C wire is only needed if your thermostat has no batteries, so you can tape it off, and toss it. It won't be needed.
Honeywell (and others such as Trane) use a C wire on models that use WiFi or voice recognition or Z-wave so they can have a 24V connection. All thermostats use low voltage from the other connectors and typically use the batteries as a backup when there's no C wire.
If you're installing a new thermostat, but your existing one is missing a C-Wire, you have the following options: Check for an unused C-Wire. Use a C-Wire Adapter. Contact a HVAC Pro.
Do all Smart Thermostats Require a C-Wire? Though all smart thermostats can use a C-wire and arguably may be more reliable with the use of one, not all smart thermostats require a C-wire to function. Some models, such as Google Nest, are designed to work even if your home doesn't have a C-wire.
You don't need a C wire for a programmable thermostat. The other channels provide power, the C wire just provides more. It is useful if you want to run a color LCD screen or WiFi. If you have a thermostat with a black & white calculator-like LCD, it likely doesn't have a C wire running to it.
Add an Adapter
Some smart thermostats include an adapter in case there's no C-wire in your home. You can also find thermostat adapters at a hardware store or online. If you have previous electrical experience, you can follow the instructions included with the adapter to install it.
You need a "C" (common) adapter if you have a 4 wire setup, if you have a 5 wire setup then it is not needed. Many modern digital thermostats have the "C" wire adapter built-in and it is called a "Power stealing circuit" by many professionals.
Option #3: Use a G-Wire as a C-Wire
If there is no hidden C-wire, you can use a G-wire instead. However, you will not be able to use your fan independently when the heating or cooling isn't running. Also, many HVAC systems are incompatible with this solution, including: HVAC systems using electric heat.
With a Nest Thermostat E or Nest Learning Thermostat, you'll need to install a C wire if the thermostat has power issues or its battery often drains.
The RTH2300 series does not allow for a C wire connection and the C wire should not be use. Tape the wire off with electrical tape and tuck it back in the wall.
In many recently-constructed homes, the HVAC c-wire is already installed. However, in homes that are only a few years old or older, the wire may need to be installed as part of the new smart thermostat installation.
This Honeywell programmable thermostat uses an internal disposable battery for its primary power. A "C" wire is not required. It will work with a 2 wire system.
Wires labeled B typically should go into a Nest thermostat's O/B connector. But for some systems the wire in the thermostat's B connector is actually a common or C wire. Common wires should go in your Nest thermostat's C connector.
Your best bet is to hire a local electrician to complete the C-wire installation for you. These electrical pros have the skills, tools, and expertise necessary to wire your thermostat quickly and safely.
An extra unused wire in the wall can be used as the C wire for your new thermostat. The extra wire will also need to be connected to the C (common) terminal at the heating and cooling system. This will provide power to your new thermostat.
The C, or common wire, provides smart thermostats with continual power. It's usually blue, but it may also be black, brown or purple. The O or orange wire connects to your heat pump (if applicable).
A USB Type C cable. With these cables, the type is whichever end of the cable isn't the standard USB Type-A connector. So, for example, a cable with both a USB Type-A and a Type-C connector is a USB Type-C cable.
To further help, many Honeywell Home T-Series thermostats are mounted on a Universal Wall Plate that allows you to change models by simply 'popping' one in place of the other.
No, the T9 Smart Thermostat comes with a c-wire adapter so it's compatible with homes that do not have a c-wire.
Q: what is a C wire
A: C stands for common. The common wire is the ground or negative wire. To complete the circuit that provides power to the thermostat you need a positive and negative wire from the 24V transformer.