"Fault Rating" is the actual "PSC" = "Prospective Short Circuit Current", at any point in an electrical network.
So you may have a mccb which has a designated operating current of 30 Amps, trips in a few seconds at 40 Amps, and trips in an hour at 32 Amps - this is all quite normal.
The Fault Current Rating designates the maximum short circuit which is available at the connection point of the circuit breaker.
So...A large Industrial Switchboard may have a PSC rating of 30MVA.
That means that all switchgear, contactors connected must be able to safely withstand a fault of that magnitude.
To determine the PSC at any point in a network is quite complex, normally left to a combination of Supply Authority Engineer, and the Electrical Engineer or Electrical Contractor on the job.
Supply Frequency/Impedance, Cable Impedances, and other variables need to be factored into the calculations.
Any error in the above calculations may have extreme effects later, if some fault develops.
Hope that assist you.
Kind Regards....
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mccb
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