If a 3-phase 208V system carries a 50 kVA load, what is the current in amps?

If a 3-phase 208V system carries a 50 kVA load, what is the current in amps?

• A. 72.0 A
• B. 115.0 A
• C. 138.7 A
• D. 166.0 A

Answer: (C)

In a three-phase system, the apparent power S relates to line current I and line-to-line voltage V_L by S = √3 · V_L · I. Here S is 50 kVA (50,000 VA) and V_L is 208 V. Solve for the current: I = S / (√3 · V_L) = 50,000 / (1.732 × 208) ≈ 138.7 A. So the current is about 138.7 amps. This uses apparent power; if the power factor were less than 1, the real power would be lower and the current for that real power would be higher, but for a given 50 kVA load, the current calculation above is correct.

In a three-phase system, the apparent power S relates to line current I and line-to-line voltage V_L by S = √3 · V_L · I. Here S is 50 kVA (50,000 VA) and V_L is 208 V. Solve for the current: I = S / (√3 · V_L) = 50,000 / (1.732 × 208) ≈ 138.7 A. So the current is about 138.7 amps. This uses apparent power; if the power factor were less than 1, the real power would be lower and the current for that real power would be higher, but for a given 50 kVA load, the current calculation above is correct.