According to Speedy Jim :
Filipo wrote:
(Chris Lewis) wrote in message
...:
I always use 2 pole for 220V.

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?

Chance? Yes, but extremely remote (assumes for example, circuit is otherwise
miswired, heater malfunctions). Significant enough to pay a bit extra?
That's something only you can answer.

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.

I kill the breakers to all the heaters regardless. Saves money if
a T-stat gets accidentally fiddled or fails on. Makes winter startup
a distinct process of cleaning them, turning them on, and
checking them all at once.

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.

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.

Notice how that's "one family"? It's one of those exemptions specifically
intended to lower the cost of wiring in the least risky environment.
[Even tho in many cases it makes no difference to the cost of the device,
and only a slight difference in labour.]

Notice how that doesn't apply to commercial, industrial, or multi-person
dwellings. There's a strong hint there.

Obviously, the NEC has made a tradeoff judgement here. The question is, do you
agree with their judgement for _your_ specific circumstances?

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

Aye, there's the rub ... some people don't. It really shouldn't
be hinted that _not_ turning off the breaker before working on a
circuit is acceptable practise.

I personally prefer exceeding code as far as is practical. So
if I stupidly forget to switch off the breaker, or something else
like the thermostat contacts sticking, then I don't find out the hard way.

When the cost difference is minor (or non-existant), as there would be
with, say, just one T-stat to buy, there's no contest - 2 pole it is.

If I already had a single-pole T-stat, I likely would decide to use
2 pole. But if I had three? Probably not.

If I was wiring whole subdivisions, I almost certainly wouldn't bother with
two pole.

Etc.