COC including supplies from UPS

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  • RegElec
    Full Member

    • Oct 2012
    • 72

    #1

    COC including supplies from UPS

    I would be interested to hear how members of this group are carrying out COC's for UPS feeds. I seem to be getting more of these all the time now. All of them are in industrial environments and sometimes involve the UPS feed to a DB or a feed from the UPS DB to 230V instruments in the filed.
    My biggest concern is the PSCC and ELI.
    There aren't any fault levels marked on the UPS. I presume that this would in any event change according to the amount of batteries installed.
    I have heard people say that in the event of a fault the inverter will switch back to mains so therefore test the mains circuit to get the values however, this still presents problems in getting the readings.

    Second question is testing of 525V feeds from MCC's to motors etc. I have one at the moment where I am to issue a COC for a 525V feed from MCC to 0.4KW motorised valve. My tester cannot test this voltage even though it will be 303V phase to earth. I am trying to get the engineers to give me the PSCC at the MCC but from previous experience they will give me the main switch kA rating and not the actual PSCC. Anyone else had these problems.
  • GCE
    Platinum Member

    • Jun 2017
    • 1473

    #2
    The fault levels on a UPS will be the max level it will hold an inrush for which is generally at 1,5 times nominal - Is often on the rating plate.The fault level is low due to the electronics that will cut the system out on a short circuit.

    You can use the incoming mains fault level which will generally be higher than the UPS.

    The batteries have no influence on the 220v side fault levels - The internal fault level on the batteries within the machine is a different story but not relevant to us
    Same as a generator .The fault level will never be more than 1,5 times rating . If you double the load on a genset it just " dies"

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    • RegElec
      Full Member

      • Oct 2012
      • 72

      #3
      Originally posted by GCE
      The fault levels on a UPS will be the max level it will hold an inrush for which is generally at 1,5 times nominal - Is often on the rating plate.The fault level is low due to the electronics that will cut the system out on a short circuit.

      You can use the incoming mains fault level which will generally be higher than the UPS.

      The batteries have no influence on the 220v side fault levels - The internal fault level on the batteries within the machine is a different story but not relevant to us
      Same as a generator .The fault level will never be more than 1,5 times rating . If you double the load on a genset it just " dies"
      Thank you for the feedback. I have spoken to UPS manufacturers and installers of major equipment and none of them have told me that. I will use that in future.

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