POWER BY INNOVATION… INNOVATION THROUGH PARTNERSHIPS
A member of the Group
A division of ATC (Pty) Ltd
Registration No. 1955/003773/07
CBI-electric: african cables
B-BBEE Level 2 contributor
PO Box 172, Vereeniging 1930 - Steel Road, Peacehaven, Vereeniging 1939, South Africa
Tel: +27 16 430 6000 - Fax: +27 16 430 6235 - www.cbi-electric.com
Directors: AE Dickson, PJ Banda, GW Eddey, TA Pooe, Z Mjali
Alternate Director: PW de Villiers
Low Voltage Cables
Rating Factors for Cables Laid Direct in Ground
RATING
FACTORS
Table 1 – Rating factor for variation in soil temperature (k
1
)
Insulation
Type
Max. Conductor
Soil temperature °C
Temperature °C
10
15
20
25
30
35
40
PVC D2
70
1.15
1.11
1.05
1.00
0.94
0.88
0.82
XLPE
90
1.11
1.07
1.04
1.00
0.96
0.92
0.88
PVC D5
105
1.12
1.08
1.04
1.00
0.97
0.94
0.87
Table 2 – Rating factor for variation in depth of laying (k
2
)
Table 3 – Rating factor for variation in thermal resistivity of soil (k
3
)
Standard laying conditions
Other laying conditions
Soil thermal resistivity 1.2K.m/W
I
standard
= Standard current rating in
ground
Depth of burial 500mm
I
rated
= I
standard
x k
1
x k
2
x k
3
x k
4
Soil temperature 25°C
k
1
= Table 1
k
2
= Table 2
k
3
= Table 3
k
4
= Table 4 to Table 7
Depth of laying (m)
0.5
0.8
1.0
1.2
1.5
Laid direct in Ground
1.00
0.95
0.94
0.92
0.91
Drawn into single way
Ducts
1.00
0.97
0.96
0.95
0.93
Soil thermal resistivity K.m/W
0.7
1.0
1.2
1.5
2.0
2.5
3.0
Laid direct in Ground
1.16
1.07
1.00
0.92
0.88
0.74
0.68
Drawn into single way
Ducts
1.08
1.04
1.00
0.95
0.89
0.84
0.79
Page 2 of 3
Low Voltage Cables
Rating Factors for Cables Laid Direct in Ground
RATING
FACTORS
Table 4 – Group Rating factors for twin or multicore cables in horizontal formation, laid direct in
ground (k
4
)
Cable Voltage
Number
of
Circuits
Touching
150mm
300mm
450mm
600mm
600/1000V
2
0.81
0.87
0.91
0.93
0.95
3
0.70
0.78
0.84
0.88
0.90
4
0.63
0.74
0.81
0.86
0.89
5
0.59
0.70
0.78
0.84
0.87
6
0.55
0.68
0.77
0.83
0.87
1900/3300V
2
0.80
0.85
0.89
0.91
0.93
3
0.68
0.76
0.81
0.84
0.87
4
0.62
0.71
0.77
0.81
0.84
5
0.57
0.66
0.73
0.78
0.82
6
0.54
0.64
0.71
0.77
0.81
Table 5 – Group Rating factors for ciruits of three single core cables in Trefoil formation touching,
laid direct in ground (k
4
)
Cable Voltage
Number
of Circuits
Touching
150mm
300mm
450mm
600mm
600/1000V
2
0.78
0.83
0.88
0.91
0.93
3
0.66
0.73
0.79
0.84
0.87
4
0.61
0.68
0.73
0.81
0.85
5
0.56
0.64
0.72
0.79
0.83
6
0.53
0.61
0.71
0.78
0.82
1900/3300V
2
0.78
0.82
0.86
0.89
0.91
3
0.66
0.71
0.77
0.80
0.83
4
0.59
0.65
0.72
0.77
0.8
5
0.55
0.61
0.68
0.74
0.78
6
0.52
0.58
0.66
0.72
0.76