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BasicGroundingSafetygrounding
LightningprotectionGroundloops
ReasonsforthisPresentation• Safety• ProtectionoftheequipmentfoundinatypicalHAMshack.• DuringthisresearchIhavefoundthat:
– Grounding/lightningprotectionisarelativelycomplexsubject.– Thereisasignificantlevelofmiss-informationand/ormultiplicityof
opinion.– Theaveragehamcannotusuallyimplementanidealgroundsystem.– Practicalsystemswillbesomethingofacompromisebasedonhome
layoutandavailableresources(cost,time,etc).– Therearesomekeythingsthatcanbedonetohelpoptimizea
practicalsystem.
Motivation(continued)• Thispresentationstrivesto:– Provideinformationonlightningandappreciationforthedifficultyoflightningprotection.
– Summarizethekeyfeaturesandprinciplesofaneffectivelightningprotectiongroundsystem.
– Helpothersachieveandeffectivesystemfortheirparticularlayoutandresource.
– Themainreasonforthispresentationistoincreaseawareness!
• Disclaimer – Youareresponsible fordeterminingwhatyouinstalloruseforgrounding!NotinformationyougetfromawellintentionedpresentationJ
Code• Followyourlocal/statecodes.• Whichcodetofollow:– NEC (NationalElectricalCode)– NFPA(NationalFireProtectionAssociation)– NEMA(NationalElectricalManufacturesAssoc.)– NEIS(NationalElectricalInstallationStandards)– NESC(NationalElectricSafetyCode)…
• Therearemanystandardsorganizationsacrossthecountrybutyoushouldalwaysfollowthecodethatyourareahasadopted.
Section1SafetyGrounding
Groundwires
GroundRodBasics(Servicepanel)• Secondgroundrod. Asinglegroundrodthathasaresistancetogroundof25ohmsorlessmustbeaugmentedbyasecondgroundrod.Oncethesecondgroundrodisinstalled,it'snotnecessaryforthetwotomeettheresistancerequirement.Asapracticalmatter,fewelectriciansdotheresistancemeasurement.
• Youcannotuseasimpleohmmetertotestthisbecausethatwouldrequireaknownperfectground.Specialequipmentandproceduresareneeded.– It'scommonpracticetosimplydriveasecondgroundrod.– Youmustlocatethematleast8ormorefeetapart.Greaterdistanceisevenbetter.
• Groundresistancewillbefurtherdiminishedifbothrodsandthebaregroundelectrodeconductoraredirectlyunderthedriplineoftheroof(bad).
Groundrodbasics(continued)• Duringcurrentsurgetheeartharoundthegroundrodbecomes“saturated”loweringit’sresistivity(duetolocalizedundergroundarcing).
• Optimalrodplacement/spacingisaboutequalto2rodlengths,thusavoidingoverlapofactiveearthvolumes.
CommonGroundRods
Whydoyouneedgroundrods?
Section2– LightningProtection
SourceofLightning• OriginatesfromchargedCumulonimbusclouds.• Typicallyinvolveselectronmovementfromcloudtoearth
(althoughpositivelightningcanoccuroccasionally).• Cloudtocloudlightningisthemostfrequent.• Intenseelectricfieldcreatesionizationchannels(plasma)in
randomsequentialsteps.• Largecurrentdischargesoccursinseveralrepetitivestrokes.
Lightningstatistics• AverageUSyearlylightningstrikes– 22million.• NumberofyearlyUSinsuranceclaimsfiledforlightningdamage– 307,000.• EstimatedyearlyUSlightningdamagecosts- $330milliondollars.• Lightningionizationchanneltemperature– 15,000to30,000deg.C(about3timesthesurfacetemperatureofthesun).• Averagepeakcurrent– 25,000Amps.• Averagestrokesperflash– 4.• Averagechannelblastwaveenergy– Equivalentto200poundsofTNT.
MechanismsofLightningInvasionNumberedbyCommonality
• Directstrikesondwellingisrare.• Conductionthroughutilitiessystemstrikesarecommon.• Localstrikesgenerateelectromagneticfieldsthatcoupleto
electrical/signallines.• Themainphysicalcouplingmechanismsare:
• Conduction• CapacitiveCoupling• MagneticCoupling
Whyshouldweprotectagainstlightning?DamageCausedbyLightning
MoreLightningDamage
MoreLightningDamage
Evenbreakersarenotsafefromlightning
BasicHAMShack
• Mosthamstation groundrodsystemswillhavealowerimpedancethanthefeeblepowercompanygroundrodnearourservicepanel.
• Lightningtransientonpowerlinewillseekoutthebestgroundpath
• Panel/strap/rodsystemwithnobondingallowsthepathtogothroughourhamequipment– thisisverydangerous
SimplisticGroundingFacts
Towergrounding• Thegreenareaiswhere
mostlightningcurrentpasses.
• Thebondingshouldbewideflashingusingeitherhightemperaturesilversolderorcadweldingtothegroundrods.
• Groundingdoesnotpreventlightningstrikes.Itreducesthechanceofthecableshieldsandcontrolwiresfrombeingthesolepathfromalightningstrike.
Basictowerground
• Inthisdiagramthereisonegroundrodpertowerleg.
• Eachlegistiedtoitsownrod.
• Allrodsarebondedtogether.
Tower– ShackGround
Thisslideshowsmanypointswhereyoushouldground atower,antenna,andyourshack.Weoften forgettobond allconnectionstogether. Seethereddotswhereground rodsarespacedevery8orsofeetalong theground wireused.FollowtheNECguidelines.
BallGapLightningProtectionInsulated towersrequireruggedlightningdischargepoints
GroundConnections
Grounding- WaterPipes
Goodandbad
What'swrongwiththis?
BondingGroundRods
• Bonding (connecting)ground rods.
• Whenbonding ground rods,followyour localelectricalcode.NEC810.21(J)
• TheNECcodestatethatallground rodsneedtobebonded toequalizeimpedance.
• Somepeopleprefertouse4AWGasthebondingjumper.
MakingconnectionsExothermic(cad)Welding
Video ofCadWelding- 2:38https://youtu.be/T5DoB26TFtI
HighTempSilverSoldering
ShackEntrance
• Shackgroundrod– steelcladcopper.
• Stainlesssteelfasteners.• Attachedlightningarrestors.• Braidedgroundcablefeedingtoshack.
• Incorrectlyusedpipeclampatthebottomwithattachedsolidcopperwire.
• Thegroundrodhasapipeoverittoincreasetherodssize.L
Notforeveryone
Practicalsystemswillbesomethingofacompromisebasedonhomelayoutandavailableresources(cost,time,etc)
Section3GroundLoops
Whataregroundloops?• Unwantedelectriccurrentpathinacircuitresultinginstraysignalsorinterferenceoccurring,e.g.,whentwoearthedpointsinthesamecircuithavedifferentpotentials.
• Video 3:11
– Groundloopscan=Noiseinyourradio– https://youtu.be/WIfcNKkkuvE
GroundLoops• Whatisagroundloop(noise)• Pictureofcommongroundloop
Manyloops
Somesimplefixestogroundloops
Warning– Donoteliminateyoursafetyground!!!
Transformers/Isolator Prepackagedsolutions
Eliminateredundant grounding
Whatelsemightbeneeded
Wholehousesurgeprotection
Therearemanypossibleproblemsandsolutions
• Groundingissues.• Antennaandcablingissues.• Radios,Antennaturners,coaxswitches,powersupplies…
• NowisthetimetobringinyourfriendsandElmer's!
ThemostimportantthingtoknowishaveFun withyourhobby!