A system to measure alternating current, AC, voltage in an insulated conductor, the system comprising: a housing; a conductive electrode physically coupled to the housing, the conductive electrode selectively positionable proximate the insulated conductor without galvanically contacting the insulated conductor, wherein, when positioned proximate the insulated conductor the conductive electrode capacitively couples with the insulated conductor such that the conductive electrode comprises a first electrode of a capacitor (C O) and the insulated conductor comprises a second electrode of the capacitor; a conductive internal ground guard which at least partially surrounds the conductive electrode and is galvanically isolated from the conductive electrode, the internal ground guard sized and dimensioned to shield the conductive electrode from stray currents; a conductive reference shield which surrounds at least a portion of the housing and is galvanically insulated from the internal ground guard, the conductive reference shield sized and dimensioned to reduce currents between the internal ground guard and an external ground; a common mode reference voltage source which, in operation, generates an alternating current, AC, reference voltage having a reference frequency, the common mode reference voltage source electrically coupled between the internal ground guard and the conductive reference shield; a current measurement subsystem electrically coupled to the conductive electrode, wherein the current measurement subsystem, in operation, generates a sensor current signal indicative of current conducted through the conductive electrode; and at least one processor (140, 508) communicatively coupled to the current measurement subsystem, wherein, in operation, the at least one processor is configured to: receive the sensor current signal from the current measurement subsystem; and determine the AC voltage in the insulated conductor based at least in part on the received sensor current signal, the AC reference voltage and the reference frequency; wherein the common mode reference voltage source is also coupled to the at least one processor. a housing; a conductive electrode physically coupled to the housing, the conductive electrode selectively positionable proximate the insulated conductor without galvanically contacting the insulated conductor, wherein, when positioned proximate the insulated conductor the conductive electrode capacitively couples with the insulated conductor such that the conductive electrode comprises a first electrode of a capacitor (C O) and the insulated conductor comprises a second electrode of the capacitor; a conductive internal ground guard which at least partially surrounds the conductive electrode and is galvanically isolated from the conductive electrode, the internal ground guard sized and dimensioned to shield the conductive electrode from stray currents; a conductive reference shield which surrounds at least a portion of the housing and is galvanically insulated from the internal ground guard, the conductive reference shield sized and dimensioned to reduce currents between the internal ground guard and an external ground; a common mode reference voltage source which, in operation, generates an alternating current, AC, reference voltage having a reference frequency, the common mode reference voltage source electrically coupled between the internal ground guard and the conductive reference shield; a current measurement subsystem electrically coupled to the conductive electrode, wherein the current measurement subsystem, in operation, generates a sensor current signal indicative of current conducted through the conductive electrode; and at least one processor (140, 508) communicatively coupled to the current measurement subsystem, wherein, in operation, the at least one processor is configured to: receive the sensor current signal from the current measurement subsystem; and determine the AC voltage in the insulated conductor based at least in part on the received sensor current signal, the AC reference voltage and the reference frequency; wherein the common mode reference voltage source is also coupled to the at least one processor. receive the sensor current signal from the current measurement subsystem; and determine the AC voltage in the insulated conductor based at least in part on the received sensor current signal, the AC reference voltage and the reference frequency; wherein the common mode reference voltage source is also coupled to the at least one processor.