Re: Lightening damage

Posted by k6dgw on Nov 07, 2017; 1:05am
URL: http://elecraft.85.s1.nabble.com/Lightening-damage-tp7635695p7635702.html

Nearly every direct strike will fry something (or manythings), connected
or not.  An arc that could involve a kilometer or two probably isn't
going to be deterred by a meter or so of disconnected coax.  The
grandson of my Elmer in the early 50's [who now holds his Grandpa's
call] became a lightning scientist.

His advice:  Very little [if any] electronic equipment will survive a
direct strike on your antenna.  There are many 10's of thousands of
amperes dashing around, and lightning arcs very often fork and take more
than one path in what appears to be random fashion.  For non-direct
hits, this electrical mayhem all still creates EMP's.  The goal is to
have everything conductive in your shack to float at the *same*
potential.  This means bonding everything together. Connecting that bond
to an earth electrode is problematical.  If you do, that electrode
should be bonded to the one at the service entrance [which more often
than not is a UFER electrode in most late 20th and 21st century
construction].

Disconnecting outside can be helpful in some cases.  However, my good
friend Tom, K5RC, who operates the Comstock Memorial Station near
Virginia City NV, with 7 [or so, I haven't counted lately] towers, some
well over 30 m, notes:  "Lightning will just as likely strike a 1 meter
sagebrush bush as a 47 meter tower with a 3-el 80 meter yagi at the top."

That said, in the rare times when we had close lightning while living in
the foothills of the Sierra Nevada, I did the disconnect at the base of
the tower out back.

73,

Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 11/6/2017 4:12 PM, Gmail wrote:

> I’m sure there are others with more expertise on this subject then me, however several texts including the new ARRL grounding book say it may be dangerous to disconnect antenna coax in the house. It should only be done outside.
>    My daughters vertical was hit by lightening and the lightening leaped 5 feet from a cable on the floor to a power outlet.
> Ray
> W8LYJ
>
> Sent from my iPad
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