Bare Conductors

Bare soft drawn stranded copper conductor
is used for grounding electrical system where higher conductivity and flexibility are required.

Over-head distribution power line
The conductor of these wires is made of:

  • bare hard drawn stranded copper conductor
  • bare hard drawn stranded aluminum (H-14) conductor ACC
  • bare hard drawn stranded aluminum (H-14) conductor with steel reinforced (ACSR)

Specification of Copper & Aluminum Conductors

Specifications

Copper

Aluminum

Resistivity at 20°C ohm mm 2/ meter

0.017241

0.028264

Specific gravity Kg/Dem 3

8 - 89

2.703

Coefficient of linear expansion /°C

17 x 10 - 6

23 x 10 – 6

Mass constant temperature /°C

0.00393

0.00403

Modulus of elasticity Kg/ mm 2

8520

6300

 

Assembly and Stranding of Conductor Wires
Aluminum & Copper Conductors
Factor Constants

Number of wires in stranded conductor

7

19

37

61

91

Assembly constant

3

5

7

9

11

Stranding constant by weight

7.091

19.34

37.74

62.35

93.26

 

Lay Ratios
Defined as ratios between the length of path which the wire draws in one cycle to the outer diameter of circle path.

 

Number of wires in stranded conductor
Lay Ratio
6 - wires layer
12 – wires layers
18 – wires layers
24 – wires layers
30 – wires layers
 

Min

Max

Min

Max

Min

Max

Min

Max

Min

Max

7

10

14

 

 

 

 

 

 

 

 

19

10

16

10

14

 

 

 

 

 

37

10

17

10

16

10

14

 

 

 

 

 

Aluminum Conductor Steel Reinforced (ACSR)
Stranding Constants

Number of Wires

Stranding Constants

by weight

Electrical resistance W / km

Aluminum

Steel

Aluminum

Steel

6

1

6.091

1.000

0.1692

26

7

26.56

7.032

0.03928

 

Lay Ratios for ACSR

Number of wires

Ratio of aluminum wire diameter to steel wire diameter

Lay ratio for steel core

Lay ratio for aluminum wire

6- wires layer

12- wire layer

Outside layer

Layer immediately beneath outside layer

Aluminum

 

Steel

 

Min

Max

Min

Max

Min

Max

Min

Max

6

1

1

-

-

-

-

10

14

-

-

26

7

1.286

13

28

-

-

10

14

10

16

 

Moduli of Elasticity and Coefficients of Linear Expansion (ACSR)

Number of wires

Final modulus of elasticity (practical)

Coefficient of linear expansion (calculated)

Aluminum

Steel

Kg/mm 2

Lb/in 2

/°C

/°F

6

1

8100

11.5 x 10 6

19.1 x 10 -6

10.6 x 10 -6

26

7

7700

10.9 x 10 6

18.9 x 10 -6

10.5 x 10 -6

 

Steel Wire Specifications

  • The steel strand shall be high density grade with class B coating in accordance with ASTM A 475 or equivalent.
  • Density of wire is 7.8 gm /am 2
  • Coefficient of linear expansion is 11.5 x 10 -6 /°C
  • The zinc coating on the steel wire is either by hot dip process or electrical process and must resist corrosion (the quantity of zinc according to the size of steel wire diameter cleared in separate cards attached to our catalogue).
  • The surface of the wire should be smooth, clean and completely free from dark spots, corrosied parts, any traces of Zn salt and non acceptable surface.

 

Stress

Stress – Strain Diagram for Wire Conductor

Yield Point

Tensile Working Stress

 

 

CALCULATED AREA
Stranding Constants (Area) – Table A 

Material

Number of Wires in Conductor

3

7

19

37

Copper-annealed

2.94118

6.88235

18.6471

36.2941

Hard-drawn

2.977

6.942

18.77

36.499

Cadmium-copper

2.977

6.942

18.77

36.499

The calculated (electrical) area of a stranded conductor is the area of a solid wire of equal resistance, obtained by multiplying the area of one of the wires by the appropriate stranding constant from Table A. these constants allow for the increase in length of each component wire, except that in the center, for laying up, the increase being of the order of 2 percent, depending on the lay of the wires.

 

RESISTANCE
Stranding Constants (Resistance) – Table B

Material

Number of Wires in Conductor

3

7

19

37

Copper-annealed

.3400

.145299

.0536278

.0275527

Hard-drawn

.3360

.1440

.05328

.027398

Cadmium-copper

.3360

.1440

.05328

.027398

Resistances are derived from the values of volume resistivity given in Table D and include the appropriate factor from Table B to allow for stranding where necessary. The International Electrotechnical Commission defines copper which has a resistivity at 20°C of 1/58 = .017241 ohm-mm 2 / m as having a conductivity of 100 per cent.

 

WEIGHTS
Stranding Constants (Weight) – Table C

Material

Number of Wires in Conductor

3

7

19

37

Copper-annealed

3.060

7.120

19.36

37.72

Hard-drawn

3.024

7.058

19.24

37.509

Cadmium-copper

3.024

7.058

19.24

37.509

The nominal weights of stranded conductors are obtained by multiplying the weight of one wire by the appropriate stranding constant from Table C. The density of high-conductivity annealed copper, adopted by the International Electrotechnical Commission, is 8.89g/cm 3 at 20°C. Densities for other materials are included in Table D.

Table D: Characteristics of Conductor Materials

 

Annealed Copper

Hard-drawn Copper

Cadmium Copper

Conductivity, per cent

… 100

97
(average)

79.2
(minimum)

Volume resistivity at 20°C

 

 

 

ohm-mm 2/m

Microhm-inch 3 … …

… … .017241*
(standard)
.67879

.01771 Ä
(average)
.69712

.021769
(maximum)
.85705

Mass resitivity at 20°C

 

 

 

ohm-gramme/m

ohm-pound/mile

 

… 15328
… 875.20

15741
898.83

.19472
1111.9

Resistance at 20°C

 

 

 

ohm-inch 2/mile

…043008

.044170

.054302

ohm-inch 2/1000 yd

…024437

.025096

.030854

ohm-inch 2/1000 ft

…0081455

.0083655

.010285

ohm-inch 2/km … …

 

17.241

17.71

21.769

Density at 20°C

 

 

 

Gramme/cm 3

… … 8.89

8.89

8.945

 

 

 

 

Weight

 

 

 

lb/ inch 2/mile

… …20349

20349

20475

lb/ inch 2/1000 yd

…11562

11562

11634

lb/ inch 2/1000 ft

…3854.1

3854.1

3877.9

Kg/mm 2/km

……8.89

8.89

8.945

 

 

 

 

Temperature coefficient of resistance at 20°C per °C

.00393

.00381

.0031

Coefficient of linear expansion at 20°C

 

 

 

per °C

…… ..17 x 10 6

17 x 10 6

17 x 10 6

per °F

…… ..9_444 x 10 6

9_444 x 10 6

9_444 x 10 6

 

 

 

 

Ultimate tensile stress

(approximate)

 

  

 

lb/inch 2

… … …36.000

60.000

90.000

kg/mm 2 … … …

25.3

42.2

63.3

 

 

 

 

Modulus of elasticity

 

 

 

lb/inch 2

… … …13 to 15 x 10 6

18 x 10 6

18 x 10 6

kg/mm 2

… … …9 to 10.5 x 10 3

12.66 x 10 3

12.66 x 10 3

 * For calculations, this value has been extended to .017241379
Ä Assumed average ultimate tensile strength: 27 tons/ inch2

 

Resistance Temperature Conversion
Table E: Constants and Reciprocals of Constants

For converting resistances between various temperatures and the standard temperature of 20 °C

Temperature °C

Annealed high conductivity copper

Hard-drawn high conductivity copper

Hard-drawn cadmium-copper

Muliplier constant

Reciprocat of constant

Muliplier constant

Reciprocat of constant

Muliplier constant

Reciprocat of constant

5

1.0626

0.9411

1.0606

0.9429

1.0488

0.9535

6

1.0582

0.9450

1.0563

0.9467

1.0454

0.9566

7

1.0538

0.9489

1.0521

0.9505

1.0420

0.9597

8

1.0495

0.9528

1.0479

0.9543

1.0386

0.9628

9

1.0452

0.9568

1.0437

0.9581

1.0353

0.9659

10

1.0409

0.9607

1.0396

0.9619

1.0320

0.9690

11

1.0367

0.9646

1.0355

0.9657

1.0287

0.9721

12

1.0325

0.9686

1.0314

0.9695

1.0254

0.9752

13

1.0283

0.9725

1.0274

0.9733

1.0222

0.9783

14

1.0241

0.9764

1.0234

0.9771

1.0189

0.9814

15

1.0200

0.9804

1.0194

0.9810

1.0157

0.9845

16

1.0160

0.9843

1.0155

0.9848

1.0125

0.9876

17

1.0119

0.9882

1.0116

0.9886

1.0094

0.9907

18

1.0079

0.9921

1.0077

0.9924

1.0062

0.9938

19

1.0039

0.9961

1.0038

0.9962

1.0031

0.9969

20

1.0000

1.0000

1.0000

1.0000

1.0000

1.0000

21

0.9961

1.0093

0.9962

1.0038

0.9969

1.0031

22

0.9922

1.0079

0.9924

1.0076

0.9938

1.0062

23

0.9883

1.0118

0.9887

1.0114

0.9908

1.0093

24

0.9845

1.0157

0.9850

1.0152

0.9877

1.0124

25

0.9807

1.0197

0.9813

1.0191

0.9847

1.0155

26

0.9770

1.0236

0.9777

1.0229

0.9817

1.0186

27

0.9732

1.0275

0.9740

1.0267

0.9788

1.0217

28

0.9695

1.0314

0.9704

1.0305

0.9758

1.0248

29

0.9658

1.0354

0.9668

1.0343

0.9728

1.0279

30

0.9622

1.0393

0.9633

1.0381

0.9699

1.0310

35

0.9443

1.0589

0.9459

1.0572

0.9556

1.0465

40

0.9271

1.0786

0.9292

1.0762

0.9416

1.0620

45

0.9105

1.0982

0.9130

1.053

0.9281

1.0775

50

0.8945

1.1179

0.8945

1.1143

0.9149

1.0930

55

0.8791

1.1375

0.8823

1.1334

0.9021

1.1085

60

0.8642

1.1572

0.8678

1.1524

0.8897

1.1240

65

0.8498

1.1768

0.8536

1.1715

0.8776

1.1395

 

 

 

 

 

 

 

70

0.8358

1.1965

0.8400

1.1905

0.8658

1.1550

 

The above constants are based on the standard expressions R = R 20 [R 1 + a (20-t)] and

R
R 20 =
ـــــــــــــــــــــــــــــــــــــــــــــ
[ 1 + a (20-t)]

 

[ 1 + a (20-t)]

Rt = resistance at temperature t°C R 20 = resistance at 20°C
a = standard resistance temperature coefficient at 20°C (see table D)    

The multipilier constant in the table is calculated from

1
ــــــــــــــــــــــــــــــــــــ
[ 1 + a (20-t)]

 

 

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