RBFU 1.05 ST Field Unit is used for controlling up to two Belimo 24 V fire damper actuators (BF24..-ST, BFG24..-ST, BLF24..-ST). The unit is connected to RingBus master controller via the 4 wire Ringbus communication. The Belimo ST actuators are equipped with connectors that are plugged directly in to RBFU 1.05 ST Field Unit. The actuators are isolated from mains by a transformer. Each unit has a predefined address and therefore has not to be addressed during the system commissioning. RBFU 1.05 ST unit is able to work without 230 V, but then it is only sending data about actuator position to the Ringbus master controller and is not able to turn on/off the actuators.