The two-wire switch connects a load (46) to an a.c. supply (18) and includes a bridge rectifier network (20) that supplies a semiconductor circuit which is initiated by a proximity switch (10). The output of the bridge is applied to a stabilisied auxiliary supply (12) to produce a low-voltage, pulsating d.c. that charges a reservoir capacitor (32) and supplies a transistor (24) that is controlled by the proximity switch. A control current flows through a reference diode (34) and decoupling diodes (38,40) to the gate electrodes of two thyristors (42,44) which are connected in opposite/parallel across the ac supply flowing through a single thyristor which is turned on towards the end of an a.c. phase.
