Just read some info. on Metal Oxide Varisters (MOV's) recommending a fuse must be installed with a MOV to prevent fires.

 

"It's crucial to include a fuse in series with the MOV. If the MOV experiences a short circuit due to a surge, the fuse will blow, preventing further damage to the circuit." Ai.

Yup, give them a fuse or breaker, particularly those on the mains supply.

 

They do (mostly) have internal overheat protection but a fuse or breaker guarantees safety.

 

The problem is that each time they absorb a surge the trigger voltage goes DOWN slightly. Eventually they are triggering on the normal supply voltage and can generat a LOT of heat.

 

In addition to what Crossy said.

The saying that lightning never strikes twice is not quite true.

The following is what you need a fuse for:

Nearby lightning strike generates EMP which causes MOV to degrade a bit.

Next strike a few seconds later the EMP may ignore the MOV and start partying around the electrics.

The fuse will blow and stop the second EMP pulse doing damage.

If the fuse does blow then it would be sensible to replace the MOV at the same time as it would have been stressed to a greater or lesser degree..