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Appendix
Glossary
15/10
Siemens ET B1 · 10/2008
15
Rated breaking capacity
I
en
(
I
er
)
The rated breaking capacity of a miniature circuit breaker is the
value of the short-circuit current that it can switch off at the rated
operational voltage, rated frequency and specified power factor
p.f. (or specified time constant). The value of the prospective
current applies (in the case of alternating current: r.m.s. value of
the AC components) as specified by the manufacturer.
Rated current
I
n
(
I
r
)
The current for which the electrical equipment is rated and to
which specific characteristics refer, e.g. rated power S
n
(
S
r
).
Rated frequency
The rated frequency is the frequency for which the electrical
equipment is designed and to which the device characteristics
refer.
Rated impulse withstand voltage
(
U
imp
)
The peak value of a surge voltage of specified form and polarity
to which, under specified test conditions, the electrical equip-
ment can be subjected without failing and to which the clear-
ance refers.
The rated impulse withstand voltage of an electrical device must
correspond to, or be greater than, the transient overvoltages that
occur in the system in which the electrical equipment is installed.
Rated input voltage U
1
n
(
U
1
r
)
Input voltage (in the case of three-phase currents, the phase-to-
phase voltage) with which a transformer can be excited at the
rated frequency.
Rated insulation voltage U
i
The voltage value, which specifies the insulation resistance of
the electrical equipment and accessories and to which the insu-
lation tests and creepage distances and clearances refer.
On no account must the rated operational voltage exceed the
rated insulation voltage.
Note:
In the case of electrical equipment without specified rated insu-
lation voltage, the highest rated operational voltage should be
taken as the rated insulation voltage.
Rated making capacity
The highest current that a switching device can switch on under
certain conditions.
Rated making capacity
I
em
The rated making capacity of a miniature circuit breaker is the
value of the short-circuit current as specified by the manufactur-
er that it can switch on at the rated operational voltage, rated fre-
quency and specified power factor p.f. (or specified time con-
stant). It is expressed by the maximum peak value of the pro-
spective current.
Rated operational current
I
e
The rated operational current is the current that is determined by
the specified conditions of an electrical equipment. It takes into
account the rated voltage and frequency, the rated duty and the
degree of protection.
Rated operational voltage U
e
The rated operational voltage of a circuit is the voltage value
which, together with the rated current, determines the usability
of the circuit. In the case of multiphase circuits, the voltage be-
tween the outer conductors is specified.
Rated peak withstand current
I
p
(
peak short-circuit current)
The largest permissible instantaneous value (peak value) of the
prospective short-circuit current in the most stressed conduct-
ing path. It characterizes the dynamic short-circuit strength of an
electrical equipment.
Rated residual current
I
n
The value specified by the manufacturer for the RCD for the re-
sidual operating current at which the RCD must switch off under
prescribed conditions.
Rated short-time current
Permissible r.m.s. value of the AC components of the prospec-
tive short-circuit current, which can control the electrical
equipment, e.g. a control room, for a specific length of time,
e.g. from 0.05 s to 1 s (1-s current) (thermal short-circuit
strength). This is specified as an r.m.s. value of the short-circuit
current.
Rated switching capacity
Rated making and rated breaking capacity. The switching ca-
pacity for short-circuit currents is expressed by the prospective
sustained short-circuit current at the installation site of the minia-
ture circuit breaker. In the case of alternating current, the r.m.s.
value of the symmetric components applies.
Rated voltage U
n
(
U
r
)
The voltage of an electrical equipment to which its other charac-
teristics refer. In the case of three-phase circuits, the phase-to-
phase voltage of the system is taken as the rated voltage. For
switchgear assemblies, the manufacturer must specify the volt-
age limits within which the problem-free function of the main and
auxiliary circuits can be guaranteed. These limits must always
be such that, under normal load conditions, the voltage at the
terminals of the control circuits of the installed device stay within
the limit values specified in the standards applicable for the re-
spective equipment.
Reactive power
The power required to create electromagnetic fields, e.g. in
electrical motors and transformers, for AC or three-phase cur-
rents. It is essential for the operation of all inductive loads but, in
contrast to active power, cannot be converted to a useful form of
energy. It is therefore an "unnecessary" load on cables and
plants, particularly the systems of electrical supply companies.
Capacitor control units, reactive-power compensation equip-
ment and capacitors that have to be subsequently installed pro-
vide loads with the necessary capacitive reactive power, thus
compensating electromagnetic fields and relieving the energy
supply.
Release (of a mechanical switching device)
A device connected to a mechanical switching device, which
trips latching if the prescribed variables (e.g. current, voltage)
are exceeded or fallen below, thus enabling the opening or clos-
ing of the switching device.
Response current, ground fault (g)
Ground-fault current, which, when reached or exceeded, acti-
vates and triggers the ground-fault release (g), e.g. a miniature
circuit breaker.
Response current, instantaneous (n)
Current, which, when exceeded causes instantaneous tripping.
Response current, overload (a)
Continuous current, which when exceeded, causes tripping
within a specified time (current-dependent delayed release!)
Response current, short-time delay (z)
Current, which when exceeded causes tripping after a user-de-
finable delay time.
Ring network
In a ring network, several transformers supply a closed cable
ring to which all loads are connected. If the ring is separated at
any point, the loads are supplied from one side as in a radial net-
work. The ring network is a type of energy supply network
(
meshed network).
© Siemens AG 2008