On 9/17/12 7:23 AM, Jeff DePolo wrote:
See NEC 250.52 for some basics on ufer ground requirements. However, I
wouldn't consider meeting the bare minimums of 250.52 to necessarily be
adequate for the sake of a tower ground system. Fanning out the ground
system via additional electrodes could make a significant improvement over
the ufer alone without costing much money. Also keep in mind that the
effectiveness of any ground system varies greatly with soil conductivity, so
what may be an adequate ground system in one place may be wholly inadequate
somewhere else...
Bear in mind that the NEC required concrete encased grounding electrode
isn't necessarily the be-all for lightning dissipation. It will safety
handle the current, but you might have an unacceptably high "step"
potential: That is, the voltage gradient in a kilovolts per meter on the
surface of the soil will be quite high, so the voltage between something
at point A on the ground and something else at Point B, some distance
away, would be unacceptably high. This is why people do radial grounds
or ring grounds, etc. (everything within the ring is at pretty much
the same potential)
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