[TowerTalk] More comments on lightning - second hand from an expert

[Tom Wagner]

>dave@egh.com wrote:
>consider a 30m high tower.  use a 45 degree angle down from the top of
>the tower (a 45 degree angle is a commonly used estimate for 
>how big of an area is 'protected' by a tall pole or wire).  
>This means that any stroke in an area of  about 2800 square meters 
>around the tower may strike the tower instead of the ground.  
>i don't remember the statistics for your area, but
>out here in western mass there are about 4 strokes per square kilometer
>per year on the average.  this means 4 strokes in 1,000,000 
>square meters per year.... so your 2800 square meter area 
>would get   4*2800/1000000 or about .0112 strokes per year, 
>or about one stroke every 89 years that may hit the
>tower itself, or may ignore it and still hit the ground.

Thanks for interjecting some new facts into this debate, Dave.  

89 years seems to be too far between strikes.  Perhaps
thats because In your analysis, you didn't mention that a strike 
near the tower might induce current into the antenna system and 
cause damage.  Damage that might seem like a direct strike,
but really isn't.  

Tom - N1MM


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