CABLE STRAPPING USING GLASS FIBRE FILAMENT TAPE
This bulletin provides guidelines for the application of reinforced glass fibre polypropylene filament tape for strapping cables together, particularly single core cables in trefoil formation. This is essential to ensure that cables stay in formation during short-circuit forces so as to minimise circuit disturbance and damage.
Purpose of Glass Fibre Filament Tape
As an alternative to stainless steel straps for strapping cables together in trefoil formation, other non-magnetic or non-metal strapping may be used in conjunction with cable cleats, provided it has sufficient strength and can withstand the corrosive effect of the atmosphere in which it is installed.
For such purpose, reinforced glass fibre polypropylene filament strapping tape may be used to strap single core cables together in trefoil formation or in flat formation provided it meets the requirements as stipulated in this technical bulletin.
Glass Fibre Filament Tape Requirements:
- Backing shall be reinforced glass fibre polypropylene.
- Minimum fibre strands: 9
- Minimum Tape width: 18mm
- Rubber resin adhesive
- Operating temperature range: -5ºC to 70ºC
- Cleats are required in conjunction with fibre filament straps, particularly at the substation or switching yards.
- Ensure that cleats for single core cables, whether installed in flat formation or in close trefoil formation, are non-magnetic. Such cleats are usually cast from non-ferrous alloy or made from treated wood which has been approved and tested.
- Cables at the substation or switching yard should be cleated in close trefoil every 3m to 4m and strapped with the glass fibre filament tape every 1m on straight sections and 0.3m on bends.
- A minimum of 15 layers of filament tape should be applied over the trefoil cable group. The tape layers should be applied with no overlap, that is, on top of itself.
- Black PVC insulating tape may be applied over the filament tape to cover it for aesthetic reasons.
- Where cables are laid in ground, apply the glass fibre filament tape every 3m along the cable route.
Guidelines for installing cables in trefoil formation:
- Single core cables need to be straight and installed together in close proximity.
- Cables should be spaced close together so that a sling or similar item can be used to shape the trefoil formation (triangular) in conjunction with a turning device such as a steel pin or similar object.
- Shape the cables in trefoil with one phase on top and the remaining phases in the bottom position.(Normally red and blue is in the bottom position)
- Wrap a suitable nylon sling around the cables and lift together so that the required trefoil shape is obtained.
- Turn the sling to tighten the trefoil, hold together and apply the filament tapes as described above.
- The trefoil group can now be loosened and put down on the sand bagged trench.
- Care should be taken not to pick cables up to high when taped as this will create a movement of the cable and tapes from each other.