[TowerTalk] Tower grounding

[David Gilbert]

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
>