Thermostat connection assistance

Discussion in 'Electrical Forum discussion & Blog' started by user32, Oct 13, 2010.

  1. user32

    user32 New Member

    Messages:
    3
    Location:
    US
    Hi, I'm trying to connect a new programmable thermostat to replace the old analog one. However, nothing seems to work. My father is a retired electrician who is coaching me over the phone 2 states away, but he's been out of the game for almost 20 years and without seeing it, it is a little difficult, so I could use some extra help.

    Here's the deal - I have a 4 wire system 2 12/2's coming in. If I run a volt meter over both blacks I get a 240 reading. If I run the meter over either black to either white, or both whites together, my meter reads 0. I have 2 baseboard heaters connected to the thermostat - 8' and a 2'. The thermostat is connected to the original fuse box 'range' fuse with 2 30amp fuses in it. Also connected to that 'range' fuse are 2 outlets and a set of overhead lights.

    The old thermostat is a double pole system, as is the new one. The new thermostat has 4 wires. My thermostat has 2 black and 2 red wires. It is a honeywell model livevolt pro 8000 TL8230A. It is rated at 240VAC 50/60Hz 15A 3600W | 208VAC 50/60Hz 3120w. One set of the thermostat wires are labeled 'lead' and the other shows a circle with a tilde in it (AC symbol, I think).

    When I connect the thermostat I get no power to the thermostat. The digital display does not come on. I have tried switching the 12/2's in case the wrong one was on the 'lead', but that didn't help either. Normally, I understand that the thermostat has a line from the box and a line to the baseboad, but is that not the case since both black complete the 240 circuit?

    Oh, I also tried a new Honeywell RLV430 using the 4 wire connection instructions (it is a two wire non polarity thermostat) which says I should be able to connect both whites to each other and connect each black to each of the thermostat's 2 wires. But, all that did was blow the fuse and trip the breaker. :(

    Any help would be appreciated.
    Last edited: Oct 14, 2010
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,242
    Location:
    Cave Creek, Arizona
    WE would have to test the wires ourselves, since we are not sure how you are doing it. The "hot wires" WILL be 240 volts between/across them. But we do not know how you are testing for the load wires.
  3. Jim Port

    Jim Port Electrical Contractor

    Messages:
    156
    Location:
    Maryland
    By 12-3s do you mean black/red/white and ground?
  4. user32

    user32 New Member

    Messages:
    3
    Location:
    US
    I mistakenly said 12/3 - I meant 12/2. They are black/white/neutral. I fixed it in the original post. Sorry.
  5. user32

    user32 New Member

    Messages:
    3
    Location:
    US
    By this, are you asking how I am determining line vs load? If so, the thermostat connection is right next to the fuse box (fuse box inside the closet, thermostat on the wall outside the closet), and I can follow the wires through a drop ceiling that clearly shows where each wire is going to/from.
  6. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    If I imagine the system wiring correctly, with all power off whatever two conductors go to the load should read a few ohms, possibly more than 16 ohms.

    On your t'stat, if it has a DPDT electromechanical relay inside, the two line/source terminals should read some ohms and all other terminals taken two at time should read infinite ohms. Use a DVM for this measurement.

    I'd take this
    ~
    to mean the AC input.
    Last edited: Oct 14, 2010
  7. Andrew21

    Andrew21 Member

    Messages:
    163
    Location:
    New York
    Take pics and post them up.

    Also, if you call the thermostat manufacturer, they have people on that line that will call you back to help you out.
  8. Bobelectric

    Bobelectric Electrical Contractor

    Messages:
    39
    Location:
    Eighty Four,Pa. 15330
    honeywell.com
  9. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    It seems unusual for a supply cable to be 2 blacks, and the load cable to be 2 whites. I suspect you may not have your system wires identified correctly. Some pictures would help.


    Look at the diagram here for the wiring: http://customer.honeywell.com/techlit/pdf/69-0000s/69-2023.pdf

    I don't think what you described is correct connection of your wires. Your incoming power, which should be a black/red or black/white, goes the the terminals marked ~, and a set of black/red or black/white should go to the LOAD terminals. You might need an electrcian to find out what wires are what.
    Last edited: Oct 16, 2010
  10. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    The diagram Jimbo posted shows the inboard terminals to be power in, and the outboard terminals to be the load.

    If it doesn't work it may already be clobbered but usually the manuf. puts in circuitry that guards against foreseeable wiring errors. There might even be an internal fuse.
    To test it independently, using clip leads you could hook it up to a known good 240 v supply like an elec. dryer outlet, and use two 120v, 60 w incand. lamps in series for a 240 v load. The voltage won't share equally between the bulbs but for a short test it should be OK.

    Load or no load, I'd think as soon as the 240 v is hooked up the display should work, but

    "The thermostat’s screen is blank. [could mean] The thermostat’s switch is set to Off."
    Last edited: Oct 16, 2010
  11. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,242
    Location:
    Cave Creek, Arizona
    IF we try to diagnose this without a better understanding of what you have, we are just the blind leading the blind. But if the thermostat was connected to the wires when they tripped the breakers and/or blow the fuse, (and from your posting it looks like you have BOTH, and then the question becomes WHY?), then you may have fryed the circuits. What is connected to the fuse/breaker, TWO blacks or a black and a white? Two blacks would normally mean a conduit system since Romex would be a black and a white.
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    Pull the cover off the CB panel (if you feel comfortable about this...it can be dangerous behind there - that's why it has a cover!), then look at the CB feeding that circuit. That should give you an indication of what the feed wires are (unless it's cobbled through something else inbetween - not a good idea!).

    With just the bare wires in the box for the thermostat, you should only get 240vac between two leads...those should be your line input to the thermostat. The other two leads should go to the heater, and if you have an ohmmeter, you should read maybe 10-20 ohms (depends on the wattage) between them. That would be the load wires. Now, if there are more than two pair of cables in the box, there may be several loads, one pair going to each radiator (assuming there is more than one - don't remember).

    Generally, it's not a good idea to feed the heating circuit AND something else. Suppose you could if the load wasn't too high, but the other circuit might get a voltage drop when they kicked in, and that could be annoying.
    Last edited: Oct 16, 2010
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