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# which wire goes where

#1
02-04-13, 02:16 PM
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Join Date: Feb 2013
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which wire goes where

Hi This is my 1st post. I have 4 wires at the wall thermostat box. I know 2 goes to the circuit breakers and 2 goes to the heater. How can I find which pair goes to the heater? I am thinking if I put a multi meter on a wire at the heater, I can touch each wire in the box (1 at a time) until I get a reading. This will tell me if the wire is the same one being touched on both ends. Is this correct? What would I set the dial at on the multimeter to do it? Thanks Paul

#2
02-04-13, 02:23 PM
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The two that go to the circuit breaker will read either 240 volts or 120 volts depending on the supply voltage. Since you seem to have a two pole thermostat best guess is 240 volts. Is that what the breaker is? If your multimeter is not self ranging set to ac voltage in the range that will give you 240 volts at about mid point.

#3
02-04-13, 04:46 PM
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can't I figure out which wires go to the heater without turning on the electricity?This is what it looks like now, on the left. The switch on the right is the new one. I would like to be able to figure out if wire 1 or wire 2 goes to the heater.

#4
02-04-13, 04:53 PM
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Turning on the breaker is the easiest way. If your worried about working around a live cable either buy a pair of alligator clips for you multimeter probes or tightly tape the wires to your probe before turning on the breaker.

#5
02-04-13, 04:53 PM
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If you have a multimeter that has probes that are long enough to touch o wire end in the heater and one on the box for the thermostat at the same time, you could test for continuity. But I would trust testing for power over that any day. Why do you not want to do that?

Is anything molded into the back of your old thermostat to indicate LINE or IN, or LOAD or OUT?

Tech note: #12 AWG is a wire. 12-2 is a cable.

#6
02-04-13, 04:57 PM
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Okay-I do have a multimeter. How do I check for electric power? Just touch one probe to each wire in the cable then turn on the electricity? Where do I set the meter?

#7
02-04-13, 05:07 PM
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Disconnect and separate the wires. Turn the breaker on. Set your meter to the lowest value for AC voltage that is greater than 240. Touch the probes to the two wires in one cable and then to the two wires in the other cable. One pair should show 240V. That's the feed from the panel. The other pair should show 0V. That's the feed to the heater.

#8
02-04-13, 06:19 PM
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Thanks guys. I did it both ways and they both show the same. Best explaination I have read yet.

#9
02-04-13, 09:24 PM
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Nice pics......however you're current pic is not drawn correctly. I don't know if just the pic is drawn incorrectly or you have your wiring connected incorrectly.

Pic doesn't really make a difference.....just make sure L1 and L2 go to the breaker and T1 and T2 go to the heater.

#10
02-05-13, 09:00 AM
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thanks - but that is how it was wired. I never wired it. It's been like that for 30 years
And yes-the wires in pic 2 on the thermostat and the pictures in the instruction sheet were very clear which wires were L1, L2, T2,and T2.
The real PITA after learning this from you guys was stuffing the wire back in the box. they are wicked stiff and almost filled the box. Didn't leave room for the thermostat. But after some wrestling I got in in.

#11
02-05-13, 01:30 PM
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Glad you got it, and thanks for letting us know.

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