its not just a matter of inductance, it is also the current flowing in the
radial wire is dissipating into the soil as it travels.
As a rule of thumb radial wires more than about 50' long don't help much for
lightning, and more than 8 radials probably
won't contribute much to the protection. Adding rods along the radials is also
not that productive, though one
is often added at the end but lots of time more to act as an anchor than for
electrical effects.
NOTE, this is based on protection against lightning, NOT for minimizing step or
touch potential from AC power
system faults.. that has its own requirements that may require different ground
systems.
Jan 29, 2015 08:38:29 AM, john@kk9a.com wrote:
At what distance from the tower will ground rods be ineffective due to
wire inductance?
John KK9A
To: Ray Benny
Subject: Re: [TowerTalk] Lightning protection - length of grounding rods
runs from tower?
From: Chad WE9V
Date: Wed, 28 Jan 2015 22:27:40 -0600
On Wed, Jan 28, 2015 at 6:37 PM, Ray Benny
wrote:
> My question, or request for your thoughts, is it better to run 3 grounding
> wires out 40, 50 or 60 ft (8 ft ground rods about every 16 ft connected
> with bare #4 wire) or to run say 6 ground wires out, perhaps 30 - 40 ft
> outwards? I have room in all but one direction to trench out a 100 ft if
> that would be even better yet.
>
More shorter wires, not less long wires. The long wires are higher
impedance(inductance). More wires lowers inductance.
See page number 11, start of Chapter 2, of this PDF:
http://www.radio2way.net/Polyphaser%20Guide.pdf
Polyphaser knows what they're talking about. The entire book is good.
Chad WE9V
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