A system is provided to detect a breach of an insulative sheath in a bipolar electrosurgical instrument the system including: a first pulse detection circuit to detect a first high frequency (HF) signal component of a HF signal conducted on a lead of the bipolar instrument; a second pulse detection circuit to detect a second HF signal component of the HF signal conducted on a conductive shield surrounding the lead; magnitude difference sampling logic to produce sample values indicative of magnitude difference between the first HF signal component and the second HF signal component; and current detection logic to detect current flow between the shield and anatomical tissue based upon the sample values.