Abstract: A current sensor for measuring a time-varying electrical current (Im) in a portion of primary conductor (1), the sensor including a sensor conductor comprising first and second ends (3,4) for connection to a signal processing circuit, a first conductor portion extending from the first end and having a plurality of windings (5) to form a first coil portion, and a second conductor portion returning to the second end. Centres of the windings define a median coil place substantially parallel to the magnetic field (Hm) generated by the time-varying current (Im) to be measured, the sensor conductor defining one or a plurality of interference field surfaces as seen projected on a plane parallel to the median plane enclosed by clockwise or anti-clockwise interference field current circulating portions (22,23) of the sensor conductor.