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Re: HV wiring
Tesla List wrote:
>
> Original Poster: "Coiler" <mycroft-at-access1-dot-net>
>
> Jim: see comments below, and note to readers: Major snippage was done.
>
> Michael Baumann
> Coiler, Homebrewer, Nerd. mycroft-at-access1-dot-net
>
> >
> > Original Poster: Jim Lux <jimlux-at-jpl.nasa.gov>
> >
> > Tesla List wrote:
> > >
> > > Original Poster: "Kent & Kim Schaffer" <santoken-at-bright-dot-net>
> > >
> >> Neon Sign Wire (GTO-15) a polyethylene jacket on a 14 ga stranded
> > copper wire.
> > RG 58/59 (if, and
> > only if the dielectric is a clear plastic and not white (the white is
> > actually foam) works fine for Neon Sign transformer voltages, the
> > thicker RG-8, RG-213, RG-11, etc. (about 1/2 inch in diam) works up to
> > around 30-50 kV.
> You left out what is rare, but great. Surplus X-Ray system wire. I managed
> to luck into about 200ft of 250KV rated cable. Not really sure what the
> dielectric is - appears to be an inner core of silicone, with a 1/2" thick
> rubber outer wrapping. I can still pick up a healthy electrostatic field
> at 14.4KV 60hz
Of course, yes, real HV cable would be nice.. It typically has the
semiconducting layer next to the HV lead which makes the effective
diameter larger to reduce the field strength and the corona.
> >
> > I personally leave the shield on coax and ground it.
> Interesting.. I have been warned against this, and actually have seen
> where this is a major problem on our synchrotron. Basically, you've just
> built the mother of all caps. I know that with my xray cable, I got
> surprising large arcs across the output end until I stripped the braid
and the
> semiconductor tape off.
Arcs from the center to the shield? Not surprising. I find that I have
to strip the shield back several inches to prevent surface arcing at 30
kV. You're not going to be able to use an unmodified PL-259 connector
with the stuff, anyway.
> We did have one guy get kicked on his butt by a
> 3KV 200nA power supply for an ion chamber. The bozo did not de-energize
> the power supply before disconnecting from the chamber to re-terminate,
> and left it lying out there. It bit hard when he went touched it as it
> was close to 400ft long. Big cap.
If the cable was 30 pF/ft, its only about .05 Joule.. Enough to make you
jump.. About like getting shocked by an automobile sparkplug wire.
However, if there was any storage in the power supply.....
Well.... if you leave the cap charged up you sort of get what you
deserve. I presume that the HV leads have some sort of high impedance
bleeder to ground, and that the shield was actually grounded. Of
course, RG-8 is only about 30pf/Ft, so even 100 ft is going to be 3 nF,
and at 25 kV, that is about a joule, which would sting, but probably not
kill you. At 50 kV and a couple of hundred feed, you're looking at a
real problem.
> >