 This technique uses a combination filament–cathode at each end of the lamp in conjunction with a mechanical or automatic (bi-metallic) switch (see circuit diagram to the right) that initially connect the filaments in series with the ballast to preheat them; when the arc is struck the filaments are disconnected.This system is described as "preheat" in some countries and "switchstart" in others.These systems are standard equipment in 200–240 V countries (and for 100–120 V lamps up to about 30 watts).