Abstract: Disclosed herein is a device that detects overcurrents and the loss of one or two phases occurring suddenly in the supply line of electrically operated devices. In both cases, the aforementioned detection is followed by generation of a deenergization signal so as to disconnect the circuits from the electricity mains. The phase loss is detected when, in one or two phases of the line, the line current is below, for a predetermined time, an established value. The overcurrent detection takes place when a line current exceeds, for a predetermined time, a threshold value. In one form or embodiment, the device trips immediately; in another, it operates with a time lag that is a function of the ratio between the line overcurrent and the threshold value, and it again becomes nonoperative when the overcurrent ceases, as a function of the said ratio. According to the invention, when all three phases experience an undercurrent, generation of the deenergization signal is inhibited.