If a generator separately derived system has overcurrent protection, which NEC table is used to size the equipment grounding conductors?

The correct choice is indeed related to Table 250.122, which is used for sizing equipment grounding conductors based on the rating of the overcurrent protective device. In the context of a separately derived system, the requirement emphasizes that the equipment grounding conductors must be sized adequately to safely conduct any fault current that may occur.

This table provides specific guidelines for determining the minimum size of equipment grounding conductors depending on the size of the feeder or branch circuit conductors that the overcurrent protection device is protecting. Each size corresponds with certain ampacities, ensuring that the grounding system remains effective and reliable.

In contrast, the other tables mentioned serve different purposes. Table 250.118 outlines acceptable types of equipment grounding conductors, not their sizing. Table 250.90 deals with the general grounding and bonding requirements, and Table 250.143 addresses grounding conductors within specific installations but does not focus on sizing based directly on overcurrent protective devices. Thus, using Table 250.122 ensures compliance with NEC requirements for safety and fault protection in a separately derived system.