Polyphaser's The Grounds for Lightning and EMP Protection, Second
Edition, has this to say about radial grounds on rocky soil (p.22):
In this situation [rocky soil], numerous slightly shorter lengths
[radials], along with using solid flat strap radial conductors, has been
proven to work. The copper strap's sharp edge will concentrate the E fields
that are present due to the existing L di/dt voltage drop and breakdown or
arc onto the surface of the rock or soil.
On solid bare rock, straps will help spread out the charge on to the
surface of the rock.
What I take away from these passages is that, on rocky soil, one should
use a multitude of copper straps that are not too long (< 75 feet) and that
cover a wide area. (And keep your fingers crossed.)
Gene Smar AD3F
----- Original Message -----
From: "Steve London" <email@example.com>
Sent: Wednesday, August 03, 2005 4:41 PM
Subject: Re: [TowerTalk] Sparky Pays a Visit
> So, just for amusement, let's see what folks would do in my situation...
> I live on a very dry hilltop in SW New Mexico. There are large limestone
> boulders at the surface, or within a few inches of the surface. You don't
> this stuff with a shovel or backhoe - it takes a jackhammer or excavator
> jackhammer attachment. There is no moisture in the ground, except for a
> after a monsoon rain event.
> For what small good it might do, I have ground rods at each end of my
> The deepest I could get them was about 2 feet. The resistance between
> ground rods (which are about 500 feet apart) is around 5M ohms. We're
> DRY here !
> Frankly, what the local power company does for grounding seems worthless.
> drill a hole in the ground for their pole, run their copper ground wire to
> bottom of the pole, loop the copper wire in a spiral around the bottom of
> pole, and plop the pole in the ground. With no moisture in the ground, I
> believe that does anything. When my house was built, they didn't even try
> drive in a ground rod, they just used the rebar and concrete in the
> as a Ufer ground. I understand that is okay for safety grounding, but
> completely worthless for lightning protection.
> Now, as far as radio goes, I have a 105' guyed tower, about 100 feet from
> house, and two 30' guyed towers about 30 and 50 feet from the house. The
> tower has the typical Rohn-approved concrete base and guy anchors. No
> rods, buried copper wires, etc. All of the cables, from all of the towers
> on top of the ground, and terminate at an aluminum plate ("bulkhead")
> about 30' from the house. There is a separate set of cables that can be
> connected to the bulkhead connectors, running underground, through plastic
> conduit, to the ground-floor hamshack. When the hamshack cables are not
> connected to the bulkhead, they sit in a covered plastic bucket, about 3
> from the bulkhead. The bulkhead is not intentionally grounded or connected
> the house Ufer ground. My strategy is simple - I don't care what happens
> tower, but keep the lightning out of the house.
> I haven't had a direct hit yet, but that's only a matter of time on this
> It does make me feel like I'm playing with a loaded gun !
> So, short of doing a major excavation to lay a circle of copper tubing
> the house and bonding everything to it, what might make sense to protect
the house ?
> Steve London, N2IC/5
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
> TowerTalk mailing list
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
TowerTalk mailing list