Surge Suppression App Guide - Eaton

7/30/2019 Surge Suppression App Guide - Eaton

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Eatons guide to

surge suppressionApplications notes


2/28EATON CORPORATION Eatons guide to surge suppression2

Contents

Description Page

Summary of applicable UL and IEEE standardsfor surge protection devices ........................................................ 4

High-resistance grounding and wye or deltasurge protection devices .............................................................. 9

Surge current per phase (industry definition) .................................. 10

Facility-wide surge suppression ...................................................... 10

Debunking the surge current myth,Why excessive surge current ratings are not required ............ 11

Surge arrestor vs. surge suppressor ............................................... 12

Benefits of hybrid filtering in surge protection devices .................. 14

Factory automation (PLCs) and their need forsurge suppression .............. ............... .............. ............... .............. 16

Surge protection devices with replaceable modules ...................... 17

Why silicon avalanche diodes are not recommendedfor AC powerline suppressors ..................................................... 18

Surge protective device frequently asked questions ...................... 20


3/28EATON CORPORATION Eatons guide to surge suppression

Why Eaton?

As a premier diversifiedindustrial manufacturer, EatonCorporation meets your electri-cal challenges with advancedelectrical control and powerdistribution products, industrialautomation, world-class manu-facturing, and global engineeringservices and support.Customer-driven solutions comein the form of industry-preferred

product brands such as Cutler-Hammer, MEM, Holec,Powerware and InnovativeTechnology.

Eaton has an extensive fam-ily of surge protective devices(SPD) for any facility or applica-tion. Using our Cutler-Hammer,Powerware and InnovativeTechnology branded productswill ensure that the quality ofpower required to maximizeproductivity in todays competi-tive environment will besupplied in the most reliable,safe and cost-effective manner.

Eaton has developed specificsurge protection solutions forcommercial, industrial, insti-tutional, telecommunication,military, medical and residentialapplicationsboth for NorthAmerica and throughoutthe world.

Cutler-Hammer

Eatons Cutler-Hammer SPDsare designed to be fully inte-grated into new switchgearand new panels for the closestpossible electrical connection.

When installing a surge suppres-sor, it is important to mount it asclose to the electrical equipmentas possible in order to keep thewiring (lead length) betweenthe electrical equipment and thesuppressor as short as possible.As such, Eaton was the firstto introduce the Direct-Onbus bar connected SPD thatprovides customers with thelowest system let-throughvoltage at the bus bar whencompared to traditional cableconnected surge protectors. Byutilizing a direct bus bar con-

nection, Cutler-Hammer SPDsachieve the industrys lowestlet-through voltage to effectivelysuppress both high and lowenergy transient events and

provide protection for allconnected electronic loads.This design provides superiorsuppression ratings and elimi-nates poor performance thatresult from poor cableconnections and long leadlengths. Integrated transientvoltage surge suppression(TVSS) is the number one choicefor surge suppression in new-construction applications.

In addition to the extensiveintegrated SPD offering, theCutler-Hammer SPD productline includes a wide variety ofsurge current ratings, monitoringfeatures and external enclosureoptions. The Cutler-HammerSPDs are available from autho-rized Cutler-Hammer electricalwholesalers. For informationon Eatons Cutler-Hammer SPDproduct line, please visitwww.eaton.com/tvss.

Powerware

Lightning and other transient

voltage and current-producingphenomena are harmful tomost UPS equipment andelectronic load equipmentconnected to the UPS. Forexample, the transient mayreach the critical load via anunwanted activation of anunprotected static-switchbypass path around a UPS.Therefore, it is recommendedpractice that both the inputcircuit to the UPS and theassociated UPS bypass cir-cuits (including the manualmaintenance bypass circuit)

be equipped with effectiveCategory B surge protectivedevice, as specified in IEEE Std.C62.41-1991. Low-inductanceconnections should beemployed for this protection.

Eaton's Powerware surgeprotective devices can be fullyintegrated into power distri-bution units (PDUs), and aredesigned to meet thedemanding needs of the samemission-critical applications andfacilities that utilize Powerwareuninterruptible power systems(UPS). Powerware surge protec-tion devices are available in awide variety of surge currentratings, monitoring features andenclosure options.

Source: IEEE RDP Std. 1100-1999.

For information onEatons Powerware SPDproduct line, please visitwww.powerware.com/tvss.

Innovative Technology

Since 1980, InnovativeTechnology products havesolved the most difficult elec-trical transient problems forbusiness, industry, governmentand defense sectors. Innovative

Technology products andTechnologies protect electrical,data, telecom circuits, andelectronic equipment from theeffects of lightning-inducedvoltages, external switchingtransients, and internally gener-ated electrical transients.

As a part of Eatons electricalbusiness since 2003, InnovativeTechnology SPD products areeven better positioned to deliverstate-of-the-art customer solu-tions. Innovative Technologyproducts are designed to be themost rugged and durable SPDs

in the market. Based on exten-sive proven field performance,Innovative Technology wasthe first to offer a 20-year fullreplacement warranty. Electricalengineers around the worldrecognize Innovative Technologyas a leader in the SPD industry.A leading research company ina survey of over 10,000 usersrated Innovative Technologynumber one in both productquality and service.

Innovative Technology SPDproducts are available in a widerange of voltages (including volt-ages up to 5 kV), surge currentratings, monitoring features andenclosure options.

For information on EatonsInnovative Technology products,please visit www.itvss.com.



Summary of applicable UL and IEEE standards for surge protection devices

TABLE 1. STANDARD DESCRIPTIONS

Standard(Current revision date) Purpose of standard/comments

UL 1449 (1987)Transient voltage surge suppressors(TVSS)

1. Safety test (constructed of approved components in a safe manner).

2. Suppressed voltage rating (let-through voltage using the IEEE C62.41 C1 test wave).

Other IEEE recommended waveforms such as the C3 and B3 Ringwave are not tested by UL.

UL 1449 (2nd Edition 1996) 1. Additional safety tests. Test for other standards used to improve safety of products.

2. Surge test. Let-through voltage tested at lower current than 1st Edition.10 kA (IEEE Cat. C3) used for the first time; however, it was used only to see if products fail safely.

UL 1449 (2nd Edition 2007) 1. Stringent new safety requirements. New tests subject TVSS units to prolonged AC overvoltageconditions to ensure safe failure modes

2. UL label changes to the wording of the short circuit current rating.

3. New Testing at 10, 100, 500 and 1000A and system voltage were added to ensure the unitsfail in a safe manner.

UL 1449 (3rd Edition 2009) 1. TVSS wil l now be referred to as SPD (surge protective devices).

2. UL 1449 is now ANSI/UL 1449.

3. Addition of four types of SPDs to cover surge arrestors, TVSS, surge strips and component SPDs.

UL 1283 (1996)Electromagnetic interference filters

This safety standard covers EMI filters connected to 600V or lower circuits. The UL 1283 is a safety stan-dard and does not include performance tests such as MIL-STD-220A insertion loss or Cat. B3 Ringwavelet-through voltage tests.

UL 497, 497A, 497B Safety standard for primary telephone line protectors, isolated signal loops and surge protection used oncommunication/data lines. No performance tests conducted for data/communication lines.

IEEE C62.41.1 (2002) IEEE Guide on the Surge Environment in Low-Voltage AC Power Circuits. This is a guide describing thesurge voltage, surge current, and temporary overvoltages (TOV) environment in low-voltage [up to

1000V root mean square (Rms)] AC power circuits.

IEEE C62.41.2 (2002) IEEE-recommended practice on characterization of surges in low-voltage AC power ci rcuits.This document defines the test waves for SPDs.

IEEE C62.45 (2002) Guide on surge testing for low voltage equipment (ANSI). This document describes the testmethodology for testing SPDs.

IEEE Emerald Book Reference manual for the operation of electronic loads (includes grounding, power requirements, and so on).

NEMAT LS-1 NEMA Technical Committee guide for the specification of surge protection devices including physical andoperating parameters.

NECT National Electrical Code Articles 245, 680 and 800.

NFPAT 780 Lightning protection code recommendations for the use of surge protection devices at a facilityservice entrance.

Underwriter laboratoriesUL 1449 (Revision 7-2-87),Transient voltage surgesuppressors (TVSS)

UL 1449 is the standard forall equipment installed on theload side of the AC electricalservice and throughout the facil-ity for AC distribution systems.This includes both hardwireand plug-in products. To obtaina UL listing, the suppressormust meet the required safetystandards and pass a duty cycletest. In addition, UL conducts alet-through voltage test on thesuppressor and assigns a sup-pressed voltage rating (SVR).UL 1449 ratings represent acomponent rating and not theactual let-through voltage of the

UL 1449 does not require a maximum surge current test.

electrical distribution system(i.e., UL 1449 does not includethe effects of installation leadlength and overcurrent protec-tion). A duty cycle test is basedon a 26-shot withstand test. TheUL test uses waveforms similarto those recommended in IEEE62.41. To pass UL 1449, theTVSS unit must withstand theduty cycle test and not degradeby more than 10% from its initiallet-through voltage value.

All UL-listed TVSS equipmentdisplays the SVR rating for eachapplicable protection mode.If this rating is not affixed to theTVSS, then one must assumethe device is not UL 1449 listed.

Notes

UL 1449 Second Edition doesnot test a suppressor to otherimportant test waveforms suchas the IEEE Cat. C3 serviceentrance surge (20 kV, 10 kA)or the B3 Ringwave (6 kV, 100kHz), the most common type oftransient inside a facility.

UL does not verify the TVSSdevice will achieve themanufacturers published surgecurrent ratings. NEMA LS-1provides the guidelines for

product specification.Plug-in products are testeddifferently and cannot becompared to hardwired devices.



UL 1449 (1996 and 20072nd Edition)

Underwriters Laboratoriesstandard for safety for transientvoltage surge suppressors (UL1449) is the primary safety stan-dard for transient voltage surgesuppressors (TVSS). This stan-dard covers all TVSS productsoperating at 50 or 60 Hz, at volt-ages 600V and below.

The UL 1449 safety standard

was first published in August of1985. As TVSS products haveevolved in the marketplace, thestandard has been updated toensure the continued safety ofthe increasing sizes, optionsand performance of new TVSSdesigns. The second editionof UL 1449 was published in1996. The second edition of theUL 1449 TVSS standard wasrevised in February 2005 andrequired compliance by February9, 2007. All TVSS productsmanufactured after February9, 2007 must comply with the

February update to the standard.A third edition of UL 1449 waspublished in September of 2006with compliance required byOctober of 2009. This articlerelates to the latest revision ofthe second edition of UL 1449,which is currently in effect andis acceptable until Octoberof 2009.

To obtain a UL listing, a suppres-sor must pass a series of testsdesigned to ensure it does notcreate any shock or fire hazardsthroughout its useful life. EachTVSS product is subjected to the

following electrical and mechani-cal tests: leakage current,temperature, ground continuity,enclosure impact, adequacy ofmounting, and many others.Each test evaluates a differ-ent function or potential failuremode of a TVSS. To obtain ULcertification, the TVSS unit mustpass all tests. Two of the mostsignificant tests performed ona TVSS are the measured limit-ing voltage test and a series ofabnormal overvoltage tests.

The measured limiting voltagetest is used to assign each TVSSa suppressed voltage rating(SVR), which appears on all ULcertified units. This rating takesthe average let-through voltagesof three 6000V, 500A combina-tion wave impulses (IEEE 62.41cat C1 test waves) and roundsup to the next highest stan-dard SVR class set by UL. Thestandard SVR classes are 330,400, 500, 600, 800, 1000, 1200,

1500, 2000, 2500, 3000, 4000,5000 and 6000V. For example,a 401V average let-through volt-age is rounded up to a 500VSVR. The test is conducted withsix inches of lead length, (lengthof wire from TVSS to testequipment connection point).Let-through voltages are signifi-cantly affected by lead length.Therefore, a six-inch lead lengthis used to standardize the test.The SVR value allows somecomparison from one TVSS toanother, but does not representan expected field installed let-

through voltage since actualinstalled lead length will varyfrom installation to installation.

The last major series of tests arethe abnormal overvoltage tests.The purpose of these tests is toensure that the TVSS willnot create a shock or fire hazard,even if the unit is misappliedor subjected to a sustainedovervoltage event. TVSS aredesigned to prevent high ener-gy, short duration (typically twomilliseconds or less) transientvoltages from causing damageto an electrical installation. TVSS

are not designed to sustainlong-term overvoltages. Duringthe abnormal overvoltage test,the TVSS unit is subjected to avoltage higher than its normaloperating voltage, typically neardouble the design voltage. Theovervoltage test is performedwith current limited to the fol-lowing current levels: 10, 100,500 and 1000A. Every mode ofthe TVSS is subjected to theabnormal overvoltage tests.The testing of each mode issustained for up to seven hours.During this time, the TVSS can-

not create a fire or shock hazard.

In addition to successfullypassing all applicable tests, allUL-listed TVSS units must besuitably and plainly marked.These markings include name ofthe manufacturer, a distinctivecatalog number, the electricalrating, short circuit current rat-ing (SCCR), SVR, and the dateor period of manufacture. TheTVSS must also be marked withthe words transient voltagesurge suppressor or TVSS,

and is able to be additionallymarked immediately followingin parentheses with the words(surge protective device)or (SPD).

The best way to verify that par-ticular TVSS unit is UL listed isto conduct a search on the ULWeb site at www.ul.com. Thecertification category for TVSSis UL category code XUHT.An alternate way to verify avendors listing is to call UL at1-847-272-8800. A listed prod-uct provides a user with theconfidence their TVSS unit willnot create a shock or fire hazardduring use.

UL 1283 electromagneticinterference filters

Surge suppressors must belisted (or recognized) under UL1449. Those devices employingan EMI filter can also be compli-mentary listed under UL 1283 toensure the filter components areproperly designed to withstandthe required duty cycle andstress requirements. UL 1283covers EMI filters installed on,

or connected to, 600V or lowercircuits. These filters consist ofcapacitors and inductors usedalone or in combination witheach other. Included under thisrequirement are facility filters,hardwired and plug-in devices.UL 1283 reviews all internalcomponents and enclosures,insulating material, flamma-bility characteristics, wiringand spacing, leakage current,temperature ratings, dielectricwithstand and overload char-acteristics. UL 1283 does notinclude performance tests such

as the MIL-STD-220A insertionloss test to determine the dBrating of the filter at the desiredfrequency (i.e., 100 kHz for hard-wired AC power systems) or thelet-through voltage test usingthe IEEE Cat. B3 Ringwave.

UL 1449 (2009 3rd Edition) UL1449 3rd Edition is now ANSIUL 1449. The change in designation helps the standard gainrelevance in North America anbrings it closer to the IEC standards. By becoming a nationastandard and forming a votingcommittee, the standard alsoensures conformance to NAFThis revision changes the designation of the TVSS devices,from TVSS to Type 2 surge

protective devices (SPDs). ThSPD is used as an umbrella deignation and includes all typessurge protective products. Thtype designation of the SPDwill be determined based on tinstallation location within anelectrical system. Some examples are surge arrestors (Type1 SPD), cord connected TVSS(Type 3 SPD) and a new cat-egory of component SPD (Typ4 SPD). The last nomenclaturemodification is the change ofSVR (suppressed voltage rat-ing) to VPL (voltage protection

level). The new VPL ratings arrequired to be displayed on thUL tags for the each SPD unit

The revised standard includessome testing modificationsthat include tests for nominaldischarge current, tests to detmine VPL and measured limitvoltage at 6 kV/3 kA.



Data/communication lineprotectors (UL 497,497A, 497B)

UL 497 is the safety standard forsingle or multi-pair Telco primaryprotectors. Every telephone lineprovided by a telephone opera-tor must have an UL-approvedT1 protector (gas tube or car-bon arrestor) in accordancewith Article 800 of the NationalElectric Code (NEC).

A primary protector is requiredto protect equipment andpersonnel from the excessivepotential or current in telephonelines caused by lightning,contact with power conductorsand rises in ground potential.UL 497A applies to secondaryprotectors for communicationcircuits. Secondary protectorsare intended to be used on theprotected side of telecommu-nication networks (it assumesprimary protectors are in place)that have operating Rms voltageto ground less than 150V. These

protectors are typically used atthe facility incoming service orother areas where communica-tion circuits require protection.UL 497B applies to data com-munication and fire alarm circuitprotectors (communication alarminitiating or alarm indicating loopcircuits). This includes mostdataline protectors in theelectrical industry.

ANSI/IEEE C62.41 (2002)recommended practice onsurge voltages in low voltageAC power circuits (ANSI)

This document describes a typi-cal surge environment based onlocation within a facility, power-line impedance to the surge andtotal wire length. Other param-eters include proximity, type ofelectrical loads, wiring qualityand geographic location.

The document only describestypical surge environments anddoes not specify a performancetest. The waveforms includedin the document are meant asstandardized waveforms thatcan be used to test protectiveequipment. Any statementwhere a manufacturer advertis-es that its protector meets therequirement of, or is certifiedto IEEE C62.41," is inappropriateand misleading.

Two selected voltage/currentwaveforms (see Figures 1and 2) are identified asrepresentative of typicalelectrical environments:

1. Combination wave: a unipolarpulse that occurs most oftenoutside a facility (e.g., alightning strike)

2. 100 kHz Ringwave: anoscillating waveform thatoccurs most often insidea facility

10,000

8000

6000

4000

2000

00 10 20 30 40

FIGURE 1. COMBINATION WAVE

8000

6000

4000

2000

0

2000

400010 0 10 20 30 40

FIGURE 2. RINGWAVE

The amplitude and availableenergy of the standard wave-forms are dependent uponlocation within a facility.

As shown in Figure 3,locations are classified intothree categories:

Category A: outlets and longbranch circuits

All outlets at more that 10m(30 ft) from Category B

All outlets at more than 20m(60 ft) from Category C

Category B: feeders and shortbranch circuits

Distribution panel devices

Bus and feeder distribution

Heavy appliance outlets withshort connections toservice entrance

Lighting systems inlarge buildings

Category C: outside andservice entrances

Service drops from poleto building

Runs between meterand panel

Overhead lines todetached building

Underground lines towell pump

The Category C surges canenter the building at the serviceentrance. SPDs must be sized towithstand these types of surgeswhen installed at switchgear orservice entrance switchboard.The second variable used toclassify the environment of apower disturbance is exposure.As shown in Figure 4, IEEEhas defines three exposure

levels that characterize the rateof surge occurrence versusvoltage level at an unprotectedsite. The three exposurecategories include:

Low exposure: applicationsknown for low lightningactivity, little load switching

Medium exposure: systemsand geographical areas knownfor medium to high lightningactivity or with significantswitching transients or both

High exposure: those rareinstallations that have greater

surge exposure than thosedefined as low or medium



10

10

10

10

10

1

0.5 1 2 20105

Number of surges per yearexceeding surge crest of abscissa

Surge crest kV

Highexposure

Medium

exposure

Sparkoverclearances

Lowexposure

FIGURE 4. COMBINATION WAVE

Category A Long branch circuits

Indoor receptacle

Category B Major feeders

Short branch circuits

Indoor service panels

Category C Outdoor overhead lines

Service entrance

Isokeraunic maps provide a goodbaseline for evaluating lightningoccurrence within a region.Discussions with local utilitiesand other major power userscombined with power qualitysurveys are useful for measuringthe likely occurrences from loadswitching and power factorcorrection capacitors.

For each category and exposurelevel, IEEE has defined the testwaveform that should be usedby a specifier when determining

performance requirements. Forexample, most SPDs installedat the main service panel afterthe meter are in a Category Cenvironment. Table 2 details theC62.41 test waveforms forcategories A, B and C.

In the C62.41 (2002) document,special waveforms have beenidentified to address large banksof switching capacitors or theoperation of fuses at the endof long cables. These situationswarrant the consideration ofadditional waveforms whereenergy is greater than thosestipulated for Category A, B andC environments.

Many specifiers are confusedabout the recommendationscontained in C62.41. Often thedocument is misapplied becausecategory environments and testwaveforms are used as perfor-mance standards (e.g., abilityto meet C62.41).

The C62.41 recommendationsshould be used for selecting spec-ifications appropriate to the needsof a given designer or end user.

FIGURE 3. IEEE C62.41 LOCATION CATEGORIES



IEEE C62.45 (2002)Guide onSurge Testing for EquipmentConducted to Low Voltage ACPower Circuits

This document providesappropriate surge testing guide-lines for equipment survivability,methods of test connection,surge coupling mode definitions,testing safety requirementsand various theories of surgesuppression techniques. The

intent is to provide backgroundinformation that can helpdetermine if specific equipmentor a circuit has adequatewithstand capability.

An important objective of thedocument is to call attention tothe safety aspects of surgetesting. Signal and datalinesare not addressed.

IEEE Std. 1100 (2005) EmeraldBook Recommended Practicefor Powering and GroundingSensitive ElectronicEquipment

This publication presents recom-mended engineering principlesand practices for powering andgrounding sensitive electronicequipment. This standard is therecommended reference bookfor facility-wide power quality

solutions. The scope of thispublication is to recommenddesign, installation and main-tenance practices for electricalpower and grounding of sensi-tive electronic processingequipment used in commercialand industrial applications.The following sections apply tosurge protection devices:

Chapter 3 (particularly 3.4.2and 3.4.3)

Chapter 4 (particularly 4.2and 4.4)

Chapter 8 (particularly 7.2)

Chapter 9 (particularly 8.6)

CAT. LEVELVOLTAGE(KV)

0.5S X 100 KHZRING WAVECURRENT (A)

1.2 X 5S (V)8 X 20S (A)COMBINATION WAVECURRENT (KA)

A1

A2

A3

Low

Medium

High

2

3

6

70

130

200

B1

B2

B3

Low

Medium

High

2

4

6

170

330

500

1

2

3

C1C2

C3

LowMedium

High

610

20

35

10

NEMA LS-1

This document is a specifica-tion guide for surge protectiondevices for low voltage ACpower applications (less than1000V). The document identifieskey parameters and evaluationprocedures for specifications.NEMA employed establishedreferences such as IEEE andUL guidelines. The followingparameters are included in

the LS-1 document: Maximum continuous

operating voltage (MCOV)

Modes of protection

Maximum surge currentper mode

Clamping voltage (A3, B3Ringwave, B3/C1 impulse,C3 impulse)

EMI noise rejection(insertion loss)

Safety UL approvals (includingUL 1449, UL 1283)

Application environment

NEMA LS-1 (and other organiza-tions) do not recommend theuse of Joule ratings or responsetime as a performance criteriafor SPDs.

National Electrical Code(United States): NECarticle280, 285, 645 and 800surge arrestors

The adequacy section of thecode clearly states thatcompliance with the code willnot ensure the proper equip-ment performance. This factis often overlooked by endusers/customers consideringelectrical designs from a low-bid perspective.

Article 280 covers the gen-eral requirements, installationrequirements and connectionrequirements for surge arrestorsinstalled on premiseswiring systems.

Article 285 covers the gen-eral requirements, installationrequirements, and connectionrequirements for transientvoltage surge suppressorspermanently installed onpremise wiring systems.

Article 645 covers electroniccomputer/data processingEquipment and referencesNational Fire ProtectionAssociation (NFPA) 75.6.4regarding the protection ofelectronic computer/dataprocessing equipment.

Article 800 reviews protectionrequirements (800-31),secondary protector require-ments (800-32) and cable andprotector grounding (800-40)for communication circuits.

National Fire ProtectionAssociation (NFPA)780lightning-protection code

NFPA 780 is the code forlightning protection systemsand addresses the protectionrequirements for ordinarystructures, miscellaneousstructures and special occu-pancies, industrial operatingenvironments, and so forth. Thefollowing paragraphs are relatedto surge protection: 3-21 surgesuppression. Devices suitablefor protection of the structureshall be installed on electric andtelephone service entrances,and on radio and televisionantenna lead-ins.

Note: Electrical systems andutilization equipment within the

structure may require furthersurge suppression.

Shall indicate a mandatoryrequirement.

TABLE 2. IEEE C62.41 CURRENT/VOLTAGE WAVEFORMS FORVARIOUS EXPOSURE LOCATIONS



High-resistance groundingand wye or delta surgeprotection devices

In todays manufacturingfacilities, ground faults canwreak havoc on production andprocess equipment. These man-ufacturing facilities may have ahigh-resistance grounding (HRG)system. In an HRG system, aresistance, which is connectedbetween the neutral of the

transformer secondary and earthground, is used that effectivelylimits the fault current to a lowvalue current under ground faultconditions. Usually, the currentis limited to 10A or less. As aresult, the system will continueto operate normally, even underthe ground fault condition.

Figure 5 depicts a systemthat has a resistance ground-ing scheme. In the case wheresurge suppression is requiredfor a three-phase, four-wire wyesystem with a neutral groundresistance (NGR), a three-phase,

three-wire delta SPD will wantto be specified and used.

In a wye system, the neutraland ground are both locatedat the center, as shown inFigure 6. If the neutral isbonded to the ground, thesystem will remain unchangedunder fault conditions.

In the case where the neutral isnot bonded to ground and a faultcondition is present, the groundwill move towards the phasethat has the fault.

Figure 7 shows a fault condi-

tion on phase C. The result isphase A to ground and phase Bto ground are now at line to linevoltage instead of line to neutralvoltage. If a three-phase, four-wire wye SPD was installed inan application where the neutralwas not bonded to ground and afault condition occurred on oneof the phases, the result wouldbe SPD failure.

In todays electrical systems,with many different groundingsystems and various voltages,determining which SPD voltageconfiguration to specify can beconfusing. Following are sev-eral helpful guidelines to followwhen specifying SPDs:

Only apply a wye (three-phase, four-wire) configuredSPD if the neutral is physicallyconnected to the SPD andif the neutral is directly andsolidly bonded to ground

Use a delta (three-phase,three-wire) configured SPDfor any type of impedance(resistive, inductive) groundedsystem

Use a delta (three-phase,three-wire) configured SPDfor a solidly grounded wyesystem where the neutralwire is not pulled through tothe SPD location

Use a delta (three-phase,three-wire) configured SPD if

the presence of a neutral wireis not known

A B

R

C

Ground

FIGURE 5. RESISTANCE GROUNDING SCHEME

FIGURE 6. WYE SYSTEM

FIGURE 7. PHASE C FAULT CONDITION

A

B

C

NeutralGround

A

B

C

Ground

Neutral



Surge current per phase(industry definition)

Engineers/specifiers routinelyinstall TVSS devices at the ser-vice entrance and key branchpanels to protect sensitivemicroprocessor loads such ascomputers or industrial controldevices from damaging surgesand noise. These devices areavailable in a wide range ofsizes to meet different applica-

tion requirements. Suppressorslocated at the facilitys serviceentrance must handle higherenergy surges than those locat-ed at branch panels.

TVSS devices are classified bythe units maximum surge cur-rent measured on a per phasebasis. Surge current per phase(expressed as kA/phase) is themaximum amount of surgecurrent that can be shunted(through each phase of thedevice) without failure and isbased on the IEEE standard8 x 20 microsecond

test waveform.As per NEMA LS-1, TVSS manu-facturers are required to publishthe level of surge protectionon each mode. A delta systemcan employ suppression com-ponents in two modes (L-L orL-G). For wye systems, shuntcomponents are connected L-G,L-N and/or N-Gs.

How to calculate surgecurrent per phase

The per-phase rating is the totalsurge current capacityconnected to a given phaseconductor. For example in a wyesystem, L1-N and L1-G modesare added together becausesurge current can flow on eitherparallel path. If the device hasonly one mode (e.g., L1-G), thenthe per-phase rating is equal to

the per-mode rating becausethere is no protection on theL1-N mode.

Note: N-G mode is not includedin the surge current per-phasecalculation.

Almost all suppressor manufac-turers follow this convention.However, there are some com-panies who attempt to causeconfusion by inflating their surgecurrent ratings using a non-standard method for calculatingsurge current per phase. Asshown below, the correct modeand phase ratings are displayed.

Summary

Surge current per phase (kA/phase) has become the standardparameter for comparingsuppression devices. Mostreputable manufacturers pub-lish surge current ratings on aper-mode and per-phase basis.Some suppression manufactur-ers may hide surge currentratings or make up their ownmethod to calculate surgeratings. Avoid manufacturerswho do not clearly publish these

industry standardsper-phaseand per-mode surge capabilities.

Facility-wide surgesuppression

As recommended by IEEE(Emerald Book 1992), TVSSunits need to be coordinated ina staged or cascaded approach.IEEE provides the followingrecommendations:

...For large surge currents,(transient) diversion is bestaccomplished in two stages:the first diversion should be per-

formed at the service entranceto the building. Then, anyresidual voltage resulting fromthe action (of the suppressiondevice) can be dealt with by asecond protective device at thepower panel of the computerroom (or other critical load). Inthis manner, the wiring insidethe building is not required tocarry the large surge current toand from the diverter at the endof a branch circuit.

...proper attention must begiven to coordination of cascad-ed surge protection devices.

Figure 8 demonstrates theeffectiveness of a suppressionsystem when used in a two-stage (cascaded) approach.

As demonstrated, the two-stageapproach ensures that bothtypes of disturbances are sup-pressed to negligible levels atthe branch panel (



Debunking the surgecurrent myth, Whyexcessive surge currentratings are not required

When will it stop?

It seems that every year surgesuppressor manufacturers areincreasing the surge currentratings of their devices. Forexample, a well-known TVSSmanufacturer has made the

following recommendations tothe consulting community formain panel surge protection:

TABLE 4. MANUFACTURERRECOMMENDATIONS

YEAR

RECOMMENDED SURGECURRENT RATING(KA/PHASE)

1993 250 kA/phase

1994 350 kA/phase

1995 >500 kA/phase

2006 >1000 kA/phase

The same model has changedsurge ratings three times in last

several years! In fact in 1998,the company also introduced aunit that is theoretically rated to650,000A per phase. The aboveexample illustrates how somemanufacturers use irrelevantjustifications to promote the saleof a premium-priced suppressor.

We believe it is time to debunkthe game and present the factson what is an acceptable levelof surge current for serviceentrance locations.

Why stroke current isnot related to TVSSsurge current

The stroke current associatedwith lightning is not related to asuppressors surge current rat-ing. It is physically impossible tohave the energy associated witha lightning stroke travel downthe AC power conductors.

Figure 9 is a graph published bythe IEEE Std. 1100 (the EmeraldBook) and by the ANSI/IEEEC62.42 committee responsiblefor surge protection devices.The IEEE lightning research pro-vides the following conclusions:

Stroke current is related tothe lightning strike (travelingbetween a cloud and earthor between clouds)

50% of recorded directlightning strokes are lessthan 18,000A

0.02% of the strokes couldhave a surge currentof 220 kA

An unusual event wasrecorded that had a strokeof approximately 450 kA;however, this is acontroversial measurement

TVSS myth

A TVSS manufacturer maysuggest a one in a millionlightning stroke will be con-ducted on the AC distributionsystem and enter a facilitysservice entrance. To bullet-proofa facility against this strokecurrent, a surge suppressorwith a surge current rating of400 kA/phase is required.

Reality

Stroke current has no relation-ship to the surge current

conducted on the AC powerdistribution system. There is notechnical reason to specify asurge suppressor having 400 kA/phase surge current rating.

Discussion

In Florida (worst case in theU.S.), there are six groundflashes/year/km2 (IEEE C62.41).A facility occupying one acrewill experience one direct strikeevery 40 years. Based on thepercentages in Figure 9, thefacility will experience one

stroke exceeding 200 kAevery 800 years.

The crest current magnitude ofan actual lightning strike varieswidely. Typical surges conductedor induced into wire line facilitieswould be considerably smallerbecause of the availability ofalternate paths. As a result,protectors at the termination ofthese facilities are normally notdesigned to withstand the fullcrest current of direct strokes.

When lightning hits the earth,a powerline or facility, most ofthe energy flashes to ground oris shunted through utility surgearrestors. The remaining energythat is induced on the AC powersystem is called surge current(measured in kA). The surge cur-rent shunted by a suppressor isa small fraction of the lightningstroke current.

Based on available research,IEEE recommends using the20 kV, 10 kA combination waveas the representative test forinduced lightning surges at ser-vice entrance locations. Abovethis amount, the voltage willexceed BIL ratings causingarcing in the conductors ordistribution system.

In summary, low voltage wir-ing (



Surge arrestor vs. surgesuppressor

The use of surge protectiondevices (surge suppressors) isgrowing at over 20% per year.Suppressors are now routinelyinstalled at the service entranceand key down-stream panel-board or motor control center(MCC) locations to provideclean power to solid-state loads.Currently, there is some confu-

sion between the application ofsurge arrestors and surge sup-pressorsespecially in industrialfacilities, water treatment plantsand other areas where arrestorswere predominately used. Thissection explains the differencesin performance and applicationbetween the two technologies.

The evolution of surge/lightning arrestors

In the past, when nonlinear orsolid-state devices such ascomputers, programmable logiccontrollers (PLCs) and drives

were not yet in use, relays,coils, step switches, motors,resistors and other linear loadswere the standard. Utility com-panies and end users wereconcerned with how to protectelectrical distribution systemsfrom lightning surges. Theirobjective was to ensure thatvoltage surges did not exceedthe basic insulation level (BIL)of the conductor wires, trans-formers and other equipment.Consequently, arrestors weredeveloped for use in low, medi-um and high voltage applications

at various points in the transmis-sion and distribution system.The fact that these devices cre-ated a crowbar between thephase conductor and ground didnot matter to these loads if itcleared within a few cycles.

Arrestors are still used in theelectrical industry primarilyalong the transmission lines andupstream of a facilitys serviceentrance. Arrestors are availablein various classes dependingupon their withstand capabil-ity (e.g., station vs. distributionclass). At the service entrancelocation on low voltage systems(600V and below), surge sup-pressors are now replacing theuse of arrestors.

The evolution of surgeprotection devices(also called TVSS)

In todays computer age, theuse of solid-state (nonlinear)loads is increasing dramatically.Research by utilities and othergroups estimated that 70% ofutility loads are consumed byelectronic equipment such asdrives, PLCs, computers,electronic ballasts, telecommuni-

cation equipment, and so forth.Modern-day electronic equip-ment is getting faster, smaller,more efficient and very complex.These improvements have beenmade in all microprocessor-based equipment over the years,and this progress will continue.

The tradeoff in faster speed andlower cost is that the micro-processor loads are becomingincreasingly more susceptibleto the effects of transientsand surges.

As a design objective, the IEEE

Emerald Book (and the CBEMAcurve) recommend reducing20,000V-induced lightning surgedisturbances down to two timesnominal voltage (< 330V peak).To achieve this level of perfor-mance, surge suppressors weredeveloped. Since the mid-1980s,these devices have become thepreferred choice for protectingloads within any facility.

Lightning arrestors weredesigned to protect the electricaldistribution system and not thesensitive solid-state equipmentfrom the effects of lightning.

As in Table 5, lightning arrestorshave a high let-through voltage,the key performance factorfor protecting electronic loads.Under the IEEE Category C3test wave (20 kV, 10 kA), thelet-through voltage is typicallyover 1200V (on a 120 Vacsystem).

This is satisfactory for insulationprotection on transformers,panelboards and wiring. Forvariable frequency drives (VFDs),computers, PLCs and othersensitive equipment,however, the solid-state com-ponents will be damaged orupset by these surges.Using suppressors at the serviceentrance and key branch panels,the surge will be effectivelyreduced to under 100V.

Note: If a TVSS and lightningarrestor are both used at a ser-vice entrance switchboard, theTVSS will do all of the work. Itwill turn on earlier and shuntmost of the surge current.

Many water-treatment plants,telecommunication facilities,hospitals, schools and heavyindustrial plants utilize TVSSsinstead of surge arrestors toprovide protection againstthe effects of lightning, utilityswitching, switching electricmotors, and so on. New sup-

pressor designs can now beintegrated into motor controlbuckets, switchboards and otherdistribution equipment, providingmore effective performance andeliminating installation problems.

When selecting a suppressor,look for a quality device havingthe following features:

Low let-through under IEEECategory B3, C1 and C3test waves

Independently tested to thepublished surge currentratings (per phase)

Includes internal fuses

Includes internal monitoring

features (for both open andshorted MOV failures)

Includes electrical noisefiltering (55 dB at 100 kHz)

Small footprint design formore effective installation

Listed under UL 1449, UL1283, and CSA approved



TABLE 5. DIFFERENCE BETWEEN ARRESTORS AND SUPPRESSORS

DESCRIPTION

SURGE ARRESTOR SURGE SUPPRESSOR

480V (277V L-N) 208V (120V L-N) 480V (277V L-N) 208V (120V L-N)

Let-through voltages(based IEEE test waves):

Cat. C3 (20 kV, 10 kA)

Cat. C1 (6 kV, 3 kA)

Cat. B3 (6 kV, 500A, 100 kHz)

>1500V

>1200V

>1500V

>1000V

>1000V

>1000V

900V

800V

200V

470V

400V

25 years(if sized appropriately)

>25 years(if sized appropriately)



Benefits of hybrid filtering insurge protection devices

A surge suppressor (TVSSdevice) prevents harmful surgevoltages from damaging ordisrupting sensitive electronicequipment. There are two typesof suppression devices:

Basic suppressor devicesTransient suppressors thatuse only voltage-dependentcomponents such as metal

oxide varistors (MOVs) orsilicon avalanche diodes (SADs).

Hybrid filter devicesHybriddevices that employ a parallelcapacitive filter circuit in addi-tion to MOVs. Since theseproducts are able to eliminatelow-amplitude transients andhigh-frequency EMI/RFI noise,they are widely specified forcommercial, hospital and indus-trial facility construction projects.(See Figure 10.)

Unfortunately, it is often difficultto distinguish between hybrid

filter and basic suppressorswhen reviewing the perfor-mance specifications providedby the manufacturer of eithertype of device. In addition,specifying consultants are oftenunsure of the practical benefitsoffered by the filter compo-nents. This section describesthe differences between thetwo technologies wheninstalled in an electricaldistribution system.

A hybrid filter protects sensitiveelectronic equipment againsthigh-amplitude lightning

impulses, low-level ringing

transients and EMI/RFI noisedisturbances. In comparison,basic suppressors do not havefilter components and can onlysuppress high voltage distur-bances. Table 6 summarizes thekey differences between thetwo technologies.

a) Ringing transientsuppression

Studies performed by ANSI/IEEEand other organizations indicate

the oscillatory ringwave is themost common type of transientwaveform occurring within afacilitys electrical distributionsystem. Normal impedancecharacteristics of a low voltagedistribution system createringing oscillatory waves atfrequencies between 50 kHzand 250 kHz.

Internal transients at thesefrequencies are common andcan result in damaged inte-grated circuits, system lock-ups,reboots or other operationalproblems. To model this ringing

effect, ANSI/IEEE C62.41(2002) recommends testingall suppression devices to the100 kHz Ringwave (CategoryB3; 6000V, 500A waveform).(See Figure 11.)

Published let-through voltagesare then used to comparesuppression performance.

Basic suppressor (MOV Only)

Filter

MOVs

Hybrid filter

Surgecurrent

Surgecurrent

Load

L

N

L

N

Load

FIGURE 10. BASIC SUPPRESSOR AND HYBRID FILTER

FIGURE 11. RINGWAVE

TABLE 6. COMPARISON OF SUPPRESSOR TECHNOLOGIES

TVSS performance criteria Hybrid filter Basic suppressor

Repetitive surge withstand capability Longer life expectancy Limited life

Ringing transient suppression 900V let-throughElectrical noise attenuation 50 dB @ 100 kHz Poor attenuation

Facility-wide noise filtering Coordinated from service entrance to branch panels Not achievable

6000

4000

4000

2000

2000

0

0 10 20

Ringwave (Cat. B3,

6000V 100 kHz)



FIGURE 12. RINGWAVE SUPPRESSION CAPABILITIES

Figure 12 illustrates the superiorperformance of a hybrid filtersuppressors when tested to thestandard IEEE B3 Ringwave.Filter components provide alow-impedance path at higherfrequencies (e.g., 100 kHz)allowing impulses to be shuntedaway from sensitive loads, atany phase angle along the 60 HzAC sine wave. This sine wavetracking feature suppressesdisturbances at much lower

levels than possible with a basicsuppressor (nonfiltered device).

Without a filter, the MOVs areable to clamp the transient onlyonce when the voltage exceedsthe turn on point of the MOV.As shown in Figure 12, theMOV let-through voltage issignificantly higher due to theimpedance associated withwire lead lengths and the MOVoperating characteristics. This isover three times the let-throughvoltage of the TVSS filter. As aresult, the level of protectionprovided is limited.

b) EMI/RFI noise attenuation

Filters remove high-frequencyEMI/RFI noise associated withloads such as:

Variable speed drives

Photocopiers

Large UPSs

Arc welders

SCR controlled loads

Light dimmers

These types of noise generat-ing loads are found in almostevery facility. IEEE defines noiseas disturbances less than twotimes peak voltage (e.g., lessthan 340V peak on 120Vsystems).

The key performance filtertesting standard is the MIL-STD-220A, 50 Ohm insertionloss test. Manufacturers shouldpublish noise attenuation lev-els measured in decibels (dB)obtained at 100 kHz. Test databased on computer simulations

such as SPICE programs are notreflective of actual environmen-tal conditions, and are thereforenot acceptable for comparingfilter performance. Also notethat published dB ratings atfrequencies over 1 MHz aremeaningless for panel hybridfilter products. Above 1 MHz,EMI/RFI noise does not travel onthe conductor (i.e., it is radiatedand travels in the atmosphere).

For premium performance, thefilter attenuation should exceed50 dB at 100 kHz (based onMIL-STD-220).

Note: Have the suppressor sup-plier provide actual test resultsto ensure this level of filtering isbeing provided.

c) System noise/suppression capability

TVSS filters installed at

the service entrance andbranch panels meet with theIEEE-recommended approachto facility protection. Pleasesee Facility-wide surgesuppression on page 9 foradditional information.

In addition, a system-widesuppression design providesenhanced normal mode andcommon mode noise attenua-tionsignificantly greater thana stand-alone device.

Summary

TVSS filters offer significantbenefits that enhance the powquality within a facility. Thissection illustrates why TVSSfilters are now the most com-monly specified suppressiontechnology.

Manufacturers may offermisleading claims and avoidpublishing accurate performanstandards. Engineers should

ensure the suppressiondevice chosen offers sufficienringwave suppression, noiseattenuation and provides coordinated facility protection. TVSmanufacturers claiming to offsine wave tracking or filter coponents must support theseclaims by submitting test resuand spectrum analysis. Withothese submittals, it is likely alow-end suppressor will besupplied rather than therequired hybrid filter.

Input wave: IEEE B3 ringwave

(6000V, 500A, 100 kHz)

No filter

Poor filter

Quality filter

(55 dB at 100 kHz)

Time (microseconds)

0 50 100 150

Voltage(volts)

600

400

200

0

200

400

600



Factory automation (PLCs)and their need for surgesuppression

End users often ask us why oursurge protection is necessaryfor protecting process controlsystems. Most people assumethat programmable controls andautomation equipment are fullyprotected from power distur-bances. As the following sectionexplains, PLC manufacturers and

service technicians recommendthe use of surge suppressorsand filters to prevent downtimeand equipment damage due tosurges and electrical line noise.

A major study on how powerdisturbances affect processcontrol systems has been con-ducted by Dranetz Technologiesand PowerCet corporation.Results of the study indicatethat impulses, surges andelectrical noise cause thefollowing equipment problems:

Scrambled memory

Process interruption Circuit board failure

AC detection circuits causefalse shutdown

Setting calibration drift

Power supply failure

Lock up

SCR failures

Program loss

Digital/analog controlmalfunction

Sensitivity to electricalinterference varies dramaticallyfrom one system to another,depending upon grounding con-ditions, equipment sensitivity,system design and quantity ofelectronic equipment inthe area.

Facility downtime and repaircosts associated with thesepower quality problems repre-sent a growing concern forengineers and maintenancestaff. Power protection is nowwidely recognized as an impor-tant factor in the design ofprocess control systems. Major

PLC manufacturers such asAllen-Bradley and Siemensprovide the following recom-mendations: Dranetz Field Handbook For Power

Quality Analysis, 1991

1. Allen-Bradley SLC500operational manual17471002, Series A

Most industrial environmentsare susceptible to powertransients or spikes. To helpensure fault-free operation andprotection of equipment, werecommend surge suppressiondevices on power to theequipment in addition toisolation equipment.

Lack of surge suppression oninductive loads may contributeto processor faults and sporadicoperation. RAM can be corrupt-ed (lost) and I/O modules mayappear to be faulty orreset themselves.

2. Siemens AG automationgroup EWA 4NEB 811 6130-02

Measures to suppress interfer-ence are frequently only takenwhen the controller is alreadyin operation and receptionof a signal has already beenaffected. The overhead for suchmeasures (e.g., special contac-tors) can often be considerablyreduced by observing the follow-ing points when you install your

controller. These points include: Physical arrangements of

devices and cables

Grounding of all inactivemetal parts

Filtering of power andsignal cables

Shielding of devicesand cables

Special measures forinterference suppression

3. Allen-Bradley publication1785-6.6.1

Electromagnetic interference(EMI) can be generated when-ever inductive loads such asrelays, solenoids, motor startersor motors are operated by hardcontacts such as pushbuttonsor selector switches. Followingthe proper wiring and groundingpractices guards the processorsystem against the effects of

EMI. However, in some casesyou can use suppression net-works to suppress EMI atits source.

Regardless of the manufacturer,electronic equipment is suscep-tible to power disturbances.This results from twocontributing factors:

1. Processors themselves areincreasingly complex with higherchip density and loweroperating voltages.

2. The growing use of distur-bance generating loads such

as adjustable frequency drives,capacitor banks, inductiveloads and a wide variety ofrobotic equipment.

Eatons series type TVSS filterswere developed exclusively forthe protection of automationequipment used in industrialenvironments. With up to 85dB of noise attenuation andoutstanding transient suppres-sion, these products are wellsuited for the protection ofsophisticated microprocessorloads. A series power line filteris extremely cost-effective and

less than one third the cost of atypical service call.

Consider improving yourcontrol system and your bottomline reliability.



Surge protection devices withreplaceable modules

A surge protective device (SPD)design that is offered by sev-eral manufactures is knownas a modular design. Modulardesigns include parts that canbe replaced in the field. Themost common replaceable mod-ule version is a metal box withreplaceable surge componentshoused in a smaller plug in

plastic box.In an SPD, the most commonlyused surge suppression com-ponent is an MOV (metal oxidevaristor). The MOV becomes aconductive component whenthe voltage across it exceedsa certain level known as themaximum continuous operatingvoltage (MCOV). Once the volt-age exceeds MCOV, the currentis allowed to flow through theMOV, which then passes thesurge to ground. For SPDs thatare modular, the MOVs are builtinto these plastic boxes that are

available for field replacement ifthe internal MOV was damaged.

Some SPD manufacturerspromote modular design tominimize their production costs.Plus, the use of modules createan aftermarket business for theSPD manufacturer. However,there are a number of potentialtechnical flaws with modulardesigns.

If one module is damaged,the remaining undamagedmodules begin to compen-sate for the lost module,

resulting in stress to theundamaged modules. Thismay lead to a second failurebefore the first moduleis replaced

Many failures result inunacceptable damage to theinterior of the metal box.Replacement of the modulesis not sufficient to get the unitback to operating condition.These failures require replace-ment of the complete unit

A damaged module may alsocause unbalanced protection,in which the surge current is

not equally shared across theMOVs. Most manufacturesmatch the performance ofthe MOVs to achieve thespecified performance. A newmodule will not be matchedto the modules already inthe product

Many manufacturers of mod-ular designs utilize bananapin connectors instead of low-impedance bolt-on connectionor leads. During high surgecurrents, the mechanicalforces can rip these con-nectors out of their sockets.Many environmental condi-tions can degrade theseconnectors, as they relysolely on spring force tokeep the connection

Performance specificationscan be misleading. Oftenthe published suppressionratings are for the individualmodule and not for the entireSPD unit. Some manufactur-ers have designed modular

products just for this reason.It is important to get the SVR(ULs surge voltage ratings,markings required on allUL- listed products) ratingsand surge current ratings forboth the module and for thecomplete product

Another aspect to look at closelyis theoretical surge currentratings. In order for accuratetheoretical surge current ratings,there are two design criteria thatmust be considered.

1. Integrity of internal wiring

Low-end surge suppressiondevices may use small diametercircuit traces or wires, whichcannot handle the rated surgecurrent. Exposure to a largetransient the modules cansurvive, but the total productcannot survive, leaving down-stream loads unprotected.

Most of the time these potentialwiring deficiencies are inside ofthe SPD and hidden from thecustomer or specifying engineer.

2. Equal current sharing toeach MOV

The SPDs internal wiring mustensure that each component iselectrically balanced. In otherwords, a suppressor manufac-turer must ensure the followingperformance criteria are met:

Integrity of ratedsurge performance

All surge paths must achievethe rated surge current

Life expectancy

The total device must meet itslifetime performance rating.

A possible result to SPDs thatdo not share surge currentequally is premature failure.Premature failure is a commonproblem in modular designssince newer and oldermodules do not have the sameMOV voltage, and thereforeexperience a reduction in surgecurrent capacity.

The Clipper Power System,

Visor series (CPS) and EatonTVSS units are designed to uti-lize the benefits of ground planetechnology in the constructionof suppressors. The electricalfoundation of all our Visor SPDsemploy a multilayer, low-imped-ance SurgePlane circuitry.

Because power surges andelectrical line noise are high-frequency disturbances, thecurrent travels on the surfaceof the plane due to skin effect.The surge plane design providesthe largest possible conduct-ing area without the drawbacksof heavy gauge wire. At thesefrequencies, the impedance (selfand mutual inductance) of thesolid copper plane is significantlylower than even large diameterwire or bus bars.

Since all MOVs attached to thplane are at the same potentiaand all the MOVs are electri-cally matched, surge current iequally shared. Stress on theMOVs is reduced because eacMOV carries a smaller and eqproportion of the total surge,resulting in significantly longelife expectancy compared todevices that do not provideequal current sharing.

Features of theSurgePlane include:

Lowest possible self-induc-tance due to the highsurface area

Mutual inductance is reducdue to the geometry ofthe circuitry

Reduced let-through voltag

Improved reliability

Since there are significantquality differences among surprotection devices (SPDs), weencourage engineers to checkthe SPDs electrical founda-tion. The consulting engineershould verify that surge cur-rent is equally shared amongcomponents and other possibproblems are dealt with beforaccepting them as equal.



Why silicon avalanche diodesare not recommended for ACpowerline suppressors

A surge protection device, alsocalled a TVSS device, is usedto protect semiconductor loadsfrom powerline transients. SPDsare installed in the AC powersystem at the service entranceand panelboards, and some-times at the load. SPDs are alsorequired on data communication

lines to prevent ground loopsand induced surges, which candamage equipment.

In AC power applications, over95% of SPDs use metal oxidevaristors because of their high-energy capability and reliableclamping performance. Foradded performance, hybriddesigns (MOVs and capacitivefilter) are typically specified.

A small number of SPD manu-facturers still promote the use ofsilicon avalanche diodes for ACapplications. These companiesattempt to scare customersinto buying a premium-pricedunit by publishing misleadinginformation about MOV surgecomponents. The following sec-tion summarizes the marketingclaims and technical insightsregarding SADs suppressors.

Three SAD myths and reality

Myth number one: SADs havea faster response time (e.g., 5picosecond compared to 1 nano-second for MOVs). The fasterSAD response time results inimproved SPD performance.

1. NEMA LS-1 and IEEE commit-tees do not mention the use ofresponse time as an SPD speci-fication. All SPDs have sufficientresponse time to turn on andshunt surges. The responsetime of an MOV is 1000 timesfaster than the time it takes fora surge to reach full current (i.e.,8 microseconds). Response timeis not an appropriate criteria touse when specifying SPDs.

2. The response time for a SADdevice is equivalent to that of anMOV device. Response time of

the device is affected more bythe internal wiring/connectionthan the speed of the SAD (orMOV). For example, a SAD mayreact in one picosecond, but theinternal wiring and connectingleads within the SPD add induc-tance (about 1 to 10 nanohenrysper inch). This inductive effect isthe dominating factor in overallresponse timenot the SADreaction time.

3. Note that hybrid filters (MOVscombined with capacitive filter-ing) react the fastest becausethe capacitors activateinstantaneously to any highfrequency surge.

Myth number two: MOVsdegrade resulting in short lifeexpectancy of the SPD andunsafe failures. SADs do notdegrade and are safer to use.

Life expectancy of SADs ismuch lower than that of anMOV (see Figure 13). A singleSAD will be damaged by a surgeunder 1000A. Given that IEEE

C62.41 requires SPDs to with-stand 10,000A surges, SADsdo not have sufficient energycapabilities for service entranceor branch panel applications. Tohide this weakness, SAD devic-es often publish Joule ratingsor wattage instead of publishingsurge current capacity per phase(a more reflective performancecriteria).

Note: IEEE and NEMA do notrecommend the use of Jouleratings for SPD comparison.

MOVs are rated from 6500A to40,000A, making them morereliable for AC power systems.

Quality SPDs often parallelMOVs to achieve surge currentratings in excess of 250,000Aper phase. These results can beverified through independenttesting at lightning labs. Atthese ratings, the SPD willoperate effectively for over 25years in IEEE-classified highexposure environments.

Paralleling SADs is more difficultthan with MOVs. Suppressorsusing parallel SADs require a sig-nificant amount of components,which reduce the overalldevice reliability.

Given the limited energy ratingsof SADs, these devices are notrecommended for panelboardor switchboard applications.

Similarly, hybrid designs usingMOVs and SADs do not achievecomponent synergies. Inhigh-energy applications,for example, the SADs arethe weak link because theSADs and MOVs cannot becoordinated to work together.

Failure mode. SAD manufactur-ers claim that their units do notdegrade. Rather than degrade,the SAD fails in a short circuitmode at much lower energylevels than a MOV. A properlyconstructed MOV suppressorwill not degrade, even when

exposed to thousands ofhigh-energy strikes. Ask yoursupplier to provide indepen-dent testing to guarantee thedevice achieves the publishedsurge current ratings (and thus,the required life expectancy).Degradation problems do existwith the very inexpensive surgebars. These devices are usu-ally manufactured offshore andare poorly constructed utilizingunderrated MOVs. These low-quality devices should not becompared to the SPDs typicallyused at panelboards or service

entrance locations.

Small MOV (20 mm)

Large SAD (5 kW)SAD

Failure

MOV

Failure

Silicon avalanche diode: Note 52 SADs are

equivalent surge current rating as the 1 small MOV

illustrated. For a complete device, a significantnumber of SADs are required.

1000010001001010

100

200

300

400

500

600

700

Voltage(V)

Surge current (A)

FIGURE 13. SILICON AVALANCHE DIODES HAVE LIMITED ENERGY CAPABILITY



Myth number three: SADsprovide tighter clampingthan MOVs.

When exposed to IEEE-definedtest waveforms and UL 1449test results, both MOV and SADdevices have the same suppres-sion voltage ratings. Accordingly,UL does not regard SAD devicesas providing any better clampingthan MOV based SPDs.

Summary

There are a number of mythsin the SPD industry. Whenevaluating SPDs, it is importantto evaluate the performanceof the suppressor unit and notcompare individual internal ele-ments. In other words, SPDconstruction methods and inter-nal wiring/fusing limitations arecritical to overall performance.Independent testing is essential

when comparing the perfor-mance of these units.

TABLE 7. COMPARISON OF COMPONENTS USED IN SURGE PROTECTION DEVICES

SPD component Advantages and Disadvantages

Metal oxide varistor (MOV) Highest energy capability, excellent reliability and consistent performance, better mechanical connectivity forparalleling multiple components. Nonlinear clamping curve gradually degrades over repeated use (only at highsurge levels), moderate capacitance.

Silicon avalanche diode (SAD) Flatter clamping curve, excellent reliability and consistent performance. Very low energy capability, expensive.

Selenium cells Moderate to high-energy capability. Very high leakage current, high clamping voltage, bulky, expensive,obsolete components.

Gas tubes High-energy capability, very low capacitive (requirement for data line applications). Unpredictable and unstablerepetitive behavior, crowbar to ground (unsuitable for AC systems), expensive.

Hybrid SPD MOV/fil ter is most common hybrid; incorporates the advantages of other components while overcoming theproblems associated with each individual component (achieves long life expectancy, faster response, betterclamping performance). Inherent problems with hybrid SPDs using MOV and SAD, or devices using seleniumcells (inability to have the various components work together).

Based on the proven trackrecord of performance, MOV-based suppressors are highlyreliable. That is why almostall suppressors still employMOV components. For serviceentrance or panelboardlocations, SADs are not recom-mended because of their limitedenergy capability. SADs areprimarily used to protect datalineand communication wires.



Surge protective devicefrequently asked questions

1. What are surges (also calledtransients, impulses, spikes)?

An electrical surge (transientvoltage) is a random, high-energy, short duration electricaldisturbance. As shown inFigure 14, it has a very fastrise time (110 microseconds).Surges, by definition, are sub-cycle events and should not be

confused with longer durationevents such as swells ortemporary overvoltages.

High-energy surges can disrupt,damage or destroy sensitivemicroprocessor-based equip-ment. Microprocessor failureresults from a breakdown in theinsulation or dielectric capabilityof the electronics.

Approximately 80% of recordedsurges are due to internalswitching transients caused byturning on/off motors, transform-ers, photocopiers or other loads.

The IEEE C62.41 surge standardhas created the Category B3ringwave and the B3/C1 combi-nation wave to represent higherenergy internal surges.

Externally generated surgesdue to induced lightning, gridswitching or from adjacent build-ings account for the remainingrecorded surges. The CategoryC3 combination wave (20 kV,10 kA) represents high-energysurges due to lightning. Refer tothe CPS Technote #1 for moreinformation on IEEEsurge standards.

FIGURE 14. AN EXTERNALLY CREATED ELECTRICAL SURGE CAUSED BYINDUCED LIGHTNING

TABLE 8. SUMMARY OF MAJOR SURVEY RESULTS ON THEEFFECTS OF SURGES ON DIFFERENT MICROPROCESSOREQUIPMENT

Impact toelectronic loads

Impulse 4X Impulse 2X

Repetitivedisturbance(noise)

Circuit board failure Yes Yes

Datatransmission errors

Yes Yes Yes

Memory scramble Yes Yes Yes

Hard disk crash Yes

SCR failure Yes

Process interrupt Yes Yes Yes

Power supply failure Yes

Program lock-up Yes Yes Yes

Source: Dranetz Handbook for Power Quality

2. Why is there a need forsurge protective devices?

In the coming years, electronicdevices will represent half ofthe electrical demand in theUnited States. Electronics,consist of microprocessors thatrely on digital signals: fast on/off coded sequences. Distortionon the power or signal linesmay disrupt the sensitive signalsequence. As electronic compo-nents become smaller and morepowerful, they become moresensitive. The tremendous pro-liferation in the use of sensitiveelectronic equipmentsensi-tive by virtue of circuit density(microchips having literally thou-sands of transistors on a singlechip)is now incorporatedinto almost every new electri-cal device. Surge protection isnow the standard technologyfor increasing the reliability anduptime of microprocessors.

Microprocessors can beupset, degraded or

damaged by surge events.Depending on the magnitudeof the surge, the system con-figuration and the sensitivity ofthe load. Table 8 summarizesthe results of a major surveyconducted by Dranetz on theeffects of surges on differentmicroprocessor equipment.

Other references for the recom-mendation of surge protectivedevices includes:

IEEE Emerald Book(Std. 1100)

FIPS 94

IEEE C62.41

Manufacturers (Allan-Bradley, Motorola,other suppliers)

NEMA LS-1

NFPA 780

As a design objective, the IEEEEmerald Book (and the CBEMAcurve) recommends reducing20,000V induced lightning surgedisturbances down to two times

nominal voltage (



3. Where do I need an SPD?Why do I need to implementa two-stage approach?

As recommended by IEEE(Emerald Book 2005), SPDsshould be coordinated in astaged or cascaded approach.The starting point is at the ser-vice entrance. (Service entranceprotection is also required byNFPA 780.) The first surgediversion occurs at the serviceentrance, then any residualvoltage can be dealt with by asecond SPD at the power panelof the computer room, or othercritical load (see Figure 15). Thistwo-stage approach will reduce20,000V induced lightningsurges well under 330V peakas recommended by IEEEand CBEMA.

4. Is there a differencebetween a TVSS and an SPD?

No, Underwriters Laboratories(UL) uses the term transientvoltage surge suppressor, whileNEMA, IEC and IEEE use surge

protective device (SPD). AnSPD/TVSS is a device that atten-uates (reduces in magnitude)transient voltages.

5. How does an SPD work?

The design goal is to divert asmuch of the transient distur-bance away from the load aspossible. This is accomplishedby shunting the energy toground through a low-impedance path (i.e., thesurge suppressor).

Metal oxide varistors are themost reliable and proven tech-nology to reduce transientvoltages. Under normalconditions, the MOV is a high-impedance component. Whensubjected to a voltage surge(i.e., voltage is over 125% of

the nominal system voltage), theMOV will quickly become a low-impedance path to divert surgesaway from loads. The MOVreaction time is nanoseconds1000 times faster than theincoming surge.

In AC power applications, over95% of SPDs use metal oxidevaristors because of their high-energy capability and reliableclamping performance. Foradded performance and SPD lifeexpectancy, a filter element isused in conjunction withthe MOVs.

Silicon avalanche diodes (SADs)are frequently used in datalineor communication surge protec-tors. They are not recommendedfor use in high-exposure ACapplications due to their limitedenergy capabilities.

Selenium cells were once usedin surge applications, but arenow an outdated technology.They were used in the 1920s,but were replaced in the 1960s

by the more efficient SADs andMOVs. One TVSS companycontinues to use selenium-enhanced surge protection as amarketing ploy to createconfusion with engineers.Selenium cells are metallicrectifiers (diodes) having amaximum reverse voltage of25 Vdc. Many selenium platesare stacked together to createsufficient voltage breakdown foruse in AC power circuits. Whenmounted in parallel with MOVcomponents, selenium offers noperformance, cost or application

advantages. In fact, they areexpensive and add considerablespace (which makes installationmore difficult). There are no pat-ents on selenium cells.

SPD

SPD480V 120V/

208V

Compute

sensitive

loads

20,000V

25 uS

Time (microseconds)

50

System test parameters:

IEEE C62.41 and C62.45 test procedures using C3 Impulse480V main entrance panels; 100 feet of entrance wire;480/208V distribution transformer; and 120/208V branch

Inputhigh energy transient disturbance:IEEE Category C3 Impulse 20,000V

Best achievableperformance with single TVSSat main panel (800V at Stage 1)

Two stage (cascade approach)achieves best possible protection(less than 100V at Stage 2)

Stage 1 protection(service entrance)

Stage 2 protection(branch location)

FIGURE 15. FACILITY-WIDE PROTECTION SOLUTIONS IEEE EMERALD BOOKRECOMMENDS A CASCADED (OR 2-STAGE) APPROACH

6. What criteria areimportant when specifyinga suppressor?

A specification should focuson the essential performance,installation and safety require-ments. A number of surgespecifications contain misleadingcriteria that do not follow NEMALS-1 or other recommendedperformance standards.

The following are considered

essential performance/safety/installation criteria fora specification:

A. Surge current per phase250 kA/phase for serviceentrance, 120 kA/phase forpanelboards or other locations

B. Let-through voltagespecithe performance voltage ratinbased on the three standardIEEE test waveforms (IEEEC62.41 Category C3 and B3combination waves; and BEringwave). Specify the requireratings for applicable nominalvoltages (i.e., 208 vs. 480). Thdata should be requested as pof the project submittal proce



C. Effective filternoise attenu-ation at 100 kHz based on theMIL-STD-220 insertion loss test.The attenuation should exceed45 dB (L-N modes). Specify thatinsertion loss bode plots areprovided as submittals.

D. Integrated installationfactory installed as part of thedistribution equipment. Check toensure the installation minimizeslead length.

E. Internal fusingsafety andovercurrent protection. 200 kAICinternal fusing system.

F. Reliability monitor andDiagnostic systemfoolproofstatus indication for each phase.A popular option is to includeForm C contacts forremote monitoring.

G. Independent testingtoensure a reliable constructionand design, specify that all man-ufacturers submit results froman independent test lab verifyingthe device can achieve the pub-

lished surge current ratings (on aper mode and per phase basis).

For more information on speci-fication recommendations or acopy of sample specification,contact Eaton.

7. What is surgecurrent capacity?

Defined by NEMA LS-1 as: Themaximum 8/20 U.S. surge cur-rent pulse the SPD device iscapable of surviving on a singleimpulse basis without sufferingeither performance or degrada-tion of more than 10 percent

deviation of clamping voltage.Listed by mode, since numberand type of components in anySPD may vary by mode.

The industry standard is to pub-lish surge current per phaseby summing modes L-N + L-G ina wye system and L-L + L-G indelta systems.

Surge current capacity is usedto indicate the protectioncapability of a particular SPDdesign, and should be used ona per phase and per mode basiswhen specifying an SPD for agiven application.

Beware: Manufacturers arenot required to have their unitsindependently tested to theirpublished surge current capacityrating. Most published ratingsare theoretical, and calculatedby summing the individual MOVcapabilities. Manufacturer Amay claim a rating of 100 kA,but due to the poor construc-tion integrity, the unit is unableto share current equally to eachMOV. Without equal currentsharing, the published surgecurrent rating cannot be met.Specifiers should request that

manufacturers submit indepen-dent test reports from lightninglabs confirming the publishedsurge ratings.

All clipper units have beenindependently tested to meetor exceed their published surgecurrent capacities.

8. What surge current capacityis required?

Surge current capacity is depen-dent on the application and theamount of required protection.What is the geographic locationof the facility and the exposure

to transients? How critical is theequipment to the organization(impact of downtime,repair costs)?

Based on available research, themaximum amplitude of a light-ning-related surge on the facilityservice entrance is 20 kV, 10 kAcombination wave (refer to IEEEC62.41). Above this amount, thevoltage will exceed BIL ratingscausing arcing in the conductorsor distribution system.

Eaton recommends 250 kAper phase for service entranceapplications (large facilities inhigh-exposure locations), andnot more than 120 kA per phaseat branch panel locations.

If IEEE and other research speci-fies the maximum surge to be10 kA, why do many suppliers,including Eaton, suggest up toa 250 kA per phase device beinstalled? The answer is reliabil-ity, or, more appropriately, lifeexpectancy. By increasing thekA rating of the suppressor, youare not increasing performance,but instead the life expectancyof the suppressor.

A service entrance suppressor

will experience thousands ofsurges of various magnitudes.Based on statistical data, we candetermine the life expectancyof a suppressor. A properly con-structed suppressor having a250 kA per phase surge currentrating will have a life expectancygreater than 25 years in highexposure locations.

Beware: Some manufacturersrecommend installing SPDs hav-ing surge current ratings over250 kA per phase. In fact, someare promoting ratings up to 600or 700 kA per phase. This levelof capacity is ridiculous andoffers no benefits to custom-ers. A 400 kA per phase devicewould have approximately 500-year life expectancy for mediumexposure locationwell beyondreasonable design parameters.

(Eaton is forced to build higherrated units to meet competitorspecifications, however, westrongly recommend that con-sultants question suppliers whopromote excessive ratings forcommercial reasons.)

Todays SPDs will not fail due tolightning surges. Based on twodecades of experience, the fail-ure rate of an SPD is extremelylow (



1,000

14 AWG

Installation criteria order

of importance:

1. Lead length 75% reduction

2. Twisting wires 23% reduction

3. Large wire minimal reduction

209V (23%)

Loose wiring

3 ft. lead length

Twisted wires

1 ft. lead length

twisted wires

67V (75%)

10 AWG

4 AWG

900

800

700

600

500

400

300

200100

0

Installation lead length can increase let-through voltageby 15 to 25V per inch

Additional let-through voltage (additional to UL 1449 rating)

FIGURE 17. ADDITIONAL LET-THROUGH VOLTAGE USING IEEE C1 (6000V, 3000A) WAVEFORM (UL1449 TEST WAVE)

.

As one specifier said, Nomatter which TVSS deviceyou buy, it is the installationrequirements/inspection that

are the most important factorof the surge specification.

Published let-through voltageratings are for the device/mod-ule only. These ratings do notinclude installation lead length(which is dependent on theelectrician installing the unit).The actual let-through voltagefor the system is measured atthe bus bar and is based ontwo factors:

1. Surge waveforms (defined by IEEE C62.41 1991)

2. Let-through voltage test

Cat. C3 Impulse(20 kV, 10 kA)

Cat. B3 Ringwave(6 kV, 500 A, 100 kHz)

Measured let-through voltage

Test surgewaveform

Surgegenerator

SPD

Time (microseconds)Time (us)

Surgecurrent(A)

Surgecurrent(V)

Cat. C1 Impulse(6 kV, 3 kA) -

-

-

9. What is let-throughvoltage (clampingvoltage)?

Let-through voltage is theamount of voltage that is notsuppressed by the SPD andpasses through to the load.Figure 16 is an example oflet-through voltage.

Let-through voltage is a per-formance measurement of asurge suppressors ability to

attenuate a defined surge.IEEE C62.41 has specifiedtest waveforms for serviceentrance and branch loca-tions. A surge manufacturershould be able to providelet-through voltage testsunder the key waveforms(i.e., Category C3 and C1combination waveforms;Category B3 Ringwave).

Beware: The UL 1449 (2ndEdition, 1988) conducts a500A let-through voltagetest. This test does notprovide any performance

data and is not a keyspecification criterion.

Clamping voltage is oftenconfused with let-throughvoltage. Clamping voltagerefers to the operating char-acteristic of a metal oxidevaristor component and isnot useful for comparing theperformance of an SPD. Theclamping voltage is the volt-age when 1 mA of currentpasses through an MOV.Clamping voltage does notinclude the effects of inter-

nal wiring, fusing, mountinglugs, or installation leadlength.

Let-through voltage is a moreapplicable test for SPDs, andrefers to the amount of volt-age that is not suppressedby an SPD when tested to anIEEE defined surgewaveform and test setup.

1. The device rating (quality ofthe suppressor).

2. The quality of the installatio

For example, consider an SPDhaving a 400V rating (based oIEEE Cat. C1 test waveform).

Connected to a panelboardwith just 14 inches of #14 wirapproximately 300V are addedto the let-through voltage.

The true let-through at the bubar is thus 700V.

10. Why is installation important?What effect does it have on anSPDs performance?

Installation lead length (wiring) reduc-

es the performance of any surgesuppressor. As a rule of thumb,assume that each inch of installa-tion lead length will add between 15and 25V per inch of wiring. Becausesurges occur at high frequencies(approximately 100 kHz), the leadlength from the bus bar to thesuppression elements createsimpedance in the surge path.

FIGURE 16. EXAMPLE OF LET-THROUGH VOLTAGES AND DIFFERENT IEEE DEFINED SURGE WAVEFORMS



11. Why should suppressorsbe integrated into the electri-cal distribution equipment(panelboards, switchboards)?

Most consulting specifiers arenow requiring the gear manufac-turer integrate the suppressorinside the switchboard, panel-board or MCC. Integratedsuppression offers a numberof key benefits compared toexternally mounted applications:

1. PerformanceIntegrating theSPD into the electrical distribu-tion equipment eliminates theinstallation lead length, ensuringsignificantly improvedperformance (much lowerlet-through values).

2. ControlThere is no chancethat field installation is doneincorrectly. By having the sup-pressor factory installed andtested, the specifier does nothave to check the installationand force the contractor toreinstall the device (a costlyand time-consuming process).

This reduces future claims andproblems for the engineer andend customer.

3. Reduce wall space.Integrating the suppressoreliminates the wall space takenup by the externally mountedsuppressor (between two andthree feet!).

4. One source for warrantyclaims. Should a problemoccur, the customer eliminatespotential warranty conflictsbetween manufacturers.

5. Reduced installation costs.

There is no contractor fees formounting SPDs.

The Cutler-Hammer ClipperPower System is integratedinto all of our low voltagedistribution equipment.

Through our innovative directbus bar connection, we limitthe lead length between theSPD and electrical equipment.For example, the Clipper PowerSystem carries a UL 1449 let-through voltage rating of 400V.

Through our zero lead lengthdirect bus bar connection, we

obtain a let-through voltage of420V at the panelboard busbar. A significant performanceadvantage over traditional cableconnected designs.

N

G

SPD

N

G

CPS

1000

800

600

400

200

0

200

Surgeevent

2.00 0.00 2.00 4.00 6.00 8.00 10.00

Microseconds

Side mounted SPDused for retrofitapplications

Benefits of integrated (clipper):- Less lead length = lower let-through voltage- Eliminates installation costs- Less wall space- Factory installed and quality tested- Higher performance

SPD Integratedinto panelboards,switchboards, MCCs

208Y/120 panelboard(integrated vs. side-mounted SPD)

Side-mounted SPD device(assuming 14" lead length to bus)

Clipper: Integrated SPD(direct bus bar connection)

FIGURE 18. INTEGRATED SPD PERFORMANCE

Some SPD manufacturers haveobtained a UL procedure forinstalling their SPD into anothermanufacturers panelboard.When this occurs, the originalpanelboard manufacturers ULlabel (UL67) is void, as is thewarranty provided by that manu-facturer. The SPD manufacturerthen modifies and integratesthe SPD into its panelboard, andmust assume all warranty andliability issues regarding thepanelboard and SPD.

In most cases, the originalpanelboard manufacturersnameplate data is not removedand replaced by that of the SPDmanufacturer. This can causeproblems for the end customeras different panelboards withinthis facility carry the nameplatesfrom the original panelboardmanufacturer, but two separatecompanies cover the warranty.



FIGURE 19. INTERNALLY GENERATED RINGWAVE

Note: Ringwaves typically resonate within a facility at frequenciesbetween 50 kHz and 250 kHz.

FIGURE 20. EMI/RFI ELECTRICAL LI

Documents

Surge Suppression App Guide - Eaton