What should the largest motor's FLA be multiplied by to get the appropriate protection for a feeder?

To determine the appropriate level of protection for a feeder serving a motor, it is common practice to multiply the Full Load Amperage (FLA) of the largest motor by a specific multiplier. The industry standard, as outlined in the National Electrical Code (NEC), recommends using a multiplier of 1.25.

Multiplying the largest motor's FLA by 1.25 accounts for potential inrush current, which can occur when the motor starts. This ensures that the feeder circuit can handle this higher initial demand without tripping the protection devices too early, while still providing adequate protection under normal operating conditions.

If a lower multiplier, such as 1.10 or 1.00, were used, there might not be sufficient capacity to accommodate the starting currents, which could lead to nuisance tripping of protective devices or inadequate protection of the feeder itself. Therefore, adhering to the 1.25 multiplier is crucial for both safety and functionality in motor applications.