A method of installing a wind turbine, the method comprising: - installing a transition piece for a wind turbine tower on a tower foundation, the transition piece being configured to be installed on a tower foundation and to carry a tower piece, the transition piece comprising a high voltage joint, the high voltage joint comprising: - a grid input terminal for receiving and connecting to an array cable from a power grid, - a wind turbine generator connecting output terminal, operatively connected to the grid input terminal, for receiving and connecting to an input cable leading to a switchgear, - a WTG connecting input terminal for receiving and connecting to an output cable from the switchgear, and - a grid output terminal, operatively connected to the WTG connecting input terminal, for receiving and connecting to an array cable leading to the power grid, - then connecting a first array cable from a power grid to the grid input terminal of the high voltage joint, and - connecting a second array cable leading to the power grid to the grid output terminal of the high voltage joint, - then, installing a tower piece on top of the transition piece, and - thereafter connecting an output cable between the WTG connecting output terminal of the high voltage joint and a high voltage input terminal of a switchgear, and connecting an input cable between a high voltage output terminal of the switchgear and the WTG connecting input terminal of the high voltage joint, characterised in the method further comprising: - before connecting the output cable and the input cable between the high voltage joint and the switchgear, applying a jumper to the WTG connecting output terminal and the WTG connecting input terminal of the high voltage joint and thereby establishing an electrical connection therebetween, - keeping the jumper attached during a subsequent phase of the installation process, and at the end of said subsequent phase, removing the jumper and - thereafter connecting the output cable and the input cable between the high voltage joint and the switchgear. - installing a transition piece for a wind turbine tower on a tower foundation, the transition piece being configured to be installed on a tower foundation and to carry a tower piece, the transition piece comprising a high voltage joint, the high voltage joint comprising: - a grid input terminal for receiving and connecting to an array cable from a power grid, - a wind turbine generator connecting output terminal, operatively connected to the grid input terminal, for receiving and connecting to an input cable leading to a switchgear, - a WTG connecting input terminal for receiving and connecting to an output cable from the switchgear, and - a grid output terminal, operatively connected to the WTG connecting input terminal, for receiving and connecting to an array cable leading to the power grid, - a grid input terminal for receiving and connecting to an array cable from a power grid, - a wind turbine generator connecting output terminal, operatively connected to the grid input terminal, for receiving and connecting to an input cable leading to a switchgear, - a WTG connecting input terminal for receiving and connecting to an output cable from the switchgear, and - a grid output terminal, operatively connected to the WTG connecting input terminal, for receiving and connecting to an array cable leading to the power grid, - then connecting a first array cable from a power grid to the grid input terminal of the high voltage joint, and - connecting a second array cable leading to the power grid to the grid output terminal of the high voltage joint, - then, installing a tower piece on top of the transition piece, and - thereafter connecting an output cable between the WTG connecting output terminal of the high voltage joint and a high voltage input terminal of a switchgear, and connecting an input cable between a high voltage output terminal of the switchgear and the WTG connecting input terminal of the high voltage joint, characterised in the method further comprising: - before connecting the output cable and the input cable between the high voltage joint and the switchgear, applying a jumper to the WTG connecting output terminal and the WTG connecting input terminal of the high voltage joint and thereby establishing an electrical connection therebetween, - keeping the jumper attached during a subsequent phase of the installation process, and at the end of said subsequent phase, removing the jumper and - thereafter connecting the output cable and the input cable between the high voltage joint and the switchgear.