A 240 VAC source is connected to a 1200 Watt 3-phase motor. How much current is flowing to the motor?

• A. 288 kA
• B. 5 A
• C. 0.2 A
• D. 1.75 hp

Answer: (B)

In a three-phase system, the electrical power relates to current by P = √3 × V_LL × I_L × cosφ. That means the exact current depends on both the power factor (cosφ) and how efficiently the motor converts electrical power to mechanical power. With only the motor’s wattage and the line voltage given, you can’t determine the exact current without those two factors.

Using a quick estimation that neglects those details and treats the load as if the full 1200 W were simply across 240 V, you’d compute I ≈ P / V = 1200 / 240 = 5 A. That aligns with the provided answer.

In reality, the current would usually be lower because of the √3 factor and a power factor less than 1. For example, using more typical values for a motor (cosφ around 0.8) gives I ≈ 1200 / (√3 × 240 × 0.8) ≈ 3.6 A. The key idea is that the exact current depends on PF and efficiency, but the 5 A result reflects a common quick-estimate approach used in practice.