NEMA Ratings

NEMA is the trade association of choice for the electrical manufacturing industry. Founded in 1926 and headquartered near Washington, D.C., its approximately 450 member companies manufacture products used in the generation, transmission and distribution, control, and end-use of electricity.

NEMA provides a forum for the development of technical standards that are in the best interests of the industry and users, advocacy of industry policies on legislative and regulatory matters, and collection, analysis, and dissemination of industry data.

The NEMA standard on outdoor enclosures and cabinets provides general information on the definitions of NEMA Enclosure Types to architects, engineers, installers, inspectors and other interested parties. Purcell Systems manufactures outdoor enclosures and cabinets to meet both NEMA 3 and NEMA 3R ratings. Although the NEMA standard supports a range of NEMA ratings from 1 through 12, most enclosures for wireline, wireless, and energy applications require NEMA 3 or NEMA 3R ratings. Most general industrial applications will require NEMA 3 or NEMA 4 variants. A summary of the most relevant NEMA ratings for outdoor industrial enclosures and cabinets is listed below.

Type 3

Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt and windblown dust); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow); and that will be undamaged by the external formation of ice on the enclosure.

Type 3R

Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow); and that will be undamaged by the external formation of ice on the enclosure. Relative to the NEMA 3 standard, this style of enclosure does not have a gasketed sealing surface. So, it subsequently excludes protection against windblown dust and allows the ingress of external air into the enclosure. Most enclosures or cabinets that house wireless, wireline, or energy electronics specify a NEMA 3R enclosure.

Type 4

Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt and windblown dust); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow, splashing water, and hose directed water); and that will be undamaged by the external formation of ice on the enclosure. NEMA 4 enclosures are typically used in many applications where; an occasional wash-down occurs, a machine tool cutter coolant is used, or a pressurized stream of water is used. NEMA 4 enclosures are gasketed and the door is clamped for maximum sealing from outside air penetration. They have continuous hinges, mounting feet, and padlock hasps.

Type 4X

Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (windblown dust); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow, splashing water, and hose directed water); that provides an additional level of protection against corrosion; and that will be undamaged by the external formation of ice on the enclosure. NEMA 4X enclosures are used in more corrosive environments than standard NEMA 4 units. Applications where corrosive materials and caustic cleaners are used necessitate the use of a NEMA 4X enclosure. Applications include food/meat/poultry processing facilities, where total wash-down with disinfectants occur repeatedly, and petro-chemical facilities. NEMA 4X is used when protection from the worst environments is required.

NEMA Standard Publication

The NEMA Standard Publication 250-2008, "Enclosures for Electrical Equipment (1000 Volts Maximum)” addresses all NEMA ratings. The standard assesses the enclosure relative to its desired NEMA rating from three perspectives – construction review, markings review, and design tests.

The construction review assesses; material, corrosion protection (indoor, outdoor), openings (equipment, ventilation, drainage), mounting, conduit connection, hubs, fittings, knockouts, access to interior, closing hardware, gaskets, and observation windows.

The markings review assesses; type of designations, location of markings, enclosure orientation, conduit hubs, closure plates, equipment openings, and drainage openings.

The design tests assess: protection against access to hazardous parts, protection against ingress of water (dripping, splashing, rain, hose, submersion), protection against ingress of solid foreign objects (dust, lint, fibers, flyings), external icing, corrosion protection (indoor, outdoor), oil exclusion, and gasket tests.

NEMA does not require independent testing and leaves compliance completely up to the manufacturer. However, the UL 50 type 3R standard is identical to the NEMA 3R rating. Purcell Systems contracts with UL to verify that their enclosures meet the requirements of UL 50 type 3R. Therefore, Purcell Systems offers independent third-party verification that our enclosures comply with both the NEMA 3R rating and the UL 50 type 3R standard.