There's a generator. And generators need changeover switching to flip the power connection from main line to generator's line.
Initially did it with a manual change over switch. But that was tiresome. Every time the power fails you need to flip the changeover switch to connect with the generators power, turn on the generator and when power returns flip it back to mains.
Then discovered the automatic change over switches when I discarded the manual one, and started to use this.
There's still a change over switch at home, but not this large. Now I do it with 220V relays which are one tenth this size.
And large ones aren't durable either.
