JPH0135575B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a POF cable line, and in particular,
It is designed to easily absorb thermal expansion and contraction of the cable.

Figure 1 shows a schematic diagram of a conventional POF cable line. 10 is a steel pipe, 20 is a cable, 22
is the cable connection.

In the straight portions of the track, the steel pipe 10 is not intentionally provided with any bends, except for the purpose of avoiding obstacles, height differences, and the like.

Stretching due to thermal expansion of cable 20 is absorbed by its own snake 24. cable 20
is normally fixed to the steel pipe 10 only at the cable connection portion 22, so snakes occur concentrated near the cable connection portion 22.

As a result, the radius of curvature of the snake becomes smaller,
Paper wrinkles and soft spots may occur, which may even lead to dielectric breakdown.

The present invention solves the above-mentioned drawbacks by providing an offset in the steel pipe 10 at the straight section so that the elongation of the cable 20 can be absorbed at that section.

That is, as shown in FIG. 2, an offset 12 is provided on the steel pipe 10 in a straight section of the line.

The offset 12 may be a horizontal offset, a vertical offset, or a combination thereof.

The number of offsets 12 made in one manhole section, their spacing, width F, length L, etc. are determined depending on the amount of expansion and contraction of the cable 20, etc.

Note that the offset 12 in this case is different from the offset of a general cable, and is not intended to absorb the expansion and contraction of the steel pipe 10. This is because the cable 20 is likely to snake in this situation. Also
In POF cables, there is sufficient clearance for the cable 20 to snake inside the steel pipe 10 (the inner diameter of the steel pipe is about 2.7 times the outer diameter of one cable core), so there is no need to make extreme bends as the offset 12. .

Let us describe its effect.

(1) For example, when the cable 20 is under no load (when it is contracted), it is slightly curved within the offset 12 and is in contact with the inner wall surface 120, as shown in FIG.

(2) When the cable 20 expands and stretches due to thermal expansion, since it was originally slightly bent within the offset 12, this part is the easiest to bend.
Snake 24 as shown in "Figure 4". The cable 20 is connected to the outer wall 11 of the offset 12.
Bend until it touches 2.

(3) When the elongation of the cable 20 cannot be absorbed within the offset 12, the cable 20 has multiple extensions near the offset 12 and the cable connection part 22, as shown in "Figure 5" and "Figure 6". snake 2
4 occurs and absorbs it.

This is because, as mentioned above, the inner diameter of the steel pipe is approximately 2.7 times the outer diameter of one cable core, and there is sufficient clearance for the cable 20 to snake inside the steel pipe 10. It is a characteristic.

In this case, at each offset 12, the cable 20 is connected to the inner wall 120 and the outer wall 122.
Stretching of the cable 20 between the offsets 12 is absorbed by the snakes 24 in that section because of the increased frictional resistance to longitudinal movement. The same applies between the offset 12 and the cable connection section 22. Unlike in the past, snakes do not concentrate near cable connections.

Therefore, the cable elongation that must be absorbed by one snake 24 is small. It becomes uniform again.

Effects of the invention Since the offset 12 of the steel pipe 10 is provided, the elongation of the cable 20 is reduced by the offset 12 as described above.
It can be absorbed internally. Furthermore, if it cannot be absorbed completely by itself, it can be absorbed by the offset 12 and the snake 24 near the cable connection part 22.

Therefore, the snakes 24 are not concentrated in one part as in the conventional case, and the accompanying troubles such as paper cuts do not occur.

In addition, since the offset 12 is only installed on a portion of the steel pipe on the straight section of the track, the cost and man-hours for laying the steel pipe are almost the same as in the conventional case, and it is also particularly difficult to pull in the cable core. There is no.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the prior art, and FIGS. 2 and 6 are schematic explanatory diagrams of an embodiment of the present invention. FIG. 2 shows the cable 20 before it is stretched, and FIG. Indicates the condition. Further, FIGS. 3, 4, and 5 are explanatory diagrams of the operation. DESCRIPTION OF SYMBOLS 10... Steel pipe, 12... Offset, 20... Cable, 22... Cable connection part, 24... Snake.

Claims (1)

[Claims] 1. In a POF cable line consisting of a steel pipe 10 and a cable 20 drawn into the steel pipe 10, a curved offset 12 is provided in a part of the steel pipe 10 so that the cable 20 can easily snake, and the offset A POF characterized in that a plurality of snakes are generated in one of the cables 12 to easily absorb the thermal expansion of the cable 20.
cable line.