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Thread: Bank of Inverters - conductor sizing

  1. #1
    Join Date
    Jun 2009
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    Bank of Inverters - conductor sizing

    Hello all - I have a bank of (11) 50kW inverters feeding a 480V piece of gear. Sizing the output circuits is easy enough 50k/831.38*1.25 = 75A.
    My next logical move is to multiply 75*11=826A and determine the conductor size and OCPD from there. Right? I'm seeing different ideas all over and need some clarity.
    My thought would be the same if I had a bank of other continuous operating equipment.

  2. #2
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    Quote Originally Posted by fossil112 View Post
    Hello all - I have a bank of (11) 50kW inverters feeding a 480V piece of gear. Sizing the output circuits is easy enough 50k/831.38*1.25 = 75A.
    My next logical move is to multiply 75*11=826A and determine the conductor size and OCPD from there. Right? I'm seeing different ideas all over and need some clarity.
    My thought would be the same if I had a bank of other continuous operating equipment.
    The inverter current is not necessarily equal to power/voltage/sqrt(3). Some inverters have headroom on this value in case the voltage is lower than nominal, or if the inverter is built to offset power factor. So you need to check the datasheets and manuals, which may specify values that override your basic calculation. Once you have the actual maximum operating current, you add this up among the group of inverters, and use that value for sizing your main output conductors and main OCPD. You have to round your OCPD up to the next size available, which would be 1000A.

  3. #3
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    Quote Originally Posted by Carultch View Post
    The inverter current is not necessarily equal to power/voltage/sqrt(3). Some inverters have headroom on this value in case the voltage is lower than nominal, or if the inverter is built to offset power factor. So you need to check the datasheets and manuals, which may specify values that override your basic calculation. Once you have the actual maximum operating current, you add this up among the group of inverters, and use that value for sizing your main output conductors and main OCPD. You have to round your OCPD up to the next size available, which would be 1000A.
    This is implicit in what you said, but to be clear, the nameplate maximum inverter current is to be used in all calculations, including the individual inverter OCPD and conductor sizing.

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