What should the neutral conductor be sized for, according to safety precautions?

The appropriate sizing of the neutral conductor according to safety precautions is based on the normal neutral unbalance current. This is because the neutral conductor's primary function is to carry current that is not balanced across the phase conductors in a multi-phase system.

In electrical systems, particularly those utilizing multiple phases, the currents in the phase conductors can differ due to imbalances caused by single-phase loads. This unbalanced current, which flows through the neutral, can be significant, especially in systems where different phases supply varying loads. By sizing the neutral conductor to accommodate the normal neutral unbalance current, it ensures that the conductor can safely handle the excess current without overheating or experiencing undue stress.

Sizing the neutral for full load current may not account for the realities of load distribution in systems and could lead to an underestimation of the required neutral sizing in practice. Similarly, considering peak load potential does not provide an accurate representation of the ongoing operational conditions that the neutral conductor will face. Lastly, minimum system load does not reflect the maximum unbalanced conditions that the neutral may need to support.

Therefore, to maintain safety and efficiency, the neutral conductor must be sized for the normal neutral unbalance current encountered in daily operation.