What is the principle of Selectivity?
Q: What is the principle of Selectivity?
A: The principle of Selectivity (Discrimination) is based upon an analysis of several circuit breaker characteristics.
Q: Which circuit breaker characteristics are analyzed in Selectivity?
A: The circuit breaker characteristics analyzed in Selectivity include time-current (tripping) curves, peak-let-through-current (Ipeak) and energy let-through (I²T).
Q: What is Selectivity level?
A: Selectivity level is the maximum level with two nominated breakers in series under short-circuit conditions.
Q: How is Selectivity enhanced beyond the breaking capacity of the downstream breaker?
A: Selectivity can be enhanced beyond the breaking capacity of the downstream breaker provided it is backed up by an appropriately selected upstream breaker, which should not trip (unlatch) under the stated short circuit current.
Q: How does Selectivity work?
A: Selectivity works as the upstream breaker heats up under fault conditions providing impedance in the fault circuit reducing the overall fault severity.
Q: What is the importance of Technical Reference Manuals?
A: Technical Reference Manuals often state the maximum selectivity level with two nominated breakers in series under short-circuit conditions.
Q: What is the purpose of providing impedance in the fault circuit?
A: The purpose of providing impedance in the fault circuit is to reduce the overall fault severity.
