Journeyman Electrician Exam (NEC)Equipment and DevicesMedium
A technician is installing a 3-phase, 480-volt, 30-horsepower squirrel-cage induction motor. The motor nameplate indicates a full-load current (FLA) of 40 amperes. According to NEC Table 430.250, what is the full-load current for a 30-horsepower, 480-volt, 3-phase motor, which should be used for sizing conductors and overcurrent protection?
- A40 amperes
- B34 amperes
- C52 amperes
- D48 amperes
Show answer & explanationAnswer & explanation
Correct answer: B. 34 amperes
NEC 430.6(A)(1) states that for motors, the values of full-load current (FLA) to be used in the calculations for conductor sizing, overcurrent protection, and switch ratings shall be taken from the appropriate tables in Article 430 (e.g., Table 430.250 for 3-phase AC motors), not the motor nameplate. According to NEC Table 430.250, a 30-horsepower, 480-volt, 3-phase motor has a full-load current of 34 amperes.
Why the other options are wrong
- A. 40 amperes is the motor nameplate FLA, but NEC requires using table values for sizing conductors and OCPD.
- C. 52 amperes is incorrect and does not correspond to the NEC table value for this motor.
- D. 48 amperes is incorrect and does not correspond to the NEC table value for this motor.
Motor Full-Load Current (FLA) for Sizing
For sizing conductors, overcurrent protection, and disconnects for motors, the NEC requires using full-load current values from Article 430 tables, not the motor's nameplate FLA.
- NEC 430.6(A)(1) mandates using table values.
- Tables account for worst-case conditions and design factors.
- Nameplate FLA is for motor overload protection only.
Memory trick: Motor Sizing: Table Trumps Tag for True Current.