METHOD OF MANUFACTURING ELECTRICAL CABLE, AND RESULTING PRODUCT, WITH REDUCED REQUIRED INSTALLATION PULLING FORCE

Abstract

Disclosed are cable types, including a type THHN cable, the cable types having a reduced surface coefficient of friction, and the method of manufacture thereof, in which the central conductor core and insulating layer are surrounded by a material containing nylon or thermosetting resin. A silicone based pulling lubricant for said cable, or alternatively, erucamide or stearyl erucamide for small cable gauge wire, is incorporated, by alternate methods, with the resin material from which the outer sheath is extruded, and is effective to reduce the required pulling force between the formed cable and a conduit during installation.

Claims

1-19) (canceled)

20) A thermoplastic high heat-resistant nylon-coated (THHN) electrical cable having a reduced installation pulling force through a building passageway defined by a PVC conduit setup sized to accomodate the THHN electrical cable and having at least two 90 bends within the PVC conduit setup, the THHN electrical cable comprising: at least one conductor capable of carrying an electrical current through the THHN electrical cable, wherein the conductor is formed at least in part from a metal; and, a sheath for protecting the conductor, wherein the sheath comprises: an insulating layer surrounding the conductor and providing electrical insulation to the conductor, wherein the insulating layer is formed at least in part from extruded polyvinyl chloride (PVC); and an outer layer surrounding, contacting, and forming a coating for the insulating layer, wherein the outer layer comprises a solidified extrusion of a material mixture, the material mixture comprising: a nylon material; and a pulling lubricant mixed within at least a portion of the nylon material, wherein at least a portion of the pulling lubricant is present at an exterior surface of the sheath to reduce the amount of force required to pull the cable through the building passageway; and wherein the outer layer is both resistant to heat, moisture, oil, and gasoline and provides the THHN electrical cable with the physical characteristic of requiring at least about 30% less force to pull the electrical cable through the building passageway compared to an amount of force required to pull a non-lubricated THHN electrical cable having an extruded sheath without the pulling lubricant mixed therein through the building passageway.

21) The thermoplastic high heat-resistant nylon-coated (THHN) electrical cable of claim 20, wherein the pulling lubricant comprises a silicone oil.

22) The thermoplastic high heat-resistant nylon-coated (THHN) electrical cable of claim 20, wherein the pulling lubricant comprises a high molecular weight silicone based pulling lubricant.

23) The thermoplastic high heat-resistant nylon-coated (THHN) electrical cable of claim 20, wherein the pulling lubricant comprises a low molecular weight silicone based pulling lubricant.

24) The thermoplastic high heat-resistant nylon-coated (THHN) electrical cable of claim 20, wherein the pulling lubricant comprises erucamide.

25) The thermoplastic high heat-resistant nylon-coated (THHN) electrical cable of claim 20, wherein the at least one conductor comprises a plurality of grouped conductors.

26) The thermoplastic high heat-resistant nylon-coated (THHN) electrical cable of claim 20, wherein the at least one conductor is a large gauge conductor.

27) The thermoplastic high heat-resistant nylon-coated (THHN) electrical cable of claim 26, wherein the at least one conductor comprises an AWG 4/0 conductor.

28) The thermoplastic high heat-resistant nylon-coated (THHN) electrical cable of claim 20, wherein the sheath is formed with geometrical characteristics that are not altered relative to the geometrical characteristics of the extruded sheath of the non-lubricated THHN cable.

29) The thermoplastic high heat-resistant nylon-coated (THHN) electrical cable of claim 28, wherein the sheath has a round profile.

30) The thermoplastic high heat-resistant nylon-coated (THHN) electrical cable of claim 20, wherein the THHN electrical cable is rated for use in dry locations at temperatures not to exceed 90 C.

31) The thermoplastic high heat-resistant nylon-coated (THHN) electrical cable of claim 20, wherein the THHN electrical cable is rated to carry current at voltages not to exceed 600 Volts.

32) A thermoplastic high heat-resistant nylon-coated (THHN) electrical cable having a reduced installation pulling force through a building passageway defined by a PVC conduit setup sized to accomodate the THHN electrical cable and having at least two 90 bends within the PVC conduit setup, the THHN electrical cable comprising: at least one conductor capable of carrying an electrical current through the THHN electrical cable, wherein the conductor is formed at least in part from a metal; and, a sheath for protecting the conductor, wherein the sheath comprises: an insulating layer surrounding the conductor and providing electrical insulation to the conductor, wherein the insulating layer is formed at least in part from extruded polyvinyl chloride (PVC); and an outer layer surrounding, contacting, and forming a coating for the insulating layer, wherein the outer layer comprises a solidified extrusion of a material mixture, the material mixture comprising: a nylon material; and a pulling lubricant mixed within at least a portion of the nylon material, wherein at least a portion of the pulling lubricant is present at an exterior surface of the sheath to reduce the amount of force required to pull the cable through the building passageway; and wherein the outer layer is both resistant to heat, moisture, oil, and gasoline and provides the THHN electrical cable with the physical characteristic of requiring at least about 50% less force to pull the electrical cable through the building passageway compared to an amount of force required to pull a non-lubricated THHN electrical cable having an extruded sheath without the pulling lubricant mixed therein through the building passageway.

33) The thermoplastic high heat-resistant nylon-coated (THHN) electrical cable of claim 32, wherein the sheath is formed with geometrical characteristics that are not altered relative to the geometrical characteristics of the extruded sheath of the non-lubricated THHN cable.

34) The thermoplastic high heat-resistant nylon-coated (THHN) electrical cable of claim 33, wherein the sheath has a round profile.

35) A non-metallic sheathed (NM-B) electrical cable having a reduced installation pulling force through a building passageway extending through throughholes drilled at a 15 degree angle through a broadface of each of four 24 wood blocks, wherein the wood blocks are lineaerly spaced apart from one another and are offset such that a centerline of each of the throughholes is offset by 10 relative to one another, the NM-B electrical cable comprising: a conductor core comprising at least two insulated metal conductors capable of carrying an electrical current through the NM-B electrical cable, wherein the conductor is formed at least in part from metal; and a sheath for protecting the conductor core, wherein the sheath comprises a solidified extrusion of a material mixture, the material mixture comprising: an insulating material providing electrical insulation to the conductor core, wherein the insulating material comprises polyvinyl chloride; and a pulling lubricant mixed with at least a portion of the insulating material, wherein at least a portion of the pulling lubricant is present at an exterior surface of the sheath to reduce the amount of force required to pull the cable through the building passageway; and wherein the sheath provides the NM-B electrical cable with the physical characteristic of requiring at least about 30% less force to pull the electrical cable through the building passageway compared to an amount of force required to pull a non-lubricated NM-B electrical cable having an extruded PVC jacket without the pulling lubricant mixed therein through the building passageway.

36) The NM-B electrical cable of claim 35, wherein the pulling lubricant comprises one of erucamide or oleamide.

37) The NM-B electrical cable of claim 36, wherein the pulling lubricant comprises a silicone pulling lubricant.

38) The NM-B electrical cable of claim 36, wherein each of the at least two metal conductors are 14-gauge metal conductors.

39) The NM-B electrical cable of claim 36, wherein each of the at least two metal conductors are 12-gauge metal conductors.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] These and other details and aspects of the invention, as well as the advantages thereof, will be more readily understood and appreciated by those skilled in the art from the following detailed description, taken in conjunction with the accompanying drawings, in which:

[0012] FIG. 1 is a diagrammatic representation of typical equipment used in the manufacture of cable in accordance with the present invention, when mixing the lubricant with the nylon material prior to extrusion;

[0013] FIG. 2 is a graphical representation of test data comparing the effect of different pulling lubricants in small size THHN cable in which the outer sheath material is nylon;

[0014] FIG. 3 is a graphical representation of test data comparing both the effects of different pulling lubricants and different percentages of pulling lubricant in large size THHN cable in which the outer sheath material is nylon;

[0015] FIGS. 4 and 5 are representations of test devices which may be used to create the aforementioned test data; and

[0016] FIG. 6 is a section view of a THHN cable produced in accordance with the process of the present invention.

DESCRIPTION

[0017] Referring initially to FIG. 1, there is depicted typical equipment 11 for manufacturing electrical cable 12 in accordance with one process of the present invention. The outer sheath of the cable is of an extruded polymer material, specifically nylon. The equipment 11 may include a reel 13 which supplies conductor wire 14 to an extruding head 15. In flow communication with the extrusion head is a tank 16 of the nylon pellets 17. A tank 18 with the desired pulling lubricant 19 is adapted to be in flow communication with the tank 16 by way of conduit 22, thus enabling the mixing of the pulling lubricant with the nylon pellets 17, the mixture thereafter introduced into the extruder. Alternatively, the tank may be adapted to be in fluid communication with the extruder or extrusion head 15, by way of conduit 23, downstream from the point of entry of the nylon material, thus allowing the pulling lubricant to mix with the nylon material while in its molten state in the extruder or extruder head. A cooling box 20 for cooling the extruded product is provided, and a reel 21 is positioned for taking up the resulting cable assembly 12. When the final cable construction is such that there are multiple layers of sheath material, the pulling lubricant should desirably be incorporated into the outermost layer.

[0018] As is therefore evident, the pulling lubricant can be mixed with the material from which the outer sheath is to be extruded prior to extrusion or, alternatively, introduced into the extruding head for subsequent mixing with the molten extrusion material as the sheath is being formed. As a further alternative, the pulling lubricant can be initially compounded with the polymeric material of the pellets themselves in a process upstream of that depicted in FIG. 1, thereby forming lubricated polymeric pellets, thus eliminating the need for tank 18 and conduits 22 and 23.

[0019] Polymeric materials that can be used for an insulating layer or outer sheath of different type of cable include polyethylene, polypropylene, polyvinylchloride, organic polymeric thermosetting and thermoplastic resins and elastomers, polyolefins, copolymers, vinyls, olefin-vinyl copolymers, polyamides, acrylics, polyesters, fluorocarbons, and the like. As previously described, for the THHN cable of the present invention, the conductor core of a single solid or stranded conductor is surrounded by an insulating layer of PVC covered by an outer sheath of a polyamide (e.g., nylon).

[0020] In accordance with the testing subsequently described, it has been determined that, for THHN cable, silicone oil is the preferred pulling lubricant. For small gauge THHN wire, erucamide is an alternative preferred pulling lubricant, to be incorporated in the nylon sheath.

[0021] The efficacy of these pulling lubricants for the nylon sheath, and specifically an optimum range for the quantity of such lubricants, in accordance with the invention, has been proven by the use of various tests. Prior to discussing the results of such tests, these test methods and their equipment are described as follows:

Testing Methods

[0022] Coefficient of Friction Test

[0023] Referring now to FIG. 4, diagrammatically illustrated is the apparatus for a coefficient of friction test. The coefficient of friction test apparatus was developed to give a consistent way to determine the input values necessary to use the industry-standard program published by PolyWater Corporation to calculate a real-world coefficient of friction for a given cable being pulled in conduit. Given the inputs for the conduit setup, the back tension on the wire, and the pulling tension on the pulling rope, this program back-calculated a coefficient of friction for the cable by subtracting the back tension from the pulling tension and attributing the remaining tension on the rope to frictional forces between the cable and the conduit.

[0024] The overall setup used a pulling rope threaded through 40 of PVC conduit (appropriately sized for the cable being pulled) with two 90 bends. Three 100 pieces of THHN cable were cut and laid out parallel to one another in line with the first straight section of conduit, and the rope connected to them using industry-standard practice. The other end of the THHN cable was attached to a metal cable which was wrapped around a cylinder with an air brake to allow the application of constant back tension on the setup.

[0025] The metal cable was threaded through a load cell so that it could be monitored in real-time, and continuously logged. The pulling rope was similarly threaded through a load cell and constantly monitored and logged. Values for both back tension and pulling tension were logged for the time it took to pull cable through the conduit run. These values were then averaged and used in the PolyWater program to calculate coefficient of friction.

[0026] Specific Type THHN Tests

[0027] Initial tests of small gauge Type THHN wire were performed using the small-scale tension tester shown in FIG. 5. In this test, multiple individual American Wire Gauge (AWG) size 12 THHN wires were provided on the payoff and attached to a metal pulling tape that was threaded through an arrangement of conduit that included about 50 feet of straight conduit and four 90 bends. A pulling rope was attached to the other end of the pulling tape and a tugger was used to pull the cable arrangement through the conduit. The rope was threaded through a pulley arrangement that used a load cell to monitor rope tension while the wire was pulled through the conduit. This tension was continuously logged and averaged to give an average pulling force for the pull. This force correlated directly to the coefficient of friction for the cable.

[0028] Using the data obtained from the small scale pull test of FIG. 5, FIG. 2 illustrates a comparison of the different required pulling forces for a small gauge cable consisting of multiple (AWG) size 12 THHN conductors. The test subjects had 0.25-0.85% of two different potential pulling lubricants, erucamide and stearyl erucamide, mixed into the outer nylon sheath. Results of the test are shown in FIG. 2 and compared to the results for the standard THHN product without any pulling lubricant and with the externally applied industry-standard Y77. This test shows that erucamide is one preferred lubricant for small gauge THHN cable, in an optimum percentage of approximately 0.85%, by weight.

[0029] Next, large gauge Type THHN cable was tested. Using the coefficient of friction test of FIG. 4, FIG. 3 illustrates the different values of surface coefficient of friction of the exterior surface of the sheath, for cables consisting of three individual large gauge AWG 4/0 THHN conductors, for varying percentages of the pulling lubricant, silicone oil, of varying molecular weights. The two lubricants compared in FIG. 3 are a high-molecular weight silicone oil (HMW Si) and a lower molecular weight silicone oil (LMW Si). Comparison results are shown for this same THHN cable arrangement lubricated with industry-standard Y77, as well as with respect to three other trial pulling lubricants, fluorinated oil, molydisulfide, and stearyl erucamide. The results in FIG. 3 illustrate that, while other pulling lubricants can reduce the coefficient of friction of the exterior surface of the cable, the preferred pulling lubricant for THHN cable, and particularly large gauge THHN cable, is a high molecular weight silicone oil added at a level of approximately 9%, by weight, or higher.

[0030] In accordance with an advantage of the present invention, the pulling lubricant that is incorporated in the sheath is present at the outer surface of the sheath when the cable engages, or in response to the cable's engagement with, the duct or other structure through which the cable is to be pulled. For the THHN cable of the present invention, where the outer sheath is of nylon and the preferred pulling lubricant is high molecular weight silicone oil, this silicon-based lubricant permeates the entire nylon sheath portion and is, in effect, continuously squeezed to the sheath surface in what is referred to as the sponge effect, when the cable is pulled through the duct.

[0031] Compounding with Pulling Lubricant

[0032] As previously described, the pulling lubricant may be incorporated into the extruded sheath (or the outer layer of the cable sheath if the sheath is of multiple layers) by initially compounding the lubricant with the (outer) sheath material to be extruded. To prepare the lubricated blend of the present invention, the resin and additional components, including the pulling lubricant, are fed into any one of a number of commonly used compounding machines, such as a twin-screw compounding extruder, Buss kneader, Banbury mixer, two-roll mill, or other heated shear-type mixer. The melted, homogeneous blend is then extruded into strands or cut into strips that may be subsequently chopped into easily handled pellets. The so-prepared lubricated pellets are then fed into the extruder for forming the outer sheath.

[0033] THHN Cable

[0034] THHN and THWN-2 are types of insulated electrical conductors that cover a broad range of wire sizes and applications. THHN or THWN-2 conductors are typically 600 volt copper conductors with a sheath comprising an outer layer of nylon surrounding a layer of thermoplastic insulation and are heat, moisture, oil, and gasoline resistant. THHN cable is primarily used in conduit and cable trays for services, feeders, and branch circuits in commercial or industrial applications as specified in the National Electrical Code and is suitable for use in dry locations at temperatures not to exceed 90 C. Type THWN-2 cable is suitable for use in wet or dry locations at temperatures not to exceed 90 C. or not to exceed 75 C. when exposed to oil or coolant. Type THHN or THWN-2 conductors are usually annealed (soft) copper, insulated with a tough, heat and moisture resistant polyvinylchloride (PVC), over which a polyamide layer, specifically nylon, is applied. Many cables, including those addressed by the present invention, can be multi-rated, simultaneously qualifying for rating as THHN or THWN-2.

[0035] Referring now to FIG. 6, there is illustrated a THHN cable 24 constructed in accordance with the process of the invention. The cable is characterized by a sheath comprising an extruded layer 25 of PVC insulation material and an overlying extruded thin layer 26 of nylon, the sheath surrounding a central electric conductor 27 which is usually, though not exclusively, of copper. The only limitation on the type of pulling lubricant to be incorporated into the extruded outer nylon sheath is that it be sufficiently compatible with nylon to be co-processed with it, and particularly when compounded with nylon, that it be robust enough to withstand the high processing temperature for nylon, which is typically about 500 F. However, it has been found that for THHN cable, this lubricant is preferably a high molecular weight, high viscosity silicone fluid; for small gauge THHN wire, as an alternative, erucamide or stearyl erucamide.

[0036] Two industry-standard processes can be used to produce this product, the so called co-extrusion method and the tandem extrusion method. In both processes, the conductor, either solid or stranded, is first introduced into the extrusion head where the heated, melted PVC insulation compound is introduced and applied to the circumference of the conductor. In the co-extrusion process, the melted nylon compound is introduced into the same extrusion head and applied together with the PVC to the conductor, in a two-layer orientation. In the tandem process the PVC-coated conductor leaves the first extrusion head and is introduced into a second, separate extrusion head where the melted nylon is applied to the surface. In both cases, the final product is then introduced into a cooling water bath and ultimately the cooled product is wound onto reels. In either case, the nylon material is preferably initially compounded with the pulling lubricant to provide the so-lubricated extrusion pellets.

[0037] As shown in FIG. 2, small gauge THHN cable prepared, as described, with nylon as the outer layer of the sheath, and containing 0.25%, 0.50% and 0.85%, by weight, of stearyl erucamide, had an average pulling force of 18.1 lbs, 16 lbs and 18.5 lbs, respectively. Even better, small gauge THHN cable containing 0.25%, 0.50% and 0.85%, by weight, of erucamide had an average pulling force of 13.2 lbs, 10.3 lbs and 9.6 lbs, respectively. Comparably, the pulling force for a THHN cable with no pulling lubricant was measured at 38.5 lbs, and THHN cable with only Y 77 applied to the exterior surface was measured at 15.3 lbs. FIG. 3, on the other hand, illustrates the results when silicone oil is used in THHN cable, compared to other potential lubricants, illustrating silicone oil as a much preferred pulling lubricant for this type cable.

[0038] Although the aforementioned description references specific embodiments and processing techniques of the invention, it is to be understood that these are only illustrative. For example, although the description has been with respect to electrical cable, it is also applicable to other types of non-electrical cable such as, for example, fiber optic cable. Additional modifications may be made to the described embodiments and techniques without departing from the spirit and the scope of the invention as defined solely by the appended claims.