What is the maximum percentage of phase current that can be found through the neutral?

The maximum percentage of phase current that can flow through the neutral conductor in a three-phase system is 173%. This situation occurs under certain conditions in a balanced three-phase load, particularly in the case of a scenario leading to maximum current in the neutral due to harmonic distortion or unbalanced loads.

When loads on the three phases are perfectly balanced, the currents theoretically cancel each other out in the neutral, resulting in minimal or no current flowing through it. However, if there is an unbalanced load or if there are third harmonics present, the current in the neutral can increase significantly due to the additive nature of these unbalanced currents.

In this context, the 173% figure is derived from the scenario involving harmonics, particularly the third harmonic. In an unbalanced load condition, when all three phase currents are in phase at the third harmonic frequency, the resultant current in the neutral can be equal to three times the phase current. The total becomes 1.732 (the square root of 3) times the phase current for balanced loads, leading to the calculation of 173% of the phase current for specific conditions. This ensures that professionals in the field are aware of the maximum stress that can be placed on the neutral in real-world applications