250.52A4 says "A ground ring encircling the building or structure, in direct contact with the earth, consisting of at least 6.0 m (20 ft) of bare copper conductor not smaller than 2 AWG."
Circle: Ellipse in which the two axes are of equal length; a plane curve generated by one point moving at a constant distance from a fixed point.
Encircle: Form a circle around.
so... not many circular buildings... we can assume that we probably don't need to form a perfect circle around the building, but do you assume that going completely around the builidng is required? some guys tell me that it doesn't really mean what it says about encirlcing the building, just use at least 20 feet of 2awg Cu... but how is that as good as a ufer since that is ok as an alternative? so i don't buy that... but then again, if you calculate a 20 foot circumference around a building, then it would probably be a dog house.
so my question is.... what does the NEC intend for us to do if we decide to use a ground ring? entirely encircle the building? go 20 feet along one side of the building?
Bob, I asked because 7-strand has ~61% of the surface area of 19-strand for the same cross-sectional area. Soil corrosion seems to vary quite a bit across the country. The “double-edged sword” of sorts is that more corrosive soil usually makes for lower ground-electrode resistance, which is usually desirable, but then, corrosion affects the working life of buried conductors.
I had always believed that the twenty foot minimum was to cope with well houses, gaurd shacks, and similar small structures in order to insure that there would be not less then twenty feet of wire in contact with the soil. -- Tom
"This alternating current stuff is just a fad. It is much too dangerous for general use" Thomas Alva Edison
The definition for a structure in article 100 is simply "that which is built or constructed." So couldn't a footing or column qualify as a structure? Then the ground ring would only have to encircle a footing, and not the entire building.
Article 100 also has a definition of a building; "A structure that stands alone or is cut off from adjoining structures...". The NEC handbook states that a "building" can also be a pole, a billboard sign, or a water tower.