What is the required size for an ungrounded feeder conductor needed for a 150-ampere rated panel board in an individual dwelling unit?

For a 150-ampere rated panel board in an individual dwelling unit, the required size for an ungrounded feeder conductor can be determined by referring to the National Electrical Code (NEC) which provides guidelines on conductor sizing based on the current carrying capacity and insulation type.

In this scenario, the conductor size needs to accommodate the continuous load that the panel board might experience. The correct choice, which is 1 AWG THWN-2, is appropriate because it has the capacity to handle up to 150 amperes safely without overheating. THWN-2 insulation type is designed for wet and dry locations, enhancing its versatility and reliability in various environments.

Considering other conductor sizes, 2 AWG would be inadequate in terms of providing enough capacity under typical load conditions for a 150-amp circuit, while 3 AWG and 4 AWG would significantly underperform, leading to possible overheating and increased risk of failure.

Choosing 1 AWG THWN-2 ensures compliance with electrical codes while providing a safe operating margin for a 150-amp load in a residential setting, making it the most suitable option.