Filipo wrote:

(Chris Lewis) wrote in message ...:

240V has two hot wires (no neutral). Preferably and ideally you should
use two pole thermostats for 240V heaters, so that both hot wires are
simultaneously detached - otherwise, the element would be live even when
the thermostat has the heater turned off. However, most codes do not seem to
insist on that - which has always seemed very odd to me.

I always use 2 pole for 220V.


Thanks, Chris, your explanation is crystal-clear and most
enlightening. Now I can actually visualize a circle where a single
pole circuit resembles a dented egg (only one side broken) while a
double pole circuit resembles a halved egg (both sides sliced through
and broken).

Now here's my problem - I'm stuck with 3 brand-new thermostats that I
have already purchased on-line based on my Internet research - a
2-wire Honeywell CT1950A, a 2-wire Ouellet OTH510, and a 2-wire Aube
Technologies TH106. It seems that in Canada (I'm actually in the US),
they don't make any distinction between single pole and double pole
switches for 240-volt baseboard heaters - they use 2-wire thermostats
intechangeably for both 2-wire and 4-wire applications.

So I'm focusing on your statement that "preferably and ideally ...use
2 pole thermostats... etc." They sound like permissive, not mandatory,
requirements, i.e., I should but I don't have to. I guess my question
is - is there a safety issue if 1 wire remains live in a 240-V
circuit? Since the 2nd wire is disconnected, is there any chance the
live wire could find a way to return to ground and form a complete
circuit? Does this constitute, God forbid, a fire hazard? Given the
new information that you so kindly provided, I'm thinking that maybe
when winter's gone, I'll just go to my breaker panel and turn off the
live feed to all baseboard circuits.

It makes me wonder why thermostat manufacturers continue to market
2-wire thermostats as suited for 240 volt applications, instead of
reserving 2-wire units only for 120 volts and 4-wire units for 240
volts.

Thanks for any additional input.

It's covered in Art. 424-19 (NEC).

Basically, in a one-family house, you are permitted to use a
single-pole (2W) thermostat and then either the branch circuit
(breaker) or the service disconnect (main breaker) serves as
the disconnect for the heater.

So, if you were going to work on the heater, you should
remember to switch off the breaker first...

Jim