RE: X-ray HV cables

["Tesla list" <tesla@xxxxxxxxxx>]

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.

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.

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.
 >
 >