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Re: RG-58 core as high voltage wire? (fwd)
---------- Forwarded message ----------
Date: Thu, 15 Jan 1998 14:27:49 -0700
From: Bill Lemieux <gomez-at-netherworld-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: RG-58 core as high voltage wire? (fwd)
Alfred C. Erpe wrote:
> If you strip off the outer insulation, and braid immediately under it,
> from a standard RG-58 coax cable, you're left with an inner core of 20 ga
> wire surrounded by .042 thickness of plastic insulation. I don't know what
> type of plastic this is,
The solid stuff is polyethylene, usually. I don't know what the foam
core stuff
is.
> but most plastics have a dielectric strength of
> around 400-500volts /.001 inch. So it seems to me that this remaining core
> would be good for up to 16,000 volts DC or maybe 8000 volts AC.
Folks, don't forget that volts/mil ratings are for _one_mil_. It does
_not_ multiply
linearly with added thickness. In other words, .125" of 500v/mil
plastic is NOT good
for 62.5kv! I have seen several different scales for how the voltage
goes up, but they tended to disagree quite a lot. Over a few mills, I
just derate by 400%, ie, divide by 4, for DC voltages. With voltage
reversal, you need to derate by another factor of 2, at least.
Pick up a copy of an Alpha wire catalog or a Newark catalog- their best
RG-58 wire is listed as being good for only a few kv, if you're lucky.
Look for RG-8 with solid poly insulation. I've seen that stuff hold off
15KVAC (60hz)
forever, even in high voltage gradient situations such as where it
passes through a
chassis. In fact, on that stuff, you can leave the shield on, and just
strip it back enough on the ends that it doesn't flash over. (if you
can't leave the shield on a piece of coax, for fear of it breaking
through the core insulation, then it isn't really safe to use it
stripped, is it?)
You can often find "scrap" RG-8 cable at hamfests or at surplus stores.
-Gomez
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