Limit values for stationary low-frequency and direct current installations

To date, electric energy has been transmitted from the power plant to the consumer almost exclusively through high-voltage lines carrying alternating current at a frequency of 50 hertz. In the course of the energy transition, high-voltage direct current (HVDC) installations are also planned in Germany.

The 26th BlmSchV entered into force in 1996 and was amended in 2013. In addition to limit values, the ordinance also contains precautionary requirements.

The "Bund/Länder-Arbeitsgemeinschaft für Immissionsschutz (LAI)" (Federal/Länder Working Group on Immission Protection) has published information on the implementation of the Ordinance on Electromagnetic Fields with the purpose of promoting a uniform enforcement by the authorities, but also of providing operators or those affected with minimum requirements.

Bases for the limit values

Low-frequency fields

Upon exposure of the human body to low-frequency electric or magnetic fields, electric fields and currents are produced in the tissues. When certain – frequency-dependent - thresholds are exceeded, nerve and muscle cells are acutely stimulated. The limit values are defined so that the fields induced in the body remain below the thresholds. They limit the electric and magnetic fields that can be measured outside the body and therefore refer directly to the immissions by the installations.

Static fields

Health effects of static fields that can be directly attributed to biological effects are known only for very high magnetic field strengths.

Occasionally even weaker magnetic fields pose an indirect risk as they exert forces on magnetic objects and may cause interference with implants. The limit value for static magnetic fields has therefore been determined so as to also avoid interference with implants. No limits have been set for static electric fields.

Compliance with limit values

The limit values for 50-hertz fields apply to places intended for not only temporary presence of humans. These include

• housing
• workplaces
• schools and
• hospitals.

Low-frequency installations covered by the 26^th BlmSchV have to be erected and operated in a way that the limit values for these places are met even when the installations are operating at maximum capacity. Other immission sources (such as other low-frequency installations) also have to be taken into account.

Direct current installations located at places intended for temporary or permanent human presence have to comply with the relevant magnetic field limit. The electricity grid operators are responsible for ensuring compliance with limit values in practice.

DIN standards

In addition to legal regulations, technical details for the design of high-voltage lines have been defined in various DIN standards. They specify minimum clearance distances for example, between the live parts of high-voltage lines and buildings. These specifications, however, are made primarily for fire protection and operational reasons and not for reasons of radiation protection.