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What is a "C" wire & do I need one?

Last Updated: Oct 25, 2014 02:58PM UTC
A "C" or "Common" wire is used to power the thermostat and if installed, the radio. The C wire is 24 volt common wire that comes for the furnace or air handler 24 volt transformer.

You will need one if you have a CT80 or CT80B thermostat or have a Wi-Fi radio installed.


For information on installing a C wire if you don't have one check out our other C wire articles.
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