An engagement detection system (“EDS”) adapted to be positioned between, and in electrical communication with, an electrosurgical generator and an electrosurgical instrument. The EDS adapted to electronically detect that the electrosurgical instrument is inserted into a trocar cannula, and thereafter deliver electrosurgical energy to the instrument. A method of operating an endoscopic electrosurgical instrument inserted into a trocar cannula, as well as a switch assembly are also provided.