Permissible bending radii
When laying power cables, the radii should not be smaller than the values given in the table below. For single bends, e.g. in front of sealing ends, these radii may in the extreme case be reduced by half, if proper handling – heating to approx. 30 °C, bending over a former – is ensured.
Permissible pulling forces
When laying power cables by machine, particular attention must be paid to the permissible tensile forces. The formulae for obtaining these values are given in the table below.
If three single-core cables are laid simultaneously with a common pulling grip the same max. pulling forces as they are applicable for single-core cables, are valid. For 3 laid-up single-core cables the calculation of the permissible pulling forces is based on 3 cables, where as it is based on 2 cables if the 3 single-core cables are not laid-up.
S = Total conductor cross-section in mm2 (without screen and concentric protective conductor)
D = Outer diameter of the cable in mm
Permissible laying temperatures
For laying the temperatures of power cables should not fall below:
plastic-insulated cable with PVC sheath – 05 °C
XLPE-insulated cable with PE sheath – 20 °C
with H sheath – 20 °C
At lower temperatures the cables must be adequately warmed up in advance.
This can be done by storing them in a heated area (approx. 20 °C) for several days or by means of special hot air equipment.
Cables in ducts
The inner diameter of conduits and ducts must be at least 1.5 times of the cable diameter or of the bundle diameter of stranded single-core cables.
If cables of an AC or three phase system should laid in a steel pipe than all cables of the system must be laid together in one pipe.
When cables are laid in conduits, the current carrying capacity must be reduced by a factor of 0.85 or must be calculated especially in difficulty cases.