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What size wire and breaker?

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  • What size wire and breaker?

    Hi there! I have been lurking around this forum for some time now and I am totally impressed by all the help you guys give out.
    My problem is this; I am installing 3 new Dimplex 2500w 240v baseboard heaters in my rental property. I have all the 12/3 and 10/3 wire I need. I also have 20amp, 30amp and 40 amp double pole breakers at my disposial. And I have a new double pole thermostat. My question is, what wire and breaker should I use? I have done lots of 110v wiring, wired in some stoves and dryers, put this is my first time with baseboard heaters, so I want to make sure it's right. Any help would be greatly appriciated.

  • #2
    Re: What size wire and breaker?

    When you are dealing with bbh on 240V you dont use 12/3 or 10/3 wire you just need two conductors as there is no connection to the "grounded" also once called the "neutral" conductor. I am wondering what made you decide to purchase 2500w units ie what size rooms do you have to heat? More info please. Thanks.
    Last edited by Sparky1969; 03-18-2010, 02:05 AM.


    • #3
      Re: What size wire and breaker?

      You can use the 12/3 or the 10/3 but you do not need the white conductor as Sparky1969 said.

      2500 watts divided by 240 volts equals 10.4 amps. So you actually could use #14 wire. But since you have 12/3, use it with the 20 amp breaker you also have handy. Just cut the white off at each end or better yet, fold it back and tape it to the cable.
      Licensed Electrician


      • #4
        Re: What size wire and breaker?

        what John stated in power draw was for one heater.

        not three of them on one circuit,

        the normal breaker size for wire size is,
        #14 wire 15 amp breaker,
        #12 wire 20 amp breaker,
        #10 wire 30 amp breaker,
        but should not be loaded for a continuous load of more the 80%, of rate amps, so in a heater type application, a
        15 amp breaker and #14 wire, 12 amps,
        20 amp breaker and #12 wire, 16 amps,
        30 amp breaker and #10 wire, 24 amps,

        so with what you have you will need to run at least two circurts or get heaver wire and the 40 amp breaker,

        If I am under standing things correctly,
        Last edited by BHD; 03-18-2010, 10:53 AM.
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        • #5
          Re: What size wire and breaker?

          Thanks so much for the help.

          Sparky1696, what made me choose 2500w heaters is that my tenant runs a hair salon, and all of her customers are elderly. They like it hot "fast". The space is about 750 square feet, the calculation I found said 8w per square foot. So about 6000w needed. The door is opening and closing a lot during the day. And its on the north side of the building. And we get some pretty nasty winter weather. And that's what my renter wanted, so I try to keep her happy. Her rent buys the christmas presents afterall.

          Again, thank you for your help.


          • #6
            Re: What size wire and breaker?

            I understand your need for wanting hot fast believe me I understand Canadian winters. My main concern was your circuit loading factors which BHD consequently addressed.( i.e too much load for one 20 or 30A ckt) Thanks for the info. Keep those ladies happy.


            • #7
              Re: What size wire and breaker?

              Not sure about Canada, but in the US, the majority of jurisdictions (maybe all) do not allow a landlord (unless he is a licensed electrician) to do wiring in his rental property. Base on your question I assume you are not an electrician.