SIST IEC 61241-1-2:1998

Electrical apparatus for use in the presence of combustible dust - Part 1-2: Electrical apparatus protected by enclosures and surface temperature limitation - Selection, installation and maintenance

Gives guidance on the selection, installation and maintenance of electrical apparatus protected by enclosures and surface temperature limitation for use in areas where combustible dust may be present in quantities which could lead to a fire or explosion hazard. Note - IEC 61241-1-1 specifies requirements for the design, construction and testing of electrical apparatus. Apparatus within the scope of this standard may also be subject to additional requirements in other standards - for example IEC 60079-0.

Matériels électriques destinés ŕ ętre utilisés en présence de poussičres combustibles - Partie 1-2: Matériels électriques protégés par enveloppes et limitation de la température de surface - Sélection, installation et maintenance

Električne naprave za uporabo v prisotnosti gorljivega prahu - 1. del: Preskusne metode -2. oddelek: izbira, vgraditev, in vzdrževanje

General Information

• Status: Published
• Publication Date: 31-Mar-1998
• ICS: 29.260.20 - Electrical apparatus for explosive atmospheres
• Technical Committee: EXP - Product for explosive atmospheres
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Apr-1998
• Due Date: 01-Apr-1998
• Completion Date: 01-Apr-1998
• Ref Project: IEC 61241-1-2:1999 - Electrical apparatus for use in the presence of combustible dust - Part 1-2: Electrical apparatus protected by enclosures and surface temperature limitation - Selection, installation and maintenance

Standards Content (Sample)

SLOVENSKI STANDARD
01-april-1998
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installation and maintenance
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Ta slovenski standard je istoveten z: IEC 61241-1-2 Ed. 2.0
ICS:
29.260.20 (OHNWULþQLDSDUDWL]D Electrical apparatus for
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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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INTERNATIONAL IEC
STANDARD
61241-1-2
Second edition
1999-06
Electrical apparatus for use in the presence
of combustible dust –
Part 1-2:
Electrical apparatus protected by
enclosures and surface temperature limitation –
Selection, installation and maintenance
Matériels électriques destinés à être utilisés en présence
de poussières combustibles –
Partie 1-2:
Matériels électriques protégés par enveloppes et limitation
de la température de surface –
Sélection, installation et maintenance

Reference number
Numbering
As from 1 January 1997 all IEC publications are issued with a designation in the
60000 series.
Consolidated publications
Consolidated versions of some IEC publications including amendments are

available. For example, edition numbers 1.0, 1.1 and 1.2 refer, respectively, to the
base publication, the base publication incorporating amendment 1 and the base

publication incorporating amendments 1 and 2.

Validity of this publication
The technical content of IEC publications is kept under constant review by the IEC,
thus ensuring that the content reflects current technology.
Information relating to the date of the reconfirmation of the publication is available
in the IEC catalogue.
Information on the subjects under consideration and work in progress undertaken
by the technical committee which has prepared this publication, as well as the list
of publications issued, is to be found at the following IEC sources:
• IEC web site*
•
Catalogue of IEC publications
Published yearly with regular updates
(On-line catalogue)*
• IEC Bulletin
Available both at the IEC web site* and as a printed periodical
Terminology, graphical and letter symbols
For general terminology, readers are referred to IEC 60050: International
Electrotechnical Vocabulary (IEV).
For graphical symbols, and letter symbols and signs approved by the IEC for
general use, readers are referred to publications IEC 60027: Letter symbols to be
used in electrical technology, IEC 60417: Graphical symbols for use on equipment.
Index, survey and compilation of the single sheets and IEC 60617: Graphical symbols
for diagrams.
* See web site address on title page.

INTERNATIONAL IEC
STANDARD
61241-1-2
Second edition
1999-06
Electrical apparatus for use in the presence
of combustible dust –
Part 1-2:
Electrical apparatus protected by
enclosures and surface temperature limitation –
Selection, installation and maintenance
Matériels électriques destinés à être utilisés en présence
de poussières combustibles –
Partie 1-2:
Matériels électriques protégés par enveloppes et limitation
de la température de surface –
Sélection, installation et maintenance

 IEC 1999  Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission 3, rue de Varembé Geneva, Switzerland
Telefax: [phone] e-mail: [e-mail] IEC web site http://www.iec.ch
Commission Electrotechnique Internationale
PRICE CODE
R
International Electrotechnical Commission
For price, see current catalogue

– 2 – 61241-1-2 © IEC:1999(E)
CONTENTS
Page
FOREWORD . 3

INTRODUCTION .5

Clause
1 Scope.6

2 Normative references . 6
3 Definitions. 7
4 Area classification . 9
5 Practices A and B. 9
5.1 Practice A.9
5.2 Practice B.10
6 Selection according to temperature . 10
6.1 Temperature limitation.10
6.2 Maximum permissible surface temperature. 12
7 Selection of apparatus. 12
7.1 Selection of practice A dust ignition protected apparatus . 12
7.2 Selection of practice B dust ignition protected apparatus . 13
7.3 Selection of radiating equipment. 13
7.4 Selection of ultrasonic equipment . 14
8 Installation . . 14
9 Wiring systems .15
10 Inspection and maintenance . 18
Annex A (informative) Examples of dust layers of excessive thickness . 19

61241-1-2 © IEC:1999(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
ELECTRICAL APPARATUS FOR USE IN THE PRESENCE OF

COMBUSTIBLE DUST –
Part 1-2: Electrical apparatus protected by enclosures and

surface temperature limitation –

Selection, installation and maintenance
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the 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, the IEC publishes International Standards. 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. The 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 the 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 National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61241-1-2 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 second edition cancels and replaces the first edition, published in 1993, and constitutes a

technical revision.
The text of this standard is based on the following documents:
FDIS Report on voting
31H/91/FDIS 31H/97/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.
Annex A is for information only.
A bilingual version of this standard may be issued at a later date.

– 4 – 61241-1-2 © IEC:1999(E)
IEC 61241 consists of the following parts under the general title: Electrical apparatus for use in

the presence of combustible dust:

– Part 1: Electrical apparatus protected by enclosures and surface temperature limitation

– Part 2: Test methods
– Part 3: Classification of areas where combustible dusts are or may be present

1)
– Part 4: Type of protection pressurization "p"

1)
– Part 5: Intrinsically safe apparatus

________
1)
Under consideration.
61241-1-2 © IEC:1999(E) – 5 –
INTRODUCTION
Combustible dust can be ignited by electrical apparatus in several main 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 (for example 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 this standard
– 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 of igniting combustible dust;
• any other ignition sources are avoided.
The protection specified in this standard will not provide the required level of safety unless 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.
Two different types of practice, A and B, are specified in this standard. Both are intended to
provide an equivalent level of protection.

– 6 – 61241-1-2 © IEC:1999(E)
ELECTRICAL APPARATUS FOR USE IN THE PRESENCE OF

COMBUSTIBLE DUST –
Part 1-2: Electrical apparatus protected by enclosures and

surface temperature limitation –

Selection, installation and maintenance

1 Scope
This part of IEC 61241 gives guidance on the selection, installation and maintenance of
electrical apparatus protected by enclosures and surface temperature limitation for use in
areas where combustible dust may be present in quantities which could lead to a fire or
explosion hazard.
NOTE – IEC 61241-1-1 specifies requirements for the design, construction and testing of electrical apparatus.
Apparatus within the scope of this standard may also be subject to additional requirements in other standards – for
example, IEC 60079-0.
The ignition protection is based on the limitation of the maximum surface temperature of the
enclosure, and other surfaces which could be in contact with dust, and on the restriction of dust
ingress into the enclosure by the use of "dust-tight" or "dust-protected" enclosures.
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.
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.
The principles of this standard may also be followed when combustible fibres or flyings cause a
hazard.
This standard does not apply to dusts of explosives which 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 firedamp
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.
This standard does not include other types of protection and is only applicable to protection by

enclosures and surface temperature limitation.
2 Normative references
The following normative documents contain provisions which, through reference in this text,
constitute provisions of this part of IEC 61241. For dated references, subsequent amendments
to, or revisions of, any of these publications do not apply. However, parties to agreements
based on this part of IEC 61241 are encouraged to investigate the possibility of applying the
most recent editions of the normative documents indicated below. For undated references, the
latest edition of the normative document referred to applies. Members of IEC and ISO maintain
registers of currently valid International Standards.
IEC 60050(426):1990, International Electrotechnical Vocabulary (IEV) – Chapter 426: Electrical
apparatus for explosive atmospheres

61241-1-2 © IEC:1999(E) – 7 –
IEC 60079-0:1998, Electrical apparatus for explosive gas atmospheres – Part 0: General
requirements
IEC 60079-14:1996, Electrical apparatus for explosive gas atmospheres – Part 14: Electrical
installation in hazardous areas (other than mines)

IEC 60364 (all parts), Electrical installations of buildings

IEC 60529:1989, Degrees of protection provided by enclosures (IP Code)

IEC 61241-1-1:1993, Electrical apparatus for use in the presence of combustible dust – Part 1:
electrical apparatus protected by enclosures – Section 1: Specification for apparatus
IEC 61241-2-1:1994, Electrical apparatus for use in the presence of combustible dust – Part 2:
Test methods – Section 1: Methods for determining the minimum ignition temperatures of dust
IEC 61241-3:1997, Electrical apparatus for use in the presence of combustible dust – Part 3:
Classification of areas where combustible dusts are or may be present
ISO 4225:1994, Air quality – General aspects – Vocabulary
3 Definitions
For the purpose of this part of IEC 61241, the following definitions apply.
3.1
dust
small solid particles 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
or fibres in which, after ignition, combustion spreads throughout the unconsumed mixture
[IEV 426-02-04]
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 [see IEC 61241-2-1]

– 8 – 61241-1-2 © IEC:1999(E)
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 [see IEC 61241-2-1]

3.7
dust ignition protection (DIP)

all relevant measures specified in this standard (for example dust ingress protection and

surface temperature limitation) applied to electrical apparatus to avoid ignition of a dust layer

or cloud
3.8
dust-tight enclosure
enclosure capable of preventing the ingress of all observable dust particles
3.9
dust-protected enclosure
enclosure in which the ingress of dust is not totally prevented but dust does not enter in
sufficient quantity to interfere with the safe operation of the equipment. Dust should not
accumulate in a position within the enclosure where it is liable to cause an ignition hazard
3.10
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 blanket conditions
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.
3.11
maximum permissible surface temperature:
highest temperature a surface of electrical apparatus is allowed to reach in practical service to
avoid ignition. 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
NOTE – For details, see clause 6.
3.12
zones
classified areas are divided into zones based upon the frequency and duration of the
occurrence of explosive dust/air mixtures. Dust layers should also be taken into consideration

3.13
zone 20
area in which combustible dust, as a cloud, is present continuously or frequently, during normal
operation, in sufficient quantity to be capable of producing an explosive concentration of
combustible dust in mixture with air and/or where layers of dust of uncontrollable and
excessive thickness can be formed. This can be the case inside dust containment where dust
can form explosive mixtures frequently or for long periods of time. This occurs typically inside
equipment
3.14
zone 21
area not classified as zone 20 in which combustible dust, as a cloud, is likely to occur during
normal operation, in sufficient quantities to be capable of producing an explosive concentration
of combustible dust in mixture with air

61241-1-2 © IEC:1999(E) – 9 –
This zone can include, among others, areas in the immediate vicinity of powder filling or
emptying points and areas where dust layers occur and are likely in normal operation to give
rise to an explosive concentration of combustible dust in mixture with air

3.15
zone 22
area not classified as zone 21 in which combustible dust clouds may occur infrequently, and

persist for only a short period, or in which accumulations or layers of combustible dust may be
present under abnormal conditions and give rise to combustible mixtures of dust in air. Where,
following an abnormal condition, the removal of dust accumulations or layers cannot be

assured, then the area is to be classified zone 21.

This zone can include, among others, areas in the vicinity of equipment containing dust, which
dust can escape from leaks and form deposits (such as milling rooms in which dust can escape
from the mills and then settle)
4 Area classification
The dust exclusion efficiency of the apparatus needs to be matched to the environmental
conditions likely to be encountered, and a three-way zone system has been adopted.
The present zonal classification of gases and vapour is for three zones: 0, 1 and 2, but there is
general consensus that a common zonal classification of both gases and dust is not feasible.
Unlike gas or vapour zones, areas where combustible dust may be present cannot be divided
into normal or abnormal conditions dependent upon time, since dust, unlike gas or vapour, is
not necessarily self-correcting by ventilation over a stipulated period. In fact, it can be the very
opposite, in that accelerated ventilation may lead to dust clouds and therefore give a greater,
not a lesser, hazardous condition.
Once a dust layer has been formed, it is cumulative and semi-permanent, unless physically
cleared or capable of being safely exhausted into a collector. Therefore, equipment which is
placed in a dust atmosphere shall be dust-tight and have a surface temperature limitation
below the temperature at which a dust cloud or layer will ignite.
Equipment placed in areas outside the main dust hazard zone, but which may be temporarily
subjected to a dust-laden atmosphere due to an occasional failure in the plant, or any untoward
happening, shall be dust-protected and have a surface temperature limitation below the dust
minimum ignition temperatures.
See IEC 61241-3 for details regarding classification of areas where combustible dusts are, or
may be, present.
5 Practices A and B
Two different types of practice are specified in this standard, both intended to provide an
equivalent level of protection against ignition.
5.1 Practice A
Design details and test methods are as follows:
• minimum ignition temperatures of a dust layer determined as specified in IEC 61241-2-1;
• maximum surface temperature measured under dust-free conditions as specified in
20.4.5.4 of IEC 61241-1-1;
– 10 – 61241-1-2 © IEC:1999(E)

• maximum permissible surface temperature for apparatus having dust layers up to a

thickness of 5 mm, calculated as specified in 6.1.2.1;

• construction of enclosure meeting the general requirements as specified in IEC 61241-1-1;

• dust tightness tested by the method specified in IEC 60529 for category 1 (using artificial

depression) meeting the requirements of table 1.

Table 1 – Dust tightness (practice A)

Zone 20
Zone 21 Zone 22
Zone 22 with conductive dust
IP6X IP5X
Marking DIP A20 or DIP A21 Marking DIP A22
5.2 Practice B
Design details and test methods are as follows:
• minimum ignition temperature of a dust layer determined as specified in IEC 61241-2-1;
• maximum surface temperatures measured under dust blanket conditions as specified
in 20.4.5.5 of IEC 61241-1-1;
• maximum permissible surface temperature for apparatus having dust layers up to a
thickness of 12,5 mm, calculated as specified in 6.1.2.2;
• construction of enclosure meeting the general requirements specified in IEC 61241-1-1;
• dust-tightness tested by the heat cycling dust test using the inherent depression of the
apparatus, as specified in IEC 61241-1-1.
Table 2 – Dust tightness (practice B)
Zone 20
Zone 21 Zone 22
Zone 22 with conductive dust
Dust-tight as specified in 20.4.3.4 of IEC 61241-1-1 Dust protected as specified in 20.4.3.5
of IEC 61241-1-1
Additional requirements as specified in clause 13
of IEC 61241-1-1 Clause 13 of IEC 61241-1-1 is not applicable
Marking DIP B20 or DIP B21 Marking DIP B22

6 Selection according to temperature
6.1 Temperature limitation
The maximum surface temperature permitted for apparatus operating in either zone 21 or
zone 22 is determined by the deduction of a safety margin from the minimum ignition
temperature of the dust concerned, when tested in accordance with the methods specified in
IEC 61241-2-1 for both dust clouds and layers up to a thickness of 5 mm or 12,5 mm. Dust
layers exhibit two properties as layer thickness increases, a reduction in minimum ignition
temperature and an increase in thermal insulation.

61241-1-2 © IEC:1999(E) – 11 –

6.1.1 Temperature limitations because of the presence of dust clouds

The maximum surface temperature of the apparatus
...