A scanning cannula for scanning an electrosurgical instrument for electrical insulation defects includes an elongated sleeve having a receiving end, an opposite exit end, and a passageway extending from the receiving end to the exit end. At least one sweeping contact is disposed in the passageway with a limit switch or photocell upstream. A circuit is electrically connected to the at least one sweeping contact. A communication device is connected to the circuit to transmit signals from the circuit to a controller of a surgical instrument. An electrosurgical instrument inserted into the receiving end of the sleeve passes through the at least one sweeping contact, and any electrical defect of the electrosurgical instrument detected by the at least one sweeping contact and assessed by the software is relayed as an error signal to the circuit, which communicates the error signal to the controller. The controller cuts current to the electrosurgical instrument and signals an alarm. The scanning cannula also discloses a cannula with an added capability for testing the insulated shafts of any incoming devices for insulation defects, and not allow electricity to flow to the device from the generator unless the insulation of the shaft has been tested and found to be free of defects (or when the OVERRIDE function is activated). The scanning cannula further may include the use of an attachable scanning chamber to commercially available non-scanning cannulas, thus allowing virtually all users of endoscopic cannulas to add vital safety feature: RF insulation scan as last step before the incoming RF electrosurgical instrument is used on the patient.