1. Maximum permissible conductor temperature in continuous operation

· PVC and XLPE insulated 1 kV cables 70 °C

· XLPE insulated cables over 1 kV and XLPE insulated 1 kV cables in specific circumstances 90 °C

 

2. Distance between single-core cables

· in flat formation the free space between the cables is equal to the cable diameter

· in trefoil formation the cables are touching each other

 

3. Coupling the metallic screen circuit of single-core cables

· open: screen circuits of the cables are connected together and earthed at one end only

· closed: screen circuits of the cables are connected together at both ends and earthed at least at one end

 

4. Installation in air

· ambient air temperature is 25 °C

· air can move freely around the installed conductors and cables

 

5. Underground installation

· ground temperature is 15 °C

· installation depth is 0.7 m for ≤ 36 kV cables and 1.0 m for ≥ 45 kV

· thermal resistivity of the ground is 1.0 Km/W

 

If XLPE insulated cables are laid underground, it is important to remember that a continuous conductor temperature of 90 °C may dry up the surrounding ground, causing an overload of the cable. For this reason, the continuous conductor temperature should not exceed 65 °C.

 

Current carrying capacities are valid for a separate multi-core cable or for a separate group of three single-core cables without any other heat generating sources nearby.

 

If the conditions differ from the above assumed premises, the load current values shall be adjusted with appropriate correction factors or shall be calculated with professional software.