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NEMA vs UL and CSA - Enclosure Ratings Defined

Hammond Manufacturing 3/28/2013

Enclosure Ratings DefinedEnclosures and Cabinets, used to house electronic equipment, are often listed with NEMA, UL and/or CSA ratings. But what do they really mean and what is the difference? If you purchased an enclosure or cabinet that was advertised as being dust-tight but does not indicate a rating inside the enclosure, should you be concerned?

In a recent interview with the Team Lead of Enclosure Product Development at Hammond Manufacturing; Kevin Hawker explained that while Hammond chooses to offer NEMA, UL and CSA rated products there is a major difference between the two. “NEMA, UL and CSA ratings are based on similar application descriptions and follow similar guidelines. The key difference between the three ratings is that NEMA does not require third-party testing and leaves compliance completely up to the manufacturer.”

To explore the difference in more detail, we compare application descriptions for NEMA and Type 12, a common rating used in industrial indoor environments.

-National Electrical Manufacturers’ Association (NEMA): Enclosures constructed (without knockouts) for indoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment, to provide a degree of protection against falling dirt, against circulating dust, lint and fiber flyings, and against dripping and light splashing of liquids. 

-Underwriters’ Laboratories Inc. (UL): Indoor use primarily to provide a degree of protection against circulating dust, falling dirt, and dripping non-corrosive liquids.

-Canadian Standards Association (CSA): An enclosure for indoor use, constructed so as to provide a degree of protection against circulating and settling dust and lint, fibre flyings; dripping and light splashing of non-corrosive liquids; not provided with knockouts. 

While many manufacturers simply apply a gasket to their enclosure and label it as NEMA 12, the UL test is a bit more complicated.

To achieve a UL/CSA Type 12 Rating, the enclosure must undergo a rigorous testing:

-The enclosure shall be placed in its intended mounting position in an airtight chamber having an internal volume not less than 0.169 m3 (6 cubic feet). The volume of the chamber shall be not be less than 150 percent of the volume of the enclosure under test (L x W x H). The test chamber shall be maintained at ambient room temperature and 20 - 50 percent relative humidity.

-?At least 1.5 kilograms (1.5 ounce per cubic foot) of dry Type 1 general-purpose Portland cement per cubic meter of test chamber shall be circulated by means of a blower suction unit for 5 minutes so as to completely envelop the enclosure under test. The air velocity at the outlet of the blower shall be maintained at approximately 305 meters per minute (1000 feet per minute).
  
-The enclosure shall be subjected to a spray of atomized water using a nozzle that produces a round pattern 75 - 100 mm in diameter when measured 300 mm from the nozzle (3 - 4 inches in diameter when measured 12 inches from the nozzle). The air pressure shall be 200 kPa (30 psi). Not less than 4.8 mL/linear cm (5 ounce per-linear foot) shall be applied at a rate of 11.4 L/h (3 gallons Per hour). The nozzle shall be held 300 - 380 mm (12 - 15 inches) from the enclosure and the spray of water shall be directed once at all points of potential dust entry such as seams, joints, and. External operating mechanisms. A conduit -may be installed to equalizer the internal and external pressures, but shall not serve as a drain. The test specimen shall have at least one seam representative of each of the types of seams of the enclosure(s). A seam is the junction of, or the joint between, two pieces. When two covers or doors are adjacent, their common edges shall be considered a single seam.

If at the conclusion of the tests no dust or water has entered the enclosure it shall be considered to have met the requirements. In addition to enclosures passing the above tests, the manufacturer test is scrutinized by UL/CSA inspectors to ensure compliance. UL also inspects enclosure manufacturing facilities as well as field sites to ensure adherence to the prescribed guidelines. 

Headquartered in Guelph, Ontario, Canada; Hammond Manufacturing is a leading manufacturer of enclosures and cabinets and has over 2000 UL and CSA rated enclosures.