[TowerTalk] Tower grounding

[Jim Lux]

On 7/18/13 6:29 AM, Grant Saviers wrote:
> "extrapolation" may have been a poor word choice, but my reasoning is
> that copper pipes are not buried without special precautions for
> domestic water service because of corrosion.  Another reason is that the
> galvanic cells and/or stray currents that exist in soils can cause
> electrolytic erosion.  Copper clad ground rods are known to have finite
> life, sometimes quite short in certain soils.  Some concrete mixtures
> were a disaster with buried radiant heating copper tubes and that
> application now very rarely uses copper in concrete. There are
> discussions on this reflector that AM broadcast station copper ground
> screens disappear over time. Copper alloys in marine environments are
> protected with sacrificial anodes or impressed voltage systems.  Copper
> in air lasts a long time, in an electrolytic or hostile chemical
> environment not so.
>
> So, why expose a Ufer ground lead to what might be an environment that
> significantly shortens its life, particularly if it isn't possible to
> inspect it?  As I have read the Ufer literature and codes, steel rebar
> is the conductor, not buried copper wire, and the connection is to a
> protected rebar exit point from the concrete.
>
> wikipedia re Ufer: "Ufer's original grounding scheme used copper encased
> in concrete. However, the high pH of concrete often causes the copper to
> chip and flake. For this reason, steel is often used instead of copper."
>
> see http://www.psihq.com/iread/ufergrnd.htm and
> http://en.wikipedia.org/wiki/Ufer_ground
>

I'd be interested in seeing a reference for the "chip and flake"

I'm not too impressed by the Wikipedia entry. For one thing, they don't 
cite Ufer's paper, nor any of the subsequent ones on the subject.  And 
that comment about "flash into steam", as you can imagine from this 
discussion, is one that I would not agree with. Unfortunately, the cited 
reference is too general to actually find it.


Ufer's original paper
IEEE CP 61-978 (Conference Paper), Herbert G. Ufer

Then there's all of these, among others..


Herbert G. Ufer  "Investigation of footing-type grounding electrodes for 
electrical installations" IEEE Trans. Power Apparatus and Systems, Vol. 
83 p. 1042-1048 October 1964

Fagan, E.J. and Lee, R.H. (July/August 1970). The Use of 
Concrete-encased Reinforcing Rods as Grounding Electrodes", IEEE Trans. 
on Industry and General Applications, Vol. IGA-6, No. 4, pp. 337-348

Harding, G. and Harris C.A. (1970). Some Engineering Objections to Using 
Reinforcing Steel as Grounding Electrodes", IEEE IGA Conference 
Proceedings, pp. 181-187. Discussion by Lee, R.H.

Preminger, Julius. (Nov./Dec. 1975). "Evaluation of Concrete-encased 
Electrodes", IEEE Trans. on Industry Applications, Vol. IA-11, No. 6, 
pp. 664-668.

Kawai, M. (1965). "Studies of Tower Footing Resistance on Transmission 
Lines", IEEE Conference Paper No. 31 CP 65-704.

> Grant KZ1W
>
> On 7/17/2013 6:26 PM, David Gilbert wrote:
>>
>> Why is that a "reasonable extrapolation"?  Copper wire won't corrode,
>> and rust/corrosion is the ONLY reason that codes require rebar to be
>> fully embedded in the concrete.  Please explain ...
>>
>> Dave   AB7E
>>
>>
>>
>>
>> On 7/17/2013 12:52 PM, Grant Saviers wrote:
>>> Building codes now REQUIRE Ufer grounds in many jurisdictions for new
>>> foundations.  Codes also REQUIRE that rebar be covered with concrete,
>>> usually a minimum of 3" to prevent corrosion ingress along the rods.
>>> So it is reasonable to extrapolate that ground wires connected to the
>>> rebar should not exit the concrete below grade ... <snip>
>>>
>>> Grant KZ1W
>>
>>
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