An electrosurgical generator includes a radio frequency output stage, a sensor for sensing current and an active lead (228a). The radio frequency output stage is configured to output at least one radio frequency waveform. The sensor includes a current sensor coil (302) including an outer coil (407) including an opening (303) therethrough and an inner coil (405) coupled to and disposed within the outer coil. The active lead is coupled to the radio frequency output stage and passes through the current sensor coil opening. The current sensor coil is configured to output a first signal indicative of differential mode currents.
