Once the power leaves the electrical service panel through the black wire and does its work through the electrical device (light bulb, motor, etc.) the electrical current returns back to the service panel through the Neutral circuit white wire which is connected to the Neutral bar.
The Neutral bar is attached to the service panel and collects all the neutral white wires from the various circuits. The bar connects to the main circuit neutral wire where it returns the current back to the electric utility company's transformer, usually the source of the electricity.
