Breach detection in bipolar electrosurgical instrument sheath

A method to detect a breach of an outer insulative sheath in a bipolar electrosurgical instrument that includes, an end effector;

• a conductive lead to electrically couple the end effector to an electrosurgical generator unit;
• and an electrically conductive shield surrounding the conductive lead;
• wherein the outer insulating sheath surrounds the conductive shield, the method comprising:
• detecting pulses of a first high frequency (HF) signal component of an HF signal conducted on the conductive lead;
• detecting pulses of a second HF signal component of the HF signal conducted on the conductive shield;
• producing a succession of sample values of the pulses of the first HF signal component and of the pulses of the second HF signal component;
• determining, using the succession of sample values, phase differences between the pulses of the first HF signal component and the pulses of the second HF signal component;
• detecting aberrant current flow between the conductive shield and anatomical tissue when the phase differences differ by at least a threshold phase amount.