The invention relates to a device (1) for protecting an installation against electrical disturbances, comprising a case (4) in which the following components are mounted, namely: arc-generation means (5) which are formed by two pieces (6, 7) between which an arc (8) is formed in the event of a disturbance, and an arc-extinguishing chamber (9) comprising a series of splitter plates (12) which are spaced apart such as to divide the arc (8) into a plurality of basic arcs (13). The invention is characterised in that the device also comprises at least one isolating spark gap (15) which is mounted in series with the aforementioned chamber and which has a sufficient interrupting capacity in order, in the event of a chamber failure, to extinguish the arc (8) at current zero-crossing, thereby preventing the reignition of the arc (8). The invention relates to devices used to protect electrical installations against electrical disturbances.