If you connect your standby generator up to an Automatic Transfer Switch (ATS) you have a fully automated change over system.
In the event of a mains power failure the ATS will automatically start the generator providing your home or business with electricity and when the mains power supply is restored the ATS will stop the generator and automatically switch back to mains power.
The ATS must be sized correctly for the generator set and the main incoming Amperage. This is to ensure that when the incoming mains power is live that the ATS box can handle it. If this is done incorrectly, the ATS will overheat and cease to function correctly. Hence the sizing of the ATS should be done by a professional taking into account the mains incoming power and the Generator output when being used.