Start of construction of underground cable line from Freienbach to Altendorf

To secure the future supply of energy, Axpo is increasing the operating voltage of its power cables from 50 to 110 kilovolts in the region south of Lake Zurich. As part of this project, the existing overhead cable line in the area from the Freienbach substation to Altendorf (Steinegg) in the Canton of Schwyz will be laid underground. Construction work will start in May 2026. 

In brief:

• Axpo is replacing the existing overhead cable line with an underground cable line, which will ensure less disruption to nature and the natural beauty of the area in the long term.
• By converting the voltage from 50 to 110 kilovolts (kV), more electricity can be transported and grid losses reduced.
• The project will boost the regional energy supply and prepare the power grid to meet growing demands, such as the increasing supply of energy from solar plants and higher loads due to heat pumps and electromobility.

The high-voltage grid on the southern side of Lake Zurich safeguards the energy supply of the local communities. To ensure a reliable and sustainable security of supply of energy, Axpo is increasing the operating voltage of its cable lines in this region from 50 to 110 kilovolts (kV). This will increase transmission capacities and reduce transmission losses. As a measure for the voltage conversion, Axpo is building a new 8.1 km 110 kV underground cable line from Freienbach substation of Axpo to Steinegg in the municipality of Altendorf. The Swiss Federal Office of Energy (SFOE) granted planning approval in October 2025. Construction will start in May 2026. Construction site traffic is to be expected from this point onwards. During the construction period, the electricity supply via the existing line will remain guaranteed at all times.

Once the new line has been commissioned, the overhead cable line that is no longer required will be dismantled, thus restoring the natural beauty of the area.

Route

From the Freienbach substation, the new cable line follows the A3 motorway to “Buechberg” and then continues eastwards to the existing cable line that feeds into the Etzel substation in the municipality of Altendorf. From this cable line, the new cable line will run largely eastwards to Steinegg in Altendorf. There, it will be connected to the existing overhead cable line by means of two new masts.

Voltage changeover

Axpo is gradually converting its existing interregional distribution grid from 50 to 110 kV. This will allow for more electricity to be transported and reduce grid losses by up to 75%. In these terms, the voltage conversion will make an important contribution to environmentally friendly and efficient grid operation. Thanks to the voltage conversion, the grid will be reliably equipped to cope with increasing demands, such as the growing supply of energy from solar panels and higher loads due to heat pumps and electromobility. Thanks to the voltage conversion, bottlenecks will be eliminated and the increasing demand for energy also accommodated. A high-performance, modern and efficient power grid is an essential prerequisite for a reliably large and sustainable supply of energy throughout Northeastern Switzerland – now and in the future.

In recent years, Axpo has realised a wide range of voltage conversion projects in the region south of Lake Zurich. Following the completion of the section from Freienbach to Altendorf, some of the operating voltage in this region can be switched from 50 to 110 kV.