Understanding OCPD Selectivity: What Is OCPD Selectivity?
Selectivity refers to the proper coordination between overcurrent protective devices so that only the affected device trips during a fault, leaving other parts of the system operational.
If one or both of OCPD is a circuit breaker, then their tripping characteristics must be compared with each other or with fuse characteristics,
If Upstream circuit-breaker and downstream fuse
Selectivity is obtained by comparing time-current characteristics.
It is advisable to maintain a safety margin between the maximum tripping time of the fuse characteristic and the minimum tripping time of the circuit-breaker characteristic.
Generally, a delta time ≥ 1s is enough for thermal-magnetic breakers and 100 ms in case of electronic trip units.
More selectivity technical issue please refer to OCPD device manufacture’s manual
Prosurge’s SPD overcurrent protective device -SCB
PROSURGE SCB provides backup over-current protection for the SPD, which is fully coordinated with the surge protective device according to the choice of different models.
Comparing to normal backup circuit breaker/fuse, the PROSURGE SCB achieve a better balance between surge withstand performance (no tripping while expected surge occurs) and sharp reaction against short circuit and abnormal leakage current.
Comparison of OCPD: Fuse,MCB,MCCB,SCB
Protective range of CB, fuse and SCB
Conclusion
Achieving optimum selectivity between overcurrent protective devices is key to both safety and reliability in electrical systems. Whether you utilize traditional fuses, MCBs, MCCBs, or advanced solutions like PROSURGE’s SCB, proper coordination and adherence to recommended safety margins are essential. For more detailed technical insights, always consult the OCPD manufacturer’s documentation.
