What is the required ampacity for a circuit supplying a continuous load?

When determining the required ampacity for a circuit that supplies a continuous load, the proper approach is to account for the continuous nature of the load, which is defined as a load expected to run for three hours or more. The National Electrical Code (NEC) requires that conductors be sized to handle this type of load safely without overheating, and this is achieved by applying a multiplier to the load.

The required ampacity is 125% of the continuous load. This includes the load itself plus an additional margin to ensure the circuit operates within safe temperature limits and can handle variations in demand without risk of overheating. By sizing the conductors in this way, we account for factors such as potentially increased resistance over time and the need for reliable operation under continuous usage.

The other options reflect incorrect multipliers for sizing conductors supplying a continuous load. A lower percentage, such as 110% or 100%, would not provide adequate capacity, especially considering the potential fluctuations within a continuous load over extended periods. The 150% option would unnecessarily overestimate what is needed for a continuous load, potentially leading to unnecessary costs and inefficiencies in conductor sizing.