Thermostat wire size requirement?


Old 10-22-15, 08:33 PM
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Thermostat wire size requirement?

I want to replace my old 3-wire thermostat cable with a 7-wire cable. For now I'm just going to use 4 wires (adding the C) but I don't want to change the cable again in the future.

The ones I found at local hardware stores are 18/7. They are quite stiff to fish/pull through walls. What is the thinnest allowed by code and where can I buy them? I need less than 50 feet.

Location around Seattle WA.
Old 10-22-15, 08:47 PM
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That's it. Thermostat wiring is #18 solid. Most home improvement stores carry it. Some have it on master rolls and will cut to length.

50 ft 18-AWG 7-Conductor Thermostat Wire at Your Lowes
Old 10-22-15, 10:10 PM
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Maybe you can get lucky as I did. I don't remember if it was Lowes or Home Depot but I picked up a fifty foot spool of nine conductor and when I got to the checkout noticed it didn't have a price code sticker. The clerk called for a price check and after a couple of minutes with no response he said, "Free today" and put it in the bag.

Although I don't recommend it, I have seen four-pair telephone cable used for thermostats.

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