Hi, TTs;
Ground resistance and ground impedance are not nearly as important for
lightning protection as is preventing differences among the several
grounds involved and preventing excessive surges on all ungrounded
connections. All the stations grounds may be at very high voltage as
long as they are all the same and all the antenna, control lines, power,
telephone, and other utilities are clamped with respect to that ground.
It is very important to tie all the utility grounds to the station
grounds with as little impedance as possible and to employ lightning or
surge arrestors, each tied to that common ground, to limit surges on
every feedline, power line, computer connection, etc. Other conductors,
like water pipes, should be close enough to that ground potential that
there is no danger of a spark between them and the ground system and is
no danger of an injurious voltage difference that might affect a person
who may contact both. The whole system must be grounded well enough to
prevent reaching a voltage that initiates a discharge to the air, but
that is thousands of volts and shouldn't be a problem if things are
grounded at all.
The emphasis must be on limiting potential differences among ALL the
conductors connected to the station.
I recommend these references:
Lightning: Physics and Effects, Dr. Vladimir A. Rakov and Dr. Martin A.
Uman. 2003. Cambridge University Press. This is an undergraduate text,
not too technical, that provides useful explanations of why lightning
does what it does as well as the latest findings and data from lightning
research and information regarding lightning protection. It is not
commonly available at local public libraries. I borrowed a copy via
inter-library loan from U of MN.
All About Lightning, Prof. Dr. Martin A. Uman. U of Fl, Gainesville.
1971, reprint 1984 with revisions. Layman’s level describing some of the
attributes of lightning. Some of the information is superseded by
information in Lightning Protection and Physics.
Protection of Electronic Circuits from Overvoltages, by Ronald B.
Standler, 1989; John Wiley & Sons, Inc., particularly Part 2, Chapters 7
through 15, for information about gas tubes, varistors, avalanche and
Zener Diodes, semiconducor diodes and rectifiers, thyristors, impedances
and current limiters, filters, isolation devices, and parasitic
inductance and how these devices may be used to protect electronic
equipment from overvoltage stresses such as those associated with
lightning. This book may not be available in many public libraries but
is available on inter-library loan from college and university libraries.
The Lightning Book, Peter E. Viemeister. Doubleday & Company. 1961.
Layman’s level. Not up to date but very readable and still informative.
Lightning Protection and Grounding Solutions for Communication Sites, by
Ken R. Rand; 1st ed., 2000, Polyphaser Corporation. Available by request
to Polyphaser. Some of the information in it is not up to date and I
disagree with the diagram for deploying ground rods.
Lightning Protection for the Amateur Station, Parts 1, 2, and 3, by Ron
Block, KB2UYT, QST, June, July and August of 2002. Ron Block is a
brother of Roger Block, founder of PolyPhaser. In my opinion, the
recommended grounding diagram uses ground rods ineffectively and does
not adequately address the utility grounds.
There is lots of other information available, including many items from
ICE and PolyPhaser. Read them critically. They are not totally unbiased
and up to date.
73 de WOØW
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