Selectivity / discrimination
Selectiviteit
Also known as: selectief, selectivity, protection-coordination, discriminatie, cascade-trip, cascadering, graded-protection, upstream-protection, stroomopwaartse-beveiliging, trip-coordination, back-up-beveiliging
Property that only the nearest protection trips on a fault, keeping the rest of the installation operational. Requires current and/or time step difference between upstream and downstream fuses (typical factor 1.6:1 or an S-type RCD before 30 mA).
Practical example
Selectivity: A fault on a final circuit trips only the 16 A branch MCB, while the 40 A main MCB in the distribution board remains closed due to sufficient current and time discrimination.
Common mistake
Selectivity: Placing two breakers with nearly identical ratings in series (e.g., 16 A and 20 A) without time delay—during a fault, the upstream breaker may also trip.
See also
Related terms
- Residual Current Device (RCD)
- Miniature Circuit Breaker (MCB)
- Breaking capacity
- Fuse
- Active harmonic filter
- Directional Earth-Fault Protection (Compensated Network)
- Zone-Selective Interlocking (ZSI) — Power Circuit Breaker
- Adjustable Ground-Fault Protection (Ig)
- Earthing Switch — Maintenance Earthing (HV/MV)
- Earthing transformer (zig-zag transformer)
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