A three-phase motor in principle works like a three-phase transformer whose secondary winding can be rotated within the field of the primary or stator winding. In the case of the squirrel cage motor the rotor winding consists of copper bars placed isolated inside the grooves of the rotor and interconnected at the front end. The picture of the resulting short-circuited rotor winding looks like a treadmill or squirrel cage and gave the name to this type of motor. In this secondary / rotor winding, a voltage from the stator winding is induced and – because the winding is short-circuited – there is also a current flow. This current generates an electromagnetic field in the rotor, which is attracted by the field of the stator winding. Since the field of the stator winding rotates around its axis (rotating field) due to the mechanical arrangement of the windings and the phase sequence of the AC current, also the rotor of the motor rotates. The squirrel cage motor is an inexpensive, robust and universally applicable drive that has made its way into nearly all fields of application. The downside aspects are its high starting current and the hard start. It can be switched on directly or via soft starts and the speed can be controlled via frequency converters. An inexpensive way of limiting the high starting torque is also the introduction of a resistor into the phase during the start (stator-resistance starting circuit).