A fully rated system is defined as all overcurrent protection devices having an interrupting rating at least as great as the available fault current at their point of application.

A fully rated system is defined as all overcurrent protection devices having an interrupting rating at least as great as the available fault current at their point of application.

• A. True
• B. False
• C. Not specified
• D. Both

Answer: (A)

A fully rated system means every overcurrent protective device has an interrupting rating at least as high as the fault current that could occur at its point of installation. This ensures that, in a fault condition, the device can safely interrupt the current without being overstressed or failing to clear the fault. The available fault current is the maximum current that could flow at that location, determined by the source and the impedances in the system. The interrupting rating is the maximum current the device is designed to interrupt safely. When each device meets or exceeds the local fault current, the protection scheme can trip and stop the fault effectively, protecting equipment and people. If a device’s interrupting rating were lower than the fault current it might experience, it could fail to interrupt or be damaged, defeating proper protection. Hence the statement is true.

A fully rated system means every overcurrent protective device has an interrupting rating at least as high as the fault current that could occur at its point of installation. This ensures that, in a fault condition, the device can safely interrupt the current without being overstressed or failing to clear the fault. The available fault current is the maximum current that could flow at that location, determined by the source and the impedances in the system. The interrupting rating is the maximum current the device is designed to interrupt safely. When each device meets or exceeds the local fault current, the protection scheme can trip and stop the fault effectively, protecting equipment and people. If a device’s interrupting rating were lower than the fault current it might experience, it could fail to interrupt or be damaged, defeating proper protection. Hence the statement is true.