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

[Jim Lux]

On 11/16/12 9:48 AM, K1TTT wrote:
> 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.
>

I sort of assumed that insulation would be punctured..  but sometimes 
it's easier to get insulated wire.

Interesting stuff.. some years ago I was in the back yard trying to make 
fulgurites with a bunch of energy discharge capacitors and I realized 
that the "fine scale" behavior is pretty un-researched and there wasn't 
much theory to look at.

I think in lightning (as opposed to antennas), efficiency isn't such a 
big deal: after all, if you heat the wires up, that's just the same as 
heating up the soil, as long as the wire doesn't melt.  So I see it as a 
"get the current density below some magic number where bad things 
happen", and then, as a secondary goal, keep the voltage rise minimized.

Reliability of the grounding system is another thing that I think needs 
attention.  One of the appeals (for me) of distributed grounding systems 
without ground rods is that you're not dependent on the local properties 
of the soil next to the rod.  You can focus more on mechanical 
ruggedness. Whether the radial is laying on top of the soil, buried 6" 
or buried 6 feet probably doesn't make much difference in performance 
(in places where the soil doesn't freeze), but there's a BIG difference 
in survivability.

Can't get much more rugged than a block or bar of concrete.  I seem to 
recall an IEEE paper (but I can't find it on my computer here now) that 
described a lightning ground that was basically a concrete encased wire 
scheme but entirely on top of the soil/rock.  It was for somewhere that 
they couldn't dig down for a conventional foundation for some reason 
(maybe a rocky site on an island?  I can't remember..it was somewhat 
unusual, like an atoll).


Freezing soil (brr.. I live in SoCal, so I never think about that).. 
what effect does that have on lightning grounding?  frozen water is very 
different than liquid:  epsilon is very low, very low dielectric loss as 
well.  Would a "ring ground" work in frozen soil?