An openable toroidal current transformer is intended to close over at least one electrical conductor in which an electrical current to be measured circulates. The current transformer includes a magnetic circuit, and an electrically conducting coil wound around the magnetic circuit and electrically insulated from the magnetic circuit. The coil comprises a single winding or several distinct windings coupled in series. The magnetic circuit comprises a set of wires of magnetic material assembled in the form of a strand, allowing having uniform flexibility in all directions for the magnetic circuit.