"Gary Schafer" wrote
What isolates the shield of the coax from carrying current?
As long as it is connected to the tower at one end it is going to have
strike current on it whether you want it there or not. Nothing you can
do about it. Paralleling other conductors will reduce it's total
current but you still have to deal with it on the coax line.

Incorrect. First, a strike termination device is placed higher than other
equipment with its own down conductor. Then a lightning arrestor and shield
bonding are specified at the top of the tower, shield bonding along the path
(up to three times) and at the bottom, then more shield grounding and
another lightning arrestor at the facility entrance.

If you don't want to call the coax shield a grounding conductor that's
ok but that won't stop the current on it.

Current is maintained at a safe level on the coax center conductor and
shielding by the above.

Who told you that you should put lightning protectors at the tower as
well as at the building entrance? What good do you think they do at
the tower other than cost more money?

National telecommunication companies who specify them in white papers and
engineering plans for lightning protection. I have been studying these
systems for 18 months now and find this procedure consistently applied. The
specific information is proprietary but all I had to do was ask for it. I
found the information available via the USAF and other agencies I normally
deal with was somewhat old, so I started asking commercial companies what
they currently use, and could I have copies of their plans. That's where
this information comes from. That and the National Electrical Code and
National Fire Protection Association, October 2004 editions. Studying the
NEC 250 grounding and bonding and the NFPA-780 offers more information to
safely operate communication sequipment, especially during thunderstorms,
than all the amatuer radio operators advice put together. Most of the
amatuers giving this advice have no personal understanding of why or how
this works, they just repeat stories or instructions they heard from someone
else. Probably the biggest collection of dangerous information ever shared
is what hams offer about lightning protection. Even the ARRL which makes an
incredible effort to educate at the issue, has information so old in many
cases it has not been used in best available practice for over ten years.

With buried coax the ground acts like a large choke on the cable also.
Exactly what you want. The ground increases the cables natural
inductance.
/clipped

Your mistaken on this stuff Gary, we either shed or prevent lightning energy
from coax by shield grounding, surge protection devices and sometimes
encasement in grounded conduit. No plan or specification calls for
earth-burying coax to deliver what you promise, and I believe your theory is
electrically impossible, unless as I said over and over, the dialectric
breakdown occurs, which means the installation was improper in the first
place, or overcome by statistically rare events.

73,
Jack Painter
Virginia Beach VA