[Amps] RG8-U for HV cable

[Will Matney <craxd1@ezwv.com>]

While reading an add I received, I visited Spellman's website and found 
this interesting. It involves using RG8-U cable as a high voltage supply 
cable for remote power supplies up to 8KV. Spellman manufacturers 
supplies for X-Ray equipment, etc.. If I recall, a while back, someone 
was interested in doing this. Below is a quote from their website.

Will Matney

*AN-07* Application Note
What's the voltage rating of RG8-U coaxial cable?

Output cable and connectors are not trivial items for power supplies 
where output voltages can be 100,000 volts or higher. The cables and 
connectors used must function together as a system to safely and 
reliably access and provide the power supplies output for customer usage.

In many high voltage power supply applications, a shielded polyethylene 
coaxial cable is used. Polyethylene cables provide excellent high 
voltage dielectric isolation characteristics in a small but robust form 
factor. The shield conductor provided in a coaxial cable functions as a 
"Faraday Shield" for the center conductor of the cable that is 
referenced to the high voltage potential. If any breakdown in the main 
insulator occurs, the high voltage current will be bypassed to the 
grounded shield conductor that surrounds the main insulator. This 
inherent safety feature is one benefit of using a coaxial high voltage 
output cable.

RG8-U has long been used as a high voltage output cable in the high 
voltage industry. There is a variation of RG8-U that utilizes a solid 
polyethylene core. Specifications for this cable do not specify actual 
"high voltage" ratings, since this cable was not designed and fabricated 
with high voltage usage in mind. So the reality is, there are no high 
voltage ratings for RG8-U. Over the years others in the HV industry have 
used this cable at 20kV, 30kV and even higher voltages. Spellman does 
use RG8-U cable, but limits it usage to applications where the maximum 
voltage that will be applied to the cable is 8kV or less.

For voltages above 8kV where a coaxial polyethylene cable is desired, 
Spellman uses cables specifically designed and manufactured for high 
voltage usage.

These cables are of the same general design; as described above but the 
insulating core material diameter has been increased appropriately to 
obtain the desired dielectric insulating capability required. Frequently 
higher voltage versions of these cables utilize a thin semiconductor 
"corona shield". This corona shield is located between the metallic 
center conductor and the main polyethylene insulating core. This corona 
shield helps equalize the geometric voltage gradients of the conductor 
and by doing so reduces the generation of corona.

A high voltage cable and connector system can only be as good as the 
materials used to make it. Using cables that are designed, specified and 
tested specifically for high voltage usage assures that these materials 
are used within their design guidelines.

http://www.spellmanhv.com/tech/app_an07.asp
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