IEC TR 60479-5:2007

IEC/TR 60479-5
Edition 1.0 2007-11
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
Effects of current on human beings and livestock –
Part 5: Touch voltage threshold values for physiological effects

Effets du courant sur l’homme et les animaux domestiques –
Partie 5: Valeurs des seuils de tension de contact pour les effets physiologiques

IEC/TR 60479-5:2007
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IEC/TR 60479-5
Edition 1.0 2007-11
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
Effects of current on human beings and livestock –
Part 5: Touch voltage threshold values for physiological effects

Effets du courant sur l’homme et les animaux domestiques –
Partie 5: Valeurs des seuils de tension de contact pour les effets physiologiques

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XA
CODE PRIX
ICS 13.200; 29.020 ISBN 2-8318-9346-1

– 2 – TR 60479-5 © IEC:2007
CONTENTS
FOREWORD.5
INTRODUCTION.7

1 Scope.8
2 Normative references .8
3 Terms and definitions .9
4 Conditions and threshold values .9
4.1 General .9
4.2 Physiological effects of touch current .10
4.3 Body impedance.14
4.4 Impedance external to the body.15
4.5 Other factors affecting voltage thresholds .15
4.6 Touch voltage thresholds as a function of duration .16
4.7 Touch voltage thresholds for long durations .17
5 Touch voltage thresholds – Presentation of voltage-time curves .19

Annex A (informative) Body impedance.30
Annex B (informative) Touch voltage – Explanation of a method to derive estimates of
touch voltages thresholds for strong muscular reactions and ventricular fibrillation from
the body impedance tables and current limits in IEC/TS 60479-1 .36
Annex C (informative) Determination of voltage thresholds under selected conditions.53
Annex D (informative) Limits of applicability.54

Bibliography.56

Figure 1 – Physiological thresholds for a.c. (50/60-Hz) and d.c. flowing hand-to-hand
(transversely) through the human body .11
Figure 2 – Physiological thresholds for a.c. (50/60-Hz) and d.c. flowing from both
hands to both feet (longitudinally) through the human body .12
Figure 3 – Physiological thresholds for a.c. (50/60-Hz) and d.c. flowing from hand-to
seat (longitudinal) through the human body .13
Figure 4 – Flow chart to be used for the selection of the appropriate figure providing
the maximum duration for each touch voltage threshold.17
Figure 5 – Conventional time/voltage zones of effects of a.c. current (50/60 Hz) on a

person for saltwater-wet condition and large contact area.20
Figure 6 – Conventional time/voltage zones of effects of a.c. current (50/60 Hz) on a
person for saltwater-wet condition and medium contact area .21
Figure 7 – Conventional time/voltage zones of effects of a.c. current (50/60 Hz) on a
person for saltwater-wet condition and small contact area .21
Figure 8 – Conventional time/voltage zones of effects of a.c. current (50/60 Hz) on a

person for water-wet condition and large contact area .22
Figure 9 – Conventional time/voltage zones of effects of a.c. current (50/60 Hz) on a
person for water-wet condition and medium contact area.22
Figure 10 – Conventional time/voltage zones of effects of a.c. current (50/60 Hz) on a
person for water-wet condition and small contact area .23

TR 60479-5 © IEC:2007 – 3 –
Figure 11 – Conventional time/voltage zones of effects of a.c. current (50/60 Hz) on a
person for dry condition and large contact area .23
Figure 12 – Conventional time/voltage zones of effects of a.c. current (50/60 Hz) on a
person for dry condition and medium contact area .24
Figure 13 – Conventional time/voltage zones of effects of a.c. current (50/60 Hz) on a
person for dry condition and small contact area .24
Figure 14 – Conventional time/voltage zones of effects of d.c. current on a person for
saltwater-wet condition and large contact area .25
Figure 15 – Conventional time/voltage zones of effects of d.c. current on a person for
saltwater-wet condition and medium contact area .25
Figure 16 – Conventional time/voltage zones of effects of d.c. current on a person for
saltwater-wet condition and small contact area .26
Figure 17 – Conventional time/voltage zones of effects of d.c. current on a person for
water-wet condition and large contact area .26
Figure 18 – Conventional time/voltage zones of effects of d.c. current on a person for
water-wet condition and medium contact area.27
Figure 19 – Conventional time/voltage zones of effects of d.c. current on a person for
water-wet condition and small contact area.27
Figure 20 – Conventional time/voltage zones of effects of d.c. current on a person for
dry condition and large contact area .28
Figure 21 – Conventional time/voltage zones of effects of d.c. current on a person for
dry condition and medium contact area.28
Figure 22 – Conventional time/voltage zones of effects of d.c. current on a person for
dry condition and small contact area.29
Figure A.1 – Model for hand-to-hand contact .33
Figure A.2 – Model for both-hands-to-feet contact .34
Figure A.3 – Model for hand-to-seat contact .35
Figure B.1 – Estimation of the variation of the skin resistance as a function of electric
shock duration .38
Figure B.2 – Example of extrapolation of the hand-to-hand body impedance at 0 V in
dry conditions with large contact area .42
Figure B.3 – Percentage of internal resistance of the human body for the part of the
body concerned .43
Figure B.4 – Example of diagram for the estimation of the strong muscular reactions
and ventricular fibrillation threshold for a.c. current hand-to-hand current path, large
contact area and dry condition for a current duration of 10 ms .47

Table 1 – Current threshold values for each condition and for long duration.14
Table 2 – Tables providing minimum touch voltage threshold for a.c. and d.c.
corresponding to startle reaction, strong muscular reaction and ventricular fibrillation
(see Table 1 notes).18
Table 2a – Startle reaction for alternating current 50/60 Hz .18
Table 2b – Strong muscular reaction for alternating current 50/60 Hz .18
Table 2c – Ventricular fibrillation for alternating current 50/60 Hz .18
Table 2d – Startle reaction for direct current .19
Table 2e – Strong muscular reaction for direct current .19
Table 2f – Ventricular fibrillation for direct current.19
Table A.1 – Total body impedance in ohms for dry, hand-to-hand, 50/60 Hz a.c., large
surface area contact (IEC/TS 60479-1 Table 1) .31

– 4 – TR 60479-5 © IEC:2007
Table A.2 – Total body impedance in ohms for dry, hand-to-hand, d.c., large surface
area contact (IEC/TS 60479-1 Table 10) .31
Table B.1 – Nature and number of the parameters influencing the human body
impedance which are taken into consideration by IEC/TS 60479-1.37
Table B.2 – Additional parameters influencing the human body impedance.37
Table B.3 – Maximum a.c. current threshold corresponding to current flow duration for
each current effect considered and for a hand-to-hand current path.46
Table B.4 – Maximum a.c. current threshold corresponding to current flow duration for
each current effect considered for both-hands-to-feet current path.47
Table B.5 – Maximum a.c. current threshold corresponding to current flow duration for
each current effect considered for a hand-to-seat current path.48
Table B.6 – Maximum d.c. current threshold corresponding to current flow duration for
each current effect considered for the hand-to-hand current path.51
Table B.7 – Maximum d.c. current threshold corresponding to current flow duration for
each current effect considered for the both-hands-to-feet current path.52
Table B.8 – Maximum d.c. current threshold corresponding to current flow duration for
each current effect considered for the hand-to-seat current path.52
Table C.1 – Example of touch voltage thresholds for a.c. and d.c. corresponding to
muscular effects and ventricular fibrillation for the above specified environmental
situations .53

TR 60479-5 © IEC:2007 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
EFFECTS OF CURRENT ON HUMAN BEINGS AND LIVESTOCK –

Part 5: Touch voltage threshold values for physiological effects

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC/TR 60479-5, which is a technical report, has been prepared by IEC technical committee
64: Electrical installations and protection against electric shock.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
64/1585/DTS 64/1611/RVC
Full information on the voting for the approval of this technical report can be found in the
report on voting indicated in the above table.

– 6 – TR 60479-5 © IEC:2007
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 60479 series, under the general title Effects of current on
human beings and livestock, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
The contents of the corrigendum of July 2013 have been included in this copy.

TR 60479-5 © IEC:2007 – 7 –
INTRODUCTION
This technical report provides a methodology for estimating voltage thresholds which are
intended to give guidance to IEC technical committees on the selection and application of
voltage limits with regard to protection against electric shock. Technical committees may use
this methodology to recalculate proposed voltage thresholds or to determine new voltage
threshold values based on different pathways, other current threshold values, different
alternating current frequencies, other skin capacitances values, etc.
To estimate the type and severity of physiological effects that might be caused by electricity,
the magnitude and pathway of current through a person’s body needs to be determined.
However, from an equipment design point of view, it is advantageous to be able to predict
whether unwanted physiological effects are possible or probable, given only information about
voltage levels on accessible conductive surfaces. If the maximum available voltage is
sufficiently low under the expected circumstances to be unable to cause enough touch current
to cause unwanted physiological effects, then the safeguards normally required to avoid the
occurrence of these physiological effects may be reduced or eliminated. Voltages below
critical levels that are unlikely to be hazardous in this respect have normally been called
extra-low voltage (ELV). Based on this information technical committees may wish to review
their defined values of extra-low voltage.
The objective of this technical report being to derive touch voltage threshold values
corresponding to zones of physiological effects (as presented in Figures 20 and 22 of IEC/TS
60479-1), the introduction of such techniques gives designers the ability to provide a larger
variety of circuits that give the expected level of user protection under a broader set of
circumstances than previously considered.
The physiological effects corresponding to the threshold voltage values should be the same
as those for touch current that appear in IEC/TS 60479-1. Physiological effects considered in
this technical report are startle reaction of current, effects involving muscular contractions
such as inability to let-go and ventricular fibrillation. Current thresholds are based on curves
a, b and c in IEC/TS 60479-1 which remains the prime standard. The touch voltage
thresholds are related to the touch current thresholds by the body impedance according to
Ohm’s law. However, in this case, the application of Ohm’s law is not straightforward. Body
impedance is a function of a number of variables including the voltage across the body, the
current pathway, the area of contact between the skin and the conductive surface, the level of
moisture in the contact area, and the duration of voltage across (or current through) the body.
When voltage is applied to the body and current begins to flow, the resistive component of the
skin impedance changes to a lower value within a few tens of milliseconds.
This technical report discusses 50/60Hz sinusoidal alternating voltage and pure direct voltage
having no significant alternating component. Higher frequency alternating voltage is not
included in this type of analysis as this would require a more complex body impedance model
and would require the use of frequency factors for the current thresholds for the unwanted
physiological effects. As this technical report does not cover frequencies above 50/60Hz,
technical committees are requested to inform IEC/TC 64 about experience gained on this
subject. Suggestions for modifications and additions to the report should be submitted to
IEC/TC 64.
This work does not relieve the responsibility of IEC technical committees to consider the usual
touch current commonly measured in product evaluations.

– 8 – TR 60479-5 © IEC:2007
EFFECTS OF CURRENT ON HUMAN BEINGS AND LIVESTOCK –

Part 5: Touch voltage threshold values for physiological effects

1 Scope
IEC/TR 60479-5, which is a technical report, provides touch voltage-duration combination
thresholds based on analysis of information concerning body impedances and current
thresholds of physiological effects, as given in IEC/TS 60479-1. Such threshold combinations
relate to specific environmental and contact conditions that determine body impedance for
particular current pathways.
This technical report considers only
(i) 50/60 Hz sinusoidal alternating voltage having no other frequency components and no
significant direct voltage component, and
(ii) direct voltage with no significant alternating component.
This technical report provides thresholds as a result of calculations based on values from
IEC/TS 60479-1, with uncertainties. Therefore thresholds proposed in this report also
correspond to values with uncertainties.
This technical report does not consider immersion of body parts and medical application.
Touch voltage-duration combination thresholds are for use by technical committees as
guidance for the determination of limits for touch voltage and touch voltage durations in
various environmental situations.
Determination of limits needs to be based on risk assessment. Factors that are part of risk
assessment include voltage threshold values (taking into account contact area, skin moisture
condition, body current pathway) provided by this technical report, as well as other factors not
covered such as:
– reduction of the likelihood of contact (by obstacles, barriers, warnings, placing out of
reach, training, etc.); or
– reduction of touch voltage compared to the fault voltage (such as by equipotential
bonding); or
– additional resistance in series with the human body (such as gloves, shoes, carpet, etc.).
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60050-195, International Electrotechnical Vocabulary – Part 195: Earthing and protection
against electric shock
IEC/TS 60479-1:2005, Effects of current on human beings and livestock – Part 1: General
aspects
IEC 60990, Methods of measurement of touch current and protective conductor current

TR 60479-5 © IEC:2007 – 9 –
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
touch current
electric current passing through a human body or through an animal body when it touches one
or more accessible parts of an installation or of equipment
[IEV-195-05-21]
3.2
touch voltage
voltage between conductive parts when touched simultaneously by a person or an animal
[IEV 195-05-11]
NOTE The touch voltage may be different from the open-circuit voltage between those conductive parts.
3.3
threshold
level of stimulus just strong enough to produce a response
NOTE A threshold is not the same as a limit which includes risk assessment, safety margins, etc.
3.3.1
voltage threshold for startle reaction
minimum derived value of touch voltage for a population for which a current flowing through
the body is just enough to cause involuntary muscular contraction to the person through which
it is flowing
3.3.2
voltage threshold for strong muscular reaction
minimum derived value of touch voltage for a population for which a current flowing through
the body is just enough to cause involuntary contraction of a muscle, such as inability to let-
go from an electrode (a.c.), but not including startle reaction
3.3.3
voltage threshold for ventricular fibrillation
minimum derived value of touch voltage for a population for which a current flowing through
the body is just enough to cause ventricular fibrillation
3.4
long duration
duration corresponding to the vertical asymptote of the “b” and “c ” curves of IEC/TS 60479-1
(e.g. 10 s)
3.5
short duration
any duration less than long duration
4 Conditions and threshold values
4.1 General
Physiological effects of electricity through the human body are caused by current passing
through the body. In order to estimate the type and severity of physiological effects that might
be caused by electricity, the magnitude and pathway of current through a person’s body must
be determined. However, from an equipment design point of view, it is advantageous to be

– 10 – TR 60479-5 © IEC:2007
able to predict whether unwanted physiological effects are possible or probable, armed only
with information concerning voltage levels on accessible conductive surfaces. If the maximum
available voltage is sufficiently low to be unable to cause enough touch current to cause
unwanted physiological effects, then the safeguards normally required to avoid the
occurrence of these physiological effects may be reduced or eliminated.
NOTE This technical report only estimates the touch voltage and not the effect of the source impedance. This
results in the worst case situation. In this report the prospective touch voltage is considered as equal to the
effective touch voltage, as defined in IEC 60050-195.
4.2 Physiological effects of touch current
Thresholds for the physiological effects associated with electric current through a human body
are reported in IEC/TS 60479-1.
This technical report addresses startle reaction from current, strong involuntary muscular
reaction such as inability to let go an electrode in a.c. and ventricular fibrillation. Other
effects, such as perception of current, might be important for some applications but are not
addressed. It should be noted that current thresholds corresponding to strong muscular
reaction and to ventricular fibrillation depend on touch current magnitude, while current
threshold corresponding to startle reaction depends more on current density. Nevertheless,
IEC/TS 60479-1 addresses a current startle reaction threshold in mA which contributes to
considerations in this report that the current startle reaction threshold only depends on the
current magnitude.
For the purposes of this report, the threshold of physiological effects of greatest interest are
curves a, b and c . Curve a is the level beyond which startle reaction of current becomes
possible. Curve b is the lower boundary of current levels beyond which more serious and
undesirable physiological effects begin to occur. Curve c is the level beyond which the
likelihood of ventricular fibrillation begins to become a concern.
Figures 1 to 3 below show the thresholds for touch current on which the voltage thresholds
are based. These figures are based only on information from IEC/TS 60479-1. Figures 1, 2
and 3 respectively show the threshold current values for hand-to-hand; both-hands-to-feet or
hand-to-seat (longitudinal) current.
Figure 2 directly reproduces Figures 20 and 22 from IEC/TS 60479-1. Other figures are
derived from IEC/TS 60479-1 using the appropriate factors of Table 5 to adapt the threshold
current to the hand-to-hand pathway.
The values in Table 1 refer to long duration current passing through the torso. For a.c., the
main concern is the inability to let go with reference to current passing through each arm.
Therefore, the a.c. current value in Table 1 and in Figure 2 has been doubled for the ‘both-
hands-to-feet’ pathway for longer current duration (only above the intersection with the d.c.
line). For d.c. and for shorter a.c. duration, the value is not doubled because continuous d.c.
and short duration a.c. current do not cause inability to let go (which results in coincidence of
both lines) (see note 1 of Table 1).
For direct current, a lower magnitude of current is needed to produce ventricular fibrillation
when the current flows upward from feet to hands (feet positive with respect to the upper
body) through the torso rather than downward. This technical report assumes upward current
in all cases involving direct current. The ventricular fibrillation current threshold for a d.c.
downwards current is about twice that of the current threshold corresponding to the upward
current.
Short duration currents (less than one heart cycle) are always assumed to coincide with the
vulnerable portion of the heart beat cycle.

TR 60479-5 © IEC:2007 – 11 –
10 aa
bb
c1 c1
AC/DC-4:
risk of
ventricular
fibrillation
0,1
AC/DC-3:
risk of
AC/DC-2:
muscular
risk of
reactions
startle
a.c.
reaction
d.c.
0,01
Body
0,1 1 10 100 1000 10000
current (mA)
NOTE The “c ” curve is modified according to Table 12 of IEC/TS 60479-1; see also last paragraph of 4.1 of that
standard.
Figure 1 – Physiological thresholds for a.c. (50/60 Hz) and d.c. flowing hand-to-hand
(transversely) through the human body
Duration of current flow (s)
– 12 – TR 60479-5 © IEC:2007
aa
bb
c1 c1
AC/DC-4:
risk of
ventricular
fibrillation
AC/DC-2:
risk of
startle
reaction
0,1
AC/DC-3:
risk of
muscular
a.c.
reactions
d.c.
0,01
Body
0,1 1 10 100 1000
current (mA)
NOTE Modifications to Figures 20 and 22 of IEC/TS 60479-1 include:
– doubling of threshold corresponding to curve “b” for a.c., explained in note 1 of Table 1;
– below the intersection of the double a.c. curve and the d.c. curve, both curves were made coincident with the
th
more conservative d.c. curve; see explanation in the 4 paragraph of 4.1 of IEC/TS 60479-1.
Figure 2 – Physiological thresholds for a.c. (50/60 Hz) and d.c. flowing from both hands
to both feet (longitudinally) through the human body
Duration of current flow (s)
TR 60479-5 © IEC:2007 – 13 –
aa
bb
c1 c1
AC/DC-4:
risk of
ventricular
fibrillation
AC/DC:-2:
risk of
startle
reaction
0,1
AC/DC-3:
risk of
muscular
reactions
a.c.
d.c.
ac
0,01
Body
0,1 1 10 100 1000
current (mA)
Figure 3 – Physiological thresholds for a.c. (50/60 Hz) and d.c. flowing from hand-to
seat (longitudinal) through the human body
For the determination of voltage threshold, the following long duration current thresholds have
been considered. They have been determined from Figures 20 and 22 and Table 12 of
IEC/TS 60479-1 which correspond to the upper end of the b or c curves in Figures 1 to 3
above.
Duration of current flow (s)
– 14 – TR 60479-5 © IEC:2007
Table 1 – Current threshold values for each condition and for long duration
Type of threshold Current Current path mA
Current of startle reaction a.c. Hand-to-hand 0,5
Both-hands-to-feet 0,5
One-hand-to-seat 0,5
d.c. Hand-to-hand 2
Both-hands-to-feet 2
One-hand-to-seat 2
Strong muscular reactions a.c. Hand-to-hand 5
1)
(Note
Both-hands-to-feet 10
One-hand-to-seat 5
d.c. Hand-to-hand 25
Both-hands-to-feet 25
One-hand-to-seat 25
Ventricular fibrillation
a.c. Hand-to-hand 100
(Note 3)
Both-hands-to-feet 40
One-hand-to-seat 57
d.c. Hand-to-hand 350
2)
(Note
Feet-to-both-hands 140
2)
(Note
Seat-to-one-hand 200
NOTE 1 The values in this table refer to current through the torso. For a.c. the
main concern is the inability to let go which refers to the current through each arm.
Therefore, the total touch current value in the table has been doubled for longer
current durations.
NOTE 2 Current path in the direction of feet-to-both-hands is referred to as
upward current. The ventricular fibrillation current threshold for a d.c. downwards
current is about twice that of the current threshold corresponding to the upward
current.
NOTE 3 Current values other than values corresponding to ventricular fibrillation
may cause other severe effects such as respiratory arrest as described in IEC/TS
60479-1.
4.3 Body impedance
Touch voltage thresholds are related to touch current thresholds by the body’s impedance
according to Ohm’s law. However, the application of Ohm’s law is not straightforward because
the appropriate value of body impedance to use is a function of many factors. The selection of
the proper value should include consideration of
• the type of power source (a.c. or d.c.), and
• the magnitude of the touch voltage, and
• the pathway of the current through the body (hand-to-hand or both-hands-to-feet or hand-
to-seat), and
TR 60479-5 © IEC:2007 – 15 –
NOTE 1 These different pathways have been selected for their characteristics. The reason comes from the body
impedance model described in Annex A. The voltage thresholds determined for the current path both-hands-to-feet
may be generally considered conservative compared to the current path one hand-to-feet.
• the area of contact with the skin, and
• the condition of the skin contact area (saltwater-wet, water-wet, dry), and
• duration of the current flow.
The body impedance only includes skin impedance and internal tissue impedance.
Skin resistance changes as a function of the voltage applied to it. At low voltages, the change
is reversible. The value quickly changes back to the original resistance once the voltage is
removed. At high voltage, permanent injury to the skin can occur. In this case, the change in
skin resistance that results from the applied voltage is not reversible.
NOTE 2 A finger can be assumed to have a resistance of approximately 1 000 Ω. Therefore, contact with a finger
tip rather than with the palm of the hand will significantly increase the body impedance. The conditions described
by the contact with the palm of the hand are therefore conservative.
IEC/TS 60479-1 contains information about body impedance that was obtained from
measurements of live human volunteers and from measurements of cadavers. Annex A
provides more details about body impedances and body impedance models. There are
variations in impedance between different individuals and this is shown in the tables of Annex
A by the percentile values.
Typically, physically large people have lower internal body resistance because of their larger
cross-sectional area. Physically small people generally have higher internal body resistance.
Some measurements [1] of body impedances show that the body impedance is not greatly
influenced by the body weight. Therefore, there is not sufficient correlation between the body
weight (children or adults) and the physiological current values corresponding to a particular
th th
effect. Three percentiles of the population are considered in IEC/TS 60479-1 (5 , 50 and
th th
95 ). This report only considers the values of body impedance corresponding to the 5
percentile of the population which covers more than 95 % of the population.
4.4 Impedance external to the body
It is assumed that the voltage source applied to the body has a low output impedance relative
to the body impedance (which is the worst case). The magnitude of the touch current is
determined solely by the combination of the applied voltage and the human body impedance.
Consideration of any significant circuit impedance that might be in series with the body, and
that can affect the available touch current from the voltage source, is outside the scope of this
technical report.
NOTE In some instances, with large inductive impedance in series with the body, the touch voltage might be
higher than the open-circuit voltage of the source. This effect can become significant for 50/60Hz at inductances
larger than 100 mH.
External impedance from clothing, including gloves or shoes, is not considered in this report.
4.5 Other factors affecting voltage thresholds
The factors considered are as follows:
• Source: 50/60 Hz alternating sinusoidal voltage with no d.c. component or direct voltage
with no alternating component.
• Skin condition: saltwater-wet, water-wet and dry.

___________
Figures in square brackets refer to the bibliography.

– 16 – TR 60479-5 © IEC:2007
NOTE ’Dry’ skin condition corresponds to normal indoor condition, water-wet skin condition corresponds to skin
that has been immersed for more than 1 min in normal water (average value ρ = 35 Ω × m, pH = 7,7 - 9), and a
saltwater-wet skin condition is considered as skin that has been immersed for more than 1 min in a solution of 3 %
NaCl in water (average value ρ = 0,25 Ω × m, pH = 7,5 - 8,5).
Perspiration may be considered as lying between a water-wet and saltwater-wet condition.
The conductivity of some sea water is slightly higher than the saltwater-wet condition.
• Pathway: hand-to-hand contact or both-hands-to-feet contact or hand-to-seat contact with
accessible conductive parts.
• Contact area: large area contact, medium area contact, or small area contact with
accessible conductive parts.
For the purposes of calculation, a large, full hand contact (L) is considered to have a surface
contact hand area of 82 cm². A medium contact area (M) is considered to be 12,5 cm and
might represent touching a conductive part in the palm of each hand. A small contact area (S)
is considered to be 1 cm and might represent touching a small conductive part with the hand.
All contacts, except for hand-to-seat, are assumed to be symmetrical for the purposes of this
analysis. It is assumed that contact between each foot and a conductive supporting surface
will be the same size as for each hand surface contact.
It should be noted that contact area may be affected by the use of conductive tools or
interconnected equipment (accessible conductive parts).
• Duration: 10 ms to 10 s.
The worst case presented in this report corresponds to the following situation: a.c. current,
long duration, saltwater-wet condition and large contact area.
4.6 Touch voltage thresholds as a function of duration
Based on human body impedances and on current-time curves as provided in
IEC/TS 60479-1, a set of diagrams (see Figures 5 to 22) provide the maximum time
acceptable for a given touch voltage applied to a human body. These curves have been
established by using the method described in Annex B and with the model described in
Annex A.
These curves should be used as a guide by IEC technical committees when prescribing the
disconnecting time of the protective device used for the automatic disconnection of supply.
The limits chosen for the disconn
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