Technical Committee 61 · PDF fileChairman IEC Technical Committee 61 ... CHAPTER TWO Child 3 -14 years ... such as blades in kitchen machines, the blades in a fan,

TC 61

Technical Committee 61

SAFETY OF HOUSEHOLD AND SIMILAR ELECTRICAL APPLIANCES

TC 61

Ensuring performance and safety of household electrical appliances

in industrializing countries

Seattle, Washington, USA: 2010-13-10

Derek JohnsChairman IEC Technical Committee 61SAFETY OF HOUSEHOLD AND SIMILAR ELECTRICAL APPLIANCES

TC 61

Contents

IntroductionElectric shock hazardsThermal hazardsAbnormal operationMechanical and other hazardsRadiation, toxicity and similar hazardsFire and abnormal heat hazardsConclusions

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TC 61

Contents

IntroductionElectric shock hazardsThermal hazardsAbnormal operationMechanical and other hazardsRadiation, toxicity and similar hazardsFire and abnormal heat hazardsConclusions

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CHAPTER ONE

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Introduction

Legislation relating to household appliances is enacted in many countries in order to protect the health and safety of the consumer.Enforcement of this legislation normally follows one of two models:– Pre-market intervention;– Performance based (post-market intervention).

In order to manage compliance with legislation manufacturers use standards and government regulators accept compliance with standards as proof of compliance with legislation.

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CHAPTER ONE

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Introduction - continued

Pre-market intervention as a legislation enforcement tool makes compliance with standards mandatory in order to obtain approval to sell: – The manufacturer must show proof of compliance

with appropriate standards before placing the product on the market.

Post-market intervention as a legislation enforcement tool accepts compliance with standards as a deemed to comply solution to the legislation:– Prudent manufacturers hold proof of compliance

with appropriate standards to present in case of a regulatory challenge that may arise due to market surveillance.

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CHAPTER ONE

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Introduction - continued

The safety standards in the IEC 60335 series include requirements and test criteria to cover the following hazards.– Electric shock;– Thermal – burns, overheated surrounds, insulation;– Mechanical – cutting, crushing, explosion;– Fire – ignition of appliances due to internal faults;– Radiation and toxicity – non-ionising radiation

poisonous gases;These hazards are addressed during normal use and abnormal operation of the appliance

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CHAPTER ONE

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Contents

IntroductionElectric shock hazardsThermal hazardsAbnormal operationMechanical and other hazardsRadiation, toxicity and similar hazardsFire and heat hazardsConclusions

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CHAPTER TWO

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Electric shock hazardsSpecial probes used to check for adequacy of protection against access to live parts and for other than class O appliances, basic insulation.

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Test pinTest finger

CHAPTER TWO

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Electric shock hazards - continued

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Special probes are used where children are likely to use an appliance without adequate prior training in its use.

CHAPTER TWO

Child 3 -14 years

Child up to 3 years

57,9 ± 0,15101,6 ± 0,3451,6 ± 0,8

R 4,3 ± 0,05Ø 38,1 ± 0,3

Ø 38,4 ± 0,3

Ø 8,6 ± 0,1

Extension of handle

Axes of joints

Hemispherical

‘A’

View ‘A’

Collar

44 ± 0,15101,6 ± 0,3464,3 ± 0,8

R 2,8 ± 0,05

Ø 25,9 ± 0,2

Ø 25,4 ± 0,2

Extension of handle

View ‘A’

Hemispherical

Axes of joints

‘A’

Collar

Ø 5,6 ± 0,1

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Electric shock hazard - continued

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A frequency compensated circuit weighted for perception or reaction is used to check touch current values – these are then compared with the limits based on the data in the IEC 60479 series of standards.

T e s t te rm in a ls

A

B

C SR S

R B U 1

W e ig h te d to u c h c u r r e n t(p e rc e p t io n / re a c t io n )

U 2

5 0 0= (p e a k v a lu e )

U 2

R 1

C 1

IE C 1 0 7 8 /9 9

U2 is measured using an instrument with an approximately flat frequency response 0 to 1 MHz

CHAPTER TWO

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CHAPTER TWO

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Adequate earthing is needed as a second level of protection in class I appliances;The effectiveness of earthing circuits is checked by measuring the earthing circuit resistances to ensure that they do not exceed 0,1 Ω;Enhanced insulation is needed as a second level of protection in class II appliances;Isolation from the supply mains and a voltage limitation is needed as a second level protection in class III appliances.

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CHAPTER TWO

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Some other aspects that contribute to the electric shock hazard are:–Effects of heat, humidity and moisture on insulation dielectric strength;–Effects of pollution on creepage distances over insulated surfaces;–Effects of over-voltage on clearances between live parts and accessible surfaces.

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CHAPTER TWO

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These aspects can be amplified by the climate and infrastructure that are specific to individual countries, for example:–Enhanced effects of heat, humidity and moisture on insulation dielectric strength in counties having a warm damp equable (WDaE) climate (commonly referred to as tropical countries);–Ineffective protective earthing in the power supply system;–Effects of altitude on adequacy of clearances between live parts and accessible surfaces.

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CHAPTER TWO

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Options exist in the 60335 series to cover these country specific climate and infrastructure issues.–WDaE climates – enhanced damp heat test based on the data in IEC 60721-2-1;–Ineffective protective earthing – Class II;–Effects of altitude – impulse testing of clearances.

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CHAPTER TWO

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Pollution in a 4 slice toaster

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Pollution in a bathroom 3-in-1 fan/heater/luminaire after 5 years of use

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Contents


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CHAPTER THREE

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Thermal hazardsTemperature limits on appliance surrounds are selected to prevent pyrolysis of timber structures.Temperature limits for accessible surfaces are based on touch times to avoid a superficial partial thickness burn of the skin.Different materials give different temperature spreads for the burn thresholds. The burn thresholds are related to the thermal inertia of the material in question. Thermal inertia is the product of the density, thermal conductivity and specific thermal capacity of material.

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CHAPTER THREE

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Thermal hazards - continuedFor short contact periods the burn thresholds (contact temperature/time graphs) are not drawn as lines but are drawn as spreads.

Illustration of general relationship between the burn threshold and contact period when a hot surface is touched by the skin

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CHAPTER THREE

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Thermal hazards - continued

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Key1. Plastics2. ceramics3. Metals

Specific relationship between burn threshold and contact period when hot surface is touched by skin using logarithmic interpolation for contact times exceeding 10 s

CHAPTER THREE

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Burn hazards - continued

This takes into account the fact that for short contact periods the knowledge of the temperature boundary between non-burning and the onset of burning is not complete. The burn threshold depends on several factors which include:

– thickness of the skin at the touching point;– moisture of the skin’s surface (sweating);– contamination of the skin (e.g. grease);– touching force; – differences between the heat conductivity properties of

materials which have been combined in one group; – uncertainties of the scientific determination of the burn

threshold values.23

CHAPTER THREE

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When setting surface temperature limits, touchable surfaces of an appliance are generally considered to be one of the following:

– Hot non-functional surfaces;– Adjacent surfaces;– Surfaces of handles, knobs, grips and similar

parts which are continuously held in normal use;– Surfaces of handles, knobs, grips and similar

parts which are held for short periods only in normal use (e.g. switches);

– Other touchable surfaces.

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CHAPTER THREE

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Burn threshold values for the contact of the skin with water are derived from the lower limit of the burn threshold spread established for bare metals.The temperature limits are selected based on the use of individual appliances.For example the existing temperature limit for the glass in an oven door will be reduced based on a touch time of 15 s. This will minimise the risk of burns to the hands of very young children but will not completely alleviate it without the additional protection afforded by care giver supervision.

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CHAPTER THREE

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Right hand of an 18 month old child 11 days after prolonged contact with the glass of an oven door

CHAPTER THREE

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Contents


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CHAPTER FOUR

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Abnormal operation

The electric shock hazard, certain aspects of the thermal hazard and fire hazard are also assessed during abnormal operation of the appliance such as:–Failure of the normal temperature control;–Overloads and locking of moving parts such as the rotor of a motor and the contacts of a relay;–Failure of electronic components;–Failure of safety related embedded software;–The effects of electromagnetic phenomena on stand-by circuits and electronic disconnections.

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CHAPTER FOUR

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Abnormal operation - continued

Protection against the effects of abnormal operation is usually provided by the use of electromechanical devices or protective electronic circuits (PECs)

If the PEC is programmable the software must contain measures to control “stuck-at” faults and for certain appliances “DC faults”

PECs must be designed so that electromagnetic phenomena does not affect the ability of the PEC to perform its safety function

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CHAPTER FOUR

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Abnormal operation does not cover absurd use of an appliance.Sometimes additional requirements need to be specified due to hazards revealed by field experience with new appliance designs

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CHAPTER FOUR

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Fire as a result of careless use – laundry basket placed on a hob. The placement turned the heating

elements on

CHAPTER FOUR

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Fire as a result of arcing due to failure of extruded insulation on a heating element

CHAPTER FOUR

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The net result

CHAPTER FOUR

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Contents


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CHAPTER FIVE

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Mechanical and other hazards - continued

Some typical mechanical hazards resulting from operation of the appliance are–Crushing due to •operation of drives for doors, gates etc,• pinch points in amusement machines such as kiddie rides;–Injury due to access to moving parts of appliances such as blades in kitchen machines, the blades in a fan, the drum in spin extractors, the interface mechanism between drives for gates etc and the driven part;–Explosion due to excessive pressure in closed containers.

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CHAPTER FIVE

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The effect of these types of hazards are minimized by the use of–Non-contact presence sensors (infrared detectors) and contact presence sensors (pressure pads);–Increasing the dimensions of potential pinch points based on the physical size of body parts such as the head;–Restricting finger access to moving parts or placing them out of reach;–Restricting the rotational energy and hardness of fan blades;–Use of pressure relief devices and enhanced mechanical strength requirements.

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CHAPTER FIVE

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Explosions caused by leakage of flammable refrigerant

CHAPTER FIVE

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Explosion caused by leakage of flammable refrigerant

CHAPTER FIVE

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Damage due to an out of balance washing machine

CHAPTER FIVE


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Some typical mechanical hazards resulting from the normal construction of an appliance are:–Child entrapment in appliances with enclosed cavities such as refrigerators, tumble dryers, drying cabinets;–Presence of sharp edges “excluding functional sharp edges”;–Toppling due to inadequate stability;–Enclosures shaped or decorated like a toy.

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CHAPTER FIVE

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Some examples of “toy” type appliances

CHAPTER FIVE


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TC 61

ContentsIntroductionElectric shock hazardsThermal hazardsAbnormal operationMechanical and other hazardsRadiation, toxicity and similar hazardsFire and heat hazardsConclusions

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CHAPTER SIX

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Radiation, toxicity and similar hazards

Hazardous substances cannot be used in the construction of an appliance–Asbestos and oils containing polychlorinated biphenyl are specifically prohibited in IEC 60335-1;–The presence of substances such as Lead, Mercury, Cadmium, Hexavalent Chromium, Polybrominated Biphenyls, Polybrominated Diphenyl Ethers is controlled by legislation (RHoS) in various countries.

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CHAPTER SIX

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Some appliances produce toxic substances as a result of their operation and limits based on WHO guidelines are specified–Pyrolytic self cleaning ovens produce CO;–Air-cleaning appliances produce 03 .

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CHAPTER SIX

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Appliances are available that use non-ionizing radiation to perform their function. –Microwaves are used in cooking appliances;–Ultraviolet radiation (UVa and UVb ) is used in skin treatment appliances;–Ultraviolet radiation (UVc ) is used in water treatment appliances;–Infrared radiation is used in heating appliances.Radiation limits based on ICNIRP guidelines are specified.

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CHAPTER SIX

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Contents


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CHAPTER SEVEN

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Fire and heat hazards

An electric shock hazard or fire hazard exists if an appliance with non-metallic parts is affected by the heat generated during either normal or abnormal operation.A ball pressure test is applied to non-metallic parts– forming the enclosure; or –Supporting live parts; or–Providing supplementary or reinforced insulation.

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CHAPTER SEVEN

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Ball pressure apparatus

The apparatus is applied to the sample at a temperature related to the temperature rise values obtained during normal and abnormal operation of the appliance

CHAPTER SEVENFire and heat hazards

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Base of a cordless kettle after exposure to heat from abnormal operation


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Terminal cover in wall oven after exposure to heat from normal operation


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Fires related to appliances have many causes some of which are–Failure of components;–Mechanical failure of heating element supports;–High resistance joints in current carrying connections;–Careless use of an appliance such as•Leaving an unattended pot of cooking oil on an energized hob;•Incorrect installation of appliances such as electrically heatedbedding;•Inadvertent covering or placement of portable room heaters.

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CHAPTER SEVEN

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Mechanical failure of heating element supports


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Locked rotor plus thermostat failure plus incorrect positioning of thermal cut-out


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Fire and heat hazards - continued

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High resistance joints in current carrying connections

CHAPTER SEVEN

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Fire and heat hazards - continued

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Tracking in pollution degree 3 environment

CHAPTER SEVEN

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Design solutions to address these problems are assessed by

Abnormal operation tests for component failure;Drop tests and impact tests for mechanical

support failure;Fire simulation tests for bad connections;Review of user instructions for careless use.

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CHAPTER SEVEN

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The fire test used for simulating a current carrying bad connection, is the glow-wire end product test from IEC 60695-2-11;

A heated wire tip is applied to the material likely to be ignited by the bad connection and the results are observed;

The tip temperature (severity) applied is selected according to the expected current through the connection and typical use of the appliance (attended, unattended etc).

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CHAPTER SEVEN

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Glow-wire test apparatus


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Glow-wire test


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Many materials flame during and after application of the glow-wire tip.

This shows that this material may be source of ignition for other non-metallic materials in the vicinity.

In order to limit the spread of fire these other materials are subject to a consequential test using the needle flame described in IEC 60695-11-5.

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CHAPTER SEVEN

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Contents


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CHAPTER EIGHT

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Conclusions

The IEC 60335 series of standards are written in a manner that is timely, efficient and which keeps pace with modern technology. They are written so as to set prudent and realistic requirements–That facilitate international trade in electrical appliances;–That minimise the need for national differences;–That enable certification bodies to issue test reports containing repeatable and reproducible test results;–That manufacturers can apply to their designs;–That governments can confidently recognize in their regulations;–That provide protection for consumers.

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CHAPTER SEVEN

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Conclusions

To ensure that these requirements are relevant for your country we need your help;

Please participate actively in the work of TC 61;

If it is possible to participate s a P-member then do as an O-member.

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CHAPTER SEVEN

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THANK YOU

Copyright © IEC, Geneva, Switzerland

Documents

Technical Committee 61 · PDF fileChairman IEC Technical Committee 61 ... CHAPTER TWO Child 3 -14 years ... such as blades in kitchen machines, the blades in a fan,