SIST EN 50123-1:2003

SLOVENSKI STANDARD
01-maj-2003
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SIST EN 50123-1:1998
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Railway applications - Fixed installations - D.C. switchgear -- Part 1: General
Bahnanwendungen - Ortsfeste Anlagen - Gleichstrom-Schalteinrichtungen -- Teil 1:
Allgemeines
Applications ferroviaires - Installations fixes - Appareillage à courant continu -- Partie 1:
Généralités
Ta slovenski standard je istoveten z: EN 50123-1:2003
ICS:
29.130.99 Druge stikalne in krmilne Other switchgear and
naprave controlgear
29.280 (OHNWULþQDYOHþQDRSUHPD Electric traction equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN 50123-1
NORME EUROPÉENNE
EUROPÄISCHE NORM February 2003

ICS 29.120.60; 45.020 Supersedes EN 50123-1:1995

English version
Railway applications –
Fixed installations – D.C. switchgear
Part 1: General
Applications ferroviaires –  Bahnanwendungen –
Installations fixes – Ortsfeste Anlagen –
Appareillage à courant continu Gleichstrom-Schalteinrichtungen
Partie 1: Généralités Teil 1: Allgemeines

This European Standard was approved by CENELEC on 2002-09-01. CENELEC members are bound to
comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and
notified to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic,
Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta,
Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2003 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 50123-1:2003 E
Foreword
This European Standard was prepared by SC 9XC, Electric supply and earthing systems for public
transport equipment and ancillary apparatus (fixed installations), of the Technical Committee CENELEC
TC 9X, Electrical and electronic applications for railways.
The text of the draft was submitted to the formal vote and was approved by CENELEC as EN 50123-1 on
2002-09-01.
This European Standard supersedes EN 50123-1:1995. It has been prepared taking into account
IEC document 9/578/FDIS (61992-1) in order to align technically as much as possible this EN 50123-1
and IEC 61992-1. These documents are to be considered as technically equivalent except for those
references and peculiarities which are due to the European standardisation in the railway application field.
The following dates were fixed:
- latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2003-09-01

- latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2005-09-01

Annexes designated “normative” are part of the body of the standard.
Annexes designated “informative” are given for information only.
In this standard, Annexes A, B and C are normative and Annexes D and E are informative.
_____________
– 3 – EN 50123-1:2003
Contents
1 Scope.4
2 Normative references .4
3 Definitions .6
3.1 General terms.6
3.2 Performance characteristics.9
3.3 Components .13
3.4 Terms relating to d.c. circuit breakers, switch-disconnectors and associated relays .17
4 Service conditions and requirements.22
4.1 Environmental conditions .22
4.2 Insulation levels .22
5 Standard features and conventional assumptions.24
5.1 Standard features and conventional parameters for the main circuit .24
5.2 Standard features for auxiliary and control circuits.26
6 Temperature-rise limits.26
7 Tests .27
7.1 General .27
7.2 Test tolerances .28
7.3 Tests on movable devices.28
7.4 Temperature-rise test .30
7.5 Dielectric tests .32
7.6 Short circuit and load switching conditions .32
7.7 Verification of the behaviour during short-time withstand current test.34
7.8 Verification of the manual control device for sturdiness and position indicator
reliability.34
Annex A (normative) Diagrams for tests.36
Annex B (normative)  Environmental conditions for indoor installations .38
Annex C (normative) Search of critical currents for d.c. circuit breakers and switches.40
Annex D (informative) Recommended creepage distances .42
Annex E (informative) Determination of maximum energy fault location .43
Bibliography.46
Figure A.1 - Diagram of the test circuit for checking the making and breaking capacities
in short-circuit and load/overload switching conditions .37
Figure A.2 - Typical calibrations and interruption under short-circuit and load/overload
switching conditions .38
Figure E.1 - Equivalent circuit of a d.c. traction system .46
Figure E.2 - Ratio of I /I to T /T .46
maxE ss s c
Table 1 - Insulation levels.24
Table 2 - Test circuit parameters for maximum circuit energy .25
Table 3 - Preferred voltages for auxiliary and control circuits [V] .27
Table 4 - Temperature-rise limits for insulated coils.27
Table 5 - Temperature-rise limits for various components.28
Table 6 - Test tolerances.29
Table 7 - Recommended quantities and dimensions of copper bars .32
Table 8 - Values of forces or torques for the tests.36
Table B.1 - Limits of sinusoidal vibrations.40
Table D.1 - Material group identification .43
Table D.2 - Recommended creepage distances, in mm/kV (base U ).43
Nm
1 Scope
The EN 50123 series specifies requirements for d.c. switchgear and controlgear and is intended to be
used in fixed electrical installations with nominal voltage not exceeding 3 000 V d.c., which supply
electrical power to vehicles for public guided transport, i.e. railway vehicles, tramway vehicles,
underground vehicles and trolley-buses.
Part 1 specifies general requirements.
The other parts are covering
Part 2 D.C. circuit breakers,
Part 3 Indoor d.c. disconnectors, switch-disconnectors and earthing switches,
Part 4 Outdoor d.c. disconnectors, switch-disconnectors and earthing switches,
Part 5 Surge arresters and low voltage limiters for specific use in d.c. systems,
Part 6 D.C. switchgear assemblies,
Part 7-1 Measurement, control and protection devices for specific use in d.c. traction systems –
Application guide,
Part 7-2 Measurement, control and protection devices for specific use in d.c. traction systems –
Isolating current transducers and other current measuring devices,
Part 7-3 Measurement, control and protection devices for specific use in d.c. traction systems –
Isolating voltage transducers and other voltage measuring devices
2 Normative references
This European Standard series incorporates by dated or undated references, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of
these publications apply to this European Standard series only when incorporated in it by amendment or
revision. For undated references the latest edition of the publication referred to applies (including
amendments).
EN 50119 2001 Railway applications – Fixed installations – Electric traction overhead contact
lines
EN 50121 Series Railway applications – Electromagnetic compatibility
EN 50122-1 1997 Railway applications – Fixed installations – Part 1: Protective provisions relating
to electrical safety and earthing
EN 50124-1 2001 Railway applications – Insulation coordination – Part 1: Basic requirements –
Clearances and creepage distances for electrical and electronic equipment
EN 50125-2 2002 Railway applications – Environmental conditions for equipment – Part 2: Fixed
electrical installations
EN 50126 1999 Railway applications – The specification and demonstration of Reliability,
Availability, Maintainability and Safety (RAMS)
EN 50163 1995 Railway applications – Supply voltage of traction systems (IEC 60850:2000)
EN 60099-1 1994 Surge arresters – Part 1: Non-linear resistor type gapped surge arresters for a.c.
systems (IEC 60099-1:1991)
– 5 – EN 50123-1:2003
EN 60099-4 1993 Surge arresters – Part 4: Metal-oxide surge arresters without gaps for a.c.
systems (IEC 60099-4:1991)
EN 60129 1994 Alternating current disconnectors and earthing switches
+ A1 1994 (IEC 60129:1984 + A1:1992 + A2:1996)
+ A2 1996
EN 60243-1 1998 Electrical strength of insulating materials – Test methods – Part 1: Tests at
power frequencies (IEC 60243-1:1998)
EN 60269 series Low-voltage fuses (IEC 60269 series)
EN 60298 1996 AC metal-enclosed switchgear and controlgear for rated voltages above 1 kV
and up to and including 52 kV (IEC 60298:1990 + corr. April 1995 + A1:1994)
EN 60507 1993 Artificial pollution tests on high-voltage insulators to be used on a.c. systems
(IEC 60507:1991)
EN 60529 1991 Degrees of protection provided by enclosures (IP Code) (IEC 60529:1989)
EN 60694 1996 Common specifcations for high-voltage switchgear and controlgear standards
(IEC 60694:1996)
EN 60721 series Classification of environmental conditions (IEC 60721 series)
EN 60947-1 1999 Low-voltage switchgear and controlgear – Part 1: General rules
(IEC 60947-1:1999, mod.)
EN 60947-2 1996 Low-voltage switchgear and controlgear – Part 2: Circuit breakers
+ A1 1997 (IEC 60947-2:1995 + A1:1997)
HD 214 S2 1980 Method for determining the comparative and the proof tracking indices of solid
insulating materials under moist conditions (IEC 60112:1979)
HD 380 S2 1987 Test methods for evaluating resistance to tracking and erosion of electrical
insulating materials used under severe ambient conditions (IEC 60587:1984)
HD 588.1 S1 1991 High-voltage test techniques – Part 1: General definitions and test requirements
(IEC 60060-1:1989 + corr. March 1990)
IEC 60050-441 1984 International Electrotechnical Vocabulary (IEV) – Chapter 441: Switchgear,
controlgear and fuses
IEC 60050-446 1983 International Electrotechnical Vocabulary (IEV) – Chapter 446: Electrical relays
IEC 60050-605 1983 International Electrotechnical Vocabulary (IEV) – Chapter 605: Generation,
transmission and distribution of electricity – Substations
IEC 60050-811 1991 International Electrotechnical Vocabulary (IEV) – Chapter 811: Electric traction
IEC 60466 1987 A.C. insulation-enclosed switchgear and controlgear for rated voltages above
1 kV and up to and including 38 kV
IEC 61245 1993 Artificial pollution tests on high voltage insulators to be used in d.c. systems

3 Definitions
For the purpose of this European Standard series, the definitions given in IEC 60050-441, IEC 60050-446,
IEC 60050-605, IEC 60050-811, EN 50124-1, EN 60099-1, EN 60099-4, EN 60298 and EN 60947 apply
together with the following:
3.1 General terms
3.1.1
switchgear
general term covering switching devices and their combination with associated control, measuring,
protective and regulating equipment; it covers also assemblies of such devices and equipment with
associated interconnections, accessories, enclosures and supporting structures
NOTE For the sake of simplicity in this standard the term “switchgear” means “switchgear and controlgear”.
3.1.1.1
d.c. switchgear and controlgear assembly
combination of one or more d.c. switching devices together with associated control, measuring, signalling,
protective, regulating equipment, etc., completely assembled under the responsibility of the supplier, with
all the internal electrical and mechanical interconnections and structural parts
NOTE 1 Throughout the Standard, the abbreviation switchgear assembly is used for a d.c. switchgear and controlgear assembly.
NOTE 2 The components of the switchgear assembly may be electromechanical or electronic.
NOTE 3 An enclosure, but not an integral enclosure, when housing a switching device and some associated controlgear, may be
considered as a switchgear assembly.
3.1.2
switching device
device designed to make or break the current in one or more electric circuits
[IEV 441-14-01]
3.1.3
d.c. circuit breaker
switching device capable of making, carrying and breaking direct currents under normal circuit conditions
and also making, carrying (up to a specified limit and for a specified time) and breaking currents under
specified abnormal conditions, such as those of short-circuit
3.1.4
d.c. disconnector
mechanical switching device, which provides, in the open position, for safety reasons, an isolating
distance in accordance with specified requirements
NOTE 1 The disconnector is capable of opening and closing a circuit when either negligible d.c. current is broken or made, or
when no significant change in the voltage across the terminals of the disconnector occurs. It is also capable of carrying d.c.
currents under normal circuit conditions and carrying, for a specified time, currents under abnormal conditions such as those of
short-circuit.
NOTE 2 A disconnector is not suitable for making or breaking load current, fault current or other current arising from the effects of
lightning or transient phenomena.
NOTE 3 A disconnector is only able to make or break current of very limited magnitude such as those arising from electrostatic
charging or discharges across undamaged insulation. The ability to make or break minimum currents due to eventual marginal
transient conditions of the network is subject to agreement between purchaser and supplier.

– 7 – EN 50123-1:2003
3.1.5
switch-disconnector
mechanical switching device capable of making, carrying and breaking currents in normal circuit
conditions and, when specified, in given operating overload conditions. In addition, it is able to carry, for a
specified time, currents under specified abnormal circuit conditions, such as short-circuit conditions.
Moreover, it complies with the requirements for a disconnector (see 3.1.4)

When specified, a switch-disconnector may be designed for making short-circuit currents, but not for
breaking the same.
NOTE Outdoor switch-disconnectors, in given special conditions, may be required to be suitable for breaking overload currents of
specified amplitude.
3.1.6
earthing switch
mechanical switching device for earthing parts of the circuit, capable of withstanding for a specified time,
currents under abnormal conditions such as those of short-circuit, but not required to carry currents under
normal conditions of the circuit
NOTE An earthing switch may have a short-circuit making capacity (see 3.2.23).
[IEV 441-14-11]
3.1.7
low-voltage limiter
device intended to be in parallel in those parts of a traction system where overvoltages are expected
having the function of limiting the voltage to predetermined values
3.1.8
d.c. sensor
device used for detecting a current or a voltage in d.c. main circuit, which produces an output signal,
proportional to and linear (over a range) with the primary input, for connection to a secondary device
which acts on the signal
3.1.9
d.c. shunt
device connected in the primary circuit, usually composed of metal grids, that provides a millivolt output
proportional to the current following in the primary circuit
3.1.10
isolating transducer
device which is interposed between the output of a sensor in the main circuit and the input of a secondary
device used for measurement or protection, and used to provide an output isolated from the main circuit
and, usually, at lower voltage
3.1.11
hall effect sensor
type of sensor which fits around the main circuit current carrying conductor and uses a single or multiple
Hall effect cells situated in the magnetic field of an iron circuit and which is energised by the current in the
main conductor
3.1.12
divider
bank of resistors connected across the main supply with a footing resistor used as the output, which gives
a voltage proportional to the main supply. This output is connected either directly or indirectly through an
isolation transducer to the voltage terminals of the secondary device

3.1.13
operation
motion of the moving contact(s) from one position to another position, for example open to close or open
to earth
NOTE 1 This may be a closing operation or an opening operation.
NOTE 2 If a distinction is necessary, the terms "electrical operation" (for example make and break) and "mechanical operation"
(for example closing and opening) should be used.
NOTE 3 The position of a switching device where the continuity of the main circuit is assured is indicated as "close" position.
NOTE 4 The position of a switching device where the prescribed distance between the contacts of the switching device is assured
is indicated as "open" position.
3.1.14
operating cycle (of a mechanical switching device)
succession of operations from one position to another and back to the first position through all other
positions, if any [IEV 441-16-02]
3.1.15
dependent manual operation (of a mechanical switching device)
operation solely by means of directly applied manual energy, such that the speed and force of the
operation are dependent upon the action of the operator [IEV 441-16-13]
3.1.16
stored energy operation (of a mechanical switching device)
operation by means of energy stored in the device itself prior to the completion of the operation and
sufficient to complete it under predetermined conditions
NOTE This kind of operation may be subdivided according to
a) the energy storage mode (spring, weight, etc.);
b) the origin of energy (manual, electric, etc.);
c) the energy releasing mode (manual, electric, etc.).
[IEV 441-16-15]
3.1.17
independent manual operation (of a mechanical switching device)
stored-energy operation where the energy originates from manual power, stored and released in one
continuous operation, in such a way that the speed and force of the operation are independent from the
action of the operator [IEV 441-16-16]
3.1.18
independent power operation
operation by means of energy where the energy originates from an external power source and is released
in a single continuous operation, in such a way that the speed and force of the operation are independent
from the action of the operator
3.1.19
switching device with interlock preventing opening and/or closing operations
switching device in which an operation (closing and/or opening) is prevented by interlocking means
reflecting given system conditions
3.1.20
utilisation category (of a switching device)
combination of specified requirements related to the condition in which the switching device fulfils its
purpose, selected to represent a characteristic group of practical applications [IEV 441-17-19]
NOTE The specified requirements may concern, for example the values of the making capacities, if applicable, breaking
capacities and other characteristics, the associated circuits and the relevant conditions of use and behaviour. The term "duty" used
elsewhere in the standard corresponds to a particular aspect of the utilisation category.

– 9 – EN 50123-1:2003
3.1.21
unidirectional switching device
switching device (for example a circuit breaker), the purpose of which is to interrupt d.c. current which is
flowing in a prescribed direction through that device, and which is identified accordingly
3.1.22
bidirectional switching device
switching device (for example a circuit breaker), the purpose of which is to interrupt d.c. current which
flows in either direction through that device, and which is identified accordingly
NOTE Proof of bidirectional ability is included in the interrupting type tests.
3.2 Performance characteristics
3.2.1 Voltages
3.2.1.1
nominal voltage (U )
n
voltage by which an installation or part of an installation is designated
3.2.1.2 Limits of system voltages
3.2.1.2.1
highest system voltage (U )
max
highest value given for the voltage in the continuous operating conditions U specified in EN 50163
max1
3.2.1.2.2
lowest system voltage (U )
min
lowest value given for the voltage in the continuous operating conditions U specified in EN 50163
min1
3.2.2
rated insulation voltage (U )
Nm
maximum value of the d.c. voltage for which the equipment is designed in respect to its insulation
3.2.3
rated voltage (U )
Ne
voltage value, given by the manufacturer, which, combined with rated service current, determines the
utilisation of the equipment and to which the corresponding tests and utilisation categories, if any, relate
NOTE The rated voltage may differ from the nominal voltage by a quantity within permitted tolerances.
3.2.3.1
rated auxiliary and control supply voltage
voltage measured at the circuit terminals of the apparatus during its operation, including, if necessary, the
auxiliary resistors or accessories supplied or required by the manufacturer to be installed in series with it,
but not including the conductors to the electrical supply
3.2.3.2
rated voltage of a gapped arrester (U )
r
maximum d.c. voltage value between terminals at which the surge arrester is designated to withstand
continuously
3.2.3.3
rated voltage of a gapless arrester (U )
r
the maximum d.c. voltage value between terminals at which the surge arrester is designated to operate
correctly under temporary overvoltage conditions as established in the operating duty tests (see 4.7.5 of
EN 50123-5). The rated voltage is used as a reference parameter for the specification of the operating
characteristics
3.2.3.4
rated voltage of a low-voltage limiter (U )
r
the maximum d.c. voltage value between terminals which the low-voltage limiter is designed to withstand
continuously
3.2.3.5
maximum continuous operating voltage of a gapless arrester (U )
c
voltage which corresponds to U defined in 3.2.1.2.1
max
3.2.3.6
protective voltage level of a gapped arrester (U )
p
crest value, declared by the supplier, higher than the maximum of the three voltage values between the
surge arrester terminals: residual voltage at I , maximum standard lightning impulse sparkover voltage,
n
maximum front of wave impulse sparkover voltage, the latter divided by 1,15
3.2.3.7
protective voltage level for gapless arrester (U )
p
impulse protection level of the arrester covering the maximum residual voltage for the nominal discharge
current I
n
3.2.3.8
maximum withstand voltage of a low-voltage limiter (U )
w
maximum peak voltage value between terminals at which the current in the voltage limiter is zero or
limited to specified values (leakage current)
3.2.3.9
maximum sparkover voltage of a low-voltage limiter (U )
s
maximum voltage value between terminals at which a gapped voltage limiter is designated to make a
connection between terminals such as to limit the difference of potential between the same to a safe value
3.2.3.10
rated supply voltage in a switchgear
voltage measured at the circuit terminals of the apparatus itself during its operation, including, if
necessary, the auxiliary resistors or accessories supplied or required by the manufacturer to be installed
in series with it, but not including the conductors from the connection to the electrical supply
3.2.4
rated impulse withstand voltage (U )
Ni
the peak value of an impulse voltage of prescribed form and polarity which the equipment is capable of
withstanding to, without failure, under the specified test conditions
3.2.5
power-frequency voltage withstand level (dry and wet) (U )
a
power-frequency test voltage level which, when withstood by the equipment, proves the integrity of its
insulation in operating conditions
3.2.6
Transient voltages
3.2.6.1
recovery voltage
voltage which appears across the terminals of a switching device after the breaking of the current
[IEV 441-17-25]
3.2.6.2
maximum arc voltage (Û )
arc
maximum voltage appearing across the switching device during arcing

– 11 – EN 50123-1:2003
3.2.7
prospective current
current that would flow in the circuit if the device was replaced by a conductor of negligible impedance
[IEV 441-17-01]
NOTE The prospective current may be qualified in the same way as a real current: prospective broken current, peak value of the
prospective current, etc.
3.2.8
conventional free-air thermal current (I )
th
current which may be used for the temperature-rise test of an equipment in free-air (see notes 1 and 2).
This value is equal to or greater than the maximum value of the rated service current I of the equipment
Ne
NOTE 1 Free-air is the indoor air existing in normal conditions, reasonably free from dust and external radiations.
NOTE 2 A free-air device is a device supplied by the manufacturer without an enclosure (see 3.3.16) or a device supplied by the
manufacturer with an integral enclosure (see 3.3.17).
3.2.9
conventional enclosed thermal current (I )
the
current stated by the manufacturer which may be used for the temperature-rise tests of the equipment
when mounted in a specified enclosure
This value is equal to or greater than the maximum value of the rated service current I of the enclosed
Ne
equipment
3.2.10
rated service current (I )
Ne
value of current stated by the manufacturer taking into account the rated voltage (see 3.2.3), the
continuous duty and the utilisation category (see 3.1.20) and the protective enclosure type, if any
NOTE 1 Any current, exceeding I is an overload condition.
Ne
NOTE 2 If a load cycle is specified by the purchaser, it should define the steady-state currents before and after the load cycle. If
the temperature-rises resulting from the load cycle exceed the temperature-rise limits, then a higher rated service current needs to
be used.
3.2.10.1
nominal discharge current of a gapped arrester (I )
n
peak value of discharge current, having an 8/20 waveshape, which is used to classify an arrester. It is also
the discharge current which is used to initiate follow-through current in the operating duty test
3.2.10.2
nominal discharge current of a gapless arrester (I )
n
peak value of lightning current impulse (see EN 60099-4) which is used to classify an arrester
3.2.10.3
long term withstand current of a low-voltage limiter (I )
w
current that a low-voltage limiter is able to withstand for 1 800 s in specified conditions
3.2.10.4
leakage current of a low-voltage limiter
current which flows between terminals of a low-voltage limiter when U is applied under nominal service

conditions
3.2.11
rated short-time withstand current (I )
Ncw
current that a circuit or a switching device in the closed position can carry, during a specified short time
under prescribed conditions of use and behaviour

3.2.11.1
rated earth fault current (of a switchgear assembly) (I )
Ncwe
maximum short-time withstand current which can be carried in the earthing circuit
3.2.12
short-circuit current (I )
ss
prospective sustained current resulting from a short circuit due to a fault or an incorrect connection in an
electric circuit
3.2.12.1
rated short-circuit current (I )
Nss
maximum value of the prospective sustained short-circuit current that the device will carry
3.2.13
peak of the short-circuit current (Î )
ss
peak prospective value of the short-circuit current under transient conditions
3.2.14
cut-off current
maximum instantaneous value of current attained during the breaking operation of a switching device
[IEV 441-17-12]
3.2.15
circuit time constant (t )
c
value of the ratio of inductance over resistance of the circuit
3.2.16 Time constants of the d.c. traction system
3.2.16.1
track time constant (of a line) (T )
c
time constant of the track itself plus all parts on the load side of a switching device, including the contact
line (overhead contact line or third rail), the return circuit and any low-frequency or high-frequency
impedance bonds
3.2.16.2
rated track time constant (of a switching device) (T )
Nc
conventional value assigned to a switching device describing the capability of the device to break inductive
short circuit currents under specified conditions
3.2.16.3
source time constant (T )
s
time constant of the d.c. source on the incoming supply side of a switching device, including the a.c.
supply network, the rectifier conversion equipment, smoothing reactors, the d.c. connections in the
substation and the feeder and return connections between substation and track
3.2.17
breaking current
current of a switching device at the instant of initiation of the contact separation during a breaking process
3.2.18
breaking capacity
value of the prospective breaking current that a switching device is capable of breaking at a stated voltage
and under prescribed conditions of use and behaviour [IEV 441-17-08]

– 13 – EN 50123-1:2003
3.2.19
rated short-circuit breaking capacity
breaking capacity for which prescribed conditions include a short circuit at the load terminals of the
switching device
3.2.20
critical current (I )
c
value of breaking current, less than rated short circuit breaking current, at which the arcing time is a
maximum and is significantly longer than at the rated short circuit breaking current
NOTE It can be a current or a range of currents which produce this effect. See Annex C.
3.2.21
maximum circuit-energy short-circuit (I )
max E
short circuit having the maximum possible value of circuit energy, which normally occurs at a short
distance along the track from the substation
3.2.22
making capacity
value of the prospective making current that a switching device is capable of making at a stated voltage,
under prescribed conditions of use and behaviour [IEV 441-17-09]
3.2.23
rated short-circuit making capacity
making capacity for which the prescribed conditions include a short circuit at the load side terminals of the
switching device
3.2.24
distant fault short-circuit
short circuit at a position remote from the switching device interrupting the fault
3.2.25
disruptive discharge
phenomenon associated with the failure of insulation, under electrical stress, in which the discharge
completely bridges the insulation under test, reducing the voltage between the electrodes to zero or nearly
to zero
NOTE 1 The term applies to discharges in solid, liquid and gaseous dielectrics and to combination of these.
NOTE 2 A disruptive discharge in a solid dielectric produces permanent loss of dielectric strength (non-self restoring insulation).
NOTE 3 The term “sparkover” is used when a discharge occurs in a gaseous or liquid dielectric.
NOTE 4 The term “flashover” is used when a disruptive discharge occurs over the surface of a solid dielectric in gaseous or liquid
medium.
NOTE 5 The term “puncture” is used when a disruptive discharge occurs through a solid dielectric.
3.2.26
ambient air temperature (of a switchgear)
temperature, determined under prescribed conditions, of the air surrounding the enclosure or switchgear
3.3 Components
3.3.1
component
essential part of the switchgear which serves a specific function (for example, circuit-breaker,
disconnector, switch, fuse, shunt, voltage and current transducers, bushing, busbar, etc)

3.3.2
conductive part
part capable of conducting current, although it may not necessarily be used for carrying service current
[IEV 441-11-09]
3.3.3
exposed conductive part
conductive part which can be readily touched and which is not normally live, but which may become live
under fault conditions [IEV 441-11-10]
NOTE 1 A conductive part of electrical equipment which can only become live under fault conditions through an exposed
conductive part is not considered to be an exposed conductive part.
NOTE 2 Typical exposed conductive parts are enclosure walls, etc.
3.3.4
live part
conductor or conductive part intended to be energised in normal use, including, if applicable, the return
conductor
NOTE The return circuit of the switchgear may be considered as either a live or an earthed part. The rated insulation voltage of
the return circuit is stated by the purchaser.
3.3.5
clearance
distance between two conductive parts along a string stretched along the shortest distance between these
conductive parts
3.3.6
clearance to earth
distance between any conductive part and any part earthed or intended to be earthed
3.3.7
clearance between open contacts
distance between the contacts, or any conductive part connected to the contacts, of a mechanical
switching device in the open position
3.3.7.1
isolating distance
clearance between open contacts satisfying the safety requirements specified for switching devices
3.3.8
creepage distance
shortest distance along the surface of the insulating material between two conductive parts
NOTE A seal between two portions of insulating material is considered to be a part of the surface.
3.3.9 Circuits at main supply voltage
3.3.9.1
main circuit (of a switching device)
all conductive parts of a switching device included in the circuit which is designed to close and open
3.3.9.2
main circuit (of a switchgear assembly)
all conductive parts of a switchgear assembly which are at the main supply voltage, carrying power
current, but excluding the busbars

– 15 – EN 50123-1:2003
3.3.9.3
busbars (of a switchgear assembly)
conductive parts of a switchgear assembly, at the main supply voltage, which are intended to distribute
power current to one or more functional units
3.3.10 Main circuit contacts
3.3.10.1
main contact (of a mechanical switching device)
contact included in the main circuit of a mechanical switching device, intended to carry, in the close
position, the current of the main circuit
3.3.10.2
arcing contact
contact on which the arc (if any) is intended to be established
NOTE An arcing contact may serve as a main contact: it may be a separate contact so designed that it opens after, and closes
before, another contact which it is intended to protect from damage.
3.3.11
control circuit (of a switching device)
conductive parts of a switching device, other than those parts forming the main circuit, forming a circuit
used to control and actuate the making and breaking operations of the switching device
3.3.12
auxiliary circuit (of a switching device)
conductive parts of a switching device forming a circuit differing from the main circuit and the control
circuit
3.3.13
auxiliary circuit (of a switchgear assembly)
all conductive parts of switchgear included in a circuit (other than the main circuit) intended to control,
measure, signal and regulate
NOTE The auxiliary circuits of a switchgear include the control and auxiliary circuits of the switching devices.
3.3.14
transport unit
part of a switchgear suitable for shipment without being dismantled
3.3.15
functional unit
part of a switchgear comprising all the components of the main circuits and auxiliary circuits that
contribute to the fulfilment of a single function
NOTE Functional units may be distinguished according to the function for which they are intended, e.g.: incoming unit, outgoing
unit, etc.
3.3.16
enclosure
part providing a specified degree of protection of the equipment against certain external influences
specified and a specified degree of protection against approach to or contact with live parts and against
contact with moving parts
3.3.17
integral enclosure
enclosure which forms an integral part of the equipment

3.3.18
compartment
part of switchgear enclosed except for openings necessary for interconnections, control and/or ventilation
NOTE 1 A compartment may be designated by the main component contained therein, for example, circuit-breaker compartment,
a busbar compartment, etc.
NOTE 2 Openings necessary for interconnections between compartments are closed with bushings or other equivalent means.
NOTE 3 Busbar compartments may extend through several functional units without the need for bushings or other equivalent
means.
3.3.19
partition
part of switchgear separating one compartment from other compartments
3.3.20
shutter
part of switchgear that can be moved from a position where it is a part of the enclosure or partition
shielding the live parts to a position where it permits contacts of a removable part to engage live parts
3.3.21
bushing
structure carrying one or more conductors through an enclosure and insulating it therefrom, including the
means of attachment
3.3.22
removable part
part of switchgear that may be removed entirely from the metal-enclosed switchgear and replaced, even
when the main circuit is alive
3.3.23
withdrawable part
removable part of a switchgear that can be moved to positions in which an isolating distance (see Table 1)
or segregation between open contacts is established, while the part remains mechanically attached to the
enclosure
3.3.24
service position (connected position) of a removable part
position of a removable part in which it is fully connected for its intended function
3.3.25
test position (of a withdrawable part)
position of a withdrawable part in which an isolating distance or segregation is established in the main
circuit and in which the control circuits are connected
3.3.26
disconnected position (of a withdrawable part)
position of a withdrawable part in which an isolating distance or segregation is established in the circuits of
the withdrawable part, that part remaining mechanically attached to the enclosure
NOTE In switchgear the auxiliary circuits may not be disconnected.
3.3.27
removed position (of a removable part)
position of a removable part when it is outside and mechanically and electrically separated from the
enclosure
– 17 – EN 50123-1:2003
3.3.28
metal-enclosed switchgear
switchgear assemblies with an external metallic enclosure intended to be earthed and complete except for
external connections
NOTE The metal-enclosed switchgear is subdivided into three types:
- metal-clad switchgear;
- compartmented switchgear (with one or more non-metallic partitions);
- cubicle switchgear.
3.3.28.1
metal-clad switchgear
metal-enclosed switchgear in which components are arranged in separate compartments with metal
partitions intended to be earthed
NOTE 1 This term applies to metal-enclosed switchgear with metal partitions providing the degree of protection (or higher)
included in EN 50123-6 and having separate compartments at least for the following components:
- each main switching device;
- components connected to one side of a main switching device, for example, feeder circuit;
- components connected to the other side of the main switching device, for example, busbars; where more than one set of
busbars is provided, each set is in a separate compartment.
NOTE 2 Metal-enclosed switchgear having metal partitions and meeting all the requirements of note 1 may utilise an insulating
shutter barrier as a part of a shutter arrangement, the combination of which provides the degree of protection included in Table 1 of
EN 50123-6 (or higher) and satisfies the requirements of the standard for partitions and shutters made of insulating material.
3.3.28.2
compartmented switch
...