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Product Safety Newsletter •

What's InsideTheProductSafetyNewsletter

Vol. 8, No. 5 Nov. - Dec. 1995

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

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

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

Technically Speaking ................................ 4

Area Activities ........................................... 5

The Road to CE Marking ........................... 6

Upcoming Requirements for

Clearance and Creepage

Distance for IEC 950 ................................. 7

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

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

Chairman's Message

Tech Council UpdateMany of you have expressed interest in

another update on our proposed restructuringwithin the IEEE. To review, TC-8 has long had adesire to grow from a technical committee withinthe EMC Society to a Technical Council that willhave formal ties with several IEEE Societies. Ihad the opportunity to present our proposal to theIEEE Society Presidents Forum a few weeks ago.Here are my key points:

1. The lack of an adequate forum andprofessional association of product safety engi-neers is not being addressed in the engineeringcommunity as a whole. This deficiency exists inspite of the increase in product safety activityglobally, including:

- European Union and its product safetydirectives,

- International safety standards work atIEC (through ANSI for the U.S.A.),

- Intense product safety assessment andcertification activity in industry,

- Increased product safety activity withincertain industry groups, shown by accel-erated wholesale upgrading of standards(for example, semiconductor manufac-turing equipment industry).

Continued on Page 20


TheProductSafetyNewsletter

The Product Safety Newsletter is published bimonthly by the Product Safety Technical Committee of the Institute ofElectronic and Electrical Engineers EMC Society. No part of this newsletter may be reproduced without writtenpermission of the authors. All rights to the articles remain with the authors. Opinions expressed in this newsletter arethose of the authors and do not necessarily represent the opinions of the Technical Committee or its members. Indeed,there may be and often are substantial disagreements with some of the opinions expressed by the authors. Permissionto copy without fee all or part of any material without a copyright notice is granted provided that the copies are notmade or distributed for direct commercial advantage, and the title of the publication and its date appear on each copy.To copy material with a copyright notice requires specific permission. Please direct all inquiries or requests to IEEECopyrights office. Subscriptions are free and may be obtained by contacting Dave McChesney at 1865 Farndon Ave.,Los Altos, CA 94024

Chairman: Brian Claes Phone: (510) 659-6574Fax: (510) 659-6852

Vice Chair: Richard Pescatore Phone: (408) 447-6607 e-mail: [email protected]/ John McBain Phone: (408) 746-5016 e-mail: [email protected]: Fax: (408) 746-5551Symposium: Mark Montrose Phone: (408) 247-5715

Central Committee

Local GroupsChicagoChairman: John Allen Phone: (708) 238-0188Southern California/Orange CountyChair/Secretary: Charlie Bayhi Phone: (714) 367-0919Vice-Chair/Treas: Ercell Bryant Phone: (714) 589-0700PortlandChairman/ Scott Varner Phone: (503) 656-8841 e-mail: [email protected]/Treasuer: Scott VarnerSanta Clara ValleyChairman: Murlin Marks Phone: (408) 985-2400x2353 e-mail: [email protected] Chair/Program: Edward Karl Phone: (408) 986-7184Treasurer: Mark Montrose Phone: (408) 247-5715Secretary: Parviz Boozarpour Phone: (510) 527-7593SeattleChairman: Walt Hart Phone: (206) 356-5177 e-mail: [email protected] Chair: John Quigley Phone: (206) 226-1660Texas (Central)Chairman: Vic Baldwin Phone: (512) 990-6145Vice Chair Charlie GoertzSecretary/Treasurer: Daniece CarpenterColoradoChairman: Richard Georgerian Phone: (303) 417-7537 e-mail: [email protected]

Fax: (303) 417-7829

Editor: Roger Volgstadt Fax: (408) 285-2553 e-mail: [email protected] & Notes: John Rolleston Fax: (614) 438-4355 e-mail: [email protected] Editor: Kevin Ravo Fax: (408) 296-3256 e-mail: [email protected] Layout: Kristin Eckhardt Fax: (804) 560-5342 e-mail: [email protected]: Dave McChesney Fax: (408) 296-3256Institutional Listings: Ervin Gomez e-mail: [email protected]

Newsletter Committee


Letters to the Editor

Continued on page 9

Dear Editor,

Congratulations on another excellent issue(March-April, 1995) of the PSN. Best wishes fora fruitful process of “organizational affiliation”considerations. I trust there will be no tendency tomix the disciplines of product safety and those ofoccupational/plant safety. There have been somehigh level efforts in the past to combine the twoorganizationally, which in my opinion would leadto critical omissions/conflicts for product safety.

I enjoyed the edifying article by WernerPoster, page 7 and following. Your coverage ofthe international issue(s) can continue to be a mostvaluable service to your readers, as the variousdifferences in safety philosophy and legal/stan-dards issues among countries are harmonized.

Mr. Poster’s good article contains one ratherperplexing point under Risk Assessment, page 14.The concern is the basing of risk assessment/riskanaylsis on only probability and severity. Mostregulatory strategy/protocol and product liabilitydisciplines in the U.S. seem to necessitate the useof three distinct criteria for risk assessment that ispractical enough to be used and can stand thescrutiny of practitioners and the courts.

The three are frequency, vulnerability (as-sumption of risk), and severity. Each of theseneeds to be separately identified, analyzed, andquantified if the accident prevention-design pro-cess and product liability demands ofreasonabileness are to be satisfied. Safety perfor-mance and hazard analysis have traditionallyapplied the questions of only frequency and sever-ity and these were seriously flawed due to the

omission of “assump-tion-of-risk” consider-ations. Becauseawareness and avoid-ance are the bottom-line of accident pre-

vention, the courts have rightfully taught us thatthe criteria for determining unreasonable risk”must include the human behavior/human factorsdisciplines which drive assumption of risk/vulner-ability analysis. **

When the many elements of “frequency”(number of products in use, use environment ofthe product, how often and under what conditionsexposure to hazard occurs, etc.) are combinedwith the many elements of “Vulnerability” (be-low) under a single heading of “Probability,” theanalysis become so complex, time consuming,and indecisive that practitioners usually end up blue-skying/omitting so much as to make conclusionsquite indefensible in court. On the other hand, withthree numerically compatible scales for Frequency,Vulnerability and Severity, the quantification pro-cess is quite simple and usually leads to a defini-tive conclusion as to whether a hazard is reason-able or unreasonable.

Supportive experience and rationale for theabove are included in the materials of mine you sokindly chose to publish in past PSN’ s (Volume 3,Numbers 4 and 5; Volume 7, Numbers 1 and 6).

Experience in Europe with Deere and Com-pany (1967 -1982) helped me understand the howand why of significant differences in safety phi-losophy between the U.S. and Europe. I believe it


Continued on page 15

Technically Speaking

A colleague recently asked what the powerdistribution system designations “IT” and “TN”mean.

The “power distribution system” is all partsof an electric system between the “bulk powersource” and the consumer’s service-entrance equip-ment. For the purposes of this discussion, the“bulk power source” is the secondary of a powerdistribution transformer, where the output voltage is the utilization voltage, commonly taken as 100,120, 127,220,230, or 240 volts.

There are three basic power distributionsystems, TN, TT, and IT. Within the TN system,there are three variations, designated TN-S, TN-C, and TN-C-S. We will examine what thesedesignations mean, and how they affect safety ofthe system and of products connected to the sys-tem.

Also, we will define “polarization” as itapplies to the power distribution system and to thesafety of products.

And, we will discuss power distributionsystem grounding.

Here is what the letters mean:

T = terra (earth)N = neutral (the neutral conductor of the

power system)I = impedance (value not specified)C = combinedS = separate

Terra (or earth) means, literally, the body ofthe earth. For the purposes of this discussion, itmeans an electrical connection to the earth bymeans of a ground rod buried in the earth.

Neutral means the neutral conductor of thepower system. There are two definitions. Con-ventionally, the neutral conductor is the commonpoint of a three-phase, four-wire (“wye”) bulkpower source. This is the first definition.

In two of the three systems, TN and IT, theneutral conductor is connected to the earth bymeans of a ground rod. From this, we have asecond definition: the neutral conductor is the oneconnected to ground. This definition is importantbecause it is used to identify the neutral conductor

Power Systems and Polarization

Copyright 1995 by Richard Nutevoice: (34) 3-582-13-89; fax: (34) 3-582-25-15e-mail:[email protected]


Area Activities


Effective this issue, I will be taking over forJohn Reynolds for this column. I have to start byextending a note of thanks to John for all hiscontribution to the Area Activities column in thepast. I hope I can continue to provide informationand news of interest from the chapters around thecountry. I welcome any suggestions regardingcontent and format of the column. I will try to takeit as complete yet concise and timely as possible.

In addition to suggestions on content andformat, I would like to invite anyone to send in any‘activity’ information you think may be of interestto the readers of the Newsletter. In addition, I willbe contacting officers in the Local Groups to getinformation on a regular basis - basically makinga pest of myself!

Now, on with the Area Activities:(Note:some information dates back to Sep ’95)

September Meeting:This was an annual planning/dinner meeting

hosted by the Committee. Several items of interestwere discussed as follows:

Financial Report - There is a fund balance.Funds are generated through participation in eventssuch as the Colloquium, and meeting attendance.Ideas for how the funds could best be used weresolicited and should be forwarded to: MarkMontrose voice: 408-247-5715

Future Programs - Ideas for future programswere solicited and the Survey form should be usedto submit these ideas. If you need a form or wantto pass along an idea contact:

Ed Karlvoice: 408-563-7184e-mail: [email protected]

EMC Symposium - A call for papers for the1996 EMC Symposium was made by MarkMontrose.

PSTC Status with IEEE - Brian Claes gavean update on the status of the Committee. Heindicated that the Committee had the support ofthe EMC Society (from the highest levels). Therewill be more of a move under way to establish thePSTC as a “Working Group” a designation whichallows for operation with less restrictions. InOctober, a Task Force will be launched to evalu-ate the scope of and develop a charter for a “Safety

by Kevin RavoUnderwriters Laboratories

voice: (408) 985-2400 ext. 32311;fax: (408) 296-3256; e-mail: [email protected]

Santa Clara Product Safety


The Road to CE Marking


The following article was re-printed with permissionfrom the European Communitv Quarterlv Review(Vol. III, Issue 3, 3rd Quarter 1995), a publication ofTechnology International, Inc. Technology Interna-tional is the US. subsidiary of Interference Technol-ogy International, Ltd., a UK. appointed Competent

Body, and can be reached at (800) 242-8399.

In 1993, Abbott Diagnostics Division be-came aware of the product Directives coming outof the European Community with regard to prod-uct safety. In particular, we were interested in theElectromagnetic or EMC Directive. As a manu-facturer of In-Vitro Diagnostic equipment whoseproducts fall under the scope of the FDA chapter,ADD was accustomed to working in a regulatedenvironment. We had just completed certificationto the ISO 9001 standard. The conventional wis-dom at that time was that these new “CE Mark”Directives were just another piece of the ever-tightening regulatory landscape. After investigat-ing the requirements of the Directives and themethods that could be used to declare compliance,ADD chose to perform testing on it’s newestproduct in an attempt to be in compliance with theEMC Directive before product launch at the end ofthat year.

Looking back on that period of time when the“CE Mark” was just a phrase, we can assess themistakes that we made and come away with aclearer picture of how to comply with the EMC

Directive. During thatinitial certification, thetime, resources and theexpense of this task wasconsistently underes-timated by the projectengineers and pro-gram managers.Much know ledgewas gained thehard waythrough trialand error. ADD has come a long way since thattime, and we have managed to successfully obtaintechnical certification for a total of 4 of ourcurrent products. We expect work to be completedon an additional 14 products by the end of thisyear, in time to meet the 1996 deadline. We havesuccessfully implemented a Division proceduredetailing how to obtain the CE Marking for ourproducts, and integrated the maintenance of theCE Marking into our change procedure.

So how do you meet the compliance deadlinewithout the luxury of a 2 year learning curve?First of all, don’t panic! Although it can seemoverwhelming at first glance, a calm head andgood plan are all that are required to successfully)meet the requirements. First take a deep breath.Now, take the following steps:

by Ann Been, CE Mark Project Manager- Instrument Systems,Abbott Diagnostic Division, a Division of Abbott Laboratories


Upcoming Requirements for Clearance andCreepage Distances for IEC 950


Basic Safety publication, IEC 664-1 (1992),Insulation Coordination for Equipment WithinLow- Voltage Systems, Part 1: Principles, re-quirements and tests, was developed and pub-lished in 1992 by SC28A. According to IECGuide 104, all technical committees of IEC, shallalign the requirements of equipment standardswith those of the basic safety publications wherepossible. Working Group 6 of technical commit-tee TC-74 for IEC 950, has started to work onrevising sub-clauses 2.9 and 5.3 of IEC Publica-tion 950, Safety of information Technology Equip-ment. Sub-clause 2.9 deals with clearances, creep-age distances and distance through insulation whileSub-clause 5.3 deals with electric strength test-ing.

REQUIREMENT FOR CLEARANCES

Present requirements for clearances in IEC950 are based on a mixture of mains supplyvoltage, pollution degree and the applicable over-voltage category. These were based on previouspublications of SC28A namely IEC 664 (1980)and 664A (1981). SC28A has published 28A/-,OO/CDV, which will be later published as anamendment no. 1 to IEC 664-1. WG6 has lookeddeeply into IEC 664-1 and this upcoming amend-ment and determined that there were differencesbetween IEC 950 and IEC 664-1 and its would beamendment no. 1.

IEC 950, Table 3 gives three different clear-ances for 4000V peak impulse voltage and pollu-tion degree 2, as follows.

A. 3.2 mm for basic insulation witha mains voltage of up to150V r.m.s.

B. 3.2 mm for basic insulation up toa mains voltage of up to 300Vr.m.s.

C. 2.0 mm for operational insula-tion up to 150V r.m.s and 2.5 mmup to 300V r.m.s.

In item “C” above the value of 2.0 mm and2.5mm, are actually smaller than required byIEC 664-1, which is 3.0 mm and may result in aflashover.

Requirements for clearances in IEC 664-1are based on impulse withstand voltages. Accord-ing to the recent paper

28A/100/CDV of SC28A, it is now knownthat pollution has no effect on clearances. Previ-ous separation was not supported by the analysisof the available test data. Pollution definitely hasa worsening effect on creepage distances but noton clearances.

by Lal Bahra, P. Eng., UL Northbrookvoice: (708) 272-8800fax: (708) 272-2474


News and Notes


The following material comes from DaveEdmunds of Xerox who has graciously kept thePSN up to date on a variety of newsworthy items.

CDRH RECORD KEEPING

The Federal Register Dated 19 Septemberpages 48374 to 48387 amends the report andrecord keeping requirements for products coveredunder CDRH requirements. A majority of thechanges simplify or reduce the details required forreport and record keeping.

It is anticipated that some additional clarifi-cation and correction to this document will bepublished in the near future.

The products covered are the X -ray; Televi-sion Products; Microwave; Lasers; Sun Lamps;Mercury Vapor Lamps; Ultrasonics and Ultra-sound.

CDRH ISSUES @ LASER NOTICES(LASER #44, #45)

Laser Notice 44 is related to manufacturersof medical equipment that use a laser; wouldpermit manufacturers to supply information asrequired by ANSI Z136.l & Z1356.3 to be ac-ceptable to meet the requirements of 21 CHR140.10 10 (b) (1) (I).

Laser Notice 45 relates to CDRH acceptingthe labeling requirements as defined in IEC 825-2. There are differences between CDRH and IEC825-1 with regard to test, measurement, classifi-

cation, accessible limits, and numerical class des-ignation. CDRH has proposed that one label withboth CDRH and lEC 825 classifications be markedon the product.

The following material comes from M.A.Lamothe and Associates / Ultratech EngineeringLabs “Approvals Review,” Fall, 1995, Vol. 7,Number 4. Subscriptions are available by calling905-569-2550 or 905-877-2203.

REMINDER: SAFETY APPROVALSNEEDED IN MEXICO

All products must be tested in Mexico, evenif the application is processed through TUV orUL. Usually the test lab in Mexico will acceptmost of the testing done by approval houses suchas CSA, UL, and TUV, but it [testing] is theiroption.

You need to remember that the basic require-ments for Mexico are still the same - all productsentering Mexico must bear the NOM mark andNOM mark is issued only to companies resident inMexico. This means that you must work with youragent in Mexico since a company located outsideof Mexico can’t own the approval.

The new Mexican Electrical Code, which isbased on the US National Electrical Code, wasadopted on Oct. 15, 1994.


Letters to the Editor, Continued From page 3

is even more important now that each entityunderstand the other’s basis for its philosophy/strategy if harmonization of standards and freetrade are to be genuinely encouraged.

I would welcome an opportunity to ex-change thoughts with Mr. Poster if it could helpmove this vital process along.

Cordially,Keith Pfundstein

** Vulnerability can be described as: degreeof user/bystander susceptibility to injury whenexposed to a hazard; likelihood that personalinjury will occur once exposure to a hazard hasoccurred; detectability of a hazard, surprise ele-ment, risk assumption, presence of certain envi-ronmental or stress conditions, skills and attitudesof those exposed.

Our Author’s response:It was not my intention to write an article on

risk assessment but rather one on machinery safety.Therefore the short paragraph on risk as-

sessment was placed in my article to mention thislimited amounts of time to dedicate to regulatoryimportant topic because it is crucial for evaluatingthe risks originating from machinery.

However, it is certainly true that there aremore than the two factors to be taken into accountassessing risk and I like to refer to the standardprEN 1050: Safety of Machinery - Risk Assess-ment for a detailed and important tool for assess-ing risk. Paragraph 7 refers to the four factorsinfluencing risk as: severity, exposure, probabil-

ity of occurence and lack of possibilities of avoid-ance. I consider severity and exposure the impor-tant ones and not the only ones as mentioned in Mr.Pfundstein’s letter. The above mentioned standardtogether with other applicable EN standards isused by European experts in reducing risks duringdesign, construction and modification of machin-ery within the scope of the machinery directive.

Sincerely,Werner W. Paster

Kudos to Technically Speaking

Dear Editor,

I want to thank you [Rich Nute] for theTECHNICALLY SPEAKING articles you write.I have been reading them for the last few years.Your column is the first (and usually the only) partof the Newsletter I read.

I appreciate the logical straight forwardapproach you make in your presentations. It isalways fact based and there are no leaps in logic.I have not found this kind of rationale in any kindsafety of Safety related literature.

For circuit designers like myself, who havelimited amounts of time to dedicate to regulatoryissues, the column serves as an important teacher.

You are to be commended....and please keepup the good work!

Dennis Carter ��


Continued

Clearance and Creepage Distance,

Continued From page 7

Also, the name “pollution degree (PD)” isproposed to be replaced by “Micro EnvironmentalCategory (MEC)” and the term “Operational in-sulation” is proposed to be replaced by a newname “Functional Insulation”. The four columnsin table 2 of IEC 664-1 for pollution degrees 1 to4, are proposed to be replaced by a single columnsignifying that pollution degree does not changethe clearance.

The above document has received favorableapproach from National Committees and will besent out as a final draft international standard(FDIS) in the near future. Table 1 of IEC 664-1gives maximum peak value of the transient ex-pected to appear on the mains supply as seen bythe equipment. Table 2 of IEC 664-1 has clear-ance requirements for both inhomogeneous andhomogenous fields.

WG6 of TC74 of IEC 950 proposes thefollowing:

a) IEC 664-1, Table 2 clearances forinhomogeneous fields for functional in-sulation (formerly operational insulation).

b) IEC 664-1, Table 2 clearances forinhomogeneous fields with an approx.33 percent safety margin, for basic andsupplementary insulations and with nomargin for functional insulation takinginto account Table 1 of IEC 664-1 formaximum peak transient voltages associ-ated with the nominal voltage supplysystems according to IEC 38.

c) A single table for clearances for allinsulations (Which will replace presentTables 3, 4 and 5 of IEC 950).

d) Table 2 of IEC 664-1 for clearances,the manufacturer has an acceptable qual-ity control system i.e., with an acceptablequality control system in place, a 1.5 mmclearance instead of 2 mm for basic orsupplementary insulation for 2500V peakmains transients, will still be permitted.

With this new thinking, clearances will bebased on the maximum value of the peak impulsevoltage, which it can withstand. A single table willreplace the present Tables 3, 4 and 5. The sametable will be applicable to both primary andsecondary circuits. Internally generated transientsof a repetitive nature, will also be handled by thesame table.

Table 1 of IEC 664-1 gives a maximumtransient rating of 1500V peak for voltage sys-tems up to 150V r.m.s. and 2500V peak forvoltage systems up to 300V r.m.s. for overvoltageCategory II, which is the assumed overvoltagecategory for IT equipment. IEC 950 has adoptedthese two overvoltage categories from IEC 664-1

There are two types of voltages generatedwithin the IT equipment as follows:

Case A:If the peak value of d.c. or r.m.s. voltages orimpulse type voltages of a repetitive nature, gen-erated in the equipment, does not exceed the peakvalue of the main suppl y voltage, then a clearancewill see a voltage not exceeding the maximumtransient rating of the mains supply voltage sys-tem, i.e., the clearance does not have to be morethan required for the maximum transient rating ofthe mains supply voltage.



CaseB:Of the peak value of a d.c. or r.m.s. voltage orimpulse type voltage of a repetitive nature, gener-ated in the equipment, exceeds the peak value ofthe mains supply voltage, then a clearance may seea voltage which may exceed the maximum tran-sient rating of the system. The maximum peak’voltage which the clearance will experience, cancalculated as follows:

Maximum working peak voltage =Maximum transient rating of the mainssupply system + peak value of inter-nally generated voltage - peak value ofthe mains supply voltage.

ELECTRIC STRENGTH FORCLEARANCES

After the maximum peak voltage which aclearance should be designed for, has been deter-mined, then the clearance can be verified byapplying an impulse voltage test. This test will becontained in another table which will complement(Copenhagen decision to have alternate test per-mitted) the present Table 18 of IEC 950. Therequired impulse voltage for verification of clear-ances will be approximately 1.06 to 1.25 timeshigher than the maximum peak voltage for whicha clearance should be designed. For example,equipment connected to 125V mains supply sys-tem having no internal voltage higher than 212V

FIG. 1: Maximum peak voltage for determining aclearance, when internally generate volt-ages will not exceed the maximum tran-sient rating of the mains supply system.

FIG 2: Maximum peak voltage for determininga clearance, when internally generated voltages exceed the transient rating of the mains supplysystem.

FIG. 1: FIG. 2:


Area Activities, Continued From page 5

Continued

Society”. Any comments or questions may bedirected to: Brian Claes

voice: 510-659-6574fax: 510-659-6852

October Meeting:This meeting was the first formal meeting of

the new season. Attendees were encouraged to joinIEEE to take advantage of the many benefits ofmembership.

Articles for the Product Safety Newsletterwere solicited.

Mr. Jean-Pierre Wolff gave a very enter-taining presentation on electrical safety. Varioustopics covered included Safety Engineering, SafetyEssentials, Types of Safety Hazards and a “Cookthe Hot Dog via Electrocution” demonstration.For more information, please contact: Jean-PierreWolff

Electro Test, Inc.voice: (510) 824-0330fax: (510) 824-0333

November Meeting:This meeting included Gene Panger, TUV

PS, as the main speaker. Gene discussed the CEMarking, particularly in relation to the EMCDirective.

For more information, contact:Gene PangerTUV PSvoice: (612) 631-2487fax: (612) 631-3515

Future Activities:December 12. 1995: Joint meeting with

EMC Society, Test Methodolody for EMC Direc-tive.

January 23. 1996: Philosophy of Meetingthe Low Voltage Directive from a Manufacturer’sStandpoint, Dave Adams, Hewlett Packard.

No activity in this area for some time now.There is a need to get some interested members inand active to pick up the ball. Anyone interested,please contact: Scott Varner

voice: 360-817-5500 (ext. 55613)fax: 360-817-6000e-mail: [email protected]

September - No meeting

October - Presentation by Bob Hunter.

For more information of future activitiescontact: Vic Baldwin

voice: 512-990-6145

September Meeting:Presentation - Jeff Gray discussed theMachinery Directive.

Announcements- The new Bi-National Stan-dard, UL 1950/CSA Third Edition is now beingdistributed. ECMA has published the latest edi-tion of the Alphabetical Index for IEC 950. Itincludes Amendments 1,2 and 3. The documentTR/63 (2nd edition) is available free of chargeYou can obtain the document by contacting ECMAat: ECMA

voice: 41 22849.60.00fax: 41 22786.52.31

Northeast Area

Texas Area

Southern California Area


It can also be downloaded from file T063-DOC.EXE or file T063-PSC.EXE fromECMANEWS.

UL has published it’s Practical ApplicationGuidelines for UL 1950. The Guidelines are avail-able for $100 ($80 for Subscribers of UL’s Stan-dards Subscription Service) and will soon beavailable on UL’s 1950 Electronic Bulletin BoardSystem.

Elections - Charlie Bayhi was re-elected asChairman/Secretary and Ercell Bryant was re-elected as Vice Chairman / Treasurer.

October Meeting: Round table discussionregarding product safety.

November/December Meeting: Re-organi-zation discussions to enlist help of new membersand generate some enthusiasm.

For more info contact:Charlie BayhiVoice: 714-367-0919

John Allen of the Chicago Area needshelp getting a local Chapter started. Anyone interestedin helping John or just getting together to shareinformation should contact:

John AllenVoice: 708-238-0188

September Meeting:The meeting was hosted by Dave Pedersen of

the UL Local Engineering Services Office inBoulder, CO.

The guest speaker at the meeting was GregRocha, Engineering Team Leader form UL’s SantaCla ra Office. Greg discussed the Bulletin Board

System (BBS) that was being developed for UL1950. The topics covered included:

1. History of developing the BBS2. Content of the BBS3. Service levels of the BBS4. Annual fees for the BBS5. Other features such as e-mail, chat, pag-

ing, announcements. Greg also gave a brief dem-onstration of the BBS which was quite impressive.

October Meeting:The meeting was hosted by Mark

Hassebrock, Agency Administrator for Data RayCorporation. The main topic was CE Markingrequirements, Declaration of Conformity for com-plex components and system level devices. Dec-larations of Conformity were shared and dis-cussed and it was a lively meeting.

November Meeting:Richard Georgerian and Kent Shown, Com-

pliance Engineers at Exabyte in Boulder were thehosts for the meeting.

This was the last ‘business’ meeting of theyear. Richard Georgerian was elected to serve aschairperson for another year and Dave Pedersonof Underwriters Laboratories was elected to beactivities leader. Ideas for next year are tours ofnearby facilities, bi-monthly meetings and morevaried topics for discussion.

For more information, contactRichard Georgerianvoice: 303-417-7537fax: 303-417-7829e- mail:[email protected]

That’s it for this issue. Remember to send inyour comments and Area information!

Best RegardsKevin Ravo � � � � �

Chicago Area

Colorado Area


The Product Safety Newsletter is looking forvolunteers for the following:

AdministrativeAssistance

NewsletterLayout

News & NotesColumn

If interested contact Roger Volgstadt, Editor, at(408) 285-2540.

** HELP WANTED **URGENT

Clearance and Creepage Distance,

Continued From page 11

peak, will be required to withstand an impulse test voltage of 1750V peak instead of the maxi-mum 1414 V peak or d.c., required at the present.;ame way equipment connected to 250V mainssupply system having no internal voltage higherthan 424V peak, will be required to withstand animpulse voltage of 2959V peak instead of 2121 Vpeak or d.c. required at the present. These higherpeak values may be taken care of when designingclearances in the equipment. But components usedn the IT equipment are not evaluated to thesehigher peak voltages, and might pose a problem.[hey may not be able to withstand these highervoltages as they are designed to the present re-quirements. There is no major move ahead tochange requirements for component standards towithstand higher electric strength voltages. There-fore the present electric strength test as given inEC 950, 2nd Edition will still be permitted as analternative.

As proposed, there are five choices given forconducting the electric strength test as follows:

a) 10 impulses of alternatingpolarity using l.2/50 s im-pulses;

b) 10 impulses of alternatingpolarity using 10 ms d.c.impulses;

c) An a.c. r.m.s. voltage test but fora minimum of 5 cycles only;

d) A d.c. voltage test for aduration of 60 seconds.

The above four use a higher peak value whenconducting the test.

e) Present electric strength test withvoltage values as given in 5.3 of lEC 950,2nd Edition is an alternative to “a”, “b”,“c” and “d” above.

CREEPAGE DISTANCES

Creepage distances Table 6 of present IEC950, 2nd Edition, is proposed to be kept the same.However, for MEC 1, the table will refer to theclearances table which has been modified. There-fore, creepage distances will change for MEC 1only.

In the document no. 28A/1 OO/CDV SC28Ais also proposing lower creepage distances thanpresently required. When accepted, WG6 mayintroduce these lower creepage distances to IEC950 in the near future. ��


Continued

for three-phase, three-wire (“delta”) and single-phase, two-wire distribution systems where thereis no common point. (The USA National Electri-cal Code uses the term “grounded conductor”rather than neutral conductor.)

(In the National Electrical Code, thegroundED conductor is also designated as the“identified” conductor. The neutral conductor is“identified” by means of insulation color. In theUSA and Canada, the color is white. In Europe,the color is blue.)

Impedance means an impedance is connectedin series between the neutral conductor and theground rod. I have heard that the value of thisimpedance is from 1000 to 10000 ohms.

Combined means that the function of twoconductors is performed by (combined into) oneconductor.

Separate means that the function of twoconductors is performed (separately) by each ofthe two conductors.

The power system designations use twoletters, TN, TT, and IT. The first letter indicatesthe means of grounding of the neutral conductor.The second letter indicates the means of ground-ing of the protective conductor.

Now we can define the three major powerdistribution systems:

TN: The TN system has its neutral con-nected to a ground rod, and has its protectiveconductor connected to the neutral.

The TN system is the predominant system inthe USA and Canada.

The advantage of the TN system is a verylow impedance between the protective conductorand the neutral conductor, thus assuring operationof the overcurrent device.

The disadvantage of the TN system is that at,

the point of a ground fault, there is a voltage dropacross the protective conductor. This raises thepotential of accessible grounded parts with re-spect to the earth, which could result in a shock.

A disadvantage with the USA TN system isthat the neutral is grounded at two or more places,one being at the bulk power source and the otherat the service entrance. This means that the earthis in parallel with the neutral, and that some of theneutral current will flow in the earth.

In turn, signal grounds between buildings(or even between parts of buildings) can also carrypart of the neutral current (which has accountedfor fires in some products).

TT: The TT system has its neutral con-nected to a ground rod, and has its protectiveconductor connected to its own, separate groundrod.

The TT system is the predominant system inthe U.K.

The advantage of the TT system is that itovercomes the disadvantage of the TN system.Because the protective conductor has its own,separate earthing, accessible grounded parts ofthe system are always at earth potential, even inthe event of a fault.

The disadvantage of the TT system is thatthe impedance between the protective conductorand the neutral conductor is not necessarily low,thus compromising operation of the overcurrentdevice.

IT: The IT system has its neutral connectedto an impedance which is connected to ground, andhas its protective conductor connected to its own,separate ground rod. (The impedance is 1000ohms or greater.)

The IT system is the predominant system inFrance and Norway and other countries. It is also

Technically Speaking, Continued From Page4


Continued

One advantage of the IT system is that it over-comes the disadvantage of the TN system. Be-cause the protective conductor has its own, sepa-rate earthing, accessible grounded parts of thesystem are always at earth potential, even in theevent of a fault.

Another advantage of the IT system is that inthe event of an earth fault, the system intentionallyremains operational, i.e., the overcurrent devicedoes not operate until the second earth fault.

(Often, the system employs an earth-faultmonitor such that an alarm is activiated when anearth-fault occurs and corrective action can betaken.)

The disadvantage of the IT system is that,when an earth-fault occurs, the voltages withrespect to earth change. For example, consider thevarious voltages with respect to ground in a threephase distribution system having 220 volts phase-to-neutral and 380 volts phase-to-phase:

Phase Normal Earth-faultconditions conditions

N - Ground 0 volts 220 voltsA - Ground 220 0 (fault to earth)B - Ground 220 380C - Ground 220 380A - N 220 220B - N 220 220C - N 220 220A. - B 380 380A. - C 380 380B - C 380 380

where N, A, B, and C are Neutral, Phase A,phase B, and Phase C, respectively.

(Note that the phase-to-neutral and phase-to-phase voltages do not change. Since all equip-ment is connected either phase-to-neutral or phase

to-phase, all equipment continues to operate nor-mally even though the system has a ground fault.)

Let’s now look at the variations of the TNsystem.

TN-S: The TN-S system has separate neu-tral and protective conductors throughout thesystem.

This is the normal system in the USA andCanada.

TN-C: The TN-C system has combinedneutral and protective conductors throughout thesystem.

TN-C-S: The TN-C-S system has part ofthe system with combined neutral and protectiveconductors and part of the system with separateneutral and protective conductors.

This is normal for USA households whereplug-and-socket connected dryers and ranges havethe neutral connected directly to the frame of thedryer or range.

Note that, no matter the system, TN, TT, orIT, the scheme of grounding the neutral largelyhas no impact on the design of the product.

Some authorities do tend to be concernedabout the voltage rating of mains-to-ground-con-nected components where the equipment is in-tended to be connected to an IT system. They areconcerned about those components being sub-jected to the higher phase-to-ground voltageoccuring during a system ground fault.

Some authorities also tend to be concernedabout the magnitude of leakage current where theequipment is intended to be connected to an ITsystem. Again, they are concerned about thehigher phase-to-ground voltage occuring during asystem ground fault.

Some authorites tend to be concerned aboutthe electric strength and hi-pot test voltage of themains circuits where the equipment is intended to


be connected to an IT system. Note, however, thatI the magnitude of transient over-voltages does notnecessarily change due to a phase-to-ground fault.

Let’s now turn to polarization. For thepurposes of this discussion, polarization is theidentification of one or more terminals of a supplysystem, whether the neutral terminal or a phaseterminal. As we have seen, all the conductors of apower distribution system are identified.

For the most part, the neutral conductor —even though it is usually grounded — is treated asif it were a phase conductor.

As mentioned, the TN-C system combinesthe neutral conductor with the protective conduc-tor. In TN-C systems and equipment, it is essentialfor safety that polarization be observed, i.e.,that the neutral in the equipment be connected tothe neutral in the supply system. Consider thehome electric dryer which has its metal enclosureconnected to the neutral terminal of the supplycord. For prevention of electric shock, it isimperative that the dryer neutral only be con-nected to the supply neutral. Polarity must beobserved.

In the USA, lamps employing Edison-basesockets are required to be provided with a polar-ized plug. The neutral terminal of the plug isconnected to the screwshell of the socket. Thismeans that the screwshell, being accessible, is atground potential. This improves the safety of theEdison-base socket.

Polarization can be used to improve thesafety of equipment where both poles of the supplyare not treated equally.

Polarization via socket outlets is not consis-tent in various power distribution systems. In theUS and Canada, polarization is maintained in the120- volt, IS-amp outlets by one blade being widerthan the other. The wider blade is the neutral

conductor. (Note that the grounding terminal doesnot provide the polarization.)

In the U.K., polarization is maintained in the13-amp socket -outlet by the three L, N, and Eblade postions. The wiring is indicated by mark-ings on the plug. Note that two-wire plugs requirea dummy grounding terminal for both polarizationand for activating the shutters in the socket-outlet.

In Australia and New Zealand, polarizationis maintained by the angled blade orientation. Thewiring is indicated by markings on the plug.

Polarization is not maintained by the Euro-pean Schuko, French, Danish, and Swiss socketoutlets. Note that the French, Danish, and Swissplugs can only be inserted one way. But, polarityof the wiring to the socket-outlet is not maintained.

Be careful not to assume that just because aplug can only be installed one way in a socket-outlet that it is polarized.

ACKNOWLEDGEMENTS

Ron Wellman of HP Corporate ProductRegulations suggested this topic.

The TN, TT, and IT systems are defined inIEC 364 and repeated in IEC 950.

For more information on neutral grounding,see the Standard Handbook for Electrical Engi-neers, Donald G. Fink and H. Wayne Berry,Editors. Published by McGraw-Hill Book Com-pany. ISBN 0-07-020975-8. ��

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The Road to CE Marking,Continued From page 6

Do your research. Read the actualEMC Directive. If you don’t have a copy

of the Directive - get one. Make a list of questionsand/or concerns. There are many resources avail-able to you. The U.S. Department of Commerce isa source of information and there are many con-sultants and Competent Bodies to utilize. If youare in a government regulated industry, talk withthe agency that works with your product.

Interview enough consultants.Competent Bodies and test labs until

you feel comfortable about what the real require-ments of the Directive are. Remember, the betteryou understand the requirements, the less chanceyou have of making costly mistakes. Learn tocommunicate with the people in your companythat are responsible for the funding of the activity.Help them understand what the requirements are,and why the work is critical. Make sure you haveenough money and technical resources to do thejob right. It will be much easier to hand back themoney in December than to miss the deadline dueto lack of dollars or resources.

Understand the different routes tocompliance for EMC. If you have more

than one product, sort them by which method ofcompliance you are going to employ. Some of thequestions you should consider as you use the“standards” route or the “Technical ConstructionFile” route are:

1. Does the product exist in more than oneversion?

2. Are modifications to the products likely?3. Are there existing test results?

4. Will the products be hard to test due tophysical size or intended use?

5. Is the life-cycle of the productgreater than 5 years?

6. Is the product technically complicated?Does it mix several technologies or havedifferent applications?

If the answer to any of these questions is yes,it makes good sense to employ the TechnicalConstruction File route to compliance.

If the answer to these questions is no, and youfeel confident that the product will meet the stan-dards, it may be appropriate to use the Standardsroute.

Choose and establish a good work-ing relationship with a European Com-

petent Body. With the deadline looming nearer,this decision could be critical to your success.Make sure you are comfortable with the company.Clearly document what role they will play, andwhat you expect from them.

Make a list of products that you aredealing with. Prioritize them in order of

importance. Maybe the priority is based on pro-jected sales volume for 1996 in the EU. Maybe itis based on a critical customer account in Europe.However it is decided, make sure that everyone inthe management team understands what the orderis and why it was set up that way.

Draft a process flow chart for thecompliance work. What is the acceptance

criteria that will be used to determine if yourcompany is ready to declare compliance and applythe CE Marking?

Continued


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HELP WANTED!!The Product Safety Newsletter

Committee is looking forsomeone interested in writing

the News & Notes column.If interested contact

Roger Volgstadt, Editor,at (408) 285-2540.

How will your company incorporate productchanges if they are required? Do you have a goodclosed loop engineering change process to ensureon-going compliance and maintenance of the CEMarking? Create a document that outlines theprocedure that will be used to declare complianceto the Directive. Identify your company’s signa-tory for the Declaration of Compliance. Ensurethat the signatory understands the process andtheir liability. Review your process with the Com-petent Body. Ensure that the process meets therequirements.

Gather all customer literature andproduct documentation. This should in-

clude the Operations Manual, any technical speci-fications and descriptions of the equipment andit’s operating environment. If the previous testinghas been done, obtain the test reports.

Meet with the Competent Body.Ask them to review your list and ratio-

nale for the routes you have chosen. Review thetechnical documentation and product manuals.Discuss which products will require testing, whichcan declare compliance based on previous testing,and other information unique to the product. De-tail a plan and time line. Set the milestones, andthen meet them.

Do the work. Arrange the test timeas required and assess the products’ abil-

ity to comply to the standards without modifica-tion. If you identify products that pass the stan-dards, use the test information as a basis for claimto compliance. If you are using the TCF route,document the test results, complete the TechnicalConstruction File and have it assessed. If you areusing the standards route, compile a Technical

File including the standards applied and test de-tails. If your product requires modification, con-sult with the Competent Body and the chosen testlab. Use their expertise to help determine theminimum amount of modification to meet therequirements. Determine if you need to rethinkyour method of compliance.

If extensive modification is re-quired. reassess your priority list. If you

spend the resources required on this product, itwill mean not meeting the deadline on other prod-ucts. Ensure that the management team under-stands the impact of their decisions.

When the Technical Certificate isissued. draft the Declaration. Remem-

ber, the Declaration is the legal document requiredto claim compliance. When the Declaration issigned, link the CE Marking label to the product.

There, you’re finished, or at least you havebegun. With the 1996 deadline drawing close, it’simperative that you begin as soon as possible. Atthis late date, there is no guarantee that you willmeet the deadline. But is you start now, you willbe 5 months closer by December! ��


Chairman's MessageContinued From page 1

2. Within the IEEE, there are small pock-ets of product safety focus:

- Our organization in the EMC Society(TC-8)

- CPMT Society (shown by theirTechnical Interest Profile item)

- Social Implications of TechnologySociety (electrical safety technicalcommittee)

- TAB’s Environment, Health andSafety Committee

However, taken as a whole, we believe theIEEE is overlooking this segment of engineering.

3. The EMC Society’s TC-8 began as agroup of product safety engineers in the SantaClara Valley in the mid-80’s. Many of the originalgroup were also members of the IEEE and EMCSociety and were active in both product safety andEMC engineering. Within a year or so, member-ship had increased enough that 200 of us plannedto petition the IEEE for Society status. We weretold there already were too many Societies andthat we were too inexperienced and few in num-ber. However, it was suggested that we could jointhe IEEE as a Technical Committee of one Soci-ety, grow to a Technical Council supported byseveral Societies, and eventually petition for So-ciety sta-tus. So about 8 years ago, we joined theEMC Society as TC-8, or the Product SafetyTechnical Committee.

4. Some of TC-8 s activities include:- sponsoring Workshops and technical

paper reviews at International Symposia,- publishing the Product Safety

Newsletter, which regularly containstechnical articles in addition to reportson developments in areas of interest.(We have published the newslettersince our inception. Circulation hasexceeded 1000 for several years andpresently is about 1300.),

- sponsoring local area groups and theirregular meetings which include techni-cal presentations, done in conjunctionwith local EMC Society chapters.

5. In conclusion, we believe the IEEE needsto provide a better focus for product safety,because:

- Thousands, perhaps tens of thousands,of engineers are involved in productsafety work world-wide, but there is nofocus for coordinated activitywithin the IEEE.

- Outside the IEEE there is no otherorganization that meets the productsafety engineer’s professional needsand interests. Professional organiza-tions such as System Safety Society,ASSE, Semiconductor Safety Associa-tion at best occasionally addressproduct safety issues and then fre-quently only tangentially.

- There are several other IEEE Societiesbesides the EMC Society interested inthe safety of electrical and electronic

Continued


News & NotesContinued From page 8

products. We have already receivedinquiries from another Societywhose product safety interests arenot being adequately met (CPMT).A Technical Council will serve as afocal point for interested groups withinIEEE Societies.

- TC-8 is presently the largest groupfor product safety in the IEEE and we want to continue to expand ourpresent activities. We would like tobe an IEEE Society, but we’re not ready.We believe a Product Safety TechnicalCouncil will increase visibility forproduct safety and attract members.

Our next step is to approach the Societies toassess their level of interest. At the President’sForum, I was approached by the leaders of twosocieties who expressed keen interest in such anassociation. In a more formal vein, I will send allthe presidents a letter outlining the proposal toform a Product Safety Technical Council.

The most aggressive timetable for accom-plishing this goal is 12 to 15 months.

In the meantime, we are continuing ourcooperation with the IEEE TAB EHS Committeewhich also is assessing its future growth plans.Those of you who are members of other IEEESocieties that have product safety related inter-ests, please share this proposal with your leader-ship. We will continue to keep you posted on ourprogress.

Brian ClaesPhone: (510)572-6574Fax: (510)572-8260E-mail: [email protected] � � � � �

WORK ON MRA’S

From the ITI “Washington Letter,” dated Nov.17,1995, it is noted that a meeting between US andEuropean CED’ s at the Transatlantic Business Dia-logue in Seville discussed adoption of the principleof “tested once, accepted everywhere” throughMutual Recognition Agreements for telecom andITE by January 1, 1997. Acceptance of this objec-tive will hinge on a Dec. 3rd meeting betweenPresident Clinton, the European Commission Presi-dent Santer and European Union Prime MinisterGonalez in Madrid.

The following material comes from ArtMichael, Editor, Int’l Product Safety News([email protected]).

SAFETY LINK IS ONLINE!

The Safety Link (http://www.safetylink.com)serves as a jumping-off point for those interested inproduct safety compliance and related topics. Due tothe comprehensive set of links found here, it is likelythat this is the only “product safety link” you willneed.

Links to many worldwide product safety re-sources are included as well as one to “InternationalProduct Safety News” (the sponsor of the site).

Product safety professionals can easily accessthe test labs & safety agencies, standards bodies,government resources including the FCC, OSHAand NIST as well as links to related areas of exper-tise such as EMC, Ergonomics, Quality, Telecom,Newsgroup, and the Northeast Product Safety Soci-ety.

In addition, a number of useful Internet tools,resources, and indices are included to ease the entryof product safety professionals new to the Internet.

The URL is: http://www.safetylink.com ��


Institutional Listings


We are grateful for the assistance given by these firms and invite application for Institutional Listings

from other firms interested in the product safety field. An Institutional Listing recognizes contributions

to support publication of the Product Safety Newsletter of the IEEE EMC Society Product Safety

Technical Committee. Please direct inquiries to:

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

Give us a call andGive us a call andGive us a call andGive us a call andGive us a call andplace your listingplace your listingplace your listingplace your listingplace your listing

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

TheProductSafetyNewsletter

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