Re: [TowerTalk] Station grounding on granite

["Jerry Keller" <k3bz@arrl.net>]

Martin... I have a similar situation but with quite a bit more soil over the 
rock. I have a terrible
time getting a ground rod down more than about 4 feet, so I put them in on the 
slant. I surrounded
my house with a circle of #4 bare solid copper with 8' copper-clad ground rods 
about every 16 feet,
and tied everything to that circle.

The AC service ground is near the front corner of the house and its ground rod 
is right on the
circle. The SPG box is by the edge of the deck in the rear of the house, and is 
joined by a 20 foot
PVC pipe under the deck to the house where the shack is in the basement, below 
grade. The metal SPG
box is right on the circle also, and has a ground rod directly under it joined 
to the circle. The
metal SPG box contains a 3/16" thick sheet of copper (from local salvage yard...cheap) 
about 12"x12"
on which are mounted I.C.E. coaxial lightning/EMP suppressors (one for each 
antenna line, plus 2 to
protect the SteppIR control line and one for the rotator control line.12"x12" 
gives plenty of room
for expansion if you stagger the suppressors so the coax lines can go in 
between them.)

I have a 30' run of #4 bare solid copper running from the SPG out under the lawn to the base of the
40M vertical, and another to the tower base about 60' out. The tower has 3 ground rods for each 
tower leg, spaced 16' apart and connected by #4 bare solid copper running out from each leg. The 40M 
vertical has a rod at its base. For every run >16'  I put in another
ground rod about every 16 feet (twice the length of the ground rods). The feedline coax also runs
under the lawn in PVC pipes. If I were to install lightning rods on top of the house, I'd join them
to the ground circle also (unless the local code said different).

I have a long piece of copper pipe running the length of the back of my 
operating table. Every piece
of gear is grounded to that single pipe, and it is tied to the SPG panel with 
as short a run as
possible of #4 solid copper.

I got most of the ideas from the guys right here on TowerTalk, plus the info 
provided on the
Polyphaser and I.C.E. websites. The main point I followed was to insure that 
everything was tied
together so potentials will rise and fall at the same rate and time in the 
whole system. I even went
through my water pipe system and made sure it was all tied together with #4 
since there is some
copper pipe and some PVC pipe in the house.

I could have done it better, and I'll be making some improvements as time and $ 
permits. I want to
improve the ground run from the SPG into the shack. I want to change to 3" wide 
copper strap in some
places. And I'm sure other ideas will come up that make sense. I'm no expert, 
but what I did made
sense to me at the time. There's a lot of different opinions about what is best 
in the lightning
protection area, and I guess everyone has to make up their own mind as to what 
will work best for
them at their location. I hope this helps get you started. And I'm sure there 
will be lots of
additional opinions offered to you.

73,  Jerry K3BZ

----- Original Message ----- 
From: "Martin Ewing" <martin@aa6e.net>
To: <towertalk@contesting.com>
Sent: Saturday, November 20, 2004 11:45 PM
Subject: [TowerTalk] Station grounding on granite


> Folks,
>
> Having invested in a SteppIR, a roof-top tower, a
> rotor, and several wire antennas, I find I have a lot
> of copper running out to the sky from my shack.  Too
> much to easily disconnect when I hear thunder.  Time
> to think about a better protective ground system.
>
> Inside the shack, I am thinking of a single-point
> ground plane near the feedline entrances.  All
> connections including AC power, telephone, computer,
> SteppIR/rotor control, etc. pass through surge devices
> on that plane, and all equipment is hopefully
> connected by low inductance strapping to the SPG.
>
> My problem is how to get a good "earth ground" for the
> SPG.  My house is on a granite ledge with only 1-2 ft
> of soil nearby. We are about 80 ft from salt water,
> but that doesn't help. The house does have lightning
> rods with 3 or 4 downleads (more on this in a moment).
> The 20-ft rooftop tower is connected to a lightning
> rod ground, but feedlines are not.
>
> I was wondering how the lightning rod grounds were set
> up, so I partly excavated one.  The results are
> visible on my web site:
> http://www.aa6e.net/aa6e/grounding .
>
> Is this approach - dual buried horizontal ground rods
> - good enough even for home protection?  Should I do
> something like this for my station? (The shack is not
> near any of the existing ground connections.)
>
> It's clear that not even an "excellent" ground
> connection can prevent kilovolt surges from a near
> hit, because that is what happens to the earth itself.
> And full protection from a direct hit to the house is
> hard to achieve (IMO) no matter how you try in a
> typical home retrofit. The whole shack should be
> inside a grounded metal box...
>
> My philosophy now is to concentrate on the SPG system
> and not to obsess on the low-Z ground, which must be
> pretty hard to realize over rock.  (I would put in
> something like what I see on the existing lightning
> rod system.) If the SPG is really good, and the
> equipment is all referred to that carefully, then it
> shouldn't matter if the whole system floats up and
> down by kilovolts.  (Hopefully the op is elsewhere!)
>
> The "kilovolt" scenario doesn't quite catch the full
> impact of a direct hit to the antenna.  10,000 amps
> into a one ohm ground (?) is 10 kV.  No one expects
> the Spanish Inquisition! (i.e., worst-case event)
>
> I would appreciate suggestions, especially from anyone
> who has faced a similar problem -- and survived the
> worst.
>
> 73, Martin, AA6E
>
> p.s. Fortunately here in CT, we have fairly low
> lightning incidence.  Even so, we had a close strike a
> couple of years ago.  A BIG crack, and both my close
> neighbors lost their telephones and other electronics.
> We had no troubles here.  My tower was down then;
> maybe our lightning rods actually caught one. Thank
> you, Ben Franklin.
>
>
> _______________________________________________
>
> 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.
>
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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.

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