At 11:53 AM 6/21/2006, Beat Meier wrote:
>Hello
>
>I'm looking for an "easy" method to calculate more or less a tower base
>for my tower.
>The tower is NOT self supporting.
>Height: 66m (220ft)
>Shape: triangle
>Material: Painted steel, not galvanized.
>What is mounted are only "small" parabolid grids (1mx0.7m) and omni antennas.
>
>
>Every 6m there are the cables. From the base to half of the tower the
>cables go to 25m point
>from the half to top to a 50m point
>
> 50m
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>I want to use UFER ground. If read a lot of articles found in the forum
>and the internet
>but no one tells about how many metall grid you should put in a tower base.
The 'electrical code' name for a UFER ground is "concrete encased grounding
electrode" or words to that effect.
Usually, they require some length of conductor that is encased. For
instance, when my house was built (1998), the local code required no less
than 20 ft of AWG 4 copper wire, as one alternative.
As far as the electrical code goes it's in section 250.52(A)(3)
Concrete-Encased Electrode.
There's a discussion of just what you're wondering about at:
http://www.iaei.org/subscriber/magazine/05_e/johnston.htm
This article seems to imply that the Code requires 20 ft of conductor
(without saying what the conductor has to be). Amazingly, it would appear
that the requirement is just that there's 20 ft of metal in the concrete,
and it doesn't have to be contiguous, or even connected. I suppose that
the real issue is that there is enough conductor length to make the overall
conductivity of the whole assembly low enough, and small gaps in the metal
might not make any difference. (Concrete in contact with soil is a fairly
good conductor)
>Does for example a hole 1m (3ft) diameter, 2m deep (7ft) filled with
>concred and steel meshes to the job?
>
>Are there any good sites with calculations? I have nothing found.
>
>Thanks a lot for any info
>
>Beat
>--
>
>
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