On Nov 21, 9:22*pm, (Doug Miller) wrote:


Have you checked the rating plate on the heater to make sure it really is a
240V heater? Sounds more to me like it's a 120V unit connected to a 240V
circuit, which of course would explain the instant breaker trip.

That's a reasonable guess, but I didn't supply all the information.
The house is from 1960 with no changes.

And I'm not sure that would have to trip the breaker immediately.
That would double the amps, but 8.6 doubled is only 17.2, within the
breaker rating and the 22 amp thermostat rating. I think it would
overheat and trip something in short order, but not instantly.

No, something either goes to ground or shorts hot to hot the instant
the stat makes.

Or something is wrong in the breaker panel. But it's not obvious to
me what that could be. Or why a fuse did not trip but a breaker
does.