An electric motor with a squirrel-cage rotor is termed a squirrel-cage motor. A squirrel-cage rotor is the rotating part used in the most common form of AC induction motor. It consists of a cylinder of steel with aluminum or copper conductors embedded in its surface. It consist of a stationary and a rotating parts. The rotating rotor is known as the squirrel cage rotor as it resembles a squirrel cage, whereas the stator is completely wound by copper wires with a proper insulation. Three phase squirrel cage induction motors can also be used as generators. For this to work the motor must either be connected to a grid supply or an arrangement of capacitors to provide excitation current. For the motor to work as a generator instead of a motor the rotor must be spun faster than its stator's synchronous speed. This will cause the motor to generate power after building up its residual magnetism.