I think this is the official IRC requirement for a "concrete encased
electrode". It always seemed kind of marginal to me, but this is
minimum spec:
"An electrode encased by at least 2 inches of concrete, located within
and near the bottom of a concrete foundation or footing that is in
direct contact with the earth, consisting of at least 20 feet of one or
more bare or galvanized or other electrically conductive steel
reinforcing rods or bars not less than 1/2 inch diameter, or consisting
of at least 20 feet of bare copper conductor not smaller than No. 4
shall be considered as a grounding electrode."
In our county they want to see 20 feet of #4 solid copper laid out along
the footing and more or less wrapped around the rebar. When I built
this house I ran 20 feet of #4 copper wire in BOTH directions from the
service entrance and I clamped the wire to the rebar with bronze clamps,
but who knows whether that added anything.
73,
Dave AB7E
p.s. to the list: Yes, I realize that the spec says to keep the
electrodes encased by at least 2 inches of concrete, but I figured that
was because they accept steel as the electrode and everyone already
agrees (I think) that it is a bad idea to have reinforcing steel exposed
to a rusting environment. In this part of the country (true, this isn't
Florida), the #4 copper wire often exits the footing below grade before
coming up along the wall (usually protected by a PVC tube or something)
to the service panel.
Michael Tope wrote:
>
> Jim, Larry, et al:
>
> I haven't followed this entire thread, so I apologize if this has already
> been
> discussed. Is there anything in the code about electrode surface area in
> contact with the concrete? I mean if you put enough current density
> through any conductor or semicondutor it will suffer damage, but if you
> make the electrode surface area large enough, the current density won't
> ever get high enough to damage anything. Seems to me that the encased
> electode in a UFER ground would tend to have a pretty large surface
> area.
>
> 73 Mike, W4EF....................
>
>
>
>
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