A meter apparatus is provided for determining parameters of an AC electric signal in first and second wires, the AC signal including an AC electric current and an AC electric voltage, the apparatus including a measurement section to provide first and second measure signals each one indicative of the AC voltage based on a first capacitive coupling with the first wire and on a second capacitive coupling with the second wire, the first and second measure signals depending on capacitance values of the first and second capacitive couplings, and a control unit to determine said capacitance values of the first and second capacitive couplings according to the first and second measure signals, and determining the amplitude of the AC voltage according to the first or second measure signal, and to the capacitance values of the first and second capacitive couplings.