The required feeder conductor ampacity must be at least what?

The required feeder conductor ampacity must be at least what?

• A. Noncontinuous load plus 125 percent of the continuous load
• B. Total load plus 50 percent of the continuous load
• C. Continuous load only
• D. Noncontinuous load only

Answer: (A)

When sizing feeder conductors, you must account for two kinds of load: continuous and noncontinuous. A continuous load is one that can be on for long periods (often defined as 3 hours or more) and carries a risk of heating the conductors if it runs that long. To prevent overheating, the continuous portion is multiplied by 125%. Noncontinuous loads don’t run long enough to cause sustained heating, so they can be added at their full rating. Therefore, the feeder’s ampacity must be at least the sum of the noncontinuous load and 125% of the continuous load. For example, if the continuous load is 20 A and the noncontinuous load is 10 A, the required feeder ampacity would be 10 A + (1.25 × 20 A) = 10 A + 25 A = 35 A. Using only the continuous load would ignore the noncontinuous demand, risking an insufficient feeder when the noncontinuous load is present. Using total load plus only 50% of the continuous load wouldn’t provide the necessary 125% safety factor for the continuous portion. Using noncontinuous load only would neglect the continuous demand entirely.

When sizing feeder conductors, you must account for two kinds of load: continuous and noncontinuous. A continuous load is one that can be on for long periods (often defined as 3 hours or more) and carries a risk of heating the conductors if it runs that long. To prevent overheating, the continuous portion is multiplied by 125%. Noncontinuous loads don’t run long enough to cause sustained heating, so they can be added at their full rating. Therefore, the feeder’s ampacity must be at least the sum of the noncontinuous load and 125% of the continuous load.

For example, if the continuous load is 20 A and the noncontinuous load is 10 A, the required feeder ampacity would be 10 A + (1.25 × 20 A) = 10 A + 25 A = 35 A.

Using only the continuous load would ignore the noncontinuous demand, risking an insufficient feeder when the noncontinuous load is present. Using total load plus only 50% of the continuous load wouldn’t provide the necessary 125% safety factor for the continuous portion. Using noncontinuous load only would neglect the continuous demand entirely.