In the present times a greater awareness is generated by the problems of harmonic voltages and currents produced by non-linear loads like the power electronic converters. The influence of voltage and current harmonics on equipment connected to electrical supply systems can cause serious problems. Customers need to be protected from other customers producing excessive distortion on the supply and damaging equipment or causing inconvenient mailfunction. This paper focuses on the set of national standards regulating the rate of indices, which characterize the nonsinusoidality of the supply voltage Keywords-voltage harmonics, national standards, reduction of the losses.I.