Annex B
(informative)
Tabulated continuous current ratings for cables having extruded insulation and a rated voltage from 3,6/6 kV up to 18/30 kV
B.1 General
This annex deals solely with the steady-state continuous current ratings of single-core and three-core cables having extruded insulation. The tabulated current ratings provided in this annex have been calculated for cables having a rated voltage of 6/10 kV and constructions as detailed in Clause B.2.
These ratings can be applied to cables of similar constructions in the voltage range of 3,6/6 kV to 18/30 kV.
Some parameters such as screen cross-sectional area and oversheath thickness have an influence on the rating of large cables. In addition, the method of screen bonding has to be taken into account in the rating of single-core cables.
The tabulated current ratings have been calculated using the methods set out in IEC 60287.
NOTE 1 For cyclic current ratings, see IEC 60853.
NOTE 2 For short-circuit temperature limits, see IEC 60986.
B.2 Cable constructions
The cable constructions and dimensions for which current ratings have been tabulated are based on those given in this standard. The constructions and dimensions used are not related to specific national designs but reflect different model cables. Armoured three-core cables are assumed to have flat wire armour and single-core cables are assumed to be unarmoured. All the cables have copper tape core screens except the single-core XLPE insulated cable, which has a copper wire screen. The nominal cross-sectional areas of the screens for the model cables is given in Table B.1.
Table B.1 – Nominal screen cross-sectional areas
Nominal area of conductor, mm²
|
16
|
25
|
35
|
50
|
70
|
95
|
120
|
150
|
185
|
240
|
300
|
400
|
Nominal cross-sectional area of screen, per core, mm²
|
||||||||||||
EPR insulated cable
|
3
|
3
|
4
|
4
|
4
|
5
|
5
|
5
|
6
|
6
|
7
|
8
|
XLPE insulated cable
|
16
|
16
|
16
|
16
|
16
|
16
|
16
|
25
|
25
|
25
|
25
|
35
|
The oversheath is taken to be polyethylene for the single core cables and PVC for the three- core cables.
B.3 Temperatures
The maximum conductor temperature for which the tabulated cable ratings have been calculated is 90 °C.
The reference ambient temperatures assumed are as follows:
– for cables in air: 30 °C
– for buried cables, either directly in the soil
or in ducts in the ground: 20 °C
Correction factors for other ambient temperatures are given in Tables B.10 and B.11.
The current ratings for cables in air do not take account of the increase, if any, due to solar or other infra-red radiation. Where the cables are subject to such radiation, the current rating should be derived by the methods specified in IEC 60287.
B.4 Soil thermal resistivity
The tabulated current ratings for cables in ducts or direct in the ground relate to a soil thermal resistivity of 1,5 K.m/W. Information on the likely soil thermal resistivity in various
countries is given in IEC 60287-3-1. Correction factors for other values of thermal resistivity are given in Tables B.14 to B.17.
It is assumed that the soil properties are uniform, no allowance has been made for the possibility of moisture migration which can lead to a region of high thermal resistivity around the cable. If partial drying-out of the soil is foreseen, the permissible current rating should be derived by the methods specified in IEC 60287.
B.5 Methods of installation
Current ratings are tabulated for cables installed in the following conditions.
B.5.1 Single-core cables in air
The cables are assumed to be spaced at least 0,5 times the cable diameter from any vertical surface and installed on brackets or ladder racks as follows:
a) three cables in trefoil formation touching throughout their length;
b) three cables in horizontal flat formation touching throughout their length;
c) three cables in horizontal flat formation with a clearance of one cable diameter.

where De is the external diameter of the cable.
Figure B.1 – Single-core cables in air
B.5.2 Single-core cables buried direct
Current ratings are given for cables buried direct in the ground at a depth of 0,8 m under the following conditions:
a) three cables in trefoil formation touching throughout their length;
b) three cables in horizontal flat formation with a clearance of one cable diameter, De. a) b)
Figure B.2 – Single-core cables buried direct
The cable depth is measured to the cable axis or centre of the trefoil group.
B.5.3 Single-core cables in earthenw are ducts
Current ratings are given for cables in earthenware ducts buried at a depth of 0,8 m with one cable per duct as follows:
a) three cables in trefoil ducts touching throughout their length;
b) three cables in horizontal flat formation, ducts touching throughout their length. a) b)
Figure B.3 – Single-core cables in earthenw are ducts
The ducts are assumed to be earthenware having an inside diameter of 1,5 times the outside diameter of the cable and a wall thickness equal to 6 % of the duct inside diameter. The ratings are based on the assumption that the ducts are air filled. If the ducts have been filled with a material such as Bentonite, then it is usual to adopt the current ratings for cables buried direct.
The tabulated ratings may be applied to cables in ducts having an inside diameter of between
1,2 and 2 times the outside diameter of the cables. For this range of diameters the variation in the rating is less than 2 % of the tabulated value.
B.5.4 Three-core cables
Current ratings are given for three-core cables installed under the following conditions:
a) single cable in air spaced at least 0,3 times the cable diameter from any vertical surface;
b) single cable buried direct in the ground at a depth of 0,8 m;
c) single cable in a buried earthenware duct having dimensions calculated in the same manner as for the single-core cables in ducts. The depth of burial of the duct is 0,8 m.
a) b) c)
Figure B.4 – Three-core cables
B.6 Screen bonding
All the tabulated ratings for single-core cables assume that the cable screens are solidly bonded, i.e. bonded at both ends of the cables.
B.7 Cable loading
The tabulated ratings relate to circuits carrying a balanced three-phase load at a rated frequency of 50 Hz.
B.8 Rating factors for grouped circuits
The tabulated current ratings apply to a set of three single-core cables or one three-core cable forming a three-phase circuit. When a number of circuits are installed in close proximity the rating should be reduced by the appropriate factor from Tables B.18 to B.23.
These rating factors should also be applied to groups of parallel cables forming the same circuit. In such cases, attention should also be given to the arrangement of the cables to ensure that the load current is shared equally between the parallel cables.
B.9 Correction factors
The correction factors given in Tables B.10 to B.23 for temperature, installation conditions and grouping are averages over a range of conductor sizes and cable types. For particular cases, the correction factor may be calculated using the methods in IEC 60287-2-1.
Table B.2 – Current ratings for single-core cables w ith XLPE insulation – Rated voltage 3,6/6 kV to 18/30 kV * –
Copper conductor
Nominal area of
conductor
|
Buried direct
in the ground
|
In single-w ay ducts
|
In air
|
||||
Trefoil
|
Flat spaced
|
Trefoil ducts
|
Flat
touching ducts
|
Trefoil
|
Flat
touching
|
Flat spaced
|
|
|
|||||||
mm2
|
A
|
A
|
A
|
A
|
A
|
A
|
A
|
16
25
35
50
70
95
120
150
185
240
300
400
|
109
140
166
196
239
285
323
361
406
469
526
590
|
113
144
172
203
246
293
332
366
410
470
524
572
|
103
132
157
186
227
271
308
343
387
447
504
564
|
104
133
159
188
229
274
311
347
391
453
510
571
|
125
163
198
238
296
361
417
473
543
641
735
845
|
128
167
203
243
303
369
426
481
550
647
739
837
|
150
196
238
286
356
434
500
559
637
745
846
938
|
Maximum conductor temperature 90 °C
Ambient air temperature 30 °C Ground temperature 20 °C Depth of laying 0,8 m
Thermal resistivity of soil 1,5 K.m/W
Thermal resistivity of earthenware ducts 1,2 K.m/W Screens bonded at both ends.
|
|||||||
* Current rating calculated for cables having a rated voltage of 6/10 kV.
|
Table B.3 – Current ratings for single-core cables w ith XLPE insulation – Rated voltage 3,6/6 kV to 18/30 kV * –
Aluminium conductor
Nominal area of
conductor
|
Buried direct in the ground
|
In single-w ay ducts
|
In air
|
||||
Trefoil
|
Flat spaced
|
Trefoil ducts
|
Flat
touching ducts
|
Trefoil
|
Flat
touching
|
Flat spaced
|
|
|
|||||||
mm2
|
A
|
A
|
A
|
A
|
A
|
A
|
A
|
16
25
35
50
70
95
120
150
185
240
300
400
|
84
108
129
152
186
221
252
281
317
367
414
470
|
88
112
134
157
192
229
260
288
324
373
419
466
|
80
102
122
144
176
210
240
267
303
351
397
451
|
81
103
123
146
178
213
242
271
307
356
402
457
|
97
127
154
184
230
280
324
368
424
502
577
673
|
99
130
157
189
236
287
332
376
432
511
586
676
|
116
153
185
222
278
338
391
440
504
593
677
769
|
Maximum conductor temperature 90 °C
Ambient air temperature 30 °C Ground temperature 20 °C Depth of laying 0,8 m
Thermal resistivity of soil 1,5 K.m/W
Thermal resistivity of earthenware ducts 1,2 K.m/W Screens bonded at both ends.
|
|||||||
* Current rating calculated for cables having a rated voltage of 6/10 kV.
|
Table B.4 – Current ratings for single-core cables w ith EPR insulation – Rated voltage 3,6/6 kV to 18/30 kV * –
Copper conductor
Nominal area of
conductor
|
Buried direct in the ground
|
In single-w ay ducts
|
In air
|
||||
Trefoil
|
Flat spaced
|
Trefoil ducts
|
Flat
touching ducts
|
Trefoil
|
Flat
touching
|
Flat spaced
|
|
mm2
|
A
|
A
|
A
|
A
|
A
|
A
|
A
|
16
25
35
50
70
95
120
150
185
240
300
400
|
106
136
162
192
234
280
319
357
403
467
526
597
|
109
140
167
198
242
289
329
369
417
484
545
618
|
99
128
153
181
222
266
303
341
386
449
509
580
|
100
129
154
183
224
269
306
344
390
454
515
588
|
116
153
186
224
280
343
398
454
522
619
712
825
|
119
156
190
229
287
352
407
465
534
634
728
843
|
138
181
221
266
334
409
474
540
621
736
843
977
|
Maximum conductor temperature 90 °C
Ambient air temperature 30 °C Ground temperature 20 °C Depth of laying 0,8 m
Thermal resistivity of soil 1,5 K.m/W
Thermal resistivity of earthenware ducts 1,2 K.m/W Screens bonded at both ends.
|
|||||||
* Current rating calculated for cables having a rated voltage of 6/10 kV.
|
Table B.5 – Current ratings for single-core cables w ith EPR insulation – Rated voltage 3,6/6 kV to 18/30 kV * –
Aluminium conductor
Nominal area of
conductor
|
Buried direct in the ground
|
In single-w ay ducts
|
In air
|
||||
Trefoil
|
Flat spaced
|
Trefoil ducts
|
Flat
touching ducts
|
Trefoil
|
Flat
touching
|
Flat spaced
|
|
mm2
|
A
|
A
|
A
|
A
|
A
|
A
|
A
|
16
25
35
50
70
95
120
150
185
240
300
400
|
82
105
126
149
182
217
247
277
314
364
411
471
|
84
109
130
153
188
224
256
287
325
377
426
487
|
77
99
118
140
172
206
235
264
300
350
397
456
|
78
100
120
142
174
208
238
267
303
354
401
462
|
90
119
144
174
218
266
309
352
406
483
556
651
|
92
121
147
178
223
273
317
361
417
495
570
667
|
107
141
171
207
259
317
368
419
484
575
659
770
|
Maximum conductor temperature 90 °C Ambient air temperature 30 °C Ground temperature 20 °C Depth of laying 0,8 m
Thermal resistivity of soil 1,5 K.m/W
Thermal resistivity of earthenware ducts 1,2 K.m/W Screens bonded at both ends.
|
|||||||
* Current rating calculated for cables having a rated voltage of 6/10 kV.
|
Table B.6 – Current rating for three-core XLPE insulated cables – Rated voltage 3,6/6 kV to 18/30 kV * –
Copper conductor, armoured and unarmoured
Nominal area of conductor
|
Unarmoured
|
Armoured
|
||||
Buried direct in ground
|
In a buried duct
|
In air
|
Buried direct in ground
|
In a buried duct
|
In air
|
|
mm2
|
A
|
A
|
A
|
A
|
A
|
A
|
16
25
35
50
70
95
120
150
185
240
300
400
|
101
129
153
181
221
262
298
334
377
434
489
553
|
87
112
133
158
193
231
264
297
336
390
441
501
|
109
142
170
204
253
304
351
398
455
531
606
696
|
101
129
154
181
220
263
298
332
374
431
482
541
|
88
112
134
158
194
232
264
296
335
387
435
492
|
110
143
172
205
253
307
352
397
453
529
599
683
|
Maximum conductor temperature 90 °C
Ambient air temperature 30 °C Ground temperature 20 °C Depth of laying 0,8 m
Thermal resistivity of soil 1,5 K.m/W
Thermal resistivity of earthenware ducts 1,2 K.m/W
|
||||||
* Current rating calculated for cables having a rated voltage of 6/10 kV.
|
Table B.7 – Current rating for three-core XLPE insulated cables – Rated voltage 3,6/6 kV to 18/30 kV * –
Aluminium conductor, armoured and unarmoured
Nominal area of conductor
|
Unarmoured
|
Armoured
|
||||
Buried direct in ground
|
In a buried duct
|
In air
|
Buried direct in ground
|
In a buried duct
|
In air
|
|
mm2
|
A
|
A
|
A
|
A
|
A
|
A
|
16
25
35
50
70
95
120
150
185
240
300
400
|
78
100
119
140
171
203
232
260
294
340
384
438
|
67
87
103
122
150
179
205
231
262
305
346
398
|
84
110
132
158
196
236
273
309
355
415
475
552
|
78
100
119
140
171
204
232
259
293
338
380
432
|
68
87
104
123
150
180
206
231
262
304
343
393
|
85
111
133
159
196
238
274
309
354
415
472
545
|
Maximum conductor temperature 90 °C
Ambient air temperature 30 °C Ground temperature 20 °C Depth of laying 0,8 m
Thermal resistivity of soil 1,5 K.m/W
Thermal resistivity of earthenware ducts 1,2 K.m/W
|
||||||
* Current rating calculated for cables having a rated voltage of 6/10 kV.
|
Table B.8 – Current rating for three-core EPR insulated cables – Rated voltage 3,6/6 kV to 18/30 kV * –
Copper conductor, armoured and unarmoured
Nominal area of conductor
|
Unarmoured
|
Armoured
|
||||
Buried direct in ground
|
In a buried duct
|
In air
|
Buried direct in ground
|
In a buried duct
|
In air
|
|
|
||||||
mm2
|
A
|
A
|
A
|
A
|
A
|
A
|
16
25
35
50
70
95
120
150
185
240
300
400
|
98
125
150
176
216
258
292
328
371
429
482
545
|
84
109
130
154
189
227
258
291
330
384
434
494
|
104
135
164
195
243
296
339
385
441
519
590
678
|
98
125
150
177
216
257
292
327
368
424
475
534
|
85
109
131
155
190
227
259
291
328
381
429
485
|
104
136
164
197
244
296
339
385
439
513
583
666
|
Maximum conductor temperature 90 °C
Ambient air temperature 30 °C Ground temperature 20 °C Depth of laying 0,8 m
Thermal resistivity of soil 1,5 K.m/W
Thermal resistivity of earthenware ducts 1,2 K.m/W
|
||||||
* Current rating calculated for cables having a rated voltage of 6/10 kV.
|
Table B.9 – Current rating for three-core EPR insulated cables – Rated voltage 3,6/6 kV to 18/30 kV * –
Aluminium conductor, armoured and unarmoured
Nominal area of conductor
|
Unarmoured
|
Armoured
|
||||
Buried direct in ground
|
In a buried duct
|
In air
|
Buried direct in ground
|
In a buried duct
|
In air
|
|
mm2
|
A
|
A
|
A
|
A
|
A
|
A
|
16
25
35
50
70
95
120
150
185
240
300
400
|
76
97
116
137
167
200
227
255
289
335
378
432
|
65
84
101
119
147
176
201
226
257
300
340
392
|
80
105
127
151
189
229
263
299
343
406
462
538
|
76
97
116
137
168
200
227
254
288
332
374
426
|
66
85
101
120
147
176
201
226
257
299
338
387
|
81
105
127
153
190
230
264
300
343
402
459
530
|
Température maximale de l’âme 90 °C
Température ambiante 30 °C Température du sol 20 °C Profondeur de pose 0,8 m
Résistivité thermique du sol 1,5 K.m/W
Résistivité thermique du conduit en terre cuite 1,2 K.m/W
|
||||||
* Current rating calculated for cables having a rated voltage of 6/10 kV.
|
Table B.10 – Correction factors for ambient air temperatures other than 30 °C
Maximum conductor temperature
°C
|
Ambient air temperature
°C
|
|||||||
20
|
25
|
35
|
40
|
45
|
50
|
55
|
60
|
|
90
|
1,08
|
1,04
|
0,96
|
0,91
|
0,87
|
0,82
|
0,76
|
0,71
|
Table B.11 – Correction factors for ambient ground temperatures other than 20 °C
Maximum conductor temperature
°C
|
Ambient ground temperature
°C
|
|||||||
10
|
15
|
25
|
30
|
35
|
40
|
45
|
50
|
|
90
|
1,07
|
1,04
|
0,96
|
0,93
|
0,89
|
0,85
|
0,80
|
0,76
|
Table B.12 – Correction factors for depths of laying other than 0,8 m for direct buried cables
Depth of laying
m
|
Single-core cables
|
Three-core cables
|
|
Nominal conductor size
mm2
|
|||
≤185 mm2
|
>185 mm2
|
||
0,5
0,6
1
1,25
1,5
1,75
2
2,5
3
|
1,04
1,02
0,98
0,96
0,95
0,94
0,93
0,91
0,90
|
1,06
1,04
0,97
0,95
0,93
0,91
0,90
0,88
0,86
|
1,04
1,03
0,98
0,96
0,95
0,94
0,93
0,91
0,90
|
Table B.13 – Correction factors for depths of laying other than 0,8 m for cables in ducts
Depth of laying
m
|
Single-core cables
|
Three-core cable
|
|
Nominal conductor size
mm2
|
|||
≤185 mm2
|
>185 mm2
|
||
0,5
0,6
1
1,25
1,5
1,75
2
2,5
3
|
1,04
1,02
0,98
0,96
0,95
0,94
0,93
0,91
0,90
|
1,05
1,03
0,97
0,95
0,93
0,92
0,91
0,89
0,88
|
1,03
1,02
0,99
0,97
0,96
0,95
0,94
0,93
0,92
|
Table B.14 – Correction factors for soil thermal resistivities other than 1,5 K.m/W for direct buried single-core cables
Nominal area of
conductor
mm2
|
Values of soil thermal resistivity
|
||||||
0,7
|
0,8
|
0,9
|
1
|
2
|
2,5
|
3
|
|
16
25
35
50
70
95
120
150
185
240
300
400
|
1,29
1,30
1,30
1,32
1,33
1,34
1,34
1,35
1,35
1,36
1,36
1,37
|
1,24
1,25
1,25
1,26
1,27
1,28
1,28
1,28
1,29
1,29
1,30
1,30
|
1,19
1,20
1,21
1,21
1,22
1,22
1,22
1,23
1,23
1,23
1,24
1,24
|
1,15
1,16
1,16
1,16
1,17
1,18
1,18
1,18
1,18
1,18
1,19
1,19
|
0,89
0,89
0,89
0,89
0,89
0,89
0,88
0,88
0,88
0,88
0,88
0,88
|
0,82
0,81
0,81
0,81
0,81
0,80
0,80
0,80
0,80
0,80
0,80
0,79
|
0,75
0,75
0,75
0,74
0,74
0,74
0,74
0,74
0,74
0,73
0,73
0,73
|
Table B.15 – Correction factors for soil thermal resistivities other than 1,5 K.m/W single-core cables in buried ducts
Nominal area of
conductor
mm2
|
Values of soil thermal resistivity
|
||||||
0,7
|
0,8
|
0,9
|
1
|
2
|
2,5
|
3
|
|
16
25
35
50
70
95
120
150
185
240
300
400
|
1,20
1,21
1,21
1,21
1,22
1,23
1,23
1,24
1,24
1,25
1,25
1,25
|
1,17
1,17
1,18
1,18
1,19
1,19
1,20
1,20
1,20
1,21
1,21
1,21
|
1,14
1,14
1,15
1,15
1,15
1,16
1,16
1,16
1,17
1,17
1,17
1,17
|
1,11
1,12
1,12
1,12
1,12
1,13
1,13
1,13
1,13
1,14
1,14
1,14
|
0,92
0,91
0,91
0,91
0,91
0,91
0,91
0,91
0,91
0,90
0,90
0,90
|
0,85
0,85
0,84
0,84
0,84
0,84
0,84
0,83
0,83
0,83
0,83
0,83
|
0,79
0,79
0,79
0,78
0,78
0,78
0,78
0,78
0,78
0,77
0,77
0,77
|
Table B.16 – Correction factors for soil thermal resistivities other than 1,5 K.m/W for direct buried three-core cables
Nominal area of conductor
mm2
|
Values of soil thermal resistivity
K•m/W
|
||||||
0,7
|
0,8
|
0,9
|
1
|
2
|
2,5
|
3
|
|
16
25
35
50
70
95
120
150
185
240
300
400
|
1,23
1,24
1,25
1,25
1,26
1,26
1,26
1,27
1,27
1,28
1,28
1,28
|
1,19
1,20
1,21
1,21
1,21
1,22
1,22
1,22
1,23
1,23
1,23
1,23
|
1,16
1,16
1,17
1,17
1,18
1,18
1,18
1,18
1,18
1,19
1,19
1,19
|
1,13
1,13
1,13
1,14
1,14
1,14
1,14
1,15
1,15
1,15
1,15
1,15
|
0,91
0,91
0,91
0,91
0,90
0,90
0,90
0,90
0,90
0,90
0,90
0,90
|
0,84
0,84
0,83
0,83
0,83
0,83
0,83
0,83
0,83
0,83
0,82
0,82
|
0,78
0,78
0,78
0,77
0,77
0,77
0,77
0,77
0,77
0,77
0,77
0,76
|
Table B.17 – Correction factors for soil thermal resistivities other than 1,5 K•m/W for three-core cables in ducts
Nominal area of
conductor
|
Values of soil thermal resistivity
K•m/W
|
||||||
mm2
|
0,7
|
0,8
|
0,9
|
1
|
2
|
2,5
|
3
|
16
25
35
50
70
95
120
150
185
240
300
400
|
1,12
1,14
1,14
1,14
1,15
1,15
1,15
1,16
1,16
1,16
1,17
1,17
|
1,11
1,12
1,12
1,12
1,13
1,13
1,13
1,13
1,14
1,14
1,14
1,14
|
1,09
1,10
1,10
1,10
1,11
1,11
1,11
1,11
1,11
1,12
1,12
1,12
|
1,08
1,08
1,08
1,08
1,09
1,09
1,09
1,09
1,09
1,10
1,10
1,10
|
0,94
0,94
0,94
0,94
0,94
0,94
0,93
0,93
0,93
0,93
0,93
0,92
|
0,89
0,89
0,88
0,88
0,88
0,88
0,88
0,88
0,87
0,87
0,87
0,86
|
0,84
0,84
0,84
0,84
0,83
0,83
0,83
0,83
0,83
0,82
0,82
0,81
|
Table B.18 – Correction factors for groups of three-core cables in horizontal formation laid direct in the ground
Number of cables in group
|
Spacing betw een cable centres
mm
|
||||
Touching
|
200
|
400
|
600
|
800
|
|
2
3
4
5
6
7
8
9
10
11
12
|
0,80
0,69
0,62
0,57
0,54
0,51
0,49
0,47
0,46
0,45
0,43
|
0,86
0,77
0,72
0,68
0,65
0,63
0,61
0,60
0,59
0,57
0,56
|
0,90
0,82
0,79
0,76
0,74
0,72
0,71
0,70
0,69
0,69
0,68
|
0,92
0,86
0,83
0,81
0,80
0,78
0,78
0,77
-
-
-
|
0,94
0,89
0,87
0,85
0,84
0,83
-
-
-
-
|
Table B.19 – Correction factors for groups of three-phase circuits of single-core cables laid direct in the ground
Number of cables in group
|
Spacing betw een group centres
mm
|
||||
Touching
|
200
|
400
|
600
|
800
|
|
2
3
4
5
6
7
8
9
10
11
12
|
0,73
0,60
0,54
0,49
0,46
0,43
0,41
0,39
0,37
0,36
0,35
|
0,83
0,68
0,63
0,61
0,58
0,57
0,55
0,54
0,53
0,52
|
0,88
0,79
0,75
0,72
0,70
0,68
0,67
0,66
0,65
0,64
0,64
|
0,90
0,83
0,80
0,78
0,76
0,75
0,74
0,73
-
-
-
|
0,92
0,86
0,84
0,82
0,81
0,80
-
-
-
-
-
|
Table B.20 – Correction factors for groups of three-core cables in single w ay ducts in horizontal formation
Number of cables in group
|
Spacing betw een duct centres
mm
|
||||
Touching
|
200
|
400
|
600
|
800
|
|
2
3
4
5
6
7
8
9
10
11
12
|
0,85
0,75
0,69
0,65
0,62
0,59
0,57
0,55
0,54
0,52
0,51
|
0,88
0,80
0,75
0,72
0,69
0,67
0,65
0,64
0,63
0,62
0,61
|
0,92
0,85
0,82
0,79
0,77
0,76
0,75
0,74
0,73
0,73
0,72
|
0,94
0,88
0,86
0,84
0,83
0,82
0,81
0,80
-
-
-
|
0,95
0,91
0,89
0,87
0,87
0,86
-
-
-
-
-
|
Table B.21 – Correction factors for groups of three-phase circuits of single-core cables in single-w ay ducts
Number of cables in group
|
Spacing betw een duct group centres
mm
|
||||
Touching
|
200
|
400
|
600
|
800
|
|
2
3
4
5
6
7
8
9
10
11
12
|
0,78
0,66
0,59
0,55
0,51
0,48
0,46
0,44
0,43
0,42
0,40
|
0,85
0,75
0,70
0,66
0,64
0,61
0,60
0,58
0,57
0,56
0,55
|
0,89
0,81
0,77
0,74
0,72
0,71
0,70
0,69
0,68
0,67
0,67
|
0,91
0,85
0,82
0,80
0,78
0,77
0,76
0,76
-
-
-
|
0,93
0,88
0,86
0,84
0,83
0,82
-
-
-
-
-
|
Table B.22 – Reduction factors for groups of more than one multi-core cable in air – To be applied to the current-carrying capacity for one multi-core cable in free air
Method of installation
|
Number of trays
|
Number of cables
|
||||||
1
|
2
|
3
|
4
|
6
|
9
|
|||
Cables on
perforated trays
|
1
2
3
|
1,00
1,00
1,00
|
0,88
0,87
0,86
|
0,82
0,80
0,79
|
0,79
0,77
0,76
|
0,76
0,73
0,71
|
0,73
0,68
0,66
|
|
1
2
3
|
1,00
1,00
1,00
|
1,00
0,99
0,98
|
0,98
0,96
0,95
|
0,95
0,92
0,91
|
0,91
0,87
0,85
|
-
-
-
|
||
Cables on vertical perforated trays
|
|
1
2
|
1,00
1,00
|
0,88
0,88
|
0,82
0,81
|
0,78
0,76
|
0,73
0,71
|
0,72
0,70
|
|
1
2
|
1,00
1,00
|
0,91
0,91
|
0,89
0,88
|
0,88
0,87
|
0,87
0,85
|
-
-
|
|
Cables on ladder supports, cleats, etc.
|
1
2
3
|
1,00
1,00
1,00
|
0,87
0,86
0,85
|
0,82
0,80
0,79
|
0,80
0,78
0,76
|
0,79
0,76
0,73
|
0,78
0,73
0,70
|
|
1
2
3
|
1,00
1,00
1,00
|
1,00
0,99
0,98
|
1,00
0,98
0,97
|
1,00
0,97
0,96
|
1,00
0,96
0,93
|
-
-
-
|
||
NOTE 1 Values given are averages for the cable types and range of conductor sizes considered. The spread of values is generally less than 5 %.
NOTE 2 Factors apply to single layer groups of cables as shown above and do not apply when cables are installed in more than one layer touching each other. Values for such installations may be significantly lower and must be determined by an appropriate method.
NOTE 3 Values are given for vertical spacings between trays of 300 mm and at least 20 mm between trays and wall. For closer spacing, the factors should be reduced.
NOTE 4 Values are given for horizontal spacing between trays of 225 mm with trays mounted back to back. For closer spacing, the factors should be reduced.
|
Table B.23 – Reduction factors for groups of more than one circuit of single-core cables (Note 2) –
To be applied to the current-carrying capacity for one circuit of single-core cables in free air
Method of installation
|
Number of trays
|
Number of three-phase circuits (Note 5)
|
Use as a
multiplier to rating for
|
|||
1
|
2
|
3
|
||||
Perforated trays
(Note 3)
|
1
2
3
|
0,98
0,96
0,95
|
0,91
0,87
0,85
|
0,87
0,81
0,78
|
Three cables in horizontal
formation
|
|
Ladder
supports, cleats etc.
(Note 3)
|
1
2
3
|
1,00
0,98
0,97
|
0,97
0,93
0,90
|
0,96
0,89
0,86
|
Three cables in horizontal
formation
|
|
Perforated trays
(Note 3)
|
|
1
2
3
|
1,00
0,97
0,96
|
0,98
0,93
0,92
|
0,96
0,89
0,86
|
Three cables in trefoil formation
|
Vertical
perforated trays
(Note 4)
|
1
2
|
1,00
1,00
|
0,91
0,90
|
0,89
0,86
|
||
Ladder
supports,
cleats, etc.
(Note 3)
|
|
1
2
3
|
1,00
0,97
0,96
|
1,00
0,95
0,94
|
1,00
0,93
0,90
|
|
NOTE 1 Values given are averages for the cable types and range of conductor sizes considered. The spread of values is generally less than 5 %.
NOTE 2 Factors are given for single layers of cables (or trefoil groups) as shown in the table and do not
apply when cables are installed in more than one layer touching each other. Values for such installations may be significantly lower and should be determined by an appropriate method.
NOTE 3 Values are given for vertical spacings between trays of 300 mm. For closer spacing, the factors should be reduced.
NOTE 4 Values are given for horizontal spacing between trays of 225 mm with trays mounted back to back. For closer spacing, the factors should be reduced.
NOTE 5 For circuits having more than one cable in parallel per phase, each three phase set of conductors should be considered as a circuit for the purpose of this table.
|