Scott Bullock KA1CLX <firstname.lastname@example.org> wrote:
>>Basically, in a Ufer ground system, you use either copper wires inside the
>>concrete tower base, or the rebar cage if you have one, as part of your
>>ground system. The tower is tied to the cage, and the cage is tied to a
>>soil ground radial/rod system.
>I always thought this was a big no no, because the rebar would then have a
>potential difference on it, and that would cause the water molecules to
>heat up during a lightning strike thereby causing the concrete to explode.
>I'll stick to the tried and true methods of using external rods with heavy
>strap to each tower leg. Once you pour the base, it's there for life! If it
>ever turned out later for this way of grounding that it was wrong, i'd feel
>nervous when every electrical storm approached.
The PolyPhaser author states, "In my many years of experience, I have only
seen one tower base with cracks that could be considered as lightning
induced. Ufers should always be used to augment your grounding system and
not to be the entire system. Radials or radials with ground rods should be
used together with the Ufer...
"For those who are afraid to use the Ufer, think about this: The heating of
the concrete is more likely if the current is high or concentrated in a
given area. This is known as current density J. The more surface area you
have to spread out the current, the less the current density. YOUR TOWER'S
ANCHOR BOLTS ARE IN THE CONCRETE ANYWAY. If your ground system is poor,
the current density surrounding the bolts will be high and can blow apart
your concrete. At least if you tie in your rebar, the area is increased
and the current density is decreased."
73 Scott KA9FOX
INTERNET SOLUTIONS - Affordable web page design and storage
Scott Neader 608-788-1234 / FAX 608-787-0100
neader@QTH.com 3323 South 29th Street, La Crosse WI, 54601
Internet Solutions web: http://QTH.com/is Ham web: http://QTH.com
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Administrative requests: towertalk-REQUEST@contesting.com