This standard is concerned with conducted disturbances in the frequency range from 0 to 9 kHz with an extension up to 148.5 kHz specifically for mains signalling systems. It gives compatibility levels for public low voltage a.c. distribution systems having a nominal voltage up to 420 V, single-phase or 690 V, three-phase and a nominal frequency of 50 Hz or 60 Hz. The compatibility levels specified in this standard apply at the point of common coupling. At the power input terminals of equipment receiving its supply from the above systems the severity levels of the disturbances can,for the most part, be taken to be the same as the levels at the point of common coupling. In some situations this is not so, particularly in the case of a disturbances generated or amplified within the installation of which the equipment forms a part.