Bsi bs en 61241 2 2 1996 (1999)

00677390 PDF BRITISH STANDARD BS EN 61241 2 2 1996 Electrical apparatus for use in the presence of combustible dust — Part 2 Test methods — Section 2 2 Method for determining the electrical resistivit[.]

BRITISH STANDARD BS EN

61241-2-2:1996

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

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

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:

Department of the Environment (Building Research Establishment)

Amendments issued since publication

Amd No Date Comments

BS EN 61241-2-2:1996

Contents

Page

Annex ZA (normative) Normative references to international publications with their corresponding European publications 6

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

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.

Cross-reference

Publication referred to Corresponding British Standard

ISO 4225:1980a BS 6069 Characterization of air quality

Part 2:1994 Glossary

a ISO 4225:1980 has been superseded by ISO 4225:1994.

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

EUROPEAN STANDARD

NORME EUROPÉENNE

EUROPÄISCHE NORM

EN 61241-2-2 August 1995

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

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:

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

— 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

EN 61241-2-2:1995

Introduction

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

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 Definitions

For the purpose of this standard 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

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).

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

6 Procedure

6.1 Preliminary measurement

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

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

Calculate the resistivity for each value of the applied voltage

7 Test report

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

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.

EN 61241-2-2:1995

Figure 1 — Test cell

Figure 2 — Circuit diagram

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.

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 — —

BS EN 61241-2-2:1996

© BSI 10-1999

List of references

See national foreword