What is the NEMA Enclosure Rating?
NEMA Enclosures Protect Against Environment Conditions and Hazards
NEMA offers standards for electrical equipment enclosures intended for use in industrial environments. These standards cover enclosures of both metallic and non-metallic types, and include enclosures without associate equipment installed, enclosures forming part of other products, enclosures intended for use in specific applications, and associated products offering a part of the environmental protection when used with these enclosures.
NEMA Standards for Enclosures
The National Electrical Manufacturers Association (NEMA) defines standards for enclosures and actively works on regional standards through CANENA with US, Canadian, and Mexican bodies. While actively promoting standardized product specifications for electrical apparatus, NEMA does not test products actively, it only establishes the performance criteria for enclosures intended for specific environments.
NEMA Classification of Enclosures
NEMA classifies enclosures to provide a degree of protection against non-hazardous environmental conditions such as:
- Incidental contact with the equipment enclosed within the enclosure
- Dirt falling on the enclosure
- Liquids falling on the enclosure and light splashing of liquids
- Dust, lint, fibers, and flying objects falling on the enclosure
- Enclosure hosed down and splashed with water
- Oil and coolant seepage onto the enclosure
- Oil or coolant spraying and splashing on the enclosure
- Enclosures affected by corrosive agents
- Occasional temporary submersion of enclosure
- Occasional prolonged submersion of enclosure
The NEMA classification ranges from 1 to 13, with each numeral signifying an enclosure meant for either indoor or outdoor use, with a defined range of protection:
Note that the above example transformer has a NEMA Enclosure Rating of 3R, enabling it for indoor/outdoor applications.
Enclosures designed to comply with NEMA 1 are meant for protecting electrical controls and terminations from inadvertent and incidental contact with objects and personnel. Such enclosures offer only a latched door, and there may not be a gasket sealing. Therefore, NEMA 1 enclosures should be used in environments where dust, oil, and water are not present.
Enclosures designed to comply with NEMA 2 are meant for indoor use and offer protection from limited quantities of water and dirt falling on it.
Enclosures designed to comply with NEMA 3 are meant for outdoor use and offer protection from windblown dust, rain, sleet, and formation of external ice on the enclosure.
Enclosures certified for NEMA 3R can be used in indoor/outdoor applications such as for wiring and junction boxes. While not having any surface sealed with a gasket, some models may provide hasps for padlocking. For indoor use, these enclosures will protect against dripping water. During outdoor use, NEMA 3R enclosures protect against falling rain, sleet, snow, and formation of external ice on it.
Enclosures certified for NEMA 3S are meant for outdoor use, where they provide protection against windblown dust, rain, and sleet. In addition, these enclosures allow operation of external mechanisms even when the enclosure is laden with ice.
Enclosures rated for NEMA 4 can be used in environments where the application is subject to occasional wash-downs such as near machines using coolants for a tool cutter. In addition, such an enclosure will also protect against a pressurized stream of water directed against it. The NEMA 4 compliant enclosure will have a gasket, with maximum sealing when its door is clamped.
Used in harsh environments where caustic cleaners and corrosive materials are in use, NEMA 4X compliant enclosures are made of aluminum, stainless steel, polycarbonate, or fiberglass. Applications include offshore petroleum sites, petro-chemical facilities, and in food industries, such as in poultry/meat processing facilities, where total wash-downs may occur repeatedly using disinfectants.
Enclosures designed to comply with NEMA 5 are meant for indoor use where they will offer protection against falling dirt, settling airborne dust, and non-corrosive dripping liquids.
Enclosures designed to comply with NEMA 6 are meant for indoor/outdoor use and provide protection against the entry of water if the enclosure is submersed occasionally or temporarily to a limited depth.
Meant for indoor/outdoor use, NEMA 6P compliant enclosures offer protection against entry of water when the enclosure is immersed to a limited depth during prolonged submersions.
Intended for indoor use, NEMA 11 compliant enclosures offer protection against the corrosive effects of liquids and gases.
Intended for indoor use, NEMA 12 compliant enclosures offer protection against falling dirt, drips, and non-corrosive dripping liquids. These enclosures have a gasket seal on the door to protect against ingress of airborne contaminants and non-pressurized oil and water.
NEMA 12K compliant enclosures contain knock-outs and are meant for indoor use, offering protection against falling dirt, dust, and non-corrosive dripping liquids, but not at the knock-outs.
Enclosures designed to comply with NEMA 13 are meant for indoor use and provide protection against the ingress of dust, and spray of water, oil, and non-corrosive coolants.
Precautions When Using NEMA Enclosures
NEMA standards do not provide any reference to constructional details, but describe each type of enclosure in general and functional terms. Therefore, NEMA standards specify only what an enclosure must do, but not how to manufacture it.