A return pad contact detection system for use with at least two pairs of patient return pads adapted for contacting a patient, each pair of said at least two pairs of patient return pads having two conductors attached to a corresponding patient return pad for connecting the pad to a source of a.c. energy passing through the pad, said return pad contact detection system comprising: means for producing and applying a corresponding current signal for each of said at least two pairs of patient return pads resonant circuitry means responsive to the impedance between said at least two pairs of patient return pads for producing at least one signal which is a function of said impedance and measurement means for receiving said at least one signal for determining the impedance between said at least two pairs of patient return pads, wherein the frequency of said corresponding current signal for each of said at least two pairs of patient return pads is substantially equal to the frequency of at least a portion of said resonant circuitry means.
