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2.4
Selectivity
Switching devices connected in series, e.g. molded case circuit breakers and fuses, work
together to ensure graded tripping of these switching devices. The closest, upstream
switching device before the location of the short-circuit must trip. The other switching devices
on the same current run do not trip. The purpose of selectivity is to minimize the effects of a
fault in terms of its duration and the area affected by the fault.
Selectivity is achieved when the circuit breakers are matched to each other by means of
selection, configuring and trip settings in such a way that, in the event of a fault, only the
breaker closest to the location of the fault trips.
Selective behavior
The selective behavior of molded case circuit breakers is mainly influenced by the following
factors:
● Tripping value settings of the trip unit
● Tripping and break times
● Let-through current values
● Modes of switching of the relevant circuit breakers
– Zero-current interrupter
– Current limiter
3VA molded case circuit breakers with IEC certificate
Manual, 03/2019, A5E03603177010-03
Short-circuit location
Description
2.4 Selectivity
53
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