On Sun, 1 Feb 2004 13:04:47 +0200, "don bryant"
wrote:

Man, this one goes back a ways.

But back to the main question...How far should a fence be place around a
tower. Most of the answers given referred to the "step voltage" case. There
is another important factor, Side Flashes. A person or animal should not be
to near a tower since the flash heading to ground can take a parallel path

There are just too many things to be taken into consideration.
There are ground currents which produce some pretty impressive voltage
drops per foot as you go away from the tower base.

There are induced currents in metal objects which of course produces
voltages. Sometimes those volt ages can be as much as several
thousand volts per meter in the conductor from a strike a mile away.
Typically, most damage, as I understand, is done by induced current
and voltage from nearby strikes rather than direct hits.

if one is standing close by. I don;t know the distance, but I would stay
10/15 feet away, just in case. It is side flashes that get people standing
under trees. Plus, there is the danger under trees from fragments of the
tree, as well as part of it falling on you. In Johannesburg, we get terrific

The problem with "nearby" is the ground current and its associated
voltages as well as the "side flashes". Most livestock farmers have
seen cows, and horses laying near an electric fence that have been
killed by lightening. Generally they were killed due to the voltage
difference between their feet which sent a current through their
bodies.

Even a ground fault in the electrical system that applies 110 volts
directly to a ground rod at the base of a vertical can produce lethal
voltage drops over a few feet near the base of the vertical. I had
one grab me and refuse to let go until I fell over and my knees broke
contact with the wet ground. (and I was hanging onto a bare copper
wire tied to a ground rod.)

Which brings me to... Some times with a truely impressive strike that
has hundreds of thousands of amps and a very steep rise time, the
current in the tower rises so quickly, it produces one whale of a
magnetic field that quenches the current flow. When that happens the
lightening has to go some where and it gets off the tower. It may
even get off near the top and follow a guy wire, or just jump through
the air.

A fence around a tower, or even around a lot with a tower in the
center can have some very impressive currents and voltages induced
when the tower takes a strike.

Were I going to fence a tower, then I think I'd fence my entire back
yard.

73

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

lighting and all thatch roof houses are required to have a vertical rod
about 1/4 wave on 40 meters).I know all this because my uncle was a musical
genius, a truly fabulous conductor. He was hit by lighting.
Joke...sorry)Don ZS6BTP