AC Power Protection

[Robert Barrell]

In article <319 at pallas.athenanet.com>, kabra437 at pallas.athenanet.com (Ken Abrams) writes:
> If you think you can save yourself from a direct lightning strike that
> occurs within a couple of hundred yards of your location, you are fooling
> yourself.  NOTHING will prevent damage in that case except having the
> system disconnected from ALL external wiring (grounds included).
> Lightening is nasty stuff and doesn't follow any rules.

     As an illustration of Ken's point, let me relate something which actually
happened to my boss's home machine.  

     My boss's house is located at the top of a hill, in semi-rural surroundings
(a prime target for lightning strikes - his sattelite dish has already been hit
twice).  He is aware of the proper procedures for preventing lightning damage,
and always disconnects all power cords during a storm.  A year or so ago, a
particularly bad storm arose a few hours after I had just installed a new,
external modem for him.  At the time, I had been short by one wire , so I had
not been able to leave the modem connected to the phone line.  In keeping with
common practice, though, I did set the phone on top of the modem before I left.
When the storm started to approach that night, my boss disconnected all the
power cords to the modem, external tape drive, computer, terminals, etc.  Since
the modem was not connected to the phone line, there was nothing to disconnect
there, yet.  He did NOT, however, disconnect the PHONE from the phone line.
Sure enough, THAT'S what got hit by the lightning.  That would not have been
too bad, but the brand of modem we had just connected (SmartLink - a Hayes look-
alike) had a metal case.  The lightning arc'ed from a rivet in the foot of the
phone, into the case of the modem.  Of course, the case was part of the ground
connection, so the strike quickly blew-out (and arc'ed through) the filter
capacitors for the RS232 lines.  From there, it proceeded directly into the
computer's serial board, melting two IC's and exploding two others.  It also
fried a terminal which had been attached to the second serial port on the same
board, and also managed to fry the primary hard drive (but, oddly enough, NOT
the controller, nor the secondary hard drive). 

     All of this happened on a machine where all external connections HAD been
removed, and only the spark-gap between a telephone foot's rivet and a modem's
metal case remained.  BTW, the NEW modem (another brand) has a plastic case,
as does the new phone, and *ALL* connections (including the phone lines) are
removed during a storm.

-- 
Robert Barrell      | ...!cbmvax!gvlv2!lock60!rdb1!root | Cody Computer Services
Milo's Meadow BBS   | root at rdb1         CIS: 70575,1312 | 55 East High Street
login: nuucp or bbs |-----------------------------------| Pottstown, PA   19464
(215) 323-0497      | Business and Police Dept Software | (215) 326-7476