A protective device for an electrical installation, having at least two electrodes between which an elastic arc can electric arc can form, and a device for interrupting (6) the arc, formed by an assembly of divider plates (7) and extending between an upstream end (6A) and a downstream end (6B), with an entry region (E) for the arc at the upstream end (6A) thereof. The interrupter device (6) has an insulation means (10), formed by caps (13) that form a partial insulating barrier between the electrodes and the upstream end (6A), the caps (13) are provided with teeth (16) housed between two adjacent plates (7). The invention further relates to overload and short-circuit protection devices.