Selective tripping refers to which behavior?

Selective tripping refers to which behavior?

• A. Selective tripping of breakers caused by the time-current characteristic so that the breaker closest to the fault opens first
• B. Manual tripping of a breaker or switch
• C. Tripping all breakers in the panel at once
• D. Tripping only when a fault is detected by residual current

Answer: (A)

Selective tripping means coordinating protective devices so that, when a fault occurs, the breaker closest to the fault clears it first, keeping the rest of the system energized. Breakers have time-current characteristics that determine how quickly they trip based on the fault current; in a coordinated setup, the downstream breaker trips sooner for the same fault than the upstream ones. This localizes the disturbance to the affected circuit, minimizes outage to other parts of the system, and protects equipment along the path. Manual tripping is an intentional action not tied to fault conditions, so it isn’t about coordination. Tripping all breakers at once is nonselective and defeats the purpose of protecting only the faulted circuit. A residual-current device trips on leakage to earth and operates by a different protection principle, not the general overcurrent coordination described here.

Selective tripping means coordinating protective devices so that, when a fault occurs, the breaker closest to the fault clears it first, keeping the rest of the system energized. Breakers have time-current characteristics that determine how quickly they trip based on the fault current; in a coordinated setup, the downstream breaker trips sooner for the same fault than the upstream ones. This localizes the disturbance to the affected circuit, minimizes outage to other parts of the system, and protects equipment along the path. Manual tripping is an intentional action not tied to fault conditions, so it isn’t about coordination. Tripping all breakers at once is nonselective and defeats the purpose of protecting only the faulted circuit. A residual-current device trips on leakage to earth and operates by a different protection principle, not the general overcurrent coordination described here.