Final answer:
Without the full NEC code tables, a precise answer for the smallest size copper grounded wire for a 480/277-volt feeder at 400 amperes cannot be given. Typically, a lower AWG number indicates a higher capacity, and #1/0 AWG might be a suitable size for higher currents such as 400 amperes. Professional consultation with existing NEC code tables is required for a precise determination.
Step-by-step explanation:
The student's question pertains to the selection of an appropriately sized grounded conductor for a 480/277-volt electrical feeder rated at 400 amperes running between two buildings. The size of a grounded conductor, or neutral wire, in an electrical system is determined by the National Electrical Code (NEC) based on factors such as current-carrying capacity, resistance, and potential heating effects. In applications involving motors or continuous loads, it is especially important to ensure that the conductor size can handle the full capacity of the current without overheating.
In practice, the size of the wire will be specified in the NEC tables considering insulation type and installation conditions, but the question does not provide all the necessary information to make a precise determination. Therefore, this question cannot be definitively answered without referring to NEC codebooks or similar standards, which provide guidelines for wire size required based on amperage and conditions.
However, it is important to note that the gauge numbers listed in the question options inversely relate to the diameter and current-carrying capacity of the wire. Hence, a lower gauge number indicates a larger diameter and higher current-carrying capacity. Of the options given, #1/0 AWG would typically be suitable for higher current applications such as 400 amperes. Nonetheless, professional consultation with current NEC code tables is necessary for a precise and safe determination of wire size.