In a residential installation, which of the following is an acceptable size for a service entrance conductor?

In residential installations, the size of the service entrance conductor must be adequate to handle the expected load while also considering factors such as the material of the conductor and the length of the run. The choice of 3/0 THWN copper is appropriate because it provides a sufficient ampacity for most residential service requirements. Copper conductors have a higher ampacity compared to aluminum, meaning they can carry more current per gauge size, making 3/0 a reliable choice for many applications.

Using 3/0 THWN copper often complies with the National Electrical Code (NEC) requirements for residential service entrances, ensuring safety and efficiency in electrical distribution. This size can typically handle 200 amps, which accommodates the needs of modern residential appliances and systems.

The other sizes presented, while also potentially acceptable depending on specific circumstances, may either be too large or unnecessary for standard residential service needs. Focusing on appropriate sizing in accordance with NEC and local codes is crucial for electrical safety and functionality.