Systems and methods provide a portable, verified voltage source that allows safe testing of separate non-contact voltage measurement systems. A proving unit of the present disclosure provides a known or specified alternating current (AC) voltage output across an insulated wire, which AC voltage may be fixed or may be user-selectable through a suitable user interface. The proving unit may include a visual indicator and/or an audible indicator that provides the user with an indication confirming that the proving unit is supplying an output voltage with the specifications of the proving unit, so the user will know that the proving unit is operating normally and is ready for testing a non-contact voltage measurement system. If the proving unit cannot provide the specified voltage output, the indicator(s) provides a signal to the user that the proving unit is currently non-functional.