[TowerTalk] strike variability---sometimes you can't outrun the bear

[Jim Jarvis]

While it is true that you don't have to be faster than the bear,
just faster than the next guy...sometimes you MAY find a bear intent
on chasing things that run.  One down, you're next.

The variability of the lightning phenomenon is such that all you can
do is take reasonable precautions, and buy insurance.

Will a dissipative ground structure help?  Of course.
Will a system to increase the effective size of the tower top help?
Of course.

Can all of these things dissipate enough charge that it will stop
all direct strikes?  Of course not.

But it can mitigate a bunch of them, and dissipate current from those
which DO strike, potentially reducing damage.

My comment about porcupines, which several have replied to privately, was
purely intended
to caution against reliance upon any one technique.

The evidence, for the empiricists among us, is that having a porcupine
on top of your tower tends to keep saber toothed tigers away, just as
well as lightning.  At least, nobody who put one up has reported an attack
so far.

n2ea



Message: 1
Date: Wed, 5 Jul 2006 10:46:16 -0500
From: "Keith Dutson" <kdutson at sbcglobal.net>
Subject: Re: [TowerTalk] Porcupines and other wives tales
To: <towertalk at contesting.com>
Message-ID: <002101c6a04a$27c05ce0$a8c3db40 at KEITHSUPPORT>
Content-Type: text/plain;	charset="us-ascii"

I think the timing and dynamics of a strike are not that well understood.
Little of what has been published is based on actual strike measurements but
rather on "triggered" strikes using rockets and long, thin wires.  The
theory of being able to dissipate massive charge fields using devices like
the porcupine has pretty well been shot down by several studies and
experiments.

In some cases it has been found that a strike causes extensive damage even
when the object being struck has been equipped with the best known strike
management systems (e.g. very low impedance ground).  These are sometimes
called mega-strikes and are fortunately few and far between.  The consensus
seems to be that a good ground system will handle the majority of hits with
little or no damage.

73, Keith NM5G