[Amps] HV Fuses

[Fuqua, Bill L]

If I recall the fusing current for a #30 wire is about 10 amps continuous current.
Eimac suggest that a #30 wire in series with the plate of a tube survives a discaharge the tube would not be damaged. 
This is from  an application note on construction and testing of crowbar circuits.

   I have thought a #30 wire or somewhat smaller wire was stretched inside a grounded piece of copper
pipe  such that there would be no discharge when HV was applied would be a great fuse. This is because if 
an arc in the tube  would vaporize the wire and producing a plasma that would short the B+ to 
ground via the surrounding copper tube or pipe.  Also, it would be easy to replace.

73
Bill wa4lav

________________________________________
From: amps-bounces at contesting.com [amps-bounces at contesting.com] On Behalf Of K1SG at aol.com [K1SG at aol.com]
Sent: Tuesday, February 16, 2010 6:59 PM
To: amps at contesting.com
Subject: [Amps] HV Fuses

In recent threads, there have been a number of comments about high voltage
fuses.
Carl mentioned sand-filled fuses, something I hadn't heard of.
I checked the Mouser catalog for HV fuses, and was stricken with
sticker-shock...$38 for a fuse?
OK, we re-think this one...
I know that an old but workable approach is  to use  a thin piece of wire
as a fuse...mount it between a couple of  standoff insulators, and it should
function fine, and if current is  substantially too high, the fuse wire
blows. How do you figure the appropriate  size wire to use? And then, how do you
go about ordering 6" of #30 wire, or  whatever it is? If you need more
current capacity, to use the above example, can  I put two strands of #30 wire
in parallel, and expect them to function as a  reliable fuse?  I'm always
worried about kinking the wire, or if it's  enameled, sanding off more than
just the insulation.
The plan is to fuse the HV output of a 5KV 2A supply to a 3X3, which of
course will only be used at the legal limit or into a dummy load.

Steve  Gilbert
K1SG
K1SG at AOL.com
508-435-9133
FN42fe


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