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Re: [TowerTalk] tower ground question

To: jim Jarvis <>
Subject: Re: [TowerTalk] tower ground question
From: David Gilbert <>
Date: Thu, 29 May 2008 12:13:33 -0700
List-post: <">>

Actually, we may be approaching some common ground here ...

Yes, I would agree that a good shunt path outside the foundation would 
be desirable for the reasons you mention (ability to monitor corrosion, 
potentially straighter path to ground with less bends, etc).  I had some 
practical reasons for wanting to avoid doing that, though, (the wall 
around my foundation, etc) and electrically I can't see any difference 
whether the shunt path goes through or around the concrete.

I also had another reason for wanting to install ground wires that 
exited the foundation underground.  The foundation for my 
self-supporting tower (AN Wireless HD-70) is spec'd at 9 feet on a side 
and 5 feet deep.  The tower base is 5 feet long and is spec'd to be 
embedded almost it's entire length into the base ... there is only about 
6 inches of concrete between the bottom of the tower base and the bottom 
of the concrete foundation.  The tower base is absolutely the lowest 
impedance path to anywhere, and it leads to within six inches of the 
soil under the foundation.  It seemed highly prudent to me to provide as 
many short, direct paths to ground that would hopefully shunt and energy 
that might otherwise want to go from the bottom of the tower base 
directly through the bulk concrete to ground.  I tried to do that by 
bonding the tower base to the rebar cage to make a Ufer ground (required 
by the zoning regulations in my area anyway), and additionally by 
bonding several copper wires to the tower base inside the concrete 
foundation and bringing them out the side of the foundation for bonding 
to ground rods in a radial pattern around the tower.  I still see no 
jeopardy in doing any of this other than possible long term corrosion of 
the copper wire.  I was and still am more concerned about a lightning 
strike blowing a chunk out of the bottom of my foundation rather than 
the side, and in my opinion the situation would be similar for most 
other non-insulated towers out there with embedded bases.

Also keep in mind that Ufer grounds for houses are constructed in this 
exact same manner, with a copper wire embedded in concrete, so if 
corrosion is a concern there are a several million homes out there with 
the same issue.

Dave   AB7E

jim Jarvis wrote:
> David,
> I would venture to say there are more insulated, serial fed towers in 
> the air, than grounded
> through the foundation amateur towers, by a fair margin.   But I could 
> be wrong, and it's totally
> academic.
> You are right that a good conductor through the concrete represents a 
> shunt path.    So long as it
> has the current carrying capacity,  and isn't degraded by corrosion,  
> it's better than not.
> I think, reading what you wrote, that you would agree that having that 
> shunt path OUTSIDE the
> concrete is preferable.   We don't differ on the question of brute 
> force grounding.    But I believe
> strongly .. STRONGLY ...  that the routing of the current path through 
> the concrete is equally
> important.   i.e.  no right angles,  gentle bends,  lots of surface 
> area  from copper strap,  etc.
> I've seen what corrosion happens with copper pipe in concrete, after 
> 15 years.    All the heating pipes
> in my VT house were run inside a slab, and not inside pvc conduit.    
> For the longest time, I wondered
> why my basement floor was pleasantly warm in the winter, until I 
> realized we were leaking hot water.
> And where the copper tube for the oil input came through the 
> foundation?   It, too, became leaky.
> So, while I will accept arguments supporting in-concrete ground 
> systems, when they're first installed,
> I will remain skeptical of their downstream value.   I want my 
> lightning protection grounds to be where
> i can see them and maintain them, if required.
> n2ea

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