"Larry Fishel" wrote in message
...
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.

That's right; it's "metal fatigue" and those fuses which carry current close
to their limits do wear out faster. I'll also add corrosion. The metal at
the contact points of the fuse corrodes and makes for an intermittent
contact. I had a car once with all kinds of electrical problems -- wouldn't
start, lights flashed, horn didn't work, then it did. Finally replaced all
the fuses and the problems disappeared.

Tomsic