NEMA & UL Ratings for Enclosures

NEMA Standards rate different grades of electrical enclosures based on the level of protection in various environments. Natural elements like wind, dust and water are included in the criteria, along with chemicals, coolants, oil, and corrosive elements like gasoline.

There are more than 13 total NEMA ratings for industrial applications in the United States, ranging from general-purpose ratings for light dust indoors, like NEMA 1 to Hazardous materials covered in NEMA 7-9. Official NEMA Standards Website

American Fittings and NEMA Ratings


NEMA Standards Publication FB 1-2014
Fittings, Cast Metal Boxes, and Conduit Bodies
for Conduit, Electrical Metallic Tubing, and Cable

This Standards Publication covers fittings that are a part of electrical raceway systems designed for use as intended by the requirements of the National Electrical Code® (NEC), NFPA 70. Specifically, this standard covers fittings for use with non-flexible tubular raceways: Rigid and Intermediate Metal Conduit and Electrical Metallic Tubing. Also included are fittings for use with flexible conduit and cable raceways, including Flexible Metal Conduit and liquidtight flexible conduits, Armored Cable, Metal Clad Cable, Tray Cable, Mineral Insulated Cable, Flexible Cord, Nonmetallic Sheathed Cable, and Service Entrance Cable.

This standard also includes cast metal outlet boxes and covers, as well as conduit bodies and covers, which when designed for the purpose, serve as a box intended to house conductor splices and/or wiring devices; and cast metal junction boxes, pull boxes, and covers.

This standard does not include standard conduit couplings of the type provided with lengths of Rigid and Intermediate Metal Conduit, or threaded conduit nipples, or threaded or unthreaded factory-made bends derived from Rigid and Intermediate Metal Conduit or Electrical Metallic Tubing.

This standard does not apply to fittings, boxes, or enclosures that are for use in Class I, Division 1; Class II, Division 1; Class III, Division 1; Class I, Zones 0, 1, 2; Zones 20, 21, or 22 hazardous (classified) locations. Exceptions are those ordinary (unclassified) location fittings and enclosures that are specifically permitted by the NEC in these locations.


NEMA (National Electrical Manufacturers Association) standards provide guidelines on the design and manufacture of enclosures used for electrical equipment. These standards primarily deal with the protection that the enclosure provides against certain environmental conditions. When it comes to electrical enclosures and fittings in the US, particularly as referenced in the NEC (National Electrical Code), NEMA 4 and NEMA 4X are two common designations that indicate a specific level of protection. Here’s a summary of the differences between the two:

NEMA 4 – Watertight and Dust-Tight Enclosures:

  • Designed primarily for indoor or outdoor use.
  • Provides a degree of protection to the equipment inside the enclosure against the ingress of solid foreign objects (windblown dust).
  • Protects against water (rain, sleet, snow, splashing water, and hose-directed water).
  • Provides protection for equipment against the harmful effects of ice formation on the exterior of the enclosure due to freezing.

NEMA 4X – Watertight, Dust-Tight, and Corrosion-Resistant Enclosures:

  • Offers all the protections of NEMA 4.
  • Additionally, it provides an extra layer of protection against corrosion, making it suitable for environments where corrosion is a concern, such as in certain industrial settings or coastal areas.
  • Typically made from materials like stainless steel or non-metallic polymers which resist corrosion.

In summary, while both NEMA 4 and 4X provide protection against dust, water ingress, and the external formation of ice, NEMA 4X adds an extra layer of protection against corrosion. When selecting fittings and enclosures, it’s crucial to consider the environment in which they will be used. If corrosion from chemicals or salty air is a potential concern, NEMA 4X might be the better choice.

Always consult the NEC and local codes when making these decisions to ensure safety and compliance.


View  Chart Showing NEMA vs UL Enclosure Criteria  

In the US, the two main organizations that set electrical safety standards for electrical enclosures are NEMA (National Electrical Manufacturers Association) and UL (Underwriters Laboratories). Although the standards for each enclosure type are independent from each other, the protection expectations are mostly the same. UL ratings are often described in more technical language, but after reviewing the summarized protections in the “NEMA and UL Ratings Equivalency Chart” below, you’ll quickly see that the enclosure protection expectations are almost identical.

So what’s the main difference between NEMA and UL ratings?

Besides the specific language used to define each enclosure rating, the main difference lies in the testing requirements.

UL Testing Requirements:

To receive a UL certification mark, the manufacturer must send samples of the enclosure to a third-party qualified evaluator to determine if it’s compliant. Afterward, the third-party evaluator will continue to do periodic audits of the manufacturing specifications and the enclosure materials.

NEMA Testing Requirements:

NEMA does not require third-party testing to verify the NEMA rating. The manufacturer alone can determine if the enclosure is in compliance.