For a 125 hp motor supplied by a 120/240 V panel, what is the minimum size of conductors that are required?

To determine the minimum size of conductors required for a 125 hp motor supplied by a 120/240 V panel, we need to refer to the National Electrical Code (NEC) for guidance on motor conductor sizing.

For motors, the NEC provides specific guidelines in Article 430. The full-load current (FLC) for a motor can be found in NEC Table 430.250, which gives the FLC based on horsepower and voltage. A 125 hp motor at 240 V typically has an FLC of approximately 375 amps.

When selecting conductor sizes, it is crucial to consider not only the FLC but also any applicable adjustment factors, such as ambient temperature, number of conductors in a raceway, and other derating factors. According to NEC Table 310.16, which lists copper and aluminum conductor ampacity, the appropriate conductor size needs to be selected based on the FLC calculated.

For a 375 amps requirement, a 3/0 AWG copper conductor is often adequate since it has an ampacity that meets or exceeds this FLC under standard conditions. However, the next step is to ensure that the conductor size complies with NEC requirements for motor circuits, including providing sufficient capacity for starting