Single-phase motors do not create their own magnetic field so they must be activated via a switch or other device to make their rotor move. Only after the rotor is set in motion is a magnetic field created, thus making it operate.
Single-phase motors are ideal in machines that are small with low horsepower, usually fractions of one horsepower, like fans, pumps, refrigerators, portable drills and compressors.
There are several types of single-phase motors, including split-phase, capacitor-start, two-valve capacitor, permanent-split capacitor, shaded-pole and wound rotor. They all have advantages and disadvantages.
Single-phase motors are less expensive to manufacture than other motors. All types of single-phase motors are very efficient in their own way. Capacitor-start motors are good general purpose motors and they are ideal for most occasions.
The mechanics behind single-phase motors are relatively simple, but this does not mean that nothing can go wrong. Sometimes they fail to start, overheat or run slow. If a shock is felt while touching the motor, there is a problem that needs to be addressed.