> The 'rolling ball' theory of lightning protection is an ancient method
> said basically that you take a ball (in your mind of course) as tall as a
> vertical object and roll it around the object and any area inside where
> ball rolls is safe from lightning... basically it is something like a 45
And you can find instances of a tower being hit on top but the lightning
gets off part way down and arcs over to something else or even the ground.
The "rolling ball" assumes the maximum charge to be centered on the tower,
but that is often not the case.
> degree angle from the highest point down to the ground, also known as the
> 'cone of protection'. this has been shown to be untrue many times,
> photographic evidence of lightning hitting sides of buildings, near the
> of towers, the bottom wires on power lines, and many other spots that
> be 'safe' according to the rolling ball theory exist.
With conductors, rise time plays a big part in where the object actually
shows the strike getting on or off.
With short rise times the magnetic field is so strong the current is
"quenched' and the lightning fines it easier to go some where else. Hence
you see it get off a grounded tower part way down.
Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
> David Robbins K1TTT
> e-mail: mailto:firstname.lastname@example.org
> web: http://www.k1ttt.net
> AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
>> -----Original Message-----
>> From: email@example.com [mailto:towertalk-
>> firstname.lastname@example.org] On Behalf Of email@example.com
>> Sent: Tuesday, July 04, 2006 15:33
>> To: firstname.lastname@example.org
>> Subject: Re: [TowerTalk] Water tower omni
>> Can you tell me more about the 'Rolling Ball' concept and lightning?
>> I've never heard of it.
>> Someone, I think it was in the forum, said that lightning protection is
>> like an insurance policy. The more you spend, the better your
>> protection, but you couldn't guarantee that you weren't going to get
>> taken out. Of course, there's the people who say that's silly, that
>> professional broadcasters have to stay on all the time, through
>> lightning hits etc. Of course their equipment is a bit heavier and a lot
>> more expensive the typical equipment I install.
>> The side tank mounting has been, at least so far, a relatively safe
>> method. I think we've had one side tank mounted antenna taken out at
>> most. (Actually the antenna wasn't taken out, but the coax as it was an
>> old installation that wasn't properly grounded, if I remember correctly.)
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