What's Inside The Product Safety Newsletter - IEEE · Product Safety Newsletter •1 What's ... of San Anselmo and the late James DeMartini. He also leaves two sisters, Judith Morris

Product Safety Newsletter •1

What's Inside

Vol. 7, No. 2 March-April 1994

Chairman's Message

Continued on page 17

Chairman's Message .................................. 1

Officers of the PSTC's ............................... 2

Letters to the Editor ................................... 3

In Memorium ............................................. 4

Michael James DeMartini ......................... 5

EEA Agreement ......................................... 6

Technically Speaking ................................ 7

News and Notes ......................................... 8

Earth Grounding ......................................... 9

Area Activities ......................................... 10

EMC Symposium 1994 ............................ 11

Institutional Listings ................................ 22

Employment Wanted ................... back page

1994 EMC SYMPOSIUM

Very shortly you will receive the advance program notice for the 1994 EMC Society Symposium to be held in Chicago this Au-gust. There are three events in particular that you

need to be aware of for your planning. For the firsttime, there will be a formal paper session devoted atleast in part to product safety. On Tuesday morning,August 23, “Product Safety and Spectrum Manage-ment” will be a featured session. Additionally, theposter session will also include a paper on safety. It’snot coincidental that all featured papers deal withbiological effects of exposure to various electromag-netic phenomena. Special thanks are due the TC-8paper reviewers, Dan Weinberg, Mike Harris, MurlinMarks and Dave Dini for their timely and insightfulanalyses.

Additionally, the TC-8 Annual Meeting will takeplace on Thursday afternoon, August 25, from 5 to 7PM. This meeting is an opportunity to review ouractivities and progress against our goals and toreassess and recast our future goals. All are welcometo attend and participate.

TheProductSafetyNewsletter


Officers of the Product SafetyTechnical Committees

Local

Central

Chairman Brian Claes (510) 659 6574(510) 659 6852 (fax)

Vice-Chairman Richard Pescatore (408) 447 6607Secretary-Treasurer John McBain (408) 746 5016

(408) 746 5258 (fax)Standards Paul McDonald (415) 592 5111

(415) 592 6052 (fax)Symposium Murlin Marks (408) 985 2400

The Product Safety Newsletter is pub-

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Technical Committee of the IEEE EMC

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the articles remain with the authors.

Opinions expressed in this newsletter

are those of the authors and do not

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bers. Indeed, there may be and often

are substantial disagreements with

some of the opinions expressed by

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Editor: Roger Volgstadt

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The

ProductSafetyNewsletter

ChicagoChair John Allen (708) 238 0188

(708) 238 0269 (fax)Orange County/Southern CaliforniaChair Charlie Bayhi (714) 367 0919Vice-Chair Ercell Bryant (714) 966 3459Secretary/Treasurer Deborah Tinsley (714) 773 7977Program Co-Chair Michael Dastmalchian (310) 604 8739Program Co-Chair Ray Jimenez (619) 726 9303

PortlandChair Jim Pierce (503) 626 6694Secretary-Treasurer Scott Varner (503) 656 8841

Santa Clara ValleyChairman Mike Campi (408) 987 6527Vice/Program Chair Murlin Marks (408) 985 2400 X2353Treasurer Mark Montrose (408) 247 5715Secretary Travis Lee (408) 294 7600

SeattleChairman Walt Hart (206) 356 5177Membership Chair John Quigley (206) 226 1660

Texas (Central)Chairman Vic Baldwin (512) 990 6145


turns ratio and the core material.

Secondly, the transformer has a small interwindingcapacitance. The transients, being very narrow highrise-time pulses, are transmitted to the secondarywithout any appreciable reduction in value. This is anormal condition.

However if a large capacitance (compared to theinterwinding capacitance of the transformer) is con-nected from the secondary to earth, then the largecapacitance acts as a low impedance path for thetransients. For such a case transients in the secondarywould have been reduced. This is the reason forhaving the Condition No. 5 to Table 5 of IEC Publi-cation 950 (Secondary Edition).

Best Regards and Thanks,Lal Bahra, P. Eng.Engineering Project ManagerEngineering and Quality AssuranceCertification DivisionCanadian Standards Association

[Note: See the Technically Speaking column in thisissue for a discussion of transmission of transientvoltages through transformers and power suppliesinto secondary circuits. -Ed.] ❏

Dear Editor,

In the Technically Speaking column by Rich Nute,entitled “Working Voltage, Electric Strength andSpacings” (July-August-September 1993), the au-thor states “...secondary dc circuits are examples ofthis kind of circuit. It is an abnormal condition thatsecondary dc circuits have transient overvoltage”.The author implies that secondary circuits are freefrom transients except under abnormal operatingconditions.

Secondary circuits which are isolated from the mainsby an earthed metal screen or circuits which have oneside of the secondary connected to earth, are ex-amples of the circuits mentioned in the above para-graph. However, a floating secondary circuit (notisolated by an earthed metal screen) is subjected tofull mains transients.

First of all, due to induction effect, some transientsdo get through to the secondary, depending upon the

Letters to the Editor

Small interwinding Capacitance

Secondary

Capacitance connected to ground

Primary


In Memorium: A Friend andColleague Passes On

In addition to his dedication to the profession, Mike’sleadership abilities have been recognized and ac-knowledged by his colleagues and co-workers alike.His integrity, fairness, compassion, understanding,caring, respect for others and winning attitude wereappreciated by all. One co-worker characterizedMike as “the absolute best boss - a true leader with avision.”

Mike is survived by his mother, daughter, two sisters,and fiancee.

Those of us who knew Mike have lost a great friendand colleague. He will be missed not only by hisloved ones, but also by those of us who were proud tohave known him, to have been his friend and to haveworked with him all these many years. o

by Richard Pescatore

It is with deep personal regret and sadness that Iinform you of the unexpected and untimely deathof Mike De Martini, Managing Engineer at Un-

derwriters Laboratories Inc. (UL) in Santa Clara,California.

Mike passed away suddenly and without warning,apparently of heart failure, while at home on theevening of January 15.

Mike spent his entire career in the field of productsafety, having worked at UL since 1969. His dedica-tion and personal efforts were evident through hisinvolvement with the profession at various levels.

In addition to his work within UL, Mike was active inthe International Electrotechnical Commission (IEC),the IEEE Product Safety Technical Committee(PSTC) and the National Fire Protection Association(NFPA). He served in various positions of leadershipat UL, in the IEC and the NFPA. He supported thegoals of the PSTC by participation as a technicalspeaker.

Mike will be remembered for his dedication to prod-uct safety, both nationally and internationally. Hisprogressive approach to the discipline was welcomeas he applied his formal engineering training and hiscreativity to problem resolution and the setting ofstandards. On several occasions, Mike shared hisfeelings of personal commitment to the betterment ofmankind. He viewed his work as his contribution tosociety.

1969 - BSEE Univ of Santa Clara

1969 - Assist Engr, UL, Sec B

1970 - Proj Engr,UL, Sec B

1976 - Senior Proj Engr, UL, Sec A

1977 - Registered Professional Engineer

1980 - MBA Univ of Santa Clara

1981 - 1985 grew Sec B from 19 to 49 persons

1989 - Managing Engineer, Electrical Dept

1992 - Managing Engineer, Engr. Services

Developed and Published UL 114/UL478

Developed draft harmonizing UL 478/IEC 950

Introduced USA requirements into IEC 950

Developed and published UL 1950


Michael James DeMartini1947-1994


[The following is extracted from UL's Feb. '94 issueof CONNECTION and is reprinted here with permis-sion- Ed.]

UL has lost a highly respected employee anda totally dedicated professional in MichaelJames DeMartini, 46, who died from ap-

parent heart failure on January 15.

Mike was Managing Engineer of Engineering Ser-vices, Department 313, and would have celebrated 25years with UL in July.A native Californian, Mike was father of TraceyDeMartini of San Jose, and son of Eleanor DeMartini

of San Anselmo and the late James DeMartini. He alsoleaves two sisters, Judith Morris of Point Reyes andGinny DeMartini of Hayward, and his fiancee, LouiseRoy, of Hollister.

On January 20 more than 200 relatives, friends, co-workers, and associates attended memorial servicesfor Mike at Transfiguration Church in San Jose. Thelarge attendance indicated the high regard people inUL and his associates outside the company had for him.

Mike earned his BSEE and MBA degrees from theUniversity of Santa Clara. He was a Registered Pro-fessional Engineer in the State of California (SafetyEngineering) and a member of numerous engineeringcommittees.

Among his professional achievements was the ULProfessional Engineer’s award he received in 1983. Hewon this recognition for his work in development andpublication of a combined Standard, UL 478, fifthedition, which comprehended older office appliancesand equipment with newer information processingequipment.

The award also acknowledged his significant contri-bution in harmonizing UL 478 with IEC 950, aninternational standard for information technologyequipment. Subsequently, Mike was instrumental inthe further harmonization of UL 478 with IEC 950 intoa document now known as UL 1950.



European Economic Area (EEA)Agreement - Looking Ahead!

by Rainer Gehrmann,Hewlett-Packard GmbH

The long negotiated agreement between theEuropean Community (EC) and the Euro-pean Free Trade Association (EFTA) was

finally signed on 17 December 1993.

The agreement was originally planned to come intoforce on 1 January 1993, but was delayed by oneyear. The delay was due to the referendum inSwitzerland, which voted against the EEA (and whichconsequently is NOT part of the EEA), and morerecently by parliamentary elections in Spain andPortugal. It has now been in effect since 1 January1994.

The agreement aims at establishing a uniform Euro-pean wide economic area allowing free movement ofgoods, capital, people and services.

Beyond the more general implications of such an

agreement, I would like to draw your attention to theimplementation and consequences in the field ofproduct regulations.The harmonization process within the EC will beextended to the signatory EFTA countries, whichmeans that local product standards shall be harmo-nized with European Standards (ENs) and local lawsshall be harmonized with European requirementsand directives. Product conformity assessment pro-cedures including testing shall be harmonized withthe EC, as well as market supervision and productsurveillance methods.

Significant changes will take effect, not ALL on 1January 1994, but according to a timetable, whichpartly is already aligned with the transition periods ofEuropean directives and standards.

- Existing pre-sales and border “product” control willdisappear and be replaced by methods focusing onmarket surveillance and “process” control.

- Conformity testing and verification done in accor-dance with the European schemes will be sufficientwith proof of conformance by CE marking and dec-laration of conformity.

Without going into details of changes on a country-by-country level, I would like to highlight just a fewopen issues.

- In some areas where mandatory testing was re-quired in the past, but not regulated from the EC, thismust cease. However, laboratories involved in suchtesting in the past have launched awareness cam-paigns, and market pressure may exist to obtain


by Richard NuteCopyright 1994

Technically Speaking

He further said that a floating secondary circuit issubject to full mains transients.

In this issue, I’ll examine how transformers behavewhen subjected to transient overvoltage, both mag-netically and capacitively.

I’ll also examine the functions of rectification andcapacitive smoothing when subjected to transientovervoltage.

And, I’ll describe some transient overvoltage testson a 40-watt transformer, a 20-watt unregulated dcpower supply, and on two 50-watt switching-modepower supplies.

Let’s first examine how transformers behave, mag-netically, in the presence of transient overvoltages.

Power transformers are designed to transform powerat 50 or 60 Hertz or both.

Transformers operate as transformers when the fluxis within the limits of the design. Flux increases withinput voltage. Flux increases with frequency. If theflux increases too much, the core will saturate, andthere will be no magnetic coupling from primary tosecondary.

Transient overvoltages are comprised of high volt-ages and high frequencies. The transient voltagesoften are greater than the rated transformer inputvoltage. The frequencies contained in the transientare much greater than the rated transformer fre-quency, usually in the hundreds of kilohertz to lowmegahertz range.

In the July-August-September issue of The Pro-duct Safety Newsletter, I discussed “workingvoltage,” and its relevance to the safety of the

equipment. Included in that discussion was a discus-sion of transient overvoltages.

I said that primary circuits normally have transientovervoltages, but that “Equipment secondary dccircuits are examples of “...circuits that have virtuallyno transient overvoltages.”

I further stated, “It is an abnormal condition thatsecondary dc circuits have transient overvoltages.”

One reader said that such statements are only true forsecondary circuits separated from primary by anearthed metal screen, or for secondary circuits hav-ing one pole connected to earth.


TRANSIENTS IN SECONDARY CIRCUITS


News and Notes


CANADIAN/US ITE SAFETY STANDARD

The PRE-RELEASE DRAFT of the Canadian/USBi-National standard for the safety of InformationTechnology Equipment is now being reviewed. Thisstandard will become THE safety standard for ITEequipment in both Canada and the US. The standardwill apply to all IT and telecommunications equipmentand replaces the four standards currently in use today(CSA 225 & 950, UL 1459 and 1950). It is thereforeimportant to those companies involved with IT andtelecom equipment. The document presently is 263pages long and includes requirements for connectionto telecommunications circuits and for connection tocentralized DC power sources. The FIRST RELEASEDRAFT for general industry review and commentwill become available sometime after the IAC meetingin mid-March, 1994.Submitted by John McBain

[Rich Pescatore, PSTC Vice-Chairman, is a memberof the bi-national committee and may be able toprovide more information. - Ed.]

UL ANNOUNCED QUEBEC RECOGNITION OF UL MARK

Underwriters Laboratories Inc. (UL) announced thatthe Regie du Baument du Quebec has officiallyrecognized the UL Mark for Canada for all productsectors, including gas and electrical, giving ULprovincial acceptance throughout Canada.

The appropriate legislative act regarding buildingand construction on Quebec has been amended, aspublished in the December 15, 1993 issue of theGazette Officielle du Quebec, to recognize UL andthe UL Mark for Canada.

According to a press release dated December 15,1993, UL says UL's acceptance in Quebec makes itthe first certification organization outside of Canadaaccredited by the Standards Council of Canada (SCC)to secure complete approval for Canada.

UL was also the first certification organization outsideof Canada to be granted Certification Organization(CO) and Testing Organization (TO) accreditation'sby the SCC.

For further information, contact:Sara J. Payne, 708/272-8800, Ext. 43436Media Relations AssociateNorthbrook, Illinois, USA-or-John R. Woods, 613/742-6965Executive Liaison Canadian Affairs

by Dave Edmundsfax: (716) 422-6449



Earth Grounding

not required to satisfy impedance, current carryingcapacity, special color coding or other requirementsof safety earth grounds.

Each safety earth ground must satisfy the electricaland mechanical characteristics of sections 1 through7 if it is to comply with recognized electrical safetystandards and certification requirements.

DEDICATED SAFETY CIRCUIT

The safety earth ground terminal must be a dedicatedtermination point and should not provide terminationfor other conductors. This avoids the need to disturbthe safety earth ground connection once is has beenestablished and tested. All power-on servicing mustbe done with the safety earth ground connected,unless the servicing requires removal of the unit fromits enclosure. In such cases an equivalent safety earthground must be used for all for power-on benchtesting.

Should there be both safety earth grounds andfunctional grounds in the same area in equipment,each type should have separate termination points.While standards may permit both safetyearth ground and functional earth ground conductorsto be terminated on the same binding post or terminal,it is not considered good design practice to do so.

Safety earth ground terminations should not be subjectto disruption or exposed to the risk of not beingreplaced once disconnected for servicing or relocationof the equipment. Once disrupted the safety earthtermination is difficult to maintain to the strictelectrical properties established at the point of

by Paul W. Hill & Associates© 1990

[We are grateful to the author for providing anotherinstallment condensed from his book "ProductSafeness As A Design Parameter", 2nd Edition,1990. The text is a registered copyright of Paul W. Hill &Associates, Inc., and is reproduced with permission.Details about the purchase of the book may beobtained by calling (407) 368 2538 - Ed.]

Earth grounding circuits are critical in theprevention of electric shock. Earth groundis the second level of protection in Class I

devices should the basic insulation fail. Due to itsimportance in the prevention of electric shock safetystandards have stringent requirements for safety earthground circuits. Safety earth ground in this discussionalways concerns the ground circuit provided forsafety reasons in Class I equipment. It is the earthground conductor identified as the green or green/yellow conductor. This material does not addressfunctional grounds which are required only for properoperation of the equipment. Functional grounds are


Area Activities

by John Reynolds381 Los Pinos WaySan Jose, CA 95123-5118voice: 415-390-1344fax: 415-962-9439e-Mail: [email protected] [email protected]

COMMUNICATION

You will notice I have included my voice phonenumber and a new e-mail address. Communicationand the NII, or National Information Infrastructure,are the buzzwords of the day. At least they areaccording to Vice President Al Gore. It is also key toour professional lives. Without a facsimile machine,telephone and e-Mail my job would be much moretedious. In fact, if I was to take a time study, I wouldmost likely find that 80 to 90% of my job involvedcommunication.

Either receiving or transmitting, the volume of infor-mation is great. Communication must also be timely,

to be of value. A meeting notice, no matter howinformative is of no use if it arrives after the event.Communication is also key to the life of our groups.With this in mind I would like to encourage anyonewho has items of interest associated with the localgroup activities to contact me.

CENTRAL TEXAS

The January 26th meeting of the Product SafetyTechnical Committee of Central Texas featured anupdates on the "EC Product Safety Directive" by Mr.R. Krumme of TÜV. The meeting was held at ROLMCorp., 2205 Grand Avenue Parkway in Austin Texas.The Social and refreshments started at 6:30 with themeeting at 7:00 pm. For details of future meetingscontact Vic Baldwin at ROLM phone 512-990-6342,fax 512-990-6145.

NORTHEAST PRODUCT SAFETY SOCIETY - (non-IEEE)The January 26th meeting featured a talk by Mr.Stuart Chappel of Voltech on the IEC 555 standard.The February 23rd meeting will feature a presenta-tion by Mr. Carl Lindquist of SAN-O on fuse design,and on March 23, Mr. Joe Guerriero of AssociatedResearch will discuss Hipot Testing Theory.

The meetings of the Northeast Product Safety Soci-ety are held at 7:30 pm, with time for social from 7-7:30 pm. To get further details on location contactDave Lorusso Committee Secretary at Tel: 508-435-5067.

The January Northeast Product Safety Society News-letter featured an interesting article on "RegulatoryDesign Guidelines for Using Lithium Batteries" by



EMC Symposium 1994

Fees are as follows: $30 for IEEE Member; $35 for Non-IEEE Member; $10 for Students. Exhibits OnlyAdmission is Free. Colloquium Record: $15 at the Colloquium or FREE to advanced registrants.

Make check payable to IEEE SCV EMC ‘94. Mail to IEEE SCV EMC ‘94, PO Box 2102, Cupertino, CA95015-2102. Advance registration for IEEE SCV EMC 94 ends March 15.

For further details, contact: David Hanttula, Chairman, (415) 390-1071 or Ghery Pettit, Registration, (408)285-2528.

Tuesday, March 297:00 - 8:45 Registration Registration8:45 - 9:00 Welcome Welcome9:00 - 9:30 1A Compliance Overview 1B Fundamental EMC9:30 - 9:45 Break Break9:45 - 10:45 2A Managing Compliance 2B Fundamental EMC10:45 - 11:00 Break Break11:00 - 12:00 3A Demo Shielding 3B Fundamental EMC12:00 - 1:15 Lunch Lunch1:15 - 2:15 4A CE/RE Emiss. Measrmnt 4B Filtering2:15 - 2:30 Break Break2:30 - 3:30 5A Compliance Stds 5B PCB Layout3:30 - 3:45 Break Break3:45 - 4:45 6A Compliance Stds 6B Demo Freq Resp.

Wednesday, March 307:00 - 8:30 Registration Registration8:30 - 9:30 1C Safety 1D EMC Trouble Shooting9:30 - 9:45 Break Break9:45 - 10:45 2C Safety 2D EMC Trouble Shooting10:45 - 11:00 Break Break11:00 - 12:00 3C Safety 3D Demo Trouble

Shooting12:00 - 1:15 Lunch Lunch1:15 - 2:15 4C Safety 4D Demo Immunity2:15 - 2:30 Break Break2:30 - 3:30 5C Telecom 5D Immunity3:30 - 3:45 Break Break3:45 - 4:45 EMC Panel Discussion Q&A 6D Immunity ❏


duration of the fault.

The likely fault currents, identified by abnormaloperation and fault testing, dictates the earth groundconductor size. It is clear that the earth groundconductors can not be smaller than that required tohandle the currents expected in the safety earth groundcircuit. Some product safety standards require thatsafety earth ground circuits be capable of conductingfrom 10 A (ten amperes) to 25 A (twenty-five amperes)for a period of one minute. Some test and certificationagencies may require such a test as part of themanufacturing process.

RELIABILITY

Due to the critical function of the safety earth groundcircuit it must be in place and remain at low impedancelevels during the operational life of the equipment.No components, switches, or fuses are permitted inthis circuit because of the possible risk of discontinuityin the circuit, such as a blown fuse or open switch.Components such as coils or resistors would increasethe circuit impedance of safety earth ground circuits.

Connections and terminations in the safety earthground circuit must not be subject to electro-chemicalor other corrosive actions. Corrosion at connectionsincrease the impedance of the circuit and possiblyelectrical discontinuity at such points. Safety earthground circuits with several connections, splices,daisy chaining, and other possible discontinuity pointsshould be avoided. Good design practice is to havesafety earth ground circuits as electrically uniformand continuous as possible.

CONNECT AND DISCONNECT

For all connect and disconnect operations, the earthground conductor must be the first to make electricalcontact and the last to break electrical contact. Earthground conductors must be terminated such that

manufacture.

Good servicing practice is to retest the safety earthground circuits for continuity and impedance afterany disturbance of the earth ground wiring orterminations. Instructions for these tests should beincluded in the equipment installation and servicemanuals.

The point at which the safety earth ground isterminated must be identified by an easily recognizedpermanent marking or symbol. Some standards permitthe word GROUND or the letter G, or the abbreviationGND to identify the termination point. The mostwidely accepted identification of the safety earthground is the conventional ground symbol within acircle, symbol number 5019 of IEC Publication 417.The safety earth grounding symbol, abbreviation orcolor coding must be explained in the installationinstructions and service manuals.

LOW IMPEDANCE

All electrical safety standards fix the maximumimpedance in the safety earth ground at 0.1 Ohm(one tenth of an Ohm). The impedance measurementis between any accessible part likely to assumehazardous conditions and the safety earth groundpoint of the equipment indicated by the safety earthground symbol.

FAULT CLEARING CAPACITY

The main purpose of the safety earth ground is toconduct a fault current to earth until the fault isremoved or reduced to a safe level. These currentsmay flow in a faulted circuit for some period of timebefore the fault current is removed or reduced to asafe level. The conductors in the earth ground circuitmust be capable of sustaining such currents for the

Earth GroundingContinued From page 9


should a stress be placed on it causing it to disconnect,the earth ground conductor must be the last to breakelectrical contact. The earth ground pin of a plug ismade longer than the phase or neutral pins to satisfythis “make first, break last” safety requirement.

CONDUCTIVE COATINGS

Conductive coatings or films applied by spraying,dipping, painting or plating materials on tonon-conductive surfaces must not be relied upon tobe a conductive link in the safety earth ground circuit.Under fault conditions conductive films and coatingstend to quickly burn away the film at the point ofcontact with the fault current. This non-conductingpoint is now a discontinuity in the safety earth groundcircuit.

UNGROUNDED ACCESSIBLE PARTS

Accessible conductive parts not electrically connectedto the earth ground circuit must be identified ininstallation instructions and service manuals. Theymust also be marked with a warning sign or label toalert individuals that the part is not earth groundedand to test for the presence of hazardous potentialsbefore touching.

PRODUCTION TESTS

Most all safety standards require each unit ofequipment produced to be tested for continuity andlow impedance as part of the manufacturing process.These tests are made on the completely assembledunit, even if all subassemblies have been previouslytested. Some standards also require the currentcarrying test of the safety earth ground circuit as partof the manufacturing process. All safety earth groundtests conducted as a formal part of the manufacturingprocess and a record of the test results maintained.These tests can be grouped or combined, includingthe dielectric strength test into one production teststation. The test sequence should be arranged to

avoid damaging units which are repairable should theearth ground circuit be defective. The test sequenceis:

1. Low voltage continuity and impedance test, ifacceptable then,

2. Dielectric strength test, if acceptable then,3. Current carrying capacity test.

If certain components in the equipment could bedamaged during test 2) or 3), the parts should beremoved, disconnected or shorted. If removal,disconnection or shorting is not practical DC testpotentials should be used. The equivalent DC testpotentials are given in the safety standard.

For high speed testing, or testing of more than oneunit at a time, care must be taken that the testpotentials applied reach the required level and hold atthat level for the time period specified by the standard.At multiple unit test stations a single source of the testpotential applied simultaneously to more than oneunit should be avoided. This is advisable because theimpedance of two or more completed units is notlikely to be closely matched. In such cases one unitis over stressed and the other under tested.

Good test practice suggests that each unit under testhave its own test potential source. All earth groundtests, at single or multiple unit test stations, shouldhave test potential vs time profiles made periodicallyto assure the full test potential is applied for therequired minimum time period.

Manufacturing test records should include calibrationof safety earth ground test equipment. Goodengineering practice is to specify the frequency oftest equipment calibration, record adjustments or anyrepairs made to the test equipment, specify the formatin which the test data will be recorded and the lengthof time test records are to be maintained. ❏


adjacent turns.

At any particular point between two windings, asingle turn is adjacent to one or more single turns inanother winding. Each set of two single turns indifferent windings constitute the plates of one of themany capacitances that exist between the two wind-ings.

In between the individual turns constituting one plateof a capacitor are a number of other turns of thewinding. These turns constitute inductances and donot contribute to the interwinding capacitance. So,the distributed capacitors are connected by means ofinductors.

At high frequencies, the various capacitances aredistributed throughout each individual winding. Thevarious incremental capacitances are connected bymeans of the turns of the winding. The turns consti-tute inductances. So, the distributed capacitors areconnected by means of inductors as well as by thecapacitance between layers of a single winding.

Series inductors attenuate high frequencies. Shuntcapacitors attenuate high frequencies. Series capaci-tors couple high frequency to the adjacent winding.This results in a very complex high-frequency cir-cuit.

Since the series capacitors between windings are justone part of the complex high-frequency circuit, verylittle transient overvoltage energy is transmitted tothe secondary windings. Most of the energy is dissi-pated within the primary winding, or from the pri-mary winding to ground.

At the high frequencies found in a transient overvolt-age situation, the interwinding capacitance cannotbe represented as a single capacitor from primary tosecondary. Likewise, the capacitance from a wind-ing to the core or to the earth cannot be representedas a single capacitor.

Because the core is optimized for the power linefrequency, it is very lossy at higher frequencies. Infact, the core is so lossy in the presence of transientfrequencies, the device ceases to be a transformer.

Due to the high frequencies, the core saturates atrelatively low transient voltages. (In fact, at highfrequencies, the core will saturate at voltages muchlower than the rated input voltage of the trans-former.) When the core saturates, there is no mag-netic coupling primary-to-secondary. With no mag-netic coupling, there is no coupling of the transientvoltage to the secondary winding.

Likewise, due to the high voltage of the transient, thecore will saturate. When the core saturates, there isno coupling of the transient voltage to the secondarywinding.

So, transformers simply do not operate as transform-ers in the presence of transient overvoltages. Thereis no output of the transient from the transformer due tothe operation of the device as a transformer.

Next, let’s examine the effect of capacitance be-tween input and output windings of a transformerwhen the transformer is subjected to transient over-voltages.

Two conductors separated by an insulator constitutea capacitor. In an isolating transformer, the input andoutput windings are separated by an insulator, andtherefore constitute a capacitor.

Similarly, there is capacitance from each winding tothe core.

Recall that transformers are wound with insulatedwire. Each turn of a winding is fully insulated from

Technically SpeakingContinued From page 7


Off-line rectifiers have lots of capacitance across thejunction, but that capacitance is very small com-pared to the bulk capacitor. In a series circuit of twocapacitors, the voltage division is inversely propor-tional to the value of capacitance. Therefore, there isa small proportion of the transient overvoltage acrossthe large capacitor (the bulk capacitor) and a largeproportion across the small capacitor (the rectifier).

Primary and secondary dc circuits have negligibletransient overvoltages due to transient overvoltageson the power line.

To confirm these hypotheses, I tested a 40-watttransformer, a 20-watt transformer-rectifier withsmoothing capacitor, and two 50-watt switching-mode power supplies.

The two 60-Hertz transformers were of triple-flangebobbin construction. The switching-mode powersupplies use reinforced insulation between primaryand secondary.

I injected 1.2 x 50 microsecond transient voltagesonto the power line for each device. I monitored theoutput with a scope (through an isolating amplifierto eliminate any affects of connecting the circuit toground through the scope).

I started with 500 volts, line-to-neutral, and workedup to 2.0 or 2.5 kilovolts. I also applied the pulse line-to-ground.

With 1.5 kilovolts input to the transformer, the tran-sient output was about 70 volts. The transient outputvoltage remained about 70 volts regardless whetherthe pulse was applied line-to-neutral or line-to-ground, and regardless whether the output wasgrounded or floating.

With up to 2.5 kilovolts applied to both the trans-former-rectifier and the switching-mode power sup-

So, while there is capacitance from primary tosecondary, there are also inductors in series withthose capacitances, and there are capacitances fromprimary to core and primary to ground, all of whichserve to highly attenuate the energy coupled to thesecondary windings.

Now, let’s examine rectification and capacitivesmoothing of the secondary output voltage whensubjected to transient overvoltages.

The action of a full-wave rectifier is such that nomatter the polarity of the input voltage, only onepolarity is present at the output. This means thattransient overvoltages (exceeding the peak-to-peakmains voltage), regardless of polarity or phaseposition with respect to the ac input voltage, willappear at the output of the rectifier (assuming therectifier diode has sufficient frequency response toturn on during the transient).

The energy in the transient is then stored in thesmoothing capacitor and should raise the capacitorvoltage depending on the value of transient voltage,the duration it is above the voltage on the capacitor,and the available current.

Since the transient voltage is attenuated by the trans-former, and since the time is very short, and sincecurrent is small due to the inductance of the trans-former, the voltage increase on the smoothing ca-pacitor is almost imperceptible.

The same action takes place in the off-line rectifier-capacitor circuits of switching-mode power sup-plies. The input EMI filter attenuates the transientovervoltage. The off-line rectifier usually is slow,and may not turn on during the transient overvoltageevent. If it does turn on, or is late in the event, onlya small amount of the energy is dumped into thecapacitor and there is negligible voltage change.


plies, there was no more than 1 volt change for nomore than 2 milliseconds in the nominal 30-volt and25-volt outputs, respectively.

CONCLUSIONSTransient overvoltages are not magnetically coupledto the output windings of 50-60 Hertz transformers.

Transient overvoltages are capacitively coupled fromprimary to other transformer windings. The magni-tude of the transient across the output winding is afunction of the capacitance between the windings,the capacitances of all windings to the core, and thecapacitances of all windings to ground.

Since the transformer output transient overvoltage iscapacitively coupled and not magnetically coupled,the value of the output transient voltage is dependenton transformer insulation construction, and indepen-dent of the output winding voltage.

At least for triple-flange bobbin construction, themagnitude of the transient across the output windingis largely independent of whether the output windingis grounded.

The magnitude of a capacitively-coupled transientacross the output winding of a triple-flange bobbin-constructed transformer is largely independent ofwhether the transient is applied pole-to-pole or pole-to-ground.

Rectification and capacitive smoothing of an acwaveform containing a transient overvoltage virtu-ally eliminates the transient from appearing on the dcvoltage.

For the evaluation of insulation (spacings) in pri-mary and secondary dc circuits, the value of “work-ing voltage” determines both clearance distances andcreepage distances, whereas in primary ac circuitsthe value of transient overvoltage determines clear-

ance distances and the value of working voltagedetermines creepage distances.

ACKNOWLEDGMENTThanks to Tinny Srinivasen, Western Transformers,Portland, Oregon, who provided me with the techni-cal details of transformer operation in the presencetransient overvoltages.

Thanks also to Daven Tester, Nick Manwell, andKevin Cyrus, all of Hewlett-Packard, for help intesting the hardware. ❏

A new PSTC group is forming inColorado! If you would like furtherinformation, please contact:

Andrew DoeringTÜV Product Service5541 Central Ave.Boulder, CO 80301303-449-4165

Dave Lorusso is back! Please sendany safety related articles to:

Dave Lorusso, EMC Corporation, 171South Street, Hopkinton, MA 01748

508-435-1000, x2130 (phone) or508-435-5222 (fax)


EEAContinued From page 6

Chairman's MessageContinued From page 1

Finally, on Friday morning, there will be a safetyworkshop on ANSI C95.1 safe exposure values. Thefocus will be on philosophy and technical consider-ations behind published requirements for EM fieldexposure, particularly that associated with varioustypes of intentional transmitting devices.

“WHAT’S THE RISK?”On a somewhat related topic, it should be noted thatmuch of the Symposium’s product safety focus is notassociated with how to design to or get approvals tostandards. Rather, the focus is on whether the pre-sumptions and ultimately the standards we use actu-ally are adequate. As I’ve shared with you before, Idon’t think we are as aggressive as we should be inassessing the adequacy of the requirements we’veadopted and the assumptions that support them. Thisnewsletter has carried, and will continue to carry,articles that deal with the technical as well as theenvironmental and human factors aspects of productsafety that challenge current practice. I’d like to seethis effort stepped up.

There is a danger in defaulting to the recommenda-tions of other specialized disciplines and passivelypermitting systems of requirements to be developedthat don’t properly reflect responsible application ofsound risk-sensitive safety practice. To address this,we must become familiar with what is going on inthese disciplines and interact constructively withthem. We also must be well-versed in dealing withrisk assessment and prioritization to be of value todecision-making processes, whether within busi-nesses, in standards developing bodies or elsewhere.❏

such marks on a voluntary basis.

- Alternative control schemes are not yet establishedand problems during a transition period can be ex-pected.

- In areas where harmonized standards are missing(e.g. Common Technical Regulations [CTRs] fortelecom), national schemes will continue to exist,and the EEA won't change anything.

Here are a few predictions of what you might expect:

- EC directives that already have existed for yearswill be implemented as soon as practicable, some-times on 1 January 1994. Where new directives haveimplementations pending, or during the transitiontimes specified by directives, these will be imple-mented according to the transition end dates.

- Systems or equipment with different requirementsusually will not be harmonized at the lowest level, butthe more stringent rules will be combined.

- The effects will not be visible in all countries andaccording to the same timetable but gradually overthe next four years. Some positive changes alreadywent into effect a couple of months ago, in anticipa-tion of this event (e.g. dropping laser certifications inSweden).

The danger of increasing bureaucracy concentratedat the European level exists, but the “rethinking”process fueled by the discussion on the MaastrichtTreaty has taken off and led to consensus that thedecision-making mechanisms must be both tightenedup and democratized. At the moment enthusiasmprevails, and I hope it will last. o


Dave Lorusso. For information about this articleplease contact the Northeast Product Safety Societyc/o Dave Lorusso, 21 Highwood Drive, Franklin,MA 02038.

1994 Administrative Committee Officers -President, Tony Nikolassy of T-Tech EngineeringVice President, Werner Paster of EuroconsultTreasurer, Michael Rains of Foxboro Co.Secretary, Dave Lorusso of EMC Corp.

There were several openings listed in the newsletter.Please contact Dave Lorusso for details and phonenumbers.

Thank you everyone on the NPSS administrativecommittee and Dave Lorusso for a very informativenewsletter.

SANTA CLARA VALLEY GROUP

*The January meeting featured our first field trip. Wemet about 50 miles away from Silicon Valley in SanFrancisco at the headquarters of Dolby LaboratoriesInc. While the tour of Dolby Labs did not directlyrelate to Product Safety, we did have a good time andlearned quite a few things. Approximately 35 peopleturned out for the tour. We had dinner before the tourat about 6 and finished the meeting at about 9.

There were at least 3 impressive features about Dolby:1) Their innovative sound reduction techniques (andhardware!) are everywhere around us from use inpersonal cassette players to television to movies toFM broadcast stations and more.2) The company was immensely successful with itsaudio cassette noise reduction but continued to inno-vate in other fields involving sound recording and

Area ActivitiesContinued From page 10 reproduction.

3) They have implemented a system of quality con-trol that includes initial test of products and fieldinspections. They even have sound consultants thatvisit movie studios to advise on sound recording/reproduction.

We viewed film clips in Dolby's state-of-the-art in-house movie theater. We saw and heard examples offilms using everything from pre-Dolby sound to thelatest innovation, Dolby Stereo Digital (VERY im-pressive). The latest development uses a printedoptical multi-digital sound track BETWEEN thesprocket holes of conventional film.

Dolby manufactures their professional equipmentthemselves and licences other manufacturers to makeconsumer equipment using Dolby technologies.

If you would like further information about DolbyLaboratories, please contact Joe Hull at(415) 558 0213.

* The February meeting will be on Wednesday the23rd instead of the usual Tuesday night. Dinner andSocial will be at Carlos Murphy's at 5:00 pm. Themeeting will start at 7:15 pm at Apple Computer inCupertino. Contact Murlin Marks (UL) at 408-985-2400 x2353 for details and dinner reservations.

* The speaker will be Mr. Gene Panger of TÜV -Product Service. Mr. Panger is Director of Sales withTÜV Product Service. His responsibilities includemonitoring European Conformity Assessment de-velopments in a variety of areas including medicalproducts, telecommunications, and scientific equip-ment. The topic will be "FDA and Notified Bodies:Comparing the Roles."

* Mr. Panger will discuss how the coming Medical


Device Directive will join the existing Active Im-plantable Medical Device and the pending In VitroDiagnostic directives in transforming the way medi-cal products are approved in Europe. Notified Bod-ies play a central role in Europe's evolving schemefor medical products. How will this role differ fromthat of the FDA here in the U.S.? How will they besimilar, and where are the areas of overlap?

* This presentation will address similarities anddifferences between the FDA and Notified Bodies inthe following areas: structure, philosophical back-drop, role of accreditation, documentation, standardsutilization, quality systems, and inspections.

* March Meeting - The March meeting will be onWednesday the 16th instead of the usual Tuesdaynight. Check in for the Social will be at 5:30 pm, withdinner at 6:00 pm. Location: Wyndham Garden Ho-tel, 1300 Chesapeak Terrace, Sunnyvale. To getdirections and reservations for dinner, contact MurlinMarks at (UL) 408-985-2400 x2353.

* This will be a combined meeting of the ProductSafety Technical Committee and the Systems SafetySociety. The topic is Software Safety/Reliability.

* Speaker - Dr. Norman Schneidewind. Dr.Schneidewind is professor of information sciences atthe Naval Postgraduate School where he teaches andperforms research in software engineering and com-puter networks. He is the developer of theSchneidewind software reliability model used byIBM-Houston to assist in the prediction of softwarereliability of the NASA Space Shuttle. This modelis recommended by the American Institute of Aeronau-tics and Astronautics, the American National Stan-dards Institute and others.

* April Meeting - The April meeting will be on

Tuesday the 26th. Check in for the Social will be at5:00 pm, with dinner at 5:30 pm. Location: AppleComputer, Valley Green 6. For directions and reser-vations for dinner contact Murlin Marks (UL)(408) 985-2400 x2353.

* This will be a presentation on Follow-Up Servicesby representatives from (we hope) Underwriters Labo-ratories, Canadian Standards Association and TÜV.

ORANGE COUNTY/SOUTHERN CALIFORNIA GROUP

* March Meeting - Date: Tuesday the 1st. Time 6:00pm. Location: QSC Audio, 1675 Macarthur Blvd.,Costa Mesa, CA. Program: "On Going Compliance- Safety & EMC" - Dan Modi of Compatible Electron-ics.

* April Meeting - Date: Tuesday the 5th. Program:"February CBEMA Meeting"- by Ercell Bryant ofCompatible Electronics.

* May Meeting - Date: Tuesday night the 3rd. Pro-gram: "ISO 9000 as applied to Product Safety, EMIand RFI" - by Gilbert Walter of Safety & ComplianceEng. For details contact Ercell Bryant Tel:(714) 589-0700

COLORADO GROUP

Andy Doering has been busy lately...he and his wife,Kim, welcomed their first child, Madeline Elizabeth,born on December 14.

Andy says there have been 2 meetings so far with atotal attendence of 32 people. As we go to press, athird meeting is scheduled to set the ground rules anddirection of the group. Meetings are on secondTuesday of the month. Contact Andy Doering(303) 449 4165 for more details. o


Mike DeMartiniContinued From page 5

In addition, he successfully managed Section B througha period of rapid growth, from 19 persons in April1981 to 49 persons in July 1985. He later managed theElectrical Department 313 and, most recently, Engi-neering Services Department 313.

Electrical Engineer Kevin Ravo was Mike’s traineewhen Kevin first joined UL 17 years ago, and the twohad been fast friends and close professional associatesever since. “Mike wouldn’t have wanted to have a bigfuss made over him. If he had wanted to be remem-bered for anything in particular, it would probablyhave been for his commitment and his vision, a visionof how much we could all accomplish working to-gether,” Kevin said.

“Everything he did supported that vision. He wasespecially adept at getting others to understand andshare his vision. He was a true leader, absolutelyrespected everyone and, in turn, was respected by all.”

“Mike lived life to the fullest and enjoyed being withfamily and friends, good food, good wine and playinggolf. At the time of his death, Kevin said, “he wasprobably at the happiest time in his life. He hadaccomplished what he set out to do. Perhaps, he wasjust ready to move on.”

Bob Miller, our OIC, remembers Mike “as a completeprofessional, a man of ideas and ideals and, mostimportantly, a thoroughly decent human being. “Hewas highly respected for his capabilities and character,and his patient willingness to lead, teach, and helpthose who depended on him for his support.

“All in all, he was a very good person who will bemissed by all who knew him well or just a little bit,”Bob stated. ❏

Ottawa, Ontario, Canada

UL IS OFFERING THE FOLLOWING COURSES IN 1994:The ISO 9000 Seminar (Cost: $ 795):Internal Auditing to ISO 9000 (Cost: $ 845)Preparing Quality Manuals & Procedures for ISO9000 (Cost: $ 795)Applying ISO 9001 to Software - Using the ISO9000-3 Guidelines (Cost: $ 375)For further information, please contact Joan Soslowitzat UL Melville (N.Y.), (516) 271-6200, ext. 22824.

Globalability: The Key to International Compliance(Cost: $ 995)UL 1950: Workshop on Information TechnologyEquipment (Cost: $895)Specifying Plastics for Electronic and ElectricalProducts (Cost: $ 895)For further information on the above, please contactBrenda Sorrenson at UL Northbrook (Ill) at(708) 272-8800, ext. 43481.

EMCS SYMPOSIUM MEETINGS 1994 - 2000August 22-26, 1994, Palmer House Hotel - Chicago,IL, contact Bob Hofman (708) 979-3627

August 21-25, 1995, Marriott Marquis Hotel -AtlantaGA, contact John Rohbaugh (404) 894-8235

August 19-23, 1996, Doubletree Hotel-Santa ClaraConvention Center, Santa Clara, CA, contact DavidHanttula (415) 335-1071

August 18-22, 1997, Austin Convention Center,Hyatt Hotel,Austin, TX, contact John Osburn(512)835-4684

News and NotesContinued From page 8


August 9-14, 1998, Radisson Hotel Denver, ContactTBD

August, 1999 (TBD)

August, 2000, Washington DC, contact Bill Duff(703) 914-8450from IEEE EMC Society Newsletter, Fall 1993

SECURITY TECHNOLOGY MEETING

The 28th annual IEEE International CarnahanConference on Security Technology is scheduled forOctober 10-12 1994 in Albuquerque NM, ContactDr.Estelle Zannes at 505-277-4422 or FAX 505 277-4206 for details.

FAX BIRTHDAY

December 6, was the birthday of Professor AdolpheFax the inventor of the Fax machine.

NAMEPLATES & LABELS

Appliance magazine December issue's "Buyers Guideto Decorative , Trim, and Nameplates" had an articleTitled "How to Select the Correct AgencyRecognization Rating & Nameplate Label", onpages BG2 to BGF-07.

ELECTRIC /MAGNETIC FIELDS

The December issue of Professional Safety has aarticle titled "Should Electric and Magnetic Fieldsbe Regulated ?" by Rob Thomas. This is brief overviewof the research and list the state laws applicable topower transmission and fields.

FORTHCOMING GENERAL MEETING OF IECThe list of IEC General Meeting for next severalyears are : 58th General Meeting Sept 3-17 1994Nice, France in conjunction with ISO GeneralAssembly 59th General Meeting October 16-281995 Durbin South Africa 60th General Meeting

Date Fall 1996 ( firm dates are TBD) in DresdenGermany 1997 several countries are consideringoffered invitation - 1) New Delhi, India 2) VancouverCanada in conjunction with ISO General Assemblyand 3) Japan.

TC PLENARY MEETING

74 (ITE ) September 12-16 1994 in Niece,TC 76 (laser) October 14-16 1994 in Kista Sweden

THE ROLE OF CSAAn article authored by John E. Kean President ofCSA appear in the ASTM Standardization NewsJanuary 1994 issue. This article reviews the historyand development of CSA and a looks at its future.

IEC LASER DOCUMENT

The 1993 revision to IEC 825 has been issued and isavailable ANSI for $199.00 plus shipping andhandling. This revision is a complete republicationof IEC 825. IEC 825 -1, "Safety of Laser Products- Part 1 Equipment Classification, Requirementsand User Guide". With the issuing of this document,IEC 825, "Electrical Safety of Laser Equipment andInstallation", has been withdrawn.

A major change is that LEDs are now considered aslaser with the same AEL. An new standard, IEC 825-2, Safety of Laser Products - Part 2: "Safety ofOptical Fiber Communication System" has alsobeen issued and is available from the same source asabove; US price is $59.00 plus shipping and handling.❏

EMC '94See Page 11


Institutional Listings

NCB Laboratory for Global Certification

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We are grateful for the assistance given by these firms and invite application for Institutional Listingsfrom other firms interested in the product safety field. An Institutional Listing recognizes contributionsto support publication of the Product Safety Newsletter of the IEEE EMC Society Product SafetyTechnical Committee. Please direct inquiries to:

Ervin Gomez at (408) 553-7684 (phone) or (408) 553-7694 (fax)-

YourListingHere?


BULK RATEU.S. POSTAGE PAIDCUPERTINO, CAPERMIT NO. 138

c/o Tandem Computers Incorporated10300 North Tantau Avenue, Loc 55-53Cupertino, CA 95014Attn: Roger Volgstadt

TheProductSafetyNewsletter

ADDRESS CORRECTION REQUESTED

As a free service to our readers, the Product Safety Newsletter willperiodically list Regulatory Compliance professionals who are availablefor employment. Those with employment opportunities are encouraged tocontact the following individuals directly.

Seeking employment as a Regulatory Engineer:

Employment Wanted

Wayne L. GloverTampa, Florida(813) 887 2534

Bogdan M. MatogaHollister, CA

(408) 636 8182

Naftali ShaniBrampton, Ontario

(905) 846 0930

What's Inside The Product Safety Newsletter - IEEE · Product Safety Newsletter •1 What's ... of San Anselmo and the late James DeMartini. He also leaves two sisters, Judith Morris

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