What is the name/purpose of this component?

This component is a undervoltage protection device. When the voltage is high enough the device will close a make contact so current can flow. When the voltage is to low the contact will open or stay open. This is a over voltage-relay, but imagine it with the smaller than(<) character.

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The red square is an undervoltage trip. It prevents the breaker from remaining or being closed when there is not enough voltage.
Commonly found on equipment and machinery that for safety reasons may never start automatically when power returns after a failure.

The black wire provides AC back from the motor as long as the thermal protector is closed indicating normal temperature. The device in the red box probably opens the switch when the thermal protector opens.