Where does the C wire connect?

A common wire (C-Wire) provides Wi-Fi thermostats continuous power by connecting it to a heating and cooling system (e.g. furnace).

What is the C terminal on the furnace?





The c wire is an extra wire that can be used to provide a return path for continuous 24V power for any application. It’s normally used to provide a return path to power the thermostat. The “c” stands for common. It is often labeled as “c” on thermostat backplates.

Where does C wire go on furnace transformer?

I think you got the C (blue) wire connection right, it is really just the negative side of the of the transformer. If you have HVAC (forced air) furnace, usually all the terminals for the thermostat are on a control board and pretty well labeled for where to connect all the colors of leads.

What is the C terminal on a transformer?

By definition the R terminal is one end of the transformer winding and the C terminal is the other end. Simple thermostats (bimetal strip, or battery-powered programmable) simply short R to W or G to call for heat or cooling.

How do I run C wire?

A C wire transformer has two output wires; connect one wire to Rc terminal and the other wire to the C terminal of your thermostat. Once you finish this connection, plug the transformer into your mains power outlet. The installation is complete now and the thermostat will be powered upon switching ON the power outlet.

What color is C wire?





Blue wires

Blue wires are also called “C” wires because they are the Common wire. C wires are necessary for any “smart” thermostat that needs to be connected to a power source 24/7, regardless of your heat pump type.

What is C wire?

WHAT IS A C-WIRE? A C-wire, or a common wire, runs from your low voltage heating system (24v) and carries continuous power to your thermostat. In today’s electric market, most newer heating and cooling systems have C-wires, which guarantees compatibility for the installation of all smart thermostats.

How do I know if my C wire is working?

Easiest way to check is pull any batteries out of the old thermostat and look for a wire (normally blue) is connected to the C spot. If the old unit supports being powered by the common wire, then the unit will turn on without batteries.

What has C wire but no power?



Quick Check for an Existing C-wire:

If it has batteries, remove them. If the thermostat loses power it does not have a C-wire, and you may need an add-a-wire kit. If it doesn’t lose power, locate your breaker panel. Flip the breaker for the wall with the thermostat on it.

What voltage is C wire?

The C wire, a.k.a. the “common wire”, allows a constant flow of 24 VAC (volts AC) power to a smart thermostat.

Can I use RC wire as C wire?



No the Rc is the red wire. You need 5 wires or more for this to run with all the functions. You can use one of the other wires but you have to drop control of the fan. It will only come on when furnace comes on.