What is the formula to calculate current for a 3-phase load given apparent power S and line voltage V?

• A. I = V / (√3 × S)
• B. I = S / (√3 × V)
• C. I = S / (V × 3)
• D. I = S / (√3 × V)

Answer: (D)

In a balanced three-phase system, the apparent power S relates to line voltage V and line current I by S = √3 × V × I. Solve for the current to get I = S ÷ (√3 × V). This uses the line-to-line (line) voltage and is the standard form for three-phase power when S is given in volt-amperes and V is the line voltage. The other forms mix up the placement of S and V or use 3 instead of √3, which does not preserve the correct relationship between apparent power, voltage, and current. (If you were using phase quantities, you'd use S = 3 × V_phase × I_phase, leading to I_phase = S ÷ (3 × V_phase).)