Current Carrying Capacity, Correction Factors, Short Circuit Capacity

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
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 iB ( R cos ϕ + λ sinϕ )

With:

ƒ¢u  voltage drop (in Volts)
coefficient equal to ã3 for three-phases circuits, or 2 for single-phase circuits
electrical resistance of conductors in normal service (in Ħ/km)
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)
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

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