Transfer Switches: Understanding Why UL 1008 Is A Critical .
Transfer Switches: Understanding WhyUL 1008 Is a Critical RequirementJointly published by
Executive SummaryThere is a growing need foremergency backup powersystems in data centers,hospitals and many otherfacilities. A critical componentof many of those systems isthe transfer switch.Transfer switches shouldbe certified to UL 1008requirements. UL 1008requires rigorous testing oftransfer switches. It isdesigned to ensure reliabilityand durability.Despite the importance of UL1008, most facility executivesare not aware of what ULstandard their transferswitches are certified to.It’s easy to take transfer switches for granted.But it’s also risky.With the growing emphasis onemergency and standby power,facility executives are taking acloser look at the elements ofthe backup power system. Onecritical element of that systemis the transfer switch. Facilityexecutives count on their transferswitches to perform when theyneed to switch from the utility’selectricity supply to backupgenerators. Mostly, transferswitches perform. But there havebeen notable failures.At an Amazon Web Services datacenter in Virginia, an automatictransfer switch didn’t workproperly in May 2010, when thedata center needed to shift fromutility power to its generatorsafter a vehicle hit a utility polenearby. As a result, some Amazoncustomers lost cloud computing service for an hour. In 2010,Codero’s Phoenix data centerexperienced a power outage. Thegenerators started as expected,2but an automatic transfer switchfailed. In January 2010, a NaviSitedata center lost power when atransfer switch failed during autility outage caused by a thunderstorm.of switching devices do not haveto meet UL 1008 and thus do notoffer the assurance of having metthe strict testing requirementsneeded for qualification to thatstandard.To ensure that transfer switchesperform as expected, it’s important that they comply with UL1008. That standard sets out a series of rigorous requirements thatinclude “withstand & closing ratings or WCR” (which cover severefault currents, bolted faults andshort circuits within the electrical distribution system); tests toensure that the device can carryrated currents; and endurancetests specifying the number ofcycles that the transfer switchmust achieve and still perform itsintended function.Most transfer switch failuresdon’t make the news the waythe ones cited above did. Butfailures do occur. In a survey cosponsored by Building Operating Management magazine andASCO Power Technologies, 20percent of respondents whosefacilities have transfer switchesreported at least one failure ofa switch in the past five years.(See Figure 1 on page 3.) In onecase, “both sides of the switchclosed at the same time duringa test. The switch exploded,” arespondent reported. Anotherrespondent indicated the transferswitch failure “caused elevatorsto lock out.” A third commentedthat the transfer switch “failed toenergize a critical Intensive CareUnit circuit.”But transfer switches are notthe only devices that are used totransfer power. And other types
Figure 1. Have you had any failure of a transferswitch in the past 5 years? R 647Figure 4. Did any of the transfer switch failuresleave your facility without power? R 125YesNoYesNoNot applicable20%80%Transfer switch failures happen in a variety of ways.But a third of respondents who experienced failuresreported that the switch completely failed and becametotally inoperational. (See Figure 2.)Figure 2. Which of the following accuratelydescribes the transfer switch failure(s)? R 123Controls failed but mechanical switchcontinued to operateSwitch completely failed and becametotally inoperationalSwitch mechanically locked up withcontrols workingFailure of switch caused damage toother equipmentOthers49%33%20%5%7%(Responses add to more than 100 percent becausemultiple answers were allowed.)The transfer switches that failed were notnecessarily old units. (See Figure 3.) The samenumber of failures was reported in the survey forunits less than five years old and units 15 ormore years old.Figure 3. How long was the transfer switch(es) inservice when the first failure(s) occurred? R 107Less than 1 year1 year to less than 5 years5 years to less than 10 years10 years to less than 15 years15 years to less than 20 years20 years or more7%18%29%21%9%16%(Responses add to more than 100 percent becausemultiple answers were allowed.)And transfer switch failures left a significant numberof facilities without power, the survey shows. Ofrespondents who experienced failures, 42 percentreported that their facilities lost power. (See Figure4.) And more than half who lost power said that facility loads were without power for an hour or more.(See Figure 5.)42%56%2%Figure 5. How long were your facility loadswithout power? R 53A minute or lessMore than a minute to 30 minutesMore than 30 minutes to 1 hourMore than 1 hour to 2 hoursMore than 2 hours to 6 hoursMore than 6 hours to 1 dayGreater than 1 day11%26%13%13%21%11%6%(Responses add to more than 100 percent becausemultiple answers were allowed.)According to the survey, failures can be traced toa variety of issues, including power surges, lack ofmaintenance, age of equipment and poor design.(See Figure 6.)Figure 6. What were the major reasons fortransfer switch failure(s)? R 125Power surgeLack of maintenanceAgePoor designPoor applicationOperator errorOther22%21%18%14%7%3%31%(Responses add to more than 100 percent becausemultiple answers were allowed.)Jacob L. Huske, PE, vice president of Environmental SystemsDesign, says that the most common causes of failures ofcontactor-based transfer switches that he has heard about werepoor maintenance, or a misapplication of the transfer switch thatresulted in power outages due to nuisance tripping of a circuitbreaker external to the transfer switch during a transfer.“I have found that many transfer switch failures are the result ofshorted-out rectifiers,” observes Christopher A. Wade, principalconsultant for Resilient Mission Critical Solutions. Previously,Wade oversaw the global strategy, planning, engineering andfacilities operations for mission critical data centers for a Fortune100 company.Another potential problem Wade mentions is human error. In onecase, he says, the transfer switch was left in manual mode for acouple of months following completion of maintenance work. So,when needed, the transfer switch did not operate. “Needless tosay, that was a career limiting situation,” notes Wade.3
Ensuring Transfer Switch ReliabilityDespite failures, transfer switchescan be extremely reliable, providedthat they are properly selected andmaintained. The starting point is toensure that the switch is qualifiedand certified to the correct UL standard. For transfer switches, that’sUL 1008.“Transfer switch equipment tendsto be very reliable when properlyapplied and maintained, so failuresof UL 1008 transfer switches arerare,” says Huske.UL 1008 was established in 1970 byUnderwriters Laboratories to guardagainst transfer switch failuresand resultant potential fires. Aperformance standard as well as adesign and construction standard,UL 1008 requires transfer switchesto undergo rigorous testing by anindependent testing and certification agency.According to the Seventh Editionof UL 1008, published in July 2012,the standard applies to automatictransfer switches (ATS), manualtransfer switches, closed transitiontransfer switches, and hybrid transfer switches. UL 1008 also coversfire pump transfer switches, bypass/isolation switches, softload transferswitches and transfer switches usedas service equipment.4To meet UL 1008 listing requirements, a transfer switch must meetthe construction requirementsspecified in the standard and passa series of stringent tests. From thefacility executive’s perspective, UL1008 transfer switches offer safeand dependable transfer of electrical power from the utility main tobackup emergency power generators during mandatory compliancetesting and when emergency poweris actually needed.“UL 1008 is almost always the standard used for enclosed, contactortype transfer switch equipmentapplied in the United States, including equipment installed in missioncritical facilities,” explains Huske.“Where transfer switch equipment is used for transferringcritical load in legally requiredemergency power applicationsor healthcare facilities, UL 1008 isgenerally the only standard thatthe authority having jurisdiction(AHJ) will accept.”The dependability and safety of UL1008 transfer switches are “veryimportant,” says John Ferguson,director of facilities for RegionalWest Medical Center in Nebraska.“As a hospital, we have to keep ouroperations safely going, even inpower outage situations, to protectthe lives of our patients and ourstaff who are caring for them.”Ferguson isn’t alone in seeingthe importance of UL 1008 listedtransfer switches. Harris of Cushman & Wakefield calls the UL 1008automatic open transition transferswitches his client uses for its lifesafety generator “very important.”And Ken Cooper, chief engineer atSands Regency Casino Hotel, saysthat UL 1008 transfer switchesperform “very well, as long as theyhave proper maintenance” and aretested periodically.From Wade’s point of view, thereare two major benefits of using UL1008. One is that it simplifies the inspection process on code-requiredemergency power systems. “Thereliability of backup power systemsis impacted by switchgear design,”says Wade. “The UL 1008 standardhas typically been specified forlegally required standby and emergency power systems (e.g., systemsused for critical loads in hospitals).It is applicable for equipment up to600 V (it does not address mediumvoltage), and is written for thesimple standalone transfer switches. The basic UL 1008 standard doesnot address the reliability requirements as the system becomes morecomplex with multiple sources ofpower (utility and generators) andwith the introduction of tie circuitbreakers.”
Figure 7. Which of the following UL Standards isyour transfer switch(es) certified to? R 633UL 67UL 98UL891UL1008Not sureOthers1%2%2%5%92%1%(Responses add to more than 100 percent becausemultiple answers were allowed.)The other major benefit of UL 1008revolves around the device testingrequirements of the standard. “UL1008 really relates to testing devices to validate that they will operatesafely and reliably as intended,” saysWade. “UL 1008 is designed to be aself-contained standard for a switchassembly and has very stringentrequirements for endurance testing. It contains overload, enduranceand interruption testing criteria inaddition to all mechanical construction requirements to ensure safeoperation of the switch.”Wade points out that the mechanical interlocking requirements ofUL 1008 are significant. Mechanical interlocking is a useful safetyfeature for the open transitiontransfer of two sources. “Somemodern circuit breakers surpassthe endurance requirements in theindustry standards,” Wade says.“Therefore, the key specificationitem is the circuit breaker endurance. Mechanical interlocking canbe specified for open transitiontransfer on simple systems wherethe switchgear arrangement makesit physically possible. However, mechanical interlocking is not possiblein many switchgear arrangements,and electrical interlocks have successfully been employed for manyyears. Either method of interlocking(mechanical or electrical) preventsthe accidental paralleling of the twosources, thus increasing safety.”Despite the importance of UL 1008,the results of the survey suggeststhat most facility executives are unfamiliar with it. Among respondentswith transfer switches, only 5 percent said that their switches werecertified to UL 1008. (See Figure 7.)The overwhelming majority — 92percent — said that they weren’tsure about the standard to whichtheir devices were certified. Thisis eye opening information whenthe transfer switch is consideredby most people knowledgeable onpower distribution systems to bethe “heart” of power systems.As noted earlier, 20 percent ofsurvey respondents experiencedtransfer switch failures in the pastfive years. In those cases, 97 percentof survey respondents were notsure what certification those failedswitches had, if any.One reason that some facility executives may not know which standard their devices are certified to isthat transfer switches can last a verylong time. For example, Dave Lopes,chief engineer for ABM Engineering,has some experience with failedtransfer switches and is replacingthem with UL 1008 listed units. He’sunsure whether the replaced unitswere UL listed “because they werevintage units.” He guesses the original switches were installed around1970 to protect power transfer tothe commercial high-rise’s elevators, the main building emergencyriser, and the emergency generator.5
Figure 8. Who ensured that your transfer switch(es)was certified to its appropriate standard? R 649YouDesign Engineer who designed your facilityInstalling ContractorAuthorities who approved occupancy certificateNo oneNot sure10%49%47%26%1%15%(Responses add to more than 100 percent becausemultiple answers were allowed.)Finding ExpertiseScott Blackman, facilities management and commissioning regionalmanager at Syska Hennessy, recommends that facilities executivesconsider tapping the resources of areputable engineering firm to helpthem select the proper transferswitches for their business’ needs.“The facility manager has tremendous experience across a broadrange of operations for his or herbuilding,” says Blackman. “Theadvantage an engineering firmoffers is that it has multiple clientswith various business needs usingtransfer switches in many differentbuildings. That expertise allowsthe engineer to refine the transferswitch selection process, basedon his or her experience with whatworks and what doesn’t for numerous buildings and situations.”Huske agrees: “There are manyapplication-specific considerationsthat must be addressed for any typeof transfer equipment that will beused, and the best way to avoidproblems is to have someone withextensive experience assist.”The survey shows that most facilityexecutives rely on outside partiesto ensure that transfer switchesare certified to the appropriate ULstandard. (See Figure 8.)6No matter who is involved in helping select transfer equipment, it’simportant for the facility executiveto take steps to ensure that the correct UL standard has been followed.It’s a red flag if transfer switchliterature says the device merely“meets UL standards,” Drengenbergsays. “(The device) may even haveundergone independent testingbut it might not be UL at all. Theymay not have tested under loadconditions,” he points out. Similarly,facility executives should be wary of“per UL 1008 standards” and similarterms that suggest a product complies with UL 1008 but does not saythat outright.He recommends looking for the ULinside a circle logo and the word“listed” as well as the exact transferswitch words cited in the standard.UL 1008 transfer switches are specifically labeled as “non-automatictransfer switch,” “automatic transfer switch” or “transfer and bypassisolation switch.” These labelingrequirements are spelled out in UL’sElectrical Construction EquipmentDirectory, commonly referred toas the “Green Book.” UL also placesa code on the switch that identifies the manufacturer, accordingto Drengenberg. And literature orspecifications should say somethinglike “UL1008 Listed” or “tested andcertified by UL 1008.”
Figure9. Howare yourtransferFigure9. Howare yourtransferswitch(es)maintained?R 631switch(es) maintained?R sing in-house ization22%22%Using original manufacturer’s service organizationOther1% 1%Other(Responsesadd tomorethanthan100 100percentbecause(Responsesaddto multipleanswersallowed.)Put UL 1008 in writingTo avoid any misunderstanding, facilities executives who are purchasing transfer switches on their ownare spelling out UL 1008 in theirmaster construction specifications.The Unified Facilities Guide Specification on automatic transfer switches cites UL 1008 (2012 edition) in itsspecifications for the Army Corps ofEngineers, Naval Facilities Engineer-ing Command (NAVFAC), Air ForceCivil Engineer Support Agency(AFCESA) and NASA projects. Itis also referenced in the MIL-PRF17773C(SH), which is the Navystandard for automatic bus transferswitches installed on Navy combatvessels.Proactive StepsAlthough proper UL certification fortransfer switches is essential, it’s notthe whole story. Maintenance andtesting are also crucial to ensurethat the transfer switch will respondwhen needed.“All transfer switch equipmentmanufacturers publish recommended schedules for maintenanceand testing, so obtaining andunderstanding these recommendations is the best place to start,”suggests Huske. “Facility executivesalso should engage a qualified service company to regularly performinspections and maintenance ontransfer switch equipment in theirbuildings.”8Regional West Medical Center inNebraska relies on a third party todo load-bank testing, as well as anyrepair needs uncovered, when theemergency backup system mustbe operated for four hours to meetJoint Commission requirements,according to Ferguson.Harris has his transfer equipment maintained under a thirdparty contract. Monthly testingis performed in-house, but it iswitnessed under the third-partyagreement at least once a year.sure his transfer switches and circuitbreakers perform as expected fordata center/call center operations.The majority of survey respondentsuse third-party service providersto maintain their transfer switches,though many also rely on in-houseexpertise. (See Figure 9.)Cooper, of the Sands RegencyCasino Hotel, also relies on a thirdparty electrical contractor to make7
Figure 10. How often do you test transferswitches? R 630MonthlyQuarterlySemiannuallyAnnuallyLess often than once a yearNot sureFigure 11. What are the steps taken whenmaintaining your transfer switch(es)? R 63246%16%12%26%5%8%(Responses add to more than 100 percent becausemultiple answers were allowed.)Contact inspectionInfrared scans of live electrical componentsLubrication of jointsTesting of sub-systemsRemoval of dirt/debris from electrical pathNot sure69%53%48%47%47%23%(Responses add to more than 100 percent becausemultiple answers were allowed.)On-siteTestingAutomatic transfer switches areelectromechanical devices that havemoving parts. Those moving partscan seize if they’re left in the sameposition for months or years.Operating those moving partsregularly helps to ensure they willcontinue to move smoothly.The survey shows that monthlyis the most common frequencyfor testing transfer switches.(See Figure 10.)That’s the case at Regional WestMedical Center, where the emergency backup power system and itstransfer switches are put through anhour of performance testing monthly, as well as periodic load-bank testing for four-hour runs per Joint Commission requirements, according toFerguson. Two licensed electriciansare on hand and, although he’s hadsome problems with the emergencypower system, “there have been noproblems with transfer switches,”says Ferguson.The National Fire Protection Association Standard 110 for emergencyand standby power systems says,“the monthly test of a transferswitch shall consist of electricallyoperating the transfer switch from8the standard position to the alternate position and then a return tothe standard position.”NFPA 110 also requires the entireemergency power supply systemto be exercised at least monthly. Asmany emergency generators arediesel, running under light or no loadconditions can cause wet stacking,which is carbon buildup in the cylinders and exhaust system, a potentialfire hazard. Generator loads of 30percent or more often are requiredby NFPA for monthly testing, whichmeans the transfer switches also arebeing tested.Experts suggest the best way to testthe automatic transfer switch andthe emergency generator to meetNFPA 110 requirements is to operatethe transfer switch’s test toggle andconfirm that it is properly signalingthe generator to start and run. Onceproper signaling is verified, the building load is transferred.Load banks offer a valuable tool forimproving the reliability of an emergency power system. They are usedto test the system without interrupting the critical loads. In the survey,however, only 28 percent of respondents reported using load banks fortesting transfer switches. Facilityexecutives who aren’t now usingload banks should evaluate whetherto incorporate them into a plannedmaintenance strategy.Maintenance is another key to ensuring that the transfer switch will function reliably.Asked how their transfer switcheswere maintained, 23 percent of survey respondents said they were unsure, raising the question of whetherthey understand the importance ofregular maintenance. (See Figure 11.)“We know maintenance is paramount. Building managers need toinspect UL 1008 transfer switchesmonthly,” Drengenberg says.
MethodologyThe ASCO Transfer Switches Survey was sent via email to arandom sample of 15,000 Building Operating Managementsubscribers on Feb. 14, 2013. Reminders were sent to nonrespondents on Feb. 20, and Feb. 22, 2013. A total of 147 subscribers chose to opt out of the survey or failed to respond dueto an invalid email address, yielding a final sample of 14,853.The survey was closed for responses on March 1, 2013. With1,134 qualified responses returned and with a net sample of14,853, the rate of response for the email survey was computed to be 7.6 percent. The overall estimated margin of errorfor this study is /- 2.89 percent at the 95 percent confidencelevel.What type of facilities are youresponsible for? R 1,133Educational (K-12, Colleges/Universities)Commercial OfficeMedical/HealthcareData 4%33%21%13%13%10%8%6%5%Download a full versionof the white paperRememberthe businessmodelThe type of UL 1008 transfer switch to usedepends on many factors, but possibly themost critical one is the organization’s business model.To that end, Blackman recommends regularly commissioning and evaluating transferswitches to see if they still satisfy the businessmodel. “Today’s business is constantly changing and the infrastructure, including transferswitches, often is overlooked,” he notes.He recalls a client with open-transitiontransfer switches that were performing as designed to an older business model. However,lights flickering and other interrupting factorsof regular testing were problematic under thenew business model. As a result, the organization opted to retrofit with closed-transitionswitches.For new construction or renovation projects,facility executives have an important role toplay in making sure the organization getswhat it needs. “Facility executives must knowwhat the actual function of the facility is going to be – data center, hospital, office building – and work with the design engineers todetermine what is needed,” says Wade.And, when automatic transfer switches areneeded in the United States, facilities executives must be sure they are UL 1008 listed.Otherwise, they probably will not pass inspections by the authorities having jurisdictionover the facility.9
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Jul 09, 2013 · UL 1008. “Transfer switch equipment tends . to be very reliable when properly applied and maintained, so failures of UL 1008 transfer switches are rare,” says Huske. UL 1008 was established in 1970 by Underwriters Laboratories to guard . against transfer switch failures and resultant potential fi
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