Abstract: The invention relates to an installation for transmitting electrical power which includes a safety device for providing protection against the effects of electric arcs, said installation including a metal casing (5) filled with a dielectric gas under pressure and having a coaxial central conductor (1,2). In such an installation, where a conductor (1,2) and a casing (5) are held in position relative to each other by a transverse insulator (8), said safety device comprises a tubular electrode (9) situated close to the casing (5) and to the insulator (8) and upstream therefrom relative to the direction of power transmission. The tubular electrode is electrically connected to the casing (5) by conductors (12) which are disposed at a small number of points around its periphery. The invention applies to protecting high-tension electric installations contained in metal casings.