Under certain circumstances, the grounded (neutral) conductors of a residential service are permitted to be sized smaller than which conductors?

The grounded (neutral) conductors in a residential service can indeed be sized smaller than the phase conductors under specific conditions. This is grounded in the National Electrical Code (NEC) guidelines, which allow for reduced sizing of neutral conductors when certain conditions are met, such as when the load is balanced and the system is designed accordingly.

In a typical residential setting where both single-phase and multi-phase systems are employed, the phase conductors carry the current to the load. The neutral conductor's sizing can often be less than that of the phase conductors because it may only carry the imbalance of current, rather than the total current load experienced by each phase conductor. This situation is particularly common in circuits where the loads are predominantly resistive and balanced, such as residential lighting and receptacles.

It’s essential to maintain proper circuit design and adherence to local codes to ensure safety and functionality. The sizing practices serve to optimize material costs without compromising safety or code requirements.