How to Wire a Smart Thermostat

Gregg in Illinois asks: My current wiring only has 4 wires but I understand I can use the fan wire and make it a common wire. How to Wire a Smart Thermostat, Change the Wiring for a Smart Thermostat.

Wiring a Smart Thermostat
Electrical Question: My current wiring only has 4 wires but I understand I can use the fan wire and make it a common wire.

I am trying to install a smart thermostat. My current wiring only has 4 wires but I understand I can use the fan wire and make it a common wire. The attached photo is a photo inside the HVAC. ‘Y’ is empty, ‘W’R”G’ are wired then there is a “C’ with a wire attached. On my current thermostat I have a white wire into W, Green into Green, a blue wire into Y, and a red wire into R. I’m just confused why there is a ‘C’ wire on my HVAC and not on my thermostat. Any help would be greatly appreciate. Thanks

This electrical wiring question came from Gregg, a Homeowner in Plainfield, Illinois.

Dave’s Reply:
Thanks for your electrical wiring question Gregg.

How to Wire a Smart Thermostat

Application: Wire a Smart Thermostat – Change the Wiring of a HVAC Thermostat.
Skill Level: Intermediate to Advanced – Best performed by a Licensed Electrical Contractor, a Certified Electrician or an HVAC Technician.
Electrical Tools Required: Basic Electricians Pouch Hand Tools, Voltage Tester, and appropriate Safety Gear.
Estimated Time: Depends on the personal level experience, ability to work with tools, install electrical circuit wiring, and the available access to the project area.
Electrical Safety: Identify the electrical power source to the HVAC Thermostat, turn it OFF and Tag with a Note before working with the electrical wiring.
Electrical Wiring Parts and Materials: Electrical parts and materials for the HVAC Thermostat should be approved for the specific project and compliant with local and national electrical codes.
Electrical Codes and Inspections: Installing or changing home electrical wiring should be done according to local and national electrical codes as adopted in Plainfield, Illinois. A permit and inspections may also be required.

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Change the Wiring for a Smart Thermostat

This electrical wiring project is about How to Change the Wiring of a HVAC Thermostat that will be replaced by a Smart Thermostat.

Smart Thermostat Wiring: What You Need to do to Make it Work for You

• A Smart Thermostat requires a constant power supply, which in this case is 24volts that will be supplied from the HVAC system.
• Normally, a non smart thermostat has only the Power wire of the 24volts to the thermostat, which is used for switching the HVAC unit on and off. Therefore a the Common wire of the 24volts is not available.
• In order to make a smart thermostat work, we will need the Common wire of the 24volts. If there are no spare wires available withing the thermostat cable, then we will need to create one, but you will have to sacrifice another option, and in this case we will be sacrificing the blower switch function, buy using the blower switch wire for the common wire required by the smart thermostat.
• IMPORTANT: In order to make this work, the change will need to be made not only at the thermostat location, but also at the HVAC system, otherwise it will not work as needed.

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» You Can Avoid Costly Mistakes! « Here's How to Do It: Wire It Right with the help of my Illustrated Wiring Book Great for any Home Wiring Project. Complete Guide to Home Electrical Wiring Perfect for Homeowners, Students, Handyman, Handywomen, and Electricians Includes: Wiring GFCI Outlets Wiring Home Electric Circuits 120 Volt and 240 Volt Outlet Circuits Wiring Light Switches Wiring 3-Wire and 4-Wire Electric Range Wiring 3-Wire and 4-Wire Dryer Cord and Dryer Outlet How to Troubleshoot and Repair Electrical Wiring Wiring Methods for Upgrading Electrical Wiring NEC Codes for Home Electrical Wiring ....and much more.

Be Careful and Be Safe - Never Work on Energized Circuits!
Consult your Local Building Department about Permits and Inspections for all Electric Wiring Projects.

Electrical Tips to Help You Wire it Right The Safest Way to Test Electrical Devices and Identify Electric Wires! The Non-Contact Electrical Tester This is a testing tool that I have had in my personal electrical tool pouch for years, and is the first test tool I grab to help identify electrical wiring. It is a Non-contact tester that I use to easily Detect Voltage in Cables, Cords, Circuit Breakers, Lighting Fixtures, Switches, Outlets and Wires. Simply insert the end of the tester into an outlet, lamp socket, or hold the end of the tester against the wire you wish to test. Very handy and easy to use. The Quickest Way to Check for Faulty Electrical Wiring! The Plug-In Outlet Tester This is the first tool I grab to troubleshoot a problem with outlet circuit wiring. This popular tester is also used by most inspectors to test for power and check the polarity of circuit wiring. It detects probable improper wiring conditions in standard 110-125 VAC outlets Provides 6 probable wiring conditions that are quick and easy to read for ultimate efficiency Lights indicate if wiring is correct and indicator light chart is included Tests standard 3-wire outlets UL Listed Light indicates if wiring is incorrect Very handy and easy to use. Strip Off Wire Insulation without Nicking and Damaging the Electric Wire! The Wire Stripper and Wire Cutter My absolute favorite wire stripping tool that I have had in my personal electrical tool pouch for years, and this is the tool I use to safely strip electrical wires. This handy tool has multiple uses: The wire gauges are shown on the side of the tool so you know which slot to use for stripping insulation. The end of the tool can be used to grip and bend wire which is handy for attaching wire onto the screw terminals of switches and outlets.. The wire stripper will work on both solid and stranded wire. This tool is Very Handy and Easy to Use.

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Home Electrical Wiring and Electrical Repairs Please Note: Unless otherwise posted, please refer to the following Guidelines when working on Electrical Projects: Skill Level: Intermediate to Advanced - Electrical Repairs and Circuit Wiring is Best Performed by a Certified Electrician or Licensed Electrical Contractor. Electrical Tools Required: Basic Electricians Pouch of Hand Tools, a Voltage Tester and a Multi Meter. Estimated Time: Depends on personal level experience, ability to work with tools, work with electrical wiring, and the available access to the project area. Precaution: Identify the project circuit, turn it OFF and Tag it with a Note before working with the wiring. Important: Modifying existing electrical circuits or installing additional electrical wiring should be done according to local and National Electrical Codes, with a permit and be inspected.

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