IEC 60287-3-1:2017

IEC 60287-3-1 ®
Edition 2.0 2017-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electric cables – Calculation of the current rating –
Part 3-1: Operating conditions – Site reference conditions

Câbles électriques – Calcul du courant admissible –
Partie 3-1: Conditions de fonctionnement – Conditions du site de référence

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IEC 60287-3-1 ®
Edition 2.0 2017-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electric cables – Calculation of the current rating –

Part 3-1: Operating conditions – Site reference conditions

Câbles électriques – Calcul du courant admissible –

Partie 3-1: Conditions de fonctionnement – Conditions du site de référence

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.060.20 ISBN 978-2-8322-4348-0

– 2 – IEC 60287-3-1:2017 © IEC 2017
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Reference ambient temperatures and thermal resistivities of soil in various
countries . 6
4.1 Operating conditions – Site reference conditions . 6
4.2 Procedure when values are not provided in national tables . 7
4.2.1 General . 7
4.2.2 Ambient temperatures at sea level . 7
4.2.3 Thermal resistivity of soil . 7
4.2.4 Solar radiation . 7
Annex A (informative) Values relating to the operating conditions in various countries . 8
A.1 Australia . 8
A.2 Austria . 8
A.3 Canada . 9
A.4 China . 10
A.5 Egypt . 10
A.6 Finland . 11
A.7 France . 12
A.8 Germany . 13
A.9 Italy . 14
A.10 Japan. 14
A.11 Mexico . 14
A.12 Netherlands . 17
A.13 New Zealand . 18
A.14 Norway . 18
A.15 Oman . 19
A.16 Poland . 19
A.17 Portugal . 20
A.18 Spain . 20
A.19 South Africa . 21
A.20 Sweden . 21
A.21 Switzerland . 22
A.22 United Kingdom . 22
A.22.1 HV . 22
A.22.2 LV/MV . 23
A.23 United States of America . 23
Bibliography . 24

Table 1 – Ambient temperatures at sea level . 7
Table 2 – Thermal resistivity of soil . 7

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRIC CABLES –
CALCULATION OF THE CURRENT RATING –

Part 3-1: Operating conditions –
Site reference conditions
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
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6) All users should ensure that they have the latest edition of this publication.
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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.
International Standard IEC 60287-3-1 has been prepared by IEC technical committee 20:
Electric cables.
This second edition cancels and replaces the first edition published in 1995 and
Amendment 1:1999. This edition constitutes a technical revision. This edition includes the
following significant technical changes with respect to the previous edition:
a) the updated list of national laying conditions is now covered in Annex A;
b) Clause 5 about the information required from the purchaser for the selection of the
appropriate type of cable has been removed.

– 4 – IEC 60287-3-1:2017 © IEC 2017
The text of this standard is based on the following documents:
FDIS Report on voting
20/1714/FDIS 20/1730/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60287 series, published under the general title Electric cables –
Calculation of the current rating, can be found on the IEC website.
The reader's attention is drawn to the fact that Annex A lists all of the “in-some-country”
clauses on differing practices of a less permanent nature relating to the subject of this
standard.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website 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.
INTRODUCTION
IEC 60287 has been divided into three parts so that revisions of, and additions to the
document can be carried out more conveniently.
Each part is subdivided into subparts which are published as separate standards.
Part 1: Formulae for ratings (100 % load factor) and power losses
Part 2: Formulae for thermal resistance
Part 3: Operating conditions
This part of IEC 60287-3 contains reference ambient temperatures and thermal resistivities of
soil in various countries.
Quantities related to the operating conditions of cables are liable to vary considerably from
one country to another. For instance, with respect to the ambient temperature and soil thermal
resistivity, the values are governed in various countries by different considerations.
Superficial comparisons between the values used in the various countries may lead to
erroneous conclusions if they are not based on common criteria: for example, there may be
different expectations for the life of the cables, and in some countries design is based on
maximum values of soil thermal resistivity, whereas in others average values are used.
Particularly, in the case of soil thermal resistivity, it is well known that this quantity is very
sensitive to soil moisture content and may vary significantly with time, depending on the soil
type, the topographical and meteorological conditions, and the cable loading.
The following procedure for choosing the values for the various parameters should, therefore,
be adopted.
Numerical values should preferably be based on results of suitable measurements. Often
such results are already included in national specifications as recommended values, so that
the calculation may be based on these values generally used in the country in question; a
survey of such values is given in this part of IEC 60287-3.

– 6 – IEC 60287-3-1:2017 © IEC 2017
ELECTRIC CABLES –
CALCULATION OF THE CURRENT RATING –

Part 3-1: Operating conditions –
Site reference conditions
1 Scope
This part of IEC 60287-3 is applicable to the conditions of steady-state operation of cables at
all voltages, buried directly in the ground, in ducts, troughs or in steel pipes, both with and
without partial drying-out of the soil, as well as cables in air. The term "steady state" is
intended to mean a continuous constant current (100 % load factor) just sufficient to produce
asymptotically the maximum conductor temperature, the surrounding ambient conditions being
assumed constant.
This document defines site reference conditions, however the general values are superseded
by specific national requirements.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
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 Reference ambient temperatures and thermal resistivities of soil in various
countries
4.1 Operating conditions – Site reference conditions
In order to use the formulae given in the various parts of IEC 60287, numerical values for the
physical quantities should be chosen relating to the operating conditions.
It is obviously possible to compare the results of two calculations of current rating only when
the assumptions made and the numerical values of the parameters are known.
In particular, the quantities related to the operating conditions of cables are likely to vary
considerably from one country to another. An enquiry into this subject has been carried out
and a number of countries have replied.
Annex A summarizes the operating conditions used in various countries. Attention is drawn
to the fact that the information in Annex A is intended only as a guide for cable installation
designers when data provided by a user is incomplete. Care should be taken not to draw
unjustified conclusions from comparisons of values for different countries. It should be
remembered that the values adopted in any particular country are governed by many factors
some of which might not be of equal importance in other countries.
Values relating to the operating conditions are given in Annex A for the following countries:
Australia Italy Portugal
Austria Japan Spain
Canada Mexico South Africa
China Netherlands Sweden
Egypt New Zealand Switzerland
Finland Norway United Kingdom
France Oman United States of America
Germany Poland
4.2 Procedure when values are not provided in national tables
4.2.1 General
It is recommended that when there is no value laid down in the national tables for the
reference ambient temperature, thermal resistivity of the soil or solar radiation, the values
given in 4.2.2, 4.2.3 and 4.2.4 should be adopted.
4.2.2 Ambient temperatures at sea level
See Table 1.
Table 1 – Ambient temperatures at sea level
Ambient air Ambient ground temperature
temperature at a depth of 1 m
Climate
Min. Max. Min. Max.
°C °C °C °C
Tropical 25 55 25 40
Subtropical 10 40 15 30
Temperate 0 25 10 20
It is essential that current ratings should be valid for the maximum temperatures given. The
lower values are for winter ratings if required. The values correspond with the temperature
limits of winter and summer, alternatively rainy and dry seasons.
When no information about the depth of laying is given, the standard depth is to be taken
as 1 m.
4.2.3 Thermal resistivity of soil
See Table 2.
Table 2 – Thermal resistivity of soil
Thermal resistivity Soil conditions Weather
conditions
K∙m/W
0,7 Very moist Continuously moist
1,0 Moist Regular rainfall
2,0 Dry Seldom rains
3,0 Very dry Little or no rain

4.2.4 Solar radiation
When no information about the intensity of solar radiation a value of 1 000 W/m is adopted.

– 8 – IEC 60287-3-1:2017 © IEC 2017
Annex A
(informative)
Values relating to the operating conditions in various countries
A.1 Australia
Thermal characteristics of the soil
Thermal resistivity, nominal 1,2 K·m/W
Soil ambient temperature, summer 25 °C
Soil ambient temperature, winter 18 °C
a
Depth of laying of cables
Voltage range 1: L.V. cables
under footways 0,5 m
under roadways 0,75 m
Voltage range 2: 11 kV cables
under footways and roadways 0,8 m

Voltage range 3: 33 kV cables and higher voltages

under footways and roadways
1,0 m
Air ambient temperature
Maximum , summer °C
+40
Maximum, winter °C
+30
a
Measured from the ground surface to the centre of the cable, or to the centre of a trefoil group.

A.2 Austria
Thermal characteristics of the soil
Thermal resistivity, nominal, season 1 (wet) 1,0 K·m/W
Thermal resistivity, dry zone, season 1 (dry) 2,5 K·m/W
Temperature, season 1 20 °C
Depth of laying of cables
Voltage range 1: up to 1 kV 0,7 m
0,8 m
Voltage range 2: > 1 kV up to 30 kV
1,2 m
Voltage range 3: > 30 kV
Air ambient temperature
Average value 20 °C
Maximum +40 °C
Minimum -20 °C
A.3 Canada
There are no recognized Canadian national values of soil thermal resistivity and temperature,
and depth of laying, however the values shown below are typical. It is recommended that,
where feasible, soil tests are performed for cable installations.
Thermal characteristics of the soil

Thermal resistivity, nominal 0,5 to 3,0 K·m/W
(Critical temperature 50 °C)
Temperature, season 1 (summer) 25 °C
Temperature, season 2 (winter) -5 °C
Depth of laying of cables (minimum cover)
Paper insulated, solid and non-draining cables for voltages up 1,1 m
to 69 kV
Solid insulation (butyl, ethylene propylene rubber, p.v.c., cross- 0,9 m
linked polyethylene, etc.) cables for voltages up to 46 kV
Oil filled cables for voltages up to 345 kV 1,1 m
Pipe-type (gas or oil pressure) cables for voltages up to 345 kV 1,1 m
Air ambient temperature
Maximum 5 to 40 °C
Minimum -55 to -20 °C
Cyclic ratings
Critical temperature 50 °C
Drying out is not considered for cables in concrete duct banks

Where direct measurements of soil thermal resistivity are not available, it is usual to assume a
thermal resistivity of 0,9 K·m/W. However in cases where it is foreseen that there may be a
progressive deterioration of the thermal characteristics of the environment over a period of
years, and in cases where the climatic conditions may give rise to significant seasonal
variations, it is recommended that the current-carrying capacity be based on a thermal
resistivity of 1,2 K·m/W.
Reference is not made to lower values of resistivity, during winter, as a basis for system
design to any significant extent.

– 10 – IEC 60287-3-1:2017 © IEC 2017
A.4 China
Thermal characteristics of the soil
Thermal resistivity 1,0 to 1,2 K·m/W
Temperature, summer 30 °C
Temperature, winter 5 °C
Depth of laying of cables
≤1 kV 0,7 m
m
>1 kV up to 35 kV 0,7
1,0 m
≥110 kV up to 500 kV
Air ambient temperature
Maximum 40 °C
Minimum -10 °C
Solar radiation
Intensity of solar radiation 1 000
W/m
A.5 Egypt
Thermal characteristics of the soil
Thermal resistivity 1,2 K·m/W
Temperature, summer 35 °C
Temperature, winter 0 °C
Depth of laying of cables
≤1 kV 0,4 m
>1 kV up to 35 kV 0,8 m
a
1,2 m
≥110 kV up to 500 kV
Air ambient temperature
Maximum 47 °C
Minimum -5 °C
Solar radiation
Intensity of solar radiation ≥1 000
W/m
a
Note at soil temperature 25 °C.

A.6 Finland
Thermal characteristics of the soil
Thermal resistivity
Average value to be used for rating calculations. 1,0 K·m/W
For submarine cables where the soil is completely saturated with 0,4 K·m/W
water
Temperature
Maximum value 15 °C
Minimum value 0 °C
(average value 5 °C to 10 °C, exceptional maximum 20 °C)
Depth of laying of cables
All cables up to 36 kV 0,7 m
All cables up to 52 kV 1,0 m
All cables up to 123 kV 1,3 m
All cables up to 245 kV 1,5 m
The actual depth depends on local conditions
Air ambient temperature
Reference value for rating calculations 25 °C
Maximum value 35 °C
Minimum value -20 °C
– 12 – IEC 60287-3-1:2017 © IEC 2017
A.7 France
Thermal characteristics of the soil
Thermal resistivity, nominal, summer 1,20 K·m/W
Thermal resistivity, nominal, winter 0,85 K·m/W
a
2,5 K·m/W
Thermal resistivity, dry zone , summer
a
2,5 K·m/W
Thermal resistivity, dry zone , winter
Temperature, summer
20 kV cables 20 °C
63 kV, 90 kV, 225 kV, 400 kV cables
hot area 25 °C
intermediate area 22 °C
cold area 20 °C
Temperature, winter
20 kV cables 10 °C
63 kV, 90 kV, 225 kV and 400 kV cables
hot region 17 °C
intermediate region 15 °C
cold region 13 °C
Depth of laying of cables
20 kV cables
in Paris 1,0 to 1,2 m
outside Paris city 0,8 m
63 kV, 90 kV, 225 kV and 400 kV cables 1,3 m
Air ambient temperature
Maximum 30 °C
Minimum 20 °C
Cyclic ratings
Critical temperature, summer 55 °C
Critical temperature, winter 60 °C
Solar radiation
Intensity of solar radiation 1 000
W/m
a
Drying out of the soil is only considered for high voltage systems.

A.8 Germany
The indicated values are taken as a basis as standard values for current rating calculations
unless there are any requirements specified for the thermal resistivity of the soil, the
temperature and the depth of laying.
Thermal characteristics of the soil

Thermal resistivity, average value 1,0 K·m/W
Thermal resistivity, for calculations considering a dry zone near 2,5 K·m/W
the cable – for the dry zone
Temperature, maximum value 20 °C
Temperature, minimum value 0 °C
Temperature, average value 10 °C
Depth of laying of cables
For cables ≥ 60 kV 1,2 m
a
For cables < 60 kV m
0,7
Air ambient temperature
Maximum 30 °C
Minimum -20 °C
Average value 10 °C
a
In spite of being calculated for 0,7 m, often cables at 20 kV to 30 kV are laid at 0,9 m to 1,0 m depth.

– 14 – IEC 60287-3-1:2017 © IEC 2017
A.9 Italy
Thermal characteristics of the soil
Thermal resistivity, maximum value 1,0 K·m/W
If the thermal characteristics of the soil are found to be poor, a suitable backfill is used and reference is made to
a thermal resistivity intermediate between that of the backfill and that of the surrounding soil.
Temperature, maximum value (to be used in calculations) 20 °C
Temperature, minimum value 5 °C
Depth of laying of cables
This depth is the maximum adopted unless otherwise specified.
Up to 12 kV 0,8 m
Up to 17,5 kV 1,0 m
Up to 24 kV 1,2 m
Up to 36 kV 1,5 m
Up to 72 kV 1,8 m
Up to 220 kV 2,2 m
Air ambient temperature
Maximum value (to be used in calculations) 30 °C
Minimum value 0 °C
Maximum daily excursion 20 °C
In summer, the maximum temperature may sometimes, for a few hours daily, be higher
by 5 °C (and in special cases even more) than the above-mentioned maximum value. Such an
occurrence is considered to be acceptable due to its short duration.
A.10 Japan
Thermal characteristics of the soil
Thermal resistivity, nominal 1,0 K·m/W
1,5 K⋅m/W, 1,0 K⋅m/W and 0,6 K m/W for dry, normal and wet soil respectively. No distinction for seasons
Temperature, summer 25 °C
Depth of laying of cables
Direct burial: 1,2 m for places where the pressure of vehicle or other heavy goods may be applied. 0,6 m for
other places
In duct: the use of duct which withstands the pressure of vehicle or other heavy goods is required (there is no
regulation for the depth of duct).
Air ambient temperature
Maximum, summer 40 °C
Solar radiation
Intensity of solar radiation 1 000
W/m
Japanese Cable Makers’ Association Standard JCS 0501, gives the calculation formulae of
thermal resistance of soil for a 2 layer model having two different thermal resistivities divided
by the boundary such as ground water level. Therefore, the ground water level is one
parameter for variations in thermal resistivity.

A.11 Mexico
Thermal characteristics of the soil

Thermal resistivity, nominal season 1 (summer)
Southern Mexico 0,8 to 2,4 K·m/W
Central Mexico 1,0 to 2,5 K·m/W
Northern Mexico 0,5 to 4,0 K·m/W
Coast Mexico 0,5 to 3,0 K·m/W
Thermal resistivity, nominal season 2 (winter)
Southern Mexico 1,0 to 2,0 K·m/W
Central Mexico 1,3 to 2,1 K·m/W
Northern Mexico 0,8 to 3,6 K·m/W
Coast Mexico 0,8 to 2,7 K·m/W
Thermal resistivity, dry zone season 1 (summer)
Southern Mexico 1,4 to 3,9 K·m/W
Central Mexico 1,6 to 4,0 K·m/W
Northern Mexico 1,0 to 5,5 K·m/W
Coast Mexico 0,9 to 3,5 K·m/W
Thermal resistivity, dry zone season 2 (winter)
Southern Mexico 1,1 to 2,8 K·m/W
Central Mexico 1,0 to 3,0 K·m/W
Northern Mexico 0,8 to 4,7 K·m/W
Coast Mexico 0,6 to 2,9 K·m/W
Where direct measurements of soil thermal resistivity are not available, it is usual to assume a thermal resistivity
of 1,5 K·m/W, however it is recommended that a survey of the thermal characteristics of the soil is carried out
for critical cable links.
Temperature, season 1 (summer)

Southern Mexico 30 °C
Central Mexico 25 °C
Northern Mexico 35 °C
Coast Mexico 30 °C
Temperature, season 2 (winter)

Southern Mexico 25 °C
Central Mexico 20 °C
Northern Mexico 30 °C
Coast Mexico 25 °C
(Critical temperature 50 °C)
When soil temperature measurements are not available a reference value of 25 °C is often used for rating
calculations
– 16 – IEC 60287-3-1:2017 © IEC 2017
A.11 Mexico (continued)
a b
Depth of laying of cables
Voltage range 1: up to 1 kV cables (maximum 2 circuits)
Under footways 0,3 m
Under roads 0,5 m
Voltage range 2: > 1 kV up to 35 kV cables (5 kV, 15 kV, 25 kV

and 35 kV, maximum 4 circuits)
Under footways 0,3 m
Under roads 0,5 m
Voltage range 3: > 35 kV up to138 kV cables (69 kV, 85 kV,

115 kV and 138 kV, maximum 2 circuits)
Only under roadways (normal terrain) 1,0 m
Only under roadways (phreatic zone or rock soils) 0,5 m
Voltage range 4: > 161 kV up to 230 kV cables (161 kV and

230 kV, maximum 2 circuits)
Only under roadways (normal terrain) 1,2 m
Only under roadways (phreatic zone or rock soils) 0,7 m

Voltage range 5: ≥ 400 kV cables (maximum 2 circuits)
Only under roadways (normal terrain) 1,4 m
Only under roadways (phreatic zone or rock soils) 0,9 m
Air ambient temperature
Maximum (annually)
Southern Mexico 25 to 35 °C
Central Mexico 20 to 26 °C
Northern Mexico 36 to 45 °C
Coast Mexico 26 to 36 °C
Minimum (annually)
Southern Mexico 8 to 18 °C
Central Mexico 1 to 12 °C
Northern Mexico -5 to +10 °C
Coast Mexico 12 to 20 °C
Average (annually)
Southern Mexico 28 °C
Central Mexico 21 °C
Northern Mexico 30 °C
Coast Mexico 29 °C
Cyclic ratings
Critical temperature or temperature rise 35 to 50 °C
The critical temperature is highly dependant on the soil composition and location. It may also vary due to
seasonal influences and/or cyclic loading. It is recommended to investigate the critical temperature during a soil
survey, unless it can be demonstrated that no drying out of the soil will occur.

A.11 Mexico (concluded)
c
Solar radiation
Intensity of solar radiation
Southern Mexico 650 to 850
W/m
Central Mexico 700 to 900
W/m
Northern Mexico 850 to 1 100 W/m
Coast Mexico 800 to 1 000
W/m
The values given above for soil thermal resistivity and temperature correspond to measurements made at
different locations in Mexico at different depths (0,9 m, 1,2 m and 1,5 m). It is recommended that, where
feasible, soil measurements are made for cable installations.
a
Measured from the ground surface to the top of the cable ducts, or to the top of a trefoil duct group. Cables
are always laid in HDPE ducts.
b
Depths may be greater depending on any underground obstacles along the cable route.
c
Direct normal irradiance or beam solar radiation value, maximum annual values present for short time
periods.
A.12 Netherlands
Thermal characteristics of the soil
Thermal resistivity, nominal 1,00 K·m/W
It is recommended that a survey of the thermal characteristics of the soil is carried out for critical cable links.
Thermal resistivity, dry zone 2,5 K·m/W
It is recommended that a survey of the thermal characteristics of the soil is carried out for critical cable links.
Temperature, maximum 20 °C
Temperature, winter 5 °C
Temperature, average 15 °C
Depth of laying of cables
Up to 30 kV 0,7 to 1,0 m
Above 30 kV 1,2 m
Air ambient temperature
Maximum 30 °C
Minimum -10 °C
Average 20 °C
Cyclic ratings
Critical temperature 30 °C
The critical temperature is highly dependent on soil composition and location. It may also vary due to seasonal
influences and/or cyclic loading. It is recommended to investigate the critical temperature during a soil survey,
unless it can be demonstrated that no drying out of the soil will occur.
Solar radiation
Intensity of solar radiation 1 000
W/m
The two zone model is regularly used to calculate the current rating of MV cable systems and
incidentally for HV systems. The parameter used to define the boundary between wet and dry
zones is the absolute temperature, isotherm at this boundary, usually in the range between
30 °C (MV cables) and 50 °C (HV cables).
Cable circuits are taken to be thermally independent if the separation is not less than 3 m. For
cables installed deeper than 3 m, such as in horizontal directional drilling, the minimum
separation is not less than 5 m to consider a cable circuit as thermally independent.

– 18 – IEC 60287-3-1:2017 © IEC 2017
A.13 New Zealand
Thermal characteristics of the soil
Thermal resistivity, nominal 1,2 K·m/W
Soil ambient temperature, summer 15 °C
Soil ambient temperature, winter 15 °C

a
Depth of laying of cables
This depth is the minimum adopted unless otherwise specified
Voltage range 1: L.V.
under footways 0,5 m
under roadways 0,75 M
Voltage range 2: 11kV
under footways and roadways 1,0 m
Voltage range 3: 33kV and higher
under footways and roadways 1,0 m

Air ambient temperature
Maximum summer +30 °C
Maximum winter +30 °C
a
Measured from the ground surface to the centre of the cable, or to the centre of a trefoil group.

A.14 Norway
Thermal characteristics of the soil
Thermal resistivity, average value to be used in calculations 1,0 K·m/W
Temperature, Southern Norway max./min. 17/0 °C
Temperature, Central Norway max./min. 15/0 °C
Temperature, Northern Norway max./min. 13/-5 °C
Depth of laying of cables (minimum value)

1 kV 0,5 m
above 1 kV 0,7 m
Air ambient temperature
Maximum value (to be used in calculations) 25 °C

A.15 Oman
Thermal characteristics of the soil
Thermal resistivity, nominal 2,5 K·m/W
No distinction for seasons
Temperature, maximum 40 °C
Temperature, minimum 10 °C
Depth of laying of cables
All cables up to 1 kV 0,5 m
All cables above 1 kV 0,8 m
Air ambient temperature
Maximum 55 °C
Minimum 10 °C
Solar radiation
Intensity of solar radiation 1 200 W/m

A.16 Poland
Thermal characteristics of the soil
Thermal resistivity, average value to be used in calculations 1,0 K·m/W
Thermal resistivity, nominal, season 2
Temperature, average value to be used in calculations 20 °C
Temperature, minimum value 5 °C
Depth of laying of cables
up to and including 36 kV 0,7 m
above 36 kV 1,0 m
Air ambient temperature
Average value to be used in calculations 25 °C

– 20 – IEC 60287-3-1:2017 © IEC 2017
A.17 Portugal
Thermal characteristics of the soil
Thermal resistivity, nominal, summer 1,2
K·m/W
Thermal resistivity, nominal, winter 0,85
K·m/W
Thermal resistivity, nominal, submarine cables 1,0 K·m/W

Soil ambient temperature, summer 20 °C
Soil ambient temperature, winter 10 °C

Depth of laying of cables
This depth is the minimum adopted unless otherwise specified
Voltage range up to 1 kV 0,7 m
Voltage range up to 30 kV 1,0 m
Voltage range up to 400 kV 1,2 m

Air ambient temperature
Air ambient temperature, summer (at sea level) 30 °C
Air ambient temperature, winter (at sea level) 20 °C
Air ambient temperature, minimum 0 °C

Solar radiation
Intensity of solar radiation 1 000
W/m
A.18 Spain
There are no recognized Spanish national values of soil thermal resistivities, ambient
temperatures and depth of laying, the values shown below are typical
Thermal characteristics of the soil
Thermal resistivity, Cables ≤0,6/1 kV 1 K·m/W
Thermal resistivity, Cables >0,6/1 kV and ≤18/30 kV 1,5 K·m/W
Thermal resistivity, Cables >18/30 kV 1 K·m/W
Where concrete is used for the cable installation it should be
considered for the calculation a value of 0,85 K m/W for the 0,85 K·m/W
volume occupied by the concrete
Temperature 25 °C
Depth of laying of cables
0,6 to 1,5 m
Air ambient temperature
Maximum 40 °C
Solar radiation
Intensity of solar radiation 1 000 W/m

A.19 South Africa
Thermal characteristics of the soil
Thermal resistivity, nominal 1,2 K·m/W
No distinction for seasons
Temperature, season 1 25 °C
No distinction for seasons °C
Depth of laying of cables
Voltage range 1: low voltage 0,5 m
Voltage range 2: all higher voltages 0,8 m
Air ambient temperature
Nominal 30 °C
Solar radiation
Intensity of solar radiation (inland) 1 250
W/m
Intensity of solar radiation (coast) 1 000 W/m

A.20 Sweden
Thermal characteristics of the soil
Thermal resistivity, average value to be used in calculations 1,0 K·m/W
Where the soil is completely saturated with water and for 0,4 K·m/W
submarine cables where the bottom is covered with sand
Maximum value for submarine cables 1,0 K·m/W
For important cables, a measurement of the resistivity and soil 0,6 K·m/W
conditions on the sea bottom is recommended, otherwise:

Temperature, maximum value 15 °C
Temperature, minimum value 0 °C
(for main part of the year between 5 °C and 10 °C)
Depth of laying of cables
For directly buried cables and for short road crossings by means of ducts
All cables up to 24 kV 0,7 m
Paper-insulated cables up to 52 kV 0,7 m
a
Oil-filled cables up to 420 kV m
1,0 to 1,5
a
The depth depends on local conditions. Less than 1 000 mm is not used.

– 22 – IEC 60287-3-1:2017 © IEC 2017
A.21 Switzerland
Thermal characteristics of the soil
Thermal resistivity, nominal, summer (May – October) 1,0 K·m/W
Thermal resistivity, nominal, winter (November – April) 0,85 K·m/W
Thermal resistivity, rocky soil, summer 1,3 K·m/W
Thermal resistivity, rocky soil, winter 1,3 K·m/W
Temperature, summer 20 °C
Temperature, winter 10 °C
Depth of laying of cables
Voltage range 10 kV to 30 kV 0,8 m
Voltage range 50 kV to 400 kV 1,0 m
Air ambient temperature
Maximum, outdoor 30 °C
Minimum, outdoor -25 °C
Solar radiation
Intensity of solar radiation, Swiss plateau (Mittelland) 1 000
W/m
Intensity of solar radiation, Alpine region (Alpenraum) 1 200
W/m
Cables are usually laid in HDPE pipes.
Drying out is usually not considered (otherwise, rho_dry is 2,5 K·m/W; T_boundary is 50 °C).
A.22 United Kingdom
A.22.1 HV
Thermal characteristics of the soil
Thermal resistivity, nominal, winter 1,05 K·m/W
Thermal resistivity, nominal, summer 1,2 K·m/W
Thermal resistivity, dry zone, winter 1,05 K·m/W
Thermal resistivity, dry zone, summer K·m/W
3,0
(critical temperature 50 °C)
Temperature, winter 10 °C
Temperature, summer 15 °C
Depth of laying of cables
0,9 min. (general) m
132 kV and above 0,75 min. (substation sites) m
0,825 min. (Scotland) m
Air ambient temperature
Maximum 30 °C
Minimum 10 °C
Solar radiation
Intensity of solar radiation 1 000 W/m

A.22.2 LV/MV
Thermal characteristics of the soil
Thermal resistivity, nominal 1,2 K·m/W
No distinction for
Thermal resistivity, nominal, season 2
seasons
Thermal resistivity, dry zone K·m/W
1,2
(critical temperature 50 °C)
Temperature, season 1 15 °C
No distinction
...