EP1150305A2

EP1150305A2 - Electrical cable apparatus having reduced attenuation and method for making

Info

Publication number: EP1150305A2
Application number: EP01303769A
Authority: EP
Inventors: Bruce J. Clark; John T. Milsaps; Paul Emilien Neveux Jr.
Original assignee: Avaya Technology LLC
Current assignee: Avaya Technology LLC
Priority date: 2000-04-26
Filing date: 2001-04-25
Publication date: 2001-10-31
Also published as: EP1150305A3; BR0101479A; JP2001357731A

Abstract

Embodiments of the invention include an electrical communication cable apparatus and method for making. The electrical communication cable comprises an information transmission medium such as an insulated electrical conductor or a pair of electrical conductors, a separator layer formed around the transmission medium, and a protective, low smoke polyvinyl chloride (LSPVC) jacket formed around the separator layer. The separator layer is made of, e.g., polytetrafluoroethylene (PTFE) or other suitable dielectric material. Alternatively, the communication cable apparatus includes a flute for separating insulated electrical conductors therein.

A method for making communication cable comprises providing a transmission medium such as an electrical conductor, a pair of electrical conductors or a plurality of electrical conductor pairs, forming a separator layer around the transmission medium, and forming a protective LSPVC jacket around the separator layer. The separator layer is made of a suitable dielectric material such as PTFE or PTFE tape.

The separator layer improves the dielectric properties of the cable in such a way that attenuation of signals propagating along conductors within the cable are reduced. Also, the separator layer reduces tightness between the protective jacket and the transmission medium, further improving attenuation characteristics of the cable and allowing portions of the protective jacket to be stripped away more readily than in conventional communication cable configurations.

Description

Background of the Invention

1. Field of the Invention

The invention relates to electrical cabling. More particularly, the invention relates to electrical cabling having reduced attenuation.

2. Description of the Related Art

Electrical cables typically are used to transmit large amounts of information great distances, e.g., between and within various communication networks including local area networks (LANs). Electrical communication cables typically are comprised of a plurality of twisted pair of individually insulated, electrically conductive elements such as insulated copper wires surrounded by a protective, dielectric jacket made of, e.g., ethylenechlorotrifluoroethylene (ECTFE), low smoke polyvinyl chloride (LSPVC), or fluoroethylenepropylene (FEP).
In addition to exhibiting sufficient transmission characteristics, electrical communication cables used for indoor applications typically have flame retardancy and low smoke requirements. Electrical communication cables having copper insulation materials formed from fluoropolymers such as FEP must pass standardized fire tests, e.g., the Underwriter's Laboratory Standard 910 test (the Steiner Tunnel test) or NFPA 262, which qualifies these cables for use in plenum space inside buildings.
To meet existing fire test requirements, many electrical comiuunication cables having FEP-insulated conductor elements use jackets made of materials such as LSPVC, which has more favorable fire test burn characteristics than, e.g., conventional PVC jackets. However, jackets made of materials such as LSPVC have poorer dielectric properties, thus contributing to increased attenuation of signals propagated along the conductor elements.
Furthermore, jackets used in conventional cabling configurations (including jackets made of LSPVC) often are formed relatively tightly around the transmission media therein to improve the protection thereof. However, such configurations often make it difficult for a portion of the jacket to be stripped away, e.g., during installation, repair, splicing and other operations. Also, such relatively tight arrangements further contribute to increased attenuation.
Accordingly, it is desirable to have electrical communication cables with improved attenuation characteristics while maintaining suitable burn and low smoke properties.

Summary of the Invention

The invention is embodied in a communication cable apparatus and method for making a communication cable apparatus. The communication cable apparatus comprises an information transmission medium such as an insulated electrical conductor or a pair of electrical conductors, which may or may not be separated by a dielectric spacer tape or cross-piece or flute; a separator layer formed around the transmission medium; and a protective, low smoke polyvinyl chloride (LSPVC) jacket formed around the separator layer. The separator layer is made of, e.g., polytetrafluoroethylene (PTFE) or other suitable dielectric material.
According to embodiments of the invention, a method for making communication cables comprises providing a transmission medium such as an insulated electrical conductor, a pair of insulated electrical conductors or a plurality of insulated electrical conductor pairs, forming a separator layer around the transmission medium, and forming a protective LSPVC jacket around the separator layer. The separator layer is made of a suitable dielectric material such as PTFE tape.
The separator layer improves the dielectric properties of the cable in such a way that attenuation of signals propagated along the electrical conductors is reduced. Also, the separator layer reduces tightness between the protective jacket and the transmission medium, further reducing attenuation in the cable and allowing portions of the protective jacket to be stripped away more readily than in conventional communication cable configurations.

Brief Description of the Drawings

In the drawings:
Fig. 1 is a cross-sectional view of an electrical cable according to an embodiment of the invention;
Fig. 2 is a perspective view of an electrical cable according to an alternative embodiment of the invention; and
Fig. 3 is a cross-sectional view of a fluted electrical cable according to an embodiment of the invention;
Fig. 4 is a perspective view of a fluted electrical cable according to an alternative embodiment of the invention; and
Fig. 5 is a simplified block diagram of a method for making an electrical cable according to embodiments of the invention.

Detailed Description

In the following description similar components are referred to by the same reference numeral in order to enhance the understanding of the invention through the description of the drawings.
Although specific features, configurations and arrangements are discussed hereinbelow, it should be understood that such is done for illustrative purposes only. A person skilled in the relevant art will recognize that other steps, configurations and arrangements are useful without departing from the spirit and scope of the invention.
Referring to Fig. 1, an electrical communications cable 10 according to embodiments of the invention is shown. The electrical communications cable 10 includes an electrically conductive transmission medium such as a plurality of conductor elements 12 such as twisted pairs of copper wire 13 individually insulated with a layer 14 of, e.g., fluoroethylenepropylene (FEP) or other suitable material such as polytetrafluoroethylene (PTFE), ethylenetetrafluoroethylene (ETFE) and perfluoroalkoxy polymers (PFA). Although four pairs of electrical conductors are shown, it is possible for the electrical communications cable 10 according to embodiments of the invention to have any suitable number of electrical conductor pairs or other electrically conductive transmission medium.
The electrical communications cable 10 further comprises a separator layer 16 formed around the conductor pairs 12 and a protective jacket 18 formed around the separator layer 16. The separator layer is wrapped around the conductor pairs, e.g., either longitudinally (shown generally in Fig. 1) or helically (shown generally in Fig. 2). The protective jacket 18 typically is made of a suitable dielectric material, such as low smoke polyvinyl chloride (LSPVC), ethylenechlorotrifluoroethylene (ECTFE) or fluoroethylenepropylene (FEP), and typically has a thickness of approximately 10 to approximately 25 mils.
When the protective jacket is made of LSPVC, the relatively high dielectric constant of the LSPVC degrades the overall dielectric properties of the cable, sometimes to the extent that the cable fails industry standard attenuation tests (e.g., Category 6B test). Also, the relative tightness of existing electrical cable arrangements, including those having LSPVC protective jackets, tends to cause unacceptable degrees of attenuation. However, LSPVC often is the material of choice for electrical cable protective jackets because LSPVC performs better in burn tests than many other materials.
Embodiments of the invention are based on the realization that attenuation of signals propagated within electrical cables having protective jackets made of LSPVC is reduced by having a separator layer (e.g., the separator layer 16) with a low dielectric constant and a low dissipation factor. Also, according to embodiments of the invention, the separator layer does not contribute smoke or heat to the cable 10 during a burn test, is relatively easy to apply to the conductor pairs 12, and is relatively flexible so as not to add to the overall stiffness of the cable 10. Also, the separator layer 16 does not stick to the conductor pairs 12, thus allowing the protective jacket 18 to be removed relatively easily.
According to embodiments of the invention, the separator layer 16 is made of, e.g., polytetrafluoroethylene (PTFE) or other suitable dielectric material. Having the separator layer 16 made of, e.g., PTFE, satisfies the requirements set forth above for reducing attenuation within electrical communication cables without sacrificing burn test performance characteristics. PTFE tape, when wrapped around the conductor pairs 12, e.g., longitudinally or helically, improves the transmission characteristics of the cable 10 by reducing attenuation therein of signals propagating along conductors therein. According to embodiments of the invention, the PTFE tape has a thickness, e.g., within the range from approximately 1 mil to approximately 10 mils.
Also, in addition to having favorable burn test characteristics, a PTFE separator layer does not flow like some other materials (e.g., FEP) during burn tests and thus does not contribute to the breach of the protective jacket 18, which is believed to add additional smoke during burn tests. Moreover, a PTFE tape separator layer does not stick to the conductor pairs 12, thus allowing the protective jacket 18 to be removed more easily, e.g., during installation, repair, splicing and other operations.
Also, according to embodiments of the invention, PTFE tape is beneficial as a separator layer because PTFE forms around the transmission media relatively easily using conventional techniques. For example, as shown in Fig. 1, the PTFE tape separator layer 16 is wound around the conductor pairs 12 longitudinally. Such configuration also is known as cigarette wrapping. Alternatively, as shown generally in Fig. 2, the communication cable 10 includes the PTFE tape separator layer 16 wound around the conductor pairs 12 in a helical manner.
Referring now to Figs. 3-4, according to alternative embodiments of the invention, the communication cable includes a flute for maintaining separation between the conductor pairs. For example, Fig. 3 illustrates an alternative embodiment of the invention in which a fluted electrical cable 30 includes a flute 19, and the separator layer 16 wrapped longitudinally around the conductor pairs 12 and between the conductor pairs 12 and the LSPVC jacket 18. Similarly, Fig. 4 illustrates another embodiment of the invention in which the fluted electrical cable 30 includes the flute 19, and the separator layer 16 wrapped helically around the conductor pairs 12 and between the conductor pairs 12 and the LSPVC jacket 18. The flute is, e.g., a conventional flute made of a low dielectric plastic or other suitable material having relatively low flammability.
Referring now to Fig. 5, a simplified block diagram of a method 50 for making a communication cable according to embodiments of the invention is shown. The method 50 includes a first step 52 of providing an information transmission medium such as a plurality of electrical conductor pairs or a plurality of optical fibers, as discussed hereinabove.
The next step 54 is to form the separator layer around the transmission medium, e.g., using conventional techniques. According to embodiments of the invention, the separator layer is made of PTFE or other suitable dielectric material, and has a thickness within the range from approximately 1 mil to approximately 10 mils. The separator layer is wrapped or wound around the transmission medium longitudinally (e.g., as shown in Figs. 1 and 3) or helically (e.g., as shown in Figs. 2 and 4).
The next step 56 is to form the LSPVC protective jacket around the separator layer. The protective jacket formation step 56 is performed by any suitable technique, including, e.g., conventional extrusion techniques.
As discussed hereinabove, embodiments of the invention use a separator layer made of a suitable dielectric material, e.g., PTFE or PTFE tape, between the electrical conductors and the LSPVC protective jacket. The separator layer reduces attenuation by improving the overall dielectric properties of the electrical communication cable. Because LSPVC has a relatively high dielectric constant, cables with jackets made of LSPVC jackets tend to have a relatively high overall dielectric constant, which increases attenuation. Thus, according to embodiments of the invention, a separator layer made of PTFE or PTFE tape, with its relatively low dielectric constant, improves the overall dielectric properties of the cable. Also, the dielectric separator layer provides a suitable degree of separation between the conductor elements and the LSPVC jacket, which separation also contributes to reduced attenuation.
Electrical cables made according to embodiments of the invention offer other advantages. For example, PTFE separator layers do not contribute smoke or heat to the cable 10 during a burn test. Also, separator layers made of PTFE and other suitable materials according to embodiments of the invention tend to be relatively flexible and thus do not add to the overall stiffness of the cable 10. Also, PTFE and other separator layers do not stick to the conductor pairs 12, thus allowing relatively easy removal of the protective jacket 18, e.g., when repairing the cable 10.
It will be apparent to those skilled in the art that many changes and substitutions can be made to the embodiments of the electrical cables herein described without departing from the spirit and scope of the invention as defined by the appended claims and their full scope of equivalents.

Claims

An electrical cabling apparatus, comprising:

at least one insulated conductive element;

at least one separator layer formed around the at least one insulated conductive element; and

a low smoke polyvinyl chloride (LSPVC) jacket formed around the separator layer,

wherein the separator layer has dielectric properties that reduce attenuation of signals propagated along the at least one conductive element.
The apparatus as recited in claim 1, wherein the separator layer is made of polytetrafluoroethylene (PTFE).
The apparatus as recited in claim 2, wherein the separator layer has a thickness within the range from approximately 1 mil to approximately 10 mils.
The apparatus as recited in claim 1, wherein the separator layer is wound helically around the at least one conductive element.
The apparatus as recited in claim 1, wherein the separator layer is wound longitudinally around the at least one conductive element.
The apparatus as recited in claim 1, wherein the low smoke polyvinyl chloride (LSPVC) jacket has a thickness within the range from approximately 12 mils to approximately 25 mils.
The apparatus as recited in claim 1, wherein the at least one insulated conductive element further comprises at least two insulated conductive elements, and wherein the electrical cabling apparatus further comprises at least one flute for separating the at least two conductive elements.
The electrical cable as recited in claim 1, wherein the at least one insulated conductive element further comprises a plurality of twisted pairs of individually insulated copper wires.
The electrical cable as recited in claim 8, wherein the twisted pairs of individually insulated copper wires are insulated with one or more materials selected from the group consisting of fluoroethylenepropylene (FEP), ethylenetetrafluoroethylene (ETFE), perfluoroalkoxy polymers (PFA) and polytetrafluoroethylene (PTFE).
A method for making a communication cable, comprising the steps of:

providing at least one insulated conductive element;

forming at least one separator layer around the at least one insulated conductive element; and

forming a low smoke polyvinyl chloride (LSPVC) jacket around the separator layer,

wherein the at least one separator layer has dielectric properties that reduce attenuation of signals propagated along the at least one conductive element.
The method as recited in claim 10, wherein the step of forming the at least one separator layer around the at least one conductive element further comprises forming a PTFE separator layer around the at least one conductive element.
The method as recited in claim 11, wherein the step of forming the at least one separator layer around the at least one conductive element further comprises forming a separator layer having a thickness within the range from approximately 1 mil to approximately 10 mils around the at least one conductive element.
The method as recited in claim 10, wherein the step of forming the at least one separator layer around the at least one conductive element further comprises wrapping the at least one separator layer helically around the at least one conductive element.
The method as recited in claim 10, wherein the step of forming the at least one separator layer around the at least one conductive element further comprises wrapping the at least one separator layer longitudinally around the at least one conductive element.
The method as recited in claim 10, wherein the at least one conductive element further comprises at least two conductive elements, and wherein the method further comprises the step of providing a flute for separating the at least two conductive elements.
The method as recited in claim 10, wherein the step of forming the low smoke polyvinyl chloride (LSPVC) jacket around the separator layer further comprises forming a low smoke polyvinyl chloride (LSPVC) jacket having a thickness within the range from approximately 12 mils to approximately 25 mils around the separator layer.