[TowerTalk] Tower grounding

[David Gilbert]

I have to ask, though ... what in your mind makes any of this relevant 
to whether or not bringing a copper wire out from a tower foundation 
below grade in any way is deleterious to the foundation??  That was the 
original discussion, remember?   Please connect the imaginary dots for me.

Dave   AB7E



On 7/18/2013 12:43 PM, David Gilbert wrote:
>
> I didn't say it wasn't possible to do so.  I said that the majority of 
> residential Ufer grounds in the footing bring the ground wire up to 
> the breaker panel from outside the footing. E3508.1.2 of the IRC gives 
> almost the same description of a Ufer as you quoted below, and neither 
> specify that the connecting electrode conductor needs to exit the 
> concrete above grade.  In fact, those same codes specify that grounded 
> electrodes formed by simple ground rods must be below the surface of 
> the soil in order to physically protect the wire at the connection to 
> the ground rod (unless other means are in place to protect it).
>
> If still in doubt, check out Exhibit 250.27 of the NEC for examples of 
> accepted grounding systems, some of which leave the concrete below grade.
>
> Dave   AB7E
>
>
>
>
> On 7/18/2013 12:03 PM, Grant Saviers wrote:
>>
>> On 7/18/2013 9:29 AM, David Gilbert wrote:
>>>
>>> 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?
>> The copper wire attaches to the exposed inside the structure rebar 
>> stub and goes to the entrance panel ground and the steel building 
>> frame. Per code and an inspection of my Ufer ground foundation. For 
>> the tower the copper ground wire connects to an anchor bolt which is 
>> tack welded/wire tied to the larger rebar cage, then to the tower 
>> bottom ground panel. No buried copper in concrete anywhere, tower or 
>> building.
>>>
>>> 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.
>> Incorrect. Grade beams are usually exposed inside the structure, dry 
>> and protected and in contact with the soil. As are side walls in 
>> contact with the earth. Footings are also exposed on the interior for 
>> steel structures. Structural steel (my building) also connects to the 
>> rebar via frame anchor bolts wired to the rebar. So there are 
>> multiple ways to have dry & protected connections to rebar without 
>> copper in the concrete.
>>
>> NEC 250.52A(3) (in my 2008 edition)
>>
>> (3) Concrete-Encased Electrode. An electrode encased
>> by at least 50 mm (2 in.) of concrete, located horizontally
>> near the bottom or vertically, and within that portion of a
>> concrete foundation or footing that is in direct contact with
>> the earth, consisting of at least 6.0 m (20 ft) of one or more
>> bare or zinc galvanized or other electrically conductive
>> coated steel reinforcing bars or rods of not less than 13 mm
>> (1⁄2 in.) in diameter, or consisting of at least 6.0 m (20 ft) of
>> bare copper conductor not smaller than 4 AWG. Reinforcing
>> bars shall be permitted to be bonded together by the
>> usual steel tie wires or other effective means. Where multiple
>> concrete-encased electrodes are present at a building
>> or structure, it shall be permissible to bond only one into
>> the grounding electrode system.
>>
>>> Dave AB7E
>>>
>>>
>>>
>>>
>> snip
>>
>