I thought that the point of a lightning rod or similar device was that a
house being a poor conductor, if hit, gets hit by a huge charge. By
putting up a lightning rod which is a good conductor with a good path to
ground, the lightning can discharge earlier as a smaller charge, and
hopefully do less damage.
As for towers, I see lots of commercial radio and electrical utility
towers that are insulated and have lightning rods (or other) mounted on
them. Isn't that how we should work? I am confused by the call by some
to ground the tower instead. Maybe both systems work ok, but I don't
understand wanting to intentionally use the tower as the lightning rod.
Maybe one of you experts could explain this to me before its too late,
and I put up a lightning research station instead of an antenna.
On Fri, 18 Mar 2005 17:20:48 -0500 "Jim Jarvis" <jimjarvis@comcast.net>
writes:
>
> We've got experts onboard here, but it's still worth
> observing that static drain devices...be they hedgehogs
> on tower tops, or short whips trailing from several points
> on aircraft wings are STILL limited in the amount of charge
> they can dissipate.
>
> At some point, charge builds up faster than they can drain,
> and there is a greater arc. It was the stbd wing of a 747
> en-route to London that took the hit, as we climbed out from
> EWR 10 years ago. Once our hearing recovered from the thunder
> clap, Cap'n came on the intercom and said, Folks,
> that surely was exciting, but it was only a static discharge,
> we weren't hit by lightning, not to worry...
>
> Right. I was on the overwing exit row and looking at the
> wingtip when the ESD hit, and the acoustic wave rattled the
> airframe.
> Flying through T-storms will do that. But we WERE still flying,
> and all systems were apparently still working, so what the hey.
>
> Similarly, fast moving storms will cause strikes to towers,
> or sailboat masts, I don't care how many discharge points you've
> got.
>
> It's interesting that the secondary strike, or streamer, damage
> from hits is a function of the quality of the discharge path.
> A sailboat in salt water, with a properly grounded mast, may be
> hit, but likely won't sustain hull damage. Properly grounded
> is defined by Lloyds as a 1 sq. ft. discharge plate connected by
> #4 cable.
>
> Take that same boat in fresh water, and you'll need 100 sq. ft.
> to provide the same drain. The result? Sailboats in fresh water
> tend to have scads of holes punched or burned through the hull,
> when they're hit. AND, they tend to be hit more frequently than
> those in salt water.
>
> I virtually never heard of a problem in coastal waters, whereas
> in Lake Champlain, VT, there were at least 2 or 3 a year, over a
> 10 year period.
>
> On a more serious note, I don't recall pidgeon shit on the Tour
> Eiffel.
> Either the observation decks are above their service ceiling, or
> those
> pointy things work for something!
>
> n2ea
> jimjarvis@ieee.org
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers",
> "Wireless Weather Stations", and lot's more. Call Toll Free,
> 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
>
> _______________________________________________
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> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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