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Furnace Thermostat Electrical Wiring

Understanding Furnace Thermostat Electrical Wiring

 

Understanding Furnace Thermostat Electrical Wiring
  Electrical Repair Question: I started having problems with the thermostat for my furnace.

I recently installed a hanging light fixture in my dining room. Previously, there has not been any fixture upon the ceiling light fixture prior to this. When I removed the cap the the ceiling light mount, I noticed two pairs of power cables (i.e. 2 positive, 2 negative, 2 grounds) tucked in the mount. There are also 2 power switches for this fixture mount, as I’m assuming there was ever a need to mount a ceiling fan & light unit. When I first attached the new light, I connected only one pair of power cables (1 black, 1 white, 1 ground)cable to the new light. I noticed however, when powering on, the new light worked, but the rest of the devices (another set of ceiling lights, floor lamps, etc) did not power ‘on.’ I had covered with electrical tape, the remaining white/black/ground cable. I then connected those remaining ‘unused’ cables, to the light fixture as well. Now, the light fixture comes ‘on’ with either light switch on the wall, but at least the rest of my ceiling lights, floor lamps, etc are now powering ‘on’ as well. Since this, I’ve noticed now that my thermostat does not power on properly and does not activate my furnace. The new light fixture and the thermostat/AC/Furnace are on Separate circuits. At times, I’ve had to power off/on my thermostat or trip the circuit in my Power Supply box, to get the furnace to now ‘kick’ on, when the temperature in the house drops. I started having problems with the thermostat powering on the furnace, since I installed this additional light fixture. Any suggestions? Remember, I ended up using the 2 black/white/ground cables to connect the new ceiling light. Thank you so much.

This electrical question came from: John, a Homeowner from Kansas City, MO, Missouri.
See more about Home Wiring for Missouri

Additional Comments: Great site!

Dave’s Reply:
Thanks for your electrical repair question John.

Furnace Thermostat Electrical Wiring

John, the interesting thing is that the thermostat for a typical furnace is low voltage which comes from the circuit at the furnace, which should be a dedicated circuit and should have nothing to do with the lighting circuit. Not knowing the history of your home or anything further about the electrical wiring I would suggest that the wiring that you have recently worked with should be positively identified for a full understanding of what the wiring truly is.

The Following will assist you with your thermostat wiring:

How to Install Ceiling Fans and Wiring

Step-by-step pictures – Easy wiring diagrams and installation guide – Light and fan switch variations.

Circuit Wiring

Wiring Diagrams

electrical circuit
home-electrical-circuits
Electric Circuit Listing
The size of the home electrical service panel is designed by calculating the square footage of the home and factoring in the code requirements for the electrical circuits that are required.


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Wiring GFCI Outlets
Wiring Home Electric Circuits
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How to Troubleshoot and Repair Electrical Wiring
Wiring Methods for Upgrading Electrical Wiring
NEC Codes for Home Electrical Wiring
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