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From: bob@islenet.UUCP (Bob Cunningham)
Newsgroups: net.dcom
Subject: Re: lightning, PACXs and computers (followup)
Message-ID: <1465@islenet.UUCP>
Date: Sat, 10-Aug-85 20:14:22 EDT
Article-I.D.: islenet.1465
Posted: Sat Aug 10 20:14:22 1985
Date-Received: Sat, 17-Aug-85 06:09:07 EDT
References: <1397@islenet.UUCP> <29116@lanl.ARPA>, <1028@ulysses.UUCP> <1831@ecsvax.UUCP>
Organization: Hawaii Institute of Geophysics
Lines: 79

At last count, over 40% of the zapped terminals we had were repairable only by
replacing the 1488 and/or 1489 chips (usually the 1488).  An
industrial-quality solder remover (heater + vacuum pump) is highly
recommended.  The percentage seems to be slightly higher (better) for port
selector boards (Gandalf & Micom).  Needless to say, we've been installing
sockets for those chips where practical.

On the computer side, all the port/multiplexer (DZ or whatever) boards
were just swapped out.  Not sure what percentage just had driver chips
burned out or not.  Subsidiary damage (one tape unit and some memory
boards) was limited to just 2 systems, and my opinion is that not all
the equipment at those locations was solidly tied to a single ground.

Besides the followup articles in this newsgroup, I've received a
considerable number of mail messages (all appreciated, though
I've not had time to send individual replies), falling into
two categories:

	1) similar horror stories
	2) thoughtful advice on lightning protection

Apparently, similar incidents (lightning damage via local data comm lines)
are much more common & widespread than I'd have thought.  Unless you're in
a very unusual location, if you've got comm lines going between buildings,
be warned:  something similar might just happen to you.

While I've received a number of very sensible suggestions on lightning
protection, there doesn't seem to be one single solution we could adopt
in all cases.  Suggestions have ranged from using opto-isolators,
diodes (of various sorts, including MOVs), to using telco-type
spark gap devices, to fiber optics.  Each approach has some good points.

However, the thought of having to install any particular suggestion
on the 800 or so data comm lines around campus which probably should have
protection is a sobering thought.  Schemes cheap in material (e.g. diodes)
look to be rather labor-intensive (if both terminal and computer/port
selector ends both need protection -- which seems optimal).  Schemes
cheap in time (e.g. fiber optics) look a bit expensive in parts
(though the thought of pulling a lot of fiber optic cables to replace
twisted-pair lines is also rather sobering).

So far, I think our best approach here is to stick to the basics.

For starters, going over all of the central grounds.  All Computer
equipment and auxiliary racks within a room should be securely grounded
to a single point with generous-size braided ground straps.
The objective is to minimize any possible ground differences between
computers and their peripherals (including port selectors).
It seems to be a good idea to tie down all incoming terminal
grounds (RS232 pin 7) to that same point -- as the lines come in
(typically on punch blocks).  This should localize damage (typically to the
port selectors).  It also seems reasonable to dedicate whole computer-side
port/multiplexer boards to PACX lines ... no more mixing direct-connect
and port selector terminals.  Typically, the only terminals I want
to leave directly connected will be those in the same building
(preferrably the same wing) as the computer site.  This should also
minimize computer-side damage.

Fortunately, port selector boards are MUCH cheaper to repair/replace
than computer port/multiplexer boards.

Relatively expensive terminals (graphics types, for the most part) should
get some special form of isolation at their end from the RS232 lines
(preferrably something simple that plugs in between the RS232 line
and the terminal).

Cheaper terminals (< $1,000) I think are best left as-is for now.

All NEW inter-building trunks (multiple data comm lines) that I have
any control over will be fiber optic lines (stat muxes at each end,
of course).

We do have some plans for a couple of real LANs around campus.  I
do believe that specs for those will now definitely include some
form of lightning protection.
-- 
Bob Cunningham  {dual|vortex|ihnp4}!islenet!bob
Hawaii Institute of Geophysics Computing Facilities
Honolulu, Hawaii