Methods of implementing selectivity using circuit breakers
3.3 Current selectivity
Selectivity for 3VA molded case circuit breakers
Configuration Manual, 08/2016, A5E03603181010-01
21
3.3.2 Tripping characteristics of circuit breakers
Figure 3-4 Current-time diagram: Tripping characteristics in current selectivity applications
In order to achieve successful current selectivity, the characteristics of the two circuit
breakers must meet the following criteria:
● No contacts between the characteristics including tolerance ranges until the operating
current of the I release at the upstream 2500 A circuit breaker is reached.
For the purpose of the selectivity evaluation, the characteristics of the upstream circuit
breaker must be in the top, right-hand area (blue characteristic) and those of the
downstream circuit breaker in the bottom, left-hand area (green characteristic).
As a result of the changes to the parameters of the I release, a significantly higher degree of
selectivity is achieved as compared to pure overload zone selectivity (see "Selectivity in the
ove
rload zone (Page 15)"), but selectivity in the overl
oad zone is also assured.
The selectivity limit current (I
s
) has been raised to 2500 A. The selectivity in the short-circuit
zone up to 10,000 A is still only partial.
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