# thermostat wiring- replacing single pole w/ double pole



## gorbengt (Oct 4, 2011)

Greetings,

current setup: Three small rooms, each with its own 120 volt baseboard electric heat, each with a 25 year old wall mount single pole, line voltage thermostat. All 3 room heaters are on the same breaker. Current single pole thermostat connections have 3 wires: black, red and white.

I need to replace with double pole thermostats so I can selectively turn off individual room heaters.

I purchased 3 new Cadet (Honeywell) line thermostats, T410B Bimetal 22amp Double Post Wall.
They have (2) black and (2) red connections... labelled L1, L2, T1 and T2.

I plan to:

(1) disconnect power
(2) remove old thermostat
(3) reconnect power
(4) determine which wire to thermostat is the hot feed
(5) disconnect power
(6) wirenut L1, L2 and hot feed together
(7) wirenut T1, T2 and load wire together
(8) Terminate white wire???

Is this correct?

Thanks!
- Gordon


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## Jim Port (Sep 21, 2007)

You only need single pole t-stats for 120 volt heaters.


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## gorbengt (Oct 4, 2011)

The problem is that the single pole t-stats don't completely turn off, so I have all 3 heaters going when the majority of the time I only want one to function. Two pole provide the off setting I need.
Thanks,
- gordon


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## kbsparky (Sep 11, 2008)

You can use double-pole thermostats as single pole units.

Most double-pole line voltage thermostats will break only one pole when cycling on and off.

Connecting the poles together in parallel as you planned will not work.

To make them work properly as single pole units, wire the 2 poles in series:

Wire-nut T1 and T2 leads together, and tuck into the box.

Use the remaining L1 and L2 leads to control your heaters.


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## Jim Port (Sep 21, 2007)

Did you mean 
Wire-nut L2 and T2 leads together, and tuck into the box.

Use the remaining L1 and T1 leads to control your heaters.

I can't see how you would have any t-stat output with T1 and T2 wire nutted and in the back of the box.


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## gorbengt (Oct 4, 2011)

The parallel connection comment took a while to sink in.
I now believe I understand the correct serial solution is:

(1) Connect the hot line feed wire to L1.
(2) Connect/jumper T1 to L2.
(3) Connect the heater load wire to T2.

Does this sound correct?
What about the white wire?

Thanks!


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## a7ecorsair (Jun 1, 2010)

gorbengt said:


> The parallel connection comment took a while to sink in.
> I now believe I understand the correct serial solution is:
> 
> (1) Connect the hot line feed wire to L1.
> ...


I have several of these thermostats installed in my house and they are listed for both 120 and 240 operation.
In 120 volt operation L1 and T1 are the only terminals used. Do not use L2, T2 as these only interrupt power when the thermostat is dialed to *OFF*

For 120 connection, connect incoming hot to L1 and the heater to T1. Wirenut the incoming white neutral to the heater white neutral.
To the OP for educational purposes. 240 line voltage thermostats that have an *OFF* position on the dial open both contacts when dialed to OFF. When controlling temperature, only one contact is cycled.


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## Pvandoren (Nov 24, 2020)

gorbengt said:


> Greetings,
> 
> current setup: Three small rooms, each with its own 120 volt baseboard electric heat, each with a 25 year old wall mount single pole, line voltage thermostat. All 3 room heaters are on the same breaker. Current single pole thermostat connections have 3 wires: black, red and white.
> 
> ...





gorbengt said:


> Greetings,
> 
> current setup: Three small rooms, each with its own 120 volt baseboard electric heat, each with a 25 year old wall mount single pole, line voltage thermostat. All 3 room heaters are on the same breaker. Current single pole thermostat connections have 3 wires: black, red and white.
> 
> ...


I have a thermostat with 2 black wires and 2 white I want to replace and the new thermostat has only 2 black wires what do I do with the white wires


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## seharper (Mar 17, 2020)

a7ecorsair said:


> I have several of these thermostats installed in my house and they are listed for both 120 and 240 operation.
> In 120 volt operation L1 and T1 are the only terminals used. Do not use L2, T2 as these only interrupt power when the thermostat is dialed to *OFF*




Correct, but OP wants that capability. After all, the existing 1-pole thermostats _already_ can be turned down to 45F or whatever. OP wants a hard-off. 

There is nothing wrong with wiring it so the two poles are in series. Least, it gives you more interrupt capacity. 



> To the OP for educational purposes. 240 line voltage thermostats that have an *OFF* position on the dial open both contacts when dialed to OFF. When controlling temperature, only one contact is cycled.


Are you *entirely sure* the thermostatically controlled leg also has a hard mechanical shutoff in the OFF position? If the knob were OFF and the room chilled to 30 degrees, are you sure the thermostatic side wouldn't close? That would surprise me; thermostats are not maintenance disconnects.


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