Which of the following THHN/THWN copper conductors is the smallest size permitted for a 150 A feeder to a subpanel for an addition to an existing dwelling?

The correct choice indicates that a 1/0 THHN/THWN copper conductor is the smallest size permitted for a 150 A feeder to a subpanel for an addition to an existing dwelling. This determination is based on the National Electrical Code (NEC) requirements for conductor ampacity, specifically addressing the current-carrying capacity of copper conductors.

For a 150 A feeder, the NEC specifies that a minimum conductor size must be used to safely handle the designated load without exceeding the wire's ampacity rating. According to NEC Table 310.16, a 1/0 copper conductor has an allowable ampacity of 150 amps in typical conditions. This makes it suitable for a 150 A feeder application.

Using a conductor size larger than necessary, such as 2/0, 3/0, or 4/0, while permissible, is not required for this specific application since the 1/0 meets the need efficiently. Selecting the correct size is crucial for ensuring safety, effective operation, and compliance with electrical codes. Conductors that are too large may incur unnecessary costs and are not typically required for this amperage rating.

In summary, the 1/0 THHN/THWN copper conductor aligns