Building ventilation system connection detection

A building ventilation system comprising a central control unit and at least one electrical operating unit for adjusting a movable member of a ventilation device, the central control unit is connected to the at least one electrical operating unit by two power supply wires and configured to provide an operating voltage for operation of the at least one electrical operating unit via the two power supply wires, wherein the two power supply wires are connected to an end module and the central control unit further is configured to provide a test voltage via the power supply wires being lower than the operating voltage, wherein the end module is configured to temporarily vary its load impedance with a predetermined pattern, and wherein the end module is configured to temporarily vary its load impedance by being switchable between a low impedance state and a high impedance state, wherein the end module provides an alternative circuit path circumventing the at least one electrical operating unit when the end module is in the low impedance state, when the test voltage is provided, the end module is in high impedance state, and the central control unit is configured to detect the temporarily varying load impedance of the end module.