1、 AMERICAN NATIONAL STANDARD ANSI/ISA-60079-25 (12.02.05)-2011 Explosive Atmospheres - Part 25: Intrinsically safe electrical systems Approved 2 December 2011 ANSI/ISA-60079-25 (12.02.05)-2011 Explosive Atmospheres - Part 25: Intrinsically safe electrical systems ISBN: 978-1-937560-17-1 Copyright 201
2、1 by IEC and ISA, the International Society of Automation. All rights reserved. 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, recor
3、ding, or otherwise), without the prior written permission of the Publisher. ISA 67 Alexander Drive P.O. Box 12277 Research Triangle Park, North Carolina 27709 USA - 3 - ANSI/ISA-60079-25 (12.02.05)-2011 Preface This preface, as well as all footnotes and annexes, is included for information purposes
4、and is not part of ANSI/ISA-60079-25 (12.02.05)-2011. 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 Soci
5、ety 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: standardsisa.org. The ISA Standards and Practice
6、s 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
7、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 greates
8、t extent possible. Standard for Use of the International System of Units (SI): The Modern Metric System, published by the American Society for Testing figures to be deleted are marked with the overlay “X.“ There are ten annexes in this standard. Annexes B, D, G and I are normative and are considered
9、 part of this standard. Annexes A, B, E, F, H and J are informative and are not considered part of this standard. This page intentionally left blank. - 11 - ANSI/ISA-60079-25 (12.02.05)-2011 1 Scope This part of IEC 60079 standard contains the specific requirements for construction and assessment of
10、 intrinsically safe electrical systems, type of protection “i”, intended for use, as a whole or in part, in Class I, Zone 0, 1, or 2, or Zone 20, 21, or 22 hazardous (classified) locations as defined by the National Electrical Code(NEC), ANSI/NFPA 70in locations in which the use of Group I, II or II
11、I apparatus is required. NOTE 1 This standard is intended for use by the designer of the system who may be a manufacturer, a specialist consultant or a member of the end-users staff. This standard supplements and modifies the general requirements of ANSI/ISA-60079-0 and ANSI/ISA-61241-0 IEC 60079-0
12、and the intrinsic safety standard ANSI/ISA-60079-11 and ANSI/ISA-61241-11 IEC 60079-11. Where a requirement of this standard conflicts with a requirement of ANSI/ISA-60079-0, ANSI/ISA-60079-11, ANSI/ISA-61241-0IEC 60079-0 or ANSI/ISA-61241-11 IEC 60079-11, the requirement of this standard takes prec
13、edence. This standard supplements IEC 60079-11, the requirements of which apply to electrical apparatus used in intrinsically safe electrical systems. The installation requirements of Group II or Group III systems designed in accordance with this standard are specified in the National Electrical Cod
14、e ANSI/NFPA 70 IEC 60079-14. NOTE 2 Group I installation requirements are presently not provided in IEC 60079-14. 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 refere
15、nces, the latest edition of the referenced document (including any amendments) applies. IEC 60060-1, High-voltage test techniques Part 1: General definitions and test requirements IEC 60079-0, Explosive atmospheres Part 0: Equipment General requirements ANSI/ISA-60079-0 (12.00.01)-2009, Explosive at
16、mospheres Part 0: Equipment General Requirements IEC 60079-11:2006, Explosive atmospheres Part 11: Equipment protection by intrinsic safety “i” ANSI/ISA-60079-11 (12.02.01), Explosive Atmospheres Part 11: Equipment protection by intrinsic safety “i” IEC 60079-14:2007, Explosive atmospheres Part 14:
17、Electrical installations design, selection and erection IEC 60079-15, Electrical apparatus for explosive gas atmospheres Part 15: Construction, test and marking of type of protection “n“ electrical apparatus ANSI/ISA-60079-15 (12.12.02)-2009 Electrical Apparatus for Use in Class I, Zone 2 Hazardous
18、(Classified) Locations: Type of Protection “n“ IEC 60079-27:2008, Explosive atmospheres Part 27: Fieldbus intrinsically safe concept (FISCO) ANSI/ISA-60079-27 (12.02.04)-2006, Fieldbus Intrinsically Safe Concept (FISCO) and Fieldbus Non-Incendive Concept (FNICO) ANSI/ISA-60079-25 (12.02.05)-2011 - 1
19、2 - IEC 61158-2, Industrial communication networks Fieldbus specifications Part 2: Physical layer specification and service definition IEC 61241-0, Electrical apparatus for use in the presence of combustible dust Part 0: General requirements ANSI/ISA-61241-0(12.10.02), Electrical Apparatus for Use i
20、n Zone 20, Zone 21 and Zone 22 Hazardous (Classified) Locations General Requirements IEC 61241-11, Electrical apparatus for use in the presence of combustible dust Part 11: Protection by intrinsic safety iD ANSI/ISA-61241-11(12.10.04), Electrical Apparatus for Use in Zone 20, 21, and Zone 22 Hazardo
21、us (Classified) Locations Protection by Intrinsic Safety “iD“ ANSI/NFPA 70:2011, National Electrical Code 3 Terms, definitions and abbreviations 3.1 Terms and definitions For the purposes of this document, the following terms and definitions, specific to intrinsically safe electrical systems, apply.
22、 They supplement the terms and definitions which are given in ANSI/ISA-60079-0, ANSI/ISA-60079-11, ANSI/ISA-61241-0 IEC 60079-0 and ANSI/ISA-61241-11 IEC 60079-11. 3.1.1 intrinsically safe electrical system assembly of interconnected items of electrical apparatus, described in a descriptive system d
23、ocument, in which the circuits or parts of circuits, intended to be used in an explosive atmosphere, are intrinsically safe circuits 3.1.2 listed certified listed intrinsically safe electrical system intrinsically safe electrical system conforming to 3.1.1 listed against for which a certificate has
24、been issued confirming that the electrical system complies with ANSI/ISA-60079-25 IEC 60079-25 3.1.3 uncertified intrinsically safe electrical system intrinsically safe electrical system conforming to 3.1.1 for which the knowledge of the electrical parameters of the items of certified intrinsically
25、safe electrical apparatus, certified associated apparatus, simple apparatus and the knowledge of the electrical and physical parameters of the interconnecting wiring permit the unambiguous deduction that intrinsic safety is preserved 3.1.4 descriptive system document document in which the items of e
26、lectrical apparatus, their electrical parameters and those of the interconnecting wiring are specified 3.1.5 system designer person who is responsible for the descriptive system document, has the necessary competence to fulfil the task and who is empowered to enter into the commitments on behalf of
27、his employer - 13 - ANSI/ISA-60079-25 (12.02.05)-2011 3.1.6 maximum cable capacitance Ccmaximum capacitance of the interconnecting cable that can be connected into an intrinsically safe circuit without invalidating intrinsic safety 3.1.7 maximum cable inductance Lcmaximum inductance of the interconn
28、ecting cable that can be connected into an intrinsically safe circuit without invalidating intrinsic safety 3.1.8 maximum cable inductance to resistance ratio Lc/Rcmaximum value of the ratio inductance (Lc) to resistance (Rc) of the interconnecting cable that can be connected into an intrinsically s
29、afe circuit without invalidating intrinsic safety 3.1.9 linear power supply power source from which the available output current is determined by a resistor; the output voltage decreases linearly as the output current increases. 3.1.10 non-linear power supply power supply where the output voltage an
30、d output current have a non-linear relationship NOTE For example, a supply with a constant voltage output that can reach a constant current limit controlled by semiconductors. 3.2 Abbreviations FISCO Fieldbus Intrinsically Safe Concept FNICO Fieldbus Non-Incendive Concept 4 Descriptive system docume
31、nt A descriptive system document shall be created for all systems. The descriptive system document shall provide an adequate analysis of the safety achieved by the system. NOTE Annex E comprises examples of typical diagrams, which illustrate the requirements of the descriptive system document. The m
32、inimum requirements are as follows: a) block diagram of the system listing all the items of apparatus within the system including simple apparatus and the interconnecting wiring. An example of such a diagram is shown in Figure E.1; b) a statement of the group subdivision (for Groups II and III), the
33、 level of protection for each part of the system, the temperature classification, and the ambient temperature rating in accordance with Clauses 5, 6 and 7; c) the requirements and permitted parameters of the interconnecting wiring in accordance with Clause 8; d) details of the earthing and bonding p
34、oints of the systems in accordance with Clause 11. When surge protection devices are used, an analysis in accordance with Clause 12 shall also be included; ANSI/ISA-60079-25 (12.02.05)-2011 - 14 - e) where applicable, the justification of the assessment of apparatus as simple apparatus in accordance
35、 with ANSI/ISA-60079-11 IEC 60079-11 shall be included; f) where the intrinsically safe circuit contains several pieces of intrinsically safe apparatus the analysis of the summation of their parameters shall be available. This shall include all simple apparatus and listed certified intrinsically saf
36、e apparatus; g) a unique identification of the descriptive system document shall be created; h) the system designer shall sign and date the document. NOTE The descriptive systems drawing is not the same as the Control Drawing referred to in ANSI/ISA-60079-11 or ANSI/ISA-61241-11IEC 60079-11. 5 Group
37、ing and classification Intrinsically safe electrical systems shall be placed in a Group I, Group II or Group III as defined in ANSI/ISA-60079-0 IEC 60079-0. Groups II and III intrinsically safe electrical systems as a whole or parts thereof shall be given a further subdivision of the Group as approp
38、riate. Apparatus within Groups II and III intrinsically safe electrical system, intended for use in explosive gas or dust atmospheres, shall be given a temperature class or maximum surface temperature in accordance with ANSI/ISA-60079-0 IEC 60079-0, ANSI/ISA-60079-11 IEC 60079-11, ANSI/ISA-61214-0,
39、IEC 61241-0 and ANSI/ISA-61241-11 IEC 61241-11 as applicable. NOTE 1 In Group II and Group III intrinsically safe electrical systems, or parts thereof, the subdivisions A, B, C may be different from those of the particular intrinsically safe electrical apparatus and associated electrical apparatus i
40、ncluded in the system. NOTE 2 Different parts of the same intrinsically safe electrical system may have different subdivisions (A, B, C). The apparatus used may have different temperature classes and different ambient temperature ratings. 6 Levels of protection 6.1 General Each part of an intrinsica
41、lly safe electrical system intended for use in an explosive atmosphere will have a level of protection of “ia”, “ib” or “ic” in accordance with ANSI/ISA-60079-11 or ANSI/ISA-61241-11 IEC 60079-11. The complete system need not necessarily have a single level of protection. NOTE 1 For example, where a
42、n instrument is primarily an “ib” instrument but which is designed for the connection of an “ia” sensor, such as a pH measuring instrument with its connected probe, the part of the system up to the instrument is “ib” and the sensor and its connections “ia”. NOTE 2 An “ia” field instrument powered vi
43、a an “ib” associated apparatus would be considered as an “ib” system. NOTE 3 A system may be “ib” in normal operation with external power, but when power is removed under defined safety circumstances (ventilation failure) then the system could become “ia” under back up battery power. The level of pr
44、otection will be clearly defined for foreseeable circumstances. Clause 13 contains details of the required assessment. 6.2 Level of protection “ia” Where the requirements applicable to electrical apparatus of level of protection “ia” (see ANSI/ISA-60079-11 and ANSI/ISA-61241-11 IEC 60079-11) are sat
45、isfied by an intrinsically safe system or part of a system considered as an entity, then that system or part of a system shall be placed in level of protection “ia”. 6.3 Level of protection “ib” Where the requirements applicable to electrical apparatus of level of protection “ib” (see ANSI/ISA-60079
46、-11 and ANSI/ISA-61241-11 IEC 60079-11) are satisfied by an intrinsically safe system or part of a system considered as an entity, then that system or part of a system shall be placed in level of protection “ib”. - 15 - ANSI/ISA-60079-25 (12.02.05)-2011 6.4 Level of protection “ic” Where the require
47、ments applicable to electrical apparatus level of protection “ic” (see ANSI/ISA-60079-11IEC 60079-11) are satisfied by an intrinsically safe system or part of a system considered as an entity, then the system or part of a system shall be placed in level of protection “ic”. 7 Ambient temperature rati
48、ng Where part or all the intrinsically safe system is specified as being suitable for operation outside the normal operating temperature range of 20 C and +40 C, this shall be specified in the descriptive system document. 8 Interconnecting wiring / cables used in an intrinsically safe electrical sys
49、tem The electrical parameters of the interconnecting wiring upon which intrinsic safety depends and the derivation of these parameters shall be specified in the descriptive system document. Alternatively, a specific type of cable shall be specified and the justification for its use included in the documentation. Cables for the interconnecting wiring shall comply with the relevant requirements of Clause 9. NOTE: The requirements for intrinsically safe wiring are contained within the National Electrical Code(NEC) 504.10. Where relevant, the descriptive
