W7QD wrote:
"The final analysis is that you must not, under any circumstance,
permit an electric current to run through the concrete. Even if
a good conductor is embedded in the concrete, a lightning strike
will cause current to flow in the concrete immediately in contact
with the conductor and the degradation process will take place."
-0-
To which I will append a personal experience. At WBRW, in Somerville,NJ,
we put up a 4 tower array. The re-bar cage was tied to ground, and there
were 4 straps outside the foundation to the perimeter strap and radial
system,
at ground level.
Within a week of installation, and while we were doing the proof of
performance, a line squall blew through. All towers took direct hits.
After the storm, as we were at the tuning units, I observed cracks in
all the concrete bases. Not huge...but enough that water incursion and
freeze/thaw cycles would be of concern.
A hurricane two weeks later caused the river to rise and put 10kt current
across the river bottom pasture where our antenna was. All foundations were
undercut by the current...and two had large hunks of concrete fall off,
where the lightning cracks were. We had to straighten them up, and build
supporting foundations around them, to stabilize the structures.
-0-
I suspect the Ufer ground concept is simple: If we lose some concrete, so
what?
At least we don't light off the ordnance! I still don't know what's right
for an amateur installation, but if preservation of the structure is
paramount,
getting the strike current off of it cleanly would seem to be paramount.
Running it THROUGH the rebar seems counter-intuitive.
n2ea
Jim Jarvis, President
The Morse Group, LLC
www.themorsegroup.net
results@themorsegroup.net
Strategic Planning and Success Strategies
for Sales Professionals and Entrepreneurs.
Sales Excellence Series beginning October 2, 2007
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