FTTH - installation of a distribution frame/box

Implementations of FTTH installations based on fiber optic subscriber lines arranged in a star topology are currently the most popular way of deploying fiber optics in multi-family buildings. The main advantages of the solution include a relatively low cost and a simple installation. The reasons of the low cost:
  • application of cheap distribution cables – the most popular indoor distribution cable Ultimode L7102 is nearly two times cheaper than good quality Cat 5 UTP cable
  • no need for additional installation activities such as splicing fibers in some intermediate boxes, making breakout windows, pulling out fibers, installation of breakout units (necessary in the case of breakout/easy access cables)
A disadvantage of this solution can be problems with holding multiple cables in proper arrangement in the distribution frame (to preserve the minimum bending radius for each cable/fiber). In some cases, the solution requires the application of additional distribution frame(s) for getting more space, despite the fact that the number of connections would be sufficient.
Fiber Optic Box: ULTIMODE MT-524 (19Fiber Optic Box: ULTIMODE MT-524 (19Indoor Cable: ULTIMODE ILB-2SM-A (2xG.657A1, limited bending radius)
The architecture of an FTTH system based on star topology

The most popular cable used in these applications is ULTIMODE ILB-2SM-A L7102. A special construction of the cable with rectangular cross-section of the jacket plus built-in FRP reinforcing rods naturally limit the bending capability in one plane to a safe bending radius range. Thanks to reduced minimum bending radius of the G.657.A single-mode fibers, the cable and individual fibers can be formed into tight coils (the minimum bending radius is only 7.5 mm).
Due to an increased use of RACK cabinets in multi-dwelling units, the distribution frames often have the form of 19" RACK boxes/panels. The example of such an optical distribution frame is Ultimode MT-524 L5124. The presented implementation involves the application of L7102 cables and single-mode pigtails PG-52S2 L35522.
Top view of the distribution frame/box. The front panel holds Ultimode A-522D L4322 duplex adapters (each adapter terminates one L7102 cable with two fibers going to one apartment or other premises).

The installation should be begun with inserting pigtails into the suitable adapters (the ferrule end faces should be cleaned with the L5916 tool). The pigtails must be adequately marked, so as to avoid problems after splicing them with the fibers of the distribution cables. Otherwise, the connections would have to be identified with the use of a visual fault locator, e.g. L5935. In the case of cables deployed in the whole building, the testing procedure would be very time-consuming.

The fibers of the pigtails should be placed around the brackets lying on both sides of the tray with splices. Cable ties provide suitable cable management.

The ends of the L7102 cables have to be inserted into the box, with spare lengths of the fibers coiled around the dedicated ring on the tray. The lengths should allow for splicing the fiber ends with pigtails outside the box.

The splicing operations have been performed with the use of EasySplicer L5810 fusion splicer. Worthy of note is the fact that the L35522 pigtails have loose tube construction. In this case, it is recommended to remove the 900 μm coating at a slightly greater length, and use the holders dedicated for 250 μm fibers. It eliminates any instability when placing the fibers in the splicer (the 900 μm holders are intended for fibers with tight buffer construction).

In the example, the box accommodates four L7102 cables (with total of 8 fibers). Potentially, the box with the included tray can accommodate up to 16 such cables (32 fibers). After adding L5506 tray, the total capacity grows to 48 fibers (after mounting 24 duplex adapters).

The spare lengths of the cables should allow for drawing the box out of the RACK cabinet.