Laying Cables in the Ground According to N-SEP-E-004

Guidelines for Laying Electric Cables in the Ground 

• For budget-conscious projects, investors may choose to install electric cables underground on their own. 
• The conditions and methods for laying electric cables underground are outlined in N-SEP-E-004, which replaced the PN-76/E-05125 standard in 2014. This standard provides comprehensive guidance on various methods for laying cables, depending on the soil type and structure. 
• In areas with sandy soil, the standard suggests placing the cable at the bottom of the trench. However, if the soil is inconsistent, it recommends laying a layer of sand at least 10 cm thick at the trench’s bottom, placing the cable on top, and then covering it with another 10 cm layer of sand. The subsequent layer can consist of native soil. 
• It is crucial to mark the entire length and width of the cable trench with blue plastic mesh or tape for cables with a nominal voltage of up to 1 kV, or red for those above 1 kV. The tape should be buried at a depth of no less than 25 cm and no more than 35 cm above the cable. 

Is it possible to lay a power cable in the ground without using sand? 

The standard typically recommends sand for this purpose due to its thermal resistivity, which does not exceed 2.5 K∙m/W. However, newer materials such as bentonite now comply with the N-SEP-E-004 standard. These alternative mixtures can be used as sand substitutes and offer a thermal resistivity of up to 2 K∙m/W. 

It is crucial to compact the sand or any alternative material after backfilling the power cables to ensure that the soil density reaches at least 1.6 t/m². For safety reasons, it is advisable to choose alternative materials from reputable manufacturers who provide product certifications. 

At what depth should power cables be buried in the ground? 

The N-SEP-E-004 standard outlines the necessary depths for cable installation as follows:

• • Cables supplying power to traffic signals, road signs, or street lighting with a nominal voltage of less than 1 kV should be buried 50 cm beneath sidewalks or roads. 
  • For cables with a nominal voltage under 1 kV that are installed outside agricultural land, a minimum depth of 70 cm is required. Cables with a nominal voltage ranging from 1 to 20 kV, also laid outside agricultural land, must be buried at least 80 cm deep. 
  • For cables with a nominal voltage between 20 and 30 kV that are placed on agricultural land, the required burial depth is at least 90 cm.
  • Cables exceeding 30 kV should be installed at a minimum depth of 1 meter, regardless of their intended use. If multiple cables are being installed, they must be spaced vertically by at least 70 cm. 

In cases where environmental, geological, or other conditions make it impossible to bury the cables at the recommended depth, they may be laid at a shallower depth but must have additional protective covering. 

Selecting a Cable Route 

The cable route must be established following the guidelines outlined in the N-SEP-E-004 standard: 

• Cables should be installed in a manner that prevents mechanical damage.
• When placed underground, the cable route should align with roads, streets, or designated grassy areas.
• Along the banks of rivers and lakes, the path should avoid areas prone to erosion.
• In agricultural regions, cables may be installed beneath drainage ditches.
• For agricultural zones, the standard advises using additional protective coverings or increasing the minimum burial depth to:
  • 1 m for cables with a nominal voltage of up to 30 kV.
  • 1.2 m for cables with a nominal voltage exceeding 30 kV.

Reserve lines should be routed separately from the main lines.

Cable Route Marking 

It is crucial to ensure that underground cables are clearly marked with permanent markers placed at intervals of no more than 10 meters, as well as at joints and in non-standard locations, such as intersections, duct entrances, and areas around protective covers. 

This information has been developed in accordance with the N-SEP-E-004 standard. 

For more details, please consult the N-SEP-E-004 standard or contact the technical support team via email at: wsparcie.techniczne@bitner.com.pl