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Wednesday, 23 October 2013

Cable current rating


Cable current rating 
cable current rating


Current carrying capacity is defined as the maximum amperage that can flow through an insulated wire or cable before reaching a temperature high enough to melt the insulation or the conductor.
Amperage refers to the strength of the current in its unit of measure. One ampere is the current that one volt of electricity can send through one ohm of resistance.
The amount of current a wire can carry is determined by several factors, including:
Conductor Size - Larger circular mil area increases current carrying capacity.
Insulation – Higher maximum temperature ratings for insulation allow for higher current carrying capacity. Heat generated by the current cannot exceed the maximum temperature rating of the insulation.
Ambient Temperature - Higher surrounding temperatures lower current carrying capacity. Less heat can be produced by the current before reaching the maximum temperature rating of the insulation.
Conductor Number – Increased numbers of individually insulated conductors bundled together decrease heat dissipation, lowering current carrying capacity.
Installation Conditions – Restricted heat dissipation faced by conductors installed in conduit, duct, trays, or raceways lowers current carrying capacity. However, proper ventilation methods like forced air cooling can mitigate this problem.
Basic assumptions and conditions of installation:
1) Maximum Conductor Temperature:  90° C
2) Ambient Ground Temperature:         30° C
3) Ambient Air Temperature:                 40° C
4) Thermal resistivity of soil:                150° C. Cm/W
Depth of laying (to the highest point of the cables laid direct in the ground)
1)    3.3, 6.6 & 11kV Cables:                      90 cm
2)    22 and 33kV Cables:                            105 cm
3) Maximum Conductor temperature at the end of a short circuit:  250° C
To obtain the maximum current carrying capacity of a cable operating at different conditions from the standard, various rating factors are to be multiplied.
Table-1: current rating (ac) for twin 650/1100volt armoured/unarmoured aluminium/copper PVC cable IS: 1554
Size in
Laid direct in the ground
In ducts
In air
mm2
Al
Cu
Al
Cu
Al
Cu
1.5
18
23
16
20
16
20
2.5
25
32
21
27
21
27
4
32
41
27
35
27
35
6
40
50
34
44
35
45
10
55
70
45
58
47
60
16
70
90
58
75
59
78
25
90
115
76
97
78
102
35
110
140
92
120
99
125
50
135
165
115
145
125
155
70
160
205
140
180
150
195
95
190
240
170
215
185
230
120
210
275
190
235
210
265
150
240
310
210
270
240
305
185
275
350
240
300
275
350
240
320
405
275
345
325
410
300
355
450
305
385
365
465

Table-2: current rating (ac) for three-four 650/1100volt armoured/unarmoured aluminium/ copper PVC cable IS: 1554
Size in
Laid direct in the ground
In ducts
In air
mm2
Al
Cu
Al
Cu
Al
Cu
1.5
16
21
14
17
13
17
2.5
21
27
18
24
18
24
4
28
36
23
30
23
30
6
35
45
30
38
30
39
10
46
60
39
50
40
52
16
60
77
50
64
51
66
25
76
99
63
81
70
90
35
92
120
77
99
86
110
50
110
145
95
125
105
135
70
135
175
115
150
130
165
95
165
210
140
175
155
200
120
185
240
155
195
180
230
150
210
270
175
225
205
265
185
235
300
200
255
240
305
240
275
345
235
295
280
355
300
305
385
260
335
315
400

Table-3: current rating (ac) of 1.1 KV XLPE aluminium conductor power cable
Size in
Single core in 3 cables
Multi core
mm2
In ground
In air
In ground
In air
6
45
40
43
40
10
59
53
57
53
16
76
70
78
70
25
99
115
95
99
35
117
140
116
117
50
138
170
140
140
70
168
210
170
176
95
204
255
200
221
120
230
300
225
258
150
265
342
255
294
185
295
385
285
339
240
340
450
325
402
300
390
519
370
461

Table-4: current rating (ac) for three core armoured XLPE cable, IS: 7098
Size
Voltage 3.8/6.6, 6.35/11, 11/11 KV
mm2
Copper conductor
Aluminium conductor

In ground
In duct
In air
In ground
In duct
In air
25
120
105
135
95
82
105
35
145
125
165
115
97
125
50
170
150
195
130
115
150
70
210
180
240
160
140
190
95
250
215
295
190
165
230
120
280
240
335
220
190
260
150
310
270
380
245
210
295
185
350
305
430
275
240
335
240
400
350
500
315
275
395
300
445
390
570
355
310
450
400
500
440
650
400
350
520

Table-5: current rating (ac) for three single core armoured XLPE cable, IS: 7098 part-2

Size
Voltage 12.7/22,19/33
Aluminium conductor
In ground
In duct
In air
mm2
Trefoil
Flat
Trefoil
Flat
Trefoil
Flat
25
100
100
90
90
120
120
35
115
120
100
100
145
145
50
135
140
120
120
170
175
70
165
170
145
150
215
220
95
195
200
170
175
260
265
120
225
225
295
195
300
300
150
250
250
215
215
340
340
185
280
280
240
240
385
385
240
320
315
275
275
450
450
300
355
345
305
300
510
500
400
400
385
345
330
600
570

Book reference :
A practical guide to cable installation and tool box talk
Available with book shop and -


Price: Rs. 375/- excluding delivery charges

3 comments:

  1. I admired those who has able to create a blog as wonderful as this! You are truly a hard working person. Keep up the good work and keep on posting.

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    ReplyDelete
  2. Pl share for DC cables also. Multistrand single core copper cables..size up to 300 sq mm...

    ReplyDelete