Journeyman Electrician Exam (NEC)Equipment and DevicesMedium
A journeyman electrician is installing a 3-phase, 480-volt, 30-horsepower squirrel-cage induction motor. According to NEC Table 430.250, what is the motor's full-load current (FLA) for the purpose of sizing overcurrent protection and conductors?
- A40 amperes
- B45 amperes
- C27 amperes
- D34 amperes
Show answer & explanationAnswer & explanation
Correct answer: D. 34 amperes
According to NEC Table 430.250 for three-phase AC motors, a 30-horsepower motor operating at 460 volts has a full-load current of 34 amperes. The 480V motor is considered to operate at 460V for table lookup purposes.
Why the other options are wrong
- A. This is the FLA for a 40 HP motor at 200V, or a 15 HP motor at 230V, not 30 HP at 460V.
- B. This is the FLA for a 20 HP motor at 230V, not 30 HP at 460V.
- C. This is the FLA for a 20 HP motor at 460V, not 30 HP.
Motor Full-Load Current (FLA) from NEC Tables
The Full-Load Current (FLA) for motors, used for sizing conductors and overcurrent protection, is typically obtained from NEC Tables 430.247 through 430.250, rather than the motor nameplate, for consistency and safety.
- NEC Tables 430.247-430.250 provide standardized FLA values.
- These values are used for sizing branch-circuit conductors and overcurrent protection.
- Nameplate FLA is used for motor running overcurrent protection.
Memory trick: For motor sizing, the NEC table knows the true current.