240v single pole?

Discussion in 'Electrical Forum discussion & Blog' started by hids2000, Jul 20, 2007.

  1. hids2000

    hids2000 New Member

    Messages:
    63
    Location:
    Belleville NJ
    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. Rancher

    Rancher Guest

    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. hids2000

    hids2000 New Member

    Messages:
    63
    Location:
    Belleville NJ

    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: Jul 20, 2007
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,138
    Location:
    New England
    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.
  5. 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 voilà 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
  6. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,540
    Location:
    North Carolina
    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.
  7. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Unfortunately, something did happen to the bulletin board. It's a long story! Let's just let it go at that!
  8. hids2000

    hids2000 New Member

    Messages:
    63
    Location:
    Belleville NJ
    I got a hold a buddy of my and I understand it fully now. My problem is I work with DC all the time so I am always thinking + goes to - and in my mind I didn't understand how a 240AC since both are hot (in my mind +) can work without a return (-). And I totally forgot that AC switches from + to - back and forth. Now I understand the drawing and how to run the wires to the heater.
    Thanks everyone for their support and help.
  9. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    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. leejosepho

    leejosepho DIY scratch-pad engineer

    Here you go, and the ground wire goes directly and only to the heater.

    Attached Files:

    Last edited: Jul 20, 2007
  11. abikerboy

    abikerboy DIY Senior Member

    Messages:
    202
    Location:
    VA
    If you work with dc current, forget the ground completely, and relate an ac circuit to your dc 2 cell flashlight, and then imagine it this way...as the batteries running your flashlight! A flashlight battery is 1.5 volt. The bulb in a 2 cell flashlight is 3 volt. Stack two batteries in a flashlight, and measure from the bottom of the lower battery to the top of the upper battery (where the bulb is) and you get 3 volts. Now, leaving one lead at the bottom (or the top), stick the other lead in between the two batteries, and you get 1.5 volt. It works exactly the same. The two "top" leads (the hot leads) bring 240 into your house, while the center lead (the neutral tap of the power companies transformer) in combination with either of the other two leads will bring you 120. Just like the switch in your flashlight, the thermostat switch will break one of these "top" or "bottom" leads, and your heater is off. Again, just like your flashlight, the center tap, or neutral, wont really matter. As for the ground on an ac circuit, ground just attaches to the housing, just in case there is a short, or bare wire somewhere. As for the relation between ac and dc, with dc, there is a plus and a minus...with ac, the plus and minus reverses itself 60 times a second, so for one instant, one lead is a plus, and the next instant, this lead becomes a minus, and the other lead becomes the plus.
    Last edited: Jul 23, 2007
  12. bucknljake

    bucknljake New Member

    Messages:
    1
    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 ?
  13. leejosepho

    leejosepho DIY scratch-pad engineer

    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.
  14. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    "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.
  15. leejosepho

    leejosepho DIY scratch-pad engineer

    Yes, mere belief never makes *anything* actually true.

    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.
  16. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    If you are cleaning an electric baseboard heater with a bucket of water you deserve a shock anyway. :p

    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.
  17. leejosepho

    leejosepho DIY scratch-pad engineer

    No big argument there, yet there must be some reason for double-pole controls being preferable ...
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