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Thermostat wiring too thick?

FizzFizz Member Posts: 522
Wiring from boiler to t-stat is heavy gauge, more likd used in electric heating. Would this affect the function of a heat anticipator?


  • Jamie HallJamie Hall Member Posts: 12,719
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • FizzFizz Member Posts: 522
    Thanks Jamie!
  • BobCBobC Member Posts: 5,101
    That depends on the electrons in your system, a boiler or furnace thermostat is only seeing a few tenths of an amp. If the electrons are not very bright they may get lost in all that copper and never find their way to the end :p

    Using "house wiring is overkill, maybe he thought he was connecting a electric baseboard thermostat that carries the current flowing through the baseboard elements (15-20Amps).

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • FizzFizz Member Posts: 522
    So, use amp meter to get flow measurement?
  • ZmanZman Member Posts: 5,752
    Bob is kidding with you. The wire will work fine.
    Do make sure that it does not have 120 volt attached, some systems are set up that way. You may need to wire nut a whip of smaller gauge wire on the end in order to connect to the small terminals on the t-stat.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 6,947
    Yes you need a low range amprobe. If you don't have one wrap a wire around your amprobe 10 times then take a reading and divide the reading by 10
  • ZmanZman Member Posts: 5,752
    edited May 2019
    I don't understand why he would need to measure amps. If it is an old school anticipator, it gets set for the rating amperage of the attached load (zone valve motor or relay coil). Are folks making an additional adjustment for the size and length of the wire?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • FizzFizz Member Posts: 522
    Wire is not connected to 120v.
  • pecmsgpecmsg Member Posts: 1,393
    Fizz said:

    Wiring from boiler to t-stat is heavy gauge, more likd used in electric heating. Would this affect the function of a heat anticipator?

    Heat Anticipator?

    that went out with Mercury!
  • HVACNUTHVACNUT Member Posts: 3,280
    > @pecmsg said:
    > Heat Anticipator?
    > that went out with Mercury!

    In the digital age we've gone to CPH but I miss the K.I.S.S. mercury thermostats. Except maybe the Honeywell analog chronotherm with the red and blue pins that always seemed to go missing.
  • Jean-David BeyerJean-David Beyer Member Posts: 2,663
    My original heating system kept the boiler hot all the time, but the thermostat turned the circulator on when it felt cold. The thermostat was 120 volt contacts and BX cable ran in the wall back to where the boiler and circulator were. I never thought about that and when someone gave me a fancy (low voltage) thermostat, I put it in and fried it in 15 seconds or less.

    When I had the mod-con put in, the contractor was all all upset because the wire was too big and the thermostat would not work right. But he did not want to chop through my plaster walls to run low voltage wire either. I assured that the BX wire would work just fine with the thermostat. It did require wire nuts to put thinner wire at each end to fit the thermostat inside the house, and the boiler at the other end. But at least the contractor did not have to chop down my walls to run low voltage thermostat wiring.
  • HomerJSmithHomerJSmith Member Posts: 891
    edited May 2019
    You can't have too big a wire, but you can have too small a wire. Wire is rated for current carrying capacity. There are several reasons that you don't use a larger wire than necessary, one is cost.

    Gosh! Maybe all those electrons get lost in the molecules of copper in those big wires. Hmmm
  • Alan (California Radiant) ForbesAlan (California Radiant) Forbes Member Posts: 2,278
    edited May 2019
    I once went to a job where they wired all the pumps using 18 gauge thermostat wire. It had been working fine for years. The pumps were all Taco 007's; less than 1 amp.
    Often wrong, never in doubt.

    Click here to learn more about this contractor.
  • HomerJSmithHomerJSmith Member Posts: 891
    edited May 2019
    Aside from current carrying capacity, wire insulation is important to handle pressure (volts) as insulation can break down leading to leakage and possibly a ground fault.

    If you don't have the right wire in your truck you use what you have, I say. Problems are for the next guy. Hey, wait a minute, I am the next guy!
    Alan (California Radiant) ForbesZman
  • ratioratio Member Posts: 2,351
    IIRC type CM (thermostat wire) is a 300 volt insulation class, so by that it's ok. Not sure what the Code says about it, though.
  • ScottSecorScottSecor Member Posts: 384
    We were on a job that had we were forced to use 14 gauge Romex for thermostat wire. The office thermostat was about a 300 foot run from the gas fired steam boiler powered with a standard millivolt generator. Originally we used 20 or 18 gauge stat wire and had lots of no heat calls. Ran the Romex wire and it solved the problem. Just a fyi, probably not at all related to this house.
  • FizzFizz Member Posts: 522
    Thanks guys! Interesting reads.
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