Which factor contributes to the selection of conduit size for a specific number of conductors?

The correct choice focuses on the minimum fill percentage because it directly affects the sizing of conduits to ensure safe and efficient operation. When multiple conductors are placed within a conduit, adhering to established minimum fill percentages is crucial to prevent overheating and to allow for adequate airflow, which prevents excessive heat buildup.

The National Electrical Code (NEC) provides guidelines on the maximum number of conductors that can be placed in a conduit without going over the recommended fill percentage. This is important because too many conductors can lead to increased resistance, heat generation, and ultimately potential failures in the system. Sizing the conduit properly based on these fill requirements ensures that conductors can operate reliably under expected load conditions.

The other factors mentioned may influence installation practices or overall system performance, but they do not primarily dictate conduit size related to the number of conductors. Conduit material may affect strength and durability, ambient temperature can impact performance but not in a straightforward manner of fill percentage, and voltage level primarily pertains to electrical insulation requirements rather than the physical space required for conductors in a conduit. Hence, the minimum fill percentage stands out as the primary consideration for conduit sizing.