The current carrying capacity of copper or aluminum conductors or wires or cables depend on number of cores, method of sheathing like PVC or XLPE and method of laying like ground laying, Dust laying or Air Laying.. But all practical purpose the current carrying capacity is within 3% of the any current carrying rating. Hence, for all practical purpose the maximum safe value current is given here.
| Sl. No | Cond. Area in MM | Copper Conductor | Aluminum Conductor |
|---|---|---|---|
|
1 |
0.5 |
3 |
- |
|
2 |
0.75 |
6 |
- |
|
3 |
1.0 |
10 |
- |
|
4 |
1.5 |
16 |
13 |
|
5 |
2.5 |
20-25 |
18 |
|
6 |
4.0 |
25-32 |
23 |
|
7 |
6.0 |
40 |
30 |
|
8 |
10.0 |
63 |
40 |
|
9 |
16 |
98 |
51 |
|
10 |
25 |
129 |
70 |
|
11 |
35 |
158 |
86 |
|
12 |
50 |
198 |
105 |
|
13 |
70 |
245 |
130 |
|
14 |
95 |
292 |
155 |
|
15 |
120 |
344 |
180 |
|
16 |
150 |
391 |
205 |
|
17 |
185 |
448 |
240 |
|
18 |
240 |
528 |
280 |
|
19 |
300 |
608 |
315 |
|
20 |
400 |
726 |
375 |
|
21 |
500 |
830 |
585 |
Factors affecting the Current Rating
Basic assumption and conditions of installation
(1)Max. Conductor temperature at continuous operation – 90OC
(2) Ambient Air temperature – 40 degree C
(3) Ground temperature – 30 degree C
(4) Thermal Resistivity of soil – 150 degree C Cm/W
(5) Depth of laying – 750 mm
(6) Max. Conductor temperature for short circuit – 250 degree C
Rating Factors for Variation in Ground Temperature
| Ground temperature OC | 15 | 20 | 25 | 30 | 35 | 40 |
| Rating Factor | 1.12 | 1.08 | 1.03 | 1.00 | 0.96 | 0.91 |
Rating Factors for Variation in Ambient Air Temperature
| Air temperature OC | 25 | 30 | 35 | 40 | 45 | 50 |
| Rating Factor | 1.14 | 1.10 | 1.04 | 1.00 | 0.95 | 0.90 |
Rating factors cables laid directly laid in ground in horizontal formation
No. of Cables | Distance of Cables | ||||
Touching | 15 cm | 30 cm | 45 cm | ||
2 | 0.79 | 0.82 | 0.87 | 0.90 | |
3 | 0.69 | 0.75 | 0.79 | 0.83 | |
4 | 0.62 | 0.69 | 0.74 | 0.79 | |
5 | 0.58 | 0.65 | 0.72 | 0.76 | |
6 | 0.54 | 0.61 | 0.69 | 0.75 | |
Rating factor for variation in depth of laying in ground
|
Depth of laying |
Size |
|||
|
Upto 25 mm2 |
25 to 300 mm2 |
Above 300 mm2 |
||
|
75 cm |
1.00 |
1.00 |
1.00 |
|
|
90 cm |
0.99 |
0.98 |
0.97 |
|
|
105 cm |
0.98 |
0.97 |
0.96 |
|
|
120 cm |
0.97 |
0.96 |
0.95 |
|
|
150 cm |
0.96 |
0.94 |
0.92 |
|
|
180 > |
0.95 |
0.93 |
0.91 |
|