What is the minimum conductor size for a motor having a 75 hp rating in a 277/480-V setup?

To determine the minimum conductor size for a motor with a 75 horsepower (hp) rating operating at a 277/480-V setup, it is important to refer to the National Electrical Code (NEC) guidelines, specifically Table 310. The requirements for conductor sizing take into account both the horsepower of the motor and the system voltage.

For a motor rated at 75 hp, you typically need to consider the full-load current (FLC) that the motor draws. At 480 volts, the FLC for a 75 hp motor is approximately 90 amps. According to NEC guidelines, conductors must be sized adequately to handle this FLC, and you must also consider factors such as the conductor's insulation type and length of the run—although these details are often standardized for common applications.

When you look at conductor sizes, the most commonly used sizes for this amperage are found in the context of copper or aluminum conductors. For example, a 4/0 AWG conductor made of copper typically supports up to 230 amps at 75°C, making it more than sufficient for the 90 amps of full-load current for a 75 hp motor.

The option that suggests a conductor size of 1 AWG would