On 1/19/15 9:30 AM, Brian Carling wrote:
I have not heard of this concrete ground before. Is it made with conductive
concrete?
No.. but regular concrete is more conductive than most soil (not to
mention that concrete often has reinforcing steel in it, which makes it
more conductive, too)
Look up "Ufer Ground" (after the inventor's name)
or "Concrete Encased Grounding Electrode". (what they call it in the
electrical code)
Basically, you have at least 20 feet of wire or other conductor in the
concrete that serves as the connection. You can use the rebar as a
conductor: there are Ufer grounds where they just bring one of the rebar
rods up through the surface and you connect to that. More commonly,
it's just a bare copper wire 23-25 feet long (so that you have 20 feet
in the concrete, and 3-5 feet sticking out to connect to the electrical
panel ground, or the conduit feeding the electrical panel.
So you have really good contact between the wire and the concrete
(because it's cast in place), and also good contact area between the
concrete and surrounding soil (because it's big, and it's heavy).
In my area (Southern California), a single rod can't serve as the system
ground, you have to use a Ufer ground, or one of the other substitutes.
Cold water pipe also can't be used as the sole ground (too much plastic
pipe these days).
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