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Thread: Common 'C' wire reading 29V rather than 24V, any ideas?

  1. #13
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    Quote Originally Posted by cflury View Post
    The Nest will not work if the voltage is above 27.6V.
    Where does this info come from? Your installer? Or did you find it documented somewhere?


  2. #14
    HVAC Thermostat Specialist

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    Quote Originally Posted by SkinnyRaven View Post
    Where does this info come from? Your installer? Or did you find it documented somewhere?
    On the Nest website it states that the Nest will work with 24vac +/- 15%

  3. #15
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    I had the same concerns. I installed a new Taco controller to finally get a C wire and to my surprise I was getting 29+ volts at the C wire. Being paranoid I called Taco and was told this is not unusual at all. Then I called Nest customer support and I was told this is not a good idea. He recommended no more than 27.5V at the C wire. Sooo I called Nest support again to see if I'd get the same answer twice and was told not to worry and that the Nest thermostat will handle this fine. He was surprised I got that info from another tech. So I took his word for it and no problems since.
    Last edited by VidPro; 02-04-2013 at 04:51 AM.

  4. #16
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    Quote Originally Posted by VidPro View Post
    I had the same concerns. I installed a new Taco controller to finally get a C wire and to my surprise I was getting 29+ volts at the C wire. Being paranoid I called Taco and was told this is not unusual at all. Then I called Nest customer support and I was told this is not a good idea. He recommended no more than 27.5V at the C wire. Sooo I called Nest support again to see if I'd get the same answer twice and was told not to worry and that the Nest will handle this fine. He was surprised I got that info from another tech. So I took his word for it and no problems since.
    That's good to know. Thanks.

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