Rich said:
>HV fuses normally contain silica sand to quench the metal vapor arc.
Asbestos powder has also been used in the past, but not these days. The
filling is called 'anti rupture powder': the idea is to keep the fuse wire
intact although molten until it reaches a sufficiently high temperature to
explode apart. It's not just used in high voltage fuses, either, but where
you need a high fault current interruption capability. Interesting subject,
fuses.
Personally, I've found that suitable thin wire between two ceramic
insulators is quite adequate: insulator about 4 inches apart and the wire
not too tight between them, and about 42awg. In the event of an arc (and I
also use a 50 ohm, 100 watt, 12 inch long wirewound glitch resistor) the
wire just disappears. Of course, you need to allow plenty of clearance
around the insulators: I have 4 inch high insulators mounted horizontally
so the wire falls away from them, although teh few occasions it has failed,
I've never found enough signs of any wire to judge where it did go.
73
Peter G3RZP
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