1、 ANSI/ISA-TR12.12.04-2011 (formerly ISA-TR12.06.01-1999) ANSI Technical Report prepared by ISA Electrical Equipment in a Class I, Division 2/Zone 2 Hazardous Location Approved 20 June 2011 ANSI/ISA-TR12.12.04-2011 (formerly ISA-TR12.06.01-1999), Electrical Equipment in a Class I, Division 2/Zone 2 H
2、azardous Location ISBN: 978-1-936007-95-0 Copyright .2011 by the International Society of Automation. All rights reserved. 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, me
3、chanical, 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 -3- ANSI/ISA-TR12.12.04-2011 Preface This preface, as well as all footnotes and annexes, is included for informa
4、tion purposes and is not part of ANSI/ISA-TR12.12.04-2011. 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
5、 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: standardsisa.org. The ISA Standards and Pra
6、ctices 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 incorpora
7、ting 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 gr
8、eatest extent possible. Standard for Use of the International System of Units (SI): The Modern Metric System, published by the American Society for Testing 67 Alexander Drive; P. O. Box 12277; Research Triangle Park, NC 27709. This page intentionally left blank. -11- ANSI/ISA-TR12.12.04-2011 1 Intro
9、duction When electrical equipment is used in locations in which fire or explosion hazards may exist due to flammable gases or vapours, flammable liquids, combustible dust, or ignitable fibers or flyings, the National Electrical Code(NEC), ANSI/NFPA 70 requires special precautions to be taken in equi
10、pment construction and installation to minimize risks of fire and explosions. There are several protection techniques in common use, each of which has its own set of advantages and disadvantages. Other countries, including Canada, utilize varying wiring methods, so the contents of this report may no
11、t be applicable to countries other than the United States. A location in which the fire or explosion hazard exists infrequently and for short periods is designated as a Division 2 or Zone 2 location. Two of the primary protection techniques for Division 2 or Zone 2 locations are “Nonincendive equipm
12、ent” or “Non-sparking equipment”. This Technical Report is intended to explain these protection techniques and to clarify the associated terminology. This Technical Report also addresses field wiring for Division 2/Zone 2 locations. Division 2 equipment is permitted to be marked and used in Zone 2 h
13、azardous locations per the NEC, Section 505.9(C)(1). Zone 2 equipment, in accordance with ANSI/ISA-60079-15, is permitted to be marked and used in Division 2 hazardous location per the NEC, Section 501.5. The term “combustible material” will be used throughout this Technical Report to refer to mater
14、ials mentioned above, i.e., flammable gases, flammable liquid produced vapours, or combustible liquid produced vapours. Similarly, the term “hazardous location” will be used in place of the phrase “hazardous (classified) location” used in the NECand in the product standards. Finally, although combus
15、tible materials pose a fire hazard, the primary concern is an explosion. 2 Hazardous locations 2.1 General To understand this Technical Report, it is necessary to know the terminology associated with hazardous locations as defined in the NEC. Although there are numerous hazards such as high voltages
16、, carcinogens and moving objects, the term “hazardous locations” only refers to areas made hazardous by the presence of a combustible material that may create an explosion hazard when mixed with air. A much fuller discussion of hazardous locations can be found in numerous publications, including ANS
17、I/ISA-12.01.01, “Definitions and Information Pertaining to Electrical Apparatus in Hazardous (Classified) Locations.” The following is provided as an overview. In some cases, terms have been defined in a simplified manner to ease understanding. There are four essential elements used to define a haza
18、rdous location in North America: Class, Division or Zone, Group, and Temperature Class. 2.2 Class Hazardous locations are divided into three classes: Class I for flammable gases or vapours. ANSI/ISA-TR12.12.04-2011 - 12 - Class II for combustible dusts. Class III for ignitible fibers. 2.3 Division E
19、ach Class is further divided into two Divisions: Division 1 hazardous locations, for the most part, are areas in which the flammable atmosphere occurs during normal operation. Examples of Division 1 areas are locations in which paint-spraying operations occur or in which flammable liquids could esca
20、pe from open tanks, and inadequately ventilated locations containing pumps handling flammable fluids. Division 2 hazardous locations are areas in which the flammable atmosphere only occurs because of abnormal operation of equipment, such as leakage from pump and valve packings or failure of pressuri
21、zing or ventilating systems. 2.4 Group (Division system) The combustible materials are divided into groups to describe the nature of the material. Gases are divided into four groups A, B, C and D as defined in Article 500 of the NEC. Dusts are divided into three groups E, F and G as defined in Artic
22、le 500 of the NEC. Fibers are not further divided into groups. The classification for a specific combustible material can be found in ANSI/NFPA 497 for gases, vapours, and liquids and NFPA 499 for combustible dusts. 2.5 Zone In the international vocabulary, the zone concept is essentially equivalent
23、 to the Division concept, except that Division 1 has been subdivided into Zone 0 and Zone 1. For practical purposes, Zone 2 and Division 2 are equivalent. The Zones are defined as follows: Zone 0 locations are areas in which the flammable atmosphere is present continuously or for long periods. Zone
24、1 locations are areas in which the flammable atmosphere is likely to occur in normal operation. Zone 2 locations are areas in which the flammable atmosphere is not likely to occur in normal operation and, if it does occur, is likely to do so only infrequently and will exist for short periods only. 2
25、.6 Group (Zone system) Under the Zone classification system, groups are defined as follows: Group I equipment is intended for use in mines susceptible to firedamp. NOTE 1 Firedamp is a flammable mixture of gases, predominantly methane, naturally occurring in a mine NOTE 2 US mines are under the juri
26、sdiction of the federal agency Mine Safety and Health Administration (MSHA) where the term Group I is not currently used Group II equipment is intended for use in locations with an explosive gas atmosphere other than mines susceptible to firedamp and is further subdivided into three groups IIA, -13-
27、 ANSI/ISA-TR12.12.04-2011 IIB and IIC as defined in Article 505 of the NEC. Group III equipment is intended for use in locations with an explosive dust atmosphere and is further subdivided into three groups IIIA, IIIB and IIIC as defined in ANSI/ISA-60079-0. NOTE The 2011 NEC does not define Group I
28、IIA, IIIB, or IIIC, but identifies equipment as suitable for Zone 20, 21, or 22. 2.7 Temperature classification A temperature class (T Code) is assigned based on the maximum surface temperature of the equipment. The maximum surface temperature may be that of the enclosure, or it may be that of the i
29、nternal components, depending upon the type of equipment. The equipment may not be used where the combustible material has an auto-ignition temperature less than the temperature class indicated by the T code. 3 The nonincendive equipment concept 3.1 General A Division 2 or Zone 2 location is a locat
30、ion where the ignitible concentrations of combustible materials do not exist under normal operating conditions. Nonincendive/non-sparking equipment is not a source of ignition under normal conditions. The probability of an ignitable concentration existing simultaneously with the equipment becoming a
31、 source of ignition is unlikely. 3.1.1 Risk of release of combustible materials Locations in which explosion hazards may exist are classified, in part, based on how frequently the hazard may be present. The hazard occurs because of the presence of a combustible material-in-air mixture that is within
32、 the flammable limits. A Division 2/Zone 2 Hazardous Location is defined as a location in which the combustible material is only a hazard because of an abnormal occurrence such as failure of ventilation equipment or damage to a container. Therefore, the hazard will only exist infrequently and for sh
33、ort periods. 3.1.2 Risk of equipment becoming a source of ignition Equipment that does not contain make/break components or components that have surface temperatures in excess of the ignition temperature of the combustible material is generally considered acceptable. Equipment that contains make/bre
34、ak components would also be considered acceptable if these components were prevented from causing ignition by a Division2/Zone 2 protection technique. Equipment that has been verified to not present an ignition hazard in normal operation is frequently referred to as “Nonincendive equipment.” This eq
35、uipment is evaluated to standards such as ANSI/ISA-12.12.01. A nonincendive evaluation verifies that such equipment does not contain unprotected make/break components such as relays, motor brushes and switches. The evaluation also determines the maximum surface temperature of components during norma
36、l operation. A number of other factors also must be evaluated. These factors include the ability of connectors to resist vibration and the evaluation of components (for example, fuses or lamps) that could become an ignition source during replacement. ANSI/ISA-TR12.12.04-2011 - 14 - 4 Nonincendive an
37、d non-sparking terminology 4.1 Nonincendive The term “nonincendive,” coined by ISA in the 1960s, often is confusing for installers and manufacturers due to its broad application. The confusion has resulted from the use of this term to mean “energy limited” when referring to a circuit, but not “energ
38、y limited” when referring to a component. The terms “nonincendive component” and “nonincendive circuit” were created to describe concepts that allow the use of switches in Division 2/Zone 2 hazardous locations. The definition of “nonincendive” is broad enough to cover high-energy components that do
39、not have make/break contacts. The following text will clarify the meaning of the terms “nonincendive circuit,” “nonincendive component,” “nonincendive equipment,” and “nonincendive field wiring.” The “nonincendive circuit” concept relies on limiting energy based on voltage, current, capacitance, and
40、 inductance. See ANSI/ISA-12.12.01 for additional information. The ANSI/ISA-12.12.01 definition for a nonincendive circuit is: nonincendive circuit a circuit, other than nonincendive field wiring, in which any arc or thermal effect produced under normal operating conditions, is not capable of igniti
41、ng the flammable gas-, vapor-, dust-air mixture, fibers or flyings. The circuit is evaluated under prescribed test conditions. “Nonincendive components” have been tested and found not to cause ignition of the relevant test-gas mixture (see ANSI/ISA-12.12.01). Make/Break components (e.g. switches) th
42、at are nonincendive components may be used in circuits that are otherwise ignition capable. The definition for a nonincendive component from ANSI/ISA-12.12.01 follows: nonincendive component a component having contacts for making or breaking an incendive circuit and the contacting mechanism is const
43、ructed so that the component, under normal operating conditions, is not capable of igniting the flammable gas or vapor-air mixture. The housing of a nonincendive component is not intended to exclude the flammable atmosphere or contain an explosion. The component is evaluated under prescribed test co
44、nditions. In the late 1970s, ISA12.12 was formed to create a standard for nonincendive equipment. This standard permitted equipment to be assembled using make/break components that were individually protected with various techniques. These techniques included limiting energy, sealing, and restrictin
45、g access to manually operated components. As discussed previously, the term “nonincendive equipment” has been used by some in a very restricted sense to apply only to equipment used in a nonincendive circuit. The correct usage also includes equipment that has some circuits that are not energy-limite
46、d, but where make/break components have been protected so that the equipment is not an ignition source in normal operation. The ANSI/ISA-12.12.01 definition for nonincendive equipment follows: nonincendive equipment equipment having electrical/electronic circuitry that is not capable, under normal o
47、perating conditions, of causing ignition of a specified flammable gas-, vapor-, dust-air mixture fibers or flyings due to arcing or thermal means. Circuits internal and external to nonincendive equipment may operate at ignition-capable energy levels. Where the energy has been limited to non-ignition
48、-capable levels in an external circuit, -15- ANSI/ISA-TR12.12.04-2011 the field-installed wiring is referred to as nonincendive field wiring. The ANSI/ISA-12.12.01 definition for nonincendive field wiring follows: nonincendive field wiring wiring that enters or leaves an equipment enclosure and, und
49、er normal operating conditions of the equipment, is not capable, due to arcing or thermal effects, of igniting the flammable gas-, vapor-, dust- air mixture, fibers or flyings. Normal operation includes opening, shorting, or grounding the field wiring. 4.2 Type of protection “n” IEC 60079-15, adopted in the US as ANSI/ISA-60079-15, introduced the terms “non-sparking”, “sparking apparatus with the contacts suitably protected” and “restricted breathing” in 1987. The concept has been expanded to include several different types of protection as outlined
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