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Slide1:AircraftElectricalWiringInterconnectSystem(EWIS)BestPractices
JobAid
Revision: 2.0
[Speakernotes]
Thisjobaidcoversapplicable14CFRpart25aircraft(althoughitisalsowidelyacceptablefor
usewithothertypesofaircraftsuchasmilitary,smallairplanes,androtorcraft). Thisjobaid
addressespolicy;industryEWISpractices;primaryfactorsassociatedwithEWISdegradation;
informationonTC/STCdatapackagerequirements;EWISselectionandprotection;routing,
splicingandterminationpractices;andEWISmaintenanceconcepts (includinghowtoperform
aEWISgeneralvisualinspection). ThejobaidalsoincludesnumerousactualaircraftEWIS
photosandexamples.
[Endspeakernotes]
Slide2:AdditionalNotes
Thisslidedoesnotpertaintothisaccessibleversion:
Thispresentationcontainsadditionalspeakernotesformostslides. Itsadvisabletoreadthesenoteswhileviewingtheslidepresentation
Slide3:PrintingtheAdditionalNotes
Thisslidedoesnotpertaintothisaccessibleversion:
To
the
slides
and
accompanying
speaker
notes:
NavigatebacktotheFAAAircraftCertificationjobaidswebpage OpenandprintPrintableSlidesandNotes.
Slide4:Background
1. WhytheneedforEWISbestpracticesJobAid?a. Accident/IncidentServiceHistoryb. AgingTransportSystemsRulemakingAdvisoryCommittee(ATSRAC)c. EnhancedAirworthinessProgramforAirplaneSystem(EAPAS)d. EAPASRuleMaking
[Speakernotes]
Historically,wiringandassociatedcomponentswereinstalledwithoutmuchthoughtgivento
theagingaspects:
Fitandforget. Unanticipatedfailuremodesandtheirseverity.
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Arctracking. Arcing. Insulationflashover.
Maintenanceprogramsoftendidnotaddresstheseagingaspects. Servicehistoryalsoindicates
thatForeignObjectDamage(FOD)suchasdrillshavings,causticliquids,etc.doescauseEWIS
degradationthat
can
lead
to
EWIS
faults.
[Endspeakernotes]
Slide5:Introduction
Late1980s,wiringsafetyconcernsraisedduetoaccidents&incidents
Investigationsfoundcommondegradingfactorsinairplaneelectricalwiringsystems
Investigationintowiring
issuesdonebyindustry,
civil
aviation
authorities,
othergovernment
agencies
[Speakernotes]
Theagingissuesinwiringsystemsweremadeknownbythefollowing:
Inthelate1980s,wiringsafetyconcernswereraisedduetoaccidents&incidents Investigationsfoundcommondegradingfactorsinairplaneelectricalwiringsystems Investigationintowiringissuesdonebyindustry,civilaviationauthorities,government
agencies
[Endspeakernotes]
Slide6:WiringInvestigationFindings
Design Maintenance Operation Training Repair Installation
[Speakernotes]
Aslistedhere,theinvestigationoftheaircraftwiringrevealedthereareseveralfactors,
togetherwithtime,thatplayaroleinwiringdegradation.
[Endspeakernotes]
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Slide7:AgingTransportSystemsRulemakingAdvisoryCommittee
(ATSRAC)PhaseI
TaskedtodevelopandproposerecommendationsforairworthinessenhancementstotheFAA.
TaskscompletedandreportsapprovedbyATSRACinJanuary2001.PhaseII
TaskedtodevelopedandproposeairworthinessenhancementsbasedontherecommendationsdevelopedinPhaseI.
TaskscompletedandreportsapprovedbyATSRACinJanuary2003.PhaseIII
TaskedtoassistFAAwiththeimplementationoftheenhancementsdevelopedinPhaseII.
[Speakernotes]
AgingTransport
Systems
Rulemaking
Advisory
Committee
PhaseIThefollowingtaskswereundertakenbyATSRACinthisphasefordevelopingand
proposingrecommendationsforairworthinessenhancementstotheFAA:
Samplinginspectionofthefleet
Reviewoffleetservicehistory
Improvementofmaintenancecriteria
Reviewandupdatestandardpracticeforwiring
Reviewaircarrierandrepairstationinspectionandrepairtrainingprograms
PhaseIIThefollowingtaskswereundertakenbyATSRACinthisphasetodevelopand
proposeairworthinessenhancementsbasedontherecommendationsdevelopedinPhaseI:
Improving
wire
system
certification
requirements
Enhancingwiringmaintenanceproceduresandinstructions
Enhancingandaugmentcurrenttrainingprograms
StandardizingtheformatofStandardWiringPracticesManual
Studyofagingissuesinsmalltransportairplaneselectricalwiring
PhaseIII ThefollowingtasksarecurrentlyundertakenbyATSRACinthisphasetoassistFAA
withtheimplementationoftheenhancementsdevelopedinPhaseII:
Provideassistanceinimplementationoftheairworthinessenhancementsand,ifrequested,
developalternativestorulemakingforimplementationoftrainingandmaintenance
enhancements.
Assistinreviewandimplementationofnewtechnologiesdevelopedformitigatingtheaging
issuesin
aircraft
wiring
systems.
Studyanddevelopenhancementsforwiringmaintenanceproceduresforsmalltransport
airplanes(withapassengercapacitybetween6to30andlessthan7,500poundpayload).
[Endspeakernotes]
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Slide8:Routing/ChafingIn-ServiceExamples
[Graphic]
Wireschafingagainstmetalframeandchaffngagainsteachother
[Endgraphic]
[Speakernotes]
Thesephotosshowexamplesoffindings.Theseexamplesshowthepotentialforchafingand
arcing.
[Endspeakernotes]
Slide9:AccumulationofDirtandLint
[Graphic]
Wirescoveredindirtandlint
[Endgraphic]
[Speakernotes]
Accumulationofdirtandlintcreateapotentialforsmokeandfire,makinginspectionofthe
EWISimpossible.
[Endspeakernotes]
Slide10:CoilandStowIn-ServiceExample/Result
[Graphic]
Cutwireswithendsexposedandcutantennathatisexposed
[Endgraphic]
[Speakernotes]
Thisslideshowsanexampleofimproperterminationofunusedwires. Ontheleftside,there
arenoterminationcapsanditsimproperlystowed.
Ontherightsideisaphotoofanimpropermaintenanceaction. Coaxialcablewasleft
attachedtoanantennainsteadofbeingremovedinitsentiretyatleastitshouldhavebeen
detachedfromtheantenna. Consequently,lightningattachedtotheantenna,traveledalong
theEWIS,andcausedafireinthecabin.
[Endspeakernotes]
Slide11:BendRadiusProblemIn-ServiceExample
[Graphic]
Wiresbent180degreesandbundledtogether
[Endgraphic]
[Speakernotes]
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Thisphotoshowsanimproperbendradiusinstallationofelectricalwire.Theproperbend
radiusforwireonaircraftshouldbe10timestheoutsidediameterofthelargestdiameterwire
inthebundleforonesidesupported(3timesfortwosidessupported.) Standardindustrial
practiceandisinAC43.131bandStandardWiringPracticesManual(SWPM).
[Endspeakernotes]
Slide12:ArcingEvent
[Graphic]
Arcingresultswithterminalsandwires
[Endgraphic]
[Speakernotes]
Thesephotosillustrateanimpropermaintenanceactioncausedwhentheairplanes
airworthinesscertificatewasrelocated. Theattachscrewpenetratedthepowercables. The
FAA
maintenance
inspector
riding
on
the
jump
seat
caught
his
clothing
on
fire.
Thearcingevent,whichoriginatedfrominsidetheelectricalpowercenter,burnedahole
throughtheleftsideofthehallway(lookingforward)betweenthecockpitandcabin.
[Endspeakernotes]
Slide13:EffectofImproperMaintenance
[Graphic]
Topshowschafingwirescausedconduitburnthroughongeneratedpowerfeederinconduit.
Thebottomshowsthatheatfromarcingcausedholesinfuelline.
[Endgraphic]
[Speakernotes]
Theleftsideofthisphotoshowsfailureofwireduetochafinginsideametallicconduit.
Createdanarc,whichcreatedholesinthefuellinebelowtheconduit. Causedbyimproperly
replacinganexistingpowerfeeder.
[Endspeakernotes]
Slide14:EffectofPoorDesign
[Graphic]
Burnholesonsideofairplaneandinthefloorunderapassengerseat
[Endgraphic]
[Speakernotes]
ThisshowsarcingduetolavatoryservicinglinesleakingondamagedEWIS,creatinganarcthat
causedafirethatledtoextensivedamageinsideandoutsideoftheairplane.Businessclass
lavatorydripshieldnotinstalledwatershortedcannonpluginwirebundlebelowdeck.
Maintenance,design,training,operationsallneedimprovement.
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[Endspeakernotes]
Slide15:PreviousRegulationsInadequate
Previousregulationsfellshortofprovidingspecificwiringrelatedrequirements. Specificwiringrelatedrequirementsneededtobeincludedincertificationand
operationalregulations.
Slide16:CultureShift: EAPASSafetyInitiative
RecognizingimportanceofEWISinsafeoperationofairplanesleadstobeingmoreproactive;FAAis
o Treatingwiringasasystemo MandatingDAHsupportoftheinitiativeo IntegratingFAAlinesofbusiness;
jointAFS/AIRactivity;andcooperationwith&betweenDAHsandoperators
[Speakernotes]
Tocompletelyandthoroughlyaddresstheagingissuesinaircraftwiringrequiredaculturalshift
comprisingof:
Recognizingimportanceofelectricalwiringinsafeoperationofairplanesleadstobeingmore
proactive;FAAis
Treatingwiringasasystem MandatingDAHsupportoftheinitiative IntegratingFAAlinesofbusiness:
jointAFS/AIRactivity;andcooperationwith&betweenDAHsandoperators
[Endspeakernotes]
Slide17:GoalofEPASRule
Bannerwithmotto:Enhancesafetybyimprovingallaspectsofaircraftelectricalwiring
Goalisbasedono Industry/governmentcommitteedatadriven
recommendations
o Maximizingharmonization[Speakernotes]
ThegoalofEAPASwastoenhancesafetybyimprovingallaspectsofaircraftelectricalwiring
Goalis
based
on
Industry/governmentcommitteedatadrivenrecommendations
MaximizingharmonizationwithinternationalauthoritiesSonowyouhopefullyhaveabetterunderstandingofthehistorybehindtheEAPASrulemaking
andhowitcameintobeing.WearenextgoingtoprovideadefinitionforanEWIS.
[Endspeakernotes]
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Slide18:EWIS
E Electrical
W Wiring
IInterconnection
S System
[Speakernotes]
Wiringneedstobetreatedasanimportantsystemonairplanes.Wiringisnowreferredtoas
theElectricalWiringInterconnectionSystem(EWIS).
[Endspeakernotes]
Slide19:EWISDefinition
AnEWIS
isis
[per
new
25.1701(a)]:
Anywire,wiringdevice,orcombinationofthese,includingterminationdevices,installedin
anyareaoftheairplaneforthepurposeoftransmittingelectricalenergybetweentwoormore
intendedterminationpoints....
Slide20:EEWWIISSiissnotnot[25.1701(a)]
Electricalequipmentoravionicsqualifiedtoacceptableenvironmentalconditionsandtestingprocedures
Portable
electrical
devices
not
part
of
airplanes
type
design
Fiberoptics
Slide21:KeyPointtoRemember...
WWiirreeaannddaassssoocciiaatteeddccoommppoonneennttssnnoowwttrreeaatteeddaassaannaaiirrppllaanneessyysstteemm
Slide22:EWISDegradationFactors
[Graphic]
Inthecenter,EWISDegradationsurroundedPhysicalProperties,Age,Installation,Maintenance
andEnvironmentpointingintoEWISDegradation.
[Endgraphic]
[Speakernotes]
EWISdegradation
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EWISdegradationisaprocessthatisafunctionofseveralvariables;agingisonlyoneofthese. OthermainfactorsthatinfluenceEWISdegradationarethe:
Environmentinwhichitisinstalled.
PhysicalpropertiesoftheEWIS.
ActualphysicalinstallationoftheEWIS.
Maintenance(cleaning
and
repair)
of
the
EWIS.
CharacteristicsofagingEWIS
ThemannerinwhichEWISdegradesisthereforedependentupontheEWIStype,howitwasoriginallyinstalled,theoveralltimeandenvironmentexposedtoin
service,andhowtheEWISwasmaintained.
ServicehistoryshowsthathowtheEWISisinstalledhasadirecteffectonEWISdegradation. Inotherwords,EWISthatisnotselectedorinstalledproperlyhas
anincreasedpotentialtodegradeatanacceleratedrate. Therefore,good
aircraftEWISpracticesarefundamentalrequirementsforEWIStoremainsafely
intact.
[Endspeakernotes]
Slide23:CausesofEWISDegradation
Vibration Moisture Maintenance
[Speakernotes]
VibrationHighvibrationareastendtoacceleratedegradationovertime,resultingin
"chattering"contacts
and
intermittent
symptoms.
High
vibration
can
also
cause
tie
wraps,
or
stringtiestodamageinsulation. Inaddition,highvibrationwillexacerbateanyexisting
problemwithwireinsulationcracking.
MoistureHighmoistureareasgenerallyacceleratecorrosionofterminals,pins,sockets,and
conductors. ItshouldbenotedthatEWISinstalledinclean,dryareaswithmoderate
temperaturesappearstoholdupwell.
MaintenanceUnscheduledmaintenanceactivities,ifdoneimproperly,maycontributetolong
termproblemsandEWISdegradation. Repairsthatdonotmeetminimumairworthiness
standardsmayhavelimiteddurability. Repairsthatconformtomanufacturersrecommended
maintenancepracticesaregenerallyconsideredpermanentandshouldnotrequirereworkif
properlymaintained.
Metalshavingsanddebrishavebeendiscoveredonwirebundlesaftermaintenanceorrepairshavebeenconducted. Careshouldbetakentoprotect
wirebundlesandconnectorsduringmodificationwork,andtoensureall
shavingsanddebrisarecleanedupafterworkiscompleted.
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Asageneralrule,EWISthatisundisturbedwillhavelessdegradationthanEWISthatisreworked. AsEWISbecomemorebrittlewithage,thiseffectbecomes
morepronounced.
[Endspeakernotes]
Slide24:CausesofEWISDegradation,cont.
Indirectdamage Chemicalcontamination Heat Installation
[Speakernotes]
IndirectdamageEventssuchaspneumaticductrupturescancausedamagethat,whilenot
initiallyevident,canlatercauseEWISproblems.Whensuchaneventhasoccurred,
surroundingEWIS
should
be
carefully
inspected
to
ensure
no
damage
is
evident.
ChemicalcontaminationChemicalssuchashydraulicfluid,batteryelectrolytes,fuel,
corrosioninhibitingcompounds,wastesystemchemicals,cleaningagents,deicingfluids,paint,
andsoftdrinkscancontributetodegradationofEWIS. EWISinthevicinityofthesechemicals
shouldbeinspectedfordamageordegradation.Recommendedoriginalequipment
manufacturercleaninginstructionsshouldbefollowed.
Hydraulicfluids,forexample,requirespecialconsideration. Hydraulicfluidisverydamagingtoconnectorgrommetandwirebundleclamps,leadingto
indirectdamage,suchasarcingandchafing. EWIScomponentsthatmayhave
beenexposedtohydraulicfluidshouldbegivenspecialattentionduringEWIS
inspections.
HeatEWIScomponentsexposedtohighheatcanacceleratedegradation,insulationdryness,andcracking. Directcontactwithahighheatsourcecanquicklydamageinsulation. Evenlow
levelsofheatcandegradeEWISoverlongperiodsoftime. Thistypeofdegradationis
sometimesseenonengines,ingalleys,andbehindlights.
InstallationEWISnotinstalledproperlycanfurtheracceleratetheEWISdegradationprocess.
Improperrouting,clamping,andterminatingduringinitialinstallationorduringamodifications
canleadtoEWISdamage.
[Endspeakernotes]
Slide25:
Current
FAA
Guidance
[Graphic]
Inthecenter,EWISPractices,surroundedwithPart25,Part26,AC25.17011,PolicyANM01
04,AC2510,AC2516,AC43.131bandAC25.27A
[Endgraphic]
[Speakernotes]
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Therearedirectspecificpart25andpart26EWISpracticesrelatedto14CFR.
Therearesomespecificelectricalpowerwiringrequirements,suchas25.1353,buttheydo
notspecificallyaddressallaircraftEWIS.
14CFR25.1729requiresthatinstructionsforcontinuedairworthinessaredevelopedusing
analyticalprocedures,whichwouldincludemaintenancetasksandintervalsforEWIS.Alarge
bodyof
FAA
general
guidance
for
wiring
practices
is
in
Chapter
11
of
AC
43.13
1b.
[Endspeakernotes]
Slide26:Part25
Newpart25requirementsforcertificationofelectricalwiringinterconnectionsystems(EWIS)
o RevisedexistingEWISrelatedcertificationrequirementsandrelocatedsomeofthem
o CreatednewEWIScertificationrequirementsand
placed
them
in
anew
subpart
H
o NewEWISICArequirements
Slide27:Part26
Affectscontinuedairworthinessissuesand/orsafetyimprovementsfortransportairplanesaddressedviaoperationalrules
Supportstheabilityofoperatorstocomplywiththeoperationalrulerequirements EAPASPart26RequiresactionsofDesignApprovalHolders(DAHs),suchas:
o instructionsforcontinuedairworthiness,o
distribution
of
information
to
affected
operators
Slide28:Part26ModelApplicability
Existingairplaneswithamaximumtypecertificatedpassengercapacityof30ormore,or
Existingairplaneswithamaximumpayloadcapacityof7,500poundsormore(reference119.3)
ExistingairplanemodelswithatypecertificateissuedonorafterJanuary1,1958.
Slide29:AC25.1701-1
ThisAdvisoryCircular(AC)providesguidanceforcertificationofelectricalwiringinterconnectionsystems(EWIS)ontransportcategoryairplanes
o 14CFRpart25,subpartH,sections25.1701through25.1733o H25.4andH25.5ofAppendixHtopart25.
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Slide30:AC25.27A
ProvidesguidancefordevelopingmaintenanceandinspectioninstructionsforEWIS Usesanenhancedzonalanalysisprocedure(EZAP). Forairplanemodelswhosemaintenanceprogramsalreadyincludeazonalinspection
program,thelogicdescribedhereprovidesguidanceonimprovingthoseprograms.
Slide31:AC25.27A,cont.
Forairplaneswithoutazonalinspectionprogram,useofthislogicwillproducezonalinspectionsforEWISthatcanbeaddedtotheexistingmaintenanceprogram.
ContainsinformationthatcanbeusedbyoperatorstoImproveEWISmaintenancepractices.
StressestheimportanceofinspectingEWISandpromotesaphilosophyofprotectandcleanasyougowhenperformingmaintenance,repair,oralterationsonanairplane.
Slide32:PolicyANM-01-04
DesigndatashouldNOTleavetheinstallationtothediscretionoftheinstaller. RoutingofEWISshouldfollowthecriteriaestablishedbytheFAAinthecertification
basis,asreflectedintheholdersoriginalorsubsequentlyapprovedtypedesign.
Installationdrawings/instructionsshouldcompletelydefinetherequiredroutingandinstallationwithsufficientdetailtoallowrepeatabilityoftheinstallation.
Slide33:Guidance:AC43.13-1b
AC43.131b: AcceptableMethods,Techniques,andPractices AircraftInspectionandRepair
AC43.13
1b:
o FlightStandardsACo Chapter11 AircraftElectricalSystems
NOTE: TheguidanceprovidedinAC43.131bisgeneralinnatureandisnottobereferencedor
usedasasubstituteforEWISinstallationdrawingsand/orEWISdiagrams.
[Speakernotes]
AC43.131bcoversafairlycomprehensivewiderangeofbasicEWISpracticestopics.
NOTE:The
guidance
provided
in
AC
43.13
1b
is
general
in
nature
and
is
not
to
be
referenced
or
usedasasubstituteforEWISinstallationdrawingsand/orEWISdiagrams.
[Endspeakernotes]
Slide34:Guidance:AC25-16
AC25 16: ElectricalFaultandFirePreventionandProtection(4/5/91)AC25 16:
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o Providesacceptablemeanstoaddresselectricallycausedfaults,overheat,smoke,andfireintransportcategoryairplanes
[Speakernotes]
AC2516provideswiringpracticesguidanceasitrelatestoaircraftfireandsmokesafetywith
emphasison
wiring
flammability,
circuit
breaker
protection,
wiring
near
flammable
fluids,
and
associatedacceptabletestmethods.
ThisACiscurrentlybeingconsideredforupdating.
[Endspeakernotes]
Slide35:Guidance:AC25-10
AC25 10: GuidanceforInstallationofMiscellaneous,NonrequiredElectricalEquipment(3/6/87)
AC25 10:
o Providesacceptablemeanstocomplywithapplicable14CFRsassociatedwithinstallation
of
electrical
equipment
such
as
galleys
and
passenger
entertainment
systems
[Speakernotes]
AC2510mainlycoversnonrequiredequipmentinstallationssuchasgalleys,passenger
entertainmentsystems,etc. Fromawiringstandpoint,allsystemsshouldbetreatedequally,
regardlessofthefunctionscriticalitybecauseofpotentialfireandsmokehazards.
ThisACcontainsminimalwiringpracticesspecifics,includinggeneralloadanalysisrequirements
andcircuitbreakerprotectionrequirements,whicharemorethoroughlycoveredinAC43.13
1bandAC2516,sowearenotgoingtobecovering2510inanydetail.
[Endspeakernotes]
Slide36:ElectricalLoadDetermination
Loadanalysiso Ensurethattotalelectricalloadcanbesafelycontrolledormanagedwithinrated
limitsofaffectedcomponentsofaircraftselectricalsystem(25.1351)
o Neworadditionalelectricaldevicesshouldnotbeinstalledwithoutanelectricalloadanalysis
(AC43.131b)
[Speakernotes]
Electricalloaddeterminationistoensureeachaircraftelectricalbuscansafelysupporta
predeterminedamountofelectricalloadthatisbasedontheelectricalcapacityoftheaircraft
generatorsandtheaircraftsoverallelectricaldistributionsystem.
25.1351requirement: Itmustbedeterminedthroughanalysisthatallelectricaldevicescan
besafelycontrolledormanagedbytheaircraftselectricalsystem.
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AC43.131b:Wheneveranelectricaldeviceisadded,aloadanalysisshouldbeperformedto
ensurethatthenewloadonthebuscanbepoweredadequatelysuchthatthereisadequate
electricalpowermargintoavoidoverloadingthebus.
Wherenecessaryasdeterminedbyaloadanalysis,wire,wirebundles,andcircuitprotective
deviceshavingthecorrectratingsshouldbeaddedorreplaced.
[Endspeaker
notes]
Slide37:CircuitBreakerDevices
Mustbesizedtoopenbeforecurrentratingofattachedwireisexceeded,orbefore
cumulativeratingofallconnectedloadsisexceeded,whicheverislower(25.1357)
[Speakernotes]
Section25.1357requiresthatautomaticprotectivedevicesbeusedtominimizedistresstothe
electricalsystemandminimizehazardtotheairplaneintheeventofwiringfaultsorserious
malfunction
of
the
system
or
connected
equipment.
[Endspeakernotes]
Slide38:CircuitBreakerProtection
Acircuitbreakermustalwaysopenbeforeanycomponentdownstreamcanoverheatandgeneratesmoke
orfire.(AC43.131b,para.1148)
Circuitbreakersaredesignedascircuitprotectionforthewire,notforprotectionofblackboxesorcomponents...(AC43.131b,
para.1151)
[Speakernotes]
AC43.131bcontainssomeconflictingstatements. Thebulletsinthisslidearesomewhat
contradictory. Thefirstbulletsaysthatthebreakermustprotectagainstanydownstream
componentfailure. ThesecondbulletsaysbreakersaredesignedsuchthattheyDONOT
protectcomponentsorLRUs.
Inreality,breakersaresizedtoprotecttheaircraftwiringasthemaindesignconstraint. Any
furtherprotectionofcomponentsorLRUsisdesirablebutnotmandatory.
Ideally,circuitbreakersshouldprotectagainstanywiringfaultthatleadstoarcing,sparking,
flames,orsmoke. Butaswewilllearn,thermalcircuitbreakersdonotalwaysdetectarcing
events.
[Endspeakernotes]
Slide39:CircuitBreakerProtection,cont. Useofacircuitbreakerasaswitchisnotrecommended
o Repeatedopeningandclosingofcontactscanleadtodamageandprematurefailureofcircuitbreakers
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Theyshouldnotbeusedinapplicationswheretheywillbesubjectedtoexcessivevibration,
repeatedbending,orfrequentdisconnectionfromscrewtermination.
[Endspeakernotes]
Slide42:
Wire
Selection,
cont.
Conductorstrandingo Minimizesfatiguebreakage
Platingsforallcopperaircraftwiringo Platedbecausebarecopperdevelops
surfaceoxidefilmapoorconductor
Tin
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Slide44:DeterminingWireSystemDesign
AC43.131b,Section5:tablesandfiguresprovideanacceptablemethodof determiningwire
systemdesign
[Speakernotes]
Theapplicant
should
ensure
that
the
maximum
ambient
temperature
that
the
wire
bundles
will
besubjectedto,plusthetemperatureriseduetothewirecurrentloads,doesnotexceedthe
maximumconductortemperaturerating.
Insmallerharnesses,theallowablepercentageoftotalcurrentmaybeincreasedastheharness
approachesthesinglewireconfiguration.
ThecontinuouscurrentratingscontainedinthetablesandfiguresinAC43.131bwerederived
onlyforwireapplication,andcannotbeapplieddirectlytoassociatedwireterminationdevices
(e.g.,connectorcontacts,relays,circuitbreakers,switches). Thecurrentratingsfordevicesare
limitedbythedesigncharacteristicsofthedevice. Careshouldbetakentoensurethatthe
continuouscurrentvaluechosenforaparticularsystemcircuitshallnotcreatehotspotswithin
anycircuit
element
which
could
lead
to
premature
failure.
[Endspeakernotes]
Slide45:WireSubstitutionforRepairsandMaintenance
Whenreplacementwireisrequired,reviewaircraftmaintenancemanualtodetermineiforiginalaircraftmanufacturer(OAM)hasapprovedanysubstitution
o Ifnotapproved,thencontactOAMforanacceptablereplacement
[Speaker
notes]
MostaircraftEWISdesignsaretospecificationsthatrequiremanufacturerstopassrigorous
testingofwiresbeforetheyareapprovedoraddedtoaQualifiedProductsList. Aircraft
manufacturerswhomaintaintheirownwirespecificationsexerciseclosecontroloftheir
approvedsources. Therefore,itisimportanttoreviewtheaircraftmaintenancemanualor
contacttheoriginalaircraftmanufacturer(OAM)whenwiresubstitutionsarenecessary.
TheOAMmayhavespecialconcernsregardingshielding,insulation,etc.forcertainwiringon
theaircraftthatperformcriticalfunctionsorwiringthatischosenbasedonasetofunique
circumstances.
[Endspeakernotes]
Slide46:EWISRouting
Eliminatepotentialforchafingagainststructureorothercomponents Positiontoeliminate/minimizeuseashandholdorsupport Minimizeexposuretodamagebymaintenancecrewsorshiftingcargo Avoidbatteryelectrolytesorothercorrosivefluids
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[Endspeakernotes]
Slide50:EWISasaHandhold
[Graphic]
Showspersons
hand
holding
onto
the
EWIS
with
international
not
symbol
superimposed
acrossit.
[EndGraphic]
[Speakernotes]
RouteEWISsothatitisnotusedasahandholdorasasupportformaintenancepersonnel.
Inaddition,routeEWISsothatitavoids:
Damagebypersonnelmovingwithintheaircraft. Damagebystowageorshiftingcargo. Damagebybatteryoracidicfumesorfluids.
Abrasion
in
wheel
wells
where
exposed
to
rocks,
ice,
mud,
etc.
Damagefromexternalevents(zonalanalysis/particularrisksanalysisdemands). Harshenvironmentssuchasseverewindandmoistureprone(SWAMP)areas,
hightemperatures,orareassusceptibletosignificantfluidorfume
concentration.
EWISshouldberoutedtopermitfreemovementofshockandvibrationmountedequipment,
designedtopreventstrainonwires,junctions,andsupports,and,theEWISinstallationshould
permitshiftingofEWISandequipmentnecessarytoperformmaintenancewithintheaircraft.
Inaddition,wirelengthsshouldbechosentoallowforatleasttworeterminations.
[Endspeakernotes]
Slide51:
EWIS
Routing,
cont.
ProtectEWISinwheelwellsandotherexposedareas RouteEWISabovefluidlines,ifpracticable Usedriploopstocontrolfluidsorcondensedmoisture Keepslacktoallowmaintenanceandpreventmechanicalstrain
[Speakernotes]
EnsurethatEWIScomponentsareadequatelyprotectedinwheelwellsandotherareaswhere
theymaybeexposedtodamagefromimpactofrocks,ice,mud,etc. (IfreroutingofEWISis
notpracticable,
protective
jacketing
may
be
installed.)
This
type
of
installation
must
be
held
to
aminimum.
Wherepractical,routeEWISsandcablesabovefluidlines.Wiresandcablesroutedwithin6
inchesofanyflammableliquid,fuel,oroxygenlineshouldbecloselyclampedandrigidly
supported. Aminimumof2inchesmustbemaintainedbetweenwiringandsuchlinesor
relatedequipment,exceptwhenthewiringispositivelyclampedtomaintainatleast1/2inch
separationorwhenitmustbeconnecteddirectlytothefluidcarryingequipment.
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Ensurethatatrapordriploopisprovidedtopreventfluidsorcondensedmoisturefrom
runningintoEWISandothercomponents.EWIS installedinbilgesandotherlocationswhere
fluidsmaybetrappedareroutedasfarfromthelowestpointaspossibleorotherwiseprovided
withamoistureproofcovering.
[Endspeakernotes]
Slide52:EWISAboveFluidLines
Brokenwireshallnotmakecontactwithfluidline
[Graphic]
Showsbrokenwireexposedendtouchingthefluidline
[EndGraphic]
[Speakernotes]
EWIS
above
fluid
lines.
The
clamps
should
be
a
compression
type
and
should
be
spaced
so
that,assumingawirebreak,thebrokenwirewillnotcontacthydrauliclines,oxygenlines,
pneumaticlines,orotherequipmentwhosesubsequentfailurecausedbyarcingcouldcause
furtherdamage.
[Endspeakernotes]
Slide53:Graphic
Wiresimproperlytied,ridingonhydrauliclines,contaminatedwithcausticfluid
[Graphic]
Showswires
touching
hydraulic
lines
[EndGraphic]
[Speakernotes]
Thisexampleshowsanumberofproblems:
Wiresinthebundlesarenottiedproperly. Thewirebundleisridinghardonthehydrauliclines. Thewirebundleappearstobecontaminatedwithhydraulicfluidresidue.
[Endspeakernotes]
Slide54:YTypeWireBundleBreakouts
[Graphic]
Bundleshowingfigure8loopasbundlesplitsintotwobundles.GraphicsaysFigure8loopmay
belocatedbeforeoraftertailofYandHeadofstrapshallnotbelocatedinthisareaortouching
anythingtocausechafing
[Endgraphic]
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[Speakernotes]
Wirebundlebreakouts. Therearethreebasicwirebundlebreakouttypesusedinrouting
aircraftEWIS. TheyarecalledtheY,T,andComplextypes.
TheYtypeofbreakoutisusedwhenaportionofEWISfromonedirectionofthewirebundle
departsthe
bundle
to
be
routed
in
another
direction.
Careshouldbetakenwhenplastictiewrapsareusedtoprovidewirecontainmentatthebreakoutsothatthetiewrapheaddoesnotcausechafing
damagetothewirebundleatthebreakoutjunction.
[Endspeakernotes]
Slide55:TTypeWireBundleBreakouts
[Graphic]
BundleshowsaTtypebundlewithacrisscrosstieatjunctionaroundtheT.Gradphicsays
Headof
strap
shall
not
be
located
in
this
area
or
touching
anything
to
cause
chafing
referring
to
the
topofthebundleandthesideoftheTgoingup.
[Endgraphic]
[Speakernotes]
TheTtypeofbreakout(alsocalled90breakout)isusedwhenportionsofEWISfromboth
directionsinthewirebundledepartthebundletoberoutedinanotherdirection.
[Endspeakernotes]
Slide56:ComplexTypeWireBundleBreakouts
[Graphic]
Showsaterminalblockwiththewireconnections
[Endgraphic]
[Speakernotes]
AComplextypeofbreakoutisgenerallyusedtoroutecertainwiresoutofawirebundletoa
terminalstrip,moduleblock,orothertermination.
Foralltypesofbreakouts,thereshouldbesufficientslackinthewiresthatarebeingbrokenout
ofthebundletoavoidstrainonthewirebetweenthewirebundleandthetermination.
[Endspeakernotes]
Slide57:Stand-offs
UsestandoffstomaintainclearancebetweenEWISandstructureo Employingtapeortubingisgenerallynotacceptableasanalternativenot
ExceptionException:WhereimpossibletoinstalloffangleclampstomaintainEWISseparationinholes,bulkheads,floors,etc.
:
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[Speakernotes]
TheEWISdesignshouldprecludewirebundlesfromcontactingstructure. Standoffsshouldbe
usedtomaintainclearancebetweenEWISandstructure.
Employingtapeorprotectivetubingasanalternativetostandoffsshouldbeavoidedasa
primarymeans
of
preventing
EWIS
contact
with
structure.
Exception: Usingtapeortubingisallowedincaseswhereitisimpossibletoinstalloffangle
clampstomaintainEWISseparationinholes,bulkheads,floors,etc.
[Endspeakernotes]
Slide58:UsingStand-offs
[Graphic]
GraphicshowstheImpropermethodwithwiresimmediatelytouchingthebaseafterusinga
standoff.Propermethodshowswiresinstandoffnottouchingbase.
[End
graphic]
[Speakernotes]
Whenusingstandoffsforadditionalclearance,clampsshouldnotbeinstalledinamannerthat
defeatsthestandoffspurposeofprovidingadditionalclearancebetweenEWISandstructure.
[Endspeakernotes]
Slide59:Bundleridingonstructure
[Graphic]
showingbundletouchingaircraftstructure
[Endgraphic]
[Speakernotes]
OneofthemorecommonaircraftEWISproblemsischafingduetowirebundlescominginto
contactwithaircraftstructureorotheraircraftequipment.
[Endspeakernotes]
Slide60:Graphic
[Graphic]
Wirebundle
too
close
to
control
cable
[Endgraphic]
[Speakernotes]
Thispictureshowsawirebundlethatisinclosecontactwithacontrolcable. Adequate
distancebetweenEWISandcontrolcablesshouldbemaintainedtoaccountformovementdue
toslackandmaintenance.
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[Speakernotes]
AcommonprobleminaircraftEWISisclamppinching. Thisoccurswhentheclampis
improperlyinstalledortheclampistoosmall. Clampsonwirebundlesshouldbeselectedso
thattheyhaveasnugfitwithoutpinchingwires.
[Endspeaker
notes]
Slide69:TypicalNylonClosed-FaceClampInstallation
[Graphic]
Showsbundleofwiresinclamponastandoff.Itsaysdonotpinchherereferringtothepoint
wheretheclampcomestogether.
[Endgraphic]
[Speakernotes]
It
is
important
when
adding
wiring
to
an
existing
wire
bundle
to
evaluate
the
existing
clamp
sizinginordertoavoidpossibleclamppinching. Insomecasesitmaybenecessarytoincrease
thesizeoftheclampstoaccommodatethenewwiring.
[Endspeakernotes]
Slide70:EngageClampTabinSlot
[Graphic]
Showsimproperwhereclamptabshaveaseparationandproperwhereclamptabsandtight
andflushtoeachother
[Endgraphic]
[Speakernotes]
Whenusingclamptabs,makesurethatthetabsareproperlyengaged. Otherwise,thetab
couldbecomelooseandcausesubsequentwiredamage.
DuringEWISinstallationinspections,ensurethattheclampissnappedbeforeinstallingandtighteningthebolt.
[Endspeakernotes]
Slide71:ClampPinching
[Graphic]
Shows improperwherethewiresarepinchedatwheretheclampcomestogetherandproper
wherethewiresdonotpinchintheclamp.
[Endgraphic]
[Speakernotes]Thisslidefurtherillustrateshowwirescanbepinchedanddamageddueto
improperclampinstallation.[Endspeakernotes]
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Slide72:ClampPinching,cont.
[Graphic]
Shows improperwheretherearetwowiresintheclampcausingpinchingandproperwhere
theright
sized
clamp
is
used
and
not
causing
any
pinching.
[Endgraphic]
[Speakernotes]
Toomuchwiringinaclamporimproperlyinstalledclampscanleadtopinchingofthewires
[Endspeakernotes]
Slide73:Graphic
[Graphic]
Openfaced
nylon
clamp
with
cable
build
up
(missing
hardware)
[Endgraphic]
[Speakernotes]
ThispicturewastakenduringageneralvisualEWISinspectionofawidebodytransportaircraft.
Notethemissingclamphardware. Alsonotethattheblackcableusedatapebuildupatthe
clamp. SomemanufacturersEWISspecificationsallowforwirecablebuildupundercertain
circumstances.
[Endspeakernotes]
Slide74:
Wire
Bend
Radii
Minimumbendradius 10timestheoutsidediameterofthelargestwireorcableinthegroupunsupported
o Exceptions Terminations/reversingdirectioninbundle(supportedatbothendsof
loop) 3timesthediameter
RFcables 6timesthediameter Thermocouplewire 20timesthediameter
[Speakernotes]
Theminimum
radius
of
bends
in
wire
groups
or
bundles
must
not
be
less
than
10
times
the
outsidediameterofthelargestwireorcable,exceptthatattheterminalstripswherewires
breakoutatterminationsorreversedirectioninabundle.
Wherethewireissuitablysupported,theradiusmaybe3timesthediameterofthewireor
cable.
Whereitisnotpracticaltoinstallwiringorcableswithintheradiusrequirements,thebend
shouldbeenclosedininsulatingtubing.
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Theradiusforthermocouplewireis20timesthediameter. (Thisisverydelicatewire.)
EnsurethatRFcables,(forexample,coaxialandtriaxial,arebentataradiusofnolessthan6
timestheoutsidediameterofthecable.
[Endspeakernotes]
Slide75:MinimumBendRadii
[Graphic]
Wirebundleillustrating
Nosupportatendofbendo Min.bendradius10xparameterofwireorcable
Supportatendofbendo Min.bendradius3xdiameterofwire
Ttypebendo Min.bendradius3xdiameterofwire
[Endgraphic]
[Speakernotes]
Thisillustrationshowstheproperbendradiiforthreedifferentscenarios.
[Endspeakernotes]
Slide76: Graphic
[Graphic]
Bendradiiokay Greaterthan3timesdiameter(securedatbothendsofloop)
[Endgraphic]
[Speakernotes]
Thisphotographshowsawireloopsecuredatbothendsoftheloop. Inthiscase,thebend
radiusshouldbenolessthan3timesthediameterofthelargestwireinthewirebundle.
[Endspeakernotes]
Slide77:Graphic
[Graphic]
Bendradiiproblem Lessthan3timesthediameter
[Endgraphic]
[Speakernotes]
Alsosupportedateachendoftheloop,thiswirebundledoesnotmeetbendradiusstandards
duetothelargewiresinthebundle.
[Endspeakernotes]
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Slide82:SpareWireTerminationUsingEndcap
[Graphic]
Showing
Wireandcapinpositionforcaptoslideoverwire Installendcapoverwireendandshrinkinplace Bundleusingadhesiveandfiberglasstyingtape
[Endgraphic]
[Speakernotes]
Installingprefabricatedendcapsareaneffectivemethodofprotectingunusedwireswith
exposedconductors.
Thisslidedepictsatypicalexampleoftheuseofaprefabricatedendcap.[Endspeakernotes]
Slide83:UnusedWires
[Graphic]
Unusedwiring Improperterminationwithexposed conductor(shouldbeproperlyinsulated
andsecuredtobundle)
[Endgraphic]
[Speakernotes]
FoundduringageneralEWISvisualinspection,thisexampleshowstwounusedwiresthathave
beencutandtheconductorsareunprotected. Inaddition,theunusedwiresarenotsecuredto
thewirebundle.
[Endspeakernotes]
Slide84:CoilandStowMethods
Coilandstowshortwirebundlesinlowvibrationareas
[Graphic]
wirebundlecoiledinaloopwithaclampandwire tiestoholdittogether[Endgraphic]
[Speakernotes]
Coilandstowmethodsareoftenusedtosecureexcesslengthofawirebundleortosecure
wirebundlesthatarenotconnectedtoanyequipment,suchaswiringprovisioningforafuture
installation.
[Endspeakernotes]
Slide85:CoilandStowMethods,cont.Coilandstowlongwirebundlesinlowvibrationareas
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[Graphic]
excesswireloopedbackandforthtoremovetheexcess.Useswiretiesandclamp
tobundletogether[Endgraphic]
[Speakernotes]
Thekeyobjectivetocoilingandstowingwiringistosafelysecurethewirebundletoprevent
excessivemovementorcontactwithotherequipmentthatcoulddamagetheEWIS.
[Endspeakernotes]
Slide86:CoilandStowMethods,cont.
Coilandstowinmediumandhighvibrationareas
[Graphic]
wirebundle,
with
aradius
between
two
bundles,
tied
to
awire
bundle
at
the
top
andbottomusingTeflontape[Endgraphic]
[Speakernotes]
Coilandstowinmediumandhighvibrationareasrequiresadditionaltiestraps,sleeving,and
support.
[Endspeakernotes]
Slide
87:
Stowing
Unused
Wires
[Graphic]
Impropermethodwithbundletiedtoasinglewireaboveit.Propermethodwith
bundletiedandnottiedtoanythingelse[Endgraphic]
[Speakernotes]
Thesephotosshowimproperandproperstowingofunusedwires.
[Endspeakernotes]
Slide88:EWISReplacement
EWIScomponentsshouldbereplacedwhen:o Chafedorfrayedo Insulationsuspectedofbeingpenetratedo Outerinsulationiscrackingo Damagedbyorknowntohavebeenexposedtoelectrolyte,oil,hydraulic
fluid,etc.
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o Evidenceofoverheatingcanbeseen[Speakernotes]
EWISneedstobereplacedunderanumberofcircumstances:
Wiringthathasbeensubjectedtochafingorfraying,thathasbeendamaged,orthat
primary
insulation
is
suspected
of
being
penetrated.
Wiringonwhichtheouterinsulationisbrittlewhenslightflexingcausesittocrack.
Wiringthathasweathercrackedouterinsulation. NOTE:somewireinsulationtypesappearstobewrinkledwhenthewireisbentandmaynotbedamaged.
Wiringthatisknowntohavebeenexposedtoelectrolyteoronwhichtheinsulationappearstobe,orissuspectedofbeing,inaninitialstageof
deteriorationduetotheeffectsofelectrolyte.
Thereisvisibleevidenceofinsulationdamageduetooverheating.[Endspeakernotes]
Slide89:HeatDiscoloration
[Speakernotes]
Thisphotographshowsanexampleofheatdiscolorationonprotectivesleevingwhichispartof
thewirebundle. Thelargeclampwasmovedtoseethedifferenceincolor. Inthiscase,the
wiringthatisnotcoveredinsleevingshowsnosignsofheatdistress. Anadjacentlightbulb
wasradiatingenoughheattocausediscolorationovertimetotheprotectivesleeving.
Althoughthisconditionisnotideal,itisacceptable.
[Endspeaker
notes]
Slide90:WireReplacement
Wireshouldbereplacedwhen:o Wirebearsevidenceofbeingcrushedorkinkedo Shieldonshieldedwireiffrayedand/orcorrodedo Wireshowsevidenceofbreaks,cracks,dirt,ormoistureinplasticsleevingo Sectionsofwirehavesplicesoccurringatlessthan10ftintervals
[Speakernotes]
Continuing,theseareadditionalcircumstancesthatwarrantreplacingEWIS:
EWISthatbearsevidenceofhavingbeencrushedorseverelykinked. ShieldedEWISonwhichthemetallicshieldisfrayedand/orcorroded. Cleaning
agents(whichcancausewiredamage)orpreservativesshouldnotbeusedto
minimizetheeffectsofcorrosionordeteriorationofwireshields.
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EWISshowingevidenceofbreaks,cracks,dirt,ormoistureintheplasticsleevesplacedoverwiresplicesorterminallugs.
Sectionsofwireinwhichsplicesoccuratlessthan10footintervals,unlessspecificallyauthorized,duetoparallelconnections,locations,orinaccessibility.
[Endspeakernotes]
Slide91:WireReplacement,cont.
Shieldingrequirementso Replacementwiresmusthavethesameshieldingcharacteristicsastheoriginal
wire,suchasshieldopticalcoverageandresistanceperunitlength
o Replacementwiresshouldnotbeinstalledoutsidethebundleshield[Speakernotes]
Replacementwiresshouldhavethesameshieldingcharacteristicsastheoriginalwires,suchas
shieldoptical
coverage
and
resistance
per
unit
length.
Ifanywiresaregoingtobereplacedinsideashieldedwirebundle,thereplacementwires
shouldnotbeinstalledoutsidethebundleshield.
Formoreinformationonshielding,theLightning/HIRFVideoandSelfstudyGuideisavailable.
(Toobtain,seeyourDirectoratetrainingmanager.)
[Endspeakernotes]
Slide92:AddingorReplacingWiresonaBundle
[Graphic]
Improperprocedurewithloosewiresnottieddownbetweenclamps.Proper
procedure
with
all
wires
tied
to
the
bundle
between
clamps.
[Endgraphic]
[Speakernotes]
Whenaddingorreplacingwiresonorinawirebundle,thereplacementoraddedwireshould
beroutedinthesamemannerastheotherwiresinthewirebundle.
Wirebundleclampsand/ortiesmayneedtobeloosenedorremovedinordertoproperlyaddorreplacewires.
Whenthenewwireisinstalled,thetiesandclampsshouldbeopenedoneatatimetoavoidexcessivedisassemblyofthewirebundles.
[Endspeakernotes]
Slide93:AddingWiresonaBundle
[Graphic]
FirstimageshowsImproperlyroutedoutsideofthetiewrapthatsecuresthe
clampandthesecondimageshowwiringroutedcorrectly[Endgraphic]
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[Speakernotes]
Properandimproperlyroutedwiresinabundle
[Endspeakernotes]
Slide94:
Wire
Splicing
Keeptoaminimum Avoidinhighvibrationareas Locatetopermitinspection Staggerinbundlestominimizeincreaseinbundlesize Useselfinsulatedspliceconnector,ifpossible
[Speakernotes]
SplicingispermittedonEWISaslongasitdoesnotaffectthereliabilityandtheelectro
mechanicalcharacteristicsoftheEWIS. Splicingofpowerwires,coaxialcables,multiplexbus,
andlarge
gauge
wire
should
be
avoided.
If
it
cant
be
avoided,
then
the
power
wire
splicing
musthaveapproveddata.
Splicingofelectricalwireshouldbekepttoaminimumandavoidedentirelyinlocationssubjecttoextremevibrations. Splicingofindividualwiresinagroupor
bundleshouldhaveengineeringapprovalandthesplice(s)shouldbelocatedto
allowperiodicinspection.
Manytypesofaircraftspliceconnectorsareavailableforusewhensplicingindividualwires.
Useofaselfinsulatedspliceconnectorispreferred;however,anoninsulatedspliceconnectormaybeusedprovidedthespliceiscoveredwithplasticsleeving
thatissecuredatbothends.
EnvironmentallysealedsplicesthatconformtoMILT7928provideareliablemeansofsplicinginSWAMPareas. However,anoninsulatedspliceconnector
maybeused,providedthespliceiscoveredwithdualwallshrinksleevingofa
suitablematerial.
[Endspeakernotes]
Slide95:StaggeredSplices
[Graphic]
Imageshowsasmallsectionwith4splicesandthewiretieplacedsothattwo
splicesareononesideandtwoontheother[Endgraphic]
[Speakernotes]
Splicesinbundlesshouldbestaggeredsoastominimizeanyincreaseinthesizeofthebundle
thatwould:
Preventbundlefromfittingintodesignatedspace. Causecongestionadverselyaffectingmaintenance.
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Causestressonthewires.[Endspeakernotes]
Slide96:Graphic
[Graphic]
Overheatedwireatthesplice
[Endgraphic]
[Speakernotes]
Splicesthatarenotcrimpedproperly(underorover)cancauseincreasedresistanceleadingto
overheatconditions.
[Endspeakernotes]
Slide
97:
Graphic
[Graphic]
Gangedwiresplices
[Endgraphic]
[Speakernotes]
Ifsplicesarenotstaggered,properstrainreliefshouldbeprovidedinordertoavoidstresson
thewires. Inthisparticularinstallation,strainreliefwasappliedtoavoidstressonthewires.
[Endspeakernotes]
Slide98:
Graphic
[Graphic]
Gangedwiresplices,9spliceswith7spliceswithslackand2splicesthataretauntbetweenthe
clamps.
[Endgraphic]
[Speakernotes]
Thetoptwowiresinthisphotoareexperiencingstressduetoapreloadcondition. Alsonote
thatthewirebundleisnotproperlyclamped
[Endspeakernotes]
Slide99:Terminals
Tensilestrengthofthewiretoterminaljointshouldbeatleasttheequivalenttensilestrengthofthewire
Resistanceofthewiretoterminaljointshouldbenegligiblerelativetothenormalresistanceofthewire
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[Speakernotes]
Tensilestrengthterminalsareattachedtotheendsofelectricalwirestofacilitateconnectionof
thewirestoterminalstripsoritemsofequipment. Thetensilestrengthofthewiretoterminal
jointshould
be
at
least
equivalent
to
the
tensile
strength
of
the
wire
itself.
Resistanceofwiretoterminaljointshouldbenegligible,relativetothenormalresistanceof
thewire.
Selectionofwireterminals. Thefollowingshouldbeconsideredintheselectionofwireterminals.
Currentrating.
Wiresize(gauge)andinsulationdiameter.
Conductormaterialcompatibility.
Studsize.
Insulationmaterialcompatibility.
Applicationenvironment.
Solder/solderless.
[Endspeakernotes]
Slide100:BendingofStraightCopperTerminals
[Graphic]
Firstimageshowscopperterminalendbent90degreesmaxtotheleftorright.Secondimage
showsterminalendbentupordown30degreesmax.Thirdimageshowscopperterminalbent
upordown45degreesmax.Fourthimageshowsabrazedjointwithamax30degreeandthe
tongueshouldbeevenwiththeendoftheterminal.
[Endgraphic]
[Speakernotes]
Ifbendingofaterminalisnecessary,careshouldbetakentoavoidoverbendingtheterminal
whichcancausedamagetotheterminal. Also,aterminalcanonlybebentoncesinceany
additionalbendingcancausedamage.
Preinsulatedcrimptyperingtongueterminalsarepreferred. Thestrength,size,and
supportingmeansofstudsandbindingposts,aswellasthewiresize,shouldbeconsidered
whendeterminingthenumberofterminalstobeattachedtoanyonepost.
Inhightemperatureapplications,theterminaltemperatureratingmustbegreaterthanthe
ambienttemperature
plus
current
related
temperature
rise.
Use
of
nickel
plated
terminals
and
ofuninsulatedterminalswithhightemperatureinsulatingsleevesshouldbeconsidered.
Terminalblocksshouldbeprovidedwithadequateelectricalclearanceorinsulationstrips
betweenmountinghardwareandconductiveparts.
Terminalsaresensitivetobendingatthejunctionbetweentheterminalringandtheterminal
crimpbarrel. Bendingtheterminalmorethanonceorexceedingpredeterminedterminal
bendlimitswillusuallyresultinmechanicalweakeningordamagetotheterminal.
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ThisslideisanexampleoflimitsestablishedbytheOAMwithregardtobendingtheterminal
priortoinstallation.
[Endspeakernotes]
Slide101:
Terminal
Strips
Barrierstopreventadjacentstudsfromcontactingeachother Currentshouldbecarriedbyterminalcontactsurfaceandnotbystud Studsanchoredagainstrotation Replacedefectivestudswithstudsofsamesizeandmaterial,mountsecurely,tighten
terminalsecuringnut
[Speakernotes]
Wiresareusuallyjoinedatterminalstrips. Aterminalstripfittedwithbarriersshouldbeused
toprevent
the
terminals
on
adjacent
studs
from
contacting
each
other.
Studsshouldbeanchoredagainstrotation.Whenmorethanfourterminalsaretobeconnectedtogether,asmallmetalbusshouldbemountedacrosstwoor
moreadjacentstuds. Inallcases,thecurrentshouldbecarriedbytheterminal
contactsurfacesandnotbythestuditself.
Defectivestudsshouldbereplacedwithstudsofthesamesizeandmaterialsinceterminalstripstudsofthesmallersizesmayshearduetoovertightening
thenut. Thereplacementstudshouldbesecurelymountedintheterminalstrip
andtheterminalsecuringnutshouldbetight.
[Endspeakernotes]
Slide102:TerminalStrips,cont.
Mountstripssoloosemetallicobjectscannotfallacrossterminal
Providesparestudforbreaksandfutureexpansion
Inspectterminalperiodicallyforlooseconnections,metallicobjects,dirt,andgrease
accumulation
Cancausearcing,resultinginfireorsystemsfailure
[Speakernotes]
[Endspeaker
notes]
Slide103:Terminalsoncircuitbreakers
[Graphic]
terminalwiresconnectedtocircuitbreakerswithseparatescrews
[Endgraphic]
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[Speakernotes]
Connectorsandterminalsinaircraftrequirespecialattentiontoensureasafeandsatisfactory
installation. Everypossibilityofterminalsnotbeingtorquedproperly,duetomisinstallation,
poormaintenance,andservicelife,shouldbeaddressedinthedesign.
Electricalequipmentmalfunctionhasfrequentlybeentracedtopoorterminalconnectionsatterminalboards.
Loosecontactsurfacescanproducelocalizedheatingthatmayignitenearbycombustiblematerialsoroverheatadjacentwireinsulation.
Notethegreentorquestripespaintedontheterminalfastenersinthispicture. Thisisan
excellentmethodtoquicklydetermineifaterminalfastenerisstilltorquedtoitsoriginalvalue.
[Endspeakernotes]
Slide104:Graphic
[Graphic]
Powerfeederterminals
[Endgraphic]
[Speakernotes]
Again,youcanseetheredcoloredtorquestripesappliedtothesehighcurrentpowerfeeder
terminations. Highcurrentterminalsaremoresensitivetoincreasedresistanceduetoa
improperlytorquedterminal.
Asasidenote,thepowerfeedercablesshouldnotbetouchingeachotherwithoutbeingsuitablytiedwithspacersorothersecuringdevice.
[Endspeaker
notes]
Slide105:TerminalLugs
Connectwiringtoterminalblockstuds Nomorethan4lugs,or3lugsand
abusbar,perstud
Lugholesizeshouldmatchstuddiametero Greatestdiameteronbottom,
smallestontop
o Tighteningterminalconnectionsshouldnotdeformlugs
[Speakernotes]
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Wireterminallugsshouldbeusedtoconnectwiringtoterminalblockstudsorequipment
terminalstuds. Nomorethanfourterminallugsorthreeterminallugsandabusshouldbe
connectedtoanyonestud.
Totalnumberofterminallugsperstudincludesacommonbusbarjoiningadjacentstuds. Fourterminallugsplusacommonbusbarthusarenot
permittedon
one
stud.
Terminallugsshouldbeselectedwithastudholediameterthatmatchesthediameterofthe
stud. However,whentheterminallugsattachedtoastudvaryindiameter,thegreatest
diametershouldbeplacedonthebottomandthesmallestdiameterontop.
Tighteningterminalconnectionsshouldnotdeformtheterminallugsorthestuds. Terminal
lugsshouldbesopositionedthatbendingoftheterminallugisnotrequiredtoremovethe
fasteningscrewornut,andmovementoftheterminallugswilltendtotightentheconnection.
[Endspeakernotes]
Slide106:TerminalLugs,cont.
Aluminumlugso Crimpedtoaluminumwireonly
Specialattentionneededtoguardagainstexcessivevoltagedropatterminaljunction
Inadequateterminalcontactarea Stackingerrors Impropertorquing
o Usecalibratedcrimptools[Speakernotes]
Aluminumterminallugsshouldbecrimpedtoaluminumwireonly.Thetongueofthealuminumterminallugsorthetotalnumberoftonguesofaluminumterminal
lugswhenstacked,shouldbesandwichedbetweentwoflatwashers(cadmiumplated)when
terminatedonterminalstuds. Spacersorwashersshouldnotbeusedbetweenthetonguesof
likematerialterminallugs.
Specialattentionshouldbegiventoaluminumwireandcableinstallationstoguardagainst
conditionsthatwouldresultinexcessivevoltagedropandhighresistanceatjunctionsthatmay
ultimatelyleadtofailureofthejunction.
Examplesofsuchconditionsareimproperinstallationofterminalsandwashers,impropertorsion(torquingofnuts),andinadequateterminalcontactareas.
Notethat
aluminum
wire
is
normally
used
in
sizes
of
10
gauge
and
larger
to
carry
electrical
powerinlargetransportcategoryaircraftinordertosaveweight. Althoughnotasgooda
conductorascopper,aluminumislighterwhencomparedtocopperandtheweightsavingscan
besignificantforalargeaircraftthatmayhaveseveralhundredfeetofpowerfeedercable.
Becausealuminumisusedprimarilyforhighcurrentpowerapplications,theterminaljunctions
aremoresensitivetoconditionsleadingtoincreasedjunctionresistancewhichcancausearcing
andlocalizedheatdistress.
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[Endspeakernotes]
Slide107:TerminalStacking(likematerials)[Graphic]
ExplodediagramofTerminalstacking.Frombottomtotop:terminalstud,copperterminallugs,
flatwasher,
lock
washer
and
nut.
[Endgraphic]
[Speakernotes]
Terminalstackingmaterialsandmethods
Multiplewiresoftenterminateontoasingleterminalstud. Careshouldbetakentoinstalltheterminalproperly. Thematerialsthattheterminalsareconstructed
ofwillimpactthetypeofstackingmethodsused. Dissimilarmetals,whenin
contact,canproduceelectrolysisthatcancausecorrosion,thusdegradingthe
terminaljunctionresistanceandcausingarcingorhotspots.
For
stacking
terminals
that
are
made
of
like
materials,
the
terminals
can
be
stackeddirectlyontopofeachother.
[Endspeakernotes]
Slide108:TerminalStacking(unlikematerials)[Graphic]
ExplodediagramofTerminalstacking.Frombottomtotop:terminalstud,flatwasher,
aluminumterminal,flatwasher,copperterminal,flatwasher,aluminumterminal,flatwasher,
lockwasherandnut
[Endgraphic]
[Speakernotes]
Whenstackingunlikematerialstogether(forexample,aluminumandcopper),acadmium
platedflatwasherisusuallyneededtoisolatethedissimilarmetals.
[Endspeakernotes]
Slide109:TerminalStackingMethods
[Graphic]
Explodediagramof"onesidedentrywithtwoterminals.".Frombottomtotop:terminalstud,
crimpbarrel
(belly
down),
crimp
barrel
(belly
up),
flat
washer,
lock
washer
and
nut
[Endgraphic]
[Speakernotes]
Whentwoterminalsareinstalledononesideoftheterminalstrip,careshouldbetakento
ensurethattheterminalcrimpbarrelsdonotinterferewithoneanother. Onemethodtoavoid
thisproblemistoinstalltheterminalswiththebarrelsbacktoback.
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[Endspeakernotes]
Slide110:TerminalStackingMethods,cont.
[Graphic]
Explodediagram
of
"one
sided
entry
with
3terminals."
From
bottom
to
top:
terminal
stud,
crimpbarrel(bellydown)in"V"split,crimpbarrel(bellydown)in"V"split,crimpbarrel(belly
up))incenterof"V"split,flatwasher,lockwasherandnut
[Endgraphic]
[Speakernotes]
Thisillustrationdepictsaterminalinstallationwiththreeterminalsenteringononeside.
[Endspeakernotes]
Slide
111:
Terminal
Stacking
Methods,
cont.
[Graphic]
Explodediagramof"onesidedentrywith4terminals"..Frombottomtotop:terminalstud,
crimpbarrel(bellydown)in"V"split,crimpbarrel(bellydown)in"V"split,crimpbarrel(belly
up))incenterof"V"split,crimpbarrel(bellyup))incenterof"V"split,flatwasher,lock
washerandnut
[Endgraphic]
[Speakernotes]
Thisillustrationdepictsaterminalinstallationwithfourterminalsenteringononeside.
Thestackingmethodusedtoconnectterminalstoterminalstripsshouldcausenointerference
betweenterminals
that
could
compromise
the
integrity
of
the
terminal
junction.
[Endspeakernotes]
Slide112:TerminalTighteningHardware
[Graphic]
Impropertightening:terminalstud,flatwasher,terminals,flatwasher,lockwashernot
compressed,space,andnut.Propertightening:terminalstud,flatwasher,terminals,flat
washer,lockwashercompressed,andnut.
[Endgraphic]
[Speakernotes]
Servicehistoryhasshownthathardwarestackupatterminalsispronetohumanerror.
Omissionoflockwashers,incorrectwashers,impropersizingofwashers,etc.hasbeena
definiteproblem.
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Slide116:Grounding
Typesofgroundingo ACreturnso DCreturnso Others
Avoidmixingreturncurrentsfromvarioussourceso Noisewillbecoupledfromonesourcetoanotherandcanbeamajorproblem
fordigitalsystems
[Speakernotes]
Groundingtypes: ACreturns,DCreturns,andothers.
Mixingreturncurrents. Ifwirescarryingreturncurrentsfromdifferenttypesofsources,such
assignalsorDCandACgenerators,areconnectedtothesamegroundpointorhavea
commonconnectioninthereturnpaths,aninteractionofthecurrentswilloccur. This
interactionmaynotbeaproblem,oritcouldbeamajornonrepeatableanomaly.
Tominimizetheinteractionbetweenvariousreturncurrents,differenttypesofgroundsshouldbeidentifiedandused. Asaminimum,thedesignshoulduse
threegroundtypes: (1)ACreturns,(2)DCreturns,and(3)allothers.
Fordistributedpowersystems,thepowerreturnpointforanalternativepowersourcewouldbeseparated.
Forexample,inatwoACgeneratorsystem(oneontherightsideand
theotherontheleftside),iftherightACgenerator weresupplying
backuppowertoequipmentlocatedintheleftside,(leftequipment
rack)thebackupACgroundreturnshouldbelabeledACRight. The
returncurrentsfortheleftgeneratorshouldbeconnectedtoaground
pointlabeledACLeft.
[Endspeakernotes]
Slide117:Grounding,cont.
Designofgroundpathshouldbegivenasmuchattentionasotherleadsinthesystem Groundingshouldprovideaconstantimpedance Groundequipmentitemsexternallyevenwheninternallygrounded
o Avoiddirectconnectionstomagnesiumstructureforgroundreturn[Speakernotes]
Designof
ground
paths.
The
design
of
the
ground
return
circuit
should
be
given
as
much
attentionastheotherleadsofacircuit.
Constantimpedance. Arequirementforpropergroundconnectionsisthattheymaintainan
impedancethatisessentiallyconstant.
Groundreturncircuitsshouldhaveacurrentratingandvoltagedropadequateforsatisfactoryoperationoftheconnectedelectricalandelectronicequipment.
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EMIproblems,thatcanbecausedbyasystemspowerwire,canbereducedsubstantiallybylocatingtheassociatedgroundreturnneartheoriginofthe
powerwiring(e.g.,circuitbreakerpanel)androutingthepowerwireandits
groundreturninatwistedpair.
Specialcareshouldbeexercisedtoensurereplacementongroundreturnleads.The
use
of
numbered
insulated
wire
leads
instead
of
bare
grounding
jumpers
mayaidinthisrespect.
Externalgroundingofequipmentitems. Ingeneral,equipmentitemsshouldhaveanexternal
groundconnection,evenwheninternallygrounded. Directconnectionstoamagnesium
structure(whichmaycreateafirehazard)mustnotbeusedforgroundreturn.
[Endspeakernotes]
Slide118:Grounding,cont. Heavycurrentgrounds
oAttach
to
individual
grounding
brackets
attached
to
aircraft
structure
with
a
propermetaltometalbond
o Accommodatenormalandfaultcurrentsofsystemwithoutcreatingexcessivevoltagedropordamagetostructure
o Givespecialattentiontocompositeaircraft[Speakernotes]
Heavycurrentgrounds. Powergroundconnectionsforgenerators,transformerrectifiers,
batteries,externalpowerreceptacles,andotherheavycurrentloadsmustbeattachedto
individualgroundingbracketsthatareattachedtoaircraftstructurewithapropermetalto
metalbondingattachment.
Thisattachmentandthesurroundingstructuremustprovideadequateconductivitytoaccommodatenormalandfaultcurrentsofthesystemwithout
creatingexcessivevoltagedropordamagetothestructure.
Atleastthreefasteners,locatedinatriangularorrectangularpattern,mustbeusedtosecuresuchbracketsinordertominimizesusceptibilitytoloosening
undervibration.
Ifthestructureisfabricatedofamaterialsuchascarbonfibercomposite(CFC),whichhasahigherresistivitythanaluminumorcopper,itwillbenecessaryto
provideanalternativegroundpath(s)forpowerreturncurrent.
[Endspeakernotes]
Slide119:Bonding
Equipmentbondingo Lowimpedancepathstoaircraftstructurerequiredforelectronicequipmentto
provideradiofrequencyreturncircuits
o FacilitatesreductioninEMIformostelectricalequipment
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CasesofcomponentsthatproduceEMIshouldbegroundedtostructure[Speakernotes]
Equipmentbonding. Lowimpedancepathstoaircraftstructurearenormallyrequiredfor
electronicequipmenttoprovideradiofrequencyreturncircuitsandformostelectrical
equipmentto
facilitate
reduction
in
EMI.
The
cases
of
components
that
produce
electromagneticenergyshouldbegroundedtostructure.
Toensureproperoperationofelectronicequipment,itisparticularlyimportanttoconformthesystemsinstallationspecificationwheninterconnections,
bonding,andgroundingarebeingaccomplished.
[Endspeakernotes]
Slide120:Bonding,cont.
Metallicsurfacebondingo Electricallyconnectingconductiveexteriorairframecomponentsthroughmechanicaljoints,conductivehinges,orbondstraps
Protectsagainststaticchargesandlightningstrikes[Speakernotes]
Metallicsurfacebonding. Allconductingobjectsontheexterioroftheairframemustbe
electricallyconnectedtotheairframethroughmechanicaljoints,conductivehinges,orbond
strapscapableofconductingstaticchargesandlightningstrikes.
Exceptionsmaybenecessaryforsomeobjectssuchasantennaelements,whosefunctionrequiresthemtobeelectricallyisolatedfromtheairframe. Such items
shouldbeprovidedwithanalternativemeanstoconductstaticchargesand/or
lightningcurrents,
as
appropriate.
[Endspeakernotes]
Slide121:Bonding,cont. Staticbonds
o Requiredforallisolatedconductingpartswithareagreaterthan3in2 andalineardimensionover3"subjectedtoappreciableelectrostaticchargingdueto
precipitation,fluid,orairinmotion
Resistanceoflessthan1ohmwhencleananddryusuallyensuresstaticdissipationonlargerobjects
[Speakernotes]
Staticbonds. Allisolatedconductingpartsinsideandoutsidetheaircraft,havinganarea
greaterthan3in2andalineardimensionover3inches,thataresubjectedtoappreciable
electrostaticchargingduetoprecipitation,fluid,orairinmotion,shouldhaveamechanically
secureelectricalconnectiontotheaircraftstructureofsufficientconductivitytodissipate
possiblestaticcharges.
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Aresistanceoflessthan1ohmwhencleananddrywillgenerallyensuresuchdissipationonlargerobjects. Higherresistancesarepermissibleinconnecting
smallerobjectstoairframestructure.
[Endspeakernotes]
Slide122:EWISIdentification
Necessaryfor:o Safetyofoperationo Safetytomaintenancepersonnelo Easeofmaintenance
Toidentifyperformancecapability,usewirematerialpartnumberandfivedigit/lettercodeidentifyingmanufacturer
[Speakernotes]
Purpose.The
proper
identification
of
EWIS
components
with
their
circuits
and
voltages
is
necessarytoprovidesafetyofoperation,safetytomaintenancepersonnel,andeaseof
maintenance.
Commonmanufacturermarkingprocess. Eachwireandcableshouldbemarkedwithapart
number. Itiscommonpracticeforwiremanufacturerstofollowthewirematerialpartnumber
withthefivedigit/letterC.A.G.E.codeidentifyingthewiremanufacturer. Usingthiscode,
existinginstalledwirethatneedsreplacementcanbeidentifiedastoitsperformance
capabilities. Thishelpstopreventtheinadvertentuseoflowerperformanceandunsuitable
replacementwire.
NOTE:Specialcareshouldbetakenwhenhotstampingwire. Servicehistoryhasshownproblemsassociatedwithhotstampingduetoinsulationdamagecaused
duringthe
process.
ThemethodofidentificationshouldnotimpairthecharacteristicsoftheEWIS. Originalwireidentification. Tofacilitateinstallationandmaintenance,retain
theoriginalwiremarkingidentification. Thewireidentificationmarksshould
consistofacombinationoflettersandnumbersthatidentifythewire,thecircuit
itbelongsto,itsgaugesize,andanyotherinformationtorelatethewiretoa
EWISdiagram. Allmarkingsshouldbelegibleinsize,type,andcolor.
IdentificationandinformationrelatedtotheEWISdiagrams. Thewireidentificationmarkingshouldconsistofsimilarinformationtorelatethewireto
aEWISdiagram.
[Endspeaker
notes]
Slide123:EWISIdentification,cont. Wireidentificationmarksidentifywire,circuit,andgaugesize Markingsshouldbelegibleinsize,type,andcolorat15inchmaximumintervalsalong
thewire(directlyonwireorindirect[sleeve/tag])
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Lessthan3inchesneedsnomarkingo Readablewithoutremovingclamps,ties,orsupportingdevices
[Speakernotes]
MarkingEWISinaircraft. Identificationmarkingsgenerallyareplacedateachendofthewire
andat
15
inch
maximum
intervals
along
the
length
of
the
wire.
Wireslessthan3incheslongneednotbeidentified. Wires3to7inchesinlengthshouldbeidentifiedapproximatelyatthecenter. Addedidentificationmarkersleevesshouldbelocatedsothatties,clamps,or
supportingdevicesneednotberemovedinordertoreadtheidentification.
Thewireidentificationcodemustbeprintedtoreadhorizontally(fromlefttoright)orvertically(fromtoptobottom). Thetwomethodsofmarkingwireor
cableareasfollows:
(1) Directmarkingisaccomplishedbyprintingthecablesouter
covering.
(2)
Indirect
marking
is
accomplished
by
printing
a
heat
shrinkable
sleeveandinstallingtheprintedsleeveonthewireorcablesouter
covering. Indirectmarkedwireorcableshouldbeidentifiedwithprinted
sleevesateachendandatintervalsnotlongerthan6feet. Theindividual
wiresinsideacableshouldbeidentifiedwithin3inchesoftheir
termination.
Themarkingshouldbepermanentsuchthatenvironmentalstressesduringoperationandmaintenancedonotadverselyaffectlegibility.
[Endspeakernotes]
Slide124:MarkingaWireBundle
[Graphic]
Firstimageshowsbundlewithnomarkingandthesecondimageshowsbundlemarkedwith
identificationnumberonatag.
[Endgraphic]
[Speakernotes]
Therecanbeseriousrepercussionswhenthereisasituationinwhichanumberofunmarked
cablesaredisconnected.Whenthecablesreconnected,thechancesarehighthattheywillbe
connectedincorrectly,
thus
causing
numerous
problems.
[Endspeakernotes]
Slide125:Connectors
Manytypes,howevercrimpedcontactsgenerallyused
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o Circulartypeo Rectangularo Moduleblocks
Selectedtoprovidemaximumdegreeofsafetyandreliabilitygivenelectricalandenvironmentalrequirements
o Useenvironmentallysealedconnectorstopreventmoisturepenetration[Speakernotes]
Connectors. ThenumberandcomplexityofEWIShaveresultedinanincreaseduseofelectrical
connectors. Theproperchoiceandapplicationofconnectorsisasignificantpartoftheaircraft
EWISsystem. Connectorsshouldbekepttoaminimum,selected,andinstalledtoprovidethe
maximumdegreeofsafetyandreliabilitytotheaircraft. Fortheinstallationofanyparticular
connectorassembly,thespecificationofthemanufacturershouldbefollowed.
Purposeandtypes. Theconnectorusedforeachapplicationshouldbeselectedonlyaftera
carefuldeterminationoftheelectricalandenvironmental requirements. Considerthesize,
weight,
tooling,
logistic,
maintenance
support,
and
compatibility
with
standardization
programs.
Foreaseofassemblyandmaintenance,connectorsusingcrimpedcontactsaregenerallychosenforallapplicationsexceptthoserequiringahermeticseal.
Areplacementconnectorofthesamebasictypeanddesignastheconnectoritreplacesshouldbeused.
Withacrimptypeconnectorforanyelectricalconnection,theproperinsertion,orextractiontoolshouldbeusedtoinstallorremovewiresfromsucha
connector. Refertomanufactureroraircraftinstructionmanual.
Aftertheconnectorisdisconnected,inspectitforloosesolderedconnectionstopreventunintentionalgrounding.
Connectorsthataresusceptibletocorrosiondifficultiesmaybetreatedwithachemicallyinertwaterproofjellyoranenvironmentallysealedconnectormaybe
used.
NOTE: AlthoughnotrequiredbyAC43.131b,moistureproofconnectorsshouldbeusedinallareasoftheaircraft,includingthecabin. Servicehistoryindicates
thatmostconnectorfailuresoccurduetosomeformofmoisturepenetration.
Eveninthepressurized,environmentallycontrolledareasofthecockpitand
cabin,moisturecanoccurduetorainintheplanetypeofcondensationthat
generallyisaprobleminallmoderntransportcategoryaircraft.
[Endspeaker
notes]
Slide126:CircularConnectors
[graphic]
Threeimagesshowing6differenttypesofcircularconnectors
[Endgraphic]
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[Speakernotes]
AlthoughAC43.131bdoesnotaddresspinlayoutdesignaspects,considerationshouldbe
giventothedesignofthepinarrangementtoavoidsituationswherepintopinshortscould
resultinmultiplelossoffunctionsand/orpowersupplies. Forexample,youwouldavoid115
Vac,400Hzbeinglocatedadjacenttolowpowerwires,suchas28and5Vdc.
Awide
variety
of
circular
environment
resistant
connectors
are
used
in
applications
where
theywillprobablybesubjectedtofluids,vibration,thermal,mechanicalshock,corrosive
elements,etc. Inaddition,firewallclassconnectorsincorporatingthesesamefeaturesshould
beabletopreventthepenetrationofthefirethroughtheaircraftfirewallconnectoropening
andcontinuetofunctionwithoutfailureforaspecifiedperiodoftimewhenexposedtofire.
Hermeticconnectorsprovideapressuresealformaintainingpressurizedareas.
WhenEMI/RFIprotectionisrequired,specialattentionshouldbegiventotheterminationofindividualandoverallshields. Backshelladaptersdesignedfor
shieldtermination,connectorswithconductivefinishes,andEMIgrounding
fingersareavailableforthispurpose.
[Endspeakernotes]
Slide127:CircularConnectors,cont.[graphic]
Imagesshows3differentlockingdevices
[Endgraphic]
[Speakernotes]
Inmediumorhighvibrationareasitmaybenecessarytoprovidealockingdevicetokeepthe
connectorsfrom
loosening.
[Endspeakernotes]
Slide128:ImproperLockWireInstallation
[Speakernotes]
Thisslideshowsalockwireimproperlyinstalled. Thelockwireisinstalledonthe"loosening
sideoftheconnector;itshouldbeonthelighteningside.
[Endspeaker
notes]
Slide129:ProperLockWireInstallation
[Speakernotes]
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Thisisanexampleofaproperlyinstalledlockwireonthelighteningside.
[Endspeakernotes]
Slide130:
Rectangular
Connectors
[graphic]
Imageshowsfourtypesofrectangularconnectors
[Endgraphic]
[Speakernotes]
Rectangularconnectorsaretypicallyusedinapplicationswhereaverylargenumberofcircuits
areaccommodatedinasinglematedpair. Theyareavailablewithagreatvarietyofcontacts,
whichcanincludeamixofstandard,coaxial,andlargepowertypes. Couplingisaccomplished
byvariousmeans.
Smallertypesaresecuredwithscrewsthatholdtheirflangetogether.
Larger
ones
have
integral
guide
pins
that
ensure
correct
alignment,
or
jackscrews
thatbothalignandlocktheconnectors.
Rackandpanelconnectorsuseintegralorrackmountedpinsforalignmentandboxmounting
hardwareforcouplings.
[Endspeakernotes]
Slide131:ModuleBlocks(TerminalBlocks)
[Graphic]
Showstwotypesofmodularblocks
[Endgraphic]
[Speakernotes]
Moduleblocksacceptcrimpedcontactssimilartothoseonconnectors. Someuseinternal
busingtoprovideavarietyofcircuitarrangements.
Moduleblocks(orterminalblocks)areusefulwhereanumberofwiresareconnectedforpowerorsignaldistribution.Whenusedasgroundingmodules,
theysaveandreducehardwareinstallationontheaircraft.
Standardizedmodulesareavailablewithwireendgrommetsealsforenvironmentalapplicationsandaretrackmounted.
[Endspeakernotes]
Slide132:TerminalBlockGrommetDistortion
[Speakernotes]
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Forcomplexwirebreakoutsthatareterminatedintoterminalblocks,caremustbetakento
allowenoughslacktopreventexcessiveforcesfrompullingtheterminatedwiresthatare
insertedintotheterminalblock.
Thisconditioncanleadtoterminalblockgrommetdistortion,whichcanleadtowiredamageorawirethatwillbepulledfreefromtheterminalblock.
[Endspeaker
notes]
Slide133:GrommetDistortion
[Graphic]
FirstimageshowsImproper:grommetdistortionduetotightwires;notenoughslack.Second
imageshowsProper:noexcessivetensiononwires;enoughslacktoavoidgrommetdistortion
[Endgraphic]
Slide
134:
Conduits
Purposeo Mechanicalprotectionofwiresandcableso Groupingandroutingwires
Standardso Absenceofabrasionatendfittingso Properclampingo Adequatedrainholesfreeofobstructionso Minimizeddamagefrommovingobjectso Properbendradii
[Speakernotes]
Purpose. Primarilythepurposeofconduitsisformechanicalprotectionofcablesorwires.
Secondarily,conduitsareusedforenvironmentalprotectionandgroupingofwiresbysignal
type.
Standards
Conduitshouldbeinspectedfor: properendfittings;absenceofabrasionattheendfittings;properclamping;distortion;adequatedrainholesthatarefreeof
dirt,grease,orotherobstructions;andfreedomfromabrasionordamagedueto
movingobjects,suchasaircraftcontrolcablesorshiftingcargo.
Sizeofconduit. Conduitsizeshouldbeselectedforaspecificwirebundleapplication
to
allow
for
ease
in
maintenance,
and
possible
future
circuit
expansion,byspecifyingtheconduitinnerdiameter(I.D.)about25percent
largerthanthemaximumdiameterofthewirebundle.
Conduitfittings.Wireisvulnerabletoabrasionatconduitends. Suitablefittingsshouldbe
affixedtoconduitendsinsuchamannerthatasmoothsurfacecomesincontactwiththewire.
Whenfittingsarenotused,theendoftheconduitshouldbeflaredtopreventwireinsulation
damage. Conduitshouldbesupportedbyuseofclampsalongtheconduitrun.
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[Endspeakernotes]
Slide135:ConduitInstallationGuidelines
Donotlocateconduitwhereserviceormaintenancepersonnelmightuseashandholdor
footstep
Provideinspectabledrainholesatthelowestpointinconduitrunremovedrillingburrscarefully
Supportconduittopreventchafingagainststructureandavoidstressingendfittings[Speakernotes]
Conduitinstallation. Conduitproblemscanbeavoidedbyfollowingtheseguidelines:
Donotlocateconduitwhereserviceormaintenancepersonnelmightuseitasahandholdorfootstep.
Provideinspectabledrainholesatthelowestpointinaconduitrun. Drillingburrs
should
be
carefully
removed.
Supportconduittopreventchafingagainststructureandtoavoidstressingits
endfittings.
[Endspeakernotes]
Slide136:ConduitCovering
[Graphic]
Firstimageshowsdamagedconduitcovering.Secondimageshowsanacceptableconduit
coveringwithnodamage
[Endgraphic]
[Speakernotes]
FODisabigproblemwithdamagedconduitcovering.
[Endspeakernotes]
Slide137:WireInsulationSelection
Chosecharacteristicsbasedonenvironmento Abrasionresistanceo Arcresistanceo Corrosionresistanceo Cutthroughstrengtho Dielectricstrengtho Flameresistanto Mechanicalstrength
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o Smokeemissiono Fluidresistanceo Heatdistortion
[Speakernotes]
Environmentalcharacteristics. Asshowninthisslide,therearemanyinsulationmaterialsand
combinationsusedinaircraftwiring.Wireinsulationcharacteristicshouldbechosenbasedon
meetingFAAflameresistanceandsmokeemissionrequirements(25.869)andtheenvironment
inwhichthewireistobeinstalled.
[Endspeakernotes]
Slide138:FlameResistantInsulatingMaterials
Polymer MilSpec
PTFE 22759/12
ETFE 22759/16
Aromaticpolyamide 81381
Composite 22759/8092
[Speakernotes]
Thesearethefourmostcommontypesofinsulationmaterialsusedinaircrafttoday. Allofthe
wireinsulatingmaterialsinthisslidemeettheminimumFAAsmokeandflammability
standards.
[Endspeakernotes]
Slide139:SelectingInsulatingMaterials
FFAACCTT:: Thereisnnooppeerrffeeccttiinnssuullaattiioonnssyysstteemmforaerospacewireandcable
TThheeddeessiiggnneerrssttaasskk::
Considertradeoffstosecurebestbalanceofproperties Considerinfluenceofdesign,
installationand
maintenance
..........ffoorreeaacchhaapppplliiccaattiioonn!!
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Slide140:HowtoChooseWireInsulation
Seekthebestbalanceofproperties:o Electricalo Mechanicalo Chemicalo Thermal
PPlluuss
Nonflammabilityandlowsmoke
Slide141:ComparativePropertiesofWireInsulationSystems
Ranking1ismostdesirableand4istheleastdesirable
RelativeRanking 1 2 3 4
Weight
PIE
TFE
COMP
PTFE
Temperature PTFE COMP PI ETFE
Abrasionresistance PI ETFE COMP PTFE
Cutthroughresistance PI COMP ETFE PTFE
Chemicalresistance PTFE ETFE COMP PI
Flammability PTFE COMP PI ETFE
Smokegeneration PI COMP PTFE ETFE
Flexibility PTFE ETFE COMP PI
Creep(attemperature) PI COMP PTFE ETFE
Arcpropagation
resistance
PTFE ETFE COMP PI
[Speakernotes]
PI[AromaticPolyimide(KAPTON)] (milspec81381)
Desirableproperties: abrasion/cutthrough,lowsmoke/nonflame,weight/space
Limitations: arctrackresistance,flexibilityETFE(TEFZEL) (milspec22759/16)
Desirableproperties: chemicalresistance,abrasionresistance,easeofuse Limitations: hightemperature,cutthrough, thermalrating(150C)
Composite
(TKT)
(mil
spec
22759/80
92)
Desirableproperties:hightemperaturerating(260C),cutthroughresistance,arctrackresistance
Limitations:outerlayerscuffingPTFE(TEFLON) (milspec22759/12)
Desirableproperties: 260Cthermalrating,lowsmoke/nonflame,highflexibility
Limitations: Cutthroughresistance,creepattemperature
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[Endspeakernotes]
Slide142:ConclusiononInsulation
Aircraftdesignercanchooseamongmanypolymericmaterials Physicalandchemicalpropertiesareequallyimportant Safestsystemcombinesbalanceofpropertieswithinherentflameand/orsmoke
resistance
Slide143:AC25-16:ElectricalFaultandFireDetection
SupplementsexistingguidanceprovidedinAC43.131b Shouldapplytonewairplanes,aswellasmodifications Notintendedtotaketheplaceofinstructionsorprecautionsprovidedby
aircraft/equipmentmanufacturers
[Speakernotes]
ThepurposeofAC2516,ElectricalFaultAndFirePrevention,istoprovideinformationon
electricallycausedfaults,overheat,smoke,andfireintransportcategoryairplanes. Acceptable
meansareprovidedtominimizethepotentialfortheseconditionstooccur,andtominimizeor
containtheireffectswhentheydooccur. Anapplicantmayelecttouseanyothermeansfound
tobeacceptablebytheFAA.
ThisACiscurrentlybeingreviewedandwillberevisedbasedonrecentservicehistoryand
ATSRACrecommendations.
[End
speaker
notes]
Slide144:AC25-16: CircuitProtectionDevices(CPDs)
Circuitbreakerresetso Cansignificantlyworsenanarcingevento Crewshouldonlyattempttoresetatrippedbreakeriffunctionisabsolutely
required
InformationshouldbeprovidedinAFMsorAFMrevisionsorsupplements
[Speakernotes]
InformationshouldbeprovidedinFAAapprovedAirplaneFlightManuals(AFM)orAFM
revisionsorsupplementsthatthecrewshouldonlyattempttorestoreanautomatically
disconnectedpowersourceorresetorreplaceanautomaticallydisconnectedcircuitprotection
device(CPD)thataffectsflightoperationsorsafety.
NOTE: Itisstronglyrecommendedthatcircuitbreakersfornonessentialsystemsnotberesetinflight.
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MosttransportOAMsandoperatorsarerevisingtheirprocedurestonotallowcircuitbreaker
resetsinflightfollowingacircuitbreakertripevent. Servicehistoryhasshownthatresettinga
circuitbreakercangreatlyinfluencethedegreeofarcingdamagetotheEWIS. Eachsuccessive
attempttorestoreanautomaticallydisconnectedCPD,canresultinprogressivelyworsening
effectsfromarcing.
[Endspeaker
notes]
Slide145:ArcTrackingandInsulationFlashover
(Causedbymultiplecircuitbreakerresets)[Graphic]
showswiringburnedandbrokenfromarcing
[Endgraphic]
[Speakernotes]
Thispictureshowstheeffectsofmultiplecircuitbreakerresets. Inthiscase,theoriginalarcing
eventwas
not
able
to
be
determined
due
to
the
severe
secondary
damage
following
the
circuit
breakerresets.
[Endspeakernotes]
Slide146:EWISSeparation
Regulatoryrequirementso Sections25.1707,25.1709,25.903(d),25.631
Manufacturersstandardso Power/signalwireseparation
EMI
concerns
[Speakernotes]
EWISseparation/segregationisafundamentaldesigntechniqueusedtoisolatefailureeffects
suchthatcertainsinglefailuresthatcancompromiseredundancyareminimized. EWIS
separationisalsousedtocontroltheeffectsofEMIinaircraftEWIS.
Fromaregulatorystandpoint,wehaveregulationsinplacethatmayinfluenceEWISdesignwithrespecttoseparation/segregation.
Inaddition,manufacturersmayhavecompanydesignstandardswhichestablishEWISseparationrequirementswithrespecttopowerandsignalroutingwhich
areusuallydrivenfromaEMIstandpoint.
Thenext
few
slides
briefly
present
the
primary
regulations
associated
with
EWIS
separation/segregation.
[Endspeakernotes]
Slide147:SystemSeparation:EWIS25.1707
AppliestoeachEWISonairplane
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RequiresadequatephysicalseparationbetweenEWISandcertainairplanesystemsknowntohavepotentialforcreatingahazardouscondition,forexample:
o Fuelsystemso Hydraulicsystemso Oxygensystemso Water/wastesystems
Slide148:SystemSeparation:EWIS25.1707,cont.
Adequatephysicalseparationmustbeachievedbyseparationdistanceorbyabarrierthatprovidesprotectionequivalenttothatseparationdistance
Hazardous mustperformaqualitativedesignassessmentofinstalledEWISo Useengineering&manufacturingjudgmento EvaluaterelevantservicehistorytodecidewhetheranEWIS,anyothertypeof
system,or
any
structural
component
could
fail
so
that
acondition
affecting
the
airplanesabilitytocontinuesafeoperationcouldresult
Slide149:SystemSafety:EWIS2