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Enclosure - Basic Properties, Teminology, and Theories

What is an Enclosure?

Enclosures An enclosure, according to the National Electrical Manufacturers Association (NEMA), is a surrounding case constructed to provide a degree of protection to personnel against incidental contact with the enclosed equipment and to provide a degree of protection to the enclosed equipment against specified environmental conditions. NEMA 250-1997.

While NEMA does not actually test products, it establishes the performance criteria for enclosures intended for specific environments. NEMA standards describe each type of enclosure in general and functional terms, and specifically omits reference to construction details. That means that NEMA specifies what an enclosure must do, not how to manufacture it. Underwriters Laboratories (UL) and Canadian Standards Association (CSA) use NEMA performance criteria and test methods as guidelines for investigation and listing of electrical enclosures. The tested enclosures are then authorized to carry a label by UL or CSA to prove it has passed the required tests and meets the applicable UL and CSA standard.
Definitions Pertaining to Non-Hazardous Locations
  • Type 1 Enclosures constructed for indoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment, and to provide a degree of protection against falling dirt. NEMA 250-1997.
  • Type 2 Enclosures constructed for indoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment, to provide a degree of protection against falling dirt, and to provide a degree of protection against dripping and light splashing of liquids. NEMA 250-1997.
  • Type 3 Enclosures constructed for either indoor or outdoor use to provides a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt, rain, sleet, snow, and windblown dust; and that will be undamaged by the external formation of ice on the enclosure. NEMA 250-1997.
  • Type 3R Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt, rain, sleet, snow; and that will be undamaged by the external formation of ice on the enclosure. NEMA 250-1997.
  • Type 35 Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt, rain, sleet, snow, and windblown dust; and in which the external mechanism(s) remain operable when ice laden. NEMA 250-1997.
  • Type 4 Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt, rain, sleet, snow, windblown dust, splashing water, and hose-directed water; and that will be undamaged by the external formation of ice on the enclosure. NEMA 250-1997.
  • Type 4X Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt, rain, sleet, snow, windblown dust, splashing water, hose-directed water; and corrosion; and that will be undamaged by the external formation of ice on the enclosure. NEMA 250-1997.
  • Type 5 Enclosures constructed for indoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt; against settling airborne dust, lint, fibers, and flyings; and to provide a degree of protection against dripping and light splashing of liquids. NEMA 250-1997.
  • Type 6 Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt; against hose-directed water and the entry of water during occasional temporary submersion at a limited depth; and that will be undamaged by the external formation of ice on the enclosure. NEMA 250-1997.
  • Type 6P Enclosures constructed for either indoor or out-door use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt; against hose-directed water and the entry of water during prolonged submersion at a limited depth; and that will be undamaged by the external formation of ice on the enclosure. NEMA 250-1997.
  • Type 12 Enclosures constructed (without knockouts) for indoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt; against circulating dust, lint, fibers, and flyings; and against dripping and light splashing of liquids. NEMA 250-1997.
  • Type 13 Enclosures constructed for indoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt; against circulating dust, lint, fibers, and flyings; and against spraying splashing, and seepage of water, oil and non-corrosive coolants. NEMA 250-1997.
Definitions Pertaining to Hazardous (Classified) Locations
  • Type 7 Enclosures constructed for indoor use in hazardous locations classified as Class I, Division 1, Groups A, B, C, or D, as defined in NFPA70. NEMA 250-1997.
  • Type 8 Enclosures constructed for either indoor or outdoor use in hazardous locations classified as Class I, Division 1, Groups A, 8, C, or D, as defined in NFPA70. NEMA 250-1997.
  • Type 9 Enclosures constructed for indoor use in hazardous locations classified as Class II, Division 1,Groups E, F, or G, as defined in NFPA70. NEMA 250-1997.
  • Type 10 Enclosures constructed to meet the requirements of the Mine Safety and health Administration, 30 CPR, Part 18. NEMA 250-1997. NEMA 250-1997.
Characteristics of Enclosure Materials and Suggested Applications
  • Hot Rolled Pickled and Oiled Steel Sheets (ASTM A569) - general indoor and outdoor use after a suitable finish has been applied to protect against corrosion.
  • Cold Rolled Steel (ASTM A366) - general indoor and outdoor use after a suitable finish has been applied to protect against corrosion.
  • Galvanized Steel (ASTM A526) - indoor or outdoor use in neutral pH. Resists oil, gas, glycerine, dichromates, borates, and silicates. Most frequent application is outdoor including seacoast atmospheres. Additional finishes may be applied to improve corrosion resistance.
  • 18-8 Stainless Steel (Type 302-304) - indoor or outdoor use. Ideally suited for use in food processing areas, dairies, breweries, or any wet area. Also works well in areas where caustic elements or alkalis are present.
  • 316 or 316L Stainless Steel - indoor or outdoor use in almost any environment. Corrosion resistant and a superior material choice for marine environments.
  • 5052 Aluminum - indoor or outdoor use, particularly in marine environments. An excellent choice for enclosures exposed to solvents, petrochemicals, some acids, most sulfates and nitrates.
Applications for Enclosure Types:
  • Type 1 general-purpose enclosures suitable for general-purpose application indoors, where atmospheric conditions are normal. These enclosures serve as protection against falling dirt but are not dust tight.
  • Type 2 drip-tight (indoor) enclosures are similar to Type 1 enclosures, suitable for application where condensation may be severe, such as that encountered in cooling rooms or laundries.
  • Type 3 provides proper protection against wind-blown dust and weather hazards such as dirt, rain, sleet, or snow. They are suitable for application outdoors on ship docks, canal locks, construction work, and for application in subways and tunnels; use indoors where dripping water is a problem.
  • Type 3N provide proper protection falling dirt, rain, sleet, snow, undamaged by external formation of ice. They are suitable for application outdoors; they will not withstand wind blown dust.
  • Type 4 watertight enclosures are suitable for dairies, breweries, etc., where the enclosure may be subjected to large amounts of water from any angle. (They are not submersible).
  • Type 4X corrosion resistant enclosures satisfy the same requirements of Type 4; in addition, they are suitable for food processing plants, dairies, refineries, and other industries where corrosion is prominent.
  • Type 6 submersible enclosures are suitable for application where the equipment may be subject to occasional temporary submersion, such as quarries, mines, and manholes. The enclosure design will depend upon the specified conditions of pressure and time.
  • Type 9 hazardous location enclosures–Class II, Group E, F, or G. These enclosures are designed to meet the requirements of the "Canadian Electrical Code" Part I for Class II hazardous locations, and CSA codes section 18, Class II, Group E, F, and G.
    • Class II, Group E – atmospheres containing metal dust
    • Class II, Group F – atmospheres containing carbon black, coal, or coke dust
    • Class II, Group G – atmospheres containing flour, starch, or grain dust
  • Type 12 industrial use enclosures protect against dripping and light splashing of liquids.
  • Type 12K industrial use enclosure same as type 12 but includes knockouts in the top & bottom end walls.
  • Type 13 industrial use enclosures, protection against dust, spraying of water, oil, and non-corrosive coolant. These enclosures are suitable for application to machine tools and other industrial processing machines.
Enclosures are available in a variety of finishes, knockouts door and mounting options. Dimensions range from the small 4x4x3 to extremely large versions.
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