Touch (Leakage) CurrentST 07Version 3.0 Overall Session Objectives:1. To understand the rationale for the Touch (leakage) Current Test, instrumentation, connections, test procedures and limits2. To understand limitations of test and alternative approaches Touch (Leakage) CurrentTouch (Leakage) Current Topics Definitions (UL 101, IEC 60990) Touch current paths Physiological effects of touch current (electric shock) Body impedance models and “safe” voltage limits Touch (Leakage) Current TestTouch current instruments (meters)Measurement circuits and proceduresLimitsSpecial SituationsDEFINITIONSLEAKAGE CURRENT (UL101-2002): Electric current which flows through a person upon contact, between accessible parts of an appliance and (1) ground, or (2) other accessible parts of the applianceTOUCH CURRENT (IEC 60990): Electric current through a human body or an animal body when it touches one or more accessible parts of an installation or of equipment.Touch (Leakage) Current PathsAccessible metalLoadLoadElectrical insulation SystemLNG+_VSUngrounded ConductorGrounded ConductorGrounding(protective earthing) Conductor?Touch currentReturnPathTouch Current PathsLoadLoadExample: Ungrounded 2 wire Cord and Plug-Connected Appliancestouchable metalElectrical InsulationSystemTo Electrical SupplyCan openerToaster ovenTVradioCoffee makerironblenderExamples of 2-wire Non-Grounded AppliancesTouch Current PathsGrounded applianceTouchable metalLoadLoadUngrounded 2 wire applianceTouchable Metalof Grounded AppliancesElectrical insulation SystemEquipment Grounding Conductor (protective earthing conductor)GLNG+_VSUngrounded ConductorGrounded ConductorGrounding(protective earthing) ConductorTouch CurrentTouchable metal Return PathsdishwasherrangemicrowaverefrigeratorExamples of 3-wire Grounded AppliancesCan openerToaster ovenTVradioCoffee makerironblenderExamples of 2-wire Non-Grounded AppliancesPlumbingFixturesConstruction GroundsMetallic Piping SystemBonding connectionto water pipeTouch CurrentTouchable metalTouchable metalLoadLoadUngrounded 2 wire applianceElectrical insulation SystemGLNG+_VSUngrounded ConductorGrounded ConductorGrounding(protective earthing) Conductor Return PathsTouch Current PathsSinkExamples of Construction Grounds Baseboard heatingExamples of 3-wire Grounded AppliancesExamples of 2-wire Non-Grounded AppliancesdishwasherrangemicrowaverefrigeratorCan openerToaster ovenTVradioCoffee makerironblenderTouch Current PathsUngrounded 2 wire applianceLoadLoadPathway through earthTouchable metalElectrical insulation SystemSoilL LNGG+_VSUngrounded ConductorGrounded ConductorGrounding(protective earthing) ConductorTouch CurrentReturn PathscCopyright 1998 Underwriters Laboratories Inc.Touch Current PathsTouchable metalLoadLoadElectrical insulation SystemLNG+_VSUngrounded ConductorGrounded ConductorGrounding(protective earthing) ConductorExample: Three - Wire Grounded Cord and Plug Connected productPotential Touch CurrentcCopyright 1998 Underwriters Laboratories Inc.Touch Current PathsTouchable metalLoadLoadElectrical insulation SystemLNG+_VSUngrounded ConductorGrounded ConductorGrounding(protective earthing) ConductorExample: Three - Wire Grounded Cord and Plug Connected productGrounded metal2-wirereceptacle(normal- old construction)OR3 to 2 adapterConnection to Ungrounded ReceptacleTouch CurrentTouchable metalLoadElectrical insulation SystemLNG+_VSUngrounded ConductorGrounded ConductorGrounding(protective earthing) ConductorExample: Three - Wire Grounded Cord and Plug Connected productOpen circuit or highimpedance (fault)Touch Current Pathstouchable metalLoadLNG+_VSUngrounded ConductorGrounded ConductorGrounding(protective earthing) ConductorTouch Current From Simultaneously Touchable Parts of same productLoadZTouch CurrentTouch (Leakage) Current Topics Definitions (UL 101, IEC 60990) Touch current paths Physiological effects of touch current (electric shock)Physiological Effects of Touch Current(sinusoidal, rms, 60 Hz) Perception (microamperes to 0.5 mA) Startle reaction ( 0.5 mA) Muscle tetanization (inability to let go) ( 5 mA) Ventricular fibrillation ( 50 mA) Electrical burns ( 70 mA)V10-00151061010-10.51510102035102103102103104VentricularFibrillationLet-GoStartle Reaction1I = 0.954 f0.716f 70 HzI 0.0007 ff 1 kHzIEC ThresholdUL LimitEffects of Frequency on Electric Shock Thresholdsand Limits for Continuous AC currentBody Current (rms mA)Frequency (Hz)22. In the case of let-go, IECcurve represents average value1. threshold/limit = 2 mA at 0 Hz (dc)(see note 3)3. respiratory arrest observedin dogs at 20, 30, and 40 mA Current Density Duration* Pathway through bodyV10-015cCopyright 1998 Underwriters Laboratories Inc. (skin contact location) Other Touch Current Variables* See Special Situations for Touch Current Measurements Waveshape*Touch (Leakage) Current Topics Definitions (UL 101, IEC 60990) Touch current paths Physiological effects of touch current (electric shock) Body impedance models and “safe” voltage limits+_ZBVsZSIBZB= body impedanceVs= source open circuit voltageZS= source impedanceIB= body currentVSZS(ZB= f , ,.)ZBZS+VsIB= Determining Touch CurrentVoltage SourceR3C1C2R2R1Five Component Body Impedance ModelImpedance representingone skin-electrodecontactInternal body impedance(less the skin)Impedance representingother skin-electrodecontactFactors Affecting Body Impedance condition of skin (affects R1 and R2) other factors:pressure of skin contacttype of skinduration of contacttemperature of skin current pathway through body (affects R3) body size and shape (affects R3) voltage across the body (affects R1 and R2) area of skin contact (affects R1, R2, C1 and C2)R3C1C2R2R1Impedancerepresentingone skin-electrodecontactImpedancerepresentingother skin-electrodecontactInternal body impedance(less the skin)Effect of Current Pathway on Internal Body ImpedanceInternal BodyImpedance (R3)(typical adult)Elbow- 200 ohmsElbow- 200 ohmsTorso-100 ohmsWrist-300 ohmsWrist-300 ohmsKnee-150 ohmsKnee-150 ohmsAnkle-350 ohmsAnkle-350 ohmsWhat is the internal body impedance: Hand to hand? _ohms One hand to both feet? _ohms Both hands to both feet? _ ohmsCLASS EXERCISE:102050100050020010010010000500020001000500200Total body impedance (ohms)50/60 Hz AC voltage (v rms)95%5%Effect of voltage on total body impedance, current path hand to hand, for large surface areas of contact, dry skin (based on IEC 60479)Experiment60075060005000400030002000100002 000500100501000Total body impedance (ohms)Frequency (Hz)Effect of Frequency on Total Body Impedance11. From IEC 60479. Total body impedance of a population for a percentile rank of 50%Current path hand to hand or hand to foot, dry skin conditions, large area contact10 V a.c.25 V 50 V 100 V220 V.0.110100100010,00010.1110100100010,000Total Body ImpedanceKTouch Area of Contactmm 2example for typicaladult male (hand tohand, dry skin,25-150 vac, 50 Hz)(based on IEC 60479-1)25 vac25 vac25 vac25 vac25 vac150 vac150 vac150 vac150 vac150 vactip ofsmall wirepalm of handforefingerpadEffect of surface area ofcontact on total body impedanceohmsSimplified Body Impedance Models3-component model fordry-moist contact andlow touch voltageConservative model forlow skin impedance (e.g.,wet contact, high voltages,and/or high frequency)0.22Microfarad1500 ohms500 ohms500 ohmsCombination two large area skin contactsInternalbodyimpedanceE = I x ZFrequency in Hertz10101010010010010001000100010,00010,00010,000Body Current Threshold for Let-GoApplied Voltage ThresholdFor Let-GoBody ImpedanceZICombined Effects of Frequency on BodyImpedance and Electric Shock ThresholdsFrequency in HertzFrequency in HertzExamples of Safe Voltage Criteria(Check the specific end-product standard) 15 V AC rms ( 100 Hz) 30 V DC 30 V AC rms ( 100 Hz) 60 V DC 42.4 V peak ( 100 Hz)(including dc) 42.4 V peak ( 100 Hz) 60 V DC 71 V peak ( 0.2 secsingle fault conditionsfor time 0.2 secLet-go and fibrillation,dry locations (UL, NEC)Let-go and fibrillation,wet locations, not includingimmersion (UL, NEC)Immersion conditionsGenerally no “safe” voltagesElectrical Insulation:Basic Equipment SafeguardAgainst Electric Shock+_VsZsZBZIITVs= source voltageZI= insulation impedanceZB= body impedanceIT= Touch currentZs= source impedanceHazardous voltage and current source:VS exceeds “safe” voltage ANDIS = VS / Zs exceeds “safe” available currentISIS = available source currentElectricalinsulationmodelInsulationResistanceTestTouch (Leakage)Current TestDielectricWithstandTest (Hi-pot)Basic Tests on Electrical InsulationTouch (Leakage) Current Topics Definitions (UL 101, IEC 60990) Touch current paths Physiological effects of touch current (electric shock) Body impedance models and “safe” voltage limits Touch (Leakage) Current TestTouch current instruments (meters)Touch (Leakage) Current TestAccessible metalLoadLoadElectrical insulation SystemLNG+_VSUngrounded ConductorGrounded ConductorGrounding(protective earthing) ConductorMEASUREMENTINSTRUMENT applies when source exceeds “safe” voltage levels represent body impedance as function of frequency represent physiological effect as a function of frequencyRationale for LimitsRationale for Flexible Metal FoilRationale for Products Requiring EMI Filtering to Meet FCC RequirementsRationale for Humidity ConditioningRationale for Higher Leakage Current LevelsRationale for Choice of Meter, and Alternative MetersRationale for Measurement CircuitsUL 101- Leakage Current for AppliancesSelection of Measurement InstrumentInstrument SpecificationsANSI C101- 1986 - Average Responding System (ARS) (Still specified in mostUL standards)UL 101- 2002 (Replaced ANSI C101)(Specified in some UL end product standards and most harmonized UL standards) IEC 60990 - 1999 SPECIFICATIONS FOR REACTION:SPECIFICATIONS FOR LET-GO:IEC 60990 1999 SPECIFICATIONS FOR ELECTRICAL BURNS:IEC 60990 - 1999 UL101- 2002(0.5 mA rms limit 60 Hz)(3.5 mA rms, 5 mA rms limits 60 Hz)(70 mA rms)Ammeter(averageresponding)0.15 uFC1 Measurement Instrument Specifications for Reaction1500R1(ANSI C101- 1986)(a) Input impedance (Z) (b) Meter type and location(intended to combine effect of frequency on body impedance and physiological response) Average Responding System (ARS)MMVoltmeter(averageresponding)(d) Circuit frequency response ( 0 to 100 kHz)IAIA = actual current to networkI1 = indicated current to network ( = V1/R1 rms for sinusoid)IAII/Z / R1=Z = R1par C1(0 - 100 kHz)Indication (current) =1.11 x VM (ave)/1500 VMI1= I 1 = V1 / R1( rms for sinusoid) (c) Meter indicationMax 5% error indication of 0.75 mA 0.15uFC1 Measurement Instrument Specifications for Reaction1500R1(ANSI C101- 1986)(a) Input impedance (Z) (b) Meter type and location(combines effect of frequency on body impedance and physiological response) Average Responding System (ARS)V1Simpson Model 229 (ANSI C101- 1986)1500R1C1Revised body impedance model500R2Voltmeter0.22uFM10 K0.022uFR3C2Frequency sensitive network for reactionRevised Measurement Instrument for ReactionUL101-2002, IEC 60990- 1999Rms reading(ANSI C101)Peak reading(IEC 60990)1500R1C1Revised body impedance model500R2Voltmeter0.22uFM10 K0.022uFR3C2Frequency sensitive network for reaction(a) Input impedance (UL 101):V1I1Revised Measurement Instrument for ReactionUL 101-1992, IEC 60990- 1999Z= V1 / I1 (20 Hz - 1 MHz) Rms reading(UL101)Peak reading(IEC 60990) 20 50 60 100 200 500 1000 2000 5000 10000 20000 50000 100000 200000 5000001000000Freq (Hz) 1998 1990 1986 1961 1857 1433 973 661 512 485 479 477 476 476 476 476V1 / I1 500 499 498 495 480 405 284 162.9 68.3 34.4 17.21 6.89 3.45 1.722 0.680 0.345V3 / I1(b) Transfer impedance (UL101):Z= V3 / I1 (d) Meter indication (IIndicated): = V3 / R2 = V3 / 500 (weighted mA -IEC 60990; MIU- ANSI C101)(c) Input voltage per mA indication (IEC 60990): 2.00 2.00 1.99 1.98 1.93 1.77 1.71 2.03 3.75 7.06 13.9 34.6 69.1 138 346 691 V1 / IIndicatedV1 / I Indicated (mA) V3Frequency sensitive network for reaction10 KR31500R1C1Body impedance model500R20.22uFIEC 60990- 1999Measurement Instrument for Let-GoFrequency sensitive network for Let-GoM0.0062uF0.0091uF20 KR4C2C3 20 50 60 100 200 500 1000 2000 5000 10000 20000 50000 100000 200000 5000001000000Freq (Hz) 0.250 0.251 0.251 0.253 0.261 0.298 0.348 0.377 0.280 0.164 0.0860 0.0349 0.0175 0.00874 0.00350 0.00175V3 / V1 2.00 1.99 1.99 1.98 1.92 1.68 1.44 1.33 1.79 3.04 5.81 14.3 28.6 57.2 143 286 V1 / IIndicatedV3V1VoltmeterPeak reading(IEC 60990)(a) Output voltage to input voltage ratio:V3 / V1 (20 Hz - 1 MHz) (c) Input voltage per milliampere indication:(b) Meter indication (scale): IIndicated = V3 (peak) / 500Weighted mAV1 / Iindicated (mA) Measurement Instrument for Burns1500R1C1500R20.22uFM( true rmsresponding)Body impedance modelTouch (Leakage) Current Topics Definitions (UL101, IEC 60990) Touch current paths Physiological effects of touch current (electric shock) Body impedance models and “safe” voltage limits Touch (Leakage) Current TestTouch current instruments (meters)Measurement circuits and proceduresMeasurementInstrumentEUT (Equipment Under Test)PowerconnectionsTouch (Leakage) Current Test Measurement Circuit ComponentsPower supplySwitchingnetworkMeasurement Equipment Connections120 VGNDOPENAABBS2S12-pole, 2-wire15 ampnon-polarizedN15 amppolarizedApplicable EUT Plug Configurations2-pole, 3-wireEQUIPMENT UNDER TEST (EUT)LoadPowerSupply20 ampGN15 ampGNLNPolarity reversing switchGrounded conductorswitchMEASUREMENTINSTRUMENTConnection to grounded supply conductorMeasurement Circuit for 120 Volt EquipmentINSULATING TABLEUL101Switching Network120 VAABBS2S12-pole, 2-wire15 ampnon-polarized20 ampG15 ampGN15 amppolarizedApplicable EUT Plug Configurations2-pole, 3-wireEQUIPMENT UNDER TEST (EUT)LoadS3Optionaltransformer1.6 x r ms value (r ms meters)00510152025304.217.1COMPOSITE CURRENT (AC+DC)DC CURRENT - mAAC+DC =-ln (DC/30).68FOR 4.21 DC 30+ DCAC + DC = 7.1FOR DC 4.2151015202530mA peaktitiV10-018cCopyright 1998 Underwriters Laboratories Inc.Let-Go Limits for Combinationsof AC and DC CurrentitititDC COMPONENT IN mACOMPOSITE AC & DC CURRENTIN mA PEAK402605040302010020204.21102020230405060402Ventricular Fibrillation Limits for ContinuousCombinations of AC and DC CurrentVentricular fibrillation threshold and UL limitcurve for single current pulses of short durationCURRENT - mA (rms)20 mAI=20T- 0.7I=6.3T- 0.7300 mAVentricular fibrillation threshold andUL limit curve for 50/60-Hz ACVentricular Fibrillationvs Duration of Current Flow for AC and Single PulsesDuration-secondsIEC-60479 VFThresholds:LowLikelihoodof VFULsGeneralLimitDuration-seconds.00001100100010000100000.0001.001.01.111010CURRENT - mADURATION - SECONDS10000100010010.010.1110Ventricular Fibrillation vs Duration of DC Current300 mAI=20 t- 0.7I = 56.6 t- 0.2556.6 mAIEC-60479 VFThresholds forDC: LowLikelihood ofVFULs Limitfor DCElectrical Stimulation and Electropathology- J. Patrick Reilly- 1992 Cambridge University Press ISBN 0-521-41791-0Physiological Effects of Capacitive DischargeSUMMARY Definitions (UL 101, IEC 60990) Touch current paths Physiological effects of touch current (electric shock) Body impedance models and “safe” voltage limits Touch (Leakage) Current TestTouch current instruments (meters)Measurement circuits and proceduresLimitsSpecial Situations