Abstract: Embodiments of the invention provide a hollow cable for conveying radiofrequency and/or microwave frequency energy to an electrosurgical instrument that can fit within, e.g. slide relative to, the hollow cable. The hollow cable provides a bipolar electrical connection to the electrosurgical instrument that is maintained when the electrosurgical instrument is rotated relative to the hollow cable. The cable may comprise a hollow coaxial transmission line having a rotatable component mounted at its distal end. The rotatable component comprises a longitudinal passageway continuous with the hollow coaxial transmission line. The rotatable component is rotatable relative to the transmission line and comprises a first and second conductive portions that are respectively electrically connected to first and second terminals on the coaxial transmission line and which are configured to maintain an electrical connection with their respective terminal when rotated relative to the coaxial transmission line.