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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Status
Published
Publication Date
14-Sep-2017
Current Stage
PPUB - Publication issued
Start Date
15-Sep-2017
Completion Date
15-Sep-2017
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IEC TS 62996:2017 - 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
IEC TS 62996:2017-09(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
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

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 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

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IEC TS 62996:2017 © IEC 2017 – 3 –

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

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– 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

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IEC TS 62996:2017 © IEC 2017 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL ELECTROHEATING AND ELECTROMAGNETIC PROCESSING
EQUIPMENT – REQUIREMENTS ON TOUCH CURRENTS, VOLTAGES
AND ELECTRIC FIELDS FROM 1 kHz TO 6 MHz
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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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. In

exceptional circumstances, a technical committee may propose the publication of a technical

specification when

• the required support cannot be obtained for the publication of an International Standard,

despite repeated efforts, or

• the subject is still under technical development or where, for any other reason, there is the

future but no immediate possibility of an agreement on an International Standard.

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.
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– 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.
---------------------- Page: 8 ----------------------
IEC TS 62996:2017 © IEC 2017 – 7 –
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.
---------------------- Page: 9 ----------------------
– 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.
---------------------- Page: 10 ----------------------
IEC TS 62996:2017 © IEC 2017 – 9 –
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.
---------------------- Page: 11 ----------------------
– 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.
...

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