Each tap conductor to a common grounding electrode conductor for multiple separately derived systems shall be sized in accordance with ______, based on the derived ungrounded conductors of the separately derived system it serves.
See answer and applicable Code reference
The correct answer is: a) 250.66
Article 250 covers the general requirements for grounding and bonding. System grounding requirements are specifically outlined in Part II of this Article. As we drill further down into this Article, we find the requirements for grounding separately derived alternating-current systems in Sec. 250.30. As per 250.30(A)(6)(b), "Each tap conductor shall be sized in accordance with 250.66 based on the derived ungrounded conductors of the separately derived system it serves."