Cables traveling beneath roadways must be routed through complete round ducts located 600 mm below ground level for cables up to 1 kV and 1100 mm below ground level for cables up to 11 kV. Cables installed in unmade ground must be buried a minimum of 600 mm below ground level for a 1 kV rating and 800 mm for an 11 kV rating. These distances may need to be greater if soil conditions are difficult to dig through.
For underground cables, the maximum depth depends on the voltage class of the cable and the type of construction used for the conduit. The typical depths required by different types of conduits are as follows: Steel pipe - 500-600 mm; Self-lining plastic pipe (SIPP) - 400-500 mm; Concrete pipe (CP) - 300-400 mm; Block - 200-300 mm.
The minimum distance between anchor points depends on the type of connector used. For earth anchors, the minimum distance between holes is 250 mm for surface-mounted connectors and 350 mm for socket connectors. For mechanical locks, the minimum distance between holes is 450 mm.
Underground power cables are often hidden in ducts between 0.45m and 1m below the ground's surface, or they may be covered with a layer of tiles, boards, or colored plastic tape 150mm above the ground. The latter method is used for urban streets where there is not enough space under buildings to bury cables.
The depth that cables need to be buried depends on several factors such as the soil type and its moisture content, the distance between poles, and whether the cable will be exposed to weather conditions. For example, if the soil is dry and well-drained, cables can be placed at a depth of 300-500mm; if it is wet, then only 100mm or less might be able to support the weight of traffic signals and street lights. Cables used in marine environments must be placed at least 250mm below sea level and cannot be placed deeper than this for safety reasons.
In general, the closer together electrical lines are buried, the better because this makes them easier to find and maintain. However, this also means that they take up more space when being installed, which may not be possible due to local regulations regarding the maximum size of conduits that can be used on some roads. For example, some cities require that electrical cables be no larger than 2.5cm in diameter for road construction projects.
Because the cables used must be constructed for subterranean electricity, the insulation on the wires must be double-insulated and armoured. Trenching project managers will then review their regulatory manuals and burial depth tables. A directly buried 1.5 kV electrical line, for example, should go deeper, maybe as far as 750 mm. The maximum allowed depth depends on the regulatory authority overseeing the project.
The requirement for double insulation means that the conductor itself must be insulated with a material capable of withstanding the voltage applied to it while still allowing it to be bent without damage to the insulation. This is usually done by wrapping the conductor several times in thick layers of paper or plastic tape. The outer layer protects the inner layer from voltage exposure and any moisture which may enter through small holes in the tape wrapper. The number of wraps varies depending on the type of insulation used but it should be enough to cover the conductor about six times.
Armed cable is also called "dead" cable because the metal sheath provides protection against lightning strikes. The distance between joints in an armoured cable should be at least twice the height of a man. The overall depth of burial of an armoured cable system depends on the density of placement of the poles and the thickness of the cable wrap: the closer together they are placed, the less space there is between them, so thicker wraps are required.
Non-armoured cable is only protected from mechanical injury and not from electrical stress.
Cables that are buried directly Direct burial is the typical method of installing high-voltage wires in both urban and rural regions. Each single cable circuit necessitates 1.5m wide and 1.2m deep trenches (see indicative diagram on page 12). The trench is filled with asphalt or concrete, and the wire is laid inside it. The depth of the trench depends on several factors such as soil conditions, etc.
Indirect burial means that an empty conduit is first placed in the ground parallel to the electrical service conductors. The high-voltage cable is then run into this conduit, which acts as a protective casing for the cable. At each end of the conduit, the cable must be spliced to other cables which will lead to other parts of the building. These splices should be made using special equipment and techniques to prevent voltage leaks through them. After all the conduits are connected together, they are filled with cement to form a solid surface across which no current can flow.
The depth that cables should be buried depends on various factors such as soil conditions, etc. Generally, underground cables should be at least as deep as the maximum expected water depth. For example, if you expect water to drain through your yard every time it rains heavily, then you should install your cables so that they are at least as deep as the base of the tree trunks or other vegetation.