ABSTRACT
This chapter continues with barriers against radiated disturbances. At low frequencies, these disturbances are independent electric or magnetic fields. Time-varying magnetic fields caused by currents are not limited to alternating current installations. Magnetic fields only induce a voltage in a loop, when the field lines penetrate the loop of the field. Any magnetic field is strongest near its source and rapidly decreases when the distance increases. A cable with four conductors and a screen as protective earth will have in practical situations a lower stray field than a cable with five cores. Enclosures can be used to attenuate disturbing magnetic and electric fields on the inside in order to shield the environment from a disturbance source. There are a variety of standardized test methods for performing pre-compliance shielding tests of enclosures and large shielded rooms and components used in such enclosures. The International Electrotechnical Commission describes an electromagnetic shielding performance test for empty cabinets and sub-racks.
