SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/eng-three-phase-120-degrees

In three-phase power, how far apart in phase are the three voltages?

120 degrees, one third of a cycle each.

Start playing free

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

Why: In a balanced system, three voltages have the same frequency and amplitude, each shifted by one third of a cycle. Their combined power is constant for a balanced load.

Huh, didn't know that: In a balanced three-phase system, the three instantaneous phase voltages sum to zero.

The dad joke
Three-phase power is like a good band. Everyone takes turns, a third of a cycle apart.
Like this card?
Play the game

References

Answer: 120 degrees. In a balanced system, three voltages have the same frequency and amplitude, each shifted by one third of a cycle. Their combined power is constant for a balanced load.

  1. IEEE Technology Navigator, Three-phase Electric Power technav.ieee.org/topic/three-phase-electric-power
    three conductors carry sinusoidal voltages of identical frequency and amplitude, each displaced by 120 degrees from the others
    Checked 2026-10-10.

Think this answer is wrong? Tap "Challenge this answer" on the card in the game and tell us why.

Test yourself in the game

EngineeringNorth America's grid runs at 60 Hz. What frequency does Europe's grid use?EngineeringHow many base units does the International System of Units (SI) have?EngineeringSince the SI redefinition voted in 2018, what defines the kilogram?

That's stuff everyone should know.