[TowerTalk] Ground Rods

[Eric Gustafson]

Dan,

What part of Arizona are you in?  I'm in the Rincon Creek valley
on the far east side of Tucson.

I just last week finished installing 10 ground rods at my
property.  Actually, we didn't use rods at all.  It was
impossible to drive in a standard ground rod and have it survive
the ordeal in a useful state.  Too many football sized rocks
mixed in with the clay and sand.

We ended up having a drilling company drill 10 foot deep holes 7
inches in diameter.  They used a hollow stem drill.  Once the
hole is drilled, we placed a length of 2 ought (#00) copper
grounding conductor all the way down the center of the drill stem
to the bottom of the hole.  Then we poured "GEM" or Ground
Enhancment Material down the stem to backfill the hole around the
conductor as we removed the drill stem.  The GEM is available as
a premix or you can make your own on site.  The mix is 75%
gypsum, 20% bentonite clay, 5% sodium sulfate.

I haven't watered the installations down yet.  I have been
letting the backfill settle a bit first.  But the ground
resistance of each "rod" is already far lower than for driven
rods I've measured in the area.  Once the backfill is moistened
and cures, the resistance will fall far lower yet.

We will also be trenching between the earth terminals.  The
interconnections will be buried horizontal conductors.  The
trenches will be at least 18 inches deep and will also get the
GEM backfill treatment.

Horizontal conductors can be used alone.  But the system needs to
be a lot more extensive and buried deeper than you describe.
Otherwise you can create a personnel and/or pet safety hazard.

73, Eric  N7CL



>Date: Fri, 16 Oct 1998 21:58:08 -0700
>From: Dan Baldwin <baldwin@primenet.com>
>
>I have been following the comments made earlier about driving
>ground rods.  Living in Arizona I had tried to drive a ground rod
>but gave up because of the soil (rock & clay) conditions here. I
>just read comments on the (antenna) reflector from a fellow
>Arizonian who also had the same problem.  I also was wondering
>like he did (thought it might be a dumb question) why do ground
>rods have to be buried vertically ? Why can't a few (#12 six
>feet) wires be layed out horizontally just a few inches down?
>Since he has asked the question on that reflector I thought I
>would pose the same question here. If anyone has any ideas on
>this I sure would like to know.
>
>Thanks Dan 73, KK7JZ

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