On Tue, 07 Jul 2009 10:34:04 -0500, Scott Neader KA9FOX wrote:
>1) How much distance from the tower to the first ground rod?
The FIRST ground electrode is the concrete itself. Spacing between
electrodes should be roughly equal to the length of the rod(s), so I'd
put the first rod at a spacing equal to the depth of the base.
>2) How much distance from the first ground rod to the second ground
>rod? I am assuming it should be 16 feet, based on past research (add
>up the length of each ground rod, as if you had laid them on the
ground)
Spacing equal to the length of the rod(s).
>3) How to attach this 3/4" braided copper strap to the ground rods?
Most experts advise against BRAID -- it corrodes much faster than solid
copper. For my tower project, I'm using solid copper strips that I
bought from DXE.
>4) How to attach this 3/4" braided copper strap to the tower? I see
>Polyphaser has various sized "TK" clamps for this purpose (see
>http://www.dxengineering.com/products.asp?ID=103 ) -- are these
>OK?
That's what I'm using.
>5) How far underground does the braid need to go?
Uninsulated conductors in the earth act as additional ground electrodes,
and lower is likely to get them into soil that is more moist (and thus
more conductive.
>And how far down
>below the ground do the ground rods need to go? Soil is largely
>"clay" with some topsoil. Do I need to go down below the frost
>line? (i.e. 2 feet ??) That sounds like a lot of work, if
>so!!
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!
73,
Jim Brown K9YC
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