Fundamental Code Calculations Practice Test 2026 – Full Exam Prep Guide

To determine the minimum size aluminum THWN grounded service-entrance conductor for a dwelling unit with a neutral load of 99 amperes, it is essential to refer to the National Electrical Code (NEC) guidelines regarding conductor sizing. The NEC provides tables that specify the appropriate conductor sizes based on the ampacity ratings, taking into account the material used (in this case, aluminum) and the type of insulation.

For aluminum conductors, the ampacity is generally lower than that of copper conductors. According to NEC Table 310.15(B)(16), the minimum size of aluminum conductors is defined based on the load they need to carry.

When assessing the ampacity, for a dwelling unit with a neutral load of 99 amperes, the code typically requires a conductor size that exceeds the load to ensure safety and performance under the maximum expected load conditions. In this scenario, the calculated requirement leads us to determine that the minimum necessary size is indeed 1 AWG THWN aluminum, which is rated to safely carry a load exceeding 99 amperes under typical installation conditions without overheating or becoming a hazard.

This size accounts for factors such as the conductor's ambient temperature, any potential derating due to multiple conductors in a race