How and when lightning strikesgreenspun.com : LUSENET : Unk's Troll-free Private Saloon : One Thread
-- (email@example.com), December 07, 2001
Interesting. Of course, way back before there were ultra-high-speed cameras and satellites and computer image enhancement, we knew more than this article seems to imply. For example, the basic mechanism (ionization due to collisions between H20 molecules in different states) was well understood decades ago.
We radio people had a crash course in lightning as soon as the first tower was erected[g]. The first thing any neophyte in Da Bidness learns is that lightning DOES strike the same place twice, too.
One thing that the survey didn't look at -- and which I'd like to know -- is the average *intensity* of the strikes in a given area. The chart doesn't seem to bear out my experience in NC and AL. In NC, in a typical storm, you seemed to get a lot of short, brief lightning bolts. Here in 'Bama, we seem to get fewer total bolts, but the ones we do get are WHOPPERS -- sky-filling, world-eating monsters that are as big around as some of my towers, and which last for a quarter second or more.
Of course, that's subjective, and the numbers for NC don't seem to bear this out.
All I know is, when lightning strikes a tower, you could have several million volts at tens of thousands of amperes, and you've got to get rid of it -- FAST -- before it gets into the equipment. We use spark gaps (they've been around forever), dissipators and ground rod "farms" with 2/0 or 4/0 cable runs. We STILL take a lick now and then.
By the way, at your house, one of the most effective ways to keep lightning out is to have the power company run a *buried* cable (rather than an above ground line with a lift pole in the yard).
-- Stephen M. Poole (firstname.lastname@example.org), December 08, 2001.
I hope you are not a golfer, Stephen
-- (email@example.com), December 08, 2001.