Handbook of Electrical Engineering

208 HANDBOOK OF ELECTRICAL ENGINEERING

Table 9.22. Land based Installations. 3800/6600 V. 6350/11,000 V. 8700/15,000 V. Cu/XLPE/PVC/SWA/
PVC three cores

Nominal conductor
area (mm^2 )

Air Ducts Direct

buried

Notes

25 145 125 140 Thermal resistivity of soil is 1.2◦Cm/W

35 175 150 170

50 220 180 210 Ambient air temp. is 25◦C.

70 270 215 255 Depth of laying cables is 0.5 m

95 330 255 300

120 375 290 340 Standard ground temp. is 15◦C

150 430 330 380

185 490 370 430 Conductor surface temp. is 90◦C.

240 570 425 490

300 650 470 540

400 740 530 600

Ambient air temperature◦C 2530354045505560
Rating factorKairfor cables laid in air 1.0 0.96 0.92 0.88 0.84 0.79 0.73 0.68
Ground temperature◦C 10152025303540
Rating factorKgrdfor cables laid in the ground 1.03 1.0 0.97 0.93 0.89 0.86 0.82

Table 9.23. Marine and offshore 600/1000 V Cu/EPR/CSP/GSWB or PBWB/CSP or PVC

installations. Cables run on open trays or enclosed in air. 1 to 6×single, 3 or 4 cores

Nominal conductor

area (mm^2 )

Single

cores

3and4

cores

Notes

1.0 17 12 Ambient air temperature is 45◦C

1.5 21 15

2.5 30 21

4 40 29 Conductor surface temperature is 90◦C.

65136

10 71 50

16 95 67

25 125 89

35 155 105

50 190 135

70 240 170

95 290 205

120 340 240

150 385 270

185 440 305

240 520 365

300 590 415

400 670 470

Ambient air tem- 35 40 45 50 55 60 65 70 75 80

perature◦C

Rating factor for 1.11 1.05 1.0 0.94 0.88 0.82 0.75 0.69 0.58 0.47

cables laid in air