Automatic Transfer Switch (ATS) AC3
It consists of two timing circuits - one for the mains and one for the generator.
Monitors the phase or phases for wrong phase sequence or phase failure, once a condition fails it will knock out the mains contactor and close a connection for the generator auto start (either Battery negative or positive)
Once power is available from the generator, it will activate a timing relay which can be set to any delay from 0.1 seconds to 10 days - this is to make sure the generator has enough time to get up to speed and stabilise. When the timer switches after the delay the generator contactor will come in to supply the load. If at any time the mains supply is restored the mains timing relay will activate to switch back to the mains supply.