[TowerTalk] More comments on lightning

[Chuck Lewis]

Eric Gustafson Courtesy Account wrote:
> 
> >Date: Thu, 04 Jun 1998 15:46:36 -0400
> >From: "Guy L. Olinger" <k2av@qsl.net>
> 
> Snip...  for brevity
> 
> >
> >It bothers me a bit to see some on this server discount
> >anecdotal material. If the theory cannot absorb the anecdotal
> >material (assuming no bald-faced lies), then the theory is
> >short. On the other hand, extrapolating a few anecdotes into a
> >pet theory is equally short. But MASSIVE anecdotal evidence
> >cannot be ignored for it's practical uses:
> >
> 
> Hi Guy,
> 
> I don't discount anecdotal accounts.  I very much enjoy seeing
> them.  Sometimes, I even inflict them.  I am nearly always
> educated to some degree by the accounts posted by others.  Even
> when my evaluation of the account reaches a very different
> conclusion about causality or whatever from the one being prmoted
> by the poster.  I assume others have the same experience with my
> anecdotal accounts.
> 
> >Lightning rods work (eg, protect the barn) if connected to good
> >grounds.
> >
> 
> True.  I have personally observed this.
> 
> >Massive ground fields under towers work.
> >
> 
> Also true.
> 
> >Lightning LOVES trees.
> >
> 
> Lightning loves anything that is conductive (to some degree more
> than air) and convenient.  By their nature, trees are frequently
> convenient.  We get the idea that lightning prefers trees because
> the effect of lightning on a tree is so easily observed.  You
> don't have to actually be there when it happened to see that the
> tree got hit.  If your tower is well bonded and grounded, you'll
> never know when it is hit unless you actually see it happen.
> 
> >Ungrounded or poorly grounded conductors from the vicinity of
> >poorly grounded lightning attractors create fireballs in the
> >hall and burn down people's houses (many years of fire
> >dept. experience to back this up).
> >
> 
> Amen!  Personal observation on this one too.
> 
> >  Here, simply disconnecting lines may guard against induced
> >surge, but may provide a path toward the house for a nearby
> >strike on a tower with a poorly dissipating ground system. Even
> >grounding both ends would not help if the connected grounds were
> >poor.
> >
> 
> Very true.
> 
> I have no problem with the concept of disconnecting feedlines
> from equipment as a substitute for installing commercial gas tube
> arresters.  However, I think that doing this absent first
> bringing the feedline to and bonding it to an adequately grounded
> entry panel is dangerous in the extreme.  If one must use the
> disconnect method, please be sure that there is a good ground on
> the feedline between the disconnection point and the antenna.
> You don't want to become the path.
> 
> >Moving toward massive evidence:
> >
> >Lightning doesn't strike "porcupines". Any reasonable theory
> >must explain why.
> >
> 
> I have seen lightning strike the porcupine devices on more than
> one occasion.  One time we had to scramble to get out of the rain
> of needles that resulted when the thing that held all the needles
> vaporized and released them all at once.  Those little pointy
> things are dangerous when falling from the 500 foot level on a
> tower.  We were lucky in that one of our group actually observed
> the hit and saw the things falling in time for us to step under
> the site roof overhang.  Every time we return to that site, we
> spend part of the day picking needles up so they don't puncture
> tires.
> 
> So I don't think any theory is going to be able to explain why
> they don't get hit.  They do get hit.  It would be relatively
> easy to formulate a theory to explain why people don't think they
> get hit.
> 
> >
> >I'm putting up a tower shortly. I intend to put in a large
> >ground system as soon as the base is poured. What I don't know
> >is how to measure the lightning receptivity of the ground. Any
> >help on this?
> >
> 
> I might be able to help with this one.
> 
> For the tower base (assuming it isn't located right near the
> service entry point for the house):
> 
> In most areas it is possible to rent or borrow an earth
> resistance tester.  With this device you can measure the
> connection resistance of a single ground rod.  If it is 25 ohms
> or less, you can probably do an adequate lightning protection job
> with a few in parallel.  But be sure to space them at least two
> times their length from each other.  Around here, a single 10
> foot ground rod averages between 25 and 30 ohms.
> 
> For the feedline entry into the envelope of the house:
> 
> If the house has no UFER ground for the service entrance, but
> does have metallic cold water distribution under the slab, we can
> normally get the lightning ground resistance down to 5 ohms or
> less with a pair of ground rods and the subgrade plumbing tied
> together.  If it has a UFER in the slab, the service entry ground
> is usually down in the 2 ohm range already.
> 
> I strongly recommend that you establish single point feedline
> entry panel very close to your service entry point and use the
> service entry ground.  The earth resistance meter can be used to
> evaluate the quality of your service entry ground.  If it is 5
> ohms or less, use it.  IF not, enhance it with ground rods and
> use it.

Eric, my tower is, for a number of reasons, adjacent to my shack, and my
service entrance is at the diagonally opposite corner of my house. A
90-100 foot run around the periphery of the house would be required to
bond the tower ground to the service entrance ground. Would that still
be effective even if I were to spend the effort & money? Or are there
alternatives in this case? Short of moving the tower or service
entrance, that is! 

Chuck, N4NM


--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm