Glossary
3VA molded case circuit breakers with IEC certificate
664 Manual, 03/2019, A5E03603177010-03
Permissible rms value of the AC component of the prospective short-circuit current which the
switching device is capable of conducting for a specific time period, e.g. from 0.05 s to 1 s
(thermal short-circuit strength).
Rated short-time withstand current
The rated short-time withstand current
I
cw
is specified as an rms value of the short-circuit
current and characterizes the thermal strength of a circuit of a switchgear assembly under
brief load conditions. The rated short-time withstand current calculation normally refers to a
period of 1 s. The reference time must be specified if it deviates from the above. The rated
short-time withstand current is specified for the distribution and/or main busbars of a
switchgear assembly.
Rated ultimate short-circuit breaking capacity
The rated ultimate short-circuit breaking capacity
I
cu
is the maximum short-circuit current that
a molded case circuit breaker is capable of interrupting (test sequence 0 - C0, formerly P -
1). After the molded case circuit breaker has cleared the short circuit, it is capable of tripping
with increased tolerances under overload conditions.
Limit value of rated ultimate short-circuit breaking capacity
I
cu
.
Rated uninterrupted current
The rated uninterrupted current
I
U
of a switching device, e.g. a molded case circuit breaker,
is a current that the device can conduct in uninterrupted operation (for weeks, months or
years). This current is specified by the manufacturer.
The rating is the power that a switching device is capable of switching at the associated
rated operational voltage in accordance with the utilization category, e.g. power contactor
utilization category AC-3:37 kW at 400 V.
Or AUTO; method of remote operation of the motor operators via control cables, e.g. PLC.
Connection with a negligibly low impedance between two points of different potential in an
electric circuit. The short-circuit current is a multiple of the rated operating current. Short
circuits can cause thermal or mechanical damage to switching devices and other parts of an
electrical installation.
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