Motor Starters Information

The poly-phase induction motor is most often used to drive essentially constant loads at constant speed. Direct-on-line (D.O.L) starting is the method most commonly used. Remember that the starting current of a motor may be 5 to 8 times the full-load current at the rating of the windings is proportional  to the square of the current. In many cases, induction motors can be started by simply connecting them to the power line.
However, there are sometimes good reasons for not doing this. For example, the starting current required may cause such a acceptable. The starter is an electrically operated switch. When the operating coil is energized by pushing the start button, it closes the three main contacts and starts the motor. It also closes a small auxiliary contact at the same time. Study the D.O.L later and then you will see that pushing the starting button lets current flow through the operating coil, which energizes it; it then closes all four contacts. That starts the motor and as you remove your finger from the start button, the circuit opens but the coil remains energized because the circuit to the coil, at first energized by current flowing through the start button, now remains energized by current flowing through the auxiliary contacts.
The current ratings  of cables in a circuit feeding a motor must be based upon the full load current of the motor and not upon the starting current.