Typical Requirements for a Fiber Optic Closure

Fiber optic closures that are called as joint closures are used to connect and store optical fibers of two cables safely either in the outside plant or indoor buildings. Fiber optic network operators specify the requirements for the joint closures according to the environment and application area. however, there are certain common requirements that every joint closure/splice closure shall meet. Those common requirements are discussed here.

144 cores dome fiber splicing enclosureImage courtesy: Ronhui Fiber Optics

Cable Compatibility: A fiber optic closure shall be capable of accepting any fiber optic cable as specified in the tender document. Hence it is necessary to know the cable type before deciding on the closure type. Fiber optic closure designs change according to the area of application. Thus, a fiber optic closure for aerial cable will have different design from that used for underground application. The closure shall be suitable to meet the cable diameter (cable dimension in general), cable sheath type, elements used in the cable such as metallic or dielectric, number of fibers per tube and total number of fibers in the cable, fiber protection method such as loose tube, ribbon or tight buffer etc.

Number of Ports: Also known as the cable entrance capacity, the number of ports in a fiber optic closure reflects its capacity to handle the number of cables. The cable entrance capacity of a fiber optic closure refers to the number of ports available for terminating cable within the closure. The number of ports provided in a closure depends on factors such as the network capacity and number of cables used in the network. Usually, in an attempt to reduce the physical size of high-capacity closures, smaller ports shall be utilized for branch cables and drop cables.

Additional Capacity: Closure manufacturers design closures with additional capacity for example, they provide enough capacity to handle 60 optical fibers even though the specification requirement is for 48 fibers

Termination System: The cable termination system shall be designed to provide sufficient mechanical strength between the cable and closure to ensure its performance throughout the lifetime. The cable termination system shall also include a gasket and closure seals that keep the interior of the closure dry. The materials used in optical fiber cables are susceptible to thermal expansion and contraction. Hence the materials used for fiber optic closures shall also be capable of minimizing or negating the effects of relative motion between cable components.

Bonding & Grounding: Proper bonding and grounding of conductive elements of the optical network shall be provided for the safe deployment and operation of the network. If metallic elements are used in the cable, suitable provision shall be provided to do earthing of the metallic elements inside the closure.

Hardware: Aerial fiber optic closures may need to hang on the messenger wire depending on the network configuration. Or they may be attached to the pole. In both cases, extra hardware are required along with the closures. The hardware to attach and secure shall be able to withstand wear and tear and also environmental stresses. A close co-operation with the user may be required to design the hardware as it depends on the structure of poles.

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