For several recent columns, I have been writing about splicing optical fibers. Last month, I covered managing fibers inside the splice trays and closures. But there is even more to know about splice closures.


Splice closures come in two basic styles. In inline-style closures, cables enter from either one or both ends, and the closure splits down the middle in line with the cables for access. In a dome closure, cables enter from one end on a base, and a single-piece dome drops down over the splice trays.


Splicers like to argue over which design is better, and arguments for both can be persuasive. It’s probably a matter of which type you learned on or have the most experience with. Either can work well if handled with care.


Sealing is a very important issue with splice closures. Outdoor closures must be well sealed to protect the fibers and splices from the outside environment. Allowing moisture, dirt or mud to enter the closure will surely cause long-term fiber performance and reliability degradation. 


Winter is especially hard on closures. A few winters ago, an installer sent me a photo of a closure that leaked and then froze solid. He called it a “splice-sicle.”


Splice closures generally have big O-ring seals and clamps or screws that hold the parts together to ensure seal integrity. Complaints about poor sealing on cheap closures and counterfeits are common, so buying a brand name from a reputable dealer is highly recommended.


Double-check the joints on the closure to ensure they are properly sealed. Be especially careful around the cable entrances. If the closure does not seal and moisture gets in, it will cause problems with the splices, fibers and cables. Some closures can be pressurized to test the seal, so be sure to do so.


Cables must also be firmly attached to the closure mechanically to ensure they do not pull out. Closures will have clamps near the cable entrance to clamp and tie off cable-strength members. Cables with metallic elements must also be grounded properly.


After the splices are made and the closure is sealed, it and the excess cable must be mounted in a safe location. The closure placement and excess cable should be carefully considered to ensure its safety and accessibility in case it needs to be entered in the future for repairs or rerouting fibers.


Splicing is generally done in a splice trailer where temperature can be kept at a reasonable level and dirt and dust exposure can be minimized. The trailer also has a workspace with room for the opened closure, splice trays, the splicing machine, tools and supplies. When splicing cables, it takes an extra 10­–20 meters of cable to reach into the trailer, so that excess cable will need to be stored in service loops near the closure.


If the cable is underground or direct-buried, a pedestal, vault, hand-hole or manhole will usually be installed to store the splice closure and protect it. Direct-buried cables should also have a pedestal or hand-hole for the closure, not simply buried near the cable where it is subject to leaking and hard to find when problems arise. Because pedestals are vulnerable to damage from vehicles, they should be placed as far as possible from roads.


Aerial cables are usually spliced on the ground, so there may be a lot of extra cable for storage. Sometimes the closure is placed on the ground, and the cable is coiled up on the pole or tower. The closure may be placed on the pole or tower with coils of cable nearby. Closures may even be suspended from the cable messenger itself and the excess fiber lashed to the messenger. Installers in some rural areas have told me these visible closures are popular for target practice. I have also heard of them being attacked by woodpeckers.


Our splices are almost completed, but as you are always reminded, the job is not completed until the paperwork is done. The documentation on a splice point must be comprehensive, including cables splice and every fiber splice identified as cable to cable, loose tube to loose tube and fiber to fiber. Ribbons must be noted as ribbon to ribbon. Any crossing or breaking out of fibers must also be noted. And, of course, the spreadsheet used to document this will also have test results.


That can be a lot of documentation if you are splicing two 144-fiber cables, but if a problem arises, having that documentation will make identifying fiber and splices much easier, facilitating repair or restoration.