IEC TR 60890:2014

A method of temperature-rise verification of low-voltage switchgear and controlgear assemblies by calculation

IEC TR 60890:2014 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. This second edition cancels and replaces the first edition published in 1987 and its Amendment 1:1995. It constitutes a technical revision. This edition includes the following significant technical changes with respect to the last edition:
- alignment with IEC 61439-1:2011;
- revision of Annex B;
- general editorial review.

Méthode de vérification par calcul des échauffements pour les ensembles d'appareillage à basse tension

L'IEC TR 60890:2014 décrit une méthode de vérification par calcul des échauffements pour les ENSEMBLES d'appareillage à basse tension. La méthode est applicable aux ENSEMBLES sous enveloppe ou aux sections compartimentées des ENSEMBLES sans ventilation forcée. Elle n'est pas applicable lorsque la vérification de l'échauffement a été réalisée conformément à la norme produit de la série IEC 61439. Cette deuxième édition annule et remplace la première édition parue en 1987 et son Amendement 1:1995. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à la dernière édition:
- harmonisation avec l'IEC 61439-1:2011;
- révision de l'Annexe B;
- revue éditoriale générale.

General Information

• Status: Published
• Publication Date: 06-May-2014
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 29.130.20 - Low voltage switchgear and controlgear
• Technical Committee: SC 121B - Low-voltage switchgear and controlgear assemblies
• Current Stage: DELPUB - Deleted Publication
• Start Date: 29-Sep-2022
• Completion Date: 26-Oct-2025

Relations

• Revised: IEC TR 60890:2022 - A method of temperature-rise verification of low-voltage switchgear and controlgear assemblies by calculation
• Effective Date: 05-Sep-2023

Overview

The IEC TR 60890:2014 is an important technical report published by the International Electrotechnical Commission (IEC) that specifies a method for temperature-rise verification of low-voltage switchgear and controlgear assemblies by calculation. This standard addresses the need for reliable thermal performance evaluation of enclosed or partitioned low-voltage assemblies without forced ventilation, which is critical for ensuring operational safety and longevity of electrical equipment.

This 2014 edition revokes and replaces the initial 1987 version and its 1995 amendment. The revision brings alignment with IEC 61439-1:2011, updates Annex B, and incorporates editorial improvements to enhance clarity and application consistency.

Key Topics

• Scope of Application
  The method applies to enclosed assemblies or partitioned sections of low-voltage switchgear and controlgear with no forced ventilation, excluding cases already covered by IEC 61439 series product standards.

• Calculation Procedure
  The report defines a detailed calculation method that includes:

  • Determination of the effective cooling surface area of the enclosure
  • Calculating the internal temperature rise of air at mid-height and top of the enclosure
  • Use of characteristic temperature-rise curves to predict air temperature distribution inside assemblies

• Parameters and Factors
  The method incorporates factors such as enclosure constants, surface conditions, installation type, ventilation openings, and power losses of components and conductors within the enclosure.

• Technical Changes
  Updates ensure better consistency with recent international product standards and enhanced methods for calculating operating currents and power losses, improving accuracy in thermal assessments.

Applications

The practical applications of IEC TR 60890:2014 include:

• Design Verification
  Enables equipment manufacturers and designers to verify that switchgear and controlgear assemblies meet thermal performance requirements by calculation rather than costly and time-consuming physical testing.

• Safety Assurance
  Helps prevent overheating-related failures by ensuring assemblies stay within acceptable temperature-rise limits under expected operating conditions.

• Compliance with International Standards
  Facilitates compliance with IEC 61439-1 and related series, supporting global market acceptance of low-voltage electrical assemblies.

• Optimization of Assembly Design
  Guides specifications for enclosure materials, ventilation design, and layout to optimize cooling and operational reliability.

This method is especially useful in scenarios where physical testing is impractical, where multiple design iterations need rapid thermal assessment, or for partitioned assembly sections requiring individual temperature-rise verification.

Related Standards

IEC TR 60890:2014 works in conjunction with several international standards to provide comprehensive guidance on low-voltage electrical assemblies:

• IEC 61439 Series
  Governs general specifications and verifications for low-voltage switchgear and controlgear assemblies, including temperature-rise verification by physical testing or alternative methods.

• IEC 60364-5-52
  Addresses electrical installation rules and considerations, including conductor temperature ratings and power loss calculations relevant to thermal verification.

• ISO/IEC Directives
  Provide the framework for drafting, revising, and maintaining IEC publications, ensuring consistency and international consensus.

By aligning calculation methods with the IEC 61439 standard and referencing conductor data from IEC 60364, IEC TR 60890 ensures a harmonized approach for assessing temperature rise safely and reliably.

---

Keywords: IEC TR 60890, temperature-rise verification, low-voltage switchgear, controlgear assemblies, enclosure cooling, thermal calculation method, IEC 61439, electrical safety standards, switchgear design verification, power loss calculation, low-voltage assemblies.

Standards Content (Sample)

IEC TR 60890 ®
Edition 2.0 2014-05
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
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’appareillage à basse tension

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IEC TR 60890 ®
Edition 2.0 2014-05
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
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’appareillage à basse tension

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX V
ICS 29.130.20 ISBN 978-2-8322-1566-1

– 2 – IEC TR 60890:2014 © IEC 2014
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Conditions for application . 7
5 Calculation . 8
5.1 Necessary information . 8
5.2 Calculation procedure . 8
5.2.1 General . 8
5.2.2 Determination of the effective cooling surface A of the enclosure . 8
e
5.2.3 Determination of the internal temperature rise ∆t of the air at mid-
0,5
height of the enclosure . 8
5.2.4 Determination of the internal temperature rise ∆t of air at the top of
1,0
the enclosure . 9
5.2.5 Characteristic curve for temperature rise of air inside enclosure . 9
6 Evaluation of the design . 11
Annex A (informative) Examples for the calculation of the temperature-rise of air
inside the enclosures . 20
A.1 Example 1 . 20
A.2 Example 2 . 23
Annex B (informative) Operating current and power losses of conductors . 27
Bibliography . 32

Figure 1 – Temperature-rise characteristic curve for enclosures with
A exceeding 1,25 m . 10
e
Figure 2 – Temperature-rise characteristic curve for enclosures with A
e
not exceeding 1,25 m . 10
Figure 3 – Enclosure constant k for enclosures without ventilation openings, with an
effective cooling surface A > 1,25 m . 13
e
Figure 4 – Temperature distribution factor c for enclosures without ventilation openings
and with an effective cooling surface A > 1,25 m . 14
e
Figure 5 – Enclosure constant k for enclosures with ventilation openings and an
effective cooling surface A > 1,25 m . 15
e
Figure 6 – Temperature distribution factor c for enclosures with ventilation openings
and an effective cooling surface A > 1,25 m . 16
e
Figure 7 – Enclosure constant k for enclosures without ventilation openings and with
an effective cooling surface A ≤ 1,25 m . 17
e
Figure 8 – Temperature distribution factor c for enclosures without ventilation openings
and with an effective cooling surface A ≤ 1,25 m . 18
e
Figure 9 – Calculation of temperature rise of air inside enclosures . 19
Figure A.1 – Example 1, calculation for an enclosure with exposed side faces without
ventilation openings and without internal horizontal partitions . 20
Figure A.2 – Example 1, calculation for a single enclosure . 22
Figure A.3 – Example 2, calculation for an enclosure for wall-mounting with ventilation

openings . 23

Figure A.4 – Example 2, calculation for one enclosure half . 24
Figure A.5 – Example 2, calculation for an enclosure for wall-mounting with ventilation
openings . 26

Table 1 – Method of calculation, application, formulae and characteristics . 11
Table 2 – Symbols, units and designations . 12
Table 3 – Surface factor b according to the type of installation . 12
Table 4 – Factor d for enclosures without ventilation openings and with an effective
cooling surface A >1,25 m . 12
e
Table 5 – Factor d for enclosures with ventilation openings and an effective cooling
surface A >1,25 m . 12
e
Table B.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) . 28
Table B.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) . 29
Table B.3 – Operating current and power loss of bare copper bars with rectangular
cross-section, run horizontally and arranged with their largest face vertical (ambient
temperature inside the enclosure: 55 °C, temperature of the conductor 70 °C) . 30
Table B.4 – Factor k for different temperatures of the air inside the enclosure and/or
for the conductors . 31

– 4 – IEC TR 60890:2014 © IEC 2014
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 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,
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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-
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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
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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.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC/TR 60890, which is a technical report, has been prepared by subcommittee 17D: Low-
voltage switchgear and controlgear assemblies, of IEC technical committee 17: Switchgear
and controlgear.
This second edition cancels and replaces the first edition published in 1987 and its
Amendment 1:1995. It constitutes a technical revision.
This edition includes the following significant technical changes with respect to the last
edition:
– alignment with IEC 61439-1:2011;
– revision of Annex B;
– general editorial review.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
17D/490/DTR 17D/499/RVC
Full information on the voting for the approval of this technical report can be found in the
report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until
the stability 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.
– 6 – IEC TR 60890:2014 © IEC 2014
INTRODUCTION
In IEC 61439-1, in the series of design verifications, a temperature-rise verification of low-
voltage power switchgear and controlgear assemblies (hereafter called ASSEMBLIES) is
specified. This may be by test, however, alternatives are acceptable in defined circumstances.
Selection of the method used for temperature rise verification is the responsibility of the
original manufacturer. Where applicable this technical report may also be used for
temperature rise verification of similar products in accordance with other standards. The
factors and coefficients, set out in this report have been derived from measurements on
numerous ASSEMBLIES and the method has been verified by comparison with test results.

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 temperature rise 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 temperature is deemed to be the ambient air temperature.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. 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
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61439-1 apply.
4 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;

– 8 – IEC TR 60890:2014 © IEC 2014
– 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.
5 Calculation
5.1 Necessary information
The following data is needed to calculate the temperature rise of the air inside an enclosure:
– dimensions of the enclosure: height/width/depth;
– the 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;
– effective power losses (P ) of conductors according to Annex B.
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.
5.2 Calculation procedure
5.2.1 General
For the enclosures specified in columns 4 and 5 of Table 1, the calculation of the temperature
rise of the air inside the enclosures 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 to be taken from 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 form (see Figure 9) can be used as a calculation aid.
5.2.2 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.
5.2.3 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 rises 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.
5.2.4 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:
The factor c from Figure 4, depends on the
a) For enclosures without ventilation
openings and with an effective cooling type of installation and the height/base factor
surface: f, where:
1,35
h
f=
A > 1,25 m
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.
5.2.5 Characteristic curve for temperature rise of air inside enclosure
5.2.5.1 General
To evaluate the design according to Clause 6, it is necessary to apply the calculated results of
5.2.3 and 5.2.4 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.
5.2.5.2 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
– 10 – IEC TR 60890:2014 © IEC 2014
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.
IEC  1428/14
Figure 1 – Temperature-rise characteristic curve
for enclosures with A exceeding 1,25 m
e
5.2.5.3 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.
IEC  1429/14
Figure 2 – Temperature-rise characteristic curve
for enclosures with A not exceeding 1,25 m
e
6 Evaluation of the design
It shall be determined whether the equipment within the ASSEMBLY can operate satisfactorily at the relevant calculated temperature rise.
If it is not so, the parameters will have to be changed and the calculation repeated.
Table 1 – Method of calculation, application, formulae and characteristics
1 2 3 4 5 6 7 8 9 10 11
Calculation formulae Enclosure Characteristics Characteristic curve
Temperature rise of air Factors Exponent
Plotting of
Effective cooling Effective cooling
temperature-rise
At mid-height of At (internal) top b k d c x
surface A surface A
e e
characteristics
the enclosure of enclosure see see see see
Enclosure without
Figure Table Figure
ventilation 0,804
3 4 4
openings
See 5.2.5.2
>1,25 m
x
Enclosure with
A = Σ (A × b) ∆t = k × d × P ∆t = c × ∆t
e o 0,5 1,0 0,5 Table Figure Table Figure
ventilation 0,715
3 5 5 6
(1) (2) (3)
openings
Enclosure without
Figure Figure
<1,25 m ventilation – 0,804 See 5.2.5.3
7 8
openings
For symbols, units and designations, see Table 2.

– 12 – IEC TR 60890:2014 © IEC 2014
Table 2 – Symbols, units and designations
Symbol Unit Designation
m Surfaces of external sides of enclosure
A
o
m Enclosure base surface
A
b
m Effective cooling surface of enclosure
A
e
– Surface factor
b
– Temperature distribution factor
c
– Temperature-rise factor for internal horizontal partitions inside enclosure
d
– Height/base factor
f
– Height/width factor
g
m Enclosure height
h
– Enclosure constant
k
– Number of internal horizontal partitions (up to three partitions)
n
W Effective power loss of equipment installed inside enclosure
P
W Effective power losses of conductors
P
v
m Enclosure width
w
– Exponent
x
K Temperature rise of air inside enclosure in general
A
t
K Temperature rise of air at (internal) mid-height of enclosure
∆t
0,5
K Temperature rise of air at (internal) 3/4 height of enclosure
∆t
0,75
K Temperature rise of air at (internal) top of enclosure
∆t
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 5.2) 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 partitions n 0 1 2 3
Factor d 1,00 1,05 1,15 1,30
Table 5 – Factor d for enclosures with ventilation openings
and an effective cooling surface A >1,25 m
e
Number of horizontal partitions n 0 1 2 3
Factor d 1,00 1,05 1,10 1,15
IEC  1430/14
Figure 3 – Enclosure constant k for enclosures without ventilation
openings, with an effective cooling surface A > 1,25 m
e
– 14 – IEC TR 60890:2014 © IEC 2014

IEC  1431/14
Key
1)
Height/base factor, see 5.2.4.
Figure 4 – Temperature distribution factor c for enclosures without ventilation openings and with an effective cooling surface A > 1,25 m
e
IEC  1432/14
Key
1)
The cross-section of the corresponding air outlet openings should be at least 1,1 times that of the air inlet
openings.
Figure 5 – Enclosure constant k for enclosures with ventilation
openings and an effective cooling surface A > 1,25 m
e
– 16 – IEC TR 60890:2014 © IEC 2014

IEC  1433/14
Key
1)
The cross-section of the corresponding air outlet openings should be at least 1,1 times that of the air inlet
openings.
2)
Height/base factor, see 5.2.4.
Figure 6 – Temperature distribution factor c for enclosures with ventilation
openings and an effective cooling surface A > 1,25 m
e
IEC  1434/14
Figure 7 – Enclosure constant k for enclosures without ventilation openings
and with an effective cooling surface A ≤ 1,25 m
e
– 18 – IEC TR 60890:2014 © IEC 2014

IEC  1435/14
Key
1)
Height/width factor, see 5.2.4.
Figure 8 – Temperature distribution factor c for enclosures without ventilation openings
and with an effective cooling surface A ≤ 1,25 m
e
Calculation of temperature rise of air inside enclosures

Customer/plant
Type of enclosure
Relevant height mm Type of installation:
dimensions for
width mm Ventilation openings: yes/no
temperature rise
depth mm Number of horizontal partitions:

A × b
o
Surface factor b
Dimensions A (column 3) ×
o
according to
(column 4)
Table 3
2 2
m m
m × m
2 3 4 5
Top
Front
Rear
Left-hand side
Right-hand side
A = Σ(A × b) = Total
e o
With an effective cooling surface A
e
2 2
Exceeding 1,25 m Not exceeding 1,25 m
1,35
h h
(see 5.2.4)
f= (see 5.2.4) g=
A w
b
= = = =
Air inlet openings cm
Enclosure constant k
Factor for horizontal partitions d
effective power loss P W
x …
P = P
x
∆t = k × d × P K
0,5
Temperature distribution factor c

∆t = c × ∆t K
1,0 0,5
Characteristic curve:
IEC  1436/14
Figure 9 – Calculation of temperature rise of air inside enclosures
Effective cooling surface
– 20 – IEC TR 60890:2014 © IEC 2014
Annex A
(informative)
Examples for the calculation of the temperature-rise
of air inside the enclosures
A.1 Example 1
Single enclosure with exposed side faces without ventilation openings and without internal
horizontal partitions (see Figure A.1).
Effective power loss of equipment installed in the enclosure: P = 300 W
Dimensions in mm
IEC  1437/14
Figure A.1 – Example 1, calculation for an enclosure with exposed side faces
without ventilation openings and without internal horizontal partitions
Calculation
(For entries see form, Figure A.2 on example 1.)
– The effective cooling surface A is determined according to 5.2.2.
e
The individual surfaces are calculated from the enclosure dimensions, and the surface
factor b is taken from Table 3.
– The temperature rise of air ∆t is determined according to 5.2.3.
0,5
Formula (2) from column 2 of Table 1:
x
∆t = k × d × P (A.1)
0,5
Factor k according to column 7 of Table 1 with A > 1,25 m , as shown in Figure 3:
e
for A = 6,64 m : k = 0,135
e
Factor d according to column 8 of Table 1 with A > 1,25 m , as specified in Table 4:
e
with number of horizontal partitions = 0: d = 1,0
Effective power loss (as specified) P = 300 W.

Exponent x from column 10 of Table 1 with A > 1,25 m : x = 0,804
e
With these values entered into the Formula (A.1), the following result is obtained:
x 0,804
∆t = k × d × P = 0,135 × 1,0 × 300
0,5
∆t = 13,24 K ≈ 13,2 K
0,5
– The temperature rise of air ∆t is determined according to 5.2.4.
1,0
Formula (3) from column 3 of Table 1:
∆t = c × ∆t (A.2)
1,0 0,5
Factor c according to column 9 of Table 1 with A > 1,25 m , as shown in Figure 4:
e
1,35
1,35
ℎ 2,2
𝑓 = = = 5,80
𝐴 1,0×0,5
𝑏
Curve 1 of Figure 4 follows:
c = 1,44
With this value entered into Formula (A.2), the following result is obtained:
∆t = c × ∆t = 1,44 × 13,24 = 19,07 K ≈ 19,1 K
1,0 0,5
– The temperature-rise characteristic curve is determined for enclosures with A > 1,25 m ,
e
in accordance with 5.2.5.2 (see Figure A.2 in the form on example 1).
– The evaluation of the design is made in accordance with Clause 6.
It is to be verified whether the equipment installed in the enclosure is capable of
functioning satisfactorily at the specified currents and calculated temperature rises,
considering the ambient air temperature (see Clause 1, Note 2).
If this is not so, the parameters will have to be changed and the calculation repeated.

– 22 – IEC TR 60890:2014 © IEC 2014

IEC  1438/14
Figure A.2 – Example 1, calculation for a single enclosure

A.2 Example 2
Enclosure for wall-mounting with ventilation openings
cross-section of air inlet openings = 1 220 cm
cross-section of air outlet openings = 1 800 cm
with two horizontal partitions inside the enclosure. Each horizontal partition, for example
perforated plate, has ventilation openings, the cross-sectional areas of which exceed 50 % of
the enclosure cross-section (see Figure A.3 and Figure A.4).
Effective power loss of equipment installed in the enclosure P = 2 200 W.
Dimensions in mm
IEC  1439/14
Key
A Air outlet openings
B Horizontal partitions with ventilation openings, for example perforated plate
C Air inlet openings
Figure A.3 – Example 2, calculation for an enclosure
for wall-mounting with ventilation openings
Calculation
(For entries see form Figure A.5 on example 2)
Given an expected cooling surface of the enclosure of more than 11,5 m² and an enclosure
width exceeding 1,5 m, the entire enclosure is to be divided, for calculation purposes, into
sections (partial enclosures) as indicated in 5.2. To simplify the procedure, as no structural
divisions are available, the entire enclosure is, in this example, divided into two equal
sections (enclosure halves). The power losses and ventilation openings are supposed to be
evenly distributed in both parts (enclosure halves) so that for the calculation they are divided
by two.
The calculation is carried out for only one enclosure half, the result being applicable to the
other half.
– 24 – IEC TR 60890:2014 © IEC 2014
– Necessary information according to 5.1 for one half of the enclosure
Dimensions in mm
Enclosure for wall-mounting with air
inlet openings
1 220
= = 610 cm
With air outlet openings
1 800
= = 900 cm
With two horizontal partitions, for
example perforated plate
Effective power loss
2 200
= = 1 100 W
IEC  1440/14
Figure A.4 – Example 2, calculation for one enclosure half
– The effective cooling surface of each enclosure half is determined according to 5.2.2.
The individual surfaces are calculated from the enclosure dimensions, and the surface
factor b is taken from Table 3.
The dividing surface between the two enclosure halves which has been obtained as a
result of the fictitious division, is not taken into account in accordance with Table 3.
– The temperature rise of air ∆t is determined according to 5.2.3.
0,5
Formula (2) from column 2 of Table 1
x
∆t = k × d × P (A.3)
0,5
Factor k according to column 7 of Table 1 and A > 1,25 m , as shown in Figure 5.
e
2 2
For 610 cm air inlet openings and A = 7,674 m : k = 0,071
e
Factor d according to column 8 of Table 1 and A > 1,25 m as specified in Table 5 with
e
two horizontal partitions: d = 1,10
Effective power loss (as specified) P = 1 100 W
Exponent x from column 10 of Table 1 with A > 1,25 m : x = 0,715
e
With these values entered into the above Formula (A.3), the following result is obtained:
x 0,715
∆t = k × d × P = 0,071 × 1,0 × 1 100
0,5
∆t = 11,67 K ≈ 11,7 K
0,5
– The temperature rise of air ∆t is determined according to 5.2.4.
1,0
Formula (3) from column 3 of Table 1
∆t = c × ∆t (A.4)
1,0 0,5
Factor c according to column 9 of Table 1 and A > 1,25 m , as shown in Figure 6.
e
1,35
1,35
ℎ 2,2
𝑓 = = = 2,50
𝐴 1,45×0,8
𝑏
Figure 6 shows that, for 610 cm air inlet openings:
c = 1,87
With these values entered into Formula (A.4), the following result is obtained:
∆t = c × ∆t = 1,87 × 11,67 = 21,82 K ≈ 21,8 K
1,0 0,5
– The temperature-rise characteristic curve is determined for enclosures with A > 1,25 m ,
e
in accordance with 5.2.5.2 (see Figure A.5 in the form on example 2).
– The evaluation of the design is made in accordance with Clause 6.
It is to be verified whether the equipment installed in the enclosure is capable of
functioning satisfactorily at the specified currents and calculated temperature rises,
considering the ambient air temperature (see Clause 1, Note 2).
If this is not so, the parameters will have to be changed and the calculation repeated.

– 26 – IEC TR 60890:2014 © IEC 2014

IEC  1441/14
Figure A.5 – Example 2, calculation for an enclosure
for wall-mounting with ventilation openings

Annex B
(informative)
Operating current and power losses of conductors

The maximum permissible operating current of a conductor is influenced by many factors:
– material, type of insulation and arrangement of the conductors belonging to the same
circuit;
– mutual influence of components connected to the conductor;
– mutual influence of neighbouring components and conductors belonging to other circuits;
– air temperature inside the enclosure around the conductor;
– temperature and thermal conductivity of constructional parts touching or in close vicinity of
the conductor.
The power loss of conductors depend on
– the operating current and its frequency;
– the material and the temperature of the conductor;
– the shape of the conductor (skin effect);
– the magnetic influence of neighbouring conductors and magnetic constructional parts
(proximity effect).
The following tables provide guidance values for operating currents and power losses of
single-core copper cables and bare copper bars under idealized conditions within an
enclosure. The calculation methods used to establish these values are given to enable values
to be calculated for other conditions.
The maximum operating currents given in the tables do not apply to conductors used for
ASSEMBLIES verified by test according to IEC 61439-1.
The power losses are valid for the corresponding operational current given in the tables. For a
different loading the power losses can be calculated using the following equation:
𝐼
𝑃 =𝑃� �
v
𝐼
max
where
P is the power loss in watts per metre (W/m);
I is the conductor current (loading);
I is the maximum operating current;
max
P is the power loss at I .
v max
– 28 – IEC TR 60890:2014 © IEC 2014
Table B.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)
Spacing at least one
cable diameter
Conductor
Single-core cables in a Single-core cables, Single-core cables,
arrangement
cable trunking on a wall, touching free in air or on spaced horizont
...

IEC TR 60890 ®
Edition 2.0 2014-05
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
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’appareillage à basse tension

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IEC TR 60890 ®
Edition 2.0 2014-05
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
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’appareillage à basse tension

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX V
ICS 29.130.20 ISBN 978-2-8322-1566-1

– 2 – IEC TR 60890:2014 © IEC 2014

CONTENTS
FOREWORD . 4

INTRODUCTION . 6

1 Scope . 7

2 Normative references . 7

3 Terms and definitions . 7

4 Conditions for application . 7

5 Calculation . 8
5.1 Necessary information . 8
5.2 Calculation procedure . 8
5.2.1 General . 8
5.2.2 Determination of the effective cooling surface A of the enclosure . 8
e
5.2.3 Determination of the internal temperature rise ∆t of the air at mid-
0,5
height of the enclosure . 8
5.2.4 Determination of the internal temperature rise ∆t of air at the top of
1,0
the enclosure . 9
5.2.5 Characteristic curve for temperature rise of air inside enclosure . 9
6 Evaluation of the design . 11
Annex A (informative) Examples for the calculation of the temperature-rise of air
inside the enclosures . 20
A.1 Example 1 . 20
A.2 Example 2 . 23
Annex B (informative) Operating current and power losses of conductors . 27
Bibliography . 32

Figure 1 – Temperature-rise characteristic curve for enclosures with
A exceeding 1,25 m . 10
e
Figure 2 – Temperature-rise characteristic curve for enclosures with A
e
not exceeding 1,25 m . 10
Figure 3 – Enclosure constant k for enclosures without ventilation openings, with an
effective cooling surface A > 1,25 m . 13
e
Figure 4 – Temperature distribution factor c for enclosures without ventilation openings
and with an effective cooling surface A > 1,25 m . 14

e
Figure 5 – Enclosure constant k for enclosures with ventilation openings and an
effective cooling surface A > 1,25 m . 15
e
Figure 6 – Temperature distribution factor c for enclosures with ventilation openings
and an effective cooling surface A > 1,25 m . 16
e
Figure 7 – Enclosure constant k for enclosures without ventilation openings and with
an effective cooling surface A ≤ 1,25 m . 17
e
Figure 8 – Temperature distribution factor c for enclosures without ventilation openings
and with an effective cooling surface A ≤ 1,25 m . 18
e
Figure 9 – Calculation of temperature rise of air inside enclosures . 19
Figure A.1 – Example 1, calculation for an enclosure with exposed side faces without
ventilation openings and without internal horizontal partitions . 20
Figure A.2 – Example 1, calculation for a single enclosure . 22
Figure A.3 – Example 2, calculation for an enclosure for wall-mounting with ventilation

openings . 23

Figure A.4 – Example 2, calculation for one enclosure half . 24

Figure A.5 – Example 2, calculation for an enclosure for wall-mounting with ventilation

openings . 26

Table 1 – Method of calculation, application, formulae and characteristics . 11

Table 2 – Symbols, units and designations . 12

Table 3 – Surface factor b according to the type of installation . 12

Table 4 – Factor d for enclosures without ventilation openings and with an effective

cooling surface A >1,25 m . 12
e
Table 5 – Factor d for enclosures with ventilation openings and an effective cooling
surface A >1,25 m . 12
e
Table B.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) . 28
Table B.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) . 29
Table B.3 – Operating current and power loss of bare copper bars with rectangular
cross-section, run horizontally and arranged with their largest face vertical (ambient
temperature inside the enclosure: 55 °C, temperature of the conductor 70 °C) . 30
Table B.4 – Factor k for different temperatures of the air inside the enclosure and/or
for the conductors . 31

– 4 – IEC TR 60890:2014 © IEC 2014

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
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected

data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC/TR 60890, which is a technical report, has been prepared by subcommittee 17D: Low-
voltage switchgear and controlgear assemblies, of IEC technical committee 17: Switchgear
and controlgear.
This second edition cancels and replaces the first edition published in 1987 and its
Amendment 1:1995. It constitutes a technical revision.
This edition includes the following significant technical changes with respect to the last
edition:
– alignment with IEC 61439-1:2011;
– revision of Annex B;
– general editorial review.
The text of this technical report is based on the following documents:

Enquiry draft Report on voting

17D/490/DTR 17D/499/RVC
Full information on the voting for the approval of this technical report can be found in the

report on voting indicated in the above table.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

The committee has decided that the contents of this publication will remain unchanged until
the stability 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.
– 6 – IEC TR 60890:2014 © IEC 2014

INTRODUCTION
In IEC 61439-1, in the series of design verifications, a temperature-rise verification of low-

voltage power switchgear and controlgear assemblies (hereafter called ASSEMBLIES) is

specified. This may be by test, however, alternatives are acceptable in defined circumstances.

Selection of the method used for temperature rise verification is the responsibility of the

original manufacturer. Where applicable this technical report may also be used for

temperature rise verification of similar products in accordance with other standards. The

factors and coefficients, set out in this report have been derived from measurements on

numerous ASSEMBLIES and the method has been verified by comparison with test results.

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 temperature rise 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 temperature is deemed to be the ambient air temperature.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. 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
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61439-1 apply.

4 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;

– 8 – IEC TR 60890:2014 © IEC 2014

– 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.

5 Calculation
5.1 Necessary information
The following data is needed to calculate the temperature rise of the air inside an enclosure:

– dimensions of the enclosure: height/width/depth;
– the 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;
– effective power losses (P ) of conductors according to Annex B.
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.
5.2 Calculation procedure
5.2.1 General
For the enclosures specified in columns 4 and 5 of Table 1, the calculation of the temperature
rise of the air inside the enclosures 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 to be taken from 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 form (see Figure 9) can be used as a calculation aid.
5.2.2 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.
5.2.3 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 rises 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.
5.2.4 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:
The factor c from Figure 4, depends on the
a) For enclosures without ventilation
openings and with an effective cooling type of installation and the height/base factor
surface: f, where:
1,35
h
f=
A > 1,25 m
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.
5.2.5 Characteristic curve for temperature rise of air inside enclosure
5.2.5.1 General
To evaluate the design according to Clause 6, it is necessary to apply the calculated results of
5.2.3 and 5.2.4 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.
5.2.5.2 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
– 10 – IEC TR 60890:2014 © IEC 2014

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.

IEC  1428/14
Figure 1 – Temperature-rise characteristic curve
for enclosures with A exceeding 1,25 m
e
5.2.5.3 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.

IEC  1429/14
Figure 2 – Temperature-rise characteristic curve
for enclosures with A not exceeding 1,25 m
e
6 Evaluation of the design
It shall be determined whether the equipment within the ASSEMBLY can operate satisfactorily at the relevant calculated temperature rise.
If it is not so, the parameters will have to be changed and the calculation repeated.
Table 1 – Method of calculation, application, formulae and characteristics
1 2 3 4 5 6 7 8 9 10 11
Calculation formulae Enclosure Characteristics Characteristic curve
Temperature rise of air Factors Exponent
Plotting of
Effective cooling Effective cooling
temperature-rise
At mid-height of At (internal) top b k d c x
surface A surface A
e e
characteristics
the enclosure of enclosure see see see see
Enclosure without
Figure Table Figure
ventilation 0,804
3 4 4
openings
See 5.2.5.2
>1,25 m
x
Enclosure with
A = Σ (A × b) ∆t = k × d × P ∆t = c × ∆t
e o 0,5 1,0 0,5 Table Figure Table Figure
ventilation 0,715
3 5 5 6
(1) (2) (3)
openings
Enclosure without
Figure Figure
<1,25 m ventilation – 0,804 See 5.2.5.3
7 8
openings
For symbols, units and designations, see Table 2.

– 12 – IEC TR 60890:2014 © IEC 2014

Table 2 – Symbols, units and designations

Symbol Unit Designation
m Surfaces of external sides of enclosure

A
o
m Enclosure base surface
A
b
m Effective cooling surface of enclosure
A
e
– Surface factor
b
– Temperature distribution factor
c
– Temperature-rise factor for internal horizontal partitions inside enclosure
d
– Height/base factor
f
– Height/width factor
g
m Enclosure height
h
– Enclosure constant
k
– Number of internal horizontal partitions (up to three partitions)
n
W Effective power loss of equipment installed inside enclosure
P
W Effective power losses of conductors
P
v
m Enclosure width
w
– Exponent
x
K Temperature rise of air inside enclosure in general
A
t
K Temperature rise of air at (internal) mid-height of enclosure
∆t
0,5
K Temperature rise of air at (internal) 3/4 height of enclosure
∆t
0,75
K Temperature rise of air at (internal) top of enclosure
∆t
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 5.2) 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 partitions n 0 1 2 3
Factor d 1,00 1,05 1,15 1,30
Table 5 – Factor d for enclosures with ventilation openings
and an effective cooling surface A >1,25 m
e
Number of horizontal partitions n 0 1 2 3
Factor d 1,00 1,05 1,10 1,15
IEC  1430/14
Figure 3 – Enclosure constant k for enclosures without ventilation
openings, with an effective cooling surface A > 1,25 m
e
– 14 – IEC TR 60890:2014 © IEC 2014

IEC  1431/14
Key
1)
Height/base factor, see 5.2.4.
Figure 4 – Temperature distribution factor c for enclosures without ventilation openings and with an effective cooling surface A > 1,25 m
e
IEC  1432/14
Key
1)
The cross-section of the corresponding air outlet openings should be at least 1,1 times that of the air inlet
openings.
Figure 5 – Enclosure constant k for enclosures with ventilation
openings and an effective cooling surface A > 1,25 m
e
– 16 – IEC TR 60890:2014 © IEC 2014

IEC  1433/14
Key
1)
The cross-section of the corresponding air outlet openings should be at least 1,1 times that of the air inlet
openings.
2)
Height/base factor, see 5.2.4.
Figure 6 – Temperature distribution factor c for enclosures with ventilation
openings and an effective cooling surface A > 1,25 m
e
IEC  1434/14
Figure 7 – Enclosure constant k for enclosures without ventilation openings
and with an effective cooling surface A ≤ 1,25 m
e
– 18 – IEC TR 60890:2014 © IEC 2014

IEC  1435/14
Key
1)
Height/width factor, see 5.2.4.
Figure 8 – Temperature distribution factor c for enclosures without ventilation openings
and with an effective cooling surface A ≤ 1,25 m
e
Calculation of temperature rise of air inside enclosures

Customer/plant
Type of enclosure
Relevant height mm Type of installation:
dimensions for
width mm Ventilation openings: yes/no
temperature rise
depth mm Number of horizontal partitions:

A × b
o
Surface factor b
Dimensions A (column 3) ×
o
according to
(column 4)
Table 3
2 2
m m
m × m
2 3 4 5
Top
Front
Rear
Left-hand side
Right-hand side
A = Σ(A × b) = Total
e o
With an effective cooling surface A
e
2 2
Exceeding 1,25 m Not exceeding 1,25 m
1,35
h h
(see 5.2.4)
f= (see 5.2.4) g=
A w
b
= = = =
Air inlet openings cm
Enclosure constant k
Factor for horizontal partitions d
effective power loss P W
x …
P = P
x
∆t = k × d × P K
0,5
Temperature distribution factor c

∆t = c × ∆t K
1,0 0,5
Characteristic curve:
IEC  1436/14
Figure 9 – Calculation of temperature rise of air inside enclosures
Effective cooling surface
– 20 – IEC TR 60890:2014 © IEC 2014

Annex A
(informative)
Examples for the calculation of the temperature-rise

of air inside the enclosures
A.1 Example 1
Single enclosure with exposed side faces without ventilation openings and without internal

horizontal partitions (see Figure A.1).
Effective power loss of equipment installed in the enclosure: P = 300 W
Dimensions in mm
IEC  1437/14
Figure A.1 – Example 1, calculation for an enclosure with exposed side faces
without ventilation openings and without internal horizontal partitions
Calculation
(For entries see form, Figure A.2 on example 1.)

– The effective cooling surface A is determined according to 5.2.2.
e
The individual surfaces are calculated from the enclosure dimensions, and the surface
factor b is taken from Table 3.
– The temperature rise of air ∆t is determined according to 5.2.3.
0,5
Formula (2) from column 2 of Table 1:
x
∆t = k × d × P (A.1)
0,5
Factor k according to column 7 of Table 1 with A > 1,25 m , as shown in Figure 3:
e
for A = 6,64 m : k = 0,135
e
Factor d according to column 8 of Table 1 with A > 1,25 m , as specified in Table 4:
e
with number of horizontal partitions = 0: d = 1,0
Effective power loss (as specified) P = 300 W.

Exponent x from column 10 of Table 1 with A > 1,25 m : x = 0,804
e
With these values entered into the Formula (A.1), the following result is obtained:

x 0,804
∆t = k × d × P = 0,135 × 1,0 × 300
0,5
∆t = 13,24 K ≈ 13,2 K
0,5
– The temperature rise of air ∆t is determined according to 5.2.4.
1,0
Formula (3) from column 3 of Table 1:

∆t = c × ∆t (A.2)
1,0 0,5
Factor c according to column 9 of Table 1 with A > 1,25 m , as shown in Figure 4:
e
1,35
1,35
ℎ 2,2
𝑓 = = = 5,80
𝐴 1,0×0,5
𝑏
Curve 1 of Figure 4 follows:
c = 1,44
With this value entered into Formula (A.2), the following result is obtained:
∆t = c × ∆t = 1,44 × 13,24 = 19,07 K ≈ 19,1 K
1,0 0,5
– The temperature-rise characteristic curve is determined for enclosures with A > 1,25 m ,
e
in accordance with 5.2.5.2 (see Figure A.2 in the form on example 1).
– The evaluation of the design is made in accordance with Clause 6.
It is to be verified whether the equipment installed in the enclosure is capable of
functioning satisfactorily at the specified currents and calculated temperature rises,
considering the ambient air temperature (see Clause 1, Note 2).
If this is not so, the parameters will have to be changed and the calculation repeated.

– 22 – IEC TR 60890:2014 © IEC 2014

IEC  1438/14
Figure A.2 – Example 1, calculation for a single enclosure

A.2 Example 2
Enclosure for wall-mounting with ventilation openings

cross-section of air inlet openings = 1 220 cm

cross-section of air outlet openings = 1 800 cm

with two horizontal partitions inside the enclosure. Each horizontal partition, for example

perforated plate, has ventilation openings, the cross-sectional areas of which exceed 50 % of

the enclosure cross-section (see Figure A.3 and Figure A.4).

Effective power loss of equipment installed in the enclosure P = 2 200 W.
Dimensions in mm
IEC  1439/14
Key
A Air outlet openings
B Horizontal partitions with ventilation openings, for example perforated plate
C Air inlet openings
Figure A.3 – Example 2, calculation for an enclosure

for wall-mounting with ventilation openings
Calculation
(For entries see form Figure A.5 on example 2)
Given an expected cooling surface of the enclosure of more than 11,5 m² and an enclosure
width exceeding 1,5 m, the entire enclosure is to be divided, for calculation purposes, into
sections (partial enclosures) as indicated in 5.2. To simplify the procedure, as no structural
divisions are available, the entire enclosure is, in this example, divided into two equal
sections (enclosure halves). The power losses and ventilation openings are supposed to be
evenly distributed in both parts (enclosure halves) so that for the calculation they are divided
by two.
The calculation is carried out for only one enclosure half, the result being applicable to the
other half.
– 24 – IEC TR 60890:2014 © IEC 2014

– Necessary information according to 5.1 for one half of the enclosure

Dimensions in mm
Enclosure for wall-mounting with air
inlet openings
1 220
= = 610 cm
With air outlet openings
1 800
= = 900 cm
With two horizontal partitions, for

example perforated plate
Effective power loss
2 200
= = 1 100 W
IEC  1440/14
Figure A.4 – Example 2, calculation for one enclosure half
– The effective cooling surface of each enclosure half is determined according to 5.2.2.
The individual surfaces are calculated from the enclosure dimensions, and the surface
factor b is taken from Table 3.
The dividing surface between the two enclosure halves which has been obtained as a
result of the fictitious division, is not taken into account in accordance with Table 3.
– The temperature rise of air ∆t is determined according to 5.2.3.
0,5
Formula (2) from column 2 of Table 1
x
∆t = k × d × P (A.3)
0,5
Factor k according to column 7 of Table 1 and A > 1,25 m , as shown in Figure 5.
e
2 2
For 610 cm air inlet openings and A = 7,674 m : k = 0,071
e
Factor d according to column 8 of Table 1 and A > 1,25 m as specified in Table 5 with
e
two horizontal partitions: d = 1,10

Effective power loss (as specified) P = 1 100 W
Exponent x from column 10 of Table 1 with A > 1,25 m : x = 0,715
e
With these values entered into the above Formula (A.3), the following result is obtained:
x 0,715
∆t = k × d × P = 0,071 × 1,0 × 1 100
0,5
∆t = 11,67 K ≈ 11,7 K
0,5
– The temperature rise of air ∆t is determined according to 5.2.4.
1,0
Formula (3) from column 3 of Table 1
∆t = c × ∆t (A.4)
1,0 0,5
Factor c according to column 9 of Table 1 and A > 1,25 m , as shown in Figure 6.
e
1,35
1,35
ℎ 2,2
𝑓 = = = 2,50
𝐴 1,45×0,8
𝑏
Figure 6 shows that, for 610 cm air inlet openings:

c = 1,87
With these values entered into Formula (A.4), the following result is obtained:

∆t = c × ∆t = 1,87 × 11,67 = 21,82 K ≈ 21,8 K

1,0 0,5
– The temperature-rise characteristic curve is determined for enclosures with A > 1,25 m ,
e
in accordance with 5.2.5.2 (see Figure A.5 in the form on example 2).
– The evaluation of the design is made in accordance with Clause 6.
It is to be verified whether the equipment installed in the enclosure is capable of
functioning satisfactorily at the specified currents and calculated temperature rises,
considering the ambient air temperature (see Clause 1, Note 2).
If this is not so, the parameters will have to be changed and the calculation repeated.

– 26 – IEC TR 60890:2014 © IEC 2014

IEC  1441/14
Figure A.5 – Example 2, calculation for an enclosure
for wall-mounting with ventilation openings

Annex B
(informative)
Operating current and power losses of conductors

The maximum permissible operating current of a conductor is influenced by many factors:

– material, type of insulation and arrangement of the conductors belonging to the same

circuit;
– mutual influence of components connected to the conductor;
– mutual influence of neighbouring components and conductors belonging to other circuits;
– air temperature inside the enclosure around the conductor;
– temperature and thermal conductivity of constructional parts touching or in close vicinity of
the conductor.
The power loss of conductors depend on
– the operating current and its frequency;
– the material and the temperature of the conductor;
– the shape of the conductor (skin effect);
– the magnetic influence of neighbouring conductors and magnetic constructional parts
(proximity effect).
The following tables provide guidance values for operating currents and power losses of
single-core copper cables and bare copper bars under idealized conditions within an
enclosure. The calculation methods used to establish these values are given to enable values
to be calculated for other conditions.
The maximum operating currents given in the tables do not apply to conductors used for
ASSEMBLIES verified by test according to IEC 61439-1.
The power losses are valid for the corresponding operational current given in the tab
...