Question regarding fuses
Thermal fuse:
Goes open circuit when the temperature reaches a certain value. Comes in non-resettable and resettable varieties.
MOV (Metal-Oxide Varistor):
This is not a fuse at all. It is a device that begins to conduct when the voltage across it exceeds a certain value. MOVs are used to absorb high-voltage pulses, hopefully for long enough to blow a upstream fuse or circuit breaker.  

If you don't have a fuse or circuit breaker upstream from the MOV, you usually get a fire.
Polyfuse:
A Polyfuse is a self-resetting fuse. Basically, the way they work, when you have a certain amount of current flowing though a polyfuse, it goes open circuit for a period of time.

Generally, they're thermal in mechanism. Once they heat up to a certain point, their resistance increases dramatically. Then, they stay high-impedance until their temperature decays back again.




Anything else, and we'll need more information about your application. It sounds like you're in a bit over your head.