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[Towertalk] grounding system

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Subject: [Towertalk] grounding system
From: (Glenn Little)
Date: Sun, 28 Jul 2002 17:03:06 -0400
Concerning the aluminum panel, dissimular metals come to mind.  Aluminum 
oxidizes as fast as you clean it.  You will have to do some special preps 
to the aluminum panel for the connection of the brass connectors.

In a professional installation, there would be a ground ring around the 
tower and another around the building. These ground rings would be bonded 
together and bonded to the service entrance ground.  Acording to some data 
that I got from a surge suppressor company concerning lightning induced 
voltages, a lightning strike one Km away will induce 200 volts per meter of 
wire.  The second floor of you house appears to be about 10 feet or about 3 
meters above actual ground. That three meter ground wire could have 600 
volts on it from a strike one Km away.  If the strike is 100 meters away, 
the figure goes to 1KV per meter of wire.

Another thing, do NOT use braid for a lightning ground.  There are warnings 
about this in Motorola's R-56 manual and the Mil Handbook concerning 
lightning (EMP) protection. R-56 states AWG 6 inside the building and AWG 2 
outside the building. Compression fittings are to be used as a last resort 
and must be inspected periodically.

I did equipment failure analysis for lightning strike damage in my last job.

Any ground length over five feet from equipment to ground rod is almost 
useless for protection from a close lightning strike.  It is fine for a 
electrical safety ground, but too much voltage will be imposed on the 
equipment for the equipment to survive fro a close strike.

Hope that this helps.


  At 11:39 AM 7/28/02 -0700, William Hein, AA6TT wrote:
>Mike at ICE told me not to worry about installing my bulkhead
>grounding panel in the window frame of my garage with the bottom
>of the window opening about 1 foot above ground level.  (The ham
>shack is on the floor above the garage, the garage is half
>underground where the bulkhead will be.)  Mike said that this
>would be a low voltage point and I shouldn't worry about lighting
>hits causing fires in my wood-framed house due to the direct
>connection of the feedthru panel to the house.
>Mike also said aluminum would work fine for the panel (instead of
>William H. Hein, AA6TT
>10 Clark Road
>Topsham VT 05076-3086 USA
>tel 802/584-4317
>Self Supporting Towers, Wireless Weather Stations, see web site: 
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Glenn Little                  QCWA  LM 28417
Amateur Callsign:  WB4UIV     AMSAT LM 2178
QTH:  Goose Creek, SC USA (EM92xx)                      ARRL  TAPR

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