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The NEMA website provides a general description of enclosure types at www.nema.org/prod/be/enclosures/upload/NEMA_Enclosure_Types.pdf. For a complete description of enclosures, including test requirements, you will need the NEMA 250 standard. It is available for purchase from IHS, ANSI, and Techstreet.
Enclosures that meet the requirements for more than one type rating may be designated by a combination of type numbers, the smaller number being given first. The designation may include a combination of indoor, outdoor, hazardous location, and non-hazardous location ratings if they apply.
It is not possible to state that an IP rating is equivalent to a NEMA type designation. An IP rating only considers protection against ingress of solid foreign objects and ingress of water. The NEMA types consider these but also consider other items such as corrosions and construction details. For this reason, it is possible to say that a NEMA type is equivalent to an IP rating, but it is not possible to state that an IP rating is equivalent to a NEMA type. Further information is available from the NEMA website at www.nema.org/stds/briefcomparison.cfm.
NEMA 250 test requirements state that all outdoor enclosures are subject to 600 hours of salt spray and compared to G90 galvanized sheet steel. Type 4X enclosures are subject to 200 hours of salt spray and compared to American Iron and Steel Institute type 304 stainless steel.
No, NEMA 250 does not address arc flash. Arc flash protection requirements are described in NFPA 70E Standard for Electrical Safety in the Workplace. NFPA 70E requires protective equipment and clothing if the operator intends to open an electrical enclosure containing voltage greater than 50 Vac. There are no tests specified in either NEMA 250 or NFPA 70E that rate an enclosure’s resistance to arc flash energy.
There are no standard sizes for NEMA enclosures. The NEMA 250 standard provides construction and test requirements.
NEMA does not cross-reference the type ratings with these environmental descriptions; however, NFPA 70 National Electrical Code has definitions and in some cases cross-references for these descriptions.
To see a listing of testing facilities, go to www.nema.org/stds/conformity/links.cfm.
The NEMA 250 standard has correlation tables for this. The NEMA 250 standard is available from IHS, ANSI, and Techstreet.
The fittings are to be independently tested to a type number equal to or better than the enclosure type rating on which they are intended to be installed.