後備電源應急系統

一般公共設施和私人機構中都會裝置後備電源應急系統，係由兩個或以上既電源來供電，如果係低壓電，將會係一個來自電力供應商牛房另一個係來自一架後備發電機，然後經過一個特別設計既自動電源轉換制 Automatic Change Over Contactor or Auto Transfer Switch 來給電，如果係高壓電通常會有兩個或以上既電源來供電，名稱叫 Loop in Loop out or 2 in 1 out，當一個電源供給有問題時會自動轉換到另一個供應。

3Link - 不斷電系統, 後備電源- 的不斷電系統為電腦房間內設備提供後備交流電源，維持設備正常運作。http://www.3linkgroup.com/zh/page.php?page=server_room_setup_4

後備電源應急系統:
If for the whole building, say office building, there will be an emergency power generator. It is used for fire services installation, essential power and other utilities. For computer system, there will also be an UPS, uninterrupted power system for server etc.

In HK, these generators are mainly diesel fueled and located at generator room.