How to Prepare Cables To Avoid Cable Damages & Faults
Published 16 Jan 2020
Preparation of Cable & Run
A careful preparation of cable, cable drum and run can avoid a number of potential reasons for damages and faults.
Low & High Voltage Cables
Cables to be laid outdoors are usually delivered on large wooden or steel drums.
Manual laying of cables is not possible due to the excessive weight.
The cable drums are therefore placed in an uncoiling stand by crane or hydraulically. This stand can either be erected on a HGV trailer or separately, as seen in the picture on the right. The cable drum must have sufficient clearance from the ground and be able to turn freely.
The rolling direction marked on the drum must be observed.
Rolling against the rolling direction results in the loosening of the cable on the reel, which impedes uncoiling. The cable is always uncoiled at a tangent. A cable must NEVER be uncoiled over the flange. The resultant torsion can irreparably damage the cable.
This is equally true for indoor cables coiled on small and light plywood reels and for ring-wound goods.
Before laying the cable, check whether the cable ends have been correctly capped and are undamaged. Missing or improperly glued caps can lead to moisture penetration during transport or laying. The same applies to any damage to the external sheath or insufficient pressure in the case of pressurised telephone cables. Moisture in the cable generally causes deterioration in the insulation resistance and the operational capacity.
A visibly damaged cable must therefore not be wound without closer inspection and clarification of the causes.
Due to their sometimes excessive weight, outdoor cables usually can not be wound by hand. Appropriate winding aids, available in diverse motorised versions, should therefore be used. Make sure that it is possible to provide evidence of the pulling in forces (tension protocol)!
There are numerous possibilities for fastening a pulling rope to a cable and this should be chosen to suit the cable type. For telecommunications cables we recommend conductor pulling with a cable pulling head.
In our example we have used a cable sock. The fastening of the pulling rope to the cable must be undertaken with care to avoid ‘losing’ the cable on the way. Corners and edges at the cross-over point from cable to rope are to be avoided otherwise the cable can easily become stuck on ledges or bumps underground. Guide swivels should be used between the cable sock and pulling rope.
The choice of the correct cable grip is dependent on the diameter of the cable.
The Cable Run
The LV HV cable run is checked before laying the cable.
- Have the minimum bending radii prescribed by the cable manufacturer been followed during laying? If necessary the run must be modified
- Are the trench, shaft, cable duct or cable pipe free of foreign bodies, sharp edges or corners and dampness or moisture?
Inspection and examination of the run prior to laying are essential. A visual check, however, is only possible for open trenches or shafts. A brush pulled through the pipe, with monitoring of any potential tension, also permits an assessment of any inaccessible areas.
If the duct brush becomes stuck in the pipe or if there is a temporary but significant increase in tension, this indicates dirty sections or badly fitting pipe connections.
Dolly-mounted cameras can help in the inspection of a pipe or channel. Thanks to modern technology the inside of the pipe can be viewed live on screen. An accompanying meter counter gives the exact position of potential trouble spots.
Cables which are led through shafts or around corners must always run over deflector rolls. This is an effective way to avoid mechanical damage to the cable sheath.
In order to achieve this some corners require a considerable measure of imagination and clever construction. It is therefore essential to have a plentiful supply of deflector rolls and to choose them correctly.
When pulling horizontally rollers should also always be placed on the ground. The cable must not drag along the ground. An even pulling of the cable with the minimum possible resistance ensures quick and faultless laying.
- Cable Laying | The Importance of Cable Installation Instructions
- Cable Drums | Recommended Transport & Storage
- Cable Pulling | Safe Pulling of Cables Using Motorised Pullers
- Cable Pulling | Safe Pulling of Cables Using Manual Laying
- Installation of Cable Sleeves | Jointing & Splicing Cables
- Installation of Rail Foot Cables
Cable Pulling Equipment
Thorne & Derrick distribute an extensive range of Cable Pulling & Laying Equipment to enable the safe installation of fibre and copper cables within the telecommunications industry. Safely installed cables reduces operational and maintenance requirements to the network and reduced service interruption to telecom cables, wires, ducts, cabinets and exchanges – products include cable spiking tools, conduit rods, cable lubricant, cable socks and rollers.