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Thread: Honeywell has thick wires too big for Nest Learning

  1. #1
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    Honeywell has thick wires too big for Nest Learning

    Hi,

    I have two thermostats in the house, one upstairs and one downstairs. I successfully installed a Nest Learning thermostat in the downstairs area and it works fine. The upstairs however has a Honeywell T451A thermostat that uses thick black and white wires that don't fit into the Nest Learning. The wires are non-stranded.

    I don't see how it could be a high voltage 120vac system when the downstairs had regular sized red and white wires and worked fine. Can I get a relay installed to change it to 24vac if needed?






  2. #2
    Member

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    Yes, you could use a relay but first verify if it is 24vac or 120vac or something else. Get a multi-meter and measure the voltage across the wires. Better is to find the other end of these at the HVAC system and determine what they are connected to.

  3. #3
    Junior Member

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    I had to borrow my father in-laws multimeter. I can't understand it very well, but think I got how to take voltage readings after reading the manual. Can anyone possibly confirm whether or not this is saying it's 24vac or 120vac?




  4. #4
    Member

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    I think you need to put the red probe in the VΩA jack at the bottom, not MAX for that meter since you are measuring normal voltages.

  5. #5
    Junior Member

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    Okay, I re-measured the voltage with the corrected settings. When I have "ACV" on 10, 25, or 100, the meter goes all the way to the right. When I have it on 250, the meter reads as shown in the picture below -




  6. #6
    Member

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    That's definitely line voltage - reading around 118v. You are on the 250vac setting so use the scale that has 25 on the right and multiply by 10.

    You can convert to 24vac using something like https://www.amazon.com/Technologies-.../dp/B00D5YLY2G but would need to be installed at the other end where you have all of the wires.


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