Cable Pulling – Preparing Cable For Pulling Into Open Trench (2 of 2)
By Jack Nottidge, Thorne & Derrick.
In this second guest blog by Thorne & Derrick, the UK’s largest cable laying equipment distributor,we look at the equipment and process requirements for laying a cable in an open trench.
Open trench cable laying is often used as opposed to laying cables directly into cable ducts. This method of laying low, medium and high voltage power cables into the ground tends to be used where the cables in use are of a higher voltage and therefore have a greater overall diameter.
The Preparation Of The Open Trench
Prior to the cable being laid, the cable trench must be dug and prepared properly. This means that the cable trench must be of adequate size to allow for the cables and ducting required. Different cables will require different sized trenches – the higher the voltage, the bigger the cable and therefore the bigger the 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 cable trench is to be dug, it should be sufficient to allow the installer to install the cables and ducting at 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 cable pulling dimensions and without damaging the cable sheaths.
Equipment Required For Open Trench Cable Laying
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.
1. Cable Winch– The cable winch is situated at the end of the cable trench and is designed to be simple and robust. The cable 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. Cable winches vary between telecommunications, power cables and lightweight small power cabling.
2. 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.
3. 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.
4. Cable Socks –Cable socks 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.
5. Straight Cable Rollers– The straight line cable rollers are, as the name suggests, for use in the straight part of the cable trench. Varying in size and weight, the straight cable rollers are selected by the size of the trench they are to be used in. The cable 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.
6. Corner Rollers– Angled corner rollers are to be used within the cable trench where there is a bend in the trench. Typically these incorporate a vertical and horizontal cable roller to allow for the pulling of the cable. Providing the same level or protection as the straight cable rollers they are both used alongside each other.
7. Draw Off Roller– The draw off cable roller is the first piece of equipment the cable will come into contact with when pulled from the cable drum. When the cable is pulled through the open trench, the draw off roller leads the cable straight from the drum into the open cable trench. The cable is then pulled through the trench with the draw roller acting as an initial guide for the cable.
8. Cable Drum Trailer–The cable drum trailer is used to transport the cable drum. In addition the cable trailer is also used to stabilise the cable drum whilst the cable is being pulled through the trench.
Thorne & Derrick UK are distributors of LV-HV Cable, Installation, Cable Jointing & Electrical Equipment – we service UK and global businesses involved in cable installations, cable jointing, earthing, substation and electrical construction at LV, 11kV, 33kV and EHV.
T&D service utilities, power, construction, rail, mining, offshore, oil, gas and petrochemical industries.T&D distribute CatuElectrical Safety Equipment protecting workers on underground cables, overhead powerlines, switchgear and substations at LV, MV and HV.