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Old February 15th 04, 01:36 AM
w_tom
 
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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.

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.

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.

Randy wrote:
So, you claim that ALL lightning strikes can be safely shunted to
Earth, with no damage along the path? Well, I don't have 30
years experience in the electrical transmission and distribution
industry, but I do have 25 years. And I have seen properly earth
grounded transmission and distribution poles where the awg #6-#4
CU wires were mostly vaporized. Sure, there were bits and short
pieces left, but for the most part, the wire was gone. I confer
with you most of what you say, but you would be not completely
honest to say that all lightning strikes can be earthed with no
damage. Possible? Maybe. Practical? Nope.There will be strikes
of magnitude where practical techniques fail.