Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uwm.edu!bionet!apple!well!nagle
From: nagle@well.UUCP (John Nagle)
Newsgroups: sci.electronics
Subject: Re: Lightning protection
Message-ID: <13987@well.UUCP>
Date: 7 Oct 89 17:58:36 GMT
References: <11561@burdvax.PRC.Unisys.COM> <7600025@hp-lsd.COS.HP.COM> <1827@jato.Jpl.Nasa.Gov> <15337@vlsisj.VLSI.COM>
Reply-To: nagle@well.UUCP (John Nagle)
Lines: 36


      For reference, where does one get serious lightning protection devices
today?  Certainly they exist for antenna protection, but they don't seem
to be widely available for other purposes.

      What you really need is as follows.

      The first stage is a spark gap to ground, with large wire to ground,
perhaps 000 gauge.  This is followed by a inductor composed of a few turns
of about .25 inch copper busbar.  The whole unit is enclosed in a grounded
can.  Heathkit used to sell such a device for antenna protection.  The
device because a lightning stroke is a sharp enough rise that the inductor
blocks it, and the voltage arcs across the spark gap, ionizing the air
and providing a low-resistance path to ground until the charge dissipates.
Properly constructed units of this type can survive multiple lightning 
strokes and cut the output voltage to about 400V.

      Lightning arrestors aren't fundamentally expensive, but they tend
to be on the large side if they are any good, with heavy wiring and big
insulators.  Properly, there should be one on every wire that goes into
a building, and in isolated structures in thunderstorm country, there
had better be.  You don't need one on every outlet strip; you want to stop
the energy pulse before it gets into the interior wiring.

      A second stage, useful in stopping inductive surges due to lightning
strikes near, but not on, wires, is a neon glow lamp to ground.  With the
firing voltage of the lamp appropriately chosen, the unit will consume no
power until a big spike comes along.

      With one of these on the front to divert the energy of the lightning
bolt, MOV-type devices can do their job properly.

      					John Nagle

					John Nagle