A ground circuit monitor (10) is disclosed for continuously monitoring the potential of a grounding brush (12) in the grounding circuit (14) used to ground a rotating member (16) within a machine (18). A proximitor (26) generates a radio frequency signal impressed across the secondary of a coupling transformer (30). The primary of the coupling transformer (30) is in series between the grounding brush and ground. In normal operation, the capacitance of the film of lubrication between the rotating member and machine prevents oscillation in the transformer. Failure of the grounding circuit increases oscillation, generating an output from the proximitor to the relay unit (32) to generate an alarm.