123 electric dual power automatic transfer switch uses

Is simply common way to backup all the way, when a sudden power failure or power outage commonly used by dual power switch automatically into the standby power (small load standby power generator can also be powered) so that the device still running . The most common is the elevator, fire protection, monitoring, UPS uninterruptible power supply with the bank as well, but his backup is a battery pack. Some of a Class II load and load unit of factories, mines or most of them have!