Hi Mat,
Copper strap is better than wire as it has lower inductance and lower
resistance.
Do not run any wires or strap out of the concrete base below grade.
Someone mentioned that they ran wires thru the concrete base and out the
side below grade to conveniently connect the radials to the tower.
The J bolts are already going into the concrete. Bond the rebar to them
inside the concrete. No need to run anything else in or out of the concrete.
Since the J bolts go into the concrete lightning current is going to get
into the concrete whether you want it to or not. You might as well use it to
advantage.
Radials should be bonded directly to each tower leg with a longer radius
from tower to earth over the concrete base. Don't make a neat sharp bend
over the edge of the concrete. No "ground rings" around the tower.
Ground rods under the concrete do little. You are much better off using
those same ground rods connected to radials coming off the tower legs.
The deeper you go the less effective a ground rod becomes because of the
added inductance.
Someone mentioned using aluminum clamps to clamp wires to rebar inside the
concrete. Aluminum and concrete do not get along at all. The aluminum will
corrode from the acids in the concrete. If there is enough aluminum it can
expand and crack the concrete as it corrodes.
Do not connect copper wire or strap directly to galvanized towers unless you
use a stainless steel piece between the two.
Do not let any copper wire or strap hang or be placed above any galvanized
surface even if it is not connected. Rain will wash copper ions over the
galvanized surface and remove the galvanize material.
A Ufer ground by itself is not enough and can cause concrete cracking
problems. A Ufer ground is a great AUGMENT to a system of ground rods and
radials.
I have seen a few tower bases that cracked from lightning. None of those had
ground rods or radials connected to them.
73
Gary K4FMX
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of Mat Eshpeter
> Sent: Monday, April 18, 2011 9:34 PM
> To: towertalk@contesting.com
> Subject: [TowerTalk] update: grounding questions: Ufer, strap,
> exothermic welds
>
>
> An update on this thread and a new question or two:
>
> Seems to be pretty well agreed that connecting the rebar to the tower
> and radials is a good thing. The potential damage to concrete is
> attributed to poor installation technique.
>
> I am confused about the preference for copper wire over strap for use as
> a buried ground radial to interconnect ground rods, given the much lower
> inductance of strap; it may be that the longevity of a big piece of
> buried wire outweighs the lower inductance benefit of comparatively
> thinner buried strap?
>
> I called a couple of electrical supply shops today. They seem to be in
> disbelief that anyone would use solid 2/0 copper wire for anything; one
> guy claimed I would only be able to bend this size solid wire with the
> same equipment used to bend conduit or pipe. Does anyone actually use
> 2/0 solid copper for grounding? If so, what is your experience regarding
> bending / handling this wire?
>
> I have delayed my tower base pour for another week while I figure out
> the final details of my ground strategy. I do appreciate the help
> offered by all those that have taken the time to respond to this thread.
>
> 73,
> Mat
> KK1C
>
>
>
>
>
>
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