On Mar 22, 12:17*am, "Phil Allison" wrote:
"Tony Hwang"

I understand they work on bi-metal strips.

** Nope - *that is a temperature switch.

Thermal fuses like this one use the melting point of some material and rely
on a spring to open the circuit.

But I assume the same applies. The metal heats up and expands somewhat
when in use and contracts when not. That will eventually cause it to
fail.