Introduction Conducted interference current can be measured@ without making direct contact with the source conductor and without modification of either the conductor or its circuit@ by use of specially develop clamp-on current transformers. The utility of this method is self-evident: the interference in complex wiring systems@ electronic circuits@ etc@ may be measured without interruption of the normal operation or configuration. The current probe is constructed so that it may be conveniently clamped around the conductor to be measured. The conductor represents a one-turn primary winding. The secondary winding is contained within the current probe. Current probes can detect interference currents in the frequency range of 30 Hz to 1000 MHz@ although the primary measurement range is 30 Hz to 100 MHz. Beyond 100 MHz the standing interference currents in conventional power systems require that the current probe location be optimized for detection of the maximum interference current.