Mike wrote:
> Jim Brown wrote:
>> I wouldn't go nuts. Remember that INDUCTANCE dominates the equivalent
>> circuit at the frequencies where nearly all the energy of lightning is
>> located (a few octaves centered around 1 MHz), and the earth itself
>> tends to be pretty lossy (resistive), so more short parallel paths are
>> more important than a few longer paths. If your tower has has a good,
>> short electrical connection to the concrete, that's likely to be the
>> best earth electrode in your system, probably as good as the rest of
>> them in parallel!
> How do you make an electrical connection to concrete?
>
With the traditional concrete encased grounding electrode, aka Ufer
ground. 20 feet of conductor in the concrete, bonded to your grounding
system. The conductor can be the rebar (tied is good enough.. doesn't
need to be welded) but then you have the problem of rebar penetrating
the concrete surface, which is generally a no-no. 20 feet of AWG 4
solid bare copper wire in the concrete is another approach.
Herb Ufer developed this grounding scheme specifically to deal with
places where ground electrodes didn't work well (dry, desert climate,
sand, etc.). It's reliable, high performance, lasts forever, etc.
Which is why the electrical code requires it for most situations.
Concrete is hydrophilic, so it tends to have a higher moisture content
than the surrounding soil, and hence higher conductivity.
The contact area between concrete and soil is very large, so the current
density is low.
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