[TowerTalk] Mot R36 related to NUMBER of installed ground

[Jeff]

One of the docs that refers to the 50/75 is the Ham Radio Grounding doc.  On 
fresh look they say the radial should be 50-75' in length referring to the 
50' as "minimum".  So I guess that makes the basic radial construct assuming 
8' rods to be a radial of 48' with 3 rods at 16, 32 and 48' spacing from the 
base.

There is not much in the way of references in either document (Mot or the 
Polyphasers) which provide optimal layouts for a given set of radials.  One 
could intuit 3 such radial sets for a total of 9 per tower.

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

-----Original Message----- 
From: Steve, W3AHL
Sent: Friday, November 03, 2017 3:49 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Mot R36 related to NUMBER of installed ground

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..
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