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Anthony Lombardy

How to wire this wall thermostat which has 1-black, 1-red, 1-white wire but wiring has 2-black and 2-white wires & neutral?

The thermostat is a single pole, 110 volt unit. The house wiring has two lines into the box, with the white wires already banded with a wire nut, and the two black wires separated. There is also the bare neutral wire.

The old thermostat wired directly to the 2-side screws, with the neutral to the green screw. The new thermostat has a red and black wire, and a smaller white ground wire. There is also a green screw for neutral. How can you determine which black house line goes to the load, and the other the line, and where does the ground wire connect, since there was none with the old thermostat.

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1 Answer from this member:
scott d
I will need the brand and part number of the thermostat you have. Hopefully with this information I will be able to obtain the instructions or wire diagram associated with this thermostat. Normally there are no wires on a new thermostat and from what you are describing it sounds like you have an older gas furnace. It seems from what you are describing the red and black wires on the new thermostat will connect to the 2 black wires. It should not make any difference about which black wire goes to the red or black on the thermostat but again I would need to see the details of this thermostat. I would strongly recommend having a technician check this to determine if the thermostat you have will work and if so to wire it up correctly. If you need more assistance you can resubmit your question with more details and maybe a picture of your thermostat.
by scott d Earned 8,216 community points in Building Supplies
December 23rd, 2008
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