EN 50020:2002

Electrical apparatus for potentially explosive atmospheres - Intrinsic safety 'i'

To be read with EN 50014:1997 * Superseded by EN 60079-11:2007

Elektrische Betriebsmittel für explosionsgefährdete Bereiche - Eigensicherheit 'i'

Matériel électrique pour atmosphères explosibles - Sécurité intrinsèque 'i'

Električne naprave za potencialno eksplozivne atmosfere - Lastna varnost ''i''

General Information

• Status: Withdrawn
• Publication Date: 13-Jun-2002
• Withdrawal Date: 29-Jun-2003
• ICS: 29.260.20 - Electrical apparatus for explosive atmospheres
• Technical Committee: CLC/TC 31 - Electrical apparatus for explosive atmospheres - General requirements
• Drafting Committee: CLC/SC 31-3 - Intrinsically safe apparatus and systems “i”
• Parallel Committee: IEC/SC 31G - IEC_SC_31G
• Current Stage: 9960 - Withdrawal effective - Withdrawal
• Start Date: 01-Oct-2009
• Completion Date: 01-Oct-2009
• Directive: 2008/68/EC - Directve 2008/68/EC of the European Parliament and of the council of 24 September 2008 on the inland transport of the dangerous goods
• Directive: 94/9/EC - Directive 94/9/EC of the European Parliament and the Council of 23 March 1994 on the approximation of the laws of the Member States concerning equipment and protective systems intended for use in potentially explosive atmospheres
• Mandate: BC/CEN/CLC/08-92 - BC/CEN/CLC/08-92
• Ref Project: SIST EN 50020:2003 - Electrical apparatus for potentially explosive atmospheres - Intrinsic safety 'i'

Relations

• Replaces: EN 50020:1994 - Electrical apparatus for potentially explosive atmospheres - Intrinsic safety 'i'
• Effective Date: 29-Jan-2023
• Replaced By: EN 60079-11:2007 - Explosive atmospheres - Part 11: Equipment protection by intrinsic safety "i"
• Effective Date: 29-Jan-2023

Standards Content (Sample)

SLOVENSKI SIST EN 50020:2003
STANDARD
marec 2003
Električne naprave za potencialno eksplozivne atmosfere - Lastna varnost ''i''
Electrical apparatus for potentially explosive atmospheres - Intrinsic safety "i"
ICS 29.260.20 Referenčna številka
©  Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

EUROPEAN STANDARD EN 50020
NORME EUROPÉENNE
EUROPÄISCHE NORM June 2002
ICS 29.260.20 Supersedes EN 50020:1994
English version
Electrical apparatus for potentially explosive atmospheres -
Intrinsic safety 'i'
Matériel électrique Elektrische Betriebsmittel
pour atmosphères explosibles - für explosionsgefährdete Bereiche -
Sécurité intrinsèque 'i' Eigensicherheit 'i'
This European Standard was approved by CENELEC on 2002-02-01. 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
© 2002 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 50020:2002 E
Foreword
This European Standard was prepared by SC 31-3, Intrinsically safe apparatus and systems "i", of
Technical Committee CENELEC TC 31, Electrical apparatus for explosive atmospheres.
The text of the draft was submitted to the CENELEC Unique Acceptance Procedure and was approved by
CENELEC as EN 50020 on 2002-02-01.
This European Standard supersedes EN 50020:1994 and its corrigendum February 1998.
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) 2003-02-01
- latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2003-06-30
This European Standard is to be read in conjunction with EN 50014:1997, Electrical apparatus for
potentially explosive atmospheres – General requirements, and with the third editions of the European
Standards for the specific types of protection.

- 3 - EN 50020:200X
Contents
1 Scope.4
2 Normative references.6
3 Definitions.7
4 Grouping and classification of intrinsically safe apparatus
and associated apparatus .10
5 Intrinsically safe levels of protection of electrical apparatus.11
6 Apparatus construction.13
7 Components on which intrinsic safety depends .30
8 Infallible components, infallible assemblies of components
and infallible connections .36
9 Diode safety barriers.42
10 Type verification and type tests.43
11 Routine verifications and tests.52
12 Marking.52
13 Documentation .53
Annex A (normative) Assessment of intrinsically safe circuits.54
Annex B (normative) Spark test apparatus for intrinsically safe circuits.77
Annex C (informative) Measurement of creepage distances, clearances
and separation distances through casting compound and through solid insulation.86
Annex D (normative) Encapsulation .89
Annex E (normative) Certification requirements for torches.93

1 Scope
1.1 This European Standard specifies the construction and testing of intrinsically safe apparatus,
intended for use in potentially explosive atmospheres and for associated apparatus, which is intended for
connection to intrinsically safe circuits which enter such atmospheres.
1.2 This European Standard supplements EN 50014 the requirements of which apply to intrinsically safe
apparatus and to associated apparatus except as indicated in the following list.
If associated apparatus is protected by a type of protection listed in EN 50014, then the requirements of
that method of protection together with the relevant parts of EN 50014 also apply to the associated
apparatus. The list of exclusions which follows is directly applicable to associated apparatus intended for
use in situations where there is no potentially hazardous atmosphere and in other circumstances should
be used in combination with the requirements of the other method of protection.

- 5 - EN 50020:200X
Clause of EN 50014:1997 Clause excluded
Intrinsically Associated
safe apparatus
apparatus
3.1 Electrical apparatus Yes Yes
4.2.2 Marking of maximum surface temperature No Yes
5.1 Maximum surface temperature No Yes
5.3 Surface temperature and ignition temperature No Yes
6.2 Enclosure opening delay Yes Yes
7.1.1 Definition of plastics material No Yes
7.1.2 Requirements of plastics material compliance Yes Yes
7.1.3 Verification of plastics material compliance No Yes
7.2 Thermal endurance Yes Yes
7.3 Electrostatic charges on plastics enclosures No Yes
7.4 Threaded holes in plastics Yes Yes
8.1 Light metal enclosure materials No Yes
8.2 Threaded holes in light metals Yes Yes
9 Fasteners Yes Yes
10 Interlocking devices Yes Yes
11 Bushings Yes Yes
12 Materials used for cementing Yes Yes
14 Connection facilities and terminal compartments Yes Yes
15 Connection facilities for earthing or bonding conductors Yes Yes
16 Cable and conduit entries Yes Yes
17 to 22 Supplementary requirements for certain electrical Yes Yes
apparatus
23.4.3.1 Test for resistance to impact Yes Yes
23.4.3.2 Drop test (no prior impact test necessary) No Yes
23.4.3.3 Required results No Yes
23.4.5 Torque test for bushings Yes Yes
23.4.6.1 Temperature measurement No Yes
23.4.6.2 Thermal shock test Yes Yes
23.4.7.1 Tests on non-metallic enclosures Yes Yes
to 23.4.7.7
23.4.7.8 Insulation resistance test of parts of enclosures of plastics No Yes
materials
Annex B Ex cable entries Yes Yes
1.3 This standard is applicable to electrical apparatus in which the electrical circuits themselves are
incapable of causing an explosion in the surrounding explosive atmosphere.

1.4 This standard is also applicable to electrical apparatus or parts of electrical apparatus located
outside the potentially explosive atmosphere or protected by another type of protection listed in
EN 50014, where the intrinsic safety of the electrical circuits in the potentially explosive atmosphere, may
depend upon the design and construction of such electrical apparatus or parts of such electrical
apparatus. The electrical circuits exposed to the potentially explosive atmosphere are evaluated for use in
such an atmosphere by applying this standard.
NOTE  Methods of interconnection of intrinsically safe apparatus and associated apparatus are specified in EN 50039.
1.5 Where intrinsically safe apparatus is required to be Category 1 G equipment in accordance with
EN 50284 it must comply with the requirements in this standard and also comply with the relevant
requirements of EN 50284. In particular 4.3, 4.4 and 4.5 impose additional requirements.
1.6 Where intrinsically safe apparatus is required to be Category M1 equipment in accordance with
EN 50303 it must comply with the requirements of this standard and also comply with the relevant
requirements of EN 50303.
NOTE  Associated apparatus intended for interconnection to Category 1 G and Category M1 equipment only requires to comply
with the requirements of “ia” associated apparatus in accordance with this standard but should be marked in accordance with the
relevant Category 1 standard.
2 Normative references
This European Standard incorporates by dated or undated reference, 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 only when incorporated in it by amendment or revision. For undated
references the latest edition of the publication referred to applies (including amendments).
Publication Year Title
EN 50014 1997 Electrical apparatus for potentially explosive atmospheres - General
+ corr. April 1998 requirements
+ A1 1999
+ A2 1999
EN 50019 Electrical apparatus for potentially explosive atmospheres - Increased
safety ‘e’
EN 50039 Electrical apparatus for potentially explosive atmospheres - Intrinsically
safe electrical systems ‘i’
EN 50284 1999 Special requirements for construction, test and marking of electrical
apparatus for equipment group II, Category 1 G
EN 50303 2000 Group I, Category M1 equipment intended to remain functional in
atmospheres endangered by firedamp and/or coal dust
EN 60127-1 Miniature fuses - Part 1: Definitions for miniature fuses and general
requirements for miniature fuse-links (IEC 60127-1)
EN 60127-2 Miniature fuses - Part 2: Cartridge fuse-links (IEC 60127-2)
EN 60127-3 Miniature fuses - Part 3: Sub-miniature fuse-links (IEC 60127-3)
EN 60317-3 1994 Specifications for particular types of winding wires - Part 3: Polyester
+ A1 1998 enamelled round copper wire, class 155
(IEC 60317-3:1990 + A1:1997)
EN 60317-7 1994 Specifications for particular types of winding wires - Part 7: Polyimide
+ A1 1997 enamelled round copper wire, class 220
+ A2 1998 (IEC 60317-7:1990 + A1:1997 + A2:1997)

- 7 - EN 50020:200X
Publication Year Title
EN 60317-8 1994 Specifications for particular types of winding wires -
+ A1 1997 Part 8: Polyesterimide enamelled round copper wire, class 180
+ A2 1998 (IEC 60317-8:1990 + A1:1997 + A2:1997)
EN 60529 Degrees of protection provided by enclosures (IP code)
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 566 S1 1990 Thermal evaluation and classification of electrical insulation
(IEC 60085:1984)
3 Definitions
For the purpose of this European Standard, the definitions in EN 50014 and the following definitions
apply:
3.1
intrinsically safe circuit
circuit in which any spark or any thermal effect produced in the conditions specified in this standard,
which include normal operation and specified fault conditions, is not capable of causing ignition of a given
explosive gas atmosphere
3.2
electrical apparatus
assembly of electrical components, electrical circuits or parts of electrical circuits normally contained in a
single enclosure
NOTE 1 The term “normally” has been introduced to indicate that an apparatus may occasionally be in more than one enclosure,
for example, a telephone or a radio transceiver with a hand microphone.
NOTE 2 This definition is more precise than that contained in EN 50014.
3.3
intrinsically safe apparatus
electrical apparatus in which all the circuits are intrinsically safe circuits
3.4
associated apparatus
electrical apparatus, which contains both intrinsically safe circuits and non-intrinsically safe circuits and is
constructed so that the non-intrinsically safe circuit, cannot adversely affect the intrinsically safe circuits
NOTE Associated apparatus may be either
- electrical apparatus which has another type of protection listed in EN 50014 for use in the appropriate explosive gas
atmosphere, or
- electrical apparatus not so protected and which, therefore, will not be used within an explosive gas atmosphere, for example a
recorder which is not itself in an explosive gas atmosphere, but is connected to a thermocouple situated within an explosive
atmosphere where only the recorder input circuit is intrinsically safe.
3.5
normal operation
operation of intrinsically safe apparatus or associated apparatus such that it conforms electrically and
mechanically with the design specification produced by its manufacturer
3.6
fault
any defect of any component, separation, insulation or connection between components, not defined as
infallible by this standard, upon which the intrinsic safety of a circuit depends

3.7
countable fault
fault which occurs in parts of electrical apparatus conforming to the constructional requirements of this
standard
3.8
non-countable fault
fault which occurs in parts of electrical apparatus not conforming to the constructional requirements of this
standard
3.9
infallible component or infallible assembly of components
component or assembly of components that is considered as not subject to certain fault modes as
specified in this standard
The probability of such fault modes occurring in service or storage is considered to be so low that they
are not to be taken into account
3.10
infallible separation or insulation
separation or insulation between electrically conductive parts that is considered as not subject to short
circuits
The probability of such fault modes occurring in service or storage is considered to be so low that they
are not to be taken into account
3.11
simple apparatus
electrical component or combination of components of simple construction with well-defined electrical
parameters which is compatible with the intrinsic safety of the circuit in which it is used
3.12
internal wiring
wiring and electrical connections that are made within the apparatus by its manufacturer
3.13
minimum igniting current (MIC)
minimum current in resistive or inductive circuits that causes the ignition of the explosive test mixture in
the spark-test apparatus according to Annex B
3.14
minimum igniting voltage
minimum voltage of capacitive circuits that causes the ignition to the explosive test mixture in the spark-
test apparatus according to Annex B
3.15
maximum r.m.s. a.c. or d.c. voltage (U )
m
maximum voltage that can be applied to the non-intrinsically safe connection facilities of associated
apparatus without invalidating intrinsic safety
NOTE  The value of U may be different for different sets of connection facilities, and may be different for a.c. and d.c. voltages.
m
3.16
maximum input voltage (U )
i
maximum voltage (peak a.c. or d.c) that can be applied to the connection facilities for intrinsically safe
circuits without invalidating intrinsic safety

- 9 - EN 50020:200X
3.17
maximum output voltage (U )
o
maximum output voltage (peak a.c. or d.c) in an intrinsically safe circuit that can appear under open
circuit conditions at the connection facilities of the apparatus at any applied voltage up to the maximum
voltage, including U and U
m i
NOTE  Where there is more than one applied voltage, the maximum output voltage is that occurring under the most onerous
combination of applied voltages.
3.18
maximum input current (I )
i
maximum current (peak a.c. or d.c) that can be applied to the connection facilities for intrinsically safe
circuits without invalidating intrinsic safety
3.19
maximum output current (I )
o
maximum current (peak a.c. or d.c) in an intrinsically safe circuit that can be taken from the connection
facilities of the apparatus
3.20
maximum input power (P )
i
maximum input power in an intrinsically safe circuit that can be dissipated within an apparatus when it is
connected to an external source without invalidating intrinsic safety
3.21
maximum output power (P )
o
maximum electrical power in an intrinsically safe circuit that can be taken from the apparatus
3.22
maximum external capacitance (C )
o
maximum capacitance in an intrinsically safe circuit that can be connected to the connection facilities of
the apparatus without invalidating intrinsic safety
3.23
maximum internal capacitance (C )
i
total equivalent internal capacitance of the apparatus, which is considered as appearing across the
connection facilities of the apparatus
3.24
maximum external inductance (L )
o
maximum value of inductance in an intrinsically safe circuit that can be connected to the connection
facilities of the apparatus
3.25
maximum internal inductance (L )
i
total equivalent internal inductance of the apparatus, which is considered as appearing at the connection
facilities of the apparatus
3.26
maximum external inductance to resistance ratio (L /R )
o o
maximum value of ratio of inductance to resistance of any external circuit which maybe connected to the
connection facilities of the electrical apparatus without invalidating intrinsic safety
3.27
maximum internal inductance to resistance ratio (L /R )
i i
maximum value of ratio of inductance to resistance which is considered as appearing at the external
connection facilities of the electrical apparatus

3.28
clearance
shortest distance in air between two conductive parts
NOTE  This distance applies only to parts that are exposed to the atmosphere and not to parts which are insulated parts or covered
with casting compound.
3.29
distance through casting compounds
shortest distance through a casting compound between two conductive parts
3.30
distances through solid insulation
shortest distance through solid insulation between two conductive parts
3.31
creepage distance in air
shortest distance along the surface of an insulating medium in contact with air between two conductive
parts
3.32
creepage distance under coating
shortest distance between conductive parts along the surface of an insulating medium covered with
insulating coating
3.33
fuse rating (I )
n
current rating of a fuse according to EN 60127 or to its manufacturer’s specification
3.34
sealed gas tight cell or battery
cell or battery which remains closed and does not release either gas or liquid when operated within the
limits of charge or temperature specified by the manufacturer
NOTE Such cells and batteries may be equipped with a safety device to prevent dangerously high internal pressure. The cell or
battery does not require addition to the electrolyte and is designed to operate during its life in its original sealed state.
3.35
sealed valve-regulated cell or battery
cell or battery, which is closed under normal conditions but which has an arrangement which allows the
escape of gas if the internal pressure exceeds a predetermined value. The cell or battery cannot normally
receive an addition to the electrolyte
3.36
diode safety barrier
assemblies incorporating shunt diodes or diode chains (including Zener diodes) protected by fuses or
resistors or a combination of these, manufactured as an individual apparatus rather than as part of a
larger apparatus
4 Grouping and classification of intrinsically safe apparatus and associated apparatus
Intrinsically safe apparatus and associated apparatus shall be grouped and classified in accordance with
clauses 4 and 5 of EN 50014.
NOTE  Where reference is made to Directive 94/9/EC then apparatus is required to be allocated a Category as defined in
subclauses 3.26 to 3.30 of EN 50014.

- 11 - EN 50020:200X
5 Intrinsically safe levels of protection of electrical apparatus
5.1 General
Intrinsically safe apparatus and intrinsically safe parts of associated apparatus shall be allocated a level
of protection “ia” or “ib”.
The requirements of this standard shall apply to both levels of protection unless otherwise stated. In the
determination of level of protection “ia” or “ib”, failure of components and connections shall be considered
in accordance with 7.6.
NOTE 1  Apparatus may be specified as both “ia” and “ib” and may have different parameters for each level of protection.
In the determination of the permitted output parameters C , L , L /R for a source of power a safety factor
o o o o
of 1,5 shall be used in all circumstances.
Where the test apparatus specified in Annex B is used for high currents, then the permitted inductance is
very low. In these circumstances the inductance shall be accurately specified in the certification
documentation and controlled. The use of high currents in field wiring is not permitted.
The application of U includes any voltage up to that value and these values have to be taken into
m
account during assessment and testing. However a slow increase of the voltage from the rated value to
U shall not be assumed.
m
NOTE 2  Guidance on the assessment of intrinsically safe circuits for spark ignition is contained in Annex A. Details of the spark
test apparatus are given in Annex B.
5.2 Level of protection “ia”
With U and U applied, the intrinsically safe circuits in electrical apparatus of level of protection “ia” shall
m i
not be capable of causing ignition in each of the following circumstances:
a) in normal operation and with the application of those non-countable faults which give the most
onerous condition;
b) in normal operation and with the application of one countable fault plus those non-countable faults
which give the most onerous condition;
c) in normal operation and with the application of two countable faults plus those non-countable faults
which give the most onerous condition.
The non-countable faults applied may differ in each of the above circumstances.
In testing or assessing the circuits for spark ignition, the following safety factors shall be applied in
accordance with 10.4.2:
− for both a) and b) 1,5
− for c) 1,0
− for output parameters, C , L , L /R 1,5
o o o o
The safety factor applied to voltage or current for determination of surface temperature classification shall
be 1,0 in all cases.
If only one countable fault can occur, the requirements of b) are considered to give a level of protection of
“ia” if the test requirements for “ia” can be satisfied. If no countable faults can occur, the requirements of
a) are considered to give a level of protection of “ia” if the test requirements for “ia” can then be satisfied.

5.3 Level of protection “ib”
With U and U applied, the intrinsically safe circuits in electrical apparatus of level of protection “ib” shall
m i
not be capable of causing ignition in each of the following circumstances:
a) in normal operation plus the application of those non-countable faults which give the most onerous
condition;
b) in normal operation and with the application of one countable fault plus the application of those non-
countable faults which give the most onerous condition.
The non-countable faults applied may differ in each of the above circumstances.
In testing or assessing the circuits for spark ignition, a safety factor of 1,5 shall be applied in accordance
with 10.4.2. The safety factor applied to the voltage or current for the determination of surface
temperature classification shall be 1,0 in all cases. If no countable fault can occur the requirements of a)
are considered to give a level of protection of “ib” if the test requirements of “ib” can be satisfied.
5.4 Simple apparatus
The following apparatus shall be considered to be simple apparatus:
a) passive components, for example switches, junction boxes, resistors and simple semiconductor
devices;
b) sources of stored energy with well-defined parameters, for example capacitors or inductors, whose
values shall be considered when determining the overall safety of the system;
c) sources of generated energy, for example thermocouples and photocells, which do not generate more
than 1,5 V, 100 mA and 25 mW. Any inductance or capacitance present in these sources of energy
shall be considered as in b).
Simple apparatus shall conform to all relevant requirements of this standard but is not considered to
contain a potential source of ignition capable of causing an explosion and need not be marked in
accordance with clause 12. In particular, the following aspects shall always be considered:
1) simple apparatus shall not achieve safety by the inclusion of voltage and/or current-limiting and/or
suppression devices;
2) simple apparatus shall not contain any means of increasing the available voltage or current, for
example circuits for the generation of ancillary power supplies;
3) where it is necessary that the simple apparatus maintains the integrity of the isolation from earth of
the intrinsically safe circuit, it shall be capable of withstanding the test voltage to earth in accordance
with 6.4.12. Its terminals shall conform to 6.3.1;
4) non-metallic enclosures and enclosures containing light metals when located in the hazardous area
shall conform to 7.3 and 8.1 of EN 50014;
5) when simple apparatus is located in the hazardous area, it shall be temperature classified. When
used in an intrinsically safe circuit within their normal rating and at a maximum ambient temperature
of 40 °C, switches, plugs, sockets and terminals can be allocated a T6 temperature classification for
Group II applications. Other types of simple apparatus shall be temperature classified in accordance
with clauses 4 and 6 of this standard;
6) where simple apparatus is to be located such that Category 1 G or M1 equipment is normally
required, then the apparatus shall also comply with the additional requirements of EN 50284 or EN
50303 as applicable.
Where simple apparatus forms a part of an apparatus containing other electrical circuits, then the
combination of apparatus shall be considered as a whole.
NOTE  Sensors, which utilise catalytic reaction or other electro-chemical mechanisms, are not normally simple apparatus.
Specialist advice on their application should be sought.

- 13 - EN 50020:200X
6 Apparatus construction
NOTE  The requirements given in this clause apply, unless otherwise stated in the relevant subclauses, only to those features of
intrinsically safe apparatus and associated apparatus which contribute to this type of protection and they are additional to the
general requirements of EN 50014 except for those excluded in 1.2.
6.1 Enclosures
Intrinsically safe apparatus and associated apparatus require an enclosure which is adequate so as to
prevent the invalidation of the method of protection. Particular care is required where intrinsic safety can
be impaired by access to conducting parts, for example if the circuits contain infallible creepage distances
in air.
For Group I apparatus, a degree of protection of IP 54 in accordance with EN 60529 will normally be
required.
For Group II apparatus, a degree of protection of IP 20 may be acceptable if it is intended to be used only
in dry, clean and well controlled environments.
The “enclosure” may not be physically the same for protection against contact with live parts and the
ingress of solid foreign bodies and liquids.
The designation of the surfaces, which form the boundaries of the enclosure, shall be the responsibility of
the manufacturer. The manufacturer shall also specify the environment in which the apparatus is intended
to be used. This information shall be recorded in the definitive documentation (see clause 13).
6.2 Wiring and small component temperatures
6.2.1 Dust layers on Group I equipment
For the purpose of this clause where reference is made to T4 and Group I, the Group I equipment shall
be equipment in which coal dust can not form a layer in the location of or on the component being
considered.
Where it is assumed for the purpose of this standard that dust is excluded from Group I apparatus then
the 'X' marking requirement of 5.1.1 of EN 50014 shall be applied.
6.2.2 Wiring within apparatus
The maximum permissible current corresponding to the maximum wire temperature due to self-heating
shall either be taken from Table 1 for copper wires or can be calculated from the following equation for
metals in general:
�t()1+ aT �
I = I
f � �
T()1+ at
� �
where
-1
a is the temperature coefficient of resistance of the wire material (0,004 265 K for copper),
I is the maximum permissible current r.m.s., in amperes,
I is the current at which the wire melts in an ambient temperature of 40 °C, in amperes,
f
T is the melting temperature of the wire material in degrees Celsius (1 083 °C for copper),
t is the wire temperature due to self-heating and ambient temperature, in degrees Celsius.

The maximum current in insulated wiring shall not exceed the rating specified by the manufacturer of the
wire.
Table 1 – Temperature classification of copper wiring
(in a maximum ambient temperature of 40 °C)
Diameter Cross-sectional area Maximum permissible current
(see note 4) (see note 4) for temperature class
T1 to T4 and T5 T6
Group I
A A A
mm mm
0,035 0,000 962 0,53 0,48 0,43
0,05 0,001 96 1,04 0,93 0,84
0,1 0,007 85 2,1 1,9 1,7
0,2 0,031 4 3,7 3,3 3,0
0,35 0,096 2 6,4 5,6 5,0
0,5 0,196 7,7 6,9 6,7
NOTE 1 The value given for maximum permissible current, in amperes, is the r.m.s. a.c. or d.c. value.
NOTE 2 For stranded conductors, the cross-sectional area is taken as the total area of all strands of the conductor.
NOTE 3 The table also applies to flexible flat conductors, such as in ribbon cable, but not to printed circuit conductors for
which see 6.2.3.
NOTE 4 Diameter and cross-sectional area are the nominal dimensions specified by the wire manufacturer.
NOTE 5 Where the maximum input P does not exceed 1,3 W, the wiring can be awarded a temperature class of T4 and is
i
acceptable for Group I.
6.2.3 Printed circuit wiring
On printed circuit boards of at least 0,5 mm thickness, having a conducting track of at least 35 µm
thickness on one or both sides, a temperature class T4 or Group I shall be given to the printed tracks if
they have a minimum width of 0,3 mm and the continuous current in the tracks does not exceed 0,518 A.
Similarly, for minimum track widths of 0,5 mm, 1,0 mm and 2,0 mm, T4 shall be given for corresponding
maximum currents of 0,814 A, 1,388 A and 2,222 A respectively. Track lengths of 10 mm or less shall be
disregarded for temperature classification purposes.
Alternatively for other applications, the temperature classification of copper wiring of printed boards can
be determined from Table 2.
Manufacturing tolerances shall not reduce the values stated in this clause by more than 10 % or 1 mm,
whichever is the smaller.
Where the maximum input power P does not exceed 1,3 W, the printed wiring shall be given a
i
temperature classification of T4 or Group I for circumstances where coal dust cannot form a layer.

- 15 - EN 50020:200X
Table 2 – Temperature classification of printed board wiring
(in a maximum ambient temperature of 40 ºC)
Minimum track width Maximum permissible current for temperature classification
T1 to T4 and Group I T5 T6
mm
A A A
0,15 1,2 1,0 0,9
0,2 1,8 1,45 1,3
0,3 2,8 2,25 1,95
0,4 3,6 2,9 2,5
0,5 4,4 3,5 3,0
0,7 5,7 4,6 4,1
1,0 7,5 6,05 5,4
1,5 9,8 8,1 6,9
2,0 12,0 9,7 8,4
2,5 13,5 11,5 9,6
3,0 16,1 13,1 11,5
4,0 19,5 16,1 14,3
5,0 22,7 18,9 16,6
6,0 25,8 21,8 18,9
NOTE 1 The value given for maximum permissible current, in amperes is the r.m.s. a.c. or d.c. value.
NOTE 2 This table applies to printed boards 1,6 mm or thicker with a single layer of copper of 35 µm thickness.
NOTE 3 For boards with a thickness between 0,5 mm and 1,6 mm, divide the maximum current specified by 1,2.
NOTE 4 For boards with conducting tracks on both sides, divide the maximum current specified by 1,5.
NOTE 5 For multilayer boards, for the track layer under consideration, divide the maximum current specified by 2.
NOTE 6 For 18 µm copper thickness, divide the maximum current by 1,5.
NOTE 7 For 70 µm copper thickness, multiply the maximum current by 1,3.
NOTE 8 For tracks passing under components dissipating 0,25 W or more either normally or under fault conditions, divide
the maximum current specified by 1,5.
NOTE 9 At terminations of components dissipating 0,25 W or more either normally or under fault conditions, and for
1,00 mm along the conductor, either multiply the track width by 3 or divide the maximum current specified by 2. If
the track goes under the component, apply the factor specified in note 8 in addition.
6.2.4 Small components
Small components for example transistors or resistors, whose temperature exceeds that permitted for the
temperature classification, shall be acceptable providing that when tested in accordance with 10.7, small
components do not cause ignition. Alternatively, where no catalytic or other chemical reactions can result,
one of the following is acceptable:
a) for Group II T4 and Group I temperature classification components shall conform to Table 3, including
the relevant reduction of permitted maximum dissipation with increased ambient temperature listed in
Table 3b;
b) for Group II T5 classification the surface temperature of a component with a surface area smaller than
10 cm shall not exceed 150 °C.

In addition the permitted higher temperature shall not invalidate the type of protection for example by
causing the component or adjacent parts of the apparatus to exceed any safety related rating, or to
deteriorate or be distorted so as to invalidate creepage and clearance distances. In particular, with the
higher levels of permitted power, extra care shall be taken in the selection of the materials to be used
adjacent to these high temperature components, for example to prevent burning of the printed circuit
boards.
Migration of components due to solder melting shall not be taken into account.
Table 3 - Assessment of temperature classification
according to component size and ambient temperature
Table 3a - Requirements at 40 °C ambient
Total surface area Group II T4 Group I
excluding lead
Dust excluded
wires
Maximum surface Maximum Maximum Maximum
temperature power surface power
dissipation temperature dissipation
° C W ° C W
< 20 mm 275 950
2 2
≥ 20 mm ≤ 10 cm 200        or 1,3 450    or 3,3
> 10 cm 135        or 1,3 450    or 3,3
Table 3b - Variation in maximum power dissipation with ambient temperature
Maximum ambient ° C Apparatus 40 60 70 80
temperature group
Maximum power W Group II 1,3 1,2 1,1 1,0
dissipation
Group I 3,3 3,15 3,07 3,0
Where the outer surface of a component is not continuous, for example a component made up of tightly
wound wire which is not consolidated or a tube with a central hole, then the surface to be considered for
the purpose of Table 3a is the outer envelope of the component. The surface temperature of any part of
such a component to which the gas has access shall be in accordance with the maximum surface
temperature requirement of Table 3a and the maximum power criterion is not applicable in these
circumstances.
For potentiometers, the surface to be considered shall be that of the resistance element and not the
external surface of the component. The mounting arrangement and heat sinking and cooling effect of the
overall potentiometer construction shall be taken into consideration during the test. Temperature shall be
measured on the track with the current which flows under conditions of “ib” or “ia”, as appropriate. If this
results in a resistance value of less than 10 % of the track resistance value, the measurement shall be
carried out at 10 % of the track resistance value.

- 17 - EN 50020:200X
6.3 Facilities for connection of external circuits
6.3.1 Terminals
In addition to satisfying the requirements of Table 4, terminals for intrinsically safe circuits shall be
separated from terminals for non-intrinsically safe circuits by one or more of the methods given in a) or b).
These methods of separation shall also be applied where intrinsic safety can be impaired by external
wiring which, if disconnected from the terminal, can come into contact with conductors or components.
NOTE  Terminals for connection of external circuits to intrinsically safe apparatus and associated apparatus should be so arranged
that components will not be damaged when making the connections.
a) When separation is accomplished by distance then the clearance between terminals shall be such that
the clearances between the bare conducting parts of connected external conductors are at least 50
mm. Care shall be exercised in the layout of terminals and in the wiring method used so that contact
between circuits is unlikely if a wire becomes dislodged.
b) When separation is accomplished by locating terminals for intrinsically safe and non-intrinsically safe
circuits in separate enclosures by use of either an insulating partition or an earthed metal partition
between terminals with a common cover, the following applies:
1) partitions used to separate terminals shall extend to within 1,5 mm of the enclosure walls, or
alternatively shall provide a minimum distance of 50 mm between the bare conducting parts of
connected external conductors when measured in any direction around the partition;
2) metal partitions shall be earthed and shall have sufficient strength and rigidity to ensure that they
are not likely to be damaged during field wiring. Such partitions shall be at least 0,45 mm thick or
shall conform to 10.10.2 if of lesser thickness. In addition, metal partitions shall have sufficient
current-carrying capacity to prevent burn-through or loss of earth connection under fault
conditions;
3) non-metallic insulating partitions shall have an appropriate Comparative Tracking Index (CTI) and
sufficient thickness and shall be so supported that they cannot readily be deformed in a manner
that would defeat their purpose. Such partitions shall be at least 0,9 mm thick, or shall conform to
10.10.2 if of lesser thickness.
The clearance between bare conducting parts of terminals of separate intrinsically safe circuits shall be
equal to or exceed the values given in Table 4. In addition, the clearances between terminals shall be
such that the clearances between the bare conducting parts of connected external conductors are at least
6 mm when measured in accordance with Figure 1. Any possible movement of metallic parts, which are
not rigidly fixed, shall be taken into account.
The minimum clearance between the bare conducting parts of external conductors connected to terminals
and earthed metal or other conducting parts shall be 3 mm, unless the possible interconnection has been
taken into account in the safety analysis.
6.3.2 Plugs and sockets
Plugs and sockets used for connection of external intrinsically safe circuits shall be separate from and
non-interchangeable with those for non-intrinsically safe circuits.
Where intrinsically safe or associated apparatus is fitted with more than one plug and socket for external
connections and interchange could adversely affect the type of protection, such plugs and sockets shall
either be arranged, for example by keying, so that interchange is not possible, or mating plugs and
sockets shall be identified, for example by marking or colour coding, to make interchanging obvious.
Where a plug or a socket is not prefabricated with its wires, the connecting facilities shall conform to
6.3.1. If, however, the connections require the use of a special tool, for example by crimping, such that
there is no possibility of a strand of wire becoming free, then the connection facilities need only conform
to Table 4.
Where a connector carries earthed circuits and the type of protection depends on the earth connection,
then the connector shall be constructed in accordance with 6.6.
6.3.3 Determination of maximum external inductance to resistance ratio (L /R ) for resistance
o o
limited power source
The maximum external inductance to resistance ratio (L /R ) which may be connected to a resistance
o o
limited power source shall be calculated using the following formula. This formula takes account of a 1,5
factor of safety on current and shall not be used where C for the output terminals of the apparatus
i
exceeds 1 % of C .
o
L0 8eRii + (64e²R ² - 72Uo² eLi)½
= µH/Ω
R0 4,5 ²Uo
where
e is the minimum spark-test apparatus ignition energy in micro joules, and is for
− Group I apparatus 525 µJ
− Group IIA apparatus 320 µJ
− Group IIB apparatus 160 µJ
− Group IIC apparatus 40 µJ
R is the minimum output resistance of the power source, in ohms,
i
U is the maximum open circuit voltage, in volts,
o
L is the maximum inductance present at the power source terminals, in henries.
I
If L = 0
i
then
L0 32 eRi
=  µH/Ω
R0 9²Uo
NOTE  The normal application of the L /R ratio is for distributed parameters, for example cables, its use for lumped values for
o o
inductors and resistance requires special consideration.

- 19 - EN 50020:2002
Table 4 – Clearances, creepage distances and separations
1 Voltage 10 30 60 90 190 375 550 750 1 000 1 300 1 575 3,3 k 4,7 k 9,5 k 15,6 k
(peak value)
V
Clearance
2 1,5 2,0 3,0 4,0 5,0 6,0 7,0 8,0 10,0 14,0 16,0
mm
Separation
0,5 0,7 1,0 1,3 1,7 2,0 2,4 2,7 3,3 4,6 5,3 9,0 12,0 20,0 33,0
distance through
casting compound
mm
4 Separation
0,5 0,5 0,5 0,7 0,8 1,0 1,2 1,4 1,7 2,3 2,7 4,5 6,0 10,0 16,5
distance through
solid insulation
mm
Creepage distance
5 1,5 2,0 3,0 4,0 8,0 10,0 15,0 18,0 25,0 36,0 49,0
in air
mm
Creepage distance
6 0,5 0,7 1,0 1,3 2,6 3,3 5,0 6,0 8,3 12,0 16,3
under coating
mm
7 Comparative
ia 100 100 100 175 175 275 275 275 275 275
tracking index
ib 100 100 100 175 175 175 175 175 175 175
(CTI)
NOTE 1 Except for separation distances, no values for voltages higher than 1 575 V are proposed at present.
NOTE 2 At voltages up to 10 V, the CTI of insulating materials is not required to be specified.

6.3.4 Permanently connected cable
Apparatus which is constructed with a integral cable for external connections, shall be subjected to a pull
test, in accordance with 10.13, on the cable if breakage of the terminations inside the apparatus could
result in intrinsic safety being invalidated., For example, where there is more than one intrinsically safe
circuit in the cable and breakage could lead to an unsafe interconnection.
Dimensions in mm
Key T = Clearance and creepage in
...