The present invention discloses a switch circuit for controlling the supply of electrical power from an electrical power source to a load, including a power supply switch comprising input, output and control terminals. The circuit further includes an electronic switching device connected to the control terminal of the power supply switch and having an activating input terminal; a momentary switch coupled to the activating input terminal of the electronic switching device; and a charge storage element coupled to the momentary switch. In a first mode, closing the momentary switch in excess of a triggering time charges the charge storage element and trioggers the electronic switching device to turn on the circuit to supply power to the load. In a second mode, closing the momentary switch connects the charge storage element to the electronic switching device to turn off the electronic switching device and the power supply switch, thus interrupting the supply of power to the load.