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Using G Wire as C Wire

breton
breton Member Posts: 3
in Gas Heating

hi, I have forced hot water heat regulated by taco 2 zone. I want to hook up smart thermostats using the fan wire that isn’t being used. 3 wires at thermostat, red, white, green. Taco sr502 relay. I just need to know the configuration at the relay, not the thermostats. Appreciate it!

image.jpg

Comments

  • Zman
    Zman Member Posts: 7,611

    Just connect the green wire to the terminal labeled "COM" on the left side of the board. It is below the "24VAC" terminal. You can wire nut the 3 green wires together and just run one wire over.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    breton
  • breton
    breton Member Posts: 3

    hi zman, thanks man, so just to confirm, take the 3 greens - from the isolated end switch, zone1 therm, zone 2 therm and connect them all in the COM connector?

  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,214

    I think zman means just the greens on thermostat 1 and 2. Leave the isolated end switch green alone as that would probably fry the transformer on the boiler and/or the transformer on the SR502.

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
    bretonZmanSteveSan
  • breton
    breton Member Posts: 3

    hi Alan, ty for the clarification! That’s exactly what I want to avoid and the reason I asked again.

  • SteveSan
    SteveSan Member Posts: 260

    @breton Just bring the common wire from the t-stat to the com side of the 24vac/com green terminal to the left of the control. Between R & C on the Taco relay is 24v needed for these smart t-stats.

    breton
  • Zman
    Zman Member Posts: 7,611

    Sorry about that, didn't notice the end switch thanks @Alan (California Radiant) Forbes

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,562

    Check to make sure the onboard transformer can handle that additional load

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    Alan (California Radiant) ForbesSteveSanHVACNUT
  • HVACNUT
    HVACNUT Member Posts: 6,332
    edited July 20

    But that's it. No smart thermostat for the second zone (or any other power consuming control) using that transformer. It won't handle it. Anything else would need a seperate 40va transformer and isolation relay.

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,380

    depending on the age of the Taco Zone control that C wire is different

    based on the photo of the SR relay, this is the diagram youy should be using

    Screenshot 2024-07-22 at 1.04.18 PM.png

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    After you make that expensive repair and you still have the same problem, What will you check next?

    Alan (California Radiant) Forbes

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