1. The selection of cable sheath shall meet the following requirements:
(1)For AC system single-core power cables, when it is necessary to enhance the resistance of the cable to external forces, a non-magnetic metal armor layer should be used.
Effectively treated steel armor.
(2) In a humid, chemically corrosive environment or easily immersed in water, the metal layer, reinforcement layer, and armor should be covered with a polyethylene outer sheath.
The thick steel wire armor of the cable shall have an extruded outer sheath.
(3) In crowded public facilities and places with low-toxicity, flame-retardant and fire-proof requirements, a halogen-free outer protective layer such as polyvinyl chloride or ethylene-propylene rubber can be selected.
When the fire protection has low toxicity requirements, it is not suitable to use PVC outer sheath.
(4) Except for low-temperature environments below -150C or immersion in medicinal chemical liquids, and cable extrusion outer sheaths that require low toxicity and flame resistance, polyethylene should be used
In addition to olefins, PVC outer sheath can be used for others.
(5) Cross-linked polyethylene cables of 6～35kV importance or above 35kV used in places immersed in water or chemical liquids shall have suitable
Radial waterproof structure such as metal plastic composite water blocking layer and metal sleeve.
Medium and high voltage XLPE cables laid underwater should have a longitudinal water-blocking structure.
2. For the reinforcement type of self-contained oil-filled cable, the height difference between the highest and lowest point when the line is not equipped with a plug-type connector shall comply with the following regulations set:
(1) When there is only a radial reinforcement layer such as copper tape, the allowable height difference should be 40m; but it should be 30m when used in important circuits.
(2) When there are reinforcing layers such as copper tape in both the radial and vertical directions, the allowable height difference is 80m; but it should be 60m when used in important circuits.
3. The selection of the outer protective layer of the cable for direct buried laying shall meet the following requirements:
(1) When the cable is under heavy pressure or has a danger of mechanical damage, it should be equipped with a reinforced layer or steel tape armor.
(2) In the soil where displacement may occur such as the quicksand layer and backfilled land belt, the cable should be armored with steel wire.
(3) For extruded cables used in areas where termites are seriously harmed, a higher-hardness outer sheath should be selected, or a thin outer sheath with higher hardness can be extruded on the ordinary outer sheath.
The material of the protective layer can be nylon or special polyolefin copolymer, etc., or metal sheath or steel tape armor.
(4) In areas with high groundwater level, polyethylene outer sheath should be used.
(5) In addition to the above, an outer protective layer without armor can be selected.
4. The selection of the cable sheath when laying in the air should meet the following requirements:
(1) When the small cross-section extruded insulated cable is directly laid on the arm support, it should be armored with steel tape.
(2) In underground passenger transportation, commercial facilities and other places with high safety requirements and serious rodent damage, the plastic insulated cable should be armored with metal tape or steel tape.
(3) When the cable is in a high-drop stress condition, the multi-core cable should have steel wire armor, and the AC single-core cable should meet the requirements of Article 3.5.1, paragraph 1 of this code.
(4) Cables that are laid on bridges and other densely supported cables may not contain armor.
(5) When it is clear that it is necessary to coordinate with environmental protection, the outer protective layer of PVC should not be used.
(6) Except in accordance with the provisions of Article 3.5.1, Paragraphs 3 and 4 and Paragraph 5 of this Article, and heat-resistant polyethylene such as polyethylene should be used in places with high temperature above 60℃.
Outside the cable with outer sheath, PVC outer sheath should be used for others.
5. Cables that need to be bent frequently or have circuits with higher flexibility requirements, such as mobile electrical equipment, should use rubber outer sheaths.
6. The cables in the place where radiation is applied should have an outer sheath of polyvinyl chloride, neoprene rubber, and chlorosulfonated polyethylene suitable for withstanding the intensity of radiation radiation.
7. The cables laid in the protective tube shall have an extruded outer protective layer.
8. The selection of the sheath for laying cables under water shall meet the following requirements:
(1) In ditches, small rivers that are not navigable, cables that do not need to be armored to withstand tension can be armored with steel tape.
(2) For cables in rivers, lakes and seas, the steel wire armor type selected should meet the stress conditions. When the laying conditions have mechanical damage and other preventive requirements, the outer protective layer that meets the requirements of protection and corrosion resistance can be selected.
9. The selection of cable sheath when the path passes through different laying conditions shall meet the following requirements:
(1)When the total line length does not exceed the cable manufacturing length, it is advisable to select the same type or more than one type that meets the conditions of the whole line or the difference is as small as possible.
(2) When the total line length exceeds the cable manufacturing length, suitable different types can be adopted according to the corresponding section.