This is because the neutral wire carries the same amount of current as. The phase conductor size is decided simply as per. As you can see from the example the neutral wire carries less current
Why is a neutral wire thinner than a phase wire? - YouTube
That's why neutral wire are designed smaller size of the phase wire
The selection of the size.
The table below shows the minimum cross sectional area of the neutral conductor in a given electrical installation under different types of circuits: Ensure electrical safety by properly sizing neutral conductors Learn the calculation methods and critical code adjustments, including harmonic factors. The neutral conductor size can be smaller than the active size if harmonic current is < 15 %
When harmonics are between 15 % to 33 % the neutral conductor size. A neutral conductor sizing calculator helps electricians, engineers, and installers find the correct size of neutral wire based on load current, system voltage, phase. • as a result, the neutral conductor carries just the unbalanced (or) residual current, which is much lower than the phase current You appear to be talking initially about the neutral wire in a 3 phase distribution system and given certain constraints on load imbalances, the star point.
The neutral wire size or cross sectional area requirement in the circuit is a tricky thing to handle