"Tendencies, not absolutes." these are called statistics... there are LOTS of
statistics in lightning, from the number of strokes to a given area in an
average year, to the distribution of peak current, total charge, duration,
number of return strokes in a flash, etc, etc, etc... and
obviously statistics change from area to area, we know some areas get more
strokes per square mile, but also the peak currents and other
parameters change from area to area.
Jan 29, 2015 09:20:46 AM, patrick_g@windstream.net wrote:
Tendencies, not absolutes. It would be foolish to assume a charge
dissipating system would work 100% of the time. Grounding runs for
lightning rods are of considerable size and are careful to bend gently
to avoid lumps of inductance. Otherwise they would be destroyed the
first time they failed to defuse a strike. Ask yourself what the sharp
thingies are on those commercial towers for. Do you suppose they might
reduce the number and severity of strikes or are they just pretty
decorations for birds and tower climbers to appreciate?
Patrick NJ5G
On 1/29/2015 7:24 AM, David Robbins wrote:
> Sorry, I have been busy and trying to ignore the recent threads on lightning
> and grounding, but this one needs to be debunked... again.
>
> "Lots of folks think lightning rods (and other structures such a towers
> etc.) are intended to attract lightning to protect other objects from
> being hit. Not so, gentle reader, as the primary purpose of lightning
> rods is to drain away static charges such as accumulate and thereby
> prevent a lightning strike. If the grounded system is hit by lightning
> then the protection system has failed its primary goal. A secondary
> consideration is surviving the strike so as to continue with its primary
> purpose of draining charge and preventing strikes in the immediate area."
>
> No, there is no way a lightning rod system, even if using those fancy
> porcupines on a stick, will ever dissipate enough
> charge to prevent a structure getting hit. if that were the purpose there
> would be no need for heavy conductors from
> lightning rods as the current during the concentration of charge on the
> ground under a convective cell is pretty small.
> just think, how much current does it take to make your hair stand on end? or
> for the tiny corona and sparks from pine
> needles or sharp points on a structure??? its TINY... and even an entire
> patch of a forest going into corona trying to
> dissipate charge doesn't prevent it from being hit. lightning rods are
> designed to be the preferred point that gets hit,
> they do that by having a sharp point that goes into corona easily and
> initiates the upward streamer where the downward
> moving leader makes its connection to ground thus triggering what you see as
> lightning.
>
> Also note that the old 'rolling ball' or '30 degree angle' for shielding
> under a structure or wire is not reliable. there are
> many lightning triggered camera systems that have caught lightning striking
> power lines directly under a shield wire
> and buildings getting hit on their side instead of on top. there is a strong
> random component in the movement of the
> downward leaders that make the final attachment point VERY hard to control or
> predict.
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