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[TowerTalk] Ground Rods

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Subject: [TowerTalk] Ground Rods
From: (Bill Hider)
Date: Thu, 17 Apr 1997 03:48:58 -0700 wrote:
> In a message dated 97-04-16 21:44:20 EDT, (Wayne
> Wilson) writes:
> > Does the distance of the tower ground rods have any effect?
> >
> >  What is the preferred distance, 6 inches, 2 foot, 10 foot?
> >
>       The practical hemisphere of influence for ground rods is twice their
> length.  In other words, a ten foot ground rod has a hemisphere of
> approximately 20 feet.  So does the adjoining ground rod.  The rods should be
> spaced 20 feet apart so that their respective hemispheres just touch.  If the
> rods are closer together, you aren't getting the maximum effectiveness from
> them.  Farther apart is better than closer together.
>     If your question was "how far to space the ground rods from the tower"
> then the answer is to get them as close as practical to the tower legs.  The
> connecting wire should have big lazy bends in it and not sharp ones.  The
> sharp bends are high impedance points which is what you're tryin to avoid.
>  Putting a copper ground wire in direct contact with the galvanized tower leg
> is asking for trouble.  Use a little piece of stainless steel sheet between
> them and liberally apply antioxidant for best results.  You can clamp the
> thing together with an SS hoseclamp.
>      Then have several ground rods in series attached to each leg using the
> above distance to really enhance the job.
>     BTW, commercial ground systems use a value of 5 ohms for ground system
> resistance for their target value.  You've got to have a GOOD ground system
> to achieve it.
>      Once the tower legs are grounded adequately, you're ready to move on to
> the remaining steps of your ground system installation.
> 73,  Steve  K7LXC
> --
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Good response, Steve.  I'd add one followup comment.  If you space the
ground rods closer together than twice their length, you run the risk
that the lightning energy will flow UP into one or more of the ground
rods and flow back along the interconnecting ground wire.  This because
the radius=twice the length is the ground area needed by each rod for
maximum dissipation of energy by the rod.  If the rods are closer then
this, saturation may occur and the ground system then becomes the path
of least resistance to ground, and the energy may follow the ground
system to your equipment.

Bill, N3RR

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