National Electrical Installation Standards

Standards as High as Your Own

Friday, January 25, 2019


Thank you for your code insight. I am confused, (my normal state) about 250.66 requirements for grounding electrode conductor size and 250.104 for water pipe and structural steel bonding. A service fed with 5 runs of 500 KCMIL copper would require a 3/0 grounding electrode conductor to the water pipe and building steel. However, 250.104 requires a 350 KCMIL copper the water pipe and building steel.

Am I confused, missing something, or merely misinformed.





Hey Mike thanks for your question and the kind words. No, you didn't miss anything, actually you point out an unintended rule.

The references in 250.104 were changed from Table 250.66 to Table 250.102(C)(1), in several places, for the 2017 NEC because the conductor is a bonding conductor, not a grounding electrode conductor. The largest grounding electrode conductor required by Table 250.66 is a 3/0 copper or 250 kcmil aluminum but bonding conductors and jumpers do not have the same limitation. This issue has been noted, and will hopefully be corrected for the 2020 NEC, to re-establish the 3/0 copper or 250 kcmil aluminum as maximum required sizes while retaining the correct terminology.

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