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When I bought my baseboard heaters, thermostats and 220V breakers I was advised to get 12/3 wire. When I attempted to install the heaters I found that the thermostats, heaters, and even breakers have connections for only 2 wires. I have since read that 12/3 is only necessary for wiring something like a dryer that uses both 220V and 110V over the same wire. My question now is, should I get 12/2 instead of 12/3 to wire these heaters?

Niall C.
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Luke
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7 Answers7

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I'd use 12/3 -- that way, the neutral is there if you need it (for built-in outlets for instance), and you can use standard color codes. (Just about ALL /2 NM is black/white/bare.)

ThreePhaseEel
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You should use 12/2 if the 240v appliance requires two hot plus ground. If you can't find 12/2 wire that has black/red/ground... you can use the more common wire that has black/white/ground where both black and white are hot. If doing this you MUST identify the white wire as hot at the appliance (or outlet if used) and at the panel. I always use colored heat shrink tubing because electrical tape almost always falls off after many years and is not reliable. Also make sure that you're using a proper 2-pole breaker at your electrical panel and if using an outlet, use the correct type to match the circuit's amp rating.

http://cdn.instructables.com/FJX/ZDUA/HAQ3A4EL/FJXZDUAHAQ3A4EL.LARGE.gif

Andrew LB
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I had a similar situation when I wanted to add 240V baseboard heaters to my attic renovation. I was initially told I needed to run 10/3 for a 240V line (I forget who, maybe my father-in-law or the guy at Home Depot), so I ran 10/3 from the basement through two stories and up into the attic. Later I found out all I needed was 2 conductors for the heaters so I ran the 10/3 into a junction box in an attic closet and then had 10/2 go from there to the heaters and thermostat. I put a wire nut on the unused conductor in the junction box as well as at the other end inside the electrical panel.

I wish I had known that I only needed 2 conductor when I was fishing it from the basement as it would have been easier to deal with and cheaper.

Where are you located? My experience is in the USA and I am NOT an electrician (though it did pass inspection from the city).

auujay
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    I really don't like having wires that are un-connected at both ends. They act like an antenna, and can give you a shock if you touch it, particularly if they are long. That is why I always connect it to ground, or neutral. ( which one depends on the circumstances ) In this case I would hook it up like you normally would at the breaker, and just put a wirenut on the white wire in the junction box. Also if you replace your system with one that requires a neutral, you won't have to go into the breaker panel, to hook it up. – Brad Gilbert Jun 25 '11 at 06:05
  • Yes, Cadet brand heaters have a changeable faceplate on each end of the heater. You can stick different accessories there, such as a thermostat *or...* a 120V receptacle! **For *those*, you would need neutral**. This receptacle can count as the Code required receptacle along a wall, sparing the need to install other receptacles. – Harper - Reinstate Monica Dec 15 '17 at 03:54
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I wire both of my 240 heaters on the same circuit with 12/2 wire identifying the white with black electrical tape.A 240 circuit is alot cheaper than a 120 volt.

Dale
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I like the idea of using 12-2 with ground, and marking the white wire red. But, my inspector said it is not allowed to mark white to red for small wires. I don't recall the cut-off AWG.

Ted Rees
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  • Are you working in NM/... *cable*, or in *conduit*? – ThreePhaseEel Jul 25 '19 at 23:59
  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably [take our tour](//diy.stackexchange.com/tour) so you'll know how best to contribute here. – Daniel Griscom Jul 26 '19 at 00:00
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Refer to the total amps for the heater. Base the wire selection on this number. The wire size should be xx/2 WITH GROUND. Try to get wire with black and red conductors for 220 volts. If the wires are black and white the white wire MUST be pemantly marked red or black. Black and white conductors ar ok for 120 volt.

Dave
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EDIT: As comments have noted, this isn't a good answer. Thanks for the lesson! Look at the other answers on this page for wiser advice.

12/2 would be a less expensive and more obvious-to-future-electricians way to wire the heaters. However, you can use 12/3 and just ignore one of the wires. The safe way to do that is to bond the red wire to ground at every junction. That way, if it is ever wired to current somewhere in the system, the circuit will immediately short and your circuit breaker will break the circuit.

Shimon Rura
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    I have to take issue with using 12/3. The heaters need 12/2wg. If 12/3 were used, convention requires that the black and red conductors are used to carry voltage 120/240vac and the white shall be neutral and bonded to the bare ground at the panel. When the white is used for a primary voltage leg (12/2wg) it must be painted or marked black to designate it as a primary. I totally disagree with using 12/3 and especially bonding red to ground, which is NEVER done. Your solution would certainly work OK, but not a good practice. Sorry down vote. – shirlock homes May 03 '11 at 10:21
  • Good point shirlock, I didn't know that when using 12/2wg to carry 240VAC it was required to mark the white. The idea of bonding something to ground was just to make clear that one of the conductors is not being used for its normal purpose. – Shimon Rura May 03 '11 at 21:08
  • Alright, I've got a follow up question. I have since discovered that the 2 connections on the 220v breaker are for the 2 hot wires that are each 110v... Now I'm wondering how to properly hook up the breaker to get 220v over one wire... – Luke May 27 '11 at 02:04
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    @Luke: each hot wire is at 120V potential relative to the neutral wire. However, they are on opposite phases, so the potential between the two hots is 240V. You don't use the house neutral in this configuration. – Shimon Rura Jun 03 '11 at 02:16
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    I am an electrician. Red and Black are used to carry voltage and white for ground. If you are tempted to use red as a ground hire an electrician before you electrocute someone. –  Dec 19 '13 at 19:31
  • @user18737 I don't think anyone is suggesting using the red as a ground, but bonding it to the ground to ensure there isn't an unused wire that's accidentally connected with voltage. – BMitch Dec 19 '13 at 20:04
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    Also, when @user18737says white is for ground he is mistaken. I hope it was an innocent mistake. White is typically used for the neutral, but can also be used as a hot when re-marked. It should never be used for ground. – Speedy Petey Sep 23 '14 at 23:12
  • If the red/black/white wire is strung from the panel to the attic box, is there any reason why it shouldn't be wired with red and black as the two hots and white wired to neutral at the panel? That would seem much more normal, and would leave open the possibility of e.g. adding a 120V blower on the circuit. – supercat Feb 19 '15 at 01:25
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    cap off the *white* (unused neutral) wire at both ends of 12/3. use the black and red to carry the 240 volts. – Skaperen Jun 15 '15 at 11:06
  • use the green wire in the usual way for ground – Skaperen Jun 15 '15 at 11:15