Electric and magnetic fields

It is hard to imagine our daily life without the numerous electronic gadgets and tools. However, we are much less aware that electric and magnetic fields are formed everywhere electricity is present: including in the generation, transmission and distribution of electric energy.

Electric field

As soon as a device is connected to an electrical outlet, it contains a voltage. An electric field is created even if the device remains switched off and no current flows. The voltage determines the intensity of the electric field and is measured in volt per metre (V/m). As the distance from the source increases, the strength of the field decreases.

Magnetic field

Once current flows, a magnetic field is formed in addition to an electric field. The electricity volume transported through the line determines the strength of the magnetic field and is measured in microtesla (μT). As the distance to the line increases, the strength of the field decreases.

Electromagnetic spectrum – non-ionising radiation

One of the strictest limit value directives in the world

The International Commission on Non-Ionizing Radiation Protection (ICNIRP) specified the international limits in 1998. In the Swiss Ordinance on Protection from Non-Ionising Radiation, Switzerland specified limits for electric and magnetic fields which go much further and are among the strictest in the world.

International comparison of limits for electrical and magnetic fields

  Electrical fields Magnetic fields
  Immission limit System limit
ICNIRP* 5 kV/m 200 μT
Switzerland 5 kV/m 100 μT 1 μT
Germany 5 kV/m 100 μT
Netherlands 5 kV/m 100 μT **

 
* International Commission on Protection against Non-Ionising Radiation

** The Netherlands use the annual average load and not the maximum load like Switzerland as the basis for calculations. They have a system limit of 0.4 μT.

Immission limit

Applies everywhere people may be present. The lines are to be dimensioned so that this limit is never exceeded.

System limit

Applies for places with sensitive use:

  • Places where people are subjected to immissions over extended periods of time, such as in bedrooms and living rooms.
  • Places where children are frequently present, such as in classrooms or on playgrounds.
  • Areas of undeveloped land where these uses are permitted.
Magnetic fields exist around overhead lines and underground cabling

Strength of the magnetic field

The magnetic field is much stronger right above underground cabling than it is below an overhead line. On the ground, where people normally are, the magnetic field for overhead lines is a few microtesla while it can reach up to 100 microtesla for underground cabling.

Spatial expansion of the magnetic field

For overhead lines, the 1 microtesla limit is observed at a distance of approx. 60-80 metres from the conductors. For underground cabling, this distance is approx. 6-8 metres.

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Measurements and calculations

Cooperation with research

Swissgrid has entered into a partnership with the Swiss Research Foundation for Electricity and Mobile Communication (FSM), a non-profit research foundation at the ETH Zurich. The FSM promotes research on technological, biological, health-related and social issues in the context of electromagnetic fields of radio and electricity technologies. The foundation also provides consulting for the authorities, companies and organisations, hosts conferences and imparts expert knowledge to the general public.

 FSM website