For several decades developments in optical fibre and cable have centred on getting more information down higher performance fibres housed within ever more compact cables designed to be pulled, blown or pushed into their desired locations. However, in parallel with this work, cable developers have been trying to make cables easier to use.
Where network users are added progressively it’s clear that a cable that runs a considerable distance will need to be opened up several times to use the appropriate fibre(s) for that new user. In the past, this has been achieved by leaving coils of cable in chambers along the route, so that when new service is needed the cable can be broken partially stripped back to its component loose tubes, the strength member cut and the remaining loose tubes coiled at the back of the joint with one loose tube exposed so that drop fibres can be spliced to it. Even for experienced craft people this is an involved procedure, it takes considerable time and is relatively expensive to accomplish. Moreover, it requires the original cable to be of loose tubes design, always required a fibre join and, usually, involves at least 12 fibres when perhaps only one or two are required. If all that was not enough,
Rather than trying to make traditional cables fit a new requirement, it makes sense to make a cable to fit the requirement. Perhaps the best way to do this is to produce a hybrid cable-duct design where a relatively stiff, strong outer casing is used to contain a variety of fibre ‘modules’. Some of these modules will be used to drop service to individual customers, whilst others will be used for backbone traffic where the fibre passes along the entire cable section. With this kind of construction different fibre count modules can be incorporated and the mix between backbone traffic modules (typically 12 fibres) and drop traffic (typically 1 to 4 fibres) can be varied according to network requirements.
Let’s explore the properties expected of such a cable. Firstly, the cable should ideally be usable direct in a duct. There is little point in directly burying this cable type (breakout locations will have to be built from scratch) and since the outer casing is effectively a duct, it would be overkill to install the product into a sub duct. Therefore, the cable is likely to be pulled into a main duct. It should have sufficient tensile strength for this purpose, so typically a 1W or 1.5W rating is ideal. Often these cables are used in shared ducts so, from a safety perspective, an all dielectric strength member is advised. The sheathing or casing must be sufficiently robust to survive ‘window cutting’ (which we will look at below) but it must be removable by the tooling supplied. So, what exactly is the necessary tooling to use these cables? The answer to that depends on the way the user wants to operate the cable. In the original version, the cable is window-cut at the nearest chamber to the new customer. This requires the use of a tool which removes a few cms of casing to expose the fibre modules on the upper part of the cable. The tool can be manually operated, needs to have no exposed blades and must produce a repeatable ‘window’. The selected module is cut at one end of the exposed window and spliced to a drop fibre. In a different version, two window cuts are performed 10s of metres apart (with the same type of tool). The selected module is cut at the distant location and it is pulled back to the customer chamber. From there it is fed down a customer drop duct, either by pushing or air assisted pushing. There is an interesting variation of this second technique. It uses an ingenious, flexible, cutting tool to cut the selected module some metres away from a single window cut. In this way, the selected fibre can be withdrawn without having to access a second chamber. Finally, at least one installation equipment producer has attempted to store a pulled back module in a cassette arrangement on the equipment so that it can be more easily blown down the drop duct.
It is all very well chopping a hole in the cable and extracting fibres but it then needs to be made good. Inevitably this means specialised joints that cover the cut, splice the fibre (if needed) and seal against water are needed. It is important to seal each joint as this is an ‘open’ cable and one leaking joint means it’s likely the entire cable will fill with water.
Emtelle’s newly launched retractable solution RTRYVA is an incredibly flexible duct system which can be accessed at any point along its length and fibre can be easily accessed and configured to drop directly to a home/business where fibre provision is required. With various advantages over traditional cabling solutions, RTRYVA offers space, product and installation cost savings, RTRYVA offers >€80 / home for Brown Field applications due to the fact that its density of fiber can accommodate 96 home drops from a single Ø15mm duct. When planning a new build (Green Field) build, if planned before Civils / digging, then additional savings of €60 / home on access chamber costs can be achieved giving total cost savings of €140 / home.
Watch RTRYVA simple installation process here:
As with all choices, the facts dictate the option! One key consideration is the environment the cable is entering. Retractable cables are often the choice of a second network company and are therefore required to fit into a congested environment; frequently the network owner will offer a limited space and so the best choice of retractable cable will often by the one that offers the largest number of fibre modules. Joints need to be carefully considered and need to be made to fit the cables specifically. The biggest decision is whether to go for a one window cut or two window cut variant. Operationally, a single cut product is much more attractive since the time and disruption to deploy is greatly reduced. A spliced connection has the great advantage that it means any drop length can be provided, however if the customers are generally near to the chamber a more reliable solution is to withdraw the module and feed it back into a drop duct (albeit usually with a second cut). In all cases the ability to use a remote cut tool to provide sufficient fibre to handle is a near necessity. But whichever option a second operator chooses, using any retractable cable avoids the need to store cable loops in every chamber – just in case – and avoiding that means avoiding unnecessary costs!