can i use a 4 wire thermostat on a 2 wire system?


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Old 11-26-07, 01:14 PM
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can i use a 4 wire thermostat on a 2 wire system?

hi -- im replacing our thermostats on our 240v baseboard heating system. everything is wired with 12-2 wiring.

i bought the honeywell rlv430a from home depot (which has two wires on the back) and pulled out the old thermostat. there were two black wires coming from the wall screwed into the back of the old unit. i connected the two black wires that used to into the old unit to the two wires that came out of the back of the new unit. flipped on the power and the thing worked great.

now that i've tried it i'd rather have the linevoltpro 8000 by honeywell. i like the backlight and the safety of a 4 wire system.

(http://customer.honeywell.com/honeyw...px/TL8230A1003)

i called honeywell and they said it was a 4 wire thermostat and was incompatible with my system. is that true? is there any way to install it on my system?

thanks
nathan
 
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Old 11-26-07, 02:05 PM
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You need to determine if the outlet-box where the thermostat connects has a "Feed-IN" pair ( Black & White wires ), and a "Feed-Out" pair ( also B & W wires).This is "Standard" wiring for line-voltage thermostats,

It MAY be possible that you overlooked wires in the box not connected to the thermostat- so -- "have a look"!!!

Good Luck!!
 
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Old 11-26-07, 02:14 PM
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hey thanks for the note. i found an end-run heater on a different circuit in the basement that we're replacing and the wires that come into that heater are just one white and one black and one ground.

so should i just bail on the idea of getting the backlit double-pole unit? and just keep the 430 units i got at home depot?
 
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Old 11-26-07, 02:19 PM
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Answer the question. Check the wiring at the thermostat, not at the heater.
 
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Old 11-26-07, 03:52 PM
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Okay. I still don't quite get it but here's how the wiring goes...

Power comes in from the breaker box on 12-2 cable, enters the box where the thermostat is, and goes out along two lengths of 12-2 cables to two heaters.

The black line from the cable coming from the breaker box goes straight to one of the thermostat's two wires. The thermostat's other wire connects directly to BOTH black wires in the cables that head to the heaters.

The white wire from the breaker box cable enters is connected directly to BOTH white wires that head to the heaters.

All the grounds are connected together.

So, that said, can I connect a four-wire thermostat to this system?

Thanks for the advice
Nathan
 
  #6  
Old 11-26-07, 08:10 PM
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Yes, you can connect a four wire thermostat to this setup. Connect the white wires in the same manner as the black wires are connected.
 
 

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