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Conduit & Trunking Capacity Chart
CABLE
SPACING
FACTORS
Not only must it be possible to draw cables into completed conduit and trunking systems, but neither the cables nor their enclosures must be damaged in the process. If too many cables are packed into the space available, there will be a greater increase in temperature during operation than if they were given more space. It is important to appreciate that grouping factors still apply to cables enclosed in conduit or trunking. To determine the conduit size needed, multiply the quantities of each size of cable by the appropriate factor, compare the total with the conduit figures shown.
For situations not covered by these tables, the requirement is that a space factor of 45% for conduit and 45% for trunking must not be exceeded. This means that not more than 45% of the space within the conduit or trunking must be occupied by cables, and involves calculating the crosssectional area of each cable, including its insulation, for which the outside diameter must be known. To use the ({Tables 4.14 to 4.17}) the cable factors for all the conductors must be added. The conduit or trunking selected must have a factor (otherwise called 'term') at least as large as this number.
Table 4.14 - Cable factors () for conduit and trunking Type of conductor
Conductor c.s.a. (mm²)
Factor for conduit
Factor for trunking pvc insulation
Factor for trunking thermosettin g insulation
Solid
1.0
16
3.6
3.8
Solid
1.5
22
8.0
8.6
Stranded
1.5
22
8.6
9.1
Solid
2.5
30
11.9
11.9
Stranded
2.5
30
12.6
13.9
Stranded
4.0
43
16.6
18.1
Stranded
6.0
58
21.2
22.9
Stranded
10.0
105
35.3
36.3
Stranded
16.0
145
47.8
50.3
Stranded
25.0
217
73.9
75.4
Table 4.15 - Cable factors () for straight runs up to 3m. Type of conductor
Conductor c.s.a. (mm²)
Cable factor
Solid
1.0
22
Solid
1.5
27
Solid
2.5
39
Stranded
1.5
31
Stranded
2.5
43
Stranded
4.0
58
Stranded
6.0
88
Stranded
10.0
146
Conduit, straight 16mm 20mm 25mm 32mm Conduit, one bend 16mm 20mm 25mm 32mm Conduit, two bends 16mm 20mm 25mm 32mm
1
2
Table 4.16 - Conduit factors () Length of run between boxes (m) 3 4 5
6
8
10
171 278 500 878
167 270 487 857
158 256 463 818
150 244 442 783
150 244 442 783
143 233 422 750
130 213 388 692
120 196 258 643
120 196 358 643
111 182 333 600
97 159 292 529
86 141 260 474
290 460 800 1400
290 460 800 1400
290 460 800 1400
171 286 514 900 -
188 303 543 947
177 286 514 900
167 270 487 857
158 256 463 818 -
177 286 514 900
158 256 463 818
For 38mm conduit use the 32mm factor x 1.4. For 50mm conduit use the 32mm factor x 2.6. For 63mm conduit use the 32mm factor x 4.2.
143 233 422 750
130 213 388 692
Table 4.17 - Trunking factors () Dimensions of trunking (mm x mm) 37.5 x 50
Factor 767
50 x 50
1037
25 x 75
738
37.5 x 75
1146
50 x 75
1555
75 x 75
2371
25 x 100
993
37.5 x 100
1542
50 x 100
2091
75 x 100
3189
100 x 100
4252
Example 1: The following single-core p.v.c. insulated cables are to be run in a conduit 6 m long with a double set: 8x1mm2, 4x2.5mm2 and 2x6mm². Choose a suitable size. Consulting {Table 4.14} gives the following cable factors: 16 for 1 mm², 30 for 2.5 mm² and 58 for 6 mm² Total cable factor is then (8 x 16) + (4 x 30) + (2 x 58) = 128 + 120 + 116 = 364
EXAMPLE 1. What size of conduit is required for 6 No. 4mm² cables in a three metre run with no bends? 6 x 58 = 348 So the nearest size of conduit with a factor greater than 348 is 20m
CABLE
SPACING
FACTORS
Not only must it be possible to draw cables into completed conduit and trunking systems, but neither the cables nor their enclosures must be damaged in the process. If too many cables are packed into the space available, there will be a greater increase in temperature during operation than if they were given more space. It is important to appreciate that grouping factors still apply to cables enclosed in conduit or trunking. To determine the conduit size needed, multiply the quantities of each size of cable by the appropriate factor, compare the total with the conduit figures shown.
For situations not covered by these tables, the requirement is that a space factor of 45% for conduit and 45% for trunking must not be exceeded. This means that not more than 45% of the space within the conduit or trunking must be occupied by cables, and involves calculating the crosssectional area of each cable, including its insulation, for which the outside diameter must be known. To use the ({Tables 4.14 to 4.17}) the cable factors for all the conductors must be added. The conduit or trunking selected must have a factor (otherwise called 'term') at least as large as this number.
Table 4.14 - Cable factors () for conduit and trunking Type of conductor
Conductor c.s.a. (mm²)
Factor for conduit
Factor for trunking pvc insulation
Factor for trunking thermosettin g insulation
Solid
1.0
16
3.6
3.8
Solid
1.5
22
8.0
8.6
Stranded
1.5
22
8.6
9.1
Solid
2.5
30
11.9
11.9
Stranded
2.5
30
12.6
13.9
Stranded
4.0
43
16.6
18.1
Stranded
6.0
58
21.2
22.9
Stranded
10.0
105
35.3
36.3
Stranded
16.0
145
47.8
50.3
Stranded
25.0
217
73.9
75.4
Table 4.15 - Cable factors () for straight runs up to 3m. Type of conductor
Conductor c.s.a. (mm²)
Cable factor
Solid
1.0
22
Solid
1.5
27
Solid
2.5
39
Stranded
1.5
31
Stranded
2.5
43
Stranded
4.0
58
Stranded
6.0
88
Stranded
10.0
146
Conduit, straight 16mm 20mm 25mm 32mm Conduit, one bend 16mm 20mm 25mm 32mm Conduit, two bends 16mm 20mm 25mm 32mm
1
2
Table 4.16 - Conduit factors () Length of run between boxes (m) 3 4 5
6
8
10
171 278 500 878
167 270 487 857
158 256 463 818
150 244 442 783
150 244 442 783
143 233 422 750
130 213 388 692
120 196 258 643
120 196 358 643
111 182 333 600
97 159 292 529
86 141 260 474
290 460 800 1400
290 460 800 1400
290 460 800 1400
171 286 514 900 -
188 303 543 947
177 286 514 900
167 270 487 857
158 256 463 818 -
177 286 514 900
158 256 463 818
For 38mm conduit use the 32mm factor x 1.4. For 50mm conduit use the 32mm factor x 2.6. For 63mm conduit use the 32mm factor x 4.2.
143 233 422 750
130 213 388 692
Table 4.17 - Trunking factors () Dimensions of trunking (mm x mm) 37.5 x 50
Factor 767
50 x 50
1037
25 x 75
738
37.5 x 75
1146
50 x 75
1555
75 x 75
2371
25 x 100
993
37.5 x 100
1542
50 x 100
2091
75 x 100
3189
100 x 100
4252
Example 1: The following single-core p.v.c. insulated cables are to be run in a conduit 6 m long with a double set: 8x1mm2, 4x2.5mm2 and 2x6mm². Choose a suitable size. Consulting {Table 4.14} gives the following cable factors: 16 for 1 mm², 30 for 2.5 mm² and 58 for 6 mm² Total cable factor is then (8 x 16) + (4 x 30) + (2 x 58) = 128 + 120 + 116 = 364
EXAMPLE 1. What size of conduit is required for 6 No. 4mm² cables in a three metre run with no bends? 6 x 58 = 348 So the nearest size of conduit with a factor greater than 348 is 20m
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