What is a C Wire | How to Correct C Wire Issue

C Wire is a wire used for a continuous 24V power supply by providing a return path for any application. Or, in the easy language, you can say it offers a return route to power the thermostat as “C” in C wire means “Common” 

What is C-wire

It’s frequently tagged as “c” on thermostat backplates. Remember that it isn’t always classified as the cable or isn’t necessarily available in any specific color. Even though there are several best practices, there are no strict criteria that cable name and color adhere to.

To have a circuit through which electricity can flow, cables will need to link back into the HVAC controller board to finish the loop.

That is precisely what the other wires do. So, the c wire does not offer electricity. It provides a return route so the thermostat can have power without bothering the other wires used as electric on/off switches to your gear.


Why Do I Want a C?

Now that you understand what the c wire does, you could be asking yourself, why do I need it?

Now’s wireless thermostats demand more electricity than the easy calculator-screen programmable thermostats of yesteryear. Maintaining a link to a Wi-Fi router or an automation pulse is one energy necessity that never existed. In just a few days, AA batteries will drain to keep the Wi-Fi connection up.

Many good thermostats come with a large, full-color touch screen. Smart thermostats should make our lives simpler. No one would like to be replacing batteries per week or perhaps once every few months, And for its smooth functioning, it demands a continuous energy supply. Employing a c wire is the perfect approach to offer the necessary constant power.


How Can I Know Whether I Have C wire installed?

Before messing with any wiring, it is almost always a fantastic idea to shut off the power.

To check if you already have a c wire hooked up, begin by taking your present thermostat off the wall to expose the wiring.

1. Are there any additional loose cables?

Occasionally painters run the c wire from the controller board into the thermostat place but do not hook this up. You might choose to remove the thermostat backplate and pull the wires out to determine whether the additional cable is there.

2. Assess The Control Board

If you still are not positive if you’ve got a c wire, visit your HVAC control board. Check to find out whether there’s a cable attached to the “c” terminal.

When there’s absolutely no cable, you do not have a c wire and likely wish to receive one. When there’s a cable attached, note its color and return it to your thermostat. Whichever cable matches the shade should become your c wire.


Four Methods to Correct the C Wire Issue

Here’s four ways to Repair the problem:


  1. Buy An “Add-A-Wire” Kit

Generally, this remedy is the simplest and best solution to the issue.

An “add-a-wire” kit enables your thermostat to utilize your present wires and get continuous power without using electricity sneaking. The kits have been set up in the HVAC control board. Setup takes a screwdriver and also the capacity to see a wiring diagram.

You are going to need to remove the access panel into a furnace to find the panel. Subsequently, shut off the electricity before doing any job. Even though the 24V power does not pose much of a security risk to you personally, shutting off the energy lessens the danger of damaging the board.

There are a couple of distinct manufacturers who produce the add-a-wire kits. The Venstar kit includes an established history and is the cheapest price kit I’ve discovered. The technology behind those kits is pretty easy, so there is no reason to invest more if you do not need to.


  1. Buy a 24V C Wire Adapter

The 24V adapter (transformer) includes two wires that plug in the thermostat to electricity. Another end plugs into a normal socket.

This is the simplest solution, but probably my least desired. It will do the job just fine, but you are going to have an unsightly cable running out of the thermostat into the socket.

You can purchase some 24V transformers to perform the task, but this adapter is especially for thermostats. Both cable ends will be already stripped and ready to set up in the thermostat. Additionally, it has additional long wires if you don’t have an outlet close to your thermostat.


  1. Install Another Cable

This is the very best solution for me. But it is not the easiest solution. It takes running a cable from the HVAC controller board for your thermostat.

If your house is already completed, this usually means attempting to fish the cable through the walls without ruining them. Based on how much is on the management board and how your walls constructed, it can vary from easy to complex.


  1. Implement Power A Stealing thermostat

There’s a certain “threshold” current running through the cable, which reflects the change stage. Any present over the threshold is “on”, and some other present beneath the threshold is “away”.

So, there may be a small number of current running through the circuit without activating the “on” condition. That’s the present that may be utilized to power the thermostat through electricity “stealing”.



Smart Thermostats use an excessive amount of electricity to be supplied by batteries. Power stealing can operate, but it could be unreliable and can be utilizing your wiring in ways it was not designed for. A c-wire is your very best alternative, and it makes a constant electricity supply to your smart thermostat.

Since a C cable can provide power more faithfully, installing one is a safe bet for most* homes (consult an HVAC expert in your area to verify a C cable works with your machine ). Applying one will not necessarily help prevent the glitches but will definitely improve your thermostats condition Nonetheless, it can offer a little more reassurance if you are concerned about your HVAC system’s general health.

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