The generators should be powering up as soon as one of the 2 different sources goes down. It takes generators a few minutes to power up and get "warmed up". If they don't start this process until both mains sources are down, then oops, there's power outage.
I used to work next door to a "major" cable TV station's broadcast location. They had multiple generators on-site, and one of them was running 24/7 (they rotated which one was hot). A major power outage hit, and there was a thunderous roar as all of the generators fired up. The channel never went off the air.
I used to work next door to a "major" cable TV station's broadcast location. They had multiple generators on-site, and one of them was running 24/7 (they rotated which one was hot). A major power outage hit, and there was a thunderous roar as all of the generators fired up. The channel never went off the air.