Cable construction requirements
Before laying the cable, check whether the cable has mechanical damage and whether the cable reel is intact. For cables of 3kV and above, a withstand voltage test should be performed. For cables below 1kV, a 1kV megohmmeter can be used to measure the insulation resistance. The insulation resistance value is generally not less than 10MΩ.
Before starting the cable trench excavation work, the underground pipelines, soil quality and terrain of the construction area should be clearly understood. When digging trenches in areas with underground pipelines, measures should be taken to prevent damage to the pipelines. When digging trenches near poles or buildings, measures should be taken to prevent collapse.
The ratio of the cable bending radius to the cable outer diameter should not be less than the following specified values:
For paper-insulated multi-core power cables, the lead sheath is 15 times and the aluminum sheath is 25 times.
For paper-insulated single-core power cables, the lead sheath and aluminum sheath are both 25 times.
For paper-insulated control cables, the lead sheath is 10 times and the aluminum sheath is 15 times.
For rubber or plastic insulated multi-core or single-core cables, the armored cable is 10 times, and the unarmored cable is 6 times.
For the straight section of the direct buried cable line, if there is no permanent building, marker stakes should be buried, and marker stakes should also be buried at the joints and corners.
When the 10kV oil-impregnated paper insulated power cable is constructed under the condition of ambient temperature below 0℃, the heating method should be used to increase the ambient temperature or heat the cable by passing current. When heating by passing current, the current value should not exceed the rated current value allowed by the cable, and the surface temperature of the cable should not exceed 35℃.
When the length of the cable line does not exceed the manufacturer’s manufacturing length, the entire cable should be used and joints should be avoided as much as possible. If joints are necessary, they should be located at the manhole or handhole of the cable trench or cable tunnel, and well marked.
Cables directly buried underground should be protected by armor and anti-corrosion layer.
For cables directly buried underground, the bottom of the trench should be flattened and compacted before burying. The area around the cables should be filled with 100mm thick fine soil or loess. The soil layer should be covered with a fixed concrete cover plate, and the intermediate joints should be protected with a concrete jacket. Cables should not be buried in soil layers with garbage.
The depth of direct buried cables of 10kV and below is generally not less than 0.7m, and not less than 1m in farmland.
Cables laid in cable trenches and tunnels should be marked with signs at the lead-out ends, terminals, intermediate joints and places where the direction changes, indicating the cable specifications, models, circuits and uses for maintenance. When the cable enters an indoor trench or duct, the anti-corrosion layer should be stripped off (except for pipe protection) and anti-rust paint should be applied.
When cables are laid in concrete pipe blocks, manholes should be set up. The distance between manholes should not be greater than 50m.
Manholes should be installed in cable tunnels where there are bends, branches, water wells, and locations with large differences in terrain height. The distance between manholes in straight sections should not exceed 150m.
In addition to reinforced concrete protection boxes, concrete pipes or hard plastic pipes can be used as intermediate cable joints.
When the length of the cable passing through the protective tube is less than 30m, the inner diameter of the straight section protective tube should be no less than 1.5 times the outer diameter of the cable, no less than 2.0 times when there is one bend, and no less than 2.5 times when there are two bends. When the length of the cable passing through the protective tube is more than 30m (limited to straight sections), the inner diameter of the protective tube should be no less than 2.5 times the outer diameter of the cable.
The connection of the cable core wires should be made by round sleeve connection. Copper cores should be crimped or welded with copper sleeves, and aluminum cores should be crimped with aluminum sleeves. Copper-aluminum transition connecting tubes should be used to connect copper and aluminum cables.
All aluminum core cables are crimped, and the oxide film must be removed before crimping. The overall structure of the sleeve after crimping should not be deformed or bent.
All cables buried underground should be inspected for concealed works before backfilling, and a completion drawing should be drawn to indicate the specific coordinates, location and direction.
The welding of non-ferrous metals and metal seals (commonly known as lead sealing) should be firm.
For outdoor cable laying, when passing through a cable hand hole or manhole, each cable should be marked with a plastic sign, and the purpose, path, cable specification and laying date of the cable should be marked with paint.
For outdoor cable concealed laying projects, the completion drawing should be handed over to the operating unit for maintenance and management purposes when the project is completed and delivered for acceptance.
Post time: Jun-24-2024
