Motor control undervoltage

Undervoltage schemes are often included in the reacceleration control systems of individual motors or groups of motors. However, these are more appropriately considered in motor protection rather than busbar protection schemes. 

Undervoltage Protection. Undervoltage relays and three-wire control are employed to initiate the opening of a motor circuit and maintain it open on a reduction or failure of voltage. Undervoltage protection generally is applied where uncontrolled motor starting could result in potential hazards. 

Undervoltage Release. Undervoltage relays and two-wire control are employed to initate the temporary opening of a motor circuit on the rednction or failure of voltage. On restoration of full voltage, the motor is automatically restarted. 

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