Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!mailrus!purdue!bu-cs!kwe
From: kwe@bu-cs.BU.EDU (kwe@bu-it.bu.edu (Kent W. England))
Newsgroups: comp.dcom.lans
Subject: Re: Ethernet and lightning
Message-ID: <27294@bu-cs.BU.EDU>
Date: 17 Jan 89 18:44:32 GMT
References: <10315@well.UUCP> <27196@bu-cs.BU.EDU> <13433@bellcore.bellcore.com> <164@oregon.uoregon.edu>
Reply-To: kwe@buit13.bu.edu (Kent England)
Followup-To: comp.dcom.lans
Organization: Boston U. Information Technology
Lines: 37

>In article <13433@bellcore.bellcore.com>, Phil R. Karn writes:
>>> [when I said]
>>> However, many
>>>people have blissfully installed thick between buildings (including
>>>me) without any problem whatsoever.
>> Your bliss may end the next time you have a nearby lightning strike.

	Perhaps it was irresponsible of me not to say something about
lightning risk, but it hasn't ever come up in my environment.

	On our urban campus it can be difficult to tell when the
address has changed, since many of the buildings are all run together.
When a cable crosses a street, it is in a steel conduit in a concrete
jacket buried in the earth.  I don't think lightning is a real risk in
that situation.  The telephone company puts fuses in a main
distribution frame in our garage and then runs cable 300 feet down the
street thru a string of buildings to its final destination.  They
don't seem to worry about induced transients on copper pairs.  All
without benefit of conduit except to cross the street.

	My main worry in running thick Ethernet cable between
buildings is differences in ground potential due to the way the
electric power feeds are distributed and grounded.  If an Ethernet
crosses substation boundaries, then there is some risk of ground
potential differences and the thick cable won't work.

	But for the folks watching this on TV, "Don't try this at
home.  These are trained professionals paid to make the stupid
mistakes for you."  :-)  In other words, you should pay a little more
for the requisite interface hardware (the fiber optic gear) and use
fiber between buildings.  That is the sort of conservative advice I
should be giving and not making comments like "installing thick cable
without any problem whatsoever."

	That should set the record straight.

	Kent England, Boston University