On its own, a contactor is merely a switch device that allows a motor to turn on or off. However, the combination of a contactor (1) and an overload relay (3) creates a motor starter, which combines the functionality of the contactor (switching) and the overload relay (overcurrent protection to the motor) in one single device.
If the contactor does not have auxiliary contacts built in, an additional auxiliary contact (2) is added so that feedback of the contactor’s current state can be provided to external equipment to sound an alarm, activate a backup power source, or other status indicators.
A combination starter uses a motor starter protector (MSP) (4) instead of an overload relay, for additional levels of overcurrent and short-circuit protection. Each motor starter protector will come with a separate connector (5) that attaches the device to a contactor without any additional configuration required. Note: components are only physically compatible with other components of the same series.