What is NEC's definition of a continuous load and how should it be treated in sizing?

• A. A load that runs for 1 hour or more; circuits sized at 110%
• B. A load that runs for 2 hours or more; circuits sized at 115%
• C. A load that runs for 3 hours or more; circuits sized at 125% of continuous load
• D. A load that never runs

Answer: (C)

Continuous load means a load that is expected to run for three hours or more. Because such loads can heat conductors and equipment over an extended period, NEC requires sizing the circuit to handle that heat by multiplying the continuous load by 1.25. In other words, circuits must be sized at 125% of the continuous load. For example, a continuous load of 40 A would require a circuit sized to at least 50 A (40 × 1.25). Loads that don’t run for three hours, or never run, don’t meet the definition of continuous and aren’t treated with this 125% factor.