Maximum continuously permissible service voltages
Cables with UO/U 0.6/1 kV having PVC-insulation, metallic armouring and with cross sections ≥ 240mm2 may be also used for three phase systems with Um= 3.6 kV.
Cables with UO/U 0.6/1 kV are also suitable for direct current systems with highest voltages phase/phase or phase/ground ≤ 1.8 kV.
Guidelines for the current carrying capacity
The heat produced by the cable under the given conditions must be able to dissipate to the ambient medium at any point of the cable installation; the loading of the cable must be limited accordingly. The currents in the tables are based of the calculation methods according to IEC 60287 and DIN VDE with regard to the partial drying out of the soil.
The values stated for cables laid in the ground are based on standard service conditions so that the current carrying capacities can be taken without derating factor in most cases:
The current values are valid for cables laid direct in ground. Furthermore it is supposed that the soil can dry out in a limited area where the surface of the cable reaches temperatures which lead to drying out of the soil.
For installation in air continuous load – load factor 1.0 – is considered.
The values given apply to cabels laid in air at 30 °C. It is assumed here that heat dissipation by convection and radiation will not be impeded, and that there are no external heat sources. These conditions can be taken as mentioned in the Table below.