Comparing enclosure standards
As a way of standardizing enclosure performance, organizations like NEMA (National Electrical Manufacturers Association), UL (Underwriters Laboratories), CSA (Canadian Standards Association), IEC (International Electrotechnical Commission), VDE (Institute of German Electronics Engineers), and TÜV Rheinland of North America use rating systems to identify an enclosure's ability to resist external environmental influences. Resistance to everything from dripping liquid, to hose-down, to total submersion is defined by the rating systems. These ratings are intended to provide more informed choices and ultimately a safer work area. However, there are differences among them.
In North America NEMA, UL, and CSA are the commonly recognized organizations. Their ratings are based on similar application descriptions and expected performance. UL and CSA both require enclosure testing by qualified evaluator labs. They also send site inspectors to ensure manufacturers adhere to prescribed methods and material specifications. NEMA does not require independent testing and leaves compliance up to the manufacturer.
North American enclosure rating systems also include a 4X rating that indicates resistance to corrosion. This rating is based on the enclosure's ability to withstand prolonged exposure to saltwater spray.
A 4X rating is a good indicator that an enclosure can resist corrosion; it does not provide information on how a specific corrosive agent will affect a given enclosure material. It is best to analyze the specific application and environment to determine the best enclosure choice.
In Europe, IEC ratings are based on performance criteria similar to NEMA, with different interpretations of enclosure performance. For example, UL and CSA test requirements specify failure of the watertight test if a single drop of water enters the enclosure. IEC's standards for each ingress protection (IP) level specifies the amount of water allowed entering the enclosure.
IEC does not specify degrees of protection against risk of explosions or conditions such as moisture or corrosive vapors; NEMA does. Because of this reason and because tests and evaluations for other characteristics are not identical, IEC enclosure classification designations cannot be exactly equated with NEMA enclosure type numbers.
IEC uses IP ratings to define the degree of protection provided by an enclosure using a two-digit numerical classification. The first number defines the degree of protection against solid objects; and the second number defines the degree of protection against water.
To promote free trade movement to and from the European Union (EU), directives are being harmonized for health, safety, environment, and consumer protection using the CE (Conformite Europeenne) Mark.
For industrial control systems, the CE Mark appears only on enclosures containing all active control system components. Responsibility of ensuring compliance to applicable EU directives and harmonized standards belongs with the final equipment manufacturer.
This information was obtained from Hoffman (Anoka, Minn.) and Rittal (Springfield, O.). Most enclosure manufacturer catalogs and/or web sites explain enclosure related standards.
NEMA, UL, & CSA type rating
Approximate IEC/IP classification
Abbreviated protection description
Indoor protection from contact with contents.
Indoor with limited protection from dirt & water.
Outdoor with some protection from rain, sleet, windblown dust, and ice damage.
Outdoor with some protection from rain, sleet, and ice damage.
Indoor and outdoor with some protection from windblown dust, rain, splashing water, hose-directed water, and ice damage.
Indoor and outdoor with some protection from corrosion, windblown dust, rain, splashing water, hose-directed water, and ice damage.
Indoor and outdoor with protection from hose-directed water, entry of water during submersion at limited depth, ice damage.
Indoor with protection from dust, falling dirt, and dripping non-corrosive liquids.
Indoor with protection against dust, spraying water, oil, and non-corrosive liquids.
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