On 2006-10-18, Bob in Phx wrote:
But for now I was wondering if an externally powered circuit could be built

It's called a "thermal cutout" (or self-resetting thermal fuse) it's a little
thing with a flat surface that you mount in contact with the equipment to be
monitored and two terminals that you wire in series with the mains.

eg: jaycar.com.au catalogue number 3823


Bye.
Jasen