There is much confusion about the sizing of the neutral wire. The neutral wire is required in single-phase wiring. Some people say that neutral wire should be thinner than Phase Wire, some say should be thicker than phase wire and some people says neutral wire should have the same size as the phase wire. Now the question is which statement is true? In simple words, I will say it depends upon the types of wiring, loads, and some other factor. Let's discuss this in detail.

## When Neutral Wire should be the same size as Phase Wire?

The Neutral Wire should be the same size as Phase Wire in two-wire single-phase circuit.

Here you can see in the above figure, a load is connected to the single-phase supply. Here, the neutral wire is also a part of the live circuit because the same current will flow through the phase wire and neutral wire. For example, if the load consumes 2A current, then both the phase and neutral wire will carry the same 2A current.  As here, the current in both wires is equal so the size of both wires should be equal.

According to the electrical standard( IEC 60364-5-52),
1. The neutral wire should be treated as the live or phase conductor.
2. The neutral conductor should have the same cross-sectional area as the phase conductor in a two-wire single-phase circuit.

## When Neutral Wire should be thinner than Phase Wire?

The size of the neutral wire may be taken as less than the phase wire in the case of a three-phase balanced load where the neutral wire is mainly connected to the ground.

The LT side of the transformer or alternator neutral terminal is connected to the ground. Here the main purpose of the neutral wire is to ground the fault current in case of unbalance or harmonics.  Here the neutral wire does not carry the load current. In this case, the size of the neutral wire may be less than the phase wire.

According to the electrical standard( IEC 60364-5-52),

1. When each phase conductor has a cross-sectional area greater than 16 mm-square(for copper) or 25 mm-square(for aluminum) in the polyphase system, then the neutral conductor may have a smaller cross-sectional area than the individual phase conductor.
2. If the harmonic is greater than 10% in a polyphase system, then the neutral conductor should have the same size as the phase conductors.

## When Neutral Wire should be thicker than Phase Wire?

The neutral wire should be thicker than phase wire when no. of loads uses a common neutral.

Here, in the above diagram, you can see from the perspective of individual loads, they have thicker neutral wires than the phase wire. Generally, for house wiring purposes a common neutral wire is used for all loads, in this case, the neutral should be thicker than the phase wire used for individual loads because the neutral wire carries more current than phase currents consume by individual loads. Here, the neutral should have the same size as the main incoming phase where all the loads are connected.