Low frequency electromagnetic fields are associated mainly with the supply of electricity, through the generation, distribution and use of alternating current (AC), and they are always present in our surroundings. Electricity operates at the frequency of 50 Hz or 60 Hz, depending on the country. Electric power stations, high- and medium-voltage lines, transformers, electric motors and railway lines are the main sources of these electromagnetic fields. The applicable reference standards include: IEC/EN 62110 (AC power systems), IEC 61786-1 and IEC 61786-2 (measurement of DC and AC fields from 1 Hz to 100 kHz).