An over moded evacuated waveguide line was chosen to be used in the transmission system for the proposed JET-EP ECRH project. A comparison between the Quasi-Optical, atmospheric waveguide and evacuated wave guide systems was performed for the project with a strong emphasis placed on the technical and financial aspects. The evacuated waveguide line was chosen as the optimal system in light of the above criteria. The system includes 6 lines of 63.5mm waveguide for transmitting the 6.0MW(10s) at 113.3GHz from the gyrotrons to the launching antenna. The designed lines are on average 72m in length and consist of 9 miter bends for an estimated transmission efficiency of ~90%.Each line is designed to include an evacuated switch leading to a calorimetric load, two DC breaks, two gate valves, one pumpout Tee, a power monitor miter bend and a double disk CVD window near the torus. The location of waveguide supports is positioned to minimize power converted to higher order modes from waveguide sagging and misalignment. The two gate valves and CVD windoware designed to be used as tritium barriers at the torus and between the J1T and J1D buildings. The last leg of the waveguide leading to the torus has to be designed to accommodate for the torus movement during disruptions and thermal cycles. All lines are also designed to be compatible for the ITER ECRH system operating at 170GHz.