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

Subject: Re: [TowerTalk] ground rod depth problem due to rocky soil -- solutions?
From: Jim Lux <>
Date: Fri, 16 Nov 2012 10:12:12 -0800
List-post: <">>
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 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?


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