© 2001 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.

Industrial facilities in which potentially explosive gas atmospheres exist have presented a challenge for codes and standards makers for decades. Area classification, equipment standards, installation and wiring codes of practice throughout the world which deal with these areas have evolved into two basic systems.

European and a majority of other nations of the world have been influenced by the International Electrotechnical Commission’s (IEC) three tiered Zone approach. The IEC separates the potentially explosive atmosphere into Zones 0, 1, and 2 based on the probability of occurrence and length of time a potentially explosive mixture may be present. Apparatus designed for use in these areas are usually tested and approved for use by CENELEC test stations using Euronorm (EN) standards.

North America, and other parts of the world influenced by North American practices, have traditionally used a Class and Division system. Classes identify the type of hazard present as gasses or vapors, combustible dusts and flammable fibers. Divisions define the normal or abnormal condition underwhich the hazardous material may be present. Apparatus designed and manufactured for these areas are tested and approved for use by Nationally Recognized Test Laboratories (NRTL) using nationally accepted product standards. In a number of countries, both systems exist in parallel. Certain nations permit the construction of facilities by multinational companies using whichever system best suits their needs.

While not unique to hazardous locations, the reasons for the evolution of the two codes and standards systems are as diverse as the countries which employ them. National electrical installation codes are put in place to ensure correct, safe and consistent equipment installation. These codes also support the product standards developed over time which address the application specific needs of each system. Product standards, on the other hand, are developed to provide what a country views as an acceptable level of safety. These include performance and construction criteria that often contain an element of protectionism for domestic manufacturers.

The desire for free trade between nations is normally the driving force of harmonization. A good example of this is CENELEC, where the national standards of thirteen countries were harmonized to create Euronorms, strictly to facilitate the governments’ trade objectives. As the desire for global trade increases, the need for North America to harmonize with the IEC becomes an important issue. Due to the similarity of the IEC and CENELEC in this area, IEC references will be used throughout the balance of this article.

Until recently the Class and Division system was the only option for area classification and equipment installation in hazardous locations for North American industries. The introduction of an IEC based three zone system is a dramatic new development for the United States (US) and Canada.

The interest in harmonizing North American practices with those of the IEC is not a new idea. Early proposals for change in the US were submitted in 1974 with a similar effort in Canada by 1987. However, the pursuit of a three zone system sparked an unprecedented battle in what is generally considered a mature and sedate industry. It was not until the end user community became interested in an alternate system that progress began to occur.

Economic and political issues of special interest groups in the US have overshadowed the technical discussions of how to best integrate the zone system into the National Electrical Code® (NEC®). After gaining consensus on the right of users to choose the system which best fits their needs, Canada has been able to concentrate on addressing the technical issues related to integration of the new system.

The driving force behind the end user community is the right to choose the system which best fits the application from both a practical and economic standpoint in regard to design, engineering and maintenance. The rational being that both systems have excellent safety records proven over decades of use. Once this fact was established and accepted, the challenge was to create the necessary installation requirements and product standards to accommodate the new (alternate) system while maintaining the existing system.

Both the US and Canada selected the IEC as the appropriate avenue to take in adopting a three Zone system. Although IEC and CENELEC standards are similar, both countries required the ability to participate in the standards development and writing process. CENELEC, created through the European Union (EU), could not offer this option.

While the overall objective of the US and Canada is essentially the same, the structure of the codes and standards process in each country is quite different resulting in two very different outcomes. To understand the 1996 NEC and 1998 CEC proposal, each must be examined separately to avoid confusion. With the major obstacles overcome, the focus is now on the realities of the code changes and their impact on the industry.

1996 National Electrical Code® (NEC®)

The US defines areas where potentially explosive or combustible gasses, dusts or fibers and flyings as hazardous (classified) locations. Code Making Panel (CMP) - 14 is responsible for NEC Articles 500-517 which deals with classification and equipment installation in such areas. This panel is comprised of manufacturing, labor, inspection, user and certification industry representatives. They review and evaluate all proposed changes to this section of the NEC.

Early proposals to the NEC suggested elimination of the Class I, Division system in favor of a three zone system or to replace Class I, Division 1 and 2 with Division 1.0, 1.1 and 1.2. These proposals were met with great resistance since they required reclassification of all existing hazardous areas and forced retraining personnel for a completely new system.

The solution proposed by CMP-14 now forms part of the 1996 edition of the NEC as a new section titled Article 505. This new text contains the fundamental requirements for Class I, Zone 0, Zone 1 and Zone 2 hazardous (classified ) locations. The US strategy is a multi-step approach introducing various elements of the system in a controlled approach for the user to fully understand prior to full implementation. Product standards, which are developed independent of the NEC, are being rewritten to meet US requirements. As the combination of codes and standards evolves, a system emerges that is similar to the IEC.

Article 505 introduces the international area classification system and terminology to the NEC yet leaves the existing Class and Division system intact. This results in a parallel system giving the user the benefit of choice in area classification, product installation and wiring methods that best suits their application.

It must be understood at this point that Article 505 is considered a framework which contains the basic building blocks from which the system must now grow. It’s introduction is a critical first step after years of effort and political debate. Several working groups have been formed to expand on the initial text of the article and introduce technical refinements.

Being a new system, a key safeguard was added requiring that "If Article 505 is used, area classification, wiring and equipment selection shall be under the supervision of a Qualified Registered Professional Engineer." Although the term "qualified" is somewhat vague, this requirement is intended to prevent misapplication by those unfamiliar with it’s intent. The reality being that safety conscious companies employ competent Professional Engineers (PE) who will be qualified to determine the safety level of a facility for safety’s sake alone.

The fundamental elements of Article 505 are identified by each code section paragraph as follows:

Section 505-2 simply states that the general rules of the NEC shall apply to the electrical wiring and equipment installed in Class I, Zone 0, Zone 1, or Zone 2 locations. This includes the sealing requirements intended for traditional equipment used in Class I, Division 1.

Section 505-5 contains the apparatus and gas groupings for the nature of the gas atmosphere and are identical to those found in the IEC system. A Fine Print Note (FPN) was added to show the relationship of the three IEC gas groups (i.e., IIC, IIB or IIA) to the four traditional NEC gas groups (i.e., A, B, C and D). It is anticipated that gas grouping could cause as much confusion within the industry as the transition to Zones. Group A is the most hazardous gas group in the traditional NEC whereas Group IIC is the most volatile in the IEC system.

Section 505-7 addresses the definition of the three zones and area classification parameters of each. It directs the user to reference publications IEC 79-10, Electrical Apparatus for Explosive Gas Atmospheres, Classifications of Hazardous Areas; the British Institute of Petroleum’s IP15 Institute of Petroleum Area Classification Code for Petroleum Installations; and the American Petroleum Institute (API) RP 500-1991, Recommended Practice for Classification of Locations for Electrical Installations of Petroleum Facilities. The API document uses more familiar references for the traditional American user. The API is developing an equivalent publication, RP 505, to deal specifically with Zone classification. Although not specifically stated in the NEC, a key point to consider is that it is not permitted for a location in a plant to be partially classified under the Class I, Division scheme and partially under the Zone classification scheme. This does not mean that there cannot be complete areas in a plant classified under the Class I, Division system and others under the zone system. The intent is not to mix the systems together in the same area. This subject as well as area reclassification will undoubtedly be clarified in the 1999 NEC or via a Tentative Interim Amendment (TIA) to the 1996 NEC.

Section 505-10 covering Listing and Marking demands that equipment be specifically listed and marked for use in Class I, Zone 0, 1 or 2 locations. The Maximum Surface Temperature Classification given in this section maintains a pure IEC approach of having only 6 main temperature classifications T1 - T6. This deviates from the traditional NEC Temperature Class structure which has multiple subdivisions between main temperature classes.

The use of listed product presents a challenge for the US. There are presently no American National Standards Institute (ANSI) standards dedicated to the testing and certification of Zone equipment. Furthermore, the methods of protection for the Zone system are not included in Article 505 of the 1996 NEC. The International Society for Measurementation and Control (ISA) has assumed the role of ANSI standards writer for the various methods of protection for Class I, Zone 0, 1 and 2 hazardous (classified) locations and equipment. All of the ISA standards are being developed using the IEC 79 Series publications as the basis with additional requirements added, where necessary, to address special US industry concerns. The goal is to submit the ISA standards, once completed, to ANSI for national acceptance.

The ISA SP12 committee, in consultation with the German test lab, PTB, has prepared a draft of the Increased Safety "e" standard. This draft standard uses IEC 79-7 as the basis with additional test requirements not currently included in any IEC or CENELEC document. In addition work is well underway by SP12 in developing similar documents based on the IEC general requirements, flameproof "d", pressurized "p", intrinsic safety "i", encapsulation "m" and powder filled "q".

The fact that no current Zone equipment standards exist in the US and that new ANSI recognized standards are in the distant future leaves each independent Nationally Recognized Test Lab (NRTL) to interpret which existing standards to apply for equipment certification today. Underwriters Laboratories Inc. (UL) is using the applicable UL ordinary location standards, IEC 79 Series publications for explosion protection aspects and the 1996 NEC. This means that equipment will be subjected to all of the electrical , mechanical and material tests of traditional industrial product plus the additional IEC 79 explosion protection tests.

Factory Mutual Research Corporation (FM) has elected to also use the same approach of applying the IEC 79 series publications but in addition felt that this would be a good opportunity to evaluate the ISA draft standards. Therefore, products seeking Zone certification at FM must meet the requirements of the draft ISA standards. The main differentiation comes in the area of increased safety "e" terminals. Specific test procedures and requirements, in regard to pullout and vibration, are documented in the ISA draft "e" standard which are not currently included in either the IEC or CENELEC "e" documents. This of course means that existing CENELEC approved products may be required to pass a number of new tests to be suitable for the US market.

The two different test lab approaches then leads to a potential marking difference for a listed product.

· Following the UL approach, a listed product would be marked...

Class I, Zone 1
Ex de IIC T6

This combines the class and zone marking requirements of the 1996 NEC with the Ex marking format of IEC 79-0.

· Following the FM approach, a listed product would be marked...

Class I, Zone 1,
AEx de IIC T6

This again combines the class and zone marking requirements of the 1996 NEC but with the Ex marking format of the ISA draft standard which includes an "AEx" to differentiate it as being tested to an American standard.

Section 505-20 provides the details of the equipment permitted to be installed in each of the three Zone areas. As previously stated, mixing of the Class I, Division and Zone classification schemes is not allowed. However, provisions have been made in this section via exceptions that identify traditional Class I, Division equipment which is also suitable for installation in a Zone classified area. These exceptions may allow traditional equipment to remain installed in the case of area reclassification.

For Zone 1, equipment approved for use in Class I, Division 1 with the same gas group and similar temperature marking is permitted. For Zone 2, equipment suitable for Class I, Division 1 or 2 with the same gas group and similar temperature marking is permitted. The reverse is not true, Zone equipment is not currently allowed to be installed in a Class I, Division area. The terms "approved" and "suitable" are used here in place of "Listed" which indicates independent third party certification. The reality is that the marking requirements of Section 505-10(b) specifically state that the "Equipment shall be marked to show the class, zone, gas group and temperature class..." For market acceptance, this requirement leads an equipment manufacturer back to a third party test agency (i.e., UL, FM) for marking issues which ultimately results in a Zone "Listed" product.

Wiring methods Section 505-15 and Grounding and Bonding Section 505-25 are about the only two areas unchanged from the traditional Class and Division system. An installer will wire and ground Zone Listed equipment the same as Class and Division equipment. This now includes the use of Listed Metal Clad (MC) Cable for Division 1 and Zone 1 applications in addition to traditional rigid conduit and Mineral Insulated Cable. This, though not as flexible as using unarmoured cable, is the beginning of what hopes to be the expanded use of cable in hazardous (classified) locations.

1998 Canadian Electrical Code® (CEC®)

While the goal is for harmonization of North American Codes and Standards, Canada has taken a much different approach to the integration of an IEC system than the US. Given the distinct structure and political nature of the two codes it is unlikely they will merge in the foreseeable future.

The CEC is made up of a number of parts, Part 1 is the general wiring methods and Part 2 is product standards. Both are administered by The Canadian Standards Association (CSA). This close link, between electrical codes and product standards, has allowed Canada to take a systems approach to integration of a second system. From Canada’s perspective, the IEC system was deemed to provide an equivalent level of safety to the existing system. The objective of Canadian code makers was then to introduce the IEC system in it’s entirety.

The group responsible for hazardous location wiring methods is Section 18 of the CEC. Members formed a task force to make the necessary changes in CEC Part 1 and 2 to permit the use of the international system. This involves the simultaneous introduction of new product standards, wiring methods and area classification requirements, while maintaining the existing system.

The traditional Class I, Division requirements which existed in Section 18 were moved to an Appendix and the main body of the code was rewritten to deal specifically with Zone classification and wiring methods. It was decided that both IEC and CEC gas groups, temperature codes and equipment markings would be added to the main body of the code.

The most significant difference between the US and Canadian approach is that the CEC will require that all new construction use the Zone method of area classification beginning in 1998. The rational being, what is defined as Zones 0 and 1 in the IEC equates to Class 1, Division 1. This will eventually establish common terms of reference between the two systems within the industry.

The new CEC Section 18-000 (3) states; for modifications, renovations to or operation and maintenance of existing facilities employing the Division system of classification for Class I locations, the continued use of the Division system of classification is permitted. This simply means, existing facilities do not have to re-classify and can continue to wire and install Class I, Division 1 equipment if they choose.

It was determined that the rules dealing with Zone 2, in the new Section 18, and Class I, Division 2, in Appendix J, were virtually identical. The group decided that to simply eliminate the Division 2 rules would cause unnecessary confusion. A statement was therefore added to CEC Section 18-000 (4) which states; equipment permitted in the rules for installations in Class I, Zone 2 locations shall also be permitted in Class I, Division 2 locations.

A major advantage the CEC has in this transition, is the use of cable. Canada has permitted the use of Teck cable for years. Teck Cable is constructed of a PVC coated jacket, with an interlocked aluminum armour over the conductors. Teck cables are installed in a similar manner to steel wire armour (SWA) or braided cables used in the IEC.

The CEC task force determined that existing, certified IEC hazardous location type products should not be subjected to additional requirements, or testing, by a Canadian NRTL. Since the system, and equipment used within it were considered to be safe, additional construction requirements or performance testing were not justified.

To complete the system, CSA adopted the IEC 79 Series product standards for explosion protected apparatus, after an extensive review by a technical committee. Minor National deviations were added which relate to Canadian terminology and allow the use of IEC products in existing Class I, Division 2 applications. The IEC Standards adapted by CSA are as follows;

The focus of the Canadian work was to minimize the impact of a "new system" on the industry. North American manufacturers are not required to redesign or re-label existing products. Products that currently meet IEC requirements will not be subjected to additional testing. It was agreed that products will require approval by a Nationally Recognized Testing Laboratory (NRTL), such as CSA, and a certification mark applied for use in Canada.

To accommodate this goal marking requirements were added to 18-052 which state,

(1) Electrical equipment intended for use in Class I hazardous locations shall be marked with the following:

(a) the symbols Ex or EEx (Ex being IEC, EEx being CENELEC)
(b) Symbol(s) to indicate method(s) of protection used;
(c) Gas Groups as specified in rule 18-050 (2) [which are IEC IIA, IIB, IIC]
(d) Temperature Rating in accordance with subrule (4) for equipment of the heat producing type.

2) Notwithstanding subrule (1), electrical equipment approved for

(a) Class I or Class I, Division 1 or 2 locations shall be marked with the class and the group described in 18-050(3), or the specific gas or vapour [which are A, B, C or D] for which it has been approved
(b) Class I, Division 2 equipment shall be so marked.

The traditional Temperature Code structure, T1-T6 with intermediate subdivisions, of the CEC was retained. The task group felt that although CEC Temperature Codes include these intermediate steps, IEC products already meet these definitions since most are rated T6 or T5. Therefore, the existing Temperature Code structure accommodates both traditional and new IEC style product that could potentially be installed in Canada. This limits the impact of the new system on manufacturers with existing CSA approved products.

The following reference table was added to the CEC to guide the user in the selection of equipment for either system.

The work of Section 18 is presently in the ballot stage and is expected to pass by June 1996. Individual provinces are permitted and expected to adopt the new code once completed. The IEC-79 Series of standards were adopted in 1995 and are published as National Standards of Canada.

Summary

It is clear both the US and Canada are seeking harmonization, not only in North America, but globally. The IEC provides an avenue for both to achieve this goal. Task groups within CMP-14 and Section 18 meet annually to discuss common concerns and review each others’ progress. It is not an issue between the two groups of who will be first to reach the target, only that they both reach it. To achieve that goal, both countries will have electrical codes which support the Zone classification system.

To understand how "harmonized" each system will be, the following table provides the details of the basic classification system, methods of protection, product standards and installation for each system.

As indicated above, North American electrical codes will permit the option to use the IEC hazardous location system and products. Complete global harmonization, on the other hand, is still decades away. The obstacles which remain are not the system as such, but in the approach to industrial electrical products in general and the substantial installed base of North American equipment.

Killark Electric, Killark-Stahl and Hubbell Canada LP have been instrumental in bringing about the code and standards changes in both the US and Canada. Killark and Hubbell Canada LP personnel sit on key code and standards making committees for hazardous locations including CMP-14 and Section 18. While other manufacturers in the US opposed Article 505, Killark and Killark-Stahl met the needs of the users by supporting and organizing meetings to educate and dispel the myths generated by opponents to the change. Hubbell Canada LP personnel continue to be intimately involved in every aspect of the code making process, standards development and education activities in Canada. As we move forward Killark, Killark-Stahl and Hubbell Canada LP are considered the experts to consult in guiding the standards development, refining the new code articles and supporting the independent certification agencies such as UL, FM and CSA. The result of this cooperative effort has been the successful introduction of a three zone system in the US and Canada as well as the establishment of relationships and respect that no other manufacturer can claim.

For more info regarding this publication please email us here.