Article 505

Zone 0, 1, and 2 Locations

Informational Note: Text that is followed by a reference in brackets has been extracted from NFPA 497-2012, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas. Only editorial changes were made to the extracted text to make it consistent with this Code.

Scope. This article covers the requirements for the zone classification system as an alternative to the division classi‐ fication system covered in Article 500 for electrical and elec‐ tronic equipment and wiring for all voltages in Class I, Zone 0, Zone 1, and Zone 2 hazardous (classified) locations where fire or explosion hazards may exist due to flammable gases, vapors, or liquids.Informational Note: For the requirements for electrical and electronic equipment and wiring for all voltages in Class I, Divi‐ sion 1 or Division 2; Class II, Division 1 or Division 2; and Class III, Division 1 or Division 2 hazardous (classified) locations where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, or combustible dusts or fibers, refer to Articles 500 through 504.•
Definitions.Encapsulation “m”. Type of protection where electrical parts that could ignite an explosive atmosphere by either sparking or heating are enclosed in a compound in such a way that this explosive atmosphere cannot be ignited.Informational Note No. 1: See ISA-60079-18-2012, Explosive atmospheres — Part 18: Equipment protection by encapsulation “m”; and ANSI/UL 60079-18-2009, Explosive atmospheres — Part 18: Equipment protection by encapsulation “m.”Informational Note No. 2: Encapsulation is designated type of protection “ma” for use in Zone 0 locations. Encapsulation is designated type of protection “m” or “mb” for use in Zone 1 locations. Encapsulation is designated type of protection “mc” for use in Zone 2 locations.Flameproof “d”. Type of protection where the enclosure will withstand an internal explosion of a flammable mixture that has penetrated into the interior, without suffering damage and without causing ignition, through any joints or structural open‐ ings in the enclosure of an external explosive gas atmosphere consisting of one or more of the gases or vapors for which it is designed.Informational Note: See ISA-60079-1-2009, Explosive Atmospheres, Part 1: Equipment protection by flameproof enclosures “d”; and ANSI/UL 60079-1-2009, Electrical Apparatus for Explosive Gas Atmospheres
- Part 1: Flameproof Enclosures “d.”Increased Safety “e”. Type of protection applied to electrical equipment that does not produce arcs or sparks in normal serv‐ ice and under specified abnormal conditions, in which addi‐ tional measures are applied so as to give increased security against the possibility of excessive temperatures and of the occurrence of arcs and sparks.Informational Note: See ISA-60079-7-2013, Explosive Atmospheres
- Part 7: Equipment protection by increased safety “e”; and ANSI/ UL 60079-7–2008, Electrical Apparatus for Explosive Gas Atmospheres
- Part 7: Increased Safety “e.”Intrinsic Safety “i”. Type of protection where any spark or thermal effect is incapable of causing ignition of a mixture of flammable or combustible material in air under prescribed test conditions.Informational Note No. 1: See UL 913-2015, Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, II, and III, Division 1 Hazardous (Classified) Locations ; ISA-60079-11 (12.02.01)-2011, Explosive Atmospheres — Part 11: Equipment protec‐ tion by intrinsic safety “i”; and ANSI/UL 60079-11-2011, Explosive Atmospheres — Part 11: Equipment protection by intrinsic safety “i.”Informational Note No. 2: Intrinsic safety is designated type of protection “ia” for use in Zone 0 locations. Intrinsic safety is designated type of protection “ib” for use in Zone 1 locations. Intrinsic safety is designated type of protection “ic” for use in Zone 2 locations.Informational Note No. 3: Intrinsically safe associated apparatus, designated by [ia], [ib], or [ic], is connected to intrinsically safe apparatus (“ia,” “ib,” or “ic,” respectively) but is located outside the hazardous (classified) location unless also protected by another type of protection (such as flameproof).Oil Immersion “o”. Type of protection where electrical equip‐ ment is immersed in a protective liquid in such a way that an explosive atmosphere that may be above the liquid or outside the enclosure cannot be ignited.Informational Note: See ANSI/ISA-60079-6-2009, Explosive Atmospheres — Part 6: Equipment protection by oil immersion “o”; and ANSI/UL 60079-6-2009, Electrical Apparatus for Explosive Gas Atmospheres — Part 6: Oil-Immersion “o.”Powder Filling “q”. Type of protection where electrical parts capable of igniting an explosive atmosphere are fixed in posi‐ tion and completely surrounded by filling material (glass or quartz powder) to prevent the ignition of an external explosive atmosphere.Informational Note: See ANSI/ISA-60079-5-2009, Explosive Atmospheres — Part 5: Equipment protection by powder filling “q”; and ANSI/UL 60079-5-2009, Electrical Apparatus for Explosive Gas Atmospheres — Part 5: Powder Filling “q.”Pressurization “p”. Type of protection for electrical equip‐ ment that uses the technique of guarding against the ingress of the external atmosphere, which may be explosive, into an enclosure by maintaining a protective gas therein at a pressure above that of the external atmosphere.Informational Note: See ANSI/UL-60079-2-2015, Explosive Atmos‐ pheres — Part 2: Equipment protection by pressurized enclosures “p”; and IEC 60079-13-2010, Electrical apparatus for explosive gas atmos‐ pheres — Part 13: Construction and use of rooms or buildings protected by pressurization.
  Type of Protection “n”. Type of protection where electrical equipment, in normal operation, is not capable of igniting a surrounding explosive gas atmosphere and a fault capable of causing ignition is not likely to occur.Informational Note: See ANSI/UL 60079-15-2009, Electrical Apparatus for Explosive Gas Atmospheres — Part 15: Type of Protection “n”; and ANSI/ISA-60079-15-2012, Explosive Atmospheres — Part 15: Equipment protection by type of protection “n.”•
Other Articles. All other applicable rules contained inthis Code shall apply to electrical equipment and wiring instal‐ led in hazardous (classified) locations.Exception: As modified by Article 504 and this article.
General.
1. Documentation for Industrial Occupancies. All areas in industrial occupancies designated as hazardous (classified) locations shall be properly documented. This documentation shall be available to those authorized to design, install, inspect, maintain, or operate electrical equipment at the location.Informational Note No. 2: Where gas detection equipment isused as a means of protection in accordance with 505.8(I)(1), (I)(2), or (I)(3), the documentation typically includes the type of detection equipment, its listing, installation location(s), alarm and shutdown criteria, and calibration frequency.Informational Note No. 1: For examples of area classification drawings, see ANSI/API RP 505-1997, Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Zone 0, Zone 1, or Zone 2; ANSI/ ISA-60079-10-1 (12.24.01)-2014 Explosive Atmospheres — Part 10-1: Classification of Areas — Explosive gas atmospheres ; and Model Code of Safe Practice in the Petroleum Industry, Part 15: Area Classification Code for Installations Handling Flammable Fluids, EI 15 :2005, Energy Institute, London.Informational Note No. 4: For further information on ventila‐ tion, see NFPA 30 -2015, Flammable and Combustible Liquids Code, and ANSI/API RP 505-1997, Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Zone 0, Zone 1, or Zone 2.Informational Note No. 5: For further information on electrical systems for hazardous (classified) locations on offshore oil and gas producing platforms, see ANSI/API RP 14FZ-2013, Recom‐ mended Practice for Design and Installation of Electrical Systems for Fixed and Floating Offshore Petroleum Facilities for Unclassified and Class I, Zone 0, Zone 1, and Zone 2 Locations.Informational Note No. 6: For further information on the instal‐ lation of electrical equipment in hazardous (classified) locations in general, see IEC 60079-14-2013, Electrical apparatus for explosive gas atmospheres — Part 14: Electrical installations in explosive gas atmospheres (other than mines), and IEC 60079-16-1990, Electrical apparatus for explosive gas atmospheres — Part 16: Artificial ventila‐ tion for the protection of analyzer(s) houses.Informational Note No. 7: For further information on applica‐ tion of electrical equipment in hazardous (classified) locations in general, see ANSI/ISA-60079-0 (12.00.01)-2013, Explosive Atmospheres — Part 0: Equipment — General Requirements; ANSI/ ISA-12.01.01-2013, Definitions and Information Pertaining to Electri‐ cal Apparatus in Hazardous (Classified) Locations; and ANSI/ UL 60079-0:2013, Electrical Apparatus for Explosive Gas AtmospheresInformational Note No. 8: Portable or transportable equipmenthaving self-contained power supplies, such as battery-operated equipment, could potentially become an ignition source in hazardous (classified) locations. See ANSI/ISA-12.12.03-2011, Standard for Portable Electronic Products Suitable for Use in Class I and II, Division 2, Class I Zone 2 and Class III, Division 1 and 2 Hazard‐ ous (Classified) Locations.
  - Part 0: General Requirements.
2. Reference Standards. Important information relating to topics covered in Chapter 5 may be found in other publica‐ tions.
Informational Note No. 1: It is important that the authority having jurisdiction be familiar with recorded industrial experi‐ ence as well as with standards of the National Fire Protection Association (NFPA), the American Petroleum Institute (API), the International Society of Automation (ISA), and the Interna‐ tional Electrotechnical Commission (IEC) that may be of use in the classification of various locations, the determination of adequate ventilation, and the protection against static electricity and lightning hazards.Informational Note No. 2: For further information on the classi‐ fication of locations, see NFPA 497-2012, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemi‐ cal Process Areas; ANSI/API RP 505-1997, Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Zone 0, Zone 1, or Zone 2; ANSI/ ISA-60079-10-1 (12.24.01)-2014, Explosive Atmospheres — Part 10-1: Classification of Areas — Explosive gas atmospheres ; and Model Code of Safe Practice in the Petroleum Industry, Part 15: Area Classification Code for Installations Handling Flammable Fluids, EI 15 :2005, Energy Institute, London.Informational Note No. 3: For further information on protec‐ tion against static electricity and lightning hazards in hazardous (classified) locations, see NFPA 77-2014, Recommended Practice on Static Electricity; NFPA 780-2014, Standard for the Installation of Lightning Protection Systems; and API RP 2003-2008, Protection Against Ignitions Arising Out of Static Lightning and Stray Currents.
Informational Note No. 9: For additional information concern‐ing the installation of equipment utilizing optical emissions technology (such as laser equipment) that could potentially become an ignition source in hazardous (classified) locations, see ANSI/ISA-60079-28 (12.21.02)-2013, Explosive Atmospheres — Part 28: Protection of equipment and transmission systems using optical radiation.
Classifications of Locations.
1. General. Locations shall be classified depending on the properties of the flammable gases, flammable liquid–produced vapors, combustible liquid–produced vapors, combustible dusts, or fibers/flyings that could be present and the likelihood that a flammable or combustible concentration or quantity is present. Each room, section, or area shall be considered indi‐ vidually in determining its classification. Where pyrophoric materials are the only materials used or handled, these loca‐ tions are outside the scope of this article.Informational Note No. 1: See 505.7 for restrictions on area clas‐ sification.Informational Note No. 2: Through the exercise of ingenuity in the layout of electrical installations for hazardous (classified) locations, it is frequently possible to locate much of the equip‐ ment in reduced level of classification or in an unclassified loca‐ tion and, thus, to reduce the amount of special equipment required.Refrigerant machinery rooms that contain ammonia refrig‐ eration systems and are equipped with adequate mechanical ventilation that operates continuously or is initiated by a detec‐ tion system at a concentration not exceeding 150 ppm shall be permitted to be classified as “unclassified” locations.
  Informational Note: For further information regarding classifi‐ cation and ventilation of areas involving closed-circuit ammonia refrigeration systems, see ANSI/ASHRAE 15-2013, Safety Stand‐ ard for Refrigeration Systems , and ANSI/IIAR 2-2014, Standard for Safe Design of Closed-Circuit Ammonia Refrigeration Systems.
2. Class I, Zone 0, 1, and 2 Locations. Class I, Zone 0, 1, and 2 locations are those in which flammable gases or vapors are or may be present in the air in quantities sufficient to produce explosive or ignitible mixtures. Class I, Zone 0, 1, and 2 loca‐ tions shall include those specified in 505.5(B)(1), (B)(2), and (B)(3).
  1. Class I, Zone 0. A Class I, Zone 0 location is a location in which one of the following conditions exists:
1. Ignitible concentrations of flammable gases or vapors are present continuously
2. Ignitible concentrations of flammable gases or vapors are present for long periods of time
Informational Note No. 1: As a guide in determining when flam‐ mable gases or vapors are present continuously or for long peri‐ ods of time, refer to ANSI/API RP 505-1997, Recommended Practice for Classification of Locations for Electrical Installations of Petroleum Facilities Classified as Class I, Zone 0, Zone 1 or Zone 2; ANSI/ISA 60079-10-1-2014, Explosive Atmospheres — Part 10-1: Classification of Areas — explosive gas atmospheres.Informational Note No. 2: This classification includes locations inside vented tanks or vessels that contain volatile flammable liquids; inside inadequately vented spraying or coating enclo‐ sures where volatile flammable solvents are used; between the inner and outer roof sections of a floating roof tank containing volatile flammable liquids; inside open vessels, tanks, and pits containing volatile flammable liquids; the interior of an exhaust duct that is used to vent ignitible concentrations of gases or vapors; and inside inadequately ventilated enclosures that contain normally venting instruments utilizing or analyzing flammable fluids and venting to the inside of the enclosures.(2) Class I, Zone 1. A Class I, Zone 1 location is a location
1. In which ignitible concentrations of flammable gases or vapors are likely to exist under normal operating condi‐ tions; or
2. In which ignitible concentrations of flammable gases or vapors may exist frequently because of repair or mainte‐ nance operations or because of leakage; or
3. In which equipment is operated or processes are carried on, of such a nature that equipment breakdown or faulty operations could result in the release of ignitible concen‐ trations of flammable gases or vapors and also cause simultaneous failure of electrical equipment in a mode to cause the electrical equipment to become a source of ignition; or
4. That is adjacent to a Class I, Zone 0 location from which ignitible concentrations of vapors could be communica‐ ted, unless communication is prevented by adequate posi‐ tive pressure ventilation from a source of clean air and effective safeguards against ventilation failure are provi‐ ded.
Informational Note No. 1: Normal operation is considered the situation when plant equipment is operating within its design parameters. Minor releases of flammable material may be part of normal operations. Minor releases include the releases from mechanical packings on pumps. Failures that involve repair or shutdown (such as the breakdown of pump seals and flange gaskets, and spillage caused by accidents) are not considered normal operation.Informational Note No. 2: This classification usually includes locations where volatile flammable liquids or liquefied flamma‐ ble gases are transferred from one container to another. In areas in the vicinity of spraying and painting operations where flam‐ mable solvents are used; adequately ventilated drying rooms or compartments for evaporation of flammable solvents; adequately ventilated locations containing fat and oil extraction equipment using volatile flammable solvents; portions of clean‐ ing and dyeing plants where volatile flammable liquids are used; adequately ventilated gas generator rooms and other portions of gas manufacturing plants where flammable gas may escape; inadequately ventilated pump rooms for flammable gas or for volatile flammable liquids; the interiors of refrigerators and freezers in which volatile flammable materials are stored in the open, lightly stoppered, or in easily ruptured containers; and other locations where ignitible concentrations of flammable vapors or gases are likely to occur in the course of normal opera‐ tion but not classified Zone 0.(3) Class I, Zone 2. A Class I, Zone 2 location is a location
1. In which ignitible concentrations of flammable gases or vapors are not likely to occur in normal operation and, if they do occur, will exist only for a short period; or
2. In which volatile flammable liquids, flammable gases, or flammable vapors are handled, processed, or used but in which the liquids, gases, or vapors normally are confined within closed containers of closed systems from which they can escape, only as a result of accidental rupture or breakdown of the containers or system, or as a result of the abnormal operation of the equipment with which the liquids or gases are handled, processed, or used; or
3. In which ignitible concentrations of flammable gases or vapors normally are prevented by positive mechanical ventilation but which may become hazardous as a result of failure or abnormal operation of the ventilation equip‐ ment; or
4. That is adjacent to a Class I, Zone 1 location, from which ignitible concentrations of flammable gases or vapors could be communicated, unless such communication is prevented by adequate positive-pressure ventilation from a source of clean air and effective safeguards against ventilation failure are provided.
Informational Note: The Zone 2 classification usually includes locations where volatile flammable liquids or flammable gases or vapors are used but which would become hazardous only in case of an accident or of some unusual operating condition.
Material Groups. For purposes of testing, approval, and area classification, various air mixtures (not oxygen enriched) shall be grouped as required in 505.6(A), (B), and (C).Informational Note No. 1: : Group I is intended for use in describing atmospheres that contain firedamp (a mixture of gases, composed mostly of methane, found underground, usually in mines). This Code does not apply to installations underground in mines. See 90.2(B).Informational Note No. 2: The gas and vapor subdivision as described above is based on the maximum experimental safe gap (MESG), minimum igniting current (MIC), or both. Test equipment for determining the MESG is described in IEC 60079-1A-1975, Amendment No. 1 (1993), Construction and verifi‐ cation tests of flameproof enclosures of electrical apparatus; and UL Technical Report No. 58 (1993). The test equipment for deter‐ mining MIC is described in IEC 60079-11-1999, Electrical appara‐ tus for explosive gas atmospheres — Part 11: Intrinsic safety “i.” The classification of gases or vapors according to their maximum experimental safe gaps and minimum igniting currents is descri‐ bed in IEC 60079-12-1978, Classification of mixtures of gases or
vapours with air according to their maximum experimental safe gaps and minimum igniting currents.Informational Note No. 3: Group II is currently subdivided into Group IIA, Group IIB, and Group IIC. Prior marking require‐ ments permitted some types of protection to be marked without a subdivision, showing only Group II.Informational Note No. 4: It is necessary that the meanings of the different equipment markings and Group II classifications be carefully observed to avoid confusion with Class I, Divisions 1 and 2, Groups A, B, C, and D.Class I, Zone 0, 1, and 2, groups shall be as follows:
1. Group IIC. Atmospheres containing acetylene, hydrogen, or flammable gas, flammable liquid–produced vapor, or combustible liquid–produced vapor mixed with air that may burn or explode, having either a maximum experimental safe gap (MESG) value less than or equal to 0.50 mm or minimum igniting current (MIC) ratio less than or equal to 0.45. [497: 3.3.5.2.3]Informational Note: Group IIC is equivalent to a combination of Class I, Group A, and Class I, Group B, as described in 500.6(A) (1) and (A)(2).
2. Group IIB. Atmospheres containing acetaldehyde, ethyl‐ ene, or flammable gas, flammable liquid–produced vapor, or combustible liquid–produced vapor mixed with air that may burn or explode, having either maximum experimental safe gap (MESG) values greater than 0.50 mm and less than or equal to 0.90 mm or minimum igniting current ratio (MIC ratio) greater than 0.45 and less than or equal to 0.80. [497:3.3.5.2.2]Informational Note: Group IIB is equivalent to Class I, Group C, as described in 500.6(A)(3).
3. Group IIA. Atmospheres containing acetone, ammonia, ethyl alcohol, gasoline, methane, propane, or flammable gas, flammable liquid–produced vapor, or combustible liquid– produced vapor mixed with air that may burn or explode, having either a maximum experimental safe gap (MESG) value greater than 0.90 mm or minimum igniting current (MIC) ratio greater than 0.80. [497: 3.3.5.2.1]Informational Note: Group IIA is equivalent to Class I, Group D as described in 500.6(A)(4).
Special Precaution. Article 505 requires equipment construction and installation that ensures safe performance under conditions of proper use and maintenance.Informational Note No. 1: It is important that inspection author‐ ities and users exercise more than ordinary care with regard to the installation and maintenance of electrical equipment in hazardous (classified) locations.Informational Note No. 2: Low ambient conditions require special consideration. Electrical equipment depending on the protection techniques described by 505.8(A) may not be suita‐ ble for use at temperatures lower than -20°C (-4°F) unless they are identified for use at lower temperatures. However, at low ambient temperatures, flammable concentrations of vapors may not exist in a location classified Class I, Zones 0, 1, or 2 at normal ambient temperature.
1. Implementation of Zone Classification System. Classifica‐ tion of areas, engineering and design, selection of equipment and wiring methods, installation, and inspection shall be performed by qualified persons.
2. Dual Classification. In instances of areas within the same facility classified separately, Class I, Zone 2 locations shall be permitted to abut, but not overlap, Class I, Division 2 locations. Class I, Zone 0 or Zone 1 locations shall not abut Class I, Divi‐ sion 1 or Division 2 locations. [33:6.2.4]
3. Reclassification Permitted. A Class I, Division 1 or Divi‐ sion 2 location shall be permitted to be reclassified as a Class I, Zone 0, Zone 1, or Zone 2 location, provided all of the space that is classified because of a single flammable gas or vapor source is reclassified under the requirements of this article.
4. Solid Obstacles. Flameproof equipment with flanged joints shall not be installed such that the flange openings are closer than the distances shown in Table 505.7(D) to any solid obstacle that is not a part of the equipment (such as steelworks, walls, weather guards, mounting brackets, pipes, or other elec‐ trical equipment) unless the equipment is listed for a smaller distance of separation.
5. Simultaneous Presence of Flammable Gases and Combus‐ tible Dusts or Fibers/Flyings. Where flammable gases, combustible dusts, or fibers/flyings are or may be present at the same time, the simultaneous presence shall be considered during the selection and installation of the electrical equip‐ ment and the wiring methods, including the determination of the safe operating temperature of the electrical equipment.
6. Available Short-Circuit Current for Type of Protection “e”. Unless listed and marked for connection to circuits with higher available short-circuit current, the available short-circuit current for electrical equipment using type of protection “e” for the field wiring connections in Zone 1 locations shall be limited to 10,000 rms symmetrical amperes to reduce the likeli‐ hood of ignition of a flammable atmosphere by an arc during a short-circuit event.
Informational Note: Limitation of the available short-circuit current to this level may require the application of current- limiting fuses or current-limiting circuit breakers.
Protection Techniques. Acceptable protection techni‐ ques for electrical and electronic equipment in hazardous (classified) locations shall be as described in 505.8(A) through (I).Informational Note: For additional information, see ANSI/ ISA-60079-0 (12.00.01)-2009, Explosive Atmospheres — Part 0: Equipment —- General Requirements; ANSI/ISA-12.01.01-1999, Defi‐ nitions and Information Pertaining to Electrical Apparatus in Hazard‐ ous (Classified) Locations; and ANSI/UL 60079–0, Electrical Apparatus for Explosive Gas Atmospheres — Part 0: General Require‐ ments.
1. Flameproof “d”. This protection technique shall be permitted for equipment in Class I, Zone 1 or Zone 2 locations.
  Table 505.7(D) Minimum Distance of Obstructions from Flameproof “d” Flange Openings
  Gas Groupmmin.IIC40137∕64IIB3013∕16IIA1025∕64Minimum Distance
2. Pressurization “p”. This protection technique shall be permitted for equipment in those Class I, Zone 1 or Zone 2 locations for which it is identified.
3. Intrinsic Safety “i”. This protection technique shall be permitted for apparatus and associated apparatus in Class I, Zone 0, Zone 1, or Zone 2 locations for which it is listed.
4. Type of Protection “n”. This protection technique shall be permitted for equipment in Class I, Zone 2 locations. Type of protection “n” is further subdivided into nA, nC, and nR.Informational Note: See Table 505.9(C)(2)(4) for the descrip‐ tions of subdivisions for type of protection “n”.
5. Oil Immersion “o”. This protection technique shall be permitted for equipment in Class I, Zone 1 or Zone 2 locations.
6. Increased Safety “e”. This protection technique shall be permitted for equipment in Class I, Zone 1 or Zone 2 locations.
7. Encapsulation “m”. This protection technique shall be permitted for equipment in Class I, Zone 0, Zone 1, or Zone 2 locations for which it is identified.Informational Note: See Table 505.9(C)(2)(4) for the descrip‐ tions of subdivisions for encapsulation.
8. Powder Filling “q”. This protection technique shall be permitted for equipment in Class I, Zone 1 or Zone 2 locations.
9. Combustible Gas Detection System. A combustible gas detection system shall be permitted as a means of protection in industrial establishments with restricted public access and where the conditions of maintenance and supervision ensure that only qualified persons service the installation. Where such a system is installed, equipment specified in 505.8(I)(1), (I)(2), or (I)(3) shall be permitted. The type of detection equipment, its listing, installation location(s), alarm and shutdown criteria, and calibration frequency shall be documented when combus‐ tible gas detectors are used as a protection technique.
Informational Note No. 1: For further information, see ANSI/API RP 505-1997, Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Zone 0, Zone 1, and Zone 2.Informational Note No. 2: For further information, see ANSI/ ISA-60079-29-2, Explosive Atmospheres — Part 29-2: Gas detectors — Selection, installation, use and maintenance of detectors for flammable gases and oxygen.Informational Note No. 3: For further information, see ANSI/ ISA-TR12.13.03-2009, Guide for Combustible Gas Detection as a Method of Protection.
1. Inadequate Ventilation. In a Class I, Zone 1 location that is so classified due to inadequate ventilation, electrical equip‐ ment suitable for Class I, Zone 2 locations shall be permitted. Combustible gas detection equipment shall be listed for Class I, Zone 1, for the appropriate material group, and for the detec‐ tion of the specific gas or vapor to be encountered.
2. Interior of a Building. In a building located in, or with an opening into, a Class I, Zone 2 location where the interior does not contain a source of flammable gas or vapor, electrical equipment for unclassified locations shall be permitted. Combustible gas detection equipment shall be listed for Class I,
3. Interior of a Control Panel. In the interior of a control panel containing instrumentation utilizing or measuring flam‐ mable liquids, gases, or vapors, electrical equipment suitable for Class I, Zone 2 locations shall be permitted. Combustible gas detection equipment shall be listed for Class I, Zone 1, for the appropriate material group, and for the detection of the specific gas or vapor to be encountered.
Equipment.

Suitability. Suitability of identified equipment shall be determined by one of the following:
1. Equipment listing or labeling
2. Evidence of equipment evaluation from a qualified test‐ ing laboratory or inspection agency concerned with prod‐ uct evaluation
3. Evidence acceptable to the authority having jurisdiction such as a manufacturer’s self-evaluation or an owner’s engineering judgment
Informational Note: Additional documentation for equipment may include certificates demonstrating compliance with applica‐ ble equipment standards, indicating special conditions of use, and other pertinent information.
Listing.
1. Equipment that is listed for a Zone 0 location shall be permitted in a Zone 1 or Zone 2 location of the same gas or vapor, provided that it is installed in accordance with the requirements for the marked type of protection. Equipment that is listed for a Zone 1 location shall be permitted in a Zone 2 location of the same gas or vapor, provided that it is installed in accordance with the requirements for the marked type of protection.
2. Equipment shall be permitted to be listed for a specific gas or vapor, specific mixtures of gases or vapors, or any specific combination of gases or vapors.
Informational Note: One common example is equipment marked for “IIB. + H2.”
Marking. Equipment shall be marked in accordance with 505.9(C)(1) or (C)(2).
1. Division Equipment. Equipment identified for Class I, Division 1 or Class I, Division 2 shall, in addition to being marked in accordance with 500.8(C), be permitted to be marked with all of the following:
  1. Class I, Zone 1 or Class I, Zone 2 (as applicable)
  2. Applicable gas classification group(s) in accordance with Table 505.9(C)(1)(2)
  3. Temperature classification in accordance with 505.9(D)(1)
  (2) Zone Equipment. Equipment meeting one or more of the protection techniques described in 505.8 shall be marked with all of the following in the order shown:
  1. Class
  2. Zone
    Table 505.9(C)(1)(2) Material Groups
    Material Group CommentZone 1 or Class I, Zone 2, for the appropriate material group, and for the detection of the specific gas or vapor to be encoun‐ tered.IIC See 505.6(A)IIB See 505.6(B)IIA See 505.6(C)
  3. Symbol “AEx” Table 505.9(C)(2)(4) Types of Protection Designation
  4. Protection technique(s) in accordance with Table 505.9(C)(2)(4)
  5. Applicable material group in accordance with Table 505.9(C)(1)(2) or a specific gas or vapor
  6. Temperature classification in accordance with 505.9(D)(1)
  Exception No. 1: Associated apparatus NOT suitable for installation in a hazardous (classified) location shall be required to be marked only with (3), (4), and (5), but BOTH the symbol AEx (3) and the symbol for the type of protection (4) shall be enclosed within the same square brackets, for example, [AEx ia] IIC.Exception No. 2: Simple apparatus as defined in 504.2 shall not be required to have a marked operating temperature or temperature class.Exception No. 3: Fittings for the termination of cables shall not be required to have a marked operating temperature or temperature class.Informational Note No. 1: An example of the required marking for intrinsically safe apparatus for installation in Class I, Zone 0 is “Class I, Zone 0, AEx ia IIC T6.” An explanation of the mark‐ ing that is required is shown in Informational Note Figure 505.9(C)(2), No. 1.Informational Note No. 2: An example of the required marking for intrinsically safe associated apparatus mounted in a flame‐ proof enclosure for installation in Class I, Zone 1 is “Class I, Zone 1 AEx d[ia] IIC T4.”Informational Note No. 3: An example of the required marking for intrinsically safe associated apparatus NOT for installation in a hazardous (classified) location is “[AEx ia] IIC.”Informational Note No. 4: The EPL (or equipment protection level) may appear in the product marking. EPLs are designated as G for gas, D for dust, or M for mining and are then followed by a letter (a, b, or c) to give the user a better understanding as to whether the equipment provides either (a) a “very high,” (b) a “high,” or (c) an “enhanced” level of protection against igni‐ tion of an explosive atmosphere. For example, a Class I, Zone 1, AEx d IIC T4 motor (which is suitable by protection concept for application in Zone 1) may additionally be marked with an EPL of “Gb” to indicate that it was provided with a high level of protection, such as Class I, Zone 1 AEx d IIC T4 Gb.Informational Note No. 5: Equipment installed outside a Zone 0 location, electrically connected to equipment located inside a Zone 0 location, may be marked Class I, Zone 0/1. The “/” indi‐ cates that equipment contains a separation element and can be installed at the boundary between a Zone 0 and a Zone 1 loca‐ tion. See ANSI/ISA-60079-26, Electrical Apparatus for Use in Class I, Zone 0 Hazardous (Classified) Locations.
Class I Temperature. The temperature marking specified in 505.9(D)(1) shall not exceed the autoignition temperature of the specific gas or vapor to be encountered.Informational Note: For information regarding autoignition temperatures of gases and vapors, see NFPA 497-2012, Recommen‐ ded Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installa‐ tions in Chemical Process Areas; and IEC 60079-20-1996, Electrical Apparatus for Explosive Gas Atmospheres, Data for Flammable Gases and Vapours, Relating to the Use of Electrical Apparatus.
1. Temperature Classifications. Equipment shall be marked to show the operating temperature or temperature class refer‐ enced to a 40°C ambient, or at the higher ambient tempera‐ ture if the equipment is rated and marked for an ambient temperature of greater than 40°C. The temperature class, ifDesignation Technique Zone*
  1. Flameproof enclosure 1db Flameproof enclosure 1
  2. Increased safety 1
  eb Increased safety 1ia Intrinsic safety 0ib Intrinsic safety 1ic Intrinsic safety 2[ia] Associated apparatus Unclassified**[ib] Associated apparatus Unclassified**[ic] Associated apparatus Unclassified**ma Encapsulation 0m Encapsulation 1mb Encapsulation 1nANonsparking2
  equipment
  nAcNonsparking2
  equipment
  nCSparking equipment2mc Encapsulation 2in which the contacts are suitably protected other than by restricted breathing enclosurenCc Sparking equipment 2in which the contacts are suitably protected other than by restricted breathing enclosurenR Restricted breathing 2enclosurenRc Restricted breathing 2enclosureo Oil immersion 1ob Oil immersion 1px Pressurization 1pxb Pressurization 1py Pressurization 1pyb Pressurization 1pz Pressurization 2pzc Pressurization 2q Powder filled 1qb Powder filled 1*Does not address use where a combination of techniques is used.**Associated apparatus is permitted to be installed in a hazardous (classified) location if suitably protected using another type of protection.
  provided, shall be indicated using the temperature class (T code) shown in Table 505.9(D)(1).Electrical equipment designed for use in the ambient temperature range between -20°C and +40°C shall require no ambient temperature marking.
  
  Area classification
  Example: Class I Zone 0 AEx ia IIC T6NPT threaded entries into explosionproof or flameproof equipment shall be made up with at least five threads fully engaged.Symbol for equipment built to American standards
  Type(s) of protection designation Material groupTemperature classification
  Informational Note Figure 505.9(C)(2), No. 1, Equipment Marking.
  ZoneException: For listed explosionproof or flameproof equipment, factory- threaded NPT entries shall be made up with at least 41∕2 threads fully engaged.Informational Note No. 1: Thread specifications for male NPT threads are located in ASME B1.20.1-2013, Pipe Threads, General Purpose (Inch).Informational Note No. 2: Female NPT threaded entries use a modified National Standard Pipe Taper (NPT) thread with thread form per ASME B1.20.1-2013, Pipe Threads, General Purpose (Inch). See ANSI/UL 60079-1:2013, Explosive AtmospheresElectrical equipment that is designed for use in a range of ambient temperatures other than -20°C to +40°C is considered to be special; and the ambient temperature range shall then be marked on the equipment, including either the symbol “Ta” or “Tamb” together with the special range of ambient tempera‐ tures, in degrees Celsius.Informational Note: As an example, such a marking might be “-30°C to +40°C.”Exception No. 1: Equipment of the non–heat-producing type, such as conduit fittings, and equipment of the heat-producing type having a maximum temperature of not more than 100°C (212°F) shall not be required to have a marked operating temperature or temperature class.Exception No. 2: Equipment identified for Class I, Division 1 or Divi‐ sion 2 locations as permitted by 505.20(A), (B), and (C) shall be permitted to be marked in accordance with 505.8(C) and Table 500.8(C).
Threading. The supply connection entry thread form shall be NPT or metric. Conduit and fittings shall be made wrenchtight to prevent sparking when fault current flows through the conduit system, and to ensure the explosionproof or flameproof integrity of the conduit system where applicable. Equipment provided with threaded entries for field wiring connections shall be installed in accordance with 505.9(E)(1) or (E)(2) and with (E)(3).
1. Equipment Provided with Threaded Entries for NPT Threaded Conduit or Fittings. For equipment provided with threaded entries for NPT threaded conduit or fittings, listed conduit, listed conduit fittings, or listed cable fittings shall be used.All NPT threaded conduit and fittings shall be threaded with a National (American) Standard Pipe Taper (NPT) thread.— Part 1: Equipment Protection by Flameproof Enclosures “d”; and ANSI/ISA 60079-1:2013, Explosive Atmospheres — Part 1: Equip‐ ment Protection by Flameproof Enclosures “d”.
2. Equipment Provided with Threaded Entries for Metric Threaded Conduit or Fittings. For equipment with metric threaded entries, listed conduit fittings or listed cable fittings shall be used. Such entries shall be identified as being metric, or listed adapters to permit connection to conduit or NPT threaded fittings shall be provided with the equipment and shall be used for connection to conduit or NPT threaded fittings.Metric threaded fittings installed into explosionproof or flameproof equipment entries shall have a class of fit of at least 6g/6H and be made up with at least five threads fully engaged for Groups C, D, IIB, or IIA and not less than eight threads fully engaged and wrenchtight.Informational Note: Threading specifications for metric threa‐ ded entries are located in ISO 965-1-2013, ISO general purpose metric screw threads — Tolerances — Part 1: Principles and basic data; and ISO 965-3-1998, ISO general purpose metric screw threads — Tolerances — Part 3: Deviations for constructional screw threads.
3. Unused Openings. All unused openings shall be closed with close-up plugs listed for the location and shall maintain the type of protection. The plug engagement shall comply with 505.9(E)(1) or 505.9(E)(2).in accord‐
Optical Fiber Cables. An optical fiber cable, with or with‐ out current-carrying current (composite optical fiber cable), shall be installed to address the associated fire hazard and sealed to address the associated explosion hazard

ance with the requirements of 505.15 and 505.16.

505.15 Wiring Methods. Wiring methods shall maintain the integrity of protection techniques and shall comply with 505.15(A) through (C).

Table 505.9(D)(1) Classification of Maximum Surface Temperature for Group II Electrical Equipment

Maximum Surface Temperature

equipment protected by intrinsic safety “ia” and equipment protected by encapsulation “ma” shall be connected using intrinsically safe “ia” circuits with wiring methods in accordance with Article 504.

(A) Class I, Zone 0. In Class I, Zone 0 locations,

Class I, Zone 1.Temperature Class (T Code)(°C)
1. General. In Class I, Zone 1 locations, the wiring methodsT1 ≤450T2 ≤300T3 ≤200T4 ≤135T5 ≤100T6 ≤85in 505.15(B)(1)(a) through (B)(1)(i) shall be permitted.
  1. All wiring methods permitted by 505.15(A).
  2. In industrial establishments with restricted public access, where the conditions of maintenance and supervision ensure that only qualified persons service the installation, and where the cable is not subject to physical damage, Type MC-HL
    cable listed for use in Class I, Zone 1 or Division 1 locations, with a gas/vaportight continuous corrugated metallic sheath, an overall jacket of suitable polymeric material, and a separate equipment grounding conductor(s) in accordance with 250.122, and terminated with fittings listed for the application. Type MC-HL cable shall be installed in accordance with the provisions of Article 330, Part II.
  3. In industrial establishments with restricted public access, where the conditions of maintenance and supervision ensure that only qualified persons service the installation, and where the cable is not subject to physical damage, Type ITC-HL cable listed for use in Class I, Zone 1 or Division 1 locations, with a gas/vaportight continuous corrugated metallic sheath and an overall jacket of suitable polymeric material, and termi‐ nated with fittings listed for the application. Type ITC-HL cable shall be installed in accordance with the provisions of Arti‐ cle 727.Informational Note: See 727.4 and 727.5 for restrictions on use of Type ITC cable.
  4. Type MI cable terminated with fittings listed for Class I, Zone 1 or Division 1 locations. Type MI cable shall be installed and supported in a manner to avoid tensile stress at the termination fittings.
  5. Threaded rigid metal conduit, or threaded steel intermediate metal conduit.
  6. Type PVC conduit and Type RTRC conduit shall be permitted where encased in a concrete envelope a minimum of 50 mm (2 in.) thick and provided with not less than 600 mm (24 in.) of cover measured from the top of the conduit to grade. Threaded rigid metal conduit or threaded steel inter‐ mediate metal conduit shall be used for the last 600 mm (24 in.) of the underground run to emergence or to the point of connection to the aboveground raceway. An equipment grounding conductor shall be included to provide for electrical continuity of the raceway system and for grounding of non– current-carrying metal parts.
  7. Intrinsic safety type of protection “ib” shall be permit‐ ted using the wiring methods specified in Article 504.Informational Note: For entry into enclosures required to be flameproof, explosionproof, or of increased safety, see the infor‐ mation on construction, testing, and marking of cables; flame‐ proof and increased safety cable fittings; and flameproof and increased safety cord connectors in ANSI/UL 2225-2013, Cables and Cable-Fittings for Use in Hazardous (Classified) Locations.
  8. Optical fiber cable Types OFNP, OFCP, OFNR, OFCR, OFNG, OFCG, OFN, and OFC shall be permitted to be installed in raceways in accordance with 505.15(B). Optical fiber cable shall be sealed in accordance with 505.16.Informational Note: For entry into enclosures required to be flameproof, explosionproof, or of increased safety, see the infor‐ mation on construction, testing, and marking of cables; flame‐ proof and increased safety cable fittings; and flameproof and increased safety cord connectors in ANSI/UL 2225-2013, Cables and Cable-Fittings for Use in Hazardous (Classified) Locations.
  9. In industrial establishments with restricted public access, where the conditions of maintenance and supervision ensure that only qualified persons service the installation, for applications limited to 600 volts nominal or less, for cable diameters 25 mm (1 in.) or less, and where the cable is not subject to physical damage, Type TC-ER-HL cable listed for use in Class I, Zone 1 locations, with an overall jacket and a sepa‐ rate equipment grounding conductor(s) in accordance with
  250.122, and terminated with fittings listed for the location, Type TC-ER-HL cable shall be installed in accordance with the provisions of Article 336, including the restrictions of 336.10(7).
2. Flexible Connections. Where necessary to employ flexible connections, flexible fittings listed for Class I, Zone 1 or Divi‐ sion 1 locations, or flexible cord in accordance with the provi‐ sions of 505.17(A) terminated with a listed cord connector that maintains the type of protection of the terminal compartment, shall be permitted.
Class I, Zone 2.
1. General. In Class I, Zone 2 locations, the following wiring methods shall be permitted:

All wiring methods permitted by 505.15(B).
Types MC, MV, TC, or TC-ER cable, including installation in cable tray systems. The cable shall be terminated with listed fittings. Single conductor Type MV cables shall be shielded or metallic-armored.
Type ITC and Type ITC-ER cable as permitted in 727.4 and terminated with listed fittings.
Type PLTC and Type PLTC-ER cable in accordance with the provisions of Article 725, including installation in cable tray systems. The cable shall be terminated with listed fittings.
Enclosed gasketed busways, enclosed gasketed wireways.
In industrial establishments with restricted public access, where the conditions of maintenance and supervision ensure that only qualified persons service the installation, and where metallic conduit does not provide sufficient corrosion resistance, listed reinforced thermosetting resin conduit (RTRC), factory elbows, and associated fittings, all marked with the suffix -XW, and Schedule 80 PVC conduit, factory elbows, and associated fittings shall be permitted. Where seals are required for boundary condi‐ tions as defined in 505.16(C)(1)(b), the Zone 1 wiring method shall extend into the Zone 2 area to the seal, which shall be located on the Zone 2 side of the Zone 1/ Zone 2 boundary.
Intrinsic safety type of protection “ic” shall be permitted using any of the wiring methods permitted for unclassi‐ fied locations. Intrinsic safety type of protection “ic” systems shall be installed in accordance with the control drawing(s). Simple apparatus, not shown on the control drawing, shall be permitted in an intrinsic safety type of protection “ic” circuit, provided that the simple apparatus does not interconnect the intrinsic safety type of protec‐ tion “ic” systems to any other circuit.Informational Note: Simple apparatus is defined in 504.2.
Optical fiber cable of Types OFNP, OFCP, OFNR, OFCR, OFNG, OFCG, OFN, and OFC shall be permitted to be installed in cable trays or any other raceway in accord‐ ance with 505.15(C). Optical fiber cable shall be sealed in accordance with 505.16.
Cablebus.

Separate intrinsic safety type of protection “ic” systems shall be installed in accordance with one of the following:

In separate cables
In multiconductor cables where the conductors of each circuit are within a grounded metal shield
In multiconductor cables where the conductors of each circuit have insulation with a minimum thickness of 0.25 mm (0.01 in.)

(2) Flexible Connections. Where provision must be made for flexibility, flexible metal fittings, flexible metal conduit with listed fittings, liquidtight flexible metal conduit with listed fittings, liquidtight flexible nonmetallic conduit with listed fittings, or flexible cord in accordance with the provisions of

505.17 terminated with a listed cord connector that maintains the type of protection of the terminal compartment shall be permitted.

Informational Note: See 505.25(B) for grounding requirements where flexible conduit is used.

Exception: For elevator use, an identified elevator cable of Type EO, ETP, or ETT, shown under the “use” column in Table 400.4 for “hazardous (classified) locations,” that is terminated with listed connec‐ tors that maintain the type of protection of the terminal compartment, shall be permitted.

Sealing and Drainage. Seals in conduit and cable systems shall comply with 505.16(A) through (E). Sealing compound shall be used in Type MI cable termination fittings to exclude moisture and other fluids from the cable insulation.Informational Note No. 1: Seals are provided in conduit and cable systems to minimize the passage of gases and vapors and prevent the passage of flames from one portion of the electrical installation to another through the conduit. Such communica‐ tion through Type MI cable is inherently prevented by construc‐ tion of the cable. Unless specifically designed and tested for the purpose, conduit and cable seals are not intended to prevent the passage of liquids, gases, or vapors at a continuous pressure differential across the seal. Even at differences in pressure across the seal equivalent to a few inches of water, there may be a slow passage of gas or vapor through a seal and through conductors passing through the seal. See 505.16(C)(2)(b). Temperature extremes and highly corrosive liquids and vapors can affect the ability of seals to perform their intended function. See 505.16(D)(2).Informational Note No. 2: Gas or vapor leakage and propaga‐ tion of flames may occur through the interstices between the strands of standard stranded conductors larger than 2 AWG. Special conductor constructions, for example, compacted strands or sealing of the individual strands, are means of reduc‐ ing leakage and preventing the propagation of flames.
1. Zone 0. In Class I, Zone 0 locations, seals shall be located according to 505.16(A)(1), (A)(2), and (A)(3).
  1. Conduit Seals. Seals shall be provided within 3.05 m (10 ft) of where a conduit leaves a Zone 0 location. There shall be no unions, couplings, boxes, or fittings, except listed reduc‐ ers at the seal, in the conduit run between the seal and the point at which the conduit leaves the location.Exception: A rigid unbroken conduit that passes completely through the Zone 0 location with no fittings less than 300 mm (12 in.) beyond each boundary shall not be required to be sealed if the termination points of the unbroken conduit are in unclassified locations.
  2. Cable Seals. Seals shall be provided on cables at the first point of termination after entry into the Zone 0 location.
  3. Not Required to Be Explosionproof or Flameproof. Seals shall not be required to be explosionproof or flameproof.
2. Zone 1. In Class I, Zone 1 locations, seals shall be located in accordance with 505.16(B)(1) through (B)(8).
  1. Type of Protection “d” or “e” Enclosures. Conduit seals shall be provided within 50 mm (2 in.) for each conduit enter‐ ing enclosures having type of protection “d” or “e.”Exception No. 1: Where the enclosure having type of protection “d” is marked to indicate that a seal is not required.Exception No. 2: For type of protection “e,” conduit and fittings employ‐ ing only NPT to NPT raceway joints or fittings listed for type of protec‐ tion “e” shall be permitted between the enclosure and the seal, and the seal shall not be required to be within 50 mm (2 in.) of the entry.Informational Note: Examples of fittings employing other than NPT threads include conduit couplings, capped elbows, unions, and breather drains.Exception No. 3: For conduit installed between type of protection “e” enclosures employing only NPT to NPT raceway joints or conduit fittings listed for type of protection “e,” a seal shall not be required.
  2. Explosionproof Equipment. Conduit seals shall be provi‐ ded for each conduit entering explosionproof equipment according to 505.16(B)(2)(a), (B)(2)(b), and (B)(2)(c).
    1. In each conduit entry into an explosionproof enclo‐ sure where either of the following conditions apply:
      1. The enclosure contains apparatus, such as switches, circuit breakers, fuses, relays, or resistors that may produce arcs, sparks, or high temperatures that are considered to be an ignition source in normal operation. For the purposes of this section, high temperatures shall be considered to be any temperatures exceeding 80 percent of the autoignition temperature in degrees Celsius of the gas or vapor involved.Exception: Seals shall not be required for conduit entering an enclosure where such switches, circuit breakers, fuses, relays, or resistors comply with one of the following:
        Are enclosed within a chamber hermetically sealed against the entrance of gases or vapors.
        Are immersed in oil.
        Are enclosed within an enclosure, identified for the location, and marked “Leads Factory Sealed,” “Factory Sealed,” “Seal not Required,” or equivalent.
      2. The entry is metric designator 53 (trade size 2) or larger and the enclosure contains terminals, splices, or taps.An enclosure, identified for the location, and marked “Leads Factory Sealed,” or “Factory Sealed,” Seal not Required,” or equivalent shall not be considered to serve as a seal for another adjacent explosionproof enclosure that is required to have a conduit seal.
    2. Conduit seals shall be installed within 450 mm (18 in.) from the enclosure. Only explosionproof unions, couplings, reducers, elbows, capped elbows, and conduit bodies similar to L, T, and cross types that are not larger than the trade size of the conduit shall be permitted between the sealing fitting and the explosionproof enclosure.
    3. Where two or more explosionproof enclosures for which conduit seals are required under 505.16(B)(2) are connected by nipples or by runs of conduit not more than 900 mm (36 in.) long, a single conduit seal in each such nipple connection or run of conduit shall be considered sufficient if located not more than 450 mm (18 in.) from either enclosure.
  1. Pressurized Enclosures. Conduit seals shall be provided in each conduit entry into a pressurized enclosure where the conduit is not pressurized as part of the protection system.
    Conduit seals shall be installed within 450 mm (18 in.) from the pressurized enclosure.Informational Note No. 1: Installing the seal as close as possible to the enclosure reduces problems with purging the dead airspace in the pressurized conduit.Informational Note No. 2: For further information, see NFPA 496-2013, Standard for Purged and Pressurized Enclosures for Electri‐ cal Equipment.
  2. Class I, Zone 1 Boundary. Conduit seals shall be provided in each conduit run leaving a Class I, Zone 1 location. The seal‐ ing fitting shall be permitted on either side of the boundary of such location within 3.05 m (10 ft) of the boundary and shall be designed and installed so as to minimize the amount of gas or vapor within the Zone 1 portion of the conduit from being communicated to the conduit beyond the seal. Except for listed explosionproof reducers at the conduit seal, there shall be no union, coupling, box, or fitting between the conduit seal and the point at which the conduit leaves the Zone 1 location.Exception: Metal conduit containing no unions, couplings, boxes, or fittings and passing completely through a Class I, Zone 1 location with no fittings less than 300 mm (12 in.) beyond each boundary shall not require a conduit seal if the termination points of the unbroken conduit are in unclassified locations.
  3. Cables Capable of Transmitting Gases or Vapors. Conduits containing cables with a gas/vaportight continuous sheath capable of transmitting gases or vapors through the cable core shall be sealed in the Zone 1 location after removing the jacket and any other coverings so that the sealing compound surrounds each individual insulated conductor or optical fiber tube and the outer jacket.Exception: Multiconductor cables with a gas/vaportight continuous sheath capable of transmitting gases or vapors through the cable core shall be permitted to be considered as a single conductor by sealing the cable in the conduit within 450 mm (18 in.) of the enclosure and the cable end within the enclosure by an approved means to minimize the entrance of gases or vapors and prevent the propagation of flame into the cable core, or by other approved methods. For shielded cables and twisted pair cables, it shall not be required to remove the shielding mate‐ rial or separate the twisted pair.
  4. Cables Incapable of Transmitting Gases or Vapors. Each multiconductor or optical multifiber cable in conduit shall be considered as a single conductor or single optical fiber tube if the cable is incapable of transmitting gases or vapors through the cable core. These cables shall be sealed in accordance with 505.16(D).
  5. Cables Entering Enclosures. Cable seals shall be provided for each cable entering flameproof or explosionproof enclo‐ sures. The seal shall comply with 505.16(D).
  6. Class I, Zone 1 Boundary. Cables shall be sealed at the point at which they leave the Zone 1 location.
  Exception: Where cable is sealed at the termination point.
3. Zone 2. In Class I, Zone 2 locations, seals shall be located in accordance with 505.16(C)(1) and (C)(2).
  1. Conduit Seals. Conduit seals shall be located in accord‐ ance with (C)(1)(a) and (C)(1)(b).the conduit run or nipple between the seal and enclosure shall comply with 505.16(B).(b) In each conduit run passing from a Class I, Zone 2 location into an unclassified location. The sealing fitting shall be permitted on either side of the boundary of such location within 3.05 m (10 ft) of the boundary and shall be designed and installed so as to minimize the amount of gas or vapor within the Zone 2 portion of the conduit from being communi‐ cated to the conduit beyond the seal. Rigid metal conduit or threaded steel intermediate metal conduit shall be used between the sealing fitting and the point at which the conduit leaves the Zone 2 location, and a threaded connection shall be used at the sealing fitting. Except for listed explosionproof reducers at the conduit seal, there shall be no union, coupling, box, or fitting between the conduit seal and the point at which the conduit leaves the Zone 2 location. Conduits shall be sealed to minimize the amount of gas or vapor within the Class I, Zone 2 portion of the conduit from being communicated to the conduit beyond the seal. Such seals shall not be required to be flameproof or explosionproof but shall be identified for the purpose of minimizing passage of gases under normal operat‐ ing conditions and shall be accessible.Exception No. 1: Metal conduit containing no unions, couplings, boxes, or fittings and passing completely through a Class I, Zone 2 loca‐ tion with no fittings less than 300 mm (12 in.) beyond each boundary shall not be required to be sealed if the termination points of the unbro‐ ken conduit are in unclassified locations.Exception No. 2: Conduit systems terminating at an unclassified loca‐ tion where a wiring method transition is made to cable tray, cablebus, ventilated busway, Type MI cable, or cable that is not installed in a raceway or cable tray system shall not be required to be sealed where passing from the Class I, Zone 2 location into the unclassified location. The unclassified location shall be outdoors or, if the conduit system is all in one room, it shall be permitted to be indoors. The conduits shall not terminate at an enclosure containing an ignition source in normal operation.Exception No. 3: Conduit systems passing from an enclosure or room that is unclassified as a result of pressurization into a Class I, Zone 2 location shall not require a seal at the boundary.Informational Note: For further information, refer to NFPA 496-2013, Standard for Purged and Pressurized Enclosures for Electri‐ cal Equipment.Exception No. 4: Segments of aboveground conduit systems shall not be required to be sealed where passing from a Class I, Zone 2 location into an unclassified location if all the following conditions are met:
    1. No part of the conduit system segment passes through a Zone 0 or Zone 1 location where the conduit contains unions, couplings, boxes, or fittings within 300 mm (12 in.) of the Zone 0 or Zone 1 location.
    2. The conduit system segment is located entirely in outdoor loca‐ tions.
    3. The conduit system segment is not directly connected to canned pumps, process or service connections for flow, pressure, or analy‐ sis measurement, and so forth, that depend on a single compres‐ sion seal, diaphragm, or tube to prevent flammable or combustible fluids from entering the conduit system.
    4. The conduit system segment contains only threaded metal conduit, unions, couplings, conduit bodies, and fittings in the
      1. For connections to enclosures that are required to be flameproof or explosionproof, a conduit seal shall be provided in accordance with 505.16(B)(1) and (B)(2). All portions of
    unclassified location.The conduit system segment is sealed at its entry to each enclosure or fitting housing terminals, splices, or taps in Zone 2 locations.
    1. Cable Seals. Cable seals shall be located in accordance with (C)(2)(a), (C)(2)(b), and (C)(2)(c).
      1. Explosionproof and Flameproof Enclosures. Cables enter‐ ing enclosures required to be flameproof or explosionproof shall be sealed at the point of entrance. The seal shall comply with 505.16(D). Multiconductor or optical multifiber cables with a gas/vaportight continuous sheath capable of transmit‐ ting gases or vapors through the cable core shall be sealed in the Zone 2 location after removing the jacket and any other coverings so that the sealing compound surrounds each indi‐ vidual insulated conductor or optical fiber tube in such a manner as to minimize the passage of gases and vapors. Multi‐ conductor or optical multifiber cables in conduit shall be sealed as described in 505.16(B)(4).Exception No. 1: Cables passing from an enclosure or room that is unclassified as a result of Type Z pressurization into a Zone 2 location shall not require a seal at the boundary.Exception No. 2: Shielded cables and twisted pair cables shall not require the removal of the shielding material or separation of the twisted pairs, provided the termination is by an approved means to minimize the entrance of gases or vapors and prevent propagation of flame into the cable core.
      2. Cables That Will Not Transmit Gases or Vapors. Cables with a gas/vaportight continuous sheath and that will not trans‐ mit gases or vapors through the cable core in excess of the quantity permitted for seal fittings shall not be required to be sealed except as required in 505.16(C)(2)(b). The minimum length of such cable run shall not be less than the length that limits gas or vapor flow through the cable core to the rate permitted for seal fittings [200 cm3/hr (0.007 ft3/hr) of air at a pressure of 1500 pascals (6 in. of water)].Informational Note No. 1: For further information on construc‐ tion, testing, and marking of cables, cable fittings, and cord connectors, see ANSI/UL 2225-2011, Cables and Cable-Fittings for Use in Hazardous (Classified) Locations.Informational Note No. 2: The cable core does not include the interstices of the conductor strands.
      3. Cables Capable of Transmitting Gases or Vapors. Cables with a gas/vaportight continuous sheath capable of transmit‐ ting gases or vapors through the cable core shall not be required to be sealed except as required in 505.16(C)(2)(b), unless the cable is attached to process equipment or devices that may cause a pressure in excess of 1500 pascals (6 in. of water) to be exerted at a cable end, in which case a seal, barrier, or other means shall be provided to prevent migration of flammables into an unclassified area.Exception: Cables with an unbroken gas/vaportight continuous sheath shall be permitted to pass through a Class I, Zone 2 location without seals.
      4. Cables Without Gas/Vaportight Continuous Sheath. Cables that do not have gas/vaportight continuous sheath shall be sealed at the boundary of the Zone 2 and unclassified loca‐ tion in such a manner as to minimize the passage of gases or vapors into an unclassified location.
    Informational Note: The cable sheath may be either metal or a nonmetallic material.
4. Class I, Zones 0, 1, and 2. Where required, seals in Class I, Zones 0, 1, and 2 locations shall comply with 505.16(D)(1) through (D)(5).
  1. Fittings. Enclosures for connections or equipment shall be provided with an integral means for sealing, or sealing fittings listed for the location shall be used. Sealing fittings shall be listed for use with one or more specific compounds and shall be accessible.
  2. Compound. The compound shall provide a seal against passage of gas or vapors through the seal fitting, shall not be affected by the surrounding atmosphere or liquids, and shall not have a melting point less than 93°C (200°F).
  3. Thickness of Compounds. In a completed seal, the mini‐ mum thickness of the sealing compound shall not be less than the trade size of the sealing fitting and, in no case, less than 16 mm (5∕8 in.).Exception: Listed cable sealing fittings shall not be required to have a minimum thickness equal to the trade size of the fitting.
  4. Splices and Taps. Splices and taps shall not be made in fittings intended only for sealing with compound, nor shall other fittings in which splices or taps are made be filled with compound.
  5. Conductor or Optical Fiber Fill. The cross-sectional area of the conductors or optical fiber tubes (metallic or nonmetal‐ lic) permitted in a seal shall not exceed 25 percent of the cross- sectional area of a rigid metal conduit of the same trade size unless it is specifically listed for a higher percentage of fill.
5. Drainage.
  1. Control Equipment. Where there is a probability that liquid or other condensed vapor may be trapped within enclo‐ sures for control equipment or at any point in the raceway system, approved means shall be provided to prevent accumula‐ tion or to permit periodic draining of such liquid or condensed vapor.
  2. Motors and Generators. Where liquid or condensed vapor may accumulate within motors or generators, joints and conduit systems shall be arranged to minimize entrance of liquid. If means to prevent accumulation or to permit periodic draining are necessary, such means shall be provided at the time of manufacture and shall be considered an integral part of the machine.
Flexible Cables, Cords and Connections.
1. Flexible Cords, Class I, Zones 1 and 2. A flexible cord shall be permitted for connection between portable lighting equipment or other portable utilization equipment and the fixed portion of their supply circuit. Flexible cord shall also be permitted for that portion of the circuit where the fixed wiring methods of 505.15(B) and (C) cannot provide the necessary degree of movement for fixed and mobile electrical utilization equipment in an industrial establishment where conditions of maintenance and engineering supervision ensure that only qualified persons install and service the installation, and where the flexible cord is protected by location or by a suitable guard from damage. The length of the flexible cord shall be continu‐ ous. Where flexible cords are used, the cords shall comply with the following:
  1. Be of a type listed for extra-hard usage.
  2. Contain, in addition to the conductors of the circuit, an equipment grounding conductor complying with 400.23.
  3. Be connected to terminals or to supply conductors in an approved manner.
  4. Be supported by clamps or by other suitable means in such a manner that there will be no tension on the termi‐ nal connections.
  5. Be terminated with a listed cord connector that maintains the type of protection where the flexible cord enters boxes, fittings, or enclosures that are required to be explosionproof or flameproof.
  6. Cord entering an increased safety “e” enclosure shall be terminated with a listed increased safety “e” cord connec‐ tor.
  Informational Note: See 400.10 for permitted uses of flexible cords.Electric submersible pumps with means for removal without entering the wet-pit shall be considered portable utilization equipment. The extension of the flexible cord within a suitable raceway between the wet-pit and the power source shall be permitted.Electric mixers intended for travel into and out of open-type mixing tanks or vats shall be considered portable utilization equipment.Informational Note: See 505.18 for flexible cords exposed to liquids having a deleterious effect on the conductor insulation.N
2. Instrumentation Connections for Zone 2. To facilitate replacements, process control instruments shall be permitted to be connected through flexible cords, attachment plugs, and receptacles, provided that all of the following conditions apply:
1. A switch listed for Zone 2 is provided so that the attach‐ ment plug is not depended on to interrupt current, unless the circuit is type “ia,” “ib,” or “ic” protection, in which case the switch is not required.
2. The current does not exceed 3 amperes at 120 volts, nominal.
3. The power-supply cord does not exceed 900 mm (3 ft), is of a type listed for extra-hard usage or for hard usage if protected by location, and is supplied through an attach‐ ment plug and receptacle of the locking and grounding type.
4. Only necessary receptacles are provided.
5. The receptacle carries a label warning against unplugging under load.
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Conductors and Conductor Insulation.
1. Conductors. For type of protection “e,” field wiring conductors shall be copper. Every conductor (including spares) that enters Type “e” equipment shall be terminated at a Type “e” terminal.
2. Conductor Insulation. Where condensed vapors or liquids may collect on, or come in contact with, the insulation on conductors, such insulation shall be of a type identified for use under such conditions, or the insulation shall be protected by a sheath of lead or by other approved means.
Uninsulated Exposed Parts. There shall be no uninsu‐ lated exposed parts, such as electrical conductors, buses, termi‐ nals, or components that operate at more than 30 volts (15 volts in wet locations). These parts shall additionally be protected by type of protection “ia,” “ib,” or “nA” that is suita‐ ble for the location.
Equipment Requirements.

Zone 0. In Class I, Zone 0 locations, only equipment specifically listed and marked as suitable for the location shall be permitted.Exception: Intrinsically safe apparatus listed for use in Class I, Divi‐ sion 1 locations for the same gas, or as permitted by 505.9(B)(2), and with a suitable temperature class shall be permitted.
Zone 1. In Class I, Zone 1 locations, only equipment specifically listed and marked as suitable for the location shall be permitted.Exception No. 1: Equipment identified for use in Class I, Division 1 or listed for use in Zone 0 locations for the same gas, or as permitted by 505.9(B)(2), and with a suitable temperature class shall be permitted.Exception No. 2: Equipment identified for Class I, Zone 1 or Zone 2 type of protection “p” shall be permitted.
Zone 2. In Class I, Zone 2 locations, only equipment specifically listed and marked as suitable for the location shall be permitted.Exception No. 1: Equipment listed for use in Zone 0 or Zone 1 locations for the same gas, or as permitted by 505.9(B)(2), and with a suitable temperature class, shall be permitted.Exception No. 2: Equipment identified for Class I, Zone 1 or Zone 2 type of protection “p” shall be permitted.Exception No. 3: Equipment identified for use in Class I, Division 1 or Division 2 locations for the same gas, or as permitted by 505.9(B)(2), and with a suitable temperature class shall be permitted.Exception No. 4: In Class I, Zone 2 locations, the installation of open or nonexplosionproof or nonflameproof enclosed motors, such as squirrel-cage induction motors without brushes, switching mechanisms, or similar arc-producing devices that are not identified for use in a Class I, Zone 2 location shall be permitted.Informational Note No. 1: It is important to consider the temperature of internal and external surfaces that may be exposed to the flammable atmosphere.Informational Note No. 2: It is important to consider the risk of ignition due to currents arcing across discontinuities and over‐ heating of parts in multisection enclosures of large motors and generators. Such motors and generators may need equipotential bonding jumpers across joints in the enclosure and from enclo‐ sure to ground. Where the presence of ignitible gases or vapors is suspected, clean air purging may be needed immediately prior to and during start-up periods.Informational Note No. 3: For further information on the appli‐ cation of electric motors in Class I, Zone 2 hazardous (classified) locations, see IEEE 1349-2011, IEEE Guide for the Application of Electric Motors in Class I, Division 2 and Class I, Zone 2 Hazardous (Classified) Locations.
Materials. Equipment marked Group IIC shall be permit‐ ted for applications requiring Group IIA or Group IIB equip‐ ment. Similarly, equipment marked Group IIB shall be permitted for applications requiring Group IIA equipment.Equipment marked for a specific gas or vapor shall be permitted for applications where the specific gas or vapor may be encountered.Informational Note: One common example combines these markings with equipment marked IIB +H2. This equipment is
suitable for applications requiring Group IIA equipment, Group IIB equipment, or equipment for hydrogen atmospheres.
Manufacturer’s Instructions. Electrical equipment instal‐ led in hazardous (classified) locations shall be installed in accordance with the instructions (if any) provided by the manufacturer.

505.22 Increased Safety “e” Motors and Generators. In Class I, Zone 1 locations, increased safety “e” motors and gener‐ ators of all voltage ratings shall be listed for Zone 1 locations, and shall comply with all of the following:

Motors shall be marked with the current ratio, IA /IN , and time, tE .
Motors shall have controllers marked with the model or identification number, output rating (horsepower or kilo‐ watt), full-load amperes, starting current ratio (IA /IN ), and time (tE ) of the motors that they are intended to protect; the controller marking shall also include the specific overload protection type (and setting, if applica‐ ble) that is listed with the motor or generator.
Connections shall be made with the specific terminals listed with the motor or generator.
Terminal housings shall be permitted to be of substantial, nonmetallic, nonburning material, provided an internal grounding means between the motor frame and the equipment grounding connection is incorporated within the housing.
The provisions of Part III of Article 430 shall apply regardless of the voltage rating of the motor.
The motors shall be protected against overload by a sepa‐ rate overload device that is responsive to motor current. This device shall be selected to trip or shall be rated in accordance with the listing of the motor and its overload protection.
Sections 430.32(C) and 430.44 shall not apply to such motors.
The motor overload protection shall not be shunted or cut out during the starting period.

Informational Note: Reciprocating engine-driven generators, compressors, and other equipment installed in Class I, Zone 2 locations may present a risk of ignition of flammable materials associated with fuel, starting, compression, and so forth, due to inadvertent release or equipment malfunction by the engine ignition system and controls. For further information on the requirements for ignition systems for reciprocating engines installed in Class I, Zone 2 hazardous (classified) locations, see ANSI/UL 122001:2014, General Requirements for Electrical Ignition Systems for Internal Combustion Engines in Class I, Division 2 or Zone 2, Hazardous (Classified) Locations.

Grounding and Bonding. Regardless of the voltage of the electrical system, grounding and bonding shall comply with Article 250 and the requirements in 505.25(A) and (B).
1. Bonding. The locknut-bushing and double-locknut types of contacts shall not be depended on for bonding purposes, but bonding jumpers with proper fittings or other approved means of bonding shall be used. Such means of bonding shall apply to all intervening raceways, fittings, boxes, enclosures, and so forth, between Class I locations and the point of grounding for service equipment or point of grounding of a separately derived system.Exception: The specific bonding means shall be required only to the nearest point where the grounded circuit conductor and the grounding electrode are connected together on the line side of the building or struc‐ture disconnecting means as specified in 250.32(B), provided the branch-circuit overcurrent protection is located on the load side of the disconnecting means.
2. Types of Equipment Grounding Conductors. Flexible metal conduit and liquidtight flexible metal conduit shall include an equipment bonding jumper of the wire type in compliance with 250.102.Exception: In Class I, Zone 2 locations, the bonding jumper shall be permitted to be deleted where all of the following conditions are met:
  1. Listed liquidtight flexible metal conduit 1.8 m (6 ft) or less in length, with fittings listed for grounding, is used.
  2. Overcurrent protection in the circuit is limited to 10 amperes or less.
  3. The load is not a power utilization load.
Process Sealing. This section shall apply to process- connected equipment, which includes, but is not limited to, canned pumps, submersible pumps, flow, pressure, tempera‐ ture, or analysis measurement instruments. A process seal is a device to prevent the migration of process fluids from the designed containment into the external electrical system. Proc‐ ess connected electrical equipment that incorporates a single process seal, such as a single compression seal, diaphragm, or tube to prevent flammable or combustible fluids from entering a conduit or cable system capable of transmitting fluids, shall be provided with an additional means to mitigate a single proc‐ ess seal failure. The additional means may include, but is not limited to, the following:

A suitable barrier meeting the process temperature and pressure conditions that the barrier is subjected to upon failure of the single process seal. There shall be a vent or drain between the single process seal and the suitable barrier. Indication of the single process seal failure shall be provided by visible leakage, an audible whistle, or other means of monitoring.
A listed Type MI cable assembly, rated at not less than 125 percent of the process pressure and not less than125 percent of the maximum process temperature (in degrees Celsius), installed between the cable or conduit and the single process seal.
A drain or vent located between the single process seal and a conduit or cable seal. The drain or vent shall be sufficiently sized to prevent overpressuring the conduit or cable seal above 6 in. water column (1493 Pa). Indication of the single process seal failure shall be provided by visi‐ ble leakage, an audible whistle, or other means of moni‐ toring.
An add-on secondary seal marked “secondary seal” and rated for the pressure and temperature conditions to which it will be subjected upon failure of the single proc‐ ess seal.

Process-connected electrical equipment that does not rely on a single process seal or is listed and marked “single seal” or “dual seal” shall not be required to be provided with an addi‐ tional means of sealing.

Informational Note: For construction and testing requirements for process sealing for listed and marked single seal, dual seal, or secondary seal equipment, refer to ANSI/ISA-12.27.01-2011, Requirements for Process Sealing Between Electrical Systems and Flam‐ mable or Combustible Process Fluids.

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