Electricity: conductors and insulators – Conduits – cables or conductors – Combined
Reexamination Certificate
2001-04-27
2003-06-03
Nguyen, Chau N. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Combined
C174S093000
Reexamination Certificate
active
06573455
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a cable closure, by means of which environmental protection may be provided around a cable splice, termination or other cable portion. The invention may be used with power cables, CATV cables or telephony or other communications cables. The invention is likely to find most use in protecting splices in, and terminations of, optical fibre cables.
BACKGROUND OF THE INVENTION
The use of closures for environmental sealing of cable splices is of course well known. Cables are produced in finite lengths and therefore lengths of cable frequently need to be joined together. The function of a closure is to provide a seal that bridges the jackets of the spliced cables. A closure may also provide other functions in addition to environmental protection, such as mechanical protection and axial-pull strength. Closures may be used around simple end-to-end splices between cables, but frequently more complex splices require sealing. For example, a large cable containing many conductors (by which term I include optical fibres as well as electrical conductors) may be split into two or more smaller cables. Ultimately, a cable will be effectively terminated where it is broken down to single conductors or small groups of conductors. Such terminations also require cable closures to protect them.
It is frequently necessary to install a cable closure around a cable splice (or termination) where access to ends of the cables is not available. In such circumstances the closure clearly cannot be permanently of closed cross-section: the closure needs to be “wrapped around” the cables, rather than slid onto the cables from one end. This term “wrap around” derives from cable closures that were formed from flexible sleeves or longitudinally-slit tubes. It is, however, a general term that merely refers to the capability of installation around a cable at some point between its ends. Thus, the term includes substantially rigid half shells that are assembled around the splice. The shells may be hinged or otherwise linked together by moulded-in strips or by tapes or living hinges etc. The term “half shells” does not imply any particular shape, and the two half shells may be different or generally similar in shape to one another. Thus, each half shell will have a periphery that abuts the periphery of the other half shell, and each will have a hollow body portion, roughly semi-circular in cross-section, so that when the two half shells are brought together they define a roughly rectangular or circular cylindrical enclosed space within which the splice will lie. Half shells may, however, differ from one another, so that one might be described as a base plate, and the other as a cover. These terms “wrap around” and “half shells” are well-known in the art.
Many cable closures have been proposed that make use of half shells. Unfortunately, many problems remain. The performance requirements of a closure are very difficult to meet. The problem arises largely because a closure must be very quick and easy to install, usually with unskilled labour, and under difficult conditions, but must meet very stringent performance specifications. As a general rule a cable closure is expected to have a life time comparable to that of the cables which it protects, typically twenty or more years. Cables are generally situated out of doors and are subjected to extremes of temperature and humidity. Various tests have been devised to mirror this long-term performance. Although different tests are applicable to different cables in different situations, typical tests involve pressurisation of the closure whilst it is subjected to temperature cycling, often under wet or humid conditions. A closure is expected not to leak for a certain number of such cycles. Clearly, closures of the half shell design start out at a disadvantage because a seal must be provided between the half shells as well as between the incoming and outgoing cables and each half shell. A particularly severe problem arises at the region where a seal between the half shells meets a seal between the cables and each half shell. This region is known as the “triple point”. It can therefore be seen that design of such a closure is a difficult matter.
The difficulties are, as usual, increased by the need for low cost. The requirement for low cost means that it is not possible to supply different designs of closure for each cable size and for each splice or termination configuration. Thus, a single design of closure must be able to accommodate, for example, a simple in-line splice between two cables, a butt splice between two cables (where the two cables lie side-by-side), and various configurations, such as “one in-two out” where one cable enters one end of a closure and two leave at an opposite end. In order to accommodate a range of splice configurations, one may decide to provide a closure that has four cables seals, two at each end. Cable seals are, unfortunately, expensive and such a closure would need to be provided with four such seals. Each of these seals would need to be capable, not only of sealing to an incoming cable, but also be capable of being closed in case the full compliment of cables was not to be employed. The present invention provides a particularly simple and elegant solution to these problems.
Before the invention is described in detail it may be worth noting some prior art closures of the half shell type. U.S. Pat. No. 5,322,973 discloses an aerial closure for protecting a cable splice. It has a central header portion and wing-like housing segments that may enclose the splice. The wing-like housing segments may be raised to provide access to the splice. Each end of the closure has a seal assembly for sealingly engaging the ends of the incoming cables. These assemblies have concentrically circular and corrugated features thereon so that an appropriately size hole may be cut to allow entry of 1, 2 or 3 cables of various sizes.
U.S. Pat. No. 4,805,979 discloses a fibre optic splice closure comprising a base to which a cable may be anchored, and a cover which overlies the base. Seals are provided around the cables at the position where the base meets the cover.
U.S. Pat. No. 4,492,816 discloses half shells for forming a cable splice. Half shells have flanges which abut one another in the assembled configuration. The adjacent flanges define a duct into which sealing material in the form of a paste may be introduced. Opposite ends of the resulting closure are provided with jaws which clamp against the incoming cables. Two jaws define between them a chamber which communicates with the sealing duct by means of a channel formed around the entire periphery of a jaw adjacent to the chamber.
EP 0543350 discloses a cable enclosure formed from a base and a cover which are secured together by bolts through flanged portions thereof. Various cable guide sections are located at the interface between the base and the cover.
GB 1260273 discloses a housing for electrical connections, which comprises a cylindrical central part and end parts that form a seal between the central housing and each incoming cable. The end parts are moulded to provide a number of cable entry ports. The ports are initially blind. The extreme ends of the ports are cut off as and when required to allow cables to pass through. The ports are heat-shrinkable so that after insertion of a cable a port can be shrunk to make sealing contact with it.
U.S. Pat. No. 5,109,467 discloses an optical fibre interconnect cabinet in the form of a box with a lid. The side walls of the box are provided with slots which can receive removable blanks. With the blanks in place, and the lid closed, the box is sealed. With the lid open, a blank can be removed to provide a port for cable entry.
Whilst each of those prior art designs provides some of the benefits that I now seek, each unfortunately suffers from one or more problems. For example, some of the designs are not fully “wraparound”, some are not suited for environmental protection out of doors, some are too complex and expensi
Myers Bigel & Sibley & Sajovec
Nguyen Chau N.
Tyco Electronics Raychem N.V.
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