The ATS, or automatic transfer switches, are basically the go-between utility power and generator power. There is a common load fed from the transfer switch usually to all your emergency panels. During a test or an actual power failure, there is a time delay before the ATS sends a signal to your generator, starting it. When the voltage and frequency of your generator is acceptable by the voltage sensing network, it sends a signal over to the mechanism. It will open up normal power and then close the generator. Now you're online and everything is stable at this point. When normal power, or utility comes back online there is a time delay preventing the generator from switching back- just in case normal power is unstable for a while.

