[TowerTalk] Tower grounding

[David Gilbert]

Consider what is used to connect the Ufer rebar system to a tower, or to 
the electrical panel, or to anything else being grounded. Except for the 
rare instances of rebar being hard welded directly to the protected 
structure, it is done with copper wire also encased inside the 
concrete.  Assuming you grounded your tower to the rebar cage per code, 
how did you do it without using copper wire?

In any case, I don't use the copper wire instead of a Ufer ... mine are 
in addition to it.  My soil here is bone dry much of the year so in 
addition to the Ufer system in the foundation I ran six 30 foot long 
wires radially out from the tower, each with a cadwelded ground rod 
every ten feet.  Those wires are brought out from the side of the 
foundation below ground level so that nobody will trip over them.

And no, the copper wire that connects to a standard Ufer ground system 
does not attach to a portion of rebar protruding from the concrete.  I 
have never seen a house built that way, and every code book I've ever 
seen shows the copper wire going into the footing and then wrapped 
around the rebar for at least 20 feet.  In most cases the footing is 
below grade and the stem wall elevates the walls above grade, so there 
really is no such thing as a "protected protrusion" anyway ... it would 
be below grade and violate code to be exposed that way.

Dave   AB7E




On 7/18/2013 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
>
> 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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