WO1996005601A1

WO1996005601A1 - Twisted-pair cable

Info

Publication number: WO1996005601A1
Application number: PCT/US1995/009800
Authority: WO
Inventors: Daniel John Kennefick; Niall Duncan Mckee; John Louis Netta; Stuart Karl Randa; Rajeev Arvind Vaidya
Original assignee: E.I. Du Pont De Nemours And Company
Priority date: 1994-08-08
Filing date: 1995-08-01
Publication date: 1996-02-22

Abstract

Twisted-pair cable is disclosed which has an attenuation no greater than 22dB/100 m at 100 MHz and wherein each conductor of the cable has dual layer insulation, the inner layer of solid FEP or PFA and the outer layer of solid ETFE or ECTFE.

Description

TITLE

TWISTED-PAIR CABLE This application is a continuation-in-part of Serial No. 08/317,494, filed October 4, 1994, which is a continuation-in-part of Serial No. 08/287,379 filed August 8, 1994.

FIELD OF THE INVENTION This invention relates to twisted-pair cable that meets category 5 performance specifications so as to be useful for computer networking. BACKGROUND OF THE INVENTION Twisted-pair cable which satisfies category 5 specifications

(standard established by the Electrical Industry Association (EIA)/Telecommunications Industry Association (TIA)) are required to transmit electrical signals at frequencies over the range of 1 to 100 MHz. By way of comparison, the category 3 specification requires the twisted-pair cable to transmit electiical signals at frequencies only up to only 16 MHz. The twisted-pair cable consists of a pair of electiical conductors, e.g., approximately solid AWG 24 size, each of which is surrounded by polymer insulation, with each insulated conductor being twisted around one another. Each insulated conductor is veiy fine, i.e., the total thickness is generally no greater than about 40 mils ( 1.02 mm) of which the electiical conductor itself comprises about 20 mils (0.508 mm) and the polymer insulation comprises a wall thickness of about 7 mils (0.178 mm). The polymer insulation of choice for use in plenum environment to meet the category 5 electrical and environmental requirements for the cable has been tetrafluoroethylene/hexafluoropropylene copolymer commonly known as FEP in the form of solid (unfoamed) insulation. The cable with FEP insulation exhibits low transmission loss, having for example an attenuation of no greater than 8.2 dB/100 m at a frequency of 16 MHz and no greater than 22 dB/100 at 100 MHz. By way of comparison, the less stringent category 3 specification requires that the cable have an attenuation of no greater than 13.6 dB/100 m at 16 MHz frequency. This attenuation difference between the category 5 cable and the category 3 cable is substantial, because of the logarithmic basis for the decibel scale.

Wires insulated with other well known fiuoropolymers such as ethylene/tetrafluoroethylene copolymer and ethylene/chlorotrifluoroethylene copolymer satisfy the category 3 specification for twisted-pair cable, but not in the categoiy 5 specification because of the relatively high attenuation exhibited when these polymers are used as the solid insulation for each conductor of the cable. SUMMARY OF THE INVENTION

It has been discovered that the outer part of the FEP insulation in the above-described twisted-pair cable can be replaced by either ETFE or ECTFE (same total insulation thickness) without appreciable harm to the attenuation of the twisted-pair cable enabling it to still meet the category 5 specification. This same result can be obtained when tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer is used in place of the FEP insulation. Thus, the present invention comprises a twisted-pair cable having an attenuation of not more than 22 dB/100 m at 100 MHz wherein each insulated conductor of the cable has dual insulation comprising an inner layer of either solid tetrafluoroethylene/hexafluoropiOpylene copolymer or solid tetrafluoroethylene/perfluoiO(alkyl vinyl) ether copolymer (PFA) and an outer layer of solid polymer selected from the group consisting of ethylene/tetrafluoroethylene copolymer (ETFE) and ethylene/chlorotiifluoroethylene copolymer (ECTFE).

Each insulated conductor is very fine, having a total thickness (diameter) generally no greater than about 50 mil (1.27 mm). Despite the relatively poor attenuation characteristic of the outer layer polymers when used by themselves as solid wire insulation in twisted-pair cable, when used in combination with the solid FEP or PFA inner layer insulation of reduced thickness so that the overall thickness of the combined layers forming the insulation is about the same as the FEP or PFA insulation used by itself, the resultant electrical properties, especially attenuation, still satisfies the category 5 specification of being no greater than 22 dB/100 m at 100 MHz. DETAILED DESCRIPTION OF THE INVENTION

The polymers used in the present invention are well known. They are all melt fabricable so as to be melt extrudable and have sufficient molecular weight to provide the properties needed for the conductor insulation, preferably exhibiting a tensile strength of at least 10 MPa and elongation at break of at least 150%. With respect to FEP and PFA, the molecular weight is generally such that the melt viscosity of the copolymer will fall within the range of 0.5 x 10⁴ to 10 x 10⁵ poise (0.5 x 10³ to 10 x 10⁴ Pa s) at 372°C when calculated from melt flow rate (MFR) as measured according to ASTM D-2116 and ASTM D-3307, respectively. In general, the copolymer will contain at least 5 wt% of HFP. With respect to PFA, the perfluoro alkyl group of the perfiuoro(alkyl vinyl) ether (PAVE) will preferably contain from 1 to 5 carbon atoms, more preferably 1 to 3 carbon atoms. The amount of PAVE will generally be at least 2 wt%, preferably at least 3 wt%. The ETFE and ECTFE copolymers will generally contain 40 to 60 mol% ethylene and 60 to 40 mol% of tetrafluoroethylene or chloiOtrifluoroethylene, as the case may be. These copolymers preferably have melt viscosity in the range of 0.5 x 10⁴ to 1 x 10⁴ poises (0.5 x 10³ to 1 x 10³ Pa s) at 298°C as determined from melt flow measurement in accordance with ATSM D-1238 using standard conditions for each resin. Any of the copolymers used in the present invention may also contain one or more additional copolymerizable monomer(s) which provides improved melt extrusion or mechanical properties.

For use with the popular R-J electrical connector, the diameter of each insulated conductor of twisted-pair cable is limited to no more than about 40 mils ( 1.02 mm) which is the maximum insulated conductor size which is accepted by this connector, so as to be useful with this connector, which has become the industry standard. Some of these connectors will accept slightly larger insulated conductors; e.g.. 41 mils ( 1.04 mm). The diameter of each insulated conductor can be less than 40 mils ( 1.02 mm) provided electrical requirements are met. and indeed the single-insulation conductors satisfying category 5 have been as small as 31 to 37 mils (0.79 to 0.94 mm) in diameter. The insulated conductors of twisted-pair cable of the present invention can fall within this same size range. For patch cable satisfying category 5, the cable diameter can be somewhat larger, e.g., 48 or 50 mils ( 1.22 or 1.27 mm), permitting the use of thicker insulation and/or larger diameter conductor.

When FEP or PFA is used as the sole solid polymer insulation for each conductor of the twisted-pair cable, the cable is made by extruding the polymer insulation around the wire and subsequently doubling up a pair of the so-prepared insulated wires by twisting them together (twinning). Generally the twisting provides at least one turn per inch (25.4 mm) and the resultant cable can consist of one or more twisted pairs of insulated conductors, the twisting being done by conventional means. In accordance with the present invention the twisting application can be the same, but the manufacture of each insulated conductor differs by a dual insulation layer being applied to each conductor. Application of the dual insulation layer has the problem of any air space between the insulation layers causing deficiency in electrical performance, especially that which is measured by structural return loss, which is a measure of reflectance of the transmission (backwards transmission) of the transmitted electiical signal caused by insulation defects. Air pockets between insulation layers show up as insulation defects. This problem is exacerbated by the fact that neither the ETFE or the ECTFE stick very well to the FEP or PFA inner insulation layer. Nevertheless, it has been found that coextrusion of these polymers onto the electiical conductor, i.e., simultaneously extruding them onto the electrical conductor, achieves intimacy even though adhesion between the layers is not obtained, such that air is apparently sufficiently excluded that the structural return loss for the dual insulation layer is about the same as for the insulation layer made solely of FEP or PFA.

Generally, for the total insulation thickness, the inner FEP or PFA layer will comprise 40 to 90% of the thickness, with the ETFE or ECTFE comprising the remainder. For the typical 6 to 7 or 7.5 mil (0.152 - 0.178 or 0.191 mm) thick insulation, the ETFE or ECTFE will comprise at least 1 mil (0.025 mm) of the total insulation thickness and the FEP or PFA will comprise at least 3.0 mils (0.076 mm) of the total thickness. Typically, the outer layer will comprise 25 to 60% of the total thickness of the insulation. The Examples disclose a number of wire insulation thicknesses.

When FEP solid insulation is used by itself in the twisted-pair cable used in category 5 application, the FEP typically contains a colorant which provides circuit identification guidance in installations of the cable. Generally, colorants detract from the attenuation performance of the cable. In accordance with the present invention, the colorant can be omitted from the inner FEP layer and provided solely in the outer ETFE or ECTFE layer. The beneficial effect of this aspect of the invention on attenuation is twofold, less colorant can be used to thereby lessen the adverse effect on the electrical performance of the cable, and the colorant is displaced from immediately adjacent the conductor where its adverse effect on attenuation is magnified. This same beneficial effect is obtained when PFA is used in place of FEP. The twisted-pair cable of the present invention can be composed of single or multiple twisted pairs, e.g., the cable can consist of one to four twisted pairs, or five to twenty-five twisted pairs. The insulation polymers can contain other additives that improve extrusion or electrical performance. The cable furthermore can be shielded or unshielded and will normally have a polymer jacket such as of polyvinyl chloride (PVC).

The best mode contemplated for carrying out the present invention is set forth in the following Examples.

EXAMPLES In the following Examples 1-3, the equipment described below is used to make dual (solid) insulated conductor for twisted-pair cable: Nokia Maillefer 45 mm 30/1 L/D ratio main extruder Maillefer 4/6 crosshead for dual coating Auxiliaiy extruder: 1 inch (25.4 mm) Entwistle 30/1 L/D ratio Screw Designs: Standard per Dupont "Extrusion Guide for Melt Processible Fluoropolymers" (3/92)

226022A Die Diameter: 0.150 inch (3.80 mm)

Tip Outer Diameter: 0.075 inch ( 1.90 mm) Draw Down Ratio: 24/1

Example 1

MAIN EXTRUDER

Resin: TEFLON® FEP fluoropolymer resin grade 4100N MFR 22 Settings (temperatures) °F °C

Rear 572 300

Center rear 644 340

Center 644 340

Center front 644 340 F Frroonntt 6 64444 340

Adapter 644 340

Crosshead 626 330

Die 626 370

Screw Speed: 6 RPM

Wire Speed: 220 ft/min (36 m/m)

AUXILIARY EXTRUDER

Resin: TEFZEL® ETFE fluoropolymer resin grade 210 MFR 20

Settings (temperatures) °F ^C

Rear 572 300

Middle 608 320

Front 608 320

Adapter 572 300

Screw Speed: 10 RPM

Wire: AWG 24 solid copper diameter 20.1 mils (0.51 mm) The result of this Example is a dual coated (solid) wire insulation as follows:

Inner FEP insulation thickness: 4.3 mils (0.109 mm) Outer ETFE insulation thickness: 2.5 mils (0.064 mm)

Similar conditions can be used to make insulated cable using oversized wire, i.e., between AWG 23 and 24 gauge, wherein the FEP inner insulation thickness is 3 mils (0.076 mm) and the outer insulation thickness is 3.5 mils (0.088 mm).

Example 2

MAIN EXTRUDER

Resin: TEFLON® fluoropolymer resin grade 4100 MFR 25

Settings (temperatures) °F °C R Reeaarr 5 57722 300

Center rear 644 340

Center 644 340

Center from t 644 340

Front 644 340 A Addaapptteerr 6 64444 340

Crosshead 554 290

Die 563 295

Screw Speed: 3 RPM

Wire Speed: 1 I00 ft/min (60 m/m)

AUXILIARY EXTRUDER

Resin: HALAR® ECTFE resin grade 500 MFR 20

Settings (temperatures) °F °C

Rear 482 250 Middle 482 250

Front 536 280 Adapter 500 260 Screw Speed: 5 RPM

Wire: AWG 24 undersized wire diameter 19.5 mils (0.50 mm) Coated Wire Insulation:

Inner FEP insulation thickness: 5.5 mils (0.14 mm) Outer ECTFE insulation thickness: 2 mils (0.051 mm) A pair of insulated conductors made in each Example are twinned by conventional means. The resultant twisted-pair cable is satisfactory for the demanding categoiy 5 use and exhibits an attenuation factor of less than 22 dB/100 m at 100 MHz. The structural return loss is also satisfactory.

More specifically, the attenuations of the cable constructions of Examples 1 and 2 have been calculated by computer modelling and the accuracy of this determination has been verified by actual attenuation measurements.

For the cable construction of Example 1, the calculated attenuation is 71.9 dB/1000 ft (23.6 dB/100 m) at 100 MHz which exceeds the attenuation limit for category 5 application. Redesign of the cable, however, wherein each insulated conductor consists of a 19.5 mil (0.49 mm) diameter conductor, 5.5 mil (0.14 mm) thick inner layer of FEP and 2.0 mil (0.05 mm) thick outer layer of ETFE yields a calculated attenuation of 64.7 dB/1000 ft (21.22 dB/100 m) at 100 MHz, which is satisfactory.

For the cable construction of Example 2, the attenuation calculates to 59 dB/1000 ft ( 19.4 dB/100 m) at 100 MHz. For additional FEP/ECTFE insulated cable constructions, additional attenuation calculations were made, as follows:

Construction Wire Dia. FFP ECTFE Attenuation (mil/mm) inner layer outer layer dB/100 m at

(mil/min) (mil/mm) 100 MHz

(a) 20.1/0.51 4.3/0.109 1.5/0.063 20.77

(b) 20.5/0.52 3.0/0.076 3.5/0.089 22.77

The attenuation of Construction (b) above exceeds the attenuation limit for the categoiy 5 application; this construction has the largest diameter conductor and thickest ECTFE outer layer as compared to the constructions of Example 2 and (a) above, which indicate how to obtain an FEP/ECTFE dual-layer insulated cable which has satisfactory attenuation.

To verify the accuracy of the calculated attenuations, a comparison was made between calculated attenuation and measured attenuation on a commercially available twisted-pair cable in which each insulated conductor consisted of a 20.1 mil (0.51 mm) diameter conductor and FEP insulation thickness of 6.0 mil (0.152 mm). The calculated attenuation was 60 dB/1000 ft ( 19.7 dB/100 m) at 100 MHz and the measured attenuation was 59.0 dB/1000 ft ( 19.4 dB/100 m) at 100 MHz. The measurement of attenuation is done by standard method known as EIA/TIA standard procedure 2840A (TIA EIA 566A), and the 22 dB/100 m at 100 MHz as the upper limit for the categoiy 5 application is determined this way.

Example 3 Results similar to Examples 1 and 2 can be obtained by replacing the

TEFLON® FEP by TEFLON® TE 9771 PFA using essentially the same conditions of operation. For cable in which each insulated conductor consists of a 19.5 mils (0.50 mm) diameter conductor surrounded by an inner PFA insulation layer which is 5.5 mils (0.14 mm) thick and an outer ECTFE insulation layer which is 2.0 mils (0.051 mm) thick, the attenuation calculates as 58.4 dB/1000 ft ( 19.2 dB/100 m) at 100 MHz.

Example 4

The equipment described below was used to make dual (solid) insulated conductor for twisted-pair cable:

Nokia Maillefer 60 mm 30/1 L/D ratio main extruder

Maillefer 4/6 crosshead for dual coating

Auxiliary extruder: 1.5 inch (38.1 mm) Davis Standard 30/1 L/D ratio

Screw Designs: Standard per Dupont "Extrusion Guide for Melt Processible Fluoropolymers" (3/92) 226022A

Die Diameter: 0.250 inch (6.35 mm) Tip Outer Diameter: 0.136 inch (3.45 mm)

Draw Down Ratio: 60/1

The extrusion wire coating process conditions were as follows:

MAIN EXTRUDER

Resin: TEFLON® FEP fluoropolymer resin grade 4100 MFR 22

Settings (temperatures) °F °C

Rear 540 282

Center rear 540 282

Center 540 282

Center front 580 304

Front 570 299

Adapter 570 299

Crosshead 580 304

Die 500 278

Screw Speed: 6 RPM

Wire Speed: 220 ft/min (26 m/m)

AUXILIARY EXTRUDER

Resin: TEFZEL® ETFE fluoropolymer resin grade 210 MFR 20

Settings (temperatures) °F °£_ Rear 480 249

Middle 470 242 Front 480 249 Adapter 490 254 Screw Speed: 10 RPM Wire: AWG 24 solid copper diameter 20.1 mils (0.51 mm)

The result of this Example was a dual coated (solid) wire insulation as follows:

Inner FEP insulation thickness: 4.6 mils (0.1 17 mm) Outer ETFE insulation thickness: 2.7 mils (0.069 mm) A pair of insulated conductors in this Example were twinned by conventional means and a flame retardant PVC jacket 15 mil (0.381 mm) thick was applied. The resultant four-pair twisted cable was satisfactory for categoiy 5 use, exhibiting the following electrical properties: a. attenuation: from 20.5 to 21.3 dB/100 m at 100 MHz (4 tests), b. fitted impedance: between 105 and 1 10 ohms (category 5 specification = 100 ± 15 ohms), c. crosstalk and structural return loss measured on 328 ft. ( 100 m) of cable was well within category 5 specification. Comparison Example

The Comparison Example shows the relative poorer attenuation of cable insulated solely with ECTFE as compared to FEP, which makes it surprising that the combination of these polymers satisfies the attenuation demand for category 5 application. The cables tested were cables qualified for category 3 which has been the highest category achieved by ECTFE twisted-pair cable insulation. Each insulated conductor consisted of 20.1 mil (0.51 mm) diameter conductor surrounded by 5 mil (0.127 mm) insulation thickness of either ECTFE or FEP. Measurement of the attenuation of each cable gave the following results:

Attenuation in dB/100 m at 100 MHz ECTFE - insulated cable 34.4

FEP - insulated cable 25.9

Example 5 The equipment described below was used to make dual (solid) insulated conductor for twisted-pair cable:

Nokia Maillefer 60 mm 30/1 L/D ratio main extruder Maillefer 4/6 crosshead for dual coating Auxiliaiy extruder: 1.5 inch (38.1 mm) Davis Standard 30/1 L/D ratio Screw Designs: Standard per DuPont "Extrusion Guide for Melt Processible Fluoropolymers" (3/92) 226022A Die Diameter: 0.250 inch (6.35 mm)

Tip Outer Diameter: 0.136 inch (3.45 mm) Draw Down Ratio: 60/1 The extrusion wire coating process conditions were as follows:

MAIN EXTRUDER

Resin: TEFLON® FEP fluoropolymer resin grade 4100 MFR 24 Settings (temperatures) °F °£_

Rear 540 282

Center rear 540 282

Center 540 282

Center front 560 293

Front 570 299

Adapter 570 299

Crosshead 560 293

Die 560 293

Screw Speed: 6 RPM

Wire Speed: 497 ft/min ( 151 m/min)

AUXILIARY EXTRUDER

Resin: Halar® ECTFE resin grade 500, MFR 18 Settings (temperatures) °F _

Rear 480 249

Center rear 470 244

Center front 460 238

Front 490 254

Adapter 480 249

Screw Speed: 15.4 RPM

Wire: AWG 24 solid copper diameter 20.1 mils (0.51 mm)

The melt temperatures of the ECTFE and FEP copolymers in the die (the ECTFE from its respective adapter flows through the die through which the FEP flows, to obtain coextrusion of these two copolymers), which is common to both copolymers. were 510°C and 580°C, respectively. This relatively low melt temperature for the ECTFE enables it to form the outer layer on the co-extrudate, containing the hotter inner layer of FEP, without causing degradation of the ECTFE.

Inner FEP insulation thickness: 5.2 mils (0.13 mm) Outer ECTFE insulation thickness: 2.4 mils (0.06 mm) A pair of insulated conductors in this Example were twinned by conventional means and a flame retardant PVC jacket 15 mil (0.381 mm) thick was applied. The resultant four-pair twisted cable was satisfactory for category 5 use, exhibiting the following electrical properties: a. attenuation: from 20.5 to 21.3 dB/100 m at 100 MHz (4 tests), b. fitted impedance: between 105 and 110 ohms (category 5 specification = 100 ± 15 ohms), c. crosstalk and structural return loss measured on 328 ft (100 m) of cable were well within category 5 specification. In one embodiment of the experiment of this Example, the coextrusion of the FEP and ECTFE copolymer was started up in the conventional way of first extruding outer-layer polymer through the coextrusion die. and when this polymer filled the die, i.e., was extruded from the die, then commencing the extrusion of the inner-layer polymer. This conventional order of start-up for coextrusion prevents the inner-layer polymer from flowing into the extrusion channel of the outer-layer polymer within the die. Application of this conventional order of start-up in this experiment resulted in black specks being present in the dual-layer coated conductor, believed to be degraded ECTFE resulting from ECTFE being first to fill the die being trapped within the die and subsequently contaminating the coextruded insulation.

In another embodiment of this Example, using the same extrusion conditions as the embodiment described above, the order of coextrusion start-up was reversed from the conventional way, i.e., the inner-layer copolymer was extruded first to fill up the die, followed by extrusion of the outer-layer copolymer until it exits the die, and then coextruding both copolymers to form the inner and outer layers of insulation on the conductor. Surprisingly, this order of start-up solved the black-speck problem; none appeared. In addition, surprisingly, the FEP inner-layer copolymer did not restrict the extrusion channel for the ECTFE copolymer within the die. The electrical measurements and details of the dimensions of the resultant insulated cable were obtained on coated conductor and twisted-pair cable made by this embodiment of this Example.

Example 6 The same equipment described in Example 5 was used to make dual

(solid) insulated conductor for twisted-pair cable, except for the following: Die Diameter: 0.297 inch (7.54 mm)

Tip Outer Diameter: 0.163 inch (4.14 mm) Draw Down Ratio: 74/1

The extrusion wire coating process conditions were as follows:

MAIN EXTRUDER

Resin: TEFLON® FEP fluoropolymer resin grade 4100, MFR 21 Settings (temperatures) °F °£_

Rear 680 360

Center rear 710 377

Center 710 377

Center front 710 377

Front 710 377

Adapter 710 377

Crosshead 685 363

Die 660 349

Screw Speed: 10 RPM

Wire Speed: 1005 ft/min ( 306 m/min)

AUXILIARY EXTRUDER

Resin: TEFZEL® ETFE fluoropolymer resin grade HT-2127,

MFR 9

Settings (temperatures) °F _

Rear 570 299

Center rear 600 316

Center front 600 316

Front 610 321

Adapter 600 316

Screw Speed: 22.7 RPM

Wire: AWG 23 solid copper diameter 22 .6 mils (0.57 mm)

The coextrusion was started up in the same way as the second-mentioned embodiment of Example 5.

Inner FEP insulation thickness: 4.7 mils (0.1 19 mm) Outer ETFE insulation thickness: 1.7 mils (0.043 mm) A pair of insulated conductors in this Example were twinned by conventional means and a flame retardant PVC jacket 15 mil (0.381 mm) thick was applied. The resultant four-pair twisted cable was satisfactory for category 5 use, exhibiting the following electrical properties: a. attenuation: from 21.2 to 22.1 dB/100 m at 100 MHz (4 tests), b. fitted impedance: between 98 and 103 ohms (category 5 specification = 100 ± 15 ohms), c. crosstalk and structural return loss measured on 328 ft (100 m) of cable were well within category 5 specification.

Claims

WHAT IS CLAIMED IS:

1. A twisted-pair cable having an attenuation of not more than 22 dB/100 m at 100 MHz wherein each insulated conductor of the cable has dual insulation comprising a solid inner layer of either tetrafluoroethylene/hexafluoropropylene copolymer or tetrafluoroethylene/perfluoro(alkyl vinyl) ether copolymer and a solid outer layer selected from the group consisting of ethylene tetrafluoroethylene copolymer and ethylene/chlorotrifluoroethylene copolymer.

2. The twisted-pair cable of claim 1 wherein the outer layer polymer comprises 10 to 60% of the total thickness of the insulation.

3. The twisted-pair cable of claim 1 wherein the inner layer is colorant-free and the outer layer contains colorant.

4. The twisted-pair cable of claim 1 wherein each insulated conductor is made by coextrusion of the inner and outer insulation layers through a common extrusion die onto the conductor.

5. The twisted-pair cable of claim 4 wherein the coextrusion is commenced by first extiuding the inner-layer copolymer to fill up the extrusion die, followed by extruding the outer-layer copolymer until it exits said die, and then coextruding both said copolymers to form the inner and outer layers of insulation on said conductor.

6. The twisted-pair cable of claim 1 wherein each insulated conductor of the cable has a total thickness of no greater than about 50 mils.

7. The twisted-pair cable of claim 6 wherein said thickness is no greater than about 40 mils.

8. A cable containing multiple twisted-pair cables of claim 1.