NEMA Enclosure Ratings Explained

When I landed my first job here at Royal Electric early in 2014, I’ll admit I knew next to nothing about the Electric Supply industry. From Variable Frequency Drives to UL Ratings and everything in between, I knew I needed to catch up quick or I’d soon find myself looking for a new job. One of the most difficult pieces of information for me to wrap my head around was NEMA Ratings for Enclosures. With 13 different types, each with their own separate classifications and configurations, I constantly found myself going back to Google to find out if I had my facts straight. The worst thing was many of the pages that came up contradicted each other and excluded some important information; not-to-mention that they weren’t clearly worded which made it really hard to get a handle on it all. When digging, I came across a recent survey that claimed, “…over 70% of engineers were confused by the different NEMA ratings…[and]…40% of all enclosures that require protection are specified at the wrong level.” (Haas, Blair) No wonder I had trouble tracking the correct information.

With that in mind, my goal is to set the record straight and give you The Definitive Guide to NEMA Enclosure Ratings.

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NEMA stands for National Electrical Manufacturers Association. It was formed in 1926 when the Associated Manufacturers of Electrical Supplies merged with the Electric Power Club to form an organization to set the standards for the manufacture of safe and effective electrical products. This merger not only served to set the standards for the burgeoning electrical industry, but also ensured compatibility between devices made by different manufacturers. Since its creation, NEMA has continued to develop and promote standards for the constantly evolving electrical industry.

NEMA Enclosures can be made out of fiberglass, polycarbonate, ABS, Polyester (PBT), mild steel, stainless steel, zinc, and aluminum. As you might guess, each material exhibits specific traits that present both advantages and disadvantages depending on its use and location. For example, “a fiberglass enclosure exposed to direct sunlight for several years will likely experience fiberbloom, and a mild steel enclosure will rust in wet or corrosive environments. (Hoffman)” When thinking about which material you want for your enclosures, you must take into account the price, the aesthetics, the weight, and the thermal issues of each material, as selecting the correct enclosure material is a key element in ensuring long enclosure life.

Enclosures made from fiberglass are lightweight and strong, demonstrating high impact strength, rigidity, and a working temperature range from -31 ̊F-300 ̊F. They are also known to exhibit above average moisture-resistance. Fiberglass enclosures can be made by either compression molding, or using a spray process that provides a heavy corrosion-resistant outer coating. Enclosures made from this material have a much higher unit price than other enclosure types despite fiberglass being notoriously known as a hard material to modify due to it’s many strengths in other areas.

Polycarbonate enclosures, made from a thermoplastic resin, are created by either an injection molding process or a sheet extrusion process. While their temperature range isn’t at large as their fiberglass counterparts, they sport a range from -31 ̊F-180 ̊F and can be formulated to offer fire retention and UV stabilizing qualities. They also have a low unit price, can be made transparent if needed/specified, and offer, “good corrosion resistance in some acidic surroundings, but it is not suitable for environments with strong alkalis and organic solvents. (Hoffman)” Polycarbonate enclosures are great for job-site modifications as thermoplastic is considered the most flexible of the enclosure materials to work with.

ABS is also a type of thermoplastic resin, and enclosures made out of ABS exhibit many of the same qualities as those made from Polycarbonate. This materials temperature range is only from 0 ̊F-125 ̊F, but ABS enclosures have better chemical resistance to some acids and alkalis than Polycarbonate enclosures. One drawback to using an enclosure built from ABS is that this material is not UL/CSA certified (though enclosure constructions meet NEMA 4X requirements). They are viewed as a “good low-cost alternative for indoor and moderately corrosive environments where a rating is not required. (Hoffman)” Enclosures made from ABS are also considered to be highly suitable for job-site modifications as thermoplastic is the most flexible of the enclosure materials to work with.

Polyester (PBT) enclosures were introduced as a non-metallic enclosure material option for those looking for an inexpensive enclosure that offers a broad range of benefits. Some of those benefits include it being a lightweight material that offers high impact resistance, great chemical and moisture resistance, and a temperature range from -40 ̊F-248 ̊F. This material may not be the best for outdoor applications where it is exposed to direct sunlight as it might cause a slight yellowing of the material that would detract from its overall aesthetic appeal.

Mild Steel enclosures are made from hot-or-cold rolled steel, and are known to be very durable and easy to modify. While they are good enclosures for many indoor and outdoor applications, they do not perform well when tested against the other materials with respect to corrosion-resistance. This can be helped by applying the proper powder paint finish which raises it’s corrosion-resistance rating. Some drawbacks to using this material include its weight, as mild steel is heavy, and its price point, though modifications such as custom shapes, sizes, and knockouts are much more inexpensive and easier to perform on mild steel then on any other material.

Stainless Steel enclosures have many of the same properties as those made from Mild Steel, but have the added benefit of being corrosion-resistant without the need for any finishing.

“Stainless steel’s ability to resist corrosion comes from its chemical composition. Type 304 stainless steel (18-8) was named to reflect its 18% chromium and 8% nickel composition. Type 316 stainless steel, a higher-grade version, has a 10% nickel, 16% chromium and 2% molybdenum content. Nickel and molybdenum provide increased corrosion resistance to chlorides and many common industrial chemicals, while chromium provides a protective surface film. Stainless steel can cost up to three times as much as mild steel, and since the cost of stainless steel is directly related to its chemical composition, an increase in nickel content equals an increase in material cost. (Hoffman)”

Similar to mild steel enclosures, some drawbacks to using this material include its weight, and its price point. Modifications such as custom shapes, sizes, and knockouts are harder to make on stainless steel due to its hardness.

Enclosures made out of Aluminum or Zinc are typically made through a metal process known as Die Casting. Die-cast enclosures are known to be extremely rugged and lightweight, provide internal equipment shielding and relatively easy to modify. Aluminum enclosures in particular are rated to NEMA 4, are corrosion resistant, and ideal for both indoor and outdoor locations as well as marine environments containing solvents, petrochemicals, some acids and most sulfates and nitrates. Zinc or aluminum as the primary enclosure material both offer high impact strength and are relatively easy to modify.

NEMA Enclosures are rated on a scale of 1-13, 1 being for the most basic applications and 13 being used for more specific applications. On top of that, there are letter classifications that often go along with the number scale. They are as follows:

  • X: Corrosion-Resistant
  • R: Susceptible to Windblown Particles
  • S: External Operating Mechanisms are Operable when Ice-Covered
  • P: Capable of being submerged in Water for Prolonged Periods of Time
  • K: Constructed with Knockouts

Each letter classification can be combined with another, so for example you can have a NEMA 3RX rated enclosure that is both corrosion-resistant and susceptible to windblown particles.

When dealing with the NEMA classification of certain boxes, you may come across something called an IP rating. “The IP rating is set out in standard IEC EN 60529 and rates electrical enclosures by the level of ingress protection against solids (1st digit) and against liquids (2nd digit). The higher number for each digit, the better the protection” (Rotork). These IP ratings directly correspond to NEMA classifications for enclosures meant for non-hazardous locations only, and work almost like a cheat sheet once you know what information correlates to each digit.

To even further complicate matters, enclosures can either be made for use in Hazardous or Non-Hazardous locations. To start off the guide we’re going to begin with the Enclosures for Non-Hazardous locations.

Non-Hazardous Location Enclosures:

All NEMA non-hazardous enclosure types, when properly installed, provide protection to personnel against access to hazardous parts, and prevent falling dirt from getting inside the enclosure and potentially interfering with the equipment you’re trying to protect.

NEMA Type 1 enclosures are the most basic classification, typically used in indoor general-purpose applications for protecting controls or housing motor stop/start stations. Type 1 enclosures also feature latching doors, but do not come with gasketed sealing surfaces that are used in applications where sealing out dust, oil, and water is required. These boxes may also be ventilated. The IP equivalent to this rating is ‘IP30’.

NEMA Type 2 enclosures are also used for indoor general-purpose applications and have all of the features of the Type 1 enclosure with the added benefit being water-resistant. Type 2 enclosures provide protection for the equipment being housed inside against light dripping and splashing. These boxes may also be ventilated. The IP equivalent to this rating is ‘IP31’.

NEMA Type 3 enclosures are capable of being used for both indoor and outdoor applications, and improve on the Type 2 design by being resistant to rain, sleet, and snow as opposed to just light dripping and splashing. As they are often used in outdoor locations, they have the added benefit of providing protection against the external formation of ice, though the external operating mechanisms are not required to be operable when enclosure is ice-covered. Type 3 enclosures are also made to prevent and protect against the ingress of solid foreign objects, including windblown dust, lint, fibers, and flyings. The IP equivalent to this rating is ‘IP64’.

NEMA Type 3R enclosures are have all of the capabilities of the Type 3 except for the ability to prevent and protect the internal equipment from the ingress of windblown dust, lint, fibers, and flyings. These enclosures are typically used for wiring and junction boxes, and some models come with hasps for padlocking or lock-out/tag-out. These boxes may also be ventilated.

NEMA Type 3S enclosures also have all of the capabilities of the Type 3 enclosures (including the ability to prevent and protect against the ingress of windblown dust, lint, fibers, and flyings) with the added benefit of having operable external mechanisms even when covered in ice. As a result, this type of specialty enclosure is often used outside in cold locations where it may be covered by snow or ice for much of the year. The IP equivalent to this rating is ‘IP64’.

NEMA Type 3X enclosures are capable of being used for both indoor and outdoor applications, are resistant to rain, sleet, and snow as well as the ability to prevent and protect against the ingress of windblown dust, lint, fibers, and flyings. As they are often used in outdoor locations, they are constructed to provide protection against the external formation of ice, though the external operating mechanisms are not required to be operable when enclosure is ice-covered. As stated above, the X designation means that this particular type of enclosure is corrosion-resistant.

NEMA Type 3RX enclosures are capable of being used for both indoor and outdoor applications, are resistant to rain, sleet, and snow. As they are often used in outdoor locations, they provide protection against the external formation of ice, though the external operating mechanisms are not required to be operable when enclosure is ice-covered. This particular type of enclosure is also corrosion-resistant, and may also be ventilated.

NEMA Type 3SX enclosures are capable of being used for both indoor and outdoor applications, are resistant to rain, sleet, and snow as well as the ability to prevent and protect against the ingress of solid foreign objects, including windblown dust, lint, fibers, and flyings. As they are often used in outdoor locations, they are made to provide protection against the external formation of ice, and also offer the added benefit of having operable external mechanisms even when covered in ice. This particular type of enclosure is also corrosion-resistant.

NEMA Type 4 enclosures are capable of being used for both indoor and outdoor applications, are resistant to rain, sleet, and snow, but does not have the ability to prevent and protect against the ingress of solid foreign objects, including windblown dust, lint, fibers, and flyings. These enclosures are usually made of steel or plastic. One feature that sets the Type 4 apart from the previous configurations we’ve reviewed is the ability to prevent the ingress of water in the event of a ‘Washdown’, which is the high-pressure cleaning with water and/or chemicals in industries such as food and beverage and pharmaceuticals. The external operating mechanisms on these enclosures are not required to be operable when enclosure is ice-covered. The IP equivalent to this rating is ‘IP66’.

NEMA Type 4X enclosures are also used for applications in the food & beverage and the pharmaceutical industries and have all of the features of the Type 4 enclosure with the added benefit being corrosion-resistant. This means that 4X enclosures are typically used in harsher environments than the normal Type 4 configurations. Applications where corrosive materials and caustic cleaners are used typically necessitate the use of a NEMA 4X enclosure. They are often used in Petro-Chemical facilities including offshore petroleum sites where protection from the worst environments is required. The IP equivalent to this rating is ‘IP66’.

NEMA Type 5 enclosures are constructed for indoor applications, and like the Type 2 enclosures are water-resistant, providing protection for the equipment being housed inside against light dripping and splashing. These types of enclosures also prevent and protects against the ingress of solid foreign objects, including windblown dust, lint, fibers, and flyings, as well as providing protection against the external formation of ice.

NEMA Type 6 enclosures are one of the only two NEMA types that provide a degree of protection for the ingress of water from a wash-down, as well as full submersion into water at a limited depth. They are made for indoor and outdoor use, are corrosion-resistant, and provide protection against the external formation of ice. The IP equivalent to this rating is ‘IP67’.

NEMA Type 6P enclosures are constructed for indoor and outdoor applications, and like the Type 6 enclosures are one of the only two NEMA types that provide a degree of protection for the ingress of water from a wash-down. The main difference between these and the Type 6 enclosures is whereas the Type 6 enclosures are protected from full submersion into water at a limited depth, the Type 6P can be submerged for prolonged periods of time without it’s contents being compromised. They are also are corrosion-resistant and provide protection against the external formation of ice. The IP equivalent to this rating is ‘IP67’.

NEMA Type 12 enclosures are constructed for indoor use, and are made to prevent against the ingress of solid foreign objects, including windblown dust, lint, fibers, and flyings, as well as light splashing and dripping from non-corrosive liquids. A gasketed sealing surface ensures protection from oil and coolant seepage. These types of enclosures are usually used to house automation control and electronic drive systems. These enclosures have no protection against significant environmental risks due to icing. NEMA Type 12K Enclosures are exactly the same as the NEMA Type 12’s except that it’s constructed with knockouts. The IP equivalent to both of these ratings is ‘IP64’.

NEMA Type 4 & 12 enclosures are a special case (Pun Intended!). They are made by a company called ‘Wiegmann”, and combine the attributes of the NEMA 4 and the NEMA 12 enclosures. This enclosure is made to prevent against the ingress of solid foreign objects, including windblown dust, lint, fibers, and flyings, as well as light splashing and dripping from non-corrosive liquids. A gasketed sealing surface ensures protection from oil and coolant seepage. It has reversible doors for right or left opening, concealed hinges, and rear mounting holes for a more aesthetically pleasing look, while affording the housed equipment the protection it needs. Like the Type 12, these enclosures have no protection against significant environmental risks due to icing as it’s used primarily for indoor applications.

NEMA Type 13 is the last classification for enclosures used in non-hazardous locations. It’s made for indoor use and is made to prevent against the ingress of solid foreign objects, including windblown dust, lint, fibers, and flyings, as well as light splashing and dripping from non-corrosive liquids. A gasketed sealing surface ensures protection from the spraying, splashing, or seepage of oil and coolant. The IP equivalent to this rating is ‘IP67’.





Hazardous Location Enclosures:

NEMA classifications for Hazardous locations are another issue entirely. While there are only 4 different number types (7-10), one must take in to account the class that goes along with them. There are four classes (I, II,III, and MSHA), and each class contains its own groups (lettered A-G depending on the enclosure Type), which correspond to atmospheres containing different chemicals including:

  • Acetylene – Class I Group A for NEMA Types 7 and 8
  • Hydrogen, Manufactured Gas – Class I Group B for NEMA Types 7 and 8
  • Diethyl Ether, Ethylene, Cyclopropane – Class I Group C for NEMA Types 7 and 8
  • Gasoline, Hexane, Butane, Naphtha, Propane, Acetone, Toluene, Isoprene – Class I Group D for NEMA Types 7 and 8
  • Metal Dust – Class II Group E for NEMA Type 9
  • Carbon Black, Coal Dust, Coke Dust – Class II Group F for NEMA Type 9
  • Flour, Starch, Grain Dust – Class II Group G
  • Fibers, Flyings – Class III Group
  • Methane (with or without Coal Dust) – Class MSHA Group 10

NEMA Type 7 enclosures are made specifically for indoor use, and when completely and properly installed and maintained this enclosure is designed to contain an internal explosion without causing an external hazard. Type 7 enclosures are classified as Class I, Division 1, Groups A, B, C, or D. This means that Type 7 enclosures can be made to provide protection against:

  • Acetylene
  • Hydrogen, Manufactured Gas
  • Diethyl Ether, Ethylene, Cyclopropane
  • Gasoline, Hexane, Butane, Naphtha, Propane, Acetone, Toluene, Isoprene

NEMA Type 8 enclosures are made for indoor and outdoor use, and when completely and properly installed and maintained this enclosure is designed to prevent combustion through the use of oil-immersed equipment. Type 8 enclosures are classified as Class I, Division 1, Groups A, B, C, or D. This means that Type 8 enclosures can be made to provide protection against:

  • Acetylene
  • Hydrogen, Manufactured Gas
  • Diethyl Ether, Ethylene, Cyclopropane
  • Gasoline, Hexane, Butane, Naphtha, Propane, Acetone, Toluene, Isoprene

NEMA Type 9 enclosures are made specifically for indoor use, and when completely and properly installed and maintained this enclosure is designed to prevent the ignition of combustible dust. These enclosures are classified as Class II, Division 1, Groups E, F, or G. This means that Type 9 enclosures can be made to provide protection against:

  • Metal Dust
  • Carbon Black, Coal Dust, Coke Dust
  • Flour, Starch, Grain Dust

NEMA Type 10 enclosures are made for indoor and outdoor use, and when completely and properly installed and maintained this enclosure, like the Type 7, are designed to contain an internal explosion without causing an external hazard. These enclosures are constructed to meet the requirements of the Mine Safety and Health Administrations.

Works Cited:

NEMA. “NEMA Enclosure Types.” Nema.org. 1 Nov. 2005. Web. 22 Jan. 2015. .

Hoffman. “Specifying the Correct Enclosure Material.” Hoffman Enclosures Inc.,01 January 2008. Web. 28 Jan. 2015. .