Technical Resources

We have gathered together a number of technical resources for use as reference on electrical projects.

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.

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
16	290
20	460
25	800
32	1400

Cable Factors

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

Type of Conductor	Conductor cross-sectional area (mmu00b2)	Factor
Solid	1.0	22
	1.5	27
	2.5	39
Standard	1.5	31
	2.5	43
	4.0	58
	6.0	88
	10.0	146

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 Conductor	Conductor cross-sectional area (mmu00b2)	Factor
Solid or Stranded	1.0	16
	1.5	22
	2.5	30
	4.0	43
	6.0	58
	10.0	105

Conduit Capacity Factors (Exceeding 3M in length)

LENGTH OF RUN (m)	CONDUIT DIAMETER (mm)
	16	20	25	32	16	20	25	32	16	20	25	32	16	20	25	32	16	20	25	32
	STRAIGHT				ONE BEND				TWO BENDS				THREE BENDS				FOUR BENDS
1.0	-	-	-	-	188	303	543	947	177	286	514	900	158	256	463	818	130	213	388	692
1.5	-	-	-	-	182	294	528	923	167	270	487	857	143	233	422	750	111	182	333	600
2.0	-	-	-	-	177	286	514	900	158	256	463	818	130	213	388	692	97	159	292	529
2.5	-	-	-	-	171	278	500	878	150	244	442	783	120	196	358	643	86	141	260	474
3.0	-	-	-	-	167	270	487	857	143	233	422	750	111	182	333	600	-	-	-	-
3.5	179	290	521	911	162	263	475	837	136	222	404	720	103	169	311	563	-	-	-	-
4.0	177	286	514	900	158	256	463	818	130	213	388	692	97	159	2925	529	-	-	-	-
4.5	174	282	507	889	154	250	452	800	125	204	3736	667	91	149	275	500	-	-	-	-
5.0	171	278	500	878	150	244	442	783	120	196	358	643	86	141	260	474	-	-	-	-
6.0	167	270	487	857	143	233	422	750	111	182	333	600	-	-	-	-	-	-	-	-
7.0	162	263	475	837	136	222	404	720	103	169	311	563	-	-	-	-	-	-	-	-
8.0	158	256	463	818	130	213	388	692	97	159	292	529	-	-	-	-	-	-	-	-
9.0	154	250	452	800	125	204	373	667	91	149	275	500	-	-	-	-	-	-	-	-
10.0	150	244	442	783	120	196	385	643	86	141	260	474	-	-	-	-	-	-	-	-

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 mmu00b2	1.5 Solid	1.5 Standard	2.5 Solid	2.5 Standard	4	6	10	16	25	35	50	70	95
Factor copper or aluminium	8.6	9.6	11.9	13.9	18.1	22.9	36.3	50.3	75.4	95	133	177	227

Standard Trunking Capacity Factors

Trunk Size	Capacity Factor	Trunk Size2	Capacity Factor3
50mm x 50mm	1,037	150mm x 75mm	4,743
75mm x 50mm	1,555	150mm x 100mm	6,394
75mm x 75mm	2,371	150mm x 150mm	9,697
100mm x 50mm	2,091	200mm x 100mm	8,572
100mm x 75mm	3,189	225mm x 150mm	14,652
100mm x 100mm	4,252	300mm x 150mm	19,607