A 0.25 horsepower motor at 240 V, 90% efficiency, draws how many amperes from the supply?

• A. 1.20 A
• B. 0.86 A
• C. 0.50 A
• D. 2.00 A

Answer: (B)

The number of amps drawn depends on the electrical input power and the supply voltage. Start with the mechanical output in watts: 0.25 hp equals about 186.5 watts (0.25 × 746). With 90% efficiency, the electrical input power must be P_in = 186.5 / 0.90 ≈ 207 W. At a 240 V supply, the current is I = P_in / V ≈ 207 / 240 ≈ 0.86 A. So the motor draws about 0.86 amperes from the supply. The other currents would require different input powers to still yield 0.25 hp output at the given efficiency and voltage, so they don’t fit the given data.