Overvoltage and undervoltage protectors are mainly used in the incoming lines of residential household distribution boxes or distribution lines that need to protect single-phase electrical equipment, such as power supply systems in homes and small offices, providing overvoltage and undervoltage protection for various electrical equipment such as air conditioners, refrigerators, and televisions.Generally installed at the incoming line of the household distribution box in a residential building or at the front end of the distribution line where single-phase electrical equipment needs to be protected.