Maximum fuse rating before a MOV (varistor)
Commonly, for example in multiple outlet powerboards that include a MOV for surge protection, a thermal fuse is also used.

The thermal fuse is in contact with the body of the MOV.
When the MOV starts to fail, its power dissipation and temperature increases, and the thermal fuse opens in that case.

Often, an indicator LED shows that the thermal fuse is OK. When it goes out, it means that MOV has failed, the thermal fuse has blown, and surge protection is no longer available.