?
Thursday, May 11, 2017
Question:
What size ground rod and how many do I need for a 1200amp 480volt three phase service. I have a 3/0 wire.
Patrick Rosenauer
A
Answer:
Hey Patrick thanks for your question. Rod type grounding electrodes must be at least 8 ft in length and must be at least 5/8 inch in diameter unless listed as stated in 250.52(A)(5). All grounding electrodes, that meet 250.52(A)1) through 250.52(A)(7) and are present at each building or structure served , must be bonded together as stated in 250.50. If other electrodes are present they must be used and you might not need any rod type electrodes.
If there are no grounding electrodes present then a rod type electrode is allowed as stated in the second sentence of 250.50. A single rod type grounding electrode must be supplemented by an additional electrode (could be a 2nd rod) as stated in 250.53(A)(2) unless the resistance is not more than 25 ohms as stated in the exception. Grounding electrode conductors are sized using 250.66 and if only rod type grounding electrode(s) exist, then a 6 AWG copper or 4 AWG aluminum is acceptable.