An apparatus is provided to detect electrical contact between anatomical tissue and a shield conductor: a transformer; an alternating current (AC) reference frequency signal generator to inject a reference frequency signal to a primary winding of the transformer; a reactive impedance coupled in parallel with a secondary winding of the transformer between a first node and a second node; and a phase match detector circuit to detect a phase match between the reference frequency signal and a reflected reference frequency signal that is reflected from the secondary winding to the primary winding.