T&EIssue16 - Washington Laboratories, Ltd.
Contents
1. prevent hazardous voltages from being accessible to the user during a fault or large currents being drawn by the equip ment Fusing and circuit protection are determined during the design phase as well as during fault testing where shorts and or overloads will be imposed to ensure that hazards can not be created Guarding Barriers or covers over hazardous parts can be used to reduce risk Such guards can prevent access to high voltages energy levels and mechan ical hazards The standards generally identify the requirements for guards such as e a tool must be required to remove the guard e sizes of openings do not allow access and e the guard must be attached in some way so that it can not be completely removed and misplaced Interlocks Interlocks operate to remove hazards prior to access Interlocks dis able electrical sources and or mechanical hazards Means for interlocking must be reliable often the switch or device must be cycle tested The interlock should consist of electro mechanical components only and should not rely on logic circuits or semiconductors An analysis should show that a single fault can not render the interlock circuit inoperable Should it fail it must fail in the safe mode i e hazard locked out Other general considerations include e all hazards must be removed before the cover can be opened the interlock switch cannot be defeated by hand or without a tool e the door or cover2. are subject to corrosion due to galvanic action or differences in electro potentials EMI FILTER MECHANICALLY SECURED GROUND GREEN YELLOW WIRE requirements A question that often aris es is What is the ratio of green to yel low Some but not all standards answer this 30 of one color and 70 of the other Further it is recommended and specified in some standards that green OR yellow is not used where there is a possibility of confusion no this does not apply to multi conductor signal or other cables the intent is to reduce confusion with the AC supply wiring J P SOLDER C GROUND WIRES f CHASSIS CHASSIS CONNECTION TO OTHER GROUNDS SAME GAUGE AS OR BIGGER THAN SUPPLY Terminal Markings Mark the terminals for the supply connections with L and N for single phase systems and with L1 L2 L3 for the US or with U V W for Europe in three phase equipment PE is generally identified by the symbol and or by the letters PE Other terminals should be identified in the product and should correlate with the documentation for use and service Alpha numeric designations are usually acceptable Wire Colors and Markings In the United States black and white are generally used to identify Line and Neutral respectively Brown and blue are the preferred colors in Europe for Line and Neutral respectively Wire colors will be corre
3. cannot be closed with the switch defeated Enclosures serve to prevent access to hazards as well as to contain fire The standards outline a variety of require ments for example UL1950 EN60950 Information Technology Equipment specifies limits for sizes and location of openings plus the flammability ratings and thickness requirements for materials Mechanical Strength Enclosures intend ed to prevent access to hazards must be strong enough to withstand anticipated environmental conditions Hand held products should not break open when dropped and other equipment should not create hazards if tipped over Further the enclosure must not bend or bow and reduce spacings or cause short circuits Various tests are employed to evaluate the strength of enclosures among them steady forces and impacts are applied and drop tests are per continued on page 4 i TOO S continued trom pave 3 formed Following such tests the prod uct must remain safe in accordance with the standard Flammability Plastic or other non metallic parts must not present a fire hazard Most often UL 94 ratings are acceptable for determining compliance with this requirement Generally parts with enough material to support and sustain a fire must not be flammable PC boards may also have to be adequately rated many boards are 94V 0 which meet most if not all requirements The required ratings are based on size weight or mounting of the eq
4. inlets or plugs sockets provide distinct advantages over fixed cords appliance inlets are available with integral fuse holders and means for volt age selection and they can have built in EMC filters Inlets and plugs sockets allow easy changeover to cord sets for different countries Any inlets plugs and sockets must bear approvals for the countries of intended use and must be rated for the particular application continued on page 2 i TOO S continues trom pase 1 Sizing the Wires Phase Connections Terminals and or connections for Line and Neutral must be adequately sized often dictated by the standard and must provide adequate protection against loosening Methods for provid ing such protection often referred to as double securement include double crimp terminals shrink sleeving cable ties lock washers looping and hooking soldered connections etc The goal is to prevent a loose conductor from shorting against other parts or circuits Protective Earthing grounding for electrical safety Earthing or bonding often abbreviated PE for Protective Earth offers a level of protection by providing a path for fault currents which by design will blow a fuse or trip a circuit breaker Some equipment may include a Residual Current Device RCD for Europe or a Ground Fault Circuit Interrupter GFCI for the US These devices detect fault currents and open the circuit as a fuse or circuit breaker
5. to provide the separation between circuits The standard will identify the ways in which the separa tion may be provided as well as specific requirements for each method L PRIMARY SELV N DOUBLE OR REINFORCED INSULATION Working Voltage One of the considera tions for determining spacing require ments is Working Voltage That is the maximum voltage that the relevant insulation will be subjected to The voltage is measured between any two points in the circuit including voltages to ground It is recommended that the derived Working Voltage should never be less than the supply voltage in a primary circuit regardless of the circuit configuration or the measured values Further periodic spikes that exceed the nominal value e g switching spikes are considered but transient over voltages are not Installation Category Another factor that may be used to determine spacings is Installation Category Where is the product installed in relation to the power source Is it before or after the branch circuit protection Is it connect ed to a low voltage power supply There are four Installation Categories that cover most products Of these four the vast majority of products fall under two Category II is for equipment that is powered by 100 240V after the branch circuit protection and Category III covers low voltage products such as keyboards mice etc For example in a notebo
6. you may be encountering with current R amp D designs Se a EMC and Military Standards Workshop Hands On Safety Compliance Join us at our lab in Frederick for hands on practical workshops to assist you with Product Safety Compliance You ll not only hear and learn about the design tips and information to help you with new product design to ensure safety but you ll roll up your sleeves and work with practical demonstrations and test simulations all geared to provide you with a 3 D picture of designing for compliance L Since the inception of MIL STD 461 the evolution of EMC technology has rapidly increased At the Washington Labs November workshop on EMC and Military Standards speakers included Steve Ferguson Washington Labs VP of Operations left photo Steve led the discussion on MIL STD 461E which covers the requirements for electronic equipment to be sold to the Department of Defense During the workshop practical session right photo attendees participated in test technique demos on EMC design methods for making radiated and conducted meaurements conducted and radiated susceptbility and EMP requirements For more information on our 2002 workshops see the article above or give Patty or Ann a call to register at 800 839 1649 Washington Laboratories Approved As UL Certificated Agency Washington Laboratories recently received notification from Underwriters Laboratories UL that the lab has
7. 1 417 0220 800 839 1649 Fax 301 417 9069 Washington Laboratories Ltd 7560 Lindbergh Drive Gaithersburg MD 20879 Presort Standard U S Postage PAID Permit No 110 Frederick MD 21701
8. IgE Issue 16 Update Testing Engineering Consulting Tools of the Trade Safety Design for Harmonized Compliance INTRODUCTION There are literally thousands of safety standards in use around the world The good news is that harmonization allows the manufacturer to design a single product that complies with the require ments of numerous markets The intent of this Tools of the Trade installment is to provide criteria that will assist designers working with the more common products on the market Computers Medical Devices Machinery Household Appliances and Home Entertainment Equipment While this guide provides general and some times more detailed information the reader is advised to refer to the standard that is applicable to his her product for specific requirements WHAT ARE HAZARDS Many of us think of hazards as harmful to people Hazards to the environment animals and sometimes damage to the work in process are also considered The following are generally considered when evaluating the hazards associated with equipment Conditions of normal use service and single faults or abnor mal operation are reviewed as well Energy The common PC power supply is very happy sourcing 25 amps or more at 5V Even though the voltage will not hurt anyone there is enough current available to melt insulation or start a fire under certain conditions Current limiting is provided to reduce the risk of th
9. area of Bellcore Testing and related NRTL approvals Safety Link safetylink com Website dedicated to Worldwide Regulatory Compliance Syvax Design syvaxdesign com Electronic product and systems develop ers specializing in state of the art digital design Technology International Inc techintl com Competent and Notified Body for the European Union Equipment Reliability Institute equipment reliability com Specialized technical training aimed at increasing the reliability of equipment Example Vibration and Shock Training Regulatory Compliance Information Center rcic com RCIC is designated to provide the updated compliance information to the compliance industry The Reliability Center Inc reliability com Reliability Consulting Services Training Programs and Software Tools for Business Government amp Industry The Northeast Product Safety Society Inc nepss org Technical Presentations on EMC Immunity Principles of IEC61010 1 North American Telecom Standards Hazard Analysis Demonstrations in Inductance International Product Safety Conformity in China Product Safety Labeling GR 63 Central Office Equipment Restricted Substances CE Marking Process Understanding IEC60950 Hazardous Locations Telecom Regulatory Update International Approvals Machinery Directive Laser Safety and lots more to be announced e mail info wll com web www wll com Washington Laboratories Ltd Phone 30
10. been approved under the UL Engineering CAP Asa UL Certificated Engineering Agency WLL can now perform UL test ing without engineer witnessing from a UL representative They are currently approved for testing to UL60950 and UL1950 and additional standards will be added to the approval designation over time Previously UL had to witness every test This means WLL will have greater freedom in scheduling their clients and not be held to witnessing timing This is great news as it will greatly improve our level of service to our clients No longer will we require UL in order to schedule and begin testing of products requiring compliance with domestic safety standards The process will improve our turn around time and limit redundant testing said Mike Violette President of Washington Laboratories WLL will be able to retest any failures without UL having to return for a sec ond visit therefore non compliance issues can also be resolved before any data is forwarded to UL Additionally UL and travel fees will decrease Per WLL Safety Manager Berri Remenick WLL is now certified to perform testing under the CAP program at both the Gaithersburg and Frederick lab facilities The time to market for our customers should greatly improve because of this new certification and streamlined process The process WLL sends project request and proposed test plan to UL UL approves test plan and provides cost lim
11. ct in a cord which bears approvals for the intended market Protective Earth is usually green US or green yellow International however green yellow can generally be used so that one model will meet most market Some standards recommend specific col ors for wires in other circuits but there are few actual requirements beside the above Do note that the customer may demand wire color standards to provide consistency for service personnel or for other site standards The machinery standard mandates that all wires must be marked or identified in the product and the service documentation Other agencies require replaceable cables to be identified as well ISOLATION FOR ELECTRICAL PROTECTION Separation of Circuits One of the fundamental means of preventing hazards is to minimize the possibility of hazardous circuits coming in contact with other parts or circuits which in turn may be accessible to the user of the equipment The means may consist of Creepage Distance i e distance between two parts over a surface or Clearance distance through air continued on page 3 TOOIS continues trom pave 2 Creepage and Clearance are also known as spacings Spacings are measured by the shortest distance between bare con ductive parts Mounting hardware used to install PC boards metal screws and standoffs can reduce the spacings below acceptable values Insulation may be used either alone or in conjunction with spacings
12. for some product categories such as household goods must always be translated while others like those for machinery labora tory equipment or medical products may remain in English Service Instruc tions should include all information required to maintain the equipment replacement parts should be identified and any other special considerations should be explained Presented here are merely fundamental issues affecting a product s compliance with various safety standards The read er is urged to procure the standard s appropriate for his or her equipment Remember too that there may be more than one applicable standard quite often the primary standard will list a number of others for components or other aspects of the equipment and declaring or certifying compliance with the base standard implies compliance with all It is also feasible to create one product model that meets the requirements for a number of markets Of course labeling and language will change but the basic construction of the equipment may not have to just apply the more stringent requirements and look for ways to meet the intent of all standards Remember that the standards generally tell you what to do but not how to do it so with a little effort your design can be deemed to comply with all standards relevant to your product In addition to an evaluation of a product s physical characteristics a number of tests are performed among t
13. hem Dielectric Strength Humidity Preconditioning Insulation Resistance Enclosure Strength Leakage Current Sound Level Ground Impedance Heating Faults Abnormals And others as specified in the relevant standard You can reach us at WASHINGTON LABORATORIES LTD 7560 Lindbergh Drive Gaithersburg MD 20879 301 417 0220 800 839 1649 Fax 301 417 9069 e mail info wll com web www will com 2002 Testing Workshop Series GAITHERSBURG LAB FEBRUARY 15 MAY 17 AUGUST 16 NOVEMBER 8 FREDERICK LAB MARCH 15 JUNE 7 OCTOBER 18 Norman Violette will be the featured speaker at our Feb 15 workshop with his popular discussion on The Principles of Design for EMC Washington Labs has announced its Free Workshop Schedule for 2002 These popular seminar practical workshops will include demonstrations guest speakers the latest EMC and Safety compliance news and lunch Each workshop will have a specific theme and guest speaker Be sure to register early as positions fill up quickly Call Patty or Ann at 800 839 1649 to register today EMC Testing and Measurements Designing to Avoid EMC Problems Down the Road Watch as our Gaithersburg Lab engineers demonstrate several testing techniques that uncover EMC flaws in electrical and electronic equipment problems which can be avoided before the testing stage You ll have the opportunity to get specific with the engineering staff on particular problems
14. human exposure to these sources Other Hazards There is a tremendous variety of products on the market each with unique characteristics and potential hazards The applicable standards will usually address the hazards associated with the particular product or the risks will usually be recognized and addressed by product safety specialists GETTING POWER TO THE UNIT Plugging In There are essentially three ways to get power to your product Permanent wiring fixed cord and appliance inlet or plug socket There are specific requirements for each of these 1 For permanent wiring often found in industrial machinery terminals are usually provided within the equipment The terminals should be located close together and should be sized to carry the rated and anticipated fault currents for the particular product Installation is often performed by an authorized individual in accordance with the electrical codes in force at the site 2 Fixed cords non detachable are often used in appliances There may be several different options allowed by the standard depending upon the complexity of cord replacement These options may range from user replaceable to non replaceable that is throw the device away if the cord is damaged Requirements for fixed cords may include the type s of strain relief allowed the type of cord and wire gauge required for a particular applica tion and or the maximum length of the cord 3 Appliance
15. is hazard Shock This is the most widely recog nized hazard Studies have been done to determine the voltages and currents which are hazardous to people As a rule voltages exceeding approximately 30Vrms 42 2Vpeak or 60Vdc are con sidered hazardous Currents that may cause harm are in the 10 s of microamps to 10 s of milliamps and the particular standard provides the limits The frequency of the waveform of interest is also important lower frequencies are more dangerous because they tend to travel deeper through human tissue and are more likely to affect the heart Higher frequencies present greater danger of burns Mechanical Moving parts required for correct function of the equipment or ancillary to it fans etc present a physical hazard to the user of the equipment Guarding interlocking or other means should be provided to minimize the risks Also the likelihood that a product will tip over during use is considered during the evaluation Heating Excessive temperatures can cause burns start a fire or degrade insulation within the equipment The standards generally provide temperature limits for various internal and external parts Installation or mounting methods are considered when evaluating the product under counter installed in a cabinet etc Radiation Lasers RF emissions audible noise X rays and other radiation sources are all potential hazards The equipment design must reduce the risk of
16. it UL confirms if auditing will be required for that project WLL performs all testing completes UL report sends test data and report to UL along with sample for construction review and auditing if required UL reviews data and report performs audit testing if required UL issues approval Washington Laboratories is a full service EMC and safety compliance testing facility with offices in Gaithersburg and Frederick Maryland For more information on this new certification or other services please call Berri Remenick at 301 417 0220 Compliance Links American Telecommunications Certification Body Inc ATCB americantcb com The FCC has designated ATCB to issue Equipment Authorizations under Part 2 960 of 47 CFR FCC Rules and Regulations Prior to this program the only route for product certifications was by submitting a formal application to the FCC for Equipment Certifications including formerly referred to applica tions called Type Acceptance Under the TCB program ATCB under its accredi tation by American National Standards Institute ANSI provides ISO Guide 65 Certification Services for electronic products requiring FCC Certification National Technical Systems Corporation ntscorp com NTS provides an extensive variety of integrated services including testing managed personnel and standards com pliance Washington Laboratories and NTS have signed agreements to work together in the
17. ok computer with a brick power supply the power supply would be Category II and the computer itself Category MI Pollution Degree Yet another considera tion for determining spacings is Pollution Degree This addresses where the product is to be used and what envi ronmental conditions it will be subjected to Circuits components or products that are likely to be exposed to moisture or particulates in the air will require larger spacings than items that are encapsulated used in a clean room etc For example take a look at the ventila tion slots on a desk top computer power supply they re likely to have dust bun nies stuck to them The build up of dust and other solid matter is likely to cover the power supply board as well and may become moist on a humid day Proper creepage distances are intended to reduce the possibility that a conduc tive track and short circuit could occur Proper clearances help assure that arcing between live parts will not occur PROTECTION It is important to protect people ani mals and the environment from harm Electric shock energy fire radiation and mechanical hazards are among the issues that are considered in setting safe ty design criteria While the protection provided should not impair the function of the equipment adequate safeguards should be in place to meet these safety objectives Protection may consist of some or all of the following Fusing Fuse protection will help
18. turer in the US it is a copy of the UL yellow card and elsewhere it would be a copy of an agency license or similar certificate LABELING AND INSTRUCTIONS The standards identify the information that must appear on the product and or in the manuals General requirements are e the manufacturer s name or e rated voltage registered trademark e current or power e model number requirement and frequency e serial number or date code must be on the product Additionally inputs and outputs indicators and controls and operator replaceable fuses should be marked All markings should be identified and described in the manuals INSTALLATION USER AND SERVICE Instructions should be provided in man uals The Installation Manual should include all information necessary to install the equipment Examples are supply connections power air water etc disconnect switches over current protection ventilation requirements and other information appropriate for the particular equipment The User Manual should contain all warnings and cau tions along with all information for proper operation cleaning etc The User Instructions MUST NOT direct the user to expose him herself to hazards even when replenishing consumables or making adjustments Language of User Instructions as well as labeling has always been a difficult topic Generally they should be in a language appropriate for the intended market User Instructions
19. uipment along with quantities and locations of materials present Be aware that the flammability rating is often based on material thickness and an enclosure may not meet the require ments because it is too thin UL 94V 0 Least flammable UL 94V 1 UL 94V 2 UL 94HB Most flammable COMPONENTS Safety related components must meet their relevant standards and must be used in accordance with their ratings Such components include e fuses and fuse holders e power supplies and transformers e circuit breakers e relays e supply connectors e switches in hazardous circuits and terminals e wiring and terminals The component vendor will usually pro vide the information needed to use the part correctly These parts will be iden tified and evaluated during the certifica tion process and changes that involve these critical components must be evalu ated to ensure continued compliance Buy Pre Approved Parts It is always better to procure parts that already bear the required approvals The components should meet the requirements in force in the intended market That is UL for the US IEC or EN for Europe etc It is possible to use unapproved components and many times evaluate them in the end product Be aware however that you are responsible for the continued compliance of those parts and must ensure that the component manufactur er does not make changes that affect safety Get the certificate from the manufac
20. would do These are often used in damp areas and in medical devices where small but lethal leakage currents can flow There are many requirements for PE A primary requirement is that double securement be used The protection of PE connections must be taken care of at the terminations themselves That is a cable tie or sleeving is not an option Double crimp terminals lock washers or hooking wires prior to soldering must be used There are fast on con nectors available which meet the requirements these connectors provide a double crimp which secures the insula tion and conductor independently and have a positive locking mechanism which prevents the terminal from sliding off by means of a tab and mating hole A tool may be required to remove such a connector PE must make first and break last when provided in a connector for example where an auxiliary outlet is available to plug in an accessory Approved plugs and sockets will meet this requirement and many connector manufacturers now provide pins of different lengths to satisfy this requirement The current path must be robust PE conductors and connections must provide a low impedance path from all conductive surfaces to the supply earth Bare metal to metal mating surfaces should be provided this may mean that surfaces may need to be masked prior to painting Also attention should be given to the types of metals being used dissimilar metals
Download Pdf Manuals
Related Search