Actually Gary, what you say would be true in theory, but for the mortal
character of wire resistance. That is what allowed the surge to come
down the coax shield, (low R) and travel thru the coax connector, (low
R, to the circuit board traces to the power leads (higher R) and then
out the power negative (medium R) to the Astron negative terminal that
was tied to its case (higher R), which was also tied to the 3rd pin AC
ground wire (Highest R).
Enough current was dissipated at each of the changes of wire/ conductor
gauge, to burn out components in the Astron; and in the rig, it
vaporized a section of circuit trace.
Yes, in theory, you bond all grounds (outside the shack). In practice,
if you have coax in parallel with a Chassis ground braid wire and AC
third pin wire, you may have a failure, if you also have a high
resistance crossing of AC and DC grounds inside the equipment. The
change of gauges of the conductors was the resistance choke point for
the surge.
This same surge took out the top of a power pole across a parking lot
from the shack. Apparently a two stroke leader from the main lightning
event! The pole was toothpicks down to the guy wire, which grounded out
the stroke, since it was larger and lower R than the copper pole ground
wire.
AC grounds, antenna coaxes, and phone and internet ground connections
should all bond outside the building per NEC electrical code. There
should be a metal entry panel with surge devices grounded to the
perimeter ground conductor placed to protect the whole building. Even
this will not prevent some damage but mitigates most lightning events to
radio and TV stations. Their towers are designed to take hits and come
right back on the air in most cases. Their feedline gauge and element
diameters are typically much larger than ham grade antennas and towers
and feeds to enable this.
-Stuart Rohre
K5KVH
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