Editing Uninterruptible power supply (section)

===Multiple redundancy===
Many computer servers offer the option of redundant [[Power supply unit (computer)|power supplies]], so that in the event of one power supply failing, one or more other power supplies are able to power the load. This is a critical point – each power supply must be able to power the entire server by itself.

Redundancy is further enhanced by plugging each power supply into a different circuit (i.e. to a different [[circuit breaker]]).

Redundant protection can be extended further yet by connecting each power supply to its own UPS. This provides double protection from both a power supply failure and a UPS failure, so that continued operation is assured. This configuration is also referred to as 1&nbsp;+&nbsp;1 or 2''N'' redundancy. If the budget does not allow for two identical UPS units then it is common practice to plug one power supply into [[mains power]] and the other into the UPS.<ref>Detailed explanation of UPS redundancy options{{cite web|url=http://www.emersonnetworkpower.com/en-US/Brands/Liebert/Documents/White%20Papers/High-Availability%20Power%20Systems,%20Part%20II_Redundancy%20Options.pdf|title=High-Availability Power Systems, Part II: Redundancy Options|access-date=2018-12-11|archive-url=https://web.archive.org/web/20130326072431/http://www.emersonnetworkpower.com/en-US/Brands/Liebert/Documents/White%20Papers/High-Availability%20Power%20Systems,%20Part%20II_Redundancy%20Options.pdf|archive-date=2013-03-26|url-status=dead}}</ref><ref>{{Cite journal|last=Heydari-doostabad|first=Hamed|date=January 2019|title=A new approach to design an observer for load current of UPS based on Fourier series theory in model predictive control system|url=https://www.sciencedirect.com/science/article/pii/S0142061517316083|journal=International Journal of Electrical Power & Energy Systems|volume=104|issue=1|pages=898–909|doi=10.1016/j.ijepes.2018.07.047|bibcode=2019IJEPE.104..898H |s2cid=116458248 |issn=0142-0615}}</ref>