Since it is used the receiving it is only rated at 300v. I'd be concerned
about transmitting with high power or a high SWR.
That is NOT the voltage breakdown of the coax from center to shield. That is
some a wiring class voltage, similar to the jacket punch through to a bare
external conductor.
If you take regular foam dielectric "RG6" (which is almost never a real RG6
style) cable and strip back the end, and high pot the cable, the center to
shield dielectric breakdown of cable with a flaw is over 12 kV.
The weakest points, by far, will be the ends. That is where it is just an
air gap with no dielectric. The breakdown there will depend on the connector
style, but is typically a few kV for a properly installed F fitting.
If you obtain cable with internal manufacturing flaws, like a center
conductor that has seriously migrated off to the side, an air gap in the
insulation, or a powdered area where the foam didn't form, the voltage will
be considerably lower.
I test all of my cables with high voltage. A properly installed UHF
connector, on ANY type of RG8X through LMR400 or RG8 cables, will high pot
over 4-5kV. That will be the air gap voltage in the connector. If you get
just one little sharp shield strand near the center, that voltage can drop
to 1000 volts or less.
A typical RG8X cable, even foam dielectric, will high pot to 10 kV or more.
8X is typically less than "F6" (RG6) type cables, because the internal
spacing is less, but still more than the connector.
The worse connectors are BNC, F, and type N. Type HN and others, including
UHF, are far more.
Anyone looking at cable advertised voltage ratings for power is making a
mistake. With a reasonable SWR, other than connector voltage failures, the
issue will always be heating.
In intermittent duty, I certainly wouldn't worry about RG6 type cables at
1500 watts below ~15 MHz.
73 Tom
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