In a 4-wire, 3-phase wye circuit, what type of load makes the neutral conductors current-carrying?

In a 4-wire, 3-phase wye circuit, neutral conductors can carry current primarily when there are nonlinear loads present. Nonlinear loads are those which do not draw current in a sinusoidal manner and instead generate harmonics in the electrical system. Examples of nonlinear loads include computers, LED lighting, and variable frequency drives.

When these harmonic currents occur, they can lead to an imbalance between the phases, which forces current to return through the neutral wire. In the case of a balanced resistive or inductive load, the currents in each of the three phases ideally cancel each other out, resulting in no current flowing in the neutral. However, with nonlinear loads, the harmonics can add up in such a way that the neutral must carry the resulting unbalanced current. This characteristic makes nonlinear loads particularly significant in terms of neutral conductor sizing and the overall electrical system design, as they can lead to increased heating and potential overload conditions if not properly accounted for.