A master/slave system on operating means of the building technology, in particular for light sources (14, 31), having a master operating device and a slave operating device, wherein the master operating device and the slave operating device are designed to be able to connect to a communication bus, wherein: - the master operating device has: - a control unit; - a first bus connection and a second connection, wherein the second connection is designed for connecting with a slave-connection of the slave operating device; and - a switch, which is designed, to connect the first bus-connection and the second connection and to selectively forward a DC voltage to the second connection, wherein: - through the selective forwarding of the DC voltage a data transmission from the master operating device is made to the slave operating device, - the DC voltage is a voltage, which is generated internally in the master operating device or is supplied to the first bus-connection by the communication bus, and the control unit is designed to make the data transmission from the master operating device to the slave operating device by the actuation of the switch; - the slave operating device has the slave-connection for connecting to the second connection of the master; - the slave operating device has a voltage supply independent of the data transmission from the master operating device to the slave operating device. - the master operating device has: - a control unit; - a first bus connection and a second connection, wherein the second connection is designed for connecting with a slave-connection of the slave operating device; and - a switch, which is designed, to connect the first bus-connection and the second connection and to selectively forward a DC voltage to the second connection, wherein: - through the selective forwarding of the DC voltage a data transmission from the master operating device is made to the slave operating device, - the DC voltage is a voltage, which is generated internally in the master operating device or is supplied to the first bus-connection by the communication bus, and the control unit is designed to make the data transmission from the master operating device to the slave operating device by the actuation of the switch; - the slave operating device has the slave-connection for connecting to the second connection of the master; - the slave operating device has a voltage supply independent of the data transmission from the master operating device to the slave operating device. - a control unit; - a first bus connection and a second connection, wherein the second connection is designed for connecting with a slave-connection of the slave operating device; and - a switch, which is designed, to connect the first bus-connection and the second connection and to selectively forward a DC voltage to the second connection, wherein: - through the selective forwarding of the DC voltage a data transmission from the master operating device is made to the slave operating device, - the DC voltage is a voltage, which is generated internally in the master operating device or is supplied to the first bus-connection by the communication bus, and the control unit is designed to make the data transmission from the master operating device to the slave operating device by the actuation of the switch; - the slave operating device has the slave-connection for connecting to the second connection of the master; - the slave operating device has a voltage supply independent of the data transmission from the master operating device to the slave operating device. - through the selective forwarding of the DC voltage a data transmission from the master operating device is made to the slave operating device, - the DC voltage is a voltage, which is generated internally in the master operating device or is supplied to the first bus-connection by the communication bus, and the control unit is designed to make the data transmission from the master operating device to the slave operating device by the actuation of the switch; - the slave operating device has the slave-connection for connecting to the second connection of the master; - the slave operating device has a voltage supply independent of the data transmission from the master operating device to the slave operating device.