Direct start is the simplest starting mode of an electric motor, with the stator connected directly to the mains Gates A25 Hi-Power II Belts. The motor starts with its natural characteristics and when it is started, the motor behaves as a transformer in which the secondary, formed by the very low resistive rotor cage, is short-circuited. The current induced in the rotor is high and the primary and secondary currents being substantially proportional, the resulting current peak is high; I start = 5.0 to 7.5 I nominal. The starting torque will be on average; C starting = 0.5 to 1.5 C nominal.
Despite its advantages such as simple equipment, high starting torque, fast starting, low price, direct starting is only interesting in cases where the power of the motor is low relative to the available power in the network, so that it limits the disturbances originated by the peak current, also when the driven machine does not need a progressive acceleration and is equipped with a mechanical device (for example reducer) which prevents a very fast start, and the starting torque has to be raised.