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Glossary
Breaking capacity
The breaking capacity is the rms value of the current at a specific cos φ (power factor) and a
specific voltage that can be safely interrupted by a switching device or fuse under prescribed
conditions. The rms value of the symmetrical component applies in the case of alternating
current.
I2t characteristic
The I
relation to breaking times as a function of the prospective current under defined operating
conditions.
I2t value
The I
through current).
Let-through current
The let-through current ID is the maximum instantaneous current value during the breaking
time of a switching device or fuse. Limited short-circuit currents occur if the switching device
reduces the amplitude of the short-circuit current due to, for example, resistance, switching
delay or peak arc voltage. The let-through current of a device such as a current-limiting fuse
or a current-limiting molded case circuit breaker determines the thermal load (I
imposed on equipment connected downstream of the device (current limiting).
Making capacity
The making capacity is the value of the prospective making current that the switching device
can safely conduct at the instant of closing under prescribed conditions for a specific circuit.
For load break switches, the making capacity is expressed as the maximum possible
instantaneous value of the potential prospective current at the input terminals for the
specified voltage.
Rated breaking capacity
The rated breaking capacity is the maximum current that can be interrupted by a switching
device under certain conditions.
Rated frequency
Rated frequency of a switching device and reference value for other characteristics of the
device.
3KF switch disconnectors with fuses
Manual, 09/2019, L1V30580914002A-01
t characteristic is a curve that represents the minimum or maximum values of I
2
t value is the thermal value of a prospective or a limited short-circuit current (let-
2
t in
2
t value)
2
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