A cable distribution box is a device used for tapping, branching, splicing, and circuit switching of cable lines. As a supporting equipment for the cable-based transformation of urban power grids, it can be installed outdoors, indoors, or in buried locationss. It can connect power cables with box-type substations, load switch cabinets, fuse combination electrical cabinets, ring network power supply units, etc., playing the role of tapping, branching, relaying, or switching, and providing great convenience for cable networking.
Cable distribution boxes are divided into two categories according to their electrical composition: one type does not contain any switching equipment, and the cabinet only has accessories for processing and connecting cable terminations. It has a simple structure, small size, and single function, and can be called an ordinary distribution box; the other type not only includes the accessories of an ordinary distribution box but also contains one or more switching equipment. It has a relatively complex structure, large size, many connecting devices, high manufacturing technical difficulty, and high cost, and can be called an advanced distribution box.
1. Ordinary Distribution Box
There is no switching equipment in an ordinary distribution box. The incoming and outgoing lines are electrically connected together with the same potential, making it suitable for tapping or branching connections. It is usually customary to refer to the sum of the number of incoming circuits and outgoing circuits as the number of branches. For example, a three-branch cable distribution box has three equipotential connection points on each phase, which can be used for one incoming and two outgoing lines or two incoming and one outgoing line. The cable distribution box contains U, V, and W three phases, with the same three-phase circuit structure arranged in sequence.
2. Advanced Distribution Box
An advanced distribution box contains switching equipment, which can not only play the tapping and branching role of an ordinary distribution box but also control and switch the power supply circuit and change the operation mode. The switch break roughly divides the cable circuit into the incoming side and the outgoing side, and the potentials of the two sides can be different. The switching equipment itself has a relatively large volume, so the overall dimensions of the advanced distribution box are relatively large: the height is generally 1.4–1.8 m, the depth is about 0.9–1.0 m, and the length depends on the number of switching equipment included, mostly between 1.0 m and 2.4 m. The appearance of the cabinet is similar to that of an outdoor box-type transformer. There are several movable doors on the cabinet shell: some doors are designed for the operation of switching equipment, and others are for the installation, construction, maintenance, or inspection of cable connection devices.
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