Electronic monitoring circuit for monitoring the electrical connection of at least two devices

Electronic monitoring circuit (A, B) for monitoring the electrical connection of at least two devices (1, 2), which supply line are connected at least by means of a first (5) and a second (6), of these two supply lines (5, 6) is supplied with electrical power at least one of the devices (2) and wherein the electronic monitoring circuit (a, B) is connected to one of the supply lines (5), wherein the monitoring circuit (a, B) a control unit (F) (for generating a test signal Ip) (for testing the line impedance R