Fault Current Rating. The short time current rating is used by the engineer to determine the ability of the circuit breaker to protect itself and to coordinate with other circuit. The short time current rating of a circuit breaker is the ability of the circuit breaker to withstand the effects of the rated short time current level over defined time duration.
The short time current rating of a circuit breaker is the ability of the circuit breaker to withstand the effects of the rated short time current level over defined time duration. Where one transformer is larger than the others in the bank use the fault current value for the larger transformer. It demonstrates the ability of the breaker to remain closed for a time interval under high fault current conditions.
For example if 65 000 amperes of fault current are available at the service entrance every circuit protection device must have an interrupting rating of 65 000 amperes.
Once the fault currents have been calculated you can then select overcurrent protection equipment breakers and fuses with a fault current rating equal to or greater than those values nec 110 9. When there is a short circuit the resistance becomes very small and that means the current becomes very large. Step 1b insert the the kva rating power factor pf and impedance z of the transformer is not required to continue. The equipment must be able to withstand this fault current without experiencing a meltdown explosion or similar catastrophe.
