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From: bob@islenet.UUCP (Bob Cunningham)
Newsgroups: net.dcom
Subject: Re: lightning, PACXs and computers
Message-ID: <1420@islenet.UUCP>
Date: Mon, 29-Jul-85 18:18:44 EDT
Article-I.D.: islenet.1420
Posted: Mon Jul 29 18:18:44 1985
Date-Received: Sat, 3-Aug-85 03:12:42 EDT
References: <1397@islenet.UUCP> <646@mcnc.mcnc.UUCP>
Distribution: net
Organization: Hawaii Institute of Geophysics
Lines: 55

> ... In particular I wonder
> if your communications lines are above or below ground?  What about 
> your power lines?  Are they above or below ground? Secondly, do your 
> communications lines have any type lightning or surge protection?  
> Were any of the affected lines shielded?  Do you have surge protection
> on your power lines?  

All of the comm lines are underground, in conduits (not steam tunnels,
which we don't have out here).  In some cases these were leased "4-wire
control circuits" from the local phone company (Hawaiian Telephone Co.,
a GTE subsidiary); in other cases, self-installed.  All power lines are
also underground (separate conduit, usually completely different trenches).
Note that power lines were not affected, nor were regular phone lines (not
a single modem was zapped, and no phone problems of any kind were
reported).  None of the comm lines had lightning or surge protection.  Some
(a few) were shielded -- though I'm not sure how well the shielding was
grounded.  Some power lines have surge protection, some not; in any case
the path was NOT thru the power lines.

Interestingly, some of the affected lines were entirely within a single
building, typically of reinforced concrete (and for ordinary r.f. signals,
the rebar cage usually provides some shielding).  My theory is that -- at
some point -- those comm lines were bundled with other lines passing from
building to building.

> We are in a lightning prone area, and I have been attempting to
> understand the intricacies of lightning protection recently.  I
> confess that the more I hear the more confused I get.  I have
> concentrated on power protection, but your problems seem to have resulted
> from a communications line hit.

That's what the evidence definitely indicates.  Surprised us.

> I wouldn't have thought that such a
> hit would spread to so many machines, unless you had a tremendous
> earth current transient that affected buried lines in a wide area,
> or were unlucky enough to get a hit on some central distribution
> point.

There was no central distribution point -- several completely separate
computer "centers" were involved, none tied together in any way.  I'd say
the ground current transient (or, perhaps several as a charge briefly
"bounded" back and forth from the clouds to the earth and back again until
settling) seems likely.

> Am I wrong in this evaluation?  Is there some other way such
> a strike could get into a widespread communications network?  How
> does one go about protecting such a network from lightning?

I'd like some of those answers myself.  Anyone else with experience care to
comment?
-- 
Bob Cunningham  {dual|vortex|ihnp4}!islenet!bob
Hawaii Institute of Geophysics Computing Facilities
Honolulu, Hawaii