Aman Technical_Handbook.pdf

8/16/2019 Aman Technical_Handbook.pdf

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Oman Cables Industry (SAOG)

In a journey spanning over two decades, Oman Cables Industry

(SAOG) has always strived towards excellence and quality in all its

activities. The various awards won by OCI bear testimony to this, be

it being the five-time winner of His Majesty’s trophies for the best

industry or the various Flame of Excellence and Exporter of the Yearawards. OCI exports its products across the globe to Europe, UK, Far

East, Asia, Middle East and the Pacific Rim. Having started with just

10 employees and sales of 0.2 million USD in 1984, today OCI is

proud of the fact that it employs 52% Omani nationals amongst its

600 employees, and has a sales turnover of 800 million USD.

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Table of Contents

Sr. No. Details Page

1 Product Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

2 Criteria for selection of Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

3 Conductor details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

4 Electric Field in MV cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

5 General characteristics of Insulating Materials . . . . . . . . . . . . . . . . . . . . . . . . .15

6 General characteristics of Sheathing Materials . . . . . . . . . . . . . . . . . . . . . . . .16

7 Continuous Current Ratings and rating factors . . . . . . . . . . . . . . . . . . . . . . . .20

8 Short Circuit Current ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41

9 Cables Storage and Installation Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

10 Testing of Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46

11 Insulation Resistance Test and significance . . . . . . . . . . . . . . . . . . . . . . . . . . .50

12 Voltage drop – utility and values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53

13 Earthing and Bonding methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56

14 PVC vs XLPE cables – Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57

15 Overhead Conductor – Characteristics and Applications . . . . . . . . . . . . . . . . .61

16 Frequently Asked Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62

17 Conversion Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64


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OCI Product Range

Oman Cables offers a wide range of cables for demands made upon electrical, mechanical and

thermal qualities. The products listed below are the most popular ones. However, OCI can meet

a customer’s special requirements.

1) Electric Wires:

a) Building wires from 1.5 mm2 to 630 mm2

b) Single core PVC and LSF insulated wires 450/750 Volts to BS 6004, BS 7211, IEC60227

c) Multicore 300/500 Volts Circular, PVC Insulated, PVC Sheathed Wires to BS 6004,

IEC 60227

d) 2 Core, 3 Core Flat Wires with and without earth continuity conductor to BS 6004

e) PVC Insulated Flexible Cords to IEC 60227

f) 300/500 Volts Flexible Cables BS 6500, IEC 60227

2) 0.6/1 kv, XLPE and PVC insulated, PVC and LSF Sheathed Cables to IEC 60502-

1, BS 6346, BS 7889, BS 5467, BS 6724 and specific customer requirements

with:

a) Copper and Stranded Aluminium Conductors

b) Single core and multicore cables

c) Unarmoured cables

d) Aluminium wire armoured single core cables

e) Galvanized Steel Wire and Galvanized Steel Tape armoured multicore cables.

f) Control cables with and without armour, with and without screen (copper

tape/copper wire).


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3. Medium Voltage XLPE insulated cables to IEC 60502-2, BS 6622, BS 7835, BS

7870 and specific customer requirements up to and including 46 kV:

Copper and Aluminium Conductors:

a) Single core cables 25 mm2 to 1000 mm2

b) Three core cables 25 mm2 to 500 mm2

c) Single core and Three core un-armoured cables with copper tape/copper wire screen.

d) Aluminium wire armoured single core cables.

e) Galvanized Steel Wire and Galvanized Steel Tape armoured multicore cables.

We can offer cables with Optional Features such as:

Watertight Conductors

Bonded or Strippable Insulation Screen

Copper Wire/Copper Tape Screen

Cables with longitudinal water barriers at screen and armour level.

Cables with Radial water barrier (PE Laminated Aluminium Tape).

Cables with LLDPE, MDPE, HDPE, FRRT, FRLS Outer Sheath.

4) Overhead Conductors to IEC, BS, ASTM, DIN, VDE, AS Standards

a) Bare and PVC/XLPE Insulated Hard Drawn Copper Conductors

b) Bare and PVC/XLPE insulated all Aluminium conductors (AAC, AAC/PVC,

AAC/XLPE).

c) All Aluminium Alloy conductors (AAAC)

d) Aluminium Conductors Steel Reinforced (ACSR)

e) Aluminium Conductors Aluminium Clad Steel Reinforced (ACSR/AW).

f) Aluminium Conductors Aluminium Alloy Reinforced (ACAR).

g) Aluminium Alloy Conductor Steel Reinforced (AACSR).

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h) Galvanized Steel and Alumoweld Earth Wires.

i) Aerial Bundle Cables (Duplex, Triplex, Quadruplex).

5. Special Cables

a) Watertight Cables

b) Fire Retardant Cables to IEC 60332-3-24, IEC 60332-3-23, IEC 60332-3-22.

c) Cables with LLDPE, MDPE, HDPE, FRRT, FRLS Outer Sheath.

d) Cable with Oil Resistant and/or Termite Resistant and/or FRRT and/or FRLS Outer

Sheath.

e) Instrumentation Cables.

6) PVC Compounds for Insulation and Sheathing of Electric Cables. To name a few:

Type A,T11, T13, Type 6, Type 9, Type ST2, FR, FRLS, FRRT, ATR etc.

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Criteria for selection of Power Cables

Cable Type and Size should be selected keeping in the view the following:1) Application

2) Working Voltage, Earthed or Unearthed System

3) Load Current, Duty Cycle, Frequency

4) Installation methods and conditions

5) Short time duty and system protection

6) Acceptable Voltage drop

7) Economics

How do these factors influence the choice of cables?

1) Application of the cable determines the basic factors for choice of cable type.

a) Conductor material – Copper is the virtually unchallenged material as a conductor.

Aluminium, can also be used as Conductor material as it is very economical.

b) Insulating Material – good insulating material should have low thermal resistivity and

low dielectric losses. Please refer to the chart for major characteristics of different

materials.

c) Power cables are usually with armour to carry earth fault current and to give

mechanical protection against damage during installation and service. For higher fault

rating and higher tensile strength steel wires are used in multicore cables. Single core

in AC circuits, use non magnetic material. Stainless steel is difficult to justify on cost

grounds and Aluminium is the normal choice.

d) External covering/sheaths are used over the armour. Polyethylene or PVC is material

most often used. Please refer to the chart for properties of sheathing material.

2) System voltage determines Voltage class of cables.

3) Current rating and intermittent load is the decisive factor for fixing conductor size. Factors

such as Ground & Air temperature, thermal resistivity of soil, depth of laying, number of

cables in circuit etc. affect specified current ratings.

4) Chemical substances in the environment might need special requirements on outer

covering. Cables are vulnerable to termite and rodent attacks.


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5) The short circuit current and its duration determines the size of conductor and thermal

requirement of insulation.

6) Voltage drop is also major factor in deciding the conductor size of the cable. Voltage drop

of the cable for a given route length should not exceed the statutory requirements.

7) The design of the cable for a particular application must be optimised taking into account

all the above factors. In case expert guidance is desired, please contact OCI.

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Class of Conductors:

Class 1: Solid Conductor - used in cables for fixed installations.

Class 2: Started Conductor - used in cables for fixed installations.

Class 5: Flexible conductor - used in flexible cables and cords.

Class 6: Flexible Conductor - used in flexible cables and cords. Conductors are more

flexible than Class 5 when more flexibility is required

Table – Class 1 solid conductors for single core and multicore cables

1 2 3 4

Nominal Maximum resistance of conductor at 20˚C

cross Circular, annealed copper Aluminium and aluminium

sectional conductors alloy conductors, circular

area Plain Metal-Coated or shaped

m2 Ω /km Ω /km Ω /km

0.5 36.0 36.7 –

0.75 24.5 24.8 –

1.0 18.1 18.2 –1.5 12.1 12.2 –

2.5 7.41 7.56 –

4 4.61 4.70 –

6 3.08 3.11 –

10 1.83 1.84 3.08(a

16 1.15 1.16 1.91(a

25 0.727(b – 1.20(a

35 0.524(b – 0.868(a

50 0.387(b – 0.641

70 0.268(b – 0.443

95 0.193(b – 0.320(d

120 0.153(b – 0.253(d

150 0.124(b – 0.206(d

185 0.101(b – 0.164(d

240 0.0775(b – 0.125(d

300 0.0620

(b

– 0.100

(d


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Table – Class 1 solid conductors for single core and

multicore cables

1 2 3 4

Nominal Maximum resistance of conductor at 20˚C

cross Circular, annealed copper Aluminium and aluminium

sectional conductors alloy conductors, circular

area Plain Metal-Coated or shape

m2 Ω /km Ω /km Ω /km

400 0.0465(b – 0.0778

500 – – 0.0605

630 – – 0.0469800 – – 0.0367

1000 – – 0.0291

1200 – – 0.0247

a) Aluminium conductors 10 mm2 to 35 mm2 circular only.

b) Solid copper conductors having nominal cross-sectional areas of 25mm2 and above are

used for particular types of cable e.g., mineral insulated, and not for general purpose.

c) For solid aluminium alloy conductors having the same nominal cross-sectional area as

an aluminium conductor, the resistance value should be multiplied by 1.162 unlessotherwise agreed between manufacturer and purchaser.

d) For single core cables, four sectoral shaped conductors may be assembled into a single

circular conductor. The maximum resistance to the assembled conductor should be

25% of that of the individual component conductors.

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mm2 Ω/km Ω/km Ω/km

0.5 7 – – – 36.0 36.7 –

0.75 7 – – – 24.5 24.8 –1.0 7 – – – 18.1 18.2 –

1.5 7 – 6 – 12.1 12.2 –

2.5 7 – 6 – 7.41 7.56 –

4 7 – 6 – 4.61 4.70 –

6 7 – 6 – 3.08 3.11 –

10 7 7 6 6 – 1.83 1.84 3.08

16 7 7 6 6 – 1.15 1.16 1.91

25 7 7 6 6 6 6 0.727 0.734 1.20

35 7 7 6 6 6 6 0.524 0.529 0.868

50 19 19 6 6 6 6 0.387 0.391 0.641

70 19 19 12 12 12 12 0.268 0.270 0.443

95 19 19 15 15 15 15 0.193 0.195 0.320

120 37 37 18 15 18 15 0.153 0.154 0.253

150 37 37 18 15 18 15 0.124 0.126 0.206

185 37 37 30 30 30 30 0.0991 0.100 0.164

240 37 37 34 30 34 30 0.0754 0.0762 0.125

300 61 61 34 30 34 30 0.0601 0.0607 0.100

400 61 61 53 53 53 53 0.0470 0.0475 0.0778

500 61 61 53 53 53 53 0.0366 0.0369 0.0605

630 91 91 53 53 53 53 0.0283 0.0286 0.0469

800 91 91 53 53 – – 0.0221 0.0224 0.03671000 91 91 53 53 – – 0.0176 0.0177 0.0291

1200 b) – – 0.0151 0.0151 0.0247

1400 a b) 0.0129 0.0129 0.0212

1600 b) 0.0113 0.0113 0.0186

1800 a b) 0.0101 0.0101 0.0165

2000 b) 0.0090 0.0090 0.0149

2500 b) 0.0072 0.0072 0.0127

a) These sizes are non-preferred. Other non-preferred sizes are recognized for some specialized applications but are

not within the scope of this standard

b) The minimum number of wires for these sizes is not specified. These sizes may be constructed from 4, 5 or 6

equal segments (Milliken)

c) For stranded aluminium alloy conductors having the same nominal cross-sectional area as an aluminium conductor

the resistance value should be agreed between the manufacturer and the purchaser.

Class 2 stranded conductors for single-core and multi-core cables

1 2 3 4 5 6 7 8 9 10

Nominal

cross-

section

al area

Minimum number of wires in

the conductor

CircularCircular

Compacted Shaped Annealed copper

conductor

Plain

wiresMetal-coated

wires

Aluminium or

aluminium alloy

conductors

Plain wires

Maximum resistance of conductor at 20˚C

Cu Al Cu Al Cu Al


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Class 5 flexible copper conductors for single core

and multi-core cables

1 2 3 4

Nominal Maximum diameter of wires in Maximum resistance of

cross- conductor (mm) conductor at 20˚C

sectional area

Class 5 Class 6 Plain wires Metal-coated wires

mm2 Ω/km Ω/km

0.5 0.21 0.16 39.0 40.1

0.75 0.21 0.16 26.0 26.7

1.0 0.21 0.16 19.5 20.0

1.5 0.26 0.16 13.3 13.7

2.5 0.26 0.16 7.98 8.21

4 0.31 0.16 4.95 5.09

6 0.31 0.21 3.30 3.39

10 0.41 0.21 1.91 1.95

16 0.41 0.21 1.21 1.24

25 0.41 0.21 0.780 0.795

35 0.41 0.21 0.554 0.565

50 0.41 0.31 0.386 0.393

70 0.51 0.31 0.272 0.277

95 0.51 0.31 0.206 0.210

120 0.51 0.31 0.161 0.164

150 0.51 0.31 0.129 0.132

185 0.51 0.41 0.106 0.108

240 0.51 0.41 0.0801 0.0817

300 0.51 0.41 0.0641 0.0654

400 0.51 0.0486 0.0495

500 0.61 0.0384 0.0391

630 0.61 0.0287 0.0292

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Electric Field in Medium Voltage XLPE Cables

As shown in the figure below, the electric field is the highest at conductor surface, reducingtowards the outer surface of the insulation.

Field distribution within a high voltage XLPE cable

Purpose of Semiconducting screens for such cables –

Conductor Screening:-

1. To provide uniform stress over the relatively rough stranded conductor surface.

2. To provide close bonding between the conductor and adjacent insulation so as to exclude

any interspersed voids that may constitute sources of partial discharge.

Insulation Screening

1. With the outer shield grounded, the electric field of the conductor attains radial symmetry

and is confined to Insulation for safety consideration.2. To distribute electrical stress uniformly along the periphery of the cable

3. Intimate contact between Insulation and semiconducting layer prevents partial discharge.

4. To prevent surface discharges and reduce electrical interferences

Please see the difference between shape of Electric field of shielded (screened) cable and

unshielded cable

Non-Shielded Shielded


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Outer Covering materials selection chart

Mechanical PVC Polyethylene

Abrasion Resistance Good Excellent

Tensile Strength Excellent Excellent

Elongation Good Excellent

Compression Resistance Good Excellent

Flexibility Good Fair

Environmental – –

Flame Good Poor

Moisture – –

Fresh or salt water Good Exceptional

Petroleum oils – –Motor oil – Excellent

Fuel oil Good (Slight swelling

Crude oil – above 60˚C)

Creosote Poor Good

Paraffinic Hydrocarbons – –

Gasoline Good Excellent

Kerosene – (Slight swelling at

higher temperatures)

Alcohols – –

Isopropyl – –

Wood Fair Good

Grain – –

Mineral Acids – –

Sulfuric Acid – –

Nitric Acid Excellent Excellent

Hydrochloric Acid – –

Fixed Alkalis Sodium hydroxide (lye) – –

Potassium hydroxide (potash) – –

Calcium hydroxide (lime) Good Excellent

Ketones – –

Acetone – –

Methyl ethyl ketone (MEK) Poor Good

Esters – –

Ethyl Acetate – –

Most lacquer thinners Poor Good

Halogenated Hydrocarbons – –

Chloroform – –

Carbon Tetrachloride – –

Methyl Chloride Poor Poor

General

Leaves protective residue after combustion Yes No

Oxygen Index (ASTM D-2863) 23-30% 17-18%

Halogen content – % Wt. 26 0

Minimum installation temperature 14˚F (-10˚C) -40˚F (-40˚C)Dimensional stability under heat Fair Fair

Maximum operating temperature 80˚C 80˚C


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Insulation Material Characteristics

Sl. Description Unit PVC XLPE LSF

No. (Type A) (0.6/1 kV) (0.45/.75 kV)1 Tensile Strength and Elongation at break

Min. tensile strength N/mm2 12.5 12.5 10Min. elongation at break % 150 200 125

2 Accelerated ageing for specified period atspecified temp. followed by Tensile Strength andElongation at breakNo. of days ageing Days 7 7 7Ageing temperature ˚C 100±2 135±3 135±3Max. variation of tensile strength from N/mm2 12.5 – –unaged specimen % ±25 ±25 ±30Max. variation of elongation from % 150 – –

unaged specimen % ±25 ±25 ±303 Hot Set Test:– Temperature ˚C N/A 200±3 200±3– Time under load Minutes N/A 15 15– Mechanical stress N/cm2 N/A 20 20Max. elongation under load % N/A 175 100Max. permanent elongation after cooling % N/A 15 25

4 Low temperature bend test:Temperature at which specimen shall not crack ˚C -15±2 N/A -15±2

5 Low temperature elongation test:Test temperature ˚C -15±2 N/A -15±2Minimum Elongation % 20 N/A 30

6 Low temperature impact test:

Temperature at which specimen shall not crack ˚C N/A N/A -15±27 Pressure test at high temperature:

Test temperature ˚C 80±2 N/A 110±2Maximum indentation % 50 N/A 50

8 Loss of Mass (only for T11 insulation as per BS)Ageing: Number of days Days 7 N/A N/AAgeing Temperature ˚C 80±2 N/A N/AMaximum loss of mass mg/cm2 2.0 N/A N/A

9 Resistance to cracking (Heat shock test)Temperature at which the specimen shall not crack ˚C 150±2 N/A N/A

10 Water absorption – electrical methodTemperature at which specimen shall not crack ˚C 70±2 85±2 N/A

Duration Hours 240 336 (14 days) N/AMaximum variation of mass mg/cm2 – 1.0 N/A

11 Maximum permissible shrinkage:– Temperature ˚C N/A 130±3 N/A– Duration Hours N/A 1 N/AMaximum permissible shrinkage % N/A 4 N/A

12 Insulation Resistance const (Ki) at max. rated temp. M.Ohm.Km 0.037 (70˚C) 3.67 (90˚C) 0.002 (90˚C)

13 Volume Resistivity at maximum rated temperature Ohm.cm 1010(70˚C) 1012(90˚C) 1011(20˚C)

14 Ozone Resistance testTemperature at which specimen shall not crack ˚C N/A N/A 25±2Duration Hours N/A N/A 24Ozone Concentration ppm N/A N/A 250 to 300

15 Acidic (corrosive) gases evolvedLevel of HCl % N/A N/A


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Sheathing Material

Characteristics

Sl. Description Unit PVC LSFNo. (ST2/Type 9)

1 Tensile Strength and Elongation at break

Min. tensile strength N/mm2 12.5 10

Min. elongation at break % 150 100

2 Accelerated ageing for specified period at specified temp.

followed by Tensile Strength and Elongation at break

No. of days ageing Days 7 7

Ageing temperature ˚C 100±2 100±2

Minimum tensile strength after ageing N/mm2 12.5 10

Max. variation of tensile strength from unaged specimen % ±25 40

Minimum Elongation % 150 100Max. variation of elongation from unaged specimen % ±25 40

3 Low temperature bend test:

Temperature at which specimen shall not crack ˚C -15±2 -15±2

4 Low temperature elongation test:

Test temperature ˚C -15±2 -15±2

Minimum Elongation % 20 30

5 Low temperature impact test:

Temperature at which specimen shall not crack ˚C -15±2 -15±2

6 Pressure test at high temperature:

Test temperature ˚C 90±2 80±2

Maximum indentation % 50 50

7 Resistance to cracking (Heat shock test)

Temperature at which the specimen shall not crack ˚C 150±2 N/A

8 Loss of Mass

Ageing: Number of days Days 7 N/A

Ageing Temperature ˚C 100±2 N/A

Maximum loss of mass mg/cm2 1.5 N/A

9 Water absorption

No. of days ageing Hours N/A 24

Aging Temperature ˚C N/A 70±2

Maximum increase in mass mg/cm2 N/A 10

10 Tear Resistance test to B5 6469 (sec 99.1)Minimum Value N/mm N/A 5

11 Water immersion test to BS 6469 (sec. 99.1)

Aging temperature ˚C N/A 7

Number of days aging Days N/A 70±2

Max variation in tensile strength % N/A 30

Max. variation in elongation at break % N/A 30

12 Acidic (corrosive) gases evolved

Level of Hcl % N/A


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Special PVC Compounds with additional requirements

provided by OCI:

Property Material

FR FRLS FRRT

Oxygen Index (Min.) 30 30 30

Temperature Index (Min) 250 250 250

Smoke Density (Max.) – 60 –

Acid Gas Generation (Max.) – 20% 17%

Flammability Test* IEC 60332-1 and IEC 60332-1 and IEC 60332-1 and

IEC 60332-3-24 IEC 60332-3-24 IEC 60332-3-24

*Based on specific requests, we can provide compounds which can meet flammability requirements of IEC 60332-3-23 and

IEC 60332-3-22

Properties of Polyethylene Sheathing Material:

Properties LDPE MDPE HDPE

Dissipation factor

60 Hz 0.0002 0.0002 0.0002

103 Hz 0.0002 0.0002 0.0002106 Hz 0.0002 0.0002 0.0002

Arc resistance, s (ASTM D495) Melts Melts > 125

Density, g/cm3 0.910-0.925 0.926-0.940 0.941-0.965

Modulus of elasticity in tension, psi x 105 0.17-0.35 0.25-0.55 0.8-1.5

Percent elongation, % (ult.) (Max.) 300 300 400

Tensile strength, yield, psi x 102 14-19 19-26 26-45

Compressive strength, psi x 103 – – 2.4

Rockwell hardness R10 R15 R30-R50

Impact strength, ft-Ib/in. – – 1-23Heat distortion temperature (at 66 psi), ̊ F 105-121 120-150 140-185

Thermal conductivity, cal/cm.s. ˚C x 10-4 8 – 11-12

Thermal expansion, in./in. per ˚C x 10-5 11-30 15-30 15-30

Water absorption, %


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OCI can supply installing cables with special requirements

for the following

Utility Voltage Rating Requirement

SEC-EOA 35 KV * Swellable tape under and over metallic screen.

* Metal polyethylene laminate over metallic screen.

* Polyethylene or PVC Outer Sheath.

ARAMCO 10 kV to 35 kV Optional Requirement:

* Watertight Conductor with TR-XLPE Insulation

* Semi-conducting water blocking swellable tapes under

and over the metallic screen or concentric neutral.

* Plastic coated laminated aluminium or copper tape underthe outer jacket and firmly bonded to it.

SABIC 5 to 35 kV * Water swellable tape over copper tape screen

* Water Swellable tape over 3 core assembly

* Polyethylene bedding under Armour and PVC Outer

Sheath

DEWA 11 and 33 kV Single Core:

* Watertight Conductor

* Swellable tape in metallic screen region.

* Metal polyethylene laminate in metallic screen region.

* Polyethylene Outer Sheath.

Multi Core:


* Swellable tape in metallic screen region.

* Metal polyethylene laminate in metallic screen region.

* Polyethylene Outer Sheath over steel wire armour

FEWA 33 kV Single Core:


* Water swellable tape over insulation screen

* Non-conductive water swellable tape over copper screen

* Copolymer Coated Laminated Tape

* Polyethylene Outer Sheath ADWEA 33 kV 33 kV Cables 3 Core Cables:

* Watertight conductor

* TR-XLPE insulation.

* Polyethylene inner sheath

* Polyethylene outer sheath over steel tape armour

KAHRAMAA 0.6/1 kV * Armour: Galvanized steel + tinned copper wires.

Conductivity of copper wires alone shall be at least 50%

of any phase conductor at normal working temperature

and shall not be less than 25% of the total number of

armour wires.

* Armour to be embedded and covered by material suitable

to prevent movement of water traversely.

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Utility Voltage Rating Requirement

KAHRAMAA 11 KV * Fillers of non-hygroscopic material to inhibit flow of water.

* Armour to be embedded in or overlaid by substance ormaterial to inhibit flow of water.

KUWAIT 11 kV * 3 Core 11 kV Cable without Metallic Screen over

individual cores.

* Steel Wire armour over Semi-conductivity bedding.

SYRIA 12 to 20 kV * Swellable tape under and over insulation screen

* PVC outer sheath

IRAQ 11 to 33 kV Single Core:

* Waterproof tape over metallic screen

* PVC outer sheath

Three core:* Extruded EPR fillers

* Waterproof tape over bedding.

* PVC outer sheath over steel tape armour

JORDAN 33 kV Single Core

* Swellable tapes over metallic screen

* PE (ST7) outer sheath

TUNISIA 10 to 30 kV Single Core:

* Longitudinally watertight at metallic screen

* Radial Watertightness to be ensured by Outer sheath.


21/70

Current Ratings for Voltage grade

from 6 kV to 30 kV

Basic Assumption:- Conductor Material – Copper Single Core Cables (Unarmoured)

Ground Temperature – 20˚C

Air Temperature – 30˚C

Thermal resistivity of soil – 150˚C-cm/w

Depth of Laying – 800 mm

Double point bonding, Flat spacing – 2 OD from centre to centre

Ground In Single way Duct In Air

Single core, Unarmoured Single core, Unarmoured Single core, Unarmoured

Size Amp Amp Amp Amp Amp AmpTrefoil Flat spaced Trefoil Flat Touching Trefoil Flat Touching

duct

25 140 144 132 133 163 167

35 166 172 157 159 198 203

50 196 203 186 188 238 243

70 239 246 227 229 296 303

95 285 293 271 274 361 369

120 323 332 308 311 417 426

150 361 366 343 347 473 481

185 406 410 387 391 543 550

240 469 470 447 453 641 647

300 526 524 504 510 735 739

400 590 572 564 571 845 837

500 649 680 617 647 952 1000

630 718 766 683 728 1067 1154

800 796 842 757 801 1221 1310

1000 865 918 823 873 1346 1454

20


22/7021

Current Ratings for Voltage grade from

6 kV to 30 kV

Basic Assumption:- Conductor Material – Copper Single Core Cables (Armoured)







Single core, Armoured Single core, Armoured Single core, Armoured

Size Amp Amp Amp Amp Amp Amp

Trefoil Flat spaced Trefoil Flat spaced Trefoil Flat spaced

25 126 130 119 120 147 150

35 149 155 141 143 178 183

50 176 183 167 169 214 219

70 215 221 204 206 266 273

95 257 264 244 247 325 332

120 291 299 277 280 375 383

150 325 329 309 312 426 433

185 365 369 348 352 489 495

240 422 423 402 408 577 582

300 473 472 454 459 662 665

400 531 515 508 514 761 753

500 584 612 556 582 857 900

630 646 689 615 656 961 1039

800 717 758 681 721 1099 1179

1000 779 826 741 786 1212 1309


23/7022


from 6 kV to 30 kV

Basic Assumption:- Conductor Material – Aluminium Single Core Cables (Unarmoured)







Single core, Unarmoured Single core, Unarmoured Single core, Unarmoured


Trefoil Flat spaced Trefoil Flat Touching Trefoil Flat Touching

duct

25 108 112 102 103 127 130

35 129 134 122 123 154 157

50 152 157 144 146 184 189

70 186 192 176 178 230 236

95 221 229 210 213 280 287

120 252 260 240 242 324 332150 281 288 267 271 368 376

185 317 324 303 307 424 432

240 367 373 351 356 502 511

300 414 419 397 402 577 586

400 470 466 451 457 673 676

500 527 540 501 514 760 799

630 588 616 559 586 875 932

800 666 691 633 657 1019 1077

1000 735 766 699 728 1144 1221


24/7023


from 6 kV to 30 kV

Basic Assumption:- Conductor Material – Aluminium Single Core Cables (Armoured)







Single core, Armoured Single core, Armoured Single core, Armoured


Trefoil Flat spaced Trefoil Flat spaced Trefoil Flat spaced

25 97 101 92 93 114 117

35 116 121 110 111 139 141

50 137 141 130 131 166 170

70 167 173 158 160 207 212

95 199 206 189 192 252 258

120 227 234 216 218 292 299

150 253 259 240 244 331 338

185 285 292 273 276 382 389

240 330 336 316 320 452 460

300 373 377 357 362 519 527

400 423 419 406 411 606 608

500 474 486 451 462 684 719

630 529 554 503 527 788 839

800 599 622 570 591 917 969

1000 662 689 629 656 1030 1099


25/70


from 6 kV to 30 kV

Basic Assumption:- Conductor Material – Copper Three Core Cables

Ground Temperature – 20˚C Armoured/Unarmoured




Double point bonding



Unarmoured Armoured Unarmoured Armoured Unarmoured Armoured

25 129 129 112 112 142 143

35 153 154 133 134 170 172

50 181 181 158 158 204 205

70 221 220 193 194 253 253

95 262 263 231 232 304 307

120 298 298 264 264 351 352

150 334 332 297 296 398 397

185 377 374 336 335 455 453

240 434 431 390 387 531 529

300 489 482 441 435 606 599

400 553 541 501 492 696 683

24


26/7025

Current Ratings for Voltage grade from 6 kV to 30 kV

Basic Assumption:- Conductor Material – Aluminium Three Core Cables

Ground Temperature – 20˚C Armoured/Unarmoured




Double point bonding



Unarmoured Armoured Unarmoured Armoured Unarmoured Armoured

25 100 100 87 87 110 111

35 119 119 103 104 132 133

50 140 140 122 123 158 159

70 171 171 150 150 196 196

95 203 204 179 180 236 238

120 232 232 205 206 273 274

150 260 259 231 231 309 309

185 294 293 262 262 355 354

240 340 338 305 304 415 415

300 384 380 346 343 475 472

400 438 432 398 393 552 545


27/7026

0.6/1 kV - 1C & 2 Core Copper, XLPE insulated

Armoured/Unarmoured Cables

Thermal Resistivity of Soil: 1.5 K.m/WGround temperature: 20˚C

Depth of laying: 0.8 m

Ambient Air temperature: 30˚C

Area In Air In Ground In Duct

mm2Single core Trefoil Two Core

Single coreTwo core

Single coreTwo core

Trefoil Trefoil

Unarmoured Armoured Unarm Armoured Armoured Armoured Armoured Armoured

1.5 27 27 27 30 28 34 27 29

2.5 37 37 37 39 38 43 37 38

4 48 48 48 53 50 57 48 49

6 60 60 62 67 63 71 61 62

10 82 82 82 91 83 95 82 82

16 112 112 119 121 109 123 106 106

25 151 151 150 157 141 160 140 135

35 178 178 185 194 166 190 159 162

50 214 222 226 234 198 224 200 19370 273 283 286 294 241 272 241 237

95 338 348 353 363 288 326 283 286

120 396 403 412 420 327 371 317 322

150 456 464 471 479 365 416 343 362

185 529 533 546 553 411 469 375 411

240 632 628 651 653 473 541 419 476

300 731 715 752 744 528 607 458 535

400 852 817 875 856 573 670 486 604

500 986 924 635 527

630 1139 1041 698 569

800 1293 1131 737 593

1000 1443 1227 782 623


28/7027

0.6/1 kV - 1C & 2 Core Aluminium, XLPE insulated

Armoured/Unarmoured Cables

Thermal Resistivity of Soil: 1.5 K.m/WGround temperature: 20˚C

Depth of laying: 0.8 m




Single coreTwo core

Single coreTwo core

Trefoil Trefoil


1.5 21 21 22 22 22 23 22 21

2.5 29 29 29 29 31 32 31 27

4 37 37 37 37 40 41 38 35

6 48 48 48 48 50 51 47 44

10 64 64 64 64 65 70 65 58

16 88 88 89 91 85 95 83 81

25 115 115 111 117 110 121 107 102

35 144 144 136 143 128 143 128 123

50 158 166 165 173 152 170 154 14670 203 212 210 218 185 206 187 180

95 251 260 259 268 220 247 221 216

120 292 301 288 288 251 268 249 243

150 337 348 329 329 280 306 273 269

185 393 400 377 377 317 351 300 308

240 469 474 445 445 367 408 340 352

300 544 543 500 500 403 453 375 391

400 596 596 575 575 412 488 351 442

500 658 658 438 376

630 747 747 497 427

800 844 844 562 483

1000 948 948 631 542


29/7028

0.6/1 kV - 3 and 4 Core Copper and Aluminium XLPE insulated cables

Thermal Resistivity of Soil: 1.5 K.m/W

Ground temperature: 20˚CDepth of laying: 0.8 m



mm2Unarmoured Armoured Armoured Armoured

Copper Aluminium Copper Aluminium Copper Aluminium Copper Aluminium

1.5 23 18 25 18 28 21 24 18

2.5 33 25 34 25 37 27 32 23

4 41 32 45 32 49 36 41 29

6 53 41 57 41 60 45 52 38

10 71 55 79 55 81 59 69 50

16 103 78 103 78 104 80 89 68

25 129 97 134 102 133 102 113 87

35 158 119 165 124 158 120 136 103

50 193 145 201 151 188 143 162 123

70 246 184 252 190 228 174 199 152

95 303 228 311 234 273 209 240 183

120 354 266 361 272 311 238 271 208

150 406 304 413 311 348 266 305 234

185 469 353 475 360 392 302 345 266

240 559 420 561 426 453 350 399 309

300 645 487 639 488 507 395 448 349

400 749 514 735 514 560 425 515 372


30/7029

0.6/1 kV - 1C & 2 Core Copper, PVC insulated cables






Single coreTwo core

Single coreTwo core

Trefoil Trefoil


1.5 23 23 23 23 25 28 23 24

2.5 31 31 31 31 33 36 32 31

4 40 40 40 41 43 48 42 41

6 51 51 52 53 55 59 53 51

10 69 69 68 72 72 79 71 69

16 94 94 91 96 95 102 92 89

25 127 127 122 128 123 135 122 115

35 150 150 149 156 144 161 139 138

50 173 181 182 189 170 191 169 164

70 219 228 229 237 206 232 204 20195 273 280 284 293 246 279 239 242

120 318 326 330 338 280 316 264 273

150 365 371 378 384 312 354 290 306

185 423 425 436 445 351 401 315 348

240 505 500 519 525 403 462 352 402

300 583 571 598 598 450 517 385 451

400 679 649 695 685 488 569 410 508

500 782 729 536 439

630 900 817 586 473

800 1018 881 614 493

1000 1134 949 648 516


31/7030

0.6/1 kV - 1C & 2 Core Aluminium, PVC insulated cables






Single coreTwo core

Single coreTwo core

Trefoil Trefoil


16 74 74 70 72 74 78 72 68

25 97 97 90 92 96 101 93 86

35 121 121 110 113 111 120 111 103

50 129 133 134 136 129 142 133 122

70 164 166 169 174 156 175 163 152

95 202 205 209 213 188 210 192 182

120 236 239 242 242 213 233 216 212

150 271 272 276 276 239 266 240 234

185 315 317 316 316 271 305 262 267

240 376 375 374 374 313 355 298 306

300 436 431 420 420 352 394 329 340

400 500 500 483 483 359 425 305 384

500 552 552 381 327

630 627 627 432 371

800 709 709 489 420

1000 796 796 549 472


32/7031

0.6/1 kV - 3C and 4 Core Copper and Aluminium PVC insulated cables





mm2Unarmoured Armoured Armoured Armoured

Copper Aluminium Copper Aluminium Copper Aluminium Copper Aluminium

1.5 20 15 20 15 23 18 20 16

2.5 28 21 26 21 30 23 26 20

4 35 26 36 26 41 31 34 26

6 45 35 45 35 51 39 43 33

10 59 46 62 46 67 51 58 43

16 79 59 82 61 87 66 75 56

25 103 78 109 80 113 86 96 72

35 128 96 133 98 135 102 115 87

50 156 117 162 120 159 121 137 104

70 197 149 205 151 195 148 170 129

95 243 183 252 188 234 179 204 156

120 284 212 291 218 266 204 230 176

150 324 243 334 248 298 228 258 197

185 374 281 383 288 336 259 293 225

240 446 336 451 344 388 302 338 264

300 512 387 514 396 434 341 379 299

400 593 431 589 431 477 370 433 323


33/70

Table 1 – Correction factors for ambient

air temperatures other than 30˚C

Maximum

conductor Ambient air temperature

temperature ˚C

˚C20 25 35 40 45 50 55 60

90 1,08 1,04 0,96 0,91 0,87 0,82 0,76 0,71

Table 2 – Correction factors for ambient ground

temperatures other than 20˚C

Maximum conductor Ground temperature

temperature ˚C

˚C10 15 25 30 35 40 45 50

90 1,07 1,04 0,96 0,93 0,89 0,85 0,80 0,76

Table 3 – Correction factors for depth of laying

Other than 0.8 m for direct buried cables

Single-core cables

Depth of laying Nominal conductor size Three-core

m cables

≤185 mm2 >185 mm2

0,5 1,04 1,06 1,04

0,6 1,02 1,04 1,03

1 0,98 0,97 0,98

1,25 0,96 0,95 0,96

1,5 0,95 0,93 0,95

1,75 0,94 0,91 0,94

2 0,93 0,90 0,93

2,5 0,91 0,88 0,91

3 0,90 0,86 0,90

32


34/7033

Table 4 – Correction factors for depths of laying

other than 0.8 m for cables in ducts

Single-core cables

Depth of laying Nominal conductor size Three-core

m cables

≤185 mm2 >185 mm2

0,5 1,04 1,05 1,03

0,6 1,02 1,03 1,02

1 0,98 0,97 0,99

1,25 0,96 0,95 0,97

1,5 0,95 0,93 0,96

1,75 0,94 0,92 0,95

2 0,93 0,91 0,94

2,5 0,91 0,89 0,93

3 0,90 0,88 0,92

Table 5 – Correction factors for soil thermal resistivities

other than 1,5 K.m/W for direct buried single-core cables

Nominal area Values of soil thermal resistivity

of conductor K.m/W

mm20,7 0,8 0,9 1 2 2.5 3

16 1,29 1,24 1,19 1,15 0,89 0,82 0,75

25 1,30 1,25 1,20 1,16 0,89 0,81 0,75

35 1,30 1,25 1,21 1,16 0,89 0,81 0,75

50 1,32 1,26 1,21 1,16 0,89 0,81 0,74

70 1,33 1,27 1,22 1,17 0,89 0,81 0,74

95 1,34 1,28 1,22 1,18 0,89 0,80 0,74

120 1,34 1,28 1,22 1,18 0,88 0,80 0,74

150 1,35 1,28 1,23 1,18 0,88 0,80 0,74

185 1,35 1,29 1,23 1,18 0,88 0,80 0,74

240 1,36 1,29 1,23 1,18 0,88 0,80 0,73

300 1,36 1,30 1,24 1,19 0,88 0,80 0,73

400 1,37 1,30 1,24 1,19 0,88 0,79 0,73


35/70


other than 1,5 K.m/W single-core cables in buried ducts


of conductor K.m/W

mm20,7 0,8 0,9 1 2 2.5 3

16 1,20 1,17 1,14 1,11 0,92 0,85 0,79

25 1,21 1,17 1,14 1,12 0,91 0,85 0,79

35 1,21 1,18 1,15 1,12 0,91 0,84 0,79

50 1,21 1,18 1,15 1,12 0,91 0,84 0,78

70 1,22 1,19 1,15 1,12 0,91 0,84 0,7895 1,23 1,19 1,16 1,13 0,91 0,84 0,78

120 1,23 1,20 1,16 1,13 0,91 0,84 0,78

150 1,24 1,20 1,16 1,13 0,91 0,83 0,78

185 1,24 1,20 1,17 1,13 0,91 0,83 0,78

240 1,25 1,21 1,17 1,14 0,90 0,83 0,77

300 1,25 1,21 1,17 1,14 0,90 0,83 0,77

400 1,25 1,21 1,17 1,14 0,90 0,83 0,77

Table 7 – Correction factors for soil thermal resistivitiesother than 1,5 K.m/W for direct buried three-core cables


of conductor K.m/W

mm20,7 0,8 0,9 1 2 2.5 3

16 1,23 1,19 1,16 1,13 0,91 0,84 0,78

25 1,24 1,20 1,16 1,13 0,91 0,84 0,78

35 1,25 1,21 1,17 1,13 0,91 0,83 0,78

50 1,25 1,21 1,17 1,14 0,91 0,83 0,77

70 1,26 1,21 1,18 1,14 0,90 0,83 0,77

95 1,26 1,22 1,18 1,14 0,90 0,83 0,77

120 1,26 1,22 1,18 1,14 0,90 0,83 0,77

150 1,27 1,22 1,18 1,15 0,90 0,83 0,77

185 1,27 1,23 1,18 1,15 0,90 0,83 0,77

240 1,28 1,23 1,19 1,15 0,90 0,83 0,77

300 1,28 1,23 1,19 1,15 0,90 0,82 0,77

400 1,28 1,23 1,19 1,15 0,90 0,82 0,76

34


36/7035


other than 1,5 K.m/W for three-core cables in ducts


of conductor K.m/W

mm20,7 0,8 0,9 1 2 2.5 3

16 1,12 1,11 1,09 1,08 0,94 0,89 0,84

25 1,14 1,12 1,10 1,08 0,94 0,89 0,84

35 1,14 1,12 1,10 1,08 0,94 0,88 0,84

50 1,14 1,12 1,10 1,08 0,94 0,88 0,84

70 1,15 1,13 1,11 1,09 0,94 0,88 0,8395 1,15 1,13 1,11 1,09 0,94 0,88 0,83

120 1,15 1,13 1,11 1,09 0,93 0,88 0,83

150 1,16 1,13 1,11 1,09 0,93 0,88 0,83

185 1,16 1,14 1,11 1,09 0,93 0,87 0,83

240 1,16 1,14 1,12 1,10 0,93 0,87 0,82

300 1,17 1,14 1,12 1,10 0,93 0,87 0,82

400 1,17 1,14 1,12 1,10 0,92 0,86 0,81

Table 9 – Correction factors for groups of three-core cablesIn horizontal formation laid direct in the ground

Number of Spacing between cable centres

cables in mm

groupTouching 200 400 600 800

2 0,80 0,86 0,90 0,92 0,94

3 0,69 0,77 0,82 0,86 0,89

4 0,62 0,72 0,79 0,83 0,87

5 0,57 0,68 0,76 0,81 0,856 0,54 0,65 0,74 0,80 0,84

7 0,51 0,63 0,72 0,78 0,83

8 0,49 0,61 0,71 0,78 –

9 0,47 0,60 0,70 0,77 –

10 0,46 0,59 0,69 – –

11 0,45 0,57 0,69 – –

12 0,43 0,56 0,68 – –


37/70

Table 10 – Correction factors for groups of three-phase circuits

of single-core cables laid direct in the ground

Number of Spacing between group centres

cables in mm


2 0,73 0,83 0,88 0,90 0.92

3 0,60 0,73 0,79 0,83 0,86

4 0,54 0,68 0,75 0,80 0,84

5 0,49 0,63 0,72 0,78 0,82

6 0,46 0,61 0,70 0,76 0,81

7 0,43 0,58 0,68 0,75 0,80

8 0,41 0,57 0,67 0,74 –

9 0,39 0,55 0,66 0,73 –

10 0,37 0,54 0,65 – –

11 0,36 0,53 0,64 – –

12 0,35 0,52 0,64 – –

Table 11 – Correction factors for groups of three-core cablesIn single way ducts in horizontal formation

Number of Spacing between duct centres

cables in mm


2 0,85 0,88 0,92 0,94 0,95

3 0,75 0,80 0,85 0,88 0,91

4 0,69 0,75 0,82 0,86 0,89

5 0,65 0,72 0,79 0,84 0,87

6 0,62 0,69 0,77 0,83 0,87

7 0,59 0,67 0,76 0,82 0,86

8 0,57 0,65 0,75 0,81 –

9 0,55 0,64 0,74 0,80 –

10 0,54 0,63 0,73 – –

11 0,52 0,62 0,73 – –

12 0,51 0,61 0,72 – –

36


38/7037

Table 12 – Correction factors for groups of three-phase circuits

of single-core cables in single-way ducts

Number of Spacing between duct group centres

cables in mm


2 0,78 0,85 0,89 0,91 0,93

3 0,66 0,75 0,81 0,85 0,88

4 0,59 0,70 0,77 0,82 0,86

5 0,55 0,66 0,74 0,80 0,84

6 0,51 0,64 0,72 0,78 0,83

7 0,48 0,61 0,71 0,77 0,82

8 0,46 0,60 0,70 0,76 –

9 0,44 0,58 0,69 0,76 –

10 0,43 0,57 0,68 – –

11 0,42 0,56 0,67 – –

12 0,40 0,55 0,67 – –


39/70

Table 13 – Reduction factors for groups of more than one multi-

core cable in air – To be applied to the current-carrying capacity

for one multi-core cable in free air

Method of Installation Number Number of cables

of trays 1 2 3 4 6 9

Touching 1 1,00 0,88 0,82 0,79 0,76 0,73

Cables on 2 1,00 0,87 0,80 0,77 0,73 0,68

perforated trays 3 1,00 0,86 0,79 0,76 0,71 0,66

Spaced 1 1,00 1,00 0,98 0,95 0,91 –

2 1,00 0,99 0,96 0,92 0,87 –3 1,00 0,98 0,95 0,91 0,85 –

Touching 1 1,00 0,88 0,82 0,78 0,73 0,72

2 1,00 0,88 0,81 0,76 0,71 0,70

Cables on vertical

perforated trays

1 1,00 0,91 0,89 0,88 0,87 –Spaced 2 1,00 0,91 0,88 0,87 0,85 –

Touching 1 1,00 0,87 0,82 0,80 0,79 0,78

2 1,00 0,86 0,80 0,78 0,76 0,73

Cables on ladder 3 1,00 0,85 0,79 0,76 0,73 0,70

supports, cleats

etc. Spaced 1 1,00 1,00 1,00 1,00 1,00 –

2 1,00 0,99 0,98 0,97 0,96 –

3 1,00 0,98 0,97 0,96 0,93 –

NOTE 1: Values given are averages for the cable types and range of conductor sizes considered. The

spread of values is generally less than 5%.

NOTE 2: Factors apply to single layer groups of cables as shown above and do not apply when cables

are installed in more than one layer touching each other. Values for such installations may be

significantly lower and must be determined by an appropriate method.

NOTE 3: Values are given for vertical spacing between trays of 300 mm and at least 20 mm between

trays and wall. For closer spacing, the factors should be reduced.

NOTE 4: Values are given for horizontal spacing between trays of 225 mm with trays mounted back to

back. For closer spacing, the factors should be reduced.

38


40/7039

Table 14 – Reduction factors for groups of more than one circuit of

single-core cables (Note 2) –

To be applied to the current-carrying capacity for one circuit ofsingle-core cables in free air

Method of Installation Number ofNumber of three-phase Use as a

trayscircuits (Note 5) multiplier to

1 2 3 rating for

Touching 1 0,98 0,91 0,87 Three cables

Perforated trays in horizontal

(Note 3) 2 0,96 0,87 0,81 formation

3 0,95 0,85 0,78

Touching 1 1,00 0,97 0,96

Ladder Three cables

supports, 2 0,98 0,93 0,89 in horizontal

cleats etc. formation

(Note 3) 3 0,97 0,90 0,86

Perforated 1 1,00 0,98 0,96

trays 2 0,97 0,93 0,89

(Note 3) 3 0,96 0,92 0,86

Vertical 1 1,00 0,91 0,89

Perforated Three cables

trays 2 1,00 0,90 0,86 in trefoil

(Note 4)Spaced

formation

Ladder 1 1,00 1,00 1,00

supports.

cleats, etc. 2 0,97 0,95 0,93

(Note 3)

3 0,96 0,94 0,90

NOTE 1: Values given are averages for the cable types and range of conductor sizes considered. The

spread of values is generally less than 5%.

NOTE 2: Factors are given for single layers of cables (or trefoil groups) as shown in the table and do

not apply when cables are installed in more than one layer touching each other. Values for such

installations may be significantly lower and should be determined by an appropriate method.

NOTE 3: Values are given for vertical spacings between trays of 300 mm. For closer spacing, the factors

should be reduced.

NOTE 4: Values are given for horizontal spacing between trays of 225 mm with trays mounted back to

back. For closer spacing, the factors should be reduced.

NOTE 5: For circuits having more than one cable in parallel per phase, each three phase set of

conductors should be considered as a circuit for the purpose of this table.


41/70

Permissible short-circuit temperatures and rated short-time current

densities

1 2 3 4 5 6 7 8 9 10

Permissible short circuit Conductor temperature at the beginning of short circuit in ˚C

temperature in ̊C 90 80 70 60 50 40 30 20

Rated short-time current density in A/mm2 for a rated

short-circuit duration of 1 second

Copper Conductors 250 143 149 154 159 165 170 176 181

Aluminium Conductors 250 94 98 102 105 109 113 116 120

1 2 3 4 5 6 7 8 9 10

Permissible short circuit Conductor temperature at the beginning of short circuit in ˚C

temperature in ̊C 90 80 70 60 50 40 30 20

Rated short-time current density in A/mm2 for a rated

short-circuit duration of 1 second

≤ 300 mm2 160 – – 115 122 129 136 143 150

300 mm2 140 – – 103 111 118 126 133 140

40

Cables with

(PVC Insulation)

Copper Conductor

Cables with

(XLPE Insulation)


42/7041

Permissible Short Circuit current of XLPE

insulated power cables (copper conductors)


43/7042

Permissible Short Circuit current of XLPE

insulated power cables (Aluminum conductors)


44/7043

Recommended Cables Storage Practices

Storage and Storage Maintenance:

1. Finished cables have no established shelf-life. Moisture and atmospheric conditions can

cause exposed conductors to oxidize and discolor. Uncovered/unsheltered cable will

degrade due to exposure to direct sunlight and/or the elements. If the cables are

protected, there should be no degradation of the insulation.

2. In general, any cable for use indoors should be stored indoors. Any cable suitable for

installation outdoors is suitable for storage outdoors. Cables stored outdoors should

have the ends sealed to prevent moisture ingress into the cable.

3. Cables should be stored in a sheltered area. While on the reel, cable should be covered

with Masonite or a dark film wrap (to block the sun’s rays and shield them from the

elements).

4. Cable reels must remain in an upright position. Cable reels must not be stored on their

sides.Reels must not be stacked.

5. Cable reels should be stored with the protective covering or lagging in place. If a length

of cable has been cut from the reel, the cable end should be immediately resealed to

prevent moisture from entering it. If a part length is returned to storage, the reel’s

protective covering should be restored.

6. Wooden reels should be stored off the ground to prevent rotting. Reels should be stored

on a flat, hard surface so that the flanges do not sink into the earth. The weight of the

reel and cable must be carried at all times by the reel flanges.7. Cable reels and lagging must not be stored in direct contact with water or dampness

for extended periods of time. Timbers or metal supports must be placed under the reel

flanges to provide elevated storage of the reels away from direct contact with water or

damp soil.

8. Reels should be stored in an area where construction equipment, falling or flying

objects or other materials will not touch the cable.

9. Cable should be stored in an area where chemicals or petroleum products will not be

spilled or sprayed on the cables.

10. Cables should be stored in an area away from open fires or sources of high heat.

11. If the cables are stored in a secure area and not exposed to the effects of the weather,

an annual inspection should be satisfactory.

12. Where the reels are exposed to the weather, a bi-monthly inspection should be

performed to observe any sign of deterioration.

13. If the reels are exposed in a non-secure area, policing of the area at frequent intervals

may be required depending on circumstances.

14. Records of delivery date, manufacturer, installation date, any extenuating

circumstances, along with all test reports should be kept on file.


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Guideline for permissible pulling force for laying of low voltage

and medium voltage cables:

Means of pulling Type of Cables Formula Factor

With pulling head All types of Cables P = σ . A σ = 50 N/mm2 (Copper Conductor)

attached to conductor σ = 30 N/mm2 (Aluminium Conductor)

With pulling stocking Unarmoured cable1) P = σ . A σ = 50 N/mm2 (Copper Conductor)

σ = 30 N/mm2 (Aluminium Conductor)

All Wire armoured Cables P = K.D2 K = 9 N/mm2

1) when laying 3 single core cables simultaneously with a common pulling stocking, the same

maximum pulling force applies, whereas the pulling force for 3 laid-up single core cables is 3times that of a single-core and for 3 non-laid-up single core cables is 2 times that of a single

core.

P = Pull in Newtons

A = total cross-sectional area in mm2 of all conductors (screen/concentric conductor not to be

included)

D = Overall diameter of cable

σ = permissible tensile stress of conductor in N/mm2

K = empirically derived factor in N/mm2.

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Minimum Installation Bending Radius

Cables for fixed wiring up to and including 450/750 V:

Insulation Conductors Construction Overall diameter Minimum

(mm) radius

XLPE or PVC Copper and Aluminium, Unarmoured Upto 10 mm 3Da

Solid or Stranded circular 10 to 25 mm 4Db

Above 25 mm 6D

D = overall diametera 2D for single-core cables with circular stranded conductors installed in conduits, ducting or

trunking.b 3D for single-core cables with circular stranded conductors installed in conduits, ducting or

trunking.

XLPE and PVC insulated cables rated 0.6/1 kV and 1.9/3.3 kV:

Conductor Construction Minimum

radius

Circular Copper Both Armoured and Unarmoured 6D

Shaped Copper Both Armoured and Unarmoured 8D

Solid Alumiuium Both Armoured and Unarmoured 8D

XLPE and insulated cables 6.6 kV to 33 kV:

Type of Cable Minimum Radius

During Laying Adjacent to joints or

terminations

Single Core:(a) Unarmoured 20D 15D

(b) Armoured 15D 12D

Three Core:

(c) Unarmoured 15D 12D

(d) Armoured 12D 10D


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D.C. Voltage Test:The purpose of the test is to check that the cable laying has been done correctly. The cable

may, for example, have been accidentally damaged during shipping, handling, storing, pullingand backfilling. Since it can be assumed that the cable insulation has not been damaged as long

as the jacket is intact, the same can be checked by a d.c. voltage-withstand test.

A direct voltage of 4 kV per millimeter of specified thickness of extruded oversheath shall be

applied with a maximum of 10 kV for a period of 1 minute between each metal sheath or

metallic screen and the ground.

For the test to be effective, it is necessary that the ground makes good contact with all of the

outer surfaces of the oversheath. A conductive layer on the oversheath can assist in this

regard.

Electrical tests after installation

Voltage Test after installation:

1) Insulation test:

a) Test for 5 minutes with the phase to phase voltage of the system applied between the

conductor and the metallic screen/sheath.

b) Test for 24 hours with the normal operating voltage of the system.

2) DC Testing:

As an alternative to a.c. test, a d.c. test as per IEC 60502-2 OR BS 6622 mentioned below

may be applied for 15 minutes.

These tests are intended for cables immediately after installation and not for cables that

have been in service.

The test voltage is to be applied between each conductor and the armour and/or screens

after all terminating and jointing has been completed, but before connection to the

system.

Cable Voltage Designation D.C. Voltage D.C. Voltage

as per IEC 60502 (4Uo) as per BS 6622

kV kV kV

3.5/6 kV (IEC), 3.8/6.6 kV (BS) 14 15

6/10 kV (IEC), 6.35/11 kV (BS) 24 25

8.7/15 kV (IEC), 8.7/15 kV (BS) 35 37

12/20 kV (IEC) 12.7/22 kV (BS) 48 50

18/30 kV (IEC), 19/33 kV (BS) 72 76

Note 1: A d.c. test may endanger the insulation system under test.

Note 2: For installations which have been in use, lower voltages and/or shorter durations may be used.Values should be negotiated taking into account the age, environment, history of breakdowns and the

purpose of carrying out the test.

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Definition of Tests for Cables1) Routine Tests:

Tests made by the manufacturer on each manufactured length of cable to check that eachlength meets the specified requirements.

Tests:

a) Measurement of electrical resistance of conductors

b) Voltage tests

c) Partial Discharge test (for XLPE cables with rated voltages 6 kV and above)

2) Sample Tests:

Tests made by the manufacturer on samples of completed length or components taken

from a completed cable, at a frequency, to verify that the finished product meets the

specified requirements.

Tests:

a) Conductor examination

b) Check of dimensions

c) 4 hour voltage test for cables with rated voltage 6 kV and above

d) Hot set test for XLPE insulation.

3) Type Tests:

Tests made before supplying on a general commercial basis, a type of cable covered by IEC

standard, in order to demonstrate satisfactory performance characteristics to meet the

intended application.

Note: These tests are such that, after they have been made, need not be repeated, unless

changes are made in the cable materials or manufacturing processes which might change

the performance characteristics.

Tests: Shall be as per attached Table for Cables.


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List of Routine, Sample and Type tests for LV Cables

Test Designation

No. Description of the Test Routine Sample Type

Elec. Non

Elec.

1 Measurement of electrical resistance of conductor

2 Voltage test (2.5Uo + 2 kV)

3 Measurement of thickness of insulation and non-metallic sheaths

4 Measurement of Cable armour dimensions

5 Measurement of Cable overall diameter

6 Hot set test for XLPE insulation

7 Insulation resistance measurement at normal and operating temp.

8 Measurement of volume resistivity for XLPE insulation

9 4 hours voltage test (4Uo)

10 Determining the mechanical properties of insulation before and

after ageing

11 Determining the mechanical properties of non-metallic sheath

before and after ageing.

12 Ageing tests on pieces of complete cable to check compatibility

13 Loss of mass test on PVC sheath

14 Pressure test at high temperature on sheaths

15 Heat shock test for PVC sheaths

16 Tests on PVC sheaths at low temperature

17 Water absorption test for XLPE insulation

18 Shrinkage test for XLPE insulation

19 Carbon black content of PE sheaths

20 Test under fire conditions (if required)

21 Smoke emission test for Halogen free cables

22 Acid Gas emission test for Halogen free cables

23 pH, conductivity, fluorine content test for Halogen free cables

24 Water absorption test for halogen free sheath


50/7049

List of Routine, Sample and Type tests for MV Cables

Test Designation

No. Description of the Test Routine Sample Type

Elec. Non

Elec.

1 Measurement of electrical resistance of conductor

2 Partial discharge test

3 Voltage test (3.5Uo)

4 Measurement of thickness of insulation and non-metallic sheaths

5 Measurement of armour dimensions

6 Measurement of Cable overall diameter

7 Hot set test for XLPE insulation

8 Bending test followed by partial discharge

9 Tangent Delta Measurement

10 Heating cycle voltage test, followed by partial discharge test

11 Impulse withstand test followed by a power frequency voltage test

12 4 hours Voltage test (4Uo)

13 Resistivity of semiconducting layers

14 Insulation resistance measurement at normal and operating temp.

15 Determining the mechanical properties of insulation before

and after ageing

16 Determining the mechanical properties of non-metallic sheath

before and after ageing

17 Ageing tests on pieces of complete cable to check compatibility

18 Loss of mass test on PVC sheath

19 Pressure test at high temperature on sheaths

20 Heat shock test for PVC sheaths

21 Tests on PVC sheaths at low temperature

22 Water absorption test for XLPE insulation

23 Shrinkage test for XLPE insulation

24 Shrinkage test for PE outer sheath

25 Strippability test (for strippable insulation screen only)

26 Carbon black content of PE sheaths

27 Test under fire conditions (if required)

28 Water penetration test (if required)


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Insulation Resistance – Significance and Use

Insulation Resistance (IR) evaluates Insulation integrityIR is used as:

a) A Quality Tool at the time of manufacturing of cable

b) After installation, to check proper installation.

c) As a preventive maintenance task

d) For Trouble shooting

Method of Measurement

IR is measured by applying voltage (generally stabilised DC) cross a dielectric, measuring the

amount of current flowing through the dielectric and then calculating resistance.

Let’s clarify our use of the term “current.” We’re talking about leakage current. The resistance

measurement is in megohms.

After connection, the test voltage is applied for 1 min. (This is a standard industry parameter

that allows the client to make relatively accurate comparisons of reading from past tests done

by other technicians.) During this interval, the resistance reading should drop or remain

relatively steady. Larger insulation systems will show a steady decrease; smaller systems will

remain steady because the capacity and absorption currents drop to zero faster than on large

systems. After 1 minute the reading should be recorded.

Precautions –

1) When performing insulation resistance testing, consistency must be maintained because

electrical insulation will exhibit dynamic behavior during the course of the test; whether the

dielectric is “good” or “bad” To evaluate a number of test results on the same piece of

equipment, the test should be conducted the same way and under the relatively same

environmental parameters, each and every time.

2) Insulation resistance is temperature-sensitive. When temperature increases, insulation

resistance decreases, and vice versa.

For a cable length of L,

IR = VR x Loge

D

2πL d

Where VR = Volume Resistivity of Insulation in ohm – cm

D = Outer dia over insulation (mm)

d = Inner dia of insulation. (mm)

L = Length of cable in cm.

IR = Insulation Resistance in ohms.

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( )


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Calculated Minimum Insulation Resistance

Values for

0.6/1 kV XLPE Insulated and PVC Insulated Cables:

Size PVC Insulated Cables XLPE Insulated Cables

mm2 (M.ohm-km) at 20˚C (M.ohm-km) at 20˚C

1.5 10 895

2.5 9 840

4 8 700

6 7 590

10 7 475

16 6 385

25 5 390

35 5 335

50 5 320

70 5 295

95 5 255

120 5 245

150 5 260

185 5 265

240 5 245

300 5 230

400 5 230

500 5 225

630 5 235


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Calculated Minimum Insulation Resistance Values for Medium

Voltage XLPE Insulated Cables:

Size

Minimum Insulation Resistance at 20˚C

(mm2)6 kV 10 kV 15 kV 20 kV 30 kV

M.ohm-km M.ohm-km M.ohm-km M.ohm-km M.ohm-km

25 845 1060 1300 – –

35 765 970 1185 1365 –

50 680 870 1075 1240 1590

70 600 770 955 1110 1435

95 530 685 855 995 1300

120 480 625 785 910 1205

150 445 580 730 855 1130

185 405 530 670 785 1045

240 370 470 600 705 945

300 360 430 550 650 875

400 345 385 495 590 795

500 330 350 450 535 725

630 295 310 400 480 655

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What is voltage drop?

A voltage drop in an electrical circuit normally occurs when current is passed

through the wire.

The greater the resistance of the circuit, the higher the voltage drop.

How much voltage drop is acceptable?

The National Electrical Code states that a voltage drop of 4% at the furthest

receptacle in a branch wiring circuit is acceptable for normal efficiency. In a

120 volt 15 ampere circuit, this means that there should be no more than a

4.8 volt drop (115.2 volts)

What causes “excess voltage drop” in a branch circuit?

The cause is usually:

1. High resistance connections at wiring junctions or outlet terminals,

usually caused by:-

• poor splices anywhere in the circuit

• loose or intermittent connections anywhere in the circuit

• corroded connections anywhere in the circuit

• Inadequate seating of wire in the slot connection on backwired “push-

in-type” receptacles and switches.

2. The wire does not meet code standards (not heavy enough gauge for the

length of the run).

What are the consequences of “excess” voltage drop in a circuit?

Excess voltage drop can cause the following conditions:

1. Low voltage to the equipment being powered, causing improper, erratic,

or no operation – and damage to the equipment.

2. Poor efficiency and wasted energy.

3. Heating at a high resistance connection/splice may result in a fire at high

ampere loads.

At what % of voltage drop, does a circuit become hazardous?

That would depend on how much current is flowing through the high

resistance connector; resistance of connector, and the following factors:-

1. Is the high resistance connection in contact with a combustible material?

2. Is there air flow to dissipate the heat?

3. Is the area around the connection insulated, so that heat cannot escape.


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Voltage Drop

The size of every bare conductor or cable conductor should be such that the drop in voltagefrom consumer’s terminals to any point in the installation does not exceed 4% of the declared

or nominal voltage when the conductors are carrying full load, but disregarding the starting

conditions. This requirement shall not apply to wiring fed from extra low voltage secondary of

a transformer. The approximate voltage drop in average circuits such as lighting and domestic

heating loads for XLPE insulated cables is:

Conductor cross- Permissible Voltage Permissible Voltage Permissible Voltage

sectional area Drop (Vp) Drop (Vp) Drop (Vp)

(Single Core Cables) (Two Core Cables) (3 & 4 Core Cables)

mm2 mV/A/m mV/A/m mV/A/m

1.5 – 30.86 26.72

2.5 – 18.9 16.36

4 – 11.76 10.18

6 – 7.86 6.804

10 4.05 4.67 4.04

16 2.55 2.94 2.54

25 1.618 1.86 1.612

35 1.173 1.348 1.166

50 0.874 1.0 0.866

70 0.616 0.702 0.607

95 0.456 0.516 0.446

120 0.373 0.418 0.362

150 0.316 0.351 0.304

185 0.267 0.295 0.255

240 0.223 0.244 0.211300 0.197 – 0.185

400 0.179 – 0.165

500 0.165 – 0.151

630 0.162 – 0.142

800 0.15 – –

1000 0.144 – –

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Selection of Cable Size Based on Voltage Drop:

Based on the required ampacity and installation conditions, a suitable cable size is chosen,cross-checked with the voltage drop as follows:

Vp x 1000 x VVcal =

I x L x 100

where:

Vp = Max. permissible voltage drop (say 4%)

V = System voltage (say 415 V)

L = Length in meters

I = Current in Amps

Suppose a 300 meters 3 core XLPE insulated cable is to carry 100 Amps and the supply voltage

is 415 V then Vcal = 4 x 1000 x 415 = 0.553 mV/A/m. Therefore a cable size whose voltage

100 x 300 x 100

drop is less than 0.553 is to be selected. Hence, for the case above , cable size 95 mm2 may

be selected.


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Bonding and

Earthing Methods

Method Induced Voltage at Sheath voltage Application

Cable ends limiters required

Both Ends Bonded No No Substations, short lengths

Single point bonded Yes Yes circuit length upto 1 Km.

Cross Bonding Only at cross Yes Long length circuits

bonding points

Both Ends Bonded Single point bonded

Surge arrester

Earth continuity wire

Induced Voltage Distribution Induced Voltage Distribution

Most safe but due to circulating More ampacity. Surge arrester required at open end.

current ampacity reduces Induced voltage is proportional to length of cable andso limitations on circuit length.

Cross Bonding

Induced Voltage Distribution

Most popular system of earthing for long circuits.

Ampacity is like single point bonded system but costly installations due to requirement of

more number of Surge limiters, each at crossing.

56


58/7057

Comparison of XLPE & PVC Insulated Power Cables

PVC XLPE1. Operating Conductor Temperature: 70˚C Operating Conductor Temperature: 90˚C

2. Lower current carrying capacity. Higher current carrying capacity.

3. Maximum Temperature Limit under Maximum Temperature Limit under

short circuit: 160˚C short circuit: 250˚C

4. Lower emergency overload capacity. Higher emergency overload capacity.

5. Lower moisture resistance High moisture resistance.

6. Insulation Resistance Lower Insulation Resistance almost 1000 times

higher

7. Inferior properties to withstand vibration & Higher properties to withstand vibrationheat impacts. and heat impacts.

8. Heavier as specific gravity is 1.42, Lighter as specific gravity is 0.92 and

therefore more difficult to install. easier to install.

9. Heat dissipation slower as Thermal Insulation dissipation heat faster as

Resistivity is 7˚C m/w. Thermal Resistivity is 3.5˚Cm/w.

10. Higher “Loss angle” of 0.01 Lower “Loss angle” of 0.004

11. Installation Technique: simple Installation Technique: simple.


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Nominal thickness of PVC/A insulation

as per IEC 60502-1

Nominal cross-sectional Nominal thickness of insulation at rated voltage

area of conductor Uo/U (Um)

0,6/1 (1,2) kV 1,8/3 (3,6) kv

mm2 mm mm

1,5 and 2,5 0,8 –

4 and 6 1,0 –

10 and 16 1,0 2,2

25 and 35 1,2 2,2

50 and 70 1,4 2,2

95 and 120 1,6 2,2150 1,8 2,2

185 2,0 2,2

240 2,2 2,2

300 2,4 2,4

400 2,6 2,6

500 to 800 2,8 2,8

1000 3.0 3,0

Note: Any conductor cross-section smaller than those given in this table is not recommended

Nominal thickness of XLPE Insulation as per IEC 60502-1

Nominal cross-sectional Nominal thickness of insulation at rated voltage

area of conductor Uo/U (Um)

0,6/1 (1,2) kV 1,8/3 (3,6) kv

mm2 mm mm

1,5 and 2,5 0,7 –

4 and 6 0,7 –

10 and 16 0,7 2,0

25 and 35 0,9 2,0

50 1,0 2,070 and 95 1,1 2,0

120 1,2 2,0

150 1,4 2,0

185 1,6 2,0

240 1,7 2,0

300 1,8 2,0

400 2,0 2,0

500 2,2 2,2

630 2,4 2,4

800 2,6 2,6

1000 2,8 2,8

NOTE: Any conductor cross-section smaller than those given in this table is not recommended

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60/7059

Nominal thickness of XLPE insulation

as per IEC 60502-2

Nominal cross Nominal thickness of insulation at rated voltage

sectional area of Uo/U (Um)

conductor 3,6/6 (7,2) kV 6/10 (7,2) kV 8,7/15 (17,5) kV 12/20 (24) kV 18/30 (36) kV

mm2 mm mm mm mm mm

10 2,5 – – – –

16 2,5 3,4 – – –

25 2,5 3,4 4,5 – –

35 2,5 3,4 4,5 5,5 –

50 to 185 2,5 3,4 4,5 5,5 8,0240 2,6 3,4 4,5 5,5 8,0

300 2,8 3,4 4,5 5,5 8,0

400 3,0 3,4 4,5 5,5 8,0

500 to 1000 3,2 3,4 4,5 5,5 8,0

Note: Any smaller conductor cross-section than those given in this table is not

recommended. However, if a smaller cross-section is needed, either the diameter of the

conductor shall be increased by a conductor screen, or the insulation thickness shall be

increased in order to limit, at the values calculated with the smallest conductor size given

in this table, the maximum electrical stresses applied to the insulation under test voltage.


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Old and New Core BS Core Colours

BS 6004 (PVC insulated PVC Sheathed Cables)

Cable Type Old Core Colour New Core Colour

Single Core Red or Black Brown or Blue

Two Core Red, Black Brown, Blue

Three Core Red, Yellow, Blue Brown, Black, Grey

BS 6500


Two Core Blue, Brown No Change

Three Core Green-Yellow, Blue, Brown No Change

Four Core Green-Yellow, Black, Blue, Brown Green-Yellow, Brown, Black, Grey

or Green-Yellow, Blue, Brown,

Black

Five Core Green-Yellow, Black, Blue, Brown, Green and Yellow, Blue, Brown,

Black Black, Grey

BS 6346, BS 5467, BS 6724


Single Core Red or Black Brown or Blue

Two Core Red, Black Brown, Blue

Three Core Red, Yellow, Blue Brown, Black, Grey

Four Core Red, Yellow, Blue, Black Blue, Brown, Black, Grey

Five Core Red, Yellow, Blue, Black, Green/Yellow, Blue, Brown

Green/Yellow Black, Grey

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Overhead conductors are manufactured in a variety of sizes and strandings and several different

materials. This range of choices enables selection of specific line conductors with

characteristics such as conductance, diameter, strength, weight & coefficient of thermal

expansion, stress strain, creep & thermal less of strength characteristics. Proper conductor

selection takes into account the interaction of these characteristics with requirements of

lines its voltage, capacity, load factor etc. These material are compared in the table given

below:

Material AAC AAAC ACSR Copper

Conductivity %IACS 61 53 20 97

Temperature co-efficient

for Resistance OHM-MM2/KM 0.00403 0.0036 0.0051 0.00331

Co-efficient of linear 10-6 23 23 12.96 17

expansion per ˚C

Ultimate tensile strength Mpa 160-200 295 1100-1344 414

Modulus of elasticity Gpa 70 70 162 125

Typical applications Short ACSR Low sag and Maximum

Span replacement high tensile current

with for strength capacity

maximum corrosive Severe

current atmosphere loading

capacity conditions

For Current ratings, size and dimensions, please refer to our catalogue. We also provide covered

conductors. Covered conductors with insulation are good for environments carrying pollution

and can withstand contact with conducting materials.


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Frequently Asked Questions

Cables can be divided into a large number of types based on a combination of classificationsas follows:

Voltage ratings low voltage, high voltage, extra high voltage cables, etc.

Conductor material Copper conductor or Aluminium conductor.

Insulating material Paper Insulated, PVC insulated, Rubber insulated, XLPE insulated, etc.

Armoured or Unarmoured cables.

Sheathing material as PVC Sheathed, Rubber Sheathed, Lead Sheathed, Aluminium Sheathed,

etc.

Number of cores as single core, two core, three core, three-and-a-half core, four core, multicore,

etc.

Cross-section of the conductor.

Type of conductor, solid, stranded, sector shaped, etc.

The details of various cable types can be checked in catalogues.

Should cables be single core or 3-core?

Single core cables can be cost-effective where impedance earthed systems are used which

require relatively small screen sizes so that the cost for three core cables is economical. This is

also true for large conductor sized cables. Single core cables are more easily water-blacked.

For 10/11 kV systems the trend is for 3-phase cables. At higher voltages and higher fault levels,

this issue of circulatory current in large screens of single core cables is a significant factor. The

subject therefore of 3-core vs single core is an important issue.

Which is best system, direct-buried or in-conduit, and what is its impact on cable

design?

In-conduit systems might enable simpler, low-cost cable designs to be used. In many densely

populated cities conduit systems are the only appropriate form of cabling, as it is impossible totake advantage of longer drum lengths with direct-buried systems. Due to frequent presence of

water in ducts, it becomes necessary to apply water barriers into the cable. On the other hand,

there is an increasing interest in direct-burying using modern installation methods.

What are the factors which reduce cable life?

Voltage surges

As with any electrical insulation, life expectancy is reduced when the insulation is subjected to

“over voltage”, in the form of surges and impulses. It is recommended that appropriate

protection devices be installed and the nature and frequency of all such occurrences be

monitored and recorded, so that protective measures can be installed.


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Excess operating temperatures

The cables are designed for a maximum operating temperature with limited overload periods as

defined in the relevant Standard. Changes in the environment, depth of cover, adjacent servicesand micro biological effects in the soil, can increase operating temperatures and thus reduce

cable life time. The circuit protection system also needs to ensure adequate protection from

excess current loading. The nature of frequency of all such occurrences should be monitored

and recorded.

To protect the investment and ensure the life of the cable, continuous monitoring of all key

circuits is required.

Adverse environmental conditions

Environmental conditions can adversely affect the conditions for the cable. Microbiological

effects from fungus and bacteria can induce increases in soil temperature thus affecting thetemperature of the cable and causing unseen overloads. Increases in the thermal conductivity

of the soil must be monitored and recorded.

Poor installation practices

The lifetime of cables is dependent on the cable being installed correctly. Poor

supervision/management and adverse installation conditions may cause the cable to be

damaged, over tensioned, twisted, bendings radii exceeded, excessive sidewall pressure

induced, over compaction of backfill and other life threatening factors.

Compatibility of design for cable and accessories

Poor co-ordination of designs will result in incorrect/incompatible accessories, fixing methods,

stresses induced by mechanical vibration, thermal movement and lack of compensation for

seismic conditions. It is essential that correct methods of fixing and environmental assessment

be undertaken to ensure the materials are not subjected to unforseen or unexpected stresses

in service.


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Conversion Tables

To Convert: Multiply by:

Mils to millimetres (1,000 mils=one inch).......................................................................................0.0254Inches to centimetres ...............................................................................................................................2.540

Centimetres to inches ............................................................................................................................0.3937

Feet to metres..........................................................................................................................................0.3048

Metres to feet .............................................................................................................................................3.281

Yards to metres........................................................................................................................................0.9144

Metres to yards........................................................................................................................................1.0936

Miles to kilometres.....................

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