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From: irwin@m.cs.uiuc.edu
Newsgroups: sci.electronics
Subject: Re: St Elmo's Fire (was Re: Lightni
Message-ID: <21000090@m.cs.uiuc.edu>
Date: 30 Jul 90 20:03:00 GMT
References: <8528@inco.UUCP>
Lines: 59
Nf-ID: #R:inco.UUCP:8528:m.cs.uiuc.edu:21000090:000:2739
Nf-From: m.cs.uiuc.edu!irwin    Jul 30 15:03:00 1990


/* Written  7:37 am  Jul 30, 1990 by jboggs@inco.UUCP in m.cs.uiuc.edu:sci.electronics */
/* ---------- "Re: St Elmo's Fire (was Re: Lightni" ---------- */
In article <2253@vela.acs.oakland.edu> amaranth@vela.acs.oakland.edu (Paul 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 afternoon
+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 lean-
+ing against an ungrounded aluminum strip which holds the weather boards in
+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 friend
+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 the
+storm.  Any explanations of how this occurred?  As far as we can tell, the
	---------------------------------------
			^
			|
See below---------------

+lightning did NOT strike any part of the boat directly.

-- 
+John Boggs

+McDonnell Douglas Electronic Systems Company
+McLean, Virginia, USA
/* End of text from m.cs.uiuc.edu:sci.electronics */

When a lightning bolt strikes, the ionized air is a current carrying
conductor, and there is a strong magnetic field around it as is the
case with any conductor carrying current.

This field will induce a voltage into metalic objects, same as in
a transformer, electric motor or other devices which have magnetic
fields crossing conductors.

The lightning need not strike an object for it to shock you, the
high field of magnetic energy only need come in contact, and induce
a voltage. The field travels a considerable distance from where the
bolt actually takes place, so it could induce a voltage in the strip
of aluminum strong enough to shock you and then some.

Years ago, the University of Illinois AM radio station had two
tall towers, with a dublet antenna stretched between them. There
was a 600 ohm open line feeder from the transmitter to the doublet,
the conductors were about 4" apart in spacing. I can recall many
times seeing lightning strike in the distance, and an arc would
travel down the feeder like a jacobs ladder, until it got to the
spark gap arrester on the side of the building, where it was shunted
off to ground.

Al Irwin
irwin@cs.uiuc.edu