Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 135)

ƒ Signaling of the operational state
ƒ Signaling
of tripping
ƒ Operational
switching
ƒ Remote
control
ƒ Disconnection
ƒ Locking functions by means of a padlock
Depending on design, they can be used not only as short-circuit protection devices but also as
motor protection circuit breakers, load switches, main switches or disconnectors.
With respect to selectivity between short-circuit protective equipment, IEC 60947-2 distin-
guishes between two utilization categories (
Copyright © IEC, Geneva, Switzerland, www.iec.ch ).
- Utilization category A Æ Circuit breakers without tripping delay
IEC-Definition: Circuit-breakers not specifically intended for selectivity under short-circuit
conditions with respect to other short-circuit protective devices in series on the load side, i.e.
without an intentional short-time delay provided for selectivity under short-circuit conditions,
and therefore without a short-time withstand current rating according to 4.3.5.4.
1)
- Utilization category B Æ Circuit breakers with short-time delay
IEC-Definition: Circuit-breakers specifically intended for selectivity under short-circuit condi-
tions with respect to other short-circuit protective devices in series on the load side, i.e. with
an intentional short-time delay (which may be adjustable), provided for selectivity under
short-circuit conditions. Such circuit breakers have a short-time withstand rating according to
4.3.5.4.
1)
1) Rated short-time withstand current (I
CW
): At a.c. this is the r.m.s. value of the a.c.-component
of the prospective short-circuit current during the time of short-time delay.
The large majority of circuit breakers is used at the load-end of circuits and corresponds to
utilization category A.
Circuit breakers with motor protection characteristic also comply with the utilization categories
for switching loads, for example AC-3 under IEC 60947-4-1.
LVSAM-WP001A-EN-P - April 2009 4-27