[TowerTalk] Tower grounding

[Grant Saviers]

On 7/18/2013 9:29 AM, David Gilbert wrote:
>
> Consider what is used to connect the Ufer rebar system to a tower, or 
> to the electrical panel, or to anything else being grounded. Except 
> for the rare instances of rebar being hard welded directly to the 
> protected structure, it is done with copper wire also encased inside 
> the concrete. Assuming you grounded your tower to the rebar cage per 
> code, how did you do it without using copper wire?
The copper wire attaches to the exposed inside the structure rebar stub 
and goes to the entrance panel ground and the steel building frame. Per 
code and an inspection of my Ufer ground foundation. For the tower the 
copper ground wire connects to an anchor bolt which is tack welded/wire 
tied to the larger rebar cage, then to the tower bottom ground panel. No 
buried copper in concrete anywhere, tower or building.
>
> In any case, I don't use the copper wire instead of a Ufer ... mine 
> are in addition to it. My soil here is bone dry much of the year so in 
> addition to the Ufer system in the foundation I ran six 30 foot long 
> wires radially out from the tower, each with a cadwelded ground rod 
> every ten feet. Those wires are brought out from the side of the 
> foundation below ground level so that nobody will trip over them.
>
> And no, the copper wire that connects to a standard Ufer ground system 
> does not attach to a portion of rebar protruding from the concrete. I 
> have never seen a house built that way, and every code book I've ever 
> seen shows the copper wire going into the footing and then wrapped 
> around the rebar for at least 20 feet. In most cases the footing is 
> below grade and the stem wall elevates the walls above grade, so there 
> really is no such thing as a "protected protrusion" anyway ... it 
> would be below grade and violate code to be exposed that way.
Incorrect. Grade beams are usually exposed inside the structure, dry and 
protected and in contact with the soil. As are side walls in contact 
with the earth. Footings are also exposed on the interior for steel 
structures. Structural steel (my building) also connects to the rebar 
via frame anchor bolts wired to the rebar. So there are multiple ways to 
have dry & protected connections to rebar without copper in the concrete.

NEC 250.52A(3) (in my 2008 edition)

(3) Concrete-Encased Electrode. An electrode encased
by at least 50 mm (2 in.) of concrete, located horizontally
near the bottom or vertically, and within that portion of a
concrete foundation or footing that is in direct contact with
the earth, consisting of at least 6.0 m (20 ft) of one or more
bare or zinc galvanized or other electrically conductive
coated steel reinforcing bars or rods of not less than 13 mm
(1⁄2 in.) in diameter, or consisting of at least 6.0 m (20 ft) of
bare copper conductor not smaller than 4 AWG. Reinforcing
bars shall be permitted to be bonded together by the
usual steel tie wires or other effective means. Where multiple
concrete-encased electrodes are present at a building
or structure, it shall be permissible to bond only one into
the grounding electrode system.

> Dave AB7E
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