What is the minimum size of feeder conductors permitted between the breaker and wireway in a 277/480-volt system?

In a 277/480-volt system, the minimum size of feeder conductors is determined by factors such as ampacity, voltage drop, and the specific requirements set forth by the National Electric Code (NEC). The correct answer, 1/0 AWG, is based on providing sufficient conductor size to handle expected loads while ensuring safety and compliance with electrical standards.

1/0 AWG conductors are capable of carrying higher currents without overheating and maintain a balance between conductance and physical manageability. This size helps to reduce voltage drop over longer distances, which is crucial in maintaining efficiency in a higher voltage system. Supporting calculations such as minimum ampacity tables from the NEC confirm that 1/0 AWG is adequate for most feeder applications in commercial settings where 277/480-volt systems are common.

Larger sizes, such as 2/0, 2 AWG, and 3/0, while capable of carrying more current, are not necessary for typical feeder applications under standard load calculations in these systems, ensuring that 1/0 AWG is indeed the minimum acceptable size. Following NEC guidelines is essential for safety and efficiency, making 1/0 AWG a compliant and practical choice.