The switch control subassembly (WST-BG) is an electronic subassembly for actuating switch mechanisms whereby the changing and monitoring logic is executed as a redundant computer system. Actuation is realised in accordance to the four-wire circuit principle and switching over between the setting and monitoring operating modes is carried out via positively driven, pluggable signal relays (Hengstler). One WST-BG can control up to 4 sets of switches.