It is an voltage protection which protects and extends the service-life of connected electrical equipment (TV,Telephone,etc.)safe. We can adjust the voltage according to equipment work voltage. When voltage is higher or lower than normal voltage, it  cut off to protect the equipment  safe.   

We can set the hither and lower voltage according to our normal voltage.(such as 180V to 260V, when voltage lower than 180V or higher than 260V, it cut off to protect the equipment safe.)           

 Green lamp means voltage is normal, when green lamp is cut off and red lamp works it means the voltage is higher or lower Voltage rate:16A,220V