How should you size a feeder for a continuous load of 60 A and a non-continuous load of 15 A?

How should you size a feeder for a continuous load of 60 A and a non-continuous load of 15 A?

• A. 60 A
• B. Continuous load is multiplied by 125% (60 × 1.25 = 75 A); add non-continuous load (75 + 15 = 90 A); select the next standard feeder size at least 90 A
• C. 75 A
• D. 105 A

Answer: (B)

Feeder sizing takes into account how long the load runs. A continuous load (one that operates for three hours or more) needs extra margin to prevent overheating, so you multiply it by 1.25. Then you add any non-continuous load, since that part doesn’t require the extra margin. After you have the total, you round up to the next standard feeder size. Here, the continuous load is 60 A, so 60 × 1.25 = 75 A. Add the non-continuous load of 15 A to get 90 A. The next standard feeder size at least 90 A is typically 100 A, so a 100 A feeder would be chosen. This approach—derate the continuous portion, add the non-continuous load, then size up to the next standard rating—is the correct method.

Feeder sizing takes into account how long the load runs. A continuous load (one that operates for three hours or more) needs extra margin to prevent overheating, so you multiply it by 1.25. Then you add any non-continuous load, since that part doesn’t require the extra margin. After you have the total, you round up to the next standard feeder size.

Here, the continuous load is 60 A, so 60 × 1.25 = 75 A. Add the non-continuous load of 15 A to get 90 A. The next standard feeder size at least 90 A is typically 100 A, so a 100 A feeder would be chosen. This approach—derate the continuous portion, add the non-continuous load, then size up to the next standard rating—is the correct method.