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[TowerTalk] Length of Mast

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Subject: [TowerTalk] Length of Mast
From: (Joe Giacobello)
Date: Sun Jun 1 11:51:19 2003
You guys have raised an issue that I have wondered about for some time 
now.  I also live out in the country and have noticed that the number of 
houses and other structures with lightning rods seems to have diminished 
over the years.  Why has the use of lightning rods fallen out of favor?

It was always my belief that the purpose of the rods was to slowly and 
continuously bleed off electrical charge in the air so that the 
likelihood of generating a voltage in excess of the the breakdown 
voltage for air in the vicinity of the structure was minimized.  The 
ultimate objective was to prevent a sudden, instantaneous, potentially 
destructive, high current discharge through the structure itself.  When 
I proposed on the Antennas mailing list that this mechanism most likely 
also applied to a properly grounded tower near one's house, my 
description was corrected by one of the readers.  Apparently, the 
effectiveness of the rod or tower depends on the formation of a cloud of 
charge in the air surrounding the tip.  In windy conditions, the cloud 
becomes unstable and must continually reform.  (Although I'm not sure 
that it makes any practical difference, I was also informed that the 
flow of charge was from the ground through the rod into the cloud.)  Is 
it because windy conditions reduce the effectiveness of lightning rods 
that they are less used today?  I'd be interested  in hearing some 
comments on this question.

I should also add that I have a pointed multiwire attachment strapped to 
the top of my tower which (allegedly) provides multiple paths for 
discharge and reduces the voltage necessary for (slow) discharge to 
occur.  (It can be purchased from the Wireman, and Pres swears that it 
works.) I also have a pretty good ground system with about eight ground 
rods connected in a large circle that includes the house ground.  I have 
observed major lightning strikes on a ridge about the same height as 
mine and about 3/4 of a mile away, but I have never been hit. Have I 
been lucky or is the system really working?

73, Joe

Pete Smith wrote:

> At 06:45 PM 5/31/03 -0700, Michael Tope wrote:
>> Actually it brings up a good question for the lightning technology 
>> experts
>> on Towertalk. How come you only see lightning rods on barns and not
>> houses? Is that just because most barns are old, and people have stopped
>> using lightning rods, or is the their some other reason?
> My house -- a farmhouse -- came with an array of 6 lightning rods, 
> complete with woven aluminum down-conductors.  Lightning rods are 
> fairly common on houses out here.  I am very unclear on whether they 
> offer any protection at all, because the ground conductors seem to 
> violate the low-inductance requirement that we hear from Polyphaser.  
> It's not clear to me why lightning would "prefer" the rods to other 
> ground conductors that might be available in the neighborhood, or on 
> nearby power poles.
> 73, Pete N4ZR
> The World HF Contest Station Database was updated 9 May 03.
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