Abstract: An electrosurgical generator arranged to supply radio frequency (RF) energy to fuse tissue is provided. The generator is arranged to supply RF energy through a removably coupled electrosurgical instrument to fuse tissue grasped by the instrument. The generator monitors a phase angle of the supplied RF energy and adjusts or terminates the supplied RF energy based on the monitored phase angle in comparison to predetermined thresholds and conditions to optimally fuse the tissue. The electrosurgical instrument conducts radio frequency energy to fuse tissue captured between the jaws and a blade to mechanically cut tissue between the jaws.