Path: utzoo!attcan!uunet!cs.utexas.edu!sun-barr!rutgers!bellcore!ka9q.bellcore.com!karn
From: karn@ka9q.bellcore.com (Phil Karn)
Newsgroups: comp.dcom.lans
Subject: Re: high speed networking between buildings
Message-ID: <17700@bellcore.bellcore.com>
Date: 23 Sep 89 05:24:37 GMT
References: <4574@ursa-major.SPDCC.COM> <337@ai.etl.army.mil> <1130@svx.SV.DG.COM> <12204@ulysses.homer.nj.att.com>
Sender: news@bellcore.bellcore.com
Reply-To: karn@ka9q.bellcore.com (Phil Karn)
Organization: Secular Humanists for No-Code
Lines: 26

In article <12204@ulysses.homer.nj.att.com> smb@ulysses.homer.nj.att.com (Steven M. Bellovin) writes:
>Lightning is quirky stuff, and damned hard to defend against.

Agreed. Its effects are a little less mysterious, though, if you analyze
everything in terms of ground loops. When you're talking about peak currents
of 10,000 to 50,000 amperes, there's just no such thing as "common ground
potential". I've read reports of lightning hits that killed only certain
people and animals apparently at random out of a much larger group that was
standing or lying near the hit. When the case was analyzed, however, it was
discovered that the fatalities were generally among those people or animals
who were lying or standing either towards or away from the point the
lightning struck. This exposed them to larger voltage gradients along the
ground. Those lying or standing perpendicular to the line to the strike
point had a much greater chance of surviving.

The point is that IR drops are everywhere during a lightning hit, especially
in the ground itself (which is not a particularly good conductor, even when
wet). It's impossible to get rid of them altogether with even the heaviest
of ground conductors. The best you can do is to use single-point grounding
schemes so that everything rides up and down together during the strike, but
this takes considerable attention to detail even in small systems. It's
practically impossible between large buildings.

If at all possible, I *strongly* recommend fiber between buildings.

Phil