4 wire T-stat to 2 wire setup?


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Old 03-03-09, 08:29 AM
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4 wire T-stat to 2 wire setup?

I'm interested in purchasing a programmable T-stat to reduce heating cost. I removed the old dial T-stat and revealed a two wire set-up. One, black and one white wire. Which is a 240 volt system. I have not pulled out the Volt meter just yet, so I can't be certain it's a 240v system just yet.

After looking around, I've only seen one T-stat out there that would be compatible with my system.(baseboard)

So my question is, being there are many 4 wire T-stats out there, can I use one of those for my 2 wire system?
 
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Old 03-03-09, 10:52 AM
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Short answer, Yes, you can use a four wire stat with a 2 wire system. You just do not connect the other pole.

You need to check it with a meter. Since you only have two wires you may have a 120 volt heater.
 
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Old 03-03-09, 11:10 AM
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What type of heating device is this controlling? Most gas furnaces use 24 volts from a transformer in the furnace for control circuits.
 
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Old 03-03-09, 11:54 AM
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Originally Posted by goldstar
What type of heating device is this controlling? Most gas furnaces use 24 volts from a transformer in the furnace for control circuits.
I didn't mention gas furnaces. It controls electric baseboard heat.
 
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Old 03-03-09, 12:32 PM
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If you only have a single black wire and a single white wire, then you have a 1-pole switch loop configuration. You can use any line-voltage programmable thermostat so long as it is self-powered with a battery. You cannot use many of the thermostats which require power from the line as you only have a partial circuit at the t-stat box.
 
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Old 03-03-09, 01:32 PM
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Originally Posted by ibpooks
If you only have a single black wire and a single white wire, then you have a 1-pole switch loop configuration. You can use any line-voltage programmable thermostat so long as it is self-powered with a battery. You cannot use many of the thermostats which require power from the line as you only have a partial circuit at the t-stat box.
Incorrect, I just tested it. Reading is 240. This is not a low volt system and I would fry a low volt Stat!
 
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Old 03-03-09, 03:02 PM
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Originally Posted by DonM77
Incorrect, I just tested it. Reading is 240. This is not a low volt system and I would fry a low volt Stat!
IF you only have 2 wires (not cables) in the box, and you get 240 volts between them, this is not going to work. All the stat does is close the circuit like a switch. If you put those two wires, on a single pole in the stat, your stat will last about 1/186,000 second.

Do you have more info? Are there more wires in the box?
 
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Old 03-03-09, 03:12 PM
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Originally Posted by Tolyn Ironhand
IF you only have 2 wires (not cables) in the box, and you get 240 volts between them, this is not going to work. All the stat does is close the circuit like a switch. If you put those two wires, on a single pole in the stat, your stat will last about 1/186,000 second.

Do you have more info? Are there more wires in the box?
I only see two wires connected to the back of the exsisting stat. Each wire reads 120v.
 
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Old 03-03-09, 03:25 PM
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You have a 240V heater, which has power fed at the heater, and runs one pole of the circuit through the t-stat loop. As I said before, you need a 240V line-voltage one-pole or two-pole t-stat which does not require power from the circuit.
 
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Old 03-03-09, 03:40 PM
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Originally Posted by ibpooks
You have a 240V heater, which has power fed at the heater, and runs one pole of the circuit through the t-stat loop. As I said before, you need a 240V line-voltage one-pole or two-pole t-stat which does not require power from the circuit.
As you stated in your last post, one that is battery powered? I'm having a difficult time finding one online. Off hand do you know of a model and brand?
 
 

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