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?
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.
Dave AB7E
On 7/18/2013 6:29 AM, Grant Saviers wrote:
"extrapolation" may have been a poor word choice, but my reasoning is
that copper pipes are not buried without special precautions for
domestic water service because of corrosion. Another reason is that
the galvanic cells and/or stray currents that exist in soils can cause
electrolytic erosion. Copper clad ground rods are known to have
finite life, sometimes quite short in certain soils. Some concrete
mixtures were a disaster with buried radiant heating copper tubes and
that application now very rarely uses copper in concrete. There are
discussions on this reflector that AM broadcast station copper ground
screens disappear over time. Copper alloys in marine environments are
protected with sacrificial anodes or impressed voltage systems.
Copper in air lasts a long time, in an electrolytic or hostile
chemical environment not so.
So, why expose a Ufer ground lead to what might be an environment that
significantly shortens its life, particularly if it isn't possible to
inspect it? As I have read the Ufer literature and codes, steel rebar
is the conductor, not buried copper wire, and the connection is to a
protected rebar exit point from the concrete.
wikipedia re Ufer: "Ufer's original grounding scheme used copper
encased in concrete. However, the high pH of concrete often causes the
copper to chip and flake. For this reason, steel is often used instead
of copper."
see http://www.psihq.com/iread/ufergrnd.htm and
http://en.wikipedia.org/wiki/Ufer_ground
Grant KZ1W
On 7/17/2013 6:26 PM, David Gilbert wrote:
Why is that a "reasonable extrapolation"? Copper wire won't corrode,
and rust/corrosion is the ONLY reason that codes require rebar to be
fully embedded in the concrete. Please explain ...
Dave AB7E
On 7/17/2013 12:52 PM, Grant Saviers wrote:
Building codes now REQUIRE Ufer grounds in many jurisdictions for
new foundations. Codes also REQUIRE that rebar be covered with
concrete, usually a minimum of 3" to prevent corrosion ingress along
the rods. So it is reasonable to extrapolate that ground wires
connected to the rebar should not exit the concrete below grade ...
<snip>
Grant KZ1W
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