RE: X-ray HV cables

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Carl Litton" <Carl_Litton@xxxxxxxxxx>

Mike,

We remove all coverings (outer insulation, braided mesh, and plastic
semi-conducting layer) for the entire length of the stripping (8" in
your case), leaving only the rubber inner core insulation exposed.  At
the point 8 inches back where these layers were cut off, we cover the
frayed end of the braided shield and about 2 inches in either direction
with 2 layers of rubber tape followed by a layer of regular plastic
electrical tape.

I will post some photos of properly prepared cable on the site for you.

Hope this helps.

Carl



-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Saturday, November 05, 2005 1:37 PM
To: tesla@xxxxxxxxxx
Subject: Re: X-ray HV cables

Original poster: "MIKE HARDY" <MHARDY@xxxxxxxxxx>


----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Wednesday, November 02, 2005 2:51 PM
Subject: RE: X-ray HV cables


 > Original poster: "Carl Litton" <Carl_Litton@xxxxxxxxxx>
 >
 > Hello Mike,
 >
 > At lower voltages (below 30 kV), you will be fine if you remove all
 > coverings down to the thick rubber layer for 8 " back and then strip
and
 > combine the center conductors.  We use a few layers of rubber
splicing
 > tape followed by electrical tape over the raw ends of the shielding
 > material that has been stripped back.  The two insulated center
 > conductors should have their insulation removed and the strands of
all 3
 > conductors twisted together and soldered.
 >
Are you saying cover the entire 'black shield with rubber tape, or just
a
few inches
where it starts?


 > I am curious about the 150 kV cable and where you obtained it - I
would
 > love to get some!  Standard x-ray cabling is rated for 75 kV DC and
must
 > be derated considerably for AC use.
 >
I think other replies to this comment were correct. It's probably 75KV.
I
assumed it was 150 because the max potential on our xray equipment is
150 KV.

 > We make extensive use of the 75 kV cable in our group projects.  At
 > higher voltages (100 to 250 kVAC), with the cable laying on the
ground
 > and coverings stripped back 18", the current will arc completely
through
 > the insulation directly into the ground quite readily, necessitating
 > frequent repairs.  Up to about 150 kVAC, this may be prevented by
 > keeping the cables off of the ground on non-conductive supports.  We
 > have used it at higher voltages (up to around a quarter Megavolt) by
 > running the cable through an outer jacket of heavy wall 1-1/4" I.D.
 > vinyl tubing and/or inside of PVC pipe.
 >
 > We just had to go through all of this for our Halloween Jacob's
Ladder
 > running at 215,000 VAC.   Here is a not-so-good PowerPoint slide show
of
 > it operating at about 175,000 volts using standard 75 kV rated x-ray
 > cable prepared as above with 18" stripping on both ends and run
through
 > PVC for the greater part of the run:
 >
 > http://www.dawntreader.net/hvgroup/ladder.ppt
 >
 >
 > Good luck!
 >
 >
 > Carl
 >
 >
 > -----Original Message-----
 > From: Tesla list [mailto:tesla@xxxxxxxxxx]
 > Sent: Wednesday, November 02, 2005 9:45 AM
 > To: tesla@xxxxxxxxxx
 > Subject: Re: X-ray HV cables
 >
 > Original poster: "MIKE HARDY" <MHARDY@xxxxxxxxxx>
 >
 > I'll answer my own inquiry. On the surface of this remaining HV cable
is
 > a
 > black hard plastic covering about 0.5 Mil thick. Then about 3/8 " red
 > rubber-like insulation, and the center conductors. Seems the black
 > plastic
 > is what's conductive. I sanded off the black plastic, down to the
red.
 > The
 > red doesn't conduct. If I remove say 8" of this black coating on each
 > end,
 > do you think I'll be alright? Will this conductive "shield" cause the
 > same
 > kind of  capacitive resonance problems a true braded shield might. I
 > don't
 > intend to ground anything, however the cables will be laying on the
 > ground.
 > ----- Original Message -----
 > From: "Tesla list" <tesla@xxxxxxxxxx>
 > To: <tesla@xxxxxxxxxx>
 > Sent: Tuesday, November 01, 2005 1:52 PM
 > Subject: X-ray HV cables
 >
 >
 >   > Original poster: "MIKE HARDY" <MHARDY@xxxxxxxxxx>
 >   >
 >   > I got a 150 KV rated xray HV cable. Per D.C.'s recomendations, I
 >   > stripped the outer jacket, removed the braded shield, and cut off
the
 >   > 'candlestick' ends. I then reterminated to acomadate the
connections
 >   > as I needed. The outer jacket (what was under the shield CONDUCTS
!!
 >   > It nicely shorted the hv output of my PT! What's going on here?
Is
 >   > this normal? I placed the hv leads of a 15kv nst at 2 points on
the
 >   > insulation away from the conductor, and it happilly arced! Any
 >   > thoughts would be apreciated.
 >   >
 >   >
 >
 >