Electronic subassembly with user-controlled start-up, and automatic stop, having zero apparent power consumption when turned off and in standby and whose start-up requires only a low priming current, comprising: - a connection to an electrical network; - a power relay comprising at least one switch, the first pole of which is connected to a phase or a pole of the electrical network, and the second pole of which is connected to a power input of a low voltage power supply for maintaining the operating state, and, where relevant, to one or more loads external to the electronic subassembly; - a control subassembly made of wired or programmed logic for at least controlling the functional state of said power relay; - said low-voltage power supply for maintaining operating state being arranged and dimensioned to supply at least said control subassembly and the control of said power relay during an indefinite time; said electronic subassembly being characterized in that it further comprises: - a low voltage priming power supply subassembly, which is at least partially distinct from the low voltage power supply for maintaining the operating state, and which is arranged and dimensioned to supply at least momentarily said control subassembly and the control of said power relay; - at least one means for momentarily activating said priming low voltage electrical supply subassembly; - at least one means (15, 16, 17, 21, 43) for limiting the current passing through the at least one means; - means (20, A', 43) for combining voltages and/or currents originating from the low voltage priming and for maintaining the operating state power supply sub-assemblies; - said control subassembly being arranged to close the at least one switch of said power relay when it is powered on, and to open the at least one switch of said power relay upon the occurrence of an event the nature of which is determined as a function of the functional characteristics of the device which comprises said electronic subassembly and/or, where relevant, according to a choice of the user. - a connection to an electrical network; - a power relay comprising at least one switch, the first pole of which is connected to a phase or a pole of the electrical network, and the second pole of which is connected to a power input of a low voltage power supply for maintaining the operating state, and, where relevant, to one or more loads external to the electronic subassembly; - a control subassembly made of wired or programmed logic for at least controlling the functional state of said power relay; - said low-voltage power supply for maintaining operating state being arranged and dimensioned to supply at least said control subassembly and the control of said power relay during an indefinite time; - a low voltage priming power supply subassembly, which is at least partially distinct from the low voltage power supply for maintaining the operating state, and which is arranged and dimensioned to supply at least momentarily said control subassembly and the control of said power relay; - at least one means for momentarily activating said priming low voltage electrical supply subassembly; - at least one means (15, 16, 17, 21, 43) for limiting the current passing through the at least one means; - means (20, A', 43) for combining voltages and/or currents originating from the low voltage priming and for maintaining the operating state power supply sub-assemblies; - said control subassembly being arranged to close the at least one switch of said power relay when it is powered on, and to open the at least one switch of said power relay upon the occurrence of an event the nature of which is determined as a function of the functional characteristics of the device which comprises said electronic subassembly and/or, where relevant, according to a choice of the user.