Good comments, Jim is right on the money.
I would add that 6 ground rods is a good start, but you may want more.
I found copper sheet from a local metal recycling place. I bought a 3'x10'
sheet and cut it into strips to interconnect all my ground rods. I built my
own clamps, very similar to these:
http://www.dxengineering.com/Parts.asp?ID=913&PLID=103&SecID=51&DeptID=19&Pa
rtNo=PPC%2D10C%2D112S
I just couldn't stomach paying $40 a piece for these clamps, so I made my
own die and "stamped" them myself. I have 150ft. of copper strap and 13
ground rods in so far. Someday I want to completely encircle the house
(possibly when the fruit on the money tree gets ripe).
Chris
KF7P
----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: "Tower Talk List" <towertalk@contesting.com>
Sent: Tuesday, July 07, 2009 9:54 AM
Subject: Re: [TowerTalk] Tower Grounding advice
> 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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>
>
>
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