Which of the following is an advantage of a three-phase system compared with a single-phase system?

• A. Three-phase circuits require less weight of conductors than single-phase circuits, permit flexibility in voltage, can be used for one-phase loads, and have smaller, lighter, more efficient equipment.
• B. Three-phase circuits require more conductor weight than single-phase circuits and are less efficient.
• C. Three-phase circuits are only suitable for three-phase loads and cannot supply single-phase loads.
• D. Three-phase circuits have no advantage over single-phase systems.

Answer: (A)

Three-phase power delivers smoother, more efficient power delivery and makes better use of conductors and equipment. With power spread across three phases that are 120 degrees apart, the current in each conductor for the same total power is lower than in a single-phase system. That means you can use lighter, thinner conductors and still carry the same load. The three-phase configuration can be arranged (delta or wye) to provide different voltages, giving flexibility in voltage levels to suit various equipment and applications. You can also take single-phase loads from a three-phase system by using one phase to neutral (or by tapping off two phases), so you don’t need a separate supply just for lighting or small motors. Additionally, motors and other equipment run more efficiently and with less vibration in a three-phase system, often allowing smaller, lighter, and more compact designs for the same power.

So this combination of reduced conductor weight, voltage flexibility, capability to supply single-phase loads, and smaller, lighter, more efficient equipment makes the statement the best description of an advantage of three-phase over single-phase. The other options describe incorrect or overly restrictive limitations, such as claiming more conductor weight, loss of efficiency, or inability to serve single-phase loads.