An impedance monitoring circuit for an electrosurgical generator. The monitoring circuit includes an isolation transformer coupled to an active terminal and a return terminal of an electrosurgical generator. The isolation transformer includes a primary winding coupled to a reference resistor and a secondary winding coupled to a load. A driver transmits a sensor signal to the reference resistor and the load. A primary converter coupled to the reference resistor and the load detects a primary converted signal as a function of the sensor signal passing through the reference resistor and the load. A secondary converter coupled to the driver detects a secondary converted signal as a function of the sensor signal prior to passing through the reference resistor and the load. A controller determines a fault condition based on the primary and secondary converted signals.