Hi Dave,
I believe you are pretty much there. The 120' #2 wire serves as a rather good
ground for the tower and also serves the function as the equalizer (see #2).
In my opinion there are two main things you want to accomplish protecting
yourself from lightning strikes:
1) You want to discharge as much as possible of the current from the lightning.
That you do with grounding rods, grounding wires, grounding plates what have
you spread around and connected to your tower. )In my case I use 9 rods
connected with #4 wire to my tower). I guess your 120' wire is good and,
needless to say, more wires laid out is a star pattern around your tower will
help. What I understand, from reading, it is more important to have more wires
and not too long once. I would guess, and this is not based on anything but my
guts feeling, lengths of 20 - 30 feet would be optimal. Yes, the more the
better, NOT: "The longer the better" NO!
2) You want the voltage difference between your tower and your equipment to be
as small as possible. That's where the #2 cable between your tower and your
shack comes in. Here should be:" The more and the heavier the better". I
believe several wires in parallel and spread apart a few inches to a few feet
is good. (Similar effect as a Litz wire.) The idea is that in the event of a
lightning strike you want the shack to assume the same (or as close as
possible) voltage as the tower thereby reduce voltage induced current in your
feed and control wires. (I have a short, 6 inch wide, aluminum band between my
shack and my tower. The tower is only five feet away from my shack so that was
simple.)
Good luck and wishes of no lightning destruction in your tower or shack.
best 73 de,
Hans - N2JFS
-----Original Message-----
From: David Merchant <merchdl@gmail.com>
To: towertalk <towertalk@contesting.com>
Sent: Sun, May 1, 2016 1:11 pm
Subject: [TowerTalk] Ledge Lightning Ground Advice
Guys,
I could use some advice. Late last fall, I erected 40' of Rohn 25G with a
Tilt-over base. It sits on top of a ledge that only has about 2-3 feet of
rocky topsoil. When I dug the hole for the foundation, I excavated all the
loose fill and I core-drilled the rock below about 36". I then epoxied
4-pieces of rebar in the holes, and poured about 3-1/2 yards of concrete
with anchor bolts for the base plate. Unfortunately, I didn't think to bond
any of the rebar or anchor bolts.
Right now, the only grounding the tower has is a connection to a 2-ga ground
wire that runs 120' underground with the conduit that feeds the power. It's
in-turn mechanically connected to a 2-4' ground rod (the max I could
install) every 15'. The 2-ga wire is also connected to the Single-Point
Ground where the coax enters the home.
Since lightning season is about to get started, I'm concerned that this is
insufficient grounding.
I was considering bonding some 2-4" copper strap to each of the tower legs
and running it along the ground for 50' or so. Also, I do have a SteppIR
BigIR vertical about 20-feet away that has an extensive ground plane, albeit
with insulated 12-14-ga wires. This could be bonded as well, but currently
isn't.
What would you guys recommend I do to augment the existing ground?
73,
Dave
K1DLM
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