Page 61 - 4587

There may be changes in the overload trip characteristic and
increased temperature rise due to the erosion of contact material.

Rated service short-circuit interrupting capacity ICS
ICS values are usually lower than the values for ICU. Circuit
breakers that have been switching-off at the level of the service
short-circuit breaking capacity continue to be serviceable
afterward.
In plants in which interruptions to operations must be kept as
short as possible, product selection should be carried out based on
ICS.

Breaking capacity of fuses
The same applies to fuses as to circuit breakers with respect to
the ICU: at the given rated operational voltage, the rated breaking
capacity must be at least as large as the prospective short-circuit
current at the site of installation.

3 Make a written translation of the following:

Definition of switching capacity
The switching capacity is the r.m.s value of a current at a given
power factor cos φ as well as a given rated voltage at which a
switchgear or a fuse can still shut-off under specified conditions in
an operationally safe way.
Both the short-circuit making capacity as well as the short-
circuit breaking capacity of circuit breakers must be larger than or
equal to the prospective short-circuit current at the place of
installation.
If this is not the case, then a suitable backup protection (for
example a fuse) should be provided to ensure the required
switching capacity of the device combination. Data regarding
devices for backup protection are given in the technical
documentation.

4 Make the following phrases complete.
1. Both the short-circuit making capacity as well as the short-
circuit breaking capacity of circuit breakers must be … .
2. Data regarding devices for backup protection are given in
… .

60