2Telecom WIA TrainingSection 1 Fuse Definition and Telecom Circuit Protection NeedsFuse DefinitionA fuse is a calibrated, intentionally weak link in an electrical circuit that provides over-current protection.Circuit Protection Needs in the Telecom SegmentLightningESDInductiveShort Circuit/Power-CrossFuse Technology for Telecom Overcurrent Circuit ProtectionElimination of series line resistance enabling longer loop lengthsPrecise longitudinal balance allowing better transmission qualityTypical Telecom Test StandardsITU K.20 K.21Bellcore GR-1089UL 60950Typical Fuse Test StandardsIEC 60127UL 248MITI
3Fuse Definition and Telecom Circuit Protection A fuse is a calibrated, intentionally weak link in an electrical circuit.Fuses function by reacting to the heat generated from excessive current flow. Once the fuses I2t rating is exceeded, the center conductor opens.A fuse is used to prevent fires and overheating when something goes wrong with electrical equipment. This can be the result of an accident, such as unintentional contact between power and the telephone line, an improper connection/installation, poor maintenance work, or a vandalism.A fuse is intended to operate before a catastrophic event occurs and can create a safety hazard. Electrical components such as capacitors, transformers, resistors, etc., can fail due to a manufacturing defect or old age, and could draw an excessive amount of current and catch fire.A fuse does not prevent a fault from occurring, but will operate quickly to prevent further damage occurring or the equipment becoming a safety hazard. The fuse can also limit the extent of the damage to a small portion of the equipment making repairs less costlyIEC, UL, MITI, and CCC standards all provide definitions and requirements for fuses. For example, IEC-127 gives specific dimensional requirements and also specifying a series of fuse tests.
4Fuse Definition and Telecom Circuit Protection Circuit Protection Needs in Telecom SystemsThunderstorms around the world deliver 8 million lightning flashes every day. Peak current in lightning discharges range from a few KA to many hundreds of KA. Induced currents from indirect strikes range from 10A to 20KA.ESD results from the build up of electrical charge, when two non-conductive materials are brought together then separated. The potential between a human body & an object can exceed 35,000 volts. An ESD event can occur to the telecom system or portable devices through human contact and usage of the telecom devices.Inductive Load Switching is caused when an inductive load is interrupted. It occurs in factory/industrial environments where motors and relays (inductive loads) are turned on and off.Short Circuit or Power Cross events can occur due to human error (such cutting a phone and power line simultaneously during construction) or natural disaster such as hurricane, thunderstorm.One or a combination of the above threats can have obvious adverse effects on semiconductor/IC devices, electro-mechanical contacts, wiring insulation, etc., to cause interruption of telecom equipment operation, telephone service, and even fire.
5Fuse Definition and Telecom Circuit Protection Fuse Technology for Telecom Overcurrent Circuit ProtectionTelecom equipment should be protected from overcurrnent conditions using either PTCs, fuses, power/line feed resistors, or flameproof resistors.A Fuse is a series element placed in front of the overvoltage protector on either Tip or Ring for metallic applications and on both Tip and Ring for longitudinal applications. Due to their stability, fuses are one of the most popular solutions for meeting AC power cross requirements for telecommunications equipment.Littelfuse Telecom WIA Fuses are designed to only interrupt a circuit when extreme fault conditions exist and, when coordinated properly with an overvoltage protector, offer a very competitive and effective solution for transient immunity needs. Advantages include:Elimination of series line resistance enabling longer loop lengthsPrecise longitudinal balance allowing better transmission qualityRobust surge performance which eliminates costly down time due to nuisance blowsGreater surge ratings than resettable devices, ensuring regulatory complianceNon-degenerative performanceTelecommunication equipment best suited for a fuse is equipment that requires surface mount technology (and is thus sensitive to transients), accurate longitudinal balance, and regulatory compliance without the use of additional series line impedance.
6Fuse Definition and Telecom Circuit Protection Telecom System Test StandardsSwitchSLICMDFUndergroundCableOverheadStreetCabinet &SLIC (if onDLC system)NetworkInterfaceDevice(NID)CustomerPremiseEquipment(CPE)Central OfficeSubscriberPremisesDDFOutside PlantYD/T993ITU-T K.21FCC P 68UL 60950UL 497YD/T1082ITU-T K.45GR 1089YD/T 694 or YD/T 940ITU-T K.28YD/T950ITU-T K.20ToPSTNTrunk Line (T1, T3, HDSL, etc.)
8Telecom WIA TrainingSection 2 WIA Fuse Characteristics and Device PhysicsBasic Fuse CharacteristicsElectrical CharacteristicsTC CurveI2tFast Acting and Slo Blo FusesMaximum Ratings (Breaking Capacity)Fuse Voltage RatingPulse Withstanding CurveThermal CharacteristicsDe-ratingFuse Construction and How it Affects Fuse CharacteristicsFuse ConstructionFuse Physics and EquationsFuse I2t and ArcingFuse Element: Slow-blow vs. Fast ActingFuse Body Strength and Breaking Capacity
9WIA Fuse Characteristics and Device Physics Basic Fuse Electrical CharacteristicsTC CurveDefines the fuse opening timeIllustrates phase change of the fuse element stateDirectly denotes the fuse ratingDifference in Slow Blow vs. Fast ActingTypical overload 200% to 800% for electronics fuseAbove 1000% considered to be short circuitI2t1. Adiabatic Process: No heat transfer to surrounding. All energy concentrated in a specific area for a split second.2. Measure of the energy required to open a fuse when subjected to an adiabatic current pulse.3. Due to adiabatic current pulses, the fusing element is stressed both thermally and mechanically. Depending on the energy and number of pulses it could weaken due to aging:- Fatigue- Pre-diffusion- Oxidation
10WIA Fuse Characteristics and Device Physics Fast Acting vs. Slo Blo Fuse Slo Blo:Fast Acting:base=solid, pellet=liquid, mix=solid & liquid diffusion process on goingt = base=solid, pellet=solidt = base=solid, pellet=liquid diffusion process startingt =2 liquid alloy (base+pellet)t =3 Separationt =5 Plasma expands, Burn Back continuesArc Extinguished Fuse Operatedt =4 Arcing Starts and Burn Back of ElementArc Extinguished Fuse Operatedt = 0 solidt =1 liquidsolid & liquidt =2 Separationt =3 Arcing Starts and Burn Back of Elementt =4 Plasma expands, Burn Back continues
11WIA Fuse Characteristics and Device Physics Maximum Ratings (Breaking Capacity)Fuse Voltage RatingThe maximum system voltage for which the fuse can be used without affecting the breaking capacity.When Fuse is subjected to high voltages (>rated voltage) and high currents (> rated breaking capacity), the fuse may explode.Interrupt Rating = Breaking Capacity = Prospective current a fuse can interrupt safelyat rated it’s voltage:- No damage to environment- Fuse remains intact- Insulation resistance maintainedPulse Withstanding CapabilitiesAbility of fuses to sustain a number of adiabatic current pulses containing a specified amount of energy with sufficient cooling in between.- Pulse in % of I²t value- Fuse remains intact with a minimum aging
12WIA Fuse Characteristics and Device Physics Thermal CharacteristicsDe-rating Curve and Fuse Re-ratingTemp. of Fusing Element = Ambient Temp. (TA ) + Temp. Increase caused by Current Flow (dT)+dTFast Acting fusetemperature (°C)°CdTSlo-Blo fuse ( 232°C)TaThe influence of ambient temperature is for Slo Blo fuses much larger then for Fact Acting fuses.
13WIA Fuse Characteristics and Device Physics Fuse ConstructionTerminations (End Cap)Connective MaterialElement/FilamentBodyTerminationsFuse Elements normally consist of a conducting metallic strip or filament of varying geometries and materials depending upon the ampere rating and applicationConnective Material typically solder or conductive epoxyBody material selected to survive Breaking Capacity/Pulse Withstand ratings safelyFiller can aid in achieving specific ratings while maintaining safe operationSpecific Fast or Medium Acting fuse element designsSpecific Slo-Blo or Time delay fuse element designsFiller
14WIA Fuse Characteristics and Device Physics Fuse Physics EquationTC Curve EquationDefined as the difference between the heat generated and the heat lost to the surroundings by the fuse element is the remaining heat energy required to raise the temperature of the fuse element to its melting point. Written as:QI – QL = mCP ( (TE-TS)/Δt) ) = ρAXLCP ( (TE-TS)/Δt) ) where:QI = Heat Generated by Current = I²R CP = Specific Heat of conductorQL = Heat Lost to Surroundings Δt = Temperature change of conductorm = Mass of conductor L = Length of conductorI 2T EquationJoule’s Law can be written as:Power (P) = I²R = mCPΔT / Δt where:m = Mass of conductorCP = Specific Heat of conductorΔT / Δt = Rate of Temperature change of conductorSlo-Blo vs. Fast Acting EquationResistance is expressed asR = pL / A where:p = Resistivity of material (ohm-length)L = Length of materialA = Cross Sectional Area of material
15WIA Fuse Characteristics and Device Physics Fuse I2t and Arcing
16WIA Fuse Characteristics and Device Physics Fuse Elements: Slow-blow vs. Fast ActingDiffusion (Slo-Blo)Non Diffusion (Fast Acting)At high overloads a Slo-Blo in principle acts like a Fast Acting fuse because no time is available to start the diffusion process.- High overloads: about 4In (4x current rating) and higher.Diffusion starts at °C. Slo-Blo fuse elements should not be operated continuously above 150°C to prevent aging.Although no Sn pellet / plating is present it is not recommended to load Fast acting fuses continuously above °C due to:- Oxidation of the fusing-element material- Change of material propertiesNon Diffusion (Fast Acting)Diffusion (Slo-Blo)
17WIA Fuse Characteristics and Device Physics Fuse Body Strength and Breaking CapacityInterrupt Rating = Breaking capacityProspective current a fuse can interrupt safely at it’s rated voltage.- No damage to it’s environment- Fuse body remains intact- Insulation resistance maintained (> 0.5MOhm)Rated Voltage / Voltage Rating:- The maximum system voltage for which the fuse can be used without affecting the breaking capacity- Typically 32, 63, 125, 250, 600V- The rated voltage is marked on the fuse body or terminations(end caps)Breaking Capacity Factors1. Air Pressure from out-gas (due to fuse opening) cannot be larger than fuse body can withstand2. Temperature of fuse body due to fuse element melting and arcing must not be higher than the ignition temperature of the fuse body3. Fuse arcing time (time to extinguish) must not be longer than fuse body can withstand (could cause ignition or even vaporize fuse body)"Equivalent Fuse Body I2t"as Breaking Capacity.
18Section 3 WIA Fuse Telecom Applications Protection Examples Telecom WIA TrainingSection WIA Fuse Telecom Applications Protection ExamplesBasic OV - OC Connection TopologyOV-OC Unit for Telecom Circuit ProtectionCircuit Protection Based on Telecom Applications RequirementsCustomer Premises EquipmentTransformer-Coupled Tip and Ring CircuitsHigh Speed Transmission Equipment & InterfacesADSLT1/E1 ProtectionIDSNAnalog Line CardsSLIC ProtectionData Line ProtectionLAN/WAN ProtectorsLittelfuse Global Lab CapabilitiesQualification of ProductsUL-Approved Customer TestingVerification of StandardsCustomer Application Testing
19WIA Fuse Telecom Application Protection Examples Basic OV - OC Connection TopologyOC device (Fuse Open, PTC Trip)OV device to suppress transientOC device placed in front of OV devices (to help if OV device fails short)Example: Basic OV – OC Protection
20WIA Fuse Telecom Application Protection Examples Customer Premises Equipment (CPE)CPE is defined as any telephone terminal or network equipment which resides at the customer's site and is connected to the Public Switched Telephone Network (PSTN)Protection Requirements:CPE should be protected against overvoltages that can exceed 800V and against surge currents up to 100A. It should meet regulatory standards such as TIA -IS-968 and UL 60950Example: Basic CPE (Phone, Modem) Protection Application
21WIA Fuse Telecom Application Protection Examples High Speed Transmission Equipment & InterfacesHigh speed transmission equipment encompasses a broad range of transmission protocols such as T1/E1, xDSL, and ISDN. Transmission equipment is located at the central office, customer premises, or remote locations.Protection Requirements:High speed transmission equipment should be protected against overvoltages that can exceed 2500V and against surge currents up to 500A. It should meet regulatory standards such as TIA -IS-968, GR 1089-CORE, ITU K.20/K.21, and UL 60950Example: T1/E1 Protection Application
22WIA Fuse Telecom Application Protection Examples Analog Line CardsAnalogy Line cards are highly susceptible to transient voltages that are deployed at the central office and in remote switching locations.Protection Requirements:It is often necessary to protect Analogy line cards by on-hook (relay) and off-hook (SLIC) protection. It should meet regulatory standards such as TIA -IS-968, GR 1089-CORE, ITU K.20/K.21, and UL 60950Example: SLIC Protection Application
23WIA Fuse Telecom Application Protection Examples Data Line ProtectionIn many office and industrial locations, data lines such as RS-232, Ethernet, and AC power lines run in close proximity to each other, which often results in voltage spikes being induced onto data lines, possibly causing damage to sensitive equipment.Protection RequirementsData lines should be protected against overvoltages that can exceed 1500V and surge currents up to 50A.Example: 10 Base-T Longitudinal Protection Application
24WIA Fuse Telecom Application Protection Examples Global Lab CapabilitiesQualification of all LF productsUL-Approved Customer Testing in ISO Lab (Des Plaines)High power (AC/DC up to 1KV/50KA) UL approvals available in DPTelcordia approvals in DP planned (2008)Verification of Telcordia, ITU, IEC, FCC, and other industry, regulatory, and safety standardsVerification to various OC and OV standardsInsure application meets standards before submitting for approvalCustomer Application testingAssistance with design-in and performance verificationHelp with selection of appropriate technology and ratingApplication troubleshootingAssistance insuring proper OV/OC and primary/secondary protection coordinationCompetitive evaluationsCompetitive or technology performance comparisonsReliability & Tin Whisker data/testing
25Telecom WIA TrainingSection 4 WIA Fuse Telecom Application Product SelectionTypical WIA Fuse Types for Telecom and Related Design FeaturesTypical Axial Type Fuse (TR-5, Pico, 5x20, etc.)Typical Surface Mount Type Fuse (Nano, Telecom Nano)Fuse Type/Series selectionIdentify Fuse Dimensional RequirementsIdentify Fuse Breaking Capacity RequirementFuse rating selectionIdentify Fuse Opening TimeIdentify Fuse I2t RequirementIdentify Fuse De-rating Requirement
26WIA Fuse Telecom Application Product Selection Typical WIA Fuse Types for Telecom ApplicationsApplicationDesign Feature RequiredWIA fuseNetwork ModemsAnalog, xDSL, ISDN, T1Must meet UL rd Edition/UL 1549 and FCC 46 Part 68 specificationsTele-Link (461 series)2AG Slo-Blo Fuse (230 Series)Desktop/PC-Card ModemsMust meet UL rd Edition and FCC 46 Part 68 specificationsNANO Slo-Blo Fuse (452 Series)Fax Machines/Business MachinesDesktop TelephonesAnswering MachinesLine Cards and PBXsMust meet UL rd Edition/UL 1549 and FCC 46 Part 68 and Bellcore GR1089-Core specificationsTelecom/Internet GatewaysMust meet UL rd Edition/UL 1458 and Bellcore GR1089-Core specifications
27WIA Fuse Telecom Application Product Selection Fuse Type/Series selectionFuse Voltage RatingThe applied voltage fuse opens safely at (arcing occurs when fuse element melts, the voltage rating is the ability to suppress internal arcing)Covered by NEC (National Electric Code) and ULStandard voltage ratings: 32V, 63V, 125V, 250V, and 600VACFuse Current RatingFuse is sensitive to changes in currentFuse will melt after heated by over-current conditionsTC (Fuse melting time vs. current) curveTypical Power Cross Requirement for FuseMeet 250V voltage rating for power crossMeet 600V 40A (UL 60950)Meet 600V 60A (GR 1089)The TeleLink or 461 seriesRated at 250VMeet 600V 40A or 600V 60A test
30Products Expected to be Released in 2007 Telecom WIA TrainingPROJECTProducts Released in 2006Products Expected to be Released in 2007Target Segment350V Fast Acting Cartridge SeriesBallasts, UPS350V Slo Blo Cartridge SeriesTime Delay Pico SeriesConsumer ElectronicsMETI B 3AB SeriesWhite Goods - Japan MktVarious custom productsALL3.6x10mm PlatformSMPSHigh Amp Nano - 20A - 30AComputer / ServerEnhanced Telelink NanoTelecomTelecom Fuse Array1206 NanoConsumer Electronics, SMPSTE-5 100A Break CapacityTR-5 150A Break CapacityHigh I2t / HBC 215XA5x20mm SMDIndustrial500V 6x32mm FuseUPSIEC Barrier FuseIEC Pico FuseDC Rated Cartridge FusesTR-5 with 125C Operating Temperature
31Telecom WIA Training123456Physical value-added services for better overall efficiencyThe complete package – Cartridge fuse with fuse-clipCartridge fuse ( or Pigtail leaded too ) with Color coded / bandLeaded fuses with kinking / lead formingFuse ( Direct welded type ) with lead formingFuse with heat-shrink tubeFuse pigtail leaded type with longer pigtail lead length (for instance 52mm)Taped and reeled/ammo-packed
32Telecom WIA TrainingElectrical value added services for specific/customized electrical applications and specificationsEnhanced breaking capacity / Short-circuit testing at ;Higher voltagesHigher currentsVDC testingHigher i2t requestAddition of or in accordance withPSEIEC/ULIncreased of rated voltage of fuse32v-rated to 125v-rated or even 250v-rated125v-rated to 250v-rated250v-rated to 350v-rated or any rated voltage neededTighter tolerance of parametersResistance, length, i2t, etc
33Telecom WIA Training Section 6 Telecom WIA Fuse Technology Challenges Fuse TC curve definition and tolerance controlHigher Breaking Capacity/smaller packageMultiple elements in one packageIndication for open fuseFuse reset featureFuse technology combined with other technologies in one packageImproved de-rating characteristicsHigher operating temperatures