IEEE INDUSTRY APPLICATIONS MAGAZINE  NOV j DEC 2010  WWW.IEEE.ORG/IAS Are they the same? BY BHARAT MISTRY & WILLIAM G LAWRENCE E LECTRIC MOTORS HAVE BEEN USED and pressurized technique or the explosion-proof enclosure in zone and division hazardous areas for are required The large fabricated frame motors are typically many years These motors operate in hazard- protected by the purged and pressurized technique ous (classified) locations where an explosive Zone or division hazardous (classified) locations have gas or vapor atmosphere is likely to be present in a normal been defined to be essentially the same in National Fire Pro- operation Motors operating in this area require special pro- tection Association (NFPA) 70 [1], National Electrical Code tection against igniting the explosive gas or vapor To oper- (NEC), C22.1 [2], Canadian Electrical Code (CEC), and inter- ate these motors safely, special protections such as the purged national standards [International Electrotechnical Commission (IEC)] The petroleum and chemical facility environments 20 Digital Object Identifier 10.1109/MIAS.2009.935589 for IEC/NEC/CEC zone and NEC/CEC division are not 1077-2618/10/$26.00©2010 IEEE IEEE INDUSTRY APPLICATIONS MAGAZINE  NOV j DEC 2010  WWW.IEEE.ORG/IAS allows the use of type p protection (presdifferent, yet the safety requirements surized enclosure) in zone area, comand how the motors are used in these THE ENCLOSURE plying with the IEC 60079-2 standard areas are addressed from competing VOLUME FOR This article outlines the key area of vantage points The codes and standards design, construction, and testing of are transcending national barriers in an MOTORS IS large fabricated frame motors selected attempt to synchronize, without sacrifor zone and division hazardous areas ficing safety requirements; however, DEFINED AS THE protected by pressurization there are still diverging regulations These diverging requirements are disVOLUME WITHIN Hazardous Areas cussed later NEC and CEC definitions for division Fabricated induction and brushless THE ENCLOSURE and zone are almost identical and are synchronous machines are larger than also substantially equivalent to the IEC National Electric Manufacturing AssoMINUS THE 60079-10 [7] zone locations It can ciation (NEMA) frame sizes and manuVOLUME OF THE be seen from the definitions of both factured to order in voltages 2.3 kV division and zone locations that these and above They are designed and built INTERNAL are locations where the explosive atto suit specific applications, operating mosphere may exist frequently under under detailed load conditions and for COMPONENTS normal operation the petroleum and chemical process inFor division locations where the dustries located within hazardous (clasPLUS VOLUME explosive atmosphere exists continuously sified) areas under the local authority under normal operation (these would be having jurisdiction (LAHJ or AHJ) OF ROTOR defined as zone under the zone classifiThe population of these motors opercation system), motors would not be ating in zone or division areas is around 10% or less The design and application of these usually installed in such area based on the guidance given motors are very important because they operate in hazard- in the NEC and CEC This article compares the applications in zone and the ous areas where ignitable gas could be present at any time portions of division where motors are likely to be installed during normal operation For division locations, both the U.S and Canadian and used Compare the following excerpts installation standards refer to the NFPA 496 [5] standard for requirements for purged and pressurized enclosures NEC Article 500.5(B)(1) Definition for Division Comparatively, for zone locations, IEC standard 60079-0 A class I division location is a location [3] for general requirement and IEC standard 60079-2 [4] 1) in which ignitable concentrations of flammable for pressurized enclosure (p) are applicable Both the U.S gases, flammable liquid-produced vapors, or comadoption [American National Standards Institute/Internabustible liquid-produced vapors can exist under tional Society of Automation (ANSI/ISA 60079-2)] [13] normal operating conditions or and the Canadian adoption (E60079-2) [14] of the IEC 2) in which ignitable concentrations of such standard have very few national differences and, for the purflammable gases, flammable liquid-produced pose of this article, are considered nearly identical vapors, or combustible liquids above their flash The standards discussed herein are not limited to motors; points may exist frequently because of repair or they are applied equally to induction and synchronous genmaintenance operations or because of leakage or erators as well as machine accessories installed in hazardous 3) in which breakdown or faulty operation of locations The term motor used herein should be considered equipment or processes might release ignitible applicable to all rotating electrical machines concentrations of flammable gases, flammable Although the North American and the international liquid-produced vapors, or combustible liquidstandard-development groups are working to improve their produced vapors and might also cause simultaown documents, there is an ongoing effort to harmonize or neous failure of electrical equipment in such a reduce conflicts and confusion Despite this work, the fact is way as to directly cause the electrical equipment that the LAHJ is responsible for establishing which single to become a source of ignition set of codes and regulations apply to the project: either the NEC or IEC philosophy is chosen On the drawing board, NEC Article 505.5 (B)(2) Definition for Zone there are a few mechanical differences between the two A class I zone location is a location Electrically, the components are the same but output charac1) in which ignitable concentrations of flammateristics (e.g., torques and other tolerances not discussed ble gases or vapors are likely to exist under here) vary These differences are mainly due to the extra normal operating conditions or safety rules adopted to satisfy individual national standards 2) in which ignitable concentrations of flammable and/or installation codes and occasional features learned from gases or vapors may exist frequently because of application experience repair or maintenance operations or because of In addition to the NEC and CEC, the IEC 60079-14 leakage or standard [6], Electrical Installations in Hazardous Areas (Other 3) in which equipment is operated or processes are Than Mines), provides additional information on the seleccarried on, of such a nature that equipment tion of the apparatus for use in zone This standard [6] 21 IEEE INDUSTRY APPLICATIONS MAGAZINE  NOV j DEC 2010  WWW.IEEE.ORG/IAS 22 and the enclosure has been purged breakdown or faulty operwith at least ten volume of air and ations could result in the THE IEC also arranged to automatically deerelease of ignitable connergize the equipment when the centrations of flammable APPROACH IS air supply fails gases or vapors and also The external surface temperature of cause simultaneous failure MORE such a motor must not exceed in any of electrical equipment in DESCRIPTIVE AND case 80% of the ignition temperature a mode to cause the elecof the gas or vapor involved Appropritrical equipment to become DEFINITIVE ate devices shall be provided to detect a source of ignition or and automatically deenergize the motor 4) that is adjacent to a class RATHER THAN or provide an adequate alarm if there I, zone location from is any increase in the temperature of which ignitable concentraSPECIFYING THE the motor beyond design limits All tions of vapors could be auxiliary equipments shall be of a type communicated unless comDESIGN identified for the location in which it munication is prevented REQUIREMENTS is installed by an adequate positivepressure ventilation from a source of clean air and Design, Construction, and Testing effective safeguards against ventilation failure As noted earlier, the second paragraph of 501.125(A) does are provided not address design issues, construction methods, or testing of purged and pressurized motors The FPN of NEC secCEC Rule J18-006(a) Definition for Division tion 500.2 says to refer to ANSI/NFPA 496 to find those Division consists of a class I locations in which design requirements explosive gas atmospheres are likely to be present NFPA 496 was originally developed as two parts The continuously, intermittently, or periodically during first part was addressed in 1967 for purged enclosures for normal operation electrical equipment in class I hazardous (classified) locations The second part then followed with purged encloCEC Rule 18-006(b)(i) Definition for Zone sures for class II hazardous (classified) locations in 1970 Zone consists of a class I location in which 1) exploThe last revision of 2003 has major changes to align the sive gas atmospheres are likely to occur in normal document with the latest NFPA style and also with peroperation or 2) the location is adjacent to a class I, mission to use methods other than a timer to ensure that zone location, from which explosive gas atmosthe purging process has removed any flammables pheres could be communicated The design, construction, and testing requirements of NFPA 496 [5] for motors are discussed further IEC 60079-10: Clause 2.5.2 Definition for Zone A place in which an explosive atmosphere consisting General Requirements for Pressurized Enclosure of a mixture with air of flammable substances in the There are three types of pressurization systems defined in form of gas, vapor, or mist is likely to occur in normal the standard operation occasionally n Type X pressurization reduces the classification within the protected enclosure from division or zone to NEC Approach unclassified n Type Y pressurization reduces the classification within the protected enclosure from division to division General Consideration or zone to zone NEC Section 500.2 Definition for Purging and Pressurization The process of 1) purging, supplying an enclosure with n Type Z pressurization reduces the classification within a protective gas at a sufficient flow and positive presthe protected enclosure from division or zone to sure to reduce the concentration of any flammable gas unclassified or vapor initially present to an acceptable level and 2) The enclosure volume for motors is also defined as the pressurization, supplying an enclosure with a protecvolume within the enclosure minus the volume of the intertive gas with or without continuous flow at sufficient nal components, e.g., rotors, stators, and field coils pressure to prevent the entrance of a flammable gas Under the fine print note (FPN), it says for further Requirements of Pressurized Enclosure information see ANSI/NFPA 496-2003, Purged and for Class I Location Pressurized Enclosures for Electrical Equipment The following are the requirements of pressurized encloNEC section 501.125(A)(2) provides the requirement sure for class I location for motors operating in class I division The second paran The enclosure shall be constructed of materials not graph of this section states that motors may be of likely to be damaged under the conditions to which the totally enclosed type supplied with positive presit may be subjected A typical pressurized motor ensure ventilation from a source of clean air with disclosure is shown in Figure 1(a) charge to a safe area, so arranged to prevent energizing n Protection shall be taken against excessive pressure of the machine, until ventilation has been established of the protective gas supply A typical pressurization n n n n n n n n system is shown in Figure 2, which can protect the enclosure from excessive pressure A pressure-relief device shall be provided to protect the enclosure from excessive pressure in the case of a control failure A typical location of such a device is shown in Figure 1(b) The pressure-relief devices shall be designed to prevent the discharge of ignition-capable particles to a division location Normal discharge of protective gas from a designated enclosure outlet shall be to an unclassified location, unless the outlet is designed to prevent the discharge of ignition-capable particles during normal operation In division and zone locations, conduit seals shall be installed as close as practical but not more than 18 in from the pressurized enclosure Where the protective gas supply has failed to maintain the required positive pressure, the enclosure shall be purged before reenergizing Air pockets shall be avoided (during design stage) to allow free airflow through the enclosure The specified positive pressure shall be maintained inside the pressurized enclosure after purging The compartments within the main enclosure or adjacent enclosures connected to the main enclosure n shall be considered separately, and protection shall be provided accordingly as explained later n The internal compartments or adjacent enclosures shall be purged in series or shall be purged separately n The internal compartment may be vented to the main enclosure by nonrestricted top and bottom vents that are common to the main enclosure Each vent shall provide not less than 6.5 cm2 (1.0 in2) of vent area for each 6,560 cm3 (400 in3) with a minimum vent size of 6.3 mm (one-fourth inch) diameter The equipment in the internal compartment or adjacent enclosure shall be protected by other means (e.g., explosion proof, intrinsic safety, hermetic sealing, nonincendive, encapsulation, and so forth) All typical devices and boxes are shown in Figure Pressurization System n n The enclosure shall be constantly maintained at a positive pressure of at least 25 Pa (0.1 in of water) above the surrounding atmosphere during the operation of protected equipment An alarm shall be provided to indicate failure of protective gas supply to maintain required pressure in type Y and type Z pressurization Equipotential Jumper Cables Pressurization system Relief Device (b) (a) Pressurized motor enclosure without a heat exchanger (b) Pressure-relief device mounted on a heat exchanger A typical division motor IEEE INDUSTRY APPLICATIONS MAGAZINE  NOV j DEC 2010  WWW.IEEE.ORG/IAS (a) 23 n All pressurization system components that may be energized in the absence of protective gas shall be approved for the classified location in which they are installed A typical pressurization system is shown in Figure Protective Gas System n n n n IEEE INDUSTRY APPLICATIONS MAGAZINE  NOV j DEC 2010  WWW.IEEE.ORG/IAS n 24 n Testing THE PURGE TIME VERIFICATION IS THE MOST CHALLENGING AND EXPENSIVE TEST TO PERFORM Air of normal instrument quality, nitrogen, or other nonflammable gas shall be permitted as a protective gas The compressed air intake shall be located in an unclassified location The protected equipment shall not be energized for type Y and type Z pressurization until at least ten volumes of purging gas have passed through the enclosure while maintaining an internal pressure of at least 25 Pa (0.1 in of water) The time for ten-volume change out and the required purging gas volume is specified by the manufacturer A means shall be used to prevent energizing of electrical equipment in type X pressurizing until at least ten volumes of purging gas have passed through the enclosure while maintaining an internal pressure of at least 25 Pa (0.1 in of water) An interlock shall be provided to deenergize all electrical circuits for the enclosures that can be readily opened without the use of a key or special tool in type X pressurization The interlock shall be approved for the external area classification Protected enclosures that contain hot parts requiring a cooldown period shall be designed to require the use of a special key or tool for opening NFPA 496 does not specify specific type tests or routine tests to validate the design criteria stated earlier However, it is a common practice for manufacturers to validate each design function during the witness of third-party inspection or as required by the local authorities The following tests are typically required by third-party inspectors or local authorities as a minimum to validate the design criteria: 1) functional tests or checks of pressurization system 2) the overpressure test of pressurized enclosures 3) the leakage test of pressurized enclosures to ensure the leakage is kept to the minimum or less than the allowable maximum limit of the pressurization system 4) the temperature class determination by running the heat run of motor and/or winding space heaters The temperature class for the large fabricated frame motor is generally determined from the maximum surface temperature of winding space heaters, which typically run hotter than the stator winding or rotor Markings n n n n Special warning nameplates are required, as specified in the clause 4.11 of NFPA 496 The external area classification, such as class I and division The pressurizing type, e.g., type X, type Y, or type Z The temperature class (T code) or the operating temperature in degree Celsius IEC Approach Determining of Temperature Class Marking General Consideration The temperature class (T code) marked on the enclosure shall represent (under normal operating conditions) the highest of the following: 1) the hottest enclosure external surface temperature 2) the hottest internal component surface temperature, e.g., surface temperature of winding space heaters 3) the temperature of the protecting gas leaving the enclosure IEC has prepared the 60079 series of standards for electrical equipment used in an explosive gas atmosphere IEC standard 60079-0 provides the general guidelines required for motors designed for hazardous areas IEC standard 60079-2 provides the specific requirement for purged and pressurized enclosures, p type of protection The following paragraphs will refer to both standards The IEC approach is more descriptive and definitive rather than specifying the design requirements IEC 60079-2 specifies the requirements of the protected motor enclosure, safety control devices, and design validation by tests The last revision in the year of 2007, IEC 60079-2 standard, introduced the equipment protection levels (EPLs) to establish the relative risk of the product becoming a source of ignition The following three EPLs are defined in the standard for electric equipments designed for gas group II, explosive gas atmospheres n EPL Ga: equipment for explosive gas atmospheres having a very high level of protection, which is not a source of ignition in normal operation, during expected malfunctions, or during rare malfunctions It is typically provided in zone explosive gas atmospheres and cannot be achieved using pressurization n EPL Gb: equipment for explosive gas atmospheres having a high level of protection, which is not a Wiring Practices and Auxiliary Equipments The external wiring for all auxiliary devices is typically provided in rigid metal conduit, although other wiring methods suitable for the area may be used All connectors, elbows, and T joints in rigid conduit runs are required to be approved for the location Conduit seals are provided near the protected enclosure, within 18 in, and at the entry of explosion-proof boxes, as shown in Figure The main power terminal box employs a series-pressurization system All auxiliary devices must be approved for the location As a good practice, bonding jumpers across the various components in a multisectioned enclosure are typically provided Doing so achieves equal potential across all parts and mitigates the risk of ignition because of high-energy discharge A photograph of a typical equipotential jumper is shown in Figure n source of ignition in normal operation or during expected malfunctions It is typically provided in zone explosive gas atmospheres and can be achieved by px and py types of protection EPL Gc: equipment for explosive gas atmospheres having an enhanced level of protection, which is not a source of ignition in normal operation and which may have some additional protection to ensure that it remains inactive as an ignition source It is typically provided in zone explosive gas atmospheres and can be achieved by pz type of protection Design, Construction, and Testing Design and construction are very similar to NEC, with minor changes as highlighted later Construction Requirements of Pressurized Enclosure Internal manifold system Temperature Class Determination The temperature class is determined based on the hottest surface Gas/vapor Zone Type px Type py Gas/vapor Zone Type px Type pz IEEE INDUSTRY APPLICATIONS MAGAZINE  NOV j DEC 2010  WWW.IEEE.ORG/IAS The NEC protection methods used in the division system, type X, type Y, and type Z pressurization, are designated as px, py, and pz types of protection, respectively, in IEC temperature of the internal or external component of motor 60079-2 standard for the zone system The definition of As was the case with divisions, it is typically determined from these three types of protection are similar to those in the the operating surface temperature of winding space heaters, which can often run hotter than the stator or rotor NEC for the division system In a type px-pressurized enclosure, the internal compoHowever, the definition of enclosure volume in IEC 60079-2 is not the same as in NEC It is defined as follows: nent temperature may exceed the marked temperature class if the time period sufficient to permit the component to cool Enclosure volume is a volume of the empty enclosure to the marked temperature class is specified Appropriate without internal apparatus The free internal volume measures shall be taken to prevent, if pressurization ceases, of the rotating electrical machines is the volume of any explosive gas atmosphere, which may exist making conenclosure without internal apparatus plus the volume tact with the hot component surface before it has cooled displaced by the rotor A few more requirements over and above the NEC [1] below the permitted maximum value The maximum permitted value of each temperature class is provided in the for pressurized enclosure are specified later: IEC 60079-0 [3] standard This type of protection is typin The mechanical strength of an enclosure is such that the enclosure, including ducts, if any, withstand cally provided in motors operating in zone area In a type py enclosure, hot ignition-capable parts in nor1.5 times the maximum overpressure specified by the manufacturer for normal service, with all outlets mal operation are not permitted inside the enclosure This type of protection is generally provided for instrumentaclosed with a minimum of 200 Pa tion operating in zone areas n Apertures and partitions are located in the internal In a type pz enclosure, the temperature class shall be compartment in such a way that an effective purging is ensured A well-designed manifold system based on the hottest external surface of the enclosure This provided in the enclosure will help to provide effec- type of protection is typically provided to motors operating tive purging A typical manifold system is shown in in zone area Figure The internal partitions are also considered in design to avoid dead pockets Safety Provisions and Safety Devices for Hazardous Area n Internal compartments are required to be vented to the Safety provisions are discussed later for the type px-protected main enclosure or be separately purged If they are motors operating in zone hazardous area A typical pressurvented, then vents providing not less than cm2 of vent ization system shown in Figure has all the safety devices The following are the minimum key design criteria for area for each 1,000 cm3, with a minimum vent size of px protection 6.3 mm diameter are provided for adequate purging n Sealing [ingress protection (IP)] of the enclosure is n One or more automatic safety devices shall be provided maintained by any installed cable glands or conduits to operate when the pressurized enclosure overpressure If the cable glands or conduits are not sealed, they TABLE DETERMINATION OF PROTECTION TYPE have to be considered as part of the pressurized enclosure Enclosure Does A quick summary of the types Enclosure Contains Not Contain External Flammable of protection for IEC/zones is proIgnition-Capable Area Substance in Ignition-Capable vided in Table Motor Enclosure Classification Apparatus Apparatus 25 IEEE INDUSTRY APPLICATIONS MAGAZINE  NOV j DEC 2010  WWW.IEEE.ORG/IAS 26 Air of normal instrument quality, falls below the minimum value nitrogen, or other nonflammable gas is The minimum overpressure for px BONDING considered acceptable as a protective or py is 50 Pa and for pz is 25 Pa gas Typically, clean instrument air is This overpressure shall be mainJUMPERS ACROSS used in motors for purging and prestained relative to the external THE VARIOUS surization The protective gas temperapressure at every point within the ture shall not normally exceed 40 °C at pressurized enclosure COMPONENTS the inlet of the enclosure n Safety devices shall be provided to prevent electrical equipment IN A within a pressurized enclosure Wiring Practices and from becoming energized until Auxiliary Equipments MULTISECTIONED purging has been completed The wiring practice is different for motors installed in accordance with n The automated sequence of opENCLOSURE ARE IEC 60079-14 [6] In an IEC-based ineration of the safety devices for px PROVIDED stallation, the typical installation employs pressurization shall be as follows: cable and cable glands at the terminal 1) following the initiation of boxes of the pressurized enclosure the sequence, the purging flow through and the overpressure in the pressurized However, in accordance with IEC 60079-14, wiring enclosure shall be monitored; purging flow will with conduit and appropriate seals, although unusual, be as specified by the manufacturer, and the mini- are equally acceptable All other accessories shall be suitably protected for the mum overpressure of 50 Pa shall be monitored 2) the purging timer can be started after achieving location The auxiliary boxes with terminals are typically Ex e minimum flow rate and overpressure, as speci- [7] (increased safety) installed with cable and cable glands As in the NEC installation, equipotential bonding cable fied by the manufacturer 3) after finishing purge time, the internal protected jumpers are provided in large fabricated frame motors to avoid the potential of arcing or sparking across metal enclosures electrical equipment can then be energized 4) the circuit shall be arranged to reset to the beginning in the event of the failure of any step in the Testing to Validate Design sequence IEC 60079-2 requires type tests and routine tests to be performed on a pressurized enclosure to validate the design n A safety device with interlock to disconnect power supply to an electrical equipment if door or covers of criteria as specified in the standard Type tests as specified in the standard are as follows: motor can be opened without the use of a tool or key n A safety device to protect pressurized enclosure n Maximum overpressure test on the enclosure, which from exceeding maximum design pressure when is 1.5 times design pressure the regulator fails This is required for the comn Leakage test to confirm the specified maximum leakpressed air system used for pressurization age rate of the pressurized enclosure n Purging test to verify specified purge time by argon (heavier than air) and helium (lighter than air) test gases Purging Criteria and Media for px Pressurization The minimum purge flow and time is based upon a fiven Verification of minimum overpressure of 50 Pa for enclosure-volume change out It is determined from the test px enclosure This test shall be performed stopping or from the calculation by inspection authority The manuthe motor and running at its maximum speed Presfacturer shall specify the minimum purge flow and time sure is likely to be measured at the lowest pressure based on the specified test criteria provided in the standard point in an enclosure n Verifying ability of the pressurized enclosure to limit internal pressure in the case of regulator failure of safety device This is required only when the enclosure is designed for use with compressed air and where leakage vents or pressure-relief devices are relied upon to limit the maximum overpressure when a regulator fails Routine test specified in the standard are as follows: n functional test of safety devices shall be verified n leakage test (same as type test) The validations of the earlier tests are very expensive, extensive, and time consuming These tests require setting up of a completely assembled motor on the test floor to perform all tests (typically during a third-party witness) Out of all those tests, the purge time verification is the most challenging and expensive test to perform A typical test setup for the purge time verification with argon and helium gases of 18-MW, 30-pole, 10-kV, 50-Hz, synchronous motor is shown in Figure Motor test setup for purge verification test to be applied to assure safety and protection Two parallel apVerified Verified Expected proaches, North American NEC/ Quoted Purged Purge Five-Volume CEC and international IEC sysPurge Time with Time with Change tems, address the requirements Time Helium Gas Argon Gas Purge Time for the equipment installed in (min) kW/Pole (min) (min) (min) these locations Although essentially equal, the two systems are 18,000/30 45 45 28 90 not interchangeable, and it is the 1,950/32 30 32 26 60 obligation of the purchaser to advise which specific codes and/or 8,430/4 30 44.5 31.2 60 standards are appropriate for the specific installation and what (if any) third-party certification is The results of the purge time being verified with argon required It is the responsibility of the purchaser or user to and helium gases on a few motors are provided in Table satisfy the legal requirements of the AHJ The Annexure A of the standard 60079-2 [4] was followed Acknowledgments for the purge time verification methods The last 8,430-kW four-pole motor was the first pres- The authors acknowledge Mr Jason Ball, Ms Brennan surized enclosure motor tested with gases Since then, the Orr, and other colleagues for reviewing this article and proother two motors have an improved manifold system and viding their valuable input an internal enclosure design The first two motors in the table have come very close to the minimum required purge References [1] National Electrical Code (NEC), 2008 [Also known as National Fire time; however, the quoted purge time provided to the Protection Association, NFPA 70] customer is increased for the additional safety factor over [2] Canadian Electrical Code (CEC) Part 1, Canadian Standards Association the life of the motor C22.1-06, 2006 The purge time verified with gases has a major impact [3] Explosive Atmospheres—Part 0: Equipment—General Requirements, International Electrotechnical Commission (IEC) IEC 60079-0, 2007 on how the internal manifold system has been designed [4] Explosive Atmospheres—Part 2: Equipment—Protection by Pressurized and confirming that there is no blocking of the airflow to Enclosure “p,” International Electrotechnical Commission (IEC) IEC create dead pockets for hazardous gas The data in Table 60079-2, 2007 also shows the longer purge time verified from the argon [5] NFPA 496: Standard for Purged and Pressurized Enclosures for Electrical Equipment, 2003 gas test TABLE EXAMPLE OF PURGE TIMES [6] Electric Apparatus for Explosive Gas Atmospheres—Part 14: Electrical Installations in Hazardous Areas (Other Than Mines), International Electrotechnical Commission (IEC) IEC 60079-14, 2002 [7] Electric Apparatus for Explosive Gas Atmospheres—Part 10: Classification of Hazardous Areas, International Electrotechnical Commission (IEC) IEC 60079-10, 2002 [8] Explosive Atmospheres—Part 7: Equipment Protection by Increased Safety “e,” International Electrotechnical Commission (IEC) IEC 60079-7, 2006 [9] Rotating Electric Machines, Part 1: Rating and Performance, International Electrotechnical Commission (IEC) IEC 60034-1, 2004 [10] B Mistry and D Somma, “Which motor would you choose for your hazardous area? Type n, e or p!” in Proc Petroleum and Chemical Industry Conf., PCIC 2006-22, Philadelphia, PA, 2006, pp 1–10 [11] J Gardner and F Dixon, “Purged and pressurized systems for class 1, div & 2, and zone & hazardous locations,” in Proc Petroleum and Chemical Industry Conf., PCIC 2006-26, Philadelphia, PA, 2006, pp 1–7 [12] D295 Super Mini Purge Manual ML360 [13] Electrical Apparatus for Explosive Gas Atmospheres—Part Pressurization “p,” ANSI/ISA 60079-2, 2004 [14] Electrical Apparatus for Explosive Gas Atmospheres—Part Pressurization “p,” CAN/CSA-E60079-2, 2002 (re-affirmed 2006) Bharat Mistry (bharat.mistry@ge.com) is with General Electric Canada in Peterborough, Ontario William G Lawrence is with FM Approvals in Norwood, Massachusetts Mistry is a Member of the IEEE Lawrence is a Senior Member of the IEEE This article first appeared as “Purged and Pressurized Motors Made to IEC/NEC/CEC Zone (EX P) and to NEC/CEC Division (Type X): Are They the Same?” at the 2007 Petroleum and Chemical Industry Conference IEEE INDUSTRY APPLICATIONS MAGAZINE  NOV j DEC 2010  WWW.IEEE.ORG/IAS Conclusions The design, construction, and application requirements for purged and pressurized motors are very similar in both NEC and IEC standards other than a few differences discussed in the article The wiring practices for the North American and IEC worlds are generally conduit based and cable based, respectively; however, both wiring methods are accepted in both systems Despite those similarities (and wiring practice differences), there is no direct replacement of motor built for either system The purging time required by NFPA 496 has a good safety margin by requiring the ten-volume air exchanges and, thus, may not require verification by argon or helium gases In contrast, the IEC-calculated purge time may not be enough based on a five-volume air exchange The purge time based on a five-volume air exchange may be good for a smaller size enclosure; however, it has to be looked at carefully in determining purge time for the large fabricated frame motors when the verifying test has not been performed with argon and helium test gases A motor designed to meet the performance requirements of the IEC will not likely qualify to meet the purge time requirement of NEC The safety of the people working in either division or zone hazardous (classified) locations and the protection of the facility is a prime concern Worldwide, LAHJ has the legal authority to mandate the specific codes or standards 27 ... to the NFPA 496 [5] standard for requirements for purged and pressurized enclosures NEC Article 500.5(B)(1) Definition for Division Comparatively, for zone locations, IEC standard 60079-0 A class... construction, and application requirements for purged and pressurized motors are very similar in both NEC and IEC standards other than a few differences discussed in the article The wiring practices for. .. series of standards for electrical equipment used in an explosive gas atmosphere IEC standard 60079-0 provides the general guidelines required for motors designed for hazardous areas IEC standard