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[Towertalk] Lightning dissipation

To: <towertalk@contesting.com>
Subject: [Towertalk] Lightning dissipation
From: RedHaines@centurytel.net (Red)
Date: Fri, 06 Dec 2002 10:53:54 -0600
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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