Analysis and Design of Electrical Power Systems

15Selectivity and Backup Protection

15.1 Selectivity

Electrical operational and consumer equipment must be protected against stresses resulting from short‐circuit circuits by the selective disconnection of the faulty systems. IEC 60364, Part 53 requires selectivity in low‐voltage networks. The most important selectivity conditions for protective devices are described. An electrical system is equipped with several overcurrent protective devices connected in series such as fuses and circuit‐breakers, which are selective because in the event of a fault only the overcurrent protective device located directly before the fault location in the direction of current flow responds. Investigating the selectivity conditions requires a comparison of the ...