What Are the Lights on Your Surge Protector Telling You?

François D. Martzloff National Institute of Standards and Technology

Reprinted from Power Quality Assurance Magazine, July/August 1998

Significance: Part 6 - Textbook, tutorials and reviews

A trade magazine describing the confusion that exists on the market for the meaning of visible indications (“lights”) of the condition of a consumer-type surge-protective device equipped with a built-in disconnector that will operate in case of failure of the SPD component(s) in the package.

Presents a brief history of the recognition of the need for a disconnector function, and makes an appeal for more consistent practices – short of standards – on the meaning of these status indicating lights.

Also underlines the basic difference between a disconnector that only disconnects within the package the failed SPD component but leaves the load powered but unprotected and packages where the disconnector function provides maintained protection by also disconnecting the load. What Are the Lights on Your Surge Protector Telling You?

Fran~oisMarlzloff, National Institute of Standards and Technology, Gaitherburg, Maryland

Especially in a free market, sensible standards and rea- light, or pilot lights, indicating the state of the device - specifically whether pro- sonable regulations have a role to play toward providing tection is in effect or protection is lost. The original 1985 version of UL Stan- useful, reliable and safe consumer products, such as the dard 1449 stipulated that a visible or other indication of the protection status now familiar transient voltage surge suppressors (TVSS). must be provided when an overcurrent protection has operated. But that is no However, the definition of what is sensible and reasonable help to the computer user who has in- has not been stipulated in any TVSS standard. This article stalled a plug-in suppressor sandwiched between the wall and the desk. Even if provides a historical perspective of the evolution of how the TVSS is visible, there might be one, two or even three pilot lights, with or TVSS standards address the issue of a disconnector, an without clear and reliable indication of their meaning. emerging concept in TVSS design. TO place this undesirable situation in perspective, I visited three local elec- A sampling of how this concept has thrown into the deal. Arriving at the tronics and do-it-yourself stores and been implemented by the TVSS indus- designated spot in the dark pnrking lot, bought 17 different brands of TVSSs. try, including overcurrent protective de- everyone expects to find that the steer- The question was, "How would the user vices (fuses) and thermal runaway pro- ing is located on the left, controlled by be informed on the status of protection tection (thermal cut-out), shows a vari- means of a wheel, the engine is started after a temporary overvoltage caused ety of rather confusing approaches. To with an ignition key, generally near the failure of the protective element in the ~llustratethis point, let's consider three steering column, and gas and brakes are TVSS package?" temporary overvolt- familiar products: fruit cakes, automo- controlled by the right foot But what age was selected as the method of fail- biles, and TVSSs. about finding the headlight control af- ure because there is growing evidence We will all agree that our military ter you have clxed the door (it's cold that they cause a large number of the personnel serving in some desolate for- and windy out)? Worse yet, two miles failures - perhaps the majority -rather eign country are entitled to a high-qual- out of the airport, in heavy traffic, it than "large" surges. Although that state- ity product when the traditional fruit suddenly starts ro rain and the traveler ment could be the subject of one entire cake is sent to them at holiday time. To fumbles to find the windshield wiper issue of this magazine, it is only men- ensure that this happens, as reported control? Now would it not be lovely if tioned here to describe how the failures tongue-in-cheek by the media a few there were standards mandating the lo- were obtained. years ago, a lengthy specification had cation of these control;'? The point of the inquiry was not to been developed for quality-control in describe how the failure occurred (in the procurement of fruit cakes. No Common Meaning to Lights particular whether there was a potential Consider now the plight of the tired Coming now to the point of TVSS, hazard, since the devices were manu- traveler, arriving at night in an unfamil- consider the plight ofthe consumer who factured before the 1996 Second Edi- iar airport and renting a car. The agent bought a TVSS, and discarded the tion of UL 1449 became effective). The behind the counter gives the traveler the bubble package or misplaced the in- point of the inquiry is to find what in- keys and the location pf-the car in the struction sheet. This consumer is now formation is clearly conveyed to the user parking lot, and smiles with good wishes trying to find the meaning of the pilot after the TVSS has failed, and it?

68 POWER QUALITY ASSURANCE. JULY/AUGUST 1998 disconnector has operated. Neither the rating, natural aging, premature Pallure the failed dev~ccand the upstream im- new UL 1449, nor any [EEE or IEC caused by misapplication, etc. The out- pedance of the power system. standards address that practical ques- come of such failures ranges from an If left unabated. this deposited en- tion. In fact, the new 1996 version of open circuit to a very low impedance. ergy will produce severe overheating UL 1449 no longer stipulates inclusion but ral-ely a zero-impedance short cir- with attendant risk of fire or other ob- of a visible indication. As it turned out. cuit. A final open circuit may be diffi- jectionable I'ailure modes. It is to several of the packages among the 17 cult to achieve in an environment of high prevent such objectionable scenarios specimens had very little information on available fault current. If achieved. it that the concept of an SPD discor~r~ecror the significance of the indicating light implies loss of protection against sub- emerged, a\ seen in this historical per- or how the indications should be inter- sequent surges. A zero-impedance con- spective. preted. Furthermore, as mentioned ear- dition would mean no energy dissipa- The term "disconnector" is a recent lier, once the bubble package is dis- tion (no heating) in the failed SPD com- addition to the vocabulary of the SPD carded, the information is lost, because ponent and thus a relatively benign fail- industry, and the spell-checker of most it is unlikely the typical user will safe- ure mode from the point of view of the word processors flags it as unknown (as guard the back of the bubble package SPD environment, but that would re- if your processor had never discon- where the details - ~fany - might have quire interruption by an upstream nected on you?). Even the definition of appeared. overcurrcnt protection device. the tcrrn has golie through several itera- In reality, the nature of the Pallure tions in recent years. SPD Failure Modes mechanism, in particular for rnetal-ox- According to emerging standards, the Surge-protective devices (SPDs) ide varistors, (MOVs) is that the imped- disconnector function is to "disconnect components - switchmg away from the ance of the failed SPD, which is resis- an SPD from the power system in case jargon 'TVSS' to the official term of tive, is low, but not zero. Consequently. of SPD failure." This clear and simple 'SPD' approved by the IEEE and IEC - the power circuit will deliver to this concept, however, has not been consis- like any electrical component, are sub- medtum-range resistance a cut-rent tently ~rnplcnlcntedby industry, in par- ject to fallure tor a val-lcr) 01 cau\cb In- wh~ch~v~ll involvc signif~c;tntcncrgy. ticular t)! the low-voltage SPD indus- cluding severe overstl-c.;\ hcyond their depcndtrig upon the actual resistiuicc of try. In p~~~-t~cul;~r.two different devices

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CIRCLE 149 POWER QUALITY ASSURANCE. JULYIAUGUST 1998 69 SPD Indicator lights Text - --- .. Remarks-- -.. There are two possible sequences of events leading First mention that a fuse should GE Transient Suppression Manual to failure ... Accordingly, and in keeping with good be used in conjunction with an First Edition safety practices, the varistor should be placed SPD. following the equipment fuse ... 1978 ... the careful designer may wish to plan for potential The guidance is becoming mort GE Transient Suppression Manual failure modes ... mechanical rupture of the package specific, but this was still a Second Edition accompanied by expulsion ... minimize this potential recommendation, not a mandat, hazard by fusing to limit high fault currents and locating varistor away from other components ... I985 12. Supplementary Protection Implies the existence of a UL 1449 Transient Voltage Surge 'A transient voltage surge suppressor that is disconnector function but does Suppressors, First Edition provided with supplementary overcurrent protection not mandate it. in series with the suppressor shall also be provided with visual or audible indication or both of the opening of the protection device." Exception: not required if in series with the load terminals 1987 Arrester Disconnector The word 'arrester" in the title is C62.11 - IEEE Standard for metal- A means for disconnecting an arrester in anticipation unlikely to attract the attention c oxide surge arresters for of, or after, a failure in order to prevent a permanent low-voltageSPD users. alternating current power circuits. fault on the circuit and to give indication of a failed The note allows shifting the arrester function to a separate device Note- Clearing of the fault current through the (presumed to be existing). arrester during disconnection is generally done by the nearest source side overcurrent protective device.

- - .- ~ ~~ - .. -- 1994 SPD Disconnector Many options offered IEC 37A LV SPDs A Device for disconnecting an SPD from the power (Too many to be useful) Working Group Draft - SPD system in case of SPD failure. Selectton and Application At least three functions are needed ... They may be Prmaples integrated in the SPD ... or integrated to another part ...They may be used in the SPD circuit or in the mains -. -~- 3.24 - Supplementary protection device definition: 'A Has to be replaceable or UL 1449 device intended for overcurrent protections ... resettable unless the whole unit Second Edition replaceable.

12 - Supplementary Protection Visible or audible indication of operation, stipulated in the 198! edition, is no longer required.

- 1996-1997 SPD Disconnector Visible indication of failure is IEC 61 643 SPDs for LV power 'A device for disconnecting an SPD from the system implied as a requirement within dlstrlbutlon systems Performance in the event of SPD failure. It is to prevent a this definition. requrements and testmg methods persistent fault on the system and to give visible 37A/44/CDV, 37Al63lFDIS indication of the SPD failure." I -~ -- 1997 SPD Disconnector Allows separation of the -- 1 Proposed modification for "An internal or external device required for disconnector function into a 37Al63lFDIS disconnecting an SPD from the system in the event separate device. Note the of SPD failure. It is to prevent a persistent fault on insertion of 'may" in the provision the system and may give visible indication of the of a visible indication. SPD failure." ---- Consensus at last Hopefully, before the turn of the

Table 1. Brie/ history of the need for disconnector function as stated in standards and other references

70 POWER QUALITY ASSURANCE JULY/AUGUST 1998 -a fuse or a thermal cut-oft' - can serve nett of the load - or would rather take a role of a disconnector increases, one can toward that end, each covering one type chance by maintaining continuity of expect that standards are more likely to of SPD failure. In case of SPD fa~lure operation, but without protection. mandate provision of a reliable and resulting in a low impedance mode (a Standards development generally clearly defined disconnector function few ohms) an ovcl-current occurs, with lags the development of products in a lor all low-volrage SPDs. It may beeasy amplitudes in excess of the SPD rating, competitive, fast-moving technology. for an outsidcr to make judgments on so that a fuse can clear the circuit. In Low-voltage SPDs are no exception. To the apparent chaos of the marketplace case of a thermal runaway. the begin- illustrate this point, Table Ipresents a and the present standards, but there are ning of SPD failure. the current is st111 chronological tabulation of the evolu- extenuating circumstances because the too low to operate the fuse, but the con- tion of the disconnector concept, from concept as well as the implementation sequences of failure (overheating) can the introduction of metal-oxide varistors of a satisfactory disconnector are not be prevented by the operation of a ther- in the mid-seventies, to the latest amend- trivial. Some of the options, advantages mal cut-out in close proximity to the ment of the definition of a disconnector and drawbacks are briefly enumerated SPD experiencing the beginning of in the late nineties. below. overheating. The tabulation shows the reference This ambigu~tyIn rhc type ol document and cites, verbatim or in sum- disconnector des~gnand thc Ii~chofcon- mary, the implied need - and eventu- Disconnector Provisions sistency or consensus in the ~nterprcta- ally the specification - for a suitable lntegral discortr~ec~or tion of the funct~onis apparent in the disconnector function. Inspection of the o is connects only the shunt-connected wide variety of designs found on the chronology shows a clear trend toward f market, while standard-writing bodies mandating a reliable disconnector func- SPD are still working on developing an ac- tion, but also some concessions to ex- A Design challenge: requirement of ceptable consensus uvcr a hroad rangc isting product practices. Nevertheless. not opcrattng lor the expected ofappl~cations.Onc unrcolved ~siucI\ the disconnector remains the ultimate \urge\ but of' operating promptly whcthcr the usct- cxpccrs 1mrccr101ial- protection against objectionable failure upon L~tlurcol rllc 51'13 element. ter hilure - tluougll a co~~~l~lc~i.d~scoti- modes. As recognitton of this essential A LJxl ~r~tor~liat~orr:necessity to

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CIRCLE 150 ClRCLE 151 POWER QUALITY ASSURANCE JULY/AUGUST 1998 71 iPD Indicator lights SPD Status lndication Continuity Type of Indication - - 1 Protection off Maintained Not recommended

- -- ~ 2 Protection off Interrupted Desirable - - - - - 3 Protectron off Interrupted Desr rable -- 4 Protection off Interrupted Desirable ------5 Protection off Maintained Not recommended - -. 6 Protection off Interrupted Desirable - - - -. Don't Gamble When it 7 Protection off Mamtained Not recommended comes to power protection.. --- - . . 8 Protection off Interrupted Desirable Turn to a company wlth over 25 - years of power control expert~se 9 Protection off Maintained Not recommended ------and experience Controlled Power 10 Protectioc off Ma~ntained Not recommended Company manufacturers the wtdest -- - - range of power control equlpment 11 Protection off Interrupted Desirable in the Industry, ~ncludng -- 12 Protection off Mamtained Not recommended ------I Uninterruptible 13 Protection ON Maintained Misleading Power Systems (UPS) - - - 14 Protection off Maintained Not recommended Q Power Conditioning Systems -- 15 Protection off Maintained Not recommended a Electronic Line Voltage ------. 16 Protection off Maintained Not recommended Regulators --- - - : Power Distribution Centers 17 Protection ON Maintained Misleading - --- . - 1 . Power Purification Systems This comment IS based on the postulate that the user would prefer to have costly 1 equlpment protected, albeit disconnected, rather than have the power supply rnalntalned 1 When fatlure IS not an optlon, you at the risk of not protecting the equipment L. -- - need power you can depend on In Table 2. Summary of status mdrcations addrtton to prov~dtngsolutions to power problems, Controlled Power offers unsurpassed product support i.li.,~rI! \lgn;il that PI-otection installed in a manner th;u the uwr that mcludes technical assistance ity.1111\1\c~l~\ecluent sul-ges is lost. will not inspect seem.; :I poor and serwce 24 hours a day, seven choice for an uninformed user. f D~\co~~r~c.ct\the SPD and the pro days a week External disconrzecfordesigned for the tccrctl Io;~tl circltil A I~L-\I:IIchallenge: respond to ab- 111)1111~1lSl'L) c~nclition(tlicrmal f Protection of the pouJer S) \lCl1l- I\ I c~ti~\i,I\ I ,I[ current aniplitudes achieved, hut (he disconnector-I\ 1111 Iwlo\\ tI1c I-ati11.gof the SPD. likely to respond to limited I:iull CIII A I'IKilccc\\aly \tci~dy-statecurrent rents below the normal rating ol'ihc C'III-LIII~ capacity for the fuse circuit supplying the SPD. Further- ci~sct~nncc~orallows persistence more, the thermal runaway protect~on i11 I~ni~icdcurrent faults in the cannot be performed by an cxtcrrwl Y1'1). rc\~tlt~ng~nhazardous over- device which is not in closc corltai.1 "Quality solutions to IIC,I[III~,IIII!C\\ an additional pro- with the SPD conrponent power problems" 1i.cr1011 I\ p~ovidedby a thermal From the poss~bilitiesIls~ecl aho\i.. Clll OLtl. it is clear that a reliable disconnccror A Usel- ~rrfor~nation:some users function is imperative for the success- CONTZOLLSD m~ghtprefer to maintain operation ful and safe application of SPDs in POWEFZ of the load. albeit with no surge power systems. However, market pres- C0M;mNY prurection. However, if this is the sures and the resourcefulness ofdesign- modc provided by the design, it ers result in a wide range of design ap- 1955 Stephenson Hwy., Troy, MI 48083 riiust hc clearly identified on the proaches, which can be overwhelming 1-800-521-4 792 prodi~ct.and ~ndicationof protee- for the end user, just like our tired.[rav- FAX f -800-642-9625 tlon loss must be signaled - a eler arriving at the airport. Beyond the merc indicating light on an SPD basic function of a low-voltage

CIRCLE 152 SPD disconnector, the details of the in two instances, the indications were tection after failure of the SPD con, \operation and the interpretation of in- in fact misleading. Hopefully, industry ponent. dications provided by all the different and standards-writing bodies will rem- 3. Anecdotal information indicates tha manufacturers do not offer a systematic, edy this situation. devices currently on the markc. user-friendly and standardized situation. Without invoking a bureaucratic sys- might not be provided w~th, To illustrate this point, Table 2 pre- tem of regulations, it would seem that a disconnector that meets the unde- sents a summary of the visible indica- clear consensus among the manufactur- fined but expected safety in failur- tions on the 17 blind-purchase of ers would make the informed end-user modes. The second edition of U1 TVSSs, after producing their failure by much more appreciative of the industry 1449 is a very constructive step to offerings, and provide enhanced safety applying a temporary overvoltage. In ward a remedy, although it does nv- for the public. this table, it is postulated that for the address the question of statu typical consumer, ensuring protection of indication. expensive equipment is preferable, even This uncoordinated - not to say chii if it means that power is cut off for the Conclusions 4. otic - situation clearly points to th-. equipment; in other words, maintaining A survey of the low-voltage SPD need for accelerating the develor. continuity is undesirable. There may be (TVSS) products currently on the some applications where maintaining marker shows not only a variety of rnent of an industry-wide conwnil- continuity would be the first choice. Ln disconnector responses after a fail- on the design, operation, anti inre either case, a clear indication of which ure, but, in some cases, false indica- pretation of the indications of lob state prevails should be clearly stated. tion of the protection status. voltage SPD disconnectors. Hop;: From this table, it is apparent that the Information provided by several fully, this article will help tt,. two possibilities - maintained continu- manufacturers, on the product pack- process. ity o~.maintained protection - are of- xgc (soon to be discarded after pur- I'crcd by different rnanufac~urcrs.How- chase by the end-user) or on the prod- cvcl-.the implications ot'rhis choice were not clearly stated on the package, and