The power supply to certain industrial and non-industrial loads must not be interrupted, and these loads, which are classified into two types—emergency and critical—must be continuously powered by electricity. The key issue between these two types of loads is the allowable interruption time caused by a power outage and the activation of the backup power source.
For emergency loads, a few seconds or even a few minutes of interruption does not affect the process, and these types of loads are generally powered by generators, or on a smaller scale, by power engines.
If an interruption in power supply is not acceptable and the load must be supplied without even the slightest noticeable delay, a UPS must be used. These systems draw their instant power from the battery bank connected to them to immediately go online.