Recommended simplified approach for cable sizing

In order to facilitate the selection of cables, 2 simplified tables are proposed, for unburied and buried cables.
These tables summarize the most commonly used configurations and give easier access to the information.

• Unburied cables:

---

Reference methods	Number of loaded conductors and type of insulation
A1		2 PVC	3 PVC		3 XLPE	2 XLPE
A2	3 PVC	2 PVC		3 XLPE	2 XLPE
B1				3 PVC	2 PVC		3 XLPE		2 XLPE
B2			3 PVC	2 PVC		3 XLPE	2 XLPE
C					3 PVC		2 PVC	3 XLPE		2 XLPE
E						3 PVC		2 PVC	3 XLPE		2 XLPE
F							3 PVC		2 PVC	3XLPE		2 XLPE
1	2	3	4	5	6	7	8	9	10	11	12	13
Size (mm2) Copper
1.5	13	13.5	14.5	15.5	17	18.5	19.5	22	23	24	26	-
2.5	17.5	18	19.5	21	23	25	27	30	31	33	36	-
4	23	24	26	28	31	34	36	40	42	45	49	-
6	29	31	34	36	40	43	46	51	54	58	63	-
10	39	42	46	50	54	60	63	70	75	80	86	-
16	52	56	61	68	73	80	85	94	100	107	115	-
25	68	73	80	89	95	101	110	119	127	135	149	161
35	-	-	-	110	117	126	137	147	158	169	185	200
50	-	-	-	134	141	153	167	179	192	207	225	242
70	-	-	-	171	179	196	213	229	246	268	289	310
95	-	-	-	207	216	238	258	278	298	328	352	377
120	-	-	-	239	249	276	299	322	346	382	410	437
150	-	-	-	-	285	318	344	371	395	441	473	504
185	-	-	-	-	324	362	392	424	450	506	542	575
240	-	-	-	-	380	424	461	500	538	599	641	679
Aluminium
2.5	13.5	14	15	16.5	18.5	19.5	21	23	24	26	28	-
4	17.5	18.5	20	22	25	26	28	31	32	35	38	-
6	23	24	26	28	32	33	36	39	42	45	49	-
10	31	32	36	39	44	46	49	54	58	62	67	-
16	41	43	48	53	58	61	66	73	77	84	91	-
25	53	57	63	70	73	78	83	90	97	101	108	121
35	-	-	-	86	90	96	103	112	120	126	135	150
50	-	-	-	104	110	117	125	136	146	154	164	184
70	-	-	-	133	140	150	160	174	187	198	211	237
95	-	-	-	161	170	183	195	211	227	241	257	289
120	-	-	-	186	197	212	226	245	263	280	300	337
150	-	-	-	-	226	245	261	283	304	324	346	389
185	-	-	-	-	256	280	298	323	347	371	397	447
240	-	-	-	-	300	330	352	382	409	439	470	530

Fig. G21a: Current-carrying capacity in amperes (table B.52-1 of IEC 60364-5-52)

---

Correction factors are given in Figure G21b for groups of several circuits or multi-core cables:

---

Arrangement	Number of circuits or multi-core cables
	1	2	3	4	6	9	12	16	20
Embedded or enclosed	1.00	0.80	0.70	0.70	0.55	0.50	0.45	0.40	0.40
Single layer on walls, floors or on unperforated trays	1.00	0.85	0.80	0.75	0.70	0.70	-	-	-
Single layer fixed directly under a ceiling	0.95	0.80	0.70	0.70	0.65	0.60	-	-	-
Single layer on perforated horizontal trays or on vertical trays	1.00	0.90	0.80	0.75	0.75	0.70	-	-	-
Single layer on cable ladder supports or cleats, etc...	1.00	0.85	0.80	0.80	0.80	0.80	-	-	-

Fig. G21b: Reduction factors for groups of several circuits or of several multi-core cables(table B.52-3 of IEC 60364-5-52)

---

• Buried cables:

---

Installation  method	Size mm2	Number of loaded conductors and type of insulation
		Two PVC	Three PVC	Two XLPE	Three XLPE
D	Copper
	1.5	22	18	26	22
	2.5	29	24	34	29
	4	38	31	44	37
	6	47	39	56	46
	10	63	52	73	61
	16	81	67	95	79
	25	104	86	121	101
	35	125	103	146	122
	50	148	122	173	144
	70	183	151	213	178
	95	216	179	252	211
	120	246	203	287	240
	150	278	230	324	271
	185	312	258	363	304
	240	361	297	419	351
	300	408	336	474	396
D	Aluminium
	2.5	22	18.5	26	22
	4	29	24	34	29
	6	36	30	42	36
	10	48	40	56	47
	16	62	52	73	61
	25	80	66	93	78
	35	96	80	112	94
	50	113	94	132	112
	70	140	117	163	138
	95	166	138	193	164
	120	189	157	220	186
	150	213	178	249	210
	185	240	200	279	236
	240	277	230	322	272
	300	313	260	364	308

Fig. G22: Current-carrying capacity in amperes (table B.52-1 of IEC 60364-5-52)

---

Busbar trunking systems

The selection of busbar trunking systems is very straightforward, using the data provided by the manufacturer. Methods of installation, insulation materials, correction factors for grouping are not relevant parameters for this technology.

The cross section area of any given model has been determined by the manufacturer based on:

• The rated current,
• An ambient air temperature equal to 35 °C,
• 3 loaded conductors.

Rated current

The rated current can be calculated taking account of:

• The layout,
• The current absorbed by the different loads connected along the trunking system.

Ambient temperature

A correction factor has to be applied for temperature higher than 35 °C. The correction factor applicable to medium and high power range (up to 4,000 A) is given in Figure G23a.

---

°C	35	40	45	50	55
Correction factor	1	0.97	0.93	0.90	0.86

Fig. G23a: Correction factor for air temperature higher than 35 °C

---

Neutral current

Where 3^rd harmonic currents are circulating, the neutral conductor may be carrying a significant current and the corresponding additional power losses must be taken into account.
Figure G23b represents the maximum admissible phase and neutral currents (per unit) in a high power busbar trunking system as functions of 3^rd harmonic level.

---

Fig. G23b: Maximum admissible currents (p.u.) in a busbar trunking system as functions of the 3rd harmonic level.

---

The layout of the trunking system depends on the position of the current consumers, the location of the power source and the possibilities for fixing the system.
  - One single distribution line serves a 4 to 6 meter area
  - Protection devices for current consumers are placed in tap-off units, connected directly to usage points.
  - One single feeder supplies all current consumers of different powers.
Once the trunking system layout is established, it is possible to calculate the absorbed current I_n on the distribution line.
I_n is equal to the sum of absorbed currents by the current I_n consumers: I_n = Σ I_B.
The current consumers do not all work at the same time and are not permanently on full load, so we have to use a clustering coefficient k_S : In = Σ (I_B . k_S).

---

Application	Number of current consumers	Ks Coefficient
Lighting, Heating		1
Distribution (engineering workshop)	2...3	0.9
	4...5	0.8
	6...9	0.7
	10...40	0.6
	40 and over 0.9	0.5

Note: for industrial installations, remember to take account of upgrading of the machine equipment base. As for a switchboard, a 20 % margin is recommended:
I_n ≤ I_B x k_s x 1.2.

Fig G24: Clustering coefficient according to the number of current consumers