The present invention relates to a cut-off member intended to be electrically series-connected to an electric circuit comprising a device for protecting an electric installation against lightning, the cut-off member (1) comprising: a first conducting armature (7) electrically connected to a first coupling terminal (3) to the electric circuit and a second conducting armature (9) electrically connected to a second coupling terminal (5) for coupling to the electric circuit; at least one fuse element (11) disposed between the first conducting armature (7) and the second conducting armature (9) and electrically connected to the first conducting armature (7) and to the second conducting armature (9), the at least one fuse element (11) being arranged to melt when it is crossed by a current of a threshold intensity over a threshold period of time; a device for increasing a peak arc voltage (15) between the first conducting armature (7) and the second conducting armature (9) in the case of melting of the at least one fuse element (11).