Thermostat Wire

A thermostat is a vital part of any temperature control system, ensuring that the conditions stay within specified ranges. Since there are many different components involved in a temperature control system, thermostat wire has to be able to handle the different needs of these components. The thermostat would never be able to function properly without the help of a thermostat wire and cable.

This specialty cable is available in a few configurations and involves various wires to reach all of the different thermostat components. Let’s take a closer look at thermostat wire.

What Is Thermostat Wire?

Thermostat wire connects the thermostat to the device whose temperature it controls and regulates, such as the furnace and air conditioning (AC) system. It can also join these heating and cooling devices. This is generally low-voltage thermostat wiring with multiple conductors, along with numbers or colors that indicate proper connection terminals. Matching up wires to the right terminals is essential for accurate operation.

Thermostat cables typically use solid copper conductors, surrounded by unfiltered polyvinyl chloride (PVC) insulation. This insulation material resists damage from fire and sunlight.

What Size is Thermostat Wire?

Thermostat cable and wires can come in several configurations between 18 and 20 AWG with 2-8 conductors.

Most thermostat wire available will have approvals from relevant organizations, such as UL, LLC and The CSA Group.

Thermostat Wire Voltage Rating

Thermostat wire and cable are designed to endure a temperature range of between negative 20°C up to 105°C and can support up to 150 volts.

If you’re not confident in your wiring abilities, or your thermostat wire becomes damaged, it’s always a good idea to work with a professional to conduct repairs and thermostat installations.

Thermostat Wire Color Codes

While manufacturers aren’t required to make wire coding and color exactly the same with each thermostat that they make, there are some commonalities across the industry. The typical colors for thermostat wires are as follows:

• Blue: Also called the “C” wire, the blue wire is a “common” wire, which provides thermostats with continuous power. You’ll need one of these if you’re hooking up a smart thermostat, such as those with Wi-Fi connections. This wire can also be black, and some older systems won’t have it, requiring adapters or rewiring for more modern upgrades.
• Green: The green wire connects to the fan of a furnace or air handler.
• Red: Red wires may also be called “RC” or “RH” wires. Both of these run consistent power from the transformer, but the RC wires connect to a cooling system, while RH wires connect to a heating system.
• Yellow: A yellow wire connects to a compressor and helps control the AC system.
• White wire: Finally, the white wire connects to the heating system and terminates at the air handler or furnace.

Thermostat wire must only be connected to the terminal that it is supposed to be connected to and nowhere else. Identification and accurate installation are essential, and there are also several codes that match up to terminals on the thermostat itself to help with this. These codes can help minimize the uncertainty that comes with non-standardized colors.

There are many of these codes, but some of the more common ones include:

• R, RC and RH for 24-volt power to cooling or heating systems.
• Y and Y2 for cooling and 2-stage cooling.
• W and W2 for heating and 2-stage heating.
• G for indoor fans and air handlers.
• C for common wire that provides power to the thermostat.
• E for emergency heating.

You’ll probably notice that many of these overlap with the colors they typically represent — R for red wire, Y for yellow wire, etc. There are a few other colors and markings that apply to more complex systems and may indicate connections like change-over relays and auxiliary heating. Commercial thermostat systems will likely need to make use of many more conductors than a home thermostat system.

Thermostat Wire From WesBell Electronics

Here at WesBell, we strive to help our customers find the perfect wire for their application at affordable prices. Our expert staff is well-versed in evaluating your application to find the right solution. If you’re not sure which configuration of wire you need for your thermostat model, we’re always happy to help. Just give us a call and walk us through your system!

Click on the links above to browse our thermostat wire configurations. You can also reach out to us for assistance or to learn more.