Electronics Protection - November/December 2013 - (Page 12)

Feature Understanding NEMA Ratings for Electrical Enclosures Joe Wilson, Appleton Electric NEMA ratings can be a source of confusion. All too often enclosures are specified with the wrong NEMA rating, which can mean wasted money if the chosen rating is too high, or premature failure and the potential for safety incidents if the rating is too low. Here's a quick overview of NEMA ratings. What is NEMA? The National Electrical Manufacturers Association (NEMA) publishes more than 600 standards, application guides and technical papers on a wide range of topics related to electrical product function and safety, helping US manufacturers ensure the compatibility, proper function and safety of their products. One familiar example is the system of NEMA ratings for plugs used in North America to accommodate different voltage and amperage ranges. What are NEMA Ratings? Despite the broad mission of the NEMA organization, the term "NEMA ratings" is used colloquially to refer to a very specific standard for electrical enclosures. NEMA standard ICS 6 categorizes enclosure types according to their ability to protect against ingress or damage due to liquids, dust and corrosive chemicals. NEMA publishes a new review of these standards every five years, and the 2013 draft is currently in progress. These generally involve improvements in testing standards that manufacturers need to know about, but they typically do not affect what the ratings mean in terms of specifying equipment for particular applications. How are Enclosures Certified Under the NEMA Rating System? NEMA does not test products and is not affiliated with UL or any other testing laboratories. Instead, NEMA defines and publishes enclosure standards, and manufacturers' compliance with those standards is voluntary. Manufacturers can self-declare their compliance, although some manufacturers, do use thirdparty testing and certification to provide their customers with objective assurance that the products they buy will perform as expected. NEMA does provide a list of testing laboratories and certification bodies that perform this service as well. Where is Complete Information on NEMA Ratings Available? An overview of NEMA enclosure type definitions is available for free, and complete descriptions, applications, features and test criteria are available for purchase. When the 2013 revisions are completed, updated documents will be available on the NEMA website. The following summary provides the information needed to choose the enclosure type for an application. It is also recommended to check with the authority having jurisdiction for each installation. Non-Hazardous Location NEMA Enclosure Types * Type 1: General purpose. Indoor use. Provides a degree of protection against human contact with electrically-charged, live parts and against ingress of solid foreign objects. * Type 2: Drip-proof. Indoor use. Same protection as Type 1 but adds protection against dripping and light splashing of water. * Types 3R, 3RX: Rain-tight, sleet-resistant. Indoor or outdoor use. Same protection as Type 1, but adds a degree of protection against ingress of falling dirt, rain, sleet and snow; also protects against damage due to external ice formation. Rust-resistant. The "X" designation indicates corrosion-resistance. 12 * Types 3/3X: Dust-tight, rain-tight, sleet-tight. Indoor or outdoor use. Same protection as Type 3R but adds protection against windblown dust. The "X" designation indicates corrosion resistance. * Types 3S/3SX: Dust-tight, rain-tight, sleet-tight. Indoor or outdoor use. Same protection as Type 3 but includes external mechanisms that remain operable when ice-laden. The "X" designation indicates corrosion-resistance. * Types 4/4X: Water-tight, dust-tight, sleet-resistant. Indoor or outdoor use. Same protection as Type 3 with added protection against splashing and hosedirected water. The "X" designation indicates corrosion-resistance. * Type 5: Dust-tight, indoor use. Same protection as Type 2 but adds gaskets to prevent ingress of dust, lint and fibers. * Types 6/6P: Submersible. Indoor or outdoor use. Same protection as Type 4, but adds protection against temporary submersion (Type 6) or prolonged submersion (Type 6P) at limited depth. * Types 12, 12K: General purpose. Indoor use. Protects against falling dirt and circulating dust, lint, fibers and flyings. Protects against ingress of dripping and splashing water. Rust-resistant Type 12 enclosures do not include knockouts; Type 12K enclosures do include knockouts. * Type 13: General purpose. Indoor use. Same protection as * Type 12, but adds protection against ingress of spraying, splashing or seeping oil and noncorrosive coolants. Hazardous Location NEMA Enclosure Types Note that all equipment designed for use in hazardous locations must be certified by a nationally recognized testing laboratory, such as UL. In addition to the NEMA type, look for the appropriate hazardous location equipment markings. * Type 7: Explosion-proof, indoor use. Class I, Division 1 hazardous locations, Groups A, B, C and D. * Type 8: Explosion-proof. Indoor or outdoor use. Class I, Division 1 hazardous locations, Groups A, B, C and D. * Type 9: Dust ignitionproof. Indoor use. Class II, Division 1 hazardous locations, Groups E, F and G. * Type 10: MSHA. Meets the requirements of the Mine Safety and Health Administration, 30 CFR Part 18. NEMA Ratings and IP Codes The IEC system provides IP codes that specify the ingress protection afforded by electrical enclosures. IP codes are two-digit numbers, with the first digit representing the degree of protection against entry of solid objects (fingers, dust, etc.) and the second digit representing protection against ingress of water. The relationship between NEMA ratings and IP codes can be confusing. Although it is possible to determine the equivalent IP code based on the NEMA rating, the reverse is not true. This is because NEMA ratings often go beyond describing protection against ingress of water to include other factors - for example, resistance to ice, rust, corrosion or oil. For more information visit www.appletonelec.com. November/December 2013 www.ElectronicsProtectionMagazine.com http://www.appletonelec.com http://www.ElectronicsProtectionMagazine.com

Table of Contents for the Digital Edition of Electronics Protection - November/December 2013

New Features Make F-Series TeraFrame Gen 3 One of CPI’s Most Advanced Cabinets
Silicones for High Reliability and Yield in Electronic Applications
Surge and Transient Protection for Telephone, CATV & Satellite Services
Thermal Management of LEDs: Looking Beyond Thermal Conductivity Values
Understanding NEMA Ratings for Electrical Enclosures
Silent Air Cooling: A New Approach to Thermal Management
VadaTech Releases Rugged Conduction-Cooled MicroTCA Ecosystem
Directable Inverted Blowers Deliver High Volume Air Flow
Cima NanoTech Launches Ultra Low Resistance Sante EMI Shielding Film
Littelfuse Introduces Surge-Tolerant Fuses
ProTek Devices’ TVS Array Provides Circuit Protection in Computing Applications
Reell’s PolyTorq Technology Expands Capabilities For Hinge and Torque Insert Applications
Industry News

Electronics Protection - November/December 2013