Wiktor Wise
Underground electrical cables are used to transmit electricity and can be placed in concrete-reinforced troughs, directly buried, or housed in underground tunnels. The method of installation depends on the geographical features of the area. Underground cables are typically insulated with materials such as XLPE or EPR to protect against moisture, corrosion, and other environmental factors. They are often used in urban areas where overhead power lines are impractical due to aesthetic or safety reasons.
| Characteristics | Values |
|---|---|
| Installation costs | Higher than overhead cables |
| Maintenance costs | Lower than overhead cables |
| Safety | Safer than overhead cables |
| Susceptibility to weather-related outages | Lower than overhead cables |
| Susceptibility to faults | Lower than overhead cables |
| Visual impact | Lower than overhead cables |
| Installation method | Placed in concrete-reinforced troughs, directly buried, or placed in underground tunnels |
| Cable type | Plastic cables (XLPE), fluid-insulated cables, HVDC cables |
| Cable core | Copper or aluminium |
| Cable insulation | Polyethylene, cross-linked polyethylene (XLPE), EPR |
| Cable protection | Metal shield, PVC outer jacket |
| Cable depth | Depends on the type of conduit, wire, or cable |
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What You'll Learn
Plastic cables (XLPE)
Underground electrical cables are placed in a variety of materials, including metal conduits, PVC, and XLPE. XLPE, or Cross-Linked Polyethylene, is a type of plastic cable that is widely used in power transmission and distribution systems due to its excellent electrical, thermal, and mechanical properties.
XLPE cable is made of a thermoset material, which means it is highly resistant to heat, moisture, and chemicals. This makes it ideal for underground or underwater installations, as it can withstand harsh environmental conditions. The XLPE insulation material is produced by chemically cross-linking polyethylene molecules, which enhances the material's strength and stability. It can withstand high temperatures and electrical stresses, making it suitable for high-voltage applications.
One of the main benefits of XLPE cable is its versatility. It can be used for low-voltage, medium-voltage, and high-voltage power distribution networks, with voltage ratings ranging from 1kV to 500kV. XLPE is commonly used in homes, offices, industrial applications, power transmission between power plants and substations, and in the chemical, commercial, and residential heating industries.
Compared to traditional materials like galvanized steel, copper, and PVC piping, XLPE offers advantages in terms of rust resistance, cost, and circulation. It is also easier to install and provides superior insulation due to its strong bonding and higher stress tolerance. XLPE's higher stress tolerance means it can be manipulated more without showing signs of damage, making it a durable and reliable choice for underground electrical cables.
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Rigid metal conduits
RMCs are connected with clamp-style fittings that slide onto the tubing and are secured with a set screw. While they are not designed to be waterproof, RMCs are required to be corrosion-resistant and suitable for their location. They are not recommended for use in hazardous locations, such as power plants, or in areas with corrosive fumes and vapours.
When installing RMCs underground, it is important to consider the depth of burial, which can vary depending on the specific project. For heavy clay soil, rocky surfaces, or areas with tree roots, a burial depth of 15 cm is recommended to minimize digging while providing sufficient support for the cabling. For small backyard electrical projects, a depth of 30 cm is ideal, offering protection without requiring excessive digging.
It is worth noting that RMCs are generally more expensive than flexible conduits, and they may require additional costs for insulated copper wires that need to be pulled into the conduit. However, they offer a robust solution for protecting underground electrical cables and can be a good choice for specific applications where their rigidity and protective qualities are advantageous.
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Direct-burial
Underground power lines provide electricity through underground cables. They are more aesthetically pleasing, have a lower risk of starting wildfires, and are less susceptible to outages during harsh weather conditions. Underground cables are also safer for low-flying aircraft and wildlife.
The depth at which direct-burial cables are buried varies depending on the type of cable and local municipality rules. Underground Feeder (UF) cables, for example, must be buried at least 24 inches underground, while PVC conduit only needs to be buried 12 inches underground. Metal conduits and low-voltage wiring are typically buried six inches underground. It is important to note that direct-burial wire terminating above ground must be shielded with a conduit before surfacing.
Before installing direct-burial cables, it is essential to follow safety precautions and check with the local building inspection department to determine if an electrical permit and inspections are required. The electrical inspector will verify the trench depth and inspect the wiring before it is covered.
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Underground tunnels
Underground electrical cables are often used in urban areas where overhead power lines are impractical due to aesthetic or safety reasons. They are also used in areas where land is costly, environmentally sensitive, or aesthetically sensitive. Underground cables can transmit power across densely populated areas, reducing the risk of wildlife electrocution and human injury from accidental damage.
The installation of underground cables is significantly more expensive than that of overhead lines. However, once installed, they require less maintenance and are less susceptible to weather-related outages, reducing operating costs over their lifetime. Underground cables are also safer than overhead cables as they are not exposed to the same dangers.
There are several methods for laying underground cables, and the choice of method is usually based on the geographical features of the area. One such method is to place the cables in underground tunnels. This method is often used in conjunction with concrete-reinforced troughs or direct burial.
The depth of the tunnels and the specific cable placement within them can vary depending on local regulations and the type of cable used. It is important to consult with local authorities and follow safety precautions to ensure the proper installation and inspection of underground electrical cables.
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Urban areas
Underground electrical cables are often used in urban areas where overhead power lines are impractical due to aesthetic or safety reasons. Underground cables can transmit power across densely populated areas, and they are also useful in areas where land is costly, environmentally sensitive, or aesthetically sensitive.
In the past, underground cables were limited to low and medium voltages, but nowadays, they are used for a variety of voltages due to changing requirements. The use of underground cables in urban areas offers several advantages over overhead lines, including a more robust construction, higher service reliability, and increased safety. Underground cables are less susceptible to faults and have lower maintenance costs. They also have reduced interference from outside disturbances like storms, lightning, ice, and trees, resulting in fewer weather-related outages.
The installation of underground cables in urban settings involves considering the geographical features of the area. There are three main methods for laying the cables: placing them in concrete-reinforced troughs, directly burying them, or situating them in underground tunnels. The choice of method depends on the specific conditions of the urban environment.
The depth of underground cable installation in urban areas can vary depending on the type of conduit, wire, or cable used. For instance, galvanized rigid metal electrical conduits with individual insulated wires are typically installed at a depth of six inches. On the other hand, GFCI-protected direct-buried Type UF cable is installed at a depth of 12 inches, and PVC conduit with individual insulated wires are placed at a depth of 18 inches.
Underground electrical cables in urban contexts are constructed with multiple layers, each serving a specific purpose. The core is the conductor, made of copper or aluminum, which carries the electric current. This conductor is surrounded by insulation, often made of polyethylene or cross-linked polyethylene (XLPE), providing electrical insulation and safety. A metal shield offers additional protection from external interference and grounding. Finally, an outer jacket made of PVC or similar material encases the entire cable, offering mechanical protection and insulation from moisture and environmental factors.
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Frequently asked questions
Underground electrical cables are safer than overhead cables as they are not exposed to the same dangers. They are also more reliable, with a reduced risk of weather-related outages, and have lower maintenance costs.
Underground cables are more expensive to install than overhead cables and are more difficult to repair.
Underground electrical cables are placed in concrete-reinforced troughs, directly buried, or placed in underground tunnels. The method used depends on the geographical features of the area.
Underground electrical cables consist of numerous layers. At the core is a conductor, generally made of copper or aluminium. This is surrounded by insulation, often made of polyethylene or cross-linked polyethylene (XLPE). This insulation is then covered by a metal shield, which offers grounding and protection from interference. Finally, an outer jacket made from PVC encases the cable, providing mechanical protection and insulation from moisture.
Underground electrical cables are commonly used in urban areas where overhead power lines are impractical due to aesthetic or safety reasons. They are also used in areas where land is costly or environmentally sensitive.
