NEMA type ratings

The purpose of NEMA Type ratings is to provide a characterization of an enclosure’s ability to protect personnel from the contents of the enclosure and to protect the equipment in the enclosure from the environment outside, as well as to ensure overall quality of the part.

NEMA is a United States manufacturers’ organization that promotes standardized specifications for electrical products. While the organization does not test the products itself, it develops detailed construction, performance, and installation criteria as well as testing methods for electrical products. These methods are then used by manufacturers, often along with standards and independent testing from Underwriters Laboratories (UL), the Canadian Standards Association (CSA), the International Electrotechnical Commission (IEC), etc. to certify their products.

Consideration for NEMA Type ratings is an important step in the design and development of electrical products and equipment because it aligns the expectations of manufacturers and installers. By standardizing features such as nomenclature, construction and composition, dimensions and tolerances, operating characteristics, and testing, manufacturers and purchasers can eliminate miscommunications in selecting the proper equipment for a job.

The purpose of the Type ratings is to provide a characterization of an enclosure’s ability to protect personnel from the contents of the enclosure and to protect the equipment in the enclosure from the environment outside, as well as to ensure overall quality of the part. In the spirit of the rating, our conduit and our fittings do prevent ingress of large, solid foreign objects into the raceway and will perform, undamaged, should ice form externally on the raceway.

Among the enclosures used in non-hazardous locations, there are 14 different rating designations:

Table 1
[From Nema 250-2003]
Comparison of specific applications of enclosures for indoor Nonhazaradous locations

Provides a Degree of Protection Against the Following Conditions:Types of Enclosures
1* 2* 4 4X 5 6 6P 12 12K 13
Access to hazardous parts
Ingress of solid foreign objects (falling dirt)
Ingress of water (Dripping and light splashing)
Ingress of solid foreign objects
(Circulating dust, lint, fibers, flyings**)
Ingress of solid foreign objects
(Settling airborne dust, lint, fibers, and flyings **)
Ingress of water (Hosedown and splashing water)
Oil and coolant seepage
Oil or coolant spraying and splashing
Corrosive agents
Ingress of water
(Occasional temporary submersion)
Ingress of water
(Occasional prolonged submersion)

* These enclosures may be ventilated.

** These fibers and flyings are nonhazardous materials and are not considered Class III type ignitable fibers or combustible flyings. For Class III type ignitable fibers or combustible flyings see the National Electrical Code Article 500.

Table 2
[From Nema 250-2003]
Comparison of specific applications of enclosures for for outdoor Nonhazaradous locations

Provides a Degree of Protection Against the Following Conditions:Types of Enclosures
3 3X 3R* 3RX* 3S 3SX 4 4X 6 6P
Access to hazardous parts
Ingress of water (Rain, snow, and sleet**)
Sleet***
Ingress of solid foreign objects
(Windblown dust, lint, fibers, and flyings)
Ingress of water (Hosedown)
Corresive agents
Ingress of water
(Occasional temporary submersion)
Ingress of water
(Occasional prolonged submersion)

* These enclosures may be ventilated.

** External operating mechanisms are not required to be operable when the enclosure is ice covered.

*** External operating mechanisms are operable when the enclosure is ice covered.


Equivalencies between Ratings
A UL Listing, which indicates a comprehensive evaluation of the part, includes some environmental testing that parallels aspects of NEMA Type ratings. For example, testing for UL Listing of Gibson Stainless conduit bodies and device boxes includes “Wet Locations” tests. In these tests, the fittings are subjected to water spray directed at the fitting from multiple angles at a given pressure for a specified duration. This is similar to NEMA Type rating testing where a mandated volume of water is directed at the fitting over a given time period.

For more information about ratings, or for answers to any certification questions you may have, contact Gibson Stainless today.

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