What happens to the fault current's magnitude and time duration in a current-limiting OCPD when in the current-limiting range?

In a current-limiting overcurrent protective device (OCPD), when it operates in the current-limiting range, both the magnitude of the fault current and the time duration are affected in a manner that ultimately improves safety and reduces damage.

The primary function of a current-limiting OCPD is to quickly detect fault conditions and limit the current that flows during a fault event. When a fault occurs, these devices will sense the instantaneous rise in current and act very rapidly. As a result, the magnitude of the fault current is dramatically reduced because the OCPD interrupts the circuit quickly and limits how much current flows. This swift action minimizes the energy that can be released, thus reducing the potential damage to equipment and improving safety for personnel in the vicinity.

Moreover, as the fault current is limited during the operation of the OCPD in this range, the duration for which the fault current flows is also decreased. This means that the fault current is present for a shorter time, thus further reducing the risk of injury and damage.

This combination of reduced current magnitude and shortened duration is critical to ensuring that electrical systems are safer and more reliable, aligning with the principles outlined in the NFPA 70E for electrical safety in the workplace.