The device works as decribed. I don't give 5 stars only because it arrived with one side dented, probably due a transportation issue. The device has the genset control NO contact, when the main power fail the device close the contact and the genset start giving recovery power, then the device switch to recovery power. When main power come back, it switch to main power and open the contact and the genset stops. The device has a complete configuration for overvoltage and undervoltage controls and delay management for switching. Easy to install and configure. Cost effective.