IEC TR 60890:2014

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,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred t
...