What is a phase in a three-phase system?

• A. One of the three alternating voltages that are 120 degrees apart in time.
• B. A conductor that carries current back to the source.
• C. The conductor at earth potential.
• D. The ground fault path.

Answer: (A)

In a three-phase system, a phase is one of the three voltage waveforms that are offset from each other by 120 degrees in time. Each phase has the same magnitude and frequency, but its sine wave is shifted so its peak occurs at a different instant than the others. This 120-degree separation keeps power delivery smoother and supports balanced loads, which is especially important for motors and feeders. The other terms describe return or fault paths—not the phase itself—such as a conductor that carries current back to the source, the conductor at earth potential (ground), or a ground fault path.