What is the general rule for sizing the equipment grounding conductor for PV source and output circuits?

The correct choice revolves around the use of Table 250.122 from the National Electrical Code (NEC), which provides guidelines for sizing equipment grounding conductors. This table takes into account the size of the overcurrent protection device and specifies the minimum size of the equipment grounding conductor required for safety and compliance with electrical installation standards.

By referring to Table 250.122, you ensure that the grounding conductor is appropriately sized to handle potential fault currents while providing adequate protection against electrical shock and fire hazards. Proper grounding is crucial in photovoltaic (PV) systems to ensure the safety and functionality of the system under various conditions.

In contrast, the other options may lead to inadequate sizing if not backed by code requirements. For example, sizing based on inverter size or the largest connected load does not provide a standardized approach, as these parameters might not necessarily correlate with the required grounding conductor size. Setting a fixed size, like 6 AWG, ignores the specific circumstances outlined in Table 250.122, which varies according to the overcurrent protection device size and offers a more accurate sizing method tailored to the installation.