Magnetic fields exist wherever we use, produce and transmit electricity. As such, there will be magnetic fields close to all electricity supply installations, be they transformers, overhead lines or underground cables. It also means that magnetic fields will be created around electrical appliances and ordinary electrical installations when an electric current flows through them.
Field strengths depend on the amount of electric current (measured in amperes (A)) flowing through a wire or an appliance, and fields drop off rapidly with distance. The higher the amperage, the stronger the magnetic fields - and the larger the distance to the wire or the appliance, the weaker the fields. Magnetic fields are not shielded by commonly used materials. Therefore, there are also fields above underground cables.
There are also electric fields around electricity supply installations, electrical appliances and machinery. Electric field strengths depend on voltage (measured in volts (V)) and distance. The higher the voltage, the stronger the fields, and the larger the distance, the weaker the fields. Electrical fields are not shielded by plantation, buildings, soil, etc., and it is therefore not possible to measure, for example, the strength of an electric field above underground cables.