What is the key difference between a single-phase and a three-phase electrical supply?

The distinction that sets single-phase electrical supply apart from three-phase supply is that single-phase consists of only one alternating current (AC) waveform. This means that the power delivered in a single-phase system fluctuates in one cycle, leading to a relatively steady but lower power output compared to three-phase systems.

In contrast, three-phase electrical supply has three separate AC waveforms that are offset by 120 degrees from each other. This configuration helps to provide a more consistent and reliable power delivery, as the combined power from the three phases results in a smoother and more efficient operation in applications, particularly for industrial motors and HVAC systems. Three-phase systems can operate at lower currents for the same power level, leading to increased efficiency and reduced transmission losses.

The other options presented do not accurately describe the key characteristics that differentiate single-phase and three-phase electrical supplies.