Asked by: Lisbel Bernhoeft
home and garden smart home

What is the purpose of the C wire on a thermostat?

19
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.


In this manner, what color is the C wire?

Here are common uses for wire colors: Blue or Black – C – Common wire, may be unused by your existing thermostat. Enables continuous power flow from the Red wire. Red – R – 24VAC power from the furnace's transformer.

does Honeywell thermostat need C wire? C-Wires are required on most Honeywell Wi-Fi thermostats, with the exception of the Smart Round Thermostat (formerly known as the Lyric Round). How do I check if my thermostat is using a C-Wire? To protect your equipment, turn off the power at the breaker box or switch that controls your furnace or heating equipment.

what if there is no C wire for thermostat?

If your current thermostat didn't need a C-wire, it (or a wire that can be used as a C-wire) might be rolled up inside the wall. This is more likely to be true if you see all the other color wires present.

Is the C wire a ground?

The C wire is the common wire ground wire. You already have 24v ac going to the red wire. If you have an extra wire connect it to the C at the thermostat and ground it at the transformer box in the AC unit.

Related Question Answers

Shafiq Baierschmitt

Professional

Is RC and C wire the same?

Typically, the wires that provide the power (often called the “hot” wires) are labeled Rc (cooling) and Rh (heating). They provide a source of 24V power coming from the HVAC control board. Other times they are the same wire. In that case it will typically be labeled Rh/c.

Kadia Rothfuss

Professional

Does low battery affect thermostat?

Most models of programmable thermostats will display or flash some sort of low battery symbol when the batteries begin to run low. At this point, the thermostat can no longer control the HVAC system. This could possibly lead to excessive heating or cooling of your home, or no heating or cooling at all.

Erhimo Schark

Professional

How do I know if C wire is live?

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.”

Dongmei Hindriks

Explainer

Is RC WIRE same as C wire?

If the air conditioning thermostat has one transformer to power both the heating and cooling system, then the wire from the transformer goes directly to the RC terminal and is called the RC wire. Effectively there isn't a second RH wire, although there is an RH terminal.

Wenzhong Es Salehy

Explainer

Is the C wire blue?

The blue wire, or C-wire, is known as the common wire. It's there to provide power to the thermostat. Power comes into the thermostat on a wire connected to the transformer, which is usually red, and returns to the transformer on the C-wire, which is usually blue, but it can be black.

Chahrazed Dufresne

Explainer

How many wires does a thermostat need?

In the most basic system, this functionality is provided by use of a fan center relay, and the low voltage wiring to the thermostat now will require a minimum of three wires (for heat only units) and four wires (for heat / cool / fan) for control.

Tomita Huska

Pundit

What is common wire?

A common wire is a more general term and simply refers to the 0 Volt wire of a circuit, either electrical or electronic.

Mounina Vollandt

Pundit

Are there any wifi thermostats that don't require AC wire?

In most cases, a Nest Thermostat can work without a common wire. Without a common wire it charges its internal battery using power from the heating and cooling wires. With some HVAC systems, such as micro-controller-based systems and certain gas valves, will require a C-wire to work with Nest Learning Thermostat.

Nilton Corsi

Pundit

Does ecobee4 need C wire?

If you don't have a C wire, you'll need to use the Power Extender Kit (PEK) included to reliably power your ecobee. The Power Extender Kit will work with your system!

Damion Haffmanns

Teacher

Can I use G wire for C wire?

Using the g-wire as a c-wire
If you can not find an unused wire or common wire, you can also use for fan wire or g-wire as a common wire.

Fanta Brey

Teacher

Why does my thermostat only have 2 wires?

If your heating system has only two wires, the job of the thermostat is simple. All it has to do is turn the heat or the cooling on and off. There is also no thermostat blue wire, or common wire, to power the thermostat, so it has to operate on its own, either using batteries or mechanical temperature detection.

Domingas Suñe

Teacher

How much does it cost to install c wire?

If you need a C wire run, expect the installation costs to be roughly double, at $170 to $200 for the job. Including the cost of a new thermostat and installation, the total cost is around $300 on average.

Vianney Botinas

Reviewer

What color wire goes where on a thermostat?

Most thermostats have a Red wire that is the power wire that usually connects to R & RC terminals of the thermostat, a Green wire that energizes the Fan relay, connected to the “G” terminal on the thermostat, a Yellow wire that energizes the outdoor unit's contactor, (if you have air conditioning) and a white wire that

Razmik Korb

Supporter

What do the letters on a thermostat mean?

The terminals have letters that refer to functions. R is transformer power, typically 24V AC. Rc is for a separate transformer power from cooling. W is heat, C is common. Y is for cooling.

Telvina Laurkain

Supporter

What is AC wire adapter?

A C wire adapter (common wire adapter) is basically a small electronic device, which re-purposes the existing wiring between your thermostat and the furnace, to add a new wire to the system. This new wire will serve as the C wire or common wire to provide necessary power to the thermostat.

Wan Dziedzi

Beginner

How does add a wire work?

The Venstar Add-a-wire and ecobee's Power Extender Kit somehow multiplex two of your existing thermostat wires (e.g. the ones that switch on your heat or fan) into one. That frees up one wire so that you can use it for constant power.

Moon Lapitzegi

Beginner

What is the difference between nest and nest E?

The Nest Thermostat has a full-color display and a feature called Farsight that will show you the time, weather, or temperature from across the room. The Nest Thermostat E has a frosted display that only shows the indoor temperature. The Nest Thermostat works with 95 percent of homes.

Romaysa Wootton

Beginner

What color is the common wire?

The "common" is the "neutral" or "ground" wire, depending on the type of circuit. In normal US residential wiring, you'll have a black "hot" wire, a white "neutral" or "common" wire, and a green or bare "ground" wire.

Jolita Fanni

Beginner

Is common wire negative or positive?

A common wire, connected to the amplifier's common line, a wire which carries a positive voltage with respect to the common line, and a wire which carries a negative voltage with respect to the common. They're both 15 volts.

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8th June, 2020

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