Yes, but... while there are significant high frequency components to the
waveform, there is charge to be transferred mostly one direction, so you do
need the conduction pathway. And in experiments the mechanism appears to be
underground streamers rather than general ionization of large volumes of
soil... so insulation would likely end up full of holes. Plus for lower
frequency power safety grounding you would have a significantly higher
impedance. So unlike radials for a vertical antenna where you are just
worrying about transmission efficiency the insulation would probably not be
good for a lightning or safety ground.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net
-----Original Message-----
From: Jim Lux [mailto:jimlux@earthlink.net]
Sent: Friday, November 16, 2012 17:18
To: towertalk@contesting.com
Subject: Re: [TowerTalk] ground rod depth problem due to rocky soil --
solutions?
On 11/16/12 7:46 AM, K1TTT wrote:
> My program doesn't do strap, so instead of 2" strap that the OP has, I
> substituted 1" wire which gives a slightly smaller surface area... the
> OP said he was going have 700' of buried stuff so that is what I
> used... of course you can't bury in rock, but I can simulate it as a worst
case, the 1'
> of topsoil on top shows there isn't much difference.
>
From a transient behavior standpoint, I would imagine that the wire could
be insulated it and would work about the same. 700 feet x 1/3 foot is around
230 square feet of surface area, or 22 square meters..
if it's separated by 1mm from the "earth", that's a capacitance of
8.85E-12* 22/1E-3 F or about .2 uF...
At a nominal 1 MHz (for lightning), that's an impedance of a bit less than
an ohm...
and, because I'm a fan of Ufer grounds.. a 3x3x3 foot cube of concrete
in soil with the top surface exposed has a surface area of 45 square
feet, so its capacitive impedance is about 4 ohms.. a 5x5x5 cube is
about 2 ohms.. so don't worry about the vapor barrier between concrete
and soil. The concrete has lower inductance than the wire radials, too..
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