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In a three-phase system, how far apart in time are the three voltages, in degrees?

Three-phase voltages are 120 degrees apart.

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  1. 90 degrees
  2. 180 degrees
  3. 120 degrees ✔

Why: Each of the three phases peaks one third of a cycle after the previous one. Because they overlap, the combined power delivery is smooth.

Huh, didn't know that: Single-phase power pulses at 120 Hz, which Utah's notes say is not suitable for motors over about 5 hp.

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References

Answer: 120 degrees. Each of the three phases peaks one third of a cycle after the previous one. Because they overlap, the combined power delivery is smooth.

  1. King Fahd University of Petroleum and Minerals, EE213 Ch. 11 Three-Phase Circuits faculty.kfupm.edu.sa/EE/samir/EE213/EE213_Ch11_ThreePhase.pdf
    out of phase with each other by exactly 120 degrees
    Checked 2026-10-10.
  2. University of Utah ECE 3600 three-phase notes my.ece.utah.edu/~ece3600/3_phase_pwr_notes.pdf
    Single phase power pulses at 120 Hz. This is not suitable for motors or generators over about 5 hp.
    Checked 2026-10-10.

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