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Correction factors for the current carrying capacity
Correction factors for installation in air
The following tables of correction factors are to be applied to the current carrying capacity
when installation conditions vary from the given presumptions. The rating for the most conditions
can be quickly estimated by multiplying the continuous current carrying capacity value by the
correction factors given in the appropriate tables below.
Cables in air = the heat dissipation conditions are the same as if cables were in free
air.
Correction factors for different ambient air temperatures
|
Conductor temperature
°C
|
Ambient air
temperature, °C
|
|
10
|
15
|
20
|
25
|
30
|
35
|
40
|
45
|
|
+90
|
1,12
|
1,08
|
1,04
|
1,00
|
0,95
|
0,90
|
0,85
|
0,80
|
|
+80
|
1,14
|
1,09
|
1,05
|
1,00
|
0,95
|
0,89
|
0,84
|
0,77
|
|
+70
|
1,18
|
1,12
|
1,06
|
1,00
|
0,93
|
0,86
|
0,79
|
0,71
|
|
+65
|
1,20
|
1,14
|
1,07
|
1,00
|
0,93
|
0,85
|
0,77
|
0,68
|
Correction factors in aerial installation of multi-core AC cables. These values apply only
when the cable temperature does not affect the ambient air temperature.
|
Arrangement of the cables
|
|
Free space = one cable diameter
(d); Free distance from the wall >= 20 mm
|
|
|
Number of adjacent multi-core
cables
|
|
1
|
2
|
3
|
6
|
9
|
Sketch
|
|
On the floor or on flat
surface
|
|
0,95
|
0,90
|
0,88
|
0,85
|
0,84
|
 |
|
On unperforated metal
trays(restricted air circulation)
|
Number of
trays
|
|
|
|
|
|
 |
|
1
|
0,95
|
0,90
|
0,88
|
0,85
|
0,84
|
|
2
|
0,90
|
0,85
|
0,83
|
0,81
|
0,80
|
|
3
|
0,88
|
0,83
|
0,81
|
0,79
|
0,78
|
|
6
|
0,86
|
0,81
|
0,79
|
0,77
|
0,76
|
|
On metal ladders
|
Number of ladders
|
|
|
|
|
|
 |
|
1
|
1,00
|
0,98
|
0,96
|
0,93
|
0,92
|
|
2
|
1,00
|
0,95
|
0,93
|
0,90
|
0,89
|
|
3
|
1,00
|
0,94
|
0,92
|
0,89
|
0,88
|
|
6
|
1,00
|
0,93
|
0,90
|
0,87
|
0,86
|
|
Number of multi-core cables
placed on top of each other
|
|
1
|
2
|
3
|
6
|
9
|
Sketch
|
|
On structures or on the
wall
|
|
1,00
|
0,93
|
0,90
|
0,87
|
0,86
|
 |
|
Arrangements where the
reduction of current is not necessary
|
|
Unrestricted number of cables
on top of each other
|
 |
|
Arrangement of the cables
|
|
Cables touching one another and
the wall
|
|
|
Number of adjacent multi-core
cables
|
|
1
|
2
|
3
|
6
|
9
|
Sketch
|
|
On the floor or on flat
surface
|
|
0,90
|
0,84
|
0,80
|
0,75
|
0,73
|
 |
|
On unperforated metal trays
(restricted air circulation)
|
Number of trays
|
|
|
|
|
|
 |
|
1
|
0,95
|
0,84
|
0,80
|
0,75
|
0,73
|
|
2
|
0,95
|
0,80
|
0,76
|
0,71
|
0,69
|
|
3
|
0,95
|
0,78
|
0,74
|
0,70
|
0,68
|
|
6
|
0,95
|
0,76
|
0,72
|
0,68
|
0,66
|
|
On metal ladders
|
Number of ladders
|
|
|
|
|
|
 |
|
1
|
0,95
|
0,84
|
0,80
|
0,75
|
0,73
|
|
2
|
0,95
|
0,80
|
0,76
|
0,71
|
0,69
|
|
3
|
0,95
|
0,78
|
0,74
|
0,70
|
0,68
|
|
6
|
0,95
|
0,76
|
0,72
|
0,68
|
0,66
|
|
Number of multi-core cables
placed on top of each other
|
|
1
|
2
|
3
|
6
|
9
|
Sketch
|
|
On structures or on
wall
|
|
0,95
|
0,78
|
0,73
|
0,68
|
0,66
|
 |
|
Arrangements where the
reduction of current is not necessary
|
|
Unrestricted number of
adjacent cables
|
 |
Correction factors in aerial installation of single-core AC cables. These values apply only
when the cable temperature does not affect the ambient air temperature.
|
Arrangement of the
cables
|
|
Flat formation. Free space = one
cable diameter (d). Free distance from the wall >= 20 mm
|
|
|
Number of adjacent
systems
|
|
1
|
2
|
3
|
Sketch
|
|
On the floor or on flat
surface
|
|
0,92
|
0,89
|
0,88
|
 |
|
On unperforated
metal trays (restricted air circulation)
|
Number of
trays
|
|
|
|
 |
|
1
|
0,92
|
0,89
|
0,88
|
|
2
|
0,87
|
0,84
|
0,83
|
|
3
|
0,84
|
0,82
|
0,81
|
|
6
|
0,82
|
0,80
|
0,79
|
|
On metal
ladders)
|
Number of ladders
|
|
|
|
 |
|
1
|
1,00
|
0,97
|
0,96
|
|
2
|
0,97
|
0,94
|
0,93
|
|
3
|
0,96
|
0,93
|
0,92
|
|
6
|
0,94
|
0,91
|
0,89
|
|
Number of systems
placed on top of each other
|
|
1
|
2
|
3
|
Sketch
|
|
On structures or on the
wall
|
|
0,94
|
0,91
|
0,89
|
 |
|
Arrangements where
the reduction of current is not nececcary
|
|
The cooling of
cables by increased spacing will get better while the losses in metallic screens and sheaths will
increase reducing the current carrying capacity. Each case shall be calculated separately.
|
|
Arrangement of the cables
|
|
Trefoil formation. Free space =
one cable diameter (d). Free distance from the wall >= 20 mm
|
|
|
Number of adjacent
systems
|
|
1
|
2
|
3
|
Sketch
|
|
On the floor or on flat
surface
|
|
0,95
|
0,90
|
0,88
|
 |
|
On unperforated metal trays
(restricted air circulation)
|
Nymber of trays
|
|
|
|
 |
|
1
|
0,95
|
0,90
|
0,88
|
|
2
|
0,90
|
0,85
|
0,83
|
|
3
|
0,88
|
0,83
|
0,81
|
|
6
|
0,86
|
0,81
|
0,79
|
|
On metal ladders
|
Number of ladders
|
|
|
|
 |
|
1
|
1,00
|
0,98
|
0,96
|
|
2
|
1,00
|
0,95
|
0,93
|
|
3
|
1,00
|
0,94
|
0,92
|
|
6
|
1,00
|
0,93
|
0,90
|
|
Number of systems placed on top
of each other
|
|
1
|
2
|
3
|
Sketch
|
|
On structures or on the
wall
|
|
0,89
|
0,86
|
0,84
|
 |
|
Arrangements where the
reduction of current is not necessary
|
|
|
|
|
 |
|
|
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