1 pole thermostat vs 2 pole thermostat

[marmathsen]

I should probably preface by saying that I'm a residential electrician and my question pertains to residential specifically, but is probably relevant to other types of work as well.

I have always taken the approach that a 240V 2 pole heater justifies a 2 pole thermostat. However I almost never see 2 pole thermostats when I'm working on existing work performed by previous electricians, and by far more frequently see single pole thermostats controlling 2 pole heaters. Why is this allowed? I have tried to dig up something concrete in the NEC but haven't been able to find what I'm looking for.

I would love some input on the mater and in particular a code article that pertains to this.

Thanks in advance.

Rob

 

[Andy Delle]

Well a few years ago they started putting single pole contractors in single phase 240v HVAC condensers. And the unit (Goodman) was UL listed too. I guess they don't consider the contractor or thermostat in your situation a disconnecting means. So in that case it doesn't need to open all live conductors?

I still think it's somewhat dangerous for service people.

 

[jumper]

You only need to break one hot conductor to control the 240V load.

A T stat that does this though cannot qualify as the disconnecting means. 424.20

 

[infinity]

You can use the single pole to control the heater but it does not qualify as a disconnecting means.

424.20(B) Thermostats That Do Not Directly Interrupt All
Ungrounded Conductors. Thermostats that do not directly
interrupt all ungrounded conductors and thermostats that
operate remote-control circuits shall not be required to meet
the requirements of 424.20(A). These devices shall not be
permitted as the disconnecting means.

 

[mbrooke]

Agree with the above. On a straight 240 volt load you only need to break one hot conductor for single phase, 2 conductors for 3 phase.

 

[LarryFine]

Some t-stats have one pole that operates to maintain temperature, and a second that only opens at full off.

 

[JFletcher]

I dont remember the exact section (410.xx) but some 240V lights must use a double pole switch. iirc it's ones with two ungrounded conductors and double end lampholders like for quartz halogen bulbs.

Heaters just break one leg to control the unit, whereas lights may very well get changed out with just the switch off, but idk the exact reasoning of the code.

 

[jumper]

I dont remember the exact section (410.xx) but some 240V lights must use a double pole switch. iirc it's ones with two ungrounded conductors and double end lampholders like for quartz halogen bulbs.

I will take 410.93 for $100 Alex.

 

[marmathsen]

Thanks for all the quick responses. The code references were spot on.

So essentially in most of the applications I come across (wall radiant, floor radiant, small squirrel cage in-wall heaters, etc.) I can use a 1 pole thermostat on a 240 v heater but would need a lock out device. Or alternatively I could use a 2 pole thermostat with an off position and wouldn't need a lockout device.

Rob

 

[electrofelon]

I dont remember the exact section (410.xx) but some 240V lights must use a double pole switch. iirc it's ones with two ungrounded conductors and double end lampholders like for quartz halogen bulbs.

Heaters just break one leg to control the unit, whereas lights may very well get changed out with just the switch off, but idk the exact reasoning of the code.

I will take 410.93 for $100 Alex.

And 410.104(B). Not sure why electric discharge lamps supplied by 240V (or two ungrounded conductors to be precise) need a double pole switch, but LED and incandescent do not (unless its a lampholder as covered under jumper's 410.93).