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1StandardspromulgatedbytheInstituteofElectricalandElectronicsEngineers(IEEE)maybepurchasedfromtheIEEEServiceCenter,445HoesLane,Piscataway,NJ08854(800-678-4333).TheU.S.NuclearRegulatoryCommission(NRC)issuesregulatoryguidestodescribeandmakeavailabletothepublicmethodsthattheNRCstaffconsidersacceptableforuseinimplementingspecificpartsoftheagency’sregulations,techniquesthatthestaffusesinevaluatingspecificproblemsorpostulatedaccidents,anddatathatthestaffneedinreviewingapplicationsforpermitsandlicenses.Regulatoryguidesarenotsubstitutesforregulations,andcompliancewiththemisnotrequired.MethodsandsolutionsthatdifferfromthosesetforthinregulatoryguideswillbedeemedacceptableiftheyprovideabasisforthefindingsrequiredfortheissuanceorcontinuanceofapermitorlicensebytheCommission.Thisguidewasissuedafterconsiderationofcommentsreceivedfromthepublic.TheNRCstaffencouragesandwelcomescommentsandsuggestionsinconnectionwithimprovementstopublishedregulatoryguides,aswellasitemsforinclusioninregulatoryguidesthatarecurrentlybeingdeveloped.TheNRCstaffwillreviseexistingguides,asappropriate,toaccommodatecommentsandtoreflectnewinformationorexperience.WrittencommentsmaybesubmittedtotheRulesandDirectivesBranch,OfficeofAdministration,U.S.NuclearRegulatoryCommission,Washington,DC20555-0001.Regulatoryguidesareissuedin10broaddivisions:1,PowerReactors;2,ResearchandTestReactors;3,FuelsandMaterialsFacilities;4,EnvironmentalandSiting;5,MaterialsandPlantProtection;6,Products;7,Transportation;8,OccupationalHealth;9,AntitrustandFinancialReview;and10,General.Requestsforsinglecopiesofdraftoractiveregulatoryguides(whichmaybereproduced)shouldbemadetotheU.S.NuclearRegulatoryCommission,Washington,DC20555,Attention:ReproductionandDistributionServicesSection,orbyfaxto(301)415-2289;orbyemailtoDistribution@nrc.gov.ElectroniccopiesofthisguideandotherrecentlyissuedguidesareavailablethroughtheNRC’spublicWebsiteundertheRegulatoryGuidesdocumentcollectionoftheNRC’sElectronicReadingRoomat’sAgencywideDocumentsAccessandManagementSystem(ADAMS)at’sWebsiteforupdatesconcerningtheresumptionofpublicaccesstoADAMS.U.S.NUCLEARREGULATORYCOMMISSIONRevision3February2005REGULATORYGUIDEOFFICEOFNUCLEARREGULATORYRESEARCHREGULATORYGUIDE1.75(DraftwasissuedasDG-1129,datedDecember2003)CRITERIAFORINDEPENDENCEOFELECTRICALSAFETYSYSTEMSA.INTRODUCTIONSection50.55a,“CodesandStandards,”of10CFRPart50,“DomesticLicensingofProductionandUtilizationFacilities,”requiresin10CFR50.55a(h)thatprotectionsystemsforplantswithconstructionpermitsissuedafterJanuary1,1971,butbeforeMay13,1999,mustmeettherequirementsstatedineitherIEEEStd.279,“CriteriaforProtectionSystemsforNuclearPowerGeneratingStations,”1orIEEEStd.603-1991,“CriteriaforSafetySystemsforNuclearPowerGeneratingStations.”1FornuclearpowerplantswithconstructionpermitsissuedbeforeJanuary1,1971,protectionsystemsmustbeconsistentwiththeirlicensingbasisormaymeettherequirementsofIEEEStd.603-1991.ThesafetysystemsforplantswithconstructionpermitsissuedafterMay13,1999,mustmeettherequirementsofIEEEStd.603-1991.Section4.6ofIEEEStd.279-1971requires,inpart,thatchannelsthatprovidesignalsforthesameprotectivefunctionmustbeindependentandphysicallyseparated.Section5.6.1ofIEEEStd.603-1991states,“Redundantportionsofasafetysystemprovidedforasafetyfunctionshallbeindependentof,andphysicallyseparatedfrom,eachothertothedegreenecessarytoretainthecapabilityofaccomplishingthesafetyfunctionduringandfollowinganydesignbasiseventrequiringthatsafetyfunction.”GeneralDesignCriterion(GDC)17,“ElectricPowerSystems,”inAppendixAto10CFRPart50requires,inpart,thatelectricpower1.75-2fromthetransmissionnetworktotheonsiteelectricdistributionsystemshallbesuppliedbytwophysicallyindependentcircuitsthataredesignedandlocatedsoastominimizetotheextentpracticalthelikelihoodoftheirsimultaneousfailureunderoperatingandpostulatedaccidentandenvironmentalconditions.GDC21,“ProtectionSystemReliabilityandTestability,”requires,inpart,thatredundancyandindependencedesignedintotheprotectionsystemshallbesufficienttoassurethatnosinglefailureresultsinalossoftheprotectionfunction.GDC22,“ProtectionSystemIndependence,”requiresthattheeffectsofnaturalphenomena,andofnormaloperating,maintenance,testing,andpostulatedaccidentconditionsonredundantchannelsdonotresultinlossoftheprotectionfunction.ThisregulatoryguidedescribesamethodacceptabletotheNRCstaffforcomplyingwiththeNRC’sregulationswithrespecttothephysicalindependencerequirementsofthecircuitsandelectricequipmentthatcompriseorareassociatedwithsafetysystems.Thisregulatoryguidecontainsinformationcollectionsthatarecoveredbytherequirementsof10CFRPart50,whichtheOfficeofManagementandBudget(OMB)approvedunderOMBcontrolnumber3150-0011.TheNRCmayneitherconductnorsponsor,andapers