Red Seal Electrician Practice
Power factor and three-phaseQuestion 1058 of 1506

Why do triplen harmonic currents add in the neutral of a four-wire Y system instead of cancelling?

  1. They are 120 degrees apart
  2. They are in phase with each other in the three phases
  3. They are DC currents
  4. They flow only in the lines
Show answer

Correct answer: They are in phase with each other in the three phases

The 120-degree shift of the fundamentals becomes 360 degrees (zero shift) for the 3rd harmonic.

Source: Lessons in Electric Circuits II: AC (Kuphaldt), 7.7: Harmonics in Polyphase Power Systems

Practice power factor and three-phase

Questions last reviewed: 18 October 2026