Proper Grounding of Instrument and Control Systems in

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1、SessionTwo:ProperGroundingofInstrumentandControlSystemsinHazardousLocationsSessionTwo:ProperGroundingofInstrumentandControlSystemsinHazardousLocationsJoeZulloRegionalSalesManager:MTLAmericasIntroductionGroundingisdefinedaselectricalequipmentconnecteddirectlytomotherearth,ortosomeconductingbodyt

2、hatservesinplaceoftheearth,suchasthesteelframeofaplantanditsearthmatorthehullofashiporoildrillingplatform.Propergroundingisanessentialcomponentforsafelyandreliablyoperatingelectricalsystems.Impropergroundingmethodologyhasthepotentialtobringdisastrousresultsfrombothanoperationalaswellasasafetyst

3、andpoint.Therearemanydifferentcategoriesandtypesofgroundingprinciples.Thispaper’sprimaryfocusistodemonstratepropergroundingtechniquesforlowvoltageInstrumentandControlSystems(IACS)thathavebeenprovensafeandreliablewhenemployedinprocesscontrolfacilities.Forthepurposesofthispaper,IACSwillbedefineda

4、sinstrumentandcontrolsystemsthatoperateat50VDCorless.Asanexampleofatypicalplant,someoftheaccompanyingphotographsarecourtesyofWashingtonGas’facilitiesinthemetropolitanDistrictofColombia,VirginiaandMarylandareaasshowninFigure1.Figure1RockvillePeakShaving/StoragePlantExplosionProtectionandHazardou

5、sLocationsConference2009–IDCTechnologies1SessionTwo:ProperGroundingofInstrumentandControlSystemsinHazardousLocationsTypesofGroundsAnydiscussionongroundinginvariablyleadstoadiscussiononthedifferenttypesofgroundsandthecorrespondingdefinitionofeach.However,itiscommonlyacceptedthatgroundsintheproce

6、ssindustrycanbebroadlyclassifiedaseitherdirtyorclean.PleaserefertoFigure2foracomparisonofthedifferentgrounds.
DirtyGroundsDirtygroundsinsidethefacilityaretypicallythose120VAC,220VAC,480VACpowergroundsthatareassociatedwithhighcurrentlevelswitchingsuchasmotorcontrolcenters(MCC),lighting,powerdist

7、ribution,and/orgroundscorruptedbyradiofrequenciesorelectromagneticinterference.QuiteoftentheprimaryACpowercomingintotheplantcanintroducespikes,surgesor“brownouts”thatfurthererodethecleanlinessoftheACground.
CleanGroundsExamplesofc