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  1. #1
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    Standard for color coded t-stat wire.

    I was wondering if there is any document regulating the color coding used in thermostat connections. I recently finished a residential installation and another technician told me I had picked the wrong color (blue) for the Common wire. He told me the Y1 should be blue. Which makes sense, but I would like to have something more authoritative than his opinion. Inspectors have never mentioned anything about it, either.

    I could not find anything related to this topic in the IMC, IRC, NEC, etc. Also thermostat installation instructions don't usually mention color coding.

    Is there any other code or standard for this?

  2. #2
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    Most of the time black is ground but sometimes blue will be ground , and it's up to the installer really , but yellow is always on Y1 , red R , green G , white W1 , orange O ....ok now.... blue can be used for O as well , it just depends , and if you have fancy stuff like stage Y2 or W2 or E ..you pick any other universal color for those like pink tan grey ...

    Then you have brands who have the Reversing Valve energize in Cool , and others during Heat , which is stupid as he'll , but they do , and the ones using Heat will often times use Blue to let you know their brand is energized during Heat , and all others use orange

  3. #3
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    Electrons know no color!

  4. Likes bhenry1013 liked this post
  5. #4
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    It’s a rule of thumb, do what you want if you really want to be an ******* run multiple 2 wire and just make everything black and white

  6. #5
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    you will get 15 different answers for 15 people.

    but the 5 common I always wire:
    r = red
    c= blue
    g= green
    y= yellow
    w= white

    i always do orange for a heat pump RV valve.

  7. #6
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    copper
    Officially, Down for the count

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  8. #7
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    Quote Originally Posted by drivexcite View Post
    I was wondering if there is any document regulating the color coding used in thermostat connections. I recently finished a residential installation and another technician told me I had picked the wrong color (blue) for the Common wire. He told me the Y1 should be blue. Which makes sense, but I would like to have something more authoritative than his opinion. Inspectors have never mentioned anything about it, either.

    I could not find anything related to this topic in the IMC, IRC, NEC, etc. Also thermostat installation instructions don't usually mention color coding.

    Is there any other code or standard for this?
    Wouldn't it make sense for Y1 to be YELLOW?
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  9. #8
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    Thread Starter

    Common sense.

    Quote Originally Posted by kdean1 View Post
    Wouldn't it make sense for Y1 to be YELLOW?
    Well, I said it made sense for Y1 to be blue because it's call for cooling. Cooling for me sounds like blue. However, Y1 being yellow makes even more sense.
    So I don't know man, I'm getting this is not regulated and totally left up to the opinion and "common sense" of the installer.

  10. #9
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    Use whatever is standard in your region. Ideally there will be some reasoning behind it.

    Years ago, Lennox had terminals labeled R for reversing valve, M for motor (compressor contactor), and other such nonsense. Other contractors wouldn't touch Lennox equipment for that reason so I got lots of referrals.

    I often rewire units I service so the colors relate to what I consider the norm. Then there are the crazy installations, such as where a hack wired the O terminal at the thermostat instead of B for a Ruud unit and installed a relay at the furnace to break the O to the heat pump.
    The worst is multiple #18-2 conductors for a heat pump because the installer didn't have #18-8.
    That's where a Honeywell Prestige IAQ two-terminal thermostat is a real problem solver.
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    There = not here. Their = possessive pronoun. They're = they are
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    Too = also. To = expressing motion. Two = 2
    Then = after that, next. Than = indicates a comparison.
    Questions should end with a question mark "?" Statements end with a period "."

  11. #10
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    I was taught in school that R should be black and then when I got working R was always red and black was W2 unless I was working with a different guy than W2 was blue. So... just always check is the moral of the story. The same is true with higher voltage use your meter and make sure that neutral is actually a neutral.

  12. #11
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    Many of the familiar colors for thermostat wiring were established decades ago by Honeywell, but some manufacturers choose not to follow that scheme, or at least throughout the eighties and nineties there was much less agreement regarding which colors are appropriate.

    Y does indeed stand for yellow, and G does indeed stand for green, and an O wire on a reversing valve is always orange, and a B wire on a reversing valve is always blue.

    I have found very few installations that did not use a brown or a black wire for common.

    Of course, the person who is paying you is going to dictate how they want new installations to be wired, but you need to use common sense to discover what the existing wiring is and be able to check it to make sure it is correct and functional.
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  13. #12
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    The colors never were used because it made sense. Like Timebuilder said.
    Honeywell had dominated most controls and their wire colors were easy to keep in mind so there was some consistency.
    Lennox used General Controls for a long time and some of their equipment is still using the colors.
    Honeywell 24 vac hot was red but General Controls had 24vac hot as blue. Today it seems Honeywell is most common with the colors.
    24vac hot = red
    w1 first stage heat = white
    y1 first stage cool - yel
    Fan = green
    O hot when switched to cool
    B hot when switched to heat
    Other colors are usually whatever is left over.
    I always asked the electrician on the job to allow me to land the low voltage wires.
    Saves me any confusion.
    I use Honeywell colors as it's a no thought process and other techs are more likely to know them.

    I hate it when an electrician runs #12 for control wires. Often results in broken sub base.
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  14. #13
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    then throw in series 10 wiring and you need to upgrade the controls " shed the red", "blue for BTU", and......i forgot the saying for cooling
    my boss thinks its possible to repeal the laws of physics

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