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Friday, October 14, 2022
Question:
Hello Code Question of the Day, I was wondering if you can settle a debate for me when it comes to grounding electrode conductor sizing. If you were to have a 100 amp service in a dwelling unit and were to install #4 copper service entrance conductors allowed by 310.12, what is the minimum size grounding electrode conductor you would need to connect to a concrete encased electrode? 250.66 states that you use the table to size all electrode conductors and that 250.66 (A) through (C) tells you the maximum you are required to run to certain electrodes. I would say for this installation that you can use a #8 grounding electrode conductor for this 100 amp service since that is what is given in the Table. I have someone else saying that you only use the Table for water pipe and building steel electrodes and that you must use 250.66 (A) through (C) for things like ground rods and concrete encased electrodes and that those sizes in those sub-sections are a minimum. He says you MUST run a #4 to a concrete encased electrode no matter what size service you have. Can you shed some light on this discussion, please?
Thank you!!
Greg Martin
A
Answer:
Greg, based on the information in your question, the minimum size Grounding Electrode Conductor run to the Concrete Encased Electrode would need to be a #8 Copper. The sizing of a Grounding Electrode Conductor starts with Section 250.66 which states the size of a Grounding Electrode Conductor shall not be less than given in Table 250.66, except as permitted in Section 250.66(A) through (C). While Table 250.66 gives us the minimum Grounding Electrode Conductor size, Section 250.66(B) states the Grounding Electrode Conductor for a Concrete Encased Electrode shall not be required to be larger than a #4 copper.