A three-phase metal-clad electricity line insulated by gas under pressure, the line including a plurality of lengths each constituted by modules that are assembled together end-to-end, each length being sealed relative to the outside and relative to adjacent lengths, two adjacent lengths being separated by a sliding junction enabling a length to be disassembled without losing gas from the adjacent length, the line being wherein the insulating gas is nitrogen under a pressure of a few tens of hectopascals, and preferably in the range 10 hectopascals to 15 hectopascals.