Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uunet!isis!nyx!whester
From: whester@nyx.UUCP (William R. Hester)
Newsgroups: sci.electronics
Subject: Lightning (St. Elmo's Fire)
Message-ID: <1753@nyx.UUCP>
Date: 1 Aug 90 21:21:36 GMT
Reply-To: whester@nyx.UUCP (William R. Hester)
Distribution: na
Organization: Public Access Unix - University of Denver
Lines: 68















In article <8528@inco.UUCP> jboggs@inco.UUCP (John Boggs) writes:
>In article <2253@vela.acs.oakland.edu> amaranth@vela.acs.oakland.edu (Pa
l Amaranth) writes:
>>
>>Not to get off the track too much, but I had a lighting strike close
>>(*VERY* close) to my house.  I was lying in bed watching tv when the
>>windows went white immediately followed by the BOOOM.  After peeling
>>myself off the ceiling (THATS the secret of anti-gravity ;-) I went
>
>A friend and I got caught out on the river in one of our recent afternoo

>thunderstorms.  We had holed up in the cabin waiting it out as the rain 
>and lightning and thunder came down all around us.  I was sitting in the
>cabin leaning against an ungrounded aluminum trim strip.  My friend was 
ean-
>ing against an ungrounded aluminum strip which holds the weather boards 
n
>place.  A particularly close lightning strike set up some kind of charge
in
>those ungrounded pieces of metal that was sufficient to shock both my fr
end
>and I simultaneously.  Neither of us received enough of a shock to cause
any
>damage but I can tell you we kept away from metal parts for the rest of 
he
>storm.  Any explanations of how this occurred?  As far as we can tell, t
e
>lightning did NOT strike any part of the boat directly.
>
>-- 
>John Boggs
>
>McDonnell Douglas Electronic Systems Company
>McLean, Virginia, USA

John,  Any flow of electrical current through a conductor is accompanied
by a surrounding magnetic field.  The lightning discharge was a LARGE
flow of current with a BIG field...which expanded outward and cut across
the metal pieces of your boat.  This induced a voltage into the metal...
just like a generator works...which was coupled into your body --completi
g
a circuit and shocking you.  

This is a common problem with lightning protection systems...where the 
downleads conduct heavy currents into the earth.  Nearby electronic
devices are damaged...not due to any direct hit, but due to the induced
magnetic field and the resulting voltages generated in the devices.

Keep all electronic devices well away from downleads of lightning
"protection" system downleads.

This same principle is the basis behind the damage caused to electronic
devices by nuclear bombs...if the explosion doesn't hit you the electro-
magnetic pulse will.