Electrical voltage measuring apparatus

An electrical measuring apparatus for measuring an alternating voltage between a first potential and a second potential comprises a voltage measuring device (1-3), a measuring electronic circuit (7) and a transformer (37, 38) for supplying power to the measuring electronic circuit (7). The transformer comprises a primary side (37) and a secondary side (38) magnetically coupled to one another. The apparatus is characterised in that the voltage measuring device comprises a first electrode (1) arranged to be electrically connected to the first potential, a second electrode (2) arranged to be electrically connected to the second potential, and a third electrode (3) separate from the first and second electrodes (1, 2), the first and third electrodes (3) being electrically connected to the measuring electronic circuit (7), and in that the primary side (37) is disposed in the second electrode (2) and the secondary side (38) is disposed in the first electrode (1).