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Transcript
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 (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
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
Can opener
TV
Toaster oven
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
refrigerator
dishwasher
Examples of 2-wire Non-Grounded Appliances
Examples of 3-wire Grounded Appliances
iron
10
Touch Current Paths
Return Paths-2
L
Touchable metal
Ungrounded
Conductor
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
Coffee
maker
radio
TV
blender
Sink
range
Can opener
Toaster oven
refrigerator
dishwasher
Baseboard heating
Examples of 2-wire Non-Grounded Appliances
Examples of 3-wire Grounded Appliances
Examples of Construction Grounds
iron
12
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
13
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
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
16
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
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 mA)
• Startle reaction (> 0.5 mA)
• Muscle tetanization (inability to let go) (> 5 mA)
• Ventricular fibrillation (> 50 mA)
• Electrical burns (> 70 mA)
V10-001
3
19
Effects of Frequency on Electric Shock Thresholds
and Limits for Continuous AC current
Body Current (rms mA)
10
IEC Threshold
UL Limit
Ventricular
Fibrillation
10
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 kHz
5
1. threshold/limit
= 2 mA 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 mA
-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
V10-015
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
S
+
V
s_
V
I
B
Z
I
s
=
Z
S
+
Z
B
V
Z
=
B
f ( V S , Z S , .....)
B
= body current
s = source open circuit voltage
B
Z
B
I
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 (R3)
(typical adult)
Elbow- 200 ohms
Elbow- 200 ohms
Wrist300 ohms
Torso100 ohms
Wrist300 ohms
Knee150 ohms
Knee150 ohms
CLASS EXERCISE:
What is the internal body impedance:
Hand to hand? _________ohms
Ankle350 ohms
Ankle350 ohms
One hand to both feet? ________ohms
Both hands to both feet? ______ ohms
25
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
500 ohms
Internal
body
impedance
26
Combined Effects of Frequency on Body
Impedance and Electric Shock Thresholds
Z
Body Impedance
10
I
100
1000
10,000
Frequency
in Hertz
Body Current Threshold for Let-Go
E=IxZ
10
100
1000
10,000
Frequency
in Hertz
Applied Voltage Threshold
For Let-Go
10
100
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:
IT
ZB
IS
ZI = insulation impedance
ZB = body impedance
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
Instrument Specifications
SPECIFICATIONS FOR REACTION:
(0.5 mA rms limit @ 60 Hz)
ANSI C101- 1986 - Average Responding System (ARS) (Still specified in
most UL standards)
UL 101- 2002 (Replaced ANSI C101)(Specified in some UL end
product standards and most harmonized UL standards)
IEC 60990 – 1999
SPECIFICATIONS FOR LET-GO: (3.5 mA rms, 5 mA rms limits @ 60 Hz)
IEC 60990 - 1999
SPECIFICATIONS FOR ELECTRICAL BURNS:
UL101- 2002
IEC 60990 - 1999
(70 mA rms)
33
Measurement Instrument Specifications for Reaction
Average Responding System (ARS) (ANSI C101- 1986)
R1
Ammeter
M
(average
responding)
1500 Ω
C1
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 C101- 1986)
IA = actual current to network
I1 = indicated current to network ( = V1/R1 rms for sinusoid)
IA
II / IA = Z / R1
V1
I1
R1
1500 Ω
C1
0.15
Z = R1par C1(0 - 100 kHz)
VM
M
uF
(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 kHz)
Voltmeter
(average
responding)
Indication
(current) = 1.11 x
VM (ave)/1500
= I 1 = V1 / R1
( rms for sinusoid)
Max 5% error @
indication of 0.75 mA
35
Simpson Model 229 (ANSI C101- 1986)
Revised Measurement Instrument for ReactionV / I
Freq (Hz)
UL 101-1992, IEC 60990- 1999
20
1998
I1
50
1990
1
R1
1500 Ω
V1
C1
0.22uF
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
476
476
V1 / IIndicated
V 3 / I1
500
499
498
495
480
405
284
162.9
68.3
34.4
17.21
6.89
3.45
1.722
0.680
0.345
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
10 K Ω
R2
500 Ω
R3
0.022 u F
C2
M
V3
Voltmeter
Revised body impedance model Frequency sensitive network for reaction Rms reading
(UL101)
(a) Input impedance (UL 101):
Z= V1 / I1 (20 Hz - 1 MHz)
Peak reading
(b) Transfer impedance (UL101): Z= V3 / I1
(IEC 60990)
(c) Meter indication (IIndicated): = V3 / R2 = V3 / 500 (weighted mA -IEC 60990;
(d) Input voltage per mA indication (IEC 60990): V1 / I Indicated (mA)
MIU- ANSI C101)
Measurement Instrument for Let-Go
IEC 60990- 1999
R1
1500 Ω
V1
C1
0.22 uF
37
V3 / V 1
Freq (Hz)
20
50
60
100
200
500
1000
2000
5000
10000
20000
50000
100000
200000
500000
1000000
V1 / IIndicated
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
0.00175
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
10 K Ω
R2
500 Ω
R3
C2
0.0091
uF
0.0062
uF
C3
R4
M
V3
20 K Ω
Voltmeter
Body impedance model Frequency
Frequency sensitive
sensitive network
network for
for Let-Go
reaction Peak reading
(a) Output voltage to input voltage ratio: V3 / V1 (20 Hz - 1 MHz)
(b) Meter indication (scale): IIndicated = V3 (peak) / 500 Weighted mA
(c) Input voltage per milliampere indication: V1 / Iindicated (mA)
(IEC 60990)
38
39
Touch (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 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 UL101
L
Polarity reversing switch
EQUIPMENT UNDER TEST (EUT)
S2
Power
Supply
A
MEASUREMENT
INSTRUMENT
B
Load
120 V
N
A
S1
B
GND
OPEN
INSULATING TABLE
Grounded conductor
switch
Connection to grounded supply conductor
Applicable EUT Plug Configurations
G
G
N
15 amp
non-polarized
15 amp
polarized
2-pole, 2-wire
N
N
15 amp
20 amp
2-pole, 3-wire
42
Optional
transformer
Measurement Circuit for 120 Volt Equipment
IEC 60990
L
EQUIPMENT UNDER TEST (EUT)
S2
A
120 V
supply
MEASUREMENT
INSTRUMENT
B
Load
120 V
N
S1
G
S3
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)
S2
Power
Supply
A
MEASUREMENT
INSTRUMENT
B
208 or 230-240 V
Load
A
S1
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
EQUIPMENT UNDER TEST (EUT)
S2
A
120 V
B
N
208 or
240 V
Load
120 V
L
A
S1
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)
Polarity reversing switch
L
Power
Supply
S2
A
120 V
208
or 240 V
GND
OPEN
EQUIPMENT UNDER TEST (EUT)
MEASUREMENT
INSTRUMENT
B
N
Load
120 V
S1
A
B
L
INSULATING TABLE
Line and Neutral Switch
Connection to grounded supply conductor
Applicable U.S. EUT Plug Configurations
G
N
G
N
N
20 amp
30 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 mA 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
50
- END -