Underground cables

EFLA offers comprehensive consulting for concept design, detailed design, and execution of underground cable projects at all voltage levels. Our engineer's knowledge and experience has been developed over many years; undertaking cable network projects in variable and often demanding environmental circumstances. 


EFLA always strives to find safe and economical solutions for all projects and to design cable networks while considering environmental and social benefits by minimizing risk in execution and operation. 

Underground cables

Due to aesthetics and environmental concerns, underground cable systems are increasing rapidly. Projects often entail connecting new users or strengthening the existing system, but often also laying of underground cables to replace overhead lines, especially on lower voltage levels.

EFLA has participated in the design of numerous underground cable systems, such as 10 km - 220 kV Hólasandslína 3,  9 - km 132 kV Fitjalína 2,  27 - km 66 kV Grundarfjarðarlína 2 and 25 km - 32 kV Nesjavallalína and offers solutions for all underground cable projects through its experience gained while working in the challenging environments of Iceland and Norway.

Broad experience

EFLA has highly qualified staff with extensive experience in design, construction supervision, and international standards application. 

Among service provided

  • Environmental assessment
  • Planning and licencing assistance, communication with stakeholders
  • Cable network system analysis
  • Cost Estimate studies
  • Geotechnical design and research and terrain mapping
  • Project planning and task sequencing
  • Concept designs
  • Detailed electrical design of cable systems
  • Design of earthworks
  • Creation of Tender documentation for cables and accessories
  • Creation of Tender documentation for earthworks
  • Product specification and qualification
  • Procurement support
  • Tender evaluations
  • Construction supervision
  • Construction management
  • Commissioning assistance
  • Risk assessments
  • Failure Investigations

Underground cables versus Overhead lines

There are many compelling financial and technical reasons why underground cables should not always be used as a replacement for overhead lines. One of the main reasons is that the use of cables includes operational challenges because of capacitive behaviour of cables, which is many times more than in overhead lines. Capacitors create reactive power which is needed in small amount in the electrical power system, but too much reactive power restricts the power lines transmission capacity and can result in system instability.

Reactive power in underground cables is proportional to the square of the operational voltage and the problem, therefore, increases significantly with higher voltages. The reactive power can be partially removed, however, it is costly. Adding the costs for reactive power compensation to the capital cost for underground cables systems which is usually higher than for overhead line systems, makes underground networks expensive. The cost difference between underground networks and overhead lines increases with a voltage which results in underground cable systems only being considered a realistic option in exceptional cases.

Operational security of underground cables

The failure rate of underground cables is usually lower than that of overhead lines, but in return, the repair time is longer. The insulation for cables are not self-restoring as with overhead lines, thus an insulation failure in cables is normally catastrophic and requires much longer restoration times. The effect of this on operational security must be evaluated on a case basis. 

Our clients

We are committed to building a mutual and beneficial long-term relationship with our customers and partners worldwide. 

See a list of some of our customers.