This thesis contains four main chapters, which describe qualitative parameters of supply voltage and measurement and analysis received information. The theoretical part consists of three chapters. Characteristics of low voltage are described in the first chapter. Next chapter describes disturbing events, which have influence on quality supply voltage, reasons for their occurrence spreading in network, eventually arrangement leading to the disappearance of disturbing events on other electric appliances in network. Last theoretical chapter describes measuring instruments of supply voltage. The purpose of these theoretical parts is to introduce the reader into supply voltage quality issues and can be used for preparation of measurement and eva...