Path: utzoo!utgpu!watserv1!watmath!att!linac!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!rpi!bu.edu!buit13!kwe
From: kwe@buit13.bu.edu (Kent England)
Newsgroups: comp.dcom.lans
Subject: Re: Lightning protection
Summary: Use Fiber
Message-ID: <69636@bu.edu.bu.edu>
Date: 29 Nov 90 15:24:01 GMT
References: <398@alsys1.aecom.yu.edu>
Sender: news@bu.edu.bu.edu
Organization: Boston U. Information Technology
Lines: 34

In article <398@alsys1.aecom.yu.edu>
 bob@alsys1.aecom.yu.edu (Bob Lummis) writes:
>Does anyone have a recommendation for lightning protection on 10Base-T
>links that go through a direct-buried cable between two buildings?  The
>buried portion of the cable is about 300 feet long.  I plan to put 10Base-T
>transceivers at each end immediately at the building entrance points, then
>run the AUI cables upstairs to equipment locations.
>
	This is really a very bad idea.  It is not worth the apparent
savings.  If you must use twisted pair between buildings (such as for
phones) I would recommend you follow telco practice and use fuse
blocks and bus bars to ground the twisted pair cable sheath.  But
10BaseT is different from tip and ring.

	If you want to use 10BaseT, it would really be much better to
use a pair of fibers and a pair of fiber optic transceivers between a
couple of 10BaseT concentrators, one in each building.  The fiber
provides excellent ground isolation between buildings, which is the
problem you are really addressing.  Fiber also is not susceptible to
lightning strike induced potentials.

	If you insist on twisted pair, you will end up with problems
due to ground potential differences and the way that Ethernet
interface manufacturers and PC makers ground their equipment.  In any
case, it is best not to rely on the end node to deal with potentially
large ground potential differences, particularly those induced by
lightning strikes.  It is very expensive to replace lots of PC
components after every summer thunderstorm.

	Perhaps some of the many many people I have talked to over the
years about these sorts of problems will speak up and confirm my
position.  Don't make the same mistake.  10BaseT is a *local* medium. 

	--Kent