Jim Lux wrote in
:

Owen Duffy wrote:

Frank,

The existence of a tall conductor provides a measure of protection to
nearby structures. The zone is often defined by a "ball" of radius
equal to the height of the tall structure that is rolled on the
ground to rest against the tall structure, and structures between the
contact with the ground and tower, and under the ball are considered
protected by the tall structure, ie that lightning is much more
likely to strike the tall object. In this way, a tower often protects
the nearby equipment hut from direct strikes.

I believe that the latest research indicates that the "rolling ball"
isn't as accurate as once believed (or necessarily better than the
older "cone of protection"). But the difference might be in the noise
floor for most ham installations.



Agreed Jim. The case is better for the nearby equipment hut than the
typical residential building near a 50' tower.

BTW, the "rolling ball" is the recommended approach in Australian
Standard 1768-1991 which I think is still current.

Owen