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Thread: 240v single pole?

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  1. #1

    Default 240v single pole?

    first did something happen to the forum I can't search any post past june of this year. where did all the old posts go?

    ok so i am adding an programmable thermostat to my 240v baseboard heaters.
    i am looking at the user guide http://www.aubetech.com/manuel/2/TH106.pdf
    and it is calling for 2 wires only.

    So one wire is hot and one is neutral i assume. But i have no idea how to get 240v out of one single wire.

    I always used a double pole breaker and use a 12-3 wire to get 240v. but i got no idea how to get 12-2 to carry 240v. any suggestion? is there such of breaker that is 240 single pole?

  2. #2
    Rancher
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    What the diagram is depicting is that the thermostat is just a switch, it breaks only one side of the power going to the heater. The circle with the squiggle thru it is your power source, either 120 or 240, i.e. it only breaks one side of the 240 volt power, there is no neutral.

    Rancher

  3. #3

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    Quote Originally Posted by Rancher
    What the diagram is depicting is that the thermostat is just a switch, it breaks only one side of the power going to the heater. The circle with the squiggle thru it is your power source, either 120 or 240, i.e. it only breaks one side of the 240 volt power, there is no neutral.

    Rancher

    I am sorry. I just can't picture it in my mind. Out of the double pole 20 amp breaker i got 3 wires coming out correct? 2 of them are hot, let's say color black and red. the third wire is the ground. But on the back of the thermostat only got 2 wires.
    So let us say I connect one of the hot wire (black) and ground to the thermostat than to the heater. Do i than connect the other hot wire (red) directly to the heater??
    Last edited by hids2000; 07-20-2007 at 09:34 AM.

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    On a typical 240vac breaker, there are two hots and the ground (no neutral) comes off of the bus. A stove or dryer may need a neutral because they want 120vac. Your heater doesn't typically need a neutral, so 12/2 is probably all you want (the second value is the number of load carrying conductors, they don't count the ground which is extra). On any circuit, it needs to be complete round trip to work. On a 240vac home circuit, that just means two hot leads from the opposite sides of the supply transformer feeding the power to the house. Neutral is half-way between those two, which gives you 120vac if you tap it off there.

    If your thermostat can handle the current from a 240vac circuit, you only need to run one wire through it to break the total connection. This means that there is still voltage in the heater, but it can't go anywhere because one half has a switch (the thermostat) breaking the path. I think it is nicer to break both hots, but functionally, it works the same either way. Just make sure to turn the CB off if you want to do work, since there is still power going to the heater, even when the thermostat is off. If you find a path to ground, it will fry you.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    Homeowner geniescience's Avatar
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    think open circuit. When an circuit isn't working, it's only because a conducting wire is cut. Only one wire, if cut, makes the circuit go dead.

    The thermostat cuts the circuit by opening one of the wires. A single wire. The same wire, cut at one place; insert thermostat and voilą circuit works again. Thermostat makes closed cicuit. One wire only. Same color in and out. Assuming i understood it like it should be understood.

    David

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    Electrical Contractor/Instructor jwelectric's Avatar
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    First you need to learn that not every white wire is a neutral and not every neutral is a white wire.

    From a 240 volt breaker comes two conductors of what ever color I choose. It can be one black and one white as no neutral is needed for baseboard heat.

    200.7(C) of the NEC requires that if I choose to use the white wire as part of a 240 volt circuit I must re-identify it be marking it as a different color.

    If you have already installed three conductor cable just disregard the white conductor.

    The thermostat needs to break only one of the conductors supplying the heater as the diagram shows.

    If you are not able to read the diagram and install the thermostat then you need to seek help from some in you area.

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by hids2000
    I just can't picture it in my mind ...
    Here you go, and the ground wire goes directly and only to the heater.
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    Last edited by leejosepho; 07-20-2007 at 02:51 PM.

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    Plumber jimbo's Avatar
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    Quote Originally Posted by hids2000
    first did something happen to the forum I can't search any post past june of this year. where did all the old posts go?

    ?
    Unfortunately, something did happen to the bulletin board. It's a long story! Let's just let it go at that!

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    Plumber jimbo's Avatar
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    Quote Originally Posted by hids2000
    So one wire is hot and one is neutral i assume. breaker ?
    NO. I see the device is Canadian. I don't know if you are in Canada.

    In the US a pure 240 volt cirvcuit, as you have typically on a baseboard heater, would NOT have a neutral. The two wires are the 2 hot wires.

    It is preferred to switch both leads of 240, but your local inspector may allow this thermostat, which only switches one lead.

  10. #10

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    I'm sure you probably already have it in by this point, but If you are doing any new work that has to be code inspected, you may want to call your local code office and double check that a single pole thermostat is ok. I discovered (well after I already bought them for a basement finishing project) that they require double pole Thermostats for 240V heaters. I'm not sure if this is a national standard code thing or just local but he did say it was a recent change.
    I personally don't see why you have to have both poles cut... a broken circuit is a broken circuit whether you cut one pole or both correct ?

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by bucknljake
    I personally don't see why you have to have both poles cut... a broken circuit is a broken circuit whether you cut one pole or both correct ?
    Yes, a broken circuit is a broken circuit, but one hot leg could still produce a shocking experience if someone did something out of the norm either to, with or near the heater while believing "off" was truly off.

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    Licensed Electrical Contractor Speedy Petey's Avatar
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    Quote Originally Posted by leejosepho
    ......while believing "off" was truly off.
    "Believing" is NOT a safe word. If you get hit because you "thought" the circuit was off it is your OWN fault. This is Ele. 101.

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    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by Speedy Petey
    "Believing" is NOT a safe word.
    Yes, mere belief never makes *anything* actually true.

    Quote Originally Posted by Speedy Petey
    If you get hit because you "thought" the circuit was off it is your OWN fault. This is Ele. 101.
    Not necessarily. A janitor or anyone else with a bucket of water for cleaning a baseboard heater might reasonably assume it is "off" simply because the thermostat knob, display or other indicator says it is ... and at that point, the individual who installed the single-pole thermostat would be the culpable one after that bucket got spilled onto the business end of that heater.

  14. #14
    Licensed Electrical Contractor Speedy Petey's Avatar
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    If you are cleaning an electric baseboard heater with a bucket of water you deserve a shock anyway.

    Seriously, water merely spilling on a baseboard heater will NOT cause a shock. The element is sealed and wiring is in a wiring compartment. Even if the wiring does get wet it will not energize the whole unit.

    If the scenario you describe did happen, the manufacturer of the unit would be at fault, not the installer.
    At the same time, this scenario could happen to literally dozens of other electrical items.
    Just because the heater is 240v does not make it that much more dangerous. People think the get shocked with 240v, when in reality they are hit with 120v. It is HIGHLY unlikely that someone would touch BOTH hot wires, at the same time, while remaining ungrounded.

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