Oklahoma Electrical Practice Exam

The minimum ampacity for a 15-foot feeder tap wire supplying a panel board must be what fraction of the feeder's ampacity?

1. 1/2

2. 1/3

3. 1/4

4. 1/5

The correct answer is: 1/3

The correct answer states that the minimum ampacity for a 15-foot feeder tap wire supplying a panel board must be at least one-third of the feeder's ampacity. This requirement ensures that the feeder tap wire is adequately sized to handle the load that will be supplied to the panel board while considering safety and efficiency. In practice, the National Electrical Code (NEC) outlines specific guidelines for feeder taps, including their ampacity based on the length of the tap. For a feeder tap that is no longer than 15 feet, it is permitted to have a minimum ampacity equal to one-third of the feeder's total ampacity. This means if the feeder has a larger capacity, the tap wire can be smaller but must still be able to carry a significant portion of the load without overheating or causing a fuse to blow. This approach helps maintain balance in the electrical system, ensuring that while the overall feeder can handle high currents, taps that are limited by length, as in this case, can still efficiently distribute power without the risk of overloads. Thus, the choice of one-third is both a practical and a regulatory standard in maintaining safe electrical practices.