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Re: [TowerTalk] Conductive Concrete and Grounding

To: Jim Brown <>,"Tower Talk List" <>
Subject: Re: [TowerTalk] Conductive Concrete and Grounding
From: Randy <>
Date: Tue, 25 Jan 2005 23:25:16 -0500
List-post: <>
At 09:43 AM 11/19/2004, Jim Brown wrote:

I'm doing some reasearch for an applications note I'm preparing on power and
grounding for audio and video systems, and wanted to mention the use of a Ufer as a
ground electrode. This got me into a google search on the resistivity of concrete. It is
clear that resistivity varies over at least four orders of magnitude, depending on the
formulation, the mix of concrete and water, and how the concrete is poured.

I've come across an interesting webpage for what appears to be a small company
(garage?) selling specialty concrete.

There is now a lot of interest in the use of conductive concrete for snow melting, EMP
protection, and a variety of other uses. Here's a study of concrete for use as railroad
ties in electric railroads.

It seems logical that varying the formulation of concrete could significantly impact its
structural properties. But there would seem to be significant benefit from tying the
structural steel within a poured concrete foundation into the ground system of a building.


Jim Brown K9YC

My personal, layman's point-of-view is that lightning is wicked, wicked stuff, and largely refuses
to do what is expected of it. It *will* cause concrete to explode exactly like wood, trees, etc., i.e.
the sudden vaporization of the moisture within causing a violent expansion thereof. It likes to jump
into and out of conductors, I suppose due to the inductance it "sees" as well as the electrolytic
charging of whatever (normally) non-conductors it's trying to drain into, and probably a host of
other variables I'm unaware of. I locate underground water leaks for a living, and I can tell you
that lightning wreaks havoc on copper systems, "almost" always from a strike to the AC mains,
the cold pipe generally being tied to the ground/neutral buss at the breaker panel (sometimes
the hot line is also bonded to the cold at the water heater, which is where the connection to the
panel is usually made, hereabouts anyway). Personally, I wouldn't want such a system in either
a residential setting for safety of persons and equipment, nor would I want it in a tower base
for structural considerations. I have no idea whether a potent, direct hit could cause such a failure,
but in any event I think you'd want to Cadweld each and every point where the rebars crossed,
and I wonder whether the flexing of the bars during the pour might crack the joint. Also, bear
in mind that concrete is caustic to such an extent that a copper pipe in direct contact with it
will, eventually, most likely leak, so I'd have to question the long-term viability of any copper conductor
passing into the concrete; I think you'd have to bring the steel outside of the concrete and bond
to it above ground, preferably.
I was under the impression that Ufer grounds were only in use as a last resort, i.e. desert conditions,
but I could be wrong...

73 de KZ4RV



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