Application planning
5.6 Use in motor protection
3VL IEC molded case circuit breakers
System Manual, 11/2013, 110 0110 - 02 DS 03
65
This version enables the parameters and the trip class 5 to class 30 to be configured step by
step using a menu on the LCD display that is built into the trip unit.
Trip class 5 is used for motors that have very simple start-up characteristics (those with a
short start-up time and a small mass moment of inertia). The class 30 releases are used to
protect motors that have to withstand difficult start-up characteristics (long start-up time and
large mass moment of inertia). The motor must be suitable for heavy-duty starting.
The trip class must be selected so that it corresponds to the overload factor of the motor
under operating conditions. You can find further information at the end of this chapter in the
figure "Current-time curve before and after overload, with thermal image".
Definition of the trip class
The trip class specifies the release time for balanced 3-pole loads, starting from the cold
state, with 7.2 times the set current I
r
according to IEC 60947-4-1. Combinations with class
10 are normally used.
Applications that require a longer start-up time, such as fans with large blade diameters,
require a higher trip class.
Figure 5-3 ETU with trip classes 5, 10, 15, 20, 30
Tripping characteristic curve for molded case circuit breakers with electronic trip unit.
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