CURRENT RATING FACTORS FOR XLPE

Normal Installation Conditions
  • Ground temp. – 30°
  • Ambient. – air temp – 40°
  • Max. operating conductor temp 90°
  • Thermal resistivity 650°C cm/w
  • Depth of laying 75cm
  • Short circuit rating 250°C
RATING FACTOR FOR VARIATION IN AMBIENT AIR TEMP.
Ground Temp 15 20 25 30 35 40 45 50
Rating factor 1.12 1.08 1.04 1.00 0.96 0.91 0.87 0.82
RATING FACTOR FOR DEPTH OF LAYING FOR LAID DIRECTLY IN THE GROUND
Depth of laying 41 to 25 sq. mm 35 to 300 sq. mm Above 300 sq mm
750 mm 1.00 1.00 1.00
900 mm 0.99 0.98 0.97
1050 mm 0.98 0.97 0.96
1200 mm 0.97 0.96 0.95
1500 mm 0.96 0.94 0.92
1800 mm 0.95 0.93 0.91
GROUP RATING FACTOR FOR TWIN AND MULTICORE CABLE LAID DIRECTLY
IN THE GROUND IN HORIZONTAL FORMATION
No of cables in the group Touching 15 cm 30cm 45cm 60cm
2 0.79 0.82 0.87 0.90 0.92
4 0.61 0.75 0.79 0.83 0.83
6 0.53 0.69 0.74 0.79 0.80
8 0.48 0.61 0.71 0.78  
GROUP RATING FACTOR FOR THREE SINGLE CORE CABLES IN TREFOIL
LAID DIRECTLY IN THE GROUND
No of cables Touching 20 cm 40cm 60cm 80cm
2 0.76 0.83 0.87 0.90 0.92
4 0.58 0.67 0.75 0.80 0.84
6 0.50 0.69 0.69 0.76 0.80
8 0.45 0.56 0.66 0.73  
COMPARATIVE CHARACTERICS OF DIELECTRIC MATERIALS
Properties Cross Linked Polyethylene (XLPE)) PVC
Dielectric Strength kv/mm 30-35 15 – 20
Volume Resistivity (ohm-cm) More than 1015 1013 – 1014
Tensile Strength N/mm2 13 – 16 14 – 18
Elongation % 250 – 450 200 – 300
Current carrying capacity Approx. 30 % higher than PVC
Max. Conductor Temperature during short circuit (°C) 250 160
Specific Gravity 0.90/0.92 1.35 / 1.55
Power Factor 0.003 0.08
Dieelectric constant at 20°C 2.3 6 to 8
Minimum working temperature -40°C -20°C