A method for determining individual voltage values of a plurality of power lines of multi-phase power lines, comprising: operatively coupling respective contactless voltage sensing devices (508,510,512) to the plurality of power lines of the multi-phase power lines (532,534,536), wherein each of the respective contactless voltage sensing devices (508,510,512), comprises: an electrically conductive housing; a first impedance element having a first impedance, wherein the first impedance element is configured to be operatively coupled to a respective power line of the plurality of power lines; an antenna operatively coupled to the first impedance element, said antenna including a first portion and a second portion, wherein the first portion of the antenna is insulated from the electrically conductive housing by means of an electrical insulator; and wherein the second portion of the antenna is disposed outside the electrical insulator, and outside the electrically conductive housing; a second impedance element having a second impedance, wherein the second impedance element is formed in part by the antenna and a parasitic impedance element, and wherein the parasitic impedance element comprises a parasitic impedance; measurement and communication circuitry operatively coupled to the first impedance element; determining sensed voltage values (V Z1, V Z2, V Z3) for the plurality of power lines of the multi-phase power lines (532,534,536) using the respective contactless voltage sensing devices (508,510,512); determining a calibration matrix comprising cross-coupling factors, wherein the cross-coupling factors are representative of cross-coupling (540,544,548) between the respective contactless voltage sensing devices (508,510,512) and other power lines of the multi-phase power lines; and determining the individual voltage values of the respective power lines by deducting at least in part contributions of the cross-coupling from the sensed voltage values using the calibration matrix. an electrically conductive housing; a first impedance element having a first impedance, wherein the first impedance element is configured to be operatively coupled to a respective power line of the plurality of power lines; an antenna operatively coupled to the first impedance element, said antenna including a first portion and a second portion, wherein the first portion of the antenna is insulated from the electrically conductive housing by means of an electrical insulator; and wherein the second portion of the antenna is disposed outside the electrical insulator, and outside the electrically conductive housing; a second impedance element having a second impedance, wherein the second impedance element is formed in part by the antenna and a parasitic impedance element, and wherein the parasitic impedance element comprises a parasitic impedance; measurement and communication circuitry operatively coupled to the first impedance element; determining sensed voltage values (V Z1, V Z2, V Z3) for the plurality of power lines of the multi-phase power lines (532,534,536) using the respective contactless voltage sensing devices (508,510,512); determining a calibration matrix comprising cross-coupling factors, wherein the cross-coupling factors are representative of cross-coupling (540,544,548) between the respective contactless voltage sensing devices (508,510,512) and other power lines of the multi-phase power lines; and determining the individual voltage values of the respective power lines by deducting at least in part contributions of the cross-coupling from the sensed voltage values using the calibration matrix.