Glossary
3VA molded case circuit breakers with IEC certificate
Manual, 03/2019, A5E03603177010-03
663
The rated residual current
I
Δn
is the fault (residual) current for which residual current-
operated circuit breakers are designed. The residual current rating is declared on the rating
plate of the device.
Rated service short-circuit breaking capacity
The rated service short-circuit breaking capacity
I
cs
is the short-circuit current determined by
the operational voltage that a molded case circuit breaker is capable of interrupting
repeatedly (test sequence 0 - C0 - CO, formerly P - 2). After a molded case circuit breaker
has interrupted a short circuit, it can continue to carry the rated operational current despite
increased self-heating and will trip again in the event of a short circuit.
Rated short-circuit breaking capacity
The rated short-circuit breaking capacity
I
cn
of a molded case circuit breaker is the maximum
current that the circuit breaker can safely interrupt at a specific rated operational voltage and
rated frequency. It is specified as an rms value.
With AC molded case circuit breakers, the rated short-circuit breaking capacity must be
independent of the magnitude of the DC component. The rated short-circuit breaking
capacity also ensures that the molded case circuit breaker can interrupt every current up to
the rated short-circuit breaking capacity in the event of a line-frequency recovery voltage with
110% of the rated operational voltage.
This applies:
● To alternating current at every value of the power factor, but not lower than the value
defined in the relevant test specification.
● To direct current (unless otherwise specified by the manufacturer) with every time
constant, but not greater than the value defined in the relevant test specification.
The short-circuit breaking capacity does not apply in the event of a recovery voltage at line
frequency above 110% of the rated operational voltage.
Rated short-circuit making capacity
The rated short-circuit making capacity
I
cm
of a molded case circuit breaker is the maximum
current that the circuit breaker can safely interrupt at a specific rated operational voltage and
rated frequency. Unlike other characteristic data, this is specified as a peak value.
With AC molded case circuit breakers, the rated short-circuit making capacity must be at
least equal to the rated short-circuit breaking capacity multiplied by a factor n.
The rated short-circuit making capacity is calculated to allow the molded case circuit breaker
to conduct the current during closing at a voltage of up to 110% inclusive of the rated
operational voltage.
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