The invention relates to a method for applying a double sealing system to an electro-technical device and an electro-technical device with a double seal. Said Electro-technical device comprises; a container (5) housing a functional unit (2) and including one aperture (52) provided with a cover (6), wherein said cover has a first face (61) abutting an annular surface (520) which borders said aperture (52); a first sealing joint (7) accommodated in a first groove (64) provided in the first face (61) of the annular surface (520), a second groove (65) provided on said first face (61) of the annular surface (520), and surrounding the first groove (64), said second groove (65) having a closed concavity not directly accessible from the exterior of the electro-technical device (1) when the cover is applied to the annular surface (520). Said device further comprises a first channel (651) for connecting the second groove (65) to a first external point of injection (9) and a second sealing joint (8), made by injection moulding of a sealing substance (81) after the cover has been applied to said annular surface, provided in the second groove (65).