What is the maximum time-delay fuse permitted for a No. 1 AWG copper THHN motor feeder for five 480-volt, 3-phase induction motors?

The correct answer is based on the National Electrical Code (NEC) and the specific guidelines it provides for overcurrent protection, especially concerning feeders for motors. For a No. 1 AWG copper conductor, the ampacity according to NEC tables is generally recognized as 130 amperes at a temperature rating of 60°C and higher under standard conditions.

When determining the maximum time-delay fuse for motor feeders, it's essential to consider the NEC guidelines found in Article 430, which deals with motors, motor circuits, and controllers. For three-phase motors, the code allows a 125% multiplier of the motor's full-load current to be used to protect the conductors. However, this is just one aspect.

The maximum value of the fuses or circuit breakers must also comply with the ampacity of the conductors, which means that, given the number of motors and the full-load current conditions, 125 amperes is an acceptable choice that provides adequate protection while allowing for typical inrush currents associated with motors.

Selecting 125 amperes ensures the motor starts properly under load without nuisance tripping while still conforming to the conductor's rating. Therefore, this option is informed by both the permissible ampacity of the conductor and the NEC’s