Conduit and Trunking Capacity Chart

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Cable Spacing Factors

To determing 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 Example

Question: What size of conduit is required for 6 No. 4mm² cables in a three metre run with no bends?

Answer: 6 x 58 = 348 So the nearest size of coduti with a factor greater than 348 is 20mm.

Conduit Factors

Conduit Diameter (mm)Capacity Factor
16290
20460
25800
321400

Cable Factors

Single core PVC insulated cables in straight runs of conduit not exceeding 3m in length

Type of ConductorConductor cross-sectional area (mmu00b2)Factor
Solid1.022
1.527
2.539
Standard1.531
2.543
4.058
6.088
10.0146

Cable Factors

Single core PVC insulated cables in straight runs of conduit exceeding 3m in length OR in runs of any length incorporating bends or sets.

Type of ConductorConductor cross-sectional area (mmu00b2)Factor
Solid or Stranded1.016
1.522
2.530
4.043
6.058
10.0105

Conduit Capacity Factors (Exceeding 3M in length)

LENGTH OF RUN (m)CONDUIT DIAMETER (mm)                   
1620253216202532162025321620253216202532
STRAIGHTONE BENDTWO BENDSTHREE BENDSFOUR BENDS
1.0----188303543947177286514900158256463818130213388692
1.5----182294528923167270487857143233422750111182333600
2.0----17728651490015825646381813021338869297159292529
2.5----17127850087815024444278312019635864386141260474
3.0----167270487857143233422750111182333600----
3.5179290521911162263475837136222404720103169311563----
4.0177286514900158256463818130213388692971592925529----
4.5174282507889154250452800125204373666791149275500----
5.017127850087815024444278312019635864386141260474----
6.0167270487857143233422750111182333600--------
7.0162263475837136222404720103169311563--------
8.015825646381813021338869297159292529--------
9.015425045280012520437366791149275500--------
10.015024444278312019638564386141260474--------

To determine the trunking size needed, multiply the quantities of each cable by the appropriate factor, and compare the total with the trunking capacity figures shown.

For example: What size of standard trunking is needed for 10 in number 35mm² cables and 16 in number 4mm² cables?
The nearest size of standard trunking with a capacity factor greater than 1239.6 is 75 x 50mm?

(No. of Cables) 10 x 95 (Factor for 35mm² cable) = 950
(No. of Cables) 16 x 18.0 (Factor for 4mm² cable) = 289.6
Total Cable Factor = 1239.6

Standard Trunking Cable Factors

Nominal Conductor size mmu00b21.5 Solid1.5 Standard2.5 Solid2.5 Standard4610162535507095
Factor copper or aluminium8.69.611.913.918.122.936.350.375.495133177227

Standard Trunking Capacity Factors

Trunk SizeCapacity FactorTrunk Size2Capacity Factor3
50mm x 50mm1,037150mm x 75mm4,743
75mm x 50mm1,555150mm x 100mm6,394
75mm x 75mm2,371150mm x 150mm9,697
100mm x 50mm2,091200mm x 100mm8,572
100mm x 75mm3,189225mm x 150mm14,652
100mm x 100mm4,252300mm x 150mm19,607

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DISCLAIMER: The information on this page and the PDF is for information only and R&M Electrical Group Ltd can not be held liable for any information therein.