What is the color of the 24 volt power wire in a thermostat?

Author: Dylan Sipes  |  Last update: Tuesday, September 2, 2025

The wires are typically arranged as follows: red for 24-volt hot, white for heat, yellow for cooling, green for the fan, and blue for common (although the common wire may be a different color).

Which wire is 24V on a thermostat?

Red: The red wire in your thermostat is for power. It will provide a 24-hour volt of power and will originate from the system's transformer. Every air conditioning system will have a red power wire. In some systems with a dual transformer, there will be two: Rc wire and Rh wire.

What color is the power wire on a thermostat?

Power (R-Wire)

This wire is Red in color and connects to the R terminal on the thermostat, which then connects to the transformer of your HVAC system. There are typically various versions of the Red/Power wire depending on the specific function of the wire.

What letter designation identifies the 24-volt power terminal on the thermostat?

RH: This terminal is the 24-volt heating power supply. Y/O: This terminal controls the cooling condenser by sending signals to power up the condenser and the blower fan. W/B: This terminal controls the heat relay or valve by sending signals to power up the furnace and the blower fan or the boiler.

What color is the common wire on a 24-volt transformer?

Common wiring practice is black for hot and white for common/neutral. In wiring jargon there are 2 power buses. 120 volt AC black is hot and white common, 0n 240 volt single phase red is other phase. For 24 volts thermostats use black for R and RT RC and white for C common.

How To Identify A Thermostat Common Wire (C Wire) & What It Does For Smart Thermostats

What color is 24V common wire?

FOUR WIRES

The standard configuration consists of 24-volt hot (red), 24-volt common (blue), heat (white), and a fan (green).

What is the color code for 24vac wire?

article 504 of NEC, light blue is intrinsically safe, other than that your 24 VAC can be any color except green. Don't use white or grey either unless it's grounded, and make sure the wire is the type allowed for your application.

Where is the 24 volts being supplied for the thermostat?

Typically, the "hot" wires, or the wires that provide power to the unit, are the heating and cooling wires, labeled Rc and Rh respectively. They provide the source of 24V power that comes into the main HVAC control board itself.

What is the Y terminal on a thermostat?

In most systems, the Y or Y1 wire controls your cooling system. If you have a heat pump, your Y or Y1 wire controls your compressor. Your compressor is responsible for heating and cooling your home. The G or G1 wire controls your fan.

What is the difference between a line voltage thermostat and a 24 volt thermostat?

Line (high) voltage operates on 120 volts and can be found in our home outlets, while a low voltage system typically operates on 12 or 24 volts and it requires a small transformer to lower the 120 volts too low voltage.

What happens if you wire a thermostat wrong?

If you wire a thermostat wrong, you may damage the thermostat, the electrical system, or the HVAC unit itself, which makes the entire installation process more frustrating. You may find yourself testing thermostat wires for hours, trying to get them right.

What color is the power wire?

US AC power circuit wiring color codes

The protective ground is green or green with yellow stripe. The neutral is white, the hot (live or active) single phase wires are black , and red in the case of a second active. Three-phase lines are red, black, and blue.

How to identify wires for a thermostat?

Here is the industry standard color code for thermostat wires used for most systems:
  1. The W wire is connected to your heating system. ...
  2. The Y wire is yellow and connects to your air conditioning compressor.
  3. The G wire is green and connects to the fan.
  4. Rc and Rh: The red wire(s) are the power source for your thermostat.

What wire is used for 24V?

24 Volt Systems - Distance in Ft

The minimum wire gauge recommended is 14 gauge for compatibility with the terminals inside the power distribution boxes.

What is the blue wire on the Y thermostat?

Yellow is the most common color for cooling wires, but Blue is also used in some systems. The cooling wire connects the thermostat to a compressor. Black (Or Blue) Wire is the so-called C wire or common wire. It is a 24V common wire that is linked to the transformer.

What is T1 and T2 on thermostat?

The FreezeAlarm acts as a switch between your main thermostat and a brand new second thermostat. When you call up the FreezeAlarm, you can tell it to supply the low voltage power to either thermostat #1 (T1) or to thermostat #2 (T2). Whichever ther- mostat is getting power is the one controlling the furnace.

What is the difference between Y and Y2 wire on a thermostat?

In conventional cooling systems, Y/Y1 controls the first stage of cooling and Y2 controls the second stage, which helps cool down the home faster. In heat pump systems, Y1 controls your compressor, which heats and cools your home.

Which wire is 24v on thermostat?

R (red) is the 24V “hot” wire and C (black) is the common. G (green) is the fan relay. W (white) is the call for heat relay. Y (yellow) is the call for cooling relay.

What is a 24 volt common wire?

Perhaps you've heard of the C Wire (aka the common wire), a power source frequently found in thermostat installations. This wire provides a continuous power flow of 24 V to the thermostat.

How do I know if I have a 24VAC system?

You probably have a low voltage (24v) system if…
  1. You have 2 to 9 (or more) wires.
  2. Those wires are low gauge (rather thin compared to other electrical wiring)
  3. Your wires are multicolored (red, white, green, orange, blue, black)
  4. You have a furnace somewhere in your house – basement, garage, bathroom, etc.

Is red wire 24V?

Red (R, RC, or RH): The red wire supplies 24V AC power to the thermostat. A wire labeled RH carries power to the heating system, while an RC wire provides a power connection between the thermostat and your cooling unit.

Does 24vac have a neutral?

The neutral is bound to ground only at the 24V-supply's negative output terminal, so current coming from a sensor going to neutral always has the path with least resistance back to the supply through the neutral wire and then the supply's negative terminal, going through ground only makes sense if there's a disconnect ...

What color is the ground wire for 24V?

Per NFPA79 and UL508A, the suggested (but not required) color code for 24VDC grounded conductors is white with a blue stripe.

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