Motors and Motor Circuits Flashcards

Per NEC 430.24, how is a feeder sized when supplying multiple motors?

Answer: 125% of the largest motor FLC plus 100% of all other motor FLCs

NEC 430.24 requires feeder conductors to have ampacity not less than 125% of the highest-rated motor FLC plus the sum of the FLCs of all other motors on the feeder.

What is the maximum rating of the feeder overcurrent protection device when supplying multiple motors per NEC 430.62?

Answer: Largest motor's branch-circuit OCPD rating plus the sum of FLCs of all other motors

NEC 430.62(A) limits the feeder OCPD to the largest motor's maximum branch-circuit protective device rating plus the sum of the full-load currents of all other motors.

Per NEC 430.6, what current value is used for determining conductor size and overcurrent protection for a motor?

Answer: NEC table full-load current values

NEC 430.6(A)(1) requires using the full-load current values from NEC Tables 430.247-430.250 for determining conductor ampacity, switch ratings, and branch-circuit protection.

What type of motor starter provides reduced voltage during starting to limit inrush current?

Answer: Reduced-voltage starter (soft starter)

Reduced-voltage starters limit starting inrush current by reducing the voltage applied to the motor during startup.

Per NEC 430.109, which devices are acceptable as a motor disconnecting means?

Answer: Motor-circuit switch, molded case circuit breaker, molded case switch, or instantaneous-trip circuit breaker (with limitations)

NEC 430.109 lists acceptable disconnecting means types including motor-circuit switches, molded case circuit breakers, molded case switches, and instantaneous-trip breakers under specific conditions.

What condition can cause a three-phase motor to overheat even when total current appears normal?

Answer: Voltage imbalance between the three phases

Voltage imbalance between phases causes unequal current distribution in motor windings, leading to hot spots and overheating even when average current appears normal.