[TowerTalk] Mot R36 related to NUMBER of installed ground

[Steve, W3AHL]

The Polyphaser document is:  “Lightning Protection & Grounding Solutions for Communication Sites” by Ken Rand, copyright 2000.  There is no mention of the maximum distance of ground rods from a tower.  However, for rocky sites where ground rods are not possible and a radial grounding field is laid on or just  below the surface, the recommendation is that the radials be no more than 75’ long and no less than 50’.  More radials are added in parallel from the base of the tower to achieve the desired impedance, while maintaining the desired fast transient response time of the grounding system.

The same principle is implied for ground rod installations in the diagrams and calculations – more parallel runs from the tower base are better.  And more short ground rods are better than fewer long ones due to the impedance of the rod.

I couldn’t find the complete PDF document online during a recent search, although there are chapters from the document on PolyPhaser’s web site as white papers.

It’s an excellent reference for lightning protection systems.

Steve, W3AHL
-----------------------------------
Date: Fri, 3 Nov 2017 11:58:40 -0500
From: "Jeff" <keepwalking188 at ac0c.com>
To: <towertalk at contesting.com>
Subject: Re: [TowerTalk] Mot R36 related to NUMBER of installed ground
rods

In one of the Polyphaser documents they talk about the rise time and length 
of a strike duration.  Forget the details but the conclusion was that rods 
further out than about 50' would not be effective because the strike would 
be over before the outlying rods came into play.

If that's true then it seems there is an implied maximum density of the 
field based on the 50' maximum radius for rods and the 2x rod length 
spacing.

73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie
...snip..