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Three Reasons for Water Intake of Direct Burial Optic Cable Joint Box

Three Reasons for Water Intake of Direct Burial Optic Cable Joint Box

1. Tie box structure design is not rigorous

There are generally four types of cable connector boxes, namely cap type, box type, open type and semi-open type. Because the structure design is not rigorous enough, its waterproofing rate varies. Cap type connector box is mainly designed for laying optical cables in overhead and tunnel. It is used in buried lines that do not meet the requirements of waterproofing, but the moisture-proofing effect in the lines is better. According to the regulations, the joint boxes of the other three common structures, such as the open type, are used in the direct burial laying, but the moisture-proof effect is poor. Therefore, the design, structure and process of cable junction box need to be improved.

2. Poor sealing at closure of joint box structure

Although the structure and application range of these four types of connector boxes are different, there are only two parts to be waterproofed in terms of sealing technology: the closure of the upper and lower parts of the connector box and the introduction of the line cable into the connector box. The cap type connector box connects the cable with the connector box by using the thermal shrinkable sleeve seal at the leading position of the cable into the connector box. The other three joint boxes are sealed with non-vulcanized rubber belts in both parts. Water and moisture enter the joint box only through these two channels. All the three structures are sealed and moistureproof by non-vulcanized rubber belt. Non-vulcanized rubber belt is a kind of high polymer material, which has a certain viscosity. When it is subjected to a greater external force, it will produce deformation and fill the voids between objects to achieve the purpose of moisture-proof. However, it belongs to medium and low viscosity chemical substances. Its physical properties are susceptible to temperature changes. Especially when other impurities are adhering to it, its sealing performance will drop sharply. Compared with non-vulcanized rubber belts, the physical characteristics of cap joint box and line cable are more stable, and the moisture-proof treatment process is more refined, thus avoiding the occurrence of water intake failure.


3. Non-standard treatment of the lead-in part of the joint box

The incoming water fault caused by the non-standard treatment of the incoming part of the optical cable into the junction box accounts for 85.7% of the total incoming water fault. Among them, the proportion of the three commonly used direct burial optic cable junction boxes is as high as 88.3%. Therefore, it is necessary to solve this problem in engineering so as to greatly improve the moisture resistance of the direct burial optic cable junction box.

After carefully studying the water inflow situation of the three kinds of commonly used direct burial optic cable connector box and cable, it is found that there are three main reasons: (1) the line cable warps at the leading part of the connector box and cable; (2) the non-vulcanized rubber belt used for sealing the connector box has impurities; (3) There is no thorough hairing on the leading part of the cable in the junction box. Therefore, we should focus on solving the above three problems.

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