EN 60691:2003

SLOVENSKI STANDARD
01-marec-2004
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SIST EN 60691:1998
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Thermal-links - Requirements and application guide
Temperatursicherungen - Anforderungen und Anwendungshinweise
Protecteurs thermiques - Prescriptions et guide d'application
Ta slovenski standard je istoveten z: EN 60691:2003
ICS:
29.120.50 9DURYDONHLQGUXJD Fuses and other overcurrent
PHGWRNRYQD]DãþLWD protection devices
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

NORME CEI
INTERNATIONALE IEC
INTERNATIONAL
Troisième édition
STANDARD
Third edition
2002-12
Protecteurs thermiques –
Prescriptions et guide d'application
Thermal-links –
Requirements and application guide
 IEC 2002 Droits de reproduction réservés  Copyright - all rights reserved
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International Electrotechnical Commission
Международная Электротехническая Комиссия
Pour prix, voir catalogue en vigueur
For price, see current catalogue

60691  IEC:2002 – 3 –
CONTENTS
FOREWORD . 5
INTRODUCTION .9
1 Scope .11
2 Normative references.13
3 Definitions .15
4 General requirements .17
5 General notes on tests.19
6 Classification .23
7 Marking .23
8 Documentation.25
9 Mechanical requirements .25
10 Electrical requirements .33
11 Temperature tests.47
12 Resistance to rusting .49
Annex A (normative) Application guide.53
Annex B (normative) Alternative ageing test for thermal-links with T
h
greater than 250 °C for use in electric irons .55
Annex C (normative) Conductive heat ageing test .57
Annex D (informative) Extended holding temperature evaluation .67
Annex E (normative) Seal ageing test .71
Annex F (normative) Identification requirements.75
Annex G (informative) Indelibility of markings .77
Figure 1 – Bending/twist test .31
Figure C.1 – Typical test fixture assembly .63
Figure C.2 – Typical thermal-link test oven.65
Figure D.1 – Typical terminal block support test fixture .69
Figure E.1 – Conditioning time versus oven temperature for proposed temperature index .73
Figure G.1 – Apparatus for testing durability of markings .77
Table 1 – Test schedule .21
Table 2 – Strength of terminals – Minimum required tensile and thrust test forces.33
Table 3 – Creepage distances and clearances (absolute minimum values).35
Table 4 – Test voltages for dielectric strength .37
Table 5 – Test current for interrupting test.41
Table 6 – Limited short-circuit test capacity.45

60691  IEC:2002 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
THERMAL-LINKS –
REQUIREMENTS AND APPLICATION GUIDE
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International
Organization for Standardization (ISO) in accordance with conditions determined by agreement between the
two organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60691 has been prepared by subcommittee 32C: Miniature fuses,
of IEC technical committee 32: Fuses.
This third edition cancels and replaces the second edition published in 1993, its amendment 1
(1995) and its amendment 2 (2000). This third edition constitutes a technical revision.
The text of this standard is based on the following documents:
FDIS Report on voting
32C/321/FDIS 32C/329/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The US national standard UL 1020 (fifth edition) which deals with thermal cutoffs/thermal-
links, has served as a basis for the elaboration of this new edition.

60691  IEC:2002 – 7 –
The committee has decided that the contents of this publication will remain unchanged until
2005. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
60691  IEC:2002 – 9 –
INTRODUCTION
Thermal-links, defined as non-resettable devices functioning once only without refunctioning,
are widely applied for the thermal protection of equipment in which, under fault conditions,
one or more parts may reach hazardous temperatures.
As these devices have several aspects in common with miniature fuse-links and are used for
obtaining a comparable degree of protection, this standard has endeavoured to lay down a
number of basic requirements for such devices.

60691  IEC:2002 – 11 –
THERMAL-LINKS –
REQUIREMENTS AND APPLICATION GUIDE
1 Scope and object
This International Standard is applicable to thermal-links intended for incorporation in
electrical appliances, electronic equipment and component parts thereof, normally intended
for use indoors, in order to protect them against excessive temperatures under abnormal
conditions.
NOTE 1 The equipment need not be designed to generate heat.
NOTE 2 The effectiveness of the protection against excessive temperatures logically depends upon the position
and method of mounting of the thermal-link, as well as upon the current which it is carrying.
NOTE 3 Attention is drawn to the fact that the external creepage distances and clearances specified in Table 3
may in some cases be smaller than those required by certain appliance or equipment standards. In such cases,
additional means should be provided when a thermal-link is mounted in the equipment in order to adjust the
creepage distances and clearances to the values required by the relevant equipment standard.
This standard may be applicable to thermal-links for use under conditions other than indoors,
provided that the climatic and other circumstances in the immediate surroundings of such
thermal-links are comparable with those in this standard.
This standard may be applicable to thermal-links in their simplest forms (e.g. melting strips or
wires), provided that molten materials expelled during function cannot adversely interfere with
the safe use of the equipment, especially in the case of hand-held or portable equipment,
irrespective of its position.
This standard is applicable to thermal-links with a rated voltage not exceeding 690 V a.c. or
d.c. and a rated current not exceeding 63 A.
The object of this standard is
a) to establish uniform requirements for thermal-links,
b) to define methods of test,
c) to provide useful information for the application of thermal-links in equipment.
This standard is not applicable to thermal-links used under extreme conditions such as
corrosive or explosive atmospheres.
This standard is not applicable to thermal-links to be used in circuits on a.c. with a frequency
lower than 45 Hz or higher than 62 Hz.

60691  IEC:2002 – 13 –
2 Normative references
The following referenced documents are indispensable for the application 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 60065:2001, Audio, video and similar electronic apparatus – Safety requirements
IEC 60085:1984, Thermal evaluation and classification of electrical insulation
IEC 60112, Method for determining the comparative and the proof tracking indices of solid
insulating materials under moist conditions
IEC 60216-1:2001, Electrical insulating materials – Properties of thermal endurance – Part 1:
Ageing procedures and evaluation of test results
IEC 60664-1:1992, Insulation coordination for equipment within low-voltage systems – Part 1:
Principles, requirements and tests
IEC 60695-2-11:2000, Fire hazard testing – Part 2-11: Glowing/hot-wire based test methods –
Glow-wire flammability test method for end-products
IEC 60695-10-2:1995, Fire hazard testing – Part 10-2: Guidance and test methods for the
minimization of the effects of abnormal heat on electrotechnical products involved in fires –
Method for testing products made from non-metallic materials for resistance to heat using the
ball pressure test
IEC 60695-10-3:2002, Fire hazard testing – Part 10-3: Abnormal heat – Mould stress relief
distortion test
IEC 60695-11-10:1999, Fire hazard testing – Part 11-10: Test flames – 50 W horizontal and
vertical flame test methods
IEC 60695-11-20:1999, Fire hazard testing – Part 11-20: Test flames – 500 W flame test
methods
IEC 60730-1:1999, Automatic electrical controls for household and similar use – Part 1:
General requirements
IEC 61210:1993, Connecting devices – Flat quick-connect terminations for electrical copper
conductors – Safety requirements
UL 1020:1994, Thermal Cutoffs for Use in Electrical Appliances and Components
———————
A fourth edition of IEC 60112, due to be published in 2003, is being prepared.

60691  IEC:2002 – 15 –
3 Definitions
For the purposes of this International Standard, the following definitions apply.
3.1
clearance
shortest distance in air between two conductive parts
3.2
creepage distance
shortest distance along the surface of insulating material between two conductive parts
3.3
holding temperature, T
h
maximum temperature of the thermal-link at which it will not change its state of conductivity
during a specified time under specified conditions
3.4
homogeneous series (of thermal-links)
series of thermal-links having common overall construction, deviating from each other only in
such characteristics that, for a given test, the testing of one or a reduced number of particular
thermal-links of that series shall be taken as representative for all the thermal-links of the
series
3.5
interrupting current, l
b
value of the current that the thermal-link is capable of interrupting at rated voltage and under
specified circuit conditions
3.6
maximum temperature limit, T
m
temperature of the thermal-link stated by the manufacturer, up to which the mechanical and
electrical properties of the thermal-link, having changed its state of conductivity, will not be
impaired for a given time
3.7
pilot duty
class of operation in which the ultimate electrical load is controlled by an auxiliary means
such as a relay or contactor
3.8
portable equipment
equipment which is moved while in operation or which can easily be moved from one place to
another while connected to the supply
3.9
rated current, I
r
current used to classify a thermal-link
3.10
rated functioning temperature, T
f
temperature of the thermal-link which causes it to change its state of conductivity with a
detection current up to 10 mA as the only load

60691  IEC:2002 – 17 –
3.11
rated voltage, U
r
voltage used to classify a thermal-link
3.12
thermal element
metallic or non-metallic fusible material that is part of a thermal-link and is responsive to
temperature by a change of state such as from solid to liquid at the temperature for which it is
calibrated
3.13
thermal-link
non-resettable device incorporating a thermal element, which will open a circuit once only
when exposed for a sufficient length of time to a temperature in excess of that for which it has
been designed
3.14
transient overload current, l
p
direct current pulse train which the thermal-link is able to withstand without impairing its
characteristics
3.15
type test
conformity testing on the basis of one or more specimens of a product representative of the
production
3.16
extended holding temperature, T
h-100
maximum temperature at which a thermal-link can be maintained while conducting the rated
load current at the rated voltage for a period of 100 weeks which will not cause the thermal-
link to open circuit in accordance with extended holding temperature evaluation (see
Annex D)
NOTE This is a rating for user consideration during the investigation of the end product.
3.17
conductive heat ageing test
CHAT
test to evaluate a thermal-link for use in an appliance (see Annex C)
NOTE If it performs satisfactorily, the thermal-link will be assigned a CHAT rating. This rating is for end-product
user consideration during the investigation of the end-use product.
4 General requirements
Adequate protection of the equipment against excessive temperatures not only depends upon
the properties of the thermal-link but also to a large extent upon the mounting of the thermal-
link in the equipment. Therefore, in addition to good engineering practice, the requirements of
the application guide in Annex A shall be considered.
Thermal-links shall have adequate electrical and mechanical strength and shall be
constructed so as to withstand all conditions of handling likely to be encountered during
mounting and normal use, when used within the requirements of this standard.

60691  IEC:2002 – 19 –
When a thermal-link changes its state of conductivity, no arc or flame shall be maintained, nor
material expelled that might impair the surrounding area or otherwise create a risk of electric
shock or fire.
NOTE For thermal-links using melting strips or wires, care should be taken to prevent molten material from short-
circuiting or bridging creepage distances and clearances in air, so as to reduce the risk of impairing the insulation
system of the equipment.
After it has functioned, the thermal-link shall not be damaged when subjected to temperatures
not exceeding T , in such a way that the safety of the equipment with regard to risk of electric
m
shock hazard and electrical breakdown is impaired.
5 General notes on tests
Unless otherwise indicated, all tests described in this standard are type tests and shall be
carried out under room ambient conditions.
If the result of a test is influenced, to an appreciable extent, by the position and method of
mounting of the specimen, the most unfavourable condition shall be chosen for the relevant
tests and recorded.
If a thermal-link has been specifically designed for use in a special type of equipment and
cannot be tested separately, the tests of this standard shall be performed in that equipment or
in the relevant part of it, or similar.
When testing a homogeneous series of thermal-links, all the tests shall be applied to thermal-
links with the lowest and highest T . Thermal-links with intermediate rated functioning tem-
f
peratures need only be subjected to tests according to 10.6, 11.2, 11.3 and 11.4.
The total number of specimens required is 48. Out of a total of 48 specimens, 15 are kept as
spares in case some of the tests have to be repeated. Out of a total of 48 specimens, 33 are
divided into groups assigned an alphabetical letter from A to K. Each group consists of three
specimens. In general, tests shall be performed in the order indicated in Table 1 but, if so
required, tests may be repeated, for example the test on marking (see Clause 7). Additional
samples may be needed according to note 3 of Table 1.
No failures are permitted in the tests carried out in accordance with Clauses 10 and 11.
If, in any of the tests carried out in accordance with the other clauses, one failure is reported,
that test shall be repeated on twice the number of specimens and no further failures are
allowed.
The conductive heat ageing test is applicable when declared by the manufacturer. This test
shall be conducted on thermal-links with a functioning temperature (T ) rating of 175 °C or
f
above. The conductive heat ageing test is optional for thermal-links with a T rating less than
f
175 °C.
Exception: The conductive heat ageing test may be omitted if the thermal-link is of eutectic
type and is constructed without contacts.
NOTE In the USA the conductive heat ageing test is required to be declared.

60691  IEC:2002 – 21 –
Manufacturer's inspection and factory test programme
The manufacturer shall provide regular production control, inspection and tests. Details of the
programme shall be agreed to between manufacturer and the testing house.
Table 1 – Test schedule
Specimen groups
Clause or
Test
subclause
A B CDE F G H I J K
7* Marking (rub test) XX
9 Mechanical requirements
9.2* Tensile force X
9.3* Thrust force X
9.4* Bending/twist force X
12* Resistance to rusting (ferrous parts only) X
10 Electrical requirements
10.1* Creepage distances and clearances X X
10.2.1* Humidity test X X X X X
10.2.2* Temperature and humidity cycle conditioning XX X X X
(note 2)
10.3* Dielectric strength (if applicable) XX X X X
10.4* Insulation resistance (if applicable) X X X X X
10.5* Resistance to tracking X X
10.6 Interrupting current X X
10.7* Transient overload current X X X
11 Temperature tests
11.2 Check on T X X
f
11.3 Check on T followed by dielectric test X X
m
11.4 Ageing XXX XX X
step 1 (optional) 21 days
step 2 (mandatory) 21 days
step 3 (mandatory) 14 days
step 4 (mandatory) 7 days
step 5 (mandatory) 7 days
step 6 (mandatory) 24 h
10.3 Dielectric strength XX XX XXX XX X X
10.4 Insulation resistance X X X X X X X X X X X
7* Marking (visual inspection only) X X
NOTE 1 For homogeneous series, tests marked with an asterisk may be omitted for intermediate ratings.
NOTE 2 At the manufacturer's request, the humidity test of 10.2.1 can be omitted if the third humidity cycle of the
temperature and humidity condition of 10.2.2 is conducted for 168 h.
NOTE 3 If the conditions of voltage, power and current in c), d) and e) of 10.6.2 are not covered by one test, a
minimum of three samples should be tested for each condition.

60691  IEC:2002 – 23 –
6 Classification
6.1 Electrical conditions
With regard to electrical conditions, the following terms are used:
a) Voltage
1) AC
2) DC
b) Current
1) Resistive
2) Inductive
–Motor
– Pilot duty
– Electric discharge lamp
6.2 Thermal conditions
With regard to thermal conditions, the following symbols and abbreviations are used:
a) T
f
b) T
h
c) T
m
d) CHAT
e) T
h-100
6.3 Resistance to tracking
With regard to resistance to tracking, the following ranges are used:
a) Proof tracking index from 120 to 174;
b) Proof tracking index from 175 to 249;
c) Proof tracking index greater than or equal to 250.
NOTE These ranges are based on test methods for surface tracking laid down in IEC 60112.
7 Marking
Each thermal-link shall be marked with the following:
a) type or catalogue reference;
b) manufacturer’s name or trade mark;
c) rated functioning temperature T with or without the symbol T followed by the number of
f f
degrees Celsius (marked with °C or C);
d) date code which identifies the date of manufacture and which does not repeat for at least
10 years, and a factory location or code, stamped on the thermal-link or the smallest
packaging.
NOTE 1 If there is only one factory, the factory location may be omitted.

60691  IEC:2002 – 25 –
The rated functioning temperature T may be omitted if a different type or catalogue reference
f
is employed for each different functioning temperature.
Where size permits, additional markings such as rated voltage followed by V, rated current
followed by A, and other optional markings as needed, may be placed on the thermal-link.
Marking shall be indelible and legible.
Indelibility is checked by trying to remove the marking by rubbing lightly for 15 s with a piece
of cloth soaked with water. Legibility is checked by inspection. After the ageing tests of 11.4,
compliance is checked by inspection.
NOTE 2 Instead of “rubbing lightly” the apparatus shown in Figure G.1 may be used.
The marking in accordance with a), b), c) and d) above shall be printed on the packaging,
together with a reference to this standard.
Compliance is checked by inspection.
8 Documentation
The manufacturer shall provide in his technical documentation, catalogues or instructional
leaflets the following information in addition to that required in Clause 7:
a) classification in accordance with Clause 6;
b) for each of the classifications
1) characteristic temperatures T , T , T ;
f h m
2) characteristic currents l , l , l ;
r b p
3) rated voltage U ;
r
c) suitability for sealing in, or use with impregnating fluids or cleaning solvents;
NOTE 1 In order to avoid possible damage to the thermal-link, the manufacturer should be consulted when
the end-use application involves sealing in or the use of cleaning solvents.
d) information for mounting the thermal-link in the equipment.
NOTE 2 For reasons of safety, it should be made clear in the documentation that a thermal-link is a non-
repairable item and that, in case of replacement, an equivalent thermal-link from the same manufacturer and
having the same catalogue reference should be used, mounted in exactly the same way.
NOTE 3 Catalogue or reference numbers should define those parameters such as temperature, current and
voltage which together classify a thermal-link.
9 Mechanical requirements
Thermal-links shall have adequate mechanical strength and stability so as to withstand the
stresses likely to be encountered during handling, normal use and fault conditions of the
relevant end-use equipment.
Tab terminals shall be constructed in accordance with IEC 61210.

60691  IEC:2002 – 27 –
Current-carrying parts shall be constructed in such a way that contact pressure is not
transmitted through non-metallic material other than ceramic, or any material considered as
having sufficient dimensional stability over the range of temperatures to be expected, unless
there is sufficient resilience in the corresponding metal parts to compensate for any shrinkage
or distortion of the non-metallic material.
Current-carrying parts shall have the necessary mechanical strength, be capable of carrying
the rated current and shall be of a material that is acceptable for the particular application.
For current-carrying parts, temperature limits should be considered according to IEC 60730-1.
Friction shall not be used to secure uninsulated live parts (including terminals) to supporting
surfaces if there is a risk of such parts turning or shifting their position, resulting in the
reduction of spacings to less than those required elsewhere in this standard. The security of
contact assemblies shall be such that alignment of contacts is maintained.
Leads and terminal parts shall be secured so that stress on them during installation and
normal use does not impair operation of the thermal-link. Thermal-links using seals with
formed leads for use in appliances or components shall not be bent less than 3 mm from the
thermal-link seal.
Exception: Leads may be bent less than 3 mm from the seal if
a) the thermal-link manufacturer's bending fixture and procedure does not transmit stress to
the thermal-link operating mechanism, and if
b) formed test samples shall be subjected to the bending/twist lead secureness test of 9.4
and the rated functioning temperature test of 11.2.
Thermal-links with leads smaller than 0,21 mm shall be provided with application instructions
that instruct the user how to mount the device in equipment, taking into consideration the
device's temperature response. The instructions shall also include guidance on the effects
that movement and vibration in the equipment may have on the thermal-link's terminals,
connections and other mounting components.
A terminal for a soldered connection shall have provision, such as a hole, for holding the
conductor independently of solder.
When applicable, provision shall be made for securely mounting a thermal-link in position.
Exception: Types intended to be embedded in windings and the like need not have provision
for mounting.
Bolts, screws, or other parts used for mounting an assembly having a thermal-link shall be
independent of those used for securing component parts of the assembly.
Compliance is checked by the lead secureness tests of 9.1. Mounting and securement
instructions shall be provided with thermal-links for the manufacturer of the end-product in
accordance with Annex A.
60691  IEC:2002 – 29 –
9.1 Lead secureness tests
If force applied to thermal-link wire leads causes breakdown of one or more parts leading
directly or indirectly to stress being applied to the operating mechanism, the tests described in
9.2, 9.3 and 9.4 shall be conducted. There shall be no displacement of parts that would tend
to reclose a thermal-link or reduce creepages or clearances as a result of the tests specified
in 9.2 and 9.3. There shall be no displacement of parts other than the wire leads as a result of
the test specified in 9.4.
The tests shall be conducted with the samples at an ambient temperature of (25 ± 5) °C.
9.2 Tensile test
The thermal-link shall be supported in any convenient manner in order not to damage it
and a tensile force as specified in Table 2 shall be applied to each lead for 10 min.
9.3 Thrust test
The thermal-link shall be supported using any convenient means such that it is not damaged
and a thrust force as specified in Table 2 shall be applied to each lead for 10 min at
a distance of 2 mm from the thermal-link.

90°
60691  IEC:2002 – 31 –
9.4 Bending/twist test
The thermal-link shall be rigidly supported such that it is not damaged. Each lead shall be
bent through 90° at a location 10 mm from the body of the thermal-link and then twisted
through 180° as shown in Figure 1.
Thermal-link
rigidly supported
10 mm
Step 1: Bend
180°
Step 2: Twist
IEC  2769/02
Figure 1 – Bending/twist test
60691  IEC:2002 – 33 –
Table 2 – Strength of terminals – Minimum required tensile and thrust test forces
Nominal cross-sectional area of the terminal, A Tensile force Thrust force
mm N N
Up to and including 0,05 1 0,25
Over 0,05 up to and including 1,2 20 × A 5 × A
Over 1,2 40 8
NOTE A is the nominal cross-sectional area of the terminal in mm .
10 Electrical requirements
Thermal-links shall comply with the relevant requirements in this clause with regard to test
voltages, currents, insulation resistances, creepage distances and clearances in air.
Contacts used for the current path in a thermal-link shall withstand the voltage stress
determined by the voltage source in the circuit. Current-carrying elements or contacts,
together with their terminals, are usually isolated from metal parts such as mounting brackets,
metal enclosures and the like, by insulating material.
If mounting brackets or metal parts of the thermal-link's enclosure are accessible or
connected through low impedances to metal enclosures of the equipment accessible to the
user from the outside, the insulation between the current-carrying elements of the thermal-link
and such conductive enclosures shall be adequate under specified conditions of ambient
temperature and humidity.
NOTE 1 The rated voltage, U , as stated by the manufacturer is used for deriving the relevant values for test
r
voltages.
NOTE 2 The voltage rating of a thermal-link should be based on the source voltage in the circuit. The voltage
rating for the insulation between current-carrying parts of such devices and the enclosure may be increased by
additional insulation; for example, by wrapping the thermal-link in insulating foil.
10.1 Creepage distances and clearances
The creepage distances and clearances between current-carrying parts (contacts together
with their terminals) and the outside of the thermal-link housing including insulated metal
parts thereof, shall be not less than the values in Table 3. The values indicated are absolute
minimum values and inclusive of manufacturing tolerances.
These distances do not apply between the open contacts of a thermal-link.
Compliance is checked by measuring the distances concerned.
An insulating barrier or liner that is used to provide spacings, including spacings in
conjunction with the required over surface spacings, shall be at least 0,7 mm thick.
However, there are two exceptions:

60691  IEC:2002 – 35 –
Exception No. 1: A barrier or liner providing spacing in air or oil and used in conjunction with
at least one-half the required spacing shall be at least 0,3 mm thick provided the barrier or
liner
a) is an acceptable insulating material,
b) is resistant to moisture,
c) has mechanical strength for the application if exposed, or otherwise subjected to
mechanical damage,
d) is held in place,
e) is located so that it will not be adversely affected by the operation of the equipment in
service, including the effects of arcing.
Exception No. 2:
• Insulating material having a thickness less than 0,7 mm may be used if investigated and
found to be acceptable for the particular application, and equivalent in all respects to
materials of the specified thickness.
• Mica shall be at least 0,4 mm thick if used in place of the clearance required in Table 3,
provided the mica is fixed in position by the parts between which the clearance is to be
maintained.
Table 3 – Creepage distances and clearances
(absolute minimum values)
Rated voltage, U Clearance Creepage distances
r
V mm mm
0- 32 0,2 0,53
33 - 50 0,2 1,2
51 - 125 0,5 1,5
126 - 250 1,5 2,5
251 - 400 3,0 4,0
401 - 690 4,0 6,9
NOTE 1 The clearances/creepage distances are specified according to IEC 60664-1.
NOTE 2 The values specified are for typical applications of thermal-links assuming:
a) continuous voltage stress;
b) altitude of 2 000 m;
c) basic insulation;
d) inhomogeneous field;
e) overvoltage category II;
f) pollution degree 2;
g) material group IIIa.
NOTE 3 If conditions are different from those specified in note 2, adjustments in clearances/creepages will
be necessary as per IEC 60664-1.
10.2 Humidity conditioning
Thermal-links shall not be adversely influenced by humidity present in the ambient conditions
for which they are intended. Compliance is checked by subjecting the specimens to the
temperature and humidity conditioning tests of 10.2.1 and 10.2.2 below, followed immediately
by the tests for dielectric strength (see 10.3) and insulation resistance (see 10.4).

60691  IEC:2002 – 37 –
10.2.1 Humidity test
The humidity test is carried out in a humidity chamber containing air with a relative humidity
between 90 % and 95 %. The temperature, t, of the air at all places where the thermal-links
can be located, is maintained at 30 °C. Before being placed in the chamber, the specimens
− 2
are brought to a temperature between 30 °C and 40 °C, and kept at that temperature for about
1 h. The specimens are kept in the humidity chamber for seven days.
After this test, the samples shall show no damage in the sense of this standard.
The air in the chamber should be moving and the chamber so designed that mist or
condensed water cannot precipitate on specimens.
10.2.2 Temperature and humidity cycle conditioning
Thermal-link samples shall be subjected to three complete conditioning cycles. Each cycle
shall consist of 24 h at rated functioning temperature, T , minus 15 K but not less than 60 °C,
f
followed immediately by at least 96 h at (35 ± 2) °C and (90 ± 5) % relative humidity, followed
by 8 h at (0 ± 2) °C.
After the conditioning test, the samples shall be brought to a room ambient temperature of
(25 ± 5) °C before being subjected to the test sequence specified in Table 1.
10.3 Dielectric strength
The dielectric strength of thermal-links shall be adequate both before and after having
operated, and also after having been subjected to the tests of 10.2.
Compliance is checked by applying the following voltage test immediately after the tests of
10.2, if applicable, and also after the temperature tests of Clause 11.
Test voltages shall comply with the values indicated in Table 4.
The insulation is subjected to a test voltage with a substantially sine-wave form having
a frequency between 45 Hz and 62 Hz.
Initially not more than half the prescribed voltage is applied. It is then raised with a rate of rise
of approximately 500 V/s to the full value.
Immediately after the humidity test, the enclosure shall be wrapped in metal foil and the test
voltage shall be applied for 1 min across the disconnection and between the live parts and the
metal foil.
The specimens are deemed to comply with the requirements if no flashover or breakdown
occurs.
NOTE A power transformer with an output of not less than 100 VA is recommended for this test.
Table 4 – Test voltages for dielectric strength
Between Test voltage
Live parts and enclosure 2 U + 1 000 V
r
Disconnection (between open contacts) 2 U
r
60691  IEC:2002 – 39 –
10.4 Insulation resistance
The insulation resistance of thermal-links shall be adequate both before and after having
changed their state of conductivity, and also after having been subjected to the relevant tests
of 10.2.
Compliance is checked by measuring the insulation resistance after the humidity test, before
and after having operated in the temperature test of Clause 11. The insulation resistance shall
be measured with a d.c. voltage of 2 U between the current path and the enclosure, wrapped
r
in metal foil if applicable, and between the terminals.
NOTE A d.c. test voltage is used in order to eliminate possible deviations due to capacitive currents.
The specimens are deemed to comply with the requirements if the insulation resistance
measured between the current path and the enclosures is not less than 2 MΩ, and across the
disconnection is not less than 0,2 MΩ.
10.5 Resistance to tracking
If insulating material used for the support of current-carrying parts, contacts and terminals is
exposed during normal use to deposition of moisture or dust, it shall be resistant to tracking.
For material other than ceramic, compliance is checked by performing a tracking test in
accordance with IEC 60112 on specimens or flat test pieces of equivalent insulating material.
The PTI values shall be declared by the manufacturer.
In order to determine acceptability of an insulating material, consideration shall be given to
such properties as:
a) mechanical strength;
b) resistance to combustion and ignition;
c) dielectric strength;
d) insulation resistance;
e) thermal ageing;
f) the degree that a material is enclosed or protected;
g) resistance to arcing;
h) resistance to distortion and creep under conditions of normal and abnormal use and
i) any other properties in conjunction with conditions of service.
Insulating materials, such as mica, cold-molded compound, or refractory material are usually
acceptable for use as direct supports of live parts without further evaluation.
If it is necessary to investigate an insulating material, the following standards shall be used
for evaluation of the properties itemized in points a) to i) above: IEC 60085, IEC 60216-1,
IEC 60695-2-11, IEC 60695-10-2, IEC 60695-10-3, IEC 60695-11-10 and IEC 60695-11-20.
Exception: Seals and potting compounds not relied upon for contact alignment or securement
of leads may be subjected to the seal ageing test specified in Annex E.

60691  IEC:2002 – 41 –
10.6 Interrupting current
10.6.1 General
A thermal-link shall interrupt the applicable test current specified in Table 5 at 1,1 times the
rated voltage, U , under the conditions specified in items a) to i) of 10.6.2. There shall be no
r
damage to the integral leads of a thermal-link. The case of an enclosed element shall remain
intact. The 3 A fuses specified in items a) and b) of 10.6.2 shall not function (open). An
exposed element shall not arc to adjacent metal parts and material shall not be expelled
which may harm the surrounding area.
10.6.2 Specific conditions
a) Any noncurrent-carrying metal part that is an inherent part of the thermal assembly and
that may be bonded electrically to a normally-earthed exposed part of the end-product
shall be connected through a 3 A fuse to earth.
Table 5 – Test current for interrupting test
Type of rating Rated in Test current Power factor
a
AC locked rotor amperes 6 times full-load current
b
(LRA)
0,40 - 0,50
Motor
c
DC amperes 10 times full-load current
c
AC amperes 4 times rated current
Electric discharge lamp 0,40 - 0,50
AC amperes
d, b
Ampere 1,5 times rated current
0,75 - 0,80
DC amperes
1,5 times rated current
ee
Pilot duty Volt-amperes
a
Or the specified value, such as horsepower, if locked rotor ampere rating is omitted.
b
Non-inductive resistive load.
c
For 120 V supply use at least 20 A test current.
d
Power factor may be 1,0 if rated resistive only.
e
See point f).
b) For a thermal-link having an exposed element, a metal screen shall be located 12,7 mm
away from live parts. The screen shall be connected to the opposite pole of the test circuit
through a 3 A fuse. The distance is measured between the screen and the nearest point of
the element when the element is in the open position.
Exception: Based on the intended use of a thermal-link, the screen may be located at
a distance other than 12,7 mm if acceptable to both the manufacturer and the end user.
c) The test circuit shall have an open circuit voltage within a range of 100 % to 105 % of the
specified test voltage, unless a higher voltage is acceptable to both the manufacturer and
the end user. The closed circuit voltage of the test circuit with the device's rated current
flowing shall be within 2,5 % of the specified test voltage.

60691  IEC:2002 – 43 –
d) If a thermal-link has the same current rating at more than one voltage, a test at the highest
voltage is considered to be representative of tests at the lower voltages.
e) If a thermal-link has more than one voltage rating within a specific power factor group, the
tests shall cover the conditions of maximum voltage, power, and current. One test may
cover two of these conditions.
f) For thermal-links assigned a pilot duty rating, the test load shall consist of an
electromagnet representative of the magnet coil load that the thermal-link is intended to
control. The test current shall be the normal current which shall be determined from the
voltage and volt-ampere rating of the thermal-link. For an alternating current thermal-link,
the power factor shall be 0,35 or less and the in
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