The minimum feeder-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity equal to or greater than the noncontinuous load plus ___ percent of the continuous load.

The minimum feeder-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity equal to or greater than the noncontinuous load plus ___ percent of the continuous load.

• A. 100
• B. 125
• C. 75
• D. 80

Answer: (B)

When sizing feeder conductors, treat continuous loads (those expected to run for 3 hours or more) with extra margin to prevent overheating. The method is to sum the noncontinuous load and add 125% of the continuous load. In other words, the conductor’s allowable ampacity must be at least the noncontinuous load plus 1.25 times the continuous load. This 125% factor accounts for the heat buildup from continuous operation and keeps the conductor from overheating over time. That’s why 125% is the correct value. For example, if the noncontinuous load is 6 A and the continuous load is 4 A, the required ampacity is 6 + 1.25×4 = 11 A. The other percentages would either ignore the continuous-load adjustment or underestimate it, which isn’t acceptable for safe, compliant sizing.

When sizing feeder conductors, treat continuous loads (those expected to run for 3 hours or more) with extra margin to prevent overheating. The method is to sum the noncontinuous load and add 125% of the continuous load. In other words, the conductor’s allowable ampacity must be at least the noncontinuous load plus 1.25 times the continuous load. This 125% factor accounts for the heat buildup from continuous operation and keeps the conductor from overheating over time. That’s why 125% is the correct value.

For example, if the noncontinuous load is 6 A and the continuous load is 4 A, the required ampacity is 6 + 1.25×4 = 11 A. The other percentages would either ignore the continuous-load adjustment or underestimate it, which isn’t acceptable for safe, compliant sizing.