[geeks] Lightning question

[Geoffrey S. Mendelson]

On Mon, Jul 24, 2006 at 08:01:08AM -0500, Lionel Peterson wrote:


> That makes me wonder about installing lightning rods on the house - in
> the past, I've always dismissed them as "attracting" lightning. Anyone
> here take such precautions?


Oh well, here we go again. This is always a hot topic and even the "experts"
get it wrong. Lightening flows from the sky to the ground. This has been
proved experimentally, photographically, and logically. 

BUT the polarity is wrong. Electricity will only flow from one direction
to the other and the sky is the to, not the from. Then how does lightening
happen? Air is an insulator of electricity. Lightening can not flow across
air. The distance is too far for a spark to jump it, like static electricity
from your finger to a doorknob.

What happens is that a cloud of ions forms both in the sky and oppositely
charged ions forms on the ground. This is like the earth being a carpet
and the clouds being your foot.

>From a point source, the clouds of ions touch and a small current flows
from the ground up. Once the path opens, a large current flows from the
sky down.

So yes, while a lightening rod does not attract lightening as Ben Franklin
thought, it causes it. The effect is the same, the lightening strikes the
rod instead of somewhere else.

One way to prevent lightening from striking is to discharge the ions
before they are concentrated enough to make lightening happen. If you
look at antenna towers, you often see along them large balls of
something that looks like a porcupine or steel wool. These dissipate the
ions and reduce the effect of lightening. They are not 100% effective as
sometimes just too many ions build up too quickly.

In your case, they may prevent lightening from striking on your home and
due to the fact that electricity takes the path of least resistance, find
ion paths nearby instead of your home.

When I lived in the states, I had lightening problems until I put up an
antenna, a Cushcraft 2 meter (144mHz) twist beam. It was two antennas,
one horizontal and one vertical, on the same mast, about 11 feet long,
with 13 elements each about a foot apart. 

At 144mHz it was a high gain, directional antenna, at DC, which is what
lightening is, it was a large grounded "ball". 

After I installed it, I had no further lightening problems. I have no
idea if they came back after we moved and took it down, but I expect
the new owners and the people next door were unpleasantly surprised.

So my advice to you is to get a ham license, and put up a big beam
antenna that has a DC ground. :-)

Geoff.


 
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