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How can the arc fault current be greater than the bolted figure?
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Author:  Mike Frain [ Fri Feb 01, 2008 6:46 am ]
Post subject:  How can the arc fault current be greater than the bolted figure?
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:
Author:  WDeanN [ Mon Feb 04, 2008 6:47 am ]
Post subject: 
Mike Frain wrote:
Is there an explanation? Surely arc current cannot be greater than the available short circuit current?
Mike :confused:


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.
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