Specifications

VärmeKabelTeknik Switchpointheating
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11
Functiontestsandfaultdetection
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Checkingthefunctionoftheswitchpointheating
elements
Theswitchpointheatingelementsaremadeoutof
double‐insulatedself‐limitingheatingcablewithan
outputpowerof100W/mat+10°C‐230Vac≈160–
170W/mat–15°C.
Thistypefheatingelementhasacoreofdipped
fluoretheneplastic
whichhastheeffectthatits
resistanceincreaseswhenthetemperaturerises.
Thispropertyallowstheelementstoautomaticallysave
energywhentheweatheriswarm.Italsomeansthat,in
coldweathertherewillbeanextraamountofheat
added.
Resistancemeasuringofself‐limitingelementsisnot
possibleastheresistancevaluereadingdoesnotshowa
valuecorrespondingtothepoweroutput.
Elementtestsaretobeconducted,withvoltage
switchedon,throughmeasuringthecurrentafterabout
15minutes’operation.Thecurrenthasthenstabilized
andcanbecomparedwiththevaluethatwasmeasured
when
theelementwasinstalled.Itshouldbenoted,
however,thatiftestingisdoneinthesummer,thenthe
currentvaluewillbelowerthaninthewinter.Ifthe
currentislessthan0,2A,theelementshouldbe
considereddefective.
99percentofanyvoltageleakagesor
directshort‐
circuitsderivefromfeedercablesorjunctionboxes.The
elementplugscanbeeasilydisconnectedfromthe
distributionboxwhenmeasuring.
Theconnectionblocksmountedonthetracksleeper
areofrubberandcastinonepieceandsocannotcause
ashort‐circuit.Aconnectionblock’sterminalsare
fedby
separateconductorsviaan8‐polecablecastintegral
withtheblock.Currenttestscanthusbeconveniently
carriedoutoneachelement,offtrack,inajointboxin
thecableduct.
Theelementsaredouble‐insulatedandlackprotective
earthing.However,theinsulationresistancebetween
element
andrailmaybetestedbyjoiningthetwopins
oftheplugtoeachotherandthenconnectingthem
jointlytooneoftheterminalsoftheinsulationtester,
theotherterminalbeingconnectedtotherail.
Whenconductingsuchtests,youmustmakesurethat
youdonotcause
anysignallingerrors.
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