In article , David Hansen
writes
Typically the standby generator can only power a small part of the
building load. Non-essential circuits are shed as the generator starts
up. With the generator running it may not be desirable to go back to
the external supply automatically if it does become healthy, it might
fail a minute later. Thus the building may run with only essential
circuits for some time until people are happy with the external supply.


In these days where everything is computer controlled and your servers
are probably the most important business-critical device (see the cases
of various supermarkets which have to close for the day because their
accounting software is on the frizz), keeping them working also needs
air-conditioning. So when things like this happen you'll be sitting in
the dark, bathed only by the strangle glow of computer screens, unable
to do many jobs that require manual dexterity - like going for a pee in
a totally dark toilet - but in a nice, comfortably cooled environment.

--
Martin @ Strawberry Hill