[TowerTalk] Ground Rods

[LYN]

Dan Baldwin wrote:

> 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.
>

Dan,

Since you asked for ideas instead of experimentally proven facts, I
guess that opens the door for me to explain the way I have always
pictured the operation of a ground rod. Someone has suggested
that I look at other concepts and that my ideas are wrong, but
until I do have time to investigate it, I picture a ground rod as being
an infinite number of small points on the surface of a metallic
conductor.  Some of these small points are near the point of
attachment, while others are further away and thus have small
increments of resistance and inductance between them and the
point of attachment.  It appears to me that these small amounts
of inductance and resistance are not going to be changed by
the physical orientation of the rod, so we must look outside
the rod for any differences which may occur due to orientation.

Outside the rod, it appears to me that each of these small
surface points is connected to the rest of the world through a
small pie-shaped wedge which extends outward from the rod
surface point to the point at which the wedge reaches an insulator
or the surface of the ground, whichever occurs first.  All of these
pie-shaped wedges would seem to have some resistance, with
the amount depending on the material and the moisture content,
and all of these resistances are connected in parallel (except for
the small increments of resistance and inductance in the rod,
which are not going to change due to orientation).

Now to the effects of orientation:  It seems to me that a ground
rod oriented vertically  may be considered to have more or less
equal pie-shaped wedges of earth connected to all the points
for a full 360 degrees around the rod, while a rod in a horizontal
orientation has wedges on the top side which quickly terminate
in the air at the surface of the earth.  This being the case, it seems
to me that the horizontal rod would have fewer long wedge-shaped
resistors connected in parallel and would thus have greater net
resistance.

Someone mentioned that RF and lightning tend to travel outward
from the rod near the earth's surface.  These same people tell
me that the series inductance in the ground rod keeps the far
(deep end) of a vertical rod from being effective as a ground for
lightning and rf. That argument doesn't influence me because
the series inductance in the rod is going to be there whether the
rod is vertical or horizontal.  Their argument would imply that
a one-foot long vertical ground rod would be just as good as
an eight-foot long vertical ground rod and I don't believe it.
They would seem to suggest that an array of short vertical
ground rods would be as good as an array of long vertical
ground rods.  I don't believe that either.

Now, I've been wrong before and may be wrong this time, but
that is my $.02 until I get a chance to examine empirical data which
proves otherwise.  Guess I may have a little ostrich blood in my
genes somewhere, but I will try to examine the available evidence
before I put in my next ground system.

Thanks for asking for ideas.  Now I'll get off my soap box.

Good luck and have fun.

Lyn, W4WDN


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