Optika v domě
Fiber optics in homes in a few simple steps
Easy access cable - what it is and where it is used?
After many years of the presence of optical fibers in the telecommunications market, it's about time they got settled in houses and apartments. It is forced by the rate of technological progress of consumer electronics that increasingly offers its services on the basis of network connections and online applications.
While optical cables for detached houses are installed on the "one home - one cable" basis, this method can be problematic in multi-family buildings, both in technical and economic sense, especially in existing buildings. It may be costly, difficult, or sometimes impossible to insert multiple cables into existing risers. The best solution is easy access cable, also optimal for currently designed and constructed buildings.
Easy access cable is a fiber optic cable consisting of multiple fibers (e.g. 12, 24, 36 or 48) with 0.9 mm tight buffer coatings, located in LSZH tube. The fibers can be branched directly to individual subscribers without the need for splicing within the riser of the building. They are easily extracted from breaking windows in the gel-free tube. It is possible thanks to the special design of the tube and fibers, with the use of dedicated tools and accessories described in this article.
Construction of easy access cables and dedicated tools
As mentioned earlier, the cable has special tube protecting the fibers, with several unique solutions. On two opposite sides of the tube there are two strength members - aramid rods embedded in the tube wall. In the perpendicular axis there are projections (window cut markers) indicating safe areas for cutting windows with the use of dedicated knife (stripping tool).
|1. Window cut marker on the sheath.|
2. Loose central tube with fibers.
3. Aramid rod.
4. LSZH sheath.
5. 900 μm tight buffer fiber.
Thanks to a special construction of the tube and dedicated stripping tool, it is impossible to break any of the fibers when cutting out windows for drop fibers. The internal cross-sectional area of the tube is 2 times greater than the sum of cross-sectional areas of all fibers in the cable. When the blade of the tool cuts the window, the fibers freely move to the other side of the tube. The possibility of deeper cutting is eliminated by the aramid rods, so the fibers are fully secure.
Installation of easy access cables in buildings
The cables are intended for indoor use. They can be arranged both horizontally and vertically. The choice of suitable cables and their lengths is determined by the size and layout of the network in a building. Typically, easy access cables are run in risers along with other cables, and drop fibers are led to the subscribers. It is therefore necessary to count the number of floors, assess the maximum number of fibers needed (taking into account that some subscribers may need more than one fiber), and the distances from the risers to the outlets. There are some examples below:
The three examples above help understanding three practical rules that are reasonable for buildings with various numbers and layouts of apartments:
- it is better to use one "thicker" cable with some spare fibers than several "thinner" cables without a reserve
- it is good to use cables with maximum (practical) numbers of fibers that should be counted down "from the top" of the building
- if possible (it depends on the construction of a building), one cable should be used for apartments in adjacent staircases
Of course, the maximum length of a fiber that can be pulled out from the cable cannot be longer than the cable itself. Another important fact is that the maximum length of the fiber is limited by technological reasons to 30 meters from the breakout window. In the case where the end of an optical path is to be located further from the drop point, an additional splice with suitable fiber segment is needed.
The installation work is quite simple. The cable reserve left on the rack shouldn't be smaller than two turns. It prevents slippage of the fibers inside the sheath, which is very important due to the fact that the cable may remain unused for longer periods between installations in apartments. The cable should be carefully attached with respect to the minimum bending radius. Any installation work connected with pulling out fibers can be carried out only after unwinding the cable reserve from the rack. Otherwise, an excessive pulling force could destroy the fibers.
Distribution of optical fibers to apartments
The easy access cable installed in a riser is the source of fibers that are run to individual apartments. It is necessary to splice the fibers with suitable pigtails or, in the case of longer lines, with additional fiber segments. In general, there are two options:
- pulling out through the drop windows suitable lengths of fibers and running them to apartments where they are spliced with pigtails in subscriber boxes
- pulling out only relatively short fibers and splicing them in installation boxes with subscriber lines terminated with optical outlets or boxes
The first option is possible when the distance from the riser to the outlet/box in an apartment does not exceed 30 m (as mentioned, this is the maximum length of fiber that can be drawn from a window). Both the windows and bare fibers must be protected against damage. The windows are protected by suitable breakout units / distribution boxes and the fiber are placed in drop/distribution tubes. The tubes can be surface-mounted or placed in grooves in walls. In the latter case, the paths should be carefully documented for future reference - detection of optical fibers inside walls is practically impossible.
If the subscriber terminals are located at distances over 30 m, then the best solution is to use readily made pigtails, which can be spliced to the fibers close to the riser cable. The splices and some fiber reserves are placed in installation boxes located in the immediate vicinity of the riser. Ready-made pigtails can usually be ordered in jackets suitable for direct distribution of the cables to subscribers' premisses without a need for additional tubing.
Additional accessories dedicated fiber optic structured cabling in multistory buildings based on easy access cables ensure high reliability of the systems. For example, windows that are made to cut a fiber without taking it out must be secured. It is not advisable to use an insulating tape, or anything that can squeeze the partially exposed fibers. The adequate protection is provided by rigid covers. In turn, the individual fibers pulled out of the riser cable can be protected by any installation tube, but the ideal choice is the drop/distribution tube with cord VC-TUB L7211, for one or two 0.9 mm fibers.
Fiber terminations in apartments
In apartments, the fibers should be terminated with suitable adapters placed in termination boxes with dedicated front plates, to guarantee protection of users from the invisible laser radiation.
Such termination boxes are used to place one or two simplex or duplex adapters. Some pieces of the equipment are presented below.
The structured cabling based on easy access cables can also be used in any multi-dwelling units, such as office buildings. The cabling can be used for operation in active or passive optical networks. Active networks cannot be equipped with optical splitters.
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