What is the minimum size requirement for a common grounding electrode conductor for multiple separately derived systems?

For multiple separately derived systems, the minimum size requirement for a common grounding electrode conductor is determined by the National Electrical Code (NEC). The standard specifies that for copper conductors, a size of 3/0 AWG is necessary, while for aluminum conductors, the minimum size is 250 kcmil.

This requirement ensures that the grounding electrode conductor is capable of safely carrying potential fault currents without overheating, thus providing effective grounding in order to minimize electrical shock hazards. The specified sizes reflect the appropriate balance between conductivity, ampacity, and safety, allowing for adequate performance in protecting systems from electrical faults.

Other size options presented do not align with the NEC standards for this particular setup. Therefore, the response that identifies 3/0 AWG copper or 250 kcmil aluminum as the minimum size is accurate and compliant with the relevant electrical safety codes.