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Purpose of uninterruptible power supply (UPS)

The purpose of this publication is to provide guidance for facilities engineers in selecting, installing, and maintaining an uninterruptible power supply (UPS) system after the decision has been made to install it.

UPS selection, installation and maintenance guide
UPS selection, installation and maintenance guide (photo credit:

This technical manual has been prepared to provide generic guidance to agencies responsible for the selection, installation, and maintenance of UPS systems at Command, Control, Communications, Computer, Intelligence, Surveillance, and Reconnaissance (C4ISR) facilities.

Although it is written mainly for C4ISR facilities, which require a higher level of reliability, it could also be utilized as a reference in similar applications.


The process for identifying the need for an UPS system, selecting, installing, and maintaining the UPS system are covered.

Covered are: theory and principles of static and rotary UPS systems, design and selection of UPS, installation and testing of UPS, maintenance and operation of UPS systems, principles of static and rotary UPS, UPS system rating and sizing selection, operations/maintenance, batteries, troubleshooting, harmonic distortions, grounding, checklists,
and acceptance testing.

Principles and configurations

An UPS system is an alternate or backup source of power with the electric utility company being the primary source. The UPS provides protection of load against line frequency variations, elimination of power line noise and voltage transients, voltage regulation, and uninterruptible power for critical loads during failures of normal utility source.

An UPS can be considered a source of standby power or emergency power depending on the nature of the critical loads.

The amount of power that the UPS must supply also depends on these specific needs. These needs can include:

  • emergency lighting for evacuation,
  • emergency perimeter lighting for security,
  • orderly shut down of manufacturing or computer operations,
  • continued operation of life support or critical medical equipment,
  • safe operation of equipment during sags and brownouts, and
  • a combination of the preceding needs.
Title:Technical Manual: UPS Selection, Installation And Maintenance
Size:1.1 MB
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UPS selection, installation and maintenance
UPS selection, installation and maintenance

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More Information


  1. Adam Sani
    Apr 22, 2021

    What mean by G400 Ups

    Jan 29, 2020

    Dear All
    Anyone recommends providing of DG power while main Electic power source is failed. Found similar connections with DG source to UPS and failure too. If anyone interested to suggest, pls use anilpaul2k at the rate gmail

  3. Parthasarathy
    Dec 05, 2017

    I didnt get the access to download the pdf file. kindly give a guide to know about modern UPS

  4. Eugenio Roncelli
    Dec 21, 2015

    Very, very old document: nowadays, only IGBT are used in UPSs, with a lot of different (and reduced) problems.
    No mention of “on-line”, “off-line” (known also as parallel/series) functioning.
    Document not useful for modern solutions.

  5. Chandra Mouli
    Oct 24, 2013

    you told about the UPS that’s good but i want to know how to calculate the back up time for ups

    • Mahantesh
      Mar 27, 2015

      As i now i have tell . battery capacity measured by AH
      formula is there IT=AH
      I = AMPS
      T = TIME
      then we have to now what is the load we are using
      exp take 200 AH battery , and load is approximately take 10amp
      then T= AH/I
      T= 200/10
      T=20 time in second like that no battery and increase load.

      • Utpal
        Oct 17, 2019

        It is understand you are going to share your knowledge, but because of language problem it is not conveyed properly. Would like to request you to write it in proper English. Regards.

  6. Anand
    Aug 26, 2013

    Can you explain why sometimes ELR trips when isolation transformer connected on the output side of the UPS. so in this case, if it is put on the input side what is the procedure to be followed.

  7. harsha
    May 23, 2012

    The material Provided is fine. If possible can you please explain the battery , UPS sizing calculations with any practical example which would be really helpful for us.

    Nov 25, 2011

    Really, that’s well..As i pertain to Networking arena, The Topic of UPS somewhat enhanced to gather my information…. Mostly, i have observed that topics are belonged to ..Transformers, power grids and so….. In short i would like to entreat all of our scholars to sprinkle the topic of Networking Tools and Diagnose also……

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