Thermostat is an electrical component that is mainly found in heating and cooling systems. It works as a temperature sensor and helps the heating and cooling systems to maintain the targeted temperature.
Today, we are going to discuss and find out what the blue wire is on a thermostat.
What is the blue wire on a thermostat?
The blue wire on a thermostat can be a Common wire or a normal cooling wire. If it is a Common wire, then it will have to be connected to the C terminal of the HVAC system’s control panel. If it is a normal cooling wire, then it will have to be connected to the Y terminal of the control panel.
Let’s look at different kinds of thermostats and find out what the blue wire does and is on those thermostats.
Nest thermostat:
The nest thermostat is a smart thermostat designed by google. Nest thermostat is very easy to use as you can control it with your smartphone. It is known for being compatible with most of the HVAC (Heating, ventilation, and Air Conditioning) systems available out there.
The blue wire on a Nest thermostat is known as the C wire or the Common wire. The primary job of blue wire on Nest thermostat is to provide the thermostat with adequate power.
The blue wire on a Nest thermostat should be connected to the C terminal of the control panel of your HVAC system.
The older models of thermostat did not have common wires on them because their power was generated by battery. But the modern day thermostats like Nest thermostat come along with blue wire which acts as the common wire to supply the thermostat with power.
Honeywell thermostat:
Honeywell thermostat is another brand of thermostat that comes with smart features such as WIFI connection and mobile control etc. As it is a modern thermostat, there is blue wire on this thermostat.
The blue wire on the honeywell thermostat works as the Common wire just like the Nest thermostat. You will have to connect the blue wire of your honeywell thermostat to the C terminal of the HVAC system’s control panel.
The blue wire on a honeywell thermostat handles the load of supplying power to the thermostat. It is a crucial wire of the wiring system that connects the thermostat to the continuous flow of power.
While installing the honeywell thermostat, the blue wire will be found in the B terminal of the thermostat.
What is the blue wire used for on a thermostat?
The older models of thermostat did not have a blue wire on them. Because these old thermostats were powered by batteries and did not need a wire connection to receive power from the HVAC system.
But the newer model smart thermostats come with a blue wire on them. This blue wire is known as the common wire on the thermostat.
The blue wire on a thermostat is connected to the C terminal of a HVAC system’s control board. This connection made by blue wire carries power to the thermostat from the HVAC system for twenty four hours a day non-stop.
Another important thing to remember here is that while replacing an older model thermostat with a smart thermostat, you might face difficulty when it comes to finding a Common wire connection.
When this problem arises, you should contact a HVAC system profession to help you solve this problem.
Where does blue wire go on the thermostat?
The blue wire on smart thermostats works as the C wire or the Common wire. The common wire can be found on the C terminal of a smart thermostat. The blue wire is crucial when it comes to supplying power to the thermostat on a consistent basis.
The blue wire of the thermostat is connected to the C terminal of the HVAC system’s control board which forms an important connection. As a result, the thermostat receives power from the HVAC system through this common wire.
The blue wire is a must have wire on smart thermostats. The Common wire connection between the thermostat and control panel of the HVAC system can not be done if your thermostat does not have a blue wire on its C terminal.
What happens if you wire a blue thermostat wire wrong?
Wiring a blue thermostat wire wrong can have serious consequences. Let’s discuss in detail and find out about some of them.
Can cause accident:
If you are not an electrical wiring expert and want to install your thermostat yourself, you might face some difficulty while doing so. If you wire a blue thermostat wire wrong, then it can cause an accident in the form of electrical shock.
You do not want to harm yourself while trying to save some money by installing the thermostat alone.
Can damage the HVAC system:
If you fail to wire your blue thermostat wire accurately, it can damage the HVAC (Heating, ventilation, and Air Conditioning) system of your house permanently. It will increase the maintenance cost of your house instead of reducing it.
The blue wire of the thermostat is needed to be connected on the C terminal of the HVAC system’s control board. A wrong connection does have the potential to damage your entire HVAC system.
Can damage the thermostat itself:
The blue wire of the thermostat is connected to the HVAC system’s control panel for the supply of power. If you wire it inaccurately, it can certainly damage your thermostat and make it inoperable. This risk is not worth taking if you value your money.
Can delay the process:
If you wire a blue thermostat wrong, it might not cause any physical damage to you and your equipment, but it will certainly delay the process of installation until you get it right.
How do I know if I have a blue wire or C wire?
If you are installing a new thermostat and wondering if you have a blue wire or C wire, you can start by looking at the internal wiring of your thermostat.
If you see blue wire on the C terminal of your thermostat, you can be sure that you have a blue wire that is the C wire or the Common wire. If your thermostat has a blue that is not connected to the C terminal, that is not the common wire and is only a blue wire.
If you want to check the already installed thermostat to find out if it has a blue wire or C wire, you will need to stop the power of the thermostat from the breaker box and then pull out the thermostat carefully from the installed place.
If you notice a blue wire connected to the C terminal of the control panel, then your thermostat has a blue wire that is working as the common wire.
If there is no blue wire connected to the C terminal, then your thermostat does not have the Common wire or the C wire and has a blue wire only.
How to wire a thermostat with blue wire?
There are many steps involved when it comes to wiring a thermostat with blue wire. Let’s discuss in detail about those steps.
Removal of the old one:
If you are wiring a new thermostat in place of an old one, you will need to remove the old one first. Without removing the old one, you can not start wiring a new thermostat.
While removing the old one, you will need to inspect the connections used by your old thermostat to help you in this process.
Identify the number of wires:
Usually, the two wire and three wire thermostats do not have blue wire on them. Usually, four wire, five wire and six wire thermostats have blue wire on them. The method of wiring a thermostat with blue wire depends on the number of wires it contains.
Connect the wires:
After removing the old thermostat, start wiring the new thermostat to the control panel of the HVAC system. If the blue wire is a normal wire used only for cooling, then it will need to be connected to the Y terminal of the control panel.
If the blue wire is a Common wire or a C wire, then it will have to be connected to the C terminal of the thermostat. The rest of the connections should be red wire to R terminal, green wire to G terminal, black wire to C terminal (If blue wire is not the C wire).
Final Thoughts
The blue wire on a thermostat does the job of supplying power to the thermostat if it is used as a C wire or a Common wire. A normal blue wire is used to control the cooling function of your HVAC system. A blue wire that is a C wire needs to be connected to the C terminal of the control panel.