Assessment of contact current related to human exposure to electric, magnetic and electromagnetic fields

IEC/TR 62905:2018(E) is a Technical Report. Provides general information on the assessment of contact current related to human exposure to electric, magnetic and electromagnetic fields. The contact currents in this context occur when a human body comes into contact with a not electrified conductive object exposed to an electric and/or magnetic field at a different electric potential owing to electric and/or magnetic induction to the object. This is distinguished from the issue of electrical safety where contact with live parts of a conductive object is dealt with.
In reference to the international EMF guidelines, the frequency range of contact current covered in this document is direct current to 110 MHz, and only steady-state (continuous) contact currents are covered. Transient contact currents (spark discharges) which may occur immediately before the contact with the object are not covered.
Keywords: Human Exposure Electric Fields, Magnetic Fields, Electromagnetic Fields

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Status
Published
Publication Date
04-Jun-2018
Current Stage
PPUB - Publication issued
Completion Date
05-Jun-2018
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IEC TR 63167
Edition 1.0 2018-06
TECHNICAL
REPORT
colour
inside
Assessment of contact current related to human exposure to electric, magnetic
and electromagnetic fields
IEC TR 63167:2018-06(en)
---------------------- Page: 1 ----------------------
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IEC TR 63167
Edition 1.0 2018-06
TECHNICAL
REPORT
colour
inside
Assessment of contact current related to human exposure to electric, magnetic
and electromagnetic fields
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.220.20 ISBN 978-2-8322-5751-7

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

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TR 63167:2018 © IEC 2018
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 7

3 Terms and definitions ...................................................................................................... 7

4 Abbreviated terms ........................................................................................................... 8

5 Contact current in EMF exposure guidelines .................................................................... 8

6 Consideration in evaluating contact currents .................................................................... 9

6.1 General ................................................................................................................... 9

6.2 Assumed situations of human exposure to contact current ...................................... 9

6.2.1 General ........................................................................................................... 9

6.2.2 Capacitive coupling (power line) ...................................................................... 9

6.2.3 Inductive coupling (power line) ........................................................................ 9

6.2.4 Induction heating equipment ............................................................................ 9

6.2.5 Wireless power transfer (WPT) ...................................................................... 10

6.2.6 Broadcasting ................................................................................................. 10

6.3 Methods of measurement of touch current used in electrical safety standards ....... 10

6.3.1 General ......................................................................................................... 10

6.3.2 IEC standards related to electrical safety ....................................................... 10

6.3.3 Modelling human body impedance ................................................................. 12

6.4 Proposed methods of measuring contact current ................................................... 15

6.4.1 General ......................................................................................................... 15

6.4.2 Contact current measurement using a human subject .................................... 15

6.4.3 Contact current measurement using a human equivalent

impedance/circuit........................................................................................... 16

6.4.4 Contact current calculated from measurement of open-circuit voltage ............ 16

7 Consideration in standardization of evaluation method for contact current ..................... 17

Annex A (informative) Contact current limits in international EMF guidelines........................ 18

Bibliography .......................................................................................................................... 20

Figure 1 – Time/current zones of effects of alternating currents (15 Hz to 100 Hz) on

persons for a current path corresponding to left hand to feet (for explanation see

Table 2) ................................................................................................................................ 12

Figure 2 – Measuring network for unweighted touch current [16] ........................................... 13

Figure 3 – Measuring network for touch current weighted for perception or startle-

reaction [16].......................................................................................................................... 14

Figure 4 – Simulated body impedance for contact current measurements shown in

IEEE C95.3 [27] .................................................................................................................... 14

Figure 5 – Impedances of various parts of the body proposed in IEC TS 62996 for 1

kHz to 6 MHz [11] ................................................................................................................. 15

Figure 6 – Realistic computational 3D human body model and results of calculation of

current density and pathway ................................................................................................. 17

Table 1 – Selected IEC technical committees and standards related to electrical safety ........ 11

Table 2 – Time/current zones for alternating current 15 Hz to 100 Hz for hand to feet

pathway – Summary of zones in Figure 1 .............................................................................. 12

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IEC TR 63167:2018 © IEC 2018 – 3 –

Table A.1 – Reference levels in ICNIRP guidelines for time varying contact current

from conductive object [1], [2] ............................................................................................... 18

Table A.2 – Maximum permissible exposure (MPE) levels of contact current in IEEE

safety standards [3], [4] ........................................................................................................ 18

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– 4 – IEC TR 63167:2018 © IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ASSESSMENT OF CONTACT CURRENT RELATED TO HUMAN EXPOSURE
TO ELECTRIC, MAGNETIC AND ELECTROMAGNETIC FIELDS
FOREWORD

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The main task of IEC technical committees is to prepare International Standards. However, a

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data of a different kind from that which is normally published as an International Standard, for

example "state of the art".

IEC TR 63167, which is a Technical Report, has been prepared by IEC technical committee

106: Methods for the assessment of electric, magnetic and electromagnetic fields associated

with human exposure.
The text of this Technical Report is based on the following documents:
Enquiry draft Report on voting
106/422/DTR 106/436A/RVDTR

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.
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IEC TR 63167:2018 © IEC 2018 – 5 –

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

The committee has decided that the contents of this document will remain unchanged until the

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colour printer.
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– 6 – IEC TR 63167:2018 © IEC 2018
INTRODUCTION

In the guidelines limiting human exposure to electric, magnetic and electromagnetic fields

(EMF guidelines), limits for the contact current are given to avoid adverse indirect effects, i.e.

electric shocks and burn hazards caused by contact with a conductive object located in an

electric and/or magnetic field, when the object has an electric potential owing to electric or

magnetic induction to the object.

At the moment, no standardized method for evaluating the contact current, in the context of

human exposures to the above fields has been well established. On the other hand, there is a

huge amount of knowledge, as well as many standards and regulations on the issue of

electrical safety (i.e. direct contact with live part of conductive object) to avoid severe electric

shock hazards. Therefore, the evaluation methods used in the field of electrical safety might

be useful references. This document summarizes general information on the assessment of

contact current related to human exposure to electric, magnetic and electromagnetic fields.

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IEC TR 63167:2018 © IEC 2018 – 7 –
ASSESSMENT OF CONTACT CURRENT RELATED TO HUMAN EXPOSURE
TO ELECTRIC, MAGNETIC AND ELECTROMAGNETIC FIELDS
1 Scope

This document, which is a Technical Report, provides general information on the assessment

of contact current related to human exposure to electric, magnetic and electromagnetic fields.

The contact currents in this context occur when a human body comes into contact with a not

electrified conductive object exposed to an electric and/or magnetic field at a different electric

potential owing to electric and/or magnetic induction to the object. This is distinguished from

the issue of electrical safety where contact with live parts of a conductive object is dealt with.

In reference to the international EMF guidelines [1]-[4] , the frequency range of contact

current covered in this document is direct current to 110 MHz, and only steady-state

(continuous) contact currents are covered. Transient contact currents (spark discharges)

which may occur immediately before the contact with the object are not covered.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

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
3.1
contact current

current flowing into the body resulting from contact with a conductive object in an electric,

magnetic or electromagnetic field
3.2
electric field strength

magnitude of a field vector at a point that represents the force (F) on an infinitely small charge

(q) divided by the charge
3.3
exposure

state that occurs when a person is subjected to an electric, magnetic or electromagnetic field,

or to a contact current other than those originating from physiological processes in the body

and other natural phenomena
___________
Numbers in square brackets refer to the Bibliography.
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– 8 – IEC TR 63167:2018 © IEC 2018
3.4
indirect effect

effect resulting from physical contact between a person and a not electrified object, such as a

metallic structure in an electric, magnetic or electromagnetic field, at an electric potential that

is at least at a point of the object different from the potential of the person
3.5
touch current

electric current flowing through a human body when it touches one or more accessible parts

of an installation or of equipment

Note 1 to entry: The term “leakage current” had also been used as a synonym for touch current in the field of

electrical safety.
3.6
spark discharge

transfer of current through an air gap prior to making contact with another conductive object at

a different potential
4 Abbreviated terms
AM amplitude modulation
EMF electric, magnetic or electromagnetic field
EV electric vehicle
FM frequency modulation
ICNIRP International Commission on Non-Ionizing Radiation Protection
IEEE Institute of Electrical and Electronics Engineers
IH induction heating
MPE maximum permissible exposure
MRI magnetic resonance imaging
PC personal computer
RF radio frequency
WPT wireless power transfer
5 Contact current in EMF exposure guidelines
Clause 5 overviews contact currents described in the EMF guidelines [1]-[4].

In the frequency range up to approximately 10 MHz (dominantly up to 100 kHz), the flow of

electric current from an object in a field to the body of an individual may result in the

stimulation of muscles and/or peripheral nerves. With increasing current, this may be

manifested as perception, pain from an electric shock and/or burn, the inability to release the

object, difficulty in breathing and, at higher currents, cardiac ventricular fibrillation.

In the frequency range of about 100 kHz to 110 MHz, shocks and burns can result either from

an individual touching an ungrounded metal object that has acquired a charge in a field or

from contact between a charged individual and a grounded metal object.

In the EMF guidelines, reference levels for steady state (continuous) contact current are given

for frequencies up to 110 MHz to avoid shock and burn hazards (see Annex A). The reference

levels are not intended to avoid ventricular fibrillation, which is the basis of standards for

electrical safety. The upper frequency of 110 MHz is the upper frequency limit of the FM

broadcast band. Here, the transient currents resulting from spark discharges [5], which can

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IEC TR 63167:2018 © IEC 2018 – 9 –

occur when an individual comes into very close proximity with an object at a different electric

potential, are not considered in the reference levels of contact current. Instead, the effect of

spark discharge is considered in the reference levels of electric field exposure for the general

public by including a sufficient margin to prevent surface electric-charge effects such as

perception by most people.

It is noteworthy that different methods for evaluation of conformity to the guidelines are

provided for multiple-frequency exposure for low-frequency (below 100 kHz) and

high-frequency (above 10 kHz) ranges. In the frequencies between 10 kHz and 100 kHz, both

evaluation methods are applied (see Annex A).
6 Consideration in evaluating contact currents
6.1 General
Clause 6 describes items to be considered in evaluating contact currents:
a) assumed situations of human exposure to a contact current (6.2);

b) methods for evaluating a touch current used in electrical safety standards for

references (6.3);
c) some proposed methods for evaluating contact currents (6.4).
6.2 Assumed situations of human exposure to contact current
6.2.1 General

There are several situations to be considered for human exposure to a contact current.

Different cases have to be considered depending on the type of coupling between fields

(electric or magnetic) and human bodies/objects.
6.2.2 Capacitive coupling (power line)

An electric field induces, by capacitive coupling (electrostatic induction), a voltage in a person

or a conductive object that is isolated from the ground. When a person touches an object

having a different potential, a contact current flows so as to cancel the potential difference.

This can be categorized into two cases: (a) an isolated person touches a grounded object and

(b) a grounded person touches an isolated object (especially a large object such as a bus or a

truck) [6]. Comprehensive studies have been carried out for typical cases encountered under

overhead transmission lines [7].
6.2.3 Inductive coupling (power line)

By inductive coupling (electromagnetic induction), a magnetic field induces a voltage,

especially in long conductive objects such as telecommunication lines, fences and gas

pipelines, having at least one reasonable grounding, when they are installed close to and

parallel to magnetic field sources such as overhead power lines [8]. When a person touches

the object, a contact current flows. In particular, in the case of fault condition in overhead

power lines, the limit values for the open-circuit voltage in telecommunication lines are set by

an international regulation-setting body [9]. In contrast to the capacitive coupling, grounding a

conductive object at a large distance from the point of contact will actually increase the

amplitude of the open-circuit voltage, thereby increasing the contact current.
6.2.4 Induction heating equipment

Induction heating (IH) equipment is heating equipment using the Joule effect produced by

magnetically induced currents. For a domestic IH cooker, a metal pan or pot is heated by a

magnetic field, and when a person touches a conductive part of the pan or pot, a contact

current can occur typically in the frequency ranges of around 20 kHz to 100 kHz. The method

used to evaluate human exposure to magnetic fields produced by IH cookers is standardized

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– 10 – IEC TR 63167:2018 © IEC 2018

in IEC 62233 [10]; however, the contact current is not mentioned in IEC 62233. Note that it

may be appropriate to categorize this exposure situation as an issue of electrical safety.

For industrial IH equipment, a method of evaluating touch current in terms of electrical safety

is being standardized in IEC TC 27 (industrial electroheating and electromagnetic processing)

for the frequency ranges between 1 kHz and 6 MHz [11].
6.2.5 Wireless power transfer (WPT)

A wireless power transfer (WPT) system is a system capable of transferring power between a

transmitter and receiver using wireless technologies including electromagnetic induction. They

are used for wirelessly charging mobile phones, tablet PCs, electric vehicles (EV) and, so

forth. There are several types of WPT, and the frequency range used is from tens of kilohertz

to tens of megahertz. When a conductive object is placed in the immediate vicinity of a

system and a person touches it, a contact current can occur. As touching the metal body of an

EV when charging using a WPT charging system may be the case [12], it may be appropriate

to categorize the exposure situation as an issue of electrical safety. Details regarding

exposure assessment methods for WPT systems are reported in IEC TR 62905 [13].

In IEC TR 62905, contact currents are considered for the conditions where ungrounded or

grounded metal object is placed in the vicinity of WPT systems.
6.2.6 Broadcasting

Burns can occur at a point of contact between a human body and a metallic structure that is

exposed to RF electromagnetic fields from nearby sources such as AM broadcast antennas.

The contact point between the body and the structure often has a small area and the current

injected into the body is concentrated near this point. This can result in a current density near

the contact sufficiently strong to raise the local temperature and cause surface or deep

burns [13].
6.3 Methods of measurement of touch current used in electrical safety standards
6.3.1 General

When considering the evaluation method for contact currents in the context of human

exposure to electric, magnetic and electromagnetic fields, existing IEC standards related to

electrical safety may be useful inputs.
6.3.2 IEC standards related to electrical safety

There are several IEC technical committees in charge of electrical safety. These include:

– TC 64: Electrical installations and protection against electric shock;

– TC 108: Safety of electronic equipment within the field of audio/video, information

technology and communication technology;
– TC 61: Safety of household and similar electrical appliances;

– TC 99: System engineering and erection of electrical power installations in systems with

nominal voltages above 1 kV AC and 1,5 kV DC, particularly concerning safety aspects;

– TC 66: Safety of measuring, control and laboratory equipment;
– TC 62/SC 62A: Common aspects of electrical equipment used in medical practice.

Table 1 summarizes the selected standards related to the electrical safety and the committees

in which they were created [14]-[26]. Note that the “touch voltage”, the product of the touch

current and the assumed body impedance, is commonly used as a parameter for setting limits

for touch currents.

In IEC TS 60479-1 [20], a diagram of physiological effects for different touch currents and

durations is shown (reproduced in Figure 1 and Table 2), which is commonly referenced in

electrical safety standards as a basis for limiting touch currents.
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IEC TR 63167:2018 © IEC 2018 – 11 –

Table 1 – Selected IEC technical committees and standards related to electrical safety

IEC TC IEC standards related to electrical safety Notes

TC 108, Safety of electronic equipment IEC 60065:2014, Audio, video and similar Stipulates touch

within the field of audio/video, information electronic apparatus – Safety requirements voltage limits

technology and communication technology [14]
IEC 60950-1:2005, Information technology Stipulates touch
equipment – Safety – Part 1: General current limits
requirements
IEC 60950-1:2005/AMD1:2009
IEC 60950-1:2005/AMD2:2013 [15]
IEC 60990:2016, Methods of measurement of Stipulates
touch current and protective conductor measuring method
current [16] of touch current
IEC 62368-1:2014, Audio/video, information “Hazard based
and communication technology equipment – safety engineering
Part 1: Safety requirements [17] (HBSE)” is adopted

TC 61, Safety of household and similar IEC 60335-1:2010, Household and similar Stipulates touch

electrical appliances electrical appliances – Safety – Part 1: current limits
General requirements
IEC 60335-1:2010/AMD1:2013
IEC 60335-1:2010/AMD2:2016 [18]

TC 64, Electrical installations and protection IEC 60364-4-41:2005, Low-voltage electrical

against electric shock installations – Part 4-41: Protection for safety
– Protection against electric shock
IEC 60364-4-41:2005/AMD1:2017 [19]
IEC TS 60479-1:2005, Effects of current on A diagram of
human beings and livestock – Part 1: physiological
General aspects effects for different
body currents and
IEC TS 60479-1:2005/AMD1:2016 [20]
durations is shown
IEC TS 60479-2:2017, Effects of current on
human beings and livestock – Part 2: Special
aspects [21]
IEC 61140:2016, Protection against electric
shock – Common aspects for installation and
equipment [22]
IEC TS 61201:2007, Use of conventional
touch voltage limits – Application guide [23]

TC 99, Insulation coordination and system IEC 61936-1:2010, Power installations Stipulates touch

engineering of high voltage electrical power exceeding 1 kV a.c. – Part 1: Common rules voltage limits

installations above 1,0 kV AC and 1,5 kV DC
IEC 61936-1:2010/AMD1:2014 [24]

TC 66, Safety of measuring, control and IEC 61010-1:2010, Safety requirements for Stipulates touch

laboratory equipment electrical equipment for measurement, current limits
control, and laboratory use – Part 1: General
requirements
IEC 61010-1:2010/AMD1:2016 [25]

TC 62/SC 62A, Common aspects of electrical IEC 60601-1:2005, Medical electrical Stipulates “lea

...

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