Determine the minimum ampacity of conductors serving a continuous duty, Design B, 3-phase, 208-volt, 10 hp, induction-type motor.

Determine the minimum ampacity of conductors serving a continuous duty, Design B, 3-phase, 208-volt, 10 hp, induction-type motor.

• A. 46.2 amps
• B. 32.2 amps
• C. 30.8 amps
• D. 38.5 amps

Answer: (D)

Sizing motor conductors for continuous-duty uses a multiplier of 1.25 on the motor’s full-load current. For a 10 hp, three-phase motor at 208 V, the full-load current from NEC motor tables is 30.8 A. Applying 125% gives 30.8 × 1.25 = 38.5 A. So the minimum ampacity the conductors must have is 38.5 A. The other numbers would come from using a different full-load current or omitting the 125% factor.

Sizing motor conductors for continuous-duty uses a multiplier of 1.25 on the motor’s full-load current. For a 10 hp, three-phase motor at 208 V, the full-load current from NEC motor tables is 30.8 A. Applying 125% gives 30.8 × 1.25 = 38.5 A. So the minimum ampacity the conductors must have is 38.5 A. The other numbers would come from using a different full-load current or omitting the 125% factor.