JPH1131418A - cable - Google Patents

Abstract

(57) [Problem] To provide a cable in which a desired cable can be easily pulled out from a cable laid in multiple rows. SOLUTION: On the surface of a cable jacket 2 provided around a cable core 1, a projection 3 having a triangular cross section is formed so as to continuously surround the outer periphery. This cable is
When two or more books are in close contact,
When one is to be pulled out for removal or the like, since it is in contact with the adjacent cable at the apex of the protrusion 3, the state is close to a point contact, the frictional resistance is small, and the pull-out can be easily performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a cable jacket such as an optical fiber cable provided with a jacket, a wire cable for telecommunication or power supply, and the like.

[0002]

2. Description of the Related Art In many cases, a plurality of optical fiber cables and electric cables are tied together using a bundling member such as an insulated lock in a state where they are laid in a station building or the like. When only one of them is to be removed, the bundle member is removed and one of the bundles is pulled out. Since the bundling member is attached over multiple locations,
It takes time to remove this. In addition, after removal, it is necessary to perform a work of binding again with the binding member.

According to the present invention, as described later, by providing fine protrusions having a triangular cross section or an arcuate cross section extending in the length direction on the surface of the jacket of the cable, the cables come into close contact with each other. The present invention relates to a cable which can be easily pulled out when a desired one cable is pulled out of cables laid in multiple strips.

[0004] On the other hand, conventionally, there is known a cable provided with a projection or a groove on a jacket. For example, JP-A-61
The cables described in JP-A-19008, JP-A-4-28117, JP-A-6-300946, and JP-B-5-14253 are provided with protrusions and grooves in a cable jacket. is there.

The cable described in Japanese Patent Application Laid-Open No. 61-19008 is characterized by providing a groove rather than a protrusion, and the groove is filled with a fluid substance. Although the projections are formed as a result of the formation of the grooves, the cross sections of the projections are substantially rectangular, and do not attempt to bring the cables into close contact with each other, as will be described later. The optical fiber cable described in Japanese Utility Model Publication No. 5-1253 uses a light-weight foamed resin for the sheath, and grooves formed on the surface also allow a gas flow to flow so that the cable can easily float. It is provided and is not intended to bring the cables into close contact with each other. Further, the cable described in Japanese Patent Application Laid-Open No. 4-28117 has a structure in which ridges and grooves are provided alternately, and the cross section of the ridge is substantially rectangular. However, although the top is circular, the radius of curvature is the radius of the cable, and therefore, when the cables come into contact with each other, the contact state is the same as when there is no groove, and the friction resistance is Not reduced by formation. In addition, the ridges and the grooves may bite into each other to increase the resistance at the time of pulling out.
Therefore, there is no consideration about bringing the cables into contact with each other in a state close to point contact. JP-A-4-3
The optical fiber cable described in JP-A-36506 and JP-A-6-300946 has a wart-like projection.
When one cable is pulled out from the bundled cable, the protrusions engage with each other, and the protrusions become obstacles when the cable is pulled out.

Each of these conventional cables is provided with a projection or a groove in order to reduce friction with a pipe wall in consideration of drawing into a pipe, and one cable is provided from a bundled cable. It does not matter how easy the cable can be pulled out.

Therefore, the conventional cable having the projections and grooves provided on the cable jacket is not intended to assume that the cables come into close contact with each other and that one cable is pulled out of the cable laid in multiple layers. I can say.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has as its object to provide a cable that allows a desired cable to be easily pulled out of a multi-layered cable. Is what you do.

[0009]

According to a first aspect of the present invention, in a cable, a surface of a cable jacket has a triangular or arcuate mountain-shaped projection continuous in the length direction, and the projection is formed. The height from the bottom of the cable is not more than the thickness of the cable jacket except for the protrusion, and the distance between adjacent protrusions in the circumferential direction is not more than twice the width of the protrusion. Things.

[0010] According to a second aspect of the present invention, in the cable, the surface of the cable jacket has a mountain-shaped projection having an arc-shaped cross section that is continuous in the length direction, and the height of the projection from the bottom is:
While not more than the thickness of the cable jacket except for the protrusion, the radius of curvature near the top of the protrusion is 0.2 to 0.8 times the radius of the circumcircle of the cable, and The distance between the adjacent projections is not more than twice the width of the projections.

According to a third aspect of the present invention, in the cable according to the first or second aspect, the protrusion is undulated in the length direction by a variation smaller than the height of the protrusion. It is.

According to a fourth aspect of the present invention, in the cable according to any one of the first to third aspects, the cable jacket and the projection are made of polyethylene to which magnesium hydroxide is added. Is what you do.

According to a fifth aspect of the present invention, in the cable according to any one of the first to third aspects, the cable jacket including the projection or at least a surface layer thereof is made of a fluororesin. It is characterized by the following.

According to a sixth aspect of the present invention, in the cable according to any one of the first to third aspects, the cable jacket including the projection or at least a surface layer thereof has a flexural modulus of 1000 kg / cm. It is characterized by comprising ^two or more thermoplastic polyester elastomers or polyamide polymers.

According to a seventh aspect of the present invention, there is provided the cable according to any one of the first to sixth aspects, wherein a length of the cable along one of a plurality of locations on the circumference of the cable jacket is along the protrusion. A notch groove in the direction is provided.

[0016]

FIG. 1 shows a first embodiment of a cable according to the present invention.
It is sectional drawing of embodiment. In the figure, 1 is a cable core, 2 is a cable jacket, and 3 is a protrusion. The cable core 1 is a core of an optical fiber cable or a wire cable for telecommunication or power supply. The cable jacket 2 is formed of a synthetic resin, and on its surface, a projection 3 having a triangular cross section is formed so as to continuously surround the outer periphery. The longitudinal direction of the projection 3 is parallel to the central axis of the cable,
Alternatively, it is formed continuously in a spiral shape.

When a plurality of cables are in close contact with each other and one of them is to be pulled out for removal or the like, the top of the projection 3 contacts the adjacent cable. Therefore, it is in a state close to point contact, has low frictional resistance, and can be easily pulled out. Even in the case of being bound by a bundling member such as an insulation lock, it can be pulled out without removing the binding.

FIG. 2 is a sectional view of a part of a cable jacket of a cable according to a second embodiment of the present invention. In the figure, FIG.
The same parts as those described above are denoted by the same reference numerals and description thereof will be omitted. In this embodiment, the cross-sectional shape of the projection on the surface of the cable jacket 3 is an arc. Therefore, the radius of curvature of the curved surface at the top of the protrusion 3 is a value sufficiently smaller than the radius of the outer periphery of the cable.

FIG. 2 (A) shows a substantially semicircular projection formed continuously in the circumferential direction. The arc shape in the present invention is not limited to a part of a perfect circle as shown in FIG. 2A, but may be an elliptical arc as shown in FIG.
Alternatively, it includes other suitable curved surfaces. In any case, the radius of curvature at the top of the projection is preferably small, and the maximum value of this radius of curvature is preferably the radius of curvature of an arc having a diameter at the bottom of the projection.

FIG. 3 is a cross-sectional view for explaining a cable according to a third embodiment of the present invention. In the figure, the same parts as those in FIG. Reference numeral 4 denotes a holding roll, 6 denotes a cutout groove, 7 denotes an optical cord, 8 denotes a tension member, and 9 denotes a cover. In this embodiment, the cross-sectional shape of the projection 3 on the surface of the cable jacket 2 is formed in an arc shape, as in the second embodiment. The portion of the cable core may have an appropriate structure and is not specified, but in the example shown in the figure, it is a cable in which optical codes are assembled. Of course, a cable of an electric conductor or a composite cable of an electric conductor and an optical fiber core may be used. In this example, a plurality of optical cords 7 are twisted around a tension member 8 such as a twisted steel wire or a single-wire steel wire and a synthetic resin coating 9 is applied around the tension member 8. 4 to cover the cable jacket 2.

The notch grooves 6 are preferably provided at least at two locations on the circumference, and facilitate tearing of the cable jacket when the cable core is taken out from the cable jacket. The width of the groove is not always necessary, and may be cut.

The shape of the cable jacket 2 in the specific example is
This will be described with reference to FIG. FIG.
The circumcircle of the cable jacket is substantially a perfect circle, and its radius is R. The projection 3 has a slightly elliptical shape, and the radius of curvature near the top is r. Assume that the height of the projection 3 is H, and the thickness of the cable jacket at the portion excluding the projection is T. The dimensions of each part are as follows: R = 5 mm r = 2.8 mm H = 0.3 mm T = 1 mm, and the ratio of the radius of curvature near the top of the projection to the radius of the circumscribed circle, that is, r / R is 0.56 And the number of projections is eight. Note that these numerical values are merely examples, and the present invention is not limited to these numerical values.
For, as described later, it is preferable to select a value in a desirable range.

When such cables are in close contact with each other and one cable is pulled out of the cables laid in multiple strips, there is a case where the cables in orthogonal contact are pulled out. In this case, the cable of the mating cable that is in contact with the cable to be pulled out in an orthogonal state is dragged by the pulled-out cable, so that the cable jacket is shaved and damage is left.

In order to examine the state of this injury, an experiment of pulling out orthogonal cables was performed using a model as shown in the plan view of FIG. In the figure, 11 is a simulation rack,
Reference numeral 12 denotes a stacked cable, 13 denotes a cable for pulling out, and 14 denotes a bobbin.

The simulated rack 11 has an upright side wall on the outside and an open upper part. The side wall of the central portion is expanded in a direction orthogonal to the center. Stacked cable 12
Is obtained by stacking 450 pieces into about 10 layers. The cable 13 for pulling out is one from the bottom of the stacked cables.
It was inserted between the second layer and the second layer and pulled out at a speed of about 30 m / min. The length pulled out was 50 m.

As the cables used in the experiment, the same cables were used as the stacked cables and the cables to be pulled out. The above-described specific example was prepared as document 1, and a material having a smaller radius of curvature near the top of the protrusion than the radius of the circumscribed circle was prepared as document 2. The dimensions of each part of document 2 are R = 5 mm r = 0.72 mm H = 0.3 mm T = 1 mm, r / R is 0.14, and the number of protrusions is 24.

In the case of the material 1 in which the radius of curvature of the arc-shaped projection of the cable to be pulled out is large, the damage is difficult to be caused. Therefore, the cable is pulled out while swinging right and left, and the surface of the cable jacket on the mating side is pulled out. As shown in FIG. 6A showing the cross section of the portion, the portion 15 to be cut is shallow,
Due to the swing of the cable that was pulled out, it was not concentrated at one place, but resulted in shallow trauma remaining at multiple places.

On the other hand, in the case of the material 2 in which the radius of curvature of the arc-shaped projection of the cable to be pulled is small, the contact area is small and the stress is concentrated on a narrow portion. As shown in FIG. 6B, which shows a cross section of the surface portion of the cable jacket on the mating side, the portion 16 to be cut becomes deeper, and therefore, from the portion that has already been bitten, the side of the cable to be pulled out The projection of the cable was hard to come off, and concentrated in one place, resulting in deep trauma.

For the cable to be pulled out for removal,
Since the cable on the other side in contact with this is a cable in operation or a cable to be operated, large damage remains as shown in FIG. This is problematic in terms of reliability.

The magnitude of the damage caused by the pull-out is affected by the weight of the stacked cables, the coefficient of friction of the surface of the cable jacket, and the like. Therefore, it is not appropriate to evaluate the absolute value of the radius of curvature of the projection. R considering the outer diameter of the cable
The evaluation with / R is high. And r / R is 0.2
At smaller sizes, trauma often affects reliability. Therefore, it is practically desirable that r / R be 0.2 or more. On the other hand, when r / R exceeds 0.8, the outer diameter of the cable is substantially close to the outer diameter of the cable, and the pullout resistance increases. Therefore, the upper limit of r / R needs to be about 0.8.

The arc shape of the present invention is not limited to a part of a perfect circle but also includes a curved surface such as an elliptical arc. The radius of curvature varies from part to part and is not a constant value. Therefore, the radius of curvature of the arc-shaped projection is preferably evaluated using the radius of curvature near the top where contact is a problem. Also, if the shape of the envelope of the cable cross section is a perfect circle, the radius can be determined. In the cable of the present invention, the shape of the envelope of the cable jacket is not necessarily a perfect circle but may be an elliptical shape or the like. Therefore, the radius R of the circumscribed circle is not limited to the shape of the envelope of the cable jacket being circular.

In the first and second embodiments described above, the protrusions are formed such that the outer peripheral portion of the cable jacket is spaced from the adjacent protrusions to zero, ie, continuous protrusions. A non-zero interval may be provided between them. However, if this interval is large, it is difficult to realize a point contact state. As shown in FIG. 7, when the width of the protrusion is W and the interval between adjacent protrusions in the circumferential direction is S, S ≦ 2W. When the height of the projection is increased, the outer diameter of the cable is substantially increased. To avoid this, the height from the bottom of the projection is H, and the thickness of the cable jacket excluding the projection is H. If T, H ≦ T.

By satisfying this condition, it is possible to reduce the frictional resistance when pulling out the cable by preventing the portions on the circumference having no protrusion from contacting each other when the cables are bundled, while suppressing the increase in the outer diameter due to the protrusion. Can be. In addition,
The values of W and H are from about 0.1 mm to about 1 mm, and are fine projections.

As a material for the cable jacket, for example, polyethylene to which magnesium hydroxide (Mg (OH) ₂ ) is added can be used. This material is not only suitable for indoor use as a flame-retardant cable, but also is more physically fragile than ordinary polyethylene, so that when the cable is pulled out, the projections rub against each other to form fine particles. Due to the fine particles, the surface becomes rough, and the frictional resistance decreases due to the rolling of the fine particles.

A fluorine resin can be used as a material for the cable jacket including the projections. FIG. 8A shows an embodiment in which a fluorine resin is used for the surface layer of the cable jacket. In the figure,
2a is a lower layer of the cable jacket, which is made of PVC or polyethylene. The projections 3 were formed on the surface of the upper layer using a fluororesin. The cable jacket may be made of a fluorine resin including the lower layer. A cable jacket using a fluorine-based resin is excellent in slipperiness and contributes to improvement in pull-out property.
However, the material is expensive, the extrusion processability is not always good, and when the thickness is large, distortion remains. In particular, in an optical cable, the transmission loss may be increased due to shrinkage of the jacket. For this reason, as shown in FIG. 8 (B), once the jacket 2c with projections is formed of a material used for a normal cable jacket such as PVC or polyethylene, the fluororesin 2d is thinly coated on the surface. It may be applied by coating or spraying.

Also, a cable jacket including a projection, or
At least the surface layer has a flexural modulus of 1000 kg / c.
m ² or more of a thermoplastic polyester elastomer or a polyamide-based polymer. Since the material has elasticity and has slipperiness and abrasion resistance, if the flexural modulus is 1000 kg / cm ² or more, the shape of the protrusion is maintained to some extent even when the protrusions with the adjacent cable are pressed. Since the protrusions can get over each other in a state close to the point contact, the pull-out property is improved.

FIG. 9 is an explanatory view of a third embodiment of the cable according to the present invention. In the first and second embodiments, the projections are formed continuously at the same height in the longitudinal direction of the cable, but in this embodiment, the projections are
It is formed with undulations in the longitudinal direction. FIG. 9 (A)
Is a sine wave-shaped undulation, FIG. 9 (B)
Are gently trapezoidal shapes with undulations, and in each case, only the protrusion is viewed from the side. The present invention is also applied to a case where the projection is provided in a spiral shape. Of course, undulations may be provided in other shapes. The shape of the undulation may be a regular change or an irregular change.

By making the projections undulate in the longitudinal direction, even when the projections partially mesh when the cables are bundled, they do not continuously mesh in the longitudinal direction, and are close to point contact with the adjacent cable. Can contact. In the state of being bound using the bundling member, the projections are pressed and fixed to each other. However, when the projections are pulled out, the contact area is small, so that the projections can be easily pulled out while climbing over the projections. Also in this sense, it is better to provide a large number of protrusions on the circumference, and the condition of S ≦ 2W and H ≦ T is significant.

The projections may be undulated by periodically changing the extrusion discharge amount of the cable jacket when extruding and coating the material of the cable jacket, or by vibrating the inner core before the extrusion section. There is a method of varying the cable jacket thickness or outer diameter in the longitudinal direction.

FIG. 10 is an explanatory diagram of another method for undulating projections. The presser winding 4 of the cable core 1 is an open winding or a lap winding, and the projections can be undulated so that the undulations appear as they are on the outer appearance of the cable jacket. In this case, the thickness of the holding tape 4 of the cable core 1 is set to be not less than 1/2 of the height H of the projection, the tape is wound horizontally, and a cable jacket having a substantially constant thickness is applied to form the projection. . The change in the outer diameter of the presser winding can be visually expressed as a change in the outer diameter sufficient for the protrusions to get over each other.

Similarly, a method of forming a projection by applying a cable jacket having a substantially constant thickness to the polygonal inner core can be adopted. As a polygonal inner core,
For example, a bundle of a plurality of electric wires, units, or filaments, or a twisted bundle of wires without insertion of an inclusion or the like has a polygonal shape without a round outer shape.
The number of electric wires, units, or filaments is desirably about 3 to 6, and when the number is more than that, the shape becomes closer to a circle and undulation is less likely to appear.

In the case of a circular core, as shown in FIG.
The outer jacket may be provided so that the outer shape of the cable core is substantially polygonal.

As described above, when the shape of the base on which the cable jacket is applied is polygonal, the shape is formed in parallel with the case where the shape is spirally parallel to the longitudinal direction of the cable. There are cases. When the projection is formed in a spiral shape, the projection can be made uneven by forming the projection in parallel with the longitudinal direction of the cable. In this case, when the protrusions are formed in a spiral shape, the pitch may be different from the pitch of the underlying spiral, or may be a pitch in the opposite direction. In the case where the polygonal shape of the base is parallel to the longitudinal direction of the cable, the protrusions can be made uneven by forming the protrusions in a spiral shape.

FIG. 12 is a sectional view for explaining a fourth embodiment of the cable of the present invention. In the figure, the same parts as those in FIG. 6 is a notch groove. In this embodiment, tearing performance is added to the cable jacket. At one or more locations on the circumference of the cable jacket, cutout grooves 6 were formed in the length direction along the protrusions. For example, as shown in FIG. 12, if notch grooves 6 are provided at almost two positions on a diagonal line,
At the end of a cable terminal such as a cable terminal for connection work or the like, the cable jacket can be easily halved by hand along the cutout groove 6, and the efficiency of removing the cable jacket increases.

FIG. 13 is a cross-sectional view of a cable subjected to a test, which is a cord twisted optical cable having an outer diameter of 7 mm. The two optical cords 7 and the two tension members 8 were twisted, pressed and wound with a thin tape, and the cable jacket was extruded and covered. The shape of the cable core consisting of two optical cords 7 and two tension members 8 is as follows:
It has a slightly square shape and is spiral in the longitudinal direction. The outer shape of the cable jacket 2 is a square shape of the cable core, which is slightly square. Since this is helical, the projection 3 of the cable jacket 2 is slightly undulated in the longitudinal direction. The cross-sectional shape of the protrusion is triangular, and 36 protrusions are continuously formed on the circumference. The material of the cable jacket 2 is flame-retardant polyethylene (Mg (O
H) _2- added polyethylene).

The contents of the test were such that these 12 cables were closely aligned, a 2 m length was bound at a 0.3 m interval with an insulin lock, one of them was pulled out, and the tension was measured with a spring balance. The comparison cable has a normal circular cable jacket. FIG. 14 shows the results of the test. In the cable of the present invention, the tension was such that it could be easily pulled out by human power, but in the case of the comparative cable, a considerable force was required for pulling out the cable, which is a value that may affect other cables in operation. Also,
The appearance of the cable of the present invention after the cable was pulled out was such that the protrusions were rubbed, rough and whitened, indicating that the frictional resistance between the cables was reduced.

It is not necessary that all the projections have the same dimensions or the same shape.
Projections having different dimensions and shapes may be mixed.

[0048]

As is apparent from the above description, according to the first aspect of the present invention, a triangular or arc-shaped mountain-shaped projection continuous in the length direction is provided on the surface of the cable jacket. The height of the protrusion from the bottom is not more than the thickness of the cable jacket except for the protrusion, and the interval between adjacent protrusions in the circumferential direction is not more than twice the width of the protrusion. Thereby, the frictional resistance between the cables is reduced without increasing the outer diameter of the cable, and the cable can be easily pulled out from the state where the cables laid in multiple layers are in contact with each other. Further, since the shape is continuous in the longitudinal direction, manufacture is easy.

According to the second aspect of the present invention, the surface of the cable jacket has a mountain-shaped projection having an arc-shaped cross section continuous in the length direction, and the height of the projection from the bottom is equal to the height of the projection. Since the radius of curvature near the top of the projection is equal to or greater than 0.2 of the radius of the circumcircle of the cable while the thickness of the cable jacket is equal to or less than the thickness of the removed cable jacket, the cables are drawn in an orthogonal arrangement. When the cable is unplugged, it is possible to suppress damage to the cable on the other side, and the radius of curvature near the top of the protrusion is 0.8 times or less the radius of the circumscribed circle of the cable, thereby reducing the cable outer diameter. Without increasing, the frictional resistance between the cables is reduced, and the cables laid in multiple layers can be easily pulled out from the contacting state. Further, since the shape is continuous in the longitudinal direction, manufacture is easy.

According to the third aspect of the present invention, the projections are undulated in the length direction by a variation smaller than the height of the projections, so that the cables are in contact with each other by being bundled or the like. The protrusions with the adjacent cables do not engage with each other continuously in the longitudinal direction, and easily get over the protrusions when the cable is pulled out, so that the pull-out property is improved. Also, means for providing undulations is not particularly difficult, and manufacture is easy.

According to the fourth aspect of the present invention, the cable jacket and the projections are made of polyethylene to which magnesium hydroxide is added. Contributes to reducing resistance. In addition, since it has flame retardancy, it is suitable for use indoors and in tunnels.

According to the fifth and sixth aspects of the present invention, the cable jacket including the projection, or at least a surface layer thereof is made of a fluorine resin, or the cable jacket including the projection, Alternatively, at least the surface layer is made of a thermoplastic polyester elastomer or a polyamide-based polymer having a flexural modulus of 1000 kg / cm ² or more, so that at least the surface layer of the jacket including the projections has good slip and the projections can be easily separated from each other. It is a material that can be overcome, and has good pull-out properties.

According to the seventh aspect of the present invention, at one or a plurality of positions on the circumference of the cable jacket, a notch groove is provided in the length direction along the protrusion, whereby the protrusion is formed. By using the shape of the above, tearing of the cable jacket at the cable terminal outlet is easy.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of a cable according to the present invention.

FIG. 2 is a sectional view of a part of a cable jacket of a cable according to a second embodiment of the present invention.

FIG. 3 is a sectional view for explaining a third embodiment of the cable of the present invention.

FIG. 4 is an enlarged view of a part of the cable jacket of FIG. 3;

FIG. 5 is an explanatory diagram of an experiment of pulling out orthogonal cables.

FIG. 6 is an explanatory diagram of an injury due to a pull-out experiment.

FIG. 7 is an explanatory view of a projection in the cable of the present invention.

FIG. 8 is an explanatory diagram of an embodiment in which a fluorine resin is used as a material of a cable jacket including a protrusion.

FIG. 9 is an explanatory view of a third embodiment of the cable of the present invention.

FIG. 10 is an explanatory diagram of an example of a method of making a projection undulate.

FIG. 11 is an explanatory diagram of an example of another method for undulating projections.

FIG. 12 is a cross-sectional view for explaining a fourth embodiment of the cable of the present invention.

FIG. 13 is a sectional view of a cable subjected to a test.

FIG. 14 is an explanatory diagram of test results.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cable core, 2, 2a, 2b, 2c, 2d ... Cable jacket, 3 ... Projection, 4 ... Hold down, 5 ... Inclusion, 6
... Notch groove, 7 ... Optical cord, 8 ... Tension member,
9 ... Coating.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Shuzo Suzuki 1 Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture, Yokohama, Ltd. Sumitomo Electric Industries, Ltd.

Claims (7)

[Claims] 1. A surface of a cable jacket having a triangular or arc-shaped projection continuous in the length direction and having a height from the bottom of the projection outside the cable except for the projection. A cable having a thickness equal to or less than a thickness of a cover and a distance between adjacent projections in a circumferential direction being equal to or less than twice a width of the projection. 2. A cable jacket having a mountain-shaped projection having an arc-shaped cross section continuous in the length direction on a surface of the cable jacket, and the height of the projection from the bottom is equal to the thickness of the cable jacket except for the projection. And the radius of curvature near the top of the projection is 0.2 to 0.8 times the radius of the circumcircle of the cable, and the interval between adjacent projections in the circumferential direction is equal to the width of the projection. A cable characterized by being no more than twice. 3. The cable according to claim 1, wherein the projection is undulated in a length direction by a variation smaller than a height of the projection. 4. The cable according to claim 1, wherein the cable jacket and the projection are made of polyethylene to which magnesium hydroxide is added. 5. The cable according to claim 1, wherein the cable jacket including the projection, or at least a surface layer thereof, is made of a fluorocarbon resin. 6. The cable jacket including the protrusion, or at least a surface layer thereof, has a flexural modulus of 1000 kg /
^2. A thermoplastic polyester elastomer or a polyamide polymer having a size of at least ² cm ^2.
4. The cable according to any one of claims 3 to 3. 7. A cable according to claim 1, wherein a notch in a longitudinal direction is provided along one of the protrusions at one or more positions on the circumference of the cable jacket. The cable according to claim 1.