What is the minimum size THWN-2 grounded feeder conductor required for a dwelling unit with a neutral load of 85 amperes?

To determine the minimum size THWN-2 grounded feeder conductor required for a dwelling unit with a neutral load of 85 amperes, it is important to reference the National Electrical Code (NEC) which provides the necessary guidelines for conductor sizing.

When calculating conductor size for feeders, we typically use the 75°C (167°F) column in the NEC ampacity table for copper conductors, as THWN-2 conductors are often rated at this temperature rating. According to the NEC, a 4 AWG copper conductor is rated to carry up to 95 amperes under standard conditions.

Since the neutral load is 85 amperes, a 4 AWG conductor can safely handle the current load while providing a margin above the actual load (85 amperes). Choosing a conductor that is too small could lead to overheating, voltage drop issues, or even potential safety hazards, while using a too-large conductor is not necessary and can be unnecessarily costly.

In summary, the selection of a 4 AWG THWN-2 grounded feeder conductor is appropriate because it meets the requirements for safely carrying an 85-ampere load according to the NEC standards.