NEMA enclosure types explained

What a NEMA enclosure type means

NEMA 250, the National Electrical Manufacturers Association standard Enclosures for Electrical Equipment (1000 Volts Maximum), defines enclosure "Types" by the conditions they are built to withstand. NEMA now publishes it as ANSI/NEMA EN 10250; most drawings and specifications still say NEMA 250. Every type protects people against access to hazardous parts inside. Beyond that, each type adds protection for the equipment against solid objects (falling dirt, windblown or circulating dust), water (dripping, rain, splashing, hose-directed water, submersion) and, for some types, external ice, oil and coolant, and corrosion.

A type rating says nothing about size: NEMA states there are no standard sizes for NEMA enclosures, and each manufacturer designs its own. It also applies to the enclosure as installed and ready for use, with every opening closed by suitable fittings.

NEMA types at a glance

The descriptions below condense the NEMA type definitions. The IP column is the IEC 60529 code that NEMA's own conversion table (Table A-1) shows each type as meeting or exceeding.

Type 12K is Type 12 with knockouts. Types 3X, 3RX and 3SX are the corrosion-resistant versions of 3, 3R and 3S. Types 2 and 5 (indoor dripping water and settling dust) exist but are rarely specified for new equipment, and Types 7 and 9 cover hazardous (classified) locations, which are outside this guide.

Indoor types: 1, 12 and 13

Type 1 keeps fingers away from live parts and keeps falling dirt off the equipment. It is the type for clean, dry rooms: offices, labs, electrical rooms.

Type 12 is the workhorse of indoor industrial panels. The door is gasketed, so circulating dust, lint and fibers stay out, and dripping or lightly splashing water and seeping oil or coolant do not get in. It is not tested against hose-directed water, so it is the wrong choice for a line that gets hosed down. Type 13 adds protection against oil and non-corrosive coolant being sprayed or splashed, typical near machine tools.

Outdoor types: 3R, 3 and 3S

Type 3R is the rain-tight outdoor type: rain, sleet and snow stay out and external ice does not damage it, but it is not tested against windblown dust. That is why many 3R enclosures are ventilated. Type 3 adds windblown dust. Type 3S adds the requirement that external mechanisms such as disconnect handles still operate when the enclosure is covered in ice.

Hosedown and corrosion: Types 4 and 4X

Type 4 is the first type tested against hose-directed water, and it also covers windblown dust and external ice, indoors or outdoors. In the NEMA hosedown test, water from a 1 in (25.4 mm) nozzle at 65 gal/min (240 L/min) is aimed from 10 to 12 ft (3.0 to 3.7 m) along every seam, joint and operating mechanism, and no water may get in.

Type 4X is Type 4 plus corrosion resistance. NEMA explains the corrosion test like this: all outdoor enclosures are exposed to 600 hours of salt spray and compared with a G90 galvanized steel specimen; Type 4X enclosures (and 3RX, 3X, 3SX and 6P) then get another 200 hours of salt spray and are compared with an AISI 304 stainless steel specimen. Stainless steel is a common way to meet it. Food and beverage plants, wastewater, chemical areas, marine and coastal sites usually call for 4X. The next guide compares the two in detail: NEMA 4 vs 4X vs IP66.

Submersible types: 6 and 6P

Type 6 survives occasional temporary submersion at a limited depth; test-lab summaries of NEMA 250 describe the test as 30 minutes at a depth of 6 ft. Type 6P is built for prolonged submersion and adds corrosion protection. If an enclosure may end up under water, for example in a pit or a flood zone, Type 4X is not enough.

Why an IP code is not a NEMA type

IEC 60529 IP codes rate two things only: protection against solid objects and dust (first digit) and against water (second digit). NEMA types cover those too, and add tests that IEC 60529 does not have. In NEMA's words, the IEC rating "does not require a corrosion test; gasket aging test; dust test or external icing test", and NEMA 250 also tests for oil and coolants where a type calls for it. NEMA's conclusion:

• A NEMA type "meets or exceeds" a given IP rating, so the table above can be used to convert a NEMA type into a minimum IP code.
• The table "cannot be used to convert from IEC Classifications to enclosure Type numbers". An IP66 enclosure is not automatically a NEMA 4X enclosure, because it has not been through the corrosion, icing and gasket tests.
• In United States installations, the National Electrical Code is explicit: NEC 110.28 states that "IP ratings are not a substitute for Enclosure Type ratings."

Many enclosures carry both a NEMA type and an IP code, which is the easiest way to satisfy US and international specifications at once.

Who rates an enclosure: self-declared vs listed

NEMA is a standards organization, not a test lab. Its enclosure FAQ says NEMA "neither tests products nor certifies for listing" and that a manufacturer "can choose to self-certify that the product meets the enclosure requirements of NEMA 250 or to seek independent, third-party certification". Everyone may describe complying self-declared products as "NEMA 4", "NEMA 4X" and so on; the NEMA trademark itself is not a certification mark.

Third-party listing is done by certification bodies such as UL and CSA to the harmonized standard UL 50E / CSA C22.2 No. 94.2, which uses the same type numbers. Whether you need a listed enclosure is set by your specification, your customer or the authority having jurisdiction (usually the electrical inspector).

How to choose the type for your location

1. Indoors or outdoors? Outdoors rules out Types 1, 12 and 13.
2. Water: rain only points to 3R or 3; hose-directed water or washdown needs at least Type 4; possible submersion needs 6 or 6P.
3. Dust: windblown dust outdoors needs 3, 4 or 4X rather than 3R; indoor lint and fibers need at least 12.
4. Oil and coolant: seepage needs 12; spray needs 13.
5. Corrosion: salt air, de-icing salt, washdown chemicals, chlorides or process vapors call for an X type, usually 4X, and the right material (see 304 vs 316L stainless).
6. The spec and the inspector: the NEC lists which enclosure types suit which conditions in Table 110.28; the project specification may also require a listing.

Then keep the rating through installation. NEMA notes that a field-installed assembly's type rating "is always limited by the least severe Type rating of all the components involved". Every conduit hub, cable gland, pushbutton and display in the enclosure wall must be rated at least as high as the enclosure. NEMA also notes that many type-rated enclosures need mounting means outside the electrical cavity, which is why our wall-mount enclosures hang on four external wall-mount feet instead of screws through the back. The cutouts and glands guide covers the openings.

Frequently asked questions

Sources

1. NEMA, "NEMA Enclosure Types" (type definitions and Table A-1, NEMA to IEC 60529 conversion), November 2005
2. NEMA, "NEMA FAQs: Enclosures" (self-certification, UL 50E / CSA, salt spray, hose test parameters, NEC 110.28, weakest-link rule, external mounting)
3. NEMA Technical Services Bulletin No. 123, "NEMA and IP Ratings", March 2023 (Table A-1 of NEMA 250-2020; NEC Table 110.28)
4. ANSI/NEMA 250-2020, contents and scope (indoor and outdoor types)
5. ANSI webstore, ANSI/NEMA EN 10250 (the renumbered NEMA 250)
6. ANSI webstore, UL 50E, Enclosures for Electrical Equipment, Environmental Considerations (3rd ed., 2020)
7. Element, "Enclosure testing: IEC 60529 and NEMA 250" (Type 6 submersion test)