What is the minimum size EGC permitted for a 115/230-V, 3 hp motor with a 1-pole breaker in a 120/240-V panel?

To determine the minimum size equipment grounding conductor (EGC) required for a 115/230-V, 3 hp motor connected to a panel, we must consider the motor's full-load current and the National Electrical Code (NEC) guidelines for EGC sizing.

For a 3 hp motor, the full-load current at 230 volts is approximately 13 amps. According to NEC Table 250.122, the size of the EGC is based on the rating of the overcurrent protection device, which in this case is a 1-pole breaker for a 120/240-V panel. Generally, for motors with protection under 15 amps, the minimum grounding conductor size starts at 14 AWG for equipment rated under 10 amps.

However, for any motor that draws more current, in this case, one protected by a breaker sized for 15 amps or more, we need to follow the guideline that requires a minimum of 10 AWG when the circuit breaker is rated for a higher current. Since typical 3 hp motors would be protected by a breaker of at least 15 amps and considering that grounding conductors must be sized adequately to ensure proper fault current limitation, 10 AWG copper wire is suitable.