Do you know the “black box” on the ground? Yes, many people who work with FOC (fiber optic cable) may be very familiar with it. It is called Fiber Optic Splice Closure , or fiber splicing closure. In fact, except underground application, fiber optic splice closures are also used for aerial, strand-mount FTTH “tap” locations where drop cables are spliced to distribution cables. It is usually used with outdoor fiber optic cables which provides space for outdoor fiber optic cables to be spliced together. The fiber optic splice closures and the fiber trays inside will protect the spliced fiber and the joint parts of the outdoor fiber cables. What factors should I know before I decide on a splice closure for an OSP installation? 1) You must know if your stitching closure application is installed in the air or in a buried installation. 2) Know your splice Count and splice type – How many fiber splices does the closure need to hold? Are they fusion splices, mechanical splices or a combination of both? Some closures can be purchased with additional sealed ports that can be opened to accommodate new fibers that may be added in the future. 3) Be sure to match the closure, and the application, to the correct type of splice tray. 4) Ease of Reentry – Many newer types of closures, it can be sealed without requiring sealing tape or C-cement. This makes it easy to seal the closure and also to reenter it when future work is required. 5) Multilink closures use compression grommets, made of malleable material that provides a tight seal when the two halves of the closure are bolted together. I recommend using a crisscross star pattern when tightening bolts to ensure that pressure is applied evenly to the compression seal. The grommets around the cable entry and exit ports can be ordered with various hole sizes to accommodate different cable diameters. 6) Some closures have a fitting that enables the installer to fill the sealed closure with compressed air to determine if there are any leaks. A soapy solution can be applied to seams, which will show bubbles if air is leaking out.