The main function of a cable branch box is to tap or transfer cables.
(1) Cable tapping: Using multiple small-cross-section cables on a relatively long line often leads to cable waste. Therefore, when supplying power to electrical loads, a main large-cross-section cable is usually used for outgoing lines. Then, when approaching the loads, a cable branch box is used to split the main cable into several small-cross-section cables, which are connected to the loads. This wiring method is widely used for power supply to street lamps and small users in urban power grids.
(2) Cable transfer: On a relatively long line, if the length of a single cable cannot meet the line requirements, cable joints or cable transfer boxes must be used. Usually, intermediate cable joints are adopted for short distances. However, for long lines (based on experience, over 1000 meters), if there are multiple intermediate joints in the cable, a cable branch box will be considered for transfer to ensure safety.
(3) Cable branch boxes are widely used outdoors. With technological progress, the number of cable branch boxes equipped with switches is constantly increasing. Urban cables often adopt dual-circuit power supply mode, so some people directly refer to branch boxes with switches as outdoor ring main units (RMUs). However, most of these current RMUs cannot realize power distribution network automation, although some manufacturers have launched outdoor RMUs capable of distribution network automation. This has also blurred the boundary between cable branch boxes and ring main units.
Ring main units are mainly used to realize dual-circuit or multi-circuit power supply to improve power supply reliability. Currently, advanced ring main units can achieve power distribution network automation and remote operation.
Nowadays, there are more and more cable branch boxes in the form of ring main units, and it is estimated that they will be integrated in the future.
Both ring main units and cable branch boxes have incoming and outgoing lines. In my opinion, the difference lies in the power supply mode rather than the incoming and outgoing line mode. Ring main units can provide dual-circuit or multi-circuit power supply to ensure reliability, while cable branch boxes do not have the capability of multi-circuit or dual-circuit power supply. In addition, ring main units can now realize distribution network automation and remote control, which cable branch boxes basically do not have (except for outdoor ring main units equipped with switches).
Source: DAYA Electric Group Co., Ltd. Please indicate the source when reprinting: https://www.hygraphics.com/