In the power transmission network, cables are the "blood vessels" for the flow of electrical energy. And low-voltage cables are the type of power cables that are closest to our daily lives and most widely used. According to the common domestic power industry standards, low-voltage cables generally refer to power cables with a rated voltage of 0.6/1kV or below, used for transmitting and distributing electrical energy in the AC power distribution system. They are suitable for our common 380V three-phase and 220V single-phase power supply systems, and are the core carrier from the low-voltage side of the transformer to the buildings, workshops, and household electrical terminals.
The structure of low-voltage cables is clear. They are mainly composed of conductors, insulation layers, filling layers, tape, and outer sheaths. Some special cables will also add a protective layer to resist external forces such as squeezing, rat bites, and corrosion. Shanghai Shipbuilding Electric......A conductor is the path for current to flow. The main types are copper core and aluminum core: the copper core has good conductivity, large current-carrying capacity, and strong oxidation resistance, and is mostly used for residential, commercial, and precision equipment power supply; the aluminum core is lightweight and has a lower cost, and is suitable for long-distance and large-section outdoor main lines. The insulation layer is wrapped around the outside of the conductor. Common materials include cross-linked polyethylene (XLPE), polyvinyl chloride (PVC), rubber, etc. Its function is to isolate the live conductor and prevent leakage and short circuit; cross-linked polyethylene insulation has high temperature resistance and stable insulation, and is the most commonly used type in current engineering; rubber insulation has good flexibility and is mostly used for rubber-covered cables for mobile devices. The outermost sheath is the "protective coat" of the cable, isolating moisture, oil, sunlight, acid and alkali, and for armored cables, steel belts or steel wires are added inside to protect against mechanical damage, suitable for direct burial underground, crossing roads, etc.
According to the number of cores, low-voltage cables are divided into single-core, two-core, three-core, four-core, five-core and other specifications. Two-core is mostly used for single-phase circuits; three-core is used for three-phase three-wire; four-core and five-core are the mainstream for building power distribution, including phase lines, neutral lines and protective ground lines, meeting modern power distribution grounding protection requirements and ensuring electrical safety. The YJV, VV, YJLV, VLV are all typical low-voltage cable models: YJV is a copper core cross-linked polyethylene insulated cable, VV is a copper core polyvinyl chloride insulated cable, with L indicating aluminum core material.
Compared with overhead wires, low-voltage cables have very prominent advantages. They can be laid directly underground, in conduits, in cable trenches, on bridges, in tunnels, without the need to erect power poles, not occupying ground space, with less interference from external environmental factors such as rain, lightning strikes, and contact with trees, strong power supply stability, neat and beautiful lines, and obvious advantages in urban built-up areas, residential areas, underground garages, etc. Of course, it also has shortcomings: the materials and construction costs are higher than overhead lines, fault detection and maintenance are more difficult, and there are stricter requirements for laying techniques and fire and moisture protection.
Low-voltage cables are applied in almost all aspects of our daily life and production. In the civilian domain, residential area power distribution, office buildings, shopping malls, hotels, and internal main power supply for important loads such as elevators, fire pumps, and fans are all unable to do without it; in industrial scenarios, factory workshop production lines, pump rooms, warehouses, and power lines for small and medium-sized equipment are extensively using low-voltage cables; in public infrastructure, municipal street lights, underground pipe galleries, parking lots, schools, hospitals, power distribution for photovoltaic inverters, and charging station incoming lines, as well as other new energy supporting lines, are also mainly low-voltage cables. In addition, there are many special low-voltage cables, such as flame-retardant cables, fire-resistant cables, low-smoke and halogen-free cables, which can delay combustion, maintain power supply for a certain period of time, and have less smoke and low toxicity when burning, specifically used for fire passages, high-rise buildings, subways, etc., which are important guarantees for fire safety.
The selection, laying, and acceptance of low-voltage cables have strict regulations. When choosing, factors such as voltage level, current-carrying capacity, laying environment, whether flame-retardant and fire-resistant are required, whether direct burial and armor are needed should be considered; during construction, the bending radius should be controlled, the joint sealing should be done well, waterproofing and grounding should be done well; after operation, regular inspections should be carried out to monitor temperature and insulation conditions, avoiding overload operation, damage to the outer skin, and preventing leakage and fire accidents. Many sources of electrical fires are caused by long-term overload, insulation aging, and loose joints of low-voltage cables, which shows that the quality of cables and standardized operation are directly related to electrical safety.
As the "last mile" of the power distribution system, low-voltage cables may seem insignificant, but they silently undertake the task of delivering electricity to every appliance and lamp. It differs from the long-distance transmission of high-voltage cables in its positioning, focusing on terminal power distribution, while also considering power supply capacity and safety protection. With the continuous development of urban construction and the new energy industry, low-smoke, halogen-free, fire-resistant and environmentally friendly low-voltage cables are gradually becoming widespread, continuously safeguarding the safety, stability and reliability of low-voltage power distribution.
