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Old 03-03-2010, 11:26 PM   #1
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thermostat wiring for electric heater


I am wiring a thermostat to my shop electric heater. Here's what I have: a plug in 24 volt 20va transformer. Both exit terminals are identical. One terminal has a "R" in its vicinity. Since the transformer can be plugged in reversed, which 24 volt terminal should be considered hot and which neutral?

I have a Honeywell thermostat with terminals Rh, Rc, W, Y, & G. The Rh & Rc have a jumper connecting them. I want to break both leggs of my DP 240 contactor. What is the wiring connections from transformer to thermostat and then to the contactor?

My contactor has what appears to be 24 volt terminals on both sides. I assume that a hot needs to go to each side to break both legs? Does the transformer neutral connect to the ground wire in the 10/3 supply line?

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Old 03-05-2010, 05:36 AM   #2
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thermostat wiring for electric heater


To answer your first question...take your voltmeter and connect one lead to each post to the white 120volt connections...the one that reads 24 volts is your hot post. You might have to unwirenut the white neutral 120 volt connection to do this test. Since you are only dealing with heat, and not cooling, take the jumper out of the RH to RC on your thermostat. Take the thermostat wire (red wire) and connect it to your hot side post of the transformer and connect it to the RH post on your thermostat. Next take a new thermostat wire and connect the red wire to the RH post as well on the thermostat and to either side of the contactor (red or white can interchange on the contactor). Take the white thermostat wire and connect it to the transformer "common" post and then connect it to the "W" post on the thermostat. next take the other white thermostat lead from the contactor thermostat wire and connect that also to the "W" post of the thermostat. Now when the transformer is energized, it will provide the 24 volts to the contactor only when the thermostat calls for heat and energizes the W post on the thermostat.

Correction..first line...connect the lead to the 24 volt posts - not the 120 volt.

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Old 03-05-2010, 04:08 PM   #3
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thermostat wiring for electric heater


wire the TR directly to the contactor and plug it in.the contactor closes ...take the stat and cut into one of the wires going to the contactor from the TR .the wire from the TR is Rh, and the one from the contactor is W
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Old 03-05-2010, 09:48 PM   #4
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thermostat wiring for electric heater


Thanks to you both for your help.
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