Best Practice

SABP-P-063 18 March 2019

Electrical Power Cable Sizing
Document Responsibility: Electrical System Design and Automation Standards
Committee

Contents
1 Scope ................................................................ 2
2 References........................................................ 2
3 Definitions ......................................................... 3
4 Design Criteria .................................................. 3
5 Cable Sizing According to IEC .......................... 9
6 Cable Sizing According to NEC ...................... 11
7 Some Examples for Cable Sizing.................... 13
Revision Summary................................................. 17

Previous Issue: New Next Planned Update: 18 March 2029

Contacts: Sharhan, Hamad T. (sharhaht) on phone +966 13 874-1631 and

Arfaj, Haitham A. (arfajha) on phone +966 13 880-9541 Page 1 of 17

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Document Responsibility: Electrical System Design and Automation Standards Committee SABP-P-063
Issue Date: 18 March 2019
Next Planned Update: 18 March 2029 Electrical Power Cable Sizing

1 Scope

1.1 Purpose

The purpose of this document is to provide guidance for Saudi Aramco engineers
on how to properly size electrical power cables, considering short circuit
withstanding current, ampacity calculations under actual site installation
conditions, and voltage drop limitations using IEC and NEC methods for both low
voltage and high voltage (as defined in SAES-P-100) up to 34.5 kV.

1.2 Disclaimer

This Best Practice is not mandatory. In the event of a conflict between this Best
Practice (BP) and other Mandatory Saudi Aramco Engineering Requirements
(MSAER), the Mandatory Saudi Aramco Engineering Requirements take
precedence.

2 References

This Best Practice is based on the below referenced standards:

2.1 Saudi Aramco References

Saudi Aramco Engineering Standards

SAES-P-100 Basic Power System Design Criteria
SAES-P-104 Wiring Methods and Materials

2.2 Industry Codes and Standards

Institute of Electrical and Electronic Engineers
IEEE 835 IEEE Standard Power Ampacity Tables

International Electrotechnical Commission

IEC 60502-1 Power Cables with Extruded Insulation and their
Accessories for Rated Voltages from 1 kV up to
30 kV. Part 1: Cables for Rated Voltages of 1 kV
and 3 kV
IEC 60502-2 Power Cables with Extruded Insulation and their
Accessories for Rated Voltages from 1 kV up to
30 kV. Part 2: Cables for Rated Voltages from
6 kV up to 30 kV

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IEC 60364-5-52 Low-voltage Electrical Installations -

Part 5-52: Selection and Erection of Electrical
Equipment - Wiring Systems

National Fire Protection Association

NFPA 70 National Electrical Code (NEC)

3 Definitions

Text identified in bold font throughout this document is defined below.

BP: Best Practice

MSAER: Mandatory Saudi Aramco Engineering Requirement (MSAER).

These documents are corporate mandatory documents. Examples of MSAERs are Saudi
Aramco Materials System Specifications (SAMSSs), Saudi Aramco Engineering
Standards (SAESs) and Saudi Aramco Standard Drawings (SASDs).

SAES: Saudi Aramco Engineering Standard

SAMSS: Saudi Aramco Materials System Specification

Low Voltage: Voltages less than 1,000 V.

High Voltage: Voltages 1,000 V or greater unless otherwise designated in a specific

MSAER or referenced international standard.

4 Design Criteria

4.1 General

The selection of the specific type and size of power cable should be based on the
following:

4.1.1 Technical requirements; such as voltage level, current loading, ambient

temperature, short circuit current, etc.

4.1.2 Installation requirements such as duct banks, direct burial, conduit, cable
tray and thermal resistivity of soil & backfill material.

4.1.3 Economic requirements based on the selection of a suitable power cable

and required accessories (splices, terminations, and connectors).

4.1.4 Selecting three core cable or trefoil configuration for single core cable as
a preferred option for cable length more than 0.5 km.

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4.1.5 Minimum size of conductors shall meet the requirements of SAES-P-104

Table 1.

4.1.6 Maximum size of conductors rated up to 35 kV shall be 500 mm² or

1,000 kcmils for three-core power cable as specified in SAES-P-104.

4.2 Power Cable Types and Application

4.2.1 Three Conductors versus Single Conductor Cables

4.2.1.1 Single conductor cables are easy to handle, splice, terminate

and are supplied in longer lengths than three conductor cables
which will result in a longer ordered cables.

4.2.1.2 In general, the ampacity and voltage drop will be higher for
three single conductor cables when compared with a similar
size of three conductor cable.

4.2.1.3 For a very long cable installation, three core cable or three
single core cable (trefoil configuration) is recommended, to
reduce the effect of circulating currents and induced voltage.
Design of cable, lay out, arrangements, and penetration to
equipment shall minimize induced voltage and circulating
currents to safe limits as specified in SAES-P-104.

4.2.2 Conductor Size Selection

4.2.2.1 Proper sizing of a conductor involves three factors:

a) Short circuit current withstanding capability:
Short circuit current may require an increase in the
conductor size selected if it is not sufficient size, to safely
dissipate the heat generated under fault conditions.
b) Cable ampacity under actual site installation conditions:
Ampacity will determine the minimum size of conductor
that can be used for a given type of installation.
c) Voltage drop limitations:
The voltage drop limitations for a feeder or a Brach circuit
based on NEC requirements, to prevent a voltage drop
exceeding 3 percent at the farthest outlet of power circuit
where the maximum total voltage drop on both feeders and
branch circuits (combined) to the farthest outlet does not
exceed 5 percent.
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Voltage drop restrictions will determine the maximum

length of the selected conductor that can be used before an
increase in cable size is considered, to maintain the voltage
level at the load to be above the accepted minimum value
(Refer to SAES-P-100).

4.2.3 Cable Voltage Rating for Power Cables

a) As specified in SAES-P-104, LV power cable shall have cable
voltage rating level 600 /1,000 V.
b) As specified in SAES-P-104, MV power cables shall have cable
voltage rating level 6 /10 kV for 4.16 kV cables, 12 /20 kV for 13.8
kV cables and 18/30 (Insulation Thickness: 345 mils or 9 mm) for
34.5 kV cables.

4.3 According to SAES-P-104, cable sizing shall be based on NEC, IEEE, or IEC.
 ANSI manufactured cables, ampacity calculations and cable sizing shall be
based on the NEC, or from the tables in IEEE 835.
 IEC manufactured cables, ampacity calculations and cable sizing shall be
based on the IEC 60364 and IEC 60502-2 series standards.
 The Cable Derating Program of the Electrical Transient Analyzer Program
(ETAP) or other power simulation software are permitted to be used to
calculate ampacities, as an alternative to the NEC, IEC, or IEEE 835 tables.

4.4 Short Circuit Withstand of Cables

The short-circuit withstand rating of cables is based on ensuring that the conductor
size is large enough to carry the short-circuit current for a sufficient time duration
(until the short-circuit protective device interrupts and clears the fault current)
before the cable insulation is damaged by the heat rise within the cable.

The minimum cable size to comply with a short-circuit current (Isc) for duration
of time (t) is therefore given by:

𝐼𝑠𝑐 × √𝑡
𝑆≥
𝑘
Where:
k = Constant applicable to type of conductor and insulation
(143 for XLPE insulated copper conductors)
S = Cable cross-sectional area of the cable (mm2)
t = Fault duration
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Isc = Short circuit currents (A)

T1 = Initial conductor temperature, Normal Operation

T2 = Initial conductor temperature, Max. Conductor Short Circuit
Temperature

Table 1 - Maximum Conductor Temperature

For Different Types of Insulating Compound
Maximum Conductor Temp. (C)
Insulating
Compound Max. Conductor Short Circuit
Normal Operation (T1)
Temperature (T2)
PVC 70 160
XLPE 90 250

According to SAES-P-104, for cable sizing adjustment for fault conditions, the
fault location shall be assumed to be at the load end of the cable.
- For low voltage cables, fault duration time shall be a minimum of 110% of
the clearing time of the protective device providing primary protection to the
cable (maximum total clearing time in the case of fuses).
- For medium voltage cables, fault duration time shall be a minimum of 110%
of the clearing time of the protective device providing backup protection to
the cable and this time shall not exceed 1.0 second.

4.5 Ampacity Calculations

Ampacity is defined as “the current in amperes that a conductor can carry

continuously under the conditions of use (conditions of the surrounding medium
in which the cables are installed) without exceeding its temperature rating”.

The following basic parameters shall be used to evaluate the ampacities to fulfill
the load requirements:

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4.5.1 Minimum size of conductors shall meet the requirements of Table 2.

Table 2 – Minimum Copper Conductor Size

Voltage Size
600 V and below (control)* 1.5 mm²(16 AWG)
600 V and below (power)* 2.5 mm²(14 AWG)
5 kV 10 mm²(8 AWG)
15 kV 35 mm²(2 AWG)
35 kV 50 mm²(1/0 AWG)
69 kV 120 mm² (4/0 AWG)
115 kV 400 mm² (750 kcmil)
230-380 kV 500 mm2 (1,000 kcmil)
Note: * Including associated grounding conductors

4.5.2 Load Factor (LF)

LV Motor feeder cables should be rated at 125% of motor full load current
(service factor 1.15 or greater) and 115% for motors over 1,000 Volts,
Nominal (refer to NEC article 430) as a good engineering practice or as
per the trip current of overcurrent (overload) relays or other motor
protective devices. Other cables shall be rated for 100% load factor as per
SAES-P-104.

4.5.3 According to SAES-P-104, for the basis of sizing a feeder ampacity rating
which supplies distribution equipment, shall be equal to the lower of:
a) The continuous current rating of the distribution equipment main bus
b) The site rating of the upstream transformer
Exception:

Switchgear directly feeding another switchgear, shall be based upon

using 110% of the sum of the operating load plus all known future loads.

4.5.4 Cable Installation Criteria

Cable installation method should be taken into account when cable sizing
calculation to provide accurate cable sizing. Calculation results should
be verified against actual vendor equipment data and against protection
coordination study for final cable selection.

When sizing cables, the designer should pay attention to the overall
derating factor that takes into account the differences in the cable’s
actual installation and operating conditions from the base conditions.
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A derating factor should be applied against a base ampacity to calculate

the derated ampacity as stated in the following formula:

𝐼 ′ = 𝐼𝐹
Where,
(I’) Derated Ampacity at actual installation conditions.
(I) Base Ampacity
(F) Overall Derating Factor.

The overall derating factor is a correction factor that considers the

differences in the cable installation method.

Overall Derating Factor (F) is composed of several components as

indicated in the following equation:

𝐹 = 𝐹𝑓 × 𝐹𝑡 × 𝐹𝑡ℎ × 𝐹𝑔 × 𝐹𝑐

Where,
Ff = Derating factor for fire coating: As per SAES-P-104, Ff = 0.85
when cables are fireproofed by coating or wrapping with a
compound or other material. If not, then Ff equal to 1.0.
Ft = Derating factor to account for the differences in ambient and
conductor temperatures. You may refer to SAES-P-104 for
ambient temperature consideration associated with different
installation conditions.
Fth = Derating factor for underground soil thermal resistance (only
for Directly Buried cables). As per SAES-P-104, Earth Thermal
Resistivity (RHO) for Land: 1.2 K-m/watt, Concrete (for Duct
Banks): 1.0 K-m/watt, and Sea Bottom: 0.8 K-m/watt
Fg = Derating factor for cable grouping.
Fc = Derating factor for A/G tray covers (only for cables installed in
covered Tray). Fc is assumed = 0.95

Duct bank de-ratings is considered where such duct runs exceed 3 meters
and overall cable ampacity will be based on the duct portion of the entire
run.

4.6 Voltage Drop Calculations

The voltage drop in power cables shall comply with sections 6.2 and 6.3 of
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SAES-P-100 and should be computed in accordance with the following formula:

For Three-phase Load:

√3 ∗ 𝐼𝑚𝑎𝑥 ∗ 𝐿(𝑅 𝑐𝑜𝑠𝜃 + 𝑋 𝑠𝑖𝑛𝜃) ∗ 100%

%𝑉𝐷 =
𝐸𝑠

For Single-Phase Load:

2 ∗ 𝐼𝑚𝑎𝑥 ∗ 𝐿(𝑅 𝑐𝑜𝑠𝜃 + 𝑋 𝑠𝑖𝑛𝜃) ∗ 100%

%𝑉𝐷 =
𝐸𝑠
For DC Load:
2 ∗ 𝐼𝑚𝑎𝑥 ∗ 𝐿 ∗ 𝑅 ∗ 100%
%𝑉𝐷 =
𝐸𝑠
Where:
%V.D. = Percent Voltage Drop
Es = System Nominal Voltage (Volts)
Imax = Maximum Operating Current (Amperes)
L = Circuit Length (km)
R = Circuit Resistance (Ohms/km)
X = Circuit Reactance (Ohms/km)
Cos Ø = Power Factor of load
Sin Ø = Reactive Factor of load
Note: The maximum operating current used for voltage drop calculation should be
based on using 110% of the sum of the operating load(s) plus all known future
loads (Amperes) as defined in SAES-P-100.

5 Cable Sizing According to IEC

5.1 LV Power Cables (not exceeding 1 kV as per IEC 60364-5-52)

Note: All tables referenced below were extracted from IEC 60364-5-52.

5.1.1 Cable Ampacity

a) Installation reference methods forming basis of tabulated current-
carrying capacities are listed in table B.52.1.
b) Current-carrying capacities in amperes for methods of installation in
table B.52.1, are listed in tables B.52.5, B.52.12 and B.52.13.

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5.1.2 Ambient Temperature

a) The maximum conductor temperature for which the tabulated cable
ratings have been calculated is 90°C.
b) The current-carrying capacities tabulated in B.52.5, B.52.12, and
B.52.13 assume ambient temperatures of 30°C in air and 20°C in
ground.
c) Where the ambient temperature at the intended location of the
insulated conductors differs from the reference ambient temperature,
the appropriate correction factor given in tables B.52.14 and B.52.15
will be applied.

5.1.3 Soil Thermal Resistivity

a) The current-carrying capacities tabulated in B.52.5, B.52.12, and
B.52.13 for cables in the ground relate to a soil thermal resistivity of
2.5 K·m/W.
b) Correction factors for soil thermal resistivities other than 2.5 K·m/W
are given in table B.52.16.

5.1.4 Groups Containing more than One Circuit

If more insulated conductors are installed in the same group, the group
reduction factors specified in tables B.52.17 to B.52.21 will be applied.

5.2 MV Power Cables as defined in IEC 60502-2, (6 /10 kV for 4.16 kV cables,
12 /20 kV for 13.8 kV cables and 18/30 (Insulation Thickness: 345 mils or
9 mm) for 34.5 kV cables).
Note: All tables referenced below were extracted from IEC 60502-2.

5.2.1 Cable Ampacity

a) Installation reference methods forming basis of tabulated current-
carrying capacities are listed in Section B.5.
b) Current-carrying capacities in amperes for methods of installation in
Section B.5, are listed in tables B.2 to B.9.

5.2.2 Ambient Temperature

a) The maximum conductor temperature for which the tabulated cable
ratings have been calculated is 90°C.
b) The current-carrying capacities tabulated in B.2 to B.9 assume
ambient temperatures of 30°C in air and 20°C in ground.

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c) Where the ambient temperature in the intended location of the

insulated conductors differs from the reference ambient temperature,
the appropriate correction factor given in tables B.10 and B.11 will
be applied.

5.2.3 Soil Thermal Resistivity

a) The current-carrying capacities tabulated in B.2 to B.9 for cables in
the ground relate to a soil thermal resistivity of 1.5 K·m/W.
b) Correction factors for soil thermal resistivities other than 1.5 K·m/W
are given in tables B.14 to B.17.

5.2.4 Depths of Laying

a) The current-carrying capacities tabulated in B.2 to B.9 assume 0.8 m
burial depth.
b) Correction factors for burial depth other than 0.8 m are given in
tables B.12 to B.13.

5.2.5 Groups Containing more than One Circuit

If more insulated conductors are installed in the same group, the group
reduction factors specified in tables B.18 to B.23 will be applied.

6 Cable Sizing According to NEC

6.1 Ampacities for Conductors Rated 0–2,000 Volts

6.1.1 Cable Ampacity

a) Current-carrying capacities in amperes are listed in tables
310.15(B)(16), 310.15(B)(17) and 310.15(B)(20)
b) Additional cable ampacities for different installation conditions are
listed in Ch.9 tables B.310.15(B)(2)(1) and B.310.15(B)(2)(3)

6.1.2 Ambient Temperature

a) The maximum conductor temperature that shall be used for the
tabulated cable ratings is 90°C.
b) The current-carrying capacities assume ambient temperatures of
30°C and 40°C.
c) Where the ambient temperature in the intended location of the
insulated conductors differs from the reference ambient temperature,
the appropriate correction factor given in tables 310.15(B)(2)(a) and

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310.15(B)(2)(b) will be applied.

6.1.3 Soil Thermal Resistivity

a) The current-carrying capacities relate to a soil thermal resistivity of
90°C·cm/W as per NEC, section “Informative Annex B”.
b) Correction factors for soil thermal resistivities other than 90°C·cm/W
are given in tables 13-5 and 13-7 of IEEE STD 399-1997.

6.1.4 Depths of Laying

a) The current-carrying capacities are based on the minimum cover
requirements listed in Table 300.5
b) Correction factors for burial depth other than the ones listed in table
300.5 are covered under Article 310.60 (C) (2)

6.1.5 Groups Containing more than Three Current-carrying Conductors

Adjustment factors for more than three current-carrying conductors are

listed in Table 310.15(B)(3)(a).

6.2 Ampacities for Conductors Rated 2,000–35,000 Volts

6.2.1 Cable Ampacity

a) Installation reference methods forming basis of tabulated current-
carrying capacities are listed in Figure 310.60(C)(3).
b) Current-carrying capacities in amperes for methods of installation in
Figure 310.60(C)(3), are listed in Table 310.60(C)(77) through
Table 310.60(C)(86).
c) Other current-carrying capacities in amperes for different installation
methods are listed in tables 310.60(C)(67) through 310.60(C)(76).

6.2.2 Ambient Temperature

a) The maximum conductor temperature that shall be used for the
tabulated cable ratings is 90°C.
b) The current-carrying capacities assume ambient temperatures of
30°C and 40°C.
c) Where the ambient temperature in the intended location of the
insulated conductors differs from the reference ambient temperature,
the appropriate correction factor given in tables 310.15(B)(2)(a) and
and 310.15(B)(2)(b) will be applied.

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6.2.3 Soil Thermal Resistivity

a) The current-carrying capacities relate to a soil thermal resistivity of
90°C·cm/W as per NEC, section “Informative Annex B”.
b) Correction factors for soil thermal resistivities other than 90°C·cm/W
are given in tables 13-6 and 13-7 of IEEE STD 399-1997.

6.2.4 Depths of Laying

a) The current-carrying capacities are based on the minimum cover
requirements listed in Table 300.50
b) Correction factors for burial depth other than the ones listed in table
300.50 are covered under Article 310.60 (C) (2)

6.2.5 Groups Containing more than Three Current-Carrying Conductors

Adjustment factors for more than three current-carrying conductors are

listed in Table 310.15(B)(3)(a).

7 Some Examples for Cable Sizing

7.1 Cable Sizing According to IEC

It is required to size a power cable, 50 m long, installed on cable tray and

feeding a synchronous motor rated at 13.2 kV and has a capacity of 14,765 kVA
with a maximum operating current of 646 A. The maximum let-through current
at the switchgear bus is 25 kA.
 Minimum Cross Section According to Short Circuit Withstand Current
The minimum cross section of the cable should be determined by the
following formula:
𝐼𝑠𝑐 ∗ √𝑡
𝑎=
0.143
Where, Isc = maximum let-through current + the motor contribution
14765𝐾𝑉𝐴
𝐼𝑆𝑐 = 25𝐾𝐴 + 5 ∗ ( ) = 28𝐾𝐴
√3 ∗ 13.8𝐾𝑉
Therefore,

28 ∗ √0.5
𝑎= = 138.5𝑚𝑚2
0.143
The Minimum Cross Section (𝑚𝑚2 )= 150 𝑚𝑚2
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 Cable Ampacity
𝐾𝑉𝐴
𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑜𝑝𝑒𝑟𝑎𝑡𝑖𝑛𝑔 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 = 𝐼 = ( ) = 646𝐴
√3 ∗ 𝐾𝑉
𝐼 ′ = 𝐼𝐹
Where: (I’) is De-rated Ampacity, (I) is Base Ampacity and (F) is Overall
Derating Factor.
Referring to the suitable IEC 60502-2 Table B.2, we will select: 2-3 - 1/C
150 mm2 has a base ampacity of 2*481 (flat touching formation as shown
below) which will be suitable for motor load.
Where the cables are assumed to be spaced at least 0.5 times the cable
diameter from cable tray edge.

The Overall Derating Factor (F) is composed of several components as

indicated in the following Equation:
𝐹 = 𝐹𝑓 × 𝐹𝑡 × 𝐹𝑡ℎ × 𝐹𝑔

Where,
Ff = Derating factor for fire coating.
Ft = Derating factor to account for the differences in ambient and
conductor temperatures according to Table B.10 of IEC-60502-2.
Fth = Derating factor for underground soil thermal resistance (only for
Directly Buried cables).
Fg = Derating factor for cable grouping.
Therefore,
Ff =1 (considering that the cable is not fire-rated)
Ft = 0.82 (at air ambient temperature of 50°C for shaded cable tray
installation)

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Fth = not applicable as the cable is not direct buried

Fg = 0.97 (Two circuits running in parallel, according to Table B.23)
Thus, 𝐹 = 1 × 0.82 × 0.97 = 0.795
De-rated Ampacity = Base Ampacity X Overall Derating Factor
𝐼 ′ = 𝐼 × 𝐹 = (2 ∗ 481) x 0.795 = 765 A
De-rated Ampacity = 765 A
So, the selected 2-3 - 1/C 185 mm2 cable installed in horizontal flat touching
formation has a de-rated cable ampacity (765A) higher than the Maximum
Operating Current (646 A).
According to NEC, the selected conductor should have an ampacity of at
least 115 percent of the motor full-load current (FLC), which can be verified
by (De-rated cable ampacity/ maximum operating current )*100;
(765/646)*100%=1.18%
 Voltage Drop Limitations

√3 ∗ 𝐼𝑚𝑎𝑥 ∗ 𝐿(𝑅 𝑐𝑜𝑠𝜃 + 𝑋 𝑠𝑖𝑛𝜃) ∗ 100%

%𝑉𝐷 =
𝐸𝑠
Maximum Operating Current = 646 A
Circuit Length (L) = 164.05 ft (50 meters) 0.05 km
Power Factor = 0.95 which implies that Ø = 18.195 Degrees
System Nominal Voltage Es = 13,800 V
Cable Size to be verified: 2-3 - 1/C 150 mm2
Circuit Resistance, (R) = 0.159 ohms/km (parallel circuit so, R=0.08)
Circuit Reactance, (X) = 0.14 ohms/km (parallel circuit so, X=0.07)
*Note: The cable resistance and reactance are obtained from Saudi Cable MV
cable catalog.

%V.D. = 0.04%
Hence, voltage drop across the selected cable is less than 2.5% of the System
Nominal Voltage.

7.2 Cable Sizing According to NEC

Same example will be used.

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Document Responsibility: Electrical System Design and Automation Standards Committee SABP-P-063
Issue Date: 18 March 2019
Next Planned Update: 18 March 2029 Electrical Power Cable Sizing

 Minimum Cross Section According to Short Circuit Withstand Current

Short Circuit Current (Isc) = 28 kA (Calculated in the above example).
Therefore, the Minimum Cross Section (𝑚𝑚2 ) standard size= 150 𝑚𝑚2
 Cable Ampacity
Maximum Operating Current = 646 A
Type of Installation: Cable Tray (Outdoor) with Top Cover
Therefore,
𝐼 ′ = 𝐼𝐹
Where: (I’) is De-rated Ampacity, (I) is Base Ampacity and (F) is Overall
Derating Factor.
The Overall Derating Factor (F) is composed of several components as
indicated in the following Equation:
Ff =1 (considering that the cable is not fire-rated)
Ft = 0.89 (at air ambient temperature of 50°C for shaded cable tray
installation)
Fth = not applicable as the cable is not direct buried
Fg = 0.8 (Two circuits running in parallel)
Overall Derating Factor,
𝐹 = 𝐹𝑓 × 𝐹𝑡 × 𝐹𝑡ℎ × 𝐹𝑔 = 1 × 0.89 × 0.8 = 0.712

Referring to NEC Table 310.60(C)(69), we can see that:

2-3-1/C 185 mm2 (350 Kcmil) has a base ampacity of 2*550 A
De-rated Ampacity = Base Ampacity X Overall Derating Factor
𝐼 ′ = I × F = (2 ∗ 550) × 0.712 = 783A
So, the selected 2-3 - 1/C 185 mm2 cable installed in horizontal flat touching
formation has a de-rated cable ampacity (783 A) higher than the Maximum
Operating Current(646 A).
According to NEC, The selected conductor should have an ampacity of at
least 115 percent of the motor full-load current (FLC), which can be verified
by (De-rated cable ampacity/ maximum operating current)*100;
(783/646)*100%=1.21%

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Document Responsibility: Electrical System Design and Automation Standards Committee SABP-P-063
Issue Date: 18 March 2019
Next Planned Update: 18 March 2029 Electrical Power Cable Sizing

 Voltage Drop Limitations

√3 ∗ 𝐼𝑚𝑎𝑥 ∗ 𝐿(𝑅 𝑐𝑜𝑠𝜃 + 𝑋 𝑠𝑖𝑛𝜃) ∗ 100%
%𝑉𝐷 = =
𝐸𝑠
Maximum Operating Current = 646 A
Circuit Length (L) = 164.05 ft (50 m) 0.05 km
Power Factor = 0.95 which implies that θ = 18.195 degrees
System Nominal Voltage Es= 13,800 V
Cable Size to be verified: 2-3 - 1/C 185 mm2
Circuit Resistance, (R) = 0.128 ohms/km (parallel circuit so, R=0.064)
Circuit Reactance, (X) = 0.13 ohms/km (parallel circuit so, X=0.065)
*Note: The cable resistance and reactance are obtained from Saudi Cable MV
cable catalog.

%V.D. = 0.033%
Hence, voltage drop across the selected cable is less than 2.5% of the System
Nominal Voltage.

Revision Summary
18 March 2019 New Saudi Aramco Best Practice that provides guidance for Saudi Aramco engineers on
how to properly size electrical power cables, considering short circuit withstanding current,
ampacity calculations under actual site installation conditions, and voltage drop limitations
using IEC and NEC methods.

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