On Sat, 14 Feb 2004 20:36:54 -0500, w_tom wrote:
Lightning builds plasma wires that can short high energy,
utility power through other copper wires. Lightning simply
creates the short circuit. Then a higher source of energy -
AC electric utility - follows to vaporize those copper wires.
That point was described by Colin Baliss:
Although lightning strikes have impressive voltage and current
values (typically hundreds to thousands of kV and 10-100 kA)
the energy content of the discharge is relatively low and most
of the damage to power plant is caused by 'power follow-through
current'. The lightning simply provides a suitable ionized
discharge path.
Yes direct strikes have caused damage. This was a problem
in the early days of ESS-1 - the first electronic switching
computers for telephone systems. And so engineers then
reevaluated the earthing system in those few 'problem' Central
Office buildings to correct the reason for electronic damage -
human failure.
What is a problem central office building?
The telephone companys lose hundreds of "channel unit" boards to
lightning damage every year. Most if not all boards lost are in the
remote sites, not the central office. The boards that are lost aren't
due to human faillure, they are due to the fact you cannot predict
lightning, and cannot totally protect against it.
Described above is not a best solution. But then a best
solution is typically not required. Above described system
will not avoid damage from every possible direct strike. But
then many of these 'rare' direct strikes have never been
experienced by many - maybe most - people. For example,
something called hot lightning may discharge the entire cloud
in one single strike. It has been observed - just like
tornados have been observed (most people also will never
witness a tornado in their lifetime).
Defined here is effective protection for most direct
lightning strikes. It costs so little. To enhance same for
the other maybe 1%, serious facilities such as 911 systems,
cell phone towers, telephone switch stations, and nuclear
hardened maritime facilities spend far more than a few $10.
They spend $thousands more on earthing alone just to also
protect from the last 1% of worst case lightning strikes.
Cell sites have a copper ring of protection around the site. I have
been in cell sites that were so totally shielded that my cell phone
wouldn't work in them. Everything entering or leaving the site is
totally protected. Quite impratical for the normal home owner.
I cite nuclear hardened facility especially since a 1998
IEEE paper described a Norwegian maritime station damaged by a
lightning strike. They discovered major installation faults
in the earthing system for what was suppose to be a nuclear
EMP protected station. Faults that even permitted lightning
to cause damage. Again, failure directly traceable to a
human. Major construction required to repair a simple
earthing flaw.
Homes contain superior earthing systems that we still don't
use today. Ufer grounds could have been installed using
existing structure - if planned for when footing were poured.
But we still don't install superior earthing systems in new
homes 30 years after the transistor existed. Costs to use that
Ufer ground on existing homes are now extreme because Ufer
grounding was not enabled when house construction started. OP
must make do with simple earth ground rods. Properly
installed, the Original Poster is quite unlikely to suffer any
damage from direct lightning strikes. For but a few $10, he
gets a massive increase in direct lightning strike
protection. Not perfect. Just a massive improvement.
You might want to read up on the damage that has occured when the
grounds for a tower were encased in the conctrete base that was the
tower mount. They are cases were the lightning "blew" the concrete
base up.
I don't know which original poster you are talking about. My tower is
properly earthed, a direct strike didn't damage my towers or antennas.
The induced voltage that got into my network cables is what caused
most of my damage. The telephone companies have much the same
problem, most of the lightning damage isn't from direct strikes, its
from their wireline pick up of induced voltage of a close strike.
I think you need to quit reading up on it so much, and spend more time
looking at whats practical and proven to work for the CB or ham radio
operator.
Here is a good place to start:
http://lists.contesting.com/archives//html/Towertalk