6. Divide and Control
Greetings to all;
The following is copied from:
http://lightning-protection-institute.com/lightning-protect.htm
Are ten radials and 80 ground rods absolute requirements? No! The
first rod is the most effective, but is seldom sufficient. More than 80
are of little use. Each added rod and radial improves the system
proportional to the inverse of the total number. In some earths, such
as very dry and rocky earth, rods are not as effective as shallow
radials, enhanced with concrete or other conductive and capacity
increasing materials.
A station requires 3 different ground systems: HF ground, lightning
dissipation ground, and (if AC powered) the power distribution safety
ground. Each is achieved quite differently, and there are variations
depending upon such variables as the antenna used and the nature of the
earth under the station.
The radial system enhances RF grounding, but the ground rods are of
little significance to RF ground. The RF ground serves 2 purposes;
attenuation of RF potential on the equipment and enhancement of some
antenna systems (particularly verticals employing ground as part of the
system). However, a radial system that serves lightning dissipation
well is not optimal for RF grounding, and vice versa. A single ground
rod, tied to the utility ground system, is sufficient for power system
safety.
The single point ground often discussed is a part of the station, to
which each of the 3 ground systems is connected. None of them serves as
the single point ground!
I know I haven't covered the subject, I may have stated some
incorrectly. The subject is appropriate to this reflector, I'm sure,
and will probably stimulate response, including a few flames. If look
forward to learning from having posted this.
73 de WOØW
Quote:
The control of dissipating lightning strike energy requires division.
This is an absolute must for success, because of the magnitude of the
current and the resulting surge impedance of any single dissipation
path. Ten radials connected to a ground ring bonded to an antenna, will
divide lightning current up into ten smaller segments. This will help
insure that the lightning will more likely follow the designated paths
for dissipation into the earth and lower the resulting GPR to the
adjacent equipment building grounding system.
The optimum length of these ten radials is approximately 80 feet each
with interconnecting 10 foot ground rods, spaced every 20 feet. Longer
length radials will offer little dissipation improvement, because the
lightning strike energy will not remain on the radials for much over 80
feet. In very limited spaces, the recommended minimum grounding system
is at least 200 feet of buried bare ground conducting wire composed of
five radials, each 40 feet in length, with interconnecting 10 foot
ground rods, spaced every 20 feet.
A greatly improved copper wire grounding system can be easily achieved
by the use of conducting cement placed around the radials at the time of
installation. The cement will harden into concrete both protecting the
grounding system (giving it many years of additional life), and making
the system a much better (lower) ground resistance.
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