I'd prefer an installation a bit more secure<:-)) but "Usually"
something is better than nothing <LOL>
And with Lightening is a "sometimes"event that is unpredictable
event. IOW Even with a "good ground system" you can not provide
protection for all events. The bigger, the better, BUT you soon reach
the area of diminishing returns. A relatively simple and relatively
inexpensive ground system will "Probably" give you protection for a good
percentage of strikes A few more will up the percentage substantially,
but there is no way of predicying whether the next strike will be
typical, or a super strike. Wk know they "tend" to be related to the
seasons, but it's that "tend to" meaning a higher percentage of them
come in spring or fall, no that "they will" happen only in spring or
fall and not in summer. IOW, we are playing the odds
The first 6 years my tower was up with the elaborate ground system, it
took 17 visually verified direct hits. AFAIK it has received none in the
last 6 years. Why the difference? I have no idea. OTOH The first week
we spent in this house, there were several, really strong thunderstorm
with many, many major strikes within a couple hundred yards of our
house. They were the kind that sounded like a large caliber rifle shot,
and felt like someone hit the side of the house. We've had nothing like
those in many years.
73
Roger (K8RI)
On 1/21/2015 8:48 PM, Jim Lux wrote:
On 1/21/15 1:41 PM, Jim Brown wrote:
On Wed,1/21/2015 1:01 PM, Patrick Greenlee wrote:
I'm confused... (still, yet, again...)
There are recommendations to place ground rods (8 footers) 8 ft apart
in a circle (octagon.) If my 14 ft apart Ufer grounds are too close
together so as to act as a single point, what about the 8 ft rods 8 ft
apart?
Forget about "single point" with respect to these various earth
electrodes. Multiple electrodes (rods, Ufer, etc.) simply provides
multiple paths in parallel to discharge a strike. Each of those paths is
R + jwL, and the impedances to earth of the combination of those paths
adds like any other combination of resistance and inductance, except to
the extent that mutual coupling between the electrodes increases the
combined impedance.
Lightning is NOT a DC event, it is an RF event, with the energy
concentrated in very broad spectrum, roughly centered (on a log
frequency scale) around 1 MHz (in other words, spread roughly between 50
kHz and 20 MHz). Thus, the inductance dominates the impedance.
Resistance matters primarily to the extent that we would like the
conductor to carry as much as possible of the strike current before it
vaporizes. :)
And just plain old redundancy. Install 3 rods of various length in
various parts of your yard with manky old clamps cobbled together out
of stuff you found in the parts bin in your garage, don't look at them
for 10 years, and hopefully not all the clamps have fallen off. I
have used stainless steel hose clamps to connect ground wires to a
rod. Clearly not to code, clearly not a good long term solution, but
hey, I'm pretty sure that if something "bad" had happened while I had
it hooked up, it would have been a heck of a lot better than nothing.
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73
Roger (K8RI)
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