Which statement about the neutral conductor in a balanced three-phase system is correct?

• A. It carries the sum of the phase currents
• B. It carries no current in a balanced system
• C. It provides the return path for current
• D. It is only used in single-phase circuits

Answer: (C)

In a three-phase system, the neutral conductor is there to complete the circuit for any current that isn’t perfectly balanced among the phases. If the three phase currents are equal and opposite in the right way, their instantaneous sum is zero and no current flows in the neutral. But when there’s any imbalance or a load connected to neutral, current returns through the neutral back to the source. So saying that the neutral provides the return path for current captures its essential role: it’s the return path for currents that aren’t perfectly balanced. The other statements are less accurate in describing that function: the neutral doesn’t always carry the sum of the phase currents (in a balanced system that sum is zero), it isn’t exclusive to single-phase circuits, and while it may carry no current in a perfectly balanced system, its purpose is to provide a return path when imbalance occurs.