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EUROPEAN STANDARD
EN 60738-1
NORME EUROPÉENNE
June 2006
EUROPÄISCHE NORM
ICS 31.040.30
English version
Thermistors -
Directly heated positive temperature coefficient
Part 1: Generic specification
(IEC 60738-1:2006)
Thermistances à coefficient  Direkt geheizte temperaturabhängige
de température positif Widerstände mit positivem
à chauffage direct Temperaturkoeffizienten
Partie 1: Spécification générique Teil 1: Fachgrundspezifikation
(CEI 60738-1:2006) (IEC 60738-1:2006)

This European Standard was approved by CENELEC on 2006-05-01. CENELEC members are bound to comply
with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and notified
to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, the Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2006 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60738-1:2006 E
Foreword
The text of document 40/1651/FDIS, future edition 3 of IEC 60738-1, prepared by IEC TC 40, Capacitors
and resistors for electronic equipment, was submitted to the IEC-CENELEC parallel vote and was
approved by CENELEC as EN 60738-1 on 2006-05-01.
This European Standard supersedes EN 60738-1:1999.
The changes with respect to EN 60738-1:1999 refer to the tables, figures and references.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2007-02-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2009-05-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 60738-1:2006 was approved by CENELEC as a European
Standard without any modification.
__________
- 3 - EN 60738-1:2006
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

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.

NOTE  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year

IEC 60027 Series Letter symbols to be used in electrical HD 60027 Series
technology
IEC 60050 Series International Electrotechnical Vocabulary - -
(IEV)
IEC 60062 (mod) 2004 Marking codes for resistors and capacitors EN 60062 2005

IEC 60068-1 1988 Environmental testing -
+ corr. October 1988 Part 1: General and guidance
+ A1 1992 EN 60068-1 1994
IEC 60068-2-1 1990 Environmental testing - EN 60068-2-1 1993
+ A1 1993 Part 2: Tests - Tests A: Cold + A1 1993
+ A2 1994 + A2 1994
IEC 60068-2-2 1974 Basic environmental testing procedures - EN 60068-2-2 1993

+ A1 1993 Part 2: Tests - Tests B: Dry heat + A1 1993

1) 2)
IEC 60068-2-6 - Environmental testing - EN 60068-2-6 1995
Part 2: Tests - Test Fc: Vibration (sinusoidal)

1) 2)
IEC 60068-2-11 - Environmental testing - EN 60068-2-11 1999
Part 2: Tests - Test Ka: Salt mist

1) 2)
IEC 60068-2-13 - Environmental testing - EN 60068-2-13 1999
Part 2: Tests - Test M: Low air pressure

IEC 60068-2-14 1984 Environmental testing -
+ A1 1986 Part 2: Tests - Test N: Change of temperature EN 60068-2-14 1999

IEC 60068-2-20 1979 Basic environmental testing procedures -
+ A2 1987 Part 2: Tests - Test T: Soldering HD 323.2.20 S3 1988

1) 2)
IEC 60068-2-21 - Environmental testing - EN 60068-2-21 1999
Part 2-21: Tests - Test U: Robustness of
terminations and integral mounting devices

1) 2)
IEC 60068-2-27 - Basic environmental testing procedures - EN 60068-2-27 1993
Part 2: Tests - Test Ea and guidance: Shock

1) 2)
IEC 60068-2-29 - Basic environmental testing procedures - EN 60068-2-29 1993
Part 2: Tests - Test Eb and guidance: Bump

1)
Undated reference.
2)
Valid edition at date of issue.

Publication Year Title EN/HD Year
IEC 60068-2-30 2005 Environmental testing - EN 60068-2-30 2005
Part 2-30: Tests - Test Db: Damp heat, cyclic
(12 h + 12 h cycle)
IEC 60068-2-45 1980 Basic environmental testing procedures - EN 60068-2-45 1992
Part 2: Tests - Test Xa and guidance:
Immersion in cleaning solvents

1) 2)
IEC 60068-2-58 - Environmental testing - EN 60068-2-58 2004
Part 2-58: Tests - Test Td: Test methods for + corr. December 2004
solderability, resistance to dissolution of
metallization and to soldering heat of surface
mounting devices (SMD)
1) 2)
IEC 60068-2-78 - Environmental testing - EN 60068-2-78 2001
Part 2-78: Tests - Test Cab: Damp heat,
steady state
1)
IEC 60294 - Measurement of the dimensions of a - -
cylindrical component having two axial
terminations
1)
IEC 60410 - Sampling plans and procedures for inspection - -
by attributes
IEC 60617 data- Graphical symbols for diagrams - - -
base
1)
IEC 60717 - Method for the determination of the space - -
required by capacitors and resistors with
unidirectional terminations
1) 2)
IEC 61249-2-7 - Materials for printed boards and other EN 61249-2-7 2002
interconnecting structures - + corr. September 2005
Part 2-7: Reinforced base materials, clad and
unclad - Epoxide woven E-glass laminated
sheet of defined flammability (vertical burning
test), copper-clad
1) 2)
IEC 61760-1 - Surface mounting technology - EN 61760-1 2006
Part 1: Standard method for the specification
of surface mounting components (SMDs)

1)
IEC QC 001002-3 - IEC Quality Assessment System for - -
Electronic Components (IECQ) - Rules of
Procedure - Part 3: Approval procedures

1)
ISO 1000 - SI units and recommendations for the use of - -
their multiples and of certain other units

INTERNATIONAL IEC
STANDARD 60738-1
QC 440000
Third edition
2006-04
Thermistors – Directly heated positive
temperature coefficient –
Part 1:
Generic specification
 IEC 2006  Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
PRICE CODE
Commission Electrotechnique Internationale XA
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
For price, see current catalogue

– 2 – 60738-1  IEC:2006(E)
CONTENTS
FOREWORD.5

1 Scope.7
2 Normative references .7
3 Terms and definitions .8
4 Units and symbols .16
5 Preferred values.17
5.1 Climatic categories.17
5.2 Marking .17
5.3 Spacings .18
6 Quality assessment procedures.18
6.1 General .18
6.2 Primary stage of manufacture.19
6.3 Subcontracting .19
6.4 Structurally similar components.19
6.5 Qualification approval procedures .20
6.6 Rework and repair .27
6.7 Release for delivery .27
6.8 Certified test records of released lots .28
6.9 Delayed delivery.28
6.10 Alternative test methods .28
6.11 Manufacture outside the geographical limits of IECQ NSIs .28
6.12 Unchecked parameters.28
7 Test and measurement procedures.28
7.1 General .28
7.2 Standard conditions for testing .29
7.3 Drying and recovery .29
7.4 Visual examination and check of dimensions.30
7.5 Zero-power resistance.30
7.6 Temperature coefficient of resistance.31
7.7 Insulation resistance (for insulated types only) .31
7.8 Voltage proof (for insulated types only) .32
7.9 Resistance/temperature characteristic.32
7.10 Dissipation factor at U (δ) .33
max
7.11 Response time by ambient temperature change (t ) .34
a
7.12 Response time by power change (t ).34
p
7.13 Thermal time constant by ambient temperature change (τ ) .35
a
7.14 Thermal time constant by cooling (τ ).35
c
7.15 Robustness of terminations .37
7.16 Solderability .38
7.17 Resistance to soldering heat .39
7.18 Rapid change of temperature .40
7.19 Vibration.40
7.20 Bump .40
7.21 Shock.41

60738-1  IEC:2006(E) – 3 –
7.22 Climatic sequence .41
7.23 Damp heat, steady state.42
7.24 Endurance.43
7.25 Tripping current and tripping time .46
7.26 Non-tripping current .47
7.27 Residual current .47
7.28 Surface temperature.47
7.29 Inrush current.48
7.30 Mounting (for surface mount thermistors only) .49
7.31 Shear (adhesion) test .50
7.32 Substrate bending test .50

Annex A (normative) Interpretation of sampling plans and procedures as described in
IEC 60410 for use within the IEC quality assessment system for electronic
components (IECQ) .51
Annex B (informative) Mounting for electrical measurements (except surface mount
types) .52
Annex C (informative) Mounting for temperature measurements .55

Figure 1 – Typical resistance-temperature characteristic and definitions for PTC
thermistors (at zero power) .10
Figure 2 – Typical R-TNF characteristic for PTC thermistors in sensor applications .11
Figure 3 – Typical current/voltage characteristic for PTC thermistors .11
Figure 4 – I against t at U .14
in dc
Figure 5 – I against t at U .15
in rms
Figure 6 – Dissipation factor test circuit .33
Figure 7 – Temperature gradient.34
Figure 8 – Circuit for measurement of thermal time constant by cooling.36
Figure 9 – Circuit for endurance at maximum operating temperature and maximum
voltage.45
Figure 10 – Circuit for surface temperature measurement.48
Figure 11 – Measuring circuit.48
Figure B.1 – Example of a preferred mounting method for thermistors without wire
terminations.52
Figure B.2 – Example of a preferred mounting method for thermistors with wire
terminations.53
Figure B.3 – Example of a preferred mounting method for surface mount thermistors .54
Figure C.1 – Example of a preferred mounting method for temperature measurement
on cylindrical heating elements .55

Table 1 – Creepage distances and clearances .18
Table 2 – Fixed sample size test schedule for qualification approval of thermistors for
current limitation – Assessment level EZ.22
Table 3 – Fixed sample size test schedule for qualification approval of thermistors for
use as heating elements – Assessment level EZ.23
Table 4 – Fixed sample size test schedule for qualification approval of thermistors for
inrush current application – Assessment level EZ .24
Table 5 – Fixed sample size test schedule for qualification approval of thermistors for
use as temperature sensing elements, Assessment level EZ .25

– 4 – 60738-1  IEC:2006(E)
Table 6 – Quality conformance inspection for lot-by-lot inspection .26
Table 7 – Quality conformance inspection for periodic testing .27
Table 8 – Tensile force .37
Table 9 – Number of cycles per climatic category .42

60738-1  IEC:2006(E) – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
THERMISTORS – DIRECTLY HEATED POSITIVE
TEMPERATURE COEFFICIENT –
Part 1: Generic specification
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of 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, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). 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. 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 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 IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60738-1 has been prepared by IEC technical committee 40:
Capacitors and resistors for electronic equipment.
This third edition cancels and replaces the second edition published in 1998 and constitutes a
minor revision. The changes with respect to the previous edition refer to the tables, figures
and references.
The text of this standard is based on the following documents:
FDIS Report on voting
40/1651/FDIS 40/1730/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.

– 6 – 60738-1  IEC:2006(E)
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The QC number that appears on the front cover of this publication is the specification number
in the IEC Quality Assessment System for Electronic Components (IECQ).
IEC 60738 consists of the following parts, under the general title Thermistors – Directly
heated positive step-function coefficient:
Part 1: Generic specification
Part 1-1: Blank detail specification – Current limiting application – Assessment level EZ
Part 1-2: Blank detail specification – Heating element application – Assessment level EZ
Part 1-3: Blank detail specification – Inrush current application – Assessment level EZ
Part 1-4: Blank detail specification – Sensing application – Assessment level EZ
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
A bilingual version of this standard may be issued at a later date.

60738-1  IEC:2006(E) – 7 –
THERMISTORS – DIRECTLY HEATED POSITIVE
TEMPERATURE COEFFICIENT –
Part 1: Generic specification
1 Scope
This part of IEC 60738 describes terms and methods of test for positive step-function
temperature coefficient thermistors, insulated and non-insulated types typically made from
ferro-electric semi-conductor materials.
It establishes standard terms, inspection procedures and methods of test for use in detail
specifications for Qualification Approval and for Quality Assessment Systems for electronic
components.
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 60027 (all parts), Letter symbols to be used in electrical technology
IEC 60050 (all parts), International Electrotechnical Vocabulary (IEV)
IEC 60062, Marking codes for resistors and capacitors
IEC 60068-1:1988, Environmental testing – Part 1: General and guidance
Amendment 1 (1992)
IEC 60068-2-1:1990, Environmental testing – Part 2: Tests – Tests A: Cold
Amendment 1 (1993)
Amendment 2 (1994)
IEC 60068-2-2:1974, Environmental testing – Part 2: Tests – Tests B: Dry heat
Amendment 1 (1993)
IEC 60068-2-6, Environmental testing – Part 2: Tests – Test Fc: Vibration (sinusoidal)
IEC 60068-2-11, Environmental testing – Part 2: Tests – Test Ka: Salt mist
IEC 60068-2-13, Environmental testing – Part 2: Tests – Test M: Low air pressure
IEC 60068-2-14:1984, Environmental testing – Part 2: Tests – Test N: Change of temperature
Amendment 1 (1986)
IEC 60068-2-20:1979, Environmental testing – Part 2: Tests – Test T: Soldering
Amendment 2 (1987)
IEC 60068-2-21, Environmental testing – Part 2-21: Tests – Test U: Robustness of
terminations and integral mounting devices

– 8 – 60738-1  IEC:2006(E)
IEC 60068-2-27, Environmental testing – Part 2: Tests – Test Ea and guidance: Shock
IEC 60068-2-29, Environmental testing – Part 2: Tests – Test Eb and guidance: Bump
IEC 60068-2-30:2005, Environmental testing – Part 2: Tests – Test Db: Damp heat, cyclic
(12 h + 12-hour cycle)
IEC 60068-2-45:1980, Environmental testing – Part 2: Tests – Test XA and guidance –
Immersion in cleaning solvents
IEC 60068-2-58, Environmental testing – Part 2-58: Tests – Test Td: Test methods for
solderability, resistance to dissolution of metallization and to soldering heat of surface
mounting devices (SMD)
IEC 60068-2-78, Environmental testing – Part 2-78: Tests – Test Cab: Damp heat, steady
state
IEC 60294, Measurement of the dimensions of a cylindrical component having two axial
terminations
IEC 60410, Sampling plans and procedures for inspection by attributes
IEC 60617 (all parts) [DB] : Graphical symbols for diagrams
IEC 60717, Method for determination of the space required by capacitors and resistors with
unidirectional terminations
IEC 61249-2-7, Materials for printed boards and other interconnecting structures – Part 2-7:
Reinforced base materials clad and unclad – Epoxide woven E-glass laminated sheet of
defined flammability (vertical burning test), copper-clad
IEC 61760-1, Surface mounting technology – Part 1: Standard method for the specification of
surface mounting components (SMDs)
IEC QC 001002-3, Rules of Procedure of the IEC Quality Assessment System for Electronic
Components (IECQ) – Part 3: Approval procedures
ISO 1000, SI units and recommendations for the use of their multiples and of certain other
units
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
type
group of components having similar design features and the similarity of whose manufacturing
techniques enables them to be grouped together either for qualification approval or for quality
conformance inspection
They are generally covered by a single detail specification
NOTE Components described in several detail specifications, may, in some cases, be considered as belonging to
the same type but they are generally covered by a single detail specification.
—————————
“DB” refers to the IEC on-line database.

60738-1  IEC:2006(E) – 9 –
3.2
style
variation within a type having specific nominal dimensions and characteristics
3.3
thermistor
thermally sensitive semiconducting resistor which exhibits a significant change in electrical
resistance with a change in body temperature
3.4
positive temperature coefficient thermistor
thermistor, the resistance of which increases with its increasing temperature throughout the
useful part of its characteristic
3.5
positive step-function temperature coefficient thermistor
PTC
thermistor which shows a step-like increase in its resistance when the increasing temperature
reaches a specific value
A PTC thermistor will show secondary effects which are to be taken into account
3.6
zero-power resistance
R
T
value of the resistance of a PTC thermistor, at a given temperature, under conditions such
that the change in resistance due to the internal generation of heat is negligible with respect
to the total error of measurement
NOTE Any resistance value of a PTC thermistor is dependent on the value and the mode of the applied voltage
(a.c. or d.c.) and, when an a.c. source is used, on the frequency (see 3.8 and 3.9).
3.7
nominal zero-power resistance
R
n
d.c. resistance value of a thermistor measured at a specified temperature, preferably at 25 °C,
with a power dissipation low enough that any further decrease in power will result only in a
negligible change in resistance. Zero-power resistance may also be measured using a.c. if
required by the detail specification
3.8
voltage dependency
secondary effect, exhibiting a decreasing resistance with increasing voltage across the
thermistor when measured at a constant body temperature
3.9
frequency dependency
secondary effect exhibiting a substantial decrease of the positive temperature coefficient of
the thermistor with increasing frequency
3.10
resistance/temperature characteristics
relationship between the zero-power resistance of a thermistor and the temperature of the
thermo-sensitive element when measured under specified reference conditions (see Figure 1)
NOTE PTC thermistors may have more than one resistance/temperature characteristic specified. The zero-power
resistance of the resistance/temperature characteristics can be measured using a pulse voltage (U ) higher than
pulse
1,5 V, which is specified in the detail specification. The right curve in Figure 1 shows the typical
resistance/temperature characteristic when using the pulse voltage (U ).
pulse
– 10 – 60738-1  IEC:2006(E)
Log R
R
p
≤ 1,5 V
d.c.
U
pulse
R
b
R
R
min
T T T
Rmin b p T  °C
Linear scale
IEC  402/06
Figure 1 – Typical resistance-temperature characteristic
and definitions for PTC thermistors (at zero power)

60738-1  IEC:2006(E) – 11 –
(logarithmic scale)
R  Ω
4 000
1 330
R
min
–20 0 T  °C
TNF – 20
TNF – 5
TNF
TNF + 5
TNF + 15
IEC  403/06
Figure 2 – Typical R-TNF characteristic for PTC thermistors in sensor applications
3.11
current/voltage characteristic
relationship in still air at 25 °C (unless otherwise stated) between the applied voltage (d.c.
and/or a.c.) at the thermistor terminations and the current under steady-state conditions (see
Figure 3)
Log I
T = constant
ambiant
I
res
U
Log U
max
IEC  404/06
NOTE 1 U will be specified by the manufacturer.
max
NOTE 2 The breakdown voltage is the value beyond which the voltage-handling capability of the thermistor no
longer exhibits its characteristic property
Figure 3 – Typical current/voltage characteristic for PTC thermistors

– 12 – 60738-1  IEC:2006(E)
3.12
nominal functioning temperature
T
NF
nominal temperature at the steep part of the resistance temperature characteristic at which
the system controlled by the thermistor is designed to operate
NOTE T is exclusively defined for PTC resistors in sensor applications.
NF
3.13
switching temperature
T
b
temperature at which the step-like function commences
3.14
minimum resistance
R
min
minimum value of the zero-power resistance/temperature characteristic (see Figures 1 and 2)
3.15
resistance at switching temperature
R
b
value of the zero-power resistance corresponding to the switching temperature defined as R
b
= 2 × R . As an alternative definition R = 2 × R can be used. If this definition is used, this
min b 25
shall be explicitly stated in the detail specification
3.16
temperature for minimum resistance
T
Rmin
temperature at which R occurs
min
3.17
temperature
T
p
temperature, higher than T , in the PTC part of the resistance/temperature characteristic for
b
which a minimum value R of the zero-power resistance is specified
p
3.18
resistance
R
p
zero-power resistance at temperature T measured at maximum voltage or a voltage specified
p
in the detail specification and given as a minimum value
NOTE The measurement should be made under such conditions that a change in resistance due to internal
generation of heat is negligible with respect to the total error of measurement. The applied voltage and the
characteristics of any pulse used should be given in the detail specification; when applying the maximum voltage,
the maximum overload current may not be exceeded.
3.19
average temperature coefficient of resistance at a stated voltage
a
R
rate of change of resistance with temperature expressed as %/K
It is calculated from the formula:
R
p
α = × ln
R
()TT− R
pb b
where T exceeds T by a minimum of 10 K.
p b
60738-1  IEC:2006(E) – 13 –
The temperatures T and T are to be given if applicable and the measurement conditions for
p b
R and R should be the same, unless otherwise specified in the detail specification
b p
NOTE The detail specification may specify the measurement of the temperature coefficient of resistance in a
narrow temperature range where its value is a maximum, together with a suitable test method.
3.20
upper category temperature
UCT
maximum ambient temperature for which a thermistor has been designed to operate
continuously at zero power
3.21
lower category temperature
LCT
minimum ambient temperature for which a thermistor has been designed to operate
continuously at zero power
3.22
maximum voltage
U
max
maximum a.c. or d.c. voltage which may be continuously applied to the thermistor without
exceeding the maximum overload current
3.23
operating temperature range at maximum voltage
range of ambient temperatures at which the thermistor can operate continuously at the
maximum voltage without exceeding the maximum overload current
3.24
isolation voltage (applicable only to insulated thermistors)
maximum peak voltage which may be applied under continuous operating conditions between
any of the thermistor terminations and any conducting surface
3.25
maximum overload current
I
mo
value of current for the operating temperature range, which shall not be exceeded
NOTE It may be necessary to limit the current through the thermistor by the use of a series resistor R .
s
3.26
residual current
I
res
value of current in the thermistor at a specified ambient temperature (preferably 25 °C) under
steady-state conditions. The applied voltage is the maximum voltage unless otherwise
specified (see Figure 3)
3.27
tripping current
I
t
lowest current which will cause the thermistor to trip to a high resistance condition at a
specified temperature (preferably 25 °C) and within a time to be specified in the detail
specification
3.28
maximum non-tripping current
I
max nt
maximum current at a specified ambient temperature (preferably 25 °C), which the thermistor
will conduct indefinitely in its low-resistance condition

– 14 – 60738-1  IEC:2006(E)
3.29
inrush current
I
in
current occurring during the transient period from the moment of switching to the steady-state
condition
3.30
peak inrush current
I
in p
peak inrush current is the maximum value of current during the transient period (see Figure 4)
3.31
minimum peak inrush current
I
in p min
lowest specified value of the peak of the inrush current
3.32
maximum peak inrush current
I
in p max
maximum specified value of the peak inrush current
I
in
I
in p max
I
in p min
t
IEC  405/06
Figure 4 – I against t at U
in dc
3.33
peak-to-peak inrush current (for a.c. conditions only)
I
in pp
value of the inrush current measured between adjacent positive and negative peaks (see
Figure 5)
3.34
minimum peak-to-peak inrush current
I
in pp min
lowest specified value of the peak to peak inrush current
3.35
maximum peak to peak inrush current
I
in pp max
maximum specified value of the peak to peak inrush current

60738-1  IEC:2006(E) – 15 –
I
in
I
in pp min
I t
in pp max
IEC  406/06
Figure 5 – I against t at U
in rms
3.36
peak inrush power
P
in p
peak power (U × I ) measured at the maximum peak value of the current occurring during
in p
the transient period from the moment of switching to the steady-state operating condition
measured under specified conditions of ambient temperature, voltage and circuit
3.37
maximum peak inrush power
P
in p max.
maximum peak power which can occur during the transient period before the thermistor
reaches its steady-state operating condition
NOTE In the detail specification it should be specified whether the “0-peak value” or the “r.m.s. value” of the
voltage should be taken.
3.38
maximum power
P
max.
maximum power is the power (U × I ) which can be dissipated continuously by the
max. res
thermistor when the maximum voltage is applied under specified conditions of ambient
temperature, circuit and thermal dissipation when thermal equilibrium is obtained
NOTE If the power is supplied by an a.c. source then the voltage and current should be measured with true r.m.s.
meters.
3.39
dissipation factor
δ
quotient (in W/K) of the change in power dissipation in the thermistor and the resultant
change of the body temperature under specified ambient conditions (temperature, medium)
3.40
thermal resistance
R
th
quotient (in K/W) of the temperature difference between the thermistor and its ambient and
the power dissipated by the thermistor under specified ambient conditions (temperature,
medium)
NOTE "Dissipation factor" and "thermal resistance" are mutually reciprocal.

– 16 – 60738-1  IEC:2006(E)
3.41
heat capacity
C
th
energy (in J) the thermistor needs to increase its body temperature by 1 K
3.42
response time
a) response time by ambient temperature change (t )
a
time (in s) required by a thermistor to change its temperature between two defined
conditions when subjected to a change in ambient temperature
b) response time by power change (t )
p
time (in s) required by a thermistor to change its temperature between two defined
conditions of power input
3.43
thermal time constant
thermal time constant (ideal) for a thermistor is the product of its heat capacity and its thermal
resistance
a) thermal time constant by ambient temperature change (τ )
a
time required for a thermistor to respond to 63,2 % of an external step change in ambient
temperature
b) thermal time constant by cooling (τ )
c
time required for a thermistor to cool by 63,2 % of its temperature excess, due to electrical
heating, in still air
3.44
insulated thermistors
thermistors capable of meeting the requirements of the insulation-resistance and voltage-
proof tests when specified in the test schedule
3.45
surface temperature
T
s
temperature under defined conditions at the boundary layer between two media
3.46
final surface temperature
T
sf
temperature reached under defined conditions when thermal equilibrium is established
4 Units and symbols
Units, graphical symbols, letter symbols and terminology shall, whenever possible, be taken
from the following publications:
IEC 60027
IEC 60050
IEC 60617
ISO 1000
When further items are required they shall be derived in accordance with the principles of the
documents listed above.
60738-1  IEC:2006(E) – 17 –
5 Preferred values
5.1 Climatic categories
The thermistors are classified into climatic categories according to the general rules given in
the annex to IEC 60068-1. The detail specification shall prescribe the appropriate category.
5.1.1 Bump test severities
The test severity given in the detail specification shall preferably be the following:
Test Eb (IEC 60068-2-29)
Acceleration: 400 m/s
Number of bumps: 4 000 total
Thermistors shall be mounted by their normal means, in such a manner that there shall be no
parasitic vibration.
5.1.2 Shock test severities
Test severities given in detail specifications shall preferably be the following:
Test Ea (IEC 60068-2-27)
Pulse shape: Half-sine
Acceleration: 500 m/s
Pulse duration: 11 ms
Severity: Three successive shocks in each axis direction per specimen
Separate specimens to be used for each axis (six shocks total per
specimen)
NOTE The shock and bump tests are normally specified as alternatives.
5.1.3 Vibration severities
Test severities given in the detail specifications shall preferably be selected from the
following:
Test Fc (IEC 60068-2-6)
Frequency Total number of
Hz sweep cycles
10 to   55
3 × 24
10 to  500
3 × 10
10 to 2 000
3 ×  8
5.2 Marking
5.2.1 General
The following shall be clearly marked on the thermistor in the following order of precedence
as space permits.
a) Values of the primary characteristics appropriate to the application of the thermistor to be
specified in the detail specification. When these values are coded (including colour
coding), details shall be given in the detail specification or type designation.
b) Manufacturer's name and/or trade mark.

– 18 – 60738-1  IEC:2006(E)
c) Date of manufacture.
d) The number of the detail specification and style.
The package containing the thermistors shall be clearly marked with all the information listed
above.
Any additional marking shall be so applied that no confusion can arise.
5.2.2 Coding
Where coding for the date is used, the method shall be selected from those given in
IEC 60062.
5.3 Spacings
5.3.1 The spacings between parts of opposite polarity of a thermistor shall be not less than
the applicable values specified in Table 1.
Table 1 – Creepage distances and clearances
Environment Operating voltage
DCV or Vrms
≤ 32 > 32 and ≤ 50 > 50 and ≤ 300 > 300 and ≤ 600
Sealed or encapsulated Exception 1 0,4 mm 0,8 mm 0,8 mm
Clean Exception 1 1,0 mm 1,0 mm 1,0 mm
Normal and dirty Exception 1 1,0 mm 1,5 mm 1,5 mm

This applies to both creepage distances and clearances.
Exception 1: as to the creepage distances and clearances for PTC thermistors with a rated
operating voltage of less th
...