We utilize the single-phase power system more widely than three phase system for household purposes, commercial purposes and some extent in industrial uses. Because, the single-phase 
system is more economical than a three-phase system and the energy requirement in the majority of the houses, shops, offices are little, which can be easily met by an individual phase system.
The single phase AC motors are further classified as:
Solitary phase induction motors or asynchronous motors.
One phase synchronous motors.
Commutator motors.
The squirrel cage rotor includes aluminum, brass or copper bars. These aluminium or copper pubs are known as rotor conductors and positioned in the slots on the periphery of the rotor. The copper or light weight aluminum rings permanently short the rotor conductors known as the end rings.
To provide mechanical power, these rotor conductors are braced to the end ring and speed reducer therefore form a complete closed circuit resembling a cage and therefore got its name as squirrel cage induction electric motor. As end rings completely short the bars, the rotor electrical resistance is very small in fact it is not possible to add external level of resistance as the pubs get permanently shorted. The absence of slip ring and brushes make the construction of single phase induction motor very easy and robust.