Fw: Lightening Protection

Dennis W. Farrell (dfarrell@ridgecrest.ca.us)
Sun, 9 May 1999 15:28:10 -0700

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West Wight Potter Website at URL
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I saw this on the r.b.e group, and thought it might be of some interest.
-- dwf
-----Original Message-----
From: Woody White <woody.white@att.net>
Newsgroups: rec.boats.electronics
Date: Sunday, May 09, 1999 10:30
Subject: Lightening Protection

>FWIW, A reply to an email I received...
>Hello Maurice,
>Unfortunatly, protection from lightening is iffy at best.
>Not only have I been in ham radio since the 60s, but have
>had several friends with whom I have confered who were
>specialists in that field for General Electric. The only
>way to really protect from taking a lightening stroke is to
>not be in the area where it is occurring. Obviously that is
>not always practical! The next line of defense is to
>minimize any damage done by a direct hit or induced currents
>from a nearby stroke. A single point ground is important.
>If on shore power, the entry point is a often good place.
>Telephone / cable lines should all enter together. GOOD
>surge supressors can help, but are no guarentee (search for
>the company "Polyphaser" for coax and other "feedthroughs").
>The goal is to minimize differiential currents generated by
>very high currents with a very fast rise time. This is a
>bit tricky in most boats because of the motor / propeller
>system. They are a good ground in seawater, but bad in
>another way - since it is through the boat and out something
>not designed to handle high electric currents. Ideal is hard
>to achieve. Physically disconect everything possible when
>(actually before) under seige by storm. Isolation offered
>by a few thousandths inch by a switch means nothing to an
>electric arc that has already traveled miles through air.
>Bad situation examples: Antenna -> VHF -> System elecrical
>ground. The current passes through the radio to discharge
>if the antenna is hit. Thousands of volts can be applied by
>the average stroke! Another... Telephone answering machine
>while at dock. The machine is between power lines and tele
>lines, either of which could experience a high voltage spike
>- discharging to the other. Disconnecting will protect
>When at anchor or underway, friends have attempted to
>"shunt" as much energy as possible by clamping heavy bare
>copper wire to mast / stays (depends on mast material and
>rigging) and trailing about 15 feet in the water. This is a
>good idea since I have heard "tales" of holes being blown in
>hulls from embedded ground plates. The path is outside the
>boat. The path to hull plates is often through the inside
>of the craft - not good. Since lightening wants to travel
>in a straight line, avoid sharp bends in ground lines.
>Bottom line is that you can never (realistically) fully
>protect everything. You just do the right things to
>mitigate problems and hope the "gods" are smiling on you!
>Good Luck!!!
>BTW... Visited the site... Curious does "your" rabbit
>tobbacco have very velvety leaves to the naked eye? My
>identification was very tentative. Aided by a not
>thechinical (in that area) friend.
> ----------- de Woody, WB4QXE -----------
> Ham Homebrew/ATV Circuits -*- Scanning Electron
>Microscope Images
> http://www.geocities.com/capecanaveral/3722