IEC TS 62996:2017
(Main)Industrial electroheating and electromagnetic processing equipment - Requirements on touch currents, voltages and electric fields from 1 kHz to 6 MHz
Industrial electroheating and electromagnetic processing equipment - Requirements on touch currents, voltages and electric fields from 1 kHz to 6 MHz
IEC TS 62996:2017(E) addresses the safety assessments in the frequency range between 1 kHz and 6 MHz and provides limits for touch and touch currents for industrial installations or equipment for electroheating (EH) and electromagnetic processing of materials (EPM). Indirect contact by capacitive currents to parts of an earthed human body in an open space are also included, since the current is then distributed analogously in the part of the body and differs from cases of induced electric shock.
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Standards Content (Sample)
IEC TS 62996 ®
Edition 1.0 2017-09
TECHNICAL
SPECIFICATION
colour
inside
Industrial electroheating and electromagnetic processing equipment –
Requirements on touch currents, voltages and electric fields from 1 kHz
to 6 MHz
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IEC TS 62996 ®
Edition 1.0 2017-09
TECHNICAL
SPECIFICATION
colour
inside
Industrial electroheating and electromagnetic processing equipment –
Requirements on touch currents, voltages and electric fields from 1 kHz
to 6 MHz
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 25.180.10 ISBN 978-2-8322-4798-3
– 2 – IEC TS 62996:2017 © IEC 2017
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 9
2 Normative references . 9
3 Terms and definitions . 9
4 Organization and use of this document . 11
5 Prospective source voltage limits . 12
6 Assessment of the source impedance . 12
7 Touching and access considerations . 13
7.1 General . 13
7.2 Primary contact areas . 13
7.3 Special protective gloves, footwear and clothing . 13
7.4 External metallic objects and tools . 14
7.5 Considerations for the secondary contact area assessment . 14
8 Impedances of parts of the body, and touch current densities . 14
8.1 General . 14
8.2 The equivalent circuit of skin and parts of the body . 15
8.3 Touch current density consideration for large contact areas . 16
9 Capacitively coupled currents in the body due to an external electric field or
insulated live part . 16
9.1 General and measurement frequency . 16
9.2 Determination of the capacitance . 16
9.3 Assessment of the electric field and use of reference level data . 17
9.4 Measurement methods and limiting values . 17
9.4.1 Simplified measurement of the prospective current in the parts of the
body . 17
9.4.2 More accurate method for determination of currents in the parts of the
body . 17
9.4.3 Limiting touch current values . 17
10 Electric shock – immediate nerve and muscle reactions. 17
10.1 General . 17
10.2 Touch current limits – immediate nerve and muscle reactions . 17
11 Electric shock – local overheating and burns of parts of the body . 18
11.1 General and initial thermal conditions . 18
11.2 Awareness, perception and withdrawal . 19
11.2.2 Heat sensing nerves exist only in the skin region, and thus not in the
interior of for example fingers. Conditions where such interior heating
occurs while the skin sensing is insufficient for perception are dealt with
in 11.3. . 19
11.2.3 The perception conditions for hazard calculations are skin temperature
rises of at least 3 K over 5 s to 10 s and 5 K over 20 s or less. These
times then include the time for withdrawal. The high alternative value 10
s applies if the touching part of the body is large and less easy to
withdraw (i.e. the upper arm, leg or torso) than a hand or finger for
which 5 s applies. . 19
11.3 Long-term tissue overheating . 19
12 Requirements and risk group classification . 20
12.1 General . 20
12.2 Conditions for the touch current limits up to 100 kHz . 20
12.3 Requirements related to skin temperature rises and times of awareness,
perception and withdrawal . 21
12.3.1 Skin heat capacity considerations . 21
12.3.2 Skin temperature considerations . 21
12.4 Risk level categorisation as function of the prospective contact voltage . 22
12.5 Additional protection: residual current protective devices (RCDs) . 22
13 Non-sinusoidal touch currents . 22
14 Warning marking and risk group classifications . 23
Annex A (informative) Examples of calculations . 24
A.1 General . 24
A.2 Skin heating . 24
A.3 Examples of tissue heating conditions . 29
A.3.1 With 1 500 mm fingerskin area, i.e. gripping . 29
A.3.2 With the maximal fingerskin area 230 mm . 29
Annex B (informative) Rationales, references and volunteer studies in the non-thermal
case . 31
B.1 Background and observations . 31
B.2 Discussion of Figure B.1 . 31
B.3 A volunteer study at 11 kHz sinusoidal conditions . 33
B.3.1 Experimental setup and data . 33
B.3.2 Discussion and analysis of the experimental data . 33
B.4 Contact/touch current data from standards and other published documents . 34
B.5 Reference levels for the external electric field . 35
B.6 Prospective touch voltage limits . 35
B.7 Perception and pain in relation to risk levels . 35
B.8 Remarks on the slope of the curves for frequencies higher than 10 kHz . 36
B.9 Remarks on the touch current levels above 100 kHz in ICNIRP and IEEE
specifications . 36
Annex C (informative) Additional information and rationales – skin data and
impedances of parts of the body . 37
C.1 Skin anatomy . 37
C.2 Comparative calculation procedure for wet skin impedances . 38
C.3 Some data for dry skin . 38
C.4 Frequency dependence of the body tissue electrical conductivities . 39
C.5 Calculations for Table 1 . 39
Bibliography . 41
Figure 1 – Complex impedances of various parts of the body, 1 kHz to 6 MHz . 15
Figure 2 – Maximum allowed touch and touch currents, 1 kHz to 100 kHz, immediate
nerve and muscle electric shock . 18
Figure 3 – Warning markings . 23
Figure B.1 – Maximum allowed touch and touch currents in various standards, 1 kHz to
100 kHz, immediate nerve and muscle electric shock . 32
Figure B.2 – Setup for touch current and voltage measurements with index and middle
fingers on 50 mm flat conductors . 33
Figure B.3 – Current measuring circuit for unweighed touch current, from
IEC 60990:2016 . 35
Figure C.1 – Human skin anatomy (from Wikipedia) . 37
– 4 – IEC TS 62996:2017 © IEC 2017
Figure C.2 – Average electrical conductivities for homogeneous body modelling from
10 Hz to 10 MHz (from EN 50444:2008) . 39
Table 1 – Maximally allowed skin power density per surface area, under various
conditions of withdrawal . 22
Table A.1 – Comparison of impedances of parts of the body, using the equivalent
circuits in IEC 60990:2016 and in this document . 25
Table A.2 – Moist skin, finger and overall heating rate at 50 V overall effective voltage,
using equivalent circuits in IEC 60990:2016 and this document . 25
Table A.3 – Wet skin, finger and overall heating rate at 50 V overall effective voltage,
using this document, with halved skin impedances compared with Table A.2 . 26
Table A.4 – Effective contact voltage limits for the moist skin examples in Table A.2 . 27
Table A.5 – Effective contact voltage limits for the wet skin examples in Table A.3 . 28
Table C.1 – Comparison of complex impedances of moist and wet fingers . 39
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL ELECTROHEATING AND ELECTROMAGNETIC PROCESSING
EQUIPMENT – REQUIREMENTS ON TOUCH CURRENTS, VOLTAGES
AND ELECTRIC FIELDS FROM 1 kHz TO 6 MHz
FOREWORD
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Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC TS 62996, which is a technical specification, has been prepared by IEC technical
committee 27: Industrial electroheating and electromagnetic processing.
– 6 – IEC TS 62996:2017 © IEC 2017
The text of this document is based on the following documents:
Draft TS Report on voting
27/1005/DTS 27/1010/RVDTS
Full information on the voting for the approval of this document can be found in the report on
voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
In this document, the following print types are used:
• terms defined in Clause 3: in bold type.
• in Table A.4 and Table A.5, the resulting voltage limits are bolded, for clarity.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
INTRODUCTION
Touch and touch currents and voltages constitute a very important category of electrical
safety issues particularly for electroheating (EH) equipment and equipment for electro-
magnetic processing of materials (EPM). The equipment manufacturer is mandated to
adequately reduce any hazard from touching live equipment parts. For being able to do so,
assessments and verifications are necessary for determination of hazards.
During the drafting of IEC 60519-1:2015, it became apparent that there was a need for a
technical specification providing an overview, a guidance and requirements for users of that
standard, and dealing with the nearest higher frequency interval above that of IEC 61140 and
IEC 60204 (all parts). A revised IEC 61140:2016 covers issues up to 1 kHz (up to 200 Hz in
earlier editions). Thus, this document deals with touch and touch currents and voltages in the
frequency range from 1 kHz to 6 MHz. This range was adopted due to deviating frequency
dependence of skin impedances below 1 kHz.
In principle, cases with strong external electric fields where the person is not touching the live
insulated or bare live conductor are closely related to cases where the person is actually
touching an insulated live conductor. These cases of currents in parts of the body by
capacitive coupling are therefore included in this document.
NOTE A parallel IEC technical specification IEC TS 62997:2017 is developed by TC 27, dealing with the magnetic
nearfields from 1 Hz to 6 MHz.
The upper frequency limit 6 MHz is chosen due to
– higher frequencies not being expected in internal frequency converters for DC voltage
transformation in equipment,
– the free space wavelength of 6 MHz being 50 m, which results in wave phenomena that
essentially not exist with or at objects with less than 10 % spatial dimensions of this,
– the fact that the power penetration depth limitation by the equivalent complex permittivity
of body tissues has not yet set in at 6 MHz, so currents can be considered to be the same
across the two touch areas and their patterns are as with low frequencies, and
– industrial processing frequencies below this limit are typically low impedance; higher
impedance dielectric heating has its lowest ISM frequency at 6,8 MHz and is dealt with in
IEC 60519-9.
Separation of electric shock (by a current between two parts of the body, creating an internal
electric field by the tissue impedance) and induced electric shock (by an internally induced
electric field caused by an external alternating magnetic field) is generally possible in the
frequency interval considered in this document, since the latter requires a very high current in
the conductor generating the magnetic field and conductor resistive losses are low by design.
However, touching of such a conductor can occur and both mechanisms will then have to be
assessed.
Impedance considerations for skin and other parts of the body are usually not included in
sufficient detail in most existing standards, technical specifications and guidelines. With the
exception of IEC 60601 (all parts) for medical equipment, no IEC standards provide
reasonably complete touch current and voltage specifications. Equivalent test circuits tend to
be too general and in some instances even contradictory to established literature data. This
specification includes references to relevant IEC, IEEE, ICNIRP, EN and scientific literature
data. Additional inputs are from numerical calculations with model situations, and volunteer
studies.
– 8 – IEC TS 62996:2017 © IEC 2017
Local overheating of particularly skin regions can be the dominating hazard at frequencies
higher than some tens of kilohertz. Hazard limits are then to be based on skin impedances,
thermal properties and touch as well as current path cross section area considerations. In
addition, awareness, perception and withdrawal considerations become crucial. All these
factors are dealt with in this document, in a more detailed way than in any other IEC
publication.
Even if the scope of IEC TC 27 is limited to industrial electroheating and electromagnetic
processing of materials, this document can fill an important gap, with its generally applicable
and detailed specifications for higher frequencies than alternating current. It is therefore
expected to be of more general use. It should, however, be observed that in particular skin
impedances behave non-linearly for frequencies below about 1 kHz.
INDUSTRIAL ELECTROHEATING AND ELECTROMAGNETIC PROCESSING
EQUIPMENT – REQUIREMENTS ON TOUCH CURRENTS, VOLTAGES
AND ELECTRIC FIELDS FROM 1 kHz TO 6 MHz
1 Scope
This document addresses the safety assessments in the frequency range between 1 kHz and
6 MHz and provides limits for touch and touch currents for industrial installations or equipment
for electroheating (EH) and electromagnetic processing of materials (EPM). Indirect contact
by capacitive currents to parts of an earthed human body in an open space are also included,
since the current is then distributed analogously in the part of the body and differs from cases
of induced electric shock.
NOTE 1 Induced electric shock phenomena are caused by the alternating magnetic field external to a
current-carrying conductor, inducing an electric field in a part of the body in the vicinity of or directly contacting it.
The causes are thus different from those causing electric shock phenomena and are dealt with in IEC TS 62997 on
magnetic nearfield safety, developed by TC 27.
The overall safety requirements for the various types of EH or EPM equipment and
installations in general result from the joint application of the general requirements specified
in IEC 60519-1:2015 and related particular requirements covering specific types of
installations or equipment. This document complements IEC 60519-1:2015.
NOTE 2 This document complements Annex B in IEC 60519-1:2015.
On contacting, this document is based primarily on a movement of the primary contact area in
relation to the live part, resulting in a contact or touch current. The awareness, perception
and reaction times differ in comparison with a situation where a person is, for example,
leaning towards or holding a conductor which subsequently becomes live, or a similar fault
condition. Different considerations are then applicable and are dealt with in a detailed way in
this document.
Since high impedances for dry skin will result in the lowest touch current and the dryness is
typically variable, data for only moist and wet skin are used in this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements 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 60417, Graphical symbols for use on equipment (available at
http://www.graphical-symbols.info/equipment)
IEC 60519-1:2015, Safety in installations for electroheating and electromagnetic processing –
Part 1: General requirements
3 Terms and definitions
For the purposes of this document the terms and definitions given in IEC 60519-1:2015 and
the following apply.
– 10 – IEC TS 62996:2017 © IEC 2017
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
– IEC Electropedia: available at http://www.electropedia.org/
– ISO Online browsing platform: available at http://www.iso.org/obp.
NOTE General definitions are given in IEC 60050, the International Electrotechnical Vocabulary. Terms relating to
industrial electroheating are defined in IEC 60050-841.
3.1
aversion
experience that is disliked but can be accepted for a short time before voluntary withdrawal
Note 1 to entry: Reactions to aversive stimuli are consciously controlled, as opposed to reactions to pain which
can normally not.
Note 2 to entry: The strength of an internal electric field causing muscle or nerve pain is typically twice the
strength of a field causing aversion.
3.2
awareness
mental preparedness regarding an unpleasant experience if an object is touched, or that it
can become live while being held
Note 1 to entry: Lack of awareness will typically delay the action of withdrawal.
3.3
electric shock
pathophysiological effect resulting from an electric current passing through a human or animal
body
Note 1 to entry: The effects in the frequency range below 100 kHz are essentially immediate, as muscle and
nerve reactions. In the higher frequency range, these have vanished and time-dependent local overheating can
occur.
Note 2 to entry: The definition requires two contact areas, or an area of the body near a voltage source and a
contact area at another potential, between which the current flows. No induced currents are supposed to be
created, as with induced electric shock dealt with in IEC TS 62997.
[SOURCE IEC 60050-195:1998, 195-01-04, modified – The notes have been added.]
3.4
pain
unpleasant experience such that it is not readily accepted a second time by the subject
submitted to it
-6 2
EXAMPLE A capacitor discharge corresponding to 50 to 100 × 10 A s between gripping hands, the sting of a
bee, the burn of a cigarette.
Note 1 to entry: Agents at the pain level cause harm as defined in for example IEC 60050-903:2013, 903-01-01.
Note 2 to entry: The examples are objective statements for standardisation purposes. Subjective experiences
vary.
[SOURCE: IEC TS 60479-2:2017, 3.13, modified – The example has been rephrased, and the
notes have been added.]
3.5
primary capacitive current area
accessible but insulated live conductive 100 mm × 200 mm area, or the smaller area if the
accessible area is smaller
3.6
primary contact area
live part which is advertently or inadvertently touched by a part of the body closing the touch
current circuit
3.7
prospective primary capacitive current area
part of the body in its most onerous position facing the live source
3.8
prospective touch voltage
open circuit voltage between the prospective primary contact area and the secondary
contact area
Note 1 to entry: The effective touch voltage that is between the two parts of the body, with the active touch
current.
Note 2 to entry: The definition differs from 195-05-09 of IEC 60050-195:1998 by the introduction of more general
contact area definitions (in 3.5, 3.6 and 3.10).
3.9
reference levels
RL
directly measurable quantities, derived from basic restrictions and provided for practical
exposure assessment purposes
Note 1 to entry: The meaning of the term differs between some standards and guidelines, with regard to the
considerations of safety factors.
Note 2 to entry: Reference levels are as such not referring to any levels of immediate nerve and muscle
reactions, or sensations of any gradual heating of the tissue.
Note 3 to entry: Another term, used by IEEE and EU, is action level (AL).
3.10
secondary contact area
live part or ground, with or without protective insulation, through which the current flows when
the primary contact area is being contacted or touched, or through the prospective primary
capacitive current area
3.11
touch current
electric current passing between the primary contact area or prospective primary
capacitive current area, and the secondary contact area
4 Organization and use of this document
It is recommended that this document be studied in the listed order below. The order of use
then depends on what is deemed to be critical. However, this document is very detailed and
there are many cross-references. They are important for determining the most significant
hazard condition. In particular, Annex A with its Table A.4 and Table A.5 is helpful in this
respect.
a) Clause 10 presents the basic touch current limitations as function of frequency up to
100 kHz, i.e. the non-thermal case of possible muscle and nerve reactions, with
consideration of various situations where a touch current can occur. The three current
level categories are shown in Figure 2. Further requirements including risk levels are given
in 12.2 and Clause 14.
b) Hazardous heating of bodyparts including skin burns are possible, in particular at
frequencies higher than 100 kHz where painful muscle and nerve reaction no longer occur.
The basic requirements are in Clause 11. Thermal data and further requirements including
– 12 – IEC TS 62996:2017 © IEC 2017
risk levels are given in 12.3, with Table 1 being helpful. Clause 14 deals with risk levels
and warning marking.
c) There are also source voltage limits for touch currents, for avoiding initiation of arcing
effects upon touching. These are specified in Clause 5, with some important comments in
Clause B.6.
d) The kinds of contact such as by a fingertip, gripping, and through protective means are
crucial for the determination of the touch current and skin heating. Standardizing
specifications of contacting geometries are given in Clause 7.
e) It is necessary to be able to assess and calculate the relevant bodypart and skin
impedances for obtaining the possible touch currents and skin heating. These
impedances are given in Clause 8, with its Figure 1. Both the moist skin (normal) and wet
skin conditions are dealt with.
f) There is furthermore a need to know additional external impedances in the overall source
circuit. The source internal impedance is dealt with in Clause 6, and capacitive
impedances by insulating protection, gloves, etc. are dealt with in Clause 9.
g) Clause 9 also deals with capacitively coupled bodycurrents caused by the electric field
from an inaccessible source.
Clause 13 is applicable in case of source voltage harmonics. Annex A contains a number of
examples illustrating the different hazard-related criteria. Annex B provides rationales,
references and volunteer studies in the non-thermal case, and Annex C provides additional
informative material on skin anatomy, impedances for wet, moist and dry skin, and body
impedances.
5 Prospective source voltage limits
NOTE 1 The limits set out in Clause 5 apply in addition to those in Clauses 10 and 11.
NOTE 2 Rationales are given in Annex B, which also provides details and data from the references which are
used in this document.
Between the frequencies f = 1 kHz and 100 kHz, the peak source voltage U is reduced from
–0,15
400 V peak to 200 V peak, by the formula U = 400 × f , with f in kHz. It is 140 V RMS
between 100 kHz and 6 MHz.
This applies also for insulated live parts dealt with in 9.2, which specifies the measurement
method.
A higher voltage is allowed if it can be shown for the specific situation via measurements that
a higher prospective touch voltage can be tolerated without arcing.
NOTE 3 The formula for the voltage between 1 kHz and 100 kHz is linear in a log-log scale.
6 Assessment of the source impedance
Source impedances are in series with the other impedances addressed in Clauses 7, 8 and 9.
If they are known beforehand to be insignificant for the assessments, no measurements are
needed.
NOTE An overall source impedance less than approximately 25 Ω is typically considered to be insignificant.
For source impedances exceeding 25 Ω, voltage measurements across applied test resistors
and capacitors are made in turn, in addition to the prospective touch voltage measurement,
for determination of the equivalent series source complex impedance.
Any contact area insulation addressed in 9.2 is not a part of the source impedance. It is
instead included as a series capacitance to the touch area.
7 Touching and access considerations
7.1 General
The primary area is the primary contact area or the primary capacitive current area. The
secondary contact area is chosen to be a large and onerously but not unlikely located skin
area of the nearest part of the body to the primary contact area.
The touch current will increase with increasing primary contact area, and the immediate
nerve and muscle reactions dealt with in Clause 10 are a first limiting factor. The impedance
of small skin areas can, however, result in too strong heating of these for lower touch
currents, dealt with in Clause 11.
NOTE Examples of calculations are given in Annex A.
7.2 Primary contact areas
7.2.1 Unless limited by the requirements in 7.2.2 to 7.2.7, the most onerous accessible
area shall be used in the calculations.
7.2.2 The impedances of parts of the body in Figure 1 are applicable to a smallest contact
area of 3,1 mm , equivalent to a 2 mm diameter flat conductor contact area.
NOTE Smaller skin contact area impedances for flat areas, circularly cylindrical conductors, and hemispherical
conductor tips are under consideration.
7.2.3 If the live conductor area is possible to grip by the hand and has a larger diameter
than 10 mm and length than 100 mm, the gripping contact area is set to 1 500 mm . If the
length or diameter is smaller, single or parallel finger contact areas are instead calculated as
in 7.2.5 for diameters up to 12 mm, and as actual minimum contacting areas of the finger skin
on the gripping side for still larger diameters or if flat. The internal finger impedance is then
set to 0.
7.2.4 A fingertip contact area to a flat object with all diametric dimensions exceeding 8 mm
is set to 8 mm in diameter, i.e. a 50 mm contact area, unless the contacting finger papillary
surface is possible to easily position in parallel to a larger live conductor surface area. The
50 mm limit is also applicable to circularly cylindrical conductors and hemispherical tips with
diameters larger than 12 mm and 10,5 mm, respectively.
7.2.5 If the primary contact area is smaller than 50 mm , the actual contact area is
employed, with the limitations in 7.2.2 and 7.2.7.
7.2.6 If the contact area is larger than 50 mm and fulfils the particular criterion in 7.2.4,
the fingertip area is set up to a maximum of 230 mm .
NOTE This elliptical area with axes 20 mm and 15 mm represent the onerous case where a potentially hazardous
internal finger heating is possible while no fingertop skin heating is perceived. The finger power density criterion in
12.3.2 is then applicable. Also see A.3.2.
7.2.7 For finger or fingertip contact to circularly cylindrical conductors with diameters
between 12 mm and 2 mm, 90° contact angle over 10 mm length is applied, resulting in
15 mm contact area in the latter case. 90° contact angle is also used for hemispherical
2 2
conductor tip diameters between 10,5 mm and 2,6 mm, resulting in 50 mm and 3,1 mm
contact area, respectively.
7.3 Special protective gloves, footwear and clothing
In cases where wearing of special protective gloves or clothing are specified or required by
the manufacturer or user, the primary capacitive current area shall be used in the
measurements and calculations of the series impedance for the touch current.
– 14 – IEC TS 62996:2017 © IEC 2017
NOTE 1 Such gloves or clothing are usually only applicable if their use does not in any way hamper the actions of
manual operation, and the primary contact area can be completely covered by the gloves or clothing.
NOTE 2 Additional non-electrical safety requirements apply to gloves and clothing.
In the case that wearing of special protective footwear is specified or required by the
manufacturer or user in areas of secondary contact, the capacitance calculated as for the
primary capacitive current area, unless ascertained by particular measures, shall be used in
the measurements and calculations of the series impedance for the touch current. The
wetting is by 0,9 % saline solution.
NOTE 3 Such footwear is usually applicable only if the secondary contact area can be reached with the feet
while another part of the body is contacting the primary contact area, and all other areas than the primary and
secondary contact areas are either inaccessible or insulated such that the application of 7.4 and 7.5 does not
result in a more onerous situation.
The capacitance or complex impedance shall be measured according to 9.2.
7.4 External metallic objects and tools
Metallic objects and tools can become part of a more onerous touch current path than any
direct bodypart contact, and shall be considered unless clearly forbidden in user instructions
and by warning signs.
NOTE A gripped metal object such as a tool contacting a live primary contact area will reduce the skin
impedance, since the primary contact area of the skin specified in 7.2 becomes larger so that the touch current
increases.
7.5 Considerations for the secondary contact area assessment
The secondary contact area is typically not a hand or a finger, except if the corresponding
earthed or live object can be gripped by a hand or is likely to be used as support for
maintaining the body posture or balance, or is a tool or a part of the equipment intended to be
held in operation.
Cases where it is possible that the touch current path is between a hand or a finger, and a
finger on the same hand, shall be investigated as an additional case to any other in this 7.5.
The hand tissue impedance is then set to zero.
NOTE Different source impedances then typically apply when the source circuit has a galvanic separation from
earth.
Secondary contact areas being an arm, leg or the torso are considered to be naked and
providing the same skin contact impedance as a naked moistened bodypart as specified in
8.2, unless special clothing as specified in 7.3 is applicable.
If the secondary contact area is a conductor which is in practise reached by only the feet
when the primary contact area is contacted:
– either zero skin impedance shall be considered, or
– special protective footwear be provided and applies, with the restrictions in 7.3.
8 Impedances of parts of the body, and touch current densities
8.1 General
The overall touch current path consists of not only the body between the primary and
secondary contact areas, but also any protective or capacitive objects such as that of gloves
or footwear (see 7.3), tools (see 7.4) and other live part insulation as well as the source
impedance (see Clause 6). Due to the impedance variations with frequency and differences in
primary and secondary contact areas, onerous but relevant impedances of the current path
shall be used in the calculations of touch currents. More than one case is possible; see 7.5.
8.2 The equivalent circuit of skin and parts of the body
Figure 1 shows the overall equivalent reference circuit of moistened skin and parts of the
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