What's the Voltage Rating of an RG8-U Coaxial Cable?

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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.

High Voltage Power Supply Mission

The mission of this blog is to, from time to time, update this space with real world information as it relates to the daily and common use of high voltage power supply and supplies in our daily lives. For example, they are used in airport security scanners, xray machines, food and produce scanning devices and even the Genome Project!

When dealing with high voltage power and high voltage power supplies, it is most important that safety be given supreme and detailed attention. With this in mind, the first post will be on safety as it relates to high voltage power and will reference written material supplied by Spellman High Voltage Electronics Corporation:

What is a safe level of high voltage?

Safety is absolutely paramount in every aspect of Spellman's high voltage endeavors. To provide the maximum margin of safety to Spellman's employees and customers alike, we take the stand that there is no "safe" level of high voltage. Using this guideline, we treat every situation that may have any possible high voltage potential associated with it as a hazardous, life threatening condition. We strongly recommend the use of interlocked high voltage Faraday Cages or enclosures, the interlocking of all high voltage access panels, the use of ground sticks to discharge any source of high voltage, the use of external interlock circuitry, and the prudent avoidance of any point that could have the slightest chance of being energized to a high voltage potential. The rigorous enforcement of comprehensive and consistent safety practices is the best method of ensuring user safety.