Atabiq, FauzunSitumeang, Benny2022-11-032022-11-032013-07-03https://repository.polibatam.ac.id/xmlui/handle/123456789/349Quality of power supply system in an electrical circuit is needed. Poor quality power supply may cause distraction and may even damage the system hardware/ electrical circuit. One form of the disorder is the under/over voltage. To overcome this we need a protection device that can detect the presence of interference under/over voltage and secure the electrical equipment. Under/over voltage relay based microcontroller ATmega328 is designed aiming to detect the disorder under/over voltage on voltage single phase 220 V 50 Hz. Voltage limits for nuisance under voltage is -5% of normal voltage (220V), whereas disruption over voltage is +5% of the normal voltage. and delay settings for under / over voltage is 5 seconds. The output of the relay is connected to the contactor, the contactor will disconnect the power supply in case of disturbances under/over voltage. From the results of tests performed, the relay under/over voltage ATmega328 microcontroller-based designed to work properly. Relay can detect disturbances under voltage and over voltage -5% +5% of nominal voltageidTeknik ElektroElekronikaManufacture of Products for Specific UsesThesis