Electric cable provided with a ribbed ANG grooved outermost layer

Abstract

The invention relates to an electric cable comprising at least one elongated electrical conductor and an isolating / protective system surrounding said at least one elongated electrical conductor, wherein said isolating / protective system comprises an outermost superficial thickness provided with longitudinal ribs and longitudinal grooves, each longitudinal groove being interposed between two adjacent ribs, and wherein the outermost superficial layer of said isolating / protective system is designed to be in contact with the external environment.

Description

[0001] ELECTRIC CABLE PROVIDED WITH A RIBBED ANG GROOVED OUTERMOST LAYER

[0002] The invention relates to an electric cable provided with a longitudinally ribbed and grooved outermost layer and to a process for manufacturing the same.

[0003] Electrical cables generally comprise at least one conductor core and one or more insulating / protective layers positioned successively and coaxially around said central conductor core. The conductor core is usually made of copper or of aluminum. The layers surrounding the conductor cores are usually made of polymeric material.

[0004] The outermost layer of electrical cables is in contact with the environment in which they are installed. When the cable is installed in a structure such as buildings or industrial sites, it is placed in internal sections of walls and ceilings or conduits.

[0005] For their installation in said structures, cables are placed, pushed, pulled, slid, moved and / or removed in order to be relocated or repaired. During such operations or during the lifetime of the cable, frictions occur between the outermost layer (or surface layer) of the cable and either the structure surrounding the cable which may be abrasive or other cables which may be installed in the same structure. Such frictions may generate scratching, an abrasion and wear of the outermost layer of the cable(s) and, consequently, damage to the cable(s). In the long term, this abrasion and wear may result in a sufficient loss of material and in a reduction in the thickness of the outermost layer surrounding the conductor core of the cable.

[0006] At present, it is known to use a plastic flooring covering an abrasive floor to protect the cable from damage caused by floor abrasion. However, this solution is not satisfactory when the floor surface to be covered is large.

[0007] The invention therefore aims to obviate the need for protective plastic flooring covering. The resistance of the cable to friction and / or abrasion caused by handling the cable on abrasive surfaces requires a more efficient insulation / protection system for the electrical cable.

[0008] Additionally, national regulations impose a minimum thickness for the insulating / protective system surrounding the conductor core. Solutions are therefore being sought to ensure that the thickness of the insulating / protective system does not fall below this minimum legal thickness.

[0009] In the prior art, various modifications have been made mainly on electric cables to avoid such frictions. In particular, the cables may be covered by a lubrication layer which allows to pull or move said cables while limiting frictions thereof with the environing structure and / or cables. Document US 10 056 742 for example discloses a cable covered by a siloxane-based lubricant.

[0010] However, prior art lubricants may not be efficient enough to reduce frictions, may generate excesses and / or drips and may also attach environing dust.

[0011] Therefore, there is still a need to improve the outer surface of an electric cable in order to address these drawbacks.

[0012] Therefore, there is still a need to improve the insulating / protective system surrounding the conductor core of an electric cable in order to maintain the thickness of the insulating / protective system of the electric cable above the minimal thickness imposed by the regulation for a longer period of time.

[0013] There is also a need to improve the insulating / protective system surrounding the conductor core of an electric cable in order to ensure electric cable compliance with national regulations for a longer period of time, even after wear and tear.

[0014] But there is also still a need to improve the insulating / protective system surrounding the conductor core of an electric cable in order to maintain the thickness of the insulating / protective system of the electric cable at a value greater than the value of minimal thickness the insulating / protective system imposed by the national regulation, but without detrimentally increasing the mass of the electrical cable.

[0015] For these aims, the present invention concerns an electric cable comprising at least one elongated electrical conductor and an isolating / protective system surrounding said at least one elongated electrical conductor, said isolating / protective system comprising an outermost superficial thickness provided with longitudinal ribs and longitudinal grooves, each longitudinal groove being interposed between two adjacent ribs, and said outermost superficial thickness of said isolating / protective system being designed to be in contact with the external environment of the cable.

[0016] In some embodiments of the invention, the isolating / protective system is an isolating system providing isolation of said at least one elongated electrical conductor. In some embodiments, the isolating / protective system provides physical and / or chemical protection of said at least one elongated electrical conductor and isolation of said at least one elongated electrical conductor. In some embodiments, the isolating system comprises at least one layer of at least one thermoplastic polymer. In some embodiments, the isolating system comprises at least one layer comprising PVC, namely consisting of PVC. In some embodiments, the isolating system comprises at least one layer of at least one crosslinked polymer. In some embodiments, the isolating system comprises at least one layer of at least one crosslinked polyethylene.

[0017] In some embodiments of the invention, the isolating / protective system comprises an external protective sheath extending around an isolating system, the external protective sheath being longitudinally ribbed and grooved.

[0018] In some embodiments, said isolating / protective system surrounding said at least one elongated electrical conductor is in physical contact with said at least one elongated electrical conductor.

[0019] According to the invention, the outermost superficial layer of said isolating / protective system is designed to be in contact with the external environment of the electric cable.

[0020] In some embodiments, in any transverse cross-section of the cable, each longitudinal rib forms an excess thickness extending beyond the minimum thickness of an insulating / protective system required by national regulation.

[0021] The ribbed and grooved electric cable of the present invention can be pulled and / or moved and / or removed in (from) internal sections of walls and ceilings, ducts, conduits or any type of structure of a building or industrial sites with a decreased pulling force as compared to the pulling force necessary for the installation of a corresponding electric cable provided with a smooth outermost layer.

[0022] Additionally, due to longitudinal ribs and longitudinal grooves, the ribbed and grooved electric cable of the present invention limits the friction area of the electric cable to the surface area of the top of longitudinal ribs, such that the electric cable according to the invention slides more easily on the surface of a surrounding structure or of another cable. In some embodiments, the electric cable of the invention presents a better sliding capacity than a corresponding cable with smooth superficial layer.

[0023] In some embodiments, the outermost superficial thickness of said isolating / protective system is free of any lubricating compound.

[0024] According to the invention, in any transverse cross-section of the electric cable, the radial thickness of the insulating / protective system of the electric cable considered at the top of each longitudinal rib is greater than a minimal thickness of an insulating / protective system of an electric cable, as required by national regulations.

[0025] In some embodiments, in any transverse cross-section of the electric cable, the radial thickness of the insulating / protective system of the electric cable considered at the bottom of each longitudinal groove is at least equal to, namely greater than, the minimal thickness of an insulating / protective system of an electric cable, as required by national regulations.

[0026] According to the invention, the top of each longitudinal rib is radially more elevated as compared to the bottom of the adjacent grooves.

[0027] Thus, when the cable is subjected to friction or rubbing or is brought into contact with an abrasive environment, namely brought into contact with surfaces that can damage the insulating / protective system, this abrasion will occur on the longitudinal ribs without significantly affecting the longitudinal grooves, thus preserving a minimal thickness of the insulating / protective system. The minimum thickness of the insulating / protective system is therefore respected, and the national regulations requirements are fulfilled for a longer period of time of use of the cable. This also helps maintaining the integrity and performance of the cable despite the different risks of use and manipulation that may arise. In addition, providing the electric cable with longitudinal ribs and longitudinal grooves according to the invention makes it possible to distinguish an electrical cable provided with longitudinal ribs and longitudinal grooves having a first shape or arrangement or distribution of longitudinal ribs and longitudinal grooves, from an electrical cable without longitudinal ribs and longitudinal grooves or from an electrical cable provided with longitudinal ribs and longitudinal grooves having a second shape or arrangement or distribution of longitudinal ribs and longitudinal grooves, said second shape or arrangement or distribution of longitudinal ribs and longitudinal grooves being different of the first shape or arrangement or distribution of longitudinal ribs and longitudinal grooves.

[0028] Two electric cables with different shape or arrangement or distribution of longitudinal ribs and longitudinal grooves can advantageously be distinguished by touch of the outermost superficial part of the isolating / protective system. The electric cable according to the present invention provides an additional level of identification of such an electrical cable of the invention among a plurality of electric cables, in particular an additional level of identification by touch of the electric cable according to the invention among a plurality of electric cables, namely but not necessarily among a plurality of electric cables of same color.

[0029] In some embodiments, said isolating / protective system is made of one (unique) material. However, in some embodiments, nothing prevents said isolating / protective system to be made of a plurality of layers made of the same or different material(s).

[0030] In some embodiments, said isolating / protective system comprises at least one electrically insulating layer surrounding the at least one elongated electrical conductor and an electrically insulating protective sheath surrounding said at least one electrically insulating layer. In these embodiments, the outermost superficial thickness of the protective sheath is longitudinally ribbed and grooved.

[0031] In some embodiments, said at least one elongated electrical conductor is a copper or aluminum electrical conductor.

[0032] In some embodiments, the electric cable of the invention is a low to medium-voltage electric cable. In some embodiments, the electric cable of the invention is a low-voltage electric cable, particularly a low-voltage electric cable operating at less than 6 kV, namely at less than 1 kV. In some embodiments, the electric cable of the invention is a medium-voltage electric cable, particularly a medium-voltage electric cable operating in the range of 18 kV to 46 kV, preferably in the range of 30 kV to 46 kV.

[0033] In some embodiments, the electric cable of the invention is a direct current electric cable or an alternating current electric cable.

[0034] In some embodiments, each longitudinal rib presents in any transverse cross-section of the electric cable, a shape extending symmetrically according to a radial plan of the longitudinal rib.

[0035] In some embodiments, each longitudinal rib forms one unique top in any transverse cross-section of the electric cable.

[0036] In some embodiments, in any transverse cross-section of the electric cable, each longitudinal rib is substantially Gauss-curve shaped. In some embodiments, in any transverse cross-section of the electric cable, each longitudinal rib is symmetrical with respect to a radial plan of the cable. In these embodiments, in any transverse cross-section of the electric cable, each longitudinal groove is symmetrical with respect to a radial plan of the cable.

[0037] In some embodiments, in any transverse cross-section of the electric cable, at least one -namely each- longitudinal groove is in the form of a concave (recessed with respect to the electric cable) circular arc. In some of these embodiments, in any transverse cross-section of the electric cable, at least one - namely each- longitudinal rib is formed by the intersection of two adjacent concave arc-shaped longitudinal grooves.

[0038] In some embodiments, the electric cable presents radially at least 10 longitudinal ribs. In some embodiments, the electric cable presents radially at most 200 longitudinal ribs. In some embodiments, the electric cable presents from 10 to 20 longitudinal ribs. In some embodiments, the electric cable presents from 20 to 30 longitudinal ribs. In some embodiments, the electric cable presents radially from 30 to 40 longitudinal ribs. In some embodiments, the electric cable presents radially from 40 to 50 longitudinal ribs. In some embodiments, the electric cable presents radially from 50 to 60 longitudinal ribs. In some embodiments, the electric cable presents radially from 60 to 70 longitudinal ribs. In some embodiments, the electric cable presents radially from 70 to 80 longitudinal ribs. In some embodiments, the electric cable presents radially from 80 to 90 longitudinal ribs. In some embodiments, the electric cable presents radially from 90 to 100 longitudinal ribs. In some embodiments, the electric cable presents radially from 100 to 110 longitudinal ribs. In some embodiments, the electric cable presents radially from 110 to 120 longitudinal ribs. In some embodiments, the electric cable presents radially from 120 to 130 longitudinal ribs. In some embodiments, the electric cable presents radially from 130 to 140 longitudinal ribs. In some embodiments, the electric cable presents radially from 140 to 150 longitudinal ribs. In some embodiments, the electric cable presents radially from 150 to 160 longitudinal ribs. In some embodiments, the electric cable presents radially from 160 to 170 longitudinal ribs. In some embodiments, the electric cable presents radially from 170 to 180 longitudinal ribs. In some embodiments, the electric cable presents radially from 180 to 190 longitudinal ribs. In some embodiments, the electric cable presents radially from 190 to 200 longitudinal ribs.

[0039] In some embodiments, in any transverse cross-section of the electric cable, the longitudinal ribs are regularly distributed around the electric cable.

[0040] In some embodiments, in any transverse cross-section of the electric cable, the ratio of an excess thickness formed by a longitudinal rib relative to the bottom of at least one groove adjacent to said longitudinal rib -namely relative to the bottom of both grooves adjacent to said longitudinal rib-, to the radius of a circle tangent to said adjacent grooves ranges from 0.5% to 5%, namely from 0.5% to 3%. In one embodiment, said ratio ranges from 0.5% to 0.7%. In one embodiment, said ratio ranges from 0.7% to 0.9%. In one embodiment, said ratio ranges from 0.9% to 1.1%. In one embodiment, said ratio ranges from 1.1% to 1.3%. In one embodiment, said ratio ranges from 1.3% to 1.5%. In one embodiment, said ratio ranges from 1.5% to 1.7%. In one embodiment, said ratio ranges from 1.7% to 1.9%. In one embodiment, said ratio ranges from 1.9% to 2.1%. In one embodiment, said ratio ranges from 2.1% to 2.3%. In one embodiment, said ratio ranges from 2.3% to 2.5%. In one embodiment, said ratio ranges from 2.5% to 2.7%. In one embodiment, said ratio ranges from 2.7% to 3.0%.

[0041] In some embodiments, in any transverse cross-section of the electric cable, the ratio of an excess thickness provided by a longitudinal rib as compared to at least one groove adjacent to said longitudinal rib, to the radius of said adjacent groove is greater than 3.0%. In some embodiments, in any transverse cross-section of the electric cable, each longitudinal rib presents a width at half-height and each longitudinal groove presents a width at half-depth, the width at half-height of each longitudinal rib being greater than the width at half-depth of each longitudinal groove. In some embodiments, in any transverse cross-section of the electric cable, each longitudinal rib presents a width at half-height and each longitudinal groove presents a width at half-depth, the width at half-height of each longitudinal rib being greater than the width at half-depth of at least one -namely to both- longitudinal groove(s) adjacent to said longitudinal rib.

[0042] In some embodiments, in any transverse cross-section of the electric cable, each longitudinal rib presents a width at half-height and each longitudinal groove presents a width at half-depth, the width at half-depth of each longitudinal groove being greater than the width at half-height of each longitudinal rib. In some embodiments, in any transverse cross-section of the electric cable, each longitudinal groove presents a width at half-depth and each longitudinal rib presents a width at half-height, the width at half-depth of each longitudinal groove being greater than the width at half-height of at least one -namely of both- longitudinal rib(s) adjacent to said longitudinal groove.

[0043] In some embodiments, the longitudinal ribs and longitudinal grooves extend parallel to the longitudinal axis of the electric cable. In some embodiments, the longitudinal ribs and longitudinal grooves extend straight and parallel to each other and parallel the longitudinal axis of the cable.

[0044] In some embodiments, the longitudinal ribs and longitudinal grooves extend helically around the longitudinal axis of the electric cable.

[0045] In some embodiments, the isolating / protective system and the outermost superficial thickness of said isolating / protective system comprise, notably consist of, at least one polymer. In some embodiments, the at least one polymer of said isolating / protective system is a thermoplastic polymer. In some embodiments, the at least one polymer of said isolating / protective system is PVC. In some embodiments, the at least one polymer of said isolating / protective system and of the outermost superficial thickness of said isolating / protective system is a crosslinked polymer. The longitudinal ribs of the invention provide the electric cable with a increased average diameter as the longitudinal ribs acts as additional protective elements to ensure cable compliance with the thickness of the insulating / protective system of an electric cable, as required by national regulation even after wear and tear.

[0046] In some embodiments, the longitudinal ribs and longitudinal grooves present a regular alternance around the longitudinal axis of the cable in any transverse cross-section of the electric cable.

[0047] In some embodiments, the longitudinal ribs and longitudinal grooves present an irregular alternance around the longitudinal axis of the electric cable in any transverse cross-section of the electric cable.

[0048] In some embodiments, the longitudinal ribs are axially symmetrically distributed. In some embodiments, the longitudinal grooves are axially symmetrically distributed.

[0049] In some embodiments, the longitudinal ribs are axially asymmetrically distributed. In some embodiments, the longitudinal groves are axially asymmetrically distributed.

[0050] In some embodiments, in any transverse cross-section (namely in any cross-section orthogonal to the longitudinal axis) of the electric cable, a straight line pertaining to the transverse cross-section, joining the tops of two adjacent longitudinal ribs, extends beyond the bottom of the longitudinal groove extending between said two adjacent longitudinal ribs and beyond the minimum thickness of insulation / protection system required by national regulation.

[0051] The invention also extends to a process of manufacture an electric cable according to the present invention.

[0052] The invention concerns a process for manufacture an electric cable comprising at least one elongated electrical conductor and at least one isolating / protective system surrounding said at least one elongated electrical conductor, said isolating / protective system comprising a longitudinally ribbed and grooved outermost superficial layer of said at least one isolating / protective system. In some embodiments, the process comprises a step of providing an electric cable with a ribbed and grooved outermost superficial layer of an insulating / protective system, the process comprising a step of extruding a softened thermoplastic polymer composition around the at least one elongated electrical conductor through a ribbed and grooved extrusion die so as to form the electric cable with an isolating / protective system comprising an outermost superficial layer provided with longitudinal ribs and grooves.

[0053] In some embodiments, the softened thermoplastic polymer composition is extruded directly in contact with the at least one elongated electrical conductor.

[0054] In some embodiments, the softened thermoplastic polymer composition is extruded above an additional layer interposed between the at least one elongated electrical conductor and the softened thermoplastic polymer composition.

[0055] In some embodiments, the process comprises a step of extruding a softened thermoplastic polymer composition around the at least one elongated electrical conductor to form an electric cable with a substantially smooth insulating / protective system and subsequently feeding the electric cable with a substantially smooth insulating / protective system, through a die adapted and shaped to remove part of the smooth insulating / protective system and to form the electric cable with an isolating / protective system comprising an outermost superficial layer provided with longitudinal ribs and grooves.

[0056] In some embodiments, the softened thermoplastic polymer composition is extruded directly in contact with the at least one elongated electrical conductor.

[0057] In some embodiments, the softened thermoplastic polymer composition is extruded above an additional layer interposed between the at least one elongated electrical conductor and the softened thermoplastic polymer composition.

[0058] Other features and advantages of the invention will become apparent from the following description and drawings of preferred embodiments of the invention, given by way of examples.

[0059] Brief Description of the Drawings:

[0060] Figure 1 is a representation in perspective view of an embodiment of an electric cable according to the invention, Figure 2 is a schematic representation of a detail of a transverse crosssection view of another embodiment of a ribbed and grooved electric cable according to the invention,

[0061] Figure 3 is a representation of the downstream side of a first embodiment of a ribbed and grooved extrusion die used in a process according to the invention,

[0062] Figure 4 is a representation of a detail of the photograph of Figure 3, the ribbed and grooved extrusion die being provided with 87 ribs and 87 grooves,

[0063] Figure 5 is a representation of the downstream side of a second embodiment of a ribbed and grooved extrusion die used in a process according to the invention,

[0064] Figure 6 represents a detail of the photograph of Figure 4, the ribbed and grooved extrusion die being provided with 24 ribs and 24 grooves,

[0065] Figure 6 represents a photograph of the upstream side of the ribbed and grooved extrusion die according to the second embodiment of figures 5 and 6 as used in a process according to the invention.

[0066] Figure 1 is a perspective view of an embodiment electric cable 1 according to the invention. The outermost superficial thickness of the electric cable 1 presents longitudinal grooves 3 and longitudinal ribs 2, the longitudinal ribs 2 extending beyond the minimum thickness of insulation / protection system required by national regulation. In the embodiment presented in figure 1, the longitudinal ribs 2 and the longitudinal grooves 3 extend parallel to the longitudinal axis of the electric cable 1. In the embodiment represented, the top of each longitudinal rib 2 and the bottom of each longitudinal groove 3 is rounded.

[0067] Figure 2 represents a schematic representation of a detail of a transverse cross-section view of a particular embodiment of a ribbed and grooved electric cable 1 according to the invention. In this embodiment, the top of each longitudinal rib 2 is pointed in any transverse cross-section of the cable 1 and the bottom of each longitudinal groove 3 is substantially flat. The minimum thickness 5 of the insulation / protection system 6, required by national regulation is maintained due to the longitudinal ribs 2.

[0068] EXAMPLES EXAMPLE 1 - Electric cable with longitudinally ribbed and grooved superficial insulating layer for residential installations

[0069] A low-voltage cable with longitudinally ribbed and grooved superficial layer for residential use is provided. The low-voltage cable according to the invention specified in the present example is a PVC-insulated cable with low smoke emission when exposed to fire.

[0070] First, copper wires are wire-drawn to the required diameter to meet the electrical load requirements of the electric cable. Then, the wire-drawn copper wires are twisted together to form the conductor element, also named stranded conductor. An insulation layer is applied around the stranded conductor by extrusion of a molten composition of PVC at a temperature of about 180°C to 200°C around the stranded conductor. The insulation layer complies with a minimum thickness according to the standard depending on the type of use and electrical load that this cable must carry out. In one embodiment, the extrusion die used to apply the insulation layer around the stranded conductor is a grooved and ribbed die providing the cable with the grooved and ribbed insulating layer.

[0071] Thanks to the longitudinally ribbed and grooved insulating layer, the electric cable can slide more easily over an abrasive surface than a cable with a smooth surface, as shown in the comparative Example 4. The longitudinal ribs and grooves make it easier for the electrical cable to slide, particularly on an abrasive surface, due to the contact area of the cable with this surface, which is reduced to the area limited to the top of longitudinal ribs. Moreover, the abrasion that may result from this sliding affects substantially exclusively the longitudinal ribs of the cable, which makes it possible to maintain the thickness of the insulating system at a value greater than the legal minimal thickness for an insulating system.

[0072] EXAMPLE 2 - Electric cable with longitudinally ribbed and grooved superficial jacket layer

[0073] An electric cable with low fire hazard and longitudinally ribbed and grooved superficial sheath layer is provided, for example for low voltage power distribution networks.

[0074] First, soft copper wires are wire-drawn to the required diameter. Then, the wire-drawn copper wires are twisted together to form the conductor element, also named stranded conductor. An insulation layer is applied around the stranded conductor by extrusion of a molten polymer composition so chosen to form an insulating crosslinked XLPE layer. A layer of a thermoplastic halogen free, fire retardant and UV resistant (HFFR-UV) is co-extruded through a ribbed and grooved extrusion die to form the ribbed and grooved external sheath of the cable.

[0075] Thanks to the longitudinally ribbed and grooved sheath layer, the electric cable can slide more easily over an abrasive surface than a cable with a smooth surface, as shown in Example 4. The longitudinal ribs and grooves make it easier for the electrical cable to slide, particularly on an abrasive surface, because the contact area of the cable with this surface is reduced to the area limited to the top of the longitudinal ribs. Moreover, the abrasion that may result from this sliding affects substantially exclusively the longitudinal ribs of the cable, which makes it possible to maintain the thickness of the insulating system at a value greater than the legal minimal thickness for an insulating system.

[0076] EXAMPLE 3 - Electric cable with longitudinally ribbed and grooved superficial sheath layer

[0077] An electric cable with large section, namely a section greater or equal to 285 mm2, with low fire hazard and longitudinally ribbed and grooved superficial jacket layer is provided, for example for low voltage power distribution networks.

[0078] First, soft copper wires are wire-drawn to the required diameter. Then, the wire-drawn copper wires are twisted together to form the conductor element, also named stranded conductor. An insulation layer is applied around the stranded conductor by extrusion of a molten polymer composition so chosen to form an insulating crosslinked XLPE layer. A layer of a thermoplastic, halogen free, fire retardant and UV resistant (HFFR-UV) polymer is co-extruded through a ribbed and grooved extrusion die to form the ribbed and grooved external sheath of the cable.

[0079] Thanks to the longitudinally ribbed and grooved sheath layer, the electric cable slides more easily over an abrasive surface than a cable with a smooth outermost surface, as shown in Example 4. The longitudinal ribs and grooves make it easier for the electrical cable to slide, particularly on an abrasive surface, due to the reduced contact area of the cable with this surface, the reduced contact area being limited to the top of the longitudinal ribs. Moreover, the abrasion that may result from this sliding affects substantially exclusively the longitudinal ribs of the cable, which makes it possible to maintain the thickness of the insulating system of the cable at a value greater than the legal minimal thickness for an insulating system.

[0080] EXAMPLE 4 - WIRE PULLING TEST - COMPARATIVE

[0081] Comparative test to assess the pulling force (N) to be applied to a cable according to the invention and to a comparable smooth cable is performed. To this end, the wire pulling test simulates the electrical installer's operation when pulling wires through a flexible conduit. The equipment to perform the wire pulling test comprises a test bench including a 4.5-meter-long flexible conduit mounted on a bench, a dynamometer and a pulling engine. The distance between the bench and the pulling engine is greater than the length of the flexible conduit. The procedure for measuring the pulling force of one cable is described below.

[0082] From a cable coil, 10 meters of cable are pulled, 3 times. The three cable segments are taped together parallel at one end with colored duct tape and arranged to form a cable bundle. The taped end of the bundle is introduced at once through the flexible conduit from the inlet to the outlet of the flexible conduit. The exact same length of the flexible conduit is reported on the cable bundles (both smooth and ribbed cable bundles) extending at the inlet of the flexible conduit. The exact same length is identified with a sticked colored duct tape on the compared bundles of cable. At the outlet of the flexible conduit, a first end of the dynamometer is connected to the bundle and the pulling engine is connected to the second end of the dynamometer.

[0083] Measuring the wire pulling force, consists in collecting the force applied to pull the bundle of wires through the flexible conduit over the total length of the flexible conduit. The test ends when the adhesive tape is at the entrance to the flexible conduit. One operator switches on the pulling engine. The pulling speed is setup at 5m / min. A second operator collects force values every 2 seconds from the dynamometer. When the duct tape reaches the flexible conduit inlet, the pulling engine is switched off. The dynamometer is disconnected, the bundles are removed from the flexible conduit and the cables of the bundle are discarded. The average of the force values defines the pulling force (N).

[0084] The results are shown in table 1 below.

[0085] Table 1

[0086] The results demonstrate that the ribbed and grooved electric cable of the invention is pulled with a lower force than the comparative smooth cable. Thus, the electric cable according to the invention is more easily moved than the comparative smooth cable. Additionally, decreased pulling force provides the electric cable of the invention with decreased frictions between the outermost layer of the cable and either the structure surrounding the cable (which may be abrasive) or other cables which may be installed in the same structure when the cable is placed, pushed, pulled, slid, moved and / or removed in the structure. Scratches, abrasion and wear on the outer surface of the cable of the invention are reduced and, as a result, the reduction in thickness of the outermost layer surrounding the conductor core of the cable is greatly slowed.

[0087] Of course, the present invention is not limited to the examples and embodiment described and shown, but is susceptible to numerous variants accessible to those skilled in the art.

Claims

CLAIMS1. Electric cable comprising at least one elongated electrical conductor and an isolating / protective system surrounding said at least one elongated electrical conductor, wherein said isolating / protective system comprises an outermost superficial thickness provided with longitudinal ribs and longitudinal grooves, each longitudinal groove being interposed between two adjacent ribs, and wherein the outermost superficial layer of said isolating / protective system is designed to be in contact with the external environment of the cable.

2. Electric cable according to claim 1, wherein in any transverse cross-section of the electric cable, the radial thickness of the insulating / protective system of the electric cable considered at the top of each longitudinal rib is greater than the minimal thickness of an insulating / protective system of an electric cable, as required by the national regulation.

3. Electric cable according to anyone of the preceding claims, wherein in any transverse cross-section of the electric cable, the radial thickness of the insulating / protective system of the electric cable considered at the bottom of each longitudinal groove is at least equal to, namely greater than, the minimal thickness of an insulating / protective system of an electric cable, as required by national regulation.

4. Electric cable according to anyone of the claims 1 to 3, wherein said isolating / protective system is made of one material.

5. Electric cable according to anyone of the claims 1 to 3, wherein said isolating / protective system comprises at least one electrically insulating layer surrounding the at least one elongated electrical conductor and an electrically insulating protective sheath surrounding said at least one electrically insulating layer.

6. Electric cable according to anyone of the preceding claims, wherein said at least one elongated electrical conductor is a copper or aluminum electrical conductor.

7. Electric cable according to anyone of the preceding claims, wherein the electric cable is a low-voltage electric cable operating at less than 6 kV, namely at less than 1 kV.

8. Electric cable according to anyone of the preceding claims, wherein each longitudinal rib presents in any transverse cross-section of the electric cable, a shape extending symmetrically according to a radial plan of the longitudinal rib.

9. Electric cable according to anyone of the preceding claims, wherein each longitudinal rib forms one unique top in any transverse cross-section of the electric cable.

10. Electric cable according to anyone of the preceding claims, wherein in any transverse cross-section of the electric cable, each longitudinal rib is substantially Gauss-curve shaped.

11. Electric cable according to anyone of the preceding claims, wherein the electric cable presents at least 10 longitudinal ribs.

12. Electric cable according to anyone of the preceding claims, wherein the longitudinal ribs are regularly distributed around the electric cable in any transverse cross-section of the electric cable.

13. Electric cable according to anyone of the preceding claims, wherein in any transverse cross-section of the electric cable, the ratio of an excess thickness formed by a longitudinal rib relative to the bottom of at least one groove adjacent to said longitudinal rib, to the radius of a circle tangent to said adjacent grooves ranges from 0.5% to 5.0%.

14. Electric cable according to anyone of claims 1 to 13, wherein in any transverse cross-section of the electric cable, each longitudinal rib presents a width at half-height and each longitudinal groove presents a width at half-depth, the width at half-height of each longitudinal rib being greater than the width at halfdepth of each longitudinal groove.

15. Electric cable according to anyone of claims 1 to 13, wherein in any transverse cross-section of the electric cable, each longitudinal rib presents a width at half-height and each longitudinal groove presents a width at half-depth, thewidth at half-depth of each longitudinal groove being greater than the width at half-height of each longitudinal rib.

16. Electric cable according to anyone of the preceding claims, wherein the longitudinal ribs and longitudinal grooves extend parallel to the longitudinal axis of the electric cable.

17. Electric cable according to anyone of the preceding claims, wherein the outermost superficial thickness of said isolating / protective system comprises at least one polymer.

18. Electric cable according to anyone of the preceding claims, wherein in any transverse cross-section of the electric cable, a straight line pertaining to the transverse cross-section, joining the tops of two adjacent longitudinal ribs, extends beyond the bottom of the longitudinal groove extending between said two adjacent longitudinal ribs and beyond the minimum thickness of insulation / protection system required by national regulation.

19. Process for manufacture an electric cable according to anyone of claims 1 to 18, provided with a longitudinally ribbed and grooved outermost superficial layer of an insulating / protective system, wherein the process comprises a step of extruding a softened thermoplastic polymer composition around the at least one elongated electrical conductor through a ribbed and grooved extrusion die so as to form the electric cable with an isolating / protective system comprising an outermost superficial layer provided with longitudinal ribs and grooves.

20. Process according to claim 19, the process comprising a step of extruding a softened thermoplastic polymer composition around the at least one elongated electrical conductor to form an electric cable with a substantially smooth insulating / protective system and subsequently feeding the electric cable with a substantially smooth insulating / protective system through a die adapted and shaped to remove part of the smooth insulating / protective system and to form the electric cable with an isolating / protective system comprising an outermost superficial layer provided with longitudinal ribs and grooves.

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