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I'm continuing to fix the issue introduced by someone else (Why run the same phase twice to a series of outlet?).

The other room they did has this setup:

  • a 3-conductors cable brings the same phase twice, from a single breaker
  • one device is a 120V heater/fan that requires 13A
  • the rest is lighting and a power outlet
  • everything is AWG 14

(so, with the heater/fan on, we go above 15A. And anyway, the heater spec asks for a 20A circuit)

I understand electricity well, but I know nada about code. Since I don't feel like running a new cable, I though this would work:

  • split the 3-conductors cable into a MWBC 20A (I'll ask a competent electrician for this, I don't open panels)
  • use 1 phase for the heater/fan (it only needs 120v, but has two switched inputs)
  • use the other phase for everything else

What code issues (if any) would this run into? Diagram shows what I'm aiming for. The blue box is the four gang box. I'd rather no rip out anything in the walls.enter image description here

Location is Quebec, Canada.

Update: There's another cable I had dismissed, 2 conductors and bare ground, in 12 AWG, but the wires are coloured Black and Red. So I expected this to be only meant for 240v. See second picture. Maybe I can use this dedicated circuit for the heat/fan.

enter image description here

Update 2: Thanks, many excellent answers. I added the diagram that show what I must change.

enter image description here

3 Answers 3

6

I don't see any way to fix this without a new cable.

  • 14 AWG is max. 15A total, 12A continuous. A 13A heater requires a 20A circuit, and you can't run that on 14 AWG. Need 12 AWG or larger.
  • A proper MWBC requires two hot wires and a neutral wire and ground. You can't do that with just two hots and a ground, so the black/red/bare cable doesn't help for an MWBC.
  • A 120V circuit requires one hot, neutral and ground. Neutral must always be white (or gray, but that's not an option in standard cables). You can't put white tape on a black or red wire to make it neutral. There are certain exceptions the other way around where you can put colored tape on the white wire in a cable to make it into a hot wire (hot/switched hot/traveler) because standard 2-wire (plus ground) cables are black/white. In other words, if you started with a black/white cable it could (generally) be used for a 240V (two hots, white marked as hot) or 120V circuit. But a black/red cable can only be used as a 240V circuit and not as a 120V circuit.
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  • > You can't put white tape on a black or red wire to make it neutral. Sigh. Ok. Thanks this is useful. Boggles the mind, but useful info.
    – Jeffrey
    Jul 10, 2022 at 22:53
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everything is AWG 14

15A is your absolute maximum on #14 for those loads. There is no way to use that with a 20A breaker.

Does Canada require bathroom receptacle circuits to be 20A? The rest of North America does.

And since the heater's instructions are calling out a 20A circuit, that isn't really optional.

Update: There's another cable I had dismissed, 2 conductors and bare ground, in 12 AWG, but the wires are coloured Black and Red. So I expected this to be only meant for 240v. See second picture. Maybe I can use this dedicated circuit for the heat/fan.

You cannot use that for anything that is 120V. There is no neutral. You must not remark a colored wire to be neutral. You must not bootleg neutral from ground.

That would be usable for a 240V heater.

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  • 1
    So the proper course of action is to rewire the 12 AWG cable with a new one exactly the same except for the red conductor to be white instead?
    – Jeffrey
    Jul 11, 2022 at 2:55
  • 2
    @Jeffrey no, I would run a 12/3 so you can run a MWBC. You need a 20A circuit for the heater because it says so. You need a 20A circuit for bathroom receptacles because they can't be on a circuit where hardwired loads account for >50% of ampacity, and the heater does that. Jul 11, 2022 at 6:06
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The 14 AWG wire cannot be protected by a 20 amp breaker, has to be a 15 amp breaker. The heater/fan specs call for a dedicated circuit of 20 Amps so you're out of luck without running some #12 AWG.

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  • The 14 awg wire tops out at 15 amps . These wires are two small to be paralleled +
    – Ed Beal
    Jul 10, 2022 at 21:04
  • There is another cable I can repurpose. It's a 12 AWG with Red/Black/Ground in a red cable. Can This be used for 120V neutral and live ?
    – Jeffrey
    Jul 10, 2022 at 21:31
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    yes, [red + black + bare] in red outer cable. See updated picture. I only ever saw that in canada for dedicated 240v heating.
    – Jeffrey
    Jul 10, 2022 at 22:38
  • Well, that changes things a lot. Jul 10, 2022 at 22:41
  • Neutral has to be white, can't be a repurposed wire.
    – JACK
    Jul 11, 2022 at 0:13

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