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From: davidsen@steinmetz.steinmetz.UUCP (William E. Davidsen Jr)
Newsgroups: comp.dcom.modems
Subject: Re: Lightning storms zapping modems
Message-ID: <7048@steinmetz.steinmetz.UUCP>
Date: Thu, 20-Aug-87 11:14:46 EDT
Article-I.D.: steinmet.7048
Posted: Thu Aug 20 11:14:46 1987
Date-Received: Sat, 22-Aug-87 11:39:42 EDT
References: <930@bc-cis.UUCP> <18600022@clio> <3587@sdcsvax.UCSD.EDU> <747@uhccux.UUCP>
Reply-To: davidsen@crdos1.UUCP (bill davidsen)
Organization: General Electric CRD, Schenectady, NY
Lines: 18
Keywords: lightning power datacomm

Lightning strikes can enter a computer either from the power line, modem
lines, or the roof.  The first two can be isolated easily if not
cheaply.  To isolate a power line fully, a motor-generator (MG) set is
used, mechanically coupled by a large non-conducting flywheel. This
protects against almost any line problems, but not against problems in
the generator itself (we found this out the hard way).

There is (was?) a device made to isolate RS232 connections, which is
based on having a large gap bridged by bidirectional optical link. I had
one of these which used two LEDs and two photodiodes. There is better
technology today, but the old stuff worked.

Your computers can be as safe as you can afford to make them. For many
systems the risk doesn't justify the cost of protection.
-- 
	bill davidsen		(wedu@ge-crd.arpa)
  {chinet | philabs | seismo}!steinmetz!crdos1!davidsen
"Stupidity, like virtue, is its own reward" -me