I have to ask, though ... what in your mind makes any of this relevant
to whether or not bringing a copper wire out from a tower foundation
below grade in any way is deleterious to the foundation?? That was the
original discussion, remember? Please connect the imaginary dots for me.
Dave AB7E
On 7/18/2013 12:43 PM, David Gilbert wrote:
I didn't say it wasn't possible to do so. I said that the majority of
residential Ufer grounds in the footing bring the ground wire up to
the breaker panel from outside the footing. E3508.1.2 of the IRC gives
almost the same description of a Ufer as you quoted below, and neither
specify that the connecting electrode conductor needs to exit the
concrete above grade. In fact, those same codes specify that grounded
electrodes formed by simple ground rods must be below the surface of
the soil in order to physically protect the wire at the connection to
the ground rod (unless other means are in place to protect it).
If still in doubt, check out Exhibit 250.27 of the NEC for examples of
accepted grounding systems, some of which leave the concrete below grade.
Dave AB7E
On 7/18/2013 12:03 PM, Grant Saviers wrote:
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
snip
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