wire, since you aren't stuck with red and black (or marking white or gray neutrals). You can use any color you please; brown, orange, yellow, blue, purple or pink. Even my local lumberyard sells several of those by the foot. Of course green can never be anything but ground, even in a conduit. (thanks gregmac for reminding me to specify what I assume you know, but the next reader might not.)

In metal conduit you must bond the conduit to ground, but you also can let the conduit be the ground, so one less wire to pull. To make a transition from wired ground to conduit ground, the boxes have a hole tapped for 10-32 for attaching the ground wire. For convenience, they sell green screws 10 for a buck, and pre-made ground pigtails 10 for $3.

  • Small clarification: You still have to follow NEC wire color rules (eg, NEC 200.6) in a conduit. Very basic summary: Grounded (neutral) conductor must be white or gray (or marked), and Equipment grounding conductor must be green or bare (if used), and conversely, those colors can't be used for ungrounded (hot) conductors. – gregmac Mar 17 '16 at 22:40
  • Thanks, appreciated. I breezed over it because of my intuitive sense of his skill level, but I forget SE has a bigger audience. – Harper Mar 18 '16 at 0:05
  • Thanks, this is what I was hoping. I don't know why I was having a hard time finding info on it. It seems a lot of people just go with tying the fan and light(s) to the timer or the same switch. Which I wanted to avoid. – Vectorjohn Mar 18 '16 at 19:13
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If you use conduit you can run a neutral ground and 3 hots. Since these are all fed from the same hot. Flexible non metallic would be the easy way since it will be concealed in a wall it is legal as long as not above 3 floors above grade NEC 362.10. Table 1 chapter 9 says over 2 conductors the max fill is 40%. with 1/2" there is room to spare according to table 5 with #12 wire (table C-1 allows for a total of 9 ea 12awg conductors).

  • I recommend running 3/4" with minimal bends for easiest pulling, though this also helps fill. For an amateur it's not worth breaking out top-shelf binders, come-along and lube just to save pennies on conduit. Fill ceases to be an issue above about 3/4" since all conduit has a thermal limit of 9 conductors (not grounds and MWBC neutrals) before you have to start derating (10ga=20A). – Harper Mar 18 '16 at 0:03
  • The OP only has 3 current conductors with a 40% fill he is only about 25% of the total area 3/4' is a total waste of $. No derate is required . – Ed Beal Mar 18 '16 at 2:21
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If the power is at the switch box, you could simply run a single 12/4 (with ground) nonmetallic sheathed cable between the boxes. You might not find 12/4 at your local big box; or maybe not even at the local electrical supply, but you should be able to order it. Another option would be to use 12/2/2 (with ground) nonmetallic sheathed cable, which is more widely available. Though with 12/2/2, you'll have to reidentify one of the neutral conductors.

Of course as you mentioned, you could always install conduit and pull individual conductors.

You don't have to worry about sharing the neutral, as long as all the "hots" are from the same circuit. The neutral is rated for 20 amperes, and there'd be no way to pull more than that without tripping the breaker.

NOTES:

  • You might find 12/2/2 listed as 12/2-2, or 12-2-2. In any case, it's a cable with two "hots", two neutrals, and a ground.

enter image description here
example using 12-2-2 NM cable.

  • This (12-2-2) would work for me except I'll be opening up the wall or somehow fishing something anyway, so I wanted to keep it to one cable/conduit if possible, since they are and can only be used for this one self contained device. – Vectorjohn Mar 18 '16 at 19:08
  • @Vectorjohn 12-2-2 is a single cable, with 5 conductors in it. If you used it, you'd simply have to reidentify one of the "neutrals" by marking it at both ends. – Tester101 Mar 18 '16 at 19:12
  • I just meant that I need 3 hot conductors. Are you saying I could tape one of the neutrals to use it as a hot? That would work for me, but is that sufficient / good practice to do? I know it's done in some cases for switches. I just don't want to do anything non-standard. Edit: oh, I see that is what you meant. Sweet diagram BTW. – Vectorjohn Mar 18 '16 at 19:52
  • @Vectorjohn there's no problem with reidentifying a conductor, as long as it's marked at both ends. – Tester101 Mar 18 '16 at 19:57

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