The article describes the methodology used in calculating errors and uncertainty of current, voltage and power measurement channels containing Hall-effect sensors and digital measurement devices. The deliberations involved LEM-manufactured current and voltage transducers whose nominal ranges enable testing electrotechnological devices intended for welding-related applications. The recommendations of the International Organisation for Standardisation (ISO) were used to present universal dependences enabling various measurement uncertainties, i.e. absolute, relative, standard, complex and extended. For some specific cases related to the selection LEM-manufactured transducers, voltmeters or measurement cards connected to a computer, relative measurement uncertainties budgets were created.