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Re: [TowerTalk] From the perspective of a concrete technician

To: Michael Tope <>
Subject: Re: [TowerTalk] From the perspective of a concrete technician
From: David Gilbert <>
Date: Sat, 15 Sep 2007 11:07:05 -0700
List-post: <>
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.

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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