Abstract: The device checks the connection of the conducting wires of a bus such as a bus distributed in a local area network. It comprises two test modules to be connected to the terminations of the bus. The first module comprises a voltage source and detects electric discontinuities in the pairs of wires, and an abnormal crossing of two wires of one and other pair when the second termination is directly connected to terminating impedances of the bus. The second module signals a crossing of wire pairs and crossings of the wires within a pair. These different tests are carried out by working switches and their results are interpreted as a function of the activating and deactivating of current sensors such as LED.