1. The structure of the joint box is not tightly designed.

There are generally four types of Fiber Optic Splice Closure , namely, cap type, box type, open type and semi-open type. Due to the structural design is not tight enough, the waterproof rate is different. For example, the 210 km direct buried optical cable line maintained by a certain station communication company is tested, and the grounding resistance resistance test results of 74 optical cable joint boxes: 52% of the insulation resistance value is zero, 48% of the joint box There is obviously water accumulation, which leads to poor insulation of the cable to the ground. Statistics show that 67% of the direct buried Fiber Optic Splice Closure will have different levels of water ingress failure. The waterproof effects of the four cable joint boxes found in the test are: the waterproof ratio of the cap joint box is 83%, the waterproof rate of the box joint box is 75%, the waterproof ratio of the open joint box is 45%, and the semi-open joint box The water resistance is 44%. It can be seen that it is best to use a cap-type joint box to prevent water ingress, but it is not ideal. The cap-type joint box is mainly designed for the laying of optical cables for overhead and tunnels. It uses non-compliant waterproof requirements in direct-buried lines, but the moisture-proof 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 direct burial, but the moisture-proof effect is poor. Therefore, the design, structure and process of the cable joint box must be improved and improved.

2. The joint box structure is closed and the seal is poor.

Although the structure and application range of the four kinds of cable joint boxes are different, from the sealing process, there are only two parts that need to be waterproofed: the joints of the upper and lower parts of the joint box; the line cable enters the joint box. Introduction site. The cap type joint box uses the heat-shrinkable sleeve seal at the introduction part of the optical cable to enter the joint box, and connects the line optical cable and the joint box into one body, and the upper and lower cover are closed, and the rubber ring is pressed against the upper and lower covers to be waterproof. The other three types of joint boxes are sealed with non-vulcanized rubber tapes in these two parts, and water and moisture can only enter the joint box through these two channels. These three types of Fiber Optic Splice Closure cable lead-in parts are sealed with non-vulcanized rubber tape to prevent moisture. The non-vulcanized rubber belt is a polymer material which has a certain viscosity and is deformed when subjected to a large external force, and fills the gap between the objects to achieve the purpose of moisture prevention. However, it is a medium- and low-viscosity chemical substance, and its physical properties are susceptible to temperature changes, especially when other impurities are adhered, and its sealing performance is drastically lowered. The cap type joint box, the line cable enters the lead-in box of the joint box, and is sealed by the heat-shrinkable sleeve. Compared with the non-vulcanized rubber belt, the physical characteristics are more stable, and the moisture-proof treatment process is more elaborate, thus avoiding The occurrence of water ingress failure.

3. The joint part of the joint box is not processed properly.

As the line cable enters the joint box, the introduction of the cable is not standardized, resulting in 85.7% of the total water inlet failure, and the water intake ratio of the three commonly used direct buried cable joint boxes is as high as 88.3%. Therefore, this problem must be solved in the project, in order to greatly improve the moisture resistance of the direct buried Fiber Optic Splice Closure.

Careful study of the water inflow into the lead-in parts of the three commonly used direct-buried Fiber Optic Splice Closure revealed that there are three main reasons: (1) the line cable is warped at the lead-in area of ​​the connector box; (2) is used for the joint box sealing. The non-vulcanized rubber tape is stuck with impurities; (3) The line cable is not completely roughened at the introduction portion of the connector box cable. Therefore, we must focus on solving the above three problems.