Directly buried optical cable joint box

How to waterproof the direct-buried optical cable splice box? Why does the direct-buried optical cable splice box get in water? The structural design of the splice box is not suitable for direct-buried optical cables.

The cap-type splice box is mainly designed for laying optical cables in overhead and tunnels. It does not meet the waterproof requirements of the regulations when used in direct-buried lines, but the moisture-proof effect in lines is better. According to regulations, the open type and other three commonly used joint boxes are all used in direct burial laying, but the moisture-proof effect is poor.

Although the structures and scopes of application of these four types of optical cable splice boxes are different, from the perspective of sealing technology, there are only two parts that need to be waterproofed: the joint of the upper and lower covers of the splice box; the place where the line optical cable enters the splice box Introduction site.

The cap-type splice box uses a heat-shrinkable sleeve to seal the lead-in part of the optical cable into the splice box, and connects the line optical cable and the splice box as a whole. The upper and lower covers squeeze the rubber ring to make it waterproof. The other three joint boxes are sealed with non-vulcanized rubber belts at these two parts, and water and moisture can only enter the joint box through these two channels. The optical cable lead-in parts of these three types of optical cable joint boxes are sealed with non-vulcanized rubber bands to prevent moisture.

The non-vulcanized rubber belt is a polymer material with a certain viscosity. When it is subjected to a large external force, it will deform and fill the gaps between objects to achieve the purpose of moisture resistance. However, it is a medium and low viscosity chemical substance, and its physical properties are easily affected by temperature changes, especially when other impurities are attached, its sealing performance will drop sharply. In the cap-type splice box, the line optical cable enters the cable introduction part of the splice box and is sealed with a heat-shrinkable sleeve. Compared with non-vulcanized rubber belts, its physical properties are more stable, and the moisture-proof treatment process is also more refined, so the occurrence of water ingress failures is avoided.

The lead-in parts of the optical cables in the splice box are not treated properly.

The water ingress faults caused by the non-standard treatment of the line optical cable entering the joint box optical cable lead-in part accounted for 85.7% of the total water ingress faults, and the proportion of water ingress in the three commonly used direct-buried optical cable joint boxes was as high as 88.3%. After careful study of the water ingress in the cable lead-in parts of these three commonly used direct-buried optical cable splice boxes, it was found that there are three main reasons:

(1) The line optical cable is warped at the cable introduction part of the joint box;

(2) The non-vulcanized rubber tape used for the sealing of the joint box is stuck with impurities;

(3) The line optical cable is not completely roughened at the cable introduction part of the joint box.

How to prevent direct buried optical cable splice box from entering water

Treatment of the fiber optic cable lead-in part of the splice box

Commonly used optical cable splice boxes for direct burial laying, no matter what kind of structure, as long as they have a network access permit, they are equipped with instructions for their application characteristics. The operator should carefully read the manual before use, and pay close attention to the parts with a high probability of problems, especially the lead-in parts where the line optical cable enters the splice box. The following work should be done in the treatment of this part:

a. It is necessary to ensure that the line optical cable is thoroughly roughened at this part to enhance the adhesion between the non-vulcanized rubber tape and the optical cable. In the project, the optical cable at this place should be sanded with No. 8 sandpaper, and the fiber optic cable should be used as the axis to be evenly roughened in a circular shape until the luster of the outer sheath of the optical cable completely disappears, and then use cotton yarn to remove the remaining sandpaper particles on the outer sheath. Finally, the non-vulcanized rubber tape is stretched in the horizontal direction and evenly wound on the optical cable. The thickness of the winding should be higher than the extrusion recess between the upper and lower covers of the splice box. After the joint box is closed, traces of the non-vulcanized rubber band being extruded out of the box can be clearly seen from the outside of the joint box.

b. It is necessary to ensure that the non-vulcanized rubber belt is clean. Due to the limitation of the field geographical environment of some optical cable splicing points and the negligence of the operator, if the non-vulcanized rubber tape is stuck with impurities before use, its viscosity will decrease, resulting in a decrease in the moisture-proof ability of the splice box after packaging.

c. It is necessary to ensure that the non-vulcanized rubber belt is stretched and wound in accordance with the operating specifications. In order to ensure that the non-vulcanized rubber tape can connect the splice box and the line optical cable as a whole during packaging, and there is no gap between layers, the operator should stretch it evenly when winding it. If the stretching force is not enough, it is impossible to make it evenly wound, and gaps will inevitably appear after the joint box is packaged; if the stretching force is too large, it will break.

Prevents cable warping at the cable entry point of the splice box

After the optical cable splice box is packaged, the link of backfilling and soil covering is generally not paid attention to, but unqualified backfilling method is the root cause of the warping of the line optical cable in the cable introduction part of the splice box. According to statistics, 59% of direct-buried optical cable splice boxes are caused by water ingress.

Enhancing the moisture-proof performance of directly buried optical cable splice box

On the basis of maintaining the structure of the existing optical cable splice box, the non-vulcanized rubber tape is replaced by the expansion water-blocking yarn tape as the sealing material to improve the moisture-proof performance of the splice box.

Improving the Structure of Direct Buried Optical Cable Splice Box

From the perspective of the sealing performance of the splice box of the four structures, different sealing processes are used for the introduction part of the optical cable into the splice box, which brings different moisture-proof effects. The cap-type splice box uses a heat-shrinkable sleeve for waterproofing at the cable introduction part of the splice box; the other three commonly used direct-buried optical cable splice boxes such as the open type use non-vulcanized rubber belts to prevent moisture in this part. From the overall effect, it is obvious that the moisture-proof effect of heat shrinkable sleeve is better than that of non-vulcanized rubber belt. For this reason, the heat-shrinkable sleeve originally used for the sealing of the hat type splice box is used for the other three kinds of direct-buried optical cable splice boxes. The improved splice box is consistent with the original splice box in structure. The biggest difference from the original splice box is that the bayonet length of the upper and lower covers of the original splice box to introduce the optical cable is extended, and it is integrated with the upper and lower covers. In order to facilitate the sealing treatment of the heat shrinkable sleeve, the extended length should generally not be less than 4-6 cm. In this way, a P-type or W-type heat-shrinkable sleeve can be used when sealing the joint box, and the part that needs to be sealed with a non-vulcanized rubber tape can be easily replaced with a heat-shrinkable sleeve for sealing, thereby further improving the quality of direct burial. Moisture-proof performance of optical cable splice box.