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Re: Lightning hits



The utility service ground is certainly NOT the 'best in the world',
particularly
at RF frequencies- and a lightning discharge is full of RF.  You can see
this for
yourself (as I have many times) by examining a piece of lightning-struck
ladder
line or twin lead.  You often see burns spaced to indicate the discharge
has a
large component in the VHF range, plenty to vaporize the copper at
precise
intervals, typically 10-20 inches apart.   Now, let's look at your
typical utility
ground wire.   I'm going from memory, but a one foot long piece of #12
wire has
an inductance of about one microhenry, streched out in a straight line. 
Inductive
reactance is 2 X pi X freq in Hertz X inductance in Henrys.  At 10 MHz,
our
foot-long piece of wire has over 6 ohms reactance.  Ten feet at 100 MHz
is over
600 ohms!  This is hardly a good path to shunt destructive lightning
strikes
safely to ground.  What is needed is a good low-impedance path to ground
from
your antennas and tower/pole.   Three ten foot copper-clad ground rods,
spaced
equally out about 6-7 feet from your tower base, and connected to the
tower legs
with low-inductance flat copper strap, provide a MUCH better lightning
protection
setup than connecting to the utility ground.  If possible, connect your
station
ground (the metal cases of your equipment) to these same ground rods,
using the
shortest and widest copper straps you can find.  Make all your strap
runs as
short and straight as possible, since a bend in a conductor increases
its'
reactance.

Copper straps can be made by cutting three to six inch wide strips from
copper
'flashing' sheets, found in the roofing department of any large hardware
store.

By the way, I don't recommend hooking your station ground to the utility
neutral
wire, for safety reasons.  If the utility neutral connection breaks or
corrodes
you may be providing the return wire for your stove and refrigerator
through
your radio equipment grounding system.  The utility neutral should be
grounded
at only one spot- at the service entrance.

Best regards,  John  W5EME



Kevin Muenzler, WB5RUE wrote:
> 
> Sorry to hear about your lightning experiences and I can sympathize.  I have
> said over and over to NEVER connect your antenna ground to the service
> ground.  I have been told over and over that I'm full of it, "that ground is
> the 'best in the world' since it's grounded at every pole along the
> line...."  Well, you are living (thankfully) proof of why it's a very bad
> idea.  Sure the lightning will go right to the "best ground in the world"
> and take out everything in your house along the way.
> 
> 73/
> Kevin, WB5RUE
> 
> > -----Original Message-----
> > From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
> > Behalf Of Bill Miller
> > Sent: Monday, December 11, 2000 7:51 AM
> > To: G Payton; AMSAT-BB
> > Subject: [amsat-bb] Lightning hits
> >
> >
> > Hi Jerry,
> > Made first mistake on second hit when I decided to gound the second
> > tower to Fl Pwr and Lights entrance ground.  It was nine feet
> > from base
> > of tower and used #2 welding cable for feed.  That hit resulted in the
> > most damage to home a.c. utensils.  I have fouir TV sets thruout the
> > house...the tremendous magnetic field destroyed purity on
> > every set!  I
> > could go on and on but ion interest of  making this boring I
> > will say :
> > #1.  Study Poilyphasers information  #2.  Study ARRL info on
> > lightning.
> > #3 Make sure youir insurance premiums are up to date and with a
> > reputable carrier.  Never had an argument from my carrier on all three
> > strikes!
> > 73 and Good Luck - BILL
> >
> 
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