A 30-volt, 0.5-horsepower motor operating at 85% efficiency draws how many amperes from the bus?

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Enhance your understanding of the fundamentals of electricity with the AMT General Exam. Study with multiple-choice questions crafted to improve your knowledge and confidence. Prepare effectively for your success!

Multiple Choice

A 30-volt, 0.5-horsepower motor operating at 85% efficiency draws how many amperes from the bus?

Explanation:
Electrical power balance: input power equals mechanical output power divided by efficiency. The motor’s mechanical output is 0.5 hp, which is 0.5 × 746 ≈ 373 W. With 85% efficiency, the electrical input power is 373 / 0.85 ≈ 439 W. The bus supplies 30 V, so the current drawn is I = P / V ≈ 439 / 30 ≈ 14.6 A. So the motor draws about 14.6 amperes from the bus. (For contrast, at 100% efficiency it would be ~12.4 A, showing how lower efficiency increases current.)

Electrical power balance: input power equals mechanical output power divided by efficiency. The motor’s mechanical output is 0.5 hp, which is 0.5 × 746 ≈ 373 W. With 85% efficiency, the electrical input power is 373 / 0.85 ≈ 439 W. The bus supplies 30 V, so the current drawn is I = P / V ≈ 439 / 30 ≈ 14.6 A. So the motor draws about 14.6 amperes from the bus. (For contrast, at 100% efficiency it would be ~12.4 A, showing how lower efficiency increases current.)

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