Which of the electrodes listed below are not permitted for grounding, if any?
A. 60′ of #4 bare copper that is concrete-encased
B. 120′ of #2 bare copper buried in a trench that encircles the building
C. 10′ of 3/4″ dia. galvanized pipe
D. 2’x 2′ x 1/16″ solid copper plate
E. All are permitted
Answer: C
(many will answer “E” but it’s not the diameter that needs to be 3/4″ it’s the trade size does)
250.52 (A) (5) (a): “Grounding electrodes of pipe or conduit shall not be smaller than metric designator 21 (trade size 3/4″) and, where of steel, shall have the outer surface galvanized or otherwise metal-coated for corrosion protection.”
(many will answer “D” but 1/16″ is 0.0625″)
250.52 (A) (7): “Each plact electrode shall expose not less than 0.186 square meters (2′ square) of surface to exterior soil….nonferrous metal shall be at least 1.5mm (0.06in.) in thickness.”
