An electrical current sensor comprises a magnetic circuit with an air-gap, a magnetic field sensor positioned in the air-gap, and a secondary coil surrounding a branch of the magnetic circuit. The magnetic circuit comprises at least two parts (18, 20) that are assembled together, a branch portion (45, 46) of each part being insertably received in a central cavity of the secondary coil in an axial direction (A). The air-gap (30) is arranged between overlapping branch portions of each magnetic field circuit part.