ON THE BUTTON A reference guide to environmental ratings used for push button enclosures A REFERENCE GUIDE TO KEY TOPICS IN PUSH BUTTON SELECTION AND SAFETY
CONTENTS I. INTRODUCTION............................... 2 II. ENCLOSURES............................... 2 IEC Enclosures..................................... 2 NEMA / UL Enclosures............................... 3 Enclosures intended for indoor use.................... 3 NEMA / UL Type 1.............................. 3 NEMA / UL Type 2.............................. 4 NEMA / UL Type 5............................. 4 NEMA / UL Type 11............................. 4 NEMA / UL Type 12............................ 4 NEMA / UL Type 12K........................... 4 NEMA / UL Type 13............................ 4 Enclosures intended for outdoor use................... 4 NEMA / UL Type 3R............................. 4 NEMA / UL Type 3............................. 4 NEMA / UL Type 3S............................. 4 Enclosures intended for indoor or outdoor use............ 4 NEMA / UL Type 4.............................. 4 NEMA / UL Type 4X............................. 5 NEMA / UL Type 6.............................. 5 NEMA / UL Type 6P............................. 5 NEMA / UL enclosure summary....................... 5 IEC and NEMA / UL Enclosures Compared................. 6 III. INDUSTRY STANDARDS & TEST REQUIREMENTS... 7 IEC Tests......................................... 7 NEMA / UL Tests.................................... 8 Water Ingress Tests Compared.......................... 9 IV. SUMMARY.................................. 9 V. CONCLUSION................................ 11
I. INTRODUCTION A push button s protection against environmental conditions depends on the following factors: sealing construction enclosure rating and construction method of installation. The International Electrotechnical Commission (IEC) and the National Electrical Manufacturers Association (NEMA) have developed independent rating systems to identify the ability of a device or system to offer protection from the external environment. Rating systems are used for enclosures and enclosures with push buttons installed. An operator installed into the enclosure is treated as a component of the enclosure, and therefore must carry the same rating as the enclosure. Underwriters Laboratories (UL) uses a rating system which is essentially the same as the NEMA system. These rating systems provide information that helps users make informed product choices. Users must be aware that differences exists between the systems. II. ENCLOSURES Push button selection depends upon the degree of environmental protection needed to meet the conditions in which the push button will operate. The push button enclosure is a key element of the environmental protection system. Enclosures must meet environmental ratings which are minimally the same as the component s environmental rating. Enclosure material and seals must be carefully selected to ensure the required degree of protection. To standardize enclosure performance, IEC and NEMA / UL rating systems are used to identify an enclosure s ability to repel the external environment. Resistance to ingress of liquids and solids is defined by these rating systems. Liquid ingress protection ranges from protection against dripping liquids to hosedown conditions to total submersion. Protection against ingress of solid objects covers a size range from very fine dust to objects 50mm (1.97 inches) in diameter. IEC Enclosures IEC Publication 529, Classification of Degrees of Protection Provided by Enclosures, describes a system for specifying push buttons based on the degree of protection they offer. The publication defines degrees of protection for: 2 personnel equipment within the enclosure ingress of water.
The degree of protection provided by an IEC push button is indicated by the letters IP followed by two Characteristic Numerals. The first numeral indicates the degree of protection provided by the push button against ingress of personnel and solid foreign objects. The second characteristic numeral indicates the degree of protection provided by the push button station against ingress of water. The following table lists the general degree of protection indicated by specific numerals. First Numeral Protection of personnel against access to hazardous parts and protection against penetration of solid foreign objects. 0 Non-protected 0 Non-protected 1 Back of hand: objects greater than 50mm in diameter 2 Finger: objects greater than 12.5mm in diameter 3 Tools or objects greater than 2.5mm in diameter 4 Tools or objects greater than 1.0mm in diameter Second Numeral Protection against damaging ingress of water under test conditions specified in IEC 529. 1 Vertically falling drops of water 2 Vertically falling drops of water with enclosure tilted 15 degrees 3 Spraying water 4 Splashing water 5 Dust protected 5 Water jets 6 Dust tight 6 Powerful water jets 7 Temporary submersion 8 Continuous submersion For example, based on the table above, the designation IP54 would describe an enclosure which is designed to provide a degree of protection against the entry of dust, and to protect against splashing water under specified test conditions. Many IEC rated industrial control push buttons are rated IP65 or IP66. NEMA / UL Enclosures NEMA Standard Publication 250, Enclosures for Electrical Equipment, establishes requirements which must be met for an enclosure to gain a specific Type designation. UL has adopted the NEMA Type designations and UL Publication 508, Standard for Industrial Control Equipment, sets similar requirements. For a complete description of the enclosures and the detailed test criteria, see the NEMA or UL publications referenced above. Enclosures intended for indoor use NEMA / UL Type 1 enclosures are commonly called general purpose or non-sealed enclosures. They provide a degree of protection against contact with the enclosed equipment in locations where the common service conditions exist. The enclosures are designed to 3
exclude the entrance of a rod greater than 1/2 inch in diameter. Enclosures are not required to prevent the entry of dust or liquids. The enclosure is rust resistant. NEMA / UL Type 2 enclosures meet the requirements of Type 1 enclosures, and in addition provide a degree of protection against limited amounts of falling water and dirt. NEMA / UL Type 5 enclosures meet the requirements of Type 1 enclosures, and in addition provide a degree of protection against dust and falling dirt. NEMA / UL Type 11 enclosures meet the requirements of Type 1 enclosures, and in addition provide a degree of protection against the entry and corrosive effects of liquids and gases. The enclosure is corrosion resistant, and provides greater corrosion protection than Type 1. NEMA / UL Type 12 enclosures meet the requirements of Type 1 and Type 2 enclosures, and use gaskets to provide a greater degree of protection against falling water and dirt than Type 2. NEMA / UL Type 12K enclosures are essentially the same as Type 12, but have knockouts in the top and/or bottom walls. They meet the same requirements as Type 12 enclosures. 4 NEMA / UL Type 13 enclosures are commonly called oil resistant. They are often used in metal cutting applications, where they are exposed to cutting fluids. They meet the requirements of Type 12 enclosures, and provide a degree of protection against oil and non-corrosive coolants. Note: Push buttons are intentionally operated during the Type 13 test cycle. Enclosures intended for outdoor use NEMA / UL Type 3R enclosures are similar to Type 1 enclosures in that they are designed to exclude the entrance of a rod greater than 1/2 inch in diameter, and are not required to prevent the entry of dust. Type 3R enclosures, however, provide a degree of protection against falling rain and are undamaged by the formation of ice on the enclosure. The enclosure is rust resistant. NEMA / UL Type 3 enclosures are commonly called rain resistant. They meet the requirements of Type 3R enclosures, and in addition they exclude dust and have a more stringent requirement against falling rain. NEMA / UL Type 3S enclosures meet the requirements of Type 3 enclosures. In addition, while ice laden, the mechanism must be operable manually without any damage to the enclosure. Enclosures intended for indoor or outdoor use NEMA / UL Type 4 enclosures are often used in applications where they may be subjected to streams of water from a pressurized hose.
They meet all the requirements of Type 3 enclosures, and in addition they exclude water under test conditions which are intended to simulate a hosedown condition. The enclosure material is rust resistant. NEMA / UL Type 4X enclosures are commonly called corrosion resistant. They are often used in food processing applications. They meet all the requirements of Type 4 enclosures. In addition, the enclosure material is resistant to corrosion from salt spray and damage from exposure to ultraviolet (UV) energy. NEMA / UL Type 6 are intended to provide a degree of protection against the entry of water during submersion at a limited depth. Per NEMA 250, page 3, they meet all the requirements of Type 4 enclosures, and in addition they protect against the entry of water when submerged to a depth of 1.83 meters (6 feet) for a period of 30 minutes. The enclosure material is rust resistant. NEMA / UL Type 6P enclosures are commonly called submersible. Per NEMA 250, page 3, they meet all the requirements of Type 6 enclosures, and have more stringent submersion requirements. They protect against the entry of water when submerged to a depth of 1.83 meters (6 feet) for a period of 24 hours. The enclosure material is corrosion resistant. NEMA / UL enclosure summary The table below provides a summary of the more commonly used enclosure types for use in non-hazardous locations. For a detailed description of the tests used to verify specific degrees of protection, refer to NEMA Standard Publication 250, Enclosures for Electrical Equipment or UL Publication 508. 5
NEMA / UL Type Indoor Use Outdoor Use Indoor or Outdoor Use For a degree of protection against: 1 12 13 3R 3 4 4X 6P 6 Incidental contact with enclosed equipment Falling dirt Rust Circulating dust, lint, fibers, and flyings Windblown dust Falling liquids and light splashing Rain (limited water allowed inside) Rain (no water allowed inside) Snow and sleet Hosedown and splashing water Occasional prolonged submersion Oil or coolant spraying or splashing Corrosive agents Occasional temporary submersion The table shows how protection capabilities of the common enclosure types build in an incremental manner. Note that Type 4 enclosures meet all requirements of Types 1, 12, 13, 3R, and 3. Even though an enclosure may meet the requirements of several type numbers, it is industry practice to list only the highest type rating on the enclosure. Many NEMA / UL rated industrial control push buttons are rated Type 4, 4X, or 13. IEC and NEMA / UL Enclosures Compared To help users of industrial control equipment select and apply enclosures, NEMA has prepared the table below (appearing in NEMA Publication 250) which attempts a translation of NEMA / UL Type ratings to the closest comparable IEC classification designation. The comparison is based on tests specified in IEC publication 529. NEMA Publication 250 makes the following statement regarding such a conversion: IEC 529 does not specify degrees of protection against mechanical damage of equipment, risk of explosion, or conditions such as moisture (produced for example by condensation), corrosive vapors, fungus or vermin. NEMA Standards Publication 250 does test for environmental conditions such as corrosion, rust, oil and coolants. Therefore, and because the tests and evaluations for other characteristics are not identical, the IEC Enclosure 6
Classification Designations cannot be exactly equated with NEMA Enclosure Type Numbers. III. INDUSTRY STANDARDS & TEST REQUIREMENTS Enclosures and push buttons designed to meet NEMA and UL requirements may not have been designed to meet similar IEC requirements. There is a marked difference in the environmental protection capabilities of each system. This is the result of each class of device being designed to meet different standards. As mentioned above, applicable standards used to determine environmental protection capabilities are contained in NEMA Publication 250, UL Publication 508, and IEC Publication 529. Those standards were the source for much of the information presented in this paper. For more detailed information concerning the tests which must be conducted before a NEMA / UL Type number or an IEC IP classification can be assigned to a product, refer to those standards. An enclosure with properly mounted push buttons comprise a system that provides a degree of environmental protection specified by a particular test. Following is a description of the standard tests that apply to push buttons most often used in industrial applications. In the discussions relating to tests, compliance requires that the push button mechanism seals, enclosure seals, and interface seals between the push buttons and the enclosures all meet the requirements of the particular test being discussed. IEC Tests Many IEC push buttons and enclosures used in industrial control applications have been designed to meet the requirements for protection against ingress from water jets. This degree of protection is indicated by the number 5 located in the second characteristic numeral position (for example, IP_5). The hosedown test specified subjects the test device to 3.3 gallons of water per minute, at a pressure of 4.35 PSI, for three minutes.* This test actually permits water to enter and accumulate in the enclosure provided that the level of water is not sufficient to interfere with the satisfactory operation of the equipment. The term not sufficient remains subject to interpretation. Another IEC classification often used for push buttons is IP_6. This classification s test requirements are similar to IP_5, except the water flow is about 26.4 gallons per minute under a pressure of about 14.5 PSI for three minutes. This test also allows water to enter the enclosure, provided that the amount of water is not sufficient to interfere with the satisfactory operation of the equipment. *The IP_5 test is actually specified in metric terms, and have been converted here for comparison purposes. 7
NEMA / UL Tests Many NEMA / UL push buttons and enclosures used in industrial control applications have been designed to meet the requirements of standards classification Type 4. This type of enclosure is commonly called water resistant. For a device to qualify as Type 4, it must pass a hosedown test. This test subjects the test device to a stream of water applied at the rate of 65 gallons per minute, under a pressure of 4.4 PSI for five minutes. At the end of the test, The device is inspected to confirm that no water leaked past the seals, and the inside of the enclosure remains dry. Underwriters Laboratories has certified ingress ratings for applications intended to be used in the United States. The test criteria used for those ratings are similar to the NEMA / UL ingress standards described above. Products rated as Type 4X must meet the same requirements as Type 4 products. In addition, Type 4X products can withstand prolonged exposure to salt water spray. This class of product is commonly called corrosion resistant. While a 4X rating is a good indication that an enclosure can resist corrosion, it does not provide information on how a particular corrosive agent will affect the enclosure material. A full analysis of the specific environment must be conducted to determine the most suitable enclosure material choice for a given application. Another widely used class of push buttons are those rated Type 13. This type of product is commonly called oil resistant. Type 13 products meet the requirements of an oil exclusion test. This test subjects the product to a stream of test liquid for 30 minutes delivered from a 3/8 inch diameter nozzle at a rate of two gallons per minute. A 0.1% solution of water and wetting agent is directed from all angles from 12 to 18 inches. Any externally operated device is operated at 30 operations per minute. The device is inspected to confirm that no liquid leaked past the seals and the inside of the enclosure remains dry. UL also examines the seals for evidence of swelling and hardening when in contact with ASTM #3 oil. 8
Variable Water Ingress Tests Compared The following table provides a comparison of the various water and oil ingress tests. NEMA / UL Type 4 NEMA / UL Type 13 Outlet diameter (inches) 1.0 0.375 0.24 0.49 Delivery rate (gallons/minute) 65 2.0 3.3 26.4 Pressure at outlet (PSI) 4.4 N/A 4.35 14.5 Test duration (minutes) 5 30 3 3 Distance from outlet 10 to 12 feet 12 to 18 inches Approx. 10 feet Approx. 10 feet Pass/fail criteria No water in enclosure No liquid in enclosure IP_5 Water may enter Test comparable to Fire hose Water fountain Garden hose without nozzle IP_6 Water may enter Garden hose with nozzle Device operated during test No Yes No No IV. SUMMARY While IEC and NEMA / UL ratings are intended to provide information to help users make safer, more informed product choices, there are important differences between environmental systems. There is no direct correlation between IEC and NEMA / UL ratings. NEMA Standards Publication 250 provides a limited conversion of NEMA Type ratings to IEC Classification designations. IEC water ingress tests permit liquid to enter the enclosure while the NEMA / UL test requires that the enclosure interior remains dry. There is no IEC test comparable to the NEMA / UL Type 13 oil resistant test. There is no IEC test comparable to the NEMA / UL Type 4X corrosion resistant test. An IEC push button installed in a NEMA / UL enclosure, or a NEMA / UL push button installed into an IEC enclosure, requires care to insure that a proper seal is obtained. The resulting environmental rating of such a system must be carefully considered. The rating of the system will be that of the lowest rated component. A user of push buttons should be aware of how compliance to applicable standards is certified. NEMA / UL products are tested by UL, which is an independent testing organization, to verify that devices meet the requirements of a specific standard. While UL tests to its own standards, they have essentially adopted NEMA Type designations and test requirements. Many IEC 9
products are self-certified by the manufacturer with no independent verification of test results. Recently, UL has begun verifying IP ratings of products. There is an important point to consider concerning the UL listing mark which appears on the nameplate of a product. The presence of a UL listing mark on the nameplate does not automatically mean that the product has been certified as meeting the requirements of a NEMA / UL enclosure type test. Many products have UL listing for their electrical ratings only, and are entitled to carry a UL listing mark on the nameplate. Devices tested by UL show the type number on the product near the UL mark. However, UL does not require that the product be marked. In many instances products are not marked with the type designation due to limited label space. An enclosure and mounted push buttons comprise a system which offers protection from the environment for the electrical components. To maximize enclosure ratings, push buttons must have an environmental rating at least the same as the enclosure plus be properly installed to preserve the integrity of the enclosure rating. Enclosure openings must be carefully created, enclosure surfaces must not be distorted, and the seals between enclosure and push button must be correctly positioned. The table below is based on information from UL Standard 508, and lists equipment that may be mounted in specific NEMA / UL Type enclosures without compromising the enclosure rating. NEMA / UL Enclosure Type Number Openings May be Closed by Equipment Marked 2 2,3,3R, 4, 4X, 6, 6P, 12, 13 3 3, 4, 4X, 6, 6P 3R 3, 3R, 4, 4X, 6, 6P 4 4, 4X, 6, 6P 4X 4X 6 6, 6P 6P 6P 12 12, 13 13 13 Another point to consider when dealing with environmental ratings is that test durations are very limited: 5 minutes for NEMA / UL Type 4, 30 minutes for NEMA / UL Type 13, and 3 minutes for IEC IP_5 and IP_6 ratings. Even through a push button passes a specific test, it may not indicate how well the device will perform over an extended period. There are no standard tests for long term enclosure integrity. To help determine how well 10
a push button performs in an environment over time, the details of its physical construction should be considered. V. CONCLUSION Careful consideration must be given to the environment to which a push button will be exposed when placed into service. If a push button is to meet the service expectations of the user, it must be protected from physical and environmental conditions which may be detrimental. A push button must be mounted in a panel or within an enclosure in order to be a usable product. The panel or enclosure along with the push button becomes a system which provides a degree of protection against the environment. To attain expected service life of a push button or other control device, the user should take the following steps: 1. Determine the severity of the environment to which the push button will be exposed. 2. Determine the proper IEC IP designation or NEMA / UL Type rating which will provide the required degree of protection for that environment. 3. Select push buttons and an enclosure that meet or exceed the required degree of protection for that environment. Do not select push buttons with translated IP or NEMA / UL Type ratings. 4. Make sure push buttons and other components are properly installed so individual device environmental ratings are not compromised. 5. Mount the enclosure so its environmental rating is not jeopardized. The standards documents which will provide information to help with this process include: IEC Publication 529, Classification of Degrees of Protection Provided by Enclosures NEMA Standard Publication 250, Enclosures for Electrical Equipment UL Publication 508, Standard for Industrial Control Equipment. A knowledgeable supplier of industrial control equipment that offers a wide variety of industrial control products can provide valuable assistance in the selection of properly rated products for specific applications. 11