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Low Voltage Cable

Low voltage cable structure

It is composed of three parts: wire core, insulating layer and protective layer. The wire core is used to conduct current, and is generally formed by twisting multiple strands of copper wire or multiple strands of aluminum wire. There are several types of low-voltage cables, such as single-core, double-core, three-core, and four-core. Two-core cables are used for single-phase lines, and three-core and four-core cables are used for three-phase three-wire lines and three-phase four-wire lines, respectively. Single-core cables can be used for single-phase lines or three-phase lines as needed. Commonly used low-voltage cable core cross-sectional areas are 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240 mm, etc.


Insulation

Insulating materials with specific functions of withstand voltage in cables. The insulation layer is divided into two types: core insulation and tape insulation: the insulation coated on the core is called core insulation; the insulation where the insulated cores of a multi-core cable are combined and then covered is called tape insulation. The belt insulation is separated from the protective layer to form a reliable ground insulation. The insulating layer is usually made of oil-impregnated paper, plastic, rubber, etc.

(1) Paper-insulated cables are cables with impregnated cable paper as the insulating layer, and are collectively referred to as paper-insulated cables. According to the condition of paper impregnation, it can be divided into: ①oil-impregnated paper insulated cable; ②dry insulated cable; ③non-drip cable.

(2) Cables whose insulating layer is extruded and cross-linked by thermoplastic plastics are collectively referred to as plastic cables and are widely used. Plastic cables can be divided into three types: PVC cables, polyethylene cables and cross-linked polyethylene cables. Cables with natural styrene-butadiene rubber, butyl rubber and ethylene-propylene rubber as insulation layer are called rubber cables. Low-voltage cables with a voltage level of 1kV can use paper-insulated cables and plastic cables, and plastic cables are mostly used; low-voltage cables with a voltage level of 0.5 kV mostly use rubber cables.


The protective layer

A layer or layers of metal or non-metallic material covering the outside of the cable. The protective layer is used to protect the insulating layer from external force damage and moisture intrusion during transportation, laying and use.

(1) Paper insulated cable protection layer. The protective layer of the paper insulated cable is divided into two parts: the inner protective layer and the outer protective layer. The inner protective layer is directly squeezed on the insulating layer, which not only protects the insulation from moisture, but also prevents the outflow of insulating oil, and has a certain mechanical strength. There are three kinds of inner protective layer: lead, aluminum and polyvinyl chloride. The outer sheath protects the inner sheath to increase the cable's ability to withstand mechanical external forces and corrosion resistance. The outer protective layer includes an inner liner layer, a metal armor layer and an outer layer. The inner liner layer protects the metal sheath from being damaged by the metal armor layer, and can be added with anti-corrosion measures; the metal armor layer can withstand mechanical external forces; the outer layer can protect the armor metal from external corrosion.

(2) Plastic cable protective layer. Usually a PVC sheath is used outside the plastic insulation.

(3) The protective layer of the rubber cable. The protective layer of the rubber cable is divided into an inner protective layer and an outer protective layer. The inner sheath has three types: PVC sheath, neoprene sheath (non-combustible rubber) and lead sheath; the outer sheath is divided into three types: steel tape armor, rubber sheath and plastic sheath.

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