[TowerTalk] Antenna to Shack Ground Connection

[Patrick Greenlee]

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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