Electrical Cable Sizing Criteria
1
,CONTENTS
1. General 3
2. Site Conditions 3
3. Reference Documents and Standards 3
4. Cables Technical Data 4
5. Cable Sizing 4
5.1. Continuous Current Carrying Capacity (Io) 6
5.1.1. Maximum Allowed Current Carrying Capacity (Iz) 6
5.2. Voltage Drop 7
5.3. Maximum Short Circuit Current 7
6. Annex A. Standard references for MV Cables 10
7. Annex B. Standard references for LV Cables 16
2
,1. General
The present specification deals with the selection criteria for the medium voltage and low voltage
cables.
The selection shall be performed considering:
Operating current condition
Voltage drop
Short circuit current condition
Type of cable installation
2. Site Conditions
Maximum Ambient Temperature 48 °C
Minimum Ambient Temperature 1 °C
Humidity 62 %
Elevation above sea level 135 m
3. Reference Documents and Standards
Electrical Design Criteria
MV Cables Technical Specification
LV and Control Cables Technical Specification
IEC 60502-1
Power cables with extruded insulation and their accessories for rated voltages from 1 kV (Um =
1.2 kV) up to 30 kV (Um = 36 kV) – Part 1: Cables for rated voltages of 1 kV (Um = 1.2 kV)
and 3 kV (Um = 3.6 kV)
IEC 60502-2
Power cables with extruded insulation and their accessories for rated voltages from 1 kV (Um =
1.2 kV) up to 30 kV (Um = 36 kV) – Part 2: Cables for rated voltages from 6 kV (Um = 7.2 kV)
up to 30kV (Um = 36 kV)
IEC 60364-5-52
Low-voltage electrical installations – Part 5-52: Selection and erection of electrical equipment –
Wiring systems
IEC 60947-2
Low-voltage switchgear and control gear – Part 2: Circuit-breakers
IEC 61200-53
Electrical installation guide – Part 53:
Selection and erection of electrical equipment – Switchgear and control gear
3
, IEC 60364-4-43
Low-voltage electrical installations –Part 4-43: Protection for safety – Protection against
overcurrent
4. Cables Technical Data
The cables technical data is specified at “Cable Characteristic Table”. The meaning of any
designation at “cable characteristic table” is explained below (items from (1) to (7)):
(1) Cable cross section
It specifies the number of cores forming the cable and also cross section of each single conductor
(mm2); neutral/protective conductor is considered too.
(2) Conductor material
It defines the material of the conductor (e.g. Cu, Al).
(3) Insulation material
It is the code to specify the insulation material (e.g. XLPE, EPR, and PVC).
(4) Cable rated voltage
It specifies the voltage cable (U0/U/ Um):
U0: is the rated voltage between conductor and earth or metallic screen for which the cable is
designed.
U: is the rated voltage between conductors for which the cable is designed.
Um: is the maximum value of the "highest system voltage'' for which the equipment may be
used.
(5) Resistance
It is the resistance of the conductor, in (Ohm/Km) at the insulation temperature limit.
(6) Reactance
It is the reactance of the conductor, in (Ohm/Km), at the rated frequency and according to the
type of installation.
(7) Rated current
It is the rated current “I0” of the cable (in Amperes) specified from the applicable standards,
under the installation condition and the reference ambient temperature.
5. Cable Sizing
The following items shall be considered:
a) Short circuit capacity
b) Continuous current carrying capacity
c) Voltage drops in normal condition & transient conditions.
4
1
,CONTENTS
1. General 3
2. Site Conditions 3
3. Reference Documents and Standards 3
4. Cables Technical Data 4
5. Cable Sizing 4
5.1. Continuous Current Carrying Capacity (Io) 6
5.1.1. Maximum Allowed Current Carrying Capacity (Iz) 6
5.2. Voltage Drop 7
5.3. Maximum Short Circuit Current 7
6. Annex A. Standard references for MV Cables 10
7. Annex B. Standard references for LV Cables 16
2
,1. General
The present specification deals with the selection criteria for the medium voltage and low voltage
cables.
The selection shall be performed considering:
Operating current condition
Voltage drop
Short circuit current condition
Type of cable installation
2. Site Conditions
Maximum Ambient Temperature 48 °C
Minimum Ambient Temperature 1 °C
Humidity 62 %
Elevation above sea level 135 m
3. Reference Documents and Standards
Electrical Design Criteria
MV Cables Technical Specification
LV and Control Cables Technical Specification
IEC 60502-1
Power cables with extruded insulation and their accessories for rated voltages from 1 kV (Um =
1.2 kV) up to 30 kV (Um = 36 kV) – Part 1: Cables for rated voltages of 1 kV (Um = 1.2 kV)
and 3 kV (Um = 3.6 kV)
IEC 60502-2
Power cables with extruded insulation and their accessories for rated voltages from 1 kV (Um =
1.2 kV) up to 30 kV (Um = 36 kV) – Part 2: Cables for rated voltages from 6 kV (Um = 7.2 kV)
up to 30kV (Um = 36 kV)
IEC 60364-5-52
Low-voltage electrical installations – Part 5-52: Selection and erection of electrical equipment –
Wiring systems
IEC 60947-2
Low-voltage switchgear and control gear – Part 2: Circuit-breakers
IEC 61200-53
Electrical installation guide – Part 53:
Selection and erection of electrical equipment – Switchgear and control gear
3
, IEC 60364-4-43
Low-voltage electrical installations –Part 4-43: Protection for safety – Protection against
overcurrent
4. Cables Technical Data
The cables technical data is specified at “Cable Characteristic Table”. The meaning of any
designation at “cable characteristic table” is explained below (items from (1) to (7)):
(1) Cable cross section
It specifies the number of cores forming the cable and also cross section of each single conductor
(mm2); neutral/protective conductor is considered too.
(2) Conductor material
It defines the material of the conductor (e.g. Cu, Al).
(3) Insulation material
It is the code to specify the insulation material (e.g. XLPE, EPR, and PVC).
(4) Cable rated voltage
It specifies the voltage cable (U0/U/ Um):
U0: is the rated voltage between conductor and earth or metallic screen for which the cable is
designed.
U: is the rated voltage between conductors for which the cable is designed.
Um: is the maximum value of the "highest system voltage'' for which the equipment may be
used.
(5) Resistance
It is the resistance of the conductor, in (Ohm/Km) at the insulation temperature limit.
(6) Reactance
It is the reactance of the conductor, in (Ohm/Km), at the rated frequency and according to the
type of installation.
(7) Rated current
It is the rated current “I0” of the cable (in Amperes) specified from the applicable standards,
under the installation condition and the reference ambient temperature.
5. Cable Sizing
The following items shall be considered:
a) Short circuit capacity
b) Continuous current carrying capacity
c) Voltage drops in normal condition & transient conditions.
4
