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Douple pole built-in baseboard thermostat

holybuzz
16 years ago

Hi,

I just installed a baseboard thermostat, a TPI douple pole. The heather is a TPI, 240v/1500w. It's on a douple pole 20 amp breaker.

I followed this similar diagram (small pdf):

www.marleymep.com/Develop/prod_pdf/2500wiring.pdf

The thermostat has an off position (douple pole), but the thing won't go off. Even when turned to the off position, it continues to churn out the heat. Unsafe.

This is a brand new thermo that replaced a single pole installed by my electrician. I went with the double pole for safety, but now I have a practically glowing heater.

Is the thermostat a dud? I've checked the wiring over and over and everything looks right?

Any ideas?

Thanks in advance.

Keith

Comments (15)

  • bus_driver
    16 years ago

    What prompted the replacement? Did the other thermostat fail? If so, did it fail to heat or did it heat all the time?

  • holybuzz
    Original Author
    16 years ago

    Bus Driver,

    The first thermostat (it was a brand new unit) stopped working. That is, the heater stopped working, and the electrician who installed it said that it was probably a bad thermostat. When I opened it up (power off first, of course), I saw that my electrician had used a single pole thermostat, probably because that's what he had in his truck at the time. As I said, the unit is a 240v unit, so I figured that a double pole was the best way to go, especially since the single pole meant that the unit was on ALL the time.

    Now the double pole is on all the time! Arg!

    Can you diagnose?

  • bus_driver
    16 years ago

    Most baseboard heaters have the element with only one electrical connection per end. To complete the circuit, a conductor runs the length of the heater within the heater and is connected to a supply conductor at whichever end is desired. That conductor is connected to the element at the other end and is the only connection at that end. Sometimes this conductor gets pinched and shorted to the heater housing. If the pinched point happens to be the one connected to the switched line on a single-pole thermostat, the heater will be heating all the time at 120 volts due to the ground fault at the pinch point. The resistance of the element will limit current to less than the trip point of a breaker. If the circuit is fused, turning on the single-pole thermostat will blow the fuse on the pole that supplies the thermostat, but the other pole/fuse will continue to supply 120 volts to the heater. It is not a given that your heater or either thermostat was ever wired properly.

  • holybuzz
    Original Author
    16 years ago

    Bus driver,

    Not sure I follow. (BTW, I know diddly about electrical. But rest assured that I'm being super careful and following the diagrams to the letter.) You're talking about the inner workings of the heater, right, not the 12/2 that runs from one end of the heater to the thermostat on the other side?

    So what do you recommend? How do I to check to see if something got pinched and shorted? And when you say that the unit may have never been wired properly, do you mean from the factory? I know that my electrician ran the 12/2 and added the thermostat (not exactly rocket science), but he didn't do anything to the factory "guts" of the heater.

    Again, both the thermostat and heater here are TPI brand. I happen to have a brand new Fahrenheat heater and thermostat that I plan on using in the near future. Does it make sense to try those out?

  • bus_driver
    16 years ago

    It is possible that the "electrician" did not wire it correctly. But I do not know that for a fact.

    "not the 12/2 that runs from one end of the heater to the thermostat on the other side?".
    He ran a 12-2 through the full length of the heater, inside the heater? That would be all wrong. I have no idea what that is all about. The possibly-pinched conductor is a single conductor, original to the heater, installed inside the heater at the factory. If your electrician ran a 12-2 cable other than through a knockout and strain relief device about 6 inches into the heater, then it indeed is all wrong. And I suggest that if my posts are not understood, your present knowledge is inadequate for this project.

  • holybuzz
    Original Author
    16 years ago

    Bus driver,

    Believe me, if I had screwed this up, I'd be taking the...heat for it. (Pardon the pun. :)) I own a crappy little house that needs loads of work, and I post about my...renovational shortcomings on different web sites on practically a weekly basis.

    Here's what the electrician did:

    12/2 (the yellow-sheathed stuff) comes up through the wall and into one end of the heater, where it connects to another length of 12/2 (also yellow) that runs underneath (not really "through" the heater, I guess; it goes via the knockouts) to the other end. That's where the thermostat is.

    Yes, it looks suspect and should be covered somehow. (I have a call in to my electrician, but I was hoping that a simple thermostat wiring was within my grasp. Maybe not.) But beyond the code issues (and I WILL address them), what is likely my problem with the heater not turning off?

    The only difference between my stat and the one in Marley pdf above (see Step 15) is that the Marley stat has a short red wire that leads (I think) from the element wire to the fins. (Wrong terminology, I'm sure, but it's the short red wire.) In my stat that little red wire doesn't exist. Instead, there are two (not one) black wires that I've nutted. Apart from that, everything else is the same.

    BTW, you're right: my present knowledge (and probably future knowledge) is inadequate to diagnose and remedy this problem. Trust me, if my explanation doesn't give you or someone else here an aha! moment, I won't start guessing.

    Thanks for your help.

  • bus_driver
    16 years ago

    That little red wire is probably the high temperature shutoff. Those baseboard heaters now have built-in limit switches that control maximum temperature to 156 deg. F. Only one of those per heater, it may be located elsewhere.

  • holybuzz
    Original Author
    16 years ago

    Does this mean that my heater (a two-year-old TPI, looks just about identical to the Marley) also has a max shut-off? And if my wiring is correct (double- and quadruple-checked it), does that mean that the unit is internally defective?

  • holybuzz
    Original Author
    16 years ago

    Solved!

    Bad thermostat. Took it in to the supplier, they said I'd fried it. The thing didn't "click" when you turned the knob. I told them how I'd installed it, insisted that I'd gone by the book, but they wouldn't give in. $20 bucks ain't much to buy another, but it's enough for me to take my business elsewhere. Oh well.

    Anyway, for future reference, here's the diagram that I used:

    http://www.tpicorp.com/01-MenuSystem-CatalogPages/01-Built-inHeaters/MarkelBuilt-in/BaseBoard-ResidentialConvection/om.pdf

    Thanks.

  • joefixit2
    16 years ago

    Those T stats are very tempermental (excuse the pun) I can remember frying one just by reversing the line and load connections.

  • nolan17_optonline_net
    16 years ago

    You mention reversing the Line and Load. I have a double pole that I am installing and I cannot figure out if Load comes from the panel or Line comes the panel. Right now I have red Load wires going to the panel and black line wires going to the heater. Is that right?

  • itsunclebill
    16 years ago

    Line comes from the panel. Load goes to whatever is being controlled.

    The thermostat is a switch and it shouldn't really care which side the line and load are on. Any markings or instructions that indicate line or load terminals should be observed though. Many people seem to get confused with the 2 pole thermostats that have the black and red wires assuming (without reading directions or lacking them) that there should be a wire of each color tied to line and to the heater when in fact this can either work or be a direct short depending on which wires are selected.

    There is no reason to assume that a 2 pole thermostat is better in an installation than a single pole since the heater is off when either one opens a contact. Maintenance shouldn't be attempted with the breaker on, and you don't run the risk of electrons leaking out and puddling on the floor just because you're only opening one line conductor. The situation is no more unsafe than the presence of a hot wire at a receptacle that is hot all the time. It doesn't do a thing unless a path to the other line, neutral, or ground is provided. A situation that causes one set of contacts to weld itself together (at some point after a correct initial installation) will likely do the same to the other set as well and will be pretty rare.

  • bus_driver
    16 years ago

    The differences between the single pole thermostats and the double pole thermostats include that the double pole typically has a positive "Off" position while the single pole does not. The single pole simply has the lowest calibrated setting of 40 to 45 deg and a positive off requires shutting off that circuit at the panel.

  • boomedley
    16 years ago

    Thanks for the info. I will redo the wiring and then see how it works. I really appreciate the help.

  • holybuzz
    Original Author
    16 years ago

    And here's a step-by-step for the Marley/Fahrenheat that Lowes sells:

    www.marleymep.com/Develop/prod_pdf/2500wiring.pdf

    FYI