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 Johns
Chairman IEC Technical Committee 61
SAFETY OF HOUSEHOLD AND SIMILAR
ELECTRICAL APPLIANCES
TC 61
Contents
Introduction
Electric shock hazards
Thermal hazards
Abnormal operation
Mechanical and other hazards
Radiation, toxicity and similar hazards
Fire and abnormal heat hazards
Conclusions
3
CHAPTER ONE
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Contents
Introduction
Electric shock hazards
Thermal hazards
Abnormal operation
Mechanical and other hazards
Radiation, toxicity and similar hazards
Fire and abnormal heat hazards
Conclusions
4
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
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
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 TWO
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Contents
Introduction
Electric shock hazards
Thermal hazards
Abnormal operation
Mechanical and other hazards
Radiation, toxicity and similar hazards
Fire and heat hazards
Conclusions
8
CHAPTER TWO
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Electric shock hazards
Special probes used to check for adequacy of protection against access
to live parts and for other than class O appliances, basic insulation.
Test finger
Test pin
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CHAPTER TWO
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Electric shock hazards - continued
Special probes are used where children are likely to use an
appliance without adequate prior training in its use.
451,6 ± 0,8
101,6 ± 0,3
57,9 ± 0,15
Axes of joints
Child 3 -14 years
‘A’
Ø 8,6 ± 0,1
Ø 38,1 ± 0,3
R 4,3 ± 0,05
Ø 38,4 ± 0,3
Hemispherical
Collar
Extension of handle
View ‘A’
101,6 ± 0,3
464,3 ± 0,8
44 ± 0,15
Axes of joints
‘A’
Child up to 3 years
R 2,8 ± 0,05
Ø 25,4 ± 0,2
Ø 25,9 ± 0,2
Ø 5,6 ± 0,1
Hemispherical
Extension of handle
Collar
View ‘A’
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CHAPTER TWO
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Electric shock hazard - continued
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.
A
RS
CS
R1
T e s t te r m i n a ls
B
RB
U1
W e ig h t e d to u c h c u r r e n t
( p e r c e p tio n / r e a c ti o n )
U2
=
( p e a k v a lu e )
500
C1
U2
IE C
1 0 7 8 /9 9
U2 is measured using an instrument with an
approximately flat frequency response 0 to 1 MHz
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CHAPTER TWO
Electric shock hazard - continued
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CHAPTER TWO
Electric shock hazard - continued
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
Electric shock hazard - continued
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
Electric shock hazard - continued
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
Electric shock hazard - continued
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
Electric shock hazard - continued
Pollution in a 4 slice toaster
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CHAPTER TWO
Electric shock hazard - continued
Pollution in a bathroom 3-in-1
fan/heater/luminaire after 5 years of use
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CHAPTER THREE
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Contents
Introduction
Electric shock hazards
Thermal hazards
Abnormal operation
Mechanical and other hazards
Radiation, toxicity and similar hazards
Fire and heat hazards
Conclusions
19
CHAPTER THREE
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Thermal hazards
Temperature 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
Thermal hazards - continued
For 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
Thermal hazards - continued
Key
1. Plastics
2. ceramics
3. 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
22
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CHAPTER THREE
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.
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CHAPTER THREE
Thermal hazards - continued
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
Thermal hazards - continued
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
Thermal hazards - continued
Right hand of an 18 month old child 11 days after prolonged
contact with the glass of an oven door
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CHAPTER FOUR
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Contents
Introduction
Electric shock hazards
Thermal hazards
Abnormal operation
Mechanical and other hazards
Radiation, toxicity and similar hazards
Fire and heat hazards
Conclusions
27
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
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
Abnormal operation - continued
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
Abnormal operation - continued
Fire as a result of careless use – laundry basket
placed on a hob. The placement turned the heating
elements on
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CHAPTER FOUR
Abnormal operation - continued
Fire as a result of arcing due to failure of extruded
insulation on a heating element
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CHAPTER FOUR
Abnormal operation - continued
The net result
33
CHAPTER FIVE
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Contents
Introduction
Electric shock hazards
Thermal hazards
Abnormal operation
Mechanical and other hazards
Radiation, toxicity and similar hazards
Fire and heat hazards
Conclusions
34
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CHAPTER FIVE
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
Mechanical and other hazards - continued
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
Mechanical and other hazards - continued
Explosions caused by leakage of flammable refrigerant
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CHAPTER FIVE
Mechanical and other hazards - continued
Explosion caused by leakage of flammable refrigerant
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CHAPTER FIVE
Mechanical and other hazards - continued
Damage due to an out of balance washing machine
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CHAPTER FIVE
Mechanical and other hazards - continued
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
Mechanical and other hazards - continued
Some examples of “toy” type appliances
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CHAPTER SIX
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Contents
Introduction
Electric shock hazards
Thermal hazards
Abnormal operation
Mechanical and other hazards
Radiation, toxicity and similar hazards
Fire and heat hazards
Conclusions
42
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CHAPTER SIX
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 603351;
–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
Radiation, toxicity and similar hazards
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
Radiation, toxicity and similar hazards
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 SEVEN
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Contents
Introduction
Electric shock hazards
Thermal hazards
Abnormal operation
Mechanical and other hazards
Radiation, toxicity and similar hazards
Fire and heat hazards
Conclusions
46
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CHAPTER SEVEN
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
Fire and heat hazards
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
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CHAPTER SEVEN
Fire and heat hazards
Base of a cordless kettle after exposure
to heat from abnormal operation
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CHAPTER SEVEN
Fire and heat hazards
Terminal cover in wall oven after exposure to heat from
normal operation
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CHAPTER SEVEN
Fire and heat hazards
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 heated
bedding;
•Inadvertent covering or placement of portable room heaters.
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CHAPTER SEVEN
Fire and heat hazards
Mechanical failure of heating element supports
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CHAPTER SEVEN
Fire and heat hazards
Locked rotor plus thermostat failure plus incorrect
positioning of thermal cut-out
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CHAPTER SEVEN
Fire and heat hazards - continued
High resistance joints in current carrying
connections
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CHAPTER SEVEN
Fire and heat hazards - continued
Tracking in pollution degree 3 environment
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CHAPTER SEVEN
Fire and heat hazards
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
Fire and heat hazards
► 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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Fire and heat hazards
Glow-wire test apparatus
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CHAPTER SEVEN
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Fire and heat hazards
Glow-wire test
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CHAPTER SEVEN
Fire and heat hazards
► 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 EIGHT
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Contents
Introduction
Electric shock hazards
Thermal hazards
Abnormal operation
Mechanical and other hazards
Radiation, toxicity and similar hazards
Fire and heat hazards
Conclusions
61
CHAPTER SEVEN
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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
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relevant for your country we need your
help;
►Please participate actively in the work
of TC 61;
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THANK YOU
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