Description
2.5 Protection functions
3VA molded case circuit breakers with UL and IEC certification
66 Manual, 01/2019, L1V30435333-01
To design a low-voltage switchboard installation in accordance with the valid rules, the
system planner needs to select the protection settings of the molded case circuit breakers.
The settings selected for the trip unit of a molded case circuit breaker depend on the type of
equipment to be protected, e.g. switchboard and applications.
Tripping characteristics are represented graphically. In order to ease the coordination of
different protection devices, the current is sometimes specified as a multiple of the current
setting value and the time is specified in seconds.
Tripping characteristics for thermal-magnetic trip units
The graph is drawn in the log-log coordinate system.
Tripping characteristics for electronic trip units
The graph is drawn in the log-log coordinate system.
②
③
④
⑤
Response threshold of the instantaneous
protection
Response threshold of the long-time delayed
protection
Delay of the long-time-delayed protection
Response threshold of the short-time delayed
protection
Fixed tripping time or I
2
t function of the
short-time-delayed protection
Delay of the short-time delayed protection
L Overload range
S Short-time delayed short-circuit current
range
I Instantaneous short-circuit current range
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