In this issue Page Product Safetyewh.ieee.org/soc/pses/Downloads/newsletters/90v03n2.pdf · resistance or in the contact resis-tance of switches and connectors. If I increases (overcuuent),

Product Safety Newsletter • Page 1

TheProductSafetyNewsletter

Volume 3, Number 2 March-April 1990

Chairman’s Message

Rich Pescatore

In this issue Page

Chairman's Message Richard Pescatore 1

Technically Speaking Ric Nute 3

Circuit Breakers Fredrick Franklin P.E. 8

Ask Doctor Z DR Z 13

Abstracts Dave Lorusso 14

Letters to the Editor 16

Area Activity Reports 18

Guest Editorial John McBain 21

Editorial Roger Volgstadt 22

Institutional Listings 23

Calendar 24

We have completed the initialReader Survey. Your commentshave been read and tabulated. Acompilation of the results of thesurvey appears on page 21 of thisissue of the newsletter. Followingare a few observations as a resultof your input.

Technically Speaking“Technically Speaking” is, by far,the most praised column. Let meshare the following quotations(which represent the theme of mostof your comments).

“... informative, provides an in-depth analysis of safety engi-neering principles...”

“Forces one to think of safety in terms of the engineeringprocess rather than blind appli-cation of rules.”

“... provides insight wherenone existed before.”

“... provides timely, detailedinfo about pertinent subjects.”

“... clearly written...”

“... very informative, but itmust be condensed.”

My thanks to Rich Nute forsharing his knowledge and enthu-siasm with us. It is clear that mostof you want this column to con-tinue. It will.

Ask Doctor Z“Ask Doctor Z” sparked a mixedresponse. It seems some of youlove the column, while others hateit. There weren’t many middleground comments. Your com-ments ranged from “Liked” and“Informative and entertaining” to“Get rid of Dr. Z” (repeated fourtimes) and “Execution!” This

leaves your editor with a toughdecision to make regarding thecontinuation of this column.

Two major functions of thisnewsletter are to provoke thoughtand disseminate information. “AskDr. Z” does this, although in amanner that some of you appar-ently find less professional thanyou would like. On the otherhand, many of you like Dr. Z’sstyle, as it provides a bit of humorand wit, while at the same timeallows free expression of opinion.It should be clear to PSN readersthat this is an opinion column,rather than technical, with anemphasis on the less serious sideof “product safetiology.”

We certainly can’t guaranteeyou will find “Ask Dr. Z” consis-tantly hilarious or even mildlyamusing. Humor has been definedas someone else slipping on abanana peel. Your banana peel isnot very funny-obviously only asafety hazard. However, given thatmany of you do like the column,



Chariman's MessageContinued

The Product Safety News-letter is published bimonthlyby the Product Safety Techni-cal Committee of the IEEEEMC Society. No part of thisnewsletter may be reproducedwithout written permission ofthe authors. All rights to thearticles remain with theauthors. Opinions expressedin this newsletter are those ofthe authors and do not neces-sarily represent the opinionsof the Technical Committee orits members. Indeed, theremay be and often are substan-tial disagreements with someof the opinions expressed bythe authors. Comments andquestions about the newslettermay be addressed to:Product Safety Newsletter,Attention: Roger Volgstadt,c/o Tandem Computers Inc.10300 N. Tantau Ave., Loc.55-53, Cupertino, CA 95014Fax No. (408) 285-2553

EditorRoger VolgstadtNews EditorDavid EdmundsAssistant EditorsMichael BarnettJohn McBainPage LayoutKen WarwickSubscriptions ManagerJohn McBain (acting)

and that it is consistent with ourgoals, I suggest that we continueto include it in the newsletter.Read it only if you like it. And ifyou don’t like it ...tell us!

We try to present all points ofview that we receive. If Dr. Z (oranyone else) makes a point thatyou disagree with, please writeand let us know. We will attemptto publish your letter or, at theleast, express your view and askfor responses. This is your forum.

Other Columns“News and Notes” is anothercolumn that many of you said youappreciate. The only complaintwas that you wanted more news.The real need for improvementseems to be the “Calendar” andthe “Area Activity Reports.”Both must become more timelyand complete so they can be moreuseful to PSN readers. Finally, acouple of you even said youespecially like the “Chairman’sMessage” (thank you). And thenthere was the guy that thinks thatwhat needs the most improvementis the Chairman’s picture. Ohwell!

All kidding aside, your com-ments are appreciated. They willlead to change. We have receivedmany good ideas for additionaltopics that could be addressed inthe newsletter. We would love topursue all of your suggestions.

One way to get a topic included isto write about it yourself. Somereaders have already submittedarticles which were well received,and more would be very welcome.As I have said many times, this isa volunteer organization and youneed to volunteer to make thingshappen.

Saving the best for last ...somereaders could not decide whichcolumns were favorites or neededimprovement. Some generalcomments:

“PS Newsletter is always veryinformative.”

“I think you guys are doing awonderful job.”“... (the) diversity presented ishealthy ...”

“The entire newsletter is verywell done.”

“I can’t choose. It’s like askinga person dying of thirst whattype of water do you likebest?”

Thank you for your support.

Best Regards,Rich PescatoreChairman

Vol. 3, No. 2 March/April 1990


Technically SpeakingRich Nute

Hello from Vancouver, Washing-ton, USA:

Consider the “direct plug-in”Class 2 transformer-power supplycommonly used for low-powerdevices such as calculators,cassette players, and similarproducts. Consider also the larger“cousin” known in the trade as the“indirect plug-in” Class 2 trans-former (where the transformer istoo large to hang from the plug,and must, instead, reside on thefloor using attached cords forinput power and output power).

These small transformer-powersupply devices have no powerswitch, and have no fuses in theprimary circuit.

In North America, it is commonfor these Class 2 transformer-power supply devices to be safetycertified for many uses, includingmedical equipment (CSA 125 and

UL 544) and data processingequipment (CSA 220 and UL478).

However, these same trans-former-power supply devices donot comply with either IEC 601-1(medical) or IEC 950 (data proc-essing) because they have nofuses in the primary circuit. Notonly do IEC 601-1 and IEC 950require fuses, for grounded prod-ucts they require fuses in bothpoles of the supply. (The possibleexceptions to this requirementwill not be discussed in thisarticle.)

This dilemma has given mecause to pause and consider thehazards addressed by the IEC fuserequirements for single-phaseplug-and-socket connected equip-ment. (See IEC 601-1 SecondEdition, Sub-clause 57.6, and IEC950, Sub-clauses 2.7.1 and 2.7.3.)

Let’s begin by discussing thepurpose of a fuse, and the func-tion of the building overcurrentprotective device as it relates toplug-and-socket connected equip-ment. Next, we’ll discuss when touse a fuse, and whether to fuseboth poles of a single-phase, plug-and-socket connected equipment.We’ll include a discussion on howto select the value of the fuse.

The Purpose of a FuseLet’s review the function of afuse. (In the context of this articleI use the word “fuse” as a general

term for automatic overcuuentprotective device which includesbut is not limited to fuses andcircuit-breakers.)

Fuses are means to automati-cally disconnect power underovercurrent conditions.

What is overcurrent? Overcur-rent is any current exceeding themaximum current rating of wires,switches, connectors, etc.

Why are we concerned aboutovercurrent? Overcurrent resultsin overheating. And overheatingcan result in fire.

Overheating is due to I*I*Rpower dissipation in the wireresistance or in the contact resis-tance of switches and connectors.If I increases (overcuuent), thenpower dissipation increases veryrapidly with increasing I (due tothe square function in the powerequation) and the conductor orcontact overheats. When conduc-tors and contacts overheat, theirresistance goes up contributingfurther to increase power dissipa-tion and the situation approachesa thermal runaway situation.

Such overheating might raisethe temperature of nearby materi-als to their ignition temperatureand result in a fire.

In a lesser situation, the over-heating might melt plastic wireinsulation thus providing unde-sired and uncontrolled currentpathways. We assume that this

The Use of OvercurrentProtection in Plug-and-SocketConnected Equipment

Copyright 1990 by Richard NuteRich Nute

Continued


Technically Speaking

lesser situation results in a hazard,and, therefore, insulation failuredue to overheating must be pre-vented.

Disconnection must be auto-matic because the circuit may notbe continuously attended bysomeone who will manuallydisconnect the power, and becauseovercurrent conditions are notnecessarily immediately apparent.

Building ProtectionIn an electrical distribution sys-

tem, whether in a building or in aproduct, automatic prevention ofovercurrent conditions is requiredwhenever the wire size is reduced.When wire size is reduced, thecross-sectional area is reduced, andthe resistance is increased.

Overheating of wire is due toI*I*R power dissipation in the wireresistance. If I remains constant,and R increases (due to decreasedwire size), then power dissipationincreases and the wire overheats.

Therefore, when wire size isreduced, it is necessary to reducethe maximum I with a fuse.

In the event of insulation failurebetween a conductor and ground,the ground return system providesa controlled current pathway bywhich the current is returned to itssource. If the fault impedance issufficiently low, the fuse will clearthe circuit and prevent overheatingof the supply and ground returnconductors.

(Note that if the fault impedanceis high, and the current throughthe fault does not exceed the overcur-rent device rating, then the con-ductors are not subject to over-heating and the situation isacceptable insofar as the purposeof the fuse. However, power willbe dissipated in the fault and mayresult in a fire or other hazard; wewill not explore this situation.)

(The ground return system to-gether with the fuse may also playa role in the prevention of electricshock. I have already discussedthis role in a previous column.)Let’s compare the requirementsfor the ground return circuit withthe characteristics of the differentground return systems usedthroughout the world.

Operation of a fuse in the eventof an insulation fault to groundnecessarily requires the groundreturn circuit impedance be aboutthe same as that of the supplycircuit impedance.

In North America, the groundwire and the neutral wire are thesame size and are connected tothe same ground rod. This givesreasonable assurance that theground return circuit impedance isabout the same as the supplycircuit impedance.

In many European installations,the ground wire and neutral wireare the same size, but are con-nected to their own independentground rods. This construction

places the earth impedance inseries with the ground returncircuit impedance. Therefore, insuch systems, the ground imped-ance is necessarily greater thanthe supply circuit impedance.

While every effort is made toassure a low impedance betweenthe two ground rods, occasionallythe earth impedance is too high tocause sufficient current to blowthe installation fuse. This fault-condition situation is not subjectto overheating, but may result inelectric shock conditions.

When the earth impedance be-tween the two ground rods is toohigh to cause the fuse to operate,then a potential difference existsbetween those two ground rods. Ifwe assume the worst-case wherethe fault current is equal to thefuse rating, then virtually theentire supply voltage appearsbetween the two ground rods. Ifthe building metal is connected tothe ground wire, then, within thebuilding, there is no potentialdifference between groundedparts and there is no shockhazard—even though at theground rod there is a potential,gradient nearly equal to thesupply voltage.

To prevent electric shock underthese conditions, some Europeanauthorities require permanentinstallation of a “residual currentcircuit breaker” (RCCB) or “earth

Continued

Continued



leakage circuit breaker” (ELCB )on the load side of the fuse (in thebuilding installation). Thesedevices are electromagneticversions of the North AmericanGFCI (ground fault circuit inter-rupter). The RCCB or ELCB unitsopen the circuit when the differ-ence between the phase currentand the neutral current exceedsabout 5 to 20 milliamperes. Forall practical purposes, the RCCBor ELCB act as fuses for ground-faults-regardless of the faultimpedance.

Now let’s look at the situationwhen the power distributionsystem is extended to the equip-ment by means of a plug andsocket and a length of power cord.

Usually, the power cord wiresize is smaller than that of thewires supplying power to thesocket. As mentioned previously,whenever the wire size is reduced,a fuse should be required toprotect the smaller wire size fromoverheating. The UK has ad-dressed this situation by requiringa fuse in the plug.

In North America (as opposedto the UK), the fuse in the instal-lation is supposed to protect notonly the installation wiring, butalso any plugs and cords con-nected to any receptacle. Thisrequirement is independent ofwhether or not a fuse is providedwithin the equipment.

A fuse, being a series element ina circuit could be applied any-where in the circuit (at the source,at the load, or in the return wire)and still do the job. How- ever,the fuse must be located at thesource and in the “hot” leg if it isto provide protection for allpossible faults. As a general rule,a fuse should not be used toprovide protection of wires andother components on the supplyside of the fuse. Therefore, a fusein the cord-connected productdoes not provide protection forfaults in the cord, line filter, orpower switch (where located onthe supply side of the fuse).

In North America, wire sizesfor power cords, including exten-sion cords, are selected to alwaysbe capable of blowing the 15 or20 amp building fuse in the eventof a steady-state short-circuit atthe end of the power cord.

The power cord wire size to-gether with its insulation ratingmust have a sufficiently lowimpedance to withstand theoverheating of the short-circuituntil the 20-amp circuit breakerclears the circuit. (Cord-connectedelectrical heating appliances oftenhave high temperature insulationon their power cords to accountfor steady-state high current con-ditions. )

To meet this criterion, theminimum wire size for flexiblecords is A WG 18, except forspecific applications, in whichcase there are extensive insula-tion robustness tests designed topreclude insulation failure.

Ampacity ratings of cords andcordsets are given in UL 817 ,Table 90. These ratings are fornormal conditions.

Inside a ProductThus far, we have been talking

about the building power distri-bution, and protecting wires fromoverheating in the event of anovercurrent condition. For cord-connected products, electricpower distribution stops andelectric power utilization beginsat the load end of the power cord.

When we get inside a cord-connected product, we are nolonger necessarily dealing withI*I*R power dissipation in thewire resistance or in the contactresistance of switches and con-nectors as being the only sourcesof heat for a fire. Within cord-connected equipment, we haveline filters, transformers, andmany other circuit componentswhich may be subject to over-heating from E*I power dissipa-tion. Now we must consider bothI*I*R and E*I power dissipation.

Continued

Continued



And, we must consider bothinsulation and circuit componentfaults.

To protect against overheating,we must first identify those partswhich could dissipate power andwhich therefore could overheat.Only those parts which candissipate power can overheat.

Let’s look at the common 50-60 hertz transformer: The idealtransformer dissipates no power.But transformers are wound withcopper wire having a finite resis-tance; power is dissipated in thisresistance and some heatingresults. Transformers are madewith imperfect magnetic cores;more power is dissipated inovercoming core losses and moreheating results. Normally, theheating from these sources isrelatively low.

What faults can cause the trans-former to overheat?

Let’s first consider the primarywinding. Here, if the magnet wireinsulation should fail, some smallproportion of the number of turnswould be shorted, and powerwould be dissipated in thoseshorted turns. The current wouldincrease in proportion to thenumber of turns shorted whichcan rarely be a very large number.(The number of turns that couldbe shorted depends on the trans-former construction.)

With shorted turns, whetherprimary or secondary, the current

increases and the E*I power in-creases. The transformer heats up.The resulting increase in thephase-to-neutral current is notlikely be enough to cause thebuilding fuse to open.

Insulation and componentfailures at the secondary outputterminals can also cause trans-former overheating withoutcausing the building fuse to open.

Two kinds of output terminalloading simulate the worst-casetransformer overheating. One loadis the output short-circuit. Thismaximizes I*I*R heating withinthe transformer. The other load isthe output maximum power. Thismaximizes the E*I heating withinthe transformer .

If the heating resulting fromshorted turns or excessive loadingcould cause the failure of insula-tion or a fire, then some kind ofautomatic safeguard must beemployed.

For many transformers, one ormore fuses is an acceptableautomatic safeguard. (In somecases of multiple-winding secon-daries, both the primary and thesecondaries must have their ownfuses.) The fuse value is selectedat some value greater than maxi-mum normal load, and less thanthat load which produces a poten-tially damaging temperature.

Now, let’s take another look atthose fuseless transformers thatare acceptable under CSA and UL

standards, but not acceptableunder IEC standards.

For small transformers whererated input current is a fraction ofan ampere, the difference betweenrated input current and faultcurrent for an unacceptabletemperature may not be highenough to find a fuse which willnot blow under normal current butwill blow under abnormal current.In addition, low current fuses tendto have fragile elements and aresubject to failure due to mechani-cal shock.

In these cases, it is common touse a thermal switch as a safe-guard against excessive tempera-ture. Indeed, for small transform-ers, a thermal switch is a bettersafeguard against excessivetemperature than a fuse.

For compliance with IEC 601-1and with IEC 950, one wouldneed to safeguard the transformerwith a thermal switch, and thenadd a fuse. (Both IEC 601-1 andIEC 950 require that the trans-former be protected againstoverheating under overload orshort-circuit conditions; see IEC601-1, Sub-clause 57.9.1 and IEC950, Appendix C.) For a smalltransformer, the fuse is useless butrequired for compliance.

What about the requirementthat, in grounded products, a fusemust be provided in both poles of

Continued

Continued



the supply? I’ve already dis-cussed in the June, 1988, ProductSafety Newsletter that doublefusing does not compromise thesafety of the product and shouldbe permitted.

Clearly, automatic overcurrentor overtemperature safeguards arenecessary to prevent electricallycaused fire.

The building fuse safeguards thebuilding wiring and power cordsfor both phase-to-neutral andphase-to-ground overcurrentsituations.

The local product fuse safe-guards the product parts for localE*I and I*I*R overheating situ-ations.

At the load end of a powercord, a fuse or other devicesafeguards against excessivetemperature due to power dissipa-tion in line filters, transformers,and many other circuit compo-nents which may be subject tooverheating. All of these kinds ofcomponents are connected be-tween the poles of the supply. Asingle fuse adequately safeguardsagainst local overheating, regard-less of which pole is wired.

Meanwhile, the building fuseadequately safeguards againstovercurrent in the event of phase-to-ground insulation failure--whether in the building, the powercord, or in the product.

With the exception of line filtercapacitors (which are rarely

provided with fuse safeguards),there are no power dissipatingcomponents connected from poleto ground. Both poles of the

mains circuits must be every-where insulated from ground.Assuming there is no wire sizereduction on the load side of thefuse, there is nothing to safeguardagainst overheating in the event ofan insulation failure to ground(except, maybe, the insulationitself)-even in the event ofpolarity reversal.

Consequently, the building fuseprevents overheating of wires inthe event of failure of insulationbetween the phase conductor andground. (Note that this is trueregardless of plug polarity: thephase conductor in the product isthe wire that is connected to thebuilding phase conductor via theplug and not necessarily the wirewith the fuse.)

And, the product fuse preventsoverheating in the electric powerutilization components within theproduct. (Note that this is trueregardless of plug polarity:

electric power utilization in theproduct occurs between the twopoles of the supply.)

In this article, I have shown thatfusing is not the only means forsafeguarding against excessivetemperature within products.Indeed, for transformers, at least,fuses may not provide an ade-quate safeguard.

I have also shown that, whiledouble-fusing should be permit-ted, double-fusing should not berequired as double-fusing doesnot provide any safeguardingabove and beyond that of a singlefuse. (In the case of an insulationfault to ground, where the build-ing ground is connected to aground rod independent of theground wire, and where theground impedance is too high tocreate overcurrent sufficient tooperate the building fuse, a localfuse may reduce conditions forelectric shock.)

( 1) From a practical point ofview, somewhere in the neigh-bor- hood of 4 to 6 amperes andlower, no automatic preventionof overcurrent conditions is re-quired whenever the wire size isreduced. The power dissipatedin the wire or contact resistance,together with the power per unitvolume and the increase inresistance due to the heating ,usually is not capable of anoverheating condition.

Your comments on this articleare welcome. Please address yourcomments to the Product SafetyNewsletter, Attention: RogerVolgstadt, c/o Tandem Comput-ers Incorporated, 10300 N.Tantau Avenue, Loc. 55-53, Cu-pertino, CA 95014-0708.

Continued


Circuit Breakers: The Myth of SafetyFredrick F. Franklin, P.E.

Copyright 1989 by Frederick F.Franklin, p .E.

“Contrary to popular opinion, theuse of circuit breakers and fusesdoes not guarantee that shortcircuit fires will be prevented.”This was the lead sentence of anarticle regarding electrical firesthe author published in theN.F.P.A. Fire Journal in 1984.After further research, he patenteda simple electronic circuit to beadded to circuit breakers to pre-vent short circuit fires. But a yearlater, he discovered that Europeancircuit breakers have the sameeffect, because they use a (9 turn)solenoid coil inside the circuitbreaker to make them moresensitive. Efforts are under way topersuade American manufacturersto change to this European style.

By simulating 120 volt shortcircuit arcs, it was discovered thatthe arcs have a significant electri-cal resistance of their own, whichcan be as high as 0.5 ohm. Thiskeeps the electrical current belowthe magnetic or instantaneous triplevel of most North Americancircuit breakers. Most people donot realize that small 15 and 20ampere branch circuit breakershave two modes of tripping. Thefirst is the well-known b whichopens thermally, like the thermo-stat in a home. But circuit break-ers also open instantaneously (likea relay) whenever the magnetic

field induced by the electricalcurrent reaches a certain thresh-old. Unfortunately, this magnetictripping threshold is set too highin almost all North Americancircuit breakers.

Short circuit currents are simu-lated by burning through theinsulation on conductors and bycutting on their insulation tocreate arcing shorts. It wasdiscovered that the electricalcurrent levels in 120 volt arcingshort circuits are almost alwaysbetween 150 and 400 amperes.with most levels congregatingaround 200 to 250 amperes.Hundreds of arcs have beencreated and an arcing currentbelow 100 amperes has neverbeen observed.

These current levels may becompared to the magnetic orinstantaneous trip levels of 15ampere North American circuitbreakers:

Brand A: 120 to 180 AmperesBrand B: 120 to 230 AmperesBrand C: 150 to 350 AmperesBrand D: 325 AmperesBrand E: 360 AmperesBrand F: 800+ AmperesBrand G: 800+ Amperes

The corresponding levels for 20ampere breakers are:

Brand A: 160 to 240 AmperesBrand B: 150 to 280 AmperesBrand C: 200 to 465 AmperesBrand D: 435 Amperes

Brand E: 480 AmperesBrand F: 1065+ AmperesBrand G: 1065+ Amperes

It may be observed that most ofthese nipping levels are wellabove short circuit arcing currentlevels.

There is another way to com-pare circuit breakers (and fuses),which is to measure their openingtimes at 200 and 250 amperes, therange of most 120 volt shortcircuit arcs (see Figure 1 nextpage).

A third way of comparingcircuit breakers and fuses is tocompare relative energy as afunction of current. It may beobserved in Figure 2 that the let-through energy (I2t) for a 5XEuropean breaker falls drasticallyat about 75 amperes. This isbecause it suddenly begins open-ing much more quickly. The let-through energy for the midrangeAmerican breaker does not beginto drop dramatically until 400amperes (27X). The Europeansinsert a coil of nine turns or so ineach circuit breaker to greatlyincrease the magnetic forces (seeFigure 2). This lowers the mag-netic nip level to 75 amperebreaker (5X). Thus at all currentlevels above 100 amperes, Euro-pean 5X circuit breakers nip in0.004 second. This reduces theenergy in the arc to negligiblelevels, for a reported additional

Continued


Circuit Breakers: The Myth of Safety

manufacturing cost of only $0.30.This addition would reduceAmerican fires by 20 percent, orroughly one billion dollars peryear. Even if short circuits ac-counted for only two percent offires, this change would stillprevent over $100 million dollarsof fire loss each year.

On February 7, 1989, theAmerican product safety engi-neers for the television and audiomanufacturers, such as Sony,RCA, GE, Magnavox, etc., flew

to Cincinnati for a specialmeeting at which video tapes andslides were shown to illustratethese views. Afterward, this R-1Safety Committee of the Electron-ics Industries Association (E.I.A.)voted unanimously to petitionU.L., the N.I.S.T. (formerly theNational Bureau of Standards),

and the circuit breaker manufac-turers’ organization, N.E.M.A.,for change. Paragraph 2 of theirPosition Paper says: “The greatestpotential for reducing the risk offire from arcing shorts in thepower supply system as a wholeappears to lie in significantlyreducing the initial “let-through”energy under arcing short condi-tions of branch circuit breakers sothat they instantaneously trip at orabout five times their nominalcurrent rating.”

After this meeting the authorand other members of the E.I.A.

Continued

Continued



were invited to N.E.M.A. head-quarters in Washington, D.C. Atask force has been formed atN.E.M.A. to study these views,and on May 9,1989, the samevideo and slide presentations weregiven to them. One video tapeshows a power cord lying on aburning piece of cardboard andplugged into a 20 ampere outlet inthe author’s office building. Thepower cord short circuits over 30times and for two minutes beforepopping his 20 ampere circuitbreaker. In a later video, this testis repeated with blankets lyingnext to the cardboard. Flyingcopper globules from the arcsignite three blankets before pop-ping the 20 ampere breaker. Bothof these videos were taken thefirst time the tests were con-ducted. A copy of either videomay be obtained by sending$25.00 (each) to P.A.C.E. Inc.,4325 Indeco Court, Cincinnati,Ohio 45141.

For over a decade, the insur-ance industry and the electricalindustry have argued about elec-trical fires. Many in the electricalindustry argued that they couldnot simulate electrical fires, andtherefore, they do not occur .Thesimulations and video tapesmentioned above should put thatargument to rest, but the useful-ness of circuit breakers is such aningrained myth that it may not be

soon. Most people continue tomisunderstand electrical fires.Many electrical engineers main-tain that all shorts are dead shorts,and therefore that no short circuitfires occur. Their reason, in short,(0 resistance) cannot dissipate anyheating energy and therefore thatit cannot cause a fire. But ondemonstration video tapes, paperis ignited numerous times bysimply cutting on a power cordwith diagonal cutters. So areblankets. In this type of test,where the diagonal cutters firstcreate a dead short between theconductors, the alternating mag-netic forces induced at the shortby the high electrical currentspush the conductors (the wiresand the cutters) apart. Thiscreates an arc of significantenergy (and its own electricalresistance) in the air almost everytime. Thus arcs immediatelyresult from dead shorts, unless theconductors are well bondedmechanically.

The amount of energy allowedinto an arc by most Americancircuit breakers is well-known toelectricians. They have devel-oped a common saying, in whichthey point to circuit breakers in apanel and say, “you can weldwith them!”

Besides tripping times, anotherindication of relative safety is theamount of metallic meltingallowed at an arcing location by

the circuit breakers. It is wellknown that a short circuit whichcauses a fire in building wiringalways leaves a melt on the metalconductors. In fact, the energy inarcs which cause building fires isgreat enough to melt at least oneconductor completely apart over97% of the time. When a 5X Eu-ropean style circuit breaker isinserted into the circuit for simu-lations, either no melt at all or avery tiny melt develops. (Thesame is true of 15 ampere Ameri-can fuses.) 0.004 second is such ashort time that very little arcingenergy can develop.

If most American circuitbreakers do not prevent shortcircuit fires, what do they accom-plish? Their usefulness seems tobe limited to tripping on deadshorts. Most people think fusesand circuit breakers are useful forpreventing overcurrent fires. Butovercurrents great enough toovercome the large factor ofsafety built into wiring insulationare very rare. As an example, thefirst video tape shows scenes of a14 gauge copper romex-type cablethrough which 100 amperes isflowing, in both the hot and theneutral conductors. Traditionally14 gauge copper has been rated atonly 15 amperes. Yet after onehour, the paper wrapped aroundthe grounding conductor insidethe cable is not even scorched.

Continued


Table A. Total Causes1. Electrical 37 %2. Arson 11 %3. Flammable Liquids 8 %4. Fuel Gas 5 %5. Smoking 5 %6. Kerosene Heater 2 %7. Cooking 2 %8. Other Causes 10 %9. Undetermined 20 %

100%

Table B Electrical Fire Causes1. Short Circuits 30.0 %2. Overheating 5.0 %3. (H.T.L.'s too slow)

4. High "R" Aluminum 1.0 %5. Broken Neutral 0.5 %6. Overcuuent 0.1 %7. High "R" Copper 0.1 %8. Televisions 0.1 %9. Motors 0.1 %

37.0%


Thus the factor of safety built intothe insulation is more than 7:1.The video also shows scenes of a16 gauge power cord sandwichedbetween two layers of carpet andthrough which 60 amperes flowsin both conductors for one hour.The plastic insulation does noteven melt, let alone burn. Over-loads well above 60 amperes inbranch circuits are highly unlikely,because so many applianceswould have to be plugged in todraw that much current. In acareer of over 1500 fire investiga-tions, only one overcurrent fire inbuilding wiring was observed. Inthat case a circuit breaker re-mained stuck in the “on” position,after a dead short developed in thewiring. Overcurrent is a mythwhich developed when firemen re-peatedly found 30 ampere fusesand pennies behind fuses at firescenes. The real danger of the 30ampere fuses and pennies was thatthey allowed much more energyinto the arc when a short circuitoccurred than a 15 or 20 amperefuse would have. Even when apenny was used behind the fuse,there was usually a 60 ampere,or 100 ampere main fuse in placeto prevent an overcurrent fire.

The third type of electrical fireis a high resistance connection,which occurs when two conduc-tors pull apart so that only a smallcross sectional area remains incontact. It also occurs when

aluminum connections oxidize. In1500 fires, only two (significant)fires were caused by copperconnections, and six by aluminumconnections. All of the aluminumconnection-fires occurred in verylarge conductors, such as wherecables feed circuit breaker panels.No (significant) connection firehas ever been confirmed in smallbranch circuit aluminum wiring.One reason for this low incidenceis that most connections are en-closed in a metal or plastic junc-tion box. Thus the flying metallicglobules and heating energy arecontained. Many small fires, of the$50 variety, are reported by othersin outlets and wall switches, butthe incidence of significant firesdeveloping in them are very low.The energy, the flying globules,and any resulting fire are con-tained very well, even for shortcircuit arcing. Conduit has thissame effect. Once short circuitenergy is minimized, conduitmight not be needed.

Tables A and B list the inci-dence of various types of firesinvestigated during the past fiveyears. After finding a short circuitmelt on a conductor at a fire scene,the only way for an investigator toprove that it occurred prior to thefire and not during the ensuing fireis to prove that the melt is locatedat the point of origin of the burn

patterns. Every other cause at thatorigin must then also be elimi-nated. Thus an “electrical” fireexpert must also be expert at in-vestigating all types of firecauses, including arson. Anelectrical engineering degree, byitself, is not of much assistance.

During short circuit arcingsimulations, a phenomenon wasdiscovered which would be usefulfor preventing short circuit firesin higher current and highervoltage circuit breakers, where

Continued

Continued



the cost of a microprocessorwould not be prohibitive. It wasfound that in virtually all arcs, thearc extinguishes and re-ignites re-peatedly. This almost alwaysresults in missing half cycles andquarter cycles in the sine-wavewaveform. In quarter cycling, thearc does not re-ignite until nearmaximum voltage is reached at thepeak of the sinewave. It is be-lieved a computer could easilydetect these missing half cyclesand quarter cycles, and immedi-ately trip a larger circuit breakerto minimize short circuit energy.

Besides short circuit arcing, theonly other significant cause ofelectrical fires in the author’sexperience is high temperaturelimit thermostats (and fusible ele-ments) which take too long tofunction after the main thermostatsticks in the “on” position. Theyfunction only after the fire hasbegun, in appliances such ascommercial deep fat fryers, elec-tric dryers and coffeemakers.These devices could be given aquicker opening time, by usingsolid state sensors, etc. Improvinghigh temperature limits andminimizing short circuit energywould reduce electrical fires tonegligible levels, in the author’sopinion, and eliminate the mostconfusing aspect of fire investiga-tion for most people—electrical.

As of this writing, the Europe-ans are not aware that their 5Xcircuit breakers prevent arcingshort circuit fires so well, becauseapparently no one there has evermeasured the currents in house-hold short circuits arcs either.The Europeans began using thesolenoid coil in their circuitbreakers 15 to 20 years ago forother reasons. It is hoped thatU.L. and the N.F.P.A. will notdelay in insisting that NorthAmerica circuit breakers bechanged to the European style,to prevent 20% of our fires.

The tests, measurements anddiscoveries mentioned in thisarticle are the author’s.

About the Author:Frederick F. Franklin is a 1964graduate of a 5-year program atthe Ohio State University inElectrical Engineering. Heworked as an electronics engineerfor nine years before formingP.A.C.E., Inc., in Cincinnati, Ohioin 1974. P.A.C.E. is a full-timeforensic engineering firm whichhas investigated over 4,000 firesand accidents of every type inOhio and its surrounding states.Mr. Franklin has testified at over60 trials as an expert witness;97% of his cases settle out ofcourt.

According to the author, thefollowing letter appeared in theMarch, 1984 edition of the IEEESpectrum:

“I am an EE {Ohio State, 1964)who has investigated more than40 accidental electrocutionsduring my forensic engineeringactivities over the past 12 years.Over 12 of these electrocutionswere caused by120 Volts ac. In allof these cases, which involvedpower supply utility, the thirdwire ground was either nonexist-ent or was interrupted at somepoint. Third-wire grounds work.They either cause enough currentto be drawn by the short circuit topop the circuit breaker or fuse, orin the case of a soft short circuitthey keep the voltage on themachinery and equipment casingsso low that no one can be hurt. Ihave never observed an electrocu-tion to be caused by a doubleinsulated tool or [to occur] when aground fault interrupter was inplace. The one 120 V electrocu-tion that occurred with a third-wire ground intact occured be-cause a portable generator wasbeing used, and the workmandropped the junction between hispower tool’s cord and its exten-sion cord into the water in whichhe was standing. It is generallyaccepted in the industry thatcurrents of 0.1 amperes can causefatal electrocutions. Because of

Continued on page 15

Continued


Ask Doctor Z

In the world of Product Safetyand Certification, there are manypitfalls for the unwary. If youhave a problem that seems insol-uble, then it’s time to ask DoctorZ! He has the answers, derivedfrom his many years of trainingand experience in the Science ofProduct Safetiology. Pitfalls holdno terrors for Dr. Z, since he is ona first name basis with most ofthem. Any resemblance to per-sons, places, products, agencies,or good advice is purely coinci-dental, but don’t let that stop you.Write Dr. Z today!

Dear Dr. Z:Recently I was opening a UL

Standard when I noticed theForeword. What does it all mean?

-Puzzled in Peoria

Dear Puzzled,I was about to start answering

your question when I realized thatyou had not asked “What does itAll Mean?” in the cosmic sense.

A question like that would be dif-ficult, but appropriate, for me toanswer. However, since you areonly inquiring about the Forewordof a UL Standard, I will turn thisquestion over to my lab assistant,Fred. As you can see from his pic-ture, he has already made anattempt to answer the cosmicquestion. Fortunately, he survived.

Doctor Z

Dear Puzzled,Hello, this is Fred. That is, these

words are written by Fred, theyare not actually Fred. But ofcourse you knew that already, andthat wasn’t even the question youwere asking. But this is my bigchance so I want to be as preciseas possible in my answer. That is,when I start writing my answer,which I haven’t yet, but I will verysoon.

Here it is: The Foreword seemsto be a lot like the “basic speedlaw” in California, which says thatany speed is illegal if it’s danger-ous. However, I don’t think it saysthat any speed is legal if it’s notdangerous. Come to think of it,that’s a lot like strict productliability , which says that anyproduct that hurts you must havebeen defective in the first place.Anyway, let me pick out a coupleof good parts from the StandardUL 1950 Foreword.

C. A product which complies

with the text of this stan-dard will not necessarily bejudged to comply with theStandard if, when examinedand tested, it is found tohave other features whichimpair the level of safetycontemplated by these re-quirements.

D. A product employing mate-rials or having forms ofconstruction differing fromthose detailed in the re-quirements of this Standardmay be examined and testedaccording to the intent ofthese requirements and, iffound to be substantiallyequivalent, may be judgedto comply with the Stan-dard.

Part C apparently says thateven if your product agreescompletely with every word of theStandard and meets all of therequirements written down, ULdoesn’t have to accept it, but theymight. They have to look at it andtest it first to find impairmentsbefore considering rejecting it. Ofcourse you have to know aboutcontemplation because the Stan-dard is supposedly contemplatinga certain level of safety, thoughperhaps not actually describing it.

Part D apparently says thateven if your product doesn’t havethe right materials or the rightconstruction described in the

Fred



Abstractsby Dave Lorusso

The following is the beginning ofa regular feature for the ProductSafety Newsletter. Written byDave Lorusso, the column willhighlight articles of interest to theproduct safety community. Con-tributions and suggestions arealways welcome.

The following articles weresubmitted for our review:

• “The Push to Comply withEuropean Safety Standards”was published in the Novem-ber, 1989 issue of EvaluationEngineering. The author, NeilSclater, discusses the resultsof his interviews with engi-neers and managers of Ameri-can component suppliers. Thearticle focuses on WestGerman test organizations,specifically, VerbandDeutscher Electrotechniker(VDE) and Technischer Uber-wachungs Verein (TUV).Some pros and cons aredescribed in using VDE andTUV.

• “ A primer on InternationalRegulatory Standards”, waspublished in the November,1989 issue of PowertechnicsMagazine. The author, DouLeschak, provides powersupply safety design guide-lines for creepage and clear-ance spacings, insulation ap-plication, and the flammabil-ity of internal and externalplastics. Agency follow-up isdiscussed, including produc-tion line testing-

• “Selling in Europe, How toGet VDE Certification”, waspublished in the December 7,1989 issue of Machine De-sign. The author, GreggGalluccio describes theVerband Deutscher Electro-techniker, E. V. (VDE) andthe certification schemesavailable. Differences in VDEvs. UL standards are discussed.Steps to aid in obtaining VDEcertification are presented.Additionally, factory inspec-tion and EMI/RFI emissionrequirements are discussed.

• “Power Supplies -Complyingwith European Standards” waspublished in the January, 1990issue of EvaluationEngineering. The author, NeilSclater, discusses compliancewith European standards,notable safety and emissions,

for switching power supplies.Power supply manufacturersshare their views on magnet-ics used in power supplies, thecost of compliance, emissions,and the commonality of UL,CSA and IEC standards suchas: leakage current, creepagedistance and dielectric with-stand voltages.

• “Engineers Star in UL VarietyShow: on the Job” was pub-lished in the April 24, 1989issue of Electronic Engineer-ing Times. The author, TerryCostlow, describes the varietyand diversity of engineeringwork at Underwriters Labora-tories (UL) Inc. Trends in ULelectronics testing and multi- !agency testing are briefly dis-cussed.

• “DANGER, CAUTION,WARNING-Product Warn-ings” was published in the De-cember, 1989 issue of Profes-sional Safety. The author, A.V. Riswadkar , provides infor-mation on adequate warningsand instructions for products.The article discusses the dutyto warn, key elements of awarning, and effectiveness ofwarning.

• “Exposure to Low FrequencyElectromagnetic Fields andCancer Development” was

Dave Lorusso

Continued


Abstracts


some of the tests I have done tosimulate accidental electrocution,however, it is my suspicion thatcurrents even as low as 0.01amperes may sometimes causefatal electrocutions. Again, thirdwire grounds work!”

Frederick F. FranklinCincinnati, Ohio

The following infonI1ation wasreceived from the author justbefore going to print:

“At a joint UL, NEMA, and EIAmeeting on April 5, 1990, the EIAand NEMA voted to fund ULresearch efforts in this area. Theauthor was invited to participatein the writing of the test proce-dure.

After 1-1/2 years of initialresearch, UL reported that itbelieves there would be a benefitto using 5X circuit breakers incircuits where they would notnuisance trip. After some months

of initial testing, NEMA reportednuisance tripping only by windowair conditioners, table saws, andhigh power microwave ovens.”

Frederick F. (Rick) Franklin

Bibliography:1. Frederick F. Franklin, “ ASurvey of Electrical Fires,” FireJournal, Volume 78, No.2,March, 1984, Pages 41-44.

published in the November,1989 issue of ProfessionalSafety Author Daniel H. Annafocuses on extremely low fre-quency (ELF) radiation. Dis-cussion centers on current re-search about the effects ofELF exposure.

• “Nine Paths to EffectiveWarnings” was published inthe November 6, 1989 issue ofDesign News. The author,Phillip M. Davis, Esq., dis-cusses guidelines to use whendeveloping and evaluatingwarnings, labels, packaging,and instructions. The credibil-ity of warnings and the at-tempt to modify behavior arebriefly discussed.

• “More Ways to Build BetterProduct Labels” was publishedin the November 20, 1989issue of Design News. Theauthor, Phillip M. Davis,Esq., describes guidelines toapply to a warning andlabeling system to adequatelyeducate the user on safeproduct usage and to satisfythe legal responsibility of themanufacturer

About our new AbstractsEditor:

Dave Lorusso is working as aprincipal engineer for Codex/Motorola in Canton, Massa-chusetts. Dave has responsi-bility for regulatory compli-

ance of the Codex/Motorolaproduct line. He has a BSEEfrom Northwestern Universityand an Associate in Elec-tronic Engineering Technol-ogy from Wentworth Instituteof Technology. Articles ofinterest to the product safetycommunity may be sentdirectly to Dave at the follow-ing address:

Codex/Motorola20 Cabor Boulevard (Cl-20)Mansfield, MA 02048Phone: (617) 821- 7609Fax: (617) 821-4211

[The PSN staff wishes to thankDave for volunteering his valu-able time to assist in this publica-tion -Ed.]

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Letters to the Editor

EC1992Dear Sir:Being the owner of RETLIFTESTING LABORATORIES, anindependent EMC testing labora-tory and the Chairman of theAmerican Council of IndependentLaboratories (ACIL) GovernmentRelations Committee, I reviewedthe above referenced article withconsiderable interest. Clearly weall understand the importance ofthe “EC1992” and we, in theACIL, have followed it extremelycarefully to detem1ine its overallimpact to the U.S. independenttesting industry.

I found the article to be quiteinteresting and as technicallycorrect as one can be covering anissue which is changing almostdaily. However, I must takeexception to the author’s “Plan ofAction” item 6, “Get experiencewith appropriate Europeancertification labs.” WHY? Aren’tU.S. laboratory good enough toperform this testing? Sure theyare! It has nothing to do withcapabilities. The fact is the ECrefuses to accept U.S. generatedtest data on regulated goods andrefused to “notify” any U.S.laboratories.

It is clear that the Europeansare attempting to control boththeir marketplace and ours bycontrolling testing and certifica-tion. And it is extremely frustrat-ing when major corporations inthis country accept this treatment.

Small manufacturers and labora-tories can and will be seriouslyhurt if this inequity is not cor-rected. I can assure you thatthrough our efforts at ACIL withthe Dept. of Commerce, FCC andUSTR we are fighting to protectthe interest of small business andthe U.S. laboratory industry.

I would assume that the Prod-uct Safety Technical Committeeshares ACIL’s interests in thisarea since you will note that it isin basic agreement with one of thefounding positions of your com-mittee, that being “Understandingthe contribution to productsafety of the test house.”.

Very truly yours,Walter A. PoggiChairman

Circuit Breaker Article“In rebuttal”, if you publish Mr .F. Franklin’s article on CircuitBreakers: Circuit breaker manu-facturers do not agree with manyof Mr. Franklin’s test methods,conclusions and comments andhave or are addressing themthrough NEMA.

Donald FischerSquare D Company

CSA 950/IEC 950I attempted to order the CSA 9501IEC 950 and U.L. 1950 compari-

son article from Richmond officeof CSA. It is not available. I wasable to order the CSA 950, cost$98.00. This is for your informa-tion.

Fred Phillips

Oops on UL 1950 InfoThe article titled “UL Modifies1950 File Review” (“News andNotes,” Product Safety Newslet-ter, Jan/Feb 1990) might moreaccurately have been titled,“Product Safety NewsletterModifies 1950 File Review!”

Many readers were surprised tofind out out that “Products nowlist under the ITE category wouldhave to be reviewed to UL 195(prior to March 15, 1990, or betransferred “ Of course this atypo. The effective date of UL19590 is March 15, 1992-accord-ing to reliable sources at UL.

Sincerely,Paul McDonaldElectro Service Corp.

P.S.-Keep up the good work, thePSN and the monthly meetingscontinue to be beneficial sourceof information.

[The editor apologizes for theabove oversight. Our readerscontinue to keep us on our toes-Ed.]


Letters to the Editor

Ask Doctor Z

Standard it still might be OK withUL. They must decide to look atit and test it the same way theStandard intended they should,even if it didn’t mention how, soyou have to know the intentionsof the Standard. If the results arepretty much the same as a productwith all the “right stuff’ then itmight be all right.

The key seems to be to get toknow the Standard. Contemplatewith it, maybe attend yoga classestogether. That should make youmore flexible, too. But you mustbe cautious. Like the father of ateen-aged girl you may be asking,“Are your intentions honorable?”And once the two of you areclose, you will realize that all therequirements are guidelinesinstead of requirements.

The rest of the Foreword is asnap. Part A says requirementschange, Part B says you’d betterfollow them if you want Listing,Part E says it’s not their fault, andPart F says watch out when youtest. And that’s about it!

All the best,Fred

Another Offer to HelpThank you for the two copies ofthe newsletter. It looks very goodand satisfies a real need to giveproduct safety and testing expertsa forum for communication andswapping information.

I have been appointed as thenew chairman for ISA SP82.01.This committee created ANSI/ISA-S82.01 “Safety Standard forElectrical and Electronic Test,Measuring, Controlling andRelated Equipment”. Expertssuch as Richard Nute served onthis committee. Additional workwill be oriented towards harmo-nizing with CSA C22.2 No.142and IEC 1010.

I also chair ISA SP12.4 andNFP A 496 subcommittees deal-ing with purged and pressurizedequipment. My primary expertiseis in intrinsically safe and nonin-cendive equipment for use inflammable atmospheres.

I have had articles publishedand would be inclined to write onsubjects that are related to mybusiness work load or to currentcommittee work. Many of thetests described in safety standardscould use supporting instructionsto explain the purpose of the test,the equipment (where it can bepurchased), precautions whendoing tests, how to interpretresults, etc.

I hope you do not restrict thenewsletter to IEEE members andlook forward to the next issues.

Regards,Richard C. Masek, P .E.Supervisor, Product SafetyBAILY CONTROLSCOMPANY

[The PSN welcomes all contribu-tions, especially from leaders suchas Mr. Masek. Those expressingan interest in contributing to PSNwill be contacted by our Techni-cal Articles Editor in the nearfuture.-Ed]

Continued

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Area Activity Reports

Chicago ChapterThe last meeting was on January16, 1990. Mitsubishi ElectricSales was gracious enough toallow the use of their facility.Mr. Saul Rosenbaum VP/Re-search for Leviton Mfg. spoke onFGCIs and related products,including the newly requiredIDIC.(Suggestion/Ideas-Contact JohnAllen.)

The Chicago Chapter is in des-perate need of a secretary.Volun-teers, please contact John Allen.

John R. Allen, President

Los Angeles ChapterThe last meeting of the ProductSafety Technical Committee inLos Angeles was on March 5.Charlie Bayhi of MAI Basic FourInc. will present the proceedingsof the CBEMA meeting of Febru-ary 27.

The next meeting will be onMonday, April 30 or May 7, at6:30 pm at Barman Electronics,8500 Balboa Blvd., Northridge,CA 91325. Martin Quezada of LHResearch will discuss IEC 555and Power Factor Correction.

Those interested in the activi-ties of the Los Angeles chaptershould contact Mr. Rolf Burck-hardt at (818) 368-2786.

Editor

Portland/Seattle ChapterOur February meetings werehighlighted by a presentation byJack Lee of the Bonneville PowerAdministration. Jack is an Envi-ronmental Health Specialistoverseeing transmission linebiological studies since 1974.

Jack’s presentation examinedthe numerous studies that havebeen made concerning the pos-sible health hazards associatedwith exposure to power linefields. Jack pointed out that whileno concrete evidence has beenmade to show a hazard, theirresearch continues to cover abroader scope and the new higherpower transmission lines. It wasinteresting to note how using anelectric blanket all night gives youtwenty times the exposure thanwatching TV.

Two programs are coming soonthat should be interesting toProduct Safety members. OnFriday, March 23, 1990, PeterPerkins will conduct a one-dayseminar on Product Liability andSafety at 290 Smith MemorialCenter, Portland State University.Cost is $195.00 including lunchand parking.

Oregon Center for AdvancedTechnology Education (OCA TE)will sponsor John Whittaker ofthe University of Alberta talkingabout “Probability and PublicSafety” on Thursday, April 19,1990, at Oregon Graduate Center.

Want a trip to Washington DC?Provide a paper for 1990 IEEEInternational Symposium onElectromagnetic Compatibility.Contact John Kneicht at Underwrit-ers Laboratories 708/272-8800.

The Portland Section will haveits meeting on Tuesday, March 201990, at 7:30 pm at the PortlandGeneral Electric building (14655SW Old Scholls Ferry Road,Beaverton, at the south end ofMurray Road). The featuredspeaker will be Debbie Tinsley,Engineering Team Leader for theMedical and Laboratory Equip-ment Group at UL. She will ex-plain UL’ s new capabilities as a“one stop” testing house. UL cannow test to the specifications ofCSA, VDE and of course, UL.

For more information, contactFran Pelinka at (503) 641-1414 orHeber Farnsworth (206) 356-5177.

Al Van Houdt

Santa Clara Valley ChapterThe first meeting of the year washeld January 23, 1990, after abreak in the chain for December.

Mr. Creg Sato of UnderwritersLaboratories reviewed the staus ofthe File Review for UL1950. Aftercomments from industry, UL hasdecided to change the File Reviewand allow presently Listed equip-ment to remain Listed under the4th Edition of ULl14 or

Continued



UL478 instead of being re-evalu-ated to the new UL1950 standard.There are also some changes inlabeling proposed so as to identifythe type of equipment standardthat the units are Listed under.There is to be another UL Indus-try meeting in March to discussthe proposed changes to the FileReview.

The February 27th meetingmain event was a presentation byMr .Matthias Heinze of TUV onspacings and insulation thickness.

Mr. Heinze reviewed the historyof the present require-ments inEN60950. The creepage andclearance values basically camefrom VDE 110, and insula-tionthickness for transformers cameto be based on the electricstrength tests from IEC 380 and435.

He also noted some rules tofollow in designing a product:

1. If a transformer is externalto the equipment, it will berequired to meet the throughinsulation thicknessesspecified in EN60742 forIsolation Transformers. Thisalso applies to Telecomproducts.

2. For switch mode power sup-plies, TUV will use thedefinition of working volt-age in VDE 805, part 100A2, ie., peak voltage, todetermine the creepage,clearance, and insulationthickness required.

Mr. Heinze also noted thatEN60950 allows the one fuse toprotect a product and that it isassumed that there is a 16Abranch protector in the hot line;that 230/400 volts is becoming thestandard voltage in Europe; thatMOVs are not allowed line-to-earth; and use red for emergenceswitches and lights, only.

For more information about theactivities of the Santa ClaraValley chapter, please contactDavid McChesney at (408) 895-2400 extension 2771 or JohnReynolds at (408) 942-4020.

David McChesney

Northeastern ChapterThe most recent meeting of theNortheastern chapter was held onWednesday, January 24. TheCSA liaison report indicated thatthe NFPA ‘s harmonizing withCSA and CEC would attempt tobring the NEC and CEC intoalignment. CSA 950 is nowreleased and includes a telecom-munications requirement. UL andCSA are working out the differ-ences between UL 1459 and CSA0.7.

Bruce Langmuir reported thatUL is combining UL standards1270, 1409, and 1411 into adocument referred to as UL 1492.He also reported that UL isreviewing the use of printedwiring board foils to replace the

grounding wires to accessoryoutlets under the requirements ofUL 1270.

The technical presentation wasby Mr. Larry Rogers of the Qual-ity Management Institute. Mr.Rogers provided a presentation onthe implementation of qualitysystems and QMI’s registrationprogram and reviewed themotiva-tion and justification forthe institution of formal qualityprograms. He noted the costsavings and improved productquality gained through a formalprogram. To be competitive withEurope, Mr. Rogers noted that itmay well be necessary for NorthAmerican manufacturers toinstitute such programs.

The calendar provides informa-tion about upcoming events.Those interested in the activitiesof the Northeast chapter shouldcontact Mr. Bill VonAchen at(508) 263-2662.

Editor

Orange County/Southern CaliforniaChapterThe February meeting was held inconjunction with the PowerElectronics Conference held inLong Beach. The featured speakerwas Mr. Josef Kirchdorfer ofWeber AG, a manufacturer ofcircuit breakers, who gave apresentation on Overload andShort Circuit protection.

Continued

Continued



SymposiumUpdateCall For Papers

In order to properly develop oursession at the 1990 IEEE Interna-tional Symposium in August, youmay have noticed that we havehad several releases of our “Callfor Papers.”

We now are requesting a sub-mittal of a paper or tutorial whichspecifically discusses any connec-tion or conflict between electricshock protection and EMCcontrol methods.

Due to the time constraints in-volved, we have decided toorganize a tutorial instead ofsubmitting papers for publication.This means that the review pro-cess time can be reduced and theformat of the submitted materialcan be less formal. We feel thatthis allaws us to be better pre-pared for the Symposium.

Also, the format of any printedmaterial that is handed out duringthe Symposium, although techni-cally accurate and well written,will not need the additional polishrequired of a published paper.

We presently have three sub-mittals in response to our “Callfor Papers.” These are:

Methods of Protection AgainstElectric Shock- ThomasLundtveit, Staff Engineer, Under-writers Laboratories Inc. Pro-vides an overview of variousmethods of protection againstelectric shock that can be incorpo-rated into the design of a product.These include grounding, doubleinsulation, shielding, ground faultcircuit interrupter, immersiondetection circuit interrupter andpolarization.

Personnel Protection Devices forUse on Appliances-Robert L.LaRocca, Engineering GroupLeader, Underwriters Laborato-ries Inc. Presents an overview ofsome devices that have becomeavailable to the manufacturers ofappliances to reduce the risk ofelectric shock resulting frominsulation failures (ground fault)and accidental immersion. Thesedevices, known generally aspersonnel protection devices,consist of Ground Fault CircuitInterrupters (GFCI), ApplianceLeakage Current Interrupters(ALCI) and Immersion DetectionCircuit Interrupters (IDCI).

Derivation of Equipment Ground-ing Impedance Values -RichNute, Safety Engineer, HewlettPackard. Presents approaches tofinding appropriate values forequipment safety grounding andbonding impedances.

In our “Call for Papers” werequested that each paper shouldmention any connection or con-flict between the electric shockprotection means discussed andEMC control methods that mightbe used. After further considera-tion, it was decided that authors ofpapers on product safety may notnecessarily be as knowledgeableabout both electric shock protec-tion means and EMC controlmethods. Therefore we are re-questing submittal of a paper ortutorial which discusses anyconnections or conflicts betweenelectric shock protection andEMC control methods (for ex-ample, leakage current, groundingpoints, etc.)

Please send any submittal to:John KnechtUL, Northbrook333 Pfingsten RoadNorthbrook, Illinois 60062

The March meeting will pro-vide a discussion of the eventsinvolving the CBEMA meetingheld February 27 and 28, 1990.The April meeting will feature apresentation by Mr. Martin

Quezada of LH Research who willdiscuss harmonic distortion andpower factor correction.

Those interested in the activitiesof the Orange County/SouthernCalifornia Chapter should contact

Paul Herrick at (714) 770-1223.

Paul Herrick

Continued


Guest EditorialJohn McBain

Reader Survey ResultsThis survey has several purposesbesides the obvious one of findingout who wants to keep subscrib-ing to the PSN. Some resultsavailable now are worth describ-ing.

One of the main purposes of thesurvey is to establish the propor-tion of readers who are actuallyIEEE or EMC Society members.This information was requestedby the EMC-S BOD because oftheir financial backing of thePSTC, which allowed the PSTCto continue publishing and mail-ing the Product Safety Newsletterduring 1989. Although a long-term objective of the PSTC is tobecome a Technical Council,which means seeking supportfrom other IEEE Societies as well,the EMC-S BOD unilaterally waswilling to “start the ball rolling”(or “start the wave-front propagat-ing”?). Their initial sponsorshiparose from several technical andnon-technical interests in commonbetween the EMC Society and thepreviously independent ProductSafety Society. But serving theinterests of EMC Society mem-bers remains their highest priority,so they want to know how manyPSN readers are members.

Reader Survey results can besummed up roughly as follows.From a mailing list of approxi-mately 1300 names we have hadso far about 50% of the surveys

returned. This means that we willbe cutting the mailing list in halfas we start 1990 (remember, ifyou didn’t send in your survey,we warned you!), although weexpect it will grow rapidlythroughout the year .Of therespondents, about 50% arealready IEEE members, andaround 50% of IEEE members arealso EMC Society members. It isinteresting that Product SafetyNewletter readers include mem-bers from at least 27 IEEE Socie-ties, including especially theReliability, Engineering Manage-ment, Industry Applications, andDielectrics & Electrical InsulationSocieties. On the other hand,over 30% of the respondents whoare IEEE members do not belongto any Society.

Not being an expert on statis-tics, I cannot say exactly how

significant our results may be. Itseems as if interest in productsafety is quite widespread withinthe IEEE and the idea of a Tech-nical Council for Product Safetymay have broad appeal. ThePSTC still needs some assistancefrom the EMC Society, but,hopefully, other Societies inter-ested in product safety will be-come co-sponsors. If some PSNreaders are involved with otherIEEE Societies, please speak up! Iwould welcome any com-mentsor suggestions from you aboutpresenting our case to yourSociety’s BOD.

Now you may be wonderingabout the comments we receivedon the different articles publishedin the PSN. Rich Pescatore hasdiscussed that more extensively inthis issue’s “Chairman’s Mes-sage”, but I have a few statisticsfor you (see below).

Continued

Survey Results


News and Notes: “Nothing newsworthy since our last publication? Hardly! But our overwhelmed NewsEditor needs the support of our readers to make the column a reality. Would you consider sending himinformation of interest to the product safety community? If just a few of our readers did this once in thenext year or two, we would have plenty of material for publication. Please help us keep the safety com-munity informed. Material can be sent directly to Dave Edmonds in care of Xerox Corp., 800 PhillipsRoad, Mail Stop 843, Webster, New York, 14580. Fax number (716) 422-7841.”

Guest EditoralContinued from page 20

EditorialRoger Volgstadt

“What do you think of when theproduct is ready to ship and theapprovals are not in place? Longnights of testing? Working upyour resume? If you do, youknow how we feel here as welook for support for our nextedition.”

For the last year and a half,Tandem Computers Incorporatedhas very generously providedvaluable time and resourcesneeded to make this newsletter areality. Due to a change in person-nel, starting with the next edition,

we will no longer have this re-source. Consequently, we needsupportfrom those in the San Jose Areawho would be able to providetheir time to continue this publica-tion. From the comments we havereceived on the reader surveyform, we know that there areliterally hundreds in the ProductSafety profession who considerthis newsletter a very valuableresource. Unless we can findseveral individuals willing to sharethe work required to assemble,

edit, and publish this newsletter,we may not be able to continue inthe present format.

Would you seriously considercontributing perhaps a few hoursevery other month so that thispublication can continue? Train-ing and equipment are available.All we need are several willinghands. Please join us in making acontribution to the Product Safetyprofession.

Roger VolgstadtEditor

Results are somewhat skewedsince this chart leaves out themany surveys which said “Every-thing is great!” or made no com-ment at all. However, it is prettyeasy to see which items arepopular and which need improve-ment. If you would like to makeadditional comments, let me pointout the the Letter column had byfar the best ratio between “favor-

ite” and “needs improvement”.So write a letter and become partof the best column in the PSN!How’s that for statistics?

Unfortunately, several peoplereturned surveys without a name,with a name but no address, orcompletely blank. The post officeforwarded one that had beenripped in half, or, rather, theyforwarded half-the half without

the name. So there are somepeople who have diligently sent intheir forms and are expecting toreceive this newsletter, but theywill be dropped from the mailinglist. If you know someone likethat, don’t flaunt your PSN infront of them. Pity their distressand tell them to give me a call onthe PSN Subscription Hotline,(408) 447-0738.


Institutional Listings

An Institutional Listing recognizes contributions to support the publication of the Product Safety Newsletter of the IEEE EMC Society Product SafetyTechnical Committee. Minimum rates are $100.00 for listing in one issue or $400.00 for six consecutive issues. Inquiries, or contribuitions made payable to theProduct Safety Technical Committee of the IEEE EMC Society and instructions on how you would like your Institutional Listing to appear, should be send to:PSTC Product Safety Newsletter, C/O John McBain (M/S 42LS), Hewlett-Packard, 19447 Pruneridge Avenue, Cupertino, CA 95014.

The Product Safety Technical Committee of the IEEE EMC Society is grateful for the assistance given by the firmslisted below and invites applications for Institutional Listings from other firms interested in the product safety field.



CalendarThe Product Safety Technical Committee of the IEEE EMC Society

Chicago Chapter ActivitiesTuesday, March 20, 1990Subject: TVSS, Related Prod-

ucts, and an analysis ofthe UL requirementsfor such.

Time: 6:30 pmLocation: UL

333 N. Pfingsten Rd.,Northbrook, ll.,

Contact: John Allen(708) 827- 7520John Knecht(708) 272-8800(ext. 3416)

Tuesday, May, 22 1990Topic: TBALocation: TBA

Los Angeles ChapterMonday, Apri130, orMay 2, 1990Subject: IEC 555 & Power

Factor CorrectionSpeaker: Mr .Martin Quezada

LH ResearchTime: 6:30 pmLocation: Harmon Electronics

8500 Balboa Blvd.Northridge, CA 91325

Contact: Mr. Rolf Burckhardt(818) 368-2786

Portland Chapter ActivitiesTuesday, March 20, 1990Subject: Safety & the Canadian

Trade AgreementSpeaker: Debbie Tinsley, UL

Time: 7:30 pmLocation: G.E. Co

14655 SW Old SchollsFerry RoadBeaverton, OR(at the south end ofMurray Road)

Contact: Fran Pelinka(503) 641-1414

Tuesday, April 17, 1990Subject: TBDSpeaker: Bob WearsonTime: 7:30 pmLocation: G.E. Co

14655 SW Old SchollsFerry RoadBeaverton, OR(at the south end ofMurray Road)

Contact: Fran Pelinka(503) 641-1414

Seattle Chapter ActivitiesWednesday, March 21, 1990Subject: Safety & the Canadian

Trade AgreementSpeaker: Debbie Tinsley, ULTime: 7:30 pmLocation: Advanced Technology

Labs22100 Bothell High-way SEBothell, WA 98041

Contact: Heber Famsworth(206) 356-5177

Wednesday, Apri118, 1990Subject: TBDSpeaker: Bob WearsonTime: 7:30 pm

Location: Advanced TechnologyLabs22100 Bothell High-way SEBothell, WA 98041

Contact: Heber Famsworth(206) 356-5177

Northeastern Chapter Activi-tiesWednesday, March 28,1990Subject: TBDSpeaker: TBDTime: 7:00 pmLocation: Sheraton Boxborough,

MassRoutes 111 and 495

Contact: Bill Von Acher (508)263-2662

Wednesday, Apri125, 1990Subject: TBDSpeaker: TBDTime: 7:00 pmLocation: Sheraton Boxborough,


Contact: Bill Von Acher(508) 263-2662

Wednesday, May 23, 1990Subject: TBDSpeaker: TEDTime: 7:00 pmLocation: Sheraton Boxborough,


Contact: Bill Von Acher(508) 263-2662


Calendar

Santa Clara Valley ChapterTuesday, March 27,1990Subject: Ergonomics for SeatingSpeaker: J. Howard, America

SeatingTime: 7:00pmLocation: Apple Computer

20705 Valley GreenDriveCupertino, CA

Contact: John Reynolds(408) 942-4020

Tuesday, Apri124, 1990Subject: Circuit Breakers/Let

Through Characteris-tics

Speaker: Rep. from WeberTime: 7:00 pmLocation: Apple Computer



Tuesday, May 22,1990Subject: CSA 220/CSA 950

StandardsSpeaker: Grant SchmidbauerTime: 7:00 pmLocation: Apple Computer



Orange County/SouthernCaliforniaTuesday, March 6,1990Subject: CBEMA meetingSpeaker: C. BayhiTime: 7:00 pmLocation: MAl Basic Four

14101 Myford RoadTustin, CA

Contact: Paul Herrick(714) 770-1223

Tuesday, April 3, 1990Subject: HanI1onic Distortion

& PF CorrectionSpeaker: M. Quezada,

LH ResearchTime: 7:00 pmLocation: MAl Basic Four

14101 Myford RoadTustin, CA

Contact: Paul Herrick(714) 770-1223

Institutional ListingsContinued

THANKS FORYOUR SUPPORT!

Continued



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

Our Reader Survey confirmed hundredsof you are interested in continuingto read the Product Safety Newsletter.We are preparing an address directory,organized by name and by postal code,to help put readers in touch with eachother. To order a copy, please send acheck for $15.00 to the Product SafetyTechnical Committee. c/o PS Newsletter.

[Note: If you want your address deleted

from the directory, please contact us.]

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

The Product Safety Newsletter’s firstissue, Vol. 1, No.1, was ten pagespublished in Feb. 1988. We now haveavailable two years (1988, 1989) ofpast PS newsletters, with an articleindex, for those who missed them.To order a set, please send a checkfor $20.00 to the Product SafetyTechnical Committee, c/o PS Newsletter.

BACK ISSUESREADER DIRECTORY

Documents

In this issue Page Product Safetyewh.ieee.org/soc/pses/Downloads/newsletters/90v03n2.pdf · resistance or in the contact resis-tance of switches and connectors. If I increases (overcuuent),