What is the minimum size aluminum THWN grounded service-entrance conductor required for a single-family dwelling unit with a neutral load of 99 amperes?

To determine the minimum size for an aluminum THWN grounded service-entrance conductor based on a neutral load of 99 amperes, it is essential to refer to the National Electrical Code (NEC) standards and the appropriate tables describing conductor sizing.

For an aluminum conductor, the size is based on the ampacity ratings prescribed in the NEC, which are influenced by factors such as temperature rating and installation conditions. When assessing the load of 99 amperes, you would look for a conductor size that can safely carry at least that load under normal operating conditions.

In this scenario, a 1 AWG aluminum THWN conductor has the necessary ampacity to support 99 amperes, as it is rated higher than the demand required. Selecting this size ensures compliance with safety standards and allows for some margin, which is crucial in preventing overheating and potential electrical failures.

In contrast, using a smaller conductor, like 2 AWG, 3 AWG, or 4 AWG, would not provide sufficient capacity for the specified load and could lead to overheating or tripping of protective devices. Therefore, 1 AWG THWN is the correct choice because it meets the requirements adequately while ensuring safety and efficiency in the electrical system.