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From: bill@bilver.uucp (Bill Vermillion)
Newsgroups: comp.dcom.modems
Subject: Re: Which is better to have?
Message-ID: <1991Apr25.164452.1129@bilver.uucp>
Date: 25 Apr 91 16:44:52 GMT
References: <1991Apr18.162946.29336@bilver.uucp> <3921.2812b277@hayes.uucp> <1991Apr23.001558.5462@dexter.mi.org>
Organization: W. J. Vermillion - Winter Park, FL
Lines: 60

In article <1991Apr23.001558.5462@dexter.mi.org> jsr@dexter.mi.org (Jay S. Rouman) writes:
>In article <3921.2812b277@hayes.uucp> tnixon@hayes.uucp writes:
>>unpredictable and dangerous.  I've seen several cases of lighting 
>>going THROUGH an external modem, arcing all around inside, and into 
>>the computer through the EIA-232 cable, so I can't list "lighting 
>>protection" as an advantage of external modems.  It may help a
>>little, but it's no guarantee.  You need external protection,
>>whether your modem is internal or external. 
 
>Just the kind of reassuring words we wanted to hear during lightning
>season. ;-)  What's considered good external protection these days?
>Will MOV's across the line do the job?  There are tons of places
>selling phone line protection devices but you never know what's inside
>or if they have much chance of working.

First thing to do is make sure your incoming lines are protected.
Locally United has been using gas-discharge tubes for years.
So.Bell started later - probably after seeing the lower failure
rates for equipment in United.

Before these were available we were buying them locally and
installing them ourselves.

When I was having lighting damage to such things as phone answering
devices a few years ago, I had telco replace the carbon blocks on
in-coming line with gas discharge - and it cured that problem.
Local hits however may get through everything.

There is one company here in Fl (and I forget the name) that I
talked with that does total protection of incoming lines.  Had a
site that the lightning entered through the phone lines,   got into
the ground system, then came back that way and wiped out 5
terminals and all the serial ports on the CPU and totally destroyed
2 printers.    If the phone lines had been protected it MIGHT have
limited the damage.   Hit was on a pole behnd the building.

You live here, you get used to it.   I have been within 100 feet of
strikes numerous times.  The tree at a neighbors that bit the
telebit.  The tree 10 feet from the back door. Gawd that was loud.

You do your best, protect as best as you can, and make sure your
insurance covers lightning.

But gas discharge tubes seem to be a good start.
Also check to make sure your lightning protection equipment is good
and dies in a fail safe mode.  In other words, if it gets hit, it
should not stop working.  I have seen some that will die during a
hit and then you have not protection , but you don't know it.

An ovelooked source in many designs is ground strike.  That is when
it hits near your house, and comes in through your ground system
and out through the power lines.  This is reverse of what most
people think.  It does not always come IN through the power lines,
and in ground strikes it can EXIT through the power lines.


And make sure your grounds are good.
-- 
Bill Vermillion - UUCP: uunet!tarpit!bilver!bill
                      : bill@bilver.UUCP