Product Safety Newsletter 88V01N6 -...

Product Safety Society Newsletter July, 1988

THE PRODUCT SAFETY SOCIETY NEWSLETTER

ASK DOCTOR Z by DOCTOR Z

The Product Safety Society Newsletter is published monthly by the Santa Clara Valley Chapter of theProduct Safety Society. No part of this Newsletter may be reproduced without written permission of theauthors. All rights to the articles remain with the authors. Opinions expressed in this Newsletter arethose of the author and do not necessarily represent the opinions of the Society or its members. Com-ments and questions about the Newsletter may be addressed to Product Safety Society Newsletter, c/oTandem Computers, Atten-tion: Roger Volgstadt, 2550 Walsh Ave., Santa Clara, CA 95051-1392.

This Newsletter is prepared on Qume Corporation's PageLINK Controller and LaserTEN Plus printer.The editor wishes to ex-tend a special thanks to Mr. Hugh Hagel of Qume Corporation and Ms. JaneBenner of Underwriters Laboratories for their efforts in the preparing this Newsletter.

Letters to the Editor

CHAPTER ACTIVITY REPORTS

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CHAIRMAN'S MESSAGEby RICHARD PESCATORE

July, 1988 Vol 1, No. 6

TECHNICALLY SPEAKINGby RICH NUTE


by RICHARD PESCATORECHAIRMAN'S MESSAGE

As our targeted time to formally petition the IEEE for affiliation approaches, yourofficers are taking a close look at the ramifications. We have discussed in pastNewsletters several of the benefits we hope to realize. One question now comes tomind: What will the IEEE expect of the Product Safety Society?

We are investigating specific expectations held by the IEEE, but we have a generalanswer to this question: Some folks will have to commit their personal time to carryout the expected functions of an IEEE Society. These functions include runningChapters, editing publications, organizing conferences, and participating in IEEE ac-tivities and administration. With our present relatively small membership base com-pared to other IEEE Societies (hundreds of people rather than thousands), to im-mediately participate in all these activities may prove difficult.

Our most important goal is to maintain our group focus on Product Safety. Maintain-ing this focus is absolutely essential! We have been exploring options for affiliationwith the IEEE that can achieve this goal and may be more appropriate right now thanfull Society status. The most promising scenario seems to be to continue our quest fursanction as an IEEE member Society, but to make it a long term project (2 to 3 years).We recommend, as an interim step, applying to the IEEE to form a Technical Councilwith existing IEEE Societies.

A Technical Council exists in the IEEE to provide “a continuing mechanism for twoor more IEEE Societies to work together in a multidisciplinary technical area of mu-tual interest”. Both the EMC Society and the CHMT Society have expressed interestin working with our group, and other Societies may also be interested in ProductSafety. As a Technical Council, we would operate at the national level as a separatetechnical entity focusing on Product Safety. Council members from the sponsoringSocieties would provide liaison and guidance. At the local level, we would operate asindependent Chapters of the Technical Council within the various geographical IEEESections. As our membership grows, we should be in a good position to make a smoothtransition to a full-f1edged IEEE Society.

Another interim arrangement worth considering is to join the IEEE as a TechnicalCommittee of just one Society. Setting up both national and local Technical Commit-tees focusing on Product Safety can be done unilaterally within a Society, while start-ing a Technical Council requires more co-ordination between Societies and the ap-roval of the IEEE Technical Activities Board. We will be meeting with the EMCSociety Board of Directors on August lst to discuss both these possibilities.


We present this recommendation to elicit your thoughts on the subject. Please send yourcomments to me by the end of July.

Richard PescatoreHewlett Packard (M/S 42LS)

19447 Pruneridge AvenueCupertino, CA 95014(Fax: 408-257-5034)

And please continue to send in your signed petitions and membership questionaires.

Richard PescatoreChairman

Chairman's Message, Continued


TECHNICALLY SPEAKING by RICHARD NUTE

“Energy Hazard”

A History and Analysis

Hello from Vancouver, Washington, USA

Bob Lundin, through Al Brazauski, was able tofind the origins of the so-called “energy” ha-zard in UL 478. Here is a review of the origins.

History

The material dates back to a manufacturer’s(identity withheld) Corporate Standard forProduct Safety, dated February, 1962. Withinthis standard is a section titled “Effects ofElectrical Current on the Human Body”.Within this section, the following appears:

“Burn Hazards. Circuits with sufficientenergy to cause arcing when short- cir-cuited can be a potential burn hazard or asource of ignition. High energy dischargescan cause an intense arc with erosion andsplattering of the metal at the point ofcontact.

“The amount of energy required to createa hazard of this type is a function of thetype of metal. its shape. its heat sink massand the way contact is made. Since somay factors are involved. it is not practi-cal to establish a specific energy levelthat de-fines this level. However. anycircuit capa-ble of supplying 240 volt-amperes without operating overcurrentdevices should be considered a potentialburn hazard:’

In the “Electrical Design” section of the stan-dard, we find:

"Customer access areas must not have ex-posed . . . potentials below 30 volts thatcan supply more than 240 volt-amperes."

Without addressing the documents dated 1962until 1966, we finally find the following UL 478meeting report dated October 14, 1966:

“Burn Hazard -Where high current isavailable at potentials down to about 2volts, enough energy is present to meltand splatter metal from neck chains, eye-glassframes, watchbands, bracelets, rings, andother personal metal objects unintentionallyput across hot bus or between such a busand ground by operators or servicemen,thereby giving rise to severe burn hazard.One of the industry representatives re-ported that his company reduces this ha-seared by limiting the apparent power avail-able to 240 volt-amperes and the availableenergy to 10 joules:’

Elsewhere in the same document, we find:

“Energy Hazard --An energy hazard isconsidered to exist at any exposed livepart of a piece of equipment if, betweenthe exposed live part and an adjacent ex-posed live or dead metal part of differentpolarity, there exists a potential of 2 voltsor more and either an available continuouspower level of 240 volt-amperes ( or more ),or a reactive energy level of 10 joules (ormore ):’

Questions:

There are several questions here:


1. Why was the title of the requirementchanged from “burn” to “energy”?

2. What part does energy play in splatteringof molten metal?

3. By what mechanism do limitations on volt-amperes and volts prevent the splattering ofmolten metal?

4. Energy is measured in joules; why is theparameter “apparent power”, measured involt-amperes, used?

5. Molten metal results from heat. Heat arisesfrom the dissipation of watts. Why is theparameter volt-amperes used?

6. If the criterion is the product of volts andamperes, then why is there a minimum of 2volts?

Hypotheses:

I thought that I would verify the theses onwhich the “energy hazard” is based: At poten-tials between 2 volts and 30 volts rms, volt-ampere levels greater than 240 can cause me-tals to splatter.

If this statement is true, I ought to be able toproduce splattering of metal and consequentburns at something more than 240 volt-amperes at all potentials between 2 and 30volts rms. In other words, I ought to be able toconfirm the thesis that “high energydischarges can cause an intense arc with ero-sion and splattering of the metal at the pointof contact”.

In order to melt anything, we’ve gotta haveheat. Electrically-caused heat comes from dis-sipation of power. A zero-impedance short-circuit cannot dissipate any power in the short.So, the only way of getting power dissipation isin the arc. In this case, power is defined as theproduct of volts and amps in the arc.

Experiments

So, I got out my trusty 200 watt, 10 Amperepower supply, connected a 7200 uP, 75 voltcapacitor across the output ( to get instantane-ous volt-amperes greater than 240), connecteda storage scope with DC-to-50 mHz currentprobe in series, and voltage probe across a cou-ple of tinned copper wires. I wanted to meas-ure the voltage and current during the time ofarcing between the two copper wires as theywere shorted together. With these two param-eters, I can calculate power in watts.

Somewhere in the literature, I have read that airdoes not break down at less than about 300volts peak. This hypothesis is supported byTable All of IEC Publication 664. I’m sure thisis difficult to measure as the distances involvedare in the neighborhood of 0.01 millimeter!That’s 0.0002 inch!

So, I started with 2 volts. By golly, there was avery small arc. Pretty tiny, but it was there.And the current was a whopping 25 amps! (Itried the same experiment without the capaci-tor, and found the same arc, but the currentwas only about 12 to 15 amps.) So, we have twoarcs at 2 volts, one at 12 to 15 amps, and theother at 25 amps. This does not square witheither the breakdown voltage of air, nor withthe current-carrying capacity of air. And, thearcing occured in the first 1 millisecond ofbringing the conductors together. Very shorttime.

I checked at 5, 10, 15, 20, 25, 30, 35, and 40 volts.The arc was brighter with every increase involtage. The current went up to a whopping 40to 60 amps! The time for things to settle downto steady state increased from less than 1 mil-lisecond to about 20 milliseconds. The erosionof metal also increased with increased voltage.

Technically Speaking, Continued


I repeated the tests without the capacitor.About the same results, except the arc was no-ticably less bright. The current was about 1/3of that with the capacitor.

I put my finger and the back of my hand nextto the arc. It was obvious that some materialwas being emitted from the shorting process. Icould feel something blowing on my finger, butI could not feel anything on the back of myhand. There was no sensation of heat or burn-ing --even with my finger in the flame of thearc.

I was holding the wire dcuring the arc --about 1/4 inch from the end. Shortly after a 25volt or greater are -say 1 to 5 seconds -- Icould feel the wire get hot. And then it im-mediately cooled. But, if I left it shorted, it didnot get hot.

The wires tended to stick together --indicat-ing some degree of melting and “welding” ofthe wires. A close inspection of the wiresreadily proved melting of the metals.

I repeated the short using a gold chain neck-lace. About the same results insofar as the arc,except there were two arcs, one at each of thetwo places where the chain made contact withthe wires. But, between the two points of con-tact, the chain became uncomfortably hot.

Analysis

Okay. Those are the facts from the experimen-tation. Now, let’s develop some hypotheses --explanations -- that fit the facts.

Some of the facts strongly suggest a virtualshort circuit, where the current was limitedonly by the impedance and charge of thesource.

If the voltage is virtually zero, then power, if Ex I, must be virtually zero. But, this is not thecase because the conductors tend to stick to-

gether after shorting. If they stick togetherthen the metal must be melting (which is con-firmed by the marks left on each wire ). If themetal is melting, then it must be heated by theelectrical energy. If the voltage is virtuallyzero, then power must be dissipated by the I xI x R version of the power of the equationrather than the E x I version. But, the brighterarc as a function of voltage indicates that thearc is indeed E x I.

The oscilloscope display is difficult to inter-pret. We see both short-circuit and variable Eand I displays in a 1 to 10 millisecond windowwith duration increasing with voltage.Thereafter, we have a stable short-circuit.

About the only hypothesis that fits all the factsis that BOTH kinds of power dissipation areoccuring, E x I and I x I x R. And, it is not airthat is the conducting medium, but metal.

Consider the following hypothesis: At the in-stant of contact, we have a metal-to-metal con-tact of very small cross-sectional area. Be-cause of the very small cross-sectional area,there is high contact resistance, and we have Ix I x R power dissipation. This heating causesthe metal in the region of the high current tomelt. The electromotive force of the highcurrent causes the small amount of moltenmaterial to move away from the point of con-tact. As the metal moves away, an arc occurs,characterized by E x I power dissipation. Be-cause the electrodes are moving, both byexternal forces (my hand) and by electromo-tive forces, the process tends to repeat until alarge contact area is achieved.

Such a hypothesis explains all the reportedfacts: The increase in brightness of the arcwith both current and voltage; the heating ofthe wire in the vicinity of the arc; the sensa-tion of emitted material, the arcing at lessthan 300 volts, the melting and erosion of themetal on the electrodes.



Without further investigation and experimen-tation, this hypothesis explains the reportedfacts, but does not confirm a hazard -- burnsfrom splattered metal -- severe enough towarrant a 240 watt (not volt-ampere) limit. Itis difficult to convert the electrical energy tosufficient thermal energy to actually causeburns with the very small amount of moltenmetal produced and with the very small dis-tance the metal travels.

The 2 volt limit seems appropriate, as the E x Ipower at 2 volts barely results in an arc.

Interestingly, there is a more severe hazardwhich shows up in this experimentation, but isnot controlled by this requirement or any oth-er requirement: I x I x R heating in the neck-lace chain (and in a ring or watchband). Thisheating occurs quite quickly, and can causeburns at currents as low as 6 to 8 amperes. Thisis because of the square function of I in thepower equation.

Energy

Energy can be defined as a watt-second, and ismeasured in joules. Energy, in mechanics, isdefined as a newton-meter, and is also meas-ured in joules.

With the first definition, how can “energy” behazardous? That is, what is the harm or injurythat arises from energy?

If we take I watt-second (which is a joule) anddissipate it over several seconds, then we havea small amount of heating. If we take thatsame watt-second and dissipate it in a mil-lisecond, then we will have a small explosion(assuming we dissipate it at a single point inspace).

Thus, whether or not electrical energy is ha-zardous depends on the time period duringwhich the energy is expended. Note that thisis true for mechanical energy.

The energy involved in my experiments canbe calculated:

J = W x tJ = E x I x t

For the worst-case arc, I had the following:

E = 40 VI = 60 A

t = 20 mS

J = 40 x 60 x 0.020 joulesJ = 48 joules

If we store electrical energy in a capacitor, andif we assume that the energy will be dissipatedin a short-circuit, and that the hazard is thatof burns which will arise from the splatteringof molten metal, then we can specify a max-imum energy (in joules) AND VOLTAGE toproduce an acceptable level of splattered mol-ten metal. Remember that we must have a vol-tage exceeding 2 volts to produce any signifi-cant arc.

The energy stored in a capacitor is

J = 1/2 x C x V x V

For the capacitor I used,

c = 7500 uFV=40

J = 1/2 x 0.0075 x 40 x 40 joulesJ = 5.76 joules

Conclusions

First, the term “energy hazard” is a misnomer.We are dealing with a burn hazard arisingfrom molten material expelled from an arc.Contrast the inconsistent use of the term “en-ergy hazard” with the use of the terms “shockhazard” and “fire hazard”.



PRODUCT SAFETY NEWS

The following trade publications included arti-cles of interest to the Product Safety Society:

IEEE GRID. June 1988:

New Society Expands

“The group that is working towards affiliationwith the IEEE as a Society for Product Safetyis closer to its goal. The required minimum of100 IEEE member signatures on the affiliationpetition has been surpassed, and more namesare constantly being sent in. “Several peoplehave told me they are just waiting to get theirIEEE membership cards before signing and re-turning the petition;’ says John McBain, PSSSecretary- Treasurer.

Interest in the PSS continues to grow nation-wide with organizational meetings beingplanned for chapters in the Los Angeles andBoston areas. The Pacific Northwest Chapterhas already scheduled quarterly technicalmeetings on June 29 at Fluke in Everett, Wash-ington and on October 19 at Tektronix inBeaverton, Oregon

Compliance Engineering. Spring. 1988:

Product Safety Society Formed

Compliance Engineering reported on the for-mation of our Product Safety Society in itsSpring, 1988 edition. The article described theintent of the society, its charter and a partiallisting of the chapter contacts. The publica-tion’s large distribution to the engineeringcommunity provides continued great exposurefor the society.

Second, volt-amperes is not a measure of eitherpower or energy as stated and implied in thevarious standards. I deplore the fact that gra-duate and experienced engineers continue topromulgate this requirement with such obvi-ous misstatements.

Third, while energy is involved in the splatter-ing of molten metal, the principal parameter isthat of power, namely joules per second. Con-sider that the energy stored in a capacitor canonly be released as a function of time, theworst case being a short-circuit. The powerdissipated in the arc causes the splattering ofmetal and any consequent burns. For a capaci-tor, it may be convenient to specify joules, butfor continuously energized circuit, the properparameter is power.

Fourth, the 240 watt limit appears very con-servative.

Fifth, every safety requirement should be ve-rifiable as to its effectiveness in controlling asituation to a non-hazardous level. I wouldchallenge you to repeat this experiment andconvince yourself as the viability of the so-called “energy hazard” requirement.

Your comments to this article are welcome.Please address your response to the Editor. Pro-duct Safety Society Newsletter. 2550 Walsh Ave.Santa Clara. CA 95051-1392



by DOCTOR ZASK DOCTOR Z

In the world of Product Safety and Certifica-tion, there are many pitfalls for the unwary. Ifyou have problems that seem insoluable, then it'stime to ask Doctor Z! He has the answers,derived from his many years of training and ex-perience in the Science of Product Safetiology.Pitfalls hold no terrors for Dr. z, since he is ona first name basis with most of them.Remember, any resemblence to persons, places,products, agencies, or good advice is purelycoincidental, but don’t let that stop you. Writeto Dr. Z today!

Dear Dr. Z:

Can I rely on three separate agencies to catcha simple substandard clearance problem that Iam having with an GEM power supply?

Last week a power supply caused our productto fail the production line dielectric withstandtest. Upon investigation we found the failurewas due to common mode choke restingdirectly on a ground trace. A check with thevendor showed that this same constructionwas used since the design of the power supply.

A quick inspection of other samples of thesame power supply that had passed the pro-duction dielectric test revealed that the chokein question was located up to 0.8 mm abovethe ground trace to resting on the ground trace,with the varnish of the choke coil in contactwith the pc trace.

This same power supply has approvals fromthree different safety test houses! The standardwith the least restrictive clearance shows aminimum of 2.54 mm clearance is reuired.What really gets me is that

THREE different test agencies looked atthree power supplies, all which had this samecondition. I would have thought that at leastone of the three houses should have caught acommon mode choke with insufficient clear-ance to ground.

Can you tell me what is going on here???? Arethe test agencies so busy that simple things areslipping through the cracks??? What should Ido???

Sincerely, Frustrated in Manufacturing

Dear Frustrated,

Many safety certification engineers have ex-perienced the same type of problem, includingDr. Z in his younger days. It is not unusual fora safety certification engineer to assume thatpurchasing a part with agency certificationmarks on it means the part was subject to anengineering evaluation for safety.

You made two fundamental mistakes: First,you assumed that the agency marks provethat a product is safe. Second, you assumedthat the agency marks prove that a productcomplies with the standards.

A product certified by agencies such as CSA,TUV, UL, VDE, etc. does not necessarily com-ply with the standards.

A certified product is simply that: A certifiedproduct.


NEW AND FOR YOUR INFORMATION:

CERTIFICATION AGENCIES: PART I

The following is the first in a series of articles meant to aid you in your work with the variousagencies. It is important to be able to contact the right person at the right Certification Agency(defined here as a company that supports its own certification mark, rather than obtains a markon behalf of a client). We will be including different agencies in the coming months, as space andtime permit. Please let us know if you find this article useful, what improvements could be madeand which agencies you would like to see included.

Ask Dr. Z, Continued

Frustrated in Manufacturing should recognize that certification agencies are VENDORS to clients.Clients pay them money for the right to use their mark on the product. Clients, being driven byeconomics, only do what is necessary to obtain the right to use the mark. Certification houses arevendors, who make money with repeat business, in the name of safety. Frustrated in Manufactur-ing has been brainwashed by the certification agency engineers into believing they make his andother clients products safe!

Contrary to what certification agencies would have Frustrated in Manufacturing believe, safety isdesigned into products by the R & D engineer. The process is that simple. If the R & D engineerdoes not understand safety, then the result is a common-mode choke resting on a ground trace.Safety is not provided by the certification house.

The value of agency certifications on a power supply simply pushes certification liability onto thepower supply manufacturer. Such certifications make the end-product certification process easier.That’s all. Nothing more! Full stop! End! The SAFETY of a power supply MUST be determinedby the user, in this case, Frustrated in Manufacturing.

With all my love, but no tears for your predicament (which is of your own making),

Dr. Z

PS: Yes, modern-day wire coatings (not varnish) will withstand 1500 volts rms. The failure wasprobably due to rubbing between the wire and the ground trace which scoured the coating toa thin enough layer to fail the dielectric strength test.

PPS: 1 mm will barely break down at 1500 volts rms. See IEC 664, Table All. Any air gap less than1 mm would break down at 1500 volts.

PPPS: You can be quite certain that the “boiler plate” agreements between the certification agen-cies and your power supply vendor are such that the condition you discovered should never haveexisted.


TUV Rheinland of North America

TUV Rheinland of North America, Inc. is a North American subsidiary of TUV Rheinland in Cologne, West Germany. TUV Rheinlandcan test and issue the GS mark and the Bauart mark on equipment and components according to VDE, DIN, BG and IEC Standards.

Main Office, Danburry, CTPhone: (203) 798-0811

Dr. Klause Spiegel PresidentPaul Schultze Vice PresidentGisela C. Seagraves Accounting ManagerJudity Ann Colombo Admin. Coordinator, PSQAWitold Marchewicz Engineer, Medical/Prod. Safety Serv.Eli Orsoff Sr. Engineer, Product Safety ServicesWolfram Gmelin Engineer, Human Factors, Prod. SafetyJoseph DeCarlo Engineer, Product Safety ServicesJohn Tyra Engineer, Product Safety ServicesJan Komarzynski Engineer, Product Safety ServicesGary Tyra Engineer, Product Safety Services

Western Regional Office, San Ramon, CAPhone:( 415) 820-8444

Fax: (415) 820-8487

Lazlo Hasonau General ManagerMatthias Heinze Coordinator, Engineering ServicesEwald Riechert Engineer, Medical/Product SafetyJoachim Neumann Sr. Engineer, Product Safety ServicesHelmut Doebert Sr. Engineer, Marketing/Prod. SafetyKlaus Ehrlich Engineer, Human Factors/Prod. SafetyEdward Spooner Engineer, RFI/Product Safety ServicesCarrol Treece Administrative ManagerMonica Weitzel Administrative Coordinator, PSQA

Eastern Regional Office, Marlborough, MAPhone: (617) 460-0792

Mark Swank Sr. Engineer, Product Safety ServicesDavid Loebeck Sr. Engineer, RFI/Prod. Safety Servo

Central Regional Office, Austin, TXPhone: (512) 343-6321

George Jurasich Sr. Engineer, Product Safety ServicesTom Lorenzen Engineer, Product Safety Services

Canadian Office, Ontario, CanadaPhone: (416) 733-3677

Dr. Steven Draemer General ManagerPaul Morton Engineer, Product Safety Services


CHAPTER ACTIVITY REPORTS

SANTA CLARA VALLEY CHAPTER REPORT

The meeting started at 7:00 p.m. with announcements and committeereports. Rich Pescatore br ief ly descr ibed the latest discussionsabout IEEE aff i l iation for the PSS and asked for comments to bereturned to h im. (See the “Cha i rman’s Message’ . i n th isNewslet ter.) A Publicity committee Chairman for the SCV Chapterwas announced: Rick Buck wi l l be repor t ing to the PSS Newslet teron SCV Chapter meetings and activit ies and improving our localpubl ic ity as wel l. The Paci f ic Nor thWest Chapter is spearheadingthe ef for t to have a booth or table at the nat ional EMC symposiumin Seatt le at the beginning of August. Any member who wil l bea t tend i ng i s a ske d to dona te a n hou r o f t he i r t i me to he lp r unthe display. Call Walt Hart at 206-356-5177 for more information.

Committee Repor ts: The Const itut ion Commit tee (Mike Har r is) is“on hold” r ight now, pend ing more deta i ls about t he IEEEaf f i l ia t ion . The Membersh ip Commit tee (Scot t Ba r rows) hasr e c e i ve d ove r 10 0 o f t h e “ M e m b e r s h i p A p p l i c a t i o n a n dQuest ionnai re” forms that were pr inted in the last Newslet ter.Please return your fo rm today! The Chapter Commun icat ionsCommittee (Roger Volgstadt) has had one of fer of help with theNewslet ter product ion, but could use more. -Please cal l Roger at408-748-2102. The Program Committee (Brian Claes) announced thatthe speaker next month wi l l be from Underwr iters Laborator iesdiscussing the new UL478.

The guest speaker, Lewis Bass, presented “system Safety forCom merc ia l P r o duc t s Beyond c e r t i f i ca t ion” , a n ove r v i ew o fsafety considerat ions that a re not covered by acqui r ing an agencymark. Mr. Bass is both an at torney and a Professiona l SafetyEngineer and serves as legal and safety consultant for manyFortune 500 companies as wel l as smal ler organ izat ions. Heteaches un iversity courses in safety engineer ing and has wr it tennumerous ar t icles on the subject , including h is recent book“Products Liabi l ity: Design and Manufactur ing Defects” .

The presenta t ion , s ince i t was an overv iew, is impossible tosummar ize. Some of the topics ment ioned were def in it ions of“ p ro duc t” a nd “p ro duct de fe c t s”, l i ab i l i t y i ssues , r i sk fac to r sto consider, system safety techniques, warn ing labels, and manymore. For more in format ion you might want to refer to the bookment ioned above, wh ich can be ordered f rom the publ isher,Shepard’s/MCGraw-Hi l l , at 800 -525-2474.

Thi r ty- f ive people from eighteen companies at tended th is meet ing.The next meeting wi l l be held on July 26 at the same locat ion:Apple Computer, 20525 Mar ian i Ave, Cuper t ino. Th is wi l l be yourchance to hear and ask about the new UL478, so pass the word anddon’t be late!


COLORADO CALLING!

Steve Tarket is continuing to act as the contact person for people interested in startinga chapter in the Denver area. Please let Steve know of your interest.

Contact: Steve Tarket (M/S 65)Hewlett Packard3404 E. Harmony RoadFt. Collins, CO 80525telephone 303- 229- 2481; Fax 303- 229- 2692

NEWS FROM SOUTHERN CALIFORNIA:

The next meeting of the Southern California Chapter of the Product Safety Societywill be at MAl Basic Four, 14101 Myford Rd., Tustin, CA on August 1,1988 at 6:00 pm.Frank Campion of LH Research will discuss the CSA Power Supply Committee.There will also be an election of officers and committee heads. Any questions aboutthe meeting can be addressed to Charlie Bayhi as noted below:

Contact: Charlie Bayhi, MAl Basic Four, Tustin CATelephone: 714-730-2556; Fax: 714-730-3185

REPORT FROM THE NORTHWEST

On June 29th, the NWC of the Product Safety Society conducted their second forma-tive meeting at John Fluke Mfg. Co. in Everett, WA. The meeting began with a gen-eral introduction of all members and a discussion of IEEE affiliation. The pros andcons of affiliation with the EMC Society were discussed and the general concensuswas that it would be a good idea until we learn all the rules and regulations of fullindividual IEEE membership. Money to help pay for the Newsletter could be ob-tained at both the national and chapter levels of the IEEE, based on attendance.

The next meeting will be held on October 19, 1988. Pete Perkins of Tektronix inBeaverton, OR is hosting an all afternoon PSS meeting which will conclude withdinner. The topic for discussion will be “International Power Line Configurationsand Components”. Representatives from Japan, England, and the Netherlands will bethere to discuss the differences and consequences in grounding, leakage current, 50Hz vs 60 Hz, ring circuits vs branch circuits, attachment plug caps, and much more.An additional speaker from a US manufacturer or expert is this area is being soughtfor the meeting.

There will be a PSS booth at the EMC International Symposium held in Seattle onAugust 2-- 4th. This booth will be manned by volunteers from the NWC of the PSSfor one day to recruit and help spread the news about our growing society.


Northwest, Continued

Hal Mickelson of HP gave a speech on domestic product l iabi l ity. In a nutshel l, Halwa r ned t he audience t ha t i f a consumer i s i nju red by a product , t he manufactu rer i sgoing to pay. Your records could be subpoenaed a s ev idence and i t i s ver y impor t a ntto state the facts in a l l cor respondence. Be object ive and do not editor ia l ize. Writeprofessional ly and do not make someone look bad.

Ruth Redden (Dr. Ruth) of Fluke gave a speech on European product liability. TheEuropean Commission made up of 12 countries have harmonized the laws regardingproduct liability. The environment regarding product liability is very different thanwhat is found in the US. The Europeans are much more tolerant and not as likely tosue for damages. The plantiff must prove there was a defect that there was damage,and that the damage was caused by the defect. Also, there are limits to the amountthat can be claimed, especially in massive product liability cases.

Finally, there was a demonstration on surge testing given by Walt Hart and HeberFarnsworth of Fluke. Walt showed us how a product can be tested for its resistanceto lightning strikes and load switching without $ 30,000 worth of equipment. Usingabout $ 50.00 worth of locally available components, Fluke has constructed a surgetester that will allow you to test per IEC specifications. The meeting was concludedwith a dinner.

At Van HoudtProduct Safety Engineer

NEWS FROM NEW ENGLAND

The Northeast Chapter of the Product Safety Society held its second regular meetingon June 25, with 32 engineers attending. The initial enthusiasm and support continueto be very strong. The chapter membership has exceeded 100 and is still growing!

Two presentations were made at the June meeting: Bruce Langmuir from BOSE Cor-poration talked about a number of issues being considered by the EIA, CEG, R -IProduct Safety Committee, including surface adhesives and harmonization of IEC 65with IEC 950; Glen Dash of Dash, Straus & Goodhue, talked about the legal issuessurronding EMI and Product Safety Regulations in the European Common Market.

The next chapter meeting will be held on July 27, at DS & G facilities. The topic ofdiscussion will deal with teh recent changes implemented by the NFPA and NECregarding safety regulations for wire. Any interested parties can contact Jim Nor-gaard at DS & G for more information about the chapter’s activities.

Jim Norgaard617- 263- 2662.


LETTERS FROM OUR READERS

The following letters were received from ourreaders since the last issue of the Product Safe-ty Society (PSS) Newsletter:

Polarity a Problem?

“Technically Speaking” in your Junenewsletter contains some glaring omissionswhich should be addressed by readers of anytechnical journal but are quite appalling tofind in a product safety society newsletter.Any electrical product or system, with a fewexeptions to be discussed later, which can ex-perience a polarity reversal and remain oper-able is inherently unsafe. It means the systemis not grounded, a violation of the NEC,OSHA, and the IEEE Stds. The exceptions aretoasters, small portable tools which are doublyinsulated, and some unique equipment designswhich are for laboratory use only. There areinstances when it might be advisable to isolatethe system from the building ground througha transformer. Here the secondary of thetransformer becomes the “supply service” andits polarity must also remain fixed withrespect to the product or system by groundingone point.

Sincerely,

Irwin EinsohnBelmont, CA

The following response to the above was received fromthe “Technically Speaking” author; Richard Nute.

In my June column, I did not provide a clear definitionfor polarity reversal. Here is the definition I used forthat column:

In a single-phase AC supply system, polarity rever-sal is the interchanging of the phase and neutralconductors with respect to their identification.

For example, it is quite common for the ordinary 120 voltNEMA 5-15R to be miswired so that the black wire is con-nected to the wide terminal and the white wire connected tothe narrow terminal. This is indeed contrary to the US Na-tional Electrical Code and the Canadian Electrical Code.But, it does occur. Indeed, in the electrical department ofalmost any hardware store, one can find receptacle testerswhich test whether or not the NEMA 5-15R receptacle isproperly wired, including the condition of phase-neutral po-larity reversal.

Note that such interchange does not mean that the system isnot grounded. The system remains grounded in accordancewith National Electrical Code and Canadian ElectricalCode requireements, but the identification of the groundedconductor is incorrect at one or more points in the system

Fortunately, in most products, all of the primary circuits aretreated as live” conductors and are suitably insulated suchthat there are equal insulating qualities for both the phaseconductor and the neutral conductor; and any interchangewill not adversely affect the safety of the product.

Virtually all 120 Volt, plug and socket connected equipmentremain both safe and operable under polarity reversa condi-tions.

Indeed, ANSL UL, and CSA Standards require NEMA 5-l5Pconnected equipment to remain safe under polarityreversal conditions. Evidence of this is the leakage currenttest, which is done under both normal and reverse polarityconditions. (See ANSI and almost any UL or CSAstandard.) In addition, the dielectric strength test is acommon-mode test for both phase to ground and neutral toground installations.

Contrary to the above, home laundry electric dryers andhome electric ranges have no independent protective con-ductor, but have the neutral conductor connected directly tothe frame and accessible metal parts. These appliances areconnected to the supply via the NEMA 10- 30 or 10- 50series plugs and receptacles. Here, polarity reversal wouldindeed result in an inherently unsafe product and in electricshock. This construction is permitted by the National Electr-ical Code, Articles, 250-60 and 250-61(b), Exception No. 1.

Sincerely,

Richard NuteAuthor; “Technically Speaking”


July 1988Tuesday, July 26Santa Clara Valley ChapterSubject: UL478/IEC 950Speaker: Mike DeMartini, ULTime: 7:00 pmLocation: Apple Computer

20525 Mariani Ave.Cupertino, CA

Wednesday, July 27Northeastern Chapter MeetingSubject: Recent Changes to

Wire Rqmts in NEC& NFPA

Speaker: tbdTime: 7:00 pmLocation: Dash, Straus & Goodhue

593 Masschusetts Ave.Boxborough, MA

The Calendar of the Product Safety Society

August 1988Monday August 1Southern California Chapter:Subject: CSA Power Supply Comm.Speaker: Frank Campion, LH ResearchTime: 6:00 pmLocation MAI Basic Four

14101 Myford RoadTustin, CA

October 19Northwest ChapterSubject: International Power InfoSpeaker: VariousTime: tbdLocation: Tektronix, Beaverton. OR

July, 1988 VOL. 1, NO.6

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