As a circuit breaker interrupts a fault current, the contacts start to part and the ensuing arcing current is directed to the arc chutes, which stretches and cools arcing current. What is the fault current being interrupted?

• A. Fault current
• B. Normal operating current
• C. Load current
• D. Surge current

Answer: (A)

When a fault occurs, the current that must be interrupted is the fault current—the abnormal, excessive current produced by the fault such as a short circuit. The arc that forms as the contacts separate is directed into arc chutes, which stretch and cool the arc to help extinguish it. This is different from normal operating current, which is the current the system carries under normal conditions; load current, which is the current drawn by the connected load; and surge current, which is a brief inrush not caused by a fault. So the fault current being interrupted is the fault current.