I'm planning on connecting a nest thermostat in the next few days once my wifi is hooked up. In the meantime, I found an unused blue wire at the furnace and hooked it up to the C. My current thermostat doesn't use C but it has the blue cable wrapped around unused. Did I wire it correctly on the furnace end? I'm still confused about the two brown wires on C and Y. Can someone explain please!! :)enter image description hereenter image description here

  • This is very close to another question you asked recently. It would be better if you posted this new information by editing the previous question, where you already have comments and help. Also, it's quite likely that the blue wire needs to be connected at both ends.
    – jay613
    Commented Feb 24, 2022 at 11:39
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  • It is nearly identical, @jay613, and in general I'd agree with you (I even VtC at first), however, there is an error that needs to be corrected.
    – FreeMan
    Commented Feb 24, 2022 at 12:32
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    As a note for future reference, combining your images into one before posting makes it harder for us to zoom in on them to look at close details. It also makes it harder to reference them in comments/answers. Please simply post separate images, and if you're restricted in the number you can post, upload them individually to imgur.com and post the links - someone will embed them for you.
    – FreeMan
    Commented Feb 24, 2022 at 12:39

1 Answer 1


No you didn't. Look at your original picture. Notice how the brown wire on the C terminal is wrapped clockwise around the screw?

Correct wiring direction from original post

However, when you put it back on with the blue wire, it's now wrapped counterclockwise.

New image with wire wrapped in the wrong direction

Don't ever do that - tightening the screw will back the brown wire out, leaving a sketchy connection that could arc. All wires under a screw should always be wrapped clockwise so that they're drawn into the connection as the screw is tightened.

Notice in that second image in the green box how the two wires are wrapped under the Y screw, both going in the same direction. That's what you want.

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    Thanks for your input! This makes sense! Sorry for the duplicate post. I'm new to this page and I'm still learning how to use it correctly. I appreciate all of your guys help!! I will correct the wires to being clockwise and then connect the other end of the blue wire to my Nest thermostat soon! Commented Feb 24, 2022 at 15:03
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    Take the tour, @SharikhKhan, that will help you learn how things work around here. You can also browse through the help center for more in-depth info.
    – FreeMan
    Commented Feb 24, 2022 at 17:46

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