This part of IEC 61000 is concerned with conducted disturbances in the frequency range from 0 kHz to 9 kHz, with an extension up to 148,5 kHz specifically for mains signalling systems. Compatibility levels are specified for electromagnetic disturbances of the types which can be expected in public medium voltage power supply systems, for guidance in: a) the limits to be set for disturbance emission into public power supply systems (including the planning levels defined in 3.1.5); b) the immunity limits to be set by product committees and others for the equipment exposed to the conducted disturbances present in public power supply systems. The disturbance phenomena considered are: voltage fluctuations and flicker, harmonics up to and including order 50, inter-harmonics up to the 50th harmonic, voltage distortions at higher frequencies (above 50th harmonic), voltage dips and short supply interruptions, voltage unbalance, transient overvoltages, power frequency variation, d.c. components, mains signalling. The medium-voltage systems covered by this standard are public distribution systems supplying either: a) private installations in which equipment is connected directly or through transformers, or b) substations feeding public low-voltage distribution systems.