Shielding againstlow-frequency alternating electric fields
Walls, ceilings and floors of buildings usually contain numerous live electrical installation lines. These constantly emit low-frequency alternating electric fields. The same also applies to all freely laid cables such as extension cords, socket strips and supply lines to consumers of all kinds. The fields are emitted even when no current is flowing and the consumers are switched off. Shielding can be achieved either by circuitry measures, such as the use of mains disconnectors, by the use of shielded electrical installation materials, or by the use of shielding materials.
Whenever possible, line systems or consumers under mains voltage should be switched off. The switching process is usually carried out directly in the fuse box, either manually or automatically, using so-called field disconnectors. Especially for bedrooms and children’s rooms, field disconnectors are often the most uncomplicated shielding measure.
Automatic circuit breakers continuously check the connected line network for consumers. If voltage is required, the mains is switched on, otherwise the mains is switched off automatically. The indicator light in the socket of the monitored network signals that the automatic circuit breaker is switching on and off correctly.
Since dimmers, fluorescent tubes, electronic transformers and energy-saving lamps installed in the circuit are not recognized by many fields disconnectors, an additional base load resistor (GLW) must be installed for these.
Continuous loads, such as radios, television and video equipment, electric alarm clocks, and motion detectors, prevent the line system from being shut down by the mains or field disconnect switch. Therefore, they must either be removed from the circuit or disconnected. It is not sufficient to merely put them in “stand-by” mode.
By using shielded electrical installation lines (sheathed or hose lines), alternating electric fields can be reduced extremely easily and effectively, especially in new construction. These lines are connected in a completely conventional manner. They differ from conventional lines in that they have an additional aluminum or copper braided shield with two wires, which is connected separately to the potential equalization (grounding).
As distribution and junction boxes for plaster or cavity wall mounting, the use of metal-coated electrical installation boxes with ground connection is suitable. Grounding must be connected during installation.
Due to the proximity of lighting fixtures and the resulting large field strength, the use of shielded lamps and luminaires is recommended. If they are well shielded, they not only have a shielded supply cable, but also shielded light sources (bulbs).
In modern workplaces, we are surrounded by numerous mains-operated electrical devices, such as computers, monitors, printers, fax machines, telephones, and many more, which are constantly in operation and remain live even when switched off. Here, the use of shielded power cords, extension cords and power strips is advisable. To reduce exposure to radiation at office and computer workplaces, use shielded lighting, suitable monitors and adapted telephone systems, and avoid wireless networks (WLAN).
When setting up monitors at a PC workstation, we recommend paying attention to test seals, such as that of the TCO standard.