What is the required minimum-size copper bonding jumper for a metal water piping system serving the same area as a separately derived system with 4/0 AWG conductors?

The required minimum size of the copper bonding jumper for a metal water piping system, when serving the same area as a separately derived system utilizing 4/0 AWG conductors, corresponds to the specified requirements set forth in the National Electrical Code (NEC).

When determining the bonding jumper size, the code specifies that it must be sized based on the largest ungrounded conductor of the separately derived system. In this context, given the 4/0 AWG conductors, the bonding jumper must be large enough to effectively handle the ground fault current and ensure safety.

According to NEC guidelines, for conductors sized at 4/0 AWG, the corresponding bonding jumper size is commonly referenced at 2 AWG copper to ensure proper grounding and bonding for the metal piping system. This ensures that any fault current is effectively managed, providing a path for fault currents and helping to maintain the integrity of the grounding system.

Therefore, the selection of 2 AWG as the minimum size for the copper bonding jumper is correct, reflecting the necessary compliance with safety standards, and addressing electrical code requirements in bonding metal water piping systems to separately derived systems.