What is the primary disadvantage of a single-phase motor?

The primary disadvantage of a single-phase motor is that they typically have lower efficiency compared to three-phase motors. Single-phase motors are designed to operate on a single phase of power, which limits their performance in terms of both efficiency and starting torque. Three-phase motors, on the other hand, can generate a rotating magnetic field that provides smoother operation, higher efficiency, and greater torque at startup.

This lower efficiency in single-phase motors can be attributed to their design and construction, which often are not optimized for high performance as seen in three-phase systems. The reliance on only one phase for operation restricts the ability of the motor to generate the same output power as a three-phase motor of the same size, making them less desirable for applications requiring high efficiency.

While the other options highlight potential aspects of single-phase motors, they do not capture the main disadvantage in terms of efficiency. The weight and size can vary based on design but are not universally true regarding single-phase versus three-phase motors. Maintenance needs can also vary greatly based on specific motor types and usage conditions rather than being a definitive disadvantage of single-phase motors. The operation at one speed, while a characteristic of some single-phase motors, is not inherently a disadvantage, as many applications do not require variable speed.