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What is the role of Cable Sheath

2022-04-14
Cable sheath is a protective layer covering the cable insulation layer, cable sheath and conductor, insulation layer collectively referred to as the three components of the cable. Typical sheath structure, including inner sheath and outer sheath.

1.The role of Cable Inner Sheath

The inner sheath is a protective covering, covering the insulation layer of the cable to prevent the insulation layer from moisture, mechanical damage, light and chemical corrosive media, etc., and can also flow short circuit current.

Inner protective layer has metal flat aluminum sheath, wrinkled aluminum sheath, copper sheath, comprehensive sheath, as well as non-metallic plastic sheath, rubber sheath and so on. Metal sheath is mainly used for oil-impregnated paper insulated cables and 110kV and above XLPE insulated power cables; Plastic sheath can be used for all kinds of plastic insulated cable; Rubber sheath is generally used for rubber insulated cables.

2.The role of Cable Outer Sheath

The outer sheath is a protective covering covering the inner protective layer, mainly for mechanical reinforcement and corrosion prevention. Commonly used cables have metal outer sheath and plastic outer sheath.

The outer protective layer of the metal sheath is generally composed of three parts: the liner layer, the armored layer and the outer layer. The liner layer is located between the metal sheath and the armored layer, and has the anticorrosion effect of the armored liner and the metal sheath. Armored layer for metal tape or wire, mainly mechanical protection, wire can withstand tension, outer layer in the armored layer, metal armored corrosion prevention. The gasket layer and the outer layer are composed of asphalt, PVC tape, impregnated paper, PVC or POLYETHYLENE sheath and other materials. According to the different environment and conditions used by various cables, the composition of the outer layer is also different.

The outer protective layer of plastic sheath has two kinds of structure. One is no outer protective layer and only polyvinyl chloride (PVC) or polyethylene sheath; The other is the armored layer also extruded PVC or polyethylene cover, its thickness and inner sheath the same. Because of the low working temperature of PVC, the traditional PVC outer sheath is not suitable for the high voltage crosslinked polyethylene (XLPE) cable with high operating temperature and protective layer insulation requirements. Therefore, the use of high density polyethylene CHDPE or low density polyethylene (LLDPE) as outer sheath has been very common, but no flame retardant. When laying, fire prevention measures or flame-retardant cables should be considered. The insulation level of the sheath can be improved by using HDPE as the outer sheath, and the adhesive should be used between the outer sheath and the wrinkled metal sheath.


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