When calculating conductor size for two motors on the same feeder, the full load current of the largest motor must be multiplied by what factor?

When calculating conductor size for multiple motors on the same feeder, the National Electrical Code (NEC) specifies a method for determining the total load. For the largest motor in a feeder system, its full load current is multiplied by a factor to account for starting currents and any potential overloads.

In this context, multiplying the full load current of the largest motor by 1.25 is the correct approach. This factor is used to ensure that the conductors can handle not just the steady-state operation of the motor but also brief periods of increased current that may occur during motor starting. By applying this factor, you ensure that the wiring system is adequately sized for the maximum demand that can be presented by the largest motor.

Using this calculation helps to provide an additional safety margin, thus preventing potential overheating and ensuring the longevity of the wiring and equipment. This practice aligns with established electrical standards, thus making it a crucial component of safe electrical design.