Description
2.8 Electronic trip unit ETU
3VA27 molded case circuit breakers & 3WL10 air circuit breakers
Manual, 10/2018, L1V30499596002-01
49
2.8.2
Selectivity
Switching devices connected in series, e.g. circuit breakers and fuses, can work together in
a selective or discriminating manner to ensure graded tripping in the event of a fault. The
upstream switching device closest to the fault must trip in the event of a short-circuit. The
other switching devices in the circuit remain closed. This minimizes the effects of a fault in
terms of its duration (selectivity) and the area affected.
Short-circuit location
Selectivity tables for the 3WL10 are available on the Internet for simple implementation of
selective trip combinations (see Selectivity tables
https://support.industry.siemens.com/cs/ww/en/view/109748621
The parameters relevant to selectivity are:
●
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 (3WL10)
–
Current limiter (3VA27)
