# Single Pole vs. Double Pole Thermostat



## dforeid (Oct 17, 2008)

Any ideas???


----------



## kbsparky (Sep 11, 2008)

Double pole line voltage thermostats have an "off" position, which can also act as a disconnecting means for your heater units.

Single pole stats do not, and cannot be turned "off" but only "down"

You can use either to control individual heating units in your house.


----------



## HandyPete (Mar 23, 2008)

hey KB! 40 years in this business and I still didn't know why the two types existed or the difference between the two! I only do industrial and have a really limited knowledge on residential. (which I only do in my own home)

So, thanks


----------



## jerryh3 (Dec 10, 2007)

HandyPete said:


> hey KB! 40 years in this business and I still didn't know why the two types existed or the difference between the two! I only do industrial and have a really limited knowledge on residential. (which I only do in my own home)
> 
> So, thanks


I was just thinking that. What's the advantage in opening one leg vs. both? The only disconnecting means I would trust if working on the heaters would be the breakers.


----------



## kbsparky (Sep 11, 2008)

There are some cases where the circuit breaker is not readily accessible (such as in certain multi-family units, or hotels, etc) and the use of a DPST thermostat satisfies the disconnect requirements of 424.19.

It is interesting to note that most double-pole thermostats only interrupt one pole of the circuit during its normal mode of operation. 

Turning it all the way down to "off" is the only way to interrupt both circuit conductors in most cases.

IF you want to use a DPST thermostat in a single pole configuration, then you have to wire both poles in series, to ensure proper interruption of the circuit when the desired temperature is reached. Otherwise, the heater may operate continuously even after the set point has been reached. :furious:


----------



## Papa Smoke (Aug 5, 2012)

I have been considering this DPST vs SPST dilemma for a while. In my home I have ONE room which would require a DPST thermostat since it has two heating runs (radiant ceiling) in the plaster. The rest of the rooms are SPST. Here is what I have:









I have a BUNCH of new Honeywell programmable thermostats. Their wiring diagram is as such:









Is there any way I can safely & to code wire these units into the existing boxes (shown above)?

Thanks for any help. I desperately need to save $$$ this year.


----------



## electures (Dec 22, 2009)

WHat are the specs on the t-stat? Is it rated for 240V?


----------



## Papa Smoke (Aug 5, 2012)

Power supply: 240/208 VAC 50/60 Hz
Max load 15.0 A (3600 W @ 240V, 3120 W @ 208V)

The breakers are all double.


----------



## Speedy Petey (Feb 1, 2004)

You have to pull the spliced whites out of the box and separate them. Cap everything off, turn on the breaker and test to see what pair is your 240v LINE. Turn them off again and install your thermostat according to the instructions.

In your pic they are using a SP t-stat for a 240v load like they discussed long ago earlier in this thread.


----------



## Speedy Petey (Feb 1, 2004)

Papa Smoke said:


> In my home I have ONE room which would require a DPST thermostat since it has two heating runs (radiant ceiling) in the plaster.


The number of heaters on the circuit is irrelevant. Other factors determine if a SP or DP can or should be used.


----------



## AllanJ (Nov 24, 2007)

kbsparky said:


> It is interesting to note that most double-pole thermostats only interrupt one pole of the circuit during its normal mode of operation.
> 
> Turning it all the way down to "off" is the only way to interrupt both circuit conductors in most cases.s:


This is because the two poles do not always turn on together at the same temperature or turn off together at the same temperature.

Occasionally a double pole line voltage thermostat is found controling one side of each of two heater feeds because they are on different branch circuits or the total heater wattage exceeds the wattage rating of one switch pole.


----------



## Papa Smoke (Aug 5, 2012)

Speedy Petey - 

I tried wiring THIS way:









and get nothing.

You have to look at the drawing a bit on the close side but it can be made out.

On both sides of the word POWER, I have labeled the wires coming from the breaker as 240V Black & 240V white. (They ARE 240V). I ran them to the two INNER wires of the t-stat...black to black & white to red.

I then ran the two load (outer) wires from the T-stat to the LOAD wires going to the ceiling heat. Black to black & red to white. 

I do get power but the t-stat does nothing. It didn't spark or turn on. 

Thoughts?


----------



## AllanJ (Nov 24, 2007)

Papa Smoke said:


> Speedy Petey -
> 
> I tried wiring THIS way:
> 
> ...


Do you get 240 volts between the two load wires when the thermostat knob is turned all the way clockwise, and zero volts between the two load wires when the knob is turned all the way counterclockwise?


----------



## Papa Smoke (Aug 5, 2012)

Yes. It does just that.


----------

