12 ansiisa-61241-11

AMERICAN NATIONAL STANDARD

ANSI/ISA-61241-11 (12.10.04)-2006 (R2011)

Electrical Apparatus for Use in Zone 20, Zone 21 and Zone 22 Hazardous (Classified) Locations −

Protection by Intrinsic Safety “iD”

Approved 29 March 2011

Copyright International Society of Automation Provided by IHS under license with ISA

Not for ResaleNo reproduction or networking permitted without license from IHS

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ANSI/ISA-61241-11 (12.10.04)-2006 (R2011), Electrical Apparatus for Use in Zone 20, Zone 21 and Zone 22 Hazardous (Classified) Locations – Protection by Intrinsic Safety “iD” ISBN: 978-1-936007-90-5 Copyright © 2011 by ISA. Not for resale. Printed in the United States of America. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic mechanical, photocopying, recording, or otherwise), without the prior written permission of the Publisher. ISA 67 Alexander Drive P.O. Box 12277 Research Triangle Park, North Carolina 27709



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Preface

This preface, as well as all footnotes and annexes, is included for information purposes and is not part of ANSI/ISA-61241-11 (12.10.04)-2006 (R2011). This document has been prepared as part of the service of ISA toward a goal of uniformity in the field of instrumentation. To be of real value, this document should not be static but should be subject to periodic review. Toward this end, the Society welcomes all comments and criticisms and asks that they be addressed to the Secretary, Standards and Practices Board; ISA; 67 Alexander Drive; P. O. Box 12277; Research Triangle Park, NC 27709; Telephone (919) 549-8411; Fax (919) 549-8288; E-mail: [email protected]. The ISA Standards and Practices Department is aware of the growing need for attention to the metric system of units in general, and the International System of Units (SI) in particular, in the preparation of instrumentation standards. The Department is further aware of the benefits to USA users of ISA standards of incorporating suitable references to the SI (and the metric system) in their business and professional dealings with other countries. Toward this end, this Department will endeavor to introduce SI-acceptable metric units in all new and revised standards, recommended practices, and technical reports to the greatest extent possible. Standard for Use of the International System of Units (SI): The Modern Metric System, published by the American Society for Testing & Materials as IEEE/ASTM SI 10-97, and future revisions, will be the reference guide for definitions, symbols, abbreviations, and conversion factors. It is the policy of ISA to encourage and welcome the participation of all concerned individuals and interests in the development of ISA standards, recommended practices, and technical reports. Participation in the ISA standards-making process by an individual in no way constitutes endorsement by the employer of that individual, of ISA, or of any of the standards, recommended practices, and technical reports that ISA develops. CAUTION — ISA DOES NOT TAKE ANY POSITION WITH RESPECT TO THE EXISTENCE OR VALIDITY OF ANY PATENT RIGHTS ASSERTED IN CONNECTION WITH THIS DOCUMENT, AND ISA DISCLAIMS LIABILITY FOR THE INFRINGEMENT OF ANY PATENT RESULTING FROM THE USE OF THIS DOCUMENT. USERS ARE ADVISED THAT DETERMINATION OF THE VALIDITY OF ANY PATENT RIGHTS, AND THE RISK OF INFRINGEMENT OF SUCH RIGHTS, IS ENTIRELY THEIR OWN RESPONSIBILITY.

PURSUANT TO ISA’S PATENT POLICY, ONE OR MORE PATENT HOLDERS OR PATENT APPLICANTS MAY HAVE DISCLOSED PATENTS THAT COULD BE INFRINGED BY USE OF THIS DOCUMENT AND EXECUTED A LETTER OF ASSURANCE COMMITTING TO THE GRANTING OF A LICENSE ON A WORLDWIDE, NON-DISCRIMINATORY BASIS, WITH A FAIR AND REASONABLE ROYALTY RATE AND FAIR AND REASONABLE TERMS AND CONDITIONS. FOR MORE INFORMATION ON SUCH DISCLOSURES AND LETTERS OF ASSURANCE, CONTACT ISA OR VISIT WWW.ISA.ORG/STANDARDSPATENTS.

OTHER PATENTS OR PATENT CLAIMS MAY EXIST FOR WHICH A DISCLOSURE OR LETTER OF ASSURANCE HAS NOT BEEN RECEIVED. ISA IS NOT RESPONSIBLE FOR IDENTIFYING PATENTS OR PATENT APPLICATIONS FOR WHICH A LICENSE MAY BE REQUIRED, FOR CONDUCTING INQUIRIES INTO THE LEGAL VALIDITY OR SCOPE OF PATENTS, OR DETERMINING WHETHER ANY LICENSING TERMS OR CONDITIONS PROVIDED IN CONNECTION WITH SUBMISSION OF A LETTER OF ASSURANCE, IF ANY, OR IN ANY LICENSING AGREEMENTS ARE REASONABLE OR NON-DISCRIMINATORY.



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ANSI/ISA-61241-11 (12.10.04)-2006 (R2011) - 4 -

ISA REQUESTS THAT ANYONE REVIEWING THIS DOCUMENT WHO IS AWARE OF ANY PATENTS THAT MAY IMPACT IMPLEMENTATION OF THE DOCUMENT NOTIFY THE ISA STANDARDS AND PRACTICES DEPARTMENT OF THE PATENT AND ITS OWNER.

ADDITIONALLY, THE USE OF THIS DOCUMENT MAY INVOLVE HAZARDOUS MATERIALS, OPERATIONS OR EQUIPMENT. THE DOCUMENT CANNOT ANTICIPATE ALL POSSIBLE APPLICATIONS OR ADDRESS ALL POSSIBLE SAFETY ISSUES ASSOCIATED WITH USE IN HAZARDOUS CONDITIONS. THE USER OF THIS DOCUMENT MUST EXERCISE SOUND PROFESSIONAL JUDGMENT CONCERNING ITS USE AND APPLICABILITY UNDER THE USER’S PARTICULAR CIRCUMSTANCES. THE USER MUST ALSO CONSIDER THE APPLICABILITY OF ANY GOVERNMENTAL REGULATORY LIMITATIONS AND ESTABLISHED SAFETY AND HEALTH PRACTICES BEFORE IMPLEMENTING THIS DOCUMENT. THE USER OF THIS DOCUMENT SHOULD BE AWARE THAT THIS DOCUMENT MAY BE IMPACTED BY ELECTRONIC SECURITY ISSUES. THE COMMITTEE HAS NOT YET ADDRESSED THE POTENTIAL ISSUES IN THIS VERSION. The following people served as members of ISA12.10: NAME COMPANY A. Engler, Chair Det Norske Veritas DNV M. Coppler,* Managing Director Ametek Inc. S. Arnold* Ametek Drexelbrook D. Bishop David N Bishop Consultant E. Briesch Underwriters Laboratories Inc. R. Buschart Cable Tray Institute R. Fontaine FM Approvals J. Kuczka Killark E. Massey Rockwell Automation A. Page MSHA Approval & Certification Center P. Schimmoeller CSA International T. Schnaare Rosemount Inc. D. Wechsler Dow Chemical Company R. Wigg E-x Solutions International Pty. Ltd. ______ * One vote per company. The following people served as members of ISA12: NAME COMPANY T. Schnaare, Chair Rosemount Inc. W. Lawrence, Vice Chair FM Approvals M. Coppler, Managing Director Ametek Inc. N. Abbatiello Optimation Technology D. Ankele Underwriters Laboratories Inc. A. Ballard Crouse Hinds Division of Cooper Industries D. Bishop David N Bishop Consultant H. Bockle R. Stahl Inc. K. Boegli Phoenix Contact Inc. D. Burns Shell Exploration & Production Company R. Buschart Cable Tray Institute R. Cardinal Bently Nevada LLC C. Casso Nabors Industries J. Cospolich Waldemar S Nelson & Company Inc. S. Czaniecki Intrinsic Safety Concepts Inc.



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J. Dolphin PSC Solutions T. Dubaniewicz NIOSH U. Dugar Mobil Chemical Company A. Engler Det Norske Veritas DNV W. Fiske Intertek Testing Services G. Garcha GE Energy D. Hohenstein Pepperl + Fuchs Inc. D. Jagger Bifold-Fluid Power P. Jonscher Adalet PLM F. Kent Honeywell Inc. P. Kovscek Industrial Scientific Corporation J. Kuczka Killark B. Larson Turck Inc. E. Massey Rockwell Automation A. Mobley 3M Company S. Nguyen Siemens Milltronics Ltd. A. Page MSHA Approval & Certification Center P. Schimmoeller CSA International R. Seitz Artech Engineering D. Wechsler Dow Chemical Company R. Wigg E-x Solutions International Pty. Ltd. This standard was approved for publication by the ISA Standards and Practices Board on 13 July 2006. NAME COMPANY I. Verhappen, Vice President Syncrude Canada Limited F. Amir E I Du Pont Company D. Bishop David N Bishop Consultant M. Coppler Ametek Inc. B. Dumortier Schneider Electric W. Holland Consultant E. Icayan ACES Inc. A. Iverson Ivy Optiks R. Jones Consultant K. Lindner Endress + Hauser Process Solutions AG V. Maggioli Feltronics Corporation T. McAvinew Jacobs Engineering Group A. McCauley Chagrin Valley Controls Inc. G. McFarland Emerson Process Mgmt. Pwr & Water Solutions R. Reimer Rockwell Automation N. Sands E I du Pont H. Sasajima Yamatake Corporation T. Schnaare Rosemount Inc. J. Tatera Tatera & Associates Inc. R. Webb Robert C Webb PE W. Weidman Worley Parsons J. Weiss KEMA Inc. M. Widmeyer Stanford Linear Accelerator Center M. Zielinski Emerson Process Management The following members of ISA12.10 reaffirmed this standard.

NAME COMPANY A. Engler, Chair Det Norske Veritas DNV M. Coppler, Managing Director Ametek Inc.



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ANSI/ISA-61241-11 (12.10.04)-2006 (R2011) - 6 -

S. Arnold Ametek Drexelbrook D. Bishop David N Bishop Consultant S. Blais EGS Electrical Group E. Briesch Underwriters Laboratories Inc. R. Fontaine FM Approvals J. Kuczka Killark E. Leubner Cooper Crouse-Hinds R. Masek CSA International E. Massey Baldor Electric Company T. Schnaare Rosemount Inc. D. Wechsler Dow Chemical Company R. Wigg E-x Solutions International Pty. Ltd. The following members of ISA12 reaffirmed this standard.

NAME COMPANY T. Schnaare, Chair Rosemount Inc. W. Lawrence, Vice Chair FM Approvals LLC M. Coppler, Managing Director Ametek Inc. N. Akhtar Pakistan Refinery Ltd. D. Ankele Underwriters Laboratories Inc. A. Ballard Consultant R. Batra Chevron Corporation K. Boegli Phoenix Contact Inc. D. Burns Shell P&T – Innovation / R&D C. Casso Nabors Industries S. Czaniecki Intrinsic Safety Concepts Inc. J. Dolphin PSC Solutions M. Dona Santos Ltd. T. Dubaniewicz NIOSH A. Engler Det Norske Veritas DNV W. Fiske Intertek G. Garcha GE Energy C. Huntley MSHA A&CC D. Jagger Bifold-Fluid Power F. Kent Honeywell Inc. P. Kovscek Industrial Scientific Corporation J. Kuczka Killark E. Leubner Cooper Crouse-Hinds S. Leverington Zone Safe Solutions N. Ludlam FM Approvals Ltd. K. Mansoor Siemens Industry Inc. R. Masek CSA International E. Massey Baldor Electric Company J. Miller Detector Electronics Corporation A. Page Consultant R. Seitz Artech Engineering R. Sierra USCG M. Spencer Columbia Gas Transmission J. Thomas Schlumberger D. Wechsler Dow Chemical Company R. Wigg E-x Solutions International Pty. Ltd.



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This standard was reaffirmed by the Standards and Practices Board on 10 February 2011.

NAME COMPANY D. Dunn, S&P Department VP Aramco Services Co. R. Bartusiak ExxonMobil Research & Engineering P. Brett Honeywell Inc. J. Campbell ConocoPhillips M. Coppler Ametek Inc. E. Cosman The Dow Chemical Company B. Dumortier Schneider Electric J. Federlein Federlein & Associates Inc. J. Gilsinn NIST/MEL E. Icayan ACES Inc. J. Jamison EnCana Corporation Ltd. K. P. Lindner Endress + Hauser Process Solutions AG V. Maggioli Feltronics Corp. T. McAvinew Jacobs Engineering R. Reimer Rockwell Automation S. Russell Valero Energy Corp. N. Sands DuPont H. Sasajima Yamatake Corp. T. Schnaare Rosemount Inc. J. Tatera Tatera & Associates Inc. I. Verhappen Industrial Automation Networks Inc. R. Webb ICS Secure LLC W. Weidman Consultant J. Weiss Applied Control Solutions LLC M. Widmeyer Kahler Engineering Inc. M. Wilkins Yokogawa IA Global Marketing D. Zetterberg Chevron Energy Technology Company



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CONTENTS

1 Scope .......................................................................................................................... 13 2 Normative References .................................................................................................. 15 3 Terms and definitions ................................................................................................... 15 4 Grouping and classification of intrinsically safe apparatus and associated apparatus ..... 15 5 Categories Levels of protection of electrical apparatus.................................................. 16 6 Apparatus construction................................................................................................. 16

6.1 Enclosures .......................................................................................................... 16 6.2 Temperatures of apparatus immersed in dust....................................................... 16

6.2.1 General ................................................................................................... 16 6.2.2 Supplementary requirements for apparatus immersed in dust ................... 16 6.2.3 Standardized dust immersion temperature test ......................................... 17 6.2.4 Wiring within apparatus............................................................................ 18 6.2.5 Printed circuit wiring ................................................................................ 18 6.2.6 Unenclosed circuits ................................................................................. 18

6.3 Facilities for connection of external circuits .......................................................... 18 6.3.1 Terminals ................................................................................................ 18 6.3.2 Plugs and sockets ................................................................................... 18 6.3.3 Determination of maximum external inductance to resistance ratio

(Lo/Ro) for resistance limited power source .............................................. 18 6.3.4 Permanently connected cables................................................................. 18

6.4 Separation distances ........................................................................................... 18 6.5 Protection against polarity reversal ...................................................................... 18 6.6 Earth conductors, connections and terminals ....................................................... 18 6.7 Encapsulation used for exclusion of explosive dust potentially explosive

atmosphere ......................................................................................................... 18 7 Components on which intrinsic safety depends ............................................................. 19

7.1 Rating of components.......................................................................................... 19 7.2 Connectors for internal connections, plug-in cards and components ..................... 19 7.3 Fuses.................................................................................................................. 19 7.4 Primary and secondary cells and batteries ........................................................... 19 7.5 Semiconductors .................................................................................................. 19 7.6 Failure of components and connections ............................................................... 19 7.7 Piezo-electric devices.......................................................................................... 19

8 Infallible components, infallible assemblies of components and infallible connections .... 19 9 Diode safety barriers .................................................................................................... 19 10 Type verifications, assessments and type tests ............................................................. 19

10.1 Spark ignition assessment ................................................................................... 19 10.2 Temperature tests ............................................................................................... 20 10.3 Voltage tests ....................................................................................................... 20 10.4 Small component ignition test .............................................................................. 20 10.5 Determination of parameters of loosely specified components .............................. 20



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10.6 Tests for cells and batteries................................................................................. 20 10.7 Mechanical test ................................................................................................... 20

10.7.1 Casting compound ................................................................................... 20 10.7.2 Partitions ................................................................................................. 20

10.8 Tests for apparatus containing piezoelectric devices ............................................ 20 10.9 Type tests for diode safety barriers and safety shunts .......................................... 21 10.10 Cable pull test ..................................................................................................... 21

11 Routine verifications and tests ...................................................................................... 21 12 Marking........................................................................................................................ 21

12.1 General............................................................................................................... 21 12.2 Marking of connection facilities ............................................................................ 21 12.3 Control drawings ................................................................................................. 22

13 Documentation ............................................................................................................. 22 Annex A (normative) Spark test apparatus for intrinsically safe circuits ................................ 25 Annex B (informative) Measurement of creepage distances, clearances and separation ........... distances through casting compound and through solid insulation........................................ 25 Annex C (normative) Encapsulation .................................................................................... 25 Annex D (informative) US national deviations ...................................................................... 25

Table A ⎯ Exclusion of specific clauses of ANSI/ISA-61241-0 (12.10.02)-2006 ................... 13 Table 1 – Permitted dissipation within a component ............................................................ 17



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FOREWORD

All text of IEC 61241-11:2005 including Corrigendum 1 is included in this document. U.S. National Deviations are shown by strikeout through deleted text and underline under added text. There are four annexes in this standard. Annex D is informative and is not considered part of this standard. Annexes A, B and C are normative and are considered part of this standard.



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1 Scope

This standard part of IEC 61241 specifies requirements for the construction and testing of intrinsically safe apparatus intended for use in an explosive dust atmosphere potentially explosive dust cloud or dust layer environments and for associated apparatus that is intended for connection to intrinsically safe circuits which enter such atmospheres environments.

This standard supplements the general requirements of ANSI/ISA-61241-0 IEC 61241-0: except as indicated in Table A the following list. Where a requirement of this standard conflicts with a requirement of ANSI/ISA-61241-0 the requirements of this standard shall take precedence.

NOTE Intrinsically safe and associated intrinsically safe apparatus Apparatus utilized in systems willshould shall meet the requirements of IEC ANSI/ISA-RP12.06.01 IEC 60079-25.

If associated apparatus is protected by a type of protection listed in ANSI/ISA-61241-0 IEC 61241-0 or ANSI/ISA-60079-0 IEC 60079-0 then the requirements of that method of protection together with the relevant standards, parts of ISA-61241-X IEC 61241-0 or ANSI/ISA-60079-X, IEC 60079 also apply to the associated apparatus. The list of exclusions in Table A which follows is directly applicable to associated apparatus intended for use in situations where there is no explosive dust potentially hazardous atmosphere and in other circumstances should be used in combination with the requirements of the other methods of protection.

Table A ― Exclusion of specific clauses of ANSI/ISA-61241-0 (12.10.02)-2006

Clause or subclause of IEC ANSI/ISA-61241-0 Intrinsically safe apparatus

Associated apparatus

4.1 General Applies Applies

4.2 Principles for design and testing of apparatus for use in Zone 20

Applies Excluded

4.3 Opening enclosures Applies Excluded

4.4 Environmental conditions Applies Excluded

5.1 Maximum surface temperature Applies Excluded

5.2 Maximum surface temperature with respect to dust layers above 50 mm

Applies Excluded

5.3 Ambient temperature Applies Applies

6.1 Non-metallic enclosures and non-metallic parts of enclosures

Applies Excluded

6.1.1 Material specification Applies Excluded

6.1.2 Plastic materials Applies Excluded

6.1.3 Verification of compliance Applies Excluded

6.1.4 Thermal endurance Applies Excluded

6.1.5 Electrostatic charges Applies Excluded

6.2 Enclosures containing light metals Applies Excluded

6.2.1 Composition Applies Excluded

6.2.2 Threaded holes Excluded Excluded

7 Fasteners Excluded Excluded

8 Interlocking devices Excluded Excluded

9 Bushings Excluded Excluded



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Clause or subclause of IEC ANSI/ISA-61241-0 Intrinsically safe apparatus

Associated apparatus

10 Materials used for cementing Applies Excluded

11 Ex components Applies Excluded

12 Connection facilities and terminal compartments Excluded Excluded

13 Connection facilities for earthing or bonding conductors

Excluded Excluded

14 Cable and conduit entries Entries into Enclosures Applies Excluded

15 Radiating equipment Applies Excluded

16 Rotating electrical machines Excluded Excluded

17 Switchgear Excluded Excluded

18 Fuses Excluded Excluded

19 Plugs and sockets Excluded Excluded

20 Luminaires Excluded Excluded

21 Caplights, caplamps and handlamps handlights Excluded Excluded

22 Apparatus incorporating cells and batteries Applies Excluded

23.1 to 23.3

Verification and tests Applies Applies

23.4.1 General Applies Excluded

23.4.2.1 Test for resistance to impact Applies Excluded

23.4.2.2 Drop test Applies Excluded

23.4.2.3 Verification a Applies Excluded

23.4.3 Test for dust exclusion (degree of protection) Applies Excluded

23.4.4 Torque test for bushings in enclosures for use in Zone 20 or 21 Excluded Excluded

23.4.5.1 Measurement for maximum surface temperature Applies Excluded

23.4.5.2 Measurement for surface temperature under excess layer Applies Excluded

23.4.5.3 Temperature control Applies Excluded

23.4.6 Thermal shock tests Applies Excluded

23.4.7.1 to 23.4.7.5

Tests of non-metallic enclosures or of non-metallic parts of apparatus for use in Zone 20 or 21

Excluded Excluded

23.4.7.6 Mechanical tests Applies Excluded

23.4.7.7 Surface resistivity test Applies Excluded

27 Clamping tests of cable entries for non-armoured and braided cables Excluded Excluded

28 Clamping tests of cable entries for armoured cables Excluded Excluded

29 Marking Applies Applies

30 Examples of marking Applies Applies

a IEC ANSI/ISA-61241-0 pass criteria apply.



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This standard part of IEC 61241 is applicable to electrical apparatus in which the electrical circuits themselves are incapable of causing an explosion in the surrounding explosive dust atmosphere. combustible dust environment. In other circumstances, associated apparatus should be used in combination with the requirements of the other methods of protection listed in ANSI/ISA-61241-0 IEC 61241-0.

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 60079-0:1997, Electrical apparatus for potentially explosive atmospheres – Part 0: General requirements

ANIS/ISA-60079-0 (12.00.01)-2005, Electrical Apparatus for Use in Class I, Zones 0, 1 & 2 Hazardous (Classified) Locations: General Requirements

IEC 60079-11, Electrical apparatus for explosive gas atmospheres – Part 11: Intrinsic safety “I”

ANSI/ISA-60079-11 (12.02.01)-2002, Electrical Apparatus for Use in Class I, Zones 0, 1 & 2 Hazardous (Classified) Locations - Intrinsic Safety "i"

IEC 60079-25, Electrical apparatus for explosive gas atmospheres - Part 25: Intrinsically safe systems

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

IEC 61241-0:2004, Electrical apparatus for use in the presence of combustible dust - Part 0: General requirements

ANSI/ISA-61241-0 (12.10.02)-2006, Electrical Apparatus for Use in Zone 20, Zone 21 and Zone 22 Hazardous (Classified) Locations - General Requirements

IEC 61241-1, Electrical apparatus for use in the presence of combustible dust – Part 1: Protection by enclosures “tD”

ANSI/ISA-61241-1 (12.10.03)-2006, Electrical Apparatus for Use in Zone 20, Zone 21 and Zone 22 Hazardous (Classified) Locations- Protection by Enclosures “tD”

3 Terms and definitions

For the purposes of this document, the terms and definitions contained in ANSI/ISA-61241-0 IEC 61241-0, ANSI/ISA-60079-0 IEC 60079-0 and ANSI/ISA-60079-11 IEC 60079-11 apply except that where the term “explosive gas atmosphere” is used it shall be interpreted as meaning “explosive dust atmosphere” “combustible dust environment”.

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 ANSI/ISA-61241-0 IEC 61241-0.



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5 Categories Levels of protection of electrical apparatus

Clause 5 of ANSI/ISA-60079-11 IEC 60079-11 applies together with the following requirement:

Intrinsically safe apparatus and intrinsically safe parts of associated apparatus shall be placed in level of protection “iaD” or “ibD”.

Intrinsically safe apparatus complying with the requirements of 5.2 of ANSI/ISA-60079-11 and this standard shall be marked “iaD”.

Intrinsically safe apparatus complying with the requirements of 5.3 of ANSI/ISA-60079-11 and this standard shall be marked “ibD”.

Apparatus shall, at a minimum, meet the spark ignition energy level requirements for Group IIB apparatus.

6 Apparatus construction

6.1 Enclosures

In principle, intrinsically safe apparatus does not need an enclosure as the method of protection is embodied within the circuits. However, where intrinsic safety can be impaired by access to conducting parts, for example if dust of any type can bridge infallible creepage distances, an enclosure of at least IP6x in accordance with IEC 60529 and as required by IEC 61241-1 shall be provided. In all other circumstances, the degree of protection provided by the enclosure that is required will vary according to the intended purpose of the apparatus. Parts of apparatus not within an enclosure having a degree of protection of at least IP6x that are encapsulated to a depth of at least 1 mm and meet the requirements of 6.7 shall be considered to be adequately protected against dust contamination. Where parts of a circuit are not protected by an enclosure or encapsulation as indicated, for example uninsulated sensor circuits in direct contact with the explosive dust atmosphere, they shall be assessed or tested in accordance with this standard assuming that all spacings do not meet the creepage and clearance requirements of 6.4.

The enclosure construction and/or the encapsulation shall be recorded in the definitive documentation (see Clause 13).

6.2 Temperatures of apparatus immersed in dust

6.2.1 General Apparatus shall meet the requirements of 6.2 of ANSI/ISA-60079-11, taking into consideration the requirements of 5.2 and 5.3 of ANSI/ISA-60079-11 applied as appropriate for the required level of protection, and 6.2.2.1 of this standard. 6.2.2 Supplementary requirements for apparatus immersed in dust

6.2.2.1 General

Whenever possible intrinsically safe apparatus for dusts should be enclosed. This clause applies to such apparatus as temperature sensors or parts of measuring devices which cannot be enclosed and are intended for immersion in a dust. All temperatures shall be measured or assessed under the most onerous fault conditions in this standard but without applying factors of



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safety to the current, voltage or power. The following requirements are applicable to apparatus used with dusts having a minimum ignition temperature of a 5 mm layer of not less than 210 °C.

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 that current which flows under conditions of “iaD” or “ibD” 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.

6.2.2.2 Apparatus and component temperature

Apparatus is considered suitable for total immersion, or being subjected to an uncontrolled layer of such dust, if it conforms to one of the following:

a) the matched power dissipation in any component shall be in accordance with Table 1.

Table 1 – Permitted dissipation within a component

Maximum ambient temperature °C 40 70 100

Permitted dissipation mW 750 650 550

b) Where intrinsically safe electrical circuits are exposed to, or directly immersed in a flammable

dust with a dust layer smouldering temperature greater than 200 °C, no testing of temperature rise is required provided that at the point of contact the available power is less than 750 mW and the short-circuit current is less than 250 mA.

c) The apparatus shall satisfactorily comply with the standardized dust immersion test specified in 6.2.3. Apparatus which complies shall be considered as suitable for use at the maximum stated ambient temperature with any combustible dust having an ignition temperature no lower than 210 °C.

The maximum surface temperature of all components, enclosures and the wiring in contact with combustible dust atmospheres and determined during testing shall be marked on the product in accordance with 29.2 of ANSI/ISA-61241-0.

6.2.3 Standardized dust immersion temperature test

This test and the associated requirements are under further consideration.

Intrinsically safe apparatus having an enclosure meeting the requirements for at least IP6x in accordance with IEC 60529 shall be tested in accordance with 8.2.2 of ANSI/ISA-61241-1 with the temperature measurement made on the outside of the enclosure there shall be no evidence of charring of the dust.

Intrinsically safe apparatus having an enclosure which does not meet the requirements for IP6x in accordance with IEC 60529 shall be tested with a 12.5 mm layer of dust paste applied over the circuit and shall additionally comply with the requirements of 6.2.6. Temperature tests shall be conducted in accordance with 23.4.5.1 of ANSI/ISA-61241-0 with the temperature measurements made on the components and wiring, there shall be no evidence of charring of the dust.



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ANSI/ISA-61241-11 (12.10.04)-2006 (R2011) - 18 -

6.2.4 Wiring within apparatus

As for 6.2.2 of IEC 60079-11.

6.2.5 Printed circuit wiring

As for 6.2.3 of IEC 60079-11.

6.2.6 Unenclosed circuits

Circuits of intrinsically safe apparatus intended to be in direct contact with the explosive dust atmosphere shall be capable of meeting the requirements for level of protection “iaD” and at least the spark ignition requirements for Group IIB apparatus. In this case, it shall be assumed that, unless encapsulated in accordance with 6.7, all spacings do not meet the creepage and clearance distance requirements specified in 6.4 and that all connections between intrinsically safe circuits or earthed parts and conductors are in the most unfavorable condition.

6.3 Facilities for connection of external circuits

6.3.1 Terminals

As for 6.3.1 of ANSI/ISA-60079-11 IEC 60079-11.

6.3.2 Plugs and sockets


6.3.3 Determination of maximum external inductance to resistance ratio (Lo/Ro) for resistance limited power source


6.3.4 Permanently connected cables


6.4 Separation distances

As for 6.4 of ANSI/ISA-60079-11 IEC 60079-11.

6.5 Protection against polarity reversal


6.6 Earth conductors, connections and terminals


6.7 Encapsulation used for exclusion of explosive dust potentially explosive atmosphere




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- 19 - ANSI/ISA-61241-11 (12.10.04)-2006 (R2011)

7 Components on which intrinsic safety depends

7.1 Rating of components


7.2 Connectors for internal connections, plug-in cards and components


7.3 Fuses


7.4 Primary and secondary cells and batteries


7.5 Semiconductors


7.6 Failure of components and connections

As for 7.6 of ANSI/ISA-60079-11 IEC 60079-11:1999.

7.7 Piezo-electric devices


8 Infallible components, infallible assemblies of components and infallible connections

As for Clause 8 of ANSI/ISA-60079-11 IEC 60079-11.

9 Diode safety barriers


10 Type verifications, assessments and type tests

10.1 Spark ignition assessment

If testing is required this should be in accordance with ANSI/ISA-60079-11 IEC 60079-11:1999 using Group IIB gases.

A circuit may be exempted from a type test with the spark-test apparatus if its structure and its electrical parameters are sufficiently well defined for its safety to be deduced from the Group IIB reference curves figures A.1 to A.6 or tables A.1 and A.2 of ANSI/ISA-60079-11 by the methods described in Annex A of ANSI/ISA-60079-11.



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10.2 Temperature tests


10.3 Voltage tests


10.4 Small component ignition test

As for 10.7 of IEC 60079-11:1999.

10.5 Determination of parameters of loosely specified components


10.6 Tests for cells and batteries


10.7 Mechanical test

10.7.1 Casting compound

A force of 30 N shall be applied perpendicular to the surface of the casting compound with a 6 mm diameter flat ended metal rod for 10 s. No damage to or permanent deformation of the encapsulation or movement greater than 1 mm shall occur.

Where a free surface of casting compound occurs, in order to ensure that the compound is rigid but not brittle, the following impact test shall be carried out on the surface of the casting compound at (20 ± 10) °C using the test apparatus described in Annex C of ANSI/ISA-60079-0 IEC 60079-0:1997. For all applications a minimum impact energy of 2 J a 1kg test mass falling from a height of 0.2m shall be used.

The casting compound shall remain intact and no permanent deformation shall occur. Minor surface cracks shall be ignored.

10.7.2 Partitions


10.8 Tests for apparatus containing piezoelectric devices

Measure both the capacitance of the device and also the voltage appearing across it when any part of the apparatus which is accessible in service is impact tested in accordance with the 'high' column of Table 84 in IEC ANSI/ISA-60079-0 IEC 60079-0 carried out at (20 ± 10) °C using the test apparatus in Annex D of ANSI/ISA-60079-0 IEC 60079-0. For the value of voltage, the higher figure of two tests on the same sample shall be used.

When the apparatus containing the piezoelectric device includes a guard to prevent a direct physical impact, the impact test shall be carried out on the guard with both it and the apparatus mounted as intended by the manufacturer.



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- 21 - ANSI/ISA-61241-11 (12.10.04)-2006 (R2011)

The maximum energy stored by the capacitance of the crystal at the maximum measured voltage shall not exceed 0,25 mJ. Where the electrical output of the piezoelectric device is limited by protective components (including guards), these components shall not be damaged by the impact in such a way as to allow the type of protection to be invalidated.

Where it is necessary to protect the apparatus from external physical impact in order to prevent the impact energy exceeding these values, details of the requirements shall be specified as special conditions of for safe use and the apparatus shall be marked with an X in accordance with 29.2 i) of ANSI/ISA-61241-0.

10.9 Type tests for diode safety barriers and safety shunts


10.10 Cable pull test


11 Routine verifications and tests


12 Marking

12.1 General

Intrinsically safe apparatus and associated apparatus shall carry at least the minimum marking specified in 29.2 of ANSI/ISA-61241-0, IEC 61241-0 and 12.2 of this standard and a reference to the Control Drawing when required by 12.3. The marking of the serial number may be achieved by using a date or batch number code which is sufficient to ensure traceability for quality control purposes.

NOTE 1 The serial number marking may be separate from the other marking.

For associated apparatus the symbol AEx iaD or AEx ibD (or iaD or ibD if AEx is already marked) shall be enclosed in square brackets.

All relevant parameters should be marked, e.g. Um, Li, Ci, Lo, Co, wherever practicable.

NOTE 2 Standard symbols for marking and documentation are given in Clause 3 of ANSI/ISA-60079-11 IEC 60079-11.

Practical considerations may restrict or preclude the use of italic characters or of subscripts and a simplified presentation may be used, for example Uo rather than Uo.

12.2 Marking of connection facilities

Connection facilities, terminal boxes, plugs and sockets of intrinsically safe apparatus and associated apparatus shall be clearly marked and shall be clearly identifiable. Where a colour is used for this purpose, it shall be light blue.



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ANSI/ISA-61241-11 (12.10.04)-2006 (R2011) - 22 -

Where parts of an apparatus or different pieces of apparatus are interconnected using plugs and sockets, these plugs and sockets shall be identified as containing only intrinsically safe circuits. Where a colour is used for this purpose it shall be light blue.

In addition, sufficient and adequate marking shall be provided to ensure correct connection for the continued intrinsic safety of the whole.

NOTE It may be necessary to include additional labels, e.g. on or adjacent to plugs and sockets, to achieve this. If clarity of intention is maintained the apparatus label may suffice.

The following are examples of marking:

a) Self-contained intrinsically safe apparatus

C TOME LTD PAGING RECEIVER TYPE 3 AEx iaD 20 T135°C -25 °C < Ta < +50 °C ACB Ex01**** Serial No. xxxx

b) Intrinsically safe apparatus designed to be connected to other apparatus

M HULOT TRANSDUCTEUR TYPE 12 AEx ibD 21 T120°C ACB No: Ex01**** Li: 10 µH Ci: 1200 pF Ui: 28 V Ii: 250 mA Pi: 1,3 W

c) Associated apparatus

J SCHMIDT A.G. STROMVERSORGUNG TYP 4 [AEx ibD] ACB No: Ex01*.*** Um: 250 V Po: 0.9 W Io: 150 mA Uo: 24 V Lo: 14.2 mH Co: 0.93 µF

12.3 Control drawings A control drawing shall be provided for all intrinsically safe apparatus or associated apparatus that requires connection to other circuits or apparatus. See 12.3 of ANSI/ISA-60079-11.

13 Documentation

As for Clause 23 13 of ANSI/ISA-61241-0 IEC 61241-0:2004.



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- 23 - ANSI/ISA-61241-11 (12.10.04)-2006 (R2011)

In addition the documentation shall specify the maximum surface temperature of the apparatus and the conditions under which the temperature was determined. For example "maximum surface temperature 135 °C derived from the corn dust immersion temperature test of 6.2.3".

Where the apparatus is designed for use in a range of temperatures other than -20 °C to +40 °C the permitted temperature range shall be specified in the documentation.

The category level of protection (iaD or ibD) shall also be specified.

Any other information necessary to ensure a safe use of the apparatus shall also be included.



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- 25 - ANSI/ISA-61241-11 (12.10.04)-2006 (R2011)

Annex A (normative)

Spark test apparatus for intrinsically safe circuits

See Annex B of IECANSI/ISA-60079-11

Annex B (informative)

Measurement of creepage distances, clearances and separation distances through casting compound and through solid insulation

See Annex C of IECANSI/ISA-60079-11

Annex C (normative)

Encapsulation

See Annex D of IECANSI/ISA-60079-11



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- 27 ANSI/ISA-61241-11 (12.10.04)-2006 (R2011)

Annex D (informative)

US national deviations The text of Annex D has been added; the underlining has been omitted for clarity.

Clause Differences to IEC 61241-11:2005

1 A title has been added to the list of specific clauses of ANSI/ISA-61241-0 excluded by this standard. The table has been modified to align with ANSI/ISA-61241-0.

5 The term “categories” has been replaced by “levels of protection”.

5 Requirements for levels of protection “iaD” and “ibD” have been added.

6.2 Requirements for the temperatures of apparatus not immersed in dust have been added and the temperature requirements for apparatus immersed in dust clarified.

6.2 Temperature requirements for potentiometers have been deleted as these are already in the referenced ANSI/ISA-60079-11.

6.2.3 A “Standardized dust immersion temperature test” has been added.

6.2.4 Subclause 6.2.4 deleted as it is already addressed by the general requirement of 6.2.1

6.2.5 Subclause 6.2.5 deleted as it is already addressed by the general requirement of 6.2.1

6.7 The clause title has been altered to reflect the subject matter of this standard.

10.1 An exemption to allow intrinsically safe circuits to be deduced from the data in Annex A of ANSI/ISA-60079-11 has been added.

10.4 Subclause 10.4 deleted as the small component ignition is a characteristic applied to gases and vapors but not dusts.

10.7.1 Impact test requirements have been modified to align with the referenced ANSI/ISA-60079-0.

12.3 Requirement for a Control Drawing and a control drawing reference to be marked on the apparatus have been added.

Annex Titles have been added to Annexes A, B and C.



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Developing and promulgating sound consensus standards, recommended practices, and technical reports is one of ISA’s primary goals. To achieve this goal the Standards and Practices Department relies on the technical expertise and efforts of volunteer committee members, chairmen and reviewers.

ISA is an American National Standards Institute (ANSI) accredited organization. ISA administers United States Technical Advisory Groups (USTAGs) and provides secretariat support for International Electrotechnical Commission (IEC) and International Organization for Standardization (ISO) committees that develop process measurement and control standards. To obtain additional information on the Society’s standards program, please write:

ISA Attn: Standards Department 67 Alexander Drive P.O. Box 12277 Research Triangle Park, NC 27709

ISBN: 978-1-936007-90-5



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12 ansiisa-61241-11

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