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Old 04-07-2012, 09:19 PM   #1
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Thermostat assist please.


I just pulled an old thermostat out of the wall because the handle was broken on it. Got a new one to put in there, and had to put in a bigger box for it.


My problem now is that the old t-stat wasn't labelled line or load. The new one is labelled, and i have 3 black wires in this box and I didn't know which one was the line wire.

I separated them and went and flipped on the power, now all 3 black wires are hot.

What gives?

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Old 04-07-2012, 09:25 PM   #2
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Thermostat assist please.


How are you metering the wires? To ground? To the white?

You will need to meter the blacks to ground.

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Old 04-07-2012, 09:27 PM   #3
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Thermostat assist please.


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Originally Posted by k_buz View Post
How are you metering the wires? To ground? To the white?
Voltage detector.

I guess I should take voltage readings on each of the lines?
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Old 04-07-2012, 09:28 PM   #4
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Thermostat assist please.


The other way to do it is to keep the blacks separated, and separate all the whites (with the breaker off). Then turn on power and meter black to white.
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Old 04-07-2012, 09:28 PM   #5
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Thermostat assist please.


Are the heaters 120 or 240V?
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Old 04-07-2012, 09:34 PM   #6
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Thermostat assist please.


I'll check the heaters one minute.


The voltage from black to ground reads 117V on each one.
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Old 04-07-2012, 09:35 PM   #7
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Thermostat assist please.


Sounds like a single pole stat on a 240v circuit.
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Old 04-07-2012, 09:43 PM   #8
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Thermostat assist please.


The heaters have no data tag on them. I opened them both up where the connections are, and there's nothing to say 240v or 120v


So I have 3 wires in the box, and two heaters.

The thermostat was a single line break, so what i'm seeing on the wires is the voltage feeding back through the heater on one leg on two wires, and the other leg is the hot incoming to the thermostat?
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Old 04-07-2012, 09:43 PM   #9
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Thermostat assist please.


Turn off power.

Separate the whites (leave the blacks separate)

Turn on power

Meter between black and white

You should only have power on one set of wires

Mark that wire with a wirenut or something

Turn off power

Splice the whites back together

Put the wire with the wirenut on the line side and splice the other two to the load side.
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Old 04-07-2012, 09:44 PM   #10
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Thermostat assist please.


Quote:
Originally Posted by Alan View Post

The thermostat was a single line break, so what i'm seeing on the wires is the voltage feeding back through the heater on one leg on two wires, and the other leg is the hot incoming to the thermostat?
yes...
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Old 04-07-2012, 09:45 PM   #11
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Thermostat assist please.


Quote:
Originally Posted by k_buz View Post
Turn off power.

Separate the whites (leave the blacks separate)

Turn on power

Meter between black and white

You should only have power on one set of wires

Mark that wire with a wirenut or something

Turn off power

Splice the whites back together

Put the wire with the wirenut on the line side and splice the other two to the load side.
Thanks.

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