IEC 61241-0:2004

IEC 61241-0
Edition 1.0 2004-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electrical apparatus for use in the presence of combustible dust –
Part 0: General requirements
Matériels électriques pour utilisation en présence de poussières combustibles –
Partie 0: Exigences générales
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IEC 61241-0
Edition 1.0 2004-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electrical apparatus for use in the presence of combustible dust –
Part 0: General requirements
Matériels électriques pour utilisation en présence de poussières combustibles –
Partie 0: Exigences générales
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
X
CODE PRIX
ICS 29.260.20 ISBN 2-8318-7530-7

– 2 – 61241-0 © IEC:2004
CONTENTS
FOREWORD.6
INTRODUCTION.9

1 Scope.11
2 Normative references .12
3 Terms and definitions .14
4 Construction .19
4.1 General .19
4.2 Principles for design and testing of apparatus for use in Zone 20 .19
4.3 Opening enclosures.19
4.4 Environmental conditions .20
5 Temperatures .20
5.1 Maximum surface temperature .20
5.2 Maximum surface temperature with respect to dust layers above 50 mm .20
5.3 Ambient temperature .20
6 Enclosure materials .21
6.1 Non-metallic enclosures and non-metallic parts of enclosures .21
6.2 Enclosures containing light metals.22
7 Fasteners .22
7.1 Access to live parts .22
7.2 Compatible material .22
8 Interlocking devices.23
9 Bushings .23
9.1 Prevention of turning .23
9.2 Torque tests .23
10 Materials used for cementing.23
10.1 Documentation .23
10.2 Thermal stability.23
10.3 Verification .23
11 Ex components.23
11.1 General .23
11.2 Mounting .24
11.3 Internal mounting .24
11.4 External mounting .24
12 Connection facilities and terminal compartments .24
12.1 Attached cables.24
12.2 Terminal access .24
12.3 Creepage and clearance .24
13 Connection facilities for earthing or bonding conductors .24
13.1 Internal connection.24
13.2 External connection.25
13.3 Facility not required.25
13.4 Effective connection .25

61241-0 © IEC:2004 – 3 –
13.5 Effective contact.25
13.6 Environmental .25
13.7 Use of light metal .25
14 Cable and conduit entries.26
14.1 Intended use .26
14.2 Construction.26
14.3 Integral part of the apparatus .26
14.4 Prevention of twisting .26
14.5 Method of attaching.26
14.6 Blanking elements .26
14.7 Branching point temperatures.26
15 Radiating equipment.27
15.1 Lasers and other continuous wave source .27
15.2 Ultrasonic sources.28
16 Supplementary requirements for specific electrical apparatus – Rotating electrical
machines.28
16.1 Ventilation openings for external fans.28
16.2 Construction and mounting of the ventilating systems .28
16.3 Clearances for the ventilating system for use in Zone 20 or 21 .28
16.4 Materials for external fans and fanhoods .29
17 Switchgear .29
17.1 Flammable dielectric .29
17.2 Interlocking .29
17.3 Indication of open position.29
17.4 Openings.29
18 Fuses .30
19 Plugs and sockets .30
19.1 Plugs and sockets construction .30
19.2 Bolted plugs and sockets.32
19.3 For Zone 21 and Zone 22 .32
19.4 Plugs remaining energized .32
20 Luminaires .32
20.1 Light transmitting covers .32
20.2 Guards .32
20.3 Mounting .32
20.4 Covers .32
20.5 Parts remaining energized.33
20.6 Types of lamps.33
21 Caplights, caplamps and handlamps.33
21.1 Leakage .33
21.2 Separate enclosures .33
22 Apparatus incorporating cells and batteries .33
22.1 General .33
22.2 Connection of cells.33
22.3 Characteristics .33
22.4 Compatibility .35
22.5 Limits .35
22.6 Mixture of cells .35

– 4 – 61241-0 © IEC:2004
22.7 Interchangeability.35
22.8 Re-charging .35
22.9 Different cells .35
22.10 Leakage .36
22.11 Method of connection .36
22.12 Orientation .36
22.13 Identification of replacement.36
23 Verification and tests .36
23.1 General .36
23.2 Verification of documents .36
23.3 Compliance of prototype or sample with documents .36
23.4 Type tests .36
24 Routine verifications and tests.43
25 Manufacturer’s responsibility .43
26 Verifications and tests on modified or repaired electrical apparatus.43
27 Clamping tests of cable entries for non-armoured and braided cables .43
27.1 Cable entries with clamping by the sealing ring .43
27.2 Cable entries with clamping by filling compound.44
27.3 Cable entries with clamping by means of a clamping device .44
27.4 Tensile test .45
27.5 Mechanical strength .45
28 Clamping tests of cable entries for armoured cables.46
28.1 Clamping tests where the armourings are clamped by a device within the
gland.46
28.2 Clamping tests where the armourings are not clamped by a device within the
gland.46
29 Marking .46
29.1 General .46
29.2 Marking of all electrical apparatus .46
29.3 Multiple protection techniques .47
29.4 Order of marking .48
29.5 Reduced marking .48
30 Examples of marking .48
30.1 Apparatus type of protection "mD" for use in Zone 20.48
30.2 Apparatus type of protection "iaD" for use in Zone 20.48
30.3 Apparatus type of protection "pD" for use in Zone 21.49
30.4 Apparatus type of protection "tD", Practice A (see IEC 61241-1); temperature
tested under 500 mm dust layer, for use in Zone 21 .49
30.5 Apparatus type of protection "tD", Practice B (see IEC 61241-1) for use in
Zone 22.49
30.6 Apparatus type of protection "tD", Practice A (see IEC 61241-1) for use in
Zone 22.49

Bibliography.50

61241-0 © IEC:2004 – 5 –
Figure 1 – Illustration of entry points and branching points .27
Figure 2 – Tolerances and clearance for threaded fasteners .31
Figure 3 – Contact surface under head of fastener with a reduced shank.31
Figure 4 – Test piece with painted electrodes .42

Table 1 – Ambient temperatures in service and additional marking .20
Table 2 – Minimum cross-sectional areas of protective conductors .25
Table 3 – Primary cells .34
Table 4 — Secondary cells .35
Table 5 – Tests of resistance to impact.37
Table 6 – Torque to be applied to the stem of bushing used for connection facilities.39

– 6 – 61241-0 © IEC:2004
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
ELECTRICAL APPARATUS FOR USE IN THE
PRESENCE OF COMBUSTIBLE DUST –

Part 0: General requirements
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61241-0 has been prepared by subcommittee 31H: Apparatus for
use in the presence of combustible dust, of IEC technical committee 31: Electrical apparatus
for explosive atmospheres.
This first edition of IEC 61241-0, together with IEC 61241-1, cancels and replaces IEC 61241-1-1
(1999) and constitutes a technical revision.
This standard, and the other parts within this series, was developed to align protection
methods associated with electrical apparatus for use in the presence of combustible dust and
those similar protection methods associated with the IEC 60079 series of standards, where
possible.
61241-0 © IEC:2004 – 7 –
The text of this standard is based on the following documents:
FDIS Report on voting
31H/173/FDIS 31H/178/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
IEC 61241 consists of the following parts under the general title: Electrical apparatus for use
in the presence of combustible dust:
Part 0: General requirements
Part 1: Protection by enclosures ‘tD’
Part 2: Type of protection ‘pD’
Part 10: Classification of areas where combustible dusts are or may be present
Part 11: Protection by intrinsic safety ‘iD’
Part 14: Selection and installation
Part 17: Inspection and maintenance of electrical installations in hazardous areas (other
than mines)
Part 18: Protection by encapsulation ‘mD’
Part 20 : Test methods
Part 20-1: Methods for determining the minimum ignition temperatures of dust
Part 20-2: Method for determining the electrical resistivity of dust in layers
Part 20-3: Method for determining minimum ignition energy of dust/air mixtures

NOTE All references in this standard to the IEC 61241 series follows the proposed re-numbering of the dust
standards agreed by SC31H and TC31. It may be necessary to alter these numbers if the relevant standards are
not yet published.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
The contents of the corrigendum of November 2005 have been included in this copy.

—————————
To be published.
To be published.
Under consideration.
– 8 – 61241-0 © IEC:2004
REFERENCE TABLE
Anticipated
New number
Existing standard Subject date of
assigned
change
IEC 61241-0 General requirements 2004
IEC 61241-1-1
IEC 61241-1 Protection by enclosure 2004
IEC 61241-1-2 IEC 61241-14 Selection and installation 2004
IEC 61241-2-1 IEC 61241-20-1 Test methods 2005
IEC 61241-2-2 IEC 61241-20-2 Test methods 2005
IEC 61241-2-3 IEC 61241-20-3 Test methods 2005
IEC 61241-3 IEC 61241-10 Classification 2004
IEC 61241-4 IEC 61241-2 Protection by pressurization 2005
IEC 61241-11 Protection by intrinsic safety 2005
IEC 61241-17 Inspection and maintenance 2004
IEC 61241-18 Protection by encapsulation 2004
IEC 61241-19 Repair and overhaul 2006

61241-0 © IEC:2004 – 9 –
INTRODUCTION
Many dusts that are generated, processed, handled and stored, are combustible. When
ignited they can burn rapidly and with considerable explosive force if mixed with air in the
appropriate proportions. It is often necessary to use electrical apparatus in locations where
such combustible materials are present, and suitable precautions must therefore be taken to
ensure that all such apparatus is adequately protected so as to reduce the likelihood of
ignition of the external explosive atmosphere. In electrical apparatus, potential ignition
sources include electrical arcs and sparks, hot surfaces and frictional sparks.
Areas where dust, flyings and fibres in air occur in dangerous quantities are classified as
hazardous and are divided into three zones according to the level of risk.
Generally, electrical safety is ensured by the implementation of one of two considerations, i.e.
that electrical apparatus be located where reasonably practicable outside hazardous areas,
and that electrical apparatus be designed, installed and maintained in accordance with
measures recommended for the area in which the apparatus is located.
Combustible dust can be ignited by electrical apparatus in several ways:
– by surfaces of the apparatus that are above the minimum ignition temperature of the dust
concerned. The temperature at which a type of dust ignites is a function of the properties
of the dust, whether the dust is in a cloud or layer, the thickness of the layer and the
geometry of the heat source;
– by arcing or sparking of electrical parts such as switches, contacts, commutators, brushes,
or the like;
– by discharge of an accumulated electrostatic charge;
– by radiated energy (e.g. electromagnetic radiation);
– by mechanical sparking or frictional sparking or heating associated with the apparatus.
In order to avoid ignition hazards it is necessary that
– the temperature of surfaces, on which dust can be deposited, or which would be in contact
with a dust cloud, is kept below the temperature limitation specified in this standard;
– any electrical sparking parts, or parts having a temperature above the temperature limit
specified in IEC 61241-14
• are contained in an enclosure which adequately prevents the ingress of dust, or
• the energy of electrical circuits is limited so as to avoid arcs, sparks or temperatures
capable to ignite combustible dust;
– any other ignition sources are avoided.
Compliance with this standard will only provide the required level of safety if the electrical
apparatus is operated within its rating and is installed and maintained according to the
relevant codes of practice or requirements, for example in respect of protection against over-
currents, internal short-circuits, and other electrical faults. In particular, it is essential that the
severity and duration of an internal or external fault be limited to values that can be sustained
by the electrical apparatus without damage.

– 10 – 61241-0 © IEC:2004
Several techniques are available for the explosion protection of electrical apparatus in
hazardous areas. This standard describes the safety features of these types of explosion-
protection techniques and specifies the installation procedures to be adopted. It is most
important that the correct selection and installation procedures be followed to ensure the safe
use of electrical apparatus in hazardous areas.

61241-0 © IEC:2004 – 11 –
ELECTRICAL APPARATUS FOR USE IN THE
PRESENCE OF COMBUSTIBLE DUST –

Part 0: General requirements
1 Scope
This part of IEC 61241 specifies general requirements for the design, construction, testing
and marking of electrical apparatus protected by any recognized safeguard technique for use
in areas where combustible dust may be present in quantities that could lead to a fire or
explosion hazard.
This standard is supplemented or modified by the following parts of IEC 61241 concerning
specific types of protection:
– Part 1: Protection by enclosures ‘tD’
– Part 2: Protection by pressurization ‘pD’ (under consideration)
– Part 11: Intrinsically safe apparatus ‘iD’
– Part 18: Protection by encapsulation ‘mD’
NOTE IEC 61241-14 gives guidance on the selection and installation of the apparatus. Apparatus within the
scope of this standard may also be subjected to additional requirements in other standards – for example,
IEC 60079-0.
The application of electrical apparatus in atmospheres which may contain explosive gas as
well as combustible dust, whether simultaneously or separately, requires additional protective
measures.
This standard does not specify requirements for safety, other than those directly related to the
explosion risk.
Where the apparatus has to meet other environmental conditions, for example, protection
against ingress of water and resistance to corrosion, additional methods of protection may be
necessary. The method used is not to adversely affect the integrity of the enclosure.
This standard does not apply to dusts of explosives that do not require atmospheric oxygen
for combustion, or to pyrophoric substances.
This standard is not applicable to electrical apparatus intended for use in underground parts
of mines as well as those parts of surface installations of such mines endangered by fire
damp and/or combustible dust.
This standard does not take account of any risk due to an emission of flammable or toxic gas
from the dust.
– 12 – 61241-0 © IEC:2004
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60034-5:2000, Rotating electrical machines – Part 5: Degrees of protection provided by
the integral design of rotating electrical machines (IP code ) − Classification
IEC 60079-0:2004, Electrical apparatus for explosive gas atmospheres – Part 0: General
requirements
IEC 60079-7:2001, Electrical apparatus for explosive gas atmospheres – Part 7: Increased
safety 'e'
IEC 60079-11:1999, Electrical apparatus for explosive gas atmospheres – Part 11: Intrinsic
safety 'i'
IEC 60086-1:2000, Primary batteries – Part 1: General
IEC 60095 (all parts), Lead-acid starter batteries
IEC 60192:2001, Low-pressure sodium vapour lamps – Performance specifications
IEC 60216-1:2001, Electrical insulating materials – Properties of thermal endurance – Part 1:
Ageing procedures and evaluation of test results
IEC 60216-2:1990, Guide for the determination of thermal endurance properties of electrical
insulating materials – Part 2: Choice of test criteria
IEC 60243-1:1998, Electrical strength of insulating materials – Test methods – Part 1: Tests
at power frequencies
IEC 60285:1993, Alkaline secondary cells and batteries – Sealed nickel-cadmium cylindrical
rechargeable single cells
IEC 60529:1989, Degrees of protection provided by enclosures (IP Code)
IEC 60623:2001, Secondary cells and batteries containing alkaline or other non-acid
electrolytes – Vented nickel-cadmium prismatic rechargeable single cells
IEC 60662:1980, High-pressure sodium vapour lamps
IEC 60947-3:1999, Low-voltage switchgear and controlgear – Part 3: Switches, disconnectors,
switch-disconnectors and fuse-combination units
IEC 61056 (all parts), General purpose lead-acid batteries (valve-regulated types)
—————————
Cancelled and replaced by IEC 61951-1 (2003).

61241-0 © IEC:2004 – 13 –
IEC 61150:1992, Alkaline secondary cells and batteries – Sealed nickel-cadmium rechargeable
monobloc batteries in button cell design
IEC 61241-1:⎯, Electrical apparatus for use in the presence of combustible dust – Part 1:
Protection by enclosures “tD”
IEC 61241-14:⎯, Electrical apparatus for use in the presence of combustible dust – Part 14:
Selection and installation
ISO 48:1994, Rubber, vulcanized or thermoplastic – Determination of hardness (hardness
between 10 IRHD and 100 IRHD)
ISO 178:2001, Plastics – Determination of flexural properties
ISO 179 (all parts), Plastics – Determination of Charpy impact properties
ISO 262:1998, ISO general-purpose metric screw threads – Selected sizes for screws, bolts
and nuts
ISO 273:1979, Fasteners – Clearance holes for bolts and screws
ISO 286-2:1988, ISO system of limits and fits – Part 2: Tables of standard tolerance grades
and limit deviations for holes and shafts
ISO 527 (all parts), Plastics – Determination of tensile properties
ISO 965 (all parts), ISO general-purpose metric screw threads – Tolerances
ISO 1818:1975, Vulcanized rubbers of low hardness (10 to 35 IRHD) − Determination of
hardness
ISO 4014:1999, Hexagon head bolts – Product grades A and B
ISO 4017:1999, Hexagon head screws – Product grades A and B
ISO 4026:2003, Hexagon socket set screws with flat point
ISO 4027:2003, Hexagon socket set screws with cone point
ISO 4028:2003, Hexagon socket set screws with dog point
ISO 4029:2003, Hexagon socket set screws with cup point
ISO 4032:1999, Hexagon nuts, style 1 – Product grades A and B
ISO 4762:1997, Hexagon socket head cap screws
ISO 4892 (all parts), Plastics – Methods of exposure to laboratory light sources
—————————
Withdrawn standard.
– 14 – 61241-0 © IEC:2004
3 Terms and definitions
For the purposes of this document, the following definitions apply.
3.1
dust
small solid particles including fibres and flyings in the atmosphere which settle out under their
own weight, but which may remain suspended in air for some time (includes dust and grit as
defined in ISO 4225)
3.2
combustible dust
dust, fibres or flyings that can burn or glow in air and could form explosive mixtures with air at
atmospheric pressure and normal temperatures
3.3
conductive dust
dust, fibres or flyings with electrical resistivity equal to or less than 10 Ω⋅m
3.4
explosive dust atmosphere
mixture with air, under atmospheric conditions, of flammable substances in the form of dust,
fibres or flyings in which, after ignition, combustion spreads throughout the unconsumed
mixture
[IEV 426-02-04, modified]
3.5
minimum ignition temperature of a dust layer
lowest temperature of a hot surface at which ignition occurs in a dust layer of specified
thickness on this hot surface
[3.3 of IEC 61241-2-1]
3.6
minimum ignition temperature of a dust cloud
lowest temperature of the hot inner wall of a furnace at which ignition occurs in a dust cloud in
air contained therein
[3.5 of IEC 61241-2-1, modified]
3.7
electrical apparatus
items applied as a whole or in part for the utilization of electrical energy
NOTE These include, amongst others, items for the generation, transmission, distribution, storage, measurement,
regulation, conversion and consumption of electrical energy and items for telecommunications.
3.8
rating
set of rated values and operating conditions

61241-0 © IEC:2004 – 15 –
3.9
enclosure
all the walls, doors, covers, cable entries, rods, spindles, shafts, etc. which contribute to the
type of protection of and/or the degree of protection (IP) of the electrical apparatus
3.10
dust-tight enclosure
enclosure capable of preventing the ingress of all observable dust particles
3.11
dust-protected enclosure
enclosure in which the ingress of dust is not totally prevented but does not enter in sufficient
quantity to interfere with the safe operation of the equipment
NOTE Dust should not accumulate in a position within the enclosure where it is liable to cause an ignition hazard.
3.12
type of protection
specific measures applied to electrical apparatus to avoid ignition of a surrounding explosive
atmosphere by such apparatus
3.13
maximum surface temperature
highest temperature which is attained by any part of the surface of electrical apparatus when
tested under the defined dust-free or dust layer conditions at the specified maximum ambient
temperature
NOTE This temperature is attained under the test condition. Increasing the layer thickness can increase this
temperature due to the thermal insulation properties of dust.
3.14
maximum permissible surface temperature
highest temperature a surface of electrical apparatus is allowed to reach in practical service
to avoid ignition
NOTE The maximum permissible surface temperature will depend upon the type of dust, whether as a cloud or
layer; if a layer, its thickness, and the application of a safety factor (see IEC 61241-14, Clause 6).
3.15
zones
areas classified for explosive dust atmospheres are divided into zones based upon the
frequency and duration of the occurrence of explosive dust/air atmospheres
3.16
Zone 20
place in which an explosive atmosphere in the form of a cloud of combustible dust in air is
present continuously, or for long periods or frequently
3.17
Zone 21
place in which an explosive atmosphere in the form of a cloud of combustible dust in air is
likely to occur, occasionally, in normal operation

– 16 – 61241-0 © IEC:2004
3.18
Zone 22
place in which an explosive atmosphere in the form of a cloud of combustible dust in air is not
likely to occur in normal operation but, if it does occur, will persist for a short period only
3.19
cable entry
device permitting the introduction of one or more electric and/or fibre optics cables into an
electrical apparatus so as to maintain the relevant type of protection
3.20
conduit entry
means of introducing a conduit into an electrical apparatus so as to maintain the relevant type
of protection
3.21
compression element
element of a cable entry acting on the sealing ring to enable the latter to fulfil its function
3.22
clamping device
element of a cable entry for preventing tension or torsion in the cable from being transmitted
to the connections
3.23
sealing ring
ring used in a cable or conduit entry to ensure the sealing between the entry and the cable or
conduit
3.24
terminal compartment
separate compartment or part of a main enclosure, communicating, or not, with the main
enclosure, and containing connection facilities
3.25
connection facilities
terminals screws and other parts, used for the electrical connection of conductors of external
circuits
3.26
bushing
insulating device carrying one or more conductors through an internal or external wall of an
enclosure
3.27
cell
assembly of electrodes and electrolyte that constitutes the smallest electrical unit of a battery
3.28
primary cell or battery
electrochemical system capable of producing electrical energy by chemical reaction

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