Current Carrying Capacity, Correction Factors, Short Circuit Capacity

Current Carrying Capacity

Nominal cross section of conductor	XLPE or EPR	PVC	XLPE or EPR	XLPE or EPR
Nominal cross section of conductor	Single-core cable free in air in acc. with EN 50 355	Multi-cores cable three loaded cores free in air type E in acc. with IEC 60 364-5-52-12	Multi-cores cable three loaded cores free in air in acc. with IEC 60 364-5-52-12	Multi-cores cable three loaded cores on ground in acc. with IEC 60 364-5-52-12
(mm²)	(A)	(A)	(A)	(A)
1.5	29	19	23	22
2.5	38	25	32	30
4	53	34	42	40
6	69	43	54	51
10	98	60	75	71
16	127	80	100	95
25	173	101	127	121
35	219	126	158	150
50	276	153	192	182
70	345	196	246	234
95	414	238	298	283
120	489	276	346	329
150	564	318	399	375
185	644	362	456	428
240	776	424	538	511

XLPE or EPR : Conductor temperature: 90 °C/ Reference ambient temperature of 30 °C

PVC : Conductor temperature: 70 °C/ Reference ambient temperature of 30 °C

Correction factors for ambient air temperature

Ambient Temperature	PVC Insulation	XLPE or EPR Insulation
(°C)	Temperature: 70 °C	Temperature: 90 °C
10	1.22	1.15
15	1.17	1.12
20	1.12	1.08
25	1.06	1.04
30	1	1
35	0.94	0.96
40	0.87	0.91
45	0.79	0.87
50	0.71	0.82
55	0.61	0.76
60	0.5	0.71
65		0.65
70		0.58
75		0.5
80		0.41

Correction factors for reeling cables

Basis in free air (in line with EN 60204-11)

	Multilayer Reel				Monospiral Reel
Number of layers	1	2	3	4	round cable ventilated	round cable non-ventilated	flat cable ventilated
	0.85	0.65	0.45	0.35	0.85	0.75	0.65

Reduction factors for groups of several circuits or several multicores cables

	Number of 3 cores circuits
Arrangement	1	2	4	6	9	12	16	20
Bunched in air, on a surface, embedded or enclosed	1.00	0.80	0.65	0.55	0.50	0.45	0.40	0.40

Short-circuit current density in A/mm² for 1 second

	Number of 3 cores circuits
Insulating material	Permissible operating temperature	Permissible short-circuit temperature	90 °C	80 °C	70 °C	60 °C	50 °C	40 °C	30 °C
plain copper conductor + PVC	70 °C	150 °C			109	117	124	131	138
tinned copper conductor + EPR	90 °C	200 °C	122	128	135	141	147	153	159
plain copper conductor + EPR	90 °C	250 °C	143	149	154	159	165	170	176
plain copper conductor + XLPE	90 °C	250 °C	143	149	154	159	165	170	176
plain copper conductor + TPE	90 °C	250 °C	143	149	154	159	165	170	176

For other short-circuit times (lower than 5 seconds), the short-circuit current density has to be calculated with the following formula:

dt = d x 1/√t

Voltage drops are determined by using the following formula:

Δu = b x l x i_B ( R cos ϕ + λ sinϕ )

With:

ƒ¢u	voltage drop (in Volts)
b	coefficient equal to ã3 for three-phases circuits, or 2 for single-phase circuits
R	electrical resistance of conductors in normal service (in ƒ¶/km)
l	straight length of the wiring systems (in km)
cos ϕ	power factor, if no precise details, the power factor is taken equal to 0.8
	(sin .= 0.6)
ƒÉ	reactance per unit length of conductors (in ƒ¶/km)
iB	current value (in Ampere)

For the application of the formula it is necessary to know the exact cable specification.

For a fast calculation of the section it is recommended to use the following tables which give the value of the voltage drop, available for most of the low voltage cables and for different values of cos ϕ.

Voltage drops are calculated for a three-phases circuit:

3 or 4 copper cores cables
3 single cores cables

Low voltage cables with PVC insulation (max. temperature: 70 °C) 3 or 4 copper cores

Cross-section area	Voltage drop (V/ A x km)
(mm²)	cos ϕ =1	cos ϕ = 0.9	cos ϕ = 0.8	cos ϕ = 0.6
1.5	25.1	22.7	20.2	15.3
2.5	15.2	13.7	12.3	9.3
4	9.5	8.6	7.8	5.8
5	6.4	5.8	5.3	4
10	3.8	3.5	3.2	2.4
16	2.4	2.2	2	1.6
25	1.5	1.4	1.3	1.04
35	1.1	1.06	0.97	0.8
50	0.8	0.8	0.74	0.62
70	0.56	0.57	0.55	0.46
95	0.4	0.43	0.42	0.37
120	0.33	0.37	0.36	0.32
150	0.26	0.3	0.3	0.28
185	0.21	0.26	0.27	0.25
240	0.17	0.22	0.23	0.22
300	0.13	0.19	0.2	0.21

Low voltage cables with EPR or XLPE insulation (max. temperature: 90 °C) 3 or 4 copper cores

Cross-section area (mm²)	Voltage drop (V/ A x km)
Cross-section area (mm²)	cos ϕ = 1	cos ϕ = 0.9	cos ϕ = 0.8	cos ϕ = 0.6
1.5	26	24.2	21.5	16.2
2.5	15.5	14.4	12.8	9.6
4	10	9	8	6.1
5	6.6	6.1	5.4	4.2
10	3.9	3.6	3.2	2.5
16	2.5	2.3	2.1	1.5
25	1.6	1.5	1.35	1.1
35	1.15	1.1	1	0.85
50	0.85	0.8	0.75	0.65
70	0.57	0.6	0.55	0.5
95	0.42	0.45	0.42	0.4
120	0.33	0.35	0.35	0.34
150	0.27	0.3	0.3	0.31
185	0.22	0.25	0.22	0.24
240	0.17	0.2	0.21	0.23
300	0.14	0.17	0.2	0.21

Current Carrying Capacity, Correction Factors, Short Circuit Capacity

Current Carrying Capacity, Correction Factors, Short Circuit Capacity