Under normal circumstances, the requirement is supplied by the city power. When the power supply is cut off or interrupted for other reasons, standby generator set could ensure the basic production and life of the user. This type of generator sets is usually used in important sites such as telecommunications departments, hospitals, industrial and mining enterprises, airports... They stay in standby at any time and can provide continuous power supply for non-constant loads.
An Automatic Transfer Switch (ATS) is often installed where a backup generator is located, so that the generator may provide temporary electrical power if the utility source fails.