> Michael Tope wrote:
> snip:
> > 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?
>
> I'm not a lightning expert, just a fireman that answered a lot of
house
> fire/lightning hit calls. Where I live, many of the outlying
areas(used
> to be farm and barns, now filled with 500k and up houses on 1+ acre
> lots), houses grounded with ground rods and grounding systems have
> become very common.(especially after a number of homes took direct
> hits.) It's not required in the code, but many homeowners have done
> this, and the incidence of direct hits has dropped dramatically. FYI
More than likely its not the hits that has dropped, but having the
downleads has prevented the hits from causing fires by providing a low
resistance path around the outside of the house rather than through it.
On the other side of the coin, it could be that the lightning incidence
has also dropped, but this is just a statistical thing... the ammount of
lightning in any small area can change drastically from year to year so
when comparing the effectiveness of protection installations you have to
consider many years of statistics. I like to see at least 5 years, but
10 would be better when talking about small targets like houses.
And yes, the pointed 'Franklin' style lightning rods are meant to
initiate streamers that go up to make the final connection to the
downward leader from the cloud. By initiating the leader in a
relatively controlled location and sooner than most surrounding objects
it is more likely that the rod will get hit. But since the rod is well
grounded it will also safely drain away most of the energy. Barns were
done more than houses because the barn was usually taller than the house
and height matters, and since installations were not cheap many farmers
probably couldn't afford to do both.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
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