11

Foundation Earth Electrode

DS162/E/0712

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A functional earth-termination system is an elementary part of the electrical and electronic installations of alrea-dy existing buildings and new buildings. It is an impor-tant basis for the safety and functionality of installations in a building, for example, for

• personalsafety(toachievesafedisconnection fromsupplyandprotectiveequipotentialbonding),• electricsystems(powersupply),• electronicsystems(dataprocessingtechnology),• lightningprotection,• overvoltageprotection,• electromagneticcompatibility(EMC)and• antennaearthing.

Theseinstallationsaresubjecttospecialrequirementswith regard to personal protection and operation safety, asspecifiedinthevariousregulationsofthedifferentsystems.

Standard RequirementsIn Germany, for new buildings a foundation earth electrodeisrequiredaccordingtoDIN18015(Electricalinstallationsinresidentialbuildings)andthetechnicalconnectionconditions(TAB)ofthenetworkoperators.DIN18014:2007-09"Fundamenterder–AllgemeinePlanungsgrundlagen",(Englishtitle:Foundationearthelectrode–Generalplanningcriteria)basicallyregula-tes the design and installation of the earth-termination system of new buildings.

If a lightning protection system shall be installed in a buildingorstructuretheextendedrequirementsofEN62305-3(VDE0185-305-3)"Protectionagainstlightning–Part3:Physicaldamagetostructuresandlifehazard"areapplicable,ortherequirementsinEN62305-4(VDE0185-305-4)"Protectionagainstlightning–Part4:Electricalandelectronicsystemswithinstructures"consideringtheaspectsofelectromagneticcompatibility(EMC).

Smallermeshsizesofthefoundationearthelectrodearerequiredifthereareforexamplelarge-scaleITsystemsinabuilding.Alsothesystemproviderspecifications(e.g.dataprocessingtechnology)havetobeconsideredfortheearthresistanceandtobetakenintoaccountalreadywhen designing the earth-termination system.

Forbuildingswithintegratedmediumvoltageswitch-gear(MVsystems),additionallyDINVDE0101(VDE0101)"StarkstromanlagenmitNennspannungenüber1kV";(Englishtitle:Powerinstallationsexceeding1kV)GermanversionHDS1:1999,isapplicableinGermany.Potentiallyhighshort-circuitcurrents(50Hz)requirehigherearth-electrodecrosssectionsandadequateclamps/connectors.

Installation of the Earth-Termination SystemThe foundation earth electrode fulfils essential safety functions and is therefore considered as part of the electrical system. That’s why the earth-termination sys-tem shall be installed by lightning protection specialists, qualifiedelectriciansorundertheirsurveillance.

Equipotential Bonding Equipotentialbondingisrequiredforallnewlyinstalledelectrical consumer’s installations. In order to implement allrequirements,themainearthingbusbar(MEB)(pre-viouslymainequipotentialbondingbar(MEBB))shallbeconnectedtothefoundationearthelectrode.Equipoten-tialbondingaccordingtoIEC60364equalisespotentialdifferences,i.e.itpreventshazardoustouchvoltagese.g.betweentheprotectiveconductorofthelow-voltageconsumer’sinstallationandmetalinstallations(water,gasandheatingpipes).AccordingtoIEC60364-4-41,equipotentialbondingcon-sistsoftheprotectiveequipotentialbonding(previously:main equipotential bonding)andthesupplementaryprotectiveequipotentialbonding(previously:supple-mentary equipotential bonding).

Protectiveequipotentialbondingmustbeimplementedineverybuildingaccordingtotheabovementionedstandards.Thesupplementaryprotectiveequipotentialbonding is intended for those cases where special con-ditionsfordisconnectionfromsupplyhavetobeimple-mentedorforspecialareaswhichconformtotheIEC60364seriesPart7.

Lightning Equipotential Bonding Lightningequipotentialbondingisanextensionoftheprotectiveequipotentialbonding.Lightningequi-potentialbondingandequipotentialbondinghavetobeconnectedwiththemainearthingbusbar(MEB)oftheearth-terminationsystem.Lightningequipotentialbonding is that part of the internal lightning protection whichprovidesasafeintegrationofallenteringconduc-torsintotheequipotentialbondingsystemiflightningstrikestheprotectionsystemorenteringconductors.Thushazardoussparkingwillbeavoided.Electricalpow-erandITinstallationshavetobeparticularlyprotectedbecause the external lightning protection system and the building installation shall not be directly connected viatheearth-terminationsystemandtheequipotentialbonding.

Types of Earth ElectrodesFoundation earth electrodeA concrete embedded closed earth electrode ring with alarge-areaearthcontact.If,incaseof"full-perimeterinsulation"ora"whitetank",thisearthcontactisnotpossible, a ring earth electrode will be installed outside thefoundationwhichtakesoverthefunctionofthefoundation earth electrode.

Ring earth electrodeA soil embedded earth electrode as closed ring around the building or structure.

Earth rodAverticallydeepdrivenearthelectrodegenerallymadeof round steel.

Natural earth electrodeMetalpartsthataresoilorconcreteembeddedandoriginallynotintendedasearthelectrode,however,beingeffectiveinthissense(reinforcementsofconcretefoundations,pipelines,etc.).

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Terminal LugAtleast1.5mlong,strikinglymarked- StStstripsteel30x3.5mm- StSt round steel 10 mm- roundsteel10mmgalvanisedwithPVCcoating- fixed earthing terminal

Foundationearthelectrode-stripsteel30x3.5mm- round steel 10 mm

round steel diameter 10 mm acc.toEN50164-2

St/tZn

StSt

stripsteel30x3.5mmacc.toEN50164-2

St/tZn

StSt

coil

Materialsandconductortypesforthefoundationearthelectrode

Terminal lugs made of StSt

Materials for Earth-Termination SystemsThe foundation earth electrode has to be made of • roundsteel(min.diameter10mm)or• stripsteel(min.dimension30mmx3.5mm)whichhastobegalvanised(orblack)forlayinginconcrete,orStSt(V4A),materialNo.1.4571forlayinginsoil.Con-ductor materials should be selected in compliance with EN50164-2inordertosimplifyalaterintegrationofalightning protection system.

Buildingsorstructureswithintegratedtransformerstationsmayrequirelargerearthelectrodecrosssections(50Hzshort-circuitcurrents).

Connections to the Earth-termination SystemEveryearth-terminationsystemhastobeconnectedatleastoncetothemainearthingbusbar(MEB).Furtherconnectionstothefoundationearthelectrodealreadyhavetobeconsideredintheplanning.Thesearetobeprovidedfor• thesupplementaryprotectiveequipotentialbonding,• metalinstallationssuchasliftrails,steelsupports, facade elements,• downconductorsoftheexternallightningprotection (possiblyinternaldownconductors),• downpipes,• connectionstotheringearthelectrode,e.g.incase ofwhitetanksorperimeterinsulation,• EMCmeasures,• structuralextensions,• cabletraysorjunctioncanalsfromotherbuildings,• supplementaryearthingmeasures,e.g.earthrods.

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Non-corrosiveterminallugStSt(V4A)

Protectivecaponterminallug

Application of the fixed earthing terminal

Connectionstotheexternalandinternalsystemsgene-rallyhavetobecorrosion-resistant.

Suitable connection parts and materials e.g. are • high-alloyroundsteel(diameter10mm)orflatsteel (dimension30mmx3.5mm)outofStSt(V4A), materialNo.1.4571,• galvanizedroundsteel(diameter10mm)withplastic coating,• fixedearthingterminals.

Usingroundsteelwithplasticcoatingrequiresspecialmountingcareduetotheriskofbreakageoftheplasticcoating at low temperatures or extreme mechanical stressingoftheplasticcoating(e.g.bystones)whenbackfillingandcompactingthetrench.ThisriskcanbeavoidedbyusingStSt(V4A).

Terminals lugs from the entry point to the inside shall be1.5mlongandtheyshallreachoutofthegroundsurfacefor1.5m.

Incompetent staff often cut the terminal lugs carelessly which then can only be reconstructed at considerable effort and costs. During the construction phase terminal lugsthereforeshallgetastrikingmarking.Aterminallugprotectivecapbothprovidesasignificantmarkingandaprotectionagainstinjuries(e.g.byburrsoredges).

Fixedearthingterminalsforconnectiontotheearth-ter-minationsystemorequipotentialbondinghaveprovedin the past. This allows for implementing corrosion-resis-tantconnectionsorbushings.Fittedintotheformwork(flushwiththewall)theycannotbe"cutoff"andcanbeintendedforsubsequentterminals.

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tested

ApplicationoftheSVClamp

ApplicationoftheMAXIMVClamp

ApplicationoftheConnectingClampandSVClamp

ConnectionsConnectionsoffoundationearthelectrodecomponentshavetobepermanentlyelectricallyconductiveandme-chanically stable.

Naturalironcomponentssuchasreinforcingsteelmats,cagesorbarsimprovethefoundationearthelectrodeefficiency and shall therefore be connected with the foundation earth electrode. The distance between these electricallyconductiveconnectionsshallbe2 m.

Connectionscanbeimplementedbyscrewing,clampingor welding. These connections are performed efficiently byusingscrewedconnectionsaccordingtoEN50164-1"LightningProtectionComponents(LPC)–Part1:Requi-rementsforconnectioncomponents".In our Lightning Protection / Earthing catalogue corre-sponding clamps and connectors are labelled with the following symbol.

Welded connections necessitate the agreement of the responsibleconstructionengineerandspecialknowledgeof the fitter as well as the necessary welding apparatus and welding tool on site.

Wedge connectors are not allowed in case of mechanical compacting/vibratingoftheconcrete.When using clamps / connectors at earth-termination sys-temsformedium-voltageswitchgear,theirspecificationforthe50Hzshort-circuitcurrentshastobeconsidered.

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additional connection line for meshing ≤ 20 m x 20 m

clamp / connection

terminal lug

e.g. acc. to class of LPS IIIevery15m

Recommendation:Severalterminallugse.g.ineverycontrolroom

Foundationearthelectrodewithterminallugs

Foundationearthelectrodewithmeshes

Bridgingofthefoundationearthelectrode

foundation plate

expansion joint

Foundation PlatesIn case of reinforced foundation plates, the foundation earth electrode will be installed on the bottom reinforce-ment layer. A correctly installed foundation earth elec-trodeoutofgalvanisedroundorstripsteelisenclosedbya5cmthickconcretelayerandisthusitisresistantagainst corrosion. Due to the hygroscopic characteristics of concrete, usually a sufficiently low earth resistance can beachieved.

The foundation earth electrode has to be installed as a closed ring in the range along the outer edges of the foundationplate,thusprovidingthebasisofequipoten-tial bonding.

The foundation earth electrode shall be implemen-ted with meshes of ≤ 20 m x 20 m. A foundation earth electrode used as lightning protection earth electrode requiressmallermeshsizes.

Meshsectioningaswellasthenecessaryterminallugsfortheequipotentialbondinginsideandfortheconnec-tion of external lightning protection down conductors outsidehavetobeconsidered.

Modernconcretingmethodsofreinforcedfoundationsandthevibrating/compactingoftheconcreteensuresthatalsoahorizontallyinstalledflatstripwillbecomple-tely enclosed by concrete, so that corrosion resistance is achieved.Anedgewiseinstallationoftheflatstripisnolonger necessary due to the mechanical compacting of the concrete.

Expansion JointsThe foundation earth electrode must not be installed across expansion joints. At these points it can be led out near walls and connected by means of fixed earthing terminals and bridging braids.

Incaseoflarge-sizefoundationplatesthemeshesoftheinstalledfoundationearthelectrodehavetocoveralsotheseexpansionjoints(sectionsorisolatingjoints)andthere are no projecting terminal lugs. Special expansion strapscanbeusedinthiscase,withapolystyreneblockprovidingarecessintheconcreteandanintegratedflexibleconnection.Thepolystyreneblockwiththeexpansionstraphastobe inserted into one section of the foundation slab and continued with the loose end line in the next section.

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Foilunderthefoundationplate

Detail of the dimpled sheets

Application of the dimpled sheets

Foils at Foundation PlatesOftenthegranularsubbaseiscoveredwithpolyethylenefoilsofapprox.0.3mmthicknessasseparationlayer.

Thesefoilsoverlappjustslightlyandnotwaterproof.Usuallytheyonlyhavelittleinfluenceontheearth-elec-troderesistanceandthuscanbeneglected.Hencethefoundation earth electrode can be laid in the foundation plate

Dimpled Sheets Dimpled sheets are used to replace the granular subba-seforfoundationslabsandoften"enclose"thewholebasement.

These dimpled sheets are made of high density special polyethyleneandareapprox.0.6mmthick(dimplesareapprox.8mmhigh).Thesheetsareapprox.2mto4mwideandshalloverlapeachotherbyapprox.20cmto25cmsothattheyarealsoasealantagainstwater.Thusthe foundation earth electrode cannot be laid in the foundation plate. The foundation earth electrode will be installed as ring earth electrode with the corresponding meshsizeunderthedimpledsheetsinthesoil,forex-ampleincaseofperimeterinsulationorclosedtanks.ForthispurposeStSt(V4A)materialNo.1.4571shallbeused.

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Closed Tanks

Whitetankoutofwater-proofconcreteWater-proof concrete is a high water penetrationresistancetypeofconcrete.Incivilandundergroundengineeringclosedtanksoutofwater-proofconcretearealsocalled"whitetanks".

Buildingsoutofconcretewithhighwaterpenetrationresistance are constructions implemented withoutadditional external sealing coat, where just the concreteandconstructivemeasuressuchasjointsealingandcrackwidthlimitationpreventfrompenetrationofwater.Erectionofsuchwaterproofconcretebuildingsrequiresspecial care, because all structural components as, forexample, joint sealings, bushings for water, gas, power,telecommunication(multi-sectionalserviceentrances),drains, other cables or conductors, terminals for thefoundationearthelectrodeorequipotentialbondingmust be permanently watertight or pressure watertight.The builder is responsible for the structure to be water-tight.

The term water-proof concrete is no longer definedby the current standardisation in the field of concreteproduction.Theconcretequalitye.g.C20/25standsforthecompressionstrengthofacylinder/cubeinN/mm²and says nothing about the water impermeability.Thecontentofcementistheprimarilydecisivefactorforthe water impermeability of concrete mixtures. 1 m3 ofwaterproofconcreteconsistsofatleast320kgofcement(oflowhydrationheat),hasareducedshrinkageandarecommendedminimumcompressionstrengthofC25/30.Anotherimportantfactoristheso-calledwater-cement-value,whichhastobebelow0.6.

Thus, the concrete part is not electrically connected to thesoil.Approximately1.5cmisthespecifiedvalueofwater penetration depth into the used concrete. The foundationearthelectrode,however,hastobeencasedin5cmofconcretecorrosion.Thisconcretehastobeconsidered as electrical insulator. Thus the earth contact is failing.

Thereforearingearthelectrodewithameshsize≤ 20 m x 20 m has to be installed below the foundationslab in the blinding layer or soil in structures with whitetank.

If a lightning protection system is installed on thebuilding,orifEMCrequirementsareapplicable,additio-nallyanequipotentialbondingconductorwithameshsize≤ 20 m x 20 m has to be installed in the foundationslab,andaringearthelectrodewithameshsize≤ 10 m x 10 m has to be installed in the soil or in theblindinglayer,asrequiredinEN62305-3(VDE0185-305-3).

Incaseofalightningstrike,areducedmeshsizeshallpreventpossibleflashoverfromtheequipotentialbonding conductor / reinforcement through the sealing (concrete)totheringearthelectrodeinstalledbelow.The ring earth electrode installed under the foundationslabhastobeconnectedwiththe"concrete-cast"equipotentialbondingconductorandthereinforcementaswellaswitheverydownconductorofthelightningprotectionsysteminordertobeeffectiveasmeshedearthing system. These connections may be implementedabovegroundwaterlevelorbelowwithpressurewater-proof bushings.

Consideringtheserviceperiodofnewbuildingsandofpossiblechangesinuse(includingtherequirementsforlightningprotectionorEMC)ananticipatoryplanning is recommended and the ring earth electrodealreadywithameshsize≤ 10 m x 10 m and alsoanequipotentialbondingconductorinthefoundationslabshouldbeinstalledbecauseasubsequentinstalla-tion is not possible.

AnArrangementofaringearthelectrodeandequi-potentialbondingconductorincaseofawhitetankisshown in the following illustrations.

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terminal luglightning protection

water-impermeableconcrete

presswater-proofwall bushingPartNo.478530

connecting clamp PartNo.308025

insulation

moisture barrier

foundation slab

reinforcement

basementfloor

equipotential busbar (EB) main earthing busbar (MEB) )PartNo.563200

soil

sealing tape

cross unitPartNo.319209

Ref.:Acc.toDIN18014:2007-09

ring earth electrodecorrosion-resistant StSt (V4A)(MaterialNo.1.4571)

equipotential bonding conductor

Arrangementoftheringearthelectrodeandequipotentialbondingconductorincaseofawhitetank

granular sub-grade course

foil

mainearthingbusbar(MEB)

terminal lug for down conductor

ground surface

max. ground waterlevel

foundation slab

presswater-proof wall bushing

granular sub-grade course

equipotentialbondingconductor

ring earth electrode

soil

Illustrationofringearthelectrode,equipotentialbondingconductorandconnectionsbymeansofpresswater-proof wall bushings

max.groundwaterlevel

connection to reinforcement

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Wallbushingwithformworkinstallation

Set-up(crosssection)withconnectionforpresswatertest

Waterproof wall bushing

Closed Tanks

Waterproof wall bushing for white tank

Connectingterminalsoftheringearthelectrodehavetobeimpervious.Ondevelopingthewaterproofwallbush-ing,DEHN+SÖHNEhasappliedtherequirementsspecifiedforwhitetanksalsoontheproduct.Realityconform component specifications were especially impor-tant.Whendevelopingsuchcomponentsithasextremlyimportanttofulfilrealcomponentrequirements.Thespecimenswereencasedintoaconcretebody(Figure1)and then submitted to a pressure water test. Installation sitesinadepthof10m(suchasrequiredforunder-groundcarparks)arequiteusualinthefieldofbuildingtechnique.

These conditions were exerted on the specimens and a waterpressureof1barwasimposed(Figure2).Afterthe concrete hardening, the specimens were subjected to a pressure water test and examined for watertightness duringa65hourslong-termtest.Capillaryeffectsofbushingsadditionallyincreasestheseverity.Innarrowgaps,cracksortubes(capillaries)oftheconcrete,liquidssuchaswater,infactspreadquitedifferently,developingadrawingorsuctioneffectintothe interior of the building. During the hardening and theconcurrentshrinkingprocessoftheconcrete,suchnarrow gaps or capillaries may result.

Therefore a professional, competent and correct installa-tionofthewallbushingintheformwork,asdescribedindetailintheinstallationinstructions,isquiteimportant.

Waterproof wall bushing for white tank:

For example Part No. 478 550• Testedwith5barcompressedairaccordingtoFprEN 50164-5(state2008-06).Unitforformwork installation with water barrier and double thread M10/12forconnectiontoe.g.theequipotential bonding bar. • Adjustableaccordingtowallthicknesswiththread M10andlocknut.Thebushingcanbeshortened,if necessary, also at the thread.• Includingterminalfitting(St/tZn,dimension 30x4mm)withsquareholeforconnectionwith clamping frame at round conductor or with cross unit at strip conductors.

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Bituminisedsealingsheets

Black TankAconcretefoundationtankcoveredwithmultilayersofblackbitumenonthesoilfacingsideiscalled"blacktank".Forsealingpurposesthebuildingfoundationbody first has to be painted with bitumen/tar, followed by usually up to three layers of bituminous sheeting to be applied.A ring earth electrode installed in the foundation slab abovethesealingcanserveforpotentialcontrolinthestructure. Due to the high-impedance outside insulation, however,theearthelectrodeisineffective.If a lightning protection system shall be implemented onthebuildingorifEMCrequirementsareapplicable,a≤20mx20mmesh-sizedequipotentialbondingcon-ductor additionally has to be installed in the foundation slab, and a ≤10mx10mmeshsizedringearthelectrodebelow the foundation slab in the soil or in the blinding layer.ThisisrequiredinIEC62305-3(EN62305-3).

Whereverpossible,theexternalringearthelectrodeshouldbeledintothestructureabovetheseal,thatmeansabovethehighestgroundwaterlevel,inordertoensurethetightnessofthetankalsointhelongterm.Awaterproofpenetrationoftheblacktankisonlypossibleby using special components.

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Ringearthelectrodeincaseofperimeterinsulation

Arrangement of the foundation earth electrode in case of a compact foundation

terminal luglightning protection

presswater-proofwall bushingPartNo.478530

connecting clamp PartNo.308025

insulation

moisture barrier foundation slab

reinforcement

basementfloor

equipotential busbar (EB) main earthing busbar (MEB) )PartNo.563200

soil

cross unitPartNo.319209

Ref.:Acc.toDIN18014:2007-09

ring earth electrodecorrosion-resistant StSt (V4A)(MaterialNo.1.4571)

equipotential bonding conductor

granular sub-grade course

terminal lug

water-impermeableconcrete

perimeter insulation

Detailviewofringearthelectrode

Perimeter InsulationPresent-dayconstructiontechniqueallowsforaquitein-dividualstructuraldesignandthecorrespondingsealingvariantsofbuildingfoundations.

Thermalprotectionregulationshavealsoinfluencedthe structuring of the strip foundations and foundation slabs. Sealing / insulation effects the installation and arrangement of the foundation earth electrodes, which, in case of new buildings will be established in accordance withtheGermanStandardDIN18014Title(English):Foundationearthelectrode–Generalplanningcriteria.

"Perimeter"meansthewallandfloorrangeofabuil-ding which is in contact with the soil. Perimeter insulati-on is the thermal insulation which encloses the structure to the outside. The perimeter insulation encloses the sealing layer and the whole structure on the outside, thus there are no thermal bridges and the sealing is addi-tionally protected from mechanical damage.

Consideringtheeffectsofperimeterinsulationsontheearth electrode resistance of foundation earth electrodes atconventionalarrangementsinthefoundationslab,the specific resistance of the perimeter insulating plates is a significant factor.

The specific resistance of a polyurethane rigid foam with bulkdensity30kg/m2,forexample,is5.4x1012 Ωm. The specificresistanceofconcrete,however,isbetween150Ωmand500Ωm.Evenfromthesevaluesitcanbederi-vedthat,inthecaseofcompleteperimeterinsulation,aconventionallyarrangedfoundationearthelectrodevirtuallyisineffective.Thustheperimeterinsulationhasthe effect of an electrical insulator.

In case of a complete insulation of foundation slab and outerwalls(fullperimeterinsulation),thecorrespondin-glymeshsizedringearthelectrodehastobeinstalledunderneath the bedplate in the blinding layer or in the soil. A corrosion resistant material, such as high-alloy stainlesssteelStSt(V4A),materialNo.1.4571,hastobeused.

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Application of the spacer with cross unit

Foundationearthelectrodeincaseoffoundationblockswith terminal lug

Foundation Blocks / Foundation SpotsForindustrialbuildingconstructionoftenfoundationblocks,alsocalledfoundationspots,areused.Theseindividualfootingsareusedasgroundslab,e.g.forsteel supports or concrete girders of halls. A foundation plate is not erected. Also these structures need a reliable earth-termination system. Therefore earthing measures arenecessaryalsoinsuchfoundationblocks.Ifthedis-tancebetweenthefoundationblocksismorethan5m one foundation earth electrode each will be installed. Distances of ≤5mrequireafoundationearthelectrodetobeinstalledonlyintoeverysecondfoundationblock.

Theroundorstripsteel(galvanised)foundationearthelectrodeinthefoundationblocksmustbeatleast2.5m longandtheconcreteenclosureshallbeatleast5cmthick.

These"individualearth-terminationsystems"havetobeinterconnectedforgivingnorisetopotentialdifferen-ces within the earthing system. The connection shall be implementedonthelowestfloor,withearthcontactandthe connecting conductors as well as the terminals of the foundationblocksshallbeoutofcorrosionresistantStSt(V4A)material.

Ifthesefoundationblocks,forexample,areoutofhighlyimperviousconcrete(water-impermeablecon-crete),aringearthelectrodeoutofStSt(V4A)materialandameshsizeof≤ 20 m x 20 m has to be laid into the ground.

Strip Foundations (without reinforcement)Spacershavetobeusedinunreinforcedfoundations,forexample, in strip foundations of residential houses. Using spacersinintervalsofapprox.2mensuresthatthefoun-dationearthelectrodeisreliablysupported(elevated)andthuscanbeencasedintoatleast5cmofconcrete.Iftheconcretewillbemachinecompacted(vibrated),wedge connectors must not be used.

Ifbecauseofahighlycompactedunderground(wetmixaggregatewithstonesetc.)spacerscannotbeused,thefoundation earth electrode can only be installed directly onthegroundandStStmaterial(V4A)hastobeused.

Strip Foundations (with reinforcement)In case of strip foundations with reinforcement, the foundation earth electrode will be laid as closed ring in concrete. The reinforcement will also be integrated and interconnected as permanent electrical conductor. Consideringapossiblecorrosion,thefoundationearthelectrodehastobeenclosedby5cmofconcrete.Theterminals/terminallugsarerequiredtobeoutofStSt(V4A)material,asdescribedabove.

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ViewofawarehouseSource:www.bekaert.com/building

FreshconcretewithsteelfibresMoreinformationatwww.vdsev.de

Fibre ConcreteFibreconcreteisatypeofconcretewhichduetothesteelfibresaddedtotheliquidconcreteformsaheavy-duty concrete slab after hardening. Steel fibre concrete has both a high compression strength and also a high tensilestrengthand,comparedtoaconventionalcon-creteslabwithreinforcement,italsoprovidesaconside-rably higher elasticity. In many cases the usually applied concrete reinforcement can be completely replaced. Steel fibre concrete will be poured, pumped or cast directly on site.

MainfieldofapplicationinGermanyistheindustrialand residential construction. Applied steel fibres usually are50–60mmlongandhaveadiameterof0.75–1.00mm. The mostly used steel fibres are straight with end hooksorslightlywavy.Therequiredadmixtureofsteelfibres depends on the stressing of the bedplate and on the performance of the used steel fibres. Selection basis ofthenecessaryfibretypeandquantityisastatisticalcalculation.Steelfibresonlyhavelittleinfluenceontheelectricalconductivityofconcrete.Forearthingmeasuresincaseof pure steel fibre concrete plates therefore an earth electrodewithameshsizeof≤ 20 m x 20 m has to be provided.Theearthconductorcanbesetinthecon-creteand,ifitismadeofgalvanisedmaterial,itmustbeencasedin5cmofconcreteforcorrosionprotectionreasons. On site this is sometimes difficult to realise. It is therefore recommended to install a corrosion-resistant high-alloystainlesssteel(V4A)ringearthelectrode,MaterialNo.1.4571,belowthesubsequentconcretebedplate.Thecorrespondingterminallugshavetobeconsidered.

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AccordingtoDIN18014,adocumentationontheearth-terminationsystemmustbeprepared.This documentation must include the result of the continuity measurement. Implementation plants and photos of the earth-termination system, if any, must be enclosed. Aformisavailableontheinternetatwww.dehn.deandcanbedownloadedaswritablepdf.

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Intermeshed earth-termination system

Intermeshed Earth-termination System at Industrial ObjectsIf a larger structure comprises more than one building, and if these are connected by electrical and electronic conductors,combiningtheindividualearth-terminationsystemscanreducethe(total)earthresistance.Inaddi-tion, the potential differences between the structures willbereducedconsiderablyandthevoltageloadoftheelectrical and electronic connecting cables will be notice-ably reduced.

Theindividualearth-terminationsystemsofthestructu-resshouldbeinterconnectedinameshednetwork.Themeshedearthingnetworkshouldbecontactedwiththeearth-termination systems at the same points where the verticaldownconductorsofthelightningprotectionsystem are connected.

Thesmallerthemeshsizeoftheearth-terminationsystem, the lower the potential differences between the structuresincaseofalightningstrike.Thisdependsonthetotalareaofthestructure.Meshsizesof20mx20mupto40mx40mhaveprovedtobecost-effective.If,forexample,highventstacks(preferredpointsofstrike)are existing, the connections around this part of the plant should be close to each other and, if possible, star shapedwithcircularinterconnections(potentialcontrol).When selecting the material for the conductors of the earth-termination system meshes, the corrosion must be takenintoaccount.Galvanisedsteelisrecommendedtobeusedinconcrete(e.g.connectionduct)andStSt(V4A),materialNo.1.4571insoil.

50 Hz Short-circuit Current Loading of Earth Conductors, Equipotential Bonding Connection and Connection Elements

Equipmentofdifferentelectricsystemsinteractinelectri-cal facilities.

• Highvoltagetechnology(HVsystems)• Mediumvoltagetechnology(MVsystems)• Lowvoltagetechnology(LVsystems)• Informationtechnology(ITsystems)

Basisforareliablecooperationofthedifferentsystemsis a common earth-termination system and a common equipotentialbondingsystem.Itisimportantthatallconductors, clamps and connectors are specified for the different cases of application.

Forbuildingswithintegratedtransformers,DINVDE0101(VDE0101)"StarkstromanlagenmitNennwechsel-spannungenüber1kV",title(English)"Powerinstallati-onsexceeding1kV"hastobeconsidered.

ConductormaterialsandconnectionelementsforuseinHV,MVandLVsystemshavetobeabletocarry50Hzcurrents.Duetotheprospectiveshort-circuitcurrents (50Hz)thecrosssectionsoftheearthelectrodematerialfortheindividualsystems/structureshavetobedeter-minedespecially.Earthfaultcurrents(standardrequire-mentdoubleearthfaultcurrentI"kEE)mustnotleadtoinadmissible heating of these components.

Ringequipotentialbonding

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Currentcarryingcapacityofearthelectrodematerials

Without special indications by the distribution system ope-rator, 1 second as standardised duration of fault current (disconnectingtime),and300°Casmaximumpermissibletemperature for the used earth conductor and connection component/clampmaterial,aretakenasbasicdata.Thematerialandthecurrentdensity(inA/mm²)inrela-tiontothedurationofthefaultcurrentaredecisiveforselecting the earth conductor cross section.

Fordetailedvaluesoftheshort-circuitcurrent(Ik)forthecurrentflowperiodof1softheearthconductors,earth rods and different connection components / clamps, please see our main catalogue Lightning Protection or the productdatasheets(www.dehn.de–ProductData).

Calculationoftheearthfaultcurrentforthedesigningofthe earth conductor is shown by the following example:

Variant 1Specification of the 3-pole short-circuit current by the systemoperatore.g.I"k3≈15000A

Variant 2The calculation specifies a theoretical worst case, assuming thatthefeedingvoltagedoesnotcollapse(reduce).

Theshort-circuitvoltage(uk)isthebasisfordeterminingthe max. 3-pole short-circuit current. The 3-pole short-circuitcurrentI"K3isthemax.3-poleshort-circuitcurrentat the transformer, neglecting an impedance on fault site (Z=0).

The calculation example is a showcase of a transformer withfollowingdata:

NominalpowerofthetransformerS=630kVANominalvoltageonlow-voltagesideU=400VShort-circuitvoltageuk=6.05%

Designing for short-circuit

Linearconversionfortheshort-circuitvoltage(worstcase)

I"k3= S√3 . U . uK

I"k3= 630 . 103VA√3 . 400V. 0.0605

≈15000A

Fordimensioningthecrosssectionofanearthconductor,the worst case of a double earth fault in a system has to beassumed.Thereforeearth-terminationsystemshavetobedesignedforthedoubleearthfaultcurrent(I"kEE).

I"kEE=0.85.I"k3

I"kEE=0.85.15000A≈12750A

TheGermanstandardDINVDE0101"StarkstromanlagenmitNennwechselspannungenüber 1kV",title(English)"Powerinstallationsexceeding 1kV"specifiesthefactor85%forthedimensioningofthe earth fault current on the basis of the 3-pole earth fault current.

All connection lines directly to the transformer shall be dimensionedforthisdoubleearthfaultcurrentI"kEE. Iftheshort-circuitcurrentspreadsoverthedirectconnec-tion lines to the transformer into the mesh of an intermes-hed earth-termination system, the current probably will

be distributed in two directions at the nodal point of the earth-termination system. With sufficient accuracy an imba-lance in the intermeshing of the earth-termination system of65%to75%canbeexpected.

The earth fault current to be considered for the earth-ter-minationmeshisspecifiedasI"kEE(branch)inourexample.

I"kEE(branch)=0.65.I"kEE

I"kEE(branch)=0.65.12750A≈8300A

Fordimensioningofthecrosssectionoftheearth-termina-tionmeshintheshownexamplethereforethecurrentI"kEE (branch)=8304Aistakenasbasis.

Determination of the resulting cross sectionThe conductor cross section depends on the material and thedisconnectingtime.TheGermanstandardVDE0101specifies the maximum short-circuit current density G [A/mm²]fordifferentmaterials(seeVDE0101FigureB1).

timeSt/tZn Copper StSt

Table:Short-circuitcurrentdensityG

The minimum cross section Amin of the conductor is deter-minedbydividingthiscalculatedcurrentbythecurrentdensityGoftherespectivematerialandbytheassigneddisconnecting time.

Amin=I"kEE(branch)

G[mm2]

The conductor now will be selected according to the cal-culated cross section. The nominal cross section is always roundeduptothenextbiggersize.

Thediagramshowsthepermissible50Hzshort-circuitcur-rentdensity(G)fortheconductormaterialscopper,steelandhigh-alloystainlesssteelStSt(V4A)(materialNo.1.4571).

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11

Connecting Clamps for Reinforcements

The foundation earth electrode has to be connected with the reinforcement of the foundation plate in distances of 2 m. Different connections are possible.

The clamping connection has turned out to be the most economic,asitcanbecarriedoutonsitequicklyandea-sily. According to the current lightning protection stan-dards, reinforcement steels shall be used among others as natural components of the discharge system.

Thefollowingtableshowsasurveyofthenominalandouter diameters as well as cross sections of the rein-forcementsteelsaccordingtotheGermanstandardDIN1045-1.

Fortheselectionoftheconnectioncomponents/clamps,the outer diameter of the reinforcement steels is appli-cable.

Pressure U-clamp for foundation earth electrodes and reinforcementsPartNo.308031and308036

Connectingclampforfixedearthingterminalandrein-forcementsteelPartNo.308035

Connectingclampforfixedearthingterminalandrein-forcementsteelPartNo.308045

U-clampterminalforlargediametersPartNo.308045

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Moreinformationmaterialandservices,forexample•LightningProtection/Earthing MainCatalogue•Appointmentwith our local partner pleasevisitourhomepage:www.dehn.de(“Service”section)

Surge Protection Lightning Protection / Earthing Safety Equipment

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Tel.+499181906-0Fax+499181906-1100www.dehn.de info@dehn.de

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