On 5/9/2013 11:57 AM, Don Wilhelm wrote:
Option 2 only.
In fact, if you want to make it even better, run a #6 copper wire all
around the perimeter of the house with a driven ground rod anywhere it
makes a turn more than 30 degrees. That perimeter wire provides a
path for lightning instead of allowing it to punch a hole in your
building foundation.
I would also suggest at least 3 radial wires from the tower (length at
least 1/2 the tower height) with driven ground rods spaced twice the
length of the ground rod.
I like this advice, BUT -- also make sure that ALL other grounds are
also bonded to this ground. That includes the common connection of all
the gear in your shack (which should have a bond from one chassis to
another for each piece of gear), the antenna entry point, cable TV
system, telephone system, cold water (it it's metallic), structural
steel if there is any, and the green wires for all the outlets in your
shack.
A quibble though -- the "green wires" for all the outlets must be bonded
to the enclosure of the main breaker panel, and they MUST be connected
to your gear via the power cord. That combination of wires IS a
connection through the house, although it's not a very good one, both
because the conductors are small and they're long, so they're inductive.
SO -- my advice, and what I've done in MY shack (where power is on one
side of the building and the shack is on the other), is to do BOTH the
perimeter wire (#4) with rods at multiple points along the run, and
bonding the steel conduit (EMT) that carries wiring for the shack to the
operating desk common point, and to the coax entry point.
The fundamental concept is that you want to provide a robust, short path
to earth for the strike (which can come in on your antennas, the tower,
a phone line, a CATV cable, the power line, and even the wiring inside
your home), and for everything in your premises to stay as close to the
same potential as possible. To accomplish that, you want multiple paths
to earth (ideally close to every entry point), and the lowest possible
IMPEDANCE between everything in the premises, with conductors large
enough that they can carry as much current as practical before they
melt. :) Because lightning is an RF event, with a very broad energy
peak around 1 MHz, the impedance is mainly INDUCTANCE, not resistance,
which is why "short" matters, and why more parallel inductors are better
than one.
73, Jim K9YC
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