What is a Common Wire? (Everything You Need to Know)

At present, the smart thermostats come with Wi-Fi and backlit displays and require a continuous power supply or a steady supply of juice. 

The common wire or C wire helps to keep the ebb and flow of accurate power to the modern thermostat. It can complete the circuit continuously, which means 24 volts of energy. 

what is a common wire

So, the C wire is important to every current thermostat. If your thermostat doesn’t include the C-wire system, you have to install a new cable running the most modern smart thermostat model. 

Are you willing to know details about C wire or common wire? 

Go through this blog post. Read it from top to bottom fully. Here are some important questions and answers. After reading, you may understand the overall idea that you expected. 

Why A Common Wire?

A common wire is a simple wire panel design to save the wiring. Perhaps, you use the light bulb and a normal battery to built-in circuits easily. Interestingly, if you observe the house wiring, you find the same principle, just including the higher voltage and the larger scale. 

The household wire can be black or red to supply current from the basis to the bulb. Again, bulb back to the source. Wire can be hot while holding the electricity. When the wire is carrying electricity between the bulb back and the source or is a neutral wire that means common wire. Like household wire, common wire is not hot. 

What Is A C-Wire Or Common Wire? 

The C wire is one of the wires to use providing the power of 24-volts for the different applications. It is specifically designed to provide back the power of the thermostat. Here “C” indicates the word common although it is unnecessary to be labeled as C. Sometimes the common wire can not be any specific color. 

It can stay in different places to power the thermostat. When both wire- hot wire & cool wire give the power, they are known as separate, just Rc (cooling) and Rh (heating). Both supply currents of 24 volts that come from the HVAC control board. Sometimes they are different and sometimes they are the same as each other and labeled as Rh/c. 

We can say that the c wire is not able to capitalize main power. Just providing a return path powers the thermostat instead of disrupting the further wires. Remember, other wires are necessary to supply electricity for the equipment. 

How to Tell If You Have a C Wire? 

It isn’t tough to know whether you have a C wire or not. We provide you with some easy and effective steps that help to know if you have a C wire or a common wire. 

Step-1

Simply take your thermostat and keep the position of turning off the power at the switch or breaker box that regulates your heating equipment. Don’t forget to use the essential tools to do this job properly. homefourexperts provides you with must-have tools: click here. 

Step-2

In this step, you have to observe the system of the thermostat that determines whether the temperature is high or low. If the system turns on, you need to turn off this power to check the wires. This step is not for you if you have a digital thermostat. 

Step-3

Your thermostat has some screws, clasps, or buttons for attaching to the wall plate. You need to take off your thermostat from the wall plate. Keep in mind that you don’t have to eliminate the wires at this time. 

Step-4

See the existing wall plate’s wires and look at the C-Terminal. If you find this terminal, your thermostat has a C-wire. Don’t find it? That means your thermostat has no C-wire. You can install it. The installation process is also easy. The AC wire transformer contains two output wires. You can attach one wire to the C terminal of the thermostat and another wire to the Rc terminal. When finishing the process of connection, you need to plug the transformer into your main power. 

Step-5

Alternatively, if you don’t understand the previous step, you can follow this step. You can see many colors of wires and one of those can be blue. You will see the terminal where wires are attached. Look at the letter C which means C-wire or common wire. So, the C wire is blue from the five-colored wires. You can identify this wire by connecting it to ‘terminal C. Terminal C has not attached any specific wire. 

Step-6

Check out the existing thermostat system if it has a line voltage. Line voltage systems can be 120 volts or higher. It is not compatible. 

So, all steps cover understanding whether you have a C wire or not. Perhaps, you also want to know how to remove the existing wall plate? 

Look at the wire terminals. They can be push-in types to release the wire or flat-head screws

It is very simple to eliminate the push-on type wall terminals. Or, if your terminal has a flat-head screws system, you must use the screwdriver to disconnect the wires from the terminals. But, without a screwdriver, you can also unscrew the wires.  

FAQs of the Common Wire 

1. How Does A Neutral Wire And A Common Wire Differ?

There is no major difference between the common wire and neutral wire. Neutral wires are known as common wires. They are a little bit different in color. If you live in the US, you find the white color-neutral wires. These wires are available in every circuit. Homearise explained common wire as hot or neutral.  

2. Is Neutral And Ground the Same Thing?

Generally, the neutral circuit is connected to the ground. And, the ground circuit is related to earth. Both circuits are utilized in alternating current and are closely related to each other. Sometimes neutral is connected to the ground point of the electrical supply system. 

3. Is The Common Wire the Live Wire?

There are two terminals, one is marked as COM or C and the other is L1. Where C-wire is the live wire used to supply the input voltage to the switch. And, the L1 terminal is output to the light fixture.

4. Does the Common Wire Carry Current?

Yes, common wire carries current (amps) of the same amount as other wires. It could also be considered live wires. 

In A Nutshell 

There is no doubt that the common wire is crucial to running the modern thermostat with ease. C wire can be of different colors and sizes. But, most of the time, it is blue. 

By the way, we have already covered a lot of information about the C wires. So, you don’t need to wait to use the smart thermostat without all the hassles.

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About This Writer

Liam Jaxon Author pic

Hi, I am responsible for the 'Homeowners Power Solutions' category. My name is Liam Jaxon and a licensed technician with 7 years of experience in vehicle batteries, electrical gadgets, and home appliances. My working experience in different residential & light commercial electrical sectors and the automobile industry helped to acquire vast knowledge in this industry.

Hi, I am responsible for the 'Homeowners Power Solutions' category. My name is Liam Jaxon and a licensed technician with 7 years of experience in vehicle batteries, electrical gadgets, and home appliances. My working experience in different residential & light commercial electrical sectors and the automobile industry helped to acquire vast knowledge in this industry.

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