On Mon, 26 Sep 2011 12:04:21 -0700, Jim Lux
wrote:

On 9/25/2011 7:06 PM, Jeff Liebermann wrote:
The end and
highest antennas were also grounded with a undersized #4 copper wire
running down the pole to a ground rod at the base. We didn't get any
lightning hits because there was an all metal forestry lookout at the
highest point on Santiago which took all the hits.

#4 is plenty big enough for lightning grounding. The current is high,
but the duration is short. You see larger lightning conductors for
mechanical reasons (e.g. where it might get damaged, or where it has to
move repeatedly).

One of the neighboring towers took a direct hit. The #6 AWG he was
using literally exploded, spraying melted copper everywhere and
blowing pieces of concrete block all over the building.

http://en.wikipedia.org/wiki/American_wire_gauge#Table_of_AWG_wire_sizes
Fusing current (32msec) for #4 is 34,000 Amps. The average lightning
hit is about 20,000A but can go up to 200,000A.
http://www.lightningsafety.com/nlsi_info/media.html
Other references offer averages from 5,000 to 50,000A. I would call
#4 marginal but probably adequate for California, which doesn't get
much lightning.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
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