Terms like “waterproof,” “sealed,” “dust tight” and the like are used to describe electrical and electronic enclosures. Unfortunately, these terms are inherently ambiguous. Is the enclosure merely rain-proof or is it fully submersible? Is it sealed so that no air will transfer, or is it sealed against intrusion by objects?
To clarify this situation with a clear set of standards, The National Electrical Manufacturer’s Association www.nema.org developed NEMA ratings. The ratings make it easy to specify enclosures with the right level of protection, however they can also be confusing. For example, NEMA 4 offers more stringent protection than NEMA 12. Many times engineers specify the wrong level of protection, either overspending or risking equipment damage.
This guide will help you select the just-right NEMA rating for your application, like Goldilocks: neither too much nor too little.
NEMA 1:
For indoor use only.
Protects users against contact with hazardous (energized electrical) components.
Protects the components from the ingress of solid objects, such as fingers and falling dirt. The test for this is trying to stick a rod of a given size into the enclosure. A very basic level of protection. A classic example is Bud’s NEMA 1 Junction Box.
NEMA 2:
For indoor use only.
NEMA 2 protection is the same as NEMA 1 in terms of preventing ingress of large solid objects.
It adds protection against the ingress of dripping and light splashing water. This does not mean rain, as this is an indoor rating. Typically, the water comes from condensation, such as in a laundry room or around HVAC equipment.
NEMA 3:
Enclosures at this rating and higher ratings are for both indoor and outdoor use.
NEMA 3 is the same as NEMA 2, but because it may be used outside in the weather, it adds stronger protection against the ingress of water and dust. It protects against windblown dust, rain, sleet, and snow. This is accomplished by a gasket on the cover.
It will not be damaged by ice forming on the enclosure.
NEMA 3 enclosures are found on construction sites, ship docks, and in tunnels and subways subject to wet conditions.
NEMA 3R:
NEMA 3R gives the mostly the same protection as NEMA 3, but it subtracts the protection against windblown dust.
The other protections are the same as NEMA 3 regarding rain, sleet, snow, and formation of ice.
NEMA 3R enclosures are commonly used where the enclosure is in a protected structure. Typical applications include electrical switch gear, lighting contactors, and power distribution units.
Note that these are electrical applications rather than electronic applications. Printed circuit boards tend to be more vulnerable to damage from moisture than electrical components.
By the way, windblown dust can include lint, fibers and filings from manufacturing process. If these settle on surfaces (indoors, without wind), a NEMA 3 enclosure should provide sufficient protection. If there are strong fans or airflow, then a NEMA 3 enclosure may be a safer option than a NEMA 3R enclosure if these contaminants are present.
NEMA 3S:
This rating provides the same protection as NEMA 3, but it adds the provision that the external mechanism remains operable when ice laden. Generally, this applies to the door and latches. A design that covers the door from above will shield the door from ice forming on top of the enclosure, and latches that operate horizontally will still work when ice forms on top of them.
NEMA 3X, NEMA 3RX, NEMA 3SX:
The X signifies the addition of corrosion protection. Usually this is achieved by molding the enclosure out of plastic and using stainless steel parts for the latch and hinges.
Corrosion is a problem in wet areas and in locations near salty air.
NEMA 4:
A NEMA 4 rating is the same as a NEMA 3 rating, but it adds protection against hose directed water.
The testing for NEMA 4 consists of spraying the enclosure with water at 65 gallons per minute from a 1-inch hose. This is a lot more water than in the NEMA 3 test, which is a water spray at 5 psi.
At many industrial plants, such as breweries and dairies, cleaning workers wash down equipment with a hose, putting at risk the circuitry used for machine controls. To protect sensitive controls on the factory floor, NEMA 4 (and NEMA 4X) is a popularly specified enclosure rating.
NEMA 4X is the same as NEMA 4 but adds protection against corrosion. Except for steel enclosures, NEMA 4X is readily available in all plastic enclosures at a relatively low price. Therefore, most enclosures specified for outdoor and factory washdown environments are rated NEMA 4X.
NEMA 5:
NEMA 5 is for indoor applications, so it has less protection than NEMA 4. The concept that a higher numerical rating denotes a higher protection level does not apply to NEMA enclosures
NEMA 5 enclosures do have a gasket, but it’s intended to keep out dust, not rain and water. Think of settings like cement plants and steel mills.
Generally, engineers just specify a NEMA 4 enclosure for dusty environments. NEMA 5 enclosures are nearly impossible to find. Because a gasket is needed anyway, enclosure manufacturers usually pursue the higher rating of NEMA 4 and increasingly of NEMA 6.
NEMA 6:
This rating includes all the protections of lower ratings: against the ingress of objects, fingers, and falling dirt, hose directed water, and it is undamaged by ice formation.
What’s more, it protects against occasional temporary submersion to a limited depth. How deep and how long? The UL-50 standard defines the submersion test to be performed at a depth of six feet for 30 minutes.
To obtain this rating, enclosure manufactures need a tight seal on the enclosure cover. Usually this includes a continuously poured gasket of a solid material such as silicone.
NEMA 6P:
Same as NEMA 6 but adds protection of prolonged submersion to a limited depth for a prolonged period of time in water or oil.
The test defined by UL-50 is a depth of six feet for a 24-hour period. For the test, a conduit connector must be installed.
Also, NEMA 6P includes corrosion protection.
This is the rating used for mines, manholes, and quarries, assuming the submersion is not continuous.
NEMA 12:
This rating protects against the ingress of objects, fingers, falling dirt, settling dust and drips.
It is similar to NEMA 3, but it is for indoor use, so instead of protecting against windblown dust it protects against settling airborne dust, lint, fibers, and
It won’t protect against rain, sleet, and snow, as it is an indoor rating, but it does protect against seeping oil and coolant as well as dripping and light splashing water.
Despite the large number it is a basic level of protection. It may be helpful to think of it as NEMA 1.2 rather than NEMA 12.
NEMA 13:
Same as NEMA 12 but adds protection against oil and coolant splashing and spraying.
NEMA 13 provides a basic level of protection despite its high number.
Hazardous Locations
This guide, so far, has covered only non-hazardous locations. NEMA 7, 8, 9 and 10 are the ratings to look at for hazardous environments in which explosive gases may be present. You may read more about these ratings at this blog post,” Rating NEMA Boxes Versus IP Boxes.” The key to selecting the right rating is to know the classification of the hazard by class and division. For example, Class I covers explosive vapors and gases, Division 1 says they may be present every day, and Group B includes Ammonia and Ethanol. Bud offers an ATEX rated enclosure for explosion-proof applications. The web page states the classes, divisions and groups where it may be used.
NEMA vs IP
Europe, through its standards body the International Electrotechnical Commission (IEC), has its own standards for specifying the degree of enclosure protection, known as IP (ingress protection) ratings. They are similar to NEMA ratings, but the tests used are slightly different, so the ratings are not equivalent. For example, a NEMA 3 enclosure will meet the requirements of an IP45 enclosure, but it will also exceed them because the NEMA 3 tests are more rigorous. Converting NEMA to IP and IP to NEMA is a whole subject in itself. See our IP versus NEMA comparison tables.
Many North American manufacturers want to sell their products globally, so they seek enclosures with IP ratings. Bud’s extensive line of NEMA rated enclosures also carry IP ratings.
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