In this article, let us discuss what is neutral wire and its importance in electrical installations. If we look at the electrical installation of a house, we normally have two cores of cable- one for phase and another for neutral. The current flow between the phase cable, load, and neutral cable.
Additionally, for safety, a third cable is installed which is called ground where current this not supposed to flow but it is a safe path in case the phase cable is damaged and comes into contact with the chassis and does not go through people.
The neutral wire is the one that allows the current to return and serves as the return conductor of the current that circulates through single-phase circuits. For example: if a light bulb is connected only to the phase, it cannot work as it does not have a neutral so that the electrons can circulate.
In an electrical system, “Neutral wire” is a feature, not a manufacturing specification.
The term neutral is associated with the fact that it is used as part of an alternating voltage distribution system with one or more phases. In these cases, one cable has a fixed voltage (say zero) and the second cable has a variable voltage (or phase) concerning this cable.
For example, 220 volts at 50Hz or 110 volts at 60Hz. In three-phase distribution, neutral and 3-phase cables are used, or only 3-phase cables without neutral.
Is it correct to connect the neutral of an installation to the ground?
If we have a low supply from the power generation company, we will generally have three phases and a neutral, and the neutral must distribute by the company and must be grounded. The neutral of the transformer at the secondary side is grounded for the safety of persons and equipment.
But once we are in our indoor installation, it must have an independent grounding from the neutral. Hence, the colors of the cable are brown, black, and grey for phases, blue color for neutral, and the green-yellow for ground in electrical installation. This is how almost all low-voltage installations are made. Therefore, in principle, it is not correct for us to confuse neutral and earth in the installation of our house.
Why would a hot wire in a home electrical system shock us if we touched it, but a neutral one won’t?
The neutral wire is at earth potential, that is, ZERO potential. The same zero potential a person has when standing on the ground. Therefore, the electric potential difference between the neutral and a person is also ZERO, therefore no current flows from the neutral to the human body, and the person is not electrocuted.
However, the power distribution company must have the neutral effectively connected to Earth. In very dry places, the potential difference between the Neutral and Earth often exceeds 10 or 20 Volts AC, which makes it dangerous to touch the neutral wire. Therefore, earth resistance must be as minimum as possible to have the least voltage between neutral and the earth.
Why do we need a neutral wire?
We need two conductors for the transmission of electric power because the current is generated only when electrons move from one point to another. The neutral conductor provides the return path for the movement of the electrons and thus, electric current flows through the load.
In a three-phase electrical system, the neutral current is the vector sum of the three-line currents. If the power system is balanced, which the symmetry of its wave in 120 electrical degrees and with a perfectly balanced three-phase linear load, the neutral current is equal to zero. However, if the load is unbalanced then the neutral wire carries the unbalance current through it.
Difference between Neutral Wire and Ground wire
As per the international Electric Code (IEC), the ground is called protective earth (PE), and neutral is N.
Neutral Wire
The neutral is a neutral point between different phases. The voltage is less between phases and neutral than the voltage between phases. The neutral wire carries currents between the phase circuits to the neutral through the load.
Ground Wire
The ground wire is not part of the electrical circuit. It serves to protect the equipment and users in case of an electrical fault. The ground wire returns currents to the transformer to eliminate potential differences in the exposed metal objects. A well-connected ground prevents an accident by getting the differential protection relay or earth fault relay to trip when detecting the leak.
Why should the neutral be grounded in an electrical installation?
The neutral point is earthed for safety reasons. The neutral provides safety to humans as well as to equipment. In the case of insulation failures, the unbalance current flows and the neutral conductor carries this unbalance current. The protection device that senses the current of the neutral wire trips the circuit breaker and isolates the faulty section.
It also ensures that the voltage between phase and ground is the same as between phase and neutral (it seems obvious but not). When the neutral is not grounded, a high voltage from a faulty transformer or lightning can raise the voltage between phase and ground, and it induced high voltage may cause insulation failures.
In some installations, the floating neutral is used, which makes it possible to detect insulation faults before a leak occurs.
Importance of Neutral Wire
The followings are the importance of neutral wire.
- The cable connected to the neutral point creates a potential difference that allows the electrical current through the phase conductor. The flow of electric current establishes in the phase conductor because the neutral wire is at zero potential. The primary function of the neutral wire is to provide a path to the phase current for a single-phase load. And, the neutral conductor carries the unbalance phase current in a three-phase 4-wire system.
- For the transmission of electrical energy, there must be a voltage difference. The current can flow in two conductors only if there exists a voltage difference. The potential difference between the phase and neutral causes the movement of the electrons from the lower potential to the higher potential. As a result, the current flow from the power source to the load, and the current returns to the source through the neutral wire. Thus, the voltage difference between the phase cable and the neutral cable causes the flow of electric current.
- Neutral wires allow current to return and serve as the return conductor. Thus, without a neutral wire, the electric current does not complete its path.
The importance of neutral wire is paramount in electrical installation and the neutral wire size selection and other factors must be taken care of during system designing.
