Saturday, March 29, 2014

Current carrying capacity of busbars

The current-carrying capacity of a busbar is usually determined by the maximum temperature at which the bar is permitted to operate, as defined by national and international standards such as British Standard BS 159, American Standard ANSI C37.20, etc. These standards give maximum temperature rises as well as maximum ambient temperatures.

BS 159 stipulates a maximum temperature rise of 50°C above a 24 hour mean ambient temperature of up to 35°C, and a peak ambient temperature of 40°C.

ANSI C37.20 alternatively permits a temperature rise of 65°C above a maximum ambient of 40°C, provided that silver-plated (or acceptable alternative) bolted terminations are used. If not, a temperature rise of 30°C is allowed.

 

A very approximate method of estimating the current carrying capacity of a copper busbar is to assume a current density of 2 A/mm2 (1250 A/in2) in still air. This method should only be used to estimate a likely size of busbar, the final size being chosen after consideration has been given to the calculation methods. Refer catalogue of manufacturers.

The more popular thumb rule being followed in India is to assume current density of 1.0 Amps / Sq.mm for Aluminium and 1.6 Amps for Copper for any standard rectangular conductor profile.

Current carrying capacity of Cu busbar

Size in mm

Area sqmm

Weight/ km

current carrying capacity in amp ( copper ) at 35 deg.C

AC ( no. of bus)

DC ( no. of bus)

I

II

III

II II

I

II

III

II II

12X2

24

0.209

110

200

115

205

15X2

30

0.262

140

200

145

245

15X3

75

0.396

170

300

175

305

20X2

40

0.351

185

315

190

325

20X3

60

0.529

220

380

225

390

20X5

100

0.882

295

500

300

510

25X3

75

0.663

270

460

275

470

25X5

125

1.11

350

600

355

610

30X3

90

0.796

315

540

320

560

30X5

150

1.33

400

700

410

720

40X3

120

1.06

420

710

430

740

40X5

200

1.77

520

900

530

930

40X10

400

3.55

760

1350

1850

2500

770

1400

2000

50X5

250

2.22

630

1100

1650

2100

650

1150

1750

50X10

500

4.44

920

1600

2250

3000

960

1700

2500

60X5

300

2.66

760

1250

1760

2400

780

1300

1900

2500

60X10

600

5.33

1060

1900

2600

3500

1100

2000

2800

3600

80X5

400

3.55

970

1700

2300

3000

1000

1800

2500

3200

80X10

800

7.11

1380

2300

3100

4200

1450

2600

3700

4800

100X5

500

4.44

1200

2050

2850

3500

1250

2250

3150

4050

100X10

1000

8.89

1700

2800

3650

5000

1800

3200

4500

5800

120X10

1200

10.7

2000

3100

4100

5700

2150

3700

5200

6700

160X10

1600

14.2

2500

3900

5300

7300

2800

4800

6900

9000

200X10

2000

17.8

3000

4750

6350

8800

3400

6000

8500

10000