What is a common wire on a thermostat?
A common wire (or c-wire for short) refers to a wire in your heating system specifically designed to enable the completion of a circuit once the hot wire initiates it. It runs from your low voltage heating system and carries continuous power to your thermostat. The common wire often has a white casing.
Where does the 120V wire come from on a boiler?
This wiring diagram shows 120 V coming from L1 of a circuit breaker, through a switch, powering a boiler control and returning through L2, back to the neutral bar of the circuit breaker box. This is fine if the boiler is 120 V.
How do you wire a thermostat to a boiler?
It's pretty simple actually. When a thermostat calls for heat, the valve for that zone opens, and the boiler is also signaled via the auxiliary switch in the valve. To get a C wire to one or more of the thermostats, you'll simply run a wire from the other side of the transformer on the wall.
What is a C wire on a furnace?
The C wire is more like a neutral wire (in electrical terms) and it completes the electrical circuit between the furnace (or any heating system) and the thermostat, thus ensuring a flawless power supply to thermostat even when the furnace is OFF. To know if you already have a C wire in your home wiring, there are two ways.
What does the common wire connect to?
A common wire (C-Wire) provides Wi-Fi thermostats continuous power by connecting it to a heating and cooling system (e.g. furnace). C-Wires are required on most Honeywell Wi-Fi thermostats, with the exception of the Smart Round Thermostat (formerly known as the Lyric Round).
Where do you connect the common wire?
3:176:13How to Connect an Unused C Wire (Common Wire) - YouTubeYouTubeStart of suggested clipEnd of suggested clipYou would typically connect. This a/c wire to be the C terminal on the board on the control board onMoreYou would typically connect. This a/c wire to be the C terminal on the board on the control board on in the furnace. But the C terminal.
What does common wire look like?
The common wire is normally the white wire, at least in the United States, and is often called the neutral wire. It's also called common because all circuits in the house typically have the white wires tied together, which means every circuit has that wire in common.
Where do you connect the common wire on a furnace?
0:535:28HVAC Furnace Has No C Terminal? - YouTubeYouTubeStart of suggested clipEnd of suggested clipCommon in most cases the easiest way to find the 24 volt common is to go right off of theMoreCommon in most cases the easiest way to find the 24 volt common is to go right off of the transformer.
What is the common wire?
The "common" is the "neutral" or "ground" wire, depending on the type of circuit. In normal US residential wiring, you'll have a black "hot" wire, a white "neutral" or "common" wire, and a green or bare "ground" wire.
What color is the common wire?
Blue wires are also called “C” wires because they are the Common wire.
Does the common wire always have power?
First and foremost, a common wire may not always carry electrical current, but a hot wire will. Also, a common wire can usually be handled with care while a hot wire, which definitely has electricity flowing through it, should be handled with extreme caution.
Does a common wire have power?
A C-wire, or a common wire, runs from your low voltage heating system (24v) and carries continuous power to your thermostat.
Is common wire the same as ground?
1:308:05Is Common and Ground The Same Thing? - YouTubeYouTubeStart of suggested clipEnd of suggested clipThere is a problem if there's an electrical short or maybe there's some hot wire shorting outMoreThere is a problem if there's an electrical short or maybe there's some hot wire shorting out somewhere the ground wire is usually a thick bare copper wire or sometimes a green wire.
Is the C wire a ground?
No way! A "return" is not the same thing as a "ground". In certain situations it is, but not here. The C wire (together with "the other half of the circuit") forms a circuit through the secondary of the 24V transformer.
What does a common wire do in a thermostat?
The C wire, or “common wire” enables the continuous flow of 24 VAC power to the thermostat. Technically speaking, power flows from the R (red) wire, but not continuously (not on its own, anyway). To make it continuous requires a common wire to complete the circuit.
Does C wire have voltage?
The C wire, a.k.a. the "common wire", allows a constant flow of 24 VAC (volts AC) power to a smart thermostat. However, the C wire doesn't provide the actual source of power to the thermostat. The wires that provide the source of power are the R wires (or hot wires).
Does the common wire always have power?
First and foremost, a common wire may not always carry electrical current, but a hot wire will. Also, a common wire can usually be handled with care while a hot wire, which definitely has electricity flowing through it, should be handled with extreme caution.
Is common wire the same as ground?
1:308:05Is Common and Ground The Same Thing? - YouTubeYouTubeStart of suggested clipEnd of suggested clipThere is a problem if there's an electrical short or maybe there's some hot wire shorting outMoreThere is a problem if there's an electrical short or maybe there's some hot wire shorting out somewhere the ground wire is usually a thick bare copper wire or sometimes a green wire.
Is common live or neutral?
A one way light switch has two terminals which is a common marked as COM or C. The common is for the live wire that supplies the input voltage to the switch. The other terminal is marked as L1 and is the output to the light fixture.
What is a common wire on a switch?
Black wire: This is a hot wire that carries electricity from the power source to the first switch in a typical 3-way setup. It's also called the “common wire” or the “line wire.” Unless the breaker is off, this black wire is always hot.
What is the color of the C wire on a furnace?
C wire from furnace circuit board going to thermostat – source. If you observe the terminals, you can see two wires are tapped from ‘C’ terminal. The ‘black’ color wire is part of the set that goes to the thermostat. The ‘white’ color wire is part of the set that goes to the condenser unit. In another image given below, you can see ...
What is the difference between a C and R wire?
Well, the R wire is a power source but it does not ensure a continuous supply when the furnace is OFF. The C wire is more like a neutral wire (in electrical terms) and it completes the electrical circuit between the furnace (or any heating system) and the thermostat, thus ensuring a flawless power supply to thermostat even when the furnace is OFF.
How many volts does a thermostat need?
Thus modern thermostats require a continuous power supply and the C wire or Common wire is required for most thermostats to ensure 24 volts AC supply continuously. Note: You might be thinking the R wire ...
How to tell if your thermostat has a common wire?
Examine Backside of your Current Thermostat. The easiest way to know if your home wiring already has a common wire is to examine the backside of your current thermostat. To do this examination, you may remove the face plate and take the thermostat out of the wall.
What color wire is connected to the C terminal?
Yellow color wire connected in ‘C’ terminal – Source. In some cases, your old thermostat may not have a ‘C’ terminal. In such cases, there are chances that a ‘C wire’ is already in place but left unconnected. Look for any wire that is tucked away behind your thermostat.
What color wire goes into a thermostat?
In the above image, a “Blue” coloured wire is coming into terminal marked “C”. Usually “C wire” or the Common Wire will be a blue coloured wire. But there is no particular standard for thermostat wires, so it can be any color like Yellow, Brown, Green or any other color.
What to do if you don't have a C wire?
If you don’t have a C wire running from the furnace, you’ve the following options. Install a new C wire. Use a C wire Adapter. Choose a thermostat that doesn’t need C wire or has an alternative solution.
How many wires does an HVAC thermostat have?
If the current thermostat has at least 3 wires and your HVAC control board has a common terminal, we can use the Thermostat Wire Adapter ( https://store.idevicesinc.com/thermostat-wire-adapter/) to power the iDevices Thermostat. The Thermostat Wire Adapter works by running two signal wires for your HVAC system over one wire, freeing up the other to be used as the common wire. Use the steps above to locate the HVAC control board, and identify the common terminal.
What wire do I need for an iDevice thermostat?
Locating the Required 24V Common Wire. iDevices Thermostat requires a 24V common or ‘C’ wire, which provides continuous power for features like Wi-Fi connectivity and the backlit display. If the previous thermostat did not have a common wire and used batteries for power or you had a mercury thermostat, there are several options available ...
Where are extra wires tucked?
Extra wires may also be tucked behind the thermostat or in the wall, pull gently on the bundle of wires or shine a flash light into the wall to see if any extra wires are present. If you located an extra wire, we’ll want to ensure the wire is connected to Common terminal at the HVAC control board.
Can you connect a mercury thermostat to a common wire?
If the previous thermostat did not have a common wire and used batteries for power or you had a mercury thermostat, there are several options available to connect a common wire. All options require a common terminal at your HVAC control board.
What wire should go on each of the W terminals of the existing t'stats?
You should have a WHITE wire on each of the W terminals of the existing t'stats, and that should go to one each of the YELLOW wires from the zone valves in a wire nut as shown.
What does it mean when wire colors match?
In the future, having the wire colors 'match' will mean that you won't need to remember what you did the last time... or the new owners won't have to know either (if you have an altruistic streak and you care!)
How many thermostats are connected to Xformer?
There will actually be 3 thermostats connected. They also have batteries so the way I understand it, they would use the battery power if the line power was not enough. Do you think adding 3 thermostats would overload the xformer?
What color is a 120V house?
With regular 120VAC house wiring, we know that the 'neutral' is always white, and the 'hot' black or red.
Where does the other yellow wire go in a transformer?
The OTHER YELLOW from each valve should all come together and go to the WHITE wire from the transformer.
Can you leave wires as is?
There's no FUNCTIONAL reason that you can't leave the wiring as-is and just make the proper connections... as long as the wires land at the proper place everything will play fine.
Can you hook up an A/C to a thermostat?
When you go to hook up the A/C to one of the new thermostats as you've indicated you wish to do, you need to be extremely careful that you REMEMBER which wire color is which. The A/C installers may have used the proper colors... and hooking them up backwards can end up with the heating transformer in SERIES with the cooling transformer... and you could end up with 48 VAC going to the controls... and you DON'T want to do that!
What is a C wire?
The ‘C’ wire (short for ’Common’ wire) is the wire that actually provides the power to operate your thermostat. Although there are some options available if you do not have a ‘C’ wire (see below), ...
How to tell if thermostat has C wire?
The easiest way to check if your existing thermostat has a ‘C’ wire already installed is to take the front of the thermostat off and look. The cover is either held onto the back plate by snap clips or one or two small screws. On the back plate, you will see a number of letters. If there is a wire going to letter ‘C’, you have a ‘C’ wire.
Is it worth having a spare wire included in a cable?
It will be an added expense, but will ’future proof’ you if further developments that require additional wires are needed. If you are going to have a new cable, it is worth considering having a spare wire included. The additional cost will be minimal and may be of use in the future.
Does Nest use a C wire?
It is recommended that the Nest uses a ‘C’ wire to avoid this. Note, even though the Wi-Fi may drop out the Nest will still continue to. function, you just won’t be able to remotely access it during that time.
Do you need a C wire for a thermostat?
In all likelihood, as thermostats continue to develop that are going to need more wires rather than less. If you do not at present have a ‘C’ wire, or a spare that wire that you can use, it may be worth considering having a new cable run from your heating / cooling control box to the new thermostat. It will be an added expense, but will ’future proof’ you if further developments that require additional wires are needed. If you are going to have a new cable, it is worth considering having a spare wire included. The additional cost will be minimal and may be of use in the future.
Can you wire a power extender to a thermostat?
They can be wired directly to the C terminal. Although this will supply the necessary power to your thermostat, you are then either left with an exposed wire coming from the device or you need to find a way to conceal this wire.
Can You Still Have a Wi-Fi Thermostat if You Do Not Have a ‘C’ Wire?
In a word – yes. The Sensi Wi-Fi Smart Programmable Thermostat 1F86U-42WF works very well without a ‘C’ wire. The Nest learning, 2 nd Generation also claims to be able to work without a ‘C’ wire as it ‘borrows’ the power from the ‘D’ and ‘G’ wire. Some users have commented that the Wi-Fi has a tendency to drop out from time to time. This happens when there is insufficient spare power for the Wi-Fi to operate. It is recommended that the Nest uses a ‘C’ wire to avoid this. Note, even though the Wi-Fi may drop out the Nest will still continue to
How does a boiler signal a thermostat?
It's pretty simple actually. When a thermostat calls for heat, the valve for that zone opens, and the boiler is also signaled via the auxiliary switch in the valve.
What is the white wire on a thermostat?
NOTE: If this diagram is accurate, the white wire to the thermostat is R, while the red wire is W.
Where do you run the blue wire on a thermostat?
Then you'll run the blue wire from the white transformer lead, up to the C terminal on the thermostat.
Can you run a 4th wire with Rc?
You also may be able to run a 4th wire with the constant power if you're heat only and split Rh and Rc. Emerson has an article about that using a wall wart, but same concept would apply to running a fourth wire straight to the transformer on the boiler. Not sure if this is common for most Wi-Fi thermostats or not...it relies on then sourcing power from Rc only and Rh just being a dumb switch. https://sensicomfort.com/support/article/adding-a-24-vac-external-transformer
