What does a blue wire do in plug?

The blue wire in a plug is the neutral wire. The neutral wire completes the circuit between the appliance and the power source, allowing the current to flow back to the power source. The blue wire has a negative charge and is often used in conjunction with the brown or black live wire, which has a positive charge. The brown or black live wire carries the current from the power source to the appliance, and the blue neutral wire carries the current back to the power source. The earth (green and yellow) wire provides a safety path for the current in the event of a fault, and the blue neutral wire is also used to balance the power load in the circuit.