Line Voltage Thermostat

[A/A Fuel GTX]

Regarding 240V baseboard heaters, I normally use a double pole thermostat to open both lines when the set point is satisfied. I am facing a situation where the load would exceed the thermostat's rating if wired as described above. My question is, in a situation where the heating load is 8kw@240V which would translate to 33.33A, could I use a double pole thermostat rated at 25A and bring two circuits in and just break one leg of each circuit through the thermostat? One problem I can see is that I would have one thermostat being fed from two double pole breakers and I wonder if 210.4 (B) would prohibit this installation? Secondly, is it legal to break just one side of a 240V circuit as described above?

 

[ptonsparky]

Breaking just 1 leg of a circuit that pulls 33 amps will not save a thermostat that is designed for a max of 25. The load thru it will still be 33 amps. We use a contactor(s) controled by the thermostat for this type of application. Yes, switching one line is OK for control purposes but not if the thermostat is being used as a disconnecting means.

 

[A/A Fuel GTX]

Actually, breaking one line of a circuit that pulls 4KW would only be a load of 17A. What I meant to say was if I take a load of 8kw, break it down to 2ea loads of 4kw each and run the entire load through a single double pole thermostat but only breaking one line of each circuit through each pole of the thermostat.

 

[electricman2]

As I understand the OP, he was going to use the thermostat to break one side of half the load or about 17A. The answer is use contactors as Tom said.

 

[A/A Fuel GTX]

Yes, switching one line is OK for control purposes but not if the thermostat is being used as a disconnecting means.

Would the OCPD be acceptable as the disconnecting means if it were in another area of the building?

 

[LarryFine]

My question is, in a situation where the heating load is 8kw@240V which would translate to 33.33A, could I use a double pole thermostat rated at 25A and bring two circuits in and just break one leg of each circuit through the thermostat?

It won't work anyway. 2-pole T-stats only open one line for temperature control. The second line opens only during 'off' operation.

 

[A/A Fuel GTX]

Good point, Larry....I'll just go with the contactor controlled by the stat....