Siemens SENTRON - Example

Methods of implementing selectivity using circuit breakers
3.2 Selectivity in the overload zone
Selectivity for 3VA molded case circuit breakers
16 Configuration Manual, 08/2016, A5E03603181010-01
breaker, both of which are equipped with an electronic trip unit with adjustable LI/LSI
protective function. To make the examples shown below in chapters 3.2 - 3.4 easier to
understand, the tolerances of the tripping characteristics are not shown.
3.2.1 Example
The rated operational currents are as follows in the starting situation described in chapter
3.1:
• S1
• S2.2
• S3.3
Rated operational current I
rated
= 630 A
Rated operational current I
rated
= 250 A
Rated operational current I
rated
= 100 A
Figure 3-2 Fault scenario with overload zone selectivity
The analysis below will focus solely on the selectivity between circuit breaker S2.2 and
circuit breaker S3.3.