In three-phase calculations, which factor introduces the difference from single-phase results?

• A. Phase relationships between voltages and currents
• B. Conductor color
• C. Surface area of conductors
• D. Frequency variation

Answer: (A)

The main thing being tested is that in a three-phase system the voltages and currents in the three paths are not in step with each other. They are 120 degrees apart, so you must treat them as vectors (phasors) and combine them accordingly. Because of these phase angles, the line-to-line voltages, line currents, and total power don’t follow the simple add-magnitudes rule you’d use in a single-phase circuit. This phasor relationship is what makes three-phase calculations different, including the way line voltage relates to phase voltage and how total power is computed.

Conductor color and surface area don’t create the difference between three-phase and single-phase results; they affect practical aspects like identification and resistance, but not the fundamental phase relationships. Frequency variation can change impedance, but it’s the 120-degree phase shifts that drive why three-phase analysis yields different results from a single-phase approach.