What minimum size THW copper conductors are required for a feeder supplying motors of 1-5hp, 1-10hp, and 1-20hp at 208 volts?

The minimum size THW copper conductors required for a feeder supplying motors is determined by the load current of the motors and taking into consideration the applicable National Electrical Code (NEC) guidelines.

For motors rated between 1-5hp, 1-10hp, and 1-20hp at 208 volts, the code specifies a certain calculation to determine the full-load current of the motors. Generally, the full-load current for these horsepower ratings at 208 volts is approximately 28 amps for 5hp, 48 amps for 10hp, and around 76 amps for 20hp.

When deciding on the conductor size, it’s important to ensure that the conductors not only carry the necessary current but also account for any potential derating factors due to installation conditions (like temperature and bundling). Based on NEC Table 310.16 and considering the continuous load rule, the conductor needs to be able to handle the load reliably.

A 2 AWG copper conductor is rated to handle 95 amps at 60°C (140°F), which provides sufficient capacity for the maximum loads expected from motors rated up to 20hp at 208 volts. Therefore, selecting a 2 AWG conductor allows for