JPH0219688B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an offset portion of a plastic cable, and more particularly to an offset portion of a plastic cable in which the laid plastic cable is curved in an S-shape within a manhole.

Conventionally, when installing plastic insulated cables, holes were created at every fixed length of the conduit.
A predetermined offset portion is formed in the manhole by arranging a plastic cable in an S-shape.

FIGS. 1 and 2 are explanatory diagrams showing the installation state of such a cable offset section. FIG. 1 is an example of a general S-shaped offset section, and FIG.
The figure shows an example of a state in which the middle part of the cable is supported in the offset part curved in an S-shape, and 1 is a plastic cable which is curved in an S-shape in the manhole to form a predetermined offset part; 2 is a cable connection box placed in the manhole, 3 is a trumpet tube, and 4 is an intermediate support section.

In the case of a structure in which the plastic cable 1 is not reinforced, the elongation of the plastic cable 1 itself is absorbed by the change in the radius of curvature of its S-shaped portion; on the other hand, in the case of a structure in which the plastic cable 1 is reinforced. In other words, the bending rigidity of the plastic cable at the offset portion is increased, or in other words, the deformation of the offset portion is reduced so that the extension of the plastic cable 1 is absorbed by snake deformation within the conduit.

However, these structures have the following problems. That is, in the case of a structure in which the plastic cable 1 is not reinforced, the size of the offset portion becomes large, and as a result, a large-sized manhole is required.

On the other hand, in the case of a structure in which the plastic cable 1 is reinforced, the cost of reinforcing materials and construction increases, making it uneconomical.

The present invention has been made in view of the above-mentioned circumstances, and allows the plastic cable to be accommodated in a small hole by reducing the offset dimension, and to average out the overall displacement absorption of the offset portion due to the extension of the cable. It is an object of the present invention to provide an offset portion of a plastic cable which can effectively absorb heat expansion and contraction by dispersing the heat and is economically advantageous.

That is, in the present invention, with respect to an offset portion of the plastic cable in which the laid plastic cable is curved in an S-shape in the manhole, the plastic cable in the offset portion extends at least by an extension portion of the plastic cable. The length of the cable is short, and the cable is previously formed into an S-shape, and is slidably supported along the length of the cable at approximately the center of the offset section between the front ends, and one end is attached to the conduit entrance side. and has a flexible guide tube fixed at the other end on the cable junction box side, and the plastic cable of the offset portion is inserted into the guide tube so as to be able to go in and out from the conduit entrance side. It is characterized by this.

An embodiment of the present invention will be explained below with reference to FIG. 3.

FIG. 3 shows a preferred embodiment of the offset portion of the plastic cable according to the present invention, partially cut away from the side. The same parts and the same working parts as in FIGS. The same reference numerals as those given in the drawings are used; therefore, 1 is a plastic cable that is curved in an S-shape from the pipe entrance into the manhole to form a predetermined offset portion, and 2 is a plastic cable in the manhole. It is a cable junction box located in the center of the interior.

In the figure, 5 is a flexible guide tube, 6 is a fixed end portion thereof, 7 is an intermediate support portion of the guide tube 5, and 8 is a conduit through which a plastic cable is laid.

The offset part of a conventional plastic cable is different from the plastic cable 1 which is curved in an S-shape to obtain a predetermined offset shape, and is shorter by at least the extension length of the plastic cable 1. The cable is curved into an S-shape, and is supported by an intermediate support 7 at the center of the offset portion so as to be slidable in the longitudinal direction of the cable, and one end is fixed to the end fixing portion 6 on the conduit entrance side. In addition, a flexible guide tube 5 is provided with the other end fixed to an end fixing part 6 on the cable junction box side, and the plastic cable 1 at the offset portion is inserted into the guide tube 5 at the conduit opening. The point is that it is inserted so that it can be entered and exited from the side.

That is, in this embodiment, the change in the radius of curvature that occurs in the S-shaped portion of the plastic cable 1 when energized is controlled by making the radii of curvature of portions A and B at the front and rear of the intermediate support body 7 the same in advance. The stress applied to the plastic cable 1 is suppressed by the S-shaped shape of the guide tube 5 that has been formed, and the stress applied to the plastic cable 1 is averaged over the whole, and the length of extension of the plastic cable 1 due to energization is averaged over the entire offset part length. The idea is to disperse and absorb it.

Generally, the change in the radius of curvature of the S-shape due to the extension of the plastic cable 1 due to energization is as follows:
The radius of curvature tends to be small on the exit side from the conduit 8, that is, on the A section side, and the curvature radius tends to become relatively large on the B section on the cable junction box 2 side.In other words, the A section side is significantly deformed due to stretching. becomes.

Therefore, at the initial point in time when the cable elongation within the conduit 8 appears as an extension from the conduit entrance due to energization, the length of the cable extending from the conduit entrance side of the plastic cable 1 in the offset section, that is, the section A side, is the same. The cable enters from the end of the guide tube 5, and in order to absorb the elongation, the cable portion on the A section side begins to bend so that the radius of curvature becomes smaller, and as the bending occurs, internal pressure is applied to the A section side of the guide tube 5. Therefore, the guide tube 5 tries to deform itself, but each end of the guide tube 5 is fixed by an end fixing part 6 at the conduit mouth and an end fixing part 6 on the cable junction box 2 side. Therefore, the bending deformation applied to the cable itself is suppressed, and at the same time, a stretching force acts, and this stretching force suppresses the bending change of the cable on the side A, and accordingly, an axial force acts on the cable portion.

Then, due to the axial force acting on itself, the part A side cable moves within the guide tube 5 by the amount of extension relative to the part A side cable, moves to the part B side of the offset part, and moves to the part B side of the offset part. A bending deformation corresponding to the cable extension occurs on the side, and as a result of this bending, internal pressure is applied on the B side of the guide tube 5 and the guide tube itself tries to deform, but the guide tube 5 As described above, since both ends are fixed, bending deformation applied to the cable itself is suppressed, and at the same time, stretching force acts, and this stretching force suppresses bending changes in the cable on the B side.

As described above, in the process of bending and deforming both the A section and the B section, when the guide tube 5 starts to curve on the A section side, the B section side slides on the intermediate support section 7 and moves to the A section side. Furthermore, when the B part side begins to be curved and deformed, it slides back on the intermediate support part 7 by the amount that it has moved to the A part side, and the state where both such curving ends, that is, both A and B parts When the shapes are made uniform, portions A and B are in a balanced state with the intermediate support portion 7 as a fulcrum.

Therefore, if the amount of movement of the cable from the conduit 8 is m, then a bending deformation equivalent to the amount of movement of m/2 is applied equally to the offset portions of parts A and B, respectively, and the cable is evenly deformed as a whole. Therefore, the expansion and contraction can be absorbed and suppressed.

As explained above, according to the present invention, the offset dimension of the plastic cable can be reduced so that it can be accommodated in a small manhole, and the displacement absorption of the offset part due to the extension of the cable is distributed evenly over the whole, so that the plastic cable can be thermally expanded and contracted. The intended purpose of providing an offset portion of a plastic cable that can effectively absorb the amount of water and is economically advantageous has been achieved, and the practical effects are significant.

[Brief explanation of drawings]

Figure 1 shows the S of a conventional general plastic cable.
FIG. 2 is an explanatory diagram showing a conventional S-shaped offset part with an intermediate support part. FIG. 3 is an explanatory diagram showing an embodiment of the offset part of a plastic cable according to the present invention. It is a diagram. In the code, 1 is plastic cable, 2
is a cable connection box, 3 is a trumpet tube, 4 is an intermediate support section, 5 is a flexible guide tube, 6 is an end fixing section, 7
is an intermediate support, and 8 is a conduit.

Claims (1)

[Claims] 1. At the offset part of the plastic cable where the plastic cable is laid in the manhole and is curved in an S-shape, the plastic cable in the offset part is shortened by at least the length of the extension of the plastic cable, and furthermore, the plastic cable has been curved into an S-shape in the manhole. In the formed state, the cable is slidably supported along the length direction of the cable at approximately the center of the offset part, and one end is fixed on the conduit entrance side and the other end is fixed on the cable junction box side. 1. An offset section for a plastic cable, characterized in that it has a flexible guide tube, into which the plastic cable of the offset section is inserted so as to be able to go in and out from the conduit opening side.