Abstract: A perforating gun assembly for perforating wellbores, comprising a shaped charge carrier assembly, a detonating cord for initiation OF shaped charges in the carrier assembly, an initiator attached to the detonating cord for initiating the cord on application of an electrical control signal to the detonator, and a pressure safety switch connected to the initiator. The pressure safety switch electrically connects the initiator to an electrical cable for carrying the control signal, when a preselected pressure is applied to the pressure safety switch.