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Electrical Equipment in aClass I, Division 2/Zone 2Hazardous Location

Approved 1 January 2000

ANSI/ISATR12.06.011999

T E C H N IC A L R E P O R T

ISA The Instrumentation,Systems, and

Automation Society

TM

NOTICE OF COPYRIGHTThis is a copyrighted document and may not be copied or distributed in any

form or manner without the permission of ISA. This copy of the document was

made for the sole use of the person to whom ISA provided it and is subject to

the restrictions stated in ISAs license to that person. It may not be provided to

any other person in print, electronic, or any other form. Violations of ISAs

copyright will be prosecuted to the fullest extent of the law and may result in

substantial civil and criminal penalties.

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Copyright

1999 by the Instrument Society of America. All rights reserved. Printed in the UnitedStates of America. No part of this publication may be reproduced, stored in a retrieval system, ortransmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or

otherwise), without the prior written permission of the Publisher.

ISA67 Alexander Drive

P.O. Box 12277Research Triangle Park, North Carolina 27709

ANSI/ISATR12.06.011999

Electrical Equipment in a Class I, Division 2/Zone 2 Hazardous Location

ISBN: 1-55617-706-2

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Preface

This preface, as well as all footnotes, is included for informational purposes and is not part ofANSI/ISA-TR12.06.01-1999.

This technical report has been prepared as part of the service of ISA, the international society formeasurement and control, 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 Societywelcomes all comments and criticisms and asks that they be addressed to the Standards and Practices

Board Secretary; ISA; 67 Alexander Drive; P.O. Box 12277; Research Triangle Park, NC 27709; Telephone(919) 549-8411; Fax (919) 549-8288; Internet: standards@isa.org.

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, recommended practices, and technical reports. The Department is furtheraware 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, thisDepartment will endeavor to introduce SI and acceptable metric units as optional alternatives to English

units in all new and revised standards, recommended practices, and technical reports to the greatestextent 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 interestsin 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 thatindividual, of ISA, or of any of the standards that ISA develops.

CAUTION ISA ADHERES TO THE POLICY OF THE AMERICAN NATIONAL STANDARDS

INSTITUTE WITH REGARD TO PATENTS. IF ISA IS INFORMED OF AN EXISTING PATENT THAT IS

REQUIRED FOR USE OF THE STANDARD, IT WILL REQUIRE THE OWNER OF THE PATENT TO

EITHER GRANT A ROYALTY-FREE LICENSE FOR USE OF THE PATENT BY USERS COMPLYINGWITH THE STANDARD OR A LICENSE ON REASONABLE TERMS AND CONDITIONS THAT ARE

FREE FROM UNFAIR DISCRIMINATION.

EVEN IF ISA IS UNAWARE OF ANY PATENT COVERING THIS STANDARD, THE USER IS

CAUTIONED THAT IMPLEMENTATION OF THE STANDARD MAY REQUIRE USE OF TECHNIQUES,

PROCESSES, OR MATERIALS COVERED BY PATENT RIGHTS. ISA TAKES NO POSITION ON THE

EXISTENCE OR VALIDITY OF ANY PATENT RIGHTS THAT MAY BE INVOLVED IN IMPLEMENTING

THE STANDARD. ISA IS NOT RESPONSIBLE FOR IDENTIFYING ALL PATENTS THAT MAY

REQUIRE A LICENSE BEFORE IMPLEMENTATION OF THE STANDARD OR FOR INVESTIGATING

THE VALIDITY OR SCOPE OF ANY PATENTS BROUGHT TO ITS ATTENTION. THE USER SHOULD

CAREFULLY INVESTIGATE RELEVANT PATENTS BEFORE USING THE STANDARD FOR THE

USERS INTENDED APPLICATION.

HOWEVER, ISA ASKS THAT ANYONE REVIEWING THIS STANDARD WHO IS AWARE OF ANY

PATENTS THAT MAY IMPACT IMPLEMENTATION OF THE STANDARD NOTIFY THE ISA

STANDARDS AND PRACTICES DEPARTMENT OF THE PATENT AND ITS OWNER.

ADDITIONALLY, THE USE OF THIS STANDARD MAY INVOLVE HAZARDOUS MATERIALS,

OPERATIONS OR EQUIPMENT. THE STANDARD CANNOT ANTICIPATE ALL POSSIBLE

APPLICATIONS OR ADDRESS ALL POSSIBLE SAFETY ISSUES ASSOCIATED WITH USE IN

HAZARDOUS CONDITIONS. THE USER OF THIS STANDARD MUST EXERCISE SOUND

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PROFESSIONAL JUDGMENT CONCERNING ITS USE AND APPLICABILITY UNDER THE USERS

PARTICULAR CIRCUMSTANCES. THE USER MUST ALSO CONSIDER THE APPLICABILITY OF ANY

GOVERNMENTAL REGULATORY LIMITATIONS AND ESTABLISHED SAFETY AND HEALTH

PRACTICES BEFORE IMPLEMENTING THIS STANDARD.

The following people served as members of ISA SP12.6:

NAME COMPANY

R. Masek, Chairman Bailey Controls Company

D. Bishop, Managing Director Chevron Petroleum Technology CompanyN. Abbatiello Eastman Kodak Company

P. Austen Electronic Controls Design, Inc.J. Bossert Hazloc, Inc.

R. Cardinal Bently Nevada Corporation

S. Czaniecki Intrinsic Safety Concepts, Inc.T. Dubaniewicz Pittsburgh Research Laboratory

A. Engler EGS Electrical GroupT. Feindel R. Stahl, Inc.

W. Fiske Intertek Testing ServicesL. Goettsche ConsultantD. Hohenstein Pepperl+Fuchs, Inc.

F. Kent Honeywell, Inc.B. Larson Turck, Inc.

F. McGowan Factory Mutual Research Corp.J. Miller Detector Electronics Corporation

A. Mobley* 3M CompanyE. Olson* 3M Company

C. Oudar ExLoc CorporationA. Page MSHA Certification CenterC. Sawyer MI Cable Company, Inc.

B. Schaefer Underwriters Laboratories, Inc.

T. Schnaare Rosemount, Inc.W. Shao Canadian Standards AssociationD. Wechsler Union Carbide Corporation

R. Weinzler Consultant

The following people served as members of ISA Committee SP12:

NAME COMPANY

F. McGowan, Chairman* Factory Mutual Research Corp.

D. Bishop, Managing Director* Chevron Petroleum Technology CompanyN. Abbatiello* Eastman Kodak Company

S. Arnold Drexelbrook Engineering Company

P. Babiarz* Crouse-Hinds CompanyA. Ballard* Crouse-Hinds Company

G. Bentinck E.I. du PontR. Berthold* Chevron Petroleum Technology Company

K. Blayden Upjohn CompanyH. Bockle Killark-Stahl, Inc.

______* One vote per company.

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J. Bossert Hazloc, Inc.

R. Brodin Fisher Controls International, Inc.M. Buettner Ralston Purina Company

R. Buschart PC & E, Inc.W. Calder III* Factory Mutual Research Corp.

R. Cardinal Bently Nevada Corp.R. Castillo Corpoven SAH. Conner Consultant

M. Coppler Ametek, Inc.J. Cospolich Waldemar S. Nelson & Company, Inc.

J. Costello Henkel Corp.E. Cranch* Drexelbrook Engineering Company

A. Czyz INERISW. Dill DMT

U. Dugar Mobil Chemical Company

A. Engler* EGS Electrical GroupT. Feindel R. Stahl, Inc.

W. Fiske Inchcape Testing ServicesS. Florence Motorola Inc.

G. Garcha PCS EngineeringB. Gibson ABB Kent-Taylor, Inc.J. Greenwald Rexene Corp.

E. Henning Fischer & Porter CompanyD. Hohenstein Pepperl + Fuchs

D. Jagger Hawke AmericaX. Jianping Shanghai Inst. of Process Automation Instr.

P. Kelly* Underwriters Laboratories, Inc.F. Kent* Honeywell, Inc.

J. Kuczka KillarkT. Lagana BE&K Inc.R. Landman International Marine Products Inc.

B. Larson* Turck Inc.

W. Lawrence* Factory Mutual Research Corp.W. Leber* EGS Electrical GroupT. Lewis, Jr. Applied Automation

D. Li Canadian Standards AssociationV. Maggioli Feltronics Corp.E. Magison Consultant

F. Maltby* Drexelbrook Engineering CompanyR. Masek Bailey Controls Company

D. McDermott Dexion HouseI. McMurchie OPC Engineering Inc.

R. McNeal Weidmuller Inc.J. Miller Detector Electronics Corp.

A. Mobley* 3M Company

W Mueller* Pepperl + Fuchs, Inc.E. Nesvig Erdco Engineering Corp.

E. Olson* 3M CompanyA. Page III MSHA Certification Center

J. Propst Shell Development CompanyC. Sandberg Raychem Corp.

______* One vote per company.

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J. Schaffer Endress & Hauser

P. Schimmoeller Weidmuller Inc.T. Schnaare Rosemount, Inc.

A. Stafford Foxboro CompanyD. Stevens* Chevron Petroleum Technology Company

D. Styrcula* Underwriters Laboratories Inc.J. Thomason OMNI Industrial Systems, Inc.P. Thurnherr Thuba, Ltd.

L. Truscott Motorola, Inc.P. Turner* 3M Company

T. Vu Milltronics Inc.D. Wechsler Union Carbide Corp.

R. Weinzler* Eastman Kodak CompanyZ. Zborovszky U.S. Bureau of Mines

This technical report was approved for publication by the ISA Standards and Practices Board on15 June 1999.

NAME COMPANY

H. Dammeyer The Ohio State UniversityH. Baumann H. D. Baumann, Inc.

D. Bishop Chevron Petroleum Technology Co.P. Brett Honeywell, Inc.

M. Cohen Senior Flexonics, Inc.M. Coppler Ametek, Inc.

W. Holland Southern CompanyA. Iverson Ivy Optiks

R. Jones Dow Chemical Co.V. Maggioli Feltronics Corp.T. McAvinew Instrumentation & Control Engineering LLC

A. McCauley, Jr. Chagrin Valley Controls, Inc.

R. McFarland Honeywell, Inc.R. Reimer Rockwell AutomationJ. Rennie Factory Mutual Research Corp.

R. Webb Altran Corp.W. Weidman Parsons Energy & Chemicals GroupJ. Weiss EPRI

J. Whetstone National Institute of Standards & TechnologyM. Widmeyer Consultant

R. Wiegle CANUS Corp.C. Williams Eastman Kodak Co.

G. Wood Graeme Wood ConsultingM. Zielinski Fisher-Rosemount Systems, Inc.

______* One vote per company.

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CONTENTS

1 Introduction........................................................................................................................................ 9

2 Hazardous locations .......................................................................................................................... 9

3 The nonincendive equipment technique .......................................................................................... 11

4 Nonincendive terminology ............................................................................................................... 11

5 Related terminology......................................................................................................................... 13

6 General design requirements .......................................................................................................... 14

7 Field wiring ...................................................................................................................................... 14

8 Maintenance .................................................................................................................................... 15

9 References ...................................................................................................................................... 15

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1 Introduction

1.1 When electrical equipment is used in locations in which fire or explosion hazards may exist due to

flammable gases or vapors, flammable liquids, combustible dust, or ignitible fibers or flyings, the NationalElectrical Code (NEC), ANSI/NFPA 70 requires special precautions to be taken in equipment construction

and installation to minimize risks of fire and explosions. There are several protection techniques in commonuse, 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 not be applicable to countries other than

the United States.

1.2 A location in which the fire or explosion hazard exists infrequently and for short periods is designatedas a Division 2/Zone 2 location. One suitable protection technique for a Division 2/Zone 2 location is

Nonincendive Equipment. This Technical Report is intended to explain this protection technique and toclarify the associated terminology. Clarification of the term Nonincendive Equipment is very important since

it has been used in two different ways. This Technical Report also addresses field wiring for

Division 2/Zone 2 locations.

1.3 The term flammable material will be used throughout this Technical Report to refer to any of thematerials mentioned above, i.e., flammable gases or vapors, flammable liquids, combustible dusts, or ignitible

fibers or flyings. Similarly, the term hazardous location will be used in place of the phrase hazardous(classified) location used in the NEC. Finally, although flammable materials pose a fire hazard, the primaryconcern is an explosion.

2 Hazardous locations

2.1 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,carcinogens and moving objects, the term hazardous locations only refers to areas made hazardous bythe presence of a flammable material that may create an explosion hazard when mixed with air.

2.2 A much fuller discussion of hazardous locations can be found in numerous publications, including ISA

standard S12.1.01, 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 simplifiedmanner to ease understanding. There are three general terms used to describe a hazardous location inNorth American terminology: class, division, and group. The international terminology primarily uses onlytwo terms: zone and group. The term zone has been adopted in the National Electrical Code as Article 505.

2.3 Class - Hazardous locations are divided into three classes:

Class I for flammable gases or vapors.

Class II for combustible dusts.

Class III for ignitible fibers.

2.4 Division - Each class is further divided into two divisions:

Division 1 hazardous locations, for the most part, are areas in which the flammable atmosphere occursduring normal operation. Examples of Division 1 areas are locations in which paint-spraying

operations occur or in which flammable liquids could escape from open tanks, and inadequatelyventilated locations containing pumps handling flammable fluids.

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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 ofpressurizing or ventilating systems.

2.5 Group - The flammable materials are divided into groups to describe the nature of the material.

Gases are divided into four groups:

Group A for acetylene,

Group B for hydrogen and similar gases,

Group C for ethylene and similar gases,

Group D for propane and similar gases.

Dusts are divided into three groups:

Group E for metal dusts,

Group F for carbonaceous dusts,

Group G for chemical and agricultural dusts.

Fibers are not divided into groups.

2.6 The classification for a specific material can be found in ANSI/NFPA 497 for gases and liquids thatmay evolve a flammable gas and in ANSI/NFPA 499 for dusts.

2.7 In the international vocabulary, the zone concept is essentially equivalent 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 longperiods.

Zone 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 normaloperation and, if it does occur, is likely to do so only infrequently and will exist for short periods only.

2.8 In the international vocabulary, Group covers the gas groupings as follows:

Group I - underground mines (such as coal mines) where methane may be present

Group IIC - hydrogen or similar gases (similar to the combination of North American Groups A and B)

Group IIB - ethylene or similar gases (equivalent to North American Group C)

Group IIA - propane or similar gases (equivalent to North American Group D)

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2.9 A temperature identification or temperature code is assigned based on the hottest surface of the

equipment. The equipment may not be used where the flammable material has an ignition temperature lessthan the temperature indicated by the temperature code.

3 The nonincendive equipment technique

3.1 Locations in which explosion hazards may exist are classified, in part, based on how frequently thehazard may be present. The hazard occurs because of the presence of a flammable material-in-air mixture

that is within the flammable limits. A Division 2/Zone 2 Hazardous Location is defined as a location in whichthe flammable 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 short periods.

3.2 Ordinary location equipment that does not contain make/break components or components that havesurface temperatures in excess of the ignition temperature of the flammable material is generally considered

acceptable. Equipment that contains make/break components would also be considered acceptable if these

components were prevented from causing ignition by a Division2/Zone 2 protection technique. Equipmentthat has been verified to not present an ignition hazard in normal operation is frequently referred to as

Nonincendive Equipment. This equipment is evaluated to standards such as ANSI/ISA S12.12.

3.3 A nonincendive evaluation verifies that such equipment does not contain unprotected make/breakcomponents such as relays, motor brushes and switches. The evaluation also determines the maximumsurface temperature of components during normal 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.

3.4 External wiring of nonincendive equipment may consist of conductors in conduit or certain types of

metallic and nonmetallic cables [see NEC Section 501-4(b)]. These wiring methods provide adequatemechanical protection; thus the opening, shorting and grounding of the conductors is considered abnormal

and is not considered in evaluating the safety of the system.

3.5 Under very limited circumstances, external wiring of nonincendive equipment may consist of certain

types of cables that do not provide the level of mechanical protection afforded by wiring methods described

in 3.4. These circumstances require that the energy be limited to levels that will not cause an ignition hazardwhen the external wiring is opened, shorted, or grounded. This type of wiring may be connected only toterminals that are identified as being suitable for Nonincendive Field Wiring. These terminals will be marked

on the equipment or identified in the manufacturers literature. The terminal markings or literature also willinclude electrical parameters for the circuit connected to the terminals.

3.6 The manufacturer of Division 2/Zone 2 equipment may provide cables or wiring harnesses forinterconnecting parts of the system. These cables and wiring harnesses must be installed in accordance

with Division 2/Zone 2 wiring methods unless the circuits have been evaluated and determined to benonincendive.

4 Nonincendive terminology

4.1 The term nonincendive, coined by ISA in the 1960s, often is confusing for installers andmanufacturers 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 energy limited when referring to a component. The termsnonincendive component and nonincendive circuit were created to describe concepts that allow the use

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of switches in Division 2/Zone 2 hazardous locations. The definition of nonincendive is broad enough to

cover high-energy components that do not have make/break contacts. A bus bar is an example of such acomponent. The following text will clarify the meaning of the terms nonincendive circuit, nonincendive

component, nonincendive equipment, and nonincendive field wiring.

4.2 The nonincendive circuit concept relies on limiting energy based on voltage, current, capacitance,and inductance. See ANSI/ISA S12.12 for additional information. The 1999 NEC definition for a nonincendivecircuit follows:

nonincendive circuit:

a circuit, other than field wiring, in which any arc or thermal effect produced, under intended operatingconditions of the equipment, is not capable, under specified test conditions, of igniting the flammable

gas-, vapor-, or dust-air mixture.

4.3 Nonincendive components have been tested and found not to cause ignition of the relevant test-gas

mixture (see ANSI/ISA-S12.12). Switching devices that are nonincendive components may be used incircuits that are otherwise ignition capable. The definition for a nonincendive component from

ANSI/ISAS12.1.01 follows:

nonincendive component:a component having contacts for making or breaking an ignition-capable circuit and in which the contactingmechanism is constructed so that the component is incapable of igniting the specified explosive

atmosphere. The housing of a nonincendive component is not intended to (1) exclude the flammableatmosphere or (2) contain an explosion.

NOTE Ignition is prevented because of the geometry of the contacts, the contact material, speed of contact mechanism, or

combinations of these factors.

4.4 In the late 1970s, ISA SP12.12 was formed to create a standard for nonincendive equipment. This

standard permitted equipment to be assembled using make/break components that were individuallyprotected with various techniques. These techniques included limiting energy, sealing, and restricting access

to the component.

4.5 As discussed previously, the term nonincendive equipment has been used by some in a veryrestricted sense to apply only to equipment used in a nonincendive circuit. The correct usage also includesequipment that has some circuits that are not energy-limited, but where make/break components have been

protected so that the equipment is not an ignition source in normal operation. The 1999 NEC definition fornonincendive equipment follows:

nonincendive equipment:

equipment having electrical/electronic circuitry that is incapable, under normal operating conditions, ofcausing ignition of a specified flammable gas or vapor or dust-air mixture due to arcing or thermal means.

4.6 Circuits internal and external to nonincendive equipment may operate at ignition-capable energylevels. Where the energy has been limited to non-ignition-capable levels in an external circuit, the field-

installed wiring is referred to as nonincendive field wiring. The 1999 NEC definition for nonincendive fieldwiring follows:

nonincendive field wiring:

wiring that enters or leaves an equipment enclosure and, under normal operating conditions of theequipment, is not capable, due to arcing or thermal effect, of igniting a specified flammable gas, vapor-in-air mixture, dust, fibers, or flyings. Normal operating conditions include opening, shorting, or grounding the

field wiring.

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5 Related terminology

5.1 Type n is the protection technique designation used by standards such as ISA dS12.12.02

(IEC 60079-15 Mod). The "n" designation was based on the word non-sparking. The terms "non-sparking"and "non-arcing" are considered by some as synonymous, but others use the terms to designate such factors

as

a) the absence of an ignition-capable arc;

b) the absence of ignition-capable particles; and

c) the absence of make/break contacts.

5.2 Standards describing equipment suitable for Division 2/Zone 2 generally use a term to designate the

components that must be investigated because they have "arcing" contacts. The term used in the ISA SP12

series of standards is make/break component. The ANSI/ISA-S12.12 definition follows:

make/break components:components having contacts that can interrupt a circuit (even if the interrupting is transient in nature).

Examples of make/break components are relays, circuit breakers, servo potentiometers, adjustableresistors, switches, and connectors.

5.3 It is necessary to determine and evaluate the amount of inductance and capacitance added tononincendive field-wiring circuits when adding components, cable, or equipment. Components defined as

simple apparatus are known to have insignificant energy storage and may be added to these circuits withoutfurther analysis. The 1999 NEC definition follows:

simple apparatus:

a device that will neither generate nor store more than 1.2 V, 0.1 A, 25 mW, or 20 uJ.

Examples are switches, thermocouples, light-emitting diodes, connectors, and resistance temperature

detectors (RTDs).

5.4 Certain types of make/break components only present an ignition hazard during maintenance. Thesecomponents include most connectors, lamp holders and fuse holders. For each of these components, a

decision must be made as to whether it could be an ignition source under normal operation. A significantfactor is operator accessibility. If an item can be replaced by an operator because it is both readily accessibleand does not require a tool to replace, then its replacement should be considered normal. However, if an

item is not readily accessible or if it requires a tool for its removal, its replacement should be consideredmaintenance and not normal.

Similarly, if operators have ready access to connectors and the connector may be separated without using

a tool, then disconnecting or connecting the connectors should be considered normal. Even if aconnector is not readily accessible, an evaluation must be made to determine if it may separate due to

vibration. Connectors that have a latch or other means to prevent separation, or connectors that require a

separating force of at least 15 N, are considered not likely to separate. Low-mass components pluggedinto sockets are exempt from the 15 N separating force requirement.

Connectors, fuse holders and lamp holders that are made non-arcing by the methods described above and

are marked (when applicable) to prevent disconnection while powered are referred to as normallynonarcing components.

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6 General design requirements

6.1 The following is provided as a simplification of the design and testing required for nonincendive

equipment by standards such as ANSI/ISAS12.12, UL 1604, and FM Class 3611.

6.2 These standards focus on components that may be either a thermal ignition source or an arc ignitionsource. The design standards permit using a system of temperature identification numbers referred to asT Codes. As examples, for equipment with which the hottest component is less than 85C, the T code is

T6. If the hottest component is less than 135C, the T code is T4. Most process control equipment will havea T4, T5, or T6 rating.

The complete sets of T codes can be found in Table 500-5(d) and Table 505-10(b)(3) of the 1999 NEC. It

is also important to note that the T Codes marked on equipment are generally based on a 40C ambienttemperature. Equipment may have ambient temperature/T Code ratings at more than one ambient

temperature or a T Code based on a higher temperature.

6.3 After determining the hottest component, the next step is to find all the components capable of creating

an arc, even if only in transient conditions. Some components with arcing contacts are relays, switches,circuit breakers, thermostats, thermal protectors, motor brushes, servo potentiometers, wire-wound

potentiometers, adjustable resistors, and automatic counter resets. Other make/break components thatmay arc when maintenance is performed include connectors, fuse holders and lamp holders. Once this listof components capable of creating an arc is compiled, each component must be examined to see if it is

protected.

6.4 Typical methods of protecting a make/break component are as follows:

a) Limiting the energy in the circuit connected to the component (a nonincendive circuit).

b) Using a solid-state component instead of one with mechanical contacts.

c) Using a component that renders the arc incapable of igniting the flammable atmosphere (a

nonincendive component).

d) Preventing the flammable atmosphere from reaching the arc (a sealed component).

e) Preventing the arc from occurring during normal operation (a normally nonarcing component).

7 Field wiring

7.1 As previously stated, one of the confusing issues with Nonincendive Equipment is the field wiring.

Nonincendive equipment is quite varied and may be a simple switch, a thermocouple, a 4-20 mA two-wiretransmitter, a sensor with a coaxial cable, or a controller powered by 120 Vac. Section 501-4(b) of the NECspecifies the type of wiring materials that may be used in Division 2 locations. Section 505-15(c) of the NEC

specifies the type of wiring materials that may be used in Zone 2 locations.

7.2 Installation of nonincendive equipment in a Division 2/Zone 2 hazardous location requires that specificwiring methods be used. Explosionproof seals are not required at the entry to the nonincendive equipment

(conduit or cable). A seal is required at area classification boundaries if conduit leaves the Class I,Division 2/Zone 2 location.

7.3 Metallic and nonmetallic cable constructions are permitted by the NEC. Examples include Types ITC,MC, PLTC and TC. However, none of these constructions include coaxial cable, flat (ribbon) cable, or

modular phone cables. The use of Type PLTC cable is restricted to power-limited circuits in accordancewith Article 725 of the NEC.

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7.4 The NEC permits nonincendive field wiring to be installed using any of the methods suitable for wiring

in ordinary locations. It is essential to understand that very few terminals on equipment installed in aDivision 2/Zone 2 location are identified for use with nonincendive field wiring. Most equipment must be

connected using approved Division 2/Zone 2 wiring methods such as wiring in conduit or Types ITC, MCor TC cable.

7.5 Equipment that may be connected with nonincendive field wiring must be identified with parametersthat specify the maximum open-circuit voltage, the maximum short-circuit current and the maximum-allowed

capacitance and inductance. The user must then investigate the wiring to be used, as well as equipmentintended to be connected (such as meters, solenoids, and transducers). The "effective" capacitance and

inductance of the equipment and cable must be obtained and calculations made to show that the allowedvalues are not exceeded. Alternatively, the equipment manufacturer may specify the allowed cable and

associated equipment that may be connected to the nonincendive field wiring terminals.

8 Maintenance

8.1 Maintenance should only be executed in accordance with the safety guidelines and regulations of the

facility and the electrical equipment manufacturers instructions.

9 References

FMRC 3611 Electrical Equipment For Use In Class I, II Div. 2 & Class III, Division 1 & 2

Hazardous Locations

ISAS12.1.011999 Definitions and Information Pertaining to Electrical Instruments in Hazardous(Classified) Locations

ANSI/ISAS12.121994 Electrical Equipment for Use in Class 1, Division 2 Hazardous (Classified) Locations

ANSI/NFPA 70 National Electrical Code

NFPA 497 Recommended Practice For the Classification of Flammable Liquids, Gases,or Vapors and of Hazardous (Classified) Locations for Electrical Installationsin Chemical Process Areas

NFPA 499 Recommended Practice for the Classification of Combustible Dusts and ofHazardous (Classified) Locations for Electrical Installations in Chemical

Process Areas

UL 1604 Electrical Equipment for Use in Class I and Class II, Division 2, and Class IIIHazardous (Classified) Locations

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ISBN 1 55617 706 2

Developing and promulgating technically sound consensus standards, recommended practices, andtechnical reports is one of ISAs primary goals. To achieve this goal, the Standards and PracticesDepartment relies on the technical expertise and efforts of volunteer committee members, chairmen,

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ISA is an American National Standards Institute (ANSI) accredited organization. ISA administersUnited 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 additionalinformation on the Societys standards program, please write:

ISA

Attn: Standards Department67 Alexander Drive

P.O. Box 12277Research Triangle Park, NC 27709