Page 581 - Industrial Power Engineering and Applications Handbook

Arrangement No. of racks No. of circuits per rack
pJ& & 2 3
25 mm
&,& + i. 1 1 .oo 0.98 .~
0.96
i && 2 I .oo . 0.95 0.93
1 .oo
0.92
0.94
3
1 .oo
2d 1 6 0.93 0.90

Table A16.21 Rating factors for groups of twin and multicore Table A16.25 Rating factors for variation in thermal resistivity
cables laid directly in ground in horizontal formation of soil (multicore cables laid directly in the ground)

No. of Rating factor for axial spacing Nominal Rating factor for value of thermal resistivity of soil in
.~
Touching 15cm 30 cm 45 cm 60cm area of C cm/W
conductor
~~
2 0.79 0.82 0.87 0.90 0.91 (mm’) 100 120 150 200 250 300
3 0.69 0.75 0.79 0.83 0.86
4 0.62 0.69 0.74 0.79 0.82 25 1.14 1.08 1.00 0.91 0.84 0.78
6 0.54 0.61 0.69 0.75 0.78 35 1.15 1.08 1.00 0.9 1 0.84 0.77
8 0.50 0.57 0.66 0.72 0.76 50 1.15 1.08 1.00 0.9 1 0.84 0.77
70 1.15 1.08 1.00 0.90 0.83 0.76
95 1.15 1.08 1.00 0.90 0.83 0.76
120 1.17 1.09 1.00 0.90 0.82 0.76
Table A16.22 Group rating factors for circuits of two single-
core cables, side by side and touching, in horizontal formation, 150 1.17 1.09 1.00 0.90 0.82 0.76
laid directly in ground 185 1.18 1.09 1.00 0.89 0.81 0.75
240 1.18 1.09 1.00 0.89 0.81 0.75
No. of Spacing (between centres of circuits) 300 1.18 1.09 1.00 0.89 0.81 0.75
circuits Touching 15 cm 30 cm 45 cm 60 cm 400 1.19 1.10 1.00 0.89 0.81 0.75
500 1.21 1.10 1.00 0.89 0.81 0.75
2 0.79 0.86 0.91 0.93 0.95 630 1.22 1.10 1.00 0.89 0.81 0.74
3 0.69 0.78 0.84 0.88 0.91 ~~ ~~
4 0.64 0.73 0.81 0.86 0.88
6 0.56 0.67 0.77 0.83 0.87
8 0.51 0.65 0.75 0.82 0.86
Table A16.26 Rating factors for variation in thermal resistivity
of soil, three single-core cables laid directly in the ground
(three cables in trefoil, touching)
Table A16.23 Group rating factors for circuits of three single
core cables in trefoil and touching, horizontal formation laid directly Nominal Rating for value of thermal resistivity of soil in
in ground area of C cm/W
conductor
No. of Spucing (Between centres of circuits) (mm’) 100 120 150 200 250 300
circuits Touching 15 cm 30 ern 45 ern 60 cm
25 1.19 1.09 1.00 0.88 0.80 0.74
2 0.78 0.81 0.85 0.88 0.90 35 1.20 1.09 1.00 0.88 0.80 0.74
3 0.68 0.71 0.77 0.81 0.83 50 1.20 1.09 1.00 0.88 0.80 0.74
4 0.61 0.65 0.72 0.76 0.79 70 1.21 1.10 1.00 0.88 0.80 0.74
6 0.53 0.58 0.66 0.71 0.76 95 1.22 1.10 1.00 0.88 0.80 0.74
8 0 48 0.54 0.62 0.67 0.72
I20 1.22 1.10 1.00 0.88 0.79 0.74
150 1.22 1.10 1.00 0.88 0.79 0.73
Table A16.24 Rating factor for groups of twin and multicore 185 1.22 1.10 1.00 0.88 0.79 0.73
cables laid directly in ground in tier formation
240 1.22 1.10 1.00 0.88 0.79 0.73
300 1.22 1.10 1.00 0.88 0.79 0.72
No. of Rating factor for axial spacing
.~ 400 1.24 1.11 1.00 0.88 0.79 0.72
circuits Touching 15 cm 30 cm 45 cm 60 cm 500 1.24 1.11 1.00 0.88 0.79 0.72
4 0.60 0.67 0.73 0.76 0.78 630 to 1.24 1.11 1.00 0.88 0.79 0.72
6 0.51 0.57 0.63 0.67 0.69 1000
8 0.45 0.51 0.57 0.57 0.61
Courtesy: CCI