Sensi SupportTouch Wi-Fi ThermostatInstallation › What is a common wire or “c-wire,” and how do I know if I have a c-wire?

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What is a common wire or “c-wire,” and how do I know if I have a c-wire?

Many conventional, non-connected thermostats don’t need a “c-wire” to function. But today, most Wi-Fi thermostats have new features such as Wi-Fi radios and LED color screens that require the unit be powered at all times. Thermostats can get this constant power through a common wire or “c-wire.”

It is easy to see if you already have a c-wire connected to your system. Simply remove your current thermostat face from its baseplate and look for the terminal labeled with the letter “c.” If this terminal has a wire attached to it, you have an active “c-wire.”

If you don’t see a wire connected to your “c” terminal, you have a few options. See our c-wire assistance page for more information and helpful videos.

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