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Thread: Wiring Multiple Wall Thermostat Controlled (Cadet) 240v Baseboard Heaters

  1. #1
    sea-bee chuck b's Avatar
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    Default Wiring Multiple Wall Thermostat Controlled (Cadet) 240v Baseboard Heaters

    I have correctly wired a single 240v heater from a thermostat in my home, but in my cottage I wish to control several baseboard heaters with a single wall thermostat. In a 240v 20-amp circuit, I understand that 80% of max is the norm, i.e. 3750 watts and 16 amps...correct? Use 12-2 gauge wire right?

    But what I am confused about is the difference between "series" and "parallel" wiring. I believe that multiple baseboard heaters must be wired with "parallel" wiring. Please confirm.

    A BLACK and WHITE wire enter the first heater from the thermostat. A BLACK and WHITE wire will be there from the 1st heater, and a BLACK and WHITE wire from the next (2nd) heater via a length of wire. I imagine your instruction would also apply to the 3rd and 4th heater wiring which will of course be calcualted properly in terms of wattage and amperage as explained above.

    Not sure how to wire them. My guess is to pigtail the white and black wires from the thermostat to the same color wires from the 1st and 2nd heaters. Am I correct. Thinking that would be parallel wiring.

    Series wiring (which is wrong - correct) would be what, connecting one thermostat wire to the black wire from the 1st heater, and making a large "loop" of black to black, and black to white back to the 1st heater and to the thermostat white. I realize that a piece of black tape is required on the white wires as they will be hot.

    It's probably simple, but I don't want to do this wrong.

    Also, how are thermostats rated for a 20-amp double pole circuit? Is there some kind of calculation needed just like the 80% rule above for its rated value?

    Thanks for your advice.

    Much appreciated.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    A parallel circuit has each load connected directly to the source. A series connection has the current flowing through each load, end-to-end. The heaters need to run in parallel. If you did run them in series, they'd put out about half the heat since the resistance would go up, the current flow goes down.

    If the thermostat is rated for 20A, you should be able to put up to a 20A load on it. It would likely last a little longer if the load was less, but not necessarily so.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Plumber jimbo's Avatar
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    Nothing in your house is wired in "series". If you put two heaters in series, each would produce 1/4 of its rated watts.

  4. #4
    Electrician ActionDave's Avatar
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    Quote Originally Posted by chuck b View Post
    But what I am confused about is the difference between "series" and "parallel" wiring. I believe that multiple baseboard heaters must be wired with "parallel" wiring. Please confirm......
    The only way to hook one baseboard heater to another in series is to complete circuit through the heating elements, i.e. Romexes at both ends of the first heater and so on down the line.

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    There's daisy chain, then there's series...two different things.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    sea-bee chuck b's Avatar
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    Default Still confused - Baseboard Heater Parallel wiring

    Hi Jim,

    thanks for the reply. Still need a simple diagramatic explanation.

    A white and black, both hot come from the thermostat. There are two blacks in the 1st heater, and a black and white (wire) coming from the 2nd heater. What connects to what?

    Thanks again.

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    To be in parallel, each wire from the thermostat needs to go to each heater. So, and on 240vac, it doesn't matter on most things (a heater doesn't care), hook say the white from the thermostat to one wire from the first heater and one wire from the second heater, then hook the second wire from the thermostat to the other leads. Functionally, each wire goes to each thing. Think of parallel like a power strip...each thing connects to the power strip and the strip powers each thing individually. Unless overloaded, each thing is functionally independent since it gets its power in parallel.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    sea-bee chuck b's Avatar
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    Hi Jim, Thanks - understand it now! Chuck B.


    Quote Originally Posted by jadnashua View Post
    To be in parallel, each wire from the thermostat needs to go to each heater. So, and on 240vac, it doesn't matter on most things (a heater doesn't care), hook say the white from the thermostat to one wire from the first heater and one wire from the second heater, then hook the second wire from the thermostat to the other leads. Functionally, each wire goes to each thing. Think of parallel like a power strip...each thing connects to the power strip and the strip powers each thing individually. Unless overloaded, each thing is functionally independent since it gets its power in parallel.

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