Free Air Installation

B. CABLES INSTALLED IN FREE AIR

B1. Rating Factor for Variation in Air Temperature

Air Temperature 10 15 20 25 30 35 40 45 50
Rating factor XLPE / EPR Cables 1.15 1.12 1.08 1.04 1.00 0.96 0.91 0.87 0.82
PVC Cables 1.22 1.17 1.12 1.06 1.00 0.94 0.87 0.79 0.71

B2. Rating Factor for Group in Air for Single-core cables in three-phase systems

Arrangement of Cables

Number of cable trays or cable racks

Installed in one plane
Clearance = cable diameter d
distance from wall ≥ 2 cm

Installation in bunches
Clearance = 2d
distance from wall ≥ 2 c

Number of group
Number of group

1

2

3

1

2

3

On the floor

-

0.92

0.89

0.88

0.95

0.90

0.88

On Cable trays

1

0.92

0.89

0.88

0.95

0.90

0.88

2

0.87

0.84

0.83

0.90

0.85

0.83

3

0.84

0.82

0.81

0.88

0.83

0.81

6

0.82

0.80

0.79

0.86

0.81

0.79

On cable racks

1

1.00

0.97

0.96

1.00

0.98

0.96

2

0.97

0.94

0.93

1.00

0.95

0.93

3

0.96

0.93

0.92

1.00

0.94

0.92

6

0.94

0.91

0.90

1.00

0.93

0.90

On support

or

on the wall

-

0.94

0.91

0.89

0.89

0.86

0.84

B3. Rating Factor for Group in Air for Multi-core cables in three-phase systems

Arrangement of Cables

Number of cable trays or cable racks
Clearance = cable diameter d
Distance from wall ≥ 2 cm
Side by side without clearance
And touching wall

Number of group

Number of group

1

2

3

6 9

 

1

2

3

6 9

On the floor

- 0.95 0.90 0.88 0.85 0.84

0.90 0.84 0.80 0.75 0.73

On Cable trays

 

 

1

0.95

0.90

0.88

0.85

0.84

0.90

0.84

0.80

0.75

0.73

2

0.90

0.85

0.83

0.81

0.80

0.85

0.80

0.76

0.71

0.69

3

0.88

0.83

0.81

0.79

0.78

0.83

0.78

0.74

0.70

0.68

6

0.86

0.81

0.79

0.77

0.76

0.81

0.76

0.72

0.68

0.66

 

 

On cable racks

 

 

 

 

1

1.00

0.98

0.96

0.93

0.92

0.9 0

0.84

0.80

0.75

0.73

2

1.00

0.95

0.93

0.90

0.89

0.85

0.80

0.76

0.71

0.69

3

1.00

0.94

0.92

0.89

0.88

0.83

0.78

0.74

0.70

0.68

6

1.00

0.93

0.90

0.87

0.86

0.81

0.76

0.72

0.68

0.66

 

 

On support

or

on the wall

- 1.00 0.93 0.90 0.87 0.86

0.95 0.78 0.73 0.68 0.66

EXAMPLE :

Two XLPE three core cables N2XSEY 3x240 cm 6/10 kV are loaded. The cable is laid ground under conditions :
Permissible operating temperature : 90°C
Load Factor : 0.7
Depth of laying : 1 meter
Ground temperature : 35°C
Resistivity of soil : 1.2 °K.m/watt
Clearance between cables : 7 cm
The current-carrying capacity of the cable is calculated as follow :
From brochure N2XSEY 3x240 cm, we get current : 491 Amp.
Rating factor :
Depth of lay : 0.98
Ground temperature 35 °C : 0.96
Resistivity of soil 1.2 °K.m/watt : 0.95
Two group of multi core cables in three-phase system : 0.85
So, current-carrying capacity is :
| load = 491 x 0.98 x 0.96 x 0.95 x 0.85 (Amp.)
| load = 373 (Amp.) (Load factor : 0.7)