If you have chosen an automatic standby generator, you will also need a separate device called an Automatic Transfer Switch to connect the generator to your existing electrical system. Most automatic standby generators are pre-packaged with a transfer switch.
Although the generator creates the power, the transfer switch is really the core of your generator system. It is an electrical panel that allows you to safely connect a generator to your home's electrical circuits and is permanently installed near your main circuit breaker panel. It constantly monitors incoming utility power and determines when a true power outage is occurring, switching from utility power to emergency generator power and back again when utility power returns. Options include transfer switches that provide power to only essential circuits or every circuit for whole-house coverage, and some allow for prioritization of optional circuits or load shedding, such as heating and cooling.
Do not attempt to install a transfer switch yourself. Installation of transfer switches may require local permits - but it always requires a professional electrician. The model of transfer switch will depend mainly on the size of your generator.