What's in a rating?

As a way of standardizing environmental performance, organizations like NEMA, UL, CSA, and IEC use rating systems to identify a device's ability to repel the outside environment. Resistance to everything from dripping liquid to hose-down to total submersion is defined by the ratings systems.

While these ratings are all intended to provide information to help you make a safer, more informed product choice, there are differences between them. NEMA, UL, and CSA are the organizations most commonly reffered to in North America. Their ratings are based on similar application descriptions and expected performance. UL and CSA both require testing by qualified evaluators in their labs. They also send site inspectors to make sure a manufacturer adheres to prescribed manufacturing methods and material specifications. NEMA, on the other hand, does not require independent testing and leaves compliance completely to the manufacturer.

In Europe, IEC ratings are based on test methods that are similar to UL and CSA. Nevertheless, there are differences in how performance is interpreted. For example, UL and CSA test requirements specify that even a single drop of water entering an enclosure is considered a test failure. In the IEC standards for each protection level (IP) a certain amount of water is allowed to enter the enclosure.

North American rating systems also include a 4X rating that indicates resistance to corrosion. This rating is based on the device's ability to withstand prolonged exposure to salt water spray.

While a 4X rating is a good indicator that a device can resist corrosion, it does not provide information on how a specific corrosive agent will affect a given material. It is best to conduct a full analysis of the specific application and environment to determine the best device choice.

CSA (Canadian Standards Association) is a non-profit, non-governmental association established as a national standardization body for Canada. Included in its scope of activities is the responsibility of investigating and approving products and materials in the interest of safety.

NEMA (National Electrical Manufacturer's Association) prepares standards which define a product, process or procedure with reference to one or more of the following: nomenclature, composition, construction, dimensions, tolerances, safety, operating characteristics, performance, quality, electrical rating, testing, and the service for which designed. The reference standards herein reflect the latest data in the NEMA Standards Publication #250 - 1985.

IEC (International Electrotechnical Commission) is the European equivalent to the above.

The formal decisions or agreements of the IEC on technical matters, prepared by Technical Committees on which all the National Committees having a special interest therein are represented, express, as nearly as possible, an international consensus of opinion on the subjects dealt with.

They have the form of recommendations for international use and they are accepted by the National Committees in that sense.

In order to promote international unification, the IEC expresses the wish that all National Committees should adopt text of the IEC recommendation for their national rules in so far as national conmditions will permit. Any divergence between the IEC recommendation and the corresponding national rules should, as far as possible, be clearly indicated in the latter.

The IEC has not laid down any procedure concerning marking as an indication of approval and has no responsibility when an item of equipment is declared to comply with one of its recommendations.