Above picture is that of a Belden surge protector with some kind of cloth covered over the MOV and thermal fuse for isolation to promote more conduction. I don't want to cover the whole thing with compound but something akin to cloth or other cover.. do you know what kind of cloth can't burn? or what more solid cover I can put that won't conduct and short the other elements? What do others use?
I'm designing a circuit and want to embed MOVs (Metal Oxide Varistors). I'd like to know two things:
I'm thinking of adding a thermal fuse. I read that the basic purpose of them is for temporary overvoltage (TOV) event when they can open before the MOV gets so hot and at end of life stage (where the MCOV kept decreasing gradually from each surge until it conducts at normal voltage initiating thermal runaway). But how about in actual surges.. if the MOV is rated at 3kA and you have a surge that is, say, 50kA, would it make the MOV initiate thermal runaway or not? How big should surges be compared to the MOV surge current rating before thermal runaway (bursting into flame) can occur?
Normal design is to put the thermal fuse beside the MOV. But does it depend on ambient temperature? If the room is cold with aircon.. can it prevent the thermal fuse from working?