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From: bob@islenet.UUCP (Bob Cunningham)
Newsgroups: net.dcom
Subject: Re: lightning, PACXs and computers (followup)
Message-ID: <1507@islenet.UUCP>
Date: Sat, 17-Aug-85 06:32:59 EDT
Article-I.D.: islenet.1507
Posted: Sat Aug 17 06:32:59 1985
Date-Received: Tue, 20-Aug-85 21:25:49 EDT
References: <1397@islenet.UUCP> <29116@lanl.ARPA> <1028@ulysses.UUCP> <1831@ecsvax.UUCP> <1465@islenet.UUCP> <1242@umcp-cs.UUCP>
Organization: Hawaii Institute of Geophysics
Lines: 22

> >... All Computer equipment and auxiliary racks within a room should
> >be securely grounded to a single point with generous-size braided
> >ground straps.  It seems to be a good idea to tie down all incoming
> >terminal grounds (RS232 pin 7) to that same point. . . .
> 
> Everything I thought I knew about grounding says you never tie signal
> ground (pin 7) to frame ground.  Am I wrong, or is this a Big Mistake?

This is an almost-counter-intuitive trick I picked up at another site where
we were having a few seemingly-weird problems with RS232 signals that
seemed to "float" far too much.  The point is to make sure
that -- at the computer port side -- all the signal grounds sit at the same
potential.  Easiest way to accomplish this is to tie them all to the
reference ground.  We don't carry pin 1 (frame ground) from the terminals
to the computer.  From my experience, it works, even though there is
potential (no pun intended) ground loop problem with remote terminals
that also tie pin 7 to their frame ground, and have a different reference
ground (say, in another building).
-- 
Bob Cunningham  {dual|vortex|ihnp4}!islenet!bob
Hawaii Institute of Geophysics Computing Facilities
Honolulu, Hawaii