The Principles of Fiber-optic Cable Installation - Cabling Install

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How to install fiber optics in the ground

Transcript of The Principles of Fiber-optic Cable Installation - Cabling Install

  • 23.03.2015 TheprinciplesoffiberopticcableinstallationCablingInstall

    http://www.cablinginstall.com/articles/print/volume20/issue2/features/theprinciplesoffiberopticcableinstallation.html 1/17

    TheprinciplesoffiberopticcableinstallationFebruary1,2012

    FromtheFebruary,2012IssueofCablingInstallation&MaintenanceMagazine

    Followingappropriatestepswillensureinstallersachievethefourgoalsofcableinstallation.

    ByEricR.Pearson,PearsonTechnologiesInc.

    Whenexaminingwhatmakesafiberopticnetworksuccessfulfromthestandpointsofinstallationandperformance,thecharacteristicscanbeorganizedintogroupsoffour.Asuccessfulfiberopticnetworkinstallationwillhavefourcharacteristics:1)lowopticalpowerloss,2)lowinstallationcost,3)lowtimeofinstallation,and4)highreliability.Likewise,therearefourgoalsoffiberopticcableinstallation:1)avoidbreakage,2)avoidreducedpoweratthereceiver,3)avoidreductionsinreliability,and4)proceedinasafemanner.Tomeetthesefourgoals,theinstallermustrecognizeandrespectcertainprinciples.Inthisarticle,Iorganizetheseprinciplesintofourgroups:1)environmentallimits,2)installationlimits,3)NationalElectricalCodecompliance,and4)endpreparation.

    Environmentallimits

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    Thenetworkdesignerisresponsibleforspecificationofacableproperfortheintendedenvironment.Withthisdefinitionofresponsibility,theinstallermightnotneedtobeconcernedwithenvironmentlimitations.However,networkdesignersmaynotrecognizeallrelevantenvironmentalconditions.Inorderthattheinstallerrecognizeandavoidcommonfieldproblems,weprovidethisfirstprinciple:Respectenvironmentallimits

    Theinstallerinstallsthecableinenvironmentalconditionsthatarewithinthelimits.Shouldthecablebeexposedtoconditionsinexcessofitslimits,thecablecanfailtoprotectthefibers.Suchfailurecanleadtofiberbreakageandexcessiveattenuationrate.

    Whilenotexhaustive,thislistoffiveenvironmentalconditionsrepresentsmostoftheconditionsthathaveresultedininstallationproblems:moisture,operatingtemperaturerange,bendradii,crushloadanduseloadalongwithverticalrisedistance.

    Moisture.Aninstallercaninstallacablethatisnotmoistureresistantinanenvironmentthatcontainsmoisture.Insuchacase,thecablecanchannelmoistureintoelectronics,developincreasedattenuationrateandfiberbreakageduetofrozenwater,and/orexperiencereducedfiberstrengthandbreakageduetoattackfromthechemicalsingroundwater.

    Operatingtemperaturerange.Ifaninstallerinstallscableinanenvironmentwithtemperaturesoutsideofthecablesoperatingrange,thecablecanexhibitincreasedattenuationand/ordegradationofcablematerials.Intheformercase,theremaybeinsufficientpoweratthereceiverforproperlinkoperation.Inthelattercase,thefibersmaybreak.

    Bendradii.Duringinstallation,theinstallercanbendacabletolessthaneithertheshorttermbendradius(20xcablediameter)orthelongtermbendradius(10xcablediameter).Inthesecases,thecablecandevelopanincreasedattenuationrate,fiberbreakageorreductioninfiberstrength.Suchasituationcanoccurinanundergroundconduitpath,inwhichtheconduitsweep,orelbow,hasaradiuslessthaneitherbendradius(20xor10x)ofthecable.Inthissituationthecablepathitsenvironmentisforcingaviolationofthebendradius.

    Crushloads.Ifaninstallerinstallsacableinanenvironmentthatimposeseitheralongorshorttermcrushloadinexcessofthecableslimit,thecablecanexperienceincreasedattenuationrateandfiberbreakage.Suchasituationcanoccurwhenanindoor,tighttubecableisdirectlyburied.

    Useload.Aninstallercaninstallacablewithlongterm,oruse,loadonthecableinexcessofthecablesrating.Suchaconditioncanoccurwhenthecableisinstalledbetweenwidelyspacedbuildings,widelyspacedtelephonepoles,widelyspacedpowertransmission

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    towers,andupalongverticalrise.Twoproblemscanoccurincreasedattenuationrateandfiberbreakage.

    Aninstallershouldlimitthelongtermloadtoavaluelessthanorequaltothecablesrating.Todoso,theinstallerobtainstheuseloadfromthemanufacturer,typicallyfromadatasheetorfromthemanufacturerswebsite.

    Theinstalleralsoshouldlimitverticalrisedistance.Theuseloadandtheverticalrisedistancearedifferentstatementsofthesamecharacteristic.Theverticalrisedistanceisthedistancetowhichthecablecanbeinstalledverticallywithoutsupport.Theinstallerlimitsthecabletoaverticaldistancelessthantheverticalriselimit.Todoso,theinstallerobtainstheverticalriselimitfromadatasheet.Theinstallercanachieveatotalverticalrisedistanceinexcessofthislimitbysupportingthecableataseparationnogreaterthanthislimit.

    Indoorloosetubecablescanallowthefiberstoslideoutofthecable.Thustheinstallerinstallsserviceloopsinverticalloosetubecable.

    Installationlimits

    Therearetwotypesofcableinstallation:1)pullingthecableintoitspath,and2)placingthecableinitslocation.Theinstallerinstallsthecablewithconditionsthatarewithinthelimitsofthecable.Theoverallprincipleistorespectinstallationlimits.

    Duringthecablepull,theinstallerrespectsfiveinstallationlimits:1)notwisting,2)installationload,3)installationbendradius,4)installationtemperaturerange,5)storagetemperaturerange.

    Notwisting.Avoidanceoffiberbreakagerequiresthatfibercablesbeinstalledwithouttwisting.Inordertoavoidtwisting,theinstallerusesapullingswivelbetweenthepullingropeandthecable.Theinstallerattachesthepullropeandthecabletothepullingeye.

    Inordertocomplywiththeinstallationloadlimit,theinstallermustknowtheloadlimitandhaveamethodforlimitingtheloadappliedtothecable.Theinstallerwilllearnthelimitfromthedatasheetforthecable,creatingtwoprinciples:1)Knowtheinstallationloadlimit2)Limittheinstallationload.

    Therearethreemethodsbywhichaninstallercanlimittheshortterm,orinstallation,loadappliedtoacable.Inaddition,therearetwomethodsforreducingtheappliedinstallationload.

    Thethreemethodshavetheadvantageofprovidingconcreteevidencethattheinstallationloadhasnotbeenexceeded.Thesemethodsaretheuseof1)apullingeyewithaswivelwithashearpin,2)apullingdevicewithaslipclutch,and3)apullingdevicewithaload

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    gage.

    Theeyehasashearpin,whichisratedataloadlessthanthemaximuminstallationloadofthecable.Forexample,acablewitharatingof600poundsforcewouldrequireashearpinrated500500poundsforce.Iftheinstallerexceedstherating,theshearpin(notthecable)breaks.

    Theinstallercanuseapullingeyewithaswivelwithoutashearpiniftheinstallerhassomeothermethodoflimitingtheloadappliedtothecable.Pullershavetwomethodstoprovidesuchlimitation.Thesemethodsareaslipclutchandaloadgage.

    Aninstallercansettheslipclutchofapullertoalevellessthantheinstallationloadofthecable.Shouldtheappliedloadexceedthelevelset,theclutchclips,eliminatingfiberdamage.

    Aninstallercansettheloadgageofapullertoalevellessthantheinstallationloadofthecable.Shouldtheappliedloadexceedthelevelset,theloadgagestopsthepullingmotorwithoutfiberbreakageordamage.Theloadgagehasanadditionaladvantageitallowsattachmentofachartrecorder,whichprovidesproofthattheinstallerdidnotloadthecableinexcessofitsrating.

    Reducingtheload

    Thesethreemethodslimittheloadbutdonothingtoreducetheload.Therearetwomethodsforreducingtheloadappliedtothecable:lubricantandaFigure8installation.

    Theinstallerusesacablelubricanttoreducefrictionandloadonthecable.Whilecoppercablelubricantsexist,theinstallerusesafibercablelubricant,assuchalubricantismatchedtothejacketofthecable.

    Thesecondmethodforreducingtheloadispullingthecablebyhandinmultiple,reducedlengthpulls.Breakingalongpullintomultiplepullsofreducedlengthreducestheloadonthecable.Iftheinstallerinstallsthecableinmultiplepulls,heorshewillstorethecableatintermediatelocationsinaFigure8pattern.Theadvantageofthismethodisreducedload.Thedisadvantageisincreasedlaborcost.

    DuringaFigure8pull,theinstallerpullsthecableintothefirstmanholeandoutofasubsequentmanhole.Thesubsequentmanholemaybethenextmanholealongthecablepath,ortheNthmanholealongthecablepath.Theinstallerdeterminesthismanholebytheloadtheinstalleriswillingtoimposeonthecable.

    Astheinstallerpullsthecablefromthemanhole,heorsheplacesthecableonthegroundinaFigure8pattern.Thispatterncanbe12feetlongand4to6feetwide.Forpractical

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    reasons,thepatternisrarelystackedmorethan24incheshigh.

    Whentheinstallerhaspulledthecableoutofthemanhole,theinstallerandseveralhelperspickuptheFigure8andflipitoversothecableendisontop.Theinstallerputsthecablebackintothesamemanholealongthecablepath.Atthismanhole,theinstallerrepeatstheFigure8patternontheground.Theinstallercanrepeatthisprocessasmanytimesasdesired,untilthecableisinstalledalongtheentirepath.

    TheinstallercanusetheFigure8methodforbothunidirectionalpulls,andmidpulls.Inamidpull,theinstallerpullsthecableinonedirection.TheinstallerplacestheremainingcableinaFigure8patternontheground.Finally,theinstallerpullsthecablefromtheFigure8patternintheoppositedirection.

    Someprofessionalinstallersuseafourthmethodforlimitingtheloadtheyapplyduringinstallation.Thismethodrequirespullinga600poundforcecablebyhand.Theassumptionisthatitisessentiallyimpossibletocreatea600poundloadbyhandpullinginahorizontalaxis.Thismethoddoesnothavetheadvantageofprovidingconcreteevidencet