In a message dated 99-09-06 14:03:37 EDT, smidtca@sprint.ca writes:
> Would someone please let me know what a UFER ground is and what is its
> purpose.
An Ufer ground is a technique where the tower base rebar cage and
concrete base is either part of the ground system or IS the ground system.
For towers that are on small plots of soil (i.e. TV tower in the city), this
may be the ENTIRE ground system. Since the concrete is conductive and there
is lots of concrete area in contact with the soil, it does a pretty
reasonable job.
The important thing here is that the rebar connections must be bonded -
either by brazing or exothermic (Cadweld, etc.) techniques. Of course, the
tower must be connected to this system as well using good mechanical or
exothermic means.
If you've got plenty of land that the tower sits on and you can build a
more traditional ground system, a direct connection from the tower leg to the
ground system negates the need for an Ufer system.
A 'tower urban legend' is that a lightning strike can break the concrete
in the base. What happens is that with a non-bonded rebar cage, the lightning
can arc between the pieces of rebar resulting in super-heating of the
moisture in the concrete. This can create internal pressures that can result
in cracking of the concrete. The lightning doesn't cause the concrete to
"explode". This can result from a poor ground system - poor tower to ground
rod connections, lack of ground rods and minimal ground system, etc.
Cheers, Steve K7LXC
Tower Tech
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