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?
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
>> 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
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