CA1236184A - Communications cable joining system - Google Patents
Communications cable joining systemInfo
- Publication number
- CA1236184A CA1236184A CA000486517A CA486517A CA1236184A CA 1236184 A CA1236184 A CA 1236184A CA 000486517 A CA000486517 A CA 000486517A CA 486517 A CA486517 A CA 486517A CA 1236184 A CA1236184 A CA 1236184A
- Authority
- CA
- Canada
- Prior art keywords
- cable
- air
- distribution
- feeder
- end portion
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Abstract
ABSTRACT OF THE DISCLOSURE
A multi-conductor communications cable joining system includes a multi-conductor pair feeder cable having an air core adapted to be filled with pressurized air. A
continuous multi-conductor pair distribution cable has a filling compound therein which surrounds the conductor pairs therein to prevent the ingress of moisture. This distribution cable includes an elongated dry end portion devoid of the filling compound with the conductor pairs in the dry end portion being free of the filling compound. A single air tight splice connects selected conductor pairs of the feeder cable to the conductor pairs in the dry end portion of the distribution cable.
This splice is in air tight sealed relation to the feeder and distribution cables to prevent escape of air to the external environment. A dam is located in the dry end portion of the distribution cable and acts in use as a barrier preventing the flow of air from the pressurized feeder cable into and along the distribution cable, and also acts to avoid contamination of the pressurized feeder cable by filling compound from the distribution cable.
A multi-conductor communications cable joining system includes a multi-conductor pair feeder cable having an air core adapted to be filled with pressurized air. A
continuous multi-conductor pair distribution cable has a filling compound therein which surrounds the conductor pairs therein to prevent the ingress of moisture. This distribution cable includes an elongated dry end portion devoid of the filling compound with the conductor pairs in the dry end portion being free of the filling compound. A single air tight splice connects selected conductor pairs of the feeder cable to the conductor pairs in the dry end portion of the distribution cable.
This splice is in air tight sealed relation to the feeder and distribution cables to prevent escape of air to the external environment. A dam is located in the dry end portion of the distribution cable and acts in use as a barrier preventing the flow of air from the pressurized feeder cable into and along the distribution cable, and also acts to avoid contamination of the pressurized feeder cable by filling compound from the distribution cable.
Description
8~
COM~IUNICATIONS CABLE JOINING SYSTEM
-BACKGROUND OF T~E INVENTION
This invention relates to improvements in ~ulti-conductor communications cable joining systems and, in particular, to improvements in underground systems wherein a pressuri~ed air core feeder cable is spliced to a local area or distribution cable.
In urban areas, telephone utilities typically use an air pressurized feeder cable system in underground ducts between switching centres and distribution areas;
the feeder cables are typically of the air core type with cellular extruded insulation. To service a local area, a connection is provided from the feeder system to a distribution box serving such area; a typical box has provision for 900 pairs of local service although the 900 pairs may not be used immediately. A distribution cable of the cellular insulation compound filled type (e.g. 900 pairs no.26AWG) is installed between the distribution box and the feeder cable to which it is connected in the nearest manhole. However, a filled cable cannot be spliced directly to a pressurized feeder system because it is important to avoid (a) contamination by filling compound and (b) the possibility of air pressure leakage through the filled cable. "Contamination by filling compound" means contamination of the splice area by filling compound (usually a grease-like material) in the distribution cable. This is of particular consequence if the feeder cable includes paper or pulp insulation. It is also possible that the filling compound could act as a partial pressure block in the feeder system if allowed to migrate into it. Until now, the splice has been achieved by splicing a short length (in the order of 6 m) of air core cable between the feeder cable and the distribution ~ ~3~
cable; furthermore, it has been part of the installation practice to make a dam in this short length of intermediate cable, according to a well known procedure to prevent air leakage from the feeder cable to the aistribution cable.
While the above described joining system provides reasonably good results in many respects, it is unsatisfactory in several other respects in that it requires an extra length of air core cable which must be spliced to the distribution cable. This necessitates an extra splice (two splices per connection), thus giving rise to high installation and maintenance costs.
SUMMARY OF INVENTION
It is an object of the invention to provide an improved communications cable joining system at modest cost with good reliability.
A further object is to provide such a joining system while reducing the number of splices needed from two to one thus increasing the amount of room available in the manhole while at the same time reducing installation costs and increasing the reliability of the system.
Thus the invention, in one aspect, provides a multi conductor communications cable joining system comprisillg:
~ a multi-conductor pair feeder cable having an air -core adapted to be filled with pressurized air: -- a continuous multi-conductor pair distribution cable having a filling compound therein which ; surrounds the conductor pairs therein to prevent the ingress of moisture, said distribution cable including an elongated dry end portion devoid of said filling compound with the conductor pairs in said dry end portion being free of said filling compound;
- a single air tight splice connecting selected conductor pairs of the feeder cable to the conductor pairs in said dry end portion of the distribution cable, said splice being in air tight sealed relation to said feeder and distribution cables to prevent escape of air to the external environment;
- a dam located in said dry end portion of the distribution cable and acting in use as a barrier preventing the flow of air from the pressusized feeder cable into and along the distribution cable and also acting to avoid contamination of the pressurized cable by filling compound from the distribution cable.
Further objects, a~pects and advantages of the invention will become apparent from the following description of a prefexred embodiment, reference being had to the drawings appended hereto.
BRIEF DESCRIPTIO~ OF T~E DRAWI~GS
Fig. 1 is a schematic view of a system for joining a distribution cable to a feeder cable in accordance with the invention;
Fig. 2 is a simplified view of "dry end"
distribution cable;
Fig. 3 and 4 are cross section views along 3-3 and 4-4 of Fig. 2.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
Referring to Fig. 1 there is shown an underground system including a typical manhole enclosure 10 into which passes a main feeder cable 12 of a conventional air core type (typically including cellular extruded insulation) such as that made by Pirelli Cables Inc. and described in Pirelli Cables Inc. specification PC-1010 Issue l-May 1982, and supplied with air pressure e.g. about 10 p.s.i.
from a source (not shown). Main feeder cable 12 originates at a central office and typically enters and ~3~
exits several such manholes 10, one being provided at each distribution point. A suitable duct surrounds cable 12 between manholes and protects the same.
A distribution cable 14 exits the manhole 10 and extends to a distribution box 11. Cable 14 (Figs. 2,3 and 4) is, except for its dry end portion, filled with a petroleum jelly based grease-like compound 15 (again known in itself), which surrounds the conductors 16 located within t}-~ cable wrapping and jacket and completely fills the interstices between such conductors. A typical distribution cable will include 900 twisted conductor pairs 16, each being 26AWG size, the conductors 16 being collectively surrounded by a metal shield 18, a core wrap 20, a layer of filling compound 22, and an outer cable jacket 24 of a tough plastics material.
The cable dry end portion 26 (Figs. 2 & 4) includes the components noted above except for the grease-like compound 15 which is absent, so that the insulated conductors 16 are surrounded by air in this end portion of the cable. The dry end portion is readily provided considering the fact that telephone cables are typically filled at either the bunching or laying up stages (i.e. where the pairs or units of pairs are laid together) or at the sheathing stage where the final shield and/or jacket is applied. The filling compound may be introduced by passing the cable through a liquid bath of the compound or a solid, semi-solid or liquid pressure filling head. The dry end 26 is formed by periodically emptying the bath or the head of filling compound thus allowing lengths of dry cable to be made. It is thus possible to provide a fairly sharp line of demarcation 2 between the dry end portion 26 and the filled portion of the cable, and since such filling compound is practically solid until temperatures of 50 to 55C are reached, the ~3~
filling compound does not tend to flow into the dry end during normal use.
Distribution cable 14 communicates with feeder cable 12 via an air tight splice 30, again well known in the art, such as that described in section V of "Underground Catalog" from Preformed Line Products Company, Cleveland, Ohio, (copyright lg78). Cables 12 and 14 are both sealed to splice 30 so that no air escapes to atmospha-e at the splice. Within the splice 30 the paired conductors 16 are joined to selected conductors of the main feeder cable 12 in a well known fashion. Although the splice 30 is air tight to external enviromnent, it - presents no barrier to air flow from the main ~eeder cable 12 to the unpressurized distribution cable 14.
15Referring again to Fig. 1, a dam 34 is located in the dry end portion 26 of cable 14. The main function of the dam 34 is to block the flow of air from the pressurized feeder cable 12 to the unpressurized distribution cable 14. It also inherently serves as a barrier to prevent migration of the filliny compound 15 back into the feeder cable 12 although this would not normally tend to occur for the reasons stated earlier.
Dam 34 is formed by techniques well known per se in the art. These techniques involve the formation of an opening in the cable jacket. The conductors are then mechanically separated from one another by core and channeling pins and the damming compound is then injected and allowed to flow around the conductors and to make good contact with them and with the interior wall of the cable jacket or sheath. The damming compound, typically Hexcel Corporation compound 174 or 3M Company SCOTCHCAST*4407 encapsulating and blocking compound, is then allowed to cure and harden and the opening in the cable jacket is t~e~ sealed wi~h a sultHble patch. Por ~urther detalls of the procedure, reference may be had to the publication *Trademark "Air Core Cable Damming" Issue 2, April 1976, Hexcel Corp., Chatsworth, California.
In theory, the dAm 34 should be placed close to the filled portion of the distribution cable 14 so as to ensure that as short a portion as possible of air core (dry end) cable is left unpressurized and hence susceptible to water ingress. In practice it has been found that a meter or so of unpressuri~ed air core cable has not tended to cause any transmission problems. The only limit as to how close to the filled part of the cable the dam 34 might be placed is related to the possibility of there being a slight residue of filling compound on the conductor pairs which would preclude an air-tight bond being formed by the damming compound. In practice, a distance of 0.5 to about 1 meter should give good results provided care is taken during the filling procedure to ensure that a reasonably sharp line of demarcation exists between the filled and unfilled portions of the cable.
The system described has several advantages over the prior art. Firstly the need for a separate length of air core cable is eliminated. Secondly, the need for a second splice to connect the air core cable to the filled distribution cable is eliminated. Considering the large number of conductors to be spliced, this greatly reduces installation costs and increases the reliability of the system. Thirdly, manhole conditions are improved by virtue of the reduction in cable length and by the elimination of the extra splice i.e. more room is available within the normally cramped manhole.
COM~IUNICATIONS CABLE JOINING SYSTEM
-BACKGROUND OF T~E INVENTION
This invention relates to improvements in ~ulti-conductor communications cable joining systems and, in particular, to improvements in underground systems wherein a pressuri~ed air core feeder cable is spliced to a local area or distribution cable.
In urban areas, telephone utilities typically use an air pressurized feeder cable system in underground ducts between switching centres and distribution areas;
the feeder cables are typically of the air core type with cellular extruded insulation. To service a local area, a connection is provided from the feeder system to a distribution box serving such area; a typical box has provision for 900 pairs of local service although the 900 pairs may not be used immediately. A distribution cable of the cellular insulation compound filled type (e.g. 900 pairs no.26AWG) is installed between the distribution box and the feeder cable to which it is connected in the nearest manhole. However, a filled cable cannot be spliced directly to a pressurized feeder system because it is important to avoid (a) contamination by filling compound and (b) the possibility of air pressure leakage through the filled cable. "Contamination by filling compound" means contamination of the splice area by filling compound (usually a grease-like material) in the distribution cable. This is of particular consequence if the feeder cable includes paper or pulp insulation. It is also possible that the filling compound could act as a partial pressure block in the feeder system if allowed to migrate into it. Until now, the splice has been achieved by splicing a short length (in the order of 6 m) of air core cable between the feeder cable and the distribution ~ ~3~
cable; furthermore, it has been part of the installation practice to make a dam in this short length of intermediate cable, according to a well known procedure to prevent air leakage from the feeder cable to the aistribution cable.
While the above described joining system provides reasonably good results in many respects, it is unsatisfactory in several other respects in that it requires an extra length of air core cable which must be spliced to the distribution cable. This necessitates an extra splice (two splices per connection), thus giving rise to high installation and maintenance costs.
SUMMARY OF INVENTION
It is an object of the invention to provide an improved communications cable joining system at modest cost with good reliability.
A further object is to provide such a joining system while reducing the number of splices needed from two to one thus increasing the amount of room available in the manhole while at the same time reducing installation costs and increasing the reliability of the system.
Thus the invention, in one aspect, provides a multi conductor communications cable joining system comprisillg:
~ a multi-conductor pair feeder cable having an air -core adapted to be filled with pressurized air: -- a continuous multi-conductor pair distribution cable having a filling compound therein which ; surrounds the conductor pairs therein to prevent the ingress of moisture, said distribution cable including an elongated dry end portion devoid of said filling compound with the conductor pairs in said dry end portion being free of said filling compound;
- a single air tight splice connecting selected conductor pairs of the feeder cable to the conductor pairs in said dry end portion of the distribution cable, said splice being in air tight sealed relation to said feeder and distribution cables to prevent escape of air to the external environment;
- a dam located in said dry end portion of the distribution cable and acting in use as a barrier preventing the flow of air from the pressusized feeder cable into and along the distribution cable and also acting to avoid contamination of the pressurized cable by filling compound from the distribution cable.
Further objects, a~pects and advantages of the invention will become apparent from the following description of a prefexred embodiment, reference being had to the drawings appended hereto.
BRIEF DESCRIPTIO~ OF T~E DRAWI~GS
Fig. 1 is a schematic view of a system for joining a distribution cable to a feeder cable in accordance with the invention;
Fig. 2 is a simplified view of "dry end"
distribution cable;
Fig. 3 and 4 are cross section views along 3-3 and 4-4 of Fig. 2.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
Referring to Fig. 1 there is shown an underground system including a typical manhole enclosure 10 into which passes a main feeder cable 12 of a conventional air core type (typically including cellular extruded insulation) such as that made by Pirelli Cables Inc. and described in Pirelli Cables Inc. specification PC-1010 Issue l-May 1982, and supplied with air pressure e.g. about 10 p.s.i.
from a source (not shown). Main feeder cable 12 originates at a central office and typically enters and ~3~
exits several such manholes 10, one being provided at each distribution point. A suitable duct surrounds cable 12 between manholes and protects the same.
A distribution cable 14 exits the manhole 10 and extends to a distribution box 11. Cable 14 (Figs. 2,3 and 4) is, except for its dry end portion, filled with a petroleum jelly based grease-like compound 15 (again known in itself), which surrounds the conductors 16 located within t}-~ cable wrapping and jacket and completely fills the interstices between such conductors. A typical distribution cable will include 900 twisted conductor pairs 16, each being 26AWG size, the conductors 16 being collectively surrounded by a metal shield 18, a core wrap 20, a layer of filling compound 22, and an outer cable jacket 24 of a tough plastics material.
The cable dry end portion 26 (Figs. 2 & 4) includes the components noted above except for the grease-like compound 15 which is absent, so that the insulated conductors 16 are surrounded by air in this end portion of the cable. The dry end portion is readily provided considering the fact that telephone cables are typically filled at either the bunching or laying up stages (i.e. where the pairs or units of pairs are laid together) or at the sheathing stage where the final shield and/or jacket is applied. The filling compound may be introduced by passing the cable through a liquid bath of the compound or a solid, semi-solid or liquid pressure filling head. The dry end 26 is formed by periodically emptying the bath or the head of filling compound thus allowing lengths of dry cable to be made. It is thus possible to provide a fairly sharp line of demarcation 2 between the dry end portion 26 and the filled portion of the cable, and since such filling compound is practically solid until temperatures of 50 to 55C are reached, the ~3~
filling compound does not tend to flow into the dry end during normal use.
Distribution cable 14 communicates with feeder cable 12 via an air tight splice 30, again well known in the art, such as that described in section V of "Underground Catalog" from Preformed Line Products Company, Cleveland, Ohio, (copyright lg78). Cables 12 and 14 are both sealed to splice 30 so that no air escapes to atmospha-e at the splice. Within the splice 30 the paired conductors 16 are joined to selected conductors of the main feeder cable 12 in a well known fashion. Although the splice 30 is air tight to external enviromnent, it - presents no barrier to air flow from the main ~eeder cable 12 to the unpressurized distribution cable 14.
15Referring again to Fig. 1, a dam 34 is located in the dry end portion 26 of cable 14. The main function of the dam 34 is to block the flow of air from the pressurized feeder cable 12 to the unpressurized distribution cable 14. It also inherently serves as a barrier to prevent migration of the filliny compound 15 back into the feeder cable 12 although this would not normally tend to occur for the reasons stated earlier.
Dam 34 is formed by techniques well known per se in the art. These techniques involve the formation of an opening in the cable jacket. The conductors are then mechanically separated from one another by core and channeling pins and the damming compound is then injected and allowed to flow around the conductors and to make good contact with them and with the interior wall of the cable jacket or sheath. The damming compound, typically Hexcel Corporation compound 174 or 3M Company SCOTCHCAST*4407 encapsulating and blocking compound, is then allowed to cure and harden and the opening in the cable jacket is t~e~ sealed wi~h a sultHble patch. Por ~urther detalls of the procedure, reference may be had to the publication *Trademark "Air Core Cable Damming" Issue 2, April 1976, Hexcel Corp., Chatsworth, California.
In theory, the dAm 34 should be placed close to the filled portion of the distribution cable 14 so as to ensure that as short a portion as possible of air core (dry end) cable is left unpressurized and hence susceptible to water ingress. In practice it has been found that a meter or so of unpressuri~ed air core cable has not tended to cause any transmission problems. The only limit as to how close to the filled part of the cable the dam 34 might be placed is related to the possibility of there being a slight residue of filling compound on the conductor pairs which would preclude an air-tight bond being formed by the damming compound. In practice, a distance of 0.5 to about 1 meter should give good results provided care is taken during the filling procedure to ensure that a reasonably sharp line of demarcation exists between the filled and unfilled portions of the cable.
The system described has several advantages over the prior art. Firstly the need for a separate length of air core cable is eliminated. Secondly, the need for a second splice to connect the air core cable to the filled distribution cable is eliminated. Considering the large number of conductors to be spliced, this greatly reduces installation costs and increases the reliability of the system. Thirdly, manhole conditions are improved by virtue of the reduction in cable length and by the elimination of the extra splice i.e. more room is available within the normally cramped manhole.
Claims (6)
1. A multi conductor communications cable joining system comprising:
- a multi-conductor pair feeder cable having an air core adapted to be filled with pressurized air;
- a continuous multi-conductor pair distribution cable having a filling compound therein which surrounds the conductor pairs therein to prevent the ingress of moisture, said distribution cable including an elongated dry end portion devoid of said filling compound with the conductor pairs in said dry end portion being free of said filling compound;
- a single air tight splice connecting selected conductor pairs of the feeder cable to the conductor pairs in said dry end portion of the distribution cable, said splice being in air tight sealed relation to said feeder and distribution cables to prevent escape of air to the external environment;
- a dam located in said dry end portion of the distribution cable and acting in use as a barrier preventing the flow of air from the pressurized feeder cable into and along the distribution cable, and also acting to avoid contamination of the pressurized feeder cable by filling compound from the distribution cable.
- a multi-conductor pair feeder cable having an air core adapted to be filled with pressurized air;
- a continuous multi-conductor pair distribution cable having a filling compound therein which surrounds the conductor pairs therein to prevent the ingress of moisture, said distribution cable including an elongated dry end portion devoid of said filling compound with the conductor pairs in said dry end portion being free of said filling compound;
- a single air tight splice connecting selected conductor pairs of the feeder cable to the conductor pairs in said dry end portion of the distribution cable, said splice being in air tight sealed relation to said feeder and distribution cables to prevent escape of air to the external environment;
- a dam located in said dry end portion of the distribution cable and acting in use as a barrier preventing the flow of air from the pressurized feeder cable into and along the distribution cable, and also acting to avoid contamination of the pressurized feeder cable by filling compound from the distribution cable.
2. The communications cable joining system of claim 1 wherein said dam comprises a compound which is injected into said dry end portion so as to cure and effect an air tight bond with the conductors and an interior wall of the cable cover or jacket.
3. The communications cable joining system of claim 2 wherein said filling compound comprises a grease-like material.
4. The communications cable joining system of claim 3 wherein said dam is spaced from both said splice and from said filling compound.
5. The communications cable joining system of claim 1, 2 or 3 wherein said splice, adjoining portions of the feeder cable and said distribution cable dry end portion are located within a manhole.
6. The communications cable joining system of claim 1, 2 or 3 wherein said splice does not afford a barrier against the flow of air therethrough from the interior of the feeder cable to the interior of the distribution cable.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000486517A CA1236184A (en) | 1985-07-09 | 1985-07-09 | Communications cable joining system |
| AU59820/86A AU585365B2 (en) | 1985-07-09 | 1986-07-07 | Communications cable joining system |
| NZ21678286A NZ216782A (en) | 1985-07-09 | 1986-07-08 | Cable joint |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000486517A CA1236184A (en) | 1985-07-09 | 1985-07-09 | Communications cable joining system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1236184A true CA1236184A (en) | 1988-05-03 |
Family
ID=4130956
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000486517A Expired CA1236184A (en) | 1985-07-09 | 1985-07-09 | Communications cable joining system |
Country Status (3)
| Country | Link |
|---|---|
| AU (1) | AU585365B2 (en) |
| CA (1) | CA1236184A (en) |
| NZ (1) | NZ216782A (en) |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1348749A (en) * | 1972-06-08 | 1974-03-20 | Standard Telephones Cables Ltd | Gas blocks for electric cable joints and terminations |
-
1985
- 1985-07-09 CA CA000486517A patent/CA1236184A/en not_active Expired
-
1986
- 1986-07-07 AU AU59820/86A patent/AU585365B2/en not_active Ceased
- 1986-07-08 NZ NZ21678286A patent/NZ216782A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| AU5982086A (en) | 1987-01-15 |
| AU585365B2 (en) | 1989-06-15 |
| NZ216782A (en) | 1989-09-27 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |