When must the allowable ampacity for the minimum branch-circuit size be equal to the maximum load being served?

The correct choice indicates that the allowable ampacity for the minimum branch-circuit size must be equal to the maximum load being served only after the application of any adjustment or correction factors. This is essential because the ampacity of conductors can be affected by various conditions, such as ambient temperature, installation conditions, and the number of conductors bundled together.

In practice, when determining the appropriate branch-circuit conductors, it is crucial to consider these factors to ensure that the conductors can safely carry the load without overheating. Before any adjustments or corrections are made, the initial allowable ampacity may not reflect the actual conditions under which the circuit operates. Therefore, a proper calculation involving these factors ensures that the conductors are adequately sized to handle the load, maintaining safety and compliance with the National Electrical Code (NEC) standards.

This approach ultimately ensures that the circuit operates safely over its intended lifespan, which is critical in preventing failures or hazards associated with undersized wiring.