With the acceleration of urban construction, the conflict between 10kV line corridor planning and urban development and construction is becoming increasingly severe. To meet the needs of social development and ensure safe, stable, and reliable power supply, cable lines are being implemented in key urban streets and areas, adhering to the principles of “typical planning, optimized operation, and safety and reliability.” Cable branch boxes are being used as a key component of power distribution. This optimizes the cable network and enables multi-circuit branching. This not only beautifies the city but also improves operational reliability and safety, and has been successfully implemented in urban construction. Commonly used cable branch boxes include ring main unit (RMU), cable branch connector (JB), disconnector (DJ), cable butt connector (JB), and cable branch with switch.
1. Introduction to Cable Branch Boxes
Cable branch boxes are devices used to branch, split, connect, and convert cable lines. They play an important role and value in various industries and fields. They are primarily used outdoors and are useful for branching and splitting cables. Cable junction boxes and cable branch boxes can be categorized into different types and styles based on different classification methods. Generally, they fall into two categories: The first type does not contain any switchgear; the box contains only accessories for handling and connecting cable ends. These types of junction boxes and cable branch boxes are relatively simple in structure, small in size, and have a limited function, yet they can play an important role and provide valuable value in their applications. The second type contains not only the accessories of a simple junction box and cable branch box, but also one or more switchgear. These types are more complex in structure, larger in size, and have numerous connecting components, making their production technically challenging and expensive, resulting in relatively high operational costs. Different types of cable junction boxes and cable branch boxes can be used in different environments and fields, with varying structural designs and advantages, playing an important role and contributing significantly to their respective fields. When using cable junction boxes and cable branch boxes, it is important to select the appropriate type to ensure proper protection of cable equipment in the power industry and to perform the functions of branching, branching, connecting, and converting cable lines.
2. Functions of Cable Branch Boxes
2.1 Cable Branching Running multiple small cables on a long line often results in wasted cable usage. Therefore, a large backbone cable is often used to connect the cables to the load. Near the load, a cable branch box is used to split the backbone cable into several smaller cables, which are then connected to the load. This wiring method is widely used in urban power grids to power streetlights and other small consumers.
2.2 Cable Transfer. On a long line, if the cable length does not meet the line requirements, cable connectors or cable transfer boxes are necessary. Generally, cable center connectors are used for short distances. However, for longer lines (over 1000m in length), if there are multiple center connectors, a cable branch box is often used for safety reasons.
2.3 Branch boxes are widely used outdoors. With technological advancements, the number of cable branch boxes with switches is increasing. Since urban cables often use dual-circuit power supply, some people simply refer to branch boxes with switches as outdoor ring main units (RMUs). RMUs are primarily used to implement dual-circuit or multi-circuit power supply, improving power supply reliability. Modern RMUs can automate distribution networks and enable remote operation.
3. Technical Design of Cable Branch Boxes
3.1 Structure, Features, and Performance of Cable Branch Boxes
Fully enclosed, fully protected, and resistant to contamination and corrosion, they meet all-weather outdoor operating conditions and can adapt to various working environments.
Cable branch boxes are floor-standing, compact, and require minimal floor space. For example, some have a footprint of 0.65 m², while those with SF6 switches occupy only 1.45 m². They also have an aesthetically pleasing appearance and do not detract from the urban landscape. The conductor connectors within the branch box are crimped, allowing for quick installation and flexible wiring. Up to 6 to 8 branch lines can be used, enabling multi-route power distribution within a residential area. This provides technical support for reaching load centers, shortening the power supply radius, and reducing line losses. The cable branch box can be equipped with power indicators, fault indicators, fully insulated silicone rubber lightning arresters, mechanical programmable locks, and earthing switches to ensure safe operation and maintenance. In conjunction with a ring-network cable power supply, SF6 and other ring-network load switches can be installed to meet local power outage maintenance requirements without disrupting main grid operation, enabling regional outages and minimizing outage scope. The ring-network cable branch box also supports ring-network power supply, laying the foundation for future adjustments to the 10kV line network structure.
3.2 Cable Branch Box Installation and Use and Precautions
Currently, my country produces a wide variety of 10kV outdoor cable branch boxes, making their installation and construction crucial. Correct operation procedures for connecting the cable branch box to the cable connector assembly, familiarity with the cable connector assembly process, the order in which the internal components of the cable branch box and the cable connector parts are assembled, and compliance with the supplied installation specifications and instructions will all directly impact the service life and proper operation of the cable branch box.
Before operating the cable branch box, it is necessary to check that the grounding wires of each branch cable are securely connected to the grounding terminals on the box. Furthermore, the box casing must be directly connected to the ground grid or have a clear connection point. After installation, the cable components must be tested in accordance with relevant test standards and conditions.
3.3 Successful Application of Cable Branch Boxes in Urban Construction
Based on urban layout and development plans, and adhering to the principles of practicality, reliability, safety, and maintainability, the following three key points are primarily considered in the design and application of cable branch boxes: First, a comprehensive analysis of real-time data on the city’s 10kV distribution network, including user data, grid structure, equipment parameters, and geographic information, is conducted to optimize the distribution of cable branch boxes and further optimize their design. Second, branch boxes equipped with sectionalizers and ring network switches are being used in backbone streets to enhance grid operation flexibility and power supply reliability. Third, testing and monitoring efforts are being strengthened, with follow-up testing to ensure timely monitoring of all technical parameters and indicators during cable branch box operation. This is primarily aimed at rapidly locating faults, isolating them, and restoring power to non-faulty areas in the event of an incident. Currently, most urban backbone streets have undergone cable conversion for 10kV lines, employing high-performance cable branch boxes and transformers. After years of operation, no line or equipment failures have occurred, ensuring safe line operation.
4. Advantages of Using Cable Branch Boxes for Cable Lines
Based on experience in numerous cities, the use of cable branch boxes in power grid construction and renovation has proven to offer the following advantages: It reshapes the way line planning is thought about, breaking the traditional pattern of planning influenced by geography and buildings and opening up new avenues for line planning.
Flexible and easy to install, especially in difficult line corridors, it facilitates access to load centers, reduces the power supply radius, improves power quality, and satisfies users’ urgent desire to improve their electricity consumption, creating an excellent environment for social and economic development.
Cable branch boxes offer comprehensive functions, superior performance, simple installation, flexible input and output lines, and the ability to provide ring-shaped power supply, providing technical support and assurance for improving and optimizing network structures.
Although the initial investment for cable branch boxes is higher than for overhead lines, they reduce the risk and incidence of accidents, resulting in significant economic and social benefits for reliable power supply.
Using cable branch boxes, civil engineering, cable laying, and box assembly and commissioning can all be carried out without interrupting the power supply. During a power outage, only the installation of the cable lead-downs is required, shortening outage duration and improving operational efficiency.
5. Conclusion
Currently, cable branch boxes have been widely promoted and implemented not only in cities but also in some towns. Their excellent power supply performance has been widely praised by the public and electricity users. I believe that in the near future, cable branch boxes will be used in more and more situations and gradually demonstrate their superiority.
Post time: Aug-13-2025
