In a single-phase electrical system, a neutral wire is also present along with the live wire. The neutral wire in a single-phase system serves the same purpose as in a three-phase system, carrying electrical current back to the source after it has completed the circuit.
It is important to note that the neutral wire and the ground wire are different things. The neutral wire is used to carry electrical current, while the ground wire is used to provide a safe path for electrical current to flow to the earth in case of a fault or other problem in the system. Despite this difference, it is still important to ground the neutral wire in both three-phase and single-phase systems to ensure the safety of users and protect against electrical hazards. If the neutral wire is not grounded, the circuit will not be complete and could pose a danger to users.
In a three-phase alternating current (AC) electrical system, there are three phases that oscillate between high and low potentials, with each phase also having a reverse polarity at different times. The neutral wire in this system does not undergo any such changes in potential and remains at ground potential.
Any time a conductor in the system is energized by one of the phases, it will be at a higher or lower potential than the neutral wire for most of the time. However, there may be a few short instances where the phase approaches a "0" potential, meaning it is neither high nor low.
When a load is connected across a phase and the neutral wire, the changing potential difference between the two causes electrical current to flow from the phase to the neutral and back again. This is because the load consumes electricity, and the flow of current through the load helps to balance the potential difference between the phase and neutral wires.
Overall, the purpose of the neutral wire in a three-phase AC system is to provide a reference point for the other phases and to ensure that the electrical current flows smoothly through the system. It is grounded to provide a safe path for the current to return to the source and to protect against electrical hazards.