Underground Cable Installation: Best Practices and Safety
The conductor of cables used in underground lines will be copper or aluminum and be insulated with appropriate mixtures of polymeric compounds. It should also be adequately protected from corrosion that may be caused by the ground where they are installed and will have sufficient strength to withstand the stresses to which they may be subjected.
Cables may contain one or more conductors and have a rated voltage not less than 0.6 / 1 kV. The cross-section of these conductors will be adequate for the currents and voltage drops. In any case, this section shall not be less than 6 mm2 for copper and 16 mm2 for aluminum.
Implementation of Underground Cable Facilities
Installation of Insulated Cables
Pipes are arranged, usually in public lands and well-defined areas, preferably under sidewalks. The layout should be as straight as possible, with references fixed and parallel to front lines and curbs. It should also take into account the minimum bend radius, set by the manufacturer (or otherwise indicated on the standards UNE 20435 series), to observe the changes of direction.
In the design stage, consult with utilities and service potential owners to know the position of their facilities in the affected area. Once known, prior to opening the trenches, open bays of recognition to confirm or reverse the planned route in the project.
Insulated cables may be installed in any of the following ways:
Directly Buried Cables
The depth to the bottom of the cable should not be less than 0.60 m in pavement, or 0.80 m in the carriageway.
Parallel Wired Circuits
When the strength to carry more current than permissible for a single conductor is needed, install more than one conductor per phase, following these criteria:
- Use conductors of the same material, section, and length.
- Group wires into triads arranged in staggered rows, in one or several levels:
- Three triples in one level: RST TSR RST
- Three slates stacked on three levels: RST
R TS
RST
The minimum distance for cross and stud is 20cm with other services.
The maximum admissible intensities depend on permanent duty. In each case, consider the maximum temperature that the insulation can withstand without alteration of their electrical, mechanical, or chemical properties. This temperature depends on the type of insulation and flow rate.
Connections (Service Connections)
In the event of crossing or parallel runs between electrical cables and conduits of other services, maintain a minimum distance of 0.20 m where they approach a building.
Cables in Galleries
There are two types of gallery: galleries that can be visited, with internal dimensions sufficient for the movement of people, and tunnels, or prefabricated trenches, which are not provided for the movement of people and where the manhole covers require mechanical handling.
The galleries will be reinforced concrete or other material with equivalent stiffness, tightness, and duration. They should be sized to support the load of land and floor above and the corresponding traffic loads.
Walk-In Galleries
Limitation of Existing Services
Walk-in galleries will be used, preferably, for electrical power, control, and telecommunications cables. In no case may electric and gas facilities coexist in the same gallery.
It is also not recommended to have water pipes. Even in cases where necessary, water pipes will be at a lower level than the rest of the facility, with the indispensable condition that the gallery has a drain located above the altitude sewer or sanitation pipeline evacuating.
Recordable Galleries or Trenches
In these galleries, you can support the installation of high voltage electrical cables, low voltage lighting, control, and communication cables. The existence of gas pipelines is not permitted. The existence of water pipes is only admitted if you can ensure that in case of leakage, the water does not affect the other services (for example, in a double body design in which one body has a pipe concreted pipes for water and communication cables, and another body, sealed from the previous cap on when you register, you have low voltage cables, high voltage, lighting, traffic lights, control and communication).
The most notable security conditions to be met by this type of installation are:
- Watertight closures, and
- Good air exchange in the body occupied by electrical cables to avoid accumulations of gas and condensation of moisture, and improve heat dissipation.