The connecting device contains a bus coupler (BA) which can be connected to a data line (11) and which contains a microprocessor and is connected to an access unit (AU) via internal communication lines (12). The access unit is connected via optical fibre cables (18) to a number of control elements (13) which do not contain any electric components and exhibit a control member (22, 23) which renders the light path from a light source to a light receiver transparent in a first position and interrupts this light path in a second position.
