Cable Laying & Pulling – Installing LV-HV Cables Into Trench
Published 29 Apr 2021
Uploaded By Chris Dodds – Thorne & Derrick Sales & Marketing Manager
Today, in Part 2 of a 2 part series covering Cable Pulling & Laying Equipment, Thorne & Derrick look at the equipment requirements and preparation for cable pulling when installing cables into cable trench. In Part 1, we discussed the procedures and equipment requirements for cable pulling and laying into ducts.
Cable Pulling Equipment & Preparation
In Part 2 of our series of articles about Cable Laying & Pulling Equipment, we look at the equipment and process requirements for pulling and laying cables in an open trench.
Open trench cable laying is often used as opposed to laying cables directly into cable ducts. This method of laying cables into the ground tends to be used where the cables in use are of a higher voltage (MV HV Cables) and therefore have a greater outside cable diameter.
The Preparation Of The Cable Trench
Prior to the cable being laid, the cable trench must be dug and prepared properly.
This means that the trench must be of adequate size to allow for the cables and ducting required.
Different cables will require different sized cable trenches – the higher the cable voltage, the bigger the cable and therefore the bigger the cable trench required.
The trench width and depth also depends on the where the cable trench is being dug. For instance, a cable being laid underneath a public footway will not be laid as deep as one under arable land that is to be ploughed.
When a trench is to be dug, it should be sufficient to allow the installer to install the cables and ducting at the correct depth for the cable being used.
It should also allow the cables to be installed within the bending radii specified.
The cable should be installed within the specified pulling dimensions and without damaging the cable sheaths.
When laying a cable into an open trench, there are 8 key components within the typical equipment layout used excluding the trench and the cable.
- Cable Winch – the cable winch is situated at the end of cable trench and is designed to be simple and robust. The winch provides smooth and controlled pulling of the cables through the trench. It is the cable pulling winch that provides the actual pulling of the cable. There is a number of different cable winches available dependant on the type of cable being pulled. Winches vary between telecommunications, power cables and lightweight cabling.
- Winch Wire Rope – the winch wire rope is attached to the cable in order for it to be pulled through. The wire rope gives extra strength and allows for heavier cables to be pulled through. In addition, the use of the winch wire prevents any potential damage being caused to the cable sheath.
- Swivel Link – the swivel link provides the connection between the cable and the winch wire rope. Each swivel link is designed and used to allow the wire to rotate when being pulled and avoid kinking or twisting. The extra layer of protection provided by the swivel link means damage to the cable sheath is reduced even further.
- Cable Socks – cable socks or stockings are available in either stainless steel or Kevlar but are traditionally constructed of high tensile, galvanised steel wire. Often called cable socks or grips, these are another level of protection between the cable and the cable winch. Fitted to the end of the cable, they are attached to the swivel link and avoid direct contact with the cable. All pilot and telephone, LV, 11kV, 20kV, 33kV, 66kV and 132kV cables should be normally pulled in using a correctly sized cable sock which is securely fixed to the LV-HV cable. More complex cable pulls may require the use of a cable pulling eye attached directly to the cable conductors.
- Straight Cable Rollers – the straight line rollers are, as the name suggests, for use in the straight part of the trench. Varying in size and weight, the straight rollers are selected by the size of the trench they are to be used in. The rollers enable to the cable to be pulled through without making contact with the base of the trench which would damage the cable outer sheath. Full range of cable trench rollers are available – cable pullers should check that cable rollers are in serviceable condition moving easily on their spindle and with rolling surfaces free from damage. Leading cable rollers are usually placed at the cable trench side at the cable pulling end with slide rollers on bends and “hoop” type rollers along straight cable section runs. Contractors can use inverted skid plates shall be used to prevent the cable or pulling wire rising into obstructions. At cable duct entries a bell mouth should be attached at end end with cable rollers positioned to give central access into the bell mouth.
- Corner Rollers – Angled corner rollers are to be used within the trench where there is a bend in the trench. Typically these incorporate a vertical and horizontal roller to allow for the pulling of the cable. Providing the same level or protection as the straight rollers they are both used alongside each other.
- Draw Off Roller – the draw off roller is the first piece of equipment the cable will come into contact with. When the cable is pulled through the open trench, the draw off roller leads the cable straight from the drum into the trench. The cable is then pulled through the trench with the draw roller acting as an initial guide for the cable.
- Cable Drum Trailer – the cable drum trailer is used to transport the cable drum. In addition the trailer is also used to stabilise the cable drum whilst the cable is being pulled through the trench.
Installation Of Cable Trench Covers & Cable Protection Tiles
All cables and ducts laid into cable trrench should be over-protected by a cable protection cover or tape depending upon the highest voltage cable to be protected within the cable duct – typically in the UK the following cable protection tapes and covers are used for LV, MV and HV cables.
Marker tile tapes or Stokbord covers are installed over the cable in the appropriate trench drawings – usually there is no requirement to install either above approved cable ducts installed using trenchless techniques (i.e. directional drill) but either may be installed if it is deemed that additional MV-HV cable protection is required. When Tile Tape is used it should be cut cleanly and installed so that the medium/high voltage cable is fully covered along the whole length of the installed cable duct.
- LV Service Cable 40m x 200mm x 2.5mm Tile Tape
- LV Mains Cable 40m x 200mm x 2.5mm Tile Tape
- 11kV MV Cables 40m x 200mm x 2.5mm Tile Tape
- 22kV MV Cables 40m x 200mm x 2.5mm Tile Tape
- 33kV MV Cables 1000mm x 244mm x 9mm Stokbord
- 66kV MV Cables 1000mm x 244mm x 9mm Stokbord
- 132kV MV Cables 1000mm x 244mm x 9mm Stokbord
Where electricity, pilot and telephone cables are installed into electricity cable ducts the utility engineering standard would normally recommend all cable ducts entering substations and buildings to be duct sealed to prevent the ingress of water and gas – this also applies to 33kV, 66kV and 132kV high voltage substation cables where cable transits are required.
Cable Pulling & Cable Laying Equipment Suppliers & Distributors
Thorne & Derrick International distribute the most extensive range of Cable Pulling & Cable Laying Equipment to enable the installation of low, medium and high voltage power cables into underground trench or duct – products also supplied for fibre optic blowing, subsea trenching, offshore umbilical installations and pulling armoured cables onto cable tray.
- SEB Cable Pulling and Laying Equipment Catalogue Size: 7.37 MB