Electrical motors should be protected against overloads and short circuits. Moreover, they should be isolated from the main supply. In the combination of the manual motor starter and contactor, the former provides the protection and isolation functions.
After detecting an overload or short circuit, the manual motor starter disconnects all phases from the supply, isolating the motor from the supply. By reacting very quickly manual motor starters also increase the device’s reliability. They protect load-side circuits against damage.