Cable Laying | The Importance of Cable Installation Instructions
Published 14 Jan 2020
Usually the only people who take any notice of cables and wires are those who work with them. Most of us use the telephone, watch television or surf the Internet without thinking about how the underlying infrastructure, the network of cables, has been assembled.
Cables are rarely heeded; they are ‘simply there’.
General knowledge about cables is equally lacking. Very few people know what high technology is wrapped up in the inconspicuous black, grey or coloured wires. Indoor cables in particular are subjected to heavy handling by the user: office chairs are rolled over telephone connection wires, computer patch cables are trodden on by people or nibbled by their amusing pets.
Outdoor cables are affected by huge differences in temperature and high bending and pulling forces while they are being laid. The thicker the cable the stronger it may appear. However thick as well as thin wires are subject to the same physical conditions and limits.
The following Blogs aim to raise awareness about cables and explain terms such as bending radius, temperature ranges or permissible tension. Furthermore you will find instructions and tips for correct and safe installation.
Initially people have the idea, ‘We should/ must modernise or expand our network’.
An engineering consultancy is hired to transform the idea into a feasible plan.
Basic conditions and objectives are decided together with the customer. At the same time many technical parameters must also be considered along with the questions related to infrastructure.
During the realisation phase for the plans numerous trades work closely together. One of these is concerned with the laying of the physical network of wires or cables.
The installation company responsible for laying the cables must heed the following parameters:
- temperature range of the cable,
- bending radius of the cable,
- maximum tension of the cable,
- weight of the cable as well as
- storage and cutting.
The temperature range of the cable is of great importance for both the user and fitter.
After all the cable is meant to function equally well in cold and hot temperatures. It is particularly during the fitting process that powerful mechanical forces act on the cable. The plastic used serves as the limiting element for the possible temperature range.
At overly warm temperatures the plastic becomes very soft and can change into a thermoplastic state (up to melting point), which causes irreversible changes in the cable.
At very cold temperatures, however, the material stiffens and becomes hard and inflexible. Here, too, irreparable damage can occur.
Tears in the sheath allow dampness and moisture in and impair the transmission rate.
Details about the permissible temperature range during laying and use (following successful fitting) can be found in the information sheets of the cable manufacturer. Since the mechanical strain on the cable in its laid form is significantly less, the permissible temperature range is greater than the range valid for the installation period.
The VDE 0816 gives the following values:
During Cable Laying
PE-sheath, from -20 ° C to + 50 ° C
PVC-sheath, from – 5 ° C to + 50 ° C
Before & After Cable Laying
PE-sheath, from -20 ° C to + 70 ° C
PVC-sheath, from – 5 ° C to + 70 ° C
Cable Bending Radius
Regarding the bending radius we distinguish between multiple and single bending (shaping into the final position). Multiple bending occurs mainly during the laying process.
Cables are laid under tension around deflector rolls. The particular stress of multiple bending lies in the alternating stress on the materials, which can be stretched several times as well as compressed during the laying process. To prevent permanent damage there are prescribed minimum bending radii of, for example, 10 x cable external diameter for multiple bending.
The stress on the material during final bending is not characterised by alternating stress.
The cable is bent into form a final time and stays in this position for the duration of its use. The minimum bending radius in this case is, for example, 7.5 x cable external diameter. During final bending the cable can, therefore, be bent more tightly.
Exact minimum bending radii for specific cables can be found in the information sheets of the cable manufacturer.
During laying of the cable particular attention must be paid to the maximum possible tension. The cable is very quickly damaged by the use of too much force and must then be replaced. The maximum possible tension depends in the first place on the overall cross section and the tensile strength of the conducting materials used.
For cables with steel tape or copper wire spiral armouring it is the internal copper conductors alone which determine the maximum tension! The armouring has no influence on the maximum tension or can possibly reduce it through additional weight.
For armouring with steel or steel profile wires, however, the tension is determined solely by the steel and steel profile wires.
The cable weight of larger cable dimensions can take weights of up to more than 9 t/km (without the reel!).
Storage & Cable Cutting
Cables for delivery as well as cut cables must generally be protected against moisture penetration. This best occurs through the use of shrink caps with fusible glue. Loose-fitting caps or temporary measures with plastic adhesive tape are not watertight and are unsuitable.
Moisture penetration leads to corrosion and deterioration of the transmission rate.
If two cable ends are to be connected with a sleeve, this must take place immediately and with protection against moisture and rain. For the period of the sleeve installation an installation tent must be erected.
- Cable Drums | Recommended Transport & Storage
- How to Prepare Cables To Avoid Cable Damages & Faults
- 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.
Further Reading | Cable Drum Handling & Laying Cables | A Guide from Nexans