Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 42)

- Coordination type 1 permits damage to the starter so that further operation may only be
possible after repair or replacement.
- With coordination type 2 the contactor or starter must be suitable for further use after the
short-circuit. Slight welding of contacts is acceptable. An early replacement of the starter
components is usually required (depending on the severity of the short-circuit) due to the
erosion of contact material by the short-circuit current, however this can be carried out at an
operationally convenient time.
- Coordination type “CPS” requires in accordance with IEC 60947-6-2 that a load feeder
continues to be usable after a short-circuit, in order to maximize operational continuity. The
guaranteed residual electrical life span based on a new device is 6000 cycles. In this case
too, the replacement of the starter components as in coordination type 2 is required and
may be carried out at a time that is convenient from an operational viewpoint. Load feeders
under coordination type “CPS” can be realized in any design (see also
Fig. 2.3-4 ).
Type “1” Type “2” Type “CPS”
Finding and rectifying cause of short-circuit X X X
Checking starter X X
Replacing devices X 1) 1)
Separating welded contacts, if any X
Resume operation X X X
Planned maintenance (device replacement) X X
Tab. 2.3-5
The selection of the coordination type with respect to duration of the interruption to operation
1)
Replacement of fuses, if used
2.3.4.6 Short-circuit 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 documen-
tation.
2.3.4.6.1 Rated short-circuit making capacity I
cm
The rated short-circuit making capacity I
cm
is a quantity that according to regulations must be in
a certain ratio to the rated ultimate short-circuit breaking capacity I
cu
and that has to be guaran-
teed by the device manufacturer. This is not a variable that must be considered by the user,
however it ensures that a circuit breaker is in the position to connect onto a short-circuit – and to
disconnect it subsequently.
2.3.4.6.2 Rated short-circuit breaking capacity I
cu
and I
cs
IEC 60947-2 makes distinction between the rated ultimate short-circuit breaking capacity I
CU
and the rated service short-circuit breaking capacity I
CS
:
- Rated ultimate short-circuit breaking capacity I
CU
:
I
CU
is the maximum breaking capacity of a circuit breaker at an associated rated operational
voltage and under specified conditions. I
CU
is expressed in kA and must be at least as large
as the prospective short-circuit current at the site of installation.
Circuit breakers that have switched-off at the level of the ultimate short-circuit breaking ca-
pacity, are reduced serviceable afterwards and should at least be checked regarding func-
tionality. There may be changes in the overload trip characteristic and increased temperature
rise due to the erosion of contact material.
LVSAM-WP001A-EN-P - April 2009 2-14