Siemens SENTRON - Page 77

Glossary
Selectivity for 3VA molded case circuit breakers
Configuration Manual, 08/2016, A5E03603181010-01
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Rated operational voltage U
e
Voltage value to which the making capacity, the breaking capacity and the utilization
categories of a circuit breaker are referred.
A circuit breaker can have more than one rated operational voltage.
Rated short-circuit breaking capacity I
cn
A short-circuit current specified by the manufacturer that a circuit breaker can safely interrupt
at the rated operational voltage U
e
, the rated frequency and a defined power factor (or
defined time constant).
The rated short-circuit breaking capacity is applicable to alternating voltages or to a defined
time constant in the case of direct voltages. It is expressed by the prospective current I
p
(or
by the rms value of the AC component) under specified conditions.
Rated short-time withstand current I
cw
Value of the AC component of the prospective short-circuit current which a circuit breaker is
capable of conducting for a specific time period, e.g. from 0.05 s to 1 s (1 s current).
A high rated short-time withstand current is typical of a circuit breaker of utilization
category B.
Rated ultimate short-circuit breaking capacity I
cu
Limit value of rated short-circuit breaking capacity I
cn
.
The rated ultimate short-circuit breaking capacity is the maximum value of the short-circuit
current which the protective device is capable of interrupting in accordance with regulations.
Rated uninterrupted current I
u
The rated uninterrupted current of a device is specified by the manufacturer and refers to the
current that the device can conduct continuously.
Response current, I release
When this current limit is exceeded, the circuit breaker trips instantaneously.
Response current, L release
When this uninterrupted current limit is exceeded within a predefined time period, the circuit
breaker trips (inverse-time delay tripping!).
Response current, S release
When this current limit is exceeded, the circuit breaker trips after a predefined time delay.