Brian--
I worked in a 1000 acre plant that developed Rockets, for 38 years. Every
building was on an Ufer ground system, but they were not as simple as has
been described here. The buildings had "Franklin" type rods at high points,
coupled to the Ufer system by large copper cables. The Ufer system was
supplemented with additional Copper cables in ditches around the perimeter.
Concrete needs no additional ingredients to be conductive. The Ufer system
consists of the incorporation of a distributed set of conductors within the
concrete which are, in turn, connected to a dissipation arrangement exterior
to the protected structure.
I only remember one case of structure Lightning damage in that 38 years,
and that was caused by a painting crew having cut a cable and not reporting
it for repair. In that incident, the failure was not in the Ufer
arrangement, but in damage to the "Franklin" part. The damage was above the
cut in the cable.
Bill--W4BSG
-----Original Message-----
From: Brian Carling
Sent: Monday, January 19, 2015 7:29 PM
To: Chuck Dietz
Cc: towertalk@contesting.com ; jim@audiosystemsgroup.com
Subject: Re: [TowerTalk] RF Ground is a Myth
The advice varies about this considerably. This week is the first time I've
even heard of UF ER or conductive concrete!
The professional experts that I know recommend putting a 20 to 30 foot
ground rod into the ground at each corner of your house and connecting heavy
gauge copper conductors up to lightning rodsup on the roof.
It seems like if the only thing you need is a large area of this allegedly
conductive concrete stuck in the ground, why not ground everything to the
concrete slab your house sits on!!
Best regards - Brian Carling
AF4K Crystals Co.
117 Sterling Pine St.
Sanford, FL 32773
Tel: +USA 321-262-5471
On Jan 19, 2015, at 8:19 PM, Chuck Dietz <w5prchuck@gmail.com> wrote:
From what you have said, I take it that putting a single (or even 2 or 3)
ground rods on a tower base that is in a good bit of concrete is
wasted effort? The tower base and concrete should dissipate most of a
lightning strike?
Chuck W5PR
On Mon, Jan 19, 2015 at 12:59 PM, Jim Brown <jim@audiosystemsgroup.com>
wrote:
The real issue is that the concept of "RF Ground" is a myth and the
result
of fuzzy thinking. Part of the reason is what Jim has addressed below.
The
other reason is simply that a connection to earth does NOT make TX
antennas
work better, and is NOT part of a solution to hum, buzz, or RFI. The
earth
is NOT a sink into which noise and RF is dumped. The ONLY reasons for an
earth connection are to sink lightning current and other
equipment-related
surge currents on the AC line.
My late colleague, Neil Muncy, ex-W3WJE, taught classes on power and
grounding for many years to audio professionals, and I took over those
classes when he no longer had the health to do them. He is also the guy
who
alerted the world to "The Pin One Problem" back in 1994. He gave one of
my
favorite teaching examples. He would say to a class, "park yourself at
the
end of the runway of the nearest major airport with a good pair of
binoculars, and call me collect when you see an aircraft take off
trailing
a ground wire."
73, Jim K9YC
On Mon,1/19/2015 9:15 AM, Jim Lux wrote:
Are there different answers depending on why we have the ground rod?
(RF
ground, power line ground, or lightning protection)
Yes..
ground rods make terrible RF grounds, in general (where RF is HF and
up):
skin effect means that wires and rods have high ac resistance. (skin
depth
in copper at 10 MHz is about 0.8 mils/0.02 mm.)
They also have significant series L (1 microhenry/meter for a wire.. so
a
30 foot run to the rod is a 10 uH inductor, that's 600 ohms reactive
impedance.
Rods are really for electrical safety ground and/or lightning ground.
And
they don't work all that well for that, unless deployed in large
numbers.
The advantage of a rod is that it's easy to install by driving, but as
an
electrical connection to the earth, it's just not that wonderful: the
surface area is quite small (8 foot rod, 1" in diameter is only 300
square
inches. You could probably do better, electrically, by burying a 1 foot
square plate (288 square inches).
Rods are also used in phone and power line applications.. you drive a
rod
at every pole (or wrap the ground wire around the foot of the pole when
planting it). Even if any one rod has crummy characteristics, there's
lots
of other rods in the circuit to help establish the common voltage
reference
and provide a fault current return. I've had telco installers drive a
new
rod next to the existing rods on the general principle that at least
they
knew the new rod was in good condition: faster to just do a new rod than
to
test the existing one
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