What is the minimum size of a service entrance conductor for a residential building?

The minimum size of a service entrance conductor for a residential building is determined by the National Electrical Code (NEC) and is based on the material of the conductor and the expected load. In this case, option B states the correct sizes: 3 AWG for copper conductors and 1 AWG for aluminum conductors.

Copper conductors have a higher conductivity compared to aluminum, which allows for a smaller gauge to handle the same current. This is why a 3 AWG copper conductor is sufficient, while a larger 1 AWG aluminum conductor is needed to carry the same load, due to aluminum's lower conductivity.

The NEC specifies these minimum sizes to ensure safety and reliability in electrical installations, as undersized conductors can lead to overheating and potentially create fire hazards. Ensuring that the service entrance conductors meet these minimum size requirements is crucial for the overall safety and functionality of the electrical system in a residential building.