Cable Laying & Pulling – Installing LV-HV Cables Into Duct
Published 29 Apr 2021
Uploaded By Chris Dodds – Thorne & Derrick Sales & Marketing Manager
Today, in Part 1 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 ducts. In Part 2, we discuss the requirements for cable pulling and laying into cable trench.
Cable Pulling Equipment
& Preparation Duct
Cables installed into cable ducts are typically used on projects where the cable duct is buried deep into the ground, sometimes up to 1200mm depth – this includes LV Low Voltage, MV Medium Voltage or HV High Voltage ducted power cables.
Guidelines for the minimum depths for the installation of underground cables are stipulated by the DNO depending on whether cables are laid direct into cable trench or installed in suitable cable ducts depending on ground location types:
- Footways, Grass Verges Or Private Property
- Carriageways (including Road Crossings)
- Normal Agricultural Land
Arrangement of the cable trench will depend upon the cable voltages typically LV, 11kV, 20kV, 33kV, 66kV and 132kV.
LV cables could include Service Cables (Single Phase Concentric | 3 Phase Concentric | Split Concentric) and Mains Cables (3 Phase Waveform).
Auxiliary multi-core and multi-pair cables are usually laid at similar depths to the power cable with which they are associated. Pilot and telephone cables installed alongside 11kV and 33kV cable circuits shall normally be installed at LV cable minimum depths of cover.
So for instance, the installation of 33kV power cables into class 1 cable duct is usually covered in the local DNO’s Approved Equipment Register, Guidelines or Excavation and Cable Installation Manual. Additionally, engineering construction standards provided by UK DNO’s will cover the installation of new LV, 11kV, 20kV, 33kV, 66kV and 132kV cables, plus associated pilot and telephone cables.
Prior To Cable Pulling
Due to the nature of the cables that are often installed in these applications, there are a number of checks that must be carried out prior to beginning the cable pull:
- The cable duct lines must be checked for any obstructions and anything that is found must be removed. This is often done with the use of duct brushes or ‘foam pigs’ which are pulled through the duct.
- It is essential to ensure that the cable duct is of adequate size to accommodate the cable due to be pulled. This is done by pulling through a 3 metre length of cable through the duct which is subsequently checked for damage prior to the full cable being installed.
- If, during these checks, the 3 metre length of cable has any damage greater than half the depth of the outer sheath the duct route must be repaired before the full length cable is pulled through. This protects the integrity of the final cable.
There are a number of items of cable pulling equipment to be used when installing cables into duct lines. Cables can vary in size and voltage, however the same process and equipment is used. When installing cables, there is typically up to 9 different pieces of equipment used.
- Cable Winch – the cable winch is used for physically pulling the cable through the duct, reducing the need for manpower and increasing productivity. Electrically powered, the cable winch is much safer and reliable than manually pulling cables through.
- Rope Guide Roller – the rope guide roller is exactly as the name suggests – a roller to guide the draw ropes or cabling ropes that are coming out of the jointboxes or manhole. This is to reduce the damage and strain put on the ropes therefore prolonging the lifespan of the equipment used. The rope guide roller is made from an aluminium roller mounted onto a frame that has been plated with zinc.
- Cable Bellmouth – the duct bellmouth is used as a means of providing additional protection to the cable when it is being pulled through the duct. The rollers on the bellmouth ensure that the cable can be pulled in any required direction without any damage being caused. The bellmouth is located at the exit of the cable duct through which the cable is being pulled.
- Cable Drum Trailer Or Cable Jacks – the cable drum trailers and cable jacks are used as a means of storing and transporting cable drums. Cable drums are large wooden wheels which are used to hold cable. Cable drum trailers make the transportation of extremely heavy cable drums easier, safer and more reliable. Often equipped with braking and road lighting, the cable drum trailers are attached to the back of an appropriate vehicle such as a tractor to assist in the transportation of cables. Cable jacks are used as a means of supporting and stabilising the cable drums. Cable drums are located at the edge of the manhole cover or opening when installing cable into underground ducts for the cable to be easily rolled off.
- Swivel Link – the swivel link is zinc plated, solid steel link that is attached to the winch rope. This link can, as the name suggests, swivel a full 360° allowing the rope to be pulled through without any twists occurring.
- Conduit Rod – the conduit rod is fed through the manhole cover opening and is used to install draw or winch ropes. The rod is manually fed through the underground duct and is extremely easy to handle. The conduit rod comes with a range of accessories available such as flexible guide tips, end connectors and rod repair kits.
- Cable Socks – cable socks or stockings can also be called cable socks or grips. These cable socks are used to support the pulling of cables through a duct. Attached to the end of a cable prior to pulling, the cable stocking is an efficient method of support when pulling the cable
- Manhole Roller – the manhole roller is specifically designed to be placed at the entrance of the manhole to assist in the guiding of the cable. Not only does the roller make the cable installation easier, it also protects the cable from being scraped on the edge of the manhole. The manhole roller is constructed of a steel frame and aluminium rollers. Complete range of cable rollers are available also for cable trench applications.
- Cable Lubricant – cable lubricant is applied to the outside of the cables when being pulled through the duct. The lubricant assists in the pulling process by removing friction between the cable and the rollers. This not only speeds up the process but also prevents snagging and therefore damage to the cable.
All cables and ducts 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:
- 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