Bsi bs en 61241 2 2 1996 (1999)

BRITISH STANDARD

Electrical apparatus for
use in the presence of
combustible dust —
Part 2: Test methods —
Section 2.2 Method for determining the
electrical resistivity of dust in layers

The European Standard EN 61241-2-2:1995 has the status of a
British Standard

ICS 29.260.20

BS EN
61241-2-2:1996


BS EN 61241-2-2:1996

Committees responsible for this
British Standard
The preparation of this British Standard was entrusted to Technical
Committee GEL/31, Electrical apparatus for explosive atmospheres, upon
which the following bodies were represented:
Association of British Mining Equipment Companies
British Cables Makers Confederation
British Electrical Systems Association (BEAMA Ltd.)
British Gas plc
British Lighting Association for the Preparation of Standards (Britlaps)
Council for Electrical Equipment for Flammable Atmospheres (BEAMA Ltd.)

Department of Trade and Industry (Standards Policy Unit)
ERA Technology Ltd.
Electric Trace Heating Industrial Council (Ethic)
Electrical Contractors Association
Electroheat Manufacturers’ Association of BEAMA (EMAB)
Energy Industries Council
Engineering Equipment and Materials Users’ Association
GAMBICA (BEAMA Ltd.)
Gland Manufacturers Technical Committee
Health and Safety Executive
Institute of Petroleum
Lighting Industry Federation Ltd.
Loss Prevention Council
Marine Safety Agency
Ministry of Defence
National Inspection Council for Electrical Installation Contracting
Rotating Electrical Machines Association (BEAMA Ltd.)
Sira Limited
Trades Union Congress
United Kingdom Offshore Operators Association
The following body was also represented in the drafting of the standard,
through sub-committees and panels:
This British Standard, having
been prepared under the
direction of the Electrotechnical
Sector Board, was published
under the authority of the
Standards Board and comes
into effect on
15 March 1996

© BSI 10-1999
The following BSI references
relate to the work on this
standard:
Committee reference GEL/31
Draft for comment 90/32582 DC
ISBN 0 580 25239 6

Department of the Environment (Building Research Establishment)

Amendments issued since publication
Amd. No.

Date

Comments


BS EN 61241-2-2:1996

Contents
Page
Committees responsible
Inside front cover
National foreword
ii
Foreword
2
Introduction
3

1
Scope
3
2
Normative references
3
3
Definitions
3
4
Test apparatus
3
5
Test sample
4
6
Procedure
4
7
Test report
4
Annex ZA (normative) Normative references to international
publications with their corresponding European publications
6
Figure 1 — Test cell
5
Figure 2 — Circuit diagram
5
List of references
Inside back cover

© BSI 10-1999

i


BS EN 61241-2-2:1996

National foreword
This British Standard has been prepared by Technical Committee GEL/31 and is
the English language version of EN 61241-2-2:1995 Electrical apparatus for use
in the presence of combustible dust — Part 2: Test methods Section 2: Method for
determining the electrical resistivity of dust in layers published by the European
Committee for Electrotechnical Standardization (CENELEC).
It is identical with IEC 1241-2-2:1993 incorporating corrigendum May 1994,
published by the International Electrotechnical Commission (IEC), except that
in EN 61241-1-1 “technical report” has been replaced by “standard” throughout
the text.
Cross-reference
Publication referred to

Corresponding British Standard

ISO 4225:1980

BS 6069 Characterization of air quality
Part 2:1994 Glossary

a

a

ISO 4225:1980 has been superseded by ISO 4225:1994.

A British Standard does not purport to include all the necessary provisions of a
contract. Users of British Standards are responsible for their correct application.
Compliance with a British Standard does not of itself confer immunity
from legal obligations.

Summary of pages
This document comprises a front cover, an inside front cover, pages i and ii,
the EN title page, pages 2 to 6, an inside back cover and a back cover.
This standard has been updated (see copyright date) and may have had
amendments incorporated. This will be indicated in the amendment table on the
inside front cover.
ii

© BSI 10-1999


EUROPEAN STANDARD

EN 61241-2-2

NORME EUROPÉENNE
August 1995

EUROPÄISCHE NORM
ICS 29.260.20

Descriptors: Electric equipment, explosive atmosphere, explosion proofing, fire protection, dust, combustible dust, test, resistivity

English version

Electrical apparatus for use in the presence of combustible
dust Part 2: Test methods
Section 2: Method for determining the electrical resistivity
of dust in layers
(IEC 1241-2-2:1993 + corrigendum 1994)
Matériels électriques destinés à être utilisés en
présence de poussières combustibles
Partie 2: Méthodes d’essais
Section 2: Méthode de détermination de la
résistivité électrique des couches de poussières
(CEI 1241-2-2:1993 + corrigendum 1994)

Elektrische Betriebsmittel zur Verwendung in
Bereichen mit brennbarem Staub
Teil 2: Untersuchungsverfahren
Hauptabschnitt 2: Verfahren zur Bestimmung
des elektrischen Widerstandes von
Staubschüttungen
(IEC 1241-2-2:1993 + Corrigendum 1994)

This European Standard was approved by CENELEC on 1995-03-06.
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, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy,
Luxembourg, Netherlands, Norway, Portugal, 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
© 1995 Copyright reserved to CENELEC members

Ref. No. EN 61241-2-2:1995 E


EN 61241-2-2:1995

Foreword
The text of the technical report IEC 1241-2-2:1993
with its corrigendum May 1994, prepared by
SC 31H, Apparatus for use in the presence of
ignitable dust, of IEC TC 31, Electrical apparatus
for explosive atmospheres, was submitted to the
formal vote and was approved by CENELEC
as EN 61241-2-2 on 1995-03-06 without any

modification.
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) 1996-03-01
— latest date by which the
national standards
conflicting with the EN
have to be withdrawn
(dow) 1996-03-01
Annexes designated “normative” are part of the
body of the standard. In this standard, Annex ZA is
normative. Annex ZA has been added by
CENELEC.

2

© BSI 10-1999


EN 61241-2-2:1995

Introduction

3 Definitions

This standard is applicable to the determination of
the electrical resistivity of dust in layers.
The test method is not suitable for use with
recognized explosives, gunpowder, dynamite, or
substances or mixtures of substances which may,
under some circumstances, behave in a similar
manner. Where any doubt exists about the existence
of a hazard due to explosive properties, an
indication may be obtained by placing a very small
quantity of the dust in question on the heated
surface of the apparatus prescribed in
IEC 1241-2-11), heated to 400 °C.
The test for explosivity will not always reveal the
explosive nature of a dust so that a “fail to danger”
situation could arise.

For the purpose of this standard the following
definitions apply.

NOTE Precautions should be taken to safeguard the health of
personnel conducting the tests against the risk of fire, explosion
and/or the effects, including toxic effects, of combustion.

This test method is applicable to the construction
and application of electrical apparatus for use in the
presence of combustible dust.

1 Scope
This standard specifies a method of test to
determine, by application of a d.c. voltage, the

electrical resistivity of a layer of dust. It is intended
to be used in the design, construction, testing, and
application of electrical apparatus for use in the
presence of combustible dust.
The test method is not suitable for use with
recognized explosives or substances having
explosive properties.

2 Normative references
The following normative documents contain
provisions which, through reference in this text,
constitute provisions of this standard. At the time of
publication, the editions indicated were valid. All
normative documents are subject to revision, and
parties to agreements based on this standard are
encouraged to investigate the possibility of applying
the most recent editions of the normative documents
indicated below. Members of IEC and ISO maintain
registers of currently valid International Standards.
ISO 565:1990, Test sieves — Metal wire cloth,
perforated metal plate and electroformed sheet —
Nominal sizes of openings.
ISO 4225:1980, Air quality — General aspects —
Vocabulary.

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

NOTE This definition includes what are defined in ISO 4225 as
“dust” and “grit”.

3.2
conductive dust
dust with electrical resistivity equal to or less
than 103 7.m
3.3
non-conductive dust
dust with electrical resistivity greater than 103 7.m
3.4
electrical resistivity
minimum value of the electrical resistance of a dust
layer measured between electrodes spaced at unit
distance apart, and each having unit area in contact
with the dust
NOTE For the purpose of this standard, electrical resistivity is
measured in ohm metre.

4 Test apparatus
Figure 1 and Figure 2 give details for the
construction of the test apparatus. The test cell
(see Figure 1) is of open construction, and consists of
two stainless steel bars with nominal dimensions:
length (W) – 100 mm, height (H) – 10 mm,
breadth (B) – 20 mm to 40 mm. These bars are
placed at a nominal distance apart of (L) – 10 mm on
a base with a thickness between 5 mm and 10 mm.
NOTE Glass or polytetrafluorethylene (PTFE) have been found
to be suitable materials for the base.

Two glass bars, also with a nominal height
of 10 mm, are placed across the ends of the
electrodes to keep the dust layer in place.
Figure 2 illustrates an example of a suitable
electrical circuit for making the resistivity
measurement. It contains a 10 k7 resistor to
restrict the breakdown current to a maximum value
of 0,2 A at a maximum supply voltage of 2 000 V d.c.
Other circuits with comparable characteristics and
accuracy may be used.

1)

IEC 1241-2-1:1993, Electrical apparatus for use in the presence of combustible dust — Part 2: Test methods — Section 1
(under consideration).

© BSI 10-1999

3


EN 61241-2-2:1995

The current-to-voltage converter has six ranges to
deal with the various values of supply voltage and
dust resistivity. A voltage inverter is present to
provide a positive output. All resistors
are 5 %, 0,5 W high-stability carbon-film type.

5 Test sample
The test sample shall be homogeneous and
representative of the dust received for testing.
When dust is received, it should be put in a closed
vessel until tested, or it should be conditioned, or it
should be tested directly, and the moisture content
measured at the same time and reported.
The sample of dust to be tested shall, in general, be
able to pass through a woven metal wire cloth, or a
square hole perforated plate test sieve with a
nominal size aperture of 71 4m (supplementary
size, see ISO 565). If it is required to test coarser
dust, a test sieve with a nominal size of aperture up
to 500 4m may be used. State the nominal size of
aperture of the sieve used in the report of the test.
State the moisture content of the dust sample as
tested in the report of the test, and describe the
method of measurement.
State in the test report any apparent changes in the
properties of the dust, for example moisture content
or particle shape, resulting from the preparation of
the test sample, for example in sieving.

Measure the resistance of the filled test cell Rs with
the following values of d.c. voltage applied:
110, 220, 300, 500, 1 000, 1 500, 2 000 V
Apply each value of voltage for at least 10 s, and
longer if polarization is evident.
The same sample of dust in the test cell may be used
for all the tests at any one of the values of voltage.

6.3 Calculation of resistivity
Generally, Ro is greater than 10 Rs, and the
resistivity of the dust is calculated from the
equation
@ = 0,001 Rs [H × W/L]
If Ro is less than 10 Rs, the resistivity is calculated
from the equation
@ = 0,001 Rs × Ro/[Ro – Rs] × H × W/L
where
@
is the resistivity in 7.m
Ro

is the resistance of empty test cell in 7;

Rs

is the resistance of the filled test cell in 7;

H

is the height of the electrode in mm;

W

is the length of the electrode in mm;

L

is the space between electrodes in mm.

Calculate the resistivity for each value of the
applied voltage.

6 Procedure

7 Test report

6.1 Preliminary measurement

The test report shall include the results of the
measurements, the name, source and chemical
description (if not implicit in the name) of the dust
tested, the particle size and moisture content of the
test sample, and the date and identification number
of the test. Report the mass of the dust in the test
cell, and the ambient temperature at the time of the
test.
The report shall state that the determination of
electrical resistivity of the dust has been carried out
in accordance with this standard.

Measure the resistance Ro of the empty test cell with
the two glass bars in position.
6.2 Measurement of resistance
Pour a weighed quantity of the test sample into the
test cell. Remove excess dust by running a
straight-edge along the top of the stainless steel
electrodes. Collect and weigh the excess. Calculate
the mass of dust in the test cell.

4

© BSI 10-1999


EN 61241-2-2:1995

Figure 1 — Test cell

Figure 2 — Circuit diagram

© BSI 10-1999

5


EN 61241-2-2:1995

Annex ZA (normative)
Normative references to international publications with their corresponding
European publications
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).
NOTE When the international publication has been modified by CENELEC common modifications, indicated by (mod), the relevant
EN/HD applies.
Publication

Year

Title

ISO 565

1990

ISO 4225

1980

Test sieves
—
Metal wire cloth, perforated metal plate and electroformed sheet —
Nominal sizes of openings
Air quality
—
General aspects — Vocabulary

6

EN/HD

Year

—

—

© BSI 10-1999


BS EN 61241-2-2:1996

List of references
See national foreword.

© BSI 10-1999


BS EN
61241-2-2:1996

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