The invention concerns a device for protecting an electrical installation designed to be mounted as a by-pass with respect to the electrical installation and comprising at least two electrically conductive contact members (3, 4) capable of shifting from a closing position to an opening position when the protecting device (1) is traversed by a current (I) of intensity higher than a predetermined threshold value. The invention is characterized in that in the closing position, the contact members are separated from each other by a potentially insulating component (15), forming thereby a protective spark-gap (E) against voltage surges between the contact members (3, 4). The invention is useful for protecting electrical installations.