Date   : Mon, 14 May 1984 09:25:00 MDT (Mon)
From   : Keith Petersen <W8SDZ@Simtel20.ARPA>
Subject: Lightning Protection

Date: 12/03/81
From: DAVE HARDY
To:   All
Re:   Preventing system failures due to transcients

  After losing 3 PMMI couplers at TCBBS in about 3 months,
I contacted the local telco (who naturally could do nothing
about my problem) and PMMI.  PMMI gave me a new style
coupler that has been working, without problems, since
it was installed (about 6 or 7 storms ago).

  If you don't have a new style coupler, then try a fused
varistor across the phone line (telco CAN give you permission,
but first you have to find somebody there who knows what a
varistor is, and then convince him the the telco's fuses aren't
doing the job).  The function of the varistor here isn't to
eliminate the lightning induced transients.  It's to REDUCE
the transients to a point where the poor PMMI can tolerate
the "shock" (down to, say, a mere 100,000 volts for 1/10th sec).

  The telco puts fuses of its own in series with your phone line,
but, unfortunately, the telco equipment is more rugged than
your PMMI (although the PMMI coupler meets or exceeds the FCC's
definition of "lightning-proof.").

  The system here has survived at least one "direct hit" on the
phone lines since I installed the varistors in it.  It wouldn't
have been able to stand that before.  Because I had the line
fused in front of the varistor, all it did was cost me $1 for
a new fuse.

  You should also put varistors across the AC power lines that
supply EACH of the peripherals of your system.  Otherwise, a
lightning zap could get into one device by traveling through
another.

  The trick with using varistors is to figure out which of the
little beggars to use in each location, and what type and value
of fuse to use along with it.  You could just buy several
"canned" transient suppressors and plug them into every outlet
that your computer is connected to, but to be really safe, you
should consider using the proper type for each application.

  If you aren't incredibly familiar with varistors and their
use (who is?), trot on down to your local GE parts supplier
and grab a copy of the "GE VARISTOR HANDBOOK."  It explains
the theory behind varistors, tells how and where to use them,
and even gives examples and recommendations for their use with
(surprise!) micros and minis and telephone lines.