Enclosures are designed to isolate apparatus from certain conditions. In addition they are used to protect personnel from unsafe, accidental contact with the apparatus. An enclosure protection rating is a standardized way of identifying the ability of an enclosure to isolate an apparatus from the outside environment. The purpose of the rating system is to provide the user with the information about the degree of protection provided by the enclosure.
The rating number indicates the external conditions in which the enclosure can be used. North America and Europe use different rating systems.
In North America, enclosures are tested by agencies and the enclosure rating is set according to standards set by the agency based on the ANSI/NEMA 250 standards.
NEMA specifies the design and testing requirements for each type of housing and does not require independent laboratory testing. The individual manufacturer must ensure that the enclosure meets the specified standards.
The Table 1 below provides the listing of NEMA ratings for the enclosures.
Table 1 NEMA Ratings for Enclosures
| Type | Rating | Description |
| 1 | General Purpose | -Enclosures constructed for indoor use. – Provides a degree of protection against access to hazardous parts and against ingress of solid foreign objects (falling dirt). |
| 2 | Drip Proof | -Enclosures constructed for either indoor or outdoor use. -Provides a degree of protection against access to hazardous parts, against ingress of solid foreign objects (falling dirt) and ingress of water (dripping and light splashing). |
| 3 | Dust-Tight | -Enclosures constructed for either indoor or outdoor use. -Provides a degree of protection against access to hazardous parts, against ingress of solid foreign objects (falling dirt and windblown dust); ingress of water (rain sleet, snow) and have they will be undamaged by the external formation of ice on the enclosure. |
| 3R | Rainproof | -Enclosures constructed for either indoor or outdoor use. -They provide a degree of protection against access to hazardous parts, against ingress of solid foreign objects (falling dirt); ingress of water (rain, sleet, snow) and they will be undamaged by the external formation of ice on the enclosure. |
| 3S | Dust-Tight, Rainproof | -Enclosures constructed for either indoor or outdoor use. -These enclosures provide a degree of protection against access to hazardous parts, against ingress of solid foreign objects (falling dirt and windblown dust); ingress of water (rain, sleet, snow) and for which the external mechanism(s) remain operable when ice laden. |
| 3X | -Enclosures constructed for either indoor or outdoor use. -The enclosures provide a degree of protection against access to hazardous parts, against ingress of solid foreign objects (falling dirt and windblown dust); ingress of water (rain, sleet, snow); and provides an additional level of protection against corrosion, additionally they will be undamaged by the external formation of ice on the enclosure. | |
| 3RX | -These includes Enclosures constructed for either indoor or outdoor use. -They provide a degree of protection against access to hazardous parts, against ingress of solid foreign objects (falling dirt); ingress of water (rain, sleet, snow); and provides an additional level of protection against corrosion and they will be undamaged by the external formation of ice on the enclosure. | |
| 3SX | -Enclosures constructed for either indoor or outdoor use. -Provides a degree of protection against access of hazardous parts, against ingress of solid foreign objects (falling dirt and windblown dust); ingress of water (rain, sleet, and snow); and provides an additional level of protection against corrosion and for which the external mechanism(s) remain operable when ice laden. | |
| 4 | Water-Tight | -These are enclosures constructed for either indoor or outdoor use. -These enclosures provide a degree of protection against access to hazardous parts, against ingress of solid foreign objects (falling dirt and windblown dust); ingress of water (rain, sleet, snow, splashing water and hose-directed water); additionally they will be undamaged by the external formation of ice on the enclosure. |
| 4X | Water-Tight, Dust-Tight | -Includes enclosures that are constructed for either for indoor or outdoor use. -The enclosures with this rating provide a degree of protection against access to hazardous parts, against ingress of solid foreign objects (windblown dust), ingress of water and hose-directed water. -Provides an additional level of protection against corrosion. -Provides the ability to be undamaged by the external formation of ice on the enclosure. |
| 5 | -Enclosures constructed for indoor use. -These enclosures provide a degree of protection against access to hazardous parts, against ingress of solid foreign objects (falling dirt, settling airborne dust, lint, fiber and flyings); ingress of water (dripping and light splashing). | |
| 6 | Submersible, Water-Tight, Dust-Tight and Sleet (Ice) Resistant | -Enclosures constructed for indoor or outdoor use. -Provides a degree of protection against access to hazardous parts, against ingress of solid foreign objects (falling dirt); ingress of water (hose-directed and occasional temporary submersion at a limited depth and will be undamaged by the external formation of ice on the enclosure. |
| 6P | Submersible, Water-Tight, Dust-Tight, and Sleet (Ice) Resistant | -Enclosures for either indoor or outdoor use. -They provide a degree of protection against access to hazardous parts, against ingress of solid foreign objects (falling dirt); ingress of water (hose-directed and prolonged submersion at a limited depth) and an additional level of protection against corrosion and undamaged by the external formation of ice on the enclosure. |
| 7 | Class I, Group A, B, C or D indoor hazardous locations Air break equipment | Enclosures for indoor use in hazardous (locations) classified as Class I, Division 1, Groups A, B, C, D as defined in NFPA 70. |
| 8 | Class I, Group A, B, C, or D indoor hazardous locations Oil-immersed equipment | Enclosures constructed for either indoor or outdoor use in hazardous locations classified as Class I, Division 1, Groups A, B, C, D as defined in NFPA 70. |
| 9 | Class II, Group E, F and G indoor hazardous locations Air-break equipment | Enclosures for indoor use in hazardous locations classified as Class II, Division 1, Groups E, F & G as defined in NFPA 70. |
| 10 | Bureau of Mines | These are enclosures constructed to meet the requirements of the Mine Safety and Health Administration, 30 CFT, part 18. |
| 11 | Corrosion resistant and drip proof-oil immersed | -These are enclosure intended for indoor use. -These enclosures protect against dripping, seepage and external condensation of corrosive liquids. -The enclosures protects against the corrosive effect of fumes and gases by oil immersion; watertight connectors and external mounting. |
| 12 | Industrial Use Dust-Tight and Drip-Tight | -Enclosures constructed (without knockouts) for indoor use. -They provide a degree of protection against access to hazardous parts, against ingress of solid foreign objects (falling dirt, circulation dust, lint, fibers and flyings. -They also provide a protection against ingress of water (dripping and light splashing). |
| 13 | Industrial Use Dust-Tight and Drip-Tight | -Enclosures constructed (with knockouts) for indoor use. -Provides a degree of protection against access to hazardous parts, against ingress of solid foreign objects (falling dirt, circulation dust, lint, fibers and flyings; ingress of water (dripping and light splashing). -These enclosures also provide a degree of protection against spraying, splashing, and seepage of oil and non-corrosive coolants. |
Related: Hazardous Locations Classifications
Recommended: The Ultimate Guide to Electrical Maintenance
In the European Union, enclosures are tested by qualified evaluators and site inspectors to ensure that the manufacturers adhere to prescribed manufacturing methods and material specification.
The IEC enclosure ratings covered byIEC Publication 529, Classification of Degrees of Protection Provided by Enclosure are based on ingress protection and are called IP ratings. IP ratings are based on protection against touch and foreign bodies and protection against water. There no classification particularly for corrosion resistance.
For enclosures the rating code considers two types of protection:
The type of protection is defined by two digits, the first digit relates to accessibility and the second digit relates to environmental protection. The two numbers are preceded by the letter IP.
Table 2 explains the meaning of the digits used in the IEC ingress protection ratings.
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Table 2 IEC IP Ratings
You can also read: Methods of Protecting Instruments from Explosive Atmospheres
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