When calculating the feeder load for a motor control center, which statement is correct?

The correct approach when calculating the feeder load for a motor control center is to sum all motor loads and then add 25% of the largest motor load. This method is in line with standard practices used to ensure that feeders are adequately sized to handle starting currents and possible overload conditions without exceeding the rating of the feeder.

This rule acknowledges that motors draw a significantly higher current during startup than during normal operation. By adding 25% of the largest motor load, the calculation accounts for potential inrush current that the largest motor might require. This ensures that the power system is capable of handling these immediate demands without tripping breakers or causing voltage dips.

Including 25% gives a safety margin that can assist in avoiding operational issues and ensures that the feeder can manage fluctuating loads effectively. This practice adheres to standard industry guidelines, as well as the relevant sections of the National Electrical Code (NEC), which outlines how to effectively size conductors and feeders for motor-driven equipment.