These motors require six phase conductors so as to operate the star-delta transition within the motor starter cubicle. There are six terminals within the motor terminal box for these.

Each motor winding has two ends and there are three sets of windings giving six terminals. Hence you have six wires coming from the motor to the switchgear. One end of the windings is connected via a contactor to each of the three phases (not shown in the diagram) while the other ends of the windings are connected together (by Q13 in the diagram below) to form a star, once sufficient speed is reached Q13 opens and Q15 closes connecting the appropriate phases in the correct order. Nowadays inverters are so cheap they are often used for soft starting motors, reducing shock loads. SDS is useful in limiting inrush current.

http://www.wiringmanual.com/motor039.html