Motor starters and contactors are specialized switches which turn on and off heavy loads such as electric motors. The principal of operation is based on using an electro-magnetic coil which draws a small amount of power to pull in a heavy set of contacts (switches) which turn on an electric motor or other heavy load, such as heaters or a long string of lights in a building. This enables a small push-button switch or other electronic control to turn on and off the load.
The difference between a starter and contactor is that the contactor is the switch mechanism only with an electro-magnetic coil. A starter has addtional components such as overload protection and possibly swtiches and an enclosure too.
Siemens Class 14 starters are the industry standard for motor control and protection. Each Siemens starter comes with an ESP200 programmable overload, which will shut down the motor in case of overloads, ground faults, phase loss, and other fault conditions.