What efficiency rating is specified for the 460-volt motor in the horsepower calculation?

What efficiency rating is specified for the 460-volt motor in the horsepower calculation?

• A. 92%
• B. 94%
• C. 96%
• D. 98%

Answer: (B)

Efficiency determines how much electrical input power becomes shaft power in a motor, which is essential for converting watts into horsepower. In a horsepower calculation for a 460-volt motor, you must use the motor’s efficiency to find the actual mechanical output: P_mech = P_in × η, then HP = P_mech / 746. The problem specifies an efficiency rating of 94% for this motor, so you multiply the electrical input power by 0.94 to get the shaft power used in the horsepower conversion. That’s why 94% is the correct value to use—the calculation is built around that given efficiency. Using a different efficiency would change the resulting horsepower and wouldn’t match the scenario described.

Efficiency determines how much electrical input power becomes shaft power in a motor, which is essential for converting watts into horsepower. In a horsepower calculation for a 460-volt motor, you must use the motor’s efficiency to find the actual mechanical output: P_mech = P_in × η, then HP = P_mech / 746. The problem specifies an efficiency rating of 94% for this motor, so you multiply the electrical input power by 0.94 to get the shaft power used in the horsepower conversion. That’s why 94% is the correct value to use—the calculation is built around that given efficiency. Using a different efficiency would change the resulting horsepower and wouldn’t match the scenario described.