250.166 Size of the Direct-Current Grounding Electrode Conductor.
Code Change Summary: Code language was added to clarify that a DC grounding electrode conductor is never required to be larger than 3/0 copper or 250 kcmil aluminum.
The code change occurred only in the parent text of this section. The subsections that followed the parent text, 250.166(A) through (E), were unchanged.
One of the requirements in 250.166(B) is that the DC grounding electrode conductor (GEC) cannot be smaller than the largest conductor supplied by the system. If that was the case, then if 500 kcmil ungrounded conductors were supplied by the DC system, then the DC GEC would also need to be 500 kcmil. This has never been the intent of this section.
The new code language in the parent text of 250.166 makes it clear that the DC GEC is never required to be larger than 3/0 copper or 250 kcmil aluminum even if the conductors supplied by the DC system exceed those values.
Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code).
2011 Code Language:
250.166 Size of the Direct-Current Grounding Electrode Conductor. The size of the grounding electrode conductor for a dc system shall be as specified in 250.166(A) and (B), except as permitted by 250.166(C) through (E).
2014 Code Language:
250.166 Size of the Direct-Current Grounding Electrode Conductor. The size of the grounding electrode conductor for a dc system shall be as specified in 250.166(A) and (B), except as permitted by 250.166(C) through (E). The grounding electrode conductor for a dc system shall meet the sizing requirements in this section but shall not be required to be larger than 3/0 copper or 250 kcmil aluminum.
