External electrical installation should be carried out in compliance with the highest level of safety and applicable standards and regulations. One of the key issues is the selection and routing of electrical cables.
In this article you will learn:
- When is it worth doing an external electrical installation?
- What electrical cables are used in it?
- Guidelines and good practices for laying cables in the ground.
- What to consider when selecting underground cables.
External electrical installation – when is it worth doing it?
Underground cables are used to transmit electricity in various conditions . You will need them if your property has garden lighting, outdoor devices or one or more socket posts. Power cables for underground installations are extremely resistant to high and low temperatures . They can withstand conditions from -40 to even 70 degrees Celsius.
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Types of underground cables – which underground cable to use?
There are several types of ground cables on the market, differing in structure and purpose. Each of them is insulated and equipped with a protective PVC sheath , resistant to solvents and providing it with high mechanical strength. The bending radius of the cables is (depending on the number of cores in the braid) 10-20 degrees.
When choosing underground cables, low voltage (LV) and medium voltage (MV) power cables are usually used. These include:
Aluminum underground cables (YAKY)
Aluminum underground cables are designed for low (0.6/1 kV) and medium voltage (3.6/6 kV, 6/10 kV 8.7/15 kV, 12/20 kV, 18/30 kV) operation. Aluminum is not a durable material , so each cable core is separated from the others and then insulated using a PVC outer sheath. MV power cables are usually single-core . They have a cross-section from 70 to even 1000 mm . It is selected depending on the cable operating conditions. If the aluminum underground cable operates in difficult conditions, dense aluminum is used.
Aluminum underground cable is typically used in city centers, in the construction of low-voltage power lines, indoors and outdoors or in cable ducts laid directly beneath the ground surface.
Copper underground power cables (YKY)
Copper electrical cables are used in installations with different voltages. Copper conducts electricity better than aluminum. It is more durable, flexible and more resistant . This ensures low failure rate , which is why copper wiring is more popular than aluminum.
Underground electric cables with copper are most often made of double insulation (the material is usually PVC). This provides them with better electrical conductivity, high water resistance and failure-free operation at low temperatures .
This type of cables are commonly used in residential construction - power supply for property lighting, socket posts, external devices (e.g. pumps), etc. In our shop you will find.
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Copper cables with multi-wire conductors
Their material is also copper. They are characterized by an uneven structure of the veins. They are also distinguished by double insulation. Used in municipal energy installations.
Halogen-free underground cables
Halogen-free cables are characterized by freedom of installation - installation can be performed under- or over-plaster, in concrete and brick walls or floor. Power cables of this type can be installed directly outside the building . They are distinguished by cross-linked polyethylene insulation.
Halogen-free ground cable has a core cross-section ranging from 2 to 5 cores. It is also distinguished by the possibility of working in low-voltage networks . It is mainly used in public places and those with an increased risk of fire.
Methods of laying electric cables in the ground - regulations, standards, good practices
The first step before starting work should be to determine the route of the cable line . It is best if it is as short as possible and does not interfere with infrastructure elements . In the event of a failure, access to the cables cannot be hindered. The regulations and requirements for laying cables in the ground are specified in the N-SEP-E-004:2014 standard.
Earth conduit and soil type
If the soil is sandy , the cables can be laid on the bottom of the trench. If the ground is uneven , a layer of sand should be poured on the bottom, the earth cable should be placed on it and covered with another layer. The thickness of the layers is at least 10 cm. The next layer can be native soil.
Cable line marking
It is important to mark the cable line along its entire length and width. This can be done using a mesh or plastic foil in the following colors:
- blue – for cables with a rated voltage of up to 1 kV,
- red – for cables with a rated voltage above 1 kV.
The material used to mark electrical cables should be covered with a layer of sand to a height of at least 25 cm, but not more than 35 cm above the laid cable.
At what depth should electric cables be laid in the ground?
The N-SEP-E-004 standard defines it in relation to the use and rated voltage of cables:
- minimum depth of 0.5 m – for cables with a rated voltage of less than 1 kV in urban power installations (road signals, lanterns, etc.), located under the pavement or road;
- min. 0.7 m – for cables with a rated voltage of less than 1 kV, located outside agricultural areas;
- min. 0.8 m – for cables with a rated voltage in the range of 1–20 kV, located outside agricultural areas;
- min. 0.9 m – for cables with a rated voltage in the range of 20–30 kV, installed on agricultural land;
A cable with a rated voltage exceeding 30 kV should be laid at a depth of at least 1 metre, regardless of its application. If the design requires the installation of several such cables, their vertical distance cannot be less than 0.7 m . The depth of laying lines in agricultural areas is usually:
- 1.0 m for lines with a rated voltage of no more than 30 kV,
- 1.2 m for lines with a rated voltage above 30 kV.
If the cable laid in the ground is exposed to damage due to low temperatures , it must be routed below the level of the depth of the ground freezing. In Poland, where there are 4 freezing zones, this depth is respectively:
- zone I – 0.8 m,
- II – 1m,
- III – 1.2 m,
- IV – 1.4 m.
By installing underground cables below these depths, you will not expose them to the risk of freezing.
What to consider when selecting underground cables?
The ground cable (and any other) is always selected with regard to the installation in which it will work . It is often a good idea to consult the choice with an electrician or the target energy supplier. When thinking about buying cabling, pay attention primarily to:
- type of installation (two-, three-, four-phase, etc.),
- conductive material (aluminum or copper),
- rated voltage (designation U0/U, e.g. 18/30 kV),
- external conditions,
- route and length of cables.
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An earth cable is an NN or SN power cable. Pay attention primarily to the thickness of the wire and the number of cores . The further away the power source is, the thicker the wire should be to properly transmit electricity. In the case of an external electrical installation in the garden , earth cables compliant with the PN-93/-90401 / PN-HD 603 standard for a voltage of 0.6/1.0 kV are used with the symbols: YKY and YAKY. Three-core cables are dedicated for single-phase receivers, and five-core earth cables for single-phase receivers.
What cable material is best to choose?
Aluminum is nearly 4 times cheaper and about 70% lighter than copper . It is much worse at conducting electricity, temperature changes or stretching. It is less flexible and more prone to failures. Copper is used in modern installations - safer, more flexible and thinner than aluminum. However, better properties mean a higher price.
Get your underground cables from the Onninen installation wholesaler
When creating a safe and efficient external electrical installation, get the necessary cables from our wholesaler. In the offer of the Onninen electrical wholesaler you will find aluminum cables and copper cables of various brands, with different parameters. Adapt them to your needs and the parameters of your installation!