What describes the short circuit breaking capacity of an overcurrent protective device?

• A. The maximum current a device will carry indefinitely without tripping
• B. How much current the device can break without exploding
• C. The time delay before tripping under overload
• D. The voltage rating of the device

Answer: (B)

Short circuit breaking capacity is the highest fault current that an overcurrent protective device can interrupt safely without sustaining damage. It tells you how much current the device can clear during a short circuit at the system’s voltage. This rating ensures the device can open the circuit without welding contacts or exploding, even when the fault current is very large.

This is different from how much current the device can carry continuously—that’s the normal current rating for steady operation. It’s also different from the time it takes to trip under overload; that describes the device’s time characteristics, not its ability to interrupt a high fault current. And it’s not about the voltage the device can handle—that’s a separate voltage rating. For proper protection, the device’s breaking capacity must be at least as large as the prospective short-circuit current in the system.