IEC TR 60890:2022
(Main)A method of temperature-rise verification of low-voltage switchgear and controlgear assemblies by calculation
A method of temperature-rise verification of low-voltage switchgear and controlgear assemblies by calculation
IEC TR 60890:2022 specifies a method of air temperature-rise calculation inside enclosures for low-voltage switchgear and controlgear assemblies or similar products in accordance with their respective standard. The method is primarily applicable to enclosed assemblies or partitioned sections of assemblies without forced ventilation. This third edition cancels and replaces the second edition published in 2014. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- alignment with IEC 61439-1:2020;
- addition of individual annexes for guidance of technical explanations related to:
--- effect of an uneven power distribution;
--- additional temperature-rise due to solar radiation;
--- effect of different enclosure materials;
--- effect of different natural ventilation management;
--- forced ventilation management;
--- power losses calculation;
--- impact of an adjacent wall can have on the assembly cooling surface(s);
- maximum internal ambient temperature limit into an assembly;
- validity area of the calculation extended from 3 150 A to 3 200 A;
- addition of an algebraic equation to the different curves included in the document.
Méthode de vérification par calcul des échauffements pour les ensembles d'appareillages à basse tension
L'IEC TR 60890:2022 spécifie une méthode de calcul des échauffements de l'air à l'intérieur d'une enveloppe pour les ensembles d'appareillages à basse tension ou produits analogues selon leur norme respective.
La méthode s'applique principalement aux ensembles sous enveloppe ou aux sections compartimentées des ensembles sans ventilation forcée.
Cette troisième édition annule et remplace la deuxième édition parue en 2014. Cette édition constitue une révision technique.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
alignement sur l'IEC 61439-1:2020;
ajout d'annexes spécifiques qui contiennent à titre de recommandations des explications techniques concernant:
l'effet d'une répartition de puissance non uniforme;
l'échauffement supplémentaire dû au rayonnement solaire;
l'effet des différents matériaux d'enveloppe;
l'effet des différents moyens de gestion par ventilation naturelle;
la gestion par ventilation forcée;
le calcul des puissances dissipées;
l'impact que peut avoir une paroi adjacente sur la ou les surfaces de refroidissement de l'ensemble;
ajout d'une limite maximale pour la température ambiante interne d'un ensemble;
extension du domaine de validité du calcul de 3 150 A à 3 200 A;
ajout d'une équation algébrique pour les différentes courbes incluses dans le document.
La présente version bilingue (2023-01) correspond à la version anglaise monolingue publiée en 2022-09.
La version française de cette norme n'a pas été soumise au vote.
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Standards Content (Sample)
IEC TR 60890 ®
Edition 3.0 2022-09
TECHNICAL
REPORT
colour
inside
A method of temperature-rise verification of low-voltage switchgear and
controlgear assemblies by calculation
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IEC TR 60890 ®
Edition 3.0 2022-09
TECHNICAL
REPORT
colour
inside
A method of temperature-rise verification of low-voltage switchgear and
controlgear assemblies by calculation
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.130.20 ISBN 978-2-8322-5762-3
– 2 – IEC TR 60890:2022 © IEC 2022
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 8
4 Verification conditions . 9
5 Calculation method . 9
5.1 Assumptions made in this calculation . 9
5.2 Necessary information . 10
5.3 Calculation procedure . 10
5.3.1 General . 10
5.3.2 Determination of the effective cooling surface A of the enclosure . 10
e
5.3.3 Determination of the internal temperature-rise ∆t of the air at mid-
0,5
height of the enclosure . 10
5.3.4 Determination of the internal temperature-rise ∆t of air at the top of
1,0
the enclosure . 11
5.3.5 Characteristic curve for temperature-rise of air inside enclosure . 11
5.4 Maximum internal air temperature limits . 13
6 Further considerations . 13
6.1 General . 13
6.2 Guidance on the effects of an uneven power distribution . 13
6.3 Guidance on the additional temperature-rise effect due to solar radiation . 14
7 Evaluation of the design . 15
Annex A (informative) Examples for the calculation of the temperature-rise of air
inside enclosures . 26
A.1 Example 1 . 26
A.2 Example 2 . 29
Annex B (informative) Guidance on the effects of an uneven power distribution . 33
B.1 Horizontal partition . 33
B.2 Calculation of internal air temperature-rise for assemblies with ventilation
openings with even power distribution and less than 50 % perforation in
horizontal partitions . 33
B.3 Calculation of internal air temperature-rise with an uneven power distribution . 34
Annex C (informative) Guidance on the additional temperature-rise effect due to solar
radiation . 35
C.1 General . 35
C.2 Solar radiation phenomena . 35
C.3 Solar radiation – consequences for thermal calculation . 36
C.4 Solar radiation of enclosures with air ventilation openings . 37
Annex D (informative) Guidance on the effect of different enclosure materials,
construction and finishes . 38
D.1 General . 38
D.2 Validity criteria . 38
D.3 Material of enclosure . 38
D.4 Results . 38
Annex E (informative) Guidance on the effects of different natural ventilation
arrangements. 40
Annex F (informative) Guidance on forced ventilation management . 42
F.1 General . 42
F.2 Forced ventilation installation system . 42
F.3 Installation considerations . 42
Annex G (informative) Power loss values calculation . 44
G.1 General . 44
G.2 Power losses of low-voltage switchgear and controlgear . 44
G.3 Power losses of conductors connecting low-voltage switchgear and
controlgear . 44
G.4 Power losses of busbars . 45
G.5 Power losses of electronic devices . 45
Annex H (informative) Guidance on the impact of an adjacent wall on the assembly
cooling surfaces . 46
Annex I (informative) Operating current and power loss of copper conductors. 48
Annex J (informative) Guidance to magnetic and eddy-current power losses. 53
Annex K (informative) Forced ventilation airflow calculation . 54
K.1 General . 54
K.2 Ventilation airflow calculation . 55
Bibliography . 57
Figure 1 – Temperature-rise characteristic curve for enclosures with A exceeding
e
1,25 m . 12
Figure 2 – Temperature-rise characteristic curve for enclosures with A not exceeding
e
1,25 m . 13
Figure 3 – Enclosure constant k for enclosures without ventilation openings, with an
effective cooling surface A > 1,25 m . 18
e
Figure 4 – Temperature distribution factor c for enclosures without ventilation openings
and with an effective cooling surface A > 1,25 m . 19
e
Figure 5 – Enclosure constant k for enclosures with ventilation openings and an
effective cooling surface A > 1,25 m . 20
e
Figure 6 – Temperature distribution factor c for enclosures with ventilation openings
and an effective cooling surface A > 1,25 m . 21
e
Figure 7 – Enclosure constant k for enclosures without ventilation openings and with
an effective cooling surface A ≤ 1,25 m . 22
e
Figure 8 – Temperature distribution factor c for enclosures without ventilation
openings and with an effective cooling surface A ≤ 1,25 m . 23
e
Figure 9 – Calculation of temperature-rise of air inside enclosures . 25
Figure A.1 – Example 1, calculation for an enclosure with exposed side faces without
ventilation openings and without internal horizontal partitions . 26
Figure A.2 – Example 1, calculation for a single enclosure . 28
Figure A.3 – Example 2, calculation for an enclosure for wall-mounting with ventilation
openings . 29
Figure A.4 – Example 2, calculation for one enclosure half . 30
– 4 – IEC TR 60890:2022 © IEC 2022
Figure A.5 – Example 2, calculation for an enclosure for wall-mounting with ventilation
openings . 32
Figure B.1 – Examples of assemblies with horizontal partitions . 33
Figure B.2 – Temperature-rise verification of a higher-power circuit . 34
Figure C.1 – Solar radiation phenomena . 35
Figure C.2 – Interpolation curve . 36
Figure D.1 – Results of comparison tests . 39
Figure E.1 – Examples of crossing diagonal installation . 40
Figure E.2 – Effect of additional filters . 41
Figure F.1 – Examples of forced ventilation arrangements . 43
Figure H.1 – Wall-mounted assembly . 46
Figure H.2 – Floor-standing assembly . 47
Figure J.1 – Power losses distribution for different gland plates with the same rating . 53
Table 1 – Method of calculation, application, formulas and characteristics . 15
Table 2 – Symbols, units and designations . 16
Table 3 – Surface factor b according to the type of installation . 17
Table 4 – Factor d for enclosures without ventilation openings and with an effective
cooling surface A > 1,25 m . 17
e
Table 5 – Factor d for enclosures with ventilation openings and an effective cooling
surface A > 1,25 m . 17
e
Table 6 – Equation for Figure 3 . 18
Table 7 – Equations for Figure 4 . 19
Table 8 – Equations for Figure 5 . 20
Table 9 – Equations for Figure 6 . 22
Table 10 – Equation for Figure 7 . 23
Table 11 – Equation for Figure 8 . 24
Table C.1 – Approximate solar absorption radiation coefficients (according to colour) . 36
Table I.1 – Operating current and power loss of single-core copper cables with a
permissible conductor temperature of 70 °C (ambient temperature inside the
enclosure: 55 °C) . 49
Table I.2 – Reduction factor k for cables with a permissible conductor temperature of
70 °C (extract from IEC 60364-5-52:2009, Table B.52.14) . 50
Table I.3 – Operating current and power loss of bare copper bars with rectangular
cross-section, run horizontally and arranged with their largest face vertical, for DC and
AC frequencies 16 2/3 Hz, 50 Hz to 60 Hz (ambient temperature inside the enclosure:
55 °C, temperature of the conductor 70 °C) . 51
Table I.4 – Factor k for different temperatures of the air inside the enclosure and/or
for the conductors . 52
Table K.1 – Factor k for altitudes above sea level . 55
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
A METHOD OF TEMPERATURE-RISE VERIFICATION OF LOW-VOLTAGE
SWITCHGEAR AND CONTROLGEAR ASSEMBLIES BY CALCULATION
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
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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.
IEC TR 60890 has been prepared by subcommittee 121B: Low-voltage switchgear and
controlgear assemblies, of IEC technical committee 121: Switchgear and controlgear and their
assemblies for low-voltage. It is a Technical Report.
This third edition cancels and replaces the second edition published in 2014. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
• alignment with IEC 61439-1:2020;
• addition of individual annexes for guidance of technical explanations related to:
– effect of an uneven power distribution;
– additional temperature-rise due to solar radiation;
– effect of different enclosure materials;
– effect of different natural ventilation management;
– forced ventilation management;
– 6 – IEC TR 60890:2022 © IEC 2022
– power losses calculation;
– impact of an adjacent wall can have on the assembly cooling surface(s);
• maximum internal ambient temperature limit into an assembly;
• validity area of the calculation extended from 3 150 A to 3 200 A;
• addition of an algebraic equation to the different curves included in the document.
The text of this Technical Report is based on the following documents:
Draft Report on voting
121B/136/DTR 121B/147/RVDTR
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Report is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The “colour inside” logo on the cover page of this publication indicates that it
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INTRODUCTION
In the series of design verifications of IEC 61439-1 a temperature-rise verification of low-voltage
power switchgear and controlgear assemblies is specified. This can be by test, however,
alternatives are acceptable under defined circumstances. Selection of the method used for
temperature-rise verification is the responsibility of the original manufacturer. Where applicable
this document can also be used for temperature-rise verification of similar products in
accordance with other standards (e.g. IEC 60204-1). The method of calculation can also be
used to determine the thermal power dissipation capability of an enclosure in accordance with
IEC 62208 for a given internal air temperature-rise. The factors and coefficients, set out in this
document have been derived from measurements on numerous assemblies and the method has
been verified by comparison with test results.
– 8 – IEC TR 60890:2022 © IEC 2022
A METHOD OF TEMPERATURE-RISE VERIFICATION OF LOW-VOLTAGE
SWITCHGEAR AND CONTROLGEAR ASSEMBLIES BY CALCULATION
1 Scope
This document specifies a method of air temperature-rise calculation inside enclosures for low-
voltage switchgear and controlgear assemblies or similar products in accordance with their
respective standard.
The method is primarily applicable to enclosed assemblies or partitioned sections of assemblies
without forced ventilation. However, some technical guidance to adapt it for the use of forced
ventilation is given in this document. The results obtained by using this method are directly
influenced by the accuracy of the evaluation of power losses used as inputs to perform the
thermal calculations.
NOTE The air temperature within the enclosure is equal to the ambient air temperature outside the enclosure plus
the temperature-rise of the air inside the enclosure caused by the power losses of the installed equipment.
For the method to be applied, the maximum daily average ambient air temperature outside the
assembly at the place of installation is specified between 10 °C and 50 °C. The maximum daily
temperature does not exceed the maximum daily average temperature by more than 5 K.
Several annexes in this document provide guidance on how temperature-rise within assemblies
can be affected by influences which are not considered in the calculation method included in
this document, for example, when the assembly is subject to solar radiation. In such cases,
different means of verification to that given in this document can be applied to ensure a definitive
result and verification of the design.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 61439 (all parts), Low-voltage switchgear and controlgear assemblies
IEEE C37.24-2017, IEEE Guide for Evaluating the Effect of Solar Radiation on Outdoor Metal-
Enclosed Switchgear
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61439 (all parts)
apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
4 Verification conditions
When this method of calculation is applied to low-voltage switchgear and controlgear
assemblies the following conditions shall be fulfilled:
– the assembly is designed for AC currents and frequencies up to and including 1 600 A, 60
Hz. For higher current ratings or frequencies, the method could be used with additional
verifications taking into account the effect of eddy-currents on the temperature distribution
inside the assembly as required by the relevant product standards.
NOTE 1 In IEC 61439-2, additional requirements for currents in excess of 1 600 A are specified to take into
account the considerably increased power losses due to magnetic effects (eddy currents, proximity effect, skin
effect)
– the assembly is designed for DC currents up to and including 3 200 A. For higher current
ratings the method could be used with additional verifications as required by the relevant
product standards;
– conductors carrying currents in excess of 200 A AC, and the adjacent structural parts are
so arranged that eddy-current and hysteresis losses are negligible;
– there is an approximately even distribution of power losses inside the enclosure;
– the power losses data for all built-in components are available or can be calculated
(see Clause 5);
– the installed equipment is so arranged that air circulation is not significantly impeded.
NOTE 2 When this method is used to determine the thermal power dissipation capability of an empty enclosure in
accordance with IEC 62208, the above conditions do not apply.
5 Calculation method
5.1 Assumptions made in this calculation
To use the calculation method of this document, the following assumptions are deemed valid:
– the enclosure is made of metal (steel, aluminium, stainless steel) coated (both sides, inside
and outside), insulating material like thermoplastic or thermoset or similar (see Annex D);
– the enclosure is made of a single layer material or multiple layers without air-gap;
– for enclosures with or without natural ventilation, there are no more than five horizontal
partitions in the assembly or in a section of it;
– the enclosure is designed without ventilation openings or;
– the enclosure is designed with free air inlet and outlet ventilation openings, without the
inclusion of any additional filter (see Annex E);
• the cross-section of the air outlet openings is at least 10 % bigger than that of the inlet
openings to permit the chimney effect;
• the minimum cross section of air inlet openings is 10 cm ;
NOTE 1 Figure 3 and the formula given in Table 7 are not usable for lower cross sections. Assemblies with a
sum of the air inlet openings less than 10 cm are considered as assemblies without an air inlet.
• if the enclosure has air inlet and outlet openings with filters for an IP5X rating or higher
then these openings are not considered for the calculation;
• for IP ratings lower than IP5X the effective free air cross section of the openings shall
be used for calculation (see Annex E);
– where enclosures with natural ventilation openings have compartments, the surface of each
horizontal partition shall be provided with free air ventilation openings of at least 50 % of
the horizontal cross-section of the partition (see Clause B.1);
– power losses are considered as a sum of the followings:
• power losses of low-voltage switchgear and controlgear (see Clause G.2);
– 10 – IEC TR 60890:2022 © IEC 2022
• power losses of conductors connecting low-voltage switchgear and controlgear (see
Clause G.3);
• power losses of busbars (see Clause G.4);
• power losses of electronic devices (see Clause G.5);
– the enclosure is not subject to solar radiation.
5.2 Necessary information
The following data shall be used to calculate the temperature-rise of the air inside an enclosure:
– dimensions of the enclosure: height/width/depth;
– type of installation of the enclosure according to Figure 4;
– design of enclosure, i.e. with or without ventilation openings;
– number of internal horizontal partitions;
– effective power loss of equipment installed in the enclosure, see Annex G;
– effective power loss (P ) of conductors according to Annex I.
v
5.3 Calculation procedure
5.3.1 General
For the enclosures specified in columns 4 and 5 of Table 1, the calculation of the temperature-
rise of the air inside the enclosure is carried out using the formulae laid down in columns 1 to
3 of Table 1.
The pertinent factors and exponents (characteristics) are obtained from columns 6 to 10 of
Table 1.
The symbols, units and designations are stated in Table 2.
For enclosures having more than one section with vertical partitions, the temperature-rise of
the air inside the enclosure shall be determined separately for each section.
Where enclosures without vertical partitions or individual sections have an effective cooling
or a width greater than about 1,5 m, they should be divided for
surface greater than 11,5 m
the calculation into fictitious sections, whose dimensions approximate to the foregoing values.
NOTE The template (see Figure 9) can be used as a calculation aid.
5.3.2 Determination of the effective cooling surface A of the enclosure
e
The calculation is carried out according to Formula (1) in column 1 of Table 1.
The effective cooling surface A of an enclosure is the sum of the individual surfaces A
e o
multiplied by the surface factor b. This factor takes into account the heat dissipation of the
individual surfaces according to the type of installation of the enclosure (see Annex H for
additional explanations).
5.3.3 Determination of the internal temperature-rise ∆t of the air at mid-height of
0,5
the enclosure
The calculation is carried out according to Formula (2) in column 2 of Table 1.
In Formula (2) the enclosure constant k allows for the size of the effective cooling surface for
enclosures without ventilation openings and, in addition, for the cross-section of the air inlet
openings for enclosures with ventilation openings.
The dependence of the temperature-rise occurring in the enclosure on the effective power loss
P is expressed by the exponent x.
The factor d allows for the dependence of the temperature-rise on the number of internal
horizontal partitions.
5.3.4 Determination of the internal temperature-rise ∆t of air at the top of the
1,0
enclosure
The calculation is made according to Formula (3) in column 3 of Table 1.
Factor c allows for the temperature distribution inside an enclosure. Its determination varies
with the design and installation of the assembly as follows:
a) For enclosures without ventilation The factor c from Figure 4, depends on the
openings and with an effective cooling type of installation and the height/base
surface: factor f, where:
1,35
h
A > 1,25 m f=
e
A
b
b) For enclosures with ventilation openings The factor c from Figure 6, depends on the
and with an effective cooling surface: cross-section of air inlet openings and the
height/base factor f, where:
1,35
h
A > 1,25 m
e f=
A
b
c) For enclosures without ventilation The factor c from Figure 8, depends on the
openings and with an effective cooling
height/width factor g, where:
surface:
h
A ≤ 1,25 m
g=
e
w
where
h is the enclosure height, in m;
A is the surface area of the enclosure base, in m ;
b
w is the enclosure width, in m.
5.3.5 Characteristic curve for temperature-rise of air inside enclosure
5.3.5.1 General
To evaluate the design according to Clause 7, the calculated results of 5.3.3 and 5.3.4 shall be
applied with the proper characteristic curve for temperature-rise of air inside the enclosure as
a function of the enclosure height. The air temperatures within horizontal levels are practically
constant.
5.3.5.2 Temperature-rise characteristic curve for enclosures with an effective
cooling surface A exceeding 1,25 m
e
As a general rule, the characteristic curve of temperature-rise is adequately well defined by a
straight line which runs through the points ∆t and ∆t (see Figure 1).
1,0 0,5
– 12 – IEC TR 60890:2022 © IEC 2022
The internal air temperature-rise at the bottom of the enclosure is close to zero, i.e. the
characteristic curve flattens out towards zero. In practice, the dotted part of the characteristic
curve is of secondary importance.
Figure 1 – Temperature-rise characteristic curve
for enclosures with A exceeding 1,25 m
e
5.3.5.3 Temperature-rise characteristic curve for enclosures with an effective
cooling surface A not exceeding 1,25 m
e
For this type of enclosure, the maximum temperature-rise in the upper quarter is constant and
the values for ∆t and ∆t are identical (see Figure 2).
1,0 0,75
The characteristic curve is obtained by connecting the temperature-rise values at an enclosure
level of 0,75 and 0,5 (see Figure 2).
The internal air temperature-rise at the bottom of the enclosure is close to zero, i.e. the
characteristic curve flattens out towards zero. In practice, the dotted part of the characteristic
curve is of secondary importance.
Figure 2 – Temperature-rise characteristic curve
for enclosures with A not exceeding 1,25 m
e
5.4 Maximum internal air temperature limits
This document contains a method to calculate the internal air temperature within an enclosure.
The resulting temperature shall not exceed the maximum absolute temperature allowed by
different types of devices and products installed inside.
The user of this document should refer to the manufacturer’s instructions regarding the
maximum operational temperature allowed for the devices used inside the assembly.
NOTE The value of internal air temperature has a direct influence on the ageing and operation of built-in
components.
6 Further considerations
6.1 General
The means of temperature-rise calculation in this document relate to specific arrangements of
assembly in the conditions as defined. These arrangements and conditions do not cover all
designs of assembly or the conditions in which some are installed. Where good practises are
applied the calculation methods in this document can lead to conservative results.
Annex B, Annex C, Annex D, Annex E, Annex F, Annex H, Annex J and Annex K detail good
practice that can lead to an improvement in thermal performance or some aspects not
considered in the calculation method in this document. However, when using these additional
considerations, to ensure a defined performance of an assembly, further verification, e.g. test,
shall be performed.
6.2 Guidance on the effects of an uneven power distribution
The aim of Annex B is to determine the temperature-rise where there is not an even power
distribution within an assembly using as a starting point the temperature-rise of a reference
design or calculation in accordance with Clause 5.
– 14 – IEC TR 60890:2022 © IEC 2022
6.3 Guidance on the additional temperature-rise effect due to solar radiation
In case of outdoor assemblies that are subject to direct sunlight, solar irridiance can significantly
increase internal air temperature-rise and require a derating of the rated currents of the
assembly. See Annex C.
7 Evaluation of the design
It shall be determined whether the equipment within the assembly can operate satisfactorily at the relevant calculated internal air temperature-rise.
If it is not so, the parameters will have to be changed and the calculation repeated.
Table 1 – Method of calculation, application, formulas and characteristics
a
1 2 3 4 6 7 8 9 10 11
Calculation formulae Enclosure Characteristics Characteristic
curve
Temperature-rise of air Factors Exponent
Effective
Plotting of
Effective cooling
cooling
temperature-rise
At mid-height of At (internal) top surface A b k d c x
e
surface A
characteristics
e
the enclosure of enclosure see see see see
Enclosure without
Figure 3 Table 4 Figure 4 0,804
ventilation openings
>1,25 m See 5.3.5.2
x
A = Σ (A × b) ∆t = c × ∆t
∆t = k × d × P
e o 1,0 0,5
Enclosure with
0,5
Table 3 Figure 5 Table 5 Figure 6 0,715
ventilation openings
(1) (3)
(2)
Enclosure without
≤1,25 m Figure 7 d=1 Figure 8 0,804 See 5.3.5.3
ventilation openings
a 2
For enclosure with ventilation openings with effective surface A ≤ 1,25 m the criteria of enclosures without ventilation openings can be used.
e
For symbols, units and designations, see Table 2.
For method of calculation, see also the examples given in Annex A.
– 16 – IEC TR 60890:2022 © IEC 2022
Table 2 – Symbols, units and designations
Symbol Unit Designation
A Surfaces of external sides of enclosure
m
o
A Enclosure base surface
m
b
A Effective cooling surface of enclosure
m
e
A Surface area, which can transport heat (usually excluding the bottom area)
m
s
α Heat transfer coefficient (includes conduction and radiation of heat)
W/m K
b – Surface factor
c – Temperature distribution factor
c J/kg*K Heat capacity (of air)
p
d – Temperature-rise factor for internal horizontal partitions inside enclosure
f – Height/base factor
g – Height/width factor
h m Enclosure height
k – Enclosure constant
n – Number of internal horizontal partitions (up to five partitions)
P W Effective power loss of equipment installed inside enclosure (determined according to
Annex G)
P W Calculated power dissipation of the enclosure according to this document, without
considering natural ventilation
P W Power losses dissipated by forced ventilation
fan
P W Effective power losses of conductors
v
P
W Total dissipated power
w
ρ Mass density (of air) at T
kg/m
a
V Volume flow rate of the air flow through the enclosure
m /s
S Cross-section of air inlet openings
cm
air
T °C Ambient temperature
a
T °C Temperature inside the enclosure
int
T °C Maximum temperature allowed inside the enclosure (limited e.g. by devices)
int,max
w m Enclosure width
x – Exponent
K Temperature-rise of air inside enclosure in general
∆t
K Temperature-rise of air at (internal) mid-height of enclosure
∆t
0,5
K Temperature-rise of air at (internal) three quarters height of enclosure
∆t
0,75
∆t K Temperature-rise of air at (internal) top of enclosure
1,0
Table 3 – Surface factor b according to the type of installation
Type of installation Surface factor
b
Exposed top surface 1,4
Covered top surface, e.g. of built-in enclosures 0,7
Exposed side faces, e.g. front, rear and side walls 0,9
Covered side faces, e.g. rear side of wall-mounted enclosures 0,5
Side faces of central enclosures 0,5
Floor surface not taken into account
Fictitious side faces of sections (see 5.3) which have been introduced only for calculation purposes are not taken
into account
Table 4 – Factor d for enclosures without ventilation openings
and with an effective cooling surface A > 1,25 m
e
Number of horizontal
0 1 2 3 4 5
partitions n
Factor d 1,00 1,05 1,15 1,30 1,45 1,55
NOTE Alternative factor d values than those of Table 4 can be used according to comparison with test results of
similar configurations.
Table 5 – Factor d for enclosures with ventilation openings
and an effective cooling surface A > 1,25 m
e
Number of horizontal
0 1 2 3 4 5
partitions n
Factor d 1,00 1,05 1,10 1,15 1,2 1,25
NOTE Alternative factor d values than those of Table 5 can be used according to comparison with test results of
similar configurations.
– 18 – IEC TR 60890:2022 © IEC 2022
Key
A effective cooling surface (see 5.3.2)
e
k enclosure constant (see 5.3.3)
NOTE See Table 6 for the algebraic expression related to the curve.
Figure 3 – Enclosure constant k for enclosures without ventilation
openings, with an effective cooling surface A > 1,25 m
e
shall be higher than 1,25 and not exceed 12.
Boundary conditions: the factor A
e
Table 6 – Equation for Figure 3
Variable Algebraic expression
−0,795
k
k = 0,58 × (𝐴𝐴 )
e
Key
A effective cooling surface (m )
e
k enclosure constant
Key
f height/base factor (see 5.3.4)
c temperature distribution factor (see Figure 6 and Figure 8)
NOTE See Table 7 for the algebraic expressions related to the curves.
Boundary conditions: the factor f shall be higher than 0,3 and not exceed 16.
Figure 4 – Temperature distribution factor c for enclosures without ventilation
openings and with an effective cooling surface A > 1,25 m
e
Table 7 – Equations for Figure 4
In
...
IEC TR 60890 ®
Edition 3.0 2022-09
REDLINE VERSION
TECHNICAL
REPORT
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A method of temperature-rise verification of low-voltage switchgear and
controlgear assemblies by calculation
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IEC TR 60890 ®
Edition 3.0 2022-09
REDLINE VERSION
TECHNICAL
REPORT
colour
inside
A method of temperature-rise verification of low-voltage switchgear and
controlgear assemblies by calculation
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.130.20 ISBN 978-2-8322-5822-4
– 2 – IEC TR 60890:2022 RLV © IEC 2022
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 Verification conditions for application. 9
5 Calculation method . 10
5.1 Assumptions made in this calculation . 10
5.2 Necessary information . 10
5.3 Calculation procedure . 11
5.3.1 General . 11
5.3.2 Determination of the effective cooling surface A of the enclosure . 11
e
5.3.3 Determination of the internal temperature-rise ∆t of the air at mid-
0,5
height of the enclosure . 11
5.3.4 Determination of the internal temperature-rise ∆t of air at the top of
1,0
the enclosure . 11
5.3.5 Characteristic curve for temperature-rise of air inside enclosure . 12
5.4 Maximum internal air temperature limits . 14
6 Further considerations . 14
6.1 General . 14
6.2 Guidance on the effects of an uneven power distribution . 14
6.3 Guidance on the additional temperature-rise effect due to solar radiation . 14
7 Evaluation of the design . 15
Annex A (informative) Examples for the calculation of the temperature-rise of air
inside enclosures . 34
A.1 Example 1 . 34
A.2 Example 2 . 38
Annex B (informative) Guidance on the effects of an uneven power distribution . 43
B.1 Horizontal partition . 43
B.2 Calculation of internal air temperature-rise for assemblies with ventilation
openings with even power distribution and less than 50 % perforation in
horizontal partitions . 43
B.3 Calculation of internal air temperature-rise with an uneven power distribution . 44
Annex C (informative) Guidance on the additional temperature-rise effect due to solar
radiation . 45
C.1 General . 45
C.2 Solar radiation phenomena . 45
C.3 Solar radiation – consequences for thermal calculation . 46
C.4 Solar radiation of enclosures with air ventilation openings . 47
Annex D (informative) Guidance on the effect of different enclosure materials,
construction and finishes . 48
D.1 General . 48
D.2 Validity criteria . 48
D.3 Material of enclosure . 48
D.4 Results . 48
Annex E (informative) Guidance on the effects of different natural ventilation
arrangements. 50
Annex F (informative) Guidance on forced ventilation management . 52
F.1 General . 52
F.2 Forced ventilation installation system . 52
F.3 Installation considerations . 52
Annex G (informative) Power loss values calculation . 54
G.1 General . 54
G.2 Power losses of low-voltage switchgear and controlgear . 54
G.3 Power losses of conductors connecting low-voltage switchgear and
controlgear . 54
G.4 Power losses of busbars . 55
G.5 Power losses of electronic devices . 55
Annex H (informative) Guidance on the impact of an adjacent wall on the assembly
cooling surfaces . 56
Annex I (informative) Operating current and power losses of copper conductors . 58
Annex J (informative) Guidance to magnetic and eddy-current power losses. 63
Annex K (informative) Forced ventilation airflow calculation . 64
K.1 General . 64
K.2 Ventilation airflow calculation . 65
Bibliography . 67
Figure 1 – Temperature-rise characteristic curve for enclosures with A exceeding
e
1,25 m . 13
Figure 2 – Temperature-rise characteristic curve for enclosures with A not exceeding
e
1,25 m . 13
Figure 3 – Enclosure constant k for enclosures without ventilation openings, with an
effective cooling surface A > 1,25 m . 19
e
Figure 4 – Temperature distribution factor c for enclosures without ventilation openings
and with an effective cooling surface A > 1,25 m . 21
e
Figure 5 – Enclosure constant k for enclosures with ventilation openings and an
effective cooling surface A > 1,25 m . 23
e
Figure 6 – Temperature distribution factor c for enclosures with ventilation openings
and an effective cooling surface A > 1,25 m . 25
e
Figure 7 – Enclosure constant k for enclosures without ventilation openings and with
an effective cooling surface A ≤ 1,25 m . 28
e
Figure 8 – Temperature distribution factor c for enclosures without ventilation openings
and with an effective cooling surface A ≤ 1,25 m . 30
e
Figure 9 – Calculation of temperature-rise of air inside enclosures . 33
Figure A.1 – Example 1, calculation for an enclosure with exposed side faces without
ventilation openings and without internal horizontal partitions . 34
Figure A.2 – Example 1, calculation for a single enclosure . 37
Figure A.3 – Example 2, calculation for an enclosure for wall-mounting with ventilation
openings . 38
Figure A.4 – Example 2, calculation for one enclosure half . 39
– 4 – IEC TR 60890:2022 RLV © IEC 2022
Figure A.5 – Example 2, calculation for an enclosure for wall-mounting with ventilation
openings . 42
Figure B.1 – Examples of assemblies with horizontal partitions . 43
Figure B.2 – Temperature-rise verification of a higher-power circuit . 44
Figure C.1 – Solar radiation phenomena . 45
Figure C.2 – Interpolation curve . 46
Figure D.1 – Results of comparison tests . 49
Figure E.1 – Examples of crossing diagonal installation . 50
Figure E.2 – Effect of additional filters . 51
Figure F.1 – Examples of forced ventilation arrangements . 53
Figure H.1 – Wall-mounted assembly . 56
Figure H.2 – Floor-standing assembly . 57
Figure J.1 – Power losses distribution for different gland plates with the same rating . 63
Table 1 – Method of calculation, application, formulas and characteristics . 15
Table 2 – Symbols, units and designations . 16
Table 3 – Surface factor b according to the type of installation . 17
Table 4 – Factor d for enclosures without ventilation openings and with an effective
cooling surface A > 1,25 m . 17
e
Table 5 – Factor d for enclosures with ventilation openings and an effective cooling
surface A > 1,25 m . 17
e
Table 6 – Equation for Figure 3 . 19
Table 7 – Equations for Figure 4 . 21
Table 8 – Equations for Figure 5 . 23
Table 9 – Equations for Figure 6 . 26
Table 10 – Equation for Figure 7 . 28
Table 11 – Equation for Figure 8 . 30
Table C.1 – Approximate solar absorption radiation coefficients (according to colour) . 46
Table I.1 – Operating current and power loss of single-core copper cables with a
permissible conductor temperature of 70 °C (ambient temperature inside the
enclosure: 55 °C) . 59
Table I.2 – Reduction factor k for cables with a permissible conductor temperature of
70 °C (extract from IEC 60364-5-52:2009, Table B.52.14) . 60
Table I.3 – Operating current and power loss of bare copper bars with rectangular
cross-section, run horizontally and arranged with their largest face vertical, for DC and
, 50 Hz to 60 Hz (ambient temperature inside the enclosure:
AC frequencies 16 2/3 Hz
55 °C, temperature of the conductor 70 °C) . 61
Table I.4 – Factor k for different temperatures of the air inside the enclosure and/or
for the conductors . 62
Table K.1 – Factor k for altitudes above sea level . 65
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
A METHOD OF TEMPERATURE-RISE VERIFICATION OF LOW-VOLTAGE
SWITCHGEAR AND CONTROLGEAR ASSEMBLIES BY CALCULATION
FOREWORD
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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.
This redline version of the official IEC Standard allows the user to identify the changes made to
the previous edition IEC TR 60890:2014. A vertical bar appears in the margin wherever a change
has been made. Additions are in green text, deletions are in strikethrough red text.
– 6 – IEC TR 60890:2022 RLV © IEC 2022
IEC TR 60890 has been prepared by subcommittee 121B: Low-voltage switchgear and
controlgear assemblies, of IEC technical committee 121: Switchgear and controlgear and their
assemblies for low-voltage. It is a Technical Report.
This third edition cancels and replaces the second edition published in 2014. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
• alignment with IEC 61439-1:2020;
• addition of individual annexes for guidance of technical explanations related to:
– effect of an uneven power distribution;
– additional temperature-rise due to solar radiation;
– effect of different enclosure materials;
– effect of different natural ventilation management;
– forced ventilation management;
– power losses calculation;
– impact of an adjacent wall can have on the assembly cooling surface(s);
• maximum internal ambient temperature limit into an assembly;
• validity area of the calculation extended from 3 150 A to 3 200 A;
• addition of an algebraic equation to the different curves included in the document.
The text of this Technical Report is based on the following documents:
Draft Report on voting
121B/136/DTR 121B/147/RVDTR
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Report is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The “colour inside” logo on the cover page of this publication indicates that it
the correct understanding of its
contains colours which are considered to be useful for
contents. Users should therefore print this publication using a colour printer.
INTRODUCTION
In the series of design verifications of IEC 61439-1 a temperature-rise verification of low-voltage
power switchgear and controlgear assemblies (hereafter called ASSEMBLIES) is specified. This
may can be by test, however, alternatives are acceptableunder defined circumstances.
Selection of the method used for temperature-rise verification is the responsibility of the original
manufacturer. Where applicable this document may can also be used for temperature-rise
verification of similar products in accordance with other standards (e.g. IEC 60204-1). The
method of calculation can also be used to determine the thermal power dissipation capability of
an enclosure in accordance with IEC 62208 for a given internal air temperature-rise. The factors
and coefficients, set out in this document have been derived from measurements on numerous
assemblies and the method has been verified by comparison with test results.
– 8 – IEC TR 60890:2022 RLV © IEC 2022
A METHOD OF TEMPERATURE-RISE VERIFICATION OF LOW-VOLTAGE
SWITCHGEAR AND CONTROLGEAR ASSEMBLIES BY CALCULATION
1 Scope
This Technical Report specifies a method of temperature-rise verification of low-voltage
switchgear and controlgear assemblies by calculation.
The method is applicable to enclosed ASSEMBLIES or partitioned sections of ASSEMBLIES without
forced ventilation. It is not applicable where temperature rise verification to the relevant product
standard of the IEC 61439 series has been established
NOTE 1 The influence of the materials and wall thicknesses usually used for enclosures can have some effect on
the steady state temperatures. However, the generalised approach used in this technical report ensures it is
applicable to enclosures made of sheet steel, sheet aluminium, cast iron, insulating material and the like.
The proposed method is intended to determine the temperature rise of the air inside the
enclosure.
NOTE 2 The air temperature within the enclosure is equal to the ambient air temperature outside the enclosure plus
the temperaturerise of the air inside the enclosure caused by the power losses of the installed equipment.
Unless otherwise specified, the ambient air temperature outside the ASSEMBLY is the air temperature indicated for
the installation (average value over 24 h) of 35 °C. If the ambient air temperature outside the assembly at the place
of use exceeds 35 °C, this higher temperatureis deemed to be the ambient air temperature.
This document specifies a method of air temperature-rise calculation inside enclosures for low-
voltage switchgear and controlgear assemblies or similar products in accordance with their
respective standard.
The method is primarily applicable to enclosed assemblies or partitioned sections of assemblies
without forced ventilation. However, some technical guidance to adapt it for the use of forced
ventilation is given in this document. The results obtained by using this method are directly
influenced by the accuracy of the evaluation of power losses used as inputs to perform the
thermal calculations.
NOTE The air temperature within the enclosure is equal to the ambient air temperature outside the enclosure plus
the temperature-rise of the air inside the enclosure caused by the power losses of the installed equipment.
For the method to be applied, the maximum daily average ambient air temperature outside the
assembly at the place of installation is specified between 10 °C and 50 °C. The maximum daily
temperature does not exceed the maximum daily average temperature by more than 5 K.
Several annexes in this document provide guidance on how temperature-rise within assemblies
can be affected by influences which are not considered in the calculation method included in
this document, for example, when the assembly is subject to solar radiation. In such cases,
different means of verification to that given in this document can be applied to ensure a definitive
result and verification of the design.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 61439-1:2011, Low-voltage switchgear and controlgear assemblies – Part 1: General rules
IEC 61439 (all parts), Low-voltage switchgear and controlgear assemblies
IEEE C37.24-2017, IEEE Guide for Evaluating the Effect of Solar Radiation on Outdoor Metal-
Enclosed Switchgear
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61439-1 (all parts)
apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
4 Verification conditions for application
This method of calculation is only applicable if the following conditions are fulfilled:
– the power loss data for all built in components is available;
– there is an approximately even distribution of power losses inside the enclosure;
– the installed equipment is so arranged that air circulation is not significantly impeded;
– the equipment installed is designed for direct current or alternating current up to and
including 60 Hz with the total of supply currents not exceeding 3 150 A;
– conductors carrying currents in excess of 200 A, and the adjacent structural parts are so
arranged that eddy-current and hysteresis losses are minimised;
– for enclosures with natural ventilation, the cross-section of the air outlet openings is at least
1,1 times the cross-section of the air inlet openings;
– there are no more than three horizontal partitions in the ASSEMBLY or in a section of it;
– where enclosures with external ventilation openings have compartments, the surface of the
ventilation openings in each horizontal partition shall be at least 50 % of the horizontal
cross-section of the compartment.
When this method of calculation is applied to low-voltage switchgear and controlgear
assemblies the following conditions shall be fulfilled:
– the assembly is designed for AC currents and frequencies up to and including 1 600 A, 60
Hz. For higher current ratings or frequencies, the method could be used with additional
verifications taking into account the effect of eddy-currents on the temperature distribution
inside the assembly as required by the relevant product standards.
NOTE 1 In IEC 61439-2, additional requirements for currents in excess of 1 600 A are specified to take into
account the considerably increased power losses due to magnetic effects (eddy currents, proximity effect, skin
effect)
– the assembly is designed for DC currents up to and including 3 200 A. For higher current
ratings the method could be used with additional verifications as required by the relevant
product standards;
– conductors carrying currents in excess of 200 A AC, and the adjacent structural parts are
so arranged that eddy-current and hysteresis losses are negligible;
– there is an approximately even distribution of power losses inside the enclosure;
– 10 – IEC TR 60890:2022 RLV © IEC 2022
– the power losses data for all built-in components are available or can be calculated
(see Clause 5);
– the installed equipment is so arranged that air circulation is not significantly impeded.
NOTE 2 When this method is used to determine the thermal power dissipation capability of an empty enclosure in
accordance with IEC 62208, the above conditions do not apply.
5 Calculation method
5.1 Assumptions made in this calculation
To use the calculation method of this document, the following assumptions are deemed valid:
– the enclosure is made of metal (steel, aluminium, stainless steel) coated (both sides, inside
and outside), insulating material like thermoplastic or thermoset or similar (see Annex D);
– the enclosure is made of a single layer material or multiple layers without air-gap;
– for enclosures with or without natural ventilation, there are no more than five horizontal
partitions in the assembly or in a section of it;
– the enclosure is designed without ventilation openings or;
– the enclosure is designed with free air inlet and outlet ventilation openings, without the
inclusion of any additional filter (see Annex E);
• the cross-section of the air outlet openings is at least 10 % bigger than that of the inlet
openings to permit the chimney effect;
• the minimum cross section of air inlet openings is 10 cm ;
NOTE 1 Figure 3 and the formula given in Table 7 are not usable for lower cross sections. Assemblies with a
sum of the air inlet openings less than 10 cm are considered as assemblies without an air inlet.
• if the enclosure has air inlet and outlet openings with filters for an IP5X rating or higher
then these openings are not considered for the calculation;
• for IP ratings lower than IP5X the effective free air cross section of the openings shall
be used for calculation (see Annex E);
– where enclosures with natural ventilation openings have compartments, the surface of each
horizontal partition shall be provided with free air ventilation openings of at least 50 % of
the horizontal cross-section of the partition (see Clause B.1);
– power losses are considered as a sum of the followings:
• power losses of low-voltage switchgear and controlgear (see Clause G.2);
• power losses of conductors connecting low-voltage switchgear and controlgear (see
Clause G.3);
• power losses of busbars (see Clause G.4);
• power losses of electronic devices (see Clause G.5);
– the enclosure is not subject to solar radiation.
5.2 Necessary information
The following data is needed shall be used to calculate the temperature-rise of the air inside an
enclosure:
– dimensions of the enclosure: height/width/depth;
– type of installation of the enclosure according to Figure 4;
– design of enclosure, i.e. with or without ventilation openings;
– number of internal horizontal partitions;
– effective power loss of equipment installed in the enclosure, see Annex G;
– effective power loss (P ) of conductors according to Annex I.
v
NOTE The effective power losses of the equipment installed in the circuits of the ASSEMBLY used for this calculation
are the power losses at the rated currents of the various circuits.
5.3 Calculation procedure
5.3.1 General
For the enclosures specified in columns 4 and 5 of Table 1, the calculation of the temperature-
rise of the air inside the enclosure is carried out using the formulae laid down in columns 1 to
3 of Table 1.
The pertinent factors and exponents (characteristics) are obtained from columns 6 to 10 of
Table 1.
The symbols, units and designations are stated in Table 2.
For enclosures having more than one section with vertical partitions, the temperature-rise of
the air inside the enclosure shall be determined separately for each section.
Where enclosures without vertical partitions or individual sections have an effective cooling
surface greater than 11,5 m or a width greater than about 1,5 m, they should be divided for
the calculation into fictitious sections, whose dimensions approximate to the foregoing values.
NOTE The template (see Figure 9) can be used as a calculation aid.
5.3.2 Determination of the effective cooling surface A of the enclosure
e
The calculation is carried out according to Formula (1) in column 1 of Table 1.
The effective cooling surface A of an enclosure is the sum of the individual surfaces A
e o
multiplied by the surface factor b. This factor takes into account the heat dissipation of the
individual surfaces according to the type of installation of the enclosure (see Annex H for
additional explanations).
5.3.3 Determination of the internal temperature-rise ∆t of the air at mid-height of
0,5
the enclosure
The calculation is carried out according to Formula (2) in column 2 of Table 1.
In Formula (2) the enclosure constant k allows for the size of the effective cooling surface for
enclosures without ventilation openings and, in addition, for the cross-section of the air inlet
openings for enclosures with ventilation openings.
The dependence of the temperature-rise occurring in the enclosure on the effective power loss
P is expressed by the exponent x.
The factor d allows for the dependence of the temperature-rise on the number of internal
horizontal partitions.
5.3.4 Determination of the internal temperature-rise ∆t of air at the top of the
1,0
enclosure
The calculation is made according to Formula (3) in column 3 of Table 1.
– 12 – IEC TR 60890:2022 RLV © IEC 2022
Factor c allows for the temperature distribution inside an enclosure. Its determination varies
with the design and installation of the assembly as follows:
a) For enclosures without ventilation The factor c from Figure 4, depends on the
openings and with an effective cooling type of installation and the height/base
surface: factor f, where:
1,35
h
A > 1,25 m f =
e
A
b
b) For enclosures with ventilation openings The factor c from Figure 6, depends on the
and with an effective cooling surface: cross-section of air inlet openings and the
height/base factor f, where:
1,35
h
A > 1,25 m
f =
e
A
b
c) For enclosures without ventilation The factor c from Figure 8, depends on the
openings and with an effective cooling height/width factor g, where:
surface:
h
A ≤ 1,25 m
g =
e
w
where
h is the enclosure height, in m;
A is the surface area of the enclosure base, in m ;
b
w is the enclosure width, in m.
5.3.5 Characteristic curve for temperature-rise of air inside enclosure
5.3.5.1 General
To evaluate the design according to Clause 7, it is necessary to apply, the calculated results of
5.3.3 and 5.3.4 shall be applied with the proper characteristic curve for temperature-rise of air
inside the enclosure as a function of the enclosure height. The air temperatures within horizontal
levels are practically constant.
5.3.5.2 Temperature-rise characteristic curve for enclosures with an effective
cooling surface A exceeding 1,25 m
e
As a general rule, the characteristic curve of temperature-rise is adequately well defined by a
straight line which runs through the points ∆t and ∆t (see Figure 1).
1,0 0,5
The internal air temperature-rise at the bottom of the enclosure is close to zero, i.e. the
characteristic curve flattens out towards zero. In practice, the dotted part of the characteristic
curve is of secondary importance.
Figure 1 – Temperature-rise characteristic curve
for enclosures with A exceeding 1,25 m
e
5.3.5.3 Temperature-rise characteristic curve for enclosures with an effective
cooling surface A not exceeding 1,25 m
e
For this type of enclosure, the maximum temperature-rise in the upper quarter is constant and
and ∆t are identical (see Figure 2).
the values for ∆t
1,0 0,75
The characteristic curve is obtained by connecting the temperature-rise values at an enclosure
level of 0,75 and 0,5 (see Figure 2).
The internal air temperature-rise at the bottom of the enclosure is close to zero, i.e. the
characteristic curve flattens out towards zero. In practice, the dotted part of the characteristic
curve is of secondary importance.
Figure 2 – Temperature-rise characteristic curve
for enclosures with A not exceeding 1,25 m
e
– 14 – IEC TR 60890:2022 RLV © IEC 2022
5.4 Maximum internal air temperature limits
This document contains a method to calculate the internal air temperature within an enclosure.
The resulting temperature shall not exceed the maximum absolute temperature allowed by
different types of devices and products installed inside.
The user of this document should refer to the manufacturer’s instructions regarding the
maximum operational temperature allowed for the devices used inside the assembly.
NOTE The value of internal air temperature has a direct influence on the ageing and operation of built-in
components.
6 Further considerations
6.1 General
The means of temperature-rise calculation in this document relate to specific arrangements of
assembly in the conditions as defined. These arrangements and conditions do not cover all
designs of assembly or the conditions in which some are installed. Where good practises are
applied the calculation methods in this document can lead to conservative results.
Annex B, Annex C, Annex D, Annex E, Annex F, Annex H, Annex J and Annex K detail good
practice that can lead to an improvement in thermal performance or some aspects not
considered in the calculation method in this document. However, when using these additional
considerations, to ensure a defined performance of an assembly, further verification, e.g. test,
shall be performed.
6.2 Guidance on the effects of an uneven power distribution
The aim of Annex B is to determine the temperature-rise where there is not an even power
distribution within an assembly using as a starting point the temperature-rise of a reference
design or calculation in accordance with Clause 5.
6.3 Guidance on the additional temperature-rise effect due to solar radiation
In case of outdoor assemblies that are subject to direct sunlight, solar irridiance can significantly
increase internal air temperature-rise and require a derating of the rated currents of the
assembly. See Annex C.
7 Evaluation of the design
It shall be determined whether the equipment within the assembly can operate satisfactorily at the relevant calculated internal air temperature-rise.
If it is not so, the parameters will have to be changed and the calculation repeated.
Table 1 – Method of calculation, application, formulas and characteristics
a
1 2 3 4 6 7 8 9 10 11
Calculation formulae Enclosure Characteristics Characteristic
curve
Temperature-rise of air Factors Exponent
Effective
Plotting of
Effective cooling
cooling
temperature-rise
At mid-height of At (internal) top surface A b k d c x
e
surface A
characteristics
e
the enclosure of enclosure see see see see
Enclosure without
Figure 3 Table 4 Figure 4 0,804
ventilation openings
>1,25 m See 5.3.5.2
x
A = Σ (A × b) ∆t = c × ∆t
∆t = k × d × P
e o 1,0 0,5
Enclosure with
0,5
Table 3 Figure 5 Table 5 Figure 6 0,715
ventilation openings
(1) (3)
(2)
Enclosure without
≤1,25 m Figure 7 d=1 Figure 8 0,804 See 5.3.5.3
ventilation openings
a 2
For enclosure with ventilation openings with effective surface A ≤ 1,25 m the criteria of enclosures without ventilation openings can be used.
e
For symbols, units and designations, see Table 2.
For method of calculation, see also the examples given in Annex A.
– 16 – IEC TR 60890:2022 RLV © IEC 2022
Table 2 – Symbols, units and designations
Symbol Unit Designation
A Surfaces of external sides of enclosure
m
o
A Enclosure base surface
m
b
A Effective cooling surface of enclosure
m
e
A Surface area, which can transport heat (usually excluding the bottom area)
m
s
α Heat transfer coefficient (includes conduction and radiation of heat)
W/m K
b – Surface factor
c – Temperature distribution factor
c J/kg*K Heat capacity (of air)
p
d – Temperature-rise factor for internal horizontal partitions inside enclosure
f – Height/base factor
g – Height/width factor
h m Enclosure height
k – Enclosure constant
n – Number of internal horizontal partitions (up to three five partitions)
P W Effective power loss of equipment installed inside enclosure (determined according to
Annex G)
P W Calculated power dissipation of the enclosure according to this document, without
considering natural ventilation
P W Power losses dissipated by forced ventilation
fan
P W Effective power losses of conductors
...
IEC TR 60890 ®
Edition 3.0 2022-09
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
colour
inside
A method of temperature-rise verification of low-voltage switchgear and
controlgear assemblies by calculation
Méthode de vérification par calcul des échauffements pour les ensembles
d'appareillages à basse tension
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IEC TR 60890 ®
Edition 3.0 2022-09
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
colour
inside
A method of temperature-rise verification of low-voltage switchgear and
controlgear assemblies by calculation
Méthode de vérification par calcul des échauffements pour les ensembles
d'appareillages à basse tension
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.130.20 ISBN 978-2-8322-6368-6
– 2 – IEC TR 60890:2022 © IEC 2022
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 8
4 Verification conditions . 9
5 Calculation method . 9
5.1 Assumptions made in this calculation . 9
5.2 Necessary information . 10
5.3 Calculation procedure . 10
5.3.1 General . 10
5.3.2 Determination of the effective cooling surface A of the enclosure . 10
e
5.3.3 Determination of the internal temperature-rise ∆t of the air at mid-
0,5
height of the enclosure . 10
5.3.4 Determination of the internal temperature-rise ∆t of air at the top of
1,0
the enclosure . 11
5.3.5 Characteristic curve for temperature-rise of air inside enclosure . 11
5.4 Maximum internal air temperature limits . 13
6 Further considerations . 13
6.1 General . 13
6.2 Guidance on the effects of an uneven power distribution . 13
6.3 Guidance on the additional temperature-rise effect due to solar radiation . 14
7 Evaluation of the design . 15
Annex A (informative) Examples for the calculation of the temperature-rise of air
inside enclosures . 26
A.1 Example 1 . 26
A.2 Example 2 . 29
Annex B (informative) Guidance on the effects of an uneven power distribution . 33
B.1 Horizontal partition . 33
B.2 Calculation of internal air temperature-rise for assemblies with ventilation
openings with even power distribution and less than 50 % perforation in
horizontal partitions . 33
B.3 Calculation of internal air temperature-rise with an uneven power distribution . 34
Annex C (informative) Guidance on the additional temperature-rise effect due to solar
radiation . 35
C.1 General . 35
C.2 Solar radiation phenomena . 35
C.3 Solar radiation – consequences for thermal calculation . 36
C.4 Solar radiation of enclosures with air ventilation openings . 37
Annex D (informative) Guidance on the effect of different enclosure materials,
construction and finishes . 38
D.1 General . 38
D.2 Validity criteria . 38
D.3 Material of enclosure . 38
D.4 Results . 38
Annex E (informative) Guidance on the effects of different natural ventilation
arrangements. 40
Annex F (informative) Guidance on forced ventilation management . 42
F.1 General . 42
F.2 Forced ventilation installation system . 42
F.3 Installation considerations . 42
Annex G (informative) Power loss values calculation . 44
G.1 General . 44
G.2 Power losses of low-voltage switchgear and controlgear . 44
G.3 Power losses of conductors connecting low-voltage switchgear and
controlgear . 44
G.4 Power losses of busbars . 45
G.5 Power losses of electronic devices . 45
Annex H (informative) Guidance on the impact of an adjacent wall on the assembly
cooling surfaces . 46
Annex I (informative) Operating current and power loss of copper conductors. 48
Annex J (informative) Guidance to magnetic and eddy-current power losses. 53
Annex K (informative) Forced ventilation airflow calculation . 54
K.1 General . 54
K.2 Ventilation airflow calculation . 55
Bibliography . 57
Figure 1 – Temperature-rise characteristic curve for enclosures with A exceeding
e
1,25 m . 12
Figure 2 – Temperature-rise characteristic curve for enclosures with A not exceeding
e
1,25 m . 13
Figure 3 – Enclosure constant k for enclosures without ventilation openings, with an
effective cooling surface A > 1,25 m . 18
e
Figure 4 – Temperature distribution factor c for enclosures without ventilation openings
and with an effective cooling surface A > 1,25 m . 19
e
Figure 5 – Enclosure constant k for enclosures with ventilation openings and an
effective cooling surface A > 1,25 m . 20
e
Figure 6 – Temperature distribution factor c for enclosures with ventilation openings
and an effective cooling surface A > 1,25 m . 21
e
Figure 7 – Enclosure constant k for enclosures without ventilation openings and with
an effective cooling surface A ≤ 1,25 m . 22
e
Figure 8 – Temperature distribution factor c for enclosures without ventilation
openings and with an effective cooling surface A ≤ 1,25 m . 23
e
Figure 9 – Calculation of temperature-rise of air inside enclosures . 25
Figure A.1 – Example 1, calculation for an enclosure with exposed side faces without
ventilation openings and without internal horizontal partitions . 26
Figure A.2 – Example 1, calculation for a single enclosure . 28
Figure A.3 – Example 2, calculation for an enclosure for wall-mounting with ventilation
openings . 29
Figure A.4 – Example 2, calculation for one enclosure half . 30
– 4 – IEC TR 60890:2022 © IEC 2022
Figure A.5 – Example 2, calculation for an enclosure for wall-mounting with ventilation
openings . 32
Figure B.1 – Examples of assemblies with horizontal partitions . 33
Figure B.2 – Temperature-rise verification of a higher-power circuit . 34
Figure C.1 – Solar radiation phenomena . 35
Figure C.2 – Interpolation curve . 36
Figure D.1 – Results of comparison tests . 39
Figure E.1 – Examples of crossing diagonal installation . 40
Figure E.2 – Effect of additional filters . 41
Figure F.1 – Examples of forced ventilation arrangements . 43
Figure H.1 – Wall-mounted assembly . 46
Figure H.2 – Floor-standing assembly . 47
Figure J.1 – Power losses distribution for different gland plates with the same rating . 53
Table 1 – Method of calculation, application, formulas and characteristics . 15
Table 2 – Symbols, units and designations . 16
Table 3 – Surface factor b according to the type of installation . 17
Table 4 – Factor d for enclosures without ventilation openings and with an effective
cooling surface A > 1,25 m . 17
e
Table 5 – Factor d for enclosures with ventilation openings and an effective cooling
surface A > 1,25 m . 17
e
Table 6 – Equation for Figure 3 . 18
Table 7 – Equations for Figure 4 . 19
Table 8 – Equations for Figure 5 . 20
Table 9 – Equations for Figure 6 . 22
Table 10 – Equation for Figure 7 . 23
Table 11 – Equation for Figure 8 . 24
Table C.1 – Approximate solar absorption radiation coefficients (according to colour) . 36
Table I.1 – Operating current and power loss of single-core copper cables with a
permissible conductor temperature of 70 °C (ambient temperature inside the
enclosure: 55 °C) . 49
Table I.2 – Reduction factor k for cables with a permissible conductor temperature of
70 °C (extract from IEC 60364-5-52:2009, Table B.52.14) . 50
Table I.3 – Operating current and power loss of bare copper bars with rectangular
cross-section, run horizontally and arranged with their largest face vertical, for DC and
AC frequencies 16 2/3 Hz, 50 Hz to 60 Hz (ambient temperature inside the enclosure:
55 °C, temperature of the conductor 70 °C) . 51
Table I.4 – Factor k for different temperatures of the air inside the enclosure and/or
for the conductors . 52
Table K.1 – Factor k for altitudes above sea level . 55
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
A METHOD OF TEMPERATURE-RISE VERIFICATION OF LOW-VOLTAGE
SWITCHGEAR AND CONTROLGEAR ASSEMBLIES BY CALCULATION
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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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.
IEC TR 60890 has been prepared by subcommittee 121B: Low-voltage switchgear and
controlgear assemblies, of IEC technical committee 121: Switchgear and controlgear and their
assemblies for low-voltage. It is a Technical Report.
This third edition cancels and replaces the second edition published in 2014. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
• alignment with IEC 61439-1:2020;
• addition of individual annexes for guidance of technical explanations related to:
– effect of an uneven power distribution;
– additional temperature-rise due to solar radiation;
– effect of different enclosure materials;
– effect of different natural ventilation management;
– forced ventilation management;
– 6 – IEC TR 60890:2022 © IEC 2022
– power losses calculation;
– impact of an adjacent wall can have on the assembly cooling surface(s);
• maximum internal ambient temperature limit into an assembly;
• validity area of the calculation extended from 3 150 A to 3 200 A;
• addition of an algebraic equation to the different curves included in the document.
The text of this Technical Report is based on the following documents:
Draft Report on voting
121B/136/DTR 121B/147/RVDTR
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Report is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The “colour inside” logo on the cover page of this publication indicates that it
contains colours which are considered to be useful for the correct understanding of its
contents. Users should therefore print this publication using a colour printer.
INTRODUCTION
In the series of design verifications of IEC 61439-1 a temperature-rise verification of low-voltage
power switchgear and controlgear assemblies is specified. This can be by test, however,
alternatives are acceptable under defined circumstances. Selection of the method used for
temperature-rise verification is the responsibility of the original manufacturer. Where applicable
this document can also be used for temperature-rise verification of similar products in
accordance with other standards (e.g. IEC 60204-1). The method of calculation can also be
used to determine the thermal power dissipation capability of an enclosure in accordance with
IEC 62208 for a given internal air temperature-rise. The factors and coefficients, set out in this
document have been derived from measurements on numerous assemblies and the method has
been verified by comparison with test results.
– 8 – IEC TR 60890:2022 © IEC 2022
A METHOD OF TEMPERATURE-RISE VERIFICATION OF LOW-VOLTAGE
SWITCHGEAR AND CONTROLGEAR ASSEMBLIES BY CALCULATION
1 Scope
This document specifies a method of air temperature-rise calculation inside enclosures for low-
voltage switchgear and controlgear assemblies or similar products in accordance with their
respective standard.
The method is primarily applicable to enclosed assemblies or partitioned sections of assemblies
without forced ventilation. However, some technical guidance to adapt it for the use of forced
ventilation is given in this document. The results obtained by using this method are directly
influenced by the accuracy of the evaluation of power losses used as inputs to perform the
thermal calculations.
NOTE The air temperature within the enclosure is equal to the ambient air temperature outside the enclosure plus
the temperature-rise of the air inside the enclosure caused by the power losses of the installed equipment.
For the method to be applied, the maximum daily average ambient air temperature outside the
assembly at the place of installation is specified between 10 °C and 50 °C. The maximum daily
temperature does not exceed the maximum daily average temperature by more than 5 K.
Several annexes in this document provide guidance on how temperature-rise within assemblies
can be affected by influences which are not considered in the calculation method included in
this document, for example, when the assembly is subject to solar radiation. In such cases,
different means of verification to that given in this document can be applied to ensure a definitive
result and verification of the design.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 61439 (all parts), Low-voltage switchgear and controlgear assemblies
IEEE C37.24-2017, IEEE Guide for Evaluating the Effect of Solar Radiation on Outdoor Metal-
Enclosed Switchgear
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61439 (all parts)
apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
4 Verification conditions
When this method of calculation is applied to low-voltage switchgear and controlgear
assemblies the following conditions shall be fulfilled:
– the assembly is designed for AC currents and frequencies up to and including 1 600 A, 60
Hz. For higher current ratings or frequencies, the method could be used with additional
verifications taking into account the effect of eddy-currents on the temperature distribution
inside the assembly as required by the relevant product standards.
NOTE 1 In IEC 61439-2, additional requirements for currents in excess of 1 600 A are specified to take into
account the considerably increased power losses due to magnetic effects (eddy currents, proximity effect, skin
effect)
– the assembly is designed for DC currents up to and including 3 200 A. For higher current
ratings the method could be used with additional verifications as required by the relevant
product standards;
– conductors carrying currents in excess of 200 A AC, and the adjacent structural parts are
so arranged that eddy-current and hysteresis losses are negligible;
– there is an approximately even distribution of power losses inside the enclosure;
– the power losses data for all built-in components are available or can be calculated
(see Clause 5);
– the installed equipment is so arranged that air circulation is not significantly impeded.
NOTE 2 When this method is used to determine the thermal power dissipation capability of an empty enclosure in
accordance with IEC 62208, the above conditions do not apply.
5 Calculation method
5.1 Assumptions made in this calculation
To use the calculation method of this document, the following assumptions are deemed valid:
– the enclosure is made of metal (steel, aluminium, stainless steel) coated (both sides, inside
and outside), insulating material like thermoplastic or thermoset or similar (see Annex D);
– the enclosure is made of a single layer material or multiple layers without air-gap;
– for enclosures with or without natural ventilation, there are no more than five horizontal
partitions in the assembly or in a section of it;
– the enclosure is designed without ventilation openings or;
– the enclosure is designed with free air inlet and outlet ventilation openings, without the
inclusion of any additional filter (see Annex E);
• the cross-section of the air outlet openings is at least 10 % bigger than that of the inlet
openings to permit the chimney effect;
• the minimum cross section of air inlet openings is 10 cm ;
NOTE 1 Figure 3 and the formula given in Table 7 are not usable for lower cross sections. Assemblies with a
sum of the air inlet openings less than 10 cm are considered as assemblies without an air inlet.
• if the enclosure has air inlet and outlet openings with filters for an IP5X rating or higher
then these openings are not considered for the calculation;
• for IP ratings lower than IP5X the effective free air cross section of the openings shall
be used for calculation (see Annex E);
– where enclosures with natural ventilation openings have compartments, the surface of each
horizontal partition shall be provided with free air ventilation openings of at least 50 % of
the horizontal cross-section of the partition (see Clause B.1);
– power losses are considered as a sum of the followings:
• power losses of low-voltage switchgear and controlgear (see Clause G.2);
– 10 – IEC TR 60890:2022 © IEC 2022
• power losses of conductors connecting low-voltage switchgear and controlgear (see
Clause G.3);
• power losses of busbars (see Clause G.4);
• power losses of electronic devices (see Clause G.5);
– the enclosure is not subject to solar radiation.
5.2 Necessary information
The following data shall be used to calculate the temperature-rise of the air inside an enclosure:
– dimensions of the enclosure: height/width/depth;
– type of installation of the enclosure according to Figure 4;
– design of enclosure, i.e. with or without ventilation openings;
– number of internal horizontal partitions;
– effective power loss of equipment installed in the enclosure, see Annex G;
– effective power loss (P ) of conductors according to Annex I.
v
5.3 Calculation procedure
5.3.1 General
For the enclosures specified in columns 4 and 5 of Table 1, the calculation of the temperature-
rise of the air inside the enclosure is carried out using the formulae laid down in columns 1 to
3 of Table 1.
The pertinent factors and exponents (characteristics) are obtained from columns 6 to 10 of
Table 1.
The symbols, units and designations are stated in Table 2.
For enclosures having more than one section with vertical partitions, the temperature-rise of
the air inside the enclosure shall be determined separately for each section.
Where enclosures without vertical partitions or individual sections have an effective cooling
or a width greater than about 1,5 m, they should be divided for
surface greater than 11,5 m
the calculation into fictitious sections, whose dimensions approximate to the foregoing values.
NOTE The template (see Figure 9) can be used as a calculation aid.
5.3.2 Determination of the effective cooling surface A of the enclosure
e
The calculation is carried out according to Formula (1) in column 1 of Table 1.
The effective cooling surface A of an enclosure is the sum of the individual surfaces A
e o
multiplied by the surface factor b. This factor takes into account the heat dissipation of the
individual surfaces according to the type of installation of the enclosure (see Annex H for
additional explanations).
5.3.3 Determination of the internal temperature-rise ∆t of the air at mid-height of
0,5
the enclosure
The calculation is carried out according to Formula (2) in column 2 of Table 1.
In Formula (2) the enclosure constant k allows for the size of the effective cooling surface for
enclosures without ventilation openings and, in addition, for the cross-section of the air inlet
openings for enclosures with ventilation openings.
The dependence of the temperature-rise occurring in the enclosure on the effective power loss
P is expressed by the exponent x.
The factor d allows for the dependence of the temperature-rise on the number of internal
horizontal partitions.
5.3.4 Determination of the internal temperature-rise ∆t of air at the top of the
1,0
enclosure
The calculation is made according to Formula (3) in column 3 of Table 1.
Factor c allows for the temperature distribution inside an enclosure. Its determination varies
with the design and installation of the assembly as follows:
a) For enclosures without ventilation The factor c from Figure 4, depends on the
openings and with an effective cooling type of installation and the height/base
surface: factor f, where:
1,35
h
A > 1,25 m f=
e
A
b
b) For enclosures with ventilation openings The factor c from Figure 6, depends on the
and with an effective cooling surface: cross-section of air inlet openings and the
height/base factor f, where:
1,35
h
A > 1,25 m
e f=
A
b
c) For enclosures without ventilation The factor c from Figure 8, depends on the
openings and with an effective cooling height/width factor g, where:
surface:
h
A ≤ 1,25 m
g=
e
w
where
h is the enclosure height, in m;
A is the surface area of the enclosure base, in m ;
b
w is the enclosure width, in m.
5.3.5 Characteristic curve for temperature-rise of air inside enclosure
5.3.5.1 General
To evaluate the design according to Clause 7, the calculated results of 5.3.3 and 5.3.4 shall be
applied with the proper characteristic curve for temperature-rise of air inside the enclosure as
a function of the enclosure height. The air temperatures within horizontal levels are practically
constant.
5.3.5.2 Temperature-rise characteristic curve for enclosures with an effective
cooling surface A exceeding 1,25 m
e
As a general rule, the characteristic curve of temperature-rise is adequately well defined by a
straight line which runs through the points ∆t and ∆t (see Figure 1).
1,0 0,5
– 12 – IEC TR 60890:2022 © IEC 2022
The internal air temperature-rise at the bottom of the enclosure is close to zero, i.e. the
characteristic curve flattens out towards zero. In practice, the dotted part of the characteristic
curve is of secondary importance.
Figure 1 – Temperature-rise characteristic curve
for enclosures with A exceeding 1,25 m
e
5.3.5.3 Temperature-rise characteristic curve for enclosures with an effective
cooling surface A not exceeding 1,25 m
e
For this type of enclosure, the maximum temperature-rise in the upper quarter is constant and
the values for ∆t and ∆t are identical (see Figure 2).
1,0 0,75
The characteristic curve is obtained by connecting the temperature-rise values at an enclosure
level of 0,75 and 0,5 (see Figure 2).
The internal air temperature-rise at the bottom of the enclosure is close to zero, i.e. the
characteristic curve flattens out towards zero. In practice, the dotted part of the characteristic
curve is of secondary importance.
Figure 2 – Temperature-rise characteristic curve
for enclosures with A not exceeding 1,25 m
e
5.4 Maximum internal air temperature limits
This document contains a method to calculate the internal air temperature within an enclosure.
The resulting temperature shall not exceed the maximum absolute temperature allowed by
different types of devices and products installed inside.
The user of this document should refer to the manufacturer’s instructions regarding the
maximum operational temperature allowed for the devices used inside the assembly.
NOTE The value of internal air temperature has a direct influence on the ageing and operation of built-in
components.
6 Further considerations
6.1 General
The means of temperature-rise calculation in this document relate to specific arrangements of
assembly in the conditions as defined. These arrangements and conditions do not cover all
designs of assembly or the conditions in which some are installed. Where good practises are
applied the calculation methods in this document can lead to conservative results.
Annex B, Annex C, Annex D, Annex E, Annex F, Annex H, Annex J and Annex K detail good
practice that can lead to an improvement in thermal performance or some aspects not
considered in the calculation method in this document. However, when using these additional
considerations, to ensure a defined performance of an assembly, further verification, e.g. test,
shall be performed.
6.2 Guidance on the effects of an uneven power distribution
The aim of Annex B is to determine the temperature-rise where there is not an even power
distribution within an assembly using as a starting point the temperature-rise of a reference
design or calculation in accordance with Clause 5.
– 14 – IEC TR 60890:2022 © IEC 2022
6.3 Guidance on the additional temperature-rise effect due to solar radiation
In case of outdoor assemblies that are subject to direct sunlight, solar irridiance can significantly
increase internal air temperature-rise and require a derating of the rated currents of the
assembly. See Annex C.
7 Evaluation of the design
It shall be determined whether the equipment within the assembly can operate satisfactorily at the relevant calculated internal air temperature-rise.
If it is not so, the parameters will have to be changed and the calculation repeated.
Table 1 – Method of calculation, application, formulas and characteristics
a
1 2 3 4 6 7 8 9 10 11
Calculation formulae Enclosure Characteristics Characteristic
curve
Temperature-rise of air Factors Exponent
Effective
Plotting of
Effective cooling
cooling
temperature-rise
At mid-height of At (internal) top surface A b k d c x
e
surface A
characteristics
e
the enclosure of enclosure see see see see
Enclosure without
Figure 3 Table 4 Figure 4 0,804
ventilation openings
>1,25 m See 5.3.5.2
x
A = Σ (A × b) ∆t = c × ∆t
∆t = k × d × P
e o 1,0 0,5
Enclosure with
0,5
Table 3 Figure 5 Table 5 Figure 6 0,715
ventilation openings
(1) (3)
(2)
Enclosure without
≤1,25 m Figure 7 d=1 Figure 8 0,804 See 5.3.5.3
ventilation openings
a 2
For enclosure with ventilation openings with effective surface A ≤ 1,25 m the criteria of enclosures without ventilation openings can be used.
e
For symbols, units and designations, see Table 2.
For method of calculation, see also the examples given in Annex A.
– 16 – IEC TR 60890:2022 © IEC 2022
Table 2 – Symbols, units and designations
Symbol Unit Designation
A Surfaces of external sides of enclosure
m
o
A Enclosure base surface
m
b
A Effective cooling surface of enclosure
m
e
A Surface area, which can transport heat (usually excluding the bottom area)
m
s
α Heat transfer coefficient (includes conduction and radiation of heat)
W/m K
b – Surface factor
c – Temperature distribution factor
c J/kg*K Heat capacity (of air)
p
d – Temperature-rise factor for internal horizontal partitions inside enclosure
f – Height/base factor
g – Height/width factor
h m Enclosure height
k – Enclosure constant
n – Number of internal horizontal partitions (up to five partitions)
P W Effective power loss of equipment installed inside enclosure (determined according to
Annex G)
P W Calculated power dissipation of the enclosure according to this document, without
considering natural ventilation
P W Power losses dissipated by forced ventilation
fan
P W Effective power losses of conductors
v
P
W Total dissipated power
w
ρ Mass density (of air) at T
kg/m
a
V Volume flow rate of the air flow through the enclosure
m /s
S Cross-section of air inlet openings
cm
air
T °C Ambient temperature
a
T °C Temperature inside the enclosure
int
T °C Maximum temperature allowed inside the enclosure (limited e.g. by devices)
int,max
w m Enc
...
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