What is three-phase phasing?

• A. The color code used for three-phase conductors.
• B. The order of three circuit breakers in a three-phase system.
• C. The relative timing of three alternating voltages, which are 120 degrees apart.
• D. The maximum voltage difference among the three conductors.

Answer: (C)

Three-phase phasing is the timing relationship among the three AC voltages in a three-phase system. Each phase is a sine wave of the same frequency and amplitude, but they are offset in time by 120 degrees, so the voltages reach their peaks at different moments. This 120-degree separation creates a rotating magnetic field and delivers power smoothly with less torque ripple, which is why three-phase systems power efficient motors and generators. The other choices aren’t about timing between the phases: the color code is simply conductor insulation labeling, the order of circuit breakers refers to switching sequence, and the maximum voltage difference among the conductors describes line-to-line voltage rather than how the phases are timed relative to each other.