[TowerTalk] ground rod depth problem due to rocky soil -- solutions?

[Jim Lux]

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..