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How can the arc fault current be greater than the bolted figure?

Discussion in 'IEEE 1584 - IEEE Guide for Performing Arc-Flash Ha' started by Mike Frain, Feb 1, 2008.

  1. Mike Frain Administrator

    I have calculated the arcing current for a 900 volt supply and came up with an unexpected result. The bolted fault current is 20kA and the current in the arc came back as 24.88kA. I checked this with the web arc analyser and came back with the same result. Is there an explanation? Surely arc current cannot be greater than the available short circuit current?

    I am using the following parameters; 900volts, MCC panel, 32mm gap, 457mm working distance, grounded supply, 20kA bolted current.

    Any ideas?

    Mike:confused:
    Mike Frain, Feb 1, 2008
    #1

  2. WDeanN Sparks Level

    Congratulations! You've found one of the few anomolies with the 1584 equations! For more information, you should read http://us.ferrazshawmut.com/arcflash/getting_help/downloads/ICPS-wilkins011904_web.pdf

    Hopefully these will be ironed out with the upcoming (someday, soon, sometime, almost here:rolleyes: ) NFPA/IEEE effort.
    WDeanN, Feb 4, 2008
    #2

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