A fiber optic closure is defined as an enclosure and the associated hardware that is intended to restore the mechanical and environmental integrity of one or more fiber cables entering the enclosure and providing some internal function for fiber organization, splicing, termination or interconnection.
There are two principle configurations for splice closures: butt closures and inline closures.
- Butt closures permit cables to enter the closure from one end only. This design may also be referred to as a dome closure. These closures can be used in a variety of applications including branch splicing. They cannot be used, however, for taut sheath splicing
- In-line closures provide for the entry of cables at both ends of the closure. They can be used in a variety of applications including branch splicing and taut-sheath splicing. In-line closures can also be used in a butt configuration by restricting cable access to one end of the closure
A fiber optic closure type is defined by the functional design characteristics and, for the most part, is independent of specific deployment environments or applications. The most common types of fiber optic closures include:
- Environmentally Sealed Closures (ESCs)
- Free-Breathing Closures (FBCs)
- Taut Sheath Closures (TSCs)
- Pre-Terminated Closures (PTCs)
- Hybrid Fiber Closures (HFCs)
- Thin-Walled Closures (TWCs)
2. Closure Type by Application
Environmentally Sealed Closures (ESC)
Used in buried or underground plant and in any other deployment scenario where exposure to chemicals or corrosive agents is expected.
Free-Breathing Closures (FBC)
Deployment of FBCs in the OSP should be restricted to aerial and ground level applications where there is no risk of water immersion or exposure to chemicals.
Taut Sheath Closures (TSC)
TSCs can be used in buried or underground plant when they are ESC.
Should be restricted to aerial and ground level applications where there is no risk of water immersion or exposure to
chemicals when they are FBC.
Pre-Terminated Closures (PTC)
PTCs are intended for use in drop cable applications.
Hybrid Fiber Closures (HFC)
The HFC provides fiber and splice organization as well as copper splicing facilities and service terminals. The closure
may also be used with composite fiber-copper stub cables.
Thin-Walled Closures (TWC)
The TWC is a closure that serves a limited number of customers, has no express or distribution cables, and is
intended to provide only drop cables or connectors.
In some cases, it may be possible that a particular closure encompasses the characteristics of more than one closure type. For example, a TSC may be either free-breathing for use in aerial applications or environmentally sealed for use in the underground environment. Below is a more detailed description of each type.
2.1 Environmentally Sealed Closures (ESCs)
ESCs provide all of the features an dnd functions expected of a typical splice closure inn an enclosure that prevents the intrusion of liquid and d vapor into the closure interior. This is accomplisheed through the use of an environmental sealing system m such as rubber gaskets or hot-melt adhesives. Fol llloowing installation, an ESC can be pressurized in the fif eield to check the integrity of the environmental se eaal. ESCs represent the most robust environmental prootection available for fiber optic closures. ESCs are ggenerally required for deployment in the buried or underground plant and in any other deploymennt scenario where exposure to chemicals or corrosive e a agents is expecte.
2.2 Free-Breathing Closurures (FBCs)
FBCs provide all of the features andnd functions expected of a typical splice closure inn an enclosure that prevents the intrusion of wind-drivveen rain, dust, and insects. Such a closure, howeveerr, permits the free exchange of air with the outside eenvironment. Therefore, it is possible that cond deensation will form inside the closure. It is thus necesessary to provide adequate drainage to prevent thhee accumulation of water inside the closure. The absenence of elaborate environmental sealing systems foouund in ESCs results in less costly closures and simplifieded installation procedures. Deployment of FBCs in tthe OSP should be restricted to aerial and ground-leveel applications where there is no risk of water imm meersion or exposure to chemicals.
2.3 Taut Sheath Closures s (TSCs)
TSCs are designed to be installed ovover an existing fiber optic cable, called the express ccable, in situations where no cable slack is available. . In many cases, it is possible that the fiber opttiicc cable is already providing service. A taut sheath clclosure permits splicing select fibers from the exprreess cable when no fiber slack is available and doing so o without interrupting the services provided by uninnvvolved fibers. Due to the absence of large amounts of f slack fiber from the express cable, splicing and thee storage of splices are difficult. Particular attention mmust be paid to ensure that torsion and/or tensillee stresses are not imparted on the fiber or splices.
2.4 Pre-Terminated Closures (PTCs)
PTCs are intended for use in drop cable applications. A drop cable of specified length is spliced into the main cable at the manufacturer’s location and enclosed in a low profile, hermetically sealed closure. These closures may or may not be re-enterable. The main cable, drop cable and PTC are often wound on the cable reel prior to shipment. However, other methods of shipment are possible. The PTC installed in a below-grade application and intended to be pulled through a duct must be small enough to be pulled into 100mm diameter conduit along with the cables (distribution and drop) themselves. PTCs must also restore the full tensile strength of the main cable to ensure adequate pulling strength when being installed in conduit.
Some pre-terminated closures are part of a Factory Installed Termination System (FITS). A FITS is one that includes field-deployed products that are pre-assembled in the factory. Normally, cables, cable assemblies, closures and distribution hubs are shipped to a work site and assembled in the field. A FITS would send a completed, distribution-feeder cabling network on a reel directly from the factory with an overmold that breaks out the distribution cable to a drop cable, and may have a hardened fiber optic connector and a stub terminal closure.
2.5 Hybrid Fiber Closures (HFCs)
HFCs are intended for use in support of Fiber-In-The-Loop (FITL) initiatives. Generally, the closure will be located in close proximity to a stubbed Optical Network Unit (ONU). In addition to fiber cable termination, the closure will be used to terminate one or more of the following stub cables: power cable or customer service wires. These cables may be either twisted copper pairs or coaxial (COAX) cables. The hybrid fiber closure provides fiber and splice organization as well as copper splicing facilities and service terminals. The closure may also be used with composite fiber-copper stub cables.
2.6 Thin-Walled Closures (TWCs
A closure that serves a limited number of customers, has no express or distribution cables, and is intended to provide only drop cables or connectors. Because of the reduced number of customers served and/or deployment conditions, the criteria for this type of product may be less severe.
3. Recommended Closure by Deployment Environment
There are a variety of deployment scenarios QNBN may encouter.
The environmentally sealed (ESC) butt closure shall be used in the below ground and above ground environments as described below:
Outside Plant (OSP) – Below Ground Deployment Environments
Outside Plant (OSP) – Above Ground Deployment Environments
- Aerial – Attached to poles or supporting structure
- Wall Mount — Closure designed for attachment to building exterior. The closure may be required to be flood proof or fire resistant in some applications
Free-Breathing Closures (FBC) are acceptable in the following environments: Inside Plant (ISP)
- Customer Premises
- Central Office (CO)
- Indoor/Premises Wall
4. Closure Requirements by Operating Environment
4.1 Closures deployed in customer premises, CO, or other protected environments, shall meet
minimal environmental protection criteria and fire-spread ratings.
4.2 The expected worst case operating environment for a splice closure is defined at temperatures between -40°C and 65°C. At these temperatures, the closure shall not experience any functional degradation that could affect the performance of the closure.
4.3 Underground environments do not experience the same level of severity as the above ground outdoor environment, thus the operating environment for a closure located in an underground environment is defined at temperatures between -30°C and 60°C (Refer ITU-T L.13, Performance Requirements for Passive Optical Nodes: Sealed Closures for Outdoor Environments) and the closures shall not experience any functional degradation that could affect the performance of the closure.
4.4 Under extreme environmental and mechanical conditions to which a closure may be subjected in certain deployment configurations, to include flood water or chemical exposure, submersion in ice, and exposure to steam or fire. Under such extreme conditions, the closures shall not experience any functional degradation that could affect the performance of the closure.
5. Metallic Closures
5.1 Metals shall be resistant and/or protected against general corrosion and various forms of localized corrosion (e.g., stress corrosion, cracking, pitting, etc.)
5.2 The metallic closure material shall be selected to help minimize the risk of inducing significant galvanic corrosion effects when in contact with other metals likely to be present in the closure’s environment
5.3 The use of additional external wraps or coatings shall not be necessary for corrosion protection
6. Non-Metallic Closures
6.1 Non-metallic materials shall be resistant to solvents and stress cracking, and shall be selected to minimize creep.
6.2 These non-metallic materials shall be compatible with chemicals and other materials to which they might be exposed in normal applications and in normal concentrations and amounts
7. Common Closure Requiremen
This section identifies general features and functions that all closures are expected to provide for QNBN deployment. Minor variations are to be expected due to the unique requirements of certain closure applications.
- Cable Compatibility: A fiber optic closure shall be capable of accepting any fiber optic cable as specified by the closure manufacturer, for its intended use (e.g., aerial, below ground, etc.). The closure manufacturer cable compatibility specifications shall include: cable size (maximum and minimum), cable sheath type (dielectric and armored), cable core type (loose tube, ribbon), and cable profile.
- Cable Entrance Capacity: 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 by a closure may depend on the application and deployment environment. In order to reduce the physical size of high-capacity closures, smaller ports shall be utilized for branch cables and drop cables.
- Cable Termination System: A closure that is not full to capacity shall be capable of accepting additional cables without removal of the sheath retention or strength member clamping hardware on previously terminated cables or disturbing existing fiber pathways. The cable termination system shall be designed to provide sufficient mechanical strength between the cable and closure to perform properly in a communications environment. 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 inherently susceptible to thermal expansion and contraction and fiber optic closures shall 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 QNBN FTTH network.
- Where used in brownfield, aerial closures shall be supplied with the necessary hardware to attach and secure the closure to aerial strand, as specified by the end user. Mounting hardware for aerial closures should permit the closure to be temporarily supported on the strand during installation.
7.1 Corrosion Resistance
7.1.1 A closure shall show no evidence of corrosion after exposure to one of the following corrosive environments (see Table 4-3). Corrosion shall be determined per ASTM D610, Standard Test Method for Evaluating Degree of Rusting on Painted Steel Surfaces. A rust grade of 9 or better is required.
7.1.2 If required to address a “heavy salt fog” or highly acidic soil (pH < 5) environment, the closure shall show no evidence of corrosion after a long-term exposure to one of the environments for a period not less than 90 days.
- Deployment Environment： uried, Underground, Aerial Pole & Strand, Outdoor Wall Mount, Indoor Wall Mount
- Corrosion Environment: Acidified Saltwater, Salt Fog, N/A
- Test Duration: 30 days, 30 days, N/A
7.1.3 Material Degradation
The material samples shall show no evidence of cracking following exposure to the chemicals listed:
• WD-40 — water displacing lubricant
• 10% IGEPAL
• Cable Filling Compound, as used in the field
• Splice Encapsulating Compound, as used in the field
• Isopropyl Alcohol Grade HPLC
• Insect Spray, as used in the field Chemical Immersion:
126.96.36.199 An underground closure shall show no change in sealing ability after submersion in a specified chemical test fluid for 7 days.
188.8.131.52 The closure seal of all closures shall be checked by performing the Water Resistance test in below table.
184.108.40.206 Samples of external, non-metallic closure materials shall not experience a change in weight greater than 10% after immersion in the chemicals listed as below.
220.127.116.11 These materials shall not experience a reduction in either tensile yield strength or yield elongation properties greater than 20%. If the material does not exhibit a yield point, the breaking strength and elongation are applicable.
7.1.4 Ultraviolet Resistance
18.104.22.168 Samples of external, non-metallic materials from an aerial or outdoor wall-mounted closure shall not have a reduction in tensile yield strength or yield elongation properties greater than 20% of their original value, after being exposed to one of the conditions outlined as below. If the sample does not exhibit a yield point, the breaking strength and elongation are applicable.
- Standard: ASTM G 154 (Cycle 1), ASTM G 155 (Cycle 1), ASTM G 154 (Cycle 3)1
- Source: UVA: 340nm, Xenon Arc: 340nm, UVB: type 313
- Duration of Exposure: 2,160 hours, 1,000 hours, 2,160 hours
Use of these test standard results in slightly more UV radiation than the alternative cycles. Manufacturers may choose to use this cycle for equipment utilization purposes with the understanding that it may put the product at increased risk of test failure.
7.1.5 Rodent Resistance
22.214.171.124 Rodent resistance is desirable in areas susceptible to gnawing by rodents. Use of selected materials and design geometry can help minimize the likelihood of product damage due to rodents.
126.96.36.199 The following design features in combination are suggested for non-metallic closures in order to meet the rodent-resistance requirement.
NOTE: The following recommendations do not apply to aspects of the closure that could be damaged without affecting the operation or integrity of the closure. The rodent-resistance criteria are applicable to non-metallic closures only. The criteria are considered non-applicable to metallic closures.
188.8.131.52 Closures shall have a minimum material hardness of Rockwell R87 per ASTM D785 or equivalent
184.108.40.206 Closures should have a minimum outside radii of 25mm
220.127.116.11 Closures should have smooth external surfaces with minimum protrusions
7.1.6 Steam Resistance
Closures designed as steam resistant shall show no indication of moisture in the area containing fiber optic splices or components after exposure to saturated steam for a period of 14 days.
7.1.7 Fire Resistance
18.104.22.168 Plastic materials shall have a flammability rating of 94 V-0 when tested per UL 94, or alternatively a rating of 94 V-1 with a minimum oxygen index of 28 as determined by ASTM D2863
22.214.171.124 If a wall-mounted closure or exterior parts of the closure are constructed of polymeric materials, the housing shall be constructed of polymeric material with a flammability rating of UL 94-5VA when tested per UL 94