Hazard Based Safety Engineering Touch Leakage Current 2

Hazard Based Safety Engineering - Touch (Leakage) Current

2 Touch (Leakage) Current Overall Session Objectives: 1. To understand the rationale for the Touch (leakage) Current Test, instrumentation, connections, test procedures and limits 2. To understand limitations of test and alternative approaches

3 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 • Touch (Leakage) Current Test –Touch current instruments (meters) –Measurement circuits and procedures –Limits

4 DEFINITIONS LEAKAGE CURRENT (UL 101 -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 appliance TOUCH 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.

5 Touch (Leakage) Current Paths L Ungrounded Conductor Accessible metal Load + VS Load _ N Grounded Conductor Electrical insulation System G Touch current Grounding (protective earthing) Conductor Return Path ?

Touch Current Paths 6 Example: Ungrounded 2 wire Cord and Plug-Connected Appliances Load To Electrical Supply Load touchable metal Electrical Insulation System

7 radio TV Toaster oven Can opener blender Examples of 2 -wire Non-Grounded Appliances Coffee iron maker

8 Touch Current Paths Return Paths-1 L Ungrounded Conductor Ungrounded 2 wire appliance Touchable metal Load + Touchable metal VS Load _ Grounded appliance Grounded N Conductor G Electrical insulation System Grounding (protective earthing) Conductor G Touchable Metal of Grounded Appliances Equipment Grounding Conductor (protective earthing conductor) Touch Current

9 microwave Coffee maker radio TV blender range Can opener Toaster oven dishwasher Examples of 2 -wire Non-Grounded Appliances Examples of 3 -wire Grounded Appliances refrigerator iron

10 Touch Current Paths Return Paths-2 Touchable metal Ungrounded Conductor L Ungrounded 2 wire appliance Load + Touchable metal VS Load _ Plumbing Fixtures Grounded N Conductor G Electrical insulation System Grounding (protective earthing) Conductor Construction Grounds G Bonding connection to water pipe Metallic Piping System Touch Current

11 microwave radio TV blender Sink range Coffee maker Can opener Toaster oven dishwasher refrigerator Baseboard heating Examples of 2 -wire Non-Grounded Appliances Examples of 3 -wire Grounded Appliances Examples of Construction Grounds iron

Touch Current Paths Return Paths-3 L Ungrounded Conductor Touchable metal Ungrounded 2 wire appliance Load + VS Load _ Grounded N Conductor G Electrical insulation System Grounding (protective earthing) Conductor Pathway through earth Soil Touch Current 12

Touch Current Paths 13 Example: Three - Wire Grounded Cord and Plug Connected product L Ungrounded Conductor Load + Touchable metal VS Load _ Grounded N Conductor G Grounding (protective earthing) Conductor Electrical insulation System Potential Touch Current

Touch Current Paths Example: Three - Wire Grounded Cord and Plug Connected product L Ungrounded Conductor Load + Touchable metal VS Load _ Grounded N Conductor G Grounding (protective earthing) Conductor Electrical insulation System 14

15 Example: Three - Wire Grounded Cord and Plug Connected product Connection to Ungrounded Receptacle L Touchable metal Ungrounded Conductor + VS Load _ Grounded N Conductor G Grounded metal Open circuit or high impedance (fault) Grounding (protective earthing) Conductor 3 to 2 adapter OR Electrical insulation System 2 -wire receptacle (normal- old construction) Touch Current

Touch Current Paths-4 Touch Current From Simultaneously Touchable Parts of same product L Ungrounded Conductor Load + touchable metal VS Load _ Grounded N Conductor G Grounding (protective earthing) Conductor Touch Current Z 16

17 Touch (Leakage) Current Topics • Definitions (UL 101, IEC 60990) • Touch current paths • Physiological effects of touch (electric shock) current

18 Physiological Effects of Touch Current (sinusoidal, rms, 60 Hz) • Perception (microamperes to 0. 5 m. A) • Startle reaction (> 0. 5 m. A) • Muscle tetanization (inability to let go) (> 5 m. A) • Ventricular fibrillation (> 50 m. A) • Electrical burns (> 70 m. A) V 10 -001

3 19 Effects of Frequency on Electric Shock Thresholds and Limits for Continuous AC current Body Current (rms m. A) 10 10 IEC Threshold UL Limit Ventricular Fibrillation 2 I = 0. 954 f 0. 716 f > 70 Hz (see note 3) 35 20 2 Let-Go I ~ 0. 0007 f 10 f > 1 k. Hz 5 1. threshold/limit = 2 m. A at 0 Hz (dc) 1 Startle Reaction 1 2. In the case of let-go, IEC curve represents average value 0. 5 3. respiratory arrest observed in dogs at 20, 30, and 40 m. A -1 10 10 10 2 3 4 10 10 Frequency (Hz) 5 10 6 10

20 Other Touch Current Variables • Waveshape* • Duration* • Current Density • Pathway through body • (skin contact location) * See Special Situations for Touch Current Measurements V 10 -015

21 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

22 Determining Touch Current Voltage Source Z + V Z B B = = Z Z s_ V I S S I s + Z B f ( V S , Z S , . . . ) B V Z B I B = body current s = source open circuit voltage S Z B = source impedance = body impedance

23 Five Component Body Impedance Model C R 1 1 R Internal body impedance (less the skin) 3 C 2 Impedance representing one skin-electrode contact R 2 Impedance representing other skin-electrode contact

Effect of Current Pathway on Internal Body Impedance 24 Internal Body Impedance (R 3) (typical adult) Elbow- 200 ohms Wrist 300 ohms Torso 100 ohms Elbow- 200 ohms Wrist 300 ohms Knee 150 ohms CLASS EXERCISE: What is the internal body impedance: Hand to hand? _____ohms Ankle 350 ohms One hand to both feet? ____ohms Both hands to both feet? ______ ohms

Simplified Body Impedance Models 3 -component model for dry-moist contact and low touch voltage 0. 22 Microfarad Combination two large area skin contacts 1500 ohms Conservative model for low skin impedance (e. g. , wet contact, high voltages, and/or high frequency) 500 ohms Internal body impedance 25

26 Combined Effects of Frequency on Body Impedance and Electric Shock Thresholds Z Body Impedance 10 I 1000 10, 000 Frequency in Hertz Body Current Threshold for Let-Go E=Ix. Z 10 1000 10, 000 Frequency in Hertz Applied Voltage Threshold For Let-Go 10 1000 10, 000 Frequency in Hertz

Examples of "Safe" Voltage Criteria (Check the specific end-product standard) Let-go and fibrillation, dry locations (UL, NEC) 30 V AC rms (< 100 Hz) 60 V DC Let-go and fibrillation, wet locations, not including immersion (UL, NEC) 15 V AC rms (< 100 Hz) 30 V DC Immersion conditions Dry locations where startle reaction cannot be tolerated (UL) Generally no “safe” voltages 42. 4 V peak (< 100 Hz) (including dc) IEC SELV circuits: normal conditions and single fault conditions for time > 0. 2 sec 42. 4 V peak (< 100 Hz) 60 V DC single fault conditions for time < 0. 2 sec 71 V peak (< 100 Hz) 120 V DC 27

28 Electrical Insulation: Basic Equipment Safeguard Against Electric Shock Zs ZI + Vs _ Vs = source voltage Zs = source impedance Hazardous voltage and current source: IS ZI = insulation impedance ZB = body impedance IT ZB IS = available source current IT = Touch current VS exceeds “safe” voltage AND IS = VS / Zs exceeds “safe” available current

29 Basic Tests on Electrical Insulation Electrical insulation model Insulation Resistance Test Touch (Leakage) Current Test Dielectric Withstand Test (Hi-pot)

30 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 • Touch (Leakage) Current Test –Touch current instruments (meters)

31 Touch (Leakage) Current Test L Ungrounded Conductor Accessible metal MEASUREMENT INSTRUMENT Load + VS Load _ N Grounded Conductor Electrical insulation System G Grounding (protective earthing) Conductor • applies when source exceeds “safe” voltage levels • represent body impedance as function of frequency • represent physiological effect as a function of frequency

32 Selection of Measurement Instrument Specifications SPECIFICATIONS FOR REACTION: (0. 5 m. A rms limit @ 60 Hz) ANSI C 101 - 1986 - Average Responding System (ARS) (Still specified in most UL standards) UL 101 - 2002 (Replaced ANSI C 101)(Specified in some UL end product standards and most harmonized UL standards) IEC 60990 – 1999 SPECIFICATIONS FOR LET-GO: (3. 5 m. A rms, 5 m. A rms limits @ 60 Hz) IEC 60990 - 1999 SPECIFICATIONS FOR ELECTRICAL BURNS: (70 m. A rms) UL 101 - 2002 IEC 60990 - 1999

33 Measurement Instrument Specifications for Reaction Average Responding System (ARS) (ANSI C 101 - 1986) R 1 Ammeter M (average responding) 1500 Ω C 1 0. 15 u F (a) Input impedance (Z) (intended to combine effect of frequency on body impedance and physiological response) (b) Meter type and location

34 Measurement Instrument Specifications for Reaction Average Responding System (ARS) (ANSI C 101 - 1986) IA = actual current to network I 1 = indicated current to network ( = V 1/R 1 rms for sinusoid) IA II / IA = Z / R 1 V 1 I 1 R 1 1500 Ω C 1 0. 15 Z = R 1 par C 1(0 - 100 k. Hz) VM u. F (a) Input impedance (Z) (combines effect of frequency on body (b) Meter type and location impedance and physiological response) (c) Meter indication (d) Circuit frequency response ( 0 to 100 k. Hz) M Voltmeter (average responding) Indication (current) = 1. 11 x VM (ave)/1500 = I 1 = V 1 / R 1 ( rms for sinusoid) Max 5% error @ indication of 0. 75 m. A

35 Simpson Model 229 (ANSI C 101 - 1986)

Revised Measurement Instrument for Reaction Freq (Hz) V / I UL 101 -1992, IEC 60990 - 1999 20 1998 I 1 50 1990 1 R 1 1500 Ω V 1 C 1 0. 22 u. F 60 100 200 500 1000 2000 5000 10000 20000 50000 100000 200000 500000 1000000 36 1 1986 1961 1857 1433 973 661 512 485 479 477 476 476 V 1 / IIndicated V 3 / I 1 500 499 498 495 480 405 284 162. 9 68. 3 34. 4 17. 21 6. 89 3. 45 1. 722 0. 680 0. 345 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 10 K Ω R 2 500 Ω R 3 0. 022 u F C 2 M V 3 Voltmeter Revised body impedance model Frequency sensitive network for reaction Rms reading (UL 101) (a) Input impedance (UL 101): Z= V 1 / I 1 (20 Hz - 1 MHz) Peak reading (b) Transfer impedance (UL 101): Z= V 3 / I 1 (IEC 60990) (c) Meter indication (IIndicated): = V 3 / R 2 = V 3 / 500 (weighted m. A -IEC 60990; (d) Input voltage per m. A indication (IEC 60990): V 1 / I Indicated (m. A) MIU- ANSI C 101)

Measurement Instrument for Let-Go IEC 60990 - 1999 R 1 1500 Ω V 1 C 1 0. 22 u. F 37 V 3 / V 1 Freq (Hz) 20 50 60 100 200 500 1000 2000 5000 10000 20000 50000 100000 200000 500000 1000000 V 1 / IIndicated 0. 250 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. 00175 2. 00 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 10 K Ω R 2 500 Ω R 3 C 2 0. 0091 u. F 0. 0062 u. F C 3 R 4 M V 3 20 K Ω Voltmeter Body impedance model Frequency sensitive network for Let-Go reaction Peak reading (a) Output voltage to input voltage ratio: V 3 / V 1 (20 Hz - 1 MHz) (b) Meter indication (scale): IIndicated = V 3 (peak) / 500 Weighted m. A (c) Input voltage per milliampere indication: V 1 / Iindicated (m. A) (IEC 60990)

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39 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 • Touch (Leakage) Current Test –Touch current instruments (meters) –Measurement circuits and procedures

Touch (Leakage) Current Test Measurement Circuit Components Power supply Power connections EUT (Equipment Under Test) Measurement Instrument Switching network Measurement Equipment Connections 40

41 Measurement Circuit for 120 Volt Equipment Switching Network UL 101 L Polarity reversing switch EQUIPMENT UNDER TEST (EUT) S 2 Power Supply A MEASUREMENT INSTRUMENT B Load 120 V N A S 1 B GND OPEN INSULATING TABLE Grounded conductor switch Connection to grounded supply conductor Applicable EUT Plug Configurations G N 15 amp non-polarized 15 amp polarized 2 -pole, 2 -wire N 15 amp G N 20 amp 2 -pole, 3 -wire

Optional transformer 42 Measurement Circuit for 120 Volt Equipment IEC 60990 L EQUIPMENT UNDER TEST (EUT) S 2 A 120 V supply MEASUREMENT INSTRUMENT B Load 120 V N S 1 G S 3 A B < 1% line voltage For 3 -wire applications Applicable EUT Plug Configurations G G 15 amp 20 amp N 15 amp non-polarized 15 amp polarized 2 -pole, 2 -wire 2 -pole, 3 -wire

43 Measurement circuit for 2 - pole 208 or 230 -240 Volt equipment suitable for use on 230 -240 volt to ground circuit (U. S. Commercial / Industrial) (European 230/400 v residential) L Polarity reversing switch EQUIPMENT UNDER TEST (EUT) S 2 Power Supply A MEASUREMENT INSTRUMENT B 208 or 230 -240 V Load A S 1 L N B GND OPEN INSULATING TABLE Line Switch Connection to grounded supply conductor Applicable U. S. EUT Plug Configurations 15 amp 20 amp 2 -pole, 2 -wire G G 15 amp 20 amp 2 -pole, 3 -wire

Measurement circuit for 2 - pole 208 and 240 volt equipment for connection only to 120 volts to ground circuits (120/208, 120/240) (U. S. Residential) Power Supply Polarity reversing switch L S 2 A 120 V 208 or 240 V EQUIPMENT UNDER TEST (EUT) B N Load 120 V L A S 1 B GND OPEN Line Switch INSULATING TABLE Connection to grounded supply conductor Applicable U. S. EUT Plug Configurations 15 amp 20 amp 2 -pole, 2 -wire G G 15 amp 20 amp 2 -pole, 3 -wire MEASUREMENT INSTRUMENT 44

Measurement circuit for single phase, 3 - pole, 208 or 240 Volt Equipment (e. g. , electric ranges, clothes dryers) Power Supply 208 or 240 V Polarity reversing switch L S 2 120 V A GND OPEN EQUIPMENT UNDER TEST (EUT) MEASUREMENT INSTRUMENT B N Load 120 V S 1 A B L INSULATING TABLE Line and Neutral Switch Connection to grounded supply conductor Applicable U. S. EUT Plug Configurations G N N 20 amp 3 -pole, 3 -wire N G N 15 amp 20 amp 3 -pole, 4 -wire 30 amp 45

46 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 • Touch (Leakage) Current Test –Touch current instruments (meters) –Measurement circuits and procedures –Limits

47 Touch (Leakage) Current Test Limits UL 101 - 2002 Recommendations Type of appliance Indication in MIU Two-wire cord- and plugconnected appliance 0. 50 MIU Three-wire (including grounding conductor) cord- and plug- connected portable appliance 0. 50 MIU Three-wire (including grounding conductor) cord- and plug- connected stationary or fixed appliance 0. 75 MIU All 70 m. A rms (electric burn)

48 SUMMARY • 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 Test –Touch current instruments (meters) –Measurement circuits and procedures –Limits

49 Questions and Answers

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