In a balanced three-phase system, what is the neutral current?

• A. Zero
• B. Approaches zero
• C. Equal to line current
• D. Twice the line current

Answer: (B)

The key point is that the neutral current is the vector sum of the three phase currents. In a perfectly balanced three-phase system, each phase current has the same magnitude and is 120 degrees apart, so these three phasors cancel out and the neutral current is zero. In real systems, small mismatches in load, impedance in the lines, or transformer effects mean the phasors don’t sum to exactly zero. These slight imbalances leave a very small current flowing in the neutral, so it effectively approaches zero rather than being exactly zero. That’s why the best answer is that the neutral current approaches zero. It's not exactly zero in practice, and it certainly isn't equal to the line current or twice the line current.