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BSI PD IEC/TS 62996:2017

BSI PD IEC/TS 62996:2017

$189.07

Industrial electroheating and electromagnetic processing equipment. Requirements on touch currents, voltages and electric fields from 1 kHz to 6 MHz

Published By Publication Date Number of Pages
BSI 2017 46
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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.

PDF Catalog

PDF Pages PDF Title
2 undefined
4 CONTENTS
7 FOREWORD
9 INTRODUCTION
11 1 Scope
2 Normative references
3 Terms and definitions
13 4 Organization and use of this document
14 5 Prospective source voltage limits
6 Assessment of the source impedance
15 7 Touching and access considerations
7.1 General
7.2 Primary contact areas
7.3 Special protective gloves, footwear and clothing
16 7.4 External metallic objects and tools
7.5 Considerations for the secondary contact area assessment
8 Impedances of parts of the body, and touch current densities
8.1 General
17 8.2 The equivalent circuit of skin and parts of the body
Figures
Figure 1 – Complex impedances of various parts of the body, 1 kHz to 6 MHz
18 8.3 Touch current density consideration for large contact areas
9 Capacitively coupled currents in the body due to an external electric field or insulated live part
9.1 General and measurement frequency
9.2 Determination of the capacitance
19 9.3 Assessment of the electric field and use of reference level data
9.4 Measurement methods and limiting values
9.4.1 Simplified measurement of the prospective current in the parts of the body
9.4.2 More accurate method for determination of currents in the parts of the body
9.4.3 Limiting touch current values
10 Electric shock – immediate nerve and muscle reactions
10.1 General
10.2 Touch current limits – immediate nerve and muscle reactions
20 11 Electric shock – local overheating and burns of parts of the body
11.1 General and initial thermal conditions
Figure 2 – Maximum allowed touch and touch currents, 1 kHz to 100 kHz,immediate nerve and muscle electric shock
21 11.2 Awareness, perception and withdrawal
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.
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 p…
11.3 Long-term tissue overheating
22 12 Requirements and risk group classification
12.1 General
12.2 Conditions for the touch current limits up to 100 kHz
23 12.3 Requirements related to skin temperature rises and times of awareness, perception and withdrawal
12.3.1 Skin heat capacity considerations
12.3.2 Skin temperature considerations
24 12.4 Risk level categorisation as function of the prospective contact voltage
12.5 Additional protection: residual current protective devices (RCDs)
13 Non-sinusoidal touch currents
Tables
Table 1 – Maximally allowed skin power density per surface area,under various conditions of withdrawal
25 14 Warning marking and risk group classifications
Figure 3 – Warning markings
26 Annex A (informative) Examples of calculations
A.1 General
A.2 Skin heating
27 Table A.1 – Comparison of impedances of parts of the body, using the equivalentcircuits in IEC 60990:2016 and in this document
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
28 Table A.3 – Wet skin, finger and overall heating rate at 50 V overall effective voltage,using this document, with halved skin impedances comparedwith Table A.2
29 Table A.4 – Effective contact voltage limits for the moist skin examples in Table A.2
30 Table A.5 – Effective contact voltage limits for the wet skin examples in Table A.3
31 A.3 Examples of tissue heating conditions
A.3.1 With 1 500 mm2 fingerskin area, i.e. gripping
A.3.2 With the maximal fingerskin area 230 mm2
33 Annex B (informative) Rationales, references and volunteer studies in the non-thermal case
B.1 Background and observations
B.2 Discussion of Figure B.1
34 Figure B.1 – Maximum allowed touch and touch currents in various standards, 1 kHzto 100 kHz, immediate nerve and muscle electric shock
35 B.3 A volunteer study at 11 kHz sinusoidal conditions
B.3.1 Experimental setup and data
B.3.2 Discussion and analysis of the experimental data
Figure B.2 – Setup for touch current and voltage measurements with indexand middle fingers on 50 mm2 flat conductors
36 B.4 Contact/touch current data from standards and other published documents
37 B.5 Reference levels for the external electric field
B.6 Prospective touch voltage limits
B.7 Perception and pain in relation to risk levels
Figure B.3 – Current measuring circuit for unweighed touch current,from IEC 60990:2016
38 B.8 Remarks on the slope of the curves for frequencies higher than 10 kHz
B.9 Remarks on the touch current levels above 100 kHz in ICNIRP and IEEE specifications
39 Annex C (informative) Additional information and rationales – skin data and impedances of parts of the body
C.1 Skin anatomy
Figure C.1 – Human skin anatomy (from Wikipedia)
40 C.2 Comparative calculation procedure for wet skin impedances
C.3 Some data for dry skin
41 C.4 Frequency dependence of the body tissue electrical conductivities
C.5 Calculations for Table 1
Figure C.2 – Average electrical conductivities for homogeneous body modellingfrom 10 Hz to 10 MHz (from EN 50444:2008)
Table C.1 – Comparison of complex impedances of moist and wet fingers
43 Bibliography

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