Siemens 3RW40 Soft Starter 400V ac, 11 kW, 3 Phase, IP20

This high-quality soft starter from Siemens is designed to provide a safer alternative to the ramp-up and ramp-down of three-phase asynchronous motors. It works by applying increasing voltages to the motor, resulting in a smooth acceleration of power and reducing the damage that could be caused by a sudden burst of energy. The unit is equipped with thyristors that control alternating currents, which means the motor won't suddenly switch off when its polarity is changed. It also features bypass contactors that divert the current flow through the soft starter switching circuits. This reduces heat buildup for improved performance and a longer working life.

• Compact dimensions of 154 (length) x 45 (width) x 125mm (depth)

The difference between the two components is that, while a VFD can alter the speed of the motor, a soft starter only controls its start and stop functions.