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7/3/2015 ELECTRICALTHEORYANDAPPLICATIONFORELECTRICKILNS|L&LElectricKilnsBuilttoLast

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ELECTRICAL THEORY AND APPLICATION FORELECTRIC KILNS

ELECTRICAL BASICS

ELECTRICAL SAFETYElectricityisawonderfulutility,butcanbedangerousifnotapproachedcarefully.Therearethreebasichazardsthatcauseinjuryordeathshock,arcflash,andarcblast.Itisimportanttorememberthatevenasmallamountofcurrentpassingthroughthechestcancausedeath.Mostdeathsoccurringforcircuitsoflessthan600voltshappenwhenpeopleareworkingonhot,energizedequipmentPLEASEDISCONNECTANDLOCKOUTALLELECTRICALPOWERBEFOREATTEMPTINGKILNREPAIRS!

ELECTRICAL HAZARDSSHOCKAnelectricalshockisacurrentthatpassesthroughthehumanbody.Anyelectricalcurrentflowsthroughthepathofleastresistancetowardsgroundifanexternalvoltagecontactsahumanbody,e.g.bytouchingalivewirewiththehand,thevoltagewilltrytofindaground,andacurrentwilldevelopthatflowsthroughthebodysnervoussystemorvascularsystem,andexitthroughtheclosestpartofthebodytoground(e.g.,theotherhandwhichmaybetouchingametalpipe.)Nerveshockdisruptsthebodysnormalelectricalfunctions,andcanstoptheheartorthelungs,orboth,causingsevereinjuryordeath.

ARCFLASHAnarcflashisanextremelyhightemperatureconductivemixtureofplasmaandgases,whichcausesveryseriousburnswhenitcomesintocontactwiththebody,andcanigniteflammableclothing.Arctemperaturesreachupto35,000F!

ARCBLASTArcblastisapressurewaveresultingfromarcing,whichcancarrymoltenmetalfragmentsandplasmagassesatveryhighspeedsanddistances.Thiscannotonlycarryveryhotshrapneltoinjureaperson,butcanactuallybestrongenoughtodestroystructuresorknockworkersoffladders.

SAFETY PRINCIPLESBesafe!Makesureanyequipmentthatisbeinginstalledorservicedisdisconnectedfromallsourcesofpower.Inindustry,itisimportanttohaveLockoutandtagoutproceduresinplacetomakesurethatpowerstaysdisconnectedwhilepeopleareservicingequipment.ItisjustasimportantinresidentialandcommercialsitesDONOTWORKONLIVEEQUIPMENTUNLESSABSOLUTELYNECESSARY!

Usetherighttoolsforthejobdonotimprovise.Forinstance,useaproperfusepullerdontuseascrewdrivertopryoutthatopenfuse.

Protectthepersonusepropergloves,shoes,andclothing.Inindustryitisrecommendedtowearsafetygogglesorfaceshieldstopreventarcflashorarcblastinjuries.Wearrubbersoledshoes.

Makesuretheenvironmentaroundtheequipmentbeingservicedissafe.Forinstance,whenworkingaroundelectricity,italwaysverydangerousforthefloortobewet.Makesurethereisadequatespacetoworksafely.

Beawarethatcurrentflowacrossyourchestcanbefatal.Ifpossible,useonlyonehandtomanipulatetestleadswhenconductinganynecessarymeasurementsonliveequipment.Useaclampforonelead,anduseonehandtoguidetheothertestlead.Keeptheotherhandasfaraspossiblefromthelivecircuitcomponents.

INSTRUMENTS COMMONLY USED TO MEASURE ELECTRICITY

Anelectricianortechnicianchargedwiththeresponsibilityofmaintainingorinstallingdevicesthatuseelectricityneedstohaveanumberoftoolscloseathand.Inadditiontohandandpowertools,theseshouldincludeinstrumentsthatcanbeusedtodiagnoseelectricaltrouble.CAUTION!Besuretofollowallinstructionsandsafetyproceduresthatareincludedwiththeintrumentmanufacturerspackage.

TESTLAMP

Thisconsistsofarubberinsulatedsocketwithanincandescentlightbulb(ratedforthehighestvoltagetowhichitmightbesubjected),towhichisattached(2)twoprobesforattachingtothepowersourcebeingdiagnosed.Atleastoneoftheseprobesshouldbefittedwithaclampsothatitcanbeattachedtooneofthepowersourceleads,whiletheotheris



manipulated(withonehandonly).Thisisusedforveryroughdiagnosticsonopenfuses,interiorlighting,motor,andresistancecircuits.

CLAMPONAMMETER

Theseareveryconvenienttestinstruments,usedfordeterminingthenumberofamperesflowinginacable.Onlyone(1)cablecanbemeasuredatatime,andthecablecaneitherbebareorinsulated.Thecabletobemeasuredis(carefully)segregatedfromothercurrentcarryingcables,andshiftedenoughsothatthejawsoftheclamponammetercanbeopened,slippedaroundthecable,andthenclosed.Assoonasthejawsclose,aclearandaccuratereadingisregisteredonthescale.Thejawsareinsulated,andtheBakelitehandleandshieldprotectthetechnicianfromshock.Themeterisoperatedbythemagneticfieldsetupbythecurrent.

OHMMETER

Thisisusedtomeasuretheresistanceofacircuit.Usuallythisisfoundincombinationwithavoltmeter,andmilliammeter,inadeviceknownasaMULTIMETER(seebelow).SomeOhmmetersareveryprecise,forlaboratoryuse.

CAUTION!Neverconnectanohmmetertoacircuituntilthecircuithasbeendisconnectedfromthepowersource.Theohmmeterhasitsowninternalpowersupply,andconnectingitacrossanotherpowersourcecancauseseriousdamage.

VOLTMETER

Voltmetersareusedtomeasurethevoltagethatexistsinacircuit.Typically,thetechnicianselectsanappropriatescale(0150volts,0250volts,0500volts,etc.),andthenclampsoneoftheprobestooneofthehotlines.Theotherprobeisthencarefullyputincontactwiththeotherhotline,andthemeterregistersthevoltage.Voltmetershaveveryhighresistance,intherangeof15,000W,sothatverylittlecurrentflowsinthevoltmetercircuitjustenoughtotocausethevoltmetertoindicatevoltageacrossitsscale.

DIGITALMULTIMETER

Thisisprobablythemostusefulinstrumentinanelectricianstoolbox.Itisacombinationohmmeter,voltmeter,andmilliammeter.Agoodmetermeasuresohms,ACvolts,DCvolts,andACandDCamperes(atleastupto300milliamperes),aswellasprovidesacontinuitytester(audible)thatmeasurescontinuitywithinacomponent(suchasafuse).Typicallythemultimeterhasdifferentsocketsfortheprobestoconnectto.OneprobegoestoCommon,andtheotherisconnectedeithertoVolts/Ohms,ortoAmps.(Clickheretoseehowtouseamultimeter)

CAUTION!NeverconnectthemultimeterHotprobetotheAmpssocketwhenmeasuringVolts.ThereisaninternalpowersourcewhichsuppliesitsownvoltagewhenmakingAmperagemeasurementsapplyinganexternalvoltagetothisinternalcircuitcancauseseriousdamage.Mostgoodmultimetershaveaninternalfusetopreventthemostseriousdamagehowever,itisstillanuisancetoreplacefuses.

Afterconnectingtheprobestotheappropriatesockets,thetechnicianselectsthetypeofmeasurementbeingmade.Thecorrectscalemayhavetobeselectedalso,ifthemultimeterisnotautoscaling.Oneprobeshouldthenbeclampedtoonepartofthecircuitbeingmeasuredforsafety,andthentheothercarefullyputintocontactwiththeotherside.Themeterdisplaysthevalue,andusuallytheunitofmeasurement.

SOME BASIC ELECTRICAL THEORYSimplyput,electricityisnothingmorethantheflowofelectronsthroughaconductor.Someunderstandingofthestructureofmatterisnecessaryinordertounderstandthefundamentalnatureofelectricity.

ATOMS,PROTONS,NEUTRONS,ANDELECTRONSMatterisanythingthatoccupiesspaceandhasmass.Someexamplesarewater,glass,wood,andsteel.Allmatterconsistsofmolecules,whichareextremelysmallparticles.Theseparticles,eventhoughtiny,stillretainsomechemicalproperties.Moleculescanbefurtherdivided,intoatoms,orelements.Dividingmoleculesintoatomscreatesachemicalchangei.e.,watermoleculesundergoachemicaltransitiontobecome2partsofhydrogenand1partoxygen(2hydrogenatomsand1oxygenatom.)

Atoms,orelements,areknownasthebuildingblocksofmatter.Singly,orincombination,atomsarethematerialsthatconstituteallmatter.Someexamplesofelementsareiron,hydrogen,andcarbon.Thereareapproximately115knownelements.Thestructureofeachatomcanberoughlycomparedtoastaranditsplanetarysystem.Likethestar,thenucleusofanatomisatthecenter.Surroundingthenucleusaretinyelectrons,whichhaveanegativecharge,thequantitydependingontheelement.Thenucleusconsistsofprotons,whichhaveapositivecharge,andneutrons,whichcarrynocharge.

Thesimplestatomisthehydrogenatom,whichhasasingleproton(+)inthenucleus,andasingleelectron()orbitingthenucleus.Amorecomplexatomisthecopperatom,whichhas29protons(+)and35neutrons(nocharge)inthenucleus,and29electrons()orbitingthenucleus.Intheirnaturalstateatomscontainanequalnumberofprotonsandelectrons,andhaveaneutralcharge.Theelectronsarearrangedinseverallayers,orrings,aroundthenucleus,andtheseringsarecalledshells.Thenumberoftheshelldeterminesthemaximum



numberofelectronsthatcanexistinashellthefirstshellisclosesttothenucleus,andthenumbersincreaseconsecutivelythefurtherawaytheyarefromthenucleus.Themaximumnumberofelectronsthatcanexistinashellisasfollows:2electronsinthefirstshell,8inthesecond,18inthethird,32inthefourth,18eachinthefifthandsixth,and2intheseventh.

Theabilityofamaterialtoletgoofitselectronsiscalledconductivity.Forvariousreasons,materialsthataregoodconductorshavefrom1to4electronsintheiroutermostshells.Forexample,thetwomostcommonconductorsusedforelectricalwiringarecopper,whichhas1electroninitslastshell,andaluminum,whichhas3.Atomswith5,6,or7electronsintheiroutermostshellsarecallednonmetalsandarepoorconductorsatomswith8electronsareinsulators.

STATICELECTRICITYStaticelectricityisanelectricchargethatbuildsupinanobject.Frictioncanbuildanelectricchargeupinanobject.Weareallfamiliarwithrubbingourstockingfeetonacarpet,buildingupachargeinourbodies,andthentouchinganuncharged(neutral)objecttoreleasethecharge(sometimeswithanaudiblecrackandavisiblespark.)Thischargeconsistsofanexcessnumberofelectronsrelativetotheprotonsintheobject,andthisexcessbuildsupfromrubbingagainstadifferentmaterialthatreleaseitselectronsmorequicklythantheobjectbeingcharged.

Thischargecanaccumulateinanobjectifisnotdischarged.Forinstance,rubbingaglassrodwithsilkcauseselectronstoflowfromthesilktotheglassrod,andthusbuildsupachargeinboththesilkandtheglassrod.Also,rubbingarubberrodwithfurcauseselectronstoflowfromthefurtotherubberrod.Iftheglassrodisbroughtinproximitytotheanothersimilarlychargedglassrod,theyrepeleachother.Also,tworubberrodsrepeleachother.Butifaglassrodisbroughtclosetoarubberrod,theyattracteachother,becausetheyhaveoppositecharges.Thestorageofthischargeiscalledelectricityatrest,orstaticelectricity.

Therearetwobasicrulesforelectricalcharges:

1. Likechargesrepel,andoppositechargesattract.2. Thestrengthofthisrepulsionorattractionisdirectlyproportionaltothestrengtyhofthe

electricalchargeandinverselyproportionaltothesquareofthedistancebetweenthechargedobjects.

ELECTRICITYINMOTIONMostelectricitythatweusetodoworkisintheformofanelectriccurrent,whichiselectricityinmotion.Electronsmovethroughaconductorbypassingfromoneatomtoanother.Amaterialthathassomeelectronsthatarefreetoflowinthismannerarecalledconductorsmaterialsthatdonothavefreeelectronsareinsulators.Rubberandceramicsaretypicallygoodinsulatorsmetalsaretypicallygoodconductors.Ifacopperwireisconnectedbetweentwobodiesofoppositecharge,electronswillflowfreelythroughthewire,attemptingtobalancethecharge.

Therearetwocommontypesofelectriccurrents,DCordirectcurrent,andACoralternatingcurrent.DCisacurrentthatalwaysflowsinthesamedirection.Commonexamplesareautomobilecircuitsthatarepoweredbybatteries,andflashlights,alsopoweredbybatteries.Abatteryisadevicethatuseschemicalstocreateanunbalancedchargebetweenitsterminals,andthuscausesadirectcurrenttoflowfroma(+)terminaltoa()terminal.ThisDCelectricitycanbeharnessedtoperformsuchtasksaslighting,playingmusiconaradio,etc.

ACelectricityistypicalinhouseholdsandbusinesses.Inthisformofcurrent,thedirectionofelectronflowisreversedatregularintervalsbytheelectricalgeneratorthatproducestheAC.Thevoltage(levelorpressureofelectricity)asitisgeneratedincreasesfromzerotoamaximumvalueinonedirection,thenreversesdowntozero,andcontinuestoamaximumvalueintheotherdirection,andincreasesbacktozerointheoriginaldirection,andsoon.Ifplottedonagraph,thecurveappearsliketheoneintheaccompanyingfigure.

Electricityhasfourbasiccharacteristics:Voltage(Pressure),Amperes(Flow),Ohms(Resistance),andWatts(Power).Theflowofelectronsthroughacircuitcan(andcommonlyis)becomparedtotheflowofwaterthroughapipe.TherateofflowofwaterisanalogoustoAmperes,Ohmstopipediameter,waterpressuretoVoltage,andWattstogallonsofwater.Wecantalkabouteachoftheseindividually,andthendiscussspecifictypesofelectricalcircuitssuchasSeriesCircuitsandParallelCircuits.

ELECTRICCURRENT(AMPERE)Thebasicunitofelectricityisthecoulomb,andisequaltoapproximately628x1016electrons.Sincetherateofflowofelectricityiswhatistypicallyofinterest,ratherthanthe



totalquantityofelectricity,thecoulombisnotgenerallyofpracticaluse,exceptasthefundamentalquantityonwhichotherelectricalcharacteristicsarebased.

AnAmpererepresentstheflowof1Coulombpersecond.TherelationshipbetweentheAmpereandtheCoulombcanberepresentedmathematicallyas:

Q=It

WhereQ=quantityofcoulombs(C)

I=current,inamperes(A)

t=time,inseconds.

Amperagewouldbeanalogoustotherateingallonsofwaterflowthroughapipe.

ELECTRICALRESISTANCE(OHMS)Allmaterialshavesomeoppositiontocurrentflow,andthisoppositionresultsinsomeoftheelectricalenergybeingconvertedtoheat.Thisconversionisinaccordancewiththeformula,W=I2R,whereWisWatts,I=Intensityofelectricalcurrent(Amperes),andRisresistanceinOhms.SeethesectiononOHMsLaw,below.Electricalresistanceisanalogoustotherestrictionofthepipediametertotheflowofwater.

Aswesawabove,differentmaterialshavedifferentquantitiesoffreeelectrons.Theoppositioniscausedbythetypeofmaterialthatthecurrentisattemptingtopassthrough,aswellasbyfrictioncausedbythemotionofelectrons.Thisfrictionisaffectedbythediameterofthewire,aswellasbythelengthofthewire.

Theoppositionoftheflowofelectronsiscalledresistance.Theunitofresistancemeasurementistheohm(W).One(1)Ohmistheoppositiontoelectricalflowthatresultsinelectricalenergybeingconvertedintoheatattherateofone(1)WattperAmpereofeffectivecurrent.Theinstrumentthatisusedtomeasureresistanceistheohmmeter.

Somematerialsthataregoodconductors:Copper,silver,gold

Somematerialsthataregoodinsulators:Rubber,glass,bakelite,wood,porcelain(especiallyelectricalgradeporcelain)

Othermaterialsareconductorsdespitehavingsomeinsulatingpropertiesthesearecalledresistors.Examplesofresistorsarealloyssuchasironaluminumchrome,andnickelchrome,whichareusedasheatingelementsinkilns,furnaces,andovens.

ELECTROMOTIVEFORCE(VOLTAGE)AvoltisaunitofEMF,orelectromotiveforce,andisinternationallydefinedasthatemfwhichwillestablishacurrentof1Amperethrougharesistanceof1Ohm().Voltageisanalogoustowaterpressure,andistheforcethatpushesthewaterthroughapipe.

Referringtothepreviousdiscussionconcerningatoms,electrons,andmatter,itcanbesaidthatallmatterconsistsofelectricity.Instrictterms,electricitycannotbegenerateditcanonlybemadetomove,andthereforetransmitpowerfromonesourcetoanother.Electricalenergy(asopposedtoelectricity)canandisgenerated(orconverted)fromotherformsofenergy.Thereareseveralcommonmethodsofgeneratingelectricalenergy,someofwhicharemechanicalinduction,chemical,thermoelectric,andfriction.Thisishowvoltageissuppliedinmostcommonapplications.

Forinstance,mechanicalinductionisthemethodwhichACproducesvoltage.AnACgeneratorproducesavoltagefirstinonedirection,andthenanother.Thisisdonebyrotatingalargecoilofwirethroughamagneticfield(orviceversa).Asthewirecoilmovesthroughthemagneticfield,avoltagedevelops.

ELECTRICALPOWER(WATTS)Strictlyspeaking,poweristhetimeratefordoingwork.Thefasterworkisdone,thegreaterthepowerthatwillberequiredtodoit.Horsepoweristhebasicunitmeasurementofpower,andisdefinedas33,000ftlb/min.Theformulais:

hp=LxW=ftlb/min

33,000xt33,000

wherehp=horsepower,L=distanceinfeetthroughwhichWisraisedorovercome,W=weightinpoundsoftheobjectbeingmoved(orthepushorpullinpoundsofforcebeingexertec),andtistimeinminutesrequiredtomoveweightWthroughdistanceL.

Electricpoweristherateofdoingelectricalwork.Itsunitisthewatt,orkilowatt,whichis1000watts.One(1)wattisdevelopedwhen(1)ampereismaintainedthrougharesistancebyanemfof(1)volt.TherelationshipbetweenkWandhpis:

(1)hp=746W

Electricalenergyisexpressedintermsofkilowatthours(kWh),and(1)kWhistheenergyexpendedifworkisdoneatarateof(1)kWfor1hour.



OHMSLAWTherelationshipbetweenelectricalpower,current,voltage,andresistanceiscalledOhmsLaw.Themathematicalformulaisexpressed:

P=E*Ior:I=E/Ror:R=E/I

Where

P=Power,inkW

I=current,inamperes(A)

E=electromotiveforce,involts(V)

R=resistance,inohms()

Thefollowingdiagramexpressesmostofthecommonrelationshipsingraphicalform.

Ohmslawcanbeappliedtoanentirecircuit,ortoanyportionofit.Thismaybestated:

Thetotalcurrentflowinginacircuitisequaltothetotalvoltageappliedtothecircuitdividedbythetotalresistanceofthecircuit.Thecurrentflowinginanypartofacircuitisequaltothevoltageacrossthatpartofthecircuitdividedbytheresistanceofthatpartofthecircuit.

ELECTRIC CIRCUITSAnelectriccircuitisthepathoverwhichelectronsflow.Thetwobasickindsofcircuitsareseriesandparallel.Acombination(orseriesparallel)circuithaselementsofbothbasickindsofcircuits,wherecomecomponentsareconnectedinseriesandothersarejoinedinparallel.

Allcircuitsarecomposedofthesamebasiccomponents:

Avoltagesource(1)Ormoreelectricalloads(1)Ormorecontroldevices(switches,relays,etc.)

Asimplecircuitasillustratedconsistsofavoltagesource(L1andN),aSPSTswitch,andaheater.

SERIESCIRCUITSAcircuitthatonlyhasonepathoverwhichcurrentcanflowisaseriescircuit.Abreakinanypartofaseriescircuitstopscurrentflow.Allcomponentsinaseriescircuitseethesameamountofcurrenttherefore,eachcomponentmustbecapableofcarryingthatnumberofamperes.

RULESFORSERIESCIRCUITS

Thevalueofacurrentflowinginaseriescircuitisthesamethroughallpartsofthecircuit.Thetotalvoltageofaseriescircuitisequaltothesumofthevoltagesacrosseachpartofthecircuit.Thetotalresistanceofaseriescircuitisequaltothesumoftheresistancesacrosseachpartofthecircuit.

Linevoltageisdividedacrosseachcomponentinaseriescircuitinproportiontothecomponentresistancevalues.Referringtotheschematicbelow,thetotalresistanceis(25+30=55).VoltagemeasuredbetweenpointsAandBis(240Voltsx25/55)=



109Volts.

Iftherewere(2)resistanceswhosevalueswereequal,thevoltagewouldbedividedequallyinhalf,andwouldmeasure120Volts.

PARALLELCIRCUITSAcircuitthathastwoorcurrentpathsisaparallelcircuit.Eachcomponentisconnectedtolinevoltage,andcurrentstillflowsthroughpartofthecircuitifonecomponentfails.Eachcomponentmustbecapableofwithstandinglinevoltage.Thenumberofamperesvariesaccordingtotheresistanceofthecomponent.

Themorecircuitpaths,thelessoppositiontotheflowofelectrons.Totalcircuitresistancedecreaseswhenmorepathsareadded.

RULESFORPARALLELCIRCUITS

Thetotalcurrentsuppliedtoaparallelcircuitisequaltothesumofthecurrentsthroughthebranches.Thevoltageacrossanybranchofaparallelcircuitisequaltothesupplyvoltage.Thetotalresistanceofaparallelcircuitisalwayslessthantheresistanceofanyofthebranches.

ThefollowingparallelcircuitistypicaloftheDavinciandJ2900kilnringsthereare(3)elementsperring,connectedinparallel.Inthisexample,eachelementhasaresistanceof49.8at240VAC,eachelementdevelops(240VAC/49.8)=4.82Amperes.Thetotalcircuitamperes,then,is4.82+4.82+4.82=14.46Amperes.

SERIES/PARALLELOrCOMBINATIONCIRCUITSCertaincircumstancesrequiretheuseofSeries/Parallel,orCombination,circuits,inwhichseriesandparallelcircuitsarecombined.Insomefrontloadingindustrialfurnacesthesecircuitsareusedtocombine,forinstance,sidewallheatingelementsandbackwallheatingelements(oftenshorterthansidewall)inabranchcircuitthatiscontrolledbyapowerrelay.

Intheaboveexample,thetotalresistancecanbefoundbyfirstdealingwitheachbranchcircuitindividually.Startingfromtheright,thiscircuitisaseriescircuitaddthe(24+24=48).Theothertwocircuitsareparallelandareequalinvalue(12each)therefore,theresistancevalueofthesetwocircuitsisequalto(12/2=6).Drawinganequivalentcircuitwith(2)parallelcircuits,oneof6andoneof48,lookslikethefollowing:

Solvingforthiscircuit:Rt=(6*48)/(6+48)=5.33.

Thetotalresistanceislowerthanthatforanyofthebranchcircuits.

CONDUCTORS AND WIRING METHODS

CONDUCTORSAconductorisanymaterialthatofferslittleopposition(resistance)totheflowofanelectriccurrent.Mostfamiliarconductorsareeithercopperoraluminumwire,coveredinanyofvariousformsofinsulation.Thesizeofconductorsvariesgreatlywiththeamountofcurrent



theycarry,andtheirintendeduseandenvironment.Becausemostconductorsarerelativelysmallindiameter,theunitcalledcircularmilshasbeenselectedtomeasurethesizeofconductors.Onemilisequaltoonethousandthofaninch(.001inch).Onecircularmilistheareaofacircleonemilindiameter.Thesymbolformilism,andforcircularmiliscm(nottobeconfusedwiththemetricsymbolsformeterandcentimeter).TheformulaA=m2canbeusedtodeterminethecircularmilareaofwire,where

A=area,incircularmils(cm)

M=diameter,inmils(m)

IntheU.S.,aspecialscalehasbeendevelopedforthemostcommonwiresizes.ThisistheAmericanWireGauge,orAWG.Thefollowingtableisbasedonthe1999NationalElectricCode,Tables31016and31018.ThisistheallowableampacitiesofInsulatedConductors,(3)currentcarryingconductorsinaracewayorcable,andisbasedonanambienttemperatureof86F.

AWG/

kcmilCircularMils

MaximumAmpacityofCopperWirewith60CInsulation



14 4,110 20 25 34

12 6,530 25 30 43

10 10,380 30 40 55

8 16,510 40 55 76

6 26,240 55 75 96

4 41,740 70 95 120

3 52,620 85 110 143

2 66,360 95 130 160

1 83,690 110 150 186

1/0 105,600 125 170 215

2/0 133,100 145 195 251

3/0 167,800 165 225 288

4/0 211,600 195 260 332

250 250,000 215 290 X

300 300,000 240 320 X

350 350,000 260 350 X

400 400,000 280 380 X

Inpractice,mostelectriciansuseTable31016,andusethevaluesforthe60Cinsulation,becausethesearethemostconservativevaluesofampacity.Therearecorrectionfactorsthatmustbetakenintoaccountforsuchvariablesasambienttemperature(lessampacityastheambienttemperarurerises)andnumberofconductorsinacableorracewaythesefactorsarefullydetailedintheNationalElectricalCode.

INSULATION TYPESVarioustypesofplasticarebyfarthemostcommoninsulationsusedonconductors.Forgeneralpurposebuildingwire,typesTW,THW,andTHWNareusedmorethananyothertype.Othertypeshavebeendevelopedformachinetools(MTW)wheretheconductorsarelikelytoencounterharshcuttingfluids.Likewise,forhighambienttemperaturesseveraltypesofinsulationhavebeendeveloped,includingthetypefavoredbyL&L,whichisSEWF.Thisisahightemperaturesiliconrubberbasedinsulation.

VOLTAGEDROP220VVersus230VVersus240VWherelongwirerunsareexperiencedbetweenthepowersupplyandthepointofconnection,itispossibleforthemeasuredvoltageatthepointofconnectiontobelowerthanthemeasuredvoltageatthepowersupply.Thisiscausedbytransmissionlossesthroughthewires,andcanalsobeaggravatedbyhavingexcessiveconnectionsfromonetransformerinaneighborhoodpowergrid,orwithinasinglefacility.Forinstance,manyoftheU.S.electricalutilitiessupply240Vfromthetransformer,butthemeasuredvoltage



comingintoaresidencemaybe230Voreven220V.Forresistanceheatingdevicessuchaselectrickilns(andovensorranges)thislowervoltagecanresultinslightlyslowerfiringsthanwouldbethecaseiftheactualvoltagewere240Vbutinpracticethisdoesnotusuallycauseproblems.

Topreventoramelioratethisvoltagedrop,largersizeconductorscanbeusedforlongruns.Oneruleofthumbistouseonesizelargerwireforevery50feetofrunfromthepowersupplytotheconnectionpointtheelectricianshouldbeabletomakethisdeterminationonsite.

Also,usingawirematerialoflowresistivitycankeepvoltagedroptoacceptablelevels.Aluminumwirehasaresistivity(Ohmscircularmilperfoot)of17.0copperhasaresistivityof10.4.Therefore,theresistivityofcopperis10.4/17.0=0.61,or61%ofaluminumsresistivity.L&Lrecommendsusingonlycopperwireforconnectionfromakilntoanypowersupplyinadditiontotheresistivitydifference,therearedifferencesintherateofcorrosionthatareaggravatedbythehighambienttemperaturescommonatthekilnconnectionpoint.

WHY 230V AND 460V RATINGS?Undervoltageconditionscanaffecttheoperationandservicelifeofmotorstheseareusuallyratedat10%ofnameplatevoltagethusthecommonratingof230Vor460Vformotors,whichcanusuallybesafelyoperatedatthelowervoltagessometimesfoundatserviceconnectionpoints.Inmanyindustrialplantsthemostcommonequipmentisoperatedbyelectricmotors,anditiscommontorefertotheactualpowersupplyas230Vor460Veventhoughthenormalsupplyvoltagefromtheutilityis240Vor480V.

FUSESANDCIRCUITBREAKERSFusesandcircuitbreakersareovercurrentdevicesdesignedtoprotectelectricalcircuitcomponents.Ifacircuitdevelopstoomanyamperes,theyaredesignedtoopen,interruptingtheflowofcurrentinthecircuit.Fusesselfdestructwhentheysenseanoverloadinthecircuit.Circuitbreakersarecommonlyusedinnewconstructiontheytrip(turnoffpower)whentheysenseanoverload,andcanbereset(turnedbackon)whenthecircuitisreturnedtonormal.

Circuitbreakersaremoreconvenientbecauseofthisfeature.However,theycancausenuisancetrippingandruinkilnfiringswhentheytrippartwaythroughafiring.Thisisbecausemostcircuitbreakersareactivatedthermallyifthecircuitbreakertemperaturerisesaboveapresetlevel,abimetallicelementinsidethecircuitbreakeropens,andthepoweristurnedoff.Thisworkswellmostofthetimehowever,overtimethebimetallicelementbecomesweakerbecauseresistanceheatingcircuitsareattheirratedloadlongerthanothertypesofelectricalloadssuchasmotors.Eventuallythecircuitbreakerbecomestooweaktoholditselfclosedoveralongenoughtimetofinishakilnfiring,unlessthecircuitisdrasticallyoversizedtocompensateforthisgradualagingprocess.

Therearemanydifferenttypesoffuses,includingdualelementtimedelay,onetime,subcycle,etc.Mostofthesedesignationsrelatetohowquicklyafusewillblowinresponsetoanoverload,andthesetypesoffuseshavebeendevelopedtoprotectnotonlythecircuits,butalsovaryingtypesofequipment.Forinstance,SCRs(siliconcontrolledrectifiers)needtobeprotectedfromvoltagespikeswhichcanoccurwithin1/60ofasecondanddestroythedevicetheseareusuallyprotectedbysemiconductorfuseswhichareveryfastacting,currentlimiting,andhavenotimedelay.

Anotherconsiderationinselectingfusesistheinterruptingcapacityinamperesinotherwords,howbigashortcircuitcanbeopenedbythefuse.Inlargeindustrialplantsthiscanbeanimportantfactor,becauseifenoughpowerisavailableitwouldbepossiblethatashortcircuitwouldallowtoomanyamperestoflowintoacircuitforageneralpurposetypefusetointerruptwhichcouldpotentiallycauseanelectricalfire.Mostresidencesandsmallcommercialshopsdonothaveenoughpoweravailablebeforethemaincircuitprotector(usuallya200ampcircuitbreaker)wouldopen,andasmallinterruptingrating(10,000Ampsor50,000Amps)isenough.

Forprotectingkilncircuits,onetimegeneralpurposetypefusesshouldbeused.Theseareinexpensive,havenoappreciabletimedelay,andareavailableinalargevarietyofsizes.Theyarealsowidelyandeasilyavailable,andaremadebyseverallargefusemanufacturers.Differentmanufacturershavedifferentdesignationsfortheironetimefusessomeofthemorecommononesare:

MANUFACTURER MAXRATEDVOLTSINTERRUPTRATING

FUSEDESIGNATION

LITTELFUSE 250VOLTS 50,000AMPS NLN

BUSSMAN 250VOLTS 50,000AMPS NON

GOULDSHAWMUT 250VOLTS 50,000AMPS OT

LITTELFUSE 600VOLTS 50,000AMPS NLS

BUSSMAN 600VOLTS 50,000AMPS NOS



GOULDSHAWMUT 600VOLTS 50,000AMPS OTS

Allovercurrentdevicesmustbesizedtocarry125%ofthecontinuousampereloadforinstance,a240V/1PhaseModelJ230kilnisratedat44amperes.Theovercurrentdevicemustberatedat125%,or(1.25x44=55Amperes)minimum.Theclosestcommerciallyavailabledeviceisratedfor60Amperesa50Amperedeviceisnotadequate.

ELECTRICAL DISTRIBUTIONElectricaldistributionfromtheelectriccompanyspowergenerationplantisgenerallybyhighvoltage3phaselines.Thesecanbebranchedtosubstationsthattransformtheasgeneratedpowertoalower(butstillrelativelyhigh)voltageforfurtherdistribution.Ultimately,foreachservice(whetherasingleindustrialplant,shopsinashoppingcenter,orhousesinaresidentialneighborhood)thissupplyisconnectedtoatransformer,whichchangesthehighvoltagesupplytolinevoltagesrangingfrom208Vto480V.

SINGLE PHASE SERVICESMostresidentialservicesaresinglephase,butmanyofthesearedistributedfrom3PhaseWyetransformers.TheyincludetwohotlegsfromtheWyeplusagroundedneutral,and,ofcourse,asystemground.Atruesinglephaseservicecomesfromatransformerthatisconnectedtoonlyonephasefromasubstationhighvoltagesupply.Thesecanbefoundinmanyresidentialneighborhoods,andsometimesinindustrialplants.Usuallythevoltagesuppliedis240V,with120Vfromphasetoneutral.

120/240VOLTS/1PHASEThisthemostcommonhouseholdpowersupplyfoundintheU.S.Theprimaryofasinglephasetransformerisconnectedtotoonephaseofthethreephasedistributionsystem.Thesecondarycontainstwocoilsconnectedinserieswithamidpointtaptoprovideasinglephase,threewiresystem.Thetwohotwires,orlines,provide240Volts,andeitherofthehotlinestoneutralprovides120Volts.Youwillsometimesseethisexpresseda110/220.(Forpurposesoforderelementsyouwillstillget240voltelementswhenyousee110/220.)

120/208VOLTS1PHASEForsomecommercialfacilitiesandsomenewerresidentialsupplies,theelectricalsupplyisdistributedwithinaneighborhoodpowergrid,andeachsupplyis120/208V1Phase.Twohotlegsat208V,agroundedneutralfor(2)120Vcircuits,andofcoursethesystemground,comprisetheelectricalsupply.Inthesecasesappliancesareratedfor208V1Phase,andkilnsshouldbeorderedassuch.

THREE PHASE SERVICES

WYEVERSUSDELTA3PHASESYTEMSA3PhasepowersupplyisclassifiedasDeltaifthehotlegsareconnectedphasetophase,withagroundedneutral.Whendiagrammed,thecircuitlookslikeatriangle(thereforethetermDelta),withthehotlegsshownasthethreepointsdefiningthetriangle,andthethreepowercircuitsdrawnbetweenthem.Thevoltagebetweenthegroundedneutralandanyoneofthehotlegsmeasuresofthesuppliedphasetophasevoltage.Avariationofthiscanbesuppliedwheretwoofthephasetoneutralvoltagesaremeasuredasthephasetophasevoltage,andtheotherismeasuredatanothercommonlyseenvoltagesuchas208V.Thistypeofelectricalserviceisusuallyfoundinindustrialplants,andthephasetoneutralvoltageisnotcommonlyusedforelectricalcircuits.

InaWyepowersupplythehotlegsofthe3phasesystemareeachconnectedtoagroundedneutral.WhendiagrammedthecircuitlooksliketheletterYwitheachofthehotlegsshownatoneoftheouterarmsoftheYandthegroundedneutralatthecentraljunctionpoint.Thephasetoneutralvoltageisreducedbythe3phasefactor(SquareRootof3=1.73).E.g.,foraphasetophasevoltageof208V,divide(208Vby1.73=)120Vcircuitvoltage.Thistypeofservicecanbefoundinindustrialplants,commercialsites,andresidentialareasthephasetophasevoltagesandphasetoneutralvoltagesareallcommonlyusedforelectricalcircuits.



240VOLTS/3PHASEMost240Volts/3PhasesystemsareprovidedasDelta,withagroundedneutraltosupply120Voltsasaphasetoneutralvoltage.Averycommontypeis240VACDelta,threewirewithagroundedcentertapononeofthephaseshighlegtoobtain120Voltsbetweentwoofthephasestoneutraland208Voltsbetweenthethirdphasetoneutral.Anothercommonserviceissimilar,butis120voltstoneutralonallthreephases.

Agroundedneutralconductorisalsousuallyincludedwiththesetypesofelectricservicetoobtainlowervoltagessuchas110120oreven208volts,andmaybeusedinmanyresidentialorcommercialinstallationstohelpindistributingthetypical110120lightingandoutletcircuits.Iftheloadsbetweenthephasetoneutralcircuitsareclosetobeingbalanced(similarinamperes),theneutralconductorendsupcarryinglittleornoamperesbecausethethreephasesaregenerated120apartintime,andthereforecanceleachotheroutwhenconnectedtogetherontheneutral(hencethenomenclatureneutral.)

208VOLTS/3PHASEManyschools,institutions,andcommercialorlightindustrialfacilitiesarewiredwith120/208Volts,3Phase,Wyeconnectionelectricalpowersupply.Thistypeofsupplyisanefficientmethodofsupplyingheavy120Vloads,andisalsoincreasinglybeingusedinresidentialserviceforthatreason.

TheWyeconnectionworksbyputtinganelectricalcircuitfromonehotlegofthe3phasesystemtoagroundedneutral.Thisreducestheeffectivevoltagebythe3phasefactor(SquareRootof3=1.73).Therefore,withaphasetophasevoltageof208V,dividethe208Vby1.73=120V.

Innonresidentialuse,mostfacilitiesaresuppliedwiththefull120/208Vsystem,andthedistributionisdoneinsidethefacilityforthe120Vcircuitsandforthe208V3Phasecircuits.Itisgenerallymosteconomicaltousethe3Phasesupplyforequipmenttherefore,itisrecommendedthatsuch208Volt/3phasekilnsbeorderedforthesefacilities.Singlephasekilnscanbeusedhowever,theywouldrequireheaviergaugewireforhookup,andwouldtendtounbalancethedistributionsysteminsidethefacility.

480VOLTS/3PHASEDELTAANDWYEManyindustrialfacilitiesareequippedwith480Vservices,whichareveryefficientforsupplyingequipmentwithhighpowerrequirements.ThesecanbefoundaseitherDeltaorWye.Ineithercase,linetolinevoltageis480Volts.WhensuppliedasaWyesystem,phasetoneutralvoltageis277Volts,whichisveryefficientforsupplyinglightingloads.Inbuildingswherethisserviceisfound,astepdowntransformerisusedtosupply208120Volts/3PhaseWye,for120Voltloads.Thismakesforaversatilepowersupply,butcancauseconfusionastowhatvoltageisavailableforequipment.Besuretomeasurelinetolinevoltagesonallthreephasessothatthetypeofvoltageavailablecanbedeterminedforcertain.Itisagoodideatotalktothebuildingsuperintendentorelectrcianwhenorderingkilnsoranyotherkindofelectricalequipment,becausetheywouldknowforsurewhichofthepowersupplieswouldbeavailable.Itiscostlytoconverttoadifferentvoltagethantheoneorderedafterthefact.

ELECTRICAL CONNECTION NOTES FOR L&L KILNS

208,220AND240VOLT,SINGLEPHASECONNECTIONMoststandardL&Lkilnsaresuppliedfor208,220or240volt,singlephaseservice.Connectingthesekilnstoapowersupplyisrelativelystraightforward.Thereare(2)hotlinesandaground.SinglephaseL&LKilnsdonotuseaneutralwiretopoweranyofthecircuitsallcircuitsarebasedonlinevoltage.Forsinglephasekilnsratedfor44Amperesandless,aNEMA650Pcordsetisprovided.ThepowersupplymustfeedaNEMA650Rreceptacle.TheexceptiontothisistheModelGS1714,whichusesa30AmpNEMA1430Pcordset,whichisthetypicaldryercordfoundinmostpartsoftheU.S.AllsinglephaseL&LKilnsratedformorethan48Amperesmustbewireddirectthesearenocordsetsprovided.

1PHASE,30AMPEREDRYERCIRCUITPOWERSUPPLYFORJUPITERKILNS

L&LsuppliessinglephaseJUPITERKilnswithaspeciallyconfigured,hightemperatureNEMA650Pcordset,eventhoughforsomemodelsitwouldbepermissibletousea30Ampcordsetbasedontheampacitiesinvolved.TheseKilnshavebeenlistedtoUL499standardsthislistingisdependentoncertainspecificcomponentsthataretestedtoULstandardsunderstrictguidelines.

Becausetherearedifferent"standard"dryeroutletconfigurations,indifferentjurisdictions



anddependingonwhentheoutletwasoriginallyinstalled,thereisnosetanswertothequestionofwhetheryoucanutilizeanexistingdryercircuitforasinglephaseJupiterkilnequippedwiththeNEMA650PplugandcordassemblythatL&Lusesonthesekilns.IfaKilnownerdecidestomakethischangeonhis/herown,beadvisedthattheULlistingnolongerappliesbecausethislistingisdependentoncertainspecificcomponentsthataretestedtoULstandardsunderstrictguidelines.Oneofthemostimportantofthesecomponentsisthemainpowercord,whichwouldnecessarilybemodifiedtomakethischange.UNDERNOCIRCUMSTANCESSHOULDANYONEEVERSUBSTITUTEANOFFTHESHELFDRYERCORDFORTHENEMA650PCORDSUPPLIEDBYL&LSUCHOFFTHESHELFCORDSARENOTRATEDFORTHETEMPERATURESTHATARENORMALATTHEKILNPOWERTERMINALBLOCK.

NEMACONFIGURATIONSFORL&LPOWERCORDSETSL&Lsuppliescordsetsfor1phaseKilns(andsome3phasekilns),ratedfor48Amperesorless.MostoftheseareNEMA650P.The3PhaseplugweuseontheEasyFirekilnsisa1550P.TheDoll/TestkilnissuppliedwithwitheraNEMA515Ror520R.LibertyBellekilnsuseavarietyof30ampcordsets(seetheLibertyBelleSpecificationsheetformoreinformation).

208,220AND240VOLT,THREEPHASEDELTACONNECTIONALLSTANDARDL&LKILNSSUPPLIEDFOR208OR240VOLT,THREEPHASESERVICEMUSTBEWIREDINDELTA,ORPHASETOPHASE,RATHERTHANPHASETONEUTRAL.DELTAmeansthattheelectricalload(s)areconnectedbetweenthehotleads,thatis,oneloadisconnectedbetweenL1andL2,anotherisconnectedbetweenL2andL3,andthethirdisconnectedbetweenL1andL3.

Thereisalotofconfusionconcerningthreephaseservices,becausetherearesomanydifferenttypesthatarecommonintheU.S.A.However,whenorderinganL&LKilnfor208OR240Volt,ThreePhaseoperation,makesuretomeasurethevoltagesbetweenallcombinationsoftheLinewires(L1toL2,L2toL3,andL3toL1.)Thisshouldbeclosetoeither240VACacrossallthreephases,or208VAC,withsometolerance(nomorethan10%)allowedforvoltagedrops.

IntheseStandardL&LKilnsalltheheatingandcontrolcircuitsaredesignedtooperatefromLinevoltage,andtherearenocircuitsthatareoperatedfromthepossiblereducedvoltagesavailablefromLinetogroundedneutral.

480/277VOLTAnd380/220VOLT,THREEPHASEWYECONNECTIONTherearesomeexceptionstotheaboverule:therearesomespeciallydesignedkilnstooperateon480VAC/277VAC,threephaseWYE,inwhichtheheatingcircuitsoperatefromLinetoneutral,andthecontrolcircuitisoperatedfromanisolatedcontroltransformer.Inaddition,somekilnsforoverseasoperationarewiredfor380VAC/220VAC,threephaseWYE,inwhichtheboththeheatingandcontrolcircuitsareoperatedfromLinetogroundedneutral.

OVERSEAS ELECTRICAL DISTRIBUTIONOverseaselectricalvoltagesvaryfromcountrytocountry,andrangefrom220/380VWyepowersupplywhere220Visacommonhouseholdvoltage,to240/415VWyewhere240Viscommon,andcangoashighas575or600VoltsDelta,whichisrelativelycommoninCanada.ThelowervoltageinWyesystemsisdeterminedbythe3Phasefactor,whichisthesquarerootof3(approximately1.73).Dividethephasetophaselinevoltagebythe3phasefactortoobtainthephasetoneutralvoltage(e.g.,380/1.73=220V).L&LKilnsareavailablefor380/220V3PhaseWye,aswellas220V1Phaseand415/240V3Phase"Wye".

ELECTRONICS AND KILN CONTROLWiththeadventofAutomatic,orComputercontrol,Kilns,Electronicshastakenonmoreimportanceintheceramicsindustry.ElectronicKilncontrollersarecalledupontocontroltheflowofelectricitytotheheatingelements,inordertoachieveadesiredtime/temperatureprogram.Thereisabasicfeedbackloopinvolved,inwhichameasurementoftemperatureiscomparedbytheelectronicmicroprocessortoadesiredprogramwhichisstoredinthememoryofthecontroller.Inresponsetotheoffsetbetweenthemeasuredtemperatureandtheprogrammedsetpoint,thecontrollerallowselectricityflowtotheheatingelements.

THERMOELECTRIC EFFECTSReferringtothediscussioninprevioussectionsconcerningatoms,ittakesalotofenergytodislodgeaprotonoraneutronfromanatom.Butelectronsmovewiththeslightestnudge,especiallyinmetals,whereasmallvoltage,atinyamountofheat,ortheimpactofafewphotonsisallittakes.Thermalandelectricalenergyworktogether,oneenhancingtheeffectsoftheother,asseveralscientistsisthe19thcenturydiscovered.Threeinparticular,



(c)2015L&LKilnMfgInc.AllRightsReserved.505SharptownRoad|Swedesboro,NJ08085|8007508350

ThomasJ.Seebeck,JeanPeltier,andSirWilliamThomson(LordKelvin),madesomediscoveriesthatareveryinfluentialintheheatprocessingindustrytoday.

In1821,Seebeckdiscoveredthatapairofwiresmadefromdissimilarmetalsandjoinedatbothends,wouldmoveamagneticneedleiftheendswereheldatdifferenttemperatures.Theneedledeflectionindicateselectronflow,orcurrent.Afurtherdevelopmenthasbeentoopenoneoftheends,andexposethejoinedendtotemperature.Averysmallvoltage,whichdependsonthetemperatureatthejunctionandthecompositionofthetwometals,canbedetectedattheopenend,andthisiscalledtheSeebeckvoltage.ThisvoltageisproportionaltothechangeintemperaturetheproportionalityconstantisknownastheSeebeckcoefficient.Thiscircuitisknownasathermocouple.Thevoltagesfoundareverysmall,andmeasuredinunitsofthousandthsofavolt,calledmillivolts.

Thermocouplesaremadewithvarioustypesofdissimilarmetals.AutomaticL&LKilnsareequippedwithavariationofTypeKthermocouplesasstandardequipment.ThesearemadewithanegativeNickelChromium(Chromel)wirejoinedtoapositiveNickelAluminum(Alumel)wireThesearetwoalloysmadefrombasemetalswhichhavebeendevelopedtoworkwellinthetemperaturesnormallyfoundinceramickilns.

Overthedecades,thermocoupletechnologyhasbecomeverymature.Standardindustrialpracticehasbeendevelopedtoidentifythermocouplewires.Allnegativethermocouplewiresareidentifiedwitharedinsulationcovering.ForTypeKthermocouples,thepositivewireismarkedwithayellowcovering.Anotherthermocouplegrade,TypeS,ismadefromplatinumandplatinumrhodium,whicharepreciousmetalsthatstandupverywelltothehightemperaturesandoxidizingconditionsencounteredinceramickilns.TheyusuallyhaveamuchlongerlifethanTypeKthermocouples,butareverycostly.TheyareavailableforL&LKilnsbyspecialorder.

FEEDBACK CONTROLAsappliedtoKilns,feedbackcontrolisthemeanswherebytheKilntemperatureiscontrolled.Theoperatorprogramsadesiredtime/temperaturecycleintothememoryofthecontroller.Whenthecontrollerisstarted,itimmediatelystartstocomparetheSetpointasitisgeneratedfromtheinternalprocessor,totheKilntemperature.TheKilntemperatureismeasuredbyathermocouple,whichgeneratesamillivoltage,whichflowstotheControllerinputterminals.TheControllercalculatestheoffsetbetweenthegeneratedSetpointandtheKilntemperature,andattemptstocorrecttheoffset.IftheKilntemperatureislowcomparedtoSetpoint,thecontrollercallsforheat.IfthekilntemperatureishighcomparedtoSetpoint,thecontrollerrefrainsfromcallingforheat,andtheKilntemperaturedropsduetoheatlossesthroughtheinsulationwall.ForL&LKilns,heatissuppliedbyclosingthecontactsofpowerrelays,whichcarryelectricalenergytotheheatingelements.Thefeedbacklooplookslikethefollowing.

ThetemperatureinsidetheKilnisconstantlybeingadjustedbythecontrollerinresponsetothethermocouplesignal.

THREEZONECONTROL(DYNATROL)L&LisoneofthepioneersofthreezonecontrolwiththeDYNATROL.Inthismethodofcontrol,threethermocouplesareplacedinsidetheKilnfromtoptobottom,andconnectedtothecontroller.Thecontrollerhasthreeinputconnections,andthreeassociatedoutputs.Theoutputsareconnectedtopowerrelays.TheDYNATROLisconstantlyadjustingthethreeoutputsinresponsetothesignalsfromthethreeinputs,andtherebycontrollingtheKilntemperatureineachofthethreezones.Toptobottomtemperaturegradients,ordifferences,canbecontrolledveryaccurately.Fordetailedinformationonthis,pleaserefertodynatrolinstructblue.pdf.