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Underground electrical wiring

Designing Underground Electrical Wiring Systems

To design an underground electrical wiring system properly, it is important to pay attention to installation methods and safety distances

One of the requirements of a well-designed garden is outdoor lighting, a fundamental aspect to enhance these spaces, make them functional, and enjoy them without any limitations.

Outdoor lighting almost always requires the installation of an underground electrical wiring system.

In this article, we will understand how to best design underground systems and carefully consider installation methods without neglecting aesthetic and safety aspects.

Finally, a video will demonstrate the advantages of design and sizing using a 3D modeling software for electrical systems.

What is an Underground Electrical Wiring System

An underground electrical wiring system is a system that involves placing a part of the entire system beneath the ground surface. This type of system is commonly used to provide outdoor lighting in areas such as gardens, parks, courtyards, and driveways, offering a discreet and aesthetically pleasing solution.

Below is a brief list of what constitutes an underground electrical wiring system. This will allow you to better understand what you need to design the electrical system more precisely:

  1. wiring and cables – the heart of an underground electrical system consists of cables and wiring that carry electricity from power points to lights or other electrical devices. These cables are usually protected by sturdy insulating material to ensure safety and durability over time. The cables are also characterized by an IP (Ingress Protection or International Protecting rating) code, indicating the degree of protection of the element and, therefore, its effectiveness against dust and moisture, ensuring safe operation even in outdoor environments exposed to atmospheric agents;
  2. lighting fixtures – lighting fixtures, such as spotlights, wall lights, or recessed lights, are connected to the electrical system and serve to emit light uniformly and discreetly;
  3. excavations or conduits – before installation, it is necessary to carry out excavations in the ground or use suitable conduits to accommodate cables and lighting fixtures. This step is essential to protect the system components from atmospheric agents and accidental damage;
  4. corrugated tubes – these tubes are essential components for the construction of an underground electrical system. Characterized by a corrugated structure, these tubes provide excellent mechanical protection and electrical insulation to the cables inside. Their corrugated shape allows greater flexibility and adaptability during installation, facilitating laying even in the presence of irregular or difficult-to-cross terrain. Corrugated tubes are available in a variety of colors, each indicating a specific use. For completeness of information, it is good to know that tubes can have different colors. Black tubes are commonly used for power distribution, while blue ones are used in audio/video and intercom systems. Green tubes are reserved for telephone cables or TV reception lines, while brown ones are used for security systems, such as alarms or fire alarms;
  5. protections and sheaths – to ensure the safety and durability of the system, it is important to use protective sheaths around cables and other electrical components. These sheaths wrap around the cables, providing an additional layer of insulation and protection against external agents, thus ensuring greater durability and reliability of the system over time. They are made of materials resistant to moisture, corrosion, and external agents;
  6. power supply and control – the underground electrical system is powered by an external power source, which can be connected to the domestic network or a dedicated power supply. Additionally, it can be equipped with control and automation systems to manage the switching on, off, and light intensity of the lights automatically or programmatically;
  7. maintenance and assistance – although underground electrical systems are designed to withstand weather conditions and wear over time, it is advisable to carry out regular checks and maintenance to ensure the correct operation and safety of the system over time.
Laying of Underground Cables

Laying of Underground Cables

  1. Concrete trench
  2. Metal conduit resistant to stresses
  3. Metal protection
  4. Monitoring tape
  5. Non-stress resistant tube
  6. Armored cable

Design Phases of an Underground Electrical Wiring System

Designing an underground electrical wiring system requires careful and detailed planning to ensure optimal outdoor lighting and user safety. Here is a more detailed overview of the steps involved in the design.

  1. Requirements analysis
    The first step is to understand the external lighting requirements. This may include determining the necessary light points, required light intensity, and the surrounding environment;
  2. Soil evaluation
    It is essential to evaluate the soil in which the electrical system will be installed. This evaluation includes analyzing soil composition, drainage, and moisture conditions;
  3. Material selection
    Based on the project requirements and soil characteristics, suitable materials for cables and pipes are selected. These materials must be resistant to moisture, weather conditions, and mechanical stress;
  4. Layout design
    The layout of the electrical system is planned, determining the arrangement of cables and pipes. This process takes into account garden elements such as trees, shrubs, paths, and areas of interest;
  5. Sizing of sheaths and protections
    Protective sheaths for underground cables must be sized according to project specifications. They must be able to withstand crushing, damage from excavations, and environmental stresses;
  6. Installation depth
    The burial depth of underground cables is a critical aspect to ensure adequate protection against atmospheric agents and compliance with safety regulations. In general, a minimum depth of at least 0.5 m is recommended to ensure adequate cable protection;
  7. Signaling and protection
    Proper signaling of the position of underground cables and protection against accidental damage during and after installation is essential. This may include the use of monitoring tapes for armored cables and the installation of additional mechanical protections;
  8. Pit installation
    Pits are created in strategic areas of the garden to allow access to cables and connections. These pits must be correctly sized and positioned to facilitate maintenance and repair operations;
  9. Verification and testing
    Once installation is complete, the underground electrical system undergoes verification and testing to ensure that all connections are intact and that the lighting functions correctly;
  10. Scheduled maintenance
    Finally, it is important to plan scheduled maintenance of the underground electrical system to ensure its longevity and user safety. This includes periodic checks of sheaths, connections, and protections.

Installation Methods and Safety Distances

In the context of designing and installing underground electrical systems, choosing installation methods and respecting safety distances are crucial aspects that require special attention and care. Let’s see in detail what are the main considerations to keep in mind.

Installation methods:

  1. Context consideration – cable laying methods may vary depending on the specific context, including direct burial in the ground, on sand layers, or inside conduits, tunnels, or concrete ducts. The choice depends on soil characteristics, the presence of other underground infrastructure, and the specific requirements of the system;
  2. Adequate protections – it is essential for cables to have adequate protections against crushing and damage resulting from excavations, especially those carried out with mechanical means. This may include the use of protective sheaths, metal armor, or other supplementary mechanical protections along their length;
  3. Burial depth – the burial depth of cables in the ground is a critical aspect to ensure the necessary protection against atmospheric agents and to comply with safety regulations. In general, a minimum depth of at least 0.5 m is recommended to ensure adequate cable protection;
  4. Proper cable positioning – cables in the same pit should be aligned as much as possible. Also, suitable conditions should be created even when there is a crossing of two cables placed in a perpendicular direction (as can be seen in the first case of the following image).
Identification of the Correct Bending Radius of Cables

Identification of the Correct Bending Radius of Cables

Safety distances:

  1. Regulatory compliance – it is essential to comply with regulated safety distances to avoid interference and damage between electrical cables and other underground infrastructures, such as pipes and tanks. These distances are established by industry regulations and must be strictly observed during the design and installation of systems;
  2. Crossings and parallels – safety distances are particularly crucial at points where cables intersect with other underground infrastructures, such as telecommunications cables or pipes. A minimum distance must be maintained, and if necessary, cables should be protected with conduits or metal boxes;
  3. Preventive agreements – in some cases, it is possible to deviate from safety distances by agreement between the involved entities. However, it is essential that such waivers are carefully negotiated and that additional protective measures are adopted to ensure the safety of the systems.

Overall, both installation methods and safety distances must be carefully evaluated during all stages of the design and installation process of underground electrical systems to ensure their safety, efficiency, and longevity.

Minimum Distances to Be Respected

Minimum Distances to Be Respected

How to Design an Electrical System with BIM Software

In this video, you can see how to use a BIM software for electrical systems design and sizing.